blob: a4ab856a24d914ee61fb2f610502cdce16bc225c [file] [log] [blame]
rjw1f884582022-01-06 17:20:42 +08001 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_no_watchdog [HW,ACPI,WDT]
141 Ignore the ACPI-based watchdog interface (WDAT) and let
142 a native driver control the watchdog device instead.
143
144 acpi_rsdp= [ACPI,EFI,KEXEC]
145 Pass the RSDP address to the kernel, mostly used
146 on machines running EFI runtime service to boot the
147 second kernel for kdump.
148
149 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
150 Format: To spoof as Windows 98: ="Microsoft Windows"
151
152 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
153 of 2 which is mandated by ACPI 6) as the supported ACPI
154 specification revision (when using this switch, it may
155 be necessary to carry out a cold reboot _twice_ in a
156 row to make it take effect on the platform firmware).
157
158 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
159 acpi_osi="string1" # add string1
160 acpi_osi="!string2" # remove string2
161 acpi_osi=!* # remove all strings
162 acpi_osi=! # disable all built-in OS vendor
163 strings
164 acpi_osi=!! # enable all built-in OS vendor
165 strings
166 acpi_osi= # disable all strings
167
168 'acpi_osi=!' can be used in combination with single or
169 multiple 'acpi_osi="string1"' to support specific OS
170 vendor string(s). Note that such command can only
171 affect the default state of the OS vendor strings, thus
172 it cannot affect the default state of the feature group
173 strings and the current state of the OS vendor strings,
174 specifying it multiple times through kernel command line
175 is meaningless. This command is useful when one do not
176 care about the state of the feature group strings which
177 should be controlled by the OSPM.
178 Examples:
179 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
180 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
181 can make '_OSI("Windows 2000")' TRUE.
182
183 'acpi_osi=' cannot be used in combination with other
184 'acpi_osi=' command lines, the _OSI method will not
185 exist in the ACPI namespace. NOTE that such command can
186 only affect the _OSI support state, thus specifying it
187 multiple times through kernel command line is also
188 meaningless.
189 Examples:
190 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
191 FALSE.
192
193 'acpi_osi=!*' can be used in combination with single or
194 multiple 'acpi_osi="string1"' to support specific
195 string(s). Note that such command can affect the
196 current state of both the OS vendor strings and the
197 feature group strings, thus specifying it multiple times
198 through kernel command line is meaningful. But it may
199 still not able to affect the final state of a string if
200 there are quirks related to this string. This command
201 is useful when one want to control the state of the
202 feature group strings to debug BIOS issues related to
203 the OSPM features.
204 Examples:
205 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
206 '_OSI("Module Device")' FALSE.
207 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
208 '_OSI("Module Device")' TRUE.
209 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
210 equivalent to
211 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
212 and
213 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
214 they all will make '_OSI("Windows 2000")' TRUE.
215
216 acpi_pm_good [X86]
217 Override the pmtimer bug detection: force the kernel
218 to assume that this machine's pmtimer latches its value
219 and always returns good values.
220
221 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
222 Format: { level | edge | high | low }
223
224 acpi_skip_timer_override [HW,ACPI]
225 Recognize and ignore IRQ0/pin2 Interrupt Override.
226 For broken nForce2 BIOS resulting in XT-PIC timer.
227
228 acpi_sleep= [HW,ACPI] Sleep options
229 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
230 old_ordering, nonvs, sci_force_enable }
231 See Documentation/power/video.txt for information on
232 s3_bios and s3_mode.
233 s3_beep is for debugging; it makes the PC's speaker beep
234 as soon as the kernel's real-mode entry point is called.
235 s4_nohwsig prevents ACPI hardware signature from being
236 used during resume from hibernation.
237 old_ordering causes the ACPI 1.0 ordering of the _PTS
238 control method, with respect to putting devices into
239 low power states, to be enforced (the ACPI 2.0 ordering
240 of _PTS is used by default).
241 nonvs prevents the kernel from saving/restoring the
242 ACPI NVS memory during suspend/hibernation and resume.
243 sci_force_enable causes the kernel to set SCI_EN directly
244 on resume from S1/S3 (which is against the ACPI spec,
245 but some broken systems don't work without it).
246
247 acpi_use_timer_override [HW,ACPI]
248 Use timer override. For some broken Nvidia NF5 boards
249 that require a timer override, but don't have HPET
250
251 add_efi_memmap [EFI; X86] Include EFI memory map in
252 kernel's map of available physical RAM.
253
254 agp= [AGP]
255 { off | try_unsupported }
256 off: disable AGP support
257 try_unsupported: try to drive unsupported chipsets
258 (may crash computer or cause data corruption)
259
260 ALSA [HW,ALSA]
261 See Documentation/sound/alsa/alsa-parameters.txt
262
263 alignment= [KNL,ARM]
264 Allow the default userspace alignment fault handler
265 behaviour to be specified. Bit 0 enables warnings,
266 bit 1 enables fixups, and bit 2 sends a segfault.
267
268 align_va_addr= [X86-64]
269 Align virtual addresses by clearing slice [14:12] when
270 allocating a VMA at process creation time. This option
271 gives you up to 3% performance improvement on AMD F15h
272 machines (where it is enabled by default) for a
273 CPU-intensive style benchmark, and it can vary highly in
274 a microbenchmark depending on workload and compiler.
275
276 32: only for 32-bit processes
277 64: only for 64-bit processes
278 on: enable for both 32- and 64-bit processes
279 off: disable for both 32- and 64-bit processes
280
281 alloc_snapshot [FTRACE]
282 Allocate the ftrace snapshot buffer on boot up when the
283 main buffer is allocated. This is handy if debugging
284 and you need to use tracing_snapshot() on boot up, and
285 do not want to use tracing_snapshot_alloc() as it needs
286 to be done where GFP_KERNEL allocations are allowed.
287
288 amd_iommu= [HW,X86-64]
289 Pass parameters to the AMD IOMMU driver in the system.
290 Possible values are:
291 fullflush - enable flushing of IO/TLB entries when
292 they are unmapped. Otherwise they are
293 flushed before they will be reused, which
294 is a lot of faster
295 off - do not initialize any AMD IOMMU found in
296 the system
297 force_isolation - Force device isolation for all
298 devices. The IOMMU driver is not
299 allowed anymore to lift isolation
300 requirements as needed. This option
301 does not override iommu=pt
302
303 amd_iommu_dump= [HW,X86-64]
304 Enable AMD IOMMU driver option to dump the ACPI table
305 for AMD IOMMU. With this option enabled, AMD IOMMU
306 driver will print ACPI tables for AMD IOMMU during
307 IOMMU initialization.
308
309 amd_iommu_intr= [HW,X86-64]
310 Specifies one of the following AMD IOMMU interrupt
311 remapping modes:
312 legacy - Use legacy interrupt remapping mode.
313 vapic - Use virtual APIC mode, which allows IOMMU
314 to inject interrupts directly into guest.
315 This mode requires kvm-amd.avic=1.
316 (Default when IOMMU HW support is present.)
317
318 amijoy.map= [HW,JOY] Amiga joystick support
319 Map of devices attached to JOY0DAT and JOY1DAT
320 Format: <a>,<b>
321 See also Documentation/input/joystick.txt
322
323 analog.map= [HW,JOY] Analog joystick and gamepad support
324 Specifies type or capabilities of an analog joystick
325 connected to one of 16 gameports
326 Format: <type1>,<type2>,..<type16>
327
328 apc= [HW,SPARC]
329 Power management functions (SPARCstation-4/5 + deriv.)
330 Format: noidle
331 Disable APC CPU standby support. SPARCstation-Fox does
332 not play well with APC CPU idle - disable it if you have
333 APC and your system crashes randomly.
334
335 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
336 Change the output verbosity whilst booting
337 Format: { quiet (default) | verbose | debug }
338 Change the amount of debugging information output
339 when initialising the APIC and IO-APIC components.
340
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
345 backup of CPU 0
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
348 shot down by NMI
349
350 autoconf= [IPV6]
351 See Documentation/networking/ipv6.txt.
352
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
361
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
364
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
367
368 ataflop= [HW,M68k]
369
370 atarimouse= [HW,MOUSE] Atari Mouse
371
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
374
375 atkbd.reset= [HW] Reset keyboard during initialization
376
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
379
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
381 keyboards
382
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
385
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
388
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
398 auditd.
399 Default: unset
400
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
403 Default: 64
404
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
408 0 - Disable the BAU.
409 1 - Enable the BAU.
410 unset - Disable the BAU.
411
412 baycom_epp= [HW,AX25]
413 Format: <io>,<mode>
414
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
416 Format: <io>,<mode>
417 See header of drivers/net/hamradio/baycom_par.c.
418
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
423
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
428
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
432
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
435 no delay (0).
436 Format: integer
437
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
439
440 bert_disable [ACPI]
441 Disable BERT OS support on buggy BIOSes.
442
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
445 kernel args too.
446 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
447 bttv.tuner=
448
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
451 at a time.
452
453 c101= [NET] Moxa C101 synchronous serial card
454
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
461
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
464 trust validation.
465 format: { id:<keyid> | builtin }
466
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
471 others).
472
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
475
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
480 a single hierarchy
481 - foo isn't visible as an individually mountable
482 subsystem
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
486
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
491
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
493 Format: <string>
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
496
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
506
507 cio_ignore= [S390]
508 See Documentation/s390/CommonIO for details.
509 clk_ignore_unused
510 [CLK]
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
520
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
522 [Deprecated]
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
527
528 clocksource= Override the default clocksource
529 Format: <string>
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
533 the platform:
534 [all] jiffies (this is the base, fallback clocksource)
535 [ACPI] acpi_pm
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
540 [MIPS] MIPS
541 [PARISC] cr16
542 [S390] tod
543 [SH] SuperH
544 [SPARC64] tick
545 [X86-64] hpet,tsc
546
547 clocksource.arm_arch_timer.evtstrm=
548 [ARM,ARM64]
549 Format: <bool>
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
553 systems.
554
555 clearcpuid=BITNUM [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
560 ones should be.
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
566 some critical bits.
567
568 cma=nn[MG]@[start[MG][-end[MG]]]
569 [ARM,X86,KNL]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
576
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
581 a hypervisor.
582 Default: yes
583
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
587
588 code_bytes [X86] How many bytes of object code to print
589 in an oops report.
590 Range: 0 - 8192
591 Default: 64
592
593 com20020= [HW,NET] ARCnet - COM20020 chipset
594 Format:
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
596
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 Format: <io>[,<irq>]
599
600 com90xx= [HW,NET]
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
603
604 condev= [HW,S390] console device
605 conmode=
606
607 console= [KNL] Output console device and options.
608
609 tty<n> Use the virtual console device <n>.
610
611 ttyS<n>[,options]
612 ttyUSB0[,options]
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
618
619 See Documentation/admin-guide/serial-console.rst for more
620 information. See
621 Documentation/networking/netconsole.txt for an
622 alternative.
623
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
638
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
641
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
644 console=brl,ttyS0
645 For now, only VisioBraille is supported.
646
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. Defaults to 10*60 = 10mins. A value of 0
649 disables the blank timer.
650
651 coredump_filter=
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
655
656 coresight_cpu_debug.enable
657 [ARM,ARM64]
658 Format: <bool>
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
662
663 cpuidle.off=1 [CPU_IDLE]
664 disable the cpuidle sub-system
665
666 cpufreq.off=1 [CPU_FREQ]
667 disable the cpufreq sub-system
668
669 cpu_init_udelay=N
670 [X86] Delay for N microsec between assert and de-assert
671 of APIC INIT to start processors. This delay occurs
672 on every CPU online, such as boot, and resume from suspend.
673 Default: 10000
674
675 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
676 Format:
677 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
678
679 crashkernel=size[KMG][@offset[KMG]]
680 [KNL] Using kexec, Linux can switch to a 'crash kernel'
681 upon panic. This parameter reserves the physical
682 memory region [offset, offset + size] for that kernel
683 image. If '@offset' is omitted, then a suitable offset
684 is selected automatically. Check
685 Documentation/kdump/kdump.txt for further details.
686
687 crashkernel=range1:size1[,range2:size2,...][@offset]
688 [KNL] Same as above, but depends on the memory
689 in the running system. The syntax of range is
690 start-[end] where start and end are both
691 a memory unit (amount[KMG]). See also
692 Documentation/kdump/kdump.txt for an example.
693
694 crashkernel=size[KMG],high
695 [KNL, x86_64] range could be above 4G. Allow kernel
696 to allocate physical memory region from top, so could
697 be above 4G if system have more than 4G ram installed.
698 Otherwise memory region will be allocated below 4G, if
699 available.
700 It will be ignored if crashkernel=X is specified.
701 crashkernel=size[KMG],low
702 [KNL, x86_64] range under 4G. When crashkernel=X,high
703 is passed, kernel could allocate physical memory region
704 above 4G, that cause second kernel crash on system
705 that require some amount of low memory, e.g. swiotlb
706 requires at least 64M+32K low memory, also enough extra
707 low memory is needed to make sure DMA buffers for 32-bit
708 devices won't run out. Kernel would try to allocate at
709 at least 256M below 4G automatically.
710 This one let user to specify own low range under 4G
711 for second kernel instead.
712 0: to disable low allocation.
713 It will be ignored when crashkernel=X,high is not used
714 or memory reserved is below 4G.
715
716 cryptomgr.notests
717 [KNL] Disable crypto self-tests
718
719 cs89x0_dma= [HW,NET]
720 Format: <dma>
721
722 cs89x0_media= [HW,NET]
723 Format: { rj45 | aui | bnc }
724
725 dasd= [HW,NET]
726 See header of drivers/s390/block/dasd_devmap.c.
727
728 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
729 (one device per port)
730 Format: <port#>,<type>
731 See also Documentation/input/joystick-parport.txt
732
733 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
734 time. See
735 Documentation/admin-guide/dynamic-debug-howto.rst for
736 details. Deprecated, see dyndbg.
737
738 debug [KNL] Enable kernel debugging (events log level).
739
740 debug_locks_verbose=
741 [KNL] verbose self-tests
742 Format=<0|1>
743 Print debugging info while doing the locking API
744 self-tests.
745 We default to 0 (no extra messages), setting it to
746 1 will print _a lot_ more information - normally
747 only useful to kernel developers.
748
749 debug_objects [KNL] Enable object debugging
750
751 no_debug_objects
752 [KNL] Disable object debugging
753
754 debug_guardpage_minorder=
755 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
756 parameter allows control of the order of pages that will
757 be intentionally kept free (and hence protected) by the
758 buddy allocator. Bigger value increase the probability
759 of catching random memory corruption, but reduce the
760 amount of memory for normal system use. The maximum
761 possible value is MAX_ORDER/2. Setting this parameter
762 to 1 or 2 should be enough to identify most random
763 memory corruption problems caused by bugs in kernel or
764 driver code when a CPU writes to (or reads from) a
765 random memory location. Note that there exists a class
766 of memory corruptions problems caused by buggy H/W or
767 F/W or by drivers badly programing DMA (basically when
768 memory is written at bus level and the CPU MMU is
769 bypassed) which are not detectable by
770 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
771 tracking down these problems.
772
773 debug_pagealloc=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter enables the feature at boot time. In
776 default, it is disabled. We can avoid allocating huge
777 chunk of memory for debug pagealloc if we don't enable
778 it at boot time and the system will work mostly same
779 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
780 on: enable the feature
781
782 debugpat [X86] Enable PAT debugging
783
784 decnet.addr= [HW,NET]
785 Format: <area>[,<node>]
786 See also Documentation/networking/decnet.txt.
787
788 default_hugepagesz=
789 [same as hugepagesz=] The size of the default
790 HugeTLB page size. This is the size represented by
791 the legacy /proc/ hugepages APIs, used for SHM, and
792 default size when mounting hugetlbfs filesystems.
793 Defaults to the default architecture's huge page size
794 if not specified.
795
796 dhash_entries= [KNL]
797 Set number of hash buckets for dentry cache.
798
799 disable_1tb_segments [PPC]
800 Disables the use of 1TB hash page table segments. This
801 causes the kernel to fall back to 256MB segments which
802 can be useful when debugging issues that require an SLB
803 miss to occur.
804
805 disable= [IPV6]
806 See Documentation/networking/ipv6.txt.
807
808 disable_radix [PPC]
809 Disable RADIX MMU mode on POWER9
810
811 disable_cpu_apicid= [X86,APIC,SMP]
812 Format: <int>
813 The number of initial APIC ID for the
814 corresponding CPU to be disabled at boot,
815 mostly used for the kdump 2nd kernel to
816 disable BSP to wake up multiple CPUs without
817 causing system reset or hang due to sending
818 INIT from AP to BSP.
819
820 disable_ddw [PPC/PSERIES]
821 Disable Dynamic DMA Window support. Use this if
822 to workaround buggy firmware.
823
824 disable_ipv6= [IPV6]
825 See Documentation/networking/ipv6.txt.
826
827 disable_mtrr_cleanup [X86]
828 The kernel tries to adjust MTRR layout from continuous
829 to discrete, to make X server driver able to add WB
830 entry later. This parameter disables that.
831
832 disable_mtrr_trim [X86, Intel and AMD only]
833 By default the kernel will trim any uncacheable
834 memory out of your available memory pool based on
835 MTRR settings. This parameter disables that behavior,
836 possibly causing your machine to run very slowly.
837
838 disable_timer_pin_1 [X86]
839 Disable PIN 1 of APIC timer
840 Can be useful to work around chipset bugs.
841
842 dis_ucode_ldr [X86] Disable the microcode loader.
843
844 dm= [DM] Allows early creation of a device-mapper device.
845 See Documentation/device-mapper/boot.txt.
846
847 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
848 this option disables the debugging code at boot.
849
850 dma_debug_entries=<number>
851 This option allows to tune the number of preallocated
852 entries for DMA-API debugging code. One entry is
853 required per DMA-API allocation. Use this if the
854 DMA-API debugging code disables itself because the
855 architectural default is too low.
856
857 dma_debug_driver=<driver_name>
858 With this option the DMA-API debugging driver
859 filter feature can be enabled at boot time. Just
860 pass the driver to filter for as the parameter.
861 The filter can be disabled or changed to another
862 driver later using sysfs.
863
864 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
865 Broken monitors, graphic adapters, KVMs and EDIDless
866 panels may send no or incorrect EDID data sets.
867 This parameter allows to specify an EDID data sets
868 in the /lib/firmware directory that are used instead.
869 Generic built-in EDID data sets are used, if one of
870 edid/1024x768.bin, edid/1280x1024.bin,
871 edid/1680x1050.bin, or edid/1920x1080.bin is given
872 and no file with the same name exists. Details and
873 instructions how to build your own EDID data are
874 available in Documentation/EDID/HOWTO.txt. An EDID
875 data set will only be used for a particular connector,
876 if its name and a colon are prepended to the EDID
877 name. Each connector may use a unique EDID data
878 set by separating the files with a comma. An EDID
879 data set with no connector name will be used for
880 any connectors not explicitly specified.
881
882 dscc4.setup= [NET]
883
884 dt_cpu_ftrs= [PPC]
885 Format: {"off" | "known"}
886 Control how the dt_cpu_ftrs device-tree binding is
887 used for CPU feature discovery and setup (if it
888 exists).
889 off: Do not use it, fall back to legacy cpu table.
890 known: Do not pass through unknown features to guests
891 or userspace, only those that the kernel is aware of.
892
893 dump_apple_properties [X86]
894 Dump name and content of EFI device properties on
895 x86 Macs. Useful for driver authors to determine
896 what data is available or for reverse-engineering.
897
898 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
899 module.dyndbg[="val"]
900 Enable debug messages at boot time. See
901 Documentation/admin-guide/dynamic-debug-howto.rst
902 for details.
903
904 nompx [X86] Disables Intel Memory Protection Extensions.
905 See Documentation/x86/intel_mpx.txt for more
906 information about the feature.
907
908 nopku [X86] Disable Memory Protection Keys CPU feature found
909 in some Intel CPUs.
910
911 module.async_probe [KNL]
912 Enable asynchronous probe on this module.
913
914 early_ioremap_debug [KNL]
915 Enable debug messages in early_ioremap support. This
916 is useful for tracking down temporary early mappings
917 which are not unmapped.
918
919 earlycon= [KNL] Output early console device and options.
920
921 When used with no options, the early console is
922 determined by the stdout-path property in device
923 tree's chosen node.
924
925 cdns,<addr>[,options]
926 Start an early, polled-mode console on a Cadence
927 (xuartps) serial port at the specified address. Only
928 supported option is baud rate. If baud rate is not
929 specified, the serial port must already be setup and
930 configured.
931
932 uart[8250],io,<addr>[,options]
933 uart[8250],mmio,<addr>[,options]
934 uart[8250],mmio32,<addr>[,options]
935 uart[8250],mmio32be,<addr>[,options]
936 uart[8250],0x<addr>[,options]
937 Start an early, polled-mode console on the 8250/16550
938 UART at the specified I/O port or MMIO address.
939 MMIO inter-register address stride is either 8-bit
940 (mmio) or 32-bit (mmio32 or mmio32be).
941 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
942 to be equivalent to 'mmio'. 'options' are specified
943 in the same format described for "console=ttyS<n>"; if
944 unspecified, the h/w is not initialized.
945
946 pl011,<addr>
947 pl011,mmio32,<addr>
948 Start an early, polled-mode console on a pl011 serial
949 port at the specified address. The pl011 serial port
950 must already be setup and configured. Options are not
951 yet supported. If 'mmio32' is specified, then only
952 the driver will use only 32-bit accessors to read/write
953 the device registers.
954
955 meson,<addr>
956 Start an early, polled-mode console on a meson serial
957 port at the specified address. The serial port must
958 already be setup and configured. Options are not yet
959 supported.
960
961 msm_serial,<addr>
962 Start an early, polled-mode console on an msm serial
963 port at the specified address. The serial port
964 must already be setup and configured. Options are not
965 yet supported.
966
967 msm_serial_dm,<addr>
968 Start an early, polled-mode console on an msm serial
969 dm port at the specified address. The serial port
970 must already be setup and configured. Options are not
971 yet supported.
972
973 owl,<addr>
974 Start an early, polled-mode console on a serial port
975 of an Actions Semi SoC, such as S500 or S900, at the
976 specified address. The serial port must already be
977 setup and configured. Options are not yet supported.
978
979 smh Use ARM semihosting calls for early console.
980
981 s3c2410,<addr>
982 s3c2412,<addr>
983 s3c2440,<addr>
984 s3c6400,<addr>
985 s5pv210,<addr>
986 exynos4210,<addr>
987 Use early console provided by serial driver available
988 on Samsung SoCs, requires selecting proper type and
989 a correct base address of the selected UART port. The
990 serial port must already be setup and configured.
991 Options are not yet supported.
992
993 lantiq,<addr>
994 Start an early, polled-mode console on a lantiq serial
995 (lqasc) port at the specified address. The serial port
996 must already be setup and configured. Options are not
997 yet supported.
998
999 lpuart,<addr>
1000 lpuart32,<addr>
1001 Use early console provided by Freescale LP UART driver
1002 found on Freescale Vybrid and QorIQ LS1021A processors.
1003 A valid base address must be provided, and the serial
1004 port must already be setup and configured.
1005
1006 ar3700_uart,<addr>
1007 Start an early, polled-mode console on the
1008 Armada 3700 serial port at the specified
1009 address. The serial port must already be setup
1010 and configured. Options are not yet supported.
1011
1012 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1013 earlyprintk=vga
1014 earlyprintk=efi
1015 earlyprintk=sclp
1016 earlyprintk=xen
1017 earlyprintk=serial[,ttySn[,baudrate]]
1018 earlyprintk=serial[,0x...[,baudrate]]
1019 earlyprintk=ttySn[,baudrate]
1020 earlyprintk=dbgp[debugController#]
1021 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1022 earlyprintk=xdbc[xhciController#]
1023
1024 earlyprintk is useful when the kernel crashes before
1025 the normal console is initialized. It is not enabled by
1026 default because it has some cosmetic problems.
1027
1028 Append ",keep" to not disable it when the real console
1029 takes over.
1030
1031 Only one of vga, efi, serial, or usb debug port can
1032 be used at a time.
1033
1034 Currently only ttyS0 and ttyS1 may be specified by
1035 name. Other I/O ports may be explicitly specified
1036 on some architectures (x86 and arm at least) by
1037 replacing ttySn with an I/O port address, like this:
1038 earlyprintk=serial,0x1008,115200
1039 You can find the port for a given device in
1040 /proc/tty/driver/serial:
1041 2: uart:ST16650V2 port:00001008 irq:18 ...
1042
1043 Interaction with the standard serial driver is not
1044 very good.
1045
1046 The VGA and EFI output is eventually overwritten by
1047 the real console.
1048
1049 The xen output can only be used by Xen PV guests.
1050
1051 The sclp output can only be used on s390.
1052
1053 The optional "force" to "pciserial" enables use of a
1054 PCI device even when its classcode is not of the
1055 UART class.
1056
1057 edac_report= [HW,EDAC] Control how to report EDAC event
1058 Format: {"on" | "off" | "force"}
1059 on: enable EDAC to report H/W event. May be overridden
1060 by other higher priority error reporting module.
1061 off: disable H/W event reporting through EDAC.
1062 force: enforce the use of EDAC to report H/W event.
1063 default: on.
1064
1065 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1066 ekgdboc=kbd
1067
1068 This is designed to be used in conjunction with
1069 the boot argument: earlyprintk=vga
1070
1071 edd= [EDD]
1072 Format: {"off" | "on" | "skip[mbr]"}
1073
1074 efi= [EFI]
1075 Format: { "old_map", "nochunk", "noruntime", "debug" }
1076 old_map [X86-64]: switch to the old ioremap-based EFI
1077 runtime services mapping. 32-bit still uses this one by
1078 default.
1079 nochunk: disable reading files in "chunks" in the EFI
1080 boot stub, as chunking can cause problems with some
1081 firmware implementations.
1082 noruntime : disable EFI runtime services support
1083 debug: enable misc debug output
1084
1085 efi_no_storage_paranoia [EFI; X86]
1086 Using this parameter you can use more than 50% of
1087 your efi variable storage. Use this parameter only if
1088 you are really sure that your UEFI does sane gc and
1089 fulfills the spec otherwise your board may brick.
1090
1091 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1092 Add arbitrary attribute to specific memory range by
1093 updating original EFI memory map.
1094 Region of memory which aa attribute is added to is
1095 from ss to ss+nn.
1096 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1097 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1098 attribute is added to range 0x100000000-0x180000000 and
1099 0x10a0000000-0x1120000000.
1100
1101 Using this parameter you can do debugging of EFI memmap
1102 related feature. For example, you can do debugging of
1103 Address Range Mirroring feature even if your box
1104 doesn't support it.
1105
1106 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1107 that is to be dynamically loaded by Linux. If there are
1108 multiple variables with the same name but with different
1109 vendor GUIDs, all of them will be loaded. See
1110 Documentation/acpi/ssdt-overlays.txt for details.
1111
1112
1113 eisa_irq_edge= [PARISC,HW]
1114 See header of drivers/parisc/eisa.c.
1115
1116 elanfreq= [X86-32]
1117 See comment before function elanfreq_setup() in
1118 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1119
1120 elevator= [IOSCHED]
1121 Format: {"cfq" | "deadline" | "noop"}
1122 See Documentation/block/cfq-iosched.txt and
1123 Documentation/block/deadline-iosched.txt for details.
1124
1125 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1126 Specifies physical address of start of kernel core
1127 image elf header and optionally the size. Generally
1128 kexec loader will pass this option to capture kernel.
1129 See Documentation/kdump/kdump.txt for details.
1130
1131 enable_mtrr_cleanup [X86]
1132 The kernel tries to adjust MTRR layout from continuous
1133 to discrete, to make X server driver able to add WB
1134 entry later. This parameter enables that.
1135
1136 enable_timer_pin_1 [X86]
1137 Enable PIN 1 of APIC timer
1138 Can be useful to work around chipset bugs
1139 (in particular on some ATI chipsets).
1140 The kernel tries to set a reasonable default.
1141
1142 enforcing [SELINUX] Set initial enforcing status.
1143 Format: {"0" | "1"}
1144 See security/selinux/Kconfig help text.
1145 0 -- permissive (log only, no denials).
1146 1 -- enforcing (deny and log).
1147 Default value is 0.
1148 Value can be changed at runtime via /selinux/enforce.
1149
1150 erst_disable [ACPI]
1151 Disable Error Record Serialization Table (ERST)
1152 support.
1153
1154 ether= [HW,NET] Ethernet cards parameters
1155 This option is obsoleted by the "netdev=" option, which
1156 has equivalent usage. See its documentation for details.
1157
1158 evm= [EVM]
1159 Format: { "fix" }
1160 Permit 'security.evm' to be updated regardless of
1161 current integrity status.
1162
1163 failslab=
1164 fail_page_alloc=
1165 fail_make_request=[KNL]
1166 General fault injection mechanism.
1167 Format: <interval>,<probability>,<space>,<times>
1168 See also Documentation/fault-injection/.
1169
1170 floppy= [HW]
1171 See Documentation/blockdev/floppy.txt.
1172
1173 force_pal_cache_flush
1174 [IA-64] Avoid check_sal_cache_flush which may hang on
1175 buggy SAL_CACHE_FLUSH implementations. Using this
1176 parameter will force ia64_sal_cache_flush to call
1177 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1178
1179 forcepae [X86-32]
1180 Forcefully enable Physical Address Extension (PAE).
1181 Many Pentium M systems disable PAE but may have a
1182 functionally usable PAE implementation.
1183 Warning: use of this parameter will taint the kernel
1184 and may cause unknown problems.
1185
1186 ftrace=[tracer]
1187 [FTRACE] will set and start the specified tracer
1188 as early as possible in order to facilitate early
1189 boot debugging.
1190
1191 ftrace_dump_on_oops[=orig_cpu]
1192 [FTRACE] will dump the trace buffers on oops.
1193 If no parameter is passed, ftrace will dump
1194 buffers of all CPUs, but if you pass orig_cpu, it will
1195 dump only the buffer of the CPU that triggered the
1196 oops.
1197
1198 ftrace_filter=[function-list]
1199 [FTRACE] Limit the functions traced by the function
1200 tracer at boot up. function-list is a comma separated
1201 list of functions. This list can be changed at run
1202 time by the set_ftrace_filter file in the debugfs
1203 tracing directory.
1204
1205 ftrace_notrace=[function-list]
1206 [FTRACE] Do not trace the functions specified in
1207 function-list. This list can be changed at run time
1208 by the set_ftrace_notrace file in the debugfs
1209 tracing directory.
1210
1211 ftrace_graph_filter=[function-list]
1212 [FTRACE] Limit the top level callers functions traced
1213 by the function graph tracer at boot up.
1214 function-list is a comma separated list of functions
1215 that can be changed at run time by the
1216 set_graph_function file in the debugfs tracing directory.
1217
1218 ftrace_graph_notrace=[function-list]
1219 [FTRACE] Do not trace from the functions specified in
1220 function-list. This list is a comma separated list of
1221 functions that can be changed at run time by the
1222 set_graph_notrace file in the debugfs tracing directory.
1223
1224 ftrace_graph_max_depth=<uint>
1225 [FTRACE] Used with the function graph tracer. This is
1226 the max depth it will trace into a function. This value
1227 can be changed at run time by the max_graph_depth file
1228 in the tracefs tracing directory. default: 0 (no limit)
1229
1230 gamecon.map[2|3]=
1231 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1232 support via parallel port (up to 5 devices per port)
1233 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1234 See also Documentation/input/joystick-parport.txt
1235
1236 gamma= [HW,DRM]
1237
1238 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1239 Format: off | on
1240 default: on
1241
1242 gcov_persist= [GCOV] When non-zero (default), profiling data for
1243 kernel modules is saved and remains accessible via
1244 debugfs, even when the module is unloaded/reloaded.
1245 When zero, profiling data is discarded and associated
1246 debugfs files are removed at module unload time.
1247
1248 goldfish [X86] Enable the goldfish android emulator platform.
1249 Don't use this when you are not running on the
1250 android emulator
1251
1252 gpt [EFI] Forces disk with valid GPT signature but
1253 invalid Protective MBR to be treated as GPT. If the
1254 primary GPT is corrupted, it enables the backup/alternate
1255 GPT to be used instead.
1256
1257 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1258 the "Enable 0" bit of the configuration register.
1259 Format: 0 | 1
1260 Default: 0
1261 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1262 the "Enable 0" bit of the configuration register.
1263 Format: 0 | 1
1264 Default: 0
1265 grcan.select= [HW] Select which physical interface to use.
1266 Format: 0 | 1
1267 Default: 0
1268 grcan.txsize= [HW] Sets the size of the tx buffer.
1269 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1270 Default: 1024
1271 grcan.rxsize= [HW] Sets the size of the rx buffer.
1272 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1273 Default: 1024
1274
1275 gpio-mockup.gpio_mockup_ranges
1276 [HW] Sets the ranges of gpiochip of for this device.
1277 Format: <start1>,<end1>,<start2>,<end2>...
1278
1279 hardlockup_all_cpu_backtrace=
1280 [KNL] Should the hard-lockup detector generate
1281 backtraces on all cpus.
1282 Format: <integer>
1283
1284 hashdist= [KNL,NUMA] Large hashes allocated during boot
1285 are distributed across NUMA nodes. Defaults on
1286 for 64-bit NUMA, off otherwise.
1287 Format: 0 | 1 (for off | on)
1288
1289 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1290
1291 hd= [EIDE] (E)IDE hard drive subsystem geometry
1292 Format: <cyl>,<head>,<sect>
1293
1294 hest_disable [ACPI]
1295 Disable Hardware Error Source Table (HEST) support;
1296 corresponding firmware-first mode error processing
1297 logic will be disabled.
1298
1299 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1300 size of <nn>. This works even on boxes that have no
1301 highmem otherwise. This also works to reduce highmem
1302 size on bigger boxes.
1303
1304 highres= [KNL] Enable/disable high resolution timer mode.
1305 Valid parameters: "on", "off"
1306 Default: "on"
1307
1308 hisax= [HW,ISDN]
1309 See Documentation/isdn/README.HiSax.
1310
1311 hlt [BUGS=ARM,SH]
1312
1313 hpet= [X86-32,HPET] option to control HPET usage
1314 Format: { enable (default) | disable | force |
1315 verbose }
1316 disable: disable HPET and use PIT instead
1317 force: allow force enabled of undocumented chips (ICH4,
1318 VIA, nVidia)
1319 verbose: show contents of HPET registers during setup
1320
1321 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1322 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1323
1324 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1325 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1326 On x86-64 and powerpc, this option can be specified
1327 multiple times interleaved with hugepages= to reserve
1328 huge pages of different sizes. Valid pages sizes on
1329 x86-64 are 2M (when the CPU supports "pse") and 1G
1330 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1331
1332 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1333 terminal devices. Valid values: 0..8
1334 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1335 If specified, z/VM IUCV HVC accepts connections
1336 from listed z/VM user IDs only.
1337
1338 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1339 hardware thread id mappings.
1340 Format: <cpu>:<hwthread>
1341
1342 keep_bootcon [KNL]
1343 Do not unregister boot console at start. This is only
1344 useful for debugging when something happens in the window
1345 between unregistering the boot console and initializing
1346 the real console.
1347
1348 i2c_bus= [HW] Override the default board specific I2C bus speed
1349 or register an additional I2C bus that is not
1350 registered from board initialization code.
1351 Format:
1352 <bus_id>,<clkrate>
1353
1354 i8042.debug [HW] Toggle i8042 debug mode
1355 i8042.unmask_kbd_data
1356 [HW] Enable printing of interrupt data from the KBD port
1357 (disabled by default, and as a pre-condition
1358 requires that i8042.debug=1 be enabled)
1359 i8042.direct [HW] Put keyboard port into non-translated mode
1360 i8042.dumbkbd [HW] Pretend that controller can only read data from
1361 keyboard and cannot control its state
1362 (Don't attempt to blink the leds)
1363 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1364 i8042.nokbd [HW] Don't check/create keyboard port
1365 i8042.noloop [HW] Disable the AUX Loopback command while probing
1366 for the AUX port
1367 i8042.nomux [HW] Don't check presence of an active multiplexing
1368 controller
1369 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1370 controllers
1371 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1372 i8042.reset [HW] Reset the controller during init, cleanup and
1373 suspend-to-ram transitions, only during s2r
1374 transitions, or never reset
1375 Format: { 1 | Y | y | 0 | N | n }
1376 1, Y, y: always reset controller
1377 0, N, n: don't ever reset controller
1378 Default: only on s2r transitions on x86; most other
1379 architectures force reset to be always executed
1380 i8042.unlock [HW] Unlock (ignore) the keylock
1381 i8042.kbdreset [HW] Reset device connected to KBD port
1382
1383 i810= [HW,DRM]
1384
1385 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1386 indicates that the driver is running on unsupported
1387 hardware.
1388 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1389 does not match list of supported models.
1390 i8k.power_status
1391 [HW] Report power status in /proc/i8k
1392 (disabled by default)
1393 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1394 capability is set.
1395
1396 i915.invert_brightness=
1397 [DRM] Invert the sense of the variable that is used to
1398 set the brightness of the panel backlight. Normally a
1399 brightness value of 0 indicates backlight switched off,
1400 and the maximum of the brightness value sets the backlight
1401 to maximum brightness. If this parameter is set to 0
1402 (default) and the machine requires it, or this parameter
1403 is set to 1, a brightness value of 0 sets the backlight
1404 to maximum brightness, and the maximum of the brightness
1405 value switches the backlight off.
1406 -1 -- never invert brightness
1407 0 -- machine default
1408 1 -- force brightness inversion
1409
1410 icn= [HW,ISDN]
1411 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1412
1413 ide-core.nodma= [HW] (E)IDE subsystem
1414 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1415 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1416 .cdrom .chs .ignore_cable are additional options
1417 See Documentation/ide/ide.txt.
1418
1419 ide-generic.probe-mask= [HW] (E)IDE subsystem
1420 Format: <int>
1421 Probe mask for legacy ISA IDE ports. Depending on
1422 platform up to 6 ports are supported, enabled by
1423 setting corresponding bits in the mask to 1. The
1424 default value is 0x0, which has a special meaning.
1425 On systems that have PCI, it triggers scanning the
1426 PCI bus for the first and the second port, which
1427 are then probed. On systems without PCI the value
1428 of 0x0 enables probing the two first ports as if it
1429 was 0x3.
1430
1431 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1432 Claim all unknown PCI IDE storage controllers.
1433
1434 idle= [X86]
1435 Format: idle=poll, idle=halt, idle=nomwait
1436 Poll forces a polling idle loop that can slightly
1437 improve the performance of waking up a idle CPU, but
1438 will use a lot of power and make the system run hot.
1439 Not recommended.
1440 idle=halt: Halt is forced to be used for CPU idle.
1441 In such case C2/C3 won't be used again.
1442 idle=nomwait: Disable mwait for CPU C-states
1443
1444 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1445 Format: { strict | legacy | 2008 | relaxed }
1446 Default: strict
1447
1448 Choose which programs will be accepted for execution
1449 based on the IEEE 754 NaN encoding(s) supported by
1450 the FPU and the NaN encoding requested with the value
1451 of an ELF file header flag individually set by each
1452 binary. Hardware implementations are permitted to
1453 support either or both of the legacy and the 2008 NaN
1454 encoding mode.
1455
1456 Available settings are as follows:
1457 strict accept binaries that request a NaN encoding
1458 supported by the FPU
1459 legacy only accept legacy-NaN binaries, if supported
1460 by the FPU
1461 2008 only accept 2008-NaN binaries, if supported
1462 by the FPU
1463 relaxed accept any binaries regardless of whether
1464 supported by the FPU
1465
1466 The FPU emulator is always able to support both NaN
1467 encodings, so if no FPU hardware is present or it has
1468 been disabled with 'nofpu', then the settings of
1469 'legacy' and '2008' strap the emulator accordingly,
1470 'relaxed' straps the emulator for both legacy-NaN and
1471 2008-NaN, whereas 'strict' enables legacy-NaN only on
1472 legacy processors and both NaN encodings on MIPS32 or
1473 MIPS64 CPUs.
1474
1475 The setting for ABS.fmt/NEG.fmt instruction execution
1476 mode generally follows that for the NaN encoding,
1477 except where unsupported by hardware.
1478
1479 ignore_loglevel [KNL]
1480 Ignore loglevel setting - this will print /all/
1481 kernel messages to the console. Useful for debugging.
1482 We also add it as printk module parameter, so users
1483 could change it dynamically, usually by
1484 /sys/module/printk/parameters/ignore_loglevel.
1485
1486 ignore_rlimit_data
1487 Ignore RLIMIT_DATA setting for data mappings,
1488 print warning at first misuse. Can be changed via
1489 /sys/module/kernel/parameters/ignore_rlimit_data.
1490
1491 ihash_entries= [KNL]
1492 Set number of hash buckets for inode cache.
1493
1494 ima_appraise= [IMA] appraise integrity measurements
1495 Format: { "off" | "enforce" | "fix" | "log" }
1496 default: "enforce"
1497
1498 ima_appraise_tcb [IMA]
1499 The builtin appraise policy appraises all files
1500 owned by uid=0.
1501
1502 ima_canonical_fmt [IMA]
1503 Use the canonical format for the binary runtime
1504 measurements, instead of host native format.
1505
1506 ima_hash= [IMA]
1507 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1508 | sha512 | ... }
1509 default: "sha1"
1510
1511 The list of supported hash algorithms is defined
1512 in crypto/hash_info.h.
1513
1514 ima_policy= [IMA]
1515 The builtin policies to load during IMA setup.
1516 Format: "tcb | appraise_tcb | secure_boot"
1517
1518 The "tcb" policy measures all programs exec'd, files
1519 mmap'd for exec, and all files opened with the read
1520 mode bit set by either the effective uid (euid=0) or
1521 uid=0.
1522
1523 The "appraise_tcb" policy appraises the integrity of
1524 all files owned by root. (This is the equivalent
1525 of ima_appraise_tcb.)
1526
1527 The "secure_boot" policy appraises the integrity
1528 of files (eg. kexec kernel image, kernel modules,
1529 firmware, policy, etc) based on file signatures.
1530
1531 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1532 Load a policy which meets the needs of the Trusted
1533 Computing Base. This means IMA will measure all
1534 programs exec'd, files mmap'd for exec, and all files
1535 opened for read by uid=0.
1536
1537 ima_template= [IMA]
1538 Select one of defined IMA measurements template formats.
1539 Formats: { "ima" | "ima-ng" | "ima-sig" }
1540 Default: "ima-ng"
1541
1542 ima_template_fmt=
1543 [IMA] Define a custom template format.
1544 Format: { "field1|...|fieldN" }
1545
1546 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1547 Format: <min_file_size>
1548 Set the minimal file size for using asynchronous hash.
1549 If left unspecified, ahash usage is disabled.
1550
1551 ahash performance varies for different data sizes on
1552 different crypto accelerators. This option can be used
1553 to achieve the best performance for a particular HW.
1554
1555 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1556 Format: <bufsize>
1557 Set hashing buffer size. Default: 4k.
1558
1559 ahash performance varies for different chunk sizes on
1560 different crypto accelerators. This option can be used
1561 to achieve best performance for particular HW.
1562
1563 init= [KNL]
1564 Format: <full_path>
1565 Run specified binary instead of /sbin/init as init
1566 process.
1567
1568 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1569 for working out where the kernel is dying during
1570 startup.
1571
1572 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1573 initcall functions. Useful for debugging built-in
1574 modules and initcalls.
1575
1576 initrd= [BOOT] Specify the location of the initial ramdisk
1577
1578 init_pkru= [x86] Specify the default memory protection keys rights
1579 register contents for all processes. 0x55555554 by
1580 default (disallow access to all but pkey 0). Can
1581 override in debugfs after boot.
1582
1583 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1584 Format: <irq>
1585
1586 int_pln_enable [x86] Enable power limit notification interrupt
1587
1588 integrity_audit=[IMA]
1589 Format: { "0" | "1" }
1590 0 -- basic integrity auditing messages. (Default)
1591 1 -- additional integrity auditing messages.
1592
1593 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1594 on
1595 Enable intel iommu driver.
1596 off
1597 Disable intel iommu driver.
1598 igfx_off [Default Off]
1599 By default, gfx is mapped as normal device. If a gfx
1600 device has a dedicated DMAR unit, the DMAR unit is
1601 bypassed by not enabling DMAR with this option. In
1602 this case, gfx device will use physical address for
1603 DMA.
1604 forcedac [x86_64]
1605 With this option iommu will not optimize to look
1606 for io virtual address below 32-bit forcing dual
1607 address cycle on pci bus for cards supporting greater
1608 than 32-bit addressing. The default is to look
1609 for translation below 32-bit and if not available
1610 then look in the higher range.
1611 strict [Default Off]
1612 With this option on every unmap_single operation will
1613 result in a hardware IOTLB flush operation as opposed
1614 to batching them for performance.
1615 sp_off [Default Off]
1616 By default, super page will be supported if Intel IOMMU
1617 has the capability. With this option, super page will
1618 not be supported.
1619 ecs_off [Default Off]
1620 By default, extended context tables will be supported if
1621 the hardware advertises that it has support both for the
1622 extended tables themselves, and also PASID support. With
1623 this option set, extended tables will not be used even
1624 on hardware which claims to support them.
1625 tboot_noforce [Default Off]
1626 Do not force the Intel IOMMU enabled under tboot.
1627 By default, tboot will force Intel IOMMU on, which
1628 could harm performance of some high-throughput
1629 devices like 40GBit network cards, even if identity
1630 mapping is enabled.
1631 Note that using this option lowers the security
1632 provided by tboot because it makes the system
1633 vulnerable to DMA attacks.
1634
1635 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1636 0 disables intel_idle and fall back on acpi_idle.
1637 1 to 9 specify maximum depth of C-state.
1638
1639 intel_pstate= [X86]
1640 disable
1641 Do not enable intel_pstate as the default
1642 scaling driver for the supported processors
1643 passive
1644 Use intel_pstate as a scaling driver, but configure it
1645 to work with generic cpufreq governors (instead of
1646 enabling its internal governor). This mode cannot be
1647 used along with the hardware-managed P-states (HWP)
1648 feature.
1649 force
1650 Enable intel_pstate on systems that prohibit it by default
1651 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1652 instead of acpi-cpufreq may disable platform features, such
1653 as thermal controls and power capping, that rely on ACPI
1654 P-States information being indicated to OSPM and therefore
1655 should be used with caution. This option does not work with
1656 processors that aren't supported by the intel_pstate driver
1657 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1658 no_hwp
1659 Do not enable hardware P state control (HWP)
1660 if available.
1661 hwp_only
1662 Only load intel_pstate on systems which support
1663 hardware P state control (HWP) if available.
1664 support_acpi_ppc
1665 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1666 Description Table, specifies preferred power management
1667 profile as "Enterprise Server" or "Performance Server",
1668 then this feature is turned on by default.
1669 per_cpu_perf_limits
1670 Allow per-logical-CPU P-State performance control limits using
1671 cpufreq sysfs interface
1672
1673 intremap= [X86-64, Intel-IOMMU]
1674 on enable Interrupt Remapping (default)
1675 off disable Interrupt Remapping
1676 nosid disable Source ID checking
1677 no_x2apic_optout
1678 BIOS x2APIC opt-out request will be ignored
1679 nopost disable Interrupt Posting
1680
1681 iomem= Disable strict checking of access to MMIO memory
1682 strict regions from userspace.
1683 relaxed
1684
1685 iommu= [x86]
1686 off
1687 force
1688 noforce
1689 biomerge
1690 panic
1691 nopanic
1692 merge
1693 nomerge
1694 forcesac
1695 soft
1696 pt [x86, IA-64]
1697 nobypass [PPC/POWERNV]
1698 Disable IOMMU bypass, using IOMMU for PCI devices.
1699
1700 iommu.passthrough=
1701 [ARM64] Configure DMA to bypass the IOMMU by default.
1702 Format: { "0" | "1" }
1703 0 - Use IOMMU translation for DMA.
1704 1 - Bypass the IOMMU for DMA.
1705 unset - Use IOMMU translation for DMA.
1706
1707 io7= [HW] IO7 for Marvel based alpha systems
1708 See comment before marvel_specify_io7 in
1709 arch/alpha/kernel/core_marvel.c.
1710
1711 io_delay= [X86] I/O delay method
1712 0x80
1713 Standard port 0x80 based delay
1714 0xed
1715 Alternate port 0xed based delay (needed on some systems)
1716 udelay
1717 Simple two microseconds delay
1718 none
1719 No delay
1720
1721 ip= [IP_PNP]
1722 See Documentation/filesystems/nfs/nfsroot.txt.
1723
1724 irqaffinity= [SMP] Set the default irq affinity mask
1725 The argument is a cpu list, as described above.
1726
1727 irqfixup [HW]
1728 When an interrupt is not handled search all handlers
1729 for it. Intended to get systems with badly broken
1730 firmware running.
1731
1732 irqpoll [HW]
1733 When an interrupt is not handled search all handlers
1734 for it. Also check all handlers each timer
1735 interrupt. Intended to get systems with badly broken
1736 firmware running.
1737
1738 isapnp= [ISAPNP]
1739 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1740
1741 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1742 The argument is a cpu list, as described above.
1743
1744 This option can be used to specify one or more CPUs
1745 to isolate from the general SMP balancing and scheduling
1746 algorithms. You can move a process onto or off an
1747 "isolated" CPU via the CPU affinity syscalls or cpuset.
1748 <cpu number> begins at 0 and the maximum value is
1749 "number of CPUs in system - 1".
1750
1751 This option is the preferred way to isolate CPUs. The
1752 alternative -- manually setting the CPU mask of all
1753 tasks in the system -- can cause problems and
1754 suboptimal load balancer performance.
1755
1756 iucv= [HW,NET]
1757
1758 ivrs_ioapic [HW,X86_64]
1759 Provide an override to the IOAPIC-ID<->DEVICE-ID
1760 mapping provided in the IVRS ACPI table. For
1761 example, to map IOAPIC-ID decimal 10 to
1762 PCI device 00:14.0 write the parameter as:
1763 ivrs_ioapic[10]=00:14.0
1764
1765 ivrs_hpet [HW,X86_64]
1766 Provide an override to the HPET-ID<->DEVICE-ID
1767 mapping provided in the IVRS ACPI table. For
1768 example, to map HPET-ID decimal 0 to
1769 PCI device 00:14.0 write the parameter as:
1770 ivrs_hpet[0]=00:14.0
1771
1772 ivrs_acpihid [HW,X86_64]
1773 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1774 mapping provided in the IVRS ACPI table. For
1775 example, to map UART-HID:UID AMD0020:0 to
1776 PCI device 00:14.5 write the parameter as:
1777 ivrs_acpihid[00:14.5]=AMD0020:0
1778
1779 js= [HW,JOY] Analog joystick
1780 See Documentation/input/joystick.txt.
1781
1782 nokaslr [KNL]
1783 When CONFIG_RANDOMIZE_BASE is set, this disables
1784 kernel and module base offset ASLR (Address Space
1785 Layout Randomization).
1786
1787 kasan_multi_shot
1788 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1789 report on every invalid memory access. Without this
1790 parameter KASAN will print report only for the first
1791 invalid access.
1792
1793 keepinitrd [HW,ARM]
1794
1795 kernelcore= [KNL,X86,IA-64,PPC]
1796 Format: nn[KMGTPE] | "mirror"
1797 This parameter
1798 specifies the amount of memory usable by the kernel
1799 for non-movable allocations. The requested amount is
1800 spread evenly throughout all nodes in the system. The
1801 remaining memory in each node is used for Movable
1802 pages. In the event, a node is too small to have both
1803 kernelcore and Movable pages, kernelcore pages will
1804 take priority and other nodes will have a larger number
1805 of Movable pages. The Movable zone is used for the
1806 allocation of pages that may be reclaimed or moved
1807 by the page migration subsystem. This means that
1808 HugeTLB pages may not be allocated from this zone.
1809 Note that allocations like PTEs-from-HighMem still
1810 use the HighMem zone if it exists, and the Normal
1811 zone if it does not.
1812
1813 Instead of specifying the amount of memory (nn[KMGTPE]),
1814 you can specify "mirror" option. In case "mirror"
1815 option is specified, mirrored (reliable) memory is used
1816 for non-movable allocations and remaining memory is used
1817 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1818 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1819 time.
1820
1821 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1822 Format: <Controller#>[,poll interval]
1823 The controller # is the number of the ehci usb debug
1824 port as it is probed via PCI. The poll interval is
1825 optional and is the number seconds in between
1826 each poll cycle to the debug port in case you need
1827 the functionality for interrupting the kernel with
1828 gdb or control-c on the dbgp connection. When
1829 not using this parameter you use sysrq-g to break into
1830 the kernel debugger.
1831
1832 kgdboc= [KGDB,HW] kgdb over consoles.
1833 Requires a tty driver that supports console polling,
1834 or a supported polling keyboard driver (non-usb).
1835 Serial only format: <serial_device>[,baud]
1836 keyboard only format: kbd
1837 keyboard and serial format: kbd,<serial_device>[,baud]
1838 Optional Kernel mode setting:
1839 kms, kbd format: kms,kbd
1840 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1841
1842 kgdbwait [KGDB] Stop kernel execution and enter the
1843 kernel debugger at the earliest opportunity.
1844
1845 kmac= [MIPS] korina ethernet MAC address.
1846 Configure the RouterBoard 532 series on-chip
1847 Ethernet adapter MAC address.
1848
1849 kmemleak= [KNL] Boot-time kmemleak enable/disable
1850 Valid arguments: on, off
1851 Default: on
1852 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1853 the default is off.
1854
1855 kpti= [ARM64] Control page table isolation of user
1856 and kernel address spaces.
1857 Default: enabled on cores which need mitigation.
1858 0: force disabled
1859 1: force enabled
1860
1861 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1862 Default is 0 (don't ignore, but inject #GP)
1863
1864 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1865 KVM MMU at runtime.
1866 Default is 0 (off)
1867
1868 kvm.nx_huge_pages=
1869 [KVM] Controls the software workaround for the
1870 X86_BUG_ITLB_MULTIHIT bug.
1871 force : Always deploy workaround.
1872 off : Never deploy workaround.
1873 auto : Deploy workaround based on the presence of
1874 X86_BUG_ITLB_MULTIHIT.
1875
1876 Default is 'auto'.
1877
1878 If the software workaround is enabled for the host,
1879 guests do need not to enable it for nested guests.
1880
1881 kvm.nx_huge_pages_recovery_ratio=
1882 [KVM] Controls how many 4KiB pages are periodically zapped
1883 back to huge pages. 0 disables the recovery, otherwise if
1884 the value is N KVM will zap 1/Nth of the 4KiB pages every
1885 minute. The default is 60.
1886
1887 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1888 Default is 1 (enabled)
1889
1890 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1891 for all guests.
1892 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1893
1894 kvm-arm.vgic_v3_group0_trap=
1895 [KVM,ARM] Trap guest accesses to GICv3 group-0
1896 system registers
1897
1898 kvm-arm.vgic_v3_group1_trap=
1899 [KVM,ARM] Trap guest accesses to GICv3 group-1
1900 system registers
1901
1902 kvm-arm.vgic_v3_common_trap=
1903 [KVM,ARM] Trap guest accesses to GICv3 common
1904 system registers
1905
1906 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1907 (virtualized MMU) support on capable Intel chips.
1908 Default is 1 (enabled)
1909
1910 kvm-intel.emulate_invalid_guest_state=
1911 [KVM,Intel] Enable emulation of invalid guest states
1912 Default is 0 (disabled)
1913
1914 kvm-intel.flexpriority=
1915 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1916 Default is 1 (enabled)
1917
1918 kvm-intel.nested=
1919 [KVM,Intel] Enable VMX nesting (nVMX).
1920 Default is 0 (disabled)
1921
1922 kvm-intel.unrestricted_guest=
1923 [KVM,Intel] Disable unrestricted guest feature
1924 (virtualized real and unpaged mode) on capable
1925 Intel chips. Default is 1 (enabled)
1926
1927 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1928 CVE-2018-3620.
1929
1930 Valid arguments: never, cond, always
1931
1932 always: L1D cache flush on every VMENTER.
1933 cond: Flush L1D on VMENTER only when the code between
1934 VMEXIT and VMENTER can leak host memory.
1935 never: Disables the mitigation
1936
1937 Default is cond (do L1 cache flush in specific instances)
1938
1939 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1940 feature (tagged TLBs) on capable Intel chips.
1941 Default is 1 (enabled)
1942
1943 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1944 affected CPUs
1945
1946 The kernel PTE inversion protection is unconditionally
1947 enabled and cannot be disabled.
1948
1949 full
1950 Provides all available mitigations for the
1951 L1TF vulnerability. Disables SMT and
1952 enables all mitigations in the
1953 hypervisors, i.e. unconditional L1D flush.
1954
1955 SMT control and L1D flush control via the
1956 sysfs interface is still possible after
1957 boot. Hypervisors will issue a warning
1958 when the first VM is started in a
1959 potentially insecure configuration,
1960 i.e. SMT enabled or L1D flush disabled.
1961
1962 full,force
1963 Same as 'full', but disables SMT and L1D
1964 flush runtime control. Implies the
1965 'nosmt=force' command line option.
1966 (i.e. sysfs control of SMT is disabled.)
1967
1968 flush
1969 Leaves SMT enabled and enables the default
1970 hypervisor mitigation, i.e. conditional
1971 L1D flush.
1972
1973 SMT control and L1D flush control via the
1974 sysfs interface is still possible after
1975 boot. Hypervisors will issue a warning
1976 when the first VM is started in a
1977 potentially insecure configuration,
1978 i.e. SMT enabled or L1D flush disabled.
1979
1980 flush,nosmt
1981
1982 Disables SMT and enables the default
1983 hypervisor mitigation.
1984
1985 SMT control and L1D flush control via the
1986 sysfs interface is still possible after
1987 boot. Hypervisors will issue a warning
1988 when the first VM is started in a
1989 potentially insecure configuration,
1990 i.e. SMT enabled or L1D flush disabled.
1991
1992 flush,nowarn
1993 Same as 'flush', but hypervisors will not
1994 warn when a VM is started in a potentially
1995 insecure configuration.
1996
1997 off
1998 Disables hypervisor mitigations and doesn't
1999 emit any warnings.
2000 It also drops the swap size and available
2001 RAM limit restriction on both hypervisor and
2002 bare metal.
2003
2004 Default is 'flush'.
2005
2006 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2007
2008 l2cr= [PPC]
2009
2010 l3cr= [PPC]
2011
2012 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2013 disabled it.
2014
2015 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2016 value for LAPIC timer one-shot implementation. Default
2017 back to the programmable timer unit in the LAPIC.
2018
2019 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2020 in C2 power state.
2021
2022 libata.dma= [LIBATA] DMA control
2023 libata.dma=0 Disable all PATA and SATA DMA
2024 libata.dma=1 PATA and SATA Disk DMA only
2025 libata.dma=2 ATAPI (CDROM) DMA only
2026 libata.dma=4 Compact Flash DMA only
2027 Combinations also work, so libata.dma=3 enables DMA
2028 for disks and CDROMs, but not CFs.
2029
2030 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2031 libata.ignore_hpa=0 keep BIOS limits (default)
2032 libata.ignore_hpa=1 ignore limits, using full disk
2033
2034 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2035 when set.
2036 Format: <int>
2037
2038 libata.force= [LIBATA] Force configurations. The format is comma
2039 separated list of "[ID:]VAL" where ID is
2040 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2041 matching port, link or device. Basically, it matches
2042 the ATA ID string printed on console by libata. If
2043 the whole ID part is omitted, the last PORT and DEVICE
2044 values are used. If ID hasn't been specified yet, the
2045 configuration applies to all ports, links and devices.
2046
2047 If only DEVICE is omitted, the parameter applies to
2048 the port and all links and devices behind it. DEVICE
2049 number of 0 either selects the first device or the
2050 first fan-out link behind PMP device. It does not
2051 select the host link. DEVICE number of 15 selects the
2052 host link and device attached to it.
2053
2054 The VAL specifies the configuration to force. As long
2055 as there's no ambiguity shortcut notation is allowed.
2056 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2057 The following configurations can be forced.
2058
2059 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2060 Any ID with matching PORT is used.
2061
2062 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2063
2064 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2065 udma[/][16,25,33,44,66,100,133] notation is also
2066 allowed.
2067
2068 * [no]ncq: Turn on or off NCQ.
2069
2070 * [no]ncqtrim: Turn off queued DSM TRIM.
2071
2072 * nohrst, nosrst, norst: suppress hard, soft
2073 and both resets.
2074
2075 * rstonce: only attempt one reset during
2076 hot-unplug link recovery
2077
2078 * dump_id: dump IDENTIFY data.
2079
2080 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2081
2082 * disable: Disable this device.
2083
2084 If there are multiple matching configurations changing
2085 the same attribute, the last one is used.
2086
2087 memblock=debug [KNL] Enable memblock debug messages.
2088
2089 load_ramdisk= [RAM] List of ramdisks to load from floppy
2090 See Documentation/blockdev/ramdisk.txt.
2091
2092 lockd.nlm_grace_period=P [NFS] Assign grace period.
2093 Format: <integer>
2094
2095 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2096 Format: <integer>
2097
2098 lockd.nlm_timeout=T [NFS] Assign timeout value.
2099 Format: <integer>
2100
2101 lockd.nlm_udpport=M [NFS] Assign UDP port.
2102 Format: <integer>
2103
2104 locktorture.nreaders_stress= [KNL]
2105 Set the number of locking read-acquisition kthreads.
2106 Defaults to being automatically set based on the
2107 number of online CPUs.
2108
2109 locktorture.nwriters_stress= [KNL]
2110 Set the number of locking write-acquisition kthreads.
2111
2112 locktorture.onoff_holdoff= [KNL]
2113 Set time (s) after boot for CPU-hotplug testing.
2114
2115 locktorture.onoff_interval= [KNL]
2116 Set time (s) between CPU-hotplug operations, or
2117 zero to disable CPU-hotplug testing.
2118
2119 locktorture.shuffle_interval= [KNL]
2120 Set task-shuffle interval (jiffies). Shuffling
2121 tasks allows some CPUs to go into dyntick-idle
2122 mode during the locktorture test.
2123
2124 locktorture.shutdown_secs= [KNL]
2125 Set time (s) after boot system shutdown. This
2126 is useful for hands-off automated testing.
2127
2128 locktorture.stat_interval= [KNL]
2129 Time (s) between statistics printk()s.
2130
2131 locktorture.stutter= [KNL]
2132 Time (s) to stutter testing, for example,
2133 specifying five seconds causes the test to run for
2134 five seconds, wait for five seconds, and so on.
2135 This tests the locking primitive's ability to
2136 transition abruptly to and from idle.
2137
2138 locktorture.torture_runnable= [BOOT]
2139 Start locktorture running at boot time.
2140
2141 locktorture.torture_type= [KNL]
2142 Specify the locking implementation to test.
2143
2144 locktorture.verbose= [KNL]
2145 Enable additional printk() statements.
2146
2147 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2148 Format: <irq>
2149
2150 loglevel= All Kernel Messages with a loglevel smaller than the
2151 console loglevel will be printed to the console. It can
2152 also be changed with klogd or other programs. The
2153 loglevels are defined as follows:
2154
2155 0 (KERN_EMERG) system is unusable
2156 1 (KERN_ALERT) action must be taken immediately
2157 2 (KERN_CRIT) critical conditions
2158 3 (KERN_ERR) error conditions
2159 4 (KERN_WARNING) warning conditions
2160 5 (KERN_NOTICE) normal but significant condition
2161 6 (KERN_INFO) informational
2162 7 (KERN_DEBUG) debug-level messages
2163
2164 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2165 in bytes. n must be a power of two and greater
2166 than the minimal size. The minimal size is defined
2167 by LOG_BUF_SHIFT kernel config parameter. There is
2168 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2169 that allows to increase the default size depending on
2170 the number of CPUs. See init/Kconfig for more details.
2171
2172 logo.nologo [FB] Disables display of the built-in Linux logo.
2173 This may be used to provide more screen space for
2174 kernel log messages and is useful when debugging
2175 kernel boot problems.
2176
2177 lp=0 [LP] Specify parallel ports to use, e.g,
2178 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2179 lp=reset first parallel port). 'lp=0' disables the
2180 lp=auto printer driver. 'lp=reset' (which can be
2181 specified in addition to the ports) causes
2182 attached printers to be reset. Using
2183 lp=port1,port2,... specifies the parallel ports
2184 to associate lp devices with, starting with
2185 lp0. A port specification may be 'none' to skip
2186 that lp device, or a parport name such as
2187 'parport0'. Specifying 'lp=auto' instead of a
2188 port specification list means that device IDs
2189 from each port should be examined, to see if
2190 an IEEE 1284-compliant printer is attached; if
2191 so, the driver will manage that printer.
2192 See also header of drivers/char/lp.c.
2193
2194 lpj=n [KNL]
2195 Sets loops_per_jiffy to given constant, thus avoiding
2196 time-consuming boot-time autodetection (up to 250 ms per
2197 CPU). 0 enables autodetection (default). To determine
2198 the correct value for your kernel, boot with normal
2199 autodetection and see what value is printed. Note that
2200 on SMP systems the preset will be applied to all CPUs,
2201 which is likely to cause problems if your CPUs need
2202 significantly divergent settings. An incorrect value
2203 will cause delays in the kernel to be wrong, leading to
2204 unpredictable I/O errors and other breakage. Although
2205 unlikely, in the extreme case this might damage your
2206 hardware.
2207
2208 ltpc= [NET]
2209 Format: <io>,<irq>,<dma>
2210
2211 machvec= [IA-64] Force the use of a particular machine-vector
2212 (machvec) in a generic kernel.
2213 Example: machvec=hpzx1_swiotlb
2214
2215 machtype= [Loongson] Share the same kernel image file between different
2216 yeeloong laptop.
2217 Example: machtype=lemote-yeeloong-2f-7inch
2218
2219 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2220 than or equal to this physical address is ignored.
2221
2222 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2223 will bring up during bootup. maxcpus=n : n >= 0 limits
2224 the kernel to bring up 'n' processors. Surely after
2225 bootup you can bring up the other plugged cpu by executing
2226 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2227 only takes effect during system bootup.
2228 While n=0 is a special case, it is equivalent to "nosmp",
2229 which also disables the IO APIC.
2230
2231 max_loop= [LOOP] The number of loop block devices that get
2232 (loop.max_loop) unconditionally pre-created at init time. The default
2233 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2234 of statically allocating a predefined number, loop
2235 devices can be requested on-demand with the
2236 /dev/loop-control interface.
2237
2238 mce [X86-32] Machine Check Exception
2239
2240 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2241
2242 md= [HW] RAID subsystems devices and level
2243 See Documentation/admin-guide/md.rst.
2244
2245 mdacon= [MDA]
2246 Format: <first>,<last>
2247 Specifies range of consoles to be captured by the MDA.
2248
2249 mds= [X86,INTEL]
2250 Control mitigation for the Micro-architectural Data
2251 Sampling (MDS) vulnerability.
2252
2253 Certain CPUs are vulnerable to an exploit against CPU
2254 internal buffers which can forward information to a
2255 disclosure gadget under certain conditions.
2256
2257 In vulnerable processors, the speculatively
2258 forwarded data can be used in a cache side channel
2259 attack, to access data to which the attacker does
2260 not have direct access.
2261
2262 This parameter controls the MDS mitigation. The
2263 options are:
2264
2265 full - Enable MDS mitigation on vulnerable CPUs
2266 full,nosmt - Enable MDS mitigation and disable
2267 SMT on vulnerable CPUs
2268 off - Unconditionally disable MDS mitigation
2269
2270 On TAA-affected machines, mds=off can be prevented by
2271 an active TAA mitigation as both vulnerabilities are
2272 mitigated with the same mechanism so in order to disable
2273 this mitigation, you need to specify tsx_async_abort=off
2274 too.
2275
2276 Not specifying this option is equivalent to
2277 mds=full.
2278
2279 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2280
2281 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2282 Amount of memory to be used when the kernel is not able
2283 to see the whole system memory or for test.
2284 [X86] Work as limiting max address. Use together
2285 with memmap= to avoid physical address space collisions.
2286 Without memmap= PCI devices could be placed at addresses
2287 belonging to unused RAM.
2288
2289 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2290 memory.
2291
2292 memchunk=nn[KMG]
2293 [KNL,SH] Allow user to override the default size for
2294 per-device physically contiguous DMA buffers.
2295
2296 memhp_default_state=online/offline
2297 [KNL] Set the initial state for the memory hotplug
2298 onlining policy. If not specified, the default value is
2299 set according to the
2300 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2301 option.
2302 See Documentation/memory-hotplug.txt.
2303
2304 memmap=exactmap [KNL,X86] Enable setting of an exact
2305 E820 memory map, as specified by the user.
2306 Such memmap=exactmap lines can be constructed based on
2307 BIOS output or other requirements. See the memmap=nn@ss
2308 option description.
2309
2310 memmap=nn[KMG]@ss[KMG]
2311 [KNL] Force usage of a specific region of memory.
2312 Region of memory to be used is from ss to ss+nn.
2313 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2314 which limits max address to nn[KMG].
2315 Multiple different regions can be specified,
2316 comma delimited.
2317 Example:
2318 memmap=100M@2G,100M#3G,1G!1024G
2319
2320 memmap=nn[KMG]#ss[KMG]
2321 [KNL,ACPI] Mark specific memory as ACPI data.
2322 Region of memory to be marked is from ss to ss+nn.
2323
2324 memmap=nn[KMG]$ss[KMG]
2325 [KNL,ACPI] Mark specific memory as reserved.
2326 Region of memory to be reserved is from ss to ss+nn.
2327 Example: Exclude memory from 0x18690000-0x1869ffff
2328 memmap=64K$0x18690000
2329 or
2330 memmap=0x10000$0x18690000
2331 Some bootloaders may need an escape character before '$',
2332 like Grub2, otherwise '$' and the following number
2333 will be eaten.
2334
2335 memmap=nn[KMG]!ss[KMG]
2336 [KNL,X86] Mark specific memory as protected.
2337 Region of memory to be used, from ss to ss+nn.
2338 The memory region may be marked as e820 type 12 (0xc)
2339 and is NVDIMM or ADR memory.
2340
2341 memory_corruption_check=0/1 [X86]
2342 Some BIOSes seem to corrupt the first 64k of
2343 memory when doing things like suspend/resume.
2344 Setting this option will scan the memory
2345 looking for corruption. Enabling this will
2346 both detect corruption and prevent the kernel
2347 from using the memory being corrupted.
2348 However, its intended as a diagnostic tool; if
2349 repeatable BIOS-originated corruption always
2350 affects the same memory, you can use memmap=
2351 to prevent the kernel from using that memory.
2352
2353 memory_corruption_check_size=size [X86]
2354 By default it checks for corruption in the low
2355 64k, making this memory unavailable for normal
2356 use. Use this parameter to scan for
2357 corruption in more or less memory.
2358
2359 memory_corruption_check_period=seconds [X86]
2360 By default it checks for corruption every 60
2361 seconds. Use this parameter to check at some
2362 other rate. 0 disables periodic checking.
2363
2364 memtest= [KNL,X86,ARM] Enable memtest
2365 Format: <integer>
2366 default : 0 <disable>
2367 Specifies the number of memtest passes to be
2368 performed. Each pass selects another test
2369 pattern from a given set of patterns. Memtest
2370 fills the memory with this pattern, validates
2371 memory contents and reserves bad memory
2372 regions that are detected.
2373
2374 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2375 Valid arguments: on, off
2376 Default (depends on kernel configuration option):
2377 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2378 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2379 mem_encrypt=on: Activate SME
2380 mem_encrypt=off: Do not activate SME
2381
2382 Refer to Documentation/x86/amd-memory-encryption.txt
2383 for details on when memory encryption can be activated.
2384
2385 mem_sleep_default= [SUSPEND] Default system suspend mode:
2386 s2idle - Suspend-To-Idle
2387 shallow - Power-On Suspend or equivalent (if supported)
2388 deep - Suspend-To-RAM or equivalent (if supported)
2389 See Documentation/power/states.txt.
2390
2391 meye.*= [HW] Set MotionEye Camera parameters
2392 See Documentation/video4linux/meye.txt.
2393
2394 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2395 Multi-Function General Purpose Timers on AMD Geode
2396 platforms.
2397
2398 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2399 the BIOS has incorrectly applied a workaround. TinyBIOS
2400 version 0.98 is known to be affected, 0.99 fixes the
2401 problem by letting the user disable the workaround.
2402
2403 mga= [HW,DRM]
2404
2405 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2406 physical address is ignored.
2407
2408 mini2440= [ARM,HW,KNL]
2409 Format:[0..2][b][c][t]
2410 Default: "0tb"
2411 MINI2440 configuration specification:
2412 0 - The attached screen is the 3.5" TFT
2413 1 - The attached screen is the 7" TFT
2414 2 - The VGA Shield is attached (1024x768)
2415 Leaving out the screen size parameter will not load
2416 the TFT driver, and the framebuffer will be left
2417 unconfigured.
2418 b - Enable backlight. The TFT backlight pin will be
2419 linked to the kernel VESA blanking code and a GPIO
2420 LED. This parameter is not necessary when using the
2421 VGA shield.
2422 c - Enable the s3c camera interface.
2423 t - Reserved for enabling touchscreen support. The
2424 touchscreen support is not enabled in the mainstream
2425 kernel as of 2.6.30, a preliminary port can be found
2426 in the "bleeding edge" mini2440 support kernel at
2427 http://repo.or.cz/w/linux-2.6/mini2440.git
2428
2429 mitigations=
2430 [X86,PPC,S390,ARM64] Control optional mitigations for
2431 CPU vulnerabilities. This is a set of curated,
2432 arch-independent options, each of which is an
2433 aggregation of existing arch-specific options.
2434
2435 off
2436 Disable all optional CPU mitigations. This
2437 improves system performance, but it may also
2438 expose users to several CPU vulnerabilities.
2439 Equivalent to: nopti [X86,PPC]
2440 kpti=0 [ARM64]
2441 nospectre_v1 [PPC]
2442 nobp=0 [S390]
2443 nospectre_v1 [X86]
2444 nospectre_v2 [X86,PPC,S390,ARM64]
2445 spectre_v2_user=off [X86]
2446 spec_store_bypass_disable=off [X86,PPC]
2447 ssbd=force-off [ARM64]
2448 l1tf=off [X86]
2449 mds=off [X86]
2450 tsx_async_abort=off [X86]
2451 kvm.nx_huge_pages=off [X86]
2452
2453 Exceptions:
2454 This does not have any effect on
2455 kvm.nx_huge_pages when
2456 kvm.nx_huge_pages=force.
2457
2458 auto (default)
2459 Mitigate all CPU vulnerabilities, but leave SMT
2460 enabled, even if it's vulnerable. This is for
2461 users who don't want to be surprised by SMT
2462 getting disabled across kernel upgrades, or who
2463 have other ways of avoiding SMT-based attacks.
2464 Equivalent to: (default behavior)
2465
2466 auto,nosmt
2467 Mitigate all CPU vulnerabilities, disabling SMT
2468 if needed. This is for users who always want to
2469 be fully mitigated, even if it means losing SMT.
2470 Equivalent to: l1tf=flush,nosmt [X86]
2471 mds=full,nosmt [X86]
2472 tsx_async_abort=full,nosmt [X86]
2473
2474 mminit_loglevel=
2475 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2476 parameter allows control of the logging verbosity for
2477 the additional memory initialisation checks. A value
2478 of 0 disables mminit logging and a level of 4 will
2479 log everything. Information is printed at KERN_DEBUG
2480 so loglevel=8 may also need to be specified.
2481
2482 module.sig_enforce
2483 [KNL] When CONFIG_MODULE_SIG is set, this means that
2484 modules without (valid) signatures will fail to load.
2485 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2486 is always true, so this option does nothing.
2487
2488 module_blacklist= [KNL] Do not load a comma-separated list of
2489 modules. Useful for debugging problem modules.
2490
2491 mousedev.tap_time=
2492 [MOUSE] Maximum time between finger touching and
2493 leaving touchpad surface for touch to be considered
2494 a tap and be reported as a left button click (for
2495 touchpads working in absolute mode only).
2496 Format: <msecs>
2497 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2498 reporting absolute coordinates, such as tablets
2499 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2500 reporting absolute coordinates, such as tablets
2501
2502 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2503 is similar to kernelcore except it specifies the
2504 amount of memory used for migratable allocations.
2505 If both kernelcore and movablecore is specified,
2506 then kernelcore will be at *least* the specified
2507 value but may be more. If movablecore on its own
2508 is specified, the administrator must be careful
2509 that the amount of memory usable for all allocations
2510 is not too small.
2511
2512 movable_node [KNL] Boot-time switch to make hotplugable memory
2513 NUMA nodes to be movable. This means that the memory
2514 of such nodes will be usable only for movable
2515 allocations which rules out almost all kernel
2516 allocations. Use with caution!
2517
2518 MTD_Partition= [MTD]
2519 Format: <name>,<region-number>,<size>,<offset>
2520
2521 MTD_Region= [MTD] Format:
2522 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2523
2524 mtdparts= [MTD]
2525 See drivers/mtd/cmdlinepart.c.
2526
2527 multitce=off [PPC] This parameter disables the use of the pSeries
2528 firmware feature for updating multiple TCE entries
2529 at a time.
2530
2531 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2532
2533 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2534
2535 boundary - index of last SLC block on Flex-OneNAND.
2536 The remaining blocks are configured as MLC blocks.
2537 lock - Configure if Flex-OneNAND boundary should be locked.
2538 Once locked, the boundary cannot be changed.
2539 1 indicates lock status, 0 indicates unlock status.
2540
2541 mtdset= [ARM]
2542 ARM/S3C2412 JIVE boot control
2543
2544 See arch/arm/mach-s3c2412/mach-jive.c
2545
2546 mtouchusb.raw_coordinates=
2547 [HW] Make the MicroTouch USB driver use raw coordinates
2548 ('y', default) or cooked coordinates ('n')
2549
2550 mtrr_chunk_size=nn[KMG] [X86]
2551 used for mtrr cleanup. It is largest continuous chunk
2552 that could hold holes aka. UC entries.
2553
2554 mtrr_gran_size=nn[KMG] [X86]
2555 Used for mtrr cleanup. It is granularity of mtrr block.
2556 Default is 1.
2557 Large value could prevent small alignment from
2558 using up MTRRs.
2559
2560 mtrr_spare_reg_nr=n [X86]
2561 Format: <integer>
2562 Range: 0,7 : spare reg number
2563 Default : 1
2564 Used for mtrr cleanup. It is spare mtrr entries number.
2565 Set to 2 or more if your graphical card needs more.
2566
2567 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2568
2569 netdev= [NET] Network devices parameters
2570 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2571 Note that mem_start is often overloaded to mean
2572 something different and driver-specific.
2573 This usage is only documented in each driver source
2574 file if at all.
2575
2576 nf_conntrack.acct=
2577 [NETFILTER] Enable connection tracking flow accounting
2578 0 to disable accounting
2579 1 to enable accounting
2580 Default value is 0.
2581
2582 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2583 See Documentation/filesystems/nfs/nfsroot.txt.
2584
2585 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2586 See Documentation/filesystems/nfs/nfsroot.txt.
2587
2588 nfsrootdebug [NFS] enable nfsroot debugging messages.
2589 See Documentation/filesystems/nfs/nfsroot.txt.
2590
2591 nfs.callback_nr_threads=
2592 [NFSv4] set the total number of threads that the
2593 NFS client will assign to service NFSv4 callback
2594 requests.
2595
2596 nfs.callback_tcpport=
2597 [NFS] set the TCP port on which the NFSv4 callback
2598 channel should listen.
2599
2600 nfs.cache_getent=
2601 [NFS] sets the pathname to the program which is used
2602 to update the NFS client cache entries.
2603
2604 nfs.cache_getent_timeout=
2605 [NFS] sets the timeout after which an attempt to
2606 update a cache entry is deemed to have failed.
2607
2608 nfs.idmap_cache_timeout=
2609 [NFS] set the maximum lifetime for idmapper cache
2610 entries.
2611
2612 nfs.enable_ino64=
2613 [NFS] enable 64-bit inode numbers.
2614 If zero, the NFS client will fake up a 32-bit inode
2615 number for the readdir() and stat() syscalls instead
2616 of returning the full 64-bit number.
2617 The default is to return 64-bit inode numbers.
2618
2619 nfs.max_session_cb_slots=
2620 [NFSv4.1] Sets the maximum number of session
2621 slots the client will assign to the callback
2622 channel. This determines the maximum number of
2623 callbacks the client will process in parallel for
2624 a particular server.
2625
2626 nfs.max_session_slots=
2627 [NFSv4.1] Sets the maximum number of session slots
2628 the client will attempt to negotiate with the server.
2629 This limits the number of simultaneous RPC requests
2630 that the client can send to the NFSv4.1 server.
2631 Note that there is little point in setting this
2632 value higher than the max_tcp_slot_table_limit.
2633
2634 nfs.nfs4_disable_idmapping=
2635 [NFSv4] When set to the default of '1', this option
2636 ensures that both the RPC level authentication
2637 scheme and the NFS level operations agree to use
2638 numeric uids/gids if the mount is using the
2639 'sec=sys' security flavour. In effect it is
2640 disabling idmapping, which can make migration from
2641 legacy NFSv2/v3 systems to NFSv4 easier.
2642 Servers that do not support this mode of operation
2643 will be autodetected by the client, and it will fall
2644 back to using the idmapper.
2645 To turn off this behaviour, set the value to '0'.
2646 nfs.nfs4_unique_id=
2647 [NFS4] Specify an additional fixed unique ident-
2648 ification string that NFSv4 clients can insert into
2649 their nfs_client_id4 string. This is typically a
2650 UUID that is generated at system install time.
2651
2652 nfs.send_implementation_id =
2653 [NFSv4.1] Send client implementation identification
2654 information in exchange_id requests.
2655 If zero, no implementation identification information
2656 will be sent.
2657 The default is to send the implementation identification
2658 information.
2659
2660 nfs.recover_lost_locks =
2661 [NFSv4] Attempt to recover locks that were lost due
2662 to a lease timeout on the server. Please note that
2663 doing this risks data corruption, since there are
2664 no guarantees that the file will remain unchanged
2665 after the locks are lost.
2666 If you want to enable the kernel legacy behaviour of
2667 attempting to recover these locks, then set this
2668 parameter to '1'.
2669 The default parameter value of '0' causes the kernel
2670 not to attempt recovery of lost locks.
2671
2672 nfs4.layoutstats_timer =
2673 [NFSv4.2] Change the rate at which the kernel sends
2674 layoutstats to the pNFS metadata server.
2675
2676 Setting this to value to 0 causes the kernel to use
2677 whatever value is the default set by the layout
2678 driver. A non-zero value sets the minimum interval
2679 in seconds between layoutstats transmissions.
2680
2681 nfsd.nfs4_disable_idmapping=
2682 [NFSv4] When set to the default of '1', the NFSv4
2683 server will return only numeric uids and gids to
2684 clients using auth_sys, and will accept numeric uids
2685 and gids from such clients. This is intended to ease
2686 migration from NFSv2/v3.
2687
2688 nmi_debug= [KNL,SH] Specify one or more actions to take
2689 when a NMI is triggered.
2690 Format: [state][,regs][,debounce][,die]
2691
2692 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2693 Format: [panic,][nopanic,][num]
2694 Valid num: 0 or 1
2695 0 - turn hardlockup detector in nmi_watchdog off
2696 1 - turn hardlockup detector in nmi_watchdog on
2697 When panic is specified, panic when an NMI watchdog
2698 timeout occurs (or 'nopanic' to override the opposite
2699 default). To disable both hard and soft lockup detectors,
2700 please see 'nowatchdog'.
2701 This is useful when you use a panic=... timeout and
2702 need the box quickly up again.
2703
2704 netpoll.carrier_timeout=
2705 [NET] Specifies amount of time (in seconds) that
2706 netpoll should wait for a carrier. By default netpoll
2707 waits 4 seconds.
2708
2709 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2710 emulation library even if a 387 maths coprocessor
2711 is present.
2712
2713 no_console_suspend
2714 [HW] Never suspend the console
2715 Disable suspending of consoles during suspend and
2716 hibernate operations. Once disabled, debugging
2717 messages can reach various consoles while the rest
2718 of the system is being put to sleep (ie, while
2719 debugging driver suspend/resume hooks). This may
2720 not work reliably with all consoles, but is known
2721 to work with serial and VGA consoles.
2722 To facilitate more flexible debugging, we also add
2723 console_suspend, a printk module parameter to control
2724 it. Users could use console_suspend (usually
2725 /sys/module/printk/parameters/console_suspend) to
2726 turn on/off it dynamically.
2727
2728 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2729 caches in the slab allocator. Saves per-node memory,
2730 but will impact performance.
2731
2732 noalign [KNL,ARM]
2733
2734 noaltinstr [S390] Disables alternative instructions patching
2735 (CPU alternatives feature).
2736
2737 noapic [SMP,APIC] Tells the kernel to not make use of any
2738 IOAPICs that may be present in the system.
2739
2740 noautogroup Disable scheduler automatic task group creation.
2741
2742 nobats [PPC] Do not use BATs for mapping kernel lowmem
2743 on "Classic" PPC cores.
2744
2745 nocache [ARM]
2746
2747 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2748
2749 nodelayacct [KNL] Disable per-task delay accounting
2750
2751 nodsp [SH] Disable hardware DSP at boot time.
2752
2753 noefi Disable EFI runtime services support.
2754
2755 noexec [IA-64]
2756
2757 noexec [X86]
2758 On X86-32 available only on PAE configured kernels.
2759 noexec=on: enable non-executable mappings (default)
2760 noexec=off: disable non-executable mappings
2761
2762 nosmap [X86]
2763 Disable SMAP (Supervisor Mode Access Prevention)
2764 even if it is supported by processor.
2765
2766 nosmep [X86]
2767 Disable SMEP (Supervisor Mode Execution Prevention)
2768 even if it is supported by processor.
2769
2770 noexec32 [X86-64]
2771 This affects only 32-bit executables.
2772 noexec32=on: enable non-executable mappings (default)
2773 read doesn't imply executable mappings
2774 noexec32=off: disable non-executable mappings
2775 read implies executable mappings
2776
2777 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2778
2779 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2780 register save and restore. The kernel will only save
2781 legacy floating-point registers on task switch.
2782
2783 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2784
2785 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2786 Equivalent to smt=1.
2787
2788 [KNL,x86] Disable symmetric multithreading (SMT).
2789 nosmt=force: Force disable SMT, cannot be undone
2790 via the sysfs control file.
2791
2792 nospectre_v1 [X66, PPC] Disable mitigations for Spectre Variant 1
2793 (bounds check bypass). With this option data leaks
2794 are possible in the system.
2795
2796 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2797 the Spectre variant 2 (indirect branch prediction)
2798 vulnerability. System may allow data leaks with this
2799 option.
2800
2801 nospec_store_bypass_disable
2802 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2803
2804 noxsave [BUGS=X86] Disables x86 extended register state save
2805 and restore using xsave. The kernel will fallback to
2806 enabling legacy floating-point and sse state.
2807
2808 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2809 register states. The kernel will fall back to use
2810 xsave to save the states. By using this parameter,
2811 performance of saving the states is degraded because
2812 xsave doesn't support modified optimization while
2813 xsaveopt supports it on xsaveopt enabled systems.
2814
2815 noxsaves [X86] Disables xsaves and xrstors used in saving and
2816 restoring x86 extended register state in compacted
2817 form of xsave area. The kernel will fall back to use
2818 xsaveopt and xrstor to save and restore the states
2819 in standard form of xsave area. By using this
2820 parameter, xsave area per process might occupy more
2821 memory on xsaves enabled systems.
2822
2823 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2824 wfi(ARM) instruction doesn't work correctly and not to
2825 use it. This is also useful when using JTAG debugger.
2826
2827 no_file_caps Tells the kernel not to honor file capabilities. The
2828 only way then for a file to be executed with privilege
2829 is to be setuid root or executed by root.
2830
2831 nohalt [IA-64] Tells the kernel not to use the power saving
2832 function PAL_HALT_LIGHT when idle. This increases
2833 power-consumption. On the positive side, it reduces
2834 interrupt wake-up latency, which may improve performance
2835 in certain environments such as networked servers or
2836 real-time systems.
2837
2838 nohibernate [HIBERNATION] Disable hibernation and resume.
2839
2840 nohz= [KNL] Boottime enable/disable dynamic ticks
2841 Valid arguments: on, off
2842 Default: on
2843
2844 nohz_full= [KNL,BOOT]
2845 The argument is a cpu list, as described above.
2846 In kernels built with CONFIG_NO_HZ_FULL=y, set
2847 the specified list of CPUs whose tick will be stopped
2848 whenever possible. The boot CPU will be forced outside
2849 the range to maintain the timekeeping. Any CPUs
2850 in this list will have their RCU callbacks offloaded,
2851 just as if they had also been called out in the
2852 rcu_nocbs= boot parameter.
2853
2854 noiotrap [SH] Disables trapped I/O port accesses.
2855
2856 noirqdebug [X86-32] Disables the code which attempts to detect and
2857 disable unhandled interrupt sources.
2858
2859 no_timer_check [X86,APIC] Disables the code which tests for
2860 broken timer IRQ sources.
2861
2862 noisapnp [ISAPNP] Disables ISA PnP code.
2863
2864 noinitrd [RAM] Tells the kernel not to load any configured
2865 initial RAM disk.
2866
2867 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2868 remapping.
2869 [Deprecated - use intremap=off]
2870
2871 nointroute [IA-64]
2872
2873 noinvpcid [X86] Disable the INVPCID cpu feature.
2874
2875 nojitter [IA-64] Disables jitter checking for ITC timers.
2876
2877 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2878
2879 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2880 fault handling.
2881
2882 no-vmw-sched-clock
2883 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2884 clock and use the default one.
2885
2886 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2887 steal time is computed, but won't influence scheduler
2888 behaviour
2889
2890 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2891
2892 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2893
2894 noltlbs [PPC] Do not use large page/tlb entries for kernel
2895 lowmem mapping on PPC40x and PPC8xx
2896
2897 nomca [IA-64] Disable machine check abort handling
2898
2899 nomce [X86-32] Disable Machine Check Exception
2900
2901 nomfgpt [X86-32] Disable Multi-Function General Purpose
2902 Timer usage (for AMD Geode machines).
2903
2904 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2905 shutdown the other cpus. Instead use the REBOOT_VECTOR
2906 irq.
2907
2908 nomodule Disable module load
2909
2910 nopat [X86] Disable PAT (page attribute table extension of
2911 pagetables) support.
2912
2913 nopcid [X86-64] Disable the PCID cpu feature.
2914
2915 norandmaps Don't use address space randomization. Equivalent to
2916 echo 0 > /proc/sys/kernel/randomize_va_space
2917
2918 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2919 with UP alternatives
2920
2921 nordrand [X86] Disable kernel use of the RDRAND and
2922 RDSEED instructions even if they are supported
2923 by the processor. RDRAND and RDSEED are still
2924 available to user space applications.
2925
2926 noresume [SWSUSP] Disables resume and restores original swap
2927 space.
2928
2929 no-scroll [VGA] Disables scrollback.
2930 This is required for the Braillex ib80-piezo Braille
2931 reader made by F.H. Papenmeier (Germany).
2932
2933 nosbagart [IA-64]
2934
2935 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2936
2937 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2938 and disable the IO APIC. legacy for "maxcpus=0".
2939
2940 nosoftlockup [KNL] Disable the soft-lockup detector.
2941
2942 nosync [HW,M68K] Disables sync negotiation for all devices.
2943
2944 notsc [BUGS=X86-32] Disable Time Stamp Counter
2945
2946 nowatchdog [KNL] Disable both lockup detectors, i.e.
2947 soft-lockup and NMI watchdog (hard-lockup).
2948
2949 nowb [ARM]
2950
2951 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2952
2953 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2954 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2955 Some features depend on CPU0. Known dependencies are:
2956 1. Resume from suspend/hibernate depends on CPU0.
2957 Suspend/hibernate will fail if CPU0 is offline and you
2958 need to online CPU0 before suspend/hibernate.
2959 2. PIC interrupts also depend on CPU0. CPU0 can't be
2960 removed if a PIC interrupt is detected.
2961 It's said poweroff/reboot may depend on CPU0 on some
2962 machines although I haven't seen such issues so far
2963 after CPU0 is offline on a few tested machines.
2964 If the dependencies are under your control, you can
2965 turn on cpu0_hotplug.
2966
2967 nps_mtm_hs_ctr= [KNL,ARC]
2968 This parameter sets the maximum duration, in
2969 cycles, each HW thread of the CTOP can run
2970 without interruptions, before HW switches it.
2971 The actual maximum duration is 16 times this
2972 parameter's value.
2973 Format: integer between 1 and 255
2974 Default: 255
2975
2976 nptcg= [IA-64] Override max number of concurrent global TLB
2977 purges which is reported from either PAL_VM_SUMMARY or
2978 SAL PALO.
2979
2980 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2981 could support. nr_cpus=n : n >= 1 limits the kernel to
2982 support 'n' processors. It could be larger than the
2983 number of already plugged CPU during bootup, later in
2984 runtime you can physically add extra cpu until it reaches
2985 n. So during boot up some boot time memory for per-cpu
2986 variables need be pre-allocated for later physical cpu
2987 hot plugging.
2988
2989 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2990
2991 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2992 Allowed values are enable and disable
2993
2994 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2995 'node', 'default' can be specified
2996 This can be set from sysctl after boot.
2997 See Documentation/sysctl/vm.txt for details.
2998
2999 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3000 See Documentation/debugging-via-ohci1394.txt for more
3001 info.
3002
3003 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3004 Rather than timing out after 20 ms if an EC
3005 command is not properly ACKed, override the length
3006 of the timeout. We have interrupts disabled while
3007 waiting for the ACK, so if this is set too high
3008 interrupts *may* be lost!
3009
3010 omap_mux= [OMAP] Override bootloader pin multiplexing.
3011 Format: <mux_mode0.mode_name=value>...
3012 For example, to override I2C bus2:
3013 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3014
3015 oprofile.timer= [HW]
3016 Use timer interrupt instead of performance counters
3017
3018 oprofile.cpu_type= Force an oprofile cpu type
3019 This might be useful if you have an older oprofile
3020 userland or if you want common events.
3021 Format: { arch_perfmon }
3022 arch_perfmon: [X86] Force use of architectural
3023 perfmon on Intel CPUs instead of the
3024 CPU specific event set.
3025 timer: [X86] Force use of architectural NMI
3026 timer mode (see also oprofile.timer
3027 for generic hr timer mode)
3028
3029 oops=panic Always panic on oopses. Default is to just kill the
3030 process, but there is a small probability of
3031 deadlocking the machine.
3032 This will also cause panics on machine check exceptions.
3033 Useful together with panic=30 to trigger a reboot.
3034
3035 OSS [HW,OSS]
3036 See Documentation/sound/oss/oss-parameters.txt
3037
3038 page_owner= [KNL] Boot-time page_owner enabling option.
3039 Storage of the information about who allocated
3040 each page is disabled in default. With this switch,
3041 we can turn it on.
3042 on: enable the feature
3043
3044 page_poison= [KNL] Boot-time parameter changing the state of
3045 poisoning on the buddy allocator.
3046 off: turn off poisoning
3047 on: turn on poisoning
3048
3049 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3050 timeout > 0: seconds before rebooting
3051 timeout = 0: wait forever
3052 timeout < 0: reboot immediately
3053 Format: <timeout>
3054
3055 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3056 on a WARN().
3057
3058 crash_kexec_post_notifiers
3059 Run kdump after running panic-notifiers and dumping
3060 kmsg. This only for the users who doubt kdump always
3061 succeeds in any situation.
3062 Note that this also increases risks of kdump failure,
3063 because some panic notifiers can make the crashed
3064 kernel more unstable.
3065
3066 parkbd.port= [HW] Parallel port number the keyboard adapter is
3067 connected to, default is 0.
3068 Format: <parport#>
3069 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3070 0 for XT, 1 for AT (default is AT).
3071 Format: <mode>
3072
3073 parport= [HW,PPT] Specify parallel ports. 0 disables.
3074 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3075 Use 'auto' to force the driver to use any
3076 IRQ/DMA settings detected (the default is to
3077 ignore detected IRQ/DMA settings because of
3078 possible conflicts). You can specify the base
3079 address, IRQ, and DMA settings; IRQ and DMA
3080 should be numbers, or 'auto' (for using detected
3081 settings on that particular port), or 'nofifo'
3082 (to avoid using a FIFO even if it is detected).
3083 Parallel ports are assigned in the order they
3084 are specified on the command line, starting
3085 with parport0.
3086
3087 parport_init_mode= [HW,PPT]
3088 Configure VIA parallel port to operate in
3089 a specific mode. This is necessary on Pegasos
3090 computer where firmware has no options for setting
3091 up parallel port mode and sets it to spp.
3092 Currently this function knows 686a and 8231 chips.
3093 Format: [spp|ps2|epp|ecp|ecpepp]
3094
3095 pause_on_oops=
3096 Halt all CPUs after the first oops has been printed for
3097 the specified number of seconds. This is to be used if
3098 your oopses keep scrolling off the screen.
3099
3100 pcbit= [HW,ISDN]
3101
3102 pcd. [PARIDE]
3103 See header of drivers/block/paride/pcd.c.
3104 See also Documentation/blockdev/paride.txt.
3105
3106 pci=option[,option...] [PCI] various PCI subsystem options:
3107 earlydump [X86] dump PCI config space before the kernel
3108 changes anything
3109 off [X86] don't probe for the PCI bus
3110 bios [X86-32] force use of PCI BIOS, don't access
3111 the hardware directly. Use this if your machine
3112 has a non-standard PCI host bridge.
3113 nobios [X86-32] disallow use of PCI BIOS, only direct
3114 hardware access methods are allowed. Use this
3115 if you experience crashes upon bootup and you
3116 suspect they are caused by the BIOS.
3117 conf1 [X86] Force use of PCI Configuration Access
3118 Mechanism 1 (config address in IO port 0xCF8,
3119 data in IO port 0xCFC, both 32-bit).
3120 conf2 [X86] Force use of PCI Configuration Access
3121 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3122 the function, IO port 0xCFA, also 8-bit, sets
3123 bus number. The config space is then accessed
3124 through ports 0xC000-0xCFFF).
3125 See http://wiki.osdev.org/PCI for more info
3126 on the configuration access mechanisms.
3127 noaer [PCIE] If the PCIEAER kernel config parameter is
3128 enabled, this kernel boot option can be used to
3129 disable the use of PCIE advanced error reporting.
3130 nodomains [PCI] Disable support for multiple PCI
3131 root domains (aka PCI segments, in ACPI-speak).
3132 nommconf [X86] Disable use of MMCONFIG for PCI
3133 Configuration
3134 check_enable_amd_mmconf [X86] check for and enable
3135 properly configured MMIO access to PCI
3136 config space on AMD family 10h CPU
3137 nomsi [MSI] If the PCI_MSI kernel config parameter is
3138 enabled, this kernel boot option can be used to
3139 disable the use of MSI interrupts system-wide.
3140 noioapicquirk [APIC] Disable all boot interrupt quirks.
3141 Safety option to keep boot IRQs enabled. This
3142 should never be necessary.
3143 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3144 primary IO-APIC for bridges that cannot disable
3145 boot IRQs. This fixes a source of spurious IRQs
3146 when the system masks IRQs.
3147 noioapicreroute [APIC] Disable workaround that uses the
3148 boot IRQ equivalent of an IRQ that connects to
3149 a chipset where boot IRQs cannot be disabled.
3150 The opposite of ioapicreroute.
3151 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3152 routing table. These calls are known to be buggy
3153 on several machines and they hang the machine
3154 when used, but on other computers it's the only
3155 way to get the interrupt routing table. Try
3156 this option if the kernel is unable to allocate
3157 IRQs or discover secondary PCI buses on your
3158 motherboard.
3159 rom [X86] Assign address space to expansion ROMs.
3160 Use with caution as certain devices share
3161 address decoders between ROMs and other
3162 resources.
3163 norom [X86] Do not assign address space to
3164 expansion ROMs that do not already have
3165 BIOS assigned address ranges.
3166 nobar [X86] Do not assign address space to the
3167 BARs that weren't assigned by the BIOS.
3168 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3169 assigned automatically to PCI devices. You can
3170 make the kernel exclude IRQs of your ISA cards
3171 this way.
3172 pirqaddr=0xAAAAA [X86] Specify the physical address
3173 of the PIRQ table (normally generated
3174 by the BIOS) if it is outside the
3175 F0000h-100000h range.
3176 lastbus=N [X86] Scan all buses thru bus #N. Can be
3177 useful if the kernel is unable to find your
3178 secondary buses and you want to tell it
3179 explicitly which ones they are.
3180 assign-busses [X86] Always assign all PCI bus
3181 numbers ourselves, overriding
3182 whatever the firmware may have done.
3183 usepirqmask [X86] Honor the possible IRQ mask stored
3184 in the BIOS $PIR table. This is needed on
3185 some systems with broken BIOSes, notably
3186 some HP Pavilion N5400 and Omnibook XE3
3187 notebooks. This will have no effect if ACPI
3188 IRQ routing is enabled.
3189 noacpi [X86] Do not use ACPI for IRQ routing
3190 or for PCI scanning.
3191 use_crs [X86] Use PCI host bridge window information
3192 from ACPI. On BIOSes from 2008 or later, this
3193 is enabled by default. If you need to use this,
3194 please report a bug.
3195 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3196 If you need to use this, please report a bug.
3197 routeirq Do IRQ routing for all PCI devices.
3198 This is normally done in pci_enable_device(),
3199 so this option is a temporary workaround
3200 for broken drivers that don't call it.
3201 skip_isa_align [X86] do not align io start addr, so can
3202 handle more pci cards
3203 noearly [X86] Don't do any early type 1 scanning.
3204 This might help on some broken boards which
3205 machine check when some devices' config space
3206 is read. But various workarounds are disabled
3207 and some IOMMU drivers will not work.
3208 bfsort Sort PCI devices into breadth-first order.
3209 This sorting is done to get a device
3210 order compatible with older (<= 2.4) kernels.
3211 nobfsort Don't sort PCI devices into breadth-first order.
3212 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3213 tuning and use the BIOS-configured MPS defaults.
3214 pcie_bus_safe Set every device's MPS to the largest value
3215 supported by all devices below the root complex.
3216 pcie_bus_perf Set device MPS to the largest allowable MPS
3217 based on its parent bus. Also set MRRS (Max
3218 Read Request Size) to the largest supported
3219 value (no larger than the MPS that the device
3220 or bus can support) for best performance.
3221 pcie_bus_peer2peer Set every device's MPS to 128B, which
3222 every device is guaranteed to support. This
3223 configuration allows peer-to-peer DMA between
3224 any pair of devices, possibly at the cost of
3225 reduced performance. This also guarantees
3226 that hot-added devices will work.
3227 cbiosize=nn[KMG] The fixed amount of bus space which is
3228 reserved for the CardBus bridge's IO window.
3229 The default value is 256 bytes.
3230 cbmemsize=nn[KMG] The fixed amount of bus space which is
3231 reserved for the CardBus bridge's memory
3232 window. The default value is 64 megabytes.
3233 resource_alignment=
3234 Format:
3235 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3236 [<order of align>@]pci:<vendor>:<device>\
3237 [:<subvendor>:<subdevice>][; ...]
3238 Specifies alignment and device to reassign
3239 aligned memory resources.
3240 If <order of align> is not specified,
3241 PAGE_SIZE is used as alignment.
3242 PCI-PCI bridge can be specified, if resource
3243 windows need to be expanded.
3244 To specify the alignment for several
3245 instances of a device, the PCI vendor,
3246 device, subvendor, and subdevice may be
3247 specified, e.g., 4096@pci:8086:9c22:103c:198f
3248 ecrc= Enable/disable PCIe ECRC (transaction layer
3249 end-to-end CRC checking).
3250 bios: Use BIOS/firmware settings. This is the
3251 the default.
3252 off: Turn ECRC off
3253 on: Turn ECRC on.
3254 hpiosize=nn[KMG] The fixed amount of bus space which is
3255 reserved for hotplug bridge's IO window.
3256 Default size is 256 bytes.
3257 hpmemsize=nn[KMG] The fixed amount of bus space which is
3258 reserved for hotplug bridge's memory window.
3259 Default size is 2 megabytes.
3260 hpbussize=nn The minimum amount of additional bus numbers
3261 reserved for buses below a hotplug bridge.
3262 Default is 1.
3263 realloc= Enable/disable reallocating PCI bridge resources
3264 if allocations done by BIOS are too small to
3265 accommodate resources required by all child
3266 devices.
3267 off: Turn realloc off
3268 on: Turn realloc on
3269 realloc same as realloc=on
3270 noari do not use PCIe ARI.
3271 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3272 only look for one device below a PCIe downstream
3273 port.
3274
3275 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3276 Management.
3277 off Disable ASPM.
3278 force Enable ASPM even on devices that claim not to support it.
3279 WARNING: Forcing ASPM on may cause system lockups.
3280
3281 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3282 nomsi Do not use MSI for PCI Express Native Hotplug (this
3283 makes all PCIe ports use INTx for hotplug services).
3284
3285 pcie_ports= [PCIE] PCIe ports handling:
3286 auto Ask the BIOS whether or not to use native PCIe services
3287 associated with PCIe ports (PME, hot-plug, AER). Use
3288 them only if that is allowed by the BIOS.
3289 native Use native PCIe services associated with PCIe ports
3290 unconditionally.
3291 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3292 ports driver.
3293
3294 pcie_port_pm= [PCIE] PCIe port power management handling:
3295 off Disable power management of all PCIe ports
3296 force Forcibly enable power management of all PCIe ports
3297
3298 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3299 nomsi Do not use MSI for native PCIe PME signaling (this makes
3300 all PCIe root ports use INTx for all services).
3301
3302 pcmv= [HW,PCMCIA] BadgePAD 4
3303
3304 pd_ignore_unused
3305 [PM]
3306 Keep all power-domains already enabled by bootloader on,
3307 even if no driver has claimed them. This is useful
3308 for debug and development, but should not be
3309 needed on a platform with proper driver support.
3310
3311 pd. [PARIDE]
3312 See Documentation/blockdev/paride.txt.
3313
3314 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3315 boot time.
3316 Format: { 0 | 1 }
3317 See arch/parisc/kernel/pdc_chassis.c
3318
3319 percpu_alloc= Select which percpu first chunk allocator to use.
3320 Currently supported values are "embed" and "page".
3321 Archs may support subset or none of the selections.
3322 See comments in mm/percpu.c for details on each
3323 allocator. This parameter is primarily for debugging
3324 and performance comparison.
3325
3326 pf. [PARIDE]
3327 See Documentation/blockdev/paride.txt.
3328
3329 pg. [PARIDE]
3330 See Documentation/blockdev/paride.txt.
3331
3332 pirq= [SMP,APIC] Manual mp-table setup
3333 See Documentation/x86/i386/IO-APIC.txt.
3334
3335 plip= [PPT,NET] Parallel port network link
3336 Format: { parport<nr> | timid | 0 }
3337 See also Documentation/parport.txt.
3338
3339 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3340 Override pmtimer IOPort with a hex value.
3341 e.g. pmtmr=0x508
3342
3343 pnp.debug=1 [PNP]
3344 Enable PNP debug messages (depends on the
3345 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3346 via /sys/module/pnp/parameters/debug. We always show
3347 current resource usage; turning this on also shows
3348 possible settings and some assignment information.
3349
3350 pnpacpi= [ACPI]
3351 { off }
3352
3353 pnpbios= [ISAPNP]
3354 { on | off | curr | res | no-curr | no-res }
3355
3356 pnp_reserve_irq=
3357 [ISAPNP] Exclude IRQs for the autoconfiguration
3358
3359 pnp_reserve_dma=
3360 [ISAPNP] Exclude DMAs for the autoconfiguration
3361
3362 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3363 Ranges are in pairs (I/O port base and size).
3364
3365 pnp_reserve_mem=
3366 [ISAPNP] Exclude memory regions for the
3367 autoconfiguration.
3368 Ranges are in pairs (memory base and size).
3369
3370 ports= [IP_VS_FTP] IPVS ftp helper module
3371 Default is 21.
3372 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3373 may be specified.
3374 Format: <port>,<port>....
3375
3376 powersave=off [PPC] This option disables power saving features.
3377 It specifically disables cpuidle and sets the
3378 platform machine description specific power_save
3379 function to NULL. On Idle the CPU just reduces
3380 execution priority.
3381
3382 ppc_strict_facility_enable
3383 [PPC] This option catches any kernel floating point,
3384 Altivec, VSX and SPE outside of regions specifically
3385 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3386 There is some performance impact when enabling this.
3387
3388 print-fatal-signals=
3389 [KNL] debug: print fatal signals
3390
3391 If enabled, warn about various signal handling
3392 related application anomalies: too many signals,
3393 too many POSIX.1 timers, fatal signals causing a
3394 coredump - etc.
3395
3396 If you hit the warning due to signal overflow,
3397 you might want to try "ulimit -i unlimited".
3398
3399 default: off.
3400
3401 printk.always_kmsg_dump=
3402 Trigger kmsg_dump for cases other than kernel oops or
3403 panics
3404 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3405 default: disabled
3406
3407 printk.devkmsg={on,off,ratelimit}
3408 Control writing to /dev/kmsg.
3409 on - unlimited logging to /dev/kmsg from userspace
3410 off - logging to /dev/kmsg disabled
3411 ratelimit - ratelimit the logging
3412 Default: ratelimit
3413
3414 printk.time= Show timing data prefixed to each printk message line
3415 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3416
3417 processor.max_cstate= [HW,ACPI]
3418 Limit processor to maximum C-state
3419 max_cstate=9 overrides any DMI blacklist limit.
3420
3421 processor.nocst [HW,ACPI]
3422 Ignore the _CST method to determine C-states,
3423 instead using the legacy FADT method
3424
3425 profile= [KNL] Enable kernel profiling via /proc/profile
3426 Format: [schedule,]<number>
3427 Param: "schedule" - profile schedule points.
3428 Param: <number> - step/bucket size as a power of 2 for
3429 statistical time based profiling.
3430 Param: "sleep" - profile D-state sleeping (millisecs).
3431 Requires CONFIG_SCHEDSTATS
3432 Param: "kvm" - profile VM exits.
3433
3434 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3435 before loading.
3436 See Documentation/blockdev/ramdisk.txt.
3437
3438 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3439 probe for; one of (bare|imps|exps|lifebook|any).
3440 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3441 per second.
3442 psmouse.resetafter= [HW,MOUSE]
3443 Try to reset the device after so many bad packets
3444 (0 = never).
3445 psmouse.resolution=
3446 [HW,MOUSE] Set desired mouse resolution, in dpi.
3447 psmouse.smartscroll=
3448 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3449 0 = disabled, 1 = enabled (default).
3450
3451 pstore.backend= Specify the name of the pstore backend to use
3452
3453 pt. [PARIDE]
3454 See Documentation/blockdev/paride.txt.
3455
3456 pti= [X86_64] Control Page Table Isolation of user and
3457 kernel address spaces. Disabling this feature
3458 removes hardening, but improves performance of
3459 system calls and interrupts.
3460
3461 on - unconditionally enable
3462 off - unconditionally disable
3463 auto - kernel detects whether your CPU model is
3464 vulnerable to issues that PTI mitigates
3465
3466 Not specifying this option is equivalent to pti=auto.
3467
3468 nopti [X86_64]
3469 Equivalent to pti=off
3470
3471 pty.legacy_count=
3472 [KNL] Number of legacy pty's. Overwrites compiled-in
3473 default number.
3474
3475 quiet [KNL] Disable most log messages
3476
3477 r128= [HW,DRM]
3478
3479 raid= [HW,RAID]
3480 See Documentation/admin-guide/md.rst.
3481
3482 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3483 See Documentation/blockdev/ramdisk.txt.
3484
3485 ras=option[,option,...] [KNL] RAS-specific options
3486
3487 cec_disable [X86]
3488 Disable the Correctable Errors Collector,
3489 see CONFIG_RAS_CEC help text.
3490
3491 rcu_nocbs= [KNL]
3492 The argument is a cpu list, as described above.
3493
3494 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3495 the specified list of CPUs to be no-callback CPUs.
3496 Invocation of these CPUs' RCU callbacks will
3497 be offloaded to "rcuox/N" kthreads created for
3498 that purpose, where "x" is "b" for RCU-bh, "p"
3499 for RCU-preempt, and "s" for RCU-sched, and "N"
3500 is the CPU number. This reduces OS jitter on the
3501 offloaded CPUs, which can be useful for HPC and
3502 real-time workloads. It can also improve energy
3503 efficiency for asymmetric multiprocessors.
3504
3505 rcu_nocb_poll [KNL]
3506 Rather than requiring that offloaded CPUs
3507 (specified by rcu_nocbs= above) explicitly
3508 awaken the corresponding "rcuoN" kthreads,
3509 make these kthreads poll for callbacks.
3510 This improves the real-time response for the
3511 offloaded CPUs by relieving them of the need to
3512 wake up the corresponding kthread, but degrades
3513 energy efficiency by requiring that the kthreads
3514 periodically wake up to do the polling.
3515
3516 rcutree.blimit= [KNL]
3517 Set maximum number of finished RCU callbacks to
3518 process in one batch.
3519
3520 rcutree.dump_tree= [KNL]
3521 Dump the structure of the rcu_node combining tree
3522 out at early boot. This is used for diagnostic
3523 purposes, to verify correct tree setup.
3524
3525 rcutree.gp_cleanup_delay= [KNL]
3526 Set the number of jiffies to delay each step of
3527 RCU grace-period cleanup.
3528
3529 rcutree.gp_init_delay= [KNL]
3530 Set the number of jiffies to delay each step of
3531 RCU grace-period initialization.
3532
3533 rcutree.gp_preinit_delay= [KNL]
3534 Set the number of jiffies to delay each step of
3535 RCU grace-period pre-initialization, that is,
3536 the propagation of recent CPU-hotplug changes up
3537 the rcu_node combining tree.
3538
3539 rcutree.rcu_fanout_exact= [KNL]
3540 Disable autobalancing of the rcu_node combining
3541 tree. This is used by rcutorture, and might
3542 possibly be useful for architectures having high
3543 cache-to-cache transfer latencies.
3544
3545 rcutree.rcu_fanout_leaf= [KNL]
3546 Change the number of CPUs assigned to each
3547 leaf rcu_node structure. Useful for very
3548 large systems, which will choose the value 64,
3549 and for NUMA systems with large remote-access
3550 latencies, which will choose a value aligned
3551 with the appropriate hardware boundaries.
3552
3553 rcutree.jiffies_till_sched_qs= [KNL]
3554 Set required age in jiffies for a
3555 given grace period before RCU starts
3556 soliciting quiescent-state help from
3557 rcu_note_context_switch().
3558
3559 rcutree.jiffies_till_first_fqs= [KNL]
3560 Set delay from grace-period initialization to
3561 first attempt to force quiescent states.
3562 Units are jiffies, minimum value is zero,
3563 and maximum value is HZ.
3564
3565 rcutree.jiffies_till_next_fqs= [KNL]
3566 Set delay between subsequent attempts to force
3567 quiescent states. Units are jiffies, minimum
3568 value is one, and maximum value is HZ.
3569
3570 rcutree.kthread_prio= [KNL,BOOT]
3571 Set the SCHED_FIFO priority of the RCU per-CPU
3572 kthreads (rcuc/N). This value is also used for
3573 the priority of the RCU boost threads (rcub/N)
3574 and for the RCU grace-period kthreads (rcu_bh,
3575 rcu_preempt, and rcu_sched). If RCU_BOOST is
3576 set, valid values are 1-99 and the default is 1
3577 (the least-favored priority). Otherwise, when
3578 RCU_BOOST is not set, valid values are 0-99 and
3579 the default is zero (non-realtime operation).
3580
3581 rcutree.rcu_nocb_leader_stride= [KNL]
3582 Set the number of NOCB kthread groups, which
3583 defaults to the square root of the number of
3584 CPUs. Larger numbers reduces the wakeup overhead
3585 on the per-CPU grace-period kthreads, but increases
3586 that same overhead on each group's leader.
3587
3588 rcutree.qhimark= [KNL]
3589 Set threshold of queued RCU callbacks beyond which
3590 batch limiting is disabled.
3591
3592 rcutree.qlowmark= [KNL]
3593 Set threshold of queued RCU callbacks below which
3594 batch limiting is re-enabled.
3595
3596 rcutree.rcu_idle_gp_delay= [KNL]
3597 Set wakeup interval for idle CPUs that have
3598 RCU callbacks (RCU_FAST_NO_HZ=y).
3599
3600 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3601 Set wakeup interval for idle CPUs that have
3602 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3603 Lazy RCU callbacks are those which RCU can
3604 prove do nothing more than free memory.
3605
3606 rcutree.rcu_kick_kthreads= [KNL]
3607 Cause the grace-period kthread to get an extra
3608 wake_up() if it sleeps three times longer than
3609 it should at force-quiescent-state time.
3610 This wake_up() will be accompanied by a
3611 WARN_ONCE() splat and an ftrace_dump().
3612
3613 rcuperf.gp_async= [KNL]
3614 Measure performance of asynchronous
3615 grace-period primitives such as call_rcu().
3616
3617 rcuperf.gp_async_max= [KNL]
3618 Specify the maximum number of outstanding
3619 callbacks per writer thread. When a writer
3620 thread exceeds this limit, it invokes the
3621 corresponding flavor of rcu_barrier() to allow
3622 previously posted callbacks to drain.
3623
3624 rcuperf.gp_exp= [KNL]
3625 Measure performance of expedited synchronous
3626 grace-period primitives.
3627
3628 rcuperf.holdoff= [KNL]
3629 Set test-start holdoff period. The purpose of
3630 this parameter is to delay the start of the
3631 test until boot completes in order to avoid
3632 interference.
3633
3634 rcuperf.nreaders= [KNL]
3635 Set number of RCU readers. The value -1 selects
3636 N, where N is the number of CPUs. A value
3637 "n" less than -1 selects N-n+1, where N is again
3638 the number of CPUs. For example, -2 selects N
3639 (the number of CPUs), -3 selects N+1, and so on.
3640 A value of "n" less than or equal to -N selects
3641 a single reader.
3642
3643 rcuperf.nwriters= [KNL]
3644 Set number of RCU writers. The values operate
3645 the same as for rcuperf.nreaders.
3646 N, where N is the number of CPUs
3647
3648 rcuperf.perf_runnable= [BOOT]
3649 Start rcuperf running at boot time.
3650
3651 rcuperf.perf_type= [KNL]
3652 Specify the RCU implementation to test.
3653
3654 rcuperf.shutdown= [KNL]
3655 Shut the system down after performance tests
3656 complete. This is useful for hands-off automated
3657 testing.
3658
3659 rcuperf.verbose= [KNL]
3660 Enable additional printk() statements.
3661
3662 rcuperf.writer_holdoff= [KNL]
3663 Write-side holdoff between grace periods,
3664 in microseconds. The default of zero says
3665 no holdoff.
3666
3667 rcutorture.cbflood_inter_holdoff= [KNL]
3668 Set holdoff time (jiffies) between successive
3669 callback-flood tests.
3670
3671 rcutorture.cbflood_intra_holdoff= [KNL]
3672 Set holdoff time (jiffies) between successive
3673 bursts of callbacks within a given callback-flood
3674 test.
3675
3676 rcutorture.cbflood_n_burst= [KNL]
3677 Set the number of bursts making up a given
3678 callback-flood test. Set this to zero to
3679 disable callback-flood testing.
3680
3681 rcutorture.cbflood_n_per_burst= [KNL]
3682 Set the number of callbacks to be registered
3683 in a given burst of a callback-flood test.
3684
3685 rcutorture.fqs_duration= [KNL]
3686 Set duration of force_quiescent_state bursts
3687 in microseconds.
3688
3689 rcutorture.fqs_holdoff= [KNL]
3690 Set holdoff time within force_quiescent_state bursts
3691 in microseconds.
3692
3693 rcutorture.fqs_stutter= [KNL]
3694 Set wait time between force_quiescent_state bursts
3695 in seconds.
3696
3697 rcutorture.gp_cond= [KNL]
3698 Use conditional/asynchronous update-side
3699 primitives, if available.
3700
3701 rcutorture.gp_exp= [KNL]
3702 Use expedited update-side primitives, if available.
3703
3704 rcutorture.gp_normal= [KNL]
3705 Use normal (non-expedited) asynchronous
3706 update-side primitives, if available.
3707
3708 rcutorture.gp_sync= [KNL]
3709 Use normal (non-expedited) synchronous
3710 update-side primitives, if available. If all
3711 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3712 rcutorture.gp_normal=, and rcutorture.gp_sync=
3713 are zero, rcutorture acts as if is interpreted
3714 they are all non-zero.
3715
3716 rcutorture.n_barrier_cbs= [KNL]
3717 Set callbacks/threads for rcu_barrier() testing.
3718
3719 rcutorture.nfakewriters= [KNL]
3720 Set number of concurrent RCU writers. These just
3721 stress RCU, they don't participate in the actual
3722 test, hence the "fake".
3723
3724 rcutorture.nreaders= [KNL]
3725 Set number of RCU readers. The value -1 selects
3726 N-1, where N is the number of CPUs. A value
3727 "n" less than -1 selects N-n-2, where N is again
3728 the number of CPUs. For example, -2 selects N
3729 (the number of CPUs), -3 selects N+1, and so on.
3730
3731 rcutorture.object_debug= [KNL]
3732 Enable debug-object double-call_rcu() testing.
3733
3734 rcutorture.onoff_holdoff= [KNL]
3735 Set time (s) after boot for CPU-hotplug testing.
3736
3737 rcutorture.onoff_interval= [KNL]
3738 Set time (s) between CPU-hotplug operations, or
3739 zero to disable CPU-hotplug testing.
3740
3741 rcutorture.shuffle_interval= [KNL]
3742 Set task-shuffle interval (s). Shuffling tasks
3743 allows some CPUs to go into dyntick-idle mode
3744 during the rcutorture test.
3745
3746 rcutorture.shutdown_secs= [KNL]
3747 Set time (s) after boot system shutdown. This
3748 is useful for hands-off automated testing.
3749
3750 rcutorture.stall_cpu= [KNL]
3751 Duration of CPU stall (s) to test RCU CPU stall
3752 warnings, zero to disable.
3753
3754 rcutorture.stall_cpu_holdoff= [KNL]
3755 Time to wait (s) after boot before inducing stall.
3756
3757 rcutorture.stat_interval= [KNL]
3758 Time (s) between statistics printk()s.
3759
3760 rcutorture.stutter= [KNL]
3761 Time (s) to stutter testing, for example, specifying
3762 five seconds causes the test to run for five seconds,
3763 wait for five seconds, and so on. This tests RCU's
3764 ability to transition abruptly to and from idle.
3765
3766 rcutorture.test_boost= [KNL]
3767 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3768 "Maybe" means test if the RCU implementation
3769 under test support RCU priority boosting.
3770
3771 rcutorture.test_boost_duration= [KNL]
3772 Duration (s) of each individual boost test.
3773
3774 rcutorture.test_boost_interval= [KNL]
3775 Interval (s) between each boost test.
3776
3777 rcutorture.test_no_idle_hz= [KNL]
3778 Test RCU's dyntick-idle handling. See also the
3779 rcutorture.shuffle_interval parameter.
3780
3781 rcutorture.torture_runnable= [BOOT]
3782 Start rcutorture running at boot time.
3783
3784 rcutorture.torture_type= [KNL]
3785 Specify the RCU implementation to test.
3786
3787 rcutorture.verbose= [KNL]
3788 Enable additional printk() statements.
3789
3790 rcupdate.rcu_cpu_stall_suppress= [KNL]
3791 Suppress RCU CPU stall warning messages.
3792
3793 rcupdate.rcu_cpu_stall_timeout= [KNL]
3794 Set timeout for RCU CPU stall warning messages.
3795
3796 rcupdate.rcu_expedited= [KNL]
3797 Use expedited grace-period primitives, for
3798 example, synchronize_rcu_expedited() instead
3799 of synchronize_rcu(). This reduces latency,
3800 but can increase CPU utilization, degrade
3801 real-time latency, and degrade energy efficiency.
3802 No effect on CONFIG_TINY_RCU kernels.
3803
3804 rcupdate.rcu_normal= [KNL]
3805 Use only normal grace-period primitives,
3806 for example, synchronize_rcu() instead of
3807 synchronize_rcu_expedited(). This improves
3808 real-time latency, CPU utilization, and
3809 energy efficiency, but can expose users to
3810 increased grace-period latency. This parameter
3811 overrides rcupdate.rcu_expedited. No effect on
3812 CONFIG_TINY_RCU kernels.
3813
3814 rcupdate.rcu_normal_after_boot= [KNL]
3815 Once boot has completed (that is, after
3816 rcu_end_inkernel_boot() has been invoked), use
3817 only normal grace-period primitives. No effect
3818 on CONFIG_TINY_RCU kernels.
3819
3820 rcupdate.rcu_task_stall_timeout= [KNL]
3821 Set timeout in jiffies for RCU task stall warning
3822 messages. Disable with a value less than or equal
3823 to zero.
3824
3825 rcupdate.rcu_self_test= [KNL]
3826 Run the RCU early boot self tests
3827
3828 rcupdate.rcu_self_test_bh= [KNL]
3829 Run the RCU bh early boot self tests
3830
3831 rcupdate.rcu_self_test_sched= [KNL]
3832 Run the RCU sched early boot self tests
3833
3834 rdinit= [KNL]
3835 Format: <full_path>
3836 Run specified binary instead of /init from the ramdisk,
3837 used for early userspace startup. See initrd.
3838
3839 rdrand= [X86]
3840 force - Override the decision by the kernel to hide the
3841 advertisement of RDRAND support (this affects
3842 certain AMD processors because of buggy BIOS
3843 support, specifically around the suspend/resume
3844 path).
3845
3846 rdt= [HW,X86,RDT]
3847 Turn on/off individual RDT features. List is:
3848 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3849 E.g. to turn on cmt and turn off mba use:
3850 rdt=cmt,!mba
3851
3852 reboot= [KNL]
3853 Format (x86 or x86_64):
3854 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3855 [[,]s[mp]#### \
3856 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3857 [[,]f[orce]
3858 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3859 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3860 reboot_force is either force or not specified,
3861 reboot_cpu is s[mp]#### with #### being the processor
3862 to be used for rebooting.
3863
3864 relax_domain_level=
3865 [KNL, SMP] Set scheduler's default relax_domain_level.
3866 See Documentation/cgroup-v1/cpusets.txt.
3867
3868 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3869
3870 reservetop= [X86-32]
3871 Format: nn[KMG]
3872 Reserves a hole at the top of the kernel virtual
3873 address space.
3874
3875 reservelow= [X86]
3876 Format: nn[K]
3877 Set the amount of memory to reserve for BIOS at
3878 the bottom of the address space.
3879
3880 reset_devices [KNL] Force drivers to reset the underlying device
3881 during initialization.
3882
3883 resume= [SWSUSP]
3884 Specify the partition device for software suspend
3885 Format:
3886 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3887
3888 resume_offset= [SWSUSP]
3889 Specify the offset from the beginning of the partition
3890 given by "resume=" at which the swap header is located,
3891 in <PAGE_SIZE> units (needed only for swap files).
3892 See Documentation/power/swsusp-and-swap-files.txt
3893
3894 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3895 read the resume files
3896
3897 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3898 Useful for devices that are detected asynchronously
3899 (e.g. USB and MMC devices).
3900
3901 hibernate= [HIBERNATION]
3902 noresume Don't check if there's a hibernation image
3903 present during boot.
3904 nocompress Don't compress/decompress hibernation images.
3905 no Disable hibernation and resume.
3906 protect_image Turn on image protection during restoration
3907 (that will set all pages holding image data
3908 during restoration read-only).
3909
3910 retain_initrd [RAM] Keep initrd memory after extraction
3911
3912 rfkill.default_state=
3913 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3914 etc. communication is blocked by default.
3915 1 Unblocked.
3916
3917 rfkill.master_switch_mode=
3918 0 The "airplane mode" button does nothing.
3919 1 The "airplane mode" button toggles between everything
3920 blocked and the previous configuration.
3921 2 The "airplane mode" button toggles between everything
3922 blocked and everything unblocked.
3923
3924 rhash_entries= [KNL,NET]
3925 Set number of hash buckets for route cache
3926
3927 ring3mwait=disable
3928 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3929 CPUs.
3930
3931 ro [KNL] Mount root device read-only on boot
3932
3933 rodata= [KNL]
3934 on Mark read-only kernel memory as read-only (default).
3935 off Leave read-only kernel memory writable for debugging.
3936
3937 rockchip.usb_uart
3938 Enable the uart passthrough on the designated usb port
3939 on Rockchip SoCs. When active, the signals of the
3940 debug-uart get routed to the D+ and D- pins of the usb
3941 port and the regular usb controller gets disabled.
3942
3943 root= [KNL] Root filesystem
3944 See name_to_dev_t comment in init/do_mounts.c.
3945
3946 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3947 mount the root filesystem
3948
3949 rootflags= [KNL] Set root filesystem mount option string
3950
3951 rootfstype= [KNL] Set root filesystem type
3952
3953 rootwait [KNL] Wait (indefinitely) for root device to show up.
3954 Useful for devices that are detected asynchronously
3955 (e.g. USB and MMC devices).
3956
3957 rproc_mem=nn[KMG][@address]
3958 [KNL,ARM,CMA] Remoteproc physical memory block.
3959 Memory area to be used by remote processor image,
3960 managed by CMA.
3961
3962 rw [KNL] Mount root device read-write on boot
3963
3964 S [KNL] Run init in single mode
3965
3966 s390_iommu= [HW,S390]
3967 Set s390 IOTLB flushing mode
3968 strict
3969 With strict flushing every unmap operation will result in
3970 an IOTLB flush. Default is lazy flushing before reuse,
3971 which is faster.
3972
3973 sa1100ir [NET]
3974 See drivers/net/irda/sa1100_ir.c.
3975
3976 sbni= [NET] Granch SBNI12 leased line adapter
3977
3978 sched_debug [KNL] Enables verbose scheduler debug messages.
3979
3980 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3981 Allowed values are enable and disable. This feature
3982 incurs a small amount of overhead in the scheduler
3983 but is useful for debugging and performance tuning.
3984
3985 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3986 xtime_lock contention on larger systems, and/or RCU lock
3987 contention on all systems with CONFIG_MAXSMP set.
3988 Format: { "0" | "1" }
3989 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3990 1 -- enable.
3991 Note: increases power consumption, thus should only be
3992 enabled if running jitter sensitive (HPC/RT) workloads.
3993
3994 security= [SECURITY] Choose a security module to enable at boot.
3995 If this boot parameter is not specified, only the first
3996 security module asking for security registration will be
3997 loaded. An invalid security module name will be treated
3998 as if no module has been chosen.
3999
4000 selinux= [SELINUX] Disable or enable SELinux at boot time.
4001 Format: { "0" | "1" }
4002 See security/selinux/Kconfig help text.
4003 0 -- disable.
4004 1 -- enable.
4005 Default value is set via kernel config option.
4006 If enabled at boot time, /selinux/disable can be used
4007 later to disable prior to initial policy load.
4008
4009 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4010 Format: { "0" | "1" }
4011 See security/apparmor/Kconfig help text
4012 0 -- disable.
4013 1 -- enable.
4014 Default value is set via kernel config option.
4015
4016 serialnumber [BUGS=X86-32]
4017
4018 shapers= [NET]
4019 Maximal number of shapers.
4020
4021 simeth= [IA-64]
4022 simscsi=
4023
4024 slram= [HW,MTD]
4025
4026 slab_nomerge [MM]
4027 Disable merging of slabs with similar size. May be
4028 necessary if there is some reason to distinguish
4029 allocs to different slabs, especially in hardened
4030 environments where the risk of heap overflows and
4031 layout control by attackers can usually be
4032 frustrated by disabling merging. This will reduce
4033 most of the exposure of a heap attack to a single
4034 cache (risks via metadata attacks are mostly
4035 unchanged). Debug options disable merging on their
4036 own.
4037 For more information see Documentation/vm/slub.txt.
4038
4039 slab_max_order= [MM, SLAB]
4040 Determines the maximum allowed order for slabs.
4041 A high setting may cause OOMs due to memory
4042 fragmentation. Defaults to 1 for systems with
4043 more than 32MB of RAM, 0 otherwise.
4044
4045 slub_debug[=options[,slabs]] [MM, SLUB]
4046 Enabling slub_debug allows one to determine the
4047 culprit if slab objects become corrupted. Enabling
4048 slub_debug can create guard zones around objects and
4049 may poison objects when not in use. Also tracks the
4050 last alloc / free. For more information see
4051 Documentation/vm/slub.txt.
4052
4053 slub_memcg_sysfs= [MM, SLUB]
4054 Determines whether to enable sysfs directories for
4055 memory cgroup sub-caches. 1 to enable, 0 to disable.
4056 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4057 Enabling this can lead to a very high number of debug
4058 directories and files being created under
4059 /sys/kernel/slub.
4060
4061 slub_max_order= [MM, SLUB]
4062 Determines the maximum allowed order for slabs.
4063 A high setting may cause OOMs due to memory
4064 fragmentation. For more information see
4065 Documentation/vm/slub.txt.
4066
4067 slub_min_objects= [MM, SLUB]
4068 The minimum number of objects per slab. SLUB will
4069 increase the slab order up to slub_max_order to
4070 generate a sufficiently large slab able to contain
4071 the number of objects indicated. The higher the number
4072 of objects the smaller the overhead of tracking slabs
4073 and the less frequently locks need to be acquired.
4074 For more information see Documentation/vm/slub.txt.
4075
4076 slub_min_order= [MM, SLUB]
4077 Determines the minimum page order for slabs. Must be
4078 lower than slub_max_order.
4079 For more information see Documentation/vm/slub.txt.
4080
4081 slub_nomerge [MM, SLUB]
4082 Same with slab_nomerge. This is supported for legacy.
4083 See slab_nomerge for more information.
4084
4085 smart2= [HW]
4086 Format: <io1>[,<io2>[,...,<io8>]]
4087
4088 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4089 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4090 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4091 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4092 smsc-ircc2.ircc_irq= [HW] IRQ line
4093 smsc-ircc2.ircc_dma= [HW] DMA channel
4094 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4095 0: Toshiba Satellite 1800 (GP data pin select)
4096 1: Fast pin select (default)
4097 2: ATC IRMode
4098
4099 smt [KNL,S390] Set the maximum number of threads (logical
4100 CPUs) to use per physical CPU on systems capable of
4101 symmetric multithreading (SMT). Will be capped to the
4102 actual hardware limit.
4103 Format: <integer>
4104 Default: -1 (no limit)
4105
4106 softlockup_panic=
4107 [KNL] Should the soft-lockup detector generate panics.
4108 Format: <integer>
4109
4110 softlockup_all_cpu_backtrace=
4111 [KNL] Should the soft-lockup detector generate
4112 backtraces on all cpus.
4113 Format: <integer>
4114
4115 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4116 See Documentation/laptops/sonypi.txt
4117
4118 spectre_v2= [X86] Control mitigation of Spectre variant 2
4119 (indirect branch speculation) vulnerability.
4120 The default operation protects the kernel from
4121 user space attacks.
4122
4123 on - unconditionally enable, implies
4124 spectre_v2_user=on
4125 off - unconditionally disable, implies
4126 spectre_v2_user=off
4127 auto - kernel detects whether your CPU model is
4128 vulnerable
4129
4130 Selecting 'on' will, and 'auto' may, choose a
4131 mitigation method at run time according to the
4132 CPU, the available microcode, the setting of the
4133 CONFIG_RETPOLINE configuration option, and the
4134 compiler with which the kernel was built.
4135
4136 Selecting 'on' will also enable the mitigation
4137 against user space to user space task attacks.
4138
4139 Selecting 'off' will disable both the kernel and
4140 the user space protections.
4141
4142 Specific mitigations can also be selected manually:
4143
4144 retpoline - replace indirect branches
4145 retpoline,generic - google's original retpoline
4146 retpoline,amd - AMD-specific minimal thunk
4147
4148 Not specifying this option is equivalent to
4149 spectre_v2=auto.
4150
4151 spectre_v2_user=
4152 [X86] Control mitigation of Spectre variant 2
4153 (indirect branch speculation) vulnerability between
4154 user space tasks
4155
4156 on - Unconditionally enable mitigations. Is
4157 enforced by spectre_v2=on
4158
4159 off - Unconditionally disable mitigations. Is
4160 enforced by spectre_v2=off
4161
4162 prctl - Indirect branch speculation is enabled,
4163 but mitigation can be enabled via prctl
4164 per thread. The mitigation control state
4165 is inherited on fork.
4166
4167 prctl,ibpb
4168 - Like "prctl" above, but only STIBP is
4169 controlled per thread. IBPB is issued
4170 always when switching between different user
4171 space processes.
4172
4173 seccomp
4174 - Same as "prctl" above, but all seccomp
4175 threads will enable the mitigation unless
4176 they explicitly opt out.
4177
4178 seccomp,ibpb
4179 - Like "seccomp" above, but only STIBP is
4180 controlled per thread. IBPB is issued
4181 always when switching between different
4182 user space processes.
4183
4184 auto - Kernel selects the mitigation depending on
4185 the available CPU features and vulnerability.
4186
4187 Default mitigation:
4188 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4189
4190 Not specifying this option is equivalent to
4191 spectre_v2_user=auto.
4192
4193 spec_store_bypass_disable=
4194 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4195 (Speculative Store Bypass vulnerability)
4196
4197 Certain CPUs are vulnerable to an exploit against a
4198 a common industry wide performance optimization known
4199 as "Speculative Store Bypass" in which recent stores
4200 to the same memory location may not be observed by
4201 later loads during speculative execution. The idea
4202 is that such stores are unlikely and that they can
4203 be detected prior to instruction retirement at the
4204 end of a particular speculation execution window.
4205
4206 In vulnerable processors, the speculatively forwarded
4207 store can be used in a cache side channel attack, for
4208 example to read memory to which the attacker does not
4209 directly have access (e.g. inside sandboxed code).
4210
4211 This parameter controls whether the Speculative Store
4212 Bypass optimization is used.
4213
4214 on - Unconditionally disable Speculative Store Bypass
4215 off - Unconditionally enable Speculative Store Bypass
4216 auto - Kernel detects whether the CPU model contains an
4217 implementation of Speculative Store Bypass and
4218 picks the most appropriate mitigation. If the
4219 CPU is not vulnerable, "off" is selected. If the
4220 CPU is vulnerable the default mitigation is
4221 architecture and Kconfig dependent. See below.
4222 prctl - Control Speculative Store Bypass per thread
4223 via prctl. Speculative Store Bypass is enabled
4224 for a process by default. The state of the control
4225 is inherited on fork.
4226 seccomp - Same as "prctl" above, but all seccomp threads
4227 will disable SSB unless they explicitly opt out.
4228
4229 Not specifying this option is equivalent to
4230 spec_store_bypass_disable=auto.
4231
4232 Default mitigations:
4233 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4234
4235 spia_io_base= [HW,MTD]
4236 spia_fio_base=
4237 spia_pedr=
4238 spia_peddr=
4239
4240 srbds= [X86,INTEL]
4241 Control the Special Register Buffer Data Sampling
4242 (SRBDS) mitigation.
4243
4244 Certain CPUs are vulnerable to an MDS-like
4245 exploit which can leak bits from the random
4246 number generator.
4247
4248 By default, this issue is mitigated by
4249 microcode. However, the microcode fix can cause
4250 the RDRAND and RDSEED instructions to become
4251 much slower. Among other effects, this will
4252 result in reduced throughput from /dev/urandom.
4253
4254 The microcode mitigation can be disabled with
4255 the following option:
4256
4257 off: Disable mitigation and remove
4258 performance impact to RDRAND and RDSEED
4259
4260 srcutree.counter_wrap_check [KNL]
4261 Specifies how frequently to check for
4262 grace-period sequence counter wrap for the
4263 srcu_data structure's ->srcu_gp_seq_needed field.
4264 The greater the number of bits set in this kernel
4265 parameter, the less frequently counter wrap will
4266 be checked for. Note that the bottom two bits
4267 are ignored.
4268
4269 srcutree.exp_holdoff [KNL]
4270 Specifies how many nanoseconds must elapse
4271 since the end of the last SRCU grace period for
4272 a given srcu_struct until the next normal SRCU
4273 grace period will be considered for automatic
4274 expediting. Set to zero to disable automatic
4275 expediting.
4276
4277 ssbd= [ARM64,HW]
4278 Speculative Store Bypass Disable control
4279
4280 On CPUs that are vulnerable to the Speculative
4281 Store Bypass vulnerability and offer a
4282 firmware based mitigation, this parameter
4283 indicates how the mitigation should be used:
4284
4285 force-on: Unconditionally enable mitigation for
4286 for both kernel and userspace
4287 force-off: Unconditionally disable mitigation for
4288 for both kernel and userspace
4289 kernel: Always enable mitigation in the
4290 kernel, and offer a prctl interface
4291 to allow userspace to register its
4292 interest in being mitigated too.
4293
4294 stack_guard_gap= [MM]
4295 override the default stack gap protection. The value
4296 is in page units and it defines how many pages prior
4297 to (for stacks growing down) resp. after (for stacks
4298 growing up) the main stack are reserved for no other
4299 mapping. Default value is 256 pages.
4300
4301 stacktrace [FTRACE]
4302 Enabled the stack tracer on boot up.
4303
4304 stacktrace_filter=[function-list]
4305 [FTRACE] Limit the functions that the stack tracer
4306 will trace at boot up. function-list is a comma separated
4307 list of functions. This list can be changed at run
4308 time by the stack_trace_filter file in the debugfs
4309 tracing directory. Note, this enables stack tracing
4310 and the stacktrace above is not needed.
4311
4312 sti= [PARISC,HW]
4313 Format: <num>
4314 Set the STI (builtin display/keyboard on the HP-PARISC
4315 machines) console (graphic card) which should be used
4316 as the initial boot-console.
4317 See also comment in drivers/video/console/sticore.c.
4318
4319 sti_font= [HW]
4320 See comment in drivers/video/console/sticore.c.
4321
4322 stifb= [HW]
4323 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4324
4325 sunrpc.min_resvport=
4326 sunrpc.max_resvport=
4327 [NFS,SUNRPC]
4328 SunRPC servers often require that client requests
4329 originate from a privileged port (i.e. a port in the
4330 range 0 < portnr < 1024).
4331 An administrator who wishes to reserve some of these
4332 ports for other uses may adjust the range that the
4333 kernel's sunrpc client considers to be privileged
4334 using these two parameters to set the minimum and
4335 maximum port values.
4336
4337 sunrpc.svc_rpc_per_connection_limit=
4338 [NFS,SUNRPC]
4339 Limit the number of requests that the server will
4340 process in parallel from a single connection.
4341 The default value is 0 (no limit).
4342
4343 sunrpc.pool_mode=
4344 [NFS]
4345 Control how the NFS server code allocates CPUs to
4346 service thread pools. Depending on how many NICs
4347 you have and where their interrupts are bound, this
4348 option will affect which CPUs will do NFS serving.
4349 Note: this parameter cannot be changed while the
4350 NFS server is running.
4351
4352 auto the server chooses an appropriate mode
4353 automatically using heuristics
4354 global a single global pool contains all CPUs
4355 percpu one pool for each CPU
4356 pernode one pool for each NUMA node (equivalent
4357 to global on non-NUMA machines)
4358
4359 sunrpc.tcp_slot_table_entries=
4360 sunrpc.udp_slot_table_entries=
4361 [NFS,SUNRPC]
4362 Sets the upper limit on the number of simultaneous
4363 RPC calls that can be sent from the client to a
4364 server. Increasing these values may allow you to
4365 improve throughput, but will also increase the
4366 amount of memory reserved for use by the client.
4367
4368 suspend.pm_test_delay=
4369 [SUSPEND]
4370 Sets the number of seconds to remain in a suspend test
4371 mode before resuming the system (see
4372 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4373 is set. Default value is 5.
4374
4375 swapaccount=[0|1]
4376 [KNL] Enable accounting of swap in memory resource
4377 controller if no parameter or 1 is given or disable
4378 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4379
4380 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4381 Format: { <int> | force | noforce }
4382 <int> -- Number of I/O TLB slabs
4383 force -- force using of bounce buffers even if they
4384 wouldn't be automatically used by the kernel
4385 noforce -- Never use bounce buffers (for debugging)
4386
4387 switches= [HW,M68k]
4388
4389 sysfs.deprecated=0|1 [KNL]
4390 Enable/disable old style sysfs layout for old udev
4391 on older distributions. When this option is enabled
4392 very new udev will not work anymore. When this option
4393 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4394 in older udev will not work anymore.
4395 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4396 the kernel configuration.
4397
4398 sysrq_always_enabled
4399 [KNL]
4400 Ignore sysrq setting - this boot parameter will
4401 neutralize any effect of /proc/sys/kernel/sysrq.
4402 Useful for debugging.
4403
4404 tcpmhash_entries= [KNL,NET]
4405 Set the number of tcp_metrics_hash slots.
4406 Default value is 8192 or 16384 depending on total
4407 ram pages. This is used to specify the TCP metrics
4408 cache size. See Documentation/networking/ip-sysctl.txt
4409 "tcp_no_metrics_save" section for more details.
4410
4411 tdfx= [HW,DRM]
4412
4413 test_suspend= [SUSPEND][,N]
4414 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4415 standby suspend) or "freeze" (for suspend type freeze)
4416 as the system sleep state during system startup with
4417 the optional capability to repeat N number of times.
4418 The system is woken from this state using a
4419 wakeup-capable RTC alarm.
4420
4421 thash_entries= [KNL,NET]
4422 Set number of hash buckets for TCP connection
4423
4424 thermal.act= [HW,ACPI]
4425 -1: disable all active trip points in all thermal zones
4426 <degrees C>: override all lowest active trip points
4427
4428 thermal.crt= [HW,ACPI]
4429 -1: disable all critical trip points in all thermal zones
4430 <degrees C>: override all critical trip points
4431
4432 thermal.nocrt= [HW,ACPI]
4433 Set to disable actions on ACPI thermal zone
4434 critical and hot trip points.
4435
4436 thermal.off= [HW,ACPI]
4437 1: disable ACPI thermal control
4438
4439 thermal.psv= [HW,ACPI]
4440 -1: disable all passive trip points
4441 <degrees C>: override all passive trip points to this
4442 value
4443
4444 thermal.tzp= [HW,ACPI]
4445 Specify global default ACPI thermal zone polling rate
4446 <deci-seconds>: poll all this frequency
4447 0: no polling (default)
4448
4449 threadirqs [KNL]
4450 Force threading of all interrupt handlers except those
4451 marked explicitly IRQF_NO_THREAD.
4452
4453 tmem [KNL,XEN]
4454 Enable the Transcendent memory driver if built-in.
4455
4456 tmem.cleancache=0|1 [KNL, XEN]
4457 Default is on (1). Disable the usage of the cleancache
4458 API to send anonymous pages to the hypervisor.
4459
4460 tmem.frontswap=0|1 [KNL, XEN]
4461 Default is on (1). Disable the usage of the frontswap
4462 API to send swap pages to the hypervisor. If disabled
4463 the selfballooning and selfshrinking are force disabled.
4464
4465 tmem.selfballooning=0|1 [KNL, XEN]
4466 Default is on (1). Disable the driving of swap pages
4467 to the hypervisor.
4468
4469 tmem.selfshrinking=0|1 [KNL, XEN]
4470 Default is on (1). Partial swapoff that immediately
4471 transfers pages from Xen hypervisor back to the
4472 kernel based on different criteria.
4473
4474 topology= [S390]
4475 Format: {off | on}
4476 Specify if the kernel should make use of the cpu
4477 topology information if the hardware supports this.
4478 The scheduler will make use of this information and
4479 e.g. base its process migration decisions on it.
4480 Default is on.
4481
4482 topology_updates= [KNL, PPC, NUMA]
4483 Format: {off}
4484 Specify if the kernel should ignore (off)
4485 topology updates sent by the hypervisor to this
4486 LPAR.
4487
4488 tp720= [HW,PS2]
4489
4490 tpm_suspend_pcr=[HW,TPM]
4491 Format: integer pcr id
4492 Specify that at suspend time, the tpm driver
4493 should extend the specified pcr with zeros,
4494 as a workaround for some chips which fail to
4495 flush the last written pcr on TPM_SaveState.
4496 This will guarantee that all the other pcrs
4497 are saved.
4498
4499 trace_buf_size=nn[KMG]
4500 [FTRACE] will set tracing buffer size on each cpu.
4501
4502 trace_event=[event-list]
4503 [FTRACE] Set and start specified trace events in order
4504 to facilitate early boot debugging. The event-list is a
4505 comma separated list of trace events to enable. See
4506 also Documentation/trace/events.txt
4507
4508 trace_options=[option-list]
4509 [FTRACE] Enable or disable tracer options at boot.
4510 The option-list is a comma delimited list of options
4511 that can be enabled or disabled just as if you were
4512 to echo the option name into
4513
4514 /sys/kernel/debug/tracing/trace_options
4515
4516 For example, to enable stacktrace option (to dump the
4517 stack trace of each event), add to the command line:
4518
4519 trace_options=stacktrace
4520
4521 See also Documentation/trace/ftrace.txt "trace options"
4522 section.
4523
4524 tp_printk[FTRACE]
4525 Have the tracepoints sent to printk as well as the
4526 tracing ring buffer. This is useful for early boot up
4527 where the system hangs or reboots and does not give the
4528 option for reading the tracing buffer or performing a
4529 ftrace_dump_on_oops.
4530
4531 To turn off having tracepoints sent to printk,
4532 echo 0 > /proc/sys/kernel/tracepoint_printk
4533 Note, echoing 1 into this file without the
4534 tracepoint_printk kernel cmdline option has no effect.
4535
4536 ** CAUTION **
4537
4538 Having tracepoints sent to printk() and activating high
4539 frequency tracepoints such as irq or sched, can cause
4540 the system to live lock.
4541
4542 traceoff_on_warning
4543 [FTRACE] enable this option to disable tracing when a
4544 warning is hit. This turns off "tracing_on". Tracing can
4545 be enabled again by echoing '1' into the "tracing_on"
4546 file located in /sys/kernel/debug/tracing/
4547
4548 This option is useful, as it disables the trace before
4549 the WARNING dump is called, which prevents the trace to
4550 be filled with content caused by the warning output.
4551
4552 This option can also be set at run time via the sysctl
4553 option: kernel/traceoff_on_warning
4554
4555 transparent_hugepage=
4556 [KNL]
4557 Format: [always|madvise|never]
4558 Can be used to control the default behavior of the system
4559 with respect to transparent hugepages.
4560 See Documentation/vm/transhuge.txt for more details.
4561
4562 tsc= Disable clocksource stability checks for TSC.
4563 Format: <string>
4564 [x86] reliable: mark tsc clocksource as reliable, this
4565 disables clocksource verification at runtime, as well
4566 as the stability checks done at bootup. Used to enable
4567 high-resolution timer mode on older hardware, and in
4568 virtualized environment.
4569 [x86] noirqtime: Do not use TSC to do irq accounting.
4570 Used to run time disable IRQ_TIME_ACCOUNTING on any
4571 platforms where RDTSC is slow and this accounting
4572 can add overhead.
4573
4574 tsx= [X86] Control Transactional Synchronization
4575 Extensions (TSX) feature in Intel processors that
4576 support TSX control.
4577
4578 This parameter controls the TSX feature. The options are:
4579
4580 on - Enable TSX on the system. Although there are
4581 mitigations for all known security vulnerabilities,
4582 TSX has been known to be an accelerator for
4583 several previous speculation-related CVEs, and
4584 so there may be unknown security risks associated
4585 with leaving it enabled.
4586
4587 off - Disable TSX on the system. (Note that this
4588 option takes effect only on newer CPUs which are
4589 not vulnerable to MDS, i.e., have
4590 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4591 the new IA32_TSX_CTRL MSR through a microcode
4592 update. This new MSR allows for the reliable
4593 deactivation of the TSX functionality.)
4594
4595 auto - Disable TSX if X86_BUG_TAA is present,
4596 otherwise enable TSX on the system.
4597
4598 Not specifying this option is equivalent to tsx=off.
4599
4600 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4601 for more details.
4602
4603 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4604 Abort (TAA) vulnerability.
4605
4606 Similar to Micro-architectural Data Sampling (MDS)
4607 certain CPUs that support Transactional
4608 Synchronization Extensions (TSX) are vulnerable to an
4609 exploit against CPU internal buffers which can forward
4610 information to a disclosure gadget under certain
4611 conditions.
4612
4613 In vulnerable processors, the speculatively forwarded
4614 data can be used in a cache side channel attack, to
4615 access data to which the attacker does not have direct
4616 access.
4617
4618 This parameter controls the TAA mitigation. The
4619 options are:
4620
4621 full - Enable TAA mitigation on vulnerable CPUs
4622 if TSX is enabled.
4623
4624 full,nosmt - Enable TAA mitigation and disable SMT on
4625 vulnerable CPUs. If TSX is disabled, SMT
4626 is not disabled because CPU is not
4627 vulnerable to cross-thread TAA attacks.
4628 off - Unconditionally disable TAA mitigation
4629
4630 On MDS-affected machines, tsx_async_abort=off can be
4631 prevented by an active MDS mitigation as both vulnerabilities
4632 are mitigated with the same mechanism so in order to disable
4633 this mitigation, you need to specify mds=off too.
4634
4635 Not specifying this option is equivalent to
4636 tsx_async_abort=full. On CPUs which are MDS affected
4637 and deploy MDS mitigation, TAA mitigation is not
4638 required and doesn't provide any additional
4639 mitigation.
4640
4641 For details see:
4642 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4643
4644 turbografx.map[2|3]= [HW,JOY]
4645 TurboGraFX parallel port interface
4646 Format:
4647 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4648 See also Documentation/input/joystick-parport.txt
4649
4650 udbg-immortal [PPC] When debugging early kernel crashes that
4651 happen after console_init() and before a proper
4652 console driver takes over, this boot options might
4653 help "seeing" what's going on.
4654
4655 uhash_entries= [KNL,NET]
4656 Set number of hash buckets for UDP/UDP-Lite connections
4657
4658 uhci-hcd.ignore_oc=
4659 [USB] Ignore overcurrent events (default N).
4660 Some badly-designed motherboards generate lots of
4661 bogus events, for ports that aren't wired to
4662 anything. Set this parameter to avoid log spamming.
4663 Note that genuine overcurrent events won't be
4664 reported either.
4665
4666 unknown_nmi_panic
4667 [X86] Cause panic on unknown NMI.
4668
4669 usbcore.authorized_default=
4670 [USB] Default USB device authorization:
4671 (default -1 = authorized except for wireless USB,
4672 0 = not authorized, 1 = authorized)
4673
4674 usbcore.autosuspend=
4675 [USB] The autosuspend time delay (in seconds) used
4676 for newly-detected USB devices (default 2). This
4677 is the time required before an idle device will be
4678 autosuspended. Devices for which the delay is set
4679 to a negative value won't be autosuspended at all.
4680
4681 usbcore.usbfs_snoop=
4682 [USB] Set to log all usbfs traffic (default 0 = off).
4683
4684 usbcore.usbfs_snoop_max=
4685 [USB] Maximum number of bytes to snoop in each URB
4686 (default = 65536).
4687
4688 usbcore.blinkenlights=
4689 [USB] Set to cycle leds on hubs (default 0 = off).
4690
4691 usbcore.old_scheme_first=
4692 [USB] Start with the old device initialization
4693 scheme (default 0 = off).
4694
4695 usbcore.usbfs_memory_mb=
4696 [USB] Memory limit (in MB) for buffers allocated by
4697 usbfs (default = 16, 0 = max = 2047).
4698
4699 usbcore.use_both_schemes=
4700 [USB] Try the other device initialization scheme
4701 if the first one fails (default 1 = enabled).
4702
4703 usbcore.initial_descriptor_timeout=
4704 [USB] Specifies timeout for the initial 64-byte
4705 USB_REQ_GET_DESCRIPTOR request in milliseconds
4706 (default 5000 = 5.0 seconds).
4707
4708 usbcore.nousb [USB] Disable the USB subsystem
4709
4710 usbhid.mousepoll=
4711 [USBHID] The interval which mice are to be polled at.
4712
4713 usbhid.jspoll=
4714 [USBHID] The interval which joysticks are to be polled at.
4715
4716 usb-storage.delay_use=
4717 [UMS] The delay in seconds before a new device is
4718 scanned for Logical Units (default 1).
4719
4720 usb-storage.quirks=
4721 [UMS] A list of quirks entries to supplement or
4722 override the built-in unusual_devs list. List
4723 entries are separated by commas. Each entry has
4724 the form VID:PID:Flags where VID and PID are Vendor
4725 and Product ID values (4-digit hex numbers) and
4726 Flags is a set of characters, each corresponding
4727 to a common usb-storage quirk flag as follows:
4728 a = SANE_SENSE (collect more than 18 bytes
4729 of sense data, not on uas);
4730 b = BAD_SENSE (don't collect more than 18
4731 bytes of sense data, not on uas);
4732 c = FIX_CAPACITY (decrease the reported
4733 device capacity by one sector);
4734 d = NO_READ_DISC_INFO (don't use
4735 READ_DISC_INFO command, not on uas);
4736 e = NO_READ_CAPACITY_16 (don't use
4737 READ_CAPACITY_16 command);
4738 f = NO_REPORT_OPCODES (don't use report opcodes
4739 command, uas only);
4740 g = MAX_SECTORS_240 (don't transfer more than
4741 240 sectors at a time, uas only);
4742 h = CAPACITY_HEURISTICS (decrease the
4743 reported device capacity by one
4744 sector if the number is odd);
4745 i = IGNORE_DEVICE (don't bind to this
4746 device);
4747 j = NO_REPORT_LUNS (don't use report luns
4748 command, uas only);
4749 l = NOT_LOCKABLE (don't try to lock and
4750 unlock ejectable media, not on uas);
4751 m = MAX_SECTORS_64 (don't transfer more
4752 than 64 sectors = 32 KB at a time,
4753 not on uas);
4754 n = INITIAL_READ10 (force a retry of the
4755 initial READ(10) command, not on uas);
4756 o = CAPACITY_OK (accept the capacity
4757 reported by the device, not on uas);
4758 p = WRITE_CACHE (the device cache is ON
4759 by default, not on uas);
4760 r = IGNORE_RESIDUE (the device reports
4761 bogus residue values, not on uas);
4762 s = SINGLE_LUN (the device has only one
4763 Logical Unit);
4764 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4765 commands, uas only);
4766 u = IGNORE_UAS (don't bind to the uas driver);
4767 w = NO_WP_DETECT (don't test whether the
4768 medium is write-protected).
4769 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4770 even if the device claims no cache,
4771 not on uas)
4772 Example: quirks=0419:aaf5:rl,0421:0433:rc
4773
4774 user_debug= [KNL,ARM]
4775 Format: <int>
4776 See arch/arm/Kconfig.debug help text.
4777 1 - undefined instruction events
4778 2 - system calls
4779 4 - invalid data aborts
4780 8 - SIGSEGV faults
4781 16 - SIGBUS faults
4782 Example: user_debug=31
4783
4784 userpte=
4785 [X86] Flags controlling user PTE allocations.
4786
4787 nohigh = do not allocate PTE pages in
4788 HIGHMEM regardless of setting
4789 of CONFIG_HIGHPTE.
4790
4791 vdso= [X86,SH]
4792 On X86_32, this is an alias for vdso32=. Otherwise:
4793
4794 vdso=1: enable VDSO (the default)
4795 vdso=0: disable VDSO mapping
4796
4797 vdso32= [X86] Control the 32-bit vDSO
4798 vdso32=1: enable 32-bit VDSO
4799 vdso32=0 or vdso32=2: disable 32-bit VDSO
4800
4801 See the help text for CONFIG_COMPAT_VDSO for more
4802 details. If CONFIG_COMPAT_VDSO is set, the default is
4803 vdso32=0; otherwise, the default is vdso32=1.
4804
4805 For compatibility with older kernels, vdso32=2 is an
4806 alias for vdso32=0.
4807
4808 Try vdso32=0 if you encounter an error that says:
4809 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4810
4811 vector= [IA-64,SMP]
4812 vector=percpu: enable percpu vector domain
4813
4814 video= [FB] Frame buffer configuration
4815 See Documentation/fb/modedb.txt.
4816
4817 video.brightness_switch_enabled= [0,1]
4818 If set to 1, on receiving an ACPI notify event
4819 generated by hotkey, video driver will adjust brightness
4820 level and then send out the event to user space through
4821 the allocated input device; If set to 0, video driver
4822 will only send out the event without touching backlight
4823 brightness level.
4824 default: 1
4825
4826 virtio_mmio.device=
4827 [VMMIO] Memory mapped virtio (platform) device.
4828
4829 <size>@<baseaddr>:<irq>[:<id>]
4830 where:
4831 <size> := size (can use standard suffixes
4832 like K, M and G)
4833 <baseaddr> := physical base address
4834 <irq> := interrupt number (as passed to
4835 request_irq())
4836 <id> := (optional) platform device id
4837 example:
4838 virtio_mmio.device=1K@0x100b0000:48:7
4839
4840 Can be used multiple times for multiple devices.
4841
4842 vga= [BOOT,X86-32] Select a particular video mode
4843 See Documentation/x86/boot.txt and
4844 Documentation/svga.txt.
4845 Use vga=ask for menu.
4846 This is actually a boot loader parameter; the value is
4847 passed to the kernel using a special protocol.
4848
4849 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4850 size of <nn>. This can be used to increase the
4851 minimum size (128MB on x86). It can also be used to
4852 decrease the size and leave more room for directly
4853 mapped kernel RAM.
4854
4855 vmcp_cma=nn[MG] [KNL,S390]
4856 Sets the memory size reserved for contiguous memory
4857 allocations for the vmcp device driver.
4858
4859 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4860 Format: <command>
4861
4862 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4863 Format: <command>
4864
4865 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4866 Format: <command>
4867
4868 vsyscall= [X86-64]
4869 Controls the behavior of vsyscalls (i.e. calls to
4870 fixed addresses of 0xffffffffff600x00 from legacy
4871 code). Most statically-linked binaries and older
4872 versions of glibc use these calls. Because these
4873 functions are at fixed addresses, they make nice
4874 targets for exploits that can control RIP.
4875
4876 emulate [default] Vsyscalls turn into traps and are
4877 emulated reasonably safely.
4878
4879 native Vsyscalls are native syscall instructions.
4880 This is a little bit faster than trapping
4881 and makes a few dynamic recompilers work
4882 better than they would in emulation mode.
4883 It also makes exploits much easier to write.
4884
4885 none Vsyscalls don't work at all. This makes
4886 them quite hard to use for exploits but
4887 might break your system.
4888
4889 vt.color= [VT] Default text color.
4890 Format: 0xYX, X = foreground, Y = background.
4891 Default: 0x07 = light gray on black.
4892
4893 vt.cur_default= [VT] Default cursor shape.
4894 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4895 the parameters of the <Esc>[?A;B;Cc escape sequence;
4896 see VGA-softcursor.txt. Default: 2 = underline.
4897
4898 vt.default_blu= [VT]
4899 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4900 Change the default blue palette of the console.
4901 This is a 16-member array composed of values
4902 ranging from 0-255.
4903
4904 vt.default_grn= [VT]
4905 Format: <green0>,<green1>,<green2>,...,<green15>
4906 Change the default green palette of the console.
4907 This is a 16-member array composed of values
4908 ranging from 0-255.
4909
4910 vt.default_red= [VT]
4911 Format: <red0>,<red1>,<red2>,...,<red15>
4912 Change the default red palette of the console.
4913 This is a 16-member array composed of values
4914 ranging from 0-255.
4915
4916 vt.default_utf8=
4917 [VT]
4918 Format=<0|1>
4919 Set system-wide default UTF-8 mode for all tty's.
4920 Default is 1, i.e. UTF-8 mode is enabled for all
4921 newly opened terminals.
4922
4923 vt.global_cursor_default=
4924 [VT]
4925 Format=<-1|0|1>
4926 Set system-wide default for whether a cursor
4927 is shown on new VTs. Default is -1,
4928 i.e. cursors will be created by default unless
4929 overridden by individual drivers. 0 will hide
4930 cursors, 1 will display them.
4931
4932 vt.italic= [VT] Default color for italic text; 0-15.
4933 Default: 2 = green.
4934
4935 vt.underline= [VT] Default color for underlined text; 0-15.
4936 Default: 3 = cyan.
4937
4938 watchdog timers [HW,WDT] For information on watchdog timers,
4939 see Documentation/watchdog/watchdog-parameters.txt
4940 or other driver-specific files in the
4941 Documentation/watchdog/ directory.
4942
4943 workqueue.watchdog_thresh=
4944 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4945 warn stall conditions and dump internal state to
4946 help debugging. 0 disables workqueue stall
4947 detection; otherwise, it's the stall threshold
4948 duration in seconds. The default value is 30 and
4949 it can be updated at runtime by writing to the
4950 corresponding sysfs file.
4951
4952 workqueue.disable_numa
4953 By default, all work items queued to unbound
4954 workqueues are affine to the NUMA nodes they're
4955 issued on, which results in better behavior in
4956 general. If NUMA affinity needs to be disabled for
4957 whatever reason, this option can be used. Note
4958 that this also can be controlled per-workqueue for
4959 workqueues visible under /sys/bus/workqueue/.
4960
4961 workqueue.power_efficient
4962 Per-cpu workqueues are generally preferred because
4963 they show better performance thanks to cache
4964 locality; unfortunately, per-cpu workqueues tend to
4965 be more power hungry than unbound workqueues.
4966
4967 Enabling this makes the per-cpu workqueues which
4968 were observed to contribute significantly to power
4969 consumption unbound, leading to measurably lower
4970 power usage at the cost of small performance
4971 overhead.
4972
4973 The default value of this parameter is determined by
4974 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4975
4976 workqueue.debug_force_rr_cpu
4977 Workqueue used to implicitly guarantee that work
4978 items queued without explicit CPU specified are put
4979 on the local CPU. This guarantee is no longer true
4980 and while local CPU is still preferred work items
4981 may be put on foreign CPUs. This debug option
4982 forces round-robin CPU selection to flush out
4983 usages which depend on the now broken guarantee.
4984 When enabled, memory and cache locality will be
4985 impacted.
4986
4987 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4988 default x2apic cluster mode on platforms
4989 supporting x2apic.
4990
4991 x86_intel_mid_timer= [X86-32,APBT]
4992 Choose timer option for x86 Intel MID platform.
4993 Two valid options are apbt timer only and lapic timer
4994 plus one apbt timer for broadcast timer.
4995 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4996
4997 xen_512gb_limit [KNL,X86-64,XEN]
4998 Restricts the kernel running paravirtualized under Xen
4999 to use only up to 512 GB of RAM. The reason to do so is
5000 crash analysis tools and Xen tools for doing domain
5001 save/restore/migration must be enabled to handle larger
5002 domains.
5003
5004 xen_emul_unplug= [HW,X86,XEN]
5005 Unplug Xen emulated devices
5006 Format: [unplug0,][unplug1]
5007 ide-disks -- unplug primary master IDE devices
5008 aux-ide-disks -- unplug non-primary-master IDE devices
5009 nics -- unplug network devices
5010 all -- unplug all emulated devices (NICs and IDE disks)
5011 unnecessary -- unplugging emulated devices is
5012 unnecessary even if the host did not respond to
5013 the unplug protocol
5014 never -- do not unplug even if version check succeeds
5015
5016 xen_legacy_crash [X86,XEN]
5017 Crash from Xen panic notifier, without executing late
5018 panic() code such as dumping handler.
5019
5020 xen_nopvspin [X86,XEN]
5021 Disables the ticketlock slowpath using Xen PV
5022 optimizations.
5023
5024 xen_nopv [X86]
5025 Disables the PV optimizations forcing the HVM guest to
5026 run as generic HVM guest with no PV drivers.
5027
5028 xirc2ps_cs= [NET,PCMCIA]
5029 Format:
5030 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]