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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 Support masking of GPEs numbered from 0x00 to 0x7f.
118
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
126
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
128 kernels.
129
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
139
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
144
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
147
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
153
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
159 strings
160 acpi_osi=!! # enable all built-in OS vendor
161 strings
162 acpi_osi= # disable all strings
163
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
174 Examples:
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
178
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
184 meaningless.
185 Examples:
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
187 FALSE.
188
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
199 the OSPM features.
200 Examples:
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 equivalent to
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 and
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
211
212 acpi_pm_good [X86]
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
216
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
219
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
223
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
228 s3_bios and s3_mode.
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
242
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
246
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
249
250 agp= [AGP]
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
255
256 ALSA [HW,ALSA]
257 See Documentation/sound/alsa/alsa-parameters.txt
258
259 alignment= [KNL,ARM]
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
263
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
271
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
276
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
283
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
286 Possible values are:
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
290 is a lot of faster
291 off - do not initialize any AMD IOMMU found in
292 the system
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
298
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
304
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
307 remapping modes:
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
313
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
316 Format: <a>,<b>
317 See also Documentation/input/joystick.txt
318
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
323
324 apc= [HW,SPARC]
325 Power management functions (SPARCstation-4/5 + deriv.)
326 Format: noidle
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
330
331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
336
337 apic_extnmi= [APIC,X86] External NMI delivery setting
338 Format: { bsp (default) | all | none }
339 bsp: External NMI is delivered only to CPU 0
340 all: External NMIs are broadcast to all CPUs as a
341 backup of CPU 0
342 none: External NMI is masked for all CPUs. This is
343 useful so that a dump capture kernel won't be
344 shot down by NMI
345
346 autoconf= [IPV6]
347 See Documentation/networking/ipv6.txt.
348
349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
350 Limit apic dumping. The parameter defines the maximal
351 number of local apics being dumped. Also it is possible
352 to set it to "all" by meaning -- no limit here.
353 Format: { 1 (default) | 2 | ... | all }.
354 The parameter valid if only apic=debug or
355 apic=verbose is specified.
356 Example: apic=debug show_lapic=all
357
358 apm= [APM] Advanced Power Management
359 See header of arch/x86/kernel/apm_32.c.
360
361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
362 Format: <io>,<irq>,<nodeID>
363
364 ataflop= [HW,M68k]
365
366 atarimouse= [HW,MOUSE] Atari Mouse
367
368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
369 EzKey and similar keyboards
370
371 atkbd.reset= [HW] Reset keyboard during initialization
372
373 atkbd.set= [HW] Select keyboard code set
374 Format: <int> (2 = AT (default), 3 = PS/2)
375
376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
377 keyboards
378
379 atkbd.softraw= [HW] Choose between synthetic and real raw mode
380 Format: <bool> (0 = real, 1 = synthetic (default))
381
382 atkbd.softrepeat= [HW]
383 Use software keyboard repeat
384
385 audit= [KNL] Enable the audit sub-system
386 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
387 0 - kernel audit is disabled and can not be enabled
388 until the next reboot
389 unset - kernel audit is initialized but disabled and
390 will be fully enabled by the userspace auditd.
391 1 - kernel audit is initialized and partially enabled,
392 storing at most audit_backlog_limit messages in
393 RAM until it is fully enabled by the userspace
394 auditd.
395 Default: unset
396
397 audit_backlog_limit= [KNL] Set the audit queue size limit.
398 Format: <int> (must be >=0)
399 Default: 64
400
401 bau= [X86_UV] Enable the BAU on SGI UV. The default
402 behavior is to disable the BAU (i.e. bau=0).
403 Format: { "0" | "1" }
404 0 - Disable the BAU.
405 1 - Enable the BAU.
406 unset - Disable the BAU.
407
408 baycom_epp= [HW,AX25]
409 Format: <io>,<mode>
410
411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
412 Format: <io>,<mode>
413 See header of drivers/net/hamradio/baycom_par.c.
414
415 baycom_ser_fdx= [HW,AX25]
416 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
417 Format: <io>,<irq>,<mode>[,<baud>]
418 See header of drivers/net/hamradio/baycom_ser_fdx.c.
419
420 baycom_ser_hdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
422 Format: <io>,<irq>,<mode>
423 See header of drivers/net/hamradio/baycom_ser_hdx.c.
424
425 blkdevparts= Manual partition parsing of block device(s) for
426 embedded devices based on command line input.
427 See Documentation/block/cmdline-partition.txt
428
429 boot_delay= Milliseconds to delay each printk during boot.
430 Values larger than 10 seconds (10000) are changed to
431 no delay (0).
432 Format: integer
433
434 bootmem_debug [KNL] Enable bootmem allocator debug messages.
435
436 bert_disable [ACPI]
437 Disable BERT OS support on buggy BIOSes.
438
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
441 kernel args too.
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
443 bttv.tuner=
444
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
447 at a time.
448
449 c101= [NET] Moxa C101 synchronous serial card
450
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
457
458 ca_keys= [KEYS] This parameter identifies a specific key(s) on
459 the system trusted keyring to be used for certificate
460 trust validation.
461 format: { id:<keyid> | builtin }
462
463 cca= [MIPS] Override the kernel pages' cache coherency
464 algorithm. Accepted values range from 0 to 7
465 inclusive. See arch/mips/include/asm/pgtable-bits.h
466 for platform specific values (SB1, Loongson3 and
467 others).
468
469 ccw_timeout_log [S390]
470 See Documentation/s390/CommonIO for details.
471
472 cgroup_disable= [KNL] Disable a particular controller
473 Format: {name of the controller(s) to disable}
474 The effects of cgroup_disable=foo are:
475 - foo isn't auto-mounted if you mount all cgroups in
476 a single hierarchy
477 - foo isn't visible as an individually mountable
478 subsystem
479 {Currently only "memory" controller deal with this and
480 cut the overhead, others just disable the usage. So
481 only cgroup_disable=memory is actually worthy}
482
483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
484 Format: { controller[,controller...] | "all" }
485 Like cgroup_disable, but only applies to cgroup v1;
486 the blacklisted controllers remain available in cgroup2.
487
488 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
489 Format: <string>
490 nosocket -- Disable socket memory accounting.
491 nokmem -- Disable kernel memory accounting.
492
493 checkreqprot [SELINUX] Set initial checkreqprot flag value.
494 Format: { "0" | "1" }
495 See security/selinux/Kconfig help text.
496 0 -- check protection applied by kernel (includes
497 any implied execute protection).
498 1 -- check protection requested by application.
499 Default value is set via a kernel config option.
500 Value can be changed at runtime via
501 /selinux/checkreqprot.
502
503 cio_ignore= [S390]
504 See Documentation/s390/CommonIO for details.
505 clk_ignore_unused
506 [CLK]
507 Prevents the clock framework from automatically gating
508 clocks that have not been explicitly enabled by a Linux
509 device driver but are enabled in hardware at reset or
510 by the bootloader/firmware. Note that this does not
511 force such clocks to be always-on nor does it reserve
512 those clocks in any way. This parameter is useful for
513 debug and development, but should not be needed on a
514 platform with proper driver support. For more
515 information, see Documentation/clk.txt.
516
517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
518 [Deprecated]
519 Forces specified clocksource (if available) to be used
520 when calculating gettimeofday(). If specified
521 clocksource is not available, it defaults to PIT.
522 Format: { pit | tsc | cyclone | pmtmr }
523
524 clocksource= Override the default clocksource
525 Format: <string>
526 Override the default clocksource and use the clocksource
527 with the name specified.
528 Some clocksource names to choose from, depending on
529 the platform:
530 [all] jiffies (this is the base, fallback clocksource)
531 [ACPI] acpi_pm
532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
533 pxa_timer,timer3,32k_counter,timer0_1
534 [AVR32] avr32
535 [X86-32] pit,hpet,tsc;
536 scx200_hrt on Geode; cyclone on IBM x440
537 [MIPS] MIPS
538 [PARISC] cr16
539 [S390] tod
540 [SH] SuperH
541 [SPARC64] tick
542 [X86-64] hpet,tsc
543
544 clocksource.arm_arch_timer.evtstrm=
545 [ARM,ARM64]
546 Format: <bool>
547 Enable/disable the eventstream feature of the ARM
548 architected timer so that code using WFE-based polling
549 loops can be debugged more effectively on production
550 systems.
551
552 clocksource.arm_arch_timer.fsl-a008585=
553 [ARM64]
554 Format: <bool>
555 Enable/disable the workaround of Freescale/NXP
556 erratum A-008585. This can be useful for KVM
557 guests, if the guest device tree doesn't show the
558 erratum. If unspecified, the workaround is
559 enabled based on the device tree.
560
561 clearcpuid=BITNUM [X86]
562 Disable CPUID feature X for the kernel. See
563 arch/x86/include/asm/cpufeatures.h for the valid bit
564 numbers. Note the Linux specific bits are not necessarily
565 stable over kernel options, but the vendor specific
566 ones should be.
567 Also note that user programs calling CPUID directly
568 or using the feature without checking anything
569 will still see it. This just prevents it from
570 being used by the kernel or shown in /proc/cpuinfo.
571 Also note the kernel might malfunction if you disable
572 some critical bits.
573
574 cma=nn[MG]@[start[MG][-end[MG]]]
575 [ARM,X86,KNL]
576 Sets the size of kernel global memory area for
577 contiguous memory allocations and optionally the
578 placement constraint by the physical address range of
579 memory allocations. A value of 0 disables CMA
580 altogether. For more information, see
581 include/linux/dma-contiguous.h
582
583 cmo_free_hint= [PPC] Format: { yes | no }
584 Specify whether pages are marked as being inactive
585 when they are freed. This is used in CMO environments
586 to determine OS memory pressure for page stealing by
587 a hypervisor.
588 Default: yes
589
590 coherent_pool=nn[KMG] [ARM,KNL]
591 Sets the size of memory pool for coherent, atomic dma
592 allocations, by default set to 256K.
593
594 code_bytes [X86] How many bytes of object code to print
595 in an oops report.
596 Range: 0 - 8192
597 Default: 64
598
599 com20020= [HW,NET] ARCnet - COM20020 chipset
600 Format:
601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
602
603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
604 Format: <io>[,<irq>]
605
606 com90xx= [HW,NET]
607 ARCnet - COM90xx chipset (memory-mapped buffers)
608 Format: <io>[,<irq>[,<memstart>]]
609
610 condev= [HW,S390] console device
611 conmode=
612
613 console= [KNL] Output console device and options.
614
615 tty<n> Use the virtual console device <n>.
616
617 ttyS<n>[,options]
618 ttyUSB0[,options]
619 Use the specified serial port. The options are of
620 the form "bbbbpnf", where "bbbb" is the baud rate,
621 "p" is parity ("n", "o", or "e"), "n" is number of
622 bits, and "f" is flow control ("r" for RTS or
623 omit it). Default is "9600n8".
624
625 See Documentation/admin-guide/serial-console.rst for more
626 information. See
627 Documentation/networking/netconsole.txt for an
628 alternative.
629
630 uart[8250],io,<addr>[,options]
631 uart[8250],mmio,<addr>[,options]
632 uart[8250],mmio16,<addr>[,options]
633 uart[8250],mmio32,<addr>[,options]
634 uart[8250],0x<addr>[,options]
635 Start an early, polled-mode console on the 8250/16550
636 UART at the specified I/O port or MMIO address,
637 switching to the matching ttyS device later.
638 MMIO inter-register address stride is either 8-bit
639 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
641 to be equivalent to 'mmio'. 'options' are specified in
642 the same format described for ttyS above; if unspecified,
643 the h/w is not re-initialized.
644
645 hvc<n> Use the hypervisor console device <n>. This is for
646 both Xen and PowerPC hypervisors.
647
648 If the device connected to the port is not a TTY but a braille
649 device, prepend "brl," before the device type, for instance
650 console=brl,ttyS0
651 For now, only VisioBraille is supported.
652
653 consoleblank= [KNL] The console blank (screen saver) timeout in
654 seconds. Defaults to 10*60 = 10mins. A value of 0
655 disables the blank timer.
656
657 coredump_filter=
658 [KNL] Change the default value for
659 /proc/<pid>/coredump_filter.
660 See also Documentation/filesystems/proc.txt.
661
662 cpuidle.off=1 [CPU_IDLE]
663 disable the cpuidle sub-system
664
665 cpu_init_udelay=N
666 [X86] Delay for N microsec between assert and de-assert
667 of APIC INIT to start processors. This delay occurs
668 on every CPU online, such as boot, and resume from suspend.
669 Default: 10000
670
671 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
672 Format:
673 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
674
675 crashkernel=size[KMG][@offset[KMG]]
676 [KNL] Using kexec, Linux can switch to a 'crash kernel'
677 upon panic. This parameter reserves the physical
678 memory region [offset, offset + size] for that kernel
679 image. If '@offset' is omitted, then a suitable offset
680 is selected automatically. Check
681 Documentation/kdump/kdump.txt for further details.
682
683 crashkernel=range1:size1[,range2:size2,...][@offset]
684 [KNL] Same as above, but depends on the memory
685 in the running system. The syntax of range is
686 start-[end] where start and end are both
687 a memory unit (amount[KMG]). See also
688 Documentation/kdump/kdump.txt for an example.
689
690 crashkernel=size[KMG],high
691 [KNL, x86_64] range could be above 4G. Allow kernel
692 to allocate physical memory region from top, so could
693 be above 4G if system have more than 4G ram installed.
694 Otherwise memory region will be allocated below 4G, if
695 available.
696 It will be ignored if crashkernel=X is specified.
697 crashkernel=size[KMG],low
698 [KNL, x86_64] range under 4G. When crashkernel=X,high
699 is passed, kernel could allocate physical memory region
700 above 4G, that cause second kernel crash on system
701 that require some amount of low memory, e.g. swiotlb
702 requires at least 64M+32K low memory, also enough extra
703 low memory is needed to make sure DMA buffers for 32-bit
704 devices won't run out. Kernel would try to allocate at
705 at least 256M below 4G automatically.
706 This one let user to specify own low range under 4G
707 for second kernel instead.
708 0: to disable low allocation.
709 It will be ignored when crashkernel=X,high is not used
710 or memory reserved is below 4G.
711
712 cryptomgr.notests
713 [KNL] Disable crypto self-tests
714
715 cs89x0_dma= [HW,NET]
716 Format: <dma>
717
718 cs89x0_media= [HW,NET]
719 Format: { rj45 | aui | bnc }
720
721 dasd= [HW,NET]
722 See header of drivers/s390/block/dasd_devmap.c.
723
724 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
725 (one device per port)
726 Format: <port#>,<type>
727 See also Documentation/input/joystick-parport.txt
728
729 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
730 time. See Documentation/dynamic-debug-howto.txt for
731 details. Deprecated, see dyndbg.
732
733 debug [KNL] Enable kernel debugging (events log level).
734
735 debug_locks_verbose=
736 [KNL] verbose self-tests
737 Format=<0|1>
738 Print debugging info while doing the locking API
739 self-tests.
740 We default to 0 (no extra messages), setting it to
741 1 will print _a lot_ more information - normally
742 only useful to kernel developers.
743
744 debug_objects [KNL] Enable object debugging
745
746 no_debug_objects
747 [KNL] Disable object debugging
748
749 debug_guardpage_minorder=
750 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
751 parameter allows control of the order of pages that will
752 be intentionally kept free (and hence protected) by the
753 buddy allocator. Bigger value increase the probability
754 of catching random memory corruption, but reduce the
755 amount of memory for normal system use. The maximum
756 possible value is MAX_ORDER/2. Setting this parameter
757 to 1 or 2 should be enough to identify most random
758 memory corruption problems caused by bugs in kernel or
759 driver code when a CPU writes to (or reads from) a
760 random memory location. Note that there exists a class
761 of memory corruptions problems caused by buggy H/W or
762 F/W or by drivers badly programing DMA (basically when
763 memory is written at bus level and the CPU MMU is
764 bypassed) which are not detectable by
765 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
766 tracking down these problems.
767
768 debug_pagealloc=
769 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
770 parameter enables the feature at boot time. In
771 default, it is disabled. We can avoid allocating huge
772 chunk of memory for debug pagealloc if we don't enable
773 it at boot time and the system will work mostly same
774 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
775 on: enable the feature
776
777 debugpat [X86] Enable PAT debugging
778
779 decnet.addr= [HW,NET]
780 Format: <area>[,<node>]
781 See also Documentation/networking/decnet.txt.
782
783 default_hugepagesz=
784 [same as hugepagesz=] The size of the default
785 HugeTLB page size. This is the size represented by
786 the legacy /proc/ hugepages APIs, used for SHM, and
787 default size when mounting hugetlbfs filesystems.
788 Defaults to the default architecture's huge page size
789 if not specified.
790
791 dhash_entries= [KNL]
792 Set number of hash buckets for dentry cache.
793
794 disable_1tb_segments [PPC]
795 Disables the use of 1TB hash page table segments. This
796 causes the kernel to fall back to 256MB segments which
797 can be useful when debugging issues that require an SLB
798 miss to occur.
799
800 disable= [IPV6]
801 See Documentation/networking/ipv6.txt.
802
803 disable_radix [PPC]
804 Disable RADIX MMU mode on POWER9
805
806 disable_cpu_apicid= [X86,APIC,SMP]
807 Format: <int>
808 The number of initial APIC ID for the
809 corresponding CPU to be disabled at boot,
810 mostly used for the kdump 2nd kernel to
811 disable BSP to wake up multiple CPUs without
812 causing system reset or hang due to sending
813 INIT from AP to BSP.
814
815 disable_ddw [PPC/PSERIES]
816 Disable Dynamic DMA Window support. Use this if
817 to workaround buggy firmware.
818
819 disable_ipv6= [IPV6]
820 See Documentation/networking/ipv6.txt.
821
822 disable_mtrr_cleanup [X86]
823 The kernel tries to adjust MTRR layout from continuous
824 to discrete, to make X server driver able to add WB
825 entry later. This parameter disables that.
826
827 disable_mtrr_trim [X86, Intel and AMD only]
828 By default the kernel will trim any uncacheable
829 memory out of your available memory pool based on
830 MTRR settings. This parameter disables that behavior,
831 possibly causing your machine to run very slowly.
832
833 disable_timer_pin_1 [X86]
834 Disable PIN 1 of APIC timer
835 Can be useful to work around chipset bugs.
836
837 dis_ucode_ldr [X86] Disable the microcode loader.
838
839 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
840 this option disables the debugging code at boot.
841
842 dma_debug_entries=<number>
843 This option allows to tune the number of preallocated
844 entries for DMA-API debugging code. One entry is
845 required per DMA-API allocation. Use this if the
846 DMA-API debugging code disables itself because the
847 architectural default is too low.
848
849 dma_debug_driver=<driver_name>
850 With this option the DMA-API debugging driver
851 filter feature can be enabled at boot time. Just
852 pass the driver to filter for as the parameter.
853 The filter can be disabled or changed to another
854 driver later using sysfs.
855
856 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
857 Broken monitors, graphic adapters, KVMs and EDIDless
858 panels may send no or incorrect EDID data sets.
859 This parameter allows to specify an EDID data sets
860 in the /lib/firmware directory that are used instead.
861 Generic built-in EDID data sets are used, if one of
862 edid/1024x768.bin, edid/1280x1024.bin,
863 edid/1680x1050.bin, or edid/1920x1080.bin is given
864 and no file with the same name exists. Details and
865 instructions how to build your own EDID data are
866 available in Documentation/EDID/HOWTO.txt. An EDID
867 data set will only be used for a particular connector,
868 if its name and a colon are prepended to the EDID
869 name. Each connector may use a unique EDID data
870 set by separating the files with a comma. An EDID
871 data set with no connector name will be used for
872 any connectors not explicitly specified.
873
874 dscc4.setup= [NET]
875
876 dump_apple_properties [X86]
877 Dump name and content of EFI device properties on
878 x86 Macs. Useful for driver authors to determine
879 what data is available or for reverse-engineering.
880
881 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
882 module.dyndbg[="val"]
883 Enable debug messages at boot time. See
884 Documentation/dynamic-debug-howto.txt for details.
885
886 nompx [X86] Disables Intel Memory Protection Extensions.
887 See Documentation/x86/intel_mpx.txt for more
888 information about the feature.
889
890 nopku [X86] Disable Memory Protection Keys CPU feature found
891 in some Intel CPUs.
892
893 module.async_probe [KNL]
894 Enable asynchronous probe on this module.
895
896 early_ioremap_debug [KNL]
897 Enable debug messages in early_ioremap support. This
898 is useful for tracking down temporary early mappings
899 which are not unmapped.
900
901 earlycon= [KNL] Output early console device and options.
902
903 When used with no options, the early console is
904 determined by the stdout-path property in device
905 tree's chosen node.
906
907 cdns,<addr>[,options]
908 Start an early, polled-mode console on a Cadence
909 (xuartps) serial port at the specified address. Only
910 supported option is baud rate. If baud rate is not
911 specified, the serial port must already be setup and
912 configured.
913
914 uart[8250],io,<addr>[,options]
915 uart[8250],mmio,<addr>[,options]
916 uart[8250],mmio32,<addr>[,options]
917 uart[8250],mmio32be,<addr>[,options]
918 uart[8250],0x<addr>[,options]
919 Start an early, polled-mode console on the 8250/16550
920 UART at the specified I/O port or MMIO address.
921 MMIO inter-register address stride is either 8-bit
922 (mmio) or 32-bit (mmio32 or mmio32be).
923 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
924 to be equivalent to 'mmio'. 'options' are specified
925 in the same format described for "console=ttyS<n>"; if
926 unspecified, the h/w is not initialized.
927
928 pl011,<addr>
929 pl011,mmio32,<addr>
930 Start an early, polled-mode console on a pl011 serial
931 port at the specified address. The pl011 serial port
932 must already be setup and configured. Options are not
933 yet supported. If 'mmio32' is specified, then only
934 the driver will use only 32-bit accessors to read/write
935 the device registers.
936
937 meson,<addr>
938 Start an early, polled-mode console on a meson serial
939 port at the specified address. The serial port must
940 already be setup and configured. Options are not yet
941 supported.
942
943 msm_serial,<addr>
944 Start an early, polled-mode console on an msm serial
945 port at the specified address. The serial port
946 must already be setup and configured. Options are not
947 yet supported.
948
949 msm_serial_dm,<addr>
950 Start an early, polled-mode console on an msm serial
951 dm port at the specified address. The serial port
952 must already be setup and configured. Options are not
953 yet supported.
954
955 smh Use ARM semihosting calls for early console.
956
957 s3c2410,<addr>
958 s3c2412,<addr>
959 s3c2440,<addr>
960 s3c6400,<addr>
961 s5pv210,<addr>
962 exynos4210,<addr>
963 Use early console provided by serial driver available
964 on Samsung SoCs, requires selecting proper type and
965 a correct base address of the selected UART port. The
966 serial port must already be setup and configured.
967 Options are not yet supported.
968
969 lpuart,<addr>
970 lpuart32,<addr>
971 Use early console provided by Freescale LP UART driver
972 found on Freescale Vybrid and QorIQ LS1021A processors.
973 A valid base address must be provided, and the serial
974 port must already be setup and configured.
975
976 armada3700_uart,<addr>
977 Start an early, polled-mode console on the
978 Armada 3700 serial port at the specified
979 address. The serial port must already be setup
980 and configured. Options are not yet supported.
981
982 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
983 earlyprintk=vga
984 earlyprintk=efi
985 earlyprintk=xen
986 earlyprintk=serial[,ttySn[,baudrate]]
987 earlyprintk=serial[,0x...[,baudrate]]
988 earlyprintk=ttySn[,baudrate]
989 earlyprintk=dbgp[debugController#]
990 earlyprintk=pciserial,bus:device.function[,baudrate]
991
992 earlyprintk is useful when the kernel crashes before
993 the normal console is initialized. It is not enabled by
994 default because it has some cosmetic problems.
995
996 Append ",keep" to not disable it when the real console
997 takes over.
998
999 Only one of vga, efi, serial, or usb debug port can
1000 be used at a time.
1001
1002 Currently only ttyS0 and ttyS1 may be specified by
1003 name. Other I/O ports may be explicitly specified
1004 on some architectures (x86 and arm at least) by
1005 replacing ttySn with an I/O port address, like this:
1006 earlyprintk=serial,0x1008,115200
1007 You can find the port for a given device in
1008 /proc/tty/driver/serial:
1009 2: uart:ST16650V2 port:00001008 irq:18 ...
1010
1011 Interaction with the standard serial driver is not
1012 very good.
1013
1014 The VGA and EFI output is eventually overwritten by
1015 the real console.
1016
1017 The xen output can only be used by Xen PV guests.
1018
1019 edac_report= [HW,EDAC] Control how to report EDAC event
1020 Format: {"on" | "off" | "force"}
1021 on: enable EDAC to report H/W event. May be overridden
1022 by other higher priority error reporting module.
1023 off: disable H/W event reporting through EDAC.
1024 force: enforce the use of EDAC to report H/W event.
1025 default: on.
1026
1027 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1028 ekgdboc=kbd
1029
1030 This is designed to be used in conjunction with
1031 the boot argument: earlyprintk=vga
1032
1033 edd= [EDD]
1034 Format: {"off" | "on" | "skip[mbr]"}
1035
1036 efi= [EFI]
1037 Format: { "old_map", "nochunk", "noruntime", "debug" }
1038 old_map [X86-64]: switch to the old ioremap-based EFI
1039 runtime services mapping. 32-bit still uses this one by
1040 default.
1041 nochunk: disable reading files in "chunks" in the EFI
1042 boot stub, as chunking can cause problems with some
1043 firmware implementations.
1044 noruntime : disable EFI runtime services support
1045 debug: enable misc debug output
1046
1047 efi_no_storage_paranoia [EFI; X86]
1048 Using this parameter you can use more than 50% of
1049 your efi variable storage. Use this parameter only if
1050 you are really sure that your UEFI does sane gc and
1051 fulfills the spec otherwise your board may brick.
1052
1053 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1054 Add arbitrary attribute to specific memory range by
1055 updating original EFI memory map.
1056 Region of memory which aa attribute is added to is
1057 from ss to ss+nn.
1058 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1059 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1060 attribute is added to range 0x100000000-0x180000000 and
1061 0x10a0000000-0x1120000000.
1062
1063 Using this parameter you can do debugging of EFI memmap
1064 related feature. For example, you can do debugging of
1065 Address Range Mirroring feature even if your box
1066 doesn't support it.
1067
1068 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1069 that is to be dynamically loaded by Linux. If there are
1070 multiple variables with the same name but with different
1071 vendor GUIDs, all of them will be loaded. See
1072 Documentation/acpi/ssdt-overlays.txt for details.
1073
1074
1075 eisa_irq_edge= [PARISC,HW]
1076 See header of drivers/parisc/eisa.c.
1077
1078 elanfreq= [X86-32]
1079 See comment before function elanfreq_setup() in
1080 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1081
1082 elevator= [IOSCHED]
1083 Format: {"cfq" | "deadline" | "noop"}
1084 See Documentation/block/cfq-iosched.txt and
1085 Documentation/block/deadline-iosched.txt for details.
1086
1087 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1088 Specifies physical address of start of kernel core
1089 image elf header and optionally the size. Generally
1090 kexec loader will pass this option to capture kernel.
1091 See Documentation/kdump/kdump.txt for details.
1092
1093 enable_mtrr_cleanup [X86]
1094 The kernel tries to adjust MTRR layout from continuous
1095 to discrete, to make X server driver able to add WB
1096 entry later. This parameter enables that.
1097
1098 enable_timer_pin_1 [X86]
1099 Enable PIN 1 of APIC timer
1100 Can be useful to work around chipset bugs
1101 (in particular on some ATI chipsets).
1102 The kernel tries to set a reasonable default.
1103
1104 enforcing [SELINUX] Set initial enforcing status.
1105 Format: {"0" | "1"}
1106 See security/selinux/Kconfig help text.
1107 0 -- permissive (log only, no denials).
1108 1 -- enforcing (deny and log).
1109 Default value is 0.
1110 Value can be changed at runtime via /selinux/enforce.
1111
1112 erst_disable [ACPI]
1113 Disable Error Record Serialization Table (ERST)
1114 support.
1115
1116 ether= [HW,NET] Ethernet cards parameters
1117 This option is obsoleted by the "netdev=" option, which
1118 has equivalent usage. See its documentation for details.
1119
1120 evm= [EVM]
1121 Format: { "fix" }
1122 Permit 'security.evm' to be updated regardless of
1123 current integrity status.
1124
1125 failslab=
1126 fail_page_alloc=
1127 fail_make_request=[KNL]
1128 General fault injection mechanism.
1129 Format: <interval>,<probability>,<space>,<times>
1130 See also Documentation/fault-injection/.
1131
1132 floppy= [HW]
1133 See Documentation/blockdev/floppy.txt.
1134
1135 force_pal_cache_flush
1136 [IA-64] Avoid check_sal_cache_flush which may hang on
1137 buggy SAL_CACHE_FLUSH implementations. Using this
1138 parameter will force ia64_sal_cache_flush to call
1139 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1140
1141 forcepae [X86-32]
1142 Forcefully enable Physical Address Extension (PAE).
1143 Many Pentium M systems disable PAE but may have a
1144 functionally usable PAE implementation.
1145 Warning: use of this parameter will taint the kernel
1146 and may cause unknown problems.
1147
1148 ftrace=[tracer]
1149 [FTRACE] will set and start the specified tracer
1150 as early as possible in order to facilitate early
1151 boot debugging.
1152
1153 ftrace_dump_on_oops[=orig_cpu]
1154 [FTRACE] will dump the trace buffers on oops.
1155 If no parameter is passed, ftrace will dump
1156 buffers of all CPUs, but if you pass orig_cpu, it will
1157 dump only the buffer of the CPU that triggered the
1158 oops.
1159
1160 ftrace_filter=[function-list]
1161 [FTRACE] Limit the functions traced by the function
1162 tracer at boot up. function-list is a comma separated
1163 list of functions. This list can be changed at run
1164 time by the set_ftrace_filter file in the debugfs
1165 tracing directory.
1166
1167 ftrace_notrace=[function-list]
1168 [FTRACE] Do not trace the functions specified in
1169 function-list. This list can be changed at run time
1170 by the set_ftrace_notrace file in the debugfs
1171 tracing directory.
1172
1173 ftrace_graph_filter=[function-list]
1174 [FTRACE] Limit the top level callers functions traced
1175 by the function graph tracer at boot up.
1176 function-list is a comma separated list of functions
1177 that can be changed at run time by the
1178 set_graph_function file in the debugfs tracing directory.
1179
1180 ftrace_graph_notrace=[function-list]
1181 [FTRACE] Do not trace from the functions specified in
1182 function-list. This list is a comma separated list of
1183 functions that can be changed at run time by the
1184 set_graph_notrace file in the debugfs tracing directory.
1185
1186 gamecon.map[2|3]=
1187 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1188 support via parallel port (up to 5 devices per port)
1189 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1190 See also Documentation/input/joystick-parport.txt
1191
1192 gamma= [HW,DRM]
1193
1194 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1195 Format: off | on
1196 default: on
1197
1198 gcov_persist= [GCOV] When non-zero (default), profiling data for
1199 kernel modules is saved and remains accessible via
1200 debugfs, even when the module is unloaded/reloaded.
1201 When zero, profiling data is discarded and associated
1202 debugfs files are removed at module unload time.
1203
1204 goldfish [X86] Enable the goldfish android emulator platform.
1205 Don't use this when you are not running on the
1206 android emulator
1207
1208 gpt [EFI] Forces disk with valid GPT signature but
1209 invalid Protective MBR to be treated as GPT. If the
1210 primary GPT is corrupted, it enables the backup/alternate
1211 GPT to be used instead.
1212
1213 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1214 the "Enable 0" bit of the configuration register.
1215 Format: 0 | 1
1216 Default: 0
1217 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1218 the "Enable 0" bit of the configuration register.
1219 Format: 0 | 1
1220 Default: 0
1221 grcan.select= [HW] Select which physical interface to use.
1222 Format: 0 | 1
1223 Default: 0
1224 grcan.txsize= [HW] Sets the size of the tx buffer.
1225 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1226 Default: 1024
1227 grcan.rxsize= [HW] Sets the size of the rx buffer.
1228 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1229 Default: 1024
1230
1231 gpio-mockup.gpio_mockup_ranges
1232 [HW] Sets the ranges of gpiochip of for this device.
1233 Format: <start1>,<end1>,<start2>,<end2>...
1234
1235 hardlockup_all_cpu_backtrace=
1236 [KNL] Should the hard-lockup detector generate
1237 backtraces on all cpus.
1238 Format: <integer>
1239
1240 hashdist= [KNL,NUMA] Large hashes allocated during boot
1241 are distributed across NUMA nodes. Defaults on
1242 for 64-bit NUMA, off otherwise.
1243 Format: 0 | 1 (for off | on)
1244
1245 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1246
1247 hd= [EIDE] (E)IDE hard drive subsystem geometry
1248 Format: <cyl>,<head>,<sect>
1249
1250 hest_disable [ACPI]
1251 Disable Hardware Error Source Table (HEST) support;
1252 corresponding firmware-first mode error processing
1253 logic will be disabled.
1254
1255 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1256 size of <nn>. This works even on boxes that have no
1257 highmem otherwise. This also works to reduce highmem
1258 size on bigger boxes.
1259
1260 highres= [KNL] Enable/disable high resolution timer mode.
1261 Valid parameters: "on", "off"
1262 Default: "on"
1263
1264 hisax= [HW,ISDN]
1265 See Documentation/isdn/README.HiSax.
1266
1267 hlt [BUGS=ARM,SH]
1268
1269 hpet= [X86-32,HPET] option to control HPET usage
1270 Format: { enable (default) | disable | force |
1271 verbose }
1272 disable: disable HPET and use PIT instead
1273 force: allow force enabled of undocumented chips (ICH4,
1274 VIA, nVidia)
1275 verbose: show contents of HPET registers during setup
1276
1277 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1278 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1279
1280 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1281 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1282 On x86-64 and powerpc, this option can be specified
1283 multiple times interleaved with hugepages= to reserve
1284 huge pages of different sizes. Valid pages sizes on
1285 x86-64 are 2M (when the CPU supports "pse") and 1G
1286 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1287
1288 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1289 terminal devices. Valid values: 0..8
1290 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1291 If specified, z/VM IUCV HVC accepts connections
1292 from listed z/VM user IDs only.
1293
1294 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1295 hardware thread id mappings.
1296 Format: <cpu>:<hwthread>
1297
1298 keep_bootcon [KNL]
1299 Do not unregister boot console at start. This is only
1300 useful for debugging when something happens in the window
1301 between unregistering the boot console and initializing
1302 the real console.
1303
1304 i2c_bus= [HW] Override the default board specific I2C bus speed
1305 or register an additional I2C bus that is not
1306 registered from board initialization code.
1307 Format:
1308 <bus_id>,<clkrate>
1309
1310 i8042.debug [HW] Toggle i8042 debug mode
1311 i8042.unmask_kbd_data
1312 [HW] Enable printing of interrupt data from the KBD port
1313 (disabled by default, and as a pre-condition
1314 requires that i8042.debug=1 be enabled)
1315 i8042.direct [HW] Put keyboard port into non-translated mode
1316 i8042.dumbkbd [HW] Pretend that controller can only read data from
1317 keyboard and cannot control its state
1318 (Don't attempt to blink the leds)
1319 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1320 i8042.nokbd [HW] Don't check/create keyboard port
1321 i8042.noloop [HW] Disable the AUX Loopback command while probing
1322 for the AUX port
1323 i8042.nomux [HW] Don't check presence of an active multiplexing
1324 controller
1325 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1326 controllers
1327 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1328 i8042.reset [HW] Reset the controller during init, cleanup and
1329 suspend-to-ram transitions, only during s2r
1330 transitions, or never reset
1331 Format: { 1 | Y | y | 0 | N | n }
1332 1, Y, y: always reset controller
1333 0, N, n: don't ever reset controller
1334 Default: only on s2r transitions on x86; most other
1335 architectures force reset to be always executed
1336 i8042.unlock [HW] Unlock (ignore) the keylock
1337 i8042.kbdreset [HW] Reset device connected to KBD port
1338
1339 i810= [HW,DRM]
1340
1341 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1342 indicates that the driver is running on unsupported
1343 hardware.
1344 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1345 does not match list of supported models.
1346 i8k.power_status
1347 [HW] Report power status in /proc/i8k
1348 (disabled by default)
1349 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1350 capability is set.
1351
1352 i915.invert_brightness=
1353 [DRM] Invert the sense of the variable that is used to
1354 set the brightness of the panel backlight. Normally a
1355 brightness value of 0 indicates backlight switched off,
1356 and the maximum of the brightness value sets the backlight
1357 to maximum brightness. If this parameter is set to 0
1358 (default) and the machine requires it, or this parameter
1359 is set to 1, a brightness value of 0 sets the backlight
1360 to maximum brightness, and the maximum of the brightness
1361 value switches the backlight off.
1362 -1 -- never invert brightness
1363 0 -- machine default
1364 1 -- force brightness inversion
1365
1366 icn= [HW,ISDN]
1367 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1368
1369 ide-core.nodma= [HW] (E)IDE subsystem
1370 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1371 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1372 .cdrom .chs .ignore_cable are additional options
1373 See Documentation/ide/ide.txt.
1374
1375 ide-generic.probe-mask= [HW] (E)IDE subsystem
1376 Format: <int>
1377 Probe mask for legacy ISA IDE ports. Depending on
1378 platform up to 6 ports are supported, enabled by
1379 setting corresponding bits in the mask to 1. The
1380 default value is 0x0, which has a special meaning.
1381 On systems that have PCI, it triggers scanning the
1382 PCI bus for the first and the second port, which
1383 are then probed. On systems without PCI the value
1384 of 0x0 enables probing the two first ports as if it
1385 was 0x3.
1386
1387 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1388 Claim all unknown PCI IDE storage controllers.
1389
1390 idle= [X86]
1391 Format: idle=poll, idle=halt, idle=nomwait
1392 Poll forces a polling idle loop that can slightly
1393 improve the performance of waking up a idle CPU, but
1394 will use a lot of power and make the system run hot.
1395 Not recommended.
1396 idle=halt: Halt is forced to be used for CPU idle.
1397 In such case C2/C3 won't be used again.
1398 idle=nomwait: Disable mwait for CPU C-states
1399
1400 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1401 Format: { strict | legacy | 2008 | relaxed }
1402 Default: strict
1403
1404 Choose which programs will be accepted for execution
1405 based on the IEEE 754 NaN encoding(s) supported by
1406 the FPU and the NaN encoding requested with the value
1407 of an ELF file header flag individually set by each
1408 binary. Hardware implementations are permitted to
1409 support either or both of the legacy and the 2008 NaN
1410 encoding mode.
1411
1412 Available settings are as follows:
1413 strict accept binaries that request a NaN encoding
1414 supported by the FPU
1415 legacy only accept legacy-NaN binaries, if supported
1416 by the FPU
1417 2008 only accept 2008-NaN binaries, if supported
1418 by the FPU
1419 relaxed accept any binaries regardless of whether
1420 supported by the FPU
1421
1422 The FPU emulator is always able to support both NaN
1423 encodings, so if no FPU hardware is present or it has
1424 been disabled with 'nofpu', then the settings of
1425 'legacy' and '2008' strap the emulator accordingly,
1426 'relaxed' straps the emulator for both legacy-NaN and
1427 2008-NaN, whereas 'strict' enables legacy-NaN only on
1428 legacy processors and both NaN encodings on MIPS32 or
1429 MIPS64 CPUs.
1430
1431 The setting for ABS.fmt/NEG.fmt instruction execution
1432 mode generally follows that for the NaN encoding,
1433 except where unsupported by hardware.
1434
1435 ignore_loglevel [KNL]
1436 Ignore loglevel setting - this will print /all/
1437 kernel messages to the console. Useful for debugging.
1438 We also add it as printk module parameter, so users
1439 could change it dynamically, usually by
1440 /sys/module/printk/parameters/ignore_loglevel.
1441
1442 ignore_rlimit_data
1443 Ignore RLIMIT_DATA setting for data mappings,
1444 print warning at first misuse. Can be changed via
1445 /sys/module/kernel/parameters/ignore_rlimit_data.
1446
1447 ihash_entries= [KNL]
1448 Set number of hash buckets for inode cache.
1449
1450 ima_appraise= [IMA] appraise integrity measurements
1451 Format: { "off" | "enforce" | "fix" | "log" }
1452 default: "enforce"
1453
1454 ima_appraise_tcb [IMA]
1455 The builtin appraise policy appraises all files
1456 owned by uid=0.
1457
1458 ima_canonical_fmt [IMA]
1459 Use the canonical format for the binary runtime
1460 measurements, instead of host native format.
1461
1462 ima_hash= [IMA]
1463 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1464 | sha512 | ... }
1465 default: "sha1"
1466
1467 The list of supported hash algorithms is defined
1468 in crypto/hash_info.h.
1469
1470 ima_policy= [IMA]
1471 The builtin measurement policy to load during IMA
1472 setup. Specyfing "tcb" as the value, measures all
1473 programs exec'd, files mmap'd for exec, and all files
1474 opened with the read mode bit set by either the
1475 effective uid (euid=0) or uid=0.
1476 Format: "tcb"
1477
1478 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1479 Load a policy which meets the needs of the Trusted
1480 Computing Base. This means IMA will measure all
1481 programs exec'd, files mmap'd for exec, and all files
1482 opened for read by uid=0.
1483
1484 ima_template= [IMA]
1485 Select one of defined IMA measurements template formats.
1486 Formats: { "ima" | "ima-ng" | "ima-sig" }
1487 Default: "ima-ng"
1488
1489 ima_template_fmt=
1490 [IMA] Define a custom template format.
1491 Format: { "field1|...|fieldN" }
1492
1493 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1494 Format: <min_file_size>
1495 Set the minimal file size for using asynchronous hash.
1496 If left unspecified, ahash usage is disabled.
1497
1498 ahash performance varies for different data sizes on
1499 different crypto accelerators. This option can be used
1500 to achieve the best performance for a particular HW.
1501
1502 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1503 Format: <bufsize>
1504 Set hashing buffer size. Default: 4k.
1505
1506 ahash performance varies for different chunk sizes on
1507 different crypto accelerators. This option can be used
1508 to achieve best performance for particular HW.
1509
1510 init= [KNL]
1511 Format: <full_path>
1512 Run specified binary instead of /sbin/init as init
1513 process.
1514
1515 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1516 for working out where the kernel is dying during
1517 startup.
1518
1519 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1520 initcall functions. Useful for debugging built-in
1521 modules and initcalls.
1522
1523 initrd= [BOOT] Specify the location of the initial ramdisk
1524
1525 init_pkru= [x86] Specify the default memory protection keys rights
1526 register contents for all processes. 0x55555554 by
1527 default (disallow access to all but pkey 0). Can
1528 override in debugfs after boot.
1529
1530 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1531 Format: <irq>
1532
1533 int_pln_enable [x86] Enable power limit notification interrupt
1534
1535 integrity_audit=[IMA]
1536 Format: { "0" | "1" }
1537 0 -- basic integrity auditing messages. (Default)
1538 1 -- additional integrity auditing messages.
1539
1540 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1541 on
1542 Enable intel iommu driver.
1543 off
1544 Disable intel iommu driver.
1545 igfx_off [Default Off]
1546 By default, gfx is mapped as normal device. If a gfx
1547 device has a dedicated DMAR unit, the DMAR unit is
1548 bypassed by not enabling DMAR with this option. In
1549 this case, gfx device will use physical address for
1550 DMA.
1551 forcedac [x86_64]
1552 With this option iommu will not optimize to look
1553 for io virtual address below 32-bit forcing dual
1554 address cycle on pci bus for cards supporting greater
1555 than 32-bit addressing. The default is to look
1556 for translation below 32-bit and if not available
1557 then look in the higher range.
1558 strict [Default Off]
1559 With this option on every unmap_single operation will
1560 result in a hardware IOTLB flush operation as opposed
1561 to batching them for performance.
1562 sp_off [Default Off]
1563 By default, super page will be supported if Intel IOMMU
1564 has the capability. With this option, super page will
1565 not be supported.
1566 ecs_off [Default Off]
1567 By default, extended context tables will be supported if
1568 the hardware advertises that it has support both for the
1569 extended tables themselves, and also PASID support. With
1570 this option set, extended tables will not be used even
1571 on hardware which claims to support them.
1572
1573 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1574 0 disables intel_idle and fall back on acpi_idle.
1575 1 to 9 specify maximum depth of C-state.
1576
1577 intel_pstate= [X86]
1578 disable
1579 Do not enable intel_pstate as the default
1580 scaling driver for the supported processors
1581 passive
1582 Use intel_pstate as a scaling driver, but configure it
1583 to work with generic cpufreq governors (instead of
1584 enabling its internal governor). This mode cannot be
1585 used along with the hardware-managed P-states (HWP)
1586 feature.
1587 force
1588 Enable intel_pstate on systems that prohibit it by default
1589 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1590 instead of acpi-cpufreq may disable platform features, such
1591 as thermal controls and power capping, that rely on ACPI
1592 P-States information being indicated to OSPM and therefore
1593 should be used with caution. This option does not work with
1594 processors that aren't supported by the intel_pstate driver
1595 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1596 no_hwp
1597 Do not enable hardware P state control (HWP)
1598 if available.
1599 hwp_only
1600 Only load intel_pstate on systems which support
1601 hardware P state control (HWP) if available.
1602 support_acpi_ppc
1603 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1604 Description Table, specifies preferred power management
1605 profile as "Enterprise Server" or "Performance Server",
1606 then this feature is turned on by default.
1607 per_cpu_perf_limits
1608 Allow per-logical-CPU P-State performance control limits using
1609 cpufreq sysfs interface
1610
1611 intremap= [X86-64, Intel-IOMMU]
1612 on enable Interrupt Remapping (default)
1613 off disable Interrupt Remapping
1614 nosid disable Source ID checking
1615 no_x2apic_optout
1616 BIOS x2APIC opt-out request will be ignored
1617 nopost disable Interrupt Posting
1618
1619 iomem= Disable strict checking of access to MMIO memory
1620 strict regions from userspace.
1621 relaxed
1622
1623 iommu= [x86]
1624 off
1625 force
1626 noforce
1627 biomerge
1628 panic
1629 nopanic
1630 merge
1631 nomerge
1632 forcesac
1633 soft
1634 pt [x86, IA-64]
1635 nobypass [PPC/POWERNV]
1636 Disable IOMMU bypass, using IOMMU for PCI devices.
1637
1638
1639 io7= [HW] IO7 for Marvel based alpha systems
1640 See comment before marvel_specify_io7 in
1641 arch/alpha/kernel/core_marvel.c.
1642
1643 io_delay= [X86] I/O delay method
1644 0x80
1645 Standard port 0x80 based delay
1646 0xed
1647 Alternate port 0xed based delay (needed on some systems)
1648 udelay
1649 Simple two microseconds delay
1650 none
1651 No delay
1652
1653 ip= [IP_PNP]
1654 See Documentation/filesystems/nfs/nfsroot.txt.
1655
1656 irqaffinity= [SMP] Set the default irq affinity mask
1657 The argument is a cpu list, as described above.
1658
1659 irqfixup [HW]
1660 When an interrupt is not handled search all handlers
1661 for it. Intended to get systems with badly broken
1662 firmware running.
1663
1664 irqpoll [HW]
1665 When an interrupt is not handled search all handlers
1666 for it. Also check all handlers each timer
1667 interrupt. Intended to get systems with badly broken
1668 firmware running.
1669
1670 isapnp= [ISAPNP]
1671 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1672
1673 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1674 The argument is a cpu list, as described above.
1675
1676 This option can be used to specify one or more CPUs
1677 to isolate from the general SMP balancing and scheduling
1678 algorithms. You can move a process onto or off an
1679 "isolated" CPU via the CPU affinity syscalls or cpuset.
1680 <cpu number> begins at 0 and the maximum value is
1681 "number of CPUs in system - 1".
1682
1683 This option is the preferred way to isolate CPUs. The
1684 alternative -- manually setting the CPU mask of all
1685 tasks in the system -- can cause problems and
1686 suboptimal load balancer performance.
1687
1688 iucv= [HW,NET]
1689
1690 ivrs_ioapic [HW,X86_64]
1691 Provide an override to the IOAPIC-ID<->DEVICE-ID
1692 mapping provided in the IVRS ACPI table. For
1693 example, to map IOAPIC-ID decimal 10 to
1694 PCI device 00:14.0 write the parameter as:
1695 ivrs_ioapic[10]=00:14.0
1696
1697 ivrs_hpet [HW,X86_64]
1698 Provide an override to the HPET-ID<->DEVICE-ID
1699 mapping provided in the IVRS ACPI table. For
1700 example, to map HPET-ID decimal 0 to
1701 PCI device 00:14.0 write the parameter as:
1702 ivrs_hpet[0]=00:14.0
1703
1704 ivrs_acpihid [HW,X86_64]
1705 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1706 mapping provided in the IVRS ACPI table. For
1707 example, to map UART-HID:UID AMD0020:0 to
1708 PCI device 00:14.5 write the parameter as:
1709 ivrs_acpihid[00:14.5]=AMD0020:0
1710
1711 js= [HW,JOY] Analog joystick
1712 See Documentation/input/joystick.txt.
1713
1714 nokaslr [KNL]
1715 When CONFIG_RANDOMIZE_BASE is set, this disables
1716 kernel and module base offset ASLR (Address Space
1717 Layout Randomization).
1718
1719 keepinitrd [HW,ARM]
1720
1721 kernelcore= [KNL,X86,IA-64,PPC]
1722 Format: nn[KMGTPE] | "mirror"
1723 This parameter
1724 specifies the amount of memory usable by the kernel
1725 for non-movable allocations. The requested amount is
1726 spread evenly throughout all nodes in the system. The
1727 remaining memory in each node is used for Movable
1728 pages. In the event, a node is too small to have both
1729 kernelcore and Movable pages, kernelcore pages will
1730 take priority and other nodes will have a larger number
1731 of Movable pages. The Movable zone is used for the
1732 allocation of pages that may be reclaimed or moved
1733 by the page migration subsystem. This means that
1734 HugeTLB pages may not be allocated from this zone.
1735 Note that allocations like PTEs-from-HighMem still
1736 use the HighMem zone if it exists, and the Normal
1737 zone if it does not.
1738
1739 Instead of specifying the amount of memory (nn[KMGTPE]),
1740 you can specify "mirror" option. In case "mirror"
1741 option is specified, mirrored (reliable) memory is used
1742 for non-movable allocations and remaining memory is used
1743 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1744 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1745 time.
1746
1747 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1748 Format: <Controller#>[,poll interval]
1749 The controller # is the number of the ehci usb debug
1750 port as it is probed via PCI. The poll interval is
1751 optional and is the number seconds in between
1752 each poll cycle to the debug port in case you need
1753 the functionality for interrupting the kernel with
1754 gdb or control-c on the dbgp connection. When
1755 not using this parameter you use sysrq-g to break into
1756 the kernel debugger.
1757
1758 kgdboc= [KGDB,HW] kgdb over consoles.
1759 Requires a tty driver that supports console polling,
1760 or a supported polling keyboard driver (non-usb).
1761 Serial only format: <serial_device>[,baud]
1762 keyboard only format: kbd
1763 keyboard and serial format: kbd,<serial_device>[,baud]
1764 Optional Kernel mode setting:
1765 kms, kbd format: kms,kbd
1766 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1767
1768 kgdbwait [KGDB] Stop kernel execution and enter the
1769 kernel debugger at the earliest opportunity.
1770
1771 kmac= [MIPS] korina ethernet MAC address.
1772 Configure the RouterBoard 532 series on-chip
1773 Ethernet adapter MAC address.
1774
1775 kmemleak= [KNL] Boot-time kmemleak enable/disable
1776 Valid arguments: on, off
1777 Default: on
1778 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1779 the default is off.
1780
1781 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1782 Valid arguments: 0, 1, 2
1783 kmemcheck=0 (disabled)
1784 kmemcheck=1 (enabled)
1785 kmemcheck=2 (one-shot mode)
1786 Default: 2 (one-shot mode)
1787
1788 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1789 Default is 0 (don't ignore, but inject #GP)
1790
1791 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1792 KVM MMU at runtime.
1793 Default is 0 (off)
1794
1795 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1796 Default is 1 (enabled)
1797
1798 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1799 for all guests.
1800 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1801
1802 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1803 (virtualized MMU) support on capable Intel chips.
1804 Default is 1 (enabled)
1805
1806 kvm-intel.emulate_invalid_guest_state=
1807 [KVM,Intel] Enable emulation of invalid guest states
1808 Default is 0 (disabled)
1809
1810 kvm-intel.flexpriority=
1811 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1812 Default is 1 (enabled)
1813
1814 kvm-intel.nested=
1815 [KVM,Intel] Enable VMX nesting (nVMX).
1816 Default is 0 (disabled)
1817
1818 kvm-intel.unrestricted_guest=
1819 [KVM,Intel] Disable unrestricted guest feature
1820 (virtualized real and unpaged mode) on capable
1821 Intel chips. Default is 1 (enabled)
1822
1823 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1824 feature (tagged TLBs) on capable Intel chips.
1825 Default is 1 (enabled)
1826
1827 l2cr= [PPC]
1828
1829 l3cr= [PPC]
1830
1831 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1832 disabled it.
1833
1834 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1835 value for LAPIC timer one-shot implementation. Default
1836 back to the programmable timer unit in the LAPIC.
1837
1838 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1839 in C2 power state.
1840
1841 libata.dma= [LIBATA] DMA control
1842 libata.dma=0 Disable all PATA and SATA DMA
1843 libata.dma=1 PATA and SATA Disk DMA only
1844 libata.dma=2 ATAPI (CDROM) DMA only
1845 libata.dma=4 Compact Flash DMA only
1846 Combinations also work, so libata.dma=3 enables DMA
1847 for disks and CDROMs, but not CFs.
1848
1849 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1850 libata.ignore_hpa=0 keep BIOS limits (default)
1851 libata.ignore_hpa=1 ignore limits, using full disk
1852
1853 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1854 when set.
1855 Format: <int>
1856
1857 libata.force= [LIBATA] Force configurations. The format is comma
1858 separated list of "[ID:]VAL" where ID is
1859 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1860 matching port, link or device. Basically, it matches
1861 the ATA ID string printed on console by libata. If
1862 the whole ID part is omitted, the last PORT and DEVICE
1863 values are used. If ID hasn't been specified yet, the
1864 configuration applies to all ports, links and devices.
1865
1866 If only DEVICE is omitted, the parameter applies to
1867 the port and all links and devices behind it. DEVICE
1868 number of 0 either selects the first device or the
1869 first fan-out link behind PMP device. It does not
1870 select the host link. DEVICE number of 15 selects the
1871 host link and device attached to it.
1872
1873 The VAL specifies the configuration to force. As long
1874 as there's no ambiguity shortcut notation is allowed.
1875 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1876 The following configurations can be forced.
1877
1878 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1879 Any ID with matching PORT is used.
1880
1881 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1882
1883 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1884 udma[/][16,25,33,44,66,100,133] notation is also
1885 allowed.
1886
1887 * [no]ncq: Turn on or off NCQ.
1888
1889 * [no]ncqtrim: Turn off queued DSM TRIM.
1890
1891 * nohrst, nosrst, norst: suppress hard, soft
1892 and both resets.
1893
1894 * rstonce: only attempt one reset during
1895 hot-unplug link recovery
1896
1897 * dump_id: dump IDENTIFY data.
1898
1899 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1900
1901 * disable: Disable this device.
1902
1903 If there are multiple matching configurations changing
1904 the same attribute, the last one is used.
1905
1906 memblock=debug [KNL] Enable memblock debug messages.
1907
1908 load_ramdisk= [RAM] List of ramdisks to load from floppy
1909 See Documentation/blockdev/ramdisk.txt.
1910
1911 lockd.nlm_grace_period=P [NFS] Assign grace period.
1912 Format: <integer>
1913
1914 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1915 Format: <integer>
1916
1917 lockd.nlm_timeout=T [NFS] Assign timeout value.
1918 Format: <integer>
1919
1920 lockd.nlm_udpport=M [NFS] Assign UDP port.
1921 Format: <integer>
1922
1923 locktorture.nreaders_stress= [KNL]
1924 Set the number of locking read-acquisition kthreads.
1925 Defaults to being automatically set based on the
1926 number of online CPUs.
1927
1928 locktorture.nwriters_stress= [KNL]
1929 Set the number of locking write-acquisition kthreads.
1930
1931 locktorture.onoff_holdoff= [KNL]
1932 Set time (s) after boot for CPU-hotplug testing.
1933
1934 locktorture.onoff_interval= [KNL]
1935 Set time (s) between CPU-hotplug operations, or
1936 zero to disable CPU-hotplug testing.
1937
1938 locktorture.shuffle_interval= [KNL]
1939 Set task-shuffle interval (jiffies). Shuffling
1940 tasks allows some CPUs to go into dyntick-idle
1941 mode during the locktorture test.
1942
1943 locktorture.shutdown_secs= [KNL]
1944 Set time (s) after boot system shutdown. This
1945 is useful for hands-off automated testing.
1946
1947 locktorture.stat_interval= [KNL]
1948 Time (s) between statistics printk()s.
1949
1950 locktorture.stutter= [KNL]
1951 Time (s) to stutter testing, for example,
1952 specifying five seconds causes the test to run for
1953 five seconds, wait for five seconds, and so on.
1954 This tests the locking primitive's ability to
1955 transition abruptly to and from idle.
1956
1957 locktorture.torture_runnable= [BOOT]
1958 Start locktorture running at boot time.
1959
1960 locktorture.torture_type= [KNL]
1961 Specify the locking implementation to test.
1962
1963 locktorture.verbose= [KNL]
1964 Enable additional printk() statements.
1965
1966 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1967 Format: <irq>
1968
1969 loglevel= All Kernel Messages with a loglevel smaller than the
1970 console loglevel will be printed to the console. It can
1971 also be changed with klogd or other programs. The
1972 loglevels are defined as follows:
1973
1974 0 (KERN_EMERG) system is unusable
1975 1 (KERN_ALERT) action must be taken immediately
1976 2 (KERN_CRIT) critical conditions
1977 3 (KERN_ERR) error conditions
1978 4 (KERN_WARNING) warning conditions
1979 5 (KERN_NOTICE) normal but significant condition
1980 6 (KERN_INFO) informational
1981 7 (KERN_DEBUG) debug-level messages
1982
1983 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1984 in bytes. n must be a power of two and greater
1985 than the minimal size. The minimal size is defined
1986 by LOG_BUF_SHIFT kernel config parameter. There is
1987 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1988 that allows to increase the default size depending on
1989 the number of CPUs. See init/Kconfig for more details.
1990
1991 logo.nologo [FB] Disables display of the built-in Linux logo.
1992 This may be used to provide more screen space for
1993 kernel log messages and is useful when debugging
1994 kernel boot problems.
1995
1996 lp=0 [LP] Specify parallel ports to use, e.g,
1997 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1998 lp=reset first parallel port). 'lp=0' disables the
1999 lp=auto printer driver. 'lp=reset' (which can be
2000 specified in addition to the ports) causes
2001 attached printers to be reset. Using
2002 lp=port1,port2,... specifies the parallel ports
2003 to associate lp devices with, starting with
2004 lp0. A port specification may be 'none' to skip
2005 that lp device, or a parport name such as
2006 'parport0'. Specifying 'lp=auto' instead of a
2007 port specification list means that device IDs
2008 from each port should be examined, to see if
2009 an IEEE 1284-compliant printer is attached; if
2010 so, the driver will manage that printer.
2011 See also header of drivers/char/lp.c.
2012
2013 lpj=n [KNL]
2014 Sets loops_per_jiffy to given constant, thus avoiding
2015 time-consuming boot-time autodetection (up to 250 ms per
2016 CPU). 0 enables autodetection (default). To determine
2017 the correct value for your kernel, boot with normal
2018 autodetection and see what value is printed. Note that
2019 on SMP systems the preset will be applied to all CPUs,
2020 which is likely to cause problems if your CPUs need
2021 significantly divergent settings. An incorrect value
2022 will cause delays in the kernel to be wrong, leading to
2023 unpredictable I/O errors and other breakage. Although
2024 unlikely, in the extreme case this might damage your
2025 hardware.
2026
2027 ltpc= [NET]
2028 Format: <io>,<irq>,<dma>
2029
2030 machvec= [IA-64] Force the use of a particular machine-vector
2031 (machvec) in a generic kernel.
2032 Example: machvec=hpzx1_swiotlb
2033
2034 machtype= [Loongson] Share the same kernel image file between different
2035 yeeloong laptop.
2036 Example: machtype=lemote-yeeloong-2f-7inch
2037
2038 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2039 than or equal to this physical address is ignored.
2040
2041 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2042 will bring up during bootup. maxcpus=n : n >= 0 limits
2043 the kernel to bring up 'n' processors. Surely after
2044 bootup you can bring up the other plugged cpu by executing
2045 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2046 only takes effect during system bootup.
2047 While n=0 is a special case, it is equivalent to "nosmp",
2048 which also disables the IO APIC.
2049
2050 max_loop= [LOOP] The number of loop block devices that get
2051 (loop.max_loop) unconditionally pre-created at init time. The default
2052 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2053 of statically allocating a predefined number, loop
2054 devices can be requested on-demand with the
2055 /dev/loop-control interface.
2056
2057 mce [X86-32] Machine Check Exception
2058
2059 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2060
2061 md= [HW] RAID subsystems devices and level
2062 See Documentation/admin-guide/md.rst.
2063
2064 mdacon= [MDA]
2065 Format: <first>,<last>
2066 Specifies range of consoles to be captured by the MDA.
2067
2068 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2069 Amount of memory to be used when the kernel is not able
2070 to see the whole system memory or for test.
2071 [X86] Work as limiting max address. Use together
2072 with memmap= to avoid physical address space collisions.
2073 Without memmap= PCI devices could be placed at addresses
2074 belonging to unused RAM.
2075
2076 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2077 memory.
2078
2079 memchunk=nn[KMG]
2080 [KNL,SH] Allow user to override the default size for
2081 per-device physically contiguous DMA buffers.
2082
2083 memhp_default_state=online/offline
2084 [KNL] Set the initial state for the memory hotplug
2085 onlining policy. If not specified, the default value is
2086 set according to the
2087 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2088 option.
2089 See Documentation/memory-hotplug.txt.
2090
2091 memmap=exactmap [KNL,X86] Enable setting of an exact
2092 E820 memory map, as specified by the user.
2093 Such memmap=exactmap lines can be constructed based on
2094 BIOS output or other requirements. See the memmap=nn@ss
2095 option description.
2096
2097 memmap=nn[KMG]@ss[KMG]
2098 [KNL] Force usage of a specific region of memory.
2099 Region of memory to be used is from ss to ss+nn.
2100
2101 memmap=nn[KMG]#ss[KMG]
2102 [KNL,ACPI] Mark specific memory as ACPI data.
2103 Region of memory to be marked is from ss to ss+nn.
2104
2105 memmap=nn[KMG]$ss[KMG]
2106 [KNL,ACPI] Mark specific memory as reserved.
2107 Region of memory to be reserved is from ss to ss+nn.
2108 Example: Exclude memory from 0x18690000-0x1869ffff
2109 memmap=64K$0x18690000
2110 or
2111 memmap=0x10000$0x18690000
2112
2113 memmap=nn[KMG]!ss[KMG]
2114 [KNL,X86] Mark specific memory as protected.
2115 Region of memory to be used, from ss to ss+nn.
2116 The memory region may be marked as e820 type 12 (0xc)
2117 and is NVDIMM or ADR memory.
2118
2119 memory_corruption_check=0/1 [X86]
2120 Some BIOSes seem to corrupt the first 64k of
2121 memory when doing things like suspend/resume.
2122 Setting this option will scan the memory
2123 looking for corruption. Enabling this will
2124 both detect corruption and prevent the kernel
2125 from using the memory being corrupted.
2126 However, its intended as a diagnostic tool; if
2127 repeatable BIOS-originated corruption always
2128 affects the same memory, you can use memmap=
2129 to prevent the kernel from using that memory.
2130
2131 memory_corruption_check_size=size [X86]
2132 By default it checks for corruption in the low
2133 64k, making this memory unavailable for normal
2134 use. Use this parameter to scan for
2135 corruption in more or less memory.
2136
2137 memory_corruption_check_period=seconds [X86]
2138 By default it checks for corruption every 60
2139 seconds. Use this parameter to check at some
2140 other rate. 0 disables periodic checking.
2141
2142 memtest= [KNL,X86,ARM] Enable memtest
2143 Format: <integer>
2144 default : 0 <disable>
2145 Specifies the number of memtest passes to be
2146 performed. Each pass selects another test
2147 pattern from a given set of patterns. Memtest
2148 fills the memory with this pattern, validates
2149 memory contents and reserves bad memory
2150 regions that are detected.
2151
2152 mem_sleep_default= [SUSPEND] Default system suspend mode:
2153 s2idle - Suspend-To-Idle
2154 shallow - Power-On Suspend or equivalent (if supported)
2155 deep - Suspend-To-RAM or equivalent (if supported)
2156 See Documentation/power/states.txt.
2157
2158 meye.*= [HW] Set MotionEye Camera parameters
2159 See Documentation/video4linux/meye.txt.
2160
2161 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2162 Multi-Function General Purpose Timers on AMD Geode
2163 platforms.
2164
2165 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2166 the BIOS has incorrectly applied a workaround. TinyBIOS
2167 version 0.98 is known to be affected, 0.99 fixes the
2168 problem by letting the user disable the workaround.
2169
2170 mga= [HW,DRM]
2171
2172 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2173 physical address is ignored.
2174
2175 mini2440= [ARM,HW,KNL]
2176 Format:[0..2][b][c][t]
2177 Default: "0tb"
2178 MINI2440 configuration specification:
2179 0 - The attached screen is the 3.5" TFT
2180 1 - The attached screen is the 7" TFT
2181 2 - The VGA Shield is attached (1024x768)
2182 Leaving out the screen size parameter will not load
2183 the TFT driver, and the framebuffer will be left
2184 unconfigured.
2185 b - Enable backlight. The TFT backlight pin will be
2186 linked to the kernel VESA blanking code and a GPIO
2187 LED. This parameter is not necessary when using the
2188 VGA shield.
2189 c - Enable the s3c camera interface.
2190 t - Reserved for enabling touchscreen support. The
2191 touchscreen support is not enabled in the mainstream
2192 kernel as of 2.6.30, a preliminary port can be found
2193 in the "bleeding edge" mini2440 support kernel at
2194 http://repo.or.cz/w/linux-2.6/mini2440.git
2195
2196 mminit_loglevel=
2197 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2198 parameter allows control of the logging verbosity for
2199 the additional memory initialisation checks. A value
2200 of 0 disables mminit logging and a level of 4 will
2201 log everything. Information is printed at KERN_DEBUG
2202 so loglevel=8 may also need to be specified.
2203
2204 module.sig_enforce
2205 [KNL] When CONFIG_MODULE_SIG is set, this means that
2206 modules without (valid) signatures will fail to load.
2207 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2208 is always true, so this option does nothing.
2209
2210 module_blacklist= [KNL] Do not load a comma-separated list of
2211 modules. Useful for debugging problem modules.
2212
2213 mousedev.tap_time=
2214 [MOUSE] Maximum time between finger touching and
2215 leaving touchpad surface for touch to be considered
2216 a tap and be reported as a left button click (for
2217 touchpads working in absolute mode only).
2218 Format: <msecs>
2219 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2220 reporting absolute coordinates, such as tablets
2221 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2222 reporting absolute coordinates, such as tablets
2223
2224 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2225 is similar to kernelcore except it specifies the
2226 amount of memory used for migratable allocations.
2227 If both kernelcore and movablecore is specified,
2228 then kernelcore will be at *least* the specified
2229 value but may be more. If movablecore on its own
2230 is specified, the administrator must be careful
2231 that the amount of memory usable for all allocations
2232 is not too small.
2233
2234 movable_node [KNL] Boot-time switch to enable the effects
2235 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2236
2237 MTD_Partition= [MTD]
2238 Format: <name>,<region-number>,<size>,<offset>
2239
2240 MTD_Region= [MTD] Format:
2241 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2242
2243 mtdparts= [MTD]
2244 See drivers/mtd/cmdlinepart.c.
2245
2246 multitce=off [PPC] This parameter disables the use of the pSeries
2247 firmware feature for updating multiple TCE entries
2248 at a time.
2249
2250 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2251
2252 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2253
2254 boundary - index of last SLC block on Flex-OneNAND.
2255 The remaining blocks are configured as MLC blocks.
2256 lock - Configure if Flex-OneNAND boundary should be locked.
2257 Once locked, the boundary cannot be changed.
2258 1 indicates lock status, 0 indicates unlock status.
2259
2260 mtdset= [ARM]
2261 ARM/S3C2412 JIVE boot control
2262
2263 See arch/arm/mach-s3c2412/mach-jive.c
2264
2265 mtouchusb.raw_coordinates=
2266 [HW] Make the MicroTouch USB driver use raw coordinates
2267 ('y', default) or cooked coordinates ('n')
2268
2269 mtrr_chunk_size=nn[KMG] [X86]
2270 used for mtrr cleanup. It is largest continuous chunk
2271 that could hold holes aka. UC entries.
2272
2273 mtrr_gran_size=nn[KMG] [X86]
2274 Used for mtrr cleanup. It is granularity of mtrr block.
2275 Default is 1.
2276 Large value could prevent small alignment from
2277 using up MTRRs.
2278
2279 mtrr_spare_reg_nr=n [X86]
2280 Format: <integer>
2281 Range: 0,7 : spare reg number
2282 Default : 1
2283 Used for mtrr cleanup. It is spare mtrr entries number.
2284 Set to 2 or more if your graphical card needs more.
2285
2286 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2287
2288 netdev= [NET] Network devices parameters
2289 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2290 Note that mem_start is often overloaded to mean
2291 something different and driver-specific.
2292 This usage is only documented in each driver source
2293 file if at all.
2294
2295 nf_conntrack.acct=
2296 [NETFILTER] Enable connection tracking flow accounting
2297 0 to disable accounting
2298 1 to enable accounting
2299 Default value is 0.
2300
2301 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2302 See Documentation/filesystems/nfs/nfsroot.txt.
2303
2304 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2305 See Documentation/filesystems/nfs/nfsroot.txt.
2306
2307 nfsrootdebug [NFS] enable nfsroot debugging messages.
2308 See Documentation/filesystems/nfs/nfsroot.txt.
2309
2310 nfs.callback_nr_threads=
2311 [NFSv4] set the total number of threads that the
2312 NFS client will assign to service NFSv4 callback
2313 requests.
2314
2315 nfs.callback_tcpport=
2316 [NFS] set the TCP port on which the NFSv4 callback
2317 channel should listen.
2318
2319 nfs.cache_getent=
2320 [NFS] sets the pathname to the program which is used
2321 to update the NFS client cache entries.
2322
2323 nfs.cache_getent_timeout=
2324 [NFS] sets the timeout after which an attempt to
2325 update a cache entry is deemed to have failed.
2326
2327 nfs.idmap_cache_timeout=
2328 [NFS] set the maximum lifetime for idmapper cache
2329 entries.
2330
2331 nfs.enable_ino64=
2332 [NFS] enable 64-bit inode numbers.
2333 If zero, the NFS client will fake up a 32-bit inode
2334 number for the readdir() and stat() syscalls instead
2335 of returning the full 64-bit number.
2336 The default is to return 64-bit inode numbers.
2337
2338 nfs.max_session_cb_slots=
2339 [NFSv4.1] Sets the maximum number of session
2340 slots the client will assign to the callback
2341 channel. This determines the maximum number of
2342 callbacks the client will process in parallel for
2343 a particular server.
2344
2345 nfs.max_session_slots=
2346 [NFSv4.1] Sets the maximum number of session slots
2347 the client will attempt to negotiate with the server.
2348 This limits the number of simultaneous RPC requests
2349 that the client can send to the NFSv4.1 server.
2350 Note that there is little point in setting this
2351 value higher than the max_tcp_slot_table_limit.
2352
2353 nfs.nfs4_disable_idmapping=
2354 [NFSv4] When set to the default of '1', this option
2355 ensures that both the RPC level authentication
2356 scheme and the NFS level operations agree to use
2357 numeric uids/gids if the mount is using the
2358 'sec=sys' security flavour. In effect it is
2359 disabling idmapping, which can make migration from
2360 legacy NFSv2/v3 systems to NFSv4 easier.
2361 Servers that do not support this mode of operation
2362 will be autodetected by the client, and it will fall
2363 back to using the idmapper.
2364 To turn off this behaviour, set the value to '0'.
2365 nfs.nfs4_unique_id=
2366 [NFS4] Specify an additional fixed unique ident-
2367 ification string that NFSv4 clients can insert into
2368 their nfs_client_id4 string. This is typically a
2369 UUID that is generated at system install time.
2370
2371 nfs.send_implementation_id =
2372 [NFSv4.1] Send client implementation identification
2373 information in exchange_id requests.
2374 If zero, no implementation identification information
2375 will be sent.
2376 The default is to send the implementation identification
2377 information.
2378
2379 nfs.recover_lost_locks =
2380 [NFSv4] Attempt to recover locks that were lost due
2381 to a lease timeout on the server. Please note that
2382 doing this risks data corruption, since there are
2383 no guarantees that the file will remain unchanged
2384 after the locks are lost.
2385 If you want to enable the kernel legacy behaviour of
2386 attempting to recover these locks, then set this
2387 parameter to '1'.
2388 The default parameter value of '0' causes the kernel
2389 not to attempt recovery of lost locks.
2390
2391 nfs4.layoutstats_timer =
2392 [NFSv4.2] Change the rate at which the kernel sends
2393 layoutstats to the pNFS metadata server.
2394
2395 Setting this to value to 0 causes the kernel to use
2396 whatever value is the default set by the layout
2397 driver. A non-zero value sets the minimum interval
2398 in seconds between layoutstats transmissions.
2399
2400 nfsd.nfs4_disable_idmapping=
2401 [NFSv4] When set to the default of '1', the NFSv4
2402 server will return only numeric uids and gids to
2403 clients using auth_sys, and will accept numeric uids
2404 and gids from such clients. This is intended to ease
2405 migration from NFSv2/v3.
2406
2407 objlayoutdriver.osd_login_prog=
2408 [NFS] [OBJLAYOUT] sets the pathname to the program which
2409 is used to automatically discover and login into new
2410 osd-targets. Please see:
2411 Documentation/filesystems/pnfs.txt for more explanations
2412
2413 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2414 when a NMI is triggered.
2415 Format: [state][,regs][,debounce][,die]
2416
2417 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2418 Format: [panic,][nopanic,][num]
2419 Valid num: 0 or 1
2420 0 - turn hardlockup detector in nmi_watchdog off
2421 1 - turn hardlockup detector in nmi_watchdog on
2422 When panic is specified, panic when an NMI watchdog
2423 timeout occurs (or 'nopanic' to override the opposite
2424 default). To disable both hard and soft lockup detectors,
2425 please see 'nowatchdog'.
2426 This is useful when you use a panic=... timeout and
2427 need the box quickly up again.
2428
2429 netpoll.carrier_timeout=
2430 [NET] Specifies amount of time (in seconds) that
2431 netpoll should wait for a carrier. By default netpoll
2432 waits 4 seconds.
2433
2434 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2435 emulation library even if a 387 maths coprocessor
2436 is present.
2437
2438 no_console_suspend
2439 [HW] Never suspend the console
2440 Disable suspending of consoles during suspend and
2441 hibernate operations. Once disabled, debugging
2442 messages can reach various consoles while the rest
2443 of the system is being put to sleep (ie, while
2444 debugging driver suspend/resume hooks). This may
2445 not work reliably with all consoles, but is known
2446 to work with serial and VGA consoles.
2447 To facilitate more flexible debugging, we also add
2448 console_suspend, a printk module parameter to control
2449 it. Users could use console_suspend (usually
2450 /sys/module/printk/parameters/console_suspend) to
2451 turn on/off it dynamically.
2452
2453 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2454 caches in the slab allocator. Saves per-node memory,
2455 but will impact performance.
2456
2457 noalign [KNL,ARM]
2458
2459 noapic [SMP,APIC] Tells the kernel to not make use of any
2460 IOAPICs that may be present in the system.
2461
2462 noautogroup Disable scheduler automatic task group creation.
2463
2464 nobats [PPC] Do not use BATs for mapping kernel lowmem
2465 on "Classic" PPC cores.
2466
2467 nocache [ARM]
2468
2469 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2470
2471 nodelayacct [KNL] Disable per-task delay accounting
2472
2473 nodsp [SH] Disable hardware DSP at boot time.
2474
2475 noefi Disable EFI runtime services support.
2476
2477 noexec [IA-64]
2478
2479 noexec [X86]
2480 On X86-32 available only on PAE configured kernels.
2481 noexec=on: enable non-executable mappings (default)
2482 noexec=off: disable non-executable mappings
2483
2484 nosmap [X86]
2485 Disable SMAP (Supervisor Mode Access Prevention)
2486 even if it is supported by processor.
2487
2488 nosmep [X86]
2489 Disable SMEP (Supervisor Mode Execution Prevention)
2490 even if it is supported by processor.
2491
2492 noexec32 [X86-64]
2493 This affects only 32-bit executables.
2494 noexec32=on: enable non-executable mappings (default)
2495 read doesn't imply executable mappings
2496 noexec32=off: disable non-executable mappings
2497 read implies executable mappings
2498
2499 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2500
2501 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2502 register save and restore. The kernel will only save
2503 legacy floating-point registers on task switch.
2504
2505 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2506
2507 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2508 Equivalent to smt=1.
2509
2510 noxsave [BUGS=X86] Disables x86 extended register state save
2511 and restore using xsave. The kernel will fallback to
2512 enabling legacy floating-point and sse state.
2513
2514 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2515 register states. The kernel will fall back to use
2516 xsave to save the states. By using this parameter,
2517 performance of saving the states is degraded because
2518 xsave doesn't support modified optimization while
2519 xsaveopt supports it on xsaveopt enabled systems.
2520
2521 noxsaves [X86] Disables xsaves and xrstors used in saving and
2522 restoring x86 extended register state in compacted
2523 form of xsave area. The kernel will fall back to use
2524 xsaveopt and xrstor to save and restore the states
2525 in standard form of xsave area. By using this
2526 parameter, xsave area per process might occupy more
2527 memory on xsaves enabled systems.
2528
2529 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2530 wfi(ARM) instruction doesn't work correctly and not to
2531 use it. This is also useful when using JTAG debugger.
2532
2533 no_file_caps Tells the kernel not to honor file capabilities. The
2534 only way then for a file to be executed with privilege
2535 is to be setuid root or executed by root.
2536
2537 nohalt [IA-64] Tells the kernel not to use the power saving
2538 function PAL_HALT_LIGHT when idle. This increases
2539 power-consumption. On the positive side, it reduces
2540 interrupt wake-up latency, which may improve performance
2541 in certain environments such as networked servers or
2542 real-time systems.
2543
2544 nohibernate [HIBERNATION] Disable hibernation and resume.
2545
2546 nohz= [KNL] Boottime enable/disable dynamic ticks
2547 Valid arguments: on, off
2548 Default: on
2549
2550 nohz_full= [KNL,BOOT]
2551 The argument is a cpu list, as described above.
2552 In kernels built with CONFIG_NO_HZ_FULL=y, set
2553 the specified list of CPUs whose tick will be stopped
2554 whenever possible. The boot CPU will be forced outside
2555 the range to maintain the timekeeping.
2556 The CPUs in this range must also be included in the
2557 rcu_nocbs= set.
2558
2559 noiotrap [SH] Disables trapped I/O port accesses.
2560
2561 noirqdebug [X86-32] Disables the code which attempts to detect and
2562 disable unhandled interrupt sources.
2563
2564 no_timer_check [X86,APIC] Disables the code which tests for
2565 broken timer IRQ sources.
2566
2567 noisapnp [ISAPNP] Disables ISA PnP code.
2568
2569 noinitrd [RAM] Tells the kernel not to load any configured
2570 initial RAM disk.
2571
2572 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2573 remapping.
2574 [Deprecated - use intremap=off]
2575
2576 nointroute [IA-64]
2577
2578 noinvpcid [X86] Disable the INVPCID cpu feature.
2579
2580 nojitter [IA-64] Disables jitter checking for ITC timers.
2581
2582 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2583
2584 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2585 fault handling.
2586
2587 no-vmw-sched-clock
2588 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2589 clock and use the default one.
2590
2591 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2592 steal time is computed, but won't influence scheduler
2593 behaviour
2594
2595 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2596
2597 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2598
2599 noltlbs [PPC] Do not use large page/tlb entries for kernel
2600 lowmem mapping on PPC40x and PPC8xx
2601
2602 nomca [IA-64] Disable machine check abort handling
2603
2604 nomce [X86-32] Disable Machine Check Exception
2605
2606 nomfgpt [X86-32] Disable Multi-Function General Purpose
2607 Timer usage (for AMD Geode machines).
2608
2609 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2610 shutdown the other cpus. Instead use the REBOOT_VECTOR
2611 irq.
2612
2613 nomodule Disable module load
2614
2615 nopat [X86] Disable PAT (page attribute table extension of
2616 pagetables) support.
2617
2618 norandmaps Don't use address space randomization. Equivalent to
2619 echo 0 > /proc/sys/kernel/randomize_va_space
2620
2621 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2622
2623 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2624 with UP alternatives
2625
2626 nordrand [X86] Disable kernel use of the RDRAND and
2627 RDSEED instructions even if they are supported
2628 by the processor. RDRAND and RDSEED are still
2629 available to user space applications.
2630
2631 noresume [SWSUSP] Disables resume and restores original swap
2632 space.
2633
2634 no-scroll [VGA] Disables scrollback.
2635 This is required for the Braillex ib80-piezo Braille
2636 reader made by F.H. Papenmeier (Germany).
2637
2638 nosbagart [IA-64]
2639
2640 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2641
2642 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2643 and disable the IO APIC. legacy for "maxcpus=0".
2644
2645 nosoftlockup [KNL] Disable the soft-lockup detector.
2646
2647 nosync [HW,M68K] Disables sync negotiation for all devices.
2648
2649 notsc [BUGS=X86-32] Disable Time Stamp Counter
2650
2651 nowatchdog [KNL] Disable both lockup detectors, i.e.
2652 soft-lockup and NMI watchdog (hard-lockup).
2653
2654 nowb [ARM]
2655
2656 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2657
2658 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2659 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2660 Some features depend on CPU0. Known dependencies are:
2661 1. Resume from suspend/hibernate depends on CPU0.
2662 Suspend/hibernate will fail if CPU0 is offline and you
2663 need to online CPU0 before suspend/hibernate.
2664 2. PIC interrupts also depend on CPU0. CPU0 can't be
2665 removed if a PIC interrupt is detected.
2666 It's said poweroff/reboot may depend on CPU0 on some
2667 machines although I haven't seen such issues so far
2668 after CPU0 is offline on a few tested machines.
2669 If the dependencies are under your control, you can
2670 turn on cpu0_hotplug.
2671
2672 nptcg= [IA-64] Override max number of concurrent global TLB
2673 purges which is reported from either PAL_VM_SUMMARY or
2674 SAL PALO.
2675
2676 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2677 could support. nr_cpus=n : n >= 1 limits the kernel to
2678 support 'n' processors. It could be larger than the
2679 number of already plugged CPU during bootup, later in
2680 runtime you can physically add extra cpu until it reaches
2681 n. So during boot up some boot time memory for per-cpu
2682 variables need be pre-allocated for later physical cpu
2683 hot plugging.
2684
2685 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2686
2687 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2688 Allowed values are enable and disable
2689
2690 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2691 one of ['zone', 'node', 'default'] can be specified
2692 This can be set from sysctl after boot.
2693 See Documentation/sysctl/vm.txt for details.
2694
2695 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2696 See Documentation/debugging-via-ohci1394.txt for more
2697 info.
2698
2699 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2700 Rather than timing out after 20 ms if an EC
2701 command is not properly ACKed, override the length
2702 of the timeout. We have interrupts disabled while
2703 waiting for the ACK, so if this is set too high
2704 interrupts *may* be lost!
2705
2706 omap_mux= [OMAP] Override bootloader pin multiplexing.
2707 Format: <mux_mode0.mode_name=value>...
2708 For example, to override I2C bus2:
2709 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2710
2711 oprofile.timer= [HW]
2712 Use timer interrupt instead of performance counters
2713
2714 oprofile.cpu_type= Force an oprofile cpu type
2715 This might be useful if you have an older oprofile
2716 userland or if you want common events.
2717 Format: { arch_perfmon }
2718 arch_perfmon: [X86] Force use of architectural
2719 perfmon on Intel CPUs instead of the
2720 CPU specific event set.
2721 timer: [X86] Force use of architectural NMI
2722 timer mode (see also oprofile.timer
2723 for generic hr timer mode)
2724
2725 oops=panic Always panic on oopses. Default is to just kill the
2726 process, but there is a small probability of
2727 deadlocking the machine.
2728 This will also cause panics on machine check exceptions.
2729 Useful together with panic=30 to trigger a reboot.
2730
2731 OSS [HW,OSS]
2732 See Documentation/sound/oss/oss-parameters.txt
2733
2734 page_owner= [KNL] Boot-time page_owner enabling option.
2735 Storage of the information about who allocated
2736 each page is disabled in default. With this switch,
2737 we can turn it on.
2738 on: enable the feature
2739
2740 page_poison= [KNL] Boot-time parameter changing the state of
2741 poisoning on the buddy allocator.
2742 off: turn off poisoning
2743 on: turn on poisoning
2744
2745 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2746 timeout > 0: seconds before rebooting
2747 timeout = 0: wait forever
2748 timeout < 0: reboot immediately
2749 Format: <timeout>
2750
2751 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2752 on a WARN().
2753
2754 crash_kexec_post_notifiers
2755 Run kdump after running panic-notifiers and dumping
2756 kmsg. This only for the users who doubt kdump always
2757 succeeds in any situation.
2758 Note that this also increases risks of kdump failure,
2759 because some panic notifiers can make the crashed
2760 kernel more unstable.
2761
2762 parkbd.port= [HW] Parallel port number the keyboard adapter is
2763 connected to, default is 0.
2764 Format: <parport#>
2765 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2766 0 for XT, 1 for AT (default is AT).
2767 Format: <mode>
2768
2769 parport= [HW,PPT] Specify parallel ports. 0 disables.
2770 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2771 Use 'auto' to force the driver to use any
2772 IRQ/DMA settings detected (the default is to
2773 ignore detected IRQ/DMA settings because of
2774 possible conflicts). You can specify the base
2775 address, IRQ, and DMA settings; IRQ and DMA
2776 should be numbers, or 'auto' (for using detected
2777 settings on that particular port), or 'nofifo'
2778 (to avoid using a FIFO even if it is detected).
2779 Parallel ports are assigned in the order they
2780 are specified on the command line, starting
2781 with parport0.
2782
2783 parport_init_mode= [HW,PPT]
2784 Configure VIA parallel port to operate in
2785 a specific mode. This is necessary on Pegasos
2786 computer where firmware has no options for setting
2787 up parallel port mode and sets it to spp.
2788 Currently this function knows 686a and 8231 chips.
2789 Format: [spp|ps2|epp|ecp|ecpepp]
2790
2791 pause_on_oops=
2792 Halt all CPUs after the first oops has been printed for
2793 the specified number of seconds. This is to be used if
2794 your oopses keep scrolling off the screen.
2795
2796 pcbit= [HW,ISDN]
2797
2798 pcd. [PARIDE]
2799 See header of drivers/block/paride/pcd.c.
2800 See also Documentation/blockdev/paride.txt.
2801
2802 pci=option[,option...] [PCI] various PCI subsystem options:
2803 earlydump [X86] dump PCI config space before the kernel
2804 changes anything
2805 off [X86] don't probe for the PCI bus
2806 bios [X86-32] force use of PCI BIOS, don't access
2807 the hardware directly. Use this if your machine
2808 has a non-standard PCI host bridge.
2809 nobios [X86-32] disallow use of PCI BIOS, only direct
2810 hardware access methods are allowed. Use this
2811 if you experience crashes upon bootup and you
2812 suspect they are caused by the BIOS.
2813 conf1 [X86] Force use of PCI Configuration Access
2814 Mechanism 1 (config address in IO port 0xCF8,
2815 data in IO port 0xCFC, both 32-bit).
2816 conf2 [X86] Force use of PCI Configuration Access
2817 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2818 the function, IO port 0xCFA, also 8-bit, sets
2819 bus number. The config space is then accessed
2820 through ports 0xC000-0xCFFF).
2821 See http://wiki.osdev.org/PCI for more info
2822 on the configuration access mechanisms.
2823 noaer [PCIE] If the PCIEAER kernel config parameter is
2824 enabled, this kernel boot option can be used to
2825 disable the use of PCIE advanced error reporting.
2826 nodomains [PCI] Disable support for multiple PCI
2827 root domains (aka PCI segments, in ACPI-speak).
2828 nommconf [X86] Disable use of MMCONFIG for PCI
2829 Configuration
2830 check_enable_amd_mmconf [X86] check for and enable
2831 properly configured MMIO access to PCI
2832 config space on AMD family 10h CPU
2833 nomsi [MSI] If the PCI_MSI kernel config parameter is
2834 enabled, this kernel boot option can be used to
2835 disable the use of MSI interrupts system-wide.
2836 noioapicquirk [APIC] Disable all boot interrupt quirks.
2837 Safety option to keep boot IRQs enabled. This
2838 should never be necessary.
2839 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2840 primary IO-APIC for bridges that cannot disable
2841 boot IRQs. This fixes a source of spurious IRQs
2842 when the system masks IRQs.
2843 noioapicreroute [APIC] Disable workaround that uses the
2844 boot IRQ equivalent of an IRQ that connects to
2845 a chipset where boot IRQs cannot be disabled.
2846 The opposite of ioapicreroute.
2847 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2848 routing table. These calls are known to be buggy
2849 on several machines and they hang the machine
2850 when used, but on other computers it's the only
2851 way to get the interrupt routing table. Try
2852 this option if the kernel is unable to allocate
2853 IRQs or discover secondary PCI buses on your
2854 motherboard.
2855 rom [X86] Assign address space to expansion ROMs.
2856 Use with caution as certain devices share
2857 address decoders between ROMs and other
2858 resources.
2859 norom [X86] Do not assign address space to
2860 expansion ROMs that do not already have
2861 BIOS assigned address ranges.
2862 nobar [X86] Do not assign address space to the
2863 BARs that weren't assigned by the BIOS.
2864 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2865 assigned automatically to PCI devices. You can
2866 make the kernel exclude IRQs of your ISA cards
2867 this way.
2868 pirqaddr=0xAAAAA [X86] Specify the physical address
2869 of the PIRQ table (normally generated
2870 by the BIOS) if it is outside the
2871 F0000h-100000h range.
2872 lastbus=N [X86] Scan all buses thru bus #N. Can be
2873 useful if the kernel is unable to find your
2874 secondary buses and you want to tell it
2875 explicitly which ones they are.
2876 assign-busses [X86] Always assign all PCI bus
2877 numbers ourselves, overriding
2878 whatever the firmware may have done.
2879 usepirqmask [X86] Honor the possible IRQ mask stored
2880 in the BIOS $PIR table. This is needed on
2881 some systems with broken BIOSes, notably
2882 some HP Pavilion N5400 and Omnibook XE3
2883 notebooks. This will have no effect if ACPI
2884 IRQ routing is enabled.
2885 noacpi [X86] Do not use ACPI for IRQ routing
2886 or for PCI scanning.
2887 use_crs [X86] Use PCI host bridge window information
2888 from ACPI. On BIOSes from 2008 or later, this
2889 is enabled by default. If you need to use this,
2890 please report a bug.
2891 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2892 If you need to use this, please report a bug.
2893 routeirq Do IRQ routing for all PCI devices.
2894 This is normally done in pci_enable_device(),
2895 so this option is a temporary workaround
2896 for broken drivers that don't call it.
2897 skip_isa_align [X86] do not align io start addr, so can
2898 handle more pci cards
2899 noearly [X86] Don't do any early type 1 scanning.
2900 This might help on some broken boards which
2901 machine check when some devices' config space
2902 is read. But various workarounds are disabled
2903 and some IOMMU drivers will not work.
2904 bfsort Sort PCI devices into breadth-first order.
2905 This sorting is done to get a device
2906 order compatible with older (<= 2.4) kernels.
2907 nobfsort Don't sort PCI devices into breadth-first order.
2908 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2909 tuning and use the BIOS-configured MPS defaults.
2910 pcie_bus_safe Set every device's MPS to the largest value
2911 supported by all devices below the root complex.
2912 pcie_bus_perf Set device MPS to the largest allowable MPS
2913 based on its parent bus. Also set MRRS (Max
2914 Read Request Size) to the largest supported
2915 value (no larger than the MPS that the device
2916 or bus can support) for best performance.
2917 pcie_bus_peer2peer Set every device's MPS to 128B, which
2918 every device is guaranteed to support. This
2919 configuration allows peer-to-peer DMA between
2920 any pair of devices, possibly at the cost of
2921 reduced performance. This also guarantees
2922 that hot-added devices will work.
2923 cbiosize=nn[KMG] The fixed amount of bus space which is
2924 reserved for the CardBus bridge's IO window.
2925 The default value is 256 bytes.
2926 cbmemsize=nn[KMG] The fixed amount of bus space which is
2927 reserved for the CardBus bridge's memory
2928 window. The default value is 64 megabytes.
2929 resource_alignment=
2930 Format:
2931 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2932 [<order of align>@]pci:<vendor>:<device>\
2933 [:<subvendor>:<subdevice>][; ...]
2934 Specifies alignment and device to reassign
2935 aligned memory resources.
2936 If <order of align> is not specified,
2937 PAGE_SIZE is used as alignment.
2938 PCI-PCI bridge can be specified, if resource
2939 windows need to be expanded.
2940 To specify the alignment for several
2941 instances of a device, the PCI vendor,
2942 device, subvendor, and subdevice may be
2943 specified, e.g., 4096@pci:8086:9c22:103c:198f
2944 ecrc= Enable/disable PCIe ECRC (transaction layer
2945 end-to-end CRC checking).
2946 bios: Use BIOS/firmware settings. This is the
2947 the default.
2948 off: Turn ECRC off
2949 on: Turn ECRC on.
2950 hpiosize=nn[KMG] The fixed amount of bus space which is
2951 reserved for hotplug bridge's IO window.
2952 Default size is 256 bytes.
2953 hpmemsize=nn[KMG] The fixed amount of bus space which is
2954 reserved for hotplug bridge's memory window.
2955 Default size is 2 megabytes.
2956 hpbussize=nn The minimum amount of additional bus numbers
2957 reserved for buses below a hotplug bridge.
2958 Default is 1.
2959 realloc= Enable/disable reallocating PCI bridge resources
2960 if allocations done by BIOS are too small to
2961 accommodate resources required by all child
2962 devices.
2963 off: Turn realloc off
2964 on: Turn realloc on
2965 realloc same as realloc=on
2966 noari do not use PCIe ARI.
2967 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2968 only look for one device below a PCIe downstream
2969 port.
2970
2971 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2972 Management.
2973 off Disable ASPM.
2974 force Enable ASPM even on devices that claim not to support it.
2975 WARNING: Forcing ASPM on may cause system lockups.
2976
2977 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2978 nomsi Do not use MSI for PCI Express Native Hotplug (this
2979 makes all PCIe ports use INTx for hotplug services).
2980
2981 pcie_ports= [PCIE] PCIe ports handling:
2982 auto Ask the BIOS whether or not to use native PCIe services
2983 associated with PCIe ports (PME, hot-plug, AER). Use
2984 them only if that is allowed by the BIOS.
2985 native Use native PCIe services associated with PCIe ports
2986 unconditionally.
2987 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2988 ports driver.
2989
2990 pcie_port_pm= [PCIE] PCIe port power management handling:
2991 off Disable power management of all PCIe ports
2992 force Forcibly enable power management of all PCIe ports
2993
2994 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2995 nomsi Do not use MSI for native PCIe PME signaling (this makes
2996 all PCIe root ports use INTx for all services).
2997
2998 pcmv= [HW,PCMCIA] BadgePAD 4
2999
3000 pd_ignore_unused
3001 [PM]
3002 Keep all power-domains already enabled by bootloader on,
3003 even if no driver has claimed them. This is useful
3004 for debug and development, but should not be
3005 needed on a platform with proper driver support.
3006
3007 pd. [PARIDE]
3008 See Documentation/blockdev/paride.txt.
3009
3010 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3011 boot time.
3012 Format: { 0 | 1 }
3013 See arch/parisc/kernel/pdc_chassis.c
3014
3015 percpu_alloc= Select which percpu first chunk allocator to use.
3016 Currently supported values are "embed" and "page".
3017 Archs may support subset or none of the selections.
3018 See comments in mm/percpu.c for details on each
3019 allocator. This parameter is primarily for debugging
3020 and performance comparison.
3021
3022 pf. [PARIDE]
3023 See Documentation/blockdev/paride.txt.
3024
3025 pg. [PARIDE]
3026 See Documentation/blockdev/paride.txt.
3027
3028 pirq= [SMP,APIC] Manual mp-table setup
3029 See Documentation/x86/i386/IO-APIC.txt.
3030
3031 plip= [PPT,NET] Parallel port network link
3032 Format: { parport<nr> | timid | 0 }
3033 See also Documentation/parport.txt.
3034
3035 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3036 Override pmtimer IOPort with a hex value.
3037 e.g. pmtmr=0x508
3038
3039 pnp.debug=1 [PNP]
3040 Enable PNP debug messages (depends on the
3041 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3042 via /sys/module/pnp/parameters/debug. We always show
3043 current resource usage; turning this on also shows
3044 possible settings and some assignment information.
3045
3046 pnpacpi= [ACPI]
3047 { off }
3048
3049 pnpbios= [ISAPNP]
3050 { on | off | curr | res | no-curr | no-res }
3051
3052 pnp_reserve_irq=
3053 [ISAPNP] Exclude IRQs for the autoconfiguration
3054
3055 pnp_reserve_dma=
3056 [ISAPNP] Exclude DMAs for the autoconfiguration
3057
3058 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3059 Ranges are in pairs (I/O port base and size).
3060
3061 pnp_reserve_mem=
3062 [ISAPNP] Exclude memory regions for the
3063 autoconfiguration.
3064 Ranges are in pairs (memory base and size).
3065
3066 ports= [IP_VS_FTP] IPVS ftp helper module
3067 Default is 21.
3068 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3069 may be specified.
3070 Format: <port>,<port>....
3071
3072 powersave=off [PPC] This option disables power saving features.
3073 It specifically disables cpuidle and sets the
3074 platform machine description specific power_save
3075 function to NULL. On Idle the CPU just reduces
3076 execution priority.
3077
3078 ppc_strict_facility_enable
3079 [PPC] This option catches any kernel floating point,
3080 Altivec, VSX and SPE outside of regions specifically
3081 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3082 There is some performance impact when enabling this.
3083
3084 print-fatal-signals=
3085 [KNL] debug: print fatal signals
3086
3087 If enabled, warn about various signal handling
3088 related application anomalies: too many signals,
3089 too many POSIX.1 timers, fatal signals causing a
3090 coredump - etc.
3091
3092 If you hit the warning due to signal overflow,
3093 you might want to try "ulimit -i unlimited".
3094
3095 default: off.
3096
3097 printk.always_kmsg_dump=
3098 Trigger kmsg_dump for cases other than kernel oops or
3099 panics
3100 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3101 default: disabled
3102
3103 printk.devkmsg={on,off,ratelimit}
3104 Control writing to /dev/kmsg.
3105 on - unlimited logging to /dev/kmsg from userspace
3106 off - logging to /dev/kmsg disabled
3107 ratelimit - ratelimit the logging
3108 Default: ratelimit
3109
3110 printk.time= Show timing data prefixed to each printk message line
3111 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3112
3113 processor.max_cstate= [HW,ACPI]
3114 Limit processor to maximum C-state
3115 max_cstate=9 overrides any DMI blacklist limit.
3116
3117 processor.nocst [HW,ACPI]
3118 Ignore the _CST method to determine C-states,
3119 instead using the legacy FADT method
3120
3121 profile= [KNL] Enable kernel profiling via /proc/profile
3122 Format: [schedule,]<number>
3123 Param: "schedule" - profile schedule points.
3124 Param: <number> - step/bucket size as a power of 2 for
3125 statistical time based profiling.
3126 Param: "sleep" - profile D-state sleeping (millisecs).
3127 Requires CONFIG_SCHEDSTATS
3128 Param: "kvm" - profile VM exits.
3129
3130 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3131 before loading.
3132 See Documentation/blockdev/ramdisk.txt.
3133
3134 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3135 probe for; one of (bare|imps|exps|lifebook|any).
3136 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3137 per second.
3138 psmouse.resetafter= [HW,MOUSE]
3139 Try to reset the device after so many bad packets
3140 (0 = never).
3141 psmouse.resolution=
3142 [HW,MOUSE] Set desired mouse resolution, in dpi.
3143 psmouse.smartscroll=
3144 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3145 0 = disabled, 1 = enabled (default).
3146
3147 pstore.backend= Specify the name of the pstore backend to use
3148
3149 pt. [PARIDE]
3150 See Documentation/blockdev/paride.txt.
3151
3152 pty.legacy_count=
3153 [KNL] Number of legacy pty's. Overwrites compiled-in
3154 default number.
3155
3156 quiet [KNL] Disable most log messages
3157
3158 r128= [HW,DRM]
3159
3160 raid= [HW,RAID]
3161 See Documentation/admin-guide/md.rst.
3162
3163 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3164 See Documentation/blockdev/ramdisk.txt.
3165
3166 rcu_nocbs= [KNL]
3167 The argument is a cpu list, as described above.
3168
3169 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3170 the specified list of CPUs to be no-callback CPUs.
3171 Invocation of these CPUs' RCU callbacks will
3172 be offloaded to "rcuox/N" kthreads created for
3173 that purpose, where "x" is "b" for RCU-bh, "p"
3174 for RCU-preempt, and "s" for RCU-sched, and "N"
3175 is the CPU number. This reduces OS jitter on the
3176 offloaded CPUs, which can be useful for HPC and
3177 real-time workloads. It can also improve energy
3178 efficiency for asymmetric multiprocessors.
3179
3180 rcu_nocb_poll [KNL]
3181 Rather than requiring that offloaded CPUs
3182 (specified by rcu_nocbs= above) explicitly
3183 awaken the corresponding "rcuoN" kthreads,
3184 make these kthreads poll for callbacks.
3185 This improves the real-time response for the
3186 offloaded CPUs by relieving them of the need to
3187 wake up the corresponding kthread, but degrades
3188 energy efficiency by requiring that the kthreads
3189 periodically wake up to do the polling.
3190
3191 rcutree.blimit= [KNL]
3192 Set maximum number of finished RCU callbacks to
3193 process in one batch.
3194
3195 rcutree.dump_tree= [KNL]
3196 Dump the structure of the rcu_node combining tree
3197 out at early boot. This is used for diagnostic
3198 purposes, to verify correct tree setup.
3199
3200 rcutree.gp_cleanup_delay= [KNL]
3201 Set the number of jiffies to delay each step of
3202 RCU grace-period cleanup. This only has effect
3203 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3204
3205 rcutree.gp_init_delay= [KNL]
3206 Set the number of jiffies to delay each step of
3207 RCU grace-period initialization. This only has
3208 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3209 is set.
3210
3211 rcutree.gp_preinit_delay= [KNL]
3212 Set the number of jiffies to delay each step of
3213 RCU grace-period pre-initialization, that is,
3214 the propagation of recent CPU-hotplug changes up
3215 the rcu_node combining tree. This only has effect
3216 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3217
3218 rcutree.rcu_fanout_exact= [KNL]
3219 Disable autobalancing of the rcu_node combining
3220 tree. This is used by rcutorture, and might
3221 possibly be useful for architectures having high
3222 cache-to-cache transfer latencies.
3223
3224 rcutree.rcu_fanout_leaf= [KNL]
3225 Change the number of CPUs assigned to each
3226 leaf rcu_node structure. Useful for very
3227 large systems, which will choose the value 64,
3228 and for NUMA systems with large remote-access
3229 latencies, which will choose a value aligned
3230 with the appropriate hardware boundaries.
3231
3232 rcutree.jiffies_till_sched_qs= [KNL]
3233 Set required age in jiffies for a
3234 given grace period before RCU starts
3235 soliciting quiescent-state help from
3236 rcu_note_context_switch().
3237
3238 rcutree.jiffies_till_first_fqs= [KNL]
3239 Set delay from grace-period initialization to
3240 first attempt to force quiescent states.
3241 Units are jiffies, minimum value is zero,
3242 and maximum value is HZ.
3243
3244 rcutree.jiffies_till_next_fqs= [KNL]
3245 Set delay between subsequent attempts to force
3246 quiescent states. Units are jiffies, minimum
3247 value is one, and maximum value is HZ.
3248
3249 rcutree.kthread_prio= [KNL,BOOT]
3250 Set the SCHED_FIFO priority of the RCU per-CPU
3251 kthreads (rcuc/N). This value is also used for
3252 the priority of the RCU boost threads (rcub/N)
3253 and for the RCU grace-period kthreads (rcu_bh,
3254 rcu_preempt, and rcu_sched). If RCU_BOOST is
3255 set, valid values are 1-99 and the default is 1
3256 (the least-favored priority). Otherwise, when
3257 RCU_BOOST is not set, valid values are 0-99 and
3258 the default is zero (non-realtime operation).
3259
3260 rcutree.rcu_nocb_leader_stride= [KNL]
3261 Set the number of NOCB kthread groups, which
3262 defaults to the square root of the number of
3263 CPUs. Larger numbers reduces the wakeup overhead
3264 on the per-CPU grace-period kthreads, but increases
3265 that same overhead on each group's leader.
3266
3267 rcutree.qhimark= [KNL]
3268 Set threshold of queued RCU callbacks beyond which
3269 batch limiting is disabled.
3270
3271 rcutree.qlowmark= [KNL]
3272 Set threshold of queued RCU callbacks below which
3273 batch limiting is re-enabled.
3274
3275 rcutree.rcu_idle_gp_delay= [KNL]
3276 Set wakeup interval for idle CPUs that have
3277 RCU callbacks (RCU_FAST_NO_HZ=y).
3278
3279 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3280 Set wakeup interval for idle CPUs that have
3281 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3282 Lazy RCU callbacks are those which RCU can
3283 prove do nothing more than free memory.
3284
3285 rcuperf.gp_exp= [KNL]
3286 Measure performance of expedited synchronous
3287 grace-period primitives.
3288
3289 rcuperf.holdoff= [KNL]
3290 Set test-start holdoff period. The purpose of
3291 this parameter is to delay the start of the
3292 test until boot completes in order to avoid
3293 interference.
3294
3295 rcuperf.nreaders= [KNL]
3296 Set number of RCU readers. The value -1 selects
3297 N, where N is the number of CPUs. A value
3298 "n" less than -1 selects N-n+1, where N is again
3299 the number of CPUs. For example, -2 selects N
3300 (the number of CPUs), -3 selects N+1, and so on.
3301 A value of "n" less than or equal to -N selects
3302 a single reader.
3303
3304 rcuperf.nwriters= [KNL]
3305 Set number of RCU writers. The values operate
3306 the same as for rcuperf.nreaders.
3307 N, where N is the number of CPUs
3308
3309 rcuperf.perf_runnable= [BOOT]
3310 Start rcuperf running at boot time.
3311
3312 rcuperf.shutdown= [KNL]
3313 Shut the system down after performance tests
3314 complete. This is useful for hands-off automated
3315 testing.
3316
3317 rcuperf.perf_type= [KNL]
3318 Specify the RCU implementation to test.
3319
3320 rcuperf.verbose= [KNL]
3321 Enable additional printk() statements.
3322
3323 rcutorture.cbflood_inter_holdoff= [KNL]
3324 Set holdoff time (jiffies) between successive
3325 callback-flood tests.
3326
3327 rcutorture.cbflood_intra_holdoff= [KNL]
3328 Set holdoff time (jiffies) between successive
3329 bursts of callbacks within a given callback-flood
3330 test.
3331
3332 rcutorture.cbflood_n_burst= [KNL]
3333 Set the number of bursts making up a given
3334 callback-flood test. Set this to zero to
3335 disable callback-flood testing.
3336
3337 rcutorture.cbflood_n_per_burst= [KNL]
3338 Set the number of callbacks to be registered
3339 in a given burst of a callback-flood test.
3340
3341 rcutorture.fqs_duration= [KNL]
3342 Set duration of force_quiescent_state bursts
3343 in microseconds.
3344
3345 rcutorture.fqs_holdoff= [KNL]
3346 Set holdoff time within force_quiescent_state bursts
3347 in microseconds.
3348
3349 rcutorture.fqs_stutter= [KNL]
3350 Set wait time between force_quiescent_state bursts
3351 in seconds.
3352
3353 rcutorture.gp_cond= [KNL]
3354 Use conditional/asynchronous update-side
3355 primitives, if available.
3356
3357 rcutorture.gp_exp= [KNL]
3358 Use expedited update-side primitives, if available.
3359
3360 rcutorture.gp_normal= [KNL]
3361 Use normal (non-expedited) asynchronous
3362 update-side primitives, if available.
3363
3364 rcutorture.gp_sync= [KNL]
3365 Use normal (non-expedited) synchronous
3366 update-side primitives, if available. If all
3367 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3368 rcutorture.gp_normal=, and rcutorture.gp_sync=
3369 are zero, rcutorture acts as if is interpreted
3370 they are all non-zero.
3371
3372 rcutorture.n_barrier_cbs= [KNL]
3373 Set callbacks/threads for rcu_barrier() testing.
3374
3375 rcutorture.nfakewriters= [KNL]
3376 Set number of concurrent RCU writers. These just
3377 stress RCU, they don't participate in the actual
3378 test, hence the "fake".
3379
3380 rcutorture.nreaders= [KNL]
3381 Set number of RCU readers. The value -1 selects
3382 N-1, where N is the number of CPUs. A value
3383 "n" less than -1 selects N-n-2, where N is again
3384 the number of CPUs. For example, -2 selects N
3385 (the number of CPUs), -3 selects N+1, and so on.
3386
3387 rcutorture.object_debug= [KNL]
3388 Enable debug-object double-call_rcu() testing.
3389
3390 rcutorture.onoff_holdoff= [KNL]
3391 Set time (s) after boot for CPU-hotplug testing.
3392
3393 rcutorture.onoff_interval= [KNL]
3394 Set time (s) between CPU-hotplug operations, or
3395 zero to disable CPU-hotplug testing.
3396
3397 rcutorture.shuffle_interval= [KNL]
3398 Set task-shuffle interval (s). Shuffling tasks
3399 allows some CPUs to go into dyntick-idle mode
3400 during the rcutorture test.
3401
3402 rcutorture.shutdown_secs= [KNL]
3403 Set time (s) after boot system shutdown. This
3404 is useful for hands-off automated testing.
3405
3406 rcutorture.stall_cpu= [KNL]
3407 Duration of CPU stall (s) to test RCU CPU stall
3408 warnings, zero to disable.
3409
3410 rcutorture.stall_cpu_holdoff= [KNL]
3411 Time to wait (s) after boot before inducing stall.
3412
3413 rcutorture.stat_interval= [KNL]
3414 Time (s) between statistics printk()s.
3415
3416 rcutorture.stutter= [KNL]
3417 Time (s) to stutter testing, for example, specifying
3418 five seconds causes the test to run for five seconds,
3419 wait for five seconds, and so on. This tests RCU's
3420 ability to transition abruptly to and from idle.
3421
3422 rcutorture.test_boost= [KNL]
3423 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3424 "Maybe" means test if the RCU implementation
3425 under test support RCU priority boosting.
3426
3427 rcutorture.test_boost_duration= [KNL]
3428 Duration (s) of each individual boost test.
3429
3430 rcutorture.test_boost_interval= [KNL]
3431 Interval (s) between each boost test.
3432
3433 rcutorture.test_no_idle_hz= [KNL]
3434 Test RCU's dyntick-idle handling. See also the
3435 rcutorture.shuffle_interval parameter.
3436
3437 rcutorture.torture_runnable= [BOOT]
3438 Start rcutorture running at boot time.
3439
3440 rcutorture.torture_type= [KNL]
3441 Specify the RCU implementation to test.
3442
3443 rcutorture.verbose= [KNL]
3444 Enable additional printk() statements.
3445
3446 rcupdate.rcu_cpu_stall_suppress= [KNL]
3447 Suppress RCU CPU stall warning messages.
3448
3449 rcupdate.rcu_cpu_stall_timeout= [KNL]
3450 Set timeout for RCU CPU stall warning messages.
3451
3452 rcupdate.rcu_expedited= [KNL]
3453 Use expedited grace-period primitives, for
3454 example, synchronize_rcu_expedited() instead
3455 of synchronize_rcu(). This reduces latency,
3456 but can increase CPU utilization, degrade
3457 real-time latency, and degrade energy efficiency.
3458 No effect on CONFIG_TINY_RCU kernels.
3459
3460 rcupdate.rcu_normal= [KNL]
3461 Use only normal grace-period primitives,
3462 for example, synchronize_rcu() instead of
3463 synchronize_rcu_expedited(). This improves
3464 real-time latency, CPU utilization, and
3465 energy efficiency, but can expose users to
3466 increased grace-period latency. This parameter
3467 overrides rcupdate.rcu_expedited. No effect on
3468 CONFIG_TINY_RCU kernels.
3469
3470 rcupdate.rcu_normal_after_boot= [KNL]
3471 Once boot has completed (that is, after
3472 rcu_end_inkernel_boot() has been invoked), use
3473 only normal grace-period primitives. No effect
3474 on CONFIG_TINY_RCU kernels.
3475
3476 rcupdate.rcu_task_stall_timeout= [KNL]
3477 Set timeout in jiffies for RCU task stall warning
3478 messages. Disable with a value less than or equal
3479 to zero.
3480
3481 rcupdate.rcu_self_test= [KNL]
3482 Run the RCU early boot self tests
3483
3484 rcupdate.rcu_self_test_bh= [KNL]
3485 Run the RCU bh early boot self tests
3486
3487 rcupdate.rcu_self_test_sched= [KNL]
3488 Run the RCU sched early boot self tests
3489
3490 rdinit= [KNL]
3491 Format: <full_path>
3492 Run specified binary instead of /init from the ramdisk,
3493 used for early userspace startup. See initrd.
3494
3495 reboot= [KNL]
3496 Format (x86 or x86_64):
3497 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3498 [[,]s[mp]#### \
3499 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3500 [[,]f[orce]
3501 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3502 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3503 reboot_force is either force or not specified,
3504 reboot_cpu is s[mp]#### with #### being the processor
3505 to be used for rebooting.
3506
3507 relax_domain_level=
3508 [KNL, SMP] Set scheduler's default relax_domain_level.
3509 See Documentation/cgroup-v1/cpusets.txt.
3510
3511 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3512
3513 reservetop= [X86-32]
3514 Format: nn[KMG]
3515 Reserves a hole at the top of the kernel virtual
3516 address space.
3517
3518 reservelow= [X86]
3519 Format: nn[K]
3520 Set the amount of memory to reserve for BIOS at
3521 the bottom of the address space.
3522
3523 reset_devices [KNL] Force drivers to reset the underlying device
3524 during initialization.
3525
3526 resume= [SWSUSP]
3527 Specify the partition device for software suspend
3528 Format:
3529 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3530
3531 resume_offset= [SWSUSP]
3532 Specify the offset from the beginning of the partition
3533 given by "resume=" at which the swap header is located,
3534 in <PAGE_SIZE> units (needed only for swap files).
3535 See Documentation/power/swsusp-and-swap-files.txt
3536
3537 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3538 read the resume files
3539
3540 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3541 Useful for devices that are detected asynchronously
3542 (e.g. USB and MMC devices).
3543
3544 hibernate= [HIBERNATION]
3545 noresume Don't check if there's a hibernation image
3546 present during boot.
3547 nocompress Don't compress/decompress hibernation images.
3548 no Disable hibernation and resume.
3549 protect_image Turn on image protection during restoration
3550 (that will set all pages holding image data
3551 during restoration read-only).
3552
3553 retain_initrd [RAM] Keep initrd memory after extraction
3554
3555 rfkill.default_state=
3556 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3557 etc. communication is blocked by default.
3558 1 Unblocked.
3559
3560 rfkill.master_switch_mode=
3561 0 The "airplane mode" button does nothing.
3562 1 The "airplane mode" button toggles between everything
3563 blocked and the previous configuration.
3564 2 The "airplane mode" button toggles between everything
3565 blocked and everything unblocked.
3566
3567 rhash_entries= [KNL,NET]
3568 Set number of hash buckets for route cache
3569
3570 ro [KNL] Mount root device read-only on boot
3571
3572 rodata= [KNL]
3573 on Mark read-only kernel memory as read-only (default).
3574 off Leave read-only kernel memory writable for debugging.
3575
3576 rockchip.usb_uart
3577 Enable the uart passthrough on the designated usb port
3578 on Rockchip SoCs. When active, the signals of the
3579 debug-uart get routed to the D+ and D- pins of the usb
3580 port and the regular usb controller gets disabled.
3581
3582 root= [KNL] Root filesystem
3583 See name_to_dev_t comment in init/do_mounts.c.
3584
3585 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3586 mount the root filesystem
3587
3588 rootflags= [KNL] Set root filesystem mount option string
3589
3590 rootfstype= [KNL] Set root filesystem type
3591
3592 rootwait [KNL] Wait (indefinitely) for root device to show up.
3593 Useful for devices that are detected asynchronously
3594 (e.g. USB and MMC devices).
3595
3596 rproc_mem=nn[KMG][@address]
3597 [KNL,ARM,CMA] Remoteproc physical memory block.
3598 Memory area to be used by remote processor image,
3599 managed by CMA.
3600
3601 rw [KNL] Mount root device read-write on boot
3602
3603 S [KNL] Run init in single mode
3604
3605 s390_iommu= [HW,S390]
3606 Set s390 IOTLB flushing mode
3607 strict
3608 With strict flushing every unmap operation will result in
3609 an IOTLB flush. Default is lazy flushing before reuse,
3610 which is faster.
3611
3612 sa1100ir [NET]
3613 See drivers/net/irda/sa1100_ir.c.
3614
3615 sbni= [NET] Granch SBNI12 leased line adapter
3616
3617 sched_debug [KNL] Enables verbose scheduler debug messages.
3618
3619 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3620 Allowed values are enable and disable. This feature
3621 incurs a small amount of overhead in the scheduler
3622 but is useful for debugging and performance tuning.
3623
3624 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3625 xtime_lock contention on larger systems, and/or RCU lock
3626 contention on all systems with CONFIG_MAXSMP set.
3627 Format: { "0" | "1" }
3628 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3629 1 -- enable.
3630 Note: increases power consumption, thus should only be
3631 enabled if running jitter sensitive (HPC/RT) workloads.
3632
3633 security= [SECURITY] Choose a security module to enable at boot.
3634 If this boot parameter is not specified, only the first
3635 security module asking for security registration will be
3636 loaded. An invalid security module name will be treated
3637 as if no module has been chosen.
3638
3639 selinux= [SELINUX] Disable or enable SELinux at boot time.
3640 Format: { "0" | "1" }
3641 See security/selinux/Kconfig help text.
3642 0 -- disable.
3643 1 -- enable.
3644 Default value is set via kernel config option.
3645 If enabled at boot time, /selinux/disable can be used
3646 later to disable prior to initial policy load.
3647
3648 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3649 Format: { "0" | "1" }
3650 See security/apparmor/Kconfig help text
3651 0 -- disable.
3652 1 -- enable.
3653 Default value is set via kernel config option.
3654
3655 serialnumber [BUGS=X86-32]
3656
3657 shapers= [NET]
3658 Maximal number of shapers.
3659
3660 simeth= [IA-64]
3661 simscsi=
3662
3663 slram= [HW,MTD]
3664
3665 slab_nomerge [MM]
3666 Disable merging of slabs with similar size. May be
3667 necessary if there is some reason to distinguish
3668 allocs to different slabs. Debug options disable
3669 merging on their own.
3670 For more information see Documentation/vm/slub.txt.
3671
3672 slab_max_order= [MM, SLAB]
3673 Determines the maximum allowed order for slabs.
3674 A high setting may cause OOMs due to memory
3675 fragmentation. Defaults to 1 for systems with
3676 more than 32MB of RAM, 0 otherwise.
3677
3678 slub_debug[=options[,slabs]] [MM, SLUB]
3679 Enabling slub_debug allows one to determine the
3680 culprit if slab objects become corrupted. Enabling
3681 slub_debug can create guard zones around objects and
3682 may poison objects when not in use. Also tracks the
3683 last alloc / free. For more information see
3684 Documentation/vm/slub.txt.
3685
3686 slub_max_order= [MM, SLUB]
3687 Determines the maximum allowed order for slabs.
3688 A high setting may cause OOMs due to memory
3689 fragmentation. For more information see
3690 Documentation/vm/slub.txt.
3691
3692 slub_min_objects= [MM, SLUB]
3693 The minimum number of objects per slab. SLUB will
3694 increase the slab order up to slub_max_order to
3695 generate a sufficiently large slab able to contain
3696 the number of objects indicated. The higher the number
3697 of objects the smaller the overhead of tracking slabs
3698 and the less frequently locks need to be acquired.
3699 For more information see Documentation/vm/slub.txt.
3700
3701 slub_min_order= [MM, SLUB]
3702 Determines the minimum page order for slabs. Must be
3703 lower than slub_max_order.
3704 For more information see Documentation/vm/slub.txt.
3705
3706 slub_nomerge [MM, SLUB]
3707 Same with slab_nomerge. This is supported for legacy.
3708 See slab_nomerge for more information.
3709
3710 smart2= [HW]
3711 Format: <io1>[,<io2>[,...,<io8>]]
3712
3713 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3714 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3715 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3716 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3717 smsc-ircc2.ircc_irq= [HW] IRQ line
3718 smsc-ircc2.ircc_dma= [HW] DMA channel
3719 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3720 0: Toshiba Satellite 1800 (GP data pin select)
3721 1: Fast pin select (default)
3722 2: ATC IRMode
3723
3724 smt [KNL,S390] Set the maximum number of threads (logical
3725 CPUs) to use per physical CPU on systems capable of
3726 symmetric multithreading (SMT). Will be capped to the
3727 actual hardware limit.
3728 Format: <integer>
3729 Default: -1 (no limit)
3730
3731 softlockup_panic=
3732 [KNL] Should the soft-lockup detector generate panics.
3733 Format: <integer>
3734
3735 softlockup_all_cpu_backtrace=
3736 [KNL] Should the soft-lockup detector generate
3737 backtraces on all cpus.
3738 Format: <integer>
3739
3740 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3741 See Documentation/laptops/sonypi.txt
3742
3743 spia_io_base= [HW,MTD]
3744 spia_fio_base=
3745 spia_pedr=
3746 spia_peddr=
3747
3748 stacktrace [FTRACE]
3749 Enabled the stack tracer on boot up.
3750
3751 stacktrace_filter=[function-list]
3752 [FTRACE] Limit the functions that the stack tracer
3753 will trace at boot up. function-list is a comma separated
3754 list of functions. This list can be changed at run
3755 time by the stack_trace_filter file in the debugfs
3756 tracing directory. Note, this enables stack tracing
3757 and the stacktrace above is not needed.
3758
3759 sti= [PARISC,HW]
3760 Format: <num>
3761 Set the STI (builtin display/keyboard on the HP-PARISC
3762 machines) console (graphic card) which should be used
3763 as the initial boot-console.
3764 See also comment in drivers/video/console/sticore.c.
3765
3766 sti_font= [HW]
3767 See comment in drivers/video/console/sticore.c.
3768
3769 stifb= [HW]
3770 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3771
3772 sunrpc.min_resvport=
3773 sunrpc.max_resvport=
3774 [NFS,SUNRPC]
3775 SunRPC servers often require that client requests
3776 originate from a privileged port (i.e. a port in the
3777 range 0 < portnr < 1024).
3778 An administrator who wishes to reserve some of these
3779 ports for other uses may adjust the range that the
3780 kernel's sunrpc client considers to be privileged
3781 using these two parameters to set the minimum and
3782 maximum port values.
3783
3784 sunrpc.svc_rpc_per_connection_limit=
3785 [NFS,SUNRPC]
3786 Limit the number of requests that the server will
3787 process in parallel from a single connection.
3788 The default value is 0 (no limit).
3789
3790 sunrpc.pool_mode=
3791 [NFS]
3792 Control how the NFS server code allocates CPUs to
3793 service thread pools. Depending on how many NICs
3794 you have and where their interrupts are bound, this
3795 option will affect which CPUs will do NFS serving.
3796 Note: this parameter cannot be changed while the
3797 NFS server is running.
3798
3799 auto the server chooses an appropriate mode
3800 automatically using heuristics
3801 global a single global pool contains all CPUs
3802 percpu one pool for each CPU
3803 pernode one pool for each NUMA node (equivalent
3804 to global on non-NUMA machines)
3805
3806 sunrpc.tcp_slot_table_entries=
3807 sunrpc.udp_slot_table_entries=
3808 [NFS,SUNRPC]
3809 Sets the upper limit on the number of simultaneous
3810 RPC calls that can be sent from the client to a
3811 server. Increasing these values may allow you to
3812 improve throughput, but will also increase the
3813 amount of memory reserved for use by the client.
3814
3815 suspend.pm_test_delay=
3816 [SUSPEND]
3817 Sets the number of seconds to remain in a suspend test
3818 mode before resuming the system (see
3819 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3820 is set. Default value is 5.
3821
3822 swapaccount=[0|1]
3823 [KNL] Enable accounting of swap in memory resource
3824 controller if no parameter or 1 is given or disable
3825 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3826
3827 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3828 Format: { <int> | force | noforce }
3829 <int> -- Number of I/O TLB slabs
3830 force -- force using of bounce buffers even if they
3831 wouldn't be automatically used by the kernel
3832 noforce -- Never use bounce buffers (for debugging)
3833
3834 switches= [HW,M68k]
3835
3836 sysfs.deprecated=0|1 [KNL]
3837 Enable/disable old style sysfs layout for old udev
3838 on older distributions. When this option is enabled
3839 very new udev will not work anymore. When this option
3840 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3841 in older udev will not work anymore.
3842 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3843 the kernel configuration.
3844
3845 sysrq_always_enabled
3846 [KNL]
3847 Ignore sysrq setting - this boot parameter will
3848 neutralize any effect of /proc/sys/kernel/sysrq.
3849 Useful for debugging.
3850
3851 tcpmhash_entries= [KNL,NET]
3852 Set the number of tcp_metrics_hash slots.
3853 Default value is 8192 or 16384 depending on total
3854 ram pages. This is used to specify the TCP metrics
3855 cache size. See Documentation/networking/ip-sysctl.txt
3856 "tcp_no_metrics_save" section for more details.
3857
3858 tdfx= [HW,DRM]
3859
3860 test_suspend= [SUSPEND][,N]
3861 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3862 standby suspend) or "freeze" (for suspend type freeze)
3863 as the system sleep state during system startup with
3864 the optional capability to repeat N number of times.
3865 The system is woken from this state using a
3866 wakeup-capable RTC alarm.
3867
3868 thash_entries= [KNL,NET]
3869 Set number of hash buckets for TCP connection
3870
3871 thermal.act= [HW,ACPI]
3872 -1: disable all active trip points in all thermal zones
3873 <degrees C>: override all lowest active trip points
3874
3875 thermal.crt= [HW,ACPI]
3876 -1: disable all critical trip points in all thermal zones
3877 <degrees C>: override all critical trip points
3878
3879 thermal.nocrt= [HW,ACPI]
3880 Set to disable actions on ACPI thermal zone
3881 critical and hot trip points.
3882
3883 thermal.off= [HW,ACPI]
3884 1: disable ACPI thermal control
3885
3886 thermal.psv= [HW,ACPI]
3887 -1: disable all passive trip points
3888 <degrees C>: override all passive trip points to this
3889 value
3890
3891 thermal.tzp= [HW,ACPI]
3892 Specify global default ACPI thermal zone polling rate
3893 <deci-seconds>: poll all this frequency
3894 0: no polling (default)
3895
3896 threadirqs [KNL]
3897 Force threading of all interrupt handlers except those
3898 marked explicitly IRQF_NO_THREAD.
3899
3900 tmem [KNL,XEN]
3901 Enable the Transcendent memory driver if built-in.
3902
3903 tmem.cleancache=0|1 [KNL, XEN]
3904 Default is on (1). Disable the usage of the cleancache
3905 API to send anonymous pages to the hypervisor.
3906
3907 tmem.frontswap=0|1 [KNL, XEN]
3908 Default is on (1). Disable the usage of the frontswap
3909 API to send swap pages to the hypervisor. If disabled
3910 the selfballooning and selfshrinking are force disabled.
3911
3912 tmem.selfballooning=0|1 [KNL, XEN]
3913 Default is on (1). Disable the driving of swap pages
3914 to the hypervisor.
3915
3916 tmem.selfshrinking=0|1 [KNL, XEN]
3917 Default is on (1). Partial swapoff that immediately
3918 transfers pages from Xen hypervisor back to the
3919 kernel based on different criteria.
3920
3921 topology= [S390]
3922 Format: {off | on}
3923 Specify if the kernel should make use of the cpu
3924 topology information if the hardware supports this.
3925 The scheduler will make use of this information and
3926 e.g. base its process migration decisions on it.
3927 Default is on.
3928
3929 topology_updates= [KNL, PPC, NUMA]
3930 Format: {off}
3931 Specify if the kernel should ignore (off)
3932 topology updates sent by the hypervisor to this
3933 LPAR.
3934
3935 tp720= [HW,PS2]
3936
3937 tpm_suspend_pcr=[HW,TPM]
3938 Format: integer pcr id
3939 Specify that at suspend time, the tpm driver
3940 should extend the specified pcr with zeros,
3941 as a workaround for some chips which fail to
3942 flush the last written pcr on TPM_SaveState.
3943 This will guarantee that all the other pcrs
3944 are saved.
3945
3946 trace_buf_size=nn[KMG]
3947 [FTRACE] will set tracing buffer size on each cpu.
3948
3949 trace_event=[event-list]
3950 [FTRACE] Set and start specified trace events in order
3951 to facilitate early boot debugging. The event-list is a
3952 comma separated list of trace events to enable. See
3953 also Documentation/trace/events.txt
3954
3955 trace_options=[option-list]
3956 [FTRACE] Enable or disable tracer options at boot.
3957 The option-list is a comma delimited list of options
3958 that can be enabled or disabled just as if you were
3959 to echo the option name into
3960
3961 /sys/kernel/debug/tracing/trace_options
3962
3963 For example, to enable stacktrace option (to dump the
3964 stack trace of each event), add to the command line:
3965
3966 trace_options=stacktrace
3967
3968 See also Documentation/trace/ftrace.txt "trace options"
3969 section.
3970
3971 tp_printk[FTRACE]
3972 Have the tracepoints sent to printk as well as the
3973 tracing ring buffer. This is useful for early boot up
3974 where the system hangs or reboots and does not give the
3975 option for reading the tracing buffer or performing a
3976 ftrace_dump_on_oops.
3977
3978 To turn off having tracepoints sent to printk,
3979 echo 0 > /proc/sys/kernel/tracepoint_printk
3980 Note, echoing 1 into this file without the
3981 tracepoint_printk kernel cmdline option has no effect.
3982
3983 ** CAUTION **
3984
3985 Having tracepoints sent to printk() and activating high
3986 frequency tracepoints such as irq or sched, can cause
3987 the system to live lock.
3988
3989 traceoff_on_warning
3990 [FTRACE] enable this option to disable tracing when a
3991 warning is hit. This turns off "tracing_on". Tracing can
3992 be enabled again by echoing '1' into the "tracing_on"
3993 file located in /sys/kernel/debug/tracing/
3994
3995 This option is useful, as it disables the trace before
3996 the WARNING dump is called, which prevents the trace to
3997 be filled with content caused by the warning output.
3998
3999 This option can also be set at run time via the sysctl
4000 option: kernel/traceoff_on_warning
4001
4002 transparent_hugepage=
4003 [KNL]
4004 Format: [always|madvise|never]
4005 Can be used to control the default behavior of the system
4006 with respect to transparent hugepages.
4007 See Documentation/vm/transhuge.txt for more details.
4008
4009 tsc= Disable clocksource stability checks for TSC.
4010 Format: <string>
4011 [x86] reliable: mark tsc clocksource as reliable, this
4012 disables clocksource verification at runtime, as well
4013 as the stability checks done at bootup. Used to enable
4014 high-resolution timer mode on older hardware, and in
4015 virtualized environment.
4016 [x86] noirqtime: Do not use TSC to do irq accounting.
4017 Used to run time disable IRQ_TIME_ACCOUNTING on any
4018 platforms where RDTSC is slow and this accounting
4019 can add overhead.
4020
4021 turbografx.map[2|3]= [HW,JOY]
4022 TurboGraFX parallel port interface
4023 Format:
4024 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4025 See also Documentation/input/joystick-parport.txt
4026
4027 udbg-immortal [PPC] When debugging early kernel crashes that
4028 happen after console_init() and before a proper
4029 console driver takes over, this boot options might
4030 help "seeing" what's going on.
4031
4032 uhash_entries= [KNL,NET]
4033 Set number of hash buckets for UDP/UDP-Lite connections
4034
4035 uhci-hcd.ignore_oc=
4036 [USB] Ignore overcurrent events (default N).
4037 Some badly-designed motherboards generate lots of
4038 bogus events, for ports that aren't wired to
4039 anything. Set this parameter to avoid log spamming.
4040 Note that genuine overcurrent events won't be
4041 reported either.
4042
4043 unknown_nmi_panic
4044 [X86] Cause panic on unknown NMI.
4045
4046 usbcore.authorized_default=
4047 [USB] Default USB device authorization:
4048 (default -1 = authorized except for wireless USB,
4049 0 = not authorized, 1 = authorized)
4050
4051 usbcore.autosuspend=
4052 [USB] The autosuspend time delay (in seconds) used
4053 for newly-detected USB devices (default 2). This
4054 is the time required before an idle device will be
4055 autosuspended. Devices for which the delay is set
4056 to a negative value won't be autosuspended at all.
4057
4058 usbcore.usbfs_snoop=
4059 [USB] Set to log all usbfs traffic (default 0 = off).
4060
4061 usbcore.usbfs_snoop_max=
4062 [USB] Maximum number of bytes to snoop in each URB
4063 (default = 65536).
4064
4065 usbcore.blinkenlights=
4066 [USB] Set to cycle leds on hubs (default 0 = off).
4067
4068 usbcore.old_scheme_first=
4069 [USB] Start with the old device initialization
4070 scheme (default 0 = off).
4071
4072 usbcore.usbfs_memory_mb=
4073 [USB] Memory limit (in MB) for buffers allocated by
4074 usbfs (default = 16, 0 = max = 2047).
4075
4076 usbcore.use_both_schemes=
4077 [USB] Try the other device initialization scheme
4078 if the first one fails (default 1 = enabled).
4079
4080 usbcore.initial_descriptor_timeout=
4081 [USB] Specifies timeout for the initial 64-byte
4082 USB_REQ_GET_DESCRIPTOR request in milliseconds
4083 (default 5000 = 5.0 seconds).
4084
4085 usbcore.nousb [USB] Disable the USB subsystem
4086
4087 usbhid.mousepoll=
4088 [USBHID] The interval which mice are to be polled at.
4089
4090 usb-storage.delay_use=
4091 [UMS] The delay in seconds before a new device is
4092 scanned for Logical Units (default 1).
4093
4094 usb-storage.quirks=
4095 [UMS] A list of quirks entries to supplement or
4096 override the built-in unusual_devs list. List
4097 entries are separated by commas. Each entry has
4098 the form VID:PID:Flags where VID and PID are Vendor
4099 and Product ID values (4-digit hex numbers) and
4100 Flags is a set of characters, each corresponding
4101 to a common usb-storage quirk flag as follows:
4102 a = SANE_SENSE (collect more than 18 bytes
4103 of sense data);
4104 b = BAD_SENSE (don't collect more than 18
4105 bytes of sense data);
4106 c = FIX_CAPACITY (decrease the reported
4107 device capacity by one sector);
4108 d = NO_READ_DISC_INFO (don't use
4109 READ_DISC_INFO command);
4110 e = NO_READ_CAPACITY_16 (don't use
4111 READ_CAPACITY_16 command);
4112 f = NO_REPORT_OPCODES (don't use report opcodes
4113 command, uas only);
4114 g = MAX_SECTORS_240 (don't transfer more than
4115 240 sectors at a time, uas only);
4116 h = CAPACITY_HEURISTICS (decrease the
4117 reported device capacity by one
4118 sector if the number is odd);
4119 i = IGNORE_DEVICE (don't bind to this
4120 device);
4121 j = NO_REPORT_LUNS (don't use report luns
4122 command, uas only);
4123 l = NOT_LOCKABLE (don't try to lock and
4124 unlock ejectable media);
4125 m = MAX_SECTORS_64 (don't transfer more
4126 than 64 sectors = 32 KB at a time);
4127 n = INITIAL_READ10 (force a retry of the
4128 initial READ(10) command);
4129 o = CAPACITY_OK (accept the capacity
4130 reported by the device);
4131 p = WRITE_CACHE (the device cache is ON
4132 by default);
4133 r = IGNORE_RESIDUE (the device reports
4134 bogus residue values);
4135 s = SINGLE_LUN (the device has only one
4136 Logical Unit);
4137 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4138 commands, uas only);
4139 u = IGNORE_UAS (don't bind to the uas driver);
4140 w = NO_WP_DETECT (don't test whether the
4141 medium is write-protected).
4142 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4143 even if the device claims no cache)
4144 Example: quirks=0419:aaf5:rl,0421:0433:rc
4145
4146 user_debug= [KNL,ARM]
4147 Format: <int>
4148 See arch/arm/Kconfig.debug help text.
4149 1 - undefined instruction events
4150 2 - system calls
4151 4 - invalid data aborts
4152 8 - SIGSEGV faults
4153 16 - SIGBUS faults
4154 Example: user_debug=31
4155
4156 userpte=
4157 [X86] Flags controlling user PTE allocations.
4158
4159 nohigh = do not allocate PTE pages in
4160 HIGHMEM regardless of setting
4161 of CONFIG_HIGHPTE.
4162
4163 vdso= [X86,SH]
4164 On X86_32, this is an alias for vdso32=. Otherwise:
4165
4166 vdso=1: enable VDSO (the default)
4167 vdso=0: disable VDSO mapping
4168
4169 vdso32= [X86] Control the 32-bit vDSO
4170 vdso32=1: enable 32-bit VDSO
4171 vdso32=0 or vdso32=2: disable 32-bit VDSO
4172
4173 See the help text for CONFIG_COMPAT_VDSO for more
4174 details. If CONFIG_COMPAT_VDSO is set, the default is
4175 vdso32=0; otherwise, the default is vdso32=1.
4176
4177 For compatibility with older kernels, vdso32=2 is an
4178 alias for vdso32=0.
4179
4180 Try vdso32=0 if you encounter an error that says:
4181 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4182
4183 vector= [IA-64,SMP]
4184 vector=percpu: enable percpu vector domain
4185
4186 video= [FB] Frame buffer configuration
4187 See Documentation/fb/modedb.txt.
4188
4189 video.brightness_switch_enabled= [0,1]
4190 If set to 1, on receiving an ACPI notify event
4191 generated by hotkey, video driver will adjust brightness
4192 level and then send out the event to user space through
4193 the allocated input device; If set to 0, video driver
4194 will only send out the event without touching backlight
4195 brightness level.
4196 default: 1
4197
4198 virtio_mmio.device=
4199 [VMMIO] Memory mapped virtio (platform) device.
4200
4201 <size>@<baseaddr>:<irq>[:<id>]
4202 where:
4203 <size> := size (can use standard suffixes
4204 like K, M and G)
4205 <baseaddr> := physical base address
4206 <irq> := interrupt number (as passed to
4207 request_irq())
4208 <id> := (optional) platform device id
4209 example:
4210 virtio_mmio.device=1K@0x100b0000:48:7
4211
4212 Can be used multiple times for multiple devices.
4213
4214 vga= [BOOT,X86-32] Select a particular video mode
4215 See Documentation/x86/boot.txt and
4216 Documentation/svga.txt.
4217 Use vga=ask for menu.
4218 This is actually a boot loader parameter; the value is
4219 passed to the kernel using a special protocol.
4220
4221 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4222 size of <nn>. This can be used to increase the
4223 minimum size (128MB on x86). It can also be used to
4224 decrease the size and leave more room for directly
4225 mapped kernel RAM.
4226
4227 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4228 Format: <command>
4229
4230 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4231 Format: <command>
4232
4233 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4234 Format: <command>
4235
4236 vsyscall= [X86-64]
4237 Controls the behavior of vsyscalls (i.e. calls to
4238 fixed addresses of 0xffffffffff600x00 from legacy
4239 code). Most statically-linked binaries and older
4240 versions of glibc use these calls. Because these
4241 functions are at fixed addresses, they make nice
4242 targets for exploits that can control RIP.
4243
4244 emulate [default] Vsyscalls turn into traps and are
4245 emulated reasonably safely.
4246
4247 native Vsyscalls are native syscall instructions.
4248 This is a little bit faster than trapping
4249 and makes a few dynamic recompilers work
4250 better than they would in emulation mode.
4251 It also makes exploits much easier to write.
4252
4253 none Vsyscalls don't work at all. This makes
4254 them quite hard to use for exploits but
4255 might break your system.
4256
4257 vt.color= [VT] Default text color.
4258 Format: 0xYX, X = foreground, Y = background.
4259 Default: 0x07 = light gray on black.
4260
4261 vt.cur_default= [VT] Default cursor shape.
4262 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4263 the parameters of the <Esc>[?A;B;Cc escape sequence;
4264 see VGA-softcursor.txt. Default: 2 = underline.
4265
4266 vt.default_blu= [VT]
4267 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4268 Change the default blue palette of the console.
4269 This is a 16-member array composed of values
4270 ranging from 0-255.
4271
4272 vt.default_grn= [VT]
4273 Format: <green0>,<green1>,<green2>,...,<green15>
4274 Change the default green palette of the console.
4275 This is a 16-member array composed of values
4276 ranging from 0-255.
4277
4278 vt.default_red= [VT]
4279 Format: <red0>,<red1>,<red2>,...,<red15>
4280 Change the default red palette of the console.
4281 This is a 16-member array composed of values
4282 ranging from 0-255.
4283
4284 vt.default_utf8=
4285 [VT]
4286 Format=<0|1>
4287 Set system-wide default UTF-8 mode for all tty's.
4288 Default is 1, i.e. UTF-8 mode is enabled for all
4289 newly opened terminals.
4290
4291 vt.global_cursor_default=
4292 [VT]
4293 Format=<-1|0|1>
4294 Set system-wide default for whether a cursor
4295 is shown on new VTs. Default is -1,
4296 i.e. cursors will be created by default unless
4297 overridden by individual drivers. 0 will hide
4298 cursors, 1 will display them.
4299
4300 vt.italic= [VT] Default color for italic text; 0-15.
4301 Default: 2 = green.
4302
4303 vt.underline= [VT] Default color for underlined text; 0-15.
4304 Default: 3 = cyan.
4305
4306 watchdog timers [HW,WDT] For information on watchdog timers,
4307 see Documentation/watchdog/watchdog-parameters.txt
4308 or other driver-specific files in the
4309 Documentation/watchdog/ directory.
4310
4311 workqueue.watchdog_thresh=
4312 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4313 warn stall conditions and dump internal state to
4314 help debugging. 0 disables workqueue stall
4315 detection; otherwise, it's the stall threshold
4316 duration in seconds. The default value is 30 and
4317 it can be updated at runtime by writing to the
4318 corresponding sysfs file.
4319
4320 workqueue.disable_numa
4321 By default, all work items queued to unbound
4322 workqueues are affine to the NUMA nodes they're
4323 issued on, which results in better behavior in
4324 general. If NUMA affinity needs to be disabled for
4325 whatever reason, this option can be used. Note
4326 that this also can be controlled per-workqueue for
4327 workqueues visible under /sys/bus/workqueue/.
4328
4329 workqueue.power_efficient
4330 Per-cpu workqueues are generally preferred because
4331 they show better performance thanks to cache
4332 locality; unfortunately, per-cpu workqueues tend to
4333 be more power hungry than unbound workqueues.
4334
4335 Enabling this makes the per-cpu workqueues which
4336 were observed to contribute significantly to power
4337 consumption unbound, leading to measurably lower
4338 power usage at the cost of small performance
4339 overhead.
4340
4341 The default value of this parameter is determined by
4342 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4343
4344 workqueue.debug_force_rr_cpu
4345 Workqueue used to implicitly guarantee that work
4346 items queued without explicit CPU specified are put
4347 on the local CPU. This guarantee is no longer true
4348 and while local CPU is still preferred work items
4349 may be put on foreign CPUs. This debug option
4350 forces round-robin CPU selection to flush out
4351 usages which depend on the now broken guarantee.
4352 When enabled, memory and cache locality will be
4353 impacted.
4354
4355 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4356 default x2apic cluster mode on platforms
4357 supporting x2apic.
4358
4359 x86_intel_mid_timer= [X86-32,APBT]
4360 Choose timer option for x86 Intel MID platform.
4361 Two valid options are apbt timer only and lapic timer
4362 plus one apbt timer for broadcast timer.
4363 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4364
4365 xen_512gb_limit [KNL,X86-64,XEN]
4366 Restricts the kernel running paravirtualized under Xen
4367 to use only up to 512 GB of RAM. The reason to do so is
4368 crash analysis tools and Xen tools for doing domain
4369 save/restore/migration must be enabled to handle larger
4370 domains.
4371
4372 xen_emul_unplug= [HW,X86,XEN]
4373 Unplug Xen emulated devices
4374 Format: [unplug0,][unplug1]
4375 ide-disks -- unplug primary master IDE devices
4376 aux-ide-disks -- unplug non-primary-master IDE devices
4377 nics -- unplug network devices
4378 all -- unplug all emulated devices (NICs and IDE disks)
4379 unnecessary -- unplugging emulated devices is
4380 unnecessary even if the host did not respond to
4381 the unplug protocol
4382 never -- do not unplug even if version check succeeds
4383
4384 xen_nopvspin [X86,XEN]
4385 Disables the ticketlock slowpath using Xen PV
4386 optimizations.
4387
4388 xen_nopv [X86]
4389 Disables the PV optimizations forcing the HVM guest to
4390 run as generic HVM guest with no PV drivers.
4391
4392 xirc2ps_cs= [NET,PCMCIA]
4393 Format:
4394 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]