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_nohwsig,
229 old_ordering, nonvs, sci_force_enable, nobl }
230 See Documentation/power/video.rst for information on
232 s3_beep is for debugging; it makes the PC's speaker beep
233 as soon as the kernel's real-mode entry point is called.
234 s4_nohwsig prevents ACPI hardware signature from being
235 used during resume from hibernation.
236 old_ordering causes the ACPI 1.0 ordering of the _PTS
237 control method, with respect to putting devices into
238 low power states, to be enforced (the ACPI 2.0 ordering
239 of _PTS is used by default).
240 nonvs prevents the kernel from saving/restoring the
241 ACPI NVS memory during suspend/hibernation and resume.
242 sci_force_enable causes the kernel to set SCI_EN directly
243 on resume from S1/S3 (which is against the ACPI spec,
244 but some broken systems don't work without it).
245 nobl causes the internal blacklist of systems known to
246 behave incorrectly in some ways with respect to system
247 suspend and resume to be ignored (use wisely).
249 acpi_use_timer_override [HW,ACPI]
250 Use timer override. For some broken Nvidia NF5 boards
251 that require a timer override, but don't have HPET
253 add_efi_memmap [EFI; X86] Include EFI memory map in
254 kernel's map of available physical RAM.
257 { off | try_unsupported }
258 off: disable AGP support
259 try_unsupported: try to drive unsupported chipsets
260 (may crash computer or cause data corruption)
263 See Documentation/sound/alsa-configuration.rst
266 Allow the default userspace alignment fault handler
267 behaviour to be specified. Bit 0 enables warnings,
268 bit 1 enables fixups, and bit 2 sends a segfault.
270 align_va_addr= [X86-64]
271 Align virtual addresses by clearing slice [14:12] when
272 allocating a VMA at process creation time. This option
273 gives you up to 3% performance improvement on AMD F15h
274 machines (where it is enabled by default) for a
275 CPU-intensive style benchmark, and it can vary highly in
276 a microbenchmark depending on workload and compiler.
278 32: only for 32-bit processes
279 64: only for 64-bit processes
280 on: enable for both 32- and 64-bit processes
281 off: disable for both 32- and 64-bit processes
283 alloc_snapshot [FTRACE]
284 Allocate the ftrace snapshot buffer on boot up when the
285 main buffer is allocated. This is handy if debugging
286 and you need to use tracing_snapshot() on boot up, and
287 do not want to use tracing_snapshot_alloc() as it needs
288 to be done where GFP_KERNEL allocations are allowed.
290 allow_mismatched_32bit_el0 [ARM64]
291 Allow execve() of 32-bit applications and setting of the
292 PER_LINUX32 personality on systems where only a strict
293 subset of the CPUs support 32-bit EL0. When this
294 parameter is present, the set of CPUs supporting 32-bit
295 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
296 and hot-unplug operations may be restricted.
298 See Documentation/arm64/asymmetric-32bit.rst for more
301 amd_iommu= [HW,X86-64]
302 Pass parameters to the AMD IOMMU driver in the system.
304 fullflush - Deprecated, equivalent to iommu.strict=1
305 off - do not initialize any AMD IOMMU found in
307 force_isolation - Force device isolation for all
308 devices. The IOMMU driver is not
309 allowed anymore to lift isolation
310 requirements as needed. This option
311 does not override iommu=pt
312 force_enable - Force enable the IOMMU on platforms known
313 to be buggy with IOMMU enabled. Use this
316 amd_iommu_dump= [HW,X86-64]
317 Enable AMD IOMMU driver option to dump the ACPI table
318 for AMD IOMMU. With this option enabled, AMD IOMMU
319 driver will print ACPI tables for AMD IOMMU during
320 IOMMU initialization.
322 amd_iommu_intr= [HW,X86-64]
323 Specifies one of the following AMD IOMMU interrupt
325 legacy - Use legacy interrupt remapping mode.
326 vapic - Use virtual APIC mode, which allows IOMMU
327 to inject interrupts directly into guest.
328 This mode requires kvm-amd.avic=1.
329 (Default when IOMMU HW support is present.)
331 amijoy.map= [HW,JOY] Amiga joystick support
332 Map of devices attached to JOY0DAT and JOY1DAT
334 See also Documentation/input/joydev/joystick.rst
336 analog.map= [HW,JOY] Analog joystick and gamepad support
337 Specifies type or capabilities of an analog joystick
338 connected to one of 16 gameports
339 Format: <type1>,<type2>,..<type16>
342 Power management functions (SPARCstation-4/5 + deriv.)
344 Disable APC CPU standby support. SPARCstation-Fox does
345 not play well with APC CPU idle - disable it if you have
346 APC and your system crashes randomly.
348 apic= [APIC,X86] Advanced Programmable Interrupt Controller
349 Change the output verbosity while booting
350 Format: { quiet (default) | verbose | debug }
351 Change the amount of debugging information output
352 when initialising the APIC and IO-APIC components.
353 For X86-32, this can also be used to specify an APIC
355 Format: apic=driver_name
356 Examples: apic=bigsmp
358 apic_extnmi= [APIC,X86] External NMI delivery setting
359 Format: { bsp (default) | all | none }
360 bsp: External NMI is delivered only to CPU 0
361 all: External NMIs are broadcast to all CPUs as a
363 none: External NMI is masked for all CPUs. This is
364 useful so that a dump capture kernel won't be
368 See Documentation/networking/ipv6.rst.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
385 arm64.nobti [ARM64] Unconditionally disable Branch Target
386 Identification support
388 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
391 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
396 atarimouse= [HW,MOUSE] Atari Mouse
398 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
399 EzKey and similar keyboards
401 atkbd.reset= [HW] Reset keyboard during initialization
403 atkbd.set= [HW] Select keyboard code set
404 Format: <int> (2 = AT (default), 3 = PS/2)
406 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
409 atkbd.softraw= [HW] Choose between synthetic and real raw mode
410 Format: <bool> (0 = real, 1 = synthetic (default))
412 atkbd.softrepeat= [HW]
413 Use software keyboard repeat
415 audit= [KNL] Enable the audit sub-system
416 Format: { "0" | "1" | "off" | "on" }
417 0 | off - kernel audit is disabled and can not be
418 enabled until the next reboot
419 unset - kernel audit is initialized but disabled and
420 will be fully enabled by the userspace auditd.
421 1 | on - kernel audit is initialized and partially
422 enabled, storing at most audit_backlog_limit
423 messages in RAM until it is fully enabled by the
427 audit_backlog_limit= [KNL] Set the audit queue size limit.
428 Format: <int> (must be >=0)
431 bau= [X86_UV] Enable the BAU on SGI UV. The default
432 behavior is to disable the BAU (i.e. bau=0).
433 Format: { "0" | "1" }
436 unset - Disable the BAU.
438 baycom_epp= [HW,AX25]
441 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
443 See header of drivers/net/hamradio/baycom_par.c.
445 baycom_ser_fdx= [HW,AX25]
446 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
447 Format: <io>,<irq>,<mode>[,<baud>]
448 See header of drivers/net/hamradio/baycom_ser_fdx.c.
450 baycom_ser_hdx= [HW,AX25]
451 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
452 Format: <io>,<irq>,<mode>
453 See header of drivers/net/hamradio/baycom_ser_hdx.c.
455 blkdevparts= Manual partition parsing of block device(s) for
456 embedded devices based on command line input.
457 See Documentation/block/cmdline-partition.rst
459 boot_delay= Milliseconds to delay each printk during boot.
460 Values larger than 10 seconds (10000) are changed to
465 Extended command line options can be added to an initrd
466 and this will cause the kernel to look for it.
468 See Documentation/admin-guide/bootconfig.rst
471 Disable BERT OS support on buggy BIOSes.
473 bgrt_disable [ACPI][X86]
474 Disable BGRT to avoid flickering OEM logo.
476 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
477 bttv.radio= Most important insmod options are available as
479 bttv.pll= See Documentation/admin-guide/media/bttv.rst
482 bulk_remove=off [PPC] This parameter disables the use of the pSeries
483 firmware feature for flushing multiple hpte entries
486 c101= [NET] Moxa C101 synchronous serial card
488 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
489 Sometimes CPU hardware bugs make them report the cache
490 size incorrectly. The kernel will attempt work arounds
491 to fix known problems, but for some CPUs it is not
492 possible to determine what the correct size should be.
493 This option provides an override for these situations.
496 [NET] Specifies amount of time (in seconds) that
497 the kernel should wait for a network carrier. By default
498 it waits 120 seconds.
500 ca_keys= [KEYS] This parameter identifies a specific key(s) on
501 the system trusted keyring to be used for certificate
503 format: { id:<keyid> | builtin }
505 cca= [MIPS] Override the kernel pages' cache coherency
506 algorithm. Accepted values range from 0 to 7
507 inclusive. See arch/mips/include/asm/pgtable-bits.h
508 for platform specific values (SB1, Loongson3 and
511 ccw_timeout_log [S390]
512 See Documentation/s390/common_io.rst for details.
514 cgroup_disable= [KNL] Disable a particular controller or optional feature
515 Format: {name of the controller(s) or feature(s) to disable}
516 The effects of cgroup_disable=foo are:
517 - foo isn't auto-mounted if you mount all cgroups in
519 - foo isn't visible as an individually mountable
521 - if foo is an optional feature then the feature is
522 disabled and corresponding cgroup files are not
524 {Currently only "memory" controller deal with this and
525 cut the overhead, others just disable the usage. So
526 only cgroup_disable=memory is actually worthy}
527 Specifying "pressure" disables per-cgroup pressure
528 stall information accounting feature
530 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
531 Format: { { controller | "all" | "named" }
532 [,{ controller | "all" | "named" }...] }
533 Like cgroup_disable, but only applies to cgroup v1;
534 the blacklisted controllers remain available in cgroup2.
535 "all" blacklists all controllers and "named" disables
536 named mounts. Specifying both "all" and "named" disables
539 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
541 nosocket -- Disable socket memory accounting.
542 nokmem -- Disable kernel memory accounting.
544 checkreqprot [SELINUX] Set initial checkreqprot flag value.
545 Format: { "0" | "1" }
546 See security/selinux/Kconfig help text.
547 0 -- check protection applied by kernel (includes
548 any implied execute protection).
549 1 -- check protection requested by application.
550 Default value is set via a kernel config option.
551 Value can be changed at runtime via
552 /sys/fs/selinux/checkreqprot.
553 Setting checkreqprot to 1 is deprecated.
556 See Documentation/s390/common_io.rst for details.
559 Prevents the clock framework from automatically gating
560 clocks that have not been explicitly enabled by a Linux
561 device driver but are enabled in hardware at reset or
562 by the bootloader/firmware. Note that this does not
563 force such clocks to be always-on nor does it reserve
564 those clocks in any way. This parameter is useful for
565 debug and development, but should not be needed on a
566 platform with proper driver support. For more
567 information, see Documentation/driver-api/clk.rst.
569 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
571 Forces specified clocksource (if available) to be used
572 when calculating gettimeofday(). If specified
573 clocksource is not available, it defaults to PIT.
574 Format: { pit | tsc | cyclone | pmtmr }
576 clocksource= Override the default clocksource
578 Override the default clocksource and use the clocksource
579 with the name specified.
580 Some clocksource names to choose from, depending on
582 [all] jiffies (this is the base, fallback clocksource)
584 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
585 pxa_timer,timer3,32k_counter,timer0_1
586 [X86-32] pit,hpet,tsc;
587 scx200_hrt on Geode; cyclone on IBM x440
595 clocksource.arm_arch_timer.evtstrm=
598 Enable/disable the eventstream feature of the ARM
599 architected timer so that code using WFE-based polling
600 loops can be debugged more effectively on production
603 clocksource.max_cswd_read_retries= [KNL]
604 Number of clocksource_watchdog() retries due to
605 external delays before the clock will be marked
606 unstable. Defaults to three retries, that is,
607 four attempts to read the clock under test.
609 clocksource.verify_n_cpus= [KNL]
610 Limit the number of CPUs checked for clocksources
611 marked with CLOCK_SOURCE_VERIFY_PERCPU that
612 are marked unstable due to excessive skew.
613 A negative value says to check all CPUs, while
614 zero says not to check any. Values larger than
615 nr_cpu_ids are silently truncated to nr_cpu_ids.
616 The actual CPUs are chosen randomly, with
617 no replacement if the same CPU is chosen twice.
619 clocksource-wdtest.holdoff= [KNL]
620 Set the time in seconds that the clocksource
621 watchdog test waits before commencing its tests.
622 Defaults to zero when built as a module and to
623 10 seconds when built into the kernel.
625 clearcpuid=BITNUM[,BITNUM...] [X86]
626 Disable CPUID feature X for the kernel. See
627 arch/x86/include/asm/cpufeatures.h for the valid bit
628 numbers. Note the Linux specific bits are not necessarily
629 stable over kernel options, but the vendor specific
631 Also note that user programs calling CPUID directly
632 or using the feature without checking anything
633 will still see it. This just prevents it from
634 being used by the kernel or shown in /proc/cpuinfo.
635 Also note the kernel might malfunction if you disable
638 cma=nn[MG]@[start[MG][-end[MG]]]
640 Sets the size of kernel global memory area for
641 contiguous memory allocations and optionally the
642 placement constraint by the physical address range of
643 memory allocations. A value of 0 disables CMA
644 altogether. For more information, see
645 kernel/dma/contiguous.c
649 Sets the size of kernel per-numa memory area for
650 contiguous memory allocations. A value of 0 disables
651 per-numa CMA altogether. And If this option is not
652 specificed, the default value is 0.
653 With per-numa CMA enabled, DMA users on node nid will
654 first try to allocate buffer from the pernuma area
655 which is located in node nid, if the allocation fails,
656 they will fallback to the global default memory area.
658 cmo_free_hint= [PPC] Format: { yes | no }
659 Specify whether pages are marked as being inactive
660 when they are freed. This is used in CMO environments
661 to determine OS memory pressure for page stealing by
665 coherent_pool=nn[KMG] [ARM,KNL]
666 Sets the size of memory pool for coherent, atomic dma
667 allocations, by default set to 256K.
669 com20020= [HW,NET] ARCnet - COM20020 chipset
671 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
673 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
677 ARCnet - COM90xx chipset (memory-mapped buffers)
678 Format: <io>[,<irq>[,<memstart>]]
680 condev= [HW,S390] console device
683 console= [KNL] Output console device and options.
685 tty<n> Use the virtual console device <n>.
689 Use the specified serial port. The options are of
690 the form "bbbbpnf", where "bbbb" is the baud rate,
691 "p" is parity ("n", "o", or "e"), "n" is number of
692 bits, and "f" is flow control ("r" for RTS or
693 omit it). Default is "9600n8".
695 See Documentation/admin-guide/serial-console.rst for more
697 Documentation/networking/netconsole.rst for an
700 uart[8250],io,<addr>[,options]
701 uart[8250],mmio,<addr>[,options]
702 uart[8250],mmio16,<addr>[,options]
703 uart[8250],mmio32,<addr>[,options]
704 uart[8250],0x<addr>[,options]
705 Start an early, polled-mode console on the 8250/16550
706 UART at the specified I/O port or MMIO address,
707 switching to the matching ttyS device later.
708 MMIO inter-register address stride is either 8-bit
709 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
710 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
711 to be equivalent to 'mmio'. 'options' are specified in
712 the same format described for ttyS above; if unspecified,
713 the h/w is not re-initialized.
715 hvc<n> Use the hypervisor console device <n>. This is for
716 both Xen and PowerPC hypervisors.
718 If the device connected to the port is not a TTY but a braille
719 device, prepend "brl," before the device type, for instance
721 For now, only VisioBraille is supported.
724 [KNL] Change console messages format
726 By default we print messages on consoles in
727 "[time stamp] text\n" format (time stamp may not be
728 printed, depending on CONFIG_PRINTK_TIME or
729 `printk_time' param).
731 Switch to syslog format: "<%u>[time stamp] text\n"
732 IOW, each message will have a facility and loglevel
733 prefix. The format is similar to one used by syslog()
734 syscall, or to executing "dmesg -S --raw" or to reading
737 consoleblank= [KNL] The console blank (screen saver) timeout in
738 seconds. A value of 0 disables the blank timer.
742 [KNL] Change the default value for
743 /proc/<pid>/coredump_filter.
744 See also Documentation/filesystems/proc.rst.
746 coresight_cpu_debug.enable
749 Enable/disable the CPU sampling based debugging.
750 0: default value, disable debugging
751 1: enable debugging at boot time
753 cpuidle.off=1 [CPU_IDLE]
754 disable the cpuidle sub-system
757 [CPU_IDLE] Name of the cpuidle governor to use.
759 cpufreq.off=1 [CPU_FREQ]
760 disable the cpufreq sub-system
762 cpufreq.default_governor=
763 [CPU_FREQ] Name of the default cpufreq governor or
764 policy to use. This governor must be registered in the
765 kernel before the cpufreq driver probes.
768 [X86] Delay for N microsec between assert and de-assert
769 of APIC INIT to start processors. This delay occurs
770 on every CPU online, such as boot, and resume from suspend.
773 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
775 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
777 crashkernel=size[KMG][@offset[KMG]]
778 [KNL] Using kexec, Linux can switch to a 'crash kernel'
779 upon panic. This parameter reserves the physical
780 memory region [offset, offset + size] for that kernel
781 image. If '@offset' is omitted, then a suitable offset
782 is selected automatically.
783 [KNL, X86-64] Select a region under 4G first, and
784 fall back to reserve region above 4G when '@offset'
785 hasn't been specified.
786 See Documentation/admin-guide/kdump/kdump.rst for further details.
788 crashkernel=range1:size1[,range2:size2,...][@offset]
789 [KNL] Same as above, but depends on the memory
790 in the running system. The syntax of range is
791 start-[end] where start and end are both
792 a memory unit (amount[KMG]). See also
793 Documentation/admin-guide/kdump/kdump.rst for an example.
795 crashkernel=size[KMG],high
796 [KNL, X86-64] range could be above 4G. Allow kernel
797 to allocate physical memory region from top, so could
798 be above 4G if system have more than 4G ram installed.
799 Otherwise memory region will be allocated below 4G, if
801 It will be ignored if crashkernel=X is specified.
802 crashkernel=size[KMG],low
803 [KNL, X86-64] range under 4G. When crashkernel=X,high
804 is passed, kernel could allocate physical memory region
805 above 4G, that cause second kernel crash on system
806 that require some amount of low memory, e.g. swiotlb
807 requires at least 64M+32K low memory, also enough extra
808 low memory is needed to make sure DMA buffers for 32-bit
809 devices won't run out. Kernel would try to allocate at
810 at least 256M below 4G automatically.
811 This one let user to specify own low range under 4G
812 for second kernel instead.
813 0: to disable low allocation.
814 It will be ignored when crashkernel=X,high is not used
815 or memory reserved is below 4G.
818 [KNL] Disable crypto self-tests
823 cs89x0_media= [HW,NET]
824 Format: { rj45 | aui | bnc }
826 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
827 handling. When switched on, additional debug data is
828 printed to the console in case a hanging CPU is
829 detected, and that CPU is pinged again in order to try
830 to resolve the hang situation.
831 0: disable csdlock debugging (default)
832 1: enable basic csdlock debugging (minor impact)
833 ext: enable extended csdlock debugging (more impact,
837 See header of drivers/s390/block/dasd_devmap.c.
839 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
840 (one device per port)
841 Format: <port#>,<type>
842 See also Documentation/input/devices/joystick-parport.rst
844 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
846 Documentation/admin-guide/dynamic-debug-howto.rst for
847 details. Deprecated, see dyndbg.
849 debug [KNL] Enable kernel debugging (events log level).
852 [KNL] Enable printing [hashed] pointers early in the
853 boot sequence. If enabled, we use a weak hash instead
854 of siphash to hash pointers. Use this option if you are
855 seeing instances of '(___ptrval___)') and need to see a
856 value (hashed pointer) instead. Cryptographically
857 insecure, please do not use on production kernels.
860 [KNL] verbose locking self-tests
862 Print debugging info while doing the locking API
864 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
865 (no extra messages), setting it to -1 (all bits set)
866 will print _a_lot_ more information - normally only
867 useful to lockdep developers.
869 debug_objects [KNL] Enable object debugging
872 [KNL] Disable object debugging
874 debug_guardpage_minorder=
875 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
876 parameter allows control of the order of pages that will
877 be intentionally kept free (and hence protected) by the
878 buddy allocator. Bigger value increase the probability
879 of catching random memory corruption, but reduce the
880 amount of memory for normal system use. The maximum
881 possible value is MAX_ORDER/2. Setting this parameter
882 to 1 or 2 should be enough to identify most random
883 memory corruption problems caused by bugs in kernel or
884 driver code when a CPU writes to (or reads from) a
885 random memory location. Note that there exists a class
886 of memory corruptions problems caused by buggy H/W or
887 F/W or by drivers badly programing DMA (basically when
888 memory is written at bus level and the CPU MMU is
889 bypassed) which are not detectable by
890 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
891 tracking down these problems.
894 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
895 enables the feature at boot time. By default, it is
896 disabled and the system will work mostly the same as a
897 kernel built without CONFIG_DEBUG_PAGEALLOC.
898 Note: to get most of debug_pagealloc error reports, it's
899 useful to also enable the page_owner functionality.
900 on: enable the feature
902 debugfs= [KNL] This parameter enables what is exposed to userspace
903 and debugfs internal clients.
904 Format: { on, no-mount, off }
905 on: All functions are enabled.
907 Filesystem is not registered but kernel clients can
908 access APIs and a crashkernel can be used to read
909 its content. There is nothing to mount.
910 off: Filesystem is not registered and clients
911 get a -EPERM as result when trying to register files
912 or directories within debugfs.
913 This is equivalent of the runtime functionality if
914 debugfs was not enabled in the kernel at all.
915 Default value is set in build-time with a kernel configuration.
917 debugpat [X86] Enable PAT debugging
919 decnet.addr= [HW,NET]
920 Format: <area>[,<node>]
921 See also Documentation/networking/decnet.rst.
924 [HW] The size of the default HugeTLB page. This is
925 the size represented by the legacy /proc/ hugepages
926 APIs. In addition, this is the default hugetlb size
927 used for shmget(), mmap() and mounting hugetlbfs
928 filesystems. If not specified, defaults to the
929 architecture's default huge page size. Huge page
930 sizes are architecture dependent. See also
931 Documentation/admin-guide/mm/hugetlbpage.rst.
934 deferred_probe_timeout=
935 [KNL] Debugging option to set a timeout in seconds for
936 deferred probe to give up waiting on dependencies to
937 probe. Only specific dependencies (subsystems or
938 drivers) that have opted in will be ignored. A timeout of 0
939 will timeout at the end of initcalls. This option will also
940 dump out devices still on the deferred probe list after
944 Format: { on | off | def_only | inf_only | always }
945 on: s390 zlib hardware support for compression on
946 level 1 and decompression (default)
947 off: No s390 zlib hardware support
948 def_only: s390 zlib hardware support for deflate
949 only (compression on level 1)
950 inf_only: s390 zlib hardware support for inflate
952 always: Same as 'on' but ignores the selected compression
953 level always using hardware support (used for debugging)
956 Set number of hash buckets for dentry cache.
958 disable_1tb_segments [PPC]
959 Disables the use of 1TB hash page table segments. This
960 causes the kernel to fall back to 256MB segments which
961 can be useful when debugging issues that require an SLB
965 Limits the number of kernel SLB entries, and flushes
966 them frequently to increase the rate of SLB faults
970 See Documentation/networking/ipv6.rst.
973 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
974 hardening is enabled for this boot. Hardened
975 usercopy checking is used to protect the kernel
976 from reading or writing beyond known memory
977 allocation boundaries as a proactive defense
978 against bounds-checking flaws in the kernel's
979 copy_to_user()/copy_from_user() interface.
980 on Perform hardened usercopy checks (default).
981 off Disable hardened usercopy checks.
984 Disable RADIX MMU mode on POWER9
986 radix_hcall_invalidate=on [PPC/PSERIES]
987 Disable RADIX GTSE feature and use hcall for TLB
991 Disable TLBIE instruction. Currently does not work
992 with KVM, with HASH MMU, or with coherent accelerators.
994 disable_cpu_apicid= [X86,APIC,SMP]
996 The number of initial APIC ID for the
997 corresponding CPU to be disabled at boot,
998 mostly used for the kdump 2nd kernel to
999 disable BSP to wake up multiple CPUs without
1000 causing system reset or hang due to sending
1001 INIT from AP to BSP.
1003 disable_ddw [PPC/PSERIES]
1004 Disable Dynamic DMA Window support. Use this
1005 to workaround buggy firmware.
1007 disable_ipv6= [IPV6]
1008 See Documentation/networking/ipv6.rst.
1010 disable_mtrr_cleanup [X86]
1011 The kernel tries to adjust MTRR layout from continuous
1012 to discrete, to make X server driver able to add WB
1013 entry later. This parameter disables that.
1015 disable_mtrr_trim [X86, Intel and AMD only]
1016 By default the kernel will trim any uncacheable
1017 memory out of your available memory pool based on
1018 MTRR settings. This parameter disables that behavior,
1019 possibly causing your machine to run very slowly.
1021 disable_timer_pin_1 [X86]
1022 Disable PIN 1 of APIC timer
1023 Can be useful to work around chipset bugs.
1025 dis_ucode_ldr [X86] Disable the microcode loader.
1027 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1028 this option disables the debugging code at boot.
1030 dma_debug_entries=<number>
1031 This option allows to tune the number of preallocated
1032 entries for DMA-API debugging code. One entry is
1033 required per DMA-API allocation. Use this if the
1034 DMA-API debugging code disables itself because the
1035 architectural default is too low.
1037 dma_debug_driver=<driver_name>
1038 With this option the DMA-API debugging driver
1039 filter feature can be enabled at boot time. Just
1040 pass the driver to filter for as the parameter.
1041 The filter can be disabled or changed to another
1042 driver later using sysfs.
1044 driver_async_probe= [KNL]
1045 List of driver names to be probed asynchronously.
1046 Format: <driver_name1>,<driver_name2>...
1048 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1049 Broken monitors, graphic adapters, KVMs and EDIDless
1050 panels may send no or incorrect EDID data sets.
1051 This parameter allows to specify an EDID data sets
1052 in the /lib/firmware directory that are used instead.
1053 Generic built-in EDID data sets are used, if one of
1054 edid/1024x768.bin, edid/1280x1024.bin,
1055 edid/1680x1050.bin, or edid/1920x1080.bin is given
1056 and no file with the same name exists. Details and
1057 instructions how to build your own EDID data are
1058 available in Documentation/admin-guide/edid.rst. An EDID
1059 data set will only be used for a particular connector,
1060 if its name and a colon are prepended to the EDID
1061 name. Each connector may use a unique EDID data
1062 set by separating the files with a comma. An EDID
1063 data set with no connector name will be used for
1064 any connectors not explicitly specified.
1069 Format: {"off" | "known"}
1070 Control how the dt_cpu_ftrs device-tree binding is
1071 used for CPU feature discovery and setup (if it
1073 off: Do not use it, fall back to legacy cpu table.
1074 known: Do not pass through unknown features to guests
1075 or userspace, only those that the kernel is aware of.
1077 dump_apple_properties [X86]
1078 Dump name and content of EFI device properties on
1079 x86 Macs. Useful for driver authors to determine
1080 what data is available or for reverse-engineering.
1082 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1083 <module>.dyndbg[="val"]
1084 Enable debug messages at boot time. See
1085 Documentation/admin-guide/dynamic-debug-howto.rst
1088 nopku [X86] Disable Memory Protection Keys CPU feature found
1091 <module>.async_probe [KNL]
1092 Enable asynchronous probe on this module.
1094 early_ioremap_debug [KNL]
1095 Enable debug messages in early_ioremap support. This
1096 is useful for tracking down temporary early mappings
1097 which are not unmapped.
1099 earlycon= [KNL] Output early console device and options.
1101 When used with no options, the early console is
1102 determined by stdout-path property in device tree's
1103 chosen node or the ACPI SPCR table if supported by
1106 cdns,<addr>[,options]
1107 Start an early, polled-mode console on a Cadence
1108 (xuartps) serial port at the specified address. Only
1109 supported option is baud rate. If baud rate is not
1110 specified, the serial port must already be setup and
1113 uart[8250],io,<addr>[,options]
1114 uart[8250],mmio,<addr>[,options]
1115 uart[8250],mmio32,<addr>[,options]
1116 uart[8250],mmio32be,<addr>[,options]
1117 uart[8250],0x<addr>[,options]
1118 Start an early, polled-mode console on the 8250/16550
1119 UART at the specified I/O port or MMIO address.
1120 MMIO inter-register address stride is either 8-bit
1121 (mmio) or 32-bit (mmio32 or mmio32be).
1122 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1123 to be equivalent to 'mmio'. 'options' are specified
1124 in the same format described for "console=ttyS<n>"; if
1125 unspecified, the h/w is not initialized.
1129 Start an early, polled-mode console on a pl011 serial
1130 port at the specified address. The pl011 serial port
1131 must already be setup and configured. Options are not
1132 yet supported. If 'mmio32' is specified, then only
1133 the driver will use only 32-bit accessors to read/write
1134 the device registers.
1137 Start an early console on a litex serial port at the
1138 specified address. The serial port must already be
1139 setup and configured. Options are not yet supported.
1142 Start an early, polled-mode console on a meson serial
1143 port at the specified address. The serial port must
1144 already be setup and configured. Options are not yet
1148 Start an early, polled-mode console on an msm serial
1149 port at the specified address. The serial port
1150 must already be setup and configured. Options are not
1153 msm_serial_dm,<addr>
1154 Start an early, polled-mode console on an msm serial
1155 dm port at the specified address. The serial port
1156 must already be setup and configured. Options are not
1160 Start an early, polled-mode console on a serial port
1161 of an Actions Semi SoC, such as S500 or S900, at the
1162 specified address. The serial port must already be
1163 setup and configured. Options are not yet supported.
1166 Start an early, polled-mode console on a serial port
1167 of an RDA Micro SoC, such as RDA8810PL, at the
1168 specified address. The serial port must already be
1169 setup and configured. Options are not yet supported.
1172 Use RISC-V SBI (Supervisor Binary Interface) for early
1175 smh Use ARM semihosting calls for early console.
1183 Use early console provided by serial driver available
1184 on Samsung SoCs, requires selecting proper type and
1185 a correct base address of the selected UART port. The
1186 serial port must already be setup and configured.
1187 Options are not yet supported.
1190 Start an early, polled-mode console on a lantiq serial
1191 (lqasc) port at the specified address. The serial port
1192 must already be setup and configured. Options are not
1197 Use early console provided by Freescale LP UART driver
1198 found on Freescale Vybrid and QorIQ LS1021A processors.
1199 A valid base address must be provided, and the serial
1200 port must already be setup and configured.
1204 Start an early, polled-mode, output-only console on the
1205 Freescale i.MX UART at the specified address. The UART
1206 must already be setup and configured.
1209 Start an early, polled-mode console on the
1210 Armada 3700 serial port at the specified
1211 address. The serial port must already be setup
1212 and configured. Options are not yet supported.
1215 Start an early, polled-mode console on a Qualcomm
1216 Generic Interface (GENI) based serial port at the
1217 specified address. The serial port must already be
1218 setup and configured. Options are not yet supported.
1221 Start an early, unaccelerated console on the EFI
1222 memory mapped framebuffer (if available). On cache
1223 coherent non-x86 systems that use system memory for
1224 the framebuffer, pass the 'ram' option so that it is
1225 mapped with the correct attributes.
1228 Use early console provided by Freescale LINFlexD UART
1229 serial driver for NXP S32V234 SoCs. A valid base
1230 address must be provided, and the serial port must
1231 already be setup and configured.
1233 earlyprintk= [X86,SH,ARM,M68k,S390]
1237 earlyprintk=serial[,ttySn[,baudrate]]
1238 earlyprintk=serial[,0x...[,baudrate]]
1239 earlyprintk=ttySn[,baudrate]
1240 earlyprintk=dbgp[debugController#]
1241 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1242 earlyprintk=xdbc[xhciController#]
1244 earlyprintk is useful when the kernel crashes before
1245 the normal console is initialized. It is not enabled by
1246 default because it has some cosmetic problems.
1248 Append ",keep" to not disable it when the real console
1251 Only one of vga, efi, serial, or usb debug port can
1254 Currently only ttyS0 and ttyS1 may be specified by
1255 name. Other I/O ports may be explicitly specified
1256 on some architectures (x86 and arm at least) by
1257 replacing ttySn with an I/O port address, like this:
1258 earlyprintk=serial,0x1008,115200
1259 You can find the port for a given device in
1260 /proc/tty/driver/serial:
1261 2: uart:ST16650V2 port:00001008 irq:18 ...
1263 Interaction with the standard serial driver is not
1266 The VGA and EFI output is eventually overwritten by
1269 The xen option can only be used in Xen domains.
1271 The sclp output can only be used on s390.
1273 The optional "force" to "pciserial" enables use of a
1274 PCI device even when its classcode is not of the
1277 edac_report= [HW,EDAC] Control how to report EDAC event
1278 Format: {"on" | "off" | "force"}
1279 on: enable EDAC to report H/W event. May be overridden
1280 by other higher priority error reporting module.
1281 off: disable H/W event reporting through EDAC.
1282 force: enforce the use of EDAC to report H/W event.
1285 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1288 This is designed to be used in conjunction with
1289 the boot argument: earlyprintk=vga
1291 This parameter works in place of the kgdboc parameter
1292 but can only be used if the backing tty is available
1293 very early in the boot process. For early debugging
1294 via a serial port see kgdboc_earlycon instead.
1297 Format: {"off" | "on" | "skip[mbr]"}
1300 Format: { "debug", "disable_early_pci_dma",
1301 "nochunk", "noruntime", "nosoftreserve",
1302 "novamap", "no_disable_early_pci_dma" }
1303 debug: enable misc debug output.
1304 disable_early_pci_dma: disable the busmaster bit on all
1305 PCI bridges while in the EFI boot stub.
1306 nochunk: disable reading files in "chunks" in the EFI
1307 boot stub, as chunking can cause problems with some
1308 firmware implementations.
1309 noruntime : disable EFI runtime services support
1310 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1311 attribute may cause the kernel to reserve the
1312 memory range for a memory mapping driver to
1313 claim. Specify efi=nosoftreserve to disable this
1314 reservation and treat the memory by its base type
1315 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1316 novamap: do not call SetVirtualAddressMap().
1317 no_disable_early_pci_dma: Leave the busmaster bit set
1318 on all PCI bridges while in the EFI boot stub
1320 efi_no_storage_paranoia [EFI; X86]
1321 Using this parameter you can use more than 50% of
1322 your efi variable storage. Use this parameter only if
1323 you are really sure that your UEFI does sane gc and
1324 fulfills the spec otherwise your board may brick.
1326 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1327 Add arbitrary attribute to specific memory range by
1328 updating original EFI memory map.
1329 Region of memory which aa attribute is added to is
1332 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1333 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1334 attribute is added to range 0x100000000-0x180000000 and
1335 0x10a0000000-0x1120000000.
1337 If efi_fake_mem=8G@9G:0x40000 is specified, the
1338 EFI_MEMORY_SP(0x40000) attribute is added to
1339 range 0x240000000-0x43fffffff.
1341 Using this parameter you can do debugging of EFI memmap
1342 related features. For example, you can do debugging of
1343 Address Range Mirroring feature even if your box
1344 doesn't support it, or mark specific memory as
1347 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1348 that is to be dynamically loaded by Linux. If there are
1349 multiple variables with the same name but with different
1350 vendor GUIDs, all of them will be loaded. See
1351 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1354 eisa_irq_edge= [PARISC,HW]
1355 See header of drivers/parisc/eisa.c.
1358 See comment before function elanfreq_setup() in
1359 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1361 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1362 Specifies physical address of start of kernel core
1363 image elf header and optionally the size. Generally
1364 kexec loader will pass this option to capture kernel.
1365 See Documentation/admin-guide/kdump/kdump.rst for details.
1367 enable_mtrr_cleanup [X86]
1368 The kernel tries to adjust MTRR layout from continuous
1369 to discrete, to make X server driver able to add WB
1370 entry later. This parameter enables that.
1372 enable_timer_pin_1 [X86]
1373 Enable PIN 1 of APIC timer
1374 Can be useful to work around chipset bugs
1375 (in particular on some ATI chipsets).
1376 The kernel tries to set a reasonable default.
1378 enforcing [SELINUX] Set initial enforcing status.
1380 See security/selinux/Kconfig help text.
1381 0 -- permissive (log only, no denials).
1382 1 -- enforcing (deny and log).
1384 Value can be changed at runtime via
1385 /sys/fs/selinux/enforce.
1388 Disable Error Record Serialization Table (ERST)
1391 ether= [HW,NET] Ethernet cards parameters
1392 This option is obsoleted by the "netdev=" option, which
1393 has equivalent usage. See its documentation for details.
1397 Permit 'security.evm' to be updated regardless of
1398 current integrity status.
1403 fail_make_request=[KNL]
1404 General fault injection mechanism.
1405 Format: <interval>,<probability>,<space>,<times>
1406 See also Documentation/fault-injection/.
1409 Format: { initns | none }
1410 See Documentation/admin-guide/sysctl/net.rst for
1411 fb_tunnels_only_for_init_ns
1414 See Documentation/admin-guide/blockdev/floppy.rst.
1416 force_pal_cache_flush
1417 [IA-64] Avoid check_sal_cache_flush which may hang on
1418 buggy SAL_CACHE_FLUSH implementations. Using this
1419 parameter will force ia64_sal_cache_flush to call
1420 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1423 Forcefully enable Physical Address Extension (PAE).
1424 Many Pentium M systems disable PAE but may have a
1425 functionally usable PAE implementation.
1426 Warning: use of this parameter will taint the kernel
1427 and may cause unknown problems.
1430 [FTRACE] will set and start the specified tracer
1431 as early as possible in order to facilitate early
1434 ftrace_dump_on_oops[=orig_cpu]
1435 [FTRACE] will dump the trace buffers on oops.
1436 If no parameter is passed, ftrace will dump
1437 buffers of all CPUs, but if you pass orig_cpu, it will
1438 dump only the buffer of the CPU that triggered the
1441 ftrace_filter=[function-list]
1442 [FTRACE] Limit the functions traced by the function
1443 tracer at boot up. function-list is a comma-separated
1444 list of functions. This list can be changed at run
1445 time by the set_ftrace_filter file in the debugfs
1448 ftrace_notrace=[function-list]
1449 [FTRACE] Do not trace the functions specified in
1450 function-list. This list can be changed at run time
1451 by the set_ftrace_notrace file in the debugfs
1454 ftrace_graph_filter=[function-list]
1455 [FTRACE] Limit the top level callers functions traced
1456 by the function graph tracer at boot up.
1457 function-list is a comma-separated list of functions
1458 that can be changed at run time by the
1459 set_graph_function file in the debugfs tracing directory.
1461 ftrace_graph_notrace=[function-list]
1462 [FTRACE] Do not trace from the functions specified in
1463 function-list. This list is a comma-separated list of
1464 functions that can be changed at run time by the
1465 set_graph_notrace file in the debugfs tracing directory.
1467 ftrace_graph_max_depth=<uint>
1468 [FTRACE] Used with the function graph tracer. This is
1469 the max depth it will trace into a function. This value
1470 can be changed at run time by the max_graph_depth file
1471 in the tracefs tracing directory. default: 0 (no limit)
1473 fw_devlink= [KNL] Create device links between consumer and supplier
1474 devices by scanning the firmware to infer the
1475 consumer/supplier relationships. This feature is
1476 especially useful when drivers are loaded as modules as
1477 it ensures proper ordering of tasks like device probing
1478 (suppliers first, then consumers), supplier boot state
1479 clean up (only after all consumers have probed),
1480 suspend/resume & runtime PM (consumers first, then
1482 Format: { off | permissive | on | rpm }
1483 off -- Don't create device links from firmware info.
1484 permissive -- Create device links from firmware info
1485 but use it only for ordering boot state clean
1486 up (sync_state() calls).
1487 on -- Create device links from firmware info and use it
1488 to enforce probe and suspend/resume ordering.
1489 rpm -- Like "on", but also use to order runtime PM.
1491 fw_devlink.strict=<bool>
1492 [KNL] Treat all inferred dependencies as mandatory
1493 dependencies. This only applies for fw_devlink=on|rpm.
1497 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1498 support via parallel port (up to 5 devices per port)
1499 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1500 See also Documentation/input/devices/joystick-parport.rst
1504 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1508 gcov_persist= [GCOV] When non-zero (default), profiling data for
1509 kernel modules is saved and remains accessible via
1510 debugfs, even when the module is unloaded/reloaded.
1511 When zero, profiling data is discarded and associated
1512 debugfs files are removed at module unload time.
1514 goldfish [X86] Enable the goldfish android emulator platform.
1515 Don't use this when you are not running on the
1518 gpio-mockup.gpio_mockup_ranges
1519 [HW] Sets the ranges of gpiochip of for this device.
1520 Format: <start1>,<end1>,<start2>,<end2>...
1521 gpio-mockup.gpio_mockup_named_lines
1522 [HW] Let the driver know GPIO lines should be named.
1524 gpt [EFI] Forces disk with valid GPT signature but
1525 invalid Protective MBR to be treated as GPT. If the
1526 primary GPT is corrupted, it enables the backup/alternate
1527 GPT to be used instead.
1529 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1530 the "Enable 0" bit of the configuration register.
1533 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1534 the "Enable 0" bit of the configuration register.
1537 grcan.select= [HW] Select which physical interface to use.
1540 grcan.txsize= [HW] Sets the size of the tx buffer.
1541 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1543 grcan.rxsize= [HW] Sets the size of the rx buffer.
1544 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1547 hardlockup_all_cpu_backtrace=
1548 [KNL] Should the hard-lockup detector generate
1549 backtraces on all cpus.
1552 hashdist= [KNL,NUMA] Large hashes allocated during boot
1553 are distributed across NUMA nodes. Defaults on
1554 for 64-bit NUMA, off otherwise.
1555 Format: 0 | 1 (for off | on)
1557 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1559 hd= [EIDE] (E)IDE hard drive subsystem geometry
1560 Format: <cyl>,<head>,<sect>
1563 Disable Hardware Error Source Table (HEST) support;
1564 corresponding firmware-first mode error processing
1565 logic will be disabled.
1567 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1568 size of <nn>. This works even on boxes that have no
1569 highmem otherwise. This also works to reduce highmem
1570 size on bigger boxes.
1572 highres= [KNL] Enable/disable high resolution timer mode.
1573 Valid parameters: "on", "off"
1578 hpet= [X86-32,HPET] option to control HPET usage
1579 Format: { enable (default) | disable | force |
1581 disable: disable HPET and use PIT instead
1582 force: allow force enabled of undocumented chips (ICH4,
1584 verbose: show contents of HPET registers during setup
1586 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1587 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1589 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1590 of gigantic hugepages.
1593 Reserve a CMA area of given size and allocate gigantic
1594 hugepages using the CMA allocator. If enabled, the
1595 boot-time allocation of gigantic hugepages is skipped.
1597 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1598 If this follows hugepagesz (below), it specifies
1599 the number of pages of hugepagesz to be allocated.
1600 If this is the first HugeTLB parameter on the command
1601 line, it specifies the number of pages to allocate for
1602 the default huge page size. See also
1603 Documentation/admin-guide/mm/hugetlbpage.rst.
1607 [HW] The size of the HugeTLB pages. This is used in
1608 conjunction with hugepages (above) to allocate huge
1609 pages of a specific size at boot. The pair
1610 hugepagesz=X hugepages=Y can be specified once for
1611 each supported huge page size. Huge page sizes are
1612 architecture dependent. See also
1613 Documentation/admin-guide/mm/hugetlbpage.rst.
1616 hugetlb_free_vmemmap=
1617 [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
1619 Allows heavy hugetlb users to free up some more
1620 memory (6 * PAGE_SIZE for each 2MB hugetlb page).
1621 Format: { on | off (default) }
1623 on: enable the feature
1624 off: disable the feature
1626 Built with CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON=y,
1629 This is not compatible with memory_hotplug.memmap_on_memory.
1630 If both parameters are enabled, hugetlb_free_vmemmap takes
1631 precedence over memory_hotplug.memmap_on_memory.
1634 [KNL] Should the hung task detector generate panics.
1637 A value of 1 instructs the kernel to panic when a
1638 hung task is detected. The default value is controlled
1639 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1640 option. The value selected by this boot parameter can
1641 be changed later by the kernel.hung_task_panic sysctl.
1643 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1644 terminal devices. Valid values: 0..8
1645 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1646 If specified, z/VM IUCV HVC accepts connections
1647 from listed z/VM user IDs only.
1649 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1650 which allow the hypervisor to 'idle' the
1651 guest on lock contention.
1654 Do not unregister boot console at start. This is only
1655 useful for debugging when something happens in the window
1656 between unregistering the boot console and initializing
1659 i2c_bus= [HW] Override the default board specific I2C bus speed
1660 or register an additional I2C bus that is not
1661 registered from board initialization code.
1665 i8042.debug [HW] Toggle i8042 debug mode
1666 i8042.unmask_kbd_data
1667 [HW] Enable printing of interrupt data from the KBD port
1668 (disabled by default, and as a pre-condition
1669 requires that i8042.debug=1 be enabled)
1670 i8042.direct [HW] Put keyboard port into non-translated mode
1671 i8042.dumbkbd [HW] Pretend that controller can only read data from
1672 keyboard and cannot control its state
1673 (Don't attempt to blink the leds)
1674 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1675 i8042.nokbd [HW] Don't check/create keyboard port
1676 i8042.noloop [HW] Disable the AUX Loopback command while probing
1678 i8042.nomux [HW] Don't check presence of an active multiplexing
1680 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1682 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1683 i8042.reset [HW] Reset the controller during init, cleanup and
1684 suspend-to-ram transitions, only during s2r
1685 transitions, or never reset
1686 Format: { 1 | Y | y | 0 | N | n }
1687 1, Y, y: always reset controller
1688 0, N, n: don't ever reset controller
1689 Default: only on s2r transitions on x86; most other
1690 architectures force reset to be always executed
1691 i8042.unlock [HW] Unlock (ignore) the keylock
1692 i8042.kbdreset [HW] Reset device connected to KBD port
1694 [HW] Allow deferred probing upon i8042 probe errors
1698 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1699 indicates that the driver is running on unsupported
1701 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1702 does not match list of supported models.
1704 [HW] Report power status in /proc/i8k
1705 (disabled by default)
1706 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1709 i915.invert_brightness=
1710 [DRM] Invert the sense of the variable that is used to
1711 set the brightness of the panel backlight. Normally a
1712 brightness value of 0 indicates backlight switched off,
1713 and the maximum of the brightness value sets the backlight
1714 to maximum brightness. If this parameter is set to 0
1715 (default) and the machine requires it, or this parameter
1716 is set to 1, a brightness value of 0 sets the backlight
1717 to maximum brightness, and the maximum of the brightness
1718 value switches the backlight off.
1719 -1 -- never invert brightness
1720 0 -- machine default
1721 1 -- force brightness inversion
1724 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1726 ide-core.nodma= [HW] (E)IDE subsystem
1727 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1728 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1729 .cdrom .chs .ignore_cable are additional options
1730 See Documentation/ide/ide.rst.
1732 ide-generic.probe-mask= [HW] (E)IDE subsystem
1734 Probe mask for legacy ISA IDE ports. Depending on
1735 platform up to 6 ports are supported, enabled by
1736 setting corresponding bits in the mask to 1. The
1737 default value is 0x0, which has a special meaning.
1738 On systems that have PCI, it triggers scanning the
1739 PCI bus for the first and the second port, which
1740 are then probed. On systems without PCI the value
1741 of 0x0 enables probing the two first ports as if it
1744 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1745 Claim all unknown PCI IDE storage controllers.
1748 Format: idle=poll, idle=halt, idle=nomwait
1749 Poll forces a polling idle loop that can slightly
1750 improve the performance of waking up a idle CPU, but
1751 will use a lot of power and make the system run hot.
1753 idle=halt: Halt is forced to be used for CPU idle.
1754 In such case C2/C3 won't be used again.
1755 idle=nomwait: Disable mwait for CPU C-states
1759 Allow force disabling of Shared Virtual Memory (SVA)
1760 support for the idxd driver. By default it is set to
1763 idxd.tc_override= [HW]
1765 Allow override of default traffic class configuration
1766 for the device. By default it is set to false (0).
1768 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1769 Format: { strict | legacy | 2008 | relaxed }
1772 Choose which programs will be accepted for execution
1773 based on the IEEE 754 NaN encoding(s) supported by
1774 the FPU and the NaN encoding requested with the value
1775 of an ELF file header flag individually set by each
1776 binary. Hardware implementations are permitted to
1777 support either or both of the legacy and the 2008 NaN
1780 Available settings are as follows:
1781 strict accept binaries that request a NaN encoding
1782 supported by the FPU
1783 legacy only accept legacy-NaN binaries, if supported
1785 2008 only accept 2008-NaN binaries, if supported
1787 relaxed accept any binaries regardless of whether
1788 supported by the FPU
1790 The FPU emulator is always able to support both NaN
1791 encodings, so if no FPU hardware is present or it has
1792 been disabled with 'nofpu', then the settings of
1793 'legacy' and '2008' strap the emulator accordingly,
1794 'relaxed' straps the emulator for both legacy-NaN and
1795 2008-NaN, whereas 'strict' enables legacy-NaN only on
1796 legacy processors and both NaN encodings on MIPS32 or
1799 The setting for ABS.fmt/NEG.fmt instruction execution
1800 mode generally follows that for the NaN encoding,
1801 except where unsupported by hardware.
1803 ignore_loglevel [KNL]
1804 Ignore loglevel setting - this will print /all/
1805 kernel messages to the console. Useful for debugging.
1806 We also add it as printk module parameter, so users
1807 could change it dynamically, usually by
1808 /sys/module/printk/parameters/ignore_loglevel.
1811 Ignore RLIMIT_DATA setting for data mappings,
1812 print warning at first misuse. Can be changed via
1813 /sys/module/kernel/parameters/ignore_rlimit_data.
1815 ihash_entries= [KNL]
1816 Set number of hash buckets for inode cache.
1818 ima_appraise= [IMA] appraise integrity measurements
1819 Format: { "off" | "enforce" | "fix" | "log" }
1822 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1823 The builtin appraise policy appraises all files
1826 ima_canonical_fmt [IMA]
1827 Use the canonical format for the binary runtime
1828 measurements, instead of host native format.
1831 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1835 The list of supported hash algorithms is defined
1836 in crypto/hash_info.h.
1839 The builtin policies to load during IMA setup.
1840 Format: "tcb | appraise_tcb | secure_boot |
1841 fail_securely | critical_data"
1843 The "tcb" policy measures all programs exec'd, files
1844 mmap'd for exec, and all files opened with the read
1845 mode bit set by either the effective uid (euid=0) or
1848 The "appraise_tcb" policy appraises the integrity of
1849 all files owned by root.
1851 The "secure_boot" policy appraises the integrity
1852 of files (eg. kexec kernel image, kernel modules,
1853 firmware, policy, etc) based on file signatures.
1855 The "fail_securely" policy forces file signature
1856 verification failure also on privileged mounted
1857 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1860 The "critical_data" policy measures kernel integrity
1863 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1864 Load a policy which meets the needs of the Trusted
1865 Computing Base. This means IMA will measure all
1866 programs exec'd, files mmap'd for exec, and all files
1867 opened for read by uid=0.
1870 Select one of defined IMA measurements template formats.
1871 Formats: { "ima" | "ima-ng" | "ima-sig" }
1875 [IMA] Define a custom template format.
1876 Format: { "field1|...|fieldN" }
1878 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1879 Format: <min_file_size>
1880 Set the minimal file size for using asynchronous hash.
1881 If left unspecified, ahash usage is disabled.
1883 ahash performance varies for different data sizes on
1884 different crypto accelerators. This option can be used
1885 to achieve the best performance for a particular HW.
1887 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1889 Set hashing buffer size. Default: 4k.
1891 ahash performance varies for different chunk sizes on
1892 different crypto accelerators. This option can be used
1893 to achieve best performance for particular HW.
1897 Run specified binary instead of /sbin/init as init
1900 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1901 for working out where the kernel is dying during
1904 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1905 initcall functions. Useful for debugging built-in
1906 modules and initcalls.
1908 initramfs_async= [KNL]
1911 This parameter controls whether the initramfs
1912 image is unpacked asynchronously, concurrently
1913 with devices being probed and
1914 initialized. This should normally just work,
1915 but as a debugging aid, one can get the
1916 historical behaviour of the initramfs
1917 unpacking being completed before device_ and
1920 initrd= [BOOT] Specify the location of the initial ramdisk
1922 initrdmem= [KNL] Specify a physical address and size from which to
1923 load the initrd. If an initrd is compiled in or
1924 specified in the bootparams, it takes priority over this
1926 Format: ss[KMG],nn[KMG]
1929 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1932 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1934 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1936 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1938 init_pkru= [X86] Specify the default memory protection keys rights
1939 register contents for all processes. 0x55555554 by
1940 default (disallow access to all but pkey 0). Can
1941 override in debugfs after boot.
1943 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1946 int_pln_enable [X86] Enable power limit notification interrupt
1948 integrity_audit=[IMA]
1949 Format: { "0" | "1" }
1950 0 -- basic integrity auditing messages. (Default)
1951 1 -- additional integrity auditing messages.
1953 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1955 Enable intel iommu driver.
1957 Disable intel iommu driver.
1958 igfx_off [Default Off]
1959 By default, gfx is mapped as normal device. If a gfx
1960 device has a dedicated DMAR unit, the DMAR unit is
1961 bypassed by not enabling DMAR with this option. In
1962 this case, gfx device will use physical address for
1964 strict [Default Off]
1965 Deprecated, equivalent to iommu.strict=1.
1966 sp_off [Default Off]
1967 By default, super page will be supported if Intel IOMMU
1968 has the capability. With this option, super page will
1971 Enable the Intel IOMMU scalable mode if the hardware
1972 advertises that it has support for the scalable mode
1975 Disallow use of the Intel IOMMU scalable mode.
1976 tboot_noforce [Default Off]
1977 Do not force the Intel IOMMU enabled under tboot.
1978 By default, tboot will force Intel IOMMU on, which
1979 could harm performance of some high-throughput
1980 devices like 40GBit network cards, even if identity
1982 Note that using this option lowers the security
1983 provided by tboot because it makes the system
1984 vulnerable to DMA attacks.
1986 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1987 0 disables intel_idle and fall back on acpi_idle.
1988 1 to 9 specify maximum depth of C-state.
1992 Do not enable intel_pstate as the default
1993 scaling driver for the supported processors
1995 Use intel_pstate as a scaling driver, but configure it
1996 to work with generic cpufreq governors (instead of
1997 enabling its internal governor). This mode cannot be
1998 used along with the hardware-managed P-states (HWP)
2001 Enable intel_pstate on systems that prohibit it by default
2002 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2003 instead of acpi-cpufreq may disable platform features, such
2004 as thermal controls and power capping, that rely on ACPI
2005 P-States information being indicated to OSPM and therefore
2006 should be used with caution. This option does not work with
2007 processors that aren't supported by the intel_pstate driver
2008 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2010 Do not enable hardware P state control (HWP)
2013 Only load intel_pstate on systems which support
2014 hardware P state control (HWP) if available.
2016 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2017 Description Table, specifies preferred power management
2018 profile as "Enterprise Server" or "Performance Server",
2019 then this feature is turned on by default.
2021 Allow per-logical-CPU P-State performance control limits using
2022 cpufreq sysfs interface
2024 intremap= [X86-64, Intel-IOMMU]
2025 on enable Interrupt Remapping (default)
2026 off disable Interrupt Remapping
2027 nosid disable Source ID checking
2029 BIOS x2APIC opt-out request will be ignored
2030 nopost disable Interrupt Posting
2032 iomem= Disable strict checking of access to MMIO memory
2033 strict regions from userspace.
2048 nobypass [PPC/POWERNV]
2049 Disable IOMMU bypass, using IOMMU for PCI devices.
2051 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2052 Format: { "0" | "1" }
2053 0 - Try to allocate a 32-bit DMA address first, before
2054 falling back to the full range if needed.
2055 1 - Allocate directly from the full usable range,
2056 forcing Dual Address Cycle for PCI cards supporting
2057 greater than 32-bit addressing.
2059 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2060 Format: { "0" | "1" }
2062 Request that DMA unmap operations use deferred
2063 invalidation of hardware TLBs, for increased
2064 throughput at the cost of reduced device isolation.
2065 Will fall back to strict mode if not supported by
2066 the relevant IOMMU driver.
2068 DMA unmap operations invalidate IOMMU hardware TLBs
2070 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2071 Note: on x86, strict mode specified via one of the
2072 legacy driver-specific options takes precedence.
2075 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2076 Format: { "0" | "1" }
2077 0 - Use IOMMU translation for DMA.
2078 1 - Bypass the IOMMU for DMA.
2079 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2081 io7= [HW] IO7 for Marvel-based Alpha systems
2082 See comment before marvel_specify_io7 in
2083 arch/alpha/kernel/core_marvel.c.
2085 io_delay= [X86] I/O delay method
2087 Standard port 0x80 based delay
2089 Alternate port 0xed based delay (needed on some systems)
2091 Simple two microseconds delay
2096 See Documentation/admin-guide/nfs/nfsroot.rst.
2098 ipcmni_extend [KNL] Extend the maximum number of unique System V
2099 IPC identifiers from 32,768 to 16,777,216.
2101 irqaffinity= [SMP] Set the default irq affinity mask
2102 The argument is a cpu list, as described above.
2104 irqchip.gicv2_force_probe=
2107 Force the kernel to look for the second 4kB page
2108 of a GICv2 controller even if the memory range
2109 exposed by the device tree is too small.
2111 irqchip.gicv3_nolpi=
2113 Force the kernel to ignore the availability of
2114 LPIs (and by consequence ITSs). Intended for system
2115 that use the kernel as a bootloader, and thus want
2116 to let secondary kernels in charge of setting up
2119 irqchip.gicv3_pseudo_nmi= [ARM64]
2120 Enables support for pseudo-NMIs in the kernel. This
2121 requires the kernel to be built with
2122 CONFIG_ARM64_PSEUDO_NMI.
2125 When an interrupt is not handled search all handlers
2126 for it. Intended to get systems with badly broken
2130 When an interrupt is not handled search all handlers
2131 for it. Also check all handlers each timer
2132 interrupt. Intended to get systems with badly broken
2136 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2138 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2139 [Deprecated - use cpusets instead]
2140 Format: [flag-list,]<cpu-list>
2142 Specify one or more CPUs to isolate from disturbances
2143 specified in the flag list (default: domain):
2146 Disable the tick when a single task runs.
2148 A residual 1Hz tick is offloaded to workqueues, which you
2149 need to affine to housekeeping through the global
2150 workqueue's affinity configured via the
2151 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2152 by using the 'domain' flag described below.
2154 NOTE: by default the global workqueue runs on all CPUs,
2155 so to protect individual CPUs the 'cpumask' file has to
2156 be configured manually after bootup.
2159 Isolate from the general SMP balancing and scheduling
2160 algorithms. Note that performing domain isolation this way
2161 is irreversible: it's not possible to bring back a CPU to
2162 the domains once isolated through isolcpus. It's strongly
2163 advised to use cpusets instead to disable scheduler load
2164 balancing through the "cpuset.sched_load_balance" file.
2165 It offers a much more flexible interface where CPUs can
2166 move in and out of an isolated set anytime.
2168 You can move a process onto or off an "isolated" CPU via
2169 the CPU affinity syscalls or cpuset.
2170 <cpu number> begins at 0 and the maximum value is
2171 "number of CPUs in system - 1".
2175 Isolate from being targeted by managed interrupts
2176 which have an interrupt mask containing isolated
2177 CPUs. The affinity of managed interrupts is
2178 handled by the kernel and cannot be changed via
2179 the /proc/irq/* interfaces.
2181 This isolation is best effort and only effective
2182 if the automatically assigned interrupt mask of a
2183 device queue contains isolated and housekeeping
2184 CPUs. If housekeeping CPUs are online then such
2185 interrupts are directed to the housekeeping CPU
2186 so that IO submitted on the housekeeping CPU
2187 cannot disturb the isolated CPU.
2189 If a queue's affinity mask contains only isolated
2190 CPUs then this parameter has no effect on the
2191 interrupt routing decision, though interrupts are
2192 only delivered when tasks running on those
2193 isolated CPUs submit IO. IO submitted on
2194 housekeeping CPUs has no influence on those
2197 The format of <cpu-list> is described above.
2201 ivrs_ioapic [HW,X86-64]
2202 Provide an override to the IOAPIC-ID<->DEVICE-ID
2203 mapping provided in the IVRS ACPI table. For
2204 example, to map IOAPIC-ID decimal 10 to
2205 PCI device 00:14.0 write the parameter as:
2206 ivrs_ioapic[10]=00:14.0
2208 ivrs_hpet [HW,X86-64]
2209 Provide an override to the HPET-ID<->DEVICE-ID
2210 mapping provided in the IVRS ACPI table. For
2211 example, to map HPET-ID decimal 0 to
2212 PCI device 00:14.0 write the parameter as:
2213 ivrs_hpet[0]=00:14.0
2215 ivrs_acpihid [HW,X86-64]
2216 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2217 mapping provided in the IVRS ACPI table. For
2218 example, to map UART-HID:UID AMD0020:0 to
2219 PCI device 00:14.5 write the parameter as:
2220 ivrs_acpihid[00:14.5]=AMD0020:0
2222 js= [HW,JOY] Analog joystick
2223 See Documentation/input/joydev/joystick.rst.
2226 When CONFIG_RANDOMIZE_BASE is set, this disables
2227 kernel and module base offset ASLR (Address Space
2228 Layout Randomization).
2231 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2232 report on every invalid memory access. Without this
2233 parameter KASAN will print report only for the first
2238 kernelcore= [KNL,X86,IA-64,PPC]
2239 Format: nn[KMGTPE] | nn% | "mirror"
2240 This parameter specifies the amount of memory usable by
2241 the kernel for non-movable allocations. The requested
2242 amount is spread evenly throughout all nodes in the
2243 system as ZONE_NORMAL. The remaining memory is used for
2244 movable memory in its own zone, ZONE_MOVABLE. In the
2245 event, a node is too small to have both ZONE_NORMAL and
2246 ZONE_MOVABLE, kernelcore memory will take priority and
2247 other nodes will have a larger ZONE_MOVABLE.
2249 ZONE_MOVABLE is used for the allocation of pages that
2250 may be reclaimed or moved by the page migration
2251 subsystem. Note that allocations like PTEs-from-HighMem
2252 still use the HighMem zone if it exists, and the Normal
2253 zone if it does not.
2255 It is possible to specify the exact amount of memory in
2256 the form of "nn[KMGTPE]", a percentage of total system
2257 memory in the form of "nn%", or "mirror". If "mirror"
2258 option is specified, mirrored (reliable) memory is used
2259 for non-movable allocations and remaining memory is used
2260 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2261 are exclusive, so you cannot specify multiple forms.
2263 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2264 Format: <Controller#>[,poll interval]
2265 The controller # is the number of the ehci usb debug
2266 port as it is probed via PCI. The poll interval is
2267 optional and is the number seconds in between
2268 each poll cycle to the debug port in case you need
2269 the functionality for interrupting the kernel with
2270 gdb or control-c on the dbgp connection. When
2271 not using this parameter you use sysrq-g to break into
2272 the kernel debugger.
2274 kgdboc= [KGDB,HW] kgdb over consoles.
2275 Requires a tty driver that supports console polling,
2276 or a supported polling keyboard driver (non-usb).
2277 Serial only format: <serial_device>[,baud]
2278 keyboard only format: kbd
2279 keyboard and serial format: kbd,<serial_device>[,baud]
2280 Optional Kernel mode setting:
2281 kms, kbd format: kms,kbd
2282 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2284 kgdboc_earlycon= [KGDB,HW]
2285 If the boot console provides the ability to read
2286 characters and can work in polling mode, you can use
2287 this parameter to tell kgdb to use it as a backend
2288 until the normal console is registered. Intended to
2289 be used together with the kgdboc parameter which
2290 specifies the normal console to transition to.
2292 The name of the early console should be specified
2293 as the value of this parameter. Note that the name of
2294 the early console might be different than the tty
2295 name passed to kgdboc. It's OK to leave the value
2296 blank and the first boot console that implements
2297 read() will be picked.
2299 kgdbwait [KGDB] Stop kernel execution and enter the
2300 kernel debugger at the earliest opportunity.
2302 kmac= [MIPS] Korina ethernet MAC address.
2303 Configure the RouterBoard 532 series on-chip
2304 Ethernet adapter MAC address.
2306 kmemleak= [KNL] Boot-time kmemleak enable/disable
2307 Valid arguments: on, off
2309 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2312 kprobe_event=[probe-list]
2313 [FTRACE] Add kprobe events and enable at boot time.
2314 The probe-list is a semicolon delimited list of probe
2315 definitions. Each definition is same as kprobe_events
2316 interface, but the parameters are comma delimited.
2317 For example, to add a kprobe event on vfs_read with
2318 arg1 and arg2, add to the command line;
2320 kprobe_event=p,vfs_read,$arg1,$arg2
2322 See also Documentation/trace/kprobetrace.rst "Kernel
2323 Boot Parameter" section.
2325 kpti= [ARM64] Control page table isolation of user
2326 and kernel address spaces.
2327 Default: enabled on cores which need mitigation.
2331 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2332 Default is 0 (don't ignore, but inject #GP)
2334 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2335 Default is false (don't support).
2337 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2342 [KVM] Controls the software workaround for the
2343 X86_BUG_ITLB_MULTIHIT bug.
2344 force : Always deploy workaround.
2345 off : Never deploy workaround.
2346 auto : Deploy workaround based on the presence of
2347 X86_BUG_ITLB_MULTIHIT.
2351 If the software workaround is enabled for the host,
2352 guests do need not to enable it for nested guests.
2354 kvm.nx_huge_pages_recovery_ratio=
2355 [KVM] Controls how many 4KiB pages are periodically zapped
2356 back to huge pages. 0 disables the recovery, otherwise if
2357 the value is N KVM will zap 1/Nth of the 4KiB pages every
2358 minute. The default is 60.
2360 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2361 Default is 1 (enabled)
2363 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2365 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2368 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2370 nvhe: Standard nVHE-based mode, without support for
2373 protected: nVHE-based mode with support for guests whose
2374 state is kept private from the host.
2375 Not valid if the kernel is running in EL2.
2377 Defaults to VHE/nVHE based on hardware support.
2379 kvm-arm.vgic_v3_group0_trap=
2380 [KVM,ARM] Trap guest accesses to GICv3 group-0
2383 kvm-arm.vgic_v3_group1_trap=
2384 [KVM,ARM] Trap guest accesses to GICv3 group-1
2387 kvm-arm.vgic_v3_common_trap=
2388 [KVM,ARM] Trap guest accesses to GICv3 common
2391 kvm-arm.vgic_v4_enable=
2392 [KVM,ARM] Allow use of GICv4 for direct injection of
2395 kvm_cma_resv_ratio=n [PPC]
2396 Reserves given percentage from system memory area for
2397 contiguous memory allocation for KVM hash pagetable
2399 By default it reserves 5% of total system memory.
2403 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2404 (virtualized MMU) support on capable Intel chips.
2405 Default is 1 (enabled)
2407 kvm-intel.emulate_invalid_guest_state=
2408 [KVM,Intel] Disable emulation of invalid guest state.
2409 Ignored if kvm-intel.enable_unrestricted_guest=1, as
2410 guest state is never invalid for unrestricted guests.
2411 This param doesn't apply to nested guests (L2), as KVM
2412 never emulates invalid L2 guest state.
2413 Default is 1 (enabled)
2415 kvm-intel.flexpriority=
2416 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2417 Default is 1 (enabled)
2420 [KVM,Intel] Enable VMX nesting (nVMX).
2421 Default is 0 (disabled)
2423 kvm-intel.unrestricted_guest=
2424 [KVM,Intel] Disable unrestricted guest feature
2425 (virtualized real and unpaged mode) on capable
2426 Intel chips. Default is 1 (enabled)
2428 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2431 Valid arguments: never, cond, always
2433 always: L1D cache flush on every VMENTER.
2434 cond: Flush L1D on VMENTER only when the code between
2435 VMEXIT and VMENTER can leak host memory.
2436 never: Disables the mitigation
2438 Default is cond (do L1 cache flush in specific instances)
2440 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2441 feature (tagged TLBs) on capable Intel chips.
2442 Default is 1 (enabled)
2444 l1d_flush= [X86,INTEL]
2445 Control mitigation for L1D based snooping vulnerability.
2447 Certain CPUs are vulnerable to an exploit against CPU
2448 internal buffers which can forward information to a
2449 disclosure gadget under certain conditions.
2451 In vulnerable processors, the speculatively
2452 forwarded data can be used in a cache side channel
2453 attack, to access data to which the attacker does
2454 not have direct access.
2456 This parameter controls the mitigation. The
2459 on - enable the interface for the mitigation
2461 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2464 The kernel PTE inversion protection is unconditionally
2465 enabled and cannot be disabled.
2468 Provides all available mitigations for the
2469 L1TF vulnerability. Disables SMT and
2470 enables all mitigations in the
2471 hypervisors, i.e. unconditional L1D flush.
2473 SMT control and L1D flush control via the
2474 sysfs interface is still possible after
2475 boot. Hypervisors will issue a warning
2476 when the first VM is started in a
2477 potentially insecure configuration,
2478 i.e. SMT enabled or L1D flush disabled.
2481 Same as 'full', but disables SMT and L1D
2482 flush runtime control. Implies the
2483 'nosmt=force' command line option.
2484 (i.e. sysfs control of SMT is disabled.)
2487 Leaves SMT enabled and enables the default
2488 hypervisor mitigation, i.e. conditional
2491 SMT control and L1D flush control via the
2492 sysfs interface is still possible after
2493 boot. Hypervisors will issue a warning
2494 when the first VM is started in a
2495 potentially insecure configuration,
2496 i.e. SMT enabled or L1D flush disabled.
2500 Disables SMT and enables the default
2501 hypervisor mitigation.
2503 SMT control and L1D flush control via the
2504 sysfs interface is still possible after
2505 boot. Hypervisors will issue a warning
2506 when the first VM is started in a
2507 potentially insecure configuration,
2508 i.e. SMT enabled or L1D flush disabled.
2511 Same as 'flush', but hypervisors will not
2512 warn when a VM is started in a potentially
2513 insecure configuration.
2516 Disables hypervisor mitigations and doesn't
2518 It also drops the swap size and available
2519 RAM limit restriction on both hypervisor and
2524 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2530 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2533 lapic= [X86,APIC] Do not use TSC deadline
2534 value for LAPIC timer one-shot implementation. Default
2535 back to the programmable timer unit in the LAPIC.
2536 Format: notscdeadline
2538 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2541 libata.dma= [LIBATA] DMA control
2542 libata.dma=0 Disable all PATA and SATA DMA
2543 libata.dma=1 PATA and SATA Disk DMA only
2544 libata.dma=2 ATAPI (CDROM) DMA only
2545 libata.dma=4 Compact Flash DMA only
2546 Combinations also work, so libata.dma=3 enables DMA
2547 for disks and CDROMs, but not CFs.
2549 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2550 libata.ignore_hpa=0 keep BIOS limits (default)
2551 libata.ignore_hpa=1 ignore limits, using full disk
2553 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2557 libata.force= [LIBATA] Force configurations. The format is comma-
2558 separated list of "[ID:]VAL" where ID is
2559 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2560 matching port, link or device. Basically, it matches
2561 the ATA ID string printed on console by libata. If
2562 the whole ID part is omitted, the last PORT and DEVICE
2563 values are used. If ID hasn't been specified yet, the
2564 configuration applies to all ports, links and devices.
2566 If only DEVICE is omitted, the parameter applies to
2567 the port and all links and devices behind it. DEVICE
2568 number of 0 either selects the first device or the
2569 first fan-out link behind PMP device. It does not
2570 select the host link. DEVICE number of 15 selects the
2571 host link and device attached to it.
2573 The VAL specifies the configuration to force. As long
2574 as there's no ambiguity shortcut notation is allowed.
2575 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2576 The following configurations can be forced.
2578 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2579 Any ID with matching PORT is used.
2581 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2583 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2584 udma[/][16,25,33,44,66,100,133] notation is also
2587 * [no]ncq: Turn on or off NCQ.
2589 * [no]ncqtrim: Turn off queued DSM TRIM.
2591 * nohrst, nosrst, norst: suppress hard, soft
2594 * rstonce: only attempt one reset during
2595 hot-unplug link recovery
2597 * dump_id: dump IDENTIFY data.
2599 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2601 * disable: Disable this device.
2603 If there are multiple matching configurations changing
2604 the same attribute, the last one is used.
2606 memblock=debug [KNL] Enable memblock debug messages.
2608 load_ramdisk= [RAM] [Deprecated]
2610 lockd.nlm_grace_period=P [NFS] Assign grace period.
2613 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2616 lockd.nlm_timeout=T [NFS] Assign timeout value.
2619 lockd.nlm_udpport=M [NFS] Assign UDP port.
2622 lockdown= [SECURITY]
2623 { integrity | confidentiality }
2624 Enable the kernel lockdown feature. If set to
2625 integrity, kernel features that allow userland to
2626 modify the running kernel are disabled. If set to
2627 confidentiality, kernel features that allow userland
2628 to extract confidential information from the kernel
2631 locktorture.nreaders_stress= [KNL]
2632 Set the number of locking read-acquisition kthreads.
2633 Defaults to being automatically set based on the
2634 number of online CPUs.
2636 locktorture.nwriters_stress= [KNL]
2637 Set the number of locking write-acquisition kthreads.
2639 locktorture.onoff_holdoff= [KNL]
2640 Set time (s) after boot for CPU-hotplug testing.
2642 locktorture.onoff_interval= [KNL]
2643 Set time (s) between CPU-hotplug operations, or
2644 zero to disable CPU-hotplug testing.
2646 locktorture.shuffle_interval= [KNL]
2647 Set task-shuffle interval (jiffies). Shuffling
2648 tasks allows some CPUs to go into dyntick-idle
2649 mode during the locktorture test.
2651 locktorture.shutdown_secs= [KNL]
2652 Set time (s) after boot system shutdown. This
2653 is useful for hands-off automated testing.
2655 locktorture.stat_interval= [KNL]
2656 Time (s) between statistics printk()s.
2658 locktorture.stutter= [KNL]
2659 Time (s) to stutter testing, for example,
2660 specifying five seconds causes the test to run for
2661 five seconds, wait for five seconds, and so on.
2662 This tests the locking primitive's ability to
2663 transition abruptly to and from idle.
2665 locktorture.torture_type= [KNL]
2666 Specify the locking implementation to test.
2668 locktorture.verbose= [KNL]
2669 Enable additional printk() statements.
2671 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2674 loglevel= All Kernel Messages with a loglevel smaller than the
2675 console loglevel will be printed to the console. It can
2676 also be changed with klogd or other programs. The
2677 loglevels are defined as follows:
2679 0 (KERN_EMERG) system is unusable
2680 1 (KERN_ALERT) action must be taken immediately
2681 2 (KERN_CRIT) critical conditions
2682 3 (KERN_ERR) error conditions
2683 4 (KERN_WARNING) warning conditions
2684 5 (KERN_NOTICE) normal but significant condition
2685 6 (KERN_INFO) informational
2686 7 (KERN_DEBUG) debug-level messages
2688 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2689 in bytes. n must be a power of two and greater
2690 than the minimal size. The minimal size is defined
2691 by LOG_BUF_SHIFT kernel config parameter. There is
2692 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2693 that allows to increase the default size depending on
2694 the number of CPUs. See init/Kconfig for more details.
2696 logo.nologo [FB] Disables display of the built-in Linux logo.
2697 This may be used to provide more screen space for
2698 kernel log messages and is useful when debugging
2699 kernel boot problems.
2701 lp=0 [LP] Specify parallel ports to use, e.g,
2702 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2703 lp=reset first parallel port). 'lp=0' disables the
2704 lp=auto printer driver. 'lp=reset' (which can be
2705 specified in addition to the ports) causes
2706 attached printers to be reset. Using
2707 lp=port1,port2,... specifies the parallel ports
2708 to associate lp devices with, starting with
2709 lp0. A port specification may be 'none' to skip
2710 that lp device, or a parport name such as
2711 'parport0'. Specifying 'lp=auto' instead of a
2712 port specification list means that device IDs
2713 from each port should be examined, to see if
2714 an IEEE 1284-compliant printer is attached; if
2715 so, the driver will manage that printer.
2716 See also header of drivers/char/lp.c.
2719 Sets loops_per_jiffy to given constant, thus avoiding
2720 time-consuming boot-time autodetection (up to 250 ms per
2721 CPU). 0 enables autodetection (default). To determine
2722 the correct value for your kernel, boot with normal
2723 autodetection and see what value is printed. Note that
2724 on SMP systems the preset will be applied to all CPUs,
2725 which is likely to cause problems if your CPUs need
2726 significantly divergent settings. An incorrect value
2727 will cause delays in the kernel to be wrong, leading to
2728 unpredictable I/O errors and other breakage. Although
2729 unlikely, in the extreme case this might damage your
2733 Format: <io>,<irq>,<dma>
2735 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2738 [SECURITY] Choose order of LSM initialization. This
2739 overrides CONFIG_LSM, and the "security=" parameter.
2741 machvec= [IA-64] Force the use of a particular machine-vector
2742 (machvec) in a generic kernel.
2743 Example: machvec=hpzx1
2745 machtype= [Loongson] Share the same kernel image file between
2746 different yeeloong laptops.
2747 Example: machtype=lemote-yeeloong-2f-7inch
2749 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2750 than or equal to this physical address is ignored.
2752 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2753 will bring up during bootup. maxcpus=n : n >= 0 limits
2754 the kernel to bring up 'n' processors. Surely after
2755 bootup you can bring up the other plugged cpu by executing
2756 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2757 only takes effect during system bootup.
2758 While n=0 is a special case, it is equivalent to "nosmp",
2759 which also disables the IO APIC.
2761 max_loop= [LOOP] The number of loop block devices that get
2762 (loop.max_loop) unconditionally pre-created at init time. The default
2763 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2764 of statically allocating a predefined number, loop
2765 devices can be requested on-demand with the
2766 /dev/loop-control interface.
2768 mce [X86-32] Machine Check Exception
2770 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2772 md= [HW] RAID subsystems devices and level
2773 See Documentation/admin-guide/md.rst.
2776 Format: <first>,<last>
2777 Specifies range of consoles to be captured by the MDA.
2780 Control mitigation for the Micro-architectural Data
2781 Sampling (MDS) vulnerability.
2783 Certain CPUs are vulnerable to an exploit against CPU
2784 internal buffers which can forward information to a
2785 disclosure gadget under certain conditions.
2787 In vulnerable processors, the speculatively
2788 forwarded data can be used in a cache side channel
2789 attack, to access data to which the attacker does
2790 not have direct access.
2792 This parameter controls the MDS mitigation. The
2795 full - Enable MDS mitigation on vulnerable CPUs
2796 full,nosmt - Enable MDS mitigation and disable
2797 SMT on vulnerable CPUs
2798 off - Unconditionally disable MDS mitigation
2800 On TAA-affected machines, mds=off can be prevented by
2801 an active TAA mitigation as both vulnerabilities are
2802 mitigated with the same mechanism so in order to disable
2803 this mitigation, you need to specify tsx_async_abort=off
2806 Not specifying this option is equivalent to
2809 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2811 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2812 Amount of memory to be used in cases as follows:
2815 2 when the kernel is not able to see the whole system memory;
2816 3 memory that lies after 'mem=' boundary is excluded from
2817 the hypervisor, then assigned to KVM guests.
2819 [X86] Work as limiting max address. Use together
2820 with memmap= to avoid physical address space collisions.
2821 Without memmap= PCI devices could be placed at addresses
2822 belonging to unused RAM.
2824 Note that this only takes effects during boot time since
2825 in above case 3, memory may need be hot added after boot
2826 if system memory of hypervisor is not sufficient.
2828 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2832 [KNL,SH] Allow user to override the default size for
2833 per-device physically contiguous DMA buffers.
2835 memhp_default_state=online/offline
2836 [KNL] Set the initial state for the memory hotplug
2837 onlining policy. If not specified, the default value is
2838 set according to the
2839 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2841 See Documentation/admin-guide/mm/memory-hotplug.rst.
2843 memmap=exactmap [KNL,X86] Enable setting of an exact
2844 E820 memory map, as specified by the user.
2845 Such memmap=exactmap lines can be constructed based on
2846 BIOS output or other requirements. See the memmap=nn@ss
2849 memmap=nn[KMG]@ss[KMG]
2850 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2851 Region of memory to be used is from ss to ss+nn.
2852 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2853 which limits max address to nn[KMG].
2854 Multiple different regions can be specified,
2857 memmap=100M@2G,100M#3G,1G!1024G
2859 memmap=nn[KMG]#ss[KMG]
2860 [KNL,ACPI] Mark specific memory as ACPI data.
2861 Region of memory to be marked is from ss to ss+nn.
2863 memmap=nn[KMG]$ss[KMG]
2864 [KNL,ACPI] Mark specific memory as reserved.
2865 Region of memory to be reserved is from ss to ss+nn.
2866 Example: Exclude memory from 0x18690000-0x1869ffff
2867 memmap=64K$0x18690000
2869 memmap=0x10000$0x18690000
2870 Some bootloaders may need an escape character before '$',
2871 like Grub2, otherwise '$' and the following number
2874 memmap=nn[KMG]!ss[KMG]
2875 [KNL,X86] Mark specific memory as protected.
2876 Region of memory to be used, from ss to ss+nn.
2877 The memory region may be marked as e820 type 12 (0xc)
2878 and is NVDIMM or ADR memory.
2880 memmap=<size>%<offset>-<oldtype>+<newtype>
2881 [KNL,ACPI] Convert memory within the specified region
2882 from <oldtype> to <newtype>. If "-<oldtype>" is left
2883 out, the whole region will be marked as <newtype>,
2884 even if previously unavailable. If "+<newtype>" is left
2885 out, matching memory will be removed. Types are
2886 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2887 3 = ACPI, 12 = PRAM.
2889 memory_corruption_check=0/1 [X86]
2890 Some BIOSes seem to corrupt the first 64k of
2891 memory when doing things like suspend/resume.
2892 Setting this option will scan the memory
2893 looking for corruption. Enabling this will
2894 both detect corruption and prevent the kernel
2895 from using the memory being corrupted.
2896 However, its intended as a diagnostic tool; if
2897 repeatable BIOS-originated corruption always
2898 affects the same memory, you can use memmap=
2899 to prevent the kernel from using that memory.
2901 memory_corruption_check_size=size [X86]
2902 By default it checks for corruption in the low
2903 64k, making this memory unavailable for normal
2904 use. Use this parameter to scan for
2905 corruption in more or less memory.
2907 memory_corruption_check_period=seconds [X86]
2908 By default it checks for corruption every 60
2909 seconds. Use this parameter to check at some
2910 other rate. 0 disables periodic checking.
2912 memory_hotplug.memmap_on_memory
2913 [KNL,X86,ARM] Boolean flag to enable this feature.
2914 Format: {on | off (default)}
2915 When enabled, runtime hotplugged memory will
2916 allocate its internal metadata (struct pages)
2917 from the hotadded memory which will allow to
2918 hotadd a lot of memory without requiring
2919 additional memory to do so.
2920 This feature is disabled by default because it
2921 has some implication on large (e.g. GB)
2922 allocations in some configurations (e.g. small
2924 The state of the flag can be read in
2925 /sys/module/memory_hotplug/parameters/memmap_on_memory.
2926 Note that even when enabled, there are a few cases where
2927 the feature is not effective.
2929 This is not compatible with hugetlb_free_vmemmap. If
2930 both parameters are enabled, hugetlb_free_vmemmap takes
2931 precedence over memory_hotplug.memmap_on_memory.
2933 memtest= [KNL,X86,ARM,PPC,RISCV] Enable memtest
2935 default : 0 <disable>
2936 Specifies the number of memtest passes to be
2937 performed. Each pass selects another test
2938 pattern from a given set of patterns. Memtest
2939 fills the memory with this pattern, validates
2940 memory contents and reserves bad memory
2941 regions that are detected.
2943 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2944 Valid arguments: on, off
2945 Default (depends on kernel configuration option):
2946 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2947 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2948 mem_encrypt=on: Activate SME
2949 mem_encrypt=off: Do not activate SME
2951 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2952 for details on when memory encryption can be activated.
2954 mem_sleep_default= [SUSPEND] Default system suspend mode:
2955 s2idle - Suspend-To-Idle
2956 shallow - Power-On Suspend or equivalent (if supported)
2957 deep - Suspend-To-RAM or equivalent (if supported)
2958 See Documentation/admin-guide/pm/sleep-states.rst.
2960 meye.*= [HW] Set MotionEye Camera parameters
2961 See Documentation/admin-guide/media/meye.rst.
2963 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2964 Multi-Function General Purpose Timers on AMD Geode
2967 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2968 the BIOS has incorrectly applied a workaround. TinyBIOS
2969 version 0.98 is known to be affected, 0.99 fixes the
2970 problem by letting the user disable the workaround.
2974 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2975 physical address is ignored.
2977 mini2440= [ARM,HW,KNL]
2978 Format:[0..2][b][c][t]
2980 MINI2440 configuration specification:
2981 0 - The attached screen is the 3.5" TFT
2982 1 - The attached screen is the 7" TFT
2983 2 - The VGA Shield is attached (1024x768)
2984 Leaving out the screen size parameter will not load
2985 the TFT driver, and the framebuffer will be left
2987 b - Enable backlight. The TFT backlight pin will be
2988 linked to the kernel VESA blanking code and a GPIO
2989 LED. This parameter is not necessary when using the
2991 c - Enable the s3c camera interface.
2992 t - Reserved for enabling touchscreen support. The
2993 touchscreen support is not enabled in the mainstream
2994 kernel as of 2.6.30, a preliminary port can be found
2995 in the "bleeding edge" mini2440 support kernel at
2996 https://repo.or.cz/w/linux-2.6/mini2440.git
2999 [X86,PPC,S390,ARM64] Control optional mitigations for
3000 CPU vulnerabilities. This is a set of curated,
3001 arch-independent options, each of which is an
3002 aggregation of existing arch-specific options.
3005 Disable all optional CPU mitigations. This
3006 improves system performance, but it may also
3007 expose users to several CPU vulnerabilities.
3008 Equivalent to: nopti [X86,PPC]
3010 nospectre_v1 [X86,PPC]
3012 nospectre_v2 [X86,PPC,S390,ARM64]
3013 spectre_v2_user=off [X86]
3014 spec_store_bypass_disable=off [X86,PPC]
3015 ssbd=force-off [ARM64]
3018 tsx_async_abort=off [X86]
3019 kvm.nx_huge_pages=off [X86]
3020 no_entry_flush [PPC]
3021 no_uaccess_flush [PPC]
3022 mmio_stale_data=off [X86]
3025 This does not have any effect on
3026 kvm.nx_huge_pages when
3027 kvm.nx_huge_pages=force.
3030 Mitigate all CPU vulnerabilities, but leave SMT
3031 enabled, even if it's vulnerable. This is for
3032 users who don't want to be surprised by SMT
3033 getting disabled across kernel upgrades, or who
3034 have other ways of avoiding SMT-based attacks.
3035 Equivalent to: (default behavior)
3038 Mitigate all CPU vulnerabilities, disabling SMT
3039 if needed. This is for users who always want to
3040 be fully mitigated, even if it means losing SMT.
3041 Equivalent to: l1tf=flush,nosmt [X86]
3042 mds=full,nosmt [X86]
3043 tsx_async_abort=full,nosmt [X86]
3044 mmio_stale_data=full,nosmt [X86]
3047 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3048 parameter allows control of the logging verbosity for
3049 the additional memory initialisation checks. A value
3050 of 0 disables mminit logging and a level of 4 will
3051 log everything. Information is printed at KERN_DEBUG
3052 so loglevel=8 may also need to be specified.
3055 [X86,INTEL] Control mitigation for the Processor
3056 MMIO Stale Data vulnerabilities.
3058 Processor MMIO Stale Data is a class of
3059 vulnerabilities that may expose data after an MMIO
3060 operation. Exposed data could originate or end in
3061 the same CPU buffers as affected by MDS and TAA.
3062 Therefore, similar to MDS and TAA, the mitigation
3063 is to clear the affected CPU buffers.
3065 This parameter controls the mitigation. The
3068 full - Enable mitigation on vulnerable CPUs
3070 full,nosmt - Enable mitigation and disable SMT on
3073 off - Unconditionally disable mitigation
3075 On MDS or TAA affected machines,
3076 mmio_stale_data=off can be prevented by an active
3077 MDS or TAA mitigation as these vulnerabilities are
3078 mitigated with the same mechanism so in order to
3079 disable this mitigation, you need to specify
3080 mds=off and tsx_async_abort=off too.
3082 Not specifying this option is equivalent to
3083 mmio_stale_data=full.
3086 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3089 [KNL] When CONFIG_MODULE_SIG is set, this means that
3090 modules without (valid) signatures will fail to load.
3091 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3092 is always true, so this option does nothing.
3094 module_blacklist= [KNL] Do not load a comma-separated list of
3095 modules. Useful for debugging problem modules.
3098 [MOUSE] Maximum time between finger touching and
3099 leaving touchpad surface for touch to be considered
3100 a tap and be reported as a left button click (for
3101 touchpads working in absolute mode only).
3103 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3104 reporting absolute coordinates, such as tablets
3105 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3106 reporting absolute coordinates, such as tablets
3108 movablecore= [KNL,X86,IA-64,PPC]
3109 Format: nn[KMGTPE] | nn%
3110 This parameter is the complement to kernelcore=, it
3111 specifies the amount of memory used for migratable
3112 allocations. If both kernelcore and movablecore is
3113 specified, then kernelcore will be at *least* the
3114 specified value but may be more. If movablecore on its
3115 own is specified, the administrator must be careful
3116 that the amount of memory usable for all allocations
3119 movable_node [KNL] Boot-time switch to make hotplugable memory
3120 NUMA nodes to be movable. This means that the memory
3121 of such nodes will be usable only for movable
3122 allocations which rules out almost all kernel
3123 allocations. Use with caution!
3125 MTD_Partition= [MTD]
3126 Format: <name>,<region-number>,<size>,<offset>
3128 MTD_Region= [MTD] Format:
3129 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3132 See drivers/mtd/parsers/cmdlinepart.c
3134 multitce=off [PPC] This parameter disables the use of the pSeries
3135 firmware feature for updating multiple TCE entries
3138 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3140 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3142 boundary - index of last SLC block on Flex-OneNAND.
3143 The remaining blocks are configured as MLC blocks.
3144 lock - Configure if Flex-OneNAND boundary should be locked.
3145 Once locked, the boundary cannot be changed.
3146 1 indicates lock status, 0 indicates unlock status.
3149 ARM/S3C2412 JIVE boot control
3151 See arch/arm/mach-s3c/mach-jive.c
3153 mtouchusb.raw_coordinates=
3154 [HW] Make the MicroTouch USB driver use raw coordinates
3155 ('y', default) or cooked coordinates ('n')
3157 mtrr_chunk_size=nn[KMG] [X86]
3158 used for mtrr cleanup. It is largest continuous chunk
3159 that could hold holes aka. UC entries.
3161 mtrr_gran_size=nn[KMG] [X86]
3162 Used for mtrr cleanup. It is granularity of mtrr block.
3164 Large value could prevent small alignment from
3167 mtrr_spare_reg_nr=n [X86]
3169 Range: 0,7 : spare reg number
3171 Used for mtrr cleanup. It is spare mtrr entries number.
3172 Set to 2 or more if your graphical card needs more.
3174 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3176 netdev= [NET] Network devices parameters
3177 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3178 Note that mem_start is often overloaded to mean
3179 something different and driver-specific.
3180 This usage is only documented in each driver source
3184 [NETFILTER] Enable connection tracking flow accounting
3185 0 to disable accounting
3186 1 to enable accounting
3189 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3190 See Documentation/admin-guide/nfs/nfsroot.rst.
3192 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3193 See Documentation/admin-guide/nfs/nfsroot.rst.
3195 nfsrootdebug [NFS] enable nfsroot debugging messages.
3196 See Documentation/admin-guide/nfs/nfsroot.rst.
3198 nfs.callback_nr_threads=
3199 [NFSv4] set the total number of threads that the
3200 NFS client will assign to service NFSv4 callback
3203 nfs.callback_tcpport=
3204 [NFS] set the TCP port on which the NFSv4 callback
3205 channel should listen.
3208 [NFS] sets the pathname to the program which is used
3209 to update the NFS client cache entries.
3211 nfs.cache_getent_timeout=
3212 [NFS] sets the timeout after which an attempt to
3213 update a cache entry is deemed to have failed.
3215 nfs.idmap_cache_timeout=
3216 [NFS] set the maximum lifetime for idmapper cache
3220 [NFS] enable 64-bit inode numbers.
3221 If zero, the NFS client will fake up a 32-bit inode
3222 number for the readdir() and stat() syscalls instead
3223 of returning the full 64-bit number.
3224 The default is to return 64-bit inode numbers.
3226 nfs.max_session_cb_slots=
3227 [NFSv4.1] Sets the maximum number of session
3228 slots the client will assign to the callback
3229 channel. This determines the maximum number of
3230 callbacks the client will process in parallel for
3231 a particular server.
3233 nfs.max_session_slots=
3234 [NFSv4.1] Sets the maximum number of session slots
3235 the client will attempt to negotiate with the server.
3236 This limits the number of simultaneous RPC requests
3237 that the client can send to the NFSv4.1 server.
3238 Note that there is little point in setting this
3239 value higher than the max_tcp_slot_table_limit.
3241 nfs.nfs4_disable_idmapping=
3242 [NFSv4] When set to the default of '1', this option
3243 ensures that both the RPC level authentication
3244 scheme and the NFS level operations agree to use
3245 numeric uids/gids if the mount is using the
3246 'sec=sys' security flavour. In effect it is
3247 disabling idmapping, which can make migration from
3248 legacy NFSv2/v3 systems to NFSv4 easier.
3249 Servers that do not support this mode of operation
3250 will be autodetected by the client, and it will fall
3251 back to using the idmapper.
3252 To turn off this behaviour, set the value to '0'.
3254 [NFS4] Specify an additional fixed unique ident-
3255 ification string that NFSv4 clients can insert into
3256 their nfs_client_id4 string. This is typically a
3257 UUID that is generated at system install time.
3259 nfs.send_implementation_id =
3260 [NFSv4.1] Send client implementation identification
3261 information in exchange_id requests.
3262 If zero, no implementation identification information
3264 The default is to send the implementation identification
3267 nfs.recover_lost_locks =
3268 [NFSv4] Attempt to recover locks that were lost due
3269 to a lease timeout on the server. Please note that
3270 doing this risks data corruption, since there are
3271 no guarantees that the file will remain unchanged
3272 after the locks are lost.
3273 If you want to enable the kernel legacy behaviour of
3274 attempting to recover these locks, then set this
3276 The default parameter value of '0' causes the kernel
3277 not to attempt recovery of lost locks.
3279 nfs4.layoutstats_timer =
3280 [NFSv4.2] Change the rate at which the kernel sends
3281 layoutstats to the pNFS metadata server.
3283 Setting this to value to 0 causes the kernel to use
3284 whatever value is the default set by the layout
3285 driver. A non-zero value sets the minimum interval
3286 in seconds between layoutstats transmissions.
3288 nfsd.nfs4_disable_idmapping=
3289 [NFSv4] When set to the default of '1', the NFSv4
3290 server will return only numeric uids and gids to
3291 clients using auth_sys, and will accept numeric uids
3292 and gids from such clients. This is intended to ease
3293 migration from NFSv2/v3.
3295 nmi_backtrace.backtrace_idle [KNL]
3296 Dump stacks even of idle CPUs in response to an
3297 NMI stack-backtrace request.
3299 nmi_debug= [KNL,SH] Specify one or more actions to take
3300 when a NMI is triggered.
3301 Format: [state][,regs][,debounce][,die]
3303 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3304 Format: [panic,][nopanic,][num]
3306 0 - turn hardlockup detector in nmi_watchdog off
3307 1 - turn hardlockup detector in nmi_watchdog on
3308 When panic is specified, panic when an NMI watchdog
3309 timeout occurs (or 'nopanic' to not panic on an NMI
3310 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3311 To disable both hard and soft lockup detectors,
3312 please see 'nowatchdog'.
3313 This is useful when you use a panic=... timeout and
3314 need the box quickly up again.
3316 These settings can be accessed at runtime via
3317 the nmi_watchdog and hardlockup_panic sysctls.
3319 netpoll.carrier_timeout=
3320 [NET] Specifies amount of time (in seconds) that
3321 netpoll should wait for a carrier. By default netpoll
3324 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3325 emulation library even if a 387 maths coprocessor
3328 no5lvl [X86-64] Disable 5-level paging mode. Forces
3329 kernel to use 4-level paging instead.
3331 nofsgsbase [X86] Disables FSGSBASE instructions.
3334 [HW] Never suspend the console
3335 Disable suspending of consoles during suspend and
3336 hibernate operations. Once disabled, debugging
3337 messages can reach various consoles while the rest
3338 of the system is being put to sleep (ie, while
3339 debugging driver suspend/resume hooks). This may
3340 not work reliably with all consoles, but is known
3341 to work with serial and VGA consoles.
3342 To facilitate more flexible debugging, we also add
3343 console_suspend, a printk module parameter to control
3344 it. Users could use console_suspend (usually
3345 /sys/module/printk/parameters/console_suspend) to
3346 turn on/off it dynamically.
3348 novmcoredd [KNL,KDUMP]
3349 Disable device dump. Device dump allows drivers to
3350 append dump data to vmcore so you can collect driver
3351 specified debug info. Drivers can append the data
3352 without any limit and this data is stored in memory,
3353 so this may cause significant memory stress. Disabling
3354 device dump can help save memory but the driver debug
3355 data will be no longer available. This parameter
3356 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3359 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3360 caches in the slab allocator. Saves per-node memory,
3361 but will impact performance.
3365 noaltinstr [S390] Disables alternative instructions patching
3366 (CPU alternatives feature).
3368 noapic [SMP,APIC] Tells the kernel to not make use of any
3369 IOAPICs that may be present in the system.
3371 noautogroup Disable scheduler automatic task group creation.
3373 nobats [PPC] Do not use BATs for mapping kernel lowmem
3374 on "Classic" PPC cores.
3378 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3380 delayacct [KNL] Enable per-task delay accounting
3382 nodsp [SH] Disable hardware DSP at boot time.
3384 noefi Disable EFI runtime services support.
3386 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3391 On X86-32 available only on PAE configured kernels.
3392 noexec=on: enable non-executable mappings (default)
3393 noexec=off: disable non-executable mappings
3396 Disable SMAP (Supervisor Mode Access Prevention)
3397 even if it is supported by processor.
3400 Disable SMEP (Supervisor Mode Execution Prevention)
3401 even if it is supported by processor.
3404 This affects only 32-bit executables.
3405 noexec32=on: enable non-executable mappings (default)
3406 read doesn't imply executable mappings
3407 noexec32=off: disable non-executable mappings
3408 read implies executable mappings
3410 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3412 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3413 register save and restore. The kernel will only save
3414 legacy floating-point registers on task switch.
3416 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3418 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3420 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3421 Equivalent to smt=1.
3423 [KNL,X86] Disable symmetric multithreading (SMT).
3424 nosmt=force: Force disable SMT, cannot be undone
3425 via the sysfs control file.
3427 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3428 (bounds check bypass). With this option data leaks are
3429 possible in the system.
3431 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3432 the Spectre variant 2 (indirect branch prediction)
3433 vulnerability. System may allow data leaks with this
3436 nospec_store_bypass_disable
3437 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3440 [PPC] Don't flush the L1-D cache after accessing user data.
3442 noxsave [BUGS=X86] Disables x86 extended register state save
3443 and restore using xsave. The kernel will fallback to
3444 enabling legacy floating-point and sse state.
3446 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3447 register states. The kernel will fall back to use
3448 xsave to save the states. By using this parameter,
3449 performance of saving the states is degraded because
3450 xsave doesn't support modified optimization while
3451 xsaveopt supports it on xsaveopt enabled systems.
3453 noxsaves [X86] Disables xsaves and xrstors used in saving and
3454 restoring x86 extended register state in compacted
3455 form of xsave area. The kernel will fall back to use
3456 xsaveopt and xrstor to save and restore the states
3457 in standard form of xsave area. By using this
3458 parameter, xsave area per process might occupy more
3459 memory on xsaves enabled systems.
3461 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3462 in do_idle() and not use the arch_cpu_idle()
3463 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3464 to be effective. This is useful on platforms where the
3465 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3466 correctly or when doing power measurements to evalute
3467 the impact of the sleep instructions. This is also
3468 useful when using JTAG debugger.
3470 no_file_caps Tells the kernel not to honor file capabilities. The
3471 only way then for a file to be executed with privilege
3472 is to be setuid root or executed by root.
3474 nohalt [IA-64] Tells the kernel not to use the power saving
3475 function PAL_HALT_LIGHT when idle. This increases
3476 power-consumption. On the positive side, it reduces
3477 interrupt wake-up latency, which may improve performance
3478 in certain environments such as networked servers or
3482 Force pointers printed to the console or buffers to be
3483 unhashed. By default, when a pointer is printed via %p
3484 format string, that pointer is "hashed", i.e. obscured
3485 by hashing the pointer value. This is a security feature
3486 that hides actual kernel addresses from unprivileged
3487 users, but it also makes debugging the kernel more
3488 difficult since unequal pointers can no longer be
3489 compared. However, if this command-line option is
3490 specified, then all normal pointers will have their true
3491 value printed. This option should only be specified when
3492 debugging the kernel. Please do not use on production
3495 nohibernate [HIBERNATION] Disable hibernation and resume.
3497 nohz= [KNL] Boottime enable/disable dynamic ticks
3498 Valid arguments: on, off
3501 nohz_full= [KNL,BOOT,SMP,ISOL]
3502 The argument is a cpu list, as described above.
3503 In kernels built with CONFIG_NO_HZ_FULL=y, set
3504 the specified list of CPUs whose tick will be stopped
3505 whenever possible. The boot CPU will be forced outside
3506 the range to maintain the timekeeping. Any CPUs
3507 in this list will have their RCU callbacks offloaded,
3508 just as if they had also been called out in the
3509 rcu_nocbs= boot parameter.
3511 noiotrap [SH] Disables trapped I/O port accesses.
3513 noirqdebug [X86-32] Disables the code which attempts to detect and
3514 disable unhandled interrupt sources.
3516 no_timer_check [X86,APIC] Disables the code which tests for
3517 broken timer IRQ sources.
3519 noisapnp [ISAPNP] Disables ISA PnP code.
3521 noinitrd [RAM] Tells the kernel not to load any configured
3524 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3526 [Deprecated - use intremap=off]
3530 noinvpcid [X86] Disable the INVPCID cpu feature.
3532 nojitter [IA-64] Disables jitter checking for ITC timers.
3534 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3536 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3540 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3541 clock and use the default one.
3543 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3544 accounting. steal time is computed, but won't
3545 influence scheduler behaviour
3547 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3549 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3551 noltlbs [PPC] Do not use large page/tlb entries for kernel
3552 lowmem mapping on PPC40x and PPC8xx
3554 nomca [IA-64] Disable machine check abort handling
3556 nomce [X86-32] Disable Machine Check Exception
3558 nomfgpt [X86-32] Disable Multi-Function General Purpose
3559 Timer usage (for AMD Geode machines).
3561 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3562 shutdown the other cpus. Instead use the REBOOT_VECTOR
3565 nomodule Disable module load
3567 nopat [X86] Disable PAT (page attribute table extension of
3568 pagetables) support.
3570 nopcid [X86-64] Disable the PCID cpu feature.
3572 norandmaps Don't use address space randomization. Equivalent to
3573 echo 0 > /proc/sys/kernel/randomize_va_space
3575 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3576 with UP alternatives
3578 nordrand [X86] Disable kernel use of the RDRAND and
3579 RDSEED instructions even if they are supported
3580 by the processor. RDRAND and RDSEED are still
3581 available to user space applications.
3583 noresume [SWSUSP] Disables resume and restores original swap
3586 no-scroll [VGA] Disables scrollback.
3587 This is required for the Braillex ib80-piezo Braille
3588 reader made by F.H. Papenmeier (Germany).
3592 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3594 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3596 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3597 and disable the IO APIC. legacy for "maxcpus=0".
3599 nosoftlockup [KNL] Disable the soft-lockup detector.
3601 nosync [HW,M68K] Disables sync negotiation for all devices.
3603 nowatchdog [KNL] Disable both lockup detectors, i.e.
3604 soft-lockup and NMI watchdog (hard-lockup).
3608 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3610 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3611 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3612 Some features depend on CPU0. Known dependencies are:
3613 1. Resume from suspend/hibernate depends on CPU0.
3614 Suspend/hibernate will fail if CPU0 is offline and you
3615 need to online CPU0 before suspend/hibernate.
3616 2. PIC interrupts also depend on CPU0. CPU0 can't be
3617 removed if a PIC interrupt is detected.
3618 It's said poweroff/reboot may depend on CPU0 on some
3619 machines although I haven't seen such issues so far
3620 after CPU0 is offline on a few tested machines.
3621 If the dependencies are under your control, you can
3622 turn on cpu0_hotplug.
3624 nps_mtm_hs_ctr= [KNL,ARC]
3625 This parameter sets the maximum duration, in
3626 cycles, each HW thread of the CTOP can run
3627 without interruptions, before HW switches it.
3628 The actual maximum duration is 16 times this
3630 Format: integer between 1 and 255
3633 nptcg= [IA-64] Override max number of concurrent global TLB
3634 purges which is reported from either PAL_VM_SUMMARY or
3637 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3638 could support. nr_cpus=n : n >= 1 limits the kernel to
3639 support 'n' processors. It could be larger than the
3640 number of already plugged CPU during bootup, later in
3641 runtime you can physically add extra cpu until it reaches
3642 n. So during boot up some boot time memory for per-cpu
3643 variables need be pre-allocated for later physical cpu
3646 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3648 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3649 set up a single NUMA node spanning all memory.
3651 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3653 Allowed values are enable and disable
3655 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3656 'node', 'default' can be specified
3657 This can be set from sysctl after boot.
3658 See Documentation/admin-guide/sysctl/vm.rst for details.
3660 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3661 See Documentation/core-api/debugging-via-ohci1394.rst for more
3664 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3665 Rather than timing out after 20 ms if an EC
3666 command is not properly ACKed, override the length
3667 of the timeout. We have interrupts disabled while
3668 waiting for the ACK, so if this is set too high
3669 interrupts *may* be lost!
3671 omap_mux= [OMAP] Override bootloader pin multiplexing.
3672 Format: <mux_mode0.mode_name=value>...
3673 For example, to override I2C bus2:
3674 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3676 oops=panic Always panic on oopses. Default is to just kill the
3677 process, but there is a small probability of
3678 deadlocking the machine.
3679 This will also cause panics on machine check exceptions.
3680 Useful together with panic=30 to trigger a reboot.
3683 [KNL] Boolean flag to control whether the page allocator
3684 should randomize its free lists. The randomization may
3685 be automatically enabled if the kernel detects it is
3686 running on a platform with a direct-mapped memory-side
3687 cache, and this parameter can be used to
3688 override/disable that behavior. The state of the flag
3689 can be read from sysfs at:
3690 /sys/module/page_alloc/parameters/shuffle.
3692 page_owner= [KNL] Boot-time page_owner enabling option.
3693 Storage of the information about who allocated
3694 each page is disabled in default. With this switch,
3696 on: enable the feature
3698 page_poison= [KNL] Boot-time parameter changing the state of
3699 poisoning on the buddy allocator, available with
3700 CONFIG_PAGE_POISONING=y.
3701 off: turn off poisoning (default)
3702 on: turn on poisoning
3704 page_reporting.page_reporting_order=
3705 [KNL] Minimal page reporting order
3707 Adjust the minimal page reporting order. The page
3708 reporting is disabled when it exceeds (MAX_ORDER-1).
3710 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3711 timeout > 0: seconds before rebooting
3712 timeout = 0: wait forever
3713 timeout < 0: reboot immediately
3716 panic_print= Bitmask for printing system info when panic happens.
3717 User can chose combination of the following bits:
3718 bit 0: print all tasks info
3719 bit 1: print system memory info
3720 bit 2: print timer info
3721 bit 3: print locks info if CONFIG_LOCKDEP is on
3722 bit 4: print ftrace buffer
3723 bit 5: print all printk messages in buffer
3725 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3726 Format: <hex>[,nousertaint]
3727 Hexadecimal bitmask representing the set of TAINT flags
3728 that will cause the kernel to panic when add_taint() is
3729 called with any of the flags in this set.
3730 The optional switch "nousertaint" can be utilized to
3731 prevent userspace forced crashes by writing to sysctl
3732 /proc/sys/kernel/tainted any flagset matching with the
3733 bitmask set on panic_on_taint.
3734 See Documentation/admin-guide/tainted-kernels.rst for
3735 extra details on the taint flags that users can pick
3736 to compose the bitmask to assign to panic_on_taint.
3738 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3741 crash_kexec_post_notifiers
3742 Run kdump after running panic-notifiers and dumping
3743 kmsg. This only for the users who doubt kdump always
3744 succeeds in any situation.
3745 Note that this also increases risks of kdump failure,
3746 because some panic notifiers can make the crashed
3747 kernel more unstable.
3749 parkbd.port= [HW] Parallel port number the keyboard adapter is
3750 connected to, default is 0.
3752 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3753 0 for XT, 1 for AT (default is AT).
3756 parport= [HW,PPT] Specify parallel ports. 0 disables.
3757 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3758 Use 'auto' to force the driver to use any
3759 IRQ/DMA settings detected (the default is to
3760 ignore detected IRQ/DMA settings because of
3761 possible conflicts). You can specify the base
3762 address, IRQ, and DMA settings; IRQ and DMA
3763 should be numbers, or 'auto' (for using detected
3764 settings on that particular port), or 'nofifo'
3765 (to avoid using a FIFO even if it is detected).
3766 Parallel ports are assigned in the order they
3767 are specified on the command line, starting
3770 parport_init_mode= [HW,PPT]
3771 Configure VIA parallel port to operate in
3772 a specific mode. This is necessary on Pegasos
3773 computer where firmware has no options for setting
3774 up parallel port mode and sets it to spp.
3775 Currently this function knows 686a and 8231 chips.
3776 Format: [spp|ps2|epp|ecp|ecpepp]
3778 pata_legacy.all= [HW,LIBATA]
3780 Set to non-zero to probe primary and secondary ISA
3781 port ranges on PCI systems where no PCI PATA device
3782 has been found at either range. Disabled by default.
3784 pata_legacy.autospeed= [HW,LIBATA]
3786 Set to non-zero if a chip is present that snoops speed
3787 changes. Disabled by default.
3789 pata_legacy.ht6560a= [HW,LIBATA]
3791 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3792 the secondary channel, or both channels respectively.
3793 Disabled by default.
3795 pata_legacy.ht6560b= [HW,LIBATA]
3797 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3798 the secondary channel, or both channels respectively.
3799 Disabled by default.
3801 pata_legacy.iordy_mask= [HW,LIBATA]
3803 IORDY enable mask. Set individual bits to allow IORDY
3804 for the respective channel. Bit 0 is for the first
3805 legacy channel handled by this driver, bit 1 is for
3806 the second channel, and so on. The sequence will often
3807 correspond to the primary legacy channel, the secondary
3808 legacy channel, and so on, but the handling of a PCI
3809 bus and the use of other driver options may interfere
3810 with the sequence. By default IORDY is allowed across
3813 pata_legacy.opti82c46x= [HW,LIBATA]
3815 Set to 1, 2, or 3 for Opti 82c611A on the primary
3816 channel, the secondary channel, or both channels
3817 respectively. Disabled by default.
3819 pata_legacy.opti82c611a= [HW,LIBATA]
3821 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3822 channel, the secondary channel, or both channels
3823 respectively. Disabled by default.
3825 pata_legacy.pio_mask= [HW,LIBATA]
3827 PIO mode mask for autospeed devices. Set individual
3828 bits to allow the use of the respective PIO modes.
3829 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3830 All modes allowed by default.
3832 pata_legacy.probe_all= [HW,LIBATA]
3834 Set to non-zero to probe tertiary and further ISA
3835 port ranges on PCI systems. Disabled by default.
3837 pata_legacy.probe_mask= [HW,LIBATA]
3839 Probe mask for legacy ISA PATA ports. Depending on
3840 platform configuration and the use of other driver
3841 options up to 6 legacy ports are supported: 0x1f0,
3842 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3843 of individual ports can be disabled by setting the
3844 corresponding bits in the mask to 1. Bit 0 is for
3845 the first port in the list above (0x1f0), and so on.
3846 By default all supported ports are probed.
3848 pata_legacy.qdi= [HW,LIBATA]
3850 Set to non-zero to probe QDI controllers. By default
3851 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3853 pata_legacy.winbond= [HW,LIBATA]
3855 Set to non-zero to probe Winbond controllers. Use
3856 the standard I/O port (0x130) if 1, otherwise the
3857 value given is the I/O port to use (typically 0x1b0).
3858 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3861 pata_platform.pio_mask= [HW,LIBATA]
3863 Supported PIO mode mask. Set individual bits to allow
3864 the use of the respective PIO modes. Bit 0 is for
3865 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3869 Halt all CPUs after the first oops has been printed for
3870 the specified number of seconds. This is to be used if
3871 your oopses keep scrolling off the screen.
3876 See header of drivers/block/paride/pcd.c.
3877 See also Documentation/admin-guide/blockdev/paride.rst.
3879 pci=option[,option...] [PCI] various PCI subsystem options.
3881 Some options herein operate on a specific device
3882 or a set of devices (<pci_dev>). These are
3883 specified in one of the following formats:
3885 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3886 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3888 Note: the first format specifies a PCI
3889 bus/device/function address which may change
3890 if new hardware is inserted, if motherboard
3891 firmware changes, or due to changes caused
3892 by other kernel parameters. If the
3893 domain is left unspecified, it is
3894 taken to be zero. Optionally, a path
3895 to a device through multiple device/function
3896 addresses can be specified after the base
3897 address (this is more robust against
3898 renumbering issues). The second format
3899 selects devices using IDs from the
3900 configuration space which may match multiple
3901 devices in the system.
3903 earlydump dump PCI config space before the kernel
3905 off [X86] don't probe for the PCI bus
3906 bios [X86-32] force use of PCI BIOS, don't access
3907 the hardware directly. Use this if your machine
3908 has a non-standard PCI host bridge.
3909 nobios [X86-32] disallow use of PCI BIOS, only direct
3910 hardware access methods are allowed. Use this
3911 if you experience crashes upon bootup and you
3912 suspect they are caused by the BIOS.
3913 conf1 [X86] Force use of PCI Configuration Access
3914 Mechanism 1 (config address in IO port 0xCF8,
3915 data in IO port 0xCFC, both 32-bit).
3916 conf2 [X86] Force use of PCI Configuration Access
3917 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3918 the function, IO port 0xCFA, also 8-bit, sets
3919 bus number. The config space is then accessed
3920 through ports 0xC000-0xCFFF).
3921 See http://wiki.osdev.org/PCI for more info
3922 on the configuration access mechanisms.
3923 noaer [PCIE] If the PCIEAER kernel config parameter is
3924 enabled, this kernel boot option can be used to
3925 disable the use of PCIE advanced error reporting.
3926 nodomains [PCI] Disable support for multiple PCI
3927 root domains (aka PCI segments, in ACPI-speak).
3928 nommconf [X86] Disable use of MMCONFIG for PCI
3930 check_enable_amd_mmconf [X86] check for and enable
3931 properly configured MMIO access to PCI
3932 config space on AMD family 10h CPU
3933 nomsi [MSI] If the PCI_MSI kernel config parameter is
3934 enabled, this kernel boot option can be used to
3935 disable the use of MSI interrupts system-wide.
3936 noioapicquirk [APIC] Disable all boot interrupt quirks.
3937 Safety option to keep boot IRQs enabled. This
3938 should never be necessary.
3939 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3940 primary IO-APIC for bridges that cannot disable
3941 boot IRQs. This fixes a source of spurious IRQs
3942 when the system masks IRQs.
3943 noioapicreroute [APIC] Disable workaround that uses the
3944 boot IRQ equivalent of an IRQ that connects to
3945 a chipset where boot IRQs cannot be disabled.
3946 The opposite of ioapicreroute.
3947 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3948 routing table. These calls are known to be buggy
3949 on several machines and they hang the machine
3950 when used, but on other computers it's the only
3951 way to get the interrupt routing table. Try
3952 this option if the kernel is unable to allocate
3953 IRQs or discover secondary PCI buses on your
3955 rom [X86] Assign address space to expansion ROMs.
3956 Use with caution as certain devices share
3957 address decoders between ROMs and other
3959 norom [X86] Do not assign address space to
3960 expansion ROMs that do not already have
3961 BIOS assigned address ranges.
3962 nobar [X86] Do not assign address space to the
3963 BARs that weren't assigned by the BIOS.
3964 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3965 assigned automatically to PCI devices. You can
3966 make the kernel exclude IRQs of your ISA cards
3968 pirqaddr=0xAAAAA [X86] Specify the physical address
3969 of the PIRQ table (normally generated
3970 by the BIOS) if it is outside the
3971 F0000h-100000h range.
3972 lastbus=N [X86] Scan all buses thru bus #N. Can be
3973 useful if the kernel is unable to find your
3974 secondary buses and you want to tell it
3975 explicitly which ones they are.
3976 assign-busses [X86] Always assign all PCI bus
3977 numbers ourselves, overriding
3978 whatever the firmware may have done.
3979 usepirqmask [X86] Honor the possible IRQ mask stored
3980 in the BIOS $PIR table. This is needed on
3981 some systems with broken BIOSes, notably
3982 some HP Pavilion N5400 and Omnibook XE3
3983 notebooks. This will have no effect if ACPI
3984 IRQ routing is enabled.
3985 noacpi [X86] Do not use ACPI for IRQ routing
3986 or for PCI scanning.
3987 use_crs [X86] Use PCI host bridge window information
3988 from ACPI. On BIOSes from 2008 or later, this
3989 is enabled by default. If you need to use this,
3990 please report a bug.
3991 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3992 If you need to use this, please report a bug.
3993 routeirq Do IRQ routing for all PCI devices.
3994 This is normally done in pci_enable_device(),
3995 so this option is a temporary workaround
3996 for broken drivers that don't call it.
3997 skip_isa_align [X86] do not align io start addr, so can
3998 handle more pci cards
3999 noearly [X86] Don't do any early type 1 scanning.
4000 This might help on some broken boards which
4001 machine check when some devices' config space
4002 is read. But various workarounds are disabled
4003 and some IOMMU drivers will not work.
4004 bfsort Sort PCI devices into breadth-first order.
4005 This sorting is done to get a device
4006 order compatible with older (<= 2.4) kernels.
4007 nobfsort Don't sort PCI devices into breadth-first order.
4008 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4009 tuning and use the BIOS-configured MPS defaults.
4010 pcie_bus_safe Set every device's MPS to the largest value
4011 supported by all devices below the root complex.
4012 pcie_bus_perf Set device MPS to the largest allowable MPS
4013 based on its parent bus. Also set MRRS (Max
4014 Read Request Size) to the largest supported
4015 value (no larger than the MPS that the device
4016 or bus can support) for best performance.
4017 pcie_bus_peer2peer Set every device's MPS to 128B, which
4018 every device is guaranteed to support. This
4019 configuration allows peer-to-peer DMA between
4020 any pair of devices, possibly at the cost of
4021 reduced performance. This also guarantees
4022 that hot-added devices will work.
4023 cbiosize=nn[KMG] The fixed amount of bus space which is
4024 reserved for the CardBus bridge's IO window.
4025 The default value is 256 bytes.
4026 cbmemsize=nn[KMG] The fixed amount of bus space which is
4027 reserved for the CardBus bridge's memory
4028 window. The default value is 64 megabytes.
4031 [<order of align>@]<pci_dev>[; ...]
4032 Specifies alignment and device to reassign
4033 aligned memory resources. How to
4034 specify the device is described above.
4035 If <order of align> is not specified,
4036 PAGE_SIZE is used as alignment.
4037 A PCI-PCI bridge can be specified if resource
4038 windows need to be expanded.
4039 To specify the alignment for several
4040 instances of a device, the PCI vendor,
4041 device, subvendor, and subdevice may be
4042 specified, e.g., 12@pci:8086:9c22:103c:198f
4043 for 4096-byte alignment.
4044 ecrc= Enable/disable PCIe ECRC (transaction layer
4045 end-to-end CRC checking).
4046 bios: Use BIOS/firmware settings. This is the
4050 hpiosize=nn[KMG] The fixed amount of bus space which is
4051 reserved for hotplug bridge's IO window.
4052 Default size is 256 bytes.
4053 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4054 reserved for hotplug bridge's MMIO window.
4055 Default size is 2 megabytes.
4056 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4057 reserved for hotplug bridge's MMIO_PREF window.
4058 Default size is 2 megabytes.
4059 hpmemsize=nn[KMG] The fixed amount of bus space which is
4060 reserved for hotplug bridge's MMIO and
4062 Default size is 2 megabytes.
4063 hpbussize=nn The minimum amount of additional bus numbers
4064 reserved for buses below a hotplug bridge.
4066 realloc= Enable/disable reallocating PCI bridge resources
4067 if allocations done by BIOS are too small to
4068 accommodate resources required by all child
4070 off: Turn realloc off
4072 realloc same as realloc=on
4073 noari do not use PCIe ARI.
4074 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4075 do not use PCIe ATS (and IOMMU device IOTLB).
4076 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4077 only look for one device below a PCIe downstream
4079 big_root_window Try to add a big 64bit memory window to the PCIe
4080 root complex on AMD CPUs. Some GFX hardware
4081 can resize a BAR to allow access to all VRAM.
4082 Adding the window is slightly risky (it may
4083 conflict with unreported devices), so this
4085 disable_acs_redir=<pci_dev>[; ...]
4086 Specify one or more PCI devices (in the format
4087 specified above) separated by semicolons.
4088 Each device specified will have the PCI ACS
4089 redirect capabilities forced off which will
4090 allow P2P traffic between devices through
4091 bridges without forcing it upstream. Note:
4092 this removes isolation between devices and
4093 may put more devices in an IOMMU group.
4094 force_floating [S390] Force usage of floating interrupts.
4095 nomio [S390] Do not use MIO instructions.
4096 norid [S390] ignore the RID field and force use of
4097 one PCI domain per PCI function
4099 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4102 force Enable ASPM even on devices that claim not to support it.
4103 WARNING: Forcing ASPM on may cause system lockups.
4105 pcie_ports= [PCIE] PCIe port services handling:
4106 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4107 even if the platform doesn't give the OS permission to
4108 use them. This may cause conflicts if the platform
4109 also tries to use these services.
4110 dpc-native Use native PCIe service for DPC only. May
4111 cause conflicts if firmware uses AER or DPC.
4112 compat Disable native PCIe services (PME, AER, DPC, PCIe
4115 pcie_port_pm= [PCIE] PCIe port power management handling:
4116 off Disable power management of all PCIe ports
4117 force Forcibly enable power management of all PCIe ports
4119 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4120 nomsi Do not use MSI for native PCIe PME signaling (this makes
4121 all PCIe root ports use INTx for all services).
4123 pcmv= [HW,PCMCIA] BadgePAD 4
4127 Keep all power-domains already enabled by bootloader on,
4128 even if no driver has claimed them. This is useful
4129 for debug and development, but should not be
4130 needed on a platform with proper driver support.
4133 See Documentation/admin-guide/blockdev/paride.rst.
4135 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4138 See arch/parisc/kernel/pdc_chassis.c
4140 percpu_alloc= Select which percpu first chunk allocator to use.
4141 Currently supported values are "embed" and "page".
4142 Archs may support subset or none of the selections.
4143 See comments in mm/percpu.c for details on each
4144 allocator. This parameter is primarily for debugging
4145 and performance comparison.
4148 See Documentation/admin-guide/blockdev/paride.rst.
4151 See Documentation/admin-guide/blockdev/paride.rst.
4153 pirq= [SMP,APIC] Manual mp-table setup
4154 See Documentation/x86/i386/IO-APIC.rst.
4156 plip= [PPT,NET] Parallel port network link
4157 Format: { parport<nr> | timid | 0 }
4158 See also Documentation/admin-guide/parport.rst.
4160 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4161 Override pmtimer IOPort with a hex value.
4164 pm_debug_messages [SUSPEND,KNL]
4165 Enable suspend/resume debug messages during boot up.
4168 Enable PNP debug messages (depends on the
4169 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4170 via /sys/module/pnp/parameters/debug. We always show
4171 current resource usage; turning this on also shows
4172 possible settings and some assignment information.
4178 { on | off | curr | res | no-curr | no-res }
4181 [ISAPNP] Exclude IRQs for the autoconfiguration
4184 [ISAPNP] Exclude DMAs for the autoconfiguration
4186 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4187 Ranges are in pairs (I/O port base and size).
4190 [ISAPNP] Exclude memory regions for the
4192 Ranges are in pairs (memory base and size).
4194 ports= [IP_VS_FTP] IPVS ftp helper module
4196 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4198 Format: <port>,<port>....
4200 powersave=off [PPC] This option disables power saving features.
4201 It specifically disables cpuidle and sets the
4202 platform machine description specific power_save
4203 function to NULL. On Idle the CPU just reduces
4206 ppc_strict_facility_enable
4207 [PPC] This option catches any kernel floating point,
4208 Altivec, VSX and SPE outside of regions specifically
4209 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4210 There is some performance impact when enabling this.
4214 Disable Hardware Transactional Memory
4217 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4218 none - Limited to cond_resched() calls
4219 voluntary - Limited to cond_resched() and might_sleep() calls
4220 full - Any section that isn't explicitly preempt disabled
4221 can be preempted anytime.
4223 print-fatal-signals=
4224 [KNL] debug: print fatal signals
4226 If enabled, warn about various signal handling
4227 related application anomalies: too many signals,
4228 too many POSIX.1 timers, fatal signals causing a
4231 If you hit the warning due to signal overflow,
4232 you might want to try "ulimit -i unlimited".
4236 printk.always_kmsg_dump=
4237 Trigger kmsg_dump for cases other than kernel oops or
4239 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4242 printk.console_no_auto_verbose=
4243 Disable console loglevel raise on oops, panic
4244 or lockdep-detected issues (only if lock debug is on).
4245 With an exception to setups with low baudrate on
4246 serial console, keeping this 0 is a good choice
4247 in order to provide more debug information.
4249 default: 0 (auto_verbose is enabled)
4251 printk.devkmsg={on,off,ratelimit}
4252 Control writing to /dev/kmsg.
4253 on - unlimited logging to /dev/kmsg from userspace
4254 off - logging to /dev/kmsg disabled
4255 ratelimit - ratelimit the logging
4258 printk.time= Show timing data prefixed to each printk message line
4259 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4261 processor.max_cstate= [HW,ACPI]
4262 Limit processor to maximum C-state
4263 max_cstate=9 overrides any DMI blacklist limit.
4265 processor.nocst [HW,ACPI]
4266 Ignore the _CST method to determine C-states,
4267 instead using the legacy FADT method
4269 profile= [KNL] Enable kernel profiling via /proc/profile
4270 Format: [<profiletype>,]<number>
4271 Param: <profiletype>: "schedule", "sleep", or "kvm"
4272 [defaults to kernel profiling]
4273 Param: "schedule" - profile schedule points.
4274 Param: "sleep" - profile D-state sleeping (millisecs).
4275 Requires CONFIG_SCHEDSTATS
4276 Param: "kvm" - profile VM exits.
4277 Param: <number> - step/bucket size as a power of 2 for
4278 statistical time based profiling.
4280 prompt_ramdisk= [RAM] [Deprecated]
4282 prot_virt= [S390] enable hosting protected virtual machines
4283 isolated from the hypervisor (if hardware supports
4287 psi= [KNL] Enable or disable pressure stall information
4291 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4292 probe for; one of (bare|imps|exps|lifebook|any).
4293 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4295 psmouse.resetafter= [HW,MOUSE]
4296 Try to reset the device after so many bad packets
4299 [HW,MOUSE] Set desired mouse resolution, in dpi.
4300 psmouse.smartscroll=
4301 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4302 0 = disabled, 1 = enabled (default).
4304 pstore.backend= Specify the name of the pstore backend to use
4307 See Documentation/admin-guide/blockdev/paride.rst.
4309 pti= [X86-64] Control Page Table Isolation of user and
4310 kernel address spaces. Disabling this feature
4311 removes hardening, but improves performance of
4312 system calls and interrupts.
4314 on - unconditionally enable
4315 off - unconditionally disable
4316 auto - kernel detects whether your CPU model is
4317 vulnerable to issues that PTI mitigates
4319 Not specifying this option is equivalent to pti=auto.
4322 Equivalent to pti=off
4325 [KNL] Number of legacy pty's. Overwrites compiled-in
4328 quiet [KNL] Disable most log messages
4333 See Documentation/admin-guide/md.rst.
4335 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4336 See Documentation/admin-guide/blockdev/ramdisk.rst.
4338 ramdisk_start= [RAM] RAM disk image start address
4340 random.trust_cpu={on,off}
4341 [KNL] Enable or disable trusting the use of the
4342 CPU's random number generator (if available) to
4343 fully seed the kernel's CRNG. Default is controlled
4344 by CONFIG_RANDOM_TRUST_CPU.
4346 random.trust_bootloader={on,off}
4347 [KNL] Enable or disable trusting the use of a
4348 seed passed by the bootloader (if available) to
4349 fully seed the kernel's CRNG. Default is controlled
4350 by CONFIG_RANDOM_TRUST_BOOTLOADER.
4352 randomize_kstack_offset=
4353 [KNL] Enable or disable kernel stack offset
4354 randomization, which provides roughly 5 bits of
4355 entropy, frustrating memory corruption attacks
4356 that depend on stack address determinism or
4357 cross-syscall address exposures. This is only
4358 available on architectures that have defined
4359 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4360 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4361 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4363 ras=option[,option,...] [KNL] RAS-specific options
4366 Disable the Correctable Errors Collector,
4367 see CONFIG_RAS_CEC help text.
4370 The argument is a cpu list, as described above.
4372 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4373 the specified list of CPUs to be no-callback CPUs.
4374 Invocation of these CPUs' RCU callbacks will be
4375 offloaded to "rcuox/N" kthreads created for that
4376 purpose, where "x" is "p" for RCU-preempt, and
4377 "s" for RCU-sched, and "N" is the CPU number.
4378 This reduces OS jitter on the offloaded CPUs,
4379 which can be useful for HPC and real-time
4380 workloads. It can also improve energy efficiency
4381 for asymmetric multiprocessors.
4384 Rather than requiring that offloaded CPUs
4385 (specified by rcu_nocbs= above) explicitly
4386 awaken the corresponding "rcuoN" kthreads,
4387 make these kthreads poll for callbacks.
4388 This improves the real-time response for the
4389 offloaded CPUs by relieving them of the need to
4390 wake up the corresponding kthread, but degrades
4391 energy efficiency by requiring that the kthreads
4392 periodically wake up to do the polling.
4394 rcutree.blimit= [KNL]
4395 Set maximum number of finished RCU callbacks to
4396 process in one batch.
4398 rcutree.dump_tree= [KNL]
4399 Dump the structure of the rcu_node combining tree
4400 out at early boot. This is used for diagnostic
4401 purposes, to verify correct tree setup.
4403 rcutree.gp_cleanup_delay= [KNL]
4404 Set the number of jiffies to delay each step of
4405 RCU grace-period cleanup.
4407 rcutree.gp_init_delay= [KNL]
4408 Set the number of jiffies to delay each step of
4409 RCU grace-period initialization.
4411 rcutree.gp_preinit_delay= [KNL]
4412 Set the number of jiffies to delay each step of
4413 RCU grace-period pre-initialization, that is,
4414 the propagation of recent CPU-hotplug changes up
4415 the rcu_node combining tree.
4417 rcutree.use_softirq= [KNL]
4418 If set to zero, move all RCU_SOFTIRQ processing to
4419 per-CPU rcuc kthreads. Defaults to a non-zero
4420 value, meaning that RCU_SOFTIRQ is used by default.
4421 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4423 But note that CONFIG_PREEMPT_RT=y kernels disable
4424 this kernel boot parameter, forcibly setting it
4427 rcutree.rcu_fanout_exact= [KNL]
4428 Disable autobalancing of the rcu_node combining
4429 tree. This is used by rcutorture, and might
4430 possibly be useful for architectures having high
4431 cache-to-cache transfer latencies.
4433 rcutree.rcu_fanout_leaf= [KNL]
4434 Change the number of CPUs assigned to each
4435 leaf rcu_node structure. Useful for very
4436 large systems, which will choose the value 64,
4437 and for NUMA systems with large remote-access
4438 latencies, which will choose a value aligned
4439 with the appropriate hardware boundaries.
4441 rcutree.rcu_min_cached_objs= [KNL]
4442 Minimum number of objects which are cached and
4443 maintained per one CPU. Object size is equal
4444 to PAGE_SIZE. The cache allows to reduce the
4445 pressure to page allocator, also it makes the
4446 whole algorithm to behave better in low memory
4449 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4450 Set the page-cache refill delay (in milliseconds)
4451 in response to low-memory conditions. The range
4452 of permitted values is in the range 0:100000.
4454 rcutree.jiffies_till_first_fqs= [KNL]
4455 Set delay from grace-period initialization to
4456 first attempt to force quiescent states.
4457 Units are jiffies, minimum value is zero,
4458 and maximum value is HZ.
4460 rcutree.jiffies_till_next_fqs= [KNL]
4461 Set delay between subsequent attempts to force
4462 quiescent states. Units are jiffies, minimum
4463 value is one, and maximum value is HZ.
4465 rcutree.jiffies_till_sched_qs= [KNL]
4466 Set required age in jiffies for a
4467 given grace period before RCU starts
4468 soliciting quiescent-state help from
4469 rcu_note_context_switch() and cond_resched().
4470 If not specified, the kernel will calculate
4471 a value based on the most recent settings
4472 of rcutree.jiffies_till_first_fqs
4473 and rcutree.jiffies_till_next_fqs.
4474 This calculated value may be viewed in
4475 rcutree.jiffies_to_sched_qs. Any attempt to set
4476 rcutree.jiffies_to_sched_qs will be cheerfully
4479 rcutree.kthread_prio= [KNL,BOOT]
4480 Set the SCHED_FIFO priority of the RCU per-CPU
4481 kthreads (rcuc/N). This value is also used for
4482 the priority of the RCU boost threads (rcub/N)
4483 and for the RCU grace-period kthreads (rcu_bh,
4484 rcu_preempt, and rcu_sched). If RCU_BOOST is
4485 set, valid values are 1-99 and the default is 1
4486 (the least-favored priority). Otherwise, when
4487 RCU_BOOST is not set, valid values are 0-99 and
4488 the default is zero (non-realtime operation).
4490 rcutree.rcu_nocb_gp_stride= [KNL]
4491 Set the number of NOCB callback kthreads in
4492 each group, which defaults to the square root
4493 of the number of CPUs. Larger numbers reduce
4494 the wakeup overhead on the global grace-period
4495 kthread, but increases that same overhead on
4496 each group's NOCB grace-period kthread.
4498 rcutree.qhimark= [KNL]
4499 Set threshold of queued RCU callbacks beyond which
4500 batch limiting is disabled.
4502 rcutree.qlowmark= [KNL]
4503 Set threshold of queued RCU callbacks below which
4504 batch limiting is re-enabled.
4506 rcutree.qovld= [KNL]
4507 Set threshold of queued RCU callbacks beyond which
4508 RCU's force-quiescent-state scan will aggressively
4509 enlist help from cond_resched() and sched IPIs to
4510 help CPUs more quickly reach quiescent states.
4511 Set to less than zero to make this be set based
4512 on rcutree.qhimark at boot time and to zero to
4513 disable more aggressive help enlistment.
4515 rcutree.rcu_idle_gp_delay= [KNL]
4516 Set wakeup interval for idle CPUs that have
4517 RCU callbacks (RCU_FAST_NO_HZ=y).
4519 rcutree.rcu_kick_kthreads= [KNL]
4520 Cause the grace-period kthread to get an extra
4521 wake_up() if it sleeps three times longer than
4522 it should at force-quiescent-state time.
4523 This wake_up() will be accompanied by a
4524 WARN_ONCE() splat and an ftrace_dump().
4526 rcutree.rcu_unlock_delay= [KNL]
4527 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4528 this specifies an rcu_read_unlock()-time delay
4529 in microseconds. This defaults to zero.
4530 Larger delays increase the probability of
4531 catching RCU pointer leaks, that is, buggy use
4532 of RCU-protected pointers after the relevant
4533 rcu_read_unlock() has completed.
4535 rcutree.sysrq_rcu= [KNL]
4536 Commandeer a sysrq key to dump out Tree RCU's
4537 rcu_node tree with an eye towards determining
4538 why a new grace period has not yet started.
4540 rcuscale.gp_async= [KNL]
4541 Measure performance of asynchronous
4542 grace-period primitives such as call_rcu().
4544 rcuscale.gp_async_max= [KNL]
4545 Specify the maximum number of outstanding
4546 callbacks per writer thread. When a writer
4547 thread exceeds this limit, it invokes the
4548 corresponding flavor of rcu_barrier() to allow
4549 previously posted callbacks to drain.
4551 rcuscale.gp_exp= [KNL]
4552 Measure performance of expedited synchronous
4553 grace-period primitives.
4555 rcuscale.holdoff= [KNL]
4556 Set test-start holdoff period. The purpose of
4557 this parameter is to delay the start of the
4558 test until boot completes in order to avoid
4561 rcuscale.kfree_rcu_test= [KNL]
4562 Set to measure performance of kfree_rcu() flooding.
4564 rcuscale.kfree_rcu_test_double= [KNL]
4565 Test the double-argument variant of kfree_rcu().
4566 If this parameter has the same value as
4567 rcuscale.kfree_rcu_test_single, both the single-
4568 and double-argument variants are tested.
4570 rcuscale.kfree_rcu_test_single= [KNL]
4571 Test the single-argument variant of kfree_rcu().
4572 If this parameter has the same value as
4573 rcuscale.kfree_rcu_test_double, both the single-
4574 and double-argument variants are tested.
4576 rcuscale.kfree_nthreads= [KNL]
4577 The number of threads running loops of kfree_rcu().
4579 rcuscale.kfree_alloc_num= [KNL]
4580 Number of allocations and frees done in an iteration.
4582 rcuscale.kfree_loops= [KNL]
4583 Number of loops doing rcuscale.kfree_alloc_num number
4584 of allocations and frees.
4586 rcuscale.nreaders= [KNL]
4587 Set number of RCU readers. The value -1 selects
4588 N, where N is the number of CPUs. A value
4589 "n" less than -1 selects N-n+1, where N is again
4590 the number of CPUs. For example, -2 selects N
4591 (the number of CPUs), -3 selects N+1, and so on.
4592 A value of "n" less than or equal to -N selects
4595 rcuscale.nwriters= [KNL]
4596 Set number of RCU writers. The values operate
4597 the same as for rcuscale.nreaders.
4598 N, where N is the number of CPUs
4600 rcuscale.perf_type= [KNL]
4601 Specify the RCU implementation to test.
4603 rcuscale.shutdown= [KNL]
4604 Shut the system down after performance tests
4605 complete. This is useful for hands-off automated
4608 rcuscale.verbose= [KNL]
4609 Enable additional printk() statements.
4611 rcuscale.writer_holdoff= [KNL]
4612 Write-side holdoff between grace periods,
4613 in microseconds. The default of zero says
4616 rcutorture.fqs_duration= [KNL]
4617 Set duration of force_quiescent_state bursts
4620 rcutorture.fqs_holdoff= [KNL]
4621 Set holdoff time within force_quiescent_state bursts
4624 rcutorture.fqs_stutter= [KNL]
4625 Set wait time between force_quiescent_state bursts
4628 rcutorture.fwd_progress= [KNL]
4629 Enable RCU grace-period forward-progress testing
4630 for the types of RCU supporting this notion.
4632 rcutorture.fwd_progress_div= [KNL]
4633 Specify the fraction of a CPU-stall-warning
4634 period to do tight-loop forward-progress testing.
4636 rcutorture.fwd_progress_holdoff= [KNL]
4637 Number of seconds to wait between successive
4638 forward-progress tests.
4640 rcutorture.fwd_progress_need_resched= [KNL]
4641 Enclose cond_resched() calls within checks for
4642 need_resched() during tight-loop forward-progress
4645 rcutorture.gp_cond= [KNL]
4646 Use conditional/asynchronous update-side
4647 primitives, if available.
4649 rcutorture.gp_exp= [KNL]
4650 Use expedited update-side primitives, if available.
4652 rcutorture.gp_normal= [KNL]
4653 Use normal (non-expedited) asynchronous
4654 update-side primitives, if available.
4656 rcutorture.gp_sync= [KNL]
4657 Use normal (non-expedited) synchronous
4658 update-side primitives, if available. If all
4659 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4660 rcutorture.gp_normal=, and rcutorture.gp_sync=
4661 are zero, rcutorture acts as if is interpreted
4662 they are all non-zero.
4664 rcutorture.irqreader= [KNL]
4665 Run RCU readers from irq handlers, or, more
4666 accurately, from a timer handler. Not all RCU
4667 flavors take kindly to this sort of thing.
4669 rcutorture.leakpointer= [KNL]
4670 Leak an RCU-protected pointer out of the reader.
4671 This can of course result in splats, and is
4672 intended to test the ability of things like
4673 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4676 rcutorture.n_barrier_cbs= [KNL]
4677 Set callbacks/threads for rcu_barrier() testing.
4679 rcutorture.nfakewriters= [KNL]
4680 Set number of concurrent RCU writers. These just
4681 stress RCU, they don't participate in the actual
4682 test, hence the "fake".
4684 rcutorture.nocbs_nthreads= [KNL]
4685 Set number of RCU callback-offload togglers.
4686 Zero (the default) disables toggling.
4688 rcutorture.nocbs_toggle= [KNL]
4689 Set the delay in milliseconds between successive
4690 callback-offload toggling attempts.
4692 rcutorture.nreaders= [KNL]
4693 Set number of RCU readers. The value -1 selects
4694 N-1, where N is the number of CPUs. A value
4695 "n" less than -1 selects N-n-2, where N is again
4696 the number of CPUs. For example, -2 selects N
4697 (the number of CPUs), -3 selects N+1, and so on.
4699 rcutorture.object_debug= [KNL]
4700 Enable debug-object double-call_rcu() testing.
4702 rcutorture.onoff_holdoff= [KNL]
4703 Set time (s) after boot for CPU-hotplug testing.
4705 rcutorture.onoff_interval= [KNL]
4706 Set time (jiffies) between CPU-hotplug operations,
4707 or zero to disable CPU-hotplug testing.
4709 rcutorture.read_exit= [KNL]
4710 Set the number of read-then-exit kthreads used
4711 to test the interaction of RCU updaters and
4712 task-exit processing.
4714 rcutorture.read_exit_burst= [KNL]
4715 The number of times in a given read-then-exit
4716 episode that a set of read-then-exit kthreads
4719 rcutorture.read_exit_delay= [KNL]
4720 The delay, in seconds, between successive
4721 read-then-exit testing episodes.
4723 rcutorture.shuffle_interval= [KNL]
4724 Set task-shuffle interval (s). Shuffling tasks
4725 allows some CPUs to go into dyntick-idle mode
4726 during the rcutorture test.
4728 rcutorture.shutdown_secs= [KNL]
4729 Set time (s) after boot system shutdown. This
4730 is useful for hands-off automated testing.
4732 rcutorture.stall_cpu= [KNL]
4733 Duration of CPU stall (s) to test RCU CPU stall
4734 warnings, zero to disable.
4736 rcutorture.stall_cpu_block= [KNL]
4737 Sleep while stalling if set. This will result
4738 in warnings from preemptible RCU in addition
4739 to any other stall-related activity.
4741 rcutorture.stall_cpu_holdoff= [KNL]
4742 Time to wait (s) after boot before inducing stall.
4744 rcutorture.stall_cpu_irqsoff= [KNL]
4745 Disable interrupts while stalling if set.
4747 rcutorture.stall_gp_kthread= [KNL]
4748 Duration (s) of forced sleep within RCU
4749 grace-period kthread to test RCU CPU stall
4750 warnings, zero to disable. If both stall_cpu
4751 and stall_gp_kthread are specified, the
4752 kthread is starved first, then the CPU.
4754 rcutorture.stat_interval= [KNL]
4755 Time (s) between statistics printk()s.
4757 rcutorture.stutter= [KNL]
4758 Time (s) to stutter testing, for example, specifying
4759 five seconds causes the test to run for five seconds,
4760 wait for five seconds, and so on. This tests RCU's
4761 ability to transition abruptly to and from idle.
4763 rcutorture.test_boost= [KNL]
4764 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4765 "Maybe" means test if the RCU implementation
4766 under test support RCU priority boosting.
4768 rcutorture.test_boost_duration= [KNL]
4769 Duration (s) of each individual boost test.
4771 rcutorture.test_boost_interval= [KNL]
4772 Interval (s) between each boost test.
4774 rcutorture.test_no_idle_hz= [KNL]
4775 Test RCU's dyntick-idle handling. See also the
4776 rcutorture.shuffle_interval parameter.
4778 rcutorture.torture_type= [KNL]
4779 Specify the RCU implementation to test.
4781 rcutorture.verbose= [KNL]
4782 Enable additional printk() statements.
4784 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4785 Dump ftrace buffer after reporting RCU CPU
4788 rcupdate.rcu_cpu_stall_suppress= [KNL]
4789 Suppress RCU CPU stall warning messages.
4791 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4792 Suppress RCU CPU stall warning messages and
4793 rcutorture writer stall warnings that occur
4794 during early boot, that is, during the time
4795 before the init task is spawned.
4797 rcupdate.rcu_cpu_stall_timeout= [KNL]
4798 Set timeout for RCU CPU stall warning messages.
4800 rcupdate.rcu_expedited= [KNL]
4801 Use expedited grace-period primitives, for
4802 example, synchronize_rcu_expedited() instead
4803 of synchronize_rcu(). This reduces latency,
4804 but can increase CPU utilization, degrade
4805 real-time latency, and degrade energy efficiency.
4806 No effect on CONFIG_TINY_RCU kernels.
4808 rcupdate.rcu_normal= [KNL]
4809 Use only normal grace-period primitives,
4810 for example, synchronize_rcu() instead of
4811 synchronize_rcu_expedited(). This improves
4812 real-time latency, CPU utilization, and
4813 energy efficiency, but can expose users to
4814 increased grace-period latency. This parameter
4815 overrides rcupdate.rcu_expedited. No effect on
4816 CONFIG_TINY_RCU kernels.
4818 rcupdate.rcu_normal_after_boot= [KNL]
4819 Once boot has completed (that is, after
4820 rcu_end_inkernel_boot() has been invoked), use
4821 only normal grace-period primitives. No effect
4822 on CONFIG_TINY_RCU kernels.
4824 But note that CONFIG_PREEMPT_RT=y kernels enables
4825 this kernel boot parameter, forcibly setting
4826 it to the value one, that is, converting any
4827 post-boot attempt at an expedited RCU grace
4828 period to instead use normal non-expedited
4829 grace-period processing.
4831 rcupdate.rcu_task_ipi_delay= [KNL]
4832 Set time in jiffies during which RCU tasks will
4833 avoid sending IPIs, starting with the beginning
4834 of a given grace period. Setting a large
4835 number avoids disturbing real-time workloads,
4836 but lengthens grace periods.
4838 rcupdate.rcu_task_stall_timeout= [KNL]
4839 Set timeout in jiffies for RCU task stall warning
4840 messages. Disable with a value less than or equal
4843 rcupdate.rcu_self_test= [KNL]
4844 Run the RCU early boot self tests
4848 Run specified binary instead of /init from the ramdisk,
4849 used for early userspace startup. See initrd.
4852 force - Override the decision by the kernel to hide the
4853 advertisement of RDRAND support (this affects
4854 certain AMD processors because of buggy BIOS
4855 support, specifically around the suspend/resume
4859 Turn on/off individual RDT features. List is:
4860 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4862 E.g. to turn on cmt and turn off mba use:
4866 Format (x86 or x86_64):
4867 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
4869 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4871 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4872 (prefix with 'panic_' to set mode for panic
4874 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4875 reboot_force is either force or not specified,
4876 reboot_cpu is s[mp]#### with #### being the processor
4877 to be used for rebooting.
4879 refscale.holdoff= [KNL]
4880 Set test-start holdoff period. The purpose of
4881 this parameter is to delay the start of the
4882 test until boot completes in order to avoid
4885 refscale.loops= [KNL]
4886 Set the number of loops over the synchronization
4887 primitive under test. Increasing this number
4888 reduces noise due to loop start/end overhead,
4889 but the default has already reduced the per-pass
4890 noise to a handful of picoseconds on ca. 2020
4893 refscale.nreaders= [KNL]
4894 Set number of readers. The default value of -1
4895 selects N, where N is roughly 75% of the number
4896 of CPUs. A value of zero is an interesting choice.
4898 refscale.nruns= [KNL]
4899 Set number of runs, each of which is dumped onto
4902 refscale.readdelay= [KNL]
4903 Set the read-side critical-section duration,
4904 measured in microseconds.
4906 refscale.scale_type= [KNL]
4907 Specify the read-protection implementation to test.
4909 refscale.shutdown= [KNL]
4910 Shut down the system at the end of the performance
4911 test. This defaults to 1 (shut it down) when
4912 refscale is built into the kernel and to 0 (leave
4913 it running) when refscale is built as a module.
4915 refscale.verbose= [KNL]
4916 Enable additional printk() statements.
4918 refscale.verbose_batched= [KNL]
4919 Batch the additional printk() statements. If zero
4920 (the default) or negative, print everything. Otherwise,
4921 print every Nth verbose statement, where N is the value
4925 [KNL, SMP] Set scheduler's default relax_domain_level.
4926 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4928 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4929 Format: <base1>,<size1>[,<base2>,<size2>,...]
4930 Reserve I/O ports or memory so the kernel won't use
4931 them. If <base> is less than 0x10000, the region
4932 is assumed to be I/O ports; otherwise it is memory.
4934 reservetop= [X86-32]
4936 Reserves a hole at the top of the kernel virtual
4939 reset_devices [KNL] Force drivers to reset the underlying device
4940 during initialization.
4943 Specify the partition device for software suspend
4945 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4947 resume_offset= [SWSUSP]
4948 Specify the offset from the beginning of the partition
4949 given by "resume=" at which the swap header is located,
4950 in <PAGE_SIZE> units (needed only for swap files).
4951 See Documentation/power/swsusp-and-swap-files.rst
4953 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4954 read the resume files
4956 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4957 Useful for devices that are detected asynchronously
4958 (e.g. USB and MMC devices).
4960 hibernate= [HIBERNATION]
4961 noresume Don't check if there's a hibernation image
4962 present during boot.
4963 nocompress Don't compress/decompress hibernation images.
4964 no Disable hibernation and resume.
4965 protect_image Turn on image protection during restoration
4966 (that will set all pages holding image data
4967 during restoration read-only).
4969 retain_initrd [RAM] Keep initrd memory after extraction
4971 rfkill.default_state=
4972 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4973 etc. communication is blocked by default.
4976 rfkill.master_switch_mode=
4977 0 The "airplane mode" button does nothing.
4978 1 The "airplane mode" button toggles between everything
4979 blocked and the previous configuration.
4980 2 The "airplane mode" button toggles between everything
4981 blocked and everything unblocked.
4983 rhash_entries= [KNL,NET]
4984 Set number of hash buckets for route cache
4987 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4990 ro [KNL] Mount root device read-only on boot
4993 on Mark read-only kernel memory as read-only (default).
4994 off Leave read-only kernel memory writable for debugging.
4997 Enable the uart passthrough on the designated usb port
4998 on Rockchip SoCs. When active, the signals of the
4999 debug-uart get routed to the D+ and D- pins of the usb
5000 port and the regular usb controller gets disabled.
5002 root= [KNL] Root filesystem
5003 See name_to_dev_t comment in init/do_mounts.c.
5005 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5006 mount the root filesystem
5008 rootflags= [KNL] Set root filesystem mount option string
5010 rootfstype= [KNL] Set root filesystem type
5012 rootwait [KNL] Wait (indefinitely) for root device to show up.
5013 Useful for devices that are detected asynchronously
5014 (e.g. USB and MMC devices).
5016 rproc_mem=nn[KMG][@address]
5017 [KNL,ARM,CMA] Remoteproc physical memory block.
5018 Memory area to be used by remote processor image,
5021 rw [KNL] Mount root device read-write on boot
5023 S [KNL] Run init in single mode
5025 s390_iommu= [HW,S390]
5026 Set s390 IOTLB flushing mode
5028 With strict flushing every unmap operation will result in
5029 an IOTLB flush. Default is lazy flushing before reuse,
5033 See drivers/net/irda/sa1100_ir.c.
5035 sched_verbose [KNL] Enables verbose scheduler debug messages.
5037 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5038 Allowed values are enable and disable. This feature
5039 incurs a small amount of overhead in the scheduler
5040 but is useful for debugging and performance tuning.
5042 sched_thermal_decay_shift=
5043 [KNL, SMP] Set a decay shift for scheduler thermal
5044 pressure signal. Thermal pressure signal follows the
5045 default decay period of other scheduler pelt
5046 signals(usually 32 ms but configurable). Setting
5047 sched_thermal_decay_shift will left shift the decay
5048 period for the thermal pressure signal by the shift
5050 i.e. with the default pelt decay period of 32 ms
5051 sched_thermal_decay_shift thermal pressure decay pr
5055 Format: integer between 0 and 10
5058 scftorture.holdoff= [KNL]
5059 Number of seconds to hold off before starting
5060 test. Defaults to zero for module insertion and
5061 to 10 seconds for built-in smp_call_function()
5064 scftorture.longwait= [KNL]
5065 Request ridiculously long waits randomly selected
5066 up to the chosen limit in seconds. Zero (the
5067 default) disables this feature. Please note
5068 that requesting even small non-zero numbers of
5069 seconds can result in RCU CPU stall warnings,
5070 softlockup complaints, and so on.
5072 scftorture.nthreads= [KNL]
5073 Number of kthreads to spawn to invoke the
5074 smp_call_function() family of functions.
5075 The default of -1 specifies a number of kthreads
5076 equal to the number of CPUs.
5078 scftorture.onoff_holdoff= [KNL]
5079 Number seconds to wait after the start of the
5080 test before initiating CPU-hotplug operations.
5082 scftorture.onoff_interval= [KNL]
5083 Number seconds to wait between successive
5084 CPU-hotplug operations. Specifying zero (which
5085 is the default) disables CPU-hotplug operations.
5087 scftorture.shutdown_secs= [KNL]
5088 The number of seconds following the start of the
5089 test after which to shut down the system. The
5090 default of zero avoids shutting down the system.
5091 Non-zero values are useful for automated tests.
5093 scftorture.stat_interval= [KNL]
5094 The number of seconds between outputting the
5095 current test statistics to the console. A value
5096 of zero disables statistics output.
5098 scftorture.stutter_cpus= [KNL]
5099 The number of jiffies to wait between each change
5100 to the set of CPUs under test.
5102 scftorture.use_cpus_read_lock= [KNL]
5103 Use use_cpus_read_lock() instead of the default
5104 preempt_disable() to disable CPU hotplug
5105 while invoking one of the smp_call_function*()
5108 scftorture.verbose= [KNL]
5109 Enable additional printk() statements.
5111 scftorture.weight_single= [KNL]
5112 The probability weighting to use for the
5113 smp_call_function_single() function with a zero
5114 "wait" parameter. A value of -1 selects the
5115 default if all other weights are -1. However,
5116 if at least one weight has some other value, a
5117 value of -1 will instead select a weight of zero.
5119 scftorture.weight_single_wait= [KNL]
5120 The probability weighting to use for the
5121 smp_call_function_single() function with a
5122 non-zero "wait" parameter. See weight_single.
5124 scftorture.weight_many= [KNL]
5125 The probability weighting to use for the
5126 smp_call_function_many() function with a zero
5127 "wait" parameter. See weight_single.
5128 Note well that setting a high probability for
5129 this weighting can place serious IPI load
5132 scftorture.weight_many_wait= [KNL]
5133 The probability weighting to use for the
5134 smp_call_function_many() function with a
5135 non-zero "wait" parameter. See weight_single
5138 scftorture.weight_all= [KNL]
5139 The probability weighting to use for the
5140 smp_call_function_all() function with a zero
5141 "wait" parameter. See weight_single and
5144 scftorture.weight_all_wait= [KNL]
5145 The probability weighting to use for the
5146 smp_call_function_all() function with a
5147 non-zero "wait" parameter. See weight_single
5150 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5151 xtime_lock contention on larger systems, and/or RCU lock
5152 contention on all systems with CONFIG_MAXSMP set.
5153 Format: { "0" | "1" }
5154 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5156 Note: increases power consumption, thus should only be
5157 enabled if running jitter sensitive (HPC/RT) workloads.
5159 security= [SECURITY] Choose a legacy "major" security module to
5160 enable at boot. This has been deprecated by the
5163 selinux= [SELINUX] Disable or enable SELinux at boot time.
5164 Format: { "0" | "1" }
5165 See security/selinux/Kconfig help text.
5170 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5171 Format: { "0" | "1" }
5172 See security/apparmor/Kconfig help text
5175 Default value is set via kernel config option.
5177 serialnumber [BUGS=X86-32]
5180 Maximal number of shapers.
5188 Enable merging of slabs with similar size when the
5189 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5192 Disable merging of slabs with similar size. May be
5193 necessary if there is some reason to distinguish
5194 allocs to different slabs, especially in hardened
5195 environments where the risk of heap overflows and
5196 layout control by attackers can usually be
5197 frustrated by disabling merging. This will reduce
5198 most of the exposure of a heap attack to a single
5199 cache (risks via metadata attacks are mostly
5200 unchanged). Debug options disable merging on their
5202 For more information see Documentation/vm/slub.rst.
5204 slab_max_order= [MM, SLAB]
5205 Determines the maximum allowed order for slabs.
5206 A high setting may cause OOMs due to memory
5207 fragmentation. Defaults to 1 for systems with
5208 more than 32MB of RAM, 0 otherwise.
5210 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5211 Enabling slub_debug allows one to determine the
5212 culprit if slab objects become corrupted. Enabling
5213 slub_debug can create guard zones around objects and
5214 may poison objects when not in use. Also tracks the
5215 last alloc / free. For more information see
5216 Documentation/vm/slub.rst.
5218 slub_max_order= [MM, SLUB]
5219 Determines the maximum allowed order for slabs.
5220 A high setting may cause OOMs due to memory
5221 fragmentation. For more information see
5222 Documentation/vm/slub.rst.
5224 slub_min_objects= [MM, SLUB]
5225 The minimum number of objects per slab. SLUB will
5226 increase the slab order up to slub_max_order to
5227 generate a sufficiently large slab able to contain
5228 the number of objects indicated. The higher the number
5229 of objects the smaller the overhead of tracking slabs
5230 and the less frequently locks need to be acquired.
5231 For more information see Documentation/vm/slub.rst.
5233 slub_min_order= [MM, SLUB]
5234 Determines the minimum page order for slabs. Must be
5235 lower than slub_max_order.
5236 For more information see Documentation/vm/slub.rst.
5238 slub_merge [MM, SLUB]
5239 Same with slab_merge.
5241 slub_nomerge [MM, SLUB]
5242 Same with slab_nomerge. This is supported for legacy.
5243 See slab_nomerge for more information.
5246 Format: <io1>[,<io2>[,...,<io8>]]
5248 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5249 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5250 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5251 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5252 smsc-ircc2.ircc_irq= [HW] IRQ line
5253 smsc-ircc2.ircc_dma= [HW] DMA channel
5254 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5255 0: Toshiba Satellite 1800 (GP data pin select)
5256 1: Fast pin select (default)
5259 smt [KNL,S390] Set the maximum number of threads (logical
5260 CPUs) to use per physical CPU on systems capable of
5261 symmetric multithreading (SMT). Will be capped to the
5262 actual hardware limit.
5264 Default: -1 (no limit)
5267 [KNL] Should the soft-lockup detector generate panics.
5270 A value of 1 instructs the soft-lockup detector
5271 to panic the machine when a soft-lockup occurs. It is
5272 also controlled by the kernel.softlockup_panic sysctl
5273 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5274 respective build-time switch to that functionality.
5276 softlockup_all_cpu_backtrace=
5277 [KNL] Should the soft-lockup detector generate
5278 backtraces on all cpus.
5281 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5282 See Documentation/admin-guide/laptops/sonypi.rst
5284 spectre_v2= [X86] Control mitigation of Spectre variant 2
5285 (indirect branch speculation) vulnerability.
5286 The default operation protects the kernel from
5289 on - unconditionally enable, implies
5291 off - unconditionally disable, implies
5293 auto - kernel detects whether your CPU model is
5296 Selecting 'on' will, and 'auto' may, choose a
5297 mitigation method at run time according to the
5298 CPU, the available microcode, the setting of the
5299 CONFIG_RETPOLINE configuration option, and the
5300 compiler with which the kernel was built.
5302 Selecting 'on' will also enable the mitigation
5303 against user space to user space task attacks.
5305 Selecting 'off' will disable both the kernel and
5306 the user space protections.
5308 Specific mitigations can also be selected manually:
5310 retpoline - replace indirect branches
5311 retpoline,generic - Retpolines
5312 retpoline,lfence - LFENCE; indirect branch
5313 retpoline,amd - alias for retpoline,lfence
5314 eibrs - enhanced IBRS
5315 eibrs,retpoline - enhanced IBRS + Retpolines
5316 eibrs,lfence - enhanced IBRS + LFENCE
5318 Not specifying this option is equivalent to
5322 [X86] Control mitigation of Spectre variant 2
5323 (indirect branch speculation) vulnerability between
5326 on - Unconditionally enable mitigations. Is
5327 enforced by spectre_v2=on
5329 off - Unconditionally disable mitigations. Is
5330 enforced by spectre_v2=off
5332 prctl - Indirect branch speculation is enabled,
5333 but mitigation can be enabled via prctl
5334 per thread. The mitigation control state
5335 is inherited on fork.
5338 - Like "prctl" above, but only STIBP is
5339 controlled per thread. IBPB is issued
5340 always when switching between different user
5344 - Same as "prctl" above, but all seccomp
5345 threads will enable the mitigation unless
5346 they explicitly opt out.
5349 - Like "seccomp" above, but only STIBP is
5350 controlled per thread. IBPB is issued
5351 always when switching between different
5352 user space processes.
5354 auto - Kernel selects the mitigation depending on
5355 the available CPU features and vulnerability.
5358 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
5360 Not specifying this option is equivalent to
5361 spectre_v2_user=auto.
5363 spec_store_bypass_disable=
5364 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5365 (Speculative Store Bypass vulnerability)
5367 Certain CPUs are vulnerable to an exploit against a
5368 a common industry wide performance optimization known
5369 as "Speculative Store Bypass" in which recent stores
5370 to the same memory location may not be observed by
5371 later loads during speculative execution. The idea
5372 is that such stores are unlikely and that they can
5373 be detected prior to instruction retirement at the
5374 end of a particular speculation execution window.
5376 In vulnerable processors, the speculatively forwarded
5377 store can be used in a cache side channel attack, for
5378 example to read memory to which the attacker does not
5379 directly have access (e.g. inside sandboxed code).
5381 This parameter controls whether the Speculative Store
5382 Bypass optimization is used.
5384 On x86 the options are:
5386 on - Unconditionally disable Speculative Store Bypass
5387 off - Unconditionally enable Speculative Store Bypass
5388 auto - Kernel detects whether the CPU model contains an
5389 implementation of Speculative Store Bypass and
5390 picks the most appropriate mitigation. If the
5391 CPU is not vulnerable, "off" is selected. If the
5392 CPU is vulnerable the default mitigation is
5393 architecture and Kconfig dependent. See below.
5394 prctl - Control Speculative Store Bypass per thread
5395 via prctl. Speculative Store Bypass is enabled
5396 for a process by default. The state of the control
5397 is inherited on fork.
5398 seccomp - Same as "prctl" above, but all seccomp threads
5399 will disable SSB unless they explicitly opt out.
5401 Default mitigations:
5402 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
5404 On powerpc the options are:
5406 on,auto - On Power8 and Power9 insert a store-forwarding
5407 barrier on kernel entry and exit. On Power7
5408 perform a software flush on kernel entry and
5412 Not specifying this option is equivalent to
5413 spec_store_bypass_disable=auto.
5415 spia_io_base= [HW,MTD]
5421 [X86] Enable split lock detection or bus lock detection
5423 When enabled (and if hardware support is present), atomic
5424 instructions that access data across cache line
5425 boundaries will result in an alignment check exception
5426 for split lock detection or a debug exception for
5431 warn - the kernel will emit rate-limited warnings
5432 about applications triggering the #AC
5433 exception or the #DB exception. This mode is
5434 the default on CPUs that support split lock
5435 detection or bus lock detection. Default
5436 behavior is by #AC if both features are
5437 enabled in hardware.
5439 fatal - the kernel will send SIGBUS to applications
5440 that trigger the #AC exception or the #DB
5441 exception. Default behavior is by #AC if
5442 both features are enabled in hardware.
5445 Set system wide rate limit to N bus locks
5446 per second for bus lock detection.
5449 N/A for split lock detection.
5452 If an #AC exception is hit in the kernel or in
5453 firmware (i.e. not while executing in user mode)
5454 the kernel will oops in either "warn" or "fatal"
5457 #DB exception for bus lock is triggered only when
5461 Control the Special Register Buffer Data Sampling
5464 Certain CPUs are vulnerable to an MDS-like
5465 exploit which can leak bits from the random
5468 By default, this issue is mitigated by
5469 microcode. However, the microcode fix can cause
5470 the RDRAND and RDSEED instructions to become
5471 much slower. Among other effects, this will
5472 result in reduced throughput from /dev/urandom.
5474 The microcode mitigation can be disabled with
5475 the following option:
5477 off: Disable mitigation and remove
5478 performance impact to RDRAND and RDSEED
5480 srcutree.counter_wrap_check [KNL]
5481 Specifies how frequently to check for
5482 grace-period sequence counter wrap for the
5483 srcu_data structure's ->srcu_gp_seq_needed field.
5484 The greater the number of bits set in this kernel
5485 parameter, the less frequently counter wrap will
5486 be checked for. Note that the bottom two bits
5489 srcutree.exp_holdoff [KNL]
5490 Specifies how many nanoseconds must elapse
5491 since the end of the last SRCU grace period for
5492 a given srcu_struct until the next normal SRCU
5493 grace period will be considered for automatic
5494 expediting. Set to zero to disable automatic
5498 Speculative Store Bypass Disable control
5500 On CPUs that are vulnerable to the Speculative
5501 Store Bypass vulnerability and offer a
5502 firmware based mitigation, this parameter
5503 indicates how the mitigation should be used:
5505 force-on: Unconditionally enable mitigation for
5506 for both kernel and userspace
5507 force-off: Unconditionally disable mitigation for
5508 for both kernel and userspace
5509 kernel: Always enable mitigation in the
5510 kernel, and offer a prctl interface
5511 to allow userspace to register its
5512 interest in being mitigated too.
5514 stack_guard_gap= [MM]
5515 override the default stack gap protection. The value
5516 is in page units and it defines how many pages prior
5517 to (for stacks growing down) resp. after (for stacks
5518 growing up) the main stack are reserved for no other
5519 mapping. Default value is 256 pages.
5521 stack_depot_disable= [KNL]
5522 Setting this to true through kernel command line will
5523 disable the stack depot thereby saving the static memory
5524 consumed by the stack hash table. By default this is set
5528 Enabled the stack tracer on boot up.
5530 stacktrace_filter=[function-list]
5531 [FTRACE] Limit the functions that the stack tracer
5532 will trace at boot up. function-list is a comma-separated
5533 list of functions. This list can be changed at run
5534 time by the stack_trace_filter file in the debugfs
5535 tracing directory. Note, this enables stack tracing
5536 and the stacktrace above is not needed.
5540 Set the STI (builtin display/keyboard on the HP-PARISC
5541 machines) console (graphic card) which should be used
5542 as the initial boot-console.
5543 See also comment in drivers/video/console/sticore.c.
5546 See comment in drivers/video/console/sticore.c.
5549 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5551 sunrpc.min_resvport=
5552 sunrpc.max_resvport=
5554 SunRPC servers often require that client requests
5555 originate from a privileged port (i.e. a port in the
5556 range 0 < portnr < 1024).
5557 An administrator who wishes to reserve some of these
5558 ports for other uses may adjust the range that the
5559 kernel's sunrpc client considers to be privileged
5560 using these two parameters to set the minimum and
5561 maximum port values.
5563 sunrpc.svc_rpc_per_connection_limit=
5565 Limit the number of requests that the server will
5566 process in parallel from a single connection.
5567 The default value is 0 (no limit).
5571 Control how the NFS server code allocates CPUs to
5572 service thread pools. Depending on how many NICs
5573 you have and where their interrupts are bound, this
5574 option will affect which CPUs will do NFS serving.
5575 Note: this parameter cannot be changed while the
5576 NFS server is running.
5578 auto the server chooses an appropriate mode
5579 automatically using heuristics
5580 global a single global pool contains all CPUs
5581 percpu one pool for each CPU
5582 pernode one pool for each NUMA node (equivalent
5583 to global on non-NUMA machines)
5585 sunrpc.tcp_slot_table_entries=
5586 sunrpc.udp_slot_table_entries=
5588 Sets the upper limit on the number of simultaneous
5589 RPC calls that can be sent from the client to a
5590 server. Increasing these values may allow you to
5591 improve throughput, but will also increase the
5592 amount of memory reserved for use by the client.
5594 suspend.pm_test_delay=
5596 Sets the number of seconds to remain in a suspend test
5597 mode before resuming the system (see
5598 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5599 is set. Default value is 5.
5602 Format: { on | off | y | n | 1 | 0 }
5603 This parameter controls use of the Protected
5604 Execution Facility on pSeries.
5607 [KNL] Enable accounting of swap in memory resource
5608 controller if no parameter or 1 is given or disable
5609 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5611 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5612 Format: { <int> | force | noforce }
5613 <int> -- Number of I/O TLB slabs
5614 force -- force using of bounce buffers even if they
5615 wouldn't be automatically used by the kernel
5616 noforce -- Never use bounce buffers (for debugging)
5621 Set a sysctl parameter, right before loading the init
5622 process, as if the value was written to the respective
5623 /proc/sys/... file. Both '.' and '/' are recognized as
5624 separators. Unrecognized parameters and invalid values
5625 are reported in the kernel log. Sysctls registered
5626 later by a loaded module cannot be set this way.
5627 Example: sysctl.vm.swappiness=40
5629 sysfs.deprecated=0|1 [KNL]
5630 Enable/disable old style sysfs layout for old udev
5631 on older distributions. When this option is enabled
5632 very new udev will not work anymore. When this option
5633 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5634 in older udev will not work anymore.
5635 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5636 the kernel configuration.
5638 sysrq_always_enabled
5640 Ignore sysrq setting - this boot parameter will
5641 neutralize any effect of /proc/sys/kernel/sysrq.
5642 Useful for debugging.
5644 tcpmhash_entries= [KNL,NET]
5645 Set the number of tcp_metrics_hash slots.
5646 Default value is 8192 or 16384 depending on total
5647 ram pages. This is used to specify the TCP metrics
5648 cache size. See Documentation/networking/ip-sysctl.rst
5649 "tcp_no_metrics_save" section for more details.
5653 test_suspend= [SUSPEND][,N]
5654 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5655 standby suspend) or "freeze" (for suspend type freeze)
5656 as the system sleep state during system startup with
5657 the optional capability to repeat N number of times.
5658 The system is woken from this state using a
5659 wakeup-capable RTC alarm.
5661 thash_entries= [KNL,NET]
5662 Set number of hash buckets for TCP connection
5664 thermal.act= [HW,ACPI]
5665 -1: disable all active trip points in all thermal zones
5666 <degrees C>: override all lowest active trip points
5668 thermal.crt= [HW,ACPI]
5669 -1: disable all critical trip points in all thermal zones
5670 <degrees C>: override all critical trip points
5672 thermal.nocrt= [HW,ACPI]
5673 Set to disable actions on ACPI thermal zone
5674 critical and hot trip points.
5676 thermal.off= [HW,ACPI]
5677 1: disable ACPI thermal control
5679 thermal.psv= [HW,ACPI]
5680 -1: disable all passive trip points
5681 <degrees C>: override all passive trip points to this
5684 thermal.tzp= [HW,ACPI]
5685 Specify global default ACPI thermal zone polling rate
5686 <deci-seconds>: poll all this frequency
5687 0: no polling (default)
5690 Force threading of all interrupt handlers except those
5691 marked explicitly IRQF_NO_THREAD.
5695 Specify if the kernel should make use of the cpu
5696 topology information if the hardware supports this.
5697 The scheduler will make use of this information and
5698 e.g. base its process migration decisions on it.
5701 topology_updates= [KNL, PPC, NUMA]
5703 Specify if the kernel should ignore (off)
5704 topology updates sent by the hypervisor to this
5707 torture.disable_onoff_at_boot= [KNL]
5708 Prevent the CPU-hotplug component of torturing
5709 until after init has spawned.
5711 torture.ftrace_dump_at_shutdown= [KNL]
5712 Dump the ftrace buffer at torture-test shutdown,
5713 even if there were no errors. This can be a
5714 very costly operation when many torture tests
5715 are running concurrently, especially on systems
5716 with rotating-rust storage.
5718 torture.verbose_sleep_frequency= [KNL]
5719 Specifies how many verbose printk()s should be
5720 emitted between each sleep. The default of zero
5721 disables verbose-printk() sleeping.
5723 torture.verbose_sleep_duration= [KNL]
5724 Duration of each verbose-printk() sleep in jiffies.
5728 tpm_suspend_pcr=[HW,TPM]
5729 Format: integer pcr id
5730 Specify that at suspend time, the tpm driver
5731 should extend the specified pcr with zeros,
5732 as a workaround for some chips which fail to
5733 flush the last written pcr on TPM_SaveState.
5734 This will guarantee that all the other pcrs
5737 trace_buf_size=nn[KMG]
5738 [FTRACE] will set tracing buffer size on each cpu.
5740 trace_event=[event-list]
5741 [FTRACE] Set and start specified trace events in order
5742 to facilitate early boot debugging. The event-list is a
5743 comma-separated list of trace events to enable. See
5744 also Documentation/trace/events.rst
5746 trace_options=[option-list]
5747 [FTRACE] Enable or disable tracer options at boot.
5748 The option-list is a comma delimited list of options
5749 that can be enabled or disabled just as if you were
5750 to echo the option name into
5752 /sys/kernel/debug/tracing/trace_options
5754 For example, to enable stacktrace option (to dump the
5755 stack trace of each event), add to the command line:
5757 trace_options=stacktrace
5759 See also Documentation/trace/ftrace.rst "trace options"
5763 Have the tracepoints sent to printk as well as the
5764 tracing ring buffer. This is useful for early boot up
5765 where the system hangs or reboots and does not give the
5766 option for reading the tracing buffer or performing a
5767 ftrace_dump_on_oops.
5769 To turn off having tracepoints sent to printk,
5770 echo 0 > /proc/sys/kernel/tracepoint_printk
5771 Note, echoing 1 into this file without the
5772 tracepoint_printk kernel cmdline option has no effect.
5774 The tp_printk_stop_on_boot (see below) can also be used
5775 to stop the printing of events to console at
5780 Having tracepoints sent to printk() and activating high
5781 frequency tracepoints such as irq or sched, can cause
5782 the system to live lock.
5784 tp_printk_stop_on_boot[FTRACE]
5785 When tp_printk (above) is set, it can cause a lot of noise
5786 on the console. It may be useful to only include the
5787 printing of events during boot up, as user space may
5788 make the system inoperable.
5790 This command line option will stop the printing of events
5791 to console at the late_initcall_sync() time frame.
5794 [FTRACE] enable this option to disable tracing when a
5795 warning is hit. This turns off "tracing_on". Tracing can
5796 be enabled again by echoing '1' into the "tracing_on"
5797 file located in /sys/kernel/debug/tracing/
5799 This option is useful, as it disables the trace before
5800 the WARNING dump is called, which prevents the trace to
5801 be filled with content caused by the warning output.
5803 This option can also be set at run time via the sysctl
5804 option: kernel/traceoff_on_warning
5806 transparent_hugepage=
5808 Format: [always|madvise|never]
5809 Can be used to control the default behavior of the system
5810 with respect to transparent hugepages.
5811 See Documentation/admin-guide/mm/transhuge.rst
5814 trusted.source= [KEYS]
5816 This parameter identifies the trust source as a backend
5817 for trusted keys implementation. Supported trust
5821 If not specified then it defaults to iterating through
5822 the trust source list starting with TPM and assigns the
5823 first trust source as a backend which is initialized
5824 successfully during iteration.
5826 tsc= Disable clocksource stability checks for TSC.
5828 [x86] reliable: mark tsc clocksource as reliable, this
5829 disables clocksource verification at runtime, as well
5830 as the stability checks done at bootup. Used to enable
5831 high-resolution timer mode on older hardware, and in
5832 virtualized environment.
5833 [x86] noirqtime: Do not use TSC to do irq accounting.
5834 Used to run time disable IRQ_TIME_ACCOUNTING on any
5835 platforms where RDTSC is slow and this accounting
5837 [x86] unstable: mark the TSC clocksource as unstable, this
5838 marks the TSC unconditionally unstable at bootup and
5839 avoids any further wobbles once the TSC watchdog notices.
5840 [x86] nowatchdog: disable clocksource watchdog. Used
5841 in situations with strict latency requirements (where
5842 interruptions from clocksource watchdog are not
5845 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5846 value instead. Useful when the early TSC frequency discovery
5847 procedure is not reliable, such as on overclocked systems
5848 with CPUID.16h support and partial CPUID.15h support.
5849 Format: <unsigned int>
5851 tsx= [X86] Control Transactional Synchronization
5852 Extensions (TSX) feature in Intel processors that
5853 support TSX control.
5855 This parameter controls the TSX feature. The options are:
5857 on - Enable TSX on the system. Although there are
5858 mitigations for all known security vulnerabilities,
5859 TSX has been known to be an accelerator for
5860 several previous speculation-related CVEs, and
5861 so there may be unknown security risks associated
5862 with leaving it enabled.
5864 off - Disable TSX on the system. (Note that this
5865 option takes effect only on newer CPUs which are
5866 not vulnerable to MDS, i.e., have
5867 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5868 the new IA32_TSX_CTRL MSR through a microcode
5869 update. This new MSR allows for the reliable
5870 deactivation of the TSX functionality.)
5872 auto - Disable TSX if X86_BUG_TAA is present,
5873 otherwise enable TSX on the system.
5875 Not specifying this option is equivalent to tsx=off.
5877 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5880 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5881 Abort (TAA) vulnerability.
5883 Similar to Micro-architectural Data Sampling (MDS)
5884 certain CPUs that support Transactional
5885 Synchronization Extensions (TSX) are vulnerable to an
5886 exploit against CPU internal buffers which can forward
5887 information to a disclosure gadget under certain
5890 In vulnerable processors, the speculatively forwarded
5891 data can be used in a cache side channel attack, to
5892 access data to which the attacker does not have direct
5895 This parameter controls the TAA mitigation. The
5898 full - Enable TAA mitigation on vulnerable CPUs
5901 full,nosmt - Enable TAA mitigation and disable SMT on
5902 vulnerable CPUs. If TSX is disabled, SMT
5903 is not disabled because CPU is not
5904 vulnerable to cross-thread TAA attacks.
5905 off - Unconditionally disable TAA mitigation
5907 On MDS-affected machines, tsx_async_abort=off can be
5908 prevented by an active MDS mitigation as both vulnerabilities
5909 are mitigated with the same mechanism so in order to disable
5910 this mitigation, you need to specify mds=off too.
5912 Not specifying this option is equivalent to
5913 tsx_async_abort=full. On CPUs which are MDS affected
5914 and deploy MDS mitigation, TAA mitigation is not
5915 required and doesn't provide any additional
5919 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5921 turbografx.map[2|3]= [HW,JOY]
5922 TurboGraFX parallel port interface
5924 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5925 See also Documentation/input/devices/joystick-parport.rst
5927 udbg-immortal [PPC] When debugging early kernel crashes that
5928 happen after console_init() and before a proper
5929 console driver takes over, this boot options might
5930 help "seeing" what's going on.
5932 uhash_entries= [KNL,NET]
5933 Set number of hash buckets for UDP/UDP-Lite connections
5936 [USB] Ignore overcurrent events (default N).
5937 Some badly-designed motherboards generate lots of
5938 bogus events, for ports that aren't wired to
5939 anything. Set this parameter to avoid log spamming.
5940 Note that genuine overcurrent events won't be
5944 [X86] Cause panic on unknown NMI.
5946 usbcore.authorized_default=
5947 [USB] Default USB device authorization:
5948 (default -1 = authorized except for wireless USB,
5949 0 = not authorized, 1 = authorized, 2 = authorized
5950 if device connected to internal port)
5952 usbcore.autosuspend=
5953 [USB] The autosuspend time delay (in seconds) used
5954 for newly-detected USB devices (default 2). This
5955 is the time required before an idle device will be
5956 autosuspended. Devices for which the delay is set
5957 to a negative value won't be autosuspended at all.
5959 usbcore.usbfs_snoop=
5960 [USB] Set to log all usbfs traffic (default 0 = off).
5962 usbcore.usbfs_snoop_max=
5963 [USB] Maximum number of bytes to snoop in each URB
5966 usbcore.blinkenlights=
5967 [USB] Set to cycle leds on hubs (default 0 = off).
5969 usbcore.old_scheme_first=
5970 [USB] Start with the old device initialization
5971 scheme (default 0 = off).
5973 usbcore.usbfs_memory_mb=
5974 [USB] Memory limit (in MB) for buffers allocated by
5975 usbfs (default = 16, 0 = max = 2047).
5977 usbcore.use_both_schemes=
5978 [USB] Try the other device initialization scheme
5979 if the first one fails (default 1 = enabled).
5981 usbcore.initial_descriptor_timeout=
5982 [USB] Specifies timeout for the initial 64-byte
5983 USB_REQ_GET_DESCRIPTOR request in milliseconds
5984 (default 5000 = 5.0 seconds).
5986 usbcore.nousb [USB] Disable the USB subsystem
5989 [USB] A list of quirk entries to augment the built-in
5990 usb core quirk list. List entries are separated by
5991 commas. Each entry has the form
5992 VendorID:ProductID:Flags. The IDs are 4-digit hex
5993 numbers and Flags is a set of letters. Each letter
5994 will change the built-in quirk; setting it if it is
5995 clear and clearing it if it is set. The letters have
5996 the following meanings:
5997 a = USB_QUIRK_STRING_FETCH_255 (string
5998 descriptors must not be fetched using
6000 b = USB_QUIRK_RESET_RESUME (device can't resume
6001 correctly so reset it instead);
6002 c = USB_QUIRK_NO_SET_INTF (device can't handle
6003 Set-Interface requests);
6004 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6005 handle its Configuration or Interface
6007 e = USB_QUIRK_RESET (device can't be reset
6008 (e.g morph devices), don't use reset);
6009 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6010 more interface descriptions than the
6011 bNumInterfaces count, and can't handle
6012 talking to these interfaces);
6013 g = USB_QUIRK_DELAY_INIT (device needs a pause
6014 during initialization, after we read
6015 the device descriptor);
6016 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6017 high speed and super speed interrupt
6018 endpoints, the USB 2.0 and USB 3.0 spec
6019 require the interval in microframes (1
6020 microframe = 125 microseconds) to be
6021 calculated as interval = 2 ^
6023 Devices with this quirk report their
6024 bInterval as the result of this
6025 calculation instead of the exponent
6026 variable used in the calculation);
6027 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6028 handle device_qualifier descriptor
6030 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6031 generates spurious wakeup, ignore
6032 remote wakeup capability);
6033 k = USB_QUIRK_NO_LPM (device can't handle Link
6035 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6036 (Device reports its bInterval as linear
6037 frames instead of the USB 2.0
6039 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6040 to be disconnected before suspend to
6041 prevent spurious wakeup);
6042 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6043 pause after every control message);
6044 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6045 delay after resetting its port);
6046 Example: quirks=0781:5580:bk,0a5c:5834:gij
6049 [USBHID] The interval which mice are to be polled at.
6052 [USBHID] The interval which joysticks are to be polled at.
6055 [USBHID] The interval which keyboards are to be polled at.
6057 usb-storage.delay_use=
6058 [UMS] The delay in seconds before a new device is
6059 scanned for Logical Units (default 1).
6062 [UMS] A list of quirks entries to supplement or
6063 override the built-in unusual_devs list. List
6064 entries are separated by commas. Each entry has
6065 the form VID:PID:Flags where VID and PID are Vendor
6066 and Product ID values (4-digit hex numbers) and
6067 Flags is a set of characters, each corresponding
6068 to a common usb-storage quirk flag as follows:
6069 a = SANE_SENSE (collect more than 18 bytes
6070 of sense data, not on uas);
6071 b = BAD_SENSE (don't collect more than 18
6072 bytes of sense data, not on uas);
6073 c = FIX_CAPACITY (decrease the reported
6074 device capacity by one sector);
6075 d = NO_READ_DISC_INFO (don't use
6076 READ_DISC_INFO command, not on uas);
6077 e = NO_READ_CAPACITY_16 (don't use
6078 READ_CAPACITY_16 command);
6079 f = NO_REPORT_OPCODES (don't use report opcodes
6081 g = MAX_SECTORS_240 (don't transfer more than
6082 240 sectors at a time, uas only);
6083 h = CAPACITY_HEURISTICS (decrease the
6084 reported device capacity by one
6085 sector if the number is odd);
6086 i = IGNORE_DEVICE (don't bind to this
6088 j = NO_REPORT_LUNS (don't use report luns
6090 k = NO_SAME (do not use WRITE_SAME, uas only)
6091 l = NOT_LOCKABLE (don't try to lock and
6092 unlock ejectable media, not on uas);
6093 m = MAX_SECTORS_64 (don't transfer more
6094 than 64 sectors = 32 KB at a time,
6096 n = INITIAL_READ10 (force a retry of the
6097 initial READ(10) command, not on uas);
6098 o = CAPACITY_OK (accept the capacity
6099 reported by the device, not on uas);
6100 p = WRITE_CACHE (the device cache is ON
6101 by default, not on uas);
6102 r = IGNORE_RESIDUE (the device reports
6103 bogus residue values, not on uas);
6104 s = SINGLE_LUN (the device has only one
6106 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6107 commands, uas only);
6108 u = IGNORE_UAS (don't bind to the uas driver);
6109 w = NO_WP_DETECT (don't test whether the
6110 medium is write-protected).
6111 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6112 even if the device claims no cache,
6114 Example: quirks=0419:aaf5:rl,0421:0433:rc
6116 user_debug= [KNL,ARM]
6118 See arch/arm/Kconfig.debug help text.
6119 1 - undefined instruction events
6121 4 - invalid data aborts
6124 Example: user_debug=31
6127 [X86] Flags controlling user PTE allocations.
6129 nohigh = do not allocate PTE pages in
6130 HIGHMEM regardless of setting
6134 On X86_32, this is an alias for vdso32=. Otherwise:
6136 vdso=1: enable VDSO (the default)
6137 vdso=0: disable VDSO mapping
6139 vdso32= [X86] Control the 32-bit vDSO
6140 vdso32=1: enable 32-bit VDSO
6141 vdso32=0 or vdso32=2: disable 32-bit VDSO
6143 See the help text for CONFIG_COMPAT_VDSO for more
6144 details. If CONFIG_COMPAT_VDSO is set, the default is
6145 vdso32=0; otherwise, the default is vdso32=1.
6147 For compatibility with older kernels, vdso32=2 is an
6150 Try vdso32=0 if you encounter an error that says:
6151 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6154 vector=percpu: enable percpu vector domain
6156 video= [FB] Frame buffer configuration
6157 See Documentation/fb/modedb.rst.
6159 video.brightness_switch_enabled= [0,1]
6160 If set to 1, on receiving an ACPI notify event
6161 generated by hotkey, video driver will adjust brightness
6162 level and then send out the event to user space through
6163 the allocated input device; If set to 0, video driver
6164 will only send out the event without touching backlight
6169 [VMMIO] Memory mapped virtio (platform) device.
6171 <size>@<baseaddr>:<irq>[:<id>]
6173 <size> := size (can use standard suffixes
6175 <baseaddr> := physical base address
6176 <irq> := interrupt number (as passed to
6178 <id> := (optional) platform device id
6180 virtio_mmio.device=1K@0x100b0000:48:7
6182 Can be used multiple times for multiple devices.
6184 vga= [BOOT,X86-32] Select a particular video mode
6185 See Documentation/x86/boot.rst and
6186 Documentation/admin-guide/svga.rst.
6187 Use vga=ask for menu.
6188 This is actually a boot loader parameter; the value is
6189 passed to the kernel using a special protocol.
6191 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6192 May slow down system boot speed, especially when
6193 enabled on systems with a large amount of memory.
6194 All options are enabled by default, and this
6195 interface is meant to allow for selectively
6196 enabling or disabling specific virtual memory
6199 Available options are:
6200 P Enable page structure init time poisoning
6201 - Disable all of the above options
6203 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6204 size of <nn>. This can be used to increase the
6205 minimum size (128MB on x86). It can also be used to
6206 decrease the size and leave more room for directly
6209 vmcp_cma=nn[MG] [KNL,S390]
6210 Sets the memory size reserved for contiguous memory
6211 allocations for the vmcp device driver.
6213 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6216 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6219 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6223 Controls the behavior of vsyscalls (i.e. calls to
6224 fixed addresses of 0xffffffffff600x00 from legacy
6225 code). Most statically-linked binaries and older
6226 versions of glibc use these calls. Because these
6227 functions are at fixed addresses, they make nice
6228 targets for exploits that can control RIP.
6230 emulate [default] Vsyscalls turn into traps and are
6231 emulated reasonably safely. The vsyscall
6234 xonly Vsyscalls turn into traps and are
6235 emulated reasonably safely. The vsyscall
6236 page is not readable.
6238 none Vsyscalls don't work at all. This makes
6239 them quite hard to use for exploits but
6240 might break your system.
6242 vt.color= [VT] Default text color.
6243 Format: 0xYX, X = foreground, Y = background.
6244 Default: 0x07 = light gray on black.
6246 vt.cur_default= [VT] Default cursor shape.
6247 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6248 the parameters of the <Esc>[?A;B;Cc escape sequence;
6249 see VGA-softcursor.txt. Default: 2 = underline.
6251 vt.default_blu= [VT]
6252 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6253 Change the default blue palette of the console.
6254 This is a 16-member array composed of values
6257 vt.default_grn= [VT]
6258 Format: <green0>,<green1>,<green2>,...,<green15>
6259 Change the default green palette of the console.
6260 This is a 16-member array composed of values
6263 vt.default_red= [VT]
6264 Format: <red0>,<red1>,<red2>,...,<red15>
6265 Change the default red palette of the console.
6266 This is a 16-member array composed of values
6272 Set system-wide default UTF-8 mode for all tty's.
6273 Default is 1, i.e. UTF-8 mode is enabled for all
6274 newly opened terminals.
6276 vt.global_cursor_default=
6279 Set system-wide default for whether a cursor
6280 is shown on new VTs. Default is -1,
6281 i.e. cursors will be created by default unless
6282 overridden by individual drivers. 0 will hide
6283 cursors, 1 will display them.
6285 vt.italic= [VT] Default color for italic text; 0-15.
6288 vt.underline= [VT] Default color for underlined text; 0-15.
6291 watchdog timers [HW,WDT] For information on watchdog timers,
6292 see Documentation/watchdog/watchdog-parameters.rst
6293 or other driver-specific files in the
6294 Documentation/watchdog/ directory.
6298 Set the hard lockup detector stall duration
6299 threshold in seconds. The soft lockup detector
6300 threshold is set to twice the value. A value of 0
6301 disables both lockup detectors. Default is 10
6304 workqueue.watchdog_thresh=
6305 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6306 warn stall conditions and dump internal state to
6307 help debugging. 0 disables workqueue stall
6308 detection; otherwise, it's the stall threshold
6309 duration in seconds. The default value is 30 and
6310 it can be updated at runtime by writing to the
6311 corresponding sysfs file.
6313 workqueue.disable_numa
6314 By default, all work items queued to unbound
6315 workqueues are affine to the NUMA nodes they're
6316 issued on, which results in better behavior in
6317 general. If NUMA affinity needs to be disabled for
6318 whatever reason, this option can be used. Note
6319 that this also can be controlled per-workqueue for
6320 workqueues visible under /sys/bus/workqueue/.
6322 workqueue.power_efficient
6323 Per-cpu workqueues are generally preferred because
6324 they show better performance thanks to cache
6325 locality; unfortunately, per-cpu workqueues tend to
6326 be more power hungry than unbound workqueues.
6328 Enabling this makes the per-cpu workqueues which
6329 were observed to contribute significantly to power
6330 consumption unbound, leading to measurably lower
6331 power usage at the cost of small performance
6334 The default value of this parameter is determined by
6335 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6337 workqueue.debug_force_rr_cpu
6338 Workqueue used to implicitly guarantee that work
6339 items queued without explicit CPU specified are put
6340 on the local CPU. This guarantee is no longer true
6341 and while local CPU is still preferred work items
6342 may be put on foreign CPUs. This debug option
6343 forces round-robin CPU selection to flush out
6344 usages which depend on the now broken guarantee.
6345 When enabled, memory and cache locality will be
6348 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6349 default x2apic cluster mode on platforms
6352 xen_512gb_limit [KNL,X86-64,XEN]
6353 Restricts the kernel running paravirtualized under Xen
6354 to use only up to 512 GB of RAM. The reason to do so is
6355 crash analysis tools and Xen tools for doing domain
6356 save/restore/migration must be enabled to handle larger
6359 xen_emul_unplug= [HW,X86,XEN]
6360 Unplug Xen emulated devices
6361 Format: [unplug0,][unplug1]
6362 ide-disks -- unplug primary master IDE devices
6363 aux-ide-disks -- unplug non-primary-master IDE devices
6364 nics -- unplug network devices
6365 all -- unplug all emulated devices (NICs and IDE disks)
6366 unnecessary -- unplugging emulated devices is
6367 unnecessary even if the host did not respond to
6369 never -- do not unplug even if version check succeeds
6371 xen_legacy_crash [X86,XEN]
6372 Crash from Xen panic notifier, without executing late
6373 panic() code such as dumping handler.
6375 xen_nopvspin [X86,XEN]
6376 Disables the qspinlock slowpath using Xen PV optimizations.
6377 This parameter is obsoleted by "nopvspin" parameter, which
6378 has equivalent effect for XEN platform.
6381 Disables the PV optimizations forcing the HVM guest to
6382 run as generic HVM guest with no PV drivers.
6383 This option is obsoleted by the "nopv" option, which
6384 has equivalent effect for XEN platform.
6386 xen_no_vector_callback
6387 [KNL,X86,XEN] Disable the vector callback for Xen
6388 event channel interrupts.
6390 xen_scrub_pages= [XEN]
6391 Boolean option to control scrubbing pages before giving them back
6392 to Xen, for use by other domains. Can be also changed at runtime
6393 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6394 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6396 xen_timer_slop= [X86-64,XEN]
6397 Set the timer slop (in nanoseconds) for the virtual Xen
6398 timers (default is 100000). This adjusts the minimum
6399 delta of virtualized Xen timers, where lower values
6400 improve timer resolution at the expense of processing
6401 more timer interrupts.
6403 xen.balloon_boot_timeout= [XEN]
6404 The time (in seconds) to wait before giving up to boot
6405 in case initial ballooning fails to free enough memory.
6406 Applies only when running as HVM or PVH guest and
6407 started with less memory configured than allowed at
6408 max. Default is 180.
6410 xen.event_eoi_delay= [XEN]
6411 How long to delay EOI handling in case of event
6412 storms (jiffies). Default is 10.
6414 xen.event_loop_timeout= [XEN]
6415 After which time (jiffies) the event handling loop
6416 should start to delay EOI handling. Default is 2.
6418 xen.fifo_events= [XEN]
6419 Boolean parameter to disable using fifo event handling
6420 even if available. Normally fifo event handling is
6421 preferred over the 2-level event handling, as it is
6422 fairer and the number of possible event channels is
6423 much higher. Default is on (use fifo events).
6425 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6426 Disables the PV optimizations forcing the guest to run
6427 as generic guest with no PV drivers. Currently support
6428 XEN HVM, KVM, HYPER_V and VMWARE guest.
6430 nopvspin [X86,XEN,KVM]
6431 Disables the qspinlock slow path using PV optimizations
6432 which allow the hypervisor to 'idle' the guest on lock
6435 xirc2ps_cs= [NET,PCMCIA]
6437 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6440 By default on POWER9 and above, the kernel will
6441 natively use the XIVE interrupt controller. This option
6442 allows the fallback firmware mode to be used:
6444 off Fallback to firmware control of XIVE interrupt
6445 controller on both pseries and powernv
6446 platforms. Only useful on POWER9 and above.
6448 xhci-hcd.quirks [USB,KNL]
6449 A hex value specifying bitmask with supplemental xhci
6450 host controller quirks. Meaning of each bit can be
6451 consulted in header drivers/usb/host/xhci.h.
6454 Format: { early | on | rw | ro | off }
6455 Controls if xmon debugger is enabled. Default is off.
6456 Passing only "xmon" is equivalent to "xmon=early".
6457 early Call xmon as early as possible on boot; xmon
6458 debugger is called from setup_arch().
6459 on xmon debugger hooks will be installed so xmon
6460 is only called on a kernel crash. Default mode,
6461 i.e. either "ro" or "rw" mode, is controlled
6462 with CONFIG_XMON_DEFAULT_RO_MODE.
6463 rw xmon debugger hooks will be installed so xmon
6464 is called only on a kernel crash, mode is write,
6465 meaning SPR registers, memory and, other data
6466 can be written using xmon commands.
6467 ro same as "rw" option above but SPR registers,
6468 memory, and other data can't be written using
6470 off xmon is disabled.
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