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1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
4 copy_dsdt }
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
14 are available
15
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
17
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
23
24 acpi_backlight= [HW,ACPI]
25 acpi_backlight=vendor
26 acpi_backlight=video
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
30
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
36
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
44
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
47 Format: <int>
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
58
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
68
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
72
73 acpi_enforce_resources= [ACPI]
74 { strict | lax | no }
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
88
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
92 size limitation.
93
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
96 default in APIC mode
97
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
100 default in PIC mode
101
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
104
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
106 use by PCI
107 Format: <irq>,<irq>...
108
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
113 the GPE dispatcher.
114 This facility can be used to prevent such uncontrolled
115 GPE floodings.
116 Format: <int>
117 Support masking of GPEs numbered from 0x00 to 0x7f.
118
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
126
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
128 kernels.
129
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
139
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
144
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
147
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
153
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
159 strings
160 acpi_osi=!! # enable all built-in OS vendor
161 strings
162 acpi_osi= # disable all strings
163
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
174 Examples:
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
178
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
184 meaningless.
185 Examples:
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
187 FALSE.
188
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
199 the OSPM features.
200 Examples:
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 equivalent to
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 and
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
211
212 acpi_pm_good [X86]
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
216
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
219
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
223
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
228 s3_bios and s3_mode.
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
242
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
246
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
249
250 agp= [AGP]
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
255
256 ALSA [HW,ALSA]
257 See Documentation/sound/alsa/alsa-parameters.txt
258
259 alignment= [KNL,ARM]
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
263
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
271
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
276
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
283
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
286 Possible values are:
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
290 is a lot of faster
291 off - do not initialize any AMD IOMMU found in
292 the system
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
298
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
304
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
307 remapping modes:
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
313
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
316 Format: <a>,<b>
317 See also Documentation/input/joydev/joystick.rst
318
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
323
324 apc= [HW,SPARC]
325 Power management functions (SPARCstation-4/5 + deriv.)
326 Format: noidle
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
330
331 apic= [APIC,X86] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
336 For X86-32, this can also be used to specify an APIC
337 driver name.
338 Format: apic=driver_name
339 Examples: apic=bigsmp
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/media/v4l-drivers/bttv.rst
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. A value of 0 disables the blank timer.
649 Defaults to 0.
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 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
664 to register. Example: cpufreq_driver=powernow-k8
665 Format: { none | STRING }
666
667 cpuidle.off=1 [CPU_IDLE]
668 disable the cpuidle sub-system
669
670 cpufreq.off=1 [CPU_FREQ]
671 disable the cpufreq sub-system
672
673 cpu_init_udelay=N
674 [X86] Delay for N microsec between assert and de-assert
675 of APIC INIT to start processors. This delay occurs
676 on every CPU online, such as boot, and resume from suspend.
677 Default: 10000
678
679 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
680 Format:
681 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
682
683 crashkernel=size[KMG][@offset[KMG]]
684 [KNL] Using kexec, Linux can switch to a 'crash kernel'
685 upon panic. This parameter reserves the physical
686 memory region [offset, offset + size] for that kernel
687 image. If '@offset' is omitted, then a suitable offset
688 is selected automatically. Check
689 Documentation/kdump/kdump.txt for further details.
690
691 crashkernel=range1:size1[,range2:size2,...][@offset]
692 [KNL] Same as above, but depends on the memory
693 in the running system. The syntax of range is
694 start-[end] where start and end are both
695 a memory unit (amount[KMG]). See also
696 Documentation/kdump/kdump.txt for an example.
697
698 crashkernel=size[KMG],high
699 [KNL, x86_64] range could be above 4G. Allow kernel
700 to allocate physical memory region from top, so could
701 be above 4G if system have more than 4G ram installed.
702 Otherwise memory region will be allocated below 4G, if
703 available.
704 It will be ignored if crashkernel=X is specified.
705 crashkernel=size[KMG],low
706 [KNL, x86_64] range under 4G. When crashkernel=X,high
707 is passed, kernel could allocate physical memory region
708 above 4G, that cause second kernel crash on system
709 that require some amount of low memory, e.g. swiotlb
710 requires at least 64M+32K low memory, also enough extra
711 low memory is needed to make sure DMA buffers for 32-bit
712 devices won't run out. Kernel would try to allocate at
713 at least 256M below 4G automatically.
714 This one let user to specify own low range under 4G
715 for second kernel instead.
716 0: to disable low allocation.
717 It will be ignored when crashkernel=X,high is not used
718 or memory reserved is below 4G.
719
720 cryptomgr.notests
721 [KNL] Disable crypto self-tests
722
723 cs89x0_dma= [HW,NET]
724 Format: <dma>
725
726 cs89x0_media= [HW,NET]
727 Format: { rj45 | aui | bnc }
728
729 dasd= [HW,NET]
730 See header of drivers/s390/block/dasd_devmap.c.
731
732 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
733 (one device per port)
734 Format: <port#>,<type>
735 See also Documentation/input/devices/joystick-parport.rst
736
737 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
738 time. See
739 Documentation/admin-guide/dynamic-debug-howto.rst for
740 details. Deprecated, see dyndbg.
741
742 debug [KNL] Enable kernel debugging (events log level).
743
744 debug_locks_verbose=
745 [KNL] verbose self-tests
746 Format=<0|1>
747 Print debugging info while doing the locking API
748 self-tests.
749 We default to 0 (no extra messages), setting it to
750 1 will print _a lot_ more information - normally
751 only useful to kernel developers.
752
753 debug_objects [KNL] Enable object debugging
754
755 no_debug_objects
756 [KNL] Disable object debugging
757
758 debug_guardpage_minorder=
759 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
760 parameter allows control of the order of pages that will
761 be intentionally kept free (and hence protected) by the
762 buddy allocator. Bigger value increase the probability
763 of catching random memory corruption, but reduce the
764 amount of memory for normal system use. The maximum
765 possible value is MAX_ORDER/2. Setting this parameter
766 to 1 or 2 should be enough to identify most random
767 memory corruption problems caused by bugs in kernel or
768 driver code when a CPU writes to (or reads from) a
769 random memory location. Note that there exists a class
770 of memory corruptions problems caused by buggy H/W or
771 F/W or by drivers badly programing DMA (basically when
772 memory is written at bus level and the CPU MMU is
773 bypassed) which are not detectable by
774 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
775 tracking down these problems.
776
777 debug_pagealloc=
778 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
779 parameter enables the feature at boot time. In
780 default, it is disabled. We can avoid allocating huge
781 chunk of memory for debug pagealloc if we don't enable
782 it at boot time and the system will work mostly same
783 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
784 on: enable the feature
785
786 debugpat [X86] Enable PAT debugging
787
788 decnet.addr= [HW,NET]
789 Format: <area>[,<node>]
790 See also Documentation/networking/decnet.txt.
791
792 default_hugepagesz=
793 [same as hugepagesz=] The size of the default
794 HugeTLB page size. This is the size represented by
795 the legacy /proc/ hugepages APIs, used for SHM, and
796 default size when mounting hugetlbfs filesystems.
797 Defaults to the default architecture's huge page size
798 if not specified.
799
800 dhash_entries= [KNL]
801 Set number of hash buckets for dentry cache.
802
803 disable_1tb_segments [PPC]
804 Disables the use of 1TB hash page table segments. This
805 causes the kernel to fall back to 256MB segments which
806 can be useful when debugging issues that require an SLB
807 miss to occur.
808
809 disable= [IPV6]
810 See Documentation/networking/ipv6.txt.
811
812 disable_radix [PPC]
813 Disable RADIX MMU mode on POWER9
814
815 disable_cpu_apicid= [X86,APIC,SMP]
816 Format: <int>
817 The number of initial APIC ID for the
818 corresponding CPU to be disabled at boot,
819 mostly used for the kdump 2nd kernel to
820 disable BSP to wake up multiple CPUs without
821 causing system reset or hang due to sending
822 INIT from AP to BSP.
823
824 disable_ddw [PPC/PSERIES]
825 Disable Dynamic DMA Window support. Use this if
826 to workaround buggy firmware.
827
828 disable_ipv6= [IPV6]
829 See Documentation/networking/ipv6.txt.
830
831 disable_mtrr_cleanup [X86]
832 The kernel tries to adjust MTRR layout from continuous
833 to discrete, to make X server driver able to add WB
834 entry later. This parameter disables that.
835
836 disable_mtrr_trim [X86, Intel and AMD only]
837 By default the kernel will trim any uncacheable
838 memory out of your available memory pool based on
839 MTRR settings. This parameter disables that behavior,
840 possibly causing your machine to run very slowly.
841
842 disable_timer_pin_1 [X86]
843 Disable PIN 1 of APIC timer
844 Can be useful to work around chipset bugs.
845
846 dis_ucode_ldr [X86] Disable the microcode loader.
847
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
850
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
857
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
864
865 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
866 Broken monitors, graphic adapters, KVMs and EDIDless
867 panels may send no or incorrect EDID data sets.
868 This parameter allows to specify an EDID data sets
869 in the /lib/firmware directory that are used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name. Each connector may use a unique EDID data
879 set by separating the files with a comma. An EDID
880 data set with no connector name will be used for
881 any connectors not explicitly specified.
882
883 dscc4.setup= [NET]
884
885 dt_cpu_ftrs= [PPC]
886 Format: {"off" | "known"}
887 Control how the dt_cpu_ftrs device-tree binding is
888 used for CPU feature discovery and setup (if it
889 exists).
890 off: Do not use it, fall back to legacy cpu table.
891 known: Do not pass through unknown features to guests
892 or userspace, only those that the kernel is aware of.
893
894 dump_apple_properties [X86]
895 Dump name and content of EFI device properties on
896 x86 Macs. Useful for driver authors to determine
897 what data is available or for reverse-engineering.
898
899 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
900 module.dyndbg[="val"]
901 Enable debug messages at boot time. See
902 Documentation/admin-guide/dynamic-debug-howto.rst
903 for details.
904
905 nompx [X86] Disables Intel Memory Protection Extensions.
906 See Documentation/x86/intel_mpx.txt for more
907 information about the feature.
908
909 nopku [X86] Disable Memory Protection Keys CPU feature found
910 in some Intel CPUs.
911
912 module.async_probe [KNL]
913 Enable asynchronous probe on this module.
914
915 early_ioremap_debug [KNL]
916 Enable debug messages in early_ioremap support. This
917 is useful for tracking down temporary early mappings
918 which are not unmapped.
919
920 earlycon= [KNL] Output early console device and options.
921
922 When used with no options, the early console is
923 determined by the stdout-path property in device
924 tree's chosen node.
925
926 cdns,<addr>[,options]
927 Start an early, polled-mode console on a Cadence
928 (xuartps) serial port at the specified address. Only
929 supported option is baud rate. If baud rate is not
930 specified, the serial port must already be setup and
931 configured.
932
933 uart[8250],io,<addr>[,options]
934 uart[8250],mmio,<addr>[,options]
935 uart[8250],mmio32,<addr>[,options]
936 uart[8250],mmio32be,<addr>[,options]
937 uart[8250],0x<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32 or mmio32be).
942 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
943 to be equivalent to 'mmio'. 'options' are specified
944 in the same format described for "console=ttyS<n>"; if
945 unspecified, the h/w is not initialized.
946
947 pl011,<addr>
948 pl011,mmio32,<addr>
949 Start an early, polled-mode console on a pl011 serial
950 port at the specified address. The pl011 serial port
951 must already be setup and configured. Options are not
952 yet supported. If 'mmio32' is specified, then only
953 the driver will use only 32-bit accessors to read/write
954 the device registers.
955
956 meson,<addr>
957 Start an early, polled-mode console on a meson serial
958 port at the specified address. The serial port must
959 already be setup and configured. Options are not yet
960 supported.
961
962 msm_serial,<addr>
963 Start an early, polled-mode console on an msm serial
964 port at the specified address. The serial port
965 must already be setup and configured. Options are not
966 yet supported.
967
968 msm_serial_dm,<addr>
969 Start an early, polled-mode console on an msm serial
970 dm port at the specified address. The serial port
971 must already be setup and configured. Options are not
972 yet supported.
973
974 owl,<addr>
975 Start an early, polled-mode console on a serial port
976 of an Actions Semi SoC, such as S500 or S900, at the
977 specified address. The serial port must already be
978 setup and configured. Options are not yet supported.
979
980 smh Use ARM semihosting calls for early console.
981
982 s3c2410,<addr>
983 s3c2412,<addr>
984 s3c2440,<addr>
985 s3c6400,<addr>
986 s5pv210,<addr>
987 exynos4210,<addr>
988 Use early console provided by serial driver available
989 on Samsung SoCs, requires selecting proper type and
990 a correct base address of the selected UART port. The
991 serial port must already be setup and configured.
992 Options are not yet supported.
993
994 lantiq,<addr>
995 Start an early, polled-mode console on a lantiq serial
996 (lqasc) port at the specified address. The serial port
997 must already be setup and configured. Options are not
998 yet supported.
999
1000 lpuart,<addr>
1001 lpuart32,<addr>
1002 Use early console provided by Freescale LP UART driver
1003 found on Freescale Vybrid and QorIQ LS1021A processors.
1004 A valid base address must be provided, and the serial
1005 port must already be setup and configured.
1006
1007 ar3700_uart,<addr>
1008 Start an early, polled-mode console on the
1009 Armada 3700 serial port at the specified
1010 address. The serial port must already be setup
1011 and configured. Options are not yet supported.
1012
1013 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1014 earlyprintk=vga
1015 earlyprintk=efi
1016 earlyprintk=sclp
1017 earlyprintk=xen
1018 earlyprintk=serial[,ttySn[,baudrate]]
1019 earlyprintk=serial[,0x...[,baudrate]]
1020 earlyprintk=ttySn[,baudrate]
1021 earlyprintk=dbgp[debugController#]
1022 earlyprintk=pciserial,bus:device.function[,baudrate]
1023 earlyprintk=xdbc[xhciController#]
1024
1025 earlyprintk is useful when the kernel crashes before
1026 the normal console is initialized. It is not enabled by
1027 default because it has some cosmetic problems.
1028
1029 Append ",keep" to not disable it when the real console
1030 takes over.
1031
1032 Only one of vga, efi, serial, or usb debug port can
1033 be used at a time.
1034
1035 Currently only ttyS0 and ttyS1 may be specified by
1036 name. Other I/O ports may be explicitly specified
1037 on some architectures (x86 and arm at least) by
1038 replacing ttySn with an I/O port address, like this:
1039 earlyprintk=serial,0x1008,115200
1040 You can find the port for a given device in
1041 /proc/tty/driver/serial:
1042 2: uart:ST16650V2 port:00001008 irq:18 ...
1043
1044 Interaction with the standard serial driver is not
1045 very good.
1046
1047 The VGA and EFI output is eventually overwritten by
1048 the real console.
1049
1050 The xen output can only be used by Xen PV guests.
1051
1052 The sclp output can only be used on s390.
1053
1054 edac_report= [HW,EDAC] Control how to report EDAC event
1055 Format: {"on" | "off" | "force"}
1056 on: enable EDAC to report H/W event. May be overridden
1057 by other higher priority error reporting module.
1058 off: disable H/W event reporting through EDAC.
1059 force: enforce the use of EDAC to report H/W event.
1060 default: on.
1061
1062 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1063 ekgdboc=kbd
1064
1065 This is designed to be used in conjunction with
1066 the boot argument: earlyprintk=vga
1067
1068 edd= [EDD]
1069 Format: {"off" | "on" | "skip[mbr]"}
1070
1071 efi= [EFI]
1072 Format: { "old_map", "nochunk", "noruntime", "debug" }
1073 old_map [X86-64]: switch to the old ioremap-based EFI
1074 runtime services mapping. 32-bit still uses this one by
1075 default.
1076 nochunk: disable reading files in "chunks" in the EFI
1077 boot stub, as chunking can cause problems with some
1078 firmware implementations.
1079 noruntime : disable EFI runtime services support
1080 debug: enable misc debug output
1081
1082 efi_no_storage_paranoia [EFI; X86]
1083 Using this parameter you can use more than 50% of
1084 your efi variable storage. Use this parameter only if
1085 you are really sure that your UEFI does sane gc and
1086 fulfills the spec otherwise your board may brick.
1087
1088 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1089 Add arbitrary attribute to specific memory range by
1090 updating original EFI memory map.
1091 Region of memory which aa attribute is added to is
1092 from ss to ss+nn.
1093 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1094 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1095 attribute is added to range 0x100000000-0x180000000 and
1096 0x10a0000000-0x1120000000.
1097
1098 Using this parameter you can do debugging of EFI memmap
1099 related feature. For example, you can do debugging of
1100 Address Range Mirroring feature even if your box
1101 doesn't support it.
1102
1103 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1104 that is to be dynamically loaded by Linux. If there are
1105 multiple variables with the same name but with different
1106 vendor GUIDs, all of them will be loaded. See
1107 Documentation/acpi/ssdt-overlays.txt for details.
1108
1109
1110 eisa_irq_edge= [PARISC,HW]
1111 See header of drivers/parisc/eisa.c.
1112
1113 elanfreq= [X86-32]
1114 See comment before function elanfreq_setup() in
1115 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1116
1117 elevator= [IOSCHED]
1118 Format: {"cfq" | "deadline" | "noop"}
1119 See Documentation/block/cfq-iosched.txt and
1120 Documentation/block/deadline-iosched.txt for details.
1121
1122 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1123 Specifies physical address of start of kernel core
1124 image elf header and optionally the size. Generally
1125 kexec loader will pass this option to capture kernel.
1126 See Documentation/kdump/kdump.txt for details.
1127
1128 enable_mtrr_cleanup [X86]
1129 The kernel tries to adjust MTRR layout from continuous
1130 to discrete, to make X server driver able to add WB
1131 entry later. This parameter enables that.
1132
1133 enable_timer_pin_1 [X86]
1134 Enable PIN 1 of APIC timer
1135 Can be useful to work around chipset bugs
1136 (in particular on some ATI chipsets).
1137 The kernel tries to set a reasonable default.
1138
1139 enforcing [SELINUX] Set initial enforcing status.
1140 Format: {"0" | "1"}
1141 See security/selinux/Kconfig help text.
1142 0 -- permissive (log only, no denials).
1143 1 -- enforcing (deny and log).
1144 Default value is 0.
1145 Value can be changed at runtime via /selinux/enforce.
1146
1147 erst_disable [ACPI]
1148 Disable Error Record Serialization Table (ERST)
1149 support.
1150
1151 ether= [HW,NET] Ethernet cards parameters
1152 This option is obsoleted by the "netdev=" option, which
1153 has equivalent usage. See its documentation for details.
1154
1155 evm= [EVM]
1156 Format: { "fix" }
1157 Permit 'security.evm' to be updated regardless of
1158 current integrity status.
1159
1160 failslab=
1161 fail_page_alloc=
1162 fail_make_request=[KNL]
1163 General fault injection mechanism.
1164 Format: <interval>,<probability>,<space>,<times>
1165 See also Documentation/fault-injection/.
1166
1167 floppy= [HW]
1168 See Documentation/blockdev/floppy.txt.
1169
1170 force_pal_cache_flush
1171 [IA-64] Avoid check_sal_cache_flush which may hang on
1172 buggy SAL_CACHE_FLUSH implementations. Using this
1173 parameter will force ia64_sal_cache_flush to call
1174 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1175
1176 forcepae [X86-32]
1177 Forcefully enable Physical Address Extension (PAE).
1178 Many Pentium M systems disable PAE but may have a
1179 functionally usable PAE implementation.
1180 Warning: use of this parameter will taint the kernel
1181 and may cause unknown problems.
1182
1183 ftrace=[tracer]
1184 [FTRACE] will set and start the specified tracer
1185 as early as possible in order to facilitate early
1186 boot debugging.
1187
1188 ftrace_dump_on_oops[=orig_cpu]
1189 [FTRACE] will dump the trace buffers on oops.
1190 If no parameter is passed, ftrace will dump
1191 buffers of all CPUs, but if you pass orig_cpu, it will
1192 dump only the buffer of the CPU that triggered the
1193 oops.
1194
1195 ftrace_filter=[function-list]
1196 [FTRACE] Limit the functions traced by the function
1197 tracer at boot up. function-list is a comma separated
1198 list of functions. This list can be changed at run
1199 time by the set_ftrace_filter file in the debugfs
1200 tracing directory.
1201
1202 ftrace_notrace=[function-list]
1203 [FTRACE] Do not trace the functions specified in
1204 function-list. This list can be changed at run time
1205 by the set_ftrace_notrace file in the debugfs
1206 tracing directory.
1207
1208 ftrace_graph_filter=[function-list]
1209 [FTRACE] Limit the top level callers functions traced
1210 by the function graph tracer at boot up.
1211 function-list is a comma separated list of functions
1212 that can be changed at run time by the
1213 set_graph_function file in the debugfs tracing directory.
1214
1215 ftrace_graph_notrace=[function-list]
1216 [FTRACE] Do not trace from the functions specified in
1217 function-list. This list is a comma separated list of
1218 functions that can be changed at run time by the
1219 set_graph_notrace file in the debugfs tracing directory.
1220
1221 ftrace_graph_max_depth=<uint>
1222 [FTRACE] Used with the function graph tracer. This is
1223 the max depth it will trace into a function. This value
1224 can be changed at run time by the max_graph_depth file
1225 in the tracefs tracing directory. default: 0 (no limit)
1226
1227 gamecon.map[2|3]=
1228 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1229 support via parallel port (up to 5 devices per port)
1230 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1231 See also Documentation/input/devices/joystick-parport.rst
1232
1233 gamma= [HW,DRM]
1234
1235 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1236 Format: off | on
1237 default: on
1238
1239 gcov_persist= [GCOV] When non-zero (default), profiling data for
1240 kernel modules is saved and remains accessible via
1241 debugfs, even when the module is unloaded/reloaded.
1242 When zero, profiling data is discarded and associated
1243 debugfs files are removed at module unload time.
1244
1245 goldfish [X86] Enable the goldfish android emulator platform.
1246 Don't use this when you are not running on the
1247 android emulator
1248
1249 gpt [EFI] Forces disk with valid GPT signature but
1250 invalid Protective MBR to be treated as GPT. If the
1251 primary GPT is corrupted, it enables the backup/alternate
1252 GPT to be used instead.
1253
1254 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1255 the "Enable 0" bit of the configuration register.
1256 Format: 0 | 1
1257 Default: 0
1258 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1259 the "Enable 0" bit of the configuration register.
1260 Format: 0 | 1
1261 Default: 0
1262 grcan.select= [HW] Select which physical interface to use.
1263 Format: 0 | 1
1264 Default: 0
1265 grcan.txsize= [HW] Sets the size of the tx buffer.
1266 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1267 Default: 1024
1268 grcan.rxsize= [HW] Sets the size of the rx buffer.
1269 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1270 Default: 1024
1271
1272 gpio-mockup.gpio_mockup_ranges
1273 [HW] Sets the ranges of gpiochip of for this device.
1274 Format: <start1>,<end1>,<start2>,<end2>...
1275
1276 hardlockup_all_cpu_backtrace=
1277 [KNL] Should the hard-lockup detector generate
1278 backtraces on all cpus.
1279 Format: <integer>
1280
1281 hashdist= [KNL,NUMA] Large hashes allocated during boot
1282 are distributed across NUMA nodes. Defaults on
1283 for 64-bit NUMA, off otherwise.
1284 Format: 0 | 1 (for off | on)
1285
1286 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1287
1288 hd= [EIDE] (E)IDE hard drive subsystem geometry
1289 Format: <cyl>,<head>,<sect>
1290
1291 hest_disable [ACPI]
1292 Disable Hardware Error Source Table (HEST) support;
1293 corresponding firmware-first mode error processing
1294 logic will be disabled.
1295
1296 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1297 size of <nn>. This works even on boxes that have no
1298 highmem otherwise. This also works to reduce highmem
1299 size on bigger boxes.
1300
1301 highres= [KNL] Enable/disable high resolution timer mode.
1302 Valid parameters: "on", "off"
1303 Default: "on"
1304
1305 hisax= [HW,ISDN]
1306 See Documentation/isdn/README.HiSax.
1307
1308 hlt [BUGS=ARM,SH]
1309
1310 hpet= [X86-32,HPET] option to control HPET usage
1311 Format: { enable (default) | disable | force |
1312 verbose }
1313 disable: disable HPET and use PIT instead
1314 force: allow force enabled of undocumented chips (ICH4,
1315 VIA, nVidia)
1316 verbose: show contents of HPET registers during setup
1317
1318 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1319 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1320
1321 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1322 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1323 On x86-64 and powerpc, this option can be specified
1324 multiple times interleaved with hugepages= to reserve
1325 huge pages of different sizes. Valid pages sizes on
1326 x86-64 are 2M (when the CPU supports "pse") and 1G
1327 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1328
1329 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1330 terminal devices. Valid values: 0..8
1331 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1332 If specified, z/VM IUCV HVC accepts connections
1333 from listed z/VM user IDs only.
1334
1335 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1336 hardware thread id mappings.
1337 Format: <cpu>:<hwthread>
1338
1339 keep_bootcon [KNL]
1340 Do not unregister boot console at start. This is only
1341 useful for debugging when something happens in the window
1342 between unregistering the boot console and initializing
1343 the real console.
1344
1345 i2c_bus= [HW] Override the default board specific I2C bus speed
1346 or register an additional I2C bus that is not
1347 registered from board initialization code.
1348 Format:
1349 <bus_id>,<clkrate>
1350
1351 i8042.debug [HW] Toggle i8042 debug mode
1352 i8042.unmask_kbd_data
1353 [HW] Enable printing of interrupt data from the KBD port
1354 (disabled by default, and as a pre-condition
1355 requires that i8042.debug=1 be enabled)
1356 i8042.direct [HW] Put keyboard port into non-translated mode
1357 i8042.dumbkbd [HW] Pretend that controller can only read data from
1358 keyboard and cannot control its state
1359 (Don't attempt to blink the leds)
1360 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1361 i8042.nokbd [HW] Don't check/create keyboard port
1362 i8042.noloop [HW] Disable the AUX Loopback command while probing
1363 for the AUX port
1364 i8042.nomux [HW] Don't check presence of an active multiplexing
1365 controller
1366 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1367 controllers
1368 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1369 i8042.reset [HW] Reset the controller during init, cleanup and
1370 suspend-to-ram transitions, only during s2r
1371 transitions, or never reset
1372 Format: { 1 | Y | y | 0 | N | n }
1373 1, Y, y: always reset controller
1374 0, N, n: don't ever reset controller
1375 Default: only on s2r transitions on x86; most other
1376 architectures force reset to be always executed
1377 i8042.unlock [HW] Unlock (ignore) the keylock
1378 i8042.kbdreset [HW] Reset device connected to KBD port
1379
1380 i810= [HW,DRM]
1381
1382 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1383 indicates that the driver is running on unsupported
1384 hardware.
1385 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1386 does not match list of supported models.
1387 i8k.power_status
1388 [HW] Report power status in /proc/i8k
1389 (disabled by default)
1390 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1391 capability is set.
1392
1393 i915.invert_brightness=
1394 [DRM] Invert the sense of the variable that is used to
1395 set the brightness of the panel backlight. Normally a
1396 brightness value of 0 indicates backlight switched off,
1397 and the maximum of the brightness value sets the backlight
1398 to maximum brightness. If this parameter is set to 0
1399 (default) and the machine requires it, or this parameter
1400 is set to 1, a brightness value of 0 sets the backlight
1401 to maximum brightness, and the maximum of the brightness
1402 value switches the backlight off.
1403 -1 -- never invert brightness
1404 0 -- machine default
1405 1 -- force brightness inversion
1406
1407 icn= [HW,ISDN]
1408 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1409
1410 ide-core.nodma= [HW] (E)IDE subsystem
1411 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1412 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1413 .cdrom .chs .ignore_cable are additional options
1414 See Documentation/ide/ide.txt.
1415
1416 ide-generic.probe-mask= [HW] (E)IDE subsystem
1417 Format: <int>
1418 Probe mask for legacy ISA IDE ports. Depending on
1419 platform up to 6 ports are supported, enabled by
1420 setting corresponding bits in the mask to 1. The
1421 default value is 0x0, which has a special meaning.
1422 On systems that have PCI, it triggers scanning the
1423 PCI bus for the first and the second port, which
1424 are then probed. On systems without PCI the value
1425 of 0x0 enables probing the two first ports as if it
1426 was 0x3.
1427
1428 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1429 Claim all unknown PCI IDE storage controllers.
1430
1431 idle= [X86]
1432 Format: idle=poll, idle=halt, idle=nomwait
1433 Poll forces a polling idle loop that can slightly
1434 improve the performance of waking up a idle CPU, but
1435 will use a lot of power and make the system run hot.
1436 Not recommended.
1437 idle=halt: Halt is forced to be used for CPU idle.
1438 In such case C2/C3 won't be used again.
1439 idle=nomwait: Disable mwait for CPU C-states
1440
1441 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1442 Format: { strict | legacy | 2008 | relaxed }
1443 Default: strict
1444
1445 Choose which programs will be accepted for execution
1446 based on the IEEE 754 NaN encoding(s) supported by
1447 the FPU and the NaN encoding requested with the value
1448 of an ELF file header flag individually set by each
1449 binary. Hardware implementations are permitted to
1450 support either or both of the legacy and the 2008 NaN
1451 encoding mode.
1452
1453 Available settings are as follows:
1454 strict accept binaries that request a NaN encoding
1455 supported by the FPU
1456 legacy only accept legacy-NaN binaries, if supported
1457 by the FPU
1458 2008 only accept 2008-NaN binaries, if supported
1459 by the FPU
1460 relaxed accept any binaries regardless of whether
1461 supported by the FPU
1462
1463 The FPU emulator is always able to support both NaN
1464 encodings, so if no FPU hardware is present or it has
1465 been disabled with 'nofpu', then the settings of
1466 'legacy' and '2008' strap the emulator accordingly,
1467 'relaxed' straps the emulator for both legacy-NaN and
1468 2008-NaN, whereas 'strict' enables legacy-NaN only on
1469 legacy processors and both NaN encodings on MIPS32 or
1470 MIPS64 CPUs.
1471
1472 The setting for ABS.fmt/NEG.fmt instruction execution
1473 mode generally follows that for the NaN encoding,
1474 except where unsupported by hardware.
1475
1476 ignore_loglevel [KNL]
1477 Ignore loglevel setting - this will print /all/
1478 kernel messages to the console. Useful for debugging.
1479 We also add it as printk module parameter, so users
1480 could change it dynamically, usually by
1481 /sys/module/printk/parameters/ignore_loglevel.
1482
1483 ignore_rlimit_data
1484 Ignore RLIMIT_DATA setting for data mappings,
1485 print warning at first misuse. Can be changed via
1486 /sys/module/kernel/parameters/ignore_rlimit_data.
1487
1488 ihash_entries= [KNL]
1489 Set number of hash buckets for inode cache.
1490
1491 ima_appraise= [IMA] appraise integrity measurements
1492 Format: { "off" | "enforce" | "fix" | "log" }
1493 default: "enforce"
1494
1495 ima_appraise_tcb [IMA]
1496 The builtin appraise policy appraises all files
1497 owned by uid=0.
1498
1499 ima_canonical_fmt [IMA]
1500 Use the canonical format for the binary runtime
1501 measurements, instead of host native format.
1502
1503 ima_hash= [IMA]
1504 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1505 | sha512 | ... }
1506 default: "sha1"
1507
1508 The list of supported hash algorithms is defined
1509 in crypto/hash_info.h.
1510
1511 ima_policy= [IMA]
1512 The builtin policies to load during IMA setup.
1513 Format: "tcb | appraise_tcb | secure_boot"
1514
1515 The "tcb" policy measures all programs exec'd, files
1516 mmap'd for exec, and all files opened with the read
1517 mode bit set by either the effective uid (euid=0) or
1518 uid=0.
1519
1520 The "appraise_tcb" policy appraises the integrity of
1521 all files owned by root. (This is the equivalent
1522 of ima_appraise_tcb.)
1523
1524 The "secure_boot" policy appraises the integrity
1525 of files (eg. kexec kernel image, kernel modules,
1526 firmware, policy, etc) based on file signatures.
1527
1528 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1529 Load a policy which meets the needs of the Trusted
1530 Computing Base. This means IMA will measure all
1531 programs exec'd, files mmap'd for exec, and all files
1532 opened for read by uid=0.
1533
1534 ima_template= [IMA]
1535 Select one of defined IMA measurements template formats.
1536 Formats: { "ima" | "ima-ng" | "ima-sig" }
1537 Default: "ima-ng"
1538
1539 ima_template_fmt=
1540 [IMA] Define a custom template format.
1541 Format: { "field1|...|fieldN" }
1542
1543 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1544 Format: <min_file_size>
1545 Set the minimal file size for using asynchronous hash.
1546 If left unspecified, ahash usage is disabled.
1547
1548 ahash performance varies for different data sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve the best performance for a particular HW.
1551
1552 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1553 Format: <bufsize>
1554 Set hashing buffer size. Default: 4k.
1555
1556 ahash performance varies for different chunk sizes on
1557 different crypto accelerators. This option can be used
1558 to achieve best performance for particular HW.
1559
1560 init= [KNL]
1561 Format: <full_path>
1562 Run specified binary instead of /sbin/init as init
1563 process.
1564
1565 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1566 for working out where the kernel is dying during
1567 startup.
1568
1569 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1570 initcall functions. Useful for debugging built-in
1571 modules and initcalls.
1572
1573 initrd= [BOOT] Specify the location of the initial ramdisk
1574
1575 init_pkru= [x86] Specify the default memory protection keys rights
1576 register contents for all processes. 0x55555554 by
1577 default (disallow access to all but pkey 0). Can
1578 override in debugfs after boot.
1579
1580 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1581 Format: <irq>
1582
1583 int_pln_enable [x86] Enable power limit notification interrupt
1584
1585 integrity_audit=[IMA]
1586 Format: { "0" | "1" }
1587 0 -- basic integrity auditing messages. (Default)
1588 1 -- additional integrity auditing messages.
1589
1590 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1591 on
1592 Enable intel iommu driver.
1593 off
1594 Disable intel iommu driver.
1595 igfx_off [Default Off]
1596 By default, gfx is mapped as normal device. If a gfx
1597 device has a dedicated DMAR unit, the DMAR unit is
1598 bypassed by not enabling DMAR with this option. In
1599 this case, gfx device will use physical address for
1600 DMA.
1601 forcedac [x86_64]
1602 With this option iommu will not optimize to look
1603 for io virtual address below 32-bit forcing dual
1604 address cycle on pci bus for cards supporting greater
1605 than 32-bit addressing. The default is to look
1606 for translation below 32-bit and if not available
1607 then look in the higher range.
1608 strict [Default Off]
1609 With this option on every unmap_single operation will
1610 result in a hardware IOTLB flush operation as opposed
1611 to batching them for performance.
1612 sp_off [Default Off]
1613 By default, super page will be supported if Intel IOMMU
1614 has the capability. With this option, super page will
1615 not be supported.
1616 ecs_off [Default Off]
1617 By default, extended context tables will be supported if
1618 the hardware advertises that it has support both for the
1619 extended tables themselves, and also PASID support. With
1620 this option set, extended tables will not be used even
1621 on hardware which claims to support them.
1622 tboot_noforce [Default Off]
1623 Do not force the Intel IOMMU enabled under tboot.
1624 By default, tboot will force Intel IOMMU on, which
1625 could harm performance of some high-throughput
1626 devices like 40GBit network cards, even if identity
1627 mapping is enabled.
1628 Note that using this option lowers the security
1629 provided by tboot because it makes the system
1630 vulnerable to DMA attacks.
1631
1632 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1633 0 disables intel_idle and fall back on acpi_idle.
1634 1 to 9 specify maximum depth of C-state.
1635
1636 intel_pstate= [X86]
1637 disable
1638 Do not enable intel_pstate as the default
1639 scaling driver for the supported processors
1640 passive
1641 Use intel_pstate as a scaling driver, but configure it
1642 to work with generic cpufreq governors (instead of
1643 enabling its internal governor). This mode cannot be
1644 used along with the hardware-managed P-states (HWP)
1645 feature.
1646 force
1647 Enable intel_pstate on systems that prohibit it by default
1648 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1649 instead of acpi-cpufreq may disable platform features, such
1650 as thermal controls and power capping, that rely on ACPI
1651 P-States information being indicated to OSPM and therefore
1652 should be used with caution. This option does not work with
1653 processors that aren't supported by the intel_pstate driver
1654 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1655 no_hwp
1656 Do not enable hardware P state control (HWP)
1657 if available.
1658 hwp_only
1659 Only load intel_pstate on systems which support
1660 hardware P state control (HWP) if available.
1661 support_acpi_ppc
1662 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1663 Description Table, specifies preferred power management
1664 profile as "Enterprise Server" or "Performance Server",
1665 then this feature is turned on by default.
1666 per_cpu_perf_limits
1667 Allow per-logical-CPU P-State performance control limits using
1668 cpufreq sysfs interface
1669
1670 intremap= [X86-64, Intel-IOMMU]
1671 on enable Interrupt Remapping (default)
1672 off disable Interrupt Remapping
1673 nosid disable Source ID checking
1674 no_x2apic_optout
1675 BIOS x2APIC opt-out request will be ignored
1676 nopost disable Interrupt Posting
1677
1678 iomem= Disable strict checking of access to MMIO memory
1679 strict regions from userspace.
1680 relaxed
1681
1682 iommu= [x86]
1683 off
1684 force
1685 noforce
1686 biomerge
1687 panic
1688 nopanic
1689 merge
1690 nomerge
1691 forcesac
1692 soft
1693 pt [x86, IA-64]
1694 nobypass [PPC/POWERNV]
1695 Disable IOMMU bypass, using IOMMU for PCI devices.
1696
1697 iommu.passthrough=
1698 [ARM64] Configure DMA to bypass the IOMMU by default.
1699 Format: { "0" | "1" }
1700 0 - Use IOMMU translation for DMA.
1701 1 - Bypass the IOMMU for DMA.
1702 unset - Use IOMMU translation for DMA.
1703
1704 io7= [HW] IO7 for Marvel based alpha systems
1705 See comment before marvel_specify_io7 in
1706 arch/alpha/kernel/core_marvel.c.
1707
1708 io_delay= [X86] I/O delay method
1709 0x80
1710 Standard port 0x80 based delay
1711 0xed
1712 Alternate port 0xed based delay (needed on some systems)
1713 udelay
1714 Simple two microseconds delay
1715 none
1716 No delay
1717
1718 ip= [IP_PNP]
1719 See Documentation/filesystems/nfs/nfsroot.txt.
1720
1721 irqaffinity= [SMP] Set the default irq affinity mask
1722 The argument is a cpu list, as described above.
1723
1724 irqchip.gicv2_force_probe=
1725 [ARM, ARM64]
1726 Format: <bool>
1727 Force the kernel to look for the second 4kB page
1728 of a GICv2 controller even if the memory range
1729 exposed by the device tree is too small.
1730
1731 irqfixup [HW]
1732 When an interrupt is not handled search all handlers
1733 for it. Intended to get systems with badly broken
1734 firmware running.
1735
1736 irqpoll [HW]
1737 When an interrupt is not handled search all handlers
1738 for it. Also check all handlers each timer
1739 interrupt. Intended to get systems with badly broken
1740 firmware running.
1741
1742 isapnp= [ISAPNP]
1743 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1744
1745 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1746 [Deprecated - use cpusets instead]
1747 Format: [flag-list,]<cpu-list>
1748
1749 Specify one or more CPUs to isolate from disturbances
1750 specified in the flag list (default: domain):
1751
1752 nohz
1753 Disable the tick when a single task runs.
1754 domain
1755 Isolate from the general SMP balancing and scheduling
1756 algorithms. Note that performing domain isolation this way
1757 is irreversible: it's not possible to bring back a CPU to
1758 the domains once isolated through isolcpus. It's strongly
1759 advised to use cpusets instead to disable scheduler load
1760 balancing through the "cpuset.sched_load_balance" file.
1761 It offers a much more flexible interface where CPUs can
1762 move in and out of an isolated set anytime.
1763
1764 You can move a process onto or off an "isolated" CPU via
1765 the CPU affinity syscalls or cpuset.
1766 <cpu number> begins at 0 and the maximum value is
1767 "number of CPUs in system - 1".
1768
1769 The format of <cpu-list> is described above.
1770
1771
1772
1773 iucv= [HW,NET]
1774
1775 ivrs_ioapic [HW,X86_64]
1776 Provide an override to the IOAPIC-ID<->DEVICE-ID
1777 mapping provided in the IVRS ACPI table. For
1778 example, to map IOAPIC-ID decimal 10 to
1779 PCI device 00:14.0 write the parameter as:
1780 ivrs_ioapic[10]=00:14.0
1781
1782 ivrs_hpet [HW,X86_64]
1783 Provide an override to the HPET-ID<->DEVICE-ID
1784 mapping provided in the IVRS ACPI table. For
1785 example, to map HPET-ID decimal 0 to
1786 PCI device 00:14.0 write the parameter as:
1787 ivrs_hpet[0]=00:14.0
1788
1789 ivrs_acpihid [HW,X86_64]
1790 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1791 mapping provided in the IVRS ACPI table. For
1792 example, to map UART-HID:UID AMD0020:0 to
1793 PCI device 00:14.5 write the parameter as:
1794 ivrs_acpihid[00:14.5]=AMD0020:0
1795
1796 js= [HW,JOY] Analog joystick
1797 See Documentation/input/joydev/joystick.rst.
1798
1799 nokaslr [KNL]
1800 When CONFIG_RANDOMIZE_BASE is set, this disables
1801 kernel and module base offset ASLR (Address Space
1802 Layout Randomization).
1803
1804 kasan_multi_shot
1805 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1806 report on every invalid memory access. Without this
1807 parameter KASAN will print report only for the first
1808 invalid access.
1809
1810 keepinitrd [HW,ARM]
1811
1812 kernelcore= [KNL,X86,IA-64,PPC]
1813 Format: nn[KMGTPE] | "mirror"
1814 This parameter
1815 specifies the amount of memory usable by the kernel
1816 for non-movable allocations. The requested amount is
1817 spread evenly throughout all nodes in the system. The
1818 remaining memory in each node is used for Movable
1819 pages. In the event, a node is too small to have both
1820 kernelcore and Movable pages, kernelcore pages will
1821 take priority and other nodes will have a larger number
1822 of Movable pages. The Movable zone is used for the
1823 allocation of pages that may be reclaimed or moved
1824 by the page migration subsystem. This means that
1825 HugeTLB pages may not be allocated from this zone.
1826 Note that allocations like PTEs-from-HighMem still
1827 use the HighMem zone if it exists, and the Normal
1828 zone if it does not.
1829
1830 Instead of specifying the amount of memory (nn[KMGTPE]),
1831 you can specify "mirror" option. In case "mirror"
1832 option is specified, mirrored (reliable) memory is used
1833 for non-movable allocations and remaining memory is used
1834 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1835 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1836 time.
1837
1838 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1839 Format: <Controller#>[,poll interval]
1840 The controller # is the number of the ehci usb debug
1841 port as it is probed via PCI. The poll interval is
1842 optional and is the number seconds in between
1843 each poll cycle to the debug port in case you need
1844 the functionality for interrupting the kernel with
1845 gdb or control-c on the dbgp connection. When
1846 not using this parameter you use sysrq-g to break into
1847 the kernel debugger.
1848
1849 kgdboc= [KGDB,HW] kgdb over consoles.
1850 Requires a tty driver that supports console polling,
1851 or a supported polling keyboard driver (non-usb).
1852 Serial only format: <serial_device>[,baud]
1853 keyboard only format: kbd
1854 keyboard and serial format: kbd,<serial_device>[,baud]
1855 Optional Kernel mode setting:
1856 kms, kbd format: kms,kbd
1857 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1858
1859 kgdbwait [KGDB] Stop kernel execution and enter the
1860 kernel debugger at the earliest opportunity.
1861
1862 kmac= [MIPS] korina ethernet MAC address.
1863 Configure the RouterBoard 532 series on-chip
1864 Ethernet adapter MAC address.
1865
1866 kmemleak= [KNL] Boot-time kmemleak enable/disable
1867 Valid arguments: on, off
1868 Default: on
1869 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1870 the default is off.
1871
1872 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1873 Default is 0 (don't ignore, but inject #GP)
1874
1875 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1876 KVM MMU at runtime.
1877 Default is 0 (off)
1878
1879 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1880 Default is 1 (enabled)
1881
1882 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1883 for all guests.
1884 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1885
1886 kvm-arm.vgic_v3_group0_trap=
1887 [KVM,ARM] Trap guest accesses to GICv3 group-0
1888 system registers
1889
1890 kvm-arm.vgic_v3_group1_trap=
1891 [KVM,ARM] Trap guest accesses to GICv3 group-1
1892 system registers
1893
1894 kvm-arm.vgic_v3_common_trap=
1895 [KVM,ARM] Trap guest accesses to GICv3 common
1896 system registers
1897
1898 kvm-arm.vgic_v4_enable=
1899 [KVM,ARM] Allow use of GICv4 for direct injection of
1900 LPIs.
1901
1902 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1903 (virtualized MMU) support on capable Intel chips.
1904 Default is 1 (enabled)
1905
1906 kvm-intel.emulate_invalid_guest_state=
1907 [KVM,Intel] Enable emulation of invalid guest states
1908 Default is 0 (disabled)
1909
1910 kvm-intel.flexpriority=
1911 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1912 Default is 1 (enabled)
1913
1914 kvm-intel.nested=
1915 [KVM,Intel] Enable VMX nesting (nVMX).
1916 Default is 0 (disabled)
1917
1918 kvm-intel.unrestricted_guest=
1919 [KVM,Intel] Disable unrestricted guest feature
1920 (virtualized real and unpaged mode) on capable
1921 Intel chips. Default is 1 (enabled)
1922
1923 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1924 feature (tagged TLBs) on capable Intel chips.
1925 Default is 1 (enabled)
1926
1927 l2cr= [PPC]
1928
1929 l3cr= [PPC]
1930
1931 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1932 disabled it.
1933
1934 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1935 value for LAPIC timer one-shot implementation. Default
1936 back to the programmable timer unit in the LAPIC.
1937
1938 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1939 in C2 power state.
1940
1941 libata.dma= [LIBATA] DMA control
1942 libata.dma=0 Disable all PATA and SATA DMA
1943 libata.dma=1 PATA and SATA Disk DMA only
1944 libata.dma=2 ATAPI (CDROM) DMA only
1945 libata.dma=4 Compact Flash DMA only
1946 Combinations also work, so libata.dma=3 enables DMA
1947 for disks and CDROMs, but not CFs.
1948
1949 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1950 libata.ignore_hpa=0 keep BIOS limits (default)
1951 libata.ignore_hpa=1 ignore limits, using full disk
1952
1953 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1954 when set.
1955 Format: <int>
1956
1957 libata.force= [LIBATA] Force configurations. The format is comma
1958 separated list of "[ID:]VAL" where ID is
1959 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1960 matching port, link or device. Basically, it matches
1961 the ATA ID string printed on console by libata. If
1962 the whole ID part is omitted, the last PORT and DEVICE
1963 values are used. If ID hasn't been specified yet, the
1964 configuration applies to all ports, links and devices.
1965
1966 If only DEVICE is omitted, the parameter applies to
1967 the port and all links and devices behind it. DEVICE
1968 number of 0 either selects the first device or the
1969 first fan-out link behind PMP device. It does not
1970 select the host link. DEVICE number of 15 selects the
1971 host link and device attached to it.
1972
1973 The VAL specifies the configuration to force. As long
1974 as there's no ambiguity shortcut notation is allowed.
1975 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1976 The following configurations can be forced.
1977
1978 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1979 Any ID with matching PORT is used.
1980
1981 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1982
1983 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1984 udma[/][16,25,33,44,66,100,133] notation is also
1985 allowed.
1986
1987 * [no]ncq: Turn on or off NCQ.
1988
1989 * [no]ncqtrim: Turn off queued DSM TRIM.
1990
1991 * nohrst, nosrst, norst: suppress hard, soft
1992 and both resets.
1993
1994 * rstonce: only attempt one reset during
1995 hot-unplug link recovery
1996
1997 * dump_id: dump IDENTIFY data.
1998
1999 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2000
2001 * disable: Disable this device.
2002
2003 If there are multiple matching configurations changing
2004 the same attribute, the last one is used.
2005
2006 memblock=debug [KNL] Enable memblock debug messages.
2007
2008 load_ramdisk= [RAM] List of ramdisks to load from floppy
2009 See Documentation/blockdev/ramdisk.txt.
2010
2011 lockd.nlm_grace_period=P [NFS] Assign grace period.
2012 Format: <integer>
2013
2014 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2015 Format: <integer>
2016
2017 lockd.nlm_timeout=T [NFS] Assign timeout value.
2018 Format: <integer>
2019
2020 lockd.nlm_udpport=M [NFS] Assign UDP port.
2021 Format: <integer>
2022
2023 locktorture.nreaders_stress= [KNL]
2024 Set the number of locking read-acquisition kthreads.
2025 Defaults to being automatically set based on the
2026 number of online CPUs.
2027
2028 locktorture.nwriters_stress= [KNL]
2029 Set the number of locking write-acquisition kthreads.
2030
2031 locktorture.onoff_holdoff= [KNL]
2032 Set time (s) after boot for CPU-hotplug testing.
2033
2034 locktorture.onoff_interval= [KNL]
2035 Set time (s) between CPU-hotplug operations, or
2036 zero to disable CPU-hotplug testing.
2037
2038 locktorture.shuffle_interval= [KNL]
2039 Set task-shuffle interval (jiffies). Shuffling
2040 tasks allows some CPUs to go into dyntick-idle
2041 mode during the locktorture test.
2042
2043 locktorture.shutdown_secs= [KNL]
2044 Set time (s) after boot system shutdown. This
2045 is useful for hands-off automated testing.
2046
2047 locktorture.stat_interval= [KNL]
2048 Time (s) between statistics printk()s.
2049
2050 locktorture.stutter= [KNL]
2051 Time (s) to stutter testing, for example,
2052 specifying five seconds causes the test to run for
2053 five seconds, wait for five seconds, and so on.
2054 This tests the locking primitive's ability to
2055 transition abruptly to and from idle.
2056
2057 locktorture.torture_runnable= [BOOT]
2058 Start locktorture running at boot time.
2059
2060 locktorture.torture_type= [KNL]
2061 Specify the locking implementation to test.
2062
2063 locktorture.verbose= [KNL]
2064 Enable additional printk() statements.
2065
2066 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2067 Format: <irq>
2068
2069 loglevel= All Kernel Messages with a loglevel smaller than the
2070 console loglevel will be printed to the console. It can
2071 also be changed with klogd or other programs. The
2072 loglevels are defined as follows:
2073
2074 0 (KERN_EMERG) system is unusable
2075 1 (KERN_ALERT) action must be taken immediately
2076 2 (KERN_CRIT) critical conditions
2077 3 (KERN_ERR) error conditions
2078 4 (KERN_WARNING) warning conditions
2079 5 (KERN_NOTICE) normal but significant condition
2080 6 (KERN_INFO) informational
2081 7 (KERN_DEBUG) debug-level messages
2082
2083 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2084 in bytes. n must be a power of two and greater
2085 than the minimal size. The minimal size is defined
2086 by LOG_BUF_SHIFT kernel config parameter. There is
2087 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2088 that allows to increase the default size depending on
2089 the number of CPUs. See init/Kconfig for more details.
2090
2091 logo.nologo [FB] Disables display of the built-in Linux logo.
2092 This may be used to provide more screen space for
2093 kernel log messages and is useful when debugging
2094 kernel boot problems.
2095
2096 lp=0 [LP] Specify parallel ports to use, e.g,
2097 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2098 lp=reset first parallel port). 'lp=0' disables the
2099 lp=auto printer driver. 'lp=reset' (which can be
2100 specified in addition to the ports) causes
2101 attached printers to be reset. Using
2102 lp=port1,port2,... specifies the parallel ports
2103 to associate lp devices with, starting with
2104 lp0. A port specification may be 'none' to skip
2105 that lp device, or a parport name such as
2106 'parport0'. Specifying 'lp=auto' instead of a
2107 port specification list means that device IDs
2108 from each port should be examined, to see if
2109 an IEEE 1284-compliant printer is attached; if
2110 so, the driver will manage that printer.
2111 See also header of drivers/char/lp.c.
2112
2113 lpj=n [KNL]
2114 Sets loops_per_jiffy to given constant, thus avoiding
2115 time-consuming boot-time autodetection (up to 250 ms per
2116 CPU). 0 enables autodetection (default). To determine
2117 the correct value for your kernel, boot with normal
2118 autodetection and see what value is printed. Note that
2119 on SMP systems the preset will be applied to all CPUs,
2120 which is likely to cause problems if your CPUs need
2121 significantly divergent settings. An incorrect value
2122 will cause delays in the kernel to be wrong, leading to
2123 unpredictable I/O errors and other breakage. Although
2124 unlikely, in the extreme case this might damage your
2125 hardware.
2126
2127 ltpc= [NET]
2128 Format: <io>,<irq>,<dma>
2129
2130 machvec= [IA-64] Force the use of a particular machine-vector
2131 (machvec) in a generic kernel.
2132 Example: machvec=hpzx1_swiotlb
2133
2134 machtype= [Loongson] Share the same kernel image file between different
2135 yeeloong laptop.
2136 Example: machtype=lemote-yeeloong-2f-7inch
2137
2138 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2139 than or equal to this physical address is ignored.
2140
2141 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2142 will bring up during bootup. maxcpus=n : n >= 0 limits
2143 the kernel to bring up 'n' processors. Surely after
2144 bootup you can bring up the other plugged cpu by executing
2145 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2146 only takes effect during system bootup.
2147 While n=0 is a special case, it is equivalent to "nosmp",
2148 which also disables the IO APIC.
2149
2150 max_loop= [LOOP] The number of loop block devices that get
2151 (loop.max_loop) unconditionally pre-created at init time. The default
2152 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2153 of statically allocating a predefined number, loop
2154 devices can be requested on-demand with the
2155 /dev/loop-control interface.
2156
2157 mce [X86-32] Machine Check Exception
2158
2159 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2160
2161 md= [HW] RAID subsystems devices and level
2162 See Documentation/admin-guide/md.rst.
2163
2164 mdacon= [MDA]
2165 Format: <first>,<last>
2166 Specifies range of consoles to be captured by the MDA.
2167
2168 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2169 Amount of memory to be used when the kernel is not able
2170 to see the whole system memory or for test.
2171 [X86] Work as limiting max address. Use together
2172 with memmap= to avoid physical address space collisions.
2173 Without memmap= PCI devices could be placed at addresses
2174 belonging to unused RAM.
2175
2176 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2177 memory.
2178
2179 memchunk=nn[KMG]
2180 [KNL,SH] Allow user to override the default size for
2181 per-device physically contiguous DMA buffers.
2182
2183 memhp_default_state=online/offline
2184 [KNL] Set the initial state for the memory hotplug
2185 onlining policy. If not specified, the default value is
2186 set according to the
2187 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2188 option.
2189 See Documentation/memory-hotplug.txt.
2190
2191 memmap=exactmap [KNL,X86] Enable setting of an exact
2192 E820 memory map, as specified by the user.
2193 Such memmap=exactmap lines can be constructed based on
2194 BIOS output or other requirements. See the memmap=nn@ss
2195 option description.
2196
2197 memmap=nn[KMG]@ss[KMG]
2198 [KNL] Force usage of a specific region of memory.
2199 Region of memory to be used is from ss to ss+nn.
2200 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2201 which limits max address to nn[KMG].
2202 Multiple different regions can be specified,
2203 comma delimited.
2204 Example:
2205 memmap=100M@2G,100M#3G,1G!1024G
2206
2207 memmap=nn[KMG]#ss[KMG]
2208 [KNL,ACPI] Mark specific memory as ACPI data.
2209 Region of memory to be marked is from ss to ss+nn.
2210
2211 memmap=nn[KMG]$ss[KMG]
2212 [KNL,ACPI] Mark specific memory as reserved.
2213 Region of memory to be reserved is from ss to ss+nn.
2214 Example: Exclude memory from 0x18690000-0x1869ffff
2215 memmap=64K$0x18690000
2216 or
2217 memmap=0x10000$0x18690000
2218 Some bootloaders may need an escape character before '$',
2219 like Grub2, otherwise '$' and the following number
2220 will be eaten.
2221
2222 memmap=nn[KMG]!ss[KMG]
2223 [KNL,X86] Mark specific memory as protected.
2224 Region of memory to be used, from ss to ss+nn.
2225 The memory region may be marked as e820 type 12 (0xc)
2226 and is NVDIMM or ADR memory.
2227
2228 memory_corruption_check=0/1 [X86]
2229 Some BIOSes seem to corrupt the first 64k of
2230 memory when doing things like suspend/resume.
2231 Setting this option will scan the memory
2232 looking for corruption. Enabling this will
2233 both detect corruption and prevent the kernel
2234 from using the memory being corrupted.
2235 However, its intended as a diagnostic tool; if
2236 repeatable BIOS-originated corruption always
2237 affects the same memory, you can use memmap=
2238 to prevent the kernel from using that memory.
2239
2240 memory_corruption_check_size=size [X86]
2241 By default it checks for corruption in the low
2242 64k, making this memory unavailable for normal
2243 use. Use this parameter to scan for
2244 corruption in more or less memory.
2245
2246 memory_corruption_check_period=seconds [X86]
2247 By default it checks for corruption every 60
2248 seconds. Use this parameter to check at some
2249 other rate. 0 disables periodic checking.
2250
2251 memtest= [KNL,X86,ARM] Enable memtest
2252 Format: <integer>
2253 default : 0 <disable>
2254 Specifies the number of memtest passes to be
2255 performed. Each pass selects another test
2256 pattern from a given set of patterns. Memtest
2257 fills the memory with this pattern, validates
2258 memory contents and reserves bad memory
2259 regions that are detected.
2260
2261 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2262 Valid arguments: on, off
2263 Default (depends on kernel configuration option):
2264 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2265 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2266 mem_encrypt=on: Activate SME
2267 mem_encrypt=off: Do not activate SME
2268
2269 Refer to Documentation/x86/amd-memory-encryption.txt
2270 for details on when memory encryption can be activated.
2271
2272 mem_sleep_default= [SUSPEND] Default system suspend mode:
2273 s2idle - Suspend-To-Idle
2274 shallow - Power-On Suspend or equivalent (if supported)
2275 deep - Suspend-To-RAM or equivalent (if supported)
2276 See Documentation/admin-guide/pm/sleep-states.rst.
2277
2278 meye.*= [HW] Set MotionEye Camera parameters
2279 See Documentation/media/v4l-drivers/meye.rst.
2280
2281 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2282 Multi-Function General Purpose Timers on AMD Geode
2283 platforms.
2284
2285 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2286 the BIOS has incorrectly applied a workaround. TinyBIOS
2287 version 0.98 is known to be affected, 0.99 fixes the
2288 problem by letting the user disable the workaround.
2289
2290 mga= [HW,DRM]
2291
2292 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2293 physical address is ignored.
2294
2295 mini2440= [ARM,HW,KNL]
2296 Format:[0..2][b][c][t]
2297 Default: "0tb"
2298 MINI2440 configuration specification:
2299 0 - The attached screen is the 3.5" TFT
2300 1 - The attached screen is the 7" TFT
2301 2 - The VGA Shield is attached (1024x768)
2302 Leaving out the screen size parameter will not load
2303 the TFT driver, and the framebuffer will be left
2304 unconfigured.
2305 b - Enable backlight. The TFT backlight pin will be
2306 linked to the kernel VESA blanking code and a GPIO
2307 LED. This parameter is not necessary when using the
2308 VGA shield.
2309 c - Enable the s3c camera interface.
2310 t - Reserved for enabling touchscreen support. The
2311 touchscreen support is not enabled in the mainstream
2312 kernel as of 2.6.30, a preliminary port can be found
2313 in the "bleeding edge" mini2440 support kernel at
2314 http://repo.or.cz/w/linux-2.6/mini2440.git
2315
2316 mminit_loglevel=
2317 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2318 parameter allows control of the logging verbosity for
2319 the additional memory initialisation checks. A value
2320 of 0 disables mminit logging and a level of 4 will
2321 log everything. Information is printed at KERN_DEBUG
2322 so loglevel=8 may also need to be specified.
2323
2324 module.sig_enforce
2325 [KNL] When CONFIG_MODULE_SIG is set, this means that
2326 modules without (valid) signatures will fail to load.
2327 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2328 is always true, so this option does nothing.
2329
2330 module_blacklist= [KNL] Do not load a comma-separated list of
2331 modules. Useful for debugging problem modules.
2332
2333 mousedev.tap_time=
2334 [MOUSE] Maximum time between finger touching and
2335 leaving touchpad surface for touch to be considered
2336 a tap and be reported as a left button click (for
2337 touchpads working in absolute mode only).
2338 Format: <msecs>
2339 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2340 reporting absolute coordinates, such as tablets
2341 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2342 reporting absolute coordinates, such as tablets
2343
2344 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2345 is similar to kernelcore except it specifies the
2346 amount of memory used for migratable allocations.
2347 If both kernelcore and movablecore is specified,
2348 then kernelcore will be at *least* the specified
2349 value but may be more. If movablecore on its own
2350 is specified, the administrator must be careful
2351 that the amount of memory usable for all allocations
2352 is not too small.
2353
2354 movable_node [KNL] Boot-time switch to make hotplugable memory
2355 NUMA nodes to be movable. This means that the memory
2356 of such nodes will be usable only for movable
2357 allocations which rules out almost all kernel
2358 allocations. Use with caution!
2359
2360 MTD_Partition= [MTD]
2361 Format: <name>,<region-number>,<size>,<offset>
2362
2363 MTD_Region= [MTD] Format:
2364 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2365
2366 mtdparts= [MTD]
2367 See drivers/mtd/cmdlinepart.c.
2368
2369 multitce=off [PPC] This parameter disables the use of the pSeries
2370 firmware feature for updating multiple TCE entries
2371 at a time.
2372
2373 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2374
2375 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2376
2377 boundary - index of last SLC block on Flex-OneNAND.
2378 The remaining blocks are configured as MLC blocks.
2379 lock - Configure if Flex-OneNAND boundary should be locked.
2380 Once locked, the boundary cannot be changed.
2381 1 indicates lock status, 0 indicates unlock status.
2382
2383 mtdset= [ARM]
2384 ARM/S3C2412 JIVE boot control
2385
2386 See arch/arm/mach-s3c2412/mach-jive.c
2387
2388 mtouchusb.raw_coordinates=
2389 [HW] Make the MicroTouch USB driver use raw coordinates
2390 ('y', default) or cooked coordinates ('n')
2391
2392 mtrr_chunk_size=nn[KMG] [X86]
2393 used for mtrr cleanup. It is largest continuous chunk
2394 that could hold holes aka. UC entries.
2395
2396 mtrr_gran_size=nn[KMG] [X86]
2397 Used for mtrr cleanup. It is granularity of mtrr block.
2398 Default is 1.
2399 Large value could prevent small alignment from
2400 using up MTRRs.
2401
2402 mtrr_spare_reg_nr=n [X86]
2403 Format: <integer>
2404 Range: 0,7 : spare reg number
2405 Default : 1
2406 Used for mtrr cleanup. It is spare mtrr entries number.
2407 Set to 2 or more if your graphical card needs more.
2408
2409 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2410
2411 netdev= [NET] Network devices parameters
2412 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2413 Note that mem_start is often overloaded to mean
2414 something different and driver-specific.
2415 This usage is only documented in each driver source
2416 file if at all.
2417
2418 nf_conntrack.acct=
2419 [NETFILTER] Enable connection tracking flow accounting
2420 0 to disable accounting
2421 1 to enable accounting
2422 Default value is 0.
2423
2424 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2425 See Documentation/filesystems/nfs/nfsroot.txt.
2426
2427 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2428 See Documentation/filesystems/nfs/nfsroot.txt.
2429
2430 nfsrootdebug [NFS] enable nfsroot debugging messages.
2431 See Documentation/filesystems/nfs/nfsroot.txt.
2432
2433 nfs.callback_nr_threads=
2434 [NFSv4] set the total number of threads that the
2435 NFS client will assign to service NFSv4 callback
2436 requests.
2437
2438 nfs.callback_tcpport=
2439 [NFS] set the TCP port on which the NFSv4 callback
2440 channel should listen.
2441
2442 nfs.cache_getent=
2443 [NFS] sets the pathname to the program which is used
2444 to update the NFS client cache entries.
2445
2446 nfs.cache_getent_timeout=
2447 [NFS] sets the timeout after which an attempt to
2448 update a cache entry is deemed to have failed.
2449
2450 nfs.idmap_cache_timeout=
2451 [NFS] set the maximum lifetime for idmapper cache
2452 entries.
2453
2454 nfs.enable_ino64=
2455 [NFS] enable 64-bit inode numbers.
2456 If zero, the NFS client will fake up a 32-bit inode
2457 number for the readdir() and stat() syscalls instead
2458 of returning the full 64-bit number.
2459 The default is to return 64-bit inode numbers.
2460
2461 nfs.max_session_cb_slots=
2462 [NFSv4.1] Sets the maximum number of session
2463 slots the client will assign to the callback
2464 channel. This determines the maximum number of
2465 callbacks the client will process in parallel for
2466 a particular server.
2467
2468 nfs.max_session_slots=
2469 [NFSv4.1] Sets the maximum number of session slots
2470 the client will attempt to negotiate with the server.
2471 This limits the number of simultaneous RPC requests
2472 that the client can send to the NFSv4.1 server.
2473 Note that there is little point in setting this
2474 value higher than the max_tcp_slot_table_limit.
2475
2476 nfs.nfs4_disable_idmapping=
2477 [NFSv4] When set to the default of '1', this option
2478 ensures that both the RPC level authentication
2479 scheme and the NFS level operations agree to use
2480 numeric uids/gids if the mount is using the
2481 'sec=sys' security flavour. In effect it is
2482 disabling idmapping, which can make migration from
2483 legacy NFSv2/v3 systems to NFSv4 easier.
2484 Servers that do not support this mode of operation
2485 will be autodetected by the client, and it will fall
2486 back to using the idmapper.
2487 To turn off this behaviour, set the value to '0'.
2488 nfs.nfs4_unique_id=
2489 [NFS4] Specify an additional fixed unique ident-
2490 ification string that NFSv4 clients can insert into
2491 their nfs_client_id4 string. This is typically a
2492 UUID that is generated at system install time.
2493
2494 nfs.send_implementation_id =
2495 [NFSv4.1] Send client implementation identification
2496 information in exchange_id requests.
2497 If zero, no implementation identification information
2498 will be sent.
2499 The default is to send the implementation identification
2500 information.
2501
2502 nfs.recover_lost_locks =
2503 [NFSv4] Attempt to recover locks that were lost due
2504 to a lease timeout on the server. Please note that
2505 doing this risks data corruption, since there are
2506 no guarantees that the file will remain unchanged
2507 after the locks are lost.
2508 If you want to enable the kernel legacy behaviour of
2509 attempting to recover these locks, then set this
2510 parameter to '1'.
2511 The default parameter value of '0' causes the kernel
2512 not to attempt recovery of lost locks.
2513
2514 nfs4.layoutstats_timer =
2515 [NFSv4.2] Change the rate at which the kernel sends
2516 layoutstats to the pNFS metadata server.
2517
2518 Setting this to value to 0 causes the kernel to use
2519 whatever value is the default set by the layout
2520 driver. A non-zero value sets the minimum interval
2521 in seconds between layoutstats transmissions.
2522
2523 nfsd.nfs4_disable_idmapping=
2524 [NFSv4] When set to the default of '1', the NFSv4
2525 server will return only numeric uids and gids to
2526 clients using auth_sys, and will accept numeric uids
2527 and gids from such clients. This is intended to ease
2528 migration from NFSv2/v3.
2529
2530 nmi_debug= [KNL,SH] Specify one or more actions to take
2531 when a NMI is triggered.
2532 Format: [state][,regs][,debounce][,die]
2533
2534 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2535 Format: [panic,][nopanic,][num]
2536 Valid num: 0 or 1
2537 0 - turn hardlockup detector in nmi_watchdog off
2538 1 - turn hardlockup detector in nmi_watchdog on
2539 When panic is specified, panic when an NMI watchdog
2540 timeout occurs (or 'nopanic' to override the opposite
2541 default). To disable both hard and soft lockup detectors,
2542 please see 'nowatchdog'.
2543 This is useful when you use a panic=... timeout and
2544 need the box quickly up again.
2545
2546 netpoll.carrier_timeout=
2547 [NET] Specifies amount of time (in seconds) that
2548 netpoll should wait for a carrier. By default netpoll
2549 waits 4 seconds.
2550
2551 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2552 emulation library even if a 387 maths coprocessor
2553 is present.
2554
2555 no_console_suspend
2556 [HW] Never suspend the console
2557 Disable suspending of consoles during suspend and
2558 hibernate operations. Once disabled, debugging
2559 messages can reach various consoles while the rest
2560 of the system is being put to sleep (ie, while
2561 debugging driver suspend/resume hooks). This may
2562 not work reliably with all consoles, but is known
2563 to work with serial and VGA consoles.
2564 To facilitate more flexible debugging, we also add
2565 console_suspend, a printk module parameter to control
2566 it. Users could use console_suspend (usually
2567 /sys/module/printk/parameters/console_suspend) to
2568 turn on/off it dynamically.
2569
2570 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2571 caches in the slab allocator. Saves per-node memory,
2572 but will impact performance.
2573
2574 noalign [KNL,ARM]
2575
2576 noaltinstr [S390] Disables alternative instructions patching
2577 (CPU alternatives feature).
2578
2579 noapic [SMP,APIC] Tells the kernel to not make use of any
2580 IOAPICs that may be present in the system.
2581
2582 noautogroup Disable scheduler automatic task group creation.
2583
2584 nobats [PPC] Do not use BATs for mapping kernel lowmem
2585 on "Classic" PPC cores.
2586
2587 nocache [ARM]
2588
2589 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2590
2591 nodelayacct [KNL] Disable per-task delay accounting
2592
2593 nodsp [SH] Disable hardware DSP at boot time.
2594
2595 noefi Disable EFI runtime services support.
2596
2597 noexec [IA-64]
2598
2599 noexec [X86]
2600 On X86-32 available only on PAE configured kernels.
2601 noexec=on: enable non-executable mappings (default)
2602 noexec=off: disable non-executable mappings
2603
2604 nosmap [X86]
2605 Disable SMAP (Supervisor Mode Access Prevention)
2606 even if it is supported by processor.
2607
2608 nosmep [X86]
2609 Disable SMEP (Supervisor Mode Execution Prevention)
2610 even if it is supported by processor.
2611
2612 noexec32 [X86-64]
2613 This affects only 32-bit executables.
2614 noexec32=on: enable non-executable mappings (default)
2615 read doesn't imply executable mappings
2616 noexec32=off: disable non-executable mappings
2617 read implies executable mappings
2618
2619 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2620
2621 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2622 register save and restore. The kernel will only save
2623 legacy floating-point registers on task switch.
2624
2625 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2626
2627 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2628 Equivalent to smt=1.
2629
2630 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2631 (indirect branch prediction) vulnerability. System may
2632 allow data leaks with this option, which is equivalent
2633 to spectre_v2=off.
2634
2635 noxsave [BUGS=X86] Disables x86 extended register state save
2636 and restore using xsave. The kernel will fallback to
2637 enabling legacy floating-point and sse state.
2638
2639 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2640 register states. The kernel will fall back to use
2641 xsave to save the states. By using this parameter,
2642 performance of saving the states is degraded because
2643 xsave doesn't support modified optimization while
2644 xsaveopt supports it on xsaveopt enabled systems.
2645
2646 noxsaves [X86] Disables xsaves and xrstors used in saving and
2647 restoring x86 extended register state in compacted
2648 form of xsave area. The kernel will fall back to use
2649 xsaveopt and xrstor to save and restore the states
2650 in standard form of xsave area. By using this
2651 parameter, xsave area per process might occupy more
2652 memory on xsaves enabled systems.
2653
2654 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2655 wfi(ARM) instruction doesn't work correctly and not to
2656 use it. This is also useful when using JTAG debugger.
2657
2658 no_file_caps Tells the kernel not to honor file capabilities. The
2659 only way then for a file to be executed with privilege
2660 is to be setuid root or executed by root.
2661
2662 nohalt [IA-64] Tells the kernel not to use the power saving
2663 function PAL_HALT_LIGHT when idle. This increases
2664 power-consumption. On the positive side, it reduces
2665 interrupt wake-up latency, which may improve performance
2666 in certain environments such as networked servers or
2667 real-time systems.
2668
2669 nohibernate [HIBERNATION] Disable hibernation and resume.
2670
2671 nohz= [KNL] Boottime enable/disable dynamic ticks
2672 Valid arguments: on, off
2673 Default: on
2674
2675 nohz_full= [KNL,BOOT,SMP,ISOL]
2676 The argument is a cpu list, as described above.
2677 In kernels built with CONFIG_NO_HZ_FULL=y, set
2678 the specified list of CPUs whose tick will be stopped
2679 whenever possible. The boot CPU will be forced outside
2680 the range to maintain the timekeeping. Any CPUs
2681 in this list will have their RCU callbacks offloaded,
2682 just as if they had also been called out in the
2683 rcu_nocbs= boot parameter.
2684
2685 noiotrap [SH] Disables trapped I/O port accesses.
2686
2687 noirqdebug [X86-32] Disables the code which attempts to detect and
2688 disable unhandled interrupt sources.
2689
2690 no_timer_check [X86,APIC] Disables the code which tests for
2691 broken timer IRQ sources.
2692
2693 noisapnp [ISAPNP] Disables ISA PnP code.
2694
2695 noinitrd [RAM] Tells the kernel not to load any configured
2696 initial RAM disk.
2697
2698 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2699 remapping.
2700 [Deprecated - use intremap=off]
2701
2702 nointroute [IA-64]
2703
2704 noinvpcid [X86] Disable the INVPCID cpu feature.
2705
2706 nojitter [IA-64] Disables jitter checking for ITC timers.
2707
2708 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2709
2710 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2711 fault handling.
2712
2713 no-vmw-sched-clock
2714 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2715 clock and use the default one.
2716
2717 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2718 steal time is computed, but won't influence scheduler
2719 behaviour
2720
2721 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2722
2723 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2724
2725 noltlbs [PPC] Do not use large page/tlb entries for kernel
2726 lowmem mapping on PPC40x and PPC8xx
2727
2728 nomca [IA-64] Disable machine check abort handling
2729
2730 nomce [X86-32] Disable Machine Check Exception
2731
2732 nomfgpt [X86-32] Disable Multi-Function General Purpose
2733 Timer usage (for AMD Geode machines).
2734
2735 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2736 shutdown the other cpus. Instead use the REBOOT_VECTOR
2737 irq.
2738
2739 nomodule Disable module load
2740
2741 nopat [X86] Disable PAT (page attribute table extension of
2742 pagetables) support.
2743
2744 nopcid [X86-64] Disable the PCID cpu feature.
2745
2746 norandmaps Don't use address space randomization. Equivalent to
2747 echo 0 > /proc/sys/kernel/randomize_va_space
2748
2749 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2750 with UP alternatives
2751
2752 nordrand [X86] Disable kernel use of the RDRAND and
2753 RDSEED instructions even if they are supported
2754 by the processor. RDRAND and RDSEED are still
2755 available to user space applications.
2756
2757 noresume [SWSUSP] Disables resume and restores original swap
2758 space.
2759
2760 no-scroll [VGA] Disables scrollback.
2761 This is required for the Braillex ib80-piezo Braille
2762 reader made by F.H. Papenmeier (Germany).
2763
2764 nosbagart [IA-64]
2765
2766 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2767
2768 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2769 and disable the IO APIC. legacy for "maxcpus=0".
2770
2771 nosoftlockup [KNL] Disable the soft-lockup detector.
2772
2773 nosync [HW,M68K] Disables sync negotiation for all devices.
2774
2775 notsc [BUGS=X86-32] Disable Time Stamp Counter
2776
2777 nowatchdog [KNL] Disable both lockup detectors, i.e.
2778 soft-lockup and NMI watchdog (hard-lockup).
2779
2780 nowb [ARM]
2781
2782 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2783
2784 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2785 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2786 Some features depend on CPU0. Known dependencies are:
2787 1. Resume from suspend/hibernate depends on CPU0.
2788 Suspend/hibernate will fail if CPU0 is offline and you
2789 need to online CPU0 before suspend/hibernate.
2790 2. PIC interrupts also depend on CPU0. CPU0 can't be
2791 removed if a PIC interrupt is detected.
2792 It's said poweroff/reboot may depend on CPU0 on some
2793 machines although I haven't seen such issues so far
2794 after CPU0 is offline on a few tested machines.
2795 If the dependencies are under your control, you can
2796 turn on cpu0_hotplug.
2797
2798 nps_mtm_hs_ctr= [KNL,ARC]
2799 This parameter sets the maximum duration, in
2800 cycles, each HW thread of the CTOP can run
2801 without interruptions, before HW switches it.
2802 The actual maximum duration is 16 times this
2803 parameter's value.
2804 Format: integer between 1 and 255
2805 Default: 255
2806
2807 nptcg= [IA-64] Override max number of concurrent global TLB
2808 purges which is reported from either PAL_VM_SUMMARY or
2809 SAL PALO.
2810
2811 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2812 could support. nr_cpus=n : n >= 1 limits the kernel to
2813 support 'n' processors. It could be larger than the
2814 number of already plugged CPU during bootup, later in
2815 runtime you can physically add extra cpu until it reaches
2816 n. So during boot up some boot time memory for per-cpu
2817 variables need be pre-allocated for later physical cpu
2818 hot plugging.
2819
2820 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2821
2822 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2823 Allowed values are enable and disable
2824
2825 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2826 'node', 'default' can be specified
2827 This can be set from sysctl after boot.
2828 See Documentation/sysctl/vm.txt for details.
2829
2830 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2831 See Documentation/debugging-via-ohci1394.txt for more
2832 info.
2833
2834 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2835 Rather than timing out after 20 ms if an EC
2836 command is not properly ACKed, override the length
2837 of the timeout. We have interrupts disabled while
2838 waiting for the ACK, so if this is set too high
2839 interrupts *may* be lost!
2840
2841 omap_mux= [OMAP] Override bootloader pin multiplexing.
2842 Format: <mux_mode0.mode_name=value>...
2843 For example, to override I2C bus2:
2844 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2845
2846 oprofile.timer= [HW]
2847 Use timer interrupt instead of performance counters
2848
2849 oprofile.cpu_type= Force an oprofile cpu type
2850 This might be useful if you have an older oprofile
2851 userland or if you want common events.
2852 Format: { arch_perfmon }
2853 arch_perfmon: [X86] Force use of architectural
2854 perfmon on Intel CPUs instead of the
2855 CPU specific event set.
2856 timer: [X86] Force use of architectural NMI
2857 timer mode (see also oprofile.timer
2858 for generic hr timer mode)
2859
2860 oops=panic Always panic on oopses. Default is to just kill the
2861 process, but there is a small probability of
2862 deadlocking the machine.
2863 This will also cause panics on machine check exceptions.
2864 Useful together with panic=30 to trigger a reboot.
2865
2866 OSS [HW,OSS]
2867 See Documentation/sound/oss/oss-parameters.txt
2868
2869 page_owner= [KNL] Boot-time page_owner enabling option.
2870 Storage of the information about who allocated
2871 each page is disabled in default. With this switch,
2872 we can turn it on.
2873 on: enable the feature
2874
2875 page_poison= [KNL] Boot-time parameter changing the state of
2876 poisoning on the buddy allocator.
2877 off: turn off poisoning
2878 on: turn on poisoning
2879
2880 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2881 timeout > 0: seconds before rebooting
2882 timeout = 0: wait forever
2883 timeout < 0: reboot immediately
2884 Format: <timeout>
2885
2886 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2887 on a WARN().
2888
2889 crash_kexec_post_notifiers
2890 Run kdump after running panic-notifiers and dumping
2891 kmsg. This only for the users who doubt kdump always
2892 succeeds in any situation.
2893 Note that this also increases risks of kdump failure,
2894 because some panic notifiers can make the crashed
2895 kernel more unstable.
2896
2897 parkbd.port= [HW] Parallel port number the keyboard adapter is
2898 connected to, default is 0.
2899 Format: <parport#>
2900 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2901 0 for XT, 1 for AT (default is AT).
2902 Format: <mode>
2903
2904 parport= [HW,PPT] Specify parallel ports. 0 disables.
2905 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2906 Use 'auto' to force the driver to use any
2907 IRQ/DMA settings detected (the default is to
2908 ignore detected IRQ/DMA settings because of
2909 possible conflicts). You can specify the base
2910 address, IRQ, and DMA settings; IRQ and DMA
2911 should be numbers, or 'auto' (for using detected
2912 settings on that particular port), or 'nofifo'
2913 (to avoid using a FIFO even if it is detected).
2914 Parallel ports are assigned in the order they
2915 are specified on the command line, starting
2916 with parport0.
2917
2918 parport_init_mode= [HW,PPT]
2919 Configure VIA parallel port to operate in
2920 a specific mode. This is necessary on Pegasos
2921 computer where firmware has no options for setting
2922 up parallel port mode and sets it to spp.
2923 Currently this function knows 686a and 8231 chips.
2924 Format: [spp|ps2|epp|ecp|ecpepp]
2925
2926 pause_on_oops=
2927 Halt all CPUs after the first oops has been printed for
2928 the specified number of seconds. This is to be used if
2929 your oopses keep scrolling off the screen.
2930
2931 pcbit= [HW,ISDN]
2932
2933 pcd. [PARIDE]
2934 See header of drivers/block/paride/pcd.c.
2935 See also Documentation/blockdev/paride.txt.
2936
2937 pci=option[,option...] [PCI] various PCI subsystem options:
2938 earlydump [X86] dump PCI config space before the kernel
2939 changes anything
2940 off [X86] don't probe for the PCI bus
2941 bios [X86-32] force use of PCI BIOS, don't access
2942 the hardware directly. Use this if your machine
2943 has a non-standard PCI host bridge.
2944 nobios [X86-32] disallow use of PCI BIOS, only direct
2945 hardware access methods are allowed. Use this
2946 if you experience crashes upon bootup and you
2947 suspect they are caused by the BIOS.
2948 conf1 [X86] Force use of PCI Configuration Access
2949 Mechanism 1 (config address in IO port 0xCF8,
2950 data in IO port 0xCFC, both 32-bit).
2951 conf2 [X86] Force use of PCI Configuration Access
2952 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2953 the function, IO port 0xCFA, also 8-bit, sets
2954 bus number. The config space is then accessed
2955 through ports 0xC000-0xCFFF).
2956 See http://wiki.osdev.org/PCI for more info
2957 on the configuration access mechanisms.
2958 noaer [PCIE] If the PCIEAER kernel config parameter is
2959 enabled, this kernel boot option can be used to
2960 disable the use of PCIE advanced error reporting.
2961 nodomains [PCI] Disable support for multiple PCI
2962 root domains (aka PCI segments, in ACPI-speak).
2963 nommconf [X86] Disable use of MMCONFIG for PCI
2964 Configuration
2965 check_enable_amd_mmconf [X86] check for and enable
2966 properly configured MMIO access to PCI
2967 config space on AMD family 10h CPU
2968 nomsi [MSI] If the PCI_MSI kernel config parameter is
2969 enabled, this kernel boot option can be used to
2970 disable the use of MSI interrupts system-wide.
2971 noioapicquirk [APIC] Disable all boot interrupt quirks.
2972 Safety option to keep boot IRQs enabled. This
2973 should never be necessary.
2974 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2975 primary IO-APIC for bridges that cannot disable
2976 boot IRQs. This fixes a source of spurious IRQs
2977 when the system masks IRQs.
2978 noioapicreroute [APIC] Disable workaround that uses the
2979 boot IRQ equivalent of an IRQ that connects to
2980 a chipset where boot IRQs cannot be disabled.
2981 The opposite of ioapicreroute.
2982 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2983 routing table. These calls are known to be buggy
2984 on several machines and they hang the machine
2985 when used, but on other computers it's the only
2986 way to get the interrupt routing table. Try
2987 this option if the kernel is unable to allocate
2988 IRQs or discover secondary PCI buses on your
2989 motherboard.
2990 rom [X86] Assign address space to expansion ROMs.
2991 Use with caution as certain devices share
2992 address decoders between ROMs and other
2993 resources.
2994 norom [X86] Do not assign address space to
2995 expansion ROMs that do not already have
2996 BIOS assigned address ranges.
2997 nobar [X86] Do not assign address space to the
2998 BARs that weren't assigned by the BIOS.
2999 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3000 assigned automatically to PCI devices. You can
3001 make the kernel exclude IRQs of your ISA cards
3002 this way.
3003 pirqaddr=0xAAAAA [X86] Specify the physical address
3004 of the PIRQ table (normally generated
3005 by the BIOS) if it is outside the
3006 F0000h-100000h range.
3007 lastbus=N [X86] Scan all buses thru bus #N. Can be
3008 useful if the kernel is unable to find your
3009 secondary buses and you want to tell it
3010 explicitly which ones they are.
3011 assign-busses [X86] Always assign all PCI bus
3012 numbers ourselves, overriding
3013 whatever the firmware may have done.
3014 usepirqmask [X86] Honor the possible IRQ mask stored
3015 in the BIOS $PIR table. This is needed on
3016 some systems with broken BIOSes, notably
3017 some HP Pavilion N5400 and Omnibook XE3
3018 notebooks. This will have no effect if ACPI
3019 IRQ routing is enabled.
3020 noacpi [X86] Do not use ACPI for IRQ routing
3021 or for PCI scanning.
3022 use_crs [X86] Use PCI host bridge window information
3023 from ACPI. On BIOSes from 2008 or later, this
3024 is enabled by default. If you need to use this,
3025 please report a bug.
3026 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3027 If you need to use this, please report a bug.
3028 routeirq Do IRQ routing for all PCI devices.
3029 This is normally done in pci_enable_device(),
3030 so this option is a temporary workaround
3031 for broken drivers that don't call it.
3032 skip_isa_align [X86] do not align io start addr, so can
3033 handle more pci cards
3034 noearly [X86] Don't do any early type 1 scanning.
3035 This might help on some broken boards which
3036 machine check when some devices' config space
3037 is read. But various workarounds are disabled
3038 and some IOMMU drivers will not work.
3039 bfsort Sort PCI devices into breadth-first order.
3040 This sorting is done to get a device
3041 order compatible with older (<= 2.4) kernels.
3042 nobfsort Don't sort PCI devices into breadth-first order.
3043 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3044 tuning and use the BIOS-configured MPS defaults.
3045 pcie_bus_safe Set every device's MPS to the largest value
3046 supported by all devices below the root complex.
3047 pcie_bus_perf Set device MPS to the largest allowable MPS
3048 based on its parent bus. Also set MRRS (Max
3049 Read Request Size) to the largest supported
3050 value (no larger than the MPS that the device
3051 or bus can support) for best performance.
3052 pcie_bus_peer2peer Set every device's MPS to 128B, which
3053 every device is guaranteed to support. This
3054 configuration allows peer-to-peer DMA between
3055 any pair of devices, possibly at the cost of
3056 reduced performance. This also guarantees
3057 that hot-added devices will work.
3058 cbiosize=nn[KMG] The fixed amount of bus space which is
3059 reserved for the CardBus bridge's IO window.
3060 The default value is 256 bytes.
3061 cbmemsize=nn[KMG] The fixed amount of bus space which is
3062 reserved for the CardBus bridge's memory
3063 window. The default value is 64 megabytes.
3064 resource_alignment=
3065 Format:
3066 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3067 [<order of align>@]pci:<vendor>:<device>\
3068 [:<subvendor>:<subdevice>][; ...]
3069 Specifies alignment and device to reassign
3070 aligned memory resources.
3071 If <order of align> is not specified,
3072 PAGE_SIZE is used as alignment.
3073 PCI-PCI bridge can be specified, if resource
3074 windows need to be expanded.
3075 To specify the alignment for several
3076 instances of a device, the PCI vendor,
3077 device, subvendor, and subdevice may be
3078 specified, e.g., 4096@pci:8086:9c22:103c:198f
3079 ecrc= Enable/disable PCIe ECRC (transaction layer
3080 end-to-end CRC checking).
3081 bios: Use BIOS/firmware settings. This is the
3082 the default.
3083 off: Turn ECRC off
3084 on: Turn ECRC on.
3085 hpiosize=nn[KMG] The fixed amount of bus space which is
3086 reserved for hotplug bridge's IO window.
3087 Default size is 256 bytes.
3088 hpmemsize=nn[KMG] The fixed amount of bus space which is
3089 reserved for hotplug bridge's memory window.
3090 Default size is 2 megabytes.
3091 hpbussize=nn The minimum amount of additional bus numbers
3092 reserved for buses below a hotplug bridge.
3093 Default is 1.
3094 realloc= Enable/disable reallocating PCI bridge resources
3095 if allocations done by BIOS are too small to
3096 accommodate resources required by all child
3097 devices.
3098 off: Turn realloc off
3099 on: Turn realloc on
3100 realloc same as realloc=on
3101 noari do not use PCIe ARI.
3102 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3103 only look for one device below a PCIe downstream
3104 port.
3105 big_root_window Try to add a big 64bit memory window to the PCIe
3106 root complex on AMD CPUs. Some GFX hardware
3107 can resize a BAR to allow access to all VRAM.
3108 Adding the window is slightly risky (it may
3109 conflict with unreported devices), so this
3110 taints the kernel.
3111
3112 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3113 Management.
3114 off Disable ASPM.
3115 force Enable ASPM even on devices that claim not to support it.
3116 WARNING: Forcing ASPM on may cause system lockups.
3117
3118 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3119 nomsi Do not use MSI for PCI Express Native Hotplug (this
3120 makes all PCIe ports use INTx for hotplug services).
3121
3122 pcie_ports= [PCIE] PCIe ports handling:
3123 auto Ask the BIOS whether or not to use native PCIe services
3124 associated with PCIe ports (PME, hot-plug, AER). Use
3125 them only if that is allowed by the BIOS.
3126 native Use native PCIe services associated with PCIe ports
3127 unconditionally.
3128 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3129 ports driver.
3130
3131 pcie_port_pm= [PCIE] PCIe port power management handling:
3132 off Disable power management of all PCIe ports
3133 force Forcibly enable power management of all PCIe ports
3134
3135 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3136 nomsi Do not use MSI for native PCIe PME signaling (this makes
3137 all PCIe root ports use INTx for all services).
3138
3139 pcmv= [HW,PCMCIA] BadgePAD 4
3140
3141 pd_ignore_unused
3142 [PM]
3143 Keep all power-domains already enabled by bootloader on,
3144 even if no driver has claimed them. This is useful
3145 for debug and development, but should not be
3146 needed on a platform with proper driver support.
3147
3148 pd. [PARIDE]
3149 See Documentation/blockdev/paride.txt.
3150
3151 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3152 boot time.
3153 Format: { 0 | 1 }
3154 See arch/parisc/kernel/pdc_chassis.c
3155
3156 percpu_alloc= Select which percpu first chunk allocator to use.
3157 Currently supported values are "embed" and "page".
3158 Archs may support subset or none of the selections.
3159 See comments in mm/percpu.c for details on each
3160 allocator. This parameter is primarily for debugging
3161 and performance comparison.
3162
3163 pf. [PARIDE]
3164 See Documentation/blockdev/paride.txt.
3165
3166 pg. [PARIDE]
3167 See Documentation/blockdev/paride.txt.
3168
3169 pirq= [SMP,APIC] Manual mp-table setup
3170 See Documentation/x86/i386/IO-APIC.txt.
3171
3172 plip= [PPT,NET] Parallel port network link
3173 Format: { parport<nr> | timid | 0 }
3174 See also Documentation/admin-guide/parport.rst.
3175
3176 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3177 Override pmtimer IOPort with a hex value.
3178 e.g. pmtmr=0x508
3179
3180 pnp.debug=1 [PNP]
3181 Enable PNP debug messages (depends on the
3182 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3183 via /sys/module/pnp/parameters/debug. We always show
3184 current resource usage; turning this on also shows
3185 possible settings and some assignment information.
3186
3187 pnpacpi= [ACPI]
3188 { off }
3189
3190 pnpbios= [ISAPNP]
3191 { on | off | curr | res | no-curr | no-res }
3192
3193 pnp_reserve_irq=
3194 [ISAPNP] Exclude IRQs for the autoconfiguration
3195
3196 pnp_reserve_dma=
3197 [ISAPNP] Exclude DMAs for the autoconfiguration
3198
3199 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3200 Ranges are in pairs (I/O port base and size).
3201
3202 pnp_reserve_mem=
3203 [ISAPNP] Exclude memory regions for the
3204 autoconfiguration.
3205 Ranges are in pairs (memory base and size).
3206
3207 ports= [IP_VS_FTP] IPVS ftp helper module
3208 Default is 21.
3209 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3210 may be specified.
3211 Format: <port>,<port>....
3212
3213 powersave=off [PPC] This option disables power saving features.
3214 It specifically disables cpuidle and sets the
3215 platform machine description specific power_save
3216 function to NULL. On Idle the CPU just reduces
3217 execution priority.
3218
3219 ppc_strict_facility_enable
3220 [PPC] This option catches any kernel floating point,
3221 Altivec, VSX and SPE outside of regions specifically
3222 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3223 There is some performance impact when enabling this.
3224
3225 ppc_tm= [PPC]
3226 Format: {"off"}
3227 Disable Hardware Transactional Memory
3228
3229 print-fatal-signals=
3230 [KNL] debug: print fatal signals
3231
3232 If enabled, warn about various signal handling
3233 related application anomalies: too many signals,
3234 too many POSIX.1 timers, fatal signals causing a
3235 coredump - etc.
3236
3237 If you hit the warning due to signal overflow,
3238 you might want to try "ulimit -i unlimited".
3239
3240 default: off.
3241
3242 printk.always_kmsg_dump=
3243 Trigger kmsg_dump for cases other than kernel oops or
3244 panics
3245 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3246 default: disabled
3247
3248 printk.devkmsg={on,off,ratelimit}
3249 Control writing to /dev/kmsg.
3250 on - unlimited logging to /dev/kmsg from userspace
3251 off - logging to /dev/kmsg disabled
3252 ratelimit - ratelimit the logging
3253 Default: ratelimit
3254
3255 printk.time= Show timing data prefixed to each printk message line
3256 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3257
3258 processor.max_cstate= [HW,ACPI]
3259 Limit processor to maximum C-state
3260 max_cstate=9 overrides any DMI blacklist limit.
3261
3262 processor.nocst [HW,ACPI]
3263 Ignore the _CST method to determine C-states,
3264 instead using the legacy FADT method
3265
3266 profile= [KNL] Enable kernel profiling via /proc/profile
3267 Format: [<profiletype>,]<number>
3268 Param: <profiletype>: "schedule", "sleep", or "kvm"
3269 [defaults to kernel profiling]
3270 Param: "schedule" - profile schedule points.
3271 Param: "sleep" - profile D-state sleeping (millisecs).
3272 Requires CONFIG_SCHEDSTATS
3273 Param: "kvm" - profile VM exits.
3274 Param: <number> - step/bucket size as a power of 2 for
3275 statistical time based profiling.
3276
3277 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3278 before loading.
3279 See Documentation/blockdev/ramdisk.txt.
3280
3281 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3282 probe for; one of (bare|imps|exps|lifebook|any).
3283 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3284 per second.
3285 psmouse.resetafter= [HW,MOUSE]
3286 Try to reset the device after so many bad packets
3287 (0 = never).
3288 psmouse.resolution=
3289 [HW,MOUSE] Set desired mouse resolution, in dpi.
3290 psmouse.smartscroll=
3291 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3292 0 = disabled, 1 = enabled (default).
3293
3294 pstore.backend= Specify the name of the pstore backend to use
3295
3296 pt. [PARIDE]
3297 See Documentation/blockdev/paride.txt.
3298
3299 pti= [X86_64] Control Page Table Isolation of user and
3300 kernel address spaces. Disabling this feature
3301 removes hardening, but improves performance of
3302 system calls and interrupts.
3303
3304 on - unconditionally enable
3305 off - unconditionally disable
3306 auto - kernel detects whether your CPU model is
3307 vulnerable to issues that PTI mitigates
3308
3309 Not specifying this option is equivalent to pti=auto.
3310
3311 nopti [X86_64]
3312 Equivalent to pti=off
3313
3314 pty.legacy_count=
3315 [KNL] Number of legacy pty's. Overwrites compiled-in
3316 default number.
3317
3318 quiet [KNL] Disable most log messages
3319
3320 r128= [HW,DRM]
3321
3322 raid= [HW,RAID]
3323 See Documentation/admin-guide/md.rst.
3324
3325 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3326 See Documentation/blockdev/ramdisk.txt.
3327
3328 ras=option[,option,...] [KNL] RAS-specific options
3329
3330 cec_disable [X86]
3331 Disable the Correctable Errors Collector,
3332 see CONFIG_RAS_CEC help text.
3333
3334 rcu_nocbs= [KNL]
3335 The argument is a cpu list, as described above.
3336
3337 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3338 the specified list of CPUs to be no-callback CPUs.
3339 Invocation of these CPUs' RCU callbacks will
3340 be offloaded to "rcuox/N" kthreads created for
3341 that purpose, where "x" is "b" for RCU-bh, "p"
3342 for RCU-preempt, and "s" for RCU-sched, and "N"
3343 is the CPU number. This reduces OS jitter on the
3344 offloaded CPUs, which can be useful for HPC and
3345 real-time workloads. It can also improve energy
3346 efficiency for asymmetric multiprocessors.
3347
3348 rcu_nocb_poll [KNL]
3349 Rather than requiring that offloaded CPUs
3350 (specified by rcu_nocbs= above) explicitly
3351 awaken the corresponding "rcuoN" kthreads,
3352 make these kthreads poll for callbacks.
3353 This improves the real-time response for the
3354 offloaded CPUs by relieving them of the need to
3355 wake up the corresponding kthread, but degrades
3356 energy efficiency by requiring that the kthreads
3357 periodically wake up to do the polling.
3358
3359 rcutree.blimit= [KNL]
3360 Set maximum number of finished RCU callbacks to
3361 process in one batch.
3362
3363 rcutree.dump_tree= [KNL]
3364 Dump the structure of the rcu_node combining tree
3365 out at early boot. This is used for diagnostic
3366 purposes, to verify correct tree setup.
3367
3368 rcutree.gp_cleanup_delay= [KNL]
3369 Set the number of jiffies to delay each step of
3370 RCU grace-period cleanup.
3371
3372 rcutree.gp_init_delay= [KNL]
3373 Set the number of jiffies to delay each step of
3374 RCU grace-period initialization.
3375
3376 rcutree.gp_preinit_delay= [KNL]
3377 Set the number of jiffies to delay each step of
3378 RCU grace-period pre-initialization, that is,
3379 the propagation of recent CPU-hotplug changes up
3380 the rcu_node combining tree.
3381
3382 rcutree.rcu_fanout_exact= [KNL]
3383 Disable autobalancing of the rcu_node combining
3384 tree. This is used by rcutorture, and might
3385 possibly be useful for architectures having high
3386 cache-to-cache transfer latencies.
3387
3388 rcutree.rcu_fanout_leaf= [KNL]
3389 Change the number of CPUs assigned to each
3390 leaf rcu_node structure. Useful for very
3391 large systems, which will choose the value 64,
3392 and for NUMA systems with large remote-access
3393 latencies, which will choose a value aligned
3394 with the appropriate hardware boundaries.
3395
3396 rcutree.jiffies_till_sched_qs= [KNL]
3397 Set required age in jiffies for a
3398 given grace period before RCU starts
3399 soliciting quiescent-state help from
3400 rcu_note_context_switch().
3401
3402 rcutree.jiffies_till_first_fqs= [KNL]
3403 Set delay from grace-period initialization to
3404 first attempt to force quiescent states.
3405 Units are jiffies, minimum value is zero,
3406 and maximum value is HZ.
3407
3408 rcutree.jiffies_till_next_fqs= [KNL]
3409 Set delay between subsequent attempts to force
3410 quiescent states. Units are jiffies, minimum
3411 value is one, and maximum value is HZ.
3412
3413 rcutree.kthread_prio= [KNL,BOOT]
3414 Set the SCHED_FIFO priority of the RCU per-CPU
3415 kthreads (rcuc/N). This value is also used for
3416 the priority of the RCU boost threads (rcub/N)
3417 and for the RCU grace-period kthreads (rcu_bh,
3418 rcu_preempt, and rcu_sched). If RCU_BOOST is
3419 set, valid values are 1-99 and the default is 1
3420 (the least-favored priority). Otherwise, when
3421 RCU_BOOST is not set, valid values are 0-99 and
3422 the default is zero (non-realtime operation).
3423
3424 rcutree.rcu_nocb_leader_stride= [KNL]
3425 Set the number of NOCB kthread groups, which
3426 defaults to the square root of the number of
3427 CPUs. Larger numbers reduces the wakeup overhead
3428 on the per-CPU grace-period kthreads, but increases
3429 that same overhead on each group's leader.
3430
3431 rcutree.qhimark= [KNL]
3432 Set threshold of queued RCU callbacks beyond which
3433 batch limiting is disabled.
3434
3435 rcutree.qlowmark= [KNL]
3436 Set threshold of queued RCU callbacks below which
3437 batch limiting is re-enabled.
3438
3439 rcutree.rcu_idle_gp_delay= [KNL]
3440 Set wakeup interval for idle CPUs that have
3441 RCU callbacks (RCU_FAST_NO_HZ=y).
3442
3443 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3444 Set wakeup interval for idle CPUs that have
3445 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3446 Lazy RCU callbacks are those which RCU can
3447 prove do nothing more than free memory.
3448
3449 rcutree.rcu_kick_kthreads= [KNL]
3450 Cause the grace-period kthread to get an extra
3451 wake_up() if it sleeps three times longer than
3452 it should at force-quiescent-state time.
3453 This wake_up() will be accompanied by a
3454 WARN_ONCE() splat and an ftrace_dump().
3455
3456 rcuperf.gp_async= [KNL]
3457 Measure performance of asynchronous
3458 grace-period primitives such as call_rcu().
3459
3460 rcuperf.gp_async_max= [KNL]
3461 Specify the maximum number of outstanding
3462 callbacks per writer thread. When a writer
3463 thread exceeds this limit, it invokes the
3464 corresponding flavor of rcu_barrier() to allow
3465 previously posted callbacks to drain.
3466
3467 rcuperf.gp_exp= [KNL]
3468 Measure performance of expedited synchronous
3469 grace-period primitives.
3470
3471 rcuperf.holdoff= [KNL]
3472 Set test-start holdoff period. The purpose of
3473 this parameter is to delay the start of the
3474 test until boot completes in order to avoid
3475 interference.
3476
3477 rcuperf.nreaders= [KNL]
3478 Set number of RCU readers. The value -1 selects
3479 N, where N is the number of CPUs. A value
3480 "n" less than -1 selects N-n+1, where N is again
3481 the number of CPUs. For example, -2 selects N
3482 (the number of CPUs), -3 selects N+1, and so on.
3483 A value of "n" less than or equal to -N selects
3484 a single reader.
3485
3486 rcuperf.nwriters= [KNL]
3487 Set number of RCU writers. The values operate
3488 the same as for rcuperf.nreaders.
3489 N, where N is the number of CPUs
3490
3491 rcuperf.perf_runnable= [BOOT]
3492 Start rcuperf running at boot time.
3493
3494 rcuperf.perf_type= [KNL]
3495 Specify the RCU implementation to test.
3496
3497 rcuperf.shutdown= [KNL]
3498 Shut the system down after performance tests
3499 complete. This is useful for hands-off automated
3500 testing.
3501
3502 rcuperf.verbose= [KNL]
3503 Enable additional printk() statements.
3504
3505 rcuperf.writer_holdoff= [KNL]
3506 Write-side holdoff between grace periods,
3507 in microseconds. The default of zero says
3508 no holdoff.
3509
3510 rcutorture.cbflood_inter_holdoff= [KNL]
3511 Set holdoff time (jiffies) between successive
3512 callback-flood tests.
3513
3514 rcutorture.cbflood_intra_holdoff= [KNL]
3515 Set holdoff time (jiffies) between successive
3516 bursts of callbacks within a given callback-flood
3517 test.
3518
3519 rcutorture.cbflood_n_burst= [KNL]
3520 Set the number of bursts making up a given
3521 callback-flood test. Set this to zero to
3522 disable callback-flood testing.
3523
3524 rcutorture.cbflood_n_per_burst= [KNL]
3525 Set the number of callbacks to be registered
3526 in a given burst of a callback-flood test.
3527
3528 rcutorture.fqs_duration= [KNL]
3529 Set duration of force_quiescent_state bursts
3530 in microseconds.
3531
3532 rcutorture.fqs_holdoff= [KNL]
3533 Set holdoff time within force_quiescent_state bursts
3534 in microseconds.
3535
3536 rcutorture.fqs_stutter= [KNL]
3537 Set wait time between force_quiescent_state bursts
3538 in seconds.
3539
3540 rcutorture.gp_cond= [KNL]
3541 Use conditional/asynchronous update-side
3542 primitives, if available.
3543
3544 rcutorture.gp_exp= [KNL]
3545 Use expedited update-side primitives, if available.
3546
3547 rcutorture.gp_normal= [KNL]
3548 Use normal (non-expedited) asynchronous
3549 update-side primitives, if available.
3550
3551 rcutorture.gp_sync= [KNL]
3552 Use normal (non-expedited) synchronous
3553 update-side primitives, if available. If all
3554 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3555 rcutorture.gp_normal=, and rcutorture.gp_sync=
3556 are zero, rcutorture acts as if is interpreted
3557 they are all non-zero.
3558
3559 rcutorture.n_barrier_cbs= [KNL]
3560 Set callbacks/threads for rcu_barrier() testing.
3561
3562 rcutorture.nfakewriters= [KNL]
3563 Set number of concurrent RCU writers. These just
3564 stress RCU, they don't participate in the actual
3565 test, hence the "fake".
3566
3567 rcutorture.nreaders= [KNL]
3568 Set number of RCU readers. The value -1 selects
3569 N-1, where N is the number of CPUs. A value
3570 "n" less than -1 selects N-n-2, where N is again
3571 the number of CPUs. For example, -2 selects N
3572 (the number of CPUs), -3 selects N+1, and so on.
3573
3574 rcutorture.object_debug= [KNL]
3575 Enable debug-object double-call_rcu() testing.
3576
3577 rcutorture.onoff_holdoff= [KNL]
3578 Set time (s) after boot for CPU-hotplug testing.
3579
3580 rcutorture.onoff_interval= [KNL]
3581 Set time (s) between CPU-hotplug operations, or
3582 zero to disable CPU-hotplug testing.
3583
3584 rcutorture.shuffle_interval= [KNL]
3585 Set task-shuffle interval (s). Shuffling tasks
3586 allows some CPUs to go into dyntick-idle mode
3587 during the rcutorture test.
3588
3589 rcutorture.shutdown_secs= [KNL]
3590 Set time (s) after boot system shutdown. This
3591 is useful for hands-off automated testing.
3592
3593 rcutorture.stall_cpu= [KNL]
3594 Duration of CPU stall (s) to test RCU CPU stall
3595 warnings, zero to disable.
3596
3597 rcutorture.stall_cpu_holdoff= [KNL]
3598 Time to wait (s) after boot before inducing stall.
3599
3600 rcutorture.stall_cpu_irqsoff= [KNL]
3601 Disable interrupts while stalling if set.
3602
3603 rcutorture.stat_interval= [KNL]
3604 Time (s) between statistics printk()s.
3605
3606 rcutorture.stutter= [KNL]
3607 Time (s) to stutter testing, for example, specifying
3608 five seconds causes the test to run for five seconds,
3609 wait for five seconds, and so on. This tests RCU's
3610 ability to transition abruptly to and from idle.
3611
3612 rcutorture.test_boost= [KNL]
3613 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3614 "Maybe" means test if the RCU implementation
3615 under test support RCU priority boosting.
3616
3617 rcutorture.test_boost_duration= [KNL]
3618 Duration (s) of each individual boost test.
3619
3620 rcutorture.test_boost_interval= [KNL]
3621 Interval (s) between each boost test.
3622
3623 rcutorture.test_no_idle_hz= [KNL]
3624 Test RCU's dyntick-idle handling. See also the
3625 rcutorture.shuffle_interval parameter.
3626
3627 rcutorture.torture_runnable= [BOOT]
3628 Start rcutorture running at boot time.
3629
3630 rcutorture.torture_type= [KNL]
3631 Specify the RCU implementation to test.
3632
3633 rcutorture.verbose= [KNL]
3634 Enable additional printk() statements.
3635
3636 rcupdate.rcu_cpu_stall_suppress= [KNL]
3637 Suppress RCU CPU stall warning messages.
3638
3639 rcupdate.rcu_cpu_stall_timeout= [KNL]
3640 Set timeout for RCU CPU stall warning messages.
3641
3642 rcupdate.rcu_expedited= [KNL]
3643 Use expedited grace-period primitives, for
3644 example, synchronize_rcu_expedited() instead
3645 of synchronize_rcu(). This reduces latency,
3646 but can increase CPU utilization, degrade
3647 real-time latency, and degrade energy efficiency.
3648 No effect on CONFIG_TINY_RCU kernels.
3649
3650 rcupdate.rcu_normal= [KNL]
3651 Use only normal grace-period primitives,
3652 for example, synchronize_rcu() instead of
3653 synchronize_rcu_expedited(). This improves
3654 real-time latency, CPU utilization, and
3655 energy efficiency, but can expose users to
3656 increased grace-period latency. This parameter
3657 overrides rcupdate.rcu_expedited. No effect on
3658 CONFIG_TINY_RCU kernels.
3659
3660 rcupdate.rcu_normal_after_boot= [KNL]
3661 Once boot has completed (that is, after
3662 rcu_end_inkernel_boot() has been invoked), use
3663 only normal grace-period primitives. No effect
3664 on CONFIG_TINY_RCU kernels.
3665
3666 rcupdate.rcu_task_stall_timeout= [KNL]
3667 Set timeout in jiffies for RCU task stall warning
3668 messages. Disable with a value less than or equal
3669 to zero.
3670
3671 rcupdate.rcu_self_test= [KNL]
3672 Run the RCU early boot self tests
3673
3674 rcupdate.rcu_self_test_bh= [KNL]
3675 Run the RCU bh early boot self tests
3676
3677 rcupdate.rcu_self_test_sched= [KNL]
3678 Run the RCU sched early boot self tests
3679
3680 rdinit= [KNL]
3681 Format: <full_path>
3682 Run specified binary instead of /init from the ramdisk,
3683 used for early userspace startup. See initrd.
3684
3685 rdt= [HW,X86,RDT]
3686 Turn on/off individual RDT features. List is:
3687 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3688 E.g. to turn on cmt and turn off mba use:
3689 rdt=cmt,!mba
3690
3691 reboot= [KNL]
3692 Format (x86 or x86_64):
3693 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3694 [[,]s[mp]#### \
3695 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3696 [[,]f[orce]
3697 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3698 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3699 reboot_force is either force or not specified,
3700 reboot_cpu is s[mp]#### with #### being the processor
3701 to be used for rebooting.
3702
3703 relax_domain_level=
3704 [KNL, SMP] Set scheduler's default relax_domain_level.
3705 See Documentation/cgroup-v1/cpusets.txt.
3706
3707 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3708
3709 reservetop= [X86-32]
3710 Format: nn[KMG]
3711 Reserves a hole at the top of the kernel virtual
3712 address space.
3713
3714 reservelow= [X86]
3715 Format: nn[K]
3716 Set the amount of memory to reserve for BIOS at
3717 the bottom of the address space.
3718
3719 reset_devices [KNL] Force drivers to reset the underlying device
3720 during initialization.
3721
3722 resume= [SWSUSP]
3723 Specify the partition device for software suspend
3724 Format:
3725 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3726
3727 resume_offset= [SWSUSP]
3728 Specify the offset from the beginning of the partition
3729 given by "resume=" at which the swap header is located,
3730 in <PAGE_SIZE> units (needed only for swap files).
3731 See Documentation/power/swsusp-and-swap-files.txt
3732
3733 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3734 read the resume files
3735
3736 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3737 Useful for devices that are detected asynchronously
3738 (e.g. USB and MMC devices).
3739
3740 hibernate= [HIBERNATION]
3741 noresume Don't check if there's a hibernation image
3742 present during boot.
3743 nocompress Don't compress/decompress hibernation images.
3744 no Disable hibernation and resume.
3745 protect_image Turn on image protection during restoration
3746 (that will set all pages holding image data
3747 during restoration read-only).
3748
3749 retain_initrd [RAM] Keep initrd memory after extraction
3750
3751 rfkill.default_state=
3752 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3753 etc. communication is blocked by default.
3754 1 Unblocked.
3755
3756 rfkill.master_switch_mode=
3757 0 The "airplane mode" button does nothing.
3758 1 The "airplane mode" button toggles between everything
3759 blocked and the previous configuration.
3760 2 The "airplane mode" button toggles between everything
3761 blocked and everything unblocked.
3762
3763 rhash_entries= [KNL,NET]
3764 Set number of hash buckets for route cache
3765
3766 ring3mwait=disable
3767 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3768 CPUs.
3769
3770 ro [KNL] Mount root device read-only on boot
3771
3772 rodata= [KNL]
3773 on Mark read-only kernel memory as read-only (default).
3774 off Leave read-only kernel memory writable for debugging.
3775
3776 rockchip.usb_uart
3777 Enable the uart passthrough on the designated usb port
3778 on Rockchip SoCs. When active, the signals of the
3779 debug-uart get routed to the D+ and D- pins of the usb
3780 port and the regular usb controller gets disabled.
3781
3782 root= [KNL] Root filesystem
3783 See name_to_dev_t comment in init/do_mounts.c.
3784
3785 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3786 mount the root filesystem
3787
3788 rootflags= [KNL] Set root filesystem mount option string
3789
3790 rootfstype= [KNL] Set root filesystem type
3791
3792 rootwait [KNL] Wait (indefinitely) for root device to show up.
3793 Useful for devices that are detected asynchronously
3794 (e.g. USB and MMC devices).
3795
3796 rproc_mem=nn[KMG][@address]
3797 [KNL,ARM,CMA] Remoteproc physical memory block.
3798 Memory area to be used by remote processor image,
3799 managed by CMA.
3800
3801 rw [KNL] Mount root device read-write on boot
3802
3803 S [KNL] Run init in single mode
3804
3805 s390_iommu= [HW,S390]
3806 Set s390 IOTLB flushing mode
3807 strict
3808 With strict flushing every unmap operation will result in
3809 an IOTLB flush. Default is lazy flushing before reuse,
3810 which is faster.
3811
3812 sa1100ir [NET]
3813 See drivers/net/irda/sa1100_ir.c.
3814
3815 sbni= [NET] Granch SBNI12 leased line adapter
3816
3817 sched_debug [KNL] Enables verbose scheduler debug messages.
3818
3819 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3820 Allowed values are enable and disable. This feature
3821 incurs a small amount of overhead in the scheduler
3822 but is useful for debugging and performance tuning.
3823
3824 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3825 xtime_lock contention on larger systems, and/or RCU lock
3826 contention on all systems with CONFIG_MAXSMP set.
3827 Format: { "0" | "1" }
3828 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3829 1 -- enable.
3830 Note: increases power consumption, thus should only be
3831 enabled if running jitter sensitive (HPC/RT) workloads.
3832
3833 security= [SECURITY] Choose a security module to enable at boot.
3834 If this boot parameter is not specified, only the first
3835 security module asking for security registration will be
3836 loaded. An invalid security module name will be treated
3837 as if no module has been chosen.
3838
3839 selinux= [SELINUX] Disable or enable SELinux at boot time.
3840 Format: { "0" | "1" }
3841 See security/selinux/Kconfig help text.
3842 0 -- disable.
3843 1 -- enable.
3844 Default value is set via kernel config option.
3845 If enabled at boot time, /selinux/disable can be used
3846 later to disable prior to initial policy load.
3847
3848 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3849 Format: { "0" | "1" }
3850 See security/apparmor/Kconfig help text
3851 0 -- disable.
3852 1 -- enable.
3853 Default value is set via kernel config option.
3854
3855 serialnumber [BUGS=X86-32]
3856
3857 shapers= [NET]
3858 Maximal number of shapers.
3859
3860 simeth= [IA-64]
3861 simscsi=
3862
3863 slram= [HW,MTD]
3864
3865 slab_nomerge [MM]
3866 Disable merging of slabs with similar size. May be
3867 necessary if there is some reason to distinguish
3868 allocs to different slabs, especially in hardened
3869 environments where the risk of heap overflows and
3870 layout control by attackers can usually be
3871 frustrated by disabling merging. This will reduce
3872 most of the exposure of a heap attack to a single
3873 cache (risks via metadata attacks are mostly
3874 unchanged). Debug options disable merging on their
3875 own.
3876 For more information see Documentation/vm/slub.txt.
3877
3878 slab_max_order= [MM, SLAB]
3879 Determines the maximum allowed order for slabs.
3880 A high setting may cause OOMs due to memory
3881 fragmentation. Defaults to 1 for systems with
3882 more than 32MB of RAM, 0 otherwise.
3883
3884 slub_debug[=options[,slabs]] [MM, SLUB]
3885 Enabling slub_debug allows one to determine the
3886 culprit if slab objects become corrupted. Enabling
3887 slub_debug can create guard zones around objects and
3888 may poison objects when not in use. Also tracks the
3889 last alloc / free. For more information see
3890 Documentation/vm/slub.txt.
3891
3892 slub_memcg_sysfs= [MM, SLUB]
3893 Determines whether to enable sysfs directories for
3894 memory cgroup sub-caches. 1 to enable, 0 to disable.
3895 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3896 Enabling this can lead to a very high number of debug
3897 directories and files being created under
3898 /sys/kernel/slub.
3899
3900 slub_max_order= [MM, SLUB]
3901 Determines the maximum allowed order for slabs.
3902 A high setting may cause OOMs due to memory
3903 fragmentation. For more information see
3904 Documentation/vm/slub.txt.
3905
3906 slub_min_objects= [MM, SLUB]
3907 The minimum number of objects per slab. SLUB will
3908 increase the slab order up to slub_max_order to
3909 generate a sufficiently large slab able to contain
3910 the number of objects indicated. The higher the number
3911 of objects the smaller the overhead of tracking slabs
3912 and the less frequently locks need to be acquired.
3913 For more information see Documentation/vm/slub.txt.
3914
3915 slub_min_order= [MM, SLUB]
3916 Determines the minimum page order for slabs. Must be
3917 lower than slub_max_order.
3918 For more information see Documentation/vm/slub.txt.
3919
3920 slub_nomerge [MM, SLUB]
3921 Same with slab_nomerge. This is supported for legacy.
3922 See slab_nomerge for more information.
3923
3924 smart2= [HW]
3925 Format: <io1>[,<io2>[,...,<io8>]]
3926
3927 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3928 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3929 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3930 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3931 smsc-ircc2.ircc_irq= [HW] IRQ line
3932 smsc-ircc2.ircc_dma= [HW] DMA channel
3933 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3934 0: Toshiba Satellite 1800 (GP data pin select)
3935 1: Fast pin select (default)
3936 2: ATC IRMode
3937
3938 smt [KNL,S390] Set the maximum number of threads (logical
3939 CPUs) to use per physical CPU on systems capable of
3940 symmetric multithreading (SMT). Will be capped to the
3941 actual hardware limit.
3942 Format: <integer>
3943 Default: -1 (no limit)
3944
3945 softlockup_panic=
3946 [KNL] Should the soft-lockup detector generate panics.
3947 Format: <integer>
3948
3949 A nonzero value instructs the soft-lockup detector
3950 to panic the machine when a soft-lockup occurs. This
3951 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3952 which is the respective build-time switch to that
3953 functionality.
3954
3955 softlockup_all_cpu_backtrace=
3956 [KNL] Should the soft-lockup detector generate
3957 backtraces on all cpus.
3958 Format: <integer>
3959
3960 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3961 See Documentation/laptops/sonypi.txt
3962
3963 spectre_v2= [X86] Control mitigation of Spectre variant 2
3964 (indirect branch speculation) vulnerability.
3965
3966 on - unconditionally enable
3967 off - unconditionally disable
3968 auto - kernel detects whether your CPU model is
3969 vulnerable
3970
3971 Selecting 'on' will, and 'auto' may, choose a
3972 mitigation method at run time according to the
3973 CPU, the available microcode, the setting of the
3974 CONFIG_RETPOLINE configuration option, and the
3975 compiler with which the kernel was built.
3976
3977 Specific mitigations can also be selected manually:
3978
3979 retpoline - replace indirect branches
3980 retpoline,generic - google's original retpoline
3981 retpoline,amd - AMD-specific minimal thunk
3982
3983 Not specifying this option is equivalent to
3984 spectre_v2=auto.
3985
3986 spia_io_base= [HW,MTD]
3987 spia_fio_base=
3988 spia_pedr=
3989 spia_peddr=
3990
3991 srcutree.counter_wrap_check [KNL]
3992 Specifies how frequently to check for
3993 grace-period sequence counter wrap for the
3994 srcu_data structure's ->srcu_gp_seq_needed field.
3995 The greater the number of bits set in this kernel
3996 parameter, the less frequently counter wrap will
3997 be checked for. Note that the bottom two bits
3998 are ignored.
3999
4000 srcutree.exp_holdoff [KNL]
4001 Specifies how many nanoseconds must elapse
4002 since the end of the last SRCU grace period for
4003 a given srcu_struct until the next normal SRCU
4004 grace period will be considered for automatic
4005 expediting. Set to zero to disable automatic
4006 expediting.
4007
4008 stack_guard_gap= [MM]
4009 override the default stack gap protection. The value
4010 is in page units and it defines how many pages prior
4011 to (for stacks growing down) resp. after (for stacks
4012 growing up) the main stack are reserved for no other
4013 mapping. Default value is 256 pages.
4014
4015 stacktrace [FTRACE]
4016 Enabled the stack tracer on boot up.
4017
4018 stacktrace_filter=[function-list]
4019 [FTRACE] Limit the functions that the stack tracer
4020 will trace at boot up. function-list is a comma separated
4021 list of functions. This list can be changed at run
4022 time by the stack_trace_filter file in the debugfs
4023 tracing directory. Note, this enables stack tracing
4024 and the stacktrace above is not needed.
4025
4026 sti= [PARISC,HW]
4027 Format: <num>
4028 Set the STI (builtin display/keyboard on the HP-PARISC
4029 machines) console (graphic card) which should be used
4030 as the initial boot-console.
4031 See also comment in drivers/video/console/sticore.c.
4032
4033 sti_font= [HW]
4034 See comment in drivers/video/console/sticore.c.
4035
4036 stifb= [HW]
4037 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4038
4039 sunrpc.min_resvport=
4040 sunrpc.max_resvport=
4041 [NFS,SUNRPC]
4042 SunRPC servers often require that client requests
4043 originate from a privileged port (i.e. a port in the
4044 range 0 < portnr < 1024).
4045 An administrator who wishes to reserve some of these
4046 ports for other uses may adjust the range that the
4047 kernel's sunrpc client considers to be privileged
4048 using these two parameters to set the minimum and
4049 maximum port values.
4050
4051 sunrpc.svc_rpc_per_connection_limit=
4052 [NFS,SUNRPC]
4053 Limit the number of requests that the server will
4054 process in parallel from a single connection.
4055 The default value is 0 (no limit).
4056
4057 sunrpc.pool_mode=
4058 [NFS]
4059 Control how the NFS server code allocates CPUs to
4060 service thread pools. Depending on how many NICs
4061 you have and where their interrupts are bound, this
4062 option will affect which CPUs will do NFS serving.
4063 Note: this parameter cannot be changed while the
4064 NFS server is running.
4065
4066 auto the server chooses an appropriate mode
4067 automatically using heuristics
4068 global a single global pool contains all CPUs
4069 percpu one pool for each CPU
4070 pernode one pool for each NUMA node (equivalent
4071 to global on non-NUMA machines)
4072
4073 sunrpc.tcp_slot_table_entries=
4074 sunrpc.udp_slot_table_entries=
4075 [NFS,SUNRPC]
4076 Sets the upper limit on the number of simultaneous
4077 RPC calls that can be sent from the client to a
4078 server. Increasing these values may allow you to
4079 improve throughput, but will also increase the
4080 amount of memory reserved for use by the client.
4081
4082 suspend.pm_test_delay=
4083 [SUSPEND]
4084 Sets the number of seconds to remain in a suspend test
4085 mode before resuming the system (see
4086 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4087 is set. Default value is 5.
4088
4089 swapaccount=[0|1]
4090 [KNL] Enable accounting of swap in memory resource
4091 controller if no parameter or 1 is given or disable
4092 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4093
4094 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4095 Format: { <int> | force | noforce }
4096 <int> -- Number of I/O TLB slabs
4097 force -- force using of bounce buffers even if they
4098 wouldn't be automatically used by the kernel
4099 noforce -- Never use bounce buffers (for debugging)
4100
4101 switches= [HW,M68k]
4102
4103 sysfs.deprecated=0|1 [KNL]
4104 Enable/disable old style sysfs layout for old udev
4105 on older distributions. When this option is enabled
4106 very new udev will not work anymore. When this option
4107 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4108 in older udev will not work anymore.
4109 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4110 the kernel configuration.
4111
4112 sysrq_always_enabled
4113 [KNL]
4114 Ignore sysrq setting - this boot parameter will
4115 neutralize any effect of /proc/sys/kernel/sysrq.
4116 Useful for debugging.
4117
4118 tcpmhash_entries= [KNL,NET]
4119 Set the number of tcp_metrics_hash slots.
4120 Default value is 8192 or 16384 depending on total
4121 ram pages. This is used to specify the TCP metrics
4122 cache size. See Documentation/networking/ip-sysctl.txt
4123 "tcp_no_metrics_save" section for more details.
4124
4125 tdfx= [HW,DRM]
4126
4127 test_suspend= [SUSPEND][,N]
4128 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4129 standby suspend) or "freeze" (for suspend type freeze)
4130 as the system sleep state during system startup with
4131 the optional capability to repeat N number of times.
4132 The system is woken from this state using a
4133 wakeup-capable RTC alarm.
4134
4135 thash_entries= [KNL,NET]
4136 Set number of hash buckets for TCP connection
4137
4138 thermal.act= [HW,ACPI]
4139 -1: disable all active trip points in all thermal zones
4140 <degrees C>: override all lowest active trip points
4141
4142 thermal.crt= [HW,ACPI]
4143 -1: disable all critical trip points in all thermal zones
4144 <degrees C>: override all critical trip points
4145
4146 thermal.nocrt= [HW,ACPI]
4147 Set to disable actions on ACPI thermal zone
4148 critical and hot trip points.
4149
4150 thermal.off= [HW,ACPI]
4151 1: disable ACPI thermal control
4152
4153 thermal.psv= [HW,ACPI]
4154 -1: disable all passive trip points
4155 <degrees C>: override all passive trip points to this
4156 value
4157
4158 thermal.tzp= [HW,ACPI]
4159 Specify global default ACPI thermal zone polling rate
4160 <deci-seconds>: poll all this frequency
4161 0: no polling (default)
4162
4163 threadirqs [KNL]
4164 Force threading of all interrupt handlers except those
4165 marked explicitly IRQF_NO_THREAD.
4166
4167 tmem [KNL,XEN]
4168 Enable the Transcendent memory driver if built-in.
4169
4170 tmem.cleancache=0|1 [KNL, XEN]
4171 Default is on (1). Disable the usage of the cleancache
4172 API to send anonymous pages to the hypervisor.
4173
4174 tmem.frontswap=0|1 [KNL, XEN]
4175 Default is on (1). Disable the usage of the frontswap
4176 API to send swap pages to the hypervisor. If disabled
4177 the selfballooning and selfshrinking are force disabled.
4178
4179 tmem.selfballooning=0|1 [KNL, XEN]
4180 Default is on (1). Disable the driving of swap pages
4181 to the hypervisor.
4182
4183 tmem.selfshrinking=0|1 [KNL, XEN]
4184 Default is on (1). Partial swapoff that immediately
4185 transfers pages from Xen hypervisor back to the
4186 kernel based on different criteria.
4187
4188 topology= [S390]
4189 Format: {off | on}
4190 Specify if the kernel should make use of the cpu
4191 topology information if the hardware supports this.
4192 The scheduler will make use of this information and
4193 e.g. base its process migration decisions on it.
4194 Default is on.
4195
4196 topology_updates= [KNL, PPC, NUMA]
4197 Format: {off}
4198 Specify if the kernel should ignore (off)
4199 topology updates sent by the hypervisor to this
4200 LPAR.
4201
4202 tp720= [HW,PS2]
4203
4204 tpm_suspend_pcr=[HW,TPM]
4205 Format: integer pcr id
4206 Specify that at suspend time, the tpm driver
4207 should extend the specified pcr with zeros,
4208 as a workaround for some chips which fail to
4209 flush the last written pcr on TPM_SaveState.
4210 This will guarantee that all the other pcrs
4211 are saved.
4212
4213 trace_buf_size=nn[KMG]
4214 [FTRACE] will set tracing buffer size on each cpu.
4215
4216 trace_event=[event-list]
4217 [FTRACE] Set and start specified trace events in order
4218 to facilitate early boot debugging. The event-list is a
4219 comma separated list of trace events to enable. See
4220 also Documentation/trace/events.txt
4221
4222 trace_options=[option-list]
4223 [FTRACE] Enable or disable tracer options at boot.
4224 The option-list is a comma delimited list of options
4225 that can be enabled or disabled just as if you were
4226 to echo the option name into
4227
4228 /sys/kernel/debug/tracing/trace_options
4229
4230 For example, to enable stacktrace option (to dump the
4231 stack trace of each event), add to the command line:
4232
4233 trace_options=stacktrace
4234
4235 See also Documentation/trace/ftrace.txt "trace options"
4236 section.
4237
4238 tp_printk[FTRACE]
4239 Have the tracepoints sent to printk as well as the
4240 tracing ring buffer. This is useful for early boot up
4241 where the system hangs or reboots and does not give the
4242 option for reading the tracing buffer or performing a
4243 ftrace_dump_on_oops.
4244
4245 To turn off having tracepoints sent to printk,
4246 echo 0 > /proc/sys/kernel/tracepoint_printk
4247 Note, echoing 1 into this file without the
4248 tracepoint_printk kernel cmdline option has no effect.
4249
4250 ** CAUTION **
4251
4252 Having tracepoints sent to printk() and activating high
4253 frequency tracepoints such as irq or sched, can cause
4254 the system to live lock.
4255
4256 traceoff_on_warning
4257 [FTRACE] enable this option to disable tracing when a
4258 warning is hit. This turns off "tracing_on". Tracing can
4259 be enabled again by echoing '1' into the "tracing_on"
4260 file located in /sys/kernel/debug/tracing/
4261
4262 This option is useful, as it disables the trace before
4263 the WARNING dump is called, which prevents the trace to
4264 be filled with content caused by the warning output.
4265
4266 This option can also be set at run time via the sysctl
4267 option: kernel/traceoff_on_warning
4268
4269 transparent_hugepage=
4270 [KNL]
4271 Format: [always|madvise|never]
4272 Can be used to control the default behavior of the system
4273 with respect to transparent hugepages.
4274 See Documentation/vm/transhuge.txt for more details.
4275
4276 tsc= Disable clocksource stability checks for TSC.
4277 Format: <string>
4278 [x86] reliable: mark tsc clocksource as reliable, this
4279 disables clocksource verification at runtime, as well
4280 as the stability checks done at bootup. Used to enable
4281 high-resolution timer mode on older hardware, and in
4282 virtualized environment.
4283 [x86] noirqtime: Do not use TSC to do irq accounting.
4284 Used to run time disable IRQ_TIME_ACCOUNTING on any
4285 platforms where RDTSC is slow and this accounting
4286 can add overhead.
4287 [x86] unstable: mark the TSC clocksource as unstable, this
4288 marks the TSC unconditionally unstable at bootup and
4289 avoids any further wobbles once the TSC watchdog notices.
4290
4291 turbografx.map[2|3]= [HW,JOY]
4292 TurboGraFX parallel port interface
4293 Format:
4294 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4295 See also Documentation/input/devices/joystick-parport.rst
4296
4297 udbg-immortal [PPC] When debugging early kernel crashes that
4298 happen after console_init() and before a proper
4299 console driver takes over, this boot options might
4300 help "seeing" what's going on.
4301
4302 uhash_entries= [KNL,NET]
4303 Set number of hash buckets for UDP/UDP-Lite connections
4304
4305 uhci-hcd.ignore_oc=
4306 [USB] Ignore overcurrent events (default N).
4307 Some badly-designed motherboards generate lots of
4308 bogus events, for ports that aren't wired to
4309 anything. Set this parameter to avoid log spamming.
4310 Note that genuine overcurrent events won't be
4311 reported either.
4312
4313 unknown_nmi_panic
4314 [X86] Cause panic on unknown NMI.
4315
4316 usbcore.authorized_default=
4317 [USB] Default USB device authorization:
4318 (default -1 = authorized except for wireless USB,
4319 0 = not authorized, 1 = authorized)
4320
4321 usbcore.autosuspend=
4322 [USB] The autosuspend time delay (in seconds) used
4323 for newly-detected USB devices (default 2). This
4324 is the time required before an idle device will be
4325 autosuspended. Devices for which the delay is set
4326 to a negative value won't be autosuspended at all.
4327
4328 usbcore.usbfs_snoop=
4329 [USB] Set to log all usbfs traffic (default 0 = off).
4330
4331 usbcore.usbfs_snoop_max=
4332 [USB] Maximum number of bytes to snoop in each URB
4333 (default = 65536).
4334
4335 usbcore.blinkenlights=
4336 [USB] Set to cycle leds on hubs (default 0 = off).
4337
4338 usbcore.old_scheme_first=
4339 [USB] Start with the old device initialization
4340 scheme (default 0 = off).
4341
4342 usbcore.usbfs_memory_mb=
4343 [USB] Memory limit (in MB) for buffers allocated by
4344 usbfs (default = 16, 0 = max = 2047).
4345
4346 usbcore.use_both_schemes=
4347 [USB] Try the other device initialization scheme
4348 if the first one fails (default 1 = enabled).
4349
4350 usbcore.initial_descriptor_timeout=
4351 [USB] Specifies timeout for the initial 64-byte
4352 USB_REQ_GET_DESCRIPTOR request in milliseconds
4353 (default 5000 = 5.0 seconds).
4354
4355 usbcore.nousb [USB] Disable the USB subsystem
4356
4357 usbhid.mousepoll=
4358 [USBHID] The interval which mice are to be polled at.
4359
4360 usbhid.jspoll=
4361 [USBHID] The interval which joysticks are to be polled at.
4362
4363 usb-storage.delay_use=
4364 [UMS] The delay in seconds before a new device is
4365 scanned for Logical Units (default 1).
4366
4367 usb-storage.quirks=
4368 [UMS] A list of quirks entries to supplement or
4369 override the built-in unusual_devs list. List
4370 entries are separated by commas. Each entry has
4371 the form VID:PID:Flags where VID and PID are Vendor
4372 and Product ID values (4-digit hex numbers) and
4373 Flags is a set of characters, each corresponding
4374 to a common usb-storage quirk flag as follows:
4375 a = SANE_SENSE (collect more than 18 bytes
4376 of sense data);
4377 b = BAD_SENSE (don't collect more than 18
4378 bytes of sense data);
4379 c = FIX_CAPACITY (decrease the reported
4380 device capacity by one sector);
4381 d = NO_READ_DISC_INFO (don't use
4382 READ_DISC_INFO command);
4383 e = NO_READ_CAPACITY_16 (don't use
4384 READ_CAPACITY_16 command);
4385 f = NO_REPORT_OPCODES (don't use report opcodes
4386 command, uas only);
4387 g = MAX_SECTORS_240 (don't transfer more than
4388 240 sectors at a time, uas only);
4389 h = CAPACITY_HEURISTICS (decrease the
4390 reported device capacity by one
4391 sector if the number is odd);
4392 i = IGNORE_DEVICE (don't bind to this
4393 device);
4394 j = NO_REPORT_LUNS (don't use report luns
4395 command, uas only);
4396 l = NOT_LOCKABLE (don't try to lock and
4397 unlock ejectable media);
4398 m = MAX_SECTORS_64 (don't transfer more
4399 than 64 sectors = 32 KB at a time);
4400 n = INITIAL_READ10 (force a retry of the
4401 initial READ(10) command);
4402 o = CAPACITY_OK (accept the capacity
4403 reported by the device);
4404 p = WRITE_CACHE (the device cache is ON
4405 by default);
4406 r = IGNORE_RESIDUE (the device reports
4407 bogus residue values);
4408 s = SINGLE_LUN (the device has only one
4409 Logical Unit);
4410 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4411 commands, uas only);
4412 u = IGNORE_UAS (don't bind to the uas driver);
4413 w = NO_WP_DETECT (don't test whether the
4414 medium is write-protected).
4415 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4416 even if the device claims no cache)
4417 Example: quirks=0419:aaf5:rl,0421:0433:rc
4418
4419 user_debug= [KNL,ARM]
4420 Format: <int>
4421 See arch/arm/Kconfig.debug help text.
4422 1 - undefined instruction events
4423 2 - system calls
4424 4 - invalid data aborts
4425 8 - SIGSEGV faults
4426 16 - SIGBUS faults
4427 Example: user_debug=31
4428
4429 userpte=
4430 [X86] Flags controlling user PTE allocations.
4431
4432 nohigh = do not allocate PTE pages in
4433 HIGHMEM regardless of setting
4434 of CONFIG_HIGHPTE.
4435
4436 vdso= [X86,SH]
4437 On X86_32, this is an alias for vdso32=. Otherwise:
4438
4439 vdso=1: enable VDSO (the default)
4440 vdso=0: disable VDSO mapping
4441
4442 vdso32= [X86] Control the 32-bit vDSO
4443 vdso32=1: enable 32-bit VDSO
4444 vdso32=0 or vdso32=2: disable 32-bit VDSO
4445
4446 See the help text for CONFIG_COMPAT_VDSO for more
4447 details. If CONFIG_COMPAT_VDSO is set, the default is
4448 vdso32=0; otherwise, the default is vdso32=1.
4449
4450 For compatibility with older kernels, vdso32=2 is an
4451 alias for vdso32=0.
4452
4453 Try vdso32=0 if you encounter an error that says:
4454 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4455
4456 vector= [IA-64,SMP]
4457 vector=percpu: enable percpu vector domain
4458
4459 video= [FB] Frame buffer configuration
4460 See Documentation/fb/modedb.txt.
4461
4462 video.brightness_switch_enabled= [0,1]
4463 If set to 1, on receiving an ACPI notify event
4464 generated by hotkey, video driver will adjust brightness
4465 level and then send out the event to user space through
4466 the allocated input device; If set to 0, video driver
4467 will only send out the event without touching backlight
4468 brightness level.
4469 default: 1
4470
4471 virtio_mmio.device=
4472 [VMMIO] Memory mapped virtio (platform) device.
4473
4474 <size>@<baseaddr>:<irq>[:<id>]
4475 where:
4476 <size> := size (can use standard suffixes
4477 like K, M and G)
4478 <baseaddr> := physical base address
4479 <irq> := interrupt number (as passed to
4480 request_irq())
4481 <id> := (optional) platform device id
4482 example:
4483 virtio_mmio.device=1K@0x100b0000:48:7
4484
4485 Can be used multiple times for multiple devices.
4486
4487 vga= [BOOT,X86-32] Select a particular video mode
4488 See Documentation/x86/boot.txt and
4489 Documentation/svga.txt.
4490 Use vga=ask for menu.
4491 This is actually a boot loader parameter; the value is
4492 passed to the kernel using a special protocol.
4493
4494 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4495 size of <nn>. This can be used to increase the
4496 minimum size (128MB on x86). It can also be used to
4497 decrease the size and leave more room for directly
4498 mapped kernel RAM.
4499
4500 vmcp_cma=nn[MG] [KNL,S390]
4501 Sets the memory size reserved for contiguous memory
4502 allocations for the vmcp device driver.
4503
4504 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4505 Format: <command>
4506
4507 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4508 Format: <command>
4509
4510 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4511 Format: <command>
4512
4513 vsyscall= [X86-64]
4514 Controls the behavior of vsyscalls (i.e. calls to
4515 fixed addresses of 0xffffffffff600x00 from legacy
4516 code). Most statically-linked binaries and older
4517 versions of glibc use these calls. Because these
4518 functions are at fixed addresses, they make nice
4519 targets for exploits that can control RIP.
4520
4521 emulate [default] Vsyscalls turn into traps and are
4522 emulated reasonably safely.
4523
4524 native Vsyscalls are native syscall instructions.
4525 This is a little bit faster than trapping
4526 and makes a few dynamic recompilers work
4527 better than they would in emulation mode.
4528 It also makes exploits much easier to write.
4529
4530 none Vsyscalls don't work at all. This makes
4531 them quite hard to use for exploits but
4532 might break your system.
4533
4534 vt.color= [VT] Default text color.
4535 Format: 0xYX, X = foreground, Y = background.
4536 Default: 0x07 = light gray on black.
4537
4538 vt.cur_default= [VT] Default cursor shape.
4539 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4540 the parameters of the <Esc>[?A;B;Cc escape sequence;
4541 see VGA-softcursor.txt. Default: 2 = underline.
4542
4543 vt.default_blu= [VT]
4544 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4545 Change the default blue palette of the console.
4546 This is a 16-member array composed of values
4547 ranging from 0-255.
4548
4549 vt.default_grn= [VT]
4550 Format: <green0>,<green1>,<green2>,...,<green15>
4551 Change the default green palette of the console.
4552 This is a 16-member array composed of values
4553 ranging from 0-255.
4554
4555 vt.default_red= [VT]
4556 Format: <red0>,<red1>,<red2>,...,<red15>
4557 Change the default red palette of the console.
4558 This is a 16-member array composed of values
4559 ranging from 0-255.
4560
4561 vt.default_utf8=
4562 [VT]
4563 Format=<0|1>
4564 Set system-wide default UTF-8 mode for all tty's.
4565 Default is 1, i.e. UTF-8 mode is enabled for all
4566 newly opened terminals.
4567
4568 vt.global_cursor_default=
4569 [VT]
4570 Format=<-1|0|1>
4571 Set system-wide default for whether a cursor
4572 is shown on new VTs. Default is -1,
4573 i.e. cursors will be created by default unless
4574 overridden by individual drivers. 0 will hide
4575 cursors, 1 will display them.
4576
4577 vt.italic= [VT] Default color for italic text; 0-15.
4578 Default: 2 = green.
4579
4580 vt.underline= [VT] Default color for underlined text; 0-15.
4581 Default: 3 = cyan.
4582
4583 watchdog timers [HW,WDT] For information on watchdog timers,
4584 see Documentation/watchdog/watchdog-parameters.txt
4585 or other driver-specific files in the
4586 Documentation/watchdog/ directory.
4587
4588 workqueue.watchdog_thresh=
4589 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4590 warn stall conditions and dump internal state to
4591 help debugging. 0 disables workqueue stall
4592 detection; otherwise, it's the stall threshold
4593 duration in seconds. The default value is 30 and
4594 it can be updated at runtime by writing to the
4595 corresponding sysfs file.
4596
4597 workqueue.disable_numa
4598 By default, all work items queued to unbound
4599 workqueues are affine to the NUMA nodes they're
4600 issued on, which results in better behavior in
4601 general. If NUMA affinity needs to be disabled for
4602 whatever reason, this option can be used. Note
4603 that this also can be controlled per-workqueue for
4604 workqueues visible under /sys/bus/workqueue/.
4605
4606 workqueue.power_efficient
4607 Per-cpu workqueues are generally preferred because
4608 they show better performance thanks to cache
4609 locality; unfortunately, per-cpu workqueues tend to
4610 be more power hungry than unbound workqueues.
4611
4612 Enabling this makes the per-cpu workqueues which
4613 were observed to contribute significantly to power
4614 consumption unbound, leading to measurably lower
4615 power usage at the cost of small performance
4616 overhead.
4617
4618 The default value of this parameter is determined by
4619 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4620
4621 workqueue.debug_force_rr_cpu
4622 Workqueue used to implicitly guarantee that work
4623 items queued without explicit CPU specified are put
4624 on the local CPU. This guarantee is no longer true
4625 and while local CPU is still preferred work items
4626 may be put on foreign CPUs. This debug option
4627 forces round-robin CPU selection to flush out
4628 usages which depend on the now broken guarantee.
4629 When enabled, memory and cache locality will be
4630 impacted.
4631
4632 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4633 default x2apic cluster mode on platforms
4634 supporting x2apic.
4635
4636 x86_intel_mid_timer= [X86-32,APBT]
4637 Choose timer option for x86 Intel MID platform.
4638 Two valid options are apbt timer only and lapic timer
4639 plus one apbt timer for broadcast timer.
4640 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4641
4642 xen_512gb_limit [KNL,X86-64,XEN]
4643 Restricts the kernel running paravirtualized under Xen
4644 to use only up to 512 GB of RAM. The reason to do so is
4645 crash analysis tools and Xen tools for doing domain
4646 save/restore/migration must be enabled to handle larger
4647 domains.
4648
4649 xen_emul_unplug= [HW,X86,XEN]
4650 Unplug Xen emulated devices
4651 Format: [unplug0,][unplug1]
4652 ide-disks -- unplug primary master IDE devices
4653 aux-ide-disks -- unplug non-primary-master IDE devices
4654 nics -- unplug network devices
4655 all -- unplug all emulated devices (NICs and IDE disks)
4656 unnecessary -- unplugging emulated devices is
4657 unnecessary even if the host did not respond to
4658 the unplug protocol
4659 never -- do not unplug even if version check succeeds
4660
4661 xen_nopvspin [X86,XEN]
4662 Disables the ticketlock slowpath using Xen PV
4663 optimizations.
4664
4665 xen_nopv [X86]
4666 Disables the PV optimizations forcing the HVM guest to
4667 run as generic HVM guest with no PV drivers.
4668
4669 xirc2ps_cs= [NET,PCMCIA]
4670 Format:
4671 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]