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1 accept_memory= [MM]
2 Format: { eager | lazy }
3 default: lazy
4 By default, unaccepted memory is accepted lazily to
5 avoid prolonged boot times. The lazy option will add
6 some runtime overhead until all memory is eventually
7 accepted. In most cases the overhead is negligible.
8 For some workloads or for debugging purposes
9 accept_memory=eager can be used to accept all memory
10 at once during boot.
11
12 acpi= [HW,ACPI,X86,ARM64,RISCV64]
13 Advanced Configuration and Power Interface
14 Format: { force | on | off | strict | noirq | rsdt |
15 copy_dsdt }
16 force -- enable ACPI if default was off
17 on -- enable ACPI but allow fallback to DT [arm64,riscv64]
18 off -- disable ACPI if default was on
19 noirq -- do not use ACPI for IRQ routing
20 strict -- Be less tolerant of platforms that are not
21 strictly ACPI specification compliant.
22 rsdt -- prefer RSDT over (default) XSDT
23 copy_dsdt -- copy DSDT to memory
24 For ARM64 and RISCV64, ONLY "acpi=off", "acpi=on" or
25 "acpi=force" are available
26
27 See also Documentation/power/runtime_pm.rst, pci=noacpi
28
29 acpi_apic_instance= [ACPI, IOAPIC]
30 Format: <int>
31 2: use 2nd APIC table, if available
32 1,0: use 1st APIC table
33 default: 0
34
35 acpi_backlight= [HW,ACPI]
36 { vendor | video | native | none }
37 If set to vendor, prefer vendor-specific driver
38 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
39 of the ACPI video.ko driver.
40 If set to video, use the ACPI video.ko driver.
41 If set to native, use the device's native backlight mode.
42 If set to none, disable the ACPI backlight interface.
43
44 acpi_force_32bit_fadt_addr
45 force FADT to use 32 bit addresses rather than the
46 64 bit X_* addresses. Some firmware have broken 64
47 bit addresses for force ACPI ignore these and use
48 the older legacy 32 bit addresses.
49
50 acpica_no_return_repair [HW, ACPI]
51 Disable AML predefined validation mechanism
52 This mechanism can repair the evaluation result to make
53 the return objects more ACPI specification compliant.
54 This option is useful for developers to identify the
55 root cause of an AML interpreter issue when the issue
56 has something to do with the repair mechanism.
57
58 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
59 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
60 Format: <int>
61 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
62 debug output. Bits in debug_layer correspond to a
63 _COMPONENT in an ACPI source file, e.g.,
64 #define _COMPONENT ACPI_EVENTS
65 Bits in debug_level correspond to a level in
66 ACPI_DEBUG_PRINT statements, e.g.,
67 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
68 The debug_level mask defaults to "info". See
69 Documentation/firmware-guide/acpi/debug.rst for more information about
70 debug layers and levels.
71
72 Enable processor driver info messages:
73 acpi.debug_layer=0x20000000
74 Enable AML "Debug" output, i.e., stores to the Debug
75 object while interpreting AML:
76 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
77 Enable all messages related to ACPI hardware:
78 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
79
80 Some values produce so much output that the system is
81 unusable. The "log_buf_len" parameter may be useful
82 if you need to capture more output.
83
84 acpi_enforce_resources= [ACPI]
85 { strict | lax | no }
86 Check for resource conflicts between native drivers
87 and ACPI OperationRegions (SystemIO and SystemMemory
88 only). IO ports and memory declared in ACPI might be
89 used by the ACPI subsystem in arbitrary AML code and
90 can interfere with legacy drivers.
91 strict (default): access to resources claimed by ACPI
92 is denied; legacy drivers trying to access reserved
93 resources will fail to bind to device using them.
94 lax: access to resources claimed by ACPI is allowed;
95 legacy drivers trying to access reserved resources
96 will bind successfully but a warning message is logged.
97 no: ACPI OperationRegions are not marked as reserved,
98 no further checks are performed.
99
100 acpi_force_table_verification [HW,ACPI]
101 Enable table checksum verification during early stage.
102 By default, this is disabled due to x86 early mapping
103 size limitation.
104
105 acpi_irq_balance [HW,ACPI]
106 ACPI will balance active IRQs
107 default in APIC mode
108
109 acpi_irq_nobalance [HW,ACPI]
110 ACPI will not move active IRQs (default)
111 default in PIC mode
112
113 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
114 Format: <irq>,<irq>...
115
116 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
117 use by PCI
118 Format: <irq>,<irq>...
119
120 acpi_mask_gpe= [HW,ACPI]
121 Due to the existence of _Lxx/_Exx, some GPEs triggered
122 by unsupported hardware/firmware features can result in
123 GPE floodings that cannot be automatically disabled by
124 the GPE dispatcher.
125 This facility can be used to prevent such uncontrolled
126 GPE floodings.
127 Format: <byte> or <bitmap-list>
128
129 acpi_no_auto_serialize [HW,ACPI]
130 Disable auto-serialization of AML methods
131 AML control methods that contain the opcodes to create
132 named objects will be marked as "Serialized" by the
133 auto-serialization feature.
134 This feature is enabled by default.
135 This option allows to turn off the feature.
136
137 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
138 kernels.
139
140 acpi_no_static_ssdt [HW,ACPI]
141 Disable installation of static SSDTs at early boot time
142 By default, SSDTs contained in the RSDT/XSDT will be
143 installed automatically and they will appear under
144 /sys/firmware/acpi/tables.
145 This option turns off this feature.
146 Note that specifying this option does not affect
147 dynamic table installation which will install SSDT
148 tables to /sys/firmware/acpi/tables/dynamic.
149
150 acpi_no_watchdog [HW,ACPI,WDT]
151 Ignore the ACPI-based watchdog interface (WDAT) and let
152 a native driver control the watchdog device instead.
153
154 acpi_rsdp= [ACPI,EFI,KEXEC]
155 Pass the RSDP address to the kernel, mostly used
156 on machines running EFI runtime service to boot the
157 second kernel for kdump.
158
159 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
160 Format: To spoof as Windows 98: ="Microsoft Windows"
161
162 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
163 of 2 which is mandated by ACPI 6) as the supported ACPI
164 specification revision (when using this switch, it may
165 be necessary to carry out a cold reboot _twice_ in a
166 row to make it take effect on the platform firmware).
167
168 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
169 acpi_osi="string1" # add string1
170 acpi_osi="!string2" # remove string2
171 acpi_osi=!* # remove all strings
172 acpi_osi=! # disable all built-in OS vendor
173 strings
174 acpi_osi=!! # enable all built-in OS vendor
175 strings
176 acpi_osi= # disable all strings
177
178 'acpi_osi=!' can be used in combination with single or
179 multiple 'acpi_osi="string1"' to support specific OS
180 vendor string(s). Note that such command can only
181 affect the default state of the OS vendor strings, thus
182 it cannot affect the default state of the feature group
183 strings and the current state of the OS vendor strings,
184 specifying it multiple times through kernel command line
185 is meaningless. This command is useful when one do not
186 care about the state of the feature group strings which
187 should be controlled by the OSPM.
188 Examples:
189 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
190 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
191 can make '_OSI("Windows 2000")' TRUE.
192
193 'acpi_osi=' cannot be used in combination with other
194 'acpi_osi=' command lines, the _OSI method will not
195 exist in the ACPI namespace. NOTE that such command can
196 only affect the _OSI support state, thus specifying it
197 multiple times through kernel command line is also
198 meaningless.
199 Examples:
200 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
201 FALSE.
202
203 'acpi_osi=!*' can be used in combination with single or
204 multiple 'acpi_osi="string1"' to support specific
205 string(s). Note that such command can affect the
206 current state of both the OS vendor strings and the
207 feature group strings, thus specifying it multiple times
208 through kernel command line is meaningful. But it may
209 still not able to affect the final state of a string if
210 there are quirks related to this string. This command
211 is useful when one want to control the state of the
212 feature group strings to debug BIOS issues related to
213 the OSPM features.
214 Examples:
215 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
216 '_OSI("Module Device")' FALSE.
217 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
218 '_OSI("Module Device")' TRUE.
219 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
220 equivalent to
221 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
222 and
223 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
224 they all will make '_OSI("Windows 2000")' TRUE.
225
226 acpi_pm_good [X86]
227 Override the pmtimer bug detection: force the kernel
228 to assume that this machine's pmtimer latches its value
229 and always returns good values.
230
231 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
232 Format: { level | edge | high | low }
233
234 acpi_skip_timer_override [HW,ACPI]
235 Recognize and ignore IRQ0/pin2 Interrupt Override.
236 For broken nForce2 BIOS resulting in XT-PIC timer.
237
238 acpi_sleep= [HW,ACPI] Sleep options
239 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
240 s4_nohwsig, old_ordering, nonvs,
241 sci_force_enable, nobl }
242 See Documentation/power/video.rst for information on
243 s3_bios and s3_mode.
244 s3_beep is for debugging; it makes the PC's speaker beep
245 as soon as the kernel's real-mode entry point is called.
246 s4_hwsig causes the kernel to check the ACPI hardware
247 signature during resume from hibernation, and gracefully
248 refuse to resume if it has changed. This complies with
249 the ACPI specification but not with reality, since
250 Windows does not do this and many laptops do change it
251 on docking. So the default behaviour is to allow resume
252 and simply warn when the signature changes, unless the
253 s4_hwsig option is enabled.
254 s4_nohwsig prevents ACPI hardware signature from being
255 used (or even warned about) during resume.
256 old_ordering causes the ACPI 1.0 ordering of the _PTS
257 control method, with respect to putting devices into
258 low power states, to be enforced (the ACPI 2.0 ordering
259 of _PTS is used by default).
260 nonvs prevents the kernel from saving/restoring the
261 ACPI NVS memory during suspend/hibernation and resume.
262 sci_force_enable causes the kernel to set SCI_EN directly
263 on resume from S1/S3 (which is against the ACPI spec,
264 but some broken systems don't work without it).
265 nobl causes the internal blacklist of systems known to
266 behave incorrectly in some ways with respect to system
267 suspend and resume to be ignored (use wisely).
268
269 acpi_use_timer_override [HW,ACPI]
270 Use timer override. For some broken Nvidia NF5 boards
271 that require a timer override, but don't have HPET
272
273 add_efi_memmap [EFI; X86] Include EFI memory map in
274 kernel's map of available physical RAM.
275
276 agp= [AGP]
277 { off | try_unsupported }
278 off: disable AGP support
279 try_unsupported: try to drive unsupported chipsets
280 (may crash computer or cause data corruption)
281
282 ALSA [HW,ALSA]
283 See Documentation/sound/alsa-configuration.rst
284
285 alignment= [KNL,ARM]
286 Allow the default userspace alignment fault handler
287 behaviour to be specified. Bit 0 enables warnings,
288 bit 1 enables fixups, and bit 2 sends a segfault.
289
290 align_va_addr= [X86-64]
291 Align virtual addresses by clearing slice [14:12] when
292 allocating a VMA at process creation time. This option
293 gives you up to 3% performance improvement on AMD F15h
294 machines (where it is enabled by default) for a
295 CPU-intensive style benchmark, and it can vary highly in
296 a microbenchmark depending on workload and compiler.
297
298 32: only for 32-bit processes
299 64: only for 64-bit processes
300 on: enable for both 32- and 64-bit processes
301 off: disable for both 32- and 64-bit processes
302
303 alloc_snapshot [FTRACE]
304 Allocate the ftrace snapshot buffer on boot up when the
305 main buffer is allocated. This is handy if debugging
306 and you need to use tracing_snapshot() on boot up, and
307 do not want to use tracing_snapshot_alloc() as it needs
308 to be done where GFP_KERNEL allocations are allowed.
309
310 allow_mismatched_32bit_el0 [ARM64]
311 Allow execve() of 32-bit applications and setting of the
312 PER_LINUX32 personality on systems where only a strict
313 subset of the CPUs support 32-bit EL0. When this
314 parameter is present, the set of CPUs supporting 32-bit
315 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
316 and hot-unplug operations may be restricted.
317
318 See Documentation/arch/arm64/asymmetric-32bit.rst for more
319 information.
320
321 amd_iommu= [HW,X86-64]
322 Pass parameters to the AMD IOMMU driver in the system.
323 Possible values are:
324 fullflush - Deprecated, equivalent to iommu.strict=1
325 off - do not initialize any AMD IOMMU found in
326 the system
327 force_isolation - Force device isolation for all
328 devices. The IOMMU driver is not
329 allowed anymore to lift isolation
330 requirements as needed. This option
331 does not override iommu=pt
332 force_enable - Force enable the IOMMU on platforms known
333 to be buggy with IOMMU enabled. Use this
334 option with care.
335 pgtbl_v1 - Use v1 page table for DMA-API (Default).
336 pgtbl_v2 - Use v2 page table for DMA-API.
337 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
338
339 amd_iommu_dump= [HW,X86-64]
340 Enable AMD IOMMU driver option to dump the ACPI table
341 for AMD IOMMU. With this option enabled, AMD IOMMU
342 driver will print ACPI tables for AMD IOMMU during
343 IOMMU initialization.
344
345 amd_iommu_intr= [HW,X86-64]
346 Specifies one of the following AMD IOMMU interrupt
347 remapping modes:
348 legacy - Use legacy interrupt remapping mode.
349 vapic - Use virtual APIC mode, which allows IOMMU
350 to inject interrupts directly into guest.
351 This mode requires kvm-amd.avic=1.
352 (Default when IOMMU HW support is present.)
353
354 amd_pstate= [X86]
355 disable
356 Do not enable amd_pstate as the default
357 scaling driver for the supported processors
358 passive
359 Use amd_pstate with passive mode as a scaling driver.
360 In this mode autonomous selection is disabled.
361 Driver requests a desired performance level and platform
362 tries to match the same performance level if it is
363 satisfied by guaranteed performance level.
364 active
365 Use amd_pstate_epp driver instance as the scaling driver,
366 driver provides a hint to the hardware if software wants
367 to bias toward performance (0x0) or energy efficiency (0xff)
368 to the CPPC firmware. then CPPC power algorithm will
369 calculate the runtime workload and adjust the realtime cores
370 frequency.
371 guided
372 Activate guided autonomous mode. Driver requests minimum and
373 maximum performance level and the platform autonomously
374 selects a performance level in this range and appropriate
375 to the current workload.
376
377 amijoy.map= [HW,JOY] Amiga joystick support
378 Map of devices attached to JOY0DAT and JOY1DAT
379 Format: <a>,<b>
380 See also Documentation/input/joydev/joystick.rst
381
382 analog.map= [HW,JOY] Analog joystick and gamepad support
383 Specifies type or capabilities of an analog joystick
384 connected to one of 16 gameports
385 Format: <type1>,<type2>,..<type16>
386
387 apc= [HW,SPARC]
388 Power management functions (SPARCstation-4/5 + deriv.)
389 Format: noidle
390 Disable APC CPU standby support. SPARCstation-Fox does
391 not play well with APC CPU idle - disable it if you have
392 APC and your system crashes randomly.
393
394 apic= [APIC,X86] Advanced Programmable Interrupt Controller
395 Change the output verbosity while booting
396 Format: { quiet (default) | verbose | debug }
397 Change the amount of debugging information output
398 when initialising the APIC and IO-APIC components.
399 For X86-32, this can also be used to specify an APIC
400 driver name.
401 Format: apic=driver_name
402 Examples: apic=bigsmp
403
404 apic_extnmi= [APIC,X86] External NMI delivery setting
405 Format: { bsp (default) | all | none }
406 bsp: External NMI is delivered only to CPU 0
407 all: External NMIs are broadcast to all CPUs as a
408 backup of CPU 0
409 none: External NMI is masked for all CPUs. This is
410 useful so that a dump capture kernel won't be
411 shot down by NMI
412
413 autoconf= [IPV6]
414 See Documentation/networking/ipv6.rst.
415
416 apm= [APM] Advanced Power Management
417 See header of arch/x86/kernel/apm_32.c.
418
419 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
420 Format: { "0" | "1" }
421 See security/apparmor/Kconfig help text
422 0 -- disable.
423 1 -- enable.
424 Default value is set via kernel config option.
425
426 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
427 Format: <io>,<irq>,<nodeID>
428
429 arm64.nobti [ARM64] Unconditionally disable Branch Target
430 Identification support
431
432 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
433 Set instructions support
434
435 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
436 support
437
438 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
439 support
440
441 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
442 Extension support
443
444 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
445 Extension support
446
447 ataflop= [HW,M68k]
448
449 atarimouse= [HW,MOUSE] Atari Mouse
450
451 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
452 EzKey and similar keyboards
453
454 atkbd.reset= [HW] Reset keyboard during initialization
455
456 atkbd.set= [HW] Select keyboard code set
457 Format: <int> (2 = AT (default), 3 = PS/2)
458
459 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
460 keyboards
461
462 atkbd.softraw= [HW] Choose between synthetic and real raw mode
463 Format: <bool> (0 = real, 1 = synthetic (default))
464
465 atkbd.softrepeat= [HW]
466 Use software keyboard repeat
467
468 audit= [KNL] Enable the audit sub-system
469 Format: { "0" | "1" | "off" | "on" }
470 0 | off - kernel audit is disabled and can not be
471 enabled until the next reboot
472 unset - kernel audit is initialized but disabled and
473 will be fully enabled by the userspace auditd.
474 1 | on - kernel audit is initialized and partially
475 enabled, storing at most audit_backlog_limit
476 messages in RAM until it is fully enabled by the
477 userspace auditd.
478 Default: unset
479
480 audit_backlog_limit= [KNL] Set the audit queue size limit.
481 Format: <int> (must be >=0)
482 Default: 64
483
484 bau= [X86_UV] Enable the BAU on SGI UV. The default
485 behavior is to disable the BAU (i.e. bau=0).
486 Format: { "0" | "1" }
487 0 - Disable the BAU.
488 1 - Enable the BAU.
489 unset - Disable the BAU.
490
491 baycom_epp= [HW,AX25]
492 Format: <io>,<mode>
493
494 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
495 Format: <io>,<mode>
496 See header of drivers/net/hamradio/baycom_par.c.
497
498 baycom_ser_fdx= [HW,AX25]
499 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
500 Format: <io>,<irq>,<mode>[,<baud>]
501 See header of drivers/net/hamradio/baycom_ser_fdx.c.
502
503 baycom_ser_hdx= [HW,AX25]
504 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
505 Format: <io>,<irq>,<mode>
506 See header of drivers/net/hamradio/baycom_ser_hdx.c.
507
508 bert_disable [ACPI]
509 Disable BERT OS support on buggy BIOSes.
510
511 bgrt_disable [ACPI][X86]
512 Disable BGRT to avoid flickering OEM logo.
513
514 blkdevparts= Manual partition parsing of block device(s) for
515 embedded devices based on command line input.
516 See Documentation/block/cmdline-partition.rst
517
518 boot_delay= Milliseconds to delay each printk during boot.
519 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
520 and you may also have to specify "lpj=". Boot_delay
521 values larger than 10 seconds (10000) are assumed
522 erroneous and ignored.
523 Format: integer
524
525 bootconfig [KNL]
526 Extended command line options can be added to an initrd
527 and this will cause the kernel to look for it.
528
529 See Documentation/admin-guide/bootconfig.rst
530
531 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
532 bttv.radio= Most important insmod options are available as
533 kernel args too.
534 bttv.pll= See Documentation/admin-guide/media/bttv.rst
535 bttv.tuner=
536
537 bulk_remove=off [PPC] This parameter disables the use of the pSeries
538 firmware feature for flushing multiple hpte entries
539 at a time.
540
541 c101= [NET] Moxa C101 synchronous serial card
542
543 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
544 Sometimes CPU hardware bugs make them report the cache
545 size incorrectly. The kernel will attempt work arounds
546 to fix known problems, but for some CPUs it is not
547 possible to determine what the correct size should be.
548 This option provides an override for these situations.
549
550 carrier_timeout=
551 [NET] Specifies amount of time (in seconds) that
552 the kernel should wait for a network carrier. By default
553 it waits 120 seconds.
554
555 ca_keys= [KEYS] This parameter identifies a specific key(s) on
556 the system trusted keyring to be used for certificate
557 trust validation.
558 format: { id:<keyid> | builtin }
559
560 cca= [MIPS] Override the kernel pages' cache coherency
561 algorithm. Accepted values range from 0 to 7
562 inclusive. See arch/mips/include/asm/pgtable-bits.h
563 for platform specific values (SB1, Loongson3 and
564 others).
565
566 ccw_timeout_log [S390]
567 See Documentation/arch/s390/common_io.rst for details.
568
569 cgroup_disable= [KNL] Disable a particular controller or optional feature
570 Format: {name of the controller(s) or feature(s) to disable}
571 The effects of cgroup_disable=foo are:
572 - foo isn't auto-mounted if you mount all cgroups in
573 a single hierarchy
574 - foo isn't visible as an individually mountable
575 subsystem
576 - if foo is an optional feature then the feature is
577 disabled and corresponding cgroup files are not
578 created
579 {Currently only "memory" controller deal with this and
580 cut the overhead, others just disable the usage. So
581 only cgroup_disable=memory is actually worthy}
582 Specifying "pressure" disables per-cgroup pressure
583 stall information accounting feature
584
585 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
586 Format: { { controller | "all" | "named" }
587 [,{ controller | "all" | "named" }...] }
588 Like cgroup_disable, but only applies to cgroup v1;
589 the blacklisted controllers remain available in cgroup2.
590 "all" blacklists all controllers and "named" disables
591 named mounts. Specifying both "all" and "named" disables
592 all v1 hierarchies.
593
594 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
595 Format: { "true" | "false" }
596 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
597
598 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
599 Format: <string>
600 nosocket -- Disable socket memory accounting.
601 nokmem -- Disable kernel memory accounting.
602 nobpf -- Disable BPF memory accounting.
603
604 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
605 Format: { "0" | "1" }
606 See security/selinux/Kconfig help text.
607 0 -- check protection applied by kernel (includes
608 any implied execute protection).
609 1 -- check protection requested by application.
610 Default value is set via a kernel config option.
611 Value can be changed at runtime via
612 /sys/fs/selinux/checkreqprot.
613 Setting checkreqprot to 1 is deprecated.
614
615 cio_ignore= [S390]
616 See Documentation/arch/s390/common_io.rst for details.
617
618 clearcpuid=X[,X...] [X86]
619 Disable CPUID feature X for the kernel. See
620 arch/x86/include/asm/cpufeatures.h for the valid bit
621 numbers X. Note the Linux-specific bits are not necessarily
622 stable over kernel options, but the vendor-specific
623 ones should be.
624 X can also be a string as appearing in the flags: line
625 in /proc/cpuinfo which does not have the above
626 instability issue. However, not all features have names
627 in /proc/cpuinfo.
628 Note that using this option will taint your kernel.
629 Also note that user programs calling CPUID directly
630 or using the feature without checking anything
631 will still see it. This just prevents it from
632 being used by the kernel or shown in /proc/cpuinfo.
633 Also note the kernel might malfunction if you disable
634 some critical bits.
635
636 clk_ignore_unused
637 [CLK]
638 Prevents the clock framework from automatically gating
639 clocks that have not been explicitly enabled by a Linux
640 device driver but are enabled in hardware at reset or
641 by the bootloader/firmware. Note that this does not
642 force such clocks to be always-on nor does it reserve
643 those clocks in any way. This parameter is useful for
644 debug and development, but should not be needed on a
645 platform with proper driver support. For more
646 information, see Documentation/driver-api/clk.rst.
647
648 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
649 [Deprecated]
650 Forces specified clocksource (if available) to be used
651 when calculating gettimeofday(). If specified
652 clocksource is not available, it defaults to PIT.
653 Format: { pit | tsc | cyclone | pmtmr }
654
655 clocksource= Override the default clocksource
656 Format: <string>
657 Override the default clocksource and use the clocksource
658 with the name specified.
659 Some clocksource names to choose from, depending on
660 the platform:
661 [all] jiffies (this is the base, fallback clocksource)
662 [ACPI] acpi_pm
663 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
664 pxa_timer,timer3,32k_counter,timer0_1
665 [X86-32] pit,hpet,tsc;
666 scx200_hrt on Geode; cyclone on IBM x440
667 [MIPS] MIPS
668 [PARISC] cr16
669 [S390] tod
670 [SH] SuperH
671 [SPARC64] tick
672 [X86-64] hpet,tsc
673
674 clocksource.arm_arch_timer.evtstrm=
675 [ARM,ARM64]
676 Format: <bool>
677 Enable/disable the eventstream feature of the ARM
678 architected timer so that code using WFE-based polling
679 loops can be debugged more effectively on production
680 systems.
681
682 clocksource.max_cswd_read_retries= [KNL]
683 Number of clocksource_watchdog() retries due to
684 external delays before the clock will be marked
685 unstable. Defaults to two retries, that is,
686 three attempts to read the clock under test.
687
688 clocksource.verify_n_cpus= [KNL]
689 Limit the number of CPUs checked for clocksources
690 marked with CLOCK_SOURCE_VERIFY_PERCPU that
691 are marked unstable due to excessive skew.
692 A negative value says to check all CPUs, while
693 zero says not to check any. Values larger than
694 nr_cpu_ids are silently truncated to nr_cpu_ids.
695 The actual CPUs are chosen randomly, with
696 no replacement if the same CPU is chosen twice.
697
698 clocksource-wdtest.holdoff= [KNL]
699 Set the time in seconds that the clocksource
700 watchdog test waits before commencing its tests.
701 Defaults to zero when built as a module and to
702 10 seconds when built into the kernel.
703
704 cma=nn[MG]@[start[MG][-end[MG]]]
705 [KNL,CMA]
706 Sets the size of kernel global memory area for
707 contiguous memory allocations and optionally the
708 placement constraint by the physical address range of
709 memory allocations. A value of 0 disables CMA
710 altogether. For more information, see
711 kernel/dma/contiguous.c
712
713 cma_pernuma=nn[MG]
714 [KNL,CMA]
715 Sets the size of kernel per-numa memory area for
716 contiguous memory allocations. A value of 0 disables
717 per-numa CMA altogether. And If this option is not
718 specified, the default value is 0.
719 With per-numa CMA enabled, DMA users on node nid will
720 first try to allocate buffer from the pernuma area
721 which is located in node nid, if the allocation fails,
722 they will fallback to the global default memory area.
723
724 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
725 [KNL,CMA]
726 Sets the size of kernel numa memory area for
727 contiguous memory allocations. It will reserve CMA
728 area for the specified node.
729
730 With numa CMA enabled, DMA users on node nid will
731 first try to allocate buffer from the numa area
732 which is located in node nid, if the allocation fails,
733 they will fallback to the global default memory area.
734
735 cmo_free_hint= [PPC] Format: { yes | no }
736 Specify whether pages are marked as being inactive
737 when they are freed. This is used in CMO environments
738 to determine OS memory pressure for page stealing by
739 a hypervisor.
740 Default: yes
741
742 coherent_pool=nn[KMG] [ARM,KNL]
743 Sets the size of memory pool for coherent, atomic dma
744 allocations, by default set to 256K.
745
746 com20020= [HW,NET] ARCnet - COM20020 chipset
747 Format:
748 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
749
750 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
751 Format: <io>[,<irq>]
752
753 com90xx= [HW,NET]
754 ARCnet - COM90xx chipset (memory-mapped buffers)
755 Format: <io>[,<irq>[,<memstart>]]
756
757 condev= [HW,S390] console device
758 conmode=
759
760 con3215_drop= [S390] 3215 console drop mode.
761 Format: y|n|Y|N|1|0
762 When set to true, drop data on the 3215 console when
763 the console buffer is full. In this case the
764 operator using a 3270 terminal emulator (for example
765 x3270) does not have to enter the clear key for the
766 console output to advance and the kernel to continue.
767 This leads to a much faster boot time when a 3270
768 terminal emulator is active. If no 3270 terminal
769 emulator is used, this parameter has no effect.
770
771 console= [KNL] Output console device and options.
772
773 tty<n> Use the virtual console device <n>.
774
775 ttyS<n>[,options]
776 ttyUSB0[,options]
777 Use the specified serial port. The options are of
778 the form "bbbbpnf", where "bbbb" is the baud rate,
779 "p" is parity ("n", "o", or "e"), "n" is number of
780 bits, and "f" is flow control ("r" for RTS or
781 omit it). Default is "9600n8".
782
783 See Documentation/admin-guide/serial-console.rst for more
784 information. See
785 Documentation/networking/netconsole.rst for an
786 alternative.
787
788 uart[8250],io,<addr>[,options]
789 uart[8250],mmio,<addr>[,options]
790 uart[8250],mmio16,<addr>[,options]
791 uart[8250],mmio32,<addr>[,options]
792 uart[8250],0x<addr>[,options]
793 Start an early, polled-mode console on the 8250/16550
794 UART at the specified I/O port or MMIO address,
795 switching to the matching ttyS device later.
796 MMIO inter-register address stride is either 8-bit
797 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
798 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
799 to be equivalent to 'mmio'. 'options' are specified in
800 the same format described for ttyS above; if unspecified,
801 the h/w is not re-initialized.
802
803 hvc<n> Use the hypervisor console device <n>. This is for
804 both Xen and PowerPC hypervisors.
805
806 { null | "" }
807 Use to disable console output, i.e., to have kernel
808 console messages discarded.
809 This must be the only console= parameter used on the
810 kernel command line.
811
812 If the device connected to the port is not a TTY but a braille
813 device, prepend "brl," before the device type, for instance
814 console=brl,ttyS0
815 For now, only VisioBraille is supported.
816
817 console_msg_format=
818 [KNL] Change console messages format
819 default
820 By default we print messages on consoles in
821 "[time stamp] text\n" format (time stamp may not be
822 printed, depending on CONFIG_PRINTK_TIME or
823 `printk_time' param).
824 syslog
825 Switch to syslog format: "<%u>[time stamp] text\n"
826 IOW, each message will have a facility and loglevel
827 prefix. The format is similar to one used by syslog()
828 syscall, or to executing "dmesg -S --raw" or to reading
829 from /proc/kmsg.
830
831 consoleblank= [KNL] The console blank (screen saver) timeout in
832 seconds. A value of 0 disables the blank timer.
833 Defaults to 0.
834
835 coredump_filter=
836 [KNL] Change the default value for
837 /proc/<pid>/coredump_filter.
838 See also Documentation/filesystems/proc.rst.
839
840 coresight_cpu_debug.enable
841 [ARM,ARM64]
842 Format: <bool>
843 Enable/disable the CPU sampling based debugging.
844 0: default value, disable debugging
845 1: enable debugging at boot time
846
847 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
848 Format:
849 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
850
851 cpuidle.off=1 [CPU_IDLE]
852 disable the cpuidle sub-system
853
854 cpuidle.governor=
855 [CPU_IDLE] Name of the cpuidle governor to use.
856
857 cpufreq.off=1 [CPU_FREQ]
858 disable the cpufreq sub-system
859
860 cpufreq.default_governor=
861 [CPU_FREQ] Name of the default cpufreq governor or
862 policy to use. This governor must be registered in the
863 kernel before the cpufreq driver probes.
864
865 cpu_init_udelay=N
866 [X86] Delay for N microsec between assert and de-assert
867 of APIC INIT to start processors. This delay occurs
868 on every CPU online, such as boot, and resume from suspend.
869 Default: 10000
870
871 cpuhp.parallel=
872 [SMP] Enable/disable parallel bringup of secondary CPUs
873 Format: <bool>
874 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
875 the parameter has no effect.
876
877 crash_kexec_post_notifiers
878 Run kdump after running panic-notifiers and dumping
879 kmsg. This only for the users who doubt kdump always
880 succeeds in any situation.
881 Note that this also increases risks of kdump failure,
882 because some panic notifiers can make the crashed
883 kernel more unstable.
884
885 crashkernel=size[KMG][@offset[KMG]]
886 [KNL] Using kexec, Linux can switch to a 'crash kernel'
887 upon panic. This parameter reserves the physical
888 memory region [offset, offset + size] for that kernel
889 image. If '@offset' is omitted, then a suitable offset
890 is selected automatically.
891 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
892 under 4G first, and fall back to reserve region above
893 4G when '@offset' hasn't been specified.
894 See Documentation/admin-guide/kdump/kdump.rst for further details.
895
896 crashkernel=range1:size1[,range2:size2,...][@offset]
897 [KNL] Same as above, but depends on the memory
898 in the running system. The syntax of range is
899 start-[end] where start and end are both
900 a memory unit (amount[KMG]). See also
901 Documentation/admin-guide/kdump/kdump.rst for an example.
902
903 crashkernel=size[KMG],high
904 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
905 above 4G.
906 Allow kernel to allocate physical memory region from top,
907 so could be above 4G if system have more than 4G ram
908 installed. Otherwise memory region will be allocated
909 below 4G, if available.
910 It will be ignored if crashkernel=X is specified.
911 crashkernel=size[KMG],low
912 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
913 When crashkernel=X,high is passed, kernel could allocate
914 physical memory region above 4G, that cause second kernel
915 crash on system that require some amount of low memory,
916 e.g. swiotlb requires at least 64M+32K low memory, also
917 enough extra low memory is needed to make sure DMA buffers
918 for 32-bit devices won't run out. Kernel would try to allocate
919 default size of memory below 4G automatically. The default
920 size is platform dependent.
921 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
922 --> arm64: 128MiB
923 --> riscv: 128MiB
924 --> loongarch: 128MiB
925 This one lets the user specify own low range under 4G
926 for second kernel instead.
927 0: to disable low allocation.
928 It will be ignored when crashkernel=X,high is not used
929 or memory reserved is below 4G.
930
931 cryptomgr.notests
932 [KNL] Disable crypto self-tests
933
934 cs89x0_dma= [HW,NET]
935 Format: <dma>
936
937 cs89x0_media= [HW,NET]
938 Format: { rj45 | aui | bnc }
939
940 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
941 function call handling. When switched on,
942 additional debug data is printed to the console
943 in case a hanging CPU is detected, and that
944 CPU is pinged again in order to try to resolve
945 the hang situation. The default value of this
946 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
947 Kconfig option.
948
949 dasd= [HW,NET]
950 See header of drivers/s390/block/dasd_devmap.c.
951
952 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
953 (one device per port)
954 Format: <port#>,<type>
955 See also Documentation/input/devices/joystick-parport.rst
956
957 debug [KNL] Enable kernel debugging (events log level).
958
959 debug_boot_weak_hash
960 [KNL] Enable printing [hashed] pointers early in the
961 boot sequence. If enabled, we use a weak hash instead
962 of siphash to hash pointers. Use this option if you are
963 seeing instances of '(___ptrval___)') and need to see a
964 value (hashed pointer) instead. Cryptographically
965 insecure, please do not use on production kernels.
966
967 debug_locks_verbose=
968 [KNL] verbose locking self-tests
969 Format: <int>
970 Print debugging info while doing the locking API
971 self-tests.
972 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
973 (no extra messages), setting it to -1 (all bits set)
974 will print _a_lot_ more information - normally only
975 useful to lockdep developers.
976
977 debug_objects [KNL] Enable object debugging
978
979 debug_guardpage_minorder=
980 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
981 parameter allows control of the order of pages that will
982 be intentionally kept free (and hence protected) by the
983 buddy allocator. Bigger value increase the probability
984 of catching random memory corruption, but reduce the
985 amount of memory for normal system use. The maximum
986 possible value is MAX_PAGE_ORDER/2. Setting this
987 parameter to 1 or 2 should be enough to identify most
988 random memory corruption problems caused by bugs in
989 kernel or driver code when a CPU writes to (or reads
990 from) a random memory location. Note that there exists
991 a class of memory corruptions problems caused by buggy
992 H/W or F/W or by drivers badly programming DMA
993 (basically when memory is written at bus level and the
994 CPU MMU is bypassed) which are not detectable by
995 CONFIG_DEBUG_PAGEALLOC, hence this option will not
996 help tracking down these problems.
997
998 debug_pagealloc=
999 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1000 enables the feature at boot time. By default, it is
1001 disabled and the system will work mostly the same as a
1002 kernel built without CONFIG_DEBUG_PAGEALLOC.
1003 Note: to get most of debug_pagealloc error reports, it's
1004 useful to also enable the page_owner functionality.
1005 on: enable the feature
1006
1007 debugfs= [KNL] This parameter enables what is exposed to userspace
1008 and debugfs internal clients.
1009 Format: { on, no-mount, off }
1010 on: All functions are enabled.
1011 no-mount:
1012 Filesystem is not registered but kernel clients can
1013 access APIs and a crashkernel can be used to read
1014 its content. There is nothing to mount.
1015 off: Filesystem is not registered and clients
1016 get a -EPERM as result when trying to register files
1017 or directories within debugfs.
1018 This is equivalent of the runtime functionality if
1019 debugfs was not enabled in the kernel at all.
1020 Default value is set in build-time with a kernel configuration.
1021
1022 debugpat [X86] Enable PAT debugging
1023
1024 default_hugepagesz=
1025 [HW] The size of the default HugeTLB page. This is
1026 the size represented by the legacy /proc/ hugepages
1027 APIs. In addition, this is the default hugetlb size
1028 used for shmget(), mmap() and mounting hugetlbfs
1029 filesystems. If not specified, defaults to the
1030 architecture's default huge page size. Huge page
1031 sizes are architecture dependent. See also
1032 Documentation/admin-guide/mm/hugetlbpage.rst.
1033 Format: size[KMG]
1034
1035 deferred_probe_timeout=
1036 [KNL] Debugging option to set a timeout in seconds for
1037 deferred probe to give up waiting on dependencies to
1038 probe. Only specific dependencies (subsystems or
1039 drivers) that have opted in will be ignored. A timeout
1040 of 0 will timeout at the end of initcalls. If the time
1041 out hasn't expired, it'll be restarted by each
1042 successful driver registration. This option will also
1043 dump out devices still on the deferred probe list after
1044 retrying.
1045
1046 delayacct [KNL] Enable per-task delay accounting
1047
1048 dell_smm_hwmon.ignore_dmi=
1049 [HW] Continue probing hardware even if DMI data
1050 indicates that the driver is running on unsupported
1051 hardware.
1052
1053 dell_smm_hwmon.force=
1054 [HW] Activate driver even if SMM BIOS signature does
1055 not match list of supported models and enable otherwise
1056 blacklisted features.
1057
1058 dell_smm_hwmon.power_status=
1059 [HW] Report power status in /proc/i8k
1060 (disabled by default).
1061
1062 dell_smm_hwmon.restricted=
1063 [HW] Allow controlling fans only if SYS_ADMIN
1064 capability is set.
1065
1066 dell_smm_hwmon.fan_mult=
1067 [HW] Factor to multiply fan speed with.
1068
1069 dell_smm_hwmon.fan_max=
1070 [HW] Maximum configurable fan speed.
1071
1072 dfltcc= [HW,S390]
1073 Format: { on | off | def_only | inf_only | always }
1074 on: s390 zlib hardware support for compression on
1075 level 1 and decompression (default)
1076 off: No s390 zlib hardware support
1077 def_only: s390 zlib hardware support for deflate
1078 only (compression on level 1)
1079 inf_only: s390 zlib hardware support for inflate
1080 only (decompression)
1081 always: Same as 'on' but ignores the selected compression
1082 level always using hardware support (used for debugging)
1083
1084 dhash_entries= [KNL]
1085 Set number of hash buckets for dentry cache.
1086
1087 disable_1tb_segments [PPC]
1088 Disables the use of 1TB hash page table segments. This
1089 causes the kernel to fall back to 256MB segments which
1090 can be useful when debugging issues that require an SLB
1091 miss to occur.
1092
1093 disable= [IPV6]
1094 See Documentation/networking/ipv6.rst.
1095
1096 disable_radix [PPC]
1097 Disable RADIX MMU mode on POWER9
1098
1099 disable_tlbie [PPC]
1100 Disable TLBIE instruction. Currently does not work
1101 with KVM, with HASH MMU, or with coherent accelerators.
1102
1103 disable_cpu_apicid= [X86,APIC,SMP]
1104 Format: <int>
1105 The number of initial APIC ID for the
1106 corresponding CPU to be disabled at boot,
1107 mostly used for the kdump 2nd kernel to
1108 disable BSP to wake up multiple CPUs without
1109 causing system reset or hang due to sending
1110 INIT from AP to BSP.
1111
1112 disable_ddw [PPC/PSERIES]
1113 Disable Dynamic DMA Window support. Use this
1114 to workaround buggy firmware.
1115
1116 disable_ipv6= [IPV6]
1117 See Documentation/networking/ipv6.rst.
1118
1119 disable_mtrr_cleanup [X86]
1120 The kernel tries to adjust MTRR layout from continuous
1121 to discrete, to make X server driver able to add WB
1122 entry later. This parameter disables that.
1123
1124 disable_mtrr_trim [X86, Intel and AMD only]
1125 By default the kernel will trim any uncacheable
1126 memory out of your available memory pool based on
1127 MTRR settings. This parameter disables that behavior,
1128 possibly causing your machine to run very slowly.
1129
1130 disable_timer_pin_1 [X86]
1131 Disable PIN 1 of APIC timer
1132 Can be useful to work around chipset bugs.
1133
1134 dis_ucode_ldr [X86] Disable the microcode loader.
1135
1136 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1137 this option disables the debugging code at boot.
1138
1139 dma_debug_entries=<number>
1140 This option allows to tune the number of preallocated
1141 entries for DMA-API debugging code. One entry is
1142 required per DMA-API allocation. Use this if the
1143 DMA-API debugging code disables itself because the
1144 architectural default is too low.
1145
1146 dma_debug_driver=<driver_name>
1147 With this option the DMA-API debugging driver
1148 filter feature can be enabled at boot time. Just
1149 pass the driver to filter for as the parameter.
1150 The filter can be disabled or changed to another
1151 driver later using sysfs.
1152
1153 driver_async_probe= [KNL]
1154 List of driver names to be probed asynchronously. *
1155 matches with all driver names. If * is specified, the
1156 rest of the listed driver names are those that will NOT
1157 match the *.
1158 Format: <driver_name1>,<driver_name2>...
1159
1160 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1161 Broken monitors, graphic adapters, KVMs and EDIDless
1162 panels may send no or incorrect EDID data sets.
1163 This parameter allows to specify an EDID data sets
1164 in the /lib/firmware directory that are used instead.
1165 Generic built-in EDID data sets are used, if one of
1166 edid/1024x768.bin, edid/1280x1024.bin,
1167 edid/1680x1050.bin, or edid/1920x1080.bin is given
1168 and no file with the same name exists. Details and
1169 instructions how to build your own EDID data are
1170 available in Documentation/admin-guide/edid.rst. An EDID
1171 data set will only be used for a particular connector,
1172 if its name and a colon are prepended to the EDID
1173 name. Each connector may use a unique EDID data
1174 set by separating the files with a comma. An EDID
1175 data set with no connector name will be used for
1176 any connectors not explicitly specified.
1177
1178 dscc4.setup= [NET]
1179
1180 dt_cpu_ftrs= [PPC]
1181 Format: {"off" | "known"}
1182 Control how the dt_cpu_ftrs device-tree binding is
1183 used for CPU feature discovery and setup (if it
1184 exists).
1185 off: Do not use it, fall back to legacy cpu table.
1186 known: Do not pass through unknown features to guests
1187 or userspace, only those that the kernel is aware of.
1188
1189 dump_apple_properties [X86]
1190 Dump name and content of EFI device properties on
1191 x86 Macs. Useful for driver authors to determine
1192 what data is available or for reverse-engineering.
1193
1194 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1195 <module>.dyndbg[="val"]
1196 Enable debug messages at boot time. See
1197 Documentation/admin-guide/dynamic-debug-howto.rst
1198 for details.
1199
1200 early_ioremap_debug [KNL]
1201 Enable debug messages in early_ioremap support. This
1202 is useful for tracking down temporary early mappings
1203 which are not unmapped.
1204
1205 earlycon= [KNL] Output early console device and options.
1206
1207 When used with no options, the early console is
1208 determined by stdout-path property in device tree's
1209 chosen node or the ACPI SPCR table if supported by
1210 the platform.
1211
1212 cdns,<addr>[,options]
1213 Start an early, polled-mode console on a Cadence
1214 (xuartps) serial port at the specified address. Only
1215 supported option is baud rate. If baud rate is not
1216 specified, the serial port must already be setup and
1217 configured.
1218
1219 uart[8250],io,<addr>[,options[,uartclk]]
1220 uart[8250],mmio,<addr>[,options[,uartclk]]
1221 uart[8250],mmio32,<addr>[,options[,uartclk]]
1222 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1223 uart[8250],0x<addr>[,options]
1224 Start an early, polled-mode console on the 8250/16550
1225 UART at the specified I/O port or MMIO address.
1226 MMIO inter-register address stride is either 8-bit
1227 (mmio) or 32-bit (mmio32 or mmio32be).
1228 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1229 to be equivalent to 'mmio'. 'options' are specified
1230 in the same format described for "console=ttyS<n>"; if
1231 unspecified, the h/w is not initialized. 'uartclk' is
1232 the uart clock frequency; if unspecified, it is set
1233 to 'BASE_BAUD' * 16.
1234
1235 pl011,<addr>
1236 pl011,mmio32,<addr>
1237 Start an early, polled-mode console on a pl011 serial
1238 port at the specified address. The pl011 serial port
1239 must already be setup and configured. Options are not
1240 yet supported. If 'mmio32' is specified, then only
1241 the driver will use only 32-bit accessors to read/write
1242 the device registers.
1243
1244 liteuart,<addr>
1245 Start an early console on a litex serial port at the
1246 specified address. The serial port must already be
1247 setup and configured. Options are not yet supported.
1248
1249 meson,<addr>
1250 Start an early, polled-mode console on a meson serial
1251 port at the specified address. The serial port must
1252 already be setup and configured. Options are not yet
1253 supported.
1254
1255 msm_serial,<addr>
1256 Start an early, polled-mode console on an msm serial
1257 port at the specified address. The serial port
1258 must already be setup and configured. Options are not
1259 yet supported.
1260
1261 msm_serial_dm,<addr>
1262 Start an early, polled-mode console on an msm serial
1263 dm port at the specified address. The serial port
1264 must already be setup and configured. Options are not
1265 yet supported.
1266
1267 owl,<addr>
1268 Start an early, polled-mode console on a serial port
1269 of an Actions Semi SoC, such as S500 or S900, at the
1270 specified address. The serial port must already be
1271 setup and configured. Options are not yet supported.
1272
1273 rda,<addr>
1274 Start an early, polled-mode console on a serial port
1275 of an RDA Micro SoC, such as RDA8810PL, at the
1276 specified address. The serial port must already be
1277 setup and configured. Options are not yet supported.
1278
1279 sbi
1280 Use RISC-V SBI (Supervisor Binary Interface) for early
1281 console.
1282
1283 smh Use ARM semihosting calls for early console.
1284
1285 s3c2410,<addr>
1286 s3c2412,<addr>
1287 s3c2440,<addr>
1288 s3c6400,<addr>
1289 s5pv210,<addr>
1290 exynos4210,<addr>
1291 Use early console provided by serial driver available
1292 on Samsung SoCs, requires selecting proper type and
1293 a correct base address of the selected UART port. The
1294 serial port must already be setup and configured.
1295 Options are not yet supported.
1296
1297 lantiq,<addr>
1298 Start an early, polled-mode console on a lantiq serial
1299 (lqasc) port at the specified address. The serial port
1300 must already be setup and configured. Options are not
1301 yet supported.
1302
1303 lpuart,<addr>
1304 lpuart32,<addr>
1305 Use early console provided by Freescale LP UART driver
1306 found on Freescale Vybrid and QorIQ LS1021A processors.
1307 A valid base address must be provided, and the serial
1308 port must already be setup and configured.
1309
1310 ec_imx21,<addr>
1311 ec_imx6q,<addr>
1312 Start an early, polled-mode, output-only console on the
1313 Freescale i.MX UART at the specified address. The UART
1314 must already be setup and configured.
1315
1316 ar3700_uart,<addr>
1317 Start an early, polled-mode console on the
1318 Armada 3700 serial port at the specified
1319 address. The serial port must already be setup
1320 and configured. Options are not yet supported.
1321
1322 qcom_geni,<addr>
1323 Start an early, polled-mode console on a Qualcomm
1324 Generic Interface (GENI) based serial port at the
1325 specified address. The serial port must already be
1326 setup and configured. Options are not yet supported.
1327
1328 efifb,[options]
1329 Start an early, unaccelerated console on the EFI
1330 memory mapped framebuffer (if available). On cache
1331 coherent non-x86 systems that use system memory for
1332 the framebuffer, pass the 'ram' option so that it is
1333 mapped with the correct attributes.
1334
1335 linflex,<addr>
1336 Use early console provided by Freescale LINFlexD UART
1337 serial driver for NXP S32V234 SoCs. A valid base
1338 address must be provided, and the serial port must
1339 already be setup and configured.
1340
1341 earlyprintk= [X86,SH,ARM,M68k,S390]
1342 earlyprintk=vga
1343 earlyprintk=sclp
1344 earlyprintk=xen
1345 earlyprintk=serial[,ttySn[,baudrate]]
1346 earlyprintk=serial[,0x...[,baudrate]]
1347 earlyprintk=ttySn[,baudrate]
1348 earlyprintk=dbgp[debugController#]
1349 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1350 earlyprintk=xdbc[xhciController#]
1351 earlyprintk=bios
1352
1353 earlyprintk is useful when the kernel crashes before
1354 the normal console is initialized. It is not enabled by
1355 default because it has some cosmetic problems.
1356
1357 Append ",keep" to not disable it when the real console
1358 takes over.
1359
1360 Only one of vga, serial, or usb debug port can
1361 be used at a time.
1362
1363 Currently only ttyS0 and ttyS1 may be specified by
1364 name. Other I/O ports may be explicitly specified
1365 on some architectures (x86 and arm at least) by
1366 replacing ttySn with an I/O port address, like this:
1367 earlyprintk=serial,0x1008,115200
1368 You can find the port for a given device in
1369 /proc/tty/driver/serial:
1370 2: uart:ST16650V2 port:00001008 irq:18 ...
1371
1372 Interaction with the standard serial driver is not
1373 very good.
1374
1375 The VGA output is eventually overwritten by
1376 the real console.
1377
1378 The xen option can only be used in Xen domains.
1379
1380 The sclp output can only be used on s390.
1381
1382 The bios output can only be used on SuperH.
1383
1384 The optional "force" to "pciserial" enables use of a
1385 PCI device even when its classcode is not of the
1386 UART class.
1387
1388 edac_report= [HW,EDAC] Control how to report EDAC event
1389 Format: {"on" | "off" | "force"}
1390 on: enable EDAC to report H/W event. May be overridden
1391 by other higher priority error reporting module.
1392 off: disable H/W event reporting through EDAC.
1393 force: enforce the use of EDAC to report H/W event.
1394 default: on.
1395
1396 edd= [EDD]
1397 Format: {"off" | "on" | "skip[mbr]"}
1398
1399 efi= [EFI]
1400 Format: { "debug", "disable_early_pci_dma",
1401 "nochunk", "noruntime", "nosoftreserve",
1402 "novamap", "no_disable_early_pci_dma" }
1403 debug: enable misc debug output.
1404 disable_early_pci_dma: disable the busmaster bit on all
1405 PCI bridges while in the EFI boot stub.
1406 nochunk: disable reading files in "chunks" in the EFI
1407 boot stub, as chunking can cause problems with some
1408 firmware implementations.
1409 noruntime : disable EFI runtime services support
1410 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1411 attribute may cause the kernel to reserve the
1412 memory range for a memory mapping driver to
1413 claim. Specify efi=nosoftreserve to disable this
1414 reservation and treat the memory by its base type
1415 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1416 novamap: do not call SetVirtualAddressMap().
1417 no_disable_early_pci_dma: Leave the busmaster bit set
1418 on all PCI bridges while in the EFI boot stub
1419
1420 efi_no_storage_paranoia [EFI; X86]
1421 Using this parameter you can use more than 50% of
1422 your efi variable storage. Use this parameter only if
1423 you are really sure that your UEFI does sane gc and
1424 fulfills the spec otherwise your board may brick.
1425
1426 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1427 Add arbitrary attribute to specific memory range by
1428 updating original EFI memory map.
1429 Region of memory which aa attribute is added to is
1430 from ss to ss+nn.
1431
1432 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1433 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1434 attribute is added to range 0x100000000-0x180000000 and
1435 0x10a0000000-0x1120000000.
1436
1437 If efi_fake_mem=8G@9G:0x40000 is specified, the
1438 EFI_MEMORY_SP(0x40000) attribute is added to
1439 range 0x240000000-0x43fffffff.
1440
1441 Using this parameter you can do debugging of EFI memmap
1442 related features. For example, you can do debugging of
1443 Address Range Mirroring feature even if your box
1444 doesn't support it, or mark specific memory as
1445 "soft reserved".
1446
1447 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1448 that is to be dynamically loaded by Linux. If there are
1449 multiple variables with the same name but with different
1450 vendor GUIDs, all of them will be loaded. See
1451 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1452
1453
1454 eisa_irq_edge= [PARISC,HW]
1455 See header of drivers/parisc/eisa.c.
1456
1457 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1458 Format: ekgdboc=kbd
1459
1460 This is designed to be used in conjunction with
1461 the boot argument: earlyprintk=vga
1462
1463 This parameter works in place of the kgdboc parameter
1464 but can only be used if the backing tty is available
1465 very early in the boot process. For early debugging
1466 via a serial port see kgdboc_earlycon instead.
1467
1468 elanfreq= [X86-32]
1469 See comment before function elanfreq_setup() in
1470 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1471
1472 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390]
1473 Specifies physical address of start of kernel core
1474 image elf header and optionally the size. Generally
1475 kexec loader will pass this option to capture kernel.
1476 See Documentation/admin-guide/kdump/kdump.rst for details.
1477
1478 enable_mtrr_cleanup [X86]
1479 The kernel tries to adjust MTRR layout from continuous
1480 to discrete, to make X server driver able to add WB
1481 entry later. This parameter enables that.
1482
1483 enable_timer_pin_1 [X86]
1484 Enable PIN 1 of APIC timer
1485 Can be useful to work around chipset bugs
1486 (in particular on some ATI chipsets).
1487 The kernel tries to set a reasonable default.
1488
1489 enforcing= [SELINUX] Set initial enforcing status.
1490 Format: {"0" | "1"}
1491 See security/selinux/Kconfig help text.
1492 0 -- permissive (log only, no denials).
1493 1 -- enforcing (deny and log).
1494 Default value is 0.
1495 Value can be changed at runtime via
1496 /sys/fs/selinux/enforce.
1497
1498 erst_disable [ACPI]
1499 Disable Error Record Serialization Table (ERST)
1500 support.
1501
1502 ether= [HW,NET] Ethernet cards parameters
1503 This option is obsoleted by the "netdev=" option, which
1504 has equivalent usage. See its documentation for details.
1505
1506 evm= [EVM]
1507 Format: { "fix" }
1508 Permit 'security.evm' to be updated regardless of
1509 current integrity status.
1510
1511 early_page_ext [KNL] Enforces page_ext initialization to earlier
1512 stages so cover more early boot allocations.
1513 Please note that as side effect some optimizations
1514 might be disabled to achieve that (e.g. parallelized
1515 memory initialization is disabled) so the boot process
1516 might take longer, especially on systems with a lot of
1517 memory. Available with CONFIG_PAGE_EXTENSION=y.
1518
1519 failslab=
1520 fail_usercopy=
1521 fail_page_alloc=
1522 fail_make_request=[KNL]
1523 General fault injection mechanism.
1524 Format: <interval>,<probability>,<space>,<times>
1525 See also Documentation/fault-injection/.
1526
1527 fb_tunnels= [NET]
1528 Format: { initns | none }
1529 See Documentation/admin-guide/sysctl/net.rst for
1530 fb_tunnels_only_for_init_ns
1531
1532 floppy= [HW]
1533 See Documentation/admin-guide/blockdev/floppy.rst.
1534
1535 forcepae [X86-32]
1536 Forcefully enable Physical Address Extension (PAE).
1537 Many Pentium M systems disable PAE but may have a
1538 functionally usable PAE implementation.
1539 Warning: use of this parameter will taint the kernel
1540 and may cause unknown problems.
1541
1542 ftrace=[tracer]
1543 [FTRACE] will set and start the specified tracer
1544 as early as possible in order to facilitate early
1545 boot debugging.
1546
1547 ftrace_boot_snapshot
1548 [FTRACE] On boot up, a snapshot will be taken of the
1549 ftrace ring buffer that can be read at:
1550 /sys/kernel/tracing/snapshot.
1551 This is useful if you need tracing information from kernel
1552 boot up that is likely to be overridden by user space
1553 start up functionality.
1554
1555 Optionally, the snapshot can also be defined for a tracing
1556 instance that was created by the trace_instance= command
1557 line parameter.
1558
1559 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1560
1561 The above will cause the "foo" tracing instance to trigger
1562 a snapshot at the end of boot up.
1563
1564 ftrace_dump_on_oops[=orig_cpu]
1565 [FTRACE] will dump the trace buffers on oops.
1566 If no parameter is passed, ftrace will dump
1567 buffers of all CPUs, but if you pass orig_cpu, it will
1568 dump only the buffer of the CPU that triggered the
1569 oops.
1570
1571 ftrace_filter=[function-list]
1572 [FTRACE] Limit the functions traced by the function
1573 tracer at boot up. function-list is a comma-separated
1574 list of functions. This list can be changed at run
1575 time by the set_ftrace_filter file in the debugfs
1576 tracing directory.
1577
1578 ftrace_notrace=[function-list]
1579 [FTRACE] Do not trace the functions specified in
1580 function-list. This list can be changed at run time
1581 by the set_ftrace_notrace file in the debugfs
1582 tracing directory.
1583
1584 ftrace_graph_filter=[function-list]
1585 [FTRACE] Limit the top level callers functions traced
1586 by the function graph tracer at boot up.
1587 function-list is a comma-separated list of functions
1588 that can be changed at run time by the
1589 set_graph_function file in the debugfs tracing directory.
1590
1591 ftrace_graph_notrace=[function-list]
1592 [FTRACE] Do not trace from the functions specified in
1593 function-list. This list is a comma-separated list of
1594 functions that can be changed at run time by the
1595 set_graph_notrace file in the debugfs tracing directory.
1596
1597 ftrace_graph_max_depth=<uint>
1598 [FTRACE] Used with the function graph tracer. This is
1599 the max depth it will trace into a function. This value
1600 can be changed at run time by the max_graph_depth file
1601 in the tracefs tracing directory. default: 0 (no limit)
1602
1603 fw_devlink= [KNL] Create device links between consumer and supplier
1604 devices by scanning the firmware to infer the
1605 consumer/supplier relationships. This feature is
1606 especially useful when drivers are loaded as modules as
1607 it ensures proper ordering of tasks like device probing
1608 (suppliers first, then consumers), supplier boot state
1609 clean up (only after all consumers have probed),
1610 suspend/resume & runtime PM (consumers first, then
1611 suppliers).
1612 Format: { off | permissive | on | rpm }
1613 off -- Don't create device links from firmware info.
1614 permissive -- Create device links from firmware info
1615 but use it only for ordering boot state clean
1616 up (sync_state() calls).
1617 on -- Create device links from firmware info and use it
1618 to enforce probe and suspend/resume ordering.
1619 rpm -- Like "on", but also use to order runtime PM.
1620
1621 fw_devlink.strict=<bool>
1622 [KNL] Treat all inferred dependencies as mandatory
1623 dependencies. This only applies for fw_devlink=on|rpm.
1624 Format: <bool>
1625
1626 fw_devlink.sync_state =
1627 [KNL] When all devices that could probe have finished
1628 probing, this parameter controls what to do with
1629 devices that haven't yet received their sync_state()
1630 calls.
1631 Format: { strict | timeout }
1632 strict -- Default. Continue waiting on consumers to
1633 probe successfully.
1634 timeout -- Give up waiting on consumers and call
1635 sync_state() on any devices that haven't yet
1636 received their sync_state() calls after
1637 deferred_probe_timeout has expired or by
1638 late_initcall() if !CONFIG_MODULES.
1639
1640 gamecon.map[2|3]=
1641 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1642 support via parallel port (up to 5 devices per port)
1643 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1644 See also Documentation/input/devices/joystick-parport.rst
1645
1646 gamma= [HW,DRM]
1647
1648 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1649 Format: off | on
1650 default: on
1651
1652 gather_data_sampling=
1653 [X86,INTEL] Control the Gather Data Sampling (GDS)
1654 mitigation.
1655
1656 Gather Data Sampling is a hardware vulnerability which
1657 allows unprivileged speculative access to data which was
1658 previously stored in vector registers.
1659
1660 This issue is mitigated by default in updated microcode.
1661 The mitigation may have a performance impact but can be
1662 disabled. On systems without the microcode mitigation
1663 disabling AVX serves as a mitigation.
1664
1665 force: Disable AVX to mitigate systems without
1666 microcode mitigation. No effect if the microcode
1667 mitigation is present. Known to cause crashes in
1668 userspace with buggy AVX enumeration.
1669
1670 off: Disable GDS mitigation.
1671
1672 gcov_persist= [GCOV] When non-zero (default), profiling data for
1673 kernel modules is saved and remains accessible via
1674 debugfs, even when the module is unloaded/reloaded.
1675 When zero, profiling data is discarded and associated
1676 debugfs files are removed at module unload time.
1677
1678 goldfish [X86] Enable the goldfish android emulator platform.
1679 Don't use this when you are not running on the
1680 android emulator
1681
1682 gpio-mockup.gpio_mockup_ranges
1683 [HW] Sets the ranges of gpiochip of for this device.
1684 Format: <start1>,<end1>,<start2>,<end2>...
1685 gpio-mockup.gpio_mockup_named_lines
1686 [HW] Let the driver know GPIO lines should be named.
1687
1688 gpt [EFI] Forces disk with valid GPT signature but
1689 invalid Protective MBR to be treated as GPT. If the
1690 primary GPT is corrupted, it enables the backup/alternate
1691 GPT to be used instead.
1692
1693 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1694 the "Enable 0" bit of the configuration register.
1695 Format: 0 | 1
1696 Default: 0
1697 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1698 the "Enable 0" bit of the configuration register.
1699 Format: 0 | 1
1700 Default: 0
1701 grcan.select= [HW] Select which physical interface to use.
1702 Format: 0 | 1
1703 Default: 0
1704 grcan.txsize= [HW] Sets the size of the tx buffer.
1705 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1706 Default: 1024
1707 grcan.rxsize= [HW] Sets the size of the rx buffer.
1708 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1709 Default: 1024
1710
1711 hardened_usercopy=
1712 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1713 hardening is enabled for this boot. Hardened
1714 usercopy checking is used to protect the kernel
1715 from reading or writing beyond known memory
1716 allocation boundaries as a proactive defense
1717 against bounds-checking flaws in the kernel's
1718 copy_to_user()/copy_from_user() interface.
1719 on Perform hardened usercopy checks (default).
1720 off Disable hardened usercopy checks.
1721
1722 hardlockup_all_cpu_backtrace=
1723 [KNL] Should the hard-lockup detector generate
1724 backtraces on all cpus.
1725 Format: 0 | 1
1726
1727 hashdist= [KNL,NUMA] Large hashes allocated during boot
1728 are distributed across NUMA nodes. Defaults on
1729 for 64-bit NUMA, off otherwise.
1730 Format: 0 | 1 (for off | on)
1731
1732 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1733
1734 hd= [EIDE] (E)IDE hard drive subsystem geometry
1735 Format: <cyl>,<head>,<sect>
1736
1737 hest_disable [ACPI]
1738 Disable Hardware Error Source Table (HEST) support;
1739 corresponding firmware-first mode error processing
1740 logic will be disabled.
1741
1742 hibernate= [HIBERNATION]
1743 noresume Don't check if there's a hibernation image
1744 present during boot.
1745 nocompress Don't compress/decompress hibernation images.
1746 no Disable hibernation and resume.
1747 protect_image Turn on image protection during restoration
1748 (that will set all pages holding image data
1749 during restoration read-only).
1750
1751 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1752 size of <nn>. This works even on boxes that have no
1753 highmem otherwise. This also works to reduce highmem
1754 size on bigger boxes.
1755
1756 highres= [KNL] Enable/disable high resolution timer mode.
1757 Valid parameters: "on", "off"
1758 Default: "on"
1759
1760 hlt [BUGS=ARM,SH]
1761
1762 hostname= [KNL] Set the hostname (aka UTS nodename).
1763 Format: <string>
1764 This allows setting the system's hostname during early
1765 startup. This sets the name returned by gethostname.
1766 Using this parameter to set the hostname makes it
1767 possible to ensure the hostname is correctly set before
1768 any userspace processes run, avoiding the possibility
1769 that a process may call gethostname before the hostname
1770 has been explicitly set, resulting in the calling
1771 process getting an incorrect result. The string must
1772 not exceed the maximum allowed hostname length (usually
1773 64 characters) and will be truncated otherwise.
1774
1775 hpet= [X86-32,HPET] option to control HPET usage
1776 Format: { enable (default) | disable | force |
1777 verbose }
1778 disable: disable HPET and use PIT instead
1779 force: allow force enabled of undocumented chips (ICH4,
1780 VIA, nVidia)
1781 verbose: show contents of HPET registers during setup
1782
1783 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1784 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1785
1786 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1787 If this follows hugepagesz (below), it specifies
1788 the number of pages of hugepagesz to be allocated.
1789 If this is the first HugeTLB parameter on the command
1790 line, it specifies the number of pages to allocate for
1791 the default huge page size. If using node format, the
1792 number of pages to allocate per-node can be specified.
1793 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1794 Format: <integer> or (node format)
1795 <node>:<integer>[,<node>:<integer>]
1796
1797 hugepagesz=
1798 [HW] The size of the HugeTLB pages. This is used in
1799 conjunction with hugepages (above) to allocate huge
1800 pages of a specific size at boot. The pair
1801 hugepagesz=X hugepages=Y can be specified once for
1802 each supported huge page size. Huge page sizes are
1803 architecture dependent. See also
1804 Documentation/admin-guide/mm/hugetlbpage.rst.
1805 Format: size[KMG]
1806
1807 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1808 of gigantic hugepages. Or using node format, the size
1809 of a CMA area per node can be specified.
1810 Format: nn[KMGTPE] or (node format)
1811 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1812
1813 Reserve a CMA area of given size and allocate gigantic
1814 hugepages using the CMA allocator. If enabled, the
1815 boot-time allocation of gigantic hugepages is skipped.
1816
1817 hugetlb_free_vmemmap=
1818 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1819 enabled.
1820 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1821 Allows heavy hugetlb users to free up some more
1822 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1823 Format: { on | off (default) }
1824
1825 on: enable HVO
1826 off: disable HVO
1827
1828 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1829 the default is on.
1830
1831 Note that the vmemmap pages may be allocated from the added
1832 memory block itself when memory_hotplug.memmap_on_memory is
1833 enabled, those vmemmap pages cannot be optimized even if this
1834 feature is enabled. Other vmemmap pages not allocated from
1835 the added memory block itself do not be affected.
1836
1837 hung_task_panic=
1838 [KNL] Should the hung task detector generate panics.
1839 Format: 0 | 1
1840
1841 A value of 1 instructs the kernel to panic when a
1842 hung task is detected. The default value is controlled
1843 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1844 option. The value selected by this boot parameter can
1845 be changed later by the kernel.hung_task_panic sysctl.
1846
1847 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1848 terminal devices. Valid values: 0..8
1849 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1850 If specified, z/VM IUCV HVC accepts connections
1851 from listed z/VM user IDs only.
1852
1853 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1854 which allow the hypervisor to 'idle' the
1855 guest on lock contention.
1856
1857 i2c_bus= [HW] Override the default board specific I2C bus speed
1858 or register an additional I2C bus that is not
1859 registered from board initialization code.
1860 Format:
1861 <bus_id>,<clkrate>
1862
1863 i8042.debug [HW] Toggle i8042 debug mode
1864 i8042.unmask_kbd_data
1865 [HW] Enable printing of interrupt data from the KBD port
1866 (disabled by default, and as a pre-condition
1867 requires that i8042.debug=1 be enabled)
1868 i8042.direct [HW] Put keyboard port into non-translated mode
1869 i8042.dumbkbd [HW] Pretend that controller can only read data from
1870 keyboard and cannot control its state
1871 (Don't attempt to blink the leds)
1872 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1873 i8042.nokbd [HW] Don't check/create keyboard port
1874 i8042.noloop [HW] Disable the AUX Loopback command while probing
1875 for the AUX port
1876 i8042.nomux [HW] Don't check presence of an active multiplexing
1877 controller
1878 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1879 controllers
1880 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1881 i8042.reset [HW] Reset the controller during init, cleanup and
1882 suspend-to-ram transitions, only during s2r
1883 transitions, or never reset
1884 Format: { 1 | Y | y | 0 | N | n }
1885 1, Y, y: always reset controller
1886 0, N, n: don't ever reset controller
1887 Default: only on s2r transitions on x86; most other
1888 architectures force reset to be always executed
1889 i8042.unlock [HW] Unlock (ignore) the keylock
1890 i8042.kbdreset [HW] Reset device connected to KBD port
1891 i8042.probe_defer
1892 [HW] Allow deferred probing upon i8042 probe errors
1893
1894 i810= [HW,DRM]
1895
1896 i915.invert_brightness=
1897 [DRM] Invert the sense of the variable that is used to
1898 set the brightness of the panel backlight. Normally a
1899 brightness value of 0 indicates backlight switched off,
1900 and the maximum of the brightness value sets the backlight
1901 to maximum brightness. If this parameter is set to 0
1902 (default) and the machine requires it, or this parameter
1903 is set to 1, a brightness value of 0 sets the backlight
1904 to maximum brightness, and the maximum of the brightness
1905 value switches the backlight off.
1906 -1 -- never invert brightness
1907 0 -- machine default
1908 1 -- force brightness inversion
1909
1910 ia32_emulation= [X86-64]
1911 Format: <bool>
1912 When true, allows loading 32-bit programs and executing 32-bit
1913 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
1914 boot time. When false, unconditionally disables IA32 emulation.
1915
1916 icn= [HW,ISDN]
1917 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1918
1919
1920 idle= [X86]
1921 Format: idle=poll, idle=halt, idle=nomwait
1922 Poll forces a polling idle loop that can slightly
1923 improve the performance of waking up a idle CPU, but
1924 will use a lot of power and make the system run hot.
1925 Not recommended.
1926 idle=halt: Halt is forced to be used for CPU idle.
1927 In such case C2/C3 won't be used again.
1928 idle=nomwait: Disable mwait for CPU C-states
1929
1930 idxd.sva= [HW]
1931 Format: <bool>
1932 Allow force disabling of Shared Virtual Memory (SVA)
1933 support for the idxd driver. By default it is set to
1934 true (1).
1935
1936 idxd.tc_override= [HW]
1937 Format: <bool>
1938 Allow override of default traffic class configuration
1939 for the device. By default it is set to false (0).
1940
1941 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1942 Format: { strict | legacy | 2008 | relaxed }
1943 Default: strict
1944
1945 Choose which programs will be accepted for execution
1946 based on the IEEE 754 NaN encoding(s) supported by
1947 the FPU and the NaN encoding requested with the value
1948 of an ELF file header flag individually set by each
1949 binary. Hardware implementations are permitted to
1950 support either or both of the legacy and the 2008 NaN
1951 encoding mode.
1952
1953 Available settings are as follows:
1954 strict accept binaries that request a NaN encoding
1955 supported by the FPU
1956 legacy only accept legacy-NaN binaries, if supported
1957 by the FPU
1958 2008 only accept 2008-NaN binaries, if supported
1959 by the FPU
1960 relaxed accept any binaries regardless of whether
1961 supported by the FPU
1962
1963 The FPU emulator is always able to support both NaN
1964 encodings, so if no FPU hardware is present or it has
1965 been disabled with 'nofpu', then the settings of
1966 'legacy' and '2008' strap the emulator accordingly,
1967 'relaxed' straps the emulator for both legacy-NaN and
1968 2008-NaN, whereas 'strict' enables legacy-NaN only on
1969 legacy processors and both NaN encodings on MIPS32 or
1970 MIPS64 CPUs.
1971
1972 The setting for ABS.fmt/NEG.fmt instruction execution
1973 mode generally follows that for the NaN encoding,
1974 except where unsupported by hardware.
1975
1976 ignore_loglevel [KNL]
1977 Ignore loglevel setting - this will print /all/
1978 kernel messages to the console. Useful for debugging.
1979 We also add it as printk module parameter, so users
1980 could change it dynamically, usually by
1981 /sys/module/printk/parameters/ignore_loglevel.
1982
1983 ignore_rlimit_data
1984 Ignore RLIMIT_DATA setting for data mappings,
1985 print warning at first misuse. Can be changed via
1986 /sys/module/kernel/parameters/ignore_rlimit_data.
1987
1988 ihash_entries= [KNL]
1989 Set number of hash buckets for inode cache.
1990
1991 ima_appraise= [IMA] appraise integrity measurements
1992 Format: { "off" | "enforce" | "fix" | "log" }
1993 default: "enforce"
1994
1995 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1996 The builtin appraise policy appraises all files
1997 owned by uid=0.
1998
1999 ima_canonical_fmt [IMA]
2000 Use the canonical format for the binary runtime
2001 measurements, instead of host native format.
2002
2003 ima_hash= [IMA]
2004 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2005 | sha512 | ... }
2006 default: "sha1"
2007
2008 The list of supported hash algorithms is defined
2009 in crypto/hash_info.h.
2010
2011 ima_policy= [IMA]
2012 The builtin policies to load during IMA setup.
2013 Format: "tcb | appraise_tcb | secure_boot |
2014 fail_securely | critical_data"
2015
2016 The "tcb" policy measures all programs exec'd, files
2017 mmap'd for exec, and all files opened with the read
2018 mode bit set by either the effective uid (euid=0) or
2019 uid=0.
2020
2021 The "appraise_tcb" policy appraises the integrity of
2022 all files owned by root.
2023
2024 The "secure_boot" policy appraises the integrity
2025 of files (eg. kexec kernel image, kernel modules,
2026 firmware, policy, etc) based on file signatures.
2027
2028 The "fail_securely" policy forces file signature
2029 verification failure also on privileged mounted
2030 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2031 flag.
2032
2033 The "critical_data" policy measures kernel integrity
2034 critical data.
2035
2036 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2037 Load a policy which meets the needs of the Trusted
2038 Computing Base. This means IMA will measure all
2039 programs exec'd, files mmap'd for exec, and all files
2040 opened for read by uid=0.
2041
2042 ima_template= [IMA]
2043 Select one of defined IMA measurements template formats.
2044 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2045 "ima-sigv2" }
2046 Default: "ima-ng"
2047
2048 ima_template_fmt=
2049 [IMA] Define a custom template format.
2050 Format: { "field1|...|fieldN" }
2051
2052 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2053 Format: <min_file_size>
2054 Set the minimal file size for using asynchronous hash.
2055 If left unspecified, ahash usage is disabled.
2056
2057 ahash performance varies for different data sizes on
2058 different crypto accelerators. This option can be used
2059 to achieve the best performance for a particular HW.
2060
2061 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2062 Format: <bufsize>
2063 Set hashing buffer size. Default: 4k.
2064
2065 ahash performance varies for different chunk sizes on
2066 different crypto accelerators. This option can be used
2067 to achieve best performance for particular HW.
2068
2069 init= [KNL]
2070 Format: <full_path>
2071 Run specified binary instead of /sbin/init as init
2072 process.
2073
2074 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2075 for working out where the kernel is dying during
2076 startup.
2077
2078 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2079 initcall functions. Useful for debugging built-in
2080 modules and initcalls.
2081
2082 initramfs_async= [KNL]
2083 Format: <bool>
2084 Default: 1
2085 This parameter controls whether the initramfs
2086 image is unpacked asynchronously, concurrently
2087 with devices being probed and
2088 initialized. This should normally just work,
2089 but as a debugging aid, one can get the
2090 historical behaviour of the initramfs
2091 unpacking being completed before device_ and
2092 late_ initcalls.
2093
2094 initrd= [BOOT] Specify the location of the initial ramdisk
2095
2096 initrdmem= [KNL] Specify a physical address and size from which to
2097 load the initrd. If an initrd is compiled in or
2098 specified in the bootparams, it takes priority over this
2099 setting.
2100 Format: ss[KMG],nn[KMG]
2101 Default is 0, 0
2102
2103 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
2104 zeroes.
2105 Format: 0 | 1
2106 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2107
2108 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
2109 Format: 0 | 1
2110 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2111
2112 init_pkru= [X86] Specify the default memory protection keys rights
2113 register contents for all processes. 0x55555554 by
2114 default (disallow access to all but pkey 0). Can
2115 override in debugfs after boot.
2116
2117 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2118 Format: <irq>
2119
2120 int_pln_enable [X86] Enable power limit notification interrupt
2121
2122 integrity_audit=[IMA]
2123 Format: { "0" | "1" }
2124 0 -- basic integrity auditing messages. (Default)
2125 1 -- additional integrity auditing messages.
2126
2127 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2128 on
2129 Enable intel iommu driver.
2130 off
2131 Disable intel iommu driver.
2132 igfx_off [Default Off]
2133 By default, gfx is mapped as normal device. If a gfx
2134 device has a dedicated DMAR unit, the DMAR unit is
2135 bypassed by not enabling DMAR with this option. In
2136 this case, gfx device will use physical address for
2137 DMA.
2138 strict [Default Off]
2139 Deprecated, equivalent to iommu.strict=1.
2140 sp_off [Default Off]
2141 By default, super page will be supported if Intel IOMMU
2142 has the capability. With this option, super page will
2143 not be supported.
2144 sm_on
2145 Enable the Intel IOMMU scalable mode if the hardware
2146 advertises that it has support for the scalable mode
2147 translation.
2148 sm_off
2149 Disallow use of the Intel IOMMU scalable mode.
2150 tboot_noforce [Default Off]
2151 Do not force the Intel IOMMU enabled under tboot.
2152 By default, tboot will force Intel IOMMU on, which
2153 could harm performance of some high-throughput
2154 devices like 40GBit network cards, even if identity
2155 mapping is enabled.
2156 Note that using this option lowers the security
2157 provided by tboot because it makes the system
2158 vulnerable to DMA attacks.
2159
2160 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2161 0 disables intel_idle and fall back on acpi_idle.
2162 1 to 9 specify maximum depth of C-state.
2163
2164 intel_pstate= [X86]
2165 disable
2166 Do not enable intel_pstate as the default
2167 scaling driver for the supported processors
2168 active
2169 Use intel_pstate driver to bypass the scaling
2170 governors layer of cpufreq and provides it own
2171 algorithms for p-state selection. There are two
2172 P-state selection algorithms provided by
2173 intel_pstate in the active mode: powersave and
2174 performance. The way they both operate depends
2175 on whether or not the hardware managed P-states
2176 (HWP) feature has been enabled in the processor
2177 and possibly on the processor model.
2178 passive
2179 Use intel_pstate as a scaling driver, but configure it
2180 to work with generic cpufreq governors (instead of
2181 enabling its internal governor). This mode cannot be
2182 used along with the hardware-managed P-states (HWP)
2183 feature.
2184 force
2185 Enable intel_pstate on systems that prohibit it by default
2186 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2187 instead of acpi-cpufreq may disable platform features, such
2188 as thermal controls and power capping, that rely on ACPI
2189 P-States information being indicated to OSPM and therefore
2190 should be used with caution. This option does not work with
2191 processors that aren't supported by the intel_pstate driver
2192 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2193 no_hwp
2194 Do not enable hardware P state control (HWP)
2195 if available.
2196 hwp_only
2197 Only load intel_pstate on systems which support
2198 hardware P state control (HWP) if available.
2199 support_acpi_ppc
2200 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2201 Description Table, specifies preferred power management
2202 profile as "Enterprise Server" or "Performance Server",
2203 then this feature is turned on by default.
2204 per_cpu_perf_limits
2205 Allow per-logical-CPU P-State performance control limits using
2206 cpufreq sysfs interface
2207
2208 intremap= [X86-64, Intel-IOMMU]
2209 on enable Interrupt Remapping (default)
2210 off disable Interrupt Remapping
2211 nosid disable Source ID checking
2212 no_x2apic_optout
2213 BIOS x2APIC opt-out request will be ignored
2214 nopost disable Interrupt Posting
2215
2216 iomem= Disable strict checking of access to MMIO memory
2217 strict regions from userspace.
2218 relaxed
2219
2220 iommu= [X86]
2221 off
2222 force
2223 noforce
2224 biomerge
2225 panic
2226 nopanic
2227 merge
2228 nomerge
2229 soft
2230 pt [X86]
2231 nopt [X86]
2232 nobypass [PPC/POWERNV]
2233 Disable IOMMU bypass, using IOMMU for PCI devices.
2234
2235 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2236 Format: { "0" | "1" }
2237 0 - Try to allocate a 32-bit DMA address first, before
2238 falling back to the full range if needed.
2239 1 - Allocate directly from the full usable range,
2240 forcing Dual Address Cycle for PCI cards supporting
2241 greater than 32-bit addressing.
2242
2243 iommu.strict= [ARM64, X86, S390] Configure TLB invalidation behaviour
2244 Format: { "0" | "1" }
2245 0 - Lazy mode.
2246 Request that DMA unmap operations use deferred
2247 invalidation of hardware TLBs, for increased
2248 throughput at the cost of reduced device isolation.
2249 Will fall back to strict mode if not supported by
2250 the relevant IOMMU driver.
2251 1 - Strict mode.
2252 DMA unmap operations invalidate IOMMU hardware TLBs
2253 synchronously.
2254 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2255 Note: on x86, strict mode specified via one of the
2256 legacy driver-specific options takes precedence.
2257
2258 iommu.passthrough=
2259 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2260 Format: { "0" | "1" }
2261 0 - Use IOMMU translation for DMA.
2262 1 - Bypass the IOMMU for DMA.
2263 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2264
2265 io7= [HW] IO7 for Marvel-based Alpha systems
2266 See comment before marvel_specify_io7 in
2267 arch/alpha/kernel/core_marvel.c.
2268
2269 io_delay= [X86] I/O delay method
2270 0x80
2271 Standard port 0x80 based delay
2272 0xed
2273 Alternate port 0xed based delay (needed on some systems)
2274 udelay
2275 Simple two microseconds delay
2276 none
2277 No delay
2278
2279 ip= [IP_PNP]
2280 See Documentation/admin-guide/nfs/nfsroot.rst.
2281
2282 ipcmni_extend [KNL] Extend the maximum number of unique System V
2283 IPC identifiers from 32,768 to 16,777,216.
2284
2285 irqaffinity= [SMP] Set the default irq affinity mask
2286 The argument is a cpu list, as described above.
2287
2288 irqchip.gicv2_force_probe=
2289 [ARM, ARM64]
2290 Format: <bool>
2291 Force the kernel to look for the second 4kB page
2292 of a GICv2 controller even if the memory range
2293 exposed by the device tree is too small.
2294
2295 irqchip.gicv3_nolpi=
2296 [ARM, ARM64]
2297 Force the kernel to ignore the availability of
2298 LPIs (and by consequence ITSs). Intended for system
2299 that use the kernel as a bootloader, and thus want
2300 to let secondary kernels in charge of setting up
2301 LPIs.
2302
2303 irqchip.gicv3_pseudo_nmi= [ARM64]
2304 Enables support for pseudo-NMIs in the kernel. This
2305 requires the kernel to be built with
2306 CONFIG_ARM64_PSEUDO_NMI.
2307
2308 irqfixup [HW]
2309 When an interrupt is not handled search all handlers
2310 for it. Intended to get systems with badly broken
2311 firmware running.
2312
2313 irqpoll [HW]
2314 When an interrupt is not handled search all handlers
2315 for it. Also check all handlers each timer
2316 interrupt. Intended to get systems with badly broken
2317 firmware running.
2318
2319 isapnp= [ISAPNP]
2320 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2321
2322 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2323 [Deprecated - use cpusets instead]
2324 Format: [flag-list,]<cpu-list>
2325
2326 Specify one or more CPUs to isolate from disturbances
2327 specified in the flag list (default: domain):
2328
2329 nohz
2330 Disable the tick when a single task runs.
2331
2332 A residual 1Hz tick is offloaded to workqueues, which you
2333 need to affine to housekeeping through the global
2334 workqueue's affinity configured via the
2335 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2336 by using the 'domain' flag described below.
2337
2338 NOTE: by default the global workqueue runs on all CPUs,
2339 so to protect individual CPUs the 'cpumask' file has to
2340 be configured manually after bootup.
2341
2342 domain
2343 Isolate from the general SMP balancing and scheduling
2344 algorithms. Note that performing domain isolation this way
2345 is irreversible: it's not possible to bring back a CPU to
2346 the domains once isolated through isolcpus. It's strongly
2347 advised to use cpusets instead to disable scheduler load
2348 balancing through the "cpuset.sched_load_balance" file.
2349 It offers a much more flexible interface where CPUs can
2350 move in and out of an isolated set anytime.
2351
2352 You can move a process onto or off an "isolated" CPU via
2353 the CPU affinity syscalls or cpuset.
2354 <cpu number> begins at 0 and the maximum value is
2355 "number of CPUs in system - 1".
2356
2357 managed_irq
2358
2359 Isolate from being targeted by managed interrupts
2360 which have an interrupt mask containing isolated
2361 CPUs. The affinity of managed interrupts is
2362 handled by the kernel and cannot be changed via
2363 the /proc/irq/* interfaces.
2364
2365 This isolation is best effort and only effective
2366 if the automatically assigned interrupt mask of a
2367 device queue contains isolated and housekeeping
2368 CPUs. If housekeeping CPUs are online then such
2369 interrupts are directed to the housekeeping CPU
2370 so that IO submitted on the housekeeping CPU
2371 cannot disturb the isolated CPU.
2372
2373 If a queue's affinity mask contains only isolated
2374 CPUs then this parameter has no effect on the
2375 interrupt routing decision, though interrupts are
2376 only delivered when tasks running on those
2377 isolated CPUs submit IO. IO submitted on
2378 housekeeping CPUs has no influence on those
2379 queues.
2380
2381 The format of <cpu-list> is described above.
2382
2383 iucv= [HW,NET]
2384
2385 ivrs_ioapic [HW,X86-64]
2386 Provide an override to the IOAPIC-ID<->DEVICE-ID
2387 mapping provided in the IVRS ACPI table.
2388 By default, PCI segment is 0, and can be omitted.
2389
2390 For example, to map IOAPIC-ID decimal 10 to
2391 PCI segment 0x1 and PCI device 00:14.0,
2392 write the parameter as:
2393 ivrs_ioapic=10@0001:00:14.0
2394
2395 Deprecated formats:
2396 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2397 write the parameter as:
2398 ivrs_ioapic[10]=00:14.0
2399 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2400 PCI device 00:14.0 write the parameter as:
2401 ivrs_ioapic[10]=0001:00:14.0
2402
2403 ivrs_hpet [HW,X86-64]
2404 Provide an override to the HPET-ID<->DEVICE-ID
2405 mapping provided in the IVRS ACPI table.
2406 By default, PCI segment is 0, and can be omitted.
2407
2408 For example, to map HPET-ID decimal 10 to
2409 PCI segment 0x1 and PCI device 00:14.0,
2410 write the parameter as:
2411 ivrs_hpet=10@0001:00:14.0
2412
2413 Deprecated formats:
2414 * To map HPET-ID decimal 0 to PCI device 00:14.0
2415 write the parameter as:
2416 ivrs_hpet[0]=00:14.0
2417 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2418 PCI device 00:14.0 write the parameter as:
2419 ivrs_ioapic[10]=0001:00:14.0
2420
2421 ivrs_acpihid [HW,X86-64]
2422 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2423 mapping provided in the IVRS ACPI table.
2424 By default, PCI segment is 0, and can be omitted.
2425
2426 For example, to map UART-HID:UID AMD0020:0 to
2427 PCI segment 0x1 and PCI device ID 00:14.5,
2428 write the parameter as:
2429 ivrs_acpihid=AMD0020:0@0001:00:14.5
2430
2431 Deprecated formats:
2432 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2433 PCI device ID 00:14.5, write the parameter as:
2434 ivrs_acpihid[00:14.5]=AMD0020:0
2435 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2436 PCI device ID 00:14.5, write the parameter as:
2437 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2438
2439 js= [HW,JOY] Analog joystick
2440 See Documentation/input/joydev/joystick.rst.
2441
2442 kasan_multi_shot
2443 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2444 report on every invalid memory access. Without this
2445 parameter KASAN will print report only for the first
2446 invalid access.
2447
2448 keep_bootcon [KNL]
2449 Do not unregister boot console at start. This is only
2450 useful for debugging when something happens in the window
2451 between unregistering the boot console and initializing
2452 the real console.
2453
2454 keepinitrd [HW,ARM] See retain_initrd.
2455
2456 kernelcore= [KNL,X86,IA-64,PPC]
2457 Format: nn[KMGTPE] | nn% | "mirror"
2458 This parameter specifies the amount of memory usable by
2459 the kernel for non-movable allocations. The requested
2460 amount is spread evenly throughout all nodes in the
2461 system as ZONE_NORMAL. The remaining memory is used for
2462 movable memory in its own zone, ZONE_MOVABLE. In the
2463 event, a node is too small to have both ZONE_NORMAL and
2464 ZONE_MOVABLE, kernelcore memory will take priority and
2465 other nodes will have a larger ZONE_MOVABLE.
2466
2467 ZONE_MOVABLE is used for the allocation of pages that
2468 may be reclaimed or moved by the page migration
2469 subsystem. Note that allocations like PTEs-from-HighMem
2470 still use the HighMem zone if it exists, and the Normal
2471 zone if it does not.
2472
2473 It is possible to specify the exact amount of memory in
2474 the form of "nn[KMGTPE]", a percentage of total system
2475 memory in the form of "nn%", or "mirror". If "mirror"
2476 option is specified, mirrored (reliable) memory is used
2477 for non-movable allocations and remaining memory is used
2478 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2479 are exclusive, so you cannot specify multiple forms.
2480
2481 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2482 Format: <Controller#>[,poll interval]
2483 The controller # is the number of the ehci usb debug
2484 port as it is probed via PCI. The poll interval is
2485 optional and is the number seconds in between
2486 each poll cycle to the debug port in case you need
2487 the functionality for interrupting the kernel with
2488 gdb or control-c on the dbgp connection. When
2489 not using this parameter you use sysrq-g to break into
2490 the kernel debugger.
2491
2492 kgdboc= [KGDB,HW] kgdb over consoles.
2493 Requires a tty driver that supports console polling,
2494 or a supported polling keyboard driver (non-usb).
2495 Serial only format: <serial_device>[,baud]
2496 keyboard only format: kbd
2497 keyboard and serial format: kbd,<serial_device>[,baud]
2498 Optional Kernel mode setting:
2499 kms, kbd format: kms,kbd
2500 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2501
2502 kgdboc_earlycon= [KGDB,HW]
2503 If the boot console provides the ability to read
2504 characters and can work in polling mode, you can use
2505 this parameter to tell kgdb to use it as a backend
2506 until the normal console is registered. Intended to
2507 be used together with the kgdboc parameter which
2508 specifies the normal console to transition to.
2509
2510 The name of the early console should be specified
2511 as the value of this parameter. Note that the name of
2512 the early console might be different than the tty
2513 name passed to kgdboc. It's OK to leave the value
2514 blank and the first boot console that implements
2515 read() will be picked.
2516
2517 kgdbwait [KGDB] Stop kernel execution and enter the
2518 kernel debugger at the earliest opportunity.
2519
2520 kmac= [MIPS] Korina ethernet MAC address.
2521 Configure the RouterBoard 532 series on-chip
2522 Ethernet adapter MAC address.
2523
2524 kmemleak= [KNL] Boot-time kmemleak enable/disable
2525 Valid arguments: on, off
2526 Default: on
2527 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2528 the default is off.
2529
2530 kprobe_event=[probe-list]
2531 [FTRACE] Add kprobe events and enable at boot time.
2532 The probe-list is a semicolon delimited list of probe
2533 definitions. Each definition is same as kprobe_events
2534 interface, but the parameters are comma delimited.
2535 For example, to add a kprobe event on vfs_read with
2536 arg1 and arg2, add to the command line;
2537
2538 kprobe_event=p,vfs_read,$arg1,$arg2
2539
2540 See also Documentation/trace/kprobetrace.rst "Kernel
2541 Boot Parameter" section.
2542
2543 kpti= [ARM64] Control page table isolation of user
2544 and kernel address spaces.
2545 Default: enabled on cores which need mitigation.
2546 0: force disabled
2547 1: force enabled
2548
2549 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2550 CONFIG_KUNIT to be set to be fully enabled. The
2551 default value can be overridden via
2552 KUNIT_DEFAULT_ENABLED.
2553 Default is 1 (enabled)
2554
2555 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2556 Default is 0 (don't ignore, but inject #GP)
2557
2558 kvm.eager_page_split=
2559 [KVM,X86] Controls whether or not KVM will try to
2560 proactively split all huge pages during dirty logging.
2561 Eager page splitting reduces interruptions to vCPU
2562 execution by eliminating the write-protection faults
2563 and MMU lock contention that would otherwise be
2564 required to split huge pages lazily.
2565
2566 VM workloads that rarely perform writes or that write
2567 only to a small region of VM memory may benefit from
2568 disabling eager page splitting to allow huge pages to
2569 still be used for reads.
2570
2571 The behavior of eager page splitting depends on whether
2572 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2573 disabled, all huge pages in a memslot will be eagerly
2574 split when dirty logging is enabled on that memslot. If
2575 enabled, eager page splitting will be performed during
2576 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2577 cleared.
2578
2579 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2580
2581 Default is Y (on).
2582
2583 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2584 Default is false (don't support).
2585
2586 kvm.nx_huge_pages=
2587 [KVM] Controls the software workaround for the
2588 X86_BUG_ITLB_MULTIHIT bug.
2589 force : Always deploy workaround.
2590 off : Never deploy workaround.
2591 auto : Deploy workaround based on the presence of
2592 X86_BUG_ITLB_MULTIHIT.
2593
2594 Default is 'auto'.
2595
2596 If the software workaround is enabled for the host,
2597 guests do need not to enable it for nested guests.
2598
2599 kvm.nx_huge_pages_recovery_ratio=
2600 [KVM] Controls how many 4KiB pages are periodically zapped
2601 back to huge pages. 0 disables the recovery, otherwise if
2602 the value is N KVM will zap 1/Nth of the 4KiB pages every
2603 period (see below). The default is 60.
2604
2605 kvm.nx_huge_pages_recovery_period_ms=
2606 [KVM] Controls the time period at which KVM zaps 4KiB pages
2607 back to huge pages. If the value is a non-zero N, KVM will
2608 zap a portion (see ratio above) of the pages every N msecs.
2609 If the value is 0 (the default), KVM will pick a period based
2610 on the ratio, such that a page is zapped after 1 hour on average.
2611
2612 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2613 KVM/SVM. Default is 1 (enabled).
2614
2615 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2616 a.k.a. Two-Dimensional Page Tables. Default is 1
2617 (enabled). Disable by KVM if hardware lacks support
2618 for NPT.
2619
2620 kvm-arm.mode=
2621 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2622
2623 none: Forcefully disable KVM.
2624
2625 nvhe: Standard nVHE-based mode, without support for
2626 protected guests.
2627
2628 protected: nVHE-based mode with support for guests whose
2629 state is kept private from the host.
2630
2631 nested: VHE-based mode with support for nested
2632 virtualization. Requires at least ARMv8.3
2633 hardware.
2634
2635 Defaults to VHE/nVHE based on hardware support. Setting
2636 mode to "protected" will disable kexec and hibernation
2637 for the host. "nested" is experimental and should be
2638 used with extreme caution.
2639
2640 kvm-arm.vgic_v3_group0_trap=
2641 [KVM,ARM] Trap guest accesses to GICv3 group-0
2642 system registers
2643
2644 kvm-arm.vgic_v3_group1_trap=
2645 [KVM,ARM] Trap guest accesses to GICv3 group-1
2646 system registers
2647
2648 kvm-arm.vgic_v3_common_trap=
2649 [KVM,ARM] Trap guest accesses to GICv3 common
2650 system registers
2651
2652 kvm-arm.vgic_v4_enable=
2653 [KVM,ARM] Allow use of GICv4 for direct injection of
2654 LPIs.
2655
2656 kvm_cma_resv_ratio=n [PPC]
2657 Reserves given percentage from system memory area for
2658 contiguous memory allocation for KVM hash pagetable
2659 allocation.
2660 By default it reserves 5% of total system memory.
2661 Format: <integer>
2662 Default: 5
2663
2664 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2665 a.k.a. Two-Dimensional Page Tables. Default is 1
2666 (enabled). Disable by KVM if hardware lacks support
2667 for EPT.
2668
2669 kvm-intel.emulate_invalid_guest_state=
2670 [KVM,Intel] Control whether to emulate invalid guest
2671 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2672 as guest state is never invalid for unrestricted
2673 guests. This param doesn't apply to nested guests (L2),
2674 as KVM never emulates invalid L2 guest state.
2675 Default is 1 (enabled).
2676
2677 kvm-intel.flexpriority=
2678 [KVM,Intel] Control KVM's use of FlexPriority feature
2679 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2680 hardware lacks support for it.
2681
2682 kvm-intel.nested=
2683 [KVM,Intel] Control nested virtualization feature in
2684 KVM/VMX. Default is 1 (enabled).
2685
2686 kvm-intel.unrestricted_guest=
2687 [KVM,Intel] Control KVM's use of unrestricted guest
2688 feature (virtualized real and unpaged mode). Default
2689 is 1 (enabled). Disable by KVM if EPT is disabled or
2690 hardware lacks support for it.
2691
2692 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2693 CVE-2018-3620.
2694
2695 Valid arguments: never, cond, always
2696
2697 always: L1D cache flush on every VMENTER.
2698 cond: Flush L1D on VMENTER only when the code between
2699 VMEXIT and VMENTER can leak host memory.
2700 never: Disables the mitigation
2701
2702 Default is cond (do L1 cache flush in specific instances)
2703
2704 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2705 Identification feature (tagged TLBs). Default is 1
2706 (enabled). Disable by KVM if hardware lacks support
2707 for it.
2708
2709 l1d_flush= [X86,INTEL]
2710 Control mitigation for L1D based snooping vulnerability.
2711
2712 Certain CPUs are vulnerable to an exploit against CPU
2713 internal buffers which can forward information to a
2714 disclosure gadget under certain conditions.
2715
2716 In vulnerable processors, the speculatively
2717 forwarded data can be used in a cache side channel
2718 attack, to access data to which the attacker does
2719 not have direct access.
2720
2721 This parameter controls the mitigation. The
2722 options are:
2723
2724 on - enable the interface for the mitigation
2725
2726 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2727 affected CPUs
2728
2729 The kernel PTE inversion protection is unconditionally
2730 enabled and cannot be disabled.
2731
2732 full
2733 Provides all available mitigations for the
2734 L1TF vulnerability. Disables SMT and
2735 enables all mitigations in the
2736 hypervisors, i.e. unconditional L1D flush.
2737
2738 SMT control and L1D flush control via the
2739 sysfs interface is still possible after
2740 boot. Hypervisors will issue a warning
2741 when the first VM is started in a
2742 potentially insecure configuration,
2743 i.e. SMT enabled or L1D flush disabled.
2744
2745 full,force
2746 Same as 'full', but disables SMT and L1D
2747 flush runtime control. Implies the
2748 'nosmt=force' command line option.
2749 (i.e. sysfs control of SMT is disabled.)
2750
2751 flush
2752 Leaves SMT enabled and enables the default
2753 hypervisor mitigation, i.e. conditional
2754 L1D flush.
2755
2756 SMT control and L1D flush control via the
2757 sysfs interface is still possible after
2758 boot. Hypervisors will issue a warning
2759 when the first VM is started in a
2760 potentially insecure configuration,
2761 i.e. SMT enabled or L1D flush disabled.
2762
2763 flush,nosmt
2764
2765 Disables SMT and enables the default
2766 hypervisor mitigation.
2767
2768 SMT control and L1D flush control via the
2769 sysfs interface is still possible after
2770 boot. Hypervisors will issue a warning
2771 when the first VM is started in a
2772 potentially insecure configuration,
2773 i.e. SMT enabled or L1D flush disabled.
2774
2775 flush,nowarn
2776 Same as 'flush', but hypervisors will not
2777 warn when a VM is started in a potentially
2778 insecure configuration.
2779
2780 off
2781 Disables hypervisor mitigations and doesn't
2782 emit any warnings.
2783 It also drops the swap size and available
2784 RAM limit restriction on both hypervisor and
2785 bare metal.
2786
2787 Default is 'flush'.
2788
2789 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2790
2791 l2cr= [PPC]
2792
2793 l3cr= [PPC]
2794
2795 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2796 disabled it.
2797
2798 lapic= [X86,APIC] Do not use TSC deadline
2799 value for LAPIC timer one-shot implementation. Default
2800 back to the programmable timer unit in the LAPIC.
2801 Format: notscdeadline
2802
2803 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2804 in C2 power state.
2805
2806 libata.dma= [LIBATA] DMA control
2807 libata.dma=0 Disable all PATA and SATA DMA
2808 libata.dma=1 PATA and SATA Disk DMA only
2809 libata.dma=2 ATAPI (CDROM) DMA only
2810 libata.dma=4 Compact Flash DMA only
2811 Combinations also work, so libata.dma=3 enables DMA
2812 for disks and CDROMs, but not CFs.
2813
2814 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2815 libata.ignore_hpa=0 keep BIOS limits (default)
2816 libata.ignore_hpa=1 ignore limits, using full disk
2817
2818 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2819 when set.
2820 Format: <int>
2821
2822 libata.force= [LIBATA] Force configurations. The format is a comma-
2823 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2824 PORT and DEVICE are decimal numbers matching port, link
2825 or device. Basically, it matches the ATA ID string
2826 printed on console by libata. If the whole ID part is
2827 omitted, the last PORT and DEVICE values are used. If
2828 ID hasn't been specified yet, the configuration applies
2829 to all ports, links and devices.
2830
2831 If only DEVICE is omitted, the parameter applies to
2832 the port and all links and devices behind it. DEVICE
2833 number of 0 either selects the first device or the
2834 first fan-out link behind PMP device. It does not
2835 select the host link. DEVICE number of 15 selects the
2836 host link and device attached to it.
2837
2838 The VAL specifies the configuration to force. As long
2839 as there is no ambiguity, shortcut notation is allowed.
2840 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2841 The following configurations can be forced.
2842
2843 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2844 Any ID with matching PORT is used.
2845
2846 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2847
2848 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2849 udma[/][16,25,33,44,66,100,133] notation is also
2850 allowed.
2851
2852 * nohrst, nosrst, norst: suppress hard, soft and both
2853 resets.
2854
2855 * rstonce: only attempt one reset during hot-unplug
2856 link recovery.
2857
2858 * [no]dbdelay: Enable or disable the extra 200ms delay
2859 before debouncing a link PHY and device presence
2860 detection.
2861
2862 * [no]ncq: Turn on or off NCQ.
2863
2864 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2865
2866 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2867
2868 * [no]trim: Enable or disable (unqueued) TRIM.
2869
2870 * trim_zero: Indicate that TRIM command zeroes data.
2871
2872 * max_trim_128m: Set 128M maximum trim size limit.
2873
2874 * [no]dma: Turn on or off DMA transfers.
2875
2876 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2877
2878 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2879 commands that are not a multiple of 16 bytes.
2880
2881 * [no]dmalog: Enable or disable the use of the
2882 READ LOG DMA EXT command to access logs.
2883
2884 * [no]iddevlog: Enable or disable access to the
2885 identify device data log.
2886
2887 * [no]logdir: Enable or disable access to the general
2888 purpose log directory.
2889
2890 * max_sec_128: Set transfer size limit to 128 sectors.
2891
2892 * max_sec_1024: Set or clear transfer size limit to
2893 1024 sectors.
2894
2895 * max_sec_lba48: Set or clear transfer size limit to
2896 65535 sectors.
2897
2898 * [no]lpm: Enable or disable link power management.
2899
2900 * [no]setxfer: Indicate if transfer speed mode setting
2901 should be skipped.
2902
2903 * [no]fua: Disable or enable FUA (Force Unit Access)
2904 support for devices supporting this feature.
2905
2906 * dump_id: Dump IDENTIFY data.
2907
2908 * disable: Disable this device.
2909
2910 If there are multiple matching configurations changing
2911 the same attribute, the last one is used.
2912
2913 load_ramdisk= [RAM] [Deprecated]
2914
2915 lockd.nlm_grace_period=P [NFS] Assign grace period.
2916 Format: <integer>
2917
2918 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2919 Format: <integer>
2920
2921 lockd.nlm_timeout=T [NFS] Assign timeout value.
2922 Format: <integer>
2923
2924 lockd.nlm_udpport=M [NFS] Assign UDP port.
2925 Format: <integer>
2926
2927 lockdown= [SECURITY]
2928 { integrity | confidentiality }
2929 Enable the kernel lockdown feature. If set to
2930 integrity, kernel features that allow userland to
2931 modify the running kernel are disabled. If set to
2932 confidentiality, kernel features that allow userland
2933 to extract confidential information from the kernel
2934 are also disabled.
2935
2936 locktorture.acq_writer_lim= [KNL]
2937 Set the time limit in jiffies for a lock
2938 acquisition. Acquisitions exceeding this limit
2939 will result in a splat once they do complete.
2940
2941 locktorture.bind_readers= [KNL]
2942 Specify the list of CPUs to which the readers are
2943 to be bound.
2944
2945 locktorture.bind_writers= [KNL]
2946 Specify the list of CPUs to which the writers are
2947 to be bound.
2948
2949 locktorture.call_rcu_chains= [KNL]
2950 Specify the number of self-propagating call_rcu()
2951 chains to set up. These are used to ensure that
2952 there is a high probability of an RCU grace period
2953 in progress at any given time. Defaults to 0,
2954 which disables these call_rcu() chains.
2955
2956 locktorture.long_hold= [KNL]
2957 Specify the duration in milliseconds for the
2958 occasional long-duration lock hold time. Defaults
2959 to 100 milliseconds. Select 0 to disable.
2960
2961 locktorture.nested_locks= [KNL]
2962 Specify the maximum lock nesting depth that
2963 locktorture is to exercise, up to a limit of 8
2964 (MAX_NESTED_LOCKS). Specify zero to disable.
2965 Note that this parameter is ineffective on types
2966 of locks that do not support nested acquisition.
2967
2968 locktorture.nreaders_stress= [KNL]
2969 Set the number of locking read-acquisition kthreads.
2970 Defaults to being automatically set based on the
2971 number of online CPUs.
2972
2973 locktorture.nwriters_stress= [KNL]
2974 Set the number of locking write-acquisition kthreads.
2975
2976 locktorture.onoff_holdoff= [KNL]
2977 Set time (s) after boot for CPU-hotplug testing.
2978
2979 locktorture.onoff_interval= [KNL]
2980 Set time (s) between CPU-hotplug operations, or
2981 zero to disable CPU-hotplug testing.
2982
2983 locktorture.rt_boost= [KNL]
2984 Do periodic testing of real-time lock priority
2985 boosting. Select 0 to disable, 1 to boost
2986 only rt_mutex, and 2 to boost unconditionally.
2987 Defaults to 2, which might seem to be an
2988 odd choice, but which should be harmless for
2989 non-real-time spinlocks, due to their disabling
2990 of preemption. Note that non-realtime mutexes
2991 disable boosting.
2992
2993 locktorture.rt_boost_factor= [KNL]
2994 Number that determines how often and for how
2995 long priority boosting is exercised. This is
2996 scaled down by the number of writers, so that the
2997 number of boosts per unit time remains roughly
2998 constant as the number of writers increases.
2999 On the other hand, the duration of each boost
3000 increases with the number of writers.
3001
3002 locktorture.shuffle_interval= [KNL]
3003 Set task-shuffle interval (jiffies). Shuffling
3004 tasks allows some CPUs to go into dyntick-idle
3005 mode during the locktorture test.
3006
3007 locktorture.shutdown_secs= [KNL]
3008 Set time (s) after boot system shutdown. This
3009 is useful for hands-off automated testing.
3010
3011 locktorture.stat_interval= [KNL]
3012 Time (s) between statistics printk()s.
3013
3014 locktorture.stutter= [KNL]
3015 Time (s) to stutter testing, for example,
3016 specifying five seconds causes the test to run for
3017 five seconds, wait for five seconds, and so on.
3018 This tests the locking primitive's ability to
3019 transition abruptly to and from idle.
3020
3021 locktorture.torture_type= [KNL]
3022 Specify the locking implementation to test.
3023
3024 locktorture.verbose= [KNL]
3025 Enable additional printk() statements.
3026
3027 locktorture.writer_fifo= [KNL]
3028 Run the write-side locktorture kthreads at
3029 sched_set_fifo() real-time priority.
3030
3031 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3032 Format: <irq>
3033
3034 loglevel= All Kernel Messages with a loglevel smaller than the
3035 console loglevel will be printed to the console. It can
3036 also be changed with klogd or other programs. The
3037 loglevels are defined as follows:
3038
3039 0 (KERN_EMERG) system is unusable
3040 1 (KERN_ALERT) action must be taken immediately
3041 2 (KERN_CRIT) critical conditions
3042 3 (KERN_ERR) error conditions
3043 4 (KERN_WARNING) warning conditions
3044 5 (KERN_NOTICE) normal but significant condition
3045 6 (KERN_INFO) informational
3046 7 (KERN_DEBUG) debug-level messages
3047
3048 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
3049 in bytes. n must be a power of two and greater
3050 than the minimal size. The minimal size is defined
3051 by LOG_BUF_SHIFT kernel config parameter. There is
3052 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
3053 that allows to increase the default size depending on
3054 the number of CPUs. See init/Kconfig for more details.
3055
3056 logo.nologo [FB] Disables display of the built-in Linux logo.
3057 This may be used to provide more screen space for
3058 kernel log messages and is useful when debugging
3059 kernel boot problems.
3060
3061 lp=0 [LP] Specify parallel ports to use, e.g,
3062 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3063 lp=reset first parallel port). 'lp=0' disables the
3064 lp=auto printer driver. 'lp=reset' (which can be
3065 specified in addition to the ports) causes
3066 attached printers to be reset. Using
3067 lp=port1,port2,... specifies the parallel ports
3068 to associate lp devices with, starting with
3069 lp0. A port specification may be 'none' to skip
3070 that lp device, or a parport name such as
3071 'parport0'. Specifying 'lp=auto' instead of a
3072 port specification list means that device IDs
3073 from each port should be examined, to see if
3074 an IEEE 1284-compliant printer is attached; if
3075 so, the driver will manage that printer.
3076 See also header of drivers/char/lp.c.
3077
3078 lpj=n [KNL]
3079 Sets loops_per_jiffy to given constant, thus avoiding
3080 time-consuming boot-time autodetection (up to 250 ms per
3081 CPU). 0 enables autodetection (default). To determine
3082 the correct value for your kernel, boot with normal
3083 autodetection and see what value is printed. Note that
3084 on SMP systems the preset will be applied to all CPUs,
3085 which is likely to cause problems if your CPUs need
3086 significantly divergent settings. An incorrect value
3087 will cause delays in the kernel to be wrong, leading to
3088 unpredictable I/O errors and other breakage. Although
3089 unlikely, in the extreme case this might damage your
3090 hardware.
3091
3092 ltpc= [NET]
3093 Format: <io>,<irq>,<dma>
3094
3095 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3096
3097 lsm=lsm1,...,lsmN
3098 [SECURITY] Choose order of LSM initialization. This
3099 overrides CONFIG_LSM, and the "security=" parameter.
3100
3101 machvec= [IA-64] Force the use of a particular machine-vector
3102 (machvec) in a generic kernel.
3103 Example: machvec=hpzx1
3104
3105 machtype= [Loongson] Share the same kernel image file between
3106 different yeeloong laptops.
3107 Example: machtype=lemote-yeeloong-2f-7inch
3108
3109 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
3110 than or equal to this physical address is ignored.
3111
3112 maxcpus= [SMP] Maximum number of processors that an SMP kernel
3113 will bring up during bootup. maxcpus=n : n >= 0 limits
3114 the kernel to bring up 'n' processors. Surely after
3115 bootup you can bring up the other plugged cpu by executing
3116 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3117 only takes effect during system bootup.
3118 While n=0 is a special case, it is equivalent to "nosmp",
3119 which also disables the IO APIC.
3120
3121 max_loop= [LOOP] The number of loop block devices that get
3122 (loop.max_loop) unconditionally pre-created at init time. The default
3123 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3124 of statically allocating a predefined number, loop
3125 devices can be requested on-demand with the
3126 /dev/loop-control interface.
3127
3128 mce [X86-32] Machine Check Exception
3129
3130 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
3131
3132 md= [HW] RAID subsystems devices and level
3133 See Documentation/admin-guide/md.rst.
3134
3135 mdacon= [MDA]
3136 Format: <first>,<last>
3137 Specifies range of consoles to be captured by the MDA.
3138
3139 mds= [X86,INTEL]
3140 Control mitigation for the Micro-architectural Data
3141 Sampling (MDS) vulnerability.
3142
3143 Certain CPUs are vulnerable to an exploit against CPU
3144 internal buffers which can forward information to a
3145 disclosure gadget under certain conditions.
3146
3147 In vulnerable processors, the speculatively
3148 forwarded data can be used in a cache side channel
3149 attack, to access data to which the attacker does
3150 not have direct access.
3151
3152 This parameter controls the MDS mitigation. The
3153 options are:
3154
3155 full - Enable MDS mitigation on vulnerable CPUs
3156 full,nosmt - Enable MDS mitigation and disable
3157 SMT on vulnerable CPUs
3158 off - Unconditionally disable MDS mitigation
3159
3160 On TAA-affected machines, mds=off can be prevented by
3161 an active TAA mitigation as both vulnerabilities are
3162 mitigated with the same mechanism so in order to disable
3163 this mitigation, you need to specify tsx_async_abort=off
3164 too.
3165
3166 Not specifying this option is equivalent to
3167 mds=full.
3168
3169 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3170
3171 mem=nn[KMG] [HEXAGON] Set the memory size.
3172 Must be specified, otherwise memory size will be 0.
3173
3174 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
3175 Amount of memory to be used in cases as follows:
3176
3177 1 for test;
3178 2 when the kernel is not able to see the whole system memory;
3179 3 memory that lies after 'mem=' boundary is excluded from
3180 the hypervisor, then assigned to KVM guests.
3181 4 to limit the memory available for kdump kernel.
3182
3183 [ARC,MICROBLAZE] - the limit applies only to low memory,
3184 high memory is not affected.
3185
3186 [ARM64] - only limits memory covered by the linear
3187 mapping. The NOMAP regions are not affected.
3188
3189 [X86] Work as limiting max address. Use together
3190 with memmap= to avoid physical address space collisions.
3191 Without memmap= PCI devices could be placed at addresses
3192 belonging to unused RAM.
3193
3194 Note that this only takes effects during boot time since
3195 in above case 3, memory may need be hot added after boot
3196 if system memory of hypervisor is not sufficient.
3197
3198 mem=nn[KMG]@ss[KMG]
3199 [ARM,MIPS] - override the memory layout reported by
3200 firmware.
3201 Define a memory region of size nn[KMG] starting at
3202 ss[KMG].
3203 Multiple different regions can be specified with
3204 multiple mem= parameters on the command line.
3205
3206 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3207 memory.
3208
3209 memblock=debug [KNL] Enable memblock debug messages.
3210
3211 memchunk=nn[KMG]
3212 [KNL,SH] Allow user to override the default size for
3213 per-device physically contiguous DMA buffers.
3214
3215 memhp_default_state=online/offline/online_kernel/online_movable
3216 [KNL] Set the initial state for the memory hotplug
3217 onlining policy. If not specified, the default value is
3218 set according to the
3219 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3220 option.
3221 See Documentation/admin-guide/mm/memory-hotplug.rst.
3222
3223 memmap=exactmap [KNL,X86] Enable setting of an exact
3224 E820 memory map, as specified by the user.
3225 Such memmap=exactmap lines can be constructed based on
3226 BIOS output or other requirements. See the memmap=nn@ss
3227 option description.
3228
3229 memmap=nn[KMG]@ss[KMG]
3230 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
3231 Region of memory to be used is from ss to ss+nn.
3232 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3233 which limits max address to nn[KMG].
3234 Multiple different regions can be specified,
3235 comma delimited.
3236 Example:
3237 memmap=100M@2G,100M#3G,1G!1024G
3238
3239 memmap=nn[KMG]#ss[KMG]
3240 [KNL,ACPI] Mark specific memory as ACPI data.
3241 Region of memory to be marked is from ss to ss+nn.
3242
3243 memmap=nn[KMG]$ss[KMG]
3244 [KNL,ACPI] Mark specific memory as reserved.
3245 Region of memory to be reserved is from ss to ss+nn.
3246 Example: Exclude memory from 0x18690000-0x1869ffff
3247 memmap=64K$0x18690000
3248 or
3249 memmap=0x10000$0x18690000
3250 Some bootloaders may need an escape character before '$',
3251 like Grub2, otherwise '$' and the following number
3252 will be eaten.
3253
3254 memmap=nn[KMG]!ss[KMG]
3255 [KNL,X86] Mark specific memory as protected.
3256 Region of memory to be used, from ss to ss+nn.
3257 The memory region may be marked as e820 type 12 (0xc)
3258 and is NVDIMM or ADR memory.
3259
3260 memmap=<size>%<offset>-<oldtype>+<newtype>
3261 [KNL,ACPI] Convert memory within the specified region
3262 from <oldtype> to <newtype>. If "-<oldtype>" is left
3263 out, the whole region will be marked as <newtype>,
3264 even if previously unavailable. If "+<newtype>" is left
3265 out, matching memory will be removed. Types are
3266 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3267 3 = ACPI, 12 = PRAM.
3268
3269 memory_corruption_check=0/1 [X86]
3270 Some BIOSes seem to corrupt the first 64k of
3271 memory when doing things like suspend/resume.
3272 Setting this option will scan the memory
3273 looking for corruption. Enabling this will
3274 both detect corruption and prevent the kernel
3275 from using the memory being corrupted.
3276 However, its intended as a diagnostic tool; if
3277 repeatable BIOS-originated corruption always
3278 affects the same memory, you can use memmap=
3279 to prevent the kernel from using that memory.
3280
3281 memory_corruption_check_size=size [X86]
3282 By default it checks for corruption in the low
3283 64k, making this memory unavailable for normal
3284 use. Use this parameter to scan for
3285 corruption in more or less memory.
3286
3287 memory_corruption_check_period=seconds [X86]
3288 By default it checks for corruption every 60
3289 seconds. Use this parameter to check at some
3290 other rate. 0 disables periodic checking.
3291
3292 memory_hotplug.memmap_on_memory
3293 [KNL,X86,ARM] Boolean flag to enable this feature.
3294 Format: {on | off (default)}
3295 When enabled, runtime hotplugged memory will
3296 allocate its internal metadata (struct pages,
3297 those vmemmap pages cannot be optimized even
3298 if hugetlb_free_vmemmap is enabled) from the
3299 hotadded memory which will allow to hotadd a
3300 lot of memory without requiring additional
3301 memory to do so.
3302 This feature is disabled by default because it
3303 has some implication on large (e.g. GB)
3304 allocations in some configurations (e.g. small
3305 memory blocks).
3306 The state of the flag can be read in
3307 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3308 Note that even when enabled, there are a few cases where
3309 the feature is not effective.
3310
3311 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
3312 Format: <integer>
3313 default : 0 <disable>
3314 Specifies the number of memtest passes to be
3315 performed. Each pass selects another test
3316 pattern from a given set of patterns. Memtest
3317 fills the memory with this pattern, validates
3318 memory contents and reserves bad memory
3319 regions that are detected.
3320
3321 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3322 Valid arguments: on, off
3323 Default (depends on kernel configuration option):
3324 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
3325 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
3326 mem_encrypt=on: Activate SME
3327 mem_encrypt=off: Do not activate SME
3328
3329 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3330 for details on when memory encryption can be activated.
3331
3332 mem_sleep_default= [SUSPEND] Default system suspend mode:
3333 s2idle - Suspend-To-Idle
3334 shallow - Power-On Suspend or equivalent (if supported)
3335 deep - Suspend-To-RAM or equivalent (if supported)
3336 See Documentation/admin-guide/pm/sleep-states.rst.
3337
3338 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3339 Multi-Function General Purpose Timers on AMD Geode
3340 platforms.
3341
3342 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3343 the BIOS has incorrectly applied a workaround. TinyBIOS
3344 version 0.98 is known to be affected, 0.99 fixes the
3345 problem by letting the user disable the workaround.
3346
3347 mga= [HW,DRM]
3348
3349 microcode.force_minrev= [X86]
3350 Format: <bool>
3351 Enable or disable the microcode minimal revision
3352 enforcement for the runtime microcode loader.
3353
3354 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3355 physical address is ignored.
3356
3357 mini2440= [ARM,HW,KNL]
3358 Format:[0..2][b][c][t]
3359 Default: "0tb"
3360 MINI2440 configuration specification:
3361 0 - The attached screen is the 3.5" TFT
3362 1 - The attached screen is the 7" TFT
3363 2 - The VGA Shield is attached (1024x768)
3364 Leaving out the screen size parameter will not load
3365 the TFT driver, and the framebuffer will be left
3366 unconfigured.
3367 b - Enable backlight. The TFT backlight pin will be
3368 linked to the kernel VESA blanking code and a GPIO
3369 LED. This parameter is not necessary when using the
3370 VGA shield.
3371 c - Enable the s3c camera interface.
3372 t - Reserved for enabling touchscreen support. The
3373 touchscreen support is not enabled in the mainstream
3374 kernel as of 2.6.30, a preliminary port can be found
3375 in the "bleeding edge" mini2440 support kernel at
3376 https://repo.or.cz/w/linux-2.6/mini2440.git
3377
3378 mitigations=
3379 [X86,PPC,S390,ARM64] Control optional mitigations for
3380 CPU vulnerabilities. This is a set of curated,
3381 arch-independent options, each of which is an
3382 aggregation of existing arch-specific options.
3383
3384 off
3385 Disable all optional CPU mitigations. This
3386 improves system performance, but it may also
3387 expose users to several CPU vulnerabilities.
3388 Equivalent to: if nokaslr then kpti=0 [ARM64]
3389 gather_data_sampling=off [X86]
3390 kvm.nx_huge_pages=off [X86]
3391 l1tf=off [X86]
3392 mds=off [X86]
3393 mmio_stale_data=off [X86]
3394 no_entry_flush [PPC]
3395 no_uaccess_flush [PPC]
3396 nobp=0 [S390]
3397 nopti [X86,PPC]
3398 nospectre_bhb [ARM64]
3399 nospectre_v1 [X86,PPC]
3400 nospectre_v2 [X86,PPC,S390,ARM64]
3401 retbleed=off [X86]
3402 spec_store_bypass_disable=off [X86,PPC]
3403 spectre_v2_user=off [X86]
3404 srbds=off [X86,INTEL]
3405 ssbd=force-off [ARM64]
3406 tsx_async_abort=off [X86]
3407
3408 Exceptions:
3409 This does not have any effect on
3410 kvm.nx_huge_pages when
3411 kvm.nx_huge_pages=force.
3412
3413 auto (default)
3414 Mitigate all CPU vulnerabilities, but leave SMT
3415 enabled, even if it's vulnerable. This is for
3416 users who don't want to be surprised by SMT
3417 getting disabled across kernel upgrades, or who
3418 have other ways of avoiding SMT-based attacks.
3419 Equivalent to: (default behavior)
3420
3421 auto,nosmt
3422 Mitigate all CPU vulnerabilities, disabling SMT
3423 if needed. This is for users who always want to
3424 be fully mitigated, even if it means losing SMT.
3425 Equivalent to: l1tf=flush,nosmt [X86]
3426 mds=full,nosmt [X86]
3427 tsx_async_abort=full,nosmt [X86]
3428 mmio_stale_data=full,nosmt [X86]
3429 retbleed=auto,nosmt [X86]
3430
3431 mminit_loglevel=
3432 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3433 parameter allows control of the logging verbosity for
3434 the additional memory initialisation checks. A value
3435 of 0 disables mminit logging and a level of 4 will
3436 log everything. Information is printed at KERN_DEBUG
3437 so loglevel=8 may also need to be specified.
3438
3439 mmio_stale_data=
3440 [X86,INTEL] Control mitigation for the Processor
3441 MMIO Stale Data vulnerabilities.
3442
3443 Processor MMIO Stale Data is a class of
3444 vulnerabilities that may expose data after an MMIO
3445 operation. Exposed data could originate or end in
3446 the same CPU buffers as affected by MDS and TAA.
3447 Therefore, similar to MDS and TAA, the mitigation
3448 is to clear the affected CPU buffers.
3449
3450 This parameter controls the mitigation. The
3451 options are:
3452
3453 full - Enable mitigation on vulnerable CPUs
3454
3455 full,nosmt - Enable mitigation and disable SMT on
3456 vulnerable CPUs.
3457
3458 off - Unconditionally disable mitigation
3459
3460 On MDS or TAA affected machines,
3461 mmio_stale_data=off can be prevented by an active
3462 MDS or TAA mitigation as these vulnerabilities are
3463 mitigated with the same mechanism so in order to
3464 disable this mitigation, you need to specify
3465 mds=off and tsx_async_abort=off too.
3466
3467 Not specifying this option is equivalent to
3468 mmio_stale_data=full.
3469
3470 For details see:
3471 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3472
3473 <module>.async_probe[=<bool>] [KNL]
3474 If no <bool> value is specified or if the value
3475 specified is not a valid <bool>, enable asynchronous
3476 probe on this module. Otherwise, enable/disable
3477 asynchronous probe on this module as indicated by the
3478 <bool> value. See also: module.async_probe
3479
3480 module.async_probe=<bool>
3481 [KNL] When set to true, modules will use async probing
3482 by default. To enable/disable async probing for a
3483 specific module, use the module specific control that
3484 is documented under <module>.async_probe. When both
3485 module.async_probe and <module>.async_probe are
3486 specified, <module>.async_probe takes precedence for
3487 the specific module.
3488
3489 module.enable_dups_trace
3490 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3491 this means that duplicate request_module() calls will
3492 trigger a WARN_ON() instead of a pr_warn(). Note that
3493 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3494 will always be issued and this option does nothing.
3495 module.sig_enforce
3496 [KNL] When CONFIG_MODULE_SIG is set, this means that
3497 modules without (valid) signatures will fail to load.
3498 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3499 is always true, so this option does nothing.
3500
3501 module_blacklist= [KNL] Do not load a comma-separated list of
3502 modules. Useful for debugging problem modules.
3503
3504 mousedev.tap_time=
3505 [MOUSE] Maximum time between finger touching and
3506 leaving touchpad surface for touch to be considered
3507 a tap and be reported as a left button click (for
3508 touchpads working in absolute mode only).
3509 Format: <msecs>
3510 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3511 reporting absolute coordinates, such as tablets
3512 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3513 reporting absolute coordinates, such as tablets
3514
3515 movablecore= [KNL,X86,IA-64,PPC]
3516 Format: nn[KMGTPE] | nn%
3517 This parameter is the complement to kernelcore=, it
3518 specifies the amount of memory used for migratable
3519 allocations. If both kernelcore and movablecore is
3520 specified, then kernelcore will be at *least* the
3521 specified value but may be more. If movablecore on its
3522 own is specified, the administrator must be careful
3523 that the amount of memory usable for all allocations
3524 is not too small.
3525
3526 movable_node [KNL] Boot-time switch to make hotplugable memory
3527 NUMA nodes to be movable. This means that the memory
3528 of such nodes will be usable only for movable
3529 allocations which rules out almost all kernel
3530 allocations. Use with caution!
3531
3532 MTD_Partition= [MTD]
3533 Format: <name>,<region-number>,<size>,<offset>
3534
3535 MTD_Region= [MTD] Format:
3536 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3537
3538 mtdparts= [MTD]
3539 See drivers/mtd/parsers/cmdlinepart.c
3540
3541 mtdset= [ARM]
3542 ARM/S3C2412 JIVE boot control
3543
3544 See arch/arm/mach-s3c/mach-jive.c
3545
3546 mtouchusb.raw_coordinates=
3547 [HW] Make the MicroTouch USB driver use raw coordinates
3548 ('y', default) or cooked coordinates ('n')
3549
3550 mtrr=debug [X86]
3551 Enable printing debug information related to MTRR
3552 registers at boot time.
3553
3554 mtrr_chunk_size=nn[KMG] [X86]
3555 used for mtrr cleanup. It is largest continuous chunk
3556 that could hold holes aka. UC entries.
3557
3558 mtrr_gran_size=nn[KMG] [X86]
3559 Used for mtrr cleanup. It is granularity of mtrr block.
3560 Default is 1.
3561 Large value could prevent small alignment from
3562 using up MTRRs.
3563
3564 mtrr_spare_reg_nr=n [X86]
3565 Format: <integer>
3566 Range: 0,7 : spare reg number
3567 Default : 1
3568 Used for mtrr cleanup. It is spare mtrr entries number.
3569 Set to 2 or more if your graphical card needs more.
3570
3571 multitce=off [PPC] This parameter disables the use of the pSeries
3572 firmware feature for updating multiple TCE entries
3573 at a time.
3574
3575 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3576
3577 netdev= [NET] Network devices parameters
3578 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3579 Note that mem_start is often overloaded to mean
3580 something different and driver-specific.
3581 This usage is only documented in each driver source
3582 file if at all.
3583
3584 netpoll.carrier_timeout=
3585 [NET] Specifies amount of time (in seconds) that
3586 netpoll should wait for a carrier. By default netpoll
3587 waits 4 seconds.
3588
3589 nf_conntrack.acct=
3590 [NETFILTER] Enable connection tracking flow accounting
3591 0 to disable accounting
3592 1 to enable accounting
3593 Default value is 0.
3594
3595 nfs.cache_getent=
3596 [NFS] sets the pathname to the program which is used
3597 to update the NFS client cache entries.
3598
3599 nfs.cache_getent_timeout=
3600 [NFS] sets the timeout after which an attempt to
3601 update a cache entry is deemed to have failed.
3602
3603 nfs.callback_nr_threads=
3604 [NFSv4] set the total number of threads that the
3605 NFS client will assign to service NFSv4 callback
3606 requests.
3607
3608 nfs.callback_tcpport=
3609 [NFS] set the TCP port on which the NFSv4 callback
3610 channel should listen.
3611
3612 nfs.delay_retrans=
3613 [NFS] specifies the number of times the NFSv4 client
3614 retries the request before returning an EAGAIN error,
3615 after a reply of NFS4ERR_DELAY from the server.
3616 Only applies if the softerr mount option is enabled,
3617 and the specified value is >= 0.
3618
3619 nfs.enable_ino64=
3620 [NFS] enable 64-bit inode numbers.
3621 If zero, the NFS client will fake up a 32-bit inode
3622 number for the readdir() and stat() syscalls instead
3623 of returning the full 64-bit number.
3624 The default is to return 64-bit inode numbers.
3625
3626 nfs.idmap_cache_timeout=
3627 [NFS] set the maximum lifetime for idmapper cache
3628 entries.
3629
3630 nfs.max_session_cb_slots=
3631 [NFSv4.1] Sets the maximum number of session
3632 slots the client will assign to the callback
3633 channel. This determines the maximum number of
3634 callbacks the client will process in parallel for
3635 a particular server.
3636
3637 nfs.max_session_slots=
3638 [NFSv4.1] Sets the maximum number of session slots
3639 the client will attempt to negotiate with the server.
3640 This limits the number of simultaneous RPC requests
3641 that the client can send to the NFSv4.1 server.
3642 Note that there is little point in setting this
3643 value higher than the max_tcp_slot_table_limit.
3644
3645 nfs.nfs4_disable_idmapping=
3646 [NFSv4] When set to the default of '1', this option
3647 ensures that both the RPC level authentication
3648 scheme and the NFS level operations agree to use
3649 numeric uids/gids if the mount is using the
3650 'sec=sys' security flavour. In effect it is
3651 disabling idmapping, which can make migration from
3652 legacy NFSv2/v3 systems to NFSv4 easier.
3653 Servers that do not support this mode of operation
3654 will be autodetected by the client, and it will fall
3655 back to using the idmapper.
3656 To turn off this behaviour, set the value to '0'.
3657
3658 nfs.nfs4_unique_id=
3659 [NFS4] Specify an additional fixed unique ident-
3660 ification string that NFSv4 clients can insert into
3661 their nfs_client_id4 string. This is typically a
3662 UUID that is generated at system install time.
3663
3664 nfs.recover_lost_locks=
3665 [NFSv4] Attempt to recover locks that were lost due
3666 to a lease timeout on the server. Please note that
3667 doing this risks data corruption, since there are
3668 no guarantees that the file will remain unchanged
3669 after the locks are lost.
3670 If you want to enable the kernel legacy behaviour of
3671 attempting to recover these locks, then set this
3672 parameter to '1'.
3673 The default parameter value of '0' causes the kernel
3674 not to attempt recovery of lost locks.
3675
3676 nfs.send_implementation_id=
3677 [NFSv4.1] Send client implementation identification
3678 information in exchange_id requests.
3679 If zero, no implementation identification information
3680 will be sent.
3681 The default is to send the implementation identification
3682 information.
3683
3684 nfs4.layoutstats_timer=
3685 [NFSv4.2] Change the rate at which the kernel sends
3686 layoutstats to the pNFS metadata server.
3687
3688 Setting this to value to 0 causes the kernel to use
3689 whatever value is the default set by the layout
3690 driver. A non-zero value sets the minimum interval
3691 in seconds between layoutstats transmissions.
3692
3693 nfsd.inter_copy_offload_enable=
3694 [NFSv4.2] When set to 1, the server will support
3695 server-to-server copies for which this server is
3696 the destination of the copy.
3697
3698 nfsd.nfs4_disable_idmapping=
3699 [NFSv4] When set to the default of '1', the NFSv4
3700 server will return only numeric uids and gids to
3701 clients using auth_sys, and will accept numeric uids
3702 and gids from such clients. This is intended to ease
3703 migration from NFSv2/v3.
3704
3705 nfsd.nfsd4_ssc_umount_timeout=
3706 [NFSv4.2] When used as the destination of a
3707 server-to-server copy, knfsd temporarily mounts
3708 the source server. It caches the mount in case
3709 it will be needed again, and discards it if not
3710 used for the number of milliseconds specified by
3711 this parameter.
3712
3713 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3714 See Documentation/admin-guide/nfs/nfsroot.rst.
3715
3716 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3717 See Documentation/admin-guide/nfs/nfsroot.rst.
3718
3719 nfsrootdebug [NFS] enable nfsroot debugging messages.
3720 See Documentation/admin-guide/nfs/nfsroot.rst.
3721
3722 nmi_backtrace.backtrace_idle [KNL]
3723 Dump stacks even of idle CPUs in response to an
3724 NMI stack-backtrace request.
3725
3726 nmi_debug= [KNL,SH] Specify one or more actions to take
3727 when a NMI is triggered.
3728 Format: [state][,regs][,debounce][,die]
3729
3730 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3731 Format: [panic,][nopanic,][num]
3732 Valid num: 0 or 1
3733 0 - turn hardlockup detector in nmi_watchdog off
3734 1 - turn hardlockup detector in nmi_watchdog on
3735 When panic is specified, panic when an NMI watchdog
3736 timeout occurs (or 'nopanic' to not panic on an NMI
3737 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3738 To disable both hard and soft lockup detectors,
3739 please see 'nowatchdog'.
3740 This is useful when you use a panic=... timeout and
3741 need the box quickly up again.
3742
3743 These settings can be accessed at runtime via
3744 the nmi_watchdog and hardlockup_panic sysctls.
3745
3746 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3747 emulation library even if a 387 maths coprocessor
3748 is present.
3749
3750 no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces
3751 kernel to use 3-level paging instead.
3752
3753 no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces
3754 kernel to use 4-level paging instead.
3755
3756 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3757 caches in the slab allocator. Saves per-node memory,
3758 but will impact performance.
3759
3760 noalign [KNL,ARM]
3761
3762 noaltinstr [S390] Disables alternative instructions patching
3763 (CPU alternatives feature).
3764
3765 noapic [SMP,APIC] Tells the kernel to not make use of any
3766 IOAPICs that may be present in the system.
3767
3768 noautogroup Disable scheduler automatic task group creation.
3769
3770 nocache [ARM]
3771
3772 no_console_suspend
3773 [HW] Never suspend the console
3774 Disable suspending of consoles during suspend and
3775 hibernate operations. Once disabled, debugging
3776 messages can reach various consoles while the rest
3777 of the system is being put to sleep (ie, while
3778 debugging driver suspend/resume hooks). This may
3779 not work reliably with all consoles, but is known
3780 to work with serial and VGA consoles.
3781 To facilitate more flexible debugging, we also add
3782 console_suspend, a printk module parameter to control
3783 it. Users could use console_suspend (usually
3784 /sys/module/printk/parameters/console_suspend) to
3785 turn on/off it dynamically.
3786
3787 no_debug_objects
3788 [KNL] Disable object debugging
3789
3790 nodsp [SH] Disable hardware DSP at boot time.
3791
3792 noefi Disable EFI runtime services support.
3793
3794 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3795
3796 noexec [IA-64]
3797
3798 noexec32 [X86-64]
3799 This affects only 32-bit executables.
3800 noexec32=on: enable non-executable mappings (default)
3801 read doesn't imply executable mappings
3802 noexec32=off: disable non-executable mappings
3803 read implies executable mappings
3804
3805 no_file_caps Tells the kernel not to honor file capabilities. The
3806 only way then for a file to be executed with privilege
3807 is to be setuid root or executed by root.
3808
3809 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3810
3811 nofsgsbase [X86] Disables FSGSBASE instructions.
3812
3813 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3814 register save and restore. The kernel will only save
3815 legacy floating-point registers on task switch.
3816
3817 nohalt [IA-64] Tells the kernel not to use the power saving
3818 function PAL_HALT_LIGHT when idle. This increases
3819 power-consumption. On the positive side, it reduces
3820 interrupt wake-up latency, which may improve performance
3821 in certain environments such as networked servers or
3822 real-time systems.
3823
3824 no_hash_pointers
3825 Force pointers printed to the console or buffers to be
3826 unhashed. By default, when a pointer is printed via %p
3827 format string, that pointer is "hashed", i.e. obscured
3828 by hashing the pointer value. This is a security feature
3829 that hides actual kernel addresses from unprivileged
3830 users, but it also makes debugging the kernel more
3831 difficult since unequal pointers can no longer be
3832 compared. However, if this command-line option is
3833 specified, then all normal pointers will have their true
3834 value printed. This option should only be specified when
3835 debugging the kernel. Please do not use on production
3836 kernels.
3837
3838 nohibernate [HIBERNATION] Disable hibernation and resume.
3839
3840 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to
3841 busy wait in do_idle() and not use the arch_cpu_idle()
3842 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3843 to be effective. This is useful on platforms where the
3844 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3845 correctly or when doing power measurements to evaluate
3846 the impact of the sleep instructions. This is also
3847 useful when using JTAG debugger.
3848
3849 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3850
3851 nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings.
3852
3853 nohz= [KNL] Boottime enable/disable dynamic ticks
3854 Valid arguments: on, off
3855 Default: on
3856
3857 nohz_full= [KNL,BOOT,SMP,ISOL]
3858 The argument is a cpu list, as described above.
3859 In kernels built with CONFIG_NO_HZ_FULL=y, set
3860 the specified list of CPUs whose tick will be stopped
3861 whenever possible. The boot CPU will be forced outside
3862 the range to maintain the timekeeping. Any CPUs
3863 in this list will have their RCU callbacks offloaded,
3864 just as if they had also been called out in the
3865 rcu_nocbs= boot parameter.
3866
3867 Note that this argument takes precedence over
3868 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3869
3870 noinitrd [RAM] Tells the kernel not to load any configured
3871 initial RAM disk.
3872
3873 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3874 remapping.
3875 [Deprecated - use intremap=off]
3876
3877 nointroute [IA-64]
3878
3879 noinvpcid [X86] Disable the INVPCID cpu feature.
3880
3881 noiotrap [SH] Disables trapped I/O port accesses.
3882
3883 noirqdebug [X86-32] Disables the code which attempts to detect and
3884 disable unhandled interrupt sources.
3885
3886 noisapnp [ISAPNP] Disables ISA PnP code.
3887
3888 nojitter [IA-64] Disables jitter checking for ITC timers.
3889
3890 nokaslr [KNL]
3891 When CONFIG_RANDOMIZE_BASE is set, this disables
3892 kernel and module base offset ASLR (Address Space
3893 Layout Randomization).
3894
3895 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3896 fault handling.
3897
3898 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3899
3900 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3901
3902 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3903
3904 nomca [IA-64] Disable machine check abort handling
3905
3906 nomce [X86-32] Disable Machine Check Exception
3907
3908 nomfgpt [X86-32] Disable Multi-Function General Purpose
3909 Timer usage (for AMD Geode machines).
3910
3911 nomodeset Disable kernel modesetting. Most systems' firmware
3912 sets up a display mode and provides framebuffer memory
3913 for output. With nomodeset, DRM and fbdev drivers will
3914 not load if they could possibly displace the pre-
3915 initialized output. Only the system framebuffer will
3916 be available for use. The respective drivers will not
3917 perform display-mode changes or accelerated rendering.
3918
3919 Useful as error fallback, or for testing and debugging.
3920
3921 nomodule Disable module load
3922
3923 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3924 shutdown the other cpus. Instead use the REBOOT_VECTOR
3925 irq.
3926
3927 nopat [X86] Disable PAT (page attribute table extension of
3928 pagetables) support.
3929
3930 nopcid [X86-64] Disable the PCID cpu feature.
3931
3932 nopku [X86] Disable Memory Protection Keys CPU feature found
3933 in some Intel CPUs.
3934
3935 nopti [X86-64]
3936 Equivalent to pti=off
3937
3938 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
3939 Disables the PV optimizations forcing the guest to run
3940 as generic guest with no PV drivers. Currently support
3941 XEN HVM, KVM, HYPER_V and VMWARE guest.
3942
3943 nopvspin [X86,XEN,KVM]
3944 Disables the qspinlock slow path using PV optimizations
3945 which allow the hypervisor to 'idle' the guest on lock
3946 contention.
3947
3948 norandmaps Don't use address space randomization. Equivalent to
3949 echo 0 > /proc/sys/kernel/randomize_va_space
3950
3951 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3952 with UP alternatives
3953
3954 noresume [SWSUSP] Disables resume and restores original swap
3955 space.
3956
3957 nosbagart [IA-64]
3958
3959 no-scroll [VGA] Disables scrollback.
3960 This is required for the Braillex ib80-piezo Braille
3961 reader made by F.H. Papenmeier (Germany).
3962
3963 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3964
3965 nosmap [PPC]
3966 Disable SMAP (Supervisor Mode Access Prevention)
3967 even if it is supported by processor.
3968
3969 nosmep [PPC64s]
3970 Disable SMEP (Supervisor Mode Execution Prevention)
3971 even if it is supported by processor.
3972
3973 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3974 and disable the IO APIC. legacy for "maxcpus=0".
3975
3976 nosmt [KNL,MIPS,PPC,S390] Disable symmetric multithreading (SMT).
3977 Equivalent to smt=1.
3978
3979 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
3980 nosmt=force: Force disable SMT, cannot be undone
3981 via the sysfs control file.
3982
3983 nosoftlockup [KNL] Disable the soft-lockup detector.
3984
3985 nospec_store_bypass_disable
3986 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3987
3988 nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
3989 history injection) vulnerability. System may allow data leaks
3990 with this option.
3991
3992 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3993 (bounds check bypass). With this option data leaks are
3994 possible in the system.
3995
3996 nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for
3997 the Spectre variant 2 (indirect branch prediction)
3998 vulnerability. System may allow data leaks with this
3999 option.
4000
4001 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV] Disable
4002 paravirtualized steal time accounting. steal time is
4003 computed, but won't influence scheduler behaviour
4004
4005 nosync [HW,M68K] Disables sync negotiation for all devices.
4006
4007 no_timer_check [X86,APIC] Disables the code which tests for
4008 broken timer IRQ sources.
4009
4010 no_uaccess_flush
4011 [PPC] Don't flush the L1-D cache after accessing user data.
4012
4013 novmcoredd [KNL,KDUMP]
4014 Disable device dump. Device dump allows drivers to
4015 append dump data to vmcore so you can collect driver
4016 specified debug info. Drivers can append the data
4017 without any limit and this data is stored in memory,
4018 so this may cause significant memory stress. Disabling
4019 device dump can help save memory but the driver debug
4020 data will be no longer available. This parameter
4021 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4022 is set.
4023
4024 no-vmw-sched-clock
4025 [X86,PV_OPS] Disable paravirtualized VMware scheduler
4026 clock and use the default one.
4027
4028 nowatchdog [KNL] Disable both lockup detectors, i.e.
4029 soft-lockup and NMI watchdog (hard-lockup).
4030
4031 nowb [ARM]
4032
4033 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
4034
4035 NOTE: this parameter will be ignored on systems with the
4036 LEGACY_XAPIC_DISABLED bit set in the
4037 IA32_XAPIC_DISABLE_STATUS MSR.
4038
4039 noxsave [BUGS=X86] Disables x86 extended register state save
4040 and restore using xsave. The kernel will fallback to
4041 enabling legacy floating-point and sse state.
4042
4043 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4044 register states. The kernel will fall back to use
4045 xsave to save the states. By using this parameter,
4046 performance of saving the states is degraded because
4047 xsave doesn't support modified optimization while
4048 xsaveopt supports it on xsaveopt enabled systems.
4049
4050 noxsaves [X86] Disables xsaves and xrstors used in saving and
4051 restoring x86 extended register state in compacted
4052 form of xsave area. The kernel will fall back to use
4053 xsaveopt and xrstor to save and restore the states
4054 in standard form of xsave area. By using this
4055 parameter, xsave area per process might occupy more
4056 memory on xsaves enabled systems.
4057
4058 nps_mtm_hs_ctr= [KNL,ARC]
4059 This parameter sets the maximum duration, in
4060 cycles, each HW thread of the CTOP can run
4061 without interruptions, before HW switches it.
4062 The actual maximum duration is 16 times this
4063 parameter's value.
4064 Format: integer between 1 and 255
4065 Default: 255
4066
4067 nptcg= [IA-64] Override max number of concurrent global TLB
4068 purges which is reported from either PAL_VM_SUMMARY or
4069 SAL PALO.
4070
4071 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
4072 could support. nr_cpus=n : n >= 1 limits the kernel to
4073 support 'n' processors. It could be larger than the
4074 number of already plugged CPU during bootup, later in
4075 runtime you can physically add extra cpu until it reaches
4076 n. So during boot up some boot time memory for per-cpu
4077 variables need be pre-allocated for later physical cpu
4078 hot plugging.
4079
4080 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4081
4082 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
4083 set up a single NUMA node spanning all memory.
4084
4085 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4086 NUMA balancing.
4087 Allowed values are enable and disable
4088
4089 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4090 'node', 'default' can be specified
4091 This can be set from sysctl after boot.
4092 See Documentation/admin-guide/sysctl/vm.rst for details.
4093
4094 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
4095 See Documentation/core-api/debugging-via-ohci1394.rst for more
4096 info.
4097
4098 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4099 Rather than timing out after 20 ms if an EC
4100 command is not properly ACKed, override the length
4101 of the timeout. We have interrupts disabled while
4102 waiting for the ACK, so if this is set too high
4103 interrupts *may* be lost!
4104
4105 omap_mux= [OMAP] Override bootloader pin multiplexing.
4106 Format: <mux_mode0.mode_name=value>...
4107 For example, to override I2C bus2:
4108 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4109
4110 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4111
4112 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4113
4114 boundary - index of last SLC block on Flex-OneNAND.
4115 The remaining blocks are configured as MLC blocks.
4116 lock - Configure if Flex-OneNAND boundary should be locked.
4117 Once locked, the boundary cannot be changed.
4118 1 indicates lock status, 0 indicates unlock status.
4119
4120 oops=panic Always panic on oopses. Default is to just kill the
4121 process, but there is a small probability of
4122 deadlocking the machine.
4123 This will also cause panics on machine check exceptions.
4124 Useful together with panic=30 to trigger a reboot.
4125
4126 page_alloc.shuffle=
4127 [KNL] Boolean flag to control whether the page allocator
4128 should randomize its free lists. The randomization may
4129 be automatically enabled if the kernel detects it is
4130 running on a platform with a direct-mapped memory-side
4131 cache, and this parameter can be used to
4132 override/disable that behavior. The state of the flag
4133 can be read from sysfs at:
4134 /sys/module/page_alloc/parameters/shuffle.
4135
4136 page_owner= [KNL] Boot-time page_owner enabling option.
4137 Storage of the information about who allocated
4138 each page is disabled in default. With this switch,
4139 we can turn it on.
4140 on: enable the feature
4141
4142 page_poison= [KNL] Boot-time parameter changing the state of
4143 poisoning on the buddy allocator, available with
4144 CONFIG_PAGE_POISONING=y.
4145 off: turn off poisoning (default)
4146 on: turn on poisoning
4147
4148 page_reporting.page_reporting_order=
4149 [KNL] Minimal page reporting order
4150 Format: <integer>
4151 Adjust the minimal page reporting order. The page
4152 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4153
4154 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4155 timeout > 0: seconds before rebooting
4156 timeout = 0: wait forever
4157 timeout < 0: reboot immediately
4158 Format: <timeout>
4159
4160 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
4161 Format: <hex>[,nousertaint]
4162 Hexadecimal bitmask representing the set of TAINT flags
4163 that will cause the kernel to panic when add_taint() is
4164 called with any of the flags in this set.
4165 The optional switch "nousertaint" can be utilized to
4166 prevent userspace forced crashes by writing to sysctl
4167 /proc/sys/kernel/tainted any flagset matching with the
4168 bitmask set on panic_on_taint.
4169 See Documentation/admin-guide/tainted-kernels.rst for
4170 extra details on the taint flags that users can pick
4171 to compose the bitmask to assign to panic_on_taint.
4172
4173 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4174 on a WARN().
4175
4176 panic_print= Bitmask for printing system info when panic happens.
4177 User can chose combination of the following bits:
4178 bit 0: print all tasks info
4179 bit 1: print system memory info
4180 bit 2: print timer info
4181 bit 3: print locks info if CONFIG_LOCKDEP is on
4182 bit 4: print ftrace buffer
4183 bit 5: print all printk messages in buffer
4184 bit 6: print all CPUs backtrace (if available in the arch)
4185 *Be aware* that this option may print a _lot_ of lines,
4186 so there are risks of losing older messages in the log.
4187 Use this option carefully, maybe worth to setup a
4188 bigger log buffer with "log_buf_len" along with this.
4189
4190 parkbd.port= [HW] Parallel port number the keyboard adapter is
4191 connected to, default is 0.
4192 Format: <parport#>
4193 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4194 0 for XT, 1 for AT (default is AT).
4195 Format: <mode>
4196
4197 parport= [HW,PPT] Specify parallel ports. 0 disables.
4198 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4199 Use 'auto' to force the driver to use any
4200 IRQ/DMA settings detected (the default is to
4201 ignore detected IRQ/DMA settings because of
4202 possible conflicts). You can specify the base
4203 address, IRQ, and DMA settings; IRQ and DMA
4204 should be numbers, or 'auto' (for using detected
4205 settings on that particular port), or 'nofifo'
4206 (to avoid using a FIFO even if it is detected).
4207 Parallel ports are assigned in the order they
4208 are specified on the command line, starting
4209 with parport0.
4210
4211 parport_init_mode= [HW,PPT]
4212 Configure VIA parallel port to operate in
4213 a specific mode. This is necessary on Pegasos
4214 computer where firmware has no options for setting
4215 up parallel port mode and sets it to spp.
4216 Currently this function knows 686a and 8231 chips.
4217 Format: [spp|ps2|epp|ecp|ecpepp]
4218
4219 pata_legacy.all= [HW,LIBATA]
4220 Format: <int>
4221 Set to non-zero to probe primary and secondary ISA
4222 port ranges on PCI systems where no PCI PATA device
4223 has been found at either range. Disabled by default.
4224
4225 pata_legacy.autospeed= [HW,LIBATA]
4226 Format: <int>
4227 Set to non-zero if a chip is present that snoops speed
4228 changes. Disabled by default.
4229
4230 pata_legacy.ht6560a= [HW,LIBATA]
4231 Format: <int>
4232 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4233 the secondary channel, or both channels respectively.
4234 Disabled by default.
4235
4236 pata_legacy.ht6560b= [HW,LIBATA]
4237 Format: <int>
4238 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4239 the secondary channel, or both channels respectively.
4240 Disabled by default.
4241
4242 pata_legacy.iordy_mask= [HW,LIBATA]
4243 Format: <int>
4244 IORDY enable mask. Set individual bits to allow IORDY
4245 for the respective channel. Bit 0 is for the first
4246 legacy channel handled by this driver, bit 1 is for
4247 the second channel, and so on. The sequence will often
4248 correspond to the primary legacy channel, the secondary
4249 legacy channel, and so on, but the handling of a PCI
4250 bus and the use of other driver options may interfere
4251 with the sequence. By default IORDY is allowed across
4252 all channels.
4253
4254 pata_legacy.opti82c46x= [HW,LIBATA]
4255 Format: <int>
4256 Set to 1, 2, or 3 for Opti 82c611A on the primary
4257 channel, the secondary channel, or both channels
4258 respectively. Disabled by default.
4259
4260 pata_legacy.opti82c611a= [HW,LIBATA]
4261 Format: <int>
4262 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4263 channel, the secondary channel, or both channels
4264 respectively. Disabled by default.
4265
4266 pata_legacy.pio_mask= [HW,LIBATA]
4267 Format: <int>
4268 PIO mode mask for autospeed devices. Set individual
4269 bits to allow the use of the respective PIO modes.
4270 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4271 All modes allowed by default.
4272
4273 pata_legacy.probe_all= [HW,LIBATA]
4274 Format: <int>
4275 Set to non-zero to probe tertiary and further ISA
4276 port ranges on PCI systems. Disabled by default.
4277
4278 pata_legacy.probe_mask= [HW,LIBATA]
4279 Format: <int>
4280 Probe mask for legacy ISA PATA ports. Depending on
4281 platform configuration and the use of other driver
4282 options up to 6 legacy ports are supported: 0x1f0,
4283 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4284 of individual ports can be disabled by setting the
4285 corresponding bits in the mask to 1. Bit 0 is for
4286 the first port in the list above (0x1f0), and so on.
4287 By default all supported ports are probed.
4288
4289 pata_legacy.qdi= [HW,LIBATA]
4290 Format: <int>
4291 Set to non-zero to probe QDI controllers. By default
4292 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4293
4294 pata_legacy.winbond= [HW,LIBATA]
4295 Format: <int>
4296 Set to non-zero to probe Winbond controllers. Use
4297 the standard I/O port (0x130) if 1, otherwise the
4298 value given is the I/O port to use (typically 0x1b0).
4299 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4300 0 otherwise.
4301
4302 pata_platform.pio_mask= [HW,LIBATA]
4303 Format: <int>
4304 Supported PIO mode mask. Set individual bits to allow
4305 the use of the respective PIO modes. Bit 0 is for
4306 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4307 allowed by default.
4308
4309 pause_on_oops=<int>
4310 Halt all CPUs after the first oops has been printed for
4311 the specified number of seconds. This is to be used if
4312 your oopses keep scrolling off the screen.
4313
4314 pcbit= [HW,ISDN]
4315
4316 pci=option[,option...] [PCI] various PCI subsystem options.
4317
4318 Some options herein operate on a specific device
4319 or a set of devices (<pci_dev>). These are
4320 specified in one of the following formats:
4321
4322 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4323 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4324
4325 Note: the first format specifies a PCI
4326 bus/device/function address which may change
4327 if new hardware is inserted, if motherboard
4328 firmware changes, or due to changes caused
4329 by other kernel parameters. If the
4330 domain is left unspecified, it is
4331 taken to be zero. Optionally, a path
4332 to a device through multiple device/function
4333 addresses can be specified after the base
4334 address (this is more robust against
4335 renumbering issues). The second format
4336 selects devices using IDs from the
4337 configuration space which may match multiple
4338 devices in the system.
4339
4340 earlydump dump PCI config space before the kernel
4341 changes anything
4342 off [X86] don't probe for the PCI bus
4343 bios [X86-32] force use of PCI BIOS, don't access
4344 the hardware directly. Use this if your machine
4345 has a non-standard PCI host bridge.
4346 nobios [X86-32] disallow use of PCI BIOS, only direct
4347 hardware access methods are allowed. Use this
4348 if you experience crashes upon bootup and you
4349 suspect they are caused by the BIOS.
4350 conf1 [X86] Force use of PCI Configuration Access
4351 Mechanism 1 (config address in IO port 0xCF8,
4352 data in IO port 0xCFC, both 32-bit).
4353 conf2 [X86] Force use of PCI Configuration Access
4354 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4355 the function, IO port 0xCFA, also 8-bit, sets
4356 bus number. The config space is then accessed
4357 through ports 0xC000-0xCFFF).
4358 See http://wiki.osdev.org/PCI for more info
4359 on the configuration access mechanisms.
4360 noaer [PCIE] If the PCIEAER kernel config parameter is
4361 enabled, this kernel boot option can be used to
4362 disable the use of PCIE advanced error reporting.
4363 nodomains [PCI] Disable support for multiple PCI
4364 root domains (aka PCI segments, in ACPI-speak).
4365 nommconf [X86] Disable use of MMCONFIG for PCI
4366 Configuration
4367 check_enable_amd_mmconf [X86] check for and enable
4368 properly configured MMIO access to PCI
4369 config space on AMD family 10h CPU
4370 nomsi [MSI] If the PCI_MSI kernel config parameter is
4371 enabled, this kernel boot option can be used to
4372 disable the use of MSI interrupts system-wide.
4373 noioapicquirk [APIC] Disable all boot interrupt quirks.
4374 Safety option to keep boot IRQs enabled. This
4375 should never be necessary.
4376 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4377 primary IO-APIC for bridges that cannot disable
4378 boot IRQs. This fixes a source of spurious IRQs
4379 when the system masks IRQs.
4380 noioapicreroute [APIC] Disable workaround that uses the
4381 boot IRQ equivalent of an IRQ that connects to
4382 a chipset where boot IRQs cannot be disabled.
4383 The opposite of ioapicreroute.
4384 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4385 routing table. These calls are known to be buggy
4386 on several machines and they hang the machine
4387 when used, but on other computers it's the only
4388 way to get the interrupt routing table. Try
4389 this option if the kernel is unable to allocate
4390 IRQs or discover secondary PCI buses on your
4391 motherboard.
4392 rom [X86] Assign address space to expansion ROMs.
4393 Use with caution as certain devices share
4394 address decoders between ROMs and other
4395 resources.
4396 norom [X86] Do not assign address space to
4397 expansion ROMs that do not already have
4398 BIOS assigned address ranges.
4399 nobar [X86] Do not assign address space to the
4400 BARs that weren't assigned by the BIOS.
4401 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4402 assigned automatically to PCI devices. You can
4403 make the kernel exclude IRQs of your ISA cards
4404 this way.
4405 pirqaddr=0xAAAAA [X86] Specify the physical address
4406 of the PIRQ table (normally generated
4407 by the BIOS) if it is outside the
4408 F0000h-100000h range.
4409 lastbus=N [X86] Scan all buses thru bus #N. Can be
4410 useful if the kernel is unable to find your
4411 secondary buses and you want to tell it
4412 explicitly which ones they are.
4413 assign-busses [X86] Always assign all PCI bus
4414 numbers ourselves, overriding
4415 whatever the firmware may have done.
4416 usepirqmask [X86] Honor the possible IRQ mask stored
4417 in the BIOS $PIR table. This is needed on
4418 some systems with broken BIOSes, notably
4419 some HP Pavilion N5400 and Omnibook XE3
4420 notebooks. This will have no effect if ACPI
4421 IRQ routing is enabled.
4422 noacpi [X86] Do not use ACPI for IRQ routing
4423 or for PCI scanning.
4424 use_crs [X86] Use PCI host bridge window information
4425 from ACPI. On BIOSes from 2008 or later, this
4426 is enabled by default. If you need to use this,
4427 please report a bug.
4428 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4429 If you need to use this, please report a bug.
4430 use_e820 [X86] Use E820 reservations to exclude parts of
4431 PCI host bridge windows. This is a workaround
4432 for BIOS defects in host bridge _CRS methods.
4433 If you need to use this, please report a bug to
4434 <linux-pci@vger.kernel.org>.
4435 no_e820 [X86] Ignore E820 reservations for PCI host
4436 bridge windows. This is the default on modern
4437 hardware. If you need to use this, please report
4438 a bug to <linux-pci@vger.kernel.org>.
4439 routeirq Do IRQ routing for all PCI devices.
4440 This is normally done in pci_enable_device(),
4441 so this option is a temporary workaround
4442 for broken drivers that don't call it.
4443 skip_isa_align [X86] do not align io start addr, so can
4444 handle more pci cards
4445 noearly [X86] Don't do any early type 1 scanning.
4446 This might help on some broken boards which
4447 machine check when some devices' config space
4448 is read. But various workarounds are disabled
4449 and some IOMMU drivers will not work.
4450 bfsort Sort PCI devices into breadth-first order.
4451 This sorting is done to get a device
4452 order compatible with older (<= 2.4) kernels.
4453 nobfsort Don't sort PCI devices into breadth-first order.
4454 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4455 tuning and use the BIOS-configured MPS defaults.
4456 pcie_bus_safe Set every device's MPS to the largest value
4457 supported by all devices below the root complex.
4458 pcie_bus_perf Set device MPS to the largest allowable MPS
4459 based on its parent bus. Also set MRRS (Max
4460 Read Request Size) to the largest supported
4461 value (no larger than the MPS that the device
4462 or bus can support) for best performance.
4463 pcie_bus_peer2peer Set every device's MPS to 128B, which
4464 every device is guaranteed to support. This
4465 configuration allows peer-to-peer DMA between
4466 any pair of devices, possibly at the cost of
4467 reduced performance. This also guarantees
4468 that hot-added devices will work.
4469 cbiosize=nn[KMG] The fixed amount of bus space which is
4470 reserved for the CardBus bridge's IO window.
4471 The default value is 256 bytes.
4472 cbmemsize=nn[KMG] The fixed amount of bus space which is
4473 reserved for the CardBus bridge's memory
4474 window. The default value is 64 megabytes.
4475 resource_alignment=
4476 Format:
4477 [<order of align>@]<pci_dev>[; ...]
4478 Specifies alignment and device to reassign
4479 aligned memory resources. How to
4480 specify the device is described above.
4481 If <order of align> is not specified,
4482 PAGE_SIZE is used as alignment.
4483 A PCI-PCI bridge can be specified if resource
4484 windows need to be expanded.
4485 To specify the alignment for several
4486 instances of a device, the PCI vendor,
4487 device, subvendor, and subdevice may be
4488 specified, e.g., 12@pci:8086:9c22:103c:198f
4489 for 4096-byte alignment.
4490 ecrc= Enable/disable PCIe ECRC (transaction layer
4491 end-to-end CRC checking). Only effective if
4492 OS has native AER control (either granted by
4493 ACPI _OSC or forced via "pcie_ports=native")
4494 bios: Use BIOS/firmware settings. This is the
4495 the default.
4496 off: Turn ECRC off
4497 on: Turn ECRC on.
4498 hpiosize=nn[KMG] The fixed amount of bus space which is
4499 reserved for hotplug bridge's IO window.
4500 Default size is 256 bytes.
4501 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4502 reserved for hotplug bridge's MMIO window.
4503 Default size is 2 megabytes.
4504 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4505 reserved for hotplug bridge's MMIO_PREF window.
4506 Default size is 2 megabytes.
4507 hpmemsize=nn[KMG] The fixed amount of bus space which is
4508 reserved for hotplug bridge's MMIO and
4509 MMIO_PREF window.
4510 Default size is 2 megabytes.
4511 hpbussize=nn The minimum amount of additional bus numbers
4512 reserved for buses below a hotplug bridge.
4513 Default is 1.
4514 realloc= Enable/disable reallocating PCI bridge resources
4515 if allocations done by BIOS are too small to
4516 accommodate resources required by all child
4517 devices.
4518 off: Turn realloc off
4519 on: Turn realloc on
4520 realloc same as realloc=on
4521 noari do not use PCIe ARI.
4522 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4523 do not use PCIe ATS (and IOMMU device IOTLB).
4524 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4525 only look for one device below a PCIe downstream
4526 port.
4527 big_root_window Try to add a big 64bit memory window to the PCIe
4528 root complex on AMD CPUs. Some GFX hardware
4529 can resize a BAR to allow access to all VRAM.
4530 Adding the window is slightly risky (it may
4531 conflict with unreported devices), so this
4532 taints the kernel.
4533 disable_acs_redir=<pci_dev>[; ...]
4534 Specify one or more PCI devices (in the format
4535 specified above) separated by semicolons.
4536 Each device specified will have the PCI ACS
4537 redirect capabilities forced off which will
4538 allow P2P traffic between devices through
4539 bridges without forcing it upstream. Note:
4540 this removes isolation between devices and
4541 may put more devices in an IOMMU group.
4542 force_floating [S390] Force usage of floating interrupts.
4543 nomio [S390] Do not use MIO instructions.
4544 norid [S390] ignore the RID field and force use of
4545 one PCI domain per PCI function
4546
4547 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4548 Management.
4549 off Disable ASPM.
4550 force Enable ASPM even on devices that claim not to support it.
4551 WARNING: Forcing ASPM on may cause system lockups.
4552
4553 pcie_ports= [PCIE] PCIe port services handling:
4554 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4555 even if the platform doesn't give the OS permission to
4556 use them. This may cause conflicts if the platform
4557 also tries to use these services.
4558 dpc-native Use native PCIe service for DPC only. May
4559 cause conflicts if firmware uses AER or DPC.
4560 compat Disable native PCIe services (PME, AER, DPC, PCIe
4561 hotplug).
4562
4563 pcie_port_pm= [PCIE] PCIe port power management handling:
4564 off Disable power management of all PCIe ports
4565 force Forcibly enable power management of all PCIe ports
4566
4567 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4568 nomsi Do not use MSI for native PCIe PME signaling (this makes
4569 all PCIe root ports use INTx for all services).
4570
4571 pcmv= [HW,PCMCIA] BadgePAD 4
4572
4573 pd_ignore_unused
4574 [PM]
4575 Keep all power-domains already enabled by bootloader on,
4576 even if no driver has claimed them. This is useful
4577 for debug and development, but should not be
4578 needed on a platform with proper driver support.
4579
4580 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4581 boot time.
4582 Format: { 0 | 1 }
4583 See arch/parisc/kernel/pdc_chassis.c
4584
4585 percpu_alloc= Select which percpu first chunk allocator to use.
4586 Currently supported values are "embed" and "page".
4587 Archs may support subset or none of the selections.
4588 See comments in mm/percpu.c for details on each
4589 allocator. This parameter is primarily for debugging
4590 and performance comparison.
4591
4592 pirq= [SMP,APIC] Manual mp-table setup
4593 See Documentation/arch/x86/i386/IO-APIC.rst.
4594
4595 plip= [PPT,NET] Parallel port network link
4596 Format: { parport<nr> | timid | 0 }
4597 See also Documentation/admin-guide/parport.rst.
4598
4599 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4600 Override pmtimer IOPort with a hex value.
4601 e.g. pmtmr=0x508
4602
4603 pmu_override= [PPC] Override the PMU.
4604 This option takes over the PMU facility, so it is no
4605 longer usable by perf. Setting this option starts the
4606 PMU counters by setting MMCR0 to 0 (the FC bit is
4607 cleared). If a number is given, then MMCR1 is set to
4608 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4609 remains 0.
4610
4611 pm_debug_messages [SUSPEND,KNL]
4612 Enable suspend/resume debug messages during boot up.
4613
4614 pnp.debug=1 [PNP]
4615 Enable PNP debug messages (depends on the
4616 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4617 via /sys/module/pnp/parameters/debug. We always show
4618 current resource usage; turning this on also shows
4619 possible settings and some assignment information.
4620
4621 pnpacpi= [ACPI]
4622 { off }
4623
4624 pnpbios= [ISAPNP]
4625 { on | off | curr | res | no-curr | no-res }
4626
4627 pnp_reserve_irq=
4628 [ISAPNP] Exclude IRQs for the autoconfiguration
4629
4630 pnp_reserve_dma=
4631 [ISAPNP] Exclude DMAs for the autoconfiguration
4632
4633 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4634 Ranges are in pairs (I/O port base and size).
4635
4636 pnp_reserve_mem=
4637 [ISAPNP] Exclude memory regions for the
4638 autoconfiguration.
4639 Ranges are in pairs (memory base and size).
4640
4641 ports= [IP_VS_FTP] IPVS ftp helper module
4642 Default is 21.
4643 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4644 may be specified.
4645 Format: <port>,<port>....
4646
4647 powersave=off [PPC] This option disables power saving features.
4648 It specifically disables cpuidle and sets the
4649 platform machine description specific power_save
4650 function to NULL. On Idle the CPU just reduces
4651 execution priority.
4652
4653 ppc_strict_facility_enable
4654 [PPC] This option catches any kernel floating point,
4655 Altivec, VSX and SPE outside of regions specifically
4656 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4657 There is some performance impact when enabling this.
4658
4659 ppc_tm= [PPC]
4660 Format: {"off"}
4661 Disable Hardware Transactional Memory
4662
4663 preempt= [KNL]
4664 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4665 none - Limited to cond_resched() calls
4666 voluntary - Limited to cond_resched() and might_sleep() calls
4667 full - Any section that isn't explicitly preempt disabled
4668 can be preempted anytime.
4669
4670 print-fatal-signals=
4671 [KNL] debug: print fatal signals
4672
4673 If enabled, warn about various signal handling
4674 related application anomalies: too many signals,
4675 too many POSIX.1 timers, fatal signals causing a
4676 coredump - etc.
4677
4678 If you hit the warning due to signal overflow,
4679 you might want to try "ulimit -i unlimited".
4680
4681 default: off.
4682
4683 printk.always_kmsg_dump=
4684 Trigger kmsg_dump for cases other than kernel oops or
4685 panics
4686 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4687 default: disabled
4688
4689 printk.console_no_auto_verbose=
4690 Disable console loglevel raise on oops, panic
4691 or lockdep-detected issues (only if lock debug is on).
4692 With an exception to setups with low baudrate on
4693 serial console, keeping this 0 is a good choice
4694 in order to provide more debug information.
4695 Format: <bool>
4696 default: 0 (auto_verbose is enabled)
4697
4698 printk.devkmsg={on,off,ratelimit}
4699 Control writing to /dev/kmsg.
4700 on - unlimited logging to /dev/kmsg from userspace
4701 off - logging to /dev/kmsg disabled
4702 ratelimit - ratelimit the logging
4703 Default: ratelimit
4704
4705 printk.time= Show timing data prefixed to each printk message line
4706 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4707
4708 processor.max_cstate= [HW,ACPI]
4709 Limit processor to maximum C-state
4710 max_cstate=9 overrides any DMI blacklist limit.
4711
4712 processor.nocst [HW,ACPI]
4713 Ignore the _CST method to determine C-states,
4714 instead using the legacy FADT method
4715
4716 profile= [KNL] Enable kernel profiling via /proc/profile
4717 Format: [<profiletype>,]<number>
4718 Param: <profiletype>: "schedule", "sleep", or "kvm"
4719 [defaults to kernel profiling]
4720 Param: "schedule" - profile schedule points.
4721 Param: "sleep" - profile D-state sleeping (millisecs).
4722 Requires CONFIG_SCHEDSTATS
4723 Param: "kvm" - profile VM exits.
4724 Param: <number> - step/bucket size as a power of 2 for
4725 statistical time based profiling.
4726
4727 prompt_ramdisk= [RAM] [Deprecated]
4728
4729 prot_virt= [S390] enable hosting protected virtual machines
4730 isolated from the hypervisor (if hardware supports
4731 that).
4732 Format: <bool>
4733
4734 psi= [KNL] Enable or disable pressure stall information
4735 tracking.
4736 Format: <bool>
4737
4738 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4739 probe for; one of (bare|imps|exps|lifebook|any).
4740 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4741 per second.
4742 psmouse.resetafter= [HW,MOUSE]
4743 Try to reset the device after so many bad packets
4744 (0 = never).
4745 psmouse.resolution=
4746 [HW,MOUSE] Set desired mouse resolution, in dpi.
4747 psmouse.smartscroll=
4748 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4749 0 = disabled, 1 = enabled (default).
4750
4751 pstore.backend= Specify the name of the pstore backend to use
4752
4753 pti= [X86-64] Control Page Table Isolation of user and
4754 kernel address spaces. Disabling this feature
4755 removes hardening, but improves performance of
4756 system calls and interrupts.
4757
4758 on - unconditionally enable
4759 off - unconditionally disable
4760 auto - kernel detects whether your CPU model is
4761 vulnerable to issues that PTI mitigates
4762
4763 Not specifying this option is equivalent to pti=auto.
4764
4765 pty.legacy_count=
4766 [KNL] Number of legacy pty's. Overwrites compiled-in
4767 default number.
4768
4769 quiet [KNL] Disable most log messages
4770
4771 r128= [HW,DRM]
4772
4773 radix_hcall_invalidate=on [PPC/PSERIES]
4774 Disable RADIX GTSE feature and use hcall for TLB
4775 invalidate.
4776
4777 raid= [HW,RAID]
4778 See Documentation/admin-guide/md.rst.
4779
4780 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4781 See Documentation/admin-guide/blockdev/ramdisk.rst.
4782
4783 ramdisk_start= [RAM] RAM disk image start address
4784
4785 random.trust_cpu=off
4786 [KNL] Disable trusting the use of the CPU's
4787 random number generator (if available) to
4788 initialize the kernel's RNG.
4789
4790 random.trust_bootloader=off
4791 [KNL] Disable trusting the use of the a seed
4792 passed by the bootloader (if available) to
4793 initialize the kernel's RNG.
4794
4795 randomize_kstack_offset=
4796 [KNL] Enable or disable kernel stack offset
4797 randomization, which provides roughly 5 bits of
4798 entropy, frustrating memory corruption attacks
4799 that depend on stack address determinism or
4800 cross-syscall address exposures. This is only
4801 available on architectures that have defined
4802 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4803 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4804 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4805
4806 ras=option[,option,...] [KNL] RAS-specific options
4807
4808 cec_disable [X86]
4809 Disable the Correctable Errors Collector,
4810 see CONFIG_RAS_CEC help text.
4811
4812 rcu_nocbs[=cpu-list]
4813 [KNL] The optional argument is a cpu list,
4814 as described above.
4815
4816 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4817 enable the no-callback CPU mode, which prevents
4818 such CPUs' callbacks from being invoked in
4819 softirq context. Invocation of such CPUs' RCU
4820 callbacks will instead be offloaded to "rcuox/N"
4821 kthreads created for that purpose, where "x" is
4822 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4823 for the kthreads that mediate grace periods; and
4824 "N" is the CPU number. This reduces OS jitter on
4825 the offloaded CPUs, which can be useful for HPC
4826 and real-time workloads. It can also improve
4827 energy efficiency for asymmetric multiprocessors.
4828
4829 If a cpulist is passed as an argument, the specified
4830 list of CPUs is set to no-callback mode from boot.
4831
4832 Otherwise, if the '=' sign and the cpulist
4833 arguments are omitted, no CPU will be set to
4834 no-callback mode from boot but the mode may be
4835 toggled at runtime via cpusets.
4836
4837 Note that this argument takes precedence over
4838 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4839
4840 rcu_nocb_poll [KNL]
4841 Rather than requiring that offloaded CPUs
4842 (specified by rcu_nocbs= above) explicitly
4843 awaken the corresponding "rcuoN" kthreads,
4844 make these kthreads poll for callbacks.
4845 This improves the real-time response for the
4846 offloaded CPUs by relieving them of the need to
4847 wake up the corresponding kthread, but degrades
4848 energy efficiency by requiring that the kthreads
4849 periodically wake up to do the polling.
4850
4851 rcutree.blimit= [KNL]
4852 Set maximum number of finished RCU callbacks to
4853 process in one batch.
4854
4855 rcutree.do_rcu_barrier= [KNL]
4856 Request a call to rcu_barrier(). This is
4857 throttled so that userspace tests can safely
4858 hammer on the sysfs variable if they so choose.
4859 If triggered before the RCU grace-period machinery
4860 is fully active, this will error out with EAGAIN.
4861
4862 rcutree.dump_tree= [KNL]
4863 Dump the structure of the rcu_node combining tree
4864 out at early boot. This is used for diagnostic
4865 purposes, to verify correct tree setup.
4866
4867 rcutree.gp_cleanup_delay= [KNL]
4868 Set the number of jiffies to delay each step of
4869 RCU grace-period cleanup.
4870
4871 rcutree.gp_init_delay= [KNL]
4872 Set the number of jiffies to delay each step of
4873 RCU grace-period initialization.
4874
4875 rcutree.gp_preinit_delay= [KNL]
4876 Set the number of jiffies to delay each step of
4877 RCU grace-period pre-initialization, that is,
4878 the propagation of recent CPU-hotplug changes up
4879 the rcu_node combining tree.
4880
4881 rcutree.jiffies_till_first_fqs= [KNL]
4882 Set delay from grace-period initialization to
4883 first attempt to force quiescent states.
4884 Units are jiffies, minimum value is zero,
4885 and maximum value is HZ.
4886
4887 rcutree.jiffies_till_next_fqs= [KNL]
4888 Set delay between subsequent attempts to force
4889 quiescent states. Units are jiffies, minimum
4890 value is one, and maximum value is HZ.
4891
4892 rcutree.jiffies_till_sched_qs= [KNL]
4893 Set required age in jiffies for a
4894 given grace period before RCU starts
4895 soliciting quiescent-state help from
4896 rcu_note_context_switch() and cond_resched().
4897 If not specified, the kernel will calculate
4898 a value based on the most recent settings
4899 of rcutree.jiffies_till_first_fqs
4900 and rcutree.jiffies_till_next_fqs.
4901 This calculated value may be viewed in
4902 rcutree.jiffies_to_sched_qs. Any attempt to set
4903 rcutree.jiffies_to_sched_qs will be cheerfully
4904 overwritten.
4905
4906 rcutree.kthread_prio= [KNL,BOOT]
4907 Set the SCHED_FIFO priority of the RCU per-CPU
4908 kthreads (rcuc/N). This value is also used for
4909 the priority of the RCU boost threads (rcub/N)
4910 and for the RCU grace-period kthreads (rcu_bh,
4911 rcu_preempt, and rcu_sched). If RCU_BOOST is
4912 set, valid values are 1-99 and the default is 1
4913 (the least-favored priority). Otherwise, when
4914 RCU_BOOST is not set, valid values are 0-99 and
4915 the default is zero (non-realtime operation).
4916 When RCU_NOCB_CPU is set, also adjust the
4917 priority of NOCB callback kthreads.
4918
4919 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4920 On callback-offloaded (rcu_nocbs) CPUs,
4921 RCU reduces the lock contention that would
4922 otherwise be caused by callback floods through
4923 use of the ->nocb_bypass list. However, in the
4924 common non-flooded case, RCU queues directly to
4925 the main ->cblist in order to avoid the extra
4926 overhead of the ->nocb_bypass list and its lock.
4927 But if there are too many callbacks queued during
4928 a single jiffy, RCU pre-queues the callbacks into
4929 the ->nocb_bypass queue. The definition of "too
4930 many" is supplied by this kernel boot parameter.
4931
4932 rcutree.qhimark= [KNL]
4933 Set threshold of queued RCU callbacks beyond which
4934 batch limiting is disabled.
4935
4936 rcutree.qlowmark= [KNL]
4937 Set threshold of queued RCU callbacks below which
4938 batch limiting is re-enabled.
4939
4940 rcutree.qovld= [KNL]
4941 Set threshold of queued RCU callbacks beyond which
4942 RCU's force-quiescent-state scan will aggressively
4943 enlist help from cond_resched() and sched IPIs to
4944 help CPUs more quickly reach quiescent states.
4945 Set to less than zero to make this be set based
4946 on rcutree.qhimark at boot time and to zero to
4947 disable more aggressive help enlistment.
4948
4949 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4950 Set the page-cache refill delay (in milliseconds)
4951 in response to low-memory conditions. The range
4952 of permitted values is in the range 0:100000.
4953
4954 rcutree.rcu_divisor= [KNL]
4955 Set the shift-right count to use to compute
4956 the callback-invocation batch limit bl from
4957 the number of callbacks queued on this CPU.
4958 The result will be bounded below by the value of
4959 the rcutree.blimit kernel parameter. Every bl
4960 callbacks, the softirq handler will exit in
4961 order to allow the CPU to do other work.
4962
4963 Please note that this callback-invocation batch
4964 limit applies only to non-offloaded callback
4965 invocation. Offloaded callbacks are instead
4966 invoked in the context of an rcuoc kthread, which
4967 scheduler will preempt as it does any other task.
4968
4969 rcutree.rcu_fanout_exact= [KNL]
4970 Disable autobalancing of the rcu_node combining
4971 tree. This is used by rcutorture, and might
4972 possibly be useful for architectures having high
4973 cache-to-cache transfer latencies.
4974
4975 rcutree.rcu_fanout_leaf= [KNL]
4976 Change the number of CPUs assigned to each
4977 leaf rcu_node structure. Useful for very
4978 large systems, which will choose the value 64,
4979 and for NUMA systems with large remote-access
4980 latencies, which will choose a value aligned
4981 with the appropriate hardware boundaries.
4982
4983 rcutree.rcu_min_cached_objs= [KNL]
4984 Minimum number of objects which are cached and
4985 maintained per one CPU. Object size is equal
4986 to PAGE_SIZE. The cache allows to reduce the
4987 pressure to page allocator, also it makes the
4988 whole algorithm to behave better in low memory
4989 condition.
4990
4991 rcutree.rcu_nocb_gp_stride= [KNL]
4992 Set the number of NOCB callback kthreads in
4993 each group, which defaults to the square root
4994 of the number of CPUs. Larger numbers reduce
4995 the wakeup overhead on the global grace-period
4996 kthread, but increases that same overhead on
4997 each group's NOCB grace-period kthread.
4998
4999 rcutree.rcu_kick_kthreads= [KNL]
5000 Cause the grace-period kthread to get an extra
5001 wake_up() if it sleeps three times longer than
5002 it should at force-quiescent-state time.
5003 This wake_up() will be accompanied by a
5004 WARN_ONCE() splat and an ftrace_dump().
5005
5006 rcutree.rcu_resched_ns= [KNL]
5007 Limit the time spend invoking a batch of RCU
5008 callbacks to the specified number of nanoseconds.
5009 By default, this limit is checked only once
5010 every 32 callbacks in order to limit the pain
5011 inflicted by local_clock() overhead.
5012
5013 rcutree.rcu_unlock_delay= [KNL]
5014 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5015 this specifies an rcu_read_unlock()-time delay
5016 in microseconds. This defaults to zero.
5017 Larger delays increase the probability of
5018 catching RCU pointer leaks, that is, buggy use
5019 of RCU-protected pointers after the relevant
5020 rcu_read_unlock() has completed.
5021
5022 rcutree.sysrq_rcu= [KNL]
5023 Commandeer a sysrq key to dump out Tree RCU's
5024 rcu_node tree with an eye towards determining
5025 why a new grace period has not yet started.
5026
5027 rcutree.use_softirq= [KNL]
5028 If set to zero, move all RCU_SOFTIRQ processing to
5029 per-CPU rcuc kthreads. Defaults to a non-zero
5030 value, meaning that RCU_SOFTIRQ is used by default.
5031 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5032
5033 But note that CONFIG_PREEMPT_RT=y kernels disable
5034 this kernel boot parameter, forcibly setting it
5035 to zero.
5036
5037 rcuscale.gp_async= [KNL]
5038 Measure performance of asynchronous
5039 grace-period primitives such as call_rcu().
5040
5041 rcuscale.gp_async_max= [KNL]
5042 Specify the maximum number of outstanding
5043 callbacks per writer thread. When a writer
5044 thread exceeds this limit, it invokes the
5045 corresponding flavor of rcu_barrier() to allow
5046 previously posted callbacks to drain.
5047
5048 rcuscale.gp_exp= [KNL]
5049 Measure performance of expedited synchronous
5050 grace-period primitives.
5051
5052 rcuscale.holdoff= [KNL]
5053 Set test-start holdoff period. The purpose of
5054 this parameter is to delay the start of the
5055 test until boot completes in order to avoid
5056 interference.
5057
5058 rcuscale.kfree_by_call_rcu= [KNL]
5059 In kernels built with CONFIG_RCU_LAZY=y, test
5060 call_rcu() instead of kfree_rcu().
5061
5062 rcuscale.kfree_mult= [KNL]
5063 Instead of allocating an object of size kfree_obj,
5064 allocate one of kfree_mult * sizeof(kfree_obj).
5065 Defaults to 1.
5066
5067 rcuscale.kfree_rcu_test= [KNL]
5068 Set to measure performance of kfree_rcu() flooding.
5069
5070 rcuscale.kfree_rcu_test_double= [KNL]
5071 Test the double-argument variant of kfree_rcu().
5072 If this parameter has the same value as
5073 rcuscale.kfree_rcu_test_single, both the single-
5074 and double-argument variants are tested.
5075
5076 rcuscale.kfree_rcu_test_single= [KNL]
5077 Test the single-argument variant of kfree_rcu().
5078 If this parameter has the same value as
5079 rcuscale.kfree_rcu_test_double, both the single-
5080 and double-argument variants are tested.
5081
5082 rcuscale.kfree_nthreads= [KNL]
5083 The number of threads running loops of kfree_rcu().
5084
5085 rcuscale.kfree_alloc_num= [KNL]
5086 Number of allocations and frees done in an iteration.
5087
5088 rcuscale.kfree_loops= [KNL]
5089 Number of loops doing rcuscale.kfree_alloc_num number
5090 of allocations and frees.
5091
5092 rcuscale.minruntime= [KNL]
5093 Set the minimum test run time in seconds. This
5094 does not affect the data-collection interval,
5095 but instead allows better measurement of things
5096 like CPU consumption.
5097
5098 rcuscale.nreaders= [KNL]
5099 Set number of RCU readers. The value -1 selects
5100 N, where N is the number of CPUs. A value
5101 "n" less than -1 selects N-n+1, where N is again
5102 the number of CPUs. For example, -2 selects N
5103 (the number of CPUs), -3 selects N+1, and so on.
5104 A value of "n" less than or equal to -N selects
5105 a single reader.
5106
5107 rcuscale.nwriters= [KNL]
5108 Set number of RCU writers. The values operate
5109 the same as for rcuscale.nreaders.
5110 N, where N is the number of CPUs
5111
5112 rcuscale.scale_type= [KNL]
5113 Specify the RCU implementation to test.
5114
5115 rcuscale.shutdown= [KNL]
5116 Shut the system down after performance tests
5117 complete. This is useful for hands-off automated
5118 testing.
5119
5120 rcuscale.verbose= [KNL]
5121 Enable additional printk() statements.
5122
5123 rcuscale.writer_holdoff= [KNL]
5124 Write-side holdoff between grace periods,
5125 in microseconds. The default of zero says
5126 no holdoff.
5127
5128 rcuscale.writer_holdoff_jiffies= [KNL]
5129 Additional write-side holdoff between grace
5130 periods, but in jiffies. The default of zero
5131 says no holdoff.
5132
5133 rcutorture.fqs_duration= [KNL]
5134 Set duration of force_quiescent_state bursts
5135 in microseconds.
5136
5137 rcutorture.fqs_holdoff= [KNL]
5138 Set holdoff time within force_quiescent_state bursts
5139 in microseconds.
5140
5141 rcutorture.fqs_stutter= [KNL]
5142 Set wait time between force_quiescent_state bursts
5143 in seconds.
5144
5145 rcutorture.fwd_progress= [KNL]
5146 Specifies the number of kthreads to be used
5147 for RCU grace-period forward-progress testing
5148 for the types of RCU supporting this notion.
5149 Defaults to 1 kthread, values less than zero or
5150 greater than the number of CPUs cause the number
5151 of CPUs to be used.
5152
5153 rcutorture.fwd_progress_div= [KNL]
5154 Specify the fraction of a CPU-stall-warning
5155 period to do tight-loop forward-progress testing.
5156
5157 rcutorture.fwd_progress_holdoff= [KNL]
5158 Number of seconds to wait between successive
5159 forward-progress tests.
5160
5161 rcutorture.fwd_progress_need_resched= [KNL]
5162 Enclose cond_resched() calls within checks for
5163 need_resched() during tight-loop forward-progress
5164 testing.
5165
5166 rcutorture.gp_cond= [KNL]
5167 Use conditional/asynchronous update-side
5168 primitives, if available.
5169
5170 rcutorture.gp_exp= [KNL]
5171 Use expedited update-side primitives, if available.
5172
5173 rcutorture.gp_normal= [KNL]
5174 Use normal (non-expedited) asynchronous
5175 update-side primitives, if available.
5176
5177 rcutorture.gp_sync= [KNL]
5178 Use normal (non-expedited) synchronous
5179 update-side primitives, if available. If all
5180 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5181 rcutorture.gp_normal=, and rcutorture.gp_sync=
5182 are zero, rcutorture acts as if is interpreted
5183 they are all non-zero.
5184
5185 rcutorture.irqreader= [KNL]
5186 Run RCU readers from irq handlers, or, more
5187 accurately, from a timer handler. Not all RCU
5188 flavors take kindly to this sort of thing.
5189
5190 rcutorture.leakpointer= [KNL]
5191 Leak an RCU-protected pointer out of the reader.
5192 This can of course result in splats, and is
5193 intended to test the ability of things like
5194 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5195 such leaks.
5196
5197 rcutorture.n_barrier_cbs= [KNL]
5198 Set callbacks/threads for rcu_barrier() testing.
5199
5200 rcutorture.nfakewriters= [KNL]
5201 Set number of concurrent RCU writers. These just
5202 stress RCU, they don't participate in the actual
5203 test, hence the "fake".
5204
5205 rcutorture.nocbs_nthreads= [KNL]
5206 Set number of RCU callback-offload togglers.
5207 Zero (the default) disables toggling.
5208
5209 rcutorture.nocbs_toggle= [KNL]
5210 Set the delay in milliseconds between successive
5211 callback-offload toggling attempts.
5212
5213 rcutorture.nreaders= [KNL]
5214 Set number of RCU readers. The value -1 selects
5215 N-1, where N is the number of CPUs. A value
5216 "n" less than -1 selects N-n-2, where N is again
5217 the number of CPUs. For example, -2 selects N
5218 (the number of CPUs), -3 selects N+1, and so on.
5219
5220 rcutorture.object_debug= [KNL]
5221 Enable debug-object double-call_rcu() testing.
5222
5223 rcutorture.onoff_holdoff= [KNL]
5224 Set time (s) after boot for CPU-hotplug testing.
5225
5226 rcutorture.onoff_interval= [KNL]
5227 Set time (jiffies) between CPU-hotplug operations,
5228 or zero to disable CPU-hotplug testing.
5229
5230 rcutorture.read_exit= [KNL]
5231 Set the number of read-then-exit kthreads used
5232 to test the interaction of RCU updaters and
5233 task-exit processing.
5234
5235 rcutorture.read_exit_burst= [KNL]
5236 The number of times in a given read-then-exit
5237 episode that a set of read-then-exit kthreads
5238 is spawned.
5239
5240 rcutorture.read_exit_delay= [KNL]
5241 The delay, in seconds, between successive
5242 read-then-exit testing episodes.
5243
5244 rcutorture.shuffle_interval= [KNL]
5245 Set task-shuffle interval (s). Shuffling tasks
5246 allows some CPUs to go into dyntick-idle mode
5247 during the rcutorture test.
5248
5249 rcutorture.shutdown_secs= [KNL]
5250 Set time (s) after boot system shutdown. This
5251 is useful for hands-off automated testing.
5252
5253 rcutorture.stall_cpu= [KNL]
5254 Duration of CPU stall (s) to test RCU CPU stall
5255 warnings, zero to disable.
5256
5257 rcutorture.stall_cpu_block= [KNL]
5258 Sleep while stalling if set. This will result
5259 in warnings from preemptible RCU in addition to
5260 any other stall-related activity. Note that
5261 in kernels built with CONFIG_PREEMPTION=n and
5262 CONFIG_PREEMPT_COUNT=y, this parameter will
5263 cause the CPU to pass through a quiescent state.
5264 Given CONFIG_PREEMPTION=n, this will suppress
5265 RCU CPU stall warnings, but will instead result
5266 in scheduling-while-atomic splats.
5267
5268 Use of this module parameter results in splats.
5269
5270
5271 rcutorture.stall_cpu_holdoff= [KNL]
5272 Time to wait (s) after boot before inducing stall.
5273
5274 rcutorture.stall_cpu_irqsoff= [KNL]
5275 Disable interrupts while stalling if set.
5276
5277 rcutorture.stall_gp_kthread= [KNL]
5278 Duration (s) of forced sleep within RCU
5279 grace-period kthread to test RCU CPU stall
5280 warnings, zero to disable. If both stall_cpu
5281 and stall_gp_kthread are specified, the
5282 kthread is starved first, then the CPU.
5283
5284 rcutorture.stat_interval= [KNL]
5285 Time (s) between statistics printk()s.
5286
5287 rcutorture.stutter= [KNL]
5288 Time (s) to stutter testing, for example, specifying
5289 five seconds causes the test to run for five seconds,
5290 wait for five seconds, and so on. This tests RCU's
5291 ability to transition abruptly to and from idle.
5292
5293 rcutorture.test_boost= [KNL]
5294 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5295 "Maybe" means test if the RCU implementation
5296 under test support RCU priority boosting.
5297
5298 rcutorture.test_boost_duration= [KNL]
5299 Duration (s) of each individual boost test.
5300
5301 rcutorture.test_boost_interval= [KNL]
5302 Interval (s) between each boost test.
5303
5304 rcutorture.test_no_idle_hz= [KNL]
5305 Test RCU's dyntick-idle handling. See also the
5306 rcutorture.shuffle_interval parameter.
5307
5308 rcutorture.torture_type= [KNL]
5309 Specify the RCU implementation to test.
5310
5311 rcutorture.verbose= [KNL]
5312 Enable additional printk() statements.
5313
5314 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5315 Dump ftrace buffer after reporting RCU CPU
5316 stall warning.
5317
5318 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5319 Provide RCU CPU stall notifiers, but see the
5320 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5321 option's help text. TL;DR: You almost certainly
5322 do not want rcupdate.rcu_cpu_stall_notifiers.
5323
5324 rcupdate.rcu_cpu_stall_suppress= [KNL]
5325 Suppress RCU CPU stall warning messages.
5326
5327 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5328 Suppress RCU CPU stall warning messages and
5329 rcutorture writer stall warnings that occur
5330 during early boot, that is, during the time
5331 before the init task is spawned.
5332
5333 rcupdate.rcu_cpu_stall_timeout= [KNL]
5334 Set timeout for RCU CPU stall warning messages.
5335 The value is in seconds and the maximum allowed
5336 value is 300 seconds.
5337
5338 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5339 Set timeout for expedited RCU CPU stall warning
5340 messages. The value is in milliseconds
5341 and the maximum allowed value is 21000
5342 milliseconds. Please note that this value is
5343 adjusted to an arch timer tick resolution.
5344 Setting this to zero causes the value from
5345 rcupdate.rcu_cpu_stall_timeout to be used (after
5346 conversion from seconds to milliseconds).
5347
5348 rcupdate.rcu_cpu_stall_cputime= [KNL]
5349 Provide statistics on the cputime and count of
5350 interrupts and tasks during the sampling period. For
5351 multiple continuous RCU stalls, all sampling periods
5352 begin at half of the first RCU stall timeout.
5353
5354 rcupdate.rcu_exp_stall_task_details= [KNL]
5355 Print stack dumps of any tasks blocking the
5356 current expedited RCU grace period during an
5357 expedited RCU CPU stall warning.
5358
5359 rcupdate.rcu_expedited= [KNL]
5360 Use expedited grace-period primitives, for
5361 example, synchronize_rcu_expedited() instead
5362 of synchronize_rcu(). This reduces latency,
5363 but can increase CPU utilization, degrade
5364 real-time latency, and degrade energy efficiency.
5365 No effect on CONFIG_TINY_RCU kernels.
5366
5367 rcupdate.rcu_normal= [KNL]
5368 Use only normal grace-period primitives,
5369 for example, synchronize_rcu() instead of
5370 synchronize_rcu_expedited(). This improves
5371 real-time latency, CPU utilization, and
5372 energy efficiency, but can expose users to
5373 increased grace-period latency. This parameter
5374 overrides rcupdate.rcu_expedited. No effect on
5375 CONFIG_TINY_RCU kernels.
5376
5377 rcupdate.rcu_normal_after_boot= [KNL]
5378 Once boot has completed (that is, after
5379 rcu_end_inkernel_boot() has been invoked), use
5380 only normal grace-period primitives. No effect
5381 on CONFIG_TINY_RCU kernels.
5382
5383 But note that CONFIG_PREEMPT_RT=y kernels enables
5384 this kernel boot parameter, forcibly setting
5385 it to the value one, that is, converting any
5386 post-boot attempt at an expedited RCU grace
5387 period to instead use normal non-expedited
5388 grace-period processing.
5389
5390 rcupdate.rcu_task_collapse_lim= [KNL]
5391 Set the maximum number of callbacks present
5392 at the beginning of a grace period that allows
5393 the RCU Tasks flavors to collapse back to using
5394 a single callback queue. This switching only
5395 occurs when rcupdate.rcu_task_enqueue_lim is
5396 set to the default value of -1.
5397
5398 rcupdate.rcu_task_contend_lim= [KNL]
5399 Set the minimum number of callback-queuing-time
5400 lock-contention events per jiffy required to
5401 cause the RCU Tasks flavors to switch to per-CPU
5402 callback queuing. This switching only occurs
5403 when rcupdate.rcu_task_enqueue_lim is set to
5404 the default value of -1.
5405
5406 rcupdate.rcu_task_enqueue_lim= [KNL]
5407 Set the number of callback queues to use for the
5408 RCU Tasks family of RCU flavors. The default
5409 of -1 allows this to be automatically (and
5410 dynamically) adjusted. This parameter is intended
5411 for use in testing.
5412
5413 rcupdate.rcu_task_ipi_delay= [KNL]
5414 Set time in jiffies during which RCU tasks will
5415 avoid sending IPIs, starting with the beginning
5416 of a given grace period. Setting a large
5417 number avoids disturbing real-time workloads,
5418 but lengthens grace periods.
5419
5420 rcupdate.rcu_task_lazy_lim= [KNL]
5421 Number of callbacks on a given CPU that will
5422 cancel laziness on that CPU. Use -1 to disable
5423 cancellation of laziness, but be advised that
5424 doing so increases the danger of OOM due to
5425 callback flooding.
5426
5427 rcupdate.rcu_task_stall_info= [KNL]
5428 Set initial timeout in jiffies for RCU task stall
5429 informational messages, which give some indication
5430 of the problem for those not patient enough to
5431 wait for ten minutes. Informational messages are
5432 only printed prior to the stall-warning message
5433 for a given grace period. Disable with a value
5434 less than or equal to zero. Defaults to ten
5435 seconds. A change in value does not take effect
5436 until the beginning of the next grace period.
5437
5438 rcupdate.rcu_task_stall_info_mult= [KNL]
5439 Multiplier for time interval between successive
5440 RCU task stall informational messages for a given
5441 RCU tasks grace period. This value is clamped
5442 to one through ten, inclusive. It defaults to
5443 the value three, so that the first informational
5444 message is printed 10 seconds into the grace
5445 period, the second at 40 seconds, the third at
5446 160 seconds, and then the stall warning at 600
5447 seconds would prevent a fourth at 640 seconds.
5448
5449 rcupdate.rcu_task_stall_timeout= [KNL]
5450 Set timeout in jiffies for RCU task stall
5451 warning messages. Disable with a value less
5452 than or equal to zero. Defaults to ten minutes.
5453 A change in value does not take effect until
5454 the beginning of the next grace period.
5455
5456 rcupdate.rcu_tasks_lazy_ms= [KNL]
5457 Set timeout in milliseconds RCU Tasks asynchronous
5458 callback batching for call_rcu_tasks().
5459 A negative value will take the default. A value
5460 of zero will disable batching. Batching is
5461 always disabled for synchronize_rcu_tasks().
5462
5463 rcupdate.rcu_tasks_rude_lazy_ms= [KNL]
5464 Set timeout in milliseconds RCU Tasks
5465 Rude asynchronous callback batching for
5466 call_rcu_tasks_rude(). A negative value
5467 will take the default. A value of zero will
5468 disable batching. Batching is always disabled
5469 for synchronize_rcu_tasks_rude().
5470
5471 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5472 Set timeout in milliseconds RCU Tasks
5473 Trace asynchronous callback batching for
5474 call_rcu_tasks_trace(). A negative value
5475 will take the default. A value of zero will
5476 disable batching. Batching is always disabled
5477 for synchronize_rcu_tasks_trace().
5478
5479 rcupdate.rcu_self_test= [KNL]
5480 Run the RCU early boot self tests
5481
5482 rdinit= [KNL]
5483 Format: <full_path>
5484 Run specified binary instead of /init from the ramdisk,
5485 used for early userspace startup. See initrd.
5486
5487 rdrand= [X86]
5488 force - Override the decision by the kernel to hide the
5489 advertisement of RDRAND support (this affects
5490 certain AMD processors because of buggy BIOS
5491 support, specifically around the suspend/resume
5492 path).
5493
5494 rdt= [HW,X86,RDT]
5495 Turn on/off individual RDT features. List is:
5496 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5497 mba, smba, bmec.
5498 E.g. to turn on cmt and turn off mba use:
5499 rdt=cmt,!mba
5500
5501 reboot= [KNL]
5502 Format (x86 or x86_64):
5503 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5504 [[,]s[mp]#### \
5505 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5506 [[,]f[orce]
5507 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5508 (prefix with 'panic_' to set mode for panic
5509 reboot only),
5510 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5511 reboot_force is either force or not specified,
5512 reboot_cpu is s[mp]#### with #### being the processor
5513 to be used for rebooting.
5514
5515 refscale.holdoff= [KNL]
5516 Set test-start holdoff period. The purpose of
5517 this parameter is to delay the start of the
5518 test until boot completes in order to avoid
5519 interference.
5520
5521 refscale.lookup_instances= [KNL]
5522 Number of data elements to use for the forms of
5523 SLAB_TYPESAFE_BY_RCU testing. A negative number
5524 is negated and multiplied by nr_cpu_ids, while
5525 zero specifies nr_cpu_ids.
5526
5527 refscale.loops= [KNL]
5528 Set the number of loops over the synchronization
5529 primitive under test. Increasing this number
5530 reduces noise due to loop start/end overhead,
5531 but the default has already reduced the per-pass
5532 noise to a handful of picoseconds on ca. 2020
5533 x86 laptops.
5534
5535 refscale.nreaders= [KNL]
5536 Set number of readers. The default value of -1
5537 selects N, where N is roughly 75% of the number
5538 of CPUs. A value of zero is an interesting choice.
5539
5540 refscale.nruns= [KNL]
5541 Set number of runs, each of which is dumped onto
5542 the console log.
5543
5544 refscale.readdelay= [KNL]
5545 Set the read-side critical-section duration,
5546 measured in microseconds.
5547
5548 refscale.scale_type= [KNL]
5549 Specify the read-protection implementation to test.
5550
5551 refscale.shutdown= [KNL]
5552 Shut down the system at the end of the performance
5553 test. This defaults to 1 (shut it down) when
5554 refscale is built into the kernel and to 0 (leave
5555 it running) when refscale is built as a module.
5556
5557 refscale.verbose= [KNL]
5558 Enable additional printk() statements.
5559
5560 refscale.verbose_batched= [KNL]
5561 Batch the additional printk() statements. If zero
5562 (the default) or negative, print everything. Otherwise,
5563 print every Nth verbose statement, where N is the value
5564 specified.
5565
5566 regulator_ignore_unused
5567 [REGULATOR]
5568 Prevents regulator framework from disabling regulators
5569 that are unused, due no driver claiming them. This may
5570 be useful for debug and development, but should not be
5571 needed on a platform with proper driver support.
5572
5573 relax_domain_level=
5574 [KNL, SMP] Set scheduler's default relax_domain_level.
5575 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5576
5577 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5578 Format: <base1>,<size1>[,<base2>,<size2>,...]
5579 Reserve I/O ports or memory so the kernel won't use
5580 them. If <base> is less than 0x10000, the region
5581 is assumed to be I/O ports; otherwise it is memory.
5582
5583 reservetop= [X86-32]
5584 Format: nn[KMG]
5585 Reserves a hole at the top of the kernel virtual
5586 address space.
5587
5588 reset_devices [KNL] Force drivers to reset the underlying device
5589 during initialization.
5590
5591 resume= [SWSUSP]
5592 Specify the partition device for software suspend
5593 Format:
5594 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5595
5596 resume_offset= [SWSUSP]
5597 Specify the offset from the beginning of the partition
5598 given by "resume=" at which the swap header is located,
5599 in <PAGE_SIZE> units (needed only for swap files).
5600 See Documentation/power/swsusp-and-swap-files.rst
5601
5602 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5603 read the resume files
5604
5605 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5606 Useful for devices that are detected asynchronously
5607 (e.g. USB and MMC devices).
5608
5609 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
5610 be accessible via /sys/firmware/initrd.
5611
5612 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5613 Speculative Code Execution with Return Instructions)
5614 vulnerability.
5615
5616 AMD-based UNRET and IBPB mitigations alone do not stop
5617 sibling threads from influencing the predictions of other
5618 sibling threads. For that reason, STIBP is used on pro-
5619 cessors that support it, and mitigate SMT on processors
5620 that don't.
5621
5622 off - no mitigation
5623 auto - automatically select a migitation
5624 auto,nosmt - automatically select a mitigation,
5625 disabling SMT if necessary for
5626 the full mitigation (only on Zen1
5627 and older without STIBP).
5628 ibpb - On AMD, mitigate short speculation
5629 windows on basic block boundaries too.
5630 Safe, highest perf impact. It also
5631 enables STIBP if present. Not suitable
5632 on Intel.
5633 ibpb,nosmt - Like "ibpb" above but will disable SMT
5634 when STIBP is not available. This is
5635 the alternative for systems which do not
5636 have STIBP.
5637 unret - Force enable untrained return thunks,
5638 only effective on AMD f15h-f17h based
5639 systems.
5640 unret,nosmt - Like unret, but will disable SMT when STIBP
5641 is not available. This is the alternative for
5642 systems which do not have STIBP.
5643
5644 Selecting 'auto' will choose a mitigation method at run
5645 time according to the CPU.
5646
5647 Not specifying this option is equivalent to retbleed=auto.
5648
5649 rfkill.default_state=
5650 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5651 etc. communication is blocked by default.
5652 1 Unblocked.
5653
5654 rfkill.master_switch_mode=
5655 0 The "airplane mode" button does nothing.
5656 1 The "airplane mode" button toggles between everything
5657 blocked and the previous configuration.
5658 2 The "airplane mode" button toggles between everything
5659 blocked and everything unblocked.
5660
5661 rhash_entries= [KNL,NET]
5662 Set number of hash buckets for route cache
5663
5664 ring3mwait=disable
5665 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5666 CPUs.
5667
5668 riscv_isa_fallback [RISCV]
5669 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
5670 falling back to detecting extension support by parsing
5671 "riscv,isa" property on devicetree systems when the
5672 replacement properties are not found. See the Kconfig
5673 entry for RISCV_ISA_FALLBACK.
5674
5675 ro [KNL] Mount root device read-only on boot
5676
5677 rodata= [KNL]
5678 on Mark read-only kernel memory as read-only (default).
5679 off Leave read-only kernel memory writable for debugging.
5680 full Mark read-only kernel memory and aliases as read-only
5681 [arm64]
5682
5683 rockchip.usb_uart
5684 Enable the uart passthrough on the designated usb port
5685 on Rockchip SoCs. When active, the signals of the
5686 debug-uart get routed to the D+ and D- pins of the usb
5687 port and the regular usb controller gets disabled.
5688
5689 root= [KNL] Root filesystem
5690 Usually this a a block device specifier of some kind,
5691 see the early_lookup_bdev comment in
5692 block/early-lookup.c for details.
5693 Alternatively this can be "ram" for the legacy initial
5694 ramdisk, "nfs" and "cifs" for root on a network file
5695 system, or "mtd" and "ubi" for mounting from raw flash.
5696
5697 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5698 mount the root filesystem
5699
5700 rootflags= [KNL] Set root filesystem mount option string
5701
5702 rootfstype= [KNL] Set root filesystem type
5703
5704 rootwait [KNL] Wait (indefinitely) for root device to show up.
5705 Useful for devices that are detected asynchronously
5706 (e.g. USB and MMC devices).
5707
5708 rootwait= [KNL] Maximum time (in seconds) to wait for root device
5709 to show up before attempting to mount the root
5710 filesystem.
5711
5712 rproc_mem=nn[KMG][@address]
5713 [KNL,ARM,CMA] Remoteproc physical memory block.
5714 Memory area to be used by remote processor image,
5715 managed by CMA.
5716
5717 rw [KNL] Mount root device read-write on boot
5718
5719 S [KNL] Run init in single mode
5720
5721 s390_iommu= [HW,S390]
5722 Set s390 IOTLB flushing mode
5723 strict
5724 With strict flushing every unmap operation will result
5725 in an IOTLB flush. Default is lazy flushing before
5726 reuse, which is faster. Deprecated, equivalent to
5727 iommu.strict=1.
5728
5729 s390_iommu_aperture= [KNL,S390]
5730 Specifies the size of the per device DMA address space
5731 accessible through the DMA and IOMMU APIs as a decimal
5732 factor of the size of main memory.
5733 The default is 1 meaning that one can concurrently use
5734 as many DMA addresses as physical memory is installed,
5735 if supported by hardware, and thus map all of memory
5736 once. With a value of 2 one can map all of memory twice
5737 and so on. As a special case a factor of 0 imposes no
5738 restrictions other than those given by hardware at the
5739 cost of significant additional memory use for tables.
5740
5741 sa1100ir [NET]
5742 See drivers/net/irda/sa1100_ir.c.
5743
5744 sched_verbose [KNL] Enables verbose scheduler debug messages.
5745
5746 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5747 Allowed values are enable and disable. This feature
5748 incurs a small amount of overhead in the scheduler
5749 but is useful for debugging and performance tuning.
5750
5751 sched_thermal_decay_shift=
5752 [KNL, SMP] Set a decay shift for scheduler thermal
5753 pressure signal. Thermal pressure signal follows the
5754 default decay period of other scheduler pelt
5755 signals(usually 32 ms but configurable). Setting
5756 sched_thermal_decay_shift will left shift the decay
5757 period for the thermal pressure signal by the shift
5758 value.
5759 i.e. with the default pelt decay period of 32 ms
5760 sched_thermal_decay_shift thermal pressure decay pr
5761 1 64 ms
5762 2 128 ms
5763 and so on.
5764 Format: integer between 0 and 10
5765 Default is 0.
5766
5767 scftorture.holdoff= [KNL]
5768 Number of seconds to hold off before starting
5769 test. Defaults to zero for module insertion and
5770 to 10 seconds for built-in smp_call_function()
5771 tests.
5772
5773 scftorture.longwait= [KNL]
5774 Request ridiculously long waits randomly selected
5775 up to the chosen limit in seconds. Zero (the
5776 default) disables this feature. Please note
5777 that requesting even small non-zero numbers of
5778 seconds can result in RCU CPU stall warnings,
5779 softlockup complaints, and so on.
5780
5781 scftorture.nthreads= [KNL]
5782 Number of kthreads to spawn to invoke the
5783 smp_call_function() family of functions.
5784 The default of -1 specifies a number of kthreads
5785 equal to the number of CPUs.
5786
5787 scftorture.onoff_holdoff= [KNL]
5788 Number seconds to wait after the start of the
5789 test before initiating CPU-hotplug operations.
5790
5791 scftorture.onoff_interval= [KNL]
5792 Number seconds to wait between successive
5793 CPU-hotplug operations. Specifying zero (which
5794 is the default) disables CPU-hotplug operations.
5795
5796 scftorture.shutdown_secs= [KNL]
5797 The number of seconds following the start of the
5798 test after which to shut down the system. The
5799 default of zero avoids shutting down the system.
5800 Non-zero values are useful for automated tests.
5801
5802 scftorture.stat_interval= [KNL]
5803 The number of seconds between outputting the
5804 current test statistics to the console. A value
5805 of zero disables statistics output.
5806
5807 scftorture.stutter_cpus= [KNL]
5808 The number of jiffies to wait between each change
5809 to the set of CPUs under test.
5810
5811 scftorture.use_cpus_read_lock= [KNL]
5812 Use use_cpus_read_lock() instead of the default
5813 preempt_disable() to disable CPU hotplug
5814 while invoking one of the smp_call_function*()
5815 functions.
5816
5817 scftorture.verbose= [KNL]
5818 Enable additional printk() statements.
5819
5820 scftorture.weight_single= [KNL]
5821 The probability weighting to use for the
5822 smp_call_function_single() function with a zero
5823 "wait" parameter. A value of -1 selects the
5824 default if all other weights are -1. However,
5825 if at least one weight has some other value, a
5826 value of -1 will instead select a weight of zero.
5827
5828 scftorture.weight_single_wait= [KNL]
5829 The probability weighting to use for the
5830 smp_call_function_single() function with a
5831 non-zero "wait" parameter. See weight_single.
5832
5833 scftorture.weight_many= [KNL]
5834 The probability weighting to use for the
5835 smp_call_function_many() function with a zero
5836 "wait" parameter. See weight_single.
5837 Note well that setting a high probability for
5838 this weighting can place serious IPI load
5839 on the system.
5840
5841 scftorture.weight_many_wait= [KNL]
5842 The probability weighting to use for the
5843 smp_call_function_many() function with a
5844 non-zero "wait" parameter. See weight_single
5845 and weight_many.
5846
5847 scftorture.weight_all= [KNL]
5848 The probability weighting to use for the
5849 smp_call_function_all() function with a zero
5850 "wait" parameter. See weight_single and
5851 weight_many.
5852
5853 scftorture.weight_all_wait= [KNL]
5854 The probability weighting to use for the
5855 smp_call_function_all() function with a
5856 non-zero "wait" parameter. See weight_single
5857 and weight_many.
5858
5859 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5860 xtime_lock contention on larger systems, and/or RCU lock
5861 contention on all systems with CONFIG_MAXSMP set.
5862 Format: { "0" | "1" }
5863 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5864 1 -- enable.
5865 Note: increases power consumption, thus should only be
5866 enabled if running jitter sensitive (HPC/RT) workloads.
5867
5868 security= [SECURITY] Choose a legacy "major" security module to
5869 enable at boot. This has been deprecated by the
5870 "lsm=" parameter.
5871
5872 selinux= [SELINUX] Disable or enable SELinux at boot time.
5873 Format: { "0" | "1" }
5874 See security/selinux/Kconfig help text.
5875 0 -- disable.
5876 1 -- enable.
5877 Default value is 1.
5878
5879 serialnumber [BUGS=X86-32]
5880
5881 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
5882
5883 shapers= [NET]
5884 Maximal number of shapers.
5885
5886 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
5887 Limit apic dumping. The parameter defines the maximal
5888 number of local apics being dumped. Also it is possible
5889 to set it to "all" by meaning -- no limit here.
5890 Format: { 1 (default) | 2 | ... | all }.
5891 The parameter valid if only apic=debug or
5892 apic=verbose is specified.
5893 Example: apic=debug show_lapic=all
5894
5895 simeth= [IA-64]
5896 simscsi=
5897
5898 slram= [HW,MTD]
5899
5900 slab_merge [MM]
5901 Enable merging of slabs with similar size when the
5902 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5903
5904 slab_nomerge [MM]
5905 Disable merging of slabs with similar size. May be
5906 necessary if there is some reason to distinguish
5907 allocs to different slabs, especially in hardened
5908 environments where the risk of heap overflows and
5909 layout control by attackers can usually be
5910 frustrated by disabling merging. This will reduce
5911 most of the exposure of a heap attack to a single
5912 cache (risks via metadata attacks are mostly
5913 unchanged). Debug options disable merging on their
5914 own.
5915 For more information see Documentation/mm/slub.rst.
5916
5917 slab_max_order= [MM, SLAB]
5918 Determines the maximum allowed order for slabs.
5919 A high setting may cause OOMs due to memory
5920 fragmentation. Defaults to 1 for systems with
5921 more than 32MB of RAM, 0 otherwise.
5922
5923 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5924 Enabling slub_debug allows one to determine the
5925 culprit if slab objects become corrupted. Enabling
5926 slub_debug can create guard zones around objects and
5927 may poison objects when not in use. Also tracks the
5928 last alloc / free. For more information see
5929 Documentation/mm/slub.rst.
5930
5931 slub_max_order= [MM, SLUB]
5932 Determines the maximum allowed order for slabs.
5933 A high setting may cause OOMs due to memory
5934 fragmentation. For more information see
5935 Documentation/mm/slub.rst.
5936
5937 slub_min_objects= [MM, SLUB]
5938 The minimum number of objects per slab. SLUB will
5939 increase the slab order up to slub_max_order to
5940 generate a sufficiently large slab able to contain
5941 the number of objects indicated. The higher the number
5942 of objects the smaller the overhead of tracking slabs
5943 and the less frequently locks need to be acquired.
5944 For more information see Documentation/mm/slub.rst.
5945
5946 slub_min_order= [MM, SLUB]
5947 Determines the minimum page order for slabs. Must be
5948 lower than slub_max_order.
5949 For more information see Documentation/mm/slub.rst.
5950
5951 slub_merge [MM, SLUB]
5952 Same with slab_merge.
5953
5954 slub_nomerge [MM, SLUB]
5955 Same with slab_nomerge. This is supported for legacy.
5956 See slab_nomerge for more information.
5957
5958 smart2= [HW]
5959 Format: <io1>[,<io2>[,...,<io8>]]
5960
5961 smp.csd_lock_timeout= [KNL]
5962 Specify the period of time in milliseconds
5963 that smp_call_function() and friends will wait
5964 for a CPU to release the CSD lock. This is
5965 useful when diagnosing bugs involving CPUs
5966 disabling interrupts for extended periods
5967 of time. Defaults to 5,000 milliseconds, and
5968 setting a value of zero disables this feature.
5969 This feature may be more efficiently disabled
5970 using the csdlock_debug- kernel parameter.
5971
5972 smp.panic_on_ipistall= [KNL]
5973 If a csd_lock_timeout extends for more than
5974 the specified number of milliseconds, panic the
5975 system. By default, let CSD-lock acquisition
5976 take as long as they take. Specifying 300,000
5977 for this value provides a 5-minute timeout.
5978
5979 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5980 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5981 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5982 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5983 smsc-ircc2.ircc_irq= [HW] IRQ line
5984 smsc-ircc2.ircc_dma= [HW] DMA channel
5985 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5986 0: Toshiba Satellite 1800 (GP data pin select)
5987 1: Fast pin select (default)
5988 2: ATC IRMode
5989
5990 smt= [KNL,MIPS,S390] Set the maximum number of threads (logical
5991 CPUs) to use per physical CPU on systems capable of
5992 symmetric multithreading (SMT). Will be capped to the
5993 actual hardware limit.
5994 Format: <integer>
5995 Default: -1 (no limit)
5996
5997 softlockup_panic=
5998 [KNL] Should the soft-lockup detector generate panics.
5999 Format: 0 | 1
6000
6001 A value of 1 instructs the soft-lockup detector
6002 to panic the machine when a soft-lockup occurs. It is
6003 also controlled by the kernel.softlockup_panic sysctl
6004 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6005 respective build-time switch to that functionality.
6006
6007 softlockup_all_cpu_backtrace=
6008 [KNL] Should the soft-lockup detector generate
6009 backtraces on all cpus.
6010 Format: 0 | 1
6011
6012 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6013 See Documentation/admin-guide/laptops/sonypi.rst
6014
6015 spectre_v2= [X86] Control mitigation of Spectre variant 2
6016 (indirect branch speculation) vulnerability.
6017 The default operation protects the kernel from
6018 user space attacks.
6019
6020 on - unconditionally enable, implies
6021 spectre_v2_user=on
6022 off - unconditionally disable, implies
6023 spectre_v2_user=off
6024 auto - kernel detects whether your CPU model is
6025 vulnerable
6026
6027 Selecting 'on' will, and 'auto' may, choose a
6028 mitigation method at run time according to the
6029 CPU, the available microcode, the setting of the
6030 CONFIG_RETPOLINE configuration option, and the
6031 compiler with which the kernel was built.
6032
6033 Selecting 'on' will also enable the mitigation
6034 against user space to user space task attacks.
6035
6036 Selecting 'off' will disable both the kernel and
6037 the user space protections.
6038
6039 Specific mitigations can also be selected manually:
6040
6041 retpoline - replace indirect branches
6042 retpoline,generic - Retpolines
6043 retpoline,lfence - LFENCE; indirect branch
6044 retpoline,amd - alias for retpoline,lfence
6045 eibrs - Enhanced/Auto IBRS
6046 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6047 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6048 ibrs - use IBRS to protect kernel
6049
6050 Not specifying this option is equivalent to
6051 spectre_v2=auto.
6052
6053 spectre_v2_user=
6054 [X86] Control mitigation of Spectre variant 2
6055 (indirect branch speculation) vulnerability between
6056 user space tasks
6057
6058 on - Unconditionally enable mitigations. Is
6059 enforced by spectre_v2=on
6060
6061 off - Unconditionally disable mitigations. Is
6062 enforced by spectre_v2=off
6063
6064 prctl - Indirect branch speculation is enabled,
6065 but mitigation can be enabled via prctl
6066 per thread. The mitigation control state
6067 is inherited on fork.
6068
6069 prctl,ibpb
6070 - Like "prctl" above, but only STIBP is
6071 controlled per thread. IBPB is issued
6072 always when switching between different user
6073 space processes.
6074
6075 seccomp
6076 - Same as "prctl" above, but all seccomp
6077 threads will enable the mitigation unless
6078 they explicitly opt out.
6079
6080 seccomp,ibpb
6081 - Like "seccomp" above, but only STIBP is
6082 controlled per thread. IBPB is issued
6083 always when switching between different
6084 user space processes.
6085
6086 auto - Kernel selects the mitigation depending on
6087 the available CPU features and vulnerability.
6088
6089 Default mitigation: "prctl"
6090
6091 Not specifying this option is equivalent to
6092 spectre_v2_user=auto.
6093
6094 spec_rstack_overflow=
6095 [X86] Control RAS overflow mitigation on AMD Zen CPUs
6096
6097 off - Disable mitigation
6098 microcode - Enable microcode mitigation only
6099 safe-ret - Enable sw-only safe RET mitigation (default)
6100 ibpb - Enable mitigation by issuing IBPB on
6101 kernel entry
6102 ibpb-vmexit - Issue IBPB only on VMEXIT
6103 (cloud-specific mitigation)
6104
6105 spec_store_bypass_disable=
6106 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
6107 (Speculative Store Bypass vulnerability)
6108
6109 Certain CPUs are vulnerable to an exploit against a
6110 a common industry wide performance optimization known
6111 as "Speculative Store Bypass" in which recent stores
6112 to the same memory location may not be observed by
6113 later loads during speculative execution. The idea
6114 is that such stores are unlikely and that they can
6115 be detected prior to instruction retirement at the
6116 end of a particular speculation execution window.
6117
6118 In vulnerable processors, the speculatively forwarded
6119 store can be used in a cache side channel attack, for
6120 example to read memory to which the attacker does not
6121 directly have access (e.g. inside sandboxed code).
6122
6123 This parameter controls whether the Speculative Store
6124 Bypass optimization is used.
6125
6126 On x86 the options are:
6127
6128 on - Unconditionally disable Speculative Store Bypass
6129 off - Unconditionally enable Speculative Store Bypass
6130 auto - Kernel detects whether the CPU model contains an
6131 implementation of Speculative Store Bypass and
6132 picks the most appropriate mitigation. If the
6133 CPU is not vulnerable, "off" is selected. If the
6134 CPU is vulnerable the default mitigation is
6135 architecture and Kconfig dependent. See below.
6136 prctl - Control Speculative Store Bypass per thread
6137 via prctl. Speculative Store Bypass is enabled
6138 for a process by default. The state of the control
6139 is inherited on fork.
6140 seccomp - Same as "prctl" above, but all seccomp threads
6141 will disable SSB unless they explicitly opt out.
6142
6143 Default mitigations:
6144 X86: "prctl"
6145
6146 On powerpc the options are:
6147
6148 on,auto - On Power8 and Power9 insert a store-forwarding
6149 barrier on kernel entry and exit. On Power7
6150 perform a software flush on kernel entry and
6151 exit.
6152 off - No action.
6153
6154 Not specifying this option is equivalent to
6155 spec_store_bypass_disable=auto.
6156
6157 spia_io_base= [HW,MTD]
6158 spia_fio_base=
6159 spia_pedr=
6160 spia_peddr=
6161
6162 split_lock_detect=
6163 [X86] Enable split lock detection or bus lock detection
6164
6165 When enabled (and if hardware support is present), atomic
6166 instructions that access data across cache line
6167 boundaries will result in an alignment check exception
6168 for split lock detection or a debug exception for
6169 bus lock detection.
6170
6171 off - not enabled
6172
6173 warn - the kernel will emit rate-limited warnings
6174 about applications triggering the #AC
6175 exception or the #DB exception. This mode is
6176 the default on CPUs that support split lock
6177 detection or bus lock detection. Default
6178 behavior is by #AC if both features are
6179 enabled in hardware.
6180
6181 fatal - the kernel will send SIGBUS to applications
6182 that trigger the #AC exception or the #DB
6183 exception. Default behavior is by #AC if
6184 both features are enabled in hardware.
6185
6186 ratelimit:N -
6187 Set system wide rate limit to N bus locks
6188 per second for bus lock detection.
6189 0 < N <= 1000.
6190
6191 N/A for split lock detection.
6192
6193
6194 If an #AC exception is hit in the kernel or in
6195 firmware (i.e. not while executing in user mode)
6196 the kernel will oops in either "warn" or "fatal"
6197 mode.
6198
6199 #DB exception for bus lock is triggered only when
6200 CPL > 0.
6201
6202 srbds= [X86,INTEL]
6203 Control the Special Register Buffer Data Sampling
6204 (SRBDS) mitigation.
6205
6206 Certain CPUs are vulnerable to an MDS-like
6207 exploit which can leak bits from the random
6208 number generator.
6209
6210 By default, this issue is mitigated by
6211 microcode. However, the microcode fix can cause
6212 the RDRAND and RDSEED instructions to become
6213 much slower. Among other effects, this will
6214 result in reduced throughput from /dev/urandom.
6215
6216 The microcode mitigation can be disabled with
6217 the following option:
6218
6219 off: Disable mitigation and remove
6220 performance impact to RDRAND and RDSEED
6221
6222 srcutree.big_cpu_lim [KNL]
6223 Specifies the number of CPUs constituting a
6224 large system, such that srcu_struct structures
6225 should immediately allocate an srcu_node array.
6226 This kernel-boot parameter defaults to 128,
6227 but takes effect only when the low-order four
6228 bits of srcutree.convert_to_big is equal to 3
6229 (decide at boot).
6230
6231 srcutree.convert_to_big [KNL]
6232 Specifies under what conditions an SRCU tree
6233 srcu_struct structure will be converted to big
6234 form, that is, with an rcu_node tree:
6235
6236 0: Never.
6237 1: At init_srcu_struct() time.
6238 2: When rcutorture decides to.
6239 3: Decide at boot time (default).
6240 0x1X: Above plus if high contention.
6241
6242 Either way, the srcu_node tree will be sized based
6243 on the actual runtime number of CPUs (nr_cpu_ids)
6244 instead of the compile-time CONFIG_NR_CPUS.
6245
6246 srcutree.counter_wrap_check [KNL]
6247 Specifies how frequently to check for
6248 grace-period sequence counter wrap for the
6249 srcu_data structure's ->srcu_gp_seq_needed field.
6250 The greater the number of bits set in this kernel
6251 parameter, the less frequently counter wrap will
6252 be checked for. Note that the bottom two bits
6253 are ignored.
6254
6255 srcutree.exp_holdoff [KNL]
6256 Specifies how many nanoseconds must elapse
6257 since the end of the last SRCU grace period for
6258 a given srcu_struct until the next normal SRCU
6259 grace period will be considered for automatic
6260 expediting. Set to zero to disable automatic
6261 expediting.
6262
6263 srcutree.srcu_max_nodelay [KNL]
6264 Specifies the number of no-delay instances
6265 per jiffy for which the SRCU grace period
6266 worker thread will be rescheduled with zero
6267 delay. Beyond this limit, worker thread will
6268 be rescheduled with a sleep delay of one jiffy.
6269
6270 srcutree.srcu_max_nodelay_phase [KNL]
6271 Specifies the per-grace-period phase, number of
6272 non-sleeping polls of readers. Beyond this limit,
6273 grace period worker thread will be rescheduled
6274 with a sleep delay of one jiffy, between each
6275 rescan of the readers, for a grace period phase.
6276
6277 srcutree.srcu_retry_check_delay [KNL]
6278 Specifies number of microseconds of non-sleeping
6279 delay between each non-sleeping poll of readers.
6280
6281 srcutree.small_contention_lim [KNL]
6282 Specifies the number of update-side contention
6283 events per jiffy will be tolerated before
6284 initiating a conversion of an srcu_struct
6285 structure to big form. Note that the value of
6286 srcutree.convert_to_big must have the 0x10 bit
6287 set for contention-based conversions to occur.
6288
6289 ssbd= [ARM64,HW]
6290 Speculative Store Bypass Disable control
6291
6292 On CPUs that are vulnerable to the Speculative
6293 Store Bypass vulnerability and offer a
6294 firmware based mitigation, this parameter
6295 indicates how the mitigation should be used:
6296
6297 force-on: Unconditionally enable mitigation for
6298 for both kernel and userspace
6299 force-off: Unconditionally disable mitigation for
6300 for both kernel and userspace
6301 kernel: Always enable mitigation in the
6302 kernel, and offer a prctl interface
6303 to allow userspace to register its
6304 interest in being mitigated too.
6305
6306 stack_guard_gap= [MM]
6307 override the default stack gap protection. The value
6308 is in page units and it defines how many pages prior
6309 to (for stacks growing down) resp. after (for stacks
6310 growing up) the main stack are reserved for no other
6311 mapping. Default value is 256 pages.
6312
6313 stack_depot_disable= [KNL]
6314 Setting this to true through kernel command line will
6315 disable the stack depot thereby saving the static memory
6316 consumed by the stack hash table. By default this is set
6317 to false.
6318
6319 stacktrace [FTRACE]
6320 Enabled the stack tracer on boot up.
6321
6322 stacktrace_filter=[function-list]
6323 [FTRACE] Limit the functions that the stack tracer
6324 will trace at boot up. function-list is a comma-separated
6325 list of functions. This list can be changed at run
6326 time by the stack_trace_filter file in the debugfs
6327 tracing directory. Note, this enables stack tracing
6328 and the stacktrace above is not needed.
6329
6330 sti= [PARISC,HW]
6331 Format: <num>
6332 Set the STI (builtin display/keyboard on the HP-PARISC
6333 machines) console (graphic card) which should be used
6334 as the initial boot-console.
6335 See also comment in drivers/video/console/sticore.c.
6336
6337 sti_font= [HW]
6338 See comment in drivers/video/console/sticore.c.
6339
6340 stifb= [HW]
6341 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6342
6343 strict_sas_size=
6344 [X86]
6345 Format: <bool>
6346 Enable or disable strict sigaltstack size checks
6347 against the required signal frame size which
6348 depends on the supported FPU features. This can
6349 be used to filter out binaries which have
6350 not yet been made aware of AT_MINSIGSTKSZ.
6351
6352 stress_hpt [PPC]
6353 Limits the number of kernel HPT entries in the hash
6354 page table to increase the rate of hash page table
6355 faults on kernel addresses.
6356
6357 stress_slb [PPC]
6358 Limits the number of kernel SLB entries, and flushes
6359 them frequently to increase the rate of SLB faults
6360 on kernel addresses.
6361
6362 sunrpc.min_resvport=
6363 sunrpc.max_resvport=
6364 [NFS,SUNRPC]
6365 SunRPC servers often require that client requests
6366 originate from a privileged port (i.e. a port in the
6367 range 0 < portnr < 1024).
6368 An administrator who wishes to reserve some of these
6369 ports for other uses may adjust the range that the
6370 kernel's sunrpc client considers to be privileged
6371 using these two parameters to set the minimum and
6372 maximum port values.
6373
6374 sunrpc.svc_rpc_per_connection_limit=
6375 [NFS,SUNRPC]
6376 Limit the number of requests that the server will
6377 process in parallel from a single connection.
6378 The default value is 0 (no limit).
6379
6380 sunrpc.pool_mode=
6381 [NFS]
6382 Control how the NFS server code allocates CPUs to
6383 service thread pools. Depending on how many NICs
6384 you have and where their interrupts are bound, this
6385 option will affect which CPUs will do NFS serving.
6386 Note: this parameter cannot be changed while the
6387 NFS server is running.
6388
6389 auto the server chooses an appropriate mode
6390 automatically using heuristics
6391 global a single global pool contains all CPUs
6392 percpu one pool for each CPU
6393 pernode one pool for each NUMA node (equivalent
6394 to global on non-NUMA machines)
6395
6396 sunrpc.tcp_slot_table_entries=
6397 sunrpc.udp_slot_table_entries=
6398 [NFS,SUNRPC]
6399 Sets the upper limit on the number of simultaneous
6400 RPC calls that can be sent from the client to a
6401 server. Increasing these values may allow you to
6402 improve throughput, but will also increase the
6403 amount of memory reserved for use by the client.
6404
6405 suspend.pm_test_delay=
6406 [SUSPEND]
6407 Sets the number of seconds to remain in a suspend test
6408 mode before resuming the system (see
6409 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6410 is set. Default value is 5.
6411
6412 svm= [PPC]
6413 Format: { on | off | y | n | 1 | 0 }
6414 This parameter controls use of the Protected
6415 Execution Facility on pSeries.
6416
6417 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
6418 Format: { <int> [,<int>] | force | noforce }
6419 <int> -- Number of I/O TLB slabs
6420 <int> -- Second integer after comma. Number of swiotlb
6421 areas with their own lock. Will be rounded up
6422 to a power of 2.
6423 force -- force using of bounce buffers even if they
6424 wouldn't be automatically used by the kernel
6425 noforce -- Never use bounce buffers (for debugging)
6426
6427 switches= [HW,M68k]
6428
6429 sysctl.*= [KNL]
6430 Set a sysctl parameter, right before loading the init
6431 process, as if the value was written to the respective
6432 /proc/sys/... file. Both '.' and '/' are recognized as
6433 separators. Unrecognized parameters and invalid values
6434 are reported in the kernel log. Sysctls registered
6435 later by a loaded module cannot be set this way.
6436 Example: sysctl.vm.swappiness=40
6437
6438 sysrq_always_enabled
6439 [KNL]
6440 Ignore sysrq setting - this boot parameter will
6441 neutralize any effect of /proc/sys/kernel/sysrq.
6442 Useful for debugging.
6443
6444 tcpmhash_entries= [KNL,NET]
6445 Set the number of tcp_metrics_hash slots.
6446 Default value is 8192 or 16384 depending on total
6447 ram pages. This is used to specify the TCP metrics
6448 cache size. See Documentation/networking/ip-sysctl.rst
6449 "tcp_no_metrics_save" section for more details.
6450
6451 tdfx= [HW,DRM]
6452
6453 test_suspend= [SUSPEND]
6454 Format: { "mem" | "standby" | "freeze" }[,N]
6455 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6456 standby suspend) or "freeze" (for suspend type freeze)
6457 as the system sleep state during system startup with
6458 the optional capability to repeat N number of times.
6459 The system is woken from this state using a
6460 wakeup-capable RTC alarm.
6461
6462 thash_entries= [KNL,NET]
6463 Set number of hash buckets for TCP connection
6464
6465 thermal.act= [HW,ACPI]
6466 -1: disable all active trip points in all thermal zones
6467 <degrees C>: override all lowest active trip points
6468
6469 thermal.crt= [HW,ACPI]
6470 -1: disable all critical trip points in all thermal zones
6471 <degrees C>: override all critical trip points
6472
6473 thermal.off= [HW,ACPI]
6474 1: disable ACPI thermal control
6475
6476 thermal.psv= [HW,ACPI]
6477 -1: disable all passive trip points
6478 <degrees C>: override all passive trip points to this
6479 value
6480
6481 thermal.tzp= [HW,ACPI]
6482 Specify global default ACPI thermal zone polling rate
6483 <deci-seconds>: poll all this frequency
6484 0: no polling (default)
6485
6486 threadirqs [KNL]
6487 Force threading of all interrupt handlers except those
6488 marked explicitly IRQF_NO_THREAD.
6489
6490 topology= [S390]
6491 Format: {off | on}
6492 Specify if the kernel should make use of the cpu
6493 topology information if the hardware supports this.
6494 The scheduler will make use of this information and
6495 e.g. base its process migration decisions on it.
6496 Default is on.
6497
6498 topology_updates= [KNL, PPC, NUMA]
6499 Format: {off}
6500 Specify if the kernel should ignore (off)
6501 topology updates sent by the hypervisor to this
6502 LPAR.
6503
6504 torture.disable_onoff_at_boot= [KNL]
6505 Prevent the CPU-hotplug component of torturing
6506 until after init has spawned.
6507
6508 torture.ftrace_dump_at_shutdown= [KNL]
6509 Dump the ftrace buffer at torture-test shutdown,
6510 even if there were no errors. This can be a
6511 very costly operation when many torture tests
6512 are running concurrently, especially on systems
6513 with rotating-rust storage.
6514
6515 torture.verbose_sleep_frequency= [KNL]
6516 Specifies how many verbose printk()s should be
6517 emitted between each sleep. The default of zero
6518 disables verbose-printk() sleeping.
6519
6520 torture.verbose_sleep_duration= [KNL]
6521 Duration of each verbose-printk() sleep in jiffies.
6522
6523 tp720= [HW,PS2]
6524
6525 tpm_suspend_pcr=[HW,TPM]
6526 Format: integer pcr id
6527 Specify that at suspend time, the tpm driver
6528 should extend the specified pcr with zeros,
6529 as a workaround for some chips which fail to
6530 flush the last written pcr on TPM_SaveState.
6531 This will guarantee that all the other pcrs
6532 are saved.
6533
6534 tpm_tis.interrupts= [HW,TPM]
6535 Enable interrupts for the MMIO based physical layer
6536 for the FIFO interface. By default it is set to false
6537 (0). For more information about TPM hardware interfaces
6538 defined by Trusted Computing Group (TCG) see
6539 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
6540
6541 tp_printk [FTRACE]
6542 Have the tracepoints sent to printk as well as the
6543 tracing ring buffer. This is useful for early boot up
6544 where the system hangs or reboots and does not give the
6545 option for reading the tracing buffer or performing a
6546 ftrace_dump_on_oops.
6547
6548 To turn off having tracepoints sent to printk,
6549 echo 0 > /proc/sys/kernel/tracepoint_printk
6550 Note, echoing 1 into this file without the
6551 tracepoint_printk kernel cmdline option has no effect.
6552
6553 The tp_printk_stop_on_boot (see below) can also be used
6554 to stop the printing of events to console at
6555 late_initcall_sync.
6556
6557 ** CAUTION **
6558
6559 Having tracepoints sent to printk() and activating high
6560 frequency tracepoints such as irq or sched, can cause
6561 the system to live lock.
6562
6563 tp_printk_stop_on_boot [FTRACE]
6564 When tp_printk (above) is set, it can cause a lot of noise
6565 on the console. It may be useful to only include the
6566 printing of events during boot up, as user space may
6567 make the system inoperable.
6568
6569 This command line option will stop the printing of events
6570 to console at the late_initcall_sync() time frame.
6571
6572 trace_buf_size=nn[KMG]
6573 [FTRACE] will set tracing buffer size on each cpu.
6574
6575 trace_clock= [FTRACE] Set the clock used for tracing events
6576 at boot up.
6577 local - Use the per CPU time stamp counter
6578 (converted into nanoseconds). Fast, but
6579 depending on the architecture, may not be
6580 in sync between CPUs.
6581 global - Event time stamps are synchronize across
6582 CPUs. May be slower than the local clock,
6583 but better for some race conditions.
6584 counter - Simple counting of events (1, 2, ..)
6585 note, some counts may be skipped due to the
6586 infrastructure grabbing the clock more than
6587 once per event.
6588 uptime - Use jiffies as the time stamp.
6589 perf - Use the same clock that perf uses.
6590 mono - Use ktime_get_mono_fast_ns() for time stamps.
6591 mono_raw - Use ktime_get_raw_fast_ns() for time
6592 stamps.
6593 boot - Use ktime_get_boot_fast_ns() for time stamps.
6594 Architectures may add more clocks. See
6595 Documentation/trace/ftrace.rst for more details.
6596
6597 trace_event=[event-list]
6598 [FTRACE] Set and start specified trace events in order
6599 to facilitate early boot debugging. The event-list is a
6600 comma-separated list of trace events to enable. See
6601 also Documentation/trace/events.rst
6602
6603 trace_instance=[instance-info]
6604 [FTRACE] Create a ring buffer instance early in boot up.
6605 This will be listed in:
6606
6607 /sys/kernel/tracing/instances
6608
6609 Events can be enabled at the time the instance is created
6610 via:
6611
6612 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6613
6614 Note, the "<system*>:" portion is optional if the event is
6615 unique.
6616
6617 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6618
6619 will enable the "sched_switch" event (note, the "sched:" is optional, and
6620 the same thing would happen if it was left off). The irq_handler_entry
6621 event, and all events under the "initcall" system.
6622
6623 trace_options=[option-list]
6624 [FTRACE] Enable or disable tracer options at boot.
6625 The option-list is a comma delimited list of options
6626 that can be enabled or disabled just as if you were
6627 to echo the option name into
6628
6629 /sys/kernel/tracing/trace_options
6630
6631 For example, to enable stacktrace option (to dump the
6632 stack trace of each event), add to the command line:
6633
6634 trace_options=stacktrace
6635
6636 See also Documentation/trace/ftrace.rst "trace options"
6637 section.
6638
6639 trace_trigger=[trigger-list]
6640 [FTRACE] Add a event trigger on specific events.
6641 Set a trigger on top of a specific event, with an optional
6642 filter.
6643
6644 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6645 Where more than one trigger may be specified that are comma deliminated.
6646
6647 For example:
6648
6649 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6650
6651 The above will enable the "stacktrace" trigger on the "sched_switch"
6652 event but only trigger it if the "prev_state" of the "sched_switch"
6653 event is "2" (TASK_UNINTERUPTIBLE).
6654
6655 See also "Event triggers" in Documentation/trace/events.rst
6656
6657
6658 traceoff_on_warning
6659 [FTRACE] enable this option to disable tracing when a
6660 warning is hit. This turns off "tracing_on". Tracing can
6661 be enabled again by echoing '1' into the "tracing_on"
6662 file located in /sys/kernel/tracing/
6663
6664 This option is useful, as it disables the trace before
6665 the WARNING dump is called, which prevents the trace to
6666 be filled with content caused by the warning output.
6667
6668 This option can also be set at run time via the sysctl
6669 option: kernel/traceoff_on_warning
6670
6671 transparent_hugepage=
6672 [KNL]
6673 Format: [always|madvise|never]
6674 Can be used to control the default behavior of the system
6675 with respect to transparent hugepages.
6676 See Documentation/admin-guide/mm/transhuge.rst
6677 for more details.
6678
6679 trusted.source= [KEYS]
6680 Format: <string>
6681 This parameter identifies the trust source as a backend
6682 for trusted keys implementation. Supported trust
6683 sources:
6684 - "tpm"
6685 - "tee"
6686 - "caam"
6687 If not specified then it defaults to iterating through
6688 the trust source list starting with TPM and assigns the
6689 first trust source as a backend which is initialized
6690 successfully during iteration.
6691
6692 trusted.rng= [KEYS]
6693 Format: <string>
6694 The RNG used to generate key material for trusted keys.
6695 Can be one of:
6696 - "kernel"
6697 - the same value as trusted.source: "tpm" or "tee"
6698 - "default"
6699 If not specified, "default" is used. In this case,
6700 the RNG's choice is left to each individual trust source.
6701
6702 tsc= Disable clocksource stability checks for TSC.
6703 Format: <string>
6704 [x86] reliable: mark tsc clocksource as reliable, this
6705 disables clocksource verification at runtime, as well
6706 as the stability checks done at bootup. Used to enable
6707 high-resolution timer mode on older hardware, and in
6708 virtualized environment.
6709 [x86] noirqtime: Do not use TSC to do irq accounting.
6710 Used to run time disable IRQ_TIME_ACCOUNTING on any
6711 platforms where RDTSC is slow and this accounting
6712 can add overhead.
6713 [x86] unstable: mark the TSC clocksource as unstable, this
6714 marks the TSC unconditionally unstable at bootup and
6715 avoids any further wobbles once the TSC watchdog notices.
6716 [x86] nowatchdog: disable clocksource watchdog. Used
6717 in situations with strict latency requirements (where
6718 interruptions from clocksource watchdog are not
6719 acceptable).
6720 [x86] recalibrate: force recalibration against a HW timer
6721 (HPET or PM timer) on systems whose TSC frequency was
6722 obtained from HW or FW using either an MSR or CPUID(0x15).
6723 Warn if the difference is more than 500 ppm.
6724 [x86] watchdog: Use TSC as the watchdog clocksource with
6725 which to check other HW timers (HPET or PM timer), but
6726 only on systems where TSC has been deemed trustworthy.
6727 This will be suppressed by an earlier tsc=nowatchdog and
6728 can be overridden by a later tsc=nowatchdog. A console
6729 message will flag any such suppression or overriding.
6730
6731 tsc_early_khz= [X86] Skip early TSC calibration and use the given
6732 value instead. Useful when the early TSC frequency discovery
6733 procedure is not reliable, such as on overclocked systems
6734 with CPUID.16h support and partial CPUID.15h support.
6735 Format: <unsigned int>
6736
6737 tsx= [X86] Control Transactional Synchronization
6738 Extensions (TSX) feature in Intel processors that
6739 support TSX control.
6740
6741 This parameter controls the TSX feature. The options are:
6742
6743 on - Enable TSX on the system. Although there are
6744 mitigations for all known security vulnerabilities,
6745 TSX has been known to be an accelerator for
6746 several previous speculation-related CVEs, and
6747 so there may be unknown security risks associated
6748 with leaving it enabled.
6749
6750 off - Disable TSX on the system. (Note that this
6751 option takes effect only on newer CPUs which are
6752 not vulnerable to MDS, i.e., have
6753 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6754 the new IA32_TSX_CTRL MSR through a microcode
6755 update. This new MSR allows for the reliable
6756 deactivation of the TSX functionality.)
6757
6758 auto - Disable TSX if X86_BUG_TAA is present,
6759 otherwise enable TSX on the system.
6760
6761 Not specifying this option is equivalent to tsx=off.
6762
6763 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6764 for more details.
6765
6766 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
6767 Abort (TAA) vulnerability.
6768
6769 Similar to Micro-architectural Data Sampling (MDS)
6770 certain CPUs that support Transactional
6771 Synchronization Extensions (TSX) are vulnerable to an
6772 exploit against CPU internal buffers which can forward
6773 information to a disclosure gadget under certain
6774 conditions.
6775
6776 In vulnerable processors, the speculatively forwarded
6777 data can be used in a cache side channel attack, to
6778 access data to which the attacker does not have direct
6779 access.
6780
6781 This parameter controls the TAA mitigation. The
6782 options are:
6783
6784 full - Enable TAA mitigation on vulnerable CPUs
6785 if TSX is enabled.
6786
6787 full,nosmt - Enable TAA mitigation and disable SMT on
6788 vulnerable CPUs. If TSX is disabled, SMT
6789 is not disabled because CPU is not
6790 vulnerable to cross-thread TAA attacks.
6791 off - Unconditionally disable TAA mitigation
6792
6793 On MDS-affected machines, tsx_async_abort=off can be
6794 prevented by an active MDS mitigation as both vulnerabilities
6795 are mitigated with the same mechanism so in order to disable
6796 this mitigation, you need to specify mds=off too.
6797
6798 Not specifying this option is equivalent to
6799 tsx_async_abort=full. On CPUs which are MDS affected
6800 and deploy MDS mitigation, TAA mitigation is not
6801 required and doesn't provide any additional
6802 mitigation.
6803
6804 For details see:
6805 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6806
6807 turbografx.map[2|3]= [HW,JOY]
6808 TurboGraFX parallel port interface
6809 Format:
6810 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6811 See also Documentation/input/devices/joystick-parport.rst
6812
6813 udbg-immortal [PPC] When debugging early kernel crashes that
6814 happen after console_init() and before a proper
6815 console driver takes over, this boot options might
6816 help "seeing" what's going on.
6817
6818 uhash_entries= [KNL,NET]
6819 Set number of hash buckets for UDP/UDP-Lite connections
6820
6821 uhci-hcd.ignore_oc=
6822 [USB] Ignore overcurrent events (default N).
6823 Some badly-designed motherboards generate lots of
6824 bogus events, for ports that aren't wired to
6825 anything. Set this parameter to avoid log spamming.
6826 Note that genuine overcurrent events won't be
6827 reported either.
6828
6829 unknown_nmi_panic
6830 [X86] Cause panic on unknown NMI.
6831
6832 unwind_debug [X86-64]
6833 Enable unwinder debug output. This can be
6834 useful for debugging certain unwinder error
6835 conditions, including corrupt stacks and
6836 bad/missing unwinder metadata.
6837
6838 usbcore.authorized_default=
6839 [USB] Default USB device authorization:
6840 (default -1 = authorized (same as 1),
6841 0 = not authorized, 1 = authorized, 2 = authorized
6842 if device connected to internal port)
6843
6844 usbcore.autosuspend=
6845 [USB] The autosuspend time delay (in seconds) used
6846 for newly-detected USB devices (default 2). This
6847 is the time required before an idle device will be
6848 autosuspended. Devices for which the delay is set
6849 to a negative value won't be autosuspended at all.
6850
6851 usbcore.usbfs_snoop=
6852 [USB] Set to log all usbfs traffic (default 0 = off).
6853
6854 usbcore.usbfs_snoop_max=
6855 [USB] Maximum number of bytes to snoop in each URB
6856 (default = 65536).
6857
6858 usbcore.blinkenlights=
6859 [USB] Set to cycle leds on hubs (default 0 = off).
6860
6861 usbcore.old_scheme_first=
6862 [USB] Start with the old device initialization
6863 scheme (default 0 = off).
6864
6865 usbcore.usbfs_memory_mb=
6866 [USB] Memory limit (in MB) for buffers allocated by
6867 usbfs (default = 16, 0 = max = 2047).
6868
6869 usbcore.use_both_schemes=
6870 [USB] Try the other device initialization scheme
6871 if the first one fails (default 1 = enabled).
6872
6873 usbcore.initial_descriptor_timeout=
6874 [USB] Specifies timeout for the initial 64-byte
6875 USB_REQ_GET_DESCRIPTOR request in milliseconds
6876 (default 5000 = 5.0 seconds).
6877
6878 usbcore.nousb [USB] Disable the USB subsystem
6879
6880 usbcore.quirks=
6881 [USB] A list of quirk entries to augment the built-in
6882 usb core quirk list. List entries are separated by
6883 commas. Each entry has the form
6884 VendorID:ProductID:Flags. The IDs are 4-digit hex
6885 numbers and Flags is a set of letters. Each letter
6886 will change the built-in quirk; setting it if it is
6887 clear and clearing it if it is set. The letters have
6888 the following meanings:
6889 a = USB_QUIRK_STRING_FETCH_255 (string
6890 descriptors must not be fetched using
6891 a 255-byte read);
6892 b = USB_QUIRK_RESET_RESUME (device can't resume
6893 correctly so reset it instead);
6894 c = USB_QUIRK_NO_SET_INTF (device can't handle
6895 Set-Interface requests);
6896 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6897 handle its Configuration or Interface
6898 strings);
6899 e = USB_QUIRK_RESET (device can't be reset
6900 (e.g morph devices), don't use reset);
6901 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6902 more interface descriptions than the
6903 bNumInterfaces count, and can't handle
6904 talking to these interfaces);
6905 g = USB_QUIRK_DELAY_INIT (device needs a pause
6906 during initialization, after we read
6907 the device descriptor);
6908 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6909 high speed and super speed interrupt
6910 endpoints, the USB 2.0 and USB 3.0 spec
6911 require the interval in microframes (1
6912 microframe = 125 microseconds) to be
6913 calculated as interval = 2 ^
6914 (bInterval-1).
6915 Devices with this quirk report their
6916 bInterval as the result of this
6917 calculation instead of the exponent
6918 variable used in the calculation);
6919 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6920 handle device_qualifier descriptor
6921 requests);
6922 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6923 generates spurious wakeup, ignore
6924 remote wakeup capability);
6925 k = USB_QUIRK_NO_LPM (device can't handle Link
6926 Power Management);
6927 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6928 (Device reports its bInterval as linear
6929 frames instead of the USB 2.0
6930 calculation);
6931 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6932 to be disconnected before suspend to
6933 prevent spurious wakeup);
6934 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6935 pause after every control message);
6936 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6937 delay after resetting its port);
6938 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
6939 (Reduce timeout of the SET_ADDRESS
6940 request from 5000 ms to 500 ms);
6941 Example: quirks=0781:5580:bk,0a5c:5834:gij
6942
6943 usbhid.mousepoll=
6944 [USBHID] The interval which mice are to be polled at.
6945
6946 usbhid.jspoll=
6947 [USBHID] The interval which joysticks are to be polled at.
6948
6949 usbhid.kbpoll=
6950 [USBHID] The interval which keyboards are to be polled at.
6951
6952 usb-storage.delay_use=
6953 [UMS] The delay in seconds before a new device is
6954 scanned for Logical Units (default 1).
6955
6956 usb-storage.quirks=
6957 [UMS] A list of quirks entries to supplement or
6958 override the built-in unusual_devs list. List
6959 entries are separated by commas. Each entry has
6960 the form VID:PID:Flags where VID and PID are Vendor
6961 and Product ID values (4-digit hex numbers) and
6962 Flags is a set of characters, each corresponding
6963 to a common usb-storage quirk flag as follows:
6964 a = SANE_SENSE (collect more than 18 bytes
6965 of sense data, not on uas);
6966 b = BAD_SENSE (don't collect more than 18
6967 bytes of sense data, not on uas);
6968 c = FIX_CAPACITY (decrease the reported
6969 device capacity by one sector);
6970 d = NO_READ_DISC_INFO (don't use
6971 READ_DISC_INFO command, not on uas);
6972 e = NO_READ_CAPACITY_16 (don't use
6973 READ_CAPACITY_16 command);
6974 f = NO_REPORT_OPCODES (don't use report opcodes
6975 command, uas only);
6976 g = MAX_SECTORS_240 (don't transfer more than
6977 240 sectors at a time, uas only);
6978 h = CAPACITY_HEURISTICS (decrease the
6979 reported device capacity by one
6980 sector if the number is odd);
6981 i = IGNORE_DEVICE (don't bind to this
6982 device);
6983 j = NO_REPORT_LUNS (don't use report luns
6984 command, uas only);
6985 k = NO_SAME (do not use WRITE_SAME, uas only)
6986 l = NOT_LOCKABLE (don't try to lock and
6987 unlock ejectable media, not on uas);
6988 m = MAX_SECTORS_64 (don't transfer more
6989 than 64 sectors = 32 KB at a time,
6990 not on uas);
6991 n = INITIAL_READ10 (force a retry of the
6992 initial READ(10) command, not on uas);
6993 o = CAPACITY_OK (accept the capacity
6994 reported by the device, not on uas);
6995 p = WRITE_CACHE (the device cache is ON
6996 by default, not on uas);
6997 r = IGNORE_RESIDUE (the device reports
6998 bogus residue values, not on uas);
6999 s = SINGLE_LUN (the device has only one
7000 Logical Unit);
7001 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7002 commands, uas only);
7003 u = IGNORE_UAS (don't bind to the uas driver);
7004 w = NO_WP_DETECT (don't test whether the
7005 medium is write-protected).
7006 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7007 even if the device claims no cache,
7008 not on uas)
7009 Example: quirks=0419:aaf5:rl,0421:0433:rc
7010
7011 user_debug= [KNL,ARM]
7012 Format: <int>
7013 See arch/arm/Kconfig.debug help text.
7014 1 - undefined instruction events
7015 2 - system calls
7016 4 - invalid data aborts
7017 8 - SIGSEGV faults
7018 16 - SIGBUS faults
7019 Example: user_debug=31
7020
7021 userpte=
7022 [X86] Flags controlling user PTE allocations.
7023
7024 nohigh = do not allocate PTE pages in
7025 HIGHMEM regardless of setting
7026 of CONFIG_HIGHPTE.
7027
7028 vdso= [X86,SH,SPARC]
7029 On X86_32, this is an alias for vdso32=. Otherwise:
7030
7031 vdso=1: enable VDSO (the default)
7032 vdso=0: disable VDSO mapping
7033
7034 vdso32= [X86] Control the 32-bit vDSO
7035 vdso32=1: enable 32-bit VDSO
7036 vdso32=0 or vdso32=2: disable 32-bit VDSO
7037
7038 See the help text for CONFIG_COMPAT_VDSO for more
7039 details. If CONFIG_COMPAT_VDSO is set, the default is
7040 vdso32=0; otherwise, the default is vdso32=1.
7041
7042 For compatibility with older kernels, vdso32=2 is an
7043 alias for vdso32=0.
7044
7045 Try vdso32=0 if you encounter an error that says:
7046 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7047
7048 vector= [IA-64,SMP]
7049 vector=percpu: enable percpu vector domain
7050
7051 video= [FB] Frame buffer configuration
7052 See Documentation/fb/modedb.rst.
7053
7054 video.brightness_switch_enabled= [ACPI]
7055 Format: [0|1]
7056 If set to 1, on receiving an ACPI notify event
7057 generated by hotkey, video driver will adjust brightness
7058 level and then send out the event to user space through
7059 the allocated input device. If set to 0, video driver
7060 will only send out the event without touching backlight
7061 brightness level.
7062 default: 1
7063
7064 virtio_mmio.device=
7065 [VMMIO] Memory mapped virtio (platform) device.
7066
7067 <size>@<baseaddr>:<irq>[:<id>]
7068 where:
7069 <size> := size (can use standard suffixes
7070 like K, M and G)
7071 <baseaddr> := physical base address
7072 <irq> := interrupt number (as passed to
7073 request_irq())
7074 <id> := (optional) platform device id
7075 example:
7076 virtio_mmio.device=1K@0x100b0000:48:7
7077
7078 Can be used multiple times for multiple devices.
7079
7080 vga= [BOOT,X86-32] Select a particular video mode
7081 See Documentation/arch/x86/boot.rst and
7082 Documentation/admin-guide/svga.rst.
7083 Use vga=ask for menu.
7084 This is actually a boot loader parameter; the value is
7085 passed to the kernel using a special protocol.
7086
7087 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7088 May slow down system boot speed, especially when
7089 enabled on systems with a large amount of memory.
7090 All options are enabled by default, and this
7091 interface is meant to allow for selectively
7092 enabling or disabling specific virtual memory
7093 debugging features.
7094
7095 Available options are:
7096 P Enable page structure init time poisoning
7097 - Disable all of the above options
7098
7099 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
7100 size of <nn>. This can be used to increase the
7101 minimum size (128MB on x86). It can also be used to
7102 decrease the size and leave more room for directly
7103 mapped kernel RAM.
7104
7105 vmcp_cma=nn[MG] [KNL,S390]
7106 Sets the memory size reserved for contiguous memory
7107 allocations for the vmcp device driver.
7108
7109 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7110 Format: <command>
7111
7112 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7113 Format: <command>
7114
7115 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7116 Format: <command>
7117
7118 vsyscall= [X86-64]
7119 Controls the behavior of vsyscalls (i.e. calls to
7120 fixed addresses of 0xffffffffff600x00 from legacy
7121 code). Most statically-linked binaries and older
7122 versions of glibc use these calls. Because these
7123 functions are at fixed addresses, they make nice
7124 targets for exploits that can control RIP.
7125
7126 emulate Vsyscalls turn into traps and are emulated
7127 reasonably safely. The vsyscall page is
7128 readable.
7129
7130 xonly [default] Vsyscalls turn into traps and are
7131 emulated reasonably safely. The vsyscall
7132 page is not readable.
7133
7134 none Vsyscalls don't work at all. This makes
7135 them quite hard to use for exploits but
7136 might break your system.
7137
7138 vt.color= [VT] Default text color.
7139 Format: 0xYX, X = foreground, Y = background.
7140 Default: 0x07 = light gray on black.
7141
7142 vt.cur_default= [VT] Default cursor shape.
7143 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7144 the parameters of the <Esc>[?A;B;Cc escape sequence;
7145 see VGA-softcursor.txt. Default: 2 = underline.
7146
7147 vt.default_blu= [VT]
7148 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7149 Change the default blue palette of the console.
7150 This is a 16-member array composed of values
7151 ranging from 0-255.
7152
7153 vt.default_grn= [VT]
7154 Format: <green0>,<green1>,<green2>,...,<green15>
7155 Change the default green palette of the console.
7156 This is a 16-member array composed of values
7157 ranging from 0-255.
7158
7159 vt.default_red= [VT]
7160 Format: <red0>,<red1>,<red2>,...,<red15>
7161 Change the default red palette of the console.
7162 This is a 16-member array composed of values
7163 ranging from 0-255.
7164
7165 vt.default_utf8=
7166 [VT]
7167 Format=<0|1>
7168 Set system-wide default UTF-8 mode for all tty's.
7169 Default is 1, i.e. UTF-8 mode is enabled for all
7170 newly opened terminals.
7171
7172 vt.global_cursor_default=
7173 [VT]
7174 Format=<-1|0|1>
7175 Set system-wide default for whether a cursor
7176 is shown on new VTs. Default is -1,
7177 i.e. cursors will be created by default unless
7178 overridden by individual drivers. 0 will hide
7179 cursors, 1 will display them.
7180
7181 vt.italic= [VT] Default color for italic text; 0-15.
7182 Default: 2 = green.
7183
7184 vt.underline= [VT] Default color for underlined text; 0-15.
7185 Default: 3 = cyan.
7186
7187 watchdog timers [HW,WDT] For information on watchdog timers,
7188 see Documentation/watchdog/watchdog-parameters.rst
7189 or other driver-specific files in the
7190 Documentation/watchdog/ directory.
7191
7192 watchdog_thresh=
7193 [KNL]
7194 Set the hard lockup detector stall duration
7195 threshold in seconds. The soft lockup detector
7196 threshold is set to twice the value. A value of 0
7197 disables both lockup detectors. Default is 10
7198 seconds.
7199
7200 workqueue.unbound_cpus=
7201 [KNL,SMP] Specify to constrain one or some CPUs
7202 to use in unbound workqueues.
7203 Format: <cpu-list>
7204 By default, all online CPUs are available for
7205 unbound workqueues.
7206
7207 workqueue.watchdog_thresh=
7208 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7209 warn stall conditions and dump internal state to
7210 help debugging. 0 disables workqueue stall
7211 detection; otherwise, it's the stall threshold
7212 duration in seconds. The default value is 30 and
7213 it can be updated at runtime by writing to the
7214 corresponding sysfs file.
7215
7216 workqueue.cpu_intensive_thresh_us=
7217 Per-cpu work items which run for longer than this
7218 threshold are automatically considered CPU intensive
7219 and excluded from concurrency management to prevent
7220 them from noticeably delaying other per-cpu work
7221 items. Default is 10000 (10ms).
7222
7223 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7224 will report the work functions which violate this
7225 threshold repeatedly. They are likely good
7226 candidates for using WQ_UNBOUND workqueues instead.
7227
7228 workqueue.power_efficient
7229 Per-cpu workqueues are generally preferred because
7230 they show better performance thanks to cache
7231 locality; unfortunately, per-cpu workqueues tend to
7232 be more power hungry than unbound workqueues.
7233
7234 Enabling this makes the per-cpu workqueues which
7235 were observed to contribute significantly to power
7236 consumption unbound, leading to measurably lower
7237 power usage at the cost of small performance
7238 overhead.
7239
7240 The default value of this parameter is determined by
7241 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7242
7243 workqueue.default_affinity_scope=
7244 Select the default affinity scope to use for unbound
7245 workqueues. Can be one of "cpu", "smt", "cache",
7246 "numa" and "system". Default is "cache". For more
7247 information, see the Affinity Scopes section in
7248 Documentation/core-api/workqueue.rst.
7249
7250 This can be changed after boot by writing to the
7251 matching /sys/module/workqueue/parameters file. All
7252 workqueues with the "default" affinity scope will be
7253 updated accordignly.
7254
7255 workqueue.debug_force_rr_cpu
7256 Workqueue used to implicitly guarantee that work
7257 items queued without explicit CPU specified are put
7258 on the local CPU. This guarantee is no longer true
7259 and while local CPU is still preferred work items
7260 may be put on foreign CPUs. This debug option
7261 forces round-robin CPU selection to flush out
7262 usages which depend on the now broken guarantee.
7263 When enabled, memory and cache locality will be
7264 impacted.
7265
7266 writecombine= [LOONGARCH] Control the MAT (Memory Access Type) of
7267 ioremap_wc().
7268
7269 on - Enable writecombine, use WUC for ioremap_wc()
7270 off - Disable writecombine, use SUC for ioremap_wc()
7271
7272 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
7273 default x2apic cluster mode on platforms
7274 supporting x2apic.
7275
7276 xen_512gb_limit [KNL,X86-64,XEN]
7277 Restricts the kernel running paravirtualized under Xen
7278 to use only up to 512 GB of RAM. The reason to do so is
7279 crash analysis tools and Xen tools for doing domain
7280 save/restore/migration must be enabled to handle larger
7281 domains.
7282
7283 xen_emul_unplug= [HW,X86,XEN]
7284 Unplug Xen emulated devices
7285 Format: [unplug0,][unplug1]
7286 ide-disks -- unplug primary master IDE devices
7287 aux-ide-disks -- unplug non-primary-master IDE devices
7288 nics -- unplug network devices
7289 all -- unplug all emulated devices (NICs and IDE disks)
7290 unnecessary -- unplugging emulated devices is
7291 unnecessary even if the host did not respond to
7292 the unplug protocol
7293 never -- do not unplug even if version check succeeds
7294
7295 xen_legacy_crash [X86,XEN]
7296 Crash from Xen panic notifier, without executing late
7297 panic() code such as dumping handler.
7298
7299 xen_msr_safe= [X86,XEN]
7300 Format: <bool>
7301 Select whether to always use non-faulting (safe) MSR
7302 access functions when running as Xen PV guest. The
7303 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7304
7305 xen_nopvspin [X86,XEN]
7306 Disables the qspinlock slowpath using Xen PV optimizations.
7307 This parameter is obsoleted by "nopvspin" parameter, which
7308 has equivalent effect for XEN platform.
7309
7310 xen_nopv [X86]
7311 Disables the PV optimizations forcing the HVM guest to
7312 run as generic HVM guest with no PV drivers.
7313 This option is obsoleted by the "nopv" option, which
7314 has equivalent effect for XEN platform.
7315
7316 xen_no_vector_callback
7317 [KNL,X86,XEN] Disable the vector callback for Xen
7318 event channel interrupts.
7319
7320 xen_scrub_pages= [XEN]
7321 Boolean option to control scrubbing pages before giving them back
7322 to Xen, for use by other domains. Can be also changed at runtime
7323 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7324 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7325
7326 xen_timer_slop= [X86-64,XEN]
7327 Set the timer slop (in nanoseconds) for the virtual Xen
7328 timers (default is 100000). This adjusts the minimum
7329 delta of virtualized Xen timers, where lower values
7330 improve timer resolution at the expense of processing
7331 more timer interrupts.
7332
7333 xen.balloon_boot_timeout= [XEN]
7334 The time (in seconds) to wait before giving up to boot
7335 in case initial ballooning fails to free enough memory.
7336 Applies only when running as HVM or PVH guest and
7337 started with less memory configured than allowed at
7338 max. Default is 180.
7339
7340 xen.event_eoi_delay= [XEN]
7341 How long to delay EOI handling in case of event
7342 storms (jiffies). Default is 10.
7343
7344 xen.event_loop_timeout= [XEN]
7345 After which time (jiffies) the event handling loop
7346 should start to delay EOI handling. Default is 2.
7347
7348 xen.fifo_events= [XEN]
7349 Boolean parameter to disable using fifo event handling
7350 even if available. Normally fifo event handling is
7351 preferred over the 2-level event handling, as it is
7352 fairer and the number of possible event channels is
7353 much higher. Default is on (use fifo events).
7354
7355 xirc2ps_cs= [NET,PCMCIA]
7356 Format:
7357 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7358
7359 xive= [PPC]
7360 By default on POWER9 and above, the kernel will
7361 natively use the XIVE interrupt controller. This option
7362 allows the fallback firmware mode to be used:
7363
7364 off Fallback to firmware control of XIVE interrupt
7365 controller on both pseries and powernv
7366 platforms. Only useful on POWER9 and above.
7367
7368 xive.store-eoi=off [PPC]
7369 By default on POWER10 and above, the kernel will use
7370 stores for EOI handling when the XIVE interrupt mode
7371 is active. This option allows the XIVE driver to use
7372 loads instead, as on POWER9.
7373
7374 xhci-hcd.quirks [USB,KNL]
7375 A hex value specifying bitmask with supplemental xhci
7376 host controller quirks. Meaning of each bit can be
7377 consulted in header drivers/usb/host/xhci.h.
7378
7379 xmon [PPC]
7380 Format: { early | on | rw | ro | off }
7381 Controls if xmon debugger is enabled. Default is off.
7382 Passing only "xmon" is equivalent to "xmon=early".
7383 early Call xmon as early as possible on boot; xmon
7384 debugger is called from setup_arch().
7385 on xmon debugger hooks will be installed so xmon
7386 is only called on a kernel crash. Default mode,
7387 i.e. either "ro" or "rw" mode, is controlled
7388 with CONFIG_XMON_DEFAULT_RO_MODE.
7389 rw xmon debugger hooks will be installed so xmon
7390 is called only on a kernel crash, mode is write,
7391 meaning SPR registers, memory and, other data
7392 can be written using xmon commands.
7393 ro same as "rw" option above but SPR registers,
7394 memory, and other data can't be written using
7395 xmon commands.
7396 off xmon is disabled.
7397
1 accept_memory= [MM]
2 Format: { eager | lazy }
3 default: lazy
4 By default, unaccepted memory is accepted lazily to
5 avoid prolonged boot times. The lazy option will add
6 some runtime overhead until all memory is eventually
7 accepted. In most cases the overhead is negligible.
8 For some workloads or for debugging purposes
9 accept_memory=eager can be used to accept all memory
10 at once during boot.
11
12 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
13 Advanced Configuration and Power Interface
14 Format: { force | on | off | strict | noirq | rsdt |
15 copy_dsdt | nospcr }
16 force -- enable ACPI if default was off
17 on -- enable ACPI but allow fallback to DT [arm64,riscv64]
18 off -- disable ACPI if default was on
19 noirq -- do not use ACPI for IRQ routing
20 strict -- Be less tolerant of platforms that are not
21 strictly ACPI specification compliant.
22 rsdt -- prefer RSDT over (default) XSDT
23 copy_dsdt -- copy DSDT to memory
24 nospcr -- disable console in ACPI SPCR table as
25 default _serial_ console on ARM64
26 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or
27 "acpi=nospcr" are available
28 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force"
29 are available
30
31 See also Documentation/power/runtime_pm.rst, pci=noacpi
32
33 acpi_apic_instance= [ACPI,IOAPIC,EARLY]
34 Format: <int>
35 2: use 2nd APIC table, if available
36 1,0: use 1st APIC table
37 default: 0
38
39 acpi_backlight= [HW,ACPI]
40 { vendor | video | native | none }
41 If set to vendor, prefer vendor-specific driver
42 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
43 of the ACPI video.ko driver.
44 If set to video, use the ACPI video.ko driver.
45 If set to native, use the device's native backlight mode.
46 If set to none, disable the ACPI backlight interface.
47
48 acpi_force_32bit_fadt_addr [ACPI,EARLY]
49 force FADT to use 32 bit addresses rather than the
50 64 bit X_* addresses. Some firmware have broken 64
51 bit addresses for force ACPI ignore these and use
52 the older legacy 32 bit addresses.
53
54 acpica_no_return_repair [HW, ACPI]
55 Disable AML predefined validation mechanism
56 This mechanism can repair the evaluation result to make
57 the return objects more ACPI specification compliant.
58 This option is useful for developers to identify the
59 root cause of an AML interpreter issue when the issue
60 has something to do with the repair mechanism.
61
62 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
63 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
64 Format: <int>
65 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
66 debug output. Bits in debug_layer correspond to a
67 _COMPONENT in an ACPI source file, e.g.,
68 #define _COMPONENT ACPI_EVENTS
69 Bits in debug_level correspond to a level in
70 ACPI_DEBUG_PRINT statements, e.g.,
71 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
72 The debug_level mask defaults to "info". See
73 Documentation/firmware-guide/acpi/debug.rst for more information about
74 debug layers and levels.
75
76 Enable processor driver info messages:
77 acpi.debug_layer=0x20000000
78 Enable AML "Debug" output, i.e., stores to the Debug
79 object while interpreting AML:
80 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
81 Enable all messages related to ACPI hardware:
82 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
83
84 Some values produce so much output that the system is
85 unusable. The "log_buf_len" parameter may be useful
86 if you need to capture more output.
87
88 acpi_enforce_resources= [ACPI]
89 { strict | lax | no }
90 Check for resource conflicts between native drivers
91 and ACPI OperationRegions (SystemIO and SystemMemory
92 only). IO ports and memory declared in ACPI might be
93 used by the ACPI subsystem in arbitrary AML code and
94 can interfere with legacy drivers.
95 strict (default): access to resources claimed by ACPI
96 is denied; legacy drivers trying to access reserved
97 resources will fail to bind to device using them.
98 lax: access to resources claimed by ACPI is allowed;
99 legacy drivers trying to access reserved resources
100 will bind successfully but a warning message is logged.
101 no: ACPI OperationRegions are not marked as reserved,
102 no further checks are performed.
103
104 acpi_force_table_verification [HW,ACPI,EARLY]
105 Enable table checksum verification during early stage.
106 By default, this is disabled due to x86 early mapping
107 size limitation.
108
109 acpi_irq_balance [HW,ACPI]
110 ACPI will balance active IRQs
111 default in APIC mode
112
113 acpi_irq_nobalance [HW,ACPI]
114 ACPI will not move active IRQs (default)
115 default in PIC mode
116
117 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
118 Format: <irq>,<irq>...
119
120 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
121 use by PCI
122 Format: <irq>,<irq>...
123
124 acpi_mask_gpe= [HW,ACPI]
125 Due to the existence of _Lxx/_Exx, some GPEs triggered
126 by unsupported hardware/firmware features can result in
127 GPE floodings that cannot be automatically disabled by
128 the GPE dispatcher.
129 This facility can be used to prevent such uncontrolled
130 GPE floodings.
131 Format: <byte> or <bitmap-list>
132
133 acpi_no_auto_serialize [HW,ACPI]
134 Disable auto-serialization of AML methods
135 AML control methods that contain the opcodes to create
136 named objects will be marked as "Serialized" by the
137 auto-serialization feature.
138 This feature is enabled by default.
139 This option allows to turn off the feature.
140
141 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
142 kernels.
143
144 acpi_no_static_ssdt [HW,ACPI,EARLY]
145 Disable installation of static SSDTs at early boot time
146 By default, SSDTs contained in the RSDT/XSDT will be
147 installed automatically and they will appear under
148 /sys/firmware/acpi/tables.
149 This option turns off this feature.
150 Note that specifying this option does not affect
151 dynamic table installation which will install SSDT
152 tables to /sys/firmware/acpi/tables/dynamic.
153
154 acpi_no_watchdog [HW,ACPI,WDT]
155 Ignore the ACPI-based watchdog interface (WDAT) and let
156 a native driver control the watchdog device instead.
157
158 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
159 Pass the RSDP address to the kernel, mostly used
160 on machines running EFI runtime service to boot the
161 second kernel for kdump.
162
163 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
164 Format: To spoof as Windows 98: ="Microsoft Windows"
165
166 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
167 of 2 which is mandated by ACPI 6) as the supported ACPI
168 specification revision (when using this switch, it may
169 be necessary to carry out a cold reboot _twice_ in a
170 row to make it take effect on the platform firmware).
171
172 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
173 acpi_osi="string1" # add string1
174 acpi_osi="!string2" # remove string2
175 acpi_osi=!* # remove all strings
176 acpi_osi=! # disable all built-in OS vendor
177 strings
178 acpi_osi=!! # enable all built-in OS vendor
179 strings
180 acpi_osi= # disable all strings
181
182 'acpi_osi=!' can be used in combination with single or
183 multiple 'acpi_osi="string1"' to support specific OS
184 vendor string(s). Note that such command can only
185 affect the default state of the OS vendor strings, thus
186 it cannot affect the default state of the feature group
187 strings and the current state of the OS vendor strings,
188 specifying it multiple times through kernel command line
189 is meaningless. This command is useful when one do not
190 care about the state of the feature group strings which
191 should be controlled by the OSPM.
192 Examples:
193 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
194 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
195 can make '_OSI("Windows 2000")' TRUE.
196
197 'acpi_osi=' cannot be used in combination with other
198 'acpi_osi=' command lines, the _OSI method will not
199 exist in the ACPI namespace. NOTE that such command can
200 only affect the _OSI support state, thus specifying it
201 multiple times through kernel command line is also
202 meaningless.
203 Examples:
204 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
205 FALSE.
206
207 'acpi_osi=!*' can be used in combination with single or
208 multiple 'acpi_osi="string1"' to support specific
209 string(s). Note that such command can affect the
210 current state of both the OS vendor strings and the
211 feature group strings, thus specifying it multiple times
212 through kernel command line is meaningful. But it may
213 still not able to affect the final state of a string if
214 there are quirks related to this string. This command
215 is useful when one want to control the state of the
216 feature group strings to debug BIOS issues related to
217 the OSPM features.
218 Examples:
219 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
220 '_OSI("Module Device")' FALSE.
221 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
222 '_OSI("Module Device")' TRUE.
223 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
224 equivalent to
225 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
226 and
227 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
228 they all will make '_OSI("Windows 2000")' TRUE.
229
230 acpi_pm_good [X86]
231 Override the pmtimer bug detection: force the kernel
232 to assume that this machine's pmtimer latches its value
233 and always returns good values.
234
235 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
236 Format: { level | edge | high | low }
237
238 acpi_skip_timer_override [HW,ACPI,EARLY]
239 Recognize and ignore IRQ0/pin2 Interrupt Override.
240 For broken nForce2 BIOS resulting in XT-PIC timer.
241
242 acpi_sleep= [HW,ACPI] Sleep options
243 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
244 s4_nohwsig, old_ordering, nonvs,
245 sci_force_enable, nobl }
246 See Documentation/power/video.rst for information on
247 s3_bios and s3_mode.
248 s3_beep is for debugging; it makes the PC's speaker beep
249 as soon as the kernel's real-mode entry point is called.
250 s4_hwsig causes the kernel to check the ACPI hardware
251 signature during resume from hibernation, and gracefully
252 refuse to resume if it has changed. This complies with
253 the ACPI specification but not with reality, since
254 Windows does not do this and many laptops do change it
255 on docking. So the default behaviour is to allow resume
256 and simply warn when the signature changes, unless the
257 s4_hwsig option is enabled.
258 s4_nohwsig prevents ACPI hardware signature from being
259 used (or even warned about) during resume.
260 old_ordering causes the ACPI 1.0 ordering of the _PTS
261 control method, with respect to putting devices into
262 low power states, to be enforced (the ACPI 2.0 ordering
263 of _PTS is used by default).
264 nonvs prevents the kernel from saving/restoring the
265 ACPI NVS memory during suspend/hibernation and resume.
266 sci_force_enable causes the kernel to set SCI_EN directly
267 on resume from S1/S3 (which is against the ACPI spec,
268 but some broken systems don't work without it).
269 nobl causes the internal blacklist of systems known to
270 behave incorrectly in some ways with respect to system
271 suspend and resume to be ignored (use wisely).
272
273 acpi_use_timer_override [HW,ACPI,EARLY]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
276
277 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
278 kernel's map of available physical RAM.
279
280 agp= [AGP]
281 { off | try_unsupported }
282 off: disable AGP support
283 try_unsupported: try to drive unsupported chipsets
284 (may crash computer or cause data corruption)
285
286 ALSA [HW,ALSA]
287 See Documentation/sound/alsa-configuration.rst
288
289 alignment= [KNL,ARM]
290 Allow the default userspace alignment fault handler
291 behaviour to be specified. Bit 0 enables warnings,
292 bit 1 enables fixups, and bit 2 sends a segfault.
293
294 align_va_addr= [X86-64]
295 Align virtual addresses by clearing slice [14:12] when
296 allocating a VMA at process creation time. This option
297 gives you up to 3% performance improvement on AMD F15h
298 machines (where it is enabled by default) for a
299 CPU-intensive style benchmark, and it can vary highly in
300 a microbenchmark depending on workload and compiler.
301
302 32: only for 32-bit processes
303 64: only for 64-bit processes
304 on: enable for both 32- and 64-bit processes
305 off: disable for both 32- and 64-bit processes
306
307 alloc_snapshot [FTRACE]
308 Allocate the ftrace snapshot buffer on boot up when the
309 main buffer is allocated. This is handy if debugging
310 and you need to use tracing_snapshot() on boot up, and
311 do not want to use tracing_snapshot_alloc() as it needs
312 to be done where GFP_KERNEL allocations are allowed.
313
314 allow_mismatched_32bit_el0 [ARM64,EARLY]
315 Allow execve() of 32-bit applications and setting of the
316 PER_LINUX32 personality on systems where only a strict
317 subset of the CPUs support 32-bit EL0. When this
318 parameter is present, the set of CPUs supporting 32-bit
319 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
320 and hot-unplug operations may be restricted.
321
322 See Documentation/arch/arm64/asymmetric-32bit.rst for more
323 information.
324
325 amd_iommu= [HW,X86-64]
326 Pass parameters to the AMD IOMMU driver in the system.
327 Possible values are:
328 fullflush - Deprecated, equivalent to iommu.strict=1
329 off - do not initialize any AMD IOMMU found in
330 the system
331 force_isolation - Force device isolation for all
332 devices. The IOMMU driver is not
333 allowed anymore to lift isolation
334 requirements as needed. This option
335 does not override iommu=pt
336 force_enable - Force enable the IOMMU on platforms known
337 to be buggy with IOMMU enabled. Use this
338 option with care.
339 pgtbl_v1 - Use v1 page table for DMA-API (Default).
340 pgtbl_v2 - Use v2 page table for DMA-API.
341 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
342 nohugepages - Limit page-sizes used for v1 page-tables
343 to 4 KiB.
344 v2_pgsizes_only - Limit page-sizes used for v1 page-tables
345 to 4KiB/2Mib/1GiB.
346
347
348 amd_iommu_dump= [HW,X86-64]
349 Enable AMD IOMMU driver option to dump the ACPI table
350 for AMD IOMMU. With this option enabled, AMD IOMMU
351 driver will print ACPI tables for AMD IOMMU during
352 IOMMU initialization.
353
354 amd_iommu_intr= [HW,X86-64]
355 Specifies one of the following AMD IOMMU interrupt
356 remapping modes:
357 legacy - Use legacy interrupt remapping mode.
358 vapic - Use virtual APIC mode, which allows IOMMU
359 to inject interrupts directly into guest.
360 This mode requires kvm-amd.avic=1.
361 (Default when IOMMU HW support is present.)
362
363 amd_pstate= [X86,EARLY]
364 disable
365 Do not enable amd_pstate as the default
366 scaling driver for the supported processors
367 passive
368 Use amd_pstate with passive mode as a scaling driver.
369 In this mode autonomous selection is disabled.
370 Driver requests a desired performance level and platform
371 tries to match the same performance level if it is
372 satisfied by guaranteed performance level.
373 active
374 Use amd_pstate_epp driver instance as the scaling driver,
375 driver provides a hint to the hardware if software wants
376 to bias toward performance (0x0) or energy efficiency (0xff)
377 to the CPPC firmware. then CPPC power algorithm will
378 calculate the runtime workload and adjust the realtime cores
379 frequency.
380 guided
381 Activate guided autonomous mode. Driver requests minimum and
382 maximum performance level and the platform autonomously
383 selects a performance level in this range and appropriate
384 to the current workload.
385
386 amd_prefcore=
387 [X86]
388 disable
389 Disable amd-pstate preferred core.
390
391 amijoy.map= [HW,JOY] Amiga joystick support
392 Map of devices attached to JOY0DAT and JOY1DAT
393 Format: <a>,<b>
394 See also Documentation/input/joydev/joystick.rst
395
396 analog.map= [HW,JOY] Analog joystick and gamepad support
397 Specifies type or capabilities of an analog joystick
398 connected to one of 16 gameports
399 Format: <type1>,<type2>,..<type16>
400
401 apc= [HW,SPARC]
402 Power management functions (SPARCstation-4/5 + deriv.)
403 Format: noidle
404 Disable APC CPU standby support. SPARCstation-Fox does
405 not play well with APC CPU idle - disable it if you have
406 APC and your system crashes randomly.
407
408 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
409 Change the output verbosity while booting
410 Format: { quiet (default) | verbose | debug }
411 Change the amount of debugging information output
412 when initialising the APIC and IO-APIC components.
413 For X86-32, this can also be used to specify an APIC
414 driver name.
415 Format: apic=driver_name
416 Examples: apic=bigsmp
417
418 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
419 Format: { bsp (default) | all | none }
420 bsp: External NMI is delivered only to CPU 0
421 all: External NMIs are broadcast to all CPUs as a
422 backup of CPU 0
423 none: External NMI is masked for all CPUs. This is
424 useful so that a dump capture kernel won't be
425 shot down by NMI
426
427 autoconf= [IPV6]
428 See Documentation/networking/ipv6.rst.
429
430 apm= [APM] Advanced Power Management
431 See header of arch/x86/kernel/apm_32.c.
432
433 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
434 Format: { "0" | "1" }
435 See security/apparmor/Kconfig help text
436 0 -- disable.
437 1 -- enable.
438 Default value is set via kernel config option.
439
440 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
441 Format: <io>,<irq>,<nodeID>
442
443 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of
444 32 bit applications.
445
446 arm64.nobti [ARM64] Unconditionally disable Branch Target
447 Identification support
448
449 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack
450 support
451
452 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
453 Set instructions support
454
455 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
456 support
457
458 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
459 support
460
461 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
462 Extension support
463
464 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
465 Extension support
466
467 ataflop= [HW,M68k]
468
469 atarimouse= [HW,MOUSE] Atari Mouse
470
471 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
472 EzKey and similar keyboards
473
474 atkbd.reset= [HW] Reset keyboard during initialization
475
476 atkbd.set= [HW] Select keyboard code set
477 Format: <int> (2 = AT (default), 3 = PS/2)
478
479 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
480 keyboards
481
482 atkbd.softraw= [HW] Choose between synthetic and real raw mode
483 Format: <bool> (0 = real, 1 = synthetic (default))
484
485 atkbd.softrepeat= [HW]
486 Use software keyboard repeat
487
488 audit= [KNL] Enable the audit sub-system
489 Format: { "0" | "1" | "off" | "on" }
490 0 | off - kernel audit is disabled and can not be
491 enabled until the next reboot
492 unset - kernel audit is initialized but disabled and
493 will be fully enabled by the userspace auditd.
494 1 | on - kernel audit is initialized and partially
495 enabled, storing at most audit_backlog_limit
496 messages in RAM until it is fully enabled by the
497 userspace auditd.
498 Default: unset
499
500 audit_backlog_limit= [KNL] Set the audit queue size limit.
501 Format: <int> (must be >=0)
502 Default: 64
503
504 bau= [X86_UV] Enable the BAU on SGI UV. The default
505 behavior is to disable the BAU (i.e. bau=0).
506 Format: { "0" | "1" }
507 0 - Disable the BAU.
508 1 - Enable the BAU.
509 unset - Disable the BAU.
510
511 baycom_epp= [HW,AX25]
512 Format: <io>,<mode>
513
514 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
515 Format: <io>,<mode>
516 See header of drivers/net/hamradio/baycom_par.c.
517
518 baycom_ser_fdx= [HW,AX25]
519 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
520 Format: <io>,<irq>,<mode>[,<baud>]
521 See header of drivers/net/hamradio/baycom_ser_fdx.c.
522
523 baycom_ser_hdx= [HW,AX25]
524 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
525 Format: <io>,<irq>,<mode>
526 See header of drivers/net/hamradio/baycom_ser_hdx.c.
527
528 bdev_allow_write_mounted=
529 Format: <bool>
530 Control the ability to open a mounted block device
531 for writing, i.e., allow / disallow writes that bypass
532 the FS. This was implemented as a means to prevent
533 fuzzers from crashing the kernel by overwriting the
534 metadata underneath a mounted FS without its awareness.
535 This also prevents destructive formatting of mounted
536 filesystems by naive storage tooling that don't use
537 O_EXCL. Default is Y and can be changed through the
538 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
539
540 bert_disable [ACPI]
541 Disable BERT OS support on buggy BIOSes.
542
543 bgrt_disable [ACPI,X86,EARLY]
544 Disable BGRT to avoid flickering OEM logo.
545
546 blkdevparts= Manual partition parsing of block device(s) for
547 embedded devices based on command line input.
548 See Documentation/block/cmdline-partition.rst
549
550 boot_delay= [KNL,EARLY]
551 Milliseconds to delay each printk during boot.
552 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
553 and you may also have to specify "lpj=". Boot_delay
554 values larger than 10 seconds (10000) are assumed
555 erroneous and ignored.
556 Format: integer
557
558 bootconfig [KNL,EARLY]
559 Extended command line options can be added to an initrd
560 and this will cause the kernel to look for it.
561
562 See Documentation/admin-guide/bootconfig.rst
563
564 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
565 bttv.radio= Most important insmod options are available as
566 kernel args too.
567 bttv.pll= See Documentation/admin-guide/media/bttv.rst
568 bttv.tuner=
569
570 bulk_remove=off [PPC] This parameter disables the use of the pSeries
571 firmware feature for flushing multiple hpte entries
572 at a time.
573
574 c101= [NET] Moxa C101 synchronous serial card
575
576 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
577 Sometimes CPU hardware bugs make them report the cache
578 size incorrectly. The kernel will attempt work arounds
579 to fix known problems, but for some CPUs it is not
580 possible to determine what the correct size should be.
581 This option provides an override for these situations.
582
583 carrier_timeout=
584 [NET] Specifies amount of time (in seconds) that
585 the kernel should wait for a network carrier. By default
586 it waits 120 seconds.
587
588 ca_keys= [KEYS] This parameter identifies a specific key(s) on
589 the system trusted keyring to be used for certificate
590 trust validation.
591 format: { id:<keyid> | builtin }
592
593 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
594 algorithm. Accepted values range from 0 to 7
595 inclusive. See arch/mips/include/asm/pgtable-bits.h
596 for platform specific values (SB1, Loongson3 and
597 others).
598
599 ccw_timeout_log [S390]
600 See Documentation/arch/s390/common_io.rst for details.
601
602 cgroup_disable= [KNL] Disable a particular controller or optional feature
603 Format: {name of the controller(s) or feature(s) to disable}
604 The effects of cgroup_disable=foo are:
605 - foo isn't auto-mounted if you mount all cgroups in
606 a single hierarchy
607 - foo isn't visible as an individually mountable
608 subsystem
609 - if foo is an optional feature then the feature is
610 disabled and corresponding cgroup files are not
611 created
612 {Currently only "memory" controller deal with this and
613 cut the overhead, others just disable the usage. So
614 only cgroup_disable=memory is actually worthy}
615 Specifying "pressure" disables per-cgroup pressure
616 stall information accounting feature
617
618 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
619 Format: { { controller | "all" | "named" }
620 [,{ controller | "all" | "named" }...] }
621 Like cgroup_disable, but only applies to cgroup v1;
622 the blacklisted controllers remain available in cgroup2.
623 "all" blacklists all controllers and "named" disables
624 named mounts. Specifying both "all" and "named" disables
625 all v1 hierarchies.
626
627 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
628 Format: { "true" | "false" }
629 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
630
631 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
632 Format: <string>
633 nosocket -- Disable socket memory accounting.
634 nokmem -- Disable kernel memory accounting.
635 nobpf -- Disable BPF memory accounting.
636
637 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
638 Format: { "0" | "1" }
639 See security/selinux/Kconfig help text.
640 0 -- check protection applied by kernel (includes
641 any implied execute protection).
642 1 -- check protection requested by application.
643 Default value is set via a kernel config option.
644 Value can be changed at runtime via
645 /sys/fs/selinux/checkreqprot.
646 Setting checkreqprot to 1 is deprecated.
647
648 cio_ignore= [S390]
649 See Documentation/arch/s390/common_io.rst for details.
650
651 clearcpuid=X[,X...] [X86]
652 Disable CPUID feature X for the kernel. See
653 arch/x86/include/asm/cpufeatures.h for the valid bit
654 numbers X. Note the Linux-specific bits are not necessarily
655 stable over kernel options, but the vendor-specific
656 ones should be.
657 X can also be a string as appearing in the flags: line
658 in /proc/cpuinfo which does not have the above
659 instability issue. However, not all features have names
660 in /proc/cpuinfo.
661 Note that using this option will taint your kernel.
662 Also note that user programs calling CPUID directly
663 or using the feature without checking anything
664 will still see it. This just prevents it from
665 being used by the kernel or shown in /proc/cpuinfo.
666 Also note the kernel might malfunction if you disable
667 some critical bits.
668
669 clk_ignore_unused
670 [CLK]
671 Prevents the clock framework from automatically gating
672 clocks that have not been explicitly enabled by a Linux
673 device driver but are enabled in hardware at reset or
674 by the bootloader/firmware. Note that this does not
675 force such clocks to be always-on nor does it reserve
676 those clocks in any way. This parameter is useful for
677 debug and development, but should not be needed on a
678 platform with proper driver support. For more
679 information, see Documentation/driver-api/clk.rst.
680
681 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
682 [Deprecated]
683 Forces specified clocksource (if available) to be used
684 when calculating gettimeofday(). If specified
685 clocksource is not available, it defaults to PIT.
686 Format: { pit | tsc | cyclone | pmtmr }
687
688 clocksource= Override the default clocksource
689 Format: <string>
690 Override the default clocksource and use the clocksource
691 with the name specified.
692 Some clocksource names to choose from, depending on
693 the platform:
694 [all] jiffies (this is the base, fallback clocksource)
695 [ACPI] acpi_pm
696 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
697 pxa_timer,timer3,32k_counter,timer0_1
698 [X86-32] pit,hpet,tsc;
699 scx200_hrt on Geode; cyclone on IBM x440
700 [MIPS] MIPS
701 [PARISC] cr16
702 [S390] tod
703 [SH] SuperH
704 [SPARC64] tick
705 [X86-64] hpet,tsc
706
707 clocksource.arm_arch_timer.evtstrm=
708 [ARM,ARM64,EARLY]
709 Format: <bool>
710 Enable/disable the eventstream feature of the ARM
711 architected timer so that code using WFE-based polling
712 loops can be debugged more effectively on production
713 systems.
714
715 clocksource.verify_n_cpus= [KNL]
716 Limit the number of CPUs checked for clocksources
717 marked with CLOCK_SOURCE_VERIFY_PERCPU that
718 are marked unstable due to excessive skew.
719 A negative value says to check all CPUs, while
720 zero says not to check any. Values larger than
721 nr_cpu_ids are silently truncated to nr_cpu_ids.
722 The actual CPUs are chosen randomly, with
723 no replacement if the same CPU is chosen twice.
724
725 clocksource-wdtest.holdoff= [KNL]
726 Set the time in seconds that the clocksource
727 watchdog test waits before commencing its tests.
728 Defaults to zero when built as a module and to
729 10 seconds when built into the kernel.
730
731 cma=nn[MG]@[start[MG][-end[MG]]]
732 [KNL,CMA,EARLY]
733 Sets the size of kernel global memory area for
734 contiguous memory allocations and optionally the
735 placement constraint by the physical address range of
736 memory allocations. A value of 0 disables CMA
737 altogether. For more information, see
738 kernel/dma/contiguous.c
739
740 cma_pernuma=nn[MG]
741 [KNL,CMA,EARLY]
742 Sets the size of kernel per-numa memory area for
743 contiguous memory allocations. A value of 0 disables
744 per-numa CMA altogether. And If this option is not
745 specified, the default value is 0.
746 With per-numa CMA enabled, DMA users on node nid will
747 first try to allocate buffer from the pernuma area
748 which is located in node nid, if the allocation fails,
749 they will fallback to the global default memory area.
750
751 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
752 [KNL,CMA,EARLY]
753 Sets the size of kernel numa memory area for
754 contiguous memory allocations. It will reserve CMA
755 area for the specified node.
756
757 With numa CMA enabled, DMA users on node nid will
758 first try to allocate buffer from the numa area
759 which is located in node nid, if the allocation fails,
760 they will fallback to the global default memory area.
761
762 cmo_free_hint= [PPC] Format: { yes | no }
763 Specify whether pages are marked as being inactive
764 when they are freed. This is used in CMO environments
765 to determine OS memory pressure for page stealing by
766 a hypervisor.
767 Default: yes
768
769 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
770 Sets the size of memory pool for coherent, atomic dma
771 allocations, by default set to 256K.
772
773 com20020= [HW,NET] ARCnet - COM20020 chipset
774 Format:
775 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
776
777 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
778 Format: <io>[,<irq>]
779
780 com90xx= [HW,NET]
781 ARCnet - COM90xx chipset (memory-mapped buffers)
782 Format: <io>[,<irq>[,<memstart>]]
783
784 condev= [HW,S390] console device
785 conmode=
786
787 con3215_drop= [S390,EARLY] 3215 console drop mode.
788 Format: y|n|Y|N|1|0
789 When set to true, drop data on the 3215 console when
790 the console buffer is full. In this case the
791 operator using a 3270 terminal emulator (for example
792 x3270) does not have to enter the clear key for the
793 console output to advance and the kernel to continue.
794 This leads to a much faster boot time when a 3270
795 terminal emulator is active. If no 3270 terminal
796 emulator is used, this parameter has no effect.
797
798 console= [KNL] Output console device and options.
799
800 tty<n> Use the virtual console device <n>.
801
802 ttyS<n>[,options]
803 ttyUSB0[,options]
804 Use the specified serial port. The options are of
805 the form "bbbbpnf", where "bbbb" is the baud rate,
806 "p" is parity ("n", "o", or "e"), "n" is number of
807 bits, and "f" is flow control ("r" for RTS or
808 omit it). Default is "9600n8".
809
810 See Documentation/admin-guide/serial-console.rst for more
811 information. See
812 Documentation/networking/netconsole.rst for an
813 alternative.
814
815 <DEVNAME>:<n>.<n>[,options]
816 Use the specified serial port on the serial core bus.
817 The addressing uses DEVNAME of the physical serial port
818 device, followed by the serial core controller instance,
819 and the serial port instance. The options are the same
820 as documented for the ttyS addressing above.
821
822 The mapping of the serial ports to the tty instances
823 can be viewed with:
824
825 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/*
826 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0
827
828 In the above example, the console can be addressed with
829 console=00:04:0.0. Note that a console addressed this
830 way will only get added when the related device driver
831 is ready. The use of an earlycon parameter in addition to
832 the console may be desired for console output early on.
833
834 uart[8250],io,<addr>[,options]
835 uart[8250],mmio,<addr>[,options]
836 uart[8250],mmio16,<addr>[,options]
837 uart[8250],mmio32,<addr>[,options]
838 uart[8250],0x<addr>[,options]
839 Start an early, polled-mode console on the 8250/16550
840 UART at the specified I/O port or MMIO address,
841 switching to the matching ttyS device later.
842 MMIO inter-register address stride is either 8-bit
843 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
844 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
845 to be equivalent to 'mmio'. 'options' are specified in
846 the same format described for ttyS above; if unspecified,
847 the h/w is not re-initialized.
848
849 hvc<n> Use the hypervisor console device <n>. This is for
850 both Xen and PowerPC hypervisors.
851
852 { null | "" }
853 Use to disable console output, i.e., to have kernel
854 console messages discarded.
855 This must be the only console= parameter used on the
856 kernel command line.
857
858 If the device connected to the port is not a TTY but a braille
859 device, prepend "brl," before the device type, for instance
860 console=brl,ttyS0
861 For now, only VisioBraille is supported.
862
863 console_msg_format=
864 [KNL] Change console messages format
865 default
866 By default we print messages on consoles in
867 "[time stamp] text\n" format (time stamp may not be
868 printed, depending on CONFIG_PRINTK_TIME or
869 `printk_time' param).
870 syslog
871 Switch to syslog format: "<%u>[time stamp] text\n"
872 IOW, each message will have a facility and loglevel
873 prefix. The format is similar to one used by syslog()
874 syscall, or to executing "dmesg -S --raw" or to reading
875 from /proc/kmsg.
876
877 consoleblank= [KNL] The console blank (screen saver) timeout in
878 seconds. A value of 0 disables the blank timer.
879 Defaults to 0.
880
881 coredump_filter=
882 [KNL] Change the default value for
883 /proc/<pid>/coredump_filter.
884 See also Documentation/filesystems/proc.rst.
885
886 coresight_cpu_debug.enable
887 [ARM,ARM64]
888 Format: <bool>
889 Enable/disable the CPU sampling based debugging.
890 0: default value, disable debugging
891 1: enable debugging at boot time
892
893 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
894 Format:
895 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
896
897 cpuidle.off=1 [CPU_IDLE]
898 disable the cpuidle sub-system
899
900 cpuidle.governor=
901 [CPU_IDLE] Name of the cpuidle governor to use.
902
903 cpufreq.off=1 [CPU_FREQ]
904 disable the cpufreq sub-system
905
906 cpufreq.default_governor=
907 [CPU_FREQ] Name of the default cpufreq governor or
908 policy to use. This governor must be registered in the
909 kernel before the cpufreq driver probes.
910
911 cpu_init_udelay=N
912 [X86,EARLY] Delay for N microsec between assert and de-assert
913 of APIC INIT to start processors. This delay occurs
914 on every CPU online, such as boot, and resume from suspend.
915 Default: 10000
916
917 cpuhp.parallel=
918 [SMP] Enable/disable parallel bringup of secondary CPUs
919 Format: <bool>
920 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
921 the parameter has no effect.
922
923 crash_kexec_post_notifiers
924 Only jump to kdump kernel after running the panic
925 notifiers and dumping kmsg. This option increases
926 the risks of a kdump failure, since some panic
927 notifiers can make the crashed kernel more unstable.
928 In configurations where kdump may not be reliable,
929 running the panic notifiers could allow collecting
930 more data on dmesg, like stack traces from other CPUS
931 or extra data dumped by panic_print. Note that some
932 configurations enable this option unconditionally,
933 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
934
935 crashkernel=size[KMG][@offset[KMG]]
936 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
937 upon panic. This parameter reserves the physical
938 memory region [offset, offset + size] for that kernel
939 image. If '@offset' is omitted, then a suitable offset
940 is selected automatically.
941 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
942 under 4G first, and fall back to reserve region above
943 4G when '@offset' hasn't been specified.
944 See Documentation/admin-guide/kdump/kdump.rst for further details.
945
946 crashkernel=range1:size1[,range2:size2,...][@offset]
947 [KNL] Same as above, but depends on the memory
948 in the running system. The syntax of range is
949 start-[end] where start and end are both
950 a memory unit (amount[KMG]). See also
951 Documentation/admin-guide/kdump/kdump.rst for an example.
952
953 crashkernel=size[KMG],high
954 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
955 above 4G.
956 Allow kernel to allocate physical memory region from top,
957 so could be above 4G if system have more than 4G ram
958 installed. Otherwise memory region will be allocated
959 below 4G, if available.
960 It will be ignored if crashkernel=X is specified.
961 crashkernel=size[KMG],low
962 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
963 When crashkernel=X,high is passed, kernel could allocate
964 physical memory region above 4G, that cause second kernel
965 crash on system that require some amount of low memory,
966 e.g. swiotlb requires at least 64M+32K low memory, also
967 enough extra low memory is needed to make sure DMA buffers
968 for 32-bit devices won't run out. Kernel would try to allocate
969 default size of memory below 4G automatically. The default
970 size is platform dependent.
971 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
972 --> arm64: 128MiB
973 --> riscv: 128MiB
974 --> loongarch: 128MiB
975 This one lets the user specify own low range under 4G
976 for second kernel instead.
977 0: to disable low allocation.
978 It will be ignored when crashkernel=X,high is not used
979 or memory reserved is below 4G.
980
981 cryptomgr.notests
982 [KNL] Disable crypto self-tests
983
984 cs89x0_dma= [HW,NET]
985 Format: <dma>
986
987 cs89x0_media= [HW,NET]
988 Format: { rj45 | aui | bnc }
989
990 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
991 function call handling. When switched on,
992 additional debug data is printed to the console
993 in case a hanging CPU is detected, and that
994 CPU is pinged again in order to try to resolve
995 the hang situation. The default value of this
996 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
997 Kconfig option.
998
999 dasd= [HW,NET]
1000 See header of drivers/s390/block/dasd_devmap.c.
1001
1002 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
1003 (one device per port)
1004 Format: <port#>,<type>
1005 See also Documentation/input/devices/joystick-parport.rst
1006
1007 debug [KNL,EARLY] Enable kernel debugging (events log level).
1008
1009 debug_boot_weak_hash
1010 [KNL,EARLY] Enable printing [hashed] pointers early in the
1011 boot sequence. If enabled, we use a weak hash instead
1012 of siphash to hash pointers. Use this option if you are
1013 seeing instances of '(___ptrval___)') and need to see a
1014 value (hashed pointer) instead. Cryptographically
1015 insecure, please do not use on production kernels.
1016
1017 debug_locks_verbose=
1018 [KNL] verbose locking self-tests
1019 Format: <int>
1020 Print debugging info while doing the locking API
1021 self-tests.
1022 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
1023 (no extra messages), setting it to -1 (all bits set)
1024 will print _a_lot_ more information - normally only
1025 useful to lockdep developers.
1026
1027 debug_objects [KNL,EARLY] Enable object debugging
1028
1029 debug_guardpage_minorder=
1030 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
1031 parameter allows control of the order of pages that will
1032 be intentionally kept free (and hence protected) by the
1033 buddy allocator. Bigger value increase the probability
1034 of catching random memory corruption, but reduce the
1035 amount of memory for normal system use. The maximum
1036 possible value is MAX_PAGE_ORDER/2. Setting this
1037 parameter to 1 or 2 should be enough to identify most
1038 random memory corruption problems caused by bugs in
1039 kernel or driver code when a CPU writes to (or reads
1040 from) a random memory location. Note that there exists
1041 a class of memory corruptions problems caused by buggy
1042 H/W or F/W or by drivers badly programming DMA
1043 (basically when memory is written at bus level and the
1044 CPU MMU is bypassed) which are not detectable by
1045 CONFIG_DEBUG_PAGEALLOC, hence this option will not
1046 help tracking down these problems.
1047
1048 debug_pagealloc=
1049 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1050 enables the feature at boot time. By default, it is
1051 disabled and the system will work mostly the same as a
1052 kernel built without CONFIG_DEBUG_PAGEALLOC.
1053 Note: to get most of debug_pagealloc error reports, it's
1054 useful to also enable the page_owner functionality.
1055 on: enable the feature
1056
1057 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1058 userspace and debugfs internal clients.
1059 Format: { on, no-mount, off }
1060 on: All functions are enabled.
1061 no-mount:
1062 Filesystem is not registered but kernel clients can
1063 access APIs and a crashkernel can be used to read
1064 its content. There is nothing to mount.
1065 off: Filesystem is not registered and clients
1066 get a -EPERM as result when trying to register files
1067 or directories within debugfs.
1068 This is equivalent of the runtime functionality if
1069 debugfs was not enabled in the kernel at all.
1070 Default value is set in build-time with a kernel configuration.
1071
1072 debugpat [X86] Enable PAT debugging
1073
1074 default_hugepagesz=
1075 [HW] The size of the default HugeTLB page. This is
1076 the size represented by the legacy /proc/ hugepages
1077 APIs. In addition, this is the default hugetlb size
1078 used for shmget(), mmap() and mounting hugetlbfs
1079 filesystems. If not specified, defaults to the
1080 architecture's default huge page size. Huge page
1081 sizes are architecture dependent. See also
1082 Documentation/admin-guide/mm/hugetlbpage.rst.
1083 Format: size[KMG]
1084
1085 deferred_probe_timeout=
1086 [KNL] Debugging option to set a timeout in seconds for
1087 deferred probe to give up waiting on dependencies to
1088 probe. Only specific dependencies (subsystems or
1089 drivers) that have opted in will be ignored. A timeout
1090 of 0 will timeout at the end of initcalls. If the time
1091 out hasn't expired, it'll be restarted by each
1092 successful driver registration. This option will also
1093 dump out devices still on the deferred probe list after
1094 retrying.
1095
1096 delayacct [KNL] Enable per-task delay accounting
1097
1098 dell_smm_hwmon.ignore_dmi=
1099 [HW] Continue probing hardware even if DMI data
1100 indicates that the driver is running on unsupported
1101 hardware.
1102
1103 dell_smm_hwmon.force=
1104 [HW] Activate driver even if SMM BIOS signature does
1105 not match list of supported models and enable otherwise
1106 blacklisted features.
1107
1108 dell_smm_hwmon.power_status=
1109 [HW] Report power status in /proc/i8k
1110 (disabled by default).
1111
1112 dell_smm_hwmon.restricted=
1113 [HW] Allow controlling fans only if SYS_ADMIN
1114 capability is set.
1115
1116 dell_smm_hwmon.fan_mult=
1117 [HW] Factor to multiply fan speed with.
1118
1119 dell_smm_hwmon.fan_max=
1120 [HW] Maximum configurable fan speed.
1121
1122 dfltcc= [HW,S390]
1123 Format: { on | off | def_only | inf_only | always }
1124 on: s390 zlib hardware support for compression on
1125 level 1 and decompression (default)
1126 off: No s390 zlib hardware support
1127 def_only: s390 zlib hardware support for deflate
1128 only (compression on level 1)
1129 inf_only: s390 zlib hardware support for inflate
1130 only (decompression)
1131 always: Same as 'on' but ignores the selected compression
1132 level always using hardware support (used for debugging)
1133
1134 dhash_entries= [KNL]
1135 Set number of hash buckets for dentry cache.
1136
1137 disable_1tb_segments [PPC,EARLY]
1138 Disables the use of 1TB hash page table segments. This
1139 causes the kernel to fall back to 256MB segments which
1140 can be useful when debugging issues that require an SLB
1141 miss to occur.
1142
1143 disable= [IPV6]
1144 See Documentation/networking/ipv6.rst.
1145
1146 disable_radix [PPC,EARLY]
1147 Disable RADIX MMU mode on POWER9
1148
1149 disable_tlbie [PPC]
1150 Disable TLBIE instruction. Currently does not work
1151 with KVM, with HASH MMU, or with coherent accelerators.
1152
1153 disable_ddw [PPC/PSERIES,EARLY]
1154 Disable Dynamic DMA Window support. Use this
1155 to workaround buggy firmware.
1156
1157 disable_ipv6= [IPV6]
1158 See Documentation/networking/ipv6.rst.
1159
1160 disable_mtrr_cleanup [X86,EARLY]
1161 The kernel tries to adjust MTRR layout from continuous
1162 to discrete, to make X server driver able to add WB
1163 entry later. This parameter disables that.
1164
1165 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1166 By default the kernel will trim any uncacheable
1167 memory out of your available memory pool based on
1168 MTRR settings. This parameter disables that behavior,
1169 possibly causing your machine to run very slowly.
1170
1171 disable_timer_pin_1 [X86,EARLY]
1172 Disable PIN 1 of APIC timer
1173 Can be useful to work around chipset bugs.
1174
1175 dis_ucode_ldr [X86] Disable the microcode loader.
1176
1177 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1178 this option disables the debugging code at boot.
1179
1180 dma_debug_entries=<number>
1181 This option allows to tune the number of preallocated
1182 entries for DMA-API debugging code. One entry is
1183 required per DMA-API allocation. Use this if the
1184 DMA-API debugging code disables itself because the
1185 architectural default is too low.
1186
1187 dma_debug_driver=<driver_name>
1188 With this option the DMA-API debugging driver
1189 filter feature can be enabled at boot time. Just
1190 pass the driver to filter for as the parameter.
1191 The filter can be disabled or changed to another
1192 driver later using sysfs.
1193
1194 reg_file_data_sampling=
1195 [X86] Controls mitigation for Register File Data
1196 Sampling (RFDS) vulnerability. RFDS is a CPU
1197 vulnerability which may allow userspace to infer
1198 kernel data values previously stored in floating point
1199 registers, vector registers, or integer registers.
1200 RFDS only affects Intel Atom processors.
1201
1202 on: Turns ON the mitigation.
1203 off: Turns OFF the mitigation.
1204
1205 This parameter overrides the compile time default set
1206 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1207 disabled when other VERW based mitigations (like MDS)
1208 are enabled. In order to disable RFDS mitigation all
1209 VERW based mitigations need to be disabled.
1210
1211 For details see:
1212 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1213
1214 driver_async_probe= [KNL]
1215 List of driver names to be probed asynchronously. *
1216 matches with all driver names. If * is specified, the
1217 rest of the listed driver names are those that will NOT
1218 match the *.
1219 Format: <driver_name1>,<driver_name2>...
1220
1221 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1222 Broken monitors, graphic adapters, KVMs and EDIDless
1223 panels may send no or incorrect EDID data sets.
1224 This parameter allows to specify an EDID data sets
1225 in the /lib/firmware directory that are used instead.
1226 An EDID data set will only be used for a particular
1227 connector, if its name and a colon are prepended to
1228 the EDID name. Each connector may use a unique EDID
1229 data set by separating the files with a comma. An EDID
1230 data set with no connector name will be used for
1231 any connectors not explicitly specified.
1232
1233 dscc4.setup= [NET]
1234
1235 dt_cpu_ftrs= [PPC,EARLY]
1236 Format: {"off" | "known"}
1237 Control how the dt_cpu_ftrs device-tree binding is
1238 used for CPU feature discovery and setup (if it
1239 exists).
1240 off: Do not use it, fall back to legacy cpu table.
1241 known: Do not pass through unknown features to guests
1242 or userspace, only those that the kernel is aware of.
1243
1244 dump_apple_properties [X86]
1245 Dump name and content of EFI device properties on
1246 x86 Macs. Useful for driver authors to determine
1247 what data is available or for reverse-engineering.
1248
1249 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1250 <module>.dyndbg[="val"]
1251 Enable debug messages at boot time. See
1252 Documentation/admin-guide/dynamic-debug-howto.rst
1253 for details.
1254
1255 early_ioremap_debug [KNL,EARLY]
1256 Enable debug messages in early_ioremap support. This
1257 is useful for tracking down temporary early mappings
1258 which are not unmapped.
1259
1260 earlycon= [KNL,EARLY] Output early console device and options.
1261
1262 When used with no options, the early console is
1263 determined by stdout-path property in device tree's
1264 chosen node or the ACPI SPCR table if supported by
1265 the platform.
1266
1267 cdns,<addr>[,options]
1268 Start an early, polled-mode console on a Cadence
1269 (xuartps) serial port at the specified address. Only
1270 supported option is baud rate. If baud rate is not
1271 specified, the serial port must already be setup and
1272 configured.
1273
1274 uart[8250],io,<addr>[,options[,uartclk]]
1275 uart[8250],mmio,<addr>[,options[,uartclk]]
1276 uart[8250],mmio32,<addr>[,options[,uartclk]]
1277 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1278 uart[8250],0x<addr>[,options]
1279 Start an early, polled-mode console on the 8250/16550
1280 UART at the specified I/O port or MMIO address.
1281 MMIO inter-register address stride is either 8-bit
1282 (mmio) or 32-bit (mmio32 or mmio32be).
1283 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1284 to be equivalent to 'mmio'. 'options' are specified
1285 in the same format described for "console=ttyS<n>"; if
1286 unspecified, the h/w is not initialized. 'uartclk' is
1287 the uart clock frequency; if unspecified, it is set
1288 to 'BASE_BAUD' * 16.
1289
1290 pl011,<addr>
1291 pl011,mmio32,<addr>
1292 Start an early, polled-mode console on a pl011 serial
1293 port at the specified address. The pl011 serial port
1294 must already be setup and configured. Options are not
1295 yet supported. If 'mmio32' is specified, then only
1296 the driver will use only 32-bit accessors to read/write
1297 the device registers.
1298
1299 liteuart,<addr>
1300 Start an early console on a litex serial port at the
1301 specified address. The serial port must already be
1302 setup and configured. Options are not yet supported.
1303
1304 meson,<addr>
1305 Start an early, polled-mode console on a meson serial
1306 port at the specified address. The serial port must
1307 already be setup and configured. Options are not yet
1308 supported.
1309
1310 msm_serial,<addr>
1311 Start an early, polled-mode console on an msm serial
1312 port at the specified address. The serial port
1313 must already be setup and configured. Options are not
1314 yet supported.
1315
1316 msm_serial_dm,<addr>
1317 Start an early, polled-mode console on an msm serial
1318 dm port at the specified address. The serial port
1319 must already be setup and configured. Options are not
1320 yet supported.
1321
1322 owl,<addr>
1323 Start an early, polled-mode console on a serial port
1324 of an Actions Semi SoC, such as S500 or S900, at the
1325 specified address. The serial port must already be
1326 setup and configured. Options are not yet supported.
1327
1328 rda,<addr>
1329 Start an early, polled-mode console on a serial port
1330 of an RDA Micro SoC, such as RDA8810PL, at the
1331 specified address. The serial port must already be
1332 setup and configured. Options are not yet supported.
1333
1334 sbi
1335 Use RISC-V SBI (Supervisor Binary Interface) for early
1336 console.
1337
1338 smh Use ARM semihosting calls for early console.
1339
1340 s3c2410,<addr>
1341 s3c2412,<addr>
1342 s3c2440,<addr>
1343 s3c6400,<addr>
1344 s5pv210,<addr>
1345 exynos4210,<addr>
1346 Use early console provided by serial driver available
1347 on Samsung SoCs, requires selecting proper type and
1348 a correct base address of the selected UART port. The
1349 serial port must already be setup and configured.
1350 Options are not yet supported.
1351
1352 lantiq,<addr>
1353 Start an early, polled-mode console on a lantiq serial
1354 (lqasc) port at the specified address. The serial port
1355 must already be setup and configured. Options are not
1356 yet supported.
1357
1358 lpuart,<addr>
1359 lpuart32,<addr>
1360 Use early console provided by Freescale LP UART driver
1361 found on Freescale Vybrid and QorIQ LS1021A processors.
1362 A valid base address must be provided, and the serial
1363 port must already be setup and configured.
1364
1365 ec_imx21,<addr>
1366 ec_imx6q,<addr>
1367 Start an early, polled-mode, output-only console on the
1368 Freescale i.MX UART at the specified address. The UART
1369 must already be setup and configured.
1370
1371 ar3700_uart,<addr>
1372 Start an early, polled-mode console on the
1373 Armada 3700 serial port at the specified
1374 address. The serial port must already be setup
1375 and configured. Options are not yet supported.
1376
1377 qcom_geni,<addr>
1378 Start an early, polled-mode console on a Qualcomm
1379 Generic Interface (GENI) based serial port at the
1380 specified address. The serial port must already be
1381 setup and configured. Options are not yet supported.
1382
1383 efifb,[options]
1384 Start an early, unaccelerated console on the EFI
1385 memory mapped framebuffer (if available). On cache
1386 coherent non-x86 systems that use system memory for
1387 the framebuffer, pass the 'ram' option so that it is
1388 mapped with the correct attributes.
1389
1390 linflex,<addr>
1391 Use early console provided by Freescale LINFlexD UART
1392 serial driver for NXP S32V234 SoCs. A valid base
1393 address must be provided, and the serial port must
1394 already be setup and configured.
1395
1396 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1397 earlyprintk=vga
1398 earlyprintk=sclp
1399 earlyprintk=xen
1400 earlyprintk=serial[,ttySn[,baudrate]]
1401 earlyprintk=serial[,0x...[,baudrate]]
1402 earlyprintk=ttySn[,baudrate]
1403 earlyprintk=dbgp[debugController#]
1404 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1405 earlyprintk=xdbc[xhciController#]
1406 earlyprintk=bios
1407
1408 earlyprintk is useful when the kernel crashes before
1409 the normal console is initialized. It is not enabled by
1410 default because it has some cosmetic problems.
1411
1412 Append ",keep" to not disable it when the real console
1413 takes over.
1414
1415 Only one of vga, serial, or usb debug port can
1416 be used at a time.
1417
1418 Currently only ttyS0 and ttyS1 may be specified by
1419 name. Other I/O ports may be explicitly specified
1420 on some architectures (x86 and arm at least) by
1421 replacing ttySn with an I/O port address, like this:
1422 earlyprintk=serial,0x1008,115200
1423 You can find the port for a given device in
1424 /proc/tty/driver/serial:
1425 2: uart:ST16650V2 port:00001008 irq:18 ...
1426
1427 Interaction with the standard serial driver is not
1428 very good.
1429
1430 The VGA output is eventually overwritten by
1431 the real console.
1432
1433 The xen option can only be used in Xen domains.
1434
1435 The sclp output can only be used on s390.
1436
1437 The bios output can only be used on SuperH.
1438
1439 The optional "force" to "pciserial" enables use of a
1440 PCI device even when its classcode is not of the
1441 UART class.
1442
1443 edac_report= [HW,EDAC] Control how to report EDAC event
1444 Format: {"on" | "off" | "force"}
1445 on: enable EDAC to report H/W event. May be overridden
1446 by other higher priority error reporting module.
1447 off: disable H/W event reporting through EDAC.
1448 force: enforce the use of EDAC to report H/W event.
1449 default: on.
1450
1451 edd= [EDD]
1452 Format: {"off" | "on" | "skip[mbr]"}
1453
1454 efi= [EFI,EARLY]
1455 Format: { "debug", "disable_early_pci_dma",
1456 "nochunk", "noruntime", "nosoftreserve",
1457 "novamap", "no_disable_early_pci_dma" }
1458 debug: enable misc debug output.
1459 disable_early_pci_dma: disable the busmaster bit on all
1460 PCI bridges while in the EFI boot stub.
1461 nochunk: disable reading files in "chunks" in the EFI
1462 boot stub, as chunking can cause problems with some
1463 firmware implementations.
1464 noruntime : disable EFI runtime services support
1465 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1466 attribute may cause the kernel to reserve the
1467 memory range for a memory mapping driver to
1468 claim. Specify efi=nosoftreserve to disable this
1469 reservation and treat the memory by its base type
1470 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1471 novamap: do not call SetVirtualAddressMap().
1472 no_disable_early_pci_dma: Leave the busmaster bit set
1473 on all PCI bridges while in the EFI boot stub
1474
1475 efi_no_storage_paranoia [EFI,X86,EARLY]
1476 Using this parameter you can use more than 50% of
1477 your efi variable storage. Use this parameter only if
1478 you are really sure that your UEFI does sane gc and
1479 fulfills the spec otherwise your board may brick.
1480
1481 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1482 that is to be dynamically loaded by Linux. If there are
1483 multiple variables with the same name but with different
1484 vendor GUIDs, all of them will be loaded. See
1485 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1486
1487
1488 eisa_irq_edge= [PARISC,HW]
1489 See header of drivers/parisc/eisa.c.
1490
1491 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1492 Format: ekgdboc=kbd
1493
1494 This is designed to be used in conjunction with
1495 the boot argument: earlyprintk=vga
1496
1497 This parameter works in place of the kgdboc parameter
1498 but can only be used if the backing tty is available
1499 very early in the boot process. For early debugging
1500 via a serial port see kgdboc_earlycon instead.
1501
1502 elanfreq= [X86-32]
1503 See comment before function elanfreq_setup() in
1504 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1505
1506 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1507 Specifies physical address of start of kernel core
1508 image elf header and optionally the size. Generally
1509 kexec loader will pass this option to capture kernel.
1510 See Documentation/admin-guide/kdump/kdump.rst for details.
1511
1512 enable_mtrr_cleanup [X86,EARLY]
1513 The kernel tries to adjust MTRR layout from continuous
1514 to discrete, to make X server driver able to add WB
1515 entry later. This parameter enables that.
1516
1517 enable_timer_pin_1 [X86]
1518 Enable PIN 1 of APIC timer
1519 Can be useful to work around chipset bugs
1520 (in particular on some ATI chipsets).
1521 The kernel tries to set a reasonable default.
1522
1523 enforcing= [SELINUX] Set initial enforcing status.
1524 Format: {"0" | "1"}
1525 See security/selinux/Kconfig help text.
1526 0 -- permissive (log only, no denials).
1527 1 -- enforcing (deny and log).
1528 Default value is 0.
1529 Value can be changed at runtime via
1530 /sys/fs/selinux/enforce.
1531
1532 erst_disable [ACPI]
1533 Disable Error Record Serialization Table (ERST)
1534 support.
1535
1536 ether= [HW,NET] Ethernet cards parameters
1537 This option is obsoleted by the "netdev=" option, which
1538 has equivalent usage. See its documentation for details.
1539
1540 evm= [EVM]
1541 Format: { "fix" }
1542 Permit 'security.evm' to be updated regardless of
1543 current integrity status.
1544
1545 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1546 stages so cover more early boot allocations.
1547 Please note that as side effect some optimizations
1548 might be disabled to achieve that (e.g. parallelized
1549 memory initialization is disabled) so the boot process
1550 might take longer, especially on systems with a lot of
1551 memory. Available with CONFIG_PAGE_EXTENSION=y.
1552
1553 failslab=
1554 fail_usercopy=
1555 fail_page_alloc=
1556 fail_skb_realloc=
1557 fail_make_request=[KNL]
1558 General fault injection mechanism.
1559 Format: <interval>,<probability>,<space>,<times>
1560 See also Documentation/fault-injection/.
1561
1562 fb_tunnels= [NET]
1563 Format: { initns | none }
1564 See Documentation/admin-guide/sysctl/net.rst for
1565 fb_tunnels_only_for_init_ns
1566
1567 floppy= [HW]
1568 See Documentation/admin-guide/blockdev/floppy.rst.
1569
1570 forcepae [X86-32]
1571 Forcefully enable Physical Address Extension (PAE).
1572 Many Pentium M systems disable PAE but may have a
1573 functionally usable PAE implementation.
1574 Warning: use of this parameter will taint the kernel
1575 and may cause unknown problems.
1576
1577 fred= [X86-64]
1578 Enable/disable Flexible Return and Event Delivery.
1579 Format: { on | off }
1580 on: enable FRED when it's present.
1581 off: disable FRED, the default setting.
1582
1583 ftrace=[tracer]
1584 [FTRACE] will set and start the specified tracer
1585 as early as possible in order to facilitate early
1586 boot debugging.
1587
1588 ftrace_boot_snapshot
1589 [FTRACE] On boot up, a snapshot will be taken of the
1590 ftrace ring buffer that can be read at:
1591 /sys/kernel/tracing/snapshot.
1592 This is useful if you need tracing information from kernel
1593 boot up that is likely to be overridden by user space
1594 start up functionality.
1595
1596 Optionally, the snapshot can also be defined for a tracing
1597 instance that was created by the trace_instance= command
1598 line parameter.
1599
1600 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1601
1602 The above will cause the "foo" tracing instance to trigger
1603 a snapshot at the end of boot up.
1604
1605 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> |
1606 ,<instance>=2(orig_cpu)]
1607 [FTRACE] will dump the trace buffers on oops.
1608 If no parameter is passed, ftrace will dump global
1609 buffers of all CPUs, if you pass 2 or orig_cpu, it
1610 will dump only the buffer of the CPU that triggered
1611 the oops, or the specific instance will be dumped if
1612 its name is passed. Multiple instance dump is also
1613 supported, and instances are separated by commas. Each
1614 instance supports only dump on CPU that triggered the
1615 oops by passing 2 or orig_cpu to it.
1616
1617 ftrace_dump_on_oops=foo=orig_cpu
1618
1619 The above will dump only the buffer of "foo" instance
1620 on CPU that triggered the oops.
1621
1622 ftrace_dump_on_oops,foo,bar=orig_cpu
1623
1624 The above will dump global buffer on all CPUs, the
1625 buffer of "foo" instance on all CPUs and the buffer
1626 of "bar" instance on CPU that triggered the oops.
1627
1628 ftrace_filter=[function-list]
1629 [FTRACE] Limit the functions traced by the function
1630 tracer at boot up. function-list is a comma-separated
1631 list of functions. This list can be changed at run
1632 time by the set_ftrace_filter file in the debugfs
1633 tracing directory.
1634
1635 ftrace_notrace=[function-list]
1636 [FTRACE] Do not trace the functions specified in
1637 function-list. This list can be changed at run time
1638 by the set_ftrace_notrace file in the debugfs
1639 tracing directory.
1640
1641 ftrace_graph_filter=[function-list]
1642 [FTRACE] Limit the top level callers functions traced
1643 by the function graph tracer at boot up.
1644 function-list is a comma-separated list of functions
1645 that can be changed at run time by the
1646 set_graph_function file in the debugfs tracing directory.
1647
1648 ftrace_graph_notrace=[function-list]
1649 [FTRACE] Do not trace from the functions specified in
1650 function-list. This list is a comma-separated list of
1651 functions that can be changed at run time by the
1652 set_graph_notrace file in the debugfs tracing directory.
1653
1654 ftrace_graph_max_depth=<uint>
1655 [FTRACE] Used with the function graph tracer. This is
1656 the max depth it will trace into a function. This value
1657 can be changed at run time by the max_graph_depth file
1658 in the tracefs tracing directory. default: 0 (no limit)
1659
1660 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1661 devices by scanning the firmware to infer the
1662 consumer/supplier relationships. This feature is
1663 especially useful when drivers are loaded as modules as
1664 it ensures proper ordering of tasks like device probing
1665 (suppliers first, then consumers), supplier boot state
1666 clean up (only after all consumers have probed),
1667 suspend/resume & runtime PM (consumers first, then
1668 suppliers).
1669 Format: { off | permissive | on | rpm }
1670 off -- Don't create device links from firmware info.
1671 permissive -- Create device links from firmware info
1672 but use it only for ordering boot state clean
1673 up (sync_state() calls).
1674 on -- Create device links from firmware info and use it
1675 to enforce probe and suspend/resume ordering.
1676 rpm -- Like "on", but also use to order runtime PM.
1677
1678 fw_devlink.strict=<bool>
1679 [KNL,EARLY] Treat all inferred dependencies as mandatory
1680 dependencies. This only applies for fw_devlink=on|rpm.
1681 Format: <bool>
1682
1683 fw_devlink.sync_state =
1684 [KNL,EARLY] When all devices that could probe have finished
1685 probing, this parameter controls what to do with
1686 devices that haven't yet received their sync_state()
1687 calls.
1688 Format: { strict | timeout }
1689 strict -- Default. Continue waiting on consumers to
1690 probe successfully.
1691 timeout -- Give up waiting on consumers and call
1692 sync_state() on any devices that haven't yet
1693 received their sync_state() calls after
1694 deferred_probe_timeout has expired or by
1695 late_initcall() if !CONFIG_MODULES.
1696
1697 gamecon.map[2|3]=
1698 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1699 support via parallel port (up to 5 devices per port)
1700 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1701 See also Documentation/input/devices/joystick-parport.rst
1702
1703 gamma= [HW,DRM]
1704
1705 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1706 Format: off | on
1707 default: on
1708
1709 gather_data_sampling=
1710 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1711 mitigation.
1712
1713 Gather Data Sampling is a hardware vulnerability which
1714 allows unprivileged speculative access to data which was
1715 previously stored in vector registers.
1716
1717 This issue is mitigated by default in updated microcode.
1718 The mitigation may have a performance impact but can be
1719 disabled. On systems without the microcode mitigation
1720 disabling AVX serves as a mitigation.
1721
1722 force: Disable AVX to mitigate systems without
1723 microcode mitigation. No effect if the microcode
1724 mitigation is present. Known to cause crashes in
1725 userspace with buggy AVX enumeration.
1726
1727 off: Disable GDS mitigation.
1728
1729 gcov_persist= [GCOV] When non-zero (default), profiling data for
1730 kernel modules is saved and remains accessible via
1731 debugfs, even when the module is unloaded/reloaded.
1732 When zero, profiling data is discarded and associated
1733 debugfs files are removed at module unload time.
1734
1735 goldfish [X86] Enable the goldfish android emulator platform.
1736 Don't use this when you are not running on the
1737 android emulator
1738
1739 gpio-mockup.gpio_mockup_ranges
1740 [HW] Sets the ranges of gpiochip of for this device.
1741 Format: <start1>,<end1>,<start2>,<end2>...
1742 gpio-mockup.gpio_mockup_named_lines
1743 [HW] Let the driver know GPIO lines should be named.
1744
1745 gpt [EFI] Forces disk with valid GPT signature but
1746 invalid Protective MBR to be treated as GPT. If the
1747 primary GPT is corrupted, it enables the backup/alternate
1748 GPT to be used instead.
1749
1750 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1751 the "Enable 0" bit of the configuration register.
1752 Format: 0 | 1
1753 Default: 0
1754 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1755 the "Enable 0" bit of the configuration register.
1756 Format: 0 | 1
1757 Default: 0
1758 grcan.select= [HW] Select which physical interface to use.
1759 Format: 0 | 1
1760 Default: 0
1761 grcan.txsize= [HW] Sets the size of the tx buffer.
1762 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1763 Default: 1024
1764 grcan.rxsize= [HW] Sets the size of the rx buffer.
1765 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1766 Default: 1024
1767
1768 hardened_usercopy=
1769 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1770 hardening is enabled for this boot. Hardened
1771 usercopy checking is used to protect the kernel
1772 from reading or writing beyond known memory
1773 allocation boundaries as a proactive defense
1774 against bounds-checking flaws in the kernel's
1775 copy_to_user()/copy_from_user() interface.
1776 on Perform hardened usercopy checks (default).
1777 off Disable hardened usercopy checks.
1778
1779 hardlockup_all_cpu_backtrace=
1780 [KNL] Should the hard-lockup detector generate
1781 backtraces on all cpus.
1782 Format: 0 | 1
1783
1784 hashdist= [KNL,NUMA] Large hashes allocated during boot
1785 are distributed across NUMA nodes. Defaults on
1786 for 64-bit NUMA, off otherwise.
1787 Format: 0 | 1 (for off | on)
1788
1789 hd= [EIDE] (E)IDE hard drive subsystem geometry
1790 Format: <cyl>,<head>,<sect>
1791
1792 hest_disable [ACPI]
1793 Disable Hardware Error Source Table (HEST) support;
1794 corresponding firmware-first mode error processing
1795 logic will be disabled.
1796
1797 hibernate= [HIBERNATION]
1798 noresume Don't check if there's a hibernation image
1799 present during boot.
1800 nocompress Don't compress/decompress hibernation images.
1801 no Disable hibernation and resume.
1802 protect_image Turn on image protection during restoration
1803 (that will set all pages holding image data
1804 during restoration read-only).
1805
1806 hibernate.compressor= [HIBERNATION] Compression algorithm to be
1807 used with hibernation.
1808 Format: { lzo | lz4 }
1809 Default: lzo
1810
1811 lzo: Select LZO compression algorithm to
1812 compress/decompress hibernation image.
1813
1814 lz4: Select LZ4 compression algorithm to
1815 compress/decompress hibernation image.
1816
1817 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
1818 size of <nn>. This works even on boxes that have no
1819 highmem otherwise. This also works to reduce highmem
1820 size on bigger boxes.
1821
1822 highres= [KNL] Enable/disable high resolution timer mode.
1823 Valid parameters: "on", "off"
1824 Default: "on"
1825
1826 hlt [BUGS=ARM,SH]
1827
1828 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
1829 Format: <string>
1830 This allows setting the system's hostname during early
1831 startup. This sets the name returned by gethostname.
1832 Using this parameter to set the hostname makes it
1833 possible to ensure the hostname is correctly set before
1834 any userspace processes run, avoiding the possibility
1835 that a process may call gethostname before the hostname
1836 has been explicitly set, resulting in the calling
1837 process getting an incorrect result. The string must
1838 not exceed the maximum allowed hostname length (usually
1839 64 characters) and will be truncated otherwise.
1840
1841 hpet= [X86-32,HPET] option to control HPET usage
1842 Format: { enable (default) | disable | force |
1843 verbose }
1844 disable: disable HPET and use PIT instead
1845 force: allow force enabled of undocumented chips (ICH4,
1846 VIA, nVidia)
1847 verbose: show contents of HPET registers during setup
1848
1849 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1850 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1851
1852 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1853 If this follows hugepagesz (below), it specifies
1854 the number of pages of hugepagesz to be allocated.
1855 If this is the first HugeTLB parameter on the command
1856 line, it specifies the number of pages to allocate for
1857 the default huge page size. If using node format, the
1858 number of pages to allocate per-node can be specified.
1859 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1860 Format: <integer> or (node format)
1861 <node>:<integer>[,<node>:<integer>]
1862
1863 hugepagesz=
1864 [HW] The size of the HugeTLB pages. This is used in
1865 conjunction with hugepages (above) to allocate huge
1866 pages of a specific size at boot. The pair
1867 hugepagesz=X hugepages=Y can be specified once for
1868 each supported huge page size. Huge page sizes are
1869 architecture dependent. See also
1870 Documentation/admin-guide/mm/hugetlbpage.rst.
1871 Format: size[KMG]
1872
1873 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
1874 of gigantic hugepages. Or using node format, the size
1875 of a CMA area per node can be specified.
1876 Format: nn[KMGTPE] or (node format)
1877 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1878
1879 Reserve a CMA area of given size and allocate gigantic
1880 hugepages using the CMA allocator. If enabled, the
1881 boot-time allocation of gigantic hugepages is skipped.
1882
1883 hugetlb_free_vmemmap=
1884 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1885 enabled.
1886 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1887 Allows heavy hugetlb users to free up some more
1888 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1889 Format: { on | off (default) }
1890
1891 on: enable HVO
1892 off: disable HVO
1893
1894 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1895 the default is on.
1896
1897 Note that the vmemmap pages may be allocated from the added
1898 memory block itself when memory_hotplug.memmap_on_memory is
1899 enabled, those vmemmap pages cannot be optimized even if this
1900 feature is enabled. Other vmemmap pages not allocated from
1901 the added memory block itself do not be affected.
1902
1903 hung_task_panic=
1904 [KNL] Should the hung task detector generate panics.
1905 Format: 0 | 1
1906
1907 A value of 1 instructs the kernel to panic when a
1908 hung task is detected. The default value is controlled
1909 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1910 option. The value selected by this boot parameter can
1911 be changed later by the kernel.hung_task_panic sysctl.
1912
1913 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1914 terminal devices. Valid values: 0..8
1915 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1916 If specified, z/VM IUCV HVC accepts connections
1917 from listed z/VM user IDs only.
1918
1919 hv_nopvspin [X86,HYPER_V,EARLY]
1920 Disables the paravirt spinlock optimizations
1921 which allow the hypervisor to 'idle' the guest
1922 on lock contention.
1923
1924 i2c_bus= [HW] Override the default board specific I2C bus speed
1925 or register an additional I2C bus that is not
1926 registered from board initialization code.
1927 Format:
1928 <bus_id>,<clkrate>
1929
1930 i2c_touchscreen_props= [HW,ACPI,X86]
1931 Set device-properties for ACPI-enumerated I2C-attached
1932 touchscreen, to e.g. fix coordinates of upside-down
1933 mounted touchscreens. If you need this option please
1934 submit a drivers/platform/x86/touchscreen_dmi.c patch
1935 adding a DMI quirk for this.
1936
1937 Format:
1938 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...]
1939 Where <val> is one of:
1940 Omit "=<val>" entirely Set a boolean device-property
1941 Unsigned number Set a u32 device-property
1942 Anything else Set a string device-property
1943
1944 Examples (split over multiple lines):
1945 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x:
1946 touchscreen-inverted-y
1947
1948 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920:
1949 touchscreen-size-y=1080:touchscreen-inverted-y:
1950 firmware-name=gsl1680-vendor-model.fw:silead,home-button
1951
1952 i8042.debug [HW] Toggle i8042 debug mode
1953 i8042.unmask_kbd_data
1954 [HW] Enable printing of interrupt data from the KBD port
1955 (disabled by default, and as a pre-condition
1956 requires that i8042.debug=1 be enabled)
1957 i8042.direct [HW] Put keyboard port into non-translated mode
1958 i8042.dumbkbd [HW] Pretend that controller can only read data from
1959 keyboard and cannot control its state
1960 (Don't attempt to blink the leds)
1961 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1962 i8042.nokbd [HW] Don't check/create keyboard port
1963 i8042.noloop [HW] Disable the AUX Loopback command while probing
1964 for the AUX port
1965 i8042.nomux [HW] Don't check presence of an active multiplexing
1966 controller
1967 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1968 controllers
1969 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1970 i8042.reset [HW] Reset the controller during init, cleanup and
1971 suspend-to-ram transitions, only during s2r
1972 transitions, or never reset
1973 Format: { 1 | Y | y | 0 | N | n }
1974 1, Y, y: always reset controller
1975 0, N, n: don't ever reset controller
1976 Default: only on s2r transitions on x86; most other
1977 architectures force reset to be always executed
1978 i8042.unlock [HW] Unlock (ignore) the keylock
1979 i8042.kbdreset [HW] Reset device connected to KBD port
1980 i8042.probe_defer
1981 [HW] Allow deferred probing upon i8042 probe errors
1982
1983 i810= [HW,DRM]
1984
1985 i915.invert_brightness=
1986 [DRM] Invert the sense of the variable that is used to
1987 set the brightness of the panel backlight. Normally a
1988 brightness value of 0 indicates backlight switched off,
1989 and the maximum of the brightness value sets the backlight
1990 to maximum brightness. If this parameter is set to 0
1991 (default) and the machine requires it, or this parameter
1992 is set to 1, a brightness value of 0 sets the backlight
1993 to maximum brightness, and the maximum of the brightness
1994 value switches the backlight off.
1995 -1 -- never invert brightness
1996 0 -- machine default
1997 1 -- force brightness inversion
1998
1999 ia32_emulation= [X86-64]
2000 Format: <bool>
2001 When true, allows loading 32-bit programs and executing 32-bit
2002 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
2003 boot time. When false, unconditionally disables IA32 emulation.
2004
2005 icn= [HW,ISDN]
2006 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
2007
2008
2009 idle= [X86,EARLY]
2010 Format: idle=poll, idle=halt, idle=nomwait
2011 Poll forces a polling idle loop that can slightly
2012 improve the performance of waking up a idle CPU, but
2013 will use a lot of power and make the system run hot.
2014 Not recommended.
2015 idle=halt: Halt is forced to be used for CPU idle.
2016 In such case C2/C3 won't be used again.
2017 idle=nomwait: Disable mwait for CPU C-states
2018
2019 idxd.sva= [HW]
2020 Format: <bool>
2021 Allow force disabling of Shared Virtual Memory (SVA)
2022 support for the idxd driver. By default it is set to
2023 true (1).
2024
2025 idxd.tc_override= [HW]
2026 Format: <bool>
2027 Allow override of default traffic class configuration
2028 for the device. By default it is set to false (0).
2029
2030 ieee754= [MIPS] Select IEEE Std 754 conformance mode
2031 Format: { strict | legacy | 2008 | relaxed | emulated }
2032 Default: strict
2033
2034 Choose which programs will be accepted for execution
2035 based on the IEEE 754 NaN encoding(s) supported by
2036 the FPU and the NaN encoding requested with the value
2037 of an ELF file header flag individually set by each
2038 binary. Hardware implementations are permitted to
2039 support either or both of the legacy and the 2008 NaN
2040 encoding mode.
2041
2042 Available settings are as follows:
2043 strict accept binaries that request a NaN encoding
2044 supported by the FPU
2045 legacy only accept legacy-NaN binaries, if supported
2046 by the FPU
2047 2008 only accept 2008-NaN binaries, if supported
2048 by the FPU
2049 relaxed accept any binaries regardless of whether
2050 supported by the FPU
2051 emulated accept any binaries but enable FPU emulator
2052 if binary mode is unsupported by the FPU.
2053
2054 The FPU emulator is always able to support both NaN
2055 encodings, so if no FPU hardware is present or it has
2056 been disabled with 'nofpu', then the settings of
2057 'legacy' and '2008' strap the emulator accordingly,
2058 'relaxed' straps the emulator for both legacy-NaN and
2059 2008-NaN, whereas 'strict' enables legacy-NaN only on
2060 legacy processors and both NaN encodings on MIPS32 or
2061 MIPS64 CPUs.
2062
2063 The setting for ABS.fmt/NEG.fmt instruction execution
2064 mode generally follows that for the NaN encoding,
2065 except where unsupported by hardware.
2066
2067 ignore_loglevel [KNL,EARLY]
2068 Ignore loglevel setting - this will print /all/
2069 kernel messages to the console. Useful for debugging.
2070 We also add it as printk module parameter, so users
2071 could change it dynamically, usually by
2072 /sys/module/printk/parameters/ignore_loglevel.
2073
2074 ignore_rlimit_data
2075 Ignore RLIMIT_DATA setting for data mappings,
2076 print warning at first misuse. Can be changed via
2077 /sys/module/kernel/parameters/ignore_rlimit_data.
2078
2079 ihash_entries= [KNL]
2080 Set number of hash buckets for inode cache.
2081
2082 ima_appraise= [IMA] appraise integrity measurements
2083 Format: { "off" | "enforce" | "fix" | "log" }
2084 default: "enforce"
2085
2086 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2087 The builtin appraise policy appraises all files
2088 owned by uid=0.
2089
2090 ima_canonical_fmt [IMA]
2091 Use the canonical format for the binary runtime
2092 measurements, instead of host native format.
2093
2094 ima_hash= [IMA]
2095 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2096 | sha512 | ... }
2097 default: "sha1"
2098
2099 The list of supported hash algorithms is defined
2100 in crypto/hash_info.h.
2101
2102 ima_policy= [IMA]
2103 The builtin policies to load during IMA setup.
2104 Format: "tcb | appraise_tcb | secure_boot |
2105 fail_securely | critical_data"
2106
2107 The "tcb" policy measures all programs exec'd, files
2108 mmap'd for exec, and all files opened with the read
2109 mode bit set by either the effective uid (euid=0) or
2110 uid=0.
2111
2112 The "appraise_tcb" policy appraises the integrity of
2113 all files owned by root.
2114
2115 The "secure_boot" policy appraises the integrity
2116 of files (eg. kexec kernel image, kernel modules,
2117 firmware, policy, etc) based on file signatures.
2118
2119 The "fail_securely" policy forces file signature
2120 verification failure also on privileged mounted
2121 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2122 flag.
2123
2124 The "critical_data" policy measures kernel integrity
2125 critical data.
2126
2127 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2128 Load a policy which meets the needs of the Trusted
2129 Computing Base. This means IMA will measure all
2130 programs exec'd, files mmap'd for exec, and all files
2131 opened for read by uid=0.
2132
2133 ima_template= [IMA]
2134 Select one of defined IMA measurements template formats.
2135 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2136 "ima-sigv2" }
2137 Default: "ima-ng"
2138
2139 ima_template_fmt=
2140 [IMA] Define a custom template format.
2141 Format: { "field1|...|fieldN" }
2142
2143 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2144 Format: <min_file_size>
2145 Set the minimal file size for using asynchronous hash.
2146 If left unspecified, ahash usage is disabled.
2147
2148 ahash performance varies for different data sizes on
2149 different crypto accelerators. This option can be used
2150 to achieve the best performance for a particular HW.
2151
2152 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2153 Format: <bufsize>
2154 Set hashing buffer size. Default: 4k.
2155
2156 ahash performance varies for different chunk sizes on
2157 different crypto accelerators. This option can be used
2158 to achieve best performance for particular HW.
2159
2160 init= [KNL]
2161 Format: <full_path>
2162 Run specified binary instead of /sbin/init as init
2163 process.
2164
2165 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2166 for working out where the kernel is dying during
2167 startup.
2168
2169 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2170 initcall functions. Useful for debugging built-in
2171 modules and initcalls.
2172
2173 initramfs_async= [KNL]
2174 Format: <bool>
2175 Default: 1
2176 This parameter controls whether the initramfs
2177 image is unpacked asynchronously, concurrently
2178 with devices being probed and
2179 initialized. This should normally just work,
2180 but as a debugging aid, one can get the
2181 historical behaviour of the initramfs
2182 unpacking being completed before device_ and
2183 late_ initcalls.
2184
2185 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2186
2187 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2188 load the initrd. If an initrd is compiled in or
2189 specified in the bootparams, it takes priority over this
2190 setting.
2191 Format: ss[KMG],nn[KMG]
2192 Default is 0, 0
2193
2194 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2195 zeroes.
2196 Format: 0 | 1
2197 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2198
2199 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2200 Format: 0 | 1
2201 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2202
2203 init_pkru= [X86] Specify the default memory protection keys rights
2204 register contents for all processes. 0x55555554 by
2205 default (disallow access to all but pkey 0). Can
2206 override in debugfs after boot.
2207
2208 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2209 Format: <irq>
2210
2211 int_pln_enable [X86] Enable power limit notification interrupt
2212
2213 integrity_audit=[IMA]
2214 Format: { "0" | "1" }
2215 0 -- basic integrity auditing messages. (Default)
2216 1 -- additional integrity auditing messages.
2217
2218 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2219 on
2220 Enable intel iommu driver.
2221 off
2222 Disable intel iommu driver.
2223 igfx_off [Default Off]
2224 By default, gfx is mapped as normal device. If a gfx
2225 device has a dedicated DMAR unit, the DMAR unit is
2226 bypassed by not enabling DMAR with this option. In
2227 this case, gfx device will use physical address for
2228 DMA.
2229 strict [Default Off]
2230 Deprecated, equivalent to iommu.strict=1.
2231 sp_off [Default Off]
2232 By default, super page will be supported if Intel IOMMU
2233 has the capability. With this option, super page will
2234 not be supported.
2235 sm_on
2236 Enable the Intel IOMMU scalable mode if the hardware
2237 advertises that it has support for the scalable mode
2238 translation.
2239 sm_off
2240 Disallow use of the Intel IOMMU scalable mode.
2241 tboot_noforce [Default Off]
2242 Do not force the Intel IOMMU enabled under tboot.
2243 By default, tboot will force Intel IOMMU on, which
2244 could harm performance of some high-throughput
2245 devices like 40GBit network cards, even if identity
2246 mapping is enabled.
2247 Note that using this option lowers the security
2248 provided by tboot because it makes the system
2249 vulnerable to DMA attacks.
2250
2251 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2252 0 disables intel_idle and fall back on acpi_idle.
2253 1 to 9 specify maximum depth of C-state.
2254
2255 intel_pstate= [X86,EARLY]
2256 disable
2257 Do not enable intel_pstate as the default
2258 scaling driver for the supported processors
2259 active
2260 Use intel_pstate driver to bypass the scaling
2261 governors layer of cpufreq and provides it own
2262 algorithms for p-state selection. There are two
2263 P-state selection algorithms provided by
2264 intel_pstate in the active mode: powersave and
2265 performance. The way they both operate depends
2266 on whether or not the hardware managed P-states
2267 (HWP) feature has been enabled in the processor
2268 and possibly on the processor model.
2269 passive
2270 Use intel_pstate as a scaling driver, but configure it
2271 to work with generic cpufreq governors (instead of
2272 enabling its internal governor). This mode cannot be
2273 used along with the hardware-managed P-states (HWP)
2274 feature.
2275 force
2276 Enable intel_pstate on systems that prohibit it by default
2277 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2278 instead of acpi-cpufreq may disable platform features, such
2279 as thermal controls and power capping, that rely on ACPI
2280 P-States information being indicated to OSPM and therefore
2281 should be used with caution. This option does not work with
2282 processors that aren't supported by the intel_pstate driver
2283 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2284 no_hwp
2285 Do not enable hardware P state control (HWP)
2286 if available.
2287 hwp_only
2288 Only load intel_pstate on systems which support
2289 hardware P state control (HWP) if available.
2290 support_acpi_ppc
2291 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2292 Description Table, specifies preferred power management
2293 profile as "Enterprise Server" or "Performance Server",
2294 then this feature is turned on by default.
2295 per_cpu_perf_limits
2296 Allow per-logical-CPU P-State performance control limits using
2297 cpufreq sysfs interface
2298
2299 intremap= [X86-64,Intel-IOMMU,EARLY]
2300 on enable Interrupt Remapping (default)
2301 off disable Interrupt Remapping
2302 nosid disable Source ID checking
2303 no_x2apic_optout
2304 BIOS x2APIC opt-out request will be ignored
2305 nopost disable Interrupt Posting
2306 posted_msi
2307 enable MSIs delivered as posted interrupts
2308
2309 iomem= Disable strict checking of access to MMIO memory
2310 strict regions from userspace.
2311 relaxed
2312
2313 iommu= [X86,EARLY]
2314 off
2315 force
2316 noforce
2317 biomerge
2318 panic
2319 nopanic
2320 merge
2321 nomerge
2322 soft
2323 pt [X86]
2324 nopt [X86]
2325 nobypass [PPC/POWERNV]
2326 Disable IOMMU bypass, using IOMMU for PCI devices.
2327
2328 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2329 Format: { "0" | "1" }
2330 0 - Try to allocate a 32-bit DMA address first, before
2331 falling back to the full range if needed.
2332 1 - Allocate directly from the full usable range,
2333 forcing Dual Address Cycle for PCI cards supporting
2334 greater than 32-bit addressing.
2335
2336 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2337 Format: { "0" | "1" }
2338 0 - Lazy mode.
2339 Request that DMA unmap operations use deferred
2340 invalidation of hardware TLBs, for increased
2341 throughput at the cost of reduced device isolation.
2342 Will fall back to strict mode if not supported by
2343 the relevant IOMMU driver.
2344 1 - Strict mode.
2345 DMA unmap operations invalidate IOMMU hardware TLBs
2346 synchronously.
2347 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2348 Note: on x86, strict mode specified via one of the
2349 legacy driver-specific options takes precedence.
2350
2351 iommu.passthrough=
2352 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2353 Format: { "0" | "1" }
2354 0 - Use IOMMU translation for DMA.
2355 1 - Bypass the IOMMU for DMA.
2356 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2357
2358 io7= [HW] IO7 for Marvel-based Alpha systems
2359 See comment before marvel_specify_io7 in
2360 arch/alpha/kernel/core_marvel.c.
2361
2362 io_delay= [X86,EARLY] I/O delay method
2363 0x80
2364 Standard port 0x80 based delay
2365 0xed
2366 Alternate port 0xed based delay (needed on some systems)
2367 udelay
2368 Simple two microseconds delay
2369 none
2370 No delay
2371
2372 ip= [IP_PNP]
2373 See Documentation/admin-guide/nfs/nfsroot.rst.
2374
2375 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2376 IPC identifiers from 32,768 to 16,777,216.
2377
2378 ipe.enforce= [IPE]
2379 Format: <bool>
2380 Determine whether IPE starts in permissive (0) or
2381 enforce (1) mode. The default is enforce.
2382
2383 ipe.success_audit=
2384 [IPE]
2385 Format: <bool>
2386 Start IPE with success auditing enabled, emitting
2387 an audit event when a binary is allowed. The default
2388 is 0.
2389
2390 irqaffinity= [SMP] Set the default irq affinity mask
2391 The argument is a cpu list, as described above.
2392
2393 irqchip.gicv2_force_probe=
2394 [ARM,ARM64,EARLY]
2395 Format: <bool>
2396 Force the kernel to look for the second 4kB page
2397 of a GICv2 controller even if the memory range
2398 exposed by the device tree is too small.
2399
2400 irqchip.gicv3_nolpi=
2401 [ARM,ARM64,EARLY]
2402 Force the kernel to ignore the availability of
2403 LPIs (and by consequence ITSs). Intended for system
2404 that use the kernel as a bootloader, and thus want
2405 to let secondary kernels in charge of setting up
2406 LPIs.
2407
2408 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2409 Enables support for pseudo-NMIs in the kernel. This
2410 requires the kernel to be built with
2411 CONFIG_ARM64_PSEUDO_NMI.
2412
2413 irqfixup [HW]
2414 When an interrupt is not handled search all handlers
2415 for it. Intended to get systems with badly broken
2416 firmware running.
2417
2418 irqpoll [HW]
2419 When an interrupt is not handled search all handlers
2420 for it. Also check all handlers each timer
2421 interrupt. Intended to get systems with badly broken
2422 firmware running.
2423
2424 isapnp= [ISAPNP]
2425 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2426
2427 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2428 [Deprecated - use cpusets instead]
2429 Format: [flag-list,]<cpu-list>
2430
2431 Specify one or more CPUs to isolate from disturbances
2432 specified in the flag list (default: domain):
2433
2434 nohz
2435 Disable the tick when a single task runs.
2436
2437 A residual 1Hz tick is offloaded to workqueues, which you
2438 need to affine to housekeeping through the global
2439 workqueue's affinity configured via the
2440 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2441 by using the 'domain' flag described below.
2442
2443 NOTE: by default the global workqueue runs on all CPUs,
2444 so to protect individual CPUs the 'cpumask' file has to
2445 be configured manually after bootup.
2446
2447 domain
2448 Isolate from the general SMP balancing and scheduling
2449 algorithms. Note that performing domain isolation this way
2450 is irreversible: it's not possible to bring back a CPU to
2451 the domains once isolated through isolcpus. It's strongly
2452 advised to use cpusets instead to disable scheduler load
2453 balancing through the "cpuset.sched_load_balance" file.
2454 It offers a much more flexible interface where CPUs can
2455 move in and out of an isolated set anytime.
2456
2457 You can move a process onto or off an "isolated" CPU via
2458 the CPU affinity syscalls or cpuset.
2459 <cpu number> begins at 0 and the maximum value is
2460 "number of CPUs in system - 1".
2461
2462 managed_irq
2463
2464 Isolate from being targeted by managed interrupts
2465 which have an interrupt mask containing isolated
2466 CPUs. The affinity of managed interrupts is
2467 handled by the kernel and cannot be changed via
2468 the /proc/irq/* interfaces.
2469
2470 This isolation is best effort and only effective
2471 if the automatically assigned interrupt mask of a
2472 device queue contains isolated and housekeeping
2473 CPUs. If housekeeping CPUs are online then such
2474 interrupts are directed to the housekeeping CPU
2475 so that IO submitted on the housekeeping CPU
2476 cannot disturb the isolated CPU.
2477
2478 If a queue's affinity mask contains only isolated
2479 CPUs then this parameter has no effect on the
2480 interrupt routing decision, though interrupts are
2481 only delivered when tasks running on those
2482 isolated CPUs submit IO. IO submitted on
2483 housekeeping CPUs has no influence on those
2484 queues.
2485
2486 The format of <cpu-list> is described above.
2487
2488 iucv= [HW,NET]
2489
2490 ivrs_ioapic [HW,X86-64]
2491 Provide an override to the IOAPIC-ID<->DEVICE-ID
2492 mapping provided in the IVRS ACPI table.
2493 By default, PCI segment is 0, and can be omitted.
2494
2495 For example, to map IOAPIC-ID decimal 10 to
2496 PCI segment 0x1 and PCI device 00:14.0,
2497 write the parameter as:
2498 ivrs_ioapic=10@0001:00:14.0
2499
2500 Deprecated formats:
2501 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2502 write the parameter as:
2503 ivrs_ioapic[10]=00:14.0
2504 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2505 PCI device 00:14.0 write the parameter as:
2506 ivrs_ioapic[10]=0001:00:14.0
2507
2508 ivrs_hpet [HW,X86-64]
2509 Provide an override to the HPET-ID<->DEVICE-ID
2510 mapping provided in the IVRS ACPI table.
2511 By default, PCI segment is 0, and can be omitted.
2512
2513 For example, to map HPET-ID decimal 10 to
2514 PCI segment 0x1 and PCI device 00:14.0,
2515 write the parameter as:
2516 ivrs_hpet=10@0001:00:14.0
2517
2518 Deprecated formats:
2519 * To map HPET-ID decimal 0 to PCI device 00:14.0
2520 write the parameter as:
2521 ivrs_hpet[0]=00:14.0
2522 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2523 PCI device 00:14.0 write the parameter as:
2524 ivrs_ioapic[10]=0001:00:14.0
2525
2526 ivrs_acpihid [HW,X86-64]
2527 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2528 mapping provided in the IVRS ACPI table.
2529 By default, PCI segment is 0, and can be omitted.
2530
2531 For example, to map UART-HID:UID AMD0020:0 to
2532 PCI segment 0x1 and PCI device ID 00:14.5,
2533 write the parameter as:
2534 ivrs_acpihid=AMD0020:0@0001:00:14.5
2535
2536 Deprecated formats:
2537 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2538 PCI device ID 00:14.5, write the parameter as:
2539 ivrs_acpihid[00:14.5]=AMD0020:0
2540 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2541 PCI device ID 00:14.5, write the parameter as:
2542 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2543
2544 js= [HW,JOY] Analog joystick
2545 See Documentation/input/joydev/joystick.rst.
2546
2547 kasan_multi_shot
2548 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2549 report on every invalid memory access. Without this
2550 parameter KASAN will print report only for the first
2551 invalid access.
2552
2553 keep_bootcon [KNL,EARLY]
2554 Do not unregister boot console at start. This is only
2555 useful for debugging when something happens in the window
2556 between unregistering the boot console and initializing
2557 the real console.
2558
2559 keepinitrd [HW,ARM] See retain_initrd.
2560
2561 kernelcore= [KNL,X86,PPC,EARLY]
2562 Format: nn[KMGTPE] | nn% | "mirror"
2563 This parameter specifies the amount of memory usable by
2564 the kernel for non-movable allocations. The requested
2565 amount is spread evenly throughout all nodes in the
2566 system as ZONE_NORMAL. The remaining memory is used for
2567 movable memory in its own zone, ZONE_MOVABLE. In the
2568 event, a node is too small to have both ZONE_NORMAL and
2569 ZONE_MOVABLE, kernelcore memory will take priority and
2570 other nodes will have a larger ZONE_MOVABLE.
2571
2572 ZONE_MOVABLE is used for the allocation of pages that
2573 may be reclaimed or moved by the page migration
2574 subsystem. Note that allocations like PTEs-from-HighMem
2575 still use the HighMem zone if it exists, and the Normal
2576 zone if it does not.
2577
2578 It is possible to specify the exact amount of memory in
2579 the form of "nn[KMGTPE]", a percentage of total system
2580 memory in the form of "nn%", or "mirror". If "mirror"
2581 option is specified, mirrored (reliable) memory is used
2582 for non-movable allocations and remaining memory is used
2583 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2584 are exclusive, so you cannot specify multiple forms.
2585
2586 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2587 Format: <Controller#>[,poll interval]
2588 The controller # is the number of the ehci usb debug
2589 port as it is probed via PCI. The poll interval is
2590 optional and is the number seconds in between
2591 each poll cycle to the debug port in case you need
2592 the functionality for interrupting the kernel with
2593 gdb or control-c on the dbgp connection. When
2594 not using this parameter you use sysrq-g to break into
2595 the kernel debugger.
2596
2597 kgdboc= [KGDB,HW] kgdb over consoles.
2598 Requires a tty driver that supports console polling,
2599 or a supported polling keyboard driver (non-usb).
2600 Serial only format: <serial_device>[,baud]
2601 keyboard only format: kbd
2602 keyboard and serial format: kbd,<serial_device>[,baud]
2603 Optional Kernel mode setting:
2604 kms, kbd format: kms,kbd
2605 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2606
2607 kgdboc_earlycon= [KGDB,HW,EARLY]
2608 If the boot console provides the ability to read
2609 characters and can work in polling mode, you can use
2610 this parameter to tell kgdb to use it as a backend
2611 until the normal console is registered. Intended to
2612 be used together with the kgdboc parameter which
2613 specifies the normal console to transition to.
2614
2615 The name of the early console should be specified
2616 as the value of this parameter. Note that the name of
2617 the early console might be different than the tty
2618 name passed to kgdboc. It's OK to leave the value
2619 blank and the first boot console that implements
2620 read() will be picked.
2621
2622 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2623 kernel debugger at the earliest opportunity.
2624
2625 kmac= [MIPS] Korina ethernet MAC address.
2626 Configure the RouterBoard 532 series on-chip
2627 Ethernet adapter MAC address.
2628
2629 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
2630 Valid arguments: on, off
2631 Default: on
2632 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2633 the default is off.
2634
2635 kprobe_event=[probe-list]
2636 [FTRACE] Add kprobe events and enable at boot time.
2637 The probe-list is a semicolon delimited list of probe
2638 definitions. Each definition is same as kprobe_events
2639 interface, but the parameters are comma delimited.
2640 For example, to add a kprobe event on vfs_read with
2641 arg1 and arg2, add to the command line;
2642
2643 kprobe_event=p,vfs_read,$arg1,$arg2
2644
2645 See also Documentation/trace/kprobetrace.rst "Kernel
2646 Boot Parameter" section.
2647
2648 kpti= [ARM64,EARLY] Control page table isolation of
2649 user and kernel address spaces.
2650 Default: enabled on cores which need mitigation.
2651 0: force disabled
2652 1: force enabled
2653
2654 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2655 CONFIG_KUNIT to be set to be fully enabled. The
2656 default value can be overridden via
2657 KUNIT_DEFAULT_ENABLED.
2658 Default is 1 (enabled)
2659
2660 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2661 Default is 0 (don't ignore, but inject #GP)
2662
2663 kvm.eager_page_split=
2664 [KVM,X86] Controls whether or not KVM will try to
2665 proactively split all huge pages during dirty logging.
2666 Eager page splitting reduces interruptions to vCPU
2667 execution by eliminating the write-protection faults
2668 and MMU lock contention that would otherwise be
2669 required to split huge pages lazily.
2670
2671 VM workloads that rarely perform writes or that write
2672 only to a small region of VM memory may benefit from
2673 disabling eager page splitting to allow huge pages to
2674 still be used for reads.
2675
2676 The behavior of eager page splitting depends on whether
2677 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2678 disabled, all huge pages in a memslot will be eagerly
2679 split when dirty logging is enabled on that memslot. If
2680 enabled, eager page splitting will be performed during
2681 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2682 cleared.
2683
2684 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2685
2686 Default is Y (on).
2687
2688 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86]
2689 If enabled, KVM will enable virtualization in hardware
2690 when KVM is loaded, and disable virtualization when KVM
2691 is unloaded (if KVM is built as a module).
2692
2693 If disabled, KVM will dynamically enable and disable
2694 virtualization on-demand when creating and destroying
2695 VMs, i.e. on the 0=>1 and 1=>0 transitions of the
2696 number of VMs.
2697
2698 Enabling virtualization at module lode avoids potential
2699 latency for creation of the 0=>1 VM, as KVM serializes
2700 virtualization enabling across all online CPUs. The
2701 "cost" of enabling virtualization when KVM is loaded,
2702 is that doing so may interfere with using out-of-tree
2703 hypervisors that want to "own" virtualization hardware.
2704
2705 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2706 Default is false (don't support).
2707
2708 kvm.nx_huge_pages=
2709 [KVM] Controls the software workaround for the
2710 X86_BUG_ITLB_MULTIHIT bug.
2711 force : Always deploy workaround.
2712 off : Never deploy workaround.
2713 auto : Deploy workaround based on the presence of
2714 X86_BUG_ITLB_MULTIHIT.
2715
2716 Default is 'auto'.
2717
2718 If the software workaround is enabled for the host,
2719 guests do need not to enable it for nested guests.
2720
2721 kvm.nx_huge_pages_recovery_ratio=
2722 [KVM] Controls how many 4KiB pages are periodically zapped
2723 back to huge pages. 0 disables the recovery, otherwise if
2724 the value is N KVM will zap 1/Nth of the 4KiB pages every
2725 period (see below). The default is 60.
2726
2727 kvm.nx_huge_pages_recovery_period_ms=
2728 [KVM] Controls the time period at which KVM zaps 4KiB pages
2729 back to huge pages. If the value is a non-zero N, KVM will
2730 zap a portion (see ratio above) of the pages every N msecs.
2731 If the value is 0 (the default), KVM will pick a period based
2732 on the ratio, such that a page is zapped after 1 hour on average.
2733
2734 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2735 KVM/SVM. Default is 1 (enabled).
2736
2737 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2738 a.k.a. Two-Dimensional Page Tables. Default is 1
2739 (enabled). Disable by KVM if hardware lacks support
2740 for NPT.
2741
2742 kvm-arm.mode=
2743 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
2744 operation.
2745
2746 none: Forcefully disable KVM.
2747
2748 nvhe: Standard nVHE-based mode, without support for
2749 protected guests.
2750
2751 protected: nVHE-based mode with support for guests whose
2752 state is kept private from the host.
2753
2754 nested: VHE-based mode with support for nested
2755 virtualization. Requires at least ARMv8.3
2756 hardware.
2757
2758 Defaults to VHE/nVHE based on hardware support. Setting
2759 mode to "protected" will disable kexec and hibernation
2760 for the host. "nested" is experimental and should be
2761 used with extreme caution.
2762
2763 kvm-arm.vgic_v3_group0_trap=
2764 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
2765 system registers
2766
2767 kvm-arm.vgic_v3_group1_trap=
2768 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
2769 system registers
2770
2771 kvm-arm.vgic_v3_common_trap=
2772 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
2773 system registers
2774
2775 kvm-arm.vgic_v4_enable=
2776 [KVM,ARM,EARLY] Allow use of GICv4 for direct
2777 injection of LPIs.
2778
2779 kvm-arm.wfe_trap_policy=
2780 [KVM,ARM] Control when to set WFE instruction trap for
2781 KVM VMs. Traps are allowed but not guaranteed by the
2782 CPU architecture.
2783
2784 trap: set WFE instruction trap
2785
2786 notrap: clear WFE instruction trap
2787
2788 kvm-arm.wfi_trap_policy=
2789 [KVM,ARM] Control when to set WFI instruction trap for
2790 KVM VMs. Traps are allowed but not guaranteed by the
2791 CPU architecture.
2792
2793 trap: set WFI instruction trap
2794
2795 notrap: clear WFI instruction trap
2796
2797 kvm_cma_resv_ratio=n [PPC,EARLY]
2798 Reserves given percentage from system memory area for
2799 contiguous memory allocation for KVM hash pagetable
2800 allocation.
2801 By default it reserves 5% of total system memory.
2802 Format: <integer>
2803 Default: 5
2804
2805 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2806 a.k.a. Two-Dimensional Page Tables. Default is 1
2807 (enabled). Disable by KVM if hardware lacks support
2808 for EPT.
2809
2810 kvm-intel.emulate_invalid_guest_state=
2811 [KVM,Intel] Control whether to emulate invalid guest
2812 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2813 as guest state is never invalid for unrestricted
2814 guests. This param doesn't apply to nested guests (L2),
2815 as KVM never emulates invalid L2 guest state.
2816 Default is 1 (enabled).
2817
2818 kvm-intel.flexpriority=
2819 [KVM,Intel] Control KVM's use of FlexPriority feature
2820 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2821 hardware lacks support for it.
2822
2823 kvm-intel.nested=
2824 [KVM,Intel] Control nested virtualization feature in
2825 KVM/VMX. Default is 1 (enabled).
2826
2827 kvm-intel.unrestricted_guest=
2828 [KVM,Intel] Control KVM's use of unrestricted guest
2829 feature (virtualized real and unpaged mode). Default
2830 is 1 (enabled). Disable by KVM if EPT is disabled or
2831 hardware lacks support for it.
2832
2833 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2834 CVE-2018-3620.
2835
2836 Valid arguments: never, cond, always
2837
2838 always: L1D cache flush on every VMENTER.
2839 cond: Flush L1D on VMENTER only when the code between
2840 VMEXIT and VMENTER can leak host memory.
2841 never: Disables the mitigation
2842
2843 Default is cond (do L1 cache flush in specific instances)
2844
2845 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2846 Identification feature (tagged TLBs). Default is 1
2847 (enabled). Disable by KVM if hardware lacks support
2848 for it.
2849
2850 l1d_flush= [X86,INTEL,EARLY]
2851 Control mitigation for L1D based snooping vulnerability.
2852
2853 Certain CPUs are vulnerable to an exploit against CPU
2854 internal buffers which can forward information to a
2855 disclosure gadget under certain conditions.
2856
2857 In vulnerable processors, the speculatively
2858 forwarded data can be used in a cache side channel
2859 attack, to access data to which the attacker does
2860 not have direct access.
2861
2862 This parameter controls the mitigation. The
2863 options are:
2864
2865 on - enable the interface for the mitigation
2866
2867 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
2868 affected CPUs
2869
2870 The kernel PTE inversion protection is unconditionally
2871 enabled and cannot be disabled.
2872
2873 full
2874 Provides all available mitigations for the
2875 L1TF vulnerability. Disables SMT and
2876 enables all mitigations in the
2877 hypervisors, i.e. unconditional L1D flush.
2878
2879 SMT control and L1D flush control via the
2880 sysfs interface is still possible after
2881 boot. Hypervisors will issue a warning
2882 when the first VM is started in a
2883 potentially insecure configuration,
2884 i.e. SMT enabled or L1D flush disabled.
2885
2886 full,force
2887 Same as 'full', but disables SMT and L1D
2888 flush runtime control. Implies the
2889 'nosmt=force' command line option.
2890 (i.e. sysfs control of SMT is disabled.)
2891
2892 flush
2893 Leaves SMT enabled and enables the default
2894 hypervisor mitigation, i.e. conditional
2895 L1D flush.
2896
2897 SMT control and L1D flush control via the
2898 sysfs interface is still possible after
2899 boot. Hypervisors will issue a warning
2900 when the first VM is started in a
2901 potentially insecure configuration,
2902 i.e. SMT enabled or L1D flush disabled.
2903
2904 flush,nosmt
2905
2906 Disables SMT and enables the default
2907 hypervisor mitigation.
2908
2909 SMT control and L1D flush control via the
2910 sysfs interface is still possible after
2911 boot. Hypervisors will issue a warning
2912 when the first VM is started in a
2913 potentially insecure configuration,
2914 i.e. SMT enabled or L1D flush disabled.
2915
2916 flush,nowarn
2917 Same as 'flush', but hypervisors will not
2918 warn when a VM is started in a potentially
2919 insecure configuration.
2920
2921 off
2922 Disables hypervisor mitigations and doesn't
2923 emit any warnings.
2924 It also drops the swap size and available
2925 RAM limit restriction on both hypervisor and
2926 bare metal.
2927
2928 Default is 'flush'.
2929
2930 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2931
2932 l2cr= [PPC]
2933
2934 l3cr= [PPC]
2935
2936 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
2937 disabled it.
2938
2939 lapic= [X86,APIC] Do not use TSC deadline
2940 value for LAPIC timer one-shot implementation. Default
2941 back to the programmable timer unit in the LAPIC.
2942 Format: notscdeadline
2943
2944 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
2945 in C2 power state.
2946
2947 libata.dma= [LIBATA] DMA control
2948 libata.dma=0 Disable all PATA and SATA DMA
2949 libata.dma=1 PATA and SATA Disk DMA only
2950 libata.dma=2 ATAPI (CDROM) DMA only
2951 libata.dma=4 Compact Flash DMA only
2952 Combinations also work, so libata.dma=3 enables DMA
2953 for disks and CDROMs, but not CFs.
2954
2955 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2956 libata.ignore_hpa=0 keep BIOS limits (default)
2957 libata.ignore_hpa=1 ignore limits, using full disk
2958
2959 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2960 when set.
2961 Format: <int>
2962
2963 libata.force= [LIBATA] Force configurations. The format is a comma-
2964 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2965 PORT and DEVICE are decimal numbers matching port, link
2966 or device. Basically, it matches the ATA ID string
2967 printed on console by libata. If the whole ID part is
2968 omitted, the last PORT and DEVICE values are used. If
2969 ID hasn't been specified yet, the configuration applies
2970 to all ports, links and devices.
2971
2972 If only DEVICE is omitted, the parameter applies to
2973 the port and all links and devices behind it. DEVICE
2974 number of 0 either selects the first device or the
2975 first fan-out link behind PMP device. It does not
2976 select the host link. DEVICE number of 15 selects the
2977 host link and device attached to it.
2978
2979 The VAL specifies the configuration to force. As long
2980 as there is no ambiguity, shortcut notation is allowed.
2981 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2982 The following configurations can be forced.
2983
2984 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2985 Any ID with matching PORT is used.
2986
2987 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2988
2989 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2990 udma[/][16,25,33,44,66,100,133] notation is also
2991 allowed.
2992
2993 * nohrst, nosrst, norst: suppress hard, soft and both
2994 resets.
2995
2996 * rstonce: only attempt one reset during hot-unplug
2997 link recovery.
2998
2999 * [no]dbdelay: Enable or disable the extra 200ms delay
3000 before debouncing a link PHY and device presence
3001 detection.
3002
3003 * [no]ncq: Turn on or off NCQ.
3004
3005 * [no]ncqtrim: Enable or disable queued DSM TRIM.
3006
3007 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
3008
3009 * [no]trim: Enable or disable (unqueued) TRIM.
3010
3011 * trim_zero: Indicate that TRIM command zeroes data.
3012
3013 * max_trim_128m: Set 128M maximum trim size limit.
3014
3015 * [no]dma: Turn on or off DMA transfers.
3016
3017 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
3018
3019 * atapi_mod16_dma: Enable the use of ATAPI DMA for
3020 commands that are not a multiple of 16 bytes.
3021
3022 * [no]dmalog: Enable or disable the use of the
3023 READ LOG DMA EXT command to access logs.
3024
3025 * [no]iddevlog: Enable or disable access to the
3026 identify device data log.
3027
3028 * [no]logdir: Enable or disable access to the general
3029 purpose log directory.
3030
3031 * max_sec_128: Set transfer size limit to 128 sectors.
3032
3033 * max_sec_1024: Set or clear transfer size limit to
3034 1024 sectors.
3035
3036 * max_sec_lba48: Set or clear transfer size limit to
3037 65535 sectors.
3038
3039 * [no]lpm: Enable or disable link power management.
3040
3041 * [no]setxfer: Indicate if transfer speed mode setting
3042 should be skipped.
3043
3044 * [no]fua: Disable or enable FUA (Force Unit Access)
3045 support for devices supporting this feature.
3046
3047 * dump_id: Dump IDENTIFY data.
3048
3049 * disable: Disable this device.
3050
3051 If there are multiple matching configurations changing
3052 the same attribute, the last one is used.
3053
3054 load_ramdisk= [RAM] [Deprecated]
3055
3056 lockd.nlm_grace_period=P [NFS] Assign grace period.
3057 Format: <integer>
3058
3059 lockd.nlm_tcpport=N [NFS] Assign TCP port.
3060 Format: <integer>
3061
3062 lockd.nlm_timeout=T [NFS] Assign timeout value.
3063 Format: <integer>
3064
3065 lockd.nlm_udpport=M [NFS] Assign UDP port.
3066 Format: <integer>
3067
3068 lockdown= [SECURITY,EARLY]
3069 { integrity | confidentiality }
3070 Enable the kernel lockdown feature. If set to
3071 integrity, kernel features that allow userland to
3072 modify the running kernel are disabled. If set to
3073 confidentiality, kernel features that allow userland
3074 to extract confidential information from the kernel
3075 are also disabled.
3076
3077 locktorture.acq_writer_lim= [KNL]
3078 Set the time limit in jiffies for a lock
3079 acquisition. Acquisitions exceeding this limit
3080 will result in a splat once they do complete.
3081
3082 locktorture.bind_readers= [KNL]
3083 Specify the list of CPUs to which the readers are
3084 to be bound.
3085
3086 locktorture.bind_writers= [KNL]
3087 Specify the list of CPUs to which the writers are
3088 to be bound.
3089
3090 locktorture.call_rcu_chains= [KNL]
3091 Specify the number of self-propagating call_rcu()
3092 chains to set up. These are used to ensure that
3093 there is a high probability of an RCU grace period
3094 in progress at any given time. Defaults to 0,
3095 which disables these call_rcu() chains.
3096
3097 locktorture.long_hold= [KNL]
3098 Specify the duration in milliseconds for the
3099 occasional long-duration lock hold time. Defaults
3100 to 100 milliseconds. Select 0 to disable.
3101
3102 locktorture.nested_locks= [KNL]
3103 Specify the maximum lock nesting depth that
3104 locktorture is to exercise, up to a limit of 8
3105 (MAX_NESTED_LOCKS). Specify zero to disable.
3106 Note that this parameter is ineffective on types
3107 of locks that do not support nested acquisition.
3108
3109 locktorture.nreaders_stress= [KNL]
3110 Set the number of locking read-acquisition kthreads.
3111 Defaults to being automatically set based on the
3112 number of online CPUs.
3113
3114 locktorture.nwriters_stress= [KNL]
3115 Set the number of locking write-acquisition kthreads.
3116
3117 locktorture.onoff_holdoff= [KNL]
3118 Set time (s) after boot for CPU-hotplug testing.
3119
3120 locktorture.onoff_interval= [KNL]
3121 Set time (s) between CPU-hotplug operations, or
3122 zero to disable CPU-hotplug testing.
3123
3124 locktorture.rt_boost= [KNL]
3125 Do periodic testing of real-time lock priority
3126 boosting. Select 0 to disable, 1 to boost
3127 only rt_mutex, and 2 to boost unconditionally.
3128 Defaults to 2, which might seem to be an
3129 odd choice, but which should be harmless for
3130 non-real-time spinlocks, due to their disabling
3131 of preemption. Note that non-realtime mutexes
3132 disable boosting.
3133
3134 locktorture.rt_boost_factor= [KNL]
3135 Number that determines how often and for how
3136 long priority boosting is exercised. This is
3137 scaled down by the number of writers, so that the
3138 number of boosts per unit time remains roughly
3139 constant as the number of writers increases.
3140 On the other hand, the duration of each boost
3141 increases with the number of writers.
3142
3143 locktorture.shuffle_interval= [KNL]
3144 Set task-shuffle interval (jiffies). Shuffling
3145 tasks allows some CPUs to go into dyntick-idle
3146 mode during the locktorture test.
3147
3148 locktorture.shutdown_secs= [KNL]
3149 Set time (s) after boot system shutdown. This
3150 is useful for hands-off automated testing.
3151
3152 locktorture.stat_interval= [KNL]
3153 Time (s) between statistics printk()s.
3154
3155 locktorture.stutter= [KNL]
3156 Time (s) to stutter testing, for example,
3157 specifying five seconds causes the test to run for
3158 five seconds, wait for five seconds, and so on.
3159 This tests the locking primitive's ability to
3160 transition abruptly to and from idle.
3161
3162 locktorture.torture_type= [KNL]
3163 Specify the locking implementation to test.
3164
3165 locktorture.verbose= [KNL]
3166 Enable additional printk() statements.
3167
3168 locktorture.writer_fifo= [KNL]
3169 Run the write-side locktorture kthreads at
3170 sched_set_fifo() real-time priority.
3171
3172 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3173 Format: <irq>
3174
3175 loglevel= [KNL,EARLY]
3176 All Kernel Messages with a loglevel smaller than the
3177 console loglevel will be printed to the console. It can
3178 also be changed with klogd or other programs. The
3179 loglevels are defined as follows:
3180
3181 0 (KERN_EMERG) system is unusable
3182 1 (KERN_ALERT) action must be taken immediately
3183 2 (KERN_CRIT) critical conditions
3184 3 (KERN_ERR) error conditions
3185 4 (KERN_WARNING) warning conditions
3186 5 (KERN_NOTICE) normal but significant condition
3187 6 (KERN_INFO) informational
3188 7 (KERN_DEBUG) debug-level messages
3189
3190 log_buf_len=n[KMG] [KNL,EARLY]
3191 Sets the size of the printk ring buffer, in bytes.
3192 n must be a power of two and greater than the
3193 minimal size. The minimal size is defined by
3194 LOG_BUF_SHIFT kernel config parameter. There
3195 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3196 parameter that allows to increase the default size
3197 depending on the number of CPUs. See init/Kconfig
3198 for more details.
3199
3200 logo.nologo [FB] Disables display of the built-in Linux logo.
3201 This may be used to provide more screen space for
3202 kernel log messages and is useful when debugging
3203 kernel boot problems.
3204
3205 lp=0 [LP] Specify parallel ports to use, e.g,
3206 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3207 lp=reset first parallel port). 'lp=0' disables the
3208 lp=auto printer driver. 'lp=reset' (which can be
3209 specified in addition to the ports) causes
3210 attached printers to be reset. Using
3211 lp=port1,port2,... specifies the parallel ports
3212 to associate lp devices with, starting with
3213 lp0. A port specification may be 'none' to skip
3214 that lp device, or a parport name such as
3215 'parport0'. Specifying 'lp=auto' instead of a
3216 port specification list means that device IDs
3217 from each port should be examined, to see if
3218 an IEEE 1284-compliant printer is attached; if
3219 so, the driver will manage that printer.
3220 See also header of drivers/char/lp.c.
3221
3222 lpj=n [KNL]
3223 Sets loops_per_jiffy to given constant, thus avoiding
3224 time-consuming boot-time autodetection (up to 250 ms per
3225 CPU). 0 enables autodetection (default). To determine
3226 the correct value for your kernel, boot with normal
3227 autodetection and see what value is printed. Note that
3228 on SMP systems the preset will be applied to all CPUs,
3229 which is likely to cause problems if your CPUs need
3230 significantly divergent settings. An incorrect value
3231 will cause delays in the kernel to be wrong, leading to
3232 unpredictable I/O errors and other breakage. Although
3233 unlikely, in the extreme case this might damage your
3234 hardware.
3235
3236 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3237
3238 lsm=lsm1,...,lsmN
3239 [SECURITY] Choose order of LSM initialization. This
3240 overrides CONFIG_LSM, and the "security=" parameter.
3241
3242 machtype= [Loongson] Share the same kernel image file between
3243 different yeeloong laptops.
3244 Example: machtype=lemote-yeeloong-2f-7inch
3245
3246 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3247 will bring up during bootup. maxcpus=n : n >= 0 limits
3248 the kernel to bring up 'n' processors. Surely after
3249 bootup you can bring up the other plugged cpu by executing
3250 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3251 only takes effect during system bootup.
3252 While n=0 is a special case, it is equivalent to "nosmp",
3253 which also disables the IO APIC.
3254
3255 max_loop= [LOOP] The number of loop block devices that get
3256 (loop.max_loop) unconditionally pre-created at init time. The default
3257 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3258 of statically allocating a predefined number, loop
3259 devices can be requested on-demand with the
3260 /dev/loop-control interface.
3261
3262 mce [X86-32] Machine Check Exception
3263
3264 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
3265
3266 md= [HW] RAID subsystems devices and level
3267 See Documentation/admin-guide/md.rst.
3268
3269 mdacon= [MDA]
3270 Format: <first>,<last>
3271 Specifies range of consoles to be captured by the MDA.
3272
3273 mds= [X86,INTEL,EARLY]
3274 Control mitigation for the Micro-architectural Data
3275 Sampling (MDS) vulnerability.
3276
3277 Certain CPUs are vulnerable to an exploit against CPU
3278 internal buffers which can forward information to a
3279 disclosure gadget under certain conditions.
3280
3281 In vulnerable processors, the speculatively
3282 forwarded data can be used in a cache side channel
3283 attack, to access data to which the attacker does
3284 not have direct access.
3285
3286 This parameter controls the MDS mitigation. The
3287 options are:
3288
3289 full - Enable MDS mitigation on vulnerable CPUs
3290 full,nosmt - Enable MDS mitigation and disable
3291 SMT on vulnerable CPUs
3292 off - Unconditionally disable MDS mitigation
3293
3294 On TAA-affected machines, mds=off can be prevented by
3295 an active TAA mitigation as both vulnerabilities are
3296 mitigated with the same mechanism so in order to disable
3297 this mitigation, you need to specify tsx_async_abort=off
3298 too.
3299
3300 Not specifying this option is equivalent to
3301 mds=full.
3302
3303 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3304
3305 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3306 Must be specified, otherwise memory size will be 0.
3307
3308 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3309 of memory Amount of memory to be used in cases
3310 as follows:
3311
3312 1 for test;
3313 2 when the kernel is not able to see the whole system memory;
3314 3 memory that lies after 'mem=' boundary is excluded from
3315 the hypervisor, then assigned to KVM guests.
3316 4 to limit the memory available for kdump kernel.
3317
3318 [ARC,MICROBLAZE] - the limit applies only to low memory,
3319 high memory is not affected.
3320
3321 [ARM64] - only limits memory covered by the linear
3322 mapping. The NOMAP regions are not affected.
3323
3324 [X86] Work as limiting max address. Use together
3325 with memmap= to avoid physical address space collisions.
3326 Without memmap= PCI devices could be placed at addresses
3327 belonging to unused RAM.
3328
3329 Note that this only takes effects during boot time since
3330 in above case 3, memory may need be hot added after boot
3331 if system memory of hypervisor is not sufficient.
3332
3333 mem=nn[KMG]@ss[KMG]
3334 [ARM,MIPS,EARLY] - override the memory layout
3335 reported by firmware.
3336 Define a memory region of size nn[KMG] starting at
3337 ss[KMG].
3338 Multiple different regions can be specified with
3339 multiple mem= parameters on the command line.
3340
3341 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3342 memory.
3343
3344 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3345
3346 memchunk=nn[KMG]
3347 [KNL,SH] Allow user to override the default size for
3348 per-device physically contiguous DMA buffers.
3349
3350 memhp_default_state=online/offline/online_kernel/online_movable
3351 [KNL] Set the initial state for the memory hotplug
3352 onlining policy. If not specified, the default value is
3353 set according to the
3354 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3355 option.
3356 See Documentation/admin-guide/mm/memory-hotplug.rst.
3357
3358 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3359 E820 memory map, as specified by the user.
3360 Such memmap=exactmap lines can be constructed based on
3361 BIOS output or other requirements. See the memmap=nn@ss
3362 option description.
3363
3364 memmap=nn[KMG]@ss[KMG]
3365 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3366 Region of memory to be used is from ss to ss+nn.
3367 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3368 which limits max address to nn[KMG].
3369 Multiple different regions can be specified,
3370 comma delimited.
3371 Example:
3372 memmap=100M@2G,100M#3G,1G!1024G
3373
3374 memmap=nn[KMG]#ss[KMG]
3375 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3376 Region of memory to be marked is from ss to ss+nn.
3377
3378 memmap=nn[KMG]$ss[KMG]
3379 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3380 Region of memory to be reserved is from ss to ss+nn.
3381 Example: Exclude memory from 0x18690000-0x1869ffff
3382 memmap=64K$0x18690000
3383 or
3384 memmap=0x10000$0x18690000
3385 Some bootloaders may need an escape character before '$',
3386 like Grub2, otherwise '$' and the following number
3387 will be eaten.
3388
3389 memmap=nn[KMG]!ss[KMG,EARLY]
3390 [KNL,X86] Mark specific memory as protected.
3391 Region of memory to be used, from ss to ss+nn.
3392 The memory region may be marked as e820 type 12 (0xc)
3393 and is NVDIMM or ADR memory.
3394
3395 memmap=<size>%<offset>-<oldtype>+<newtype>
3396 [KNL,ACPI,EARLY] Convert memory within the specified region
3397 from <oldtype> to <newtype>. If "-<oldtype>" is left
3398 out, the whole region will be marked as <newtype>,
3399 even if previously unavailable. If "+<newtype>" is left
3400 out, matching memory will be removed. Types are
3401 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3402 3 = ACPI, 12 = PRAM.
3403
3404 memory_corruption_check=0/1 [X86,EARLY]
3405 Some BIOSes seem to corrupt the first 64k of
3406 memory when doing things like suspend/resume.
3407 Setting this option will scan the memory
3408 looking for corruption. Enabling this will
3409 both detect corruption and prevent the kernel
3410 from using the memory being corrupted.
3411 However, its intended as a diagnostic tool; if
3412 repeatable BIOS-originated corruption always
3413 affects the same memory, you can use memmap=
3414 to prevent the kernel from using that memory.
3415
3416 memory_corruption_check_size=size [X86,EARLY]
3417 By default it checks for corruption in the low
3418 64k, making this memory unavailable for normal
3419 use. Use this parameter to scan for
3420 corruption in more or less memory.
3421
3422 memory_corruption_check_period=seconds [X86,EARLY]
3423 By default it checks for corruption every 60
3424 seconds. Use this parameter to check at some
3425 other rate. 0 disables periodic checking.
3426
3427 memory_hotplug.memmap_on_memory
3428 [KNL,X86,ARM] Boolean flag to enable this feature.
3429 Format: {on | off (default)}
3430 When enabled, runtime hotplugged memory will
3431 allocate its internal metadata (struct pages,
3432 those vmemmap pages cannot be optimized even
3433 if hugetlb_free_vmemmap is enabled) from the
3434 hotadded memory which will allow to hotadd a
3435 lot of memory without requiring additional
3436 memory to do so.
3437 This feature is disabled by default because it
3438 has some implication on large (e.g. GB)
3439 allocations in some configurations (e.g. small
3440 memory blocks).
3441 The state of the flag can be read in
3442 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3443 Note that even when enabled, there are a few cases where
3444 the feature is not effective.
3445
3446 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3447 Format: <integer>
3448 default : 0 <disable>
3449 Specifies the number of memtest passes to be
3450 performed. Each pass selects another test
3451 pattern from a given set of patterns. Memtest
3452 fills the memory with this pattern, validates
3453 memory contents and reserves bad memory
3454 regions that are detected.
3455
3456 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3457 Valid arguments: on, off
3458 Default: off
3459 mem_encrypt=on: Activate SME
3460 mem_encrypt=off: Do not activate SME
3461
3462 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3463 for details on when memory encryption can be activated.
3464
3465 mem_sleep_default= [SUSPEND] Default system suspend mode:
3466 s2idle - Suspend-To-Idle
3467 shallow - Power-On Suspend or equivalent (if supported)
3468 deep - Suspend-To-RAM or equivalent (if supported)
3469 See Documentation/admin-guide/pm/sleep-states.rst.
3470
3471 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3472 the BIOS has incorrectly applied a workaround. TinyBIOS
3473 version 0.98 is known to be affected, 0.99 fixes the
3474 problem by letting the user disable the workaround.
3475
3476 mga= [HW,DRM]
3477
3478 microcode.force_minrev= [X86]
3479 Format: <bool>
3480 Enable or disable the microcode minimal revision
3481 enforcement for the runtime microcode loader.
3482
3483 mini2440= [ARM,HW,KNL]
3484 Format:[0..2][b][c][t]
3485 Default: "0tb"
3486 MINI2440 configuration specification:
3487 0 - The attached screen is the 3.5" TFT
3488 1 - The attached screen is the 7" TFT
3489 2 - The VGA Shield is attached (1024x768)
3490 Leaving out the screen size parameter will not load
3491 the TFT driver, and the framebuffer will be left
3492 unconfigured.
3493 b - Enable backlight. The TFT backlight pin will be
3494 linked to the kernel VESA blanking code and a GPIO
3495 LED. This parameter is not necessary when using the
3496 VGA shield.
3497 c - Enable the s3c camera interface.
3498 t - Reserved for enabling touchscreen support. The
3499 touchscreen support is not enabled in the mainstream
3500 kernel as of 2.6.30, a preliminary port can be found
3501 in the "bleeding edge" mini2440 support kernel at
3502 https://repo.or.cz/w/linux-2.6/mini2440.git
3503
3504 mitigations=
3505 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
3506 CPU vulnerabilities. This is a set of curated,
3507 arch-independent options, each of which is an
3508 aggregation of existing arch-specific options.
3509
3510 Note, "mitigations" is supported if and only if the
3511 kernel was built with CPU_MITIGATIONS=y.
3512
3513 off
3514 Disable all optional CPU mitigations. This
3515 improves system performance, but it may also
3516 expose users to several CPU vulnerabilities.
3517 Equivalent to: if nokaslr then kpti=0 [ARM64]
3518 gather_data_sampling=off [X86]
3519 kvm.nx_huge_pages=off [X86]
3520 l1tf=off [X86]
3521 mds=off [X86]
3522 mmio_stale_data=off [X86]
3523 no_entry_flush [PPC]
3524 no_uaccess_flush [PPC]
3525 nobp=0 [S390]
3526 nopti [X86,PPC]
3527 nospectre_bhb [ARM64]
3528 nospectre_v1 [X86,PPC]
3529 nospectre_v2 [X86,PPC,S390,ARM64]
3530 reg_file_data_sampling=off [X86]
3531 retbleed=off [X86]
3532 spec_rstack_overflow=off [X86]
3533 spec_store_bypass_disable=off [X86,PPC]
3534 spectre_bhi=off [X86]
3535 spectre_v2_user=off [X86]
3536 srbds=off [X86,INTEL]
3537 ssbd=force-off [ARM64]
3538 tsx_async_abort=off [X86]
3539
3540 Exceptions:
3541 This does not have any effect on
3542 kvm.nx_huge_pages when
3543 kvm.nx_huge_pages=force.
3544
3545 auto (default)
3546 Mitigate all CPU vulnerabilities, but leave SMT
3547 enabled, even if it's vulnerable. This is for
3548 users who don't want to be surprised by SMT
3549 getting disabled across kernel upgrades, or who
3550 have other ways of avoiding SMT-based attacks.
3551 Equivalent to: (default behavior)
3552
3553 auto,nosmt
3554 Mitigate all CPU vulnerabilities, disabling SMT
3555 if needed. This is for users who always want to
3556 be fully mitigated, even if it means losing SMT.
3557 Equivalent to: l1tf=flush,nosmt [X86]
3558 mds=full,nosmt [X86]
3559 tsx_async_abort=full,nosmt [X86]
3560 mmio_stale_data=full,nosmt [X86]
3561 retbleed=auto,nosmt [X86]
3562
3563 mminit_loglevel=
3564 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
3565 parameter allows control of the logging verbosity for
3566 the additional memory initialisation checks. A value
3567 of 0 disables mminit logging and a level of 4 will
3568 log everything. Information is printed at KERN_DEBUG
3569 so loglevel=8 may also need to be specified.
3570
3571 mmio_stale_data=
3572 [X86,INTEL,EARLY] Control mitigation for the Processor
3573 MMIO Stale Data vulnerabilities.
3574
3575 Processor MMIO Stale Data is a class of
3576 vulnerabilities that may expose data after an MMIO
3577 operation. Exposed data could originate or end in
3578 the same CPU buffers as affected by MDS and TAA.
3579 Therefore, similar to MDS and TAA, the mitigation
3580 is to clear the affected CPU buffers.
3581
3582 This parameter controls the mitigation. The
3583 options are:
3584
3585 full - Enable mitigation on vulnerable CPUs
3586
3587 full,nosmt - Enable mitigation and disable SMT on
3588 vulnerable CPUs.
3589
3590 off - Unconditionally disable mitigation
3591
3592 On MDS or TAA affected machines,
3593 mmio_stale_data=off can be prevented by an active
3594 MDS or TAA mitigation as these vulnerabilities are
3595 mitigated with the same mechanism so in order to
3596 disable this mitigation, you need to specify
3597 mds=off and tsx_async_abort=off too.
3598
3599 Not specifying this option is equivalent to
3600 mmio_stale_data=full.
3601
3602 For details see:
3603 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3604
3605 <module>.async_probe[=<bool>] [KNL]
3606 If no <bool> value is specified or if the value
3607 specified is not a valid <bool>, enable asynchronous
3608 probe on this module. Otherwise, enable/disable
3609 asynchronous probe on this module as indicated by the
3610 <bool> value. See also: module.async_probe
3611
3612 module.async_probe=<bool>
3613 [KNL] When set to true, modules will use async probing
3614 by default. To enable/disable async probing for a
3615 specific module, use the module specific control that
3616 is documented under <module>.async_probe. When both
3617 module.async_probe and <module>.async_probe are
3618 specified, <module>.async_probe takes precedence for
3619 the specific module.
3620
3621 module.enable_dups_trace
3622 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3623 this means that duplicate request_module() calls will
3624 trigger a WARN_ON() instead of a pr_warn(). Note that
3625 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3626 will always be issued and this option does nothing.
3627 module.sig_enforce
3628 [KNL] When CONFIG_MODULE_SIG is set, this means that
3629 modules without (valid) signatures will fail to load.
3630 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3631 is always true, so this option does nothing.
3632
3633 module_blacklist= [KNL] Do not load a comma-separated list of
3634 modules. Useful for debugging problem modules.
3635
3636 mousedev.tap_time=
3637 [MOUSE] Maximum time between finger touching and
3638 leaving touchpad surface for touch to be considered
3639 a tap and be reported as a left button click (for
3640 touchpads working in absolute mode only).
3641 Format: <msecs>
3642 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3643 reporting absolute coordinates, such as tablets
3644 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3645 reporting absolute coordinates, such as tablets
3646
3647 movablecore= [KNL,X86,PPC,EARLY]
3648 Format: nn[KMGTPE] | nn%
3649 This parameter is the complement to kernelcore=, it
3650 specifies the amount of memory used for migratable
3651 allocations. If both kernelcore and movablecore is
3652 specified, then kernelcore will be at *least* the
3653 specified value but may be more. If movablecore on its
3654 own is specified, the administrator must be careful
3655 that the amount of memory usable for all allocations
3656 is not too small.
3657
3658 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
3659 NUMA nodes to be movable. This means that the memory
3660 of such nodes will be usable only for movable
3661 allocations which rules out almost all kernel
3662 allocations. Use with caution!
3663
3664 MTD_Partition= [MTD]
3665 Format: <name>,<region-number>,<size>,<offset>
3666
3667 MTD_Region= [MTD] Format:
3668 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3669
3670 mtdparts= [MTD]
3671 See drivers/mtd/parsers/cmdlinepart.c
3672
3673 mtouchusb.raw_coordinates=
3674 [HW] Make the MicroTouch USB driver use raw coordinates
3675 ('y', default) or cooked coordinates ('n')
3676
3677 mtrr=debug [X86,EARLY]
3678 Enable printing debug information related to MTRR
3679 registers at boot time.
3680
3681 mtrr_chunk_size=nn[KMG,X86,EARLY]
3682 used for mtrr cleanup. It is largest continuous chunk
3683 that could hold holes aka. UC entries.
3684
3685 mtrr_gran_size=nn[KMG,X86,EARLY]
3686 Used for mtrr cleanup. It is granularity of mtrr block.
3687 Default is 1.
3688 Large value could prevent small alignment from
3689 using up MTRRs.
3690
3691 mtrr_spare_reg_nr=n [X86,EARLY]
3692 Format: <integer>
3693 Range: 0,7 : spare reg number
3694 Default : 1
3695 Used for mtrr cleanup. It is spare mtrr entries number.
3696 Set to 2 or more if your graphical card needs more.
3697
3698 multitce=off [PPC] This parameter disables the use of the pSeries
3699 firmware feature for updating multiple TCE entries
3700 at a time.
3701
3702 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3703
3704 netdev= [NET] Network devices parameters
3705 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3706 Note that mem_start is often overloaded to mean
3707 something different and driver-specific.
3708 This usage is only documented in each driver source
3709 file if at all.
3710
3711 netpoll.carrier_timeout=
3712 [NET] Specifies amount of time (in seconds) that
3713 netpoll should wait for a carrier. By default netpoll
3714 waits 4 seconds.
3715
3716 nf_conntrack.acct=
3717 [NETFILTER] Enable connection tracking flow accounting
3718 0 to disable accounting
3719 1 to enable accounting
3720 Default value is 0.
3721
3722 nfs.cache_getent=
3723 [NFS] sets the pathname to the program which is used
3724 to update the NFS client cache entries.
3725
3726 nfs.cache_getent_timeout=
3727 [NFS] sets the timeout after which an attempt to
3728 update a cache entry is deemed to have failed.
3729
3730 nfs.callback_nr_threads=
3731 [NFSv4] set the total number of threads that the
3732 NFS client will assign to service NFSv4 callback
3733 requests.
3734
3735 nfs.callback_tcpport=
3736 [NFS] set the TCP port on which the NFSv4 callback
3737 channel should listen.
3738
3739 nfs.delay_retrans=
3740 [NFS] specifies the number of times the NFSv4 client
3741 retries the request before returning an EAGAIN error,
3742 after a reply of NFS4ERR_DELAY from the server.
3743 Only applies if the softerr mount option is enabled,
3744 and the specified value is >= 0.
3745
3746 nfs.enable_ino64=
3747 [NFS] enable 64-bit inode numbers.
3748 If zero, the NFS client will fake up a 32-bit inode
3749 number for the readdir() and stat() syscalls instead
3750 of returning the full 64-bit number.
3751 The default is to return 64-bit inode numbers.
3752
3753 nfs.idmap_cache_timeout=
3754 [NFS] set the maximum lifetime for idmapper cache
3755 entries.
3756
3757 nfs.max_session_cb_slots=
3758 [NFSv4.1] Sets the maximum number of session
3759 slots the client will assign to the callback
3760 channel. This determines the maximum number of
3761 callbacks the client will process in parallel for
3762 a particular server.
3763
3764 nfs.max_session_slots=
3765 [NFSv4.1] Sets the maximum number of session slots
3766 the client will attempt to negotiate with the server.
3767 This limits the number of simultaneous RPC requests
3768 that the client can send to the NFSv4.1 server.
3769 Note that there is little point in setting this
3770 value higher than the max_tcp_slot_table_limit.
3771
3772 nfs.nfs4_disable_idmapping=
3773 [NFSv4] When set to the default of '1', this option
3774 ensures that both the RPC level authentication
3775 scheme and the NFS level operations agree to use
3776 numeric uids/gids if the mount is using the
3777 'sec=sys' security flavour. In effect it is
3778 disabling idmapping, which can make migration from
3779 legacy NFSv2/v3 systems to NFSv4 easier.
3780 Servers that do not support this mode of operation
3781 will be autodetected by the client, and it will fall
3782 back to using the idmapper.
3783 To turn off this behaviour, set the value to '0'.
3784
3785 nfs.nfs4_unique_id=
3786 [NFS4] Specify an additional fixed unique ident-
3787 ification string that NFSv4 clients can insert into
3788 their nfs_client_id4 string. This is typically a
3789 UUID that is generated at system install time.
3790
3791 nfs.recover_lost_locks=
3792 [NFSv4] Attempt to recover locks that were lost due
3793 to a lease timeout on the server. Please note that
3794 doing this risks data corruption, since there are
3795 no guarantees that the file will remain unchanged
3796 after the locks are lost.
3797 If you want to enable the kernel legacy behaviour of
3798 attempting to recover these locks, then set this
3799 parameter to '1'.
3800 The default parameter value of '0' causes the kernel
3801 not to attempt recovery of lost locks.
3802
3803 nfs.send_implementation_id=
3804 [NFSv4.1] Send client implementation identification
3805 information in exchange_id requests.
3806 If zero, no implementation identification information
3807 will be sent.
3808 The default is to send the implementation identification
3809 information.
3810
3811 nfs4.layoutstats_timer=
3812 [NFSv4.2] Change the rate at which the kernel sends
3813 layoutstats to the pNFS metadata server.
3814
3815 Setting this to value to 0 causes the kernel to use
3816 whatever value is the default set by the layout
3817 driver. A non-zero value sets the minimum interval
3818 in seconds between layoutstats transmissions.
3819
3820 nfsd.inter_copy_offload_enable=
3821 [NFSv4.2] When set to 1, the server will support
3822 server-to-server copies for which this server is
3823 the destination of the copy.
3824
3825 nfsd.nfs4_disable_idmapping=
3826 [NFSv4] When set to the default of '1', the NFSv4
3827 server will return only numeric uids and gids to
3828 clients using auth_sys, and will accept numeric uids
3829 and gids from such clients. This is intended to ease
3830 migration from NFSv2/v3.
3831
3832 nfsd.nfsd4_ssc_umount_timeout=
3833 [NFSv4.2] When used as the destination of a
3834 server-to-server copy, knfsd temporarily mounts
3835 the source server. It caches the mount in case
3836 it will be needed again, and discards it if not
3837 used for the number of milliseconds specified by
3838 this parameter.
3839
3840 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3841 See Documentation/admin-guide/nfs/nfsroot.rst.
3842
3843 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3844 See Documentation/admin-guide/nfs/nfsroot.rst.
3845
3846 nfsrootdebug [NFS] enable nfsroot debugging messages.
3847 See Documentation/admin-guide/nfs/nfsroot.rst.
3848
3849 nmi_backtrace.backtrace_idle [KNL]
3850 Dump stacks even of idle CPUs in response to an
3851 NMI stack-backtrace request.
3852
3853 nmi_debug= [KNL,SH] Specify one or more actions to take
3854 when a NMI is triggered.
3855 Format: [state][,regs][,debounce][,die]
3856
3857 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3858 Format: [panic,][nopanic,][rNNN,][num]
3859 Valid num: 0 or 1
3860 0 - turn hardlockup detector in nmi_watchdog off
3861 1 - turn hardlockup detector in nmi_watchdog on
3862 rNNN - configure the watchdog with raw perf event 0xNNN
3863
3864 When panic is specified, panic when an NMI watchdog
3865 timeout occurs (or 'nopanic' to not panic on an NMI
3866 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3867 To disable both hard and soft lockup detectors,
3868 please see 'nowatchdog'.
3869 This is useful when you use a panic=... timeout and
3870 need the box quickly up again.
3871
3872 These settings can be accessed at runtime via
3873 the nmi_watchdog and hardlockup_panic sysctls.
3874
3875 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3876 emulation library even if a 387 maths coprocessor
3877 is present.
3878
3879 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
3880 Forces kernel to use 3-level paging instead.
3881
3882 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
3883 kernel to use 4-level paging instead.
3884
3885 noalign [KNL,ARM]
3886
3887 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
3888 IOAPICs that may be present in the system.
3889
3890 noautogroup Disable scheduler automatic task group creation.
3891
3892 nocache [ARM,EARLY]
3893
3894 no_console_suspend
3895 [HW] Never suspend the console
3896 Disable suspending of consoles during suspend and
3897 hibernate operations. Once disabled, debugging
3898 messages can reach various consoles while the rest
3899 of the system is being put to sleep (ie, while
3900 debugging driver suspend/resume hooks). This may
3901 not work reliably with all consoles, but is known
3902 to work with serial and VGA consoles.
3903 To facilitate more flexible debugging, we also add
3904 console_suspend, a printk module parameter to control
3905 it. Users could use console_suspend (usually
3906 /sys/module/printk/parameters/console_suspend) to
3907 turn on/off it dynamically.
3908
3909 no_debug_objects
3910 [KNL,EARLY] Disable object debugging
3911
3912 nodsp [SH] Disable hardware DSP at boot time.
3913
3914 noefi [EFI,EARLY] Disable EFI runtime services support.
3915
3916 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
3917
3918 noexec32 [X86-64]
3919 This affects only 32-bit executables.
3920 noexec32=on: enable non-executable mappings (default)
3921 read doesn't imply executable mappings
3922 noexec32=off: disable non-executable mappings
3923 read implies executable mappings
3924
3925 no_file_caps Tells the kernel not to honor file capabilities. The
3926 only way then for a file to be executed with privilege
3927 is to be setuid root or executed by root.
3928
3929 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3930
3931 nofsgsbase [X86] Disables FSGSBASE instructions.
3932
3933 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3934 register save and restore. The kernel will only save
3935 legacy floating-point registers on task switch.
3936
3937 no_hash_pointers
3938 [KNL,EARLY]
3939 Force pointers printed to the console or buffers to be
3940 unhashed. By default, when a pointer is printed via %p
3941 format string, that pointer is "hashed", i.e. obscured
3942 by hashing the pointer value. This is a security feature
3943 that hides actual kernel addresses from unprivileged
3944 users, but it also makes debugging the kernel more
3945 difficult since unequal pointers can no longer be
3946 compared. However, if this command-line option is
3947 specified, then all normal pointers will have their true
3948 value printed. This option should only be specified when
3949 debugging the kernel. Please do not use on production
3950 kernels.
3951
3952 nohibernate [HIBERNATION] Disable hibernation and resume.
3953
3954 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to
3955 busy wait in do_idle() and not use the arch_cpu_idle()
3956 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3957 to be effective. This is useful on platforms where the
3958 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3959 correctly or when doing power measurements to evaluate
3960 the impact of the sleep instructions. This is also
3961 useful when using JTAG debugger.
3962
3963 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
3964
3965 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
3966
3967 nohz= [KNL] Boottime enable/disable dynamic ticks
3968 Valid arguments: on, off
3969 Default: on
3970
3971 nohz_full= [KNL,BOOT,SMP,ISOL]
3972 The argument is a cpu list, as described above.
3973 In kernels built with CONFIG_NO_HZ_FULL=y, set
3974 the specified list of CPUs whose tick will be stopped
3975 whenever possible. The boot CPU will be forced outside
3976 the range to maintain the timekeeping. Any CPUs
3977 in this list will have their RCU callbacks offloaded,
3978 just as if they had also been called out in the
3979 rcu_nocbs= boot parameter.
3980
3981 Note that this argument takes precedence over
3982 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3983
3984 noinitrd [RAM] Tells the kernel not to load any configured
3985 initial RAM disk.
3986
3987 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
3988 remapping.
3989 [Deprecated - use intremap=off]
3990
3991 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
3992
3993 noiotrap [SH] Disables trapped I/O port accesses.
3994
3995 noirqdebug [X86-32] Disables the code which attempts to detect and
3996 disable unhandled interrupt sources.
3997
3998 noisapnp [ISAPNP] Disables ISA PnP code.
3999
4000 nokaslr [KNL,EARLY]
4001 When CONFIG_RANDOMIZE_BASE is set, this disables
4002 kernel and module base offset ASLR (Address Space
4003 Layout Randomization).
4004
4005 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
4006 fault handling.
4007
4008 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
4009
4010 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
4011
4012 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
4013
4014 nomce [X86-32] Disable Machine Check Exception
4015
4016 nomfgpt [X86-32] Disable Multi-Function General Purpose
4017 Timer usage (for AMD Geode machines).
4018
4019 nomodeset Disable kernel modesetting. Most systems' firmware
4020 sets up a display mode and provides framebuffer memory
4021 for output. With nomodeset, DRM and fbdev drivers will
4022 not load if they could possibly displace the pre-
4023 initialized output. Only the system framebuffer will
4024 be available for use. The respective drivers will not
4025 perform display-mode changes or accelerated rendering.
4026
4027 Useful as error fallback, or for testing and debugging.
4028
4029 nomodule Disable module load
4030
4031 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
4032 shutdown the other cpus. Instead use the REBOOT_VECTOR
4033 irq.
4034
4035 nopat [X86,EARLY] Disable PAT (page attribute table extension of
4036 pagetables) support.
4037
4038 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
4039
4040 nopku [X86] Disable Memory Protection Keys CPU feature found
4041 in some Intel CPUs.
4042
4043 nopti [X86-64,EARLY]
4044 Equivalent to pti=off
4045
4046 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
4047 Disables the PV optimizations forcing the guest to run
4048 as generic guest with no PV drivers. Currently support
4049 XEN HVM, KVM, HYPER_V and VMWARE guest.
4050
4051 nopvspin [X86,XEN,KVM,EARLY]
4052 Disables the qspinlock slow path using PV optimizations
4053 which allow the hypervisor to 'idle' the guest on lock
4054 contention.
4055
4056 norandmaps Don't use address space randomization. Equivalent to
4057 echo 0 > /proc/sys/kernel/randomize_va_space
4058
4059 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
4060 with UP alternatives
4061
4062 noresume [SWSUSP] Disables resume and restores original swap
4063 space.
4064
4065 no-scroll [VGA] Disables scrollback.
4066 This is required for the Braillex ib80-piezo Braille
4067 reader made by F.H. Papenmeier (Germany).
4068
4069 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
4070
4071 nosmap [PPC,EARLY]
4072 Disable SMAP (Supervisor Mode Access Prevention)
4073 even if it is supported by processor.
4074
4075 nosmep [PPC64s,EARLY]
4076 Disable SMEP (Supervisor Mode Execution Prevention)
4077 even if it is supported by processor.
4078
4079 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
4080 and disable the IO APIC. legacy for "maxcpus=0".
4081
4082 nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
4083 Equivalent to smt=1.
4084
4085 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
4086 nosmt=force: Force disable SMT, cannot be undone
4087 via the sysfs control file.
4088
4089 nosoftlockup [KNL] Disable the soft-lockup detector.
4090
4091 nospec_store_bypass_disable
4092 [HW,EARLY] Disable all mitigations for the Speculative
4093 Store Bypass vulnerability
4094
4095 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4096 history injection) vulnerability. System may allow data leaks
4097 with this option.
4098
4099 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4100 (bounds check bypass). With this option data leaks are
4101 possible in the system.
4102
4103 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4104 for the Spectre variant 2 (indirect branch
4105 prediction) vulnerability. System may allow data
4106 leaks with this option.
4107
4108 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY]
4109 Disable paravirtualized steal time accounting. steal time
4110 is computed, but won't influence scheduler behaviour
4111
4112 nosync [HW,M68K] Disables sync negotiation for all devices.
4113
4114 no_timer_check [X86,APIC] Disables the code which tests for
4115 broken timer IRQ sources.
4116
4117 no_uaccess_flush
4118 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4119
4120 novmcoredd [KNL,KDUMP]
4121 Disable device dump. Device dump allows drivers to
4122 append dump data to vmcore so you can collect driver
4123 specified debug info. Drivers can append the data
4124 without any limit and this data is stored in memory,
4125 so this may cause significant memory stress. Disabling
4126 device dump can help save memory but the driver debug
4127 data will be no longer available. This parameter
4128 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4129 is set.
4130
4131 no-vmw-sched-clock
4132 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4133 scheduler clock and use the default one.
4134
4135 nowatchdog [KNL] Disable both lockup detectors, i.e.
4136 soft-lockup and NMI watchdog (hard-lockup).
4137
4138 nowb [ARM,EARLY]
4139
4140 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4141
4142 NOTE: this parameter will be ignored on systems with the
4143 LEGACY_XAPIC_DISABLED bit set in the
4144 IA32_XAPIC_DISABLE_STATUS MSR.
4145
4146 noxsave [BUGS=X86] Disables x86 extended register state save
4147 and restore using xsave. The kernel will fallback to
4148 enabling legacy floating-point and sse state.
4149
4150 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4151 register states. The kernel will fall back to use
4152 xsave to save the states. By using this parameter,
4153 performance of saving the states is degraded because
4154 xsave doesn't support modified optimization while
4155 xsaveopt supports it on xsaveopt enabled systems.
4156
4157 noxsaves [X86] Disables xsaves and xrstors used in saving and
4158 restoring x86 extended register state in compacted
4159 form of xsave area. The kernel will fall back to use
4160 xsaveopt and xrstor to save and restore the states
4161 in standard form of xsave area. By using this
4162 parameter, xsave area per process might occupy more
4163 memory on xsaves enabled systems.
4164
4165 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4166 could support. nr_cpus=n : n >= 1 limits the kernel to
4167 support 'n' processors. It could be larger than the
4168 number of already plugged CPU during bootup, later in
4169 runtime you can physically add extra cpu until it reaches
4170 n. So during boot up some boot time memory for per-cpu
4171 variables need be pre-allocated for later physical cpu
4172 hot plugging.
4173
4174 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4175
4176 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4177 Disable NUMA, Only set up a single NUMA node
4178 spanning all memory.
4179
4180 numa=fake=<size>[MG]
4181 [KNL, ARM64, RISCV, X86, EARLY]
4182 If given as a memory unit, fills all system RAM with
4183 nodes of size interleaved over physical nodes.
4184
4185 numa=fake=<N>
4186 [KNL, ARM64, RISCV, X86, EARLY]
4187 If given as an integer, fills all system RAM with N
4188 fake nodes interleaved over physical nodes.
4189
4190 numa=fake=<N>U
4191 [KNL, ARM64, RISCV, X86, EARLY]
4192 If given as an integer followed by 'U', it will
4193 divide each physical node into N emulated nodes.
4194
4195 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4196 NUMA balancing.
4197 Allowed values are enable and disable
4198
4199 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4200 'node', 'default' can be specified
4201 This can be set from sysctl after boot.
4202 See Documentation/admin-guide/sysctl/vm.rst for details.
4203
4204 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4205 See Documentation/core-api/debugging-via-ohci1394.rst for more
4206 info.
4207
4208 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4209 Rather than timing out after 20 ms if an EC
4210 command is not properly ACKed, override the length
4211 of the timeout. We have interrupts disabled while
4212 waiting for the ACK, so if this is set too high
4213 interrupts *may* be lost!
4214
4215 omap_mux= [OMAP] Override bootloader pin multiplexing.
4216 Format: <mux_mode0.mode_name=value>...
4217 For example, to override I2C bus2:
4218 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4219
4220 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4221
4222 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4223
4224 boundary - index of last SLC block on Flex-OneNAND.
4225 The remaining blocks are configured as MLC blocks.
4226 lock - Configure if Flex-OneNAND boundary should be locked.
4227 Once locked, the boundary cannot be changed.
4228 1 indicates lock status, 0 indicates unlock status.
4229
4230 oops=panic [KNL,EARLY]
4231 Always panic on oopses. Default is to just kill the
4232 process, but there is a small probability of
4233 deadlocking the machine.
4234 This will also cause panics on machine check exceptions.
4235 Useful together with panic=30 to trigger a reboot.
4236
4237 page_alloc.shuffle=
4238 [KNL] Boolean flag to control whether the page allocator
4239 should randomize its free lists. This parameter can be
4240 used to enable/disable page randomization. The state of
4241 the flag can be read from sysfs at:
4242 /sys/module/page_alloc/parameters/shuffle.
4243 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.
4244
4245 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4246 Storage of the information about who allocated
4247 each page is disabled in default. With this switch,
4248 we can turn it on.
4249 on: enable the feature
4250
4251 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4252 poisoning on the buddy allocator, available with
4253 CONFIG_PAGE_POISONING=y.
4254 off: turn off poisoning (default)
4255 on: turn on poisoning
4256
4257 page_reporting.page_reporting_order=
4258 [KNL] Minimal page reporting order
4259 Format: <integer>
4260 Adjust the minimal page reporting order. The page
4261 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4262
4263 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4264 timeout > 0: seconds before rebooting
4265 timeout = 0: wait forever
4266 timeout < 0: reboot immediately
4267 Format: <timeout>
4268
4269 panic_on_taint= [KNL,EARLY]
4270 Bitmask for conditionally calling panic() in add_taint()
4271 Format: <hex>[,nousertaint]
4272 Hexadecimal bitmask representing the set of TAINT flags
4273 that will cause the kernel to panic when add_taint() is
4274 called with any of the flags in this set.
4275 The optional switch "nousertaint" can be utilized to
4276 prevent userspace forced crashes by writing to sysctl
4277 /proc/sys/kernel/tainted any flagset matching with the
4278 bitmask set on panic_on_taint.
4279 See Documentation/admin-guide/tainted-kernels.rst for
4280 extra details on the taint flags that users can pick
4281 to compose the bitmask to assign to panic_on_taint.
4282
4283 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4284 on a WARN().
4285
4286 panic_print= Bitmask for printing system info when panic happens.
4287 User can chose combination of the following bits:
4288 bit 0: print all tasks info
4289 bit 1: print system memory info
4290 bit 2: print timer info
4291 bit 3: print locks info if CONFIG_LOCKDEP is on
4292 bit 4: print ftrace buffer
4293 bit 5: print all printk messages in buffer
4294 bit 6: print all CPUs backtrace (if available in the arch)
4295 bit 7: print only tasks in uninterruptible (blocked) state
4296 *Be aware* that this option may print a _lot_ of lines,
4297 so there are risks of losing older messages in the log.
4298 Use this option carefully, maybe worth to setup a
4299 bigger log buffer with "log_buf_len" along with this.
4300
4301 parkbd.port= [HW] Parallel port number the keyboard adapter is
4302 connected to, default is 0.
4303 Format: <parport#>
4304 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4305 0 for XT, 1 for AT (default is AT).
4306 Format: <mode>
4307
4308 parport= [HW,PPT] Specify parallel ports. 0 disables.
4309 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4310 Use 'auto' to force the driver to use any
4311 IRQ/DMA settings detected (the default is to
4312 ignore detected IRQ/DMA settings because of
4313 possible conflicts). You can specify the base
4314 address, IRQ, and DMA settings; IRQ and DMA
4315 should be numbers, or 'auto' (for using detected
4316 settings on that particular port), or 'nofifo'
4317 (to avoid using a FIFO even if it is detected).
4318 Parallel ports are assigned in the order they
4319 are specified on the command line, starting
4320 with parport0.
4321
4322 parport_init_mode= [HW,PPT]
4323 Configure VIA parallel port to operate in
4324 a specific mode. This is necessary on Pegasos
4325 computer where firmware has no options for setting
4326 up parallel port mode and sets it to spp.
4327 Currently this function knows 686a and 8231 chips.
4328 Format: [spp|ps2|epp|ecp|ecpepp]
4329
4330 pata_legacy.all= [HW,LIBATA]
4331 Format: <int>
4332 Set to non-zero to probe primary and secondary ISA
4333 port ranges on PCI systems where no PCI PATA device
4334 has been found at either range. Disabled by default.
4335
4336 pata_legacy.autospeed= [HW,LIBATA]
4337 Format: <int>
4338 Set to non-zero if a chip is present that snoops speed
4339 changes. Disabled by default.
4340
4341 pata_legacy.ht6560a= [HW,LIBATA]
4342 Format: <int>
4343 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4344 the secondary channel, or both channels respectively.
4345 Disabled by default.
4346
4347 pata_legacy.ht6560b= [HW,LIBATA]
4348 Format: <int>
4349 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4350 the secondary channel, or both channels respectively.
4351 Disabled by default.
4352
4353 pata_legacy.iordy_mask= [HW,LIBATA]
4354 Format: <int>
4355 IORDY enable mask. Set individual bits to allow IORDY
4356 for the respective channel. Bit 0 is for the first
4357 legacy channel handled by this driver, bit 1 is for
4358 the second channel, and so on. The sequence will often
4359 correspond to the primary legacy channel, the secondary
4360 legacy channel, and so on, but the handling of a PCI
4361 bus and the use of other driver options may interfere
4362 with the sequence. By default IORDY is allowed across
4363 all channels.
4364
4365 pata_legacy.opti82c46x= [HW,LIBATA]
4366 Format: <int>
4367 Set to 1, 2, or 3 for Opti 82c611A on the primary
4368 channel, the secondary channel, or both channels
4369 respectively. Disabled by default.
4370
4371 pata_legacy.opti82c611a= [HW,LIBATA]
4372 Format: <int>
4373 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4374 channel, the secondary channel, or both channels
4375 respectively. Disabled by default.
4376
4377 pata_legacy.pio_mask= [HW,LIBATA]
4378 Format: <int>
4379 PIO mode mask for autospeed devices. Set individual
4380 bits to allow the use of the respective PIO modes.
4381 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4382 All modes allowed by default.
4383
4384 pata_legacy.probe_all= [HW,LIBATA]
4385 Format: <int>
4386 Set to non-zero to probe tertiary and further ISA
4387 port ranges on PCI systems. Disabled by default.
4388
4389 pata_legacy.probe_mask= [HW,LIBATA]
4390 Format: <int>
4391 Probe mask for legacy ISA PATA ports. Depending on
4392 platform configuration and the use of other driver
4393 options up to 6 legacy ports are supported: 0x1f0,
4394 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4395 of individual ports can be disabled by setting the
4396 corresponding bits in the mask to 1. Bit 0 is for
4397 the first port in the list above (0x1f0), and so on.
4398 By default all supported ports are probed.
4399
4400 pata_legacy.qdi= [HW,LIBATA]
4401 Format: <int>
4402 Set to non-zero to probe QDI controllers. By default
4403 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4404
4405 pata_legacy.winbond= [HW,LIBATA]
4406 Format: <int>
4407 Set to non-zero to probe Winbond controllers. Use
4408 the standard I/O port (0x130) if 1, otherwise the
4409 value given is the I/O port to use (typically 0x1b0).
4410 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4411 0 otherwise.
4412
4413 pata_platform.pio_mask= [HW,LIBATA]
4414 Format: <int>
4415 Supported PIO mode mask. Set individual bits to allow
4416 the use of the respective PIO modes. Bit 0 is for
4417 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4418 allowed by default.
4419
4420 pause_on_oops=<int>
4421 Halt all CPUs after the first oops has been printed for
4422 the specified number of seconds. This is to be used if
4423 your oopses keep scrolling off the screen.
4424
4425 pcbit= [HW,ISDN]
4426
4427 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
4428
4429 Some options herein operate on a specific device
4430 or a set of devices (<pci_dev>). These are
4431 specified in one of the following formats:
4432
4433 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4434 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4435
4436 Note: the first format specifies a PCI
4437 bus/device/function address which may change
4438 if new hardware is inserted, if motherboard
4439 firmware changes, or due to changes caused
4440 by other kernel parameters. If the
4441 domain is left unspecified, it is
4442 taken to be zero. Optionally, a path
4443 to a device through multiple device/function
4444 addresses can be specified after the base
4445 address (this is more robust against
4446 renumbering issues). The second format
4447 selects devices using IDs from the
4448 configuration space which may match multiple
4449 devices in the system.
4450
4451 earlydump dump PCI config space before the kernel
4452 changes anything
4453 off [X86] don't probe for the PCI bus
4454 bios [X86-32] force use of PCI BIOS, don't access
4455 the hardware directly. Use this if your machine
4456 has a non-standard PCI host bridge.
4457 nobios [X86-32] disallow use of PCI BIOS, only direct
4458 hardware access methods are allowed. Use this
4459 if you experience crashes upon bootup and you
4460 suspect they are caused by the BIOS.
4461 conf1 [X86] Force use of PCI Configuration Access
4462 Mechanism 1 (config address in IO port 0xCF8,
4463 data in IO port 0xCFC, both 32-bit).
4464 conf2 [X86] Force use of PCI Configuration Access
4465 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4466 the function, IO port 0xCFA, also 8-bit, sets
4467 bus number. The config space is then accessed
4468 through ports 0xC000-0xCFFF).
4469 See http://wiki.osdev.org/PCI for more info
4470 on the configuration access mechanisms.
4471 noaer [PCIE] If the PCIEAER kernel config parameter is
4472 enabled, this kernel boot option can be used to
4473 disable the use of PCIE advanced error reporting.
4474 nodomains [PCI] Disable support for multiple PCI
4475 root domains (aka PCI segments, in ACPI-speak).
4476 nommconf [X86] Disable use of MMCONFIG for PCI
4477 Configuration
4478 check_enable_amd_mmconf [X86] check for and enable
4479 properly configured MMIO access to PCI
4480 config space on AMD family 10h CPU
4481 nomsi [MSI] If the PCI_MSI kernel config parameter is
4482 enabled, this kernel boot option can be used to
4483 disable the use of MSI interrupts system-wide.
4484 noioapicquirk [APIC] Disable all boot interrupt quirks.
4485 Safety option to keep boot IRQs enabled. This
4486 should never be necessary.
4487 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4488 primary IO-APIC for bridges that cannot disable
4489 boot IRQs. This fixes a source of spurious IRQs
4490 when the system masks IRQs.
4491 noioapicreroute [APIC] Disable workaround that uses the
4492 boot IRQ equivalent of an IRQ that connects to
4493 a chipset where boot IRQs cannot be disabled.
4494 The opposite of ioapicreroute.
4495 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4496 routing table. These calls are known to be buggy
4497 on several machines and they hang the machine
4498 when used, but on other computers it's the only
4499 way to get the interrupt routing table. Try
4500 this option if the kernel is unable to allocate
4501 IRQs or discover secondary PCI buses on your
4502 motherboard.
4503 rom [X86] Assign address space to expansion ROMs.
4504 Use with caution as certain devices share
4505 address decoders between ROMs and other
4506 resources.
4507 norom [X86] Do not assign address space to
4508 expansion ROMs that do not already have
4509 BIOS assigned address ranges.
4510 nobar [X86] Do not assign address space to the
4511 BARs that weren't assigned by the BIOS.
4512 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4513 assigned automatically to PCI devices. You can
4514 make the kernel exclude IRQs of your ISA cards
4515 this way.
4516 pirqaddr=0xAAAAA [X86] Specify the physical address
4517 of the PIRQ table (normally generated
4518 by the BIOS) if it is outside the
4519 F0000h-100000h range.
4520 lastbus=N [X86] Scan all buses thru bus #N. Can be
4521 useful if the kernel is unable to find your
4522 secondary buses and you want to tell it
4523 explicitly which ones they are.
4524 assign-busses [X86] Always assign all PCI bus
4525 numbers ourselves, overriding
4526 whatever the firmware may have done.
4527 usepirqmask [X86] Honor the possible IRQ mask stored
4528 in the BIOS $PIR table. This is needed on
4529 some systems with broken BIOSes, notably
4530 some HP Pavilion N5400 and Omnibook XE3
4531 notebooks. This will have no effect if ACPI
4532 IRQ routing is enabled.
4533 noacpi [X86] Do not use ACPI for IRQ routing
4534 or for PCI scanning.
4535 use_crs [X86] Use PCI host bridge window information
4536 from ACPI. On BIOSes from 2008 or later, this
4537 is enabled by default. If you need to use this,
4538 please report a bug.
4539 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4540 If you need to use this, please report a bug.
4541 use_e820 [X86] Use E820 reservations to exclude parts of
4542 PCI host bridge windows. This is a workaround
4543 for BIOS defects in host bridge _CRS methods.
4544 If you need to use this, please report a bug to
4545 <linux-pci@vger.kernel.org>.
4546 no_e820 [X86] Ignore E820 reservations for PCI host
4547 bridge windows. This is the default on modern
4548 hardware. If you need to use this, please report
4549 a bug to <linux-pci@vger.kernel.org>.
4550 routeirq Do IRQ routing for all PCI devices.
4551 This is normally done in pci_enable_device(),
4552 so this option is a temporary workaround
4553 for broken drivers that don't call it.
4554 skip_isa_align [X86] do not align io start addr, so can
4555 handle more pci cards
4556 noearly [X86] Don't do any early type 1 scanning.
4557 This might help on some broken boards which
4558 machine check when some devices' config space
4559 is read. But various workarounds are disabled
4560 and some IOMMU drivers will not work.
4561 bfsort Sort PCI devices into breadth-first order.
4562 This sorting is done to get a device
4563 order compatible with older (<= 2.4) kernels.
4564 nobfsort Don't sort PCI devices into breadth-first order.
4565 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4566 tuning and use the BIOS-configured MPS defaults.
4567 pcie_bus_safe Set every device's MPS to the largest value
4568 supported by all devices below the root complex.
4569 pcie_bus_perf Set device MPS to the largest allowable MPS
4570 based on its parent bus. Also set MRRS (Max
4571 Read Request Size) to the largest supported
4572 value (no larger than the MPS that the device
4573 or bus can support) for best performance.
4574 pcie_bus_peer2peer Set every device's MPS to 128B, which
4575 every device is guaranteed to support. This
4576 configuration allows peer-to-peer DMA between
4577 any pair of devices, possibly at the cost of
4578 reduced performance. This also guarantees
4579 that hot-added devices will work.
4580 cbiosize=nn[KMG] The fixed amount of bus space which is
4581 reserved for the CardBus bridge's IO window.
4582 The default value is 256 bytes.
4583 cbmemsize=nn[KMG] The fixed amount of bus space which is
4584 reserved for the CardBus bridge's memory
4585 window. The default value is 64 megabytes.
4586 resource_alignment=
4587 Format:
4588 [<order of align>@]<pci_dev>[; ...]
4589 Specifies alignment and device to reassign
4590 aligned memory resources. How to
4591 specify the device is described above.
4592 If <order of align> is not specified,
4593 PAGE_SIZE is used as alignment.
4594 A PCI-PCI bridge can be specified if resource
4595 windows need to be expanded.
4596 To specify the alignment for several
4597 instances of a device, the PCI vendor,
4598 device, subvendor, and subdevice may be
4599 specified, e.g., 12@pci:8086:9c22:103c:198f
4600 for 4096-byte alignment.
4601 ecrc= Enable/disable PCIe ECRC (transaction layer
4602 end-to-end CRC checking). Only effective if
4603 OS has native AER control (either granted by
4604 ACPI _OSC or forced via "pcie_ports=native")
4605 bios: Use BIOS/firmware settings. This is the
4606 the default.
4607 off: Turn ECRC off
4608 on: Turn ECRC on.
4609 hpiosize=nn[KMG] The fixed amount of bus space which is
4610 reserved for hotplug bridge's IO window.
4611 Default size is 256 bytes.
4612 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4613 reserved for hotplug bridge's MMIO window.
4614 Default size is 2 megabytes.
4615 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4616 reserved for hotplug bridge's MMIO_PREF window.
4617 Default size is 2 megabytes.
4618 hpmemsize=nn[KMG] The fixed amount of bus space which is
4619 reserved for hotplug bridge's MMIO and
4620 MMIO_PREF window.
4621 Default size is 2 megabytes.
4622 hpbussize=nn The minimum amount of additional bus numbers
4623 reserved for buses below a hotplug bridge.
4624 Default is 1.
4625 realloc= Enable/disable reallocating PCI bridge resources
4626 if allocations done by BIOS are too small to
4627 accommodate resources required by all child
4628 devices.
4629 off: Turn realloc off
4630 on: Turn realloc on
4631 realloc same as realloc=on
4632 noari do not use PCIe ARI.
4633 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4634 do not use PCIe ATS (and IOMMU device IOTLB).
4635 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4636 only look for one device below a PCIe downstream
4637 port.
4638 big_root_window Try to add a big 64bit memory window to the PCIe
4639 root complex on AMD CPUs. Some GFX hardware
4640 can resize a BAR to allow access to all VRAM.
4641 Adding the window is slightly risky (it may
4642 conflict with unreported devices), so this
4643 taints the kernel.
4644 disable_acs_redir=<pci_dev>[; ...]
4645 Specify one or more PCI devices (in the format
4646 specified above) separated by semicolons.
4647 Each device specified will have the PCI ACS
4648 redirect capabilities forced off which will
4649 allow P2P traffic between devices through
4650 bridges without forcing it upstream. Note:
4651 this removes isolation between devices and
4652 may put more devices in an IOMMU group.
4653 config_acs=
4654 Format:
4655 <ACS flags>@<pci_dev>[; ...]
4656 Specify one or more PCI devices (in the format
4657 specified above) optionally prepended with flags
4658 and separated by semicolons. The respective
4659 capabilities will be enabled, disabled or
4660 unchanged based on what is specified in
4661 flags.
4662
4663 ACS Flags is defined as follows:
4664 bit-0 : ACS Source Validation
4665 bit-1 : ACS Translation Blocking
4666 bit-2 : ACS P2P Request Redirect
4667 bit-3 : ACS P2P Completion Redirect
4668 bit-4 : ACS Upstream Forwarding
4669 bit-5 : ACS P2P Egress Control
4670 bit-6 : ACS Direct Translated P2P
4671 Each bit can be marked as:
4672 '0' – force disabled
4673 '1' – force enabled
4674 'x' – unchanged
4675 For example,
4676 pci=config_acs=10x
4677 would configure all devices that support
4678 ACS to enable P2P Request Redirect, disable
4679 Translation Blocking, and leave Source
4680 Validation unchanged from whatever power-up
4681 or firmware set it to.
4682
4683 Note: this may remove isolation between devices
4684 and may put more devices in an IOMMU group.
4685 force_floating [S390] Force usage of floating interrupts.
4686 nomio [S390] Do not use MIO instructions.
4687 norid [S390] ignore the RID field and force use of
4688 one PCI domain per PCI function
4689 notph [PCIE] If the PCIE_TPH kernel config parameter
4690 is enabled, this kernel boot option can be used
4691 to disable PCIe TLP Processing Hints support
4692 system-wide.
4693
4694 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power
4695 Management.
4696 off Don't touch ASPM configuration at all. Leave any
4697 configuration done by firmware unchanged.
4698 force Enable ASPM even on devices that claim not to support it.
4699 WARNING: Forcing ASPM on may cause system lockups.
4700
4701 pcie_ports= [PCIE] PCIe port services handling:
4702 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4703 even if the platform doesn't give the OS permission to
4704 use them. This may cause conflicts if the platform
4705 also tries to use these services.
4706 dpc-native Use native PCIe service for DPC only. May
4707 cause conflicts if firmware uses AER or DPC.
4708 compat Disable native PCIe services (PME, AER, DPC, PCIe
4709 hotplug).
4710
4711 pcie_port_pm= [PCIE] PCIe port power management handling:
4712 off Disable power management of all PCIe ports
4713 force Forcibly enable power management of all PCIe ports
4714
4715 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4716 nomsi Do not use MSI for native PCIe PME signaling (this makes
4717 all PCIe root ports use INTx for all services).
4718
4719 pcmv= [HW,PCMCIA] BadgePAD 4
4720
4721 pd_ignore_unused
4722 [PM]
4723 Keep all power-domains already enabled by bootloader on,
4724 even if no driver has claimed them. This is useful
4725 for debug and development, but should not be
4726 needed on a platform with proper driver support.
4727
4728 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4729 boot time.
4730 Format: { 0 | 1 }
4731 See arch/parisc/kernel/pdc_chassis.c
4732
4733 percpu_alloc= [MM,EARLY]
4734 Select which percpu first chunk allocator to use.
4735 Currently supported values are "embed" and "page".
4736 Archs may support subset or none of the selections.
4737 See comments in mm/percpu.c for details on each
4738 allocator. This parameter is primarily for debugging
4739 and performance comparison.
4740
4741 pirq= [SMP,APIC] Manual mp-table setup
4742 See Documentation/arch/x86/i386/IO-APIC.rst.
4743
4744 plip= [PPT,NET] Parallel port network link
4745 Format: { parport<nr> | timid | 0 }
4746 See also Documentation/admin-guide/parport.rst.
4747
4748 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4749 Override pmtimer IOPort with a hex value.
4750 e.g. pmtmr=0x508
4751
4752 pmu_override= [PPC] Override the PMU.
4753 This option takes over the PMU facility, so it is no
4754 longer usable by perf. Setting this option starts the
4755 PMU counters by setting MMCR0 to 0 (the FC bit is
4756 cleared). If a number is given, then MMCR1 is set to
4757 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4758 remains 0.
4759
4760 pm_debug_messages [SUSPEND,KNL]
4761 Enable suspend/resume debug messages during boot up.
4762
4763 pnp.debug=1 [PNP]
4764 Enable PNP debug messages (depends on the
4765 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4766 via /sys/module/pnp/parameters/debug. We always show
4767 current resource usage; turning this on also shows
4768 possible settings and some assignment information.
4769
4770 pnpacpi= [ACPI]
4771 { off }
4772
4773 pnpbios= [ISAPNP]
4774 { on | off | curr | res | no-curr | no-res }
4775
4776 pnp_reserve_irq=
4777 [ISAPNP] Exclude IRQs for the autoconfiguration
4778
4779 pnp_reserve_dma=
4780 [ISAPNP] Exclude DMAs for the autoconfiguration
4781
4782 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4783 Ranges are in pairs (I/O port base and size).
4784
4785 pnp_reserve_mem=
4786 [ISAPNP] Exclude memory regions for the
4787 autoconfiguration.
4788 Ranges are in pairs (memory base and size).
4789
4790 ports= [IP_VS_FTP] IPVS ftp helper module
4791 Default is 21.
4792 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4793 may be specified.
4794 Format: <port>,<port>....
4795
4796 possible_cpus= [SMP,S390,X86]
4797 Format: <unsigned int>
4798 Set the number of possible CPUs, overriding the
4799 regular discovery mechanisms (such as ACPI/FW, etc).
4800
4801 powersave=off [PPC] This option disables power saving features.
4802 It specifically disables cpuidle and sets the
4803 platform machine description specific power_save
4804 function to NULL. On Idle the CPU just reduces
4805 execution priority.
4806
4807 ppc_strict_facility_enable
4808 [PPC,ENABLE] This option catches any kernel floating point,
4809 Altivec, VSX and SPE outside of regions specifically
4810 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4811 There is some performance impact when enabling this.
4812
4813 ppc_tm= [PPC,EARLY]
4814 Format: {"off"}
4815 Disable Hardware Transactional Memory
4816
4817 preempt= [KNL]
4818 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4819 none - Limited to cond_resched() calls
4820 voluntary - Limited to cond_resched() and might_sleep() calls
4821 full - Any section that isn't explicitly preempt disabled
4822 can be preempted anytime. Tasks will also yield
4823 contended spinlocks (if the critical section isn't
4824 explicitly preempt disabled beyond the lock itself).
4825 lazy - Scheduler controlled. Similar to full but instead
4826 of preempting the task immediately, the task gets
4827 one HZ tick time to yield itself before the
4828 preemption will be forced. One preemption is when the
4829 task returns to user space.
4830
4831 print-fatal-signals=
4832 [KNL] debug: print fatal signals
4833
4834 If enabled, warn about various signal handling
4835 related application anomalies: too many signals,
4836 too many POSIX.1 timers, fatal signals causing a
4837 coredump - etc.
4838
4839 If you hit the warning due to signal overflow,
4840 you might want to try "ulimit -i unlimited".
4841
4842 default: off.
4843
4844 printk.always_kmsg_dump=
4845 Trigger kmsg_dump for cases other than kernel oops or
4846 panics
4847 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4848 default: disabled
4849
4850 printk.console_no_auto_verbose=
4851 Disable console loglevel raise on oops, panic
4852 or lockdep-detected issues (only if lock debug is on).
4853 With an exception to setups with low baudrate on
4854 serial console, keeping this 0 is a good choice
4855 in order to provide more debug information.
4856 Format: <bool>
4857 default: 0 (auto_verbose is enabled)
4858
4859 printk.devkmsg={on,off,ratelimit}
4860 Control writing to /dev/kmsg.
4861 on - unlimited logging to /dev/kmsg from userspace
4862 off - logging to /dev/kmsg disabled
4863 ratelimit - ratelimit the logging
4864 Default: ratelimit
4865
4866 printk.time= Show timing data prefixed to each printk message line
4867 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4868
4869 proc_mem.force_override= [KNL]
4870 Format: {always | ptrace | never}
4871 Traditionally /proc/pid/mem allows memory permissions to be
4872 overridden without restrictions. This option may be set to
4873 restrict that. Can be one of:
4874 - 'always': traditional behavior always allows mem overrides.
4875 - 'ptrace': only allow mem overrides for active ptracers.
4876 - 'never': never allow mem overrides.
4877 If not specified, default is the CONFIG_PROC_MEM_* choice.
4878
4879 processor.max_cstate= [HW,ACPI]
4880 Limit processor to maximum C-state
4881 max_cstate=9 overrides any DMI blacklist limit.
4882
4883 processor.nocst [HW,ACPI]
4884 Ignore the _CST method to determine C-states,
4885 instead using the legacy FADT method
4886
4887 profile= [KNL] Enable kernel profiling via /proc/profile
4888 Format: [<profiletype>,]<number>
4889 Param: <profiletype>: "schedule" or "kvm"
4890 [defaults to kernel profiling]
4891 Param: "schedule" - profile schedule points.
4892 Param: "kvm" - profile VM exits.
4893 Param: <number> - step/bucket size as a power of 2 for
4894 statistical time based profiling.
4895
4896 prompt_ramdisk= [RAM] [Deprecated]
4897
4898 prot_virt= [S390] enable hosting protected virtual machines
4899 isolated from the hypervisor (if hardware supports
4900 that). If enabled, the default kernel base address
4901 might be overridden even when Kernel Address Space
4902 Layout Randomization is disabled.
4903 Format: <bool>
4904
4905 psi= [KNL] Enable or disable pressure stall information
4906 tracking.
4907 Format: <bool>
4908
4909 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4910 probe for; one of (bare|imps|exps|lifebook|any).
4911 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4912 per second.
4913 psmouse.resetafter= [HW,MOUSE]
4914 Try to reset the device after so many bad packets
4915 (0 = never).
4916 psmouse.resolution=
4917 [HW,MOUSE] Set desired mouse resolution, in dpi.
4918 psmouse.smartscroll=
4919 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4920 0 = disabled, 1 = enabled (default).
4921
4922 pstore.backend= Specify the name of the pstore backend to use
4923
4924 pti= [X86-64] Control Page Table Isolation of user and
4925 kernel address spaces. Disabling this feature
4926 removes hardening, but improves performance of
4927 system calls and interrupts.
4928
4929 on - unconditionally enable
4930 off - unconditionally disable
4931 auto - kernel detects whether your CPU model is
4932 vulnerable to issues that PTI mitigates
4933
4934 Not specifying this option is equivalent to pti=auto.
4935
4936 pty.legacy_count=
4937 [KNL] Number of legacy pty's. Overwrites compiled-in
4938 default number.
4939
4940 quiet [KNL,EARLY] Disable most log messages
4941
4942 r128= [HW,DRM]
4943
4944 radix_hcall_invalidate=on [PPC/PSERIES]
4945 Disable RADIX GTSE feature and use hcall for TLB
4946 invalidate.
4947
4948 raid= [HW,RAID]
4949 See Documentation/admin-guide/md.rst.
4950
4951 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4952 See Documentation/admin-guide/blockdev/ramdisk.rst.
4953
4954 ramdisk_start= [RAM] RAM disk image start address
4955
4956 random.trust_cpu=off
4957 [KNL,EARLY] Disable trusting the use of the CPU's
4958 random number generator (if available) to
4959 initialize the kernel's RNG.
4960
4961 random.trust_bootloader=off
4962 [KNL,EARLY] Disable trusting the use of the a seed
4963 passed by the bootloader (if available) to
4964 initialize the kernel's RNG.
4965
4966 randomize_kstack_offset=
4967 [KNL,EARLY] Enable or disable kernel stack offset
4968 randomization, which provides roughly 5 bits of
4969 entropy, frustrating memory corruption attacks
4970 that depend on stack address determinism or
4971 cross-syscall address exposures. This is only
4972 available on architectures that have defined
4973 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4974 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4975 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4976
4977 ras=option[,option,...] [KNL] RAS-specific options
4978
4979 cec_disable [X86]
4980 Disable the Correctable Errors Collector,
4981 see CONFIG_RAS_CEC help text.
4982
4983 rcu_nocbs[=cpu-list]
4984 [KNL] The optional argument is a cpu list,
4985 as described above.
4986
4987 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4988 enable the no-callback CPU mode, which prevents
4989 such CPUs' callbacks from being invoked in
4990 softirq context. Invocation of such CPUs' RCU
4991 callbacks will instead be offloaded to "rcuox/N"
4992 kthreads created for that purpose, where "x" is
4993 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4994 for the kthreads that mediate grace periods; and
4995 "N" is the CPU number. This reduces OS jitter on
4996 the offloaded CPUs, which can be useful for HPC
4997 and real-time workloads. It can also improve
4998 energy efficiency for asymmetric multiprocessors.
4999
5000 If a cpulist is passed as an argument, the specified
5001 list of CPUs is set to no-callback mode from boot.
5002
5003 Otherwise, if the '=' sign and the cpulist
5004 arguments are omitted, no CPU will be set to
5005 no-callback mode from boot but the mode may be
5006 toggled at runtime via cpusets.
5007
5008 Note that this argument takes precedence over
5009 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
5010
5011 rcu_nocb_poll [KNL]
5012 Rather than requiring that offloaded CPUs
5013 (specified by rcu_nocbs= above) explicitly
5014 awaken the corresponding "rcuoN" kthreads,
5015 make these kthreads poll for callbacks.
5016 This improves the real-time response for the
5017 offloaded CPUs by relieving them of the need to
5018 wake up the corresponding kthread, but degrades
5019 energy efficiency by requiring that the kthreads
5020 periodically wake up to do the polling.
5021
5022 rcutree.blimit= [KNL]
5023 Set maximum number of finished RCU callbacks to
5024 process in one batch.
5025
5026 rcutree.csd_lock_suppress_rcu_stall= [KNL]
5027 Do only a one-line RCU CPU stall warning when
5028 there is an ongoing too-long CSD-lock wait.
5029
5030 rcutree.do_rcu_barrier= [KNL]
5031 Request a call to rcu_barrier(). This is
5032 throttled so that userspace tests can safely
5033 hammer on the sysfs variable if they so choose.
5034 If triggered before the RCU grace-period machinery
5035 is fully active, this will error out with EAGAIN.
5036
5037 rcutree.dump_tree= [KNL]
5038 Dump the structure of the rcu_node combining tree
5039 out at early boot. This is used for diagnostic
5040 purposes, to verify correct tree setup.
5041
5042 rcutree.gp_cleanup_delay= [KNL]
5043 Set the number of jiffies to delay each step of
5044 RCU grace-period cleanup.
5045
5046 rcutree.gp_init_delay= [KNL]
5047 Set the number of jiffies to delay each step of
5048 RCU grace-period initialization.
5049
5050 rcutree.gp_preinit_delay= [KNL]
5051 Set the number of jiffies to delay each step of
5052 RCU grace-period pre-initialization, that is,
5053 the propagation of recent CPU-hotplug changes up
5054 the rcu_node combining tree.
5055
5056 rcutree.jiffies_till_first_fqs= [KNL]
5057 Set delay from grace-period initialization to
5058 first attempt to force quiescent states.
5059 Units are jiffies, minimum value is zero,
5060 and maximum value is HZ.
5061
5062 rcutree.jiffies_till_next_fqs= [KNL]
5063 Set delay between subsequent attempts to force
5064 quiescent states. Units are jiffies, minimum
5065 value is one, and maximum value is HZ.
5066
5067 rcutree.jiffies_till_sched_qs= [KNL]
5068 Set required age in jiffies for a
5069 given grace period before RCU starts
5070 soliciting quiescent-state help from
5071 rcu_note_context_switch() and cond_resched().
5072 If not specified, the kernel will calculate
5073 a value based on the most recent settings
5074 of rcutree.jiffies_till_first_fqs
5075 and rcutree.jiffies_till_next_fqs.
5076 This calculated value may be viewed in
5077 rcutree.jiffies_to_sched_qs. Any attempt to set
5078 rcutree.jiffies_to_sched_qs will be cheerfully
5079 overwritten.
5080
5081 rcutree.kthread_prio= [KNL,BOOT]
5082 Set the SCHED_FIFO priority of the RCU per-CPU
5083 kthreads (rcuc/N). This value is also used for
5084 the priority of the RCU boost threads (rcub/N)
5085 and for the RCU grace-period kthreads (rcu_bh,
5086 rcu_preempt, and rcu_sched). If RCU_BOOST is
5087 set, valid values are 1-99 and the default is 1
5088 (the least-favored priority). Otherwise, when
5089 RCU_BOOST is not set, valid values are 0-99 and
5090 the default is zero (non-realtime operation).
5091 When RCU_NOCB_CPU is set, also adjust the
5092 priority of NOCB callback kthreads.
5093
5094 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
5095 On callback-offloaded (rcu_nocbs) CPUs,
5096 RCU reduces the lock contention that would
5097 otherwise be caused by callback floods through
5098 use of the ->nocb_bypass list. However, in the
5099 common non-flooded case, RCU queues directly to
5100 the main ->cblist in order to avoid the extra
5101 overhead of the ->nocb_bypass list and its lock.
5102 But if there are too many callbacks queued during
5103 a single jiffy, RCU pre-queues the callbacks into
5104 the ->nocb_bypass queue. The definition of "too
5105 many" is supplied by this kernel boot parameter.
5106
5107 rcutree.nohz_full_patience_delay= [KNL]
5108 On callback-offloaded (rcu_nocbs) CPUs, avoid
5109 disturbing RCU unless the grace period has
5110 reached the specified age in milliseconds.
5111 Defaults to zero. Large values will be capped
5112 at five seconds. All values will be rounded down
5113 to the nearest value representable by jiffies.
5114
5115 rcutree.qhimark= [KNL]
5116 Set threshold of queued RCU callbacks beyond which
5117 batch limiting is disabled.
5118
5119 rcutree.qlowmark= [KNL]
5120 Set threshold of queued RCU callbacks below which
5121 batch limiting is re-enabled.
5122
5123 rcutree.qovld= [KNL]
5124 Set threshold of queued RCU callbacks beyond which
5125 RCU's force-quiescent-state scan will aggressively
5126 enlist help from cond_resched() and sched IPIs to
5127 help CPUs more quickly reach quiescent states.
5128 Set to less than zero to make this be set based
5129 on rcutree.qhimark at boot time and to zero to
5130 disable more aggressive help enlistment.
5131
5132 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
5133 Set the page-cache refill delay (in milliseconds)
5134 in response to low-memory conditions. The range
5135 of permitted values is in the range 0:100000.
5136
5137 rcutree.rcu_divisor= [KNL]
5138 Set the shift-right count to use to compute
5139 the callback-invocation batch limit bl from
5140 the number of callbacks queued on this CPU.
5141 The result will be bounded below by the value of
5142 the rcutree.blimit kernel parameter. Every bl
5143 callbacks, the softirq handler will exit in
5144 order to allow the CPU to do other work.
5145
5146 Please note that this callback-invocation batch
5147 limit applies only to non-offloaded callback
5148 invocation. Offloaded callbacks are instead
5149 invoked in the context of an rcuoc kthread, which
5150 scheduler will preempt as it does any other task.
5151
5152 rcutree.rcu_fanout_exact= [KNL]
5153 Disable autobalancing of the rcu_node combining
5154 tree. This is used by rcutorture, and might
5155 possibly be useful for architectures having high
5156 cache-to-cache transfer latencies.
5157
5158 rcutree.rcu_fanout_leaf= [KNL]
5159 Change the number of CPUs assigned to each
5160 leaf rcu_node structure. Useful for very
5161 large systems, which will choose the value 64,
5162 and for NUMA systems with large remote-access
5163 latencies, which will choose a value aligned
5164 with the appropriate hardware boundaries.
5165
5166 rcutree.rcu_min_cached_objs= [KNL]
5167 Minimum number of objects which are cached and
5168 maintained per one CPU. Object size is equal
5169 to PAGE_SIZE. The cache allows to reduce the
5170 pressure to page allocator, also it makes the
5171 whole algorithm to behave better in low memory
5172 condition.
5173
5174 rcutree.rcu_nocb_gp_stride= [KNL]
5175 Set the number of NOCB callback kthreads in
5176 each group, which defaults to the square root
5177 of the number of CPUs. Larger numbers reduce
5178 the wakeup overhead on the global grace-period
5179 kthread, but increases that same overhead on
5180 each group's NOCB grace-period kthread.
5181
5182 rcutree.rcu_kick_kthreads= [KNL]
5183 Cause the grace-period kthread to get an extra
5184 wake_up() if it sleeps three times longer than
5185 it should at force-quiescent-state time.
5186 This wake_up() will be accompanied by a
5187 WARN_ONCE() splat and an ftrace_dump().
5188
5189 rcutree.rcu_resched_ns= [KNL]
5190 Limit the time spend invoking a batch of RCU
5191 callbacks to the specified number of nanoseconds.
5192 By default, this limit is checked only once
5193 every 32 callbacks in order to limit the pain
5194 inflicted by local_clock() overhead.
5195
5196 rcutree.rcu_unlock_delay= [KNL]
5197 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5198 this specifies an rcu_read_unlock()-time delay
5199 in microseconds. This defaults to zero.
5200 Larger delays increase the probability of
5201 catching RCU pointer leaks, that is, buggy use
5202 of RCU-protected pointers after the relevant
5203 rcu_read_unlock() has completed.
5204
5205 rcutree.sysrq_rcu= [KNL]
5206 Commandeer a sysrq key to dump out Tree RCU's
5207 rcu_node tree with an eye towards determining
5208 why a new grace period has not yet started.
5209
5210 rcutree.use_softirq= [KNL]
5211 If set to zero, move all RCU_SOFTIRQ processing to
5212 per-CPU rcuc kthreads. Defaults to a non-zero
5213 value, meaning that RCU_SOFTIRQ is used by default.
5214 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5215
5216 But note that CONFIG_PREEMPT_RT=y kernels disable
5217 this kernel boot parameter, forcibly setting it
5218 to zero.
5219
5220 rcutree.enable_rcu_lazy= [KNL]
5221 To save power, batch RCU callbacks and flush after
5222 delay, memory pressure or callback list growing too
5223 big.
5224
5225 rcutree.rcu_normal_wake_from_gp= [KNL]
5226 Reduces a latency of synchronize_rcu() call. This approach
5227 maintains its own track of synchronize_rcu() callers, so it
5228 does not interact with regular callbacks because it does not
5229 use a call_rcu[_hurry]() path. Please note, this is for a
5230 normal grace period.
5231
5232 How to enable it:
5233
5234 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp
5235 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"
5236
5237 Default is 0.
5238
5239 rcuscale.gp_async= [KNL]
5240 Measure performance of asynchronous
5241 grace-period primitives such as call_rcu().
5242
5243 rcuscale.gp_async_max= [KNL]
5244 Specify the maximum number of outstanding
5245 callbacks per writer thread. When a writer
5246 thread exceeds this limit, it invokes the
5247 corresponding flavor of rcu_barrier() to allow
5248 previously posted callbacks to drain.
5249
5250 rcuscale.gp_exp= [KNL]
5251 Measure performance of expedited synchronous
5252 grace-period primitives.
5253
5254 rcuscale.holdoff= [KNL]
5255 Set test-start holdoff period. The purpose of
5256 this parameter is to delay the start of the
5257 test until boot completes in order to avoid
5258 interference.
5259
5260 rcuscale.kfree_by_call_rcu= [KNL]
5261 In kernels built with CONFIG_RCU_LAZY=y, test
5262 call_rcu() instead of kfree_rcu().
5263
5264 rcuscale.kfree_mult= [KNL]
5265 Instead of allocating an object of size kfree_obj,
5266 allocate one of kfree_mult * sizeof(kfree_obj).
5267 Defaults to 1.
5268
5269 rcuscale.kfree_rcu_test= [KNL]
5270 Set to measure performance of kfree_rcu() flooding.
5271
5272 rcuscale.kfree_rcu_test_double= [KNL]
5273 Test the double-argument variant of kfree_rcu().
5274 If this parameter has the same value as
5275 rcuscale.kfree_rcu_test_single, both the single-
5276 and double-argument variants are tested.
5277
5278 rcuscale.kfree_rcu_test_single= [KNL]
5279 Test the single-argument variant of kfree_rcu().
5280 If this parameter has the same value as
5281 rcuscale.kfree_rcu_test_double, both the single-
5282 and double-argument variants are tested.
5283
5284 rcuscale.kfree_nthreads= [KNL]
5285 The number of threads running loops of kfree_rcu().
5286
5287 rcuscale.kfree_alloc_num= [KNL]
5288 Number of allocations and frees done in an iteration.
5289
5290 rcuscale.kfree_loops= [KNL]
5291 Number of loops doing rcuscale.kfree_alloc_num number
5292 of allocations and frees.
5293
5294 rcuscale.minruntime= [KNL]
5295 Set the minimum test run time in seconds. This
5296 does not affect the data-collection interval,
5297 but instead allows better measurement of things
5298 like CPU consumption.
5299
5300 rcuscale.nreaders= [KNL]
5301 Set number of RCU readers. The value -1 selects
5302 N, where N is the number of CPUs. A value
5303 "n" less than -1 selects N-n+1, where N is again
5304 the number of CPUs. For example, -2 selects N
5305 (the number of CPUs), -3 selects N+1, and so on.
5306 A value of "n" less than or equal to -N selects
5307 a single reader.
5308
5309 rcuscale.nwriters= [KNL]
5310 Set number of RCU writers. The values operate
5311 the same as for rcuscale.nreaders.
5312 N, where N is the number of CPUs
5313
5314 rcuscale.scale_type= [KNL]
5315 Specify the RCU implementation to test.
5316
5317 rcuscale.shutdown= [KNL]
5318 Shut the system down after performance tests
5319 complete. This is useful for hands-off automated
5320 testing.
5321
5322 rcuscale.verbose= [KNL]
5323 Enable additional printk() statements.
5324
5325 rcuscale.writer_holdoff= [KNL]
5326 Write-side holdoff between grace periods,
5327 in microseconds. The default of zero says
5328 no holdoff.
5329
5330 rcuscale.writer_holdoff_jiffies= [KNL]
5331 Additional write-side holdoff between grace
5332 periods, but in jiffies. The default of zero
5333 says no holdoff.
5334
5335 rcutorture.fqs_duration= [KNL]
5336 Set duration of force_quiescent_state bursts
5337 in microseconds.
5338
5339 rcutorture.fqs_holdoff= [KNL]
5340 Set holdoff time within force_quiescent_state bursts
5341 in microseconds.
5342
5343 rcutorture.fqs_stutter= [KNL]
5344 Set wait time between force_quiescent_state bursts
5345 in seconds.
5346
5347 rcutorture.fwd_progress= [KNL]
5348 Specifies the number of kthreads to be used
5349 for RCU grace-period forward-progress testing
5350 for the types of RCU supporting this notion.
5351 Defaults to 1 kthread, values less than zero or
5352 greater than the number of CPUs cause the number
5353 of CPUs to be used.
5354
5355 rcutorture.fwd_progress_div= [KNL]
5356 Specify the fraction of a CPU-stall-warning
5357 period to do tight-loop forward-progress testing.
5358
5359 rcutorture.fwd_progress_holdoff= [KNL]
5360 Number of seconds to wait between successive
5361 forward-progress tests.
5362
5363 rcutorture.fwd_progress_need_resched= [KNL]
5364 Enclose cond_resched() calls within checks for
5365 need_resched() during tight-loop forward-progress
5366 testing.
5367
5368 rcutorture.gp_cond= [KNL]
5369 Use conditional/asynchronous update-side
5370 primitives, if available.
5371
5372 rcutorture.gp_exp= [KNL]
5373 Use expedited update-side primitives, if available.
5374
5375 rcutorture.gp_normal= [KNL]
5376 Use normal (non-expedited) asynchronous
5377 update-side primitives, if available.
5378
5379 rcutorture.gp_sync= [KNL]
5380 Use normal (non-expedited) synchronous
5381 update-side primitives, if available. If all
5382 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5383 rcutorture.gp_normal=, and rcutorture.gp_sync=
5384 are zero, rcutorture acts as if is interpreted
5385 they are all non-zero.
5386
5387 rcutorture.irqreader= [KNL]
5388 Run RCU readers from irq handlers, or, more
5389 accurately, from a timer handler. Not all RCU
5390 flavors take kindly to this sort of thing.
5391
5392 rcutorture.leakpointer= [KNL]
5393 Leak an RCU-protected pointer out of the reader.
5394 This can of course result in splats, and is
5395 intended to test the ability of things like
5396 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5397 such leaks.
5398
5399 rcutorture.n_barrier_cbs= [KNL]
5400 Set callbacks/threads for rcu_barrier() testing.
5401
5402 rcutorture.nfakewriters= [KNL]
5403 Set number of concurrent RCU writers. These just
5404 stress RCU, they don't participate in the actual
5405 test, hence the "fake".
5406
5407 rcutorture.nocbs_nthreads= [KNL]
5408 Set number of RCU callback-offload togglers.
5409 Zero (the default) disables toggling.
5410
5411 rcutorture.nocbs_toggle= [KNL]
5412 Set the delay in milliseconds between successive
5413 callback-offload toggling attempts.
5414
5415 rcutorture.nreaders= [KNL]
5416 Set number of RCU readers. The value -1 selects
5417 N-1, where N is the number of CPUs. A value
5418 "n" less than -1 selects N-n-2, where N is again
5419 the number of CPUs. For example, -2 selects N
5420 (the number of CPUs), -3 selects N+1, and so on.
5421
5422 rcutorture.object_debug= [KNL]
5423 Enable debug-object double-call_rcu() testing.
5424
5425 rcutorture.onoff_holdoff= [KNL]
5426 Set time (s) after boot for CPU-hotplug testing.
5427
5428 rcutorture.onoff_interval= [KNL]
5429 Set time (jiffies) between CPU-hotplug operations,
5430 or zero to disable CPU-hotplug testing.
5431
5432 rcutorture.read_exit_burst= [KNL]
5433 The number of times in a given read-then-exit
5434 episode that a set of read-then-exit kthreads
5435 is spawned.
5436
5437 rcutorture.read_exit_delay= [KNL]
5438 The delay, in seconds, between successive
5439 read-then-exit testing episodes.
5440
5441 rcutorture.reader_flavor= [KNL]
5442 A bit mask indicating which readers to use.
5443 If there is more than one bit set, the readers
5444 are entered from low-order bit up, and are
5445 exited in the opposite order. For SRCU, the
5446 0x1 bit is normal readers, 0x2 NMI-safe readers,
5447 and 0x4 light-weight readers.
5448
5449 rcutorture.shuffle_interval= [KNL]
5450 Set task-shuffle interval (s). Shuffling tasks
5451 allows some CPUs to go into dyntick-idle mode
5452 during the rcutorture test.
5453
5454 rcutorture.shutdown_secs= [KNL]
5455 Set time (s) after boot system shutdown. This
5456 is useful for hands-off automated testing.
5457
5458 rcutorture.stall_cpu= [KNL]
5459 Duration of CPU stall (s) to test RCU CPU stall
5460 warnings, zero to disable.
5461
5462 rcutorture.stall_cpu_block= [KNL]
5463 Sleep while stalling if set. This will result
5464 in warnings from preemptible RCU in addition to
5465 any other stall-related activity. Note that
5466 in kernels built with CONFIG_PREEMPTION=n and
5467 CONFIG_PREEMPT_COUNT=y, this parameter will
5468 cause the CPU to pass through a quiescent state.
5469 Given CONFIG_PREEMPTION=n, this will suppress
5470 RCU CPU stall warnings, but will instead result
5471 in scheduling-while-atomic splats.
5472
5473 Use of this module parameter results in splats.
5474
5475
5476 rcutorture.stall_cpu_holdoff= [KNL]
5477 Time to wait (s) after boot before inducing stall.
5478
5479 rcutorture.stall_cpu_irqsoff= [KNL]
5480 Disable interrupts while stalling if set, but only
5481 on the first stall in the set.
5482
5483 rcutorture.stall_cpu_repeat= [KNL]
5484 Number of times to repeat the stall sequence,
5485 so that rcutorture.stall_cpu_repeat=3 will result
5486 in four stall sequences.
5487
5488 rcutorture.stall_gp_kthread= [KNL]
5489 Duration (s) of forced sleep within RCU
5490 grace-period kthread to test RCU CPU stall
5491 warnings, zero to disable. If both stall_cpu
5492 and stall_gp_kthread are specified, the
5493 kthread is starved first, then the CPU.
5494
5495 rcutorture.stat_interval= [KNL]
5496 Time (s) between statistics printk()s.
5497
5498 rcutorture.stutter= [KNL]
5499 Time (s) to stutter testing, for example, specifying
5500 five seconds causes the test to run for five seconds,
5501 wait for five seconds, and so on. This tests RCU's
5502 ability to transition abruptly to and from idle.
5503
5504 rcutorture.test_boost= [KNL]
5505 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5506 "Maybe" means test if the RCU implementation
5507 under test support RCU priority boosting.
5508
5509 rcutorture.test_boost_duration= [KNL]
5510 Duration (s) of each individual boost test.
5511
5512 rcutorture.test_boost_interval= [KNL]
5513 Interval (s) between each boost test.
5514
5515 rcutorture.test_no_idle_hz= [KNL]
5516 Test RCU's dyntick-idle handling. See also the
5517 rcutorture.shuffle_interval parameter.
5518
5519 rcutorture.torture_type= [KNL]
5520 Specify the RCU implementation to test.
5521
5522 rcutorture.verbose= [KNL]
5523 Enable additional printk() statements.
5524
5525 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5526 Dump ftrace buffer after reporting RCU CPU
5527 stall warning.
5528
5529 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5530 Provide RCU CPU stall notifiers, but see the
5531 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5532 option's help text. TL;DR: You almost certainly
5533 do not want rcupdate.rcu_cpu_stall_notifiers.
5534
5535 rcupdate.rcu_cpu_stall_suppress= [KNL]
5536 Suppress RCU CPU stall warning messages.
5537
5538 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5539 Suppress RCU CPU stall warning messages and
5540 rcutorture writer stall warnings that occur
5541 during early boot, that is, during the time
5542 before the init task is spawned.
5543
5544 rcupdate.rcu_cpu_stall_timeout= [KNL]
5545 Set timeout for RCU CPU stall warning messages.
5546 The value is in seconds and the maximum allowed
5547 value is 300 seconds.
5548
5549 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5550 Set timeout for expedited RCU CPU stall warning
5551 messages. The value is in milliseconds
5552 and the maximum allowed value is 21000
5553 milliseconds. Please note that this value is
5554 adjusted to an arch timer tick resolution.
5555 Setting this to zero causes the value from
5556 rcupdate.rcu_cpu_stall_timeout to be used (after
5557 conversion from seconds to milliseconds).
5558
5559 rcupdate.rcu_cpu_stall_cputime= [KNL]
5560 Provide statistics on the cputime and count of
5561 interrupts and tasks during the sampling period. For
5562 multiple continuous RCU stalls, all sampling periods
5563 begin at half of the first RCU stall timeout.
5564
5565 rcupdate.rcu_exp_stall_task_details= [KNL]
5566 Print stack dumps of any tasks blocking the
5567 current expedited RCU grace period during an
5568 expedited RCU CPU stall warning.
5569
5570 rcupdate.rcu_expedited= [KNL]
5571 Use expedited grace-period primitives, for
5572 example, synchronize_rcu_expedited() instead
5573 of synchronize_rcu(). This reduces latency,
5574 but can increase CPU utilization, degrade
5575 real-time latency, and degrade energy efficiency.
5576 No effect on CONFIG_TINY_RCU kernels.
5577
5578 rcupdate.rcu_normal= [KNL]
5579 Use only normal grace-period primitives,
5580 for example, synchronize_rcu() instead of
5581 synchronize_rcu_expedited(). This improves
5582 real-time latency, CPU utilization, and
5583 energy efficiency, but can expose users to
5584 increased grace-period latency. This parameter
5585 overrides rcupdate.rcu_expedited. No effect on
5586 CONFIG_TINY_RCU kernels.
5587
5588 rcupdate.rcu_normal_after_boot= [KNL]
5589 Once boot has completed (that is, after
5590 rcu_end_inkernel_boot() has been invoked), use
5591 only normal grace-period primitives. No effect
5592 on CONFIG_TINY_RCU kernels.
5593
5594 But note that CONFIG_PREEMPT_RT=y kernels enables
5595 this kernel boot parameter, forcibly setting
5596 it to the value one, that is, converting any
5597 post-boot attempt at an expedited RCU grace
5598 period to instead use normal non-expedited
5599 grace-period processing.
5600
5601 rcupdate.rcu_task_collapse_lim= [KNL]
5602 Set the maximum number of callbacks present
5603 at the beginning of a grace period that allows
5604 the RCU Tasks flavors to collapse back to using
5605 a single callback queue. This switching only
5606 occurs when rcupdate.rcu_task_enqueue_lim is
5607 set to the default value of -1.
5608
5609 rcupdate.rcu_task_contend_lim= [KNL]
5610 Set the minimum number of callback-queuing-time
5611 lock-contention events per jiffy required to
5612 cause the RCU Tasks flavors to switch to per-CPU
5613 callback queuing. This switching only occurs
5614 when rcupdate.rcu_task_enqueue_lim is set to
5615 the default value of -1.
5616
5617 rcupdate.rcu_task_enqueue_lim= [KNL]
5618 Set the number of callback queues to use for the
5619 RCU Tasks family of RCU flavors. The default
5620 of -1 allows this to be automatically (and
5621 dynamically) adjusted. This parameter is intended
5622 for use in testing.
5623
5624 rcupdate.rcu_task_ipi_delay= [KNL]
5625 Set time in jiffies during which RCU tasks will
5626 avoid sending IPIs, starting with the beginning
5627 of a given grace period. Setting a large
5628 number avoids disturbing real-time workloads,
5629 but lengthens grace periods.
5630
5631 rcupdate.rcu_task_lazy_lim= [KNL]
5632 Number of callbacks on a given CPU that will
5633 cancel laziness on that CPU. Use -1 to disable
5634 cancellation of laziness, but be advised that
5635 doing so increases the danger of OOM due to
5636 callback flooding.
5637
5638 rcupdate.rcu_task_stall_info= [KNL]
5639 Set initial timeout in jiffies for RCU task stall
5640 informational messages, which give some indication
5641 of the problem for those not patient enough to
5642 wait for ten minutes. Informational messages are
5643 only printed prior to the stall-warning message
5644 for a given grace period. Disable with a value
5645 less than or equal to zero. Defaults to ten
5646 seconds. A change in value does not take effect
5647 until the beginning of the next grace period.
5648
5649 rcupdate.rcu_task_stall_info_mult= [KNL]
5650 Multiplier for time interval between successive
5651 RCU task stall informational messages for a given
5652 RCU tasks grace period. This value is clamped
5653 to one through ten, inclusive. It defaults to
5654 the value three, so that the first informational
5655 message is printed 10 seconds into the grace
5656 period, the second at 40 seconds, the third at
5657 160 seconds, and then the stall warning at 600
5658 seconds would prevent a fourth at 640 seconds.
5659
5660 rcupdate.rcu_task_stall_timeout= [KNL]
5661 Set timeout in jiffies for RCU task stall
5662 warning messages. Disable with a value less
5663 than or equal to zero. Defaults to ten minutes.
5664 A change in value does not take effect until
5665 the beginning of the next grace period.
5666
5667 rcupdate.rcu_tasks_lazy_ms= [KNL]
5668 Set timeout in milliseconds RCU Tasks asynchronous
5669 callback batching for call_rcu_tasks().
5670 A negative value will take the default. A value
5671 of zero will disable batching. Batching is
5672 always disabled for synchronize_rcu_tasks().
5673
5674 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5675 Set timeout in milliseconds RCU Tasks
5676 Trace asynchronous callback batching for
5677 call_rcu_tasks_trace(). A negative value
5678 will take the default. A value of zero will
5679 disable batching. Batching is always disabled
5680 for synchronize_rcu_tasks_trace().
5681
5682 rcupdate.rcu_self_test= [KNL]
5683 Run the RCU early boot self tests
5684
5685 rdinit= [KNL]
5686 Format: <full_path>
5687 Run specified binary instead of /init from the ramdisk,
5688 used for early userspace startup. See initrd.
5689
5690 rdrand= [X86,EARLY]
5691 force - Override the decision by the kernel to hide the
5692 advertisement of RDRAND support (this affects
5693 certain AMD processors because of buggy BIOS
5694 support, specifically around the suspend/resume
5695 path).
5696
5697 rdt= [HW,X86,RDT]
5698 Turn on/off individual RDT features. List is:
5699 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5700 mba, smba, bmec.
5701 E.g. to turn on cmt and turn off mba use:
5702 rdt=cmt,!mba
5703
5704 reboot= [KNL]
5705 Format (x86 or x86_64):
5706 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5707 [[,]s[mp]#### \
5708 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5709 [[,]f[orce]
5710 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5711 (prefix with 'panic_' to set mode for panic
5712 reboot only),
5713 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5714 reboot_force is either force or not specified,
5715 reboot_cpu is s[mp]#### with #### being the processor
5716 to be used for rebooting.
5717
5718 refscale.holdoff= [KNL]
5719 Set test-start holdoff period. The purpose of
5720 this parameter is to delay the start of the
5721 test until boot completes in order to avoid
5722 interference.
5723
5724 refscale.lookup_instances= [KNL]
5725 Number of data elements to use for the forms of
5726 SLAB_TYPESAFE_BY_RCU testing. A negative number
5727 is negated and multiplied by nr_cpu_ids, while
5728 zero specifies nr_cpu_ids.
5729
5730 refscale.loops= [KNL]
5731 Set the number of loops over the synchronization
5732 primitive under test. Increasing this number
5733 reduces noise due to loop start/end overhead,
5734 but the default has already reduced the per-pass
5735 noise to a handful of picoseconds on ca. 2020
5736 x86 laptops.
5737
5738 refscale.nreaders= [KNL]
5739 Set number of readers. The default value of -1
5740 selects N, where N is roughly 75% of the number
5741 of CPUs. A value of zero is an interesting choice.
5742
5743 refscale.nruns= [KNL]
5744 Set number of runs, each of which is dumped onto
5745 the console log.
5746
5747 refscale.readdelay= [KNL]
5748 Set the read-side critical-section duration,
5749 measured in microseconds.
5750
5751 refscale.scale_type= [KNL]
5752 Specify the read-protection implementation to test.
5753
5754 refscale.shutdown= [KNL]
5755 Shut down the system at the end of the performance
5756 test. This defaults to 1 (shut it down) when
5757 refscale is built into the kernel and to 0 (leave
5758 it running) when refscale is built as a module.
5759
5760 refscale.verbose= [KNL]
5761 Enable additional printk() statements.
5762
5763 refscale.verbose_batched= [KNL]
5764 Batch the additional printk() statements. If zero
5765 (the default) or negative, print everything. Otherwise,
5766 print every Nth verbose statement, where N is the value
5767 specified.
5768
5769 regulator_ignore_unused
5770 [REGULATOR]
5771 Prevents regulator framework from disabling regulators
5772 that are unused, due no driver claiming them. This may
5773 be useful for debug and development, but should not be
5774 needed on a platform with proper driver support.
5775
5776 relax_domain_level=
5777 [KNL, SMP] Set scheduler's default relax_domain_level.
5778 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5779
5780 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5781 Format: <base1>,<size1>[,<base2>,<size2>,...]
5782 Reserve I/O ports or memory so the kernel won't use
5783 them. If <base> is less than 0x10000, the region
5784 is assumed to be I/O ports; otherwise it is memory.
5785
5786 reserve_mem= [RAM]
5787 Format: nn[KNG]:<align>:<label>
5788 Reserve physical memory and label it with a name that
5789 other subsystems can use to access it. This is typically
5790 used for systems that do not wipe the RAM, and this command
5791 line will try to reserve the same physical memory on
5792 soft reboots. Note, it is not guaranteed to be the same
5793 location. For example, if anything about the system changes
5794 or if booting a different kernel. It can also fail if KASLR
5795 places the kernel at the location of where the RAM reservation
5796 was from a previous boot, the new reservation will be at a
5797 different location.
5798 Any subsystem using this feature must add a way to verify
5799 that the contents of the physical memory is from a previous
5800 boot, as there may be cases where the memory will not be
5801 located at the same location.
5802
5803 The format is size:align:label for example, to request
5804 12 megabytes of 4096 alignment for ramoops:
5805
5806 reserve_mem=12M:4096:oops ramoops.mem_name=oops
5807
5808 reservetop= [X86-32,EARLY]
5809 Format: nn[KMG]
5810 Reserves a hole at the top of the kernel virtual
5811 address space.
5812
5813 reset_devices [KNL] Force drivers to reset the underlying device
5814 during initialization.
5815
5816 resume= [SWSUSP]
5817 Specify the partition device for software suspend
5818 Format:
5819 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5820
5821 resume_offset= [SWSUSP]
5822 Specify the offset from the beginning of the partition
5823 given by "resume=" at which the swap header is located,
5824 in <PAGE_SIZE> units (needed only for swap files).
5825 See Documentation/power/swsusp-and-swap-files.rst
5826
5827 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5828 read the resume files
5829
5830 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5831 Useful for devices that are detected asynchronously
5832 (e.g. USB and MMC devices).
5833
5834 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
5835 be accessible via /sys/firmware/initrd.
5836
5837 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5838 Speculative Code Execution with Return Instructions)
5839 vulnerability.
5840
5841 AMD-based UNRET and IBPB mitigations alone do not stop
5842 sibling threads from influencing the predictions of other
5843 sibling threads. For that reason, STIBP is used on pro-
5844 cessors that support it, and mitigate SMT on processors
5845 that don't.
5846
5847 off - no mitigation
5848 auto - automatically select a migitation
5849 auto,nosmt - automatically select a mitigation,
5850 disabling SMT if necessary for
5851 the full mitigation (only on Zen1
5852 and older without STIBP).
5853 ibpb - On AMD, mitigate short speculation
5854 windows on basic block boundaries too.
5855 Safe, highest perf impact. It also
5856 enables STIBP if present. Not suitable
5857 on Intel.
5858 ibpb,nosmt - Like "ibpb" above but will disable SMT
5859 when STIBP is not available. This is
5860 the alternative for systems which do not
5861 have STIBP.
5862 unret - Force enable untrained return thunks,
5863 only effective on AMD f15h-f17h based
5864 systems.
5865 unret,nosmt - Like unret, but will disable SMT when STIBP
5866 is not available. This is the alternative for
5867 systems which do not have STIBP.
5868
5869 Selecting 'auto' will choose a mitigation method at run
5870 time according to the CPU.
5871
5872 Not specifying this option is equivalent to retbleed=auto.
5873
5874 rfkill.default_state=
5875 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5876 etc. communication is blocked by default.
5877 1 Unblocked.
5878
5879 rfkill.master_switch_mode=
5880 0 The "airplane mode" button does nothing.
5881 1 The "airplane mode" button toggles between everything
5882 blocked and the previous configuration.
5883 2 The "airplane mode" button toggles between everything
5884 blocked and everything unblocked.
5885
5886 ring3mwait=disable
5887 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5888 CPUs.
5889
5890 riscv_isa_fallback [RISCV,EARLY]
5891 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
5892 falling back to detecting extension support by parsing
5893 "riscv,isa" property on devicetree systems when the
5894 replacement properties are not found. See the Kconfig
5895 entry for RISCV_ISA_FALLBACK.
5896
5897 ro [KNL] Mount root device read-only on boot
5898
5899 rodata= [KNL,EARLY]
5900 on Mark read-only kernel memory as read-only (default).
5901 off Leave read-only kernel memory writable for debugging.
5902 full Mark read-only kernel memory and aliases as read-only
5903 [arm64]
5904
5905 rockchip.usb_uart
5906 [EARLY]
5907 Enable the uart passthrough on the designated usb port
5908 on Rockchip SoCs. When active, the signals of the
5909 debug-uart get routed to the D+ and D- pins of the usb
5910 port and the regular usb controller gets disabled.
5911
5912 root= [KNL] Root filesystem
5913 Usually this a a block device specifier of some kind,
5914 see the early_lookup_bdev comment in
5915 block/early-lookup.c for details.
5916 Alternatively this can be "ram" for the legacy initial
5917 ramdisk, "nfs" and "cifs" for root on a network file
5918 system, or "mtd" and "ubi" for mounting from raw flash.
5919
5920 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5921 mount the root filesystem
5922
5923 rootflags= [KNL] Set root filesystem mount option string
5924
5925 rootfstype= [KNL] Set root filesystem type
5926
5927 rootwait [KNL] Wait (indefinitely) for root device to show up.
5928 Useful for devices that are detected asynchronously
5929 (e.g. USB and MMC devices).
5930
5931 rootwait= [KNL] Maximum time (in seconds) to wait for root device
5932 to show up before attempting to mount the root
5933 filesystem.
5934
5935 rproc_mem=nn[KMG][@address]
5936 [KNL,ARM,CMA] Remoteproc physical memory block.
5937 Memory area to be used by remote processor image,
5938 managed by CMA.
5939
5940 rw [KNL] Mount root device read-write on boot
5941
5942 S [KNL] Run init in single mode
5943
5944 s390_iommu= [HW,S390]
5945 Set s390 IOTLB flushing mode
5946 strict
5947 With strict flushing every unmap operation will result
5948 in an IOTLB flush. Default is lazy flushing before
5949 reuse, which is faster. Deprecated, equivalent to
5950 iommu.strict=1.
5951
5952 s390_iommu_aperture= [KNL,S390]
5953 Specifies the size of the per device DMA address space
5954 accessible through the DMA and IOMMU APIs as a decimal
5955 factor of the size of main memory.
5956 The default is 1 meaning that one can concurrently use
5957 as many DMA addresses as physical memory is installed,
5958 if supported by hardware, and thus map all of memory
5959 once. With a value of 2 one can map all of memory twice
5960 and so on. As a special case a factor of 0 imposes no
5961 restrictions other than those given by hardware at the
5962 cost of significant additional memory use for tables.
5963
5964 sa1100ir [NET]
5965 See drivers/net/irda/sa1100_ir.c.
5966
5967 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
5968
5969 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5970 Allowed values are enable and disable. This feature
5971 incurs a small amount of overhead in the scheduler
5972 but is useful for debugging and performance tuning.
5973
5974 sched_thermal_decay_shift=
5975 [Deprecated]
5976 [KNL, SMP] Set a decay shift for scheduler thermal
5977 pressure signal. Thermal pressure signal follows the
5978 default decay period of other scheduler pelt
5979 signals(usually 32 ms but configurable). Setting
5980 sched_thermal_decay_shift will left shift the decay
5981 period for the thermal pressure signal by the shift
5982 value.
5983 i.e. with the default pelt decay period of 32 ms
5984 sched_thermal_decay_shift thermal pressure decay pr
5985 1 64 ms
5986 2 128 ms
5987 and so on.
5988 Format: integer between 0 and 10
5989 Default is 0.
5990
5991 scftorture.holdoff= [KNL]
5992 Number of seconds to hold off before starting
5993 test. Defaults to zero for module insertion and
5994 to 10 seconds for built-in smp_call_function()
5995 tests.
5996
5997 scftorture.longwait= [KNL]
5998 Request ridiculously long waits randomly selected
5999 up to the chosen limit in seconds. Zero (the
6000 default) disables this feature. Please note
6001 that requesting even small non-zero numbers of
6002 seconds can result in RCU CPU stall warnings,
6003 softlockup complaints, and so on.
6004
6005 scftorture.nthreads= [KNL]
6006 Number of kthreads to spawn to invoke the
6007 smp_call_function() family of functions.
6008 The default of -1 specifies a number of kthreads
6009 equal to the number of CPUs.
6010
6011 scftorture.onoff_holdoff= [KNL]
6012 Number seconds to wait after the start of the
6013 test before initiating CPU-hotplug operations.
6014
6015 scftorture.onoff_interval= [KNL]
6016 Number seconds to wait between successive
6017 CPU-hotplug operations. Specifying zero (which
6018 is the default) disables CPU-hotplug operations.
6019
6020 scftorture.shutdown_secs= [KNL]
6021 The number of seconds following the start of the
6022 test after which to shut down the system. The
6023 default of zero avoids shutting down the system.
6024 Non-zero values are useful for automated tests.
6025
6026 scftorture.stat_interval= [KNL]
6027 The number of seconds between outputting the
6028 current test statistics to the console. A value
6029 of zero disables statistics output.
6030
6031 scftorture.stutter_cpus= [KNL]
6032 The number of jiffies to wait between each change
6033 to the set of CPUs under test.
6034
6035 scftorture.use_cpus_read_lock= [KNL]
6036 Use use_cpus_read_lock() instead of the default
6037 preempt_disable() to disable CPU hotplug
6038 while invoking one of the smp_call_function*()
6039 functions.
6040
6041 scftorture.verbose= [KNL]
6042 Enable additional printk() statements.
6043
6044 scftorture.weight_single= [KNL]
6045 The probability weighting to use for the
6046 smp_call_function_single() function with a zero
6047 "wait" parameter. A value of -1 selects the
6048 default if all other weights are -1. However,
6049 if at least one weight has some other value, a
6050 value of -1 will instead select a weight of zero.
6051
6052 scftorture.weight_single_wait= [KNL]
6053 The probability weighting to use for the
6054 smp_call_function_single() function with a
6055 non-zero "wait" parameter. See weight_single.
6056
6057 scftorture.weight_many= [KNL]
6058 The probability weighting to use for the
6059 smp_call_function_many() function with a zero
6060 "wait" parameter. See weight_single.
6061 Note well that setting a high probability for
6062 this weighting can place serious IPI load
6063 on the system.
6064
6065 scftorture.weight_many_wait= [KNL]
6066 The probability weighting to use for the
6067 smp_call_function_many() function with a
6068 non-zero "wait" parameter. See weight_single
6069 and weight_many.
6070
6071 scftorture.weight_all= [KNL]
6072 The probability weighting to use for the
6073 smp_call_function_all() function with a zero
6074 "wait" parameter. See weight_single and
6075 weight_many.
6076
6077 scftorture.weight_all_wait= [KNL]
6078 The probability weighting to use for the
6079 smp_call_function_all() function with a
6080 non-zero "wait" parameter. See weight_single
6081 and weight_many.
6082
6083 sdw_mclk_divider=[SDW]
6084 Specify the MCLK divider for Intel SoundWire buses in
6085 case the BIOS does not provide the clock rate properly.
6086
6087 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
6088 xtime_lock contention on larger systems, and/or RCU lock
6089 contention on all systems with CONFIG_MAXSMP set.
6090 Format: { "0" | "1" }
6091 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
6092 1 -- enable.
6093 Note: increases power consumption, thus should only be
6094 enabled if running jitter sensitive (HPC/RT) workloads.
6095
6096 security= [SECURITY] Choose a legacy "major" security module to
6097 enable at boot. This has been deprecated by the
6098 "lsm=" parameter.
6099
6100 selinux= [SELINUX] Disable or enable SELinux at boot time.
6101 Format: { "0" | "1" }
6102 See security/selinux/Kconfig help text.
6103 0 -- disable.
6104 1 -- enable.
6105 Default value is 1.
6106
6107 serialnumber [BUGS=X86-32]
6108
6109 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
6110
6111 shapers= [NET]
6112 Maximal number of shapers.
6113
6114 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
6115 Limit apic dumping. The parameter defines the maximal
6116 number of local apics being dumped. Also it is possible
6117 to set it to "all" by meaning -- no limit here.
6118 Format: { 1 (default) | 2 | ... | all }.
6119 The parameter valid if only apic=debug or
6120 apic=verbose is specified.
6121 Example: apic=debug show_lapic=all
6122
6123 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]
6124 Enabling slab_debug allows one to determine the
6125 culprit if slab objects become corrupted. Enabling
6126 slab_debug can create guard zones around objects and
6127 may poison objects when not in use. Also tracks the
6128 last alloc / free. For more information see
6129 Documentation/mm/slub.rst.
6130 (slub_debug legacy name also accepted for now)
6131
6132 slab_max_order= [MM]
6133 Determines the maximum allowed order for slabs.
6134 A high setting may cause OOMs due to memory
6135 fragmentation. For more information see
6136 Documentation/mm/slub.rst.
6137 (slub_max_order legacy name also accepted for now)
6138
6139 slab_merge [MM]
6140 Enable merging of slabs with similar size when the
6141 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
6142 (slub_merge legacy name also accepted for now)
6143
6144 slab_min_objects= [MM]
6145 The minimum number of objects per slab. SLUB will
6146 increase the slab order up to slab_max_order to
6147 generate a sufficiently large slab able to contain
6148 the number of objects indicated. The higher the number
6149 of objects the smaller the overhead of tracking slabs
6150 and the less frequently locks need to be acquired.
6151 For more information see Documentation/mm/slub.rst.
6152 (slub_min_objects legacy name also accepted for now)
6153
6154 slab_min_order= [MM]
6155 Determines the minimum page order for slabs. Must be
6156 lower or equal to slab_max_order. For more information see
6157 Documentation/mm/slub.rst.
6158 (slub_min_order legacy name also accepted for now)
6159
6160 slab_nomerge [MM]
6161 Disable merging of slabs with similar size. May be
6162 necessary if there is some reason to distinguish
6163 allocs to different slabs, especially in hardened
6164 environments where the risk of heap overflows and
6165 layout control by attackers can usually be
6166 frustrated by disabling merging. This will reduce
6167 most of the exposure of a heap attack to a single
6168 cache (risks via metadata attacks are mostly
6169 unchanged). Debug options disable merging on their
6170 own.
6171 For more information see Documentation/mm/slub.rst.
6172 (slub_nomerge legacy name also accepted for now)
6173
6174 slab_strict_numa [MM]
6175 Support memory policies on a per object level
6176 in the slab allocator. The default is for memory
6177 policies to be applied at the folio level when
6178 a new folio is needed or a partial folio is
6179 retrieved from the lists. Increases overhead
6180 in the slab fastpaths but gains more accurate
6181 NUMA kernel object placement which helps with slow
6182 interconnects in NUMA systems.
6183
6184 slram= [HW,MTD]
6185
6186 smart2= [HW]
6187 Format: <io1>[,<io2>[,...,<io8>]]
6188
6189 smp.csd_lock_timeout= [KNL]
6190 Specify the period of time in milliseconds
6191 that smp_call_function() and friends will wait
6192 for a CPU to release the CSD lock. This is
6193 useful when diagnosing bugs involving CPUs
6194 disabling interrupts for extended periods
6195 of time. Defaults to 5,000 milliseconds, and
6196 setting a value of zero disables this feature.
6197 This feature may be more efficiently disabled
6198 using the csdlock_debug- kernel parameter.
6199
6200 smp.panic_on_ipistall= [KNL]
6201 If a csd_lock_timeout extends for more than
6202 the specified number of milliseconds, panic the
6203 system. By default, let CSD-lock acquisition
6204 take as long as they take. Specifying 300,000
6205 for this value provides a 5-minute timeout.
6206
6207 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
6208 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
6209 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
6210 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
6211 smsc-ircc2.ircc_irq= [HW] IRQ line
6212 smsc-ircc2.ircc_dma= [HW] DMA channel
6213 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
6214 0: Toshiba Satellite 1800 (GP data pin select)
6215 1: Fast pin select (default)
6216 2: ATC IRMode
6217
6218 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
6219 (logical CPUs) to use per physical CPU on systems
6220 capable of symmetric multithreading (SMT). Will
6221 be capped to the actual hardware limit.
6222 Format: <integer>
6223 Default: -1 (no limit)
6224
6225 softlockup_panic=
6226 [KNL] Should the soft-lockup detector generate panics.
6227 Format: 0 | 1
6228
6229 A value of 1 instructs the soft-lockup detector
6230 to panic the machine when a soft-lockup occurs. It is
6231 also controlled by the kernel.softlockup_panic sysctl
6232 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6233 respective build-time switch to that functionality.
6234
6235 softlockup_all_cpu_backtrace=
6236 [KNL] Should the soft-lockup detector generate
6237 backtraces on all cpus.
6238 Format: 0 | 1
6239
6240 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6241 See Documentation/admin-guide/laptops/sonypi.rst
6242
6243 spectre_bhi= [X86] Control mitigation of Branch History Injection
6244 (BHI) vulnerability. This setting affects the
6245 deployment of the HW BHI control and the SW BHB
6246 clearing sequence.
6247
6248 on - (default) Enable the HW or SW mitigation as
6249 needed. This protects the kernel from
6250 both syscalls and VMs.
6251 vmexit - On systems which don't have the HW mitigation
6252 available, enable the SW mitigation on vmexit
6253 ONLY. On such systems, the host kernel is
6254 protected from VM-originated BHI attacks, but
6255 may still be vulnerable to syscall attacks.
6256 off - Disable the mitigation.
6257
6258 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
6259 (indirect branch speculation) vulnerability.
6260 The default operation protects the kernel from
6261 user space attacks.
6262
6263 on - unconditionally enable, implies
6264 spectre_v2_user=on
6265 off - unconditionally disable, implies
6266 spectre_v2_user=off
6267 auto - kernel detects whether your CPU model is
6268 vulnerable
6269
6270 Selecting 'on' will, and 'auto' may, choose a
6271 mitigation method at run time according to the
6272 CPU, the available microcode, the setting of the
6273 CONFIG_MITIGATION_RETPOLINE configuration option,
6274 and the compiler with which the kernel was built.
6275
6276 Selecting 'on' will also enable the mitigation
6277 against user space to user space task attacks.
6278
6279 Selecting 'off' will disable both the kernel and
6280 the user space protections.
6281
6282 Specific mitigations can also be selected manually:
6283
6284 retpoline - replace indirect branches
6285 retpoline,generic - Retpolines
6286 retpoline,lfence - LFENCE; indirect branch
6287 retpoline,amd - alias for retpoline,lfence
6288 eibrs - Enhanced/Auto IBRS
6289 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6290 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6291 ibrs - use IBRS to protect kernel
6292
6293 Not specifying this option is equivalent to
6294 spectre_v2=auto.
6295
6296 spectre_v2_user=
6297 [X86] Control mitigation of Spectre variant 2
6298 (indirect branch speculation) vulnerability between
6299 user space tasks
6300
6301 on - Unconditionally enable mitigations. Is
6302 enforced by spectre_v2=on
6303
6304 off - Unconditionally disable mitigations. Is
6305 enforced by spectre_v2=off
6306
6307 prctl - Indirect branch speculation is enabled,
6308 but mitigation can be enabled via prctl
6309 per thread. The mitigation control state
6310 is inherited on fork.
6311
6312 prctl,ibpb
6313 - Like "prctl" above, but only STIBP is
6314 controlled per thread. IBPB is issued
6315 always when switching between different user
6316 space processes.
6317
6318 seccomp
6319 - Same as "prctl" above, but all seccomp
6320 threads will enable the mitigation unless
6321 they explicitly opt out.
6322
6323 seccomp,ibpb
6324 - Like "seccomp" above, but only STIBP is
6325 controlled per thread. IBPB is issued
6326 always when switching between different
6327 user space processes.
6328
6329 auto - Kernel selects the mitigation depending on
6330 the available CPU features and vulnerability.
6331
6332 Default mitigation: "prctl"
6333
6334 Not specifying this option is equivalent to
6335 spectre_v2_user=auto.
6336
6337 spec_rstack_overflow=
6338 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
6339
6340 off - Disable mitigation
6341 microcode - Enable microcode mitigation only
6342 safe-ret - Enable sw-only safe RET mitigation (default)
6343 ibpb - Enable mitigation by issuing IBPB on
6344 kernel entry
6345 ibpb-vmexit - Issue IBPB only on VMEXIT
6346 (cloud-specific mitigation)
6347
6348 spec_store_bypass_disable=
6349 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
6350 (Speculative Store Bypass vulnerability)
6351
6352 Certain CPUs are vulnerable to an exploit against a
6353 a common industry wide performance optimization known
6354 as "Speculative Store Bypass" in which recent stores
6355 to the same memory location may not be observed by
6356 later loads during speculative execution. The idea
6357 is that such stores are unlikely and that they can
6358 be detected prior to instruction retirement at the
6359 end of a particular speculation execution window.
6360
6361 In vulnerable processors, the speculatively forwarded
6362 store can be used in a cache side channel attack, for
6363 example to read memory to which the attacker does not
6364 directly have access (e.g. inside sandboxed code).
6365
6366 This parameter controls whether the Speculative Store
6367 Bypass optimization is used.
6368
6369 On x86 the options are:
6370
6371 on - Unconditionally disable Speculative Store Bypass
6372 off - Unconditionally enable Speculative Store Bypass
6373 auto - Kernel detects whether the CPU model contains an
6374 implementation of Speculative Store Bypass and
6375 picks the most appropriate mitigation. If the
6376 CPU is not vulnerable, "off" is selected. If the
6377 CPU is vulnerable the default mitigation is
6378 architecture and Kconfig dependent. See below.
6379 prctl - Control Speculative Store Bypass per thread
6380 via prctl. Speculative Store Bypass is enabled
6381 for a process by default. The state of the control
6382 is inherited on fork.
6383 seccomp - Same as "prctl" above, but all seccomp threads
6384 will disable SSB unless they explicitly opt out.
6385
6386 Default mitigations:
6387 X86: "prctl"
6388
6389 On powerpc the options are:
6390
6391 on,auto - On Power8 and Power9 insert a store-forwarding
6392 barrier on kernel entry and exit. On Power7
6393 perform a software flush on kernel entry and
6394 exit.
6395 off - No action.
6396
6397 Not specifying this option is equivalent to
6398 spec_store_bypass_disable=auto.
6399
6400 split_lock_detect=
6401 [X86] Enable split lock detection or bus lock detection
6402
6403 When enabled (and if hardware support is present), atomic
6404 instructions that access data across cache line
6405 boundaries will result in an alignment check exception
6406 for split lock detection or a debug exception for
6407 bus lock detection.
6408
6409 off - not enabled
6410
6411 warn - the kernel will emit rate-limited warnings
6412 about applications triggering the #AC
6413 exception or the #DB exception. This mode is
6414 the default on CPUs that support split lock
6415 detection or bus lock detection. Default
6416 behavior is by #AC if both features are
6417 enabled in hardware.
6418
6419 fatal - the kernel will send SIGBUS to applications
6420 that trigger the #AC exception or the #DB
6421 exception. Default behavior is by #AC if
6422 both features are enabled in hardware.
6423
6424 ratelimit:N -
6425 Set system wide rate limit to N bus locks
6426 per second for bus lock detection.
6427 0 < N <= 1000.
6428
6429 N/A for split lock detection.
6430
6431
6432 If an #AC exception is hit in the kernel or in
6433 firmware (i.e. not while executing in user mode)
6434 the kernel will oops in either "warn" or "fatal"
6435 mode.
6436
6437 #DB exception for bus lock is triggered only when
6438 CPL > 0.
6439
6440 srbds= [X86,INTEL,EARLY]
6441 Control the Special Register Buffer Data Sampling
6442 (SRBDS) mitigation.
6443
6444 Certain CPUs are vulnerable to an MDS-like
6445 exploit which can leak bits from the random
6446 number generator.
6447
6448 By default, this issue is mitigated by
6449 microcode. However, the microcode fix can cause
6450 the RDRAND and RDSEED instructions to become
6451 much slower. Among other effects, this will
6452 result in reduced throughput from /dev/urandom.
6453
6454 The microcode mitigation can be disabled with
6455 the following option:
6456
6457 off: Disable mitigation and remove
6458 performance impact to RDRAND and RDSEED
6459
6460 srcutree.big_cpu_lim [KNL]
6461 Specifies the number of CPUs constituting a
6462 large system, such that srcu_struct structures
6463 should immediately allocate an srcu_node array.
6464 This kernel-boot parameter defaults to 128,
6465 but takes effect only when the low-order four
6466 bits of srcutree.convert_to_big is equal to 3
6467 (decide at boot).
6468
6469 srcutree.convert_to_big [KNL]
6470 Specifies under what conditions an SRCU tree
6471 srcu_struct structure will be converted to big
6472 form, that is, with an rcu_node tree:
6473
6474 0: Never.
6475 1: At init_srcu_struct() time.
6476 2: When rcutorture decides to.
6477 3: Decide at boot time (default).
6478 0x1X: Above plus if high contention.
6479
6480 Either way, the srcu_node tree will be sized based
6481 on the actual runtime number of CPUs (nr_cpu_ids)
6482 instead of the compile-time CONFIG_NR_CPUS.
6483
6484 srcutree.counter_wrap_check [KNL]
6485 Specifies how frequently to check for
6486 grace-period sequence counter wrap for the
6487 srcu_data structure's ->srcu_gp_seq_needed field.
6488 The greater the number of bits set in this kernel
6489 parameter, the less frequently counter wrap will
6490 be checked for. Note that the bottom two bits
6491 are ignored.
6492
6493 srcutree.exp_holdoff [KNL]
6494 Specifies how many nanoseconds must elapse
6495 since the end of the last SRCU grace period for
6496 a given srcu_struct until the next normal SRCU
6497 grace period will be considered for automatic
6498 expediting. Set to zero to disable automatic
6499 expediting.
6500
6501 srcutree.srcu_max_nodelay [KNL]
6502 Specifies the number of no-delay instances
6503 per jiffy for which the SRCU grace period
6504 worker thread will be rescheduled with zero
6505 delay. Beyond this limit, worker thread will
6506 be rescheduled with a sleep delay of one jiffy.
6507
6508 srcutree.srcu_max_nodelay_phase [KNL]
6509 Specifies the per-grace-period phase, number of
6510 non-sleeping polls of readers. Beyond this limit,
6511 grace period worker thread will be rescheduled
6512 with a sleep delay of one jiffy, between each
6513 rescan of the readers, for a grace period phase.
6514
6515 srcutree.srcu_retry_check_delay [KNL]
6516 Specifies number of microseconds of non-sleeping
6517 delay between each non-sleeping poll of readers.
6518
6519 srcutree.small_contention_lim [KNL]
6520 Specifies the number of update-side contention
6521 events per jiffy will be tolerated before
6522 initiating a conversion of an srcu_struct
6523 structure to big form. Note that the value of
6524 srcutree.convert_to_big must have the 0x10 bit
6525 set for contention-based conversions to occur.
6526
6527 ssbd= [ARM64,HW,EARLY]
6528 Speculative Store Bypass Disable control
6529
6530 On CPUs that are vulnerable to the Speculative
6531 Store Bypass vulnerability and offer a
6532 firmware based mitigation, this parameter
6533 indicates how the mitigation should be used:
6534
6535 force-on: Unconditionally enable mitigation for
6536 for both kernel and userspace
6537 force-off: Unconditionally disable mitigation for
6538 for both kernel and userspace
6539 kernel: Always enable mitigation in the
6540 kernel, and offer a prctl interface
6541 to allow userspace to register its
6542 interest in being mitigated too.
6543
6544 stack_guard_gap= [MM]
6545 override the default stack gap protection. The value
6546 is in page units and it defines how many pages prior
6547 to (for stacks growing down) resp. after (for stacks
6548 growing up) the main stack are reserved for no other
6549 mapping. Default value is 256 pages.
6550
6551 stack_depot_disable= [KNL,EARLY]
6552 Setting this to true through kernel command line will
6553 disable the stack depot thereby saving the static memory
6554 consumed by the stack hash table. By default this is set
6555 to false.
6556
6557 stacktrace [FTRACE]
6558 Enabled the stack tracer on boot up.
6559
6560 stacktrace_filter=[function-list]
6561 [FTRACE] Limit the functions that the stack tracer
6562 will trace at boot up. function-list is a comma-separated
6563 list of functions. This list can be changed at run
6564 time by the stack_trace_filter file in the debugfs
6565 tracing directory. Note, this enables stack tracing
6566 and the stacktrace above is not needed.
6567
6568 sti= [PARISC,HW]
6569 Format: <num>
6570 Set the STI (builtin display/keyboard on the HP-PARISC
6571 machines) console (graphic card) which should be used
6572 as the initial boot-console.
6573 See also comment in drivers/video/console/sticore.c.
6574
6575 sti_font= [HW]
6576 See comment in drivers/video/console/sticore.c.
6577
6578 stifb= [HW]
6579 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6580
6581 strict_sas_size=
6582 [X86]
6583 Format: <bool>
6584 Enable or disable strict sigaltstack size checks
6585 against the required signal frame size which
6586 depends on the supported FPU features. This can
6587 be used to filter out binaries which have
6588 not yet been made aware of AT_MINSIGSTKSZ.
6589
6590 stress_hpt [PPC,EARLY]
6591 Limits the number of kernel HPT entries in the hash
6592 page table to increase the rate of hash page table
6593 faults on kernel addresses.
6594
6595 stress_slb [PPC,EARLY]
6596 Limits the number of kernel SLB entries, and flushes
6597 them frequently to increase the rate of SLB faults
6598 on kernel addresses.
6599
6600 sunrpc.min_resvport=
6601 sunrpc.max_resvport=
6602 [NFS,SUNRPC]
6603 SunRPC servers often require that client requests
6604 originate from a privileged port (i.e. a port in the
6605 range 0 < portnr < 1024).
6606 An administrator who wishes to reserve some of these
6607 ports for other uses may adjust the range that the
6608 kernel's sunrpc client considers to be privileged
6609 using these two parameters to set the minimum and
6610 maximum port values.
6611
6612 sunrpc.svc_rpc_per_connection_limit=
6613 [NFS,SUNRPC]
6614 Limit the number of requests that the server will
6615 process in parallel from a single connection.
6616 The default value is 0 (no limit).
6617
6618 sunrpc.pool_mode=
6619 [NFS]
6620 Control how the NFS server code allocates CPUs to
6621 service thread pools. Depending on how many NICs
6622 you have and where their interrupts are bound, this
6623 option will affect which CPUs will do NFS serving.
6624 Note: this parameter cannot be changed while the
6625 NFS server is running.
6626
6627 auto the server chooses an appropriate mode
6628 automatically using heuristics
6629 global a single global pool contains all CPUs
6630 percpu one pool for each CPU
6631 pernode one pool for each NUMA node (equivalent
6632 to global on non-NUMA machines)
6633
6634 sunrpc.tcp_slot_table_entries=
6635 sunrpc.udp_slot_table_entries=
6636 [NFS,SUNRPC]
6637 Sets the upper limit on the number of simultaneous
6638 RPC calls that can be sent from the client to a
6639 server. Increasing these values may allow you to
6640 improve throughput, but will also increase the
6641 amount of memory reserved for use by the client.
6642
6643 suspend.pm_test_delay=
6644 [SUSPEND]
6645 Sets the number of seconds to remain in a suspend test
6646 mode before resuming the system (see
6647 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6648 is set. Default value is 5.
6649
6650 svm= [PPC]
6651 Format: { on | off | y | n | 1 | 0 }
6652 This parameter controls use of the Protected
6653 Execution Facility on pSeries.
6654
6655 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY]
6656 Format: { <int> [,<int>] | force | noforce }
6657 <int> -- Number of I/O TLB slabs
6658 <int> -- Second integer after comma. Number of swiotlb
6659 areas with their own lock. Will be rounded up
6660 to a power of 2.
6661 force -- force using of bounce buffers even if they
6662 wouldn't be automatically used by the kernel
6663 noforce -- Never use bounce buffers (for debugging)
6664
6665 switches= [HW,M68k,EARLY]
6666
6667 sysctl.*= [KNL]
6668 Set a sysctl parameter, right before loading the init
6669 process, as if the value was written to the respective
6670 /proc/sys/... file. Both '.' and '/' are recognized as
6671 separators. Unrecognized parameters and invalid values
6672 are reported in the kernel log. Sysctls registered
6673 later by a loaded module cannot be set this way.
6674 Example: sysctl.vm.swappiness=40
6675
6676 sysrq_always_enabled
6677 [KNL]
6678 Ignore sysrq setting - this boot parameter will
6679 neutralize any effect of /proc/sys/kernel/sysrq.
6680 Useful for debugging.
6681
6682 tcpmhash_entries= [KNL,NET]
6683 Set the number of tcp_metrics_hash slots.
6684 Default value is 8192 or 16384 depending on total
6685 ram pages. This is used to specify the TCP metrics
6686 cache size. See Documentation/networking/ip-sysctl.rst
6687 "tcp_no_metrics_save" section for more details.
6688
6689 tdfx= [HW,DRM]
6690
6691 test_suspend= [SUSPEND]
6692 Format: { "mem" | "standby" | "freeze" }[,N]
6693 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6694 standby suspend) or "freeze" (for suspend type freeze)
6695 as the system sleep state during system startup with
6696 the optional capability to repeat N number of times.
6697 The system is woken from this state using a
6698 wakeup-capable RTC alarm.
6699
6700 thash_entries= [KNL,NET]
6701 Set number of hash buckets for TCP connection
6702
6703 thermal.act= [HW,ACPI]
6704 -1: disable all active trip points in all thermal zones
6705 <degrees C>: override all lowest active trip points
6706
6707 thermal.crt= [HW,ACPI]
6708 -1: disable all critical trip points in all thermal zones
6709 <degrees C>: override all critical trip points
6710
6711 thermal.off= [HW,ACPI]
6712 1: disable ACPI thermal control
6713
6714 thermal.psv= [HW,ACPI]
6715 -1: disable all passive trip points
6716 <degrees C>: override all passive trip points to this
6717 value
6718
6719 thermal.tzp= [HW,ACPI]
6720 Specify global default ACPI thermal zone polling rate
6721 <deci-seconds>: poll all this frequency
6722 0: no polling (default)
6723
6724 thp_anon= [KNL]
6725 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state>
6726 state is one of "always", "madvise", "never" or "inherit".
6727 Control the default behavior of the system with respect
6728 to anonymous transparent hugepages.
6729 Can be used multiple times for multiple anon THP sizes.
6730 See Documentation/admin-guide/mm/transhuge.rst for more
6731 details.
6732
6733 threadirqs [KNL,EARLY]
6734 Force threading of all interrupt handlers except those
6735 marked explicitly IRQF_NO_THREAD.
6736
6737 thp_shmem= [KNL]
6738 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy>
6739 Control the default policy of each hugepage size for the
6740 internal shmem mount. <policy> is one of policies available
6741 for the shmem mount ("always", "inherit", "never", "within_size",
6742 and "advise").
6743 It can be used multiple times for multiple shmem THP sizes.
6744 See Documentation/admin-guide/mm/transhuge.rst for more
6745 details.
6746
6747 topology= [S390,EARLY]
6748 Format: {off | on}
6749 Specify if the kernel should make use of the cpu
6750 topology information if the hardware supports this.
6751 The scheduler will make use of this information and
6752 e.g. base its process migration decisions on it.
6753 Default is on.
6754
6755 torture.disable_onoff_at_boot= [KNL]
6756 Prevent the CPU-hotplug component of torturing
6757 until after init has spawned.
6758
6759 torture.ftrace_dump_at_shutdown= [KNL]
6760 Dump the ftrace buffer at torture-test shutdown,
6761 even if there were no errors. This can be a
6762 very costly operation when many torture tests
6763 are running concurrently, especially on systems
6764 with rotating-rust storage.
6765
6766 torture.verbose_sleep_frequency= [KNL]
6767 Specifies how many verbose printk()s should be
6768 emitted between each sleep. The default of zero
6769 disables verbose-printk() sleeping.
6770
6771 torture.verbose_sleep_duration= [KNL]
6772 Duration of each verbose-printk() sleep in jiffies.
6773
6774 tpm.disable_pcr_integrity= [HW,TPM]
6775 Do not protect PCR registers from unintended physical
6776 access, or interposers in the bus by the means of
6777 having an integrity protected session wrapped around
6778 TPM2_PCR_Extend command. Consider this in a situation
6779 where TPM is heavily utilized by IMA, thus protection
6780 causing a major performance hit, and the space where
6781 machines are deployed is by other means guarded.
6782
6783 tpm_suspend_pcr=[HW,TPM]
6784 Format: integer pcr id
6785 Specify that at suspend time, the tpm driver
6786 should extend the specified pcr with zeros,
6787 as a workaround for some chips which fail to
6788 flush the last written pcr on TPM_SaveState.
6789 This will guarantee that all the other pcrs
6790 are saved.
6791
6792 tpm_tis.interrupts= [HW,TPM]
6793 Enable interrupts for the MMIO based physical layer
6794 for the FIFO interface. By default it is set to false
6795 (0). For more information about TPM hardware interfaces
6796 defined by Trusted Computing Group (TCG) see
6797 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
6798
6799 tp_printk [FTRACE]
6800 Have the tracepoints sent to printk as well as the
6801 tracing ring buffer. This is useful for early boot up
6802 where the system hangs or reboots and does not give the
6803 option for reading the tracing buffer or performing a
6804 ftrace_dump_on_oops.
6805
6806 To turn off having tracepoints sent to printk,
6807 echo 0 > /proc/sys/kernel/tracepoint_printk
6808 Note, echoing 1 into this file without the
6809 tp_printk kernel cmdline option has no effect.
6810
6811 The tp_printk_stop_on_boot (see below) can also be used
6812 to stop the printing of events to console at
6813 late_initcall_sync.
6814
6815 ** CAUTION **
6816
6817 Having tracepoints sent to printk() and activating high
6818 frequency tracepoints such as irq or sched, can cause
6819 the system to live lock.
6820
6821 tp_printk_stop_on_boot [FTRACE]
6822 When tp_printk (above) is set, it can cause a lot of noise
6823 on the console. It may be useful to only include the
6824 printing of events during boot up, as user space may
6825 make the system inoperable.
6826
6827 This command line option will stop the printing of events
6828 to console at the late_initcall_sync() time frame.
6829
6830 trace_buf_size=nn[KMG]
6831 [FTRACE] will set tracing buffer size on each cpu.
6832
6833 trace_clock= [FTRACE] Set the clock used for tracing events
6834 at boot up.
6835 local - Use the per CPU time stamp counter
6836 (converted into nanoseconds). Fast, but
6837 depending on the architecture, may not be
6838 in sync between CPUs.
6839 global - Event time stamps are synchronize across
6840 CPUs. May be slower than the local clock,
6841 but better for some race conditions.
6842 counter - Simple counting of events (1, 2, ..)
6843 note, some counts may be skipped due to the
6844 infrastructure grabbing the clock more than
6845 once per event.
6846 uptime - Use jiffies as the time stamp.
6847 perf - Use the same clock that perf uses.
6848 mono - Use ktime_get_mono_fast_ns() for time stamps.
6849 mono_raw - Use ktime_get_raw_fast_ns() for time
6850 stamps.
6851 boot - Use ktime_get_boot_fast_ns() for time stamps.
6852 Architectures may add more clocks. See
6853 Documentation/trace/ftrace.rst for more details.
6854
6855 trace_event=[event-list]
6856 [FTRACE] Set and start specified trace events in order
6857 to facilitate early boot debugging. The event-list is a
6858 comma-separated list of trace events to enable. See
6859 also Documentation/trace/events.rst
6860
6861 trace_instance=[instance-info]
6862 [FTRACE] Create a ring buffer instance early in boot up.
6863 This will be listed in:
6864
6865 /sys/kernel/tracing/instances
6866
6867 Events can be enabled at the time the instance is created
6868 via:
6869
6870 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6871
6872 Note, the "<system*>:" portion is optional if the event is
6873 unique.
6874
6875 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6876
6877 will enable the "sched_switch" event (note, the "sched:" is optional, and
6878 the same thing would happen if it was left off). The irq_handler_entry
6879 event, and all events under the "initcall" system.
6880
6881 Flags can be added to the instance to modify its behavior when it is
6882 created. The flags are separated by '^'.
6883
6884 The available flags are:
6885
6886 traceoff - Have the tracing instance tracing disabled after it is created.
6887 traceprintk - Have trace_printk() write into this trace instance
6888 (note, "printk" and "trace_printk" can also be used)
6889
6890 trace_instance=foo^traceoff^traceprintk,sched,irq
6891
6892 The flags must come before the defined events.
6893
6894 If memory has been reserved (see memmap for x86), the instance
6895 can use that memory:
6896
6897 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M
6898
6899 The above will create a "boot_map" instance that uses the physical
6900 memory at 0x284500000 that is 12Megs. The per CPU buffers of that
6901 instance will be split up accordingly.
6902
6903 Alternatively, the memory can be reserved by the reserve_mem option:
6904
6905 reserve_mem=12M:4096:trace trace_instance=boot_map@trace
6906
6907 This will reserve 12 megabytes at boot up with a 4096 byte alignment
6908 and place the ring buffer in this memory. Note that due to KASLR, the
6909 memory may not be the same location each time, which will not preserve
6910 the buffer content.
6911
6912 Also note that the layout of the ring buffer data may change between
6913 kernel versions where the validator will fail and reset the ring buffer
6914 if the layout is not the same as the previous kernel.
6915
6916 If the ring buffer is used for persistent bootups and has events enabled,
6917 it is recommend to disable tracing so that events from a previous boot do not
6918 mix with events of the current boot (unless you are debugging a random crash
6919 at boot up).
6920
6921 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq
6922
6923 Note, saving the trace buffer across reboots does require that the system
6924 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION
6925 can force a memory reset on boot which will clear any trace that was stored.
6926 This is just one of many ways that can clear memory. Make sure your system
6927 keeps the content of memory across reboots before relying on this option.
6928
6929 See also Documentation/trace/debugging.rst
6930
6931
6932 trace_options=[option-list]
6933 [FTRACE] Enable or disable tracer options at boot.
6934 The option-list is a comma delimited list of options
6935 that can be enabled or disabled just as if you were
6936 to echo the option name into
6937
6938 /sys/kernel/tracing/trace_options
6939
6940 For example, to enable stacktrace option (to dump the
6941 stack trace of each event), add to the command line:
6942
6943 trace_options=stacktrace
6944
6945 See also Documentation/trace/ftrace.rst "trace options"
6946 section.
6947
6948 trace_trigger=[trigger-list]
6949 [FTRACE] Add a event trigger on specific events.
6950 Set a trigger on top of a specific event, with an optional
6951 filter.
6952
6953 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6954 Where more than one trigger may be specified that are comma deliminated.
6955
6956 For example:
6957
6958 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6959
6960 The above will enable the "stacktrace" trigger on the "sched_switch"
6961 event but only trigger it if the "prev_state" of the "sched_switch"
6962 event is "2" (TASK_UNINTERUPTIBLE).
6963
6964 See also "Event triggers" in Documentation/trace/events.rst
6965
6966
6967 traceoff_on_warning
6968 [FTRACE] enable this option to disable tracing when a
6969 warning is hit. This turns off "tracing_on". Tracing can
6970 be enabled again by echoing '1' into the "tracing_on"
6971 file located in /sys/kernel/tracing/
6972
6973 This option is useful, as it disables the trace before
6974 the WARNING dump is called, which prevents the trace to
6975 be filled with content caused by the warning output.
6976
6977 This option can also be set at run time via the sysctl
6978 option: kernel/traceoff_on_warning
6979
6980 transparent_hugepage=
6981 [KNL]
6982 Format: [always|madvise|never]
6983 Can be used to control the default behavior of the system
6984 with respect to transparent hugepages.
6985 See Documentation/admin-guide/mm/transhuge.rst
6986 for more details.
6987
6988 transparent_hugepage_shmem= [KNL]
6989 Format: [always|within_size|advise|never|deny|force]
6990 Can be used to control the hugepage allocation policy for
6991 the internal shmem mount.
6992 See Documentation/admin-guide/mm/transhuge.rst
6993 for more details.
6994
6995 trusted.source= [KEYS]
6996 Format: <string>
6997 This parameter identifies the trust source as a backend
6998 for trusted keys implementation. Supported trust
6999 sources:
7000 - "tpm"
7001 - "tee"
7002 - "caam"
7003 - "dcp"
7004 If not specified then it defaults to iterating through
7005 the trust source list starting with TPM and assigns the
7006 first trust source as a backend which is initialized
7007 successfully during iteration.
7008
7009 trusted.rng= [KEYS]
7010 Format: <string>
7011 The RNG used to generate key material for trusted keys.
7012 Can be one of:
7013 - "kernel"
7014 - the same value as trusted.source: "tpm" or "tee"
7015 - "default"
7016 If not specified, "default" is used. In this case,
7017 the RNG's choice is left to each individual trust source.
7018
7019 trusted.dcp_use_otp_key
7020 This is intended to be used in combination with
7021 trusted.source=dcp and will select the DCP OTP key
7022 instead of the DCP UNIQUE key blob encryption.
7023
7024 trusted.dcp_skip_zk_test
7025 This is intended to be used in combination with
7026 trusted.source=dcp and will disable the check if the
7027 blob key is all zeros. This is helpful for situations where
7028 having this key zero'ed is acceptable. E.g. in testing
7029 scenarios.
7030
7031 tsc= Disable clocksource stability checks for TSC.
7032 Format: <string>
7033 [x86] reliable: mark tsc clocksource as reliable, this
7034 disables clocksource verification at runtime, as well
7035 as the stability checks done at bootup. Used to enable
7036 high-resolution timer mode on older hardware, and in
7037 virtualized environment.
7038 [x86] noirqtime: Do not use TSC to do irq accounting.
7039 Used to run time disable IRQ_TIME_ACCOUNTING on any
7040 platforms where RDTSC is slow and this accounting
7041 can add overhead.
7042 [x86] unstable: mark the TSC clocksource as unstable, this
7043 marks the TSC unconditionally unstable at bootup and
7044 avoids any further wobbles once the TSC watchdog notices.
7045 [x86] nowatchdog: disable clocksource watchdog. Used
7046 in situations with strict latency requirements (where
7047 interruptions from clocksource watchdog are not
7048 acceptable).
7049 [x86] recalibrate: force recalibration against a HW timer
7050 (HPET or PM timer) on systems whose TSC frequency was
7051 obtained from HW or FW using either an MSR or CPUID(0x15).
7052 Warn if the difference is more than 500 ppm.
7053 [x86] watchdog: Use TSC as the watchdog clocksource with
7054 which to check other HW timers (HPET or PM timer), but
7055 only on systems where TSC has been deemed trustworthy.
7056 This will be suppressed by an earlier tsc=nowatchdog and
7057 can be overridden by a later tsc=nowatchdog. A console
7058 message will flag any such suppression or overriding.
7059
7060 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
7061 value instead. Useful when the early TSC frequency discovery
7062 procedure is not reliable, such as on overclocked systems
7063 with CPUID.16h support and partial CPUID.15h support.
7064 Format: <unsigned int>
7065
7066 tsx= [X86] Control Transactional Synchronization
7067 Extensions (TSX) feature in Intel processors that
7068 support TSX control.
7069
7070 This parameter controls the TSX feature. The options are:
7071
7072 on - Enable TSX on the system. Although there are
7073 mitigations for all known security vulnerabilities,
7074 TSX has been known to be an accelerator for
7075 several previous speculation-related CVEs, and
7076 so there may be unknown security risks associated
7077 with leaving it enabled.
7078
7079 off - Disable TSX on the system. (Note that this
7080 option takes effect only on newer CPUs which are
7081 not vulnerable to MDS, i.e., have
7082 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
7083 the new IA32_TSX_CTRL MSR through a microcode
7084 update. This new MSR allows for the reliable
7085 deactivation of the TSX functionality.)
7086
7087 auto - Disable TSX if X86_BUG_TAA is present,
7088 otherwise enable TSX on the system.
7089
7090 Not specifying this option is equivalent to tsx=off.
7091
7092 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
7093 for more details.
7094
7095 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
7096 Abort (TAA) vulnerability.
7097
7098 Similar to Micro-architectural Data Sampling (MDS)
7099 certain CPUs that support Transactional
7100 Synchronization Extensions (TSX) are vulnerable to an
7101 exploit against CPU internal buffers which can forward
7102 information to a disclosure gadget under certain
7103 conditions.
7104
7105 In vulnerable processors, the speculatively forwarded
7106 data can be used in a cache side channel attack, to
7107 access data to which the attacker does not have direct
7108 access.
7109
7110 This parameter controls the TAA mitigation. The
7111 options are:
7112
7113 full - Enable TAA mitigation on vulnerable CPUs
7114 if TSX is enabled.
7115
7116 full,nosmt - Enable TAA mitigation and disable SMT on
7117 vulnerable CPUs. If TSX is disabled, SMT
7118 is not disabled because CPU is not
7119 vulnerable to cross-thread TAA attacks.
7120 off - Unconditionally disable TAA mitigation
7121
7122 On MDS-affected machines, tsx_async_abort=off can be
7123 prevented by an active MDS mitigation as both vulnerabilities
7124 are mitigated with the same mechanism so in order to disable
7125 this mitigation, you need to specify mds=off too.
7126
7127 Not specifying this option is equivalent to
7128 tsx_async_abort=full. On CPUs which are MDS affected
7129 and deploy MDS mitigation, TAA mitigation is not
7130 required and doesn't provide any additional
7131 mitigation.
7132
7133 For details see:
7134 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
7135
7136 turbografx.map[2|3]= [HW,JOY]
7137 TurboGraFX parallel port interface
7138 Format:
7139 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
7140 See also Documentation/input/devices/joystick-parport.rst
7141
7142 udbg-immortal [PPC] When debugging early kernel crashes that
7143 happen after console_init() and before a proper
7144 console driver takes over, this boot options might
7145 help "seeing" what's going on.
7146
7147 uhash_entries= [KNL,NET]
7148 Set number of hash buckets for UDP/UDP-Lite connections
7149
7150 uhci-hcd.ignore_oc=
7151 [USB] Ignore overcurrent events (default N).
7152 Some badly-designed motherboards generate lots of
7153 bogus events, for ports that aren't wired to
7154 anything. Set this parameter to avoid log spamming.
7155 Note that genuine overcurrent events won't be
7156 reported either.
7157
7158 unknown_nmi_panic
7159 [X86] Cause panic on unknown NMI.
7160
7161 unwind_debug [X86-64,EARLY]
7162 Enable unwinder debug output. This can be
7163 useful for debugging certain unwinder error
7164 conditions, including corrupt stacks and
7165 bad/missing unwinder metadata.
7166
7167 usbcore.authorized_default=
7168 [USB] Default USB device authorization:
7169 (default -1 = authorized (same as 1),
7170 0 = not authorized, 1 = authorized, 2 = authorized
7171 if device connected to internal port)
7172
7173 usbcore.autosuspend=
7174 [USB] The autosuspend time delay (in seconds) used
7175 for newly-detected USB devices (default 2). This
7176 is the time required before an idle device will be
7177 autosuspended. Devices for which the delay is set
7178 to a negative value won't be autosuspended at all.
7179
7180 usbcore.usbfs_snoop=
7181 [USB] Set to log all usbfs traffic (default 0 = off).
7182
7183 usbcore.usbfs_snoop_max=
7184 [USB] Maximum number of bytes to snoop in each URB
7185 (default = 65536).
7186
7187 usbcore.blinkenlights=
7188 [USB] Set to cycle leds on hubs (default 0 = off).
7189
7190 usbcore.old_scheme_first=
7191 [USB] Start with the old device initialization
7192 scheme (default 0 = off).
7193
7194 usbcore.usbfs_memory_mb=
7195 [USB] Memory limit (in MB) for buffers allocated by
7196 usbfs (default = 16, 0 = max = 2047).
7197
7198 usbcore.use_both_schemes=
7199 [USB] Try the other device initialization scheme
7200 if the first one fails (default 1 = enabled).
7201
7202 usbcore.initial_descriptor_timeout=
7203 [USB] Specifies timeout for the initial 64-byte
7204 USB_REQ_GET_DESCRIPTOR request in milliseconds
7205 (default 5000 = 5.0 seconds).
7206
7207 usbcore.nousb [USB] Disable the USB subsystem
7208
7209 usbcore.quirks=
7210 [USB] A list of quirk entries to augment the built-in
7211 usb core quirk list. List entries are separated by
7212 commas. Each entry has the form
7213 VendorID:ProductID:Flags. The IDs are 4-digit hex
7214 numbers and Flags is a set of letters. Each letter
7215 will change the built-in quirk; setting it if it is
7216 clear and clearing it if it is set. The letters have
7217 the following meanings:
7218 a = USB_QUIRK_STRING_FETCH_255 (string
7219 descriptors must not be fetched using
7220 a 255-byte read);
7221 b = USB_QUIRK_RESET_RESUME (device can't resume
7222 correctly so reset it instead);
7223 c = USB_QUIRK_NO_SET_INTF (device can't handle
7224 Set-Interface requests);
7225 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
7226 handle its Configuration or Interface
7227 strings);
7228 e = USB_QUIRK_RESET (device can't be reset
7229 (e.g morph devices), don't use reset);
7230 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
7231 more interface descriptions than the
7232 bNumInterfaces count, and can't handle
7233 talking to these interfaces);
7234 g = USB_QUIRK_DELAY_INIT (device needs a pause
7235 during initialization, after we read
7236 the device descriptor);
7237 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
7238 high speed and super speed interrupt
7239 endpoints, the USB 2.0 and USB 3.0 spec
7240 require the interval in microframes (1
7241 microframe = 125 microseconds) to be
7242 calculated as interval = 2 ^
7243 (bInterval-1).
7244 Devices with this quirk report their
7245 bInterval as the result of this
7246 calculation instead of the exponent
7247 variable used in the calculation);
7248 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
7249 handle device_qualifier descriptor
7250 requests);
7251 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
7252 generates spurious wakeup, ignore
7253 remote wakeup capability);
7254 k = USB_QUIRK_NO_LPM (device can't handle Link
7255 Power Management);
7256 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
7257 (Device reports its bInterval as linear
7258 frames instead of the USB 2.0
7259 calculation);
7260 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
7261 to be disconnected before suspend to
7262 prevent spurious wakeup);
7263 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
7264 pause after every control message);
7265 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
7266 delay after resetting its port);
7267 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
7268 (Reduce timeout of the SET_ADDRESS
7269 request from 5000 ms to 500 ms);
7270 Example: quirks=0781:5580:bk,0a5c:5834:gij
7271
7272 usbhid.mousepoll=
7273 [USBHID] The interval which mice are to be polled at.
7274
7275 usbhid.jspoll=
7276 [USBHID] The interval which joysticks are to be polled at.
7277
7278 usbhid.kbpoll=
7279 [USBHID] The interval which keyboards are to be polled at.
7280
7281 usb-storage.delay_use=
7282 [UMS] The delay in seconds before a new device is
7283 scanned for Logical Units (default 1).
7284 Optionally the delay in milliseconds if the value has
7285 suffix with "ms".
7286 Example: delay_use=2567ms
7287
7288 usb-storage.quirks=
7289 [UMS] A list of quirks entries to supplement or
7290 override the built-in unusual_devs list. List
7291 entries are separated by commas. Each entry has
7292 the form VID:PID:Flags where VID and PID are Vendor
7293 and Product ID values (4-digit hex numbers) and
7294 Flags is a set of characters, each corresponding
7295 to a common usb-storage quirk flag as follows:
7296 a = SANE_SENSE (collect more than 18 bytes
7297 of sense data, not on uas);
7298 b = BAD_SENSE (don't collect more than 18
7299 bytes of sense data, not on uas);
7300 c = FIX_CAPACITY (decrease the reported
7301 device capacity by one sector);
7302 d = NO_READ_DISC_INFO (don't use
7303 READ_DISC_INFO command, not on uas);
7304 e = NO_READ_CAPACITY_16 (don't use
7305 READ_CAPACITY_16 command);
7306 f = NO_REPORT_OPCODES (don't use report opcodes
7307 command, uas only);
7308 g = MAX_SECTORS_240 (don't transfer more than
7309 240 sectors at a time, uas only);
7310 h = CAPACITY_HEURISTICS (decrease the
7311 reported device capacity by one
7312 sector if the number is odd);
7313 i = IGNORE_DEVICE (don't bind to this
7314 device);
7315 j = NO_REPORT_LUNS (don't use report luns
7316 command, uas only);
7317 k = NO_SAME (do not use WRITE_SAME, uas only)
7318 l = NOT_LOCKABLE (don't try to lock and
7319 unlock ejectable media, not on uas);
7320 m = MAX_SECTORS_64 (don't transfer more
7321 than 64 sectors = 32 KB at a time,
7322 not on uas);
7323 n = INITIAL_READ10 (force a retry of the
7324 initial READ(10) command, not on uas);
7325 o = CAPACITY_OK (accept the capacity
7326 reported by the device, not on uas);
7327 p = WRITE_CACHE (the device cache is ON
7328 by default, not on uas);
7329 r = IGNORE_RESIDUE (the device reports
7330 bogus residue values, not on uas);
7331 s = SINGLE_LUN (the device has only one
7332 Logical Unit);
7333 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7334 commands, uas only);
7335 u = IGNORE_UAS (don't bind to the uas driver);
7336 w = NO_WP_DETECT (don't test whether the
7337 medium is write-protected).
7338 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7339 even if the device claims no cache,
7340 not on uas)
7341 Example: quirks=0419:aaf5:rl,0421:0433:rc
7342
7343 user_debug= [KNL,ARM]
7344 Format: <int>
7345 See arch/arm/Kconfig.debug help text.
7346 1 - undefined instruction events
7347 2 - system calls
7348 4 - invalid data aborts
7349 8 - SIGSEGV faults
7350 16 - SIGBUS faults
7351 Example: user_debug=31
7352
7353 userpte=
7354 [X86,EARLY] Flags controlling user PTE allocations.
7355
7356 nohigh = do not allocate PTE pages in
7357 HIGHMEM regardless of setting
7358 of CONFIG_HIGHPTE.
7359
7360 vdso= [X86,SH,SPARC]
7361 On X86_32, this is an alias for vdso32=. Otherwise:
7362
7363 vdso=1: enable VDSO (the default)
7364 vdso=0: disable VDSO mapping
7365
7366 vdso32= [X86] Control the 32-bit vDSO
7367 vdso32=1: enable 32-bit VDSO
7368 vdso32=0 or vdso32=2: disable 32-bit VDSO
7369
7370 See the help text for CONFIG_COMPAT_VDSO for more
7371 details. If CONFIG_COMPAT_VDSO is set, the default is
7372 vdso32=0; otherwise, the default is vdso32=1.
7373
7374 For compatibility with older kernels, vdso32=2 is an
7375 alias for vdso32=0.
7376
7377 Try vdso32=0 if you encounter an error that says:
7378 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7379
7380 video= [FB,EARLY] Frame buffer configuration
7381 See Documentation/fb/modedb.rst.
7382
7383 video.brightness_switch_enabled= [ACPI]
7384 Format: [0|1]
7385 If set to 1, on receiving an ACPI notify event
7386 generated by hotkey, video driver will adjust brightness
7387 level and then send out the event to user space through
7388 the allocated input device. If set to 0, video driver
7389 will only send out the event without touching backlight
7390 brightness level.
7391 default: 1
7392
7393 virtio_mmio.device=
7394 [VMMIO] Memory mapped virtio (platform) device.
7395
7396 <size>@<baseaddr>:<irq>[:<id>]
7397 where:
7398 <size> := size (can use standard suffixes
7399 like K, M and G)
7400 <baseaddr> := physical base address
7401 <irq> := interrupt number (as passed to
7402 request_irq())
7403 <id> := (optional) platform device id
7404 example:
7405 virtio_mmio.device=1K@0x100b0000:48:7
7406
7407 Can be used multiple times for multiple devices.
7408
7409 vga= [BOOT,X86-32] Select a particular video mode
7410 See Documentation/arch/x86/boot.rst and
7411 Documentation/admin-guide/svga.rst.
7412 Use vga=ask for menu.
7413 This is actually a boot loader parameter; the value is
7414 passed to the kernel using a special protocol.
7415
7416 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7417 May slow down system boot speed, especially when
7418 enabled on systems with a large amount of memory.
7419 All options are enabled by default, and this
7420 interface is meant to allow for selectively
7421 enabling or disabling specific virtual memory
7422 debugging features.
7423
7424 Available options are:
7425 P Enable page structure init time poisoning
7426 - Disable all of the above options
7427
7428 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
7429 exact size of <nn>. This can be used to increase
7430 the minimum size (128MB on x86, arm32 platforms).
7431 It can also be used to decrease the size and leave more room
7432 for directly mapped kernel RAM. Note that this parameter does
7433 not exist on many other platforms (including arm64, alpha,
7434 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc,
7435 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc).
7436
7437 vmcp_cma=nn[MG] [KNL,S390,EARLY]
7438 Sets the memory size reserved for contiguous memory
7439 allocations for the vmcp device driver.
7440
7441 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7442 Format: <command>
7443
7444 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7445 Format: <command>
7446
7447 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7448 Format: <command>
7449
7450 vsyscall= [X86-64,EARLY]
7451 Controls the behavior of vsyscalls (i.e. calls to
7452 fixed addresses of 0xffffffffff600x00 from legacy
7453 code). Most statically-linked binaries and older
7454 versions of glibc use these calls. Because these
7455 functions are at fixed addresses, they make nice
7456 targets for exploits that can control RIP.
7457
7458 emulate Vsyscalls turn into traps and are emulated
7459 reasonably safely. The vsyscall page is
7460 readable.
7461
7462 xonly [default] Vsyscalls turn into traps and are
7463 emulated reasonably safely. The vsyscall
7464 page is not readable.
7465
7466 none Vsyscalls don't work at all. This makes
7467 them quite hard to use for exploits but
7468 might break your system.
7469
7470 vt.color= [VT] Default text color.
7471 Format: 0xYX, X = foreground, Y = background.
7472 Default: 0x07 = light gray on black.
7473
7474 vt.cur_default= [VT] Default cursor shape.
7475 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7476 the parameters of the <Esc>[?A;B;Cc escape sequence;
7477 see VGA-softcursor.txt. Default: 2 = underline.
7478
7479 vt.default_blu= [VT]
7480 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7481 Change the default blue palette of the console.
7482 This is a 16-member array composed of values
7483 ranging from 0-255.
7484
7485 vt.default_grn= [VT]
7486 Format: <green0>,<green1>,<green2>,...,<green15>
7487 Change the default green palette of the console.
7488 This is a 16-member array composed of values
7489 ranging from 0-255.
7490
7491 vt.default_red= [VT]
7492 Format: <red0>,<red1>,<red2>,...,<red15>
7493 Change the default red palette of the console.
7494 This is a 16-member array composed of values
7495 ranging from 0-255.
7496
7497 vt.default_utf8=
7498 [VT]
7499 Format=<0|1>
7500 Set system-wide default UTF-8 mode for all tty's.
7501 Default is 1, i.e. UTF-8 mode is enabled for all
7502 newly opened terminals.
7503
7504 vt.global_cursor_default=
7505 [VT]
7506 Format=<-1|0|1>
7507 Set system-wide default for whether a cursor
7508 is shown on new VTs. Default is -1,
7509 i.e. cursors will be created by default unless
7510 overridden by individual drivers. 0 will hide
7511 cursors, 1 will display them.
7512
7513 vt.italic= [VT] Default color for italic text; 0-15.
7514 Default: 2 = green.
7515
7516 vt.underline= [VT] Default color for underlined text; 0-15.
7517 Default: 3 = cyan.
7518
7519 watchdog timers [HW,WDT] For information on watchdog timers,
7520 see Documentation/watchdog/watchdog-parameters.rst
7521 or other driver-specific files in the
7522 Documentation/watchdog/ directory.
7523
7524 watchdog_thresh=
7525 [KNL]
7526 Set the hard lockup detector stall duration
7527 threshold in seconds. The soft lockup detector
7528 threshold is set to twice the value. A value of 0
7529 disables both lockup detectors. Default is 10
7530 seconds.
7531
7532 workqueue.unbound_cpus=
7533 [KNL,SMP] Specify to constrain one or some CPUs
7534 to use in unbound workqueues.
7535 Format: <cpu-list>
7536 By default, all online CPUs are available for
7537 unbound workqueues.
7538
7539 workqueue.watchdog_thresh=
7540 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7541 warn stall conditions and dump internal state to
7542 help debugging. 0 disables workqueue stall
7543 detection; otherwise, it's the stall threshold
7544 duration in seconds. The default value is 30 and
7545 it can be updated at runtime by writing to the
7546 corresponding sysfs file.
7547
7548 workqueue.panic_on_stall=<uint>
7549 Panic when workqueue stall is detected by
7550 CONFIG_WQ_WATCHDOG. It sets the number times of the
7551 stall to trigger panic.
7552
7553 The default is 0, which disables the panic on stall.
7554
7555 workqueue.cpu_intensive_thresh_us=
7556 Per-cpu work items which run for longer than this
7557 threshold are automatically considered CPU intensive
7558 and excluded from concurrency management to prevent
7559 them from noticeably delaying other per-cpu work
7560 items. Default is 10000 (10ms).
7561
7562 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7563 will report the work functions which violate this
7564 threshold repeatedly. They are likely good
7565 candidates for using WQ_UNBOUND workqueues instead.
7566
7567 workqueue.cpu_intensive_warning_thresh=<uint>
7568 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7569 will report the work functions which violate the
7570 intensive_threshold_us repeatedly. In order to prevent
7571 spurious warnings, start printing only after a work
7572 function has violated this threshold number of times.
7573
7574 The default is 4 times. 0 disables the warning.
7575
7576 workqueue.power_efficient
7577 Per-cpu workqueues are generally preferred because
7578 they show better performance thanks to cache
7579 locality; unfortunately, per-cpu workqueues tend to
7580 be more power hungry than unbound workqueues.
7581
7582 Enabling this makes the per-cpu workqueues which
7583 were observed to contribute significantly to power
7584 consumption unbound, leading to measurably lower
7585 power usage at the cost of small performance
7586 overhead.
7587
7588 The default value of this parameter is determined by
7589 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7590
7591 workqueue.default_affinity_scope=
7592 Select the default affinity scope to use for unbound
7593 workqueues. Can be one of "cpu", "smt", "cache",
7594 "numa" and "system". Default is "cache". For more
7595 information, see the Affinity Scopes section in
7596 Documentation/core-api/workqueue.rst.
7597
7598 This can be changed after boot by writing to the
7599 matching /sys/module/workqueue/parameters file. All
7600 workqueues with the "default" affinity scope will be
7601 updated accordingly.
7602
7603 workqueue.debug_force_rr_cpu
7604 Workqueue used to implicitly guarantee that work
7605 items queued without explicit CPU specified are put
7606 on the local CPU. This guarantee is no longer true
7607 and while local CPU is still preferred work items
7608 may be put on foreign CPUs. This debug option
7609 forces round-robin CPU selection to flush out
7610 usages which depend on the now broken guarantee.
7611 When enabled, memory and cache locality will be
7612 impacted.
7613
7614 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
7615 Type) of ioremap_wc().
7616
7617 on - Enable writecombine, use WUC for ioremap_wc()
7618 off - Disable writecombine, use SUC for ioremap_wc()
7619
7620 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
7621 default x2apic cluster mode on platforms
7622 supporting x2apic.
7623
7624 xen_512gb_limit [KNL,X86-64,XEN]
7625 Restricts the kernel running paravirtualized under Xen
7626 to use only up to 512 GB of RAM. The reason to do so is
7627 crash analysis tools and Xen tools for doing domain
7628 save/restore/migration must be enabled to handle larger
7629 domains.
7630
7631 xen_emul_unplug= [HW,X86,XEN,EARLY]
7632 Unplug Xen emulated devices
7633 Format: [unplug0,][unplug1]
7634 ide-disks -- unplug primary master IDE devices
7635 aux-ide-disks -- unplug non-primary-master IDE devices
7636 nics -- unplug network devices
7637 all -- unplug all emulated devices (NICs and IDE disks)
7638 unnecessary -- unplugging emulated devices is
7639 unnecessary even if the host did not respond to
7640 the unplug protocol
7641 never -- do not unplug even if version check succeeds
7642
7643 xen_legacy_crash [X86,XEN,EARLY]
7644 Crash from Xen panic notifier, without executing late
7645 panic() code such as dumping handler.
7646
7647 xen_mc_debug [X86,XEN,EARLY]
7648 Enable multicall debugging when running as a Xen PV guest.
7649 Enabling this feature will reduce performance a little
7650 bit, so it should only be enabled for obtaining extended
7651 debug data in case of multicall errors.
7652
7653 xen_msr_safe= [X86,XEN,EARLY]
7654 Format: <bool>
7655 Select whether to always use non-faulting (safe) MSR
7656 access functions when running as Xen PV guest. The
7657 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7658
7659 xen_nopv [X86]
7660 Disables the PV optimizations forcing the HVM guest to
7661 run as generic HVM guest with no PV drivers.
7662 This option is obsoleted by the "nopv" option, which
7663 has equivalent effect for XEN platform.
7664
7665 xen_no_vector_callback
7666 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
7667 event channel interrupts.
7668
7669 xen_scrub_pages= [XEN]
7670 Boolean option to control scrubbing pages before giving them back
7671 to Xen, for use by other domains. Can be also changed at runtime
7672 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7673 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7674
7675 xen_timer_slop= [X86-64,XEN,EARLY]
7676 Set the timer slop (in nanoseconds) for the virtual Xen
7677 timers (default is 100000). This adjusts the minimum
7678 delta of virtualized Xen timers, where lower values
7679 improve timer resolution at the expense of processing
7680 more timer interrupts.
7681
7682 xen.balloon_boot_timeout= [XEN]
7683 The time (in seconds) to wait before giving up to boot
7684 in case initial ballooning fails to free enough memory.
7685 Applies only when running as HVM or PVH guest and
7686 started with less memory configured than allowed at
7687 max. Default is 180.
7688
7689 xen.event_eoi_delay= [XEN]
7690 How long to delay EOI handling in case of event
7691 storms (jiffies). Default is 10.
7692
7693 xen.event_loop_timeout= [XEN]
7694 After which time (jiffies) the event handling loop
7695 should start to delay EOI handling. Default is 2.
7696
7697 xen.fifo_events= [XEN]
7698 Boolean parameter to disable using fifo event handling
7699 even if available. Normally fifo event handling is
7700 preferred over the 2-level event handling, as it is
7701 fairer and the number of possible event channels is
7702 much higher. Default is on (use fifo events).
7703
7704 xirc2ps_cs= [NET,PCMCIA]
7705 Format:
7706 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7707
7708 xive= [PPC]
7709 By default on POWER9 and above, the kernel will
7710 natively use the XIVE interrupt controller. This option
7711 allows the fallback firmware mode to be used:
7712
7713 off Fallback to firmware control of XIVE interrupt
7714 controller on both pseries and powernv
7715 platforms. Only useful on POWER9 and above.
7716
7717 xive.store-eoi=off [PPC]
7718 By default on POWER10 and above, the kernel will use
7719 stores for EOI handling when the XIVE interrupt mode
7720 is active. This option allows the XIVE driver to use
7721 loads instead, as on POWER9.
7722
7723 xhci-hcd.quirks [USB,KNL]
7724 A hex value specifying bitmask with supplemental xhci
7725 host controller quirks. Meaning of each bit can be
7726 consulted in header drivers/usb/host/xhci.h.
7727
7728 xmon [PPC,EARLY]
7729 Format: { early | on | rw | ro | off }
7730 Controls if xmon debugger is enabled. Default is off.
7731 Passing only "xmon" is equivalent to "xmon=early".
7732 early Call xmon as early as possible on boot; xmon
7733 debugger is called from setup_arch().
7734 on xmon debugger hooks will be installed so xmon
7735 is only called on a kernel crash. Default mode,
7736 i.e. either "ro" or "rw" mode, is controlled
7737 with CONFIG_XMON_DEFAULT_RO_MODE.
7738 rw xmon debugger hooks will be installed so xmon
7739 is called only on a kernel crash, mode is write,
7740 meaning SPR registers, memory and, other data
7741 can be written using xmon commands.
7742 ro same as "rw" option above but SPR registers,
7743 memory, and other data can't be written using
7744 xmon commands.
7745 off xmon is disabled.