1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.rst, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
25 { vendor | video | native | none }
26 If set to vendor, prefer vendor-specific driver
27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
28 of the ACPI video.ko driver.
29 If set to video, use the ACPI video.ko driver.
30 If set to native, use the device's native backlight mode.
31 If set to none, disable the ACPI backlight interface.
33 acpi_force_32bit_fadt_addr
34 force FADT to use 32 bit addresses rather than the
35 64 bit X_* addresses. Some firmware have broken 64
36 bit addresses for force ACPI ignore these and use
37 the older legacy 32 bit addresses.
39 acpica_no_return_repair [HW, ACPI]
40 Disable AML predefined validation mechanism
41 This mechanism can repair the evaluation result to make
42 the return objects more ACPI specification compliant.
43 This option is useful for developers to identify the
44 root cause of an AML interpreter issue when the issue
45 has something to do with the repair mechanism.
47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
51 debug output. Bits in debug_layer correspond to a
52 _COMPONENT in an ACPI source file, e.g.,
53 #define _COMPONENT ACPI_EVENTS
54 Bits in debug_level correspond to a level in
55 ACPI_DEBUG_PRINT statements, e.g.,
56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
57 The debug_level mask defaults to "info". See
58 Documentation/firmware-guide/acpi/debug.rst for more information about
59 debug layers and levels.
61 Enable processor driver info messages:
62 acpi.debug_layer=0x20000000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
116 Format: <byte> or <bitmap-list>
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_no_watchdog [HW,ACPI,WDT]
140 Ignore the ACPI-based watchdog interface (WDAT) and let
141 a native driver control the watchdog device instead.
143 acpi_rsdp= [ACPI,EFI,KEXEC]
144 Pass the RSDP address to the kernel, mostly used
145 on machines running EFI runtime service to boot the
146 second kernel for kdump.
148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
149 Format: To spoof as Windows 98: ="Microsoft Windows"
151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
152 of 2 which is mandated by ACPI 6) as the supported ACPI
153 specification revision (when using this switch, it may
154 be necessary to carry out a cold reboot _twice_ in a
155 row to make it take effect on the platform firmware).
157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
158 acpi_osi="string1" # add string1
159 acpi_osi="!string2" # remove string2
160 acpi_osi=!* # remove all strings
161 acpi_osi=! # disable all built-in OS vendor
163 acpi_osi=!! # enable all built-in OS vendor
165 acpi_osi= # disable all strings
167 'acpi_osi=!' can be used in combination with single or
168 multiple 'acpi_osi="string1"' to support specific OS
169 vendor string(s). Note that such command can only
170 affect the default state of the OS vendor strings, thus
171 it cannot affect the default state of the feature group
172 strings and the current state of the OS vendor strings,
173 specifying it multiple times through kernel command line
174 is meaningless. This command is useful when one do not
175 care about the state of the feature group strings which
176 should be controlled by the OSPM.
178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
180 can make '_OSI("Windows 2000")' TRUE.
182 'acpi_osi=' cannot be used in combination with other
183 'acpi_osi=' command lines, the _OSI method will not
184 exist in the ACPI namespace. NOTE that such command can
185 only affect the _OSI support state, thus specifying it
186 multiple times through kernel command line is also
189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
192 'acpi_osi=!*' can be used in combination with single or
193 multiple 'acpi_osi="string1"' to support specific
194 string(s). Note that such command can affect the
195 current state of both the OS vendor strings and the
196 feature group strings, thus specifying it multiple times
197 through kernel command line is meaningful. But it may
198 still not able to affect the final state of a string if
199 there are quirks related to this string. This command
200 is useful when one want to control the state of the
201 feature group strings to debug BIOS issues related to
204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
205 '_OSI("Module Device")' FALSE.
206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
207 '_OSI("Module Device")' TRUE.
208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
213 they all will make '_OSI("Windows 2000")' TRUE.
216 Override the pmtimer bug detection: force the kernel
217 to assume that this machine's pmtimer latches its value
218 and always returns good values.
220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
221 Format: { level | edge | high | low }
223 acpi_skip_timer_override [HW,ACPI]
224 Recognize and ignore IRQ0/pin2 Interrupt Override.
225 For broken nForce2 BIOS resulting in XT-PIC timer.
227 acpi_sleep= [HW,ACPI] Sleep options
228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig,
229 s4_nohwsig, old_ordering, nonvs,
230 sci_force_enable, nobl }
231 See Documentation/power/video.rst for information on
233 s3_beep is for debugging; it makes the PC's speaker beep
234 as soon as the kernel's real-mode entry point is called.
235 s4_hwsig causes the kernel to check the ACPI hardware
236 signature during resume from hibernation, and gracefully
237 refuse to resume if it has changed. This complies with
238 the ACPI specification but not with reality, since
239 Windows does not do this and many laptops do change it
240 on docking. So the default behaviour is to allow resume
241 and simply warn when the signature changes, unless the
242 s4_hwsig option is enabled.
243 s4_nohwsig prevents ACPI hardware signature from being
244 used (or even warned about) during resume.
245 old_ordering causes the ACPI 1.0 ordering of the _PTS
246 control method, with respect to putting devices into
247 low power states, to be enforced (the ACPI 2.0 ordering
248 of _PTS is used by default).
249 nonvs prevents the kernel from saving/restoring the
250 ACPI NVS memory during suspend/hibernation and resume.
251 sci_force_enable causes the kernel to set SCI_EN directly
252 on resume from S1/S3 (which is against the ACPI spec,
253 but some broken systems don't work without it).
254 nobl causes the internal blacklist of systems known to
255 behave incorrectly in some ways with respect to system
256 suspend and resume to be ignored (use wisely).
258 acpi_use_timer_override [HW,ACPI]
259 Use timer override. For some broken Nvidia NF5 boards
260 that require a timer override, but don't have HPET
262 add_efi_memmap [EFI; X86] Include EFI memory map in
263 kernel's map of available physical RAM.
266 { off | try_unsupported }
267 off: disable AGP support
268 try_unsupported: try to drive unsupported chipsets
269 (may crash computer or cause data corruption)
272 See Documentation/sound/alsa-configuration.rst
275 Allow the default userspace alignment fault handler
276 behaviour to be specified. Bit 0 enables warnings,
277 bit 1 enables fixups, and bit 2 sends a segfault.
279 align_va_addr= [X86-64]
280 Align virtual addresses by clearing slice [14:12] when
281 allocating a VMA at process creation time. This option
282 gives you up to 3% performance improvement on AMD F15h
283 machines (where it is enabled by default) for a
284 CPU-intensive style benchmark, and it can vary highly in
285 a microbenchmark depending on workload and compiler.
287 32: only for 32-bit processes
288 64: only for 64-bit processes
289 on: enable for both 32- and 64-bit processes
290 off: disable for both 32- and 64-bit processes
292 alloc_snapshot [FTRACE]
293 Allocate the ftrace snapshot buffer on boot up when the
294 main buffer is allocated. This is handy if debugging
295 and you need to use tracing_snapshot() on boot up, and
296 do not want to use tracing_snapshot_alloc() as it needs
297 to be done where GFP_KERNEL allocations are allowed.
299 allow_mismatched_32bit_el0 [ARM64]
300 Allow execve() of 32-bit applications and setting of the
301 PER_LINUX32 personality on systems where only a strict
302 subset of the CPUs support 32-bit EL0. When this
303 parameter is present, the set of CPUs supporting 32-bit
304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
305 and hot-unplug operations may be restricted.
307 See Documentation/arm64/asymmetric-32bit.rst for more
310 amd_iommu= [HW,X86-64]
311 Pass parameters to the AMD IOMMU driver in the system.
313 fullflush - Deprecated, equivalent to iommu.strict=1
314 off - do not initialize any AMD IOMMU found in
316 force_isolation - Force device isolation for all
317 devices. The IOMMU driver is not
318 allowed anymore to lift isolation
319 requirements as needed. This option
320 does not override iommu=pt
321 force_enable - Force enable the IOMMU on platforms known
322 to be buggy with IOMMU enabled. Use this
325 amd_iommu_dump= [HW,X86-64]
326 Enable AMD IOMMU driver option to dump the ACPI table
327 for AMD IOMMU. With this option enabled, AMD IOMMU
328 driver will print ACPI tables for AMD IOMMU during
329 IOMMU initialization.
331 amd_iommu_intr= [HW,X86-64]
332 Specifies one of the following AMD IOMMU interrupt
334 legacy - Use legacy interrupt remapping mode.
335 vapic - Use virtual APIC mode, which allows IOMMU
336 to inject interrupts directly into guest.
337 This mode requires kvm-amd.avic=1.
338 (Default when IOMMU HW support is present.)
340 amijoy.map= [HW,JOY] Amiga joystick support
341 Map of devices attached to JOY0DAT and JOY1DAT
343 See also Documentation/input/joydev/joystick.rst
345 analog.map= [HW,JOY] Analog joystick and gamepad support
346 Specifies type or capabilities of an analog joystick
347 connected to one of 16 gameports
348 Format: <type1>,<type2>,..<type16>
351 Power management functions (SPARCstation-4/5 + deriv.)
353 Disable APC CPU standby support. SPARCstation-Fox does
354 not play well with APC CPU idle - disable it if you have
355 APC and your system crashes randomly.
357 apic= [APIC,X86] Advanced Programmable Interrupt Controller
358 Change the output verbosity while booting
359 Format: { quiet (default) | verbose | debug }
360 Change the amount of debugging information output
361 when initialising the APIC and IO-APIC components.
362 For X86-32, this can also be used to specify an APIC
364 Format: apic=driver_name
365 Examples: apic=bigsmp
367 apic_extnmi= [APIC,X86] External NMI delivery setting
368 Format: { bsp (default) | all | none }
369 bsp: External NMI is delivered only to CPU 0
370 all: External NMIs are broadcast to all CPUs as a
372 none: External NMI is masked for all CPUs. This is
373 useful so that a dump capture kernel won't be
377 See Documentation/networking/ipv6.rst.
379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
380 Limit apic dumping. The parameter defines the maximal
381 number of local apics being dumped. Also it is possible
382 to set it to "all" by meaning -- no limit here.
383 Format: { 1 (default) | 2 | ... | all }.
384 The parameter valid if only apic=debug or
385 apic=verbose is specified.
386 Example: apic=debug show_lapic=all
388 apm= [APM] Advanced Power Management
389 See header of arch/x86/kernel/apm_32.c.
391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
392 Format: <io>,<irq>,<nodeID>
394 arm64.nobti [ARM64] Unconditionally disable Branch Target
395 Identification support
397 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
400 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
403 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
406 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
411 atarimouse= [HW,MOUSE] Atari Mouse
413 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
414 EzKey and similar keyboards
416 atkbd.reset= [HW] Reset keyboard during initialization
418 atkbd.set= [HW] Select keyboard code set
419 Format: <int> (2 = AT (default), 3 = PS/2)
421 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
424 atkbd.softraw= [HW] Choose between synthetic and real raw mode
425 Format: <bool> (0 = real, 1 = synthetic (default))
427 atkbd.softrepeat= [HW]
428 Use software keyboard repeat
430 audit= [KNL] Enable the audit sub-system
431 Format: { "0" | "1" | "off" | "on" }
432 0 | off - kernel audit is disabled and can not be
433 enabled until the next reboot
434 unset - kernel audit is initialized but disabled and
435 will be fully enabled by the userspace auditd.
436 1 | on - kernel audit is initialized and partially
437 enabled, storing at most audit_backlog_limit
438 messages in RAM until it is fully enabled by the
442 audit_backlog_limit= [KNL] Set the audit queue size limit.
443 Format: <int> (must be >=0)
446 bau= [X86_UV] Enable the BAU on SGI UV. The default
447 behavior is to disable the BAU (i.e. bau=0).
448 Format: { "0" | "1" }
451 unset - Disable the BAU.
453 baycom_epp= [HW,AX25]
456 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
458 See header of drivers/net/hamradio/baycom_par.c.
460 baycom_ser_fdx= [HW,AX25]
461 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
462 Format: <io>,<irq>,<mode>[,<baud>]
463 See header of drivers/net/hamradio/baycom_ser_fdx.c.
465 baycom_ser_hdx= [HW,AX25]
466 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
467 Format: <io>,<irq>,<mode>
468 See header of drivers/net/hamradio/baycom_ser_hdx.c.
471 Disable BERT OS support on buggy BIOSes.
473 bgrt_disable [ACPI][X86]
474 Disable BGRT to avoid flickering OEM logo.
476 blkdevparts= Manual partition parsing of block device(s) for
477 embedded devices based on command line input.
478 See Documentation/block/cmdline-partition.rst
480 boot_delay= Milliseconds to delay each printk during boot.
481 Values larger than 10 seconds (10000) are changed to
486 Extended command line options can be added to an initrd
487 and this will cause the kernel to look for it.
489 See Documentation/admin-guide/bootconfig.rst
491 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
492 bttv.radio= Most important insmod options are available as
494 bttv.pll= See Documentation/admin-guide/media/bttv.rst
497 bulk_remove=off [PPC] This parameter disables the use of the pSeries
498 firmware feature for flushing multiple hpte entries
501 c101= [NET] Moxa C101 synchronous serial card
503 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
504 Sometimes CPU hardware bugs make them report the cache
505 size incorrectly. The kernel will attempt work arounds
506 to fix known problems, but for some CPUs it is not
507 possible to determine what the correct size should be.
508 This option provides an override for these situations.
511 [NET] Specifies amount of time (in seconds) that
512 the kernel should wait for a network carrier. By default
513 it waits 120 seconds.
515 ca_keys= [KEYS] This parameter identifies a specific key(s) on
516 the system trusted keyring to be used for certificate
518 format: { id:<keyid> | builtin }
520 cca= [MIPS] Override the kernel pages' cache coherency
521 algorithm. Accepted values range from 0 to 7
522 inclusive. See arch/mips/include/asm/pgtable-bits.h
523 for platform specific values (SB1, Loongson3 and
526 ccw_timeout_log [S390]
527 See Documentation/s390/common_io.rst for details.
529 cgroup_disable= [KNL] Disable a particular controller or optional feature
530 Format: {name of the controller(s) or feature(s) to disable}
531 The effects of cgroup_disable=foo are:
532 - foo isn't auto-mounted if you mount all cgroups in
534 - foo isn't visible as an individually mountable
536 - if foo is an optional feature then the feature is
537 disabled and corresponding cgroup files are not
539 {Currently only "memory" controller deal with this and
540 cut the overhead, others just disable the usage. So
541 only cgroup_disable=memory is actually worthy}
542 Specifying "pressure" disables per-cgroup pressure
543 stall information accounting feature
545 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
546 Format: { { controller | "all" | "named" }
547 [,{ controller | "all" | "named" }...] }
548 Like cgroup_disable, but only applies to cgroup v1;
549 the blacklisted controllers remain available in cgroup2.
550 "all" blacklists all controllers and "named" disables
551 named mounts. Specifying both "all" and "named" disables
554 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
556 nosocket -- Disable socket memory accounting.
557 nokmem -- Disable kernel memory accounting.
559 checkreqprot [SELINUX] Set initial checkreqprot flag value.
560 Format: { "0" | "1" }
561 See security/selinux/Kconfig help text.
562 0 -- check protection applied by kernel (includes
563 any implied execute protection).
564 1 -- check protection requested by application.
565 Default value is set via a kernel config option.
566 Value can be changed at runtime via
567 /sys/fs/selinux/checkreqprot.
568 Setting checkreqprot to 1 is deprecated.
571 See Documentation/s390/common_io.rst for details.
573 clearcpuid=X[,X...] [X86]
574 Disable CPUID feature X for the kernel. See
575 arch/x86/include/asm/cpufeatures.h for the valid bit
576 numbers X. Note the Linux-specific bits are not necessarily
577 stable over kernel options, but the vendor-specific
579 X can also be a string as appearing in the flags: line
580 in /proc/cpuinfo which does not have the above
581 instability issue. However, not all features have names
583 Note that using this option will taint your kernel.
584 Also note that user programs calling CPUID directly
585 or using the feature without checking anything
586 will still see it. This just prevents it from
587 being used by the kernel or shown in /proc/cpuinfo.
588 Also note the kernel might malfunction if you disable
593 Prevents the clock framework from automatically gating
594 clocks that have not been explicitly enabled by a Linux
595 device driver but are enabled in hardware at reset or
596 by the bootloader/firmware. Note that this does not
597 force such clocks to be always-on nor does it reserve
598 those clocks in any way. This parameter is useful for
599 debug and development, but should not be needed on a
600 platform with proper driver support. For more
601 information, see Documentation/driver-api/clk.rst.
603 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
605 Forces specified clocksource (if available) to be used
606 when calculating gettimeofday(). If specified
607 clocksource is not available, it defaults to PIT.
608 Format: { pit | tsc | cyclone | pmtmr }
610 clocksource= Override the default clocksource
612 Override the default clocksource and use the clocksource
613 with the name specified.
614 Some clocksource names to choose from, depending on
616 [all] jiffies (this is the base, fallback clocksource)
618 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
619 pxa_timer,timer3,32k_counter,timer0_1
620 [X86-32] pit,hpet,tsc;
621 scx200_hrt on Geode; cyclone on IBM x440
629 clocksource.arm_arch_timer.evtstrm=
632 Enable/disable the eventstream feature of the ARM
633 architected timer so that code using WFE-based polling
634 loops can be debugged more effectively on production
637 clocksource.max_cswd_read_retries= [KNL]
638 Number of clocksource_watchdog() retries due to
639 external delays before the clock will be marked
640 unstable. Defaults to two retries, that is,
641 three attempts to read the clock under test.
643 clocksource.verify_n_cpus= [KNL]
644 Limit the number of CPUs checked for clocksources
645 marked with CLOCK_SOURCE_VERIFY_PERCPU that
646 are marked unstable due to excessive skew.
647 A negative value says to check all CPUs, while
648 zero says not to check any. Values larger than
649 nr_cpu_ids are silently truncated to nr_cpu_ids.
650 The actual CPUs are chosen randomly, with
651 no replacement if the same CPU is chosen twice.
653 clocksource-wdtest.holdoff= [KNL]
654 Set the time in seconds that the clocksource
655 watchdog test waits before commencing its tests.
656 Defaults to zero when built as a module and to
657 10 seconds when built into the kernel.
659 cma=nn[MG]@[start[MG][-end[MG]]]
661 Sets the size of kernel global memory area for
662 contiguous memory allocations and optionally the
663 placement constraint by the physical address range of
664 memory allocations. A value of 0 disables CMA
665 altogether. For more information, see
666 kernel/dma/contiguous.c
670 Sets the size of kernel per-numa memory area for
671 contiguous memory allocations. A value of 0 disables
672 per-numa CMA altogether. And If this option is not
673 specificed, the default value is 0.
674 With per-numa CMA enabled, DMA users on node nid will
675 first try to allocate buffer from the pernuma area
676 which is located in node nid, if the allocation fails,
677 they will fallback to the global default memory area.
679 cmo_free_hint= [PPC] Format: { yes | no }
680 Specify whether pages are marked as being inactive
681 when they are freed. This is used in CMO environments
682 to determine OS memory pressure for page stealing by
686 coherent_pool=nn[KMG] [ARM,KNL]
687 Sets the size of memory pool for coherent, atomic dma
688 allocations, by default set to 256K.
690 com20020= [HW,NET] ARCnet - COM20020 chipset
692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
698 ARCnet - COM90xx chipset (memory-mapped buffers)
699 Format: <io>[,<irq>[,<memstart>]]
701 condev= [HW,S390] console device
704 console= [KNL] Output console device and options.
706 tty<n> Use the virtual console device <n>.
710 Use the specified serial port. The options are of
711 the form "bbbbpnf", where "bbbb" is the baud rate,
712 "p" is parity ("n", "o", or "e"), "n" is number of
713 bits, and "f" is flow control ("r" for RTS or
714 omit it). Default is "9600n8".
716 See Documentation/admin-guide/serial-console.rst for more
718 Documentation/networking/netconsole.rst for an
721 uart[8250],io,<addr>[,options]
722 uart[8250],mmio,<addr>[,options]
723 uart[8250],mmio16,<addr>[,options]
724 uart[8250],mmio32,<addr>[,options]
725 uart[8250],0x<addr>[,options]
726 Start an early, polled-mode console on the 8250/16550
727 UART at the specified I/O port or MMIO address,
728 switching to the matching ttyS device later.
729 MMIO inter-register address stride is either 8-bit
730 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
731 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
732 to be equivalent to 'mmio'. 'options' are specified in
733 the same format described for ttyS above; if unspecified,
734 the h/w is not re-initialized.
736 hvc<n> Use the hypervisor console device <n>. This is for
737 both Xen and PowerPC hypervisors.
740 Use to disable console output, i.e., to have kernel
741 console messages discarded.
742 This must be the only console= parameter used on the
745 If the device connected to the port is not a TTY but a braille
746 device, prepend "brl," before the device type, for instance
748 For now, only VisioBraille is supported.
751 [KNL] Change console messages format
753 By default we print messages on consoles in
754 "[time stamp] text\n" format (time stamp may not be
755 printed, depending on CONFIG_PRINTK_TIME or
756 `printk_time' param).
758 Switch to syslog format: "<%u>[time stamp] text\n"
759 IOW, each message will have a facility and loglevel
760 prefix. The format is similar to one used by syslog()
761 syscall, or to executing "dmesg -S --raw" or to reading
764 consoleblank= [KNL] The console blank (screen saver) timeout in
765 seconds. A value of 0 disables the blank timer.
769 [KNL] Change the default value for
770 /proc/<pid>/coredump_filter.
771 See also Documentation/filesystems/proc.rst.
773 coresight_cpu_debug.enable
776 Enable/disable the CPU sampling based debugging.
777 0: default value, disable debugging
778 1: enable debugging at boot time
780 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
782 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
784 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
785 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
786 Some features depend on CPU0. Known dependencies are:
787 1. Resume from suspend/hibernate depends on CPU0.
788 Suspend/hibernate will fail if CPU0 is offline and you
789 need to online CPU0 before suspend/hibernate.
790 2. PIC interrupts also depend on CPU0. CPU0 can't be
791 removed if a PIC interrupt is detected.
792 It's said poweroff/reboot may depend on CPU0 on some
793 machines although I haven't seen such issues so far
794 after CPU0 is offline on a few tested machines.
795 If the dependencies are under your control, you can
796 turn on cpu0_hotplug.
798 cpuidle.off=1 [CPU_IDLE]
799 disable the cpuidle sub-system
802 [CPU_IDLE] Name of the cpuidle governor to use.
804 cpufreq.off=1 [CPU_FREQ]
805 disable the cpufreq sub-system
807 cpufreq.default_governor=
808 [CPU_FREQ] Name of the default cpufreq governor or
809 policy to use. This governor must be registered in the
810 kernel before the cpufreq driver probes.
813 [X86] Delay for N microsec between assert and de-assert
814 of APIC INIT to start processors. This delay occurs
815 on every CPU online, such as boot, and resume from suspend.
818 crash_kexec_post_notifiers
819 Run kdump after running panic-notifiers and dumping
820 kmsg. This only for the users who doubt kdump always
821 succeeds in any situation.
822 Note that this also increases risks of kdump failure,
823 because some panic notifiers can make the crashed
824 kernel more unstable.
826 crashkernel=size[KMG][@offset[KMG]]
827 [KNL] Using kexec, Linux can switch to a 'crash kernel'
828 upon panic. This parameter reserves the physical
829 memory region [offset, offset + size] for that kernel
830 image. If '@offset' is omitted, then a suitable offset
831 is selected automatically.
832 [KNL, X86-64] Select a region under 4G first, and
833 fall back to reserve region above 4G when '@offset'
834 hasn't been specified.
835 See Documentation/admin-guide/kdump/kdump.rst for further details.
837 crashkernel=range1:size1[,range2:size2,...][@offset]
838 [KNL] Same as above, but depends on the memory
839 in the running system. The syntax of range is
840 start-[end] where start and end are both
841 a memory unit (amount[KMG]). See also
842 Documentation/admin-guide/kdump/kdump.rst for an example.
844 crashkernel=size[KMG],high
845 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel
846 to allocate physical memory region from top, so could
847 be above 4G if system have more than 4G ram installed.
848 Otherwise memory region will be allocated below 4G, if
850 It will be ignored if crashkernel=X is specified.
851 crashkernel=size[KMG],low
852 [KNL, X86-64] range under 4G. When crashkernel=X,high
853 is passed, kernel could allocate physical memory region
854 above 4G, that cause second kernel crash on system
855 that require some amount of low memory, e.g. swiotlb
856 requires at least 64M+32K low memory, also enough extra
857 low memory is needed to make sure DMA buffers for 32-bit
858 devices won't run out. Kernel would try to allocate
859 at least 256M below 4G automatically.
860 This one lets the user specify own low range under 4G
861 for second kernel instead.
862 0: to disable low allocation.
863 It will be ignored when crashkernel=X,high is not used
864 or memory reserved is below 4G.
866 [KNL, ARM64] range in low memory.
867 This one lets the user specify a low range in the
868 DMA zone for the crash dump kernel.
869 It will be ignored when crashkernel=X,high is not used
870 or memory reserved is located in the DMA zones.
873 [KNL] Disable crypto self-tests
878 cs89x0_media= [HW,NET]
879 Format: { rj45 | aui | bnc }
881 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
882 handling. When switched on, additional debug data is
883 printed to the console in case a hanging CPU is
884 detected, and that CPU is pinged again in order to try
885 to resolve the hang situation.
886 0: disable csdlock debugging (default)
887 1: enable basic csdlock debugging (minor impact)
888 ext: enable extended csdlock debugging (more impact,
892 See header of drivers/s390/block/dasd_devmap.c.
894 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
895 (one device per port)
896 Format: <port#>,<type>
897 See also Documentation/input/devices/joystick-parport.rst
899 debug [KNL] Enable kernel debugging (events log level).
902 [KNL] Enable printing [hashed] pointers early in the
903 boot sequence. If enabled, we use a weak hash instead
904 of siphash to hash pointers. Use this option if you are
905 seeing instances of '(___ptrval___)') and need to see a
906 value (hashed pointer) instead. Cryptographically
907 insecure, please do not use on production kernels.
910 [KNL] verbose locking self-tests
912 Print debugging info while doing the locking API
914 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
915 (no extra messages), setting it to -1 (all bits set)
916 will print _a_lot_ more information - normally only
917 useful to lockdep developers.
919 debug_objects [KNL] Enable object debugging
922 [KNL] Disable object debugging
924 debug_guardpage_minorder=
925 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
926 parameter allows control of the order of pages that will
927 be intentionally kept free (and hence protected) by the
928 buddy allocator. Bigger value increase the probability
929 of catching random memory corruption, but reduce the
930 amount of memory for normal system use. The maximum
931 possible value is MAX_ORDER/2. Setting this parameter
932 to 1 or 2 should be enough to identify most random
933 memory corruption problems caused by bugs in kernel or
934 driver code when a CPU writes to (or reads from) a
935 random memory location. Note that there exists a class
936 of memory corruptions problems caused by buggy H/W or
937 F/W or by drivers badly programing DMA (basically when
938 memory is written at bus level and the CPU MMU is
939 bypassed) which are not detectable by
940 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
941 tracking down these problems.
944 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
945 enables the feature at boot time. By default, it is
946 disabled and the system will work mostly the same as a
947 kernel built without CONFIG_DEBUG_PAGEALLOC.
948 Note: to get most of debug_pagealloc error reports, it's
949 useful to also enable the page_owner functionality.
950 on: enable the feature
952 debugfs= [KNL] This parameter enables what is exposed to userspace
953 and debugfs internal clients.
954 Format: { on, no-mount, off }
955 on: All functions are enabled.
957 Filesystem is not registered but kernel clients can
958 access APIs and a crashkernel can be used to read
959 its content. There is nothing to mount.
960 off: Filesystem is not registered and clients
961 get a -EPERM as result when trying to register files
962 or directories within debugfs.
963 This is equivalent of the runtime functionality if
964 debugfs was not enabled in the kernel at all.
965 Default value is set in build-time with a kernel configuration.
967 debugpat [X86] Enable PAT debugging
969 decnet.addr= [HW,NET]
970 Format: <area>[,<node>]
971 See also Documentation/networking/decnet.rst.
974 [HW] The size of the default HugeTLB page. This is
975 the size represented by the legacy /proc/ hugepages
976 APIs. In addition, this is the default hugetlb size
977 used for shmget(), mmap() and mounting hugetlbfs
978 filesystems. If not specified, defaults to the
979 architecture's default huge page size. Huge page
980 sizes are architecture dependent. See also
981 Documentation/admin-guide/mm/hugetlbpage.rst.
984 deferred_probe_timeout=
985 [KNL] Debugging option to set a timeout in seconds for
986 deferred probe to give up waiting on dependencies to
987 probe. Only specific dependencies (subsystems or
988 drivers) that have opted in will be ignored. A timeout
989 of 0 will timeout at the end of initcalls. If the time
990 out hasn't expired, it'll be restarted by each
991 successful driver registration. This option will also
992 dump out devices still on the deferred probe list after
995 delayacct [KNL] Enable per-task delay accounting
997 dell_smm_hwmon.ignore_dmi=
998 [HW] Continue probing hardware even if DMI data
999 indicates that the driver is running on unsupported
1002 dell_smm_hwmon.force=
1003 [HW] Activate driver even if SMM BIOS signature does
1004 not match list of supported models and enable otherwise
1005 blacklisted features.
1007 dell_smm_hwmon.power_status=
1008 [HW] Report power status in /proc/i8k
1009 (disabled by default).
1011 dell_smm_hwmon.restricted=
1012 [HW] Allow controlling fans only if SYS_ADMIN
1015 dell_smm_hwmon.fan_mult=
1016 [HW] Factor to multiply fan speed with.
1018 dell_smm_hwmon.fan_max=
1019 [HW] Maximum configurable fan speed.
1022 Format: { on | off | def_only | inf_only | always }
1023 on: s390 zlib hardware support for compression on
1024 level 1 and decompression (default)
1025 off: No s390 zlib hardware support
1026 def_only: s390 zlib hardware support for deflate
1027 only (compression on level 1)
1028 inf_only: s390 zlib hardware support for inflate
1029 only (decompression)
1030 always: Same as 'on' but ignores the selected compression
1031 level always using hardware support (used for debugging)
1033 dhash_entries= [KNL]
1034 Set number of hash buckets for dentry cache.
1036 disable_1tb_segments [PPC]
1037 Disables the use of 1TB hash page table segments. This
1038 causes the kernel to fall back to 256MB segments which
1039 can be useful when debugging issues that require an SLB
1043 Limits the number of kernel SLB entries, and flushes
1044 them frequently to increase the rate of SLB faults
1045 on kernel addresses.
1048 See Documentation/networking/ipv6.rst.
1051 Disable RADIX MMU mode on POWER9
1053 radix_hcall_invalidate=on [PPC/PSERIES]
1054 Disable RADIX GTSE feature and use hcall for TLB
1058 Disable TLBIE instruction. Currently does not work
1059 with KVM, with HASH MMU, or with coherent accelerators.
1061 disable_cpu_apicid= [X86,APIC,SMP]
1063 The number of initial APIC ID for the
1064 corresponding CPU to be disabled at boot,
1065 mostly used for the kdump 2nd kernel to
1066 disable BSP to wake up multiple CPUs without
1067 causing system reset or hang due to sending
1068 INIT from AP to BSP.
1070 disable_ddw [PPC/PSERIES]
1071 Disable Dynamic DMA Window support. Use this
1072 to workaround buggy firmware.
1074 disable_ipv6= [IPV6]
1075 See Documentation/networking/ipv6.rst.
1077 disable_mtrr_cleanup [X86]
1078 The kernel tries to adjust MTRR layout from continuous
1079 to discrete, to make X server driver able to add WB
1080 entry later. This parameter disables that.
1082 disable_mtrr_trim [X86, Intel and AMD only]
1083 By default the kernel will trim any uncacheable
1084 memory out of your available memory pool based on
1085 MTRR settings. This parameter disables that behavior,
1086 possibly causing your machine to run very slowly.
1088 disable_timer_pin_1 [X86]
1089 Disable PIN 1 of APIC timer
1090 Can be useful to work around chipset bugs.
1092 dis_ucode_ldr [X86] Disable the microcode loader.
1094 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1095 this option disables the debugging code at boot.
1097 dma_debug_entries=<number>
1098 This option allows to tune the number of preallocated
1099 entries for DMA-API debugging code. One entry is
1100 required per DMA-API allocation. Use this if the
1101 DMA-API debugging code disables itself because the
1102 architectural default is too low.
1104 dma_debug_driver=<driver_name>
1105 With this option the DMA-API debugging driver
1106 filter feature can be enabled at boot time. Just
1107 pass the driver to filter for as the parameter.
1108 The filter can be disabled or changed to another
1109 driver later using sysfs.
1111 driver_async_probe= [KNL]
1112 List of driver names to be probed asynchronously. *
1113 matches with all driver names. If * is specified, the
1114 rest of the listed driver names are those that will NOT
1116 Format: <driver_name1>,<driver_name2>...
1118 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1119 Broken monitors, graphic adapters, KVMs and EDIDless
1120 panels may send no or incorrect EDID data sets.
1121 This parameter allows to specify an EDID data sets
1122 in the /lib/firmware directory that are used instead.
1123 Generic built-in EDID data sets are used, if one of
1124 edid/1024x768.bin, edid/1280x1024.bin,
1125 edid/1680x1050.bin, or edid/1920x1080.bin is given
1126 and no file with the same name exists. Details and
1127 instructions how to build your own EDID data are
1128 available in Documentation/admin-guide/edid.rst. An EDID
1129 data set will only be used for a particular connector,
1130 if its name and a colon are prepended to the EDID
1131 name. Each connector may use a unique EDID data
1132 set by separating the files with a comma. An EDID
1133 data set with no connector name will be used for
1134 any connectors not explicitly specified.
1139 Format: {"off" | "known"}
1140 Control how the dt_cpu_ftrs device-tree binding is
1141 used for CPU feature discovery and setup (if it
1143 off: Do not use it, fall back to legacy cpu table.
1144 known: Do not pass through unknown features to guests
1145 or userspace, only those that the kernel is aware of.
1147 dump_apple_properties [X86]
1148 Dump name and content of EFI device properties on
1149 x86 Macs. Useful for driver authors to determine
1150 what data is available or for reverse-engineering.
1152 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1153 <module>.dyndbg[="val"]
1154 Enable debug messages at boot time. See
1155 Documentation/admin-guide/dynamic-debug-howto.rst
1158 nopku [X86] Disable Memory Protection Keys CPU feature found
1161 <module>.async_probe [KNL]
1162 Enable asynchronous probe on this module.
1164 early_ioremap_debug [KNL]
1165 Enable debug messages in early_ioremap support. This
1166 is useful for tracking down temporary early mappings
1167 which are not unmapped.
1169 earlycon= [KNL] Output early console device and options.
1171 When used with no options, the early console is
1172 determined by stdout-path property in device tree's
1173 chosen node or the ACPI SPCR table if supported by
1176 cdns,<addr>[,options]
1177 Start an early, polled-mode console on a Cadence
1178 (xuartps) serial port at the specified address. Only
1179 supported option is baud rate. If baud rate is not
1180 specified, the serial port must already be setup and
1183 uart[8250],io,<addr>[,options]
1184 uart[8250],mmio,<addr>[,options]
1185 uart[8250],mmio32,<addr>[,options]
1186 uart[8250],mmio32be,<addr>[,options]
1187 uart[8250],0x<addr>[,options]
1188 Start an early, polled-mode console on the 8250/16550
1189 UART at the specified I/O port or MMIO address.
1190 MMIO inter-register address stride is either 8-bit
1191 (mmio) or 32-bit (mmio32 or mmio32be).
1192 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1193 to be equivalent to 'mmio'. 'options' are specified
1194 in the same format described for "console=ttyS<n>"; if
1195 unspecified, the h/w is not initialized.
1199 Start an early, polled-mode console on a pl011 serial
1200 port at the specified address. The pl011 serial port
1201 must already be setup and configured. Options are not
1202 yet supported. If 'mmio32' is specified, then only
1203 the driver will use only 32-bit accessors to read/write
1204 the device registers.
1207 Start an early console on a litex serial port at the
1208 specified address. The serial port must already be
1209 setup and configured. Options are not yet supported.
1212 Start an early, polled-mode console on a meson serial
1213 port at the specified address. The serial port must
1214 already be setup and configured. Options are not yet
1218 Start an early, polled-mode console on an msm serial
1219 port at the specified address. The serial port
1220 must already be setup and configured. Options are not
1223 msm_serial_dm,<addr>
1224 Start an early, polled-mode console on an msm serial
1225 dm port at the specified address. The serial port
1226 must already be setup and configured. Options are not
1230 Start an early, polled-mode console on a serial port
1231 of an Actions Semi SoC, such as S500 or S900, at the
1232 specified address. The serial port must already be
1233 setup and configured. Options are not yet supported.
1236 Start an early, polled-mode console on a serial port
1237 of an RDA Micro SoC, such as RDA8810PL, at the
1238 specified address. The serial port must already be
1239 setup and configured. Options are not yet supported.
1242 Use RISC-V SBI (Supervisor Binary Interface) for early
1245 smh Use ARM semihosting calls for early console.
1253 Use early console provided by serial driver available
1254 on Samsung SoCs, requires selecting proper type and
1255 a correct base address of the selected UART port. The
1256 serial port must already be setup and configured.
1257 Options are not yet supported.
1260 Start an early, polled-mode console on a lantiq serial
1261 (lqasc) port at the specified address. The serial port
1262 must already be setup and configured. Options are not
1267 Use early console provided by Freescale LP UART driver
1268 found on Freescale Vybrid and QorIQ LS1021A processors.
1269 A valid base address must be provided, and the serial
1270 port must already be setup and configured.
1274 Start an early, polled-mode, output-only console on the
1275 Freescale i.MX UART at the specified address. The UART
1276 must already be setup and configured.
1279 Start an early, polled-mode console on the
1280 Armada 3700 serial port at the specified
1281 address. The serial port must already be setup
1282 and configured. Options are not yet supported.
1285 Start an early, polled-mode console on a Qualcomm
1286 Generic Interface (GENI) based serial port at the
1287 specified address. The serial port must already be
1288 setup and configured. Options are not yet supported.
1291 Start an early, unaccelerated console on the EFI
1292 memory mapped framebuffer (if available). On cache
1293 coherent non-x86 systems that use system memory for
1294 the framebuffer, pass the 'ram' option so that it is
1295 mapped with the correct attributes.
1298 Use early console provided by Freescale LINFlexD UART
1299 serial driver for NXP S32V234 SoCs. A valid base
1300 address must be provided, and the serial port must
1301 already be setup and configured.
1303 earlyprintk= [X86,SH,ARM,M68k,S390]
1307 earlyprintk=serial[,ttySn[,baudrate]]
1308 earlyprintk=serial[,0x...[,baudrate]]
1309 earlyprintk=ttySn[,baudrate]
1310 earlyprintk=dbgp[debugController#]
1311 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1312 earlyprintk=xdbc[xhciController#]
1314 earlyprintk is useful when the kernel crashes before
1315 the normal console is initialized. It is not enabled by
1316 default because it has some cosmetic problems.
1318 Append ",keep" to not disable it when the real console
1321 Only one of vga, serial, or usb debug port can
1324 Currently only ttyS0 and ttyS1 may be specified by
1325 name. Other I/O ports may be explicitly specified
1326 on some architectures (x86 and arm at least) by
1327 replacing ttySn with an I/O port address, like this:
1328 earlyprintk=serial,0x1008,115200
1329 You can find the port for a given device in
1330 /proc/tty/driver/serial:
1331 2: uart:ST16650V2 port:00001008 irq:18 ...
1333 Interaction with the standard serial driver is not
1336 The VGA output is eventually overwritten by
1339 The xen option can only be used in Xen domains.
1341 The sclp output can only be used on s390.
1343 The optional "force" to "pciserial" enables use of a
1344 PCI device even when its classcode is not of the
1347 edac_report= [HW,EDAC] Control how to report EDAC event
1348 Format: {"on" | "off" | "force"}
1349 on: enable EDAC to report H/W event. May be overridden
1350 by other higher priority error reporting module.
1351 off: disable H/W event reporting through EDAC.
1352 force: enforce the use of EDAC to report H/W event.
1356 Format: {"off" | "on" | "skip[mbr]"}
1359 Format: { "debug", "disable_early_pci_dma",
1360 "nochunk", "noruntime", "nosoftreserve",
1361 "novamap", "no_disable_early_pci_dma" }
1362 debug: enable misc debug output.
1363 disable_early_pci_dma: disable the busmaster bit on all
1364 PCI bridges while in the EFI boot stub.
1365 nochunk: disable reading files in "chunks" in the EFI
1366 boot stub, as chunking can cause problems with some
1367 firmware implementations.
1368 noruntime : disable EFI runtime services support
1369 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1370 attribute may cause the kernel to reserve the
1371 memory range for a memory mapping driver to
1372 claim. Specify efi=nosoftreserve to disable this
1373 reservation and treat the memory by its base type
1374 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1375 novamap: do not call SetVirtualAddressMap().
1376 no_disable_early_pci_dma: Leave the busmaster bit set
1377 on all PCI bridges while in the EFI boot stub
1379 efi_no_storage_paranoia [EFI; X86]
1380 Using this parameter you can use more than 50% of
1381 your efi variable storage. Use this parameter only if
1382 you are really sure that your UEFI does sane gc and
1383 fulfills the spec otherwise your board may brick.
1385 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1386 Add arbitrary attribute to specific memory range by
1387 updating original EFI memory map.
1388 Region of memory which aa attribute is added to is
1391 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1392 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1393 attribute is added to range 0x100000000-0x180000000 and
1394 0x10a0000000-0x1120000000.
1396 If efi_fake_mem=8G@9G:0x40000 is specified, the
1397 EFI_MEMORY_SP(0x40000) attribute is added to
1398 range 0x240000000-0x43fffffff.
1400 Using this parameter you can do debugging of EFI memmap
1401 related features. For example, you can do debugging of
1402 Address Range Mirroring feature even if your box
1403 doesn't support it, or mark specific memory as
1406 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1407 that is to be dynamically loaded by Linux. If there are
1408 multiple variables with the same name but with different
1409 vendor GUIDs, all of them will be loaded. See
1410 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1413 eisa_irq_edge= [PARISC,HW]
1414 See header of drivers/parisc/eisa.c.
1416 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1419 This is designed to be used in conjunction with
1420 the boot argument: earlyprintk=vga
1422 This parameter works in place of the kgdboc parameter
1423 but can only be used if the backing tty is available
1424 very early in the boot process. For early debugging
1425 via a serial port see kgdboc_earlycon instead.
1428 See comment before function elanfreq_setup() in
1429 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1431 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1432 Specifies physical address of start of kernel core
1433 image elf header and optionally the size. Generally
1434 kexec loader will pass this option to capture kernel.
1435 See Documentation/admin-guide/kdump/kdump.rst for details.
1437 enable_mtrr_cleanup [X86]
1438 The kernel tries to adjust MTRR layout from continuous
1439 to discrete, to make X server driver able to add WB
1440 entry later. This parameter enables that.
1442 enable_timer_pin_1 [X86]
1443 Enable PIN 1 of APIC timer
1444 Can be useful to work around chipset bugs
1445 (in particular on some ATI chipsets).
1446 The kernel tries to set a reasonable default.
1448 enforcing [SELINUX] Set initial enforcing status.
1450 See security/selinux/Kconfig help text.
1451 0 -- permissive (log only, no denials).
1452 1 -- enforcing (deny and log).
1454 Value can be changed at runtime via
1455 /sys/fs/selinux/enforce.
1458 Disable Error Record Serialization Table (ERST)
1461 ether= [HW,NET] Ethernet cards parameters
1462 This option is obsoleted by the "netdev=" option, which
1463 has equivalent usage. See its documentation for details.
1467 Permit 'security.evm' to be updated regardless of
1468 current integrity status.
1473 fail_make_request=[KNL]
1474 General fault injection mechanism.
1475 Format: <interval>,<probability>,<space>,<times>
1476 See also Documentation/fault-injection/.
1479 Format: { initns | none }
1480 See Documentation/admin-guide/sysctl/net.rst for
1481 fb_tunnels_only_for_init_ns
1484 See Documentation/admin-guide/blockdev/floppy.rst.
1486 force_pal_cache_flush
1487 [IA-64] Avoid check_sal_cache_flush which may hang on
1488 buggy SAL_CACHE_FLUSH implementations. Using this
1489 parameter will force ia64_sal_cache_flush to call
1490 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1493 Forcefully enable Physical Address Extension (PAE).
1494 Many Pentium M systems disable PAE but may have a
1495 functionally usable PAE implementation.
1496 Warning: use of this parameter will taint the kernel
1497 and may cause unknown problems.
1500 [FTRACE] will set and start the specified tracer
1501 as early as possible in order to facilitate early
1504 ftrace_boot_snapshot
1505 [FTRACE] On boot up, a snapshot will be taken of the
1506 ftrace ring buffer that can be read at:
1507 /sys/kernel/tracing/snapshot.
1508 This is useful if you need tracing information from kernel
1509 boot up that is likely to be overridden by user space
1510 start up functionality.
1512 ftrace_dump_on_oops[=orig_cpu]
1513 [FTRACE] will dump the trace buffers on oops.
1514 If no parameter is passed, ftrace will dump
1515 buffers of all CPUs, but if you pass orig_cpu, it will
1516 dump only the buffer of the CPU that triggered the
1519 ftrace_filter=[function-list]
1520 [FTRACE] Limit the functions traced by the function
1521 tracer at boot up. function-list is a comma-separated
1522 list of functions. This list can be changed at run
1523 time by the set_ftrace_filter file in the debugfs
1526 ftrace_notrace=[function-list]
1527 [FTRACE] Do not trace the functions specified in
1528 function-list. This list can be changed at run time
1529 by the set_ftrace_notrace file in the debugfs
1532 ftrace_graph_filter=[function-list]
1533 [FTRACE] Limit the top level callers functions traced
1534 by the function graph tracer at boot up.
1535 function-list is a comma-separated list of functions
1536 that can be changed at run time by the
1537 set_graph_function file in the debugfs tracing directory.
1539 ftrace_graph_notrace=[function-list]
1540 [FTRACE] Do not trace from the functions specified in
1541 function-list. This list is a comma-separated list of
1542 functions that can be changed at run time by the
1543 set_graph_notrace file in the debugfs tracing directory.
1545 ftrace_graph_max_depth=<uint>
1546 [FTRACE] Used with the function graph tracer. This is
1547 the max depth it will trace into a function. This value
1548 can be changed at run time by the max_graph_depth file
1549 in the tracefs tracing directory. default: 0 (no limit)
1551 fw_devlink= [KNL] Create device links between consumer and supplier
1552 devices by scanning the firmware to infer the
1553 consumer/supplier relationships. This feature is
1554 especially useful when drivers are loaded as modules as
1555 it ensures proper ordering of tasks like device probing
1556 (suppliers first, then consumers), supplier boot state
1557 clean up (only after all consumers have probed),
1558 suspend/resume & runtime PM (consumers first, then
1560 Format: { off | permissive | on | rpm }
1561 off -- Don't create device links from firmware info.
1562 permissive -- Create device links from firmware info
1563 but use it only for ordering boot state clean
1564 up (sync_state() calls).
1565 on -- Create device links from firmware info and use it
1566 to enforce probe and suspend/resume ordering.
1567 rpm -- Like "on", but also use to order runtime PM.
1569 fw_devlink.strict=<bool>
1570 [KNL] Treat all inferred dependencies as mandatory
1571 dependencies. This only applies for fw_devlink=on|rpm.
1575 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1576 support via parallel port (up to 5 devices per port)
1577 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1578 See also Documentation/input/devices/joystick-parport.rst
1582 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1586 gcov_persist= [GCOV] When non-zero (default), profiling data for
1587 kernel modules is saved and remains accessible via
1588 debugfs, even when the module is unloaded/reloaded.
1589 When zero, profiling data is discarded and associated
1590 debugfs files are removed at module unload time.
1592 goldfish [X86] Enable the goldfish android emulator platform.
1593 Don't use this when you are not running on the
1596 gpio-mockup.gpio_mockup_ranges
1597 [HW] Sets the ranges of gpiochip of for this device.
1598 Format: <start1>,<end1>,<start2>,<end2>...
1599 gpio-mockup.gpio_mockup_named_lines
1600 [HW] Let the driver know GPIO lines should be named.
1602 gpt [EFI] Forces disk with valid GPT signature but
1603 invalid Protective MBR to be treated as GPT. If the
1604 primary GPT is corrupted, it enables the backup/alternate
1605 GPT to be used instead.
1607 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1608 the "Enable 0" bit of the configuration register.
1611 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1612 the "Enable 0" bit of the configuration register.
1615 grcan.select= [HW] Select which physical interface to use.
1618 grcan.txsize= [HW] Sets the size of the tx buffer.
1619 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1621 grcan.rxsize= [HW] Sets the size of the rx buffer.
1622 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1626 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1627 hardening is enabled for this boot. Hardened
1628 usercopy checking is used to protect the kernel
1629 from reading or writing beyond known memory
1630 allocation boundaries as a proactive defense
1631 against bounds-checking flaws in the kernel's
1632 copy_to_user()/copy_from_user() interface.
1633 on Perform hardened usercopy checks (default).
1634 off Disable hardened usercopy checks.
1636 hardlockup_all_cpu_backtrace=
1637 [KNL] Should the hard-lockup detector generate
1638 backtraces on all cpus.
1641 hashdist= [KNL,NUMA] Large hashes allocated during boot
1642 are distributed across NUMA nodes. Defaults on
1643 for 64-bit NUMA, off otherwise.
1644 Format: 0 | 1 (for off | on)
1646 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1648 hd= [EIDE] (E)IDE hard drive subsystem geometry
1649 Format: <cyl>,<head>,<sect>
1652 Disable Hardware Error Source Table (HEST) support;
1653 corresponding firmware-first mode error processing
1654 logic will be disabled.
1656 hibernate= [HIBERNATION]
1657 noresume Don't check if there's a hibernation image
1658 present during boot.
1659 nocompress Don't compress/decompress hibernation images.
1660 no Disable hibernation and resume.
1661 protect_image Turn on image protection during restoration
1662 (that will set all pages holding image data
1663 during restoration read-only).
1665 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1666 size of <nn>. This works even on boxes that have no
1667 highmem otherwise. This also works to reduce highmem
1668 size on bigger boxes.
1670 highres= [KNL] Enable/disable high resolution timer mode.
1671 Valid parameters: "on", "off"
1676 hpet= [X86-32,HPET] option to control HPET usage
1677 Format: { enable (default) | disable | force |
1679 disable: disable HPET and use PIT instead
1680 force: allow force enabled of undocumented chips (ICH4,
1682 verbose: show contents of HPET registers during setup
1684 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1685 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1687 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1688 If this follows hugepagesz (below), it specifies
1689 the number of pages of hugepagesz to be allocated.
1690 If this is the first HugeTLB parameter on the command
1691 line, it specifies the number of pages to allocate for
1692 the default huge page size. If using node format, the
1693 number of pages to allocate per-node can be specified.
1694 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1695 Format: <integer> or (node format)
1696 <node>:<integer>[,<node>:<integer>]
1699 [HW] The size of the HugeTLB pages. This is used in
1700 conjunction with hugepages (above) to allocate huge
1701 pages of a specific size at boot. The pair
1702 hugepagesz=X hugepages=Y can be specified once for
1703 each supported huge page size. Huge page sizes are
1704 architecture dependent. See also
1705 Documentation/admin-guide/mm/hugetlbpage.rst.
1708 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1709 of gigantic hugepages. Or using node format, the size
1710 of a CMA area per node can be specified.
1711 Format: nn[KMGTPE] or (node format)
1712 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1714 Reserve a CMA area of given size and allocate gigantic
1715 hugepages using the CMA allocator. If enabled, the
1716 boot-time allocation of gigantic hugepages is skipped.
1718 hugetlb_free_vmemmap=
1719 [KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1721 Allows heavy hugetlb users to free up some more
1722 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1723 Format: { [oO][Nn]/Y/y/1 | [oO][Ff]/N/n/0 (default) }
1725 [oO][Nn]/Y/y/1: enable the feature
1726 [oO][Ff]/N/n/0: disable the feature
1728 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1731 This is not compatible with memory_hotplug.memmap_on_memory.
1732 If both parameters are enabled, hugetlb_free_vmemmap takes
1733 precedence over memory_hotplug.memmap_on_memory.
1736 [KNL] Should the hung task detector generate panics.
1739 A value of 1 instructs the kernel to panic when a
1740 hung task is detected. The default value is controlled
1741 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1742 option. The value selected by this boot parameter can
1743 be changed later by the kernel.hung_task_panic sysctl.
1745 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1746 terminal devices. Valid values: 0..8
1747 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1748 If specified, z/VM IUCV HVC accepts connections
1749 from listed z/VM user IDs only.
1751 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1752 which allow the hypervisor to 'idle' the
1753 guest on lock contention.
1756 Do not unregister boot console at start. This is only
1757 useful for debugging when something happens in the window
1758 between unregistering the boot console and initializing
1761 i2c_bus= [HW] Override the default board specific I2C bus speed
1762 or register an additional I2C bus that is not
1763 registered from board initialization code.
1767 i8042.debug [HW] Toggle i8042 debug mode
1768 i8042.unmask_kbd_data
1769 [HW] Enable printing of interrupt data from the KBD port
1770 (disabled by default, and as a pre-condition
1771 requires that i8042.debug=1 be enabled)
1772 i8042.direct [HW] Put keyboard port into non-translated mode
1773 i8042.dumbkbd [HW] Pretend that controller can only read data from
1774 keyboard and cannot control its state
1775 (Don't attempt to blink the leds)
1776 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1777 i8042.nokbd [HW] Don't check/create keyboard port
1778 i8042.noloop [HW] Disable the AUX Loopback command while probing
1780 i8042.nomux [HW] Don't check presence of an active multiplexing
1782 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1784 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1785 i8042.reset [HW] Reset the controller during init, cleanup and
1786 suspend-to-ram transitions, only during s2r
1787 transitions, or never reset
1788 Format: { 1 | Y | y | 0 | N | n }
1789 1, Y, y: always reset controller
1790 0, N, n: don't ever reset controller
1791 Default: only on s2r transitions on x86; most other
1792 architectures force reset to be always executed
1793 i8042.unlock [HW] Unlock (ignore) the keylock
1794 i8042.kbdreset [HW] Reset device connected to KBD port
1796 [HW] Allow deferred probing upon i8042 probe errors
1800 i915.invert_brightness=
1801 [DRM] Invert the sense of the variable that is used to
1802 set the brightness of the panel backlight. Normally a
1803 brightness value of 0 indicates backlight switched off,
1804 and the maximum of the brightness value sets the backlight
1805 to maximum brightness. If this parameter is set to 0
1806 (default) and the machine requires it, or this parameter
1807 is set to 1, a brightness value of 0 sets the backlight
1808 to maximum brightness, and the maximum of the brightness
1809 value switches the backlight off.
1810 -1 -- never invert brightness
1811 0 -- machine default
1812 1 -- force brightness inversion
1815 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1819 Format: idle=poll, idle=halt, idle=nomwait
1820 Poll forces a polling idle loop that can slightly
1821 improve the performance of waking up a idle CPU, but
1822 will use a lot of power and make the system run hot.
1824 idle=halt: Halt is forced to be used for CPU idle.
1825 In such case C2/C3 won't be used again.
1826 idle=nomwait: Disable mwait for CPU C-states
1830 Allow force disabling of Shared Virtual Memory (SVA)
1831 support for the idxd driver. By default it is set to
1834 idxd.tc_override= [HW]
1836 Allow override of default traffic class configuration
1837 for the device. By default it is set to false (0).
1839 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1840 Format: { strict | legacy | 2008 | relaxed }
1843 Choose which programs will be accepted for execution
1844 based on the IEEE 754 NaN encoding(s) supported by
1845 the FPU and the NaN encoding requested with the value
1846 of an ELF file header flag individually set by each
1847 binary. Hardware implementations are permitted to
1848 support either or both of the legacy and the 2008 NaN
1851 Available settings are as follows:
1852 strict accept binaries that request a NaN encoding
1853 supported by the FPU
1854 legacy only accept legacy-NaN binaries, if supported
1856 2008 only accept 2008-NaN binaries, if supported
1858 relaxed accept any binaries regardless of whether
1859 supported by the FPU
1861 The FPU emulator is always able to support both NaN
1862 encodings, so if no FPU hardware is present or it has
1863 been disabled with 'nofpu', then the settings of
1864 'legacy' and '2008' strap the emulator accordingly,
1865 'relaxed' straps the emulator for both legacy-NaN and
1866 2008-NaN, whereas 'strict' enables legacy-NaN only on
1867 legacy processors and both NaN encodings on MIPS32 or
1870 The setting for ABS.fmt/NEG.fmt instruction execution
1871 mode generally follows that for the NaN encoding,
1872 except where unsupported by hardware.
1874 ignore_loglevel [KNL]
1875 Ignore loglevel setting - this will print /all/
1876 kernel messages to the console. Useful for debugging.
1877 We also add it as printk module parameter, so users
1878 could change it dynamically, usually by
1879 /sys/module/printk/parameters/ignore_loglevel.
1882 Ignore RLIMIT_DATA setting for data mappings,
1883 print warning at first misuse. Can be changed via
1884 /sys/module/kernel/parameters/ignore_rlimit_data.
1886 ihash_entries= [KNL]
1887 Set number of hash buckets for inode cache.
1889 ima_appraise= [IMA] appraise integrity measurements
1890 Format: { "off" | "enforce" | "fix" | "log" }
1893 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1894 The builtin appraise policy appraises all files
1897 ima_canonical_fmt [IMA]
1898 Use the canonical format for the binary runtime
1899 measurements, instead of host native format.
1902 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1906 The list of supported hash algorithms is defined
1907 in crypto/hash_info.h.
1910 The builtin policies to load during IMA setup.
1911 Format: "tcb | appraise_tcb | secure_boot |
1912 fail_securely | critical_data"
1914 The "tcb" policy measures all programs exec'd, files
1915 mmap'd for exec, and all files opened with the read
1916 mode bit set by either the effective uid (euid=0) or
1919 The "appraise_tcb" policy appraises the integrity of
1920 all files owned by root.
1922 The "secure_boot" policy appraises the integrity
1923 of files (eg. kexec kernel image, kernel modules,
1924 firmware, policy, etc) based on file signatures.
1926 The "fail_securely" policy forces file signature
1927 verification failure also on privileged mounted
1928 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1931 The "critical_data" policy measures kernel integrity
1934 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1935 Load a policy which meets the needs of the Trusted
1936 Computing Base. This means IMA will measure all
1937 programs exec'd, files mmap'd for exec, and all files
1938 opened for read by uid=0.
1941 Select one of defined IMA measurements template formats.
1942 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
1947 [IMA] Define a custom template format.
1948 Format: { "field1|...|fieldN" }
1950 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1951 Format: <min_file_size>
1952 Set the minimal file size for using asynchronous hash.
1953 If left unspecified, ahash usage is disabled.
1955 ahash performance varies for different data sizes on
1956 different crypto accelerators. This option can be used
1957 to achieve the best performance for a particular HW.
1959 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1961 Set hashing buffer size. Default: 4k.
1963 ahash performance varies for different chunk sizes on
1964 different crypto accelerators. This option can be used
1965 to achieve best performance for particular HW.
1969 Run specified binary instead of /sbin/init as init
1972 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1973 for working out where the kernel is dying during
1976 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1977 initcall functions. Useful for debugging built-in
1978 modules and initcalls.
1980 initramfs_async= [KNL]
1983 This parameter controls whether the initramfs
1984 image is unpacked asynchronously, concurrently
1985 with devices being probed and
1986 initialized. This should normally just work,
1987 but as a debugging aid, one can get the
1988 historical behaviour of the initramfs
1989 unpacking being completed before device_ and
1992 initrd= [BOOT] Specify the location of the initial ramdisk
1994 initrdmem= [KNL] Specify a physical address and size from which to
1995 load the initrd. If an initrd is compiled in or
1996 specified in the bootparams, it takes priority over this
1998 Format: ss[KMG],nn[KMG]
2001 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
2004 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2006 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
2008 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2010 init_pkru= [X86] Specify the default memory protection keys rights
2011 register contents for all processes. 0x55555554 by
2012 default (disallow access to all but pkey 0). Can
2013 override in debugfs after boot.
2015 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2018 int_pln_enable [X86] Enable power limit notification interrupt
2020 integrity_audit=[IMA]
2021 Format: { "0" | "1" }
2022 0 -- basic integrity auditing messages. (Default)
2023 1 -- additional integrity auditing messages.
2025 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2027 Enable intel iommu driver.
2029 Disable intel iommu driver.
2030 igfx_off [Default Off]
2031 By default, gfx is mapped as normal device. If a gfx
2032 device has a dedicated DMAR unit, the DMAR unit is
2033 bypassed by not enabling DMAR with this option. In
2034 this case, gfx device will use physical address for
2036 strict [Default Off]
2037 Deprecated, equivalent to iommu.strict=1.
2038 sp_off [Default Off]
2039 By default, super page will be supported if Intel IOMMU
2040 has the capability. With this option, super page will
2043 Enable the Intel IOMMU scalable mode if the hardware
2044 advertises that it has support for the scalable mode
2047 Disallow use of the Intel IOMMU scalable mode.
2048 tboot_noforce [Default Off]
2049 Do not force the Intel IOMMU enabled under tboot.
2050 By default, tboot will force Intel IOMMU on, which
2051 could harm performance of some high-throughput
2052 devices like 40GBit network cards, even if identity
2054 Note that using this option lowers the security
2055 provided by tboot because it makes the system
2056 vulnerable to DMA attacks.
2058 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2059 0 disables intel_idle and fall back on acpi_idle.
2060 1 to 9 specify maximum depth of C-state.
2064 Do not enable intel_pstate as the default
2065 scaling driver for the supported processors
2067 Use intel_pstate as a scaling driver, but configure it
2068 to work with generic cpufreq governors (instead of
2069 enabling its internal governor). This mode cannot be
2070 used along with the hardware-managed P-states (HWP)
2073 Enable intel_pstate on systems that prohibit it by default
2074 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2075 instead of acpi-cpufreq may disable platform features, such
2076 as thermal controls and power capping, that rely on ACPI
2077 P-States information being indicated to OSPM and therefore
2078 should be used with caution. This option does not work with
2079 processors that aren't supported by the intel_pstate driver
2080 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2082 Do not enable hardware P state control (HWP)
2085 Only load intel_pstate on systems which support
2086 hardware P state control (HWP) if available.
2088 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2089 Description Table, specifies preferred power management
2090 profile as "Enterprise Server" or "Performance Server",
2091 then this feature is turned on by default.
2093 Allow per-logical-CPU P-State performance control limits using
2094 cpufreq sysfs interface
2096 intremap= [X86-64, Intel-IOMMU]
2097 on enable Interrupt Remapping (default)
2098 off disable Interrupt Remapping
2099 nosid disable Source ID checking
2101 BIOS x2APIC opt-out request will be ignored
2102 nopost disable Interrupt Posting
2104 iomem= Disable strict checking of access to MMIO memory
2105 strict regions from userspace.
2120 nobypass [PPC/POWERNV]
2121 Disable IOMMU bypass, using IOMMU for PCI devices.
2123 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2124 Format: { "0" | "1" }
2125 0 - Try to allocate a 32-bit DMA address first, before
2126 falling back to the full range if needed.
2127 1 - Allocate directly from the full usable range,
2128 forcing Dual Address Cycle for PCI cards supporting
2129 greater than 32-bit addressing.
2131 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2132 Format: { "0" | "1" }
2134 Request that DMA unmap operations use deferred
2135 invalidation of hardware TLBs, for increased
2136 throughput at the cost of reduced device isolation.
2137 Will fall back to strict mode if not supported by
2138 the relevant IOMMU driver.
2140 DMA unmap operations invalidate IOMMU hardware TLBs
2142 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2143 Note: on x86, strict mode specified via one of the
2144 legacy driver-specific options takes precedence.
2147 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2148 Format: { "0" | "1" }
2149 0 - Use IOMMU translation for DMA.
2150 1 - Bypass the IOMMU for DMA.
2151 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2153 io7= [HW] IO7 for Marvel-based Alpha systems
2154 See comment before marvel_specify_io7 in
2155 arch/alpha/kernel/core_marvel.c.
2157 io_delay= [X86] I/O delay method
2159 Standard port 0x80 based delay
2161 Alternate port 0xed based delay (needed on some systems)
2163 Simple two microseconds delay
2168 See Documentation/admin-guide/nfs/nfsroot.rst.
2170 ipcmni_extend [KNL] Extend the maximum number of unique System V
2171 IPC identifiers from 32,768 to 16,777,216.
2173 irqaffinity= [SMP] Set the default irq affinity mask
2174 The argument is a cpu list, as described above.
2176 irqchip.gicv2_force_probe=
2179 Force the kernel to look for the second 4kB page
2180 of a GICv2 controller even if the memory range
2181 exposed by the device tree is too small.
2183 irqchip.gicv3_nolpi=
2185 Force the kernel to ignore the availability of
2186 LPIs (and by consequence ITSs). Intended for system
2187 that use the kernel as a bootloader, and thus want
2188 to let secondary kernels in charge of setting up
2191 irqchip.gicv3_pseudo_nmi= [ARM64]
2192 Enables support for pseudo-NMIs in the kernel. This
2193 requires the kernel to be built with
2194 CONFIG_ARM64_PSEUDO_NMI.
2197 When an interrupt is not handled search all handlers
2198 for it. Intended to get systems with badly broken
2202 When an interrupt is not handled search all handlers
2203 for it. Also check all handlers each timer
2204 interrupt. Intended to get systems with badly broken
2208 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2210 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2211 [Deprecated - use cpusets instead]
2212 Format: [flag-list,]<cpu-list>
2214 Specify one or more CPUs to isolate from disturbances
2215 specified in the flag list (default: domain):
2218 Disable the tick when a single task runs.
2220 A residual 1Hz tick is offloaded to workqueues, which you
2221 need to affine to housekeeping through the global
2222 workqueue's affinity configured via the
2223 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2224 by using the 'domain' flag described below.
2226 NOTE: by default the global workqueue runs on all CPUs,
2227 so to protect individual CPUs the 'cpumask' file has to
2228 be configured manually after bootup.
2231 Isolate from the general SMP balancing and scheduling
2232 algorithms. Note that performing domain isolation this way
2233 is irreversible: it's not possible to bring back a CPU to
2234 the domains once isolated through isolcpus. It's strongly
2235 advised to use cpusets instead to disable scheduler load
2236 balancing through the "cpuset.sched_load_balance" file.
2237 It offers a much more flexible interface where CPUs can
2238 move in and out of an isolated set anytime.
2240 You can move a process onto or off an "isolated" CPU via
2241 the CPU affinity syscalls or cpuset.
2242 <cpu number> begins at 0 and the maximum value is
2243 "number of CPUs in system - 1".
2247 Isolate from being targeted by managed interrupts
2248 which have an interrupt mask containing isolated
2249 CPUs. The affinity of managed interrupts is
2250 handled by the kernel and cannot be changed via
2251 the /proc/irq/* interfaces.
2253 This isolation is best effort and only effective
2254 if the automatically assigned interrupt mask of a
2255 device queue contains isolated and housekeeping
2256 CPUs. If housekeeping CPUs are online then such
2257 interrupts are directed to the housekeeping CPU
2258 so that IO submitted on the housekeeping CPU
2259 cannot disturb the isolated CPU.
2261 If a queue's affinity mask contains only isolated
2262 CPUs then this parameter has no effect on the
2263 interrupt routing decision, though interrupts are
2264 only delivered when tasks running on those
2265 isolated CPUs submit IO. IO submitted on
2266 housekeeping CPUs has no influence on those
2269 The format of <cpu-list> is described above.
2273 ivrs_ioapic [HW,X86-64]
2274 Provide an override to the IOAPIC-ID<->DEVICE-ID
2275 mapping provided in the IVRS ACPI table. For
2276 example, to map IOAPIC-ID decimal 10 to
2277 PCI device 00:14.0 write the parameter as:
2278 ivrs_ioapic[10]=00:14.0
2280 ivrs_hpet [HW,X86-64]
2281 Provide an override to the HPET-ID<->DEVICE-ID
2282 mapping provided in the IVRS ACPI table. For
2283 example, to map HPET-ID decimal 0 to
2284 PCI device 00:14.0 write the parameter as:
2285 ivrs_hpet[0]=00:14.0
2287 ivrs_acpihid [HW,X86-64]
2288 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2289 mapping provided in the IVRS ACPI table. For
2290 example, to map UART-HID:UID AMD0020:0 to
2291 PCI device 00:14.5 write the parameter as:
2292 ivrs_acpihid[00:14.5]=AMD0020:0
2294 js= [HW,JOY] Analog joystick
2295 See Documentation/input/joydev/joystick.rst.
2298 When CONFIG_RANDOMIZE_BASE is set, this disables
2299 kernel and module base offset ASLR (Address Space
2300 Layout Randomization).
2303 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2304 report on every invalid memory access. Without this
2305 parameter KASAN will print report only for the first
2310 kernelcore= [KNL,X86,IA-64,PPC]
2311 Format: nn[KMGTPE] | nn% | "mirror"
2312 This parameter specifies the amount of memory usable by
2313 the kernel for non-movable allocations. The requested
2314 amount is spread evenly throughout all nodes in the
2315 system as ZONE_NORMAL. The remaining memory is used for
2316 movable memory in its own zone, ZONE_MOVABLE. In the
2317 event, a node is too small to have both ZONE_NORMAL and
2318 ZONE_MOVABLE, kernelcore memory will take priority and
2319 other nodes will have a larger ZONE_MOVABLE.
2321 ZONE_MOVABLE is used for the allocation of pages that
2322 may be reclaimed or moved by the page migration
2323 subsystem. Note that allocations like PTEs-from-HighMem
2324 still use the HighMem zone if it exists, and the Normal
2325 zone if it does not.
2327 It is possible to specify the exact amount of memory in
2328 the form of "nn[KMGTPE]", a percentage of total system
2329 memory in the form of "nn%", or "mirror". If "mirror"
2330 option is specified, mirrored (reliable) memory is used
2331 for non-movable allocations and remaining memory is used
2332 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2333 are exclusive, so you cannot specify multiple forms.
2335 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2336 Format: <Controller#>[,poll interval]
2337 The controller # is the number of the ehci usb debug
2338 port as it is probed via PCI. The poll interval is
2339 optional and is the number seconds in between
2340 each poll cycle to the debug port in case you need
2341 the functionality for interrupting the kernel with
2342 gdb or control-c on the dbgp connection. When
2343 not using this parameter you use sysrq-g to break into
2344 the kernel debugger.
2346 kgdboc= [KGDB,HW] kgdb over consoles.
2347 Requires a tty driver that supports console polling,
2348 or a supported polling keyboard driver (non-usb).
2349 Serial only format: <serial_device>[,baud]
2350 keyboard only format: kbd
2351 keyboard and serial format: kbd,<serial_device>[,baud]
2352 Optional Kernel mode setting:
2353 kms, kbd format: kms,kbd
2354 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2356 kgdboc_earlycon= [KGDB,HW]
2357 If the boot console provides the ability to read
2358 characters and can work in polling mode, you can use
2359 this parameter to tell kgdb to use it as a backend
2360 until the normal console is registered. Intended to
2361 be used together with the kgdboc parameter which
2362 specifies the normal console to transition to.
2364 The name of the early console should be specified
2365 as the value of this parameter. Note that the name of
2366 the early console might be different than the tty
2367 name passed to kgdboc. It's OK to leave the value
2368 blank and the first boot console that implements
2369 read() will be picked.
2371 kgdbwait [KGDB] Stop kernel execution and enter the
2372 kernel debugger at the earliest opportunity.
2374 kmac= [MIPS] Korina ethernet MAC address.
2375 Configure the RouterBoard 532 series on-chip
2376 Ethernet adapter MAC address.
2378 kmemleak= [KNL] Boot-time kmemleak enable/disable
2379 Valid arguments: on, off
2381 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2384 kprobe_event=[probe-list]
2385 [FTRACE] Add kprobe events and enable at boot time.
2386 The probe-list is a semicolon delimited list of probe
2387 definitions. Each definition is same as kprobe_events
2388 interface, but the parameters are comma delimited.
2389 For example, to add a kprobe event on vfs_read with
2390 arg1 and arg2, add to the command line;
2392 kprobe_event=p,vfs_read,$arg1,$arg2
2394 See also Documentation/trace/kprobetrace.rst "Kernel
2395 Boot Parameter" section.
2397 kpti= [ARM64] Control page table isolation of user
2398 and kernel address spaces.
2399 Default: enabled on cores which need mitigation.
2403 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2404 Default is 0 (don't ignore, but inject #GP)
2406 kvm.eager_page_split=
2407 [KVM,X86] Controls whether or not KVM will try to
2408 proactively split all huge pages during dirty logging.
2409 Eager page splitting reduces interruptions to vCPU
2410 execution by eliminating the write-protection faults
2411 and MMU lock contention that would otherwise be
2412 required to split huge pages lazily.
2414 VM workloads that rarely perform writes or that write
2415 only to a small region of VM memory may benefit from
2416 disabling eager page splitting to allow huge pages to
2417 still be used for reads.
2419 The behavior of eager page splitting depends on whether
2420 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2421 disabled, all huge pages in a memslot will be eagerly
2422 split when dirty logging is enabled on that memslot. If
2423 enabled, eager page splitting will be performed during
2424 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2427 Eager page splitting currently only supports splitting
2428 huge pages mapped by the TDP MMU.
2432 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2433 Default is false (don't support).
2436 [KVM] Controls the software workaround for the
2437 X86_BUG_ITLB_MULTIHIT bug.
2438 force : Always deploy workaround.
2439 off : Never deploy workaround.
2440 auto : Deploy workaround based on the presence of
2441 X86_BUG_ITLB_MULTIHIT.
2445 If the software workaround is enabled for the host,
2446 guests do need not to enable it for nested guests.
2448 kvm.nx_huge_pages_recovery_ratio=
2449 [KVM] Controls how many 4KiB pages are periodically zapped
2450 back to huge pages. 0 disables the recovery, otherwise if
2451 the value is N KVM will zap 1/Nth of the 4KiB pages every
2452 period (see below). The default is 60.
2454 kvm.nx_huge_pages_recovery_period_ms=
2455 [KVM] Controls the time period at which KVM zaps 4KiB pages
2456 back to huge pages. If the value is a non-zero N, KVM will
2457 zap a portion (see ratio above) of the pages every N msecs.
2458 If the value is 0 (the default), KVM will pick a period based
2459 on the ratio, such that a page is zapped after 1 hour on average.
2461 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2462 Default is 1 (enabled)
2464 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2466 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2469 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2471 none: Forcefully disable KVM.
2473 nvhe: Standard nVHE-based mode, without support for
2476 protected: nVHE-based mode with support for guests whose
2477 state is kept private from the host.
2479 Defaults to VHE/nVHE based on hardware support. Setting
2480 mode to "protected" will disable kexec and hibernation
2483 kvm-arm.vgic_v3_group0_trap=
2484 [KVM,ARM] Trap guest accesses to GICv3 group-0
2487 kvm-arm.vgic_v3_group1_trap=
2488 [KVM,ARM] Trap guest accesses to GICv3 group-1
2491 kvm-arm.vgic_v3_common_trap=
2492 [KVM,ARM] Trap guest accesses to GICv3 common
2495 kvm-arm.vgic_v4_enable=
2496 [KVM,ARM] Allow use of GICv4 for direct injection of
2499 kvm_cma_resv_ratio=n [PPC]
2500 Reserves given percentage from system memory area for
2501 contiguous memory allocation for KVM hash pagetable
2503 By default it reserves 5% of total system memory.
2507 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2508 (virtualized MMU) support on capable Intel chips.
2509 Default is 1 (enabled)
2511 kvm-intel.emulate_invalid_guest_state=
2512 [KVM,Intel] Disable emulation of invalid guest state.
2513 Ignored if kvm-intel.enable_unrestricted_guest=1, as
2514 guest state is never invalid for unrestricted guests.
2515 This param doesn't apply to nested guests (L2), as KVM
2516 never emulates invalid L2 guest state.
2517 Default is 1 (enabled)
2519 kvm-intel.flexpriority=
2520 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2521 Default is 1 (enabled)
2524 [KVM,Intel] Enable VMX nesting (nVMX).
2525 Default is 0 (disabled)
2527 kvm-intel.unrestricted_guest=
2528 [KVM,Intel] Disable unrestricted guest feature
2529 (virtualized real and unpaged mode) on capable
2530 Intel chips. Default is 1 (enabled)
2532 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2535 Valid arguments: never, cond, always
2537 always: L1D cache flush on every VMENTER.
2538 cond: Flush L1D on VMENTER only when the code between
2539 VMEXIT and VMENTER can leak host memory.
2540 never: Disables the mitigation
2542 Default is cond (do L1 cache flush in specific instances)
2544 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2545 feature (tagged TLBs) on capable Intel chips.
2546 Default is 1 (enabled)
2548 l1d_flush= [X86,INTEL]
2549 Control mitigation for L1D based snooping vulnerability.
2551 Certain CPUs are vulnerable to an exploit against CPU
2552 internal buffers which can forward information to a
2553 disclosure gadget under certain conditions.
2555 In vulnerable processors, the speculatively
2556 forwarded data can be used in a cache side channel
2557 attack, to access data to which the attacker does
2558 not have direct access.
2560 This parameter controls the mitigation. The
2563 on - enable the interface for the mitigation
2565 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2568 The kernel PTE inversion protection is unconditionally
2569 enabled and cannot be disabled.
2572 Provides all available mitigations for the
2573 L1TF vulnerability. Disables SMT and
2574 enables all mitigations in the
2575 hypervisors, i.e. unconditional L1D flush.
2577 SMT control and L1D flush control via the
2578 sysfs interface is still possible after
2579 boot. Hypervisors will issue a warning
2580 when the first VM is started in a
2581 potentially insecure configuration,
2582 i.e. SMT enabled or L1D flush disabled.
2585 Same as 'full', but disables SMT and L1D
2586 flush runtime control. Implies the
2587 'nosmt=force' command line option.
2588 (i.e. sysfs control of SMT is disabled.)
2591 Leaves SMT enabled and enables the default
2592 hypervisor mitigation, i.e. conditional
2595 SMT control and L1D flush control via the
2596 sysfs interface is still possible after
2597 boot. Hypervisors will issue a warning
2598 when the first VM is started in a
2599 potentially insecure configuration,
2600 i.e. SMT enabled or L1D flush disabled.
2604 Disables SMT and enables the default
2605 hypervisor mitigation.
2607 SMT control and L1D flush control via the
2608 sysfs interface is still possible after
2609 boot. Hypervisors will issue a warning
2610 when the first VM is started in a
2611 potentially insecure configuration,
2612 i.e. SMT enabled or L1D flush disabled.
2615 Same as 'flush', but hypervisors will not
2616 warn when a VM is started in a potentially
2617 insecure configuration.
2620 Disables hypervisor mitigations and doesn't
2622 It also drops the swap size and available
2623 RAM limit restriction on both hypervisor and
2628 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2634 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2637 lapic= [X86,APIC] Do not use TSC deadline
2638 value for LAPIC timer one-shot implementation. Default
2639 back to the programmable timer unit in the LAPIC.
2640 Format: notscdeadline
2642 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2645 libata.dma= [LIBATA] DMA control
2646 libata.dma=0 Disable all PATA and SATA DMA
2647 libata.dma=1 PATA and SATA Disk DMA only
2648 libata.dma=2 ATAPI (CDROM) DMA only
2649 libata.dma=4 Compact Flash DMA only
2650 Combinations also work, so libata.dma=3 enables DMA
2651 for disks and CDROMs, but not CFs.
2653 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2654 libata.ignore_hpa=0 keep BIOS limits (default)
2655 libata.ignore_hpa=1 ignore limits, using full disk
2657 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2661 libata.force= [LIBATA] Force configurations. The format is a comma-
2662 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2663 PORT and DEVICE are decimal numbers matching port, link
2664 or device. Basically, it matches the ATA ID string
2665 printed on console by libata. If the whole ID part is
2666 omitted, the last PORT and DEVICE values are used. If
2667 ID hasn't been specified yet, the configuration applies
2668 to all ports, links and devices.
2670 If only DEVICE is omitted, the parameter applies to
2671 the port and all links and devices behind it. DEVICE
2672 number of 0 either selects the first device or the
2673 first fan-out link behind PMP device. It does not
2674 select the host link. DEVICE number of 15 selects the
2675 host link and device attached to it.
2677 The VAL specifies the configuration to force. As long
2678 as there is no ambiguity, shortcut notation is allowed.
2679 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2680 The following configurations can be forced.
2682 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2683 Any ID with matching PORT is used.
2685 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2687 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2688 udma[/][16,25,33,44,66,100,133] notation is also
2691 * nohrst, nosrst, norst: suppress hard, soft and both
2694 * rstonce: only attempt one reset during hot-unplug
2697 * [no]dbdelay: Enable or disable the extra 200ms delay
2698 before debouncing a link PHY and device presence
2701 * [no]ncq: Turn on or off NCQ.
2703 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2705 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2707 * [no]trim: Enable or disable (unqueued) TRIM.
2709 * trim_zero: Indicate that TRIM command zeroes data.
2711 * max_trim_128m: Set 128M maximum trim size limit.
2713 * [no]dma: Turn on or off DMA transfers.
2715 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2717 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2718 commands that are not a multiple of 16 bytes.
2720 * [no]dmalog: Enable or disable the use of the
2721 READ LOG DMA EXT command to access logs.
2723 * [no]iddevlog: Enable or disable access to the
2724 identify device data log.
2726 * [no]logdir: Enable or disable access to the general
2727 purpose log directory.
2729 * max_sec_128: Set transfer size limit to 128 sectors.
2731 * max_sec_1024: Set or clear transfer size limit to
2734 * max_sec_lba48: Set or clear transfer size limit to
2737 * [no]lpm: Enable or disable link power management.
2739 * [no]setxfer: Indicate if transfer speed mode setting
2742 * dump_id: Dump IDENTIFY data.
2744 * disable: Disable this device.
2746 If there are multiple matching configurations changing
2747 the same attribute, the last one is used.
2749 load_ramdisk= [RAM] [Deprecated]
2751 lockd.nlm_grace_period=P [NFS] Assign grace period.
2754 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2757 lockd.nlm_timeout=T [NFS] Assign timeout value.
2760 lockd.nlm_udpport=M [NFS] Assign UDP port.
2763 lockdown= [SECURITY]
2764 { integrity | confidentiality }
2765 Enable the kernel lockdown feature. If set to
2766 integrity, kernel features that allow userland to
2767 modify the running kernel are disabled. If set to
2768 confidentiality, kernel features that allow userland
2769 to extract confidential information from the kernel
2772 locktorture.nreaders_stress= [KNL]
2773 Set the number of locking read-acquisition kthreads.
2774 Defaults to being automatically set based on the
2775 number of online CPUs.
2777 locktorture.nwriters_stress= [KNL]
2778 Set the number of locking write-acquisition kthreads.
2780 locktorture.onoff_holdoff= [KNL]
2781 Set time (s) after boot for CPU-hotplug testing.
2783 locktorture.onoff_interval= [KNL]
2784 Set time (s) between CPU-hotplug operations, or
2785 zero to disable CPU-hotplug testing.
2787 locktorture.shuffle_interval= [KNL]
2788 Set task-shuffle interval (jiffies). Shuffling
2789 tasks allows some CPUs to go into dyntick-idle
2790 mode during the locktorture test.
2792 locktorture.shutdown_secs= [KNL]
2793 Set time (s) after boot system shutdown. This
2794 is useful for hands-off automated testing.
2796 locktorture.stat_interval= [KNL]
2797 Time (s) between statistics printk()s.
2799 locktorture.stutter= [KNL]
2800 Time (s) to stutter testing, for example,
2801 specifying five seconds causes the test to run for
2802 five seconds, wait for five seconds, and so on.
2803 This tests the locking primitive's ability to
2804 transition abruptly to and from idle.
2806 locktorture.torture_type= [KNL]
2807 Specify the locking implementation to test.
2809 locktorture.verbose= [KNL]
2810 Enable additional printk() statements.
2812 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2815 loglevel= All Kernel Messages with a loglevel smaller than the
2816 console loglevel will be printed to the console. It can
2817 also be changed with klogd or other programs. The
2818 loglevels are defined as follows:
2820 0 (KERN_EMERG) system is unusable
2821 1 (KERN_ALERT) action must be taken immediately
2822 2 (KERN_CRIT) critical conditions
2823 3 (KERN_ERR) error conditions
2824 4 (KERN_WARNING) warning conditions
2825 5 (KERN_NOTICE) normal but significant condition
2826 6 (KERN_INFO) informational
2827 7 (KERN_DEBUG) debug-level messages
2829 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2830 in bytes. n must be a power of two and greater
2831 than the minimal size. The minimal size is defined
2832 by LOG_BUF_SHIFT kernel config parameter. There is
2833 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2834 that allows to increase the default size depending on
2835 the number of CPUs. See init/Kconfig for more details.
2837 logo.nologo [FB] Disables display of the built-in Linux logo.
2838 This may be used to provide more screen space for
2839 kernel log messages and is useful when debugging
2840 kernel boot problems.
2842 lp=0 [LP] Specify parallel ports to use, e.g,
2843 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2844 lp=reset first parallel port). 'lp=0' disables the
2845 lp=auto printer driver. 'lp=reset' (which can be
2846 specified in addition to the ports) causes
2847 attached printers to be reset. Using
2848 lp=port1,port2,... specifies the parallel ports
2849 to associate lp devices with, starting with
2850 lp0. A port specification may be 'none' to skip
2851 that lp device, or a parport name such as
2852 'parport0'. Specifying 'lp=auto' instead of a
2853 port specification list means that device IDs
2854 from each port should be examined, to see if
2855 an IEEE 1284-compliant printer is attached; if
2856 so, the driver will manage that printer.
2857 See also header of drivers/char/lp.c.
2860 Sets loops_per_jiffy to given constant, thus avoiding
2861 time-consuming boot-time autodetection (up to 250 ms per
2862 CPU). 0 enables autodetection (default). To determine
2863 the correct value for your kernel, boot with normal
2864 autodetection and see what value is printed. Note that
2865 on SMP systems the preset will be applied to all CPUs,
2866 which is likely to cause problems if your CPUs need
2867 significantly divergent settings. An incorrect value
2868 will cause delays in the kernel to be wrong, leading to
2869 unpredictable I/O errors and other breakage. Although
2870 unlikely, in the extreme case this might damage your
2874 Format: <io>,<irq>,<dma>
2876 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2879 [SECURITY] Choose order of LSM initialization. This
2880 overrides CONFIG_LSM, and the "security=" parameter.
2882 machvec= [IA-64] Force the use of a particular machine-vector
2883 (machvec) in a generic kernel.
2884 Example: machvec=hpzx1
2886 machtype= [Loongson] Share the same kernel image file between
2887 different yeeloong laptops.
2888 Example: machtype=lemote-yeeloong-2f-7inch
2890 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
2891 than or equal to this physical address is ignored.
2893 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2894 will bring up during bootup. maxcpus=n : n >= 0 limits
2895 the kernel to bring up 'n' processors. Surely after
2896 bootup you can bring up the other plugged cpu by executing
2897 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2898 only takes effect during system bootup.
2899 While n=0 is a special case, it is equivalent to "nosmp",
2900 which also disables the IO APIC.
2902 max_loop= [LOOP] The number of loop block devices that get
2903 (loop.max_loop) unconditionally pre-created at init time. The default
2904 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2905 of statically allocating a predefined number, loop
2906 devices can be requested on-demand with the
2907 /dev/loop-control interface.
2909 mce [X86-32] Machine Check Exception
2911 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2913 md= [HW] RAID subsystems devices and level
2914 See Documentation/admin-guide/md.rst.
2917 Format: <first>,<last>
2918 Specifies range of consoles to be captured by the MDA.
2921 Control mitigation for the Micro-architectural Data
2922 Sampling (MDS) vulnerability.
2924 Certain CPUs are vulnerable to an exploit against CPU
2925 internal buffers which can forward information to a
2926 disclosure gadget under certain conditions.
2928 In vulnerable processors, the speculatively
2929 forwarded data can be used in a cache side channel
2930 attack, to access data to which the attacker does
2931 not have direct access.
2933 This parameter controls the MDS mitigation. The
2936 full - Enable MDS mitigation on vulnerable CPUs
2937 full,nosmt - Enable MDS mitigation and disable
2938 SMT on vulnerable CPUs
2939 off - Unconditionally disable MDS mitigation
2941 On TAA-affected machines, mds=off can be prevented by
2942 an active TAA mitigation as both vulnerabilities are
2943 mitigated with the same mechanism so in order to disable
2944 this mitigation, you need to specify tsx_async_abort=off
2947 Not specifying this option is equivalent to
2950 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2952 mem=nn[KMG] [HEXAGON] Set the memory size.
2953 Must be specified, otherwise memory size will be 0.
2955 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2956 Amount of memory to be used in cases as follows:
2959 2 when the kernel is not able to see the whole system memory;
2960 3 memory that lies after 'mem=' boundary is excluded from
2961 the hypervisor, then assigned to KVM guests.
2962 4 to limit the memory available for kdump kernel.
2964 [ARC,MICROBLAZE] - the limit applies only to low memory,
2965 high memory is not affected.
2967 [ARM64] - only limits memory covered by the linear
2968 mapping. The NOMAP regions are not affected.
2970 [X86] Work as limiting max address. Use together
2971 with memmap= to avoid physical address space collisions.
2972 Without memmap= PCI devices could be placed at addresses
2973 belonging to unused RAM.
2975 Note that this only takes effects during boot time since
2976 in above case 3, memory may need be hot added after boot
2977 if system memory of hypervisor is not sufficient.
2980 [ARM,MIPS] - override the memory layout reported by
2982 Define a memory region of size nn[KMG] starting at
2984 Multiple different regions can be specified with
2985 multiple mem= parameters on the command line.
2987 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2990 memblock=debug [KNL] Enable memblock debug messages.
2993 [KNL,SH] Allow user to override the default size for
2994 per-device physically contiguous DMA buffers.
2996 memhp_default_state=online/offline
2997 [KNL] Set the initial state for the memory hotplug
2998 onlining policy. If not specified, the default value is
2999 set according to the
3000 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3002 See Documentation/admin-guide/mm/memory-hotplug.rst.
3004 memmap=exactmap [KNL,X86] Enable setting of an exact
3005 E820 memory map, as specified by the user.
3006 Such memmap=exactmap lines can be constructed based on
3007 BIOS output or other requirements. See the memmap=nn@ss
3010 memmap=nn[KMG]@ss[KMG]
3011 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
3012 Region of memory to be used is from ss to ss+nn.
3013 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3014 which limits max address to nn[KMG].
3015 Multiple different regions can be specified,
3018 memmap=100M@2G,100M#3G,1G!1024G
3020 memmap=nn[KMG]#ss[KMG]
3021 [KNL,ACPI] Mark specific memory as ACPI data.
3022 Region of memory to be marked is from ss to ss+nn.
3024 memmap=nn[KMG]$ss[KMG]
3025 [KNL,ACPI] Mark specific memory as reserved.
3026 Region of memory to be reserved is from ss to ss+nn.
3027 Example: Exclude memory from 0x18690000-0x1869ffff
3028 memmap=64K$0x18690000
3030 memmap=0x10000$0x18690000
3031 Some bootloaders may need an escape character before '$',
3032 like Grub2, otherwise '$' and the following number
3035 memmap=nn[KMG]!ss[KMG]
3036 [KNL,X86] Mark specific memory as protected.
3037 Region of memory to be used, from ss to ss+nn.
3038 The memory region may be marked as e820 type 12 (0xc)
3039 and is NVDIMM or ADR memory.
3041 memmap=<size>%<offset>-<oldtype>+<newtype>
3042 [KNL,ACPI] Convert memory within the specified region
3043 from <oldtype> to <newtype>. If "-<oldtype>" is left
3044 out, the whole region will be marked as <newtype>,
3045 even if previously unavailable. If "+<newtype>" is left
3046 out, matching memory will be removed. Types are
3047 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3048 3 = ACPI, 12 = PRAM.
3050 memory_corruption_check=0/1 [X86]
3051 Some BIOSes seem to corrupt the first 64k of
3052 memory when doing things like suspend/resume.
3053 Setting this option will scan the memory
3054 looking for corruption. Enabling this will
3055 both detect corruption and prevent the kernel
3056 from using the memory being corrupted.
3057 However, its intended as a diagnostic tool; if
3058 repeatable BIOS-originated corruption always
3059 affects the same memory, you can use memmap=
3060 to prevent the kernel from using that memory.
3062 memory_corruption_check_size=size [X86]
3063 By default it checks for corruption in the low
3064 64k, making this memory unavailable for normal
3065 use. Use this parameter to scan for
3066 corruption in more or less memory.
3068 memory_corruption_check_period=seconds [X86]
3069 By default it checks for corruption every 60
3070 seconds. Use this parameter to check at some
3071 other rate. 0 disables periodic checking.
3073 memory_hotplug.memmap_on_memory
3074 [KNL,X86,ARM] Boolean flag to enable this feature.
3075 Format: {on | off (default)}
3076 When enabled, runtime hotplugged memory will
3077 allocate its internal metadata (struct pages)
3078 from the hotadded memory which will allow to
3079 hotadd a lot of memory without requiring
3080 additional memory to do so.
3081 This feature is disabled by default because it
3082 has some implication on large (e.g. GB)
3083 allocations in some configurations (e.g. small
3085 The state of the flag can be read in
3086 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3087 Note that even when enabled, there are a few cases where
3088 the feature is not effective.
3090 This is not compatible with hugetlb_free_vmemmap. If
3091 both parameters are enabled, hugetlb_free_vmemmap takes
3092 precedence over memory_hotplug.memmap_on_memory.
3094 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
3096 default : 0 <disable>
3097 Specifies the number of memtest passes to be
3098 performed. Each pass selects another test
3099 pattern from a given set of patterns. Memtest
3100 fills the memory with this pattern, validates
3101 memory contents and reserves bad memory
3102 regions that are detected.
3104 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3105 Valid arguments: on, off
3106 Default (depends on kernel configuration option):
3107 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
3108 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
3109 mem_encrypt=on: Activate SME
3110 mem_encrypt=off: Do not activate SME
3112 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
3113 for details on when memory encryption can be activated.
3115 mem_sleep_default= [SUSPEND] Default system suspend mode:
3116 s2idle - Suspend-To-Idle
3117 shallow - Power-On Suspend or equivalent (if supported)
3118 deep - Suspend-To-RAM or equivalent (if supported)
3119 See Documentation/admin-guide/pm/sleep-states.rst.
3121 meye.*= [HW] Set MotionEye Camera parameters
3122 See Documentation/admin-guide/media/meye.rst.
3124 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3125 Multi-Function General Purpose Timers on AMD Geode
3128 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3129 the BIOS has incorrectly applied a workaround. TinyBIOS
3130 version 0.98 is known to be affected, 0.99 fixes the
3131 problem by letting the user disable the workaround.
3135 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3136 physical address is ignored.
3138 mini2440= [ARM,HW,KNL]
3139 Format:[0..2][b][c][t]
3141 MINI2440 configuration specification:
3142 0 - The attached screen is the 3.5" TFT
3143 1 - The attached screen is the 7" TFT
3144 2 - The VGA Shield is attached (1024x768)
3145 Leaving out the screen size parameter will not load
3146 the TFT driver, and the framebuffer will be left
3148 b - Enable backlight. The TFT backlight pin will be
3149 linked to the kernel VESA blanking code and a GPIO
3150 LED. This parameter is not necessary when using the
3152 c - Enable the s3c camera interface.
3153 t - Reserved for enabling touchscreen support. The
3154 touchscreen support is not enabled in the mainstream
3155 kernel as of 2.6.30, a preliminary port can be found
3156 in the "bleeding edge" mini2440 support kernel at
3157 https://repo.or.cz/w/linux-2.6/mini2440.git
3160 [X86,PPC,S390,ARM64] Control optional mitigations for
3161 CPU vulnerabilities. This is a set of curated,
3162 arch-independent options, each of which is an
3163 aggregation of existing arch-specific options.
3166 Disable all optional CPU mitigations. This
3167 improves system performance, but it may also
3168 expose users to several CPU vulnerabilities.
3169 Equivalent to: nopti [X86,PPC]
3170 if nokaslr then kpti=0 [ARM64]
3171 nospectre_v1 [X86,PPC]
3173 nospectre_v2 [X86,PPC,S390,ARM64]
3174 spectre_v2_user=off [X86]
3175 spec_store_bypass_disable=off [X86,PPC]
3176 ssbd=force-off [ARM64]
3179 tsx_async_abort=off [X86]
3180 kvm.nx_huge_pages=off [X86]
3181 srbds=off [X86,INTEL]
3182 no_entry_flush [PPC]
3183 no_uaccess_flush [PPC]
3184 mmio_stale_data=off [X86]
3188 This does not have any effect on
3189 kvm.nx_huge_pages when
3190 kvm.nx_huge_pages=force.
3193 Mitigate all CPU vulnerabilities, but leave SMT
3194 enabled, even if it's vulnerable. This is for
3195 users who don't want to be surprised by SMT
3196 getting disabled across kernel upgrades, or who
3197 have other ways of avoiding SMT-based attacks.
3198 Equivalent to: (default behavior)
3201 Mitigate all CPU vulnerabilities, disabling SMT
3202 if needed. This is for users who always want to
3203 be fully mitigated, even if it means losing SMT.
3204 Equivalent to: l1tf=flush,nosmt [X86]
3205 mds=full,nosmt [X86]
3206 tsx_async_abort=full,nosmt [X86]
3207 mmio_stale_data=full,nosmt [X86]
3208 retbleed=auto,nosmt [X86]
3211 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3212 parameter allows control of the logging verbosity for
3213 the additional memory initialisation checks. A value
3214 of 0 disables mminit logging and a level of 4 will
3215 log everything. Information is printed at KERN_DEBUG
3216 so loglevel=8 may also need to be specified.
3219 [X86,INTEL] Control mitigation for the Processor
3220 MMIO Stale Data vulnerabilities.
3222 Processor MMIO Stale Data is a class of
3223 vulnerabilities that may expose data after an MMIO
3224 operation. Exposed data could originate or end in
3225 the same CPU buffers as affected by MDS and TAA.
3226 Therefore, similar to MDS and TAA, the mitigation
3227 is to clear the affected CPU buffers.
3229 This parameter controls the mitigation. The
3232 full - Enable mitigation on vulnerable CPUs
3234 full,nosmt - Enable mitigation and disable SMT on
3237 off - Unconditionally disable mitigation
3239 On MDS or TAA affected machines,
3240 mmio_stale_data=off can be prevented by an active
3241 MDS or TAA mitigation as these vulnerabilities are
3242 mitigated with the same mechanism so in order to
3243 disable this mitigation, you need to specify
3244 mds=off and tsx_async_abort=off too.
3246 Not specifying this option is equivalent to
3247 mmio_stale_data=full.
3250 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3253 [KNL] When CONFIG_MODULE_SIG is set, this means that
3254 modules without (valid) signatures will fail to load.
3255 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3256 is always true, so this option does nothing.
3258 module_blacklist= [KNL] Do not load a comma-separated list of
3259 modules. Useful for debugging problem modules.
3262 [MOUSE] Maximum time between finger touching and
3263 leaving touchpad surface for touch to be considered
3264 a tap and be reported as a left button click (for
3265 touchpads working in absolute mode only).
3267 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3268 reporting absolute coordinates, such as tablets
3269 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3270 reporting absolute coordinates, such as tablets
3272 movablecore= [KNL,X86,IA-64,PPC]
3273 Format: nn[KMGTPE] | nn%
3274 This parameter is the complement to kernelcore=, it
3275 specifies the amount of memory used for migratable
3276 allocations. If both kernelcore and movablecore is
3277 specified, then kernelcore will be at *least* the
3278 specified value but may be more. If movablecore on its
3279 own is specified, the administrator must be careful
3280 that the amount of memory usable for all allocations
3283 movable_node [KNL] Boot-time switch to make hotplugable memory
3284 NUMA nodes to be movable. This means that the memory
3285 of such nodes will be usable only for movable
3286 allocations which rules out almost all kernel
3287 allocations. Use with caution!
3289 MTD_Partition= [MTD]
3290 Format: <name>,<region-number>,<size>,<offset>
3292 MTD_Region= [MTD] Format:
3293 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3296 See drivers/mtd/parsers/cmdlinepart.c
3299 ARM/S3C2412 JIVE boot control
3301 See arch/arm/mach-s3c/mach-jive.c
3303 mtouchusb.raw_coordinates=
3304 [HW] Make the MicroTouch USB driver use raw coordinates
3305 ('y', default) or cooked coordinates ('n')
3307 mtrr_chunk_size=nn[KMG] [X86]
3308 used for mtrr cleanup. It is largest continuous chunk
3309 that could hold holes aka. UC entries.
3311 mtrr_gran_size=nn[KMG] [X86]
3312 Used for mtrr cleanup. It is granularity of mtrr block.
3314 Large value could prevent small alignment from
3317 mtrr_spare_reg_nr=n [X86]
3319 Range: 0,7 : spare reg number
3321 Used for mtrr cleanup. It is spare mtrr entries number.
3322 Set to 2 or more if your graphical card needs more.
3324 multitce=off [PPC] This parameter disables the use of the pSeries
3325 firmware feature for updating multiple TCE entries
3328 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3330 netdev= [NET] Network devices parameters
3331 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3332 Note that mem_start is often overloaded to mean
3333 something different and driver-specific.
3334 This usage is only documented in each driver source
3337 netpoll.carrier_timeout=
3338 [NET] Specifies amount of time (in seconds) that
3339 netpoll should wait for a carrier. By default netpoll
3343 [NETFILTER] Enable connection tracking flow accounting
3344 0 to disable accounting
3345 1 to enable accounting
3348 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3349 See Documentation/admin-guide/nfs/nfsroot.rst.
3351 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3352 See Documentation/admin-guide/nfs/nfsroot.rst.
3354 nfsrootdebug [NFS] enable nfsroot debugging messages.
3355 See Documentation/admin-guide/nfs/nfsroot.rst.
3357 nfs.callback_nr_threads=
3358 [NFSv4] set the total number of threads that the
3359 NFS client will assign to service NFSv4 callback
3362 nfs.callback_tcpport=
3363 [NFS] set the TCP port on which the NFSv4 callback
3364 channel should listen.
3367 [NFS] sets the pathname to the program which is used
3368 to update the NFS client cache entries.
3370 nfs.cache_getent_timeout=
3371 [NFS] sets the timeout after which an attempt to
3372 update a cache entry is deemed to have failed.
3374 nfs.idmap_cache_timeout=
3375 [NFS] set the maximum lifetime for idmapper cache
3379 [NFS] enable 64-bit inode numbers.
3380 If zero, the NFS client will fake up a 32-bit inode
3381 number for the readdir() and stat() syscalls instead
3382 of returning the full 64-bit number.
3383 The default is to return 64-bit inode numbers.
3385 nfs.max_session_cb_slots=
3386 [NFSv4.1] Sets the maximum number of session
3387 slots the client will assign to the callback
3388 channel. This determines the maximum number of
3389 callbacks the client will process in parallel for
3390 a particular server.
3392 nfs.max_session_slots=
3393 [NFSv4.1] Sets the maximum number of session slots
3394 the client will attempt to negotiate with the server.
3395 This limits the number of simultaneous RPC requests
3396 that the client can send to the NFSv4.1 server.
3397 Note that there is little point in setting this
3398 value higher than the max_tcp_slot_table_limit.
3400 nfs.nfs4_disable_idmapping=
3401 [NFSv4] When set to the default of '1', this option
3402 ensures that both the RPC level authentication
3403 scheme and the NFS level operations agree to use
3404 numeric uids/gids if the mount is using the
3405 'sec=sys' security flavour. In effect it is
3406 disabling idmapping, which can make migration from
3407 legacy NFSv2/v3 systems to NFSv4 easier.
3408 Servers that do not support this mode of operation
3409 will be autodetected by the client, and it will fall
3410 back to using the idmapper.
3411 To turn off this behaviour, set the value to '0'.
3413 [NFS4] Specify an additional fixed unique ident-
3414 ification string that NFSv4 clients can insert into
3415 their nfs_client_id4 string. This is typically a
3416 UUID that is generated at system install time.
3418 nfs.send_implementation_id =
3419 [NFSv4.1] Send client implementation identification
3420 information in exchange_id requests.
3421 If zero, no implementation identification information
3423 The default is to send the implementation identification
3426 nfs.recover_lost_locks =
3427 [NFSv4] Attempt to recover locks that were lost due
3428 to a lease timeout on the server. Please note that
3429 doing this risks data corruption, since there are
3430 no guarantees that the file will remain unchanged
3431 after the locks are lost.
3432 If you want to enable the kernel legacy behaviour of
3433 attempting to recover these locks, then set this
3435 The default parameter value of '0' causes the kernel
3436 not to attempt recovery of lost locks.
3438 nfs4.layoutstats_timer =
3439 [NFSv4.2] Change the rate at which the kernel sends
3440 layoutstats to the pNFS metadata server.
3442 Setting this to value to 0 causes the kernel to use
3443 whatever value is the default set by the layout
3444 driver. A non-zero value sets the minimum interval
3445 in seconds between layoutstats transmissions.
3447 nfsd.inter_copy_offload_enable =
3448 [NFSv4.2] When set to 1, the server will support
3449 server-to-server copies for which this server is
3450 the destination of the copy.
3452 nfsd.nfsd4_ssc_umount_timeout =
3453 [NFSv4.2] When used as the destination of a
3454 server-to-server copy, knfsd temporarily mounts
3455 the source server. It caches the mount in case
3456 it will be needed again, and discards it if not
3457 used for the number of milliseconds specified by
3460 nfsd.nfs4_disable_idmapping=
3461 [NFSv4] When set to the default of '1', the NFSv4
3462 server will return only numeric uids and gids to
3463 clients using auth_sys, and will accept numeric uids
3464 and gids from such clients. This is intended to ease
3465 migration from NFSv2/v3.
3468 nmi_backtrace.backtrace_idle [KNL]
3469 Dump stacks even of idle CPUs in response to an
3470 NMI stack-backtrace request.
3472 nmi_debug= [KNL,SH] Specify one or more actions to take
3473 when a NMI is triggered.
3474 Format: [state][,regs][,debounce][,die]
3476 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3477 Format: [panic,][nopanic,][num]
3479 0 - turn hardlockup detector in nmi_watchdog off
3480 1 - turn hardlockup detector in nmi_watchdog on
3481 When panic is specified, panic when an NMI watchdog
3482 timeout occurs (or 'nopanic' to not panic on an NMI
3483 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3484 To disable both hard and soft lockup detectors,
3485 please see 'nowatchdog'.
3486 This is useful when you use a panic=... timeout and
3487 need the box quickly up again.
3489 These settings can be accessed at runtime via
3490 the nmi_watchdog and hardlockup_panic sysctls.
3492 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3493 emulation library even if a 387 maths coprocessor
3496 no5lvl [X86-64] Disable 5-level paging mode. Forces
3497 kernel to use 4-level paging instead.
3499 nofsgsbase [X86] Disables FSGSBASE instructions.
3502 [HW] Never suspend the console
3503 Disable suspending of consoles during suspend and
3504 hibernate operations. Once disabled, debugging
3505 messages can reach various consoles while the rest
3506 of the system is being put to sleep (ie, while
3507 debugging driver suspend/resume hooks). This may
3508 not work reliably with all consoles, but is known
3509 to work with serial and VGA consoles.
3510 To facilitate more flexible debugging, we also add
3511 console_suspend, a printk module parameter to control
3512 it. Users could use console_suspend (usually
3513 /sys/module/printk/parameters/console_suspend) to
3514 turn on/off it dynamically.
3516 novmcoredd [KNL,KDUMP]
3517 Disable device dump. Device dump allows drivers to
3518 append dump data to vmcore so you can collect driver
3519 specified debug info. Drivers can append the data
3520 without any limit and this data is stored in memory,
3521 so this may cause significant memory stress. Disabling
3522 device dump can help save memory but the driver debug
3523 data will be no longer available. This parameter
3524 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3527 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3528 caches in the slab allocator. Saves per-node memory,
3529 but will impact performance.
3533 noaltinstr [S390] Disables alternative instructions patching
3534 (CPU alternatives feature).
3536 noapic [SMP,APIC] Tells the kernel to not make use of any
3537 IOAPICs that may be present in the system.
3539 noautogroup Disable scheduler automatic task group creation.
3541 nobats [PPC] Do not use BATs for mapping kernel lowmem
3542 on "Classic" PPC cores.
3546 nodsp [SH] Disable hardware DSP at boot time.
3548 noefi Disable EFI runtime services support.
3550 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3555 Disable SMAP (Supervisor Mode Access Prevention)
3556 even if it is supported by processor.
3559 Disable SMEP (Supervisor Mode Execution Prevention)
3560 even if it is supported by processor.
3563 This affects only 32-bit executables.
3564 noexec32=on: enable non-executable mappings (default)
3565 read doesn't imply executable mappings
3566 noexec32=off: disable non-executable mappings
3567 read implies executable mappings
3569 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3571 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3572 register save and restore. The kernel will only save
3573 legacy floating-point registers on task switch.
3575 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3577 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3579 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3580 Equivalent to smt=1.
3582 [KNL,X86] Disable symmetric multithreading (SMT).
3583 nosmt=force: Force disable SMT, cannot be undone
3584 via the sysfs control file.
3586 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3587 (bounds check bypass). With this option data leaks are
3588 possible in the system.
3590 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3591 the Spectre variant 2 (indirect branch prediction)
3592 vulnerability. System may allow data leaks with this
3595 nospec_store_bypass_disable
3596 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3599 [PPC] Don't flush the L1-D cache after accessing user data.
3601 noxsave [BUGS=X86] Disables x86 extended register state save
3602 and restore using xsave. The kernel will fallback to
3603 enabling legacy floating-point and sse state.
3605 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3606 register states. The kernel will fall back to use
3607 xsave to save the states. By using this parameter,
3608 performance of saving the states is degraded because
3609 xsave doesn't support modified optimization while
3610 xsaveopt supports it on xsaveopt enabled systems.
3612 noxsaves [X86] Disables xsaves and xrstors used in saving and
3613 restoring x86 extended register state in compacted
3614 form of xsave area. The kernel will fall back to use
3615 xsaveopt and xrstor to save and restore the states
3616 in standard form of xsave area. By using this
3617 parameter, xsave area per process might occupy more
3618 memory on xsaves enabled systems.
3620 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3621 in do_idle() and not use the arch_cpu_idle()
3622 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3623 to be effective. This is useful on platforms where the
3624 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3625 correctly or when doing power measurements to evalute
3626 the impact of the sleep instructions. This is also
3627 useful when using JTAG debugger.
3629 no_file_caps Tells the kernel not to honor file capabilities. The
3630 only way then for a file to be executed with privilege
3631 is to be setuid root or executed by root.
3633 nohalt [IA-64] Tells the kernel not to use the power saving
3634 function PAL_HALT_LIGHT when idle. This increases
3635 power-consumption. On the positive side, it reduces
3636 interrupt wake-up latency, which may improve performance
3637 in certain environments such as networked servers or
3641 Force pointers printed to the console or buffers to be
3642 unhashed. By default, when a pointer is printed via %p
3643 format string, that pointer is "hashed", i.e. obscured
3644 by hashing the pointer value. This is a security feature
3645 that hides actual kernel addresses from unprivileged
3646 users, but it also makes debugging the kernel more
3647 difficult since unequal pointers can no longer be
3648 compared. However, if this command-line option is
3649 specified, then all normal pointers will have their true
3650 value printed. This option should only be specified when
3651 debugging the kernel. Please do not use on production
3654 nohibernate [HIBERNATION] Disable hibernation and resume.
3656 nohz= [KNL] Boottime enable/disable dynamic ticks
3657 Valid arguments: on, off
3660 nohz_full= [KNL,BOOT,SMP,ISOL]
3661 The argument is a cpu list, as described above.
3662 In kernels built with CONFIG_NO_HZ_FULL=y, set
3663 the specified list of CPUs whose tick will be stopped
3664 whenever possible. The boot CPU will be forced outside
3665 the range to maintain the timekeeping. Any CPUs
3666 in this list will have their RCU callbacks offloaded,
3667 just as if they had also been called out in the
3668 rcu_nocbs= boot parameter.
3670 noiotrap [SH] Disables trapped I/O port accesses.
3672 noirqdebug [X86-32] Disables the code which attempts to detect and
3673 disable unhandled interrupt sources.
3675 no_timer_check [X86,APIC] Disables the code which tests for
3676 broken timer IRQ sources.
3678 noisapnp [ISAPNP] Disables ISA PnP code.
3680 noinitrd [RAM] Tells the kernel not to load any configured
3683 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3685 [Deprecated - use intremap=off]
3689 noinvpcid [X86] Disable the INVPCID cpu feature.
3691 nojitter [IA-64] Disables jitter checking for ITC timers.
3693 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3695 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3699 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3700 clock and use the default one.
3702 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3703 accounting. steal time is computed, but won't
3704 influence scheduler behaviour
3706 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3708 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3710 noltlbs [PPC] Do not use large page/tlb entries for kernel
3711 lowmem mapping on PPC40x and PPC8xx
3713 nomca [IA-64] Disable machine check abort handling
3715 nomce [X86-32] Disable Machine Check Exception
3717 nomfgpt [X86-32] Disable Multi-Function General Purpose
3718 Timer usage (for AMD Geode machines).
3720 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3721 shutdown the other cpus. Instead use the REBOOT_VECTOR
3724 nomodeset Disable kernel modesetting. DRM drivers will not perform
3725 display-mode changes or accelerated rendering. Only the
3726 system framebuffer will be available for use if this was
3727 set-up by the firmware or boot loader.
3729 Useful as fallback, or for testing and debugging.
3731 nomodule Disable module load
3733 nopat [X86] Disable PAT (page attribute table extension of
3734 pagetables) support.
3736 nopcid [X86-64] Disable the PCID cpu feature.
3738 norandmaps Don't use address space randomization. Equivalent to
3739 echo 0 > /proc/sys/kernel/randomize_va_space
3741 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3742 with UP alternatives
3744 nordrand [X86] Disable kernel use of the RDRAND and
3745 RDSEED instructions even if they are supported
3746 by the processor. RDRAND and RDSEED are still
3747 available to user space applications.
3749 noresume [SWSUSP] Disables resume and restores original swap
3752 no-scroll [VGA] Disables scrollback.
3753 This is required for the Braillex ib80-piezo Braille
3754 reader made by F.H. Papenmeier (Germany).
3758 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3760 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3761 and disable the IO APIC. legacy for "maxcpus=0".
3763 nosoftlockup [KNL] Disable the soft-lockup detector.
3765 nosync [HW,M68K] Disables sync negotiation for all devices.
3767 nowatchdog [KNL] Disable both lockup detectors, i.e.
3768 soft-lockup and NMI watchdog (hard-lockup).
3772 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3774 nps_mtm_hs_ctr= [KNL,ARC]
3775 This parameter sets the maximum duration, in
3776 cycles, each HW thread of the CTOP can run
3777 without interruptions, before HW switches it.
3778 The actual maximum duration is 16 times this
3780 Format: integer between 1 and 255
3783 nptcg= [IA-64] Override max number of concurrent global TLB
3784 purges which is reported from either PAL_VM_SUMMARY or
3787 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3788 could support. nr_cpus=n : n >= 1 limits the kernel to
3789 support 'n' processors. It could be larger than the
3790 number of already plugged CPU during bootup, later in
3791 runtime you can physically add extra cpu until it reaches
3792 n. So during boot up some boot time memory for per-cpu
3793 variables need be pre-allocated for later physical cpu
3796 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3798 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3799 set up a single NUMA node spanning all memory.
3801 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3803 Allowed values are enable and disable
3805 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3806 'node', 'default' can be specified
3807 This can be set from sysctl after boot.
3808 See Documentation/admin-guide/sysctl/vm.rst for details.
3810 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3811 See Documentation/core-api/debugging-via-ohci1394.rst for more
3814 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3815 Rather than timing out after 20 ms if an EC
3816 command is not properly ACKed, override the length
3817 of the timeout. We have interrupts disabled while
3818 waiting for the ACK, so if this is set too high
3819 interrupts *may* be lost!
3821 omap_mux= [OMAP] Override bootloader pin multiplexing.
3822 Format: <mux_mode0.mode_name=value>...
3823 For example, to override I2C bus2:
3824 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3826 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3828 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3830 boundary - index of last SLC block on Flex-OneNAND.
3831 The remaining blocks are configured as MLC blocks.
3832 lock - Configure if Flex-OneNAND boundary should be locked.
3833 Once locked, the boundary cannot be changed.
3834 1 indicates lock status, 0 indicates unlock status.
3836 oops=panic Always panic on oopses. Default is to just kill the
3837 process, but there is a small probability of
3838 deadlocking the machine.
3839 This will also cause panics on machine check exceptions.
3840 Useful together with panic=30 to trigger a reboot.
3843 [KNL] Boolean flag to control whether the page allocator
3844 should randomize its free lists. The randomization may
3845 be automatically enabled if the kernel detects it is
3846 running on a platform with a direct-mapped memory-side
3847 cache, and this parameter can be used to
3848 override/disable that behavior. The state of the flag
3849 can be read from sysfs at:
3850 /sys/module/page_alloc/parameters/shuffle.
3852 page_owner= [KNL] Boot-time page_owner enabling option.
3853 Storage of the information about who allocated
3854 each page is disabled in default. With this switch,
3856 on: enable the feature
3858 page_poison= [KNL] Boot-time parameter changing the state of
3859 poisoning on the buddy allocator, available with
3860 CONFIG_PAGE_POISONING=y.
3861 off: turn off poisoning (default)
3862 on: turn on poisoning
3864 page_reporting.page_reporting_order=
3865 [KNL] Minimal page reporting order
3867 Adjust the minimal page reporting order. The page
3868 reporting is disabled when it exceeds (MAX_ORDER-1).
3870 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3871 timeout > 0: seconds before rebooting
3872 timeout = 0: wait forever
3873 timeout < 0: reboot immediately
3876 panic_print= Bitmask for printing system info when panic happens.
3877 User can chose combination of the following bits:
3878 bit 0: print all tasks info
3879 bit 1: print system memory info
3880 bit 2: print timer info
3881 bit 3: print locks info if CONFIG_LOCKDEP is on
3882 bit 4: print ftrace buffer
3883 bit 5: print all printk messages in buffer
3884 bit 6: print all CPUs backtrace (if available in the arch)
3885 *Be aware* that this option may print a _lot_ of lines,
3886 so there are risks of losing older messages in the log.
3887 Use this option carefully, maybe worth to setup a
3888 bigger log buffer with "log_buf_len" along with this.
3890 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3891 Format: <hex>[,nousertaint]
3892 Hexadecimal bitmask representing the set of TAINT flags
3893 that will cause the kernel to panic when add_taint() is
3894 called with any of the flags in this set.
3895 The optional switch "nousertaint" can be utilized to
3896 prevent userspace forced crashes by writing to sysctl
3897 /proc/sys/kernel/tainted any flagset matching with the
3898 bitmask set on panic_on_taint.
3899 See Documentation/admin-guide/tainted-kernels.rst for
3900 extra details on the taint flags that users can pick
3901 to compose the bitmask to assign to panic_on_taint.
3903 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3906 parkbd.port= [HW] Parallel port number the keyboard adapter is
3907 connected to, default is 0.
3909 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3910 0 for XT, 1 for AT (default is AT).
3913 parport= [HW,PPT] Specify parallel ports. 0 disables.
3914 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3915 Use 'auto' to force the driver to use any
3916 IRQ/DMA settings detected (the default is to
3917 ignore detected IRQ/DMA settings because of
3918 possible conflicts). You can specify the base
3919 address, IRQ, and DMA settings; IRQ and DMA
3920 should be numbers, or 'auto' (for using detected
3921 settings on that particular port), or 'nofifo'
3922 (to avoid using a FIFO even if it is detected).
3923 Parallel ports are assigned in the order they
3924 are specified on the command line, starting
3927 parport_init_mode= [HW,PPT]
3928 Configure VIA parallel port to operate in
3929 a specific mode. This is necessary on Pegasos
3930 computer where firmware has no options for setting
3931 up parallel port mode and sets it to spp.
3932 Currently this function knows 686a and 8231 chips.
3933 Format: [spp|ps2|epp|ecp|ecpepp]
3935 pata_legacy.all= [HW,LIBATA]
3937 Set to non-zero to probe primary and secondary ISA
3938 port ranges on PCI systems where no PCI PATA device
3939 has been found at either range. Disabled by default.
3941 pata_legacy.autospeed= [HW,LIBATA]
3943 Set to non-zero if a chip is present that snoops speed
3944 changes. Disabled by default.
3946 pata_legacy.ht6560a= [HW,LIBATA]
3948 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3949 the secondary channel, or both channels respectively.
3950 Disabled by default.
3952 pata_legacy.ht6560b= [HW,LIBATA]
3954 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3955 the secondary channel, or both channels respectively.
3956 Disabled by default.
3958 pata_legacy.iordy_mask= [HW,LIBATA]
3960 IORDY enable mask. Set individual bits to allow IORDY
3961 for the respective channel. Bit 0 is for the first
3962 legacy channel handled by this driver, bit 1 is for
3963 the second channel, and so on. The sequence will often
3964 correspond to the primary legacy channel, the secondary
3965 legacy channel, and so on, but the handling of a PCI
3966 bus and the use of other driver options may interfere
3967 with the sequence. By default IORDY is allowed across
3970 pata_legacy.opti82c46x= [HW,LIBATA]
3972 Set to 1, 2, or 3 for Opti 82c611A on the primary
3973 channel, the secondary channel, or both channels
3974 respectively. Disabled by default.
3976 pata_legacy.opti82c611a= [HW,LIBATA]
3978 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3979 channel, the secondary channel, or both channels
3980 respectively. Disabled by default.
3982 pata_legacy.pio_mask= [HW,LIBATA]
3984 PIO mode mask for autospeed devices. Set individual
3985 bits to allow the use of the respective PIO modes.
3986 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3987 All modes allowed by default.
3989 pata_legacy.probe_all= [HW,LIBATA]
3991 Set to non-zero to probe tertiary and further ISA
3992 port ranges on PCI systems. Disabled by default.
3994 pata_legacy.probe_mask= [HW,LIBATA]
3996 Probe mask for legacy ISA PATA ports. Depending on
3997 platform configuration and the use of other driver
3998 options up to 6 legacy ports are supported: 0x1f0,
3999 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4000 of individual ports can be disabled by setting the
4001 corresponding bits in the mask to 1. Bit 0 is for
4002 the first port in the list above (0x1f0), and so on.
4003 By default all supported ports are probed.
4005 pata_legacy.qdi= [HW,LIBATA]
4007 Set to non-zero to probe QDI controllers. By default
4008 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4010 pata_legacy.winbond= [HW,LIBATA]
4012 Set to non-zero to probe Winbond controllers. Use
4013 the standard I/O port (0x130) if 1, otherwise the
4014 value given is the I/O port to use (typically 0x1b0).
4015 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4018 pata_platform.pio_mask= [HW,LIBATA]
4020 Supported PIO mode mask. Set individual bits to allow
4021 the use of the respective PIO modes. Bit 0 is for
4022 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4026 Halt all CPUs after the first oops has been printed for
4027 the specified number of seconds. This is to be used if
4028 your oopses keep scrolling off the screen.
4033 See header of drivers/block/paride/pcd.c.
4034 See also Documentation/admin-guide/blockdev/paride.rst.
4036 pci=option[,option...] [PCI] various PCI subsystem options.
4038 Some options herein operate on a specific device
4039 or a set of devices (<pci_dev>). These are
4040 specified in one of the following formats:
4042 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4043 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4045 Note: the first format specifies a PCI
4046 bus/device/function address which may change
4047 if new hardware is inserted, if motherboard
4048 firmware changes, or due to changes caused
4049 by other kernel parameters. If the
4050 domain is left unspecified, it is
4051 taken to be zero. Optionally, a path
4052 to a device through multiple device/function
4053 addresses can be specified after the base
4054 address (this is more robust against
4055 renumbering issues). The second format
4056 selects devices using IDs from the
4057 configuration space which may match multiple
4058 devices in the system.
4060 earlydump dump PCI config space before the kernel
4062 off [X86] don't probe for the PCI bus
4063 bios [X86-32] force use of PCI BIOS, don't access
4064 the hardware directly. Use this if your machine
4065 has a non-standard PCI host bridge.
4066 nobios [X86-32] disallow use of PCI BIOS, only direct
4067 hardware access methods are allowed. Use this
4068 if you experience crashes upon bootup and you
4069 suspect they are caused by the BIOS.
4070 conf1 [X86] Force use of PCI Configuration Access
4071 Mechanism 1 (config address in IO port 0xCF8,
4072 data in IO port 0xCFC, both 32-bit).
4073 conf2 [X86] Force use of PCI Configuration Access
4074 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4075 the function, IO port 0xCFA, also 8-bit, sets
4076 bus number. The config space is then accessed
4077 through ports 0xC000-0xCFFF).
4078 See http://wiki.osdev.org/PCI for more info
4079 on the configuration access mechanisms.
4080 noaer [PCIE] If the PCIEAER kernel config parameter is
4081 enabled, this kernel boot option can be used to
4082 disable the use of PCIE advanced error reporting.
4083 nodomains [PCI] Disable support for multiple PCI
4084 root domains (aka PCI segments, in ACPI-speak).
4085 nommconf [X86] Disable use of MMCONFIG for PCI
4087 check_enable_amd_mmconf [X86] check for and enable
4088 properly configured MMIO access to PCI
4089 config space on AMD family 10h CPU
4090 nomsi [MSI] If the PCI_MSI kernel config parameter is
4091 enabled, this kernel boot option can be used to
4092 disable the use of MSI interrupts system-wide.
4093 noioapicquirk [APIC] Disable all boot interrupt quirks.
4094 Safety option to keep boot IRQs enabled. This
4095 should never be necessary.
4096 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4097 primary IO-APIC for bridges that cannot disable
4098 boot IRQs. This fixes a source of spurious IRQs
4099 when the system masks IRQs.
4100 noioapicreroute [APIC] Disable workaround that uses the
4101 boot IRQ equivalent of an IRQ that connects to
4102 a chipset where boot IRQs cannot be disabled.
4103 The opposite of ioapicreroute.
4104 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4105 routing table. These calls are known to be buggy
4106 on several machines and they hang the machine
4107 when used, but on other computers it's the only
4108 way to get the interrupt routing table. Try
4109 this option if the kernel is unable to allocate
4110 IRQs or discover secondary PCI buses on your
4112 rom [X86] Assign address space to expansion ROMs.
4113 Use with caution as certain devices share
4114 address decoders between ROMs and other
4116 norom [X86] Do not assign address space to
4117 expansion ROMs that do not already have
4118 BIOS assigned address ranges.
4119 nobar [X86] Do not assign address space to the
4120 BARs that weren't assigned by the BIOS.
4121 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4122 assigned automatically to PCI devices. You can
4123 make the kernel exclude IRQs of your ISA cards
4125 pirqaddr=0xAAAAA [X86] Specify the physical address
4126 of the PIRQ table (normally generated
4127 by the BIOS) if it is outside the
4128 F0000h-100000h range.
4129 lastbus=N [X86] Scan all buses thru bus #N. Can be
4130 useful if the kernel is unable to find your
4131 secondary buses and you want to tell it
4132 explicitly which ones they are.
4133 assign-busses [X86] Always assign all PCI bus
4134 numbers ourselves, overriding
4135 whatever the firmware may have done.
4136 usepirqmask [X86] Honor the possible IRQ mask stored
4137 in the BIOS $PIR table. This is needed on
4138 some systems with broken BIOSes, notably
4139 some HP Pavilion N5400 and Omnibook XE3
4140 notebooks. This will have no effect if ACPI
4141 IRQ routing is enabled.
4142 noacpi [X86] Do not use ACPI for IRQ routing
4143 or for PCI scanning.
4144 use_crs [X86] Use PCI host bridge window information
4145 from ACPI. On BIOSes from 2008 or later, this
4146 is enabled by default. If you need to use this,
4147 please report a bug.
4148 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4149 If you need to use this, please report a bug.
4150 use_e820 [X86] Use E820 reservations to exclude parts of
4151 PCI host bridge windows. This is a workaround
4152 for BIOS defects in host bridge _CRS methods.
4153 If you need to use this, please report a bug to
4154 <linux-pci@vger.kernel.org>.
4155 no_e820 [X86] Ignore E820 reservations for PCI host
4156 bridge windows. This is the default on modern
4157 hardware. If you need to use this, please report
4158 a bug to <linux-pci@vger.kernel.org>.
4159 routeirq Do IRQ routing for all PCI devices.
4160 This is normally done in pci_enable_device(),
4161 so this option is a temporary workaround
4162 for broken drivers that don't call it.
4163 skip_isa_align [X86] do not align io start addr, so can
4164 handle more pci cards
4165 noearly [X86] Don't do any early type 1 scanning.
4166 This might help on some broken boards which
4167 machine check when some devices' config space
4168 is read. But various workarounds are disabled
4169 and some IOMMU drivers will not work.
4170 bfsort Sort PCI devices into breadth-first order.
4171 This sorting is done to get a device
4172 order compatible with older (<= 2.4) kernels.
4173 nobfsort Don't sort PCI devices into breadth-first order.
4174 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4175 tuning and use the BIOS-configured MPS defaults.
4176 pcie_bus_safe Set every device's MPS to the largest value
4177 supported by all devices below the root complex.
4178 pcie_bus_perf Set device MPS to the largest allowable MPS
4179 based on its parent bus. Also set MRRS (Max
4180 Read Request Size) to the largest supported
4181 value (no larger than the MPS that the device
4182 or bus can support) for best performance.
4183 pcie_bus_peer2peer Set every device's MPS to 128B, which
4184 every device is guaranteed to support. This
4185 configuration allows peer-to-peer DMA between
4186 any pair of devices, possibly at the cost of
4187 reduced performance. This also guarantees
4188 that hot-added devices will work.
4189 cbiosize=nn[KMG] The fixed amount of bus space which is
4190 reserved for the CardBus bridge's IO window.
4191 The default value is 256 bytes.
4192 cbmemsize=nn[KMG] The fixed amount of bus space which is
4193 reserved for the CardBus bridge's memory
4194 window. The default value is 64 megabytes.
4197 [<order of align>@]<pci_dev>[; ...]
4198 Specifies alignment and device to reassign
4199 aligned memory resources. How to
4200 specify the device is described above.
4201 If <order of align> is not specified,
4202 PAGE_SIZE is used as alignment.
4203 A PCI-PCI bridge can be specified if resource
4204 windows need to be expanded.
4205 To specify the alignment for several
4206 instances of a device, the PCI vendor,
4207 device, subvendor, and subdevice may be
4208 specified, e.g., 12@pci:8086:9c22:103c:198f
4209 for 4096-byte alignment.
4210 ecrc= Enable/disable PCIe ECRC (transaction layer
4211 end-to-end CRC checking).
4212 bios: Use BIOS/firmware settings. This is the
4216 hpiosize=nn[KMG] The fixed amount of bus space which is
4217 reserved for hotplug bridge's IO window.
4218 Default size is 256 bytes.
4219 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4220 reserved for hotplug bridge's MMIO window.
4221 Default size is 2 megabytes.
4222 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4223 reserved for hotplug bridge's MMIO_PREF window.
4224 Default size is 2 megabytes.
4225 hpmemsize=nn[KMG] The fixed amount of bus space which is
4226 reserved for hotplug bridge's MMIO and
4228 Default size is 2 megabytes.
4229 hpbussize=nn The minimum amount of additional bus numbers
4230 reserved for buses below a hotplug bridge.
4232 realloc= Enable/disable reallocating PCI bridge resources
4233 if allocations done by BIOS are too small to
4234 accommodate resources required by all child
4236 off: Turn realloc off
4238 realloc same as realloc=on
4239 noari do not use PCIe ARI.
4240 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4241 do not use PCIe ATS (and IOMMU device IOTLB).
4242 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4243 only look for one device below a PCIe downstream
4245 big_root_window Try to add a big 64bit memory window to the PCIe
4246 root complex on AMD CPUs. Some GFX hardware
4247 can resize a BAR to allow access to all VRAM.
4248 Adding the window is slightly risky (it may
4249 conflict with unreported devices), so this
4251 disable_acs_redir=<pci_dev>[; ...]
4252 Specify one or more PCI devices (in the format
4253 specified above) separated by semicolons.
4254 Each device specified will have the PCI ACS
4255 redirect capabilities forced off which will
4256 allow P2P traffic between devices through
4257 bridges without forcing it upstream. Note:
4258 this removes isolation between devices and
4259 may put more devices in an IOMMU group.
4260 force_floating [S390] Force usage of floating interrupts.
4261 nomio [S390] Do not use MIO instructions.
4262 norid [S390] ignore the RID field and force use of
4263 one PCI domain per PCI function
4265 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4268 force Enable ASPM even on devices that claim not to support it.
4269 WARNING: Forcing ASPM on may cause system lockups.
4271 pcie_ports= [PCIE] PCIe port services handling:
4272 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4273 even if the platform doesn't give the OS permission to
4274 use them. This may cause conflicts if the platform
4275 also tries to use these services.
4276 dpc-native Use native PCIe service for DPC only. May
4277 cause conflicts if firmware uses AER or DPC.
4278 compat Disable native PCIe services (PME, AER, DPC, PCIe
4281 pcie_port_pm= [PCIE] PCIe port power management handling:
4282 off Disable power management of all PCIe ports
4283 force Forcibly enable power management of all PCIe ports
4285 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4286 nomsi Do not use MSI for native PCIe PME signaling (this makes
4287 all PCIe root ports use INTx for all services).
4289 pcmv= [HW,PCMCIA] BadgePAD 4
4293 Keep all power-domains already enabled by bootloader on,
4294 even if no driver has claimed them. This is useful
4295 for debug and development, but should not be
4296 needed on a platform with proper driver support.
4299 See Documentation/admin-guide/blockdev/paride.rst.
4301 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4304 See arch/parisc/kernel/pdc_chassis.c
4306 percpu_alloc= Select which percpu first chunk allocator to use.
4307 Currently supported values are "embed" and "page".
4308 Archs may support subset or none of the selections.
4309 See comments in mm/percpu.c for details on each
4310 allocator. This parameter is primarily for debugging
4311 and performance comparison.
4314 See Documentation/admin-guide/blockdev/paride.rst.
4317 See Documentation/admin-guide/blockdev/paride.rst.
4319 pirq= [SMP,APIC] Manual mp-table setup
4320 See Documentation/x86/i386/IO-APIC.rst.
4322 plip= [PPT,NET] Parallel port network link
4323 Format: { parport<nr> | timid | 0 }
4324 See also Documentation/admin-guide/parport.rst.
4326 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4327 Override pmtimer IOPort with a hex value.
4330 pmu_override= [PPC] Override the PMU.
4331 This option takes over the PMU facility, so it is no
4332 longer usable by perf. Setting this option starts the
4333 PMU counters by setting MMCR0 to 0 (the FC bit is
4334 cleared). If a number is given, then MMCR1 is set to
4335 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4338 pm_debug_messages [SUSPEND,KNL]
4339 Enable suspend/resume debug messages during boot up.
4342 Enable PNP debug messages (depends on the
4343 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4344 via /sys/module/pnp/parameters/debug. We always show
4345 current resource usage; turning this on also shows
4346 possible settings and some assignment information.
4352 { on | off | curr | res | no-curr | no-res }
4355 [ISAPNP] Exclude IRQs for the autoconfiguration
4358 [ISAPNP] Exclude DMAs for the autoconfiguration
4360 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4361 Ranges are in pairs (I/O port base and size).
4364 [ISAPNP] Exclude memory regions for the
4366 Ranges are in pairs (memory base and size).
4368 ports= [IP_VS_FTP] IPVS ftp helper module
4370 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4372 Format: <port>,<port>....
4374 powersave=off [PPC] This option disables power saving features.
4375 It specifically disables cpuidle and sets the
4376 platform machine description specific power_save
4377 function to NULL. On Idle the CPU just reduces
4380 ppc_strict_facility_enable
4381 [PPC] This option catches any kernel floating point,
4382 Altivec, VSX and SPE outside of regions specifically
4383 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4384 There is some performance impact when enabling this.
4388 Disable Hardware Transactional Memory
4391 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4392 none - Limited to cond_resched() calls
4393 voluntary - Limited to cond_resched() and might_sleep() calls
4394 full - Any section that isn't explicitly preempt disabled
4395 can be preempted anytime.
4397 print-fatal-signals=
4398 [KNL] debug: print fatal signals
4400 If enabled, warn about various signal handling
4401 related application anomalies: too many signals,
4402 too many POSIX.1 timers, fatal signals causing a
4405 If you hit the warning due to signal overflow,
4406 you might want to try "ulimit -i unlimited".
4410 printk.always_kmsg_dump=
4411 Trigger kmsg_dump for cases other than kernel oops or
4413 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4416 printk.console_no_auto_verbose=
4417 Disable console loglevel raise on oops, panic
4418 or lockdep-detected issues (only if lock debug is on).
4419 With an exception to setups with low baudrate on
4420 serial console, keeping this 0 is a good choice
4421 in order to provide more debug information.
4423 default: 0 (auto_verbose is enabled)
4425 printk.devkmsg={on,off,ratelimit}
4426 Control writing to /dev/kmsg.
4427 on - unlimited logging to /dev/kmsg from userspace
4428 off - logging to /dev/kmsg disabled
4429 ratelimit - ratelimit the logging
4432 printk.time= Show timing data prefixed to each printk message line
4433 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4435 processor.max_cstate= [HW,ACPI]
4436 Limit processor to maximum C-state
4437 max_cstate=9 overrides any DMI blacklist limit.
4439 processor.nocst [HW,ACPI]
4440 Ignore the _CST method to determine C-states,
4441 instead using the legacy FADT method
4443 profile= [KNL] Enable kernel profiling via /proc/profile
4444 Format: [<profiletype>,]<number>
4445 Param: <profiletype>: "schedule", "sleep", or "kvm"
4446 [defaults to kernel profiling]
4447 Param: "schedule" - profile schedule points.
4448 Param: "sleep" - profile D-state sleeping (millisecs).
4449 Requires CONFIG_SCHEDSTATS
4450 Param: "kvm" - profile VM exits.
4451 Param: <number> - step/bucket size as a power of 2 for
4452 statistical time based profiling.
4454 prompt_ramdisk= [RAM] [Deprecated]
4456 prot_virt= [S390] enable hosting protected virtual machines
4457 isolated from the hypervisor (if hardware supports
4461 psi= [KNL] Enable or disable pressure stall information
4465 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4466 probe for; one of (bare|imps|exps|lifebook|any).
4467 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4469 psmouse.resetafter= [HW,MOUSE]
4470 Try to reset the device after so many bad packets
4473 [HW,MOUSE] Set desired mouse resolution, in dpi.
4474 psmouse.smartscroll=
4475 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4476 0 = disabled, 1 = enabled (default).
4478 pstore.backend= Specify the name of the pstore backend to use
4481 See Documentation/admin-guide/blockdev/paride.rst.
4483 pti= [X86-64] Control Page Table Isolation of user and
4484 kernel address spaces. Disabling this feature
4485 removes hardening, but improves performance of
4486 system calls and interrupts.
4488 on - unconditionally enable
4489 off - unconditionally disable
4490 auto - kernel detects whether your CPU model is
4491 vulnerable to issues that PTI mitigates
4493 Not specifying this option is equivalent to pti=auto.
4496 Equivalent to pti=off
4499 [KNL] Number of legacy pty's. Overwrites compiled-in
4502 quiet [KNL] Disable most log messages
4507 See Documentation/admin-guide/md.rst.
4509 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4510 See Documentation/admin-guide/blockdev/ramdisk.rst.
4512 ramdisk_start= [RAM] RAM disk image start address
4514 random.trust_cpu={on,off}
4515 [KNL] Enable or disable trusting the use of the
4516 CPU's random number generator (if available) to
4517 fully seed the kernel's CRNG. Default is controlled
4518 by CONFIG_RANDOM_TRUST_CPU.
4520 random.trust_bootloader={on,off}
4521 [KNL] Enable or disable trusting the use of a
4522 seed passed by the bootloader (if available) to
4523 fully seed the kernel's CRNG. Default is controlled
4524 by CONFIG_RANDOM_TRUST_BOOTLOADER.
4526 randomize_kstack_offset=
4527 [KNL] Enable or disable kernel stack offset
4528 randomization, which provides roughly 5 bits of
4529 entropy, frustrating memory corruption attacks
4530 that depend on stack address determinism or
4531 cross-syscall address exposures. This is only
4532 available on architectures that have defined
4533 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4534 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4535 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4537 ras=option[,option,...] [KNL] RAS-specific options
4540 Disable the Correctable Errors Collector,
4541 see CONFIG_RAS_CEC help text.
4543 rcu_nocbs[=cpu-list]
4544 [KNL] The optional argument is a cpu list,
4547 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4548 enable the no-callback CPU mode, which prevents
4549 such CPUs' callbacks from being invoked in
4550 softirq context. Invocation of such CPUs' RCU
4551 callbacks will instead be offloaded to "rcuox/N"
4552 kthreads created for that purpose, where "x" is
4553 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4554 for the kthreads that mediate grace periods; and
4555 "N" is the CPU number. This reduces OS jitter on
4556 the offloaded CPUs, which can be useful for HPC
4557 and real-time workloads. It can also improve
4558 energy efficiency for asymmetric multiprocessors.
4560 If a cpulist is passed as an argument, the specified
4561 list of CPUs is set to no-callback mode from boot.
4563 Otherwise, if the '=' sign and the cpulist
4564 arguments are omitted, no CPU will be set to
4565 no-callback mode from boot but the mode may be
4566 toggled at runtime via cpusets.
4569 Rather than requiring that offloaded CPUs
4570 (specified by rcu_nocbs= above) explicitly
4571 awaken the corresponding "rcuoN" kthreads,
4572 make these kthreads poll for callbacks.
4573 This improves the real-time response for the
4574 offloaded CPUs by relieving them of the need to
4575 wake up the corresponding kthread, but degrades
4576 energy efficiency by requiring that the kthreads
4577 periodically wake up to do the polling.
4579 rcutree.blimit= [KNL]
4580 Set maximum number of finished RCU callbacks to
4581 process in one batch.
4583 rcutree.dump_tree= [KNL]
4584 Dump the structure of the rcu_node combining tree
4585 out at early boot. This is used for diagnostic
4586 purposes, to verify correct tree setup.
4588 rcutree.gp_cleanup_delay= [KNL]
4589 Set the number of jiffies to delay each step of
4590 RCU grace-period cleanup.
4592 rcutree.gp_init_delay= [KNL]
4593 Set the number of jiffies to delay each step of
4594 RCU grace-period initialization.
4596 rcutree.gp_preinit_delay= [KNL]
4597 Set the number of jiffies to delay each step of
4598 RCU grace-period pre-initialization, that is,
4599 the propagation of recent CPU-hotplug changes up
4600 the rcu_node combining tree.
4602 rcutree.use_softirq= [KNL]
4603 If set to zero, move all RCU_SOFTIRQ processing to
4604 per-CPU rcuc kthreads. Defaults to a non-zero
4605 value, meaning that RCU_SOFTIRQ is used by default.
4606 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4608 But note that CONFIG_PREEMPT_RT=y kernels disable
4609 this kernel boot parameter, forcibly setting it
4612 rcutree.rcu_fanout_exact= [KNL]
4613 Disable autobalancing of the rcu_node combining
4614 tree. This is used by rcutorture, and might
4615 possibly be useful for architectures having high
4616 cache-to-cache transfer latencies.
4618 rcutree.rcu_fanout_leaf= [KNL]
4619 Change the number of CPUs assigned to each
4620 leaf rcu_node structure. Useful for very
4621 large systems, which will choose the value 64,
4622 and for NUMA systems with large remote-access
4623 latencies, which will choose a value aligned
4624 with the appropriate hardware boundaries.
4626 rcutree.rcu_min_cached_objs= [KNL]
4627 Minimum number of objects which are cached and
4628 maintained per one CPU. Object size is equal
4629 to PAGE_SIZE. The cache allows to reduce the
4630 pressure to page allocator, also it makes the
4631 whole algorithm to behave better in low memory
4634 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4635 Set the page-cache refill delay (in milliseconds)
4636 in response to low-memory conditions. The range
4637 of permitted values is in the range 0:100000.
4639 rcutree.jiffies_till_first_fqs= [KNL]
4640 Set delay from grace-period initialization to
4641 first attempt to force quiescent states.
4642 Units are jiffies, minimum value is zero,
4643 and maximum value is HZ.
4645 rcutree.jiffies_till_next_fqs= [KNL]
4646 Set delay between subsequent attempts to force
4647 quiescent states. Units are jiffies, minimum
4648 value is one, and maximum value is HZ.
4650 rcutree.jiffies_till_sched_qs= [KNL]
4651 Set required age in jiffies for a
4652 given grace period before RCU starts
4653 soliciting quiescent-state help from
4654 rcu_note_context_switch() and cond_resched().
4655 If not specified, the kernel will calculate
4656 a value based on the most recent settings
4657 of rcutree.jiffies_till_first_fqs
4658 and rcutree.jiffies_till_next_fqs.
4659 This calculated value may be viewed in
4660 rcutree.jiffies_to_sched_qs. Any attempt to set
4661 rcutree.jiffies_to_sched_qs will be cheerfully
4664 rcutree.kthread_prio= [KNL,BOOT]
4665 Set the SCHED_FIFO priority of the RCU per-CPU
4666 kthreads (rcuc/N). This value is also used for
4667 the priority of the RCU boost threads (rcub/N)
4668 and for the RCU grace-period kthreads (rcu_bh,
4669 rcu_preempt, and rcu_sched). If RCU_BOOST is
4670 set, valid values are 1-99 and the default is 1
4671 (the least-favored priority). Otherwise, when
4672 RCU_BOOST is not set, valid values are 0-99 and
4673 the default is zero (non-realtime operation).
4674 When RCU_NOCB_CPU is set, also adjust the
4675 priority of NOCB callback kthreads.
4677 rcutree.rcu_nocb_gp_stride= [KNL]
4678 Set the number of NOCB callback kthreads in
4679 each group, which defaults to the square root
4680 of the number of CPUs. Larger numbers reduce
4681 the wakeup overhead on the global grace-period
4682 kthread, but increases that same overhead on
4683 each group's NOCB grace-period kthread.
4685 rcutree.qhimark= [KNL]
4686 Set threshold of queued RCU callbacks beyond which
4687 batch limiting is disabled.
4689 rcutree.qlowmark= [KNL]
4690 Set threshold of queued RCU callbacks below which
4691 batch limiting is re-enabled.
4693 rcutree.qovld= [KNL]
4694 Set threshold of queued RCU callbacks beyond which
4695 RCU's force-quiescent-state scan will aggressively
4696 enlist help from cond_resched() and sched IPIs to
4697 help CPUs more quickly reach quiescent states.
4698 Set to less than zero to make this be set based
4699 on rcutree.qhimark at boot time and to zero to
4700 disable more aggressive help enlistment.
4702 rcutree.rcu_kick_kthreads= [KNL]
4703 Cause the grace-period kthread to get an extra
4704 wake_up() if it sleeps three times longer than
4705 it should at force-quiescent-state time.
4706 This wake_up() will be accompanied by a
4707 WARN_ONCE() splat and an ftrace_dump().
4709 rcutree.rcu_unlock_delay= [KNL]
4710 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4711 this specifies an rcu_read_unlock()-time delay
4712 in microseconds. This defaults to zero.
4713 Larger delays increase the probability of
4714 catching RCU pointer leaks, that is, buggy use
4715 of RCU-protected pointers after the relevant
4716 rcu_read_unlock() has completed.
4718 rcutree.sysrq_rcu= [KNL]
4719 Commandeer a sysrq key to dump out Tree RCU's
4720 rcu_node tree with an eye towards determining
4721 why a new grace period has not yet started.
4723 rcuscale.gp_async= [KNL]
4724 Measure performance of asynchronous
4725 grace-period primitives such as call_rcu().
4727 rcuscale.gp_async_max= [KNL]
4728 Specify the maximum number of outstanding
4729 callbacks per writer thread. When a writer
4730 thread exceeds this limit, it invokes the
4731 corresponding flavor of rcu_barrier() to allow
4732 previously posted callbacks to drain.
4734 rcuscale.gp_exp= [KNL]
4735 Measure performance of expedited synchronous
4736 grace-period primitives.
4738 rcuscale.holdoff= [KNL]
4739 Set test-start holdoff period. The purpose of
4740 this parameter is to delay the start of the
4741 test until boot completes in order to avoid
4744 rcuscale.kfree_rcu_test= [KNL]
4745 Set to measure performance of kfree_rcu() flooding.
4747 rcuscale.kfree_rcu_test_double= [KNL]
4748 Test the double-argument variant of kfree_rcu().
4749 If this parameter has the same value as
4750 rcuscale.kfree_rcu_test_single, both the single-
4751 and double-argument variants are tested.
4753 rcuscale.kfree_rcu_test_single= [KNL]
4754 Test the single-argument variant of kfree_rcu().
4755 If this parameter has the same value as
4756 rcuscale.kfree_rcu_test_double, both the single-
4757 and double-argument variants are tested.
4759 rcuscale.kfree_nthreads= [KNL]
4760 The number of threads running loops of kfree_rcu().
4762 rcuscale.kfree_alloc_num= [KNL]
4763 Number of allocations and frees done in an iteration.
4765 rcuscale.kfree_loops= [KNL]
4766 Number of loops doing rcuscale.kfree_alloc_num number
4767 of allocations and frees.
4769 rcuscale.nreaders= [KNL]
4770 Set number of RCU readers. The value -1 selects
4771 N, where N is the number of CPUs. A value
4772 "n" less than -1 selects N-n+1, where N is again
4773 the number of CPUs. For example, -2 selects N
4774 (the number of CPUs), -3 selects N+1, and so on.
4775 A value of "n" less than or equal to -N selects
4778 rcuscale.nwriters= [KNL]
4779 Set number of RCU writers. The values operate
4780 the same as for rcuscale.nreaders.
4781 N, where N is the number of CPUs
4783 rcuscale.perf_type= [KNL]
4784 Specify the RCU implementation to test.
4786 rcuscale.shutdown= [KNL]
4787 Shut the system down after performance tests
4788 complete. This is useful for hands-off automated
4791 rcuscale.verbose= [KNL]
4792 Enable additional printk() statements.
4794 rcuscale.writer_holdoff= [KNL]
4795 Write-side holdoff between grace periods,
4796 in microseconds. The default of zero says
4799 rcutorture.fqs_duration= [KNL]
4800 Set duration of force_quiescent_state bursts
4803 rcutorture.fqs_holdoff= [KNL]
4804 Set holdoff time within force_quiescent_state bursts
4807 rcutorture.fqs_stutter= [KNL]
4808 Set wait time between force_quiescent_state bursts
4811 rcutorture.fwd_progress= [KNL]
4812 Specifies the number of kthreads to be used
4813 for RCU grace-period forward-progress testing
4814 for the types of RCU supporting this notion.
4815 Defaults to 1 kthread, values less than zero or
4816 greater than the number of CPUs cause the number
4819 rcutorture.fwd_progress_div= [KNL]
4820 Specify the fraction of a CPU-stall-warning
4821 period to do tight-loop forward-progress testing.
4823 rcutorture.fwd_progress_holdoff= [KNL]
4824 Number of seconds to wait between successive
4825 forward-progress tests.
4827 rcutorture.fwd_progress_need_resched= [KNL]
4828 Enclose cond_resched() calls within checks for
4829 need_resched() during tight-loop forward-progress
4832 rcutorture.gp_cond= [KNL]
4833 Use conditional/asynchronous update-side
4834 primitives, if available.
4836 rcutorture.gp_exp= [KNL]
4837 Use expedited update-side primitives, if available.
4839 rcutorture.gp_normal= [KNL]
4840 Use normal (non-expedited) asynchronous
4841 update-side primitives, if available.
4843 rcutorture.gp_sync= [KNL]
4844 Use normal (non-expedited) synchronous
4845 update-side primitives, if available. If all
4846 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4847 rcutorture.gp_normal=, and rcutorture.gp_sync=
4848 are zero, rcutorture acts as if is interpreted
4849 they are all non-zero.
4851 rcutorture.irqreader= [KNL]
4852 Run RCU readers from irq handlers, or, more
4853 accurately, from a timer handler. Not all RCU
4854 flavors take kindly to this sort of thing.
4856 rcutorture.leakpointer= [KNL]
4857 Leak an RCU-protected pointer out of the reader.
4858 This can of course result in splats, and is
4859 intended to test the ability of things like
4860 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4863 rcutorture.n_barrier_cbs= [KNL]
4864 Set callbacks/threads for rcu_barrier() testing.
4866 rcutorture.nfakewriters= [KNL]
4867 Set number of concurrent RCU writers. These just
4868 stress RCU, they don't participate in the actual
4869 test, hence the "fake".
4871 rcutorture.nocbs_nthreads= [KNL]
4872 Set number of RCU callback-offload togglers.
4873 Zero (the default) disables toggling.
4875 rcutorture.nocbs_toggle= [KNL]
4876 Set the delay in milliseconds between successive
4877 callback-offload toggling attempts.
4879 rcutorture.nreaders= [KNL]
4880 Set number of RCU readers. The value -1 selects
4881 N-1, where N is the number of CPUs. A value
4882 "n" less than -1 selects N-n-2, where N is again
4883 the number of CPUs. For example, -2 selects N
4884 (the number of CPUs), -3 selects N+1, and so on.
4886 rcutorture.object_debug= [KNL]
4887 Enable debug-object double-call_rcu() testing.
4889 rcutorture.onoff_holdoff= [KNL]
4890 Set time (s) after boot for CPU-hotplug testing.
4892 rcutorture.onoff_interval= [KNL]
4893 Set time (jiffies) between CPU-hotplug operations,
4894 or zero to disable CPU-hotplug testing.
4896 rcutorture.read_exit= [KNL]
4897 Set the number of read-then-exit kthreads used
4898 to test the interaction of RCU updaters and
4899 task-exit processing.
4901 rcutorture.read_exit_burst= [KNL]
4902 The number of times in a given read-then-exit
4903 episode that a set of read-then-exit kthreads
4906 rcutorture.read_exit_delay= [KNL]
4907 The delay, in seconds, between successive
4908 read-then-exit testing episodes.
4910 rcutorture.shuffle_interval= [KNL]
4911 Set task-shuffle interval (s). Shuffling tasks
4912 allows some CPUs to go into dyntick-idle mode
4913 during the rcutorture test.
4915 rcutorture.shutdown_secs= [KNL]
4916 Set time (s) after boot system shutdown. This
4917 is useful for hands-off automated testing.
4919 rcutorture.stall_cpu= [KNL]
4920 Duration of CPU stall (s) to test RCU CPU stall
4921 warnings, zero to disable.
4923 rcutorture.stall_cpu_block= [KNL]
4924 Sleep while stalling if set. This will result
4925 in warnings from preemptible RCU in addition
4926 to any other stall-related activity.
4928 rcutorture.stall_cpu_holdoff= [KNL]
4929 Time to wait (s) after boot before inducing stall.
4931 rcutorture.stall_cpu_irqsoff= [KNL]
4932 Disable interrupts while stalling if set.
4934 rcutorture.stall_gp_kthread= [KNL]
4935 Duration (s) of forced sleep within RCU
4936 grace-period kthread to test RCU CPU stall
4937 warnings, zero to disable. If both stall_cpu
4938 and stall_gp_kthread are specified, the
4939 kthread is starved first, then the CPU.
4941 rcutorture.stat_interval= [KNL]
4942 Time (s) between statistics printk()s.
4944 rcutorture.stutter= [KNL]
4945 Time (s) to stutter testing, for example, specifying
4946 five seconds causes the test to run for five seconds,
4947 wait for five seconds, and so on. This tests RCU's
4948 ability to transition abruptly to and from idle.
4950 rcutorture.test_boost= [KNL]
4951 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4952 "Maybe" means test if the RCU implementation
4953 under test support RCU priority boosting.
4955 rcutorture.test_boost_duration= [KNL]
4956 Duration (s) of each individual boost test.
4958 rcutorture.test_boost_interval= [KNL]
4959 Interval (s) between each boost test.
4961 rcutorture.test_no_idle_hz= [KNL]
4962 Test RCU's dyntick-idle handling. See also the
4963 rcutorture.shuffle_interval parameter.
4965 rcutorture.torture_type= [KNL]
4966 Specify the RCU implementation to test.
4968 rcutorture.verbose= [KNL]
4969 Enable additional printk() statements.
4971 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4972 Dump ftrace buffer after reporting RCU CPU
4975 rcupdate.rcu_cpu_stall_suppress= [KNL]
4976 Suppress RCU CPU stall warning messages.
4978 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4979 Suppress RCU CPU stall warning messages and
4980 rcutorture writer stall warnings that occur
4981 during early boot, that is, during the time
4982 before the init task is spawned.
4984 rcupdate.rcu_cpu_stall_timeout= [KNL]
4985 Set timeout for RCU CPU stall warning messages.
4986 The value is in seconds and the maximum allowed
4987 value is 300 seconds.
4989 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
4990 Set timeout for expedited RCU CPU stall warning
4991 messages. The value is in milliseconds
4992 and the maximum allowed value is 21000
4993 milliseconds. Please note that this value is
4994 adjusted to an arch timer tick resolution.
4995 Setting this to zero causes the value from
4996 rcupdate.rcu_cpu_stall_timeout to be used (after
4997 conversion from seconds to milliseconds).
4999 rcupdate.rcu_expedited= [KNL]
5000 Use expedited grace-period primitives, for
5001 example, synchronize_rcu_expedited() instead
5002 of synchronize_rcu(). This reduces latency,
5003 but can increase CPU utilization, degrade
5004 real-time latency, and degrade energy efficiency.
5005 No effect on CONFIG_TINY_RCU kernels.
5007 rcupdate.rcu_normal= [KNL]
5008 Use only normal grace-period primitives,
5009 for example, synchronize_rcu() instead of
5010 synchronize_rcu_expedited(). This improves
5011 real-time latency, CPU utilization, and
5012 energy efficiency, but can expose users to
5013 increased grace-period latency. This parameter
5014 overrides rcupdate.rcu_expedited. No effect on
5015 CONFIG_TINY_RCU kernels.
5017 rcupdate.rcu_normal_after_boot= [KNL]
5018 Once boot has completed (that is, after
5019 rcu_end_inkernel_boot() has been invoked), use
5020 only normal grace-period primitives. No effect
5021 on CONFIG_TINY_RCU kernels.
5023 But note that CONFIG_PREEMPT_RT=y kernels enables
5024 this kernel boot parameter, forcibly setting
5025 it to the value one, that is, converting any
5026 post-boot attempt at an expedited RCU grace
5027 period to instead use normal non-expedited
5028 grace-period processing.
5030 rcupdate.rcu_task_collapse_lim= [KNL]
5031 Set the maximum number of callbacks present
5032 at the beginning of a grace period that allows
5033 the RCU Tasks flavors to collapse back to using
5034 a single callback queue. This switching only
5035 occurs when rcupdate.rcu_task_enqueue_lim is
5036 set to the default value of -1.
5038 rcupdate.rcu_task_contend_lim= [KNL]
5039 Set the minimum number of callback-queuing-time
5040 lock-contention events per jiffy required to
5041 cause the RCU Tasks flavors to switch to per-CPU
5042 callback queuing. This switching only occurs
5043 when rcupdate.rcu_task_enqueue_lim is set to
5044 the default value of -1.
5046 rcupdate.rcu_task_enqueue_lim= [KNL]
5047 Set the number of callback queues to use for the
5048 RCU Tasks family of RCU flavors. The default
5049 of -1 allows this to be automatically (and
5050 dynamically) adjusted. This parameter is intended
5053 rcupdate.rcu_task_ipi_delay= [KNL]
5054 Set time in jiffies during which RCU tasks will
5055 avoid sending IPIs, starting with the beginning
5056 of a given grace period. Setting a large
5057 number avoids disturbing real-time workloads,
5058 but lengthens grace periods.
5060 rcupdate.rcu_task_stall_info= [KNL]
5061 Set initial timeout in jiffies for RCU task stall
5062 informational messages, which give some indication
5063 of the problem for those not patient enough to
5064 wait for ten minutes. Informational messages are
5065 only printed prior to the stall-warning message
5066 for a given grace period. Disable with a value
5067 less than or equal to zero. Defaults to ten
5068 seconds. A change in value does not take effect
5069 until the beginning of the next grace period.
5071 rcupdate.rcu_task_stall_info_mult= [KNL]
5072 Multiplier for time interval between successive
5073 RCU task stall informational messages for a given
5074 RCU tasks grace period. This value is clamped
5075 to one through ten, inclusive. It defaults to
5076 the value three, so that the first informational
5077 message is printed 10 seconds into the grace
5078 period, the second at 40 seconds, the third at
5079 160 seconds, and then the stall warning at 600
5080 seconds would prevent a fourth at 640 seconds.
5082 rcupdate.rcu_task_stall_timeout= [KNL]
5083 Set timeout in jiffies for RCU task stall
5084 warning messages. Disable with a value less
5085 than or equal to zero. Defaults to ten minutes.
5086 A change in value does not take effect until
5087 the beginning of the next grace period.
5089 rcupdate.rcu_self_test= [KNL]
5090 Run the RCU early boot self tests
5094 Run specified binary instead of /init from the ramdisk,
5095 used for early userspace startup. See initrd.
5098 force - Override the decision by the kernel to hide the
5099 advertisement of RDRAND support (this affects
5100 certain AMD processors because of buggy BIOS
5101 support, specifically around the suspend/resume
5105 Turn on/off individual RDT features. List is:
5106 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5108 E.g. to turn on cmt and turn off mba use:
5112 Format (x86 or x86_64):
5113 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5115 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5117 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5118 (prefix with 'panic_' to set mode for panic
5120 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5121 reboot_force is either force or not specified,
5122 reboot_cpu is s[mp]#### with #### being the processor
5123 to be used for rebooting.
5125 refscale.holdoff= [KNL]
5126 Set test-start holdoff period. The purpose of
5127 this parameter is to delay the start of the
5128 test until boot completes in order to avoid
5131 refscale.loops= [KNL]
5132 Set the number of loops over the synchronization
5133 primitive under test. Increasing this number
5134 reduces noise due to loop start/end overhead,
5135 but the default has already reduced the per-pass
5136 noise to a handful of picoseconds on ca. 2020
5139 refscale.nreaders= [KNL]
5140 Set number of readers. The default value of -1
5141 selects N, where N is roughly 75% of the number
5142 of CPUs. A value of zero is an interesting choice.
5144 refscale.nruns= [KNL]
5145 Set number of runs, each of which is dumped onto
5148 refscale.readdelay= [KNL]
5149 Set the read-side critical-section duration,
5150 measured in microseconds.
5152 refscale.scale_type= [KNL]
5153 Specify the read-protection implementation to test.
5155 refscale.shutdown= [KNL]
5156 Shut down the system at the end of the performance
5157 test. This defaults to 1 (shut it down) when
5158 refscale is built into the kernel and to 0 (leave
5159 it running) when refscale is built as a module.
5161 refscale.verbose= [KNL]
5162 Enable additional printk() statements.
5164 refscale.verbose_batched= [KNL]
5165 Batch the additional printk() statements. If zero
5166 (the default) or negative, print everything. Otherwise,
5167 print every Nth verbose statement, where N is the value
5171 [KNL, SMP] Set scheduler's default relax_domain_level.
5172 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5174 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5175 Format: <base1>,<size1>[,<base2>,<size2>,...]
5176 Reserve I/O ports or memory so the kernel won't use
5177 them. If <base> is less than 0x10000, the region
5178 is assumed to be I/O ports; otherwise it is memory.
5180 reservetop= [X86-32]
5182 Reserves a hole at the top of the kernel virtual
5185 reset_devices [KNL] Force drivers to reset the underlying device
5186 during initialization.
5189 Specify the partition device for software suspend
5191 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5193 resume_offset= [SWSUSP]
5194 Specify the offset from the beginning of the partition
5195 given by "resume=" at which the swap header is located,
5196 in <PAGE_SIZE> units (needed only for swap files).
5197 See Documentation/power/swsusp-and-swap-files.rst
5199 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5200 read the resume files
5202 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5203 Useful for devices that are detected asynchronously
5204 (e.g. USB and MMC devices).
5206 retain_initrd [RAM] Keep initrd memory after extraction
5208 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5209 Speculative Code Execution with Return Instructions)
5213 auto - automatically select a migitation
5214 auto,nosmt - automatically select a mitigation,
5215 disabling SMT if necessary for
5216 the full mitigation (only on Zen1
5217 and older without STIBP).
5218 ibpb - mitigate short speculation windows on
5219 basic block boundaries too. Safe, highest
5221 unret - force enable untrained return thunks,
5222 only effective on AMD f15h-f17h
5224 unret,nosmt - like unret, will disable SMT when STIBP
5227 Selecting 'auto' will choose a mitigation method at run
5228 time according to the CPU.
5230 Not specifying this option is equivalent to retbleed=auto.
5232 rfkill.default_state=
5233 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5234 etc. communication is blocked by default.
5237 rfkill.master_switch_mode=
5238 0 The "airplane mode" button does nothing.
5239 1 The "airplane mode" button toggles between everything
5240 blocked and the previous configuration.
5241 2 The "airplane mode" button toggles between everything
5242 blocked and everything unblocked.
5244 rhash_entries= [KNL,NET]
5245 Set number of hash buckets for route cache
5248 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5251 ro [KNL] Mount root device read-only on boot
5254 on Mark read-only kernel memory as read-only (default).
5255 off Leave read-only kernel memory writable for debugging.
5258 Enable the uart passthrough on the designated usb port
5259 on Rockchip SoCs. When active, the signals of the
5260 debug-uart get routed to the D+ and D- pins of the usb
5261 port and the regular usb controller gets disabled.
5263 root= [KNL] Root filesystem
5264 See name_to_dev_t comment in init/do_mounts.c.
5266 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5267 mount the root filesystem
5269 rootflags= [KNL] Set root filesystem mount option string
5271 rootfstype= [KNL] Set root filesystem type
5273 rootwait [KNL] Wait (indefinitely) for root device to show up.
5274 Useful for devices that are detected asynchronously
5275 (e.g. USB and MMC devices).
5277 rproc_mem=nn[KMG][@address]
5278 [KNL,ARM,CMA] Remoteproc physical memory block.
5279 Memory area to be used by remote processor image,
5282 rw [KNL] Mount root device read-write on boot
5284 S [KNL] Run init in single mode
5286 s390_iommu= [HW,S390]
5287 Set s390 IOTLB flushing mode
5289 With strict flushing every unmap operation will result in
5290 an IOTLB flush. Default is lazy flushing before reuse,
5293 s390_iommu_aperture= [KNL,S390]
5294 Specifies the size of the per device DMA address space
5295 accessible through the DMA and IOMMU APIs as a decimal
5296 factor of the size of main memory.
5297 The default is 1 meaning that one can concurrently use
5298 as many DMA addresses as physical memory is installed,
5299 if supported by hardware, and thus map all of memory
5300 once. With a value of 2 one can map all of memory twice
5301 and so on. As a special case a factor of 0 imposes no
5302 restrictions other than those given by hardware at the
5303 cost of significant additional memory use for tables.
5306 See drivers/net/irda/sa1100_ir.c.
5308 sched_verbose [KNL] Enables verbose scheduler debug messages.
5310 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5311 Allowed values are enable and disable. This feature
5312 incurs a small amount of overhead in the scheduler
5313 but is useful for debugging and performance tuning.
5315 sched_thermal_decay_shift=
5316 [KNL, SMP] Set a decay shift for scheduler thermal
5317 pressure signal. Thermal pressure signal follows the
5318 default decay period of other scheduler pelt
5319 signals(usually 32 ms but configurable). Setting
5320 sched_thermal_decay_shift will left shift the decay
5321 period for the thermal pressure signal by the shift
5323 i.e. with the default pelt decay period of 32 ms
5324 sched_thermal_decay_shift thermal pressure decay pr
5328 Format: integer between 0 and 10
5331 scftorture.holdoff= [KNL]
5332 Number of seconds to hold off before starting
5333 test. Defaults to zero for module insertion and
5334 to 10 seconds for built-in smp_call_function()
5337 scftorture.longwait= [KNL]
5338 Request ridiculously long waits randomly selected
5339 up to the chosen limit in seconds. Zero (the
5340 default) disables this feature. Please note
5341 that requesting even small non-zero numbers of
5342 seconds can result in RCU CPU stall warnings,
5343 softlockup complaints, and so on.
5345 scftorture.nthreads= [KNL]
5346 Number of kthreads to spawn to invoke the
5347 smp_call_function() family of functions.
5348 The default of -1 specifies a number of kthreads
5349 equal to the number of CPUs.
5351 scftorture.onoff_holdoff= [KNL]
5352 Number seconds to wait after the start of the
5353 test before initiating CPU-hotplug operations.
5355 scftorture.onoff_interval= [KNL]
5356 Number seconds to wait between successive
5357 CPU-hotplug operations. Specifying zero (which
5358 is the default) disables CPU-hotplug operations.
5360 scftorture.shutdown_secs= [KNL]
5361 The number of seconds following the start of the
5362 test after which to shut down the system. The
5363 default of zero avoids shutting down the system.
5364 Non-zero values are useful for automated tests.
5366 scftorture.stat_interval= [KNL]
5367 The number of seconds between outputting the
5368 current test statistics to the console. A value
5369 of zero disables statistics output.
5371 scftorture.stutter_cpus= [KNL]
5372 The number of jiffies to wait between each change
5373 to the set of CPUs under test.
5375 scftorture.use_cpus_read_lock= [KNL]
5376 Use use_cpus_read_lock() instead of the default
5377 preempt_disable() to disable CPU hotplug
5378 while invoking one of the smp_call_function*()
5381 scftorture.verbose= [KNL]
5382 Enable additional printk() statements.
5384 scftorture.weight_single= [KNL]
5385 The probability weighting to use for the
5386 smp_call_function_single() function with a zero
5387 "wait" parameter. A value of -1 selects the
5388 default if all other weights are -1. However,
5389 if at least one weight has some other value, a
5390 value of -1 will instead select a weight of zero.
5392 scftorture.weight_single_wait= [KNL]
5393 The probability weighting to use for the
5394 smp_call_function_single() function with a
5395 non-zero "wait" parameter. See weight_single.
5397 scftorture.weight_many= [KNL]
5398 The probability weighting to use for the
5399 smp_call_function_many() function with a zero
5400 "wait" parameter. See weight_single.
5401 Note well that setting a high probability for
5402 this weighting can place serious IPI load
5405 scftorture.weight_many_wait= [KNL]
5406 The probability weighting to use for the
5407 smp_call_function_many() function with a
5408 non-zero "wait" parameter. See weight_single
5411 scftorture.weight_all= [KNL]
5412 The probability weighting to use for the
5413 smp_call_function_all() function with a zero
5414 "wait" parameter. See weight_single and
5417 scftorture.weight_all_wait= [KNL]
5418 The probability weighting to use for the
5419 smp_call_function_all() function with a
5420 non-zero "wait" parameter. See weight_single
5423 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5424 xtime_lock contention on larger systems, and/or RCU lock
5425 contention on all systems with CONFIG_MAXSMP set.
5426 Format: { "0" | "1" }
5427 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5429 Note: increases power consumption, thus should only be
5430 enabled if running jitter sensitive (HPC/RT) workloads.
5432 security= [SECURITY] Choose a legacy "major" security module to
5433 enable at boot. This has been deprecated by the
5436 selinux= [SELINUX] Disable or enable SELinux at boot time.
5437 Format: { "0" | "1" }
5438 See security/selinux/Kconfig help text.
5443 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5444 Format: { "0" | "1" }
5445 See security/apparmor/Kconfig help text
5448 Default value is set via kernel config option.
5450 serialnumber [BUGS=X86-32]
5452 sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
5455 Maximal number of shapers.
5463 Enable merging of slabs with similar size when the
5464 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5467 Disable merging of slabs with similar size. May be
5468 necessary if there is some reason to distinguish
5469 allocs to different slabs, especially in hardened
5470 environments where the risk of heap overflows and
5471 layout control by attackers can usually be
5472 frustrated by disabling merging. This will reduce
5473 most of the exposure of a heap attack to a single
5474 cache (risks via metadata attacks are mostly
5475 unchanged). Debug options disable merging on their
5477 For more information see Documentation/vm/slub.rst.
5479 slab_max_order= [MM, SLAB]
5480 Determines the maximum allowed order for slabs.
5481 A high setting may cause OOMs due to memory
5482 fragmentation. Defaults to 1 for systems with
5483 more than 32MB of RAM, 0 otherwise.
5485 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5486 Enabling slub_debug allows one to determine the
5487 culprit if slab objects become corrupted. Enabling
5488 slub_debug can create guard zones around objects and
5489 may poison objects when not in use. Also tracks the
5490 last alloc / free. For more information see
5491 Documentation/vm/slub.rst.
5493 slub_max_order= [MM, SLUB]
5494 Determines the maximum allowed order for slabs.
5495 A high setting may cause OOMs due to memory
5496 fragmentation. For more information see
5497 Documentation/vm/slub.rst.
5499 slub_min_objects= [MM, SLUB]
5500 The minimum number of objects per slab. SLUB will
5501 increase the slab order up to slub_max_order to
5502 generate a sufficiently large slab able to contain
5503 the number of objects indicated. The higher the number
5504 of objects the smaller the overhead of tracking slabs
5505 and the less frequently locks need to be acquired.
5506 For more information see Documentation/vm/slub.rst.
5508 slub_min_order= [MM, SLUB]
5509 Determines the minimum page order for slabs. Must be
5510 lower than slub_max_order.
5511 For more information see Documentation/vm/slub.rst.
5513 slub_merge [MM, SLUB]
5514 Same with slab_merge.
5516 slub_nomerge [MM, SLUB]
5517 Same with slab_nomerge. This is supported for legacy.
5518 See slab_nomerge for more information.
5521 Format: <io1>[,<io2>[,...,<io8>]]
5523 smp.csd_lock_timeout= [KNL]
5524 Specify the period of time in milliseconds
5525 that smp_call_function() and friends will wait
5526 for a CPU to release the CSD lock. This is
5527 useful when diagnosing bugs involving CPUs
5528 disabling interrupts for extended periods
5529 of time. Defaults to 5,000 milliseconds, and
5530 setting a value of zero disables this feature.
5531 This feature may be more efficiently disabled
5532 using the csdlock_debug- kernel parameter.
5534 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5535 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5536 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5537 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5538 smsc-ircc2.ircc_irq= [HW] IRQ line
5539 smsc-ircc2.ircc_dma= [HW] DMA channel
5540 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5541 0: Toshiba Satellite 1800 (GP data pin select)
5542 1: Fast pin select (default)
5545 smt= [KNL,S390] Set the maximum number of threads (logical
5546 CPUs) to use per physical CPU on systems capable of
5547 symmetric multithreading (SMT). Will be capped to the
5548 actual hardware limit.
5550 Default: -1 (no limit)
5553 [KNL] Should the soft-lockup detector generate panics.
5556 A value of 1 instructs the soft-lockup detector
5557 to panic the machine when a soft-lockup occurs. It is
5558 also controlled by the kernel.softlockup_panic sysctl
5559 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5560 respective build-time switch to that functionality.
5562 softlockup_all_cpu_backtrace=
5563 [KNL] Should the soft-lockup detector generate
5564 backtraces on all cpus.
5567 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5568 See Documentation/admin-guide/laptops/sonypi.rst
5570 spectre_v2= [X86] Control mitigation of Spectre variant 2
5571 (indirect branch speculation) vulnerability.
5572 The default operation protects the kernel from
5575 on - unconditionally enable, implies
5577 off - unconditionally disable, implies
5579 auto - kernel detects whether your CPU model is
5582 Selecting 'on' will, and 'auto' may, choose a
5583 mitigation method at run time according to the
5584 CPU, the available microcode, the setting of the
5585 CONFIG_RETPOLINE configuration option, and the
5586 compiler with which the kernel was built.
5588 Selecting 'on' will also enable the mitigation
5589 against user space to user space task attacks.
5591 Selecting 'off' will disable both the kernel and
5592 the user space protections.
5594 Specific mitigations can also be selected manually:
5596 retpoline - replace indirect branches
5597 retpoline,generic - Retpolines
5598 retpoline,lfence - LFENCE; indirect branch
5599 retpoline,amd - alias for retpoline,lfence
5600 eibrs - enhanced IBRS
5601 eibrs,retpoline - enhanced IBRS + Retpolines
5602 eibrs,lfence - enhanced IBRS + LFENCE
5603 ibrs - use IBRS to protect kernel
5605 Not specifying this option is equivalent to
5609 [X86] Control mitigation of Spectre variant 2
5610 (indirect branch speculation) vulnerability between
5613 on - Unconditionally enable mitigations. Is
5614 enforced by spectre_v2=on
5616 off - Unconditionally disable mitigations. Is
5617 enforced by spectre_v2=off
5619 prctl - Indirect branch speculation is enabled,
5620 but mitigation can be enabled via prctl
5621 per thread. The mitigation control state
5622 is inherited on fork.
5625 - Like "prctl" above, but only STIBP is
5626 controlled per thread. IBPB is issued
5627 always when switching between different user
5631 - Same as "prctl" above, but all seccomp
5632 threads will enable the mitigation unless
5633 they explicitly opt out.
5636 - Like "seccomp" above, but only STIBP is
5637 controlled per thread. IBPB is issued
5638 always when switching between different
5639 user space processes.
5641 auto - Kernel selects the mitigation depending on
5642 the available CPU features and vulnerability.
5644 Default mitigation: "prctl"
5646 Not specifying this option is equivalent to
5647 spectre_v2_user=auto.
5649 spec_store_bypass_disable=
5650 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5651 (Speculative Store Bypass vulnerability)
5653 Certain CPUs are vulnerable to an exploit against a
5654 a common industry wide performance optimization known
5655 as "Speculative Store Bypass" in which recent stores
5656 to the same memory location may not be observed by
5657 later loads during speculative execution. The idea
5658 is that such stores are unlikely and that they can
5659 be detected prior to instruction retirement at the
5660 end of a particular speculation execution window.
5662 In vulnerable processors, the speculatively forwarded
5663 store can be used in a cache side channel attack, for
5664 example to read memory to which the attacker does not
5665 directly have access (e.g. inside sandboxed code).
5667 This parameter controls whether the Speculative Store
5668 Bypass optimization is used.
5670 On x86 the options are:
5672 on - Unconditionally disable Speculative Store Bypass
5673 off - Unconditionally enable Speculative Store Bypass
5674 auto - Kernel detects whether the CPU model contains an
5675 implementation of Speculative Store Bypass and
5676 picks the most appropriate mitigation. If the
5677 CPU is not vulnerable, "off" is selected. If the
5678 CPU is vulnerable the default mitigation is
5679 architecture and Kconfig dependent. See below.
5680 prctl - Control Speculative Store Bypass per thread
5681 via prctl. Speculative Store Bypass is enabled
5682 for a process by default. The state of the control
5683 is inherited on fork.
5684 seccomp - Same as "prctl" above, but all seccomp threads
5685 will disable SSB unless they explicitly opt out.
5687 Default mitigations:
5690 On powerpc the options are:
5692 on,auto - On Power8 and Power9 insert a store-forwarding
5693 barrier on kernel entry and exit. On Power7
5694 perform a software flush on kernel entry and
5698 Not specifying this option is equivalent to
5699 spec_store_bypass_disable=auto.
5701 spia_io_base= [HW,MTD]
5707 [X86] Enable split lock detection or bus lock detection
5709 When enabled (and if hardware support is present), atomic
5710 instructions that access data across cache line
5711 boundaries will result in an alignment check exception
5712 for split lock detection or a debug exception for
5717 warn - the kernel will emit rate-limited warnings
5718 about applications triggering the #AC
5719 exception or the #DB exception. This mode is
5720 the default on CPUs that support split lock
5721 detection or bus lock detection. Default
5722 behavior is by #AC if both features are
5723 enabled in hardware.
5725 fatal - the kernel will send SIGBUS to applications
5726 that trigger the #AC exception or the #DB
5727 exception. Default behavior is by #AC if
5728 both features are enabled in hardware.
5731 Set system wide rate limit to N bus locks
5732 per second for bus lock detection.
5735 N/A for split lock detection.
5738 If an #AC exception is hit in the kernel or in
5739 firmware (i.e. not while executing in user mode)
5740 the kernel will oops in either "warn" or "fatal"
5743 #DB exception for bus lock is triggered only when
5747 Control the Special Register Buffer Data Sampling
5750 Certain CPUs are vulnerable to an MDS-like
5751 exploit which can leak bits from the random
5754 By default, this issue is mitigated by
5755 microcode. However, the microcode fix can cause
5756 the RDRAND and RDSEED instructions to become
5757 much slower. Among other effects, this will
5758 result in reduced throughput from /dev/urandom.
5760 The microcode mitigation can be disabled with
5761 the following option:
5763 off: Disable mitigation and remove
5764 performance impact to RDRAND and RDSEED
5766 srcutree.big_cpu_lim [KNL]
5767 Specifies the number of CPUs constituting a
5768 large system, such that srcu_struct structures
5769 should immediately allocate an srcu_node array.
5770 This kernel-boot parameter defaults to 128,
5771 but takes effect only when the low-order four
5772 bits of srcutree.convert_to_big is equal to 3
5775 srcutree.convert_to_big [KNL]
5776 Specifies under what conditions an SRCU tree
5777 srcu_struct structure will be converted to big
5778 form, that is, with an rcu_node tree:
5781 1: At init_srcu_struct() time.
5782 2: When rcutorture decides to.
5783 3: Decide at boot time (default).
5784 0x1X: Above plus if high contention.
5786 Either way, the srcu_node tree will be sized based
5787 on the actual runtime number of CPUs (nr_cpu_ids)
5788 instead of the compile-time CONFIG_NR_CPUS.
5790 srcutree.counter_wrap_check [KNL]
5791 Specifies how frequently to check for
5792 grace-period sequence counter wrap for the
5793 srcu_data structure's ->srcu_gp_seq_needed field.
5794 The greater the number of bits set in this kernel
5795 parameter, the less frequently counter wrap will
5796 be checked for. Note that the bottom two bits
5799 srcutree.exp_holdoff [KNL]
5800 Specifies how many nanoseconds must elapse
5801 since the end of the last SRCU grace period for
5802 a given srcu_struct until the next normal SRCU
5803 grace period will be considered for automatic
5804 expediting. Set to zero to disable automatic
5807 srcutree.srcu_max_nodelay [KNL]
5808 Specifies the number of no-delay instances
5809 per jiffy for which the SRCU grace period
5810 worker thread will be rescheduled with zero
5811 delay. Beyond this limit, worker thread will
5812 be rescheduled with a sleep delay of one jiffy.
5814 srcutree.srcu_max_nodelay_phase [KNL]
5815 Specifies the per-grace-period phase, number of
5816 non-sleeping polls of readers. Beyond this limit,
5817 grace period worker thread will be rescheduled
5818 with a sleep delay of one jiffy, between each
5819 rescan of the readers, for a grace period phase.
5821 srcutree.srcu_retry_check_delay [KNL]
5822 Specifies number of microseconds of non-sleeping
5823 delay between each non-sleeping poll of readers.
5825 srcutree.small_contention_lim [KNL]
5826 Specifies the number of update-side contention
5827 events per jiffy will be tolerated before
5828 initiating a conversion of an srcu_struct
5829 structure to big form. Note that the value of
5830 srcutree.convert_to_big must have the 0x10 bit
5831 set for contention-based conversions to occur.
5834 Speculative Store Bypass Disable control
5836 On CPUs that are vulnerable to the Speculative
5837 Store Bypass vulnerability and offer a
5838 firmware based mitigation, this parameter
5839 indicates how the mitigation should be used:
5841 force-on: Unconditionally enable mitigation for
5842 for both kernel and userspace
5843 force-off: Unconditionally disable mitigation for
5844 for both kernel and userspace
5845 kernel: Always enable mitigation in the
5846 kernel, and offer a prctl interface
5847 to allow userspace to register its
5848 interest in being mitigated too.
5850 stack_guard_gap= [MM]
5851 override the default stack gap protection. The value
5852 is in page units and it defines how many pages prior
5853 to (for stacks growing down) resp. after (for stacks
5854 growing up) the main stack are reserved for no other
5855 mapping. Default value is 256 pages.
5857 stack_depot_disable= [KNL]
5858 Setting this to true through kernel command line will
5859 disable the stack depot thereby saving the static memory
5860 consumed by the stack hash table. By default this is set
5864 Enabled the stack tracer on boot up.
5866 stacktrace_filter=[function-list]
5867 [FTRACE] Limit the functions that the stack tracer
5868 will trace at boot up. function-list is a comma-separated
5869 list of functions. This list can be changed at run
5870 time by the stack_trace_filter file in the debugfs
5871 tracing directory. Note, this enables stack tracing
5872 and the stacktrace above is not needed.
5876 Set the STI (builtin display/keyboard on the HP-PARISC
5877 machines) console (graphic card) which should be used
5878 as the initial boot-console.
5879 See also comment in drivers/video/console/sticore.c.
5882 See comment in drivers/video/console/sticore.c.
5885 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5890 Enable or disable strict sigaltstack size checks
5891 against the required signal frame size which
5892 depends on the supported FPU features. This can
5893 be used to filter out binaries which have
5894 not yet been made aware of AT_MINSIGSTKSZ.
5896 sunrpc.min_resvport=
5897 sunrpc.max_resvport=
5899 SunRPC servers often require that client requests
5900 originate from a privileged port (i.e. a port in the
5901 range 0 < portnr < 1024).
5902 An administrator who wishes to reserve some of these
5903 ports for other uses may adjust the range that the
5904 kernel's sunrpc client considers to be privileged
5905 using these two parameters to set the minimum and
5906 maximum port values.
5908 sunrpc.svc_rpc_per_connection_limit=
5910 Limit the number of requests that the server will
5911 process in parallel from a single connection.
5912 The default value is 0 (no limit).
5916 Control how the NFS server code allocates CPUs to
5917 service thread pools. Depending on how many NICs
5918 you have and where their interrupts are bound, this
5919 option will affect which CPUs will do NFS serving.
5920 Note: this parameter cannot be changed while the
5921 NFS server is running.
5923 auto the server chooses an appropriate mode
5924 automatically using heuristics
5925 global a single global pool contains all CPUs
5926 percpu one pool for each CPU
5927 pernode one pool for each NUMA node (equivalent
5928 to global on non-NUMA machines)
5930 sunrpc.tcp_slot_table_entries=
5931 sunrpc.udp_slot_table_entries=
5933 Sets the upper limit on the number of simultaneous
5934 RPC calls that can be sent from the client to a
5935 server. Increasing these values may allow you to
5936 improve throughput, but will also increase the
5937 amount of memory reserved for use by the client.
5939 suspend.pm_test_delay=
5941 Sets the number of seconds to remain in a suspend test
5942 mode before resuming the system (see
5943 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5944 is set. Default value is 5.
5947 Format: { on | off | y | n | 1 | 0 }
5948 This parameter controls use of the Protected
5949 Execution Facility on pSeries.
5953 Enable accounting of swap in memory resource
5954 controller if no parameter or 1 is given or disable
5955 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5957 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5958 Format: { <int> | force | noforce }
5959 <int> -- Number of I/O TLB slabs
5960 force -- force using of bounce buffers even if they
5961 wouldn't be automatically used by the kernel
5962 noforce -- Never use bounce buffers (for debugging)
5967 Set a sysctl parameter, right before loading the init
5968 process, as if the value was written to the respective
5969 /proc/sys/... file. Both '.' and '/' are recognized as
5970 separators. Unrecognized parameters and invalid values
5971 are reported in the kernel log. Sysctls registered
5972 later by a loaded module cannot be set this way.
5973 Example: sysctl.vm.swappiness=40
5975 sysfs.deprecated=0|1 [KNL]
5976 Enable/disable old style sysfs layout for old udev
5977 on older distributions. When this option is enabled
5978 very new udev will not work anymore. When this option
5979 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5980 in older udev will not work anymore.
5981 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5982 the kernel configuration.
5984 sysrq_always_enabled
5986 Ignore sysrq setting - this boot parameter will
5987 neutralize any effect of /proc/sys/kernel/sysrq.
5988 Useful for debugging.
5990 tcpmhash_entries= [KNL,NET]
5991 Set the number of tcp_metrics_hash slots.
5992 Default value is 8192 or 16384 depending on total
5993 ram pages. This is used to specify the TCP metrics
5994 cache size. See Documentation/networking/ip-sysctl.rst
5995 "tcp_no_metrics_save" section for more details.
5999 test_suspend= [SUSPEND]
6000 Format: { "mem" | "standby" | "freeze" }[,N]
6001 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6002 standby suspend) or "freeze" (for suspend type freeze)
6003 as the system sleep state during system startup with
6004 the optional capability to repeat N number of times.
6005 The system is woken from this state using a
6006 wakeup-capable RTC alarm.
6008 thash_entries= [KNL,NET]
6009 Set number of hash buckets for TCP connection
6011 thermal.act= [HW,ACPI]
6012 -1: disable all active trip points in all thermal zones
6013 <degrees C>: override all lowest active trip points
6015 thermal.crt= [HW,ACPI]
6016 -1: disable all critical trip points in all thermal zones
6017 <degrees C>: override all critical trip points
6019 thermal.nocrt= [HW,ACPI]
6020 Set to disable actions on ACPI thermal zone
6021 critical and hot trip points.
6023 thermal.off= [HW,ACPI]
6024 1: disable ACPI thermal control
6026 thermal.psv= [HW,ACPI]
6027 -1: disable all passive trip points
6028 <degrees C>: override all passive trip points to this
6031 thermal.tzp= [HW,ACPI]
6032 Specify global default ACPI thermal zone polling rate
6033 <deci-seconds>: poll all this frequency
6034 0: no polling (default)
6037 Force threading of all interrupt handlers except those
6038 marked explicitly IRQF_NO_THREAD.
6042 Specify if the kernel should make use of the cpu
6043 topology information if the hardware supports this.
6044 The scheduler will make use of this information and
6045 e.g. base its process migration decisions on it.
6048 topology_updates= [KNL, PPC, NUMA]
6050 Specify if the kernel should ignore (off)
6051 topology updates sent by the hypervisor to this
6054 torture.disable_onoff_at_boot= [KNL]
6055 Prevent the CPU-hotplug component of torturing
6056 until after init has spawned.
6058 torture.ftrace_dump_at_shutdown= [KNL]
6059 Dump the ftrace buffer at torture-test shutdown,
6060 even if there were no errors. This can be a
6061 very costly operation when many torture tests
6062 are running concurrently, especially on systems
6063 with rotating-rust storage.
6065 torture.verbose_sleep_frequency= [KNL]
6066 Specifies how many verbose printk()s should be
6067 emitted between each sleep. The default of zero
6068 disables verbose-printk() sleeping.
6070 torture.verbose_sleep_duration= [KNL]
6071 Duration of each verbose-printk() sleep in jiffies.
6075 tpm_suspend_pcr=[HW,TPM]
6076 Format: integer pcr id
6077 Specify that at suspend time, the tpm driver
6078 should extend the specified pcr with zeros,
6079 as a workaround for some chips which fail to
6080 flush the last written pcr on TPM_SaveState.
6081 This will guarantee that all the other pcrs
6085 Have the tracepoints sent to printk as well as the
6086 tracing ring buffer. This is useful for early boot up
6087 where the system hangs or reboots and does not give the
6088 option for reading the tracing buffer or performing a
6089 ftrace_dump_on_oops.
6091 To turn off having tracepoints sent to printk,
6092 echo 0 > /proc/sys/kernel/tracepoint_printk
6093 Note, echoing 1 into this file without the
6094 tracepoint_printk kernel cmdline option has no effect.
6096 The tp_printk_stop_on_boot (see below) can also be used
6097 to stop the printing of events to console at
6102 Having tracepoints sent to printk() and activating high
6103 frequency tracepoints such as irq or sched, can cause
6104 the system to live lock.
6106 tp_printk_stop_on_boot [FTRACE]
6107 When tp_printk (above) is set, it can cause a lot of noise
6108 on the console. It may be useful to only include the
6109 printing of events during boot up, as user space may
6110 make the system inoperable.
6112 This command line option will stop the printing of events
6113 to console at the late_initcall_sync() time frame.
6115 trace_buf_size=nn[KMG]
6116 [FTRACE] will set tracing buffer size on each cpu.
6118 trace_clock= [FTRACE] Set the clock used for tracing events
6120 local - Use the per CPU time stamp counter
6121 (converted into nanoseconds). Fast, but
6122 depending on the architecture, may not be
6123 in sync between CPUs.
6124 global - Event time stamps are synchronize across
6125 CPUs. May be slower than the local clock,
6126 but better for some race conditions.
6127 counter - Simple counting of events (1, 2, ..)
6128 note, some counts may be skipped due to the
6129 infrastructure grabbing the clock more than
6131 uptime - Use jiffies as the time stamp.
6132 perf - Use the same clock that perf uses.
6133 mono - Use ktime_get_mono_fast_ns() for time stamps.
6134 mono_raw - Use ktime_get_raw_fast_ns() for time
6136 boot - Use ktime_get_boot_fast_ns() for time stamps.
6137 Architectures may add more clocks. See
6138 Documentation/trace/ftrace.rst for more details.
6140 trace_event=[event-list]
6141 [FTRACE] Set and start specified trace events in order
6142 to facilitate early boot debugging. The event-list is a
6143 comma-separated list of trace events to enable. See
6144 also Documentation/trace/events.rst
6146 trace_options=[option-list]
6147 [FTRACE] Enable or disable tracer options at boot.
6148 The option-list is a comma delimited list of options
6149 that can be enabled or disabled just as if you were
6150 to echo the option name into
6152 /sys/kernel/debug/tracing/trace_options
6154 For example, to enable stacktrace option (to dump the
6155 stack trace of each event), add to the command line:
6157 trace_options=stacktrace
6159 See also Documentation/trace/ftrace.rst "trace options"
6163 [FTRACE] enable this option to disable tracing when a
6164 warning is hit. This turns off "tracing_on". Tracing can
6165 be enabled again by echoing '1' into the "tracing_on"
6166 file located in /sys/kernel/debug/tracing/
6168 This option is useful, as it disables the trace before
6169 the WARNING dump is called, which prevents the trace to
6170 be filled with content caused by the warning output.
6172 This option can also be set at run time via the sysctl
6173 option: kernel/traceoff_on_warning
6175 transparent_hugepage=
6177 Format: [always|madvise|never]
6178 Can be used to control the default behavior of the system
6179 with respect to transparent hugepages.
6180 See Documentation/admin-guide/mm/transhuge.rst
6183 trusted.source= [KEYS]
6185 This parameter identifies the trust source as a backend
6186 for trusted keys implementation. Supported trust
6191 If not specified then it defaults to iterating through
6192 the trust source list starting with TPM and assigns the
6193 first trust source as a backend which is initialized
6194 successfully during iteration.
6198 The RNG used to generate key material for trusted keys.
6201 - the same value as trusted.source: "tpm" or "tee"
6203 If not specified, "default" is used. In this case,
6204 the RNG's choice is left to each individual trust source.
6206 tsc= Disable clocksource stability checks for TSC.
6208 [x86] reliable: mark tsc clocksource as reliable, this
6209 disables clocksource verification at runtime, as well
6210 as the stability checks done at bootup. Used to enable
6211 high-resolution timer mode on older hardware, and in
6212 virtualized environment.
6213 [x86] noirqtime: Do not use TSC to do irq accounting.
6214 Used to run time disable IRQ_TIME_ACCOUNTING on any
6215 platforms where RDTSC is slow and this accounting
6217 [x86] unstable: mark the TSC clocksource as unstable, this
6218 marks the TSC unconditionally unstable at bootup and
6219 avoids any further wobbles once the TSC watchdog notices.
6220 [x86] nowatchdog: disable clocksource watchdog. Used
6221 in situations with strict latency requirements (where
6222 interruptions from clocksource watchdog are not
6225 tsc_early_khz= [X86] Skip early TSC calibration and use the given
6226 value instead. Useful when the early TSC frequency discovery
6227 procedure is not reliable, such as on overclocked systems
6228 with CPUID.16h support and partial CPUID.15h support.
6229 Format: <unsigned int>
6231 tsx= [X86] Control Transactional Synchronization
6232 Extensions (TSX) feature in Intel processors that
6233 support TSX control.
6235 This parameter controls the TSX feature. The options are:
6237 on - Enable TSX on the system. Although there are
6238 mitigations for all known security vulnerabilities,
6239 TSX has been known to be an accelerator for
6240 several previous speculation-related CVEs, and
6241 so there may be unknown security risks associated
6242 with leaving it enabled.
6244 off - Disable TSX on the system. (Note that this
6245 option takes effect only on newer CPUs which are
6246 not vulnerable to MDS, i.e., have
6247 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6248 the new IA32_TSX_CTRL MSR through a microcode
6249 update. This new MSR allows for the reliable
6250 deactivation of the TSX functionality.)
6252 auto - Disable TSX if X86_BUG_TAA is present,
6253 otherwise enable TSX on the system.
6255 Not specifying this option is equivalent to tsx=off.
6257 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6260 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
6261 Abort (TAA) vulnerability.
6263 Similar to Micro-architectural Data Sampling (MDS)
6264 certain CPUs that support Transactional
6265 Synchronization Extensions (TSX) are vulnerable to an
6266 exploit against CPU internal buffers which can forward
6267 information to a disclosure gadget under certain
6270 In vulnerable processors, the speculatively forwarded
6271 data can be used in a cache side channel attack, to
6272 access data to which the attacker does not have direct
6275 This parameter controls the TAA mitigation. The
6278 full - Enable TAA mitigation on vulnerable CPUs
6281 full,nosmt - Enable TAA mitigation and disable SMT on
6282 vulnerable CPUs. If TSX is disabled, SMT
6283 is not disabled because CPU is not
6284 vulnerable to cross-thread TAA attacks.
6285 off - Unconditionally disable TAA mitigation
6287 On MDS-affected machines, tsx_async_abort=off can be
6288 prevented by an active MDS mitigation as both vulnerabilities
6289 are mitigated with the same mechanism so in order to disable
6290 this mitigation, you need to specify mds=off too.
6292 Not specifying this option is equivalent to
6293 tsx_async_abort=full. On CPUs which are MDS affected
6294 and deploy MDS mitigation, TAA mitigation is not
6295 required and doesn't provide any additional
6299 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6301 turbografx.map[2|3]= [HW,JOY]
6302 TurboGraFX parallel port interface
6304 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6305 See also Documentation/input/devices/joystick-parport.rst
6307 udbg-immortal [PPC] When debugging early kernel crashes that
6308 happen after console_init() and before a proper
6309 console driver takes over, this boot options might
6310 help "seeing" what's going on.
6312 uhash_entries= [KNL,NET]
6313 Set number of hash buckets for UDP/UDP-Lite connections
6316 [USB] Ignore overcurrent events (default N).
6317 Some badly-designed motherboards generate lots of
6318 bogus events, for ports that aren't wired to
6319 anything. Set this parameter to avoid log spamming.
6320 Note that genuine overcurrent events won't be
6324 [X86] Cause panic on unknown NMI.
6326 usbcore.authorized_default=
6327 [USB] Default USB device authorization:
6328 (default -1 = authorized except for wireless USB,
6329 0 = not authorized, 1 = authorized, 2 = authorized
6330 if device connected to internal port)
6332 usbcore.autosuspend=
6333 [USB] The autosuspend time delay (in seconds) used
6334 for newly-detected USB devices (default 2). This
6335 is the time required before an idle device will be
6336 autosuspended. Devices for which the delay is set
6337 to a negative value won't be autosuspended at all.
6339 usbcore.usbfs_snoop=
6340 [USB] Set to log all usbfs traffic (default 0 = off).
6342 usbcore.usbfs_snoop_max=
6343 [USB] Maximum number of bytes to snoop in each URB
6346 usbcore.blinkenlights=
6347 [USB] Set to cycle leds on hubs (default 0 = off).
6349 usbcore.old_scheme_first=
6350 [USB] Start with the old device initialization
6351 scheme (default 0 = off).
6353 usbcore.usbfs_memory_mb=
6354 [USB] Memory limit (in MB) for buffers allocated by
6355 usbfs (default = 16, 0 = max = 2047).
6357 usbcore.use_both_schemes=
6358 [USB] Try the other device initialization scheme
6359 if the first one fails (default 1 = enabled).
6361 usbcore.initial_descriptor_timeout=
6362 [USB] Specifies timeout for the initial 64-byte
6363 USB_REQ_GET_DESCRIPTOR request in milliseconds
6364 (default 5000 = 5.0 seconds).
6366 usbcore.nousb [USB] Disable the USB subsystem
6369 [USB] A list of quirk entries to augment the built-in
6370 usb core quirk list. List entries are separated by
6371 commas. Each entry has the form
6372 VendorID:ProductID:Flags. The IDs are 4-digit hex
6373 numbers and Flags is a set of letters. Each letter
6374 will change the built-in quirk; setting it if it is
6375 clear and clearing it if it is set. The letters have
6376 the following meanings:
6377 a = USB_QUIRK_STRING_FETCH_255 (string
6378 descriptors must not be fetched using
6380 b = USB_QUIRK_RESET_RESUME (device can't resume
6381 correctly so reset it instead);
6382 c = USB_QUIRK_NO_SET_INTF (device can't handle
6383 Set-Interface requests);
6384 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6385 handle its Configuration or Interface
6387 e = USB_QUIRK_RESET (device can't be reset
6388 (e.g morph devices), don't use reset);
6389 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6390 more interface descriptions than the
6391 bNumInterfaces count, and can't handle
6392 talking to these interfaces);
6393 g = USB_QUIRK_DELAY_INIT (device needs a pause
6394 during initialization, after we read
6395 the device descriptor);
6396 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6397 high speed and super speed interrupt
6398 endpoints, the USB 2.0 and USB 3.0 spec
6399 require the interval in microframes (1
6400 microframe = 125 microseconds) to be
6401 calculated as interval = 2 ^
6403 Devices with this quirk report their
6404 bInterval as the result of this
6405 calculation instead of the exponent
6406 variable used in the calculation);
6407 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6408 handle device_qualifier descriptor
6410 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6411 generates spurious wakeup, ignore
6412 remote wakeup capability);
6413 k = USB_QUIRK_NO_LPM (device can't handle Link
6415 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6416 (Device reports its bInterval as linear
6417 frames instead of the USB 2.0
6419 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6420 to be disconnected before suspend to
6421 prevent spurious wakeup);
6422 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6423 pause after every control message);
6424 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6425 delay after resetting its port);
6426 Example: quirks=0781:5580:bk,0a5c:5834:gij
6429 [USBHID] The interval which mice are to be polled at.
6432 [USBHID] The interval which joysticks are to be polled at.
6435 [USBHID] The interval which keyboards are to be polled at.
6437 usb-storage.delay_use=
6438 [UMS] The delay in seconds before a new device is
6439 scanned for Logical Units (default 1).
6442 [UMS] A list of quirks entries to supplement or
6443 override the built-in unusual_devs list. List
6444 entries are separated by commas. Each entry has
6445 the form VID:PID:Flags where VID and PID are Vendor
6446 and Product ID values (4-digit hex numbers) and
6447 Flags is a set of characters, each corresponding
6448 to a common usb-storage quirk flag as follows:
6449 a = SANE_SENSE (collect more than 18 bytes
6450 of sense data, not on uas);
6451 b = BAD_SENSE (don't collect more than 18
6452 bytes of sense data, not on uas);
6453 c = FIX_CAPACITY (decrease the reported
6454 device capacity by one sector);
6455 d = NO_READ_DISC_INFO (don't use
6456 READ_DISC_INFO command, not on uas);
6457 e = NO_READ_CAPACITY_16 (don't use
6458 READ_CAPACITY_16 command);
6459 f = NO_REPORT_OPCODES (don't use report opcodes
6461 g = MAX_SECTORS_240 (don't transfer more than
6462 240 sectors at a time, uas only);
6463 h = CAPACITY_HEURISTICS (decrease the
6464 reported device capacity by one
6465 sector if the number is odd);
6466 i = IGNORE_DEVICE (don't bind to this
6468 j = NO_REPORT_LUNS (don't use report luns
6470 k = NO_SAME (do not use WRITE_SAME, uas only)
6471 l = NOT_LOCKABLE (don't try to lock and
6472 unlock ejectable media, not on uas);
6473 m = MAX_SECTORS_64 (don't transfer more
6474 than 64 sectors = 32 KB at a time,
6476 n = INITIAL_READ10 (force a retry of the
6477 initial READ(10) command, not on uas);
6478 o = CAPACITY_OK (accept the capacity
6479 reported by the device, not on uas);
6480 p = WRITE_CACHE (the device cache is ON
6481 by default, not on uas);
6482 r = IGNORE_RESIDUE (the device reports
6483 bogus residue values, not on uas);
6484 s = SINGLE_LUN (the device has only one
6486 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6487 commands, uas only);
6488 u = IGNORE_UAS (don't bind to the uas driver);
6489 w = NO_WP_DETECT (don't test whether the
6490 medium is write-protected).
6491 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6492 even if the device claims no cache,
6494 Example: quirks=0419:aaf5:rl,0421:0433:rc
6496 user_debug= [KNL,ARM]
6498 See arch/arm/Kconfig.debug help text.
6499 1 - undefined instruction events
6501 4 - invalid data aborts
6504 Example: user_debug=31
6507 [X86] Flags controlling user PTE allocations.
6509 nohigh = do not allocate PTE pages in
6510 HIGHMEM regardless of setting
6513 vdso= [X86,SH,SPARC]
6514 On X86_32, this is an alias for vdso32=. Otherwise:
6516 vdso=1: enable VDSO (the default)
6517 vdso=0: disable VDSO mapping
6519 vdso32= [X86] Control the 32-bit vDSO
6520 vdso32=1: enable 32-bit VDSO
6521 vdso32=0 or vdso32=2: disable 32-bit VDSO
6523 See the help text for CONFIG_COMPAT_VDSO for more
6524 details. If CONFIG_COMPAT_VDSO is set, the default is
6525 vdso32=0; otherwise, the default is vdso32=1.
6527 For compatibility with older kernels, vdso32=2 is an
6530 Try vdso32=0 if you encounter an error that says:
6531 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6534 vector=percpu: enable percpu vector domain
6536 video= [FB] Frame buffer configuration
6537 See Documentation/fb/modedb.rst.
6539 video.brightness_switch_enabled= [ACPI]
6541 If set to 1, on receiving an ACPI notify event
6542 generated by hotkey, video driver will adjust brightness
6543 level and then send out the event to user space through
6544 the allocated input device. If set to 0, video driver
6545 will only send out the event without touching backlight
6550 [VMMIO] Memory mapped virtio (platform) device.
6552 <size>@<baseaddr>:<irq>[:<id>]
6554 <size> := size (can use standard suffixes
6556 <baseaddr> := physical base address
6557 <irq> := interrupt number (as passed to
6559 <id> := (optional) platform device id
6561 virtio_mmio.device=1K@0x100b0000:48:7
6563 Can be used multiple times for multiple devices.
6565 vga= [BOOT,X86-32] Select a particular video mode
6566 See Documentation/x86/boot.rst and
6567 Documentation/admin-guide/svga.rst.
6568 Use vga=ask for menu.
6569 This is actually a boot loader parameter; the value is
6570 passed to the kernel using a special protocol.
6572 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6573 May slow down system boot speed, especially when
6574 enabled on systems with a large amount of memory.
6575 All options are enabled by default, and this
6576 interface is meant to allow for selectively
6577 enabling or disabling specific virtual memory
6580 Available options are:
6581 P Enable page structure init time poisoning
6582 - Disable all of the above options
6584 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6585 size of <nn>. This can be used to increase the
6586 minimum size (128MB on x86). It can also be used to
6587 decrease the size and leave more room for directly
6590 vmcp_cma=nn[MG] [KNL,S390]
6591 Sets the memory size reserved for contiguous memory
6592 allocations for the vmcp device driver.
6594 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6597 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6600 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6604 Controls the behavior of vsyscalls (i.e. calls to
6605 fixed addresses of 0xffffffffff600x00 from legacy
6606 code). Most statically-linked binaries and older
6607 versions of glibc use these calls. Because these
6608 functions are at fixed addresses, they make nice
6609 targets for exploits that can control RIP.
6611 emulate [default] Vsyscalls turn into traps and are
6612 emulated reasonably safely. The vsyscall
6615 xonly Vsyscalls turn into traps and are
6616 emulated reasonably safely. The vsyscall
6617 page is not readable.
6619 none Vsyscalls don't work at all. This makes
6620 them quite hard to use for exploits but
6621 might break your system.
6623 vt.color= [VT] Default text color.
6624 Format: 0xYX, X = foreground, Y = background.
6625 Default: 0x07 = light gray on black.
6627 vt.cur_default= [VT] Default cursor shape.
6628 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6629 the parameters of the <Esc>[?A;B;Cc escape sequence;
6630 see VGA-softcursor.txt. Default: 2 = underline.
6632 vt.default_blu= [VT]
6633 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6634 Change the default blue palette of the console.
6635 This is a 16-member array composed of values
6638 vt.default_grn= [VT]
6639 Format: <green0>,<green1>,<green2>,...,<green15>
6640 Change the default green palette of the console.
6641 This is a 16-member array composed of values
6644 vt.default_red= [VT]
6645 Format: <red0>,<red1>,<red2>,...,<red15>
6646 Change the default red palette of the console.
6647 This is a 16-member array composed of values
6653 Set system-wide default UTF-8 mode for all tty's.
6654 Default is 1, i.e. UTF-8 mode is enabled for all
6655 newly opened terminals.
6657 vt.global_cursor_default=
6660 Set system-wide default for whether a cursor
6661 is shown on new VTs. Default is -1,
6662 i.e. cursors will be created by default unless
6663 overridden by individual drivers. 0 will hide
6664 cursors, 1 will display them.
6666 vt.italic= [VT] Default color for italic text; 0-15.
6669 vt.underline= [VT] Default color for underlined text; 0-15.
6672 watchdog timers [HW,WDT] For information on watchdog timers,
6673 see Documentation/watchdog/watchdog-parameters.rst
6674 or other driver-specific files in the
6675 Documentation/watchdog/ directory.
6679 Set the hard lockup detector stall duration
6680 threshold in seconds. The soft lockup detector
6681 threshold is set to twice the value. A value of 0
6682 disables both lockup detectors. Default is 10
6685 workqueue.watchdog_thresh=
6686 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6687 warn stall conditions and dump internal state to
6688 help debugging. 0 disables workqueue stall
6689 detection; otherwise, it's the stall threshold
6690 duration in seconds. The default value is 30 and
6691 it can be updated at runtime by writing to the
6692 corresponding sysfs file.
6694 workqueue.disable_numa
6695 By default, all work items queued to unbound
6696 workqueues are affine to the NUMA nodes they're
6697 issued on, which results in better behavior in
6698 general. If NUMA affinity needs to be disabled for
6699 whatever reason, this option can be used. Note
6700 that this also can be controlled per-workqueue for
6701 workqueues visible under /sys/bus/workqueue/.
6703 workqueue.power_efficient
6704 Per-cpu workqueues are generally preferred because
6705 they show better performance thanks to cache
6706 locality; unfortunately, per-cpu workqueues tend to
6707 be more power hungry than unbound workqueues.
6709 Enabling this makes the per-cpu workqueues which
6710 were observed to contribute significantly to power
6711 consumption unbound, leading to measurably lower
6712 power usage at the cost of small performance
6715 The default value of this parameter is determined by
6716 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6718 workqueue.debug_force_rr_cpu
6719 Workqueue used to implicitly guarantee that work
6720 items queued without explicit CPU specified are put
6721 on the local CPU. This guarantee is no longer true
6722 and while local CPU is still preferred work items
6723 may be put on foreign CPUs. This debug option
6724 forces round-robin CPU selection to flush out
6725 usages which depend on the now broken guarantee.
6726 When enabled, memory and cache locality will be
6729 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6730 default x2apic cluster mode on platforms
6733 xen_512gb_limit [KNL,X86-64,XEN]
6734 Restricts the kernel running paravirtualized under Xen
6735 to use only up to 512 GB of RAM. The reason to do so is
6736 crash analysis tools and Xen tools for doing domain
6737 save/restore/migration must be enabled to handle larger
6740 xen_emul_unplug= [HW,X86,XEN]
6741 Unplug Xen emulated devices
6742 Format: [unplug0,][unplug1]
6743 ide-disks -- unplug primary master IDE devices
6744 aux-ide-disks -- unplug non-primary-master IDE devices
6745 nics -- unplug network devices
6746 all -- unplug all emulated devices (NICs and IDE disks)
6747 unnecessary -- unplugging emulated devices is
6748 unnecessary even if the host did not respond to
6750 never -- do not unplug even if version check succeeds
6752 xen_legacy_crash [X86,XEN]
6753 Crash from Xen panic notifier, without executing late
6754 panic() code such as dumping handler.
6756 xen_nopvspin [X86,XEN]
6757 Disables the qspinlock slowpath using Xen PV optimizations.
6758 This parameter is obsoleted by "nopvspin" parameter, which
6759 has equivalent effect for XEN platform.
6762 Disables the PV optimizations forcing the HVM guest to
6763 run as generic HVM guest with no PV drivers.
6764 This option is obsoleted by the "nopv" option, which
6765 has equivalent effect for XEN platform.
6767 xen_no_vector_callback
6768 [KNL,X86,XEN] Disable the vector callback for Xen
6769 event channel interrupts.
6771 xen_scrub_pages= [XEN]
6772 Boolean option to control scrubbing pages before giving them back
6773 to Xen, for use by other domains. Can be also changed at runtime
6774 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6775 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6777 xen_timer_slop= [X86-64,XEN]
6778 Set the timer slop (in nanoseconds) for the virtual Xen
6779 timers (default is 100000). This adjusts the minimum
6780 delta of virtualized Xen timers, where lower values
6781 improve timer resolution at the expense of processing
6782 more timer interrupts.
6784 xen.balloon_boot_timeout= [XEN]
6785 The time (in seconds) to wait before giving up to boot
6786 in case initial ballooning fails to free enough memory.
6787 Applies only when running as HVM or PVH guest and
6788 started with less memory configured than allowed at
6789 max. Default is 180.
6791 xen.event_eoi_delay= [XEN]
6792 How long to delay EOI handling in case of event
6793 storms (jiffies). Default is 10.
6795 xen.event_loop_timeout= [XEN]
6796 After which time (jiffies) the event handling loop
6797 should start to delay EOI handling. Default is 2.
6799 xen.fifo_events= [XEN]
6800 Boolean parameter to disable using fifo event handling
6801 even if available. Normally fifo event handling is
6802 preferred over the 2-level event handling, as it is
6803 fairer and the number of possible event channels is
6804 much higher. Default is on (use fifo events).
6806 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6807 Disables the PV optimizations forcing the guest to run
6808 as generic guest with no PV drivers. Currently support
6809 XEN HVM, KVM, HYPER_V and VMWARE guest.
6811 nopvspin [X86,XEN,KVM]
6812 Disables the qspinlock slow path using PV optimizations
6813 which allow the hypervisor to 'idle' the guest on lock
6816 xirc2ps_cs= [NET,PCMCIA]
6818 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6821 By default on POWER9 and above, the kernel will
6822 natively use the XIVE interrupt controller. This option
6823 allows the fallback firmware mode to be used:
6825 off Fallback to firmware control of XIVE interrupt
6826 controller on both pseries and powernv
6827 platforms. Only useful on POWER9 and above.
6829 xive.store-eoi=off [PPC]
6830 By default on POWER10 and above, the kernel will use
6831 stores for EOI handling when the XIVE interrupt mode
6832 is active. This option allows the XIVE driver to use
6833 loads instead, as on POWER9.
6835 xhci-hcd.quirks [USB,KNL]
6836 A hex value specifying bitmask with supplemental xhci
6837 host controller quirks. Meaning of each bit can be
6838 consulted in header drivers/usb/host/xhci.h.
6841 Format: { early | on | rw | ro | off }
6842 Controls if xmon debugger is enabled. Default is off.
6843 Passing only "xmon" is equivalent to "xmon=early".
6844 early Call xmon as early as possible on boot; xmon
6845 debugger is called from setup_arch().
6846 on xmon debugger hooks will be installed so xmon
6847 is only called on a kernel crash. Default mode,
6848 i.e. either "ro" or "rw" mode, is controlled
6849 with CONFIG_XMON_DEFAULT_RO_MODE.
6850 rw xmon debugger hooks will be installed so xmon
6851 is called only on a kernel crash, mode is write,
6852 meaning SPR registers, memory and, other data
6853 can be written using xmon commands.
6854 ro same as "rw" option above but SPR registers,
6855 memory, and other data can't be written using
6857 off xmon is disabled.
git.samba.org / sfrench / cifs-2.6.git / blob