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 - enable flushing of IO/TLB entries when
305 they are unmapped. Otherwise they are
306 flushed before they will be reused, which
308 off - do not initialize any AMD IOMMU found in
310 force_isolation - Force device isolation for all
311 devices. The IOMMU driver is not
312 allowed anymore to lift isolation
313 requirements as needed. This option
314 does not override iommu=pt
315 force_enable - Force enable the IOMMU on platforms known
316 to be buggy with IOMMU enabled. Use this
319 amd_iommu_dump= [HW,X86-64]
320 Enable AMD IOMMU driver option to dump the ACPI table
321 for AMD IOMMU. With this option enabled, AMD IOMMU
322 driver will print ACPI tables for AMD IOMMU during
323 IOMMU initialization.
325 amd_iommu_intr= [HW,X86-64]
326 Specifies one of the following AMD IOMMU interrupt
328 legacy - Use legacy interrupt remapping mode.
329 vapic - Use virtual APIC mode, which allows IOMMU
330 to inject interrupts directly into guest.
331 This mode requires kvm-amd.avic=1.
332 (Default when IOMMU HW support is present.)
334 amijoy.map= [HW,JOY] Amiga joystick support
335 Map of devices attached to JOY0DAT and JOY1DAT
337 See also Documentation/input/joydev/joystick.rst
339 analog.map= [HW,JOY] Analog joystick and gamepad support
340 Specifies type or capabilities of an analog joystick
341 connected to one of 16 gameports
342 Format: <type1>,<type2>,..<type16>
345 Power management functions (SPARCstation-4/5 + deriv.)
347 Disable APC CPU standby support. SPARCstation-Fox does
348 not play well with APC CPU idle - disable it if you have
349 APC and your system crashes randomly.
351 apic= [APIC,X86] Advanced Programmable Interrupt Controller
352 Change the output verbosity while booting
353 Format: { quiet (default) | verbose | debug }
354 Change the amount of debugging information output
355 when initialising the APIC and IO-APIC components.
356 For X86-32, this can also be used to specify an APIC
358 Format: apic=driver_name
359 Examples: apic=bigsmp
361 apic_extnmi= [APIC,X86] External NMI delivery setting
362 Format: { bsp (default) | all | none }
363 bsp: External NMI is delivered only to CPU 0
364 all: External NMIs are broadcast to all CPUs as a
366 none: External NMI is masked for all CPUs. This is
367 useful so that a dump capture kernel won't be
371 See Documentation/networking/ipv6.rst.
373 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
374 Limit apic dumping. The parameter defines the maximal
375 number of local apics being dumped. Also it is possible
376 to set it to "all" by meaning -- no limit here.
377 Format: { 1 (default) | 2 | ... | all }.
378 The parameter valid if only apic=debug or
379 apic=verbose is specified.
380 Example: apic=debug show_lapic=all
382 apm= [APM] Advanced Power Management
383 See header of arch/x86/kernel/apm_32.c.
385 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
386 Format: <io>,<irq>,<nodeID>
388 arm64.nobti [ARM64] Unconditionally disable Branch Target
389 Identification support
391 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
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 output can only be used by Xen PV guests.
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
1696 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1697 indicates that the driver is running on unsupported
1699 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1700 does not match list of supported models.
1702 [HW] Report power status in /proc/i8k
1703 (disabled by default)
1704 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1707 i915.invert_brightness=
1708 [DRM] Invert the sense of the variable that is used to
1709 set the brightness of the panel backlight. Normally a
1710 brightness value of 0 indicates backlight switched off,
1711 and the maximum of the brightness value sets the backlight
1712 to maximum brightness. If this parameter is set to 0
1713 (default) and the machine requires it, or this parameter
1714 is set to 1, a brightness value of 0 sets the backlight
1715 to maximum brightness, and the maximum of the brightness
1716 value switches the backlight off.
1717 -1 -- never invert brightness
1718 0 -- machine default
1719 1 -- force brightness inversion
1722 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1724 ide-core.nodma= [HW] (E)IDE subsystem
1725 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1726 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1727 .cdrom .chs .ignore_cable are additional options
1728 See Documentation/ide/ide.rst.
1730 ide-generic.probe-mask= [HW] (E)IDE subsystem
1732 Probe mask for legacy ISA IDE ports. Depending on
1733 platform up to 6 ports are supported, enabled by
1734 setting corresponding bits in the mask to 1. The
1735 default value is 0x0, which has a special meaning.
1736 On systems that have PCI, it triggers scanning the
1737 PCI bus for the first and the second port, which
1738 are then probed. On systems without PCI the value
1739 of 0x0 enables probing the two first ports as if it
1742 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1743 Claim all unknown PCI IDE storage controllers.
1746 Format: idle=poll, idle=halt, idle=nomwait
1747 Poll forces a polling idle loop that can slightly
1748 improve the performance of waking up a idle CPU, but
1749 will use a lot of power and make the system run hot.
1751 idle=halt: Halt is forced to be used for CPU idle.
1752 In such case C2/C3 won't be used again.
1753 idle=nomwait: Disable mwait for CPU C-states
1757 Allow force disabling of Shared Virtual Memory (SVA)
1758 support for the idxd driver. By default it is set to
1761 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1762 Format: { strict | legacy | 2008 | relaxed }
1765 Choose which programs will be accepted for execution
1766 based on the IEEE 754 NaN encoding(s) supported by
1767 the FPU and the NaN encoding requested with the value
1768 of an ELF file header flag individually set by each
1769 binary. Hardware implementations are permitted to
1770 support either or both of the legacy and the 2008 NaN
1773 Available settings are as follows:
1774 strict accept binaries that request a NaN encoding
1775 supported by the FPU
1776 legacy only accept legacy-NaN binaries, if supported
1778 2008 only accept 2008-NaN binaries, if supported
1780 relaxed accept any binaries regardless of whether
1781 supported by the FPU
1783 The FPU emulator is always able to support both NaN
1784 encodings, so if no FPU hardware is present or it has
1785 been disabled with 'nofpu', then the settings of
1786 'legacy' and '2008' strap the emulator accordingly,
1787 'relaxed' straps the emulator for both legacy-NaN and
1788 2008-NaN, whereas 'strict' enables legacy-NaN only on
1789 legacy processors and both NaN encodings on MIPS32 or
1792 The setting for ABS.fmt/NEG.fmt instruction execution
1793 mode generally follows that for the NaN encoding,
1794 except where unsupported by hardware.
1796 ignore_loglevel [KNL]
1797 Ignore loglevel setting - this will print /all/
1798 kernel messages to the console. Useful for debugging.
1799 We also add it as printk module parameter, so users
1800 could change it dynamically, usually by
1801 /sys/module/printk/parameters/ignore_loglevel.
1804 Ignore RLIMIT_DATA setting for data mappings,
1805 print warning at first misuse. Can be changed via
1806 /sys/module/kernel/parameters/ignore_rlimit_data.
1808 ihash_entries= [KNL]
1809 Set number of hash buckets for inode cache.
1811 ima_appraise= [IMA] appraise integrity measurements
1812 Format: { "off" | "enforce" | "fix" | "log" }
1815 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1816 The builtin appraise policy appraises all files
1819 ima_canonical_fmt [IMA]
1820 Use the canonical format for the binary runtime
1821 measurements, instead of host native format.
1824 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1828 The list of supported hash algorithms is defined
1829 in crypto/hash_info.h.
1832 The builtin policies to load during IMA setup.
1833 Format: "tcb | appraise_tcb | secure_boot |
1834 fail_securely | critical_data"
1836 The "tcb" policy measures all programs exec'd, files
1837 mmap'd for exec, and all files opened with the read
1838 mode bit set by either the effective uid (euid=0) or
1841 The "appraise_tcb" policy appraises the integrity of
1842 all files owned by root.
1844 The "secure_boot" policy appraises the integrity
1845 of files (eg. kexec kernel image, kernel modules,
1846 firmware, policy, etc) based on file signatures.
1848 The "fail_securely" policy forces file signature
1849 verification failure also on privileged mounted
1850 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1853 The "critical_data" policy measures kernel integrity
1856 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1857 Load a policy which meets the needs of the Trusted
1858 Computing Base. This means IMA will measure all
1859 programs exec'd, files mmap'd for exec, and all files
1860 opened for read by uid=0.
1863 Select one of defined IMA measurements template formats.
1864 Formats: { "ima" | "ima-ng" | "ima-sig" }
1868 [IMA] Define a custom template format.
1869 Format: { "field1|...|fieldN" }
1871 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1872 Format: <min_file_size>
1873 Set the minimal file size for using asynchronous hash.
1874 If left unspecified, ahash usage is disabled.
1876 ahash performance varies for different data sizes on
1877 different crypto accelerators. This option can be used
1878 to achieve the best performance for a particular HW.
1880 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1882 Set hashing buffer size. Default: 4k.
1884 ahash performance varies for different chunk sizes on
1885 different crypto accelerators. This option can be used
1886 to achieve best performance for particular HW.
1890 Run specified binary instead of /sbin/init as init
1893 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1894 for working out where the kernel is dying during
1897 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1898 initcall functions. Useful for debugging built-in
1899 modules and initcalls.
1901 initramfs_async= [KNL]
1904 This parameter controls whether the initramfs
1905 image is unpacked asynchronously, concurrently
1906 with devices being probed and
1907 initialized. This should normally just work,
1908 but as a debugging aid, one can get the
1909 historical behaviour of the initramfs
1910 unpacking being completed before device_ and
1913 initrd= [BOOT] Specify the location of the initial ramdisk
1915 initrdmem= [KNL] Specify a physical address and size from which to
1916 load the initrd. If an initrd is compiled in or
1917 specified in the bootparams, it takes priority over this
1919 Format: ss[KMG],nn[KMG]
1922 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1925 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1927 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1929 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1931 init_pkru= [X86] Specify the default memory protection keys rights
1932 register contents for all processes. 0x55555554 by
1933 default (disallow access to all but pkey 0). Can
1934 override in debugfs after boot.
1936 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1939 int_pln_enable [X86] Enable power limit notification interrupt
1941 integrity_audit=[IMA]
1942 Format: { "0" | "1" }
1943 0 -- basic integrity auditing messages. (Default)
1944 1 -- additional integrity auditing messages.
1946 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1948 Enable intel iommu driver.
1950 Disable intel iommu driver.
1951 igfx_off [Default Off]
1952 By default, gfx is mapped as normal device. If a gfx
1953 device has a dedicated DMAR unit, the DMAR unit is
1954 bypassed by not enabling DMAR with this option. In
1955 this case, gfx device will use physical address for
1957 strict [Default Off]
1958 With this option on every unmap_single operation will
1959 result in a hardware IOTLB flush operation as opposed
1960 to batching them for performance.
1961 sp_off [Default Off]
1962 By default, super page will be supported if Intel IOMMU
1963 has the capability. With this option, super page will
1966 By default, scalable mode will be disabled even if the
1967 hardware advertises that it has support for the scalable
1968 mode translation. With this option set, scalable mode
1969 will be used on hardware which claims to support it.
1970 tboot_noforce [Default Off]
1971 Do not force the Intel IOMMU enabled under tboot.
1972 By default, tboot will force Intel IOMMU on, which
1973 could harm performance of some high-throughput
1974 devices like 40GBit network cards, even if identity
1976 Note that using this option lowers the security
1977 provided by tboot because it makes the system
1978 vulnerable to DMA attacks.
1980 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1981 0 disables intel_idle and fall back on acpi_idle.
1982 1 to 9 specify maximum depth of C-state.
1986 Do not enable intel_pstate as the default
1987 scaling driver for the supported processors
1989 Use intel_pstate as a scaling driver, but configure it
1990 to work with generic cpufreq governors (instead of
1991 enabling its internal governor). This mode cannot be
1992 used along with the hardware-managed P-states (HWP)
1995 Enable intel_pstate on systems that prohibit it by default
1996 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1997 instead of acpi-cpufreq may disable platform features, such
1998 as thermal controls and power capping, that rely on ACPI
1999 P-States information being indicated to OSPM and therefore
2000 should be used with caution. This option does not work with
2001 processors that aren't supported by the intel_pstate driver
2002 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2004 Do not enable hardware P state control (HWP)
2007 Only load intel_pstate on systems which support
2008 hardware P state control (HWP) if available.
2010 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2011 Description Table, specifies preferred power management
2012 profile as "Enterprise Server" or "Performance Server",
2013 then this feature is turned on by default.
2015 Allow per-logical-CPU P-State performance control limits using
2016 cpufreq sysfs interface
2018 intremap= [X86-64, Intel-IOMMU]
2019 on enable Interrupt Remapping (default)
2020 off disable Interrupt Remapping
2021 nosid disable Source ID checking
2023 BIOS x2APIC opt-out request will be ignored
2024 nopost disable Interrupt Posting
2026 iomem= Disable strict checking of access to MMIO memory
2027 strict regions from userspace.
2042 nobypass [PPC/POWERNV]
2043 Disable IOMMU bypass, using IOMMU for PCI devices.
2045 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2046 Format: { "0" | "1" }
2047 0 - Try to allocate a 32-bit DMA address first, before
2048 falling back to the full range if needed.
2049 1 - Allocate directly from the full usable range,
2050 forcing Dual Address Cycle for PCI cards supporting
2051 greater than 32-bit addressing.
2053 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2054 Format: { "0" | "1" }
2056 Request that DMA unmap operations use deferred
2057 invalidation of hardware TLBs, for increased
2058 throughput at the cost of reduced device isolation.
2059 Will fall back to strict mode if not supported by
2060 the relevant IOMMU driver.
2061 1 - Strict mode (default).
2062 DMA unmap operations invalidate IOMMU hardware TLBs
2064 Note: on x86, the default behaviour depends on the
2065 equivalent driver-specific parameters, but a strict
2066 mode explicitly specified by either method takes
2070 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2071 Format: { "0" | "1" }
2072 0 - Use IOMMU translation for DMA.
2073 1 - Bypass the IOMMU for DMA.
2074 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2076 io7= [HW] IO7 for Marvel-based Alpha systems
2077 See comment before marvel_specify_io7 in
2078 arch/alpha/kernel/core_marvel.c.
2080 io_delay= [X86] I/O delay method
2082 Standard port 0x80 based delay
2084 Alternate port 0xed based delay (needed on some systems)
2086 Simple two microseconds delay
2091 See Documentation/admin-guide/nfs/nfsroot.rst.
2093 ipcmni_extend [KNL] Extend the maximum number of unique System V
2094 IPC identifiers from 32,768 to 16,777,216.
2096 irqaffinity= [SMP] Set the default irq affinity mask
2097 The argument is a cpu list, as described above.
2099 irqchip.gicv2_force_probe=
2102 Force the kernel to look for the second 4kB page
2103 of a GICv2 controller even if the memory range
2104 exposed by the device tree is too small.
2106 irqchip.gicv3_nolpi=
2108 Force the kernel to ignore the availability of
2109 LPIs (and by consequence ITSs). Intended for system
2110 that use the kernel as a bootloader, and thus want
2111 to let secondary kernels in charge of setting up
2114 irqchip.gicv3_pseudo_nmi= [ARM64]
2115 Enables support for pseudo-NMIs in the kernel. This
2116 requires the kernel to be built with
2117 CONFIG_ARM64_PSEUDO_NMI.
2120 When an interrupt is not handled search all handlers
2121 for it. Intended to get systems with badly broken
2125 When an interrupt is not handled search all handlers
2126 for it. Also check all handlers each timer
2127 interrupt. Intended to get systems with badly broken
2131 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2133 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2134 [Deprecated - use cpusets instead]
2135 Format: [flag-list,]<cpu-list>
2137 Specify one or more CPUs to isolate from disturbances
2138 specified in the flag list (default: domain):
2141 Disable the tick when a single task runs.
2143 A residual 1Hz tick is offloaded to workqueues, which you
2144 need to affine to housekeeping through the global
2145 workqueue's affinity configured via the
2146 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2147 by using the 'domain' flag described below.
2149 NOTE: by default the global workqueue runs on all CPUs,
2150 so to protect individual CPUs the 'cpumask' file has to
2151 be configured manually after bootup.
2154 Isolate from the general SMP balancing and scheduling
2155 algorithms. Note that performing domain isolation this way
2156 is irreversible: it's not possible to bring back a CPU to
2157 the domains once isolated through isolcpus. It's strongly
2158 advised to use cpusets instead to disable scheduler load
2159 balancing through the "cpuset.sched_load_balance" file.
2160 It offers a much more flexible interface where CPUs can
2161 move in and out of an isolated set anytime.
2163 You can move a process onto or off an "isolated" CPU via
2164 the CPU affinity syscalls or cpuset.
2165 <cpu number> begins at 0 and the maximum value is
2166 "number of CPUs in system - 1".
2170 Isolate from being targeted by managed interrupts
2171 which have an interrupt mask containing isolated
2172 CPUs. The affinity of managed interrupts is
2173 handled by the kernel and cannot be changed via
2174 the /proc/irq/* interfaces.
2176 This isolation is best effort and only effective
2177 if the automatically assigned interrupt mask of a
2178 device queue contains isolated and housekeeping
2179 CPUs. If housekeeping CPUs are online then such
2180 interrupts are directed to the housekeeping CPU
2181 so that IO submitted on the housekeeping CPU
2182 cannot disturb the isolated CPU.
2184 If a queue's affinity mask contains only isolated
2185 CPUs then this parameter has no effect on the
2186 interrupt routing decision, though interrupts are
2187 only delivered when tasks running on those
2188 isolated CPUs submit IO. IO submitted on
2189 housekeeping CPUs has no influence on those
2192 The format of <cpu-list> is described above.
2196 ivrs_ioapic [HW,X86-64]
2197 Provide an override to the IOAPIC-ID<->DEVICE-ID
2198 mapping provided in the IVRS ACPI table. For
2199 example, to map IOAPIC-ID decimal 10 to
2200 PCI device 00:14.0 write the parameter as:
2201 ivrs_ioapic[10]=00:14.0
2203 ivrs_hpet [HW,X86-64]
2204 Provide an override to the HPET-ID<->DEVICE-ID
2205 mapping provided in the IVRS ACPI table. For
2206 example, to map HPET-ID decimal 0 to
2207 PCI device 00:14.0 write the parameter as:
2208 ivrs_hpet[0]=00:14.0
2210 ivrs_acpihid [HW,X86-64]
2211 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2212 mapping provided in the IVRS ACPI table. For
2213 example, to map UART-HID:UID AMD0020:0 to
2214 PCI device 00:14.5 write the parameter as:
2215 ivrs_acpihid[00:14.5]=AMD0020:0
2217 js= [HW,JOY] Analog joystick
2218 See Documentation/input/joydev/joystick.rst.
2221 When CONFIG_RANDOMIZE_BASE is set, this disables
2222 kernel and module base offset ASLR (Address Space
2223 Layout Randomization).
2226 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2227 report on every invalid memory access. Without this
2228 parameter KASAN will print report only for the first
2233 kernelcore= [KNL,X86,IA-64,PPC]
2234 Format: nn[KMGTPE] | nn% | "mirror"
2235 This parameter specifies the amount of memory usable by
2236 the kernel for non-movable allocations. The requested
2237 amount is spread evenly throughout all nodes in the
2238 system as ZONE_NORMAL. The remaining memory is used for
2239 movable memory in its own zone, ZONE_MOVABLE. In the
2240 event, a node is too small to have both ZONE_NORMAL and
2241 ZONE_MOVABLE, kernelcore memory will take priority and
2242 other nodes will have a larger ZONE_MOVABLE.
2244 ZONE_MOVABLE is used for the allocation of pages that
2245 may be reclaimed or moved by the page migration
2246 subsystem. Note that allocations like PTEs-from-HighMem
2247 still use the HighMem zone if it exists, and the Normal
2248 zone if it does not.
2250 It is possible to specify the exact amount of memory in
2251 the form of "nn[KMGTPE]", a percentage of total system
2252 memory in the form of "nn%", or "mirror". If "mirror"
2253 option is specified, mirrored (reliable) memory is used
2254 for non-movable allocations and remaining memory is used
2255 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2256 are exclusive, so you cannot specify multiple forms.
2258 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2259 Format: <Controller#>[,poll interval]
2260 The controller # is the number of the ehci usb debug
2261 port as it is probed via PCI. The poll interval is
2262 optional and is the number seconds in between
2263 each poll cycle to the debug port in case you need
2264 the functionality for interrupting the kernel with
2265 gdb or control-c on the dbgp connection. When
2266 not using this parameter you use sysrq-g to break into
2267 the kernel debugger.
2269 kgdboc= [KGDB,HW] kgdb over consoles.
2270 Requires a tty driver that supports console polling,
2271 or a supported polling keyboard driver (non-usb).
2272 Serial only format: <serial_device>[,baud]
2273 keyboard only format: kbd
2274 keyboard and serial format: kbd,<serial_device>[,baud]
2275 Optional Kernel mode setting:
2276 kms, kbd format: kms,kbd
2277 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2279 kgdboc_earlycon= [KGDB,HW]
2280 If the boot console provides the ability to read
2281 characters and can work in polling mode, you can use
2282 this parameter to tell kgdb to use it as a backend
2283 until the normal console is registered. Intended to
2284 be used together with the kgdboc parameter which
2285 specifies the normal console to transition to.
2287 The name of the early console should be specified
2288 as the value of this parameter. Note that the name of
2289 the early console might be different than the tty
2290 name passed to kgdboc. It's OK to leave the value
2291 blank and the first boot console that implements
2292 read() will be picked.
2294 kgdbwait [KGDB] Stop kernel execution and enter the
2295 kernel debugger at the earliest opportunity.
2297 kmac= [MIPS] Korina ethernet MAC address.
2298 Configure the RouterBoard 532 series on-chip
2299 Ethernet adapter MAC address.
2301 kmemleak= [KNL] Boot-time kmemleak enable/disable
2302 Valid arguments: on, off
2304 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2307 kprobe_event=[probe-list]
2308 [FTRACE] Add kprobe events and enable at boot time.
2309 The probe-list is a semicolon delimited list of probe
2310 definitions. Each definition is same as kprobe_events
2311 interface, but the parameters are comma delimited.
2312 For example, to add a kprobe event on vfs_read with
2313 arg1 and arg2, add to the command line;
2315 kprobe_event=p,vfs_read,$arg1,$arg2
2317 See also Documentation/trace/kprobetrace.rst "Kernel
2318 Boot Parameter" section.
2320 kpti= [ARM64] Control page table isolation of user
2321 and kernel address spaces.
2322 Default: enabled on cores which need mitigation.
2326 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2327 Default is 0 (don't ignore, but inject #GP)
2329 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2330 Default is false (don't support).
2332 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2337 [KVM] Controls the software workaround for the
2338 X86_BUG_ITLB_MULTIHIT bug.
2339 force : Always deploy workaround.
2340 off : Never deploy workaround.
2341 auto : Deploy workaround based on the presence of
2342 X86_BUG_ITLB_MULTIHIT.
2346 If the software workaround is enabled for the host,
2347 guests do need not to enable it for nested guests.
2349 kvm.nx_huge_pages_recovery_ratio=
2350 [KVM] Controls how many 4KiB pages are periodically zapped
2351 back to huge pages. 0 disables the recovery, otherwise if
2352 the value is N KVM will zap 1/Nth of the 4KiB pages every
2353 minute. The default is 60.
2355 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2356 Default is 1 (enabled)
2358 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2360 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2363 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2365 nvhe: Standard nVHE-based mode, without support for
2368 protected: nVHE-based mode with support for guests whose
2369 state is kept private from the host.
2370 Not valid if the kernel is running in EL2.
2372 Defaults to VHE/nVHE based on hardware support.
2374 kvm-arm.vgic_v3_group0_trap=
2375 [KVM,ARM] Trap guest accesses to GICv3 group-0
2378 kvm-arm.vgic_v3_group1_trap=
2379 [KVM,ARM] Trap guest accesses to GICv3 group-1
2382 kvm-arm.vgic_v3_common_trap=
2383 [KVM,ARM] Trap guest accesses to GICv3 common
2386 kvm-arm.vgic_v4_enable=
2387 [KVM,ARM] Allow use of GICv4 for direct injection of
2390 kvm_cma_resv_ratio=n [PPC]
2391 Reserves given percentage from system memory area for
2392 contiguous memory allocation for KVM hash pagetable
2394 By default it reserves 5% of total system memory.
2398 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2399 (virtualized MMU) support on capable Intel chips.
2400 Default is 1 (enabled)
2402 kvm-intel.emulate_invalid_guest_state=
2403 [KVM,Intel] Enable emulation of invalid guest states
2404 Default is 0 (disabled)
2406 kvm-intel.flexpriority=
2407 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2408 Default is 1 (enabled)
2411 [KVM,Intel] Enable VMX nesting (nVMX).
2412 Default is 0 (disabled)
2414 kvm-intel.unrestricted_guest=
2415 [KVM,Intel] Disable unrestricted guest feature
2416 (virtualized real and unpaged mode) on capable
2417 Intel chips. Default is 1 (enabled)
2419 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2422 Valid arguments: never, cond, always
2424 always: L1D cache flush on every VMENTER.
2425 cond: Flush L1D on VMENTER only when the code between
2426 VMEXIT and VMENTER can leak host memory.
2427 never: Disables the mitigation
2429 Default is cond (do L1 cache flush in specific instances)
2431 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2432 feature (tagged TLBs) on capable Intel chips.
2433 Default is 1 (enabled)
2435 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2438 The kernel PTE inversion protection is unconditionally
2439 enabled and cannot be disabled.
2442 Provides all available mitigations for the
2443 L1TF vulnerability. Disables SMT and
2444 enables all mitigations in the
2445 hypervisors, i.e. unconditional L1D flush.
2447 SMT control and L1D flush control via the
2448 sysfs interface is still possible after
2449 boot. Hypervisors will issue a warning
2450 when the first VM is started in a
2451 potentially insecure configuration,
2452 i.e. SMT enabled or L1D flush disabled.
2455 Same as 'full', but disables SMT and L1D
2456 flush runtime control. Implies the
2457 'nosmt=force' command line option.
2458 (i.e. sysfs control of SMT is disabled.)
2461 Leaves SMT enabled and enables the default
2462 hypervisor mitigation, i.e. conditional
2465 SMT control and L1D flush control via the
2466 sysfs interface is still possible after
2467 boot. Hypervisors will issue a warning
2468 when the first VM is started in a
2469 potentially insecure configuration,
2470 i.e. SMT enabled or L1D flush disabled.
2474 Disables SMT and enables the default
2475 hypervisor mitigation.
2477 SMT control and L1D flush control via the
2478 sysfs interface is still possible after
2479 boot. Hypervisors will issue a warning
2480 when the first VM is started in a
2481 potentially insecure configuration,
2482 i.e. SMT enabled or L1D flush disabled.
2485 Same as 'flush', but hypervisors will not
2486 warn when a VM is started in a potentially
2487 insecure configuration.
2490 Disables hypervisor mitigations and doesn't
2492 It also drops the swap size and available
2493 RAM limit restriction on both hypervisor and
2498 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2504 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2507 lapic= [X86,APIC] Do not use TSC deadline
2508 value for LAPIC timer one-shot implementation. Default
2509 back to the programmable timer unit in the LAPIC.
2510 Format: notscdeadline
2512 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2515 libata.dma= [LIBATA] DMA control
2516 libata.dma=0 Disable all PATA and SATA DMA
2517 libata.dma=1 PATA and SATA Disk DMA only
2518 libata.dma=2 ATAPI (CDROM) DMA only
2519 libata.dma=4 Compact Flash DMA only
2520 Combinations also work, so libata.dma=3 enables DMA
2521 for disks and CDROMs, but not CFs.
2523 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2524 libata.ignore_hpa=0 keep BIOS limits (default)
2525 libata.ignore_hpa=1 ignore limits, using full disk
2527 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2531 libata.force= [LIBATA] Force configurations. The format is comma-
2532 separated list of "[ID:]VAL" where ID is
2533 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2534 matching port, link or device. Basically, it matches
2535 the ATA ID string printed on console by libata. If
2536 the whole ID part is omitted, the last PORT and DEVICE
2537 values are used. If ID hasn't been specified yet, the
2538 configuration applies to all ports, links and devices.
2540 If only DEVICE is omitted, the parameter applies to
2541 the port and all links and devices behind it. DEVICE
2542 number of 0 either selects the first device or the
2543 first fan-out link behind PMP device. It does not
2544 select the host link. DEVICE number of 15 selects the
2545 host link and device attached to it.
2547 The VAL specifies the configuration to force. As long
2548 as there's no ambiguity shortcut notation is allowed.
2549 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2550 The following configurations can be forced.
2552 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2553 Any ID with matching PORT is used.
2555 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2557 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2558 udma[/][16,25,33,44,66,100,133] notation is also
2561 * [no]ncq: Turn on or off NCQ.
2563 * [no]ncqtrim: Turn off queued DSM TRIM.
2565 * nohrst, nosrst, norst: suppress hard, soft
2568 * rstonce: only attempt one reset during
2569 hot-unplug link recovery
2571 * dump_id: dump IDENTIFY data.
2573 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2575 * disable: Disable this device.
2577 If there are multiple matching configurations changing
2578 the same attribute, the last one is used.
2580 memblock=debug [KNL] Enable memblock debug messages.
2582 load_ramdisk= [RAM] [Deprecated]
2584 lockd.nlm_grace_period=P [NFS] Assign grace period.
2587 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2590 lockd.nlm_timeout=T [NFS] Assign timeout value.
2593 lockd.nlm_udpport=M [NFS] Assign UDP port.
2596 lockdown= [SECURITY]
2597 { integrity | confidentiality }
2598 Enable the kernel lockdown feature. If set to
2599 integrity, kernel features that allow userland to
2600 modify the running kernel are disabled. If set to
2601 confidentiality, kernel features that allow userland
2602 to extract confidential information from the kernel
2605 locktorture.nreaders_stress= [KNL]
2606 Set the number of locking read-acquisition kthreads.
2607 Defaults to being automatically set based on the
2608 number of online CPUs.
2610 locktorture.nwriters_stress= [KNL]
2611 Set the number of locking write-acquisition kthreads.
2613 locktorture.onoff_holdoff= [KNL]
2614 Set time (s) after boot for CPU-hotplug testing.
2616 locktorture.onoff_interval= [KNL]
2617 Set time (s) between CPU-hotplug operations, or
2618 zero to disable CPU-hotplug testing.
2620 locktorture.shuffle_interval= [KNL]
2621 Set task-shuffle interval (jiffies). Shuffling
2622 tasks allows some CPUs to go into dyntick-idle
2623 mode during the locktorture test.
2625 locktorture.shutdown_secs= [KNL]
2626 Set time (s) after boot system shutdown. This
2627 is useful for hands-off automated testing.
2629 locktorture.stat_interval= [KNL]
2630 Time (s) between statistics printk()s.
2632 locktorture.stutter= [KNL]
2633 Time (s) to stutter testing, for example,
2634 specifying five seconds causes the test to run for
2635 five seconds, wait for five seconds, and so on.
2636 This tests the locking primitive's ability to
2637 transition abruptly to and from idle.
2639 locktorture.torture_type= [KNL]
2640 Specify the locking implementation to test.
2642 locktorture.verbose= [KNL]
2643 Enable additional printk() statements.
2645 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2648 loglevel= All Kernel Messages with a loglevel smaller than the
2649 console loglevel will be printed to the console. It can
2650 also be changed with klogd or other programs. The
2651 loglevels are defined as follows:
2653 0 (KERN_EMERG) system is unusable
2654 1 (KERN_ALERT) action must be taken immediately
2655 2 (KERN_CRIT) critical conditions
2656 3 (KERN_ERR) error conditions
2657 4 (KERN_WARNING) warning conditions
2658 5 (KERN_NOTICE) normal but significant condition
2659 6 (KERN_INFO) informational
2660 7 (KERN_DEBUG) debug-level messages
2662 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2663 in bytes. n must be a power of two and greater
2664 than the minimal size. The minimal size is defined
2665 by LOG_BUF_SHIFT kernel config parameter. There is
2666 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2667 that allows to increase the default size depending on
2668 the number of CPUs. See init/Kconfig for more details.
2670 logo.nologo [FB] Disables display of the built-in Linux logo.
2671 This may be used to provide more screen space for
2672 kernel log messages and is useful when debugging
2673 kernel boot problems.
2675 lp=0 [LP] Specify parallel ports to use, e.g,
2676 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2677 lp=reset first parallel port). 'lp=0' disables the
2678 lp=auto printer driver. 'lp=reset' (which can be
2679 specified in addition to the ports) causes
2680 attached printers to be reset. Using
2681 lp=port1,port2,... specifies the parallel ports
2682 to associate lp devices with, starting with
2683 lp0. A port specification may be 'none' to skip
2684 that lp device, or a parport name such as
2685 'parport0'. Specifying 'lp=auto' instead of a
2686 port specification list means that device IDs
2687 from each port should be examined, to see if
2688 an IEEE 1284-compliant printer is attached; if
2689 so, the driver will manage that printer.
2690 See also header of drivers/char/lp.c.
2693 Sets loops_per_jiffy to given constant, thus avoiding
2694 time-consuming boot-time autodetection (up to 250 ms per
2695 CPU). 0 enables autodetection (default). To determine
2696 the correct value for your kernel, boot with normal
2697 autodetection and see what value is printed. Note that
2698 on SMP systems the preset will be applied to all CPUs,
2699 which is likely to cause problems if your CPUs need
2700 significantly divergent settings. An incorrect value
2701 will cause delays in the kernel to be wrong, leading to
2702 unpredictable I/O errors and other breakage. Although
2703 unlikely, in the extreme case this might damage your
2707 Format: <io>,<irq>,<dma>
2709 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2712 [SECURITY] Choose order of LSM initialization. This
2713 overrides CONFIG_LSM, and the "security=" parameter.
2715 machvec= [IA-64] Force the use of a particular machine-vector
2716 (machvec) in a generic kernel.
2717 Example: machvec=hpzx1
2719 machtype= [Loongson] Share the same kernel image file between
2720 different yeeloong laptops.
2721 Example: machtype=lemote-yeeloong-2f-7inch
2723 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2724 than or equal to this physical address is ignored.
2726 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2727 will bring up during bootup. maxcpus=n : n >= 0 limits
2728 the kernel to bring up 'n' processors. Surely after
2729 bootup you can bring up the other plugged cpu by executing
2730 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2731 only takes effect during system bootup.
2732 While n=0 is a special case, it is equivalent to "nosmp",
2733 which also disables the IO APIC.
2735 max_loop= [LOOP] The number of loop block devices that get
2736 (loop.max_loop) unconditionally pre-created at init time. The default
2737 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2738 of statically allocating a predefined number, loop
2739 devices can be requested on-demand with the
2740 /dev/loop-control interface.
2742 mce [X86-32] Machine Check Exception
2744 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2746 md= [HW] RAID subsystems devices and level
2747 See Documentation/admin-guide/md.rst.
2750 Format: <first>,<last>
2751 Specifies range of consoles to be captured by the MDA.
2754 Control mitigation for the Micro-architectural Data
2755 Sampling (MDS) vulnerability.
2757 Certain CPUs are vulnerable to an exploit against CPU
2758 internal buffers which can forward information to a
2759 disclosure gadget under certain conditions.
2761 In vulnerable processors, the speculatively
2762 forwarded data can be used in a cache side channel
2763 attack, to access data to which the attacker does
2764 not have direct access.
2766 This parameter controls the MDS mitigation. The
2769 full - Enable MDS mitigation on vulnerable CPUs
2770 full,nosmt - Enable MDS mitigation and disable
2771 SMT on vulnerable CPUs
2772 off - Unconditionally disable MDS mitigation
2774 On TAA-affected machines, mds=off can be prevented by
2775 an active TAA mitigation as both vulnerabilities are
2776 mitigated with the same mechanism so in order to disable
2777 this mitigation, you need to specify tsx_async_abort=off
2780 Not specifying this option is equivalent to
2783 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2785 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2786 Amount of memory to be used in cases as follows:
2789 2 when the kernel is not able to see the whole system memory;
2790 3 memory that lies after 'mem=' boundary is excluded from
2791 the hypervisor, then assigned to KVM guests.
2793 [X86] Work as limiting max address. Use together
2794 with memmap= to avoid physical address space collisions.
2795 Without memmap= PCI devices could be placed at addresses
2796 belonging to unused RAM.
2798 Note that this only takes effects during boot time since
2799 in above case 3, memory may need be hot added after boot
2800 if system memory of hypervisor is not sufficient.
2802 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2806 [KNL,SH] Allow user to override the default size for
2807 per-device physically contiguous DMA buffers.
2809 memhp_default_state=online/offline
2810 [KNL] Set the initial state for the memory hotplug
2811 onlining policy. If not specified, the default value is
2812 set according to the
2813 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2815 See Documentation/admin-guide/mm/memory-hotplug.rst.
2817 memmap=exactmap [KNL,X86] Enable setting of an exact
2818 E820 memory map, as specified by the user.
2819 Such memmap=exactmap lines can be constructed based on
2820 BIOS output or other requirements. See the memmap=nn@ss
2823 memmap=nn[KMG]@ss[KMG]
2824 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2825 Region of memory to be used is from ss to ss+nn.
2826 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2827 which limits max address to nn[KMG].
2828 Multiple different regions can be specified,
2831 memmap=100M@2G,100M#3G,1G!1024G
2833 memmap=nn[KMG]#ss[KMG]
2834 [KNL,ACPI] Mark specific memory as ACPI data.
2835 Region of memory to be marked is from ss to ss+nn.
2837 memmap=nn[KMG]$ss[KMG]
2838 [KNL,ACPI] Mark specific memory as reserved.
2839 Region of memory to be reserved is from ss to ss+nn.
2840 Example: Exclude memory from 0x18690000-0x1869ffff
2841 memmap=64K$0x18690000
2843 memmap=0x10000$0x18690000
2844 Some bootloaders may need an escape character before '$',
2845 like Grub2, otherwise '$' and the following number
2848 memmap=nn[KMG]!ss[KMG]
2849 [KNL,X86] Mark specific memory as protected.
2850 Region of memory to be used, from ss to ss+nn.
2851 The memory region may be marked as e820 type 12 (0xc)
2852 and is NVDIMM or ADR memory.
2854 memmap=<size>%<offset>-<oldtype>+<newtype>
2855 [KNL,ACPI] Convert memory within the specified region
2856 from <oldtype> to <newtype>. If "-<oldtype>" is left
2857 out, the whole region will be marked as <newtype>,
2858 even if previously unavailable. If "+<newtype>" is left
2859 out, matching memory will be removed. Types are
2860 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2861 3 = ACPI, 12 = PRAM.
2863 memory_corruption_check=0/1 [X86]
2864 Some BIOSes seem to corrupt the first 64k of
2865 memory when doing things like suspend/resume.
2866 Setting this option will scan the memory
2867 looking for corruption. Enabling this will
2868 both detect corruption and prevent the kernel
2869 from using the memory being corrupted.
2870 However, its intended as a diagnostic tool; if
2871 repeatable BIOS-originated corruption always
2872 affects the same memory, you can use memmap=
2873 to prevent the kernel from using that memory.
2875 memory_corruption_check_size=size [X86]
2876 By default it checks for corruption in the low
2877 64k, making this memory unavailable for normal
2878 use. Use this parameter to scan for
2879 corruption in more or less memory.
2881 memory_corruption_check_period=seconds [X86]
2882 By default it checks for corruption every 60
2883 seconds. Use this parameter to check at some
2884 other rate. 0 disables periodic checking.
2886 memory_hotplug.memmap_on_memory
2887 [KNL,X86,ARM] Boolean flag to enable this feature.
2888 Format: {on | off (default)}
2889 When enabled, runtime hotplugged memory will
2890 allocate its internal metadata (struct pages)
2891 from the hotadded memory which will allow to
2892 hotadd a lot of memory without requiring
2893 additional memory to do so.
2894 This feature is disabled by default because it
2895 has some implication on large (e.g. GB)
2896 allocations in some configurations (e.g. small
2898 The state of the flag can be read in
2899 /sys/module/memory_hotplug/parameters/memmap_on_memory.
2900 Note that even when enabled, there are a few cases where
2901 the feature is not effective.
2903 This is not compatible with hugetlb_free_vmemmap. If
2904 both parameters are enabled, hugetlb_free_vmemmap takes
2905 precedence over memory_hotplug.memmap_on_memory.
2907 memtest= [KNL,X86,ARM,PPC,RISCV] Enable memtest
2909 default : 0 <disable>
2910 Specifies the number of memtest passes to be
2911 performed. Each pass selects another test
2912 pattern from a given set of patterns. Memtest
2913 fills the memory with this pattern, validates
2914 memory contents and reserves bad memory
2915 regions that are detected.
2917 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2918 Valid arguments: on, off
2919 Default (depends on kernel configuration option):
2920 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2921 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2922 mem_encrypt=on: Activate SME
2923 mem_encrypt=off: Do not activate SME
2925 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2926 for details on when memory encryption can be activated.
2928 mem_sleep_default= [SUSPEND] Default system suspend mode:
2929 s2idle - Suspend-To-Idle
2930 shallow - Power-On Suspend or equivalent (if supported)
2931 deep - Suspend-To-RAM or equivalent (if supported)
2932 See Documentation/admin-guide/pm/sleep-states.rst.
2934 meye.*= [HW] Set MotionEye Camera parameters
2935 See Documentation/admin-guide/media/meye.rst.
2937 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2938 Multi-Function General Purpose Timers on AMD Geode
2941 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2942 the BIOS has incorrectly applied a workaround. TinyBIOS
2943 version 0.98 is known to be affected, 0.99 fixes the
2944 problem by letting the user disable the workaround.
2948 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2949 physical address is ignored.
2951 mini2440= [ARM,HW,KNL]
2952 Format:[0..2][b][c][t]
2954 MINI2440 configuration specification:
2955 0 - The attached screen is the 3.5" TFT
2956 1 - The attached screen is the 7" TFT
2957 2 - The VGA Shield is attached (1024x768)
2958 Leaving out the screen size parameter will not load
2959 the TFT driver, and the framebuffer will be left
2961 b - Enable backlight. The TFT backlight pin will be
2962 linked to the kernel VESA blanking code and a GPIO
2963 LED. This parameter is not necessary when using the
2965 c - Enable the s3c camera interface.
2966 t - Reserved for enabling touchscreen support. The
2967 touchscreen support is not enabled in the mainstream
2968 kernel as of 2.6.30, a preliminary port can be found
2969 in the "bleeding edge" mini2440 support kernel at
2970 https://repo.or.cz/w/linux-2.6/mini2440.git
2973 [X86,PPC,S390,ARM64] Control optional mitigations for
2974 CPU vulnerabilities. This is a set of curated,
2975 arch-independent options, each of which is an
2976 aggregation of existing arch-specific options.
2979 Disable all optional CPU mitigations. This
2980 improves system performance, but it may also
2981 expose users to several CPU vulnerabilities.
2982 Equivalent to: nopti [X86,PPC]
2984 nospectre_v1 [X86,PPC]
2986 nospectre_v2 [X86,PPC,S390,ARM64]
2987 spectre_v2_user=off [X86]
2988 spec_store_bypass_disable=off [X86,PPC]
2989 ssbd=force-off [ARM64]
2992 tsx_async_abort=off [X86]
2993 kvm.nx_huge_pages=off [X86]
2994 no_entry_flush [PPC]
2995 no_uaccess_flush [PPC]
2998 This does not have any effect on
2999 kvm.nx_huge_pages when
3000 kvm.nx_huge_pages=force.
3003 Mitigate all CPU vulnerabilities, but leave SMT
3004 enabled, even if it's vulnerable. This is for
3005 users who don't want to be surprised by SMT
3006 getting disabled across kernel upgrades, or who
3007 have other ways of avoiding SMT-based attacks.
3008 Equivalent to: (default behavior)
3011 Mitigate all CPU vulnerabilities, disabling SMT
3012 if needed. This is for users who always want to
3013 be fully mitigated, even if it means losing SMT.
3014 Equivalent to: l1tf=flush,nosmt [X86]
3015 mds=full,nosmt [X86]
3016 tsx_async_abort=full,nosmt [X86]
3019 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3020 parameter allows control of the logging verbosity for
3021 the additional memory initialisation checks. A value
3022 of 0 disables mminit logging and a level of 4 will
3023 log everything. Information is printed at KERN_DEBUG
3024 so loglevel=8 may also need to be specified.
3027 [KNL] When CONFIG_MODULE_SIG is set, this means that
3028 modules without (valid) signatures will fail to load.
3029 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3030 is always true, so this option does nothing.
3032 module_blacklist= [KNL] Do not load a comma-separated list of
3033 modules. Useful for debugging problem modules.
3036 [MOUSE] Maximum time between finger touching and
3037 leaving touchpad surface for touch to be considered
3038 a tap and be reported as a left button click (for
3039 touchpads working in absolute mode only).
3041 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3042 reporting absolute coordinates, such as tablets
3043 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3044 reporting absolute coordinates, such as tablets
3046 movablecore= [KNL,X86,IA-64,PPC]
3047 Format: nn[KMGTPE] | nn%
3048 This parameter is the complement to kernelcore=, it
3049 specifies the amount of memory used for migratable
3050 allocations. If both kernelcore and movablecore is
3051 specified, then kernelcore will be at *least* the
3052 specified value but may be more. If movablecore on its
3053 own is specified, the administrator must be careful
3054 that the amount of memory usable for all allocations
3057 movable_node [KNL] Boot-time switch to make hotplugable memory
3058 NUMA nodes to be movable. This means that the memory
3059 of such nodes will be usable only for movable
3060 allocations which rules out almost all kernel
3061 allocations. Use with caution!
3063 MTD_Partition= [MTD]
3064 Format: <name>,<region-number>,<size>,<offset>
3066 MTD_Region= [MTD] Format:
3067 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3070 See drivers/mtd/parsers/cmdlinepart.c
3072 multitce=off [PPC] This parameter disables the use of the pSeries
3073 firmware feature for updating multiple TCE entries
3076 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3078 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3080 boundary - index of last SLC block on Flex-OneNAND.
3081 The remaining blocks are configured as MLC blocks.
3082 lock - Configure if Flex-OneNAND boundary should be locked.
3083 Once locked, the boundary cannot be changed.
3084 1 indicates lock status, 0 indicates unlock status.
3087 ARM/S3C2412 JIVE boot control
3089 See arch/arm/mach-s3c/mach-jive.c
3091 mtouchusb.raw_coordinates=
3092 [HW] Make the MicroTouch USB driver use raw coordinates
3093 ('y', default) or cooked coordinates ('n')
3095 mtrr_chunk_size=nn[KMG] [X86]
3096 used for mtrr cleanup. It is largest continuous chunk
3097 that could hold holes aka. UC entries.
3099 mtrr_gran_size=nn[KMG] [X86]
3100 Used for mtrr cleanup. It is granularity of mtrr block.
3102 Large value could prevent small alignment from
3105 mtrr_spare_reg_nr=n [X86]
3107 Range: 0,7 : spare reg number
3109 Used for mtrr cleanup. It is spare mtrr entries number.
3110 Set to 2 or more if your graphical card needs more.
3112 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3114 netdev= [NET] Network devices parameters
3115 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3116 Note that mem_start is often overloaded to mean
3117 something different and driver-specific.
3118 This usage is only documented in each driver source
3122 [NETFILTER] Enable connection tracking flow accounting
3123 0 to disable accounting
3124 1 to enable accounting
3127 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3128 See Documentation/admin-guide/nfs/nfsroot.rst.
3130 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3131 See Documentation/admin-guide/nfs/nfsroot.rst.
3133 nfsrootdebug [NFS] enable nfsroot debugging messages.
3134 See Documentation/admin-guide/nfs/nfsroot.rst.
3136 nfs.callback_nr_threads=
3137 [NFSv4] set the total number of threads that the
3138 NFS client will assign to service NFSv4 callback
3141 nfs.callback_tcpport=
3142 [NFS] set the TCP port on which the NFSv4 callback
3143 channel should listen.
3146 [NFS] sets the pathname to the program which is used
3147 to update the NFS client cache entries.
3149 nfs.cache_getent_timeout=
3150 [NFS] sets the timeout after which an attempt to
3151 update a cache entry is deemed to have failed.
3153 nfs.idmap_cache_timeout=
3154 [NFS] set the maximum lifetime for idmapper cache
3158 [NFS] enable 64-bit inode numbers.
3159 If zero, the NFS client will fake up a 32-bit inode
3160 number for the readdir() and stat() syscalls instead
3161 of returning the full 64-bit number.
3162 The default is to return 64-bit inode numbers.
3164 nfs.max_session_cb_slots=
3165 [NFSv4.1] Sets the maximum number of session
3166 slots the client will assign to the callback
3167 channel. This determines the maximum number of
3168 callbacks the client will process in parallel for
3169 a particular server.
3171 nfs.max_session_slots=
3172 [NFSv4.1] Sets the maximum number of session slots
3173 the client will attempt to negotiate with the server.
3174 This limits the number of simultaneous RPC requests
3175 that the client can send to the NFSv4.1 server.
3176 Note that there is little point in setting this
3177 value higher than the max_tcp_slot_table_limit.
3179 nfs.nfs4_disable_idmapping=
3180 [NFSv4] When set to the default of '1', this option
3181 ensures that both the RPC level authentication
3182 scheme and the NFS level operations agree to use
3183 numeric uids/gids if the mount is using the
3184 'sec=sys' security flavour. In effect it is
3185 disabling idmapping, which can make migration from
3186 legacy NFSv2/v3 systems to NFSv4 easier.
3187 Servers that do not support this mode of operation
3188 will be autodetected by the client, and it will fall
3189 back to using the idmapper.
3190 To turn off this behaviour, set the value to '0'.
3192 [NFS4] Specify an additional fixed unique ident-
3193 ification string that NFSv4 clients can insert into
3194 their nfs_client_id4 string. This is typically a
3195 UUID that is generated at system install time.
3197 nfs.send_implementation_id =
3198 [NFSv4.1] Send client implementation identification
3199 information in exchange_id requests.
3200 If zero, no implementation identification information
3202 The default is to send the implementation identification
3205 nfs.recover_lost_locks =
3206 [NFSv4] Attempt to recover locks that were lost due
3207 to a lease timeout on the server. Please note that
3208 doing this risks data corruption, since there are
3209 no guarantees that the file will remain unchanged
3210 after the locks are lost.
3211 If you want to enable the kernel legacy behaviour of
3212 attempting to recover these locks, then set this
3214 The default parameter value of '0' causes the kernel
3215 not to attempt recovery of lost locks.
3217 nfs4.layoutstats_timer =
3218 [NFSv4.2] Change the rate at which the kernel sends
3219 layoutstats to the pNFS metadata server.
3221 Setting this to value to 0 causes the kernel to use
3222 whatever value is the default set by the layout
3223 driver. A non-zero value sets the minimum interval
3224 in seconds between layoutstats transmissions.
3226 nfsd.nfs4_disable_idmapping=
3227 [NFSv4] When set to the default of '1', the NFSv4
3228 server will return only numeric uids and gids to
3229 clients using auth_sys, and will accept numeric uids
3230 and gids from such clients. This is intended to ease
3231 migration from NFSv2/v3.
3233 nmi_backtrace.backtrace_idle [KNL]
3234 Dump stacks even of idle CPUs in response to an
3235 NMI stack-backtrace request.
3237 nmi_debug= [KNL,SH] Specify one or more actions to take
3238 when a NMI is triggered.
3239 Format: [state][,regs][,debounce][,die]
3241 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3242 Format: [panic,][nopanic,][num]
3244 0 - turn hardlockup detector in nmi_watchdog off
3245 1 - turn hardlockup detector in nmi_watchdog on
3246 When panic is specified, panic when an NMI watchdog
3247 timeout occurs (or 'nopanic' to not panic on an NMI
3248 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3249 To disable both hard and soft lockup detectors,
3250 please see 'nowatchdog'.
3251 This is useful when you use a panic=... timeout and
3252 need the box quickly up again.
3254 These settings can be accessed at runtime via
3255 the nmi_watchdog and hardlockup_panic sysctls.
3257 netpoll.carrier_timeout=
3258 [NET] Specifies amount of time (in seconds) that
3259 netpoll should wait for a carrier. By default netpoll
3262 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3263 emulation library even if a 387 maths coprocessor
3266 no5lvl [X86-64] Disable 5-level paging mode. Forces
3267 kernel to use 4-level paging instead.
3269 nofsgsbase [X86] Disables FSGSBASE instructions.
3272 [HW] Never suspend the console
3273 Disable suspending of consoles during suspend and
3274 hibernate operations. Once disabled, debugging
3275 messages can reach various consoles while the rest
3276 of the system is being put to sleep (ie, while
3277 debugging driver suspend/resume hooks). This may
3278 not work reliably with all consoles, but is known
3279 to work with serial and VGA consoles.
3280 To facilitate more flexible debugging, we also add
3281 console_suspend, a printk module parameter to control
3282 it. Users could use console_suspend (usually
3283 /sys/module/printk/parameters/console_suspend) to
3284 turn on/off it dynamically.
3286 novmcoredd [KNL,KDUMP]
3287 Disable device dump. Device dump allows drivers to
3288 append dump data to vmcore so you can collect driver
3289 specified debug info. Drivers can append the data
3290 without any limit and this data is stored in memory,
3291 so this may cause significant memory stress. Disabling
3292 device dump can help save memory but the driver debug
3293 data will be no longer available. This parameter
3294 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3297 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3298 caches in the slab allocator. Saves per-node memory,
3299 but will impact performance.
3303 noaltinstr [S390] Disables alternative instructions patching
3304 (CPU alternatives feature).
3306 noapic [SMP,APIC] Tells the kernel to not make use of any
3307 IOAPICs that may be present in the system.
3309 noautogroup Disable scheduler automatic task group creation.
3311 nobats [PPC] Do not use BATs for mapping kernel lowmem
3312 on "Classic" PPC cores.
3316 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3318 delayacct [KNL] Enable per-task delay accounting
3320 nodsp [SH] Disable hardware DSP at boot time.
3322 noefi Disable EFI runtime services support.
3324 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3329 On X86-32 available only on PAE configured kernels.
3330 noexec=on: enable non-executable mappings (default)
3331 noexec=off: disable non-executable mappings
3334 Disable SMAP (Supervisor Mode Access Prevention)
3335 even if it is supported by processor.
3338 Disable SMEP (Supervisor Mode Execution Prevention)
3339 even if it is supported by processor.
3342 This affects only 32-bit executables.
3343 noexec32=on: enable non-executable mappings (default)
3344 read doesn't imply executable mappings
3345 noexec32=off: disable non-executable mappings
3346 read implies executable mappings
3348 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3350 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3351 register save and restore. The kernel will only save
3352 legacy floating-point registers on task switch.
3354 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3356 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3358 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3359 Equivalent to smt=1.
3361 [KNL,X86] Disable symmetric multithreading (SMT).
3362 nosmt=force: Force disable SMT, cannot be undone
3363 via the sysfs control file.
3365 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3366 (bounds check bypass). With this option data leaks are
3367 possible in the system.
3369 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3370 the Spectre variant 2 (indirect branch prediction)
3371 vulnerability. System may allow data leaks with this
3374 nospec_store_bypass_disable
3375 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3378 [PPC] Don't flush the L1-D cache after accessing user data.
3380 noxsave [BUGS=X86] Disables x86 extended register state save
3381 and restore using xsave. The kernel will fallback to
3382 enabling legacy floating-point and sse state.
3384 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3385 register states. The kernel will fall back to use
3386 xsave to save the states. By using this parameter,
3387 performance of saving the states is degraded because
3388 xsave doesn't support modified optimization while
3389 xsaveopt supports it on xsaveopt enabled systems.
3391 noxsaves [X86] Disables xsaves and xrstors used in saving and
3392 restoring x86 extended register state in compacted
3393 form of xsave area. The kernel will fall back to use
3394 xsaveopt and xrstor to save and restore the states
3395 in standard form of xsave area. By using this
3396 parameter, xsave area per process might occupy more
3397 memory on xsaves enabled systems.
3399 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3400 in do_idle() and not use the arch_cpu_idle()
3401 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3402 to be effective. This is useful on platforms where the
3403 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3404 correctly or when doing power measurements to evalute
3405 the impact of the sleep instructions. This is also
3406 useful when using JTAG debugger.
3408 no_file_caps Tells the kernel not to honor file capabilities. The
3409 only way then for a file to be executed with privilege
3410 is to be setuid root or executed by root.
3412 nohalt [IA-64] Tells the kernel not to use the power saving
3413 function PAL_HALT_LIGHT when idle. This increases
3414 power-consumption. On the positive side, it reduces
3415 interrupt wake-up latency, which may improve performance
3416 in certain environments such as networked servers or
3420 Force pointers printed to the console or buffers to be
3421 unhashed. By default, when a pointer is printed via %p
3422 format string, that pointer is "hashed", i.e. obscured
3423 by hashing the pointer value. This is a security feature
3424 that hides actual kernel addresses from unprivileged
3425 users, but it also makes debugging the kernel more
3426 difficult since unequal pointers can no longer be
3427 compared. However, if this command-line option is
3428 specified, then all normal pointers will have their true
3429 value printed. Pointers printed via %pK may still be
3430 hashed. This option should only be specified when
3431 debugging the kernel. Please do not use on production
3434 nohibernate [HIBERNATION] Disable hibernation and resume.
3436 nohz= [KNL] Boottime enable/disable dynamic ticks
3437 Valid arguments: on, off
3440 nohz_full= [KNL,BOOT,SMP,ISOL]
3441 The argument is a cpu list, as described above.
3442 In kernels built with CONFIG_NO_HZ_FULL=y, set
3443 the specified list of CPUs whose tick will be stopped
3444 whenever possible. The boot CPU will be forced outside
3445 the range to maintain the timekeeping. Any CPUs
3446 in this list will have their RCU callbacks offloaded,
3447 just as if they had also been called out in the
3448 rcu_nocbs= boot parameter.
3450 noiotrap [SH] Disables trapped I/O port accesses.
3452 noirqdebug [X86-32] Disables the code which attempts to detect and
3453 disable unhandled interrupt sources.
3455 no_timer_check [X86,APIC] Disables the code which tests for
3456 broken timer IRQ sources.
3458 noisapnp [ISAPNP] Disables ISA PnP code.
3460 noinitrd [RAM] Tells the kernel not to load any configured
3463 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3465 [Deprecated - use intremap=off]
3469 noinvpcid [X86] Disable the INVPCID cpu feature.
3471 nojitter [IA-64] Disables jitter checking for ITC timers.
3473 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3475 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3479 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3480 clock and use the default one.
3482 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3483 accounting. steal time is computed, but won't
3484 influence scheduler behaviour
3486 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3488 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3490 noltlbs [PPC] Do not use large page/tlb entries for kernel
3491 lowmem mapping on PPC40x and PPC8xx
3493 nomca [IA-64] Disable machine check abort handling
3495 nomce [X86-32] Disable Machine Check Exception
3497 nomfgpt [X86-32] Disable Multi-Function General Purpose
3498 Timer usage (for AMD Geode machines).
3500 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3501 shutdown the other cpus. Instead use the REBOOT_VECTOR
3504 nomodule Disable module load
3506 nopat [X86] Disable PAT (page attribute table extension of
3507 pagetables) support.
3509 nopcid [X86-64] Disable the PCID cpu feature.
3511 norandmaps Don't use address space randomization. Equivalent to
3512 echo 0 > /proc/sys/kernel/randomize_va_space
3514 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3515 with UP alternatives
3517 nordrand [X86] Disable kernel use of the RDRAND and
3518 RDSEED instructions even if they are supported
3519 by the processor. RDRAND and RDSEED are still
3520 available to user space applications.
3522 noresume [SWSUSP] Disables resume and restores original swap
3525 no-scroll [VGA] Disables scrollback.
3526 This is required for the Braillex ib80-piezo Braille
3527 reader made by F.H. Papenmeier (Germany).
3531 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3533 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3535 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3536 and disable the IO APIC. legacy for "maxcpus=0".
3538 nosoftlockup [KNL] Disable the soft-lockup detector.
3540 nosync [HW,M68K] Disables sync negotiation for all devices.
3542 nowatchdog [KNL] Disable both lockup detectors, i.e.
3543 soft-lockup and NMI watchdog (hard-lockup).
3547 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3549 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3550 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3551 Some features depend on CPU0. Known dependencies are:
3552 1. Resume from suspend/hibernate depends on CPU0.
3553 Suspend/hibernate will fail if CPU0 is offline and you
3554 need to online CPU0 before suspend/hibernate.
3555 2. PIC interrupts also depend on CPU0. CPU0 can't be
3556 removed if a PIC interrupt is detected.
3557 It's said poweroff/reboot may depend on CPU0 on some
3558 machines although I haven't seen such issues so far
3559 after CPU0 is offline on a few tested machines.
3560 If the dependencies are under your control, you can
3561 turn on cpu0_hotplug.
3563 nps_mtm_hs_ctr= [KNL,ARC]
3564 This parameter sets the maximum duration, in
3565 cycles, each HW thread of the CTOP can run
3566 without interruptions, before HW switches it.
3567 The actual maximum duration is 16 times this
3569 Format: integer between 1 and 255
3572 nptcg= [IA-64] Override max number of concurrent global TLB
3573 purges which is reported from either PAL_VM_SUMMARY or
3576 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3577 could support. nr_cpus=n : n >= 1 limits the kernel to
3578 support 'n' processors. It could be larger than the
3579 number of already plugged CPU during bootup, later in
3580 runtime you can physically add extra cpu until it reaches
3581 n. So during boot up some boot time memory for per-cpu
3582 variables need be pre-allocated for later physical cpu
3585 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3587 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3588 set up a single NUMA node spanning all memory.
3590 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3592 Allowed values are enable and disable
3594 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3595 'node', 'default' can be specified
3596 This can be set from sysctl after boot.
3597 See Documentation/admin-guide/sysctl/vm.rst for details.
3599 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3600 See Documentation/core-api/debugging-via-ohci1394.rst for more
3603 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3604 Rather than timing out after 20 ms if an EC
3605 command is not properly ACKed, override the length
3606 of the timeout. We have interrupts disabled while
3607 waiting for the ACK, so if this is set too high
3608 interrupts *may* be lost!
3610 omap_mux= [OMAP] Override bootloader pin multiplexing.
3611 Format: <mux_mode0.mode_name=value>...
3612 For example, to override I2C bus2:
3613 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3615 oops=panic Always panic on oopses. Default is to just kill the
3616 process, but there is a small probability of
3617 deadlocking the machine.
3618 This will also cause panics on machine check exceptions.
3619 Useful together with panic=30 to trigger a reboot.
3622 [KNL] Boolean flag to control whether the page allocator
3623 should randomize its free lists. The randomization may
3624 be automatically enabled if the kernel detects it is
3625 running on a platform with a direct-mapped memory-side
3626 cache, and this parameter can be used to
3627 override/disable that behavior. The state of the flag
3628 can be read from sysfs at:
3629 /sys/module/page_alloc/parameters/shuffle.
3631 page_owner= [KNL] Boot-time page_owner enabling option.
3632 Storage of the information about who allocated
3633 each page is disabled in default. With this switch,
3635 on: enable the feature
3637 page_poison= [KNL] Boot-time parameter changing the state of
3638 poisoning on the buddy allocator, available with
3639 CONFIG_PAGE_POISONING=y.
3640 off: turn off poisoning (default)
3641 on: turn on poisoning
3643 page_reporting.page_reporting_order=
3644 [KNL] Minimal page reporting order
3646 Adjust the minimal page reporting order. The page
3647 reporting is disabled when it exceeds (MAX_ORDER-1).
3649 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3650 timeout > 0: seconds before rebooting
3651 timeout = 0: wait forever
3652 timeout < 0: reboot immediately
3655 panic_print= Bitmask for printing system info when panic happens.
3656 User can chose combination of the following bits:
3657 bit 0: print all tasks info
3658 bit 1: print system memory info
3659 bit 2: print timer info
3660 bit 3: print locks info if CONFIG_LOCKDEP is on
3661 bit 4: print ftrace buffer
3662 bit 5: print all printk messages in buffer
3664 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3665 Format: <hex>[,nousertaint]
3666 Hexadecimal bitmask representing the set of TAINT flags
3667 that will cause the kernel to panic when add_taint() is
3668 called with any of the flags in this set.
3669 The optional switch "nousertaint" can be utilized to
3670 prevent userspace forced crashes by writing to sysctl
3671 /proc/sys/kernel/tainted any flagset matching with the
3672 bitmask set on panic_on_taint.
3673 See Documentation/admin-guide/tainted-kernels.rst for
3674 extra details on the taint flags that users can pick
3675 to compose the bitmask to assign to panic_on_taint.
3677 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3680 crash_kexec_post_notifiers
3681 Run kdump after running panic-notifiers and dumping
3682 kmsg. This only for the users who doubt kdump always
3683 succeeds in any situation.
3684 Note that this also increases risks of kdump failure,
3685 because some panic notifiers can make the crashed
3686 kernel more unstable.
3688 parkbd.port= [HW] Parallel port number the keyboard adapter is
3689 connected to, default is 0.
3691 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3692 0 for XT, 1 for AT (default is AT).
3695 parport= [HW,PPT] Specify parallel ports. 0 disables.
3696 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3697 Use 'auto' to force the driver to use any
3698 IRQ/DMA settings detected (the default is to
3699 ignore detected IRQ/DMA settings because of
3700 possible conflicts). You can specify the base
3701 address, IRQ, and DMA settings; IRQ and DMA
3702 should be numbers, or 'auto' (for using detected
3703 settings on that particular port), or 'nofifo'
3704 (to avoid using a FIFO even if it is detected).
3705 Parallel ports are assigned in the order they
3706 are specified on the command line, starting
3709 parport_init_mode= [HW,PPT]
3710 Configure VIA parallel port to operate in
3711 a specific mode. This is necessary on Pegasos
3712 computer where firmware has no options for setting
3713 up parallel port mode and sets it to spp.
3714 Currently this function knows 686a and 8231 chips.
3715 Format: [spp|ps2|epp|ecp|ecpepp]
3717 pata_legacy.all= [HW,LIBATA]
3719 Set to non-zero to probe primary and secondary ISA
3720 port ranges on PCI systems where no PCI PATA device
3721 has been found at either range. Disabled by default.
3723 pata_legacy.autospeed= [HW,LIBATA]
3725 Set to non-zero if a chip is present that snoops speed
3726 changes. Disabled by default.
3728 pata_legacy.ht6560a= [HW,LIBATA]
3730 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3731 the secondary channel, or both channels respectively.
3732 Disabled by default.
3734 pata_legacy.ht6560b= [HW,LIBATA]
3736 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3737 the secondary channel, or both channels respectively.
3738 Disabled by default.
3740 pata_legacy.iordy_mask= [HW,LIBATA]
3742 IORDY enable mask. Set individual bits to allow IORDY
3743 for the respective channel. Bit 0 is for the first
3744 legacy channel handled by this driver, bit 1 is for
3745 the second channel, and so on. The sequence will often
3746 correspond to the primary legacy channel, the secondary
3747 legacy channel, and so on, but the handling of a PCI
3748 bus and the use of other driver options may interfere
3749 with the sequence. By default IORDY is allowed across
3752 pata_legacy.opti82c46x= [HW,LIBATA]
3754 Set to 1, 2, or 3 for Opti 82c611A on the primary
3755 channel, the secondary channel, or both channels
3756 respectively. Disabled by default.
3758 pata_legacy.opti82c611a= [HW,LIBATA]
3760 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3761 channel, the secondary channel, or both channels
3762 respectively. Disabled by default.
3764 pata_legacy.pio_mask= [HW,LIBATA]
3766 PIO mode mask for autospeed devices. Set individual
3767 bits to allow the use of the respective PIO modes.
3768 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3769 All modes allowed by default.
3771 pata_legacy.probe_all= [HW,LIBATA]
3773 Set to non-zero to probe tertiary and further ISA
3774 port ranges on PCI systems. Disabled by default.
3776 pata_legacy.probe_mask= [HW,LIBATA]
3778 Probe mask for legacy ISA PATA ports. Depending on
3779 platform configuration and the use of other driver
3780 options up to 6 legacy ports are supported: 0x1f0,
3781 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3782 of individual ports can be disabled by setting the
3783 corresponding bits in the mask to 1. Bit 0 is for
3784 the first port in the list above (0x1f0), and so on.
3785 By default all supported ports are probed.
3787 pata_legacy.qdi= [HW,LIBATA]
3789 Set to non-zero to probe QDI controllers. By default
3790 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3792 pata_legacy.winbond= [HW,LIBATA]
3794 Set to non-zero to probe Winbond controllers. Use
3795 the standard I/O port (0x130) if 1, otherwise the
3796 value given is the I/O port to use (typically 0x1b0).
3797 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3800 pata_platform.pio_mask= [HW,LIBATA]
3802 Supported PIO mode mask. Set individual bits to allow
3803 the use of the respective PIO modes. Bit 0 is for
3804 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3808 Halt all CPUs after the first oops has been printed for
3809 the specified number of seconds. This is to be used if
3810 your oopses keep scrolling off the screen.
3815 See header of drivers/block/paride/pcd.c.
3816 See also Documentation/admin-guide/blockdev/paride.rst.
3818 pci=option[,option...] [PCI] various PCI subsystem options.
3820 Some options herein operate on a specific device
3821 or a set of devices (<pci_dev>). These are
3822 specified in one of the following formats:
3824 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3825 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3827 Note: the first format specifies a PCI
3828 bus/device/function address which may change
3829 if new hardware is inserted, if motherboard
3830 firmware changes, or due to changes caused
3831 by other kernel parameters. If the
3832 domain is left unspecified, it is
3833 taken to be zero. Optionally, a path
3834 to a device through multiple device/function
3835 addresses can be specified after the base
3836 address (this is more robust against
3837 renumbering issues). The second format
3838 selects devices using IDs from the
3839 configuration space which may match multiple
3840 devices in the system.
3842 earlydump dump PCI config space before the kernel
3844 off [X86] don't probe for the PCI bus
3845 bios [X86-32] force use of PCI BIOS, don't access
3846 the hardware directly. Use this if your machine
3847 has a non-standard PCI host bridge.
3848 nobios [X86-32] disallow use of PCI BIOS, only direct
3849 hardware access methods are allowed. Use this
3850 if you experience crashes upon bootup and you
3851 suspect they are caused by the BIOS.
3852 conf1 [X86] Force use of PCI Configuration Access
3853 Mechanism 1 (config address in IO port 0xCF8,
3854 data in IO port 0xCFC, both 32-bit).
3855 conf2 [X86] Force use of PCI Configuration Access
3856 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3857 the function, IO port 0xCFA, also 8-bit, sets
3858 bus number. The config space is then accessed
3859 through ports 0xC000-0xCFFF).
3860 See http://wiki.osdev.org/PCI for more info
3861 on the configuration access mechanisms.
3862 noaer [PCIE] If the PCIEAER kernel config parameter is
3863 enabled, this kernel boot option can be used to
3864 disable the use of PCIE advanced error reporting.
3865 nodomains [PCI] Disable support for multiple PCI
3866 root domains (aka PCI segments, in ACPI-speak).
3867 nommconf [X86] Disable use of MMCONFIG for PCI
3869 check_enable_amd_mmconf [X86] check for and enable
3870 properly configured MMIO access to PCI
3871 config space on AMD family 10h CPU
3872 nomsi [MSI] If the PCI_MSI kernel config parameter is
3873 enabled, this kernel boot option can be used to
3874 disable the use of MSI interrupts system-wide.
3875 noioapicquirk [APIC] Disable all boot interrupt quirks.
3876 Safety option to keep boot IRQs enabled. This
3877 should never be necessary.
3878 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3879 primary IO-APIC for bridges that cannot disable
3880 boot IRQs. This fixes a source of spurious IRQs
3881 when the system masks IRQs.
3882 noioapicreroute [APIC] Disable workaround that uses the
3883 boot IRQ equivalent of an IRQ that connects to
3884 a chipset where boot IRQs cannot be disabled.
3885 The opposite of ioapicreroute.
3886 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3887 routing table. These calls are known to be buggy
3888 on several machines and they hang the machine
3889 when used, but on other computers it's the only
3890 way to get the interrupt routing table. Try
3891 this option if the kernel is unable to allocate
3892 IRQs or discover secondary PCI buses on your
3894 rom [X86] Assign address space to expansion ROMs.
3895 Use with caution as certain devices share
3896 address decoders between ROMs and other
3898 norom [X86] Do not assign address space to
3899 expansion ROMs that do not already have
3900 BIOS assigned address ranges.
3901 nobar [X86] Do not assign address space to the
3902 BARs that weren't assigned by the BIOS.
3903 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3904 assigned automatically to PCI devices. You can
3905 make the kernel exclude IRQs of your ISA cards
3907 pirqaddr=0xAAAAA [X86] Specify the physical address
3908 of the PIRQ table (normally generated
3909 by the BIOS) if it is outside the
3910 F0000h-100000h range.
3911 lastbus=N [X86] Scan all buses thru bus #N. Can be
3912 useful if the kernel is unable to find your
3913 secondary buses and you want to tell it
3914 explicitly which ones they are.
3915 assign-busses [X86] Always assign all PCI bus
3916 numbers ourselves, overriding
3917 whatever the firmware may have done.
3918 usepirqmask [X86] Honor the possible IRQ mask stored
3919 in the BIOS $PIR table. This is needed on
3920 some systems with broken BIOSes, notably
3921 some HP Pavilion N5400 and Omnibook XE3
3922 notebooks. This will have no effect if ACPI
3923 IRQ routing is enabled.
3924 noacpi [X86] Do not use ACPI for IRQ routing
3925 or for PCI scanning.
3926 use_crs [X86] Use PCI host bridge window information
3927 from ACPI. On BIOSes from 2008 or later, this
3928 is enabled by default. If you need to use this,
3929 please report a bug.
3930 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3931 If you need to use this, please report a bug.
3932 routeirq Do IRQ routing for all PCI devices.
3933 This is normally done in pci_enable_device(),
3934 so this option is a temporary workaround
3935 for broken drivers that don't call it.
3936 skip_isa_align [X86] do not align io start addr, so can
3937 handle more pci cards
3938 noearly [X86] Don't do any early type 1 scanning.
3939 This might help on some broken boards which
3940 machine check when some devices' config space
3941 is read. But various workarounds are disabled
3942 and some IOMMU drivers will not work.
3943 bfsort Sort PCI devices into breadth-first order.
3944 This sorting is done to get a device
3945 order compatible with older (<= 2.4) kernels.
3946 nobfsort Don't sort PCI devices into breadth-first order.
3947 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3948 tuning and use the BIOS-configured MPS defaults.
3949 pcie_bus_safe Set every device's MPS to the largest value
3950 supported by all devices below the root complex.
3951 pcie_bus_perf Set device MPS to the largest allowable MPS
3952 based on its parent bus. Also set MRRS (Max
3953 Read Request Size) to the largest supported
3954 value (no larger than the MPS that the device
3955 or bus can support) for best performance.
3956 pcie_bus_peer2peer Set every device's MPS to 128B, which
3957 every device is guaranteed to support. This
3958 configuration allows peer-to-peer DMA between
3959 any pair of devices, possibly at the cost of
3960 reduced performance. This also guarantees
3961 that hot-added devices will work.
3962 cbiosize=nn[KMG] The fixed amount of bus space which is
3963 reserved for the CardBus bridge's IO window.
3964 The default value is 256 bytes.
3965 cbmemsize=nn[KMG] The fixed amount of bus space which is
3966 reserved for the CardBus bridge's memory
3967 window. The default value is 64 megabytes.
3970 [<order of align>@]<pci_dev>[; ...]
3971 Specifies alignment and device to reassign
3972 aligned memory resources. How to
3973 specify the device is described above.
3974 If <order of align> is not specified,
3975 PAGE_SIZE is used as alignment.
3976 A PCI-PCI bridge can be specified if resource
3977 windows need to be expanded.
3978 To specify the alignment for several
3979 instances of a device, the PCI vendor,
3980 device, subvendor, and subdevice may be
3981 specified, e.g., 12@pci:8086:9c22:103c:198f
3982 for 4096-byte alignment.
3983 ecrc= Enable/disable PCIe ECRC (transaction layer
3984 end-to-end CRC checking).
3985 bios: Use BIOS/firmware settings. This is the
3989 hpiosize=nn[KMG] The fixed amount of bus space which is
3990 reserved for hotplug bridge's IO window.
3991 Default size is 256 bytes.
3992 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3993 reserved for hotplug bridge's MMIO window.
3994 Default size is 2 megabytes.
3995 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3996 reserved for hotplug bridge's MMIO_PREF window.
3997 Default size is 2 megabytes.
3998 hpmemsize=nn[KMG] The fixed amount of bus space which is
3999 reserved for hotplug bridge's MMIO and
4001 Default size is 2 megabytes.
4002 hpbussize=nn The minimum amount of additional bus numbers
4003 reserved for buses below a hotplug bridge.
4005 realloc= Enable/disable reallocating PCI bridge resources
4006 if allocations done by BIOS are too small to
4007 accommodate resources required by all child
4009 off: Turn realloc off
4011 realloc same as realloc=on
4012 noari do not use PCIe ARI.
4013 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4014 do not use PCIe ATS (and IOMMU device IOTLB).
4015 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4016 only look for one device below a PCIe downstream
4018 big_root_window Try to add a big 64bit memory window to the PCIe
4019 root complex on AMD CPUs. Some GFX hardware
4020 can resize a BAR to allow access to all VRAM.
4021 Adding the window is slightly risky (it may
4022 conflict with unreported devices), so this
4024 disable_acs_redir=<pci_dev>[; ...]
4025 Specify one or more PCI devices (in the format
4026 specified above) separated by semicolons.
4027 Each device specified will have the PCI ACS
4028 redirect capabilities forced off which will
4029 allow P2P traffic between devices through
4030 bridges without forcing it upstream. Note:
4031 this removes isolation between devices and
4032 may put more devices in an IOMMU group.
4033 force_floating [S390] Force usage of floating interrupts.
4034 nomio [S390] Do not use MIO instructions.
4035 norid [S390] ignore the RID field and force use of
4036 one PCI domain per PCI function
4038 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4041 force Enable ASPM even on devices that claim not to support it.
4042 WARNING: Forcing ASPM on may cause system lockups.
4044 pcie_ports= [PCIE] PCIe port services handling:
4045 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4046 even if the platform doesn't give the OS permission to
4047 use them. This may cause conflicts if the platform
4048 also tries to use these services.
4049 dpc-native Use native PCIe service for DPC only. May
4050 cause conflicts if firmware uses AER or DPC.
4051 compat Disable native PCIe services (PME, AER, DPC, PCIe
4054 pcie_port_pm= [PCIE] PCIe port power management handling:
4055 off Disable power management of all PCIe ports
4056 force Forcibly enable power management of all PCIe ports
4058 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4059 nomsi Do not use MSI for native PCIe PME signaling (this makes
4060 all PCIe root ports use INTx for all services).
4062 pcmv= [HW,PCMCIA] BadgePAD 4
4066 Keep all power-domains already enabled by bootloader on,
4067 even if no driver has claimed them. This is useful
4068 for debug and development, but should not be
4069 needed on a platform with proper driver support.
4072 See Documentation/admin-guide/blockdev/paride.rst.
4074 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4077 See arch/parisc/kernel/pdc_chassis.c
4079 percpu_alloc= Select which percpu first chunk allocator to use.
4080 Currently supported values are "embed" and "page".
4081 Archs may support subset or none of the selections.
4082 See comments in mm/percpu.c for details on each
4083 allocator. This parameter is primarily for debugging
4084 and performance comparison.
4087 See Documentation/admin-guide/blockdev/paride.rst.
4090 See Documentation/admin-guide/blockdev/paride.rst.
4092 pirq= [SMP,APIC] Manual mp-table setup
4093 See Documentation/x86/i386/IO-APIC.rst.
4095 plip= [PPT,NET] Parallel port network link
4096 Format: { parport<nr> | timid | 0 }
4097 See also Documentation/admin-guide/parport.rst.
4099 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4100 Override pmtimer IOPort with a hex value.
4103 pm_debug_messages [SUSPEND,KNL]
4104 Enable suspend/resume debug messages during boot up.
4107 Enable PNP debug messages (depends on the
4108 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4109 via /sys/module/pnp/parameters/debug. We always show
4110 current resource usage; turning this on also shows
4111 possible settings and some assignment information.
4117 { on | off | curr | res | no-curr | no-res }
4120 [ISAPNP] Exclude IRQs for the autoconfiguration
4123 [ISAPNP] Exclude DMAs for the autoconfiguration
4125 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4126 Ranges are in pairs (I/O port base and size).
4129 [ISAPNP] Exclude memory regions for the
4131 Ranges are in pairs (memory base and size).
4133 ports= [IP_VS_FTP] IPVS ftp helper module
4135 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4137 Format: <port>,<port>....
4139 powersave=off [PPC] This option disables power saving features.
4140 It specifically disables cpuidle and sets the
4141 platform machine description specific power_save
4142 function to NULL. On Idle the CPU just reduces
4145 ppc_strict_facility_enable
4146 [PPC] This option catches any kernel floating point,
4147 Altivec, VSX and SPE outside of regions specifically
4148 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4149 There is some performance impact when enabling this.
4153 Disable Hardware Transactional Memory
4156 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4157 none - Limited to cond_resched() calls
4158 voluntary - Limited to cond_resched() and might_sleep() calls
4159 full - Any section that isn't explicitly preempt disabled
4160 can be preempted anytime.
4162 print-fatal-signals=
4163 [KNL] debug: print fatal signals
4165 If enabled, warn about various signal handling
4166 related application anomalies: too many signals,
4167 too many POSIX.1 timers, fatal signals causing a
4170 If you hit the warning due to signal overflow,
4171 you might want to try "ulimit -i unlimited".
4175 printk.always_kmsg_dump=
4176 Trigger kmsg_dump for cases other than kernel oops or
4178 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4181 printk.devkmsg={on,off,ratelimit}
4182 Control writing to /dev/kmsg.
4183 on - unlimited logging to /dev/kmsg from userspace
4184 off - logging to /dev/kmsg disabled
4185 ratelimit - ratelimit the logging
4188 printk.time= Show timing data prefixed to each printk message line
4189 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4191 processor.max_cstate= [HW,ACPI]
4192 Limit processor to maximum C-state
4193 max_cstate=9 overrides any DMI blacklist limit.
4195 processor.nocst [HW,ACPI]
4196 Ignore the _CST method to determine C-states,
4197 instead using the legacy FADT method
4199 profile= [KNL] Enable kernel profiling via /proc/profile
4200 Format: [<profiletype>,]<number>
4201 Param: <profiletype>: "schedule", "sleep", or "kvm"
4202 [defaults to kernel profiling]
4203 Param: "schedule" - profile schedule points.
4204 Param: "sleep" - profile D-state sleeping (millisecs).
4205 Requires CONFIG_SCHEDSTATS
4206 Param: "kvm" - profile VM exits.
4207 Param: <number> - step/bucket size as a power of 2 for
4208 statistical time based profiling.
4210 prompt_ramdisk= [RAM] [Deprecated]
4212 prot_virt= [S390] enable hosting protected virtual machines
4213 isolated from the hypervisor (if hardware supports
4217 psi= [KNL] Enable or disable pressure stall information
4221 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4222 probe for; one of (bare|imps|exps|lifebook|any).
4223 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4225 psmouse.resetafter= [HW,MOUSE]
4226 Try to reset the device after so many bad packets
4229 [HW,MOUSE] Set desired mouse resolution, in dpi.
4230 psmouse.smartscroll=
4231 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4232 0 = disabled, 1 = enabled (default).
4234 pstore.backend= Specify the name of the pstore backend to use
4237 See Documentation/admin-guide/blockdev/paride.rst.
4239 pti= [X86-64] Control Page Table Isolation of user and
4240 kernel address spaces. Disabling this feature
4241 removes hardening, but improves performance of
4242 system calls and interrupts.
4244 on - unconditionally enable
4245 off - unconditionally disable
4246 auto - kernel detects whether your CPU model is
4247 vulnerable to issues that PTI mitigates
4249 Not specifying this option is equivalent to pti=auto.
4252 Equivalent to pti=off
4255 [KNL] Number of legacy pty's. Overwrites compiled-in
4258 quiet [KNL] Disable most log messages
4263 See Documentation/admin-guide/md.rst.
4265 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4266 See Documentation/admin-guide/blockdev/ramdisk.rst.
4268 ramdisk_start= [RAM] RAM disk image start address
4270 random.trust_cpu={on,off}
4271 [KNL] Enable or disable trusting the use of the
4272 CPU's random number generator (if available) to
4273 fully seed the kernel's CRNG. Default is controlled
4274 by CONFIG_RANDOM_TRUST_CPU.
4276 randomize_kstack_offset=
4277 [KNL] Enable or disable kernel stack offset
4278 randomization, which provides roughly 5 bits of
4279 entropy, frustrating memory corruption attacks
4280 that depend on stack address determinism or
4281 cross-syscall address exposures. This is only
4282 available on architectures that have defined
4283 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4284 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4285 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4287 ras=option[,option,...] [KNL] RAS-specific options
4290 Disable the Correctable Errors Collector,
4291 see CONFIG_RAS_CEC help text.
4294 The argument is a cpu list, as described above.
4296 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4297 the specified list of CPUs to be no-callback CPUs.
4298 Invocation of these CPUs' RCU callbacks will be
4299 offloaded to "rcuox/N" kthreads created for that
4300 purpose, where "x" is "p" for RCU-preempt, and
4301 "s" for RCU-sched, and "N" is the CPU number.
4302 This reduces OS jitter on the offloaded CPUs,
4303 which can be useful for HPC and real-time
4304 workloads. It can also improve energy efficiency
4305 for asymmetric multiprocessors.
4308 Rather than requiring that offloaded CPUs
4309 (specified by rcu_nocbs= above) explicitly
4310 awaken the corresponding "rcuoN" kthreads,
4311 make these kthreads poll for callbacks.
4312 This improves the real-time response for the
4313 offloaded CPUs by relieving them of the need to
4314 wake up the corresponding kthread, but degrades
4315 energy efficiency by requiring that the kthreads
4316 periodically wake up to do the polling.
4318 rcutree.blimit= [KNL]
4319 Set maximum number of finished RCU callbacks to
4320 process in one batch.
4322 rcutree.dump_tree= [KNL]
4323 Dump the structure of the rcu_node combining tree
4324 out at early boot. This is used for diagnostic
4325 purposes, to verify correct tree setup.
4327 rcutree.gp_cleanup_delay= [KNL]
4328 Set the number of jiffies to delay each step of
4329 RCU grace-period cleanup.
4331 rcutree.gp_init_delay= [KNL]
4332 Set the number of jiffies to delay each step of
4333 RCU grace-period initialization.
4335 rcutree.gp_preinit_delay= [KNL]
4336 Set the number of jiffies to delay each step of
4337 RCU grace-period pre-initialization, that is,
4338 the propagation of recent CPU-hotplug changes up
4339 the rcu_node combining tree.
4341 rcutree.use_softirq= [KNL]
4342 If set to zero, move all RCU_SOFTIRQ processing to
4343 per-CPU rcuc kthreads. Defaults to a non-zero
4344 value, meaning that RCU_SOFTIRQ is used by default.
4345 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4347 But note that CONFIG_PREEMPT_RT=y kernels disable
4348 this kernel boot parameter, forcibly setting it
4351 rcutree.rcu_fanout_exact= [KNL]
4352 Disable autobalancing of the rcu_node combining
4353 tree. This is used by rcutorture, and might
4354 possibly be useful for architectures having high
4355 cache-to-cache transfer latencies.
4357 rcutree.rcu_fanout_leaf= [KNL]
4358 Change the number of CPUs assigned to each
4359 leaf rcu_node structure. Useful for very
4360 large systems, which will choose the value 64,
4361 and for NUMA systems with large remote-access
4362 latencies, which will choose a value aligned
4363 with the appropriate hardware boundaries.
4365 rcutree.rcu_min_cached_objs= [KNL]
4366 Minimum number of objects which are cached and
4367 maintained per one CPU. Object size is equal
4368 to PAGE_SIZE. The cache allows to reduce the
4369 pressure to page allocator, also it makes the
4370 whole algorithm to behave better in low memory
4373 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4374 Set the page-cache refill delay (in milliseconds)
4375 in response to low-memory conditions. The range
4376 of permitted values is in the range 0:100000.
4378 rcutree.jiffies_till_first_fqs= [KNL]
4379 Set delay from grace-period initialization to
4380 first attempt to force quiescent states.
4381 Units are jiffies, minimum value is zero,
4382 and maximum value is HZ.
4384 rcutree.jiffies_till_next_fqs= [KNL]
4385 Set delay between subsequent attempts to force
4386 quiescent states. Units are jiffies, minimum
4387 value is one, and maximum value is HZ.
4389 rcutree.jiffies_till_sched_qs= [KNL]
4390 Set required age in jiffies for a
4391 given grace period before RCU starts
4392 soliciting quiescent-state help from
4393 rcu_note_context_switch() and cond_resched().
4394 If not specified, the kernel will calculate
4395 a value based on the most recent settings
4396 of rcutree.jiffies_till_first_fqs
4397 and rcutree.jiffies_till_next_fqs.
4398 This calculated value may be viewed in
4399 rcutree.jiffies_to_sched_qs. Any attempt to set
4400 rcutree.jiffies_to_sched_qs will be cheerfully
4403 rcutree.kthread_prio= [KNL,BOOT]
4404 Set the SCHED_FIFO priority of the RCU per-CPU
4405 kthreads (rcuc/N). This value is also used for
4406 the priority of the RCU boost threads (rcub/N)
4407 and for the RCU grace-period kthreads (rcu_bh,
4408 rcu_preempt, and rcu_sched). If RCU_BOOST is
4409 set, valid values are 1-99 and the default is 1
4410 (the least-favored priority). Otherwise, when
4411 RCU_BOOST is not set, valid values are 0-99 and
4412 the default is zero (non-realtime operation).
4414 rcutree.rcu_nocb_gp_stride= [KNL]
4415 Set the number of NOCB callback kthreads in
4416 each group, which defaults to the square root
4417 of the number of CPUs. Larger numbers reduce
4418 the wakeup overhead on the global grace-period
4419 kthread, but increases that same overhead on
4420 each group's NOCB grace-period kthread.
4422 rcutree.qhimark= [KNL]
4423 Set threshold of queued RCU callbacks beyond which
4424 batch limiting is disabled.
4426 rcutree.qlowmark= [KNL]
4427 Set threshold of queued RCU callbacks below which
4428 batch limiting is re-enabled.
4430 rcutree.qovld= [KNL]
4431 Set threshold of queued RCU callbacks beyond which
4432 RCU's force-quiescent-state scan will aggressively
4433 enlist help from cond_resched() and sched IPIs to
4434 help CPUs more quickly reach quiescent states.
4435 Set to less than zero to make this be set based
4436 on rcutree.qhimark at boot time and to zero to
4437 disable more aggressive help enlistment.
4439 rcutree.rcu_idle_gp_delay= [KNL]
4440 Set wakeup interval for idle CPUs that have
4441 RCU callbacks (RCU_FAST_NO_HZ=y).
4443 rcutree.rcu_kick_kthreads= [KNL]
4444 Cause the grace-period kthread to get an extra
4445 wake_up() if it sleeps three times longer than
4446 it should at force-quiescent-state time.
4447 This wake_up() will be accompanied by a
4448 WARN_ONCE() splat and an ftrace_dump().
4450 rcutree.rcu_unlock_delay= [KNL]
4451 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4452 this specifies an rcu_read_unlock()-time delay
4453 in microseconds. This defaults to zero.
4454 Larger delays increase the probability of
4455 catching RCU pointer leaks, that is, buggy use
4456 of RCU-protected pointers after the relevant
4457 rcu_read_unlock() has completed.
4459 rcutree.sysrq_rcu= [KNL]
4460 Commandeer a sysrq key to dump out Tree RCU's
4461 rcu_node tree with an eye towards determining
4462 why a new grace period has not yet started.
4464 rcuscale.gp_async= [KNL]
4465 Measure performance of asynchronous
4466 grace-period primitives such as call_rcu().
4468 rcuscale.gp_async_max= [KNL]
4469 Specify the maximum number of outstanding
4470 callbacks per writer thread. When a writer
4471 thread exceeds this limit, it invokes the
4472 corresponding flavor of rcu_barrier() to allow
4473 previously posted callbacks to drain.
4475 rcuscale.gp_exp= [KNL]
4476 Measure performance of expedited synchronous
4477 grace-period primitives.
4479 rcuscale.holdoff= [KNL]
4480 Set test-start holdoff period. The purpose of
4481 this parameter is to delay the start of the
4482 test until boot completes in order to avoid
4485 rcuscale.kfree_rcu_test= [KNL]
4486 Set to measure performance of kfree_rcu() flooding.
4488 rcuscale.kfree_rcu_test_double= [KNL]
4489 Test the double-argument variant of kfree_rcu().
4490 If this parameter has the same value as
4491 rcuscale.kfree_rcu_test_single, both the single-
4492 and double-argument variants are tested.
4494 rcuscale.kfree_rcu_test_single= [KNL]
4495 Test the single-argument variant of kfree_rcu().
4496 If this parameter has the same value as
4497 rcuscale.kfree_rcu_test_double, both the single-
4498 and double-argument variants are tested.
4500 rcuscale.kfree_nthreads= [KNL]
4501 The number of threads running loops of kfree_rcu().
4503 rcuscale.kfree_alloc_num= [KNL]
4504 Number of allocations and frees done in an iteration.
4506 rcuscale.kfree_loops= [KNL]
4507 Number of loops doing rcuscale.kfree_alloc_num number
4508 of allocations and frees.
4510 rcuscale.nreaders= [KNL]
4511 Set number of RCU readers. The value -1 selects
4512 N, where N is the number of CPUs. A value
4513 "n" less than -1 selects N-n+1, where N is again
4514 the number of CPUs. For example, -2 selects N
4515 (the number of CPUs), -3 selects N+1, and so on.
4516 A value of "n" less than or equal to -N selects
4519 rcuscale.nwriters= [KNL]
4520 Set number of RCU writers. The values operate
4521 the same as for rcuscale.nreaders.
4522 N, where N is the number of CPUs
4524 rcuscale.perf_type= [KNL]
4525 Specify the RCU implementation to test.
4527 rcuscale.shutdown= [KNL]
4528 Shut the system down after performance tests
4529 complete. This is useful for hands-off automated
4532 rcuscale.verbose= [KNL]
4533 Enable additional printk() statements.
4535 rcuscale.writer_holdoff= [KNL]
4536 Write-side holdoff between grace periods,
4537 in microseconds. The default of zero says
4540 rcutorture.fqs_duration= [KNL]
4541 Set duration of force_quiescent_state bursts
4544 rcutorture.fqs_holdoff= [KNL]
4545 Set holdoff time within force_quiescent_state bursts
4548 rcutorture.fqs_stutter= [KNL]
4549 Set wait time between force_quiescent_state bursts
4552 rcutorture.fwd_progress= [KNL]
4553 Enable RCU grace-period forward-progress testing
4554 for the types of RCU supporting this notion.
4556 rcutorture.fwd_progress_div= [KNL]
4557 Specify the fraction of a CPU-stall-warning
4558 period to do tight-loop forward-progress testing.
4560 rcutorture.fwd_progress_holdoff= [KNL]
4561 Number of seconds to wait between successive
4562 forward-progress tests.
4564 rcutorture.fwd_progress_need_resched= [KNL]
4565 Enclose cond_resched() calls within checks for
4566 need_resched() during tight-loop forward-progress
4569 rcutorture.gp_cond= [KNL]
4570 Use conditional/asynchronous update-side
4571 primitives, if available.
4573 rcutorture.gp_exp= [KNL]
4574 Use expedited update-side primitives, if available.
4576 rcutorture.gp_normal= [KNL]
4577 Use normal (non-expedited) asynchronous
4578 update-side primitives, if available.
4580 rcutorture.gp_sync= [KNL]
4581 Use normal (non-expedited) synchronous
4582 update-side primitives, if available. If all
4583 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4584 rcutorture.gp_normal=, and rcutorture.gp_sync=
4585 are zero, rcutorture acts as if is interpreted
4586 they are all non-zero.
4588 rcutorture.irqreader= [KNL]
4589 Run RCU readers from irq handlers, or, more
4590 accurately, from a timer handler. Not all RCU
4591 flavors take kindly to this sort of thing.
4593 rcutorture.leakpointer= [KNL]
4594 Leak an RCU-protected pointer out of the reader.
4595 This can of course result in splats, and is
4596 intended to test the ability of things like
4597 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4600 rcutorture.n_barrier_cbs= [KNL]
4601 Set callbacks/threads for rcu_barrier() testing.
4603 rcutorture.nfakewriters= [KNL]
4604 Set number of concurrent RCU writers. These just
4605 stress RCU, they don't participate in the actual
4606 test, hence the "fake".
4608 rcutorture.nocbs_nthreads= [KNL]
4609 Set number of RCU callback-offload togglers.
4610 Zero (the default) disables toggling.
4612 rcutorture.nocbs_toggle= [KNL]
4613 Set the delay in milliseconds between successive
4614 callback-offload toggling attempts.
4616 rcutorture.nreaders= [KNL]
4617 Set number of RCU readers. The value -1 selects
4618 N-1, where N is the number of CPUs. A value
4619 "n" less than -1 selects N-n-2, where N is again
4620 the number of CPUs. For example, -2 selects N
4621 (the number of CPUs), -3 selects N+1, and so on.
4623 rcutorture.object_debug= [KNL]
4624 Enable debug-object double-call_rcu() testing.
4626 rcutorture.onoff_holdoff= [KNL]
4627 Set time (s) after boot for CPU-hotplug testing.
4629 rcutorture.onoff_interval= [KNL]
4630 Set time (jiffies) between CPU-hotplug operations,
4631 or zero to disable CPU-hotplug testing.
4633 rcutorture.read_exit= [KNL]
4634 Set the number of read-then-exit kthreads used
4635 to test the interaction of RCU updaters and
4636 task-exit processing.
4638 rcutorture.read_exit_burst= [KNL]
4639 The number of times in a given read-then-exit
4640 episode that a set of read-then-exit kthreads
4643 rcutorture.read_exit_delay= [KNL]
4644 The delay, in seconds, between successive
4645 read-then-exit testing episodes.
4647 rcutorture.shuffle_interval= [KNL]
4648 Set task-shuffle interval (s). Shuffling tasks
4649 allows some CPUs to go into dyntick-idle mode
4650 during the rcutorture test.
4652 rcutorture.shutdown_secs= [KNL]
4653 Set time (s) after boot system shutdown. This
4654 is useful for hands-off automated testing.
4656 rcutorture.stall_cpu= [KNL]
4657 Duration of CPU stall (s) to test RCU CPU stall
4658 warnings, zero to disable.
4660 rcutorture.stall_cpu_block= [KNL]
4661 Sleep while stalling if set. This will result
4662 in warnings from preemptible RCU in addition
4663 to any other stall-related activity.
4665 rcutorture.stall_cpu_holdoff= [KNL]
4666 Time to wait (s) after boot before inducing stall.
4668 rcutorture.stall_cpu_irqsoff= [KNL]
4669 Disable interrupts while stalling if set.
4671 rcutorture.stall_gp_kthread= [KNL]
4672 Duration (s) of forced sleep within RCU
4673 grace-period kthread to test RCU CPU stall
4674 warnings, zero to disable. If both stall_cpu
4675 and stall_gp_kthread are specified, the
4676 kthread is starved first, then the CPU.
4678 rcutorture.stat_interval= [KNL]
4679 Time (s) between statistics printk()s.
4681 rcutorture.stutter= [KNL]
4682 Time (s) to stutter testing, for example, specifying
4683 five seconds causes the test to run for five seconds,
4684 wait for five seconds, and so on. This tests RCU's
4685 ability to transition abruptly to and from idle.
4687 rcutorture.test_boost= [KNL]
4688 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4689 "Maybe" means test if the RCU implementation
4690 under test support RCU priority boosting.
4692 rcutorture.test_boost_duration= [KNL]
4693 Duration (s) of each individual boost test.
4695 rcutorture.test_boost_interval= [KNL]
4696 Interval (s) between each boost test.
4698 rcutorture.test_no_idle_hz= [KNL]
4699 Test RCU's dyntick-idle handling. See also the
4700 rcutorture.shuffle_interval parameter.
4702 rcutorture.torture_type= [KNL]
4703 Specify the RCU implementation to test.
4705 rcutorture.verbose= [KNL]
4706 Enable additional printk() statements.
4708 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4709 Dump ftrace buffer after reporting RCU CPU
4712 rcupdate.rcu_cpu_stall_suppress= [KNL]
4713 Suppress RCU CPU stall warning messages.
4715 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4716 Suppress RCU CPU stall warning messages and
4717 rcutorture writer stall warnings that occur
4718 during early boot, that is, during the time
4719 before the init task is spawned.
4721 rcupdate.rcu_cpu_stall_timeout= [KNL]
4722 Set timeout for RCU CPU stall warning messages.
4724 rcupdate.rcu_expedited= [KNL]
4725 Use expedited grace-period primitives, for
4726 example, synchronize_rcu_expedited() instead
4727 of synchronize_rcu(). This reduces latency,
4728 but can increase CPU utilization, degrade
4729 real-time latency, and degrade energy efficiency.
4730 No effect on CONFIG_TINY_RCU kernels.
4732 rcupdate.rcu_normal= [KNL]
4733 Use only normal grace-period primitives,
4734 for example, synchronize_rcu() instead of
4735 synchronize_rcu_expedited(). This improves
4736 real-time latency, CPU utilization, and
4737 energy efficiency, but can expose users to
4738 increased grace-period latency. This parameter
4739 overrides rcupdate.rcu_expedited. No effect on
4740 CONFIG_TINY_RCU kernels.
4742 rcupdate.rcu_normal_after_boot= [KNL]
4743 Once boot has completed (that is, after
4744 rcu_end_inkernel_boot() has been invoked), use
4745 only normal grace-period primitives. No effect
4746 on CONFIG_TINY_RCU kernels.
4748 But note that CONFIG_PREEMPT_RT=y kernels enables
4749 this kernel boot parameter, forcibly setting
4750 it to the value one, that is, converting any
4751 post-boot attempt at an expedited RCU grace
4752 period to instead use normal non-expedited
4753 grace-period processing.
4755 rcupdate.rcu_task_ipi_delay= [KNL]
4756 Set time in jiffies during which RCU tasks will
4757 avoid sending IPIs, starting with the beginning
4758 of a given grace period. Setting a large
4759 number avoids disturbing real-time workloads,
4760 but lengthens grace periods.
4762 rcupdate.rcu_task_stall_timeout= [KNL]
4763 Set timeout in jiffies for RCU task stall warning
4764 messages. Disable with a value less than or equal
4767 rcupdate.rcu_self_test= [KNL]
4768 Run the RCU early boot self tests
4772 Run specified binary instead of /init from the ramdisk,
4773 used for early userspace startup. See initrd.
4776 force - Override the decision by the kernel to hide the
4777 advertisement of RDRAND support (this affects
4778 certain AMD processors because of buggy BIOS
4779 support, specifically around the suspend/resume
4783 Turn on/off individual RDT features. List is:
4784 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4786 E.g. to turn on cmt and turn off mba use:
4790 Format (x86 or x86_64):
4791 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4793 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4795 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4796 (prefix with 'panic_' to set mode for panic
4798 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4799 reboot_force is either force or not specified,
4800 reboot_cpu is s[mp]#### with #### being the processor
4801 to be used for rebooting.
4803 refscale.holdoff= [KNL]
4804 Set test-start holdoff period. The purpose of
4805 this parameter is to delay the start of the
4806 test until boot completes in order to avoid
4809 refscale.loops= [KNL]
4810 Set the number of loops over the synchronization
4811 primitive under test. Increasing this number
4812 reduces noise due to loop start/end overhead,
4813 but the default has already reduced the per-pass
4814 noise to a handful of picoseconds on ca. 2020
4817 refscale.nreaders= [KNL]
4818 Set number of readers. The default value of -1
4819 selects N, where N is roughly 75% of the number
4820 of CPUs. A value of zero is an interesting choice.
4822 refscale.nruns= [KNL]
4823 Set number of runs, each of which is dumped onto
4826 refscale.readdelay= [KNL]
4827 Set the read-side critical-section duration,
4828 measured in microseconds.
4830 refscale.scale_type= [KNL]
4831 Specify the read-protection implementation to test.
4833 refscale.shutdown= [KNL]
4834 Shut down the system at the end of the performance
4835 test. This defaults to 1 (shut it down) when
4836 refscale is built into the kernel and to 0 (leave
4837 it running) when refscale is built as a module.
4839 refscale.verbose= [KNL]
4840 Enable additional printk() statements.
4842 refscale.verbose_batched= [KNL]
4843 Batch the additional printk() statements. If zero
4844 (the default) or negative, print everything. Otherwise,
4845 print every Nth verbose statement, where N is the value
4849 [KNL, SMP] Set scheduler's default relax_domain_level.
4850 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4852 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4853 Format: <base1>,<size1>[,<base2>,<size2>,...]
4854 Reserve I/O ports or memory so the kernel won't use
4855 them. If <base> is less than 0x10000, the region
4856 is assumed to be I/O ports; otherwise it is memory.
4858 reservetop= [X86-32]
4860 Reserves a hole at the top of the kernel virtual
4863 reset_devices [KNL] Force drivers to reset the underlying device
4864 during initialization.
4867 Specify the partition device for software suspend
4869 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4871 resume_offset= [SWSUSP]
4872 Specify the offset from the beginning of the partition
4873 given by "resume=" at which the swap header is located,
4874 in <PAGE_SIZE> units (needed only for swap files).
4875 See Documentation/power/swsusp-and-swap-files.rst
4877 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4878 read the resume files
4880 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4881 Useful for devices that are detected asynchronously
4882 (e.g. USB and MMC devices).
4884 hibernate= [HIBERNATION]
4885 noresume Don't check if there's a hibernation image
4886 present during boot.
4887 nocompress Don't compress/decompress hibernation images.
4888 no Disable hibernation and resume.
4889 protect_image Turn on image protection during restoration
4890 (that will set all pages holding image data
4891 during restoration read-only).
4893 retain_initrd [RAM] Keep initrd memory after extraction
4895 rfkill.default_state=
4896 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4897 etc. communication is blocked by default.
4900 rfkill.master_switch_mode=
4901 0 The "airplane mode" button does nothing.
4902 1 The "airplane mode" button toggles between everything
4903 blocked and the previous configuration.
4904 2 The "airplane mode" button toggles between everything
4905 blocked and everything unblocked.
4907 rhash_entries= [KNL,NET]
4908 Set number of hash buckets for route cache
4911 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4914 ro [KNL] Mount root device read-only on boot
4917 on Mark read-only kernel memory as read-only (default).
4918 off Leave read-only kernel memory writable for debugging.
4921 Enable the uart passthrough on the designated usb port
4922 on Rockchip SoCs. When active, the signals of the
4923 debug-uart get routed to the D+ and D- pins of the usb
4924 port and the regular usb controller gets disabled.
4926 root= [KNL] Root filesystem
4927 See name_to_dev_t comment in init/do_mounts.c.
4929 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4930 mount the root filesystem
4932 rootflags= [KNL] Set root filesystem mount option string
4934 rootfstype= [KNL] Set root filesystem type
4936 rootwait [KNL] Wait (indefinitely) for root device to show up.
4937 Useful for devices that are detected asynchronously
4938 (e.g. USB and MMC devices).
4940 rproc_mem=nn[KMG][@address]
4941 [KNL,ARM,CMA] Remoteproc physical memory block.
4942 Memory area to be used by remote processor image,
4945 rw [KNL] Mount root device read-write on boot
4947 S [KNL] Run init in single mode
4949 s390_iommu= [HW,S390]
4950 Set s390 IOTLB flushing mode
4952 With strict flushing every unmap operation will result in
4953 an IOTLB flush. Default is lazy flushing before reuse,
4957 See drivers/net/irda/sa1100_ir.c.
4959 sbni= [NET] Granch SBNI12 leased line adapter
4961 sched_verbose [KNL] Enables verbose scheduler debug messages.
4963 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4964 Allowed values are enable and disable. This feature
4965 incurs a small amount of overhead in the scheduler
4966 but is useful for debugging and performance tuning.
4968 sched_thermal_decay_shift=
4969 [KNL, SMP] Set a decay shift for scheduler thermal
4970 pressure signal. Thermal pressure signal follows the
4971 default decay period of other scheduler pelt
4972 signals(usually 32 ms but configurable). Setting
4973 sched_thermal_decay_shift will left shift the decay
4974 period for the thermal pressure signal by the shift
4976 i.e. with the default pelt decay period of 32 ms
4977 sched_thermal_decay_shift thermal pressure decay pr
4981 Format: integer between 0 and 10
4984 scftorture.holdoff= [KNL]
4985 Number of seconds to hold off before starting
4986 test. Defaults to zero for module insertion and
4987 to 10 seconds for built-in smp_call_function()
4990 scftorture.longwait= [KNL]
4991 Request ridiculously long waits randomly selected
4992 up to the chosen limit in seconds. Zero (the
4993 default) disables this feature. Please note
4994 that requesting even small non-zero numbers of
4995 seconds can result in RCU CPU stall warnings,
4996 softlockup complaints, and so on.
4998 scftorture.nthreads= [KNL]
4999 Number of kthreads to spawn to invoke the
5000 smp_call_function() family of functions.
5001 The default of -1 specifies a number of kthreads
5002 equal to the number of CPUs.
5004 scftorture.onoff_holdoff= [KNL]
5005 Number seconds to wait after the start of the
5006 test before initiating CPU-hotplug operations.
5008 scftorture.onoff_interval= [KNL]
5009 Number seconds to wait between successive
5010 CPU-hotplug operations. Specifying zero (which
5011 is the default) disables CPU-hotplug operations.
5013 scftorture.shutdown_secs= [KNL]
5014 The number of seconds following the start of the
5015 test after which to shut down the system. The
5016 default of zero avoids shutting down the system.
5017 Non-zero values are useful for automated tests.
5019 scftorture.stat_interval= [KNL]
5020 The number of seconds between outputting the
5021 current test statistics to the console. A value
5022 of zero disables statistics output.
5024 scftorture.stutter_cpus= [KNL]
5025 The number of jiffies to wait between each change
5026 to the set of CPUs under test.
5028 scftorture.use_cpus_read_lock= [KNL]
5029 Use use_cpus_read_lock() instead of the default
5030 preempt_disable() to disable CPU hotplug
5031 while invoking one of the smp_call_function*()
5034 scftorture.verbose= [KNL]
5035 Enable additional printk() statements.
5037 scftorture.weight_single= [KNL]
5038 The probability weighting to use for the
5039 smp_call_function_single() function with a zero
5040 "wait" parameter. A value of -1 selects the
5041 default if all other weights are -1. However,
5042 if at least one weight has some other value, a
5043 value of -1 will instead select a weight of zero.
5045 scftorture.weight_single_wait= [KNL]
5046 The probability weighting to use for the
5047 smp_call_function_single() function with a
5048 non-zero "wait" parameter. See weight_single.
5050 scftorture.weight_many= [KNL]
5051 The probability weighting to use for the
5052 smp_call_function_many() function with a zero
5053 "wait" parameter. See weight_single.
5054 Note well that setting a high probability for
5055 this weighting can place serious IPI load
5058 scftorture.weight_many_wait= [KNL]
5059 The probability weighting to use for the
5060 smp_call_function_many() function with a
5061 non-zero "wait" parameter. See weight_single
5064 scftorture.weight_all= [KNL]
5065 The probability weighting to use for the
5066 smp_call_function_all() function with a zero
5067 "wait" parameter. See weight_single and
5070 scftorture.weight_all_wait= [KNL]
5071 The probability weighting to use for the
5072 smp_call_function_all() function with a
5073 non-zero "wait" parameter. See weight_single
5076 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5077 xtime_lock contention on larger systems, and/or RCU lock
5078 contention on all systems with CONFIG_MAXSMP set.
5079 Format: { "0" | "1" }
5080 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5082 Note: increases power consumption, thus should only be
5083 enabled if running jitter sensitive (HPC/RT) workloads.
5085 security= [SECURITY] Choose a legacy "major" security module to
5086 enable at boot. This has been deprecated by the
5089 selinux= [SELINUX] Disable or enable SELinux at boot time.
5090 Format: { "0" | "1" }
5091 See security/selinux/Kconfig help text.
5096 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5097 Format: { "0" | "1" }
5098 See security/apparmor/Kconfig help text
5101 Default value is set via kernel config option.
5103 serialnumber [BUGS=X86-32]
5106 Maximal number of shapers.
5114 Enable merging of slabs with similar size when the
5115 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5118 Disable merging of slabs with similar size. May be
5119 necessary if there is some reason to distinguish
5120 allocs to different slabs, especially in hardened
5121 environments where the risk of heap overflows and
5122 layout control by attackers can usually be
5123 frustrated by disabling merging. This will reduce
5124 most of the exposure of a heap attack to a single
5125 cache (risks via metadata attacks are mostly
5126 unchanged). Debug options disable merging on their
5128 For more information see Documentation/vm/slub.rst.
5130 slab_max_order= [MM, SLAB]
5131 Determines the maximum allowed order for slabs.
5132 A high setting may cause OOMs due to memory
5133 fragmentation. Defaults to 1 for systems with
5134 more than 32MB of RAM, 0 otherwise.
5136 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5137 Enabling slub_debug allows one to determine the
5138 culprit if slab objects become corrupted. Enabling
5139 slub_debug can create guard zones around objects and
5140 may poison objects when not in use. Also tracks the
5141 last alloc / free. For more information see
5142 Documentation/vm/slub.rst.
5144 slub_max_order= [MM, SLUB]
5145 Determines the maximum allowed order for slabs.
5146 A high setting may cause OOMs due to memory
5147 fragmentation. For more information see
5148 Documentation/vm/slub.rst.
5150 slub_min_objects= [MM, SLUB]
5151 The minimum number of objects per slab. SLUB will
5152 increase the slab order up to slub_max_order to
5153 generate a sufficiently large slab able to contain
5154 the number of objects indicated. The higher the number
5155 of objects the smaller the overhead of tracking slabs
5156 and the less frequently locks need to be acquired.
5157 For more information see Documentation/vm/slub.rst.
5159 slub_min_order= [MM, SLUB]
5160 Determines the minimum page order for slabs. Must be
5161 lower than slub_max_order.
5162 For more information see Documentation/vm/slub.rst.
5164 slub_merge [MM, SLUB]
5165 Same with slab_merge.
5167 slub_nomerge [MM, SLUB]
5168 Same with slab_nomerge. This is supported for legacy.
5169 See slab_nomerge for more information.
5172 Format: <io1>[,<io2>[,...,<io8>]]
5174 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5175 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5176 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5177 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5178 smsc-ircc2.ircc_irq= [HW] IRQ line
5179 smsc-ircc2.ircc_dma= [HW] DMA channel
5180 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5181 0: Toshiba Satellite 1800 (GP data pin select)
5182 1: Fast pin select (default)
5185 smt [KNL,S390] Set the maximum number of threads (logical
5186 CPUs) to use per physical CPU on systems capable of
5187 symmetric multithreading (SMT). Will be capped to the
5188 actual hardware limit.
5190 Default: -1 (no limit)
5193 [KNL] Should the soft-lockup detector generate panics.
5196 A value of 1 instructs the soft-lockup detector
5197 to panic the machine when a soft-lockup occurs. It is
5198 also controlled by the kernel.softlockup_panic sysctl
5199 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5200 respective build-time switch to that functionality.
5202 softlockup_all_cpu_backtrace=
5203 [KNL] Should the soft-lockup detector generate
5204 backtraces on all cpus.
5207 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5208 See Documentation/admin-guide/laptops/sonypi.rst
5210 spectre_v2= [X86] Control mitigation of Spectre variant 2
5211 (indirect branch speculation) vulnerability.
5212 The default operation protects the kernel from
5215 on - unconditionally enable, implies
5217 off - unconditionally disable, implies
5219 auto - kernel detects whether your CPU model is
5222 Selecting 'on' will, and 'auto' may, choose a
5223 mitigation method at run time according to the
5224 CPU, the available microcode, the setting of the
5225 CONFIG_RETPOLINE configuration option, and the
5226 compiler with which the kernel was built.
5228 Selecting 'on' will also enable the mitigation
5229 against user space to user space task attacks.
5231 Selecting 'off' will disable both the kernel and
5232 the user space protections.
5234 Specific mitigations can also be selected manually:
5236 retpoline - replace indirect branches
5237 retpoline,generic - google's original retpoline
5238 retpoline,amd - AMD-specific minimal thunk
5240 Not specifying this option is equivalent to
5244 [X86] Control mitigation of Spectre variant 2
5245 (indirect branch speculation) vulnerability between
5248 on - Unconditionally enable mitigations. Is
5249 enforced by spectre_v2=on
5251 off - Unconditionally disable mitigations. Is
5252 enforced by spectre_v2=off
5254 prctl - Indirect branch speculation is enabled,
5255 but mitigation can be enabled via prctl
5256 per thread. The mitigation control state
5257 is inherited on fork.
5260 - Like "prctl" above, but only STIBP is
5261 controlled per thread. IBPB is issued
5262 always when switching between different user
5266 - Same as "prctl" above, but all seccomp
5267 threads will enable the mitigation unless
5268 they explicitly opt out.
5271 - Like "seccomp" above, but only STIBP is
5272 controlled per thread. IBPB is issued
5273 always when switching between different
5274 user space processes.
5276 auto - Kernel selects the mitigation depending on
5277 the available CPU features and vulnerability.
5280 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
5282 Not specifying this option is equivalent to
5283 spectre_v2_user=auto.
5285 spec_store_bypass_disable=
5286 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5287 (Speculative Store Bypass vulnerability)
5289 Certain CPUs are vulnerable to an exploit against a
5290 a common industry wide performance optimization known
5291 as "Speculative Store Bypass" in which recent stores
5292 to the same memory location may not be observed by
5293 later loads during speculative execution. The idea
5294 is that such stores are unlikely and that they can
5295 be detected prior to instruction retirement at the
5296 end of a particular speculation execution window.
5298 In vulnerable processors, the speculatively forwarded
5299 store can be used in a cache side channel attack, for
5300 example to read memory to which the attacker does not
5301 directly have access (e.g. inside sandboxed code).
5303 This parameter controls whether the Speculative Store
5304 Bypass optimization is used.
5306 On x86 the options are:
5308 on - Unconditionally disable Speculative Store Bypass
5309 off - Unconditionally enable Speculative Store Bypass
5310 auto - Kernel detects whether the CPU model contains an
5311 implementation of Speculative Store Bypass and
5312 picks the most appropriate mitigation. If the
5313 CPU is not vulnerable, "off" is selected. If the
5314 CPU is vulnerable the default mitigation is
5315 architecture and Kconfig dependent. See below.
5316 prctl - Control Speculative Store Bypass per thread
5317 via prctl. Speculative Store Bypass is enabled
5318 for a process by default. The state of the control
5319 is inherited on fork.
5320 seccomp - Same as "prctl" above, but all seccomp threads
5321 will disable SSB unless they explicitly opt out.
5323 Default mitigations:
5324 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
5326 On powerpc the options are:
5328 on,auto - On Power8 and Power9 insert a store-forwarding
5329 barrier on kernel entry and exit. On Power7
5330 perform a software flush on kernel entry and
5334 Not specifying this option is equivalent to
5335 spec_store_bypass_disable=auto.
5337 spia_io_base= [HW,MTD]
5343 [X86] Enable split lock detection or bus lock detection
5345 When enabled (and if hardware support is present), atomic
5346 instructions that access data across cache line
5347 boundaries will result in an alignment check exception
5348 for split lock detection or a debug exception for
5353 warn - the kernel will emit rate-limited warnings
5354 about applications triggering the #AC
5355 exception or the #DB exception. This mode is
5356 the default on CPUs that support split lock
5357 detection or bus lock detection. Default
5358 behavior is by #AC if both features are
5359 enabled in hardware.
5361 fatal - the kernel will send SIGBUS to applications
5362 that trigger the #AC exception or the #DB
5363 exception. Default behavior is by #AC if
5364 both features are enabled in hardware.
5367 Set system wide rate limit to N bus locks
5368 per second for bus lock detection.
5371 N/A for split lock detection.
5374 If an #AC exception is hit in the kernel or in
5375 firmware (i.e. not while executing in user mode)
5376 the kernel will oops in either "warn" or "fatal"
5379 #DB exception for bus lock is triggered only when
5383 Control the Special Register Buffer Data Sampling
5386 Certain CPUs are vulnerable to an MDS-like
5387 exploit which can leak bits from the random
5390 By default, this issue is mitigated by
5391 microcode. However, the microcode fix can cause
5392 the RDRAND and RDSEED instructions to become
5393 much slower. Among other effects, this will
5394 result in reduced throughput from /dev/urandom.
5396 The microcode mitigation can be disabled with
5397 the following option:
5399 off: Disable mitigation and remove
5400 performance impact to RDRAND and RDSEED
5402 srcutree.counter_wrap_check [KNL]
5403 Specifies how frequently to check for
5404 grace-period sequence counter wrap for the
5405 srcu_data structure's ->srcu_gp_seq_needed field.
5406 The greater the number of bits set in this kernel
5407 parameter, the less frequently counter wrap will
5408 be checked for. Note that the bottom two bits
5411 srcutree.exp_holdoff [KNL]
5412 Specifies how many nanoseconds must elapse
5413 since the end of the last SRCU grace period for
5414 a given srcu_struct until the next normal SRCU
5415 grace period will be considered for automatic
5416 expediting. Set to zero to disable automatic
5420 Speculative Store Bypass Disable control
5422 On CPUs that are vulnerable to the Speculative
5423 Store Bypass vulnerability and offer a
5424 firmware based mitigation, this parameter
5425 indicates how the mitigation should be used:
5427 force-on: Unconditionally enable mitigation for
5428 for both kernel and userspace
5429 force-off: Unconditionally disable mitigation for
5430 for both kernel and userspace
5431 kernel: Always enable mitigation in the
5432 kernel, and offer a prctl interface
5433 to allow userspace to register its
5434 interest in being mitigated too.
5436 stack_guard_gap= [MM]
5437 override the default stack gap protection. The value
5438 is in page units and it defines how many pages prior
5439 to (for stacks growing down) resp. after (for stacks
5440 growing up) the main stack are reserved for no other
5441 mapping. Default value is 256 pages.
5443 stack_depot_disable= [KNL]
5444 Setting this to true through kernel command line will
5445 disable the stack depot thereby saving the static memory
5446 consumed by the stack hash table. By default this is set
5450 Enabled the stack tracer on boot up.
5452 stacktrace_filter=[function-list]
5453 [FTRACE] Limit the functions that the stack tracer
5454 will trace at boot up. function-list is a comma-separated
5455 list of functions. This list can be changed at run
5456 time by the stack_trace_filter file in the debugfs
5457 tracing directory. Note, this enables stack tracing
5458 and the stacktrace above is not needed.
5462 Set the STI (builtin display/keyboard on the HP-PARISC
5463 machines) console (graphic card) which should be used
5464 as the initial boot-console.
5465 See also comment in drivers/video/console/sticore.c.
5468 See comment in drivers/video/console/sticore.c.
5471 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5473 sunrpc.min_resvport=
5474 sunrpc.max_resvport=
5476 SunRPC servers often require that client requests
5477 originate from a privileged port (i.e. a port in the
5478 range 0 < portnr < 1024).
5479 An administrator who wishes to reserve some of these
5480 ports for other uses may adjust the range that the
5481 kernel's sunrpc client considers to be privileged
5482 using these two parameters to set the minimum and
5483 maximum port values.
5485 sunrpc.svc_rpc_per_connection_limit=
5487 Limit the number of requests that the server will
5488 process in parallel from a single connection.
5489 The default value is 0 (no limit).
5493 Control how the NFS server code allocates CPUs to
5494 service thread pools. Depending on how many NICs
5495 you have and where their interrupts are bound, this
5496 option will affect which CPUs will do NFS serving.
5497 Note: this parameter cannot be changed while the
5498 NFS server is running.
5500 auto the server chooses an appropriate mode
5501 automatically using heuristics
5502 global a single global pool contains all CPUs
5503 percpu one pool for each CPU
5504 pernode one pool for each NUMA node (equivalent
5505 to global on non-NUMA machines)
5507 sunrpc.tcp_slot_table_entries=
5508 sunrpc.udp_slot_table_entries=
5510 Sets the upper limit on the number of simultaneous
5511 RPC calls that can be sent from the client to a
5512 server. Increasing these values may allow you to
5513 improve throughput, but will also increase the
5514 amount of memory reserved for use by the client.
5516 suspend.pm_test_delay=
5518 Sets the number of seconds to remain in a suspend test
5519 mode before resuming the system (see
5520 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5521 is set. Default value is 5.
5524 Format: { on | off | y | n | 1 | 0 }
5525 This parameter controls use of the Protected
5526 Execution Facility on pSeries.
5529 [KNL] Enable accounting of swap in memory resource
5530 controller if no parameter or 1 is given or disable
5531 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5533 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5534 Format: { <int> | force | noforce }
5535 <int> -- Number of I/O TLB slabs
5536 force -- force using of bounce buffers even if they
5537 wouldn't be automatically used by the kernel
5538 noforce -- Never use bounce buffers (for debugging)
5543 Set a sysctl parameter, right before loading the init
5544 process, as if the value was written to the respective
5545 /proc/sys/... file. Both '.' and '/' are recognized as
5546 separators. Unrecognized parameters and invalid values
5547 are reported in the kernel log. Sysctls registered
5548 later by a loaded module cannot be set this way.
5549 Example: sysctl.vm.swappiness=40
5551 sysfs.deprecated=0|1 [KNL]
5552 Enable/disable old style sysfs layout for old udev
5553 on older distributions. When this option is enabled
5554 very new udev will not work anymore. When this option
5555 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5556 in older udev will not work anymore.
5557 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5558 the kernel configuration.
5560 sysrq_always_enabled
5562 Ignore sysrq setting - this boot parameter will
5563 neutralize any effect of /proc/sys/kernel/sysrq.
5564 Useful for debugging.
5566 tcpmhash_entries= [KNL,NET]
5567 Set the number of tcp_metrics_hash slots.
5568 Default value is 8192 or 16384 depending on total
5569 ram pages. This is used to specify the TCP metrics
5570 cache size. See Documentation/networking/ip-sysctl.rst
5571 "tcp_no_metrics_save" section for more details.
5575 test_suspend= [SUSPEND][,N]
5576 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5577 standby suspend) or "freeze" (for suspend type freeze)
5578 as the system sleep state during system startup with
5579 the optional capability to repeat N number of times.
5580 The system is woken from this state using a
5581 wakeup-capable RTC alarm.
5583 thash_entries= [KNL,NET]
5584 Set number of hash buckets for TCP connection
5586 thermal.act= [HW,ACPI]
5587 -1: disable all active trip points in all thermal zones
5588 <degrees C>: override all lowest active trip points
5590 thermal.crt= [HW,ACPI]
5591 -1: disable all critical trip points in all thermal zones
5592 <degrees C>: override all critical trip points
5594 thermal.nocrt= [HW,ACPI]
5595 Set to disable actions on ACPI thermal zone
5596 critical and hot trip points.
5598 thermal.off= [HW,ACPI]
5599 1: disable ACPI thermal control
5601 thermal.psv= [HW,ACPI]
5602 -1: disable all passive trip points
5603 <degrees C>: override all passive trip points to this
5606 thermal.tzp= [HW,ACPI]
5607 Specify global default ACPI thermal zone polling rate
5608 <deci-seconds>: poll all this frequency
5609 0: no polling (default)
5612 Force threading of all interrupt handlers except those
5613 marked explicitly IRQF_NO_THREAD.
5617 Specify if the kernel should make use of the cpu
5618 topology information if the hardware supports this.
5619 The scheduler will make use of this information and
5620 e.g. base its process migration decisions on it.
5623 topology_updates= [KNL, PPC, NUMA]
5625 Specify if the kernel should ignore (off)
5626 topology updates sent by the hypervisor to this
5629 torture.disable_onoff_at_boot= [KNL]
5630 Prevent the CPU-hotplug component of torturing
5631 until after init has spawned.
5633 torture.ftrace_dump_at_shutdown= [KNL]
5634 Dump the ftrace buffer at torture-test shutdown,
5635 even if there were no errors. This can be a
5636 very costly operation when many torture tests
5637 are running concurrently, especially on systems
5638 with rotating-rust storage.
5640 torture.verbose_sleep_frequency= [KNL]
5641 Specifies how many verbose printk()s should be
5642 emitted between each sleep. The default of zero
5643 disables verbose-printk() sleeping.
5645 torture.verbose_sleep_duration= [KNL]
5646 Duration of each verbose-printk() sleep in jiffies.
5650 tpm_suspend_pcr=[HW,TPM]
5651 Format: integer pcr id
5652 Specify that at suspend time, the tpm driver
5653 should extend the specified pcr with zeros,
5654 as a workaround for some chips which fail to
5655 flush the last written pcr on TPM_SaveState.
5656 This will guarantee that all the other pcrs
5659 trace_buf_size=nn[KMG]
5660 [FTRACE] will set tracing buffer size on each cpu.
5662 trace_event=[event-list]
5663 [FTRACE] Set and start specified trace events in order
5664 to facilitate early boot debugging. The event-list is a
5665 comma-separated list of trace events to enable. See
5666 also Documentation/trace/events.rst
5668 trace_options=[option-list]
5669 [FTRACE] Enable or disable tracer options at boot.
5670 The option-list is a comma delimited list of options
5671 that can be enabled or disabled just as if you were
5672 to echo the option name into
5674 /sys/kernel/debug/tracing/trace_options
5676 For example, to enable stacktrace option (to dump the
5677 stack trace of each event), add to the command line:
5679 trace_options=stacktrace
5681 See also Documentation/trace/ftrace.rst "trace options"
5685 Have the tracepoints sent to printk as well as the
5686 tracing ring buffer. This is useful for early boot up
5687 where the system hangs or reboots and does not give the
5688 option for reading the tracing buffer or performing a
5689 ftrace_dump_on_oops.
5691 To turn off having tracepoints sent to printk,
5692 echo 0 > /proc/sys/kernel/tracepoint_printk
5693 Note, echoing 1 into this file without the
5694 tracepoint_printk kernel cmdline option has no effect.
5696 The tp_printk_stop_on_boot (see below) can also be used
5697 to stop the printing of events to console at
5702 Having tracepoints sent to printk() and activating high
5703 frequency tracepoints such as irq or sched, can cause
5704 the system to live lock.
5706 tp_printk_stop_on_boot[FTRACE]
5707 When tp_printk (above) is set, it can cause a lot of noise
5708 on the console. It may be useful to only include the
5709 printing of events during boot up, as user space may
5710 make the system inoperable.
5712 This command line option will stop the printing of events
5713 to console at the late_initcall_sync() time frame.
5716 [FTRACE] enable this option to disable tracing when a
5717 warning is hit. This turns off "tracing_on". Tracing can
5718 be enabled again by echoing '1' into the "tracing_on"
5719 file located in /sys/kernel/debug/tracing/
5721 This option is useful, as it disables the trace before
5722 the WARNING dump is called, which prevents the trace to
5723 be filled with content caused by the warning output.
5725 This option can also be set at run time via the sysctl
5726 option: kernel/traceoff_on_warning
5728 transparent_hugepage=
5730 Format: [always|madvise|never]
5731 Can be used to control the default behavior of the system
5732 with respect to transparent hugepages.
5733 See Documentation/admin-guide/mm/transhuge.rst
5736 trusted.source= [KEYS]
5738 This parameter identifies the trust source as a backend
5739 for trusted keys implementation. Supported trust
5743 If not specified then it defaults to iterating through
5744 the trust source list starting with TPM and assigns the
5745 first trust source as a backend which is initialized
5746 successfully during iteration.
5748 tsc= Disable clocksource stability checks for TSC.
5750 [x86] reliable: mark tsc clocksource as reliable, this
5751 disables clocksource verification at runtime, as well
5752 as the stability checks done at bootup. Used to enable
5753 high-resolution timer mode on older hardware, and in
5754 virtualized environment.
5755 [x86] noirqtime: Do not use TSC to do irq accounting.
5756 Used to run time disable IRQ_TIME_ACCOUNTING on any
5757 platforms where RDTSC is slow and this accounting
5759 [x86] unstable: mark the TSC clocksource as unstable, this
5760 marks the TSC unconditionally unstable at bootup and
5761 avoids any further wobbles once the TSC watchdog notices.
5762 [x86] nowatchdog: disable clocksource watchdog. Used
5763 in situations with strict latency requirements (where
5764 interruptions from clocksource watchdog are not
5767 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5768 value instead. Useful when the early TSC frequency discovery
5769 procedure is not reliable, such as on overclocked systems
5770 with CPUID.16h support and partial CPUID.15h support.
5771 Format: <unsigned int>
5773 tsx= [X86] Control Transactional Synchronization
5774 Extensions (TSX) feature in Intel processors that
5775 support TSX control.
5777 This parameter controls the TSX feature. The options are:
5779 on - Enable TSX on the system. Although there are
5780 mitigations for all known security vulnerabilities,
5781 TSX has been known to be an accelerator for
5782 several previous speculation-related CVEs, and
5783 so there may be unknown security risks associated
5784 with leaving it enabled.
5786 off - Disable TSX on the system. (Note that this
5787 option takes effect only on newer CPUs which are
5788 not vulnerable to MDS, i.e., have
5789 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5790 the new IA32_TSX_CTRL MSR through a microcode
5791 update. This new MSR allows for the reliable
5792 deactivation of the TSX functionality.)
5794 auto - Disable TSX if X86_BUG_TAA is present,
5795 otherwise enable TSX on the system.
5797 Not specifying this option is equivalent to tsx=off.
5799 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5802 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5803 Abort (TAA) vulnerability.
5805 Similar to Micro-architectural Data Sampling (MDS)
5806 certain CPUs that support Transactional
5807 Synchronization Extensions (TSX) are vulnerable to an
5808 exploit against CPU internal buffers which can forward
5809 information to a disclosure gadget under certain
5812 In vulnerable processors, the speculatively forwarded
5813 data can be used in a cache side channel attack, to
5814 access data to which the attacker does not have direct
5817 This parameter controls the TAA mitigation. The
5820 full - Enable TAA mitigation on vulnerable CPUs
5823 full,nosmt - Enable TAA mitigation and disable SMT on
5824 vulnerable CPUs. If TSX is disabled, SMT
5825 is not disabled because CPU is not
5826 vulnerable to cross-thread TAA attacks.
5827 off - Unconditionally disable TAA mitigation
5829 On MDS-affected machines, tsx_async_abort=off can be
5830 prevented by an active MDS mitigation as both vulnerabilities
5831 are mitigated with the same mechanism so in order to disable
5832 this mitigation, you need to specify mds=off too.
5834 Not specifying this option is equivalent to
5835 tsx_async_abort=full. On CPUs which are MDS affected
5836 and deploy MDS mitigation, TAA mitigation is not
5837 required and doesn't provide any additional
5841 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5843 turbografx.map[2|3]= [HW,JOY]
5844 TurboGraFX parallel port interface
5846 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5847 See also Documentation/input/devices/joystick-parport.rst
5849 udbg-immortal [PPC] When debugging early kernel crashes that
5850 happen after console_init() and before a proper
5851 console driver takes over, this boot options might
5852 help "seeing" what's going on.
5854 uhash_entries= [KNL,NET]
5855 Set number of hash buckets for UDP/UDP-Lite connections
5858 [USB] Ignore overcurrent events (default N).
5859 Some badly-designed motherboards generate lots of
5860 bogus events, for ports that aren't wired to
5861 anything. Set this parameter to avoid log spamming.
5862 Note that genuine overcurrent events won't be
5866 [X86] Cause panic on unknown NMI.
5868 usbcore.authorized_default=
5869 [USB] Default USB device authorization:
5870 (default -1 = authorized except for wireless USB,
5871 0 = not authorized, 1 = authorized, 2 = authorized
5872 if device connected to internal port)
5874 usbcore.autosuspend=
5875 [USB] The autosuspend time delay (in seconds) used
5876 for newly-detected USB devices (default 2). This
5877 is the time required before an idle device will be
5878 autosuspended. Devices for which the delay is set
5879 to a negative value won't be autosuspended at all.
5881 usbcore.usbfs_snoop=
5882 [USB] Set to log all usbfs traffic (default 0 = off).
5884 usbcore.usbfs_snoop_max=
5885 [USB] Maximum number of bytes to snoop in each URB
5888 usbcore.blinkenlights=
5889 [USB] Set to cycle leds on hubs (default 0 = off).
5891 usbcore.old_scheme_first=
5892 [USB] Start with the old device initialization
5893 scheme (default 0 = off).
5895 usbcore.usbfs_memory_mb=
5896 [USB] Memory limit (in MB) for buffers allocated by
5897 usbfs (default = 16, 0 = max = 2047).
5899 usbcore.use_both_schemes=
5900 [USB] Try the other device initialization scheme
5901 if the first one fails (default 1 = enabled).
5903 usbcore.initial_descriptor_timeout=
5904 [USB] Specifies timeout for the initial 64-byte
5905 USB_REQ_GET_DESCRIPTOR request in milliseconds
5906 (default 5000 = 5.0 seconds).
5908 usbcore.nousb [USB] Disable the USB subsystem
5911 [USB] A list of quirk entries to augment the built-in
5912 usb core quirk list. List entries are separated by
5913 commas. Each entry has the form
5914 VendorID:ProductID:Flags. The IDs are 4-digit hex
5915 numbers and Flags is a set of letters. Each letter
5916 will change the built-in quirk; setting it if it is
5917 clear and clearing it if it is set. The letters have
5918 the following meanings:
5919 a = USB_QUIRK_STRING_FETCH_255 (string
5920 descriptors must not be fetched using
5922 b = USB_QUIRK_RESET_RESUME (device can't resume
5923 correctly so reset it instead);
5924 c = USB_QUIRK_NO_SET_INTF (device can't handle
5925 Set-Interface requests);
5926 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5927 handle its Configuration or Interface
5929 e = USB_QUIRK_RESET (device can't be reset
5930 (e.g morph devices), don't use reset);
5931 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5932 more interface descriptions than the
5933 bNumInterfaces count, and can't handle
5934 talking to these interfaces);
5935 g = USB_QUIRK_DELAY_INIT (device needs a pause
5936 during initialization, after we read
5937 the device descriptor);
5938 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5939 high speed and super speed interrupt
5940 endpoints, the USB 2.0 and USB 3.0 spec
5941 require the interval in microframes (1
5942 microframe = 125 microseconds) to be
5943 calculated as interval = 2 ^
5945 Devices with this quirk report their
5946 bInterval as the result of this
5947 calculation instead of the exponent
5948 variable used in the calculation);
5949 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5950 handle device_qualifier descriptor
5952 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5953 generates spurious wakeup, ignore
5954 remote wakeup capability);
5955 k = USB_QUIRK_NO_LPM (device can't handle Link
5957 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5958 (Device reports its bInterval as linear
5959 frames instead of the USB 2.0
5961 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5962 to be disconnected before suspend to
5963 prevent spurious wakeup);
5964 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5965 pause after every control message);
5966 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5967 delay after resetting its port);
5968 Example: quirks=0781:5580:bk,0a5c:5834:gij
5971 [USBHID] The interval which mice are to be polled at.
5974 [USBHID] The interval which joysticks are to be polled at.
5977 [USBHID] The interval which keyboards are to be polled at.
5979 usb-storage.delay_use=
5980 [UMS] The delay in seconds before a new device is
5981 scanned for Logical Units (default 1).
5984 [UMS] A list of quirks entries to supplement or
5985 override the built-in unusual_devs list. List
5986 entries are separated by commas. Each entry has
5987 the form VID:PID:Flags where VID and PID are Vendor
5988 and Product ID values (4-digit hex numbers) and
5989 Flags is a set of characters, each corresponding
5990 to a common usb-storage quirk flag as follows:
5991 a = SANE_SENSE (collect more than 18 bytes
5992 of sense data, not on uas);
5993 b = BAD_SENSE (don't collect more than 18
5994 bytes of sense data, not on uas);
5995 c = FIX_CAPACITY (decrease the reported
5996 device capacity by one sector);
5997 d = NO_READ_DISC_INFO (don't use
5998 READ_DISC_INFO command, not on uas);
5999 e = NO_READ_CAPACITY_16 (don't use
6000 READ_CAPACITY_16 command);
6001 f = NO_REPORT_OPCODES (don't use report opcodes
6003 g = MAX_SECTORS_240 (don't transfer more than
6004 240 sectors at a time, uas only);
6005 h = CAPACITY_HEURISTICS (decrease the
6006 reported device capacity by one
6007 sector if the number is odd);
6008 i = IGNORE_DEVICE (don't bind to this
6010 j = NO_REPORT_LUNS (don't use report luns
6012 k = NO_SAME (do not use WRITE_SAME, uas only)
6013 l = NOT_LOCKABLE (don't try to lock and
6014 unlock ejectable media, not on uas);
6015 m = MAX_SECTORS_64 (don't transfer more
6016 than 64 sectors = 32 KB at a time,
6018 n = INITIAL_READ10 (force a retry of the
6019 initial READ(10) command, not on uas);
6020 o = CAPACITY_OK (accept the capacity
6021 reported by the device, not on uas);
6022 p = WRITE_CACHE (the device cache is ON
6023 by default, not on uas);
6024 r = IGNORE_RESIDUE (the device reports
6025 bogus residue values, not on uas);
6026 s = SINGLE_LUN (the device has only one
6028 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6029 commands, uas only);
6030 u = IGNORE_UAS (don't bind to the uas driver);
6031 w = NO_WP_DETECT (don't test whether the
6032 medium is write-protected).
6033 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6034 even if the device claims no cache,
6036 Example: quirks=0419:aaf5:rl,0421:0433:rc
6038 user_debug= [KNL,ARM]
6040 See arch/arm/Kconfig.debug help text.
6041 1 - undefined instruction events
6043 4 - invalid data aborts
6046 Example: user_debug=31
6049 [X86] Flags controlling user PTE allocations.
6051 nohigh = do not allocate PTE pages in
6052 HIGHMEM regardless of setting
6056 On X86_32, this is an alias for vdso32=. Otherwise:
6058 vdso=1: enable VDSO (the default)
6059 vdso=0: disable VDSO mapping
6061 vdso32= [X86] Control the 32-bit vDSO
6062 vdso32=1: enable 32-bit VDSO
6063 vdso32=0 or vdso32=2: disable 32-bit VDSO
6065 See the help text for CONFIG_COMPAT_VDSO for more
6066 details. If CONFIG_COMPAT_VDSO is set, the default is
6067 vdso32=0; otherwise, the default is vdso32=1.
6069 For compatibility with older kernels, vdso32=2 is an
6072 Try vdso32=0 if you encounter an error that says:
6073 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6076 vector=percpu: enable percpu vector domain
6078 video= [FB] Frame buffer configuration
6079 See Documentation/fb/modedb.rst.
6081 video.brightness_switch_enabled= [0,1]
6082 If set to 1, on receiving an ACPI notify event
6083 generated by hotkey, video driver will adjust brightness
6084 level and then send out the event to user space through
6085 the allocated input device; If set to 0, video driver
6086 will only send out the event without touching backlight
6091 [VMMIO] Memory mapped virtio (platform) device.
6093 <size>@<baseaddr>:<irq>[:<id>]
6095 <size> := size (can use standard suffixes
6097 <baseaddr> := physical base address
6098 <irq> := interrupt number (as passed to
6100 <id> := (optional) platform device id
6102 virtio_mmio.device=1K@0x100b0000:48:7
6104 Can be used multiple times for multiple devices.
6106 vga= [BOOT,X86-32] Select a particular video mode
6107 See Documentation/x86/boot.rst and
6108 Documentation/admin-guide/svga.rst.
6109 Use vga=ask for menu.
6110 This is actually a boot loader parameter; the value is
6111 passed to the kernel using a special protocol.
6113 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6114 May slow down system boot speed, especially when
6115 enabled on systems with a large amount of memory.
6116 All options are enabled by default, and this
6117 interface is meant to allow for selectively
6118 enabling or disabling specific virtual memory
6121 Available options are:
6122 P Enable page structure init time poisoning
6123 - Disable all of the above options
6125 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6126 size of <nn>. This can be used to increase the
6127 minimum size (128MB on x86). It can also be used to
6128 decrease the size and leave more room for directly
6131 vmcp_cma=nn[MG] [KNL,S390]
6132 Sets the memory size reserved for contiguous memory
6133 allocations for the vmcp device driver.
6135 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6138 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6141 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6145 Controls the behavior of vsyscalls (i.e. calls to
6146 fixed addresses of 0xffffffffff600x00 from legacy
6147 code). Most statically-linked binaries and older
6148 versions of glibc use these calls. Because these
6149 functions are at fixed addresses, they make nice
6150 targets for exploits that can control RIP.
6152 emulate [default] Vsyscalls turn into traps and are
6153 emulated reasonably safely. The vsyscall
6156 xonly Vsyscalls turn into traps and are
6157 emulated reasonably safely. The vsyscall
6158 page is not readable.
6160 none Vsyscalls don't work at all. This makes
6161 them quite hard to use for exploits but
6162 might break your system.
6164 vt.color= [VT] Default text color.
6165 Format: 0xYX, X = foreground, Y = background.
6166 Default: 0x07 = light gray on black.
6168 vt.cur_default= [VT] Default cursor shape.
6169 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6170 the parameters of the <Esc>[?A;B;Cc escape sequence;
6171 see VGA-softcursor.txt. Default: 2 = underline.
6173 vt.default_blu= [VT]
6174 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6175 Change the default blue palette of the console.
6176 This is a 16-member array composed of values
6179 vt.default_grn= [VT]
6180 Format: <green0>,<green1>,<green2>,...,<green15>
6181 Change the default green palette of the console.
6182 This is a 16-member array composed of values
6185 vt.default_red= [VT]
6186 Format: <red0>,<red1>,<red2>,...,<red15>
6187 Change the default red palette of the console.
6188 This is a 16-member array composed of values
6194 Set system-wide default UTF-8 mode for all tty's.
6195 Default is 1, i.e. UTF-8 mode is enabled for all
6196 newly opened terminals.
6198 vt.global_cursor_default=
6201 Set system-wide default for whether a cursor
6202 is shown on new VTs. Default is -1,
6203 i.e. cursors will be created by default unless
6204 overridden by individual drivers. 0 will hide
6205 cursors, 1 will display them.
6207 vt.italic= [VT] Default color for italic text; 0-15.
6210 vt.underline= [VT] Default color for underlined text; 0-15.
6213 watchdog timers [HW,WDT] For information on watchdog timers,
6214 see Documentation/watchdog/watchdog-parameters.rst
6215 or other driver-specific files in the
6216 Documentation/watchdog/ directory.
6220 Set the hard lockup detector stall duration
6221 threshold in seconds. The soft lockup detector
6222 threshold is set to twice the value. A value of 0
6223 disables both lockup detectors. Default is 10
6226 workqueue.watchdog_thresh=
6227 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6228 warn stall conditions and dump internal state to
6229 help debugging. 0 disables workqueue stall
6230 detection; otherwise, it's the stall threshold
6231 duration in seconds. The default value is 30 and
6232 it can be updated at runtime by writing to the
6233 corresponding sysfs file.
6235 workqueue.disable_numa
6236 By default, all work items queued to unbound
6237 workqueues are affine to the NUMA nodes they're
6238 issued on, which results in better behavior in
6239 general. If NUMA affinity needs to be disabled for
6240 whatever reason, this option can be used. Note
6241 that this also can be controlled per-workqueue for
6242 workqueues visible under /sys/bus/workqueue/.
6244 workqueue.power_efficient
6245 Per-cpu workqueues are generally preferred because
6246 they show better performance thanks to cache
6247 locality; unfortunately, per-cpu workqueues tend to
6248 be more power hungry than unbound workqueues.
6250 Enabling this makes the per-cpu workqueues which
6251 were observed to contribute significantly to power
6252 consumption unbound, leading to measurably lower
6253 power usage at the cost of small performance
6256 The default value of this parameter is determined by
6257 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6259 workqueue.debug_force_rr_cpu
6260 Workqueue used to implicitly guarantee that work
6261 items queued without explicit CPU specified are put
6262 on the local CPU. This guarantee is no longer true
6263 and while local CPU is still preferred work items
6264 may be put on foreign CPUs. This debug option
6265 forces round-robin CPU selection to flush out
6266 usages which depend on the now broken guarantee.
6267 When enabled, memory and cache locality will be
6270 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6271 default x2apic cluster mode on platforms
6274 xen_512gb_limit [KNL,X86-64,XEN]
6275 Restricts the kernel running paravirtualized under Xen
6276 to use only up to 512 GB of RAM. The reason to do so is
6277 crash analysis tools and Xen tools for doing domain
6278 save/restore/migration must be enabled to handle larger
6281 xen_emul_unplug= [HW,X86,XEN]
6282 Unplug Xen emulated devices
6283 Format: [unplug0,][unplug1]
6284 ide-disks -- unplug primary master IDE devices
6285 aux-ide-disks -- unplug non-primary-master IDE devices
6286 nics -- unplug network devices
6287 all -- unplug all emulated devices (NICs and IDE disks)
6288 unnecessary -- unplugging emulated devices is
6289 unnecessary even if the host did not respond to
6291 never -- do not unplug even if version check succeeds
6293 xen_legacy_crash [X86,XEN]
6294 Crash from Xen panic notifier, without executing late
6295 panic() code such as dumping handler.
6297 xen_nopvspin [X86,XEN]
6298 Disables the qspinlock slowpath using Xen PV optimizations.
6299 This parameter is obsoleted by "nopvspin" parameter, which
6300 has equivalent effect for XEN platform.
6303 Disables the PV optimizations forcing the HVM guest to
6304 run as generic HVM guest with no PV drivers.
6305 This option is obsoleted by the "nopv" option, which
6306 has equivalent effect for XEN platform.
6308 xen_no_vector_callback
6309 [KNL,X86,XEN] Disable the vector callback for Xen
6310 event channel interrupts.
6312 xen_scrub_pages= [XEN]
6313 Boolean option to control scrubbing pages before giving them back
6314 to Xen, for use by other domains. Can be also changed at runtime
6315 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6316 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6318 xen_timer_slop= [X86-64,XEN]
6319 Set the timer slop (in nanoseconds) for the virtual Xen
6320 timers (default is 100000). This adjusts the minimum
6321 delta of virtualized Xen timers, where lower values
6322 improve timer resolution at the expense of processing
6323 more timer interrupts.
6325 xen.event_eoi_delay= [XEN]
6326 How long to delay EOI handling in case of event
6327 storms (jiffies). Default is 10.
6329 xen.event_loop_timeout= [XEN]
6330 After which time (jiffies) the event handling loop
6331 should start to delay EOI handling. Default is 2.
6333 xen.fifo_events= [XEN]
6334 Boolean parameter to disable using fifo event handling
6335 even if available. Normally fifo event handling is
6336 preferred over the 2-level event handling, as it is
6337 fairer and the number of possible event channels is
6338 much higher. Default is on (use fifo events).
6340 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6341 Disables the PV optimizations forcing the guest to run
6342 as generic guest with no PV drivers. Currently support
6343 XEN HVM, KVM, HYPER_V and VMWARE guest.
6345 nopvspin [X86,XEN,KVM]
6346 Disables the qspinlock slow path using PV optimizations
6347 which allow the hypervisor to 'idle' the guest on lock
6350 xirc2ps_cs= [NET,PCMCIA]
6352 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6355 By default on POWER9 and above, the kernel will
6356 natively use the XIVE interrupt controller. This option
6357 allows the fallback firmware mode to be used:
6359 off Fallback to firmware control of XIVE interrupt
6360 controller on both pseries and powernv
6361 platforms. Only useful on POWER9 and above.
6363 xhci-hcd.quirks [USB,KNL]
6364 A hex value specifying bitmask with supplemental xhci
6365 host controller quirks. Meaning of each bit can be
6366 consulted in header drivers/usb/host/xhci.h.
6369 Format: { early | on | rw | ro | off }
6370 Controls if xmon debugger is enabled. Default is off.
6371 Passing only "xmon" is equivalent to "xmon=early".
6372 early Call xmon as early as possible on boot; xmon
6373 debugger is called from setup_arch().
6374 on xmon debugger hooks will be installed so xmon
6375 is only called on a kernel crash. Default mode,
6376 i.e. either "ro" or "rw" mode, is controlled
6377 with CONFIG_XMON_DEFAULT_RO_MODE.
6378 rw xmon debugger hooks will be installed so xmon
6379 is called only on a kernel crash, mode is write,
6380 meaning SPR registers, memory and, other data
6381 can be written using xmon commands.
6382 ro same as "rw" option above but SPR registers,
6383 memory, and other data can't be written using
6385 off xmon is disabled.
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