| blob | fb8752b42ec8582b8750d7e014c4d76166fa2fc1 |
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.
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 | nospcr }
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 nocmcff -- Disable firmware first mode for corrected
25 errors. This disables parsing the HEST CMC error
26 source to check if firmware has set the FF flag. This
27 may result in duplicate corrected error reports.
28 nospcr -- disable console in ACPI SPCR table as
29 default _serial_ console on ARM64
30 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or
31 "acpi=nospcr" are available
32 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force"
33 are available
35 See also Documentation/power/runtime_pm.rst, pci=noacpi
37 acpi_apic_instance= [ACPI,IOAPIC,EARLY]
38 Format: <int>
39 2: use 2nd APIC table, if available
40 1,0: use 1st APIC table
41 default: 0
43 acpi_backlight= [HW,ACPI]
44 { vendor | video | native | none }
45 If set to vendor, prefer vendor-specific driver
46 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
47 of the ACPI video.ko driver.
48 If set to video, use the ACPI video.ko driver.
49 If set to native, use the device's native backlight mode.
50 If set to none, disable the ACPI backlight interface.
52 acpi_force_32bit_fadt_addr [ACPI,EARLY]
53 force FADT to use 32 bit addresses rather than the
54 64 bit X_* addresses. Some firmware have broken 64
55 bit addresses for force ACPI ignore these and use
56 the older legacy 32 bit addresses.
58 acpica_no_return_repair [HW, ACPI]
59 Disable AML predefined validation mechanism
60 This mechanism can repair the evaluation result to make
61 the return objects more ACPI specification compliant.
62 This option is useful for developers to identify the
63 root cause of an AML interpreter issue when the issue
64 has something to do with the repair mechanism.
66 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
67 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
68 Format: <int>
69 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
70 debug output. Bits in debug_layer correspond to a
71 _COMPONENT in an ACPI source file, e.g.,
72 #define _COMPONENT ACPI_EVENTS
73 Bits in debug_level correspond to a level in
74 ACPI_DEBUG_PRINT statements, e.g.,
75 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
76 The debug_level mask defaults to "info". See
77 Documentation/firmware-guide/acpi/debug.rst for more information about
78 debug layers and levels.
80 Enable processor driver info messages:
81 acpi.debug_layer=0x20000000
82 Enable AML "Debug" output, i.e., stores to the Debug
83 object while interpreting AML:
84 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
85 Enable all messages related to ACPI hardware:
86 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
88 Some values produce so much output that the system is
89 unusable. The "log_buf_len" parameter may be useful
90 if you need to capture more output.
92 acpi_enforce_resources= [ACPI]
93 { strict | lax | no }
94 Check for resource conflicts between native drivers
95 and ACPI OperationRegions (SystemIO and SystemMemory
96 only). IO ports and memory declared in ACPI might be
97 used by the ACPI subsystem in arbitrary AML code and
98 can interfere with legacy drivers.
99 strict (default): access to resources claimed by ACPI
100 is denied; legacy drivers trying to access reserved
101 resources will fail to bind to device using them.
102 lax: access to resources claimed by ACPI is allowed;
103 legacy drivers trying to access reserved resources
104 will bind successfully but a warning message is logged.
105 no: ACPI OperationRegions are not marked as reserved,
106 no further checks are performed.
108 acpi_force_table_verification [HW,ACPI,EARLY]
109 Enable table checksum verification during early stage.
110 By default, this is disabled due to x86 early mapping
111 size limitation.
113 acpi_irq_balance [HW,ACPI]
114 ACPI will balance active IRQs
115 default in APIC mode
117 acpi_irq_nobalance [HW,ACPI]
118 ACPI will not move active IRQs (default)
119 default in PIC mode
121 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
122 Format: <irq>,<irq>...
124 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
125 use by PCI
126 Format: <irq>,<irq>...
128 acpi_mask_gpe= [HW,ACPI]
129 Due to the existence of _Lxx/_Exx, some GPEs triggered
130 by unsupported hardware/firmware features can result in
131 GPE floodings that cannot be automatically disabled by
132 the GPE dispatcher.
133 This facility can be used to prevent such uncontrolled
134 GPE floodings.
135 Format: <byte> or <bitmap-list>
137 acpi_no_auto_serialize [HW,ACPI]
138 Disable auto-serialization of AML methods
139 AML control methods that contain the opcodes to create
140 named objects will be marked as "Serialized" by the
141 auto-serialization feature.
142 This feature is enabled by default.
143 This option allows to turn off the feature.
145 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
146 kernels.
148 acpi_no_static_ssdt [HW,ACPI,EARLY]
149 Disable installation of static SSDTs at early boot time
150 By default, SSDTs contained in the RSDT/XSDT will be
151 installed automatically and they will appear under
152 /sys/firmware/acpi/tables.
153 This option turns off this feature.
154 Note that specifying this option does not affect
155 dynamic table installation which will install SSDT
156 tables to /sys/firmware/acpi/tables/dynamic.
158 acpi_no_watchdog [HW,ACPI,WDT]
159 Ignore the ACPI-based watchdog interface (WDAT) and let
160 a native driver control the watchdog device instead.
162 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
163 Pass the RSDP address to the kernel, mostly used
164 on machines running EFI runtime service to boot the
165 second kernel for kdump.
167 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
168 Format: To spoof as Windows 98: ="Microsoft Windows"
170 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
171 of 2 which is mandated by ACPI 6) as the supported ACPI
172 specification revision (when using this switch, it may
173 be necessary to carry out a cold reboot _twice_ in a
174 row to make it take effect on the platform firmware).
176 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
177 acpi_osi="string1" # add string1
178 acpi_osi="!string2" # remove string2
179 acpi_osi=!* # remove all strings
180 acpi_osi=! # disable all built-in OS vendor
181 strings
182 acpi_osi=!! # enable all built-in OS vendor
183 strings
184 acpi_osi= # disable all strings
186 'acpi_osi=!' can be used in combination with single or
187 multiple 'acpi_osi="string1"' to support specific OS
188 vendor string(s). Note that such command can only
189 affect the default state of the OS vendor strings, thus
190 it cannot affect the default state of the feature group
191 strings and the current state of the OS vendor strings,
192 specifying it multiple times through kernel command line
193 is meaningless. This command is useful when one do not
194 care about the state of the feature group strings which
195 should be controlled by the OSPM.
196 Examples:
197 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
198 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
199 can make '_OSI("Windows 2000")' TRUE.
201 'acpi_osi=' cannot be used in combination with other
202 'acpi_osi=' command lines, the _OSI method will not
203 exist in the ACPI namespace. NOTE that such command can
204 only affect the _OSI support state, thus specifying it
205 multiple times through kernel command line is also
206 meaningless.
207 Examples:
208 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
209 FALSE.
211 'acpi_osi=!*' can be used in combination with single or
212 multiple 'acpi_osi="string1"' to support specific
213 string(s). Note that such command can affect the
214 current state of both the OS vendor strings and the
215 feature group strings, thus specifying it multiple times
216 through kernel command line is meaningful. But it may
217 still not able to affect the final state of a string if
218 there are quirks related to this string. This command
219 is useful when one want to control the state of the
220 feature group strings to debug BIOS issues related to
221 the OSPM features.
222 Examples:
223 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
224 '_OSI("Module Device")' FALSE.
225 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
226 '_OSI("Module Device")' TRUE.
227 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
228 equivalent to
229 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
230 and
231 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
232 they all will make '_OSI("Windows 2000")' TRUE.
234 acpi_pm_good [X86]
235 Override the pmtimer bug detection: force the kernel
236 to assume that this machine's pmtimer latches its value
237 and always returns good values.
239 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
240 Format: { level | edge | high | low }
242 acpi_skip_timer_override [HW,ACPI,EARLY]
243 Recognize and ignore IRQ0/pin2 Interrupt Override.
244 For broken nForce2 BIOS resulting in XT-PIC timer.
246 acpi_sleep= [HW,ACPI] Sleep options
247 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
248 s4_nohwsig, old_ordering, nonvs,
249 sci_force_enable, nobl }
250 See Documentation/power/video.rst for information on
251 s3_bios and s3_mode.
252 s3_beep is for debugging; it makes the PC's speaker beep
253 as soon as the kernel's real-mode entry point is called.
254 s4_hwsig causes the kernel to check the ACPI hardware
255 signature during resume from hibernation, and gracefully
256 refuse to resume if it has changed. This complies with
257 the ACPI specification but not with reality, since
258 Windows does not do this and many laptops do change it
259 on docking. So the default behaviour is to allow resume
260 and simply warn when the signature changes, unless the
261 s4_hwsig option is enabled.
262 s4_nohwsig prevents ACPI hardware signature from being
263 used (or even warned about) during resume.
264 old_ordering causes the ACPI 1.0 ordering of the _PTS
265 control method, with respect to putting devices into
266 low power states, to be enforced (the ACPI 2.0 ordering
267 of _PTS is used by default).
268 nonvs prevents the kernel from saving/restoring the
269 ACPI NVS memory during suspend/hibernation and resume.
270 sci_force_enable causes the kernel to set SCI_EN directly
271 on resume from S1/S3 (which is against the ACPI spec,
272 but some broken systems don't work without it).
273 nobl causes the internal blacklist of systems known to
274 behave incorrectly in some ways with respect to system
275 suspend and resume to be ignored (use wisely).
277 acpi_use_timer_override [HW,ACPI,EARLY]
278 Use timer override. For some broken Nvidia NF5 boards
279 that require a timer override, but don't have HPET
281 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
282 kernel's map of available physical RAM.
284 agp= [AGP]
285 { off | try_unsupported }
286 off: disable AGP support
287 try_unsupported: try to drive unsupported chipsets
288 (may crash computer or cause data corruption)
290 ALSA [HW,ALSA]
291 See Documentation/sound/alsa-configuration.rst
293 alignment= [KNL,ARM]
294 Allow the default userspace alignment fault handler
295 behaviour to be specified. Bit 0 enables warnings,
296 bit 1 enables fixups, and bit 2 sends a segfault.
298 align_va_addr= [X86-64]
299 Align virtual addresses by clearing slice [14:12] when
300 allocating a VMA at process creation time. This option
301 gives you up to 3% performance improvement on AMD F15h
302 machines (where it is enabled by default) for a
303 CPU-intensive style benchmark, and it can vary highly in
304 a microbenchmark depending on workload and compiler.
306 32: only for 32-bit processes
307 64: only for 64-bit processes
308 on: enable for both 32- and 64-bit processes
309 off: disable for both 32- and 64-bit processes
311 alloc_snapshot [FTRACE]
312 Allocate the ftrace snapshot buffer on boot up when the
313 main buffer is allocated. This is handy if debugging
314 and you need to use tracing_snapshot() on boot up, and
315 do not want to use tracing_snapshot_alloc() as it needs
316 to be done where GFP_KERNEL allocations are allowed.
318 allow_mismatched_32bit_el0 [ARM64,EARLY]
319 Allow execve() of 32-bit applications and setting of the
320 PER_LINUX32 personality on systems where only a strict
321 subset of the CPUs support 32-bit EL0. When this
322 parameter is present, the set of CPUs supporting 32-bit
323 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
324 and hot-unplug operations may be restricted.
326 See Documentation/arch/arm64/asymmetric-32bit.rst for more
327 information.
329 amd_iommu= [HW,X86-64]
330 Pass parameters to the AMD IOMMU driver in the system.
331 Possible values are:
332 fullflush - Deprecated, equivalent to iommu.strict=1
333 off - do not initialize any AMD IOMMU found in
334 the system
335 force_isolation - Force device isolation for all
336 devices. The IOMMU driver is not
337 allowed anymore to lift isolation
338 requirements as needed. This option
339 does not override iommu=pt
340 force_enable - Force enable the IOMMU on platforms known
341 to be buggy with IOMMU enabled. Use this
342 option with care.
343 pgtbl_v1 - Use v1 page table for DMA-API (Default).
344 pgtbl_v2 - Use v2 page table for DMA-API.
345 irtcachedis - Disable Interrupt Remapping Table (IRT) caching.
346 nohugepages - Limit page-sizes used for v1 page-tables
347 to 4 KiB.
348 v2_pgsizes_only - Limit page-sizes used for v1 page-tables
349 to 4KiB/2Mib/1GiB.
352 amd_iommu_dump= [HW,X86-64]
353 Enable AMD IOMMU driver option to dump the ACPI table
354 for AMD IOMMU. With this option enabled, AMD IOMMU
355 driver will print ACPI tables for AMD IOMMU during
356 IOMMU initialization.
358 amd_iommu_intr= [HW,X86-64]
359 Specifies one of the following AMD IOMMU interrupt
360 remapping modes:
361 legacy - Use legacy interrupt remapping mode.
362 vapic - Use virtual APIC mode, which allows IOMMU
363 to inject interrupts directly into guest.
364 This mode requires kvm-amd.avic=1.
365 (Default when IOMMU HW support is present.)
367 amd_pstate= [X86,EARLY]
368 disable
369 Do not enable amd_pstate as the default
370 scaling driver for the supported processors
371 passive
372 Use amd_pstate with passive mode as a scaling driver.
373 In this mode autonomous selection is disabled.
374 Driver requests a desired performance level and platform
375 tries to match the same performance level if it is
376 satisfied by guaranteed performance level.
377 active
378 Use amd_pstate_epp driver instance as the scaling driver,
379 driver provides a hint to the hardware if software wants
380 to bias toward performance (0x0) or energy efficiency (0xff)
381 to the CPPC firmware. then CPPC power algorithm will
382 calculate the runtime workload and adjust the realtime cores
383 frequency.
384 guided
385 Activate guided autonomous mode. Driver requests minimum and
386 maximum performance level and the platform autonomously
387 selects a performance level in this range and appropriate
388 to the current workload.
390 amd_prefcore=
391 [X86]
392 disable
393 Disable amd-pstate preferred core.
395 amijoy.map= [HW,JOY] Amiga joystick support
396 Map of devices attached to JOY0DAT and JOY1DAT
397 Format: <a>,<b>
398 See also Documentation/input/joydev/joystick.rst
400 analog.map= [HW,JOY] Analog joystick and gamepad support
401 Specifies type or capabilities of an analog joystick
402 connected to one of 16 gameports
403 Format: <type1>,<type2>,..<type16>
405 apc= [HW,SPARC]
406 Power management functions (SPARCstation-4/5 + deriv.)
407 Format: noidle
408 Disable APC CPU standby support. SPARCstation-Fox does
409 not play well with APC CPU idle - disable it if you have
410 APC and your system crashes randomly.
412 apic [APIC,X86-64] Use IO-APIC. Default.
414 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
415 Change the output verbosity while booting
416 Format: { quiet (default) | verbose | debug }
417 Change the amount of debugging information output
418 when initialising the APIC and IO-APIC components.
419 For X86-32, this can also be used to specify an APIC
420 driver name.
421 Format: apic=driver_name
422 Examples: apic=bigsmp
424 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
425 Format: { bsp (default) | all | none }
426 bsp: External NMI is delivered only to CPU 0
427 all: External NMIs are broadcast to all CPUs as a
428 backup of CPU 0
429 none: External NMI is masked for all CPUs. This is
430 useful so that a dump capture kernel won't be
431 shot down by NMI
433 apicpmtimer Do APIC timer calibration using the pmtimer. Implies
434 apicmaintimer. Useful when your PIT timer is totally
435 broken.
437 autoconf= [IPV6]
438 See Documentation/networking/ipv6.rst.
440 apm= [APM] Advanced Power Management
441 See header of arch/x86/kernel/apm_32.c.
443 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
444 Format: { "0" | "1" }
445 See security/apparmor/Kconfig help text
446 0 -- disable.
447 1 -- enable.
448 Default value is set via kernel config option.
450 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
451 Format: <io>,<irq>,<nodeID>
453 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of
454 32 bit applications.
456 arm64.nobti [ARM64] Unconditionally disable Branch Target
457 Identification support
459 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack
460 support
462 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory
463 Set instructions support
465 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
466 support
468 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
469 support
471 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
472 Extension support
474 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
475 Extension support
477 ataflop= [HW,M68k]
479 atarimouse= [HW,MOUSE] Atari Mouse
481 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
482 EzKey and similar keyboards
484 atkbd.reset= [HW] Reset keyboard during initialization
486 atkbd.set= [HW] Select keyboard code set
487 Format: <int> (2 = AT (default), 3 = PS/2)
489 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
490 keyboards
492 atkbd.softraw= [HW] Choose between synthetic and real raw mode
493 Format: <bool> (0 = real, 1 = synthetic (default))
495 atkbd.softrepeat= [HW]
496 Use software keyboard repeat
498 audit= [KNL] Enable the audit sub-system
499 Format: { "0" | "1" | "off" | "on" }
500 0 | off - kernel audit is disabled and can not be
501 enabled until the next reboot
502 unset - kernel audit is initialized but disabled and
503 will be fully enabled by the userspace auditd.
504 1 | on - kernel audit is initialized and partially
505 enabled, storing at most audit_backlog_limit
506 messages in RAM until it is fully enabled by the
507 userspace auditd.
508 Default: unset
510 audit_backlog_limit= [KNL] Set the audit queue size limit.
511 Format: <int> (must be >=0)
512 Default: 64
514 bau= [X86_UV] Enable the BAU on SGI UV. The default
515 behavior is to disable the BAU (i.e. bau=0).
516 Format: { "0" | "1" }
517 0 - Disable the BAU.
518 1 - Enable the BAU.
519 unset - Disable the BAU.
521 baycom_epp= [HW,AX25]
522 Format: <io>,<mode>
524 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
525 Format: <io>,<mode>
526 See header of drivers/net/hamradio/baycom_par.c.
528 baycom_ser_fdx= [HW,AX25]
529 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
530 Format: <io>,<irq>,<mode>[,<baud>]
531 See header of drivers/net/hamradio/baycom_ser_fdx.c.
533 baycom_ser_hdx= [HW,AX25]
534 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
535 Format: <io>,<irq>,<mode>
536 See header of drivers/net/hamradio/baycom_ser_hdx.c.
538 bdev_allow_write_mounted=
539 Format: <bool>
540 Control the ability to open a mounted block device
541 for writing, i.e., allow / disallow writes that bypass
542 the FS. This was implemented as a means to prevent
543 fuzzers from crashing the kernel by overwriting the
544 metadata underneath a mounted FS without its awareness.
545 This also prevents destructive formatting of mounted
546 filesystems by naive storage tooling that don't use
547 O_EXCL. Default is Y and can be changed through the
548 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED.
550 bert_disable [ACPI]
551 Disable BERT OS support on buggy BIOSes.
553 bgrt_disable [ACPI,X86,EARLY]
554 Disable BGRT to avoid flickering OEM logo.
556 blkdevparts= Manual partition parsing of block device(s) for
557 embedded devices based on command line input.
558 See Documentation/block/cmdline-partition.rst
560 boot_delay= [KNL,EARLY]
561 Milliseconds to delay each printk during boot.
562 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
563 and you may also have to specify "lpj=". Boot_delay
564 values larger than 10 seconds (10000) are assumed
565 erroneous and ignored.
566 Format: integer
568 bootconfig [KNL,EARLY]
569 Extended command line options can be added to an initrd
570 and this will cause the kernel to look for it.
572 See Documentation/admin-guide/bootconfig.rst
574 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
575 bttv.radio= Most important insmod options are available as
576 kernel args too.
577 bttv.pll= See Documentation/admin-guide/media/bttv.rst
578 bttv.tuner=
580 bulk_remove=off [PPC] This parameter disables the use of the pSeries
581 firmware feature for flushing multiple hpte entries
582 at a time.
584 c101= [NET] Moxa C101 synchronous serial card
586 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
587 Sometimes CPU hardware bugs make them report the cache
588 size incorrectly. The kernel will attempt work arounds
589 to fix known problems, but for some CPUs it is not
590 possible to determine what the correct size should be.
591 This option provides an override for these situations.
593 carrier_timeout=
594 [NET] Specifies amount of time (in seconds) that
595 the kernel should wait for a network carrier. By default
596 it waits 120 seconds.
598 ca_keys= [KEYS] This parameter identifies a specific key(s) on
599 the system trusted keyring to be used for certificate
600 trust validation.
601 format: { id:<keyid> | builtin }
603 cca= [MIPS,EARLY] Override the kernel pages' cache coherency
604 algorithm. Accepted values range from 0 to 7
605 inclusive. See arch/mips/include/asm/pgtable-bits.h
606 for platform specific values (SB1, Loongson3 and
607 others).
609 ccw_timeout_log [S390]
610 See Documentation/arch/s390/common_io.rst for details.
612 cgroup_disable= [KNL] Disable a particular controller or optional feature
613 Format: {name of the controller(s) or feature(s) to disable}
614 The effects of cgroup_disable=foo are:
615 - foo isn't auto-mounted if you mount all cgroups in
616 a single hierarchy
617 - foo isn't visible as an individually mountable
618 subsystem
619 - if foo is an optional feature then the feature is
620 disabled and corresponding cgroup files are not
621 created
622 {Currently only "memory" controller deal with this and
623 cut the overhead, others just disable the usage. So
624 only cgroup_disable=memory is actually worthy}
625 Specifying "pressure" disables per-cgroup pressure
626 stall information accounting feature
628 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
629 Format: { { controller | "all" | "named" }
630 [,{ controller | "all" | "named" }...] }
631 Like cgroup_disable, but only applies to cgroup v1;
632 the blacklisted controllers remain available in cgroup2.
633 "all" blacklists all controllers and "named" disables
634 named mounts. Specifying both "all" and "named" disables
635 all v1 hierarchies.
637 cgroup_favordynmods= [KNL] Enable or Disable favordynmods.
638 Format: { "true" | "false" }
639 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS.
641 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
642 Format: <string>
643 nosocket -- Disable socket memory accounting.
644 nokmem -- Disable kernel memory accounting.
645 nobpf -- Disable BPF memory accounting.
647 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
648 Format: { "0" | "1" }
649 See security/selinux/Kconfig help text.
650 0 -- check protection applied by kernel (includes
651 any implied execute protection).
652 1 -- check protection requested by application.
653 Default value is set via a kernel config option.
654 Value can be changed at runtime via
655 /sys/fs/selinux/checkreqprot.
656 Setting checkreqprot to 1 is deprecated.
658 cio_ignore= [S390]
659 See Documentation/arch/s390/common_io.rst for details.
661 clearcpuid=X[,X...] [X86]
662 Disable CPUID feature X for the kernel. See
663 arch/x86/include/asm/cpufeatures.h for the valid bit
664 numbers X. Note the Linux-specific bits are not necessarily
665 stable over kernel options, but the vendor-specific
666 ones should be.
667 X can also be a string as appearing in the flags: line
668 in /proc/cpuinfo which does not have the above
669 instability issue. However, not all features have names
670 in /proc/cpuinfo.
671 Note that using this option will taint your kernel.
672 Also note that user programs calling CPUID directly
673 or using the feature without checking anything
674 will still see it. This just prevents it from
675 being used by the kernel or shown in /proc/cpuinfo.
676 Also note the kernel might malfunction if you disable
677 some critical bits.
679 clk_ignore_unused
680 [CLK]
681 Prevents the clock framework from automatically gating
682 clocks that have not been explicitly enabled by a Linux
683 device driver but are enabled in hardware at reset or
684 by the bootloader/firmware. Note that this does not
685 force such clocks to be always-on nor does it reserve
686 those clocks in any way. This parameter is useful for
687 debug and development, but should not be needed on a
688 platform with proper driver support. For more
689 information, see Documentation/driver-api/clk.rst.
691 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
692 [Deprecated]
693 Forces specified clocksource (if available) to be used
694 when calculating gettimeofday(). If specified
695 clocksource is not available, it defaults to PIT.
696 Format: { pit | tsc | cyclone | pmtmr }
698 clocksource= Override the default clocksource
699 Format: <string>
700 Override the default clocksource and use the clocksource
701 with the name specified.
702 Some clocksource names to choose from, depending on
703 the platform:
704 [all] jiffies (this is the base, fallback clocksource)
705 [ACPI] acpi_pm
706 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
707 pxa_timer,timer3,32k_counter,timer0_1
708 [X86-32] pit,hpet,tsc;
709 scx200_hrt on Geode; cyclone on IBM x440
710 [MIPS] MIPS
711 [PARISC] cr16
712 [S390] tod
713 [SH] SuperH
714 [SPARC64] tick
715 [X86-64] hpet,tsc
717 clocksource.arm_arch_timer.evtstrm=
718 [ARM,ARM64,EARLY]
719 Format: <bool>
720 Enable/disable the eventstream feature of the ARM
721 architected timer so that code using WFE-based polling
722 loops can be debugged more effectively on production
723 systems.
725 clocksource.verify_n_cpus= [KNL]
726 Limit the number of CPUs checked for clocksources
727 marked with CLOCK_SOURCE_VERIFY_PERCPU that
728 are marked unstable due to excessive skew.
729 A negative value says to check all CPUs, while
730 zero says not to check any. Values larger than
731 nr_cpu_ids are silently truncated to nr_cpu_ids.
732 The actual CPUs are chosen randomly, with
733 no replacement if the same CPU is chosen twice.
735 clocksource-wdtest.holdoff= [KNL]
736 Set the time in seconds that the clocksource
737 watchdog test waits before commencing its tests.
738 Defaults to zero when built as a module and to
739 10 seconds when built into the kernel.
741 cma=nn[MG]@[start[MG][-end[MG]]]
742 [KNL,CMA,EARLY]
743 Sets the size of kernel global memory area for
744 contiguous memory allocations and optionally the
745 placement constraint by the physical address range of
746 memory allocations. A value of 0 disables CMA
747 altogether. For more information, see
748 kernel/dma/contiguous.c
750 cma_pernuma=nn[MG]
751 [KNL,CMA,EARLY]
752 Sets the size of kernel per-numa memory area for
753 contiguous memory allocations. A value of 0 disables
754 per-numa CMA altogether. And If this option is not
755 specified, the default value is 0.
756 With per-numa CMA enabled, DMA users on node nid will
757 first try to allocate buffer from the pernuma area
758 which is located in node nid, if the allocation fails,
759 they will fallback to the global default memory area.
761 numa_cma=<node>:nn[MG][,<node>:nn[MG]]
762 [KNL,CMA,EARLY]
763 Sets the size of kernel numa memory area for
764 contiguous memory allocations. It will reserve CMA
765 area for the specified node.
767 With numa CMA enabled, DMA users on node nid will
768 first try to allocate buffer from the numa area
769 which is located in node nid, if the allocation fails,
770 they will fallback to the global default memory area.
772 cmo_free_hint= [PPC] Format: { yes | no }
773 Specify whether pages are marked as being inactive
774 when they are freed. This is used in CMO environments
775 to determine OS memory pressure for page stealing by
776 a hypervisor.
777 Default: yes
779 coherent_pool=nn[KMG] [ARM,KNL,EARLY]
780 Sets the size of memory pool for coherent, atomic dma
781 allocations, by default set to 256K.
783 com20020= [HW,NET] ARCnet - COM20020 chipset
784 Format:
785 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
787 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
788 Format: <io>[,<irq>]
790 com90xx= [HW,NET]
791 ARCnet - COM90xx chipset (memory-mapped buffers)
792 Format: <io>[,<irq>[,<memstart>]]
794 condev= [HW,S390] console device
795 conmode=
797 con3215_drop= [S390,EARLY] 3215 console drop mode.
798 Format: y|n|Y|N|1|0
799 When set to true, drop data on the 3215 console when
800 the console buffer is full. In this case the
801 operator using a 3270 terminal emulator (for example
802 x3270) does not have to enter the clear key for the
803 console output to advance and the kernel to continue.
804 This leads to a much faster boot time when a 3270
805 terminal emulator is active. If no 3270 terminal
806 emulator is used, this parameter has no effect.
808 console= [KNL] Output console device and options.
810 tty<n> Use the virtual console device <n>.
812 ttyS<n>[,options]
813 ttyUSB0[,options]
814 Use the specified serial port. The options are of
815 the form "bbbbpnf", where "bbbb" is the baud rate,
816 "p" is parity ("n", "o", or "e"), "n" is number of
817 bits, and "f" is flow control ("r" for RTS or
818 omit it). Default is "9600n8".
820 See Documentation/admin-guide/serial-console.rst for more
821 information. See
822 Documentation/networking/netconsole.rst for an
823 alternative.
825 <DEVNAME>:<n>.<n>[,options]
826 Use the specified serial port on the serial core bus.
827 The addressing uses DEVNAME of the physical serial port
828 device, followed by the serial core controller instance,
829 and the serial port instance. The options are the same
830 as documented for the ttyS addressing above.
832 The mapping of the serial ports to the tty instances
833 can be viewed with:
835 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/*
836 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0
838 In the above example, the console can be addressed with
839 console=00:04:0.0. Note that a console addressed this
840 way will only get added when the related device driver
841 is ready. The use of an earlycon parameter in addition to
842 the console may be desired for console output early on.
844 uart[8250],io,<addr>[,options]
845 uart[8250],mmio,<addr>[,options]
846 uart[8250],mmio16,<addr>[,options]
847 uart[8250],mmio32,<addr>[,options]
848 uart[8250],0x<addr>[,options]
849 Start an early, polled-mode console on the 8250/16550
850 UART at the specified I/O port or MMIO address,
851 switching to the matching ttyS device later.
852 MMIO inter-register address stride is either 8-bit
853 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
854 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
855 to be equivalent to 'mmio'. 'options' are specified in
856 the same format described for ttyS above; if unspecified,
857 the h/w is not re-initialized.
859 hvc<n> Use the hypervisor console device <n>. This is for
860 both Xen and PowerPC hypervisors.
862 { null | "" }
863 Use to disable console output, i.e., to have kernel
864 console messages discarded.
865 This must be the only console= parameter used on the
866 kernel command line.
868 If the device connected to the port is not a TTY but a braille
869 device, prepend "brl," before the device type, for instance
870 console=brl,ttyS0
871 For now, only VisioBraille is supported.
873 console_msg_format=
874 [KNL] Change console messages format
875 default
876 By default we print messages on consoles in
877 "[time stamp] text\n" format (time stamp may not be
878 printed, depending on CONFIG_PRINTK_TIME or
879 `printk_time' param).
880 syslog
881 Switch to syslog format: "<%u>[time stamp] text\n"
882 IOW, each message will have a facility and loglevel
883 prefix. The format is similar to one used by syslog()
884 syscall, or to executing "dmesg -S --raw" or to reading
885 from /proc/kmsg.
887 consoleblank= [KNL] The console blank (screen saver) timeout in
888 seconds. A value of 0 disables the blank timer.
889 Defaults to 0.
891 coredump_filter=
892 [KNL] Change the default value for
893 /proc/<pid>/coredump_filter.
894 See also Documentation/filesystems/proc.rst.
896 coresight_cpu_debug.enable
897 [ARM,ARM64]
898 Format: <bool>
899 Enable/disable the CPU sampling based debugging.
900 0: default value, disable debugging
901 1: enable debugging at boot time
903 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
904 Format:
905 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
907 cpuidle.off=1 [CPU_IDLE]
908 disable the cpuidle sub-system
910 cpuidle.governor=
911 [CPU_IDLE] Name of the cpuidle governor to use.
913 cpufreq.off=1 [CPU_FREQ]
914 disable the cpufreq sub-system
916 cpufreq.default_governor=
917 [CPU_FREQ] Name of the default cpufreq governor or
918 policy to use. This governor must be registered in the
919 kernel before the cpufreq driver probes.
921 cpu_init_udelay=N
922 [X86,EARLY] Delay for N microsec between assert and de-assert
923 of APIC INIT to start processors. This delay occurs
924 on every CPU online, such as boot, and resume from suspend.
925 Default: 10000
927 cpuhp.parallel=
928 [SMP] Enable/disable parallel bringup of secondary CPUs
929 Format: <bool>
930 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise
931 the parameter has no effect.
933 crash_kexec_post_notifiers
934 Only jump to kdump kernel after running the panic
935 notifiers and dumping kmsg. This option increases
936 the risks of a kdump failure, since some panic
937 notifiers can make the crashed kernel more unstable.
938 In configurations where kdump may not be reliable,
939 running the panic notifiers could allow collecting
940 more data on dmesg, like stack traces from other CPUS
941 or extra data dumped by panic_print. Note that some
942 configurations enable this option unconditionally,
943 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP.
945 crashkernel=size[KMG][@offset[KMG]]
946 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
947 upon panic. This parameter reserves the physical
948 memory region [offset, offset + size] for that kernel
949 image. If '@offset' is omitted, then a suitable offset
950 is selected automatically.
951 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
952 under 4G first, and fall back to reserve region above
953 4G when '@offset' hasn't been specified.
954 See Documentation/admin-guide/kdump/kdump.rst for further details.
956 crashkernel=range1:size1[,range2:size2,...][@offset]
957 [KNL] Same as above, but depends on the memory
958 in the running system. The syntax of range is
959 start-[end] where start and end are both
960 a memory unit (amount[KMG]). See also
961 Documentation/admin-guide/kdump/kdump.rst for an example.
963 crashkernel=size[KMG],high
964 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
965 above 4G.
966 Allow kernel to allocate physical memory region from top,
967 so could be above 4G if system have more than 4G ram
968 installed. Otherwise memory region will be allocated
969 below 4G, if available.
970 It will be ignored if crashkernel=X is specified.
971 crashkernel=size[KMG],low
972 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
973 When crashkernel=X,high is passed, kernel could allocate
974 physical memory region above 4G, that cause second kernel
975 crash on system that require some amount of low memory,
976 e.g. swiotlb requires at least 64M+32K low memory, also
977 enough extra low memory is needed to make sure DMA buffers
978 for 32-bit devices won't run out. Kernel would try to allocate
979 default size of memory below 4G automatically. The default
980 size is platform dependent.
981 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
982 --> arm64: 128MiB
983 --> riscv: 128MiB
984 --> loongarch: 128MiB
985 This one lets the user specify own low range under 4G
986 for second kernel instead.
987 0: to disable low allocation.
988 It will be ignored when crashkernel=X,high is not used
989 or memory reserved is below 4G.
991 cryptomgr.notests
992 [KNL] Disable crypto self-tests
994 cs89x0_dma= [HW,NET]
995 Format: <dma>
997 cs89x0_media= [HW,NET]
998 Format: { rj45 | aui | bnc }
1000 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU
1001 function call handling. When switched on,
1002 additional debug data is printed to the console
1003 in case a hanging CPU is detected, and that
1004 CPU is pinged again in order to try to resolve
1005 the hang situation. The default value of this
1006 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT
1007 Kconfig option.
1009 dasd= [HW,NET]
1010 See header of drivers/s390/block/dasd_devmap.c.
1012 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
1013 (one device per port)
1014 Format: <port#>,<type>
1015 See also Documentation/input/devices/joystick-parport.rst
1017 debug [KNL,EARLY] Enable kernel debugging (events log level).
1019 debug_boot_weak_hash
1020 [KNL,EARLY] Enable printing [hashed] pointers early in the
1021 boot sequence. If enabled, we use a weak hash instead
1022 of siphash to hash pointers. Use this option if you are
1023 seeing instances of '(___ptrval___)') and need to see a
1024 value (hashed pointer) instead. Cryptographically
1025 insecure, please do not use on production kernels.
1027 debug_locks_verbose=
1028 [KNL] verbose locking self-tests
1029 Format: <int>
1030 Print debugging info while doing the locking API
1031 self-tests.
1032 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
1033 (no extra messages), setting it to -1 (all bits set)
1034 will print _a_lot_ more information - normally only
1035 useful to lockdep developers.
1037 debug_objects [KNL,EARLY] Enable object debugging
1039 debug_guardpage_minorder=
1040 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
1041 parameter allows control of the order of pages that will
1042 be intentionally kept free (and hence protected) by the
1043 buddy allocator. Bigger value increase the probability
1044 of catching random memory corruption, but reduce the
1045 amount of memory for normal system use. The maximum
1046 possible value is MAX_PAGE_ORDER/2. Setting this
1047 parameter to 1 or 2 should be enough to identify most
1048 random memory corruption problems caused by bugs in
1049 kernel or driver code when a CPU writes to (or reads
1050 from) a random memory location. Note that there exists
1051 a class of memory corruptions problems caused by buggy
1052 H/W or F/W or by drivers badly programming DMA
1053 (basically when memory is written at bus level and the
1054 CPU MMU is bypassed) which are not detectable by
1055 CONFIG_DEBUG_PAGEALLOC, hence this option will not
1056 help tracking down these problems.
1058 debug_pagealloc=
1059 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
1060 enables the feature at boot time. By default, it is
1061 disabled and the system will work mostly the same as a
1062 kernel built without CONFIG_DEBUG_PAGEALLOC.
1063 Note: to get most of debug_pagealloc error reports, it's
1064 useful to also enable the page_owner functionality.
1065 on: enable the feature
1067 debugfs= [KNL,EARLY] This parameter enables what is exposed to
1068 userspace and debugfs internal clients.
1069 Format: { on, no-mount, off }
1070 on: All functions are enabled.
1071 no-mount:
1072 Filesystem is not registered but kernel clients can
1073 access APIs and a crashkernel can be used to read
1074 its content. There is nothing to mount.
1075 off: Filesystem is not registered and clients
1076 get a -EPERM as result when trying to register files
1077 or directories within debugfs.
1078 This is equivalent of the runtime functionality if
1079 debugfs was not enabled in the kernel at all.
1080 Default value is set in build-time with a kernel configuration.
1082 debugpat [X86] Enable PAT debugging
1084 default_hugepagesz=
1085 [HW] The size of the default HugeTLB page. This is
1086 the size represented by the legacy /proc/ hugepages
1087 APIs. In addition, this is the default hugetlb size
1088 used for shmget(), mmap() and mounting hugetlbfs
1089 filesystems. If not specified, defaults to the
1090 architecture's default huge page size. Huge page
1091 sizes are architecture dependent. See also
1092 Documentation/admin-guide/mm/hugetlbpage.rst.
1093 Format: size[KMG]
1095 deferred_probe_timeout=
1096 [KNL] Debugging option to set a timeout in seconds for
1097 deferred probe to give up waiting on dependencies to
1098 probe. Only specific dependencies (subsystems or
1099 drivers) that have opted in will be ignored. A timeout
1100 of 0 will timeout at the end of initcalls. If the time
1101 out hasn't expired, it'll be restarted by each
1102 successful driver registration. This option will also
1103 dump out devices still on the deferred probe list after
1104 retrying.
1106 delayacct [KNL] Enable per-task delay accounting
1108 dell_smm_hwmon.ignore_dmi=
1109 [HW] Continue probing hardware even if DMI data
1110 indicates that the driver is running on unsupported
1111 hardware.
1113 dell_smm_hwmon.force=
1114 [HW] Activate driver even if SMM BIOS signature does
1115 not match list of supported models and enable otherwise
1116 blacklisted features.
1118 dell_smm_hwmon.power_status=
1119 [HW] Report power status in /proc/i8k
1120 (disabled by default).
1122 dell_smm_hwmon.restricted=
1123 [HW] Allow controlling fans only if SYS_ADMIN
1124 capability is set.
1126 dell_smm_hwmon.fan_mult=
1127 [HW] Factor to multiply fan speed with.
1129 dell_smm_hwmon.fan_max=
1130 [HW] Maximum configurable fan speed.
1132 dfltcc= [HW,S390]
1133 Format: { on | off | def_only | inf_only | always }
1134 on: s390 zlib hardware support for compression on
1135 level 1 and decompression (default)
1136 off: No s390 zlib hardware support
1137 def_only: s390 zlib hardware support for deflate
1138 only (compression on level 1)
1139 inf_only: s390 zlib hardware support for inflate
1140 only (decompression)
1141 always: Same as 'on' but ignores the selected compression
1142 level always using hardware support (used for debugging)
1144 dhash_entries= [KNL]
1145 Set number of hash buckets for dentry cache.
1147 disable_1tb_segments [PPC,EARLY]
1148 Disables the use of 1TB hash page table segments. This
1149 causes the kernel to fall back to 256MB segments which
1150 can be useful when debugging issues that require an SLB
1151 miss to occur.
1153 disable= [IPV6]
1154 See Documentation/networking/ipv6.rst.
1156 disable_radix [PPC,EARLY]
1157 Disable RADIX MMU mode on POWER9
1159 disable_tlbie [PPC]
1160 Disable TLBIE instruction. Currently does not work
1161 with KVM, with HASH MMU, or with coherent accelerators.
1163 disable_ddw [PPC/PSERIES,EARLY]
1164 Disable Dynamic DMA Window support. Use this
1165 to workaround buggy firmware.
1167 disable_ipv6= [IPV6]
1168 See Documentation/networking/ipv6.rst.
1170 disable_mtrr_cleanup [X86,EARLY]
1171 The kernel tries to adjust MTRR layout from continuous
1172 to discrete, to make X server driver able to add WB
1173 entry later. This parameter disables that.
1175 disable_mtrr_trim [X86, Intel and AMD only,EARLY]
1176 By default the kernel will trim any uncacheable
1177 memory out of your available memory pool based on
1178 MTRR settings. This parameter disables that behavior,
1179 possibly causing your machine to run very slowly.
1181 disable_timer_pin_1 [X86,EARLY]
1182 Disable PIN 1 of APIC timer
1183 Can be useful to work around chipset bugs.
1185 dis_ucode_ldr [X86] Disable the microcode loader.
1187 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1188 this option disables the debugging code at boot.
1190 dma_debug_entries=<number>
1191 This option allows to tune the number of preallocated
1192 entries for DMA-API debugging code. One entry is
1193 required per DMA-API allocation. Use this if the
1194 DMA-API debugging code disables itself because the
1195 architectural default is too low.
1197 dma_debug_driver=<driver_name>
1198 With this option the DMA-API debugging driver
1199 filter feature can be enabled at boot time. Just
1200 pass the driver to filter for as the parameter.
1201 The filter can be disabled or changed to another
1202 driver later using sysfs.
1204 reg_file_data_sampling=
1205 [X86] Controls mitigation for Register File Data
1206 Sampling (RFDS) vulnerability. RFDS is a CPU
1207 vulnerability which may allow userspace to infer
1208 kernel data values previously stored in floating point
1209 registers, vector registers, or integer registers.
1210 RFDS only affects Intel Atom processors.
1212 on: Turns ON the mitigation.
1213 off: Turns OFF the mitigation.
1215 This parameter overrides the compile time default set
1216 by CONFIG_MITIGATION_RFDS. Mitigation cannot be
1217 disabled when other VERW based mitigations (like MDS)
1218 are enabled. In order to disable RFDS mitigation all
1219 VERW based mitigations need to be disabled.
1221 For details see:
1222 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
1224 driver_async_probe= [KNL]
1225 List of driver names to be probed asynchronously. *
1226 matches with all driver names. If * is specified, the
1227 rest of the listed driver names are those that will NOT
1228 match the *.
1229 Format: <driver_name1>,<driver_name2>...
1231 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1232 Broken monitors, graphic adapters, KVMs and EDIDless
1233 panels may send no or incorrect EDID data sets.
1234 This parameter allows to specify an EDID data sets
1235 in the /lib/firmware directory that are used instead.
1236 An EDID data set will only be used for a particular
1237 connector, if its name and a colon are prepended to
1238 the EDID name. Each connector may use a unique EDID
1239 data set by separating the files with a comma. An EDID
1240 data set with no connector name will be used for
1241 any connectors not explicitly specified.
1243 dscc4.setup= [NET]
1245 dt_cpu_ftrs= [PPC,EARLY]
1246 Format: {"off" | "known"}
1247 Control how the dt_cpu_ftrs device-tree binding is
1248 used for CPU feature discovery and setup (if it
1249 exists).
1250 off: Do not use it, fall back to legacy cpu table.
1251 known: Do not pass through unknown features to guests
1252 or userspace, only those that the kernel is aware of.
1254 dump_apple_properties [X86]
1255 Dump name and content of EFI device properties on
1256 x86 Macs. Useful for driver authors to determine
1257 what data is available or for reverse-engineering.
1259 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1260 <module>.dyndbg[="val"]
1261 Enable debug messages at boot time. See
1262 Documentation/admin-guide/dynamic-debug-howto.rst
1263 for details.
1265 early_ioremap_debug [KNL,EARLY]
1266 Enable debug messages in early_ioremap support. This
1267 is useful for tracking down temporary early mappings
1268 which are not unmapped.
1270 earlycon= [KNL,EARLY] Output early console device and options.
1272 When used with no options, the early console is
1273 determined by stdout-path property in device tree's
1274 chosen node or the ACPI SPCR table if supported by
1275 the platform.
1277 cdns,<addr>[,options]
1278 Start an early, polled-mode console on a Cadence
1279 (xuartps) serial port at the specified address. Only
1280 supported option is baud rate. If baud rate is not
1281 specified, the serial port must already be setup and
1282 configured.
1284 uart[8250],io,<addr>[,options[,uartclk]]
1285 uart[8250],mmio,<addr>[,options[,uartclk]]
1286 uart[8250],mmio32,<addr>[,options[,uartclk]]
1287 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1288 uart[8250],0x<addr>[,options]
1289 Start an early, polled-mode console on the 8250/16550
1290 UART at the specified I/O port or MMIO address.
1291 MMIO inter-register address stride is either 8-bit
1292 (mmio) or 32-bit (mmio32 or mmio32be).
1293 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1294 to be equivalent to 'mmio'. 'options' are specified
1295 in the same format described for "console=ttyS<n>"; if
1296 unspecified, the h/w is not initialized. 'uartclk' is
1297 the uart clock frequency; if unspecified, it is set
1298 to 'BASE_BAUD' * 16.
1300 pl011,<addr>
1301 pl011,mmio32,<addr>
1302 Start an early, polled-mode console on a pl011 serial
1303 port at the specified address. The pl011 serial port
1304 must already be setup and configured. Options are not
1305 yet supported. If 'mmio32' is specified, then only
1306 the driver will use only 32-bit accessors to read/write
1307 the device registers.
1309 liteuart,<addr>
1310 Start an early console on a litex serial port at the
1311 specified address. The serial port must already be
1312 setup and configured. Options are not yet supported.
1314 meson,<addr>
1315 Start an early, polled-mode console on a meson serial
1316 port at the specified address. The serial port must
1317 already be setup and configured. Options are not yet
1318 supported.
1320 msm_serial,<addr>
1321 Start an early, polled-mode console on an msm serial
1322 port at the specified address. The serial port
1323 must already be setup and configured. Options are not
1324 yet supported.
1326 msm_serial_dm,<addr>
1327 Start an early, polled-mode console on an msm serial
1328 dm port at the specified address. The serial port
1329 must already be setup and configured. Options are not
1330 yet supported.
1332 owl,<addr>
1333 Start an early, polled-mode console on a serial port
1334 of an Actions Semi SoC, such as S500 or S900, at the
1335 specified address. The serial port must already be
1336 setup and configured. Options are not yet supported.
1338 rda,<addr>
1339 Start an early, polled-mode console on a serial port
1340 of an RDA Micro SoC, such as RDA8810PL, at the
1341 specified address. The serial port must already be
1342 setup and configured. Options are not yet supported.
1344 sbi
1345 Use RISC-V SBI (Supervisor Binary Interface) for early
1346 console.
1348 smh Use ARM semihosting calls for early console.
1350 s3c2410,<addr>
1351 s3c2412,<addr>
1352 s3c2440,<addr>
1353 s3c6400,<addr>
1354 s5pv210,<addr>
1355 exynos4210,<addr>
1356 Use early console provided by serial driver available
1357 on Samsung SoCs, requires selecting proper type and
1358 a correct base address of the selected UART port. The
1359 serial port must already be setup and configured.
1360 Options are not yet supported.
1362 lantiq,<addr>
1363 Start an early, polled-mode console on a lantiq serial
1364 (lqasc) port at the specified address. The serial port
1365 must already be setup and configured. Options are not
1366 yet supported.
1368 lpuart,<addr>
1369 lpuart32,<addr>
1370 Use early console provided by Freescale LP UART driver
1371 found on Freescale Vybrid and QorIQ LS1021A processors.
1372 A valid base address must be provided, and the serial
1373 port must already be setup and configured.
1375 ec_imx21,<addr>
1376 ec_imx6q,<addr>
1377 Start an early, polled-mode, output-only console on the
1378 Freescale i.MX UART at the specified address. The UART
1379 must already be setup and configured.
1381 ar3700_uart,<addr>
1382 Start an early, polled-mode console on the
1383 Armada 3700 serial port at the specified
1384 address. The serial port must already be setup
1385 and configured. Options are not yet supported.
1387 qcom_geni,<addr>
1388 Start an early, polled-mode console on a Qualcomm
1389 Generic Interface (GENI) based serial port at the
1390 specified address. The serial port must already be
1391 setup and configured. Options are not yet supported.
1393 efifb,[options]
1394 Start an early, unaccelerated console on the EFI
1395 memory mapped framebuffer (if available). On cache
1396 coherent non-x86 systems that use system memory for
1397 the framebuffer, pass the 'ram' option so that it is
1398 mapped with the correct attributes.
1400 linflex,<addr>
1401 Use early console provided by Freescale LINFlexD UART
1402 serial driver for NXP S32V234 SoCs. A valid base
1403 address must be provided, and the serial port must
1404 already be setup and configured.
1406 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
1407 earlyprintk=vga
1408 earlyprintk=sclp
1409 earlyprintk=xen
1410 earlyprintk=serial[,ttySn[,baudrate]]
1411 earlyprintk=serial[,0x...[,baudrate]]
1412 earlyprintk=ttySn[,baudrate]
1413 earlyprintk=dbgp[debugController#]
1414 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1415 earlyprintk=xdbc[xhciController#]
1416 earlyprintk=bios
1418 earlyprintk is useful when the kernel crashes before
1419 the normal console is initialized. It is not enabled by
1420 default because it has some cosmetic problems.
1422 Append ",keep" to not disable it when the real console
1423 takes over.
1425 Only one of vga, serial, or usb debug port can
1426 be used at a time.
1428 Currently only ttyS0 and ttyS1 may be specified by
1429 name. Other I/O ports may be explicitly specified
1430 on some architectures (x86 and arm at least) by
1431 replacing ttySn with an I/O port address, like this:
1432 earlyprintk=serial,0x1008,115200
1433 You can find the port for a given device in
1434 /proc/tty/driver/serial:
1435 2: uart:ST16650V2 port:00001008 irq:18 ...
1437 Interaction with the standard serial driver is not
1438 very good.
1440 The VGA output is eventually overwritten by
1441 the real console.
1443 The xen option can only be used in Xen domains.
1445 The sclp output can only be used on s390.
1447 The bios output can only be used on SuperH.
1449 The optional "force" to "pciserial" enables use of a
1450 PCI device even when its classcode is not of the
1451 UART class.
1453 edac_report= [HW,EDAC] Control how to report EDAC event
1454 Format: {"on" | "off" | "force"}
1455 on: enable EDAC to report H/W event. May be overridden
1456 by other higher priority error reporting module.
1457 off: disable H/W event reporting through EDAC.
1458 force: enforce the use of EDAC to report H/W event.
1459 default: on.
1461 edd= [EDD]
1462 Format: {"off" | "on" | "skip[mbr]"}
1464 efi= [EFI,EARLY]
1465 Format: { "debug", "disable_early_pci_dma",
1466 "nochunk", "noruntime", "nosoftreserve",
1467 "novamap", "no_disable_early_pci_dma" }
1468 debug: enable misc debug output.
1469 disable_early_pci_dma: disable the busmaster bit on all
1470 PCI bridges while in the EFI boot stub.
1471 nochunk: disable reading files in "chunks" in the EFI
1472 boot stub, as chunking can cause problems with some
1473 firmware implementations.
1474 noruntime : disable EFI runtime services support
1475 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1476 attribute may cause the kernel to reserve the
1477 memory range for a memory mapping driver to
1478 claim. Specify efi=nosoftreserve to disable this
1479 reservation and treat the memory by its base type
1480 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1481 novamap: do not call SetVirtualAddressMap().
1482 no_disable_early_pci_dma: Leave the busmaster bit set
1483 on all PCI bridges while in the EFI boot stub
1485 efi_no_storage_paranoia [EFI,X86,EARLY]
1486 Using this parameter you can use more than 50% of
1487 your efi variable storage. Use this parameter only if
1488 you are really sure that your UEFI does sane gc and
1489 fulfills the spec otherwise your board may brick.
1491 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1492 that is to be dynamically loaded by Linux. If there are
1493 multiple variables with the same name but with different
1494 vendor GUIDs, all of them will be loaded. See
1495 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1498 eisa_irq_edge= [PARISC,HW]
1499 See header of drivers/parisc/eisa.c.
1501 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
1502 Format: ekgdboc=kbd
1504 This is designed to be used in conjunction with
1505 the boot argument: earlyprintk=vga
1507 This parameter works in place of the kgdboc parameter
1508 but can only be used if the backing tty is available
1509 very early in the boot process. For early debugging
1510 via a serial port see kgdboc_earlycon instead.
1512 elanfreq= [X86-32]
1513 See comment before function elanfreq_setup() in
1514 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1516 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
1517 Specifies physical address of start of kernel core
1518 image elf header and optionally the size. Generally
1519 kexec loader will pass this option to capture kernel.
1520 See Documentation/admin-guide/kdump/kdump.rst for details.
1522 enable_mtrr_cleanup [X86,EARLY]
1523 The kernel tries to adjust MTRR layout from continuous
1524 to discrete, to make X server driver able to add WB
1525 entry later. This parameter enables that.
1527 enable_timer_pin_1 [X86]
1528 Enable PIN 1 of APIC timer
1529 Can be useful to work around chipset bugs
1530 (in particular on some ATI chipsets).
1531 The kernel tries to set a reasonable default.
1533 enforcing= [SELINUX] Set initial enforcing status.
1534 Format: {"0" | "1"}
1535 See security/selinux/Kconfig help text.
1536 0 -- permissive (log only, no denials).
1537 1 -- enforcing (deny and log).
1538 Default value is 0.
1539 Value can be changed at runtime via
1540 /sys/fs/selinux/enforce.
1542 erst_disable [ACPI]
1543 Disable Error Record Serialization Table (ERST)
1544 support.
1546 ether= [HW,NET] Ethernet cards parameters
1547 This option is obsoleted by the "netdev=" option, which
1548 has equivalent usage. See its documentation for details.
1550 evm= [EVM]
1551 Format: { "fix" }
1552 Permit 'security.evm' to be updated regardless of
1553 current integrity status.
1555 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
1556 stages so cover more early boot allocations.
1557 Please note that as side effect some optimizations
1558 might be disabled to achieve that (e.g. parallelized
1559 memory initialization is disabled) so the boot process
1560 might take longer, especially on systems with a lot of
1561 memory. Available with CONFIG_PAGE_EXTENSION=y.
1563 failslab=
1564 fail_usercopy=
1565 fail_page_alloc=
1566 fail_skb_realloc=
1567 fail_make_request=[KNL]
1568 General fault injection mechanism.
1569 Format: <interval>,<probability>,<space>,<times>
1570 See also Documentation/fault-injection/.
1572 fb_tunnels= [NET]
1573 Format: { initns | none }
1574 See Documentation/admin-guide/sysctl/net.rst for
1575 fb_tunnels_only_for_init_ns
1577 floppy= [HW]
1578 See Documentation/admin-guide/blockdev/floppy.rst.
1580 forcepae [X86-32]
1581 Forcefully enable Physical Address Extension (PAE).
1582 Many Pentium M systems disable PAE but may have a
1583 functionally usable PAE implementation.
1584 Warning: use of this parameter will taint the kernel
1585 and may cause unknown problems.
1587 fred= [X86-64]
1588 Enable/disable Flexible Return and Event Delivery.
1589 Format: { on | off }
1590 on: enable FRED when it's present.
1591 off: disable FRED, the default setting.
1593 ftrace=[tracer]
1594 [FTRACE] will set and start the specified tracer
1595 as early as possible in order to facilitate early
1596 boot debugging.
1598 ftrace_boot_snapshot
1599 [FTRACE] On boot up, a snapshot will be taken of the
1600 ftrace ring buffer that can be read at:
1601 /sys/kernel/tracing/snapshot.
1602 This is useful if you need tracing information from kernel
1603 boot up that is likely to be overridden by user space
1604 start up functionality.
1606 Optionally, the snapshot can also be defined for a tracing
1607 instance that was created by the trace_instance= command
1608 line parameter.
1610 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1612 The above will cause the "foo" tracing instance to trigger
1613 a snapshot at the end of boot up.
1615 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> |
1616 ,<instance>=2(orig_cpu)]
1617 [FTRACE] will dump the trace buffers on oops.
1618 If no parameter is passed, ftrace will dump global
1619 buffers of all CPUs, if you pass 2 or orig_cpu, it
1620 will dump only the buffer of the CPU that triggered
1621 the oops, or the specific instance will be dumped if
1622 its name is passed. Multiple instance dump is also
1623 supported, and instances are separated by commas. Each
1624 instance supports only dump on CPU that triggered the
1625 oops by passing 2 or orig_cpu to it.
1627 ftrace_dump_on_oops=foo=orig_cpu
1629 The above will dump only the buffer of "foo" instance
1630 on CPU that triggered the oops.
1632 ftrace_dump_on_oops,foo,bar=orig_cpu
1634 The above will dump global buffer on all CPUs, the
1635 buffer of "foo" instance on all CPUs and the buffer
1636 of "bar" instance on CPU that triggered the oops.
1638 ftrace_filter=[function-list]
1639 [FTRACE] Limit the functions traced by the function
1640 tracer at boot up. function-list is a comma-separated
1641 list of functions. This list can be changed at run
1642 time by the set_ftrace_filter file in the debugfs
1643 tracing directory.
1645 ftrace_notrace=[function-list]
1646 [FTRACE] Do not trace the functions specified in
1647 function-list. This list can be changed at run time
1648 by the set_ftrace_notrace file in the debugfs
1649 tracing directory.
1651 ftrace_graph_filter=[function-list]
1652 [FTRACE] Limit the top level callers functions traced
1653 by the function graph tracer at boot up.
1654 function-list is a comma-separated list of functions
1655 that can be changed at run time by the
1656 set_graph_function file in the debugfs tracing directory.
1658 ftrace_graph_notrace=[function-list]
1659 [FTRACE] Do not trace from the functions specified in
1660 function-list. This list is a comma-separated list of
1661 functions that can be changed at run time by the
1662 set_graph_notrace file in the debugfs tracing directory.
1664 ftrace_graph_max_depth=<uint>
1665 [FTRACE] Used with the function graph tracer. This is
1666 the max depth it will trace into a function. This value
1667 can be changed at run time by the max_graph_depth file
1668 in the tracefs tracing directory. default: 0 (no limit)
1670 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
1671 devices by scanning the firmware to infer the
1672 consumer/supplier relationships. This feature is
1673 especially useful when drivers are loaded as modules as
1674 it ensures proper ordering of tasks like device probing
1675 (suppliers first, then consumers), supplier boot state
1676 clean up (only after all consumers have probed),
1677 suspend/resume & runtime PM (consumers first, then
1678 suppliers).
1679 Format: { off | permissive | on | rpm }
1680 off -- Don't create device links from firmware info.
1681 permissive -- Create device links from firmware info
1682 but use it only for ordering boot state clean
1683 up (sync_state() calls).
1684 on -- Create device links from firmware info and use it
1685 to enforce probe and suspend/resume ordering.
1686 rpm -- Like "on", but also use to order runtime PM.
1688 fw_devlink.strict=<bool>
1689 [KNL,EARLY] Treat all inferred dependencies as mandatory
1690 dependencies. This only applies for fw_devlink=on|rpm.
1691 Format: <bool>
1693 fw_devlink.sync_state =
1694 [KNL,EARLY] When all devices that could probe have finished
1695 probing, this parameter controls what to do with
1696 devices that haven't yet received their sync_state()
1697 calls.
1698 Format: { strict | timeout }
1699 strict -- Default. Continue waiting on consumers to
1700 probe successfully.
1701 timeout -- Give up waiting on consumers and call
1702 sync_state() on any devices that haven't yet
1703 received their sync_state() calls after
1704 deferred_probe_timeout has expired or by
1705 late_initcall() if !CONFIG_MODULES.
1707 gamecon.map[2|3]=
1708 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1709 support via parallel port (up to 5 devices per port)
1710 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1711 See also Documentation/input/devices/joystick-parport.rst
1713 gamma= [HW,DRM]
1715 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
1716 Format: off | on
1717 default: on
1719 gather_data_sampling=
1720 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
1721 mitigation.
1723 Gather Data Sampling is a hardware vulnerability which
1724 allows unprivileged speculative access to data which was
1725 previously stored in vector registers.
1727 This issue is mitigated by default in updated microcode.
1728 The mitigation may have a performance impact but can be
1729 disabled. On systems without the microcode mitigation
1730 disabling AVX serves as a mitigation.
1732 force: Disable AVX to mitigate systems without
1733 microcode mitigation. No effect if the microcode
1734 mitigation is present. Known to cause crashes in
1735 userspace with buggy AVX enumeration.
1737 off: Disable GDS mitigation.
1739 gbpages [X86] Use GB pages for kernel direct mappings.
1741 gcov_persist= [GCOV] When non-zero (default), profiling data for
1742 kernel modules is saved and remains accessible via
1743 debugfs, even when the module is unloaded/reloaded.
1744 When zero, profiling data is discarded and associated
1745 debugfs files are removed at module unload time.
1747 goldfish [X86] Enable the goldfish android emulator platform.
1748 Don't use this when you are not running on the
1749 android emulator
1751 gpio-mockup.gpio_mockup_ranges
1752 [HW] Sets the ranges of gpiochip of for this device.
1753 Format: <start1>,<end1>,<start2>,<end2>...
1754 gpio-mockup.gpio_mockup_named_lines
1755 [HW] Let the driver know GPIO lines should be named.
1757 gpt [EFI] Forces disk with valid GPT signature but
1758 invalid Protective MBR to be treated as GPT. If the
1759 primary GPT is corrupted, it enables the backup/alternate
1760 GPT to be used instead.
1762 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1763 the "Enable 0" bit of the configuration register.
1764 Format: 0 | 1
1765 Default: 0
1766 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1767 the "Enable 0" bit of the configuration register.
1768 Format: 0 | 1
1769 Default: 0
1770 grcan.select= [HW] Select which physical interface to use.
1771 Format: 0 | 1
1772 Default: 0
1773 grcan.txsize= [HW] Sets the size of the tx buffer.
1774 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1775 Default: 1024
1776 grcan.rxsize= [HW] Sets the size of the rx buffer.
1777 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1778 Default: 1024
1780 hardened_usercopy=
1781 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1782 hardening is enabled for this boot. Hardened
1783 usercopy checking is used to protect the kernel
1784 from reading or writing beyond known memory
1785 allocation boundaries as a proactive defense
1786 against bounds-checking flaws in the kernel's
1787 copy_to_user()/copy_from_user() interface.
1788 on Perform hardened usercopy checks (default).
1789 off Disable hardened usercopy checks.
1791 hardlockup_all_cpu_backtrace=
1792 [KNL] Should the hard-lockup detector generate
1793 backtraces on all cpus.
1794 Format: 0 | 1
1796 hashdist= [KNL,NUMA] Large hashes allocated during boot
1797 are distributed across NUMA nodes. Defaults on
1798 for 64-bit NUMA, off otherwise.
1799 Format: 0 | 1 (for off | on)
1801 hd= [EIDE] (E)IDE hard drive subsystem geometry
1802 Format: <cyl>,<head>,<sect>
1804 hest_disable [ACPI]
1805 Disable Hardware Error Source Table (HEST) support;
1806 corresponding firmware-first mode error processing
1807 logic will be disabled.
1809 hibernate= [HIBERNATION]
1810 noresume Don't check if there's a hibernation image
1811 present during boot.
1812 nocompress Don't compress/decompress hibernation images.
1813 no Disable hibernation and resume.
1814 protect_image Turn on image protection during restoration
1815 (that will set all pages holding image data
1816 during restoration read-only).
1818 hibernate.compressor= [HIBERNATION] Compression algorithm to be
1819 used with hibernation.
1820 Format: { lzo | lz4 }
1821 Default: lzo
1823 lzo: Select LZO compression algorithm to
1824 compress/decompress hibernation image.
1826 lz4: Select LZ4 compression algorithm to
1827 compress/decompress hibernation image.
1829 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact
1830 size of <nn>. This works even on boxes that have no
1831 highmem otherwise. This also works to reduce highmem
1832 size on bigger boxes.
1834 highres= [KNL] Enable/disable high resolution timer mode.
1835 Valid parameters: "on", "off"
1836 Default: "on"
1838 hlt [BUGS=ARM,SH]
1840 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
1841 Format: <string>
1842 This allows setting the system's hostname during early
1843 startup. This sets the name returned by gethostname.
1844 Using this parameter to set the hostname makes it
1845 possible to ensure the hostname is correctly set before
1846 any userspace processes run, avoiding the possibility
1847 that a process may call gethostname before the hostname
1848 has been explicitly set, resulting in the calling
1849 process getting an incorrect result. The string must
1850 not exceed the maximum allowed hostname length (usually
1851 64 characters) and will be truncated otherwise.
1853 hpet= [X86-32,HPET] option to control HPET usage
1854 Format: { enable (default) | disable | force |
1855 verbose }
1856 disable: disable HPET and use PIT instead
1857 force: allow force enabled of undocumented chips (ICH4,
1858 VIA, nVidia)
1859 verbose: show contents of HPET registers during setup
1861 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1862 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1864 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1865 If this follows hugepagesz (below), it specifies
1866 the number of pages of hugepagesz to be allocated.
1867 If this is the first HugeTLB parameter on the command
1868 line, it specifies the number of pages to allocate for
1869 the default huge page size. If using node format, the
1870 number of pages to allocate per-node can be specified.
1871 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1872 Format: <integer> or (node format)
1873 <node>:<integer>[,<node>:<integer>]
1875 hugepagesz=
1876 [HW] The size of the HugeTLB pages. This is used in
1877 conjunction with hugepages (above) to allocate huge
1878 pages of a specific size at boot. The pair
1879 hugepagesz=X hugepages=Y can be specified once for
1880 each supported huge page size. Huge page sizes are
1881 architecture dependent. See also
1882 Documentation/admin-guide/mm/hugetlbpage.rst.
1883 Format: size[KMG]
1885 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
1886 of gigantic hugepages. Or using node format, the size
1887 of a CMA area per node can be specified.
1888 Format: nn[KMGTPE] or (node format)
1889 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1891 Reserve a CMA area of given size and allocate gigantic
1892 hugepages using the CMA allocator. If enabled, the
1893 boot-time allocation of gigantic hugepages is skipped.
1895 hugetlb_free_vmemmap=
1896 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1897 enabled.
1898 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1899 Allows heavy hugetlb users to free up some more
1900 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1901 Format: { on | off (default) }
1903 on: enable HVO
1904 off: disable HVO
1906 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1907 the default is on.
1909 Note that the vmemmap pages may be allocated from the added
1910 memory block itself when memory_hotplug.memmap_on_memory is
1911 enabled, those vmemmap pages cannot be optimized even if this
1912 feature is enabled. Other vmemmap pages not allocated from
1913 the added memory block itself do not be affected.
1915 hung_task_panic=
1916 [KNL] Should the hung task detector generate panics.
1917 Format: 0 | 1
1919 A value of 1 instructs the kernel to panic when a
1920 hung task is detected. The default value is controlled
1921 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1922 option. The value selected by this boot parameter can
1923 be changed later by the kernel.hung_task_panic sysctl.
1925 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1926 terminal devices. Valid values: 0..8
1927 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1928 If specified, z/VM IUCV HVC accepts connections
1929 from listed z/VM user IDs only.
1931 hv_nopvspin [X86,HYPER_V,EARLY]
1932 Disables the paravirt spinlock optimizations
1933 which allow the hypervisor to 'idle' the guest
1934 on lock contention.
1936 i2c_bus= [HW] Override the default board specific I2C bus speed
1937 or register an additional I2C bus that is not
1938 registered from board initialization code.
1939 Format:
1940 <bus_id>,<clkrate>
1942 i2c_touchscreen_props= [HW,ACPI,X86]
1943 Set device-properties for ACPI-enumerated I2C-attached
1944 touchscreen, to e.g. fix coordinates of upside-down
1945 mounted touchscreens. If you need this option please
1946 submit a drivers/platform/x86/touchscreen_dmi.c patch
1947 adding a DMI quirk for this.
1949 Format:
1950 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...]
1951 Where <val> is one of:
1952 Omit "=<val>" entirely Set a boolean device-property
1953 Unsigned number Set a u32 device-property
1954 Anything else Set a string device-property
1956 Examples (split over multiple lines):
1957 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x:
1958 touchscreen-inverted-y
1960 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920:
1961 touchscreen-size-y=1080:touchscreen-inverted-y:
1962 firmware-name=gsl1680-vendor-model.fw:silead,home-button
1964 i8042.debug [HW] Toggle i8042 debug mode
1965 i8042.unmask_kbd_data
1966 [HW] Enable printing of interrupt data from the KBD port
1967 (disabled by default, and as a pre-condition
1968 requires that i8042.debug=1 be enabled)
1969 i8042.direct [HW] Put keyboard port into non-translated mode
1970 i8042.dumbkbd [HW] Pretend that controller can only read data from
1971 keyboard and cannot control its state
1972 (Don't attempt to blink the leds)
1973 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1974 i8042.nokbd [HW] Don't check/create keyboard port
1975 i8042.noloop [HW] Disable the AUX Loopback command while probing
1976 for the AUX port
1977 i8042.nomux [HW] Don't check presence of an active multiplexing
1978 controller
1979 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1980 controllers
1981 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1982 i8042.reset [HW] Reset the controller during init, cleanup and
1983 suspend-to-ram transitions, only during s2r
1984 transitions, or never reset
1985 Format: { 1 | Y | y | 0 | N | n }
1986 1, Y, y: always reset controller
1987 0, N, n: don't ever reset controller
1988 Default: only on s2r transitions on x86; most other
1989 architectures force reset to be always executed
1990 i8042.unlock [HW] Unlock (ignore) the keylock
1991 i8042.kbdreset [HW] Reset device connected to KBD port
1992 i8042.probe_defer
1993 [HW] Allow deferred probing upon i8042 probe errors
1995 i810= [HW,DRM]
1997 i915.invert_brightness=
1998 [DRM] Invert the sense of the variable that is used to
1999 set the brightness of the panel backlight. Normally a
2000 brightness value of 0 indicates backlight switched off,
2001 and the maximum of the brightness value sets the backlight
2002 to maximum brightness. If this parameter is set to 0
2003 (default) and the machine requires it, or this parameter
2004 is set to 1, a brightness value of 0 sets the backlight
2005 to maximum brightness, and the maximum of the brightness
2006 value switches the backlight off.
2007 -1 -- never invert brightness
2008 0 -- machine default
2009 1 -- force brightness inversion
2011 ia32_emulation= [X86-64]
2012 Format: <bool>
2013 When true, allows loading 32-bit programs and executing 32-bit
2014 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
2015 boot time. When false, unconditionally disables IA32 emulation.
2017 icn= [HW,ISDN]
2018 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
2021 idle= [X86,EARLY]
2022 Format: idle=poll, idle=halt, idle=nomwait
2024 idle=poll: Don't do power saving in the idle loop
2025 using HLT, but poll for rescheduling event. This will
2026 make the CPUs eat a lot more power, but may be useful
2027 to get slightly better performance in multiprocessor
2028 benchmarks. It also makes some profiling using
2029 performance counters more accurate. Please note that
2030 on systems with MONITOR/MWAIT support (like Intel
2031 EM64T CPUs) this option has no performance advantage
2032 over the normal idle loop. It may also interact badly
2033 with hyperthreading.
2035 idle=halt: Halt is forced to be used for CPU idle.
2036 In such case C2/C3 won't be used again.
2038 idle=nomwait: Disable mwait for CPU C-states
2040 idxd.sva= [HW]
2041 Format: <bool>
2042 Allow force disabling of Shared Virtual Memory (SVA)
2043 support for the idxd driver. By default it is set to
2044 true (1).
2046 idxd.tc_override= [HW]
2047 Format: <bool>
2048 Allow override of default traffic class configuration
2049 for the device. By default it is set to false (0).
2051 ieee754= [MIPS] Select IEEE Std 754 conformance mode
2052 Format: { strict | legacy | 2008 | relaxed | emulated }
2053 Default: strict
2055 Choose which programs will be accepted for execution
2056 based on the IEEE 754 NaN encoding(s) supported by
2057 the FPU and the NaN encoding requested with the value
2058 of an ELF file header flag individually set by each
2059 binary. Hardware implementations are permitted to
2060 support either or both of the legacy and the 2008 NaN
2061 encoding mode.
2063 Available settings are as follows:
2064 strict accept binaries that request a NaN encoding
2065 supported by the FPU
2066 legacy only accept legacy-NaN binaries, if supported
2067 by the FPU
2068 2008 only accept 2008-NaN binaries, if supported
2069 by the FPU
2070 relaxed accept any binaries regardless of whether
2071 supported by the FPU
2072 emulated accept any binaries but enable FPU emulator
2073 if binary mode is unsupported by the FPU.
2075 The FPU emulator is always able to support both NaN
2076 encodings, so if no FPU hardware is present or it has
2077 been disabled with 'nofpu', then the settings of
2078 'legacy' and '2008' strap the emulator accordingly,
2079 'relaxed' straps the emulator for both legacy-NaN and
2080 2008-NaN, whereas 'strict' enables legacy-NaN only on
2081 legacy processors and both NaN encodings on MIPS32 or
2082 MIPS64 CPUs.
2084 The setting for ABS.fmt/NEG.fmt instruction execution
2085 mode generally follows that for the NaN encoding,
2086 except where unsupported by hardware.
2088 ignore_loglevel [KNL,EARLY]
2089 Ignore loglevel setting - this will print /all/
2090 kernel messages to the console. Useful for debugging.
2091 We also add it as printk module parameter, so users
2092 could change it dynamically, usually by
2093 /sys/module/printk/parameters/ignore_loglevel.
2095 ignore_rlimit_data
2096 Ignore RLIMIT_DATA setting for data mappings,
2097 print warning at first misuse. Can be changed via
2098 /sys/module/kernel/parameters/ignore_rlimit_data.
2100 ihash_entries= [KNL]
2101 Set number of hash buckets for inode cache.
2103 ima_appraise= [IMA] appraise integrity measurements
2104 Format: { "off" | "enforce" | "fix" | "log" }
2105 default: "enforce"
2107 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
2108 The builtin appraise policy appraises all files
2109 owned by uid=0.
2111 ima_canonical_fmt [IMA]
2112 Use the canonical format for the binary runtime
2113 measurements, instead of host native format.
2115 ima_hash= [IMA]
2116 Format: { md5 | sha1 | rmd160 | sha256 | sha384
2117 | sha512 | ... }
2118 default: "sha1"
2120 The list of supported hash algorithms is defined
2121 in crypto/hash_info.h.
2123 ima_policy= [IMA]
2124 The builtin policies to load during IMA setup.
2125 Format: "tcb | appraise_tcb | secure_boot |
2126 fail_securely | critical_data"
2128 The "tcb" policy measures all programs exec'd, files
2129 mmap'd for exec, and all files opened with the read
2130 mode bit set by either the effective uid (euid=0) or
2131 uid=0.
2133 The "appraise_tcb" policy appraises the integrity of
2134 all files owned by root.
2136 The "secure_boot" policy appraises the integrity
2137 of files (eg. kexec kernel image, kernel modules,
2138 firmware, policy, etc) based on file signatures.
2140 The "fail_securely" policy forces file signature
2141 verification failure also on privileged mounted
2142 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
2143 flag.
2145 The "critical_data" policy measures kernel integrity
2146 critical data.
2148 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
2149 Load a policy which meets the needs of the Trusted
2150 Computing Base. This means IMA will measure all
2151 programs exec'd, files mmap'd for exec, and all files
2152 opened for read by uid=0.
2154 ima_template= [IMA]
2155 Select one of defined IMA measurements template formats.
2156 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
2157 "ima-sigv2" }
2158 Default: "ima-ng"
2160 ima_template_fmt=
2161 [IMA] Define a custom template format.
2162 Format: { "field1|...|fieldN" }
2164 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
2165 Format: <min_file_size>
2166 Set the minimal file size for using asynchronous hash.
2167 If left unspecified, ahash usage is disabled.
2169 ahash performance varies for different data sizes on
2170 different crypto accelerators. This option can be used
2171 to achieve the best performance for a particular HW.
2173 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
2174 Format: <bufsize>
2175 Set hashing buffer size. Default: 4k.
2177 ahash performance varies for different chunk sizes on
2178 different crypto accelerators. This option can be used
2179 to achieve best performance for particular HW.
2181 init= [KNL]
2182 Format: <full_path>
2183 Run specified binary instead of /sbin/init as init
2184 process.
2186 initcall_debug [KNL] Trace initcalls as they are executed. Useful
2187 for working out where the kernel is dying during
2188 startup.
2190 initcall_blacklist= [KNL] Do not execute a comma-separated list of
2191 initcall functions. Useful for debugging built-in
2192 modules and initcalls.
2194 initramfs_async= [KNL]
2195 Format: <bool>
2196 Default: 1
2197 This parameter controls whether the initramfs
2198 image is unpacked asynchronously, concurrently
2199 with devices being probed and
2200 initialized. This should normally just work,
2201 but as a debugging aid, one can get the
2202 historical behaviour of the initramfs
2203 unpacking being completed before device_ and
2204 late_ initcalls.
2206 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
2208 initrdmem= [KNL,EARLY] Specify a physical address and size from which to
2209 load the initrd. If an initrd is compiled in or
2210 specified in the bootparams, it takes priority over this
2211 setting.
2212 Format: ss[KMG],nn[KMG]
2213 Default is 0, 0
2215 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
2216 zeroes.
2217 Format: 0 | 1
2218 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2220 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
2221 Format: 0 | 1
2222 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2224 init_pkru= [X86] Specify the default memory protection keys rights
2225 register contents for all processes. 0x55555554 by
2226 default (disallow access to all but pkey 0). Can
2227 override in debugfs after boot.
2229 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2230 Format: <irq>
2232 int_pln_enable [X86] Enable power limit notification interrupt
2234 integrity_audit=[IMA]
2235 Format: { "0" | "1" }
2236 0 -- basic integrity auditing messages. (Default)
2237 1 -- additional integrity auditing messages.
2239 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2240 on
2241 Enable intel iommu driver.
2242 off
2243 Disable intel iommu driver.
2244 igfx_off [Default Off]
2245 By default, gfx is mapped as normal device. If a gfx
2246 device has a dedicated DMAR unit, the DMAR unit is
2247 bypassed by not enabling DMAR with this option. In
2248 this case, gfx device will use physical address for
2249 DMA.
2250 strict [Default Off]
2251 Deprecated, equivalent to iommu.strict=1.
2252 sp_off [Default Off]
2253 By default, super page will be supported if Intel IOMMU
2254 has the capability. With this option, super page will
2255 not be supported.
2256 sm_on
2257 Enable the Intel IOMMU scalable mode if the hardware
2258 advertises that it has support for the scalable mode
2259 translation.
2260 sm_off
2261 Disallow use of the Intel IOMMU scalable mode.
2262 tboot_noforce [Default Off]
2263 Do not force the Intel IOMMU enabled under tboot.
2264 By default, tboot will force Intel IOMMU on, which
2265 could harm performance of some high-throughput
2266 devices like 40GBit network cards, even if identity
2267 mapping is enabled.
2268 Note that using this option lowers the security
2269 provided by tboot because it makes the system
2270 vulnerable to DMA attacks.
2272 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2273 0 disables intel_idle and fall back on acpi_idle.
2274 1 to 9 specify maximum depth of C-state.
2276 intel_pstate= [X86,EARLY]
2277 disable
2278 Do not enable intel_pstate as the default
2279 scaling driver for the supported processors
2280 active
2281 Use intel_pstate driver to bypass the scaling
2282 governors layer of cpufreq and provides it own
2283 algorithms for p-state selection. There are two
2284 P-state selection algorithms provided by
2285 intel_pstate in the active mode: powersave and
2286 performance. The way they both operate depends
2287 on whether or not the hardware managed P-states
2288 (HWP) feature has been enabled in the processor
2289 and possibly on the processor model.
2290 passive
2291 Use intel_pstate as a scaling driver, but configure it
2292 to work with generic cpufreq governors (instead of
2293 enabling its internal governor). This mode cannot be
2294 used along with the hardware-managed P-states (HWP)
2295 feature.
2296 force
2297 Enable intel_pstate on systems that prohibit it by default
2298 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2299 instead of acpi-cpufreq may disable platform features, such
2300 as thermal controls and power capping, that rely on ACPI
2301 P-States information being indicated to OSPM and therefore
2302 should be used with caution. This option does not work with
2303 processors that aren't supported by the intel_pstate driver
2304 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2305 no_hwp
2306 Do not enable hardware P state control (HWP)
2307 if available.
2308 hwp_only
2309 Only load intel_pstate on systems which support
2310 hardware P state control (HWP) if available.
2311 support_acpi_ppc
2312 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2313 Description Table, specifies preferred power management
2314 profile as "Enterprise Server" or "Performance Server",
2315 then this feature is turned on by default.
2316 per_cpu_perf_limits
2317 Allow per-logical-CPU P-State performance control limits using
2318 cpufreq sysfs interface
2320 intremap= [X86-64,Intel-IOMMU,EARLY]
2321 on enable Interrupt Remapping (default)
2322 off disable Interrupt Remapping
2323 nosid disable Source ID checking
2324 no_x2apic_optout
2325 BIOS x2APIC opt-out request will be ignored
2326 nopost disable Interrupt Posting
2327 posted_msi
2328 enable MSIs delivered as posted interrupts
2330 iomem= Disable strict checking of access to MMIO memory
2331 strict regions from userspace.
2332 relaxed
2334 iommu= [X86,EARLY]
2336 off
2337 Don't initialize and use any kind of IOMMU.
2339 force
2340 Force the use of the hardware IOMMU even when
2341 it is not actually needed (e.g. because < 3 GB
2342 memory).
2344 noforce
2345 Don't force hardware IOMMU usage when it is not
2346 needed. (default).
2348 biomerge
2349 panic
2350 nopanic
2351 merge
2352 nomerge
2354 soft
2355 Use software bounce buffering (SWIOTLB) (default for
2356 Intel machines). This can be used to prevent the usage
2357 of an available hardware IOMMU.
2359 [X86]
2360 pt
2361 [X86]
2362 nopt
2363 [PPC/POWERNV]
2364 nobypass
2365 Disable IOMMU bypass, using IOMMU for PCI devices.
2367 [X86]
2368 AMD Gart HW IOMMU-specific options:
2370 <size>
2371 Set the size of the remapping area in bytes.
2373 allowed
2374 Overwrite iommu off workarounds for specific chipsets
2376 fullflush
2377 Flush IOMMU on each allocation (default).
2379 nofullflush
2380 Don't use IOMMU fullflush.
2382 memaper[=<order>]
2383 Allocate an own aperture over RAM with size
2384 32MB<<order. (default: order=1, i.e. 64MB)
2386 merge
2387 Do scatter-gather (SG) merging. Implies "force"
2388 (experimental).
2390 nomerge
2391 Don't do scatter-gather (SG) merging.
2393 noaperture
2394 Ask the IOMMU not to touch the aperture for AGP.
2396 noagp
2397 Don't initialize the AGP driver and use full aperture.
2399 panic
2400 Always panic when IOMMU overflows.
2402 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
2403 Format: { "0" | "1" }
2404 0 - Try to allocate a 32-bit DMA address first, before
2405 falling back to the full range if needed.
2406 1 - Allocate directly from the full usable range,
2407 forcing Dual Address Cycle for PCI cards supporting
2408 greater than 32-bit addressing.
2410 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
2411 Format: { "0" | "1" }
2412 0 - Lazy mode.
2413 Request that DMA unmap operations use deferred
2414 invalidation of hardware TLBs, for increased
2415 throughput at the cost of reduced device isolation.
2416 Will fall back to strict mode if not supported by
2417 the relevant IOMMU driver.
2418 1 - Strict mode.
2419 DMA unmap operations invalidate IOMMU hardware TLBs
2420 synchronously.
2421 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2422 Note: on x86, strict mode specified via one of the
2423 legacy driver-specific options takes precedence.
2425 iommu.passthrough=
2426 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
2427 Format: { "0" | "1" }
2428 0 - Use IOMMU translation for DMA.
2429 1 - Bypass the IOMMU for DMA.
2430 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2432 io7= [HW] IO7 for Marvel-based Alpha systems
2433 See comment before marvel_specify_io7 in
2434 arch/alpha/kernel/core_marvel.c.
2436 io_delay= [X86,EARLY] I/O delay method
2437 0x80
2438 Standard port 0x80 based delay
2439 0xed
2440 Alternate port 0xed based delay (needed on some systems)
2441 udelay
2442 Simple two microseconds delay
2443 none
2444 No delay
2446 ip= [IP_PNP]
2447 See Documentation/admin-guide/nfs/nfsroot.rst.
2449 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
2450 IPC identifiers from 32,768 to 16,777,216.
2452 ipe.enforce= [IPE]
2453 Format: <bool>
2454 Determine whether IPE starts in permissive (0) or
2455 enforce (1) mode. The default is enforce.
2457 ipe.success_audit=
2458 [IPE]
2459 Format: <bool>
2460 Start IPE with success auditing enabled, emitting
2461 an audit event when a binary is allowed. The default
2462 is 0.
2464 irqaffinity= [SMP] Set the default irq affinity mask
2465 The argument is a cpu list, as described above.
2467 irqchip.gicv2_force_probe=
2468 [ARM,ARM64,EARLY]
2469 Format: <bool>
2470 Force the kernel to look for the second 4kB page
2471 of a GICv2 controller even if the memory range
2472 exposed by the device tree is too small.
2474 irqchip.gicv3_nolpi=
2475 [ARM,ARM64,EARLY]
2476 Force the kernel to ignore the availability of
2477 LPIs (and by consequence ITSs). Intended for system
2478 that use the kernel as a bootloader, and thus want
2479 to let secondary kernels in charge of setting up
2480 LPIs.
2482 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
2483 Enables support for pseudo-NMIs in the kernel. This
2484 requires the kernel to be built with
2485 CONFIG_ARM64_PSEUDO_NMI.
2487 irqfixup [HW]
2488 When an interrupt is not handled search all handlers
2489 for it. Intended to get systems with badly broken
2490 firmware running.
2492 irqpoll [HW]
2493 When an interrupt is not handled search all handlers
2494 for it. Also check all handlers each timer
2495 interrupt. Intended to get systems with badly broken
2496 firmware running.
2498 isapnp= [ISAPNP]
2499 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2501 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2502 [Deprecated - use cpusets instead]
2503 Format: [flag-list,]<cpu-list>
2505 Specify one or more CPUs to isolate from disturbances
2506 specified in the flag list (default: domain):
2508 nohz
2509 Disable the tick when a single task runs as well as
2510 disabling other kernel noises like having RCU callbacks
2511 offloaded. This is equivalent to the nohz_full parameter.
2513 A residual 1Hz tick is offloaded to workqueues, which you
2514 need to affine to housekeeping through the global
2515 workqueue's affinity configured via the
2516 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2517 by using the 'domain' flag described below.
2519 NOTE: by default the global workqueue runs on all CPUs,
2520 so to protect individual CPUs the 'cpumask' file has to
2521 be configured manually after bootup.
2523 domain
2524 Isolate from the general SMP balancing and scheduling
2525 algorithms. Note that performing domain isolation this way
2526 is irreversible: it's not possible to bring back a CPU to
2527 the domains once isolated through isolcpus. It's strongly
2528 advised to use cpusets instead to disable scheduler load
2529 balancing through the "cpuset.sched_load_balance" file.
2530 It offers a much more flexible interface where CPUs can
2531 move in and out of an isolated set anytime.
2533 You can move a process onto or off an "isolated" CPU via
2534 the CPU affinity syscalls or cpuset.
2535 <cpu number> begins at 0 and the maximum value is
2536 "number of CPUs in system - 1".
2538 managed_irq
2540 Isolate from being targeted by managed interrupts
2541 which have an interrupt mask containing isolated
2542 CPUs. The affinity of managed interrupts is
2543 handled by the kernel and cannot be changed via
2544 the /proc/irq/* interfaces.
2546 This isolation is best effort and only effective
2547 if the automatically assigned interrupt mask of a
2548 device queue contains isolated and housekeeping
2549 CPUs. If housekeeping CPUs are online then such
2550 interrupts are directed to the housekeeping CPU
2551 so that IO submitted on the housekeeping CPU
2552 cannot disturb the isolated CPU.
2554 If a queue's affinity mask contains only isolated
2555 CPUs then this parameter has no effect on the
2556 interrupt routing decision, though interrupts are
2557 only delivered when tasks running on those
2558 isolated CPUs submit IO. IO submitted on
2559 housekeeping CPUs has no influence on those
2560 queues.
2562 The format of <cpu-list> is described above.
2564 iucv= [HW,NET]
2566 ivrs_ioapic [HW,X86-64]
2567 Provide an override to the IOAPIC-ID<->DEVICE-ID
2568 mapping provided in the IVRS ACPI table.
2569 By default, PCI segment is 0, and can be omitted.
2571 For example, to map IOAPIC-ID decimal 10 to
2572 PCI segment 0x1 and PCI device 00:14.0,
2573 write the parameter as:
2574 ivrs_ioapic=10@0001:00:14.0
2576 Deprecated formats:
2577 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2578 write the parameter as:
2579 ivrs_ioapic[10]=00:14.0
2580 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2581 PCI device 00:14.0 write the parameter as:
2582 ivrs_ioapic[10]=0001:00:14.0
2584 ivrs_hpet [HW,X86-64]
2585 Provide an override to the HPET-ID<->DEVICE-ID
2586 mapping provided in the IVRS ACPI table.
2587 By default, PCI segment is 0, and can be omitted.
2589 For example, to map HPET-ID decimal 10 to
2590 PCI segment 0x1 and PCI device 00:14.0,
2591 write the parameter as:
2592 ivrs_hpet=10@0001:00:14.0
2594 Deprecated formats:
2595 * To map HPET-ID decimal 0 to PCI device 00:14.0
2596 write the parameter as:
2597 ivrs_hpet[0]=00:14.0
2598 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2599 PCI device 00:14.0 write the parameter as:
2600 ivrs_ioapic[10]=0001:00:14.0
2602 ivrs_acpihid [HW,X86-64]
2603 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2604 mapping provided in the IVRS ACPI table.
2605 By default, PCI segment is 0, and can be omitted.
2607 For example, to map UART-HID:UID AMD0020:0 to
2608 PCI segment 0x1 and PCI device ID 00:14.5,
2609 write the parameter as:
2610 ivrs_acpihid=AMD0020:0@0001:00:14.5
2612 Deprecated formats:
2613 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2614 PCI device ID 00:14.5, write the parameter as:
2615 ivrs_acpihid[00:14.5]=AMD0020:0
2616 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2617 PCI device ID 00:14.5, write the parameter as:
2618 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2620 js= [HW,JOY] Analog joystick
2621 See Documentation/input/joydev/joystick.rst.
2623 kasan_multi_shot
2624 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2625 report on every invalid memory access. Without this
2626 parameter KASAN will print report only for the first
2627 invalid access.
2629 keep_bootcon [KNL,EARLY]
2630 Do not unregister boot console at start. This is only
2631 useful for debugging when something happens in the window
2632 between unregistering the boot console and initializing
2633 the real console.
2635 keepinitrd [HW,ARM] See retain_initrd.
2637 kernelcore= [KNL,X86,PPC,EARLY]
2638 Format: nn[KMGTPE] | nn% | "mirror"
2639 This parameter specifies the amount of memory usable by
2640 the kernel for non-movable allocations. The requested
2641 amount is spread evenly throughout all nodes in the
2642 system as ZONE_NORMAL. The remaining memory is used for
2643 movable memory in its own zone, ZONE_MOVABLE. In the
2644 event, a node is too small to have both ZONE_NORMAL and
2645 ZONE_MOVABLE, kernelcore memory will take priority and
2646 other nodes will have a larger ZONE_MOVABLE.
2648 ZONE_MOVABLE is used for the allocation of pages that
2649 may be reclaimed or moved by the page migration
2650 subsystem. Note that allocations like PTEs-from-HighMem
2651 still use the HighMem zone if it exists, and the Normal
2652 zone if it does not.
2654 It is possible to specify the exact amount of memory in
2655 the form of "nn[KMGTPE]", a percentage of total system
2656 memory in the form of "nn%", or "mirror". If "mirror"
2657 option is specified, mirrored (reliable) memory is used
2658 for non-movable allocations and remaining memory is used
2659 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2660 are exclusive, so you cannot specify multiple forms.
2662 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
2663 Format: <Controller#>[,poll interval]
2664 The controller # is the number of the ehci usb debug
2665 port as it is probed via PCI. The poll interval is
2666 optional and is the number seconds in between
2667 each poll cycle to the debug port in case you need
2668 the functionality for interrupting the kernel with
2669 gdb or control-c on the dbgp connection. When
2670 not using this parameter you use sysrq-g to break into
2671 the kernel debugger.
2673 kgdboc= [KGDB,HW] kgdb over consoles.
2674 Requires a tty driver that supports console polling,
2675 or a supported polling keyboard driver (non-usb).
2676 Serial only format: <serial_device>[,baud]
2677 keyboard only format: kbd
2678 keyboard and serial format: kbd,<serial_device>[,baud]
2679 Optional Kernel mode setting:
2680 kms, kbd format: kms,kbd
2681 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2683 kgdboc_earlycon= [KGDB,HW,EARLY]
2684 If the boot console provides the ability to read
2685 characters and can work in polling mode, you can use
2686 this parameter to tell kgdb to use it as a backend
2687 until the normal console is registered. Intended to
2688 be used together with the kgdboc parameter which
2689 specifies the normal console to transition to.
2691 The name of the early console should be specified
2692 as the value of this parameter. Note that the name of
2693 the early console might be different than the tty
2694 name passed to kgdboc. It's OK to leave the value
2695 blank and the first boot console that implements
2696 read() will be picked.
2698 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
2699 kernel debugger at the earliest opportunity.
2701 kmac= [MIPS] Korina ethernet MAC address.
2702 Configure the RouterBoard 532 series on-chip
2703 Ethernet adapter MAC address.
2705 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
2706 Valid arguments: on, off
2707 Default: on
2708 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2709 the default is off.
2711 kprobe_event=[probe-list]
2712 [FTRACE] Add kprobe events and enable at boot time.
2713 The probe-list is a semicolon delimited list of probe
2714 definitions. Each definition is same as kprobe_events
2715 interface, but the parameters are comma delimited.
2716 For example, to add a kprobe event on vfs_read with
2717 arg1 and arg2, add to the command line;
2719 kprobe_event=p,vfs_read,$arg1,$arg2
2721 See also Documentation/trace/kprobetrace.rst "Kernel
2722 Boot Parameter" section.
2724 kpti= [ARM64,EARLY] Control page table isolation of
2725 user and kernel address spaces.
2726 Default: enabled on cores which need mitigation.
2727 0: force disabled
2728 1: force enabled
2730 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2731 CONFIG_KUNIT to be set to be fully enabled. The
2732 default value can be overridden via
2733 KUNIT_DEFAULT_ENABLED.
2734 Default is 1 (enabled)
2736 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2737 Default is 0 (don't ignore, but inject #GP)
2739 kvm.eager_page_split=
2740 [KVM,X86] Controls whether or not KVM will try to
2741 proactively split all huge pages during dirty logging.
2742 Eager page splitting reduces interruptions to vCPU
2743 execution by eliminating the write-protection faults
2744 and MMU lock contention that would otherwise be
2745 required to split huge pages lazily.
2747 VM workloads that rarely perform writes or that write
2748 only to a small region of VM memory may benefit from
2749 disabling eager page splitting to allow huge pages to
2750 still be used for reads.
2752 The behavior of eager page splitting depends on whether
2753 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2754 disabled, all huge pages in a memslot will be eagerly
2755 split when dirty logging is enabled on that memslot. If
2756 enabled, eager page splitting will be performed during
2757 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2758 cleared.
2760 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2762 Default is Y (on).
2764 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86]
2765 If enabled, KVM will enable virtualization in hardware
2766 when KVM is loaded, and disable virtualization when KVM
2767 is unloaded (if KVM is built as a module).
2769 If disabled, KVM will dynamically enable and disable
2770 virtualization on-demand when creating and destroying
2771 VMs, i.e. on the 0=>1 and 1=>0 transitions of the
2772 number of VMs.
2774 Enabling virtualization at module load avoids potential
2775 latency for creation of the 0=>1 VM, as KVM serializes
2776 virtualization enabling across all online CPUs. The
2777 "cost" of enabling virtualization when KVM is loaded,
2778 is that doing so may interfere with using out-of-tree
2779 hypervisors that want to "own" virtualization hardware.
2781 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2782 Default is false (don't support).
2784 kvm.nx_huge_pages=
2785 [KVM] Controls the software workaround for the
2786 X86_BUG_ITLB_MULTIHIT bug.
2787 force : Always deploy workaround.
2788 off : Never deploy workaround.
2789 auto : Deploy workaround based on the presence of
2790 X86_BUG_ITLB_MULTIHIT.
2792 Default is 'auto'.
2794 If the software workaround is enabled for the host,
2795 guests do need not to enable it for nested guests.
2797 kvm.nx_huge_pages_recovery_ratio=
2798 [KVM] Controls how many 4KiB pages are periodically zapped
2799 back to huge pages. 0 disables the recovery, otherwise if
2800 the value is N KVM will zap 1/Nth of the 4KiB pages every
2801 period (see below). The default is 60.
2803 kvm.nx_huge_pages_recovery_period_ms=
2804 [KVM] Controls the time period at which KVM zaps 4KiB pages
2805 back to huge pages. If the value is a non-zero N, KVM will
2806 zap a portion (see ratio above) of the pages every N msecs.
2807 If the value is 0 (the default), KVM will pick a period based
2808 on the ratio, such that a page is zapped after 1 hour on average.
2810 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in
2811 KVM/SVM. Default is 1 (enabled).
2813 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables,
2814 a.k.a. Two-Dimensional Page Tables. Default is 1
2815 (enabled). Disable by KVM if hardware lacks support
2816 for NPT.
2818 kvm-arm.mode=
2819 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
2820 operation.
2822 none: Forcefully disable KVM.
2824 nvhe: Standard nVHE-based mode, without support for
2825 protected guests.
2827 protected: Mode with support for guests whose state is
2828 kept private from the host, using VHE or
2829 nVHE depending on HW support.
2831 nested: VHE-based mode with support for nested
2832 virtualization. Requires at least ARMv8.4
2833 hardware (with FEAT_NV2).
2835 Defaults to VHE/nVHE based on hardware support. Setting
2836 mode to "protected" will disable kexec and hibernation
2837 for the host. To force nVHE on VHE hardware, add
2838 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the
2839 command-line.
2840 "nested" is experimental and should be used with
2841 extreme caution.
2843 kvm-arm.vgic_v3_group0_trap=
2844 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
2845 system registers
2847 kvm-arm.vgic_v3_group1_trap=
2848 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
2849 system registers
2851 kvm-arm.vgic_v3_common_trap=
2852 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
2853 system registers
2855 kvm-arm.vgic_v4_enable=
2856 [KVM,ARM,EARLY] Allow use of GICv4 for direct
2857 injection of LPIs.
2859 kvm-arm.wfe_trap_policy=
2860 [KVM,ARM] Control when to set WFE instruction trap for
2861 KVM VMs. Traps are allowed but not guaranteed by the
2862 CPU architecture.
2864 trap: set WFE instruction trap
2866 notrap: clear WFE instruction trap
2868 kvm-arm.wfi_trap_policy=
2869 [KVM,ARM] Control when to set WFI instruction trap for
2870 KVM VMs. Traps are allowed but not guaranteed by the
2871 CPU architecture.
2873 trap: set WFI instruction trap
2875 notrap: clear WFI instruction trap
2877 kvm_cma_resv_ratio=n [PPC,EARLY]
2878 Reserves given percentage from system memory area for
2879 contiguous memory allocation for KVM hash pagetable
2880 allocation.
2881 By default it reserves 5% of total system memory.
2882 Format: <integer>
2883 Default: 5
2885 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables,
2886 a.k.a. Two-Dimensional Page Tables. Default is 1
2887 (enabled). Disable by KVM if hardware lacks support
2888 for EPT.
2890 kvm-intel.emulate_invalid_guest_state=
2891 [KVM,Intel] Control whether to emulate invalid guest
2892 state. Ignored if kvm-intel.enable_unrestricted_guest=1,
2893 as guest state is never invalid for unrestricted
2894 guests. This param doesn't apply to nested guests (L2),
2895 as KVM never emulates invalid L2 guest state.
2896 Default is 1 (enabled).
2898 kvm-intel.flexpriority=
2899 [KVM,Intel] Control KVM's use of FlexPriority feature
2900 (TPR shadow). Default is 1 (enabled). Disable by KVM if
2901 hardware lacks support for it.
2903 kvm-intel.nested=
2904 [KVM,Intel] Control nested virtualization feature in
2905 KVM/VMX. Default is 1 (enabled).
2907 kvm-intel.unrestricted_guest=
2908 [KVM,Intel] Control KVM's use of unrestricted guest
2909 feature (virtualized real and unpaged mode). Default
2910 is 1 (enabled). Disable by KVM if EPT is disabled or
2911 hardware lacks support for it.
2913 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2914 CVE-2018-3620.
2916 Valid arguments: never, cond, always
2918 always: L1D cache flush on every VMENTER.
2919 cond: Flush L1D on VMENTER only when the code between
2920 VMEXIT and VMENTER can leak host memory.
2921 never: Disables the mitigation
2923 Default is cond (do L1 cache flush in specific instances)
2925 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor
2926 Identification feature (tagged TLBs). Default is 1
2927 (enabled). Disable by KVM if hardware lacks support
2928 for it.
2930 l1d_flush= [X86,INTEL,EARLY]
2931 Control mitigation for L1D based snooping vulnerability.
2933 Certain CPUs are vulnerable to an exploit against CPU
2934 internal buffers which can forward information to a
2935 disclosure gadget under certain conditions.
2937 In vulnerable processors, the speculatively
2938 forwarded data can be used in a cache side channel
2939 attack, to access data to which the attacker does
2940 not have direct access.
2942 This parameter controls the mitigation. The
2943 options are:
2945 on - enable the interface for the mitigation
2947 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
2948 affected CPUs
2950 The kernel PTE inversion protection is unconditionally
2951 enabled and cannot be disabled.
2953 full
2954 Provides all available mitigations for the
2955 L1TF vulnerability. Disables SMT and
2956 enables all mitigations in the
2957 hypervisors, i.e. unconditional L1D flush.
2959 SMT control and L1D flush control via the
2960 sysfs interface is still possible after
2961 boot. Hypervisors will issue a warning
2962 when the first VM is started in a
2963 potentially insecure configuration,
2964 i.e. SMT enabled or L1D flush disabled.
2966 full,force
2967 Same as 'full', but disables SMT and L1D
2968 flush runtime control. Implies the
2969 'nosmt=force' command line option.
2970 (i.e. sysfs control of SMT is disabled.)
2972 flush
2973 Leaves SMT enabled and enables the default
2974 hypervisor mitigation, i.e. conditional
2975 L1D flush.
2977 SMT control and L1D flush control via the
2978 sysfs interface is still possible after
2979 boot. Hypervisors will issue a warning
2980 when the first VM is started in a
2981 potentially insecure configuration,
2982 i.e. SMT enabled or L1D flush disabled.
2984 flush,nosmt
2986 Disables SMT and enables the default
2987 hypervisor mitigation.
2989 SMT control and L1D flush control via the
2990 sysfs interface is still possible after
2991 boot. Hypervisors will issue a warning
2992 when the first VM is started in a
2993 potentially insecure configuration,
2994 i.e. SMT enabled or L1D flush disabled.
2996 flush,nowarn
2997 Same as 'flush', but hypervisors will not
2998 warn when a VM is started in a potentially
2999 insecure configuration.
3001 off
3002 Disables hypervisor mitigations and doesn't
3003 emit any warnings.
3004 It also drops the swap size and available
3005 RAM limit restriction on both hypervisor and
3006 bare metal.
3008 Default is 'flush'.
3010 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
3012 l2cr= [PPC]
3014 l3cr= [PPC]
3016 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
3017 disabled it.
3019 lapic= [X86,APIC] Do not use TSC deadline
3020 value for LAPIC timer one-shot implementation. Default
3021 back to the programmable timer unit in the LAPIC.
3022 Format: notscdeadline
3024 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
3025 in C2 power state.
3027 libata.dma= [LIBATA] DMA control
3028 libata.dma=0 Disable all PATA and SATA DMA
3029 libata.dma=1 PATA and SATA Disk DMA only
3030 libata.dma=2 ATAPI (CDROM) DMA only
3031 libata.dma=4 Compact Flash DMA only
3032 Combinations also work, so libata.dma=3 enables DMA
3033 for disks and CDROMs, but not CFs.
3035 libata.ignore_hpa= [LIBATA] Ignore HPA limit
3036 libata.ignore_hpa=0 keep BIOS limits (default)
3037 libata.ignore_hpa=1 ignore limits, using full disk
3039 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
3040 when set.
3041 Format: <int>
3043 libata.force= [LIBATA] Force configurations. The format is a comma-
3044 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
3045 PORT and DEVICE are decimal numbers matching port, link
3046 or device. Basically, it matches the ATA ID string
3047 printed on console by libata. If the whole ID part is
3048 omitted, the last PORT and DEVICE values are used. If
3049 ID hasn't been specified yet, the configuration applies
3050 to all ports, links and devices.
3052 If only DEVICE is omitted, the parameter applies to
3053 the port and all links and devices behind it. DEVICE
3054 number of 0 either selects the first device or the
3055 first fan-out link behind PMP device. It does not
3056 select the host link. DEVICE number of 15 selects the
3057 host link and device attached to it.
3059 The VAL specifies the configuration to force. As long
3060 as there is no ambiguity, shortcut notation is allowed.
3061 For example, both 1.5 and 1.5G would work for 1.5Gbps.
3062 The following configurations can be forced.
3064 * Cable type: 40c, 80c, short40c, unk, ign or sata.
3065 Any ID with matching PORT is used.
3067 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
3069 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
3070 udma[/][16,25,33,44,66,100,133] notation is also
3071 allowed.
3073 * nohrst, nosrst, norst: suppress hard, soft and both
3074 resets.
3076 * rstonce: only attempt one reset during hot-unplug
3077 link recovery.
3079 * [no]dbdelay: Enable or disable the extra 200ms delay
3080 before debouncing a link PHY and device presence
3081 detection.
3083 * [no]ncq: Turn on or off NCQ.
3085 * [no]ncqtrim: Enable or disable queued DSM TRIM.
3087 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
3089 * [no]trim: Enable or disable (unqueued) TRIM.
3091 * trim_zero: Indicate that TRIM command zeroes data.
3093 * max_trim_128m: Set 128M maximum trim size limit.
3095 * [no]dma: Turn on or off DMA transfers.
3097 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
3099 * atapi_mod16_dma: Enable the use of ATAPI DMA for
3100 commands that are not a multiple of 16 bytes.
3102 * [no]dmalog: Enable or disable the use of the
3103 READ LOG DMA EXT command to access logs.
3105 * [no]iddevlog: Enable or disable access to the
3106 identify device data log.
3108 * [no]logdir: Enable or disable access to the general
3109 purpose log directory.
3111 * max_sec_128: Set transfer size limit to 128 sectors.
3113 * max_sec_1024: Set or clear transfer size limit to
3114 1024 sectors.
3116 * max_sec_lba48: Set or clear transfer size limit to
3117 65535 sectors.
3119 * [no]lpm: Enable or disable link power management.
3121 * [no]setxfer: Indicate if transfer speed mode setting
3122 should be skipped.
3124 * [no]fua: Disable or enable FUA (Force Unit Access)
3125 support for devices supporting this feature.
3127 * dump_id: Dump IDENTIFY data.
3129 * disable: Disable this device.
3131 If there are multiple matching configurations changing
3132 the same attribute, the last one is used.
3134 load_ramdisk= [RAM] [Deprecated]
3136 lockd.nlm_grace_period=P [NFS] Assign grace period.
3137 Format: <integer>
3139 lockd.nlm_tcpport=N [NFS] Assign TCP port.
3140 Format: <integer>
3142 lockd.nlm_timeout=T [NFS] Assign timeout value.
3143 Format: <integer>
3145 lockd.nlm_udpport=M [NFS] Assign UDP port.
3146 Format: <integer>
3148 lockdown= [SECURITY,EARLY]
3149 { integrity | confidentiality }
3150 Enable the kernel lockdown feature. If set to
3151 integrity, kernel features that allow userland to
3152 modify the running kernel are disabled. If set to
3153 confidentiality, kernel features that allow userland
3154 to extract confidential information from the kernel
3155 are also disabled.
3157 locktorture.acq_writer_lim= [KNL]
3158 Set the time limit in jiffies for a lock
3159 acquisition. Acquisitions exceeding this limit
3160 will result in a splat once they do complete.
3162 locktorture.bind_readers= [KNL]
3163 Specify the list of CPUs to which the readers are
3164 to be bound.
3166 locktorture.bind_writers= [KNL]
3167 Specify the list of CPUs to which the writers are
3168 to be bound.
3170 locktorture.call_rcu_chains= [KNL]
3171 Specify the number of self-propagating call_rcu()
3172 chains to set up. These are used to ensure that
3173 there is a high probability of an RCU grace period
3174 in progress at any given time. Defaults to 0,
3175 which disables these call_rcu() chains.
3177 locktorture.long_hold= [KNL]
3178 Specify the duration in milliseconds for the
3179 occasional long-duration lock hold time. Defaults
3180 to 100 milliseconds. Select 0 to disable.
3182 locktorture.nested_locks= [KNL]
3183 Specify the maximum lock nesting depth that
3184 locktorture is to exercise, up to a limit of 8
3185 (MAX_NESTED_LOCKS). Specify zero to disable.
3186 Note that this parameter is ineffective on types
3187 of locks that do not support nested acquisition.
3189 locktorture.nreaders_stress= [KNL]
3190 Set the number of locking read-acquisition kthreads.
3191 Defaults to being automatically set based on the
3192 number of online CPUs.
3194 locktorture.nwriters_stress= [KNL]
3195 Set the number of locking write-acquisition kthreads.
3197 locktorture.onoff_holdoff= [KNL]
3198 Set time (s) after boot for CPU-hotplug testing.
3200 locktorture.onoff_interval= [KNL]
3201 Set time (s) between CPU-hotplug operations, or
3202 zero to disable CPU-hotplug testing.
3204 locktorture.rt_boost= [KNL]
3205 Do periodic testing of real-time lock priority
3206 boosting. Select 0 to disable, 1 to boost
3207 only rt_mutex, and 2 to boost unconditionally.
3208 Defaults to 2, which might seem to be an
3209 odd choice, but which should be harmless for
3210 non-real-time spinlocks, due to their disabling
3211 of preemption. Note that non-realtime mutexes
3212 disable boosting.
3214 locktorture.rt_boost_factor= [KNL]
3215 Number that determines how often and for how
3216 long priority boosting is exercised. This is
3217 scaled down by the number of writers, so that the
3218 number of boosts per unit time remains roughly
3219 constant as the number of writers increases.
3220 On the other hand, the duration of each boost
3221 increases with the number of writers.
3223 locktorture.shuffle_interval= [KNL]
3224 Set task-shuffle interval (jiffies). Shuffling
3225 tasks allows some CPUs to go into dyntick-idle
3226 mode during the locktorture test.
3228 locktorture.shutdown_secs= [KNL]
3229 Set time (s) after boot system shutdown. This
3230 is useful for hands-off automated testing.
3232 locktorture.stat_interval= [KNL]
3233 Time (s) between statistics printk()s.
3235 locktorture.stutter= [KNL]
3236 Time (s) to stutter testing, for example,
3237 specifying five seconds causes the test to run for
3238 five seconds, wait for five seconds, and so on.
3239 This tests the locking primitive's ability to
3240 transition abruptly to and from idle.
3242 locktorture.torture_type= [KNL]
3243 Specify the locking implementation to test.
3245 locktorture.verbose= [KNL]
3246 Enable additional printk() statements.
3248 locktorture.writer_fifo= [KNL]
3249 Run the write-side locktorture kthreads at
3250 sched_set_fifo() real-time priority.
3252 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
3253 Format: <irq>
3255 loglevel= [KNL,EARLY]
3256 All Kernel Messages with a loglevel smaller than the
3257 console loglevel will be printed to the console. It can
3258 also be changed with klogd or other programs. The
3259 loglevels are defined as follows:
3261 0 (KERN_EMERG) system is unusable
3262 1 (KERN_ALERT) action must be taken immediately
3263 2 (KERN_CRIT) critical conditions
3264 3 (KERN_ERR) error conditions
3265 4 (KERN_WARNING) warning conditions
3266 5 (KERN_NOTICE) normal but significant condition
3267 6 (KERN_INFO) informational
3268 7 (KERN_DEBUG) debug-level messages
3270 log_buf_len=n[KMG] [KNL,EARLY]
3271 Sets the size of the printk ring buffer, in bytes.
3272 n must be a power of two and greater than the
3273 minimal size. The minimal size is defined by
3274 LOG_BUF_SHIFT kernel config parameter. There
3275 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
3276 parameter that allows to increase the default size
3277 depending on the number of CPUs. See init/Kconfig
3278 for more details.
3280 logo.nologo [FB] Disables display of the built-in Linux logo.
3281 This may be used to provide more screen space for
3282 kernel log messages and is useful when debugging
3283 kernel boot problems.
3285 lp=0 [LP] Specify parallel ports to use, e.g,
3286 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
3287 lp=reset first parallel port). 'lp=0' disables the
3288 lp=auto printer driver. 'lp=reset' (which can be
3289 specified in addition to the ports) causes
3290 attached printers to be reset. Using
3291 lp=port1,port2,... specifies the parallel ports
3292 to associate lp devices with, starting with
3293 lp0. A port specification may be 'none' to skip
3294 that lp device, or a parport name such as
3295 'parport0'. Specifying 'lp=auto' instead of a
3296 port specification list means that device IDs
3297 from each port should be examined, to see if
3298 an IEEE 1284-compliant printer is attached; if
3299 so, the driver will manage that printer.
3300 See also header of drivers/char/lp.c.
3302 lpj=n [KNL]
3303 Sets loops_per_jiffy to given constant, thus avoiding
3304 time-consuming boot-time autodetection (up to 250 ms per
3305 CPU). 0 enables autodetection (default). To determine
3306 the correct value for your kernel, boot with normal
3307 autodetection and see what value is printed. Note that
3308 on SMP systems the preset will be applied to all CPUs,
3309 which is likely to cause problems if your CPUs need
3310 significantly divergent settings. An incorrect value
3311 will cause delays in the kernel to be wrong, leading to
3312 unpredictable I/O errors and other breakage. Although
3313 unlikely, in the extreme case this might damage your
3314 hardware.
3316 lsm.debug [SECURITY] Enable LSM initialization debugging output.
3318 lsm=lsm1,...,lsmN
3319 [SECURITY] Choose order of LSM initialization. This
3320 overrides CONFIG_LSM, and the "security=" parameter.
3322 machtype= [Loongson] Share the same kernel image file between
3323 different yeeloong laptops.
3324 Example: machtype=lemote-yeeloong-2f-7inch
3326 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
3327 will bring up during bootup. maxcpus=n : n >= 0 limits
3328 the kernel to bring up 'n' processors. Surely after
3329 bootup you can bring up the other plugged cpu by executing
3330 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
3331 only takes effect during system bootup.
3332 While n=0 is a special case, it is equivalent to "nosmp",
3333 which also disables the IO APIC.
3335 max_loop= [LOOP] The number of loop block devices that get
3336 (loop.max_loop) unconditionally pre-created at init time. The default
3337 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
3338 of statically allocating a predefined number, loop
3339 devices can be requested on-demand with the
3340 /dev/loop-control interface.
3342 mce= [X86-{32,64}]
3344 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables.
3346 off
3347 disable machine check
3349 no_cmci
3350 disable CMCI(Corrected Machine Check Interrupt) that
3351 Intel processor supports. Usually this disablement is
3352 not recommended, but it might be handy if your
3353 hardware is misbehaving.
3355 Note that you'll get more problems without CMCI than
3356 with due to the shared banks, i.e. you might get
3357 duplicated error logs.
3359 dont_log_ce
3360 don't make logs for corrected errors. All events
3361 reported as corrected are silently cleared by OS. This
3362 option will be useful if you have no interest in any
3363 of corrected errors.
3365 ignore_ce
3366 disable features for corrected errors, e.g.
3367 polling timer and CMCI. All events reported as
3368 corrected are not cleared by OS and remained in its
3369 error banks.
3371 Usually this disablement is not recommended, however
3372 if there is an agent checking/clearing corrected
3373 errors (e.g. BIOS or hardware monitoring
3374 applications), conflicting with OS's error handling,
3375 and you cannot deactivate the agent, then this option
3376 will be a help.
3378 no_lmce
3379 do not opt-in to Local MCE delivery. Use legacy method
3380 to broadcast MCEs.
3382 bootlog
3383 enable logging of machine checks left over from
3384 booting. Disabled by default on AMD Fam10h and older
3385 because some BIOS leave bogus ones.
3387 If your BIOS doesn't do that it's a good idea to
3388 enable though to make sure you log even machine check
3389 events that result in a reboot. On Intel systems it is
3390 enabled by default.
3392 nobootlog
3393 disable boot machine check logging.
3395 monarchtimeout (number)
3396 sets the time in us to wait for other CPUs on machine
3397 checks. 0 to disable.
3399 bios_cmci_threshold
3400 don't overwrite the bios-set CMCI threshold. This boot
3401 option prevents Linux from overwriting the CMCI
3402 threshold set by the bios. Without this option, Linux
3403 always sets the CMCI threshold to 1. Enabling this may
3404 make memory predictive failure analysis less effective
3405 if the bios sets thresholds for memory errors since we
3406 will not see details for all errors.
3408 recovery
3409 force-enable recoverable machine check code paths
3411 Everything else is in sysfs now.
3414 md= [HW] RAID subsystems devices and level
3415 See Documentation/admin-guide/md.rst.
3417 mdacon= [MDA]
3418 Format: <first>,<last>
3419 Specifies range of consoles to be captured by the MDA.
3421 mds= [X86,INTEL,EARLY]
3422 Control mitigation for the Micro-architectural Data
3423 Sampling (MDS) vulnerability.
3425 Certain CPUs are vulnerable to an exploit against CPU
3426 internal buffers which can forward information to a
3427 disclosure gadget under certain conditions.
3429 In vulnerable processors, the speculatively
3430 forwarded data can be used in a cache side channel
3431 attack, to access data to which the attacker does
3432 not have direct access.
3434 This parameter controls the MDS mitigation. The
3435 options are:
3437 full - Enable MDS mitigation on vulnerable CPUs
3438 full,nosmt - Enable MDS mitigation and disable
3439 SMT on vulnerable CPUs
3440 off - Unconditionally disable MDS mitigation
3442 On TAA-affected machines, mds=off can be prevented by
3443 an active TAA mitigation as both vulnerabilities are
3444 mitigated with the same mechanism so in order to disable
3445 this mitigation, you need to specify tsx_async_abort=off
3446 too.
3448 Not specifying this option is equivalent to
3449 mds=full.
3451 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3453 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
3454 Must be specified, otherwise memory size will be 0.
3456 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
3457 of memory Amount of memory to be used in cases
3458 as follows:
3460 1 for test;
3461 2 when the kernel is not able to see the whole system memory;
3462 3 memory that lies after 'mem=' boundary is excluded from
3463 the hypervisor, then assigned to KVM guests.
3464 4 to limit the memory available for kdump kernel.
3466 [ARC,MICROBLAZE] - the limit applies only to low memory,
3467 high memory is not affected.
3469 [ARM64] - only limits memory covered by the linear
3470 mapping. The NOMAP regions are not affected.
3472 [X86] Work as limiting max address. Use together
3473 with memmap= to avoid physical address space collisions.
3474 Without memmap= PCI devices could be placed at addresses
3475 belonging to unused RAM.
3477 Note that this only takes effects during boot time since
3478 in above case 3, memory may need be hot added after boot
3479 if system memory of hypervisor is not sufficient.
3481 mem=nn[KMG]@ss[KMG]
3482 [ARM,MIPS,EARLY] - override the memory layout
3483 reported by firmware.
3484 Define a memory region of size nn[KMG] starting at
3485 ss[KMG].
3486 Multiple different regions can be specified with
3487 multiple mem= parameters on the command line.
3489 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3490 memory.
3492 memblock=debug [KNL,EARLY] Enable memblock debug messages.
3494 memchunk=nn[KMG]
3495 [KNL,SH] Allow user to override the default size for
3496 per-device physically contiguous DMA buffers.
3498 memhp_default_state=online/offline/online_kernel/online_movable
3499 [KNL] Set the initial state for the memory hotplug
3500 onlining policy. If not specified, the default value is
3501 set according to the
3502 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config
3503 options.
3504 See Documentation/admin-guide/mm/memory-hotplug.rst.
3506 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact
3507 E820 memory map, as specified by the user.
3508 Such memmap=exactmap lines can be constructed based on
3509 BIOS output or other requirements. See the memmap=nn@ss
3510 option description.
3512 memmap=nn[KMG]@ss[KMG]
3513 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
3514 Region of memory to be used is from ss to ss+nn.
3515 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3516 which limits max address to nn[KMG].
3517 Multiple different regions can be specified,
3518 comma delimited.
3519 Example:
3520 memmap=100M@2G,100M#3G,1G!1024G
3522 memmap=nn[KMG]#ss[KMG]
3523 [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
3524 Region of memory to be marked is from ss to ss+nn.
3526 memmap=nn[KMG]$ss[KMG]
3527 [KNL,ACPI,EARLY] Mark specific memory as reserved.
3528 Region of memory to be reserved is from ss to ss+nn.
3529 Example: Exclude memory from 0x18690000-0x1869ffff
3530 memmap=64K$0x18690000
3531 or
3532 memmap=0x10000$0x18690000
3533 Some bootloaders may need an escape character before '$',
3534 like Grub2, otherwise '$' and the following number
3535 will be eaten.
3537 memmap=nn[KMG]!ss[KMG,EARLY]
3538 [KNL,X86] Mark specific memory as protected.
3539 Region of memory to be used, from ss to ss+nn.
3540 The memory region may be marked as e820 type 12 (0xc)
3541 and is NVDIMM or ADR memory.
3543 memmap=<size>%<offset>-<oldtype>+<newtype>
3544 [KNL,ACPI,EARLY] Convert memory within the specified region
3545 from <oldtype> to <newtype>. If "-<oldtype>" is left
3546 out, the whole region will be marked as <newtype>,
3547 even if previously unavailable. If "+<newtype>" is left
3548 out, matching memory will be removed. Types are
3549 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3550 3 = ACPI, 12 = PRAM.
3552 memory_corruption_check=0/1 [X86,EARLY]
3553 Some BIOSes seem to corrupt the first 64k of
3554 memory when doing things like suspend/resume.
3555 Setting this option will scan the memory
3556 looking for corruption. Enabling this will
3557 both detect corruption and prevent the kernel
3558 from using the memory being corrupted.
3559 However, its intended as a diagnostic tool; if
3560 repeatable BIOS-originated corruption always
3561 affects the same memory, you can use memmap=
3562 to prevent the kernel from using that memory.
3564 memory_corruption_check_size=size [X86,EARLY]
3565 By default it checks for corruption in the low
3566 64k, making this memory unavailable for normal
3567 use. Use this parameter to scan for
3568 corruption in more or less memory.
3570 memory_corruption_check_period=seconds [X86,EARLY]
3571 By default it checks for corruption every 60
3572 seconds. Use this parameter to check at some
3573 other rate. 0 disables periodic checking.
3575 memory_hotplug.memmap_on_memory
3576 [KNL,X86,ARM] Boolean flag to enable this feature.
3577 Format: {on | off (default)}
3578 When enabled, runtime hotplugged memory will
3579 allocate its internal metadata (struct pages,
3580 those vmemmap pages cannot be optimized even
3581 if hugetlb_free_vmemmap is enabled) from the
3582 hotadded memory which will allow to hotadd a
3583 lot of memory without requiring additional
3584 memory to do so.
3585 This feature is disabled by default because it
3586 has some implication on large (e.g. GB)
3587 allocations in some configurations (e.g. small
3588 memory blocks).
3589 The state of the flag can be read in
3590 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3591 Note that even when enabled, there are a few cases where
3592 the feature is not effective.
3594 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
3595 Format: <integer>
3596 default : 0 <disable>
3597 Specifies the number of memtest passes to be
3598 performed. Each pass selects another test
3599 pattern from a given set of patterns. Memtest
3600 fills the memory with this pattern, validates
3601 memory contents and reserves bad memory
3602 regions that are detected.
3604 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3605 Valid arguments: on, off
3606 Default: off
3607 mem_encrypt=on: Activate SME
3608 mem_encrypt=off: Do not activate SME
3610 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3611 for details on when memory encryption can be activated.
3613 mem_sleep_default= [SUSPEND] Default system suspend mode:
3614 s2idle - Suspend-To-Idle
3615 shallow - Power-On Suspend or equivalent (if supported)
3616 deep - Suspend-To-RAM or equivalent (if supported)
3617 See Documentation/admin-guide/pm/sleep-states.rst.
3619 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3620 the BIOS has incorrectly applied a workaround. TinyBIOS
3621 version 0.98 is known to be affected, 0.99 fixes the
3622 problem by letting the user disable the workaround.
3624 mga= [HW,DRM]
3626 microcode.force_minrev= [X86]
3627 Format: <bool>
3628 Enable or disable the microcode minimal revision
3629 enforcement for the runtime microcode loader.
3631 mini2440= [ARM,HW,KNL]
3632 Format:[0..2][b][c][t]
3633 Default: "0tb"
3634 MINI2440 configuration specification:
3635 0 - The attached screen is the 3.5" TFT
3636 1 - The attached screen is the 7" TFT
3637 2 - The VGA Shield is attached (1024x768)
3638 Leaving out the screen size parameter will not load
3639 the TFT driver, and the framebuffer will be left
3640 unconfigured.
3641 b - Enable backlight. The TFT backlight pin will be
3642 linked to the kernel VESA blanking code and a GPIO
3643 LED. This parameter is not necessary when using the
3644 VGA shield.
3645 c - Enable the s3c camera interface.
3646 t - Reserved for enabling touchscreen support. The
3647 touchscreen support is not enabled in the mainstream
3648 kernel as of 2.6.30, a preliminary port can be found
3649 in the "bleeding edge" mini2440 support kernel at
3650 https://repo.or.cz/w/linux-2.6/mini2440.git
3652 mitigations=
3653 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
3654 CPU vulnerabilities. This is a set of curated,
3655 arch-independent options, each of which is an
3656 aggregation of existing arch-specific options.
3658 Note, "mitigations" is supported if and only if the
3659 kernel was built with CPU_MITIGATIONS=y.
3661 off
3662 Disable all optional CPU mitigations. This
3663 improves system performance, but it may also
3664 expose users to several CPU vulnerabilities.
3665 Equivalent to: if nokaslr then kpti=0 [ARM64]
3666 gather_data_sampling=off [X86]
3667 kvm.nx_huge_pages=off [X86]
3668 l1tf=off [X86]
3669 mds=off [X86]
3670 mmio_stale_data=off [X86]
3671 no_entry_flush [PPC]
3672 no_uaccess_flush [PPC]
3673 nobp=0 [S390]
3674 nopti [X86,PPC]
3675 nospectre_bhb [ARM64]
3676 nospectre_v1 [X86,PPC]
3677 nospectre_v2 [X86,PPC,S390,ARM64]
3678 reg_file_data_sampling=off [X86]
3679 retbleed=off [X86]
3680 spec_rstack_overflow=off [X86]
3681 spec_store_bypass_disable=off [X86,PPC]
3682 spectre_bhi=off [X86]
3683 spectre_v2_user=off [X86]
3684 srbds=off [X86,INTEL]
3685 ssbd=force-off [ARM64]
3686 tsx_async_abort=off [X86]
3688 Exceptions:
3689 This does not have any effect on
3690 kvm.nx_huge_pages when
3691 kvm.nx_huge_pages=force.
3693 auto (default)
3694 Mitigate all CPU vulnerabilities, but leave SMT
3695 enabled, even if it's vulnerable. This is for
3696 users who don't want to be surprised by SMT
3697 getting disabled across kernel upgrades, or who
3698 have other ways of avoiding SMT-based attacks.
3699 Equivalent to: (default behavior)
3701 auto,nosmt
3702 Mitigate all CPU vulnerabilities, disabling SMT
3703 if needed. This is for users who always want to
3704 be fully mitigated, even if it means losing SMT.
3705 Equivalent to: l1tf=flush,nosmt [X86]
3706 mds=full,nosmt [X86]
3707 tsx_async_abort=full,nosmt [X86]
3708 mmio_stale_data=full,nosmt [X86]
3709 retbleed=auto,nosmt [X86]
3711 mminit_loglevel=
3712 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this
3713 parameter allows control of the logging verbosity for
3714 the additional memory initialisation checks. A value
3715 of 0 disables mminit logging and a level of 4 will
3716 log everything. Information is printed at KERN_DEBUG
3717 so loglevel=8 may also need to be specified.
3719 mmio_stale_data=
3720 [X86,INTEL,EARLY] Control mitigation for the Processor
3721 MMIO Stale Data vulnerabilities.
3723 Processor MMIO Stale Data is a class of
3724 vulnerabilities that may expose data after an MMIO
3725 operation. Exposed data could originate or end in
3726 the same CPU buffers as affected by MDS and TAA.
3727 Therefore, similar to MDS and TAA, the mitigation
3728 is to clear the affected CPU buffers.
3730 This parameter controls the mitigation. The
3731 options are:
3733 full - Enable mitigation on vulnerable CPUs
3735 full,nosmt - Enable mitigation and disable SMT on
3736 vulnerable CPUs.
3738 off - Unconditionally disable mitigation
3740 On MDS or TAA affected machines,
3741 mmio_stale_data=off can be prevented by an active
3742 MDS or TAA mitigation as these vulnerabilities are
3743 mitigated with the same mechanism so in order to
3744 disable this mitigation, you need to specify
3745 mds=off and tsx_async_abort=off too.
3747 Not specifying this option is equivalent to
3748 mmio_stale_data=full.
3750 For details see:
3751 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3753 <module>.async_probe[=<bool>] [KNL]
3754 If no <bool> value is specified or if the value
3755 specified is not a valid <bool>, enable asynchronous
3756 probe on this module. Otherwise, enable/disable
3757 asynchronous probe on this module as indicated by the
3758 <bool> value. See also: module.async_probe
3760 module.async_probe=<bool>
3761 [KNL] When set to true, modules will use async probing
3762 by default. To enable/disable async probing for a
3763 specific module, use the module specific control that
3764 is documented under <module>.async_probe. When both
3765 module.async_probe and <module>.async_probe are
3766 specified, <module>.async_probe takes precedence for
3767 the specific module.
3769 module.enable_dups_trace
3770 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set,
3771 this means that duplicate request_module() calls will
3772 trigger a WARN_ON() instead of a pr_warn(). Note that
3773 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
3774 will always be issued and this option does nothing.
3775 module.sig_enforce
3776 [KNL] When CONFIG_MODULE_SIG is set, this means that
3777 modules without (valid) signatures will fail to load.
3778 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3779 is always true, so this option does nothing.
3781 module_blacklist= [KNL] Do not load a comma-separated list of
3782 modules. Useful for debugging problem modules.
3784 mousedev.tap_time=
3785 [MOUSE] Maximum time between finger touching and
3786 leaving touchpad surface for touch to be considered
3787 a tap and be reported as a left button click (for
3788 touchpads working in absolute mode only).
3789 Format: <msecs>
3790 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3791 reporting absolute coordinates, such as tablets
3792 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3793 reporting absolute coordinates, such as tablets
3795 movablecore= [KNL,X86,PPC,EARLY]
3796 Format: nn[KMGTPE] | nn%
3797 This parameter is the complement to kernelcore=, it
3798 specifies the amount of memory used for migratable
3799 allocations. If both kernelcore and movablecore is
3800 specified, then kernelcore will be at *least* the
3801 specified value but may be more. If movablecore on its
3802 own is specified, the administrator must be careful
3803 that the amount of memory usable for all allocations
3804 is not too small.
3806 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
3807 NUMA nodes to be movable. This means that the memory
3808 of such nodes will be usable only for movable
3809 allocations which rules out almost all kernel
3810 allocations. Use with caution!
3812 MTD_Partition= [MTD]
3813 Format: <name>,<region-number>,<size>,<offset>
3815 MTD_Region= [MTD] Format:
3816 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3818 mtdparts= [MTD]
3819 See drivers/mtd/parsers/cmdlinepart.c
3821 mtouchusb.raw_coordinates=
3822 [HW] Make the MicroTouch USB driver use raw coordinates
3823 ('y', default) or cooked coordinates ('n')
3825 mtrr=debug [X86,EARLY]
3826 Enable printing debug information related to MTRR
3827 registers at boot time.
3829 mtrr_chunk_size=nn[KMG,X86,EARLY]
3830 used for mtrr cleanup. It is largest continuous chunk
3831 that could hold holes aka. UC entries.
3833 mtrr_gran_size=nn[KMG,X86,EARLY]
3834 Used for mtrr cleanup. It is granularity of mtrr block.
3835 Default is 1.
3836 Large value could prevent small alignment from
3837 using up MTRRs.
3839 mtrr_spare_reg_nr=n [X86,EARLY]
3840 Format: <integer>
3841 Range: 0,7 : spare reg number
3842 Default : 1
3843 Used for mtrr cleanup. It is spare mtrr entries number.
3844 Set to 2 or more if your graphical card needs more.
3846 multitce=off [PPC] This parameter disables the use of the pSeries
3847 firmware feature for updating multiple TCE entries
3848 at a time.
3850 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3852 netdev= [NET] Network devices parameters
3853 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3854 Note that mem_start is often overloaded to mean
3855 something different and driver-specific.
3856 This usage is only documented in each driver source
3857 file if at all.
3859 netpoll.carrier_timeout=
3860 [NET] Specifies amount of time (in seconds) that
3861 netpoll should wait for a carrier. By default netpoll
3862 waits 4 seconds.
3864 nf_conntrack.acct=
3865 [NETFILTER] Enable connection tracking flow accounting
3866 0 to disable accounting
3867 1 to enable accounting
3868 Default value is 0.
3870 nfs.cache_getent=
3871 [NFS] sets the pathname to the program which is used
3872 to update the NFS client cache entries.
3874 nfs.cache_getent_timeout=
3875 [NFS] sets the timeout after which an attempt to
3876 update a cache entry is deemed to have failed.
3878 nfs.callback_nr_threads=
3879 [NFSv4] set the total number of threads that the
3880 NFS client will assign to service NFSv4 callback
3881 requests.
3883 nfs.callback_tcpport=
3884 [NFS] set the TCP port on which the NFSv4 callback
3885 channel should listen.
3887 nfs.delay_retrans=
3888 [NFS] specifies the number of times the NFSv4 client
3889 retries the request before returning an EAGAIN error,
3890 after a reply of NFS4ERR_DELAY from the server.
3891 Only applies if the softerr mount option is enabled,
3892 and the specified value is >= 0.
3894 nfs.enable_ino64=
3895 [NFS] enable 64-bit inode numbers.
3896 If zero, the NFS client will fake up a 32-bit inode
3897 number for the readdir() and stat() syscalls instead
3898 of returning the full 64-bit number.
3899 The default is to return 64-bit inode numbers.
3901 nfs.idmap_cache_timeout=
3902 [NFS] set the maximum lifetime for idmapper cache
3903 entries.
3905 nfs.max_session_cb_slots=
3906 [NFSv4.1] Sets the maximum number of session
3907 slots the client will assign to the callback
3908 channel. This determines the maximum number of
3909 callbacks the client will process in parallel for
3910 a particular server.
3912 nfs.max_session_slots=
3913 [NFSv4.1] Sets the maximum number of session slots
3914 the client will attempt to negotiate with the server.
3915 This limits the number of simultaneous RPC requests
3916 that the client can send to the NFSv4.1 server.
3917 Note that there is little point in setting this
3918 value higher than the max_tcp_slot_table_limit.
3920 nfs.nfs4_disable_idmapping=
3921 [NFSv4] When set to the default of '1', this option
3922 ensures that both the RPC level authentication
3923 scheme and the NFS level operations agree to use
3924 numeric uids/gids if the mount is using the
3925 'sec=sys' security flavour. In effect it is
3926 disabling idmapping, which can make migration from
3927 legacy NFSv2/v3 systems to NFSv4 easier.
3928 Servers that do not support this mode of operation
3929 will be autodetected by the client, and it will fall
3930 back to using the idmapper.
3931 To turn off this behaviour, set the value to '0'.
3933 nfs.nfs4_unique_id=
3934 [NFS4] Specify an additional fixed unique ident-
3935 ification string that NFSv4 clients can insert into
3936 their nfs_client_id4 string. This is typically a
3937 UUID that is generated at system install time.
3939 nfs.recover_lost_locks=
3940 [NFSv4] Attempt to recover locks that were lost due
3941 to a lease timeout on the server. Please note that
3942 doing this risks data corruption, since there are
3943 no guarantees that the file will remain unchanged
3944 after the locks are lost.
3945 If you want to enable the kernel legacy behaviour of
3946 attempting to recover these locks, then set this
3947 parameter to '1'.
3948 The default parameter value of '0' causes the kernel
3949 not to attempt recovery of lost locks.
3951 nfs.send_implementation_id=
3952 [NFSv4.1] Send client implementation identification
3953 information in exchange_id requests.
3954 If zero, no implementation identification information
3955 will be sent.
3956 The default is to send the implementation identification
3957 information.
3959 nfs4.layoutstats_timer=
3960 [NFSv4.2] Change the rate at which the kernel sends
3961 layoutstats to the pNFS metadata server.
3963 Setting this to value to 0 causes the kernel to use
3964 whatever value is the default set by the layout
3965 driver. A non-zero value sets the minimum interval
3966 in seconds between layoutstats transmissions.
3968 nfsd.inter_copy_offload_enable=
3969 [NFSv4.2] When set to 1, the server will support
3970 server-to-server copies for which this server is
3971 the destination of the copy.
3973 nfsd.nfs4_disable_idmapping=
3974 [NFSv4] When set to the default of '1', the NFSv4
3975 server will return only numeric uids and gids to
3976 clients using auth_sys, and will accept numeric uids
3977 and gids from such clients. This is intended to ease
3978 migration from NFSv2/v3.
3980 nfsd.nfsd4_ssc_umount_timeout=
3981 [NFSv4.2] When used as the destination of a
3982 server-to-server copy, knfsd temporarily mounts
3983 the source server. It caches the mount in case
3984 it will be needed again, and discards it if not
3985 used for the number of milliseconds specified by
3986 this parameter.
3988 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3989 See Documentation/admin-guide/nfs/nfsroot.rst.
3991 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3992 See Documentation/admin-guide/nfs/nfsroot.rst.
3994 nfsrootdebug [NFS] enable nfsroot debugging messages.
3995 See Documentation/admin-guide/nfs/nfsroot.rst.
3997 nmi_backtrace.backtrace_idle [KNL]
3998 Dump stacks even of idle CPUs in response to an
3999 NMI stack-backtrace request.
4001 nmi_debug= [KNL,SH] Specify one or more actions to take
4002 when a NMI is triggered.
4003 Format: [state][,regs][,debounce][,die]
4005 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
4006 Format: [panic,][nopanic,][rNNN,][num]
4007 Valid num: 0 or 1
4008 0 - turn hardlockup detector in nmi_watchdog off
4009 1 - turn hardlockup detector in nmi_watchdog on
4010 rNNN - configure the watchdog with raw perf event 0xNNN
4012 When panic is specified, panic when an NMI watchdog
4013 timeout occurs (or 'nopanic' to not panic on an NMI
4014 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
4015 To disable both hard and soft lockup detectors,
4016 please see 'nowatchdog'.
4017 This is useful when you use a panic=... timeout and
4018 need the box quickly up again.
4020 These settings can be accessed at runtime via
4021 the nmi_watchdog and hardlockup_panic sysctls.
4023 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
4024 emulation library even if a 387 maths coprocessor
4025 is present.
4027 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
4028 Forces kernel to use 3-level paging instead.
4030 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
4031 kernel to use 4-level paging instead.
4033 noalign [KNL,ARM]
4035 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
4036 IOAPICs that may be present in the system.
4038 noapictimer [APIC,X86] Don't set up the APIC timer
4040 noautogroup Disable scheduler automatic task group creation.
4042 nocache [ARM,EARLY]
4044 no_console_suspend
4045 [HW] Never suspend the console
4046 Disable suspending of consoles during suspend and
4047 hibernate operations. Once disabled, debugging
4048 messages can reach various consoles while the rest
4049 of the system is being put to sleep (ie, while
4050 debugging driver suspend/resume hooks). This may
4051 not work reliably with all consoles, but is known
4052 to work with serial and VGA consoles.
4053 To facilitate more flexible debugging, we also add
4054 console_suspend, a printk module parameter to control
4055 it. Users could use console_suspend (usually
4056 /sys/module/printk/parameters/console_suspend) to
4057 turn on/off it dynamically.
4059 no_debug_objects
4060 [KNL,EARLY] Disable object debugging
4062 nodsp [SH] Disable hardware DSP at boot time.
4064 noefi [EFI,EARLY] Disable EFI runtime services support.
4066 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
4068 noexec32 [X86-64]
4069 This affects only 32-bit executables.
4070 noexec32=on: enable non-executable mappings (default)
4071 read doesn't imply executable mappings
4072 noexec32=off: disable non-executable mappings
4073 read implies executable mappings
4075 no_file_caps Tells the kernel not to honor file capabilities. The
4076 only way then for a file to be executed with privilege
4077 is to be setuid root or executed by root.
4079 nofpu [MIPS,SH] Disable hardware FPU at boot time.
4081 nofsgsbase [X86] Disables FSGSBASE instructions.
4083 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4084 register save and restore. The kernel will only save
4085 legacy floating-point registers on task switch.
4087 nogbpages [X86] Do not use GB pages for kernel direct mappings.
4089 no_hash_pointers
4090 [KNL,EARLY]
4091 Force pointers printed to the console or buffers to be
4092 unhashed. By default, when a pointer is printed via %p
4093 format string, that pointer is "hashed", i.e. obscured
4094 by hashing the pointer value. This is a security feature
4095 that hides actual kernel addresses from unprivileged
4096 users, but it also makes debugging the kernel more
4097 difficult since unequal pointers can no longer be
4098 compared. However, if this command-line option is
4099 specified, then all normal pointers will have their true
4100 value printed. This option should only be specified when
4101 debugging the kernel. Please do not use on production
4102 kernels.
4104 nohibernate [HIBERNATION] Disable hibernation and resume.
4106 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to
4107 busy wait in do_idle() and not use the arch_cpu_idle()
4108 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
4109 to be effective. This is useful on platforms where the
4110 sleep(SH) or wfi(ARM,ARM64) instructions do not work
4111 correctly or when doing power measurements to evaluate
4112 the impact of the sleep instructions. This is also
4113 useful when using JTAG debugger.
4115 nohpet [X86] Don't use the HPET timer.
4117 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
4119 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
4121 nohz= [KNL] Boottime enable/disable dynamic ticks
4122 Valid arguments: on, off
4123 Default: on
4125 nohz_full= [KNL,BOOT,SMP,ISOL]
4126 The argument is a cpu list, as described above.
4127 In kernels built with CONFIG_NO_HZ_FULL=y, set
4128 the specified list of CPUs whose tick will be stopped
4129 whenever possible. The boot CPU will be forced outside
4130 the range to maintain the timekeeping. Any CPUs
4131 in this list will have their RCU callbacks offloaded,
4132 just as if they had also been called out in the
4133 rcu_nocbs= boot parameter.
4135 Note that this argument takes precedence over
4136 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4138 noinitrd [RAM] Tells the kernel not to load any configured
4139 initial RAM disk.
4141 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
4142 remapping.
4143 [Deprecated - use intremap=off]
4145 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
4147 noiotrap [SH] Disables trapped I/O port accesses.
4149 noirqdebug [X86-32] Disables the code which attempts to detect and
4150 disable unhandled interrupt sources.
4152 noisapnp [ISAPNP] Disables ISA PnP code.
4154 nokaslr [KNL,EARLY]
4155 When CONFIG_RANDOMIZE_BASE is set, this disables
4156 kernel and module base offset ASLR (Address Space
4157 Layout Randomization).
4159 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
4160 fault handling.
4162 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
4164 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
4166 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
4168 nomce [X86-32] Disable Machine Check Exception
4170 nomfgpt [X86-32] Disable Multi-Function General Purpose
4171 Timer usage (for AMD Geode machines).
4173 nomodeset Disable kernel modesetting. Most systems' firmware
4174 sets up a display mode and provides framebuffer memory
4175 for output. With nomodeset, DRM and fbdev drivers will
4176 not load if they could possibly displace the pre-
4177 initialized output. Only the system framebuffer will
4178 be available for use. The respective drivers will not
4179 perform display-mode changes or accelerated rendering.
4181 Useful as error fallback, or for testing and debugging.
4183 nomodule Disable module load
4185 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
4186 shutdown the other cpus. Instead use the REBOOT_VECTOR
4187 irq.
4189 nopat [X86,EARLY] Disable PAT (page attribute table extension of
4190 pagetables) support.
4192 nopcid [X86-64,EARLY] Disable the PCID cpu feature.
4194 nopku [X86] Disable Memory Protection Keys CPU feature found
4195 in some Intel CPUs.
4197 nopti [X86-64,EARLY]
4198 Equivalent to pti=off
4200 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
4201 Disables the PV optimizations forcing the guest to run
4202 as generic guest with no PV drivers. Currently support
4203 XEN HVM, KVM, HYPER_V and VMWARE guest.
4205 nopvspin [X86,XEN,KVM,EARLY]
4206 Disables the qspinlock slow path using PV optimizations
4207 which allow the hypervisor to 'idle' the guest on lock
4208 contention.
4210 norandmaps Don't use address space randomization. Equivalent to
4211 echo 0 > /proc/sys/kernel/randomize_va_space
4213 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
4214 with UP alternatives
4216 noresume [SWSUSP] Disables resume and restores original swap
4217 space.
4219 no-scroll [VGA] Disables scrollback.
4220 This is required for the Braillex ib80-piezo Braille
4221 reader made by F.H. Papenmeier (Germany).
4223 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
4225 nosmap [PPC,EARLY]
4226 Disable SMAP (Supervisor Mode Access Prevention)
4227 even if it is supported by processor.
4229 nosmep [PPC64s,EARLY]
4230 Disable SMEP (Supervisor Mode Execution Prevention)
4231 even if it is supported by processor.
4233 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
4234 and disable the IO APIC. legacy for "maxcpus=0".
4236 nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
4237 Equivalent to smt=1.
4239 [KNL,X86,PPC] Disable symmetric multithreading (SMT).
4240 nosmt=force: Force disable SMT, cannot be undone
4241 via the sysfs control file.
4243 nosoftlockup [KNL] Disable the soft-lockup detector.
4245 nospec_store_bypass_disable
4246 [HW,EARLY] Disable all mitigations for the Speculative
4247 Store Bypass vulnerability
4249 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
4250 history injection) vulnerability. System may allow data leaks
4251 with this option.
4253 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
4254 (bounds check bypass). With this option data leaks are
4255 possible in the system.
4257 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
4258 for the Spectre variant 2 (indirect branch
4259 prediction) vulnerability. System may allow data
4260 leaks with this option.
4262 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY]
4263 Disable paravirtualized steal time accounting. steal time
4264 is computed, but won't influence scheduler behaviour
4266 nosync [HW,M68K] Disables sync negotiation for all devices.
4268 no_timer_check [X86,APIC] Disables the code which tests for broken
4269 timer IRQ sources, i.e., the IO-APIC timer. This can
4270 work around problems with incorrect timer
4271 initialization on some boards.
4273 no_uaccess_flush
4274 [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
4276 novmcoredd [KNL,KDUMP]
4277 Disable device dump. Device dump allows drivers to
4278 append dump data to vmcore so you can collect driver
4279 specified debug info. Drivers can append the data
4280 without any limit and this data is stored in memory,
4281 so this may cause significant memory stress. Disabling
4282 device dump can help save memory but the driver debug
4283 data will be no longer available. This parameter
4284 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
4285 is set.
4287 no-vmw-sched-clock
4288 [X86,PV_OPS,EARLY] Disable paravirtualized VMware
4289 scheduler clock and use the default one.
4291 nowatchdog [KNL] Disable both lockup detectors, i.e.
4292 soft-lockup and NMI watchdog (hard-lockup).
4294 nowb [ARM,EARLY]
4296 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
4298 NOTE: this parameter will be ignored on systems with the
4299 LEGACY_XAPIC_DISABLED bit set in the
4300 IA32_XAPIC_DISABLE_STATUS MSR.
4302 noxsave [BUGS=X86] Disables x86 extended register state save
4303 and restore using xsave. The kernel will fallback to
4304 enabling legacy floating-point and sse state.
4306 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
4307 register states. The kernel will fall back to use
4308 xsave to save the states. By using this parameter,
4309 performance of saving the states is degraded because
4310 xsave doesn't support modified optimization while
4311 xsaveopt supports it on xsaveopt enabled systems.
4313 noxsaves [X86] Disables xsaves and xrstors used in saving and
4314 restoring x86 extended register state in compacted
4315 form of xsave area. The kernel will fall back to use
4316 xsaveopt and xrstor to save and restore the states
4317 in standard form of xsave area. By using this
4318 parameter, xsave area per process might occupy more
4319 memory on xsaves enabled systems.
4321 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
4322 could support. nr_cpus=n : n >= 1 limits the kernel to
4323 support 'n' processors. It could be larger than the
4324 number of already plugged CPU during bootup, later in
4325 runtime you can physically add extra cpu until it reaches
4326 n. So during boot up some boot time memory for per-cpu
4327 variables need be pre-allocated for later physical cpu
4328 hot plugging.
4330 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
4332 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
4333 Disable NUMA, Only set up a single NUMA node
4334 spanning all memory.
4336 numa=fake=<size>[MG]
4337 [KNL, ARM64, RISCV, X86, EARLY]
4338 If given as a memory unit, fills all system RAM with
4339 nodes of size interleaved over physical nodes.
4341 numa=fake=<N>
4342 [KNL, ARM64, RISCV, X86, EARLY]
4343 If given as an integer, fills all system RAM with N
4344 fake nodes interleaved over physical nodes.
4346 numa=fake=<N>U
4347 [KNL, ARM64, RISCV, X86, EARLY]
4348 If given as an integer followed by 'U', it will
4349 divide each physical node into N emulated nodes.
4351 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup
4353 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or
4354 soft-reserved memory partitioning.
4356 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
4357 NUMA balancing.
4358 Allowed values are enable and disable
4360 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
4361 'node', 'default' can be specified
4362 This can be set from sysctl after boot.
4363 See Documentation/admin-guide/sysctl/vm.rst for details.
4365 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
4366 See Documentation/core-api/debugging-via-ohci1394.rst for more
4367 info.
4369 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
4370 Rather than timing out after 20 ms if an EC
4371 command is not properly ACKed, override the length
4372 of the timeout. We have interrupts disabled while
4373 waiting for the ACK, so if this is set too high
4374 interrupts *may* be lost!
4376 omap_mux= [OMAP] Override bootloader pin multiplexing.
4377 Format: <mux_mode0.mode_name=value>...
4378 For example, to override I2C bus2:
4379 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
4381 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
4383 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
4385 boundary - index of last SLC block on Flex-OneNAND.
4386 The remaining blocks are configured as MLC blocks.
4387 lock - Configure if Flex-OneNAND boundary should be locked.
4388 Once locked, the boundary cannot be changed.
4389 1 indicates lock status, 0 indicates unlock status.
4391 oops=panic [KNL,EARLY]
4392 Always panic on oopses. Default is to just kill the
4393 process, but there is a small probability of
4394 deadlocking the machine.
4395 This will also cause panics on machine check exceptions.
4396 Useful together with panic=30 to trigger a reboot.
4398 page_alloc.shuffle=
4399 [KNL] Boolean flag to control whether the page allocator
4400 should randomize its free lists. This parameter can be
4401 used to enable/disable page randomization. The state of
4402 the flag can be read from sysfs at:
4403 /sys/module/page_alloc/parameters/shuffle.
4404 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y.
4406 page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
4407 Storage of the information about who allocated
4408 each page is disabled in default. With this switch,
4409 we can turn it on.
4410 on: enable the feature
4412 page_poison= [KNL,EARLY] Boot-time parameter changing the state of
4413 poisoning on the buddy allocator, available with
4414 CONFIG_PAGE_POISONING=y.
4415 off: turn off poisoning (default)
4416 on: turn on poisoning
4418 page_reporting.page_reporting_order=
4419 [KNL] Minimal page reporting order
4420 Format: <integer>
4421 Adjust the minimal page reporting order. The page
4422 reporting is disabled when it exceeds MAX_PAGE_ORDER.
4424 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4425 timeout > 0: seconds before rebooting
4426 timeout = 0: wait forever
4427 timeout < 0: reboot immediately
4428 Format: <timeout>
4430 panic_on_taint= [KNL,EARLY]
4431 Bitmask for conditionally calling panic() in add_taint()
4432 Format: <hex>[,nousertaint]
4433 Hexadecimal bitmask representing the set of TAINT flags
4434 that will cause the kernel to panic when add_taint() is
4435 called with any of the flags in this set.
4436 The optional switch "nousertaint" can be utilized to
4437 prevent userspace forced crashes by writing to sysctl
4438 /proc/sys/kernel/tainted any flagset matching with the
4439 bitmask set on panic_on_taint.
4440 See Documentation/admin-guide/tainted-kernels.rst for
4441 extra details on the taint flags that users can pick
4442 to compose the bitmask to assign to panic_on_taint.
4444 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump
4445 on a WARN().
4447 panic_print= Bitmask for printing system info when panic happens.
4448 User can chose combination of the following bits:
4449 bit 0: print all tasks info
4450 bit 1: print system memory info
4451 bit 2: print timer info
4452 bit 3: print locks info if CONFIG_LOCKDEP is on
4453 bit 4: print ftrace buffer
4454 bit 5: print all printk messages in buffer
4455 bit 6: print all CPUs backtrace (if available in the arch)
4456 bit 7: print only tasks in uninterruptible (blocked) state
4457 *Be aware* that this option may print a _lot_ of lines,
4458 so there are risks of losing older messages in the log.
4459 Use this option carefully, maybe worth to setup a
4460 bigger log buffer with "log_buf_len" along with this.
4462 parkbd.port= [HW] Parallel port number the keyboard adapter is
4463 connected to, default is 0.
4464 Format: <parport#>
4465 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4466 0 for XT, 1 for AT (default is AT).
4467 Format: <mode>
4469 parport= [HW,PPT] Specify parallel ports. 0 disables.
4470 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4471 Use 'auto' to force the driver to use any
4472 IRQ/DMA settings detected (the default is to
4473 ignore detected IRQ/DMA settings because of
4474 possible conflicts). You can specify the base
4475 address, IRQ, and DMA settings; IRQ and DMA
4476 should be numbers, or 'auto' (for using detected
4477 settings on that particular port), or 'nofifo'
4478 (to avoid using a FIFO even if it is detected).
4479 Parallel ports are assigned in the order they
4480 are specified on the command line, starting
4481 with parport0.
4483 parport_init_mode= [HW,PPT]
4484 Configure VIA parallel port to operate in
4485 a specific mode. This is necessary on Pegasos
4486 computer where firmware has no options for setting
4487 up parallel port mode and sets it to spp.
4488 Currently this function knows 686a and 8231 chips.
4489 Format: [spp|ps2|epp|ecp|ecpepp]
4491 pata_legacy.all= [HW,LIBATA]
4492 Format: <int>
4493 Set to non-zero to probe primary and secondary ISA
4494 port ranges on PCI systems where no PCI PATA device
4495 has been found at either range. Disabled by default.
4497 pata_legacy.autospeed= [HW,LIBATA]
4498 Format: <int>
4499 Set to non-zero if a chip is present that snoops speed
4500 changes. Disabled by default.
4502 pata_legacy.ht6560a= [HW,LIBATA]
4503 Format: <int>
4504 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4505 the secondary channel, or both channels respectively.
4506 Disabled by default.
4508 pata_legacy.ht6560b= [HW,LIBATA]
4509 Format: <int>
4510 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4511 the secondary channel, or both channels respectively.
4512 Disabled by default.
4514 pata_legacy.iordy_mask= [HW,LIBATA]
4515 Format: <int>
4516 IORDY enable mask. Set individual bits to allow IORDY
4517 for the respective channel. Bit 0 is for the first
4518 legacy channel handled by this driver, bit 1 is for
4519 the second channel, and so on. The sequence will often
4520 correspond to the primary legacy channel, the secondary
4521 legacy channel, and so on, but the handling of a PCI
4522 bus and the use of other driver options may interfere
4523 with the sequence. By default IORDY is allowed across
4524 all channels.
4526 pata_legacy.opti82c46x= [HW,LIBATA]
4527 Format: <int>
4528 Set to 1, 2, or 3 for Opti 82c611A on the primary
4529 channel, the secondary channel, or both channels
4530 respectively. Disabled by default.
4532 pata_legacy.opti82c611a= [HW,LIBATA]
4533 Format: <int>
4534 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4535 channel, the secondary channel, or both channels
4536 respectively. Disabled by default.
4538 pata_legacy.pio_mask= [HW,LIBATA]
4539 Format: <int>
4540 PIO mode mask for autospeed devices. Set individual
4541 bits to allow the use of the respective PIO modes.
4542 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4543 All modes allowed by default.
4545 pata_legacy.probe_all= [HW,LIBATA]
4546 Format: <int>
4547 Set to non-zero to probe tertiary and further ISA
4548 port ranges on PCI systems. Disabled by default.
4550 pata_legacy.probe_mask= [HW,LIBATA]
4551 Format: <int>
4552 Probe mask for legacy ISA PATA ports. Depending on
4553 platform configuration and the use of other driver
4554 options up to 6 legacy ports are supported: 0x1f0,
4555 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4556 of individual ports can be disabled by setting the
4557 corresponding bits in the mask to 1. Bit 0 is for
4558 the first port in the list above (0x1f0), and so on.
4559 By default all supported ports are probed.
4561 pata_legacy.qdi= [HW,LIBATA]
4562 Format: <int>
4563 Set to non-zero to probe QDI controllers. By default
4564 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4566 pata_legacy.winbond= [HW,LIBATA]
4567 Format: <int>
4568 Set to non-zero to probe Winbond controllers. Use
4569 the standard I/O port (0x130) if 1, otherwise the
4570 value given is the I/O port to use (typically 0x1b0).
4571 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4572 0 otherwise.
4574 pata_platform.pio_mask= [HW,LIBATA]
4575 Format: <int>
4576 Supported PIO mode mask. Set individual bits to allow
4577 the use of the respective PIO modes. Bit 0 is for
4578 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4579 allowed by default.
4581 pause_on_oops=<int>
4582 Halt all CPUs after the first oops has been printed for
4583 the specified number of seconds. This is to be used if
4584 your oopses keep scrolling off the screen.
4586 pcbit= [HW,ISDN]
4588 pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
4590 Some options herein operate on a specific device
4591 or a set of devices (<pci_dev>). These are
4592 specified in one of the following formats:
4594 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4595 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4597 Note: the first format specifies a PCI
4598 bus/device/function address which may change
4599 if new hardware is inserted, if motherboard
4600 firmware changes, or due to changes caused
4601 by other kernel parameters. If the
4602 domain is left unspecified, it is
4603 taken to be zero. Optionally, a path
4604 to a device through multiple device/function
4605 addresses can be specified after the base
4606 address (this is more robust against
4607 renumbering issues). The second format
4608 selects devices using IDs from the
4609 configuration space which may match multiple
4610 devices in the system.
4612 earlydump dump PCI config space before the kernel
4613 changes anything
4614 off [X86] don't probe for the PCI bus
4615 bios [X86-32] force use of PCI BIOS, don't access
4616 the hardware directly. Use this if your machine
4617 has a non-standard PCI host bridge.
4618 nobios [X86-32] disallow use of PCI BIOS, only direct
4619 hardware access methods are allowed. Use this
4620 if you experience crashes upon bootup and you
4621 suspect they are caused by the BIOS.
4622 conf1 [X86] Force use of PCI Configuration Access
4623 Mechanism 1 (config address in IO port 0xCF8,
4624 data in IO port 0xCFC, both 32-bit).
4625 conf2 [X86] Force use of PCI Configuration Access
4626 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4627 the function, IO port 0xCFA, also 8-bit, sets
4628 bus number. The config space is then accessed
4629 through ports 0xC000-0xCFFF).
4630 See http://wiki.osdev.org/PCI for more info
4631 on the configuration access mechanisms.
4632 noaer [PCIE] If the PCIEAER kernel config parameter is
4633 enabled, this kernel boot option can be used to
4634 disable the use of PCIE advanced error reporting.
4635 nodomains [PCI] Disable support for multiple PCI
4636 root domains (aka PCI segments, in ACPI-speak).
4637 nommconf [X86] Disable use of MMCONFIG for PCI
4638 Configuration
4639 check_enable_amd_mmconf [X86] check for and enable
4640 properly configured MMIO access to PCI
4641 config space on AMD family 10h CPU
4642 nomsi [MSI] If the PCI_MSI kernel config parameter is
4643 enabled, this kernel boot option can be used to
4644 disable the use of MSI interrupts system-wide.
4645 noioapicquirk [APIC] Disable all boot interrupt quirks.
4646 Safety option to keep boot IRQs enabled. This
4647 should never be necessary.
4648 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4649 primary IO-APIC for bridges that cannot disable
4650 boot IRQs. This fixes a source of spurious IRQs
4651 when the system masks IRQs.
4652 noioapicreroute [APIC] Disable workaround that uses the
4653 boot IRQ equivalent of an IRQ that connects to
4654 a chipset where boot IRQs cannot be disabled.
4655 The opposite of ioapicreroute.
4656 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4657 routing table. These calls are known to be buggy
4658 on several machines and they hang the machine
4659 when used, but on other computers it's the only
4660 way to get the interrupt routing table. Try
4661 this option if the kernel is unable to allocate
4662 IRQs or discover secondary PCI buses on your
4663 motherboard.
4664 rom [X86] Assign address space to expansion ROMs.
4665 Use with caution as certain devices share
4666 address decoders between ROMs and other
4667 resources.
4668 norom [X86] Do not assign address space to
4669 expansion ROMs that do not already have
4670 BIOS assigned address ranges.
4671 nobar [X86] Do not assign address space to the
4672 BARs that weren't assigned by the BIOS.
4673 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4674 assigned automatically to PCI devices. You can
4675 make the kernel exclude IRQs of your ISA cards
4676 this way.
4677 pirqaddr=0xAAAAA [X86] Specify the physical address
4678 of the PIRQ table (normally generated
4679 by the BIOS) if it is outside the
4680 F0000h-100000h range.
4681 lastbus=N [X86] Scan all buses thru bus #N. Can be
4682 useful if the kernel is unable to find your
4683 secondary buses and you want to tell it
4684 explicitly which ones they are.
4685 assign-busses [X86] Always assign all PCI bus
4686 numbers ourselves, overriding
4687 whatever the firmware may have done.
4688 usepirqmask [X86] Honor the possible IRQ mask stored
4689 in the BIOS $PIR table. This is needed on
4690 some systems with broken BIOSes, notably
4691 some HP Pavilion N5400 and Omnibook XE3
4692 notebooks. This will have no effect if ACPI
4693 IRQ routing is enabled.
4694 noacpi [X86] Do not use ACPI for IRQ routing
4695 or for PCI scanning.
4696 use_crs [X86] Use PCI host bridge window information
4697 from ACPI. On BIOSes from 2008 or later, this
4698 is enabled by default. If you need to use this,
4699 please report a bug.
4700 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4701 If you need to use this, please report a bug.
4702 use_e820 [X86] Use E820 reservations to exclude parts of
4703 PCI host bridge windows. This is a workaround
4704 for BIOS defects in host bridge _CRS methods.
4705 If you need to use this, please report a bug to
4706 <linux-pci@vger.kernel.org>.
4707 no_e820 [X86] Ignore E820 reservations for PCI host
4708 bridge windows. This is the default on modern
4709 hardware. If you need to use this, please report
4710 a bug to <linux-pci@vger.kernel.org>.
4711 routeirq Do IRQ routing for all PCI devices.
4712 This is normally done in pci_enable_device(),
4713 so this option is a temporary workaround
4714 for broken drivers that don't call it.
4715 skip_isa_align [X86] do not align io start addr, so can
4716 handle more pci cards
4717 noearly [X86] Don't do any early type 1 scanning.
4718 This might help on some broken boards which
4719 machine check when some devices' config space
4720 is read. But various workarounds are disabled
4721 and some IOMMU drivers will not work.
4722 bfsort Sort PCI devices into breadth-first order.
4723 This sorting is done to get a device
4724 order compatible with older (<= 2.4) kernels.
4725 nobfsort Don't sort PCI devices into breadth-first order.
4726 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4727 tuning and use the BIOS-configured MPS defaults.
4728 pcie_bus_safe Set every device's MPS to the largest value
4729 supported by all devices below the root complex.
4730 pcie_bus_perf Set device MPS to the largest allowable MPS
4731 based on its parent bus. Also set MRRS (Max
4732 Read Request Size) to the largest supported
4733 value (no larger than the MPS that the device
4734 or bus can support) for best performance.
4735 pcie_bus_peer2peer Set every device's MPS to 128B, which
4736 every device is guaranteed to support. This
4737 configuration allows peer-to-peer DMA between
4738 any pair of devices, possibly at the cost of
4739 reduced performance. This also guarantees
4740 that hot-added devices will work.
4741 cbiosize=nn[KMG] The fixed amount of bus space which is
4742 reserved for the CardBus bridge's IO window.
4743 The default value is 256 bytes.
4744 cbmemsize=nn[KMG] The fixed amount of bus space which is
4745 reserved for the CardBus bridge's memory
4746 window. The default value is 64 megabytes.
4747 resource_alignment=
4748 Format:
4749 [<order of align>@]<pci_dev>[; ...]
4750 Specifies alignment and device to reassign
4751 aligned memory resources. How to
4752 specify the device is described above.
4753 If <order of align> is not specified,
4754 PAGE_SIZE is used as alignment.
4755 A PCI-PCI bridge can be specified if resource
4756 windows need to be expanded.
4757 To specify the alignment for several
4758 instances of a device, the PCI vendor,
4759 device, subvendor, and subdevice may be
4760 specified, e.g., 12@pci:8086:9c22:103c:198f
4761 for 4096-byte alignment.
4762 ecrc= Enable/disable PCIe ECRC (transaction layer
4763 end-to-end CRC checking). Only effective if
4764 OS has native AER control (either granted by
4765 ACPI _OSC or forced via "pcie_ports=native")
4766 bios: Use BIOS/firmware settings. This is the
4767 the default.
4768 off: Turn ECRC off
4769 on: Turn ECRC on.
4770 hpiosize=nn[KMG] The fixed amount of bus space which is
4771 reserved for hotplug bridge's IO window.
4772 Default size is 256 bytes.
4773 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4774 reserved for hotplug bridge's MMIO window.
4775 Default size is 2 megabytes.
4776 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4777 reserved for hotplug bridge's MMIO_PREF window.
4778 Default size is 2 megabytes.
4779 hpmemsize=nn[KMG] The fixed amount of bus space which is
4780 reserved for hotplug bridge's MMIO and
4781 MMIO_PREF window.
4782 Default size is 2 megabytes.
4783 hpbussize=nn The minimum amount of additional bus numbers
4784 reserved for buses below a hotplug bridge.
4785 Default is 1.
4786 realloc= Enable/disable reallocating PCI bridge resources
4787 if allocations done by BIOS are too small to
4788 accommodate resources required by all child
4789 devices.
4790 off: Turn realloc off
4791 on: Turn realloc on
4792 realloc same as realloc=on
4793 noari do not use PCIe ARI.
4794 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4795 do not use PCIe ATS (and IOMMU device IOTLB).
4796 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4797 only look for one device below a PCIe downstream
4798 port.
4799 big_root_window Try to add a big 64bit memory window to the PCIe
4800 root complex on AMD CPUs. Some GFX hardware
4801 can resize a BAR to allow access to all VRAM.
4802 Adding the window is slightly risky (it may
4803 conflict with unreported devices), so this
4804 taints the kernel.
4805 disable_acs_redir=<pci_dev>[; ...]
4806 Specify one or more PCI devices (in the format
4807 specified above) separated by semicolons.
4808 Each device specified will have the PCI ACS
4809 redirect capabilities forced off which will
4810 allow P2P traffic between devices through
4811 bridges without forcing it upstream. Note:
4812 this removes isolation between devices and
4813 may put more devices in an IOMMU group.
4814 config_acs=
4815 Format:
4816 <ACS flags>@<pci_dev>[; ...]
4817 Specify one or more PCI devices (in the format
4818 specified above) optionally prepended with flags
4819 and separated by semicolons. The respective
4820 capabilities will be enabled, disabled or
4821 unchanged based on what is specified in
4822 flags.
4824 ACS Flags is defined as follows:
4825 bit-0 : ACS Source Validation
4826 bit-1 : ACS Translation Blocking
4827 bit-2 : ACS P2P Request Redirect
4828 bit-3 : ACS P2P Completion Redirect
4829 bit-4 : ACS Upstream Forwarding
4830 bit-5 : ACS P2P Egress Control
4831 bit-6 : ACS Direct Translated P2P
4832 Each bit can be marked as:
4833 '0' – force disabled
4834 '1' – force enabled
4835 'x' – unchanged
4836 For example,
4837 pci=config_acs=10x@pci:0:0
4838 would configure all devices that support
4839 ACS to enable P2P Request Redirect, disable
4840 Translation Blocking, and leave Source
4841 Validation unchanged from whatever power-up
4842 or firmware set it to.
4844 Note: this may remove isolation between devices
4845 and may put more devices in an IOMMU group.
4846 force_floating [S390] Force usage of floating interrupts.
4847 nomio [S390] Do not use MIO instructions.
4848 norid [S390] ignore the RID field and force use of
4849 one PCI domain per PCI function
4850 notph [PCIE] If the PCIE_TPH kernel config parameter
4851 is enabled, this kernel boot option can be used
4852 to disable PCIe TLP Processing Hints support
4853 system-wide.
4855 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power
4856 Management.
4857 off Don't touch ASPM configuration at all. Leave any
4858 configuration done by firmware unchanged.
4859 force Enable ASPM even on devices that claim not to support it.
4860 WARNING: Forcing ASPM on may cause system lockups.
4862 pcie_ports= [PCIE] PCIe port services handling:
4863 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4864 even if the platform doesn't give the OS permission to
4865 use them. This may cause conflicts if the platform
4866 also tries to use these services.
4867 dpc-native Use native PCIe service for DPC only. May
4868 cause conflicts if firmware uses AER or DPC.
4869 compat Disable native PCIe services (PME, AER, DPC, PCIe
4870 hotplug).
4872 pcie_port_pm= [PCIE] PCIe port power management handling:
4873 off Disable power management of all PCIe ports
4874 force Forcibly enable power management of all PCIe ports
4876 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4877 nomsi Do not use MSI for native PCIe PME signaling (this makes
4878 all PCIe root ports use INTx for all services).
4880 pcmv= [HW,PCMCIA] BadgePAD 4
4882 pd_ignore_unused
4883 [PM]
4884 Keep all power-domains already enabled by bootloader on,
4885 even if no driver has claimed them. This is useful
4886 for debug and development, but should not be
4887 needed on a platform with proper driver support.
4889 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4890 boot time.
4891 Format: { 0 | 1 }
4892 See arch/parisc/kernel/pdc_chassis.c
4894 percpu_alloc= [MM,EARLY]
4895 Select which percpu first chunk allocator to use.
4896 Currently supported values are "embed" and "page".
4897 Archs may support subset or none of the selections.
4898 See comments in mm/percpu.c for details on each
4899 allocator. This parameter is primarily for debugging
4900 and performance comparison.
4902 pirq= [SMP,APIC] Manual mp-table setup
4903 See Documentation/arch/x86/i386/IO-APIC.rst.
4905 plip= [PPT,NET] Parallel port network link
4906 Format: { parport<nr> | timid | 0 }
4907 See also Documentation/admin-guide/parport.rst.
4909 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4910 Override pmtimer IOPort with a hex value.
4911 e.g. pmtmr=0x508
4913 pmu_override= [PPC] Override the PMU.
4914 This option takes over the PMU facility, so it is no
4915 longer usable by perf. Setting this option starts the
4916 PMU counters by setting MMCR0 to 0 (the FC bit is
4917 cleared). If a number is given, then MMCR1 is set to
4918 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4919 remains 0.
4921 pm_debug_messages [SUSPEND,KNL]
4922 Enable suspend/resume debug messages during boot up.
4924 pnp.debug=1 [PNP]
4925 Enable PNP debug messages (depends on the
4926 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4927 via /sys/module/pnp/parameters/debug. We always show
4928 current resource usage; turning this on also shows
4929 possible settings and some assignment information.
4931 pnpacpi= [ACPI]
4932 { off }
4934 pnpbios= [ISAPNP]
4935 { on | off | curr | res | no-curr | no-res }
4937 pnp_reserve_irq=
4938 [ISAPNP] Exclude IRQs for the autoconfiguration
4940 pnp_reserve_dma=
4941 [ISAPNP] Exclude DMAs for the autoconfiguration
4943 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4944 Ranges are in pairs (I/O port base and size).
4946 pnp_reserve_mem=
4947 [ISAPNP] Exclude memory regions for the
4948 autoconfiguration.
4949 Ranges are in pairs (memory base and size).
4951 ports= [IP_VS_FTP] IPVS ftp helper module
4952 Default is 21.
4953 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4954 may be specified.
4955 Format: <port>,<port>....
4957 possible_cpus= [SMP,S390,X86]
4958 Format: <unsigned int>
4959 Set the number of possible CPUs, overriding the
4960 regular discovery mechanisms (such as ACPI/FW, etc).
4962 powersave=off [PPC] This option disables power saving features.
4963 It specifically disables cpuidle and sets the
4964 platform machine description specific power_save
4965 function to NULL. On Idle the CPU just reduces
4966 execution priority.
4968 ppc_strict_facility_enable
4969 [PPC,ENABLE] This option catches any kernel floating point,
4970 Altivec, VSX and SPE outside of regions specifically
4971 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4972 There is some performance impact when enabling this.
4974 ppc_tm= [PPC,EARLY]
4975 Format: {"off"}
4976 Disable Hardware Transactional Memory
4978 preempt= [KNL]
4979 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4980 none - Limited to cond_resched() calls
4981 voluntary - Limited to cond_resched() and might_sleep() calls
4982 full - Any section that isn't explicitly preempt disabled
4983 can be preempted anytime. Tasks will also yield
4984 contended spinlocks (if the critical section isn't
4985 explicitly preempt disabled beyond the lock itself).
4986 lazy - Scheduler controlled. Similar to full but instead
4987 of preempting the task immediately, the task gets
4988 one HZ tick time to yield itself before the
4989 preemption will be forced. One preemption is when the
4990 task returns to user space.
4992 print-fatal-signals=
4993 [KNL] debug: print fatal signals
4995 If enabled, warn about various signal handling
4996 related application anomalies: too many signals,
4997 too many POSIX.1 timers, fatal signals causing a
4998 coredump - etc.
5000 If you hit the warning due to signal overflow,
5001 you might want to try "ulimit -i unlimited".
5003 default: off.
5005 printk.always_kmsg_dump=
5006 Trigger kmsg_dump for cases other than kernel oops or
5007 panics
5008 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5009 default: disabled
5011 printk.console_no_auto_verbose=
5012 Disable console loglevel raise on oops, panic
5013 or lockdep-detected issues (only if lock debug is on).
5014 With an exception to setups with low baudrate on
5015 serial console, keeping this 0 is a good choice
5016 in order to provide more debug information.
5017 Format: <bool>
5018 default: 0 (auto_verbose is enabled)
5020 printk.devkmsg={on,off,ratelimit}
5021 Control writing to /dev/kmsg.
5022 on - unlimited logging to /dev/kmsg from userspace
5023 off - logging to /dev/kmsg disabled
5024 ratelimit - ratelimit the logging
5025 Default: ratelimit
5027 printk.time= Show timing data prefixed to each printk message line
5028 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5030 proc_mem.force_override= [KNL]
5031 Format: {always | ptrace | never}
5032 Traditionally /proc/pid/mem allows memory permissions to be
5033 overridden without restrictions. This option may be set to
5034 restrict that. Can be one of:
5035 - 'always': traditional behavior always allows mem overrides.
5036 - 'ptrace': only allow mem overrides for active ptracers.
5037 - 'never': never allow mem overrides.
5038 If not specified, default is the CONFIG_PROC_MEM_* choice.
5040 processor.max_cstate= [HW,ACPI]
5041 Limit processor to maximum C-state
5042 max_cstate=9 overrides any DMI blacklist limit.
5044 processor.nocst [HW,ACPI]
5045 Ignore the _CST method to determine C-states,
5046 instead using the legacy FADT method
5048 profile= [KNL] Enable kernel profiling via /proc/profile
5049 Format: [<profiletype>,]<number>
5050 Param: <profiletype>: "schedule" or "kvm"
5051 [defaults to kernel profiling]
5052 Param: "schedule" - profile schedule points.
5053 Param: "kvm" - profile VM exits.
5054 Param: <number> - step/bucket size as a power of 2 for
5055 statistical time based profiling.
5057 prompt_ramdisk= [RAM] [Deprecated]
5059 prot_virt= [S390] enable hosting protected virtual machines
5060 isolated from the hypervisor (if hardware supports
5061 that). If enabled, the default kernel base address
5062 might be overridden even when Kernel Address Space
5063 Layout Randomization is disabled.
5064 Format: <bool>
5066 psi= [KNL] Enable or disable pressure stall information
5067 tracking.
5068 Format: <bool>
5070 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
5071 probe for; one of (bare|imps|exps|lifebook|any).
5072 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
5073 per second.
5074 psmouse.resetafter= [HW,MOUSE]
5075 Try to reset the device after so many bad packets
5076 (0 = never).
5077 psmouse.resolution=
5078 [HW,MOUSE] Set desired mouse resolution, in dpi.
5079 psmouse.smartscroll=
5080 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
5081 0 = disabled, 1 = enabled (default).
5083 pstore.backend= Specify the name of the pstore backend to use
5085 pti= [X86-64] Control Page Table Isolation of user and
5086 kernel address spaces. Disabling this feature
5087 removes hardening, but improves performance of
5088 system calls and interrupts.
5090 on - unconditionally enable
5091 off - unconditionally disable
5092 auto - kernel detects whether your CPU model is
5093 vulnerable to issues that PTI mitigates
5095 Not specifying this option is equivalent to pti=auto.
5097 pty.legacy_count=
5098 [KNL] Number of legacy pty's. Overwrites compiled-in
5099 default number.
5101 quiet [KNL,EARLY] Disable most log messages
5103 r128= [HW,DRM]
5105 radix_hcall_invalidate=on [PPC/PSERIES]
5106 Disable RADIX GTSE feature and use hcall for TLB
5107 invalidate.
5109 raid= [HW,RAID]
5110 See Documentation/admin-guide/md.rst.
5112 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
5113 See Documentation/admin-guide/blockdev/ramdisk.rst.
5115 ramdisk_start= [RAM] RAM disk image start address
5117 random.trust_cpu=off
5118 [KNL,EARLY] Disable trusting the use of the CPU's
5119 random number generator (if available) to
5120 initialize the kernel's RNG.
5122 random.trust_bootloader=off
5123 [KNL,EARLY] Disable trusting the use of the a seed
5124 passed by the bootloader (if available) to
5125 initialize the kernel's RNG.
5127 randomize_kstack_offset=
5128 [KNL,EARLY] Enable or disable kernel stack offset
5129 randomization, which provides roughly 5 bits of
5130 entropy, frustrating memory corruption attacks
5131 that depend on stack address determinism or
5132 cross-syscall address exposures. This is only
5133 available on architectures that have defined
5134 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
5135 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
5136 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
5138 ras=option[,option,...] [KNL] RAS-specific options
5140 cec_disable [X86]
5141 Disable the Correctable Errors Collector,
5142 see CONFIG_RAS_CEC help text.
5144 rcu_nocbs[=cpu-list]
5145 [KNL] The optional argument is a cpu list,
5146 as described above.
5148 In kernels built with CONFIG_RCU_NOCB_CPU=y,
5149 enable the no-callback CPU mode, which prevents
5150 such CPUs' callbacks from being invoked in
5151 softirq context. Invocation of such CPUs' RCU
5152 callbacks will instead be offloaded to "rcuox/N"
5153 kthreads created for that purpose, where "x" is
5154 "p" for RCU-preempt, "s" for RCU-sched, and "g"
5155 for the kthreads that mediate grace periods; and
5156 "N" is the CPU number. This reduces OS jitter on
5157 the offloaded CPUs, which can be useful for HPC
5158 and real-time workloads. It can also improve
5159 energy efficiency for asymmetric multiprocessors.
5161 If a cpulist is passed as an argument, the specified
5162 list of CPUs is set to no-callback mode from boot.
5164 Otherwise, if the '=' sign and the cpulist
5165 arguments are omitted, no CPU will be set to
5166 no-callback mode from boot but the mode may be
5167 toggled at runtime via cpusets.
5169 Note that this argument takes precedence over
5170 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
5172 rcu_nocb_poll [KNL]
5173 Rather than requiring that offloaded CPUs
5174 (specified by rcu_nocbs= above) explicitly
5175 awaken the corresponding "rcuoN" kthreads,
5176 make these kthreads poll for callbacks.
5177 This improves the real-time response for the
5178 offloaded CPUs by relieving them of the need to
5179 wake up the corresponding kthread, but degrades
5180 energy efficiency by requiring that the kthreads
5181 periodically wake up to do the polling.
5183 rcutree.blimit= [KNL]
5184 Set maximum number of finished RCU callbacks to
5185 process in one batch.
5187 rcutree.csd_lock_suppress_rcu_stall= [KNL]
5188 Do only a one-line RCU CPU stall warning when
5189 there is an ongoing too-long CSD-lock wait.
5191 rcutree.do_rcu_barrier= [KNL]
5192 Request a call to rcu_barrier(). This is
5193 throttled so that userspace tests can safely
5194 hammer on the sysfs variable if they so choose.
5195 If triggered before the RCU grace-period machinery
5196 is fully active, this will error out with EAGAIN.
5198 rcutree.dump_tree= [KNL]
5199 Dump the structure of the rcu_node combining tree
5200 out at early boot. This is used for diagnostic
5201 purposes, to verify correct tree setup.
5203 rcutree.gp_cleanup_delay= [KNL]
5204 Set the number of jiffies to delay each step of
5205 RCU grace-period cleanup.
5207 rcutree.gp_init_delay= [KNL]
5208 Set the number of jiffies to delay each step of
5209 RCU grace-period initialization.
5211 rcutree.gp_preinit_delay= [KNL]
5212 Set the number of jiffies to delay each step of
5213 RCU grace-period pre-initialization, that is,
5214 the propagation of recent CPU-hotplug changes up
5215 the rcu_node combining tree.
5217 rcutree.jiffies_till_first_fqs= [KNL]
5218 Set delay from grace-period initialization to
5219 first attempt to force quiescent states.
5220 Units are jiffies, minimum value is zero,
5221 and maximum value is HZ.
5223 rcutree.jiffies_till_next_fqs= [KNL]
5224 Set delay between subsequent attempts to force
5225 quiescent states. Units are jiffies, minimum
5226 value is one, and maximum value is HZ.
5228 rcutree.jiffies_till_sched_qs= [KNL]
5229 Set required age in jiffies for a
5230 given grace period before RCU starts
5231 soliciting quiescent-state help from
5232 rcu_note_context_switch() and cond_resched().
5233 If not specified, the kernel will calculate
5234 a value based on the most recent settings
5235 of rcutree.jiffies_till_first_fqs
5236 and rcutree.jiffies_till_next_fqs.
5237 This calculated value may be viewed in
5238 rcutree.jiffies_to_sched_qs. Any attempt to set
5239 rcutree.jiffies_to_sched_qs will be cheerfully
5240 overwritten.
5242 rcutree.kthread_prio= [KNL,BOOT]
5243 Set the SCHED_FIFO priority of the RCU per-CPU
5244 kthreads (rcuc/N). This value is also used for
5245 the priority of the RCU boost threads (rcub/N)
5246 and for the RCU grace-period kthreads (rcu_bh,
5247 rcu_preempt, and rcu_sched). If RCU_BOOST is
5248 set, valid values are 1-99 and the default is 1
5249 (the least-favored priority). Otherwise, when
5250 RCU_BOOST is not set, valid values are 0-99 and
5251 the default is zero (non-realtime operation).
5252 When RCU_NOCB_CPU is set, also adjust the
5253 priority of NOCB callback kthreads.
5255 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
5256 On callback-offloaded (rcu_nocbs) CPUs,
5257 RCU reduces the lock contention that would
5258 otherwise be caused by callback floods through
5259 use of the ->nocb_bypass list. However, in the
5260 common non-flooded case, RCU queues directly to
5261 the main ->cblist in order to avoid the extra
5262 overhead of the ->nocb_bypass list and its lock.
5263 But if there are too many callbacks queued during
5264 a single jiffy, RCU pre-queues the callbacks into
5265 the ->nocb_bypass queue. The definition of "too
5266 many" is supplied by this kernel boot parameter.
5268 rcutree.nohz_full_patience_delay= [KNL]
5269 On callback-offloaded (rcu_nocbs) CPUs, avoid
5270 disturbing RCU unless the grace period has
5271 reached the specified age in milliseconds.
5272 Defaults to zero. Large values will be capped
5273 at five seconds. All values will be rounded down
5274 to the nearest value representable by jiffies.
5276 rcutree.qhimark= [KNL]
5277 Set threshold of queued RCU callbacks beyond which
5278 batch limiting is disabled.
5280 rcutree.qlowmark= [KNL]
5281 Set threshold of queued RCU callbacks below which
5282 batch limiting is re-enabled.
5284 rcutree.qovld= [KNL]
5285 Set threshold of queued RCU callbacks beyond which
5286 RCU's force-quiescent-state scan will aggressively
5287 enlist help from cond_resched() and sched IPIs to
5288 help CPUs more quickly reach quiescent states.
5289 Set to less than zero to make this be set based
5290 on rcutree.qhimark at boot time and to zero to
5291 disable more aggressive help enlistment.
5293 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
5294 Set the page-cache refill delay (in milliseconds)
5295 in response to low-memory conditions. The range
5296 of permitted values is in the range 0:100000.
5298 rcutree.rcu_divisor= [KNL]
5299 Set the shift-right count to use to compute
5300 the callback-invocation batch limit bl from
5301 the number of callbacks queued on this CPU.
5302 The result will be bounded below by the value of
5303 the rcutree.blimit kernel parameter. Every bl
5304 callbacks, the softirq handler will exit in
5305 order to allow the CPU to do other work.
5307 Please note that this callback-invocation batch
5308 limit applies only to non-offloaded callback
5309 invocation. Offloaded callbacks are instead
5310 invoked in the context of an rcuoc kthread, which
5311 scheduler will preempt as it does any other task.
5313 rcutree.rcu_fanout_exact= [KNL]
5314 Disable autobalancing of the rcu_node combining
5315 tree. This is used by rcutorture, and might
5316 possibly be useful for architectures having high
5317 cache-to-cache transfer latencies.
5319 rcutree.rcu_fanout_leaf= [KNL]
5320 Change the number of CPUs assigned to each
5321 leaf rcu_node structure. Useful for very
5322 large systems, which will choose the value 64,
5323 and for NUMA systems with large remote-access
5324 latencies, which will choose a value aligned
5325 with the appropriate hardware boundaries.
5327 rcutree.rcu_min_cached_objs= [KNL]
5328 Minimum number of objects which are cached and
5329 maintained per one CPU. Object size is equal
5330 to PAGE_SIZE. The cache allows to reduce the
5331 pressure to page allocator, also it makes the
5332 whole algorithm to behave better in low memory
5333 condition.
5335 rcutree.rcu_nocb_gp_stride= [KNL]
5336 Set the number of NOCB callback kthreads in
5337 each group, which defaults to the square root
5338 of the number of CPUs. Larger numbers reduce
5339 the wakeup overhead on the global grace-period
5340 kthread, but increases that same overhead on
5341 each group's NOCB grace-period kthread.
5343 rcutree.rcu_kick_kthreads= [KNL]
5344 Cause the grace-period kthread to get an extra
5345 wake_up() if it sleeps three times longer than
5346 it should at force-quiescent-state time.
5347 This wake_up() will be accompanied by a
5348 WARN_ONCE() splat and an ftrace_dump().
5350 rcutree.rcu_resched_ns= [KNL]
5351 Limit the time spend invoking a batch of RCU
5352 callbacks to the specified number of nanoseconds.
5353 By default, this limit is checked only once
5354 every 32 callbacks in order to limit the pain
5355 inflicted by local_clock() overhead.
5357 rcutree.rcu_unlock_delay= [KNL]
5358 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
5359 this specifies an rcu_read_unlock()-time delay
5360 in microseconds. This defaults to zero.
5361 Larger delays increase the probability of
5362 catching RCU pointer leaks, that is, buggy use
5363 of RCU-protected pointers after the relevant
5364 rcu_read_unlock() has completed.
5366 rcutree.sysrq_rcu= [KNL]
5367 Commandeer a sysrq key to dump out Tree RCU's
5368 rcu_node tree with an eye towards determining
5369 why a new grace period has not yet started.
5371 rcutree.use_softirq= [KNL]
5372 If set to zero, move all RCU_SOFTIRQ processing to
5373 per-CPU rcuc kthreads. Defaults to a non-zero
5374 value, meaning that RCU_SOFTIRQ is used by default.
5375 Specify rcutree.use_softirq=0 to use rcuc kthreads.
5377 But note that CONFIG_PREEMPT_RT=y kernels disable
5378 this kernel boot parameter, forcibly setting it
5379 to zero.
5381 rcutree.enable_rcu_lazy= [KNL]
5382 To save power, batch RCU callbacks and flush after
5383 delay, memory pressure or callback list growing too
5384 big.
5386 rcutree.rcu_normal_wake_from_gp= [KNL]
5387 Reduces a latency of synchronize_rcu() call. This approach
5388 maintains its own track of synchronize_rcu() callers, so it
5389 does not interact with regular callbacks because it does not
5390 use a call_rcu[_hurry]() path. Please note, this is for a
5391 normal grace period.
5393 How to enable it:
5395 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp
5396 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1"
5398 Default is 0.
5400 rcuscale.gp_async= [KNL]
5401 Measure performance of asynchronous
5402 grace-period primitives such as call_rcu().
5404 rcuscale.gp_async_max= [KNL]
5405 Specify the maximum number of outstanding
5406 callbacks per writer thread. When a writer
5407 thread exceeds this limit, it invokes the
5408 corresponding flavor of rcu_barrier() to allow
5409 previously posted callbacks to drain.
5411 rcuscale.gp_exp= [KNL]
5412 Measure performance of expedited synchronous
5413 grace-period primitives.
5415 rcuscale.holdoff= [KNL]
5416 Set test-start holdoff period. The purpose of
5417 this parameter is to delay the start of the
5418 test until boot completes in order to avoid
5419 interference.
5421 rcuscale.kfree_by_call_rcu= [KNL]
5422 In kernels built with CONFIG_RCU_LAZY=y, test
5423 call_rcu() instead of kfree_rcu().
5425 rcuscale.kfree_mult= [KNL]
5426 Instead of allocating an object of size kfree_obj,
5427 allocate one of kfree_mult * sizeof(kfree_obj).
5428 Defaults to 1.
5430 rcuscale.kfree_rcu_test= [KNL]
5431 Set to measure performance of kfree_rcu() flooding.
5433 rcuscale.kfree_rcu_test_double= [KNL]
5434 Test the double-argument variant of kfree_rcu().
5435 If this parameter has the same value as
5436 rcuscale.kfree_rcu_test_single, both the single-
5437 and double-argument variants are tested.
5439 rcuscale.kfree_rcu_test_single= [KNL]
5440 Test the single-argument variant of kfree_rcu().
5441 If this parameter has the same value as
5442 rcuscale.kfree_rcu_test_double, both the single-
5443 and double-argument variants are tested.
5445 rcuscale.kfree_nthreads= [KNL]
5446 The number of threads running loops of kfree_rcu().
5448 rcuscale.kfree_alloc_num= [KNL]
5449 Number of allocations and frees done in an iteration.
5451 rcuscale.kfree_loops= [KNL]
5452 Number of loops doing rcuscale.kfree_alloc_num number
5453 of allocations and frees.
5455 rcuscale.minruntime= [KNL]
5456 Set the minimum test run time in seconds. This
5457 does not affect the data-collection interval,
5458 but instead allows better measurement of things
5459 like CPU consumption.
5461 rcuscale.nreaders= [KNL]
5462 Set number of RCU readers. The value -1 selects
5463 N, where N is the number of CPUs. A value
5464 "n" less than -1 selects N-n+1, where N is again
5465 the number of CPUs. For example, -2 selects N
5466 (the number of CPUs), -3 selects N+1, and so on.
5467 A value of "n" less than or equal to -N selects
5468 a single reader.
5470 rcuscale.nwriters= [KNL]
5471 Set number of RCU writers. The values operate
5472 the same as for rcuscale.nreaders.
5473 N, where N is the number of CPUs
5475 rcuscale.scale_type= [KNL]
5476 Specify the RCU implementation to test.
5478 rcuscale.shutdown= [KNL]
5479 Shut the system down after performance tests
5480 complete. This is useful for hands-off automated
5481 testing.
5483 rcuscale.verbose= [KNL]
5484 Enable additional printk() statements.
5486 rcuscale.writer_holdoff= [KNL]
5487 Write-side holdoff between grace periods,
5488 in microseconds. The default of zero says
5489 no holdoff.
5491 rcuscale.writer_holdoff_jiffies= [KNL]
5492 Additional write-side holdoff between grace
5493 periods, but in jiffies. The default of zero
5494 says no holdoff.
5496 rcutorture.fqs_duration= [KNL]
5497 Set duration of force_quiescent_state bursts
5498 in microseconds.
5500 rcutorture.fqs_holdoff= [KNL]
5501 Set holdoff time within force_quiescent_state bursts
5502 in microseconds.
5504 rcutorture.fqs_stutter= [KNL]
5505 Set wait time between force_quiescent_state bursts
5506 in seconds.
5508 rcutorture.fwd_progress= [KNL]
5509 Specifies the number of kthreads to be used
5510 for RCU grace-period forward-progress testing
5511 for the types of RCU supporting this notion.
5512 Defaults to 1 kthread, values less than zero or
5513 greater than the number of CPUs cause the number
5514 of CPUs to be used.
5516 rcutorture.fwd_progress_div= [KNL]
5517 Specify the fraction of a CPU-stall-warning
5518 period to do tight-loop forward-progress testing.
5520 rcutorture.fwd_progress_holdoff= [KNL]
5521 Number of seconds to wait between successive
5522 forward-progress tests.
5524 rcutorture.fwd_progress_need_resched= [KNL]
5525 Enclose cond_resched() calls within checks for
5526 need_resched() during tight-loop forward-progress
5527 testing.
5529 rcutorture.gp_cond= [KNL]
5530 Use conditional/asynchronous update-side
5531 normal-grace-period primitives, if available.
5533 rcutorture.gp_cond_exp= [KNL]
5534 Use conditional/asynchronous update-side
5535 expedited-grace-period primitives, if available.
5537 rcutorture.gp_cond_full= [KNL]
5538 Use conditional/asynchronous update-side
5539 normal-grace-period primitives that also take
5540 concurrent expedited grace periods into account,
5541 if available.
5543 rcutorture.gp_cond_exp_full= [KNL]
5544 Use conditional/asynchronous update-side
5545 expedited-grace-period primitives that also take
5546 concurrent normal grace periods into account,
5547 if available.
5549 rcutorture.gp_cond_wi= [KNL]
5550 Nominal wait interval for normal conditional
5551 grace periods (specified by rcutorture's
5552 gp_cond and gp_cond_full module parameters),
5553 in microseconds. The actual wait interval will
5554 be randomly selected to nanosecond granularity up
5555 to this wait interval. Defaults to 16 jiffies,
5556 for example, 16,000 microseconds on a system
5557 with HZ=1000.
5559 rcutorture.gp_cond_wi_exp= [KNL]
5560 Nominal wait interval for expedited conditional
5561 grace periods (specified by rcutorture's
5562 gp_cond_exp and gp_cond_exp_full module
5563 parameters), in microseconds. The actual wait
5564 interval will be randomly selected to nanosecond
5565 granularity up to this wait interval. Defaults to
5566 128 microseconds.
5568 rcutorture.gp_exp= [KNL]
5569 Use expedited update-side primitives, if available.
5571 rcutorture.gp_normal= [KNL]
5572 Use normal (non-expedited) asynchronous
5573 update-side primitives, if available.
5575 rcutorture.gp_poll= [KNL]
5576 Use polled update-side normal-grace-period
5577 primitives, if available.
5579 rcutorture.gp_poll_exp= [KNL]
5580 Use polled update-side expedited-grace-period
5581 primitives, if available.
5583 rcutorture.gp_poll_full= [KNL]
5584 Use polled update-side normal-grace-period
5585 primitives that also take concurrent expedited
5586 grace periods into account, if available.
5588 rcutorture.gp_poll_exp_full= [KNL]
5589 Use polled update-side expedited-grace-period
5590 primitives that also take concurrent normal
5591 grace periods into account, if available.
5593 rcutorture.gp_poll_wi= [KNL]
5594 Nominal wait interval for normal conditional
5595 grace periods (specified by rcutorture's
5596 gp_poll and gp_poll_full module parameters),
5597 in microseconds. The actual wait interval will
5598 be randomly selected to nanosecond granularity up
5599 to this wait interval. Defaults to 16 jiffies,
5600 for example, 16,000 microseconds on a system
5601 with HZ=1000.
5603 rcutorture.gp_poll_wi_exp= [KNL]
5604 Nominal wait interval for expedited conditional
5605 grace periods (specified by rcutorture's
5606 gp_poll_exp and gp_poll_exp_full module
5607 parameters), in microseconds. The actual wait
5608 interval will be randomly selected to nanosecond
5609 granularity up to this wait interval. Defaults to
5610 128 microseconds.
5612 rcutorture.gp_sync= [KNL]
5613 Use normal (non-expedited) synchronous
5614 update-side primitives, if available. If all
5615 of rcutorture.gp_cond=, rcutorture.gp_exp=,
5616 rcutorture.gp_normal=, and rcutorture.gp_sync=
5617 are zero, rcutorture acts as if is interpreted
5618 they are all non-zero.
5620 rcutorture.irqreader= [KNL]
5621 Run RCU readers from irq handlers, or, more
5622 accurately, from a timer handler. Not all RCU
5623 flavors take kindly to this sort of thing.
5625 rcutorture.leakpointer= [KNL]
5626 Leak an RCU-protected pointer out of the reader.
5627 This can of course result in splats, and is
5628 intended to test the ability of things like
5629 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
5630 such leaks.
5632 rcutorture.n_barrier_cbs= [KNL]
5633 Set callbacks/threads for rcu_barrier() testing.
5635 rcutorture.nfakewriters= [KNL]
5636 Set number of concurrent RCU writers. These just
5637 stress RCU, they don't participate in the actual
5638 test, hence the "fake".
5640 rcutorture.nocbs_nthreads= [KNL]
5641 Set number of RCU callback-offload togglers.
5642 Zero (the default) disables toggling.
5644 rcutorture.nocbs_toggle= [KNL]
5645 Set the delay in milliseconds between successive
5646 callback-offload toggling attempts.
5648 rcutorture.nreaders= [KNL]
5649 Set number of RCU readers. The value -1 selects
5650 N-1, where N is the number of CPUs. A value
5651 "n" less than -1 selects N-n-2, where N is again
5652 the number of CPUs. For example, -2 selects N
5653 (the number of CPUs), -3 selects N+1, and so on.
5655 rcutorture.object_debug= [KNL]
5656 Enable debug-object double-call_rcu() testing.
5658 rcutorture.onoff_holdoff= [KNL]
5659 Set time (s) after boot for CPU-hotplug testing.
5661 rcutorture.onoff_interval= [KNL]
5662 Set time (jiffies) between CPU-hotplug operations,
5663 or zero to disable CPU-hotplug testing.
5665 rcutorture.preempt_duration= [KNL]
5666 Set duration (in milliseconds) of preemptions
5667 by a high-priority FIFO real-time task. Set to
5668 zero (the default) to disable. The CPUs to
5669 preempt are selected randomly from the set that
5670 are online at a given point in time. Races with
5671 CPUs going offline are ignored, with that attempt
5672 at preemption skipped.
5674 rcutorture.preempt_interval= [KNL]
5675 Set interval (in milliseconds, defaulting to one
5676 second) between preemptions by a high-priority
5677 FIFO real-time task. This delay is mediated
5678 by an hrtimer and is further fuzzed to avoid
5679 inadvertent synchronizations.
5681 rcutorture.read_exit_burst= [KNL]
5682 The number of times in a given read-then-exit
5683 episode that a set of read-then-exit kthreads
5684 is spawned.
5686 rcutorture.read_exit_delay= [KNL]
5687 The delay, in seconds, between successive
5688 read-then-exit testing episodes.
5690 rcutorture.reader_flavor= [KNL]
5691 A bit mask indicating which readers to use.
5692 If there is more than one bit set, the readers
5693 are entered from low-order bit up, and are
5694 exited in the opposite order. For SRCU, the
5695 0x1 bit is normal readers, 0x2 NMI-safe readers,
5696 and 0x4 light-weight readers.
5698 rcutorture.shuffle_interval= [KNL]
5699 Set task-shuffle interval (s). Shuffling tasks
5700 allows some CPUs to go into dyntick-idle mode
5701 during the rcutorture test.
5703 rcutorture.shutdown_secs= [KNL]
5704 Set time (s) after boot system shutdown. This
5705 is useful for hands-off automated testing.
5707 rcutorture.stall_cpu= [KNL]
5708 Duration of CPU stall (s) to test RCU CPU stall
5709 warnings, zero to disable.
5711 rcutorture.stall_cpu_block= [KNL]
5712 Sleep while stalling if set. This will result
5713 in warnings from preemptible RCU in addition to
5714 any other stall-related activity. Note that
5715 in kernels built with CONFIG_PREEMPTION=n and
5716 CONFIG_PREEMPT_COUNT=y, this parameter will
5717 cause the CPU to pass through a quiescent state.
5718 Given CONFIG_PREEMPTION=n, this will suppress
5719 RCU CPU stall warnings, but will instead result
5720 in scheduling-while-atomic splats.
5722 Use of this module parameter results in splats.
5725 rcutorture.stall_cpu_holdoff= [KNL]
5726 Time to wait (s) after boot before inducing stall.
5728 rcutorture.stall_cpu_irqsoff= [KNL]
5729 Disable interrupts while stalling if set, but only
5730 on the first stall in the set.
5732 rcutorture.stall_cpu_repeat= [KNL]
5733 Number of times to repeat the stall sequence,
5734 so that rcutorture.stall_cpu_repeat=3 will result
5735 in four stall sequences.
5737 rcutorture.stall_gp_kthread= [KNL]
5738 Duration (s) of forced sleep within RCU
5739 grace-period kthread to test RCU CPU stall
5740 warnings, zero to disable. If both stall_cpu
5741 and stall_gp_kthread are specified, the
5742 kthread is starved first, then the CPU.
5744 rcutorture.stat_interval= [KNL]
5745 Time (s) between statistics printk()s.
5747 rcutorture.stutter= [KNL]
5748 Time (s) to stutter testing, for example, specifying
5749 five seconds causes the test to run for five seconds,
5750 wait for five seconds, and so on. This tests RCU's
5751 ability to transition abruptly to and from idle.
5753 rcutorture.test_boost= [KNL]
5754 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5755 "Maybe" means test if the RCU implementation
5756 under test support RCU priority boosting.
5758 rcutorture.test_boost_duration= [KNL]
5759 Duration (s) of each individual boost test.
5761 rcutorture.test_boost_interval= [KNL]
5762 Interval (s) between each boost test.
5764 rcutorture.test_no_idle_hz= [KNL]
5765 Test RCU's dyntick-idle handling. See also the
5766 rcutorture.shuffle_interval parameter.
5768 rcutorture.torture_type= [KNL]
5769 Specify the RCU implementation to test.
5771 rcutorture.verbose= [KNL]
5772 Enable additional printk() statements.
5774 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5775 Dump ftrace buffer after reporting RCU CPU
5776 stall warning.
5778 rcupdate.rcu_cpu_stall_notifiers= [KNL]
5779 Provide RCU CPU stall notifiers, but see the
5780 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig
5781 option's help text. TL;DR: You almost certainly
5782 do not want rcupdate.rcu_cpu_stall_notifiers.
5784 rcupdate.rcu_cpu_stall_suppress= [KNL]
5785 Suppress RCU CPU stall warning messages.
5787 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5788 Suppress RCU CPU stall warning messages and
5789 rcutorture writer stall warnings that occur
5790 during early boot, that is, during the time
5791 before the init task is spawned.
5793 rcupdate.rcu_cpu_stall_timeout= [KNL]
5794 Set timeout for RCU CPU stall warning messages.
5795 The value is in seconds and the maximum allowed
5796 value is 300 seconds.
5798 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5799 Set timeout for expedited RCU CPU stall warning
5800 messages. The value is in milliseconds
5801 and the maximum allowed value is 21000
5802 milliseconds. Please note that this value is
5803 adjusted to an arch timer tick resolution.
5804 Setting this to zero causes the value from
5805 rcupdate.rcu_cpu_stall_timeout to be used (after
5806 conversion from seconds to milliseconds).
5808 rcupdate.rcu_cpu_stall_cputime= [KNL]
5809 Provide statistics on the cputime and count of
5810 interrupts and tasks during the sampling period. For
5811 multiple continuous RCU stalls, all sampling periods
5812 begin at half of the first RCU stall timeout.
5814 rcupdate.rcu_exp_stall_task_details= [KNL]
5815 Print stack dumps of any tasks blocking the
5816 current expedited RCU grace period during an
5817 expedited RCU CPU stall warning.
5819 rcupdate.rcu_expedited= [KNL]
5820 Use expedited grace-period primitives, for
5821 example, synchronize_rcu_expedited() instead
5822 of synchronize_rcu(). This reduces latency,
5823 but can increase CPU utilization, degrade
5824 real-time latency, and degrade energy efficiency.
5825 No effect on CONFIG_TINY_RCU kernels.
5827 rcupdate.rcu_normal= [KNL]
5828 Use only normal grace-period primitives,
5829 for example, synchronize_rcu() instead of
5830 synchronize_rcu_expedited(). This improves
5831 real-time latency, CPU utilization, and
5832 energy efficiency, but can expose users to
5833 increased grace-period latency. This parameter
5834 overrides rcupdate.rcu_expedited. No effect on
5835 CONFIG_TINY_RCU kernels.
5837 rcupdate.rcu_normal_after_boot= [KNL]
5838 Once boot has completed (that is, after
5839 rcu_end_inkernel_boot() has been invoked), use
5840 only normal grace-period primitives. No effect
5841 on CONFIG_TINY_RCU kernels.
5843 But note that CONFIG_PREEMPT_RT=y kernels enables
5844 this kernel boot parameter, forcibly setting
5845 it to the value one, that is, converting any
5846 post-boot attempt at an expedited RCU grace
5847 period to instead use normal non-expedited
5848 grace-period processing.
5850 rcupdate.rcu_task_collapse_lim= [KNL]
5851 Set the maximum number of callbacks present
5852 at the beginning of a grace period that allows
5853 the RCU Tasks flavors to collapse back to using
5854 a single callback queue. This switching only
5855 occurs when rcupdate.rcu_task_enqueue_lim is
5856 set to the default value of -1.
5858 rcupdate.rcu_task_contend_lim= [KNL]
5859 Set the minimum number of callback-queuing-time
5860 lock-contention events per jiffy required to
5861 cause the RCU Tasks flavors to switch to per-CPU
5862 callback queuing. This switching only occurs
5863 when rcupdate.rcu_task_enqueue_lim is set to
5864 the default value of -1.
5866 rcupdate.rcu_task_enqueue_lim= [KNL]
5867 Set the number of callback queues to use for the
5868 RCU Tasks family of RCU flavors. The default
5869 of -1 allows this to be automatically (and
5870 dynamically) adjusted. This parameter is intended
5871 for use in testing.
5873 rcupdate.rcu_task_ipi_delay= [KNL]
5874 Set time in jiffies during which RCU tasks will
5875 avoid sending IPIs, starting with the beginning
5876 of a given grace period. Setting a large
5877 number avoids disturbing real-time workloads,
5878 but lengthens grace periods.
5880 rcupdate.rcu_task_lazy_lim= [KNL]
5881 Number of callbacks on a given CPU that will
5882 cancel laziness on that CPU. Use -1 to disable
5883 cancellation of laziness, but be advised that
5884 doing so increases the danger of OOM due to
5885 callback flooding.
5887 rcupdate.rcu_task_stall_info= [KNL]
5888 Set initial timeout in jiffies for RCU task stall
5889 informational messages, which give some indication
5890 of the problem for those not patient enough to
5891 wait for ten minutes. Informational messages are
5892 only printed prior to the stall-warning message
5893 for a given grace period. Disable with a value
5894 less than or equal to zero. Defaults to ten
5895 seconds. A change in value does not take effect
5896 until the beginning of the next grace period.
5898 rcupdate.rcu_task_stall_info_mult= [KNL]
5899 Multiplier for time interval between successive
5900 RCU task stall informational messages for a given
5901 RCU tasks grace period. This value is clamped
5902 to one through ten, inclusive. It defaults to
5903 the value three, so that the first informational
5904 message is printed 10 seconds into the grace
5905 period, the second at 40 seconds, the third at
5906 160 seconds, and then the stall warning at 600
5907 seconds would prevent a fourth at 640 seconds.
5909 rcupdate.rcu_task_stall_timeout= [KNL]
5910 Set timeout in jiffies for RCU task stall
5911 warning messages. Disable with a value less
5912 than or equal to zero. Defaults to ten minutes.
5913 A change in value does not take effect until
5914 the beginning of the next grace period.
5916 rcupdate.rcu_tasks_lazy_ms= [KNL]
5917 Set timeout in milliseconds RCU Tasks asynchronous
5918 callback batching for call_rcu_tasks().
5919 A negative value will take the default. A value
5920 of zero will disable batching. Batching is
5921 always disabled for synchronize_rcu_tasks().
5923 rcupdate.rcu_tasks_trace_lazy_ms= [KNL]
5924 Set timeout in milliseconds RCU Tasks
5925 Trace asynchronous callback batching for
5926 call_rcu_tasks_trace(). A negative value
5927 will take the default. A value of zero will
5928 disable batching. Batching is always disabled
5929 for synchronize_rcu_tasks_trace().
5931 rcupdate.rcu_self_test= [KNL]
5932 Run the RCU early boot self tests
5934 rdinit= [KNL]
5935 Format: <full_path>
5936 Run specified binary instead of /init from the ramdisk,
5937 used for early userspace startup. See initrd.
5939 rdrand= [X86,EARLY]
5940 force - Override the decision by the kernel to hide the
5941 advertisement of RDRAND support (this affects
5942 certain AMD processors because of buggy BIOS
5943 support, specifically around the suspend/resume
5944 path).
5946 rdt= [HW,X86,RDT]
5947 Turn on/off individual RDT features. List is:
5948 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5949 mba, smba, bmec.
5950 E.g. to turn on cmt and turn off mba use:
5951 rdt=cmt,!mba
5953 reboot= [KNL]
5954 Format (x86 or x86_64):
5955 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5956 [[,]s[mp]#### \
5957 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5958 [[,]f[orce]
5959 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5960 (prefix with 'panic_' to set mode for panic
5961 reboot only),
5962 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5963 reboot_force is either force or not specified,
5964 reboot_cpu is s[mp]#### with #### being the processor
5965 to be used for rebooting.
5967 acpi
5968 Use the ACPI RESET_REG in the FADT. If ACPI is not
5969 configured or the ACPI reset does not work, the reboot
5970 path attempts the reset using the keyboard controller.
5972 bios
5973 Use the CPU reboot vector for warm reset
5975 cold
5976 Set the cold reboot flag
5978 default
5979 There are some built-in platform specific "quirks"
5980 - you may see: "reboot: <name> series board detected.
5981 Selecting <type> for reboots." In the case where you
5982 think the quirk is in error (e.g. you have newer BIOS,
5983 or newer board) using this option will ignore the
5984 built-in quirk table, and use the generic default
5985 reboot actions.
5987 efi
5988 Use efi reset_system runtime service. If EFI is not
5989 configured or the EFI reset does not work, the reboot
5990 path attempts the reset using the keyboard controller.
5992 force
5993 Don't stop other CPUs on reboot. This can make reboot
5994 more reliable in some cases.
5996 kbd
5997 Use the keyboard controller. cold reset (default)
5999 pci
6000 Use a write to the PCI config space register 0xcf9 to
6001 trigger reboot.
6003 triple
6004 Force a triple fault (init)
6006 warm
6007 Don't set the cold reboot flag
6009 Using warm reset will be much faster especially on big
6010 memory systems because the BIOS will not go through
6011 the memory check. Disadvantage is that not all
6012 hardware will be completely reinitialized on reboot so
6013 there may be boot problems on some systems.
6016 refscale.holdoff= [KNL]
6017 Set test-start holdoff period. The purpose of
6018 this parameter is to delay the start of the
6019 test until boot completes in order to avoid
6020 interference.
6022 refscale.lookup_instances= [KNL]
6023 Number of data elements to use for the forms of
6024 SLAB_TYPESAFE_BY_RCU testing. A negative number
6025 is negated and multiplied by nr_cpu_ids, while
6026 zero specifies nr_cpu_ids.
6028 refscale.loops= [KNL]
6029 Set the number of loops over the synchronization
6030 primitive under test. Increasing this number
6031 reduces noise due to loop start/end overhead,
6032 but the default has already reduced the per-pass
6033 noise to a handful of picoseconds on ca. 2020
6034 x86 laptops.
6036 refscale.nreaders= [KNL]
6037 Set number of readers. The default value of -1
6038 selects N, where N is roughly 75% of the number
6039 of CPUs. A value of zero is an interesting choice.
6041 refscale.nruns= [KNL]
6042 Set number of runs, each of which is dumped onto
6043 the console log.
6045 refscale.readdelay= [KNL]
6046 Set the read-side critical-section duration,
6047 measured in microseconds.
6049 refscale.scale_type= [KNL]
6050 Specify the read-protection implementation to test.
6052 refscale.shutdown= [KNL]
6053 Shut down the system at the end of the performance
6054 test. This defaults to 1 (shut it down) when
6055 refscale is built into the kernel and to 0 (leave
6056 it running) when refscale is built as a module.
6058 refscale.verbose= [KNL]
6059 Enable additional printk() statements.
6061 refscale.verbose_batched= [KNL]
6062 Batch the additional printk() statements. If zero
6063 (the default) or negative, print everything. Otherwise,
6064 print every Nth verbose statement, where N is the value
6065 specified.
6067 regulator_ignore_unused
6068 [REGULATOR]
6069 Prevents regulator framework from disabling regulators
6070 that are unused, due no driver claiming them. This may
6071 be useful for debug and development, but should not be
6072 needed on a platform with proper driver support.
6074 relax_domain_level=
6075 [KNL, SMP] Set scheduler's default relax_domain_level.
6076 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
6078 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
6079 Format: <base1>,<size1>[,<base2>,<size2>,...]
6080 Reserve I/O ports or memory so the kernel won't use
6081 them. If <base> is less than 0x10000, the region
6082 is assumed to be I/O ports; otherwise it is memory.
6084 reserve_mem= [RAM]
6085 Format: nn[KNG]:<align>:<label>
6086 Reserve physical memory and label it with a name that
6087 other subsystems can use to access it. This is typically
6088 used for systems that do not wipe the RAM, and this command
6089 line will try to reserve the same physical memory on
6090 soft reboots. Note, it is not guaranteed to be the same
6091 location. For example, if anything about the system changes
6092 or if booting a different kernel. It can also fail if KASLR
6093 places the kernel at the location of where the RAM reservation
6094 was from a previous boot, the new reservation will be at a
6095 different location.
6096 Any subsystem using this feature must add a way to verify
6097 that the contents of the physical memory is from a previous
6098 boot, as there may be cases where the memory will not be
6099 located at the same location.
6101 The format is size:align:label for example, to request
6102 12 megabytes of 4096 alignment for ramoops:
6104 reserve_mem=12M:4096:oops ramoops.mem_name=oops
6106 reservetop= [X86-32,EARLY]
6107 Format: nn[KMG]
6108 Reserves a hole at the top of the kernel virtual
6109 address space.
6111 reset_devices [KNL] Force drivers to reset the underlying device
6112 during initialization.
6114 resume= [SWSUSP]
6115 Specify the partition device for software suspend
6116 Format:
6117 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
6119 resume_offset= [SWSUSP]
6120 Specify the offset from the beginning of the partition
6121 given by "resume=" at which the swap header is located,
6122 in <PAGE_SIZE> units (needed only for swap files).
6123 See Documentation/power/swsusp-and-swap-files.rst
6125 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
6126 read the resume files
6128 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
6129 Useful for devices that are detected asynchronously
6130 (e.g. USB and MMC devices).
6132 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
6133 be accessible via /sys/firmware/initrd.
6135 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
6136 Speculative Code Execution with Return Instructions)
6137 vulnerability.
6139 AMD-based UNRET and IBPB mitigations alone do not stop
6140 sibling threads from influencing the predictions of other
6141 sibling threads. For that reason, STIBP is used on pro-
6142 cessors that support it, and mitigate SMT on processors
6143 that don't.
6145 off - no mitigation
6146 auto - automatically select a migitation
6147 auto,nosmt - automatically select a mitigation,
6148 disabling SMT if necessary for
6149 the full mitigation (only on Zen1
6150 and older without STIBP).
6151 ibpb - On AMD, mitigate short speculation
6152 windows on basic block boundaries too.
6153 Safe, highest perf impact. It also
6154 enables STIBP if present. Not suitable
6155 on Intel.
6156 ibpb,nosmt - Like "ibpb" above but will disable SMT
6157 when STIBP is not available. This is
6158 the alternative for systems which do not
6159 have STIBP.
6160 unret - Force enable untrained return thunks,
6161 only effective on AMD f15h-f17h based
6162 systems.
6163 unret,nosmt - Like unret, but will disable SMT when STIBP
6164 is not available. This is the alternative for
6165 systems which do not have STIBP.
6167 Selecting 'auto' will choose a mitigation method at run
6168 time according to the CPU.
6170 Not specifying this option is equivalent to retbleed=auto.
6172 rfkill.default_state=
6173 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
6174 etc. communication is blocked by default.
6175 1 Unblocked.
6177 rfkill.master_switch_mode=
6178 0 The "airplane mode" button does nothing.
6179 1 The "airplane mode" button toggles between everything
6180 blocked and the previous configuration.
6181 2 The "airplane mode" button toggles between everything
6182 blocked and everything unblocked.
6184 ring3mwait=disable
6185 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
6186 CPUs.
6188 riscv_isa_fallback [RISCV,EARLY]
6189 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
6190 falling back to detecting extension support by parsing
6191 "riscv,isa" property on devicetree systems when the
6192 replacement properties are not found. See the Kconfig
6193 entry for RISCV_ISA_FALLBACK.
6195 ro [KNL] Mount root device read-only on boot
6197 rodata= [KNL,EARLY]
6198 on Mark read-only kernel memory as read-only (default).
6199 off Leave read-only kernel memory writable for debugging.
6200 full Mark read-only kernel memory and aliases as read-only
6201 [arm64]
6203 rockchip.usb_uart
6204 [EARLY]
6205 Enable the uart passthrough on the designated usb port
6206 on Rockchip SoCs. When active, the signals of the
6207 debug-uart get routed to the D+ and D- pins of the usb
6208 port and the regular usb controller gets disabled.
6210 root= [KNL] Root filesystem
6211 Usually this a a block device specifier of some kind,
6212 see the early_lookup_bdev comment in
6213 block/early-lookup.c for details.
6214 Alternatively this can be "ram" for the legacy initial
6215 ramdisk, "nfs" and "cifs" for root on a network file
6216 system, or "mtd" and "ubi" for mounting from raw flash.
6218 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
6219 mount the root filesystem
6221 rootflags= [KNL] Set root filesystem mount option string
6223 rootfstype= [KNL] Set root filesystem type
6225 rootwait [KNL] Wait (indefinitely) for root device to show up.
6226 Useful for devices that are detected asynchronously
6227 (e.g. USB and MMC devices).
6229 rootwait= [KNL] Maximum time (in seconds) to wait for root device
6230 to show up before attempting to mount the root
6231 filesystem.
6233 rproc_mem=nn[KMG][@address]
6234 [KNL,ARM,CMA] Remoteproc physical memory block.
6235 Memory area to be used by remote processor image,
6236 managed by CMA.
6238 rw [KNL] Mount root device read-write on boot
6240 S [KNL] Run init in single mode
6242 s390_iommu= [HW,S390]
6243 Set s390 IOTLB flushing mode
6244 strict
6245 With strict flushing every unmap operation will result
6246 in an IOTLB flush. Default is lazy flushing before
6247 reuse, which is faster. Deprecated, equivalent to
6248 iommu.strict=1.
6250 s390_iommu_aperture= [KNL,S390]
6251 Specifies the size of the per device DMA address space
6252 accessible through the DMA and IOMMU APIs as a decimal
6253 factor of the size of main memory.
6254 The default is 1 meaning that one can concurrently use
6255 as many DMA addresses as physical memory is installed,
6256 if supported by hardware, and thus map all of memory
6257 once. With a value of 2 one can map all of memory twice
6258 and so on. As a special case a factor of 0 imposes no
6259 restrictions other than those given by hardware at the
6260 cost of significant additional memory use for tables.
6262 sa1100ir [NET]
6263 See drivers/net/irda/sa1100_ir.c.
6265 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
6267 schedstats= [KNL,X86] Enable or disable scheduled statistics.
6268 Allowed values are enable and disable. This feature
6269 incurs a small amount of overhead in the scheduler
6270 but is useful for debugging and performance tuning.
6272 sched_thermal_decay_shift=
6273 [Deprecated]
6274 [KNL, SMP] Set a decay shift for scheduler thermal
6275 pressure signal. Thermal pressure signal follows the
6276 default decay period of other scheduler pelt
6277 signals(usually 32 ms but configurable). Setting
6278 sched_thermal_decay_shift will left shift the decay
6279 period for the thermal pressure signal by the shift
6280 value.
6281 i.e. with the default pelt decay period of 32 ms
6282 sched_thermal_decay_shift thermal pressure decay pr
6283 1 64 ms
6284 2 128 ms
6285 and so on.
6286 Format: integer between 0 and 10
6287 Default is 0.
6289 scftorture.holdoff= [KNL]
6290 Number of seconds to hold off before starting
6291 test. Defaults to zero for module insertion and
6292 to 10 seconds for built-in smp_call_function()
6293 tests.
6295 scftorture.longwait= [KNL]
6296 Request ridiculously long waits randomly selected
6297 up to the chosen limit in seconds. Zero (the
6298 default) disables this feature. Please note
6299 that requesting even small non-zero numbers of
6300 seconds can result in RCU CPU stall warnings,
6301 softlockup complaints, and so on.
6303 scftorture.nthreads= [KNL]
6304 Number of kthreads to spawn to invoke the
6305 smp_call_function() family of functions.
6306 The default of -1 specifies a number of kthreads
6307 equal to the number of CPUs.
6309 scftorture.onoff_holdoff= [KNL]
6310 Number seconds to wait after the start of the
6311 test before initiating CPU-hotplug operations.
6313 scftorture.onoff_interval= [KNL]
6314 Number seconds to wait between successive
6315 CPU-hotplug operations. Specifying zero (which
6316 is the default) disables CPU-hotplug operations.
6318 scftorture.shutdown_secs= [KNL]
6319 The number of seconds following the start of the
6320 test after which to shut down the system. The
6321 default of zero avoids shutting down the system.
6322 Non-zero values are useful for automated tests.
6324 scftorture.stat_interval= [KNL]
6325 The number of seconds between outputting the
6326 current test statistics to the console. A value
6327 of zero disables statistics output.
6329 scftorture.stutter_cpus= [KNL]
6330 The number of jiffies to wait between each change
6331 to the set of CPUs under test.
6333 scftorture.use_cpus_read_lock= [KNL]
6334 Use use_cpus_read_lock() instead of the default
6335 preempt_disable() to disable CPU hotplug
6336 while invoking one of the smp_call_function*()
6337 functions.
6339 scftorture.verbose= [KNL]
6340 Enable additional printk() statements.
6342 scftorture.weight_single= [KNL]
6343 The probability weighting to use for the
6344 smp_call_function_single() function with a zero
6345 "wait" parameter. A value of -1 selects the
6346 default if all other weights are -1. However,
6347 if at least one weight has some other value, a
6348 value of -1 will instead select a weight of zero.
6350 scftorture.weight_single_wait= [KNL]
6351 The probability weighting to use for the
6352 smp_call_function_single() function with a
6353 non-zero "wait" parameter. See weight_single.
6355 scftorture.weight_many= [KNL]
6356 The probability weighting to use for the
6357 smp_call_function_many() function with a zero
6358 "wait" parameter. See weight_single.
6359 Note well that setting a high probability for
6360 this weighting can place serious IPI load
6361 on the system.
6363 scftorture.weight_many_wait= [KNL]
6364 The probability weighting to use for the
6365 smp_call_function_many() function with a
6366 non-zero "wait" parameter. See weight_single
6367 and weight_many.
6369 scftorture.weight_all= [KNL]
6370 The probability weighting to use for the
6371 smp_call_function_all() function with a zero
6372 "wait" parameter. See weight_single and
6373 weight_many.
6375 scftorture.weight_all_wait= [KNL]
6376 The probability weighting to use for the
6377 smp_call_function_all() function with a
6378 non-zero "wait" parameter. See weight_single
6379 and weight_many.
6381 sdw_mclk_divider=[SDW]
6382 Specify the MCLK divider for Intel SoundWire buses in
6383 case the BIOS does not provide the clock rate properly.
6385 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
6386 xtime_lock contention on larger systems, and/or RCU lock
6387 contention on all systems with CONFIG_MAXSMP set.
6388 Format: { "0" | "1" }
6389 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
6390 1 -- enable.
6391 Note: increases power consumption, thus should only be
6392 enabled if running jitter sensitive (HPC/RT) workloads.
6394 security= [SECURITY] Choose a legacy "major" security module to
6395 enable at boot. This has been deprecated by the
6396 "lsm=" parameter.
6398 selinux= [SELINUX] Disable or enable SELinux at boot time.
6399 Format: { "0" | "1" }
6400 See security/selinux/Kconfig help text.
6401 0 -- disable.
6402 1 -- enable.
6403 Default value is 1.
6405 serialnumber [BUGS=X86-32]
6407 sev=option[,option...] [X86-64]
6409 debug
6410 Enable debug messages.
6412 nosnp
6413 Do not enable SEV-SNP (applies to host/hypervisor
6414 only). Setting 'nosnp' avoids the RMP check overhead
6415 in memory accesses when users do not want to run
6416 SEV-SNP guests.
6418 shapers= [NET]
6419 Maximal number of shapers.
6421 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
6422 Limit apic dumping. The parameter defines the maximal
6423 number of local apics being dumped. Also it is possible
6424 to set it to "all" by meaning -- no limit here.
6425 Format: { 1 (default) | 2 | ... | all }.
6426 The parameter valid if only apic=debug or
6427 apic=verbose is specified.
6428 Example: apic=debug show_lapic=all
6430 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM]
6431 Enabling slab_debug allows one to determine the
6432 culprit if slab objects become corrupted. Enabling
6433 slab_debug can create guard zones around objects and
6434 may poison objects when not in use. Also tracks the
6435 last alloc / free. For more information see
6436 Documentation/mm/slub.rst.
6437 (slub_debug legacy name also accepted for now)
6439 slab_max_order= [MM]
6440 Determines the maximum allowed order for slabs.
6441 A high setting may cause OOMs due to memory
6442 fragmentation. For more information see
6443 Documentation/mm/slub.rst.
6444 (slub_max_order legacy name also accepted for now)
6446 slab_merge [MM]
6447 Enable merging of slabs with similar size when the
6448 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
6449 (slub_merge legacy name also accepted for now)
6451 slab_min_objects= [MM]
6452 The minimum number of objects per slab. SLUB will
6453 increase the slab order up to slab_max_order to
6454 generate a sufficiently large slab able to contain
6455 the number of objects indicated. The higher the number
6456 of objects the smaller the overhead of tracking slabs
6457 and the less frequently locks need to be acquired.
6458 For more information see Documentation/mm/slub.rst.
6459 (slub_min_objects legacy name also accepted for now)
6461 slab_min_order= [MM]
6462 Determines the minimum page order for slabs. Must be
6463 lower or equal to slab_max_order. For more information see
6464 Documentation/mm/slub.rst.
6465 (slub_min_order legacy name also accepted for now)
6467 slab_nomerge [MM]
6468 Disable merging of slabs with similar size. May be
6469 necessary if there is some reason to distinguish
6470 allocs to different slabs, especially in hardened
6471 environments where the risk of heap overflows and
6472 layout control by attackers can usually be
6473 frustrated by disabling merging. This will reduce
6474 most of the exposure of a heap attack to a single
6475 cache (risks via metadata attacks are mostly
6476 unchanged). Debug options disable merging on their
6477 own.
6478 For more information see Documentation/mm/slub.rst.
6479 (slub_nomerge legacy name also accepted for now)
6481 slab_strict_numa [MM]
6482 Support memory policies on a per object level
6483 in the slab allocator. The default is for memory
6484 policies to be applied at the folio level when
6485 a new folio is needed or a partial folio is
6486 retrieved from the lists. Increases overhead
6487 in the slab fastpaths but gains more accurate
6488 NUMA kernel object placement which helps with slow
6489 interconnects in NUMA systems.
6491 slram= [HW,MTD]
6493 smart2= [HW]
6494 Format: <io1>[,<io2>[,...,<io8>]]
6496 smp.csd_lock_timeout= [KNL]
6497 Specify the period of time in milliseconds
6498 that smp_call_function() and friends will wait
6499 for a CPU to release the CSD lock. This is
6500 useful when diagnosing bugs involving CPUs
6501 disabling interrupts for extended periods
6502 of time. Defaults to 5,000 milliseconds, and
6503 setting a value of zero disables this feature.
6504 This feature may be more efficiently disabled
6505 using the csdlock_debug- kernel parameter.
6507 smp.panic_on_ipistall= [KNL]
6508 If a csd_lock_timeout extends for more than
6509 the specified number of milliseconds, panic the
6510 system. By default, let CSD-lock acquisition
6511 take as long as they take. Specifying 300,000
6512 for this value provides a 5-minute timeout.
6514 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
6515 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
6516 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
6517 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
6518 smsc-ircc2.ircc_irq= [HW] IRQ line
6519 smsc-ircc2.ircc_dma= [HW] DMA channel
6520 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
6521 0: Toshiba Satellite 1800 (GP data pin select)
6522 1: Fast pin select (default)
6523 2: ATC IRMode
6525 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
6526 (logical CPUs) to use per physical CPU on systems
6527 capable of symmetric multithreading (SMT). Will
6528 be capped to the actual hardware limit.
6529 Format: <integer>
6530 Default: -1 (no limit)
6532 softlockup_panic=
6533 [KNL] Should the soft-lockup detector generate panics.
6534 Format: 0 | 1
6536 A value of 1 instructs the soft-lockup detector
6537 to panic the machine when a soft-lockup occurs. It is
6538 also controlled by the kernel.softlockup_panic sysctl
6539 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
6540 respective build-time switch to that functionality.
6542 softlockup_all_cpu_backtrace=
6543 [KNL] Should the soft-lockup detector generate
6544 backtraces on all cpus.
6545 Format: 0 | 1
6547 sonypi.*= [HW] Sony Programmable I/O Control Device driver
6548 See Documentation/admin-guide/laptops/sonypi.rst
6550 spectre_bhi= [X86] Control mitigation of Branch History Injection
6551 (BHI) vulnerability. This setting affects the
6552 deployment of the HW BHI control and the SW BHB
6553 clearing sequence.
6555 on - (default) Enable the HW or SW mitigation as
6556 needed. This protects the kernel from
6557 both syscalls and VMs.
6558 vmexit - On systems which don't have the HW mitigation
6559 available, enable the SW mitigation on vmexit
6560 ONLY. On such systems, the host kernel is
6561 protected from VM-originated BHI attacks, but
6562 may still be vulnerable to syscall attacks.
6563 off - Disable the mitigation.
6565 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
6566 (indirect branch speculation) vulnerability.
6567 The default operation protects the kernel from
6568 user space attacks.
6570 on - unconditionally enable, implies
6571 spectre_v2_user=on
6572 off - unconditionally disable, implies
6573 spectre_v2_user=off
6574 auto - kernel detects whether your CPU model is
6575 vulnerable
6577 Selecting 'on' will, and 'auto' may, choose a
6578 mitigation method at run time according to the
6579 CPU, the available microcode, the setting of the
6580 CONFIG_MITIGATION_RETPOLINE configuration option,
6581 and the compiler with which the kernel was built.
6583 Selecting 'on' will also enable the mitigation
6584 against user space to user space task attacks.
6586 Selecting 'off' will disable both the kernel and
6587 the user space protections.
6589 Specific mitigations can also be selected manually:
6591 retpoline - replace indirect branches
6592 retpoline,generic - Retpolines
6593 retpoline,lfence - LFENCE; indirect branch
6594 retpoline,amd - alias for retpoline,lfence
6595 eibrs - Enhanced/Auto IBRS
6596 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
6597 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
6598 ibrs - use IBRS to protect kernel
6600 Not specifying this option is equivalent to
6601 spectre_v2=auto.
6603 spectre_v2_user=
6604 [X86] Control mitigation of Spectre variant 2
6605 (indirect branch speculation) vulnerability between
6606 user space tasks
6608 on - Unconditionally enable mitigations. Is
6609 enforced by spectre_v2=on
6611 off - Unconditionally disable mitigations. Is
6612 enforced by spectre_v2=off
6614 prctl - Indirect branch speculation is enabled,
6615 but mitigation can be enabled via prctl
6616 per thread. The mitigation control state
6617 is inherited on fork.
6619 prctl,ibpb
6620 - Like "prctl" above, but only STIBP is
6621 controlled per thread. IBPB is issued
6622 always when switching between different user
6623 space processes.
6625 seccomp
6626 - Same as "prctl" above, but all seccomp
6627 threads will enable the mitigation unless
6628 they explicitly opt out.
6630 seccomp,ibpb
6631 - Like "seccomp" above, but only STIBP is
6632 controlled per thread. IBPB is issued
6633 always when switching between different
6634 user space processes.
6636 auto - Kernel selects the mitigation depending on
6637 the available CPU features and vulnerability.
6639 Default mitigation: "prctl"
6641 Not specifying this option is equivalent to
6642 spectre_v2_user=auto.
6644 spec_rstack_overflow=
6645 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
6647 off - Disable mitigation
6648 microcode - Enable microcode mitigation only
6649 safe-ret - Enable sw-only safe RET mitigation (default)
6650 ibpb - Enable mitigation by issuing IBPB on
6651 kernel entry
6652 ibpb-vmexit - Issue IBPB only on VMEXIT
6653 (cloud-specific mitigation)
6655 spec_store_bypass_disable=
6656 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
6657 (Speculative Store Bypass vulnerability)
6659 Certain CPUs are vulnerable to an exploit against a
6660 a common industry wide performance optimization known
6661 as "Speculative Store Bypass" in which recent stores
6662 to the same memory location may not be observed by
6663 later loads during speculative execution. The idea
6664 is that such stores are unlikely and that they can
6665 be detected prior to instruction retirement at the
6666 end of a particular speculation execution window.
6668 In vulnerable processors, the speculatively forwarded
6669 store can be used in a cache side channel attack, for
6670 example to read memory to which the attacker does not
6671 directly have access (e.g. inside sandboxed code).
6673 This parameter controls whether the Speculative Store
6674 Bypass optimization is used.
6676 On x86 the options are:
6678 on - Unconditionally disable Speculative Store Bypass
6679 off - Unconditionally enable Speculative Store Bypass
6680 auto - Kernel detects whether the CPU model contains an
6681 implementation of Speculative Store Bypass and
6682 picks the most appropriate mitigation. If the
6683 CPU is not vulnerable, "off" is selected. If the
6684 CPU is vulnerable the default mitigation is
6685 architecture and Kconfig dependent. See below.
6686 prctl - Control Speculative Store Bypass per thread
6687 via prctl. Speculative Store Bypass is enabled
6688 for a process by default. The state of the control
6689 is inherited on fork.
6690 seccomp - Same as "prctl" above, but all seccomp threads
6691 will disable SSB unless they explicitly opt out.
6693 Default mitigations:
6694 X86: "prctl"
6696 On powerpc the options are:
6698 on,auto - On Power8 and Power9 insert a store-forwarding
6699 barrier on kernel entry and exit. On Power7
6700 perform a software flush on kernel entry and
6701 exit.
6702 off - No action.
6704 Not specifying this option is equivalent to
6705 spec_store_bypass_disable=auto.
6707 split_lock_detect=
6708 [X86] Enable split lock detection or bus lock detection
6710 When enabled (and if hardware support is present), atomic
6711 instructions that access data across cache line
6712 boundaries will result in an alignment check exception
6713 for split lock detection or a debug exception for
6714 bus lock detection.
6716 off - not enabled
6718 warn - the kernel will emit rate-limited warnings
6719 about applications triggering the #AC
6720 exception or the #DB exception. This mode is
6721 the default on CPUs that support split lock
6722 detection or bus lock detection. Default
6723 behavior is by #AC if both features are
6724 enabled in hardware.
6726 fatal - the kernel will send SIGBUS to applications
6727 that trigger the #AC exception or the #DB
6728 exception. Default behavior is by #AC if
6729 both features are enabled in hardware.
6731 ratelimit:N -
6732 Set system wide rate limit to N bus locks
6733 per second for bus lock detection.
6734 0 < N <= 1000.
6736 N/A for split lock detection.
6739 If an #AC exception is hit in the kernel or in
6740 firmware (i.e. not while executing in user mode)
6741 the kernel will oops in either "warn" or "fatal"
6742 mode.
6744 #DB exception for bus lock is triggered only when
6745 CPL > 0.
6747 srbds= [X86,INTEL,EARLY]
6748 Control the Special Register Buffer Data Sampling
6749 (SRBDS) mitigation.
6751 Certain CPUs are vulnerable to an MDS-like
6752 exploit which can leak bits from the random
6753 number generator.
6755 By default, this issue is mitigated by
6756 microcode. However, the microcode fix can cause
6757 the RDRAND and RDSEED instructions to become
6758 much slower. Among other effects, this will
6759 result in reduced throughput from /dev/urandom.
6761 The microcode mitigation can be disabled with
6762 the following option:
6764 off: Disable mitigation and remove
6765 performance impact to RDRAND and RDSEED
6767 srcutree.big_cpu_lim [KNL]
6768 Specifies the number of CPUs constituting a
6769 large system, such that srcu_struct structures
6770 should immediately allocate an srcu_node array.
6771 This kernel-boot parameter defaults to 128,
6772 but takes effect only when the low-order four
6773 bits of srcutree.convert_to_big is equal to 3
6774 (decide at boot).
6776 srcutree.convert_to_big [KNL]
6777 Specifies under what conditions an SRCU tree
6778 srcu_struct structure will be converted to big
6779 form, that is, with an rcu_node tree:
6781 0: Never.
6782 1: At init_srcu_struct() time.
6783 2: When rcutorture decides to.
6784 3: Decide at boot time (default).
6785 0x1X: Above plus if high contention.
6787 Either way, the srcu_node tree will be sized based
6788 on the actual runtime number of CPUs (nr_cpu_ids)
6789 instead of the compile-time CONFIG_NR_CPUS.
6791 srcutree.counter_wrap_check [KNL]
6792 Specifies how frequently to check for
6793 grace-period sequence counter wrap for the
6794 srcu_data structure's ->srcu_gp_seq_needed field.
6795 The greater the number of bits set in this kernel
6796 parameter, the less frequently counter wrap will
6797 be checked for. Note that the bottom two bits
6798 are ignored.
6800 srcutree.exp_holdoff [KNL]
6801 Specifies how many nanoseconds must elapse
6802 since the end of the last SRCU grace period for
6803 a given srcu_struct until the next normal SRCU
6804 grace period will be considered for automatic
6805 expediting. Set to zero to disable automatic
6806 expediting.
6808 srcutree.srcu_max_nodelay [KNL]
6809 Specifies the number of no-delay instances
6810 per jiffy for which the SRCU grace period
6811 worker thread will be rescheduled with zero
6812 delay. Beyond this limit, worker thread will
6813 be rescheduled with a sleep delay of one jiffy.
6815 srcutree.srcu_max_nodelay_phase [KNL]
6816 Specifies the per-grace-period phase, number of
6817 non-sleeping polls of readers. Beyond this limit,
6818 grace period worker thread will be rescheduled
6819 with a sleep delay of one jiffy, between each
6820 rescan of the readers, for a grace period phase.
6822 srcutree.srcu_retry_check_delay [KNL]
6823 Specifies number of microseconds of non-sleeping
6824 delay between each non-sleeping poll of readers.
6826 srcutree.small_contention_lim [KNL]
6827 Specifies the number of update-side contention
6828 events per jiffy will be tolerated before
6829 initiating a conversion of an srcu_struct
6830 structure to big form. Note that the value of
6831 srcutree.convert_to_big must have the 0x10 bit
6832 set for contention-based conversions to occur.
6834 ssbd= [ARM64,HW,EARLY]
6835 Speculative Store Bypass Disable control
6837 On CPUs that are vulnerable to the Speculative
6838 Store Bypass vulnerability and offer a
6839 firmware based mitigation, this parameter
6840 indicates how the mitigation should be used:
6842 force-on: Unconditionally enable mitigation for
6843 for both kernel and userspace
6844 force-off: Unconditionally disable mitigation for
6845 for both kernel and userspace
6846 kernel: Always enable mitigation in the
6847 kernel, and offer a prctl interface
6848 to allow userspace to register its
6849 interest in being mitigated too.
6851 stack_guard_gap= [MM]
6852 override the default stack gap protection. The value
6853 is in page units and it defines how many pages prior
6854 to (for stacks growing down) resp. after (for stacks
6855 growing up) the main stack are reserved for no other
6856 mapping. Default value is 256 pages.
6858 stack_depot_disable= [KNL,EARLY]
6859 Setting this to true through kernel command line will
6860 disable the stack depot thereby saving the static memory
6861 consumed by the stack hash table. By default this is set
6862 to false.
6864 stacktrace [FTRACE]
6865 Enabled the stack tracer on boot up.
6867 stacktrace_filter=[function-list]
6868 [FTRACE] Limit the functions that the stack tracer
6869 will trace at boot up. function-list is a comma-separated
6870 list of functions. This list can be changed at run
6871 time by the stack_trace_filter file in the debugfs
6872 tracing directory. Note, this enables stack tracing
6873 and the stacktrace above is not needed.
6875 sti= [PARISC,HW]
6876 Format: <num>
6877 Set the STI (builtin display/keyboard on the HP-PARISC
6878 machines) console (graphic card) which should be used
6879 as the initial boot-console.
6880 See also comment in drivers/video/console/sticore.c.
6882 sti_font= [HW]
6883 See comment in drivers/video/console/sticore.c.
6885 stifb= [HW]
6886 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6888 strict_sas_size=
6889 [X86]
6890 Format: <bool>
6891 Enable or disable strict sigaltstack size checks
6892 against the required signal frame size which
6893 depends on the supported FPU features. This can
6894 be used to filter out binaries which have
6895 not yet been made aware of AT_MINSIGSTKSZ.
6897 stress_hpt [PPC,EARLY]
6898 Limits the number of kernel HPT entries in the hash
6899 page table to increase the rate of hash page table
6900 faults on kernel addresses.
6902 stress_slb [PPC,EARLY]
6903 Limits the number of kernel SLB entries, and flushes
6904 them frequently to increase the rate of SLB faults
6905 on kernel addresses.
6907 sunrpc.min_resvport=
6908 sunrpc.max_resvport=
6909 [NFS,SUNRPC]
6910 SunRPC servers often require that client requests
6911 originate from a privileged port (i.e. a port in the
6912 range 0 < portnr < 1024).
6913 An administrator who wishes to reserve some of these
6914 ports for other uses may adjust the range that the
6915 kernel's sunrpc client considers to be privileged
6916 using these two parameters to set the minimum and
6917 maximum port values.
6919 sunrpc.svc_rpc_per_connection_limit=
6920 [NFS,SUNRPC]
6921 Limit the number of requests that the server will
6922 process in parallel from a single connection.
6923 The default value is 0 (no limit).
6925 sunrpc.pool_mode=
6926 [NFS]
6927 Control how the NFS server code allocates CPUs to
6928 service thread pools. Depending on how many NICs
6929 you have and where their interrupts are bound, this
6930 option will affect which CPUs will do NFS serving.
6931 Note: this parameter cannot be changed while the
6932 NFS server is running.
6934 auto the server chooses an appropriate mode
6935 automatically using heuristics
6936 global a single global pool contains all CPUs
6937 percpu one pool for each CPU
6938 pernode one pool for each NUMA node (equivalent
6939 to global on non-NUMA machines)
6941 sunrpc.tcp_slot_table_entries=
6942 sunrpc.udp_slot_table_entries=
6943 [NFS,SUNRPC]
6944 Sets the upper limit on the number of simultaneous
6945 RPC calls that can be sent from the client to a
6946 server. Increasing these values may allow you to
6947 improve throughput, but will also increase the
6948 amount of memory reserved for use by the client.
6950 suspend.pm_test_delay=
6951 [SUSPEND]
6952 Sets the number of seconds to remain in a suspend test
6953 mode before resuming the system (see
6954 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6955 is set. Default value is 5.
6957 svm= [PPC]
6958 Format: { on | off | y | n | 1 | 0 }
6959 This parameter controls use of the Protected
6960 Execution Facility on pSeries.
6962 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY]
6963 Format: { <int> [,<int>] | force | noforce }
6964 <int> -- Number of I/O TLB slabs
6965 <int> -- Second integer after comma. Number of swiotlb
6966 areas with their own lock. Will be rounded up
6967 to a power of 2.
6968 force -- force using of bounce buffers even if they
6969 wouldn't be automatically used by the kernel
6970 noforce -- Never use bounce buffers (for debugging)
6972 switches= [HW,M68k,EARLY]
6974 sysctl.*= [KNL]
6975 Set a sysctl parameter, right before loading the init
6976 process, as if the value was written to the respective
6977 /proc/sys/... file. Both '.' and '/' are recognized as
6978 separators. Unrecognized parameters and invalid values
6979 are reported in the kernel log. Sysctls registered
6980 later by a loaded module cannot be set this way.
6981 Example: sysctl.vm.swappiness=40
6983 sysrq_always_enabled
6984 [KNL]
6985 Ignore sysrq setting - this boot parameter will
6986 neutralize any effect of /proc/sys/kernel/sysrq.
6987 Useful for debugging.
6989 tcpmhash_entries= [KNL,NET]
6990 Set the number of tcp_metrics_hash slots.
6991 Default value is 8192 or 16384 depending on total
6992 ram pages. This is used to specify the TCP metrics
6993 cache size. See Documentation/networking/ip-sysctl.rst
6994 "tcp_no_metrics_save" section for more details.
6996 tdfx= [HW,DRM]
6998 test_suspend= [SUSPEND]
6999 Format: { "mem" | "standby" | "freeze" }[,N]
7000 Specify "mem" (for Suspend-to-RAM) or "standby" (for
7001 standby suspend) or "freeze" (for suspend type freeze)
7002 as the system sleep state during system startup with
7003 the optional capability to repeat N number of times.
7004 The system is woken from this state using a
7005 wakeup-capable RTC alarm.
7007 thash_entries= [KNL,NET]
7008 Set number of hash buckets for TCP connection
7010 thermal.act= [HW,ACPI]
7011 -1: disable all active trip points in all thermal zones
7012 <degrees C>: override all lowest active trip points
7014 thermal.crt= [HW,ACPI]
7015 -1: disable all critical trip points in all thermal zones
7016 <degrees C>: override all critical trip points
7018 thermal.off= [HW,ACPI]
7019 1: disable ACPI thermal control
7021 thermal.psv= [HW,ACPI]
7022 -1: disable all passive trip points
7023 <degrees C>: override all passive trip points to this
7024 value
7026 thermal.tzp= [HW,ACPI]
7027 Specify global default ACPI thermal zone polling rate
7028 <deci-seconds>: poll all this frequency
7029 0: no polling (default)
7031 thp_anon= [KNL]
7032 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state>
7033 state is one of "always", "madvise", "never" or "inherit".
7034 Control the default behavior of the system with respect
7035 to anonymous transparent hugepages.
7036 Can be used multiple times for multiple anon THP sizes.
7037 See Documentation/admin-guide/mm/transhuge.rst for more
7038 details.
7040 threadirqs [KNL,EARLY]
7041 Force threading of all interrupt handlers except those
7042 marked explicitly IRQF_NO_THREAD.
7044 thp_shmem= [KNL]
7045 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy>
7046 Control the default policy of each hugepage size for the
7047 internal shmem mount. <policy> is one of policies available
7048 for the shmem mount ("always", "inherit", "never", "within_size",
7049 and "advise").
7050 It can be used multiple times for multiple shmem THP sizes.
7051 See Documentation/admin-guide/mm/transhuge.rst for more
7052 details.
7054 topology= [S390,EARLY]
7055 Format: {off | on}
7056 Specify if the kernel should make use of the cpu
7057 topology information if the hardware supports this.
7058 The scheduler will make use of this information and
7059 e.g. base its process migration decisions on it.
7060 Default is on.
7062 torture.disable_onoff_at_boot= [KNL]
7063 Prevent the CPU-hotplug component of torturing
7064 until after init has spawned.
7066 torture.ftrace_dump_at_shutdown= [KNL]
7067 Dump the ftrace buffer at torture-test shutdown,
7068 even if there were no errors. This can be a
7069 very costly operation when many torture tests
7070 are running concurrently, especially on systems
7071 with rotating-rust storage.
7073 torture.verbose_sleep_frequency= [KNL]
7074 Specifies how many verbose printk()s should be
7075 emitted between each sleep. The default of zero
7076 disables verbose-printk() sleeping.
7078 torture.verbose_sleep_duration= [KNL]
7079 Duration of each verbose-printk() sleep in jiffies.
7081 tpm.disable_pcr_integrity= [HW,TPM]
7082 Do not protect PCR registers from unintended physical
7083 access, or interposers in the bus by the means of
7084 having an integrity protected session wrapped around
7085 TPM2_PCR_Extend command. Consider this in a situation
7086 where TPM is heavily utilized by IMA, thus protection
7087 causing a major performance hit, and the space where
7088 machines are deployed is by other means guarded.
7090 tpm_suspend_pcr=[HW,TPM]
7091 Format: integer pcr id
7092 Specify that at suspend time, the tpm driver
7093 should extend the specified pcr with zeros,
7094 as a workaround for some chips which fail to
7095 flush the last written pcr on TPM_SaveState.
7096 This will guarantee that all the other pcrs
7097 are saved.
7099 tpm_tis.interrupts= [HW,TPM]
7100 Enable interrupts for the MMIO based physical layer
7101 for the FIFO interface. By default it is set to false
7102 (0). For more information about TPM hardware interfaces
7103 defined by Trusted Computing Group (TCG) see
7104 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
7106 tp_printk [FTRACE]
7107 Have the tracepoints sent to printk as well as the
7108 tracing ring buffer. This is useful for early boot up
7109 where the system hangs or reboots and does not give the
7110 option for reading the tracing buffer or performing a
7111 ftrace_dump_on_oops.
7113 To turn off having tracepoints sent to printk,
7114 echo 0 > /proc/sys/kernel/tracepoint_printk
7115 Note, echoing 1 into this file without the
7116 tp_printk kernel cmdline option has no effect.
7118 The tp_printk_stop_on_boot (see below) can also be used
7119 to stop the printing of events to console at
7120 late_initcall_sync.
7122 ** CAUTION **
7124 Having tracepoints sent to printk() and activating high
7125 frequency tracepoints such as irq or sched, can cause
7126 the system to live lock.
7128 tp_printk_stop_on_boot [FTRACE]
7129 When tp_printk (above) is set, it can cause a lot of noise
7130 on the console. It may be useful to only include the
7131 printing of events during boot up, as user space may
7132 make the system inoperable.
7134 This command line option will stop the printing of events
7135 to console at the late_initcall_sync() time frame.
7137 trace_buf_size=nn[KMG]
7138 [FTRACE] will set tracing buffer size on each cpu.
7140 trace_clock= [FTRACE] Set the clock used for tracing events
7141 at boot up.
7142 local - Use the per CPU time stamp counter
7143 (converted into nanoseconds). Fast, but
7144 depending on the architecture, may not be
7145 in sync between CPUs.
7146 global - Event time stamps are synchronize across
7147 CPUs. May be slower than the local clock,
7148 but better for some race conditions.
7149 counter - Simple counting of events (1, 2, ..)
7150 note, some counts may be skipped due to the
7151 infrastructure grabbing the clock more than
7152 once per event.
7153 uptime - Use jiffies as the time stamp.
7154 perf - Use the same clock that perf uses.
7155 mono - Use ktime_get_mono_fast_ns() for time stamps.
7156 mono_raw - Use ktime_get_raw_fast_ns() for time
7157 stamps.
7158 boot - Use ktime_get_boot_fast_ns() for time stamps.
7159 Architectures may add more clocks. See
7160 Documentation/trace/ftrace.rst for more details.
7162 trace_event=[event-list]
7163 [FTRACE] Set and start specified trace events in order
7164 to facilitate early boot debugging. The event-list is a
7165 comma-separated list of trace events to enable. See
7166 also Documentation/trace/events.rst
7168 To enable modules, use :mod: keyword:
7170 trace_event=:mod:<module>
7172 The value before :mod: will only enable specific events
7173 that are part of the module. See the above mentioned
7174 document for more information.
7176 trace_instance=[instance-info]
7177 [FTRACE] Create a ring buffer instance early in boot up.
7178 This will be listed in:
7180 /sys/kernel/tracing/instances
7182 Events can be enabled at the time the instance is created
7183 via:
7185 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
7187 Note, the "<system*>:" portion is optional if the event is
7188 unique.
7190 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
7192 will enable the "sched_switch" event (note, the "sched:" is optional, and
7193 the same thing would happen if it was left off). The irq_handler_entry
7194 event, and all events under the "initcall" system.
7196 Flags can be added to the instance to modify its behavior when it is
7197 created. The flags are separated by '^'.
7199 The available flags are:
7201 traceoff - Have the tracing instance tracing disabled after it is created.
7202 traceprintk - Have trace_printk() write into this trace instance
7203 (note, "printk" and "trace_printk" can also be used)
7205 trace_instance=foo^traceoff^traceprintk,sched,irq
7207 The flags must come before the defined events.
7209 If memory has been reserved (see memmap for x86), the instance
7210 can use that memory:
7212 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M
7214 The above will create a "boot_map" instance that uses the physical
7215 memory at 0x284500000 that is 12Megs. The per CPU buffers of that
7216 instance will be split up accordingly.
7218 Alternatively, the memory can be reserved by the reserve_mem option:
7220 reserve_mem=12M:4096:trace trace_instance=boot_map@trace
7222 This will reserve 12 megabytes at boot up with a 4096 byte alignment
7223 and place the ring buffer in this memory. Note that due to KASLR, the
7224 memory may not be the same location each time, which will not preserve
7225 the buffer content.
7227 Also note that the layout of the ring buffer data may change between
7228 kernel versions where the validator will fail and reset the ring buffer
7229 if the layout is not the same as the previous kernel.
7231 If the ring buffer is used for persistent bootups and has events enabled,
7232 it is recommend to disable tracing so that events from a previous boot do not
7233 mix with events of the current boot (unless you are debugging a random crash
7234 at boot up).
7236 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq
7238 Note, saving the trace buffer across reboots does require that the system
7239 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION
7240 can force a memory reset on boot which will clear any trace that was stored.
7241 This is just one of many ways that can clear memory. Make sure your system
7242 keeps the content of memory across reboots before relying on this option.
7244 See also Documentation/trace/debugging.rst
7247 trace_options=[option-list]
7248 [FTRACE] Enable or disable tracer options at boot.
7249 The option-list is a comma delimited list of options
7250 that can be enabled or disabled just as if you were
7251 to echo the option name into
7253 /sys/kernel/tracing/trace_options
7255 For example, to enable stacktrace option (to dump the
7256 stack trace of each event), add to the command line:
7258 trace_options=stacktrace
7260 See also Documentation/trace/ftrace.rst "trace options"
7261 section.
7263 trace_trigger=[trigger-list]
7264 [FTRACE] Add a event trigger on specific events.
7265 Set a trigger on top of a specific event, with an optional
7266 filter.
7268 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
7269 Where more than one trigger may be specified that are comma deliminated.
7271 For example:
7273 trace_trigger="sched_switch.stacktrace if prev_state == 2"
7275 The above will enable the "stacktrace" trigger on the "sched_switch"
7276 event but only trigger it if the "prev_state" of the "sched_switch"
7277 event is "2" (TASK_UNINTERUPTIBLE).
7279 See also "Event triggers" in Documentation/trace/events.rst
7282 traceoff_on_warning
7283 [FTRACE] enable this option to disable tracing when a
7284 warning is hit. This turns off "tracing_on". Tracing can
7285 be enabled again by echoing '1' into the "tracing_on"
7286 file located in /sys/kernel/tracing/
7288 This option is useful, as it disables the trace before
7289 the WARNING dump is called, which prevents the trace to
7290 be filled with content caused by the warning output.
7292 This option can also be set at run time via the sysctl
7293 option: kernel/traceoff_on_warning
7295 transparent_hugepage=
7296 [KNL]
7297 Format: [always|madvise|never]
7298 Can be used to control the default behavior of the system
7299 with respect to transparent hugepages.
7300 See Documentation/admin-guide/mm/transhuge.rst
7301 for more details.
7303 transparent_hugepage_shmem= [KNL]
7304 Format: [always|within_size|advise|never|deny|force]
7305 Can be used to control the hugepage allocation policy for
7306 the internal shmem mount.
7307 See Documentation/admin-guide/mm/transhuge.rst
7308 for more details.
7310 transparent_hugepage_tmpfs= [KNL]
7311 Format: [always|within_size|advise|never]
7312 Can be used to control the default hugepage allocation policy
7313 for the tmpfs mount.
7314 See Documentation/admin-guide/mm/transhuge.rst
7315 for more details.
7317 trusted.source= [KEYS]
7318 Format: <string>
7319 This parameter identifies the trust source as a backend
7320 for trusted keys implementation. Supported trust
7321 sources:
7322 - "tpm"
7323 - "tee"
7324 - "caam"
7325 - "dcp"
7326 If not specified then it defaults to iterating through
7327 the trust source list starting with TPM and assigns the
7328 first trust source as a backend which is initialized
7329 successfully during iteration.
7331 trusted.rng= [KEYS]
7332 Format: <string>
7333 The RNG used to generate key material for trusted keys.
7334 Can be one of:
7335 - "kernel"
7336 - the same value as trusted.source: "tpm" or "tee"
7337 - "default"
7338 If not specified, "default" is used. In this case,
7339 the RNG's choice is left to each individual trust source.
7341 trusted.dcp_use_otp_key
7342 This is intended to be used in combination with
7343 trusted.source=dcp and will select the DCP OTP key
7344 instead of the DCP UNIQUE key blob encryption.
7346 trusted.dcp_skip_zk_test
7347 This is intended to be used in combination with
7348 trusted.source=dcp and will disable the check if the
7349 blob key is all zeros. This is helpful for situations where
7350 having this key zero'ed is acceptable. E.g. in testing
7351 scenarios.
7353 tsc= Disable clocksource stability checks for TSC.
7354 Format: <string>
7355 [x86] reliable: mark tsc clocksource as reliable, this
7356 disables clocksource verification at runtime, as well
7357 as the stability checks done at bootup. Used to enable
7358 high-resolution timer mode on older hardware, and in
7359 virtualized environment.
7360 [x86] noirqtime: Do not use TSC to do irq accounting.
7361 Used to run time disable IRQ_TIME_ACCOUNTING on any
7362 platforms where RDTSC is slow and this accounting
7363 can add overhead.
7364 [x86] unstable: mark the TSC clocksource as unstable, this
7365 marks the TSC unconditionally unstable at bootup and
7366 avoids any further wobbles once the TSC watchdog notices.
7367 [x86] nowatchdog: disable clocksource watchdog. Used
7368 in situations with strict latency requirements (where
7369 interruptions from clocksource watchdog are not
7370 acceptable).
7371 [x86] recalibrate: force recalibration against a HW timer
7372 (HPET or PM timer) on systems whose TSC frequency was
7373 obtained from HW or FW using either an MSR or CPUID(0x15).
7374 Warn if the difference is more than 500 ppm.
7375 [x86] watchdog: Use TSC as the watchdog clocksource with
7376 which to check other HW timers (HPET or PM timer), but
7377 only on systems where TSC has been deemed trustworthy.
7378 This will be suppressed by an earlier tsc=nowatchdog and
7379 can be overridden by a later tsc=nowatchdog. A console
7380 message will flag any such suppression or overriding.
7382 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
7383 value instead. Useful when the early TSC frequency discovery
7384 procedure is not reliable, such as on overclocked systems
7385 with CPUID.16h support and partial CPUID.15h support.
7386 Format: <unsigned int>
7388 tsx= [X86] Control Transactional Synchronization
7389 Extensions (TSX) feature in Intel processors that
7390 support TSX control.
7392 This parameter controls the TSX feature. The options are:
7394 on - Enable TSX on the system. Although there are
7395 mitigations for all known security vulnerabilities,
7396 TSX has been known to be an accelerator for
7397 several previous speculation-related CVEs, and
7398 so there may be unknown security risks associated
7399 with leaving it enabled.
7401 off - Disable TSX on the system. (Note that this
7402 option takes effect only on newer CPUs which are
7403 not vulnerable to MDS, i.e., have
7404 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
7405 the new IA32_TSX_CTRL MSR through a microcode
7406 update. This new MSR allows for the reliable
7407 deactivation of the TSX functionality.)
7409 auto - Disable TSX if X86_BUG_TAA is present,
7410 otherwise enable TSX on the system.
7412 Not specifying this option is equivalent to tsx=off.
7414 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
7415 for more details.
7417 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
7418 Abort (TAA) vulnerability.
7420 Similar to Micro-architectural Data Sampling (MDS)
7421 certain CPUs that support Transactional
7422 Synchronization Extensions (TSX) are vulnerable to an
7423 exploit against CPU internal buffers which can forward
7424 information to a disclosure gadget under certain
7425 conditions.
7427 In vulnerable processors, the speculatively forwarded
7428 data can be used in a cache side channel attack, to
7429 access data to which the attacker does not have direct
7430 access.
7432 This parameter controls the TAA mitigation. The
7433 options are:
7435 full - Enable TAA mitigation on vulnerable CPUs
7436 if TSX is enabled.
7438 full,nosmt - Enable TAA mitigation and disable SMT on
7439 vulnerable CPUs. If TSX is disabled, SMT
7440 is not disabled because CPU is not
7441 vulnerable to cross-thread TAA attacks.
7442 off - Unconditionally disable TAA mitigation
7444 On MDS-affected machines, tsx_async_abort=off can be
7445 prevented by an active MDS mitigation as both vulnerabilities
7446 are mitigated with the same mechanism so in order to disable
7447 this mitigation, you need to specify mds=off too.
7449 Not specifying this option is equivalent to
7450 tsx_async_abort=full. On CPUs which are MDS affected
7451 and deploy MDS mitigation, TAA mitigation is not
7452 required and doesn't provide any additional
7453 mitigation.
7455 For details see:
7456 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
7458 turbografx.map[2|3]= [HW,JOY]
7459 TurboGraFX parallel port interface
7460 Format:
7461 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
7462 See also Documentation/input/devices/joystick-parport.rst
7464 udbg-immortal [PPC] When debugging early kernel crashes that
7465 happen after console_init() and before a proper
7466 console driver takes over, this boot options might
7467 help "seeing" what's going on.
7469 uhash_entries= [KNL,NET]
7470 Set number of hash buckets for UDP/UDP-Lite connections
7472 uhci-hcd.ignore_oc=
7473 [USB] Ignore overcurrent events (default N).
7474 Some badly-designed motherboards generate lots of
7475 bogus events, for ports that aren't wired to
7476 anything. Set this parameter to avoid log spamming.
7477 Note that genuine overcurrent events won't be
7478 reported either.
7480 unknown_nmi_panic
7481 [X86] Cause panic on unknown NMI.
7483 unwind_debug [X86-64,EARLY]
7484 Enable unwinder debug output. This can be
7485 useful for debugging certain unwinder error
7486 conditions, including corrupt stacks and
7487 bad/missing unwinder metadata.
7489 usbcore.authorized_default=
7490 [USB] Default USB device authorization:
7491 (default -1 = authorized (same as 1),
7492 0 = not authorized, 1 = authorized, 2 = authorized
7493 if device connected to internal port)
7495 usbcore.autosuspend=
7496 [USB] The autosuspend time delay (in seconds) used
7497 for newly-detected USB devices (default 2). This
7498 is the time required before an idle device will be
7499 autosuspended. Devices for which the delay is set
7500 to a negative value won't be autosuspended at all.
7502 usbcore.usbfs_snoop=
7503 [USB] Set to log all usbfs traffic (default 0 = off).
7505 usbcore.usbfs_snoop_max=
7506 [USB] Maximum number of bytes to snoop in each URB
7507 (default = 65536).
7509 usbcore.blinkenlights=
7510 [USB] Set to cycle leds on hubs (default 0 = off).
7512 usbcore.old_scheme_first=
7513 [USB] Start with the old device initialization
7514 scheme (default 0 = off).
7516 usbcore.usbfs_memory_mb=
7517 [USB] Memory limit (in MB) for buffers allocated by
7518 usbfs (default = 16, 0 = max = 2047).
7520 usbcore.use_both_schemes=
7521 [USB] Try the other device initialization scheme
7522 if the first one fails (default 1 = enabled).
7524 usbcore.initial_descriptor_timeout=
7525 [USB] Specifies timeout for the initial 64-byte
7526 USB_REQ_GET_DESCRIPTOR request in milliseconds
7527 (default 5000 = 5.0 seconds).
7529 usbcore.nousb [USB] Disable the USB subsystem
7531 usbcore.quirks=
7532 [USB] A list of quirk entries to augment the built-in
7533 usb core quirk list. List entries are separated by
7534 commas. Each entry has the form
7535 VendorID:ProductID:Flags. The IDs are 4-digit hex
7536 numbers and Flags is a set of letters. Each letter
7537 will change the built-in quirk; setting it if it is
7538 clear and clearing it if it is set. The letters have
7539 the following meanings:
7540 a = USB_QUIRK_STRING_FETCH_255 (string
7541 descriptors must not be fetched using
7542 a 255-byte read);
7543 b = USB_QUIRK_RESET_RESUME (device can't resume
7544 correctly so reset it instead);
7545 c = USB_QUIRK_NO_SET_INTF (device can't handle
7546 Set-Interface requests);
7547 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
7548 handle its Configuration or Interface
7549 strings);
7550 e = USB_QUIRK_RESET (device can't be reset
7551 (e.g morph devices), don't use reset);
7552 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
7553 more interface descriptions than the
7554 bNumInterfaces count, and can't handle
7555 talking to these interfaces);
7556 g = USB_QUIRK_DELAY_INIT (device needs a pause
7557 during initialization, after we read
7558 the device descriptor);
7559 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
7560 high speed and super speed interrupt
7561 endpoints, the USB 2.0 and USB 3.0 spec
7562 require the interval in microframes (1
7563 microframe = 125 microseconds) to be
7564 calculated as interval = 2 ^
7565 (bInterval-1).
7566 Devices with this quirk report their
7567 bInterval as the result of this
7568 calculation instead of the exponent
7569 variable used in the calculation);
7570 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
7571 handle device_qualifier descriptor
7572 requests);
7573 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
7574 generates spurious wakeup, ignore
7575 remote wakeup capability);
7576 k = USB_QUIRK_NO_LPM (device can't handle Link
7577 Power Management);
7578 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
7579 (Device reports its bInterval as linear
7580 frames instead of the USB 2.0
7581 calculation);
7582 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
7583 to be disconnected before suspend to
7584 prevent spurious wakeup);
7585 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
7586 pause after every control message);
7587 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
7588 delay after resetting its port);
7589 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
7590 (Reduce timeout of the SET_ADDRESS
7591 request from 5000 ms to 500 ms);
7592 Example: quirks=0781:5580:bk,0a5c:5834:gij
7594 usbhid.mousepoll=
7595 [USBHID] The interval which mice are to be polled at.
7597 usbhid.jspoll=
7598 [USBHID] The interval which joysticks are to be polled at.
7600 usbhid.kbpoll=
7601 [USBHID] The interval which keyboards are to be polled at.
7603 usb-storage.delay_use=
7604 [UMS] The delay in seconds before a new device is
7605 scanned for Logical Units (default 1).
7606 Optionally the delay in milliseconds if the value has
7607 suffix with "ms".
7608 Example: delay_use=2567ms
7610 usb-storage.quirks=
7611 [UMS] A list of quirks entries to supplement or
7612 override the built-in unusual_devs list. List
7613 entries are separated by commas. Each entry has
7614 the form VID:PID:Flags where VID and PID are Vendor
7615 and Product ID values (4-digit hex numbers) and
7616 Flags is a set of characters, each corresponding
7617 to a common usb-storage quirk flag as follows:
7618 a = SANE_SENSE (collect more than 18 bytes
7619 of sense data, not on uas);
7620 b = BAD_SENSE (don't collect more than 18
7621 bytes of sense data, not on uas);
7622 c = FIX_CAPACITY (decrease the reported
7623 device capacity by one sector);
7624 d = NO_READ_DISC_INFO (don't use
7625 READ_DISC_INFO command, not on uas);
7626 e = NO_READ_CAPACITY_16 (don't use
7627 READ_CAPACITY_16 command);
7628 f = NO_REPORT_OPCODES (don't use report opcodes
7629 command, uas only);
7630 g = MAX_SECTORS_240 (don't transfer more than
7631 240 sectors at a time, uas only);
7632 h = CAPACITY_HEURISTICS (decrease the
7633 reported device capacity by one
7634 sector if the number is odd);
7635 i = IGNORE_DEVICE (don't bind to this
7636 device);
7637 j = NO_REPORT_LUNS (don't use report luns
7638 command, uas only);
7639 k = NO_SAME (do not use WRITE_SAME, uas only)
7640 l = NOT_LOCKABLE (don't try to lock and
7641 unlock ejectable media, not on uas);
7642 m = MAX_SECTORS_64 (don't transfer more
7643 than 64 sectors = 32 KB at a time,
7644 not on uas);
7645 n = INITIAL_READ10 (force a retry of the
7646 initial READ(10) command, not on uas);
7647 o = CAPACITY_OK (accept the capacity
7648 reported by the device, not on uas);
7649 p = WRITE_CACHE (the device cache is ON
7650 by default, not on uas);
7651 r = IGNORE_RESIDUE (the device reports
7652 bogus residue values, not on uas);
7653 s = SINGLE_LUN (the device has only one
7654 Logical Unit);
7655 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
7656 commands, uas only);
7657 u = IGNORE_UAS (don't bind to the uas driver);
7658 w = NO_WP_DETECT (don't test whether the
7659 medium is write-protected).
7660 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
7661 even if the device claims no cache,
7662 not on uas)
7663 Example: quirks=0419:aaf5:rl,0421:0433:rc
7665 user_debug= [KNL,ARM]
7666 Format: <int>
7667 See arch/arm/Kconfig.debug help text.
7668 1 - undefined instruction events
7669 2 - system calls
7670 4 - invalid data aborts
7671 8 - SIGSEGV faults
7672 16 - SIGBUS faults
7673 Example: user_debug=31
7675 userpte=
7676 [X86,EARLY] Flags controlling user PTE allocations.
7678 nohigh = do not allocate PTE pages in
7679 HIGHMEM regardless of setting
7680 of CONFIG_HIGHPTE.
7682 vdso= [X86,SH,SPARC]
7683 On X86_32, this is an alias for vdso32=. Otherwise:
7685 vdso=1: enable VDSO (the default)
7686 vdso=0: disable VDSO mapping
7688 vdso32= [X86] Control the 32-bit vDSO
7689 vdso32=1: enable 32-bit VDSO
7690 vdso32=0 or vdso32=2: disable 32-bit VDSO
7692 See the help text for CONFIG_COMPAT_VDSO for more
7693 details. If CONFIG_COMPAT_VDSO is set, the default is
7694 vdso32=0; otherwise, the default is vdso32=1.
7696 For compatibility with older kernels, vdso32=2 is an
7697 alias for vdso32=0.
7699 Try vdso32=0 if you encounter an error that says:
7700 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
7702 video= [FB,EARLY] Frame buffer configuration
7703 See Documentation/fb/modedb.rst.
7705 video.brightness_switch_enabled= [ACPI]
7706 Format: [0|1]
7707 If set to 1, on receiving an ACPI notify event
7708 generated by hotkey, video driver will adjust brightness
7709 level and then send out the event to user space through
7710 the allocated input device. If set to 0, video driver
7711 will only send out the event without touching backlight
7712 brightness level.
7713 default: 1
7715 virtio_mmio.device=
7716 [VMMIO] Memory mapped virtio (platform) device.
7718 <size>@<baseaddr>:<irq>[:<id>]
7719 where:
7720 <size> := size (can use standard suffixes
7721 like K, M and G)
7722 <baseaddr> := physical base address
7723 <irq> := interrupt number (as passed to
7724 request_irq())
7725 <id> := (optional) platform device id
7726 example:
7727 virtio_mmio.device=1K@0x100b0000:48:7
7729 Can be used multiple times for multiple devices.
7731 vga= [BOOT,X86-32] Select a particular video mode
7732 See Documentation/arch/x86/boot.rst and
7733 Documentation/admin-guide/svga.rst.
7734 Use vga=ask for menu.
7735 This is actually a boot loader parameter; the value is
7736 passed to the kernel using a special protocol.
7738 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
7739 May slow down system boot speed, especially when
7740 enabled on systems with a large amount of memory.
7741 All options are enabled by default, and this
7742 interface is meant to allow for selectively
7743 enabling or disabling specific virtual memory
7744 debugging features.
7746 Available options are:
7747 P Enable page structure init time poisoning
7748 - Disable all of the above options
7750 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an
7751 exact size of <nn>. This can be used to increase
7752 the minimum size (128MB on x86, arm32 platforms).
7753 It can also be used to decrease the size and leave more room
7754 for directly mapped kernel RAM. Note that this parameter does
7755 not exist on many other platforms (including arm64, alpha,
7756 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc,
7757 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc).
7759 vmcp_cma=nn[MG] [KNL,S390,EARLY]
7760 Sets the memory size reserved for contiguous memory
7761 allocations for the vmcp device driver.
7763 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
7764 Format: <command>
7766 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
7767 Format: <command>
7769 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
7770 Format: <command>
7772 vsyscall= [X86-64,EARLY]
7773 Controls the behavior of vsyscalls (i.e. calls to
7774 fixed addresses of 0xffffffffff600x00 from legacy
7775 code). Most statically-linked binaries and older
7776 versions of glibc use these calls. Because these
7777 functions are at fixed addresses, they make nice
7778 targets for exploits that can control RIP.
7780 emulate Vsyscalls turn into traps and are emulated
7781 reasonably safely. The vsyscall page is
7782 readable.
7784 xonly [default] Vsyscalls turn into traps and are
7785 emulated reasonably safely. The vsyscall
7786 page is not readable.
7788 none Vsyscalls don't work at all. This makes
7789 them quite hard to use for exploits but
7790 might break your system.
7792 vt.color= [VT] Default text color.
7793 Format: 0xYX, X = foreground, Y = background.
7794 Default: 0x07 = light gray on black.
7796 vt.cur_default= [VT] Default cursor shape.
7797 Format: 0xCCBBAA, where AA, BB, and CC are the same as
7798 the parameters of the <Esc>[?A;B;Cc escape sequence;
7799 see vga-softcursor.rst. Default: 2 = underline.
7801 vt.default_blu= [VT]
7802 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
7803 Change the default blue palette of the console.
7804 This is a 16-member array composed of values
7805 ranging from 0-255.
7807 vt.default_grn= [VT]
7808 Format: <green0>,<green1>,<green2>,...,<green15>
7809 Change the default green palette of the console.
7810 This is a 16-member array composed of values
7811 ranging from 0-255.
7813 vt.default_red= [VT]
7814 Format: <red0>,<red1>,<red2>,...,<red15>
7815 Change the default red palette of the console.
7816 This is a 16-member array composed of values
7817 ranging from 0-255.
7819 vt.default_utf8=
7820 [VT]
7821 Format=<0|1>
7822 Set system-wide default UTF-8 mode for all tty's.
7823 Default is 1, i.e. UTF-8 mode is enabled for all
7824 newly opened terminals.
7826 vt.global_cursor_default=
7827 [VT]
7828 Format=<-1|0|1>
7829 Set system-wide default for whether a cursor
7830 is shown on new VTs. Default is -1,
7831 i.e. cursors will be created by default unless
7832 overridden by individual drivers. 0 will hide
7833 cursors, 1 will display them.
7835 vt.italic= [VT] Default color for italic text; 0-15.
7836 Default: 2 = green.
7838 vt.underline= [VT] Default color for underlined text; 0-15.
7839 Default: 3 = cyan.
7841 watchdog timers [HW,WDT] For information on watchdog timers,
7842 see Documentation/watchdog/watchdog-parameters.rst
7843 or other driver-specific files in the
7844 Documentation/watchdog/ directory.
7846 watchdog_thresh=
7847 [KNL]
7848 Set the hard lockup detector stall duration
7849 threshold in seconds. The soft lockup detector
7850 threshold is set to twice the value. A value of 0
7851 disables both lockup detectors. Default is 10
7852 seconds.
7854 workqueue.unbound_cpus=
7855 [KNL,SMP] Specify to constrain one or some CPUs
7856 to use in unbound workqueues.
7857 Format: <cpu-list>
7858 By default, all online CPUs are available for
7859 unbound workqueues.
7861 workqueue.watchdog_thresh=
7862 If CONFIG_WQ_WATCHDOG is configured, workqueue can
7863 warn stall conditions and dump internal state to
7864 help debugging. 0 disables workqueue stall
7865 detection; otherwise, it's the stall threshold
7866 duration in seconds. The default value is 30 and
7867 it can be updated at runtime by writing to the
7868 corresponding sysfs file.
7870 workqueue.panic_on_stall=<uint>
7871 Panic when workqueue stall is detected by
7872 CONFIG_WQ_WATCHDOG. It sets the number times of the
7873 stall to trigger panic.
7875 The default is 0, which disables the panic on stall.
7877 workqueue.cpu_intensive_thresh_us=
7878 Per-cpu work items which run for longer than this
7879 threshold are automatically considered CPU intensive
7880 and excluded from concurrency management to prevent
7881 them from noticeably delaying other per-cpu work
7882 items. Default is 10000 (10ms).
7884 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7885 will report the work functions which violate this
7886 threshold repeatedly. They are likely good
7887 candidates for using WQ_UNBOUND workqueues instead.
7889 workqueue.cpu_intensive_warning_thresh=<uint>
7890 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
7891 will report the work functions which violate the
7892 intensive_threshold_us repeatedly. In order to prevent
7893 spurious warnings, start printing only after a work
7894 function has violated this threshold number of times.
7896 The default is 4 times. 0 disables the warning.
7898 workqueue.power_efficient
7899 Per-cpu workqueues are generally preferred because
7900 they show better performance thanks to cache
7901 locality; unfortunately, per-cpu workqueues tend to
7902 be more power hungry than unbound workqueues.
7904 Enabling this makes the per-cpu workqueues which
7905 were observed to contribute significantly to power
7906 consumption unbound, leading to measurably lower
7907 power usage at the cost of small performance
7908 overhead.
7910 The default value of this parameter is determined by
7911 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
7913 workqueue.default_affinity_scope=
7914 Select the default affinity scope to use for unbound
7915 workqueues. Can be one of "cpu", "smt", "cache",
7916 "numa" and "system". Default is "cache". For more
7917 information, see the Affinity Scopes section in
7918 Documentation/core-api/workqueue.rst.
7920 This can be changed after boot by writing to the
7921 matching /sys/module/workqueue/parameters file. All
7922 workqueues with the "default" affinity scope will be
7923 updated accordingly.
7925 workqueue.debug_force_rr_cpu
7926 Workqueue used to implicitly guarantee that work
7927 items queued without explicit CPU specified are put
7928 on the local CPU. This guarantee is no longer true
7929 and while local CPU is still preferred work items
7930 may be put on foreign CPUs. This debug option
7931 forces round-robin CPU selection to flush out
7932 usages which depend on the now broken guarantee.
7933 When enabled, memory and cache locality will be
7934 impacted.
7936 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
7937 Type) of ioremap_wc().
7939 on - Enable writecombine, use WUC for ioremap_wc()
7940 off - Disable writecombine, use SUC for ioremap_wc()
7942 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
7943 default x2apic cluster mode on platforms
7944 supporting x2apic.
7946 xen_512gb_limit [KNL,X86-64,XEN]
7947 Restricts the kernel running paravirtualized under Xen
7948 to use only up to 512 GB of RAM. The reason to do so is
7949 crash analysis tools and Xen tools for doing domain
7950 save/restore/migration must be enabled to handle larger
7951 domains.
7953 xen_emul_unplug= [HW,X86,XEN,EARLY]
7954 Unplug Xen emulated devices
7955 Format: [unplug0,][unplug1]
7956 ide-disks -- unplug primary master IDE devices
7957 aux-ide-disks -- unplug non-primary-master IDE devices
7958 nics -- unplug network devices
7959 all -- unplug all emulated devices (NICs and IDE disks)
7960 unnecessary -- unplugging emulated devices is
7961 unnecessary even if the host did not respond to
7962 the unplug protocol
7963 never -- do not unplug even if version check succeeds
7965 xen_legacy_crash [X86,XEN,EARLY]
7966 Crash from Xen panic notifier, without executing late
7967 panic() code such as dumping handler.
7969 xen_mc_debug [X86,XEN,EARLY]
7970 Enable multicall debugging when running as a Xen PV guest.
7971 Enabling this feature will reduce performance a little
7972 bit, so it should only be enabled for obtaining extended
7973 debug data in case of multicall errors.
7975 xen_msr_safe= [X86,XEN,EARLY]
7976 Format: <bool>
7977 Select whether to always use non-faulting (safe) MSR
7978 access functions when running as Xen PV guest. The
7979 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
7981 xen_nopv [X86]
7982 Disables the PV optimizations forcing the HVM guest to
7983 run as generic HVM guest with no PV drivers.
7984 This option is obsoleted by the "nopv" option, which
7985 has equivalent effect for XEN platform.
7987 xen_no_vector_callback
7988 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
7989 event channel interrupts.
7991 xen_scrub_pages= [XEN]
7992 Boolean option to control scrubbing pages before giving them back
7993 to Xen, for use by other domains. Can be also changed at runtime
7994 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
7995 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
7997 xen_timer_slop= [X86-64,XEN,EARLY]
7998 Set the timer slop (in nanoseconds) for the virtual Xen
7999 timers (default is 100000). This adjusts the minimum
8000 delta of virtualized Xen timers, where lower values
8001 improve timer resolution at the expense of processing
8002 more timer interrupts.
8004 xen.balloon_boot_timeout= [XEN]
8005 The time (in seconds) to wait before giving up to boot
8006 in case initial ballooning fails to free enough memory.
8007 Applies only when running as HVM or PVH guest and
8008 started with less memory configured than allowed at
8009 max. Default is 180.
8011 xen.event_eoi_delay= [XEN]
8012 How long to delay EOI handling in case of event
8013 storms (jiffies). Default is 10.
8015 xen.event_loop_timeout= [XEN]
8016 After which time (jiffies) the event handling loop
8017 should start to delay EOI handling. Default is 2.
8019 xen.fifo_events= [XEN]
8020 Boolean parameter to disable using fifo event handling
8021 even if available. Normally fifo event handling is
8022 preferred over the 2-level event handling, as it is
8023 fairer and the number of possible event channels is
8024 much higher. Default is on (use fifo events).
8026 xirc2ps_cs= [NET,PCMCIA]
8027 Format:
8028 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
8030 xive= [PPC]
8031 By default on POWER9 and above, the kernel will
8032 natively use the XIVE interrupt controller. This option
8033 allows the fallback firmware mode to be used:
8035 off Fallback to firmware control of XIVE interrupt
8036 controller on both pseries and powernv
8037 platforms. Only useful on POWER9 and above.
8039 xive.store-eoi=off [PPC]
8040 By default on POWER10 and above, the kernel will use
8041 stores for EOI handling when the XIVE interrupt mode
8042 is active. This option allows the XIVE driver to use
8043 loads instead, as on POWER9.
8045 xhci-hcd.quirks [USB,KNL]
8046 A hex value specifying bitmask with supplemental xhci
8047 host controller quirks. Meaning of each bit can be
8048 consulted in header drivers/usb/host/xhci.h.
8050 xmon [PPC,EARLY]
8051 Format: { early | on | rw | ro | off }
8052 Controls if xmon debugger is enabled. Default is off.
8053 Passing only "xmon" is equivalent to "xmon=early".
8054 early Call xmon as early as possible on boot; xmon
8055 debugger is called from setup_arch().
8056 on xmon debugger hooks will be installed so xmon
8057 is only called on a kernel crash. Default mode,
8058 i.e. either "ro" or "rw" mode, is controlled
8059 with CONFIG_XMON_DEFAULT_RO_MODE.
8060 rw xmon debugger hooks will be installed so xmon
8061 is called only on a kernel crash, mode is write,
8062 meaning SPR registers, memory and, other data
8063 can be written using xmon commands.
8064 ro same as "rw" option above but SPR registers,
8065 memory, and other data can't be written using
8066 xmon commands.
8067 off xmon is disabled.