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1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
4 copy_dsdt }
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
14 are available
15
16 See also Documentation/power/runtime_pm.rst, pci=noacpi
17
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
23
24 acpi_backlight= [HW,ACPI]
25 { vendor | video | native | none }
26 If set to vendor, prefer vendor-specific driver
27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
28 of the ACPI video.ko driver.
29 If set to video, use the ACPI video.ko driver.
30 If set to native, use the device's native backlight mode.
31 If set to none, disable the ACPI backlight interface.
32
33 acpi_force_32bit_fadt_addr
34 force FADT to use 32 bit addresses rather than the
35 64 bit X_* addresses. Some firmware have broken 64
36 bit addresses for force ACPI ignore these and use
37 the older legacy 32 bit addresses.
38
39 acpica_no_return_repair [HW, ACPI]
40 Disable AML predefined validation mechanism
41 This mechanism can repair the evaluation result to make
42 the return objects more ACPI specification compliant.
43 This option is useful for developers to identify the
44 root cause of an AML interpreter issue when the issue
45 has something to do with the repair mechanism.
46
47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
49 Format: <int>
50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
51 debug output. Bits in debug_layer correspond to a
52 _COMPONENT in an ACPI source file, e.g.,
53 #define _COMPONENT ACPI_EVENTS
54 Bits in debug_level correspond to a level in
55 ACPI_DEBUG_PRINT statements, e.g.,
56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
57 The debug_level mask defaults to "info". See
58 Documentation/firmware-guide/acpi/debug.rst for more information about
59 debug layers and levels.
60
61 Enable processor driver info messages:
62 acpi.debug_layer=0x20000000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
68
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
72
73 acpi_enforce_resources= [ACPI]
74 { strict | lax | no }
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
88
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
92 size limitation.
93
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
97
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
101
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
104
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
106 use by PCI
107 Format: <irq>,<irq>...
108
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
113 the GPE dispatcher.
114 This facility can be used to prevent such uncontrolled
115 GPE floodings.
116 Format: <byte> or <bitmap-list>
117
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
125
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
127 kernels.
128
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
138
139 acpi_no_watchdog [HW,ACPI,WDT]
140 Ignore the ACPI-based watchdog interface (WDAT) and let
141 a native driver control the watchdog device instead.
142
143 acpi_rsdp= [ACPI,EFI,KEXEC]
144 Pass the RSDP address to the kernel, mostly used
145 on machines running EFI runtime service to boot the
146 second kernel for kdump.
147
148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
149 Format: To spoof as Windows 98: ="Microsoft Windows"
150
151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
152 of 2 which is mandated by ACPI 6) as the supported ACPI
153 specification revision (when using this switch, it may
154 be necessary to carry out a cold reboot _twice_ in a
155 row to make it take effect on the platform firmware).
156
157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
158 acpi_osi="string1" # add string1
159 acpi_osi="!string2" # remove string2
160 acpi_osi=!* # remove all strings
161 acpi_osi=! # disable all built-in OS vendor
162 strings
163 acpi_osi=!! # enable all built-in OS vendor
164 strings
165 acpi_osi= # disable all strings
166
167 'acpi_osi=!' can be used in combination with single or
168 multiple 'acpi_osi="string1"' to support specific OS
169 vendor string(s). Note that such command can only
170 affect the default state of the OS vendor strings, thus
171 it cannot affect the default state of the feature group
172 strings and the current state of the OS vendor strings,
173 specifying it multiple times through kernel command line
174 is meaningless. This command is useful when one do not
175 care about the state of the feature group strings which
176 should be controlled by the OSPM.
177 Examples:
178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
180 can make '_OSI("Windows 2000")' TRUE.
181
182 'acpi_osi=' cannot be used in combination with other
183 'acpi_osi=' command lines, the _OSI method will not
184 exist in the ACPI namespace. NOTE that such command can
185 only affect the _OSI support state, thus specifying it
186 multiple times through kernel command line is also
187 meaningless.
188 Examples:
189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
190 FALSE.
191
192 'acpi_osi=!*' can be used in combination with single or
193 multiple 'acpi_osi="string1"' to support specific
194 string(s). Note that such command can affect the
195 current state of both the OS vendor strings and the
196 feature group strings, thus specifying it multiple times
197 through kernel command line is meaningful. But it may
198 still not able to affect the final state of a string if
199 there are quirks related to this string. This command
200 is useful when one want to control the state of the
201 feature group strings to debug BIOS issues related to
202 the OSPM features.
203 Examples:
204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
205 '_OSI("Module Device")' FALSE.
206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
207 '_OSI("Module Device")' TRUE.
208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
209 equivalent to
210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
211 and
212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
213 they all will make '_OSI("Windows 2000")' TRUE.
214
215 acpi_pm_good [X86]
216 Override the pmtimer bug detection: force the kernel
217 to assume that this machine's pmtimer latches its value
218 and always returns good values.
219
220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
221 Format: { level | edge | high | low }
222
223 acpi_skip_timer_override [HW,ACPI]
224 Recognize and ignore IRQ0/pin2 Interrupt Override.
225 For broken nForce2 BIOS resulting in XT-PIC timer.
226
227 acpi_sleep= [HW,ACPI] Sleep options
228 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
229 old_ordering, nonvs, sci_force_enable, nobl }
230 See Documentation/power/video.rst for information on
231 s3_bios and s3_mode.
232 s3_beep is for debugging; it makes the PC's speaker beep
233 as soon as the kernel's real-mode entry point is called.
234 s4_nohwsig prevents ACPI hardware signature from being
235 used during resume from hibernation.
236 old_ordering causes the ACPI 1.0 ordering of the _PTS
237 control method, with respect to putting devices into
238 low power states, to be enforced (the ACPI 2.0 ordering
239 of _PTS is used by default).
240 nonvs prevents the kernel from saving/restoring the
241 ACPI NVS memory during suspend/hibernation and resume.
242 sci_force_enable causes the kernel to set SCI_EN directly
243 on resume from S1/S3 (which is against the ACPI spec,
244 but some broken systems don't work without it).
245 nobl causes the internal blacklist of systems known to
246 behave incorrectly in some ways with respect to system
247 suspend and resume to be ignored (use wisely).
248
249 acpi_use_timer_override [HW,ACPI]
250 Use timer override. For some broken Nvidia NF5 boards
251 that require a timer override, but don't have HPET
252
253 add_efi_memmap [EFI; X86] Include EFI memory map in
254 kernel's map of available physical RAM.
255
256 agp= [AGP]
257 { off | try_unsupported }
258 off: disable AGP support
259 try_unsupported: try to drive unsupported chipsets
260 (may crash computer or cause data corruption)
261
262 ALSA [HW,ALSA]
263 See Documentation/sound/alsa-configuration.rst
264
265 alignment= [KNL,ARM]
266 Allow the default userspace alignment fault handler
267 behaviour to be specified. Bit 0 enables warnings,
268 bit 1 enables fixups, and bit 2 sends a segfault.
269
270 align_va_addr= [X86-64]
271 Align virtual addresses by clearing slice [14:12] when
272 allocating a VMA at process creation time. This option
273 gives you up to 3% performance improvement on AMD F15h
274 machines (where it is enabled by default) for a
275 CPU-intensive style benchmark, and it can vary highly in
276 a microbenchmark depending on workload and compiler.
277
278 32: only for 32-bit processes
279 64: only for 64-bit processes
280 on: enable for both 32- and 64-bit processes
281 off: disable for both 32- and 64-bit processes
282
283 alloc_snapshot [FTRACE]
284 Allocate the ftrace snapshot buffer on boot up when the
285 main buffer is allocated. This is handy if debugging
286 and you need to use tracing_snapshot() on boot up, and
287 do not want to use tracing_snapshot_alloc() as it needs
288 to be done where GFP_KERNEL allocations are allowed.
289
290 amd_iommu= [HW,X86-64]
291 Pass parameters to the AMD IOMMU driver in the system.
292 Possible values are:
293 fullflush - enable flushing of IO/TLB entries when
294 they are unmapped. Otherwise they are
295 flushed before they will be reused, which
296 is a lot of faster
297 off - do not initialize any AMD IOMMU found in
298 the system
299 force_isolation - Force device isolation for all
300 devices. The IOMMU driver is not
301 allowed anymore to lift isolation
302 requirements as needed. This option
303 does not override iommu=pt
304 force_enable - Force enable the IOMMU on platforms known
305 to be buggy with IOMMU enabled. Use this
306 option with care.
307
308 amd_iommu_dump= [HW,X86-64]
309 Enable AMD IOMMU driver option to dump the ACPI table
310 for AMD IOMMU. With this option enabled, AMD IOMMU
311 driver will print ACPI tables for AMD IOMMU during
312 IOMMU initialization.
313
314 amd_iommu_intr= [HW,X86-64]
315 Specifies one of the following AMD IOMMU interrupt
316 remapping modes:
317 legacy - Use legacy interrupt remapping mode.
318 vapic - Use virtual APIC mode, which allows IOMMU
319 to inject interrupts directly into guest.
320 This mode requires kvm-amd.avic=1.
321 (Default when IOMMU HW support is present.)
322
323 amijoy.map= [HW,JOY] Amiga joystick support
324 Map of devices attached to JOY0DAT and JOY1DAT
325 Format: <a>,<b>
326 See also Documentation/input/joydev/joystick.rst
327
328 analog.map= [HW,JOY] Analog joystick and gamepad support
329 Specifies type or capabilities of an analog joystick
330 connected to one of 16 gameports
331 Format: <type1>,<type2>,..<type16>
332
333 apc= [HW,SPARC]
334 Power management functions (SPARCstation-4/5 + deriv.)
335 Format: noidle
336 Disable APC CPU standby support. SPARCstation-Fox does
337 not play well with APC CPU idle - disable it if you have
338 APC and your system crashes randomly.
339
340 apic= [APIC,X86] Advanced Programmable Interrupt Controller
341 Change the output verbosity while booting
342 Format: { quiet (default) | verbose | debug }
343 Change the amount of debugging information output
344 when initialising the APIC and IO-APIC components.
345 For X86-32, this can also be used to specify an APIC
346 driver name.
347 Format: apic=driver_name
348 Examples: apic=bigsmp
349
350 apic_extnmi= [APIC,X86] External NMI delivery setting
351 Format: { bsp (default) | all | none }
352 bsp: External NMI is delivered only to CPU 0
353 all: External NMIs are broadcast to all CPUs as a
354 backup of CPU 0
355 none: External NMI is masked for all CPUs. This is
356 useful so that a dump capture kernel won't be
357 shot down by NMI
358
359 autoconf= [IPV6]
360 See Documentation/networking/ipv6.rst.
361
362 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
363 Limit apic dumping. The parameter defines the maximal
364 number of local apics being dumped. Also it is possible
365 to set it to "all" by meaning -- no limit here.
366 Format: { 1 (default) | 2 | ... | all }.
367 The parameter valid if only apic=debug or
368 apic=verbose is specified.
369 Example: apic=debug show_lapic=all
370
371 apm= [APM] Advanced Power Management
372 See header of arch/x86/kernel/apm_32.c.
373
374 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
375 Format: <io>,<irq>,<nodeID>
376
377 arm64.nobti [ARM64] Unconditionally disable Branch Target
378 Identification support
379
380 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
381 support
382
383 ataflop= [HW,M68k]
384
385 atarimouse= [HW,MOUSE] Atari Mouse
386
387 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
388 EzKey and similar keyboards
389
390 atkbd.reset= [HW] Reset keyboard during initialization
391
392 atkbd.set= [HW] Select keyboard code set
393 Format: <int> (2 = AT (default), 3 = PS/2)
394
395 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
396 keyboards
397
398 atkbd.softraw= [HW] Choose between synthetic and real raw mode
399 Format: <bool> (0 = real, 1 = synthetic (default))
400
401 atkbd.softrepeat= [HW]
402 Use software keyboard repeat
403
404 audit= [KNL] Enable the audit sub-system
405 Format: { "0" | "1" | "off" | "on" }
406 0 | off - kernel audit is disabled and can not be
407 enabled until the next reboot
408 unset - kernel audit is initialized but disabled and
409 will be fully enabled by the userspace auditd.
410 1 | on - kernel audit is initialized and partially
411 enabled, storing at most audit_backlog_limit
412 messages in RAM until it is fully enabled by the
413 userspace auditd.
414 Default: unset
415
416 audit_backlog_limit= [KNL] Set the audit queue size limit.
417 Format: <int> (must be >=0)
418 Default: 64
419
420 bau= [X86_UV] Enable the BAU on SGI UV. The default
421 behavior is to disable the BAU (i.e. bau=0).
422 Format: { "0" | "1" }
423 0 - Disable the BAU.
424 1 - Enable the BAU.
425 unset - Disable the BAU.
426
427 baycom_epp= [HW,AX25]
428 Format: <io>,<mode>
429
430 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
431 Format: <io>,<mode>
432 See header of drivers/net/hamradio/baycom_par.c.
433
434 baycom_ser_fdx= [HW,AX25]
435 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
436 Format: <io>,<irq>,<mode>[,<baud>]
437 See header of drivers/net/hamradio/baycom_ser_fdx.c.
438
439 baycom_ser_hdx= [HW,AX25]
440 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
441 Format: <io>,<irq>,<mode>
442 See header of drivers/net/hamradio/baycom_ser_hdx.c.
443
444 blkdevparts= Manual partition parsing of block device(s) for
445 embedded devices based on command line input.
446 See Documentation/block/cmdline-partition.rst
447
448 boot_delay= Milliseconds to delay each printk during boot.
449 Values larger than 10 seconds (10000) are changed to
450 no delay (0).
451 Format: integer
452
453 bootconfig [KNL]
454 Extended command line options can be added to an initrd
455 and this will cause the kernel to look for it.
456
457 See Documentation/admin-guide/bootconfig.rst
458
459 bert_disable [ACPI]
460 Disable BERT OS support on buggy BIOSes.
461
462 bgrt_disable [ACPI][X86]
463 Disable BGRT to avoid flickering OEM logo.
464
465 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
466 bttv.radio= Most important insmod options are available as
467 kernel args too.
468 bttv.pll= See Documentation/admin-guide/media/bttv.rst
469 bttv.tuner=
470
471 bulk_remove=off [PPC] This parameter disables the use of the pSeries
472 firmware feature for flushing multiple hpte entries
473 at a time.
474
475 c101= [NET] Moxa C101 synchronous serial card
476
477 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
478 Sometimes CPU hardware bugs make them report the cache
479 size incorrectly. The kernel will attempt work arounds
480 to fix known problems, but for some CPUs it is not
481 possible to determine what the correct size should be.
482 This option provides an override for these situations.
483
484 carrier_timeout=
485 [NET] Specifies amount of time (in seconds) that
486 the kernel should wait for a network carrier. By default
487 it waits 120 seconds.
488
489 ca_keys= [KEYS] This parameter identifies a specific key(s) on
490 the system trusted keyring to be used for certificate
491 trust validation.
492 format: { id:<keyid> | builtin }
493
494 cca= [MIPS] Override the kernel pages' cache coherency
495 algorithm. Accepted values range from 0 to 7
496 inclusive. See arch/mips/include/asm/pgtable-bits.h
497 for platform specific values (SB1, Loongson3 and
498 others).
499
500 ccw_timeout_log [S390]
501 See Documentation/s390/common_io.rst for details.
502
503 cgroup_disable= [KNL] Disable a particular controller or optional feature
504 Format: {name of the controller(s) or feature(s) to disable}
505 The effects of cgroup_disable=foo are:
506 - foo isn't auto-mounted if you mount all cgroups in
507 a single hierarchy
508 - foo isn't visible as an individually mountable
509 subsystem
510 - if foo is an optional feature then the feature is
511 disabled and corresponding cgroup files are not
512 created
513 {Currently only "memory" controller deal with this and
514 cut the overhead, others just disable the usage. So
515 only cgroup_disable=memory is actually worthy}
516 Specifying "pressure" disables per-cgroup pressure
517 stall information accounting feature
518
519 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
520 Format: { { controller | "all" | "named" }
521 [,{ controller | "all" | "named" }...] }
522 Like cgroup_disable, but only applies to cgroup v1;
523 the blacklisted controllers remain available in cgroup2.
524 "all" blacklists all controllers and "named" disables
525 named mounts. Specifying both "all" and "named" disables
526 all v1 hierarchies.
527
528 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
529 Format: <string>
530 nosocket -- Disable socket memory accounting.
531 nokmem -- Disable kernel memory accounting.
532
533 checkreqprot [SELINUX] Set initial checkreqprot flag value.
534 Format: { "0" | "1" }
535 See security/selinux/Kconfig help text.
536 0 -- check protection applied by kernel (includes
537 any implied execute protection).
538 1 -- check protection requested by application.
539 Default value is set via a kernel config option.
540 Value can be changed at runtime via
541 /sys/fs/selinux/checkreqprot.
542 Setting checkreqprot to 1 is deprecated.
543
544 cio_ignore= [S390]
545 See Documentation/s390/common_io.rst for details.
546 clk_ignore_unused
547 [CLK]
548 Prevents the clock framework from automatically gating
549 clocks that have not been explicitly enabled by a Linux
550 device driver but are enabled in hardware at reset or
551 by the bootloader/firmware. Note that this does not
552 force such clocks to be always-on nor does it reserve
553 those clocks in any way. This parameter is useful for
554 debug and development, but should not be needed on a
555 platform with proper driver support. For more
556 information, see Documentation/driver-api/clk.rst.
557
558 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
559 [Deprecated]
560 Forces specified clocksource (if available) to be used
561 when calculating gettimeofday(). If specified
562 clocksource is not available, it defaults to PIT.
563 Format: { pit | tsc | cyclone | pmtmr }
564
565 clocksource= Override the default clocksource
566 Format: <string>
567 Override the default clocksource and use the clocksource
568 with the name specified.
569 Some clocksource names to choose from, depending on
570 the platform:
571 [all] jiffies (this is the base, fallback clocksource)
572 [ACPI] acpi_pm
573 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
574 pxa_timer,timer3,32k_counter,timer0_1
575 [X86-32] pit,hpet,tsc;
576 scx200_hrt on Geode; cyclone on IBM x440
577 [MIPS] MIPS
578 [PARISC] cr16
579 [S390] tod
580 [SH] SuperH
581 [SPARC64] tick
582 [X86-64] hpet,tsc
583
584 clocksource.arm_arch_timer.evtstrm=
585 [ARM,ARM64]
586 Format: <bool>
587 Enable/disable the eventstream feature of the ARM
588 architected timer so that code using WFE-based polling
589 loops can be debugged more effectively on production
590 systems.
591
592 clocksource.max_cswd_read_retries= [KNL]
593 Number of clocksource_watchdog() retries due to
594 external delays before the clock will be marked
595 unstable. Defaults to three retries, that is,
596 four attempts to read the clock under test.
597
598 clocksource.verify_n_cpus= [KNL]
599 Limit the number of CPUs checked for clocksources
600 marked with CLOCK_SOURCE_VERIFY_PERCPU that
601 are marked unstable due to excessive skew.
602 A negative value says to check all CPUs, while
603 zero says not to check any. Values larger than
604 nr_cpu_ids are silently truncated to nr_cpu_ids.
605 The actual CPUs are chosen randomly, with
606 no replacement if the same CPU is chosen twice.
607
608 clocksource-wdtest.holdoff= [KNL]
609 Set the time in seconds that the clocksource
610 watchdog test waits before commencing its tests.
611 Defaults to zero when built as a module and to
612 10 seconds when built into the kernel.
613
614 clearcpuid=BITNUM[,BITNUM...] [X86]
615 Disable CPUID feature X for the kernel. See
616 arch/x86/include/asm/cpufeatures.h for the valid bit
617 numbers. Note the Linux specific bits are not necessarily
618 stable over kernel options, but the vendor specific
619 ones should be.
620 Also note that user programs calling CPUID directly
621 or using the feature without checking anything
622 will still see it. This just prevents it from
623 being used by the kernel or shown in /proc/cpuinfo.
624 Also note the kernel might malfunction if you disable
625 some critical bits.
626
627 cma=nn[MG]@[start[MG][-end[MG]]]
628 [KNL,CMA]
629 Sets the size of kernel global memory area for
630 contiguous memory allocations and optionally the
631 placement constraint by the physical address range of
632 memory allocations. A value of 0 disables CMA
633 altogether. For more information, see
634 kernel/dma/contiguous.c
635
636 cma_pernuma=nn[MG]
637 [ARM64,KNL,CMA]
638 Sets the size of kernel per-numa memory area for
639 contiguous memory allocations. A value of 0 disables
640 per-numa CMA altogether. And If this option is not
641 specificed, the default value is 0.
642 With per-numa CMA enabled, DMA users on node nid will
643 first try to allocate buffer from the pernuma area
644 which is located in node nid, if the allocation fails,
645 they will fallback to the global default memory area.
646
647 cmo_free_hint= [PPC] Format: { yes | no }
648 Specify whether pages are marked as being inactive
649 when they are freed. This is used in CMO environments
650 to determine OS memory pressure for page stealing by
651 a hypervisor.
652 Default: yes
653
654 coherent_pool=nn[KMG] [ARM,KNL]
655 Sets the size of memory pool for coherent, atomic dma
656 allocations, by default set to 256K.
657
658 com20020= [HW,NET] ARCnet - COM20020 chipset
659 Format:
660 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
661
662 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
663 Format: <io>[,<irq>]
664
665 com90xx= [HW,NET]
666 ARCnet - COM90xx chipset (memory-mapped buffers)
667 Format: <io>[,<irq>[,<memstart>]]
668
669 condev= [HW,S390] console device
670 conmode=
671
672 console= [KNL] Output console device and options.
673
674 tty<n> Use the virtual console device <n>.
675
676 ttyS<n>[,options]
677 ttyUSB0[,options]
678 Use the specified serial port. The options are of
679 the form "bbbbpnf", where "bbbb" is the baud rate,
680 "p" is parity ("n", "o", or "e"), "n" is number of
681 bits, and "f" is flow control ("r" for RTS or
682 omit it). Default is "9600n8".
683
684 See Documentation/admin-guide/serial-console.rst for more
685 information. See
686 Documentation/networking/netconsole.rst for an
687 alternative.
688
689 uart[8250],io,<addr>[,options]
690 uart[8250],mmio,<addr>[,options]
691 uart[8250],mmio16,<addr>[,options]
692 uart[8250],mmio32,<addr>[,options]
693 uart[8250],0x<addr>[,options]
694 Start an early, polled-mode console on the 8250/16550
695 UART at the specified I/O port or MMIO address,
696 switching to the matching ttyS device later.
697 MMIO inter-register address stride is either 8-bit
698 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
699 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
700 to be equivalent to 'mmio'. 'options' are specified in
701 the same format described for ttyS above; if unspecified,
702 the h/w is not re-initialized.
703
704 hvc<n> Use the hypervisor console device <n>. This is for
705 both Xen and PowerPC hypervisors.
706
707 If the device connected to the port is not a TTY but a braille
708 device, prepend "brl," before the device type, for instance
709 console=brl,ttyS0
710 For now, only VisioBraille is supported.
711
712 console_msg_format=
713 [KNL] Change console messages format
714 default
715 By default we print messages on consoles in
716 "[time stamp] text\n" format (time stamp may not be
717 printed, depending on CONFIG_PRINTK_TIME or
718 `printk_time' param).
719 syslog
720 Switch to syslog format: "<%u>[time stamp] text\n"
721 IOW, each message will have a facility and loglevel
722 prefix. The format is similar to one used by syslog()
723 syscall, or to executing "dmesg -S --raw" or to reading
724 from /proc/kmsg.
725
726 consoleblank= [KNL] The console blank (screen saver) timeout in
727 seconds. A value of 0 disables the blank timer.
728 Defaults to 0.
729
730 coredump_filter=
731 [KNL] Change the default value for
732 /proc/<pid>/coredump_filter.
733 See also Documentation/filesystems/proc.rst.
734
735 coresight_cpu_debug.enable
736 [ARM,ARM64]
737 Format: <bool>
738 Enable/disable the CPU sampling based debugging.
739 0: default value, disable debugging
740 1: enable debugging at boot time
741
742 cpuidle.off=1 [CPU_IDLE]
743 disable the cpuidle sub-system
744
745 cpuidle.governor=
746 [CPU_IDLE] Name of the cpuidle governor to use.
747
748 cpufreq.off=1 [CPU_FREQ]
749 disable the cpufreq sub-system
750
751 cpufreq.default_governor=
752 [CPU_FREQ] Name of the default cpufreq governor or
753 policy to use. This governor must be registered in the
754 kernel before the cpufreq driver probes.
755
756 cpu_init_udelay=N
757 [X86] Delay for N microsec between assert and de-assert
758 of APIC INIT to start processors. This delay occurs
759 on every CPU online, such as boot, and resume from suspend.
760 Default: 10000
761
762 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
763 Format:
764 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
765
766 crashkernel=size[KMG][@offset[KMG]]
767 [KNL] Using kexec, Linux can switch to a 'crash kernel'
768 upon panic. This parameter reserves the physical
769 memory region [offset, offset + size] for that kernel
770 image. If '@offset' is omitted, then a suitable offset
771 is selected automatically.
772 [KNL, X86-64] Select a region under 4G first, and
773 fall back to reserve region above 4G when '@offset'
774 hasn't been specified.
775 See Documentation/admin-guide/kdump/kdump.rst for further details.
776
777 crashkernel=range1:size1[,range2:size2,...][@offset]
778 [KNL] Same as above, but depends on the memory
779 in the running system. The syntax of range is
780 start-[end] where start and end are both
781 a memory unit (amount[KMG]). See also
782 Documentation/admin-guide/kdump/kdump.rst for an example.
783
784 crashkernel=size[KMG],high
785 [KNL, X86-64] range could be above 4G. Allow kernel
786 to allocate physical memory region from top, so could
787 be above 4G if system have more than 4G ram installed.
788 Otherwise memory region will be allocated below 4G, if
789 available.
790 It will be ignored if crashkernel=X is specified.
791 crashkernel=size[KMG],low
792 [KNL, X86-64] range under 4G. When crashkernel=X,high
793 is passed, kernel could allocate physical memory region
794 above 4G, that cause second kernel crash on system
795 that require some amount of low memory, e.g. swiotlb
796 requires at least 64M+32K low memory, also enough extra
797 low memory is needed to make sure DMA buffers for 32-bit
798 devices won't run out. Kernel would try to allocate at
799 at least 256M below 4G automatically.
800 This one let user to specify own low range under 4G
801 for second kernel instead.
802 0: to disable low allocation.
803 It will be ignored when crashkernel=X,high is not used
804 or memory reserved is below 4G.
805
806 cryptomgr.notests
807 [KNL] Disable crypto self-tests
808
809 cs89x0_dma= [HW,NET]
810 Format: <dma>
811
812 cs89x0_media= [HW,NET]
813 Format: { rj45 | aui | bnc }
814
815 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
816 handling. When switched on, additional debug data is
817 printed to the console in case a hanging CPU is
818 detected, and that CPU is pinged again in order to try
819 to resolve the hang situation.
820 0: disable csdlock debugging (default)
821 1: enable basic csdlock debugging (minor impact)
822 ext: enable extended csdlock debugging (more impact,
823 but more data)
824
825 dasd= [HW,NET]
826 See header of drivers/s390/block/dasd_devmap.c.
827
828 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
829 (one device per port)
830 Format: <port#>,<type>
831 See also Documentation/input/devices/joystick-parport.rst
832
833 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
834 time. See
835 Documentation/admin-guide/dynamic-debug-howto.rst for
836 details. Deprecated, see dyndbg.
837
838 debug [KNL] Enable kernel debugging (events log level).
839
840 debug_boot_weak_hash
841 [KNL] Enable printing [hashed] pointers early in the
842 boot sequence. If enabled, we use a weak hash instead
843 of siphash to hash pointers. Use this option if you are
844 seeing instances of '(___ptrval___)') and need to see a
845 value (hashed pointer) instead. Cryptographically
846 insecure, please do not use on production kernels.
847
848 debug_locks_verbose=
849 [KNL] verbose locking self-tests
850 Format: <int>
851 Print debugging info while doing the locking API
852 self-tests.
853 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
854 (no extra messages), setting it to -1 (all bits set)
855 will print _a_lot_ more information - normally only
856 useful to lockdep developers.
857
858 debug_objects [KNL] Enable object debugging
859
860 no_debug_objects
861 [KNL] Disable object debugging
862
863 debug_guardpage_minorder=
864 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
865 parameter allows control of the order of pages that will
866 be intentionally kept free (and hence protected) by the
867 buddy allocator. Bigger value increase the probability
868 of catching random memory corruption, but reduce the
869 amount of memory for normal system use. The maximum
870 possible value is MAX_ORDER/2. Setting this parameter
871 to 1 or 2 should be enough to identify most random
872 memory corruption problems caused by bugs in kernel or
873 driver code when a CPU writes to (or reads from) a
874 random memory location. Note that there exists a class
875 of memory corruptions problems caused by buggy H/W or
876 F/W or by drivers badly programing DMA (basically when
877 memory is written at bus level and the CPU MMU is
878 bypassed) which are not detectable by
879 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
880 tracking down these problems.
881
882 debug_pagealloc=
883 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
884 enables the feature at boot time. By default, it is
885 disabled and the system will work mostly the same as a
886 kernel built without CONFIG_DEBUG_PAGEALLOC.
887 Note: to get most of debug_pagealloc error reports, it's
888 useful to also enable the page_owner functionality.
889 on: enable the feature
890
891 debugfs= [KNL] This parameter enables what is exposed to userspace
892 and debugfs internal clients.
893 Format: { on, no-mount, off }
894 on: All functions are enabled.
895 no-mount:
896 Filesystem is not registered but kernel clients can
897 access APIs and a crashkernel can be used to read
898 its content. There is nothing to mount.
899 off: Filesystem is not registered and clients
900 get a -EPERM as result when trying to register files
901 or directories within debugfs.
902 This is equivalent of the runtime functionality if
903 debugfs was not enabled in the kernel at all.
904 Default value is set in build-time with a kernel configuration.
905
906 debugpat [X86] Enable PAT debugging
907
908 decnet.addr= [HW,NET]
909 Format: <area>[,<node>]
910 See also Documentation/networking/decnet.rst.
911
912 default_hugepagesz=
913 [HW] The size of the default HugeTLB page. This is
914 the size represented by the legacy /proc/ hugepages
915 APIs. In addition, this is the default hugetlb size
916 used for shmget(), mmap() and mounting hugetlbfs
917 filesystems. If not specified, defaults to the
918 architecture's default huge page size. Huge page
919 sizes are architecture dependent. See also
920 Documentation/admin-guide/mm/hugetlbpage.rst.
921 Format: size[KMG]
922
923 deferred_probe_timeout=
924 [KNL] Debugging option to set a timeout in seconds for
925 deferred probe to give up waiting on dependencies to
926 probe. Only specific dependencies (subsystems or
927 drivers) that have opted in will be ignored. A timeout of 0
928 will timeout at the end of initcalls. This option will also
929 dump out devices still on the deferred probe list after
930 retrying.
931
932 dfltcc= [HW,S390]
933 Format: { on | off | def_only | inf_only | always }
934 on: s390 zlib hardware support for compression on
935 level 1 and decompression (default)
936 off: No s390 zlib hardware support
937 def_only: s390 zlib hardware support for deflate
938 only (compression on level 1)
939 inf_only: s390 zlib hardware support for inflate
940 only (decompression)
941 always: Same as 'on' but ignores the selected compression
942 level always using hardware support (used for debugging)
943
944 dhash_entries= [KNL]
945 Set number of hash buckets for dentry cache.
946
947 disable_1tb_segments [PPC]
948 Disables the use of 1TB hash page table segments. This
949 causes the kernel to fall back to 256MB segments which
950 can be useful when debugging issues that require an SLB
951 miss to occur.
952
953 stress_slb [PPC]
954 Limits the number of kernel SLB entries, and flushes
955 them frequently to increase the rate of SLB faults
956 on kernel addresses.
957
958 disable= [IPV6]
959 See Documentation/networking/ipv6.rst.
960
961 hardened_usercopy=
962 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
963 hardening is enabled for this boot. Hardened
964 usercopy checking is used to protect the kernel
965 from reading or writing beyond known memory
966 allocation boundaries as a proactive defense
967 against bounds-checking flaws in the kernel's
968 copy_to_user()/copy_from_user() interface.
969 on Perform hardened usercopy checks (default).
970 off Disable hardened usercopy checks.
971
972 disable_radix [PPC]
973 Disable RADIX MMU mode on POWER9
974
975 radix_hcall_invalidate=on [PPC/PSERIES]
976 Disable RADIX GTSE feature and use hcall for TLB
977 invalidate.
978
979 disable_tlbie [PPC]
980 Disable TLBIE instruction. Currently does not work
981 with KVM, with HASH MMU, or with coherent accelerators.
982
983 disable_cpu_apicid= [X86,APIC,SMP]
984 Format: <int>
985 The number of initial APIC ID for the
986 corresponding CPU to be disabled at boot,
987 mostly used for the kdump 2nd kernel to
988 disable BSP to wake up multiple CPUs without
989 causing system reset or hang due to sending
990 INIT from AP to BSP.
991
992 disable_ddw [PPC/PSERIES]
993 Disable Dynamic DMA Window support. Use this
994 to workaround buggy firmware.
995
996 disable_ipv6= [IPV6]
997 See Documentation/networking/ipv6.rst.
998
999 disable_mtrr_cleanup [X86]
1000 The kernel tries to adjust MTRR layout from continuous
1001 to discrete, to make X server driver able to add WB
1002 entry later. This parameter disables that.
1003
1004 disable_mtrr_trim [X86, Intel and AMD only]
1005 By default the kernel will trim any uncacheable
1006 memory out of your available memory pool based on
1007 MTRR settings. This parameter disables that behavior,
1008 possibly causing your machine to run very slowly.
1009
1010 disable_timer_pin_1 [X86]
1011 Disable PIN 1 of APIC timer
1012 Can be useful to work around chipset bugs.
1013
1014 dis_ucode_ldr [X86] Disable the microcode loader.
1015
1016 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1017 this option disables the debugging code at boot.
1018
1019 dma_debug_entries=<number>
1020 This option allows to tune the number of preallocated
1021 entries for DMA-API debugging code. One entry is
1022 required per DMA-API allocation. Use this if the
1023 DMA-API debugging code disables itself because the
1024 architectural default is too low.
1025
1026 dma_debug_driver=<driver_name>
1027 With this option the DMA-API debugging driver
1028 filter feature can be enabled at boot time. Just
1029 pass the driver to filter for as the parameter.
1030 The filter can be disabled or changed to another
1031 driver later using sysfs.
1032
1033 driver_async_probe= [KNL]
1034 List of driver names to be probed asynchronously.
1035 Format: <driver_name1>,<driver_name2>...
1036
1037 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1038 Broken monitors, graphic adapters, KVMs and EDIDless
1039 panels may send no or incorrect EDID data sets.
1040 This parameter allows to specify an EDID data sets
1041 in the /lib/firmware directory that are used instead.
1042 Generic built-in EDID data sets are used, if one of
1043 edid/1024x768.bin, edid/1280x1024.bin,
1044 edid/1680x1050.bin, or edid/1920x1080.bin is given
1045 and no file with the same name exists. Details and
1046 instructions how to build your own EDID data are
1047 available in Documentation/admin-guide/edid.rst. An EDID
1048 data set will only be used for a particular connector,
1049 if its name and a colon are prepended to the EDID
1050 name. Each connector may use a unique EDID data
1051 set by separating the files with a comma. An EDID
1052 data set with no connector name will be used for
1053 any connectors not explicitly specified.
1054
1055 dscc4.setup= [NET]
1056
1057 dt_cpu_ftrs= [PPC]
1058 Format: {"off" | "known"}
1059 Control how the dt_cpu_ftrs device-tree binding is
1060 used for CPU feature discovery and setup (if it
1061 exists).
1062 off: Do not use it, fall back to legacy cpu table.
1063 known: Do not pass through unknown features to guests
1064 or userspace, only those that the kernel is aware of.
1065
1066 dump_apple_properties [X86]
1067 Dump name and content of EFI device properties on
1068 x86 Macs. Useful for driver authors to determine
1069 what data is available or for reverse-engineering.
1070
1071 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1072 <module>.dyndbg[="val"]
1073 Enable debug messages at boot time. See
1074 Documentation/admin-guide/dynamic-debug-howto.rst
1075 for details.
1076
1077 nopku [X86] Disable Memory Protection Keys CPU feature found
1078 in some Intel CPUs.
1079
1080 <module>.async_probe [KNL]
1081 Enable asynchronous probe on this module.
1082
1083 early_ioremap_debug [KNL]
1084 Enable debug messages in early_ioremap support. This
1085 is useful for tracking down temporary early mappings
1086 which are not unmapped.
1087
1088 earlycon= [KNL] Output early console device and options.
1089
1090 When used with no options, the early console is
1091 determined by stdout-path property in device tree's
1092 chosen node or the ACPI SPCR table if supported by
1093 the platform.
1094
1095 cdns,<addr>[,options]
1096 Start an early, polled-mode console on a Cadence
1097 (xuartps) serial port at the specified address. Only
1098 supported option is baud rate. If baud rate is not
1099 specified, the serial port must already be setup and
1100 configured.
1101
1102 uart[8250],io,<addr>[,options]
1103 uart[8250],mmio,<addr>[,options]
1104 uart[8250],mmio32,<addr>[,options]
1105 uart[8250],mmio32be,<addr>[,options]
1106 uart[8250],0x<addr>[,options]
1107 Start an early, polled-mode console on the 8250/16550
1108 UART at the specified I/O port or MMIO address.
1109 MMIO inter-register address stride is either 8-bit
1110 (mmio) or 32-bit (mmio32 or mmio32be).
1111 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1112 to be equivalent to 'mmio'. 'options' are specified
1113 in the same format described for "console=ttyS<n>"; if
1114 unspecified, the h/w is not initialized.
1115
1116 pl011,<addr>
1117 pl011,mmio32,<addr>
1118 Start an early, polled-mode console on a pl011 serial
1119 port at the specified address. The pl011 serial port
1120 must already be setup and configured. Options are not
1121 yet supported. If 'mmio32' is specified, then only
1122 the driver will use only 32-bit accessors to read/write
1123 the device registers.
1124
1125 liteuart,<addr>
1126 Start an early console on a litex serial port at the
1127 specified address. The serial port must already be
1128 setup and configured. Options are not yet supported.
1129
1130 meson,<addr>
1131 Start an early, polled-mode console on a meson serial
1132 port at the specified address. The serial port must
1133 already be setup and configured. Options are not yet
1134 supported.
1135
1136 msm_serial,<addr>
1137 Start an early, polled-mode console on an msm serial
1138 port at the specified address. The serial port
1139 must already be setup and configured. Options are not
1140 yet supported.
1141
1142 msm_serial_dm,<addr>
1143 Start an early, polled-mode console on an msm serial
1144 dm port at the specified address. The serial port
1145 must already be setup and configured. Options are not
1146 yet supported.
1147
1148 owl,<addr>
1149 Start an early, polled-mode console on a serial port
1150 of an Actions Semi SoC, such as S500 or S900, at the
1151 specified address. The serial port must already be
1152 setup and configured. Options are not yet supported.
1153
1154 rda,<addr>
1155 Start an early, polled-mode console on a serial port
1156 of an RDA Micro SoC, such as RDA8810PL, at the
1157 specified address. The serial port must already be
1158 setup and configured. Options are not yet supported.
1159
1160 sbi
1161 Use RISC-V SBI (Supervisor Binary Interface) for early
1162 console.
1163
1164 smh Use ARM semihosting calls for early console.
1165
1166 s3c2410,<addr>
1167 s3c2412,<addr>
1168 s3c2440,<addr>
1169 s3c6400,<addr>
1170 s5pv210,<addr>
1171 exynos4210,<addr>
1172 Use early console provided by serial driver available
1173 on Samsung SoCs, requires selecting proper type and
1174 a correct base address of the selected UART port. The
1175 serial port must already be setup and configured.
1176 Options are not yet supported.
1177
1178 lantiq,<addr>
1179 Start an early, polled-mode console on a lantiq serial
1180 (lqasc) port at the specified address. The serial port
1181 must already be setup and configured. Options are not
1182 yet supported.
1183
1184 lpuart,<addr>
1185 lpuart32,<addr>
1186 Use early console provided by Freescale LP UART driver
1187 found on Freescale Vybrid and QorIQ LS1021A processors.
1188 A valid base address must be provided, and the serial
1189 port must already be setup and configured.
1190
1191 ec_imx21,<addr>
1192 ec_imx6q,<addr>
1193 Start an early, polled-mode, output-only console on the
1194 Freescale i.MX UART at the specified address. The UART
1195 must already be setup and configured.
1196
1197 ar3700_uart,<addr>
1198 Start an early, polled-mode console on the
1199 Armada 3700 serial port at the specified
1200 address. The serial port must already be setup
1201 and configured. Options are not yet supported.
1202
1203 qcom_geni,<addr>
1204 Start an early, polled-mode console on a Qualcomm
1205 Generic Interface (GENI) based serial port at the
1206 specified address. The serial port must already be
1207 setup and configured. Options are not yet supported.
1208
1209 efifb,[options]
1210 Start an early, unaccelerated console on the EFI
1211 memory mapped framebuffer (if available). On cache
1212 coherent non-x86 systems that use system memory for
1213 the framebuffer, pass the 'ram' option so that it is
1214 mapped with the correct attributes.
1215
1216 linflex,<addr>
1217 Use early console provided by Freescale LINFlexD UART
1218 serial driver for NXP S32V234 SoCs. A valid base
1219 address must be provided, and the serial port must
1220 already be setup and configured.
1221
1222 earlyprintk= [X86,SH,ARM,M68k,S390]
1223 earlyprintk=vga
1224 earlyprintk=sclp
1225 earlyprintk=xen
1226 earlyprintk=serial[,ttySn[,baudrate]]
1227 earlyprintk=serial[,0x...[,baudrate]]
1228 earlyprintk=ttySn[,baudrate]
1229 earlyprintk=dbgp[debugController#]
1230 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1231 earlyprintk=xdbc[xhciController#]
1232
1233 earlyprintk is useful when the kernel crashes before
1234 the normal console is initialized. It is not enabled by
1235 default because it has some cosmetic problems.
1236
1237 Append ",keep" to not disable it when the real console
1238 takes over.
1239
1240 Only one of vga, efi, serial, or usb debug port can
1241 be used at a time.
1242
1243 Currently only ttyS0 and ttyS1 may be specified by
1244 name. Other I/O ports may be explicitly specified
1245 on some architectures (x86 and arm at least) by
1246 replacing ttySn with an I/O port address, like this:
1247 earlyprintk=serial,0x1008,115200
1248 You can find the port for a given device in
1249 /proc/tty/driver/serial:
1250 2: uart:ST16650V2 port:00001008 irq:18 ...
1251
1252 Interaction with the standard serial driver is not
1253 very good.
1254
1255 The VGA and EFI output is eventually overwritten by
1256 the real console.
1257
1258 The xen output can only be used by Xen PV guests.
1259
1260 The sclp output can only be used on s390.
1261
1262 The optional "force" to "pciserial" enables use of a
1263 PCI device even when its classcode is not of the
1264 UART class.
1265
1266 edac_report= [HW,EDAC] Control how to report EDAC event
1267 Format: {"on" | "off" | "force"}
1268 on: enable EDAC to report H/W event. May be overridden
1269 by other higher priority error reporting module.
1270 off: disable H/W event reporting through EDAC.
1271 force: enforce the use of EDAC to report H/W event.
1272 default: on.
1273
1274 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1275 ekgdboc=kbd
1276
1277 This is designed to be used in conjunction with
1278 the boot argument: earlyprintk=vga
1279
1280 This parameter works in place of the kgdboc parameter
1281 but can only be used if the backing tty is available
1282 very early in the boot process. For early debugging
1283 via a serial port see kgdboc_earlycon instead.
1284
1285 edd= [EDD]
1286 Format: {"off" | "on" | "skip[mbr]"}
1287
1288 efi= [EFI]
1289 Format: { "debug", "disable_early_pci_dma",
1290 "nochunk", "noruntime", "nosoftreserve",
1291 "novamap", "no_disable_early_pci_dma" }
1292 debug: enable misc debug output.
1293 disable_early_pci_dma: disable the busmaster bit on all
1294 PCI bridges while in the EFI boot stub.
1295 nochunk: disable reading files in "chunks" in the EFI
1296 boot stub, as chunking can cause problems with some
1297 firmware implementations.
1298 noruntime : disable EFI runtime services support
1299 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1300 attribute may cause the kernel to reserve the
1301 memory range for a memory mapping driver to
1302 claim. Specify efi=nosoftreserve to disable this
1303 reservation and treat the memory by its base type
1304 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1305 novamap: do not call SetVirtualAddressMap().
1306 no_disable_early_pci_dma: Leave the busmaster bit set
1307 on all PCI bridges while in the EFI boot stub
1308
1309 efi_no_storage_paranoia [EFI; X86]
1310 Using this parameter you can use more than 50% of
1311 your efi variable storage. Use this parameter only if
1312 you are really sure that your UEFI does sane gc and
1313 fulfills the spec otherwise your board may brick.
1314
1315 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1316 Add arbitrary attribute to specific memory range by
1317 updating original EFI memory map.
1318 Region of memory which aa attribute is added to is
1319 from ss to ss+nn.
1320
1321 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1322 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1323 attribute is added to range 0x100000000-0x180000000 and
1324 0x10a0000000-0x1120000000.
1325
1326 If efi_fake_mem=8G@9G:0x40000 is specified, the
1327 EFI_MEMORY_SP(0x40000) attribute is added to
1328 range 0x240000000-0x43fffffff.
1329
1330 Using this parameter you can do debugging of EFI memmap
1331 related features. For example, you can do debugging of
1332 Address Range Mirroring feature even if your box
1333 doesn't support it, or mark specific memory as
1334 "soft reserved".
1335
1336 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1337 that is to be dynamically loaded by Linux. If there are
1338 multiple variables with the same name but with different
1339 vendor GUIDs, all of them will be loaded. See
1340 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1341
1342
1343 eisa_irq_edge= [PARISC,HW]
1344 See header of drivers/parisc/eisa.c.
1345
1346 elanfreq= [X86-32]
1347 See comment before function elanfreq_setup() in
1348 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1349
1350 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1351 Specifies physical address of start of kernel core
1352 image elf header and optionally the size. Generally
1353 kexec loader will pass this option to capture kernel.
1354 See Documentation/admin-guide/kdump/kdump.rst for details.
1355
1356 enable_mtrr_cleanup [X86]
1357 The kernel tries to adjust MTRR layout from continuous
1358 to discrete, to make X server driver able to add WB
1359 entry later. This parameter enables that.
1360
1361 enable_timer_pin_1 [X86]
1362 Enable PIN 1 of APIC timer
1363 Can be useful to work around chipset bugs
1364 (in particular on some ATI chipsets).
1365 The kernel tries to set a reasonable default.
1366
1367 enforcing [SELINUX] Set initial enforcing status.
1368 Format: {"0" | "1"}
1369 See security/selinux/Kconfig help text.
1370 0 -- permissive (log only, no denials).
1371 1 -- enforcing (deny and log).
1372 Default value is 0.
1373 Value can be changed at runtime via
1374 /sys/fs/selinux/enforce.
1375
1376 erst_disable [ACPI]
1377 Disable Error Record Serialization Table (ERST)
1378 support.
1379
1380 ether= [HW,NET] Ethernet cards parameters
1381 This option is obsoleted by the "netdev=" option, which
1382 has equivalent usage. See its documentation for details.
1383
1384 evm= [EVM]
1385 Format: { "fix" }
1386 Permit 'security.evm' to be updated regardless of
1387 current integrity status.
1388
1389 failslab=
1390 fail_usercopy=
1391 fail_page_alloc=
1392 fail_make_request=[KNL]
1393 General fault injection mechanism.
1394 Format: <interval>,<probability>,<space>,<times>
1395 See also Documentation/fault-injection/.
1396
1397 fb_tunnels= [NET]
1398 Format: { initns | none }
1399 See Documentation/admin-guide/sysctl/net.rst for
1400 fb_tunnels_only_for_init_ns
1401
1402 floppy= [HW]
1403 See Documentation/admin-guide/blockdev/floppy.rst.
1404
1405 force_pal_cache_flush
1406 [IA-64] Avoid check_sal_cache_flush which may hang on
1407 buggy SAL_CACHE_FLUSH implementations. Using this
1408 parameter will force ia64_sal_cache_flush to call
1409 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1410
1411 forcepae [X86-32]
1412 Forcefully enable Physical Address Extension (PAE).
1413 Many Pentium M systems disable PAE but may have a
1414 functionally usable PAE implementation.
1415 Warning: use of this parameter will taint the kernel
1416 and may cause unknown problems.
1417
1418 ftrace=[tracer]
1419 [FTRACE] will set and start the specified tracer
1420 as early as possible in order to facilitate early
1421 boot debugging.
1422
1423 ftrace_dump_on_oops[=orig_cpu]
1424 [FTRACE] will dump the trace buffers on oops.
1425 If no parameter is passed, ftrace will dump
1426 buffers of all CPUs, but if you pass orig_cpu, it will
1427 dump only the buffer of the CPU that triggered the
1428 oops.
1429
1430 ftrace_filter=[function-list]
1431 [FTRACE] Limit the functions traced by the function
1432 tracer at boot up. function-list is a comma-separated
1433 list of functions. This list can be changed at run
1434 time by the set_ftrace_filter file in the debugfs
1435 tracing directory.
1436
1437 ftrace_notrace=[function-list]
1438 [FTRACE] Do not trace the functions specified in
1439 function-list. This list can be changed at run time
1440 by the set_ftrace_notrace file in the debugfs
1441 tracing directory.
1442
1443 ftrace_graph_filter=[function-list]
1444 [FTRACE] Limit the top level callers functions traced
1445 by the function graph tracer at boot up.
1446 function-list is a comma-separated list of functions
1447 that can be changed at run time by the
1448 set_graph_function file in the debugfs tracing directory.
1449
1450 ftrace_graph_notrace=[function-list]
1451 [FTRACE] Do not trace from the functions specified in
1452 function-list. This list is a comma-separated list of
1453 functions that can be changed at run time by the
1454 set_graph_notrace file in the debugfs tracing directory.
1455
1456 ftrace_graph_max_depth=<uint>
1457 [FTRACE] Used with the function graph tracer. This is
1458 the max depth it will trace into a function. This value
1459 can be changed at run time by the max_graph_depth file
1460 in the tracefs tracing directory. default: 0 (no limit)
1461
1462 fw_devlink= [KNL] Create device links between consumer and supplier
1463 devices by scanning the firmware to infer the
1464 consumer/supplier relationships. This feature is
1465 especially useful when drivers are loaded as modules as
1466 it ensures proper ordering of tasks like device probing
1467 (suppliers first, then consumers), supplier boot state
1468 clean up (only after all consumers have probed),
1469 suspend/resume & runtime PM (consumers first, then
1470 suppliers).
1471 Format: { off | permissive | on | rpm }
1472 off -- Don't create device links from firmware info.
1473 permissive -- Create device links from firmware info
1474 but use it only for ordering boot state clean
1475 up (sync_state() calls).
1476 on -- Create device links from firmware info and use it
1477 to enforce probe and suspend/resume ordering.
1478 rpm -- Like "on", but also use to order runtime PM.
1479
1480 fw_devlink.strict=<bool>
1481 [KNL] Treat all inferred dependencies as mandatory
1482 dependencies. This only applies for fw_devlink=on|rpm.
1483 Format: <bool>
1484
1485 gamecon.map[2|3]=
1486 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1487 support via parallel port (up to 5 devices per port)
1488 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1489 See also Documentation/input/devices/joystick-parport.rst
1490
1491 gamma= [HW,DRM]
1492
1493 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1494 Format: off | on
1495 default: on
1496
1497 gcov_persist= [GCOV] When non-zero (default), profiling data for
1498 kernel modules is saved and remains accessible via
1499 debugfs, even when the module is unloaded/reloaded.
1500 When zero, profiling data is discarded and associated
1501 debugfs files are removed at module unload time.
1502
1503 goldfish [X86] Enable the goldfish android emulator platform.
1504 Don't use this when you are not running on the
1505 android emulator
1506
1507 gpio-mockup.gpio_mockup_ranges
1508 [HW] Sets the ranges of gpiochip of for this device.
1509 Format: <start1>,<end1>,<start2>,<end2>...
1510 gpio-mockup.gpio_mockup_named_lines
1511 [HW] Let the driver know GPIO lines should be named.
1512
1513 gpt [EFI] Forces disk with valid GPT signature but
1514 invalid Protective MBR to be treated as GPT. If the
1515 primary GPT is corrupted, it enables the backup/alternate
1516 GPT to be used instead.
1517
1518 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1519 the "Enable 0" bit of the configuration register.
1520 Format: 0 | 1
1521 Default: 0
1522 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1523 the "Enable 0" bit of the configuration register.
1524 Format: 0 | 1
1525 Default: 0
1526 grcan.select= [HW] Select which physical interface to use.
1527 Format: 0 | 1
1528 Default: 0
1529 grcan.txsize= [HW] Sets the size of the tx buffer.
1530 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1531 Default: 1024
1532 grcan.rxsize= [HW] Sets the size of the rx buffer.
1533 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1534 Default: 1024
1535
1536 hardlockup_all_cpu_backtrace=
1537 [KNL] Should the hard-lockup detector generate
1538 backtraces on all cpus.
1539 Format: 0 | 1
1540
1541 hashdist= [KNL,NUMA] Large hashes allocated during boot
1542 are distributed across NUMA nodes. Defaults on
1543 for 64-bit NUMA, off otherwise.
1544 Format: 0 | 1 (for off | on)
1545
1546 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1547
1548 hd= [EIDE] (E)IDE hard drive subsystem geometry
1549 Format: <cyl>,<head>,<sect>
1550
1551 hest_disable [ACPI]
1552 Disable Hardware Error Source Table (HEST) support;
1553 corresponding firmware-first mode error processing
1554 logic will be disabled.
1555
1556 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1557 size of <nn>. This works even on boxes that have no
1558 highmem otherwise. This also works to reduce highmem
1559 size on bigger boxes.
1560
1561 highres= [KNL] Enable/disable high resolution timer mode.
1562 Valid parameters: "on", "off"
1563 Default: "on"
1564
1565 hlt [BUGS=ARM,SH]
1566
1567 hpet= [X86-32,HPET] option to control HPET usage
1568 Format: { enable (default) | disable | force |
1569 verbose }
1570 disable: disable HPET and use PIT instead
1571 force: allow force enabled of undocumented chips (ICH4,
1572 VIA, nVidia)
1573 verbose: show contents of HPET registers during setup
1574
1575 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1576 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1577
1578 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1579 of gigantic hugepages.
1580 Format: nn[KMGTPE]
1581
1582 Reserve a CMA area of given size and allocate gigantic
1583 hugepages using the CMA allocator. If enabled, the
1584 boot-time allocation of gigantic hugepages is skipped.
1585
1586 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1587 If this follows hugepagesz (below), it specifies
1588 the number of pages of hugepagesz to be allocated.
1589 If this is the first HugeTLB parameter on the command
1590 line, it specifies the number of pages to allocate for
1591 the default huge page size. See also
1592 Documentation/admin-guide/mm/hugetlbpage.rst.
1593 Format: <integer>
1594
1595 hugepagesz=
1596 [HW] The size of the HugeTLB pages. This is used in
1597 conjunction with hugepages (above) to allocate huge
1598 pages of a specific size at boot. The pair
1599 hugepagesz=X hugepages=Y can be specified once for
1600 each supported huge page size. Huge page sizes are
1601 architecture dependent. See also
1602 Documentation/admin-guide/mm/hugetlbpage.rst.
1603 Format: size[KMG]
1604
1605 hugetlb_free_vmemmap=
1606 [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
1607 enabled.
1608 Allows heavy hugetlb users to free up some more
1609 memory (6 * PAGE_SIZE for each 2MB hugetlb page).
1610 Format: { on | off (default) }
1611
1612 on: enable the feature
1613 off: disable the feature
1614
1615 Built with CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON=y,
1616 the default is on.
1617
1618 This is not compatible with memory_hotplug.memmap_on_memory.
1619 If both parameters are enabled, hugetlb_free_vmemmap takes
1620 precedence over memory_hotplug.memmap_on_memory.
1621
1622 hung_task_panic=
1623 [KNL] Should the hung task detector generate panics.
1624 Format: 0 | 1
1625
1626 A value of 1 instructs the kernel to panic when a
1627 hung task is detected. The default value is controlled
1628 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1629 option. The value selected by this boot parameter can
1630 be changed later by the kernel.hung_task_panic sysctl.
1631
1632 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1633 terminal devices. Valid values: 0..8
1634 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1635 If specified, z/VM IUCV HVC accepts connections
1636 from listed z/VM user IDs only.
1637
1638 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1639 which allow the hypervisor to 'idle' the
1640 guest on lock contention.
1641
1642 keep_bootcon [KNL]
1643 Do not unregister boot console at start. This is only
1644 useful for debugging when something happens in the window
1645 between unregistering the boot console and initializing
1646 the real console.
1647
1648 i2c_bus= [HW] Override the default board specific I2C bus speed
1649 or register an additional I2C bus that is not
1650 registered from board initialization code.
1651 Format:
1652 <bus_id>,<clkrate>
1653
1654 i8042.debug [HW] Toggle i8042 debug mode
1655 i8042.unmask_kbd_data
1656 [HW] Enable printing of interrupt data from the KBD port
1657 (disabled by default, and as a pre-condition
1658 requires that i8042.debug=1 be enabled)
1659 i8042.direct [HW] Put keyboard port into non-translated mode
1660 i8042.dumbkbd [HW] Pretend that controller can only read data from
1661 keyboard and cannot control its state
1662 (Don't attempt to blink the leds)
1663 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1664 i8042.nokbd [HW] Don't check/create keyboard port
1665 i8042.noloop [HW] Disable the AUX Loopback command while probing
1666 for the AUX port
1667 i8042.nomux [HW] Don't check presence of an active multiplexing
1668 controller
1669 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1670 controllers
1671 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1672 i8042.reset [HW] Reset the controller during init, cleanup and
1673 suspend-to-ram transitions, only during s2r
1674 transitions, or never reset
1675 Format: { 1 | Y | y | 0 | N | n }
1676 1, Y, y: always reset controller
1677 0, N, n: don't ever reset controller
1678 Default: only on s2r transitions on x86; most other
1679 architectures force reset to be always executed
1680 i8042.unlock [HW] Unlock (ignore) the keylock
1681 i8042.kbdreset [HW] Reset device connected to KBD port
1682
1683 i810= [HW,DRM]
1684
1685 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1686 indicates that the driver is running on unsupported
1687 hardware.
1688 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1689 does not match list of supported models.
1690 i8k.power_status
1691 [HW] Report power status in /proc/i8k
1692 (disabled by default)
1693 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1694 capability is set.
1695
1696 i915.invert_brightness=
1697 [DRM] Invert the sense of the variable that is used to
1698 set the brightness of the panel backlight. Normally a
1699 brightness value of 0 indicates backlight switched off,
1700 and the maximum of the brightness value sets the backlight
1701 to maximum brightness. If this parameter is set to 0
1702 (default) and the machine requires it, or this parameter
1703 is set to 1, a brightness value of 0 sets the backlight
1704 to maximum brightness, and the maximum of the brightness
1705 value switches the backlight off.
1706 -1 -- never invert brightness
1707 0 -- machine default
1708 1 -- force brightness inversion
1709
1710 icn= [HW,ISDN]
1711 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1712
1713 ide-core.nodma= [HW] (E)IDE subsystem
1714 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1715 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1716 .cdrom .chs .ignore_cable are additional options
1717 See Documentation/ide/ide.rst.
1718
1719 ide-generic.probe-mask= [HW] (E)IDE subsystem
1720 Format: <int>
1721 Probe mask for legacy ISA IDE ports. Depending on
1722 platform up to 6 ports are supported, enabled by
1723 setting corresponding bits in the mask to 1. The
1724 default value is 0x0, which has a special meaning.
1725 On systems that have PCI, it triggers scanning the
1726 PCI bus for the first and the second port, which
1727 are then probed. On systems without PCI the value
1728 of 0x0 enables probing the two first ports as if it
1729 was 0x3.
1730
1731 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1732 Claim all unknown PCI IDE storage controllers.
1733
1734 idle= [X86]
1735 Format: idle=poll, idle=halt, idle=nomwait
1736 Poll forces a polling idle loop that can slightly
1737 improve the performance of waking up a idle CPU, but
1738 will use a lot of power and make the system run hot.
1739 Not recommended.
1740 idle=halt: Halt is forced to be used for CPU idle.
1741 In such case C2/C3 won't be used again.
1742 idle=nomwait: Disable mwait for CPU C-states
1743
1744 idxd.sva= [HW]
1745 Format: <bool>
1746 Allow force disabling of Shared Virtual Memory (SVA)
1747 support for the idxd driver. By default it is set to
1748 true (1).
1749
1750 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1751 Format: { strict | legacy | 2008 | relaxed }
1752 Default: strict
1753
1754 Choose which programs will be accepted for execution
1755 based on the IEEE 754 NaN encoding(s) supported by
1756 the FPU and the NaN encoding requested with the value
1757 of an ELF file header flag individually set by each
1758 binary. Hardware implementations are permitted to
1759 support either or both of the legacy and the 2008 NaN
1760 encoding mode.
1761
1762 Available settings are as follows:
1763 strict accept binaries that request a NaN encoding
1764 supported by the FPU
1765 legacy only accept legacy-NaN binaries, if supported
1766 by the FPU
1767 2008 only accept 2008-NaN binaries, if supported
1768 by the FPU
1769 relaxed accept any binaries regardless of whether
1770 supported by the FPU
1771
1772 The FPU emulator is always able to support both NaN
1773 encodings, so if no FPU hardware is present or it has
1774 been disabled with 'nofpu', then the settings of
1775 'legacy' and '2008' strap the emulator accordingly,
1776 'relaxed' straps the emulator for both legacy-NaN and
1777 2008-NaN, whereas 'strict' enables legacy-NaN only on
1778 legacy processors and both NaN encodings on MIPS32 or
1779 MIPS64 CPUs.
1780
1781 The setting for ABS.fmt/NEG.fmt instruction execution
1782 mode generally follows that for the NaN encoding,
1783 except where unsupported by hardware.
1784
1785 ignore_loglevel [KNL]
1786 Ignore loglevel setting - this will print /all/
1787 kernel messages to the console. Useful for debugging.
1788 We also add it as printk module parameter, so users
1789 could change it dynamically, usually by
1790 /sys/module/printk/parameters/ignore_loglevel.
1791
1792 ignore_rlimit_data
1793 Ignore RLIMIT_DATA setting for data mappings,
1794 print warning at first misuse. Can be changed via
1795 /sys/module/kernel/parameters/ignore_rlimit_data.
1796
1797 ihash_entries= [KNL]
1798 Set number of hash buckets for inode cache.
1799
1800 ima_appraise= [IMA] appraise integrity measurements
1801 Format: { "off" | "enforce" | "fix" | "log" }
1802 default: "enforce"
1803
1804 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1805 The builtin appraise policy appraises all files
1806 owned by uid=0.
1807
1808 ima_canonical_fmt [IMA]
1809 Use the canonical format for the binary runtime
1810 measurements, instead of host native format.
1811
1812 ima_hash= [IMA]
1813 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1814 | sha512 | ... }
1815 default: "sha1"
1816
1817 The list of supported hash algorithms is defined
1818 in crypto/hash_info.h.
1819
1820 ima_policy= [IMA]
1821 The builtin policies to load during IMA setup.
1822 Format: "tcb | appraise_tcb | secure_boot |
1823 fail_securely | critical_data"
1824
1825 The "tcb" policy measures all programs exec'd, files
1826 mmap'd for exec, and all files opened with the read
1827 mode bit set by either the effective uid (euid=0) or
1828 uid=0.
1829
1830 The "appraise_tcb" policy appraises the integrity of
1831 all files owned by root.
1832
1833 The "secure_boot" policy appraises the integrity
1834 of files (eg. kexec kernel image, kernel modules,
1835 firmware, policy, etc) based on file signatures.
1836
1837 The "fail_securely" policy forces file signature
1838 verification failure also on privileged mounted
1839 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1840 flag.
1841
1842 The "critical_data" policy measures kernel integrity
1843 critical data.
1844
1845 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1846 Load a policy which meets the needs of the Trusted
1847 Computing Base. This means IMA will measure all
1848 programs exec'd, files mmap'd for exec, and all files
1849 opened for read by uid=0.
1850
1851 ima_template= [IMA]
1852 Select one of defined IMA measurements template formats.
1853 Formats: { "ima" | "ima-ng" | "ima-sig" }
1854 Default: "ima-ng"
1855
1856 ima_template_fmt=
1857 [IMA] Define a custom template format.
1858 Format: { "field1|...|fieldN" }
1859
1860 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1861 Format: <min_file_size>
1862 Set the minimal file size for using asynchronous hash.
1863 If left unspecified, ahash usage is disabled.
1864
1865 ahash performance varies for different data sizes on
1866 different crypto accelerators. This option can be used
1867 to achieve the best performance for a particular HW.
1868
1869 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1870 Format: <bufsize>
1871 Set hashing buffer size. Default: 4k.
1872
1873 ahash performance varies for different chunk sizes on
1874 different crypto accelerators. This option can be used
1875 to achieve best performance for particular HW.
1876
1877 init= [KNL]
1878 Format: <full_path>
1879 Run specified binary instead of /sbin/init as init
1880 process.
1881
1882 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1883 for working out where the kernel is dying during
1884 startup.
1885
1886 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1887 initcall functions. Useful for debugging built-in
1888 modules and initcalls.
1889
1890 initramfs_async= [KNL]
1891 Format: <bool>
1892 Default: 1
1893 This parameter controls whether the initramfs
1894 image is unpacked asynchronously, concurrently
1895 with devices being probed and
1896 initialized. This should normally just work,
1897 but as a debugging aid, one can get the
1898 historical behaviour of the initramfs
1899 unpacking being completed before device_ and
1900 late_ initcalls.
1901
1902 initrd= [BOOT] Specify the location of the initial ramdisk
1903
1904 initrdmem= [KNL] Specify a physical address and size from which to
1905 load the initrd. If an initrd is compiled in or
1906 specified in the bootparams, it takes priority over this
1907 setting.
1908 Format: ss[KMG],nn[KMG]
1909 Default is 0, 0
1910
1911 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1912 zeroes.
1913 Format: 0 | 1
1914 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1915
1916 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1917 Format: 0 | 1
1918 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1919
1920 init_pkru= [X86] Specify the default memory protection keys rights
1921 register contents for all processes. 0x55555554 by
1922 default (disallow access to all but pkey 0). Can
1923 override in debugfs after boot.
1924
1925 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1926 Format: <irq>
1927
1928 int_pln_enable [X86] Enable power limit notification interrupt
1929
1930 integrity_audit=[IMA]
1931 Format: { "0" | "1" }
1932 0 -- basic integrity auditing messages. (Default)
1933 1 -- additional integrity auditing messages.
1934
1935 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1936 on
1937 Enable intel iommu driver.
1938 off
1939 Disable intel iommu driver.
1940 igfx_off [Default Off]
1941 By default, gfx is mapped as normal device. If a gfx
1942 device has a dedicated DMAR unit, the DMAR unit is
1943 bypassed by not enabling DMAR with this option. In
1944 this case, gfx device will use physical address for
1945 DMA.
1946 strict [Default Off]
1947 With this option on every unmap_single operation will
1948 result in a hardware IOTLB flush operation as opposed
1949 to batching them for performance.
1950 sp_off [Default Off]
1951 By default, super page will be supported if Intel IOMMU
1952 has the capability. With this option, super page will
1953 not be supported.
1954 sm_on [Default Off]
1955 By default, scalable mode will be disabled even if the
1956 hardware advertises that it has support for the scalable
1957 mode translation. With this option set, scalable mode
1958 will be used on hardware which claims to support it.
1959 tboot_noforce [Default Off]
1960 Do not force the Intel IOMMU enabled under tboot.
1961 By default, tboot will force Intel IOMMU on, which
1962 could harm performance of some high-throughput
1963 devices like 40GBit network cards, even if identity
1964 mapping is enabled.
1965 Note that using this option lowers the security
1966 provided by tboot because it makes the system
1967 vulnerable to DMA attacks.
1968
1969 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1970 0 disables intel_idle and fall back on acpi_idle.
1971 1 to 9 specify maximum depth of C-state.
1972
1973 intel_pstate= [X86]
1974 disable
1975 Do not enable intel_pstate as the default
1976 scaling driver for the supported processors
1977 passive
1978 Use intel_pstate as a scaling driver, but configure it
1979 to work with generic cpufreq governors (instead of
1980 enabling its internal governor). This mode cannot be
1981 used along with the hardware-managed P-states (HWP)
1982 feature.
1983 force
1984 Enable intel_pstate on systems that prohibit it by default
1985 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1986 instead of acpi-cpufreq may disable platform features, such
1987 as thermal controls and power capping, that rely on ACPI
1988 P-States information being indicated to OSPM and therefore
1989 should be used with caution. This option does not work with
1990 processors that aren't supported by the intel_pstate driver
1991 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1992 no_hwp
1993 Do not enable hardware P state control (HWP)
1994 if available.
1995 hwp_only
1996 Only load intel_pstate on systems which support
1997 hardware P state control (HWP) if available.
1998 support_acpi_ppc
1999 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2000 Description Table, specifies preferred power management
2001 profile as "Enterprise Server" or "Performance Server",
2002 then this feature is turned on by default.
2003 per_cpu_perf_limits
2004 Allow per-logical-CPU P-State performance control limits using
2005 cpufreq sysfs interface
2006
2007 intremap= [X86-64, Intel-IOMMU]
2008 on enable Interrupt Remapping (default)
2009 off disable Interrupt Remapping
2010 nosid disable Source ID checking
2011 no_x2apic_optout
2012 BIOS x2APIC opt-out request will be ignored
2013 nopost disable Interrupt Posting
2014
2015 iomem= Disable strict checking of access to MMIO memory
2016 strict regions from userspace.
2017 relaxed
2018
2019 iommu= [X86]
2020 off
2021 force
2022 noforce
2023 biomerge
2024 panic
2025 nopanic
2026 merge
2027 nomerge
2028 soft
2029 pt [X86]
2030 nopt [X86]
2031 nobypass [PPC/POWERNV]
2032 Disable IOMMU bypass, using IOMMU for PCI devices.
2033
2034 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2035 Format: { "0" | "1" }
2036 0 - Try to allocate a 32-bit DMA address first, before
2037 falling back to the full range if needed.
2038 1 - Allocate directly from the full usable range,
2039 forcing Dual Address Cycle for PCI cards supporting
2040 greater than 32-bit addressing.
2041
2042 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2043 Format: { "0" | "1" }
2044 0 - Lazy mode.
2045 Request that DMA unmap operations use deferred
2046 invalidation of hardware TLBs, for increased
2047 throughput at the cost of reduced device isolation.
2048 Will fall back to strict mode if not supported by
2049 the relevant IOMMU driver.
2050 1 - Strict mode (default).
2051 DMA unmap operations invalidate IOMMU hardware TLBs
2052 synchronously.
2053 Note: on x86, the default behaviour depends on the
2054 equivalent driver-specific parameters, but a strict
2055 mode explicitly specified by either method takes
2056 precedence.
2057
2058 iommu.passthrough=
2059 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2060 Format: { "0" | "1" }
2061 0 - Use IOMMU translation for DMA.
2062 1 - Bypass the IOMMU for DMA.
2063 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2064
2065 io7= [HW] IO7 for Marvel-based Alpha systems
2066 See comment before marvel_specify_io7 in
2067 arch/alpha/kernel/core_marvel.c.
2068
2069 io_delay= [X86] I/O delay method
2070 0x80
2071 Standard port 0x80 based delay
2072 0xed
2073 Alternate port 0xed based delay (needed on some systems)
2074 udelay
2075 Simple two microseconds delay
2076 none
2077 No delay
2078
2079 ip= [IP_PNP]
2080 See Documentation/admin-guide/nfs/nfsroot.rst.
2081
2082 ipcmni_extend [KNL] Extend the maximum number of unique System V
2083 IPC identifiers from 32,768 to 16,777,216.
2084
2085 irqaffinity= [SMP] Set the default irq affinity mask
2086 The argument is a cpu list, as described above.
2087
2088 irqchip.gicv2_force_probe=
2089 [ARM, ARM64]
2090 Format: <bool>
2091 Force the kernel to look for the second 4kB page
2092 of a GICv2 controller even if the memory range
2093 exposed by the device tree is too small.
2094
2095 irqchip.gicv3_nolpi=
2096 [ARM, ARM64]
2097 Force the kernel to ignore the availability of
2098 LPIs (and by consequence ITSs). Intended for system
2099 that use the kernel as a bootloader, and thus want
2100 to let secondary kernels in charge of setting up
2101 LPIs.
2102
2103 irqchip.gicv3_pseudo_nmi= [ARM64]
2104 Enables support for pseudo-NMIs in the kernel. This
2105 requires the kernel to be built with
2106 CONFIG_ARM64_PSEUDO_NMI.
2107
2108 irqfixup [HW]
2109 When an interrupt is not handled search all handlers
2110 for it. Intended to get systems with badly broken
2111 firmware running.
2112
2113 irqpoll [HW]
2114 When an interrupt is not handled search all handlers
2115 for it. Also check all handlers each timer
2116 interrupt. Intended to get systems with badly broken
2117 firmware running.
2118
2119 isapnp= [ISAPNP]
2120 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2121
2122 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2123 [Deprecated - use cpusets instead]
2124 Format: [flag-list,]<cpu-list>
2125
2126 Specify one or more CPUs to isolate from disturbances
2127 specified in the flag list (default: domain):
2128
2129 nohz
2130 Disable the tick when a single task runs.
2131
2132 A residual 1Hz tick is offloaded to workqueues, which you
2133 need to affine to housekeeping through the global
2134 workqueue's affinity configured via the
2135 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2136 by using the 'domain' flag described below.
2137
2138 NOTE: by default the global workqueue runs on all CPUs,
2139 so to protect individual CPUs the 'cpumask' file has to
2140 be configured manually after bootup.
2141
2142 domain
2143 Isolate from the general SMP balancing and scheduling
2144 algorithms. Note that performing domain isolation this way
2145 is irreversible: it's not possible to bring back a CPU to
2146 the domains once isolated through isolcpus. It's strongly
2147 advised to use cpusets instead to disable scheduler load
2148 balancing through the "cpuset.sched_load_balance" file.
2149 It offers a much more flexible interface where CPUs can
2150 move in and out of an isolated set anytime.
2151
2152 You can move a process onto or off an "isolated" CPU via
2153 the CPU affinity syscalls or cpuset.
2154 <cpu number> begins at 0 and the maximum value is
2155 "number of CPUs in system - 1".
2156
2157 managed_irq
2158
2159 Isolate from being targeted by managed interrupts
2160 which have an interrupt mask containing isolated
2161 CPUs. The affinity of managed interrupts is
2162 handled by the kernel and cannot be changed via
2163 the /proc/irq/* interfaces.
2164
2165 This isolation is best effort and only effective
2166 if the automatically assigned interrupt mask of a
2167 device queue contains isolated and housekeeping
2168 CPUs. If housekeeping CPUs are online then such
2169 interrupts are directed to the housekeeping CPU
2170 so that IO submitted on the housekeeping CPU
2171 cannot disturb the isolated CPU.
2172
2173 If a queue's affinity mask contains only isolated
2174 CPUs then this parameter has no effect on the
2175 interrupt routing decision, though interrupts are
2176 only delivered when tasks running on those
2177 isolated CPUs submit IO. IO submitted on
2178 housekeeping CPUs has no influence on those
2179 queues.
2180
2181 The format of <cpu-list> is described above.
2182
2183 iucv= [HW,NET]
2184
2185 ivrs_ioapic [HW,X86-64]
2186 Provide an override to the IOAPIC-ID<->DEVICE-ID
2187 mapping provided in the IVRS ACPI table. For
2188 example, to map IOAPIC-ID decimal 10 to
2189 PCI device 00:14.0 write the parameter as:
2190 ivrs_ioapic[10]=00:14.0
2191
2192 ivrs_hpet [HW,X86-64]
2193 Provide an override to the HPET-ID<->DEVICE-ID
2194 mapping provided in the IVRS ACPI table. For
2195 example, to map HPET-ID decimal 0 to
2196 PCI device 00:14.0 write the parameter as:
2197 ivrs_hpet[0]=00:14.0
2198
2199 ivrs_acpihid [HW,X86-64]
2200 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2201 mapping provided in the IVRS ACPI table. For
2202 example, to map UART-HID:UID AMD0020:0 to
2203 PCI device 00:14.5 write the parameter as:
2204 ivrs_acpihid[00:14.5]=AMD0020:0
2205
2206 js= [HW,JOY] Analog joystick
2207 See Documentation/input/joydev/joystick.rst.
2208
2209 nokaslr [KNL]
2210 When CONFIG_RANDOMIZE_BASE is set, this disables
2211 kernel and module base offset ASLR (Address Space
2212 Layout Randomization).
2213
2214 kasan_multi_shot
2215 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2216 report on every invalid memory access. Without this
2217 parameter KASAN will print report only for the first
2218 invalid access.
2219
2220 keepinitrd [HW,ARM]
2221
2222 kernelcore= [KNL,X86,IA-64,PPC]
2223 Format: nn[KMGTPE] | nn% | "mirror"
2224 This parameter specifies the amount of memory usable by
2225 the kernel for non-movable allocations. The requested
2226 amount is spread evenly throughout all nodes in the
2227 system as ZONE_NORMAL. The remaining memory is used for
2228 movable memory in its own zone, ZONE_MOVABLE. In the
2229 event, a node is too small to have both ZONE_NORMAL and
2230 ZONE_MOVABLE, kernelcore memory will take priority and
2231 other nodes will have a larger ZONE_MOVABLE.
2232
2233 ZONE_MOVABLE is used for the allocation of pages that
2234 may be reclaimed or moved by the page migration
2235 subsystem. Note that allocations like PTEs-from-HighMem
2236 still use the HighMem zone if it exists, and the Normal
2237 zone if it does not.
2238
2239 It is possible to specify the exact amount of memory in
2240 the form of "nn[KMGTPE]", a percentage of total system
2241 memory in the form of "nn%", or "mirror". If "mirror"
2242 option is specified, mirrored (reliable) memory is used
2243 for non-movable allocations and remaining memory is used
2244 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2245 are exclusive, so you cannot specify multiple forms.
2246
2247 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2248 Format: <Controller#>[,poll interval]
2249 The controller # is the number of the ehci usb debug
2250 port as it is probed via PCI. The poll interval is
2251 optional and is the number seconds in between
2252 each poll cycle to the debug port in case you need
2253 the functionality for interrupting the kernel with
2254 gdb or control-c on the dbgp connection. When
2255 not using this parameter you use sysrq-g to break into
2256 the kernel debugger.
2257
2258 kgdboc= [KGDB,HW] kgdb over consoles.
2259 Requires a tty driver that supports console polling,
2260 or a supported polling keyboard driver (non-usb).
2261 Serial only format: <serial_device>[,baud]
2262 keyboard only format: kbd
2263 keyboard and serial format: kbd,<serial_device>[,baud]
2264 Optional Kernel mode setting:
2265 kms, kbd format: kms,kbd
2266 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2267
2268 kgdboc_earlycon= [KGDB,HW]
2269 If the boot console provides the ability to read
2270 characters and can work in polling mode, you can use
2271 this parameter to tell kgdb to use it as a backend
2272 until the normal console is registered. Intended to
2273 be used together with the kgdboc parameter which
2274 specifies the normal console to transition to.
2275
2276 The name of the early console should be specified
2277 as the value of this parameter. Note that the name of
2278 the early console might be different than the tty
2279 name passed to kgdboc. It's OK to leave the value
2280 blank and the first boot console that implements
2281 read() will be picked.
2282
2283 kgdbwait [KGDB] Stop kernel execution and enter the
2284 kernel debugger at the earliest opportunity.
2285
2286 kmac= [MIPS] Korina ethernet MAC address.
2287 Configure the RouterBoard 532 series on-chip
2288 Ethernet adapter MAC address.
2289
2290 kmemleak= [KNL] Boot-time kmemleak enable/disable
2291 Valid arguments: on, off
2292 Default: on
2293 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2294 the default is off.
2295
2296 kprobe_event=[probe-list]
2297 [FTRACE] Add kprobe events and enable at boot time.
2298 The probe-list is a semicolon delimited list of probe
2299 definitions. Each definition is same as kprobe_events
2300 interface, but the parameters are comma delimited.
2301 For example, to add a kprobe event on vfs_read with
2302 arg1 and arg2, add to the command line;
2303
2304 kprobe_event=p,vfs_read,$arg1,$arg2
2305
2306 See also Documentation/trace/kprobetrace.rst "Kernel
2307 Boot Parameter" section.
2308
2309 kpti= [ARM64] Control page table isolation of user
2310 and kernel address spaces.
2311 Default: enabled on cores which need mitigation.
2312 0: force disabled
2313 1: force enabled
2314
2315 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2316 Default is 0 (don't ignore, but inject #GP)
2317
2318 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2319 Default is false (don't support).
2320
2321 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2322 KVM MMU at runtime.
2323 Default is 0 (off)
2324
2325 kvm.nx_huge_pages=
2326 [KVM] Controls the software workaround for the
2327 X86_BUG_ITLB_MULTIHIT bug.
2328 force : Always deploy workaround.
2329 off : Never deploy workaround.
2330 auto : Deploy workaround based on the presence of
2331 X86_BUG_ITLB_MULTIHIT.
2332
2333 Default is 'auto'.
2334
2335 If the software workaround is enabled for the host,
2336 guests do need not to enable it for nested guests.
2337
2338 kvm.nx_huge_pages_recovery_ratio=
2339 [KVM] Controls how many 4KiB pages are periodically zapped
2340 back to huge pages. 0 disables the recovery, otherwise if
2341 the value is N KVM will zap 1/Nth of the 4KiB pages every
2342 minute. The default is 60.
2343
2344 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2345 Default is 1 (enabled)
2346
2347 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2348 for all guests.
2349 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2350
2351 kvm-arm.mode=
2352 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2353
2354 nvhe: Standard nVHE-based mode, without support for
2355 protected guests.
2356
2357 protected: nVHE-based mode with support for guests whose
2358 state is kept private from the host.
2359 Not valid if the kernel is running in EL2.
2360
2361 Defaults to VHE/nVHE based on hardware support.
2362
2363 kvm-arm.vgic_v3_group0_trap=
2364 [KVM,ARM] Trap guest accesses to GICv3 group-0
2365 system registers
2366
2367 kvm-arm.vgic_v3_group1_trap=
2368 [KVM,ARM] Trap guest accesses to GICv3 group-1
2369 system registers
2370
2371 kvm-arm.vgic_v3_common_trap=
2372 [KVM,ARM] Trap guest accesses to GICv3 common
2373 system registers
2374
2375 kvm-arm.vgic_v4_enable=
2376 [KVM,ARM] Allow use of GICv4 for direct injection of
2377 LPIs.
2378
2379 kvm_cma_resv_ratio=n [PPC]
2380 Reserves given percentage from system memory area for
2381 contiguous memory allocation for KVM hash pagetable
2382 allocation.
2383 By default it reserves 5% of total system memory.
2384 Format: <integer>
2385 Default: 5
2386
2387 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2388 (virtualized MMU) support on capable Intel chips.
2389 Default is 1 (enabled)
2390
2391 kvm-intel.emulate_invalid_guest_state=
2392 [KVM,Intel] Enable emulation of invalid guest states
2393 Default is 0 (disabled)
2394
2395 kvm-intel.flexpriority=
2396 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2397 Default is 1 (enabled)
2398
2399 kvm-intel.nested=
2400 [KVM,Intel] Enable VMX nesting (nVMX).
2401 Default is 0 (disabled)
2402
2403 kvm-intel.unrestricted_guest=
2404 [KVM,Intel] Disable unrestricted guest feature
2405 (virtualized real and unpaged mode) on capable
2406 Intel chips. Default is 1 (enabled)
2407
2408 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2409 CVE-2018-3620.
2410
2411 Valid arguments: never, cond, always
2412
2413 always: L1D cache flush on every VMENTER.
2414 cond: Flush L1D on VMENTER only when the code between
2415 VMEXIT and VMENTER can leak host memory.
2416 never: Disables the mitigation
2417
2418 Default is cond (do L1 cache flush in specific instances)
2419
2420 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2421 feature (tagged TLBs) on capable Intel chips.
2422 Default is 1 (enabled)
2423
2424 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2425 affected CPUs
2426
2427 The kernel PTE inversion protection is unconditionally
2428 enabled and cannot be disabled.
2429
2430 full
2431 Provides all available mitigations for the
2432 L1TF vulnerability. Disables SMT and
2433 enables all mitigations in the
2434 hypervisors, i.e. unconditional L1D flush.
2435
2436 SMT control and L1D flush control via the
2437 sysfs interface is still possible after
2438 boot. Hypervisors will issue a warning
2439 when the first VM is started in a
2440 potentially insecure configuration,
2441 i.e. SMT enabled or L1D flush disabled.
2442
2443 full,force
2444 Same as 'full', but disables SMT and L1D
2445 flush runtime control. Implies the
2446 'nosmt=force' command line option.
2447 (i.e. sysfs control of SMT is disabled.)
2448
2449 flush
2450 Leaves SMT enabled and enables the default
2451 hypervisor mitigation, i.e. conditional
2452 L1D flush.
2453
2454 SMT control and L1D flush control via the
2455 sysfs interface is still possible after
2456 boot. Hypervisors will issue a warning
2457 when the first VM is started in a
2458 potentially insecure configuration,
2459 i.e. SMT enabled or L1D flush disabled.
2460
2461 flush,nosmt
2462
2463 Disables SMT and enables the default
2464 hypervisor mitigation.
2465
2466 SMT control and L1D flush control via the
2467 sysfs interface is still possible after
2468 boot. Hypervisors will issue a warning
2469 when the first VM is started in a
2470 potentially insecure configuration,
2471 i.e. SMT enabled or L1D flush disabled.
2472
2473 flush,nowarn
2474 Same as 'flush', but hypervisors will not
2475 warn when a VM is started in a potentially
2476 insecure configuration.
2477
2478 off
2479 Disables hypervisor mitigations and doesn't
2480 emit any warnings.
2481 It also drops the swap size and available
2482 RAM limit restriction on both hypervisor and
2483 bare metal.
2484
2485 Default is 'flush'.
2486
2487 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2488
2489 l2cr= [PPC]
2490
2491 l3cr= [PPC]
2492
2493 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2494 disabled it.
2495
2496 lapic= [X86,APIC] Do not use TSC deadline
2497 value for LAPIC timer one-shot implementation. Default
2498 back to the programmable timer unit in the LAPIC.
2499 Format: notscdeadline
2500
2501 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2502 in C2 power state.
2503
2504 libata.dma= [LIBATA] DMA control
2505 libata.dma=0 Disable all PATA and SATA DMA
2506 libata.dma=1 PATA and SATA Disk DMA only
2507 libata.dma=2 ATAPI (CDROM) DMA only
2508 libata.dma=4 Compact Flash DMA only
2509 Combinations also work, so libata.dma=3 enables DMA
2510 for disks and CDROMs, but not CFs.
2511
2512 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2513 libata.ignore_hpa=0 keep BIOS limits (default)
2514 libata.ignore_hpa=1 ignore limits, using full disk
2515
2516 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2517 when set.
2518 Format: <int>
2519
2520 libata.force= [LIBATA] Force configurations. The format is comma-
2521 separated list of "[ID:]VAL" where ID is
2522 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2523 matching port, link or device. Basically, it matches
2524 the ATA ID string printed on console by libata. If
2525 the whole ID part is omitted, the last PORT and DEVICE
2526 values are used. If ID hasn't been specified yet, the
2527 configuration applies to all ports, links and devices.
2528
2529 If only DEVICE is omitted, the parameter applies to
2530 the port and all links and devices behind it. DEVICE
2531 number of 0 either selects the first device or the
2532 first fan-out link behind PMP device. It does not
2533 select the host link. DEVICE number of 15 selects the
2534 host link and device attached to it.
2535
2536 The VAL specifies the configuration to force. As long
2537 as there's no ambiguity shortcut notation is allowed.
2538 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2539 The following configurations can be forced.
2540
2541 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2542 Any ID with matching PORT is used.
2543
2544 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2545
2546 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2547 udma[/][16,25,33,44,66,100,133] notation is also
2548 allowed.
2549
2550 * [no]ncq: Turn on or off NCQ.
2551
2552 * [no]ncqtrim: Turn off queued DSM TRIM.
2553
2554 * nohrst, nosrst, norst: suppress hard, soft
2555 and both resets.
2556
2557 * rstonce: only attempt one reset during
2558 hot-unplug link recovery
2559
2560 * dump_id: dump IDENTIFY data.
2561
2562 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2563
2564 * disable: Disable this device.
2565
2566 If there are multiple matching configurations changing
2567 the same attribute, the last one is used.
2568
2569 memblock=debug [KNL] Enable memblock debug messages.
2570
2571 load_ramdisk= [RAM] [Deprecated]
2572
2573 lockd.nlm_grace_period=P [NFS] Assign grace period.
2574 Format: <integer>
2575
2576 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2577 Format: <integer>
2578
2579 lockd.nlm_timeout=T [NFS] Assign timeout value.
2580 Format: <integer>
2581
2582 lockd.nlm_udpport=M [NFS] Assign UDP port.
2583 Format: <integer>
2584
2585 lockdown= [SECURITY]
2586 { integrity | confidentiality }
2587 Enable the kernel lockdown feature. If set to
2588 integrity, kernel features that allow userland to
2589 modify the running kernel are disabled. If set to
2590 confidentiality, kernel features that allow userland
2591 to extract confidential information from the kernel
2592 are also disabled.
2593
2594 locktorture.nreaders_stress= [KNL]
2595 Set the number of locking read-acquisition kthreads.
2596 Defaults to being automatically set based on the
2597 number of online CPUs.
2598
2599 locktorture.nwriters_stress= [KNL]
2600 Set the number of locking write-acquisition kthreads.
2601
2602 locktorture.onoff_holdoff= [KNL]
2603 Set time (s) after boot for CPU-hotplug testing.
2604
2605 locktorture.onoff_interval= [KNL]
2606 Set time (s) between CPU-hotplug operations, or
2607 zero to disable CPU-hotplug testing.
2608
2609 locktorture.shuffle_interval= [KNL]
2610 Set task-shuffle interval (jiffies). Shuffling
2611 tasks allows some CPUs to go into dyntick-idle
2612 mode during the locktorture test.
2613
2614 locktorture.shutdown_secs= [KNL]
2615 Set time (s) after boot system shutdown. This
2616 is useful for hands-off automated testing.
2617
2618 locktorture.stat_interval= [KNL]
2619 Time (s) between statistics printk()s.
2620
2621 locktorture.stutter= [KNL]
2622 Time (s) to stutter testing, for example,
2623 specifying five seconds causes the test to run for
2624 five seconds, wait for five seconds, and so on.
2625 This tests the locking primitive's ability to
2626 transition abruptly to and from idle.
2627
2628 locktorture.torture_type= [KNL]
2629 Specify the locking implementation to test.
2630
2631 locktorture.verbose= [KNL]
2632 Enable additional printk() statements.
2633
2634 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2635 Format: <irq>
2636
2637 loglevel= All Kernel Messages with a loglevel smaller than the
2638 console loglevel will be printed to the console. It can
2639 also be changed with klogd or other programs. The
2640 loglevels are defined as follows:
2641
2642 0 (KERN_EMERG) system is unusable
2643 1 (KERN_ALERT) action must be taken immediately
2644 2 (KERN_CRIT) critical conditions
2645 3 (KERN_ERR) error conditions
2646 4 (KERN_WARNING) warning conditions
2647 5 (KERN_NOTICE) normal but significant condition
2648 6 (KERN_INFO) informational
2649 7 (KERN_DEBUG) debug-level messages
2650
2651 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2652 in bytes. n must be a power of two and greater
2653 than the minimal size. The minimal size is defined
2654 by LOG_BUF_SHIFT kernel config parameter. There is
2655 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2656 that allows to increase the default size depending on
2657 the number of CPUs. See init/Kconfig for more details.
2658
2659 logo.nologo [FB] Disables display of the built-in Linux logo.
2660 This may be used to provide more screen space for
2661 kernel log messages and is useful when debugging
2662 kernel boot problems.
2663
2664 lp=0 [LP] Specify parallel ports to use, e.g,
2665 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2666 lp=reset first parallel port). 'lp=0' disables the
2667 lp=auto printer driver. 'lp=reset' (which can be
2668 specified in addition to the ports) causes
2669 attached printers to be reset. Using
2670 lp=port1,port2,... specifies the parallel ports
2671 to associate lp devices with, starting with
2672 lp0. A port specification may be 'none' to skip
2673 that lp device, or a parport name such as
2674 'parport0'. Specifying 'lp=auto' instead of a
2675 port specification list means that device IDs
2676 from each port should be examined, to see if
2677 an IEEE 1284-compliant printer is attached; if
2678 so, the driver will manage that printer.
2679 See also header of drivers/char/lp.c.
2680
2681 lpj=n [KNL]
2682 Sets loops_per_jiffy to given constant, thus avoiding
2683 time-consuming boot-time autodetection (up to 250 ms per
2684 CPU). 0 enables autodetection (default). To determine
2685 the correct value for your kernel, boot with normal
2686 autodetection and see what value is printed. Note that
2687 on SMP systems the preset will be applied to all CPUs,
2688 which is likely to cause problems if your CPUs need
2689 significantly divergent settings. An incorrect value
2690 will cause delays in the kernel to be wrong, leading to
2691 unpredictable I/O errors and other breakage. Although
2692 unlikely, in the extreme case this might damage your
2693 hardware.
2694
2695 ltpc= [NET]
2696 Format: <io>,<irq>,<dma>
2697
2698 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2699
2700 lsm=lsm1,...,lsmN
2701 [SECURITY] Choose order of LSM initialization. This
2702 overrides CONFIG_LSM, and the "security=" parameter.
2703
2704 machvec= [IA-64] Force the use of a particular machine-vector
2705 (machvec) in a generic kernel.
2706 Example: machvec=hpzx1
2707
2708 machtype= [Loongson] Share the same kernel image file between
2709 different yeeloong laptops.
2710 Example: machtype=lemote-yeeloong-2f-7inch
2711
2712 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2713 than or equal to this physical address is ignored.
2714
2715 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2716 will bring up during bootup. maxcpus=n : n >= 0 limits
2717 the kernel to bring up 'n' processors. Surely after
2718 bootup you can bring up the other plugged cpu by executing
2719 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2720 only takes effect during system bootup.
2721 While n=0 is a special case, it is equivalent to "nosmp",
2722 which also disables the IO APIC.
2723
2724 max_loop= [LOOP] The number of loop block devices that get
2725 (loop.max_loop) unconditionally pre-created at init time. The default
2726 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2727 of statically allocating a predefined number, loop
2728 devices can be requested on-demand with the
2729 /dev/loop-control interface.
2730
2731 mce [X86-32] Machine Check Exception
2732
2733 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2734
2735 md= [HW] RAID subsystems devices and level
2736 See Documentation/admin-guide/md.rst.
2737
2738 mdacon= [MDA]
2739 Format: <first>,<last>
2740 Specifies range of consoles to be captured by the MDA.
2741
2742 mds= [X86,INTEL]
2743 Control mitigation for the Micro-architectural Data
2744 Sampling (MDS) vulnerability.
2745
2746 Certain CPUs are vulnerable to an exploit against CPU
2747 internal buffers which can forward information to a
2748 disclosure gadget under certain conditions.
2749
2750 In vulnerable processors, the speculatively
2751 forwarded data can be used in a cache side channel
2752 attack, to access data to which the attacker does
2753 not have direct access.
2754
2755 This parameter controls the MDS mitigation. The
2756 options are:
2757
2758 full - Enable MDS mitigation on vulnerable CPUs
2759 full,nosmt - Enable MDS mitigation and disable
2760 SMT on vulnerable CPUs
2761 off - Unconditionally disable MDS mitigation
2762
2763 On TAA-affected machines, mds=off can be prevented by
2764 an active TAA mitigation as both vulnerabilities are
2765 mitigated with the same mechanism so in order to disable
2766 this mitigation, you need to specify tsx_async_abort=off
2767 too.
2768
2769 Not specifying this option is equivalent to
2770 mds=full.
2771
2772 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2773
2774 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2775 Amount of memory to be used in cases as follows:
2776
2777 1 for test;
2778 2 when the kernel is not able to see the whole system memory;
2779 3 memory that lies after 'mem=' boundary is excluded from
2780 the hypervisor, then assigned to KVM guests.
2781
2782 [X86] Work as limiting max address. Use together
2783 with memmap= to avoid physical address space collisions.
2784 Without memmap= PCI devices could be placed at addresses
2785 belonging to unused RAM.
2786
2787 Note that this only takes effects during boot time since
2788 in above case 3, memory may need be hot added after boot
2789 if system memory of hypervisor is not sufficient.
2790
2791 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2792 memory.
2793
2794 memchunk=nn[KMG]
2795 [KNL,SH] Allow user to override the default size for
2796 per-device physically contiguous DMA buffers.
2797
2798 memhp_default_state=online/offline
2799 [KNL] Set the initial state for the memory hotplug
2800 onlining policy. If not specified, the default value is
2801 set according to the
2802 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2803 option.
2804 See Documentation/admin-guide/mm/memory-hotplug.rst.
2805
2806 memmap=exactmap [KNL,X86] Enable setting of an exact
2807 E820 memory map, as specified by the user.
2808 Such memmap=exactmap lines can be constructed based on
2809 BIOS output or other requirements. See the memmap=nn@ss
2810 option description.
2811
2812 memmap=nn[KMG]@ss[KMG]
2813 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2814 Region of memory to be used is from ss to ss+nn.
2815 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2816 which limits max address to nn[KMG].
2817 Multiple different regions can be specified,
2818 comma delimited.
2819 Example:
2820 memmap=100M@2G,100M#3G,1G!1024G
2821
2822 memmap=nn[KMG]#ss[KMG]
2823 [KNL,ACPI] Mark specific memory as ACPI data.
2824 Region of memory to be marked is from ss to ss+nn.
2825
2826 memmap=nn[KMG]$ss[KMG]
2827 [KNL,ACPI] Mark specific memory as reserved.
2828 Region of memory to be reserved is from ss to ss+nn.
2829 Example: Exclude memory from 0x18690000-0x1869ffff
2830 memmap=64K$0x18690000
2831 or
2832 memmap=0x10000$0x18690000
2833 Some bootloaders may need an escape character before '$',
2834 like Grub2, otherwise '$' and the following number
2835 will be eaten.
2836
2837 memmap=nn[KMG]!ss[KMG]
2838 [KNL,X86] Mark specific memory as protected.
2839 Region of memory to be used, from ss to ss+nn.
2840 The memory region may be marked as e820 type 12 (0xc)
2841 and is NVDIMM or ADR memory.
2842
2843 memmap=<size>%<offset>-<oldtype>+<newtype>
2844 [KNL,ACPI] Convert memory within the specified region
2845 from <oldtype> to <newtype>. If "-<oldtype>" is left
2846 out, the whole region will be marked as <newtype>,
2847 even if previously unavailable. If "+<newtype>" is left
2848 out, matching memory will be removed. Types are
2849 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2850 3 = ACPI, 12 = PRAM.
2851
2852 memory_corruption_check=0/1 [X86]
2853 Some BIOSes seem to corrupt the first 64k of
2854 memory when doing things like suspend/resume.
2855 Setting this option will scan the memory
2856 looking for corruption. Enabling this will
2857 both detect corruption and prevent the kernel
2858 from using the memory being corrupted.
2859 However, its intended as a diagnostic tool; if
2860 repeatable BIOS-originated corruption always
2861 affects the same memory, you can use memmap=
2862 to prevent the kernel from using that memory.
2863
2864 memory_corruption_check_size=size [X86]
2865 By default it checks for corruption in the low
2866 64k, making this memory unavailable for normal
2867 use. Use this parameter to scan for
2868 corruption in more or less memory.
2869
2870 memory_corruption_check_period=seconds [X86]
2871 By default it checks for corruption every 60
2872 seconds. Use this parameter to check at some
2873 other rate. 0 disables periodic checking.
2874
2875 memory_hotplug.memmap_on_memory
2876 [KNL,X86,ARM] Boolean flag to enable this feature.
2877 Format: {on | off (default)}
2878 When enabled, runtime hotplugged memory will
2879 allocate its internal metadata (struct pages)
2880 from the hotadded memory which will allow to
2881 hotadd a lot of memory without requiring
2882 additional memory to do so.
2883 This feature is disabled by default because it
2884 has some implication on large (e.g. GB)
2885 allocations in some configurations (e.g. small
2886 memory blocks).
2887 The state of the flag can be read in
2888 /sys/module/memory_hotplug/parameters/memmap_on_memory.
2889 Note that even when enabled, there are a few cases where
2890 the feature is not effective.
2891
2892 This is not compatible with hugetlb_free_vmemmap. If
2893 both parameters are enabled, hugetlb_free_vmemmap takes
2894 precedence over memory_hotplug.memmap_on_memory.
2895
2896 memtest= [KNL,X86,ARM,PPC,RISCV] Enable memtest
2897 Format: <integer>
2898 default : 0 <disable>
2899 Specifies the number of memtest passes to be
2900 performed. Each pass selects another test
2901 pattern from a given set of patterns. Memtest
2902 fills the memory with this pattern, validates
2903 memory contents and reserves bad memory
2904 regions that are detected.
2905
2906 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2907 Valid arguments: on, off
2908 Default (depends on kernel configuration option):
2909 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2910 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2911 mem_encrypt=on: Activate SME
2912 mem_encrypt=off: Do not activate SME
2913
2914 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2915 for details on when memory encryption can be activated.
2916
2917 mem_sleep_default= [SUSPEND] Default system suspend mode:
2918 s2idle - Suspend-To-Idle
2919 shallow - Power-On Suspend or equivalent (if supported)
2920 deep - Suspend-To-RAM or equivalent (if supported)
2921 See Documentation/admin-guide/pm/sleep-states.rst.
2922
2923 meye.*= [HW] Set MotionEye Camera parameters
2924 See Documentation/admin-guide/media/meye.rst.
2925
2926 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2927 Multi-Function General Purpose Timers on AMD Geode
2928 platforms.
2929
2930 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2931 the BIOS has incorrectly applied a workaround. TinyBIOS
2932 version 0.98 is known to be affected, 0.99 fixes the
2933 problem by letting the user disable the workaround.
2934
2935 mga= [HW,DRM]
2936
2937 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2938 physical address is ignored.
2939
2940 mini2440= [ARM,HW,KNL]
2941 Format:[0..2][b][c][t]
2942 Default: "0tb"
2943 MINI2440 configuration specification:
2944 0 - The attached screen is the 3.5" TFT
2945 1 - The attached screen is the 7" TFT
2946 2 - The VGA Shield is attached (1024x768)
2947 Leaving out the screen size parameter will not load
2948 the TFT driver, and the framebuffer will be left
2949 unconfigured.
2950 b - Enable backlight. The TFT backlight pin will be
2951 linked to the kernel VESA blanking code and a GPIO
2952 LED. This parameter is not necessary when using the
2953 VGA shield.
2954 c - Enable the s3c camera interface.
2955 t - Reserved for enabling touchscreen support. The
2956 touchscreen support is not enabled in the mainstream
2957 kernel as of 2.6.30, a preliminary port can be found
2958 in the "bleeding edge" mini2440 support kernel at
2959 https://repo.or.cz/w/linux-2.6/mini2440.git
2960
2961 mitigations=
2962 [X86,PPC,S390,ARM64] Control optional mitigations for
2963 CPU vulnerabilities. This is a set of curated,
2964 arch-independent options, each of which is an
2965 aggregation of existing arch-specific options.
2966
2967 off
2968 Disable all optional CPU mitigations. This
2969 improves system performance, but it may also
2970 expose users to several CPU vulnerabilities.
2971 Equivalent to: nopti [X86,PPC]
2972 kpti=0 [ARM64]
2973 nospectre_v1 [X86,PPC]
2974 nobp=0 [S390]
2975 nospectre_v2 [X86,PPC,S390,ARM64]
2976 spectre_v2_user=off [X86]
2977 spec_store_bypass_disable=off [X86,PPC]
2978 ssbd=force-off [ARM64]
2979 l1tf=off [X86]
2980 mds=off [X86]
2981 tsx_async_abort=off [X86]
2982 kvm.nx_huge_pages=off [X86]
2983 no_entry_flush [PPC]
2984 no_uaccess_flush [PPC]
2985
2986 Exceptions:
2987 This does not have any effect on
2988 kvm.nx_huge_pages when
2989 kvm.nx_huge_pages=force.
2990
2991 auto (default)
2992 Mitigate all CPU vulnerabilities, but leave SMT
2993 enabled, even if it's vulnerable. This is for
2994 users who don't want to be surprised by SMT
2995 getting disabled across kernel upgrades, or who
2996 have other ways of avoiding SMT-based attacks.
2997 Equivalent to: (default behavior)
2998
2999 auto,nosmt
3000 Mitigate all CPU vulnerabilities, disabling SMT
3001 if needed. This is for users who always want to
3002 be fully mitigated, even if it means losing SMT.
3003 Equivalent to: l1tf=flush,nosmt [X86]
3004 mds=full,nosmt [X86]
3005 tsx_async_abort=full,nosmt [X86]
3006
3007 mminit_loglevel=
3008 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3009 parameter allows control of the logging verbosity for
3010 the additional memory initialisation checks. A value
3011 of 0 disables mminit logging and a level of 4 will
3012 log everything. Information is printed at KERN_DEBUG
3013 so loglevel=8 may also need to be specified.
3014
3015 module.sig_enforce
3016 [KNL] When CONFIG_MODULE_SIG is set, this means that
3017 modules without (valid) signatures will fail to load.
3018 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3019 is always true, so this option does nothing.
3020
3021 module_blacklist= [KNL] Do not load a comma-separated list of
3022 modules. Useful for debugging problem modules.
3023
3024 mousedev.tap_time=
3025 [MOUSE] Maximum time between finger touching and
3026 leaving touchpad surface for touch to be considered
3027 a tap and be reported as a left button click (for
3028 touchpads working in absolute mode only).
3029 Format: <msecs>
3030 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3031 reporting absolute coordinates, such as tablets
3032 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3033 reporting absolute coordinates, such as tablets
3034
3035 movablecore= [KNL,X86,IA-64,PPC]
3036 Format: nn[KMGTPE] | nn%
3037 This parameter is the complement to kernelcore=, it
3038 specifies the amount of memory used for migratable
3039 allocations. If both kernelcore and movablecore is
3040 specified, then kernelcore will be at *least* the
3041 specified value but may be more. If movablecore on its
3042 own is specified, the administrator must be careful
3043 that the amount of memory usable for all allocations
3044 is not too small.
3045
3046 movable_node [KNL] Boot-time switch to make hotplugable memory
3047 NUMA nodes to be movable. This means that the memory
3048 of such nodes will be usable only for movable
3049 allocations which rules out almost all kernel
3050 allocations. Use with caution!
3051
3052 MTD_Partition= [MTD]
3053 Format: <name>,<region-number>,<size>,<offset>
3054
3055 MTD_Region= [MTD] Format:
3056 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3057
3058 mtdparts= [MTD]
3059 See drivers/mtd/parsers/cmdlinepart.c
3060
3061 multitce=off [PPC] This parameter disables the use of the pSeries
3062 firmware feature for updating multiple TCE entries
3063 at a time.
3064
3065 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3066
3067 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3068
3069 boundary - index of last SLC block on Flex-OneNAND.
3070 The remaining blocks are configured as MLC blocks.
3071 lock - Configure if Flex-OneNAND boundary should be locked.
3072 Once locked, the boundary cannot be changed.
3073 1 indicates lock status, 0 indicates unlock status.
3074
3075 mtdset= [ARM]
3076 ARM/S3C2412 JIVE boot control
3077
3078 See arch/arm/mach-s3c/mach-jive.c
3079
3080 mtouchusb.raw_coordinates=
3081 [HW] Make the MicroTouch USB driver use raw coordinates
3082 ('y', default) or cooked coordinates ('n')
3083
3084 mtrr_chunk_size=nn[KMG] [X86]
3085 used for mtrr cleanup. It is largest continuous chunk
3086 that could hold holes aka. UC entries.
3087
3088 mtrr_gran_size=nn[KMG] [X86]
3089 Used for mtrr cleanup. It is granularity of mtrr block.
3090 Default is 1.
3091 Large value could prevent small alignment from
3092 using up MTRRs.
3093
3094 mtrr_spare_reg_nr=n [X86]
3095 Format: <integer>
3096 Range: 0,7 : spare reg number
3097 Default : 1
3098 Used for mtrr cleanup. It is spare mtrr entries number.
3099 Set to 2 or more if your graphical card needs more.
3100
3101 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3102
3103 netdev= [NET] Network devices parameters
3104 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3105 Note that mem_start is often overloaded to mean
3106 something different and driver-specific.
3107 This usage is only documented in each driver source
3108 file if at all.
3109
3110 nf_conntrack.acct=
3111 [NETFILTER] Enable connection tracking flow accounting
3112 0 to disable accounting
3113 1 to enable accounting
3114 Default value is 0.
3115
3116 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3117 See Documentation/admin-guide/nfs/nfsroot.rst.
3118
3119 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3120 See Documentation/admin-guide/nfs/nfsroot.rst.
3121
3122 nfsrootdebug [NFS] enable nfsroot debugging messages.
3123 See Documentation/admin-guide/nfs/nfsroot.rst.
3124
3125 nfs.callback_nr_threads=
3126 [NFSv4] set the total number of threads that the
3127 NFS client will assign to service NFSv4 callback
3128 requests.
3129
3130 nfs.callback_tcpport=
3131 [NFS] set the TCP port on which the NFSv4 callback
3132 channel should listen.
3133
3134 nfs.cache_getent=
3135 [NFS] sets the pathname to the program which is used
3136 to update the NFS client cache entries.
3137
3138 nfs.cache_getent_timeout=
3139 [NFS] sets the timeout after which an attempt to
3140 update a cache entry is deemed to have failed.
3141
3142 nfs.idmap_cache_timeout=
3143 [NFS] set the maximum lifetime for idmapper cache
3144 entries.
3145
3146 nfs.enable_ino64=
3147 [NFS] enable 64-bit inode numbers.
3148 If zero, the NFS client will fake up a 32-bit inode
3149 number for the readdir() and stat() syscalls instead
3150 of returning the full 64-bit number.
3151 The default is to return 64-bit inode numbers.
3152
3153 nfs.max_session_cb_slots=
3154 [NFSv4.1] Sets the maximum number of session
3155 slots the client will assign to the callback
3156 channel. This determines the maximum number of
3157 callbacks the client will process in parallel for
3158 a particular server.
3159
3160 nfs.max_session_slots=
3161 [NFSv4.1] Sets the maximum number of session slots
3162 the client will attempt to negotiate with the server.
3163 This limits the number of simultaneous RPC requests
3164 that the client can send to the NFSv4.1 server.
3165 Note that there is little point in setting this
3166 value higher than the max_tcp_slot_table_limit.
3167
3168 nfs.nfs4_disable_idmapping=
3169 [NFSv4] When set to the default of '1', this option
3170 ensures that both the RPC level authentication
3171 scheme and the NFS level operations agree to use
3172 numeric uids/gids if the mount is using the
3173 'sec=sys' security flavour. In effect it is
3174 disabling idmapping, which can make migration from
3175 legacy NFSv2/v3 systems to NFSv4 easier.
3176 Servers that do not support this mode of operation
3177 will be autodetected by the client, and it will fall
3178 back to using the idmapper.
3179 To turn off this behaviour, set the value to '0'.
3180 nfs.nfs4_unique_id=
3181 [NFS4] Specify an additional fixed unique ident-
3182 ification string that NFSv4 clients can insert into
3183 their nfs_client_id4 string. This is typically a
3184 UUID that is generated at system install time.
3185
3186 nfs.send_implementation_id =
3187 [NFSv4.1] Send client implementation identification
3188 information in exchange_id requests.
3189 If zero, no implementation identification information
3190 will be sent.
3191 The default is to send the implementation identification
3192 information.
3193
3194 nfs.recover_lost_locks =
3195 [NFSv4] Attempt to recover locks that were lost due
3196 to a lease timeout on the server. Please note that
3197 doing this risks data corruption, since there are
3198 no guarantees that the file will remain unchanged
3199 after the locks are lost.
3200 If you want to enable the kernel legacy behaviour of
3201 attempting to recover these locks, then set this
3202 parameter to '1'.
3203 The default parameter value of '0' causes the kernel
3204 not to attempt recovery of lost locks.
3205
3206 nfs4.layoutstats_timer =
3207 [NFSv4.2] Change the rate at which the kernel sends
3208 layoutstats to the pNFS metadata server.
3209
3210 Setting this to value to 0 causes the kernel to use
3211 whatever value is the default set by the layout
3212 driver. A non-zero value sets the minimum interval
3213 in seconds between layoutstats transmissions.
3214
3215 nfsd.nfs4_disable_idmapping=
3216 [NFSv4] When set to the default of '1', the NFSv4
3217 server will return only numeric uids and gids to
3218 clients using auth_sys, and will accept numeric uids
3219 and gids from such clients. This is intended to ease
3220 migration from NFSv2/v3.
3221
3222 nmi_backtrace.backtrace_idle [KNL]
3223 Dump stacks even of idle CPUs in response to an
3224 NMI stack-backtrace request.
3225
3226 nmi_debug= [KNL,SH] Specify one or more actions to take
3227 when a NMI is triggered.
3228 Format: [state][,regs][,debounce][,die]
3229
3230 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3231 Format: [panic,][nopanic,][num]
3232 Valid num: 0 or 1
3233 0 - turn hardlockup detector in nmi_watchdog off
3234 1 - turn hardlockup detector in nmi_watchdog on
3235 When panic is specified, panic when an NMI watchdog
3236 timeout occurs (or 'nopanic' to not panic on an NMI
3237 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3238 To disable both hard and soft lockup detectors,
3239 please see 'nowatchdog'.
3240 This is useful when you use a panic=... timeout and
3241 need the box quickly up again.
3242
3243 These settings can be accessed at runtime via
3244 the nmi_watchdog and hardlockup_panic sysctls.
3245
3246 netpoll.carrier_timeout=
3247 [NET] Specifies amount of time (in seconds) that
3248 netpoll should wait for a carrier. By default netpoll
3249 waits 4 seconds.
3250
3251 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3252 emulation library even if a 387 maths coprocessor
3253 is present.
3254
3255 no5lvl [X86-64] Disable 5-level paging mode. Forces
3256 kernel to use 4-level paging instead.
3257
3258 nofsgsbase [X86] Disables FSGSBASE instructions.
3259
3260 no_console_suspend
3261 [HW] Never suspend the console
3262 Disable suspending of consoles during suspend and
3263 hibernate operations. Once disabled, debugging
3264 messages can reach various consoles while the rest
3265 of the system is being put to sleep (ie, while
3266 debugging driver suspend/resume hooks). This may
3267 not work reliably with all consoles, but is known
3268 to work with serial and VGA consoles.
3269 To facilitate more flexible debugging, we also add
3270 console_suspend, a printk module parameter to control
3271 it. Users could use console_suspend (usually
3272 /sys/module/printk/parameters/console_suspend) to
3273 turn on/off it dynamically.
3274
3275 novmcoredd [KNL,KDUMP]
3276 Disable device dump. Device dump allows drivers to
3277 append dump data to vmcore so you can collect driver
3278 specified debug info. Drivers can append the data
3279 without any limit and this data is stored in memory,
3280 so this may cause significant memory stress. Disabling
3281 device dump can help save memory but the driver debug
3282 data will be no longer available. This parameter
3283 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3284 is set.
3285
3286 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3287 caches in the slab allocator. Saves per-node memory,
3288 but will impact performance.
3289
3290 noalign [KNL,ARM]
3291
3292 noaltinstr [S390] Disables alternative instructions patching
3293 (CPU alternatives feature).
3294
3295 noapic [SMP,APIC] Tells the kernel to not make use of any
3296 IOAPICs that may be present in the system.
3297
3298 noautogroup Disable scheduler automatic task group creation.
3299
3300 nobats [PPC] Do not use BATs for mapping kernel lowmem
3301 on "Classic" PPC cores.
3302
3303 nocache [ARM]
3304
3305 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3306
3307 delayacct [KNL] Enable per-task delay accounting
3308
3309 nodsp [SH] Disable hardware DSP at boot time.
3310
3311 noefi Disable EFI runtime services support.
3312
3313 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3314
3315 noexec [IA-64]
3316
3317 noexec [X86]
3318 On X86-32 available only on PAE configured kernels.
3319 noexec=on: enable non-executable mappings (default)
3320 noexec=off: disable non-executable mappings
3321
3322 nosmap [X86,PPC]
3323 Disable SMAP (Supervisor Mode Access Prevention)
3324 even if it is supported by processor.
3325
3326 nosmep [X86,PPC]
3327 Disable SMEP (Supervisor Mode Execution Prevention)
3328 even if it is supported by processor.
3329
3330 noexec32 [X86-64]
3331 This affects only 32-bit executables.
3332 noexec32=on: enable non-executable mappings (default)
3333 read doesn't imply executable mappings
3334 noexec32=off: disable non-executable mappings
3335 read implies executable mappings
3336
3337 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3338
3339 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3340 register save and restore. The kernel will only save
3341 legacy floating-point registers on task switch.
3342
3343 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3344
3345 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3346
3347 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3348 Equivalent to smt=1.
3349
3350 [KNL,X86] Disable symmetric multithreading (SMT).
3351 nosmt=force: Force disable SMT, cannot be undone
3352 via the sysfs control file.
3353
3354 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3355 (bounds check bypass). With this option data leaks are
3356 possible in the system.
3357
3358 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3359 the Spectre variant 2 (indirect branch prediction)
3360 vulnerability. System may allow data leaks with this
3361 option.
3362
3363 nospec_store_bypass_disable
3364 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3365
3366 no_uaccess_flush
3367 [PPC] Don't flush the L1-D cache after accessing user data.
3368
3369 noxsave [BUGS=X86] Disables x86 extended register state save
3370 and restore using xsave. The kernel will fallback to
3371 enabling legacy floating-point and sse state.
3372
3373 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3374 register states. The kernel will fall back to use
3375 xsave to save the states. By using this parameter,
3376 performance of saving the states is degraded because
3377 xsave doesn't support modified optimization while
3378 xsaveopt supports it on xsaveopt enabled systems.
3379
3380 noxsaves [X86] Disables xsaves and xrstors used in saving and
3381 restoring x86 extended register state in compacted
3382 form of xsave area. The kernel will fall back to use
3383 xsaveopt and xrstor to save and restore the states
3384 in standard form of xsave area. By using this
3385 parameter, xsave area per process might occupy more
3386 memory on xsaves enabled systems.
3387
3388 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3389 in do_idle() and not use the arch_cpu_idle()
3390 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3391 to be effective. This is useful on platforms where the
3392 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3393 correctly or when doing power measurements to evalute
3394 the impact of the sleep instructions. This is also
3395 useful when using JTAG debugger.
3396
3397 no_file_caps Tells the kernel not to honor file capabilities. The
3398 only way then for a file to be executed with privilege
3399 is to be setuid root or executed by root.
3400
3401 nohalt [IA-64] Tells the kernel not to use the power saving
3402 function PAL_HALT_LIGHT when idle. This increases
3403 power-consumption. On the positive side, it reduces
3404 interrupt wake-up latency, which may improve performance
3405 in certain environments such as networked servers or
3406 real-time systems.
3407
3408 no_hash_pointers
3409 Force pointers printed to the console or buffers to be
3410 unhashed. By default, when a pointer is printed via %p
3411 format string, that pointer is "hashed", i.e. obscured
3412 by hashing the pointer value. This is a security feature
3413 that hides actual kernel addresses from unprivileged
3414 users, but it also makes debugging the kernel more
3415 difficult since unequal pointers can no longer be
3416 compared. However, if this command-line option is
3417 specified, then all normal pointers will have their true
3418 value printed. Pointers printed via %pK may still be
3419 hashed. This option should only be specified when
3420 debugging the kernel. Please do not use on production
3421 kernels.
3422
3423 nohibernate [HIBERNATION] Disable hibernation and resume.
3424
3425 nohz= [KNL] Boottime enable/disable dynamic ticks
3426 Valid arguments: on, off
3427 Default: on
3428
3429 nohz_full= [KNL,BOOT,SMP,ISOL]
3430 The argument is a cpu list, as described above.
3431 In kernels built with CONFIG_NO_HZ_FULL=y, set
3432 the specified list of CPUs whose tick will be stopped
3433 whenever possible. The boot CPU will be forced outside
3434 the range to maintain the timekeeping. Any CPUs
3435 in this list will have their RCU callbacks offloaded,
3436 just as if they had also been called out in the
3437 rcu_nocbs= boot parameter.
3438
3439 noiotrap [SH] Disables trapped I/O port accesses.
3440
3441 noirqdebug [X86-32] Disables the code which attempts to detect and
3442 disable unhandled interrupt sources.
3443
3444 no_timer_check [X86,APIC] Disables the code which tests for
3445 broken timer IRQ sources.
3446
3447 noisapnp [ISAPNP] Disables ISA PnP code.
3448
3449 noinitrd [RAM] Tells the kernel not to load any configured
3450 initial RAM disk.
3451
3452 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3453 remapping.
3454 [Deprecated - use intremap=off]
3455
3456 nointroute [IA-64]
3457
3458 noinvpcid [X86] Disable the INVPCID cpu feature.
3459
3460 nojitter [IA-64] Disables jitter checking for ITC timers.
3461
3462 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3463
3464 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3465 fault handling.
3466
3467 no-vmw-sched-clock
3468 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3469 clock and use the default one.
3470
3471 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3472 accounting. steal time is computed, but won't
3473 influence scheduler behaviour
3474
3475 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3476
3477 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3478
3479 noltlbs [PPC] Do not use large page/tlb entries for kernel
3480 lowmem mapping on PPC40x and PPC8xx
3481
3482 nomca [IA-64] Disable machine check abort handling
3483
3484 nomce [X86-32] Disable Machine Check Exception
3485
3486 nomfgpt [X86-32] Disable Multi-Function General Purpose
3487 Timer usage (for AMD Geode machines).
3488
3489 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3490 shutdown the other cpus. Instead use the REBOOT_VECTOR
3491 irq.
3492
3493 nomodule Disable module load
3494
3495 nopat [X86] Disable PAT (page attribute table extension of
3496 pagetables) support.
3497
3498 nopcid [X86-64] Disable the PCID cpu feature.
3499
3500 norandmaps Don't use address space randomization. Equivalent to
3501 echo 0 > /proc/sys/kernel/randomize_va_space
3502
3503 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3504 with UP alternatives
3505
3506 nordrand [X86] Disable kernel use of the RDRAND and
3507 RDSEED instructions even if they are supported
3508 by the processor. RDRAND and RDSEED are still
3509 available to user space applications.
3510
3511 noresume [SWSUSP] Disables resume and restores original swap
3512 space.
3513
3514 no-scroll [VGA] Disables scrollback.
3515 This is required for the Braillex ib80-piezo Braille
3516 reader made by F.H. Papenmeier (Germany).
3517
3518 nosbagart [IA-64]
3519
3520 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3521
3522 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3523
3524 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3525 and disable the IO APIC. legacy for "maxcpus=0".
3526
3527 nosoftlockup [KNL] Disable the soft-lockup detector.
3528
3529 nosync [HW,M68K] Disables sync negotiation for all devices.
3530
3531 nowatchdog [KNL] Disable both lockup detectors, i.e.
3532 soft-lockup and NMI watchdog (hard-lockup).
3533
3534 nowb [ARM]
3535
3536 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3537
3538 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3539 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3540 Some features depend on CPU0. Known dependencies are:
3541 1. Resume from suspend/hibernate depends on CPU0.
3542 Suspend/hibernate will fail if CPU0 is offline and you
3543 need to online CPU0 before suspend/hibernate.
3544 2. PIC interrupts also depend on CPU0. CPU0 can't be
3545 removed if a PIC interrupt is detected.
3546 It's said poweroff/reboot may depend on CPU0 on some
3547 machines although I haven't seen such issues so far
3548 after CPU0 is offline on a few tested machines.
3549 If the dependencies are under your control, you can
3550 turn on cpu0_hotplug.
3551
3552 nps_mtm_hs_ctr= [KNL,ARC]
3553 This parameter sets the maximum duration, in
3554 cycles, each HW thread of the CTOP can run
3555 without interruptions, before HW switches it.
3556 The actual maximum duration is 16 times this
3557 parameter's value.
3558 Format: integer between 1 and 255
3559 Default: 255
3560
3561 nptcg= [IA-64] Override max number of concurrent global TLB
3562 purges which is reported from either PAL_VM_SUMMARY or
3563 SAL PALO.
3564
3565 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3566 could support. nr_cpus=n : n >= 1 limits the kernel to
3567 support 'n' processors. It could be larger than the
3568 number of already plugged CPU during bootup, later in
3569 runtime you can physically add extra cpu until it reaches
3570 n. So during boot up some boot time memory for per-cpu
3571 variables need be pre-allocated for later physical cpu
3572 hot plugging.
3573
3574 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3575
3576 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3577 set up a single NUMA node spanning all memory.
3578
3579 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3580 NUMA balancing.
3581 Allowed values are enable and disable
3582
3583 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3584 'node', 'default' can be specified
3585 This can be set from sysctl after boot.
3586 See Documentation/admin-guide/sysctl/vm.rst for details.
3587
3588 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3589 See Documentation/core-api/debugging-via-ohci1394.rst for more
3590 info.
3591
3592 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3593 Rather than timing out after 20 ms if an EC
3594 command is not properly ACKed, override the length
3595 of the timeout. We have interrupts disabled while
3596 waiting for the ACK, so if this is set too high
3597 interrupts *may* be lost!
3598
3599 omap_mux= [OMAP] Override bootloader pin multiplexing.
3600 Format: <mux_mode0.mode_name=value>...
3601 For example, to override I2C bus2:
3602 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3603
3604 oops=panic Always panic on oopses. Default is to just kill the
3605 process, but there is a small probability of
3606 deadlocking the machine.
3607 This will also cause panics on machine check exceptions.
3608 Useful together with panic=30 to trigger a reboot.
3609
3610 page_alloc.shuffle=
3611 [KNL] Boolean flag to control whether the page allocator
3612 should randomize its free lists. The randomization may
3613 be automatically enabled if the kernel detects it is
3614 running on a platform with a direct-mapped memory-side
3615 cache, and this parameter can be used to
3616 override/disable that behavior. The state of the flag
3617 can be read from sysfs at:
3618 /sys/module/page_alloc/parameters/shuffle.
3619
3620 page_owner= [KNL] Boot-time page_owner enabling option.
3621 Storage of the information about who allocated
3622 each page is disabled in default. With this switch,
3623 we can turn it on.
3624 on: enable the feature
3625
3626 page_poison= [KNL] Boot-time parameter changing the state of
3627 poisoning on the buddy allocator, available with
3628 CONFIG_PAGE_POISONING=y.
3629 off: turn off poisoning (default)
3630 on: turn on poisoning
3631
3632 page_reporting.page_reporting_order=
3633 [KNL] Minimal page reporting order
3634 Format: <integer>
3635 Adjust the minimal page reporting order. The page
3636 reporting is disabled when it exceeds (MAX_ORDER-1).
3637
3638 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3639 timeout > 0: seconds before rebooting
3640 timeout = 0: wait forever
3641 timeout < 0: reboot immediately
3642 Format: <timeout>
3643
3644 panic_print= Bitmask for printing system info when panic happens.
3645 User can chose combination of the following bits:
3646 bit 0: print all tasks info
3647 bit 1: print system memory info
3648 bit 2: print timer info
3649 bit 3: print locks info if CONFIG_LOCKDEP is on
3650 bit 4: print ftrace buffer
3651 bit 5: print all printk messages in buffer
3652
3653 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3654 Format: <hex>[,nousertaint]
3655 Hexadecimal bitmask representing the set of TAINT flags
3656 that will cause the kernel to panic when add_taint() is
3657 called with any of the flags in this set.
3658 The optional switch "nousertaint" can be utilized to
3659 prevent userspace forced crashes by writing to sysctl
3660 /proc/sys/kernel/tainted any flagset matching with the
3661 bitmask set on panic_on_taint.
3662 See Documentation/admin-guide/tainted-kernels.rst for
3663 extra details on the taint flags that users can pick
3664 to compose the bitmask to assign to panic_on_taint.
3665
3666 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3667 on a WARN().
3668
3669 crash_kexec_post_notifiers
3670 Run kdump after running panic-notifiers and dumping
3671 kmsg. This only for the users who doubt kdump always
3672 succeeds in any situation.
3673 Note that this also increases risks of kdump failure,
3674 because some panic notifiers can make the crashed
3675 kernel more unstable.
3676
3677 parkbd.port= [HW] Parallel port number the keyboard adapter is
3678 connected to, default is 0.
3679 Format: <parport#>
3680 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3681 0 for XT, 1 for AT (default is AT).
3682 Format: <mode>
3683
3684 parport= [HW,PPT] Specify parallel ports. 0 disables.
3685 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3686 Use 'auto' to force the driver to use any
3687 IRQ/DMA settings detected (the default is to
3688 ignore detected IRQ/DMA settings because of
3689 possible conflicts). You can specify the base
3690 address, IRQ, and DMA settings; IRQ and DMA
3691 should be numbers, or 'auto' (for using detected
3692 settings on that particular port), or 'nofifo'
3693 (to avoid using a FIFO even if it is detected).
3694 Parallel ports are assigned in the order they
3695 are specified on the command line, starting
3696 with parport0.
3697
3698 parport_init_mode= [HW,PPT]
3699 Configure VIA parallel port to operate in
3700 a specific mode. This is necessary on Pegasos
3701 computer where firmware has no options for setting
3702 up parallel port mode and sets it to spp.
3703 Currently this function knows 686a and 8231 chips.
3704 Format: [spp|ps2|epp|ecp|ecpepp]
3705
3706 pata_legacy.all= [HW,LIBATA]
3707 Format: <int>
3708 Set to non-zero to probe primary and secondary ISA
3709 port ranges on PCI systems where no PCI PATA device
3710 has been found at either range. Disabled by default.
3711
3712 pata_legacy.autospeed= [HW,LIBATA]
3713 Format: <int>
3714 Set to non-zero if a chip is present that snoops speed
3715 changes. Disabled by default.
3716
3717 pata_legacy.ht6560a= [HW,LIBATA]
3718 Format: <int>
3719 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3720 the secondary channel, or both channels respectively.
3721 Disabled by default.
3722
3723 pata_legacy.ht6560b= [HW,LIBATA]
3724 Format: <int>
3725 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3726 the secondary channel, or both channels respectively.
3727 Disabled by default.
3728
3729 pata_legacy.iordy_mask= [HW,LIBATA]
3730 Format: <int>
3731 IORDY enable mask. Set individual bits to allow IORDY
3732 for the respective channel. Bit 0 is for the first
3733 legacy channel handled by this driver, bit 1 is for
3734 the second channel, and so on. The sequence will often
3735 correspond to the primary legacy channel, the secondary
3736 legacy channel, and so on, but the handling of a PCI
3737 bus and the use of other driver options may interfere
3738 with the sequence. By default IORDY is allowed across
3739 all channels.
3740
3741 pata_legacy.opti82c46x= [HW,LIBATA]
3742 Format: <int>
3743 Set to 1, 2, or 3 for Opti 82c611A on the primary
3744 channel, the secondary channel, or both channels
3745 respectively. Disabled by default.
3746
3747 pata_legacy.opti82c611a= [HW,LIBATA]
3748 Format: <int>
3749 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3750 channel, the secondary channel, or both channels
3751 respectively. Disabled by default.
3752
3753 pata_legacy.pio_mask= [HW,LIBATA]
3754 Format: <int>
3755 PIO mode mask for autospeed devices. Set individual
3756 bits to allow the use of the respective PIO modes.
3757 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3758 All modes allowed by default.
3759
3760 pata_legacy.probe_all= [HW,LIBATA]
3761 Format: <int>
3762 Set to non-zero to probe tertiary and further ISA
3763 port ranges on PCI systems. Disabled by default.
3764
3765 pata_legacy.probe_mask= [HW,LIBATA]
3766 Format: <int>
3767 Probe mask for legacy ISA PATA ports. Depending on
3768 platform configuration and the use of other driver
3769 options up to 6 legacy ports are supported: 0x1f0,
3770 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3771 of individual ports can be disabled by setting the
3772 corresponding bits in the mask to 1. Bit 0 is for
3773 the first port in the list above (0x1f0), and so on.
3774 By default all supported ports are probed.
3775
3776 pata_legacy.qdi= [HW,LIBATA]
3777 Format: <int>
3778 Set to non-zero to probe QDI controllers. By default
3779 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3780
3781 pata_legacy.winbond= [HW,LIBATA]
3782 Format: <int>
3783 Set to non-zero to probe Winbond controllers. Use
3784 the standard I/O port (0x130) if 1, otherwise the
3785 value given is the I/O port to use (typically 0x1b0).
3786 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3787 0 otherwise.
3788
3789 pata_platform.pio_mask= [HW,LIBATA]
3790 Format: <int>
3791 Supported PIO mode mask. Set individual bits to allow
3792 the use of the respective PIO modes. Bit 0 is for
3793 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3794 allowed by default.
3795
3796 pause_on_oops=
3797 Halt all CPUs after the first oops has been printed for
3798 the specified number of seconds. This is to be used if
3799 your oopses keep scrolling off the screen.
3800
3801 pcbit= [HW,ISDN]
3802
3803 pcd. [PARIDE]
3804 See header of drivers/block/paride/pcd.c.
3805 See also Documentation/admin-guide/blockdev/paride.rst.
3806
3807 pci=option[,option...] [PCI] various PCI subsystem options.
3808
3809 Some options herein operate on a specific device
3810 or a set of devices (<pci_dev>). These are
3811 specified in one of the following formats:
3812
3813 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3814 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3815
3816 Note: the first format specifies a PCI
3817 bus/device/function address which may change
3818 if new hardware is inserted, if motherboard
3819 firmware changes, or due to changes caused
3820 by other kernel parameters. If the
3821 domain is left unspecified, it is
3822 taken to be zero. Optionally, a path
3823 to a device through multiple device/function
3824 addresses can be specified after the base
3825 address (this is more robust against
3826 renumbering issues). The second format
3827 selects devices using IDs from the
3828 configuration space which may match multiple
3829 devices in the system.
3830
3831 earlydump dump PCI config space before the kernel
3832 changes anything
3833 off [X86] don't probe for the PCI bus
3834 bios [X86-32] force use of PCI BIOS, don't access
3835 the hardware directly. Use this if your machine
3836 has a non-standard PCI host bridge.
3837 nobios [X86-32] disallow use of PCI BIOS, only direct
3838 hardware access methods are allowed. Use this
3839 if you experience crashes upon bootup and you
3840 suspect they are caused by the BIOS.
3841 conf1 [X86] Force use of PCI Configuration Access
3842 Mechanism 1 (config address in IO port 0xCF8,
3843 data in IO port 0xCFC, both 32-bit).
3844 conf2 [X86] Force use of PCI Configuration Access
3845 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3846 the function, IO port 0xCFA, also 8-bit, sets
3847 bus number. The config space is then accessed
3848 through ports 0xC000-0xCFFF).
3849 See http://wiki.osdev.org/PCI for more info
3850 on the configuration access mechanisms.
3851 noaer [PCIE] If the PCIEAER kernel config parameter is
3852 enabled, this kernel boot option can be used to
3853 disable the use of PCIE advanced error reporting.
3854 nodomains [PCI] Disable support for multiple PCI
3855 root domains (aka PCI segments, in ACPI-speak).
3856 nommconf [X86] Disable use of MMCONFIG for PCI
3857 Configuration
3858 check_enable_amd_mmconf [X86] check for and enable
3859 properly configured MMIO access to PCI
3860 config space on AMD family 10h CPU
3861 nomsi [MSI] If the PCI_MSI kernel config parameter is
3862 enabled, this kernel boot option can be used to
3863 disable the use of MSI interrupts system-wide.
3864 noioapicquirk [APIC] Disable all boot interrupt quirks.
3865 Safety option to keep boot IRQs enabled. This
3866 should never be necessary.
3867 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3868 primary IO-APIC for bridges that cannot disable
3869 boot IRQs. This fixes a source of spurious IRQs
3870 when the system masks IRQs.
3871 noioapicreroute [APIC] Disable workaround that uses the
3872 boot IRQ equivalent of an IRQ that connects to
3873 a chipset where boot IRQs cannot be disabled.
3874 The opposite of ioapicreroute.
3875 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3876 routing table. These calls are known to be buggy
3877 on several machines and they hang the machine
3878 when used, but on other computers it's the only
3879 way to get the interrupt routing table. Try
3880 this option if the kernel is unable to allocate
3881 IRQs or discover secondary PCI buses on your
3882 motherboard.
3883 rom [X86] Assign address space to expansion ROMs.
3884 Use with caution as certain devices share
3885 address decoders between ROMs and other
3886 resources.
3887 norom [X86] Do not assign address space to
3888 expansion ROMs that do not already have
3889 BIOS assigned address ranges.
3890 nobar [X86] Do not assign address space to the
3891 BARs that weren't assigned by the BIOS.
3892 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3893 assigned automatically to PCI devices. You can
3894 make the kernel exclude IRQs of your ISA cards
3895 this way.
3896 pirqaddr=0xAAAAA [X86] Specify the physical address
3897 of the PIRQ table (normally generated
3898 by the BIOS) if it is outside the
3899 F0000h-100000h range.
3900 lastbus=N [X86] Scan all buses thru bus #N. Can be
3901 useful if the kernel is unable to find your
3902 secondary buses and you want to tell it
3903 explicitly which ones they are.
3904 assign-busses [X86] Always assign all PCI bus
3905 numbers ourselves, overriding
3906 whatever the firmware may have done.
3907 usepirqmask [X86] Honor the possible IRQ mask stored
3908 in the BIOS $PIR table. This is needed on
3909 some systems with broken BIOSes, notably
3910 some HP Pavilion N5400 and Omnibook XE3
3911 notebooks. This will have no effect if ACPI
3912 IRQ routing is enabled.
3913 noacpi [X86] Do not use ACPI for IRQ routing
3914 or for PCI scanning.
3915 use_crs [X86] Use PCI host bridge window information
3916 from ACPI. On BIOSes from 2008 or later, this
3917 is enabled by default. If you need to use this,
3918 please report a bug.
3919 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3920 If you need to use this, please report a bug.
3921 routeirq Do IRQ routing for all PCI devices.
3922 This is normally done in pci_enable_device(),
3923 so this option is a temporary workaround
3924 for broken drivers that don't call it.
3925 skip_isa_align [X86] do not align io start addr, so can
3926 handle more pci cards
3927 noearly [X86] Don't do any early type 1 scanning.
3928 This might help on some broken boards which
3929 machine check when some devices' config space
3930 is read. But various workarounds are disabled
3931 and some IOMMU drivers will not work.
3932 bfsort Sort PCI devices into breadth-first order.
3933 This sorting is done to get a device
3934 order compatible with older (<= 2.4) kernels.
3935 nobfsort Don't sort PCI devices into breadth-first order.
3936 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3937 tuning and use the BIOS-configured MPS defaults.
3938 pcie_bus_safe Set every device's MPS to the largest value
3939 supported by all devices below the root complex.
3940 pcie_bus_perf Set device MPS to the largest allowable MPS
3941 based on its parent bus. Also set MRRS (Max
3942 Read Request Size) to the largest supported
3943 value (no larger than the MPS that the device
3944 or bus can support) for best performance.
3945 pcie_bus_peer2peer Set every device's MPS to 128B, which
3946 every device is guaranteed to support. This
3947 configuration allows peer-to-peer DMA between
3948 any pair of devices, possibly at the cost of
3949 reduced performance. This also guarantees
3950 that hot-added devices will work.
3951 cbiosize=nn[KMG] The fixed amount of bus space which is
3952 reserved for the CardBus bridge's IO window.
3953 The default value is 256 bytes.
3954 cbmemsize=nn[KMG] The fixed amount of bus space which is
3955 reserved for the CardBus bridge's memory
3956 window. The default value is 64 megabytes.
3957 resource_alignment=
3958 Format:
3959 [<order of align>@]<pci_dev>[; ...]
3960 Specifies alignment and device to reassign
3961 aligned memory resources. How to
3962 specify the device is described above.
3963 If <order of align> is not specified,
3964 PAGE_SIZE is used as alignment.
3965 A PCI-PCI bridge can be specified if resource
3966 windows need to be expanded.
3967 To specify the alignment for several
3968 instances of a device, the PCI vendor,
3969 device, subvendor, and subdevice may be
3970 specified, e.g., 12@pci:8086:9c22:103c:198f
3971 for 4096-byte alignment.
3972 ecrc= Enable/disable PCIe ECRC (transaction layer
3973 end-to-end CRC checking).
3974 bios: Use BIOS/firmware settings. This is the
3975 the default.
3976 off: Turn ECRC off
3977 on: Turn ECRC on.
3978 hpiosize=nn[KMG] The fixed amount of bus space which is
3979 reserved for hotplug bridge's IO window.
3980 Default size is 256 bytes.
3981 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3982 reserved for hotplug bridge's MMIO window.
3983 Default size is 2 megabytes.
3984 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3985 reserved for hotplug bridge's MMIO_PREF window.
3986 Default size is 2 megabytes.
3987 hpmemsize=nn[KMG] The fixed amount of bus space which is
3988 reserved for hotplug bridge's MMIO and
3989 MMIO_PREF window.
3990 Default size is 2 megabytes.
3991 hpbussize=nn The minimum amount of additional bus numbers
3992 reserved for buses below a hotplug bridge.
3993 Default is 1.
3994 realloc= Enable/disable reallocating PCI bridge resources
3995 if allocations done by BIOS are too small to
3996 accommodate resources required by all child
3997 devices.
3998 off: Turn realloc off
3999 on: Turn realloc on
4000 realloc same as realloc=on
4001 noari do not use PCIe ARI.
4002 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4003 do not use PCIe ATS (and IOMMU device IOTLB).
4004 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4005 only look for one device below a PCIe downstream
4006 port.
4007 big_root_window Try to add a big 64bit memory window to the PCIe
4008 root complex on AMD CPUs. Some GFX hardware
4009 can resize a BAR to allow access to all VRAM.
4010 Adding the window is slightly risky (it may
4011 conflict with unreported devices), so this
4012 taints the kernel.
4013 disable_acs_redir=<pci_dev>[; ...]
4014 Specify one or more PCI devices (in the format
4015 specified above) separated by semicolons.
4016 Each device specified will have the PCI ACS
4017 redirect capabilities forced off which will
4018 allow P2P traffic between devices through
4019 bridges without forcing it upstream. Note:
4020 this removes isolation between devices and
4021 may put more devices in an IOMMU group.
4022 force_floating [S390] Force usage of floating interrupts.
4023 nomio [S390] Do not use MIO instructions.
4024 norid [S390] ignore the RID field and force use of
4025 one PCI domain per PCI function
4026
4027 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4028 Management.
4029 off Disable ASPM.
4030 force Enable ASPM even on devices that claim not to support it.
4031 WARNING: Forcing ASPM on may cause system lockups.
4032
4033 pcie_ports= [PCIE] PCIe port services handling:
4034 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4035 even if the platform doesn't give the OS permission to
4036 use them. This may cause conflicts if the platform
4037 also tries to use these services.
4038 dpc-native Use native PCIe service for DPC only. May
4039 cause conflicts if firmware uses AER or DPC.
4040 compat Disable native PCIe services (PME, AER, DPC, PCIe
4041 hotplug).
4042
4043 pcie_port_pm= [PCIE] PCIe port power management handling:
4044 off Disable power management of all PCIe ports
4045 force Forcibly enable power management of all PCIe ports
4046
4047 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4048 nomsi Do not use MSI for native PCIe PME signaling (this makes
4049 all PCIe root ports use INTx for all services).
4050
4051 pcmv= [HW,PCMCIA] BadgePAD 4
4052
4053 pd_ignore_unused
4054 [PM]
4055 Keep all power-domains already enabled by bootloader on,
4056 even if no driver has claimed them. This is useful
4057 for debug and development, but should not be
4058 needed on a platform with proper driver support.
4059
4060 pd. [PARIDE]
4061 See Documentation/admin-guide/blockdev/paride.rst.
4062
4063 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4064 boot time.
4065 Format: { 0 | 1 }
4066 See arch/parisc/kernel/pdc_chassis.c
4067
4068 percpu_alloc= Select which percpu first chunk allocator to use.
4069 Currently supported values are "embed" and "page".
4070 Archs may support subset or none of the selections.
4071 See comments in mm/percpu.c for details on each
4072 allocator. This parameter is primarily for debugging
4073 and performance comparison.
4074
4075 pf. [PARIDE]
4076 See Documentation/admin-guide/blockdev/paride.rst.
4077
4078 pg. [PARIDE]
4079 See Documentation/admin-guide/blockdev/paride.rst.
4080
4081 pirq= [SMP,APIC] Manual mp-table setup
4082 See Documentation/x86/i386/IO-APIC.rst.
4083
4084 plip= [PPT,NET] Parallel port network link
4085 Format: { parport<nr> | timid | 0 }
4086 See also Documentation/admin-guide/parport.rst.
4087
4088 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4089 Override pmtimer IOPort with a hex value.
4090 e.g. pmtmr=0x508
4091
4092 pm_debug_messages [SUSPEND,KNL]
4093 Enable suspend/resume debug messages during boot up.
4094
4095 pnp.debug=1 [PNP]
4096 Enable PNP debug messages (depends on the
4097 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4098 via /sys/module/pnp/parameters/debug. We always show
4099 current resource usage; turning this on also shows
4100 possible settings and some assignment information.
4101
4102 pnpacpi= [ACPI]
4103 { off }
4104
4105 pnpbios= [ISAPNP]
4106 { on | off | curr | res | no-curr | no-res }
4107
4108 pnp_reserve_irq=
4109 [ISAPNP] Exclude IRQs for the autoconfiguration
4110
4111 pnp_reserve_dma=
4112 [ISAPNP] Exclude DMAs for the autoconfiguration
4113
4114 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4115 Ranges are in pairs (I/O port base and size).
4116
4117 pnp_reserve_mem=
4118 [ISAPNP] Exclude memory regions for the
4119 autoconfiguration.
4120 Ranges are in pairs (memory base and size).
4121
4122 ports= [IP_VS_FTP] IPVS ftp helper module
4123 Default is 21.
4124 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4125 may be specified.
4126 Format: <port>,<port>....
4127
4128 powersave=off [PPC] This option disables power saving features.
4129 It specifically disables cpuidle and sets the
4130 platform machine description specific power_save
4131 function to NULL. On Idle the CPU just reduces
4132 execution priority.
4133
4134 ppc_strict_facility_enable
4135 [PPC] This option catches any kernel floating point,
4136 Altivec, VSX and SPE outside of regions specifically
4137 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4138 There is some performance impact when enabling this.
4139
4140 ppc_tm= [PPC]
4141 Format: {"off"}
4142 Disable Hardware Transactional Memory
4143
4144 preempt= [KNL]
4145 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4146 none - Limited to cond_resched() calls
4147 voluntary - Limited to cond_resched() and might_sleep() calls
4148 full - Any section that isn't explicitly preempt disabled
4149 can be preempted anytime.
4150
4151 print-fatal-signals=
4152 [KNL] debug: print fatal signals
4153
4154 If enabled, warn about various signal handling
4155 related application anomalies: too many signals,
4156 too many POSIX.1 timers, fatal signals causing a
4157 coredump - etc.
4158
4159 If you hit the warning due to signal overflow,
4160 you might want to try "ulimit -i unlimited".
4161
4162 default: off.
4163
4164 printk.always_kmsg_dump=
4165 Trigger kmsg_dump for cases other than kernel oops or
4166 panics
4167 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4168 default: disabled
4169
4170 printk.devkmsg={on,off,ratelimit}
4171 Control writing to /dev/kmsg.
4172 on - unlimited logging to /dev/kmsg from userspace
4173 off - logging to /dev/kmsg disabled
4174 ratelimit - ratelimit the logging
4175 Default: ratelimit
4176
4177 printk.time= Show timing data prefixed to each printk message line
4178 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4179
4180 processor.max_cstate= [HW,ACPI]
4181 Limit processor to maximum C-state
4182 max_cstate=9 overrides any DMI blacklist limit.
4183
4184 processor.nocst [HW,ACPI]
4185 Ignore the _CST method to determine C-states,
4186 instead using the legacy FADT method
4187
4188 profile= [KNL] Enable kernel profiling via /proc/profile
4189 Format: [<profiletype>,]<number>
4190 Param: <profiletype>: "schedule", "sleep", or "kvm"
4191 [defaults to kernel profiling]
4192 Param: "schedule" - profile schedule points.
4193 Param: "sleep" - profile D-state sleeping (millisecs).
4194 Requires CONFIG_SCHEDSTATS
4195 Param: "kvm" - profile VM exits.
4196 Param: <number> - step/bucket size as a power of 2 for
4197 statistical time based profiling.
4198
4199 prompt_ramdisk= [RAM] [Deprecated]
4200
4201 prot_virt= [S390] enable hosting protected virtual machines
4202 isolated from the hypervisor (if hardware supports
4203 that).
4204 Format: <bool>
4205
4206 psi= [KNL] Enable or disable pressure stall information
4207 tracking.
4208 Format: <bool>
4209
4210 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4211 probe for; one of (bare|imps|exps|lifebook|any).
4212 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4213 per second.
4214 psmouse.resetafter= [HW,MOUSE]
4215 Try to reset the device after so many bad packets
4216 (0 = never).
4217 psmouse.resolution=
4218 [HW,MOUSE] Set desired mouse resolution, in dpi.
4219 psmouse.smartscroll=
4220 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4221 0 = disabled, 1 = enabled (default).
4222
4223 pstore.backend= Specify the name of the pstore backend to use
4224
4225 pt. [PARIDE]
4226 See Documentation/admin-guide/blockdev/paride.rst.
4227
4228 pti= [X86-64] Control Page Table Isolation of user and
4229 kernel address spaces. Disabling this feature
4230 removes hardening, but improves performance of
4231 system calls and interrupts.
4232
4233 on - unconditionally enable
4234 off - unconditionally disable
4235 auto - kernel detects whether your CPU model is
4236 vulnerable to issues that PTI mitigates
4237
4238 Not specifying this option is equivalent to pti=auto.
4239
4240 nopti [X86-64]
4241 Equivalent to pti=off
4242
4243 pty.legacy_count=
4244 [KNL] Number of legacy pty's. Overwrites compiled-in
4245 default number.
4246
4247 quiet [KNL] Disable most log messages
4248
4249 r128= [HW,DRM]
4250
4251 raid= [HW,RAID]
4252 See Documentation/admin-guide/md.rst.
4253
4254 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4255 See Documentation/admin-guide/blockdev/ramdisk.rst.
4256
4257 ramdisk_start= [RAM] RAM disk image start address
4258
4259 random.trust_cpu={on,off}
4260 [KNL] Enable or disable trusting the use of the
4261 CPU's random number generator (if available) to
4262 fully seed the kernel's CRNG. Default is controlled
4263 by CONFIG_RANDOM_TRUST_CPU.
4264
4265 randomize_kstack_offset=
4266 [KNL] Enable or disable kernel stack offset
4267 randomization, which provides roughly 5 bits of
4268 entropy, frustrating memory corruption attacks
4269 that depend on stack address determinism or
4270 cross-syscall address exposures. This is only
4271 available on architectures that have defined
4272 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4273 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4274 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4275
4276 ras=option[,option,...] [KNL] RAS-specific options
4277
4278 cec_disable [X86]
4279 Disable the Correctable Errors Collector,
4280 see CONFIG_RAS_CEC help text.
4281
4282 rcu_nocbs= [KNL]
4283 The argument is a cpu list, as described above.
4284
4285 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4286 the specified list of CPUs to be no-callback CPUs.
4287 Invocation of these CPUs' RCU callbacks will be
4288 offloaded to "rcuox/N" kthreads created for that
4289 purpose, where "x" is "p" for RCU-preempt, and
4290 "s" for RCU-sched, and "N" is the CPU number.
4291 This reduces OS jitter on the offloaded CPUs,
4292 which can be useful for HPC and real-time
4293 workloads. It can also improve energy efficiency
4294 for asymmetric multiprocessors.
4295
4296 rcu_nocb_poll [KNL]
4297 Rather than requiring that offloaded CPUs
4298 (specified by rcu_nocbs= above) explicitly
4299 awaken the corresponding "rcuoN" kthreads,
4300 make these kthreads poll for callbacks.
4301 This improves the real-time response for the
4302 offloaded CPUs by relieving them of the need to
4303 wake up the corresponding kthread, but degrades
4304 energy efficiency by requiring that the kthreads
4305 periodically wake up to do the polling.
4306
4307 rcutree.blimit= [KNL]
4308 Set maximum number of finished RCU callbacks to
4309 process in one batch.
4310
4311 rcutree.dump_tree= [KNL]
4312 Dump the structure of the rcu_node combining tree
4313 out at early boot. This is used for diagnostic
4314 purposes, to verify correct tree setup.
4315
4316 rcutree.gp_cleanup_delay= [KNL]
4317 Set the number of jiffies to delay each step of
4318 RCU grace-period cleanup.
4319
4320 rcutree.gp_init_delay= [KNL]
4321 Set the number of jiffies to delay each step of
4322 RCU grace-period initialization.
4323
4324 rcutree.gp_preinit_delay= [KNL]
4325 Set the number of jiffies to delay each step of
4326 RCU grace-period pre-initialization, that is,
4327 the propagation of recent CPU-hotplug changes up
4328 the rcu_node combining tree.
4329
4330 rcutree.use_softirq= [KNL]
4331 If set to zero, move all RCU_SOFTIRQ processing to
4332 per-CPU rcuc kthreads. Defaults to a non-zero
4333 value, meaning that RCU_SOFTIRQ is used by default.
4334 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4335
4336 But note that CONFIG_PREEMPT_RT=y kernels disable
4337 this kernel boot parameter, forcibly setting it
4338 to zero.
4339
4340 rcutree.rcu_fanout_exact= [KNL]
4341 Disable autobalancing of the rcu_node combining
4342 tree. This is used by rcutorture, and might
4343 possibly be useful for architectures having high
4344 cache-to-cache transfer latencies.
4345
4346 rcutree.rcu_fanout_leaf= [KNL]
4347 Change the number of CPUs assigned to each
4348 leaf rcu_node structure. Useful for very
4349 large systems, which will choose the value 64,
4350 and for NUMA systems with large remote-access
4351 latencies, which will choose a value aligned
4352 with the appropriate hardware boundaries.
4353
4354 rcutree.rcu_min_cached_objs= [KNL]
4355 Minimum number of objects which are cached and
4356 maintained per one CPU. Object size is equal
4357 to PAGE_SIZE. The cache allows to reduce the
4358 pressure to page allocator, also it makes the
4359 whole algorithm to behave better in low memory
4360 condition.
4361
4362 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4363 Set the page-cache refill delay (in milliseconds)
4364 in response to low-memory conditions. The range
4365 of permitted values is in the range 0:100000.
4366
4367 rcutree.jiffies_till_first_fqs= [KNL]
4368 Set delay from grace-period initialization to
4369 first attempt to force quiescent states.
4370 Units are jiffies, minimum value is zero,
4371 and maximum value is HZ.
4372
4373 rcutree.jiffies_till_next_fqs= [KNL]
4374 Set delay between subsequent attempts to force
4375 quiescent states. Units are jiffies, minimum
4376 value is one, and maximum value is HZ.
4377
4378 rcutree.jiffies_till_sched_qs= [KNL]
4379 Set required age in jiffies for a
4380 given grace period before RCU starts
4381 soliciting quiescent-state help from
4382 rcu_note_context_switch() and cond_resched().
4383 If not specified, the kernel will calculate
4384 a value based on the most recent settings
4385 of rcutree.jiffies_till_first_fqs
4386 and rcutree.jiffies_till_next_fqs.
4387 This calculated value may be viewed in
4388 rcutree.jiffies_to_sched_qs. Any attempt to set
4389 rcutree.jiffies_to_sched_qs will be cheerfully
4390 overwritten.
4391
4392 rcutree.kthread_prio= [KNL,BOOT]
4393 Set the SCHED_FIFO priority of the RCU per-CPU
4394 kthreads (rcuc/N). This value is also used for
4395 the priority of the RCU boost threads (rcub/N)
4396 and for the RCU grace-period kthreads (rcu_bh,
4397 rcu_preempt, and rcu_sched). If RCU_BOOST is
4398 set, valid values are 1-99 and the default is 1
4399 (the least-favored priority). Otherwise, when
4400 RCU_BOOST is not set, valid values are 0-99 and
4401 the default is zero (non-realtime operation).
4402
4403 rcutree.rcu_nocb_gp_stride= [KNL]
4404 Set the number of NOCB callback kthreads in
4405 each group, which defaults to the square root
4406 of the number of CPUs. Larger numbers reduce
4407 the wakeup overhead on the global grace-period
4408 kthread, but increases that same overhead on
4409 each group's NOCB grace-period kthread.
4410
4411 rcutree.qhimark= [KNL]
4412 Set threshold of queued RCU callbacks beyond which
4413 batch limiting is disabled.
4414
4415 rcutree.qlowmark= [KNL]
4416 Set threshold of queued RCU callbacks below which
4417 batch limiting is re-enabled.
4418
4419 rcutree.qovld= [KNL]
4420 Set threshold of queued RCU callbacks beyond which
4421 RCU's force-quiescent-state scan will aggressively
4422 enlist help from cond_resched() and sched IPIs to
4423 help CPUs more quickly reach quiescent states.
4424 Set to less than zero to make this be set based
4425 on rcutree.qhimark at boot time and to zero to
4426 disable more aggressive help enlistment.
4427
4428 rcutree.rcu_idle_gp_delay= [KNL]
4429 Set wakeup interval for idle CPUs that have
4430 RCU callbacks (RCU_FAST_NO_HZ=y).
4431
4432 rcutree.rcu_kick_kthreads= [KNL]
4433 Cause the grace-period kthread to get an extra
4434 wake_up() if it sleeps three times longer than
4435 it should at force-quiescent-state time.
4436 This wake_up() will be accompanied by a
4437 WARN_ONCE() splat and an ftrace_dump().
4438
4439 rcutree.rcu_unlock_delay= [KNL]
4440 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4441 this specifies an rcu_read_unlock()-time delay
4442 in microseconds. This defaults to zero.
4443 Larger delays increase the probability of
4444 catching RCU pointer leaks, that is, buggy use
4445 of RCU-protected pointers after the relevant
4446 rcu_read_unlock() has completed.
4447
4448 rcutree.sysrq_rcu= [KNL]
4449 Commandeer a sysrq key to dump out Tree RCU's
4450 rcu_node tree with an eye towards determining
4451 why a new grace period has not yet started.
4452
4453 rcuscale.gp_async= [KNL]
4454 Measure performance of asynchronous
4455 grace-period primitives such as call_rcu().
4456
4457 rcuscale.gp_async_max= [KNL]
4458 Specify the maximum number of outstanding
4459 callbacks per writer thread. When a writer
4460 thread exceeds this limit, it invokes the
4461 corresponding flavor of rcu_barrier() to allow
4462 previously posted callbacks to drain.
4463
4464 rcuscale.gp_exp= [KNL]
4465 Measure performance of expedited synchronous
4466 grace-period primitives.
4467
4468 rcuscale.holdoff= [KNL]
4469 Set test-start holdoff period. The purpose of
4470 this parameter is to delay the start of the
4471 test until boot completes in order to avoid
4472 interference.
4473
4474 rcuscale.kfree_rcu_test= [KNL]
4475 Set to measure performance of kfree_rcu() flooding.
4476
4477 rcuscale.kfree_rcu_test_double= [KNL]
4478 Test the double-argument variant of kfree_rcu().
4479 If this parameter has the same value as
4480 rcuscale.kfree_rcu_test_single, both the single-
4481 and double-argument variants are tested.
4482
4483 rcuscale.kfree_rcu_test_single= [KNL]
4484 Test the single-argument variant of kfree_rcu().
4485 If this parameter has the same value as
4486 rcuscale.kfree_rcu_test_double, both the single-
4487 and double-argument variants are tested.
4488
4489 rcuscale.kfree_nthreads= [KNL]
4490 The number of threads running loops of kfree_rcu().
4491
4492 rcuscale.kfree_alloc_num= [KNL]
4493 Number of allocations and frees done in an iteration.
4494
4495 rcuscale.kfree_loops= [KNL]
4496 Number of loops doing rcuscale.kfree_alloc_num number
4497 of allocations and frees.
4498
4499 rcuscale.nreaders= [KNL]
4500 Set number of RCU readers. The value -1 selects
4501 N, where N is the number of CPUs. A value
4502 "n" less than -1 selects N-n+1, where N is again
4503 the number of CPUs. For example, -2 selects N
4504 (the number of CPUs), -3 selects N+1, and so on.
4505 A value of "n" less than or equal to -N selects
4506 a single reader.
4507
4508 rcuscale.nwriters= [KNL]
4509 Set number of RCU writers. The values operate
4510 the same as for rcuscale.nreaders.
4511 N, where N is the number of CPUs
4512
4513 rcuscale.perf_type= [KNL]
4514 Specify the RCU implementation to test.
4515
4516 rcuscale.shutdown= [KNL]
4517 Shut the system down after performance tests
4518 complete. This is useful for hands-off automated
4519 testing.
4520
4521 rcuscale.verbose= [KNL]
4522 Enable additional printk() statements.
4523
4524 rcuscale.writer_holdoff= [KNL]
4525 Write-side holdoff between grace periods,
4526 in microseconds. The default of zero says
4527 no holdoff.
4528
4529 rcutorture.fqs_duration= [KNL]
4530 Set duration of force_quiescent_state bursts
4531 in microseconds.
4532
4533 rcutorture.fqs_holdoff= [KNL]
4534 Set holdoff time within force_quiescent_state bursts
4535 in microseconds.
4536
4537 rcutorture.fqs_stutter= [KNL]
4538 Set wait time between force_quiescent_state bursts
4539 in seconds.
4540
4541 rcutorture.fwd_progress= [KNL]
4542 Enable RCU grace-period forward-progress testing
4543 for the types of RCU supporting this notion.
4544
4545 rcutorture.fwd_progress_div= [KNL]
4546 Specify the fraction of a CPU-stall-warning
4547 period to do tight-loop forward-progress testing.
4548
4549 rcutorture.fwd_progress_holdoff= [KNL]
4550 Number of seconds to wait between successive
4551 forward-progress tests.
4552
4553 rcutorture.fwd_progress_need_resched= [KNL]
4554 Enclose cond_resched() calls within checks for
4555 need_resched() during tight-loop forward-progress
4556 testing.
4557
4558 rcutorture.gp_cond= [KNL]
4559 Use conditional/asynchronous update-side
4560 primitives, if available.
4561
4562 rcutorture.gp_exp= [KNL]
4563 Use expedited update-side primitives, if available.
4564
4565 rcutorture.gp_normal= [KNL]
4566 Use normal (non-expedited) asynchronous
4567 update-side primitives, if available.
4568
4569 rcutorture.gp_sync= [KNL]
4570 Use normal (non-expedited) synchronous
4571 update-side primitives, if available. If all
4572 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4573 rcutorture.gp_normal=, and rcutorture.gp_sync=
4574 are zero, rcutorture acts as if is interpreted
4575 they are all non-zero.
4576
4577 rcutorture.irqreader= [KNL]
4578 Run RCU readers from irq handlers, or, more
4579 accurately, from a timer handler. Not all RCU
4580 flavors take kindly to this sort of thing.
4581
4582 rcutorture.leakpointer= [KNL]
4583 Leak an RCU-protected pointer out of the reader.
4584 This can of course result in splats, and is
4585 intended to test the ability of things like
4586 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4587 such leaks.
4588
4589 rcutorture.n_barrier_cbs= [KNL]
4590 Set callbacks/threads for rcu_barrier() testing.
4591
4592 rcutorture.nfakewriters= [KNL]
4593 Set number of concurrent RCU writers. These just
4594 stress RCU, they don't participate in the actual
4595 test, hence the "fake".
4596
4597 rcutorture.nocbs_nthreads= [KNL]
4598 Set number of RCU callback-offload togglers.
4599 Zero (the default) disables toggling.
4600
4601 rcutorture.nocbs_toggle= [KNL]
4602 Set the delay in milliseconds between successive
4603 callback-offload toggling attempts.
4604
4605 rcutorture.nreaders= [KNL]
4606 Set number of RCU readers. The value -1 selects
4607 N-1, where N is the number of CPUs. A value
4608 "n" less than -1 selects N-n-2, where N is again
4609 the number of CPUs. For example, -2 selects N
4610 (the number of CPUs), -3 selects N+1, and so on.
4611
4612 rcutorture.object_debug= [KNL]
4613 Enable debug-object double-call_rcu() testing.
4614
4615 rcutorture.onoff_holdoff= [KNL]
4616 Set time (s) after boot for CPU-hotplug testing.
4617
4618 rcutorture.onoff_interval= [KNL]
4619 Set time (jiffies) between CPU-hotplug operations,
4620 or zero to disable CPU-hotplug testing.
4621
4622 rcutorture.read_exit= [KNL]
4623 Set the number of read-then-exit kthreads used
4624 to test the interaction of RCU updaters and
4625 task-exit processing.
4626
4627 rcutorture.read_exit_burst= [KNL]
4628 The number of times in a given read-then-exit
4629 episode that a set of read-then-exit kthreads
4630 is spawned.
4631
4632 rcutorture.read_exit_delay= [KNL]
4633 The delay, in seconds, between successive
4634 read-then-exit testing episodes.
4635
4636 rcutorture.shuffle_interval= [KNL]
4637 Set task-shuffle interval (s). Shuffling tasks
4638 allows some CPUs to go into dyntick-idle mode
4639 during the rcutorture test.
4640
4641 rcutorture.shutdown_secs= [KNL]
4642 Set time (s) after boot system shutdown. This
4643 is useful for hands-off automated testing.
4644
4645 rcutorture.stall_cpu= [KNL]
4646 Duration of CPU stall (s) to test RCU CPU stall
4647 warnings, zero to disable.
4648
4649 rcutorture.stall_cpu_block= [KNL]
4650 Sleep while stalling if set. This will result
4651 in warnings from preemptible RCU in addition
4652 to any other stall-related activity.
4653
4654 rcutorture.stall_cpu_holdoff= [KNL]
4655 Time to wait (s) after boot before inducing stall.
4656
4657 rcutorture.stall_cpu_irqsoff= [KNL]
4658 Disable interrupts while stalling if set.
4659
4660 rcutorture.stall_gp_kthread= [KNL]
4661 Duration (s) of forced sleep within RCU
4662 grace-period kthread to test RCU CPU stall
4663 warnings, zero to disable. If both stall_cpu
4664 and stall_gp_kthread are specified, the
4665 kthread is starved first, then the CPU.
4666
4667 rcutorture.stat_interval= [KNL]
4668 Time (s) between statistics printk()s.
4669
4670 rcutorture.stutter= [KNL]
4671 Time (s) to stutter testing, for example, specifying
4672 five seconds causes the test to run for five seconds,
4673 wait for five seconds, and so on. This tests RCU's
4674 ability to transition abruptly to and from idle.
4675
4676 rcutorture.test_boost= [KNL]
4677 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4678 "Maybe" means test if the RCU implementation
4679 under test support RCU priority boosting.
4680
4681 rcutorture.test_boost_duration= [KNL]
4682 Duration (s) of each individual boost test.
4683
4684 rcutorture.test_boost_interval= [KNL]
4685 Interval (s) between each boost test.
4686
4687 rcutorture.test_no_idle_hz= [KNL]
4688 Test RCU's dyntick-idle handling. See also the
4689 rcutorture.shuffle_interval parameter.
4690
4691 rcutorture.torture_type= [KNL]
4692 Specify the RCU implementation to test.
4693
4694 rcutorture.verbose= [KNL]
4695 Enable additional printk() statements.
4696
4697 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4698 Dump ftrace buffer after reporting RCU CPU
4699 stall warning.
4700
4701 rcupdate.rcu_cpu_stall_suppress= [KNL]
4702 Suppress RCU CPU stall warning messages.
4703
4704 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4705 Suppress RCU CPU stall warning messages and
4706 rcutorture writer stall warnings that occur
4707 during early boot, that is, during the time
4708 before the init task is spawned.
4709
4710 rcupdate.rcu_cpu_stall_timeout= [KNL]
4711 Set timeout for RCU CPU stall warning messages.
4712
4713 rcupdate.rcu_expedited= [KNL]
4714 Use expedited grace-period primitives, for
4715 example, synchronize_rcu_expedited() instead
4716 of synchronize_rcu(). This reduces latency,
4717 but can increase CPU utilization, degrade
4718 real-time latency, and degrade energy efficiency.
4719 No effect on CONFIG_TINY_RCU kernels.
4720
4721 rcupdate.rcu_normal= [KNL]
4722 Use only normal grace-period primitives,
4723 for example, synchronize_rcu() instead of
4724 synchronize_rcu_expedited(). This improves
4725 real-time latency, CPU utilization, and
4726 energy efficiency, but can expose users to
4727 increased grace-period latency. This parameter
4728 overrides rcupdate.rcu_expedited. No effect on
4729 CONFIG_TINY_RCU kernels.
4730
4731 rcupdate.rcu_normal_after_boot= [KNL]
4732 Once boot has completed (that is, after
4733 rcu_end_inkernel_boot() has been invoked), use
4734 only normal grace-period primitives. No effect
4735 on CONFIG_TINY_RCU kernels.
4736
4737 But note that CONFIG_PREEMPT_RT=y kernels enables
4738 this kernel boot parameter, forcibly setting
4739 it to the value one, that is, converting any
4740 post-boot attempt at an expedited RCU grace
4741 period to instead use normal non-expedited
4742 grace-period processing.
4743
4744 rcupdate.rcu_task_ipi_delay= [KNL]
4745 Set time in jiffies during which RCU tasks will
4746 avoid sending IPIs, starting with the beginning
4747 of a given grace period. Setting a large
4748 number avoids disturbing real-time workloads,
4749 but lengthens grace periods.
4750
4751 rcupdate.rcu_task_stall_timeout= [KNL]
4752 Set timeout in jiffies for RCU task stall warning
4753 messages. Disable with a value less than or equal
4754 to zero.
4755
4756 rcupdate.rcu_self_test= [KNL]
4757 Run the RCU early boot self tests
4758
4759 rdinit= [KNL]
4760 Format: <full_path>
4761 Run specified binary instead of /init from the ramdisk,
4762 used for early userspace startup. See initrd.
4763
4764 rdrand= [X86]
4765 force - Override the decision by the kernel to hide the
4766 advertisement of RDRAND support (this affects
4767 certain AMD processors because of buggy BIOS
4768 support, specifically around the suspend/resume
4769 path).
4770
4771 rdt= [HW,X86,RDT]
4772 Turn on/off individual RDT features. List is:
4773 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4774 mba.
4775 E.g. to turn on cmt and turn off mba use:
4776 rdt=cmt,!mba
4777
4778 reboot= [KNL]
4779 Format (x86 or x86_64):
4780 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4781 [[,]s[mp]#### \
4782 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4783 [[,]f[orce]
4784 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4785 (prefix with 'panic_' to set mode for panic
4786 reboot only),
4787 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4788 reboot_force is either force or not specified,
4789 reboot_cpu is s[mp]#### with #### being the processor
4790 to be used for rebooting.
4791
4792 refscale.holdoff= [KNL]
4793 Set test-start holdoff period. The purpose of
4794 this parameter is to delay the start of the
4795 test until boot completes in order to avoid
4796 interference.
4797
4798 refscale.loops= [KNL]
4799 Set the number of loops over the synchronization
4800 primitive under test. Increasing this number
4801 reduces noise due to loop start/end overhead,
4802 but the default has already reduced the per-pass
4803 noise to a handful of picoseconds on ca. 2020
4804 x86 laptops.
4805
4806 refscale.nreaders= [KNL]
4807 Set number of readers. The default value of -1
4808 selects N, where N is roughly 75% of the number
4809 of CPUs. A value of zero is an interesting choice.
4810
4811 refscale.nruns= [KNL]
4812 Set number of runs, each of which is dumped onto
4813 the console log.
4814
4815 refscale.readdelay= [KNL]
4816 Set the read-side critical-section duration,
4817 measured in microseconds.
4818
4819 refscale.scale_type= [KNL]
4820 Specify the read-protection implementation to test.
4821
4822 refscale.shutdown= [KNL]
4823 Shut down the system at the end of the performance
4824 test. This defaults to 1 (shut it down) when
4825 refscale is built into the kernel and to 0 (leave
4826 it running) when refscale is built as a module.
4827
4828 refscale.verbose= [KNL]
4829 Enable additional printk() statements.
4830
4831 refscale.verbose_batched= [KNL]
4832 Batch the additional printk() statements. If zero
4833 (the default) or negative, print everything. Otherwise,
4834 print every Nth verbose statement, where N is the value
4835 specified.
4836
4837 relax_domain_level=
4838 [KNL, SMP] Set scheduler's default relax_domain_level.
4839 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4840
4841 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4842 Format: <base1>,<size1>[,<base2>,<size2>,...]
4843 Reserve I/O ports or memory so the kernel won't use
4844 them. If <base> is less than 0x10000, the region
4845 is assumed to be I/O ports; otherwise it is memory.
4846
4847 reservetop= [X86-32]
4848 Format: nn[KMG]
4849 Reserves a hole at the top of the kernel virtual
4850 address space.
4851
4852 reset_devices [KNL] Force drivers to reset the underlying device
4853 during initialization.
4854
4855 resume= [SWSUSP]
4856 Specify the partition device for software suspend
4857 Format:
4858 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4859
4860 resume_offset= [SWSUSP]
4861 Specify the offset from the beginning of the partition
4862 given by "resume=" at which the swap header is located,
4863 in <PAGE_SIZE> units (needed only for swap files).
4864 See Documentation/power/swsusp-and-swap-files.rst
4865
4866 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4867 read the resume files
4868
4869 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4870 Useful for devices that are detected asynchronously
4871 (e.g. USB and MMC devices).
4872
4873 hibernate= [HIBERNATION]
4874 noresume Don't check if there's a hibernation image
4875 present during boot.
4876 nocompress Don't compress/decompress hibernation images.
4877 no Disable hibernation and resume.
4878 protect_image Turn on image protection during restoration
4879 (that will set all pages holding image data
4880 during restoration read-only).
4881
4882 retain_initrd [RAM] Keep initrd memory after extraction
4883
4884 rfkill.default_state=
4885 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4886 etc. communication is blocked by default.
4887 1 Unblocked.
4888
4889 rfkill.master_switch_mode=
4890 0 The "airplane mode" button does nothing.
4891 1 The "airplane mode" button toggles between everything
4892 blocked and the previous configuration.
4893 2 The "airplane mode" button toggles between everything
4894 blocked and everything unblocked.
4895
4896 rhash_entries= [KNL,NET]
4897 Set number of hash buckets for route cache
4898
4899 ring3mwait=disable
4900 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4901 CPUs.
4902
4903 ro [KNL] Mount root device read-only on boot
4904
4905 rodata= [KNL]
4906 on Mark read-only kernel memory as read-only (default).
4907 off Leave read-only kernel memory writable for debugging.
4908
4909 rockchip.usb_uart
4910 Enable the uart passthrough on the designated usb port
4911 on Rockchip SoCs. When active, the signals of the
4912 debug-uart get routed to the D+ and D- pins of the usb
4913 port and the regular usb controller gets disabled.
4914
4915 root= [KNL] Root filesystem
4916 See name_to_dev_t comment in init/do_mounts.c.
4917
4918 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4919 mount the root filesystem
4920
4921 rootflags= [KNL] Set root filesystem mount option string
4922
4923 rootfstype= [KNL] Set root filesystem type
4924
4925 rootwait [KNL] Wait (indefinitely) for root device to show up.
4926 Useful for devices that are detected asynchronously
4927 (e.g. USB and MMC devices).
4928
4929 rproc_mem=nn[KMG][@address]
4930 [KNL,ARM,CMA] Remoteproc physical memory block.
4931 Memory area to be used by remote processor image,
4932 managed by CMA.
4933
4934 rw [KNL] Mount root device read-write on boot
4935
4936 S [KNL] Run init in single mode
4937
4938 s390_iommu= [HW,S390]
4939 Set s390 IOTLB flushing mode
4940 strict
4941 With strict flushing every unmap operation will result in
4942 an IOTLB flush. Default is lazy flushing before reuse,
4943 which is faster.
4944
4945 sa1100ir [NET]
4946 See drivers/net/irda/sa1100_ir.c.
4947
4948 sbni= [NET] Granch SBNI12 leased line adapter
4949
4950 sched_verbose [KNL] Enables verbose scheduler debug messages.
4951
4952 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4953 Allowed values are enable and disable. This feature
4954 incurs a small amount of overhead in the scheduler
4955 but is useful for debugging and performance tuning.
4956
4957 sched_thermal_decay_shift=
4958 [KNL, SMP] Set a decay shift for scheduler thermal
4959 pressure signal. Thermal pressure signal follows the
4960 default decay period of other scheduler pelt
4961 signals(usually 32 ms but configurable). Setting
4962 sched_thermal_decay_shift will left shift the decay
4963 period for the thermal pressure signal by the shift
4964 value.
4965 i.e. with the default pelt decay period of 32 ms
4966 sched_thermal_decay_shift thermal pressure decay pr
4967 1 64 ms
4968 2 128 ms
4969 and so on.
4970 Format: integer between 0 and 10
4971 Default is 0.
4972
4973 scftorture.holdoff= [KNL]
4974 Number of seconds to hold off before starting
4975 test. Defaults to zero for module insertion and
4976 to 10 seconds for built-in smp_call_function()
4977 tests.
4978
4979 scftorture.longwait= [KNL]
4980 Request ridiculously long waits randomly selected
4981 up to the chosen limit in seconds. Zero (the
4982 default) disables this feature. Please note
4983 that requesting even small non-zero numbers of
4984 seconds can result in RCU CPU stall warnings,
4985 softlockup complaints, and so on.
4986
4987 scftorture.nthreads= [KNL]
4988 Number of kthreads to spawn to invoke the
4989 smp_call_function() family of functions.
4990 The default of -1 specifies a number of kthreads
4991 equal to the number of CPUs.
4992
4993 scftorture.onoff_holdoff= [KNL]
4994 Number seconds to wait after the start of the
4995 test before initiating CPU-hotplug operations.
4996
4997 scftorture.onoff_interval= [KNL]
4998 Number seconds to wait between successive
4999 CPU-hotplug operations. Specifying zero (which
5000 is the default) disables CPU-hotplug operations.
5001
5002 scftorture.shutdown_secs= [KNL]
5003 The number of seconds following the start of the
5004 test after which to shut down the system. The
5005 default of zero avoids shutting down the system.
5006 Non-zero values are useful for automated tests.
5007
5008 scftorture.stat_interval= [KNL]
5009 The number of seconds between outputting the
5010 current test statistics to the console. A value
5011 of zero disables statistics output.
5012
5013 scftorture.stutter_cpus= [KNL]
5014 The number of jiffies to wait between each change
5015 to the set of CPUs under test.
5016
5017 scftorture.use_cpus_read_lock= [KNL]
5018 Use use_cpus_read_lock() instead of the default
5019 preempt_disable() to disable CPU hotplug
5020 while invoking one of the smp_call_function*()
5021 functions.
5022
5023 scftorture.verbose= [KNL]
5024 Enable additional printk() statements.
5025
5026 scftorture.weight_single= [KNL]
5027 The probability weighting to use for the
5028 smp_call_function_single() function with a zero
5029 "wait" parameter. A value of -1 selects the
5030 default if all other weights are -1. However,
5031 if at least one weight has some other value, a
5032 value of -1 will instead select a weight of zero.
5033
5034 scftorture.weight_single_wait= [KNL]
5035 The probability weighting to use for the
5036 smp_call_function_single() function with a
5037 non-zero "wait" parameter. See weight_single.
5038
5039 scftorture.weight_many= [KNL]
5040 The probability weighting to use for the
5041 smp_call_function_many() function with a zero
5042 "wait" parameter. See weight_single.
5043 Note well that setting a high probability for
5044 this weighting can place serious IPI load
5045 on the system.
5046
5047 scftorture.weight_many_wait= [KNL]
5048 The probability weighting to use for the
5049 smp_call_function_many() function with a
5050 non-zero "wait" parameter. See weight_single
5051 and weight_many.
5052
5053 scftorture.weight_all= [KNL]
5054 The probability weighting to use for the
5055 smp_call_function_all() function with a zero
5056 "wait" parameter. See weight_single and
5057 weight_many.
5058
5059 scftorture.weight_all_wait= [KNL]
5060 The probability weighting to use for the
5061 smp_call_function_all() function with a
5062 non-zero "wait" parameter. See weight_single
5063 and weight_many.
5064
5065 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5066 xtime_lock contention on larger systems, and/or RCU lock
5067 contention on all systems with CONFIG_MAXSMP set.
5068 Format: { "0" | "1" }
5069 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5070 1 -- enable.
5071 Note: increases power consumption, thus should only be
5072 enabled if running jitter sensitive (HPC/RT) workloads.
5073
5074 security= [SECURITY] Choose a legacy "major" security module to
5075 enable at boot. This has been deprecated by the
5076 "lsm=" parameter.
5077
5078 selinux= [SELINUX] Disable or enable SELinux at boot time.
5079 Format: { "0" | "1" }
5080 See security/selinux/Kconfig help text.
5081 0 -- disable.
5082 1 -- enable.
5083 Default value is 1.
5084
5085 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5086 Format: { "0" | "1" }
5087 See security/apparmor/Kconfig help text
5088 0 -- disable.
5089 1 -- enable.
5090 Default value is set via kernel config option.
5091
5092 serialnumber [BUGS=X86-32]
5093
5094 shapers= [NET]
5095 Maximal number of shapers.
5096
5097 simeth= [IA-64]
5098 simscsi=
5099
5100 slram= [HW,MTD]
5101
5102 slab_merge [MM]
5103 Enable merging of slabs with similar size when the
5104 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5105
5106 slab_nomerge [MM]
5107 Disable merging of slabs with similar size. May be
5108 necessary if there is some reason to distinguish
5109 allocs to different slabs, especially in hardened
5110 environments where the risk of heap overflows and
5111 layout control by attackers can usually be
5112 frustrated by disabling merging. This will reduce
5113 most of the exposure of a heap attack to a single
5114 cache (risks via metadata attacks are mostly
5115 unchanged). Debug options disable merging on their
5116 own.
5117 For more information see Documentation/vm/slub.rst.
5118
5119 slab_max_order= [MM, SLAB]
5120 Determines the maximum allowed order for slabs.
5121 A high setting may cause OOMs due to memory
5122 fragmentation. Defaults to 1 for systems with
5123 more than 32MB of RAM, 0 otherwise.
5124
5125 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5126 Enabling slub_debug allows one to determine the
5127 culprit if slab objects become corrupted. Enabling
5128 slub_debug can create guard zones around objects and
5129 may poison objects when not in use. Also tracks the
5130 last alloc / free. For more information see
5131 Documentation/vm/slub.rst.
5132
5133 slub_max_order= [MM, SLUB]
5134 Determines the maximum allowed order for slabs.
5135 A high setting may cause OOMs due to memory
5136 fragmentation. For more information see
5137 Documentation/vm/slub.rst.
5138
5139 slub_min_objects= [MM, SLUB]
5140 The minimum number of objects per slab. SLUB will
5141 increase the slab order up to slub_max_order to
5142 generate a sufficiently large slab able to contain
5143 the number of objects indicated. The higher the number
5144 of objects the smaller the overhead of tracking slabs
5145 and the less frequently locks need to be acquired.
5146 For more information see Documentation/vm/slub.rst.
5147
5148 slub_min_order= [MM, SLUB]
5149 Determines the minimum page order for slabs. Must be
5150 lower than slub_max_order.
5151 For more information see Documentation/vm/slub.rst.
5152
5153 slub_merge [MM, SLUB]
5154 Same with slab_merge.
5155
5156 slub_nomerge [MM, SLUB]
5157 Same with slab_nomerge. This is supported for legacy.
5158 See slab_nomerge for more information.
5159
5160 smart2= [HW]
5161 Format: <io1>[,<io2>[,...,<io8>]]
5162
5163 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5164 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5165 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5166 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5167 smsc-ircc2.ircc_irq= [HW] IRQ line
5168 smsc-ircc2.ircc_dma= [HW] DMA channel
5169 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5170 0: Toshiba Satellite 1800 (GP data pin select)
5171 1: Fast pin select (default)
5172 2: ATC IRMode
5173
5174 smt [KNL,S390] Set the maximum number of threads (logical
5175 CPUs) to use per physical CPU on systems capable of
5176 symmetric multithreading (SMT). Will be capped to the
5177 actual hardware limit.
5178 Format: <integer>
5179 Default: -1 (no limit)
5180
5181 softlockup_panic=
5182 [KNL] Should the soft-lockup detector generate panics.
5183 Format: 0 | 1
5184
5185 A value of 1 instructs the soft-lockup detector
5186 to panic the machine when a soft-lockup occurs. It is
5187 also controlled by the kernel.softlockup_panic sysctl
5188 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5189 respective build-time switch to that functionality.
5190
5191 softlockup_all_cpu_backtrace=
5192 [KNL] Should the soft-lockup detector generate
5193 backtraces on all cpus.
5194 Format: 0 | 1
5195
5196 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5197 See Documentation/admin-guide/laptops/sonypi.rst
5198
5199 spectre_v2= [X86] Control mitigation of Spectre variant 2
5200 (indirect branch speculation) vulnerability.
5201 The default operation protects the kernel from
5202 user space attacks.
5203
5204 on - unconditionally enable, implies
5205 spectre_v2_user=on
5206 off - unconditionally disable, implies
5207 spectre_v2_user=off
5208 auto - kernel detects whether your CPU model is
5209 vulnerable
5210
5211 Selecting 'on' will, and 'auto' may, choose a
5212 mitigation method at run time according to the
5213 CPU, the available microcode, the setting of the
5214 CONFIG_RETPOLINE configuration option, and the
5215 compiler with which the kernel was built.
5216
5217 Selecting 'on' will also enable the mitigation
5218 against user space to user space task attacks.
5219
5220 Selecting 'off' will disable both the kernel and
5221 the user space protections.
5222
5223 Specific mitigations can also be selected manually:
5224
5225 retpoline - replace indirect branches
5226 retpoline,generic - google's original retpoline
5227 retpoline,amd - AMD-specific minimal thunk
5228
5229 Not specifying this option is equivalent to
5230 spectre_v2=auto.
5231
5232 spectre_v2_user=
5233 [X86] Control mitigation of Spectre variant 2
5234 (indirect branch speculation) vulnerability between
5235 user space tasks
5236
5237 on - Unconditionally enable mitigations. Is
5238 enforced by spectre_v2=on
5239
5240 off - Unconditionally disable mitigations. Is
5241 enforced by spectre_v2=off
5242
5243 prctl - Indirect branch speculation is enabled,
5244 but mitigation can be enabled via prctl
5245 per thread. The mitigation control state
5246 is inherited on fork.
5247
5248 prctl,ibpb
5249 - Like "prctl" above, but only STIBP is
5250 controlled per thread. IBPB is issued
5251 always when switching between different user
5252 space processes.
5253
5254 seccomp
5255 - Same as "prctl" above, but all seccomp
5256 threads will enable the mitigation unless
5257 they explicitly opt out.
5258
5259 seccomp,ibpb
5260 - Like "seccomp" above, but only STIBP is
5261 controlled per thread. IBPB is issued
5262 always when switching between different
5263 user space processes.
5264
5265 auto - Kernel selects the mitigation depending on
5266 the available CPU features and vulnerability.
5267
5268 Default mitigation:
5269 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
5270
5271 Not specifying this option is equivalent to
5272 spectre_v2_user=auto.
5273
5274 spec_store_bypass_disable=
5275 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5276 (Speculative Store Bypass vulnerability)
5277
5278 Certain CPUs are vulnerable to an exploit against a
5279 a common industry wide performance optimization known
5280 as "Speculative Store Bypass" in which recent stores
5281 to the same memory location may not be observed by
5282 later loads during speculative execution. The idea
5283 is that such stores are unlikely and that they can
5284 be detected prior to instruction retirement at the
5285 end of a particular speculation execution window.
5286
5287 In vulnerable processors, the speculatively forwarded
5288 store can be used in a cache side channel attack, for
5289 example to read memory to which the attacker does not
5290 directly have access (e.g. inside sandboxed code).
5291
5292 This parameter controls whether the Speculative Store
5293 Bypass optimization is used.
5294
5295 On x86 the options are:
5296
5297 on - Unconditionally disable Speculative Store Bypass
5298 off - Unconditionally enable Speculative Store Bypass
5299 auto - Kernel detects whether the CPU model contains an
5300 implementation of Speculative Store Bypass and
5301 picks the most appropriate mitigation. If the
5302 CPU is not vulnerable, "off" is selected. If the
5303 CPU is vulnerable the default mitigation is
5304 architecture and Kconfig dependent. See below.
5305 prctl - Control Speculative Store Bypass per thread
5306 via prctl. Speculative Store Bypass is enabled
5307 for a process by default. The state of the control
5308 is inherited on fork.
5309 seccomp - Same as "prctl" above, but all seccomp threads
5310 will disable SSB unless they explicitly opt out.
5311
5312 Default mitigations:
5313 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
5314
5315 On powerpc the options are:
5316
5317 on,auto - On Power8 and Power9 insert a store-forwarding
5318 barrier on kernel entry and exit. On Power7
5319 perform a software flush on kernel entry and
5320 exit.
5321 off - No action.
5322
5323 Not specifying this option is equivalent to
5324 spec_store_bypass_disable=auto.
5325
5326 spia_io_base= [HW,MTD]
5327 spia_fio_base=
5328 spia_pedr=
5329 spia_peddr=
5330
5331 split_lock_detect=
5332 [X86] Enable split lock detection or bus lock detection
5333
5334 When enabled (and if hardware support is present), atomic
5335 instructions that access data across cache line
5336 boundaries will result in an alignment check exception
5337 for split lock detection or a debug exception for
5338 bus lock detection.
5339
5340 off - not enabled
5341
5342 warn - the kernel will emit rate-limited warnings
5343 about applications triggering the #AC
5344 exception or the #DB exception. This mode is
5345 the default on CPUs that support split lock
5346 detection or bus lock detection. Default
5347 behavior is by #AC if both features are
5348 enabled in hardware.
5349
5350 fatal - the kernel will send SIGBUS to applications
5351 that trigger the #AC exception or the #DB
5352 exception. Default behavior is by #AC if
5353 both features are enabled in hardware.
5354
5355 ratelimit:N -
5356 Set system wide rate limit to N bus locks
5357 per second for bus lock detection.
5358 0 < N <= 1000.
5359
5360 N/A for split lock detection.
5361
5362
5363 If an #AC exception is hit in the kernel or in
5364 firmware (i.e. not while executing in user mode)
5365 the kernel will oops in either "warn" or "fatal"
5366 mode.
5367
5368 #DB exception for bus lock is triggered only when
5369 CPL > 0.
5370
5371 srbds= [X86,INTEL]
5372 Control the Special Register Buffer Data Sampling
5373 (SRBDS) mitigation.
5374
5375 Certain CPUs are vulnerable to an MDS-like
5376 exploit which can leak bits from the random
5377 number generator.
5378
5379 By default, this issue is mitigated by
5380 microcode. However, the microcode fix can cause
5381 the RDRAND and RDSEED instructions to become
5382 much slower. Among other effects, this will
5383 result in reduced throughput from /dev/urandom.
5384
5385 The microcode mitigation can be disabled with
5386 the following option:
5387
5388 off: Disable mitigation and remove
5389 performance impact to RDRAND and RDSEED
5390
5391 srcutree.counter_wrap_check [KNL]
5392 Specifies how frequently to check for
5393 grace-period sequence counter wrap for the
5394 srcu_data structure's ->srcu_gp_seq_needed field.
5395 The greater the number of bits set in this kernel
5396 parameter, the less frequently counter wrap will
5397 be checked for. Note that the bottom two bits
5398 are ignored.
5399
5400 srcutree.exp_holdoff [KNL]
5401 Specifies how many nanoseconds must elapse
5402 since the end of the last SRCU grace period for
5403 a given srcu_struct until the next normal SRCU
5404 grace period will be considered for automatic
5405 expediting. Set to zero to disable automatic
5406 expediting.
5407
5408 ssbd= [ARM64,HW]
5409 Speculative Store Bypass Disable control
5410
5411 On CPUs that are vulnerable to the Speculative
5412 Store Bypass vulnerability and offer a
5413 firmware based mitigation, this parameter
5414 indicates how the mitigation should be used:
5415
5416 force-on: Unconditionally enable mitigation for
5417 for both kernel and userspace
5418 force-off: Unconditionally disable mitigation for
5419 for both kernel and userspace
5420 kernel: Always enable mitigation in the
5421 kernel, and offer a prctl interface
5422 to allow userspace to register its
5423 interest in being mitigated too.
5424
5425 stack_guard_gap= [MM]
5426 override the default stack gap protection. The value
5427 is in page units and it defines how many pages prior
5428 to (for stacks growing down) resp. after (for stacks
5429 growing up) the main stack are reserved for no other
5430 mapping. Default value is 256 pages.
5431
5432 stack_depot_disable= [KNL]
5433 Setting this to true through kernel command line will
5434 disable the stack depot thereby saving the static memory
5435 consumed by the stack hash table. By default this is set
5436 to false.
5437
5438 stacktrace [FTRACE]
5439 Enabled the stack tracer on boot up.
5440
5441 stacktrace_filter=[function-list]
5442 [FTRACE] Limit the functions that the stack tracer
5443 will trace at boot up. function-list is a comma-separated
5444 list of functions. This list can be changed at run
5445 time by the stack_trace_filter file in the debugfs
5446 tracing directory. Note, this enables stack tracing
5447 and the stacktrace above is not needed.
5448
5449 sti= [PARISC,HW]
5450 Format: <num>
5451 Set the STI (builtin display/keyboard on the HP-PARISC
5452 machines) console (graphic card) which should be used
5453 as the initial boot-console.
5454 See also comment in drivers/video/console/sticore.c.
5455
5456 sti_font= [HW]
5457 See comment in drivers/video/console/sticore.c.
5458
5459 stifb= [HW]
5460 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5461
5462 sunrpc.min_resvport=
5463 sunrpc.max_resvport=
5464 [NFS,SUNRPC]
5465 SunRPC servers often require that client requests
5466 originate from a privileged port (i.e. a port in the
5467 range 0 < portnr < 1024).
5468 An administrator who wishes to reserve some of these
5469 ports for other uses may adjust the range that the
5470 kernel's sunrpc client considers to be privileged
5471 using these two parameters to set the minimum and
5472 maximum port values.
5473
5474 sunrpc.svc_rpc_per_connection_limit=
5475 [NFS,SUNRPC]
5476 Limit the number of requests that the server will
5477 process in parallel from a single connection.
5478 The default value is 0 (no limit).
5479
5480 sunrpc.pool_mode=
5481 [NFS]
5482 Control how the NFS server code allocates CPUs to
5483 service thread pools. Depending on how many NICs
5484 you have and where their interrupts are bound, this
5485 option will affect which CPUs will do NFS serving.
5486 Note: this parameter cannot be changed while the
5487 NFS server is running.
5488
5489 auto the server chooses an appropriate mode
5490 automatically using heuristics
5491 global a single global pool contains all CPUs
5492 percpu one pool for each CPU
5493 pernode one pool for each NUMA node (equivalent
5494 to global on non-NUMA machines)
5495
5496 sunrpc.tcp_slot_table_entries=
5497 sunrpc.udp_slot_table_entries=
5498 [NFS,SUNRPC]
5499 Sets the upper limit on the number of simultaneous
5500 RPC calls that can be sent from the client to a
5501 server. Increasing these values may allow you to
5502 improve throughput, but will also increase the
5503 amount of memory reserved for use by the client.
5504
5505 suspend.pm_test_delay=
5506 [SUSPEND]
5507 Sets the number of seconds to remain in a suspend test
5508 mode before resuming the system (see
5509 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5510 is set. Default value is 5.
5511
5512 svm= [PPC]
5513 Format: { on | off | y | n | 1 | 0 }
5514 This parameter controls use of the Protected
5515 Execution Facility on pSeries.
5516
5517 swapaccount=[0|1]
5518 [KNL] Enable accounting of swap in memory resource
5519 controller if no parameter or 1 is given or disable
5520 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5521
5522 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5523 Format: { <int> | force | noforce }
5524 <int> -- Number of I/O TLB slabs
5525 force -- force using of bounce buffers even if they
5526 wouldn't be automatically used by the kernel
5527 noforce -- Never use bounce buffers (for debugging)
5528
5529 switches= [HW,M68k]
5530
5531 sysctl.*= [KNL]
5532 Set a sysctl parameter, right before loading the init
5533 process, as if the value was written to the respective
5534 /proc/sys/... file. Both '.' and '/' are recognized as
5535 separators. Unrecognized parameters and invalid values
5536 are reported in the kernel log. Sysctls registered
5537 later by a loaded module cannot be set this way.
5538 Example: sysctl.vm.swappiness=40
5539
5540 sysfs.deprecated=0|1 [KNL]
5541 Enable/disable old style sysfs layout for old udev
5542 on older distributions. When this option is enabled
5543 very new udev will not work anymore. When this option
5544 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5545 in older udev will not work anymore.
5546 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5547 the kernel configuration.
5548
5549 sysrq_always_enabled
5550 [KNL]
5551 Ignore sysrq setting - this boot parameter will
5552 neutralize any effect of /proc/sys/kernel/sysrq.
5553 Useful for debugging.
5554
5555 tcpmhash_entries= [KNL,NET]
5556 Set the number of tcp_metrics_hash slots.
5557 Default value is 8192 or 16384 depending on total
5558 ram pages. This is used to specify the TCP metrics
5559 cache size. See Documentation/networking/ip-sysctl.rst
5560 "tcp_no_metrics_save" section for more details.
5561
5562 tdfx= [HW,DRM]
5563
5564 test_suspend= [SUSPEND][,N]
5565 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5566 standby suspend) or "freeze" (for suspend type freeze)
5567 as the system sleep state during system startup with
5568 the optional capability to repeat N number of times.
5569 The system is woken from this state using a
5570 wakeup-capable RTC alarm.
5571
5572 thash_entries= [KNL,NET]
5573 Set number of hash buckets for TCP connection
5574
5575 thermal.act= [HW,ACPI]
5576 -1: disable all active trip points in all thermal zones
5577 <degrees C>: override all lowest active trip points
5578
5579 thermal.crt= [HW,ACPI]
5580 -1: disable all critical trip points in all thermal zones
5581 <degrees C>: override all critical trip points
5582
5583 thermal.nocrt= [HW,ACPI]
5584 Set to disable actions on ACPI thermal zone
5585 critical and hot trip points.
5586
5587 thermal.off= [HW,ACPI]
5588 1: disable ACPI thermal control
5589
5590 thermal.psv= [HW,ACPI]
5591 -1: disable all passive trip points
5592 <degrees C>: override all passive trip points to this
5593 value
5594
5595 thermal.tzp= [HW,ACPI]
5596 Specify global default ACPI thermal zone polling rate
5597 <deci-seconds>: poll all this frequency
5598 0: no polling (default)
5599
5600 threadirqs [KNL]
5601 Force threading of all interrupt handlers except those
5602 marked explicitly IRQF_NO_THREAD.
5603
5604 topology= [S390]
5605 Format: {off | on}
5606 Specify if the kernel should make use of the cpu
5607 topology information if the hardware supports this.
5608 The scheduler will make use of this information and
5609 e.g. base its process migration decisions on it.
5610 Default is on.
5611
5612 topology_updates= [KNL, PPC, NUMA]
5613 Format: {off}
5614 Specify if the kernel should ignore (off)
5615 topology updates sent by the hypervisor to this
5616 LPAR.
5617
5618 torture.disable_onoff_at_boot= [KNL]
5619 Prevent the CPU-hotplug component of torturing
5620 until after init has spawned.
5621
5622 torture.ftrace_dump_at_shutdown= [KNL]
5623 Dump the ftrace buffer at torture-test shutdown,
5624 even if there were no errors. This can be a
5625 very costly operation when many torture tests
5626 are running concurrently, especially on systems
5627 with rotating-rust storage.
5628
5629 torture.verbose_sleep_frequency= [KNL]
5630 Specifies how many verbose printk()s should be
5631 emitted between each sleep. The default of zero
5632 disables verbose-printk() sleeping.
5633
5634 torture.verbose_sleep_duration= [KNL]
5635 Duration of each verbose-printk() sleep in jiffies.
5636
5637 tp720= [HW,PS2]
5638
5639 tpm_suspend_pcr=[HW,TPM]
5640 Format: integer pcr id
5641 Specify that at suspend time, the tpm driver
5642 should extend the specified pcr with zeros,
5643 as a workaround for some chips which fail to
5644 flush the last written pcr on TPM_SaveState.
5645 This will guarantee that all the other pcrs
5646 are saved.
5647
5648 trace_buf_size=nn[KMG]
5649 [FTRACE] will set tracing buffer size on each cpu.
5650
5651 trace_event=[event-list]
5652 [FTRACE] Set and start specified trace events in order
5653 to facilitate early boot debugging. The event-list is a
5654 comma-separated list of trace events to enable. See
5655 also Documentation/trace/events.rst
5656
5657 trace_options=[option-list]
5658 [FTRACE] Enable or disable tracer options at boot.
5659 The option-list is a comma delimited list of options
5660 that can be enabled or disabled just as if you were
5661 to echo the option name into
5662
5663 /sys/kernel/debug/tracing/trace_options
5664
5665 For example, to enable stacktrace option (to dump the
5666 stack trace of each event), add to the command line:
5667
5668 trace_options=stacktrace
5669
5670 See also Documentation/trace/ftrace.rst "trace options"
5671 section.
5672
5673 tp_printk[FTRACE]
5674 Have the tracepoints sent to printk as well as the
5675 tracing ring buffer. This is useful for early boot up
5676 where the system hangs or reboots and does not give the
5677 option for reading the tracing buffer or performing a
5678 ftrace_dump_on_oops.
5679
5680 To turn off having tracepoints sent to printk,
5681 echo 0 > /proc/sys/kernel/tracepoint_printk
5682 Note, echoing 1 into this file without the
5683 tracepoint_printk kernel cmdline option has no effect.
5684
5685 The tp_printk_stop_on_boot (see below) can also be used
5686 to stop the printing of events to console at
5687 late_initcall_sync.
5688
5689 ** CAUTION **
5690
5691 Having tracepoints sent to printk() and activating high
5692 frequency tracepoints such as irq or sched, can cause
5693 the system to live lock.
5694
5695 tp_printk_stop_on_boot[FTRACE]
5696 When tp_printk (above) is set, it can cause a lot of noise
5697 on the console. It may be useful to only include the
5698 printing of events during boot up, as user space may
5699 make the system inoperable.
5700
5701 This command line option will stop the printing of events
5702 to console at the late_initcall_sync() time frame.
5703
5704 traceoff_on_warning
5705 [FTRACE] enable this option to disable tracing when a
5706 warning is hit. This turns off "tracing_on". Tracing can
5707 be enabled again by echoing '1' into the "tracing_on"
5708 file located in /sys/kernel/debug/tracing/
5709
5710 This option is useful, as it disables the trace before
5711 the WARNING dump is called, which prevents the trace to
5712 be filled with content caused by the warning output.
5713
5714 This option can also be set at run time via the sysctl
5715 option: kernel/traceoff_on_warning
5716
5717 transparent_hugepage=
5718 [KNL]
5719 Format: [always|madvise|never]
5720 Can be used to control the default behavior of the system
5721 with respect to transparent hugepages.
5722 See Documentation/admin-guide/mm/transhuge.rst
5723 for more details.
5724
5725 trusted.source= [KEYS]
5726 Format: <string>
5727 This parameter identifies the trust source as a backend
5728 for trusted keys implementation. Supported trust
5729 sources:
5730 - "tpm"
5731 - "tee"
5732 If not specified then it defaults to iterating through
5733 the trust source list starting with TPM and assigns the
5734 first trust source as a backend which is initialized
5735 successfully during iteration.
5736
5737 tsc= Disable clocksource stability checks for TSC.
5738 Format: <string>
5739 [x86] reliable: mark tsc clocksource as reliable, this
5740 disables clocksource verification at runtime, as well
5741 as the stability checks done at bootup. Used to enable
5742 high-resolution timer mode on older hardware, and in
5743 virtualized environment.
5744 [x86] noirqtime: Do not use TSC to do irq accounting.
5745 Used to run time disable IRQ_TIME_ACCOUNTING on any
5746 platforms where RDTSC is slow and this accounting
5747 can add overhead.
5748 [x86] unstable: mark the TSC clocksource as unstable, this
5749 marks the TSC unconditionally unstable at bootup and
5750 avoids any further wobbles once the TSC watchdog notices.
5751 [x86] nowatchdog: disable clocksource watchdog. Used
5752 in situations with strict latency requirements (where
5753 interruptions from clocksource watchdog are not
5754 acceptable).
5755
5756 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5757 value instead. Useful when the early TSC frequency discovery
5758 procedure is not reliable, such as on overclocked systems
5759 with CPUID.16h support and partial CPUID.15h support.
5760 Format: <unsigned int>
5761
5762 tsx= [X86] Control Transactional Synchronization
5763 Extensions (TSX) feature in Intel processors that
5764 support TSX control.
5765
5766 This parameter controls the TSX feature. The options are:
5767
5768 on - Enable TSX on the system. Although there are
5769 mitigations for all known security vulnerabilities,
5770 TSX has been known to be an accelerator for
5771 several previous speculation-related CVEs, and
5772 so there may be unknown security risks associated
5773 with leaving it enabled.
5774
5775 off - Disable TSX on the system. (Note that this
5776 option takes effect only on newer CPUs which are
5777 not vulnerable to MDS, i.e., have
5778 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5779 the new IA32_TSX_CTRL MSR through a microcode
5780 update. This new MSR allows for the reliable
5781 deactivation of the TSX functionality.)
5782
5783 auto - Disable TSX if X86_BUG_TAA is present,
5784 otherwise enable TSX on the system.
5785
5786 Not specifying this option is equivalent to tsx=off.
5787
5788 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5789 for more details.
5790
5791 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5792 Abort (TAA) vulnerability.
5793
5794 Similar to Micro-architectural Data Sampling (MDS)
5795 certain CPUs that support Transactional
5796 Synchronization Extensions (TSX) are vulnerable to an
5797 exploit against CPU internal buffers which can forward
5798 information to a disclosure gadget under certain
5799 conditions.
5800
5801 In vulnerable processors, the speculatively forwarded
5802 data can be used in a cache side channel attack, to
5803 access data to which the attacker does not have direct
5804 access.
5805
5806 This parameter controls the TAA mitigation. The
5807 options are:
5808
5809 full - Enable TAA mitigation on vulnerable CPUs
5810 if TSX is enabled.
5811
5812 full,nosmt - Enable TAA mitigation and disable SMT on
5813 vulnerable CPUs. If TSX is disabled, SMT
5814 is not disabled because CPU is not
5815 vulnerable to cross-thread TAA attacks.
5816 off - Unconditionally disable TAA mitigation
5817
5818 On MDS-affected machines, tsx_async_abort=off can be
5819 prevented by an active MDS mitigation as both vulnerabilities
5820 are mitigated with the same mechanism so in order to disable
5821 this mitigation, you need to specify mds=off too.
5822
5823 Not specifying this option is equivalent to
5824 tsx_async_abort=full. On CPUs which are MDS affected
5825 and deploy MDS mitigation, TAA mitigation is not
5826 required and doesn't provide any additional
5827 mitigation.
5828
5829 For details see:
5830 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5831
5832 turbografx.map[2|3]= [HW,JOY]
5833 TurboGraFX parallel port interface
5834 Format:
5835 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5836 See also Documentation/input/devices/joystick-parport.rst
5837
5838 udbg-immortal [PPC] When debugging early kernel crashes that
5839 happen after console_init() and before a proper
5840 console driver takes over, this boot options might
5841 help "seeing" what's going on.
5842
5843 uhash_entries= [KNL,NET]
5844 Set number of hash buckets for UDP/UDP-Lite connections
5845
5846 uhci-hcd.ignore_oc=
5847 [USB] Ignore overcurrent events (default N).
5848 Some badly-designed motherboards generate lots of
5849 bogus events, for ports that aren't wired to
5850 anything. Set this parameter to avoid log spamming.
5851 Note that genuine overcurrent events won't be
5852 reported either.
5853
5854 unknown_nmi_panic
5855 [X86] Cause panic on unknown NMI.
5856
5857 usbcore.authorized_default=
5858 [USB] Default USB device authorization:
5859 (default -1 = authorized except for wireless USB,
5860 0 = not authorized, 1 = authorized, 2 = authorized
5861 if device connected to internal port)
5862
5863 usbcore.autosuspend=
5864 [USB] The autosuspend time delay (in seconds) used
5865 for newly-detected USB devices (default 2). This
5866 is the time required before an idle device will be
5867 autosuspended. Devices for which the delay is set
5868 to a negative value won't be autosuspended at all.
5869
5870 usbcore.usbfs_snoop=
5871 [USB] Set to log all usbfs traffic (default 0 = off).
5872
5873 usbcore.usbfs_snoop_max=
5874 [USB] Maximum number of bytes to snoop in each URB
5875 (default = 65536).
5876
5877 usbcore.blinkenlights=
5878 [USB] Set to cycle leds on hubs (default 0 = off).
5879
5880 usbcore.old_scheme_first=
5881 [USB] Start with the old device initialization
5882 scheme (default 0 = off).
5883
5884 usbcore.usbfs_memory_mb=
5885 [USB] Memory limit (in MB) for buffers allocated by
5886 usbfs (default = 16, 0 = max = 2047).
5887
5888 usbcore.use_both_schemes=
5889 [USB] Try the other device initialization scheme
5890 if the first one fails (default 1 = enabled).
5891
5892 usbcore.initial_descriptor_timeout=
5893 [USB] Specifies timeout for the initial 64-byte
5894 USB_REQ_GET_DESCRIPTOR request in milliseconds
5895 (default 5000 = 5.0 seconds).
5896
5897 usbcore.nousb [USB] Disable the USB subsystem
5898
5899 usbcore.quirks=
5900 [USB] A list of quirk entries to augment the built-in
5901 usb core quirk list. List entries are separated by
5902 commas. Each entry has the form
5903 VendorID:ProductID:Flags. The IDs are 4-digit hex
5904 numbers and Flags is a set of letters. Each letter
5905 will change the built-in quirk; setting it if it is
5906 clear and clearing it if it is set. The letters have
5907 the following meanings:
5908 a = USB_QUIRK_STRING_FETCH_255 (string
5909 descriptors must not be fetched using
5910 a 255-byte read);
5911 b = USB_QUIRK_RESET_RESUME (device can't resume
5912 correctly so reset it instead);
5913 c = USB_QUIRK_NO_SET_INTF (device can't handle
5914 Set-Interface requests);
5915 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5916 handle its Configuration or Interface
5917 strings);
5918 e = USB_QUIRK_RESET (device can't be reset
5919 (e.g morph devices), don't use reset);
5920 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5921 more interface descriptions than the
5922 bNumInterfaces count, and can't handle
5923 talking to these interfaces);
5924 g = USB_QUIRK_DELAY_INIT (device needs a pause
5925 during initialization, after we read
5926 the device descriptor);
5927 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5928 high speed and super speed interrupt
5929 endpoints, the USB 2.0 and USB 3.0 spec
5930 require the interval in microframes (1
5931 microframe = 125 microseconds) to be
5932 calculated as interval = 2 ^
5933 (bInterval-1).
5934 Devices with this quirk report their
5935 bInterval as the result of this
5936 calculation instead of the exponent
5937 variable used in the calculation);
5938 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5939 handle device_qualifier descriptor
5940 requests);
5941 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5942 generates spurious wakeup, ignore
5943 remote wakeup capability);
5944 k = USB_QUIRK_NO_LPM (device can't handle Link
5945 Power Management);
5946 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5947 (Device reports its bInterval as linear
5948 frames instead of the USB 2.0
5949 calculation);
5950 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5951 to be disconnected before suspend to
5952 prevent spurious wakeup);
5953 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5954 pause after every control message);
5955 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5956 delay after resetting its port);
5957 Example: quirks=0781:5580:bk,0a5c:5834:gij
5958
5959 usbhid.mousepoll=
5960 [USBHID] The interval which mice are to be polled at.
5961
5962 usbhid.jspoll=
5963 [USBHID] The interval which joysticks are to be polled at.
5964
5965 usbhid.kbpoll=
5966 [USBHID] The interval which keyboards are to be polled at.
5967
5968 usb-storage.delay_use=
5969 [UMS] The delay in seconds before a new device is
5970 scanned for Logical Units (default 1).
5971
5972 usb-storage.quirks=
5973 [UMS] A list of quirks entries to supplement or
5974 override the built-in unusual_devs list. List
5975 entries are separated by commas. Each entry has
5976 the form VID:PID:Flags where VID and PID are Vendor
5977 and Product ID values (4-digit hex numbers) and
5978 Flags is a set of characters, each corresponding
5979 to a common usb-storage quirk flag as follows:
5980 a = SANE_SENSE (collect more than 18 bytes
5981 of sense data, not on uas);
5982 b = BAD_SENSE (don't collect more than 18
5983 bytes of sense data, not on uas);
5984 c = FIX_CAPACITY (decrease the reported
5985 device capacity by one sector);
5986 d = NO_READ_DISC_INFO (don't use
5987 READ_DISC_INFO command, not on uas);
5988 e = NO_READ_CAPACITY_16 (don't use
5989 READ_CAPACITY_16 command);
5990 f = NO_REPORT_OPCODES (don't use report opcodes
5991 command, uas only);
5992 g = MAX_SECTORS_240 (don't transfer more than
5993 240 sectors at a time, uas only);
5994 h = CAPACITY_HEURISTICS (decrease the
5995 reported device capacity by one
5996 sector if the number is odd);
5997 i = IGNORE_DEVICE (don't bind to this
5998 device);
5999 j = NO_REPORT_LUNS (don't use report luns
6000 command, uas only);
6001 k = NO_SAME (do not use WRITE_SAME, uas only)
6002 l = NOT_LOCKABLE (don't try to lock and
6003 unlock ejectable media, not on uas);
6004 m = MAX_SECTORS_64 (don't transfer more
6005 than 64 sectors = 32 KB at a time,
6006 not on uas);
6007 n = INITIAL_READ10 (force a retry of the
6008 initial READ(10) command, not on uas);
6009 o = CAPACITY_OK (accept the capacity
6010 reported by the device, not on uas);
6011 p = WRITE_CACHE (the device cache is ON
6012 by default, not on uas);
6013 r = IGNORE_RESIDUE (the device reports
6014 bogus residue values, not on uas);
6015 s = SINGLE_LUN (the device has only one
6016 Logical Unit);
6017 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6018 commands, uas only);
6019 u = IGNORE_UAS (don't bind to the uas driver);
6020 w = NO_WP_DETECT (don't test whether the
6021 medium is write-protected).
6022 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6023 even if the device claims no cache,
6024 not on uas)
6025 Example: quirks=0419:aaf5:rl,0421:0433:rc
6026
6027 user_debug= [KNL,ARM]
6028 Format: <int>
6029 See arch/arm/Kconfig.debug help text.
6030 1 - undefined instruction events
6031 2 - system calls
6032 4 - invalid data aborts
6033 8 - SIGSEGV faults
6034 16 - SIGBUS faults
6035 Example: user_debug=31
6036
6037 userpte=
6038 [X86] Flags controlling user PTE allocations.
6039
6040 nohigh = do not allocate PTE pages in
6041 HIGHMEM regardless of setting
6042 of CONFIG_HIGHPTE.
6043
6044 vdso= [X86,SH]
6045 On X86_32, this is an alias for vdso32=. Otherwise:
6046
6047 vdso=1: enable VDSO (the default)
6048 vdso=0: disable VDSO mapping
6049
6050 vdso32= [X86] Control the 32-bit vDSO
6051 vdso32=1: enable 32-bit VDSO
6052 vdso32=0 or vdso32=2: disable 32-bit VDSO
6053
6054 See the help text for CONFIG_COMPAT_VDSO for more
6055 details. If CONFIG_COMPAT_VDSO is set, the default is
6056 vdso32=0; otherwise, the default is vdso32=1.
6057
6058 For compatibility with older kernels, vdso32=2 is an
6059 alias for vdso32=0.
6060
6061 Try vdso32=0 if you encounter an error that says:
6062 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6063
6064 vector= [IA-64,SMP]
6065 vector=percpu: enable percpu vector domain
6066
6067 video= [FB] Frame buffer configuration
6068 See Documentation/fb/modedb.rst.
6069
6070 video.brightness_switch_enabled= [0,1]
6071 If set to 1, on receiving an ACPI notify event
6072 generated by hotkey, video driver will adjust brightness
6073 level and then send out the event to user space through
6074 the allocated input device; If set to 0, video driver
6075 will only send out the event without touching backlight
6076 brightness level.
6077 default: 1
6078
6079 virtio_mmio.device=
6080 [VMMIO] Memory mapped virtio (platform) device.
6081
6082 <size>@<baseaddr>:<irq>[:<id>]
6083 where:
6084 <size> := size (can use standard suffixes
6085 like K, M and G)
6086 <baseaddr> := physical base address
6087 <irq> := interrupt number (as passed to
6088 request_irq())
6089 <id> := (optional) platform device id
6090 example:
6091 virtio_mmio.device=1K@0x100b0000:48:7
6092
6093 Can be used multiple times for multiple devices.
6094
6095 vga= [BOOT,X86-32] Select a particular video mode
6096 See Documentation/x86/boot.rst and
6097 Documentation/admin-guide/svga.rst.
6098 Use vga=ask for menu.
6099 This is actually a boot loader parameter; the value is
6100 passed to the kernel using a special protocol.
6101
6102 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6103 May slow down system boot speed, especially when
6104 enabled on systems with a large amount of memory.
6105 All options are enabled by default, and this
6106 interface is meant to allow for selectively
6107 enabling or disabling specific virtual memory
6108 debugging features.
6109
6110 Available options are:
6111 P Enable page structure init time poisoning
6112 - Disable all of the above options
6113
6114 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6115 size of <nn>. This can be used to increase the
6116 minimum size (128MB on x86). It can also be used to
6117 decrease the size and leave more room for directly
6118 mapped kernel RAM.
6119
6120 vmcp_cma=nn[MG] [KNL,S390]
6121 Sets the memory size reserved for contiguous memory
6122 allocations for the vmcp device driver.
6123
6124 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6125 Format: <command>
6126
6127 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6128 Format: <command>
6129
6130 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6131 Format: <command>
6132
6133 vsyscall= [X86-64]
6134 Controls the behavior of vsyscalls (i.e. calls to
6135 fixed addresses of 0xffffffffff600x00 from legacy
6136 code). Most statically-linked binaries and older
6137 versions of glibc use these calls. Because these
6138 functions are at fixed addresses, they make nice
6139 targets for exploits that can control RIP.
6140
6141 emulate [default] Vsyscalls turn into traps and are
6142 emulated reasonably safely. The vsyscall
6143 page is readable.
6144
6145 xonly Vsyscalls turn into traps and are
6146 emulated reasonably safely. The vsyscall
6147 page is not readable.
6148
6149 none Vsyscalls don't work at all. This makes
6150 them quite hard to use for exploits but
6151 might break your system.
6152
6153 vt.color= [VT] Default text color.
6154 Format: 0xYX, X = foreground, Y = background.
6155 Default: 0x07 = light gray on black.
6156
6157 vt.cur_default= [VT] Default cursor shape.
6158 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6159 the parameters of the <Esc>[?A;B;Cc escape sequence;
6160 see VGA-softcursor.txt. Default: 2 = underline.
6161
6162 vt.default_blu= [VT]
6163 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6164 Change the default blue palette of the console.
6165 This is a 16-member array composed of values
6166 ranging from 0-255.
6167
6168 vt.default_grn= [VT]
6169 Format: <green0>,<green1>,<green2>,...,<green15>
6170 Change the default green palette of the console.
6171 This is a 16-member array composed of values
6172 ranging from 0-255.
6173
6174 vt.default_red= [VT]
6175 Format: <red0>,<red1>,<red2>,...,<red15>
6176 Change the default red palette of the console.
6177 This is a 16-member array composed of values
6178 ranging from 0-255.
6179
6180 vt.default_utf8=
6181 [VT]
6182 Format=<0|1>
6183 Set system-wide default UTF-8 mode for all tty's.
6184 Default is 1, i.e. UTF-8 mode is enabled for all
6185 newly opened terminals.
6186
6187 vt.global_cursor_default=
6188 [VT]
6189 Format=<-1|0|1>
6190 Set system-wide default for whether a cursor
6191 is shown on new VTs. Default is -1,
6192 i.e. cursors will be created by default unless
6193 overridden by individual drivers. 0 will hide
6194 cursors, 1 will display them.
6195
6196 vt.italic= [VT] Default color for italic text; 0-15.
6197 Default: 2 = green.
6198
6199 vt.underline= [VT] Default color for underlined text; 0-15.
6200 Default: 3 = cyan.
6201
6202 watchdog timers [HW,WDT] For information on watchdog timers,
6203 see Documentation/watchdog/watchdog-parameters.rst
6204 or other driver-specific files in the
6205 Documentation/watchdog/ directory.
6206
6207 watchdog_thresh=
6208 [KNL]
6209 Set the hard lockup detector stall duration
6210 threshold in seconds. The soft lockup detector
6211 threshold is set to twice the value. A value of 0
6212 disables both lockup detectors. Default is 10
6213 seconds.
6214
6215 workqueue.watchdog_thresh=
6216 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6217 warn stall conditions and dump internal state to
6218 help debugging. 0 disables workqueue stall
6219 detection; otherwise, it's the stall threshold
6220 duration in seconds. The default value is 30 and
6221 it can be updated at runtime by writing to the
6222 corresponding sysfs file.
6223
6224 workqueue.disable_numa
6225 By default, all work items queued to unbound
6226 workqueues are affine to the NUMA nodes they're
6227 issued on, which results in better behavior in
6228 general. If NUMA affinity needs to be disabled for
6229 whatever reason, this option can be used. Note
6230 that this also can be controlled per-workqueue for
6231 workqueues visible under /sys/bus/workqueue/.
6232
6233 workqueue.power_efficient
6234 Per-cpu workqueues are generally preferred because
6235 they show better performance thanks to cache
6236 locality; unfortunately, per-cpu workqueues tend to
6237 be more power hungry than unbound workqueues.
6238
6239 Enabling this makes the per-cpu workqueues which
6240 were observed to contribute significantly to power
6241 consumption unbound, leading to measurably lower
6242 power usage at the cost of small performance
6243 overhead.
6244
6245 The default value of this parameter is determined by
6246 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6247
6248 workqueue.debug_force_rr_cpu
6249 Workqueue used to implicitly guarantee that work
6250 items queued without explicit CPU specified are put
6251 on the local CPU. This guarantee is no longer true
6252 and while local CPU is still preferred work items
6253 may be put on foreign CPUs. This debug option
6254 forces round-robin CPU selection to flush out
6255 usages which depend on the now broken guarantee.
6256 When enabled, memory and cache locality will be
6257 impacted.
6258
6259 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6260 default x2apic cluster mode on platforms
6261 supporting x2apic.
6262
6263 xen_512gb_limit [KNL,X86-64,XEN]
6264 Restricts the kernel running paravirtualized under Xen
6265 to use only up to 512 GB of RAM. The reason to do so is
6266 crash analysis tools and Xen tools for doing domain
6267 save/restore/migration must be enabled to handle larger
6268 domains.
6269
6270 xen_emul_unplug= [HW,X86,XEN]
6271 Unplug Xen emulated devices
6272 Format: [unplug0,][unplug1]
6273 ide-disks -- unplug primary master IDE devices
6274 aux-ide-disks -- unplug non-primary-master IDE devices
6275 nics -- unplug network devices
6276 all -- unplug all emulated devices (NICs and IDE disks)
6277 unnecessary -- unplugging emulated devices is
6278 unnecessary even if the host did not respond to
6279 the unplug protocol
6280 never -- do not unplug even if version check succeeds
6281
6282 xen_legacy_crash [X86,XEN]
6283 Crash from Xen panic notifier, without executing late
6284 panic() code such as dumping handler.
6285
6286 xen_nopvspin [X86,XEN]
6287 Disables the qspinlock slowpath using Xen PV optimizations.
6288 This parameter is obsoleted by "nopvspin" parameter, which
6289 has equivalent effect for XEN platform.
6290
6291 xen_nopv [X86]
6292 Disables the PV optimizations forcing the HVM guest to
6293 run as generic HVM guest with no PV drivers.
6294 This option is obsoleted by the "nopv" option, which
6295 has equivalent effect for XEN platform.
6296
6297 xen_no_vector_callback
6298 [KNL,X86,XEN] Disable the vector callback for Xen
6299 event channel interrupts.
6300
6301 xen_scrub_pages= [XEN]
6302 Boolean option to control scrubbing pages before giving them back
6303 to Xen, for use by other domains. Can be also changed at runtime
6304 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6305 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6306
6307 xen_timer_slop= [X86-64,XEN]
6308 Set the timer slop (in nanoseconds) for the virtual Xen
6309 timers (default is 100000). This adjusts the minimum
6310 delta of virtualized Xen timers, where lower values
6311 improve timer resolution at the expense of processing
6312 more timer interrupts.
6313
6314 xen.event_eoi_delay= [XEN]
6315 How long to delay EOI handling in case of event
6316 storms (jiffies). Default is 10.
6317
6318 xen.event_loop_timeout= [XEN]
6319 After which time (jiffies) the event handling loop
6320 should start to delay EOI handling. Default is 2.
6321
6322 xen.fifo_events= [XEN]
6323 Boolean parameter to disable using fifo event handling
6324 even if available. Normally fifo event handling is
6325 preferred over the 2-level event handling, as it is
6326 fairer and the number of possible event channels is
6327 much higher. Default is on (use fifo events).
6328
6329 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6330 Disables the PV optimizations forcing the guest to run
6331 as generic guest with no PV drivers. Currently support
6332 XEN HVM, KVM, HYPER_V and VMWARE guest.
6333
6334 nopvspin [X86,XEN,KVM]
6335 Disables the qspinlock slow path using PV optimizations
6336 which allow the hypervisor to 'idle' the guest on lock
6337 contention.
6338
6339 xirc2ps_cs= [NET,PCMCIA]
6340 Format:
6341 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6342
6343 xive= [PPC]
6344 By default on POWER9 and above, the kernel will
6345 natively use the XIVE interrupt controller. This option
6346 allows the fallback firmware mode to be used:
6347
6348 off Fallback to firmware control of XIVE interrupt
6349 controller on both pseries and powernv
6350 platforms. Only useful on POWER9 and above.
6351
6352 xhci-hcd.quirks [USB,KNL]
6353 A hex value specifying bitmask with supplemental xhci
6354 host controller quirks. Meaning of each bit can be
6355 consulted in header drivers/usb/host/xhci.h.
6356
6357 xmon [PPC]
6358 Format: { early | on | rw | ro | off }
6359 Controls if xmon debugger is enabled. Default is off.
6360 Passing only "xmon" is equivalent to "xmon=early".
6361 early Call xmon as early as possible on boot; xmon
6362 debugger is called from setup_arch().
6363 on xmon debugger hooks will be installed so xmon
6364 is only called on a kernel crash. Default mode,
6365 i.e. either "ro" or "rw" mode, is controlled
6366 with CONFIG_XMON_DEFAULT_RO_MODE.
6367 rw xmon debugger hooks will be installed so xmon
6368 is called only on a kernel crash, mode is write,
6369 meaning SPR registers, memory and, other data
6370 can be written using xmon commands.
6371 ro same as "rw" option above but SPR registers,
6372 memory, and other data can't be written using
6373 xmon commands.
6374 off xmon is disabled.
1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
4 copy_dsdt }
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
14 are available
15
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
17
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
23
24 acpi_backlight= [HW,ACPI]
25 acpi_backlight=vendor
26 acpi_backlight=video
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
30
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
36
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
44
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
47 Format: <int>
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
58
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
68
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
72
73 acpi_enforce_resources= [ACPI]
74 { strict | lax | no }
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
88
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
92 size limitation.
93
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
97
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
101
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
104
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
106 use by PCI
107 Format: <irq>,<irq>...
108
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
113 the GPE dispatcher.
114 This facility can be used to prevent such uncontrolled
115 GPE floodings.
116 Format: <int>
117
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
125
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
127 kernels.
128
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
138
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
143
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
146
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
152
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
158 strings
159 acpi_osi=!! # enable all built-in OS vendor
160 strings
161 acpi_osi= # disable all strings
162
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
173 Examples:
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
177
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
183 meaningless.
184 Examples:
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
186 FALSE.
187
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
198 the OSPM features.
199 Examples:
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
205 equivalent to
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
207 and
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
210
211 acpi_pm_good [X86]
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
215
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
218
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
222
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
227 s3_bios and s3_mode.
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
244
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
248
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
251
252 agp= [AGP]
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
257
258 ALSA [HW,ALSA]
259 See Documentation/sound/alsa/alsa-parameters.txt
260
261 alignment= [KNL,ARM]
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
265
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
273
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
278
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
285
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
288 Possible values are:
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
292 is a lot of faster
293 off - do not initialize any AMD IOMMU found in
294 the system
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
300
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
306
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
309 remapping modes:
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
315
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
318 Format: <a>,<b>
319 See also Documentation/input/joydev/joystick.rst
320
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
325
326 apc= [HW,SPARC]
327 Power management functions (SPARCstation-4/5 + deriv.)
328 Format: noidle
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
332
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
339 driver name.
340 Format: apic=driver_name
341 Examples: apic=bigsmp
342
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
347 backup of CPU 0
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
350 shot down by NMI
351
352 autoconf= [IPV6]
353 See Documentation/networking/ipv6.txt.
354
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
363
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
366
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
369
370 ataflop= [HW,M68k]
371
372 atarimouse= [HW,MOUSE] Atari Mouse
373
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
376
377 atkbd.reset= [HW] Reset keyboard during initialization
378
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
381
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 keyboards
384
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
387
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
390
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
400 userspace auditd.
401 Default: unset
402
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
405 Default: 64
406
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
410 0 - Disable the BAU.
411 1 - Enable the BAU.
412 unset - Disable the BAU.
413
414 baycom_epp= [HW,AX25]
415 Format: <io>,<mode>
416
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
418 Format: <io>,<mode>
419 See header of drivers/net/hamradio/baycom_par.c.
420
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
425
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
430
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
434
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
437 no delay (0).
438 Format: integer
439
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441
442 bert_disable [ACPI]
443 Disable BERT OS support on buggy BIOSes.
444
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
447 kernel args too.
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bttv.tuner=
450
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
453 at a time.
454
455 c101= [NET] Moxa C101 synchronous serial card
456
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
463
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
466 trust validation.
467 format: { id:<keyid> | builtin }
468
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
473 others).
474
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
477
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
482 a single hierarchy
483 - foo isn't visible as an individually mountable
484 subsystem
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
488
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
493
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
495 Format: <string>
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
498
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
508
509 cio_ignore= [S390]
510 See Documentation/s390/CommonIO for details.
511 clk_ignore_unused
512 [CLK]
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
522
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
524 [Deprecated]
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
529
530 clocksource= Override the default clocksource
531 Format: <string>
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
535 the platform:
536 [all] jiffies (this is the base, fallback clocksource)
537 [ACPI] acpi_pm
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
542 [MIPS] MIPS
543 [PARISC] cr16
544 [S390] tod
545 [SH] SuperH
546 [SPARC64] tick
547 [X86-64] hpet,tsc
548
549 clocksource.arm_arch_timer.evtstrm=
550 [ARM,ARM64]
551 Format: <bool>
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
555 systems.
556
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
562 ones should be.
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
568 some critical bits.
569
570 cma=nn[MG]@[start[MG][-end[MG]]]
571 [ARM,X86,KNL]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
578
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
583 a hypervisor.
584 Default: yes
585
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
589
590 code_bytes [X86] How many bytes of object code to print
591 in an oops report.
592 Range: 0 - 8192
593 Default: 64
594
595 com20020= [HW,NET] ARCnet - COM20020 chipset
596 Format:
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
598
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
600 Format: <io>[,<irq>]
601
602 com90xx= [HW,NET]
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
605
606 condev= [HW,S390] console device
607 conmode=
608
609 console= [KNL] Output console device and options.
610
611 tty<n> Use the virtual console device <n>.
612
613 ttyS<n>[,options]
614 ttyUSB0[,options]
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
620
621 See Documentation/admin-guide/serial-console.rst for more
622 information. See
623 Documentation/networking/netconsole.txt for an
624 alternative.
625
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
640
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
643
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
646 console=brl,ttyS0
647 For now, only VisioBraille is supported.
648
649 console_msg_format=
650 [KNL] Change console messages format
651 default
652 By default we print messages on consoles in
653 "[time stamp] text\n" format (time stamp may not be
654 printed, depending on CONFIG_PRINTK_TIME or
655 `printk_time' param).
656 syslog
657 Switch to syslog format: "<%u>[time stamp] text\n"
658 IOW, each message will have a facility and loglevel
659 prefix. The format is similar to one used by syslog()
660 syscall, or to executing "dmesg -S --raw" or to reading
661 from /proc/kmsg.
662
663 consoleblank= [KNL] The console blank (screen saver) timeout in
664 seconds. A value of 0 disables the blank timer.
665 Defaults to 0.
666
667 coredump_filter=
668 [KNL] Change the default value for
669 /proc/<pid>/coredump_filter.
670 See also Documentation/filesystems/proc.txt.
671
672 coresight_cpu_debug.enable
673 [ARM,ARM64]
674 Format: <bool>
675 Enable/disable the CPU sampling based debugging.
676 0: default value, disable debugging
677 1: enable debugging at boot time
678
679 cpuidle.off=1 [CPU_IDLE]
680 disable the cpuidle sub-system
681
682 cpufreq.off=1 [CPU_FREQ]
683 disable the cpufreq sub-system
684
685 cpu_init_udelay=N
686 [X86] Delay for N microsec between assert and de-assert
687 of APIC INIT to start processors. This delay occurs
688 on every CPU online, such as boot, and resume from suspend.
689 Default: 10000
690
691 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
692 Format:
693 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
694
695 crashkernel=size[KMG][@offset[KMG]]
696 [KNL] Using kexec, Linux can switch to a 'crash kernel'
697 upon panic. This parameter reserves the physical
698 memory region [offset, offset + size] for that kernel
699 image. If '@offset' is omitted, then a suitable offset
700 is selected automatically. Check
701 Documentation/kdump/kdump.txt for further details.
702
703 crashkernel=range1:size1[,range2:size2,...][@offset]
704 [KNL] Same as above, but depends on the memory
705 in the running system. The syntax of range is
706 start-[end] where start and end are both
707 a memory unit (amount[KMG]). See also
708 Documentation/kdump/kdump.txt for an example.
709
710 crashkernel=size[KMG],high
711 [KNL, x86_64] range could be above 4G. Allow kernel
712 to allocate physical memory region from top, so could
713 be above 4G if system have more than 4G ram installed.
714 Otherwise memory region will be allocated below 4G, if
715 available.
716 It will be ignored if crashkernel=X is specified.
717 crashkernel=size[KMG],low
718 [KNL, x86_64] range under 4G. When crashkernel=X,high
719 is passed, kernel could allocate physical memory region
720 above 4G, that cause second kernel crash on system
721 that require some amount of low memory, e.g. swiotlb
722 requires at least 64M+32K low memory, also enough extra
723 low memory is needed to make sure DMA buffers for 32-bit
724 devices won't run out. Kernel would try to allocate at
725 at least 256M below 4G automatically.
726 This one let user to specify own low range under 4G
727 for second kernel instead.
728 0: to disable low allocation.
729 It will be ignored when crashkernel=X,high is not used
730 or memory reserved is below 4G.
731
732 cryptomgr.notests
733 [KNL] Disable crypto self-tests
734
735 cs89x0_dma= [HW,NET]
736 Format: <dma>
737
738 cs89x0_media= [HW,NET]
739 Format: { rj45 | aui | bnc }
740
741 dasd= [HW,NET]
742 See header of drivers/s390/block/dasd_devmap.c.
743
744 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
745 (one device per port)
746 Format: <port#>,<type>
747 See also Documentation/input/devices/joystick-parport.rst
748
749 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
750 time. See
751 Documentation/admin-guide/dynamic-debug-howto.rst for
752 details. Deprecated, see dyndbg.
753
754 debug [KNL] Enable kernel debugging (events log level).
755
756 debug_locks_verbose=
757 [KNL] verbose self-tests
758 Format=<0|1>
759 Print debugging info while doing the locking API
760 self-tests.
761 We default to 0 (no extra messages), setting it to
762 1 will print _a lot_ more information - normally
763 only useful to kernel developers.
764
765 debug_objects [KNL] Enable object debugging
766
767 no_debug_objects
768 [KNL] Disable object debugging
769
770 debug_guardpage_minorder=
771 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
772 parameter allows control of the order of pages that will
773 be intentionally kept free (and hence protected) by the
774 buddy allocator. Bigger value increase the probability
775 of catching random memory corruption, but reduce the
776 amount of memory for normal system use. The maximum
777 possible value is MAX_ORDER/2. Setting this parameter
778 to 1 or 2 should be enough to identify most random
779 memory corruption problems caused by bugs in kernel or
780 driver code when a CPU writes to (or reads from) a
781 random memory location. Note that there exists a class
782 of memory corruptions problems caused by buggy H/W or
783 F/W or by drivers badly programing DMA (basically when
784 memory is written at bus level and the CPU MMU is
785 bypassed) which are not detectable by
786 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
787 tracking down these problems.
788
789 debug_pagealloc=
790 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
791 parameter enables the feature at boot time. In
792 default, it is disabled. We can avoid allocating huge
793 chunk of memory for debug pagealloc if we don't enable
794 it at boot time and the system will work mostly same
795 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
796 on: enable the feature
797
798 debugpat [X86] Enable PAT debugging
799
800 decnet.addr= [HW,NET]
801 Format: <area>[,<node>]
802 See also Documentation/networking/decnet.txt.
803
804 default_hugepagesz=
805 [same as hugepagesz=] The size of the default
806 HugeTLB page size. This is the size represented by
807 the legacy /proc/ hugepages APIs, used for SHM, and
808 default size when mounting hugetlbfs filesystems.
809 Defaults to the default architecture's huge page size
810 if not specified.
811
812 dhash_entries= [KNL]
813 Set number of hash buckets for dentry cache.
814
815 disable_1tb_segments [PPC]
816 Disables the use of 1TB hash page table segments. This
817 causes the kernel to fall back to 256MB segments which
818 can be useful when debugging issues that require an SLB
819 miss to occur.
820
821 disable= [IPV6]
822 See Documentation/networking/ipv6.txt.
823
824 disable_radix [PPC]
825 Disable RADIX MMU mode on POWER9
826
827 disable_cpu_apicid= [X86,APIC,SMP]
828 Format: <int>
829 The number of initial APIC ID for the
830 corresponding CPU to be disabled at boot,
831 mostly used for the kdump 2nd kernel to
832 disable BSP to wake up multiple CPUs without
833 causing system reset or hang due to sending
834 INIT from AP to BSP.
835
836 disable_ddw [PPC/PSERIES]
837 Disable Dynamic DMA Window support. Use this if
838 to workaround buggy firmware.
839
840 disable_ipv6= [IPV6]
841 See Documentation/networking/ipv6.txt.
842
843 disable_mtrr_cleanup [X86]
844 The kernel tries to adjust MTRR layout from continuous
845 to discrete, to make X server driver able to add WB
846 entry later. This parameter disables that.
847
848 disable_mtrr_trim [X86, Intel and AMD only]
849 By default the kernel will trim any uncacheable
850 memory out of your available memory pool based on
851 MTRR settings. This parameter disables that behavior,
852 possibly causing your machine to run very slowly.
853
854 disable_timer_pin_1 [X86]
855 Disable PIN 1 of APIC timer
856 Can be useful to work around chipset bugs.
857
858 dis_ucode_ldr [X86] Disable the microcode loader.
859
860 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
861 this option disables the debugging code at boot.
862
863 dma_debug_entries=<number>
864 This option allows to tune the number of preallocated
865 entries for DMA-API debugging code. One entry is
866 required per DMA-API allocation. Use this if the
867 DMA-API debugging code disables itself because the
868 architectural default is too low.
869
870 dma_debug_driver=<driver_name>
871 With this option the DMA-API debugging driver
872 filter feature can be enabled at boot time. Just
873 pass the driver to filter for as the parameter.
874 The filter can be disabled or changed to another
875 driver later using sysfs.
876
877 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
878 Broken monitors, graphic adapters, KVMs and EDIDless
879 panels may send no or incorrect EDID data sets.
880 This parameter allows to specify an EDID data sets
881 in the /lib/firmware directory that are used instead.
882 Generic built-in EDID data sets are used, if one of
883 edid/1024x768.bin, edid/1280x1024.bin,
884 edid/1680x1050.bin, or edid/1920x1080.bin is given
885 and no file with the same name exists. Details and
886 instructions how to build your own EDID data are
887 available in Documentation/EDID/HOWTO.txt. An EDID
888 data set will only be used for a particular connector,
889 if its name and a colon are prepended to the EDID
890 name. Each connector may use a unique EDID data
891 set by separating the files with a comma. An EDID
892 data set with no connector name will be used for
893 any connectors not explicitly specified.
894
895 dscc4.setup= [NET]
896
897 dt_cpu_ftrs= [PPC]
898 Format: {"off" | "known"}
899 Control how the dt_cpu_ftrs device-tree binding is
900 used for CPU feature discovery and setup (if it
901 exists).
902 off: Do not use it, fall back to legacy cpu table.
903 known: Do not pass through unknown features to guests
904 or userspace, only those that the kernel is aware of.
905
906 dump_apple_properties [X86]
907 Dump name and content of EFI device properties on
908 x86 Macs. Useful for driver authors to determine
909 what data is available or for reverse-engineering.
910
911 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
912 module.dyndbg[="val"]
913 Enable debug messages at boot time. See
914 Documentation/admin-guide/dynamic-debug-howto.rst
915 for details.
916
917 nompx [X86] Disables Intel Memory Protection Extensions.
918 See Documentation/x86/intel_mpx.txt for more
919 information about the feature.
920
921 nopku [X86] Disable Memory Protection Keys CPU feature found
922 in some Intel CPUs.
923
924 module.async_probe [KNL]
925 Enable asynchronous probe on this module.
926
927 early_ioremap_debug [KNL]
928 Enable debug messages in early_ioremap support. This
929 is useful for tracking down temporary early mappings
930 which are not unmapped.
931
932 earlycon= [KNL] Output early console device and options.
933
934 [ARM64] The early console is determined by the
935 stdout-path property in device tree's chosen node,
936 or determined by the ACPI SPCR table.
937
938 [X86] When used with no options the early console is
939 determined by the ACPI SPCR table.
940
941 cdns,<addr>[,options]
942 Start an early, polled-mode console on a Cadence
943 (xuartps) serial port at the specified address. Only
944 supported option is baud rate. If baud rate is not
945 specified, the serial port must already be setup and
946 configured.
947
948 uart[8250],io,<addr>[,options]
949 uart[8250],mmio,<addr>[,options]
950 uart[8250],mmio32,<addr>[,options]
951 uart[8250],mmio32be,<addr>[,options]
952 uart[8250],0x<addr>[,options]
953 Start an early, polled-mode console on the 8250/16550
954 UART at the specified I/O port or MMIO address.
955 MMIO inter-register address stride is either 8-bit
956 (mmio) or 32-bit (mmio32 or mmio32be).
957 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
958 to be equivalent to 'mmio'. 'options' are specified
959 in the same format described for "console=ttyS<n>"; if
960 unspecified, the h/w is not initialized.
961
962 pl011,<addr>
963 pl011,mmio32,<addr>
964 Start an early, polled-mode console on a pl011 serial
965 port at the specified address. The pl011 serial port
966 must already be setup and configured. Options are not
967 yet supported. If 'mmio32' is specified, then only
968 the driver will use only 32-bit accessors to read/write
969 the device registers.
970
971 meson,<addr>
972 Start an early, polled-mode console on a meson serial
973 port at the specified address. The serial port must
974 already be setup and configured. Options are not yet
975 supported.
976
977 msm_serial,<addr>
978 Start an early, polled-mode console on an msm serial
979 port at the specified address. The serial port
980 must already be setup and configured. Options are not
981 yet supported.
982
983 msm_serial_dm,<addr>
984 Start an early, polled-mode console on an msm serial
985 dm port at the specified address. The serial port
986 must already be setup and configured. Options are not
987 yet supported.
988
989 owl,<addr>
990 Start an early, polled-mode console on a serial port
991 of an Actions Semi SoC, such as S500 or S900, at the
992 specified address. The serial port must already be
993 setup and configured. Options are not yet supported.
994
995 smh Use ARM semihosting calls for early console.
996
997 s3c2410,<addr>
998 s3c2412,<addr>
999 s3c2440,<addr>
1000 s3c6400,<addr>
1001 s5pv210,<addr>
1002 exynos4210,<addr>
1003 Use early console provided by serial driver available
1004 on Samsung SoCs, requires selecting proper type and
1005 a correct base address of the selected UART port. The
1006 serial port must already be setup and configured.
1007 Options are not yet supported.
1008
1009 lantiq,<addr>
1010 Start an early, polled-mode console on a lantiq serial
1011 (lqasc) port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1013 yet supported.
1014
1015 lpuart,<addr>
1016 lpuart32,<addr>
1017 Use early console provided by Freescale LP UART driver
1018 found on Freescale Vybrid and QorIQ LS1021A processors.
1019 A valid base address must be provided, and the serial
1020 port must already be setup and configured.
1021
1022 ar3700_uart,<addr>
1023 Start an early, polled-mode console on the
1024 Armada 3700 serial port at the specified
1025 address. The serial port must already be setup
1026 and configured. Options are not yet supported.
1027
1028 earlyprintk= [X86,SH,ARM,M68k,S390]
1029 earlyprintk=vga
1030 earlyprintk=efi
1031 earlyprintk=sclp
1032 earlyprintk=xen
1033 earlyprintk=serial[,ttySn[,baudrate]]
1034 earlyprintk=serial[,0x...[,baudrate]]
1035 earlyprintk=ttySn[,baudrate]
1036 earlyprintk=dbgp[debugController#]
1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1038 earlyprintk=xdbc[xhciController#]
1039
1040 earlyprintk is useful when the kernel crashes before
1041 the normal console is initialized. It is not enabled by
1042 default because it has some cosmetic problems.
1043
1044 Append ",keep" to not disable it when the real console
1045 takes over.
1046
1047 Only one of vga, efi, serial, or usb debug port can
1048 be used at a time.
1049
1050 Currently only ttyS0 and ttyS1 may be specified by
1051 name. Other I/O ports may be explicitly specified
1052 on some architectures (x86 and arm at least) by
1053 replacing ttySn with an I/O port address, like this:
1054 earlyprintk=serial,0x1008,115200
1055 You can find the port for a given device in
1056 /proc/tty/driver/serial:
1057 2: uart:ST16650V2 port:00001008 irq:18 ...
1058
1059 Interaction with the standard serial driver is not
1060 very good.
1061
1062 The VGA and EFI output is eventually overwritten by
1063 the real console.
1064
1065 The xen output can only be used by Xen PV guests.
1066
1067 The sclp output can only be used on s390.
1068
1069 edac_report= [HW,EDAC] Control how to report EDAC event
1070 Format: {"on" | "off" | "force"}
1071 on: enable EDAC to report H/W event. May be overridden
1072 by other higher priority error reporting module.
1073 off: disable H/W event reporting through EDAC.
1074 force: enforce the use of EDAC to report H/W event.
1075 default: on.
1076
1077 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1078 ekgdboc=kbd
1079
1080 This is designed to be used in conjunction with
1081 the boot argument: earlyprintk=vga
1082
1083 edd= [EDD]
1084 Format: {"off" | "on" | "skip[mbr]"}
1085
1086 efi= [EFI]
1087 Format: { "old_map", "nochunk", "noruntime", "debug" }
1088 old_map [X86-64]: switch to the old ioremap-based EFI
1089 runtime services mapping. 32-bit still uses this one by
1090 default.
1091 nochunk: disable reading files in "chunks" in the EFI
1092 boot stub, as chunking can cause problems with some
1093 firmware implementations.
1094 noruntime : disable EFI runtime services support
1095 debug: enable misc debug output
1096
1097 efi_no_storage_paranoia [EFI; X86]
1098 Using this parameter you can use more than 50% of
1099 your efi variable storage. Use this parameter only if
1100 you are really sure that your UEFI does sane gc and
1101 fulfills the spec otherwise your board may brick.
1102
1103 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1104 Add arbitrary attribute to specific memory range by
1105 updating original EFI memory map.
1106 Region of memory which aa attribute is added to is
1107 from ss to ss+nn.
1108 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1109 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1110 attribute is added to range 0x100000000-0x180000000 and
1111 0x10a0000000-0x1120000000.
1112
1113 Using this parameter you can do debugging of EFI memmap
1114 related feature. For example, you can do debugging of
1115 Address Range Mirroring feature even if your box
1116 doesn't support it.
1117
1118 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1119 that is to be dynamically loaded by Linux. If there are
1120 multiple variables with the same name but with different
1121 vendor GUIDs, all of them will be loaded. See
1122 Documentation/acpi/ssdt-overlays.txt for details.
1123
1124
1125 eisa_irq_edge= [PARISC,HW]
1126 See header of drivers/parisc/eisa.c.
1127
1128 elanfreq= [X86-32]
1129 See comment before function elanfreq_setup() in
1130 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1131
1132 elevator= [IOSCHED]
1133 Format: {"cfq" | "deadline" | "noop"}
1134 See Documentation/block/cfq-iosched.txt and
1135 Documentation/block/deadline-iosched.txt for details.
1136
1137 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1138 Specifies physical address of start of kernel core
1139 image elf header and optionally the size. Generally
1140 kexec loader will pass this option to capture kernel.
1141 See Documentation/kdump/kdump.txt for details.
1142
1143 enable_mtrr_cleanup [X86]
1144 The kernel tries to adjust MTRR layout from continuous
1145 to discrete, to make X server driver able to add WB
1146 entry later. This parameter enables that.
1147
1148 enable_timer_pin_1 [X86]
1149 Enable PIN 1 of APIC timer
1150 Can be useful to work around chipset bugs
1151 (in particular on some ATI chipsets).
1152 The kernel tries to set a reasonable default.
1153
1154 enforcing [SELINUX] Set initial enforcing status.
1155 Format: {"0" | "1"}
1156 See security/selinux/Kconfig help text.
1157 0 -- permissive (log only, no denials).
1158 1 -- enforcing (deny and log).
1159 Default value is 0.
1160 Value can be changed at runtime via /selinux/enforce.
1161
1162 erst_disable [ACPI]
1163 Disable Error Record Serialization Table (ERST)
1164 support.
1165
1166 ether= [HW,NET] Ethernet cards parameters
1167 This option is obsoleted by the "netdev=" option, which
1168 has equivalent usage. See its documentation for details.
1169
1170 evm= [EVM]
1171 Format: { "fix" }
1172 Permit 'security.evm' to be updated regardless of
1173 current integrity status.
1174
1175 failslab=
1176 fail_page_alloc=
1177 fail_make_request=[KNL]
1178 General fault injection mechanism.
1179 Format: <interval>,<probability>,<space>,<times>
1180 See also Documentation/fault-injection/.
1181
1182 floppy= [HW]
1183 See Documentation/blockdev/floppy.txt.
1184
1185 force_pal_cache_flush
1186 [IA-64] Avoid check_sal_cache_flush which may hang on
1187 buggy SAL_CACHE_FLUSH implementations. Using this
1188 parameter will force ia64_sal_cache_flush to call
1189 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1190
1191 forcepae [X86-32]
1192 Forcefully enable Physical Address Extension (PAE).
1193 Many Pentium M systems disable PAE but may have a
1194 functionally usable PAE implementation.
1195 Warning: use of this parameter will taint the kernel
1196 and may cause unknown problems.
1197
1198 ftrace=[tracer]
1199 [FTRACE] will set and start the specified tracer
1200 as early as possible in order to facilitate early
1201 boot debugging.
1202
1203 ftrace_dump_on_oops[=orig_cpu]
1204 [FTRACE] will dump the trace buffers on oops.
1205 If no parameter is passed, ftrace will dump
1206 buffers of all CPUs, but if you pass orig_cpu, it will
1207 dump only the buffer of the CPU that triggered the
1208 oops.
1209
1210 ftrace_filter=[function-list]
1211 [FTRACE] Limit the functions traced by the function
1212 tracer at boot up. function-list is a comma separated
1213 list of functions. This list can be changed at run
1214 time by the set_ftrace_filter file in the debugfs
1215 tracing directory.
1216
1217 ftrace_notrace=[function-list]
1218 [FTRACE] Do not trace the functions specified in
1219 function-list. This list can be changed at run time
1220 by the set_ftrace_notrace file in the debugfs
1221 tracing directory.
1222
1223 ftrace_graph_filter=[function-list]
1224 [FTRACE] Limit the top level callers functions traced
1225 by the function graph tracer at boot up.
1226 function-list is a comma separated list of functions
1227 that can be changed at run time by the
1228 set_graph_function file in the debugfs tracing directory.
1229
1230 ftrace_graph_notrace=[function-list]
1231 [FTRACE] Do not trace from the functions specified in
1232 function-list. This list is a comma separated list of
1233 functions that can be changed at run time by the
1234 set_graph_notrace file in the debugfs tracing directory.
1235
1236 ftrace_graph_max_depth=<uint>
1237 [FTRACE] Used with the function graph tracer. This is
1238 the max depth it will trace into a function. This value
1239 can be changed at run time by the max_graph_depth file
1240 in the tracefs tracing directory. default: 0 (no limit)
1241
1242 gamecon.map[2|3]=
1243 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1244 support via parallel port (up to 5 devices per port)
1245 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1246 See also Documentation/input/devices/joystick-parport.rst
1247
1248 gamma= [HW,DRM]
1249
1250 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1251 Format: off | on
1252 default: on
1253
1254 gcov_persist= [GCOV] When non-zero (default), profiling data for
1255 kernel modules is saved and remains accessible via
1256 debugfs, even when the module is unloaded/reloaded.
1257 When zero, profiling data is discarded and associated
1258 debugfs files are removed at module unload time.
1259
1260 goldfish [X86] Enable the goldfish android emulator platform.
1261 Don't use this when you are not running on the
1262 android emulator
1263
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1268
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1271 Format: 0 | 1
1272 Default: 0
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1275 Format: 0 | 1
1276 Default: 0
1277 grcan.select= [HW] Select which physical interface to use.
1278 Format: 0 | 1
1279 Default: 0
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1282 Default: 1024
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1285 Default: 1024
1286
1287 gpio-mockup.gpio_mockup_ranges
1288 [HW] Sets the ranges of gpiochip of for this device.
1289 Format: <start1>,<end1>,<start2>,<end2>...
1290
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1294 Format: <integer>
1295
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1300
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1302
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1305
1306 hest_disable [ACPI]
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1310
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1315
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1318 Default: "on"
1319
1320 hisax= [HW,ISDN]
1321 See Documentation/isdn/README.HiSax.
1322
1323 hlt [BUGS=ARM,SH]
1324
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1327 verbose }
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1330 VIA, nVidia)
1331 verbose: show contents of HPET registers during setup
1332
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1335
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1343
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1349
1350 keep_bootcon [KNL]
1351 Do not unregister boot console at start. This is only
1352 useful for debugging when something happens in the window
1353 between unregistering the boot console and initializing
1354 the real console.
1355
1356 i2c_bus= [HW] Override the default board specific I2C bus speed
1357 or register an additional I2C bus that is not
1358 registered from board initialization code.
1359 Format:
1360 <bus_id>,<clkrate>
1361
1362 i8042.debug [HW] Toggle i8042 debug mode
1363 i8042.unmask_kbd_data
1364 [HW] Enable printing of interrupt data from the KBD port
1365 (disabled by default, and as a pre-condition
1366 requires that i8042.debug=1 be enabled)
1367 i8042.direct [HW] Put keyboard port into non-translated mode
1368 i8042.dumbkbd [HW] Pretend that controller can only read data from
1369 keyboard and cannot control its state
1370 (Don't attempt to blink the leds)
1371 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1372 i8042.nokbd [HW] Don't check/create keyboard port
1373 i8042.noloop [HW] Disable the AUX Loopback command while probing
1374 for the AUX port
1375 i8042.nomux [HW] Don't check presence of an active multiplexing
1376 controller
1377 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1378 controllers
1379 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1380 i8042.reset [HW] Reset the controller during init, cleanup and
1381 suspend-to-ram transitions, only during s2r
1382 transitions, or never reset
1383 Format: { 1 | Y | y | 0 | N | n }
1384 1, Y, y: always reset controller
1385 0, N, n: don't ever reset controller
1386 Default: only on s2r transitions on x86; most other
1387 architectures force reset to be always executed
1388 i8042.unlock [HW] Unlock (ignore) the keylock
1389 i8042.kbdreset [HW] Reset device connected to KBD port
1390
1391 i810= [HW,DRM]
1392
1393 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1394 indicates that the driver is running on unsupported
1395 hardware.
1396 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1397 does not match list of supported models.
1398 i8k.power_status
1399 [HW] Report power status in /proc/i8k
1400 (disabled by default)
1401 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1402 capability is set.
1403
1404 i915.invert_brightness=
1405 [DRM] Invert the sense of the variable that is used to
1406 set the brightness of the panel backlight. Normally a
1407 brightness value of 0 indicates backlight switched off,
1408 and the maximum of the brightness value sets the backlight
1409 to maximum brightness. If this parameter is set to 0
1410 (default) and the machine requires it, or this parameter
1411 is set to 1, a brightness value of 0 sets the backlight
1412 to maximum brightness, and the maximum of the brightness
1413 value switches the backlight off.
1414 -1 -- never invert brightness
1415 0 -- machine default
1416 1 -- force brightness inversion
1417
1418 icn= [HW,ISDN]
1419 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1420
1421 ide-core.nodma= [HW] (E)IDE subsystem
1422 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1423 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1424 .cdrom .chs .ignore_cable are additional options
1425 See Documentation/ide/ide.txt.
1426
1427 ide-generic.probe-mask= [HW] (E)IDE subsystem
1428 Format: <int>
1429 Probe mask for legacy ISA IDE ports. Depending on
1430 platform up to 6 ports are supported, enabled by
1431 setting corresponding bits in the mask to 1. The
1432 default value is 0x0, which has a special meaning.
1433 On systems that have PCI, it triggers scanning the
1434 PCI bus for the first and the second port, which
1435 are then probed. On systems without PCI the value
1436 of 0x0 enables probing the two first ports as if it
1437 was 0x3.
1438
1439 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1440 Claim all unknown PCI IDE storage controllers.
1441
1442 idle= [X86]
1443 Format: idle=poll, idle=halt, idle=nomwait
1444 Poll forces a polling idle loop that can slightly
1445 improve the performance of waking up a idle CPU, but
1446 will use a lot of power and make the system run hot.
1447 Not recommended.
1448 idle=halt: Halt is forced to be used for CPU idle.
1449 In such case C2/C3 won't be used again.
1450 idle=nomwait: Disable mwait for CPU C-states
1451
1452 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1453 Format: { strict | legacy | 2008 | relaxed }
1454 Default: strict
1455
1456 Choose which programs will be accepted for execution
1457 based on the IEEE 754 NaN encoding(s) supported by
1458 the FPU and the NaN encoding requested with the value
1459 of an ELF file header flag individually set by each
1460 binary. Hardware implementations are permitted to
1461 support either or both of the legacy and the 2008 NaN
1462 encoding mode.
1463
1464 Available settings are as follows:
1465 strict accept binaries that request a NaN encoding
1466 supported by the FPU
1467 legacy only accept legacy-NaN binaries, if supported
1468 by the FPU
1469 2008 only accept 2008-NaN binaries, if supported
1470 by the FPU
1471 relaxed accept any binaries regardless of whether
1472 supported by the FPU
1473
1474 The FPU emulator is always able to support both NaN
1475 encodings, so if no FPU hardware is present or it has
1476 been disabled with 'nofpu', then the settings of
1477 'legacy' and '2008' strap the emulator accordingly,
1478 'relaxed' straps the emulator for both legacy-NaN and
1479 2008-NaN, whereas 'strict' enables legacy-NaN only on
1480 legacy processors and both NaN encodings on MIPS32 or
1481 MIPS64 CPUs.
1482
1483 The setting for ABS.fmt/NEG.fmt instruction execution
1484 mode generally follows that for the NaN encoding,
1485 except where unsupported by hardware.
1486
1487 ignore_loglevel [KNL]
1488 Ignore loglevel setting - this will print /all/
1489 kernel messages to the console. Useful for debugging.
1490 We also add it as printk module parameter, so users
1491 could change it dynamically, usually by
1492 /sys/module/printk/parameters/ignore_loglevel.
1493
1494 ignore_rlimit_data
1495 Ignore RLIMIT_DATA setting for data mappings,
1496 print warning at first misuse. Can be changed via
1497 /sys/module/kernel/parameters/ignore_rlimit_data.
1498
1499 ihash_entries= [KNL]
1500 Set number of hash buckets for inode cache.
1501
1502 ima_appraise= [IMA] appraise integrity measurements
1503 Format: { "off" | "enforce" | "fix" | "log" }
1504 default: "enforce"
1505
1506 ima_appraise_tcb [IMA]
1507 The builtin appraise policy appraises all files
1508 owned by uid=0.
1509
1510 ima_canonical_fmt [IMA]
1511 Use the canonical format for the binary runtime
1512 measurements, instead of host native format.
1513
1514 ima_hash= [IMA]
1515 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1516 | sha512 | ... }
1517 default: "sha1"
1518
1519 The list of supported hash algorithms is defined
1520 in crypto/hash_info.h.
1521
1522 ima_policy= [IMA]
1523 The builtin policies to load during IMA setup.
1524 Format: "tcb | appraise_tcb | secure_boot |
1525 fail_securely"
1526
1527 The "tcb" policy measures all programs exec'd, files
1528 mmap'd for exec, and all files opened with the read
1529 mode bit set by either the effective uid (euid=0) or
1530 uid=0.
1531
1532 The "appraise_tcb" policy appraises the integrity of
1533 all files owned by root. (This is the equivalent
1534 of ima_appraise_tcb.)
1535
1536 The "secure_boot" policy appraises the integrity
1537 of files (eg. kexec kernel image, kernel modules,
1538 firmware, policy, etc) based on file signatures.
1539
1540 The "fail_securely" policy forces file signature
1541 verification failure also on privileged mounted
1542 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1543 flag.
1544
1545 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1546 Load a policy which meets the needs of the Trusted
1547 Computing Base. This means IMA will measure all
1548 programs exec'd, files mmap'd for exec, and all files
1549 opened for read by uid=0.
1550
1551 ima_template= [IMA]
1552 Select one of defined IMA measurements template formats.
1553 Formats: { "ima" | "ima-ng" | "ima-sig" }
1554 Default: "ima-ng"
1555
1556 ima_template_fmt=
1557 [IMA] Define a custom template format.
1558 Format: { "field1|...|fieldN" }
1559
1560 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1561 Format: <min_file_size>
1562 Set the minimal file size for using asynchronous hash.
1563 If left unspecified, ahash usage is disabled.
1564
1565 ahash performance varies for different data sizes on
1566 different crypto accelerators. This option can be used
1567 to achieve the best performance for a particular HW.
1568
1569 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1570 Format: <bufsize>
1571 Set hashing buffer size. Default: 4k.
1572
1573 ahash performance varies for different chunk sizes on
1574 different crypto accelerators. This option can be used
1575 to achieve best performance for particular HW.
1576
1577 init= [KNL]
1578 Format: <full_path>
1579 Run specified binary instead of /sbin/init as init
1580 process.
1581
1582 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1583 for working out where the kernel is dying during
1584 startup.
1585
1586 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1587 initcall functions. Useful for debugging built-in
1588 modules and initcalls.
1589
1590 initrd= [BOOT] Specify the location of the initial ramdisk
1591
1592 init_pkru= [x86] Specify the default memory protection keys rights
1593 register contents for all processes. 0x55555554 by
1594 default (disallow access to all but pkey 0). Can
1595 override in debugfs after boot.
1596
1597 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1598 Format: <irq>
1599
1600 int_pln_enable [x86] Enable power limit notification interrupt
1601
1602 integrity_audit=[IMA]
1603 Format: { "0" | "1" }
1604 0 -- basic integrity auditing messages. (Default)
1605 1 -- additional integrity auditing messages.
1606
1607 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1608 on
1609 Enable intel iommu driver.
1610 off
1611 Disable intel iommu driver.
1612 igfx_off [Default Off]
1613 By default, gfx is mapped as normal device. If a gfx
1614 device has a dedicated DMAR unit, the DMAR unit is
1615 bypassed by not enabling DMAR with this option. In
1616 this case, gfx device will use physical address for
1617 DMA.
1618 forcedac [x86_64]
1619 With this option iommu will not optimize to look
1620 for io virtual address below 32-bit forcing dual
1621 address cycle on pci bus for cards supporting greater
1622 than 32-bit addressing. The default is to look
1623 for translation below 32-bit and if not available
1624 then look in the higher range.
1625 strict [Default Off]
1626 With this option on every unmap_single operation will
1627 result in a hardware IOTLB flush operation as opposed
1628 to batching them for performance.
1629 sp_off [Default Off]
1630 By default, super page will be supported if Intel IOMMU
1631 has the capability. With this option, super page will
1632 not be supported.
1633 ecs_off [Default Off]
1634 By default, extended context tables will be supported if
1635 the hardware advertises that it has support both for the
1636 extended tables themselves, and also PASID support. With
1637 this option set, extended tables will not be used even
1638 on hardware which claims to support them.
1639 tboot_noforce [Default Off]
1640 Do not force the Intel IOMMU enabled under tboot.
1641 By default, tboot will force Intel IOMMU on, which
1642 could harm performance of some high-throughput
1643 devices like 40GBit network cards, even if identity
1644 mapping is enabled.
1645 Note that using this option lowers the security
1646 provided by tboot because it makes the system
1647 vulnerable to DMA attacks.
1648
1649 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1650 0 disables intel_idle and fall back on acpi_idle.
1651 1 to 9 specify maximum depth of C-state.
1652
1653 intel_pstate= [X86]
1654 disable
1655 Do not enable intel_pstate as the default
1656 scaling driver for the supported processors
1657 passive
1658 Use intel_pstate as a scaling driver, but configure it
1659 to work with generic cpufreq governors (instead of
1660 enabling its internal governor). This mode cannot be
1661 used along with the hardware-managed P-states (HWP)
1662 feature.
1663 force
1664 Enable intel_pstate on systems that prohibit it by default
1665 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1666 instead of acpi-cpufreq may disable platform features, such
1667 as thermal controls and power capping, that rely on ACPI
1668 P-States information being indicated to OSPM and therefore
1669 should be used with caution. This option does not work with
1670 processors that aren't supported by the intel_pstate driver
1671 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1672 no_hwp
1673 Do not enable hardware P state control (HWP)
1674 if available.
1675 hwp_only
1676 Only load intel_pstate on systems which support
1677 hardware P state control (HWP) if available.
1678 support_acpi_ppc
1679 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1680 Description Table, specifies preferred power management
1681 profile as "Enterprise Server" or "Performance Server",
1682 then this feature is turned on by default.
1683 per_cpu_perf_limits
1684 Allow per-logical-CPU P-State performance control limits using
1685 cpufreq sysfs interface
1686
1687 intremap= [X86-64, Intel-IOMMU]
1688 on enable Interrupt Remapping (default)
1689 off disable Interrupt Remapping
1690 nosid disable Source ID checking
1691 no_x2apic_optout
1692 BIOS x2APIC opt-out request will be ignored
1693 nopost disable Interrupt Posting
1694
1695 iomem= Disable strict checking of access to MMIO memory
1696 strict regions from userspace.
1697 relaxed
1698
1699 iommu= [x86]
1700 off
1701 force
1702 noforce
1703 biomerge
1704 panic
1705 nopanic
1706 merge
1707 nomerge
1708 forcesac
1709 soft
1710 pt [x86, IA-64]
1711 nobypass [PPC/POWERNV]
1712 Disable IOMMU bypass, using IOMMU for PCI devices.
1713
1714 iommu.passthrough=
1715 [ARM64] Configure DMA to bypass the IOMMU by default.
1716 Format: { "0" | "1" }
1717 0 - Use IOMMU translation for DMA.
1718 1 - Bypass the IOMMU for DMA.
1719 unset - Use IOMMU translation for DMA.
1720
1721 io7= [HW] IO7 for Marvel based alpha systems
1722 See comment before marvel_specify_io7 in
1723 arch/alpha/kernel/core_marvel.c.
1724
1725 io_delay= [X86] I/O delay method
1726 0x80
1727 Standard port 0x80 based delay
1728 0xed
1729 Alternate port 0xed based delay (needed on some systems)
1730 udelay
1731 Simple two microseconds delay
1732 none
1733 No delay
1734
1735 ip= [IP_PNP]
1736 See Documentation/filesystems/nfs/nfsroot.txt.
1737
1738 irqaffinity= [SMP] Set the default irq affinity mask
1739 The argument is a cpu list, as described above.
1740
1741 irqchip.gicv2_force_probe=
1742 [ARM, ARM64]
1743 Format: <bool>
1744 Force the kernel to look for the second 4kB page
1745 of a GICv2 controller even if the memory range
1746 exposed by the device tree is too small.
1747
1748 irqchip.gicv3_nolpi=
1749 [ARM, ARM64]
1750 Force the kernel to ignore the availability of
1751 LPIs (and by consequence ITSs). Intended for system
1752 that use the kernel as a bootloader, and thus want
1753 to let secondary kernels in charge of setting up
1754 LPIs.
1755
1756 irqfixup [HW]
1757 When an interrupt is not handled search all handlers
1758 for it. Intended to get systems with badly broken
1759 firmware running.
1760
1761 irqpoll [HW]
1762 When an interrupt is not handled search all handlers
1763 for it. Also check all handlers each timer
1764 interrupt. Intended to get systems with badly broken
1765 firmware running.
1766
1767 isapnp= [ISAPNP]
1768 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1769
1770 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1771 [Deprecated - use cpusets instead]
1772 Format: [flag-list,]<cpu-list>
1773
1774 Specify one or more CPUs to isolate from disturbances
1775 specified in the flag list (default: domain):
1776
1777 nohz
1778 Disable the tick when a single task runs.
1779
1780 A residual 1Hz tick is offloaded to workqueues, which you
1781 need to affine to housekeeping through the global
1782 workqueue's affinity configured via the
1783 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1784 by using the 'domain' flag described below.
1785
1786 NOTE: by default the global workqueue runs on all CPUs,
1787 so to protect individual CPUs the 'cpumask' file has to
1788 be configured manually after bootup.
1789
1790 domain
1791 Isolate from the general SMP balancing and scheduling
1792 algorithms. Note that performing domain isolation this way
1793 is irreversible: it's not possible to bring back a CPU to
1794 the domains once isolated through isolcpus. It's strongly
1795 advised to use cpusets instead to disable scheduler load
1796 balancing through the "cpuset.sched_load_balance" file.
1797 It offers a much more flexible interface where CPUs can
1798 move in and out of an isolated set anytime.
1799
1800 You can move a process onto or off an "isolated" CPU via
1801 the CPU affinity syscalls or cpuset.
1802 <cpu number> begins at 0 and the maximum value is
1803 "number of CPUs in system - 1".
1804
1805 The format of <cpu-list> is described above.
1806
1807
1808
1809 iucv= [HW,NET]
1810
1811 ivrs_ioapic [HW,X86_64]
1812 Provide an override to the IOAPIC-ID<->DEVICE-ID
1813 mapping provided in the IVRS ACPI table. For
1814 example, to map IOAPIC-ID decimal 10 to
1815 PCI device 00:14.0 write the parameter as:
1816 ivrs_ioapic[10]=00:14.0
1817
1818 ivrs_hpet [HW,X86_64]
1819 Provide an override to the HPET-ID<->DEVICE-ID
1820 mapping provided in the IVRS ACPI table. For
1821 example, to map HPET-ID decimal 0 to
1822 PCI device 00:14.0 write the parameter as:
1823 ivrs_hpet[0]=00:14.0
1824
1825 ivrs_acpihid [HW,X86_64]
1826 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1827 mapping provided in the IVRS ACPI table. For
1828 example, to map UART-HID:UID AMD0020:0 to
1829 PCI device 00:14.5 write the parameter as:
1830 ivrs_acpihid[00:14.5]=AMD0020:0
1831
1832 js= [HW,JOY] Analog joystick
1833 See Documentation/input/joydev/joystick.rst.
1834
1835 nokaslr [KNL]
1836 When CONFIG_RANDOMIZE_BASE is set, this disables
1837 kernel and module base offset ASLR (Address Space
1838 Layout Randomization).
1839
1840 kasan_multi_shot
1841 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1842 report on every invalid memory access. Without this
1843 parameter KASAN will print report only for the first
1844 invalid access.
1845
1846 keepinitrd [HW,ARM]
1847
1848 kernelcore= [KNL,X86,IA-64,PPC]
1849 Format: nn[KMGTPE] | nn% | "mirror"
1850 This parameter specifies the amount of memory usable by
1851 the kernel for non-movable allocations. The requested
1852 amount is spread evenly throughout all nodes in the
1853 system as ZONE_NORMAL. The remaining memory is used for
1854 movable memory in its own zone, ZONE_MOVABLE. In the
1855 event, a node is too small to have both ZONE_NORMAL and
1856 ZONE_MOVABLE, kernelcore memory will take priority and
1857 other nodes will have a larger ZONE_MOVABLE.
1858
1859 ZONE_MOVABLE is used for the allocation of pages that
1860 may be reclaimed or moved by the page migration
1861 subsystem. Note that allocations like PTEs-from-HighMem
1862 still use the HighMem zone if it exists, and the Normal
1863 zone if it does not.
1864
1865 It is possible to specify the exact amount of memory in
1866 the form of "nn[KMGTPE]", a percentage of total system
1867 memory in the form of "nn%", or "mirror". If "mirror"
1868 option is specified, mirrored (reliable) memory is used
1869 for non-movable allocations and remaining memory is used
1870 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1871 are exclusive, so you cannot specify multiple forms.
1872
1873 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1874 Format: <Controller#>[,poll interval]
1875 The controller # is the number of the ehci usb debug
1876 port as it is probed via PCI. The poll interval is
1877 optional and is the number seconds in between
1878 each poll cycle to the debug port in case you need
1879 the functionality for interrupting the kernel with
1880 gdb or control-c on the dbgp connection. When
1881 not using this parameter you use sysrq-g to break into
1882 the kernel debugger.
1883
1884 kgdboc= [KGDB,HW] kgdb over consoles.
1885 Requires a tty driver that supports console polling,
1886 or a supported polling keyboard driver (non-usb).
1887 Serial only format: <serial_device>[,baud]
1888 keyboard only format: kbd
1889 keyboard and serial format: kbd,<serial_device>[,baud]
1890 Optional Kernel mode setting:
1891 kms, kbd format: kms,kbd
1892 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1893
1894 kgdbwait [KGDB] Stop kernel execution and enter the
1895 kernel debugger at the earliest opportunity.
1896
1897 kmac= [MIPS] korina ethernet MAC address.
1898 Configure the RouterBoard 532 series on-chip
1899 Ethernet adapter MAC address.
1900
1901 kmemleak= [KNL] Boot-time kmemleak enable/disable
1902 Valid arguments: on, off
1903 Default: on
1904 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1905 the default is off.
1906
1907 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1908 Default is 0 (don't ignore, but inject #GP)
1909
1910 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1911 Default is false (don't support).
1912
1913 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1914 KVM MMU at runtime.
1915 Default is 0 (off)
1916
1917 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1918 Default is 1 (enabled)
1919
1920 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1921 for all guests.
1922 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1923
1924 kvm-arm.vgic_v3_group0_trap=
1925 [KVM,ARM] Trap guest accesses to GICv3 group-0
1926 system registers
1927
1928 kvm-arm.vgic_v3_group1_trap=
1929 [KVM,ARM] Trap guest accesses to GICv3 group-1
1930 system registers
1931
1932 kvm-arm.vgic_v3_common_trap=
1933 [KVM,ARM] Trap guest accesses to GICv3 common
1934 system registers
1935
1936 kvm-arm.vgic_v4_enable=
1937 [KVM,ARM] Allow use of GICv4 for direct injection of
1938 LPIs.
1939
1940 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1941 (virtualized MMU) support on capable Intel chips.
1942 Default is 1 (enabled)
1943
1944 kvm-intel.emulate_invalid_guest_state=
1945 [KVM,Intel] Enable emulation of invalid guest states
1946 Default is 0 (disabled)
1947
1948 kvm-intel.flexpriority=
1949 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1950 Default is 1 (enabled)
1951
1952 kvm-intel.nested=
1953 [KVM,Intel] Enable VMX nesting (nVMX).
1954 Default is 0 (disabled)
1955
1956 kvm-intel.unrestricted_guest=
1957 [KVM,Intel] Disable unrestricted guest feature
1958 (virtualized real and unpaged mode) on capable
1959 Intel chips. Default is 1 (enabled)
1960
1961 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1962 feature (tagged TLBs) on capable Intel chips.
1963 Default is 1 (enabled)
1964
1965 l2cr= [PPC]
1966
1967 l3cr= [PPC]
1968
1969 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1970 disabled it.
1971
1972 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1973 value for LAPIC timer one-shot implementation. Default
1974 back to the programmable timer unit in the LAPIC.
1975
1976 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1977 in C2 power state.
1978
1979 libata.dma= [LIBATA] DMA control
1980 libata.dma=0 Disable all PATA and SATA DMA
1981 libata.dma=1 PATA and SATA Disk DMA only
1982 libata.dma=2 ATAPI (CDROM) DMA only
1983 libata.dma=4 Compact Flash DMA only
1984 Combinations also work, so libata.dma=3 enables DMA
1985 for disks and CDROMs, but not CFs.
1986
1987 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1988 libata.ignore_hpa=0 keep BIOS limits (default)
1989 libata.ignore_hpa=1 ignore limits, using full disk
1990
1991 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1992 when set.
1993 Format: <int>
1994
1995 libata.force= [LIBATA] Force configurations. The format is comma
1996 separated list of "[ID:]VAL" where ID is
1997 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1998 matching port, link or device. Basically, it matches
1999 the ATA ID string printed on console by libata. If
2000 the whole ID part is omitted, the last PORT and DEVICE
2001 values are used. If ID hasn't been specified yet, the
2002 configuration applies to all ports, links and devices.
2003
2004 If only DEVICE is omitted, the parameter applies to
2005 the port and all links and devices behind it. DEVICE
2006 number of 0 either selects the first device or the
2007 first fan-out link behind PMP device. It does not
2008 select the host link. DEVICE number of 15 selects the
2009 host link and device attached to it.
2010
2011 The VAL specifies the configuration to force. As long
2012 as there's no ambiguity shortcut notation is allowed.
2013 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2014 The following configurations can be forced.
2015
2016 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2017 Any ID with matching PORT is used.
2018
2019 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2020
2021 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2022 udma[/][16,25,33,44,66,100,133] notation is also
2023 allowed.
2024
2025 * [no]ncq: Turn on or off NCQ.
2026
2027 * [no]ncqtrim: Turn off queued DSM TRIM.
2028
2029 * nohrst, nosrst, norst: suppress hard, soft
2030 and both resets.
2031
2032 * rstonce: only attempt one reset during
2033 hot-unplug link recovery
2034
2035 * dump_id: dump IDENTIFY data.
2036
2037 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2038
2039 * disable: Disable this device.
2040
2041 If there are multiple matching configurations changing
2042 the same attribute, the last one is used.
2043
2044 memblock=debug [KNL] Enable memblock debug messages.
2045
2046 load_ramdisk= [RAM] List of ramdisks to load from floppy
2047 See Documentation/blockdev/ramdisk.txt.
2048
2049 lockd.nlm_grace_period=P [NFS] Assign grace period.
2050 Format: <integer>
2051
2052 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2053 Format: <integer>
2054
2055 lockd.nlm_timeout=T [NFS] Assign timeout value.
2056 Format: <integer>
2057
2058 lockd.nlm_udpport=M [NFS] Assign UDP port.
2059 Format: <integer>
2060
2061 locktorture.nreaders_stress= [KNL]
2062 Set the number of locking read-acquisition kthreads.
2063 Defaults to being automatically set based on the
2064 number of online CPUs.
2065
2066 locktorture.nwriters_stress= [KNL]
2067 Set the number of locking write-acquisition kthreads.
2068
2069 locktorture.onoff_holdoff= [KNL]
2070 Set time (s) after boot for CPU-hotplug testing.
2071
2072 locktorture.onoff_interval= [KNL]
2073 Set time (s) between CPU-hotplug operations, or
2074 zero to disable CPU-hotplug testing.
2075
2076 locktorture.shuffle_interval= [KNL]
2077 Set task-shuffle interval (jiffies). Shuffling
2078 tasks allows some CPUs to go into dyntick-idle
2079 mode during the locktorture test.
2080
2081 locktorture.shutdown_secs= [KNL]
2082 Set time (s) after boot system shutdown. This
2083 is useful for hands-off automated testing.
2084
2085 locktorture.stat_interval= [KNL]
2086 Time (s) between statistics printk()s.
2087
2088 locktorture.stutter= [KNL]
2089 Time (s) to stutter testing, for example,
2090 specifying five seconds causes the test to run for
2091 five seconds, wait for five seconds, and so on.
2092 This tests the locking primitive's ability to
2093 transition abruptly to and from idle.
2094
2095 locktorture.torture_type= [KNL]
2096 Specify the locking implementation to test.
2097
2098 locktorture.verbose= [KNL]
2099 Enable additional printk() statements.
2100
2101 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2102 Format: <irq>
2103
2104 loglevel= All Kernel Messages with a loglevel smaller than the
2105 console loglevel will be printed to the console. It can
2106 also be changed with klogd or other programs. The
2107 loglevels are defined as follows:
2108
2109 0 (KERN_EMERG) system is unusable
2110 1 (KERN_ALERT) action must be taken immediately
2111 2 (KERN_CRIT) critical conditions
2112 3 (KERN_ERR) error conditions
2113 4 (KERN_WARNING) warning conditions
2114 5 (KERN_NOTICE) normal but significant condition
2115 6 (KERN_INFO) informational
2116 7 (KERN_DEBUG) debug-level messages
2117
2118 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2119 in bytes. n must be a power of two and greater
2120 than the minimal size. The minimal size is defined
2121 by LOG_BUF_SHIFT kernel config parameter. There is
2122 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2123 that allows to increase the default size depending on
2124 the number of CPUs. See init/Kconfig for more details.
2125
2126 logo.nologo [FB] Disables display of the built-in Linux logo.
2127 This may be used to provide more screen space for
2128 kernel log messages and is useful when debugging
2129 kernel boot problems.
2130
2131 lp=0 [LP] Specify parallel ports to use, e.g,
2132 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2133 lp=reset first parallel port). 'lp=0' disables the
2134 lp=auto printer driver. 'lp=reset' (which can be
2135 specified in addition to the ports) causes
2136 attached printers to be reset. Using
2137 lp=port1,port2,... specifies the parallel ports
2138 to associate lp devices with, starting with
2139 lp0. A port specification may be 'none' to skip
2140 that lp device, or a parport name such as
2141 'parport0'. Specifying 'lp=auto' instead of a
2142 port specification list means that device IDs
2143 from each port should be examined, to see if
2144 an IEEE 1284-compliant printer is attached; if
2145 so, the driver will manage that printer.
2146 See also header of drivers/char/lp.c.
2147
2148 lpj=n [KNL]
2149 Sets loops_per_jiffy to given constant, thus avoiding
2150 time-consuming boot-time autodetection (up to 250 ms per
2151 CPU). 0 enables autodetection (default). To determine
2152 the correct value for your kernel, boot with normal
2153 autodetection and see what value is printed. Note that
2154 on SMP systems the preset will be applied to all CPUs,
2155 which is likely to cause problems if your CPUs need
2156 significantly divergent settings. An incorrect value
2157 will cause delays in the kernel to be wrong, leading to
2158 unpredictable I/O errors and other breakage. Although
2159 unlikely, in the extreme case this might damage your
2160 hardware.
2161
2162 ltpc= [NET]
2163 Format: <io>,<irq>,<dma>
2164
2165 machvec= [IA-64] Force the use of a particular machine-vector
2166 (machvec) in a generic kernel.
2167 Example: machvec=hpzx1_swiotlb
2168
2169 machtype= [Loongson] Share the same kernel image file between different
2170 yeeloong laptop.
2171 Example: machtype=lemote-yeeloong-2f-7inch
2172
2173 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2174 than or equal to this physical address is ignored.
2175
2176 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2177 will bring up during bootup. maxcpus=n : n >= 0 limits
2178 the kernel to bring up 'n' processors. Surely after
2179 bootup you can bring up the other plugged cpu by executing
2180 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2181 only takes effect during system bootup.
2182 While n=0 is a special case, it is equivalent to "nosmp",
2183 which also disables the IO APIC.
2184
2185 max_loop= [LOOP] The number of loop block devices that get
2186 (loop.max_loop) unconditionally pre-created at init time. The default
2187 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2188 of statically allocating a predefined number, loop
2189 devices can be requested on-demand with the
2190 /dev/loop-control interface.
2191
2192 mce [X86-32] Machine Check Exception
2193
2194 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2195
2196 md= [HW] RAID subsystems devices and level
2197 See Documentation/admin-guide/md.rst.
2198
2199 mdacon= [MDA]
2200 Format: <first>,<last>
2201 Specifies range of consoles to be captured by the MDA.
2202
2203 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2204 Amount of memory to be used when the kernel is not able
2205 to see the whole system memory or for test.
2206 [X86] Work as limiting max address. Use together
2207 with memmap= to avoid physical address space collisions.
2208 Without memmap= PCI devices could be placed at addresses
2209 belonging to unused RAM.
2210
2211 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2212 memory.
2213
2214 memchunk=nn[KMG]
2215 [KNL,SH] Allow user to override the default size for
2216 per-device physically contiguous DMA buffers.
2217
2218 memhp_default_state=online/offline
2219 [KNL] Set the initial state for the memory hotplug
2220 onlining policy. If not specified, the default value is
2221 set according to the
2222 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2223 option.
2224 See Documentation/memory-hotplug.txt.
2225
2226 memmap=exactmap [KNL,X86] Enable setting of an exact
2227 E820 memory map, as specified by the user.
2228 Such memmap=exactmap lines can be constructed based on
2229 BIOS output or other requirements. See the memmap=nn@ss
2230 option description.
2231
2232 memmap=nn[KMG]@ss[KMG]
2233 [KNL] Force usage of a specific region of memory.
2234 Region of memory to be used is from ss to ss+nn.
2235 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2236 which limits max address to nn[KMG].
2237 Multiple different regions can be specified,
2238 comma delimited.
2239 Example:
2240 memmap=100M@2G,100M#3G,1G!1024G
2241
2242 memmap=nn[KMG]#ss[KMG]
2243 [KNL,ACPI] Mark specific memory as ACPI data.
2244 Region of memory to be marked is from ss to ss+nn.
2245
2246 memmap=nn[KMG]$ss[KMG]
2247 [KNL,ACPI] Mark specific memory as reserved.
2248 Region of memory to be reserved is from ss to ss+nn.
2249 Example: Exclude memory from 0x18690000-0x1869ffff
2250 memmap=64K$0x18690000
2251 or
2252 memmap=0x10000$0x18690000
2253 Some bootloaders may need an escape character before '$',
2254 like Grub2, otherwise '$' and the following number
2255 will be eaten.
2256
2257 memmap=nn[KMG]!ss[KMG]
2258 [KNL,X86] Mark specific memory as protected.
2259 Region of memory to be used, from ss to ss+nn.
2260 The memory region may be marked as e820 type 12 (0xc)
2261 and is NVDIMM or ADR memory.
2262
2263 memmap=<size>%<offset>-<oldtype>+<newtype>
2264 [KNL,ACPI] Convert memory within the specified region
2265 from <oldtype> to <newtype>. If "-<oldtype>" is left
2266 out, the whole region will be marked as <newtype>,
2267 even if previously unavailable. If "+<newtype>" is left
2268 out, matching memory will be removed. Types are
2269 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2270 3 = ACPI, 12 = PRAM.
2271
2272 memory_corruption_check=0/1 [X86]
2273 Some BIOSes seem to corrupt the first 64k of
2274 memory when doing things like suspend/resume.
2275 Setting this option will scan the memory
2276 looking for corruption. Enabling this will
2277 both detect corruption and prevent the kernel
2278 from using the memory being corrupted.
2279 However, its intended as a diagnostic tool; if
2280 repeatable BIOS-originated corruption always
2281 affects the same memory, you can use memmap=
2282 to prevent the kernel from using that memory.
2283
2284 memory_corruption_check_size=size [X86]
2285 By default it checks for corruption in the low
2286 64k, making this memory unavailable for normal
2287 use. Use this parameter to scan for
2288 corruption in more or less memory.
2289
2290 memory_corruption_check_period=seconds [X86]
2291 By default it checks for corruption every 60
2292 seconds. Use this parameter to check at some
2293 other rate. 0 disables periodic checking.
2294
2295 memtest= [KNL,X86,ARM] Enable memtest
2296 Format: <integer>
2297 default : 0 <disable>
2298 Specifies the number of memtest passes to be
2299 performed. Each pass selects another test
2300 pattern from a given set of patterns. Memtest
2301 fills the memory with this pattern, validates
2302 memory contents and reserves bad memory
2303 regions that are detected.
2304
2305 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2306 Valid arguments: on, off
2307 Default (depends on kernel configuration option):
2308 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2309 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2310 mem_encrypt=on: Activate SME
2311 mem_encrypt=off: Do not activate SME
2312
2313 Refer to Documentation/x86/amd-memory-encryption.txt
2314 for details on when memory encryption can be activated.
2315
2316 mem_sleep_default= [SUSPEND] Default system suspend mode:
2317 s2idle - Suspend-To-Idle
2318 shallow - Power-On Suspend or equivalent (if supported)
2319 deep - Suspend-To-RAM or equivalent (if supported)
2320 See Documentation/admin-guide/pm/sleep-states.rst.
2321
2322 meye.*= [HW] Set MotionEye Camera parameters
2323 See Documentation/media/v4l-drivers/meye.rst.
2324
2325 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2326 Multi-Function General Purpose Timers on AMD Geode
2327 platforms.
2328
2329 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2330 the BIOS has incorrectly applied a workaround. TinyBIOS
2331 version 0.98 is known to be affected, 0.99 fixes the
2332 problem by letting the user disable the workaround.
2333
2334 mga= [HW,DRM]
2335
2336 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2337 physical address is ignored.
2338
2339 mini2440= [ARM,HW,KNL]
2340 Format:[0..2][b][c][t]
2341 Default: "0tb"
2342 MINI2440 configuration specification:
2343 0 - The attached screen is the 3.5" TFT
2344 1 - The attached screen is the 7" TFT
2345 2 - The VGA Shield is attached (1024x768)
2346 Leaving out the screen size parameter will not load
2347 the TFT driver, and the framebuffer will be left
2348 unconfigured.
2349 b - Enable backlight. The TFT backlight pin will be
2350 linked to the kernel VESA blanking code and a GPIO
2351 LED. This parameter is not necessary when using the
2352 VGA shield.
2353 c - Enable the s3c camera interface.
2354 t - Reserved for enabling touchscreen support. The
2355 touchscreen support is not enabled in the mainstream
2356 kernel as of 2.6.30, a preliminary port can be found
2357 in the "bleeding edge" mini2440 support kernel at
2358 http://repo.or.cz/w/linux-2.6/mini2440.git
2359
2360 mminit_loglevel=
2361 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2362 parameter allows control of the logging verbosity for
2363 the additional memory initialisation checks. A value
2364 of 0 disables mminit logging and a level of 4 will
2365 log everything. Information is printed at KERN_DEBUG
2366 so loglevel=8 may also need to be specified.
2367
2368 module.sig_enforce
2369 [KNL] When CONFIG_MODULE_SIG is set, this means that
2370 modules without (valid) signatures will fail to load.
2371 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2372 is always true, so this option does nothing.
2373
2374 module_blacklist= [KNL] Do not load a comma-separated list of
2375 modules. Useful for debugging problem modules.
2376
2377 mousedev.tap_time=
2378 [MOUSE] Maximum time between finger touching and
2379 leaving touchpad surface for touch to be considered
2380 a tap and be reported as a left button click (for
2381 touchpads working in absolute mode only).
2382 Format: <msecs>
2383 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2384 reporting absolute coordinates, such as tablets
2385 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2386 reporting absolute coordinates, such as tablets
2387
2388 movablecore= [KNL,X86,IA-64,PPC]
2389 Format: nn[KMGTPE] | nn%
2390 This parameter is the complement to kernelcore=, it
2391 specifies the amount of memory used for migratable
2392 allocations. If both kernelcore and movablecore is
2393 specified, then kernelcore will be at *least* the
2394 specified value but may be more. If movablecore on its
2395 own is specified, the administrator must be careful
2396 that the amount of memory usable for all allocations
2397 is not too small.
2398
2399 movable_node [KNL] Boot-time switch to make hotplugable memory
2400 NUMA nodes to be movable. This means that the memory
2401 of such nodes will be usable only for movable
2402 allocations which rules out almost all kernel
2403 allocations. Use with caution!
2404
2405 MTD_Partition= [MTD]
2406 Format: <name>,<region-number>,<size>,<offset>
2407
2408 MTD_Region= [MTD] Format:
2409 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2410
2411 mtdparts= [MTD]
2412 See drivers/mtd/cmdlinepart.c.
2413
2414 multitce=off [PPC] This parameter disables the use of the pSeries
2415 firmware feature for updating multiple TCE entries
2416 at a time.
2417
2418 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2419
2420 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2421
2422 boundary - index of last SLC block on Flex-OneNAND.
2423 The remaining blocks are configured as MLC blocks.
2424 lock - Configure if Flex-OneNAND boundary should be locked.
2425 Once locked, the boundary cannot be changed.
2426 1 indicates lock status, 0 indicates unlock status.
2427
2428 mtdset= [ARM]
2429 ARM/S3C2412 JIVE boot control
2430
2431 See arch/arm/mach-s3c2412/mach-jive.c
2432
2433 mtouchusb.raw_coordinates=
2434 [HW] Make the MicroTouch USB driver use raw coordinates
2435 ('y', default) or cooked coordinates ('n')
2436
2437 mtrr_chunk_size=nn[KMG] [X86]
2438 used for mtrr cleanup. It is largest continuous chunk
2439 that could hold holes aka. UC entries.
2440
2441 mtrr_gran_size=nn[KMG] [X86]
2442 Used for mtrr cleanup. It is granularity of mtrr block.
2443 Default is 1.
2444 Large value could prevent small alignment from
2445 using up MTRRs.
2446
2447 mtrr_spare_reg_nr=n [X86]
2448 Format: <integer>
2449 Range: 0,7 : spare reg number
2450 Default : 1
2451 Used for mtrr cleanup. It is spare mtrr entries number.
2452 Set to 2 or more if your graphical card needs more.
2453
2454 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2455
2456 netdev= [NET] Network devices parameters
2457 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2458 Note that mem_start is often overloaded to mean
2459 something different and driver-specific.
2460 This usage is only documented in each driver source
2461 file if at all.
2462
2463 nf_conntrack.acct=
2464 [NETFILTER] Enable connection tracking flow accounting
2465 0 to disable accounting
2466 1 to enable accounting
2467 Default value is 0.
2468
2469 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2470 See Documentation/filesystems/nfs/nfsroot.txt.
2471
2472 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2473 See Documentation/filesystems/nfs/nfsroot.txt.
2474
2475 nfsrootdebug [NFS] enable nfsroot debugging messages.
2476 See Documentation/filesystems/nfs/nfsroot.txt.
2477
2478 nfs.callback_nr_threads=
2479 [NFSv4] set the total number of threads that the
2480 NFS client will assign to service NFSv4 callback
2481 requests.
2482
2483 nfs.callback_tcpport=
2484 [NFS] set the TCP port on which the NFSv4 callback
2485 channel should listen.
2486
2487 nfs.cache_getent=
2488 [NFS] sets the pathname to the program which is used
2489 to update the NFS client cache entries.
2490
2491 nfs.cache_getent_timeout=
2492 [NFS] sets the timeout after which an attempt to
2493 update a cache entry is deemed to have failed.
2494
2495 nfs.idmap_cache_timeout=
2496 [NFS] set the maximum lifetime for idmapper cache
2497 entries.
2498
2499 nfs.enable_ino64=
2500 [NFS] enable 64-bit inode numbers.
2501 If zero, the NFS client will fake up a 32-bit inode
2502 number for the readdir() and stat() syscalls instead
2503 of returning the full 64-bit number.
2504 The default is to return 64-bit inode numbers.
2505
2506 nfs.max_session_cb_slots=
2507 [NFSv4.1] Sets the maximum number of session
2508 slots the client will assign to the callback
2509 channel. This determines the maximum number of
2510 callbacks the client will process in parallel for
2511 a particular server.
2512
2513 nfs.max_session_slots=
2514 [NFSv4.1] Sets the maximum number of session slots
2515 the client will attempt to negotiate with the server.
2516 This limits the number of simultaneous RPC requests
2517 that the client can send to the NFSv4.1 server.
2518 Note that there is little point in setting this
2519 value higher than the max_tcp_slot_table_limit.
2520
2521 nfs.nfs4_disable_idmapping=
2522 [NFSv4] When set to the default of '1', this option
2523 ensures that both the RPC level authentication
2524 scheme and the NFS level operations agree to use
2525 numeric uids/gids if the mount is using the
2526 'sec=sys' security flavour. In effect it is
2527 disabling idmapping, which can make migration from
2528 legacy NFSv2/v3 systems to NFSv4 easier.
2529 Servers that do not support this mode of operation
2530 will be autodetected by the client, and it will fall
2531 back to using the idmapper.
2532 To turn off this behaviour, set the value to '0'.
2533 nfs.nfs4_unique_id=
2534 [NFS4] Specify an additional fixed unique ident-
2535 ification string that NFSv4 clients can insert into
2536 their nfs_client_id4 string. This is typically a
2537 UUID that is generated at system install time.
2538
2539 nfs.send_implementation_id =
2540 [NFSv4.1] Send client implementation identification
2541 information in exchange_id requests.
2542 If zero, no implementation identification information
2543 will be sent.
2544 The default is to send the implementation identification
2545 information.
2546
2547 nfs.recover_lost_locks =
2548 [NFSv4] Attempt to recover locks that were lost due
2549 to a lease timeout on the server. Please note that
2550 doing this risks data corruption, since there are
2551 no guarantees that the file will remain unchanged
2552 after the locks are lost.
2553 If you want to enable the kernel legacy behaviour of
2554 attempting to recover these locks, then set this
2555 parameter to '1'.
2556 The default parameter value of '0' causes the kernel
2557 not to attempt recovery of lost locks.
2558
2559 nfs4.layoutstats_timer =
2560 [NFSv4.2] Change the rate at which the kernel sends
2561 layoutstats to the pNFS metadata server.
2562
2563 Setting this to value to 0 causes the kernel to use
2564 whatever value is the default set by the layout
2565 driver. A non-zero value sets the minimum interval
2566 in seconds between layoutstats transmissions.
2567
2568 nfsd.nfs4_disable_idmapping=
2569 [NFSv4] When set to the default of '1', the NFSv4
2570 server will return only numeric uids and gids to
2571 clients using auth_sys, and will accept numeric uids
2572 and gids from such clients. This is intended to ease
2573 migration from NFSv2/v3.
2574
2575 nmi_debug= [KNL,SH] Specify one or more actions to take
2576 when a NMI is triggered.
2577 Format: [state][,regs][,debounce][,die]
2578
2579 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2580 Format: [panic,][nopanic,][num]
2581 Valid num: 0 or 1
2582 0 - turn hardlockup detector in nmi_watchdog off
2583 1 - turn hardlockup detector in nmi_watchdog on
2584 When panic is specified, panic when an NMI watchdog
2585 timeout occurs (or 'nopanic' to override the opposite
2586 default). To disable both hard and soft lockup detectors,
2587 please see 'nowatchdog'.
2588 This is useful when you use a panic=... timeout and
2589 need the box quickly up again.
2590
2591 These settings can be accessed at runtime via
2592 the nmi_watchdog and hardlockup_panic sysctls.
2593
2594 netpoll.carrier_timeout=
2595 [NET] Specifies amount of time (in seconds) that
2596 netpoll should wait for a carrier. By default netpoll
2597 waits 4 seconds.
2598
2599 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2600 emulation library even if a 387 maths coprocessor
2601 is present.
2602
2603 no_console_suspend
2604 [HW] Never suspend the console
2605 Disable suspending of consoles during suspend and
2606 hibernate operations. Once disabled, debugging
2607 messages can reach various consoles while the rest
2608 of the system is being put to sleep (ie, while
2609 debugging driver suspend/resume hooks). This may
2610 not work reliably with all consoles, but is known
2611 to work with serial and VGA consoles.
2612 To facilitate more flexible debugging, we also add
2613 console_suspend, a printk module parameter to control
2614 it. Users could use console_suspend (usually
2615 /sys/module/printk/parameters/console_suspend) to
2616 turn on/off it dynamically.
2617
2618 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2619 caches in the slab allocator. Saves per-node memory,
2620 but will impact performance.
2621
2622 noalign [KNL,ARM]
2623
2624 noaltinstr [S390] Disables alternative instructions patching
2625 (CPU alternatives feature).
2626
2627 noapic [SMP,APIC] Tells the kernel to not make use of any
2628 IOAPICs that may be present in the system.
2629
2630 noautogroup Disable scheduler automatic task group creation.
2631
2632 nobats [PPC] Do not use BATs for mapping kernel lowmem
2633 on "Classic" PPC cores.
2634
2635 nocache [ARM]
2636
2637 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2638
2639 nodelayacct [KNL] Disable per-task delay accounting
2640
2641 nodsp [SH] Disable hardware DSP at boot time.
2642
2643 noefi Disable EFI runtime services support.
2644
2645 noexec [IA-64]
2646
2647 noexec [X86]
2648 On X86-32 available only on PAE configured kernels.
2649 noexec=on: enable non-executable mappings (default)
2650 noexec=off: disable non-executable mappings
2651
2652 nosmap [X86]
2653 Disable SMAP (Supervisor Mode Access Prevention)
2654 even if it is supported by processor.
2655
2656 nosmep [X86]
2657 Disable SMEP (Supervisor Mode Execution Prevention)
2658 even if it is supported by processor.
2659
2660 noexec32 [X86-64]
2661 This affects only 32-bit executables.
2662 noexec32=on: enable non-executable mappings (default)
2663 read doesn't imply executable mappings
2664 noexec32=off: disable non-executable mappings
2665 read implies executable mappings
2666
2667 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2668
2669 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2670 register save and restore. The kernel will only save
2671 legacy floating-point registers on task switch.
2672
2673 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2674
2675 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2676 Equivalent to smt=1.
2677
2678 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2679 (indirect branch prediction) vulnerability. System may
2680 allow data leaks with this option, which is equivalent
2681 to spectre_v2=off.
2682
2683 nospec_store_bypass_disable
2684 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2685
2686 noxsave [BUGS=X86] Disables x86 extended register state save
2687 and restore using xsave. The kernel will fallback to
2688 enabling legacy floating-point and sse state.
2689
2690 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2691 register states. The kernel will fall back to use
2692 xsave to save the states. By using this parameter,
2693 performance of saving the states is degraded because
2694 xsave doesn't support modified optimization while
2695 xsaveopt supports it on xsaveopt enabled systems.
2696
2697 noxsaves [X86] Disables xsaves and xrstors used in saving and
2698 restoring x86 extended register state in compacted
2699 form of xsave area. The kernel will fall back to use
2700 xsaveopt and xrstor to save and restore the states
2701 in standard form of xsave area. By using this
2702 parameter, xsave area per process might occupy more
2703 memory on xsaves enabled systems.
2704
2705 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2706 wfi(ARM) instruction doesn't work correctly and not to
2707 use it. This is also useful when using JTAG debugger.
2708
2709 no_file_caps Tells the kernel not to honor file capabilities. The
2710 only way then for a file to be executed with privilege
2711 is to be setuid root or executed by root.
2712
2713 nohalt [IA-64] Tells the kernel not to use the power saving
2714 function PAL_HALT_LIGHT when idle. This increases
2715 power-consumption. On the positive side, it reduces
2716 interrupt wake-up latency, which may improve performance
2717 in certain environments such as networked servers or
2718 real-time systems.
2719
2720 nohibernate [HIBERNATION] Disable hibernation and resume.
2721
2722 nohz= [KNL] Boottime enable/disable dynamic ticks
2723 Valid arguments: on, off
2724 Default: on
2725
2726 nohz_full= [KNL,BOOT,SMP,ISOL]
2727 The argument is a cpu list, as described above.
2728 In kernels built with CONFIG_NO_HZ_FULL=y, set
2729 the specified list of CPUs whose tick will be stopped
2730 whenever possible. The boot CPU will be forced outside
2731 the range to maintain the timekeeping. Any CPUs
2732 in this list will have their RCU callbacks offloaded,
2733 just as if they had also been called out in the
2734 rcu_nocbs= boot parameter.
2735
2736 noiotrap [SH] Disables trapped I/O port accesses.
2737
2738 noirqdebug [X86-32] Disables the code which attempts to detect and
2739 disable unhandled interrupt sources.
2740
2741 no_timer_check [X86,APIC] Disables the code which tests for
2742 broken timer IRQ sources.
2743
2744 noisapnp [ISAPNP] Disables ISA PnP code.
2745
2746 noinitrd [RAM] Tells the kernel not to load any configured
2747 initial RAM disk.
2748
2749 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2750 remapping.
2751 [Deprecated - use intremap=off]
2752
2753 nointroute [IA-64]
2754
2755 noinvpcid [X86] Disable the INVPCID cpu feature.
2756
2757 nojitter [IA-64] Disables jitter checking for ITC timers.
2758
2759 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2760
2761 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2762 fault handling.
2763
2764 no-vmw-sched-clock
2765 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2766 clock and use the default one.
2767
2768 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2769 steal time is computed, but won't influence scheduler
2770 behaviour
2771
2772 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2773
2774 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2775
2776 noltlbs [PPC] Do not use large page/tlb entries for kernel
2777 lowmem mapping on PPC40x and PPC8xx
2778
2779 nomca [IA-64] Disable machine check abort handling
2780
2781 nomce [X86-32] Disable Machine Check Exception
2782
2783 nomfgpt [X86-32] Disable Multi-Function General Purpose
2784 Timer usage (for AMD Geode machines).
2785
2786 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2787 shutdown the other cpus. Instead use the REBOOT_VECTOR
2788 irq.
2789
2790 nomodule Disable module load
2791
2792 nopat [X86] Disable PAT (page attribute table extension of
2793 pagetables) support.
2794
2795 nopcid [X86-64] Disable the PCID cpu feature.
2796
2797 norandmaps Don't use address space randomization. Equivalent to
2798 echo 0 > /proc/sys/kernel/randomize_va_space
2799
2800 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2801 with UP alternatives
2802
2803 nordrand [X86] Disable kernel use of the RDRAND and
2804 RDSEED instructions even if they are supported
2805 by the processor. RDRAND and RDSEED are still
2806 available to user space applications.
2807
2808 noresume [SWSUSP] Disables resume and restores original swap
2809 space.
2810
2811 no-scroll [VGA] Disables scrollback.
2812 This is required for the Braillex ib80-piezo Braille
2813 reader made by F.H. Papenmeier (Germany).
2814
2815 nosbagart [IA-64]
2816
2817 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2818
2819 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2820 and disable the IO APIC. legacy for "maxcpus=0".
2821
2822 nosoftlockup [KNL] Disable the soft-lockup detector.
2823
2824 nosync [HW,M68K] Disables sync negotiation for all devices.
2825
2826 notsc [BUGS=X86-32] Disable Time Stamp Counter
2827
2828 nowatchdog [KNL] Disable both lockup detectors, i.e.
2829 soft-lockup and NMI watchdog (hard-lockup).
2830
2831 nowb [ARM]
2832
2833 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2834
2835 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2836 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2837 Some features depend on CPU0. Known dependencies are:
2838 1. Resume from suspend/hibernate depends on CPU0.
2839 Suspend/hibernate will fail if CPU0 is offline and you
2840 need to online CPU0 before suspend/hibernate.
2841 2. PIC interrupts also depend on CPU0. CPU0 can't be
2842 removed if a PIC interrupt is detected.
2843 It's said poweroff/reboot may depend on CPU0 on some
2844 machines although I haven't seen such issues so far
2845 after CPU0 is offline on a few tested machines.
2846 If the dependencies are under your control, you can
2847 turn on cpu0_hotplug.
2848
2849 nps_mtm_hs_ctr= [KNL,ARC]
2850 This parameter sets the maximum duration, in
2851 cycles, each HW thread of the CTOP can run
2852 without interruptions, before HW switches it.
2853 The actual maximum duration is 16 times this
2854 parameter's value.
2855 Format: integer between 1 and 255
2856 Default: 255
2857
2858 nptcg= [IA-64] Override max number of concurrent global TLB
2859 purges which is reported from either PAL_VM_SUMMARY or
2860 SAL PALO.
2861
2862 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2863 could support. nr_cpus=n : n >= 1 limits the kernel to
2864 support 'n' processors. It could be larger than the
2865 number of already plugged CPU during bootup, later in
2866 runtime you can physically add extra cpu until it reaches
2867 n. So during boot up some boot time memory for per-cpu
2868 variables need be pre-allocated for later physical cpu
2869 hot plugging.
2870
2871 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2872
2873 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2874 Allowed values are enable and disable
2875
2876 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2877 'node', 'default' can be specified
2878 This can be set from sysctl after boot.
2879 See Documentation/sysctl/vm.txt for details.
2880
2881 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2882 See Documentation/debugging-via-ohci1394.txt for more
2883 info.
2884
2885 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2886 Rather than timing out after 20 ms if an EC
2887 command is not properly ACKed, override the length
2888 of the timeout. We have interrupts disabled while
2889 waiting for the ACK, so if this is set too high
2890 interrupts *may* be lost!
2891
2892 omap_mux= [OMAP] Override bootloader pin multiplexing.
2893 Format: <mux_mode0.mode_name=value>...
2894 For example, to override I2C bus2:
2895 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2896
2897 oprofile.timer= [HW]
2898 Use timer interrupt instead of performance counters
2899
2900 oprofile.cpu_type= Force an oprofile cpu type
2901 This might be useful if you have an older oprofile
2902 userland or if you want common events.
2903 Format: { arch_perfmon }
2904 arch_perfmon: [X86] Force use of architectural
2905 perfmon on Intel CPUs instead of the
2906 CPU specific event set.
2907 timer: [X86] Force use of architectural NMI
2908 timer mode (see also oprofile.timer
2909 for generic hr timer mode)
2910
2911 oops=panic Always panic on oopses. Default is to just kill the
2912 process, but there is a small probability of
2913 deadlocking the machine.
2914 This will also cause panics on machine check exceptions.
2915 Useful together with panic=30 to trigger a reboot.
2916
2917 OSS [HW,OSS]
2918 See Documentation/sound/oss/oss-parameters.txt
2919
2920 page_owner= [KNL] Boot-time page_owner enabling option.
2921 Storage of the information about who allocated
2922 each page is disabled in default. With this switch,
2923 we can turn it on.
2924 on: enable the feature
2925
2926 page_poison= [KNL] Boot-time parameter changing the state of
2927 poisoning on the buddy allocator.
2928 off: turn off poisoning
2929 on: turn on poisoning
2930
2931 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2932 timeout > 0: seconds before rebooting
2933 timeout = 0: wait forever
2934 timeout < 0: reboot immediately
2935 Format: <timeout>
2936
2937 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2938 on a WARN().
2939
2940 crash_kexec_post_notifiers
2941 Run kdump after running panic-notifiers and dumping
2942 kmsg. This only for the users who doubt kdump always
2943 succeeds in any situation.
2944 Note that this also increases risks of kdump failure,
2945 because some panic notifiers can make the crashed
2946 kernel more unstable.
2947
2948 parkbd.port= [HW] Parallel port number the keyboard adapter is
2949 connected to, default is 0.
2950 Format: <parport#>
2951 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2952 0 for XT, 1 for AT (default is AT).
2953 Format: <mode>
2954
2955 parport= [HW,PPT] Specify parallel ports. 0 disables.
2956 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2957 Use 'auto' to force the driver to use any
2958 IRQ/DMA settings detected (the default is to
2959 ignore detected IRQ/DMA settings because of
2960 possible conflicts). You can specify the base
2961 address, IRQ, and DMA settings; IRQ and DMA
2962 should be numbers, or 'auto' (for using detected
2963 settings on that particular port), or 'nofifo'
2964 (to avoid using a FIFO even if it is detected).
2965 Parallel ports are assigned in the order they
2966 are specified on the command line, starting
2967 with parport0.
2968
2969 parport_init_mode= [HW,PPT]
2970 Configure VIA parallel port to operate in
2971 a specific mode. This is necessary on Pegasos
2972 computer where firmware has no options for setting
2973 up parallel port mode and sets it to spp.
2974 Currently this function knows 686a and 8231 chips.
2975 Format: [spp|ps2|epp|ecp|ecpepp]
2976
2977 pause_on_oops=
2978 Halt all CPUs after the first oops has been printed for
2979 the specified number of seconds. This is to be used if
2980 your oopses keep scrolling off the screen.
2981
2982 pcbit= [HW,ISDN]
2983
2984 pcd. [PARIDE]
2985 See header of drivers/block/paride/pcd.c.
2986 See also Documentation/blockdev/paride.txt.
2987
2988 pci=option[,option...] [PCI] various PCI subsystem options:
2989 earlydump [X86] dump PCI config space before the kernel
2990 changes anything
2991 off [X86] don't probe for the PCI bus
2992 bios [X86-32] force use of PCI BIOS, don't access
2993 the hardware directly. Use this if your machine
2994 has a non-standard PCI host bridge.
2995 nobios [X86-32] disallow use of PCI BIOS, only direct
2996 hardware access methods are allowed. Use this
2997 if you experience crashes upon bootup and you
2998 suspect they are caused by the BIOS.
2999 conf1 [X86] Force use of PCI Configuration Access
3000 Mechanism 1 (config address in IO port 0xCF8,
3001 data in IO port 0xCFC, both 32-bit).
3002 conf2 [X86] Force use of PCI Configuration Access
3003 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3004 the function, IO port 0xCFA, also 8-bit, sets
3005 bus number. The config space is then accessed
3006 through ports 0xC000-0xCFFF).
3007 See http://wiki.osdev.org/PCI for more info
3008 on the configuration access mechanisms.
3009 noaer [PCIE] If the PCIEAER kernel config parameter is
3010 enabled, this kernel boot option can be used to
3011 disable the use of PCIE advanced error reporting.
3012 nodomains [PCI] Disable support for multiple PCI
3013 root domains (aka PCI segments, in ACPI-speak).
3014 nommconf [X86] Disable use of MMCONFIG for PCI
3015 Configuration
3016 check_enable_amd_mmconf [X86] check for and enable
3017 properly configured MMIO access to PCI
3018 config space on AMD family 10h CPU
3019 nomsi [MSI] If the PCI_MSI kernel config parameter is
3020 enabled, this kernel boot option can be used to
3021 disable the use of MSI interrupts system-wide.
3022 noioapicquirk [APIC] Disable all boot interrupt quirks.
3023 Safety option to keep boot IRQs enabled. This
3024 should never be necessary.
3025 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3026 primary IO-APIC for bridges that cannot disable
3027 boot IRQs. This fixes a source of spurious IRQs
3028 when the system masks IRQs.
3029 noioapicreroute [APIC] Disable workaround that uses the
3030 boot IRQ equivalent of an IRQ that connects to
3031 a chipset where boot IRQs cannot be disabled.
3032 The opposite of ioapicreroute.
3033 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3034 routing table. These calls are known to be buggy
3035 on several machines and they hang the machine
3036 when used, but on other computers it's the only
3037 way to get the interrupt routing table. Try
3038 this option if the kernel is unable to allocate
3039 IRQs or discover secondary PCI buses on your
3040 motherboard.
3041 rom [X86] Assign address space to expansion ROMs.
3042 Use with caution as certain devices share
3043 address decoders between ROMs and other
3044 resources.
3045 norom [X86] Do not assign address space to
3046 expansion ROMs that do not already have
3047 BIOS assigned address ranges.
3048 nobar [X86] Do not assign address space to the
3049 BARs that weren't assigned by the BIOS.
3050 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3051 assigned automatically to PCI devices. You can
3052 make the kernel exclude IRQs of your ISA cards
3053 this way.
3054 pirqaddr=0xAAAAA [X86] Specify the physical address
3055 of the PIRQ table (normally generated
3056 by the BIOS) if it is outside the
3057 F0000h-100000h range.
3058 lastbus=N [X86] Scan all buses thru bus #N. Can be
3059 useful if the kernel is unable to find your
3060 secondary buses and you want to tell it
3061 explicitly which ones they are.
3062 assign-busses [X86] Always assign all PCI bus
3063 numbers ourselves, overriding
3064 whatever the firmware may have done.
3065 usepirqmask [X86] Honor the possible IRQ mask stored
3066 in the BIOS $PIR table. This is needed on
3067 some systems with broken BIOSes, notably
3068 some HP Pavilion N5400 and Omnibook XE3
3069 notebooks. This will have no effect if ACPI
3070 IRQ routing is enabled.
3071 noacpi [X86] Do not use ACPI for IRQ routing
3072 or for PCI scanning.
3073 use_crs [X86] Use PCI host bridge window information
3074 from ACPI. On BIOSes from 2008 or later, this
3075 is enabled by default. If you need to use this,
3076 please report a bug.
3077 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3078 If you need to use this, please report a bug.
3079 routeirq Do IRQ routing for all PCI devices.
3080 This is normally done in pci_enable_device(),
3081 so this option is a temporary workaround
3082 for broken drivers that don't call it.
3083 skip_isa_align [X86] do not align io start addr, so can
3084 handle more pci cards
3085 noearly [X86] Don't do any early type 1 scanning.
3086 This might help on some broken boards which
3087 machine check when some devices' config space
3088 is read. But various workarounds are disabled
3089 and some IOMMU drivers will not work.
3090 bfsort Sort PCI devices into breadth-first order.
3091 This sorting is done to get a device
3092 order compatible with older (<= 2.4) kernels.
3093 nobfsort Don't sort PCI devices into breadth-first order.
3094 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3095 tuning and use the BIOS-configured MPS defaults.
3096 pcie_bus_safe Set every device's MPS to the largest value
3097 supported by all devices below the root complex.
3098 pcie_bus_perf Set device MPS to the largest allowable MPS
3099 based on its parent bus. Also set MRRS (Max
3100 Read Request Size) to the largest supported
3101 value (no larger than the MPS that the device
3102 or bus can support) for best performance.
3103 pcie_bus_peer2peer Set every device's MPS to 128B, which
3104 every device is guaranteed to support. This
3105 configuration allows peer-to-peer DMA between
3106 any pair of devices, possibly at the cost of
3107 reduced performance. This also guarantees
3108 that hot-added devices will work.
3109 cbiosize=nn[KMG] The fixed amount of bus space which is
3110 reserved for the CardBus bridge's IO window.
3111 The default value is 256 bytes.
3112 cbmemsize=nn[KMG] The fixed amount of bus space which is
3113 reserved for the CardBus bridge's memory
3114 window. The default value is 64 megabytes.
3115 resource_alignment=
3116 Format:
3117 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3118 [<order of align>@]pci:<vendor>:<device>\
3119 [:<subvendor>:<subdevice>][; ...]
3120 Specifies alignment and device to reassign
3121 aligned memory resources.
3122 If <order of align> is not specified,
3123 PAGE_SIZE is used as alignment.
3124 PCI-PCI bridge can be specified, if resource
3125 windows need to be expanded.
3126 To specify the alignment for several
3127 instances of a device, the PCI vendor,
3128 device, subvendor, and subdevice may be
3129 specified, e.g., 4096@pci:8086:9c22:103c:198f
3130 ecrc= Enable/disable PCIe ECRC (transaction layer
3131 end-to-end CRC checking).
3132 bios: Use BIOS/firmware settings. This is the
3133 the default.
3134 off: Turn ECRC off
3135 on: Turn ECRC on.
3136 hpiosize=nn[KMG] The fixed amount of bus space which is
3137 reserved for hotplug bridge's IO window.
3138 Default size is 256 bytes.
3139 hpmemsize=nn[KMG] The fixed amount of bus space which is
3140 reserved for hotplug bridge's memory window.
3141 Default size is 2 megabytes.
3142 hpbussize=nn The minimum amount of additional bus numbers
3143 reserved for buses below a hotplug bridge.
3144 Default is 1.
3145 realloc= Enable/disable reallocating PCI bridge resources
3146 if allocations done by BIOS are too small to
3147 accommodate resources required by all child
3148 devices.
3149 off: Turn realloc off
3150 on: Turn realloc on
3151 realloc same as realloc=on
3152 noari do not use PCIe ARI.
3153 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3154 only look for one device below a PCIe downstream
3155 port.
3156 big_root_window Try to add a big 64bit memory window to the PCIe
3157 root complex on AMD CPUs. Some GFX hardware
3158 can resize a BAR to allow access to all VRAM.
3159 Adding the window is slightly risky (it may
3160 conflict with unreported devices), so this
3161 taints the kernel.
3162
3163 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3164 Management.
3165 off Disable ASPM.
3166 force Enable ASPM even on devices that claim not to support it.
3167 WARNING: Forcing ASPM on may cause system lockups.
3168
3169 pcie_ports= [PCIE] PCIe port services handling:
3170 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3171 even if the platform doesn't give the OS permission to
3172 use them. This may cause conflicts if the platform
3173 also tries to use these services.
3174 compat Disable native PCIe services (PME, AER, DPC, PCIe
3175 hotplug).
3176
3177 pcie_port_pm= [PCIE] PCIe port power management handling:
3178 off Disable power management of all PCIe ports
3179 force Forcibly enable power management of all PCIe ports
3180
3181 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3182 nomsi Do not use MSI for native PCIe PME signaling (this makes
3183 all PCIe root ports use INTx for all services).
3184
3185 pcmv= [HW,PCMCIA] BadgePAD 4
3186
3187 pd_ignore_unused
3188 [PM]
3189 Keep all power-domains already enabled by bootloader on,
3190 even if no driver has claimed them. This is useful
3191 for debug and development, but should not be
3192 needed on a platform with proper driver support.
3193
3194 pd. [PARIDE]
3195 See Documentation/blockdev/paride.txt.
3196
3197 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3198 boot time.
3199 Format: { 0 | 1 }
3200 See arch/parisc/kernel/pdc_chassis.c
3201
3202 percpu_alloc= Select which percpu first chunk allocator to use.
3203 Currently supported values are "embed" and "page".
3204 Archs may support subset or none of the selections.
3205 See comments in mm/percpu.c for details on each
3206 allocator. This parameter is primarily for debugging
3207 and performance comparison.
3208
3209 pf. [PARIDE]
3210 See Documentation/blockdev/paride.txt.
3211
3212 pg. [PARIDE]
3213 See Documentation/blockdev/paride.txt.
3214
3215 pirq= [SMP,APIC] Manual mp-table setup
3216 See Documentation/x86/i386/IO-APIC.txt.
3217
3218 plip= [PPT,NET] Parallel port network link
3219 Format: { parport<nr> | timid | 0 }
3220 See also Documentation/admin-guide/parport.rst.
3221
3222 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3223 Override pmtimer IOPort with a hex value.
3224 e.g. pmtmr=0x508
3225
3226 pnp.debug=1 [PNP]
3227 Enable PNP debug messages (depends on the
3228 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3229 via /sys/module/pnp/parameters/debug. We always show
3230 current resource usage; turning this on also shows
3231 possible settings and some assignment information.
3232
3233 pnpacpi= [ACPI]
3234 { off }
3235
3236 pnpbios= [ISAPNP]
3237 { on | off | curr | res | no-curr | no-res }
3238
3239 pnp_reserve_irq=
3240 [ISAPNP] Exclude IRQs for the autoconfiguration
3241
3242 pnp_reserve_dma=
3243 [ISAPNP] Exclude DMAs for the autoconfiguration
3244
3245 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3246 Ranges are in pairs (I/O port base and size).
3247
3248 pnp_reserve_mem=
3249 [ISAPNP] Exclude memory regions for the
3250 autoconfiguration.
3251 Ranges are in pairs (memory base and size).
3252
3253 ports= [IP_VS_FTP] IPVS ftp helper module
3254 Default is 21.
3255 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3256 may be specified.
3257 Format: <port>,<port>....
3258
3259 powersave=off [PPC] This option disables power saving features.
3260 It specifically disables cpuidle and sets the
3261 platform machine description specific power_save
3262 function to NULL. On Idle the CPU just reduces
3263 execution priority.
3264
3265 ppc_strict_facility_enable
3266 [PPC] This option catches any kernel floating point,
3267 Altivec, VSX and SPE outside of regions specifically
3268 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3269 There is some performance impact when enabling this.
3270
3271 ppc_tm= [PPC]
3272 Format: {"off"}
3273 Disable Hardware Transactional Memory
3274
3275 print-fatal-signals=
3276 [KNL] debug: print fatal signals
3277
3278 If enabled, warn about various signal handling
3279 related application anomalies: too many signals,
3280 too many POSIX.1 timers, fatal signals causing a
3281 coredump - etc.
3282
3283 If you hit the warning due to signal overflow,
3284 you might want to try "ulimit -i unlimited".
3285
3286 default: off.
3287
3288 printk.always_kmsg_dump=
3289 Trigger kmsg_dump for cases other than kernel oops or
3290 panics
3291 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3292 default: disabled
3293
3294 printk.devkmsg={on,off,ratelimit}
3295 Control writing to /dev/kmsg.
3296 on - unlimited logging to /dev/kmsg from userspace
3297 off - logging to /dev/kmsg disabled
3298 ratelimit - ratelimit the logging
3299 Default: ratelimit
3300
3301 printk.time= Show timing data prefixed to each printk message line
3302 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3303
3304 processor.max_cstate= [HW,ACPI]
3305 Limit processor to maximum C-state
3306 max_cstate=9 overrides any DMI blacklist limit.
3307
3308 processor.nocst [HW,ACPI]
3309 Ignore the _CST method to determine C-states,
3310 instead using the legacy FADT method
3311
3312 profile= [KNL] Enable kernel profiling via /proc/profile
3313 Format: [<profiletype>,]<number>
3314 Param: <profiletype>: "schedule", "sleep", or "kvm"
3315 [defaults to kernel profiling]
3316 Param: "schedule" - profile schedule points.
3317 Param: "sleep" - profile D-state sleeping (millisecs).
3318 Requires CONFIG_SCHEDSTATS
3319 Param: "kvm" - profile VM exits.
3320 Param: <number> - step/bucket size as a power of 2 for
3321 statistical time based profiling.
3322
3323 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3324 before loading.
3325 See Documentation/blockdev/ramdisk.txt.
3326
3327 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3328 probe for; one of (bare|imps|exps|lifebook|any).
3329 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3330 per second.
3331 psmouse.resetafter= [HW,MOUSE]
3332 Try to reset the device after so many bad packets
3333 (0 = never).
3334 psmouse.resolution=
3335 [HW,MOUSE] Set desired mouse resolution, in dpi.
3336 psmouse.smartscroll=
3337 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3338 0 = disabled, 1 = enabled (default).
3339
3340 pstore.backend= Specify the name of the pstore backend to use
3341
3342 pt. [PARIDE]
3343 See Documentation/blockdev/paride.txt.
3344
3345 pti= [X86_64] Control Page Table Isolation of user and
3346 kernel address spaces. Disabling this feature
3347 removes hardening, but improves performance of
3348 system calls and interrupts.
3349
3350 on - unconditionally enable
3351 off - unconditionally disable
3352 auto - kernel detects whether your CPU model is
3353 vulnerable to issues that PTI mitigates
3354
3355 Not specifying this option is equivalent to pti=auto.
3356
3357 nopti [X86_64]
3358 Equivalent to pti=off
3359
3360 pty.legacy_count=
3361 [KNL] Number of legacy pty's. Overwrites compiled-in
3362 default number.
3363
3364 quiet [KNL] Disable most log messages
3365
3366 r128= [HW,DRM]
3367
3368 raid= [HW,RAID]
3369 See Documentation/admin-guide/md.rst.
3370
3371 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3372 See Documentation/blockdev/ramdisk.txt.
3373
3374 ras=option[,option,...] [KNL] RAS-specific options
3375
3376 cec_disable [X86]
3377 Disable the Correctable Errors Collector,
3378 see CONFIG_RAS_CEC help text.
3379
3380 rcu_nocbs= [KNL]
3381 The argument is a cpu list, as described above.
3382
3383 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3384 the specified list of CPUs to be no-callback CPUs.
3385 Invocation of these CPUs' RCU callbacks will
3386 be offloaded to "rcuox/N" kthreads created for
3387 that purpose, where "x" is "b" for RCU-bh, "p"
3388 for RCU-preempt, and "s" for RCU-sched, and "N"
3389 is the CPU number. This reduces OS jitter on the
3390 offloaded CPUs, which can be useful for HPC and
3391 real-time workloads. It can also improve energy
3392 efficiency for asymmetric multiprocessors.
3393
3394 rcu_nocb_poll [KNL]
3395 Rather than requiring that offloaded CPUs
3396 (specified by rcu_nocbs= above) explicitly
3397 awaken the corresponding "rcuoN" kthreads,
3398 make these kthreads poll for callbacks.
3399 This improves the real-time response for the
3400 offloaded CPUs by relieving them of the need to
3401 wake up the corresponding kthread, but degrades
3402 energy efficiency by requiring that the kthreads
3403 periodically wake up to do the polling.
3404
3405 rcutree.blimit= [KNL]
3406 Set maximum number of finished RCU callbacks to
3407 process in one batch.
3408
3409 rcutree.dump_tree= [KNL]
3410 Dump the structure of the rcu_node combining tree
3411 out at early boot. This is used for diagnostic
3412 purposes, to verify correct tree setup.
3413
3414 rcutree.gp_cleanup_delay= [KNL]
3415 Set the number of jiffies to delay each step of
3416 RCU grace-period cleanup.
3417
3418 rcutree.gp_init_delay= [KNL]
3419 Set the number of jiffies to delay each step of
3420 RCU grace-period initialization.
3421
3422 rcutree.gp_preinit_delay= [KNL]
3423 Set the number of jiffies to delay each step of
3424 RCU grace-period pre-initialization, that is,
3425 the propagation of recent CPU-hotplug changes up
3426 the rcu_node combining tree.
3427
3428 rcutree.rcu_fanout_exact= [KNL]
3429 Disable autobalancing of the rcu_node combining
3430 tree. This is used by rcutorture, and might
3431 possibly be useful for architectures having high
3432 cache-to-cache transfer latencies.
3433
3434 rcutree.rcu_fanout_leaf= [KNL]
3435 Change the number of CPUs assigned to each
3436 leaf rcu_node structure. Useful for very
3437 large systems, which will choose the value 64,
3438 and for NUMA systems with large remote-access
3439 latencies, which will choose a value aligned
3440 with the appropriate hardware boundaries.
3441
3442 rcutree.jiffies_till_sched_qs= [KNL]
3443 Set required age in jiffies for a
3444 given grace period before RCU starts
3445 soliciting quiescent-state help from
3446 rcu_note_context_switch().
3447
3448 rcutree.jiffies_till_first_fqs= [KNL]
3449 Set delay from grace-period initialization to
3450 first attempt to force quiescent states.
3451 Units are jiffies, minimum value is zero,
3452 and maximum value is HZ.
3453
3454 rcutree.jiffies_till_next_fqs= [KNL]
3455 Set delay between subsequent attempts to force
3456 quiescent states. Units are jiffies, minimum
3457 value is one, and maximum value is HZ.
3458
3459 rcutree.kthread_prio= [KNL,BOOT]
3460 Set the SCHED_FIFO priority of the RCU per-CPU
3461 kthreads (rcuc/N). This value is also used for
3462 the priority of the RCU boost threads (rcub/N)
3463 and for the RCU grace-period kthreads (rcu_bh,
3464 rcu_preempt, and rcu_sched). If RCU_BOOST is
3465 set, valid values are 1-99 and the default is 1
3466 (the least-favored priority). Otherwise, when
3467 RCU_BOOST is not set, valid values are 0-99 and
3468 the default is zero (non-realtime operation).
3469
3470 rcutree.rcu_nocb_leader_stride= [KNL]
3471 Set the number of NOCB kthread groups, which
3472 defaults to the square root of the number of
3473 CPUs. Larger numbers reduces the wakeup overhead
3474 on the per-CPU grace-period kthreads, but increases
3475 that same overhead on each group's leader.
3476
3477 rcutree.qhimark= [KNL]
3478 Set threshold of queued RCU callbacks beyond which
3479 batch limiting is disabled.
3480
3481 rcutree.qlowmark= [KNL]
3482 Set threshold of queued RCU callbacks below which
3483 batch limiting is re-enabled.
3484
3485 rcutree.rcu_idle_gp_delay= [KNL]
3486 Set wakeup interval for idle CPUs that have
3487 RCU callbacks (RCU_FAST_NO_HZ=y).
3488
3489 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3490 Set wakeup interval for idle CPUs that have
3491 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3492 Lazy RCU callbacks are those which RCU can
3493 prove do nothing more than free memory.
3494
3495 rcutree.rcu_kick_kthreads= [KNL]
3496 Cause the grace-period kthread to get an extra
3497 wake_up() if it sleeps three times longer than
3498 it should at force-quiescent-state time.
3499 This wake_up() will be accompanied by a
3500 WARN_ONCE() splat and an ftrace_dump().
3501
3502 rcuperf.gp_async= [KNL]
3503 Measure performance of asynchronous
3504 grace-period primitives such as call_rcu().
3505
3506 rcuperf.gp_async_max= [KNL]
3507 Specify the maximum number of outstanding
3508 callbacks per writer thread. When a writer
3509 thread exceeds this limit, it invokes the
3510 corresponding flavor of rcu_barrier() to allow
3511 previously posted callbacks to drain.
3512
3513 rcuperf.gp_exp= [KNL]
3514 Measure performance of expedited synchronous
3515 grace-period primitives.
3516
3517 rcuperf.holdoff= [KNL]
3518 Set test-start holdoff period. The purpose of
3519 this parameter is to delay the start of the
3520 test until boot completes in order to avoid
3521 interference.
3522
3523 rcuperf.nreaders= [KNL]
3524 Set number of RCU readers. The value -1 selects
3525 N, where N is the number of CPUs. A value
3526 "n" less than -1 selects N-n+1, where N is again
3527 the number of CPUs. For example, -2 selects N
3528 (the number of CPUs), -3 selects N+1, and so on.
3529 A value of "n" less than or equal to -N selects
3530 a single reader.
3531
3532 rcuperf.nwriters= [KNL]
3533 Set number of RCU writers. The values operate
3534 the same as for rcuperf.nreaders.
3535 N, where N is the number of CPUs
3536
3537 rcuperf.perf_type= [KNL]
3538 Specify the RCU implementation to test.
3539
3540 rcuperf.shutdown= [KNL]
3541 Shut the system down after performance tests
3542 complete. This is useful for hands-off automated
3543 testing.
3544
3545 rcuperf.verbose= [KNL]
3546 Enable additional printk() statements.
3547
3548 rcuperf.writer_holdoff= [KNL]
3549 Write-side holdoff between grace periods,
3550 in microseconds. The default of zero says
3551 no holdoff.
3552
3553 rcutorture.cbflood_inter_holdoff= [KNL]
3554 Set holdoff time (jiffies) between successive
3555 callback-flood tests.
3556
3557 rcutorture.cbflood_intra_holdoff= [KNL]
3558 Set holdoff time (jiffies) between successive
3559 bursts of callbacks within a given callback-flood
3560 test.
3561
3562 rcutorture.cbflood_n_burst= [KNL]
3563 Set the number of bursts making up a given
3564 callback-flood test. Set this to zero to
3565 disable callback-flood testing.
3566
3567 rcutorture.cbflood_n_per_burst= [KNL]
3568 Set the number of callbacks to be registered
3569 in a given burst of a callback-flood test.
3570
3571 rcutorture.fqs_duration= [KNL]
3572 Set duration of force_quiescent_state bursts
3573 in microseconds.
3574
3575 rcutorture.fqs_holdoff= [KNL]
3576 Set holdoff time within force_quiescent_state bursts
3577 in microseconds.
3578
3579 rcutorture.fqs_stutter= [KNL]
3580 Set wait time between force_quiescent_state bursts
3581 in seconds.
3582
3583 rcutorture.gp_cond= [KNL]
3584 Use conditional/asynchronous update-side
3585 primitives, if available.
3586
3587 rcutorture.gp_exp= [KNL]
3588 Use expedited update-side primitives, if available.
3589
3590 rcutorture.gp_normal= [KNL]
3591 Use normal (non-expedited) asynchronous
3592 update-side primitives, if available.
3593
3594 rcutorture.gp_sync= [KNL]
3595 Use normal (non-expedited) synchronous
3596 update-side primitives, if available. If all
3597 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3598 rcutorture.gp_normal=, and rcutorture.gp_sync=
3599 are zero, rcutorture acts as if is interpreted
3600 they are all non-zero.
3601
3602 rcutorture.n_barrier_cbs= [KNL]
3603 Set callbacks/threads for rcu_barrier() testing.
3604
3605 rcutorture.nfakewriters= [KNL]
3606 Set number of concurrent RCU writers. These just
3607 stress RCU, they don't participate in the actual
3608 test, hence the "fake".
3609
3610 rcutorture.nreaders= [KNL]
3611 Set number of RCU readers. The value -1 selects
3612 N-1, where N is the number of CPUs. A value
3613 "n" less than -1 selects N-n-2, where N is again
3614 the number of CPUs. For example, -2 selects N
3615 (the number of CPUs), -3 selects N+1, and so on.
3616
3617 rcutorture.object_debug= [KNL]
3618 Enable debug-object double-call_rcu() testing.
3619
3620 rcutorture.onoff_holdoff= [KNL]
3621 Set time (s) after boot for CPU-hotplug testing.
3622
3623 rcutorture.onoff_interval= [KNL]
3624 Set time (s) between CPU-hotplug operations, or
3625 zero to disable CPU-hotplug testing.
3626
3627 rcutorture.shuffle_interval= [KNL]
3628 Set task-shuffle interval (s). Shuffling tasks
3629 allows some CPUs to go into dyntick-idle mode
3630 during the rcutorture test.
3631
3632 rcutorture.shutdown_secs= [KNL]
3633 Set time (s) after boot system shutdown. This
3634 is useful for hands-off automated testing.
3635
3636 rcutorture.stall_cpu= [KNL]
3637 Duration of CPU stall (s) to test RCU CPU stall
3638 warnings, zero to disable.
3639
3640 rcutorture.stall_cpu_holdoff= [KNL]
3641 Time to wait (s) after boot before inducing stall.
3642
3643 rcutorture.stall_cpu_irqsoff= [KNL]
3644 Disable interrupts while stalling if set.
3645
3646 rcutorture.stat_interval= [KNL]
3647 Time (s) between statistics printk()s.
3648
3649 rcutorture.stutter= [KNL]
3650 Time (s) to stutter testing, for example, specifying
3651 five seconds causes the test to run for five seconds,
3652 wait for five seconds, and so on. This tests RCU's
3653 ability to transition abruptly to and from idle.
3654
3655 rcutorture.test_boost= [KNL]
3656 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3657 "Maybe" means test if the RCU implementation
3658 under test support RCU priority boosting.
3659
3660 rcutorture.test_boost_duration= [KNL]
3661 Duration (s) of each individual boost test.
3662
3663 rcutorture.test_boost_interval= [KNL]
3664 Interval (s) between each boost test.
3665
3666 rcutorture.test_no_idle_hz= [KNL]
3667 Test RCU's dyntick-idle handling. See also the
3668 rcutorture.shuffle_interval parameter.
3669
3670 rcutorture.torture_type= [KNL]
3671 Specify the RCU implementation to test.
3672
3673 rcutorture.verbose= [KNL]
3674 Enable additional printk() statements.
3675
3676 rcupdate.rcu_cpu_stall_suppress= [KNL]
3677 Suppress RCU CPU stall warning messages.
3678
3679 rcupdate.rcu_cpu_stall_timeout= [KNL]
3680 Set timeout for RCU CPU stall warning messages.
3681
3682 rcupdate.rcu_expedited= [KNL]
3683 Use expedited grace-period primitives, for
3684 example, synchronize_rcu_expedited() instead
3685 of synchronize_rcu(). This reduces latency,
3686 but can increase CPU utilization, degrade
3687 real-time latency, and degrade energy efficiency.
3688 No effect on CONFIG_TINY_RCU kernels.
3689
3690 rcupdate.rcu_normal= [KNL]
3691 Use only normal grace-period primitives,
3692 for example, synchronize_rcu() instead of
3693 synchronize_rcu_expedited(). This improves
3694 real-time latency, CPU utilization, and
3695 energy efficiency, but can expose users to
3696 increased grace-period latency. This parameter
3697 overrides rcupdate.rcu_expedited. No effect on
3698 CONFIG_TINY_RCU kernels.
3699
3700 rcupdate.rcu_normal_after_boot= [KNL]
3701 Once boot has completed (that is, after
3702 rcu_end_inkernel_boot() has been invoked), use
3703 only normal grace-period primitives. No effect
3704 on CONFIG_TINY_RCU kernels.
3705
3706 rcupdate.rcu_task_stall_timeout= [KNL]
3707 Set timeout in jiffies for RCU task stall warning
3708 messages. Disable with a value less than or equal
3709 to zero.
3710
3711 rcupdate.rcu_self_test= [KNL]
3712 Run the RCU early boot self tests
3713
3714 rcupdate.rcu_self_test_bh= [KNL]
3715 Run the RCU bh early boot self tests
3716
3717 rcupdate.rcu_self_test_sched= [KNL]
3718 Run the RCU sched early boot self tests
3719
3720 rdinit= [KNL]
3721 Format: <full_path>
3722 Run specified binary instead of /init from the ramdisk,
3723 used for early userspace startup. See initrd.
3724
3725 rdt= [HW,X86,RDT]
3726 Turn on/off individual RDT features. List is:
3727 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3728 mba.
3729 E.g. to turn on cmt and turn off mba use:
3730 rdt=cmt,!mba
3731
3732 reboot= [KNL]
3733 Format (x86 or x86_64):
3734 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3735 [[,]s[mp]#### \
3736 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3737 [[,]f[orce]
3738 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3739 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3740 reboot_force is either force or not specified,
3741 reboot_cpu is s[mp]#### with #### being the processor
3742 to be used for rebooting.
3743
3744 relax_domain_level=
3745 [KNL, SMP] Set scheduler's default relax_domain_level.
3746 See Documentation/cgroup-v1/cpusets.txt.
3747
3748 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3749 Format: <base1>,<size1>[,<base2>,<size2>,...]
3750 Reserve I/O ports or memory so the kernel won't use
3751 them. If <base> is less than 0x10000, the region
3752 is assumed to be I/O ports; otherwise it is memory.
3753
3754 reservetop= [X86-32]
3755 Format: nn[KMG]
3756 Reserves a hole at the top of the kernel virtual
3757 address space.
3758
3759 reservelow= [X86]
3760 Format: nn[K]
3761 Set the amount of memory to reserve for BIOS at
3762 the bottom of the address space.
3763
3764 reset_devices [KNL] Force drivers to reset the underlying device
3765 during initialization.
3766
3767 resume= [SWSUSP]
3768 Specify the partition device for software suspend
3769 Format:
3770 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3771
3772 resume_offset= [SWSUSP]
3773 Specify the offset from the beginning of the partition
3774 given by "resume=" at which the swap header is located,
3775 in <PAGE_SIZE> units (needed only for swap files).
3776 See Documentation/power/swsusp-and-swap-files.txt
3777
3778 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3779 read the resume files
3780
3781 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3782 Useful for devices that are detected asynchronously
3783 (e.g. USB and MMC devices).
3784
3785 hibernate= [HIBERNATION]
3786 noresume Don't check if there's a hibernation image
3787 present during boot.
3788 nocompress Don't compress/decompress hibernation images.
3789 no Disable hibernation and resume.
3790 protect_image Turn on image protection during restoration
3791 (that will set all pages holding image data
3792 during restoration read-only).
3793
3794 retain_initrd [RAM] Keep initrd memory after extraction
3795
3796 rfkill.default_state=
3797 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3798 etc. communication is blocked by default.
3799 1 Unblocked.
3800
3801 rfkill.master_switch_mode=
3802 0 The "airplane mode" button does nothing.
3803 1 The "airplane mode" button toggles between everything
3804 blocked and the previous configuration.
3805 2 The "airplane mode" button toggles between everything
3806 blocked and everything unblocked.
3807
3808 rhash_entries= [KNL,NET]
3809 Set number of hash buckets for route cache
3810
3811 ring3mwait=disable
3812 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3813 CPUs.
3814
3815 ro [KNL] Mount root device read-only on boot
3816
3817 rodata= [KNL]
3818 on Mark read-only kernel memory as read-only (default).
3819 off Leave read-only kernel memory writable for debugging.
3820
3821 rockchip.usb_uart
3822 Enable the uart passthrough on the designated usb port
3823 on Rockchip SoCs. When active, the signals of the
3824 debug-uart get routed to the D+ and D- pins of the usb
3825 port and the regular usb controller gets disabled.
3826
3827 root= [KNL] Root filesystem
3828 See name_to_dev_t comment in init/do_mounts.c.
3829
3830 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3831 mount the root filesystem
3832
3833 rootflags= [KNL] Set root filesystem mount option string
3834
3835 rootfstype= [KNL] Set root filesystem type
3836
3837 rootwait [KNL] Wait (indefinitely) for root device to show up.
3838 Useful for devices that are detected asynchronously
3839 (e.g. USB and MMC devices).
3840
3841 rproc_mem=nn[KMG][@address]
3842 [KNL,ARM,CMA] Remoteproc physical memory block.
3843 Memory area to be used by remote processor image,
3844 managed by CMA.
3845
3846 rw [KNL] Mount root device read-write on boot
3847
3848 S [KNL] Run init in single mode
3849
3850 s390_iommu= [HW,S390]
3851 Set s390 IOTLB flushing mode
3852 strict
3853 With strict flushing every unmap operation will result in
3854 an IOTLB flush. Default is lazy flushing before reuse,
3855 which is faster.
3856
3857 sa1100ir [NET]
3858 See drivers/net/irda/sa1100_ir.c.
3859
3860 sbni= [NET] Granch SBNI12 leased line adapter
3861
3862 sched_debug [KNL] Enables verbose scheduler debug messages.
3863
3864 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3865 Allowed values are enable and disable. This feature
3866 incurs a small amount of overhead in the scheduler
3867 but is useful for debugging and performance tuning.
3868
3869 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3870 xtime_lock contention on larger systems, and/or RCU lock
3871 contention on all systems with CONFIG_MAXSMP set.
3872 Format: { "0" | "1" }
3873 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3874 1 -- enable.
3875 Note: increases power consumption, thus should only be
3876 enabled if running jitter sensitive (HPC/RT) workloads.
3877
3878 security= [SECURITY] Choose a security module to enable at boot.
3879 If this boot parameter is not specified, only the first
3880 security module asking for security registration will be
3881 loaded. An invalid security module name will be treated
3882 as if no module has been chosen.
3883
3884 selinux= [SELINUX] Disable or enable SELinux at boot time.
3885 Format: { "0" | "1" }
3886 See security/selinux/Kconfig help text.
3887 0 -- disable.
3888 1 -- enable.
3889 Default value is set via kernel config option.
3890 If enabled at boot time, /selinux/disable can be used
3891 later to disable prior to initial policy load.
3892
3893 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3894 Format: { "0" | "1" }
3895 See security/apparmor/Kconfig help text
3896 0 -- disable.
3897 1 -- enable.
3898 Default value is set via kernel config option.
3899
3900 serialnumber [BUGS=X86-32]
3901
3902 shapers= [NET]
3903 Maximal number of shapers.
3904
3905 simeth= [IA-64]
3906 simscsi=
3907
3908 slram= [HW,MTD]
3909
3910 slab_nomerge [MM]
3911 Disable merging of slabs with similar size. May be
3912 necessary if there is some reason to distinguish
3913 allocs to different slabs, especially in hardened
3914 environments where the risk of heap overflows and
3915 layout control by attackers can usually be
3916 frustrated by disabling merging. This will reduce
3917 most of the exposure of a heap attack to a single
3918 cache (risks via metadata attacks are mostly
3919 unchanged). Debug options disable merging on their
3920 own.
3921 For more information see Documentation/vm/slub.txt.
3922
3923 slab_max_order= [MM, SLAB]
3924 Determines the maximum allowed order for slabs.
3925 A high setting may cause OOMs due to memory
3926 fragmentation. Defaults to 1 for systems with
3927 more than 32MB of RAM, 0 otherwise.
3928
3929 slub_debug[=options[,slabs]] [MM, SLUB]
3930 Enabling slub_debug allows one to determine the
3931 culprit if slab objects become corrupted. Enabling
3932 slub_debug can create guard zones around objects and
3933 may poison objects when not in use. Also tracks the
3934 last alloc / free. For more information see
3935 Documentation/vm/slub.txt.
3936
3937 slub_memcg_sysfs= [MM, SLUB]
3938 Determines whether to enable sysfs directories for
3939 memory cgroup sub-caches. 1 to enable, 0 to disable.
3940 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3941 Enabling this can lead to a very high number of debug
3942 directories and files being created under
3943 /sys/kernel/slub.
3944
3945 slub_max_order= [MM, SLUB]
3946 Determines the maximum allowed order for slabs.
3947 A high setting may cause OOMs due to memory
3948 fragmentation. For more information see
3949 Documentation/vm/slub.txt.
3950
3951 slub_min_objects= [MM, SLUB]
3952 The minimum number of objects per slab. SLUB will
3953 increase the slab order up to slub_max_order to
3954 generate a sufficiently large slab able to contain
3955 the number of objects indicated. The higher the number
3956 of objects the smaller the overhead of tracking slabs
3957 and the less frequently locks need to be acquired.
3958 For more information see Documentation/vm/slub.txt.
3959
3960 slub_min_order= [MM, SLUB]
3961 Determines the minimum page order for slabs. Must be
3962 lower than slub_max_order.
3963 For more information see Documentation/vm/slub.txt.
3964
3965 slub_nomerge [MM, SLUB]
3966 Same with slab_nomerge. This is supported for legacy.
3967 See slab_nomerge for more information.
3968
3969 smart2= [HW]
3970 Format: <io1>[,<io2>[,...,<io8>]]
3971
3972 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3973 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3974 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3975 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3976 smsc-ircc2.ircc_irq= [HW] IRQ line
3977 smsc-ircc2.ircc_dma= [HW] DMA channel
3978 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3979 0: Toshiba Satellite 1800 (GP data pin select)
3980 1: Fast pin select (default)
3981 2: ATC IRMode
3982
3983 smt [KNL,S390] Set the maximum number of threads (logical
3984 CPUs) to use per physical CPU on systems capable of
3985 symmetric multithreading (SMT). Will be capped to the
3986 actual hardware limit.
3987 Format: <integer>
3988 Default: -1 (no limit)
3989
3990 softlockup_panic=
3991 [KNL] Should the soft-lockup detector generate panics.
3992 Format: <integer>
3993
3994 A nonzero value instructs the soft-lockup detector
3995 to panic the machine when a soft-lockup occurs. This
3996 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3997 which is the respective build-time switch to that
3998 functionality.
3999
4000 softlockup_all_cpu_backtrace=
4001 [KNL] Should the soft-lockup detector generate
4002 backtraces on all cpus.
4003 Format: <integer>
4004
4005 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4006 See Documentation/laptops/sonypi.txt
4007
4008 spectre_v2= [X86] Control mitigation of Spectre variant 2
4009 (indirect branch speculation) vulnerability.
4010
4011 on - unconditionally enable
4012 off - unconditionally disable
4013 auto - kernel detects whether your CPU model is
4014 vulnerable
4015
4016 Selecting 'on' will, and 'auto' may, choose a
4017 mitigation method at run time according to the
4018 CPU, the available microcode, the setting of the
4019 CONFIG_RETPOLINE configuration option, and the
4020 compiler with which the kernel was built.
4021
4022 Specific mitigations can also be selected manually:
4023
4024 retpoline - replace indirect branches
4025 retpoline,generic - google's original retpoline
4026 retpoline,amd - AMD-specific minimal thunk
4027
4028 Not specifying this option is equivalent to
4029 spectre_v2=auto.
4030
4031 spec_store_bypass_disable=
4032 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4033 (Speculative Store Bypass vulnerability)
4034
4035 Certain CPUs are vulnerable to an exploit against a
4036 a common industry wide performance optimization known
4037 as "Speculative Store Bypass" in which recent stores
4038 to the same memory location may not be observed by
4039 later loads during speculative execution. The idea
4040 is that such stores are unlikely and that they can
4041 be detected prior to instruction retirement at the
4042 end of a particular speculation execution window.
4043
4044 In vulnerable processors, the speculatively forwarded
4045 store can be used in a cache side channel attack, for
4046 example to read memory to which the attacker does not
4047 directly have access (e.g. inside sandboxed code).
4048
4049 This parameter controls whether the Speculative Store
4050 Bypass optimization is used.
4051
4052 on - Unconditionally disable Speculative Store Bypass
4053 off - Unconditionally enable Speculative Store Bypass
4054 auto - Kernel detects whether the CPU model contains an
4055 implementation of Speculative Store Bypass and
4056 picks the most appropriate mitigation. If the
4057 CPU is not vulnerable, "off" is selected. If the
4058 CPU is vulnerable the default mitigation is
4059 architecture and Kconfig dependent. See below.
4060 prctl - Control Speculative Store Bypass per thread
4061 via prctl. Speculative Store Bypass is enabled
4062 for a process by default. The state of the control
4063 is inherited on fork.
4064 seccomp - Same as "prctl" above, but all seccomp threads
4065 will disable SSB unless they explicitly opt out.
4066
4067 Not specifying this option is equivalent to
4068 spec_store_bypass_disable=auto.
4069
4070 Default mitigations:
4071 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4072
4073 spia_io_base= [HW,MTD]
4074 spia_fio_base=
4075 spia_pedr=
4076 spia_peddr=
4077
4078 srcutree.counter_wrap_check [KNL]
4079 Specifies how frequently to check for
4080 grace-period sequence counter wrap for the
4081 srcu_data structure's ->srcu_gp_seq_needed field.
4082 The greater the number of bits set in this kernel
4083 parameter, the less frequently counter wrap will
4084 be checked for. Note that the bottom two bits
4085 are ignored.
4086
4087 srcutree.exp_holdoff [KNL]
4088 Specifies how many nanoseconds must elapse
4089 since the end of the last SRCU grace period for
4090 a given srcu_struct until the next normal SRCU
4091 grace period will be considered for automatic
4092 expediting. Set to zero to disable automatic
4093 expediting.
4094
4095 stack_guard_gap= [MM]
4096 override the default stack gap protection. The value
4097 is in page units and it defines how many pages prior
4098 to (for stacks growing down) resp. after (for stacks
4099 growing up) the main stack are reserved for no other
4100 mapping. Default value is 256 pages.
4101
4102 stacktrace [FTRACE]
4103 Enabled the stack tracer on boot up.
4104
4105 stacktrace_filter=[function-list]
4106 [FTRACE] Limit the functions that the stack tracer
4107 will trace at boot up. function-list is a comma separated
4108 list of functions. This list can be changed at run
4109 time by the stack_trace_filter file in the debugfs
4110 tracing directory. Note, this enables stack tracing
4111 and the stacktrace above is not needed.
4112
4113 sti= [PARISC,HW]
4114 Format: <num>
4115 Set the STI (builtin display/keyboard on the HP-PARISC
4116 machines) console (graphic card) which should be used
4117 as the initial boot-console.
4118 See also comment in drivers/video/console/sticore.c.
4119
4120 sti_font= [HW]
4121 See comment in drivers/video/console/sticore.c.
4122
4123 stifb= [HW]
4124 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4125
4126 sunrpc.min_resvport=
4127 sunrpc.max_resvport=
4128 [NFS,SUNRPC]
4129 SunRPC servers often require that client requests
4130 originate from a privileged port (i.e. a port in the
4131 range 0 < portnr < 1024).
4132 An administrator who wishes to reserve some of these
4133 ports for other uses may adjust the range that the
4134 kernel's sunrpc client considers to be privileged
4135 using these two parameters to set the minimum and
4136 maximum port values.
4137
4138 sunrpc.svc_rpc_per_connection_limit=
4139 [NFS,SUNRPC]
4140 Limit the number of requests that the server will
4141 process in parallel from a single connection.
4142 The default value is 0 (no limit).
4143
4144 sunrpc.pool_mode=
4145 [NFS]
4146 Control how the NFS server code allocates CPUs to
4147 service thread pools. Depending on how many NICs
4148 you have and where their interrupts are bound, this
4149 option will affect which CPUs will do NFS serving.
4150 Note: this parameter cannot be changed while the
4151 NFS server is running.
4152
4153 auto the server chooses an appropriate mode
4154 automatically using heuristics
4155 global a single global pool contains all CPUs
4156 percpu one pool for each CPU
4157 pernode one pool for each NUMA node (equivalent
4158 to global on non-NUMA machines)
4159
4160 sunrpc.tcp_slot_table_entries=
4161 sunrpc.udp_slot_table_entries=
4162 [NFS,SUNRPC]
4163 Sets the upper limit on the number of simultaneous
4164 RPC calls that can be sent from the client to a
4165 server. Increasing these values may allow you to
4166 improve throughput, but will also increase the
4167 amount of memory reserved for use by the client.
4168
4169 suspend.pm_test_delay=
4170 [SUSPEND]
4171 Sets the number of seconds to remain in a suspend test
4172 mode before resuming the system (see
4173 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4174 is set. Default value is 5.
4175
4176 swapaccount=[0|1]
4177 [KNL] Enable accounting of swap in memory resource
4178 controller if no parameter or 1 is given or disable
4179 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4180
4181 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4182 Format: { <int> | force | noforce }
4183 <int> -- Number of I/O TLB slabs
4184 force -- force using of bounce buffers even if they
4185 wouldn't be automatically used by the kernel
4186 noforce -- Never use bounce buffers (for debugging)
4187
4188 switches= [HW,M68k]
4189
4190 sysfs.deprecated=0|1 [KNL]
4191 Enable/disable old style sysfs layout for old udev
4192 on older distributions. When this option is enabled
4193 very new udev will not work anymore. When this option
4194 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4195 in older udev will not work anymore.
4196 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4197 the kernel configuration.
4198
4199 sysrq_always_enabled
4200 [KNL]
4201 Ignore sysrq setting - this boot parameter will
4202 neutralize any effect of /proc/sys/kernel/sysrq.
4203 Useful for debugging.
4204
4205 tcpmhash_entries= [KNL,NET]
4206 Set the number of tcp_metrics_hash slots.
4207 Default value is 8192 or 16384 depending on total
4208 ram pages. This is used to specify the TCP metrics
4209 cache size. See Documentation/networking/ip-sysctl.txt
4210 "tcp_no_metrics_save" section for more details.
4211
4212 tdfx= [HW,DRM]
4213
4214 test_suspend= [SUSPEND][,N]
4215 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4216 standby suspend) or "freeze" (for suspend type freeze)
4217 as the system sleep state during system startup with
4218 the optional capability to repeat N number of times.
4219 The system is woken from this state using a
4220 wakeup-capable RTC alarm.
4221
4222 thash_entries= [KNL,NET]
4223 Set number of hash buckets for TCP connection
4224
4225 thermal.act= [HW,ACPI]
4226 -1: disable all active trip points in all thermal zones
4227 <degrees C>: override all lowest active trip points
4228
4229 thermal.crt= [HW,ACPI]
4230 -1: disable all critical trip points in all thermal zones
4231 <degrees C>: override all critical trip points
4232
4233 thermal.nocrt= [HW,ACPI]
4234 Set to disable actions on ACPI thermal zone
4235 critical and hot trip points.
4236
4237 thermal.off= [HW,ACPI]
4238 1: disable ACPI thermal control
4239
4240 thermal.psv= [HW,ACPI]
4241 -1: disable all passive trip points
4242 <degrees C>: override all passive trip points to this
4243 value
4244
4245 thermal.tzp= [HW,ACPI]
4246 Specify global default ACPI thermal zone polling rate
4247 <deci-seconds>: poll all this frequency
4248 0: no polling (default)
4249
4250 threadirqs [KNL]
4251 Force threading of all interrupt handlers except those
4252 marked explicitly IRQF_NO_THREAD.
4253
4254 tmem [KNL,XEN]
4255 Enable the Transcendent memory driver if built-in.
4256
4257 tmem.cleancache=0|1 [KNL, XEN]
4258 Default is on (1). Disable the usage of the cleancache
4259 API to send anonymous pages to the hypervisor.
4260
4261 tmem.frontswap=0|1 [KNL, XEN]
4262 Default is on (1). Disable the usage of the frontswap
4263 API to send swap pages to the hypervisor. If disabled
4264 the selfballooning and selfshrinking are force disabled.
4265
4266 tmem.selfballooning=0|1 [KNL, XEN]
4267 Default is on (1). Disable the driving of swap pages
4268 to the hypervisor.
4269
4270 tmem.selfshrinking=0|1 [KNL, XEN]
4271 Default is on (1). Partial swapoff that immediately
4272 transfers pages from Xen hypervisor back to the
4273 kernel based on different criteria.
4274
4275 topology= [S390]
4276 Format: {off | on}
4277 Specify if the kernel should make use of the cpu
4278 topology information if the hardware supports this.
4279 The scheduler will make use of this information and
4280 e.g. base its process migration decisions on it.
4281 Default is on.
4282
4283 topology_updates= [KNL, PPC, NUMA]
4284 Format: {off}
4285 Specify if the kernel should ignore (off)
4286 topology updates sent by the hypervisor to this
4287 LPAR.
4288
4289 tp720= [HW,PS2]
4290
4291 tpm_suspend_pcr=[HW,TPM]
4292 Format: integer pcr id
4293 Specify that at suspend time, the tpm driver
4294 should extend the specified pcr with zeros,
4295 as a workaround for some chips which fail to
4296 flush the last written pcr on TPM_SaveState.
4297 This will guarantee that all the other pcrs
4298 are saved.
4299
4300 trace_buf_size=nn[KMG]
4301 [FTRACE] will set tracing buffer size on each cpu.
4302
4303 trace_event=[event-list]
4304 [FTRACE] Set and start specified trace events in order
4305 to facilitate early boot debugging. The event-list is a
4306 comma separated list of trace events to enable. See
4307 also Documentation/trace/events.txt
4308
4309 trace_options=[option-list]
4310 [FTRACE] Enable or disable tracer options at boot.
4311 The option-list is a comma delimited list of options
4312 that can be enabled or disabled just as if you were
4313 to echo the option name into
4314
4315 /sys/kernel/debug/tracing/trace_options
4316
4317 For example, to enable stacktrace option (to dump the
4318 stack trace of each event), add to the command line:
4319
4320 trace_options=stacktrace
4321
4322 See also Documentation/trace/ftrace.txt "trace options"
4323 section.
4324
4325 tp_printk[FTRACE]
4326 Have the tracepoints sent to printk as well as the
4327 tracing ring buffer. This is useful for early boot up
4328 where the system hangs or reboots and does not give the
4329 option for reading the tracing buffer or performing a
4330 ftrace_dump_on_oops.
4331
4332 To turn off having tracepoints sent to printk,
4333 echo 0 > /proc/sys/kernel/tracepoint_printk
4334 Note, echoing 1 into this file without the
4335 tracepoint_printk kernel cmdline option has no effect.
4336
4337 ** CAUTION **
4338
4339 Having tracepoints sent to printk() and activating high
4340 frequency tracepoints such as irq or sched, can cause
4341 the system to live lock.
4342
4343 traceoff_on_warning
4344 [FTRACE] enable this option to disable tracing when a
4345 warning is hit. This turns off "tracing_on". Tracing can
4346 be enabled again by echoing '1' into the "tracing_on"
4347 file located in /sys/kernel/debug/tracing/
4348
4349 This option is useful, as it disables the trace before
4350 the WARNING dump is called, which prevents the trace to
4351 be filled with content caused by the warning output.
4352
4353 This option can also be set at run time via the sysctl
4354 option: kernel/traceoff_on_warning
4355
4356 transparent_hugepage=
4357 [KNL]
4358 Format: [always|madvise|never]
4359 Can be used to control the default behavior of the system
4360 with respect to transparent hugepages.
4361 See Documentation/vm/transhuge.txt for more details.
4362
4363 tsc= Disable clocksource stability checks for TSC.
4364 Format: <string>
4365 [x86] reliable: mark tsc clocksource as reliable, this
4366 disables clocksource verification at runtime, as well
4367 as the stability checks done at bootup. Used to enable
4368 high-resolution timer mode on older hardware, and in
4369 virtualized environment.
4370 [x86] noirqtime: Do not use TSC to do irq accounting.
4371 Used to run time disable IRQ_TIME_ACCOUNTING on any
4372 platforms where RDTSC is slow and this accounting
4373 can add overhead.
4374 [x86] unstable: mark the TSC clocksource as unstable, this
4375 marks the TSC unconditionally unstable at bootup and
4376 avoids any further wobbles once the TSC watchdog notices.
4377
4378 turbografx.map[2|3]= [HW,JOY]
4379 TurboGraFX parallel port interface
4380 Format:
4381 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4382 See also Documentation/input/devices/joystick-parport.rst
4383
4384 udbg-immortal [PPC] When debugging early kernel crashes that
4385 happen after console_init() and before a proper
4386 console driver takes over, this boot options might
4387 help "seeing" what's going on.
4388
4389 uhash_entries= [KNL,NET]
4390 Set number of hash buckets for UDP/UDP-Lite connections
4391
4392 uhci-hcd.ignore_oc=
4393 [USB] Ignore overcurrent events (default N).
4394 Some badly-designed motherboards generate lots of
4395 bogus events, for ports that aren't wired to
4396 anything. Set this parameter to avoid log spamming.
4397 Note that genuine overcurrent events won't be
4398 reported either.
4399
4400 unknown_nmi_panic
4401 [X86] Cause panic on unknown NMI.
4402
4403 usbcore.authorized_default=
4404 [USB] Default USB device authorization:
4405 (default -1 = authorized except for wireless USB,
4406 0 = not authorized, 1 = authorized)
4407
4408 usbcore.autosuspend=
4409 [USB] The autosuspend time delay (in seconds) used
4410 for newly-detected USB devices (default 2). This
4411 is the time required before an idle device will be
4412 autosuspended. Devices for which the delay is set
4413 to a negative value won't be autosuspended at all.
4414
4415 usbcore.usbfs_snoop=
4416 [USB] Set to log all usbfs traffic (default 0 = off).
4417
4418 usbcore.usbfs_snoop_max=
4419 [USB] Maximum number of bytes to snoop in each URB
4420 (default = 65536).
4421
4422 usbcore.blinkenlights=
4423 [USB] Set to cycle leds on hubs (default 0 = off).
4424
4425 usbcore.old_scheme_first=
4426 [USB] Start with the old device initialization
4427 scheme (default 0 = off).
4428
4429 usbcore.usbfs_memory_mb=
4430 [USB] Memory limit (in MB) for buffers allocated by
4431 usbfs (default = 16, 0 = max = 2047).
4432
4433 usbcore.use_both_schemes=
4434 [USB] Try the other device initialization scheme
4435 if the first one fails (default 1 = enabled).
4436
4437 usbcore.initial_descriptor_timeout=
4438 [USB] Specifies timeout for the initial 64-byte
4439 USB_REQ_GET_DESCRIPTOR request in milliseconds
4440 (default 5000 = 5.0 seconds).
4441
4442 usbcore.nousb [USB] Disable the USB subsystem
4443
4444 usbcore.quirks=
4445 [USB] A list of quirk entries to augment the built-in
4446 usb core quirk list. List entries are separated by
4447 commas. Each entry has the form
4448 VendorID:ProductID:Flags. The IDs are 4-digit hex
4449 numbers and Flags is a set of letters. Each letter
4450 will change the built-in quirk; setting it if it is
4451 clear and clearing it if it is set. The letters have
4452 the following meanings:
4453 a = USB_QUIRK_STRING_FETCH_255 (string
4454 descriptors must not be fetched using
4455 a 255-byte read);
4456 b = USB_QUIRK_RESET_RESUME (device can't resume
4457 correctly so reset it instead);
4458 c = USB_QUIRK_NO_SET_INTF (device can't handle
4459 Set-Interface requests);
4460 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4461 handle its Configuration or Interface
4462 strings);
4463 e = USB_QUIRK_RESET (device can't be reset
4464 (e.g morph devices), don't use reset);
4465 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4466 more interface descriptions than the
4467 bNumInterfaces count, and can't handle
4468 talking to these interfaces);
4469 g = USB_QUIRK_DELAY_INIT (device needs a pause
4470 during initialization, after we read
4471 the device descriptor);
4472 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4473 high speed and super speed interrupt
4474 endpoints, the USB 2.0 and USB 3.0 spec
4475 require the interval in microframes (1
4476 microframe = 125 microseconds) to be
4477 calculated as interval = 2 ^
4478 (bInterval-1).
4479 Devices with this quirk report their
4480 bInterval as the result of this
4481 calculation instead of the exponent
4482 variable used in the calculation);
4483 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4484 handle device_qualifier descriptor
4485 requests);
4486 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4487 generates spurious wakeup, ignore
4488 remote wakeup capability);
4489 k = USB_QUIRK_NO_LPM (device can't handle Link
4490 Power Management);
4491 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4492 (Device reports its bInterval as linear
4493 frames instead of the USB 2.0
4494 calculation);
4495 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4496 to be disconnected before suspend to
4497 prevent spurious wakeup);
4498 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4499 pause after every control message);
4500 Example: quirks=0781:5580:bk,0a5c:5834:gij
4501
4502 usbhid.mousepoll=
4503 [USBHID] The interval which mice are to be polled at.
4504
4505 usbhid.jspoll=
4506 [USBHID] The interval which joysticks are to be polled at.
4507
4508 usbhid.kbpoll=
4509 [USBHID] The interval which keyboards are to be polled at.
4510
4511 usb-storage.delay_use=
4512 [UMS] The delay in seconds before a new device is
4513 scanned for Logical Units (default 1).
4514
4515 usb-storage.quirks=
4516 [UMS] A list of quirks entries to supplement or
4517 override the built-in unusual_devs list. List
4518 entries are separated by commas. Each entry has
4519 the form VID:PID:Flags where VID and PID are Vendor
4520 and Product ID values (4-digit hex numbers) and
4521 Flags is a set of characters, each corresponding
4522 to a common usb-storage quirk flag as follows:
4523 a = SANE_SENSE (collect more than 18 bytes
4524 of sense data);
4525 b = BAD_SENSE (don't collect more than 18
4526 bytes of sense data);
4527 c = FIX_CAPACITY (decrease the reported
4528 device capacity by one sector);
4529 d = NO_READ_DISC_INFO (don't use
4530 READ_DISC_INFO command);
4531 e = NO_READ_CAPACITY_16 (don't use
4532 READ_CAPACITY_16 command);
4533 f = NO_REPORT_OPCODES (don't use report opcodes
4534 command, uas only);
4535 g = MAX_SECTORS_240 (don't transfer more than
4536 240 sectors at a time, uas only);
4537 h = CAPACITY_HEURISTICS (decrease the
4538 reported device capacity by one
4539 sector if the number is odd);
4540 i = IGNORE_DEVICE (don't bind to this
4541 device);
4542 j = NO_REPORT_LUNS (don't use report luns
4543 command, uas only);
4544 l = NOT_LOCKABLE (don't try to lock and
4545 unlock ejectable media);
4546 m = MAX_SECTORS_64 (don't transfer more
4547 than 64 sectors = 32 KB at a time);
4548 n = INITIAL_READ10 (force a retry of the
4549 initial READ(10) command);
4550 o = CAPACITY_OK (accept the capacity
4551 reported by the device);
4552 p = WRITE_CACHE (the device cache is ON
4553 by default);
4554 r = IGNORE_RESIDUE (the device reports
4555 bogus residue values);
4556 s = SINGLE_LUN (the device has only one
4557 Logical Unit);
4558 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4559 commands, uas only);
4560 u = IGNORE_UAS (don't bind to the uas driver);
4561 w = NO_WP_DETECT (don't test whether the
4562 medium is write-protected).
4563 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4564 even if the device claims no cache)
4565 Example: quirks=0419:aaf5:rl,0421:0433:rc
4566
4567 user_debug= [KNL,ARM]
4568 Format: <int>
4569 See arch/arm/Kconfig.debug help text.
4570 1 - undefined instruction events
4571 2 - system calls
4572 4 - invalid data aborts
4573 8 - SIGSEGV faults
4574 16 - SIGBUS faults
4575 Example: user_debug=31
4576
4577 userpte=
4578 [X86] Flags controlling user PTE allocations.
4579
4580 nohigh = do not allocate PTE pages in
4581 HIGHMEM regardless of setting
4582 of CONFIG_HIGHPTE.
4583
4584 vdso= [X86,SH]
4585 On X86_32, this is an alias for vdso32=. Otherwise:
4586
4587 vdso=1: enable VDSO (the default)
4588 vdso=0: disable VDSO mapping
4589
4590 vdso32= [X86] Control the 32-bit vDSO
4591 vdso32=1: enable 32-bit VDSO
4592 vdso32=0 or vdso32=2: disable 32-bit VDSO
4593
4594 See the help text for CONFIG_COMPAT_VDSO for more
4595 details. If CONFIG_COMPAT_VDSO is set, the default is
4596 vdso32=0; otherwise, the default is vdso32=1.
4597
4598 For compatibility with older kernels, vdso32=2 is an
4599 alias for vdso32=0.
4600
4601 Try vdso32=0 if you encounter an error that says:
4602 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4603
4604 vector= [IA-64,SMP]
4605 vector=percpu: enable percpu vector domain
4606
4607 video= [FB] Frame buffer configuration
4608 See Documentation/fb/modedb.txt.
4609
4610 video.brightness_switch_enabled= [0,1]
4611 If set to 1, on receiving an ACPI notify event
4612 generated by hotkey, video driver will adjust brightness
4613 level and then send out the event to user space through
4614 the allocated input device; If set to 0, video driver
4615 will only send out the event without touching backlight
4616 brightness level.
4617 default: 1
4618
4619 virtio_mmio.device=
4620 [VMMIO] Memory mapped virtio (platform) device.
4621
4622 <size>@<baseaddr>:<irq>[:<id>]
4623 where:
4624 <size> := size (can use standard suffixes
4625 like K, M and G)
4626 <baseaddr> := physical base address
4627 <irq> := interrupt number (as passed to
4628 request_irq())
4629 <id> := (optional) platform device id
4630 example:
4631 virtio_mmio.device=1K@0x100b0000:48:7
4632
4633 Can be used multiple times for multiple devices.
4634
4635 vga= [BOOT,X86-32] Select a particular video mode
4636 See Documentation/x86/boot.txt and
4637 Documentation/svga.txt.
4638 Use vga=ask for menu.
4639 This is actually a boot loader parameter; the value is
4640 passed to the kernel using a special protocol.
4641
4642 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4643 size of <nn>. This can be used to increase the
4644 minimum size (128MB on x86). It can also be used to
4645 decrease the size and leave more room for directly
4646 mapped kernel RAM.
4647
4648 vmcp_cma=nn[MG] [KNL,S390]
4649 Sets the memory size reserved for contiguous memory
4650 allocations for the vmcp device driver.
4651
4652 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4653 Format: <command>
4654
4655 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4656 Format: <command>
4657
4658 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4659 Format: <command>
4660
4661 vsyscall= [X86-64]
4662 Controls the behavior of vsyscalls (i.e. calls to
4663 fixed addresses of 0xffffffffff600x00 from legacy
4664 code). Most statically-linked binaries and older
4665 versions of glibc use these calls. Because these
4666 functions are at fixed addresses, they make nice
4667 targets for exploits that can control RIP.
4668
4669 emulate [default] Vsyscalls turn into traps and are
4670 emulated reasonably safely.
4671
4672 native Vsyscalls are native syscall instructions.
4673 This is a little bit faster than trapping
4674 and makes a few dynamic recompilers work
4675 better than they would in emulation mode.
4676 It also makes exploits much easier to write.
4677
4678 none Vsyscalls don't work at all. This makes
4679 them quite hard to use for exploits but
4680 might break your system.
4681
4682 vt.color= [VT] Default text color.
4683 Format: 0xYX, X = foreground, Y = background.
4684 Default: 0x07 = light gray on black.
4685
4686 vt.cur_default= [VT] Default cursor shape.
4687 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4688 the parameters of the <Esc>[?A;B;Cc escape sequence;
4689 see VGA-softcursor.txt. Default: 2 = underline.
4690
4691 vt.default_blu= [VT]
4692 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4693 Change the default blue palette of the console.
4694 This is a 16-member array composed of values
4695 ranging from 0-255.
4696
4697 vt.default_grn= [VT]
4698 Format: <green0>,<green1>,<green2>,...,<green15>
4699 Change the default green palette of the console.
4700 This is a 16-member array composed of values
4701 ranging from 0-255.
4702
4703 vt.default_red= [VT]
4704 Format: <red0>,<red1>,<red2>,...,<red15>
4705 Change the default red palette of the console.
4706 This is a 16-member array composed of values
4707 ranging from 0-255.
4708
4709 vt.default_utf8=
4710 [VT]
4711 Format=<0|1>
4712 Set system-wide default UTF-8 mode for all tty's.
4713 Default is 1, i.e. UTF-8 mode is enabled for all
4714 newly opened terminals.
4715
4716 vt.global_cursor_default=
4717 [VT]
4718 Format=<-1|0|1>
4719 Set system-wide default for whether a cursor
4720 is shown on new VTs. Default is -1,
4721 i.e. cursors will be created by default unless
4722 overridden by individual drivers. 0 will hide
4723 cursors, 1 will display them.
4724
4725 vt.italic= [VT] Default color for italic text; 0-15.
4726 Default: 2 = green.
4727
4728 vt.underline= [VT] Default color for underlined text; 0-15.
4729 Default: 3 = cyan.
4730
4731 watchdog timers [HW,WDT] For information on watchdog timers,
4732 see Documentation/watchdog/watchdog-parameters.txt
4733 or other driver-specific files in the
4734 Documentation/watchdog/ directory.
4735
4736 workqueue.watchdog_thresh=
4737 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4738 warn stall conditions and dump internal state to
4739 help debugging. 0 disables workqueue stall
4740 detection; otherwise, it's the stall threshold
4741 duration in seconds. The default value is 30 and
4742 it can be updated at runtime by writing to the
4743 corresponding sysfs file.
4744
4745 workqueue.disable_numa
4746 By default, all work items queued to unbound
4747 workqueues are affine to the NUMA nodes they're
4748 issued on, which results in better behavior in
4749 general. If NUMA affinity needs to be disabled for
4750 whatever reason, this option can be used. Note
4751 that this also can be controlled per-workqueue for
4752 workqueues visible under /sys/bus/workqueue/.
4753
4754 workqueue.power_efficient
4755 Per-cpu workqueues are generally preferred because
4756 they show better performance thanks to cache
4757 locality; unfortunately, per-cpu workqueues tend to
4758 be more power hungry than unbound workqueues.
4759
4760 Enabling this makes the per-cpu workqueues which
4761 were observed to contribute significantly to power
4762 consumption unbound, leading to measurably lower
4763 power usage at the cost of small performance
4764 overhead.
4765
4766 The default value of this parameter is determined by
4767 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4768
4769 workqueue.debug_force_rr_cpu
4770 Workqueue used to implicitly guarantee that work
4771 items queued without explicit CPU specified are put
4772 on the local CPU. This guarantee is no longer true
4773 and while local CPU is still preferred work items
4774 may be put on foreign CPUs. This debug option
4775 forces round-robin CPU selection to flush out
4776 usages which depend on the now broken guarantee.
4777 When enabled, memory and cache locality will be
4778 impacted.
4779
4780 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4781 default x2apic cluster mode on platforms
4782 supporting x2apic.
4783
4784 x86_intel_mid_timer= [X86-32,APBT]
4785 Choose timer option for x86 Intel MID platform.
4786 Two valid options are apbt timer only and lapic timer
4787 plus one apbt timer for broadcast timer.
4788 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4789
4790 xen_512gb_limit [KNL,X86-64,XEN]
4791 Restricts the kernel running paravirtualized under Xen
4792 to use only up to 512 GB of RAM. The reason to do so is
4793 crash analysis tools and Xen tools for doing domain
4794 save/restore/migration must be enabled to handle larger
4795 domains.
4796
4797 xen_emul_unplug= [HW,X86,XEN]
4798 Unplug Xen emulated devices
4799 Format: [unplug0,][unplug1]
4800 ide-disks -- unplug primary master IDE devices
4801 aux-ide-disks -- unplug non-primary-master IDE devices
4802 nics -- unplug network devices
4803 all -- unplug all emulated devices (NICs and IDE disks)
4804 unnecessary -- unplugging emulated devices is
4805 unnecessary even if the host did not respond to
4806 the unplug protocol
4807 never -- do not unplug even if version check succeeds
4808
4809 xen_nopvspin [X86,XEN]
4810 Disables the ticketlock slowpath using Xen PV
4811 optimizations.
4812
4813 xen_nopv [X86]
4814 Disables the PV optimizations forcing the HVM guest to
4815 run as generic HVM guest with no PV drivers.
4816
4817 xirc2ps_cs= [NET,PCMCIA]
4818 Format:
4819 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]