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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
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
125
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
127 kernels.
128
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
138
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
143
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
146
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
152
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
158 strings
159 acpi_osi=!! # enable all built-in OS vendor
160 strings
161 acpi_osi= # disable all strings
162
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
173 Examples:
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
177
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
183 meaningless.
184 Examples:
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
186 FALSE.
187
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
198 the OSPM features.
199 Examples:
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
205 equivalent to
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
207 and
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
210
211 acpi_pm_good [X86]
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
215
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
218
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
222
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
227 s3_bios and s3_mode.
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
244
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
248
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
251
252 agp= [AGP]
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
257
258 ALSA [HW,ALSA]
259 See Documentation/sound/alsa/alsa-parameters.txt
260
261 alignment= [KNL,ARM]
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
265
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
273
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
278
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
285
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
288 Possible values are:
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
292 is a lot of faster
293 off - do not initialize any AMD IOMMU found in
294 the system
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
300
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
306
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
309 remapping modes:
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
315
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
318 Format: <a>,<b>
319 See also Documentation/input/joydev/joystick.rst
320
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
325
326 apc= [HW,SPARC]
327 Power management functions (SPARCstation-4/5 + deriv.)
328 Format: noidle
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
332
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
339 driver name.
340 Format: apic=driver_name
341 Examples: apic=bigsmp
342
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
347 backup of CPU 0
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
350 shot down by NMI
351
352 autoconf= [IPV6]
353 See Documentation/networking/ipv6.txt.
354
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
363
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
366
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
369
370 ataflop= [HW,M68k]
371
372 atarimouse= [HW,MOUSE] Atari Mouse
373
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
376
377 atkbd.reset= [HW] Reset keyboard during initialization
378
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
381
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 keyboards
384
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
387
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
390
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
400 userspace auditd.
401 Default: unset
402
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
405 Default: 64
406
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
410 0 - Disable the BAU.
411 1 - Enable the BAU.
412 unset - Disable the BAU.
413
414 baycom_epp= [HW,AX25]
415 Format: <io>,<mode>
416
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
418 Format: <io>,<mode>
419 See header of drivers/net/hamradio/baycom_par.c.
420
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
425
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
430
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
434
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
437 no delay (0).
438 Format: integer
439
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441
442 bert_disable [ACPI]
443 Disable BERT OS support on buggy BIOSes.
444
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
447 kernel args too.
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bttv.tuner=
450
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
453 at a time.
454
455 c101= [NET] Moxa C101 synchronous serial card
456
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
463
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
466 trust validation.
467 format: { id:<keyid> | builtin }
468
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
473 others).
474
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
477
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
482 a single hierarchy
483 - foo isn't visible as an individually mountable
484 subsystem
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
488
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
493
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
495 Format: <string>
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
498
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
508
509 cio_ignore= [S390]
510 See Documentation/s390/CommonIO for details.
511 clk_ignore_unused
512 [CLK]
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/clk.txt.
522
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
524 [Deprecated]
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
529
530 clocksource= Override the default clocksource
531 Format: <string>
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
535 the platform:
536 [all] jiffies (this is the base, fallback clocksource)
537 [ACPI] acpi_pm
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
542 [MIPS] MIPS
543 [PARISC] cr16
544 [S390] tod
545 [SH] SuperH
546 [SPARC64] tick
547 [X86-64] hpet,tsc
548
549 clocksource.arm_arch_timer.evtstrm=
550 [ARM,ARM64]
551 Format: <bool>
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
555 systems.
556
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
562 ones should be.
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
568 some critical bits.
569
570 cma=nn[MG]@[start[MG][-end[MG]]]
571 [ARM,X86,KNL]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
578
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
583 a hypervisor.
584 Default: yes
585
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
589
590 code_bytes [X86] How many bytes of object code to print
591 in an oops report.
592 Range: 0 - 8192
593 Default: 64
594
595 com20020= [HW,NET] ARCnet - COM20020 chipset
596 Format:
597 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
598
599 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
600 Format: <io>[,<irq>]
601
602 com90xx= [HW,NET]
603 ARCnet - COM90xx chipset (memory-mapped buffers)
604 Format: <io>[,<irq>[,<memstart>]]
605
606 condev= [HW,S390] console device
607 conmode=
608
609 console= [KNL] Output console device and options.
610
611 tty<n> Use the virtual console device <n>.
612
613 ttyS<n>[,options]
614 ttyUSB0[,options]
615 Use the specified serial port. The options are of
616 the form "bbbbpnf", where "bbbb" is the baud rate,
617 "p" is parity ("n", "o", or "e"), "n" is number of
618 bits, and "f" is flow control ("r" for RTS or
619 omit it). Default is "9600n8".
620
621 See Documentation/admin-guide/serial-console.rst for more
622 information. See
623 Documentation/networking/netconsole.txt for an
624 alternative.
625
626 uart[8250],io,<addr>[,options]
627 uart[8250],mmio,<addr>[,options]
628 uart[8250],mmio16,<addr>[,options]
629 uart[8250],mmio32,<addr>[,options]
630 uart[8250],0x<addr>[,options]
631 Start an early, polled-mode console on the 8250/16550
632 UART at the specified I/O port or MMIO address,
633 switching to the matching ttyS device later.
634 MMIO inter-register address stride is either 8-bit
635 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
636 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
637 to be equivalent to 'mmio'. 'options' are specified in
638 the same format described for ttyS above; if unspecified,
639 the h/w is not re-initialized.
640
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
643
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
646 console=brl,ttyS0
647 For now, only VisioBraille is supported.
648
649 console_msg_format=
650 [KNL] Change console messages format
651 default
652 By default we print messages on consoles in
653 "[time stamp] text\n" format (time stamp may not be
654 printed, depending on CONFIG_PRINTK_TIME or
655 `printk_time' param).
656 syslog
657 Switch to syslog format: "<%u>[time stamp] text\n"
658 IOW, each message will have a facility and loglevel
659 prefix. The format is similar to one used by syslog()
660 syscall, or to executing "dmesg -S --raw" or to reading
661 from /proc/kmsg.
662
663 consoleblank= [KNL] The console blank (screen saver) timeout in
664 seconds. A value of 0 disables the blank timer.
665 Defaults to 0.
666
667 coredump_filter=
668 [KNL] Change the default value for
669 /proc/<pid>/coredump_filter.
670 See also Documentation/filesystems/proc.txt.
671
672 coresight_cpu_debug.enable
673 [ARM,ARM64]
674 Format: <bool>
675 Enable/disable the CPU sampling based debugging.
676 0: default value, disable debugging
677 1: enable debugging at boot time
678
679 cpuidle.off=1 [CPU_IDLE]
680 disable the cpuidle sub-system
681
682 cpufreq.off=1 [CPU_FREQ]
683 disable the cpufreq sub-system
684
685 cpu_init_udelay=N
686 [X86] Delay for N microsec between assert and de-assert
687 of APIC INIT to start processors. This delay occurs
688 on every CPU online, such as boot, and resume from suspend.
689 Default: 10000
690
691 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
692 Format:
693 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
694
695 crashkernel=size[KMG][@offset[KMG]]
696 [KNL] Using kexec, Linux can switch to a 'crash kernel'
697 upon panic. This parameter reserves the physical
698 memory region [offset, offset + size] for that kernel
699 image. If '@offset' is omitted, then a suitable offset
700 is selected automatically. Check
701 Documentation/kdump/kdump.txt for further details.
702
703 crashkernel=range1:size1[,range2:size2,...][@offset]
704 [KNL] Same as above, but depends on the memory
705 in the running system. The syntax of range is
706 start-[end] where start and end are both
707 a memory unit (amount[KMG]). See also
708 Documentation/kdump/kdump.txt for an example.
709
710 crashkernel=size[KMG],high
711 [KNL, x86_64] range could be above 4G. Allow kernel
712 to allocate physical memory region from top, so could
713 be above 4G if system have more than 4G ram installed.
714 Otherwise memory region will be allocated below 4G, if
715 available.
716 It will be ignored if crashkernel=X is specified.
717 crashkernel=size[KMG],low
718 [KNL, x86_64] range under 4G. When crashkernel=X,high
719 is passed, kernel could allocate physical memory region
720 above 4G, that cause second kernel crash on system
721 that require some amount of low memory, e.g. swiotlb
722 requires at least 64M+32K low memory, also enough extra
723 low memory is needed to make sure DMA buffers for 32-bit
724 devices won't run out. Kernel would try to allocate at
725 at least 256M below 4G automatically.
726 This one let user to specify own low range under 4G
727 for second kernel instead.
728 0: to disable low allocation.
729 It will be ignored when crashkernel=X,high is not used
730 or memory reserved is below 4G.
731
732 cryptomgr.notests
733 [KNL] Disable crypto self-tests
734
735 cs89x0_dma= [HW,NET]
736 Format: <dma>
737
738 cs89x0_media= [HW,NET]
739 Format: { rj45 | aui | bnc }
740
741 dasd= [HW,NET]
742 See header of drivers/s390/block/dasd_devmap.c.
743
744 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
745 (one device per port)
746 Format: <port#>,<type>
747 See also Documentation/input/devices/joystick-parport.rst
748
749 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
750 time. See
751 Documentation/admin-guide/dynamic-debug-howto.rst for
752 details. Deprecated, see dyndbg.
753
754 debug [KNL] Enable kernel debugging (events log level).
755
756 debug_locks_verbose=
757 [KNL] verbose self-tests
758 Format=<0|1>
759 Print debugging info while doing the locking API
760 self-tests.
761 We default to 0 (no extra messages), setting it to
762 1 will print _a lot_ more information - normally
763 only useful to kernel developers.
764
765 debug_objects [KNL] Enable object debugging
766
767 no_debug_objects
768 [KNL] Disable object debugging
769
770 debug_guardpage_minorder=
771 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
772 parameter allows control of the order of pages that will
773 be intentionally kept free (and hence protected) by the
774 buddy allocator. Bigger value increase the probability
775 of catching random memory corruption, but reduce the
776 amount of memory for normal system use. The maximum
777 possible value is MAX_ORDER/2. Setting this parameter
778 to 1 or 2 should be enough to identify most random
779 memory corruption problems caused by bugs in kernel or
780 driver code when a CPU writes to (or reads from) a
781 random memory location. Note that there exists a class
782 of memory corruptions problems caused by buggy H/W or
783 F/W or by drivers badly programing DMA (basically when
784 memory is written at bus level and the CPU MMU is
785 bypassed) which are not detectable by
786 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
787 tracking down these problems.
788
789 debug_pagealloc=
790 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
791 parameter enables the feature at boot time. In
792 default, it is disabled. We can avoid allocating huge
793 chunk of memory for debug pagealloc if we don't enable
794 it at boot time and the system will work mostly same
795 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
796 on: enable the feature
797
798 debugpat [X86] Enable PAT debugging
799
800 decnet.addr= [HW,NET]
801 Format: <area>[,<node>]
802 See also Documentation/networking/decnet.txt.
803
804 default_hugepagesz=
805 [same as hugepagesz=] The size of the default
806 HugeTLB page size. This is the size represented by
807 the legacy /proc/ hugepages APIs, used for SHM, and
808 default size when mounting hugetlbfs filesystems.
809 Defaults to the default architecture's huge page size
810 if not specified.
811
812 dhash_entries= [KNL]
813 Set number of hash buckets for dentry cache.
814
815 disable_1tb_segments [PPC]
816 Disables the use of 1TB hash page table segments. This
817 causes the kernel to fall back to 256MB segments which
818 can be useful when debugging issues that require an SLB
819 miss to occur.
820
821 disable= [IPV6]
822 See Documentation/networking/ipv6.txt.
823
824 disable_radix [PPC]
825 Disable RADIX MMU mode on POWER9
826
827 disable_cpu_apicid= [X86,APIC,SMP]
828 Format: <int>
829 The number of initial APIC ID for the
830 corresponding CPU to be disabled at boot,
831 mostly used for the kdump 2nd kernel to
832 disable BSP to wake up multiple CPUs without
833 causing system reset or hang due to sending
834 INIT from AP to BSP.
835
836 disable_ddw [PPC/PSERIES]
837 Disable Dynamic DMA Window support. Use this if
838 to workaround buggy firmware.
839
840 disable_ipv6= [IPV6]
841 See Documentation/networking/ipv6.txt.
842
843 disable_mtrr_cleanup [X86]
844 The kernel tries to adjust MTRR layout from continuous
845 to discrete, to make X server driver able to add WB
846 entry later. This parameter disables that.
847
848 disable_mtrr_trim [X86, Intel and AMD only]
849 By default the kernel will trim any uncacheable
850 memory out of your available memory pool based on
851 MTRR settings. This parameter disables that behavior,
852 possibly causing your machine to run very slowly.
853
854 disable_timer_pin_1 [X86]
855 Disable PIN 1 of APIC timer
856 Can be useful to work around chipset bugs.
857
858 dis_ucode_ldr [X86] Disable the microcode loader.
859
860 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
861 this option disables the debugging code at boot.
862
863 dma_debug_entries=<number>
864 This option allows to tune the number of preallocated
865 entries for DMA-API debugging code. One entry is
866 required per DMA-API allocation. Use this if the
867 DMA-API debugging code disables itself because the
868 architectural default is too low.
869
870 dma_debug_driver=<driver_name>
871 With this option the DMA-API debugging driver
872 filter feature can be enabled at boot time. Just
873 pass the driver to filter for as the parameter.
874 The filter can be disabled or changed to another
875 driver later using sysfs.
876
877 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
878 Broken monitors, graphic adapters, KVMs and EDIDless
879 panels may send no or incorrect EDID data sets.
880 This parameter allows to specify an EDID data sets
881 in the /lib/firmware directory that are used instead.
882 Generic built-in EDID data sets are used, if one of
883 edid/1024x768.bin, edid/1280x1024.bin,
884 edid/1680x1050.bin, or edid/1920x1080.bin is given
885 and no file with the same name exists. Details and
886 instructions how to build your own EDID data are
887 available in Documentation/EDID/HOWTO.txt. An EDID
888 data set will only be used for a particular connector,
889 if its name and a colon are prepended to the EDID
890 name. Each connector may use a unique EDID data
891 set by separating the files with a comma. An EDID
892 data set with no connector name will be used for
893 any connectors not explicitly specified.
894
895 dscc4.setup= [NET]
896
897 dt_cpu_ftrs= [PPC]
898 Format: {"off" | "known"}
899 Control how the dt_cpu_ftrs device-tree binding is
900 used for CPU feature discovery and setup (if it
901 exists).
902 off: Do not use it, fall back to legacy cpu table.
903 known: Do not pass through unknown features to guests
904 or userspace, only those that the kernel is aware of.
905
906 dump_apple_properties [X86]
907 Dump name and content of EFI device properties on
908 x86 Macs. Useful for driver authors to determine
909 what data is available or for reverse-engineering.
910
911 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
912 module.dyndbg[="val"]
913 Enable debug messages at boot time. See
914 Documentation/admin-guide/dynamic-debug-howto.rst
915 for details.
916
917 nompx [X86] Disables Intel Memory Protection Extensions.
918 See Documentation/x86/intel_mpx.txt for more
919 information about the feature.
920
921 nopku [X86] Disable Memory Protection Keys CPU feature found
922 in some Intel CPUs.
923
924 module.async_probe [KNL]
925 Enable asynchronous probe on this module.
926
927 early_ioremap_debug [KNL]
928 Enable debug messages in early_ioremap support. This
929 is useful for tracking down temporary early mappings
930 which are not unmapped.
931
932 earlycon= [KNL] Output early console device and options.
933
934 [ARM64] The early console is determined by the
935 stdout-path property in device tree's chosen node,
936 or determined by the ACPI SPCR table.
937
938 [X86] When used with no options the early console is
939 determined by the ACPI SPCR table.
940
941 cdns,<addr>[,options]
942 Start an early, polled-mode console on a Cadence
943 (xuartps) serial port at the specified address. Only
944 supported option is baud rate. If baud rate is not
945 specified, the serial port must already be setup and
946 configured.
947
948 uart[8250],io,<addr>[,options]
949 uart[8250],mmio,<addr>[,options]
950 uart[8250],mmio32,<addr>[,options]
951 uart[8250],mmio32be,<addr>[,options]
952 uart[8250],0x<addr>[,options]
953 Start an early, polled-mode console on the 8250/16550
954 UART at the specified I/O port or MMIO address.
955 MMIO inter-register address stride is either 8-bit
956 (mmio) or 32-bit (mmio32 or mmio32be).
957 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
958 to be equivalent to 'mmio'. 'options' are specified
959 in the same format described for "console=ttyS<n>"; if
960 unspecified, the h/w is not initialized.
961
962 pl011,<addr>
963 pl011,mmio32,<addr>
964 Start an early, polled-mode console on a pl011 serial
965 port at the specified address. The pl011 serial port
966 must already be setup and configured. Options are not
967 yet supported. If 'mmio32' is specified, then only
968 the driver will use only 32-bit accessors to read/write
969 the device registers.
970
971 meson,<addr>
972 Start an early, polled-mode console on a meson serial
973 port at the specified address. The serial port must
974 already be setup and configured. Options are not yet
975 supported.
976
977 msm_serial,<addr>
978 Start an early, polled-mode console on an msm serial
979 port at the specified address. The serial port
980 must already be setup and configured. Options are not
981 yet supported.
982
983 msm_serial_dm,<addr>
984 Start an early, polled-mode console on an msm serial
985 dm port at the specified address. The serial port
986 must already be setup and configured. Options are not
987 yet supported.
988
989 owl,<addr>
990 Start an early, polled-mode console on a serial port
991 of an Actions Semi SoC, such as S500 or S900, at the
992 specified address. The serial port must already be
993 setup and configured. Options are not yet supported.
994
995 smh Use ARM semihosting calls for early console.
996
997 s3c2410,<addr>
998 s3c2412,<addr>
999 s3c2440,<addr>
1000 s3c6400,<addr>
1001 s5pv210,<addr>
1002 exynos4210,<addr>
1003 Use early console provided by serial driver available
1004 on Samsung SoCs, requires selecting proper type and
1005 a correct base address of the selected UART port. The
1006 serial port must already be setup and configured.
1007 Options are not yet supported.
1008
1009 lantiq,<addr>
1010 Start an early, polled-mode console on a lantiq serial
1011 (lqasc) port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1013 yet supported.
1014
1015 lpuart,<addr>
1016 lpuart32,<addr>
1017 Use early console provided by Freescale LP UART driver
1018 found on Freescale Vybrid and QorIQ LS1021A processors.
1019 A valid base address must be provided, and the serial
1020 port must already be setup and configured.
1021
1022 ar3700_uart,<addr>
1023 Start an early, polled-mode console on the
1024 Armada 3700 serial port at the specified
1025 address. The serial port must already be setup
1026 and configured. Options are not yet supported.
1027
1028 earlyprintk= [X86,SH,ARM,M68k,S390]
1029 earlyprintk=vga
1030 earlyprintk=efi
1031 earlyprintk=sclp
1032 earlyprintk=xen
1033 earlyprintk=serial[,ttySn[,baudrate]]
1034 earlyprintk=serial[,0x...[,baudrate]]
1035 earlyprintk=ttySn[,baudrate]
1036 earlyprintk=dbgp[debugController#]
1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1038 earlyprintk=xdbc[xhciController#]
1039
1040 earlyprintk is useful when the kernel crashes before
1041 the normal console is initialized. It is not enabled by
1042 default because it has some cosmetic problems.
1043
1044 Append ",keep" to not disable it when the real console
1045 takes over.
1046
1047 Only one of vga, efi, serial, or usb debug port can
1048 be used at a time.
1049
1050 Currently only ttyS0 and ttyS1 may be specified by
1051 name. Other I/O ports may be explicitly specified
1052 on some architectures (x86 and arm at least) by
1053 replacing ttySn with an I/O port address, like this:
1054 earlyprintk=serial,0x1008,115200
1055 You can find the port for a given device in
1056 /proc/tty/driver/serial:
1057 2: uart:ST16650V2 port:00001008 irq:18 ...
1058
1059 Interaction with the standard serial driver is not
1060 very good.
1061
1062 The VGA and EFI output is eventually overwritten by
1063 the real console.
1064
1065 The xen output can only be used by Xen PV guests.
1066
1067 The sclp output can only be used on s390.
1068
1069 edac_report= [HW,EDAC] Control how to report EDAC event
1070 Format: {"on" | "off" | "force"}
1071 on: enable EDAC to report H/W event. May be overridden
1072 by other higher priority error reporting module.
1073 off: disable H/W event reporting through EDAC.
1074 force: enforce the use of EDAC to report H/W event.
1075 default: on.
1076
1077 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1078 ekgdboc=kbd
1079
1080 This is designed to be used in conjunction with
1081 the boot argument: earlyprintk=vga
1082
1083 edd= [EDD]
1084 Format: {"off" | "on" | "skip[mbr]"}
1085
1086 efi= [EFI]
1087 Format: { "old_map", "nochunk", "noruntime", "debug" }
1088 old_map [X86-64]: switch to the old ioremap-based EFI
1089 runtime services mapping. 32-bit still uses this one by
1090 default.
1091 nochunk: disable reading files in "chunks" in the EFI
1092 boot stub, as chunking can cause problems with some
1093 firmware implementations.
1094 noruntime : disable EFI runtime services support
1095 debug: enable misc debug output
1096
1097 efi_no_storage_paranoia [EFI; X86]
1098 Using this parameter you can use more than 50% of
1099 your efi variable storage. Use this parameter only if
1100 you are really sure that your UEFI does sane gc and
1101 fulfills the spec otherwise your board may brick.
1102
1103 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1104 Add arbitrary attribute to specific memory range by
1105 updating original EFI memory map.
1106 Region of memory which aa attribute is added to is
1107 from ss to ss+nn.
1108 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1109 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1110 attribute is added to range 0x100000000-0x180000000 and
1111 0x10a0000000-0x1120000000.
1112
1113 Using this parameter you can do debugging of EFI memmap
1114 related feature. For example, you can do debugging of
1115 Address Range Mirroring feature even if your box
1116 doesn't support it.
1117
1118 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1119 that is to be dynamically loaded by Linux. If there are
1120 multiple variables with the same name but with different
1121 vendor GUIDs, all of them will be loaded. See
1122 Documentation/acpi/ssdt-overlays.txt for details.
1123
1124
1125 eisa_irq_edge= [PARISC,HW]
1126 See header of drivers/parisc/eisa.c.
1127
1128 elanfreq= [X86-32]
1129 See comment before function elanfreq_setup() in
1130 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1131
1132 elevator= [IOSCHED]
1133 Format: {"cfq" | "deadline" | "noop"}
1134 See Documentation/block/cfq-iosched.txt and
1135 Documentation/block/deadline-iosched.txt for details.
1136
1137 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1138 Specifies physical address of start of kernel core
1139 image elf header and optionally the size. Generally
1140 kexec loader will pass this option to capture kernel.
1141 See Documentation/kdump/kdump.txt for details.
1142
1143 enable_mtrr_cleanup [X86]
1144 The kernel tries to adjust MTRR layout from continuous
1145 to discrete, to make X server driver able to add WB
1146 entry later. This parameter enables that.
1147
1148 enable_timer_pin_1 [X86]
1149 Enable PIN 1 of APIC timer
1150 Can be useful to work around chipset bugs
1151 (in particular on some ATI chipsets).
1152 The kernel tries to set a reasonable default.
1153
1154 enforcing [SELINUX] Set initial enforcing status.
1155 Format: {"0" | "1"}
1156 See security/selinux/Kconfig help text.
1157 0 -- permissive (log only, no denials).
1158 1 -- enforcing (deny and log).
1159 Default value is 0.
1160 Value can be changed at runtime via /selinux/enforce.
1161
1162 erst_disable [ACPI]
1163 Disable Error Record Serialization Table (ERST)
1164 support.
1165
1166 ether= [HW,NET] Ethernet cards parameters
1167 This option is obsoleted by the "netdev=" option, which
1168 has equivalent usage. See its documentation for details.
1169
1170 evm= [EVM]
1171 Format: { "fix" }
1172 Permit 'security.evm' to be updated regardless of
1173 current integrity status.
1174
1175 failslab=
1176 fail_page_alloc=
1177 fail_make_request=[KNL]
1178 General fault injection mechanism.
1179 Format: <interval>,<probability>,<space>,<times>
1180 See also Documentation/fault-injection/.
1181
1182 floppy= [HW]
1183 See Documentation/blockdev/floppy.txt.
1184
1185 force_pal_cache_flush
1186 [IA-64] Avoid check_sal_cache_flush which may hang on
1187 buggy SAL_CACHE_FLUSH implementations. Using this
1188 parameter will force ia64_sal_cache_flush to call
1189 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1190
1191 forcepae [X86-32]
1192 Forcefully enable Physical Address Extension (PAE).
1193 Many Pentium M systems disable PAE but may have a
1194 functionally usable PAE implementation.
1195 Warning: use of this parameter will taint the kernel
1196 and may cause unknown problems.
1197
1198 ftrace=[tracer]
1199 [FTRACE] will set and start the specified tracer
1200 as early as possible in order to facilitate early
1201 boot debugging.
1202
1203 ftrace_dump_on_oops[=orig_cpu]
1204 [FTRACE] will dump the trace buffers on oops.
1205 If no parameter is passed, ftrace will dump
1206 buffers of all CPUs, but if you pass orig_cpu, it will
1207 dump only the buffer of the CPU that triggered the
1208 oops.
1209
1210 ftrace_filter=[function-list]
1211 [FTRACE] Limit the functions traced by the function
1212 tracer at boot up. function-list is a comma separated
1213 list of functions. This list can be changed at run
1214 time by the set_ftrace_filter file in the debugfs
1215 tracing directory.
1216
1217 ftrace_notrace=[function-list]
1218 [FTRACE] Do not trace the functions specified in
1219 function-list. This list can be changed at run time
1220 by the set_ftrace_notrace file in the debugfs
1221 tracing directory.
1222
1223 ftrace_graph_filter=[function-list]
1224 [FTRACE] Limit the top level callers functions traced
1225 by the function graph tracer at boot up.
1226 function-list is a comma separated list of functions
1227 that can be changed at run time by the
1228 set_graph_function file in the debugfs tracing directory.
1229
1230 ftrace_graph_notrace=[function-list]
1231 [FTRACE] Do not trace from the functions specified in
1232 function-list. This list is a comma separated list of
1233 functions that can be changed at run time by the
1234 set_graph_notrace file in the debugfs tracing directory.
1235
1236 ftrace_graph_max_depth=<uint>
1237 [FTRACE] Used with the function graph tracer. This is
1238 the max depth it will trace into a function. This value
1239 can be changed at run time by the max_graph_depth file
1240 in the tracefs tracing directory. default: 0 (no limit)
1241
1242 gamecon.map[2|3]=
1243 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1244 support via parallel port (up to 5 devices per port)
1245 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1246 See also Documentation/input/devices/joystick-parport.rst
1247
1248 gamma= [HW,DRM]
1249
1250 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1251 Format: off | on
1252 default: on
1253
1254 gcov_persist= [GCOV] When non-zero (default), profiling data for
1255 kernel modules is saved and remains accessible via
1256 debugfs, even when the module is unloaded/reloaded.
1257 When zero, profiling data is discarded and associated
1258 debugfs files are removed at module unload time.
1259
1260 goldfish [X86] Enable the goldfish android emulator platform.
1261 Don't use this when you are not running on the
1262 android emulator
1263
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1268
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1271 Format: 0 | 1
1272 Default: 0
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1275 Format: 0 | 1
1276 Default: 0
1277 grcan.select= [HW] Select which physical interface to use.
1278 Format: 0 | 1
1279 Default: 0
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1282 Default: 1024
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1285 Default: 1024
1286
1287 gpio-mockup.gpio_mockup_ranges
1288 [HW] Sets the ranges of gpiochip of for this device.
1289 Format: <start1>,<end1>,<start2>,<end2>...
1290
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1294 Format: <integer>
1295
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1300
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1302
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1305
1306 hest_disable [ACPI]
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1310
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1315
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1318 Default: "on"
1319
1320 hisax= [HW,ISDN]
1321 See Documentation/isdn/README.HiSax.
1322
1323 hlt [BUGS=ARM,SH]
1324
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1327 verbose }
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1330 VIA, nVidia)
1331 verbose: show contents of HPET registers during setup
1332
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1335
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1343
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1349
1350 keep_bootcon [KNL]
1351 Do not unregister boot console at start. This is only
1352 useful for debugging when something happens in the window
1353 between unregistering the boot console and initializing
1354 the real console.
1355
1356 i2c_bus= [HW] Override the default board specific I2C bus speed
1357 or register an additional I2C bus that is not
1358 registered from board initialization code.
1359 Format:
1360 <bus_id>,<clkrate>
1361
1362 i8042.debug [HW] Toggle i8042 debug mode
1363 i8042.unmask_kbd_data
1364 [HW] Enable printing of interrupt data from the KBD port
1365 (disabled by default, and as a pre-condition
1366 requires that i8042.debug=1 be enabled)
1367 i8042.direct [HW] Put keyboard port into non-translated mode
1368 i8042.dumbkbd [HW] Pretend that controller can only read data from
1369 keyboard and cannot control its state
1370 (Don't attempt to blink the leds)
1371 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1372 i8042.nokbd [HW] Don't check/create keyboard port
1373 i8042.noloop [HW] Disable the AUX Loopback command while probing
1374 for the AUX port
1375 i8042.nomux [HW] Don't check presence of an active multiplexing
1376 controller
1377 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1378 controllers
1379 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1380 i8042.reset [HW] Reset the controller during init, cleanup and
1381 suspend-to-ram transitions, only during s2r
1382 transitions, or never reset
1383 Format: { 1 | Y | y | 0 | N | n }
1384 1, Y, y: always reset controller
1385 0, N, n: don't ever reset controller
1386 Default: only on s2r transitions on x86; most other
1387 architectures force reset to be always executed
1388 i8042.unlock [HW] Unlock (ignore) the keylock
1389 i8042.kbdreset [HW] Reset device connected to KBD port
1390
1391 i810= [HW,DRM]
1392
1393 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1394 indicates that the driver is running on unsupported
1395 hardware.
1396 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1397 does not match list of supported models.
1398 i8k.power_status
1399 [HW] Report power status in /proc/i8k
1400 (disabled by default)
1401 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1402 capability is set.
1403
1404 i915.invert_brightness=
1405 [DRM] Invert the sense of the variable that is used to
1406 set the brightness of the panel backlight. Normally a
1407 brightness value of 0 indicates backlight switched off,
1408 and the maximum of the brightness value sets the backlight
1409 to maximum brightness. If this parameter is set to 0
1410 (default) and the machine requires it, or this parameter
1411 is set to 1, a brightness value of 0 sets the backlight
1412 to maximum brightness, and the maximum of the brightness
1413 value switches the backlight off.
1414 -1 -- never invert brightness
1415 0 -- machine default
1416 1 -- force brightness inversion
1417
1418 icn= [HW,ISDN]
1419 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1420
1421 ide-core.nodma= [HW] (E)IDE subsystem
1422 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1423 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1424 .cdrom .chs .ignore_cable are additional options
1425 See Documentation/ide/ide.txt.
1426
1427 ide-generic.probe-mask= [HW] (E)IDE subsystem
1428 Format: <int>
1429 Probe mask for legacy ISA IDE ports. Depending on
1430 platform up to 6 ports are supported, enabled by
1431 setting corresponding bits in the mask to 1. The
1432 default value is 0x0, which has a special meaning.
1433 On systems that have PCI, it triggers scanning the
1434 PCI bus for the first and the second port, which
1435 are then probed. On systems without PCI the value
1436 of 0x0 enables probing the two first ports as if it
1437 was 0x3.
1438
1439 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1440 Claim all unknown PCI IDE storage controllers.
1441
1442 idle= [X86]
1443 Format: idle=poll, idle=halt, idle=nomwait
1444 Poll forces a polling idle loop that can slightly
1445 improve the performance of waking up a idle CPU, but
1446 will use a lot of power and make the system run hot.
1447 Not recommended.
1448 idle=halt: Halt is forced to be used for CPU idle.
1449 In such case C2/C3 won't be used again.
1450 idle=nomwait: Disable mwait for CPU C-states
1451
1452 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1453 Format: { strict | legacy | 2008 | relaxed }
1454 Default: strict
1455
1456 Choose which programs will be accepted for execution
1457 based on the IEEE 754 NaN encoding(s) supported by
1458 the FPU and the NaN encoding requested with the value
1459 of an ELF file header flag individually set by each
1460 binary. Hardware implementations are permitted to
1461 support either or both of the legacy and the 2008 NaN
1462 encoding mode.
1463
1464 Available settings are as follows:
1465 strict accept binaries that request a NaN encoding
1466 supported by the FPU
1467 legacy only accept legacy-NaN binaries, if supported
1468 by the FPU
1469 2008 only accept 2008-NaN binaries, if supported
1470 by the FPU
1471 relaxed accept any binaries regardless of whether
1472 supported by the FPU
1473
1474 The FPU emulator is always able to support both NaN
1475 encodings, so if no FPU hardware is present or it has
1476 been disabled with 'nofpu', then the settings of
1477 'legacy' and '2008' strap the emulator accordingly,
1478 'relaxed' straps the emulator for both legacy-NaN and
1479 2008-NaN, whereas 'strict' enables legacy-NaN only on
1480 legacy processors and both NaN encodings on MIPS32 or
1481 MIPS64 CPUs.
1482
1483 The setting for ABS.fmt/NEG.fmt instruction execution
1484 mode generally follows that for the NaN encoding,
1485 except where unsupported by hardware.
1486
1487 ignore_loglevel [KNL]
1488 Ignore loglevel setting - this will print /all/
1489 kernel messages to the console. Useful for debugging.
1490 We also add it as printk module parameter, so users
1491 could change it dynamically, usually by
1492 /sys/module/printk/parameters/ignore_loglevel.
1493
1494 ignore_rlimit_data
1495 Ignore RLIMIT_DATA setting for data mappings,
1496 print warning at first misuse. Can be changed via
1497 /sys/module/kernel/parameters/ignore_rlimit_data.
1498
1499 ihash_entries= [KNL]
1500 Set number of hash buckets for inode cache.
1501
1502 ima_appraise= [IMA] appraise integrity measurements
1503 Format: { "off" | "enforce" | "fix" | "log" }
1504 default: "enforce"
1505
1506 ima_appraise_tcb [IMA]
1507 The builtin appraise policy appraises all files
1508 owned by uid=0.
1509
1510 ima_canonical_fmt [IMA]
1511 Use the canonical format for the binary runtime
1512 measurements, instead of host native format.
1513
1514 ima_hash= [IMA]
1515 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1516 | sha512 | ... }
1517 default: "sha1"
1518
1519 The list of supported hash algorithms is defined
1520 in crypto/hash_info.h.
1521
1522 ima_policy= [IMA]
1523 The builtin policies to load during IMA setup.
1524 Format: "tcb | appraise_tcb | secure_boot |
1525 fail_securely"
1526
1527 The "tcb" policy measures all programs exec'd, files
1528 mmap'd for exec, and all files opened with the read
1529 mode bit set by either the effective uid (euid=0) or
1530 uid=0.
1531
1532 The "appraise_tcb" policy appraises the integrity of
1533 all files owned by root. (This is the equivalent
1534 of ima_appraise_tcb.)
1535
1536 The "secure_boot" policy appraises the integrity
1537 of files (eg. kexec kernel image, kernel modules,
1538 firmware, policy, etc) based on file signatures.
1539
1540 The "fail_securely" policy forces file signature
1541 verification failure also on privileged mounted
1542 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1543 flag.
1544
1545 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1546 Load a policy which meets the needs of the Trusted
1547 Computing Base. This means IMA will measure all
1548 programs exec'd, files mmap'd for exec, and all files
1549 opened for read by uid=0.
1550
1551 ima_template= [IMA]
1552 Select one of defined IMA measurements template formats.
1553 Formats: { "ima" | "ima-ng" | "ima-sig" }
1554 Default: "ima-ng"
1555
1556 ima_template_fmt=
1557 [IMA] Define a custom template format.
1558 Format: { "field1|...|fieldN" }
1559
1560 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1561 Format: <min_file_size>
1562 Set the minimal file size for using asynchronous hash.
1563 If left unspecified, ahash usage is disabled.
1564
1565 ahash performance varies for different data sizes on
1566 different crypto accelerators. This option can be used
1567 to achieve the best performance for a particular HW.
1568
1569 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1570 Format: <bufsize>
1571 Set hashing buffer size. Default: 4k.
1572
1573 ahash performance varies for different chunk sizes on
1574 different crypto accelerators. This option can be used
1575 to achieve best performance for particular HW.
1576
1577 init= [KNL]
1578 Format: <full_path>
1579 Run specified binary instead of /sbin/init as init
1580 process.
1581
1582 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1583 for working out where the kernel is dying during
1584 startup.
1585
1586 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1587 initcall functions. Useful for debugging built-in
1588 modules and initcalls.
1589
1590 initrd= [BOOT] Specify the location of the initial ramdisk
1591
1592 init_pkru= [x86] Specify the default memory protection keys rights
1593 register contents for all processes. 0x55555554 by
1594 default (disallow access to all but pkey 0). Can
1595 override in debugfs after boot.
1596
1597 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1598 Format: <irq>
1599
1600 int_pln_enable [x86] Enable power limit notification interrupt
1601
1602 integrity_audit=[IMA]
1603 Format: { "0" | "1" }
1604 0 -- basic integrity auditing messages. (Default)
1605 1 -- additional integrity auditing messages.
1606
1607 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1608 on
1609 Enable intel iommu driver.
1610 off
1611 Disable intel iommu driver.
1612 igfx_off [Default Off]
1613 By default, gfx is mapped as normal device. If a gfx
1614 device has a dedicated DMAR unit, the DMAR unit is
1615 bypassed by not enabling DMAR with this option. In
1616 this case, gfx device will use physical address for
1617 DMA.
1618 forcedac [x86_64]
1619 With this option iommu will not optimize to look
1620 for io virtual address below 32-bit forcing dual
1621 address cycle on pci bus for cards supporting greater
1622 than 32-bit addressing. The default is to look
1623 for translation below 32-bit and if not available
1624 then look in the higher range.
1625 strict [Default Off]
1626 With this option on every unmap_single operation will
1627 result in a hardware IOTLB flush operation as opposed
1628 to batching them for performance.
1629 sp_off [Default Off]
1630 By default, super page will be supported if Intel IOMMU
1631 has the capability. With this option, super page will
1632 not be supported.
1633 ecs_off [Default Off]
1634 By default, extended context tables will be supported if
1635 the hardware advertises that it has support both for the
1636 extended tables themselves, and also PASID support. With
1637 this option set, extended tables will not be used even
1638 on hardware which claims to support them.
1639 tboot_noforce [Default Off]
1640 Do not force the Intel IOMMU enabled under tboot.
1641 By default, tboot will force Intel IOMMU on, which
1642 could harm performance of some high-throughput
1643 devices like 40GBit network cards, even if identity
1644 mapping is enabled.
1645 Note that using this option lowers the security
1646 provided by tboot because it makes the system
1647 vulnerable to DMA attacks.
1648
1649 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1650 0 disables intel_idle and fall back on acpi_idle.
1651 1 to 9 specify maximum depth of C-state.
1652
1653 intel_pstate= [X86]
1654 disable
1655 Do not enable intel_pstate as the default
1656 scaling driver for the supported processors
1657 passive
1658 Use intel_pstate as a scaling driver, but configure it
1659 to work with generic cpufreq governors (instead of
1660 enabling its internal governor). This mode cannot be
1661 used along with the hardware-managed P-states (HWP)
1662 feature.
1663 force
1664 Enable intel_pstate on systems that prohibit it by default
1665 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1666 instead of acpi-cpufreq may disable platform features, such
1667 as thermal controls and power capping, that rely on ACPI
1668 P-States information being indicated to OSPM and therefore
1669 should be used with caution. This option does not work with
1670 processors that aren't supported by the intel_pstate driver
1671 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1672 no_hwp
1673 Do not enable hardware P state control (HWP)
1674 if available.
1675 hwp_only
1676 Only load intel_pstate on systems which support
1677 hardware P state control (HWP) if available.
1678 support_acpi_ppc
1679 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1680 Description Table, specifies preferred power management
1681 profile as "Enterprise Server" or "Performance Server",
1682 then this feature is turned on by default.
1683 per_cpu_perf_limits
1684 Allow per-logical-CPU P-State performance control limits using
1685 cpufreq sysfs interface
1686
1687 intremap= [X86-64, Intel-IOMMU]
1688 on enable Interrupt Remapping (default)
1689 off disable Interrupt Remapping
1690 nosid disable Source ID checking
1691 no_x2apic_optout
1692 BIOS x2APIC opt-out request will be ignored
1693 nopost disable Interrupt Posting
1694
1695 iomem= Disable strict checking of access to MMIO memory
1696 strict regions from userspace.
1697 relaxed
1698
1699 iommu= [x86]
1700 off
1701 force
1702 noforce
1703 biomerge
1704 panic
1705 nopanic
1706 merge
1707 nomerge
1708 forcesac
1709 soft
1710 pt [x86, IA-64]
1711 nobypass [PPC/POWERNV]
1712 Disable IOMMU bypass, using IOMMU for PCI devices.
1713
1714 iommu.passthrough=
1715 [ARM64] Configure DMA to bypass the IOMMU by default.
1716 Format: { "0" | "1" }
1717 0 - Use IOMMU translation for DMA.
1718 1 - Bypass the IOMMU for DMA.
1719 unset - Use IOMMU translation for DMA.
1720
1721 io7= [HW] IO7 for Marvel based alpha systems
1722 See comment before marvel_specify_io7 in
1723 arch/alpha/kernel/core_marvel.c.
1724
1725 io_delay= [X86] I/O delay method
1726 0x80
1727 Standard port 0x80 based delay
1728 0xed
1729 Alternate port 0xed based delay (needed on some systems)
1730 udelay
1731 Simple two microseconds delay
1732 none
1733 No delay
1734
1735 ip= [IP_PNP]
1736 See Documentation/filesystems/nfs/nfsroot.txt.
1737
1738 irqaffinity= [SMP] Set the default irq affinity mask
1739 The argument is a cpu list, as described above.
1740
1741 irqchip.gicv2_force_probe=
1742 [ARM, ARM64]
1743 Format: <bool>
1744 Force the kernel to look for the second 4kB page
1745 of a GICv2 controller even if the memory range
1746 exposed by the device tree is too small.
1747
1748 irqchip.gicv3_nolpi=
1749 [ARM, ARM64]
1750 Force the kernel to ignore the availability of
1751 LPIs (and by consequence ITSs). Intended for system
1752 that use the kernel as a bootloader, and thus want
1753 to let secondary kernels in charge of setting up
1754 LPIs.
1755
1756 irqfixup [HW]
1757 When an interrupt is not handled search all handlers
1758 for it. Intended to get systems with badly broken
1759 firmware running.
1760
1761 irqpoll [HW]
1762 When an interrupt is not handled search all handlers
1763 for it. Also check all handlers each timer
1764 interrupt. Intended to get systems with badly broken
1765 firmware running.
1766
1767 isapnp= [ISAPNP]
1768 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1769
1770 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1771 [Deprecated - use cpusets instead]
1772 Format: [flag-list,]<cpu-list>
1773
1774 Specify one or more CPUs to isolate from disturbances
1775 specified in the flag list (default: domain):
1776
1777 nohz
1778 Disable the tick when a single task runs.
1779
1780 A residual 1Hz tick is offloaded to workqueues, which you
1781 need to affine to housekeeping through the global
1782 workqueue's affinity configured via the
1783 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1784 by using the 'domain' flag described below.
1785
1786 NOTE: by default the global workqueue runs on all CPUs,
1787 so to protect individual CPUs the 'cpumask' file has to
1788 be configured manually after bootup.
1789
1790 domain
1791 Isolate from the general SMP balancing and scheduling
1792 algorithms. Note that performing domain isolation this way
1793 is irreversible: it's not possible to bring back a CPU to
1794 the domains once isolated through isolcpus. It's strongly
1795 advised to use cpusets instead to disable scheduler load
1796 balancing through the "cpuset.sched_load_balance" file.
1797 It offers a much more flexible interface where CPUs can
1798 move in and out of an isolated set anytime.
1799
1800 You can move a process onto or off an "isolated" CPU via
1801 the CPU affinity syscalls or cpuset.
1802 <cpu number> begins at 0 and the maximum value is
1803 "number of CPUs in system - 1".
1804
1805 The format of <cpu-list> is described above.
1806
1807
1808
1809 iucv= [HW,NET]
1810
1811 ivrs_ioapic [HW,X86_64]
1812 Provide an override to the IOAPIC-ID<->DEVICE-ID
1813 mapping provided in the IVRS ACPI table. For
1814 example, to map IOAPIC-ID decimal 10 to
1815 PCI device 00:14.0 write the parameter as:
1816 ivrs_ioapic[10]=00:14.0
1817
1818 ivrs_hpet [HW,X86_64]
1819 Provide an override to the HPET-ID<->DEVICE-ID
1820 mapping provided in the IVRS ACPI table. For
1821 example, to map HPET-ID decimal 0 to
1822 PCI device 00:14.0 write the parameter as:
1823 ivrs_hpet[0]=00:14.0
1824
1825 ivrs_acpihid [HW,X86_64]
1826 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1827 mapping provided in the IVRS ACPI table. For
1828 example, to map UART-HID:UID AMD0020:0 to
1829 PCI device 00:14.5 write the parameter as:
1830 ivrs_acpihid[00:14.5]=AMD0020:0
1831
1832 js= [HW,JOY] Analog joystick
1833 See Documentation/input/joydev/joystick.rst.
1834
1835 nokaslr [KNL]
1836 When CONFIG_RANDOMIZE_BASE is set, this disables
1837 kernel and module base offset ASLR (Address Space
1838 Layout Randomization).
1839
1840 kasan_multi_shot
1841 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1842 report on every invalid memory access. Without this
1843 parameter KASAN will print report only for the first
1844 invalid access.
1845
1846 keepinitrd [HW,ARM]
1847
1848 kernelcore= [KNL,X86,IA-64,PPC]
1849 Format: nn[KMGTPE] | nn% | "mirror"
1850 This parameter specifies the amount of memory usable by
1851 the kernel for non-movable allocations. The requested
1852 amount is spread evenly throughout all nodes in the
1853 system as ZONE_NORMAL. The remaining memory is used for
1854 movable memory in its own zone, ZONE_MOVABLE. In the
1855 event, a node is too small to have both ZONE_NORMAL and
1856 ZONE_MOVABLE, kernelcore memory will take priority and
1857 other nodes will have a larger ZONE_MOVABLE.
1858
1859 ZONE_MOVABLE is used for the allocation of pages that
1860 may be reclaimed or moved by the page migration
1861 subsystem. Note that allocations like PTEs-from-HighMem
1862 still use the HighMem zone if it exists, and the Normal
1863 zone if it does not.
1864
1865 It is possible to specify the exact amount of memory in
1866 the form of "nn[KMGTPE]", a percentage of total system
1867 memory in the form of "nn%", or "mirror". If "mirror"
1868 option is specified, mirrored (reliable) memory is used
1869 for non-movable allocations and remaining memory is used
1870 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1871 are exclusive, so you cannot specify multiple forms.
1872
1873 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1874 Format: <Controller#>[,poll interval]
1875 The controller # is the number of the ehci usb debug
1876 port as it is probed via PCI. The poll interval is
1877 optional and is the number seconds in between
1878 each poll cycle to the debug port in case you need
1879 the functionality for interrupting the kernel with
1880 gdb or control-c on the dbgp connection. When
1881 not using this parameter you use sysrq-g to break into
1882 the kernel debugger.
1883
1884 kgdboc= [KGDB,HW] kgdb over consoles.
1885 Requires a tty driver that supports console polling,
1886 or a supported polling keyboard driver (non-usb).
1887 Serial only format: <serial_device>[,baud]
1888 keyboard only format: kbd
1889 keyboard and serial format: kbd,<serial_device>[,baud]
1890 Optional Kernel mode setting:
1891 kms, kbd format: kms,kbd
1892 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1893
1894 kgdbwait [KGDB] Stop kernel execution and enter the
1895 kernel debugger at the earliest opportunity.
1896
1897 kmac= [MIPS] korina ethernet MAC address.
1898 Configure the RouterBoard 532 series on-chip
1899 Ethernet adapter MAC address.
1900
1901 kmemleak= [KNL] Boot-time kmemleak enable/disable
1902 Valid arguments: on, off
1903 Default: on
1904 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1905 the default is off.
1906
1907 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1908 Default is 0 (don't ignore, but inject #GP)
1909
1910 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1911 Default is false (don't support).
1912
1913 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1914 KVM MMU at runtime.
1915 Default is 0 (off)
1916
1917 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1918 Default is 1 (enabled)
1919
1920 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1921 for all guests.
1922 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1923
1924 kvm-arm.vgic_v3_group0_trap=
1925 [KVM,ARM] Trap guest accesses to GICv3 group-0
1926 system registers
1927
1928 kvm-arm.vgic_v3_group1_trap=
1929 [KVM,ARM] Trap guest accesses to GICv3 group-1
1930 system registers
1931
1932 kvm-arm.vgic_v3_common_trap=
1933 [KVM,ARM] Trap guest accesses to GICv3 common
1934 system registers
1935
1936 kvm-arm.vgic_v4_enable=
1937 [KVM,ARM] Allow use of GICv4 for direct injection of
1938 LPIs.
1939
1940 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1941 (virtualized MMU) support on capable Intel chips.
1942 Default is 1 (enabled)
1943
1944 kvm-intel.emulate_invalid_guest_state=
1945 [KVM,Intel] Enable emulation of invalid guest states
1946 Default is 0 (disabled)
1947
1948 kvm-intel.flexpriority=
1949 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1950 Default is 1 (enabled)
1951
1952 kvm-intel.nested=
1953 [KVM,Intel] Enable VMX nesting (nVMX).
1954 Default is 0 (disabled)
1955
1956 kvm-intel.unrestricted_guest=
1957 [KVM,Intel] Disable unrestricted guest feature
1958 (virtualized real and unpaged mode) on capable
1959 Intel chips. Default is 1 (enabled)
1960
1961 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1962 feature (tagged TLBs) on capable Intel chips.
1963 Default is 1 (enabled)
1964
1965 l2cr= [PPC]
1966
1967 l3cr= [PPC]
1968
1969 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1970 disabled it.
1971
1972 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1973 value for LAPIC timer one-shot implementation. Default
1974 back to the programmable timer unit in the LAPIC.
1975
1976 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1977 in C2 power state.
1978
1979 libata.dma= [LIBATA] DMA control
1980 libata.dma=0 Disable all PATA and SATA DMA
1981 libata.dma=1 PATA and SATA Disk DMA only
1982 libata.dma=2 ATAPI (CDROM) DMA only
1983 libata.dma=4 Compact Flash DMA only
1984 Combinations also work, so libata.dma=3 enables DMA
1985 for disks and CDROMs, but not CFs.
1986
1987 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1988 libata.ignore_hpa=0 keep BIOS limits (default)
1989 libata.ignore_hpa=1 ignore limits, using full disk
1990
1991 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1992 when set.
1993 Format: <int>
1994
1995 libata.force= [LIBATA] Force configurations. The format is comma
1996 separated list of "[ID:]VAL" where ID is
1997 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1998 matching port, link or device. Basically, it matches
1999 the ATA ID string printed on console by libata. If
2000 the whole ID part is omitted, the last PORT and DEVICE
2001 values are used. If ID hasn't been specified yet, the
2002 configuration applies to all ports, links and devices.
2003
2004 If only DEVICE is omitted, the parameter applies to
2005 the port and all links and devices behind it. DEVICE
2006 number of 0 either selects the first device or the
2007 first fan-out link behind PMP device. It does not
2008 select the host link. DEVICE number of 15 selects the
2009 host link and device attached to it.
2010
2011 The VAL specifies the configuration to force. As long
2012 as there's no ambiguity shortcut notation is allowed.
2013 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2014 The following configurations can be forced.
2015
2016 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2017 Any ID with matching PORT is used.
2018
2019 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2020
2021 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2022 udma[/][16,25,33,44,66,100,133] notation is also
2023 allowed.
2024
2025 * [no]ncq: Turn on or off NCQ.
2026
2027 * [no]ncqtrim: Turn off queued DSM TRIM.
2028
2029 * nohrst, nosrst, norst: suppress hard, soft
2030 and both resets.
2031
2032 * rstonce: only attempt one reset during
2033 hot-unplug link recovery
2034
2035 * dump_id: dump IDENTIFY data.
2036
2037 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2038
2039 * disable: Disable this device.
2040
2041 If there are multiple matching configurations changing
2042 the same attribute, the last one is used.
2043
2044 memblock=debug [KNL] Enable memblock debug messages.
2045
2046 load_ramdisk= [RAM] List of ramdisks to load from floppy
2047 See Documentation/blockdev/ramdisk.txt.
2048
2049 lockd.nlm_grace_period=P [NFS] Assign grace period.
2050 Format: <integer>
2051
2052 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2053 Format: <integer>
2054
2055 lockd.nlm_timeout=T [NFS] Assign timeout value.
2056 Format: <integer>
2057
2058 lockd.nlm_udpport=M [NFS] Assign UDP port.
2059 Format: <integer>
2060
2061 locktorture.nreaders_stress= [KNL]
2062 Set the number of locking read-acquisition kthreads.
2063 Defaults to being automatically set based on the
2064 number of online CPUs.
2065
2066 locktorture.nwriters_stress= [KNL]
2067 Set the number of locking write-acquisition kthreads.
2068
2069 locktorture.onoff_holdoff= [KNL]
2070 Set time (s) after boot for CPU-hotplug testing.
2071
2072 locktorture.onoff_interval= [KNL]
2073 Set time (s) between CPU-hotplug operations, or
2074 zero to disable CPU-hotplug testing.
2075
2076 locktorture.shuffle_interval= [KNL]
2077 Set task-shuffle interval (jiffies). Shuffling
2078 tasks allows some CPUs to go into dyntick-idle
2079 mode during the locktorture test.
2080
2081 locktorture.shutdown_secs= [KNL]
2082 Set time (s) after boot system shutdown. This
2083 is useful for hands-off automated testing.
2084
2085 locktorture.stat_interval= [KNL]
2086 Time (s) between statistics printk()s.
2087
2088 locktorture.stutter= [KNL]
2089 Time (s) to stutter testing, for example,
2090 specifying five seconds causes the test to run for
2091 five seconds, wait for five seconds, and so on.
2092 This tests the locking primitive's ability to
2093 transition abruptly to and from idle.
2094
2095 locktorture.torture_type= [KNL]
2096 Specify the locking implementation to test.
2097
2098 locktorture.verbose= [KNL]
2099 Enable additional printk() statements.
2100
2101 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2102 Format: <irq>
2103
2104 loglevel= All Kernel Messages with a loglevel smaller than the
2105 console loglevel will be printed to the console. It can
2106 also be changed with klogd or other programs. The
2107 loglevels are defined as follows:
2108
2109 0 (KERN_EMERG) system is unusable
2110 1 (KERN_ALERT) action must be taken immediately
2111 2 (KERN_CRIT) critical conditions
2112 3 (KERN_ERR) error conditions
2113 4 (KERN_WARNING) warning conditions
2114 5 (KERN_NOTICE) normal but significant condition
2115 6 (KERN_INFO) informational
2116 7 (KERN_DEBUG) debug-level messages
2117
2118 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2119 in bytes. n must be a power of two and greater
2120 than the minimal size. The minimal size is defined
2121 by LOG_BUF_SHIFT kernel config parameter. There is
2122 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2123 that allows to increase the default size depending on
2124 the number of CPUs. See init/Kconfig for more details.
2125
2126 logo.nologo [FB] Disables display of the built-in Linux logo.
2127 This may be used to provide more screen space for
2128 kernel log messages and is useful when debugging
2129 kernel boot problems.
2130
2131 lp=0 [LP] Specify parallel ports to use, e.g,
2132 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2133 lp=reset first parallel port). 'lp=0' disables the
2134 lp=auto printer driver. 'lp=reset' (which can be
2135 specified in addition to the ports) causes
2136 attached printers to be reset. Using
2137 lp=port1,port2,... specifies the parallel ports
2138 to associate lp devices with, starting with
2139 lp0. A port specification may be 'none' to skip
2140 that lp device, or a parport name such as
2141 'parport0'. Specifying 'lp=auto' instead of a
2142 port specification list means that device IDs
2143 from each port should be examined, to see if
2144 an IEEE 1284-compliant printer is attached; if
2145 so, the driver will manage that printer.
2146 See also header of drivers/char/lp.c.
2147
2148 lpj=n [KNL]
2149 Sets loops_per_jiffy to given constant, thus avoiding
2150 time-consuming boot-time autodetection (up to 250 ms per
2151 CPU). 0 enables autodetection (default). To determine
2152 the correct value for your kernel, boot with normal
2153 autodetection and see what value is printed. Note that
2154 on SMP systems the preset will be applied to all CPUs,
2155 which is likely to cause problems if your CPUs need
2156 significantly divergent settings. An incorrect value
2157 will cause delays in the kernel to be wrong, leading to
2158 unpredictable I/O errors and other breakage. Although
2159 unlikely, in the extreme case this might damage your
2160 hardware.
2161
2162 ltpc= [NET]
2163 Format: <io>,<irq>,<dma>
2164
2165 machvec= [IA-64] Force the use of a particular machine-vector
2166 (machvec) in a generic kernel.
2167 Example: machvec=hpzx1_swiotlb
2168
2169 machtype= [Loongson] Share the same kernel image file between different
2170 yeeloong laptop.
2171 Example: machtype=lemote-yeeloong-2f-7inch
2172
2173 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2174 than or equal to this physical address is ignored.
2175
2176 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2177 will bring up during bootup. maxcpus=n : n >= 0 limits
2178 the kernel to bring up 'n' processors. Surely after
2179 bootup you can bring up the other plugged cpu by executing
2180 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2181 only takes effect during system bootup.
2182 While n=0 is a special case, it is equivalent to "nosmp",
2183 which also disables the IO APIC.
2184
2185 max_loop= [LOOP] The number of loop block devices that get
2186 (loop.max_loop) unconditionally pre-created at init time. The default
2187 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2188 of statically allocating a predefined number, loop
2189 devices can be requested on-demand with the
2190 /dev/loop-control interface.
2191
2192 mce [X86-32] Machine Check Exception
2193
2194 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2195
2196 md= [HW] RAID subsystems devices and level
2197 See Documentation/admin-guide/md.rst.
2198
2199 mdacon= [MDA]
2200 Format: <first>,<last>
2201 Specifies range of consoles to be captured by the MDA.
2202
2203 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2204 Amount of memory to be used when the kernel is not able
2205 to see the whole system memory or for test.
2206 [X86] Work as limiting max address. Use together
2207 with memmap= to avoid physical address space collisions.
2208 Without memmap= PCI devices could be placed at addresses
2209 belonging to unused RAM.
2210
2211 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2212 memory.
2213
2214 memchunk=nn[KMG]
2215 [KNL,SH] Allow user to override the default size for
2216 per-device physically contiguous DMA buffers.
2217
2218 memhp_default_state=online/offline
2219 [KNL] Set the initial state for the memory hotplug
2220 onlining policy. If not specified, the default value is
2221 set according to the
2222 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2223 option.
2224 See Documentation/memory-hotplug.txt.
2225
2226 memmap=exactmap [KNL,X86] Enable setting of an exact
2227 E820 memory map, as specified by the user.
2228 Such memmap=exactmap lines can be constructed based on
2229 BIOS output or other requirements. See the memmap=nn@ss
2230 option description.
2231
2232 memmap=nn[KMG]@ss[KMG]
2233 [KNL] Force usage of a specific region of memory.
2234 Region of memory to be used is from ss to ss+nn.
2235 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2236 which limits max address to nn[KMG].
2237 Multiple different regions can be specified,
2238 comma delimited.
2239 Example:
2240 memmap=100M@2G,100M#3G,1G!1024G
2241
2242 memmap=nn[KMG]#ss[KMG]
2243 [KNL,ACPI] Mark specific memory as ACPI data.
2244 Region of memory to be marked is from ss to ss+nn.
2245
2246 memmap=nn[KMG]$ss[KMG]
2247 [KNL,ACPI] Mark specific memory as reserved.
2248 Region of memory to be reserved is from ss to ss+nn.
2249 Example: Exclude memory from 0x18690000-0x1869ffff
2250 memmap=64K$0x18690000
2251 or
2252 memmap=0x10000$0x18690000
2253 Some bootloaders may need an escape character before '$',
2254 like Grub2, otherwise '$' and the following number
2255 will be eaten.
2256
2257 memmap=nn[KMG]!ss[KMG]
2258 [KNL,X86] Mark specific memory as protected.
2259 Region of memory to be used, from ss to ss+nn.
2260 The memory region may be marked as e820 type 12 (0xc)
2261 and is NVDIMM or ADR memory.
2262
2263 memmap=<size>%<offset>-<oldtype>+<newtype>
2264 [KNL,ACPI] Convert memory within the specified region
2265 from <oldtype> to <newtype>. If "-<oldtype>" is left
2266 out, the whole region will be marked as <newtype>,
2267 even if previously unavailable. If "+<newtype>" is left
2268 out, matching memory will be removed. Types are
2269 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2270 3 = ACPI, 12 = PRAM.
2271
2272 memory_corruption_check=0/1 [X86]
2273 Some BIOSes seem to corrupt the first 64k of
2274 memory when doing things like suspend/resume.
2275 Setting this option will scan the memory
2276 looking for corruption. Enabling this will
2277 both detect corruption and prevent the kernel
2278 from using the memory being corrupted.
2279 However, its intended as a diagnostic tool; if
2280 repeatable BIOS-originated corruption always
2281 affects the same memory, you can use memmap=
2282 to prevent the kernel from using that memory.
2283
2284 memory_corruption_check_size=size [X86]
2285 By default it checks for corruption in the low
2286 64k, making this memory unavailable for normal
2287 use. Use this parameter to scan for
2288 corruption in more or less memory.
2289
2290 memory_corruption_check_period=seconds [X86]
2291 By default it checks for corruption every 60
2292 seconds. Use this parameter to check at some
2293 other rate. 0 disables periodic checking.
2294
2295 memtest= [KNL,X86,ARM] Enable memtest
2296 Format: <integer>
2297 default : 0 <disable>
2298 Specifies the number of memtest passes to be
2299 performed. Each pass selects another test
2300 pattern from a given set of patterns. Memtest
2301 fills the memory with this pattern, validates
2302 memory contents and reserves bad memory
2303 regions that are detected.
2304
2305 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2306 Valid arguments: on, off
2307 Default (depends on kernel configuration option):
2308 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2309 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2310 mem_encrypt=on: Activate SME
2311 mem_encrypt=off: Do not activate SME
2312
2313 Refer to Documentation/x86/amd-memory-encryption.txt
2314 for details on when memory encryption can be activated.
2315
2316 mem_sleep_default= [SUSPEND] Default system suspend mode:
2317 s2idle - Suspend-To-Idle
2318 shallow - Power-On Suspend or equivalent (if supported)
2319 deep - Suspend-To-RAM or equivalent (if supported)
2320 See Documentation/admin-guide/pm/sleep-states.rst.
2321
2322 meye.*= [HW] Set MotionEye Camera parameters
2323 See Documentation/media/v4l-drivers/meye.rst.
2324
2325 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2326 Multi-Function General Purpose Timers on AMD Geode
2327 platforms.
2328
2329 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2330 the BIOS has incorrectly applied a workaround. TinyBIOS
2331 version 0.98 is known to be affected, 0.99 fixes the
2332 problem by letting the user disable the workaround.
2333
2334 mga= [HW,DRM]
2335
2336 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2337 physical address is ignored.
2338
2339 mini2440= [ARM,HW,KNL]
2340 Format:[0..2][b][c][t]
2341 Default: "0tb"
2342 MINI2440 configuration specification:
2343 0 - The attached screen is the 3.5" TFT
2344 1 - The attached screen is the 7" TFT
2345 2 - The VGA Shield is attached (1024x768)
2346 Leaving out the screen size parameter will not load
2347 the TFT driver, and the framebuffer will be left
2348 unconfigured.
2349 b - Enable backlight. The TFT backlight pin will be
2350 linked to the kernel VESA blanking code and a GPIO
2351 LED. This parameter is not necessary when using the
2352 VGA shield.
2353 c - Enable the s3c camera interface.
2354 t - Reserved for enabling touchscreen support. The
2355 touchscreen support is not enabled in the mainstream
2356 kernel as of 2.6.30, a preliminary port can be found
2357 in the "bleeding edge" mini2440 support kernel at
2358 http://repo.or.cz/w/linux-2.6/mini2440.git
2359
2360 mminit_loglevel=
2361 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2362 parameter allows control of the logging verbosity for
2363 the additional memory initialisation checks. A value
2364 of 0 disables mminit logging and a level of 4 will
2365 log everything. Information is printed at KERN_DEBUG
2366 so loglevel=8 may also need to be specified.
2367
2368 module.sig_enforce
2369 [KNL] When CONFIG_MODULE_SIG is set, this means that
2370 modules without (valid) signatures will fail to load.
2371 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2372 is always true, so this option does nothing.
2373
2374 module_blacklist= [KNL] Do not load a comma-separated list of
2375 modules. Useful for debugging problem modules.
2376
2377 mousedev.tap_time=
2378 [MOUSE] Maximum time between finger touching and
2379 leaving touchpad surface for touch to be considered
2380 a tap and be reported as a left button click (for
2381 touchpads working in absolute mode only).
2382 Format: <msecs>
2383 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2384 reporting absolute coordinates, such as tablets
2385 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2386 reporting absolute coordinates, such as tablets
2387
2388 movablecore= [KNL,X86,IA-64,PPC]
2389 Format: nn[KMGTPE] | nn%
2390 This parameter is the complement to kernelcore=, it
2391 specifies the amount of memory used for migratable
2392 allocations. If both kernelcore and movablecore is
2393 specified, then kernelcore will be at *least* the
2394 specified value but may be more. If movablecore on its
2395 own is specified, the administrator must be careful
2396 that the amount of memory usable for all allocations
2397 is not too small.
2398
2399 movable_node [KNL] Boot-time switch to make hotplugable memory
2400 NUMA nodes to be movable. This means that the memory
2401 of such nodes will be usable only for movable
2402 allocations which rules out almost all kernel
2403 allocations. Use with caution!
2404
2405 MTD_Partition= [MTD]
2406 Format: <name>,<region-number>,<size>,<offset>
2407
2408 MTD_Region= [MTD] Format:
2409 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2410
2411 mtdparts= [MTD]
2412 See drivers/mtd/cmdlinepart.c.
2413
2414 multitce=off [PPC] This parameter disables the use of the pSeries
2415 firmware feature for updating multiple TCE entries
2416 at a time.
2417
2418 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2419
2420 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2421
2422 boundary - index of last SLC block on Flex-OneNAND.
2423 The remaining blocks are configured as MLC blocks.
2424 lock - Configure if Flex-OneNAND boundary should be locked.
2425 Once locked, the boundary cannot be changed.
2426 1 indicates lock status, 0 indicates unlock status.
2427
2428 mtdset= [ARM]
2429 ARM/S3C2412 JIVE boot control
2430
2431 See arch/arm/mach-s3c2412/mach-jive.c
2432
2433 mtouchusb.raw_coordinates=
2434 [HW] Make the MicroTouch USB driver use raw coordinates
2435 ('y', default) or cooked coordinates ('n')
2436
2437 mtrr_chunk_size=nn[KMG] [X86]
2438 used for mtrr cleanup. It is largest continuous chunk
2439 that could hold holes aka. UC entries.
2440
2441 mtrr_gran_size=nn[KMG] [X86]
2442 Used for mtrr cleanup. It is granularity of mtrr block.
2443 Default is 1.
2444 Large value could prevent small alignment from
2445 using up MTRRs.
2446
2447 mtrr_spare_reg_nr=n [X86]
2448 Format: <integer>
2449 Range: 0,7 : spare reg number
2450 Default : 1
2451 Used for mtrr cleanup. It is spare mtrr entries number.
2452 Set to 2 or more if your graphical card needs more.
2453
2454 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2455
2456 netdev= [NET] Network devices parameters
2457 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2458 Note that mem_start is often overloaded to mean
2459 something different and driver-specific.
2460 This usage is only documented in each driver source
2461 file if at all.
2462
2463 nf_conntrack.acct=
2464 [NETFILTER] Enable connection tracking flow accounting
2465 0 to disable accounting
2466 1 to enable accounting
2467 Default value is 0.
2468
2469 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2470 See Documentation/filesystems/nfs/nfsroot.txt.
2471
2472 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2473 See Documentation/filesystems/nfs/nfsroot.txt.
2474
2475 nfsrootdebug [NFS] enable nfsroot debugging messages.
2476 See Documentation/filesystems/nfs/nfsroot.txt.
2477
2478 nfs.callback_nr_threads=
2479 [NFSv4] set the total number of threads that the
2480 NFS client will assign to service NFSv4 callback
2481 requests.
2482
2483 nfs.callback_tcpport=
2484 [NFS] set the TCP port on which the NFSv4 callback
2485 channel should listen.
2486
2487 nfs.cache_getent=
2488 [NFS] sets the pathname to the program which is used
2489 to update the NFS client cache entries.
2490
2491 nfs.cache_getent_timeout=
2492 [NFS] sets the timeout after which an attempt to
2493 update a cache entry is deemed to have failed.
2494
2495 nfs.idmap_cache_timeout=
2496 [NFS] set the maximum lifetime for idmapper cache
2497 entries.
2498
2499 nfs.enable_ino64=
2500 [NFS] enable 64-bit inode numbers.
2501 If zero, the NFS client will fake up a 32-bit inode
2502 number for the readdir() and stat() syscalls instead
2503 of returning the full 64-bit number.
2504 The default is to return 64-bit inode numbers.
2505
2506 nfs.max_session_cb_slots=
2507 [NFSv4.1] Sets the maximum number of session
2508 slots the client will assign to the callback
2509 channel. This determines the maximum number of
2510 callbacks the client will process in parallel for
2511 a particular server.
2512
2513 nfs.max_session_slots=
2514 [NFSv4.1] Sets the maximum number of session slots
2515 the client will attempt to negotiate with the server.
2516 This limits the number of simultaneous RPC requests
2517 that the client can send to the NFSv4.1 server.
2518 Note that there is little point in setting this
2519 value higher than the max_tcp_slot_table_limit.
2520
2521 nfs.nfs4_disable_idmapping=
2522 [NFSv4] When set to the default of '1', this option
2523 ensures that both the RPC level authentication
2524 scheme and the NFS level operations agree to use
2525 numeric uids/gids if the mount is using the
2526 'sec=sys' security flavour. In effect it is
2527 disabling idmapping, which can make migration from
2528 legacy NFSv2/v3 systems to NFSv4 easier.
2529 Servers that do not support this mode of operation
2530 will be autodetected by the client, and it will fall
2531 back to using the idmapper.
2532 To turn off this behaviour, set the value to '0'.
2533 nfs.nfs4_unique_id=
2534 [NFS4] Specify an additional fixed unique ident-
2535 ification string that NFSv4 clients can insert into
2536 their nfs_client_id4 string. This is typically a
2537 UUID that is generated at system install time.
2538
2539 nfs.send_implementation_id =
2540 [NFSv4.1] Send client implementation identification
2541 information in exchange_id requests.
2542 If zero, no implementation identification information
2543 will be sent.
2544 The default is to send the implementation identification
2545 information.
2546
2547 nfs.recover_lost_locks =
2548 [NFSv4] Attempt to recover locks that were lost due
2549 to a lease timeout on the server. Please note that
2550 doing this risks data corruption, since there are
2551 no guarantees that the file will remain unchanged
2552 after the locks are lost.
2553 If you want to enable the kernel legacy behaviour of
2554 attempting to recover these locks, then set this
2555 parameter to '1'.
2556 The default parameter value of '0' causes the kernel
2557 not to attempt recovery of lost locks.
2558
2559 nfs4.layoutstats_timer =
2560 [NFSv4.2] Change the rate at which the kernel sends
2561 layoutstats to the pNFS metadata server.
2562
2563 Setting this to value to 0 causes the kernel to use
2564 whatever value is the default set by the layout
2565 driver. A non-zero value sets the minimum interval
2566 in seconds between layoutstats transmissions.
2567
2568 nfsd.nfs4_disable_idmapping=
2569 [NFSv4] When set to the default of '1', the NFSv4
2570 server will return only numeric uids and gids to
2571 clients using auth_sys, and will accept numeric uids
2572 and gids from such clients. This is intended to ease
2573 migration from NFSv2/v3.
2574
2575 nmi_debug= [KNL,SH] Specify one or more actions to take
2576 when a NMI is triggered.
2577 Format: [state][,regs][,debounce][,die]
2578
2579 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2580 Format: [panic,][nopanic,][num]
2581 Valid num: 0 or 1
2582 0 - turn hardlockup detector in nmi_watchdog off
2583 1 - turn hardlockup detector in nmi_watchdog on
2584 When panic is specified, panic when an NMI watchdog
2585 timeout occurs (or 'nopanic' to override the opposite
2586 default). To disable both hard and soft lockup detectors,
2587 please see 'nowatchdog'.
2588 This is useful when you use a panic=... timeout and
2589 need the box quickly up again.
2590
2591 These settings can be accessed at runtime via
2592 the nmi_watchdog and hardlockup_panic sysctls.
2593
2594 netpoll.carrier_timeout=
2595 [NET] Specifies amount of time (in seconds) that
2596 netpoll should wait for a carrier. By default netpoll
2597 waits 4 seconds.
2598
2599 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2600 emulation library even if a 387 maths coprocessor
2601 is present.
2602
2603 no_console_suspend
2604 [HW] Never suspend the console
2605 Disable suspending of consoles during suspend and
2606 hibernate operations. Once disabled, debugging
2607 messages can reach various consoles while the rest
2608 of the system is being put to sleep (ie, while
2609 debugging driver suspend/resume hooks). This may
2610 not work reliably with all consoles, but is known
2611 to work with serial and VGA consoles.
2612 To facilitate more flexible debugging, we also add
2613 console_suspend, a printk module parameter to control
2614 it. Users could use console_suspend (usually
2615 /sys/module/printk/parameters/console_suspend) to
2616 turn on/off it dynamically.
2617
2618 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2619 caches in the slab allocator. Saves per-node memory,
2620 but will impact performance.
2621
2622 noalign [KNL,ARM]
2623
2624 noaltinstr [S390] Disables alternative instructions patching
2625 (CPU alternatives feature).
2626
2627 noapic [SMP,APIC] Tells the kernel to not make use of any
2628 IOAPICs that may be present in the system.
2629
2630 noautogroup Disable scheduler automatic task group creation.
2631
2632 nobats [PPC] Do not use BATs for mapping kernel lowmem
2633 on "Classic" PPC cores.
2634
2635 nocache [ARM]
2636
2637 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2638
2639 nodelayacct [KNL] Disable per-task delay accounting
2640
2641 nodsp [SH] Disable hardware DSP at boot time.
2642
2643 noefi Disable EFI runtime services support.
2644
2645 noexec [IA-64]
2646
2647 noexec [X86]
2648 On X86-32 available only on PAE configured kernels.
2649 noexec=on: enable non-executable mappings (default)
2650 noexec=off: disable non-executable mappings
2651
2652 nosmap [X86]
2653 Disable SMAP (Supervisor Mode Access Prevention)
2654 even if it is supported by processor.
2655
2656 nosmep [X86]
2657 Disable SMEP (Supervisor Mode Execution Prevention)
2658 even if it is supported by processor.
2659
2660 noexec32 [X86-64]
2661 This affects only 32-bit executables.
2662 noexec32=on: enable non-executable mappings (default)
2663 read doesn't imply executable mappings
2664 noexec32=off: disable non-executable mappings
2665 read implies executable mappings
2666
2667 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2668
2669 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2670 register save and restore. The kernel will only save
2671 legacy floating-point registers on task switch.
2672
2673 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2674
2675 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2676 Equivalent to smt=1.
2677
2678 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2679 (indirect branch prediction) vulnerability. System may
2680 allow data leaks with this option, which is equivalent
2681 to spectre_v2=off.
2682
2683 nospec_store_bypass_disable
2684 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2685
2686 noxsave [BUGS=X86] Disables x86 extended register state save
2687 and restore using xsave. The kernel will fallback to
2688 enabling legacy floating-point and sse state.
2689
2690 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2691 register states. The kernel will fall back to use
2692 xsave to save the states. By using this parameter,
2693 performance of saving the states is degraded because
2694 xsave doesn't support modified optimization while
2695 xsaveopt supports it on xsaveopt enabled systems.
2696
2697 noxsaves [X86] Disables xsaves and xrstors used in saving and
2698 restoring x86 extended register state in compacted
2699 form of xsave area. The kernel will fall back to use
2700 xsaveopt and xrstor to save and restore the states
2701 in standard form of xsave area. By using this
2702 parameter, xsave area per process might occupy more
2703 memory on xsaves enabled systems.
2704
2705 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2706 wfi(ARM) instruction doesn't work correctly and not to
2707 use it. This is also useful when using JTAG debugger.
2708
2709 no_file_caps Tells the kernel not to honor file capabilities. The
2710 only way then for a file to be executed with privilege
2711 is to be setuid root or executed by root.
2712
2713 nohalt [IA-64] Tells the kernel not to use the power saving
2714 function PAL_HALT_LIGHT when idle. This increases
2715 power-consumption. On the positive side, it reduces
2716 interrupt wake-up latency, which may improve performance
2717 in certain environments such as networked servers or
2718 real-time systems.
2719
2720 nohibernate [HIBERNATION] Disable hibernation and resume.
2721
2722 nohz= [KNL] Boottime enable/disable dynamic ticks
2723 Valid arguments: on, off
2724 Default: on
2725
2726 nohz_full= [KNL,BOOT,SMP,ISOL]
2727 The argument is a cpu list, as described above.
2728 In kernels built with CONFIG_NO_HZ_FULL=y, set
2729 the specified list of CPUs whose tick will be stopped
2730 whenever possible. The boot CPU will be forced outside
2731 the range to maintain the timekeeping. Any CPUs
2732 in this list will have their RCU callbacks offloaded,
2733 just as if they had also been called out in the
2734 rcu_nocbs= boot parameter.
2735
2736 noiotrap [SH] Disables trapped I/O port accesses.
2737
2738 noirqdebug [X86-32] Disables the code which attempts to detect and
2739 disable unhandled interrupt sources.
2740
2741 no_timer_check [X86,APIC] Disables the code which tests for
2742 broken timer IRQ sources.
2743
2744 noisapnp [ISAPNP] Disables ISA PnP code.
2745
2746 noinitrd [RAM] Tells the kernel not to load any configured
2747 initial RAM disk.
2748
2749 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2750 remapping.
2751 [Deprecated - use intremap=off]
2752
2753 nointroute [IA-64]
2754
2755 noinvpcid [X86] Disable the INVPCID cpu feature.
2756
2757 nojitter [IA-64] Disables jitter checking for ITC timers.
2758
2759 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2760
2761 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2762 fault handling.
2763
2764 no-vmw-sched-clock
2765 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2766 clock and use the default one.
2767
2768 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2769 steal time is computed, but won't influence scheduler
2770 behaviour
2771
2772 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2773
2774 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2775
2776 noltlbs [PPC] Do not use large page/tlb entries for kernel
2777 lowmem mapping on PPC40x and PPC8xx
2778
2779 nomca [IA-64] Disable machine check abort handling
2780
2781 nomce [X86-32] Disable Machine Check Exception
2782
2783 nomfgpt [X86-32] Disable Multi-Function General Purpose
2784 Timer usage (for AMD Geode machines).
2785
2786 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2787 shutdown the other cpus. Instead use the REBOOT_VECTOR
2788 irq.
2789
2790 nomodule Disable module load
2791
2792 nopat [X86] Disable PAT (page attribute table extension of
2793 pagetables) support.
2794
2795 nopcid [X86-64] Disable the PCID cpu feature.
2796
2797 norandmaps Don't use address space randomization. Equivalent to
2798 echo 0 > /proc/sys/kernel/randomize_va_space
2799
2800 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2801 with UP alternatives
2802
2803 nordrand [X86] Disable kernel use of the RDRAND and
2804 RDSEED instructions even if they are supported
2805 by the processor. RDRAND and RDSEED are still
2806 available to user space applications.
2807
2808 noresume [SWSUSP] Disables resume and restores original swap
2809 space.
2810
2811 no-scroll [VGA] Disables scrollback.
2812 This is required for the Braillex ib80-piezo Braille
2813 reader made by F.H. Papenmeier (Germany).
2814
2815 nosbagart [IA-64]
2816
2817 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2818
2819 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2820 and disable the IO APIC. legacy for "maxcpus=0".
2821
2822 nosoftlockup [KNL] Disable the soft-lockup detector.
2823
2824 nosync [HW,M68K] Disables sync negotiation for all devices.
2825
2826 notsc [BUGS=X86-32] Disable Time Stamp Counter
2827
2828 nowatchdog [KNL] Disable both lockup detectors, i.e.
2829 soft-lockup and NMI watchdog (hard-lockup).
2830
2831 nowb [ARM]
2832
2833 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2834
2835 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2836 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2837 Some features depend on CPU0. Known dependencies are:
2838 1. Resume from suspend/hibernate depends on CPU0.
2839 Suspend/hibernate will fail if CPU0 is offline and you
2840 need to online CPU0 before suspend/hibernate.
2841 2. PIC interrupts also depend on CPU0. CPU0 can't be
2842 removed if a PIC interrupt is detected.
2843 It's said poweroff/reboot may depend on CPU0 on some
2844 machines although I haven't seen such issues so far
2845 after CPU0 is offline on a few tested machines.
2846 If the dependencies are under your control, you can
2847 turn on cpu0_hotplug.
2848
2849 nps_mtm_hs_ctr= [KNL,ARC]
2850 This parameter sets the maximum duration, in
2851 cycles, each HW thread of the CTOP can run
2852 without interruptions, before HW switches it.
2853 The actual maximum duration is 16 times this
2854 parameter's value.
2855 Format: integer between 1 and 255
2856 Default: 255
2857
2858 nptcg= [IA-64] Override max number of concurrent global TLB
2859 purges which is reported from either PAL_VM_SUMMARY or
2860 SAL PALO.
2861
2862 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2863 could support. nr_cpus=n : n >= 1 limits the kernel to
2864 support 'n' processors. It could be larger than the
2865 number of already plugged CPU during bootup, later in
2866 runtime you can physically add extra cpu until it reaches
2867 n. So during boot up some boot time memory for per-cpu
2868 variables need be pre-allocated for later physical cpu
2869 hot plugging.
2870
2871 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2872
2873 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2874 Allowed values are enable and disable
2875
2876 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2877 'node', 'default' can be specified
2878 This can be set from sysctl after boot.
2879 See Documentation/sysctl/vm.txt for details.
2880
2881 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2882 See Documentation/debugging-via-ohci1394.txt for more
2883 info.
2884
2885 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2886 Rather than timing out after 20 ms if an EC
2887 command is not properly ACKed, override the length
2888 of the timeout. We have interrupts disabled while
2889 waiting for the ACK, so if this is set too high
2890 interrupts *may* be lost!
2891
2892 omap_mux= [OMAP] Override bootloader pin multiplexing.
2893 Format: <mux_mode0.mode_name=value>...
2894 For example, to override I2C bus2:
2895 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2896
2897 oprofile.timer= [HW]
2898 Use timer interrupt instead of performance counters
2899
2900 oprofile.cpu_type= Force an oprofile cpu type
2901 This might be useful if you have an older oprofile
2902 userland or if you want common events.
2903 Format: { arch_perfmon }
2904 arch_perfmon: [X86] Force use of architectural
2905 perfmon on Intel CPUs instead of the
2906 CPU specific event set.
2907 timer: [X86] Force use of architectural NMI
2908 timer mode (see also oprofile.timer
2909 for generic hr timer mode)
2910
2911 oops=panic Always panic on oopses. Default is to just kill the
2912 process, but there is a small probability of
2913 deadlocking the machine.
2914 This will also cause panics on machine check exceptions.
2915 Useful together with panic=30 to trigger a reboot.
2916
2917 OSS [HW,OSS]
2918 See Documentation/sound/oss/oss-parameters.txt
2919
2920 page_owner= [KNL] Boot-time page_owner enabling option.
2921 Storage of the information about who allocated
2922 each page is disabled in default. With this switch,
2923 we can turn it on.
2924 on: enable the feature
2925
2926 page_poison= [KNL] Boot-time parameter changing the state of
2927 poisoning on the buddy allocator.
2928 off: turn off poisoning
2929 on: turn on poisoning
2930
2931 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2932 timeout > 0: seconds before rebooting
2933 timeout = 0: wait forever
2934 timeout < 0: reboot immediately
2935 Format: <timeout>
2936
2937 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2938 on a WARN().
2939
2940 crash_kexec_post_notifiers
2941 Run kdump after running panic-notifiers and dumping
2942 kmsg. This only for the users who doubt kdump always
2943 succeeds in any situation.
2944 Note that this also increases risks of kdump failure,
2945 because some panic notifiers can make the crashed
2946 kernel more unstable.
2947
2948 parkbd.port= [HW] Parallel port number the keyboard adapter is
2949 connected to, default is 0.
2950 Format: <parport#>
2951 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2952 0 for XT, 1 for AT (default is AT).
2953 Format: <mode>
2954
2955 parport= [HW,PPT] Specify parallel ports. 0 disables.
2956 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2957 Use 'auto' to force the driver to use any
2958 IRQ/DMA settings detected (the default is to
2959 ignore detected IRQ/DMA settings because of
2960 possible conflicts). You can specify the base
2961 address, IRQ, and DMA settings; IRQ and DMA
2962 should be numbers, or 'auto' (for using detected
2963 settings on that particular port), or 'nofifo'
2964 (to avoid using a FIFO even if it is detected).
2965 Parallel ports are assigned in the order they
2966 are specified on the command line, starting
2967 with parport0.
2968
2969 parport_init_mode= [HW,PPT]
2970 Configure VIA parallel port to operate in
2971 a specific mode. This is necessary on Pegasos
2972 computer where firmware has no options for setting
2973 up parallel port mode and sets it to spp.
2974 Currently this function knows 686a and 8231 chips.
2975 Format: [spp|ps2|epp|ecp|ecpepp]
2976
2977 pause_on_oops=
2978 Halt all CPUs after the first oops has been printed for
2979 the specified number of seconds. This is to be used if
2980 your oopses keep scrolling off the screen.
2981
2982 pcbit= [HW,ISDN]
2983
2984 pcd. [PARIDE]
2985 See header of drivers/block/paride/pcd.c.
2986 See also Documentation/blockdev/paride.txt.
2987
2988 pci=option[,option...] [PCI] various PCI subsystem options:
2989 earlydump [X86] dump PCI config space before the kernel
2990 changes anything
2991 off [X86] don't probe for the PCI bus
2992 bios [X86-32] force use of PCI BIOS, don't access
2993 the hardware directly. Use this if your machine
2994 has a non-standard PCI host bridge.
2995 nobios [X86-32] disallow use of PCI BIOS, only direct
2996 hardware access methods are allowed. Use this
2997 if you experience crashes upon bootup and you
2998 suspect they are caused by the BIOS.
2999 conf1 [X86] Force use of PCI Configuration Access
3000 Mechanism 1 (config address in IO port 0xCF8,
3001 data in IO port 0xCFC, both 32-bit).
3002 conf2 [X86] Force use of PCI Configuration Access
3003 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3004 the function, IO port 0xCFA, also 8-bit, sets
3005 bus number. The config space is then accessed
3006 through ports 0xC000-0xCFFF).
3007 See http://wiki.osdev.org/PCI for more info
3008 on the configuration access mechanisms.
3009 noaer [PCIE] If the PCIEAER kernel config parameter is
3010 enabled, this kernel boot option can be used to
3011 disable the use of PCIE advanced error reporting.
3012 nodomains [PCI] Disable support for multiple PCI
3013 root domains (aka PCI segments, in ACPI-speak).
3014 nommconf [X86] Disable use of MMCONFIG for PCI
3015 Configuration
3016 check_enable_amd_mmconf [X86] check for and enable
3017 properly configured MMIO access to PCI
3018 config space on AMD family 10h CPU
3019 nomsi [MSI] If the PCI_MSI kernel config parameter is
3020 enabled, this kernel boot option can be used to
3021 disable the use of MSI interrupts system-wide.
3022 noioapicquirk [APIC] Disable all boot interrupt quirks.
3023 Safety option to keep boot IRQs enabled. This
3024 should never be necessary.
3025 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3026 primary IO-APIC for bridges that cannot disable
3027 boot IRQs. This fixes a source of spurious IRQs
3028 when the system masks IRQs.
3029 noioapicreroute [APIC] Disable workaround that uses the
3030 boot IRQ equivalent of an IRQ that connects to
3031 a chipset where boot IRQs cannot be disabled.
3032 The opposite of ioapicreroute.
3033 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3034 routing table. These calls are known to be buggy
3035 on several machines and they hang the machine
3036 when used, but on other computers it's the only
3037 way to get the interrupt routing table. Try
3038 this option if the kernel is unable to allocate
3039 IRQs or discover secondary PCI buses on your
3040 motherboard.
3041 rom [X86] Assign address space to expansion ROMs.
3042 Use with caution as certain devices share
3043 address decoders between ROMs and other
3044 resources.
3045 norom [X86] Do not assign address space to
3046 expansion ROMs that do not already have
3047 BIOS assigned address ranges.
3048 nobar [X86] Do not assign address space to the
3049 BARs that weren't assigned by the BIOS.
3050 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3051 assigned automatically to PCI devices. You can
3052 make the kernel exclude IRQs of your ISA cards
3053 this way.
3054 pirqaddr=0xAAAAA [X86] Specify the physical address
3055 of the PIRQ table (normally generated
3056 by the BIOS) if it is outside the
3057 F0000h-100000h range.
3058 lastbus=N [X86] Scan all buses thru bus #N. Can be
3059 useful if the kernel is unable to find your
3060 secondary buses and you want to tell it
3061 explicitly which ones they are.
3062 assign-busses [X86] Always assign all PCI bus
3063 numbers ourselves, overriding
3064 whatever the firmware may have done.
3065 usepirqmask [X86] Honor the possible IRQ mask stored
3066 in the BIOS $PIR table. This is needed on
3067 some systems with broken BIOSes, notably
3068 some HP Pavilion N5400 and Omnibook XE3
3069 notebooks. This will have no effect if ACPI
3070 IRQ routing is enabled.
3071 noacpi [X86] Do not use ACPI for IRQ routing
3072 or for PCI scanning.
3073 use_crs [X86] Use PCI host bridge window information
3074 from ACPI. On BIOSes from 2008 or later, this
3075 is enabled by default. If you need to use this,
3076 please report a bug.
3077 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3078 If you need to use this, please report a bug.
3079 routeirq Do IRQ routing for all PCI devices.
3080 This is normally done in pci_enable_device(),
3081 so this option is a temporary workaround
3082 for broken drivers that don't call it.
3083 skip_isa_align [X86] do not align io start addr, so can
3084 handle more pci cards
3085 noearly [X86] Don't do any early type 1 scanning.
3086 This might help on some broken boards which
3087 machine check when some devices' config space
3088 is read. But various workarounds are disabled
3089 and some IOMMU drivers will not work.
3090 bfsort Sort PCI devices into breadth-first order.
3091 This sorting is done to get a device
3092 order compatible with older (<= 2.4) kernels.
3093 nobfsort Don't sort PCI devices into breadth-first order.
3094 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3095 tuning and use the BIOS-configured MPS defaults.
3096 pcie_bus_safe Set every device's MPS to the largest value
3097 supported by all devices below the root complex.
3098 pcie_bus_perf Set device MPS to the largest allowable MPS
3099 based on its parent bus. Also set MRRS (Max
3100 Read Request Size) to the largest supported
3101 value (no larger than the MPS that the device
3102 or bus can support) for best performance.
3103 pcie_bus_peer2peer Set every device's MPS to 128B, which
3104 every device is guaranteed to support. This
3105 configuration allows peer-to-peer DMA between
3106 any pair of devices, possibly at the cost of
3107 reduced performance. This also guarantees
3108 that hot-added devices will work.
3109 cbiosize=nn[KMG] The fixed amount of bus space which is
3110 reserved for the CardBus bridge's IO window.
3111 The default value is 256 bytes.
3112 cbmemsize=nn[KMG] The fixed amount of bus space which is
3113 reserved for the CardBus bridge's memory
3114 window. The default value is 64 megabytes.
3115 resource_alignment=
3116 Format:
3117 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3118 [<order of align>@]pci:<vendor>:<device>\
3119 [:<subvendor>:<subdevice>][; ...]
3120 Specifies alignment and device to reassign
3121 aligned memory resources.
3122 If <order of align> is not specified,
3123 PAGE_SIZE is used as alignment.
3124 PCI-PCI bridge can be specified, if resource
3125 windows need to be expanded.
3126 To specify the alignment for several
3127 instances of a device, the PCI vendor,
3128 device, subvendor, and subdevice may be
3129 specified, e.g., 4096@pci:8086:9c22:103c:198f
3130 ecrc= Enable/disable PCIe ECRC (transaction layer
3131 end-to-end CRC checking).
3132 bios: Use BIOS/firmware settings. This is the
3133 the default.
3134 off: Turn ECRC off
3135 on: Turn ECRC on.
3136 hpiosize=nn[KMG] The fixed amount of bus space which is
3137 reserved for hotplug bridge's IO window.
3138 Default size is 256 bytes.
3139 hpmemsize=nn[KMG] The fixed amount of bus space which is
3140 reserved for hotplug bridge's memory window.
3141 Default size is 2 megabytes.
3142 hpbussize=nn The minimum amount of additional bus numbers
3143 reserved for buses below a hotplug bridge.
3144 Default is 1.
3145 realloc= Enable/disable reallocating PCI bridge resources
3146 if allocations done by BIOS are too small to
3147 accommodate resources required by all child
3148 devices.
3149 off: Turn realloc off
3150 on: Turn realloc on
3151 realloc same as realloc=on
3152 noari do not use PCIe ARI.
3153 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3154 only look for one device below a PCIe downstream
3155 port.
3156 big_root_window Try to add a big 64bit memory window to the PCIe
3157 root complex on AMD CPUs. Some GFX hardware
3158 can resize a BAR to allow access to all VRAM.
3159 Adding the window is slightly risky (it may
3160 conflict with unreported devices), so this
3161 taints the kernel.
3162
3163 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3164 Management.
3165 off Disable ASPM.
3166 force Enable ASPM even on devices that claim not to support it.
3167 WARNING: Forcing ASPM on may cause system lockups.
3168
3169 pcie_ports= [PCIE] PCIe port services handling:
3170 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3171 even if the platform doesn't give the OS permission to
3172 use them. This may cause conflicts if the platform
3173 also tries to use these services.
3174 compat Disable native PCIe services (PME, AER, DPC, PCIe
3175 hotplug).
3176
3177 pcie_port_pm= [PCIE] PCIe port power management handling:
3178 off Disable power management of all PCIe ports
3179 force Forcibly enable power management of all PCIe ports
3180
3181 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3182 nomsi Do not use MSI for native PCIe PME signaling (this makes
3183 all PCIe root ports use INTx for all services).
3184
3185 pcmv= [HW,PCMCIA] BadgePAD 4
3186
3187 pd_ignore_unused
3188 [PM]
3189 Keep all power-domains already enabled by bootloader on,
3190 even if no driver has claimed them. This is useful
3191 for debug and development, but should not be
3192 needed on a platform with proper driver support.
3193
3194 pd. [PARIDE]
3195 See Documentation/blockdev/paride.txt.
3196
3197 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3198 boot time.
3199 Format: { 0 | 1 }
3200 See arch/parisc/kernel/pdc_chassis.c
3201
3202 percpu_alloc= Select which percpu first chunk allocator to use.
3203 Currently supported values are "embed" and "page".
3204 Archs may support subset or none of the selections.
3205 See comments in mm/percpu.c for details on each
3206 allocator. This parameter is primarily for debugging
3207 and performance comparison.
3208
3209 pf. [PARIDE]
3210 See Documentation/blockdev/paride.txt.
3211
3212 pg. [PARIDE]
3213 See Documentation/blockdev/paride.txt.
3214
3215 pirq= [SMP,APIC] Manual mp-table setup
3216 See Documentation/x86/i386/IO-APIC.txt.
3217
3218 plip= [PPT,NET] Parallel port network link
3219 Format: { parport<nr> | timid | 0 }
3220 See also Documentation/admin-guide/parport.rst.
3221
3222 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3223 Override pmtimer IOPort with a hex value.
3224 e.g. pmtmr=0x508
3225
3226 pnp.debug=1 [PNP]
3227 Enable PNP debug messages (depends on the
3228 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3229 via /sys/module/pnp/parameters/debug. We always show
3230 current resource usage; turning this on also shows
3231 possible settings and some assignment information.
3232
3233 pnpacpi= [ACPI]
3234 { off }
3235
3236 pnpbios= [ISAPNP]
3237 { on | off | curr | res | no-curr | no-res }
3238
3239 pnp_reserve_irq=
3240 [ISAPNP] Exclude IRQs for the autoconfiguration
3241
3242 pnp_reserve_dma=
3243 [ISAPNP] Exclude DMAs for the autoconfiguration
3244
3245 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3246 Ranges are in pairs (I/O port base and size).
3247
3248 pnp_reserve_mem=
3249 [ISAPNP] Exclude memory regions for the
3250 autoconfiguration.
3251 Ranges are in pairs (memory base and size).
3252
3253 ports= [IP_VS_FTP] IPVS ftp helper module
3254 Default is 21.
3255 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3256 may be specified.
3257 Format: <port>,<port>....
3258
3259 powersave=off [PPC] This option disables power saving features.
3260 It specifically disables cpuidle and sets the
3261 platform machine description specific power_save
3262 function to NULL. On Idle the CPU just reduces
3263 execution priority.
3264
3265 ppc_strict_facility_enable
3266 [PPC] This option catches any kernel floating point,
3267 Altivec, VSX and SPE outside of regions specifically
3268 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3269 There is some performance impact when enabling this.
3270
3271 ppc_tm= [PPC]
3272 Format: {"off"}
3273 Disable Hardware Transactional Memory
3274
3275 print-fatal-signals=
3276 [KNL] debug: print fatal signals
3277
3278 If enabled, warn about various signal handling
3279 related application anomalies: too many signals,
3280 too many POSIX.1 timers, fatal signals causing a
3281 coredump - etc.
3282
3283 If you hit the warning due to signal overflow,
3284 you might want to try "ulimit -i unlimited".
3285
3286 default: off.
3287
3288 printk.always_kmsg_dump=
3289 Trigger kmsg_dump for cases other than kernel oops or
3290 panics
3291 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3292 default: disabled
3293
3294 printk.devkmsg={on,off,ratelimit}
3295 Control writing to /dev/kmsg.
3296 on - unlimited logging to /dev/kmsg from userspace
3297 off - logging to /dev/kmsg disabled
3298 ratelimit - ratelimit the logging
3299 Default: ratelimit
3300
3301 printk.time= Show timing data prefixed to each printk message line
3302 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3303
3304 processor.max_cstate= [HW,ACPI]
3305 Limit processor to maximum C-state
3306 max_cstate=9 overrides any DMI blacklist limit.
3307
3308 processor.nocst [HW,ACPI]
3309 Ignore the _CST method to determine C-states,
3310 instead using the legacy FADT method
3311
3312 profile= [KNL] Enable kernel profiling via /proc/profile
3313 Format: [<profiletype>,]<number>
3314 Param: <profiletype>: "schedule", "sleep", or "kvm"
3315 [defaults to kernel profiling]
3316 Param: "schedule" - profile schedule points.
3317 Param: "sleep" - profile D-state sleeping (millisecs).
3318 Requires CONFIG_SCHEDSTATS
3319 Param: "kvm" - profile VM exits.
3320 Param: <number> - step/bucket size as a power of 2 for
3321 statistical time based profiling.
3322
3323 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3324 before loading.
3325 See Documentation/blockdev/ramdisk.txt.
3326
3327 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3328 probe for; one of (bare|imps|exps|lifebook|any).
3329 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3330 per second.
3331 psmouse.resetafter= [HW,MOUSE]
3332 Try to reset the device after so many bad packets
3333 (0 = never).
3334 psmouse.resolution=
3335 [HW,MOUSE] Set desired mouse resolution, in dpi.
3336 psmouse.smartscroll=
3337 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3338 0 = disabled, 1 = enabled (default).
3339
3340 pstore.backend= Specify the name of the pstore backend to use
3341
3342 pt. [PARIDE]
3343 See Documentation/blockdev/paride.txt.
3344
3345 pti= [X86_64] Control Page Table Isolation of user and
3346 kernel address spaces. Disabling this feature
3347 removes hardening, but improves performance of
3348 system calls and interrupts.
3349
3350 on - unconditionally enable
3351 off - unconditionally disable
3352 auto - kernel detects whether your CPU model is
3353 vulnerable to issues that PTI mitigates
3354
3355 Not specifying this option is equivalent to pti=auto.
3356
3357 nopti [X86_64]
3358 Equivalent to pti=off
3359
3360 pty.legacy_count=
3361 [KNL] Number of legacy pty's. Overwrites compiled-in
3362 default number.
3363
3364 quiet [KNL] Disable most log messages
3365
3366 r128= [HW,DRM]
3367
3368 raid= [HW,RAID]
3369 See Documentation/admin-guide/md.rst.
3370
3371 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3372 See Documentation/blockdev/ramdisk.txt.
3373
3374 ras=option[,option,...] [KNL] RAS-specific options
3375
3376 cec_disable [X86]
3377 Disable the Correctable Errors Collector,
3378 see CONFIG_RAS_CEC help text.
3379
3380 rcu_nocbs= [KNL]
3381 The argument is a cpu list, as described above.
3382
3383 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3384 the specified list of CPUs to be no-callback CPUs.
3385 Invocation of these CPUs' RCU callbacks will
3386 be offloaded to "rcuox/N" kthreads created for
3387 that purpose, where "x" is "b" for RCU-bh, "p"
3388 for RCU-preempt, and "s" for RCU-sched, and "N"
3389 is the CPU number. This reduces OS jitter on the
3390 offloaded CPUs, which can be useful for HPC and
3391 real-time workloads. It can also improve energy
3392 efficiency for asymmetric multiprocessors.
3393
3394 rcu_nocb_poll [KNL]
3395 Rather than requiring that offloaded CPUs
3396 (specified by rcu_nocbs= above) explicitly
3397 awaken the corresponding "rcuoN" kthreads,
3398 make these kthreads poll for callbacks.
3399 This improves the real-time response for the
3400 offloaded CPUs by relieving them of the need to
3401 wake up the corresponding kthread, but degrades
3402 energy efficiency by requiring that the kthreads
3403 periodically wake up to do the polling.
3404
3405 rcutree.blimit= [KNL]
3406 Set maximum number of finished RCU callbacks to
3407 process in one batch.
3408
3409 rcutree.dump_tree= [KNL]
3410 Dump the structure of the rcu_node combining tree
3411 out at early boot. This is used for diagnostic
3412 purposes, to verify correct tree setup.
3413
3414 rcutree.gp_cleanup_delay= [KNL]
3415 Set the number of jiffies to delay each step of
3416 RCU grace-period cleanup.
3417
3418 rcutree.gp_init_delay= [KNL]
3419 Set the number of jiffies to delay each step of
3420 RCU grace-period initialization.
3421
3422 rcutree.gp_preinit_delay= [KNL]
3423 Set the number of jiffies to delay each step of
3424 RCU grace-period pre-initialization, that is,
3425 the propagation of recent CPU-hotplug changes up
3426 the rcu_node combining tree.
3427
3428 rcutree.rcu_fanout_exact= [KNL]
3429 Disable autobalancing of the rcu_node combining
3430 tree. This is used by rcutorture, and might
3431 possibly be useful for architectures having high
3432 cache-to-cache transfer latencies.
3433
3434 rcutree.rcu_fanout_leaf= [KNL]
3435 Change the number of CPUs assigned to each
3436 leaf rcu_node structure. Useful for very
3437 large systems, which will choose the value 64,
3438 and for NUMA systems with large remote-access
3439 latencies, which will choose a value aligned
3440 with the appropriate hardware boundaries.
3441
3442 rcutree.jiffies_till_sched_qs= [KNL]
3443 Set required age in jiffies for a
3444 given grace period before RCU starts
3445 soliciting quiescent-state help from
3446 rcu_note_context_switch().
3447
3448 rcutree.jiffies_till_first_fqs= [KNL]
3449 Set delay from grace-period initialization to
3450 first attempt to force quiescent states.
3451 Units are jiffies, minimum value is zero,
3452 and maximum value is HZ.
3453
3454 rcutree.jiffies_till_next_fqs= [KNL]
3455 Set delay between subsequent attempts to force
3456 quiescent states. Units are jiffies, minimum
3457 value is one, and maximum value is HZ.
3458
3459 rcutree.kthread_prio= [KNL,BOOT]
3460 Set the SCHED_FIFO priority of the RCU per-CPU
3461 kthreads (rcuc/N). This value is also used for
3462 the priority of the RCU boost threads (rcub/N)
3463 and for the RCU grace-period kthreads (rcu_bh,
3464 rcu_preempt, and rcu_sched). If RCU_BOOST is
3465 set, valid values are 1-99 and the default is 1
3466 (the least-favored priority). Otherwise, when
3467 RCU_BOOST is not set, valid values are 0-99 and
3468 the default is zero (non-realtime operation).
3469
3470 rcutree.rcu_nocb_leader_stride= [KNL]
3471 Set the number of NOCB kthread groups, which
3472 defaults to the square root of the number of
3473 CPUs. Larger numbers reduces the wakeup overhead
3474 on the per-CPU grace-period kthreads, but increases
3475 that same overhead on each group's leader.
3476
3477 rcutree.qhimark= [KNL]
3478 Set threshold of queued RCU callbacks beyond which
3479 batch limiting is disabled.
3480
3481 rcutree.qlowmark= [KNL]
3482 Set threshold of queued RCU callbacks below which
3483 batch limiting is re-enabled.
3484
3485 rcutree.rcu_idle_gp_delay= [KNL]
3486 Set wakeup interval for idle CPUs that have
3487 RCU callbacks (RCU_FAST_NO_HZ=y).
3488
3489 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3490 Set wakeup interval for idle CPUs that have
3491 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3492 Lazy RCU callbacks are those which RCU can
3493 prove do nothing more than free memory.
3494
3495 rcutree.rcu_kick_kthreads= [KNL]
3496 Cause the grace-period kthread to get an extra
3497 wake_up() if it sleeps three times longer than
3498 it should at force-quiescent-state time.
3499 This wake_up() will be accompanied by a
3500 WARN_ONCE() splat and an ftrace_dump().
3501
3502 rcuperf.gp_async= [KNL]
3503 Measure performance of asynchronous
3504 grace-period primitives such as call_rcu().
3505
3506 rcuperf.gp_async_max= [KNL]
3507 Specify the maximum number of outstanding
3508 callbacks per writer thread. When a writer
3509 thread exceeds this limit, it invokes the
3510 corresponding flavor of rcu_barrier() to allow
3511 previously posted callbacks to drain.
3512
3513 rcuperf.gp_exp= [KNL]
3514 Measure performance of expedited synchronous
3515 grace-period primitives.
3516
3517 rcuperf.holdoff= [KNL]
3518 Set test-start holdoff period. The purpose of
3519 this parameter is to delay the start of the
3520 test until boot completes in order to avoid
3521 interference.
3522
3523 rcuperf.nreaders= [KNL]
3524 Set number of RCU readers. The value -1 selects
3525 N, where N is the number of CPUs. A value
3526 "n" less than -1 selects N-n+1, where N is again
3527 the number of CPUs. For example, -2 selects N
3528 (the number of CPUs), -3 selects N+1, and so on.
3529 A value of "n" less than or equal to -N selects
3530 a single reader.
3531
3532 rcuperf.nwriters= [KNL]
3533 Set number of RCU writers. The values operate
3534 the same as for rcuperf.nreaders.
3535 N, where N is the number of CPUs
3536
3537 rcuperf.perf_type= [KNL]
3538 Specify the RCU implementation to test.
3539
3540 rcuperf.shutdown= [KNL]
3541 Shut the system down after performance tests
3542 complete. This is useful for hands-off automated
3543 testing.
3544
3545 rcuperf.verbose= [KNL]
3546 Enable additional printk() statements.
3547
3548 rcuperf.writer_holdoff= [KNL]
3549 Write-side holdoff between grace periods,
3550 in microseconds. The default of zero says
3551 no holdoff.
3552
3553 rcutorture.cbflood_inter_holdoff= [KNL]
3554 Set holdoff time (jiffies) between successive
3555 callback-flood tests.
3556
3557 rcutorture.cbflood_intra_holdoff= [KNL]
3558 Set holdoff time (jiffies) between successive
3559 bursts of callbacks within a given callback-flood
3560 test.
3561
3562 rcutorture.cbflood_n_burst= [KNL]
3563 Set the number of bursts making up a given
3564 callback-flood test. Set this to zero to
3565 disable callback-flood testing.
3566
3567 rcutorture.cbflood_n_per_burst= [KNL]
3568 Set the number of callbacks to be registered
3569 in a given burst of a callback-flood test.
3570
3571 rcutorture.fqs_duration= [KNL]
3572 Set duration of force_quiescent_state bursts
3573 in microseconds.
3574
3575 rcutorture.fqs_holdoff= [KNL]
3576 Set holdoff time within force_quiescent_state bursts
3577 in microseconds.
3578
3579 rcutorture.fqs_stutter= [KNL]
3580 Set wait time between force_quiescent_state bursts
3581 in seconds.
3582
3583 rcutorture.gp_cond= [KNL]
3584 Use conditional/asynchronous update-side
3585 primitives, if available.
3586
3587 rcutorture.gp_exp= [KNL]
3588 Use expedited update-side primitives, if available.
3589
3590 rcutorture.gp_normal= [KNL]
3591 Use normal (non-expedited) asynchronous
3592 update-side primitives, if available.
3593
3594 rcutorture.gp_sync= [KNL]
3595 Use normal (non-expedited) synchronous
3596 update-side primitives, if available. If all
3597 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3598 rcutorture.gp_normal=, and rcutorture.gp_sync=
3599 are zero, rcutorture acts as if is interpreted
3600 they are all non-zero.
3601
3602 rcutorture.n_barrier_cbs= [KNL]
3603 Set callbacks/threads for rcu_barrier() testing.
3604
3605 rcutorture.nfakewriters= [KNL]
3606 Set number of concurrent RCU writers. These just
3607 stress RCU, they don't participate in the actual
3608 test, hence the "fake".
3609
3610 rcutorture.nreaders= [KNL]
3611 Set number of RCU readers. The value -1 selects
3612 N-1, where N is the number of CPUs. A value
3613 "n" less than -1 selects N-n-2, where N is again
3614 the number of CPUs. For example, -2 selects N
3615 (the number of CPUs), -3 selects N+1, and so on.
3616
3617 rcutorture.object_debug= [KNL]
3618 Enable debug-object double-call_rcu() testing.
3619
3620 rcutorture.onoff_holdoff= [KNL]
3621 Set time (s) after boot for CPU-hotplug testing.
3622
3623 rcutorture.onoff_interval= [KNL]
3624 Set time (s) between CPU-hotplug operations, or
3625 zero to disable CPU-hotplug testing.
3626
3627 rcutorture.shuffle_interval= [KNL]
3628 Set task-shuffle interval (s). Shuffling tasks
3629 allows some CPUs to go into dyntick-idle mode
3630 during the rcutorture test.
3631
3632 rcutorture.shutdown_secs= [KNL]
3633 Set time (s) after boot system shutdown. This
3634 is useful for hands-off automated testing.
3635
3636 rcutorture.stall_cpu= [KNL]
3637 Duration of CPU stall (s) to test RCU CPU stall
3638 warnings, zero to disable.
3639
3640 rcutorture.stall_cpu_holdoff= [KNL]
3641 Time to wait (s) after boot before inducing stall.
3642
3643 rcutorture.stall_cpu_irqsoff= [KNL]
3644 Disable interrupts while stalling if set.
3645
3646 rcutorture.stat_interval= [KNL]
3647 Time (s) between statistics printk()s.
3648
3649 rcutorture.stutter= [KNL]
3650 Time (s) to stutter testing, for example, specifying
3651 five seconds causes the test to run for five seconds,
3652 wait for five seconds, and so on. This tests RCU's
3653 ability to transition abruptly to and from idle.
3654
3655 rcutorture.test_boost= [KNL]
3656 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3657 "Maybe" means test if the RCU implementation
3658 under test support RCU priority boosting.
3659
3660 rcutorture.test_boost_duration= [KNL]
3661 Duration (s) of each individual boost test.
3662
3663 rcutorture.test_boost_interval= [KNL]
3664 Interval (s) between each boost test.
3665
3666 rcutorture.test_no_idle_hz= [KNL]
3667 Test RCU's dyntick-idle handling. See also the
3668 rcutorture.shuffle_interval parameter.
3669
3670 rcutorture.torture_type= [KNL]
3671 Specify the RCU implementation to test.
3672
3673 rcutorture.verbose= [KNL]
3674 Enable additional printk() statements.
3675
3676 rcupdate.rcu_cpu_stall_suppress= [KNL]
3677 Suppress RCU CPU stall warning messages.
3678
3679 rcupdate.rcu_cpu_stall_timeout= [KNL]
3680 Set timeout for RCU CPU stall warning messages.
3681
3682 rcupdate.rcu_expedited= [KNL]
3683 Use expedited grace-period primitives, for
3684 example, synchronize_rcu_expedited() instead
3685 of synchronize_rcu(). This reduces latency,
3686 but can increase CPU utilization, degrade
3687 real-time latency, and degrade energy efficiency.
3688 No effect on CONFIG_TINY_RCU kernels.
3689
3690 rcupdate.rcu_normal= [KNL]
3691 Use only normal grace-period primitives,
3692 for example, synchronize_rcu() instead of
3693 synchronize_rcu_expedited(). This improves
3694 real-time latency, CPU utilization, and
3695 energy efficiency, but can expose users to
3696 increased grace-period latency. This parameter
3697 overrides rcupdate.rcu_expedited. No effect on
3698 CONFIG_TINY_RCU kernels.
3699
3700 rcupdate.rcu_normal_after_boot= [KNL]
3701 Once boot has completed (that is, after
3702 rcu_end_inkernel_boot() has been invoked), use
3703 only normal grace-period primitives. No effect
3704 on CONFIG_TINY_RCU kernels.
3705
3706 rcupdate.rcu_task_stall_timeout= [KNL]
3707 Set timeout in jiffies for RCU task stall warning
3708 messages. Disable with a value less than or equal
3709 to zero.
3710
3711 rcupdate.rcu_self_test= [KNL]
3712 Run the RCU early boot self tests
3713
3714 rcupdate.rcu_self_test_bh= [KNL]
3715 Run the RCU bh early boot self tests
3716
3717 rcupdate.rcu_self_test_sched= [KNL]
3718 Run the RCU sched early boot self tests
3719
3720 rdinit= [KNL]
3721 Format: <full_path>
3722 Run specified binary instead of /init from the ramdisk,
3723 used for early userspace startup. See initrd.
3724
3725 rdt= [HW,X86,RDT]
3726 Turn on/off individual RDT features. List is:
3727 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3728 mba.
3729 E.g. to turn on cmt and turn off mba use:
3730 rdt=cmt,!mba
3731
3732 reboot= [KNL]
3733 Format (x86 or x86_64):
3734 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3735 [[,]s[mp]#### \
3736 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3737 [[,]f[orce]
3738 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3739 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3740 reboot_force is either force or not specified,
3741 reboot_cpu is s[mp]#### with #### being the processor
3742 to be used for rebooting.
3743
3744 relax_domain_level=
3745 [KNL, SMP] Set scheduler's default relax_domain_level.
3746 See Documentation/cgroup-v1/cpusets.txt.
3747
3748 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3749 Format: <base1>,<size1>[,<base2>,<size2>,...]
3750 Reserve I/O ports or memory so the kernel won't use
3751 them. If <base> is less than 0x10000, the region
3752 is assumed to be I/O ports; otherwise it is memory.
3753
3754 reservetop= [X86-32]
3755 Format: nn[KMG]
3756 Reserves a hole at the top of the kernel virtual
3757 address space.
3758
3759 reservelow= [X86]
3760 Format: nn[K]
3761 Set the amount of memory to reserve for BIOS at
3762 the bottom of the address space.
3763
3764 reset_devices [KNL] Force drivers to reset the underlying device
3765 during initialization.
3766
3767 resume= [SWSUSP]
3768 Specify the partition device for software suspend
3769 Format:
3770 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3771
3772 resume_offset= [SWSUSP]
3773 Specify the offset from the beginning of the partition
3774 given by "resume=" at which the swap header is located,
3775 in <PAGE_SIZE> units (needed only for swap files).
3776 See Documentation/power/swsusp-and-swap-files.txt
3777
3778 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3779 read the resume files
3780
3781 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3782 Useful for devices that are detected asynchronously
3783 (e.g. USB and MMC devices).
3784
3785 hibernate= [HIBERNATION]
3786 noresume Don't check if there's a hibernation image
3787 present during boot.
3788 nocompress Don't compress/decompress hibernation images.
3789 no Disable hibernation and resume.
3790 protect_image Turn on image protection during restoration
3791 (that will set all pages holding image data
3792 during restoration read-only).
3793
3794 retain_initrd [RAM] Keep initrd memory after extraction
3795
3796 rfkill.default_state=
3797 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3798 etc. communication is blocked by default.
3799 1 Unblocked.
3800
3801 rfkill.master_switch_mode=
3802 0 The "airplane mode" button does nothing.
3803 1 The "airplane mode" button toggles between everything
3804 blocked and the previous configuration.
3805 2 The "airplane mode" button toggles between everything
3806 blocked and everything unblocked.
3807
3808 rhash_entries= [KNL,NET]
3809 Set number of hash buckets for route cache
3810
3811 ring3mwait=disable
3812 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3813 CPUs.
3814
3815 ro [KNL] Mount root device read-only on boot
3816
3817 rodata= [KNL]
3818 on Mark read-only kernel memory as read-only (default).
3819 off Leave read-only kernel memory writable for debugging.
3820
3821 rockchip.usb_uart
3822 Enable the uart passthrough on the designated usb port
3823 on Rockchip SoCs. When active, the signals of the
3824 debug-uart get routed to the D+ and D- pins of the usb
3825 port and the regular usb controller gets disabled.
3826
3827 root= [KNL] Root filesystem
3828 See name_to_dev_t comment in init/do_mounts.c.
3829
3830 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3831 mount the root filesystem
3832
3833 rootflags= [KNL] Set root filesystem mount option string
3834
3835 rootfstype= [KNL] Set root filesystem type
3836
3837 rootwait [KNL] Wait (indefinitely) for root device to show up.
3838 Useful for devices that are detected asynchronously
3839 (e.g. USB and MMC devices).
3840
3841 rproc_mem=nn[KMG][@address]
3842 [KNL,ARM,CMA] Remoteproc physical memory block.
3843 Memory area to be used by remote processor image,
3844 managed by CMA.
3845
3846 rw [KNL] Mount root device read-write on boot
3847
3848 S [KNL] Run init in single mode
3849
3850 s390_iommu= [HW,S390]
3851 Set s390 IOTLB flushing mode
3852 strict
3853 With strict flushing every unmap operation will result in
3854 an IOTLB flush. Default is lazy flushing before reuse,
3855 which is faster.
3856
3857 sa1100ir [NET]
3858 See drivers/net/irda/sa1100_ir.c.
3859
3860 sbni= [NET] Granch SBNI12 leased line adapter
3861
3862 sched_debug [KNL] Enables verbose scheduler debug messages.
3863
3864 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3865 Allowed values are enable and disable. This feature
3866 incurs a small amount of overhead in the scheduler
3867 but is useful for debugging and performance tuning.
3868
3869 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3870 xtime_lock contention on larger systems, and/or RCU lock
3871 contention on all systems with CONFIG_MAXSMP set.
3872 Format: { "0" | "1" }
3873 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3874 1 -- enable.
3875 Note: increases power consumption, thus should only be
3876 enabled if running jitter sensitive (HPC/RT) workloads.
3877
3878 security= [SECURITY] Choose a security module to enable at boot.
3879 If this boot parameter is not specified, only the first
3880 security module asking for security registration will be
3881 loaded. An invalid security module name will be treated
3882 as if no module has been chosen.
3883
3884 selinux= [SELINUX] Disable or enable SELinux at boot time.
3885 Format: { "0" | "1" }
3886 See security/selinux/Kconfig help text.
3887 0 -- disable.
3888 1 -- enable.
3889 Default value is set via kernel config option.
3890 If enabled at boot time, /selinux/disable can be used
3891 later to disable prior to initial policy load.
3892
3893 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3894 Format: { "0" | "1" }
3895 See security/apparmor/Kconfig help text
3896 0 -- disable.
3897 1 -- enable.
3898 Default value is set via kernel config option.
3899
3900 serialnumber [BUGS=X86-32]
3901
3902 shapers= [NET]
3903 Maximal number of shapers.
3904
3905 simeth= [IA-64]
3906 simscsi=
3907
3908 slram= [HW,MTD]
3909
3910 slab_nomerge [MM]
3911 Disable merging of slabs with similar size. May be
3912 necessary if there is some reason to distinguish
3913 allocs to different slabs, especially in hardened
3914 environments where the risk of heap overflows and
3915 layout control by attackers can usually be
3916 frustrated by disabling merging. This will reduce
3917 most of the exposure of a heap attack to a single
3918 cache (risks via metadata attacks are mostly
3919 unchanged). Debug options disable merging on their
3920 own.
3921 For more information see Documentation/vm/slub.txt.
3922
3923 slab_max_order= [MM, SLAB]
3924 Determines the maximum allowed order for slabs.
3925 A high setting may cause OOMs due to memory
3926 fragmentation. Defaults to 1 for systems with
3927 more than 32MB of RAM, 0 otherwise.
3928
3929 slub_debug[=options[,slabs]] [MM, SLUB]
3930 Enabling slub_debug allows one to determine the
3931 culprit if slab objects become corrupted. Enabling
3932 slub_debug can create guard zones around objects and
3933 may poison objects when not in use. Also tracks the
3934 last alloc / free. For more information see
3935 Documentation/vm/slub.txt.
3936
3937 slub_memcg_sysfs= [MM, SLUB]
3938 Determines whether to enable sysfs directories for
3939 memory cgroup sub-caches. 1 to enable, 0 to disable.
3940 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3941 Enabling this can lead to a very high number of debug
3942 directories and files being created under
3943 /sys/kernel/slub.
3944
3945 slub_max_order= [MM, SLUB]
3946 Determines the maximum allowed order for slabs.
3947 A high setting may cause OOMs due to memory
3948 fragmentation. For more information see
3949 Documentation/vm/slub.txt.
3950
3951 slub_min_objects= [MM, SLUB]
3952 The minimum number of objects per slab. SLUB will
3953 increase the slab order up to slub_max_order to
3954 generate a sufficiently large slab able to contain
3955 the number of objects indicated. The higher the number
3956 of objects the smaller the overhead of tracking slabs
3957 and the less frequently locks need to be acquired.
3958 For more information see Documentation/vm/slub.txt.
3959
3960 slub_min_order= [MM, SLUB]
3961 Determines the minimum page order for slabs. Must be
3962 lower than slub_max_order.
3963 For more information see Documentation/vm/slub.txt.
3964
3965 slub_nomerge [MM, SLUB]
3966 Same with slab_nomerge. This is supported for legacy.
3967 See slab_nomerge for more information.
3968
3969 smart2= [HW]
3970 Format: <io1>[,<io2>[,...,<io8>]]
3971
3972 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3973 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3974 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3975 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3976 smsc-ircc2.ircc_irq= [HW] IRQ line
3977 smsc-ircc2.ircc_dma= [HW] DMA channel
3978 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3979 0: Toshiba Satellite 1800 (GP data pin select)
3980 1: Fast pin select (default)
3981 2: ATC IRMode
3982
3983 smt [KNL,S390] Set the maximum number of threads (logical
3984 CPUs) to use per physical CPU on systems capable of
3985 symmetric multithreading (SMT). Will be capped to the
3986 actual hardware limit.
3987 Format: <integer>
3988 Default: -1 (no limit)
3989
3990 softlockup_panic=
3991 [KNL] Should the soft-lockup detector generate panics.
3992 Format: <integer>
3993
3994 A nonzero value instructs the soft-lockup detector
3995 to panic the machine when a soft-lockup occurs. This
3996 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3997 which is the respective build-time switch to that
3998 functionality.
3999
4000 softlockup_all_cpu_backtrace=
4001 [KNL] Should the soft-lockup detector generate
4002 backtraces on all cpus.
4003 Format: <integer>
4004
4005 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4006 See Documentation/laptops/sonypi.txt
4007
4008 spectre_v2= [X86] Control mitigation of Spectre variant 2
4009 (indirect branch speculation) vulnerability.
4010
4011 on - unconditionally enable
4012 off - unconditionally disable
4013 auto - kernel detects whether your CPU model is
4014 vulnerable
4015
4016 Selecting 'on' will, and 'auto' may, choose a
4017 mitigation method at run time according to the
4018 CPU, the available microcode, the setting of the
4019 CONFIG_RETPOLINE configuration option, and the
4020 compiler with which the kernel was built.
4021
4022 Specific mitigations can also be selected manually:
4023
4024 retpoline - replace indirect branches
4025 retpoline,generic - google's original retpoline
4026 retpoline,amd - AMD-specific minimal thunk
4027
4028 Not specifying this option is equivalent to
4029 spectre_v2=auto.
4030
4031 spec_store_bypass_disable=
4032 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4033 (Speculative Store Bypass vulnerability)
4034
4035 Certain CPUs are vulnerable to an exploit against a
4036 a common industry wide performance optimization known
4037 as "Speculative Store Bypass" in which recent stores
4038 to the same memory location may not be observed by
4039 later loads during speculative execution. The idea
4040 is that such stores are unlikely and that they can
4041 be detected prior to instruction retirement at the
4042 end of a particular speculation execution window.
4043
4044 In vulnerable processors, the speculatively forwarded
4045 store can be used in a cache side channel attack, for
4046 example to read memory to which the attacker does not
4047 directly have access (e.g. inside sandboxed code).
4048
4049 This parameter controls whether the Speculative Store
4050 Bypass optimization is used.
4051
4052 on - Unconditionally disable Speculative Store Bypass
4053 off - Unconditionally enable Speculative Store Bypass
4054 auto - Kernel detects whether the CPU model contains an
4055 implementation of Speculative Store Bypass and
4056 picks the most appropriate mitigation. If the
4057 CPU is not vulnerable, "off" is selected. If the
4058 CPU is vulnerable the default mitigation is
4059 architecture and Kconfig dependent. See below.
4060 prctl - Control Speculative Store Bypass per thread
4061 via prctl. Speculative Store Bypass is enabled
4062 for a process by default. The state of the control
4063 is inherited on fork.
4064 seccomp - Same as "prctl" above, but all seccomp threads
4065 will disable SSB unless they explicitly opt out.
4066
4067 Not specifying this option is equivalent to
4068 spec_store_bypass_disable=auto.
4069
4070 Default mitigations:
4071 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4072
4073 spia_io_base= [HW,MTD]
4074 spia_fio_base=
4075 spia_pedr=
4076 spia_peddr=
4077
4078 srcutree.counter_wrap_check [KNL]
4079 Specifies how frequently to check for
4080 grace-period sequence counter wrap for the
4081 srcu_data structure's ->srcu_gp_seq_needed field.
4082 The greater the number of bits set in this kernel
4083 parameter, the less frequently counter wrap will
4084 be checked for. Note that the bottom two bits
4085 are ignored.
4086
4087 srcutree.exp_holdoff [KNL]
4088 Specifies how many nanoseconds must elapse
4089 since the end of the last SRCU grace period for
4090 a given srcu_struct until the next normal SRCU
4091 grace period will be considered for automatic
4092 expediting. Set to zero to disable automatic
4093 expediting.
4094
4095 stack_guard_gap= [MM]
4096 override the default stack gap protection. The value
4097 is in page units and it defines how many pages prior
4098 to (for stacks growing down) resp. after (for stacks
4099 growing up) the main stack are reserved for no other
4100 mapping. Default value is 256 pages.
4101
4102 stacktrace [FTRACE]
4103 Enabled the stack tracer on boot up.
4104
4105 stacktrace_filter=[function-list]
4106 [FTRACE] Limit the functions that the stack tracer
4107 will trace at boot up. function-list is a comma separated
4108 list of functions. This list can be changed at run
4109 time by the stack_trace_filter file in the debugfs
4110 tracing directory. Note, this enables stack tracing
4111 and the stacktrace above is not needed.
4112
4113 sti= [PARISC,HW]
4114 Format: <num>
4115 Set the STI (builtin display/keyboard on the HP-PARISC
4116 machines) console (graphic card) which should be used
4117 as the initial boot-console.
4118 See also comment in drivers/video/console/sticore.c.
4119
4120 sti_font= [HW]
4121 See comment in drivers/video/console/sticore.c.
4122
4123 stifb= [HW]
4124 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4125
4126 sunrpc.min_resvport=
4127 sunrpc.max_resvport=
4128 [NFS,SUNRPC]
4129 SunRPC servers often require that client requests
4130 originate from a privileged port (i.e. a port in the
4131 range 0 < portnr < 1024).
4132 An administrator who wishes to reserve some of these
4133 ports for other uses may adjust the range that the
4134 kernel's sunrpc client considers to be privileged
4135 using these two parameters to set the minimum and
4136 maximum port values.
4137
4138 sunrpc.svc_rpc_per_connection_limit=
4139 [NFS,SUNRPC]
4140 Limit the number of requests that the server will
4141 process in parallel from a single connection.
4142 The default value is 0 (no limit).
4143
4144 sunrpc.pool_mode=
4145 [NFS]
4146 Control how the NFS server code allocates CPUs to
4147 service thread pools. Depending on how many NICs
4148 you have and where their interrupts are bound, this
4149 option will affect which CPUs will do NFS serving.
4150 Note: this parameter cannot be changed while the
4151 NFS server is running.
4152
4153 auto the server chooses an appropriate mode
4154 automatically using heuristics
4155 global a single global pool contains all CPUs
4156 percpu one pool for each CPU
4157 pernode one pool for each NUMA node (equivalent
4158 to global on non-NUMA machines)
4159
4160 sunrpc.tcp_slot_table_entries=
4161 sunrpc.udp_slot_table_entries=
4162 [NFS,SUNRPC]
4163 Sets the upper limit on the number of simultaneous
4164 RPC calls that can be sent from the client to a
4165 server. Increasing these values may allow you to
4166 improve throughput, but will also increase the
4167 amount of memory reserved for use by the client.
4168
4169 suspend.pm_test_delay=
4170 [SUSPEND]
4171 Sets the number of seconds to remain in a suspend test
4172 mode before resuming the system (see
4173 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4174 is set. Default value is 5.
4175
4176 swapaccount=[0|1]
4177 [KNL] Enable accounting of swap in memory resource
4178 controller if no parameter or 1 is given or disable
4179 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4180
4181 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4182 Format: { <int> | force | noforce }
4183 <int> -- Number of I/O TLB slabs
4184 force -- force using of bounce buffers even if they
4185 wouldn't be automatically used by the kernel
4186 noforce -- Never use bounce buffers (for debugging)
4187
4188 switches= [HW,M68k]
4189
4190 sysfs.deprecated=0|1 [KNL]
4191 Enable/disable old style sysfs layout for old udev
4192 on older distributions. When this option is enabled
4193 very new udev will not work anymore. When this option
4194 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4195 in older udev will not work anymore.
4196 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4197 the kernel configuration.
4198
4199 sysrq_always_enabled
4200 [KNL]
4201 Ignore sysrq setting - this boot parameter will
4202 neutralize any effect of /proc/sys/kernel/sysrq.
4203 Useful for debugging.
4204
4205 tcpmhash_entries= [KNL,NET]
4206 Set the number of tcp_metrics_hash slots.
4207 Default value is 8192 or 16384 depending on total
4208 ram pages. This is used to specify the TCP metrics
4209 cache size. See Documentation/networking/ip-sysctl.txt
4210 "tcp_no_metrics_save" section for more details.
4211
4212 tdfx= [HW,DRM]
4213
4214 test_suspend= [SUSPEND][,N]
4215 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4216 standby suspend) or "freeze" (for suspend type freeze)
4217 as the system sleep state during system startup with
4218 the optional capability to repeat N number of times.
4219 The system is woken from this state using a
4220 wakeup-capable RTC alarm.
4221
4222 thash_entries= [KNL,NET]
4223 Set number of hash buckets for TCP connection
4224
4225 thermal.act= [HW,ACPI]
4226 -1: disable all active trip points in all thermal zones
4227 <degrees C>: override all lowest active trip points
4228
4229 thermal.crt= [HW,ACPI]
4230 -1: disable all critical trip points in all thermal zones
4231 <degrees C>: override all critical trip points
4232
4233 thermal.nocrt= [HW,ACPI]
4234 Set to disable actions on ACPI thermal zone
4235 critical and hot trip points.
4236
4237 thermal.off= [HW,ACPI]
4238 1: disable ACPI thermal control
4239
4240 thermal.psv= [HW,ACPI]
4241 -1: disable all passive trip points
4242 <degrees C>: override all passive trip points to this
4243 value
4244
4245 thermal.tzp= [HW,ACPI]
4246 Specify global default ACPI thermal zone polling rate
4247 <deci-seconds>: poll all this frequency
4248 0: no polling (default)
4249
4250 threadirqs [KNL]
4251 Force threading of all interrupt handlers except those
4252 marked explicitly IRQF_NO_THREAD.
4253
4254 tmem [KNL,XEN]
4255 Enable the Transcendent memory driver if built-in.
4256
4257 tmem.cleancache=0|1 [KNL, XEN]
4258 Default is on (1). Disable the usage of the cleancache
4259 API to send anonymous pages to the hypervisor.
4260
4261 tmem.frontswap=0|1 [KNL, XEN]
4262 Default is on (1). Disable the usage of the frontswap
4263 API to send swap pages to the hypervisor. If disabled
4264 the selfballooning and selfshrinking are force disabled.
4265
4266 tmem.selfballooning=0|1 [KNL, XEN]
4267 Default is on (1). Disable the driving of swap pages
4268 to the hypervisor.
4269
4270 tmem.selfshrinking=0|1 [KNL, XEN]
4271 Default is on (1). Partial swapoff that immediately
4272 transfers pages from Xen hypervisor back to the
4273 kernel based on different criteria.
4274
4275 topology= [S390]
4276 Format: {off | on}
4277 Specify if the kernel should make use of the cpu
4278 topology information if the hardware supports this.
4279 The scheduler will make use of this information and
4280 e.g. base its process migration decisions on it.
4281 Default is on.
4282
4283 topology_updates= [KNL, PPC, NUMA]
4284 Format: {off}
4285 Specify if the kernel should ignore (off)
4286 topology updates sent by the hypervisor to this
4287 LPAR.
4288
4289 tp720= [HW,PS2]
4290
4291 tpm_suspend_pcr=[HW,TPM]
4292 Format: integer pcr id
4293 Specify that at suspend time, the tpm driver
4294 should extend the specified pcr with zeros,
4295 as a workaround for some chips which fail to
4296 flush the last written pcr on TPM_SaveState.
4297 This will guarantee that all the other pcrs
4298 are saved.
4299
4300 trace_buf_size=nn[KMG]
4301 [FTRACE] will set tracing buffer size on each cpu.
4302
4303 trace_event=[event-list]
4304 [FTRACE] Set and start specified trace events in order
4305 to facilitate early boot debugging. The event-list is a
4306 comma separated list of trace events to enable. See
4307 also Documentation/trace/events.txt
4308
4309 trace_options=[option-list]
4310 [FTRACE] Enable or disable tracer options at boot.
4311 The option-list is a comma delimited list of options
4312 that can be enabled or disabled just as if you were
4313 to echo the option name into
4314
4315 /sys/kernel/debug/tracing/trace_options
4316
4317 For example, to enable stacktrace option (to dump the
4318 stack trace of each event), add to the command line:
4319
4320 trace_options=stacktrace
4321
4322 See also Documentation/trace/ftrace.txt "trace options"
4323 section.
4324
4325 tp_printk[FTRACE]
4326 Have the tracepoints sent to printk as well as the
4327 tracing ring buffer. This is useful for early boot up
4328 where the system hangs or reboots and does not give the
4329 option for reading the tracing buffer or performing a
4330 ftrace_dump_on_oops.
4331
4332 To turn off having tracepoints sent to printk,
4333 echo 0 > /proc/sys/kernel/tracepoint_printk
4334 Note, echoing 1 into this file without the
4335 tracepoint_printk kernel cmdline option has no effect.
4336
4337 ** CAUTION **
4338
4339 Having tracepoints sent to printk() and activating high
4340 frequency tracepoints such as irq or sched, can cause
4341 the system to live lock.
4342
4343 traceoff_on_warning
4344 [FTRACE] enable this option to disable tracing when a
4345 warning is hit. This turns off "tracing_on". Tracing can
4346 be enabled again by echoing '1' into the "tracing_on"
4347 file located in /sys/kernel/debug/tracing/
4348
4349 This option is useful, as it disables the trace before
4350 the WARNING dump is called, which prevents the trace to
4351 be filled with content caused by the warning output.
4352
4353 This option can also be set at run time via the sysctl
4354 option: kernel/traceoff_on_warning
4355
4356 transparent_hugepage=
4357 [KNL]
4358 Format: [always|madvise|never]
4359 Can be used to control the default behavior of the system
4360 with respect to transparent hugepages.
4361 See Documentation/vm/transhuge.txt for more details.
4362
4363 tsc= Disable clocksource stability checks for TSC.
4364 Format: <string>
4365 [x86] reliable: mark tsc clocksource as reliable, this
4366 disables clocksource verification at runtime, as well
4367 as the stability checks done at bootup. Used to enable
4368 high-resolution timer mode on older hardware, and in
4369 virtualized environment.
4370 [x86] noirqtime: Do not use TSC to do irq accounting.
4371 Used to run time disable IRQ_TIME_ACCOUNTING on any
4372 platforms where RDTSC is slow and this accounting
4373 can add overhead.
4374 [x86] unstable: mark the TSC clocksource as unstable, this
4375 marks the TSC unconditionally unstable at bootup and
4376 avoids any further wobbles once the TSC watchdog notices.
4377
4378 turbografx.map[2|3]= [HW,JOY]
4379 TurboGraFX parallel port interface
4380 Format:
4381 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4382 See also Documentation/input/devices/joystick-parport.rst
4383
4384 udbg-immortal [PPC] When debugging early kernel crashes that
4385 happen after console_init() and before a proper
4386 console driver takes over, this boot options might
4387 help "seeing" what's going on.
4388
4389 uhash_entries= [KNL,NET]
4390 Set number of hash buckets for UDP/UDP-Lite connections
4391
4392 uhci-hcd.ignore_oc=
4393 [USB] Ignore overcurrent events (default N).
4394 Some badly-designed motherboards generate lots of
4395 bogus events, for ports that aren't wired to
4396 anything. Set this parameter to avoid log spamming.
4397 Note that genuine overcurrent events won't be
4398 reported either.
4399
4400 unknown_nmi_panic
4401 [X86] Cause panic on unknown NMI.
4402
4403 usbcore.authorized_default=
4404 [USB] Default USB device authorization:
4405 (default -1 = authorized except for wireless USB,
4406 0 = not authorized, 1 = authorized)
4407
4408 usbcore.autosuspend=
4409 [USB] The autosuspend time delay (in seconds) used
4410 for newly-detected USB devices (default 2). This
4411 is the time required before an idle device will be
4412 autosuspended. Devices for which the delay is set
4413 to a negative value won't be autosuspended at all.
4414
4415 usbcore.usbfs_snoop=
4416 [USB] Set to log all usbfs traffic (default 0 = off).
4417
4418 usbcore.usbfs_snoop_max=
4419 [USB] Maximum number of bytes to snoop in each URB
4420 (default = 65536).
4421
4422 usbcore.blinkenlights=
4423 [USB] Set to cycle leds on hubs (default 0 = off).
4424
4425 usbcore.old_scheme_first=
4426 [USB] Start with the old device initialization
4427 scheme (default 0 = off).
4428
4429 usbcore.usbfs_memory_mb=
4430 [USB] Memory limit (in MB) for buffers allocated by
4431 usbfs (default = 16, 0 = max = 2047).
4432
4433 usbcore.use_both_schemes=
4434 [USB] Try the other device initialization scheme
4435 if the first one fails (default 1 = enabled).
4436
4437 usbcore.initial_descriptor_timeout=
4438 [USB] Specifies timeout for the initial 64-byte
4439 USB_REQ_GET_DESCRIPTOR request in milliseconds
4440 (default 5000 = 5.0 seconds).
4441
4442 usbcore.nousb [USB] Disable the USB subsystem
4443
4444 usbcore.quirks=
4445 [USB] A list of quirk entries to augment the built-in
4446 usb core quirk list. List entries are separated by
4447 commas. Each entry has the form
4448 VendorID:ProductID:Flags. The IDs are 4-digit hex
4449 numbers and Flags is a set of letters. Each letter
4450 will change the built-in quirk; setting it if it is
4451 clear and clearing it if it is set. The letters have
4452 the following meanings:
4453 a = USB_QUIRK_STRING_FETCH_255 (string
4454 descriptors must not be fetched using
4455 a 255-byte read);
4456 b = USB_QUIRK_RESET_RESUME (device can't resume
4457 correctly so reset it instead);
4458 c = USB_QUIRK_NO_SET_INTF (device can't handle
4459 Set-Interface requests);
4460 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4461 handle its Configuration or Interface
4462 strings);
4463 e = USB_QUIRK_RESET (device can't be reset
4464 (e.g morph devices), don't use reset);
4465 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4466 more interface descriptions than the
4467 bNumInterfaces count, and can't handle
4468 talking to these interfaces);
4469 g = USB_QUIRK_DELAY_INIT (device needs a pause
4470 during initialization, after we read
4471 the device descriptor);
4472 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4473 high speed and super speed interrupt
4474 endpoints, the USB 2.0 and USB 3.0 spec
4475 require the interval in microframes (1
4476 microframe = 125 microseconds) to be
4477 calculated as interval = 2 ^
4478 (bInterval-1).
4479 Devices with this quirk report their
4480 bInterval as the result of this
4481 calculation instead of the exponent
4482 variable used in the calculation);
4483 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4484 handle device_qualifier descriptor
4485 requests);
4486 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4487 generates spurious wakeup, ignore
4488 remote wakeup capability);
4489 k = USB_QUIRK_NO_LPM (device can't handle Link
4490 Power Management);
4491 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4492 (Device reports its bInterval as linear
4493 frames instead of the USB 2.0
4494 calculation);
4495 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4496 to be disconnected before suspend to
4497 prevent spurious wakeup);
4498 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4499 pause after every control message);
4500 Example: quirks=0781:5580:bk,0a5c:5834:gij
4501
4502 usbhid.mousepoll=
4503 [USBHID] The interval which mice are to be polled at.
4504
4505 usbhid.jspoll=
4506 [USBHID] The interval which joysticks are to be polled at.
4507
4508 usbhid.kbpoll=
4509 [USBHID] The interval which keyboards are to be polled at.
4510
4511 usb-storage.delay_use=
4512 [UMS] The delay in seconds before a new device is
4513 scanned for Logical Units (default 1).
4514
4515 usb-storage.quirks=
4516 [UMS] A list of quirks entries to supplement or
4517 override the built-in unusual_devs list. List
4518 entries are separated by commas. Each entry has
4519 the form VID:PID:Flags where VID and PID are Vendor
4520 and Product ID values (4-digit hex numbers) and
4521 Flags is a set of characters, each corresponding
4522 to a common usb-storage quirk flag as follows:
4523 a = SANE_SENSE (collect more than 18 bytes
4524 of sense data);
4525 b = BAD_SENSE (don't collect more than 18
4526 bytes of sense data);
4527 c = FIX_CAPACITY (decrease the reported
4528 device capacity by one sector);
4529 d = NO_READ_DISC_INFO (don't use
4530 READ_DISC_INFO command);
4531 e = NO_READ_CAPACITY_16 (don't use
4532 READ_CAPACITY_16 command);
4533 f = NO_REPORT_OPCODES (don't use report opcodes
4534 command, uas only);
4535 g = MAX_SECTORS_240 (don't transfer more than
4536 240 sectors at a time, uas only);
4537 h = CAPACITY_HEURISTICS (decrease the
4538 reported device capacity by one
4539 sector if the number is odd);
4540 i = IGNORE_DEVICE (don't bind to this
4541 device);
4542 j = NO_REPORT_LUNS (don't use report luns
4543 command, uas only);
4544 l = NOT_LOCKABLE (don't try to lock and
4545 unlock ejectable media);
4546 m = MAX_SECTORS_64 (don't transfer more
4547 than 64 sectors = 32 KB at a time);
4548 n = INITIAL_READ10 (force a retry of the
4549 initial READ(10) command);
4550 o = CAPACITY_OK (accept the capacity
4551 reported by the device);
4552 p = WRITE_CACHE (the device cache is ON
4553 by default);
4554 r = IGNORE_RESIDUE (the device reports
4555 bogus residue values);
4556 s = SINGLE_LUN (the device has only one
4557 Logical Unit);
4558 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4559 commands, uas only);
4560 u = IGNORE_UAS (don't bind to the uas driver);
4561 w = NO_WP_DETECT (don't test whether the
4562 medium is write-protected).
4563 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4564 even if the device claims no cache)
4565 Example: quirks=0419:aaf5:rl,0421:0433:rc
4566
4567 user_debug= [KNL,ARM]
4568 Format: <int>
4569 See arch/arm/Kconfig.debug help text.
4570 1 - undefined instruction events
4571 2 - system calls
4572 4 - invalid data aborts
4573 8 - SIGSEGV faults
4574 16 - SIGBUS faults
4575 Example: user_debug=31
4576
4577 userpte=
4578 [X86] Flags controlling user PTE allocations.
4579
4580 nohigh = do not allocate PTE pages in
4581 HIGHMEM regardless of setting
4582 of CONFIG_HIGHPTE.
4583
4584 vdso= [X86,SH]
4585 On X86_32, this is an alias for vdso32=. Otherwise:
4586
4587 vdso=1: enable VDSO (the default)
4588 vdso=0: disable VDSO mapping
4589
4590 vdso32= [X86] Control the 32-bit vDSO
4591 vdso32=1: enable 32-bit VDSO
4592 vdso32=0 or vdso32=2: disable 32-bit VDSO
4593
4594 See the help text for CONFIG_COMPAT_VDSO for more
4595 details. If CONFIG_COMPAT_VDSO is set, the default is
4596 vdso32=0; otherwise, the default is vdso32=1.
4597
4598 For compatibility with older kernels, vdso32=2 is an
4599 alias for vdso32=0.
4600
4601 Try vdso32=0 if you encounter an error that says:
4602 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4603
4604 vector= [IA-64,SMP]
4605 vector=percpu: enable percpu vector domain
4606
4607 video= [FB] Frame buffer configuration
4608 See Documentation/fb/modedb.txt.
4609
4610 video.brightness_switch_enabled= [0,1]
4611 If set to 1, on receiving an ACPI notify event
4612 generated by hotkey, video driver will adjust brightness
4613 level and then send out the event to user space through
4614 the allocated input device; If set to 0, video driver
4615 will only send out the event without touching backlight
4616 brightness level.
4617 default: 1
4618
4619 virtio_mmio.device=
4620 [VMMIO] Memory mapped virtio (platform) device.
4621
4622 <size>@<baseaddr>:<irq>[:<id>]
4623 where:
4624 <size> := size (can use standard suffixes
4625 like K, M and G)
4626 <baseaddr> := physical base address
4627 <irq> := interrupt number (as passed to
4628 request_irq())
4629 <id> := (optional) platform device id
4630 example:
4631 virtio_mmio.device=1K@0x100b0000:48:7
4632
4633 Can be used multiple times for multiple devices.
4634
4635 vga= [BOOT,X86-32] Select a particular video mode
4636 See Documentation/x86/boot.txt and
4637 Documentation/svga.txt.
4638 Use vga=ask for menu.
4639 This is actually a boot loader parameter; the value is
4640 passed to the kernel using a special protocol.
4641
4642 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4643 size of <nn>. This can be used to increase the
4644 minimum size (128MB on x86). It can also be used to
4645 decrease the size and leave more room for directly
4646 mapped kernel RAM.
4647
4648 vmcp_cma=nn[MG] [KNL,S390]
4649 Sets the memory size reserved for contiguous memory
4650 allocations for the vmcp device driver.
4651
4652 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4653 Format: <command>
4654
4655 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4656 Format: <command>
4657
4658 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4659 Format: <command>
4660
4661 vsyscall= [X86-64]
4662 Controls the behavior of vsyscalls (i.e. calls to
4663 fixed addresses of 0xffffffffff600x00 from legacy
4664 code). Most statically-linked binaries and older
4665 versions of glibc use these calls. Because these
4666 functions are at fixed addresses, they make nice
4667 targets for exploits that can control RIP.
4668
4669 emulate [default] Vsyscalls turn into traps and are
4670 emulated reasonably safely.
4671
4672 native Vsyscalls are native syscall instructions.
4673 This is a little bit faster than trapping
4674 and makes a few dynamic recompilers work
4675 better than they would in emulation mode.
4676 It also makes exploits much easier to write.
4677
4678 none Vsyscalls don't work at all. This makes
4679 them quite hard to use for exploits but
4680 might break your system.
4681
4682 vt.color= [VT] Default text color.
4683 Format: 0xYX, X = foreground, Y = background.
4684 Default: 0x07 = light gray on black.
4685
4686 vt.cur_default= [VT] Default cursor shape.
4687 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4688 the parameters of the <Esc>[?A;B;Cc escape sequence;
4689 see VGA-softcursor.txt. Default: 2 = underline.
4690
4691 vt.default_blu= [VT]
4692 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4693 Change the default blue palette of the console.
4694 This is a 16-member array composed of values
4695 ranging from 0-255.
4696
4697 vt.default_grn= [VT]
4698 Format: <green0>,<green1>,<green2>,...,<green15>
4699 Change the default green palette of the console.
4700 This is a 16-member array composed of values
4701 ranging from 0-255.
4702
4703 vt.default_red= [VT]
4704 Format: <red0>,<red1>,<red2>,...,<red15>
4705 Change the default red palette of the console.
4706 This is a 16-member array composed of values
4707 ranging from 0-255.
4708
4709 vt.default_utf8=
4710 [VT]
4711 Format=<0|1>
4712 Set system-wide default UTF-8 mode for all tty's.
4713 Default is 1, i.e. UTF-8 mode is enabled for all
4714 newly opened terminals.
4715
4716 vt.global_cursor_default=
4717 [VT]
4718 Format=<-1|0|1>
4719 Set system-wide default for whether a cursor
4720 is shown on new VTs. Default is -1,
4721 i.e. cursors will be created by default unless
4722 overridden by individual drivers. 0 will hide
4723 cursors, 1 will display them.
4724
4725 vt.italic= [VT] Default color for italic text; 0-15.
4726 Default: 2 = green.
4727
4728 vt.underline= [VT] Default color for underlined text; 0-15.
4729 Default: 3 = cyan.
4730
4731 watchdog timers [HW,WDT] For information on watchdog timers,
4732 see Documentation/watchdog/watchdog-parameters.txt
4733 or other driver-specific files in the
4734 Documentation/watchdog/ directory.
4735
4736 workqueue.watchdog_thresh=
4737 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4738 warn stall conditions and dump internal state to
4739 help debugging. 0 disables workqueue stall
4740 detection; otherwise, it's the stall threshold
4741 duration in seconds. The default value is 30 and
4742 it can be updated at runtime by writing to the
4743 corresponding sysfs file.
4744
4745 workqueue.disable_numa
4746 By default, all work items queued to unbound
4747 workqueues are affine to the NUMA nodes they're
4748 issued on, which results in better behavior in
4749 general. If NUMA affinity needs to be disabled for
4750 whatever reason, this option can be used. Note
4751 that this also can be controlled per-workqueue for
4752 workqueues visible under /sys/bus/workqueue/.
4753
4754 workqueue.power_efficient
4755 Per-cpu workqueues are generally preferred because
4756 they show better performance thanks to cache
4757 locality; unfortunately, per-cpu workqueues tend to
4758 be more power hungry than unbound workqueues.
4759
4760 Enabling this makes the per-cpu workqueues which
4761 were observed to contribute significantly to power
4762 consumption unbound, leading to measurably lower
4763 power usage at the cost of small performance
4764 overhead.
4765
4766 The default value of this parameter is determined by
4767 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4768
4769 workqueue.debug_force_rr_cpu
4770 Workqueue used to implicitly guarantee that work
4771 items queued without explicit CPU specified are put
4772 on the local CPU. This guarantee is no longer true
4773 and while local CPU is still preferred work items
4774 may be put on foreign CPUs. This debug option
4775 forces round-robin CPU selection to flush out
4776 usages which depend on the now broken guarantee.
4777 When enabled, memory and cache locality will be
4778 impacted.
4779
4780 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4781 default x2apic cluster mode on platforms
4782 supporting x2apic.
4783
4784 x86_intel_mid_timer= [X86-32,APBT]
4785 Choose timer option for x86 Intel MID platform.
4786 Two valid options are apbt timer only and lapic timer
4787 plus one apbt timer for broadcast timer.
4788 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4789
4790 xen_512gb_limit [KNL,X86-64,XEN]
4791 Restricts the kernel running paravirtualized under Xen
4792 to use only up to 512 GB of RAM. The reason to do so is
4793 crash analysis tools and Xen tools for doing domain
4794 save/restore/migration must be enabled to handle larger
4795 domains.
4796
4797 xen_emul_unplug= [HW,X86,XEN]
4798 Unplug Xen emulated devices
4799 Format: [unplug0,][unplug1]
4800 ide-disks -- unplug primary master IDE devices
4801 aux-ide-disks -- unplug non-primary-master IDE devices
4802 nics -- unplug network devices
4803 all -- unplug all emulated devices (NICs and IDE disks)
4804 unnecessary -- unplugging emulated devices is
4805 unnecessary even if the host did not respond to
4806 the unplug protocol
4807 never -- do not unplug even if version check succeeds
4808
4809 xen_nopvspin [X86,XEN]
4810 Disables the ticketlock slowpath using Xen PV
4811 optimizations.
4812
4813 xen_nopv [X86]
4814 Disables the PV optimizations forcing the HVM guest to
4815 run as generic HVM guest with no PV drivers.
4816
4817 xirc2ps_cs= [NET,PCMCIA]
4818 Format:
4819 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1 accept_memory= [MM]
2 Format: { eager | lazy }
3 default: lazy
4 By default, unaccepted memory is accepted lazily to
5 avoid prolonged boot times. The lazy option will add
6 some runtime overhead until all memory is eventually
7 accepted. In most cases the overhead is negligible.
8 For some workloads or for debugging purposes
9 accept_memory=eager can be used to accept all memory
10 at once during boot.
11
12 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
13 Advanced Configuration and Power Interface
14 Format: { force | on | off | strict | noirq | rsdt |
15 copy_dsdt }
16 force -- enable ACPI if default was off
17 on -- enable ACPI but allow fallback to DT [arm64,riscv64]
18 off -- disable ACPI if default was on
19 noirq -- do not use ACPI for IRQ routing
20 strict -- Be less tolerant of platforms that are not
21 strictly ACPI specification compliant.
22 rsdt -- prefer RSDT over (default) XSDT
23 copy_dsdt -- copy DSDT to memory
24 For ARM64 and RISCV64, ONLY "acpi=off", "acpi=on" or
25 "acpi=force" are available
26
27 See also Documentation/power/runtime_pm.rst, pci=noacpi
28
29 acpi_apic_instance= [ACPI,IOAPIC,EARLY]
30 Format: <int>
31 2: use 2nd APIC table, if available
32 1,0: use 1st APIC table
33 default: 0
34
35 acpi_backlight= [HW,ACPI]
36 { vendor | video | native | none }
37 If set to vendor, prefer vendor-specific driver
38 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
39 of the ACPI video.ko driver.
40 If set to video, use the ACPI video.ko driver.
41 If set to native, use the device's native backlight mode.
42 If set to none, disable the ACPI backlight interface.
43
44 acpi_force_32bit_fadt_addr [ACPI,EARLY]
45 force FADT to use 32 bit addresses rather than the
46 64 bit X_* addresses. Some firmware have broken 64
47 bit addresses for force ACPI ignore these and use
48 the older legacy 32 bit addresses.
49
50 acpica_no_return_repair [HW, ACPI]
51 Disable AML predefined validation mechanism
52 This mechanism can repair the evaluation result to make
53 the return objects more ACPI specification compliant.
54 This option is useful for developers to identify the
55 root cause of an AML interpreter issue when the issue
56 has something to do with the repair mechanism.
57
58 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
59 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
60 Format: <int>
61 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
62 debug output. Bits in debug_layer correspond to a
63 _COMPONENT in an ACPI source file, e.g.,
64 #define _COMPONENT ACPI_EVENTS
65 Bits in debug_level correspond to a level in
66 ACPI_DEBUG_PRINT statements, e.g.,
67 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
68 The debug_level mask defaults to "info". See
69 Documentation/firmware-guide/acpi/debug.rst for more information about
70 debug layers and levels.
71
72 Enable processor driver info messages:
73 acpi.debug_layer=0x20000000
74 Enable AML "Debug" output, i.e., stores to the Debug
75 object while interpreting AML:
76 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
77 Enable all messages related to ACPI hardware:
78 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
79
80 Some values produce so much output that the system is
81 unusable. The "log_buf_len" parameter may be useful
82 if you need to capture more output.
83
84 acpi_enforce_resources= [ACPI]
85 { strict | lax | no }
86 Check for resource conflicts between native drivers
87 and ACPI OperationRegions (SystemIO and SystemMemory
88 only). IO ports and memory declared in ACPI might be
89 used by the ACPI subsystem in arbitrary AML code and
90 can interfere with legacy drivers.
91 strict (default): access to resources claimed by ACPI
92 is denied; legacy drivers trying to access reserved
93 resources will fail to bind to device using them.
94 lax: access to resources claimed by ACPI is allowed;
95 legacy drivers trying to access reserved resources
96 will bind successfully but a warning message is logged.
97 no: ACPI OperationRegions are not marked as reserved,
98 no further checks are performed.
99
100 acpi_force_table_verification [HW,ACPI,EARLY]
101 Enable table checksum verification during early stage.
102 By default, this is disabled due to x86 early mapping
103 size limitation.
104
105 acpi_irq_balance [HW,ACPI]
106 ACPI will balance active IRQs
107 default in APIC mode
108
109 acpi_irq_nobalance [HW,ACPI]
110 ACPI will not move active IRQs (default)
111 default in PIC mode
112
113 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
114 Format: <irq>,<irq>...
115
116 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
117 use by PCI
118 Format: <irq>,<irq>...
119
120 acpi_mask_gpe= [HW,ACPI]
121 Due to the existence of _Lxx/_Exx, some GPEs triggered
122 by unsupported hardware/firmware features can result in
123 GPE floodings that cannot be automatically disabled by
124 the GPE dispatcher.
125 This facility can be used to prevent such uncontrolled
126 GPE floodings.
127 Format: <byte> or <bitmap-list>
128
129 acpi_no_auto_serialize [HW,ACPI]
130 Disable auto-serialization of AML methods
131 AML control methods that contain the opcodes to create
132 named objects will be marked as "Serialized" by the
133 auto-serialization feature.
134 This feature is enabled by default.
135 This option allows to turn off the feature.
136
137 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
138 kernels.
139
140 acpi_no_static_ssdt [HW,ACPI,EARLY]
141 Disable installation of static SSDTs at early boot time
142 By default, SSDTs contained in the RSDT/XSDT will be
143 installed automatically and they will appear under
144 /sys/firmware/acpi/tables.
145 This option turns off this feature.
146 Note that specifying this option does not affect
147 dynamic table installation which will install SSDT
148 tables to /sys/firmware/acpi/tables/dynamic.
149
150 acpi_no_watchdog [HW,ACPI,WDT]
151 Ignore the ACPI-based watchdog interface (WDAT) and let
152 a native driver control the watchdog device instead.
153
154 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
155 Pass the RSDP address to the kernel, mostly used
156 on machines running EFI runtime service to boot the
157 second kernel for kdump.
158
159 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
160 Format: To spoof as Windows 98: ="Microsoft Windows"
161
162 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
163 of 2 which is mandated by ACPI 6) as the supported ACPI
164 specification revision (when using this switch, it may
165 be necessary to carry out a cold reboot _twice_ in a
166 row to make it take effect on the platform firmware).
167
168 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
169 acpi_osi="string1" # add string1
170 acpi_osi="!string2" # remove string2
171 acpi_osi=!* # remove all strings
172 acpi_osi=! # disable all built-in OS vendor
173 strings
174 acpi_osi=!! # enable all built-in OS vendor
175 strings
176 acpi_osi= # disable all strings
177
178 'acpi_osi=!' can be used in combination with single or
179 multiple 'acpi_osi="string1"' to support specific OS
180 vendor string(s). Note that such command can only
181 affect the default state of the OS vendor strings, thus
182 it cannot affect the default state of the feature group
183 strings and the current state of the OS vendor strings,
184 specifying it multiple times through kernel command line
185 is meaningless. This command is useful when one do not
186 care about the state of the feature group strings which
187 should be controlled by the OSPM.
188 Examples:
189 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
190 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
191 can make '_OSI("Windows 2000")' TRUE.
192
193 'acpi_osi=' cannot be used in combination with other
194 'acpi_osi=' command lines, the _OSI method will not
195 exist in the ACPI namespace. NOTE that such command can
196 only affect the _OSI support state, thus specifying it
197 multiple times through kernel command line is also
198 meaningless.
199 Examples:
200 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
201 FALSE.
202
203 'acpi_osi=!*' can be used in combination with single or
204 multiple 'acpi_osi="string1"' to support specific
205 string(s). Note that such command can affect the
206 current state of both the OS vendor strings and the
207 feature group strings, thus specifying it multiple times
208 through kernel command line is meaningful. But it may
209 still not able to affect the final state of a string if
210 there are quirks related to this string. This command
211 is useful when one want to control the state of the
212 feature group strings to debug BIOS issues related to
213 the OSPM features.
214 Examples:
215 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
216 '_OSI("Module Device")' FALSE.
217 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
218 '_OSI("Module Device")' TRUE.
219 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
220 equivalent to
221 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
222 and
223 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
224 they all will make '_OSI("Windows 2000")' TRUE.
225
226 acpi_pm_good [X86]
227 Override the pmtimer bug detection: force the kernel
228 to assume that this machine's pmtimer latches its value
229 and always returns good values.
230
231 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
232 Format: { level | edge | high | low }
233
234 acpi_skip_timer_override [HW,ACPI,EARLY]
235 Recognize and ignore IRQ0/pin2 Interrupt Override.
236 For broken nForce2 BIOS resulting in XT-PIC timer.
237
238 acpi_sleep= [HW,ACPI] Sleep options
239 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
240 s4_nohwsig, old_ordering, nonvs,
241 sci_force_enable, nobl }
242 See Documentation/power/video.rst for information on
243 s3_bios and s3_mode.
244 s3_beep is for debugging; it makes the PC's speaker beep
245 as soon as the kernel's real-mode entry point is called.
246 s4_hwsig causes the kernel to check the ACPI hardware
247 signature during resume from hibernation, and gracefully
248 refuse to resume if it has changed. This complies with
249 the ACPI specification but not with reality, since
250 Windows does not do this and many laptops do change it
251 on docking. So the default behaviour is to allow resume
252 and simply warn when the signature changes, unless the
253 s4_hwsig option is enabled.
254 s4_nohwsig prevents ACPI hardware signature from being
255 used (or even warned about) during resume.
256 old_ordering causes the ACPI 1.0 ordering of the _PTS
257 control method, with respect to putting devices into
258 low power states, to be enforced (the ACPI 2.0 ordering
259 of _PTS is used by default).
260 nonvs prevents the kernel from saving/restoring the
261 ACPI NVS memory during suspend/hibernation and resume.
262 sci_force_enable causes the kernel to set SCI_EN directly
263 on resume from S1/S3 (which is against the ACPI spec,
264 but some broken systems don't work without it).
265 nobl causes the internal blacklist of systems known to
266 behave incorrectly in some ways with respect to system
267 suspend and resume to be ignored (use wisely).
268
269 acpi_use_timer_override [HW,ACPI,EARLY]
270 Use timer override. For some broken Nvidia NF5 boards
271 that require a timer override, but don't have HPET
272
273 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
274 kernel's map of available physical RAM.
275
276 agp= [AGP]
277 { off | try_unsupported }
278 off: disable AGP support
279 try_unsupported: try to drive unsupported chipsets
280 (may crash computer or cause data corruption)
281
282 ALSA [HW,ALSA]
283 See Documentation/sound/alsa-configuration.rst
284
285 alignment= [KNL,ARM]
286 Allow the default userspace alignment fault handler
287 behaviour to be specified. Bit 0 enables warnings,
288 bit 1 enables fixups, and bit 2 sends a segfault.
289
290 align_va_addr= [X86-64]
291 Align virtual addresses by clearing slice [14:12] when
292 allocating a VMA at process creation time. This option
293 gives you up to 3% performance improvement on AMD F15h
294 machines (where it is enabled by default) for a
295 CPU-intensive style benchmark, and it can vary highly in
296 a microbenchmark depending on workload and compiler.
297
298 32: only for 32-bit processes
299 64: only for 64-bit processes
300 on: enable for both 32- and 64-bit processes
301 off: disable for both 32- and 64-bit processes
302
303 alloc_snapshot [FTRACE]
304 Allocate the ftrace snapshot buffer on boot up when the
305 main buffer is allocated. This is handy if debugging
306 and you need to use tracing_snapshot() on boot up, and
307 do not want to use tracing_snapshot_alloc() as it needs
308 to be done where GFP_KERNEL allocations are allowed.
309
310 allow_mismatched_32bit_el0 [ARM64,EARLY]
311 Allow execve() of 32-bit applications and setting of the
312 PER_LINUX32 personality on systems where only a strict
313 subset of the CPUs support 32-bit EL0. When this
314 parameter is present, the set of CPUs supporting 32-bit
315 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
316 and hot-unplug operations may be restricted.
317
318 See Documentation/arch/arm64/asymmetric-32bit.rst for more
319 information.
320
321 amd_iommu= [HW,X86-64]
322 Pass parameters to the AMD IOMMU driver in the system.
323 Possible values are:
324 fullflush - Deprecated, equivalent to iommu.strict=1
325 off - do not initialize any AMD IOMMU found in
326 the system
327 force_isolation - Force device isolation for all
328 devices. The IOMMU driver is not
329 allowed anymore to lift isolation
330 requirements as needed. This option
331 does not override iommu=pt
332 force_enable - Force enable the IOMMU on platforms known
333 to be buggy with IOMMU enabled. Use this
334 option with care.
335 pgtbl_v1 - Use v1 page table for DMA-API (Default).
336 pgtbl_v2 - Use v2 page table for DMA-API.
337 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
338
339 amd_iommu_dump= [HW,X86-64]
340 Enable AMD IOMMU driver option to dump the ACPI table
341 for AMD IOMMU. With this option enabled, AMD IOMMU
342 driver will print ACPI tables for AMD IOMMU during
343 IOMMU initialization.
344
345 amd_iommu_intr= [HW,X86-64]
346 Specifies one of the following AMD IOMMU interrupt
347 remapping modes:
348 legacy - Use legacy interrupt remapping mode.
349 vapic - Use virtual APIC mode, which allows IOMMU
350 to inject interrupts directly into guest.
351 This mode requires kvm-amd.avic=1.
352 (Default when IOMMU HW support is present.)
353
354 amd_pstate= [X86,EARLY]
355 disable
356 Do not enable amd_pstate as the default
357 scaling driver for the supported processors
358 passive
359 Use amd_pstate with passive mode as a scaling driver.
360 In this mode autonomous selection is disabled.
361 Driver requests a desired performance level and platform
362 tries to match the same performance level if it is
363 satisfied by guaranteed performance level.
364 active
365 Use amd_pstate_epp driver instance as the scaling driver,
366 driver provides a hint to the hardware if software wants
367 to bias toward performance (0x0) or energy efficiency (0xff)
368 to the CPPC firmware. then CPPC power algorithm will
369 calculate the runtime workload and adjust the realtime cores
370 frequency.
371 guided
372 Activate guided autonomous mode. Driver requests minimum and
373 maximum performance level and the platform autonomously
374 selects a performance level in this range and appropriate
375 to the current workload.
376
377 amd_prefcore=
378 [X86]
379 disable
380 Disable amd-pstate preferred core.
381
382 amijoy.map= [HW,JOY] Amiga joystick support
383 Map of devices attached to JOY0DAT and JOY1DAT
384 Format: <a>,<b>
385 See also Documentation/input/joydev/joystick.rst
386
387 analog.map= [HW,JOY] Analog joystick and gamepad support
388 Specifies type or capabilities of an analog joystick
389 connected to one of 16 gameports
390 Format: <type1>,<type2>,..<type16>
391
392 apc= [HW,SPARC]
393 Power management functions (SPARCstation-4/5 + deriv.)
394 Format: noidle
395 Disable APC CPU standby support. SPARCstation-Fox does
396 not play well with APC CPU idle - disable it if you have
397 APC and your system crashes randomly.
398
399 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
400 Change the output verbosity while booting
401 Format: { quiet (default) | verbose | debug }
402 Change the amount of debugging information output
403 when initialising the APIC and IO-APIC components.
404 For X86-32, this can also be used to specify an APIC
405 driver name.
406 Format: apic=driver_name
407 Examples: apic=bigsmp
408
409 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
410 Format: { bsp (default) | all | none }
411 bsp: External NMI is delivered only to CPU 0
412 all: External NMIs are broadcast to all CPUs as a
413 backup of CPU 0
414 none: External NMI is masked for all CPUs. This is
415 useful so that a dump capture kernel won't be
416 shot down by NMI
417
418 autoconf= [IPV6]
419 See Documentation/networking/ipv6.rst.
420
421 apm= [APM] Advanced Power Management
422 See header of arch/x86/kernel/apm_32.c.
423
424 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
425 Format: { "0" | "1" }
426 See security/apparmor/Kconfig help text
427 0 -- disable.
428 1 -- enable.
429 Default value is set via kernel config option.
430
431 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
432 Format: <io>,<irq>,<nodeID>
433
434 arm64.nobti [ARM64] Unconditionally disable Branch Target
435 Identification support
436
437 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
438 Set instructions support
439
440 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
441 support
442
443 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
444 support
445
446 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
447 Extension support
448
449 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
450 Extension support
451
452 ataflop= [HW,M68k]
453
454 atarimouse= [HW,MOUSE] Atari Mouse
455
456 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
457 EzKey and similar keyboards
458
459 atkbd.reset= [HW] Reset keyboard during initialization
460
461 atkbd.set= [HW] Select keyboard code set
462 Format: <int> (2 = AT (default), 3 = PS/2)
463
464 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
465 keyboards
466
467 atkbd.softraw= [HW] Choose between synthetic and real raw mode
468 Format: <bool> (0 = real, 1 = synthetic (default))
469
470 atkbd.softrepeat= [HW]
471 Use software keyboard repeat
472
473 audit= [KNL] Enable the audit sub-system
474 Format: { "0" | "1" | "off" | "on" }
475 0 | off - kernel audit is disabled and can not be
476 enabled until the next reboot
477 unset - kernel audit is initialized but disabled and
478 will be fully enabled by the userspace auditd.
479 1 | on - kernel audit is initialized and partially
480 enabled, storing at most audit_backlog_limit
481 messages in RAM until it is fully enabled by the
482 userspace auditd.
483 Default: unset
484
485 audit_backlog_limit= [KNL] Set the audit queue size limit.
486 Format: <int> (must be >=0)
487 Default: 64
488
489 bau= [X86_UV] Enable the BAU on SGI UV. The default
490 behavior is to disable the BAU (i.e. bau=0).
491 Format: { "0" | "1" }
492 0 - Disable the BAU.
493 1 - Enable the BAU.
494 unset - Disable the BAU.
495
496 baycom_epp= [HW,AX25]
497 Format: <io>,<mode>
498
499 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
500 Format: <io>,<mode>
501 See header of drivers/net/hamradio/baycom_par.c.
502
503 baycom_ser_fdx= [HW,AX25]
504 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
505 Format: <io>,<irq>,<mode>[,<baud>]
506 See header of drivers/net/hamradio/baycom_ser_fdx.c.
507
508 baycom_ser_hdx= [HW,AX25]
509 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
510 Format: <io>,<irq>,<mode>
511 See header of drivers/net/hamradio/baycom_ser_hdx.c.
512
513 bert_disable [ACPI]
514 Disable BERT OS support on buggy BIOSes.
515
516 bgrt_disable [ACPI,X86,EARLY]
517 Disable BGRT to avoid flickering OEM logo.
518
519 blkdevparts= Manual partition parsing of block device(s) for
520 embedded devices based on command line input.
521 See Documentation/block/cmdline-partition.rst
522
523 boot_delay= [KNL,EARLY]
524 Milliseconds to delay each printk during boot.
525 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
526 and you may also have to specify "lpj=". Boot_delay
527 values larger than 10 seconds (10000) are assumed
528 erroneous and ignored.
529 Format: integer
530
531 bootconfig [KNL,EARLY]
532 Extended command line options can be added to an initrd
533 and this will cause the kernel to look for it.
534
535 See Documentation/admin-guide/bootconfig.rst
536
537 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
538 bttv.radio= Most important insmod options are available as
539 kernel args too.
540 bttv.pll= See Documentation/admin-guide/media/bttv.rst
541 bttv.tuner=
542
543 bulk_remove=off [PPC] This parameter disables the use of the pSeries
544 firmware feature for flushing multiple hpte entries
545 at a time.
546
547 c101= [NET] Moxa C101 synchronous serial card
548
549 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
550 Sometimes CPU hardware bugs make them report the cache
551 size incorrectly. The kernel will attempt work arounds
552 to fix known problems, but for some CPUs it is not
553 possible to determine what the correct size should be.
554 This option provides an override for these situations.
555
556 carrier_timeout=
557 [NET] Specifies amount of time (in seconds) that
558 the kernel should wait for a network carrier. By default
559 it waits 120 seconds.
560
561 ca_keys= [KEYS] This parameter identifies a specific key(s) on
562 the system trusted keyring to be used for certificate
563 trust validation.
564 format: { id:<keyid> | builtin }
565
566 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
567 algorithm. Accepted values range from 0 to 7
568 inclusive. See arch/mips/include/asm/pgtable-bits.h
569 for platform specific values (SB1, Loongson3 and
570 others).
571
572 ccw_timeout_log [S390]
573 See Documentation/arch/s390/common_io.rst for details.
574
575 cgroup_disable= [KNL] Disable a particular controller or optional feature
576 Format: {name of the controller(s) or feature(s) to disable}
577 The effects of cgroup_disable=foo are:
578 - foo isn't auto-mounted if you mount all cgroups in
579 a single hierarchy
580 - foo isn't visible as an individually mountable
581 subsystem
582 - if foo is an optional feature then the feature is
583 disabled and corresponding cgroup files are not
584 created
585 {Currently only "memory" controller deal with this and
586 cut the overhead, others just disable the usage. So
587 only cgroup_disable=memory is actually worthy}
588 Specifying "pressure" disables per-cgroup pressure
589 stall information accounting feature
590
591 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
592 Format: { { controller | "all" | "named" }
593 [,{ controller | "all" | "named" }...] }
594 Like cgroup_disable, but only applies to cgroup v1;
595 the blacklisted controllers remain available in cgroup2.
596 "all" blacklists all controllers and "named" disables
597 named mounts. Specifying both "all" and "named" disables
598 all v1 hierarchies.
599
600 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
601 Format: { "true" | "false" }
602 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
603
604 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
605 Format: <string>
606 nosocket -- Disable socket memory accounting.
607 nokmem -- Disable kernel memory accounting.
608 nobpf -- Disable BPF memory accounting.
609
610 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
611 Format: { "0" | "1" }
612 See security/selinux/Kconfig help text.
613 0 -- check protection applied by kernel (includes
614 any implied execute protection).
615 1 -- check protection requested by application.
616 Default value is set via a kernel config option.
617 Value can be changed at runtime via
618 /sys/fs/selinux/checkreqprot.
619 Setting checkreqprot to 1 is deprecated.
620
621 cio_ignore= [S390]
622 See Documentation/arch/s390/common_io.rst for details.
623
624 clearcpuid=X[,X...] [X86]
625 Disable CPUID feature X for the kernel. See
626 arch/x86/include/asm/cpufeatures.h for the valid bit
627 numbers X. Note the Linux-specific bits are not necessarily
628 stable over kernel options, but the vendor-specific
629 ones should be.
630 X can also be a string as appearing in the flags: line
631 in /proc/cpuinfo which does not have the above
632 instability issue. However, not all features have names
633 in /proc/cpuinfo.
634 Note that using this option will taint your kernel.
635 Also note that user programs calling CPUID directly
636 or using the feature without checking anything
637 will still see it. This just prevents it from
638 being used by the kernel or shown in /proc/cpuinfo.
639 Also note the kernel might malfunction if you disable
640 some critical bits.
641
642 clk_ignore_unused
643 [CLK]
644 Prevents the clock framework from automatically gating
645 clocks that have not been explicitly enabled by a Linux
646 device driver but are enabled in hardware at reset or
647 by the bootloader/firmware. Note that this does not
648 force such clocks to be always-on nor does it reserve
649 those clocks in any way. This parameter is useful for
650 debug and development, but should not be needed on a
651 platform with proper driver support. For more
652 information, see Documentation/driver-api/clk.rst.
653
654 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
655 [Deprecated]
656 Forces specified clocksource (if available) to be used
657 when calculating gettimeofday(). If specified
658 clocksource is not available, it defaults to PIT.
659 Format: { pit | tsc | cyclone | pmtmr }
660
661 clocksource= Override the default clocksource
662 Format: <string>
663 Override the default clocksource and use the clocksource
664 with the name specified.
665 Some clocksource names to choose from, depending on
666 the platform:
667 [all] jiffies (this is the base, fallback clocksource)
668 [ACPI] acpi_pm
669 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
670 pxa_timer,timer3,32k_counter,timer0_1
671 [X86-32] pit,hpet,tsc;
672 scx200_hrt on Geode; cyclone on IBM x440
673 [MIPS] MIPS
674 [PARISC] cr16
675 [S390] tod
676 [SH] SuperH
677 [SPARC64] tick
678 [X86-64] hpet,tsc
679
680 clocksource.arm_arch_timer.evtstrm=
681 [ARM,ARM64,EARLY]
682 Format: <bool>
683 Enable/disable the eventstream feature of the ARM
684 architected timer so that code using WFE-based polling
685 loops can be debugged more effectively on production
686 systems.
687
688 clocksource.verify_n_cpus= [KNL]
689 Limit the number of CPUs checked for clocksources
690 marked with CLOCK_SOURCE_VERIFY_PERCPU that
691 are marked unstable due to excessive skew.
692 A negative value says to check all CPUs, while
693 zero says not to check any. Values larger than
694 nr_cpu_ids are silently truncated to nr_cpu_ids.
695 The actual CPUs are chosen randomly, with
696 no replacement if the same CPU is chosen twice.
697
698 clocksource-wdtest.holdoff= [KNL]
699 Set the time in seconds that the clocksource
700 watchdog test waits before commencing its tests.
701 Defaults to zero when built as a module and to
702 10 seconds when built into the kernel.
703
704 cma=nn[MG]@[start[MG][-end[MG]]]
705 [KNL,CMA,EARLY]
706 Sets the size of kernel global memory area for
707 contiguous memory allocations and optionally the
708 placement constraint by the physical address range of
709 memory allocations. A value of 0 disables CMA
710 altogether. For more information, see
711 kernel/dma/contiguous.c
712
713 cma_pernuma=nn[MG]
714 [KNL,CMA,EARLY]
715 Sets the size of kernel per-numa memory area for
716 contiguous memory allocations. A value of 0 disables
717 per-numa CMA altogether. And If this option is not
718 specified, the default value is 0.
719 With per-numa CMA enabled, DMA users on node nid will
720 first try to allocate buffer from the pernuma area
721 which is located in node nid, if the allocation fails,
722 they will fallback to the global default memory area.
723
724 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
725 [KNL,CMA,EARLY]
726 Sets the size of kernel numa memory area for
727 contiguous memory allocations. It will reserve CMA
728 area for the specified node.
729
730 With numa CMA enabled, DMA users on node nid will
731 first try to allocate buffer from the numa area
732 which is located in node nid, if the allocation fails,
733 they will fallback to the global default memory area.
734
735 cmo_free_hint= [PPC] Format: { yes | no }
736 Specify whether pages are marked as being inactive
737 when they are freed. This is used in CMO environments
738 to determine OS memory pressure for page stealing by
739 a hypervisor.
740 Default: yes
741
742 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
743 Sets the size of memory pool for coherent, atomic dma
744 allocations, by default set to 256K.
745
746 com20020= [HW,NET] ARCnet - COM20020 chipset
747 Format:
748 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
749
750 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
751 Format: <io>[,<irq>]
752
753 com90xx= [HW,NET]
754 ARCnet - COM90xx chipset (memory-mapped buffers)
755 Format: <io>[,<irq>[,<memstart>]]
756
757 condev= [HW,S390] console device
758 conmode=
759
760 con3215_drop= [S390,EARLY] 3215 console drop mode.
761 Format: y|n|Y|N|1|0
762 When set to true, drop data on the 3215 console when
763 the console buffer is full. In this case the
764 operator using a 3270 terminal emulator (for example
765 x3270) does not have to enter the clear key for the
766 console output to advance and the kernel to continue.
767 This leads to a much faster boot time when a 3270
768 terminal emulator is active. If no 3270 terminal
769 emulator is used, this parameter has no effect.
770
771 console= [KNL] Output console device and options.
772
773 tty<n> Use the virtual console device <n>.
774
775 ttyS<n>[,options]
776 ttyUSB0[,options]
777 Use the specified serial port. The options are of
778 the form "bbbbpnf", where "bbbb" is the baud rate,
779 "p" is parity ("n", "o", or "e"), "n" is number of
780 bits, and "f" is flow control ("r" for RTS or
781 omit it). Default is "9600n8".
782
783 See Documentation/admin-guide/serial-console.rst for more
784 information. See
785 Documentation/networking/netconsole.rst for an
786 alternative.
787
788 uart[8250],io,<addr>[,options]
789 uart[8250],mmio,<addr>[,options]
790 uart[8250],mmio16,<addr>[,options]
791 uart[8250],mmio32,<addr>[,options]
792 uart[8250],0x<addr>[,options]
793 Start an early, polled-mode console on the 8250/16550
794 UART at the specified I/O port or MMIO address,
795 switching to the matching ttyS device later.
796 MMIO inter-register address stride is either 8-bit
797 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
798 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
799 to be equivalent to 'mmio'. 'options' are specified in
800 the same format described for ttyS above; if unspecified,
801 the h/w is not re-initialized.
802
803 hvc<n> Use the hypervisor console device <n>. This is for
804 both Xen and PowerPC hypervisors.
805
806 { null | "" }
807 Use to disable console output, i.e., to have kernel
808 console messages discarded.
809 This must be the only console= parameter used on the
810 kernel command line.
811
812 If the device connected to the port is not a TTY but a braille
813 device, prepend "brl," before the device type, for instance
814 console=brl,ttyS0
815 For now, only VisioBraille is supported.
816
817 console_msg_format=
818 [KNL] Change console messages format
819 default
820 By default we print messages on consoles in
821 "[time stamp] text\n" format (time stamp may not be
822 printed, depending on CONFIG_PRINTK_TIME or
823 `printk_time' param).
824 syslog
825 Switch to syslog format: "<%u>[time stamp] text\n"
826 IOW, each message will have a facility and loglevel
827 prefix. The format is similar to one used by syslog()
828 syscall, or to executing "dmesg -S --raw" or to reading
829 from /proc/kmsg.
830
831 consoleblank= [KNL] The console blank (screen saver) timeout in
832 seconds. A value of 0 disables the blank timer.
833 Defaults to 0.
834
835 coredump_filter=
836 [KNL] Change the default value for
837 /proc/<pid>/coredump_filter.
838 See also Documentation/filesystems/proc.rst.
839
840 coresight_cpu_debug.enable
841 [ARM,ARM64]
842 Format: <bool>
843 Enable/disable the CPU sampling based debugging.
844 0: default value, disable debugging
845 1: enable debugging at boot time
846
847 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
848 Format:
849 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
850
851 cpuidle.off=1 [CPU_IDLE]
852 disable the cpuidle sub-system
853
854 cpuidle.governor=
855 [CPU_IDLE] Name of the cpuidle governor to use.
856
857 cpufreq.off=1 [CPU_FREQ]
858 disable the cpufreq sub-system
859
860 cpufreq.default_governor=
861 [CPU_FREQ] Name of the default cpufreq governor or
862 policy to use. This governor must be registered in the
863 kernel before the cpufreq driver probes.
864
865 cpu_init_udelay=N
866 [X86,EARLY] Delay for N microsec between assert and de-assert
867 of APIC INIT to start processors. This delay occurs
868 on every CPU online, such as boot, and resume from suspend.
869 Default: 10000
870
871 cpuhp.parallel=
872 [SMP] Enable/disable parallel bringup of secondary CPUs
873 Format: <bool>
874 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
875 the parameter has no effect.
876
877 crash_kexec_post_notifiers
878 Run kdump after running panic-notifiers and dumping
879 kmsg. This only for the users who doubt kdump always
880 succeeds in any situation.
881 Note that this also increases risks of kdump failure,
882 because some panic notifiers can make the crashed
883 kernel more unstable.
884
885 crashkernel=size[KMG][@offset[KMG]]
886 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
887 upon panic. This parameter reserves the physical
888 memory region [offset, offset + size] for that kernel
889 image. If '@offset' is omitted, then a suitable offset
890 is selected automatically.
891 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
892 under 4G first, and fall back to reserve region above
893 4G when '@offset' hasn't been specified.
894 See Documentation/admin-guide/kdump/kdump.rst for further details.
895
896 crashkernel=range1:size1[,range2:size2,...][@offset]
897 [KNL] Same as above, but depends on the memory
898 in the running system. The syntax of range is
899 start-[end] where start and end are both
900 a memory unit (amount[KMG]). See also
901 Documentation/admin-guide/kdump/kdump.rst for an example.
902
903 crashkernel=size[KMG],high
904 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
905 above 4G.
906 Allow kernel to allocate physical memory region from top,
907 so could be above 4G if system have more than 4G ram
908 installed. Otherwise memory region will be allocated
909 below 4G, if available.
910 It will be ignored if crashkernel=X is specified.
911 crashkernel=size[KMG],low
912 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
913 When crashkernel=X,high is passed, kernel could allocate
914 physical memory region above 4G, that cause second kernel
915 crash on system that require some amount of low memory,
916 e.g. swiotlb requires at least 64M+32K low memory, also
917 enough extra low memory is needed to make sure DMA buffers
918 for 32-bit devices won't run out. Kernel would try to allocate
919 default size of memory below 4G automatically. The default
920 size is platform dependent.
921 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
922 --> arm64: 128MiB
923 --> riscv: 128MiB
924 --> loongarch: 128MiB
925 This one lets the user specify own low range under 4G
926 for second kernel instead.
927 0: to disable low allocation.
928 It will be ignored when crashkernel=X,high is not used
929 or memory reserved is below 4G.
930
931 cryptomgr.notests
932 [KNL] Disable crypto self-tests
933
934 cs89x0_dma= [HW,NET]
935 Format: <dma>
936
937 cs89x0_media= [HW,NET]
938 Format: { rj45 | aui | bnc }
939
940 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
941 function call handling. When switched on,
942 additional debug data is printed to the console
943 in case a hanging CPU is detected, and that
944 CPU is pinged again in order to try to resolve
945 the hang situation. The default value of this
946 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
947 Kconfig option.
948
949 dasd= [HW,NET]
950 See header of drivers/s390/block/dasd_devmap.c.
951
952 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
953 (one device per port)
954 Format: <port#>,<type>
955 See also Documentation/input/devices/joystick-parport.rst
956
957 debug [KNL,EARLY] Enable kernel debugging (events log level).
958
959 debug_boot_weak_hash
960 [KNL,EARLY] Enable printing [hashed] pointers early in the
961 boot sequence. If enabled, we use a weak hash instead
962 of siphash to hash pointers. Use this option if you are
963 seeing instances of '(___ptrval___)') and need to see a
964 value (hashed pointer) instead. Cryptographically
965 insecure, please do not use on production kernels.
966
967 debug_locks_verbose=
968 [KNL] verbose locking self-tests
969 Format: <int>
970 Print debugging info while doing the locking API
971 self-tests.
972 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
973 (no extra messages), setting it to -1 (all bits set)
974 will print _a_lot_ more information - normally only
975 useful to lockdep developers.
976
977 debug_objects [KNL,EARLY] Enable object debugging
978
979 debug_guardpage_minorder=
980 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
981 parameter allows control of the order of pages that will
982 be intentionally kept free (and hence protected) by the
983 buddy allocator. Bigger value increase the probability
984 of catching random memory corruption, but reduce the
985 amount of memory for normal system use. The maximum
986 possible value is MAX_PAGE_ORDER/2. Setting this
987 parameter to 1 or 2 should be enough to identify most
988 random memory corruption problems caused by bugs in
989 kernel or driver code when a CPU writes to (or reads
990 from) a random memory location. Note that there exists
991 a class of memory corruptions problems caused by buggy
992 H/W or F/W or by drivers badly programming DMA
993 (basically when memory is written at bus level and the
994 CPU MMU is bypassed) which are not detectable by
995 CONFIG_DEBUG_PAGEALLOC, hence this option will not
996 help tracking down these problems.
997
998 debug_pagealloc=
999 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1000 enables the feature at boot time. By default, it is
1001 disabled and the system will work mostly the same as a
1002 kernel built without CONFIG_DEBUG_PAGEALLOC.
1003 Note: to get most of debug_pagealloc error reports, it's
1004 useful to also enable the page_owner functionality.
1005 on: enable the feature
1006
1007 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1008 userspace and debugfs internal clients.
1009 Format: { on, no-mount, off }
1010 on: All functions are enabled.
1011 no-mount:
1012 Filesystem is not registered but kernel clients can
1013 access APIs and a crashkernel can be used to read
1014 its content. There is nothing to mount.
1015 off: Filesystem is not registered and clients
1016 get a -EPERM as result when trying to register files
1017 or directories within debugfs.
1018 This is equivalent of the runtime functionality if
1019 debugfs was not enabled in the kernel at all.
1020 Default value is set in build-time with a kernel configuration.
1021
1022 debugpat [X86] Enable PAT debugging
1023
1024 default_hugepagesz=
1025 [HW] The size of the default HugeTLB page. This is
1026 the size represented by the legacy /proc/ hugepages
1027 APIs. In addition, this is the default hugetlb size
1028 used for shmget(), mmap() and mounting hugetlbfs
1029 filesystems. If not specified, defaults to the
1030 architecture's default huge page size. Huge page
1031 sizes are architecture dependent. See also
1032 Documentation/admin-guide/mm/hugetlbpage.rst.
1033 Format: size[KMG]
1034
1035 deferred_probe_timeout=
1036 [KNL] Debugging option to set a timeout in seconds for
1037 deferred probe to give up waiting on dependencies to
1038 probe. Only specific dependencies (subsystems or
1039 drivers) that have opted in will be ignored. A timeout
1040 of 0 will timeout at the end of initcalls. If the time
1041 out hasn't expired, it'll be restarted by each
1042 successful driver registration. This option will also
1043 dump out devices still on the deferred probe list after
1044 retrying.
1045
1046 delayacct [KNL] Enable per-task delay accounting
1047
1048 dell_smm_hwmon.ignore_dmi=
1049 [HW] Continue probing hardware even if DMI data
1050 indicates that the driver is running on unsupported
1051 hardware.
1052
1053 dell_smm_hwmon.force=
1054 [HW] Activate driver even if SMM BIOS signature does
1055 not match list of supported models and enable otherwise
1056 blacklisted features.
1057
1058 dell_smm_hwmon.power_status=
1059 [HW] Report power status in /proc/i8k
1060 (disabled by default).
1061
1062 dell_smm_hwmon.restricted=
1063 [HW] Allow controlling fans only if SYS_ADMIN
1064 capability is set.
1065
1066 dell_smm_hwmon.fan_mult=
1067 [HW] Factor to multiply fan speed with.
1068
1069 dell_smm_hwmon.fan_max=
1070 [HW] Maximum configurable fan speed.
1071
1072 dfltcc= [HW,S390]
1073 Format: { on | off | def_only | inf_only | always }
1074 on: s390 zlib hardware support for compression on
1075 level 1 and decompression (default)
1076 off: No s390 zlib hardware support
1077 def_only: s390 zlib hardware support for deflate
1078 only (compression on level 1)
1079 inf_only: s390 zlib hardware support for inflate
1080 only (decompression)
1081 always: Same as 'on' but ignores the selected compression
1082 level always using hardware support (used for debugging)
1083
1084 dhash_entries= [KNL]
1085 Set number of hash buckets for dentry cache.
1086
1087 disable_1tb_segments [PPC,EARLY]
1088 Disables the use of 1TB hash page table segments. This
1089 causes the kernel to fall back to 256MB segments which
1090 can be useful when debugging issues that require an SLB
1091 miss to occur.
1092
1093 disable= [IPV6]
1094 See Documentation/networking/ipv6.rst.
1095
1096 disable_radix [PPC,EARLY]
1097 Disable RADIX MMU mode on POWER9
1098
1099 disable_tlbie [PPC]
1100 Disable TLBIE instruction. Currently does not work
1101 with KVM, with HASH MMU, or with coherent accelerators.
1102
1103 disable_ddw [PPC/PSERIES,EARLY]
1104 Disable Dynamic DMA Window support. Use this
1105 to workaround buggy firmware.
1106
1107 disable_ipv6= [IPV6]
1108 See Documentation/networking/ipv6.rst.
1109
1110 disable_mtrr_cleanup [X86,EARLY]
1111 The kernel tries to adjust MTRR layout from continuous
1112 to discrete, to make X server driver able to add WB
1113 entry later. This parameter disables that.
1114
1115 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1116 By default the kernel will trim any uncacheable
1117 memory out of your available memory pool based on
1118 MTRR settings. This parameter disables that behavior,
1119 possibly causing your machine to run very slowly.
1120
1121 disable_timer_pin_1 [X86,EARLY]
1122 Disable PIN 1 of APIC timer
1123 Can be useful to work around chipset bugs.
1124
1125 dis_ucode_ldr [X86] Disable the microcode loader.
1126
1127 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1128 this option disables the debugging code at boot.
1129
1130 dma_debug_entries=<number>
1131 This option allows to tune the number of preallocated
1132 entries for DMA-API debugging code. One entry is
1133 required per DMA-API allocation. Use this if the
1134 DMA-API debugging code disables itself because the
1135 architectural default is too low.
1136
1137 dma_debug_driver=<driver_name>
1138 With this option the DMA-API debugging driver
1139 filter feature can be enabled at boot time. Just
1140 pass the driver to filter for as the parameter.
1141 The filter can be disabled or changed to another
1142 driver later using sysfs.
1143
1144 reg_file_data_sampling=
1145 [X86] Controls mitigation for Register File Data
1146 Sampling (RFDS) vulnerability. RFDS is a CPU
1147 vulnerability which may allow userspace to infer
1148 kernel data values previously stored in floating point
1149 registers, vector registers, or integer registers.
1150 RFDS only affects Intel Atom processors.
1151
1152 on: Turns ON the mitigation.
1153 off: Turns OFF the mitigation.
1154
1155 This parameter overrides the compile time default set
1156 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1157 disabled when other VERW based mitigations (like MDS)
1158 are enabled. In order to disable RFDS mitigation all
1159 VERW based mitigations need to be disabled.
1160
1161 For details see:
1162 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1163
1164 driver_async_probe= [KNL]
1165 List of driver names to be probed asynchronously. *
1166 matches with all driver names. If * is specified, the
1167 rest of the listed driver names are those that will NOT
1168 match the *.
1169 Format: <driver_name1>,<driver_name2>...
1170
1171 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1172 Broken monitors, graphic adapters, KVMs and EDIDless
1173 panels may send no or incorrect EDID data sets.
1174 This parameter allows to specify an EDID data sets
1175 in the /lib/firmware directory that are used instead.
1176 An EDID data set will only be used for a particular
1177 connector, if its name and a colon are prepended to
1178 the EDID name. Each connector may use a unique EDID
1179 data set by separating the files with a comma. An EDID
1180 data set with no connector name will be used for
1181 any connectors not explicitly specified.
1182
1183 dscc4.setup= [NET]
1184
1185 dt_cpu_ftrs= [PPC,EARLY]
1186 Format: {"off" | "known"}
1187 Control how the dt_cpu_ftrs device-tree binding is
1188 used for CPU feature discovery and setup (if it
1189 exists).
1190 off: Do not use it, fall back to legacy cpu table.
1191 known: Do not pass through unknown features to guests
1192 or userspace, only those that the kernel is aware of.
1193
1194 dump_apple_properties [X86]
1195 Dump name and content of EFI device properties on
1196 x86 Macs. Useful for driver authors to determine
1197 what data is available or for reverse-engineering.
1198
1199 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1200 <module>.dyndbg[="val"]
1201 Enable debug messages at boot time. See
1202 Documentation/admin-guide/dynamic-debug-howto.rst
1203 for details.
1204
1205 early_ioremap_debug [KNL,EARLY]
1206 Enable debug messages in early_ioremap support. This
1207 is useful for tracking down temporary early mappings
1208 which are not unmapped.
1209
1210 earlycon= [KNL,EARLY] Output early console device and options.
1211
1212 When used with no options, the early console is
1213 determined by stdout-path property in device tree's
1214 chosen node or the ACPI SPCR table if supported by
1215 the platform.
1216
1217 cdns,<addr>[,options]
1218 Start an early, polled-mode console on a Cadence
1219 (xuartps) serial port at the specified address. Only
1220 supported option is baud rate. If baud rate is not
1221 specified, the serial port must already be setup and
1222 configured.
1223
1224 uart[8250],io,<addr>[,options[,uartclk]]
1225 uart[8250],mmio,<addr>[,options[,uartclk]]
1226 uart[8250],mmio32,<addr>[,options[,uartclk]]
1227 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1228 uart[8250],0x<addr>[,options]
1229 Start an early, polled-mode console on the 8250/16550
1230 UART at the specified I/O port or MMIO address.
1231 MMIO inter-register address stride is either 8-bit
1232 (mmio) or 32-bit (mmio32 or mmio32be).
1233 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1234 to be equivalent to 'mmio'. 'options' are specified
1235 in the same format described for "console=ttyS<n>"; if
1236 unspecified, the h/w is not initialized. 'uartclk' is
1237 the uart clock frequency; if unspecified, it is set
1238 to 'BASE_BAUD' * 16.
1239
1240 pl011,<addr>
1241 pl011,mmio32,<addr>
1242 Start an early, polled-mode console on a pl011 serial
1243 port at the specified address. The pl011 serial port
1244 must already be setup and configured. Options are not
1245 yet supported. If 'mmio32' is specified, then only
1246 the driver will use only 32-bit accessors to read/write
1247 the device registers.
1248
1249 liteuart,<addr>
1250 Start an early console on a litex serial port at the
1251 specified address. The serial port must already be
1252 setup and configured. Options are not yet supported.
1253
1254 meson,<addr>
1255 Start an early, polled-mode console on a meson serial
1256 port at the specified address. The serial port must
1257 already be setup and configured. Options are not yet
1258 supported.
1259
1260 msm_serial,<addr>
1261 Start an early, polled-mode console on an msm serial
1262 port at the specified address. The serial port
1263 must already be setup and configured. Options are not
1264 yet supported.
1265
1266 msm_serial_dm,<addr>
1267 Start an early, polled-mode console on an msm serial
1268 dm port at the specified address. The serial port
1269 must already be setup and configured. Options are not
1270 yet supported.
1271
1272 owl,<addr>
1273 Start an early, polled-mode console on a serial port
1274 of an Actions Semi SoC, such as S500 or S900, at the
1275 specified address. The serial port must already be
1276 setup and configured. Options are not yet supported.
1277
1278 rda,<addr>
1279 Start an early, polled-mode console on a serial port
1280 of an RDA Micro SoC, such as RDA8810PL, at the
1281 specified address. The serial port must already be
1282 setup and configured. Options are not yet supported.
1283
1284 sbi
1285 Use RISC-V SBI (Supervisor Binary Interface) for early
1286 console.
1287
1288 smh Use ARM semihosting calls for early console.
1289
1290 s3c2410,<addr>
1291 s3c2412,<addr>
1292 s3c2440,<addr>
1293 s3c6400,<addr>
1294 s5pv210,<addr>
1295 exynos4210,<addr>
1296 Use early console provided by serial driver available
1297 on Samsung SoCs, requires selecting proper type and
1298 a correct base address of the selected UART port. The
1299 serial port must already be setup and configured.
1300 Options are not yet supported.
1301
1302 lantiq,<addr>
1303 Start an early, polled-mode console on a lantiq serial
1304 (lqasc) port at the specified address. The serial port
1305 must already be setup and configured. Options are not
1306 yet supported.
1307
1308 lpuart,<addr>
1309 lpuart32,<addr>
1310 Use early console provided by Freescale LP UART driver
1311 found on Freescale Vybrid and QorIQ LS1021A processors.
1312 A valid base address must be provided, and the serial
1313 port must already be setup and configured.
1314
1315 ec_imx21,<addr>
1316 ec_imx6q,<addr>
1317 Start an early, polled-mode, output-only console on the
1318 Freescale i.MX UART at the specified address. The UART
1319 must already be setup and configured.
1320
1321 ar3700_uart,<addr>
1322 Start an early, polled-mode console on the
1323 Armada 3700 serial port at the specified
1324 address. The serial port must already be setup
1325 and configured. Options are not yet supported.
1326
1327 qcom_geni,<addr>
1328 Start an early, polled-mode console on a Qualcomm
1329 Generic Interface (GENI) based serial port at the
1330 specified address. The serial port must already be
1331 setup and configured. Options are not yet supported.
1332
1333 efifb,[options]
1334 Start an early, unaccelerated console on the EFI
1335 memory mapped framebuffer (if available). On cache
1336 coherent non-x86 systems that use system memory for
1337 the framebuffer, pass the 'ram' option so that it is
1338 mapped with the correct attributes.
1339
1340 linflex,<addr>
1341 Use early console provided by Freescale LINFlexD UART
1342 serial driver for NXP S32V234 SoCs. A valid base
1343 address must be provided, and the serial port must
1344 already be setup and configured.
1345
1346 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1347 earlyprintk=vga
1348 earlyprintk=sclp
1349 earlyprintk=xen
1350 earlyprintk=serial[,ttySn[,baudrate]]
1351 earlyprintk=serial[,0x...[,baudrate]]
1352 earlyprintk=ttySn[,baudrate]
1353 earlyprintk=dbgp[debugController#]
1354 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1355 earlyprintk=xdbc[xhciController#]
1356 earlyprintk=bios
1357
1358 earlyprintk is useful when the kernel crashes before
1359 the normal console is initialized. It is not enabled by
1360 default because it has some cosmetic problems.
1361
1362 Append ",keep" to not disable it when the real console
1363 takes over.
1364
1365 Only one of vga, serial, or usb debug port can
1366 be used at a time.
1367
1368 Currently only ttyS0 and ttyS1 may be specified by
1369 name. Other I/O ports may be explicitly specified
1370 on some architectures (x86 and arm at least) by
1371 replacing ttySn with an I/O port address, like this:
1372 earlyprintk=serial,0x1008,115200
1373 You can find the port for a given device in
1374 /proc/tty/driver/serial:
1375 2: uart:ST16650V2 port:00001008 irq:18 ...
1376
1377 Interaction with the standard serial driver is not
1378 very good.
1379
1380 The VGA output is eventually overwritten by
1381 the real console.
1382
1383 The xen option can only be used in Xen domains.
1384
1385 The sclp output can only be used on s390.
1386
1387 The bios output can only be used on SuperH.
1388
1389 The optional "force" to "pciserial" enables use of a
1390 PCI device even when its classcode is not of the
1391 UART class.
1392
1393 edac_report= [HW,EDAC] Control how to report EDAC event
1394 Format: {"on" | "off" | "force"}
1395 on: enable EDAC to report H/W event. May be overridden
1396 by other higher priority error reporting module.
1397 off: disable H/W event reporting through EDAC.
1398 force: enforce the use of EDAC to report H/W event.
1399 default: on.
1400
1401 edd= [EDD]
1402 Format: {"off" | "on" | "skip[mbr]"}
1403
1404 efi= [EFI,EARLY]
1405 Format: { "debug", "disable_early_pci_dma",
1406 "nochunk", "noruntime", "nosoftreserve",
1407 "novamap", "no_disable_early_pci_dma" }
1408 debug: enable misc debug output.
1409 disable_early_pci_dma: disable the busmaster bit on all
1410 PCI bridges while in the EFI boot stub.
1411 nochunk: disable reading files in "chunks" in the EFI
1412 boot stub, as chunking can cause problems with some
1413 firmware implementations.
1414 noruntime : disable EFI runtime services support
1415 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1416 attribute may cause the kernel to reserve the
1417 memory range for a memory mapping driver to
1418 claim. Specify efi=nosoftreserve to disable this
1419 reservation and treat the memory by its base type
1420 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1421 novamap: do not call SetVirtualAddressMap().
1422 no_disable_early_pci_dma: Leave the busmaster bit set
1423 on all PCI bridges while in the EFI boot stub
1424
1425 efi_no_storage_paranoia [EFI,X86,EARLY]
1426 Using this parameter you can use more than 50% of
1427 your efi variable storage. Use this parameter only if
1428 you are really sure that your UEFI does sane gc and
1429 fulfills the spec otherwise your board may brick.
1430
1431 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI,X86,EARLY]
1432 Add arbitrary attribute to specific memory range by
1433 updating original EFI memory map.
1434 Region of memory which aa attribute is added to is
1435 from ss to ss+nn.
1436
1437 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1438 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1439 attribute is added to range 0x100000000-0x180000000 and
1440 0x10a0000000-0x1120000000.
1441
1442 If efi_fake_mem=8G@9G:0x40000 is specified, the
1443 EFI_MEMORY_SP(0x40000) attribute is added to
1444 range 0x240000000-0x43fffffff.
1445
1446 Using this parameter you can do debugging of EFI memmap
1447 related features. For example, you can do debugging of
1448 Address Range Mirroring feature even if your box
1449 doesn't support it, or mark specific memory as
1450 "soft reserved".
1451
1452 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1453 that is to be dynamically loaded by Linux. If there are
1454 multiple variables with the same name but with different
1455 vendor GUIDs, all of them will be loaded. See
1456 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1457
1458
1459 eisa_irq_edge= [PARISC,HW]
1460 See header of drivers/parisc/eisa.c.
1461
1462 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1463 Format: ekgdboc=kbd
1464
1465 This is designed to be used in conjunction with
1466 the boot argument: earlyprintk=vga
1467
1468 This parameter works in place of the kgdboc parameter
1469 but can only be used if the backing tty is available
1470 very early in the boot process. For early debugging
1471 via a serial port see kgdboc_earlycon instead.
1472
1473 elanfreq= [X86-32]
1474 See comment before function elanfreq_setup() in
1475 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1476
1477 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1478 Specifies physical address of start of kernel core
1479 image elf header and optionally the size. Generally
1480 kexec loader will pass this option to capture kernel.
1481 See Documentation/admin-guide/kdump/kdump.rst for details.
1482
1483 enable_mtrr_cleanup [X86,EARLY]
1484 The kernel tries to adjust MTRR layout from continuous
1485 to discrete, to make X server driver able to add WB
1486 entry later. This parameter enables that.
1487
1488 enable_timer_pin_1 [X86]
1489 Enable PIN 1 of APIC timer
1490 Can be useful to work around chipset bugs
1491 (in particular on some ATI chipsets).
1492 The kernel tries to set a reasonable default.
1493
1494 enforcing= [SELINUX] Set initial enforcing status.
1495 Format: {"0" | "1"}
1496 See security/selinux/Kconfig help text.
1497 0 -- permissive (log only, no denials).
1498 1 -- enforcing (deny and log).
1499 Default value is 0.
1500 Value can be changed at runtime via
1501 /sys/fs/selinux/enforce.
1502
1503 erst_disable [ACPI]
1504 Disable Error Record Serialization Table (ERST)
1505 support.
1506
1507 ether= [HW,NET] Ethernet cards parameters
1508 This option is obsoleted by the "netdev=" option, which
1509 has equivalent usage. See its documentation for details.
1510
1511 evm= [EVM]
1512 Format: { "fix" }
1513 Permit 'security.evm' to be updated regardless of
1514 current integrity status.
1515
1516 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1517 stages so cover more early boot allocations.
1518 Please note that as side effect some optimizations
1519 might be disabled to achieve that (e.g. parallelized
1520 memory initialization is disabled) so the boot process
1521 might take longer, especially on systems with a lot of
1522 memory. Available with CONFIG_PAGE_EXTENSION=y.
1523
1524 failslab=
1525 fail_usercopy=
1526 fail_page_alloc=
1527 fail_make_request=[KNL]
1528 General fault injection mechanism.
1529 Format: <interval>,<probability>,<space>,<times>
1530 See also Documentation/fault-injection/.
1531
1532 fb_tunnels= [NET]
1533 Format: { initns | none }
1534 See Documentation/admin-guide/sysctl/net.rst for
1535 fb_tunnels_only_for_init_ns
1536
1537 floppy= [HW]
1538 See Documentation/admin-guide/blockdev/floppy.rst.
1539
1540 forcepae [X86-32]
1541 Forcefully enable Physical Address Extension (PAE).
1542 Many Pentium M systems disable PAE but may have a
1543 functionally usable PAE implementation.
1544 Warning: use of this parameter will taint the kernel
1545 and may cause unknown problems.
1546
1547 fred= [X86-64]
1548 Enable/disable Flexible Return and Event Delivery.
1549 Format: { on | off }
1550 on: enable FRED when it's present.
1551 off: disable FRED, the default setting.
1552
1553 ftrace=[tracer]
1554 [FTRACE] will set and start the specified tracer
1555 as early as possible in order to facilitate early
1556 boot debugging.
1557
1558 ftrace_boot_snapshot
1559 [FTRACE] On boot up, a snapshot will be taken of the
1560 ftrace ring buffer that can be read at:
1561 /sys/kernel/tracing/snapshot.
1562 This is useful if you need tracing information from kernel
1563 boot up that is likely to be overridden by user space
1564 start up functionality.
1565
1566 Optionally, the snapshot can also be defined for a tracing
1567 instance that was created by the trace_instance= command
1568 line parameter.
1569
1570 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1571
1572 The above will cause the "foo" tracing instance to trigger
1573 a snapshot at the end of boot up.
1574
1575 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> |
1576 ,<instance>=2(orig_cpu)]
1577 [FTRACE] will dump the trace buffers on oops.
1578 If no parameter is passed, ftrace will dump global
1579 buffers of all CPUs, if you pass 2 or orig_cpu, it
1580 will dump only the buffer of the CPU that triggered
1581 the oops, or the specific instance will be dumped if
1582 its name is passed. Multiple instance dump is also
1583 supported, and instances are separated by commas. Each
1584 instance supports only dump on CPU that triggered the
1585 oops by passing 2 or orig_cpu to it.
1586
1587 ftrace_dump_on_oops=foo=orig_cpu
1588
1589 The above will dump only the buffer of "foo" instance
1590 on CPU that triggered the oops.
1591
1592 ftrace_dump_on_oops,foo,bar=orig_cpu
1593
1594 The above will dump global buffer on all CPUs, the
1595 buffer of "foo" instance on all CPUs and the buffer
1596 of "bar" instance on CPU that triggered the oops.
1597
1598 ftrace_filter=[function-list]
1599 [FTRACE] Limit the functions traced by the function
1600 tracer at boot up. function-list is a comma-separated
1601 list of functions. This list can be changed at run
1602 time by the set_ftrace_filter file in the debugfs
1603 tracing directory.
1604
1605 ftrace_notrace=[function-list]
1606 [FTRACE] Do not trace the functions specified in
1607 function-list. This list can be changed at run time
1608 by the set_ftrace_notrace file in the debugfs
1609 tracing directory.
1610
1611 ftrace_graph_filter=[function-list]
1612 [FTRACE] Limit the top level callers functions traced
1613 by the function graph tracer at boot up.
1614 function-list is a comma-separated list of functions
1615 that can be changed at run time by the
1616 set_graph_function file in the debugfs tracing directory.
1617
1618 ftrace_graph_notrace=[function-list]
1619 [FTRACE] Do not trace from the functions specified in
1620 function-list. This list is a comma-separated list of
1621 functions that can be changed at run time by the
1622 set_graph_notrace file in the debugfs tracing directory.
1623
1624 ftrace_graph_max_depth=<uint>
1625 [FTRACE] Used with the function graph tracer. This is
1626 the max depth it will trace into a function. This value
1627 can be changed at run time by the max_graph_depth file
1628 in the tracefs tracing directory. default: 0 (no limit)
1629
1630 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1631 devices by scanning the firmware to infer the
1632 consumer/supplier relationships. This feature is
1633 especially useful when drivers are loaded as modules as
1634 it ensures proper ordering of tasks like device probing
1635 (suppliers first, then consumers), supplier boot state
1636 clean up (only after all consumers have probed),
1637 suspend/resume & runtime PM (consumers first, then
1638 suppliers).
1639 Format: { off | permissive | on | rpm }
1640 off -- Don't create device links from firmware info.
1641 permissive -- Create device links from firmware info
1642 but use it only for ordering boot state clean
1643 up (sync_state() calls).
1644 on -- Create device links from firmware info and use it
1645 to enforce probe and suspend/resume ordering.
1646 rpm -- Like "on", but also use to order runtime PM.
1647
1648 fw_devlink.strict=<bool>
1649 [KNL,EARLY] Treat all inferred dependencies as mandatory
1650 dependencies. This only applies for fw_devlink=on|rpm.
1651 Format: <bool>
1652
1653 fw_devlink.sync_state =
1654 [KNL,EARLY] When all devices that could probe have finished
1655 probing, this parameter controls what to do with
1656 devices that haven't yet received their sync_state()
1657 calls.
1658 Format: { strict | timeout }
1659 strict -- Default. Continue waiting on consumers to
1660 probe successfully.
1661 timeout -- Give up waiting on consumers and call
1662 sync_state() on any devices that haven't yet
1663 received their sync_state() calls after
1664 deferred_probe_timeout has expired or by
1665 late_initcall() if !CONFIG_MODULES.
1666
1667 gamecon.map[2|3]=
1668 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1669 support via parallel port (up to 5 devices per port)
1670 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1671 See also Documentation/input/devices/joystick-parport.rst
1672
1673 gamma= [HW,DRM]
1674
1675 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1676 Format: off | on
1677 default: on
1678
1679 gather_data_sampling=
1680 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1681 mitigation.
1682
1683 Gather Data Sampling is a hardware vulnerability which
1684 allows unprivileged speculative access to data which was
1685 previously stored in vector registers.
1686
1687 This issue is mitigated by default in updated microcode.
1688 The mitigation may have a performance impact but can be
1689 disabled. On systems without the microcode mitigation
1690 disabling AVX serves as a mitigation.
1691
1692 force: Disable AVX to mitigate systems without
1693 microcode mitigation. No effect if the microcode
1694 mitigation is present. Known to cause crashes in
1695 userspace with buggy AVX enumeration.
1696
1697 off: Disable GDS mitigation.
1698
1699 gcov_persist= [GCOV] When non-zero (default), profiling data for
1700 kernel modules is saved and remains accessible via
1701 debugfs, even when the module is unloaded/reloaded.
1702 When zero, profiling data is discarded and associated
1703 debugfs files are removed at module unload time.
1704
1705 goldfish [X86] Enable the goldfish android emulator platform.
1706 Don't use this when you are not running on the
1707 android emulator
1708
1709 gpio-mockup.gpio_mockup_ranges
1710 [HW] Sets the ranges of gpiochip of for this device.
1711 Format: <start1>,<end1>,<start2>,<end2>...
1712 gpio-mockup.gpio_mockup_named_lines
1713 [HW] Let the driver know GPIO lines should be named.
1714
1715 gpt [EFI] Forces disk with valid GPT signature but
1716 invalid Protective MBR to be treated as GPT. If the
1717 primary GPT is corrupted, it enables the backup/alternate
1718 GPT to be used instead.
1719
1720 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1721 the "Enable 0" bit of the configuration register.
1722 Format: 0 | 1
1723 Default: 0
1724 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1725 the "Enable 0" bit of the configuration register.
1726 Format: 0 | 1
1727 Default: 0
1728 grcan.select= [HW] Select which physical interface to use.
1729 Format: 0 | 1
1730 Default: 0
1731 grcan.txsize= [HW] Sets the size of the tx buffer.
1732 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1733 Default: 1024
1734 grcan.rxsize= [HW] Sets the size of the rx buffer.
1735 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1736 Default: 1024
1737
1738 hardened_usercopy=
1739 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1740 hardening is enabled for this boot. Hardened
1741 usercopy checking is used to protect the kernel
1742 from reading or writing beyond known memory
1743 allocation boundaries as a proactive defense
1744 against bounds-checking flaws in the kernel's
1745 copy_to_user()/copy_from_user() interface.
1746 on Perform hardened usercopy checks (default).
1747 off Disable hardened usercopy checks.
1748
1749 hardlockup_all_cpu_backtrace=
1750 [KNL] Should the hard-lockup detector generate
1751 backtraces on all cpus.
1752 Format: 0 | 1
1753
1754 hashdist= [KNL,NUMA] Large hashes allocated during boot
1755 are distributed across NUMA nodes. Defaults on
1756 for 64-bit NUMA, off otherwise.
1757 Format: 0 | 1 (for off | on)
1758
1759 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1760
1761 hd= [EIDE] (E)IDE hard drive subsystem geometry
1762 Format: <cyl>,<head>,<sect>
1763
1764 hest_disable [ACPI]
1765 Disable Hardware Error Source Table (HEST) support;
1766 corresponding firmware-first mode error processing
1767 logic will be disabled.
1768
1769 hibernate= [HIBERNATION]
1770 noresume Don't check if there's a hibernation image
1771 present during boot.
1772 nocompress Don't compress/decompress hibernation images.
1773 no Disable hibernation and resume.
1774 protect_image Turn on image protection during restoration
1775 (that will set all pages holding image data
1776 during restoration read-only).
1777
1778 hibernate.compressor= [HIBERNATION] Compression algorithm to be
1779 used with hibernation.
1780 Format: { lzo | lz4 }
1781 Default: lzo
1782
1783 lzo: Select LZO compression algorithm to
1784 compress/decompress hibernation image.
1785
1786 lz4: Select LZ4 compression algorithm to
1787 compress/decompress hibernation image.
1788
1789 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
1790 size of <nn>. This works even on boxes that have no
1791 highmem otherwise. This also works to reduce highmem
1792 size on bigger boxes.
1793
1794 highres= [KNL] Enable/disable high resolution timer mode.
1795 Valid parameters: "on", "off"
1796 Default: "on"
1797
1798 hlt [BUGS=ARM,SH]
1799
1800 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
1801 Format: <string>
1802 This allows setting the system's hostname during early
1803 startup. This sets the name returned by gethostname.
1804 Using this parameter to set the hostname makes it
1805 possible to ensure the hostname is correctly set before
1806 any userspace processes run, avoiding the possibility
1807 that a process may call gethostname before the hostname
1808 has been explicitly set, resulting in the calling
1809 process getting an incorrect result. The string must
1810 not exceed the maximum allowed hostname length (usually
1811 64 characters) and will be truncated otherwise.
1812
1813 hpet= [X86-32,HPET] option to control HPET usage
1814 Format: { enable (default) | disable | force |
1815 verbose }
1816 disable: disable HPET and use PIT instead
1817 force: allow force enabled of undocumented chips (ICH4,
1818 VIA, nVidia)
1819 verbose: show contents of HPET registers during setup
1820
1821 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1822 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1823
1824 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1825 If this follows hugepagesz (below), it specifies
1826 the number of pages of hugepagesz to be allocated.
1827 If this is the first HugeTLB parameter on the command
1828 line, it specifies the number of pages to allocate for
1829 the default huge page size. If using node format, the
1830 number of pages to allocate per-node can be specified.
1831 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1832 Format: <integer> or (node format)
1833 <node>:<integer>[,<node>:<integer>]
1834
1835 hugepagesz=
1836 [HW] The size of the HugeTLB pages. This is used in
1837 conjunction with hugepages (above) to allocate huge
1838 pages of a specific size at boot. The pair
1839 hugepagesz=X hugepages=Y can be specified once for
1840 each supported huge page size. Huge page sizes are
1841 architecture dependent. See also
1842 Documentation/admin-guide/mm/hugetlbpage.rst.
1843 Format: size[KMG]
1844
1845 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
1846 of gigantic hugepages. Or using node format, the size
1847 of a CMA area per node can be specified.
1848 Format: nn[KMGTPE] or (node format)
1849 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1850
1851 Reserve a CMA area of given size and allocate gigantic
1852 hugepages using the CMA allocator. If enabled, the
1853 boot-time allocation of gigantic hugepages is skipped.
1854
1855 hugetlb_free_vmemmap=
1856 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1857 enabled.
1858 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1859 Allows heavy hugetlb users to free up some more
1860 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1861 Format: { on | off (default) }
1862
1863 on: enable HVO
1864 off: disable HVO
1865
1866 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1867 the default is on.
1868
1869 Note that the vmemmap pages may be allocated from the added
1870 memory block itself when memory_hotplug.memmap_on_memory is
1871 enabled, those vmemmap pages cannot be optimized even if this
1872 feature is enabled. Other vmemmap pages not allocated from
1873 the added memory block itself do not be affected.
1874
1875 hung_task_panic=
1876 [KNL] Should the hung task detector generate panics.
1877 Format: 0 | 1
1878
1879 A value of 1 instructs the kernel to panic when a
1880 hung task is detected. The default value is controlled
1881 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1882 option. The value selected by this boot parameter can
1883 be changed later by the kernel.hung_task_panic sysctl.
1884
1885 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1886 terminal devices. Valid values: 0..8
1887 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1888 If specified, z/VM IUCV HVC accepts connections
1889 from listed z/VM user IDs only.
1890
1891 hv_nopvspin [X86,HYPER_V,EARLY]
1892 Disables the paravirt spinlock optimizations
1893 which allow the hypervisor to 'idle' the guest
1894 on lock contention.
1895
1896 i2c_bus= [HW] Override the default board specific I2C bus speed
1897 or register an additional I2C bus that is not
1898 registered from board initialization code.
1899 Format:
1900 <bus_id>,<clkrate>
1901
1902 i8042.debug [HW] Toggle i8042 debug mode
1903 i8042.unmask_kbd_data
1904 [HW] Enable printing of interrupt data from the KBD port
1905 (disabled by default, and as a pre-condition
1906 requires that i8042.debug=1 be enabled)
1907 i8042.direct [HW] Put keyboard port into non-translated mode
1908 i8042.dumbkbd [HW] Pretend that controller can only read data from
1909 keyboard and cannot control its state
1910 (Don't attempt to blink the leds)
1911 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1912 i8042.nokbd [HW] Don't check/create keyboard port
1913 i8042.noloop [HW] Disable the AUX Loopback command while probing
1914 for the AUX port
1915 i8042.nomux [HW] Don't check presence of an active multiplexing
1916 controller
1917 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1918 controllers
1919 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1920 i8042.reset [HW] Reset the controller during init, cleanup and
1921 suspend-to-ram transitions, only during s2r
1922 transitions, or never reset
1923 Format: { 1 | Y | y | 0 | N | n }
1924 1, Y, y: always reset controller
1925 0, N, n: don't ever reset controller
1926 Default: only on s2r transitions on x86; most other
1927 architectures force reset to be always executed
1928 i8042.unlock [HW] Unlock (ignore) the keylock
1929 i8042.kbdreset [HW] Reset device connected to KBD port
1930 i8042.probe_defer
1931 [HW] Allow deferred probing upon i8042 probe errors
1932
1933 i810= [HW,DRM]
1934
1935 i915.invert_brightness=
1936 [DRM] Invert the sense of the variable that is used to
1937 set the brightness of the panel backlight. Normally a
1938 brightness value of 0 indicates backlight switched off,
1939 and the maximum of the brightness value sets the backlight
1940 to maximum brightness. If this parameter is set to 0
1941 (default) and the machine requires it, or this parameter
1942 is set to 1, a brightness value of 0 sets the backlight
1943 to maximum brightness, and the maximum of the brightness
1944 value switches the backlight off.
1945 -1 -- never invert brightness
1946 0 -- machine default
1947 1 -- force brightness inversion
1948
1949 ia32_emulation= [X86-64]
1950 Format: <bool>
1951 When true, allows loading 32-bit programs and executing 32-bit
1952 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
1953 boot time. When false, unconditionally disables IA32 emulation.
1954
1955 icn= [HW,ISDN]
1956 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1957
1958
1959 idle= [X86,EARLY]
1960 Format: idle=poll, idle=halt, idle=nomwait
1961 Poll forces a polling idle loop that can slightly
1962 improve the performance of waking up a idle CPU, but
1963 will use a lot of power and make the system run hot.
1964 Not recommended.
1965 idle=halt: Halt is forced to be used for CPU idle.
1966 In such case C2/C3 won't be used again.
1967 idle=nomwait: Disable mwait for CPU C-states
1968
1969 idxd.sva= [HW]
1970 Format: <bool>
1971 Allow force disabling of Shared Virtual Memory (SVA)
1972 support for the idxd driver. By default it is set to
1973 true (1).
1974
1975 idxd.tc_override= [HW]
1976 Format: <bool>
1977 Allow override of default traffic class configuration
1978 for the device. By default it is set to false (0).
1979
1980 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1981 Format: { strict | legacy | 2008 | relaxed }
1982 Default: strict
1983
1984 Choose which programs will be accepted for execution
1985 based on the IEEE 754 NaN encoding(s) supported by
1986 the FPU and the NaN encoding requested with the value
1987 of an ELF file header flag individually set by each
1988 binary. Hardware implementations are permitted to
1989 support either or both of the legacy and the 2008 NaN
1990 encoding mode.
1991
1992 Available settings are as follows:
1993 strict accept binaries that request a NaN encoding
1994 supported by the FPU
1995 legacy only accept legacy-NaN binaries, if supported
1996 by the FPU
1997 2008 only accept 2008-NaN binaries, if supported
1998 by the FPU
1999 relaxed accept any binaries regardless of whether
2000 supported by the FPU
2001
2002 The FPU emulator is always able to support both NaN
2003 encodings, so if no FPU hardware is present or it has
2004 been disabled with 'nofpu', then the settings of
2005 'legacy' and '2008' strap the emulator accordingly,
2006 'relaxed' straps the emulator for both legacy-NaN and
2007 2008-NaN, whereas 'strict' enables legacy-NaN only on
2008 legacy processors and both NaN encodings on MIPS32 or
2009 MIPS64 CPUs.
2010
2011 The setting for ABS.fmt/NEG.fmt instruction execution
2012 mode generally follows that for the NaN encoding,
2013 except where unsupported by hardware.
2014
2015 ignore_loglevel [KNL,EARLY]
2016 Ignore loglevel setting - this will print /all/
2017 kernel messages to the console. Useful for debugging.
2018 We also add it as printk module parameter, so users
2019 could change it dynamically, usually by
2020 /sys/module/printk/parameters/ignore_loglevel.
2021
2022 ignore_rlimit_data
2023 Ignore RLIMIT_DATA setting for data mappings,
2024 print warning at first misuse. Can be changed via
2025 /sys/module/kernel/parameters/ignore_rlimit_data.
2026
2027 ihash_entries= [KNL]
2028 Set number of hash buckets for inode cache.
2029
2030 ima_appraise= [IMA] appraise integrity measurements
2031 Format: { "off" | "enforce" | "fix" | "log" }
2032 default: "enforce"
2033
2034 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2035 The builtin appraise policy appraises all files
2036 owned by uid=0.
2037
2038 ima_canonical_fmt [IMA]
2039 Use the canonical format for the binary runtime
2040 measurements, instead of host native format.
2041
2042 ima_hash= [IMA]
2043 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2044 | sha512 | ... }
2045 default: "sha1"
2046
2047 The list of supported hash algorithms is defined
2048 in crypto/hash_info.h.
2049
2050 ima_policy= [IMA]
2051 The builtin policies to load during IMA setup.
2052 Format: "tcb | appraise_tcb | secure_boot |
2053 fail_securely | critical_data"
2054
2055 The "tcb" policy measures all programs exec'd, files
2056 mmap'd for exec, and all files opened with the read
2057 mode bit set by either the effective uid (euid=0) or
2058 uid=0.
2059
2060 The "appraise_tcb" policy appraises the integrity of
2061 all files owned by root.
2062
2063 The "secure_boot" policy appraises the integrity
2064 of files (eg. kexec kernel image, kernel modules,
2065 firmware, policy, etc) based on file signatures.
2066
2067 The "fail_securely" policy forces file signature
2068 verification failure also on privileged mounted
2069 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2070 flag.
2071
2072 The "critical_data" policy measures kernel integrity
2073 critical data.
2074
2075 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2076 Load a policy which meets the needs of the Trusted
2077 Computing Base. This means IMA will measure all
2078 programs exec'd, files mmap'd for exec, and all files
2079 opened for read by uid=0.
2080
2081 ima_template= [IMA]
2082 Select one of defined IMA measurements template formats.
2083 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2084 "ima-sigv2" }
2085 Default: "ima-ng"
2086
2087 ima_template_fmt=
2088 [IMA] Define a custom template format.
2089 Format: { "field1|...|fieldN" }
2090
2091 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2092 Format: <min_file_size>
2093 Set the minimal file size for using asynchronous hash.
2094 If left unspecified, ahash usage is disabled.
2095
2096 ahash performance varies for different data sizes on
2097 different crypto accelerators. This option can be used
2098 to achieve the best performance for a particular HW.
2099
2100 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2101 Format: <bufsize>
2102 Set hashing buffer size. Default: 4k.
2103
2104 ahash performance varies for different chunk sizes on
2105 different crypto accelerators. This option can be used
2106 to achieve best performance for particular HW.
2107
2108 init= [KNL]
2109 Format: <full_path>
2110 Run specified binary instead of /sbin/init as init
2111 process.
2112
2113 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2114 for working out where the kernel is dying during
2115 startup.
2116
2117 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2118 initcall functions. Useful for debugging built-in
2119 modules and initcalls.
2120
2121 initramfs_async= [KNL]
2122 Format: <bool>
2123 Default: 1
2124 This parameter controls whether the initramfs
2125 image is unpacked asynchronously, concurrently
2126 with devices being probed and
2127 initialized. This should normally just work,
2128 but as a debugging aid, one can get the
2129 historical behaviour of the initramfs
2130 unpacking being completed before device_ and
2131 late_ initcalls.
2132
2133 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2134
2135 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2136 load the initrd. If an initrd is compiled in or
2137 specified in the bootparams, it takes priority over this
2138 setting.
2139 Format: ss[KMG],nn[KMG]
2140 Default is 0, 0
2141
2142 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2143 zeroes.
2144 Format: 0 | 1
2145 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2146
2147 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2148 Format: 0 | 1
2149 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2150
2151 init_pkru= [X86] Specify the default memory protection keys rights
2152 register contents for all processes. 0x55555554 by
2153 default (disallow access to all but pkey 0). Can
2154 override in debugfs after boot.
2155
2156 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2157 Format: <irq>
2158
2159 int_pln_enable [X86] Enable power limit notification interrupt
2160
2161 integrity_audit=[IMA]
2162 Format: { "0" | "1" }
2163 0 -- basic integrity auditing messages. (Default)
2164 1 -- additional integrity auditing messages.
2165
2166 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2167 on
2168 Enable intel iommu driver.
2169 off
2170 Disable intel iommu driver.
2171 igfx_off [Default Off]
2172 By default, gfx is mapped as normal device. If a gfx
2173 device has a dedicated DMAR unit, the DMAR unit is
2174 bypassed by not enabling DMAR with this option. In
2175 this case, gfx device will use physical address for
2176 DMA.
2177 strict [Default Off]
2178 Deprecated, equivalent to iommu.strict=1.
2179 sp_off [Default Off]
2180 By default, super page will be supported if Intel IOMMU
2181 has the capability. With this option, super page will
2182 not be supported.
2183 sm_on
2184 Enable the Intel IOMMU scalable mode if the hardware
2185 advertises that it has support for the scalable mode
2186 translation.
2187 sm_off
2188 Disallow use of the Intel IOMMU scalable mode.
2189 tboot_noforce [Default Off]
2190 Do not force the Intel IOMMU enabled under tboot.
2191 By default, tboot will force Intel IOMMU on, which
2192 could harm performance of some high-throughput
2193 devices like 40GBit network cards, even if identity
2194 mapping is enabled.
2195 Note that using this option lowers the security
2196 provided by tboot because it makes the system
2197 vulnerable to DMA attacks.
2198
2199 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2200 0 disables intel_idle and fall back on acpi_idle.
2201 1 to 9 specify maximum depth of C-state.
2202
2203 intel_pstate= [X86,EARLY]
2204 disable
2205 Do not enable intel_pstate as the default
2206 scaling driver for the supported processors
2207 active
2208 Use intel_pstate driver to bypass the scaling
2209 governors layer of cpufreq and provides it own
2210 algorithms for p-state selection. There are two
2211 P-state selection algorithms provided by
2212 intel_pstate in the active mode: powersave and
2213 performance. The way they both operate depends
2214 on whether or not the hardware managed P-states
2215 (HWP) feature has been enabled in the processor
2216 and possibly on the processor model.
2217 passive
2218 Use intel_pstate as a scaling driver, but configure it
2219 to work with generic cpufreq governors (instead of
2220 enabling its internal governor). This mode cannot be
2221 used along with the hardware-managed P-states (HWP)
2222 feature.
2223 force
2224 Enable intel_pstate on systems that prohibit it by default
2225 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2226 instead of acpi-cpufreq may disable platform features, such
2227 as thermal controls and power capping, that rely on ACPI
2228 P-States information being indicated to OSPM and therefore
2229 should be used with caution. This option does not work with
2230 processors that aren't supported by the intel_pstate driver
2231 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2232 no_hwp
2233 Do not enable hardware P state control (HWP)
2234 if available.
2235 hwp_only
2236 Only load intel_pstate on systems which support
2237 hardware P state control (HWP) if available.
2238 support_acpi_ppc
2239 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2240 Description Table, specifies preferred power management
2241 profile as "Enterprise Server" or "Performance Server",
2242 then this feature is turned on by default.
2243 per_cpu_perf_limits
2244 Allow per-logical-CPU P-State performance control limits using
2245 cpufreq sysfs interface
2246
2247 intremap= [X86-64,Intel-IOMMU,EARLY]
2248 on enable Interrupt Remapping (default)
2249 off disable Interrupt Remapping
2250 nosid disable Source ID checking
2251 no_x2apic_optout
2252 BIOS x2APIC opt-out request will be ignored
2253 nopost disable Interrupt Posting
2254
2255 iomem= Disable strict checking of access to MMIO memory
2256 strict regions from userspace.
2257 relaxed
2258
2259 iommu= [X86,EARLY]
2260 off
2261 force
2262 noforce
2263 biomerge
2264 panic
2265 nopanic
2266 merge
2267 nomerge
2268 soft
2269 pt [X86]
2270 nopt [X86]
2271 nobypass [PPC/POWERNV]
2272 Disable IOMMU bypass, using IOMMU for PCI devices.
2273
2274 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2275 Format: { "0" | "1" }
2276 0 - Try to allocate a 32-bit DMA address first, before
2277 falling back to the full range if needed.
2278 1 - Allocate directly from the full usable range,
2279 forcing Dual Address Cycle for PCI cards supporting
2280 greater than 32-bit addressing.
2281
2282 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2283 Format: { "0" | "1" }
2284 0 - Lazy mode.
2285 Request that DMA unmap operations use deferred
2286 invalidation of hardware TLBs, for increased
2287 throughput at the cost of reduced device isolation.
2288 Will fall back to strict mode if not supported by
2289 the relevant IOMMU driver.
2290 1 - Strict mode.
2291 DMA unmap operations invalidate IOMMU hardware TLBs
2292 synchronously.
2293 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2294 Note: on x86, strict mode specified via one of the
2295 legacy driver-specific options takes precedence.
2296
2297 iommu.passthrough=
2298 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2299 Format: { "0" | "1" }
2300 0 - Use IOMMU translation for DMA.
2301 1 - Bypass the IOMMU for DMA.
2302 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2303
2304 io7= [HW] IO7 for Marvel-based Alpha systems
2305 See comment before marvel_specify_io7 in
2306 arch/alpha/kernel/core_marvel.c.
2307
2308 io_delay= [X86,EARLY] I/O delay method
2309 0x80
2310 Standard port 0x80 based delay
2311 0xed
2312 Alternate port 0xed based delay (needed on some systems)
2313 udelay
2314 Simple two microseconds delay
2315 none
2316 No delay
2317
2318 ip= [IP_PNP]
2319 See Documentation/admin-guide/nfs/nfsroot.rst.
2320
2321 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2322 IPC identifiers from 32,768 to 16,777,216.
2323
2324 irqaffinity= [SMP] Set the default irq affinity mask
2325 The argument is a cpu list, as described above.
2326
2327 irqchip.gicv2_force_probe=
2328 [ARM,ARM64,EARLY]
2329 Format: <bool>
2330 Force the kernel to look for the second 4kB page
2331 of a GICv2 controller even if the memory range
2332 exposed by the device tree is too small.
2333
2334 irqchip.gicv3_nolpi=
2335 [ARM,ARM64,EARLY]
2336 Force the kernel to ignore the availability of
2337 LPIs (and by consequence ITSs). Intended for system
2338 that use the kernel as a bootloader, and thus want
2339 to let secondary kernels in charge of setting up
2340 LPIs.
2341
2342 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2343 Enables support for pseudo-NMIs in the kernel. This
2344 requires the kernel to be built with
2345 CONFIG_ARM64_PSEUDO_NMI.
2346
2347 irqfixup [HW]
2348 When an interrupt is not handled search all handlers
2349 for it. Intended to get systems with badly broken
2350 firmware running.
2351
2352 irqpoll [HW]
2353 When an interrupt is not handled search all handlers
2354 for it. Also check all handlers each timer
2355 interrupt. Intended to get systems with badly broken
2356 firmware running.
2357
2358 isapnp= [ISAPNP]
2359 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2360
2361 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2362 [Deprecated - use cpusets instead]
2363 Format: [flag-list,]<cpu-list>
2364
2365 Specify one or more CPUs to isolate from disturbances
2366 specified in the flag list (default: domain):
2367
2368 nohz
2369 Disable the tick when a single task runs.
2370
2371 A residual 1Hz tick is offloaded to workqueues, which you
2372 need to affine to housekeeping through the global
2373 workqueue's affinity configured via the
2374 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2375 by using the 'domain' flag described below.
2376
2377 NOTE: by default the global workqueue runs on all CPUs,
2378 so to protect individual CPUs the 'cpumask' file has to
2379 be configured manually after bootup.
2380
2381 domain
2382 Isolate from the general SMP balancing and scheduling
2383 algorithms. Note that performing domain isolation this way
2384 is irreversible: it's not possible to bring back a CPU to
2385 the domains once isolated through isolcpus. It's strongly
2386 advised to use cpusets instead to disable scheduler load
2387 balancing through the "cpuset.sched_load_balance" file.
2388 It offers a much more flexible interface where CPUs can
2389 move in and out of an isolated set anytime.
2390
2391 You can move a process onto or off an "isolated" CPU via
2392 the CPU affinity syscalls or cpuset.
2393 <cpu number> begins at 0 and the maximum value is
2394 "number of CPUs in system - 1".
2395
2396 managed_irq
2397
2398 Isolate from being targeted by managed interrupts
2399 which have an interrupt mask containing isolated
2400 CPUs. The affinity of managed interrupts is
2401 handled by the kernel and cannot be changed via
2402 the /proc/irq/* interfaces.
2403
2404 This isolation is best effort and only effective
2405 if the automatically assigned interrupt mask of a
2406 device queue contains isolated and housekeeping
2407 CPUs. If housekeeping CPUs are online then such
2408 interrupts are directed to the housekeeping CPU
2409 so that IO submitted on the housekeeping CPU
2410 cannot disturb the isolated CPU.
2411
2412 If a queue's affinity mask contains only isolated
2413 CPUs then this parameter has no effect on the
2414 interrupt routing decision, though interrupts are
2415 only delivered when tasks running on those
2416 isolated CPUs submit IO. IO submitted on
2417 housekeeping CPUs has no influence on those
2418 queues.
2419
2420 The format of <cpu-list> is described above.
2421
2422 iucv= [HW,NET]
2423
2424 ivrs_ioapic [HW,X86-64]
2425 Provide an override to the IOAPIC-ID<->DEVICE-ID
2426 mapping provided in the IVRS ACPI table.
2427 By default, PCI segment is 0, and can be omitted.
2428
2429 For example, to map IOAPIC-ID decimal 10 to
2430 PCI segment 0x1 and PCI device 00:14.0,
2431 write the parameter as:
2432 ivrs_ioapic=10@0001:00:14.0
2433
2434 Deprecated formats:
2435 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2436 write the parameter as:
2437 ivrs_ioapic[10]=00:14.0
2438 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2439 PCI device 00:14.0 write the parameter as:
2440 ivrs_ioapic[10]=0001:00:14.0
2441
2442 ivrs_hpet [HW,X86-64]
2443 Provide an override to the HPET-ID<->DEVICE-ID
2444 mapping provided in the IVRS ACPI table.
2445 By default, PCI segment is 0, and can be omitted.
2446
2447 For example, to map HPET-ID decimal 10 to
2448 PCI segment 0x1 and PCI device 00:14.0,
2449 write the parameter as:
2450 ivrs_hpet=10@0001:00:14.0
2451
2452 Deprecated formats:
2453 * To map HPET-ID decimal 0 to PCI device 00:14.0
2454 write the parameter as:
2455 ivrs_hpet[0]=00:14.0
2456 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2457 PCI device 00:14.0 write the parameter as:
2458 ivrs_ioapic[10]=0001:00:14.0
2459
2460 ivrs_acpihid [HW,X86-64]
2461 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2462 mapping provided in the IVRS ACPI table.
2463 By default, PCI segment is 0, and can be omitted.
2464
2465 For example, to map UART-HID:UID AMD0020:0 to
2466 PCI segment 0x1 and PCI device ID 00:14.5,
2467 write the parameter as:
2468 ivrs_acpihid=AMD0020:0@0001:00:14.5
2469
2470 Deprecated formats:
2471 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2472 PCI device ID 00:14.5, write the parameter as:
2473 ivrs_acpihid[00:14.5]=AMD0020:0
2474 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2475 PCI device ID 00:14.5, write the parameter as:
2476 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2477
2478 js= [HW,JOY] Analog joystick
2479 See Documentation/input/joydev/joystick.rst.
2480
2481 kasan_multi_shot
2482 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2483 report on every invalid memory access. Without this
2484 parameter KASAN will print report only for the first
2485 invalid access.
2486
2487 keep_bootcon [KNL,EARLY]
2488 Do not unregister boot console at start. This is only
2489 useful for debugging when something happens in the window
2490 between unregistering the boot console and initializing
2491 the real console.
2492
2493 keepinitrd [HW,ARM] See retain_initrd.
2494
2495 kernelcore= [KNL,X86,IA-64,PPC,EARLY]
2496 Format: nn[KMGTPE] | nn% | "mirror"
2497 This parameter specifies the amount of memory usable by
2498 the kernel for non-movable allocations. The requested
2499 amount is spread evenly throughout all nodes in the
2500 system as ZONE_NORMAL. The remaining memory is used for
2501 movable memory in its own zone, ZONE_MOVABLE. In the
2502 event, a node is too small to have both ZONE_NORMAL and
2503 ZONE_MOVABLE, kernelcore memory will take priority and
2504 other nodes will have a larger ZONE_MOVABLE.
2505
2506 ZONE_MOVABLE is used for the allocation of pages that
2507 may be reclaimed or moved by the page migration
2508 subsystem. Note that allocations like PTEs-from-HighMem
2509 still use the HighMem zone if it exists, and the Normal
2510 zone if it does not.
2511
2512 It is possible to specify the exact amount of memory in
2513 the form of "nn[KMGTPE]", a percentage of total system
2514 memory in the form of "nn%", or "mirror". If "mirror"
2515 option is specified, mirrored (reliable) memory is used
2516 for non-movable allocations and remaining memory is used
2517 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2518 are exclusive, so you cannot specify multiple forms.
2519
2520 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2521 Format: <Controller#>[,poll interval]
2522 The controller # is the number of the ehci usb debug
2523 port as it is probed via PCI. The poll interval is
2524 optional and is the number seconds in between
2525 each poll cycle to the debug port in case you need
2526 the functionality for interrupting the kernel with
2527 gdb or control-c on the dbgp connection. When
2528 not using this parameter you use sysrq-g to break into
2529 the kernel debugger.
2530
2531 kgdboc= [KGDB,HW] kgdb over consoles.
2532 Requires a tty driver that supports console polling,
2533 or a supported polling keyboard driver (non-usb).
2534 Serial only format: <serial_device>[,baud]
2535 keyboard only format: kbd
2536 keyboard and serial format: kbd,<serial_device>[,baud]
2537 Optional Kernel mode setting:
2538 kms, kbd format: kms,kbd
2539 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2540
2541 kgdboc_earlycon= [KGDB,HW,EARLY]
2542 If the boot console provides the ability to read
2543 characters and can work in polling mode, you can use
2544 this parameter to tell kgdb to use it as a backend
2545 until the normal console is registered. Intended to
2546 be used together with the kgdboc parameter which
2547 specifies the normal console to transition to.
2548
2549 The name of the early console should be specified
2550 as the value of this parameter. Note that the name of
2551 the early console might be different than the tty
2552 name passed to kgdboc. It's OK to leave the value
2553 blank and the first boot console that implements
2554 read() will be picked.
2555
2556 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2557 kernel debugger at the earliest opportunity.
2558
2559 kmac= [MIPS] Korina ethernet MAC address.
2560 Configure the RouterBoard 532 series on-chip
2561 Ethernet adapter MAC address.
2562
2563 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
2564 Valid arguments: on, off
2565 Default: on
2566 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2567 the default is off.
2568
2569 kprobe_event=[probe-list]
2570 [FTRACE] Add kprobe events and enable at boot time.
2571 The probe-list is a semicolon delimited list of probe
2572 definitions. Each definition is same as kprobe_events
2573 interface, but the parameters are comma delimited.
2574 For example, to add a kprobe event on vfs_read with
2575 arg1 and arg2, add to the command line;
2576
2577 kprobe_event=p,vfs_read,$arg1,$arg2
2578
2579 See also Documentation/trace/kprobetrace.rst "Kernel
2580 Boot Parameter" section.
2581
2582 kpti= [ARM64,EARLY] Control page table isolation of
2583 user and kernel address spaces.
2584 Default: enabled on cores which need mitigation.
2585 0: force disabled
2586 1: force enabled
2587
2588 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2589 CONFIG_KUNIT to be set to be fully enabled. The
2590 default value can be overridden via
2591 KUNIT_DEFAULT_ENABLED.
2592 Default is 1 (enabled)
2593
2594 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2595 Default is 0 (don't ignore, but inject #GP)
2596
2597 kvm.eager_page_split=
2598 [KVM,X86] Controls whether or not KVM will try to
2599 proactively split all huge pages during dirty logging.
2600 Eager page splitting reduces interruptions to vCPU
2601 execution by eliminating the write-protection faults
2602 and MMU lock contention that would otherwise be
2603 required to split huge pages lazily.
2604
2605 VM workloads that rarely perform writes or that write
2606 only to a small region of VM memory may benefit from
2607 disabling eager page splitting to allow huge pages to
2608 still be used for reads.
2609
2610 The behavior of eager page splitting depends on whether
2611 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2612 disabled, all huge pages in a memslot will be eagerly
2613 split when dirty logging is enabled on that memslot. If
2614 enabled, eager page splitting will be performed during
2615 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2616 cleared.
2617
2618 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2619
2620 Default is Y (on).
2621
2622 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2623 Default is false (don't support).
2624
2625 kvm.nx_huge_pages=
2626 [KVM] Controls the software workaround for the
2627 X86_BUG_ITLB_MULTIHIT bug.
2628 force : Always deploy workaround.
2629 off : Never deploy workaround.
2630 auto : Deploy workaround based on the presence of
2631 X86_BUG_ITLB_MULTIHIT.
2632
2633 Default is 'auto'.
2634
2635 If the software workaround is enabled for the host,
2636 guests do need not to enable it for nested guests.
2637
2638 kvm.nx_huge_pages_recovery_ratio=
2639 [KVM] Controls how many 4KiB pages are periodically zapped
2640 back to huge pages. 0 disables the recovery, otherwise if
2641 the value is N KVM will zap 1/Nth of the 4KiB pages every
2642 period (see below). The default is 60.
2643
2644 kvm.nx_huge_pages_recovery_period_ms=
2645 [KVM] Controls the time period at which KVM zaps 4KiB pages
2646 back to huge pages. If the value is a non-zero N, KVM will
2647 zap a portion (see ratio above) of the pages every N msecs.
2648 If the value is 0 (the default), KVM will pick a period based
2649 on the ratio, such that a page is zapped after 1 hour on average.
2650
2651 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2652 KVM/SVM. Default is 1 (enabled).
2653
2654 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2655 a.k.a. Two-Dimensional Page Tables. Default is 1
2656 (enabled). Disable by KVM if hardware lacks support
2657 for NPT.
2658
2659 kvm-arm.mode=
2660 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
2661 operation.
2662
2663 none: Forcefully disable KVM.
2664
2665 nvhe: Standard nVHE-based mode, without support for
2666 protected guests.
2667
2668 protected: nVHE-based mode with support for guests whose
2669 state is kept private from the host.
2670
2671 nested: VHE-based mode with support for nested
2672 virtualization. Requires at least ARMv8.3
2673 hardware.
2674
2675 Defaults to VHE/nVHE based on hardware support. Setting
2676 mode to "protected" will disable kexec and hibernation
2677 for the host. "nested" is experimental and should be
2678 used with extreme caution.
2679
2680 kvm-arm.vgic_v3_group0_trap=
2681 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
2682 system registers
2683
2684 kvm-arm.vgic_v3_group1_trap=
2685 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
2686 system registers
2687
2688 kvm-arm.vgic_v3_common_trap=
2689 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
2690 system registers
2691
2692 kvm-arm.vgic_v4_enable=
2693 [KVM,ARM,EARLY] Allow use of GICv4 for direct
2694 injection of LPIs.
2695
2696 kvm_cma_resv_ratio=n [PPC,EARLY]
2697 Reserves given percentage from system memory area for
2698 contiguous memory allocation for KVM hash pagetable
2699 allocation.
2700 By default it reserves 5% of total system memory.
2701 Format: <integer>
2702 Default: 5
2703
2704 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2705 a.k.a. Two-Dimensional Page Tables. Default is 1
2706 (enabled). Disable by KVM if hardware lacks support
2707 for EPT.
2708
2709 kvm-intel.emulate_invalid_guest_state=
2710 [KVM,Intel] Control whether to emulate invalid guest
2711 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2712 as guest state is never invalid for unrestricted
2713 guests. This param doesn't apply to nested guests (L2),
2714 as KVM never emulates invalid L2 guest state.
2715 Default is 1 (enabled).
2716
2717 kvm-intel.flexpriority=
2718 [KVM,Intel] Control KVM's use of FlexPriority feature
2719 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2720 hardware lacks support for it.
2721
2722 kvm-intel.nested=
2723 [KVM,Intel] Control nested virtualization feature in
2724 KVM/VMX. Default is 1 (enabled).
2725
2726 kvm-intel.unrestricted_guest=
2727 [KVM,Intel] Control KVM's use of unrestricted guest
2728 feature (virtualized real and unpaged mode). Default
2729 is 1 (enabled). Disable by KVM if EPT is disabled or
2730 hardware lacks support for it.
2731
2732 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2733 CVE-2018-3620.
2734
2735 Valid arguments: never, cond, always
2736
2737 always: L1D cache flush on every VMENTER.
2738 cond: Flush L1D on VMENTER only when the code between
2739 VMEXIT and VMENTER can leak host memory.
2740 never: Disables the mitigation
2741
2742 Default is cond (do L1 cache flush in specific instances)
2743
2744 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2745 Identification feature (tagged TLBs). Default is 1
2746 (enabled). Disable by KVM if hardware lacks support
2747 for it.
2748
2749 l1d_flush= [X86,INTEL,EARLY]
2750 Control mitigation for L1D based snooping vulnerability.
2751
2752 Certain CPUs are vulnerable to an exploit against CPU
2753 internal buffers which can forward information to a
2754 disclosure gadget under certain conditions.
2755
2756 In vulnerable processors, the speculatively
2757 forwarded data can be used in a cache side channel
2758 attack, to access data to which the attacker does
2759 not have direct access.
2760
2761 This parameter controls the mitigation. The
2762 options are:
2763
2764 on - enable the interface for the mitigation
2765
2766 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
2767 affected CPUs
2768
2769 The kernel PTE inversion protection is unconditionally
2770 enabled and cannot be disabled.
2771
2772 full
2773 Provides all available mitigations for the
2774 L1TF vulnerability. Disables SMT and
2775 enables all mitigations in the
2776 hypervisors, i.e. unconditional L1D flush.
2777
2778 SMT control and L1D flush control via the
2779 sysfs interface is still possible after
2780 boot. Hypervisors will issue a warning
2781 when the first VM is started in a
2782 potentially insecure configuration,
2783 i.e. SMT enabled or L1D flush disabled.
2784
2785 full,force
2786 Same as 'full', but disables SMT and L1D
2787 flush runtime control. Implies the
2788 'nosmt=force' command line option.
2789 (i.e. sysfs control of SMT is disabled.)
2790
2791 flush
2792 Leaves SMT enabled and enables the default
2793 hypervisor mitigation, i.e. conditional
2794 L1D flush.
2795
2796 SMT control and L1D flush control via the
2797 sysfs interface is still possible after
2798 boot. Hypervisors will issue a warning
2799 when the first VM is started in a
2800 potentially insecure configuration,
2801 i.e. SMT enabled or L1D flush disabled.
2802
2803 flush,nosmt
2804
2805 Disables SMT and enables the default
2806 hypervisor mitigation.
2807
2808 SMT control and L1D flush control via the
2809 sysfs interface is still possible after
2810 boot. Hypervisors will issue a warning
2811 when the first VM is started in a
2812 potentially insecure configuration,
2813 i.e. SMT enabled or L1D flush disabled.
2814
2815 flush,nowarn
2816 Same as 'flush', but hypervisors will not
2817 warn when a VM is started in a potentially
2818 insecure configuration.
2819
2820 off
2821 Disables hypervisor mitigations and doesn't
2822 emit any warnings.
2823 It also drops the swap size and available
2824 RAM limit restriction on both hypervisor and
2825 bare metal.
2826
2827 Default is 'flush'.
2828
2829 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2830
2831 l2cr= [PPC]
2832
2833 l3cr= [PPC]
2834
2835 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
2836 disabled it.
2837
2838 lapic= [X86,APIC] Do not use TSC deadline
2839 value for LAPIC timer one-shot implementation. Default
2840 back to the programmable timer unit in the LAPIC.
2841 Format: notscdeadline
2842
2843 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
2844 in C2 power state.
2845
2846 libata.dma= [LIBATA] DMA control
2847 libata.dma=0 Disable all PATA and SATA DMA
2848 libata.dma=1 PATA and SATA Disk DMA only
2849 libata.dma=2 ATAPI (CDROM) DMA only
2850 libata.dma=4 Compact Flash DMA only
2851 Combinations also work, so libata.dma=3 enables DMA
2852 for disks and CDROMs, but not CFs.
2853
2854 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2855 libata.ignore_hpa=0 keep BIOS limits (default)
2856 libata.ignore_hpa=1 ignore limits, using full disk
2857
2858 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2859 when set.
2860 Format: <int>
2861
2862 libata.force= [LIBATA] Force configurations. The format is a comma-
2863 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2864 PORT and DEVICE are decimal numbers matching port, link
2865 or device. Basically, it matches the ATA ID string
2866 printed on console by libata. If the whole ID part is
2867 omitted, the last PORT and DEVICE values are used. If
2868 ID hasn't been specified yet, the configuration applies
2869 to all ports, links and devices.
2870
2871 If only DEVICE is omitted, the parameter applies to
2872 the port and all links and devices behind it. DEVICE
2873 number of 0 either selects the first device or the
2874 first fan-out link behind PMP device. It does not
2875 select the host link. DEVICE number of 15 selects the
2876 host link and device attached to it.
2877
2878 The VAL specifies the configuration to force. As long
2879 as there is no ambiguity, shortcut notation is allowed.
2880 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2881 The following configurations can be forced.
2882
2883 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2884 Any ID with matching PORT is used.
2885
2886 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2887
2888 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2889 udma[/][16,25,33,44,66,100,133] notation is also
2890 allowed.
2891
2892 * nohrst, nosrst, norst: suppress hard, soft and both
2893 resets.
2894
2895 * rstonce: only attempt one reset during hot-unplug
2896 link recovery.
2897
2898 * [no]dbdelay: Enable or disable the extra 200ms delay
2899 before debouncing a link PHY and device presence
2900 detection.
2901
2902 * [no]ncq: Turn on or off NCQ.
2903
2904 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2905
2906 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2907
2908 * [no]trim: Enable or disable (unqueued) TRIM.
2909
2910 * trim_zero: Indicate that TRIM command zeroes data.
2911
2912 * max_trim_128m: Set 128M maximum trim size limit.
2913
2914 * [no]dma: Turn on or off DMA transfers.
2915
2916 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2917
2918 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2919 commands that are not a multiple of 16 bytes.
2920
2921 * [no]dmalog: Enable or disable the use of the
2922 READ LOG DMA EXT command to access logs.
2923
2924 * [no]iddevlog: Enable or disable access to the
2925 identify device data log.
2926
2927 * [no]logdir: Enable or disable access to the general
2928 purpose log directory.
2929
2930 * max_sec_128: Set transfer size limit to 128 sectors.
2931
2932 * max_sec_1024: Set or clear transfer size limit to
2933 1024 sectors.
2934
2935 * max_sec_lba48: Set or clear transfer size limit to
2936 65535 sectors.
2937
2938 * [no]lpm: Enable or disable link power management.
2939
2940 * [no]setxfer: Indicate if transfer speed mode setting
2941 should be skipped.
2942
2943 * [no]fua: Disable or enable FUA (Force Unit Access)
2944 support for devices supporting this feature.
2945
2946 * dump_id: Dump IDENTIFY data.
2947
2948 * disable: Disable this device.
2949
2950 If there are multiple matching configurations changing
2951 the same attribute, the last one is used.
2952
2953 load_ramdisk= [RAM] [Deprecated]
2954
2955 lockd.nlm_grace_period=P [NFS] Assign grace period.
2956 Format: <integer>
2957
2958 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2959 Format: <integer>
2960
2961 lockd.nlm_timeout=T [NFS] Assign timeout value.
2962 Format: <integer>
2963
2964 lockd.nlm_udpport=M [NFS] Assign UDP port.
2965 Format: <integer>
2966
2967 lockdown= [SECURITY,EARLY]
2968 { integrity | confidentiality }
2969 Enable the kernel lockdown feature. If set to
2970 integrity, kernel features that allow userland to
2971 modify the running kernel are disabled. If set to
2972 confidentiality, kernel features that allow userland
2973 to extract confidential information from the kernel
2974 are also disabled.
2975
2976 locktorture.acq_writer_lim= [KNL]
2977 Set the time limit in jiffies for a lock
2978 acquisition. Acquisitions exceeding this limit
2979 will result in a splat once they do complete.
2980
2981 locktorture.bind_readers= [KNL]
2982 Specify the list of CPUs to which the readers are
2983 to be bound.
2984
2985 locktorture.bind_writers= [KNL]
2986 Specify the list of CPUs to which the writers are
2987 to be bound.
2988
2989 locktorture.call_rcu_chains= [KNL]
2990 Specify the number of self-propagating call_rcu()
2991 chains to set up. These are used to ensure that
2992 there is a high probability of an RCU grace period
2993 in progress at any given time. Defaults to 0,
2994 which disables these call_rcu() chains.
2995
2996 locktorture.long_hold= [KNL]
2997 Specify the duration in milliseconds for the
2998 occasional long-duration lock hold time. Defaults
2999 to 100 milliseconds. Select 0 to disable.
3000
3001 locktorture.nested_locks= [KNL]
3002 Specify the maximum lock nesting depth that
3003 locktorture is to exercise, up to a limit of 8
3004 (MAX_NESTED_LOCKS). Specify zero to disable.
3005 Note that this parameter is ineffective on types
3006 of locks that do not support nested acquisition.
3007
3008 locktorture.nreaders_stress= [KNL]
3009 Set the number of locking read-acquisition kthreads.
3010 Defaults to being automatically set based on the
3011 number of online CPUs.
3012
3013 locktorture.nwriters_stress= [KNL]
3014 Set the number of locking write-acquisition kthreads.
3015
3016 locktorture.onoff_holdoff= [KNL]
3017 Set time (s) after boot for CPU-hotplug testing.
3018
3019 locktorture.onoff_interval= [KNL]
3020 Set time (s) between CPU-hotplug operations, or
3021 zero to disable CPU-hotplug testing.
3022
3023 locktorture.rt_boost= [KNL]
3024 Do periodic testing of real-time lock priority
3025 boosting. Select 0 to disable, 1 to boost
3026 only rt_mutex, and 2 to boost unconditionally.
3027 Defaults to 2, which might seem to be an
3028 odd choice, but which should be harmless for
3029 non-real-time spinlocks, due to their disabling
3030 of preemption. Note that non-realtime mutexes
3031 disable boosting.
3032
3033 locktorture.rt_boost_factor= [KNL]
3034 Number that determines how often and for how
3035 long priority boosting is exercised. This is
3036 scaled down by the number of writers, so that the
3037 number of boosts per unit time remains roughly
3038 constant as the number of writers increases.
3039 On the other hand, the duration of each boost
3040 increases with the number of writers.
3041
3042 locktorture.shuffle_interval= [KNL]
3043 Set task-shuffle interval (jiffies). Shuffling
3044 tasks allows some CPUs to go into dyntick-idle
3045 mode during the locktorture test.
3046
3047 locktorture.shutdown_secs= [KNL]
3048 Set time (s) after boot system shutdown. This
3049 is useful for hands-off automated testing.
3050
3051 locktorture.stat_interval= [KNL]
3052 Time (s) between statistics printk()s.
3053
3054 locktorture.stutter= [KNL]
3055 Time (s) to stutter testing, for example,
3056 specifying five seconds causes the test to run for
3057 five seconds, wait for five seconds, and so on.
3058 This tests the locking primitive's ability to
3059 transition abruptly to and from idle.
3060
3061 locktorture.torture_type= [KNL]
3062 Specify the locking implementation to test.
3063
3064 locktorture.verbose= [KNL]
3065 Enable additional printk() statements.
3066
3067 locktorture.writer_fifo= [KNL]
3068 Run the write-side locktorture kthreads at
3069 sched_set_fifo() real-time priority.
3070
3071 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3072 Format: <irq>
3073
3074 loglevel= [KNL,EARLY]
3075 All Kernel Messages with a loglevel smaller than the
3076 console loglevel will be printed to the console. It can
3077 also be changed with klogd or other programs. The
3078 loglevels are defined as follows:
3079
3080 0 (KERN_EMERG) system is unusable
3081 1 (KERN_ALERT) action must be taken immediately
3082 2 (KERN_CRIT) critical conditions
3083 3 (KERN_ERR) error conditions
3084 4 (KERN_WARNING) warning conditions
3085 5 (KERN_NOTICE) normal but significant condition
3086 6 (KERN_INFO) informational
3087 7 (KERN_DEBUG) debug-level messages
3088
3089 log_buf_len=n[KMG] [KNL,EARLY]
3090 Sets the size of the printk ring buffer, in bytes.
3091 n must be a power of two and greater than the
3092 minimal size. The minimal size is defined by
3093 LOG_BUF_SHIFT kernel config parameter. There
3094 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3095 parameter that allows to increase the default size
3096 depending on the number of CPUs. See init/Kconfig
3097 for more details.
3098
3099 logo.nologo [FB] Disables display of the built-in Linux logo.
3100 This may be used to provide more screen space for
3101 kernel log messages and is useful when debugging
3102 kernel boot problems.
3103
3104 lp=0 [LP] Specify parallel ports to use, e.g,
3105 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3106 lp=reset first parallel port). 'lp=0' disables the
3107 lp=auto printer driver. 'lp=reset' (which can be
3108 specified in addition to the ports) causes
3109 attached printers to be reset. Using
3110 lp=port1,port2,... specifies the parallel ports
3111 to associate lp devices with, starting with
3112 lp0. A port specification may be 'none' to skip
3113 that lp device, or a parport name such as
3114 'parport0'. Specifying 'lp=auto' instead of a
3115 port specification list means that device IDs
3116 from each port should be examined, to see if
3117 an IEEE 1284-compliant printer is attached; if
3118 so, the driver will manage that printer.
3119 See also header of drivers/char/lp.c.
3120
3121 lpj=n [KNL]
3122 Sets loops_per_jiffy to given constant, thus avoiding
3123 time-consuming boot-time autodetection (up to 250 ms per
3124 CPU). 0 enables autodetection (default). To determine
3125 the correct value for your kernel, boot with normal
3126 autodetection and see what value is printed. Note that
3127 on SMP systems the preset will be applied to all CPUs,
3128 which is likely to cause problems if your CPUs need
3129 significantly divergent settings. An incorrect value
3130 will cause delays in the kernel to be wrong, leading to
3131 unpredictable I/O errors and other breakage. Although
3132 unlikely, in the extreme case this might damage your
3133 hardware.
3134
3135 ltpc= [NET]
3136 Format: <io>,<irq>,<dma>
3137
3138 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3139
3140 lsm=lsm1,...,lsmN
3141 [SECURITY] Choose order of LSM initialization. This
3142 overrides CONFIG_LSM, and the "security=" parameter.
3143
3144 machvec= [IA-64] Force the use of a particular machine-vector
3145 (machvec) in a generic kernel.
3146 Example: machvec=hpzx1
3147
3148 machtype= [Loongson] Share the same kernel image file between
3149 different yeeloong laptops.
3150 Example: machtype=lemote-yeeloong-2f-7inch
3151
3152 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
3153 than or equal to this physical address is ignored.
3154
3155 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3156 will bring up during bootup. maxcpus=n : n >= 0 limits
3157 the kernel to bring up 'n' processors. Surely after
3158 bootup you can bring up the other plugged cpu by executing
3159 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3160 only takes effect during system bootup.
3161 While n=0 is a special case, it is equivalent to "nosmp",
3162 which also disables the IO APIC.
3163
3164 max_loop= [LOOP] The number of loop block devices that get
3165 (loop.max_loop) unconditionally pre-created at init time. The default
3166 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3167 of statically allocating a predefined number, loop
3168 devices can be requested on-demand with the
3169 /dev/loop-control interface.
3170
3171 mce [X86-32] Machine Check Exception
3172
3173 mce=option [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
3174
3175 md= [HW] RAID subsystems devices and level
3176 See Documentation/admin-guide/md.rst.
3177
3178 mdacon= [MDA]
3179 Format: <first>,<last>
3180 Specifies range of consoles to be captured by the MDA.
3181
3182 mds= [X86,INTEL,EARLY]
3183 Control mitigation for the Micro-architectural Data
3184 Sampling (MDS) vulnerability.
3185
3186 Certain CPUs are vulnerable to an exploit against CPU
3187 internal buffers which can forward information to a
3188 disclosure gadget under certain conditions.
3189
3190 In vulnerable processors, the speculatively
3191 forwarded data can be used in a cache side channel
3192 attack, to access data to which the attacker does
3193 not have direct access.
3194
3195 This parameter controls the MDS mitigation. The
3196 options are:
3197
3198 full - Enable MDS mitigation on vulnerable CPUs
3199 full,nosmt - Enable MDS mitigation and disable
3200 SMT on vulnerable CPUs
3201 off - Unconditionally disable MDS mitigation
3202
3203 On TAA-affected machines, mds=off can be prevented by
3204 an active TAA mitigation as both vulnerabilities are
3205 mitigated with the same mechanism so in order to disable
3206 this mitigation, you need to specify tsx_async_abort=off
3207 too.
3208
3209 Not specifying this option is equivalent to
3210 mds=full.
3211
3212 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3213
3214 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3215 Must be specified, otherwise memory size will be 0.
3216
3217 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3218 of memory Amount of memory to be used in cases
3219 as follows:
3220
3221 1 for test;
3222 2 when the kernel is not able to see the whole system memory;
3223 3 memory that lies after 'mem=' boundary is excluded from
3224 the hypervisor, then assigned to KVM guests.
3225 4 to limit the memory available for kdump kernel.
3226
3227 [ARC,MICROBLAZE] - the limit applies only to low memory,
3228 high memory is not affected.
3229
3230 [ARM64] - only limits memory covered by the linear
3231 mapping. The NOMAP regions are not affected.
3232
3233 [X86] Work as limiting max address. Use together
3234 with memmap= to avoid physical address space collisions.
3235 Without memmap= PCI devices could be placed at addresses
3236 belonging to unused RAM.
3237
3238 Note that this only takes effects during boot time since
3239 in above case 3, memory may need be hot added after boot
3240 if system memory of hypervisor is not sufficient.
3241
3242 mem=nn[KMG]@ss[KMG]
3243 [ARM,MIPS,EARLY] - override the memory layout
3244 reported by firmware.
3245 Define a memory region of size nn[KMG] starting at
3246 ss[KMG].
3247 Multiple different regions can be specified with
3248 multiple mem= parameters on the command line.
3249
3250 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3251 memory.
3252
3253 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3254
3255 memchunk=nn[KMG]
3256 [KNL,SH] Allow user to override the default size for
3257 per-device physically contiguous DMA buffers.
3258
3259 memhp_default_state=online/offline/online_kernel/online_movable
3260 [KNL] Set the initial state for the memory hotplug
3261 onlining policy. If not specified, the default value is
3262 set according to the
3263 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3264 option.
3265 See Documentation/admin-guide/mm/memory-hotplug.rst.
3266
3267 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3268 E820 memory map, as specified by the user.
3269 Such memmap=exactmap lines can be constructed based on
3270 BIOS output or other requirements. See the memmap=nn@ss
3271 option description.
3272
3273 memmap=nn[KMG]@ss[KMG]
3274 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3275 Region of memory to be used is from ss to ss+nn.
3276 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3277 which limits max address to nn[KMG].
3278 Multiple different regions can be specified,
3279 comma delimited.
3280 Example:
3281 memmap=100M@2G,100M#3G,1G!1024G
3282
3283 memmap=nn[KMG]#ss[KMG]
3284 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3285 Region of memory to be marked is from ss to ss+nn.
3286
3287 memmap=nn[KMG]$ss[KMG]
3288 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3289 Region of memory to be reserved is from ss to ss+nn.
3290 Example: Exclude memory from 0x18690000-0x1869ffff
3291 memmap=64K$0x18690000
3292 or
3293 memmap=0x10000$0x18690000
3294 Some bootloaders may need an escape character before '$',
3295 like Grub2, otherwise '$' and the following number
3296 will be eaten.
3297
3298 memmap=nn[KMG]!ss[KMG,EARLY]
3299 [KNL,X86] Mark specific memory as protected.
3300 Region of memory to be used, from ss to ss+nn.
3301 The memory region may be marked as e820 type 12 (0xc)
3302 and is NVDIMM or ADR memory.
3303
3304 memmap=<size>%<offset>-<oldtype>+<newtype>
3305 [KNL,ACPI,EARLY] Convert memory within the specified region
3306 from <oldtype> to <newtype>. If "-<oldtype>" is left
3307 out, the whole region will be marked as <newtype>,
3308 even if previously unavailable. If "+<newtype>" is left
3309 out, matching memory will be removed. Types are
3310 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3311 3 = ACPI, 12 = PRAM.
3312
3313 memory_corruption_check=0/1 [X86,EARLY]
3314 Some BIOSes seem to corrupt the first 64k of
3315 memory when doing things like suspend/resume.
3316 Setting this option will scan the memory
3317 looking for corruption. Enabling this will
3318 both detect corruption and prevent the kernel
3319 from using the memory being corrupted.
3320 However, its intended as a diagnostic tool; if
3321 repeatable BIOS-originated corruption always
3322 affects the same memory, you can use memmap=
3323 to prevent the kernel from using that memory.
3324
3325 memory_corruption_check_size=size [X86,EARLY]
3326 By default it checks for corruption in the low
3327 64k, making this memory unavailable for normal
3328 use. Use this parameter to scan for
3329 corruption in more or less memory.
3330
3331 memory_corruption_check_period=seconds [X86,EARLY]
3332 By default it checks for corruption every 60
3333 seconds. Use this parameter to check at some
3334 other rate. 0 disables periodic checking.
3335
3336 memory_hotplug.memmap_on_memory
3337 [KNL,X86,ARM] Boolean flag to enable this feature.
3338 Format: {on | off (default)}
3339 When enabled, runtime hotplugged memory will
3340 allocate its internal metadata (struct pages,
3341 those vmemmap pages cannot be optimized even
3342 if hugetlb_free_vmemmap is enabled) from the
3343 hotadded memory which will allow to hotadd a
3344 lot of memory without requiring additional
3345 memory to do so.
3346 This feature is disabled by default because it
3347 has some implication on large (e.g. GB)
3348 allocations in some configurations (e.g. small
3349 memory blocks).
3350 The state of the flag can be read in
3351 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3352 Note that even when enabled, there are a few cases where
3353 the feature is not effective.
3354
3355 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3356 Format: <integer>
3357 default : 0 <disable>
3358 Specifies the number of memtest passes to be
3359 performed. Each pass selects another test
3360 pattern from a given set of patterns. Memtest
3361 fills the memory with this pattern, validates
3362 memory contents and reserves bad memory
3363 regions that are detected.
3364
3365 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3366 Valid arguments: on, off
3367 Default: off
3368 mem_encrypt=on: Activate SME
3369 mem_encrypt=off: Do not activate SME
3370
3371 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3372 for details on when memory encryption can be activated.
3373
3374 mem_sleep_default= [SUSPEND] Default system suspend mode:
3375 s2idle - Suspend-To-Idle
3376 shallow - Power-On Suspend or equivalent (if supported)
3377 deep - Suspend-To-RAM or equivalent (if supported)
3378 See Documentation/admin-guide/pm/sleep-states.rst.
3379
3380 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3381 Multi-Function General Purpose Timers on AMD Geode
3382 platforms.
3383
3384 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3385 the BIOS has incorrectly applied a workaround. TinyBIOS
3386 version 0.98 is known to be affected, 0.99 fixes the
3387 problem by letting the user disable the workaround.
3388
3389 mga= [HW,DRM]
3390
3391 microcode.force_minrev= [X86]
3392 Format: <bool>
3393 Enable or disable the microcode minimal revision
3394 enforcement for the runtime microcode loader.
3395
3396 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3397 physical address is ignored.
3398
3399 mini2440= [ARM,HW,KNL]
3400 Format:[0..2][b][c][t]
3401 Default: "0tb"
3402 MINI2440 configuration specification:
3403 0 - The attached screen is the 3.5" TFT
3404 1 - The attached screen is the 7" TFT
3405 2 - The VGA Shield is attached (1024x768)
3406 Leaving out the screen size parameter will not load
3407 the TFT driver, and the framebuffer will be left
3408 unconfigured.
3409 b - Enable backlight. The TFT backlight pin will be
3410 linked to the kernel VESA blanking code and a GPIO
3411 LED. This parameter is not necessary when using the
3412 VGA shield.
3413 c - Enable the s3c camera interface.
3414 t - Reserved for enabling touchscreen support. The
3415 touchscreen support is not enabled in the mainstream
3416 kernel as of 2.6.30, a preliminary port can be found
3417 in the "bleeding edge" mini2440 support kernel at
3418 https://repo.or.cz/w/linux-2.6/mini2440.git
3419
3420 mitigations=
3421 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
3422 CPU vulnerabilities. This is a set of curated,
3423 arch-independent options, each of which is an
3424 aggregation of existing arch-specific options.
3425
3426 Note, "mitigations" is supported if and only if the
3427 kernel was built with CPU_MITIGATIONS=y.
3428
3429 off
3430 Disable all optional CPU mitigations. This
3431 improves system performance, but it may also
3432 expose users to several CPU vulnerabilities.
3433 Equivalent to: if nokaslr then kpti=0 [ARM64]
3434 gather_data_sampling=off [X86]
3435 kvm.nx_huge_pages=off [X86]
3436 l1tf=off [X86]
3437 mds=off [X86]
3438 mmio_stale_data=off [X86]
3439 no_entry_flush [PPC]
3440 no_uaccess_flush [PPC]
3441 nobp=0 [S390]
3442 nopti [X86,PPC]
3443 nospectre_bhb [ARM64]
3444 nospectre_v1 [X86,PPC]
3445 nospectre_v2 [X86,PPC,S390,ARM64]
3446 reg_file_data_sampling=off [X86]
3447 retbleed=off [X86]
3448 spec_rstack_overflow=off [X86]
3449 spec_store_bypass_disable=off [X86,PPC]
3450 spectre_bhi=off [X86]
3451 spectre_v2_user=off [X86]
3452 srbds=off [X86,INTEL]
3453 ssbd=force-off [ARM64]
3454 tsx_async_abort=off [X86]
3455
3456 Exceptions:
3457 This does not have any effect on
3458 kvm.nx_huge_pages when
3459 kvm.nx_huge_pages=force.
3460
3461 auto (default)
3462 Mitigate all CPU vulnerabilities, but leave SMT
3463 enabled, even if it's vulnerable. This is for
3464 users who don't want to be surprised by SMT
3465 getting disabled across kernel upgrades, or who
3466 have other ways of avoiding SMT-based attacks.
3467 Equivalent to: (default behavior)
3468
3469 auto,nosmt
3470 Mitigate all CPU vulnerabilities, disabling SMT
3471 if needed. This is for users who always want to
3472 be fully mitigated, even if it means losing SMT.
3473 Equivalent to: l1tf=flush,nosmt [X86]
3474 mds=full,nosmt [X86]
3475 tsx_async_abort=full,nosmt [X86]
3476 mmio_stale_data=full,nosmt [X86]
3477 retbleed=auto,nosmt [X86]
3478
3479 mminit_loglevel=
3480 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
3481 parameter allows control of the logging verbosity for
3482 the additional memory initialisation checks. A value
3483 of 0 disables mminit logging and a level of 4 will
3484 log everything. Information is printed at KERN_DEBUG
3485 so loglevel=8 may also need to be specified.
3486
3487 mmio_stale_data=
3488 [X86,INTEL,EARLY] Control mitigation for the Processor
3489 MMIO Stale Data vulnerabilities.
3490
3491 Processor MMIO Stale Data is a class of
3492 vulnerabilities that may expose data after an MMIO
3493 operation. Exposed data could originate or end in
3494 the same CPU buffers as affected by MDS and TAA.
3495 Therefore, similar to MDS and TAA, the mitigation
3496 is to clear the affected CPU buffers.
3497
3498 This parameter controls the mitigation. The
3499 options are:
3500
3501 full - Enable mitigation on vulnerable CPUs
3502
3503 full,nosmt - Enable mitigation and disable SMT on
3504 vulnerable CPUs.
3505
3506 off - Unconditionally disable mitigation
3507
3508 On MDS or TAA affected machines,
3509 mmio_stale_data=off can be prevented by an active
3510 MDS or TAA mitigation as these vulnerabilities are
3511 mitigated with the same mechanism so in order to
3512 disable this mitigation, you need to specify
3513 mds=off and tsx_async_abort=off too.
3514
3515 Not specifying this option is equivalent to
3516 mmio_stale_data=full.
3517
3518 For details see:
3519 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3520
3521 <module>.async_probe[=<bool>] [KNL]
3522 If no <bool> value is specified or if the value
3523 specified is not a valid <bool>, enable asynchronous
3524 probe on this module. Otherwise, enable/disable
3525 asynchronous probe on this module as indicated by the
3526 <bool> value. See also: module.async_probe
3527
3528 module.async_probe=<bool>
3529 [KNL] When set to true, modules will use async probing
3530 by default. To enable/disable async probing for a
3531 specific module, use the module specific control that
3532 is documented under <module>.async_probe. When both
3533 module.async_probe and <module>.async_probe are
3534 specified, <module>.async_probe takes precedence for
3535 the specific module.
3536
3537 module.enable_dups_trace
3538 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3539 this means that duplicate request_module() calls will
3540 trigger a WARN_ON() instead of a pr_warn(). Note that
3541 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3542 will always be issued and this option does nothing.
3543 module.sig_enforce
3544 [KNL] When CONFIG_MODULE_SIG is set, this means that
3545 modules without (valid) signatures will fail to load.
3546 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3547 is always true, so this option does nothing.
3548
3549 module_blacklist= [KNL] Do not load a comma-separated list of
3550 modules. Useful for debugging problem modules.
3551
3552 mousedev.tap_time=
3553 [MOUSE] Maximum time between finger touching and
3554 leaving touchpad surface for touch to be considered
3555 a tap and be reported as a left button click (for
3556 touchpads working in absolute mode only).
3557 Format: <msecs>
3558 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3559 reporting absolute coordinates, such as tablets
3560 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3561 reporting absolute coordinates, such as tablets
3562
3563 movablecore= [KNL,X86,IA-64,PPC,EARLY]
3564 Format: nn[KMGTPE] | nn%
3565 This parameter is the complement to kernelcore=, it
3566 specifies the amount of memory used for migratable
3567 allocations. If both kernelcore and movablecore is
3568 specified, then kernelcore will be at *least* the
3569 specified value but may be more. If movablecore on its
3570 own is specified, the administrator must be careful
3571 that the amount of memory usable for all allocations
3572 is not too small.
3573
3574 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
3575 NUMA nodes to be movable. This means that the memory
3576 of such nodes will be usable only for movable
3577 allocations which rules out almost all kernel
3578 allocations. Use with caution!
3579
3580 MTD_Partition= [MTD]
3581 Format: <name>,<region-number>,<size>,<offset>
3582
3583 MTD_Region= [MTD] Format:
3584 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3585
3586 mtdparts= [MTD]
3587 See drivers/mtd/parsers/cmdlinepart.c
3588
3589 mtdset= [ARM]
3590 ARM/S3C2412 JIVE boot control
3591
3592 See arch/arm/mach-s3c/mach-jive.c
3593
3594 mtouchusb.raw_coordinates=
3595 [HW] Make the MicroTouch USB driver use raw coordinates
3596 ('y', default) or cooked coordinates ('n')
3597
3598 mtrr=debug [X86,EARLY]
3599 Enable printing debug information related to MTRR
3600 registers at boot time.
3601
3602 mtrr_chunk_size=nn[KMG,X86,EARLY]
3603 used for mtrr cleanup. It is largest continuous chunk
3604 that could hold holes aka. UC entries.
3605
3606 mtrr_gran_size=nn[KMG,X86,EARLY]
3607 Used for mtrr cleanup. It is granularity of mtrr block.
3608 Default is 1.
3609 Large value could prevent small alignment from
3610 using up MTRRs.
3611
3612 mtrr_spare_reg_nr=n [X86,EARLY]
3613 Format: <integer>
3614 Range: 0,7 : spare reg number
3615 Default : 1
3616 Used for mtrr cleanup. It is spare mtrr entries number.
3617 Set to 2 or more if your graphical card needs more.
3618
3619 multitce=off [PPC] This parameter disables the use of the pSeries
3620 firmware feature for updating multiple TCE entries
3621 at a time.
3622
3623 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3624
3625 netdev= [NET] Network devices parameters
3626 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3627 Note that mem_start is often overloaded to mean
3628 something different and driver-specific.
3629 This usage is only documented in each driver source
3630 file if at all.
3631
3632 netpoll.carrier_timeout=
3633 [NET] Specifies amount of time (in seconds) that
3634 netpoll should wait for a carrier. By default netpoll
3635 waits 4 seconds.
3636
3637 nf_conntrack.acct=
3638 [NETFILTER] Enable connection tracking flow accounting
3639 0 to disable accounting
3640 1 to enable accounting
3641 Default value is 0.
3642
3643 nfs.cache_getent=
3644 [NFS] sets the pathname to the program which is used
3645 to update the NFS client cache entries.
3646
3647 nfs.cache_getent_timeout=
3648 [NFS] sets the timeout after which an attempt to
3649 update a cache entry is deemed to have failed.
3650
3651 nfs.callback_nr_threads=
3652 [NFSv4] set the total number of threads that the
3653 NFS client will assign to service NFSv4 callback
3654 requests.
3655
3656 nfs.callback_tcpport=
3657 [NFS] set the TCP port on which the NFSv4 callback
3658 channel should listen.
3659
3660 nfs.delay_retrans=
3661 [NFS] specifies the number of times the NFSv4 client
3662 retries the request before returning an EAGAIN error,
3663 after a reply of NFS4ERR_DELAY from the server.
3664 Only applies if the softerr mount option is enabled,
3665 and the specified value is >= 0.
3666
3667 nfs.enable_ino64=
3668 [NFS] enable 64-bit inode numbers.
3669 If zero, the NFS client will fake up a 32-bit inode
3670 number for the readdir() and stat() syscalls instead
3671 of returning the full 64-bit number.
3672 The default is to return 64-bit inode numbers.
3673
3674 nfs.idmap_cache_timeout=
3675 [NFS] set the maximum lifetime for idmapper cache
3676 entries.
3677
3678 nfs.max_session_cb_slots=
3679 [NFSv4.1] Sets the maximum number of session
3680 slots the client will assign to the callback
3681 channel. This determines the maximum number of
3682 callbacks the client will process in parallel for
3683 a particular server.
3684
3685 nfs.max_session_slots=
3686 [NFSv4.1] Sets the maximum number of session slots
3687 the client will attempt to negotiate with the server.
3688 This limits the number of simultaneous RPC requests
3689 that the client can send to the NFSv4.1 server.
3690 Note that there is little point in setting this
3691 value higher than the max_tcp_slot_table_limit.
3692
3693 nfs.nfs4_disable_idmapping=
3694 [NFSv4] When set to the default of '1', this option
3695 ensures that both the RPC level authentication
3696 scheme and the NFS level operations agree to use
3697 numeric uids/gids if the mount is using the
3698 'sec=sys' security flavour. In effect it is
3699 disabling idmapping, which can make migration from
3700 legacy NFSv2/v3 systems to NFSv4 easier.
3701 Servers that do not support this mode of operation
3702 will be autodetected by the client, and it will fall
3703 back to using the idmapper.
3704 To turn off this behaviour, set the value to '0'.
3705
3706 nfs.nfs4_unique_id=
3707 [NFS4] Specify an additional fixed unique ident-
3708 ification string that NFSv4 clients can insert into
3709 their nfs_client_id4 string. This is typically a
3710 UUID that is generated at system install time.
3711
3712 nfs.recover_lost_locks=
3713 [NFSv4] Attempt to recover locks that were lost due
3714 to a lease timeout on the server. Please note that
3715 doing this risks data corruption, since there are
3716 no guarantees that the file will remain unchanged
3717 after the locks are lost.
3718 If you want to enable the kernel legacy behaviour of
3719 attempting to recover these locks, then set this
3720 parameter to '1'.
3721 The default parameter value of '0' causes the kernel
3722 not to attempt recovery of lost locks.
3723
3724 nfs.send_implementation_id=
3725 [NFSv4.1] Send client implementation identification
3726 information in exchange_id requests.
3727 If zero, no implementation identification information
3728 will be sent.
3729 The default is to send the implementation identification
3730 information.
3731
3732 nfs4.layoutstats_timer=
3733 [NFSv4.2] Change the rate at which the kernel sends
3734 layoutstats to the pNFS metadata server.
3735
3736 Setting this to value to 0 causes the kernel to use
3737 whatever value is the default set by the layout
3738 driver. A non-zero value sets the minimum interval
3739 in seconds between layoutstats transmissions.
3740
3741 nfsd.inter_copy_offload_enable=
3742 [NFSv4.2] When set to 1, the server will support
3743 server-to-server copies for which this server is
3744 the destination of the copy.
3745
3746 nfsd.nfs4_disable_idmapping=
3747 [NFSv4] When set to the default of '1', the NFSv4
3748 server will return only numeric uids and gids to
3749 clients using auth_sys, and will accept numeric uids
3750 and gids from such clients. This is intended to ease
3751 migration from NFSv2/v3.
3752
3753 nfsd.nfsd4_ssc_umount_timeout=
3754 [NFSv4.2] When used as the destination of a
3755 server-to-server copy, knfsd temporarily mounts
3756 the source server. It caches the mount in case
3757 it will be needed again, and discards it if not
3758 used for the number of milliseconds specified by
3759 this parameter.
3760
3761 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3762 See Documentation/admin-guide/nfs/nfsroot.rst.
3763
3764 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3765 See Documentation/admin-guide/nfs/nfsroot.rst.
3766
3767 nfsrootdebug [NFS] enable nfsroot debugging messages.
3768 See Documentation/admin-guide/nfs/nfsroot.rst.
3769
3770 nmi_backtrace.backtrace_idle [KNL]
3771 Dump stacks even of idle CPUs in response to an
3772 NMI stack-backtrace request.
3773
3774 nmi_debug= [KNL,SH] Specify one or more actions to take
3775 when a NMI is triggered.
3776 Format: [state][,regs][,debounce][,die]
3777
3778 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3779 Format: [panic,][nopanic,][num]
3780 Valid num: 0 or 1
3781 0 - turn hardlockup detector in nmi_watchdog off
3782 1 - turn hardlockup detector in nmi_watchdog on
3783 When panic is specified, panic when an NMI watchdog
3784 timeout occurs (or 'nopanic' to not panic on an NMI
3785 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3786 To disable both hard and soft lockup detectors,
3787 please see 'nowatchdog'.
3788 This is useful when you use a panic=... timeout and
3789 need the box quickly up again.
3790
3791 These settings can be accessed at runtime via
3792 the nmi_watchdog and hardlockup_panic sysctls.
3793
3794 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3795 emulation library even if a 387 maths coprocessor
3796 is present.
3797
3798 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
3799 Forces kernel to use 3-level paging instead.
3800
3801 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
3802 kernel to use 4-level paging instead.
3803
3804 noalign [KNL,ARM]
3805
3806 noaltinstr [S390,EARLY] Disables alternative instructions
3807 patching (CPU alternatives feature).
3808
3809 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
3810 IOAPICs that may be present in the system.
3811
3812 noautogroup Disable scheduler automatic task group creation.
3813
3814 nocache [ARM,EARLY]
3815
3816 no_console_suspend
3817 [HW] Never suspend the console
3818 Disable suspending of consoles during suspend and
3819 hibernate operations. Once disabled, debugging
3820 messages can reach various consoles while the rest
3821 of the system is being put to sleep (ie, while
3822 debugging driver suspend/resume hooks). This may
3823 not work reliably with all consoles, but is known
3824 to work with serial and VGA consoles.
3825 To facilitate more flexible debugging, we also add
3826 console_suspend, a printk module parameter to control
3827 it. Users could use console_suspend (usually
3828 /sys/module/printk/parameters/console_suspend) to
3829 turn on/off it dynamically.
3830
3831 no_debug_objects
3832 [KNL,EARLY] Disable object debugging
3833
3834 nodsp [SH] Disable hardware DSP at boot time.
3835
3836 noefi [EFI,EARLY] Disable EFI runtime services support.
3837
3838 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
3839
3840 noexec [IA-64]
3841
3842 noexec32 [X86-64]
3843 This affects only 32-bit executables.
3844 noexec32=on: enable non-executable mappings (default)
3845 read doesn't imply executable mappings
3846 noexec32=off: disable non-executable mappings
3847 read implies executable mappings
3848
3849 no_file_caps Tells the kernel not to honor file capabilities. The
3850 only way then for a file to be executed with privilege
3851 is to be setuid root or executed by root.
3852
3853 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3854
3855 nofsgsbase [X86] Disables FSGSBASE instructions.
3856
3857 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3858 register save and restore. The kernel will only save
3859 legacy floating-point registers on task switch.
3860
3861 nohalt [IA-64] Tells the kernel not to use the power saving
3862 function PAL_HALT_LIGHT when idle. This increases
3863 power-consumption. On the positive side, it reduces
3864 interrupt wake-up latency, which may improve performance
3865 in certain environments such as networked servers or
3866 real-time systems.
3867
3868 no_hash_pointers
3869 [KNL,EARLY]
3870 Force pointers printed to the console or buffers to be
3871 unhashed. By default, when a pointer is printed via %p
3872 format string, that pointer is "hashed", i.e. obscured
3873 by hashing the pointer value. This is a security feature
3874 that hides actual kernel addresses from unprivileged
3875 users, but it also makes debugging the kernel more
3876 difficult since unequal pointers can no longer be
3877 compared. However, if this command-line option is
3878 specified, then all normal pointers will have their true
3879 value printed. This option should only be specified when
3880 debugging the kernel. Please do not use on production
3881 kernels.
3882
3883 nohibernate [HIBERNATION] Disable hibernation and resume.
3884
3885 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to
3886 busy wait in do_idle() and not use the arch_cpu_idle()
3887 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3888 to be effective. This is useful on platforms where the
3889 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3890 correctly or when doing power measurements to evaluate
3891 the impact of the sleep instructions. This is also
3892 useful when using JTAG debugger.
3893
3894 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
3895
3896 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
3897
3898 nohz= [KNL] Boottime enable/disable dynamic ticks
3899 Valid arguments: on, off
3900 Default: on
3901
3902 nohz_full= [KNL,BOOT,SMP,ISOL]
3903 The argument is a cpu list, as described above.
3904 In kernels built with CONFIG_NO_HZ_FULL=y, set
3905 the specified list of CPUs whose tick will be stopped
3906 whenever possible. The boot CPU will be forced outside
3907 the range to maintain the timekeeping. Any CPUs
3908 in this list will have their RCU callbacks offloaded,
3909 just as if they had also been called out in the
3910 rcu_nocbs= boot parameter.
3911
3912 Note that this argument takes precedence over
3913 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3914
3915 noinitrd [RAM] Tells the kernel not to load any configured
3916 initial RAM disk.
3917
3918 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
3919 remapping.
3920 [Deprecated - use intremap=off]
3921
3922 nointroute [IA-64]
3923
3924 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
3925
3926 noiotrap [SH] Disables trapped I/O port accesses.
3927
3928 noirqdebug [X86-32] Disables the code which attempts to detect and
3929 disable unhandled interrupt sources.
3930
3931 noisapnp [ISAPNP] Disables ISA PnP code.
3932
3933 nojitter [IA-64] Disables jitter checking for ITC timers.
3934
3935 nokaslr [KNL,EARLY]
3936 When CONFIG_RANDOMIZE_BASE is set, this disables
3937 kernel and module base offset ASLR (Address Space
3938 Layout Randomization).
3939
3940 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
3941 fault handling.
3942
3943 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
3944
3945 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
3946
3947 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
3948
3949 nomca [IA-64] Disable machine check abort handling
3950
3951 nomce [X86-32] Disable Machine Check Exception
3952
3953 nomfgpt [X86-32] Disable Multi-Function General Purpose
3954 Timer usage (for AMD Geode machines).
3955
3956 nomodeset Disable kernel modesetting. Most systems' firmware
3957 sets up a display mode and provides framebuffer memory
3958 for output. With nomodeset, DRM and fbdev drivers will
3959 not load if they could possibly displace the pre-
3960 initialized output. Only the system framebuffer will
3961 be available for use. The respective drivers will not
3962 perform display-mode changes or accelerated rendering.
3963
3964 Useful as error fallback, or for testing and debugging.
3965
3966 nomodule Disable module load
3967
3968 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3969 shutdown the other cpus. Instead use the REBOOT_VECTOR
3970 irq.
3971
3972 nopat [X86,EARLY] Disable PAT (page attribute table extension of
3973 pagetables) support.
3974
3975 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
3976
3977 nopku [X86] Disable Memory Protection Keys CPU feature found
3978 in some Intel CPUs.
3979
3980 nopti [X86-64,EARLY]
3981 Equivalent to pti=off
3982
3983 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
3984 Disables the PV optimizations forcing the guest to run
3985 as generic guest with no PV drivers. Currently support
3986 XEN HVM, KVM, HYPER_V and VMWARE guest.
3987
3988 nopvspin [X86,XEN,KVM,EARLY]
3989 Disables the qspinlock slow path using PV optimizations
3990 which allow the hypervisor to 'idle' the guest on lock
3991 contention.
3992
3993 norandmaps Don't use address space randomization. Equivalent to
3994 echo 0 > /proc/sys/kernel/randomize_va_space
3995
3996 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3997 with UP alternatives
3998
3999 noresume [SWSUSP] Disables resume and restores original swap
4000 space.
4001
4002 nosbagart [IA-64]
4003
4004 no-scroll [VGA] Disables scrollback.
4005 This is required for the Braillex ib80-piezo Braille
4006 reader made by F.H. Papenmeier (Germany).
4007
4008 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
4009
4010 nosmap [PPC,EARLY]
4011 Disable SMAP (Supervisor Mode Access Prevention)
4012 even if it is supported by processor.
4013
4014 nosmep [PPC64s,EARLY]
4015 Disable SMEP (Supervisor Mode Execution Prevention)
4016 even if it is supported by processor.
4017
4018 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
4019 and disable the IO APIC. legacy for "maxcpus=0".
4020
4021 nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
4022 Equivalent to smt=1.
4023
4024 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
4025 nosmt=force: Force disable SMT, cannot be undone
4026 via the sysfs control file.
4027
4028 nosoftlockup [KNL] Disable the soft-lockup detector.
4029
4030 nospec_store_bypass_disable
4031 [HW,EARLY] Disable all mitigations for the Speculative
4032 Store Bypass vulnerability
4033
4034 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4035 history injection) vulnerability. System may allow data leaks
4036 with this option.
4037
4038 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4039 (bounds check bypass). With this option data leaks are
4040 possible in the system.
4041
4042 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4043 for the Spectre variant 2 (indirect branch
4044 prediction) vulnerability. System may allow data
4045 leaks with this option.
4046
4047 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,EARLY] Disable
4048 paravirtualized steal time accounting. steal time is
4049 computed, but won't influence scheduler behaviour
4050
4051 nosync [HW,M68K] Disables sync negotiation for all devices.
4052
4053 no_timer_check [X86,APIC] Disables the code which tests for
4054 broken timer IRQ sources.
4055
4056 no_uaccess_flush
4057 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4058
4059 novmcoredd [KNL,KDUMP]
4060 Disable device dump. Device dump allows drivers to
4061 append dump data to vmcore so you can collect driver
4062 specified debug info. Drivers can append the data
4063 without any limit and this data is stored in memory,
4064 so this may cause significant memory stress. Disabling
4065 device dump can help save memory but the driver debug
4066 data will be no longer available. This parameter
4067 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4068 is set.
4069
4070 no-vmw-sched-clock
4071 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4072 scheduler clock and use the default one.
4073
4074 nowatchdog [KNL] Disable both lockup detectors, i.e.
4075 soft-lockup and NMI watchdog (hard-lockup).
4076
4077 nowb [ARM,EARLY]
4078
4079 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4080
4081 NOTE: this parameter will be ignored on systems with the
4082 LEGACY_XAPIC_DISABLED bit set in the
4083 IA32_XAPIC_DISABLE_STATUS MSR.
4084
4085 noxsave [BUGS=X86] Disables x86 extended register state save
4086 and restore using xsave. The kernel will fallback to
4087 enabling legacy floating-point and sse state.
4088
4089 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4090 register states. The kernel will fall back to use
4091 xsave to save the states. By using this parameter,
4092 performance of saving the states is degraded because
4093 xsave doesn't support modified optimization while
4094 xsaveopt supports it on xsaveopt enabled systems.
4095
4096 noxsaves [X86] Disables xsaves and xrstors used in saving and
4097 restoring x86 extended register state in compacted
4098 form of xsave area. The kernel will fall back to use
4099 xsaveopt and xrstor to save and restore the states
4100 in standard form of xsave area. By using this
4101 parameter, xsave area per process might occupy more
4102 memory on xsaves enabled systems.
4103
4104 nps_mtm_hs_ctr= [KNL,ARC]
4105 This parameter sets the maximum duration, in
4106 cycles, each HW thread of the CTOP can run
4107 without interruptions, before HW switches it.
4108 The actual maximum duration is 16 times this
4109 parameter's value.
4110 Format: integer between 1 and 255
4111 Default: 255
4112
4113 nptcg= [IA-64] Override max number of concurrent global TLB
4114 purges which is reported from either PAL_VM_SUMMARY or
4115 SAL PALO.
4116
4117 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4118 could support. nr_cpus=n : n >= 1 limits the kernel to
4119 support 'n' processors. It could be larger than the
4120 number of already plugged CPU during bootup, later in
4121 runtime you can physically add extra cpu until it reaches
4122 n. So during boot up some boot time memory for per-cpu
4123 variables need be pre-allocated for later physical cpu
4124 hot plugging.
4125
4126 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4127
4128 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4129 Disable NUMA, Only set up a single NUMA node
4130 spanning all memory.
4131
4132 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4133 NUMA balancing.
4134 Allowed values are enable and disable
4135
4136 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4137 'node', 'default' can be specified
4138 This can be set from sysctl after boot.
4139 See Documentation/admin-guide/sysctl/vm.rst for details.
4140
4141 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4142 See Documentation/core-api/debugging-via-ohci1394.rst for more
4143 info.
4144
4145 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4146 Rather than timing out after 20 ms if an EC
4147 command is not properly ACKed, override the length
4148 of the timeout. We have interrupts disabled while
4149 waiting for the ACK, so if this is set too high
4150 interrupts *may* be lost!
4151
4152 omap_mux= [OMAP] Override bootloader pin multiplexing.
4153 Format: <mux_mode0.mode_name=value>...
4154 For example, to override I2C bus2:
4155 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4156
4157 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4158
4159 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4160
4161 boundary - index of last SLC block on Flex-OneNAND.
4162 The remaining blocks are configured as MLC blocks.
4163 lock - Configure if Flex-OneNAND boundary should be locked.
4164 Once locked, the boundary cannot be changed.
4165 1 indicates lock status, 0 indicates unlock status.
4166
4167 oops=panic [KNL,EARLY]
4168 Always panic on oopses. Default is to just kill the
4169 process, but there is a small probability of
4170 deadlocking the machine.
4171 This will also cause panics on machine check exceptions.
4172 Useful together with panic=30 to trigger a reboot.
4173
4174 page_alloc.shuffle=
4175 [KNL] Boolean flag to control whether the page allocator
4176 should randomize its free lists. The randomization may
4177 be automatically enabled if the kernel detects it is
4178 running on a platform with a direct-mapped memory-side
4179 cache, and this parameter can be used to
4180 override/disable that behavior. The state of the flag
4181 can be read from sysfs at:
4182 /sys/module/page_alloc/parameters/shuffle.
4183
4184 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4185 Storage of the information about who allocated
4186 each page is disabled in default. With this switch,
4187 we can turn it on.
4188 on: enable the feature
4189
4190 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4191 poisoning on the buddy allocator, available with
4192 CONFIG_PAGE_POISONING=y.
4193 off: turn off poisoning (default)
4194 on: turn on poisoning
4195
4196 page_reporting.page_reporting_order=
4197 [KNL] Minimal page reporting order
4198 Format: <integer>
4199 Adjust the minimal page reporting order. The page
4200 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4201
4202 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4203 timeout > 0: seconds before rebooting
4204 timeout = 0: wait forever
4205 timeout < 0: reboot immediately
4206 Format: <timeout>
4207
4208 panic_on_taint= [KNL,EARLY]
4209 Bitmask for conditionally calling panic() in add_taint()
4210 Format: <hex>[,nousertaint]
4211 Hexadecimal bitmask representing the set of TAINT flags
4212 that will cause the kernel to panic when add_taint() is
4213 called with any of the flags in this set.
4214 The optional switch "nousertaint" can be utilized to
4215 prevent userspace forced crashes by writing to sysctl
4216 /proc/sys/kernel/tainted any flagset matching with the
4217 bitmask set on panic_on_taint.
4218 See Documentation/admin-guide/tainted-kernels.rst for
4219 extra details on the taint flags that users can pick
4220 to compose the bitmask to assign to panic_on_taint.
4221
4222 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4223 on a WARN().
4224
4225 panic_print= Bitmask for printing system info when panic happens.
4226 User can chose combination of the following bits:
4227 bit 0: print all tasks info
4228 bit 1: print system memory info
4229 bit 2: print timer info
4230 bit 3: print locks info if CONFIG_LOCKDEP is on
4231 bit 4: print ftrace buffer
4232 bit 5: print all printk messages in buffer
4233 bit 6: print all CPUs backtrace (if available in the arch)
4234 bit 7: print only tasks in uninterruptible (blocked) state
4235 *Be aware* that this option may print a _lot_ of lines,
4236 so there are risks of losing older messages in the log.
4237 Use this option carefully, maybe worth to setup a
4238 bigger log buffer with "log_buf_len" along with this.
4239
4240 parkbd.port= [HW] Parallel port number the keyboard adapter is
4241 connected to, default is 0.
4242 Format: <parport#>
4243 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4244 0 for XT, 1 for AT (default is AT).
4245 Format: <mode>
4246
4247 parport= [HW,PPT] Specify parallel ports. 0 disables.
4248 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4249 Use 'auto' to force the driver to use any
4250 IRQ/DMA settings detected (the default is to
4251 ignore detected IRQ/DMA settings because of
4252 possible conflicts). You can specify the base
4253 address, IRQ, and DMA settings; IRQ and DMA
4254 should be numbers, or 'auto' (for using detected
4255 settings on that particular port), or 'nofifo'
4256 (to avoid using a FIFO even if it is detected).
4257 Parallel ports are assigned in the order they
4258 are specified on the command line, starting
4259 with parport0.
4260
4261 parport_init_mode= [HW,PPT]
4262 Configure VIA parallel port to operate in
4263 a specific mode. This is necessary on Pegasos
4264 computer where firmware has no options for setting
4265 up parallel port mode and sets it to spp.
4266 Currently this function knows 686a and 8231 chips.
4267 Format: [spp|ps2|epp|ecp|ecpepp]
4268
4269 pata_legacy.all= [HW,LIBATA]
4270 Format: <int>
4271 Set to non-zero to probe primary and secondary ISA
4272 port ranges on PCI systems where no PCI PATA device
4273 has been found at either range. Disabled by default.
4274
4275 pata_legacy.autospeed= [HW,LIBATA]
4276 Format: <int>
4277 Set to non-zero if a chip is present that snoops speed
4278 changes. Disabled by default.
4279
4280 pata_legacy.ht6560a= [HW,LIBATA]
4281 Format: <int>
4282 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4283 the secondary channel, or both channels respectively.
4284 Disabled by default.
4285
4286 pata_legacy.ht6560b= [HW,LIBATA]
4287 Format: <int>
4288 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4289 the secondary channel, or both channels respectively.
4290 Disabled by default.
4291
4292 pata_legacy.iordy_mask= [HW,LIBATA]
4293 Format: <int>
4294 IORDY enable mask. Set individual bits to allow IORDY
4295 for the respective channel. Bit 0 is for the first
4296 legacy channel handled by this driver, bit 1 is for
4297 the second channel, and so on. The sequence will often
4298 correspond to the primary legacy channel, the secondary
4299 legacy channel, and so on, but the handling of a PCI
4300 bus and the use of other driver options may interfere
4301 with the sequence. By default IORDY is allowed across
4302 all channels.
4303
4304 pata_legacy.opti82c46x= [HW,LIBATA]
4305 Format: <int>
4306 Set to 1, 2, or 3 for Opti 82c611A on the primary
4307 channel, the secondary channel, or both channels
4308 respectively. Disabled by default.
4309
4310 pata_legacy.opti82c611a= [HW,LIBATA]
4311 Format: <int>
4312 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4313 channel, the secondary channel, or both channels
4314 respectively. Disabled by default.
4315
4316 pata_legacy.pio_mask= [HW,LIBATA]
4317 Format: <int>
4318 PIO mode mask for autospeed devices. Set individual
4319 bits to allow the use of the respective PIO modes.
4320 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4321 All modes allowed by default.
4322
4323 pata_legacy.probe_all= [HW,LIBATA]
4324 Format: <int>
4325 Set to non-zero to probe tertiary and further ISA
4326 port ranges on PCI systems. Disabled by default.
4327
4328 pata_legacy.probe_mask= [HW,LIBATA]
4329 Format: <int>
4330 Probe mask for legacy ISA PATA ports. Depending on
4331 platform configuration and the use of other driver
4332 options up to 6 legacy ports are supported: 0x1f0,
4333 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4334 of individual ports can be disabled by setting the
4335 corresponding bits in the mask to 1. Bit 0 is for
4336 the first port in the list above (0x1f0), and so on.
4337 By default all supported ports are probed.
4338
4339 pata_legacy.qdi= [HW,LIBATA]
4340 Format: <int>
4341 Set to non-zero to probe QDI controllers. By default
4342 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4343
4344 pata_legacy.winbond= [HW,LIBATA]
4345 Format: <int>
4346 Set to non-zero to probe Winbond controllers. Use
4347 the standard I/O port (0x130) if 1, otherwise the
4348 value given is the I/O port to use (typically 0x1b0).
4349 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4350 0 otherwise.
4351
4352 pata_platform.pio_mask= [HW,LIBATA]
4353 Format: <int>
4354 Supported PIO mode mask. Set individual bits to allow
4355 the use of the respective PIO modes. Bit 0 is for
4356 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4357 allowed by default.
4358
4359 pause_on_oops=<int>
4360 Halt all CPUs after the first oops has been printed for
4361 the specified number of seconds. This is to be used if
4362 your oopses keep scrolling off the screen.
4363
4364 pcbit= [HW,ISDN]
4365
4366 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
4367
4368 Some options herein operate on a specific device
4369 or a set of devices (<pci_dev>). These are
4370 specified in one of the following formats:
4371
4372 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4373 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4374
4375 Note: the first format specifies a PCI
4376 bus/device/function address which may change
4377 if new hardware is inserted, if motherboard
4378 firmware changes, or due to changes caused
4379 by other kernel parameters. If the
4380 domain is left unspecified, it is
4381 taken to be zero. Optionally, a path
4382 to a device through multiple device/function
4383 addresses can be specified after the base
4384 address (this is more robust against
4385 renumbering issues). The second format
4386 selects devices using IDs from the
4387 configuration space which may match multiple
4388 devices in the system.
4389
4390 earlydump dump PCI config space before the kernel
4391 changes anything
4392 off [X86] don't probe for the PCI bus
4393 bios [X86-32] force use of PCI BIOS, don't access
4394 the hardware directly. Use this if your machine
4395 has a non-standard PCI host bridge.
4396 nobios [X86-32] disallow use of PCI BIOS, only direct
4397 hardware access methods are allowed. Use this
4398 if you experience crashes upon bootup and you
4399 suspect they are caused by the BIOS.
4400 conf1 [X86] Force use of PCI Configuration Access
4401 Mechanism 1 (config address in IO port 0xCF8,
4402 data in IO port 0xCFC, both 32-bit).
4403 conf2 [X86] Force use of PCI Configuration Access
4404 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4405 the function, IO port 0xCFA, also 8-bit, sets
4406 bus number. The config space is then accessed
4407 through ports 0xC000-0xCFFF).
4408 See http://wiki.osdev.org/PCI for more info
4409 on the configuration access mechanisms.
4410 noaer [PCIE] If the PCIEAER kernel config parameter is
4411 enabled, this kernel boot option can be used to
4412 disable the use of PCIE advanced error reporting.
4413 nodomains [PCI] Disable support for multiple PCI
4414 root domains (aka PCI segments, in ACPI-speak).
4415 nommconf [X86] Disable use of MMCONFIG for PCI
4416 Configuration
4417 check_enable_amd_mmconf [X86] check for and enable
4418 properly configured MMIO access to PCI
4419 config space on AMD family 10h CPU
4420 nomsi [MSI] If the PCI_MSI kernel config parameter is
4421 enabled, this kernel boot option can be used to
4422 disable the use of MSI interrupts system-wide.
4423 noioapicquirk [APIC] Disable all boot interrupt quirks.
4424 Safety option to keep boot IRQs enabled. This
4425 should never be necessary.
4426 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4427 primary IO-APIC for bridges that cannot disable
4428 boot IRQs. This fixes a source of spurious IRQs
4429 when the system masks IRQs.
4430 noioapicreroute [APIC] Disable workaround that uses the
4431 boot IRQ equivalent of an IRQ that connects to
4432 a chipset where boot IRQs cannot be disabled.
4433 The opposite of ioapicreroute.
4434 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4435 routing table. These calls are known to be buggy
4436 on several machines and they hang the machine
4437 when used, but on other computers it's the only
4438 way to get the interrupt routing table. Try
4439 this option if the kernel is unable to allocate
4440 IRQs or discover secondary PCI buses on your
4441 motherboard.
4442 rom [X86] Assign address space to expansion ROMs.
4443 Use with caution as certain devices share
4444 address decoders between ROMs and other
4445 resources.
4446 norom [X86] Do not assign address space to
4447 expansion ROMs that do not already have
4448 BIOS assigned address ranges.
4449 nobar [X86] Do not assign address space to the
4450 BARs that weren't assigned by the BIOS.
4451 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4452 assigned automatically to PCI devices. You can
4453 make the kernel exclude IRQs of your ISA cards
4454 this way.
4455 pirqaddr=0xAAAAA [X86] Specify the physical address
4456 of the PIRQ table (normally generated
4457 by the BIOS) if it is outside the
4458 F0000h-100000h range.
4459 lastbus=N [X86] Scan all buses thru bus #N. Can be
4460 useful if the kernel is unable to find your
4461 secondary buses and you want to tell it
4462 explicitly which ones they are.
4463 assign-busses [X86] Always assign all PCI bus
4464 numbers ourselves, overriding
4465 whatever the firmware may have done.
4466 usepirqmask [X86] Honor the possible IRQ mask stored
4467 in the BIOS $PIR table. This is needed on
4468 some systems with broken BIOSes, notably
4469 some HP Pavilion N5400 and Omnibook XE3
4470 notebooks. This will have no effect if ACPI
4471 IRQ routing is enabled.
4472 noacpi [X86] Do not use ACPI for IRQ routing
4473 or for PCI scanning.
4474 use_crs [X86] Use PCI host bridge window information
4475 from ACPI. On BIOSes from 2008 or later, this
4476 is enabled by default. If you need to use this,
4477 please report a bug.
4478 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4479 If you need to use this, please report a bug.
4480 use_e820 [X86] Use E820 reservations to exclude parts of
4481 PCI host bridge windows. This is a workaround
4482 for BIOS defects in host bridge _CRS methods.
4483 If you need to use this, please report a bug to
4484 <linux-pci@vger.kernel.org>.
4485 no_e820 [X86] Ignore E820 reservations for PCI host
4486 bridge windows. This is the default on modern
4487 hardware. If you need to use this, please report
4488 a bug to <linux-pci@vger.kernel.org>.
4489 routeirq Do IRQ routing for all PCI devices.
4490 This is normally done in pci_enable_device(),
4491 so this option is a temporary workaround
4492 for broken drivers that don't call it.
4493 skip_isa_align [X86] do not align io start addr, so can
4494 handle more pci cards
4495 noearly [X86] Don't do any early type 1 scanning.
4496 This might help on some broken boards which
4497 machine check when some devices' config space
4498 is read. But various workarounds are disabled
4499 and some IOMMU drivers will not work.
4500 bfsort Sort PCI devices into breadth-first order.
4501 This sorting is done to get a device
4502 order compatible with older (<= 2.4) kernels.
4503 nobfsort Don't sort PCI devices into breadth-first order.
4504 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4505 tuning and use the BIOS-configured MPS defaults.
4506 pcie_bus_safe Set every device's MPS to the largest value
4507 supported by all devices below the root complex.
4508 pcie_bus_perf Set device MPS to the largest allowable MPS
4509 based on its parent bus. Also set MRRS (Max
4510 Read Request Size) to the largest supported
4511 value (no larger than the MPS that the device
4512 or bus can support) for best performance.
4513 pcie_bus_peer2peer Set every device's MPS to 128B, which
4514 every device is guaranteed to support. This
4515 configuration allows peer-to-peer DMA between
4516 any pair of devices, possibly at the cost of
4517 reduced performance. This also guarantees
4518 that hot-added devices will work.
4519 cbiosize=nn[KMG] The fixed amount of bus space which is
4520 reserved for the CardBus bridge's IO window.
4521 The default value is 256 bytes.
4522 cbmemsize=nn[KMG] The fixed amount of bus space which is
4523 reserved for the CardBus bridge's memory
4524 window. The default value is 64 megabytes.
4525 resource_alignment=
4526 Format:
4527 [<order of align>@]<pci_dev>[; ...]
4528 Specifies alignment and device to reassign
4529 aligned memory resources. How to
4530 specify the device is described above.
4531 If <order of align> is not specified,
4532 PAGE_SIZE is used as alignment.
4533 A PCI-PCI bridge can be specified if resource
4534 windows need to be expanded.
4535 To specify the alignment for several
4536 instances of a device, the PCI vendor,
4537 device, subvendor, and subdevice may be
4538 specified, e.g., 12@pci:8086:9c22:103c:198f
4539 for 4096-byte alignment.
4540 ecrc= Enable/disable PCIe ECRC (transaction layer
4541 end-to-end CRC checking). Only effective if
4542 OS has native AER control (either granted by
4543 ACPI _OSC or forced via "pcie_ports=native")
4544 bios: Use BIOS/firmware settings. This is the
4545 the default.
4546 off: Turn ECRC off
4547 on: Turn ECRC on.
4548 hpiosize=nn[KMG] The fixed amount of bus space which is
4549 reserved for hotplug bridge's IO window.
4550 Default size is 256 bytes.
4551 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4552 reserved for hotplug bridge's MMIO window.
4553 Default size is 2 megabytes.
4554 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4555 reserved for hotplug bridge's MMIO_PREF window.
4556 Default size is 2 megabytes.
4557 hpmemsize=nn[KMG] The fixed amount of bus space which is
4558 reserved for hotplug bridge's MMIO and
4559 MMIO_PREF window.
4560 Default size is 2 megabytes.
4561 hpbussize=nn The minimum amount of additional bus numbers
4562 reserved for buses below a hotplug bridge.
4563 Default is 1.
4564 realloc= Enable/disable reallocating PCI bridge resources
4565 if allocations done by BIOS are too small to
4566 accommodate resources required by all child
4567 devices.
4568 off: Turn realloc off
4569 on: Turn realloc on
4570 realloc same as realloc=on
4571 noari do not use PCIe ARI.
4572 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4573 do not use PCIe ATS (and IOMMU device IOTLB).
4574 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4575 only look for one device below a PCIe downstream
4576 port.
4577 big_root_window Try to add a big 64bit memory window to the PCIe
4578 root complex on AMD CPUs. Some GFX hardware
4579 can resize a BAR to allow access to all VRAM.
4580 Adding the window is slightly risky (it may
4581 conflict with unreported devices), so this
4582 taints the kernel.
4583 disable_acs_redir=<pci_dev>[; ...]
4584 Specify one or more PCI devices (in the format
4585 specified above) separated by semicolons.
4586 Each device specified will have the PCI ACS
4587 redirect capabilities forced off which will
4588 allow P2P traffic between devices through
4589 bridges without forcing it upstream. Note:
4590 this removes isolation between devices and
4591 may put more devices in an IOMMU group.
4592 force_floating [S390] Force usage of floating interrupts.
4593 nomio [S390] Do not use MIO instructions.
4594 norid [S390] ignore the RID field and force use of
4595 one PCI domain per PCI function
4596
4597 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power
4598 Management.
4599 off Don't touch ASPM configuration at all. Leave any
4600 configuration done by firmware unchanged.
4601 force Enable ASPM even on devices that claim not to support it.
4602 WARNING: Forcing ASPM on may cause system lockups.
4603
4604 pcie_ports= [PCIE] PCIe port services handling:
4605 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4606 even if the platform doesn't give the OS permission to
4607 use them. This may cause conflicts if the platform
4608 also tries to use these services.
4609 dpc-native Use native PCIe service for DPC only. May
4610 cause conflicts if firmware uses AER or DPC.
4611 compat Disable native PCIe services (PME, AER, DPC, PCIe
4612 hotplug).
4613
4614 pcie_port_pm= [PCIE] PCIe port power management handling:
4615 off Disable power management of all PCIe ports
4616 force Forcibly enable power management of all PCIe ports
4617
4618 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4619 nomsi Do not use MSI for native PCIe PME signaling (this makes
4620 all PCIe root ports use INTx for all services).
4621
4622 pcmv= [HW,PCMCIA] BadgePAD 4
4623
4624 pd_ignore_unused
4625 [PM]
4626 Keep all power-domains already enabled by bootloader on,
4627 even if no driver has claimed them. This is useful
4628 for debug and development, but should not be
4629 needed on a platform with proper driver support.
4630
4631 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4632 boot time.
4633 Format: { 0 | 1 }
4634 See arch/parisc/kernel/pdc_chassis.c
4635
4636 percpu_alloc= [MM,EARLY]
4637 Select which percpu first chunk allocator to use.
4638 Currently supported values are "embed" and "page".
4639 Archs may support subset or none of the selections.
4640 See comments in mm/percpu.c for details on each
4641 allocator. This parameter is primarily for debugging
4642 and performance comparison.
4643
4644 pirq= [SMP,APIC] Manual mp-table setup
4645 See Documentation/arch/x86/i386/IO-APIC.rst.
4646
4647 plip= [PPT,NET] Parallel port network link
4648 Format: { parport<nr> | timid | 0 }
4649 See also Documentation/admin-guide/parport.rst.
4650
4651 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4652 Override pmtimer IOPort with a hex value.
4653 e.g. pmtmr=0x508
4654
4655 pmu_override= [PPC] Override the PMU.
4656 This option takes over the PMU facility, so it is no
4657 longer usable by perf. Setting this option starts the
4658 PMU counters by setting MMCR0 to 0 (the FC bit is
4659 cleared). If a number is given, then MMCR1 is set to
4660 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4661 remains 0.
4662
4663 pm_debug_messages [SUSPEND,KNL]
4664 Enable suspend/resume debug messages during boot up.
4665
4666 pnp.debug=1 [PNP]
4667 Enable PNP debug messages (depends on the
4668 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4669 via /sys/module/pnp/parameters/debug. We always show
4670 current resource usage; turning this on also shows
4671 possible settings and some assignment information.
4672
4673 pnpacpi= [ACPI]
4674 { off }
4675
4676 pnpbios= [ISAPNP]
4677 { on | off | curr | res | no-curr | no-res }
4678
4679 pnp_reserve_irq=
4680 [ISAPNP] Exclude IRQs for the autoconfiguration
4681
4682 pnp_reserve_dma=
4683 [ISAPNP] Exclude DMAs for the autoconfiguration
4684
4685 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4686 Ranges are in pairs (I/O port base and size).
4687
4688 pnp_reserve_mem=
4689 [ISAPNP] Exclude memory regions for the
4690 autoconfiguration.
4691 Ranges are in pairs (memory base and size).
4692
4693 ports= [IP_VS_FTP] IPVS ftp helper module
4694 Default is 21.
4695 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4696 may be specified.
4697 Format: <port>,<port>....
4698
4699 possible_cpus= [SMP,S390,X86]
4700 Format: <unsigned int>
4701 Set the number of possible CPUs, overriding the
4702 regular discovery mechanisms (such as ACPI/FW, etc).
4703
4704 powersave=off [PPC] This option disables power saving features.
4705 It specifically disables cpuidle and sets the
4706 platform machine description specific power_save
4707 function to NULL. On Idle the CPU just reduces
4708 execution priority.
4709
4710 ppc_strict_facility_enable
4711 [PPC,ENABLE] This option catches any kernel floating point,
4712 Altivec, VSX and SPE outside of regions specifically
4713 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4714 There is some performance impact when enabling this.
4715
4716 ppc_tm= [PPC,EARLY]
4717 Format: {"off"}
4718 Disable Hardware Transactional Memory
4719
4720 preempt= [KNL]
4721 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4722 none - Limited to cond_resched() calls
4723 voluntary - Limited to cond_resched() and might_sleep() calls
4724 full - Any section that isn't explicitly preempt disabled
4725 can be preempted anytime.
4726
4727 print-fatal-signals=
4728 [KNL] debug: print fatal signals
4729
4730 If enabled, warn about various signal handling
4731 related application anomalies: too many signals,
4732 too many POSIX.1 timers, fatal signals causing a
4733 coredump - etc.
4734
4735 If you hit the warning due to signal overflow,
4736 you might want to try "ulimit -i unlimited".
4737
4738 default: off.
4739
4740 printk.always_kmsg_dump=
4741 Trigger kmsg_dump for cases other than kernel oops or
4742 panics
4743 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4744 default: disabled
4745
4746 printk.console_no_auto_verbose=
4747 Disable console loglevel raise on oops, panic
4748 or lockdep-detected issues (only if lock debug is on).
4749 With an exception to setups with low baudrate on
4750 serial console, keeping this 0 is a good choice
4751 in order to provide more debug information.
4752 Format: <bool>
4753 default: 0 (auto_verbose is enabled)
4754
4755 printk.devkmsg={on,off,ratelimit}
4756 Control writing to /dev/kmsg.
4757 on - unlimited logging to /dev/kmsg from userspace
4758 off - logging to /dev/kmsg disabled
4759 ratelimit - ratelimit the logging
4760 Default: ratelimit
4761
4762 printk.time= Show timing data prefixed to each printk message line
4763 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4764
4765 processor.max_cstate= [HW,ACPI]
4766 Limit processor to maximum C-state
4767 max_cstate=9 overrides any DMI blacklist limit.
4768
4769 processor.nocst [HW,ACPI]
4770 Ignore the _CST method to determine C-states,
4771 instead using the legacy FADT method
4772
4773 profile= [KNL] Enable kernel profiling via /proc/profile
4774 Format: [<profiletype>,]<number>
4775 Param: <profiletype>: "schedule", "sleep", or "kvm"
4776 [defaults to kernel profiling]
4777 Param: "schedule" - profile schedule points.
4778 Param: "sleep" - profile D-state sleeping (millisecs).
4779 Requires CONFIG_SCHEDSTATS
4780 Param: "kvm" - profile VM exits.
4781 Param: <number> - step/bucket size as a power of 2 for
4782 statistical time based profiling.
4783
4784 prompt_ramdisk= [RAM] [Deprecated]
4785
4786 prot_virt= [S390] enable hosting protected virtual machines
4787 isolated from the hypervisor (if hardware supports
4788 that).
4789 Format: <bool>
4790
4791 psi= [KNL] Enable or disable pressure stall information
4792 tracking.
4793 Format: <bool>
4794
4795 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4796 probe for; one of (bare|imps|exps|lifebook|any).
4797 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4798 per second.
4799 psmouse.resetafter= [HW,MOUSE]
4800 Try to reset the device after so many bad packets
4801 (0 = never).
4802 psmouse.resolution=
4803 [HW,MOUSE] Set desired mouse resolution, in dpi.
4804 psmouse.smartscroll=
4805 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4806 0 = disabled, 1 = enabled (default).
4807
4808 pstore.backend= Specify the name of the pstore backend to use
4809
4810 pti= [X86-64] Control Page Table Isolation of user and
4811 kernel address spaces. Disabling this feature
4812 removes hardening, but improves performance of
4813 system calls and interrupts.
4814
4815 on - unconditionally enable
4816 off - unconditionally disable
4817 auto - kernel detects whether your CPU model is
4818 vulnerable to issues that PTI mitigates
4819
4820 Not specifying this option is equivalent to pti=auto.
4821
4822 pty.legacy_count=
4823 [KNL] Number of legacy pty's. Overwrites compiled-in
4824 default number.
4825
4826 quiet [KNL,EARLY] Disable most log messages
4827
4828 r128= [HW,DRM]
4829
4830 radix_hcall_invalidate=on [PPC/PSERIES]
4831 Disable RADIX GTSE feature and use hcall for TLB
4832 invalidate.
4833
4834 raid= [HW,RAID]
4835 See Documentation/admin-guide/md.rst.
4836
4837 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4838 See Documentation/admin-guide/blockdev/ramdisk.rst.
4839
4840 ramdisk_start= [RAM] RAM disk image start address
4841
4842 random.trust_cpu=off
4843 [KNL,EARLY] Disable trusting the use of the CPU's
4844 random number generator (if available) to
4845 initialize the kernel's RNG.
4846
4847 random.trust_bootloader=off
4848 [KNL,EARLY] Disable trusting the use of the a seed
4849 passed by the bootloader (if available) to
4850 initialize the kernel's RNG.
4851
4852 randomize_kstack_offset=
4853 [KNL,EARLY] Enable or disable kernel stack offset
4854 randomization, which provides roughly 5 bits of
4855 entropy, frustrating memory corruption attacks
4856 that depend on stack address determinism or
4857 cross-syscall address exposures. This is only
4858 available on architectures that have defined
4859 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4860 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4861 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4862
4863 ras=option[,option,...] [KNL] RAS-specific options
4864
4865 cec_disable [X86]
4866 Disable the Correctable Errors Collector,
4867 see CONFIG_RAS_CEC help text.
4868
4869 rcu_nocbs[=cpu-list]
4870 [KNL] The optional argument is a cpu list,
4871 as described above.
4872
4873 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4874 enable the no-callback CPU mode, which prevents
4875 such CPUs' callbacks from being invoked in
4876 softirq context. Invocation of such CPUs' RCU
4877 callbacks will instead be offloaded to "rcuox/N"
4878 kthreads created for that purpose, where "x" is
4879 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4880 for the kthreads that mediate grace periods; and
4881 "N" is the CPU number. This reduces OS jitter on
4882 the offloaded CPUs, which can be useful for HPC
4883 and real-time workloads. It can also improve
4884 energy efficiency for asymmetric multiprocessors.
4885
4886 If a cpulist is passed as an argument, the specified
4887 list of CPUs is set to no-callback mode from boot.
4888
4889 Otherwise, if the '=' sign and the cpulist
4890 arguments are omitted, no CPU will be set to
4891 no-callback mode from boot but the mode may be
4892 toggled at runtime via cpusets.
4893
4894 Note that this argument takes precedence over
4895 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4896
4897 rcu_nocb_poll [KNL]
4898 Rather than requiring that offloaded CPUs
4899 (specified by rcu_nocbs= above) explicitly
4900 awaken the corresponding "rcuoN" kthreads,
4901 make these kthreads poll for callbacks.
4902 This improves the real-time response for the
4903 offloaded CPUs by relieving them of the need to
4904 wake up the corresponding kthread, but degrades
4905 energy efficiency by requiring that the kthreads
4906 periodically wake up to do the polling.
4907
4908 rcutree.blimit= [KNL]
4909 Set maximum number of finished RCU callbacks to
4910 process in one batch.
4911
4912 rcutree.do_rcu_barrier= [KNL]
4913 Request a call to rcu_barrier(). This is
4914 throttled so that userspace tests can safely
4915 hammer on the sysfs variable if they so choose.
4916 If triggered before the RCU grace-period machinery
4917 is fully active, this will error out with EAGAIN.
4918
4919 rcutree.dump_tree= [KNL]
4920 Dump the structure of the rcu_node combining tree
4921 out at early boot. This is used for diagnostic
4922 purposes, to verify correct tree setup.
4923
4924 rcutree.gp_cleanup_delay= [KNL]
4925 Set the number of jiffies to delay each step of
4926 RCU grace-period cleanup.
4927
4928 rcutree.gp_init_delay= [KNL]
4929 Set the number of jiffies to delay each step of
4930 RCU grace-period initialization.
4931
4932 rcutree.gp_preinit_delay= [KNL]
4933 Set the number of jiffies to delay each step of
4934 RCU grace-period pre-initialization, that is,
4935 the propagation of recent CPU-hotplug changes up
4936 the rcu_node combining tree.
4937
4938 rcutree.jiffies_till_first_fqs= [KNL]
4939 Set delay from grace-period initialization to
4940 first attempt to force quiescent states.
4941 Units are jiffies, minimum value is zero,
4942 and maximum value is HZ.
4943
4944 rcutree.jiffies_till_next_fqs= [KNL]
4945 Set delay between subsequent attempts to force
4946 quiescent states. Units are jiffies, minimum
4947 value is one, and maximum value is HZ.
4948
4949 rcutree.jiffies_till_sched_qs= [KNL]
4950 Set required age in jiffies for a
4951 given grace period before RCU starts
4952 soliciting quiescent-state help from
4953 rcu_note_context_switch() and cond_resched().
4954 If not specified, the kernel will calculate
4955 a value based on the most recent settings
4956 of rcutree.jiffies_till_first_fqs
4957 and rcutree.jiffies_till_next_fqs.
4958 This calculated value may be viewed in
4959 rcutree.jiffies_to_sched_qs. Any attempt to set
4960 rcutree.jiffies_to_sched_qs will be cheerfully
4961 overwritten.
4962
4963 rcutree.kthread_prio= [KNL,BOOT]
4964 Set the SCHED_FIFO priority of the RCU per-CPU
4965 kthreads (rcuc/N). This value is also used for
4966 the priority of the RCU boost threads (rcub/N)
4967 and for the RCU grace-period kthreads (rcu_bh,
4968 rcu_preempt, and rcu_sched). If RCU_BOOST is
4969 set, valid values are 1-99 and the default is 1
4970 (the least-favored priority). Otherwise, when
4971 RCU_BOOST is not set, valid values are 0-99 and
4972 the default is zero (non-realtime operation).
4973 When RCU_NOCB_CPU is set, also adjust the
4974 priority of NOCB callback kthreads.
4975
4976 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4977 On callback-offloaded (rcu_nocbs) CPUs,
4978 RCU reduces the lock contention that would
4979 otherwise be caused by callback floods through
4980 use of the ->nocb_bypass list. However, in the
4981 common non-flooded case, RCU queues directly to
4982 the main ->cblist in order to avoid the extra
4983 overhead of the ->nocb_bypass list and its lock.
4984 But if there are too many callbacks queued during
4985 a single jiffy, RCU pre-queues the callbacks into
4986 the ->nocb_bypass queue. The definition of "too
4987 many" is supplied by this kernel boot parameter.
4988
4989 rcutree.qhimark= [KNL]
4990 Set threshold of queued RCU callbacks beyond which
4991 batch limiting is disabled.
4992
4993 rcutree.qlowmark= [KNL]
4994 Set threshold of queued RCU callbacks below which
4995 batch limiting is re-enabled.
4996
4997 rcutree.qovld= [KNL]
4998 Set threshold of queued RCU callbacks beyond which
4999 RCU's force-quiescent-state scan will aggressively
5000 enlist help from cond_resched() and sched IPIs to
5001 help CPUs more quickly reach quiescent states.
5002 Set to less than zero to make this be set based
5003 on rcutree.qhimark at boot time and to zero to
5004 disable more aggressive help enlistment.
5005
5006 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
5007 Set the page-cache refill delay (in milliseconds)
5008 in response to low-memory conditions. The range
5009 of permitted values is in the range 0:100000.
5010
5011 rcutree.rcu_divisor= [KNL]
5012 Set the shift-right count to use to compute
5013 the callback-invocation batch limit bl from
5014 the number of callbacks queued on this CPU.
5015 The result will be bounded below by the value of
5016 the rcutree.blimit kernel parameter. Every bl
5017 callbacks, the softirq handler will exit in
5018 order to allow the CPU to do other work.
5019
5020 Please note that this callback-invocation batch
5021 limit applies only to non-offloaded callback
5022 invocation. Offloaded callbacks are instead
5023 invoked in the context of an rcuoc kthread, which
5024 scheduler will preempt as it does any other task.
5025
5026 rcutree.rcu_fanout_exact= [KNL]
5027 Disable autobalancing of the rcu_node combining
5028 tree. This is used by rcutorture, and might
5029 possibly be useful for architectures having high
5030 cache-to-cache transfer latencies.
5031
5032 rcutree.rcu_fanout_leaf= [KNL]
5033 Change the number of CPUs assigned to each
5034 leaf rcu_node structure. Useful for very
5035 large systems, which will choose the value 64,
5036 and for NUMA systems with large remote-access
5037 latencies, which will choose a value aligned
5038 with the appropriate hardware boundaries.
5039
5040 rcutree.rcu_min_cached_objs= [KNL]
5041 Minimum number of objects which are cached and
5042 maintained per one CPU. Object size is equal
5043 to PAGE_SIZE. The cache allows to reduce the
5044 pressure to page allocator, also it makes the
5045 whole algorithm to behave better in low memory
5046 condition.
5047
5048 rcutree.rcu_nocb_gp_stride= [KNL]
5049 Set the number of NOCB callback kthreads in
5050 each group, which defaults to the square root
5051 of the number of CPUs. Larger numbers reduce
5052 the wakeup overhead on the global grace-period
5053 kthread, but increases that same overhead on
5054 each group's NOCB grace-period kthread.
5055
5056 rcutree.rcu_kick_kthreads= [KNL]
5057 Cause the grace-period kthread to get an extra
5058 wake_up() if it sleeps three times longer than
5059 it should at force-quiescent-state time.
5060 This wake_up() will be accompanied by a
5061 WARN_ONCE() splat and an ftrace_dump().
5062
5063 rcutree.rcu_resched_ns= [KNL]
5064 Limit the time spend invoking a batch of RCU
5065 callbacks to the specified number of nanoseconds.
5066 By default, this limit is checked only once
5067 every 32 callbacks in order to limit the pain
5068 inflicted by local_clock() overhead.
5069
5070 rcutree.rcu_unlock_delay= [KNL]
5071 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5072 this specifies an rcu_read_unlock()-time delay
5073 in microseconds. This defaults to zero.
5074 Larger delays increase the probability of
5075 catching RCU pointer leaks, that is, buggy use
5076 of RCU-protected pointers after the relevant
5077 rcu_read_unlock() has completed.
5078
5079 rcutree.sysrq_rcu= [KNL]
5080 Commandeer a sysrq key to dump out Tree RCU's
5081 rcu_node tree with an eye towards determining
5082 why a new grace period has not yet started.
5083
5084 rcutree.use_softirq= [KNL]
5085 If set to zero, move all RCU_SOFTIRQ processing to
5086 per-CPU rcuc kthreads. Defaults to a non-zero
5087 value, meaning that RCU_SOFTIRQ is used by default.
5088 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5089
5090 But note that CONFIG_PREEMPT_RT=y kernels disable
5091 this kernel boot parameter, forcibly setting it
5092 to zero.
5093
5094 rcutree.enable_rcu_lazy= [KNL]
5095 To save power, batch RCU callbacks and flush after
5096 delay, memory pressure or callback list growing too
5097 big.
5098
5099 rcuscale.gp_async= [KNL]
5100 Measure performance of asynchronous
5101 grace-period primitives such as call_rcu().
5102
5103 rcuscale.gp_async_max= [KNL]
5104 Specify the maximum number of outstanding
5105 callbacks per writer thread. When a writer
5106 thread exceeds this limit, it invokes the
5107 corresponding flavor of rcu_barrier() to allow
5108 previously posted callbacks to drain.
5109
5110 rcuscale.gp_exp= [KNL]
5111 Measure performance of expedited synchronous
5112 grace-period primitives.
5113
5114 rcuscale.holdoff= [KNL]
5115 Set test-start holdoff period. The purpose of
5116 this parameter is to delay the start of the
5117 test until boot completes in order to avoid
5118 interference.
5119
5120 rcuscale.kfree_by_call_rcu= [KNL]
5121 In kernels built with CONFIG_RCU_LAZY=y, test
5122 call_rcu() instead of kfree_rcu().
5123
5124 rcuscale.kfree_mult= [KNL]
5125 Instead of allocating an object of size kfree_obj,
5126 allocate one of kfree_mult * sizeof(kfree_obj).
5127 Defaults to 1.
5128
5129 rcuscale.kfree_rcu_test= [KNL]
5130 Set to measure performance of kfree_rcu() flooding.
5131
5132 rcuscale.kfree_rcu_test_double= [KNL]
5133 Test the double-argument variant of kfree_rcu().
5134 If this parameter has the same value as
5135 rcuscale.kfree_rcu_test_single, both the single-
5136 and double-argument variants are tested.
5137
5138 rcuscale.kfree_rcu_test_single= [KNL]
5139 Test the single-argument variant of kfree_rcu().
5140 If this parameter has the same value as
5141 rcuscale.kfree_rcu_test_double, both the single-
5142 and double-argument variants are tested.
5143
5144 rcuscale.kfree_nthreads= [KNL]
5145 The number of threads running loops of kfree_rcu().
5146
5147 rcuscale.kfree_alloc_num= [KNL]
5148 Number of allocations and frees done in an iteration.
5149
5150 rcuscale.kfree_loops= [KNL]
5151 Number of loops doing rcuscale.kfree_alloc_num number
5152 of allocations and frees.
5153
5154 rcuscale.minruntime= [KNL]
5155 Set the minimum test run time in seconds. This
5156 does not affect the data-collection interval,
5157 but instead allows better measurement of things
5158 like CPU consumption.
5159
5160 rcuscale.nreaders= [KNL]
5161 Set number of RCU readers. The value -1 selects
5162 N, where N is the number of CPUs. A value
5163 "n" less than -1 selects N-n+1, where N is again
5164 the number of CPUs. For example, -2 selects N
5165 (the number of CPUs), -3 selects N+1, and so on.
5166 A value of "n" less than or equal to -N selects
5167 a single reader.
5168
5169 rcuscale.nwriters= [KNL]
5170 Set number of RCU writers. The values operate
5171 the same as for rcuscale.nreaders.
5172 N, where N is the number of CPUs
5173
5174 rcuscale.scale_type= [KNL]
5175 Specify the RCU implementation to test.
5176
5177 rcuscale.shutdown= [KNL]
5178 Shut the system down after performance tests
5179 complete. This is useful for hands-off automated
5180 testing.
5181
5182 rcuscale.verbose= [KNL]
5183 Enable additional printk() statements.
5184
5185 rcuscale.writer_holdoff= [KNL]
5186 Write-side holdoff between grace periods,
5187 in microseconds. The default of zero says
5188 no holdoff.
5189
5190 rcuscale.writer_holdoff_jiffies= [KNL]
5191 Additional write-side holdoff between grace
5192 periods, but in jiffies. The default of zero
5193 says no holdoff.
5194
5195 rcutorture.fqs_duration= [KNL]
5196 Set duration of force_quiescent_state bursts
5197 in microseconds.
5198
5199 rcutorture.fqs_holdoff= [KNL]
5200 Set holdoff time within force_quiescent_state bursts
5201 in microseconds.
5202
5203 rcutorture.fqs_stutter= [KNL]
5204 Set wait time between force_quiescent_state bursts
5205 in seconds.
5206
5207 rcutorture.fwd_progress= [KNL]
5208 Specifies the number of kthreads to be used
5209 for RCU grace-period forward-progress testing
5210 for the types of RCU supporting this notion.
5211 Defaults to 1 kthread, values less than zero or
5212 greater than the number of CPUs cause the number
5213 of CPUs to be used.
5214
5215 rcutorture.fwd_progress_div= [KNL]
5216 Specify the fraction of a CPU-stall-warning
5217 period to do tight-loop forward-progress testing.
5218
5219 rcutorture.fwd_progress_holdoff= [KNL]
5220 Number of seconds to wait between successive
5221 forward-progress tests.
5222
5223 rcutorture.fwd_progress_need_resched= [KNL]
5224 Enclose cond_resched() calls within checks for
5225 need_resched() during tight-loop forward-progress
5226 testing.
5227
5228 rcutorture.gp_cond= [KNL]
5229 Use conditional/asynchronous update-side
5230 primitives, if available.
5231
5232 rcutorture.gp_exp= [KNL]
5233 Use expedited update-side primitives, if available.
5234
5235 rcutorture.gp_normal= [KNL]
5236 Use normal (non-expedited) asynchronous
5237 update-side primitives, if available.
5238
5239 rcutorture.gp_sync= [KNL]
5240 Use normal (non-expedited) synchronous
5241 update-side primitives, if available. If all
5242 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5243 rcutorture.gp_normal=, and rcutorture.gp_sync=
5244 are zero, rcutorture acts as if is interpreted
5245 they are all non-zero.
5246
5247 rcutorture.irqreader= [KNL]
5248 Run RCU readers from irq handlers, or, more
5249 accurately, from a timer handler. Not all RCU
5250 flavors take kindly to this sort of thing.
5251
5252 rcutorture.leakpointer= [KNL]
5253 Leak an RCU-protected pointer out of the reader.
5254 This can of course result in splats, and is
5255 intended to test the ability of things like
5256 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5257 such leaks.
5258
5259 rcutorture.n_barrier_cbs= [KNL]
5260 Set callbacks/threads for rcu_barrier() testing.
5261
5262 rcutorture.nfakewriters= [KNL]
5263 Set number of concurrent RCU writers. These just
5264 stress RCU, they don't participate in the actual
5265 test, hence the "fake".
5266
5267 rcutorture.nocbs_nthreads= [KNL]
5268 Set number of RCU callback-offload togglers.
5269 Zero (the default) disables toggling.
5270
5271 rcutorture.nocbs_toggle= [KNL]
5272 Set the delay in milliseconds between successive
5273 callback-offload toggling attempts.
5274
5275 rcutorture.nreaders= [KNL]
5276 Set number of RCU readers. The value -1 selects
5277 N-1, where N is the number of CPUs. A value
5278 "n" less than -1 selects N-n-2, where N is again
5279 the number of CPUs. For example, -2 selects N
5280 (the number of CPUs), -3 selects N+1, and so on.
5281
5282 rcutorture.object_debug= [KNL]
5283 Enable debug-object double-call_rcu() testing.
5284
5285 rcutorture.onoff_holdoff= [KNL]
5286 Set time (s) after boot for CPU-hotplug testing.
5287
5288 rcutorture.onoff_interval= [KNL]
5289 Set time (jiffies) between CPU-hotplug operations,
5290 or zero to disable CPU-hotplug testing.
5291
5292 rcutorture.read_exit= [KNL]
5293 Set the number of read-then-exit kthreads used
5294 to test the interaction of RCU updaters and
5295 task-exit processing.
5296
5297 rcutorture.read_exit_burst= [KNL]
5298 The number of times in a given read-then-exit
5299 episode that a set of read-then-exit kthreads
5300 is spawned.
5301
5302 rcutorture.read_exit_delay= [KNL]
5303 The delay, in seconds, between successive
5304 read-then-exit testing episodes.
5305
5306 rcutorture.shuffle_interval= [KNL]
5307 Set task-shuffle interval (s). Shuffling tasks
5308 allows some CPUs to go into dyntick-idle mode
5309 during the rcutorture test.
5310
5311 rcutorture.shutdown_secs= [KNL]
5312 Set time (s) after boot system shutdown. This
5313 is useful for hands-off automated testing.
5314
5315 rcutorture.stall_cpu= [KNL]
5316 Duration of CPU stall (s) to test RCU CPU stall
5317 warnings, zero to disable.
5318
5319 rcutorture.stall_cpu_block= [KNL]
5320 Sleep while stalling if set. This will result
5321 in warnings from preemptible RCU in addition to
5322 any other stall-related activity. Note that
5323 in kernels built with CONFIG_PREEMPTION=n and
5324 CONFIG_PREEMPT_COUNT=y, this parameter will
5325 cause the CPU to pass through a quiescent state.
5326 Given CONFIG_PREEMPTION=n, this will suppress
5327 RCU CPU stall warnings, but will instead result
5328 in scheduling-while-atomic splats.
5329
5330 Use of this module parameter results in splats.
5331
5332
5333 rcutorture.stall_cpu_holdoff= [KNL]
5334 Time to wait (s) after boot before inducing stall.
5335
5336 rcutorture.stall_cpu_irqsoff= [KNL]
5337 Disable interrupts while stalling if set.
5338
5339 rcutorture.stall_gp_kthread= [KNL]
5340 Duration (s) of forced sleep within RCU
5341 grace-period kthread to test RCU CPU stall
5342 warnings, zero to disable. If both stall_cpu
5343 and stall_gp_kthread are specified, the
5344 kthread is starved first, then the CPU.
5345
5346 rcutorture.stat_interval= [KNL]
5347 Time (s) between statistics printk()s.
5348
5349 rcutorture.stutter= [KNL]
5350 Time (s) to stutter testing, for example, specifying
5351 five seconds causes the test to run for five seconds,
5352 wait for five seconds, and so on. This tests RCU's
5353 ability to transition abruptly to and from idle.
5354
5355 rcutorture.test_boost= [KNL]
5356 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5357 "Maybe" means test if the RCU implementation
5358 under test support RCU priority boosting.
5359
5360 rcutorture.test_boost_duration= [KNL]
5361 Duration (s) of each individual boost test.
5362
5363 rcutorture.test_boost_interval= [KNL]
5364 Interval (s) between each boost test.
5365
5366 rcutorture.test_no_idle_hz= [KNL]
5367 Test RCU's dyntick-idle handling. See also the
5368 rcutorture.shuffle_interval parameter.
5369
5370 rcutorture.torture_type= [KNL]
5371 Specify the RCU implementation to test.
5372
5373 rcutorture.verbose= [KNL]
5374 Enable additional printk() statements.
5375
5376 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5377 Dump ftrace buffer after reporting RCU CPU
5378 stall warning.
5379
5380 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5381 Provide RCU CPU stall notifiers, but see the
5382 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5383 option's help text. TL;DR: You almost certainly
5384 do not want rcupdate.rcu_cpu_stall_notifiers.
5385
5386 rcupdate.rcu_cpu_stall_suppress= [KNL]
5387 Suppress RCU CPU stall warning messages.
5388
5389 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5390 Suppress RCU CPU stall warning messages and
5391 rcutorture writer stall warnings that occur
5392 during early boot, that is, during the time
5393 before the init task is spawned.
5394
5395 rcupdate.rcu_cpu_stall_timeout= [KNL]
5396 Set timeout for RCU CPU stall warning messages.
5397 The value is in seconds and the maximum allowed
5398 value is 300 seconds.
5399
5400 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5401 Set timeout for expedited RCU CPU stall warning
5402 messages. The value is in milliseconds
5403 and the maximum allowed value is 21000
5404 milliseconds. Please note that this value is
5405 adjusted to an arch timer tick resolution.
5406 Setting this to zero causes the value from
5407 rcupdate.rcu_cpu_stall_timeout to be used (after
5408 conversion from seconds to milliseconds).
5409
5410 rcupdate.rcu_cpu_stall_cputime= [KNL]
5411 Provide statistics on the cputime and count of
5412 interrupts and tasks during the sampling period. For
5413 multiple continuous RCU stalls, all sampling periods
5414 begin at half of the first RCU stall timeout.
5415
5416 rcupdate.rcu_exp_stall_task_details= [KNL]
5417 Print stack dumps of any tasks blocking the
5418 current expedited RCU grace period during an
5419 expedited RCU CPU stall warning.
5420
5421 rcupdate.rcu_expedited= [KNL]
5422 Use expedited grace-period primitives, for
5423 example, synchronize_rcu_expedited() instead
5424 of synchronize_rcu(). This reduces latency,
5425 but can increase CPU utilization, degrade
5426 real-time latency, and degrade energy efficiency.
5427 No effect on CONFIG_TINY_RCU kernels.
5428
5429 rcupdate.rcu_normal= [KNL]
5430 Use only normal grace-period primitives,
5431 for example, synchronize_rcu() instead of
5432 synchronize_rcu_expedited(). This improves
5433 real-time latency, CPU utilization, and
5434 energy efficiency, but can expose users to
5435 increased grace-period latency. This parameter
5436 overrides rcupdate.rcu_expedited. No effect on
5437 CONFIG_TINY_RCU kernels.
5438
5439 rcupdate.rcu_normal_after_boot= [KNL]
5440 Once boot has completed (that is, after
5441 rcu_end_inkernel_boot() has been invoked), use
5442 only normal grace-period primitives. No effect
5443 on CONFIG_TINY_RCU kernels.
5444
5445 But note that CONFIG_PREEMPT_RT=y kernels enables
5446 this kernel boot parameter, forcibly setting
5447 it to the value one, that is, converting any
5448 post-boot attempt at an expedited RCU grace
5449 period to instead use normal non-expedited
5450 grace-period processing.
5451
5452 rcupdate.rcu_task_collapse_lim= [KNL]
5453 Set the maximum number of callbacks present
5454 at the beginning of a grace period that allows
5455 the RCU Tasks flavors to collapse back to using
5456 a single callback queue. This switching only
5457 occurs when rcupdate.rcu_task_enqueue_lim is
5458 set to the default value of -1.
5459
5460 rcupdate.rcu_task_contend_lim= [KNL]
5461 Set the minimum number of callback-queuing-time
5462 lock-contention events per jiffy required to
5463 cause the RCU Tasks flavors to switch to per-CPU
5464 callback queuing. This switching only occurs
5465 when rcupdate.rcu_task_enqueue_lim is set to
5466 the default value of -1.
5467
5468 rcupdate.rcu_task_enqueue_lim= [KNL]
5469 Set the number of callback queues to use for the
5470 RCU Tasks family of RCU flavors. The default
5471 of -1 allows this to be automatically (and
5472 dynamically) adjusted. This parameter is intended
5473 for use in testing.
5474
5475 rcupdate.rcu_task_ipi_delay= [KNL]
5476 Set time in jiffies during which RCU tasks will
5477 avoid sending IPIs, starting with the beginning
5478 of a given grace period. Setting a large
5479 number avoids disturbing real-time workloads,
5480 but lengthens grace periods.
5481
5482 rcupdate.rcu_task_lazy_lim= [KNL]
5483 Number of callbacks on a given CPU that will
5484 cancel laziness on that CPU. Use -1 to disable
5485 cancellation of laziness, but be advised that
5486 doing so increases the danger of OOM due to
5487 callback flooding.
5488
5489 rcupdate.rcu_task_stall_info= [KNL]
5490 Set initial timeout in jiffies for RCU task stall
5491 informational messages, which give some indication
5492 of the problem for those not patient enough to
5493 wait for ten minutes. Informational messages are
5494 only printed prior to the stall-warning message
5495 for a given grace period. Disable with a value
5496 less than or equal to zero. Defaults to ten
5497 seconds. A change in value does not take effect
5498 until the beginning of the next grace period.
5499
5500 rcupdate.rcu_task_stall_info_mult= [KNL]
5501 Multiplier for time interval between successive
5502 RCU task stall informational messages for a given
5503 RCU tasks grace period. This value is clamped
5504 to one through ten, inclusive. It defaults to
5505 the value three, so that the first informational
5506 message is printed 10 seconds into the grace
5507 period, the second at 40 seconds, the third at
5508 160 seconds, and then the stall warning at 600
5509 seconds would prevent a fourth at 640 seconds.
5510
5511 rcupdate.rcu_task_stall_timeout= [KNL]
5512 Set timeout in jiffies for RCU task stall
5513 warning messages. Disable with a value less
5514 than or equal to zero. Defaults to ten minutes.
5515 A change in value does not take effect until
5516 the beginning of the next grace period.
5517
5518 rcupdate.rcu_tasks_lazy_ms= [KNL]
5519 Set timeout in milliseconds RCU Tasks asynchronous
5520 callback batching for call_rcu_tasks().
5521 A negative value will take the default. A value
5522 of zero will disable batching. Batching is
5523 always disabled for synchronize_rcu_tasks().
5524
5525 rcupdate.rcu_tasks_rude_lazy_ms= [KNL]
5526 Set timeout in milliseconds RCU Tasks
5527 Rude asynchronous callback batching for
5528 call_rcu_tasks_rude(). A negative value
5529 will take the default. A value of zero will
5530 disable batching. Batching is always disabled
5531 for synchronize_rcu_tasks_rude().
5532
5533 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5534 Set timeout in milliseconds RCU Tasks
5535 Trace asynchronous callback batching for
5536 call_rcu_tasks_trace(). A negative value
5537 will take the default. A value of zero will
5538 disable batching. Batching is always disabled
5539 for synchronize_rcu_tasks_trace().
5540
5541 rcupdate.rcu_self_test= [KNL]
5542 Run the RCU early boot self tests
5543
5544 rdinit= [KNL]
5545 Format: <full_path>
5546 Run specified binary instead of /init from the ramdisk,
5547 used for early userspace startup. See initrd.
5548
5549 rdrand= [X86,EARLY]
5550 force - Override the decision by the kernel to hide the
5551 advertisement of RDRAND support (this affects
5552 certain AMD processors because of buggy BIOS
5553 support, specifically around the suspend/resume
5554 path).
5555
5556 rdt= [HW,X86,RDT]
5557 Turn on/off individual RDT features. List is:
5558 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5559 mba, smba, bmec.
5560 E.g. to turn on cmt and turn off mba use:
5561 rdt=cmt,!mba
5562
5563 reboot= [KNL]
5564 Format (x86 or x86_64):
5565 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5566 [[,]s[mp]#### \
5567 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5568 [[,]f[orce]
5569 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5570 (prefix with 'panic_' to set mode for panic
5571 reboot only),
5572 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5573 reboot_force is either force or not specified,
5574 reboot_cpu is s[mp]#### with #### being the processor
5575 to be used for rebooting.
5576
5577 refscale.holdoff= [KNL]
5578 Set test-start holdoff period. The purpose of
5579 this parameter is to delay the start of the
5580 test until boot completes in order to avoid
5581 interference.
5582
5583 refscale.lookup_instances= [KNL]
5584 Number of data elements to use for the forms of
5585 SLAB_TYPESAFE_BY_RCU testing. A negative number
5586 is negated and multiplied by nr_cpu_ids, while
5587 zero specifies nr_cpu_ids.
5588
5589 refscale.loops= [KNL]
5590 Set the number of loops over the synchronization
5591 primitive under test. Increasing this number
5592 reduces noise due to loop start/end overhead,
5593 but the default has already reduced the per-pass
5594 noise to a handful of picoseconds on ca. 2020
5595 x86 laptops.
5596
5597 refscale.nreaders= [KNL]
5598 Set number of readers. The default value of -1
5599 selects N, where N is roughly 75% of the number
5600 of CPUs. A value of zero is an interesting choice.
5601
5602 refscale.nruns= [KNL]
5603 Set number of runs, each of which is dumped onto
5604 the console log.
5605
5606 refscale.readdelay= [KNL]
5607 Set the read-side critical-section duration,
5608 measured in microseconds.
5609
5610 refscale.scale_type= [KNL]
5611 Specify the read-protection implementation to test.
5612
5613 refscale.shutdown= [KNL]
5614 Shut down the system at the end of the performance
5615 test. This defaults to 1 (shut it down) when
5616 refscale is built into the kernel and to 0 (leave
5617 it running) when refscale is built as a module.
5618
5619 refscale.verbose= [KNL]
5620 Enable additional printk() statements.
5621
5622 refscale.verbose_batched= [KNL]
5623 Batch the additional printk() statements. If zero
5624 (the default) or negative, print everything. Otherwise,
5625 print every Nth verbose statement, where N is the value
5626 specified.
5627
5628 regulator_ignore_unused
5629 [REGULATOR]
5630 Prevents regulator framework from disabling regulators
5631 that are unused, due no driver claiming them. This may
5632 be useful for debug and development, but should not be
5633 needed on a platform with proper driver support.
5634
5635 relax_domain_level=
5636 [KNL, SMP] Set scheduler's default relax_domain_level.
5637 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5638
5639 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5640 Format: <base1>,<size1>[,<base2>,<size2>,...]
5641 Reserve I/O ports or memory so the kernel won't use
5642 them. If <base> is less than 0x10000, the region
5643 is assumed to be I/O ports; otherwise it is memory.
5644
5645 reservetop= [X86-32,EARLY]
5646 Format: nn[KMG]
5647 Reserves a hole at the top of the kernel virtual
5648 address space.
5649
5650 reset_devices [KNL] Force drivers to reset the underlying device
5651 during initialization.
5652
5653 resume= [SWSUSP]
5654 Specify the partition device for software suspend
5655 Format:
5656 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5657
5658 resume_offset= [SWSUSP]
5659 Specify the offset from the beginning of the partition
5660 given by "resume=" at which the swap header is located,
5661 in <PAGE_SIZE> units (needed only for swap files).
5662 See Documentation/power/swsusp-and-swap-files.rst
5663
5664 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5665 read the resume files
5666
5667 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5668 Useful for devices that are detected asynchronously
5669 (e.g. USB and MMC devices).
5670
5671 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
5672 be accessible via /sys/firmware/initrd.
5673
5674 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5675 Speculative Code Execution with Return Instructions)
5676 vulnerability.
5677
5678 AMD-based UNRET and IBPB mitigations alone do not stop
5679 sibling threads from influencing the predictions of other
5680 sibling threads. For that reason, STIBP is used on pro-
5681 cessors that support it, and mitigate SMT on processors
5682 that don't.
5683
5684 off - no mitigation
5685 auto - automatically select a migitation
5686 auto,nosmt - automatically select a mitigation,
5687 disabling SMT if necessary for
5688 the full mitigation (only on Zen1
5689 and older without STIBP).
5690 ibpb - On AMD, mitigate short speculation
5691 windows on basic block boundaries too.
5692 Safe, highest perf impact. It also
5693 enables STIBP if present. Not suitable
5694 on Intel.
5695 ibpb,nosmt - Like "ibpb" above but will disable SMT
5696 when STIBP is not available. This is
5697 the alternative for systems which do not
5698 have STIBP.
5699 unret - Force enable untrained return thunks,
5700 only effective on AMD f15h-f17h based
5701 systems.
5702 unret,nosmt - Like unret, but will disable SMT when STIBP
5703 is not available. This is the alternative for
5704 systems which do not have STIBP.
5705
5706 Selecting 'auto' will choose a mitigation method at run
5707 time according to the CPU.
5708
5709 Not specifying this option is equivalent to retbleed=auto.
5710
5711 rfkill.default_state=
5712 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5713 etc. communication is blocked by default.
5714 1 Unblocked.
5715
5716 rfkill.master_switch_mode=
5717 0 The "airplane mode" button does nothing.
5718 1 The "airplane mode" button toggles between everything
5719 blocked and the previous configuration.
5720 2 The "airplane mode" button toggles between everything
5721 blocked and everything unblocked.
5722
5723 rhash_entries= [KNL,NET]
5724 Set number of hash buckets for route cache
5725
5726 ring3mwait=disable
5727 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5728 CPUs.
5729
5730 riscv_isa_fallback [RISCV,EARLY]
5731 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
5732 falling back to detecting extension support by parsing
5733 "riscv,isa" property on devicetree systems when the
5734 replacement properties are not found. See the Kconfig
5735 entry for RISCV_ISA_FALLBACK.
5736
5737 ro [KNL] Mount root device read-only on boot
5738
5739 rodata= [KNL,EARLY]
5740 on Mark read-only kernel memory as read-only (default).
5741 off Leave read-only kernel memory writable for debugging.
5742 full Mark read-only kernel memory and aliases as read-only
5743 [arm64]
5744
5745 rockchip.usb_uart
5746 [EARLY]
5747 Enable the uart passthrough on the designated usb port
5748 on Rockchip SoCs. When active, the signals of the
5749 debug-uart get routed to the D+ and D- pins of the usb
5750 port and the regular usb controller gets disabled.
5751
5752 root= [KNL] Root filesystem
5753 Usually this a a block device specifier of some kind,
5754 see the early_lookup_bdev comment in
5755 block/early-lookup.c for details.
5756 Alternatively this can be "ram" for the legacy initial
5757 ramdisk, "nfs" and "cifs" for root on a network file
5758 system, or "mtd" and "ubi" for mounting from raw flash.
5759
5760 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5761 mount the root filesystem
5762
5763 rootflags= [KNL] Set root filesystem mount option string
5764
5765 rootfstype= [KNL] Set root filesystem type
5766
5767 rootwait [KNL] Wait (indefinitely) for root device to show up.
5768 Useful for devices that are detected asynchronously
5769 (e.g. USB and MMC devices).
5770
5771 rootwait= [KNL] Maximum time (in seconds) to wait for root device
5772 to show up before attempting to mount the root
5773 filesystem.
5774
5775 rproc_mem=nn[KMG][@address]
5776 [KNL,ARM,CMA] Remoteproc physical memory block.
5777 Memory area to be used by remote processor image,
5778 managed by CMA.
5779
5780 rw [KNL] Mount root device read-write on boot
5781
5782 S [KNL] Run init in single mode
5783
5784 s390_iommu= [HW,S390]
5785 Set s390 IOTLB flushing mode
5786 strict
5787 With strict flushing every unmap operation will result
5788 in an IOTLB flush. Default is lazy flushing before
5789 reuse, which is faster. Deprecated, equivalent to
5790 iommu.strict=1.
5791
5792 s390_iommu_aperture= [KNL,S390]
5793 Specifies the size of the per device DMA address space
5794 accessible through the DMA and IOMMU APIs as a decimal
5795 factor of the size of main memory.
5796 The default is 1 meaning that one can concurrently use
5797 as many DMA addresses as physical memory is installed,
5798 if supported by hardware, and thus map all of memory
5799 once. With a value of 2 one can map all of memory twice
5800 and so on. As a special case a factor of 0 imposes no
5801 restrictions other than those given by hardware at the
5802 cost of significant additional memory use for tables.
5803
5804 sa1100ir [NET]
5805 See drivers/net/irda/sa1100_ir.c.
5806
5807 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
5808
5809 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5810 Allowed values are enable and disable. This feature
5811 incurs a small amount of overhead in the scheduler
5812 but is useful for debugging and performance tuning.
5813
5814 sched_thermal_decay_shift=
5815 [KNL, SMP] Set a decay shift for scheduler thermal
5816 pressure signal. Thermal pressure signal follows the
5817 default decay period of other scheduler pelt
5818 signals(usually 32 ms but configurable). Setting
5819 sched_thermal_decay_shift will left shift the decay
5820 period for the thermal pressure signal by the shift
5821 value.
5822 i.e. with the default pelt decay period of 32 ms
5823 sched_thermal_decay_shift thermal pressure decay pr
5824 1 64 ms
5825 2 128 ms
5826 and so on.
5827 Format: integer between 0 and 10
5828 Default is 0.
5829
5830 scftorture.holdoff= [KNL]
5831 Number of seconds to hold off before starting
5832 test. Defaults to zero for module insertion and
5833 to 10 seconds for built-in smp_call_function()
5834 tests.
5835
5836 scftorture.longwait= [KNL]
5837 Request ridiculously long waits randomly selected
5838 up to the chosen limit in seconds. Zero (the
5839 default) disables this feature. Please note
5840 that requesting even small non-zero numbers of
5841 seconds can result in RCU CPU stall warnings,
5842 softlockup complaints, and so on.
5843
5844 scftorture.nthreads= [KNL]
5845 Number of kthreads to spawn to invoke the
5846 smp_call_function() family of functions.
5847 The default of -1 specifies a number of kthreads
5848 equal to the number of CPUs.
5849
5850 scftorture.onoff_holdoff= [KNL]
5851 Number seconds to wait after the start of the
5852 test before initiating CPU-hotplug operations.
5853
5854 scftorture.onoff_interval= [KNL]
5855 Number seconds to wait between successive
5856 CPU-hotplug operations. Specifying zero (which
5857 is the default) disables CPU-hotplug operations.
5858
5859 scftorture.shutdown_secs= [KNL]
5860 The number of seconds following the start of the
5861 test after which to shut down the system. The
5862 default of zero avoids shutting down the system.
5863 Non-zero values are useful for automated tests.
5864
5865 scftorture.stat_interval= [KNL]
5866 The number of seconds between outputting the
5867 current test statistics to the console. A value
5868 of zero disables statistics output.
5869
5870 scftorture.stutter_cpus= [KNL]
5871 The number of jiffies to wait between each change
5872 to the set of CPUs under test.
5873
5874 scftorture.use_cpus_read_lock= [KNL]
5875 Use use_cpus_read_lock() instead of the default
5876 preempt_disable() to disable CPU hotplug
5877 while invoking one of the smp_call_function*()
5878 functions.
5879
5880 scftorture.verbose= [KNL]
5881 Enable additional printk() statements.
5882
5883 scftorture.weight_single= [KNL]
5884 The probability weighting to use for the
5885 smp_call_function_single() function with a zero
5886 "wait" parameter. A value of -1 selects the
5887 default if all other weights are -1. However,
5888 if at least one weight has some other value, a
5889 value of -1 will instead select a weight of zero.
5890
5891 scftorture.weight_single_wait= [KNL]
5892 The probability weighting to use for the
5893 smp_call_function_single() function with a
5894 non-zero "wait" parameter. See weight_single.
5895
5896 scftorture.weight_many= [KNL]
5897 The probability weighting to use for the
5898 smp_call_function_many() function with a zero
5899 "wait" parameter. See weight_single.
5900 Note well that setting a high probability for
5901 this weighting can place serious IPI load
5902 on the system.
5903
5904 scftorture.weight_many_wait= [KNL]
5905 The probability weighting to use for the
5906 smp_call_function_many() function with a
5907 non-zero "wait" parameter. See weight_single
5908 and weight_many.
5909
5910 scftorture.weight_all= [KNL]
5911 The probability weighting to use for the
5912 smp_call_function_all() function with a zero
5913 "wait" parameter. See weight_single and
5914 weight_many.
5915
5916 scftorture.weight_all_wait= [KNL]
5917 The probability weighting to use for the
5918 smp_call_function_all() function with a
5919 non-zero "wait" parameter. See weight_single
5920 and weight_many.
5921
5922 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
5923 xtime_lock contention on larger systems, and/or RCU lock
5924 contention on all systems with CONFIG_MAXSMP set.
5925 Format: { "0" | "1" }
5926 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5927 1 -- enable.
5928 Note: increases power consumption, thus should only be
5929 enabled if running jitter sensitive (HPC/RT) workloads.
5930
5931 security= [SECURITY] Choose a legacy "major" security module to
5932 enable at boot. This has been deprecated by the
5933 "lsm=" parameter.
5934
5935 selinux= [SELINUX] Disable or enable SELinux at boot time.
5936 Format: { "0" | "1" }
5937 See security/selinux/Kconfig help text.
5938 0 -- disable.
5939 1 -- enable.
5940 Default value is 1.
5941
5942 serialnumber [BUGS=X86-32]
5943
5944 sev=option[,option...] [X86-64] See Documentation/arch/x86/x86_64/boot-options.rst
5945
5946 shapers= [NET]
5947 Maximal number of shapers.
5948
5949 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
5950 Limit apic dumping. The parameter defines the maximal
5951 number of local apics being dumped. Also it is possible
5952 to set it to "all" by meaning -- no limit here.
5953 Format: { 1 (default) | 2 | ... | all }.
5954 The parameter valid if only apic=debug or
5955 apic=verbose is specified.
5956 Example: apic=debug show_lapic=all
5957
5958 simeth= [IA-64]
5959 simscsi=
5960
5961 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]
5962 Enabling slab_debug allows one to determine the
5963 culprit if slab objects become corrupted. Enabling
5964 slab_debug can create guard zones around objects and
5965 may poison objects when not in use. Also tracks the
5966 last alloc / free. For more information see
5967 Documentation/mm/slub.rst.
5968 (slub_debug legacy name also accepted for now)
5969
5970 slab_max_order= [MM]
5971 Determines the maximum allowed order for slabs.
5972 A high setting may cause OOMs due to memory
5973 fragmentation. For more information see
5974 Documentation/mm/slub.rst.
5975 (slub_max_order legacy name also accepted for now)
5976
5977 slab_merge [MM]
5978 Enable merging of slabs with similar size when the
5979 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5980 (slub_merge legacy name also accepted for now)
5981
5982 slab_min_objects= [MM]
5983 The minimum number of objects per slab. SLUB will
5984 increase the slab order up to slab_max_order to
5985 generate a sufficiently large slab able to contain
5986 the number of objects indicated. The higher the number
5987 of objects the smaller the overhead of tracking slabs
5988 and the less frequently locks need to be acquired.
5989 For more information see Documentation/mm/slub.rst.
5990 (slub_min_objects legacy name also accepted for now)
5991
5992 slab_min_order= [MM]
5993 Determines the minimum page order for slabs. Must be
5994 lower or equal to slab_max_order. For more information see
5995 Documentation/mm/slub.rst.
5996 (slub_min_order legacy name also accepted for now)
5997
5998 slab_nomerge [MM]
5999 Disable merging of slabs with similar size. May be
6000 necessary if there is some reason to distinguish
6001 allocs to different slabs, especially in hardened
6002 environments where the risk of heap overflows and
6003 layout control by attackers can usually be
6004 frustrated by disabling merging. This will reduce
6005 most of the exposure of a heap attack to a single
6006 cache (risks via metadata attacks are mostly
6007 unchanged). Debug options disable merging on their
6008 own.
6009 For more information see Documentation/mm/slub.rst.
6010 (slub_nomerge legacy name also accepted for now)
6011
6012 slram= [HW,MTD]
6013
6014 smart2= [HW]
6015 Format: <io1>[,<io2>[,...,<io8>]]
6016
6017 smp.csd_lock_timeout= [KNL]
6018 Specify the period of time in milliseconds
6019 that smp_call_function() and friends will wait
6020 for a CPU to release the CSD lock. This is
6021 useful when diagnosing bugs involving CPUs
6022 disabling interrupts for extended periods
6023 of time. Defaults to 5,000 milliseconds, and
6024 setting a value of zero disables this feature.
6025 This feature may be more efficiently disabled
6026 using the csdlock_debug- kernel parameter.
6027
6028 smp.panic_on_ipistall= [KNL]
6029 If a csd_lock_timeout extends for more than
6030 the specified number of milliseconds, panic the
6031 system. By default, let CSD-lock acquisition
6032 take as long as they take. Specifying 300,000
6033 for this value provides a 5-minute timeout.
6034
6035 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
6036 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
6037 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
6038 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
6039 smsc-ircc2.ircc_irq= [HW] IRQ line
6040 smsc-ircc2.ircc_dma= [HW] DMA channel
6041 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
6042 0: Toshiba Satellite 1800 (GP data pin select)
6043 1: Fast pin select (default)
6044 2: ATC IRMode
6045
6046 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
6047 (logical CPUs) to use per physical CPU on systems
6048 capable of symmetric multithreading (SMT). Will
6049 be capped to the actual hardware limit.
6050 Format: <integer>
6051 Default: -1 (no limit)
6052
6053 softlockup_panic=
6054 [KNL] Should the soft-lockup detector generate panics.
6055 Format: 0 | 1
6056
6057 A value of 1 instructs the soft-lockup detector
6058 to panic the machine when a soft-lockup occurs. It is
6059 also controlled by the kernel.softlockup_panic sysctl
6060 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6061 respective build-time switch to that functionality.
6062
6063 softlockup_all_cpu_backtrace=
6064 [KNL] Should the soft-lockup detector generate
6065 backtraces on all cpus.
6066 Format: 0 | 1
6067
6068 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6069 See Documentation/admin-guide/laptops/sonypi.rst
6070
6071 spectre_bhi= [X86] Control mitigation of Branch History Injection
6072 (BHI) vulnerability. This setting affects the
6073 deployment of the HW BHI control and the SW BHB
6074 clearing sequence.
6075
6076 on - (default) Enable the HW or SW mitigation
6077 as needed.
6078 off - Disable the mitigation.
6079
6080 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
6081 (indirect branch speculation) vulnerability.
6082 The default operation protects the kernel from
6083 user space attacks.
6084
6085 on - unconditionally enable, implies
6086 spectre_v2_user=on
6087 off - unconditionally disable, implies
6088 spectre_v2_user=off
6089 auto - kernel detects whether your CPU model is
6090 vulnerable
6091
6092 Selecting 'on' will, and 'auto' may, choose a
6093 mitigation method at run time according to the
6094 CPU, the available microcode, the setting of the
6095 CONFIG_MITIGATION_RETPOLINE configuration option,
6096 and the compiler with which the kernel was built.
6097
6098 Selecting 'on' will also enable the mitigation
6099 against user space to user space task attacks.
6100
6101 Selecting 'off' will disable both the kernel and
6102 the user space protections.
6103
6104 Specific mitigations can also be selected manually:
6105
6106 retpoline - replace indirect branches
6107 retpoline,generic - Retpolines
6108 retpoline,lfence - LFENCE; indirect branch
6109 retpoline,amd - alias for retpoline,lfence
6110 eibrs - Enhanced/Auto IBRS
6111 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6112 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6113 ibrs - use IBRS to protect kernel
6114
6115 Not specifying this option is equivalent to
6116 spectre_v2=auto.
6117
6118 spectre_v2_user=
6119 [X86] Control mitigation of Spectre variant 2
6120 (indirect branch speculation) vulnerability between
6121 user space tasks
6122
6123 on - Unconditionally enable mitigations. Is
6124 enforced by spectre_v2=on
6125
6126 off - Unconditionally disable mitigations. Is
6127 enforced by spectre_v2=off
6128
6129 prctl - Indirect branch speculation is enabled,
6130 but mitigation can be enabled via prctl
6131 per thread. The mitigation control state
6132 is inherited on fork.
6133
6134 prctl,ibpb
6135 - Like "prctl" above, but only STIBP is
6136 controlled per thread. IBPB is issued
6137 always when switching between different user
6138 space processes.
6139
6140 seccomp
6141 - Same as "prctl" above, but all seccomp
6142 threads will enable the mitigation unless
6143 they explicitly opt out.
6144
6145 seccomp,ibpb
6146 - Like "seccomp" above, but only STIBP is
6147 controlled per thread. IBPB is issued
6148 always when switching between different
6149 user space processes.
6150
6151 auto - Kernel selects the mitigation depending on
6152 the available CPU features and vulnerability.
6153
6154 Default mitigation: "prctl"
6155
6156 Not specifying this option is equivalent to
6157 spectre_v2_user=auto.
6158
6159 spec_rstack_overflow=
6160 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
6161
6162 off - Disable mitigation
6163 microcode - Enable microcode mitigation only
6164 safe-ret - Enable sw-only safe RET mitigation (default)
6165 ibpb - Enable mitigation by issuing IBPB on
6166 kernel entry
6167 ibpb-vmexit - Issue IBPB only on VMEXIT
6168 (cloud-specific mitigation)
6169
6170 spec_store_bypass_disable=
6171 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
6172 (Speculative Store Bypass vulnerability)
6173
6174 Certain CPUs are vulnerable to an exploit against a
6175 a common industry wide performance optimization known
6176 as "Speculative Store Bypass" in which recent stores
6177 to the same memory location may not be observed by
6178 later loads during speculative execution. The idea
6179 is that such stores are unlikely and that they can
6180 be detected prior to instruction retirement at the
6181 end of a particular speculation execution window.
6182
6183 In vulnerable processors, the speculatively forwarded
6184 store can be used in a cache side channel attack, for
6185 example to read memory to which the attacker does not
6186 directly have access (e.g. inside sandboxed code).
6187
6188 This parameter controls whether the Speculative Store
6189 Bypass optimization is used.
6190
6191 On x86 the options are:
6192
6193 on - Unconditionally disable Speculative Store Bypass
6194 off - Unconditionally enable Speculative Store Bypass
6195 auto - Kernel detects whether the CPU model contains an
6196 implementation of Speculative Store Bypass and
6197 picks the most appropriate mitigation. If the
6198 CPU is not vulnerable, "off" is selected. If the
6199 CPU is vulnerable the default mitigation is
6200 architecture and Kconfig dependent. See below.
6201 prctl - Control Speculative Store Bypass per thread
6202 via prctl. Speculative Store Bypass is enabled
6203 for a process by default. The state of the control
6204 is inherited on fork.
6205 seccomp - Same as "prctl" above, but all seccomp threads
6206 will disable SSB unless they explicitly opt out.
6207
6208 Default mitigations:
6209 X86: "prctl"
6210
6211 On powerpc the options are:
6212
6213 on,auto - On Power8 and Power9 insert a store-forwarding
6214 barrier on kernel entry and exit. On Power7
6215 perform a software flush on kernel entry and
6216 exit.
6217 off - No action.
6218
6219 Not specifying this option is equivalent to
6220 spec_store_bypass_disable=auto.
6221
6222 spia_io_base= [HW,MTD]
6223 spia_fio_base=
6224 spia_pedr=
6225 spia_peddr=
6226
6227 split_lock_detect=
6228 [X86] Enable split lock detection or bus lock detection
6229
6230 When enabled (and if hardware support is present), atomic
6231 instructions that access data across cache line
6232 boundaries will result in an alignment check exception
6233 for split lock detection or a debug exception for
6234 bus lock detection.
6235
6236 off - not enabled
6237
6238 warn - the kernel will emit rate-limited warnings
6239 about applications triggering the #AC
6240 exception or the #DB exception. This mode is
6241 the default on CPUs that support split lock
6242 detection or bus lock detection. Default
6243 behavior is by #AC if both features are
6244 enabled in hardware.
6245
6246 fatal - the kernel will send SIGBUS to applications
6247 that trigger the #AC exception or the #DB
6248 exception. Default behavior is by #AC if
6249 both features are enabled in hardware.
6250
6251 ratelimit:N -
6252 Set system wide rate limit to N bus locks
6253 per second for bus lock detection.
6254 0 < N <= 1000.
6255
6256 N/A for split lock detection.
6257
6258
6259 If an #AC exception is hit in the kernel or in
6260 firmware (i.e. not while executing in user mode)
6261 the kernel will oops in either "warn" or "fatal"
6262 mode.
6263
6264 #DB exception for bus lock is triggered only when
6265 CPL > 0.
6266
6267 srbds= [X86,INTEL,EARLY]
6268 Control the Special Register Buffer Data Sampling
6269 (SRBDS) mitigation.
6270
6271 Certain CPUs are vulnerable to an MDS-like
6272 exploit which can leak bits from the random
6273 number generator.
6274
6275 By default, this issue is mitigated by
6276 microcode. However, the microcode fix can cause
6277 the RDRAND and RDSEED instructions to become
6278 much slower. Among other effects, this will
6279 result in reduced throughput from /dev/urandom.
6280
6281 The microcode mitigation can be disabled with
6282 the following option:
6283
6284 off: Disable mitigation and remove
6285 performance impact to RDRAND and RDSEED
6286
6287 srcutree.big_cpu_lim [KNL]
6288 Specifies the number of CPUs constituting a
6289 large system, such that srcu_struct structures
6290 should immediately allocate an srcu_node array.
6291 This kernel-boot parameter defaults to 128,
6292 but takes effect only when the low-order four
6293 bits of srcutree.convert_to_big is equal to 3
6294 (decide at boot).
6295
6296 srcutree.convert_to_big [KNL]
6297 Specifies under what conditions an SRCU tree
6298 srcu_struct structure will be converted to big
6299 form, that is, with an rcu_node tree:
6300
6301 0: Never.
6302 1: At init_srcu_struct() time.
6303 2: When rcutorture decides to.
6304 3: Decide at boot time (default).
6305 0x1X: Above plus if high contention.
6306
6307 Either way, the srcu_node tree will be sized based
6308 on the actual runtime number of CPUs (nr_cpu_ids)
6309 instead of the compile-time CONFIG_NR_CPUS.
6310
6311 srcutree.counter_wrap_check [KNL]
6312 Specifies how frequently to check for
6313 grace-period sequence counter wrap for the
6314 srcu_data structure's ->srcu_gp_seq_needed field.
6315 The greater the number of bits set in this kernel
6316 parameter, the less frequently counter wrap will
6317 be checked for. Note that the bottom two bits
6318 are ignored.
6319
6320 srcutree.exp_holdoff [KNL]
6321 Specifies how many nanoseconds must elapse
6322 since the end of the last SRCU grace period for
6323 a given srcu_struct until the next normal SRCU
6324 grace period will be considered for automatic
6325 expediting. Set to zero to disable automatic
6326 expediting.
6327
6328 srcutree.srcu_max_nodelay [KNL]
6329 Specifies the number of no-delay instances
6330 per jiffy for which the SRCU grace period
6331 worker thread will be rescheduled with zero
6332 delay. Beyond this limit, worker thread will
6333 be rescheduled with a sleep delay of one jiffy.
6334
6335 srcutree.srcu_max_nodelay_phase [KNL]
6336 Specifies the per-grace-period phase, number of
6337 non-sleeping polls of readers. Beyond this limit,
6338 grace period worker thread will be rescheduled
6339 with a sleep delay of one jiffy, between each
6340 rescan of the readers, for a grace period phase.
6341
6342 srcutree.srcu_retry_check_delay [KNL]
6343 Specifies number of microseconds of non-sleeping
6344 delay between each non-sleeping poll of readers.
6345
6346 srcutree.small_contention_lim [KNL]
6347 Specifies the number of update-side contention
6348 events per jiffy will be tolerated before
6349 initiating a conversion of an srcu_struct
6350 structure to big form. Note that the value of
6351 srcutree.convert_to_big must have the 0x10 bit
6352 set for contention-based conversions to occur.
6353
6354 ssbd= [ARM64,HW,EARLY]
6355 Speculative Store Bypass Disable control
6356
6357 On CPUs that are vulnerable to the Speculative
6358 Store Bypass vulnerability and offer a
6359 firmware based mitigation, this parameter
6360 indicates how the mitigation should be used:
6361
6362 force-on: Unconditionally enable mitigation for
6363 for both kernel and userspace
6364 force-off: Unconditionally disable mitigation for
6365 for both kernel and userspace
6366 kernel: Always enable mitigation in the
6367 kernel, and offer a prctl interface
6368 to allow userspace to register its
6369 interest in being mitigated too.
6370
6371 stack_guard_gap= [MM]
6372 override the default stack gap protection. The value
6373 is in page units and it defines how many pages prior
6374 to (for stacks growing down) resp. after (for stacks
6375 growing up) the main stack are reserved for no other
6376 mapping. Default value is 256 pages.
6377
6378 stack_depot_disable= [KNL,EARLY]
6379 Setting this to true through kernel command line will
6380 disable the stack depot thereby saving the static memory
6381 consumed by the stack hash table. By default this is set
6382 to false.
6383
6384 stacktrace [FTRACE]
6385 Enabled the stack tracer on boot up.
6386
6387 stacktrace_filter=[function-list]
6388 [FTRACE] Limit the functions that the stack tracer
6389 will trace at boot up. function-list is a comma-separated
6390 list of functions. This list can be changed at run
6391 time by the stack_trace_filter file in the debugfs
6392 tracing directory. Note, this enables stack tracing
6393 and the stacktrace above is not needed.
6394
6395 sti= [PARISC,HW]
6396 Format: <num>
6397 Set the STI (builtin display/keyboard on the HP-PARISC
6398 machines) console (graphic card) which should be used
6399 as the initial boot-console.
6400 See also comment in drivers/video/console/sticore.c.
6401
6402 sti_font= [HW]
6403 See comment in drivers/video/console/sticore.c.
6404
6405 stifb= [HW]
6406 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6407
6408 strict_sas_size=
6409 [X86]
6410 Format: <bool>
6411 Enable or disable strict sigaltstack size checks
6412 against the required signal frame size which
6413 depends on the supported FPU features. This can
6414 be used to filter out binaries which have
6415 not yet been made aware of AT_MINSIGSTKSZ.
6416
6417 stress_hpt [PPC,EARLY]
6418 Limits the number of kernel HPT entries in the hash
6419 page table to increase the rate of hash page table
6420 faults on kernel addresses.
6421
6422 stress_slb [PPC,EARLY]
6423 Limits the number of kernel SLB entries, and flushes
6424 them frequently to increase the rate of SLB faults
6425 on kernel addresses.
6426
6427 sunrpc.min_resvport=
6428 sunrpc.max_resvport=
6429 [NFS,SUNRPC]
6430 SunRPC servers often require that client requests
6431 originate from a privileged port (i.e. a port in the
6432 range 0 < portnr < 1024).
6433 An administrator who wishes to reserve some of these
6434 ports for other uses may adjust the range that the
6435 kernel's sunrpc client considers to be privileged
6436 using these two parameters to set the minimum and
6437 maximum port values.
6438
6439 sunrpc.svc_rpc_per_connection_limit=
6440 [NFS,SUNRPC]
6441 Limit the number of requests that the server will
6442 process in parallel from a single connection.
6443 The default value is 0 (no limit).
6444
6445 sunrpc.pool_mode=
6446 [NFS]
6447 Control how the NFS server code allocates CPUs to
6448 service thread pools. Depending on how many NICs
6449 you have and where their interrupts are bound, this
6450 option will affect which CPUs will do NFS serving.
6451 Note: this parameter cannot be changed while the
6452 NFS server is running.
6453
6454 auto the server chooses an appropriate mode
6455 automatically using heuristics
6456 global a single global pool contains all CPUs
6457 percpu one pool for each CPU
6458 pernode one pool for each NUMA node (equivalent
6459 to global on non-NUMA machines)
6460
6461 sunrpc.tcp_slot_table_entries=
6462 sunrpc.udp_slot_table_entries=
6463 [NFS,SUNRPC]
6464 Sets the upper limit on the number of simultaneous
6465 RPC calls that can be sent from the client to a
6466 server. Increasing these values may allow you to
6467 improve throughput, but will also increase the
6468 amount of memory reserved for use by the client.
6469
6470 suspend.pm_test_delay=
6471 [SUSPEND]
6472 Sets the number of seconds to remain in a suspend test
6473 mode before resuming the system (see
6474 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6475 is set. Default value is 5.
6476
6477 svm= [PPC]
6478 Format: { on | off | y | n | 1 | 0 }
6479 This parameter controls use of the Protected
6480 Execution Facility on pSeries.
6481
6482 swiotlb= [ARM,IA-64,PPC,MIPS,X86,EARLY]
6483 Format: { <int> [,<int>] | force | noforce }
6484 <int> -- Number of I/O TLB slabs
6485 <int> -- Second integer after comma. Number of swiotlb
6486 areas with their own lock. Will be rounded up
6487 to a power of 2.
6488 force -- force using of bounce buffers even if they
6489 wouldn't be automatically used by the kernel
6490 noforce -- Never use bounce buffers (for debugging)
6491
6492 switches= [HW,M68k,EARLY]
6493
6494 sysctl.*= [KNL]
6495 Set a sysctl parameter, right before loading the init
6496 process, as if the value was written to the respective
6497 /proc/sys/... file. Both '.' and '/' are recognized as
6498 separators. Unrecognized parameters and invalid values
6499 are reported in the kernel log. Sysctls registered
6500 later by a loaded module cannot be set this way.
6501 Example: sysctl.vm.swappiness=40
6502
6503 sysrq_always_enabled
6504 [KNL]
6505 Ignore sysrq setting - this boot parameter will
6506 neutralize any effect of /proc/sys/kernel/sysrq.
6507 Useful for debugging.
6508
6509 tcpmhash_entries= [KNL,NET]
6510 Set the number of tcp_metrics_hash slots.
6511 Default value is 8192 or 16384 depending on total
6512 ram pages. This is used to specify the TCP metrics
6513 cache size. See Documentation/networking/ip-sysctl.rst
6514 "tcp_no_metrics_save" section for more details.
6515
6516 tdfx= [HW,DRM]
6517
6518 test_suspend= [SUSPEND]
6519 Format: { "mem" | "standby" | "freeze" }[,N]
6520 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6521 standby suspend) or "freeze" (for suspend type freeze)
6522 as the system sleep state during system startup with
6523 the optional capability to repeat N number of times.
6524 The system is woken from this state using a
6525 wakeup-capable RTC alarm.
6526
6527 thash_entries= [KNL,NET]
6528 Set number of hash buckets for TCP connection
6529
6530 thermal.act= [HW,ACPI]
6531 -1: disable all active trip points in all thermal zones
6532 <degrees C>: override all lowest active trip points
6533
6534 thermal.crt= [HW,ACPI]
6535 -1: disable all critical trip points in all thermal zones
6536 <degrees C>: override all critical trip points
6537
6538 thermal.off= [HW,ACPI]
6539 1: disable ACPI thermal control
6540
6541 thermal.psv= [HW,ACPI]
6542 -1: disable all passive trip points
6543 <degrees C>: override all passive trip points to this
6544 value
6545
6546 thermal.tzp= [HW,ACPI]
6547 Specify global default ACPI thermal zone polling rate
6548 <deci-seconds>: poll all this frequency
6549 0: no polling (default)
6550
6551 threadirqs [KNL,EARLY]
6552 Force threading of all interrupt handlers except those
6553 marked explicitly IRQF_NO_THREAD.
6554
6555 topology= [S390,EARLY]
6556 Format: {off | on}
6557 Specify if the kernel should make use of the cpu
6558 topology information if the hardware supports this.
6559 The scheduler will make use of this information and
6560 e.g. base its process migration decisions on it.
6561 Default is on.
6562
6563 topology_updates= [KNL, PPC, NUMA]
6564 Format: {off}
6565 Specify if the kernel should ignore (off)
6566 topology updates sent by the hypervisor to this
6567 LPAR.
6568
6569 torture.disable_onoff_at_boot= [KNL]
6570 Prevent the CPU-hotplug component of torturing
6571 until after init has spawned.
6572
6573 torture.ftrace_dump_at_shutdown= [KNL]
6574 Dump the ftrace buffer at torture-test shutdown,
6575 even if there were no errors. This can be a
6576 very costly operation when many torture tests
6577 are running concurrently, especially on systems
6578 with rotating-rust storage.
6579
6580 torture.verbose_sleep_frequency= [KNL]
6581 Specifies how many verbose printk()s should be
6582 emitted between each sleep. The default of zero
6583 disables verbose-printk() sleeping.
6584
6585 torture.verbose_sleep_duration= [KNL]
6586 Duration of each verbose-printk() sleep in jiffies.
6587
6588 tp720= [HW,PS2]
6589
6590 tpm_suspend_pcr=[HW,TPM]
6591 Format: integer pcr id
6592 Specify that at suspend time, the tpm driver
6593 should extend the specified pcr with zeros,
6594 as a workaround for some chips which fail to
6595 flush the last written pcr on TPM_SaveState.
6596 This will guarantee that all the other pcrs
6597 are saved.
6598
6599 tpm_tis.interrupts= [HW,TPM]
6600 Enable interrupts for the MMIO based physical layer
6601 for the FIFO interface. By default it is set to false
6602 (0). For more information about TPM hardware interfaces
6603 defined by Trusted Computing Group (TCG) see
6604 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
6605
6606 tp_printk [FTRACE]
6607 Have the tracepoints sent to printk as well as the
6608 tracing ring buffer. This is useful for early boot up
6609 where the system hangs or reboots and does not give the
6610 option for reading the tracing buffer or performing a
6611 ftrace_dump_on_oops.
6612
6613 To turn off having tracepoints sent to printk,
6614 echo 0 > /proc/sys/kernel/tracepoint_printk
6615 Note, echoing 1 into this file without the
6616 tp_printk kernel cmdline option has no effect.
6617
6618 The tp_printk_stop_on_boot (see below) can also be used
6619 to stop the printing of events to console at
6620 late_initcall_sync.
6621
6622 ** CAUTION **
6623
6624 Having tracepoints sent to printk() and activating high
6625 frequency tracepoints such as irq or sched, can cause
6626 the system to live lock.
6627
6628 tp_printk_stop_on_boot [FTRACE]
6629 When tp_printk (above) is set, it can cause a lot of noise
6630 on the console. It may be useful to only include the
6631 printing of events during boot up, as user space may
6632 make the system inoperable.
6633
6634 This command line option will stop the printing of events
6635 to console at the late_initcall_sync() time frame.
6636
6637 trace_buf_size=nn[KMG]
6638 [FTRACE] will set tracing buffer size on each cpu.
6639
6640 trace_clock= [FTRACE] Set the clock used for tracing events
6641 at boot up.
6642 local - Use the per CPU time stamp counter
6643 (converted into nanoseconds). Fast, but
6644 depending on the architecture, may not be
6645 in sync between CPUs.
6646 global - Event time stamps are synchronize across
6647 CPUs. May be slower than the local clock,
6648 but better for some race conditions.
6649 counter - Simple counting of events (1, 2, ..)
6650 note, some counts may be skipped due to the
6651 infrastructure grabbing the clock more than
6652 once per event.
6653 uptime - Use jiffies as the time stamp.
6654 perf - Use the same clock that perf uses.
6655 mono - Use ktime_get_mono_fast_ns() for time stamps.
6656 mono_raw - Use ktime_get_raw_fast_ns() for time
6657 stamps.
6658 boot - Use ktime_get_boot_fast_ns() for time stamps.
6659 Architectures may add more clocks. See
6660 Documentation/trace/ftrace.rst for more details.
6661
6662 trace_event=[event-list]
6663 [FTRACE] Set and start specified trace events in order
6664 to facilitate early boot debugging. The event-list is a
6665 comma-separated list of trace events to enable. See
6666 also Documentation/trace/events.rst
6667
6668 trace_instance=[instance-info]
6669 [FTRACE] Create a ring buffer instance early in boot up.
6670 This will be listed in:
6671
6672 /sys/kernel/tracing/instances
6673
6674 Events can be enabled at the time the instance is created
6675 via:
6676
6677 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6678
6679 Note, the "<system*>:" portion is optional if the event is
6680 unique.
6681
6682 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6683
6684 will enable the "sched_switch" event (note, the "sched:" is optional, and
6685 the same thing would happen if it was left off). The irq_handler_entry
6686 event, and all events under the "initcall" system.
6687
6688 trace_options=[option-list]
6689 [FTRACE] Enable or disable tracer options at boot.
6690 The option-list is a comma delimited list of options
6691 that can be enabled or disabled just as if you were
6692 to echo the option name into
6693
6694 /sys/kernel/tracing/trace_options
6695
6696 For example, to enable stacktrace option (to dump the
6697 stack trace of each event), add to the command line:
6698
6699 trace_options=stacktrace
6700
6701 See also Documentation/trace/ftrace.rst "trace options"
6702 section.
6703
6704 trace_trigger=[trigger-list]
6705 [FTRACE] Add a event trigger on specific events.
6706 Set a trigger on top of a specific event, with an optional
6707 filter.
6708
6709 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6710 Where more than one trigger may be specified that are comma deliminated.
6711
6712 For example:
6713
6714 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6715
6716 The above will enable the "stacktrace" trigger on the "sched_switch"
6717 event but only trigger it if the "prev_state" of the "sched_switch"
6718 event is "2" (TASK_UNINTERUPTIBLE).
6719
6720 See also "Event triggers" in Documentation/trace/events.rst
6721
6722
6723 traceoff_on_warning
6724 [FTRACE] enable this option to disable tracing when a
6725 warning is hit. This turns off "tracing_on". Tracing can
6726 be enabled again by echoing '1' into the "tracing_on"
6727 file located in /sys/kernel/tracing/
6728
6729 This option is useful, as it disables the trace before
6730 the WARNING dump is called, which prevents the trace to
6731 be filled with content caused by the warning output.
6732
6733 This option can also be set at run time via the sysctl
6734 option: kernel/traceoff_on_warning
6735
6736 transparent_hugepage=
6737 [KNL]
6738 Format: [always|madvise|never]
6739 Can be used to control the default behavior of the system
6740 with respect to transparent hugepages.
6741 See Documentation/admin-guide/mm/transhuge.rst
6742 for more details.
6743
6744 trusted.source= [KEYS]
6745 Format: <string>
6746 This parameter identifies the trust source as a backend
6747 for trusted keys implementation. Supported trust
6748 sources:
6749 - "tpm"
6750 - "tee"
6751 - "caam"
6752 If not specified then it defaults to iterating through
6753 the trust source list starting with TPM and assigns the
6754 first trust source as a backend which is initialized
6755 successfully during iteration.
6756
6757 trusted.rng= [KEYS]
6758 Format: <string>
6759 The RNG used to generate key material for trusted keys.
6760 Can be one of:
6761 - "kernel"
6762 - the same value as trusted.source: "tpm" or "tee"
6763 - "default"
6764 If not specified, "default" is used. In this case,
6765 the RNG's choice is left to each individual trust source.
6766
6767 tsc= Disable clocksource stability checks for TSC.
6768 Format: <string>
6769 [x86] reliable: mark tsc clocksource as reliable, this
6770 disables clocksource verification at runtime, as well
6771 as the stability checks done at bootup. Used to enable
6772 high-resolution timer mode on older hardware, and in
6773 virtualized environment.
6774 [x86] noirqtime: Do not use TSC to do irq accounting.
6775 Used to run time disable IRQ_TIME_ACCOUNTING on any
6776 platforms where RDTSC is slow and this accounting
6777 can add overhead.
6778 [x86] unstable: mark the TSC clocksource as unstable, this
6779 marks the TSC unconditionally unstable at bootup and
6780 avoids any further wobbles once the TSC watchdog notices.
6781 [x86] nowatchdog: disable clocksource watchdog. Used
6782 in situations with strict latency requirements (where
6783 interruptions from clocksource watchdog are not
6784 acceptable).
6785 [x86] recalibrate: force recalibration against a HW timer
6786 (HPET or PM timer) on systems whose TSC frequency was
6787 obtained from HW or FW using either an MSR or CPUID(0x15).
6788 Warn if the difference is more than 500 ppm.
6789 [x86] watchdog: Use TSC as the watchdog clocksource with
6790 which to check other HW timers (HPET or PM timer), but
6791 only on systems where TSC has been deemed trustworthy.
6792 This will be suppressed by an earlier tsc=nowatchdog and
6793 can be overridden by a later tsc=nowatchdog. A console
6794 message will flag any such suppression or overriding.
6795
6796 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
6797 value instead. Useful when the early TSC frequency discovery
6798 procedure is not reliable, such as on overclocked systems
6799 with CPUID.16h support and partial CPUID.15h support.
6800 Format: <unsigned int>
6801
6802 tsx= [X86] Control Transactional Synchronization
6803 Extensions (TSX) feature in Intel processors that
6804 support TSX control.
6805
6806 This parameter controls the TSX feature. The options are:
6807
6808 on - Enable TSX on the system. Although there are
6809 mitigations for all known security vulnerabilities,
6810 TSX has been known to be an accelerator for
6811 several previous speculation-related CVEs, and
6812 so there may be unknown security risks associated
6813 with leaving it enabled.
6814
6815 off - Disable TSX on the system. (Note that this
6816 option takes effect only on newer CPUs which are
6817 not vulnerable to MDS, i.e., have
6818 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6819 the new IA32_TSX_CTRL MSR through a microcode
6820 update. This new MSR allows for the reliable
6821 deactivation of the TSX functionality.)
6822
6823 auto - Disable TSX if X86_BUG_TAA is present,
6824 otherwise enable TSX on the system.
6825
6826 Not specifying this option is equivalent to tsx=off.
6827
6828 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6829 for more details.
6830
6831 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
6832 Abort (TAA) vulnerability.
6833
6834 Similar to Micro-architectural Data Sampling (MDS)
6835 certain CPUs that support Transactional
6836 Synchronization Extensions (TSX) are vulnerable to an
6837 exploit against CPU internal buffers which can forward
6838 information to a disclosure gadget under certain
6839 conditions.
6840
6841 In vulnerable processors, the speculatively forwarded
6842 data can be used in a cache side channel attack, to
6843 access data to which the attacker does not have direct
6844 access.
6845
6846 This parameter controls the TAA mitigation. The
6847 options are:
6848
6849 full - Enable TAA mitigation on vulnerable CPUs
6850 if TSX is enabled.
6851
6852 full,nosmt - Enable TAA mitigation and disable SMT on
6853 vulnerable CPUs. If TSX is disabled, SMT
6854 is not disabled because CPU is not
6855 vulnerable to cross-thread TAA attacks.
6856 off - Unconditionally disable TAA mitigation
6857
6858 On MDS-affected machines, tsx_async_abort=off can be
6859 prevented by an active MDS mitigation as both vulnerabilities
6860 are mitigated with the same mechanism so in order to disable
6861 this mitigation, you need to specify mds=off too.
6862
6863 Not specifying this option is equivalent to
6864 tsx_async_abort=full. On CPUs which are MDS affected
6865 and deploy MDS mitigation, TAA mitigation is not
6866 required and doesn't provide any additional
6867 mitigation.
6868
6869 For details see:
6870 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6871
6872 turbografx.map[2|3]= [HW,JOY]
6873 TurboGraFX parallel port interface
6874 Format:
6875 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6876 See also Documentation/input/devices/joystick-parport.rst
6877
6878 udbg-immortal [PPC] When debugging early kernel crashes that
6879 happen after console_init() and before a proper
6880 console driver takes over, this boot options might
6881 help "seeing" what's going on.
6882
6883 uhash_entries= [KNL,NET]
6884 Set number of hash buckets for UDP/UDP-Lite connections
6885
6886 uhci-hcd.ignore_oc=
6887 [USB] Ignore overcurrent events (default N).
6888 Some badly-designed motherboards generate lots of
6889 bogus events, for ports that aren't wired to
6890 anything. Set this parameter to avoid log spamming.
6891 Note that genuine overcurrent events won't be
6892 reported either.
6893
6894 unknown_nmi_panic
6895 [X86] Cause panic on unknown NMI.
6896
6897 unwind_debug [X86-64,EARLY]
6898 Enable unwinder debug output. This can be
6899 useful for debugging certain unwinder error
6900 conditions, including corrupt stacks and
6901 bad/missing unwinder metadata.
6902
6903 usbcore.authorized_default=
6904 [USB] Default USB device authorization:
6905 (default -1 = authorized (same as 1),
6906 0 = not authorized, 1 = authorized, 2 = authorized
6907 if device connected to internal port)
6908
6909 usbcore.autosuspend=
6910 [USB] The autosuspend time delay (in seconds) used
6911 for newly-detected USB devices (default 2). This
6912 is the time required before an idle device will be
6913 autosuspended. Devices for which the delay is set
6914 to a negative value won't be autosuspended at all.
6915
6916 usbcore.usbfs_snoop=
6917 [USB] Set to log all usbfs traffic (default 0 = off).
6918
6919 usbcore.usbfs_snoop_max=
6920 [USB] Maximum number of bytes to snoop in each URB
6921 (default = 65536).
6922
6923 usbcore.blinkenlights=
6924 [USB] Set to cycle leds on hubs (default 0 = off).
6925
6926 usbcore.old_scheme_first=
6927 [USB] Start with the old device initialization
6928 scheme (default 0 = off).
6929
6930 usbcore.usbfs_memory_mb=
6931 [USB] Memory limit (in MB) for buffers allocated by
6932 usbfs (default = 16, 0 = max = 2047).
6933
6934 usbcore.use_both_schemes=
6935 [USB] Try the other device initialization scheme
6936 if the first one fails (default 1 = enabled).
6937
6938 usbcore.initial_descriptor_timeout=
6939 [USB] Specifies timeout for the initial 64-byte
6940 USB_REQ_GET_DESCRIPTOR request in milliseconds
6941 (default 5000 = 5.0 seconds).
6942
6943 usbcore.nousb [USB] Disable the USB subsystem
6944
6945 usbcore.quirks=
6946 [USB] A list of quirk entries to augment the built-in
6947 usb core quirk list. List entries are separated by
6948 commas. Each entry has the form
6949 VendorID:ProductID:Flags. The IDs are 4-digit hex
6950 numbers and Flags is a set of letters. Each letter
6951 will change the built-in quirk; setting it if it is
6952 clear and clearing it if it is set. The letters have
6953 the following meanings:
6954 a = USB_QUIRK_STRING_FETCH_255 (string
6955 descriptors must not be fetched using
6956 a 255-byte read);
6957 b = USB_QUIRK_RESET_RESUME (device can't resume
6958 correctly so reset it instead);
6959 c = USB_QUIRK_NO_SET_INTF (device can't handle
6960 Set-Interface requests);
6961 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6962 handle its Configuration or Interface
6963 strings);
6964 e = USB_QUIRK_RESET (device can't be reset
6965 (e.g morph devices), don't use reset);
6966 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6967 more interface descriptions than the
6968 bNumInterfaces count, and can't handle
6969 talking to these interfaces);
6970 g = USB_QUIRK_DELAY_INIT (device needs a pause
6971 during initialization, after we read
6972 the device descriptor);
6973 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6974 high speed and super speed interrupt
6975 endpoints, the USB 2.0 and USB 3.0 spec
6976 require the interval in microframes (1
6977 microframe = 125 microseconds) to be
6978 calculated as interval = 2 ^
6979 (bInterval-1).
6980 Devices with this quirk report their
6981 bInterval as the result of this
6982 calculation instead of the exponent
6983 variable used in the calculation);
6984 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6985 handle device_qualifier descriptor
6986 requests);
6987 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6988 generates spurious wakeup, ignore
6989 remote wakeup capability);
6990 k = USB_QUIRK_NO_LPM (device can't handle Link
6991 Power Management);
6992 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6993 (Device reports its bInterval as linear
6994 frames instead of the USB 2.0
6995 calculation);
6996 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6997 to be disconnected before suspend to
6998 prevent spurious wakeup);
6999 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
7000 pause after every control message);
7001 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
7002 delay after resetting its port);
7003 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
7004 (Reduce timeout of the SET_ADDRESS
7005 request from 5000 ms to 500 ms);
7006 Example: quirks=0781:5580:bk,0a5c:5834:gij
7007
7008 usbhid.mousepoll=
7009 [USBHID] The interval which mice are to be polled at.
7010
7011 usbhid.jspoll=
7012 [USBHID] The interval which joysticks are to be polled at.
7013
7014 usbhid.kbpoll=
7015 [USBHID] The interval which keyboards are to be polled at.
7016
7017 usb-storage.delay_use=
7018 [UMS] The delay in seconds before a new device is
7019 scanned for Logical Units (default 1).
7020
7021 usb-storage.quirks=
7022 [UMS] A list of quirks entries to supplement or
7023 override the built-in unusual_devs list. List
7024 entries are separated by commas. Each entry has
7025 the form VID:PID:Flags where VID and PID are Vendor
7026 and Product ID values (4-digit hex numbers) and
7027 Flags is a set of characters, each corresponding
7028 to a common usb-storage quirk flag as follows:
7029 a = SANE_SENSE (collect more than 18 bytes
7030 of sense data, not on uas);
7031 b = BAD_SENSE (don't collect more than 18
7032 bytes of sense data, not on uas);
7033 c = FIX_CAPACITY (decrease the reported
7034 device capacity by one sector);
7035 d = NO_READ_DISC_INFO (don't use
7036 READ_DISC_INFO command, not on uas);
7037 e = NO_READ_CAPACITY_16 (don't use
7038 READ_CAPACITY_16 command);
7039 f = NO_REPORT_OPCODES (don't use report opcodes
7040 command, uas only);
7041 g = MAX_SECTORS_240 (don't transfer more than
7042 240 sectors at a time, uas only);
7043 h = CAPACITY_HEURISTICS (decrease the
7044 reported device capacity by one
7045 sector if the number is odd);
7046 i = IGNORE_DEVICE (don't bind to this
7047 device);
7048 j = NO_REPORT_LUNS (don't use report luns
7049 command, uas only);
7050 k = NO_SAME (do not use WRITE_SAME, uas only)
7051 l = NOT_LOCKABLE (don't try to lock and
7052 unlock ejectable media, not on uas);
7053 m = MAX_SECTORS_64 (don't transfer more
7054 than 64 sectors = 32 KB at a time,
7055 not on uas);
7056 n = INITIAL_READ10 (force a retry of the
7057 initial READ(10) command, not on uas);
7058 o = CAPACITY_OK (accept the capacity
7059 reported by the device, not on uas);
7060 p = WRITE_CACHE (the device cache is ON
7061 by default, not on uas);
7062 r = IGNORE_RESIDUE (the device reports
7063 bogus residue values, not on uas);
7064 s = SINGLE_LUN (the device has only one
7065 Logical Unit);
7066 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7067 commands, uas only);
7068 u = IGNORE_UAS (don't bind to the uas driver);
7069 w = NO_WP_DETECT (don't test whether the
7070 medium is write-protected).
7071 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7072 even if the device claims no cache,
7073 not on uas)
7074 Example: quirks=0419:aaf5:rl,0421:0433:rc
7075
7076 user_debug= [KNL,ARM]
7077 Format: <int>
7078 See arch/arm/Kconfig.debug help text.
7079 1 - undefined instruction events
7080 2 - system calls
7081 4 - invalid data aborts
7082 8 - SIGSEGV faults
7083 16 - SIGBUS faults
7084 Example: user_debug=31
7085
7086 userpte=
7087 [X86,EARLY] Flags controlling user PTE allocations.
7088
7089 nohigh = do not allocate PTE pages in
7090 HIGHMEM regardless of setting
7091 of CONFIG_HIGHPTE.
7092
7093 vdso= [X86,SH,SPARC]
7094 On X86_32, this is an alias for vdso32=. Otherwise:
7095
7096 vdso=1: enable VDSO (the default)
7097 vdso=0: disable VDSO mapping
7098
7099 vdso32= [X86] Control the 32-bit vDSO
7100 vdso32=1: enable 32-bit VDSO
7101 vdso32=0 or vdso32=2: disable 32-bit VDSO
7102
7103 See the help text for CONFIG_COMPAT_VDSO for more
7104 details. If CONFIG_COMPAT_VDSO is set, the default is
7105 vdso32=0; otherwise, the default is vdso32=1.
7106
7107 For compatibility with older kernels, vdso32=2 is an
7108 alias for vdso32=0.
7109
7110 Try vdso32=0 if you encounter an error that says:
7111 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7112
7113 vector= [IA-64,SMP]
7114 vector=percpu: enable percpu vector domain
7115
7116 video= [FB,EARLY] Frame buffer configuration
7117 See Documentation/fb/modedb.rst.
7118
7119 video.brightness_switch_enabled= [ACPI]
7120 Format: [0|1]
7121 If set to 1, on receiving an ACPI notify event
7122 generated by hotkey, video driver will adjust brightness
7123 level and then send out the event to user space through
7124 the allocated input device. If set to 0, video driver
7125 will only send out the event without touching backlight
7126 brightness level.
7127 default: 1
7128
7129 virtio_mmio.device=
7130 [VMMIO] Memory mapped virtio (platform) device.
7131
7132 <size>@<baseaddr>:<irq>[:<id>]
7133 where:
7134 <size> := size (can use standard suffixes
7135 like K, M and G)
7136 <baseaddr> := physical base address
7137 <irq> := interrupt number (as passed to
7138 request_irq())
7139 <id> := (optional) platform device id
7140 example:
7141 virtio_mmio.device=1K@0x100b0000:48:7
7142
7143 Can be used multiple times for multiple devices.
7144
7145 vga= [BOOT,X86-32] Select a particular video mode
7146 See Documentation/arch/x86/boot.rst and
7147 Documentation/admin-guide/svga.rst.
7148 Use vga=ask for menu.
7149 This is actually a boot loader parameter; the value is
7150 passed to the kernel using a special protocol.
7151
7152 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7153 May slow down system boot speed, especially when
7154 enabled on systems with a large amount of memory.
7155 All options are enabled by default, and this
7156 interface is meant to allow for selectively
7157 enabling or disabling specific virtual memory
7158 debugging features.
7159
7160 Available options are:
7161 P Enable page structure init time poisoning
7162 - Disable all of the above options
7163
7164 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
7165 exact size of <nn>. This can be used to increase
7166 the minimum size (128MB on x86). It can also be
7167 used to decrease the size and leave more room
7168 for directly mapped kernel RAM.
7169
7170 vmcp_cma=nn[MG] [KNL,S390,EARLY]
7171 Sets the memory size reserved for contiguous memory
7172 allocations for the vmcp device driver.
7173
7174 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7175 Format: <command>
7176
7177 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7178 Format: <command>
7179
7180 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7181 Format: <command>
7182
7183 vsyscall= [X86-64,EARLY]
7184 Controls the behavior of vsyscalls (i.e. calls to
7185 fixed addresses of 0xffffffffff600x00 from legacy
7186 code). Most statically-linked binaries and older
7187 versions of glibc use these calls. Because these
7188 functions are at fixed addresses, they make nice
7189 targets for exploits that can control RIP.
7190
7191 emulate Vsyscalls turn into traps and are emulated
7192 reasonably safely. The vsyscall page is
7193 readable.
7194
7195 xonly [default] Vsyscalls turn into traps and are
7196 emulated reasonably safely. The vsyscall
7197 page is not readable.
7198
7199 none Vsyscalls don't work at all. This makes
7200 them quite hard to use for exploits but
7201 might break your system.
7202
7203 vt.color= [VT] Default text color.
7204 Format: 0xYX, X = foreground, Y = background.
7205 Default: 0x07 = light gray on black.
7206
7207 vt.cur_default= [VT] Default cursor shape.
7208 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7209 the parameters of the <Esc>[?A;B;Cc escape sequence;
7210 see VGA-softcursor.txt. Default: 2 = underline.
7211
7212 vt.default_blu= [VT]
7213 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7214 Change the default blue palette of the console.
7215 This is a 16-member array composed of values
7216 ranging from 0-255.
7217
7218 vt.default_grn= [VT]
7219 Format: <green0>,<green1>,<green2>,...,<green15>
7220 Change the default green palette of the console.
7221 This is a 16-member array composed of values
7222 ranging from 0-255.
7223
7224 vt.default_red= [VT]
7225 Format: <red0>,<red1>,<red2>,...,<red15>
7226 Change the default red palette of the console.
7227 This is a 16-member array composed of values
7228 ranging from 0-255.
7229
7230 vt.default_utf8=
7231 [VT]
7232 Format=<0|1>
7233 Set system-wide default UTF-8 mode for all tty's.
7234 Default is 1, i.e. UTF-8 mode is enabled for all
7235 newly opened terminals.
7236
7237 vt.global_cursor_default=
7238 [VT]
7239 Format=<-1|0|1>
7240 Set system-wide default for whether a cursor
7241 is shown on new VTs. Default is -1,
7242 i.e. cursors will be created by default unless
7243 overridden by individual drivers. 0 will hide
7244 cursors, 1 will display them.
7245
7246 vt.italic= [VT] Default color for italic text; 0-15.
7247 Default: 2 = green.
7248
7249 vt.underline= [VT] Default color for underlined text; 0-15.
7250 Default: 3 = cyan.
7251
7252 watchdog timers [HW,WDT] For information on watchdog timers,
7253 see Documentation/watchdog/watchdog-parameters.rst
7254 or other driver-specific files in the
7255 Documentation/watchdog/ directory.
7256
7257 watchdog_thresh=
7258 [KNL]
7259 Set the hard lockup detector stall duration
7260 threshold in seconds. The soft lockup detector
7261 threshold is set to twice the value. A value of 0
7262 disables both lockup detectors. Default is 10
7263 seconds.
7264
7265 workqueue.unbound_cpus=
7266 [KNL,SMP] Specify to constrain one or some CPUs
7267 to use in unbound workqueues.
7268 Format: <cpu-list>
7269 By default, all online CPUs are available for
7270 unbound workqueues.
7271
7272 workqueue.watchdog_thresh=
7273 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7274 warn stall conditions and dump internal state to
7275 help debugging. 0 disables workqueue stall
7276 detection; otherwise, it's the stall threshold
7277 duration in seconds. The default value is 30 and
7278 it can be updated at runtime by writing to the
7279 corresponding sysfs file.
7280
7281 workqueue.cpu_intensive_thresh_us=
7282 Per-cpu work items which run for longer than this
7283 threshold are automatically considered CPU intensive
7284 and excluded from concurrency management to prevent
7285 them from noticeably delaying other per-cpu work
7286 items. Default is 10000 (10ms).
7287
7288 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7289 will report the work functions which violate this
7290 threshold repeatedly. They are likely good
7291 candidates for using WQ_UNBOUND workqueues instead.
7292
7293 workqueue.cpu_intensive_warning_thresh=<uint>
7294 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7295 will report the work functions which violate the
7296 intensive_threshold_us repeatedly. In order to prevent
7297 spurious warnings, start printing only after a work
7298 function has violated this threshold number of times.
7299
7300 The default is 4 times. 0 disables the warning.
7301
7302 workqueue.power_efficient
7303 Per-cpu workqueues are generally preferred because
7304 they show better performance thanks to cache
7305 locality; unfortunately, per-cpu workqueues tend to
7306 be more power hungry than unbound workqueues.
7307
7308 Enabling this makes the per-cpu workqueues which
7309 were observed to contribute significantly to power
7310 consumption unbound, leading to measurably lower
7311 power usage at the cost of small performance
7312 overhead.
7313
7314 The default value of this parameter is determined by
7315 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7316
7317 workqueue.default_affinity_scope=
7318 Select the default affinity scope to use for unbound
7319 workqueues. Can be one of "cpu", "smt", "cache",
7320 "numa" and "system". Default is "cache". For more
7321 information, see the Affinity Scopes section in
7322 Documentation/core-api/workqueue.rst.
7323
7324 This can be changed after boot by writing to the
7325 matching /sys/module/workqueue/parameters file. All
7326 workqueues with the "default" affinity scope will be
7327 updated accordignly.
7328
7329 workqueue.debug_force_rr_cpu
7330 Workqueue used to implicitly guarantee that work
7331 items queued without explicit CPU specified are put
7332 on the local CPU. This guarantee is no longer true
7333 and while local CPU is still preferred work items
7334 may be put on foreign CPUs. This debug option
7335 forces round-robin CPU selection to flush out
7336 usages which depend on the now broken guarantee.
7337 When enabled, memory and cache locality will be
7338 impacted.
7339
7340 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
7341 Type) of ioremap_wc().
7342
7343 on - Enable writecombine, use WUC for ioremap_wc()
7344 off - Disable writecombine, use SUC for ioremap_wc()
7345
7346 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
7347 default x2apic cluster mode on platforms
7348 supporting x2apic.
7349
7350 xen_512gb_limit [KNL,X86-64,XEN]
7351 Restricts the kernel running paravirtualized under Xen
7352 to use only up to 512 GB of RAM. The reason to do so is
7353 crash analysis tools and Xen tools for doing domain
7354 save/restore/migration must be enabled to handle larger
7355 domains.
7356
7357 xen_emul_unplug= [HW,X86,XEN,EARLY]
7358 Unplug Xen emulated devices
7359 Format: [unplug0,][unplug1]
7360 ide-disks -- unplug primary master IDE devices
7361 aux-ide-disks -- unplug non-primary-master IDE devices
7362 nics -- unplug network devices
7363 all -- unplug all emulated devices (NICs and IDE disks)
7364 unnecessary -- unplugging emulated devices is
7365 unnecessary even if the host did not respond to
7366 the unplug protocol
7367 never -- do not unplug even if version check succeeds
7368
7369 xen_legacy_crash [X86,XEN,EARLY]
7370 Crash from Xen panic notifier, without executing late
7371 panic() code such as dumping handler.
7372
7373 xen_msr_safe= [X86,XEN,EARLY]
7374 Format: <bool>
7375 Select whether to always use non-faulting (safe) MSR
7376 access functions when running as Xen PV guest. The
7377 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7378
7379 xen_nopvspin [X86,XEN,EARLY]
7380 Disables the qspinlock slowpath using Xen PV optimizations.
7381 This parameter is obsoleted by "nopvspin" parameter, which
7382 has equivalent effect for XEN platform.
7383
7384 xen_nopv [X86]
7385 Disables the PV optimizations forcing the HVM guest to
7386 run as generic HVM guest with no PV drivers.
7387 This option is obsoleted by the "nopv" option, which
7388 has equivalent effect for XEN platform.
7389
7390 xen_no_vector_callback
7391 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
7392 event channel interrupts.
7393
7394 xen_scrub_pages= [XEN]
7395 Boolean option to control scrubbing pages before giving them back
7396 to Xen, for use by other domains. Can be also changed at runtime
7397 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7398 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7399
7400 xen_timer_slop= [X86-64,XEN,EARLY]
7401 Set the timer slop (in nanoseconds) for the virtual Xen
7402 timers (default is 100000). This adjusts the minimum
7403 delta of virtualized Xen timers, where lower values
7404 improve timer resolution at the expense of processing
7405 more timer interrupts.
7406
7407 xen.balloon_boot_timeout= [XEN]
7408 The time (in seconds) to wait before giving up to boot
7409 in case initial ballooning fails to free enough memory.
7410 Applies only when running as HVM or PVH guest and
7411 started with less memory configured than allowed at
7412 max. Default is 180.
7413
7414 xen.event_eoi_delay= [XEN]
7415 How long to delay EOI handling in case of event
7416 storms (jiffies). Default is 10.
7417
7418 xen.event_loop_timeout= [XEN]
7419 After which time (jiffies) the event handling loop
7420 should start to delay EOI handling. Default is 2.
7421
7422 xen.fifo_events= [XEN]
7423 Boolean parameter to disable using fifo event handling
7424 even if available. Normally fifo event handling is
7425 preferred over the 2-level event handling, as it is
7426 fairer and the number of possible event channels is
7427 much higher. Default is on (use fifo events).
7428
7429 xirc2ps_cs= [NET,PCMCIA]
7430 Format:
7431 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7432
7433 xive= [PPC]
7434 By default on POWER9 and above, the kernel will
7435 natively use the XIVE interrupt controller. This option
7436 allows the fallback firmware mode to be used:
7437
7438 off Fallback to firmware control of XIVE interrupt
7439 controller on both pseries and powernv
7440 platforms. Only useful on POWER9 and above.
7441
7442 xive.store-eoi=off [PPC]
7443 By default on POWER10 and above, the kernel will use
7444 stores for EOI handling when the XIVE interrupt mode
7445 is active. This option allows the XIVE driver to use
7446 loads instead, as on POWER9.
7447
7448 xhci-hcd.quirks [USB,KNL]
7449 A hex value specifying bitmask with supplemental xhci
7450 host controller quirks. Meaning of each bit can be
7451 consulted in header drivers/usb/host/xhci.h.
7452
7453 xmon [PPC,EARLY]
7454 Format: { early | on | rw | ro | off }
7455 Controls if xmon debugger is enabled. Default is off.
7456 Passing only "xmon" is equivalent to "xmon=early".
7457 early Call xmon as early as possible on boot; xmon
7458 debugger is called from setup_arch().
7459 on xmon debugger hooks will be installed so xmon
7460 is only called on a kernel crash. Default mode,
7461 i.e. either "ro" or "rw" mode, is controlled
7462 with CONFIG_XMON_DEFAULT_RO_MODE.
7463 rw xmon debugger hooks will be installed so xmon
7464 is called only on a kernel crash, mode is write,
7465 meaning SPR registers, memory and, other data
7466 can be written using xmon commands.
7467 ro same as "rw" option above but SPR registers,
7468 memory, and other data can't be written using
7469 xmon commands.
7470 off xmon is disabled.
7471