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.txt, 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]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
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
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joydev/joystick.rst
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
336 For X86-32, this can also be used to specify an APIC
338 Format: apic=driver_name
339 Examples: apic=bigsmp
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
351 See Documentation/networking/ipv6.txt.
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
370 atarimouse= [HW,MOUSE] Atari Mouse
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
375 atkbd.reset= [HW] Reset keyboard during initialization
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
410 unset - Disable the BAU.
412 baycom_epp= [HW,AX25]
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
417 See header of drivers/net/hamradio/baycom_par.c.
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441 Disable BERT OS support on buggy BIOSes.
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
446 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
453 c101= [NET] Moxa C101 synchronous serial card
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
465 format: { id:<keyid> | builtin }
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
481 - foo isn't visible as an individually mountable
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
508 See Documentation/s390/CommonIO for details.
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
528 clocksource= Override the default clocksource
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
534 [all] jiffies (this is the base, fallback clocksource)
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
547 clocksource.arm_arch_timer.evtstrm=
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
555 clearcpuid=BITNUM [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
568 cma=nn[MG]@[start[MG][-end[MG]]]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
588 code_bytes [X86] How many bytes of object code to print
593 com20020= [HW,NET] ARCnet - COM20020 chipset
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
604 condev= [HW,S390] console device
607 console= [KNL] Output console device and options.
609 tty<n> Use the virtual console device <n>.
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
619 See Documentation/admin-guide/serial-console.rst for more
621 Documentation/networking/netconsole.txt for an
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
645 For now, only VisioBraille is supported.
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. A value of 0 disables the blank timer.
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
656 coresight_cpu_debug.enable
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
663 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
664 to register. Example: cpufreq_driver=powernow-k8
665 Format: { none | STRING }
667 cpuidle.off=1 [CPU_IDLE]
668 disable the cpuidle sub-system
670 cpufreq.off=1 [CPU_FREQ]
671 disable the cpufreq sub-system
674 [X86] Delay for N microsec between assert and de-assert
675 of APIC INIT to start processors. This delay occurs
676 on every CPU online, such as boot, and resume from suspend.
679 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
681 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
683 crashkernel=size[KMG][@offset[KMG]]
684 [KNL] Using kexec, Linux can switch to a 'crash kernel'
685 upon panic. This parameter reserves the physical
686 memory region [offset, offset + size] for that kernel
687 image. If '@offset' is omitted, then a suitable offset
688 is selected automatically. Check
689 Documentation/kdump/kdump.txt for further details.
691 crashkernel=range1:size1[,range2:size2,...][@offset]
692 [KNL] Same as above, but depends on the memory
693 in the running system. The syntax of range is
694 start-[end] where start and end are both
695 a memory unit (amount[KMG]). See also
696 Documentation/kdump/kdump.txt for an example.
698 crashkernel=size[KMG],high
699 [KNL, x86_64] range could be above 4G. Allow kernel
700 to allocate physical memory region from top, so could
701 be above 4G if system have more than 4G ram installed.
702 Otherwise memory region will be allocated below 4G, if
704 It will be ignored if crashkernel=X is specified.
705 crashkernel=size[KMG],low
706 [KNL, x86_64] range under 4G. When crashkernel=X,high
707 is passed, kernel could allocate physical memory region
708 above 4G, that cause second kernel crash on system
709 that require some amount of low memory, e.g. swiotlb
710 requires at least 64M+32K low memory, also enough extra
711 low memory is needed to make sure DMA buffers for 32-bit
712 devices won't run out. Kernel would try to allocate at
713 at least 256M below 4G automatically.
714 This one let user to specify own low range under 4G
715 for second kernel instead.
716 0: to disable low allocation.
717 It will be ignored when crashkernel=X,high is not used
718 or memory reserved is below 4G.
721 [KNL] Disable crypto self-tests
726 cs89x0_media= [HW,NET]
727 Format: { rj45 | aui | bnc }
730 See header of drivers/s390/block/dasd_devmap.c.
732 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
733 (one device per port)
734 Format: <port#>,<type>
735 See also Documentation/input/devices/joystick-parport.rst
737 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
739 Documentation/admin-guide/dynamic-debug-howto.rst for
740 details. Deprecated, see dyndbg.
742 debug [KNL] Enable kernel debugging (events log level).
745 [KNL] verbose self-tests
747 Print debugging info while doing the locking API
749 We default to 0 (no extra messages), setting it to
750 1 will print _a lot_ more information - normally
751 only useful to kernel developers.
753 debug_objects [KNL] Enable object debugging
756 [KNL] Disable object debugging
758 debug_guardpage_minorder=
759 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
760 parameter allows control of the order of pages that will
761 be intentionally kept free (and hence protected) by the
762 buddy allocator. Bigger value increase the probability
763 of catching random memory corruption, but reduce the
764 amount of memory for normal system use. The maximum
765 possible value is MAX_ORDER/2. Setting this parameter
766 to 1 or 2 should be enough to identify most random
767 memory corruption problems caused by bugs in kernel or
768 driver code when a CPU writes to (or reads from) a
769 random memory location. Note that there exists a class
770 of memory corruptions problems caused by buggy H/W or
771 F/W or by drivers badly programing DMA (basically when
772 memory is written at bus level and the CPU MMU is
773 bypassed) which are not detectable by
774 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
775 tracking down these problems.
778 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
779 parameter enables the feature at boot time. In
780 default, it is disabled. We can avoid allocating huge
781 chunk of memory for debug pagealloc if we don't enable
782 it at boot time and the system will work mostly same
783 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
784 on: enable the feature
786 debugpat [X86] Enable PAT debugging
788 decnet.addr= [HW,NET]
789 Format: <area>[,<node>]
790 See also Documentation/networking/decnet.txt.
793 [same as hugepagesz=] The size of the default
794 HugeTLB page size. This is the size represented by
795 the legacy /proc/ hugepages APIs, used for SHM, and
796 default size when mounting hugetlbfs filesystems.
797 Defaults to the default architecture's huge page size
801 Set number of hash buckets for dentry cache.
803 disable_1tb_segments [PPC]
804 Disables the use of 1TB hash page table segments. This
805 causes the kernel to fall back to 256MB segments which
806 can be useful when debugging issues that require an SLB
810 See Documentation/networking/ipv6.txt.
813 Disable RADIX MMU mode on POWER9
815 disable_cpu_apicid= [X86,APIC,SMP]
817 The number of initial APIC ID for the
818 corresponding CPU to be disabled at boot,
819 mostly used for the kdump 2nd kernel to
820 disable BSP to wake up multiple CPUs without
821 causing system reset or hang due to sending
824 disable_ddw [PPC/PSERIES]
825 Disable Dynamic DMA Window support. Use this if
826 to workaround buggy firmware.
829 See Documentation/networking/ipv6.txt.
831 disable_mtrr_cleanup [X86]
832 The kernel tries to adjust MTRR layout from continuous
833 to discrete, to make X server driver able to add WB
834 entry later. This parameter disables that.
836 disable_mtrr_trim [X86, Intel and AMD only]
837 By default the kernel will trim any uncacheable
838 memory out of your available memory pool based on
839 MTRR settings. This parameter disables that behavior,
840 possibly causing your machine to run very slowly.
842 disable_timer_pin_1 [X86]
843 Disable PIN 1 of APIC timer
844 Can be useful to work around chipset bugs.
846 dis_ucode_ldr [X86] Disable the microcode loader.
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
865 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
866 Broken monitors, graphic adapters, KVMs and EDIDless
867 panels may send no or incorrect EDID data sets.
868 This parameter allows to specify an EDID data sets
869 in the /lib/firmware directory that are used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name. Each connector may use a unique EDID data
879 set by separating the files with a comma. An EDID
880 data set with no connector name will be used for
881 any connectors not explicitly specified.
886 Format: {"off" | "known"}
887 Control how the dt_cpu_ftrs device-tree binding is
888 used for CPU feature discovery and setup (if it
890 off: Do not use it, fall back to legacy cpu table.
891 known: Do not pass through unknown features to guests
892 or userspace, only those that the kernel is aware of.
894 dump_apple_properties [X86]
895 Dump name and content of EFI device properties on
896 x86 Macs. Useful for driver authors to determine
897 what data is available or for reverse-engineering.
899 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
900 module.dyndbg[="val"]
901 Enable debug messages at boot time. See
902 Documentation/admin-guide/dynamic-debug-howto.rst
905 nompx [X86] Disables Intel Memory Protection Extensions.
906 See Documentation/x86/intel_mpx.txt for more
907 information about the feature.
909 nopku [X86] Disable Memory Protection Keys CPU feature found
912 module.async_probe [KNL]
913 Enable asynchronous probe on this module.
915 early_ioremap_debug [KNL]
916 Enable debug messages in early_ioremap support. This
917 is useful for tracking down temporary early mappings
918 which are not unmapped.
920 earlycon= [KNL] Output early console device and options.
922 When used with no options, the early console is
923 determined by the stdout-path property in device
926 cdns,<addr>[,options]
927 Start an early, polled-mode console on a Cadence
928 (xuartps) serial port at the specified address. Only
929 supported option is baud rate. If baud rate is not
930 specified, the serial port must already be setup and
933 uart[8250],io,<addr>[,options]
934 uart[8250],mmio,<addr>[,options]
935 uart[8250],mmio32,<addr>[,options]
936 uart[8250],mmio32be,<addr>[,options]
937 uart[8250],0x<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32 or mmio32be).
942 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
943 to be equivalent to 'mmio'. 'options' are specified
944 in the same format described for "console=ttyS<n>"; if
945 unspecified, the h/w is not initialized.
949 Start an early, polled-mode console on a pl011 serial
950 port at the specified address. The pl011 serial port
951 must already be setup and configured. Options are not
952 yet supported. If 'mmio32' is specified, then only
953 the driver will use only 32-bit accessors to read/write
954 the device registers.
957 Start an early, polled-mode console on a meson serial
958 port at the specified address. The serial port must
959 already be setup and configured. Options are not yet
963 Start an early, polled-mode console on an msm serial
964 port at the specified address. The serial port
965 must already be setup and configured. Options are not
969 Start an early, polled-mode console on an msm serial
970 dm port at the specified address. The serial port
971 must already be setup and configured. Options are not
975 Start an early, polled-mode console on a serial port
976 of an Actions Semi SoC, such as S500 or S900, at the
977 specified address. The serial port must already be
978 setup and configured. Options are not yet supported.
980 smh Use ARM semihosting calls for early console.
988 Use early console provided by serial driver available
989 on Samsung SoCs, requires selecting proper type and
990 a correct base address of the selected UART port. The
991 serial port must already be setup and configured.
992 Options are not yet supported.
995 Start an early, polled-mode console on a lantiq serial
996 (lqasc) port at the specified address. The serial port
997 must already be setup and configured. Options are not
1002 Use early console provided by Freescale LP UART driver
1003 found on Freescale Vybrid and QorIQ LS1021A processors.
1004 A valid base address must be provided, and the serial
1005 port must already be setup and configured.
1008 Start an early, polled-mode console on the
1009 Armada 3700 serial port at the specified
1010 address. The serial port must already be setup
1011 and configured. Options are not yet supported.
1013 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1018 earlyprintk=serial[,ttySn[,baudrate]]
1019 earlyprintk=serial[,0x...[,baudrate]]
1020 earlyprintk=ttySn[,baudrate]
1021 earlyprintk=dbgp[debugController#]
1022 earlyprintk=pciserial,bus:device.function[,baudrate]
1023 earlyprintk=xdbc[xhciController#]
1025 earlyprintk is useful when the kernel crashes before
1026 the normal console is initialized. It is not enabled by
1027 default because it has some cosmetic problems.
1029 Append ",keep" to not disable it when the real console
1032 Only one of vga, efi, serial, or usb debug port can
1035 Currently only ttyS0 and ttyS1 may be specified by
1036 name. Other I/O ports may be explicitly specified
1037 on some architectures (x86 and arm at least) by
1038 replacing ttySn with an I/O port address, like this:
1039 earlyprintk=serial,0x1008,115200
1040 You can find the port for a given device in
1041 /proc/tty/driver/serial:
1042 2: uart:ST16650V2 port:00001008 irq:18 ...
1044 Interaction with the standard serial driver is not
1047 The VGA and EFI output is eventually overwritten by
1050 The xen output can only be used by Xen PV guests.
1052 The sclp output can only be used on s390.
1054 edac_report= [HW,EDAC] Control how to report EDAC event
1055 Format: {"on" | "off" | "force"}
1056 on: enable EDAC to report H/W event. May be overridden
1057 by other higher priority error reporting module.
1058 off: disable H/W event reporting through EDAC.
1059 force: enforce the use of EDAC to report H/W event.
1062 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1065 This is designed to be used in conjunction with
1066 the boot argument: earlyprintk=vga
1069 Format: {"off" | "on" | "skip[mbr]"}
1072 Format: { "old_map", "nochunk", "noruntime", "debug" }
1073 old_map [X86-64]: switch to the old ioremap-based EFI
1074 runtime services mapping. 32-bit still uses this one by
1076 nochunk: disable reading files in "chunks" in the EFI
1077 boot stub, as chunking can cause problems with some
1078 firmware implementations.
1079 noruntime : disable EFI runtime services support
1080 debug: enable misc debug output
1082 efi_no_storage_paranoia [EFI; X86]
1083 Using this parameter you can use more than 50% of
1084 your efi variable storage. Use this parameter only if
1085 you are really sure that your UEFI does sane gc and
1086 fulfills the spec otherwise your board may brick.
1088 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1089 Add arbitrary attribute to specific memory range by
1090 updating original EFI memory map.
1091 Region of memory which aa attribute is added to is
1093 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1094 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1095 attribute is added to range 0x100000000-0x180000000 and
1096 0x10a0000000-0x1120000000.
1098 Using this parameter you can do debugging of EFI memmap
1099 related feature. For example, you can do debugging of
1100 Address Range Mirroring feature even if your box
1103 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1104 that is to be dynamically loaded by Linux. If there are
1105 multiple variables with the same name but with different
1106 vendor GUIDs, all of them will be loaded. See
1107 Documentation/acpi/ssdt-overlays.txt for details.
1110 eisa_irq_edge= [PARISC,HW]
1111 See header of drivers/parisc/eisa.c.
1114 See comment before function elanfreq_setup() in
1115 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1118 Format: {"cfq" | "deadline" | "noop"}
1119 See Documentation/block/cfq-iosched.txt and
1120 Documentation/block/deadline-iosched.txt for details.
1122 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1123 Specifies physical address of start of kernel core
1124 image elf header and optionally the size. Generally
1125 kexec loader will pass this option to capture kernel.
1126 See Documentation/kdump/kdump.txt for details.
1128 enable_mtrr_cleanup [X86]
1129 The kernel tries to adjust MTRR layout from continuous
1130 to discrete, to make X server driver able to add WB
1131 entry later. This parameter enables that.
1133 enable_timer_pin_1 [X86]
1134 Enable PIN 1 of APIC timer
1135 Can be useful to work around chipset bugs
1136 (in particular on some ATI chipsets).
1137 The kernel tries to set a reasonable default.
1139 enforcing [SELINUX] Set initial enforcing status.
1141 See security/selinux/Kconfig help text.
1142 0 -- permissive (log only, no denials).
1143 1 -- enforcing (deny and log).
1145 Value can be changed at runtime via /selinux/enforce.
1148 Disable Error Record Serialization Table (ERST)
1151 ether= [HW,NET] Ethernet cards parameters
1152 This option is obsoleted by the "netdev=" option, which
1153 has equivalent usage. See its documentation for details.
1157 Permit 'security.evm' to be updated regardless of
1158 current integrity status.
1162 fail_make_request=[KNL]
1163 General fault injection mechanism.
1164 Format: <interval>,<probability>,<space>,<times>
1165 See also Documentation/fault-injection/.
1168 See Documentation/blockdev/floppy.txt.
1170 force_pal_cache_flush
1171 [IA-64] Avoid check_sal_cache_flush which may hang on
1172 buggy SAL_CACHE_FLUSH implementations. Using this
1173 parameter will force ia64_sal_cache_flush to call
1174 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1177 Forcefully enable Physical Address Extension (PAE).
1178 Many Pentium M systems disable PAE but may have a
1179 functionally usable PAE implementation.
1180 Warning: use of this parameter will taint the kernel
1181 and may cause unknown problems.
1184 [FTRACE] will set and start the specified tracer
1185 as early as possible in order to facilitate early
1188 ftrace_dump_on_oops[=orig_cpu]
1189 [FTRACE] will dump the trace buffers on oops.
1190 If no parameter is passed, ftrace will dump
1191 buffers of all CPUs, but if you pass orig_cpu, it will
1192 dump only the buffer of the CPU that triggered the
1195 ftrace_filter=[function-list]
1196 [FTRACE] Limit the functions traced by the function
1197 tracer at boot up. function-list is a comma separated
1198 list of functions. This list can be changed at run
1199 time by the set_ftrace_filter file in the debugfs
1202 ftrace_notrace=[function-list]
1203 [FTRACE] Do not trace the functions specified in
1204 function-list. This list can be changed at run time
1205 by the set_ftrace_notrace file in the debugfs
1208 ftrace_graph_filter=[function-list]
1209 [FTRACE] Limit the top level callers functions traced
1210 by the function graph tracer at boot up.
1211 function-list is a comma separated list of functions
1212 that can be changed at run time by the
1213 set_graph_function file in the debugfs tracing directory.
1215 ftrace_graph_notrace=[function-list]
1216 [FTRACE] Do not trace from the functions specified in
1217 function-list. This list is a comma separated list of
1218 functions that can be changed at run time by the
1219 set_graph_notrace file in the debugfs tracing directory.
1221 ftrace_graph_max_depth=<uint>
1222 [FTRACE] Used with the function graph tracer. This is
1223 the max depth it will trace into a function. This value
1224 can be changed at run time by the max_graph_depth file
1225 in the tracefs tracing directory. default: 0 (no limit)
1228 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1229 support via parallel port (up to 5 devices per port)
1230 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1231 See also Documentation/input/devices/joystick-parport.rst
1235 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1239 gcov_persist= [GCOV] When non-zero (default), profiling data for
1240 kernel modules is saved and remains accessible via
1241 debugfs, even when the module is unloaded/reloaded.
1242 When zero, profiling data is discarded and associated
1243 debugfs files are removed at module unload time.
1245 goldfish [X86] Enable the goldfish android emulator platform.
1246 Don't use this when you are not running on the
1249 gpt [EFI] Forces disk with valid GPT signature but
1250 invalid Protective MBR to be treated as GPT. If the
1251 primary GPT is corrupted, it enables the backup/alternate
1252 GPT to be used instead.
1254 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1255 the "Enable 0" bit of the configuration register.
1258 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1259 the "Enable 0" bit of the configuration register.
1262 grcan.select= [HW] Select which physical interface to use.
1265 grcan.txsize= [HW] Sets the size of the tx buffer.
1266 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1268 grcan.rxsize= [HW] Sets the size of the rx buffer.
1269 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1272 gpio-mockup.gpio_mockup_ranges
1273 [HW] Sets the ranges of gpiochip of for this device.
1274 Format: <start1>,<end1>,<start2>,<end2>...
1276 hardlockup_all_cpu_backtrace=
1277 [KNL] Should the hard-lockup detector generate
1278 backtraces on all cpus.
1281 hashdist= [KNL,NUMA] Large hashes allocated during boot
1282 are distributed across NUMA nodes. Defaults on
1283 for 64-bit NUMA, off otherwise.
1284 Format: 0 | 1 (for off | on)
1286 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1288 hd= [EIDE] (E)IDE hard drive subsystem geometry
1289 Format: <cyl>,<head>,<sect>
1292 Disable Hardware Error Source Table (HEST) support;
1293 corresponding firmware-first mode error processing
1294 logic will be disabled.
1296 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1297 size of <nn>. This works even on boxes that have no
1298 highmem otherwise. This also works to reduce highmem
1299 size on bigger boxes.
1301 highres= [KNL] Enable/disable high resolution timer mode.
1302 Valid parameters: "on", "off"
1306 See Documentation/isdn/README.HiSax.
1310 hpet= [X86-32,HPET] option to control HPET usage
1311 Format: { enable (default) | disable | force |
1313 disable: disable HPET and use PIT instead
1314 force: allow force enabled of undocumented chips (ICH4,
1316 verbose: show contents of HPET registers during setup
1318 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1319 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1321 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1322 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1323 On x86-64 and powerpc, this option can be specified
1324 multiple times interleaved with hugepages= to reserve
1325 huge pages of different sizes. Valid pages sizes on
1326 x86-64 are 2M (when the CPU supports "pse") and 1G
1327 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1329 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1330 terminal devices. Valid values: 0..8
1331 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1332 If specified, z/VM IUCV HVC accepts connections
1333 from listed z/VM user IDs only.
1335 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1336 hardware thread id mappings.
1337 Format: <cpu>:<hwthread>
1340 Do not unregister boot console at start. This is only
1341 useful for debugging when something happens in the window
1342 between unregistering the boot console and initializing
1345 i2c_bus= [HW] Override the default board specific I2C bus speed
1346 or register an additional I2C bus that is not
1347 registered from board initialization code.
1351 i8042.debug [HW] Toggle i8042 debug mode
1352 i8042.unmask_kbd_data
1353 [HW] Enable printing of interrupt data from the KBD port
1354 (disabled by default, and as a pre-condition
1355 requires that i8042.debug=1 be enabled)
1356 i8042.direct [HW] Put keyboard port into non-translated mode
1357 i8042.dumbkbd [HW] Pretend that controller can only read data from
1358 keyboard and cannot control its state
1359 (Don't attempt to blink the leds)
1360 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1361 i8042.nokbd [HW] Don't check/create keyboard port
1362 i8042.noloop [HW] Disable the AUX Loopback command while probing
1364 i8042.nomux [HW] Don't check presence of an active multiplexing
1366 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1368 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1369 i8042.reset [HW] Reset the controller during init, cleanup and
1370 suspend-to-ram transitions, only during s2r
1371 transitions, or never reset
1372 Format: { 1 | Y | y | 0 | N | n }
1373 1, Y, y: always reset controller
1374 0, N, n: don't ever reset controller
1375 Default: only on s2r transitions on x86; most other
1376 architectures force reset to be always executed
1377 i8042.unlock [HW] Unlock (ignore) the keylock
1378 i8042.kbdreset [HW] Reset device connected to KBD port
1382 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1383 indicates that the driver is running on unsupported
1385 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1386 does not match list of supported models.
1388 [HW] Report power status in /proc/i8k
1389 (disabled by default)
1390 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1393 i915.invert_brightness=
1394 [DRM] Invert the sense of the variable that is used to
1395 set the brightness of the panel backlight. Normally a
1396 brightness value of 0 indicates backlight switched off,
1397 and the maximum of the brightness value sets the backlight
1398 to maximum brightness. If this parameter is set to 0
1399 (default) and the machine requires it, or this parameter
1400 is set to 1, a brightness value of 0 sets the backlight
1401 to maximum brightness, and the maximum of the brightness
1402 value switches the backlight off.
1403 -1 -- never invert brightness
1404 0 -- machine default
1405 1 -- force brightness inversion
1408 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1410 ide-core.nodma= [HW] (E)IDE subsystem
1411 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1412 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1413 .cdrom .chs .ignore_cable are additional options
1414 See Documentation/ide/ide.txt.
1416 ide-generic.probe-mask= [HW] (E)IDE subsystem
1418 Probe mask for legacy ISA IDE ports. Depending on
1419 platform up to 6 ports are supported, enabled by
1420 setting corresponding bits in the mask to 1. The
1421 default value is 0x0, which has a special meaning.
1422 On systems that have PCI, it triggers scanning the
1423 PCI bus for the first and the second port, which
1424 are then probed. On systems without PCI the value
1425 of 0x0 enables probing the two first ports as if it
1428 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1429 Claim all unknown PCI IDE storage controllers.
1432 Format: idle=poll, idle=halt, idle=nomwait
1433 Poll forces a polling idle loop that can slightly
1434 improve the performance of waking up a idle CPU, but
1435 will use a lot of power and make the system run hot.
1437 idle=halt: Halt is forced to be used for CPU idle.
1438 In such case C2/C3 won't be used again.
1439 idle=nomwait: Disable mwait for CPU C-states
1441 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1442 Format: { strict | legacy | 2008 | relaxed }
1445 Choose which programs will be accepted for execution
1446 based on the IEEE 754 NaN encoding(s) supported by
1447 the FPU and the NaN encoding requested with the value
1448 of an ELF file header flag individually set by each
1449 binary. Hardware implementations are permitted to
1450 support either or both of the legacy and the 2008 NaN
1453 Available settings are as follows:
1454 strict accept binaries that request a NaN encoding
1455 supported by the FPU
1456 legacy only accept legacy-NaN binaries, if supported
1458 2008 only accept 2008-NaN binaries, if supported
1460 relaxed accept any binaries regardless of whether
1461 supported by the FPU
1463 The FPU emulator is always able to support both NaN
1464 encodings, so if no FPU hardware is present or it has
1465 been disabled with 'nofpu', then the settings of
1466 'legacy' and '2008' strap the emulator accordingly,
1467 'relaxed' straps the emulator for both legacy-NaN and
1468 2008-NaN, whereas 'strict' enables legacy-NaN only on
1469 legacy processors and both NaN encodings on MIPS32 or
1472 The setting for ABS.fmt/NEG.fmt instruction execution
1473 mode generally follows that for the NaN encoding,
1474 except where unsupported by hardware.
1476 ignore_loglevel [KNL]
1477 Ignore loglevel setting - this will print /all/
1478 kernel messages to the console. Useful for debugging.
1479 We also add it as printk module parameter, so users
1480 could change it dynamically, usually by
1481 /sys/module/printk/parameters/ignore_loglevel.
1484 Ignore RLIMIT_DATA setting for data mappings,
1485 print warning at first misuse. Can be changed via
1486 /sys/module/kernel/parameters/ignore_rlimit_data.
1488 ihash_entries= [KNL]
1489 Set number of hash buckets for inode cache.
1491 ima_appraise= [IMA] appraise integrity measurements
1492 Format: { "off" | "enforce" | "fix" | "log" }
1495 ima_appraise_tcb [IMA]
1496 The builtin appraise policy appraises all files
1499 ima_canonical_fmt [IMA]
1500 Use the canonical format for the binary runtime
1501 measurements, instead of host native format.
1504 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1508 The list of supported hash algorithms is defined
1509 in crypto/hash_info.h.
1512 The builtin policies to load during IMA setup.
1513 Format: "tcb | appraise_tcb | secure_boot"
1515 The "tcb" policy measures all programs exec'd, files
1516 mmap'd for exec, and all files opened with the read
1517 mode bit set by either the effective uid (euid=0) or
1520 The "appraise_tcb" policy appraises the integrity of
1521 all files owned by root. (This is the equivalent
1522 of ima_appraise_tcb.)
1524 The "secure_boot" policy appraises the integrity
1525 of files (eg. kexec kernel image, kernel modules,
1526 firmware, policy, etc) based on file signatures.
1528 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1529 Load a policy which meets the needs of the Trusted
1530 Computing Base. This means IMA will measure all
1531 programs exec'd, files mmap'd for exec, and all files
1532 opened for read by uid=0.
1535 Select one of defined IMA measurements template formats.
1536 Formats: { "ima" | "ima-ng" | "ima-sig" }
1540 [IMA] Define a custom template format.
1541 Format: { "field1|...|fieldN" }
1543 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1544 Format: <min_file_size>
1545 Set the minimal file size for using asynchronous hash.
1546 If left unspecified, ahash usage is disabled.
1548 ahash performance varies for different data sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve the best performance for a particular HW.
1552 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1554 Set hashing buffer size. Default: 4k.
1556 ahash performance varies for different chunk sizes on
1557 different crypto accelerators. This option can be used
1558 to achieve best performance for particular HW.
1562 Run specified binary instead of /sbin/init as init
1565 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1566 for working out where the kernel is dying during
1569 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1570 initcall functions. Useful for debugging built-in
1571 modules and initcalls.
1573 initrd= [BOOT] Specify the location of the initial ramdisk
1575 init_pkru= [x86] Specify the default memory protection keys rights
1576 register contents for all processes. 0x55555554 by
1577 default (disallow access to all but pkey 0). Can
1578 override in debugfs after boot.
1580 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1583 int_pln_enable [x86] Enable power limit notification interrupt
1585 integrity_audit=[IMA]
1586 Format: { "0" | "1" }
1587 0 -- basic integrity auditing messages. (Default)
1588 1 -- additional integrity auditing messages.
1590 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1592 Enable intel iommu driver.
1594 Disable intel iommu driver.
1595 igfx_off [Default Off]
1596 By default, gfx is mapped as normal device. If a gfx
1597 device has a dedicated DMAR unit, the DMAR unit is
1598 bypassed by not enabling DMAR with this option. In
1599 this case, gfx device will use physical address for
1602 With this option iommu will not optimize to look
1603 for io virtual address below 32-bit forcing dual
1604 address cycle on pci bus for cards supporting greater
1605 than 32-bit addressing. The default is to look
1606 for translation below 32-bit and if not available
1607 then look in the higher range.
1608 strict [Default Off]
1609 With this option on every unmap_single operation will
1610 result in a hardware IOTLB flush operation as opposed
1611 to batching them for performance.
1612 sp_off [Default Off]
1613 By default, super page will be supported if Intel IOMMU
1614 has the capability. With this option, super page will
1616 ecs_off [Default Off]
1617 By default, extended context tables will be supported if
1618 the hardware advertises that it has support both for the
1619 extended tables themselves, and also PASID support. With
1620 this option set, extended tables will not be used even
1621 on hardware which claims to support them.
1622 tboot_noforce [Default Off]
1623 Do not force the Intel IOMMU enabled under tboot.
1624 By default, tboot will force Intel IOMMU on, which
1625 could harm performance of some high-throughput
1626 devices like 40GBit network cards, even if identity
1628 Note that using this option lowers the security
1629 provided by tboot because it makes the system
1630 vulnerable to DMA attacks.
1632 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1633 0 disables intel_idle and fall back on acpi_idle.
1634 1 to 9 specify maximum depth of C-state.
1638 Do not enable intel_pstate as the default
1639 scaling driver for the supported processors
1641 Use intel_pstate as a scaling driver, but configure it
1642 to work with generic cpufreq governors (instead of
1643 enabling its internal governor). This mode cannot be
1644 used along with the hardware-managed P-states (HWP)
1647 Enable intel_pstate on systems that prohibit it by default
1648 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1649 instead of acpi-cpufreq may disable platform features, such
1650 as thermal controls and power capping, that rely on ACPI
1651 P-States information being indicated to OSPM and therefore
1652 should be used with caution. This option does not work with
1653 processors that aren't supported by the intel_pstate driver
1654 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1656 Do not enable hardware P state control (HWP)
1659 Only load intel_pstate on systems which support
1660 hardware P state control (HWP) if available.
1662 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1663 Description Table, specifies preferred power management
1664 profile as "Enterprise Server" or "Performance Server",
1665 then this feature is turned on by default.
1667 Allow per-logical-CPU P-State performance control limits using
1668 cpufreq sysfs interface
1670 intremap= [X86-64, Intel-IOMMU]
1671 on enable Interrupt Remapping (default)
1672 off disable Interrupt Remapping
1673 nosid disable Source ID checking
1675 BIOS x2APIC opt-out request will be ignored
1676 nopost disable Interrupt Posting
1678 iomem= Disable strict checking of access to MMIO memory
1679 strict regions from userspace.
1694 nobypass [PPC/POWERNV]
1695 Disable IOMMU bypass, using IOMMU for PCI devices.
1697 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1698 Format: { "0" | "1" }
1700 Request that DMA unmap operations use deferred
1701 invalidation of hardware TLBs, for increased
1702 throughput at the cost of reduced device isolation.
1703 Will fall back to strict mode if not supported by
1704 the relevant IOMMU driver.
1705 1 - Strict mode (default).
1706 DMA unmap operations invalidate IOMMU hardware TLBs
1710 [ARM64] Configure DMA to bypass the IOMMU by default.
1711 Format: { "0" | "1" }
1712 0 - Use IOMMU translation for DMA.
1713 1 - Bypass the IOMMU for DMA.
1714 unset - Use IOMMU translation for DMA.
1716 io7= [HW] IO7 for Marvel based alpha systems
1717 See comment before marvel_specify_io7 in
1718 arch/alpha/kernel/core_marvel.c.
1720 io_delay= [X86] I/O delay method
1722 Standard port 0x80 based delay
1724 Alternate port 0xed based delay (needed on some systems)
1726 Simple two microseconds delay
1731 See Documentation/filesystems/nfs/nfsroot.txt.
1733 irqaffinity= [SMP] Set the default irq affinity mask
1734 The argument is a cpu list, as described above.
1736 irqchip.gicv2_force_probe=
1739 Force the kernel to look for the second 4kB page
1740 of a GICv2 controller even if the memory range
1741 exposed by the device tree is too small.
1744 When an interrupt is not handled search all handlers
1745 for it. Intended to get systems with badly broken
1749 When an interrupt is not handled search all handlers
1750 for it. Also check all handlers each timer
1751 interrupt. Intended to get systems with badly broken
1755 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1757 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1758 [Deprecated - use cpusets instead]
1759 Format: [flag-list,]<cpu-list>
1761 Specify one or more CPUs to isolate from disturbances
1762 specified in the flag list (default: domain):
1765 Disable the tick when a single task runs.
1767 Isolate from the general SMP balancing and scheduling
1768 algorithms. Note that performing domain isolation this way
1769 is irreversible: it's not possible to bring back a CPU to
1770 the domains once isolated through isolcpus. It's strongly
1771 advised to use cpusets instead to disable scheduler load
1772 balancing through the "cpuset.sched_load_balance" file.
1773 It offers a much more flexible interface where CPUs can
1774 move in and out of an isolated set anytime.
1776 You can move a process onto or off an "isolated" CPU via
1777 the CPU affinity syscalls or cpuset.
1778 <cpu number> begins at 0 and the maximum value is
1779 "number of CPUs in system - 1".
1781 The format of <cpu-list> is described above.
1787 ivrs_ioapic [HW,X86_64]
1788 Provide an override to the IOAPIC-ID<->DEVICE-ID
1789 mapping provided in the IVRS ACPI table. For
1790 example, to map IOAPIC-ID decimal 10 to
1791 PCI device 00:14.0 write the parameter as:
1792 ivrs_ioapic[10]=00:14.0
1794 ivrs_hpet [HW,X86_64]
1795 Provide an override to the HPET-ID<->DEVICE-ID
1796 mapping provided in the IVRS ACPI table. For
1797 example, to map HPET-ID decimal 0 to
1798 PCI device 00:14.0 write the parameter as:
1799 ivrs_hpet[0]=00:14.0
1801 ivrs_acpihid [HW,X86_64]
1802 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1803 mapping provided in the IVRS ACPI table. For
1804 example, to map UART-HID:UID AMD0020:0 to
1805 PCI device 00:14.5 write the parameter as:
1806 ivrs_acpihid[00:14.5]=AMD0020:0
1808 js= [HW,JOY] Analog joystick
1809 See Documentation/input/joydev/joystick.rst.
1812 When CONFIG_RANDOMIZE_BASE is set, this disables
1813 kernel and module base offset ASLR (Address Space
1814 Layout Randomization).
1817 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1818 report on every invalid memory access. Without this
1819 parameter KASAN will print report only for the first
1824 kernelcore= [KNL,X86,IA-64,PPC]
1825 Format: nn[KMGTPE] | "mirror"
1827 specifies the amount of memory usable by the kernel
1828 for non-movable allocations. The requested amount is
1829 spread evenly throughout all nodes in the system. The
1830 remaining memory in each node is used for Movable
1831 pages. In the event, a node is too small to have both
1832 kernelcore and Movable pages, kernelcore pages will
1833 take priority and other nodes will have a larger number
1834 of Movable pages. The Movable zone is used for the
1835 allocation of pages that may be reclaimed or moved
1836 by the page migration subsystem. This means that
1837 HugeTLB pages may not be allocated from this zone.
1838 Note that allocations like PTEs-from-HighMem still
1839 use the HighMem zone if it exists, and the Normal
1840 zone if it does not.
1842 Instead of specifying the amount of memory (nn[KMGTPE]),
1843 you can specify "mirror" option. In case "mirror"
1844 option is specified, mirrored (reliable) memory is used
1845 for non-movable allocations and remaining memory is used
1846 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1847 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1850 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1851 Format: <Controller#>[,poll interval]
1852 The controller # is the number of the ehci usb debug
1853 port as it is probed via PCI. The poll interval is
1854 optional and is the number seconds in between
1855 each poll cycle to the debug port in case you need
1856 the functionality for interrupting the kernel with
1857 gdb or control-c on the dbgp connection. When
1858 not using this parameter you use sysrq-g to break into
1859 the kernel debugger.
1861 kgdboc= [KGDB,HW] kgdb over consoles.
1862 Requires a tty driver that supports console polling,
1863 or a supported polling keyboard driver (non-usb).
1864 Serial only format: <serial_device>[,baud]
1865 keyboard only format: kbd
1866 keyboard and serial format: kbd,<serial_device>[,baud]
1867 Optional Kernel mode setting:
1868 kms, kbd format: kms,kbd
1869 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1871 kgdbwait [KGDB] Stop kernel execution and enter the
1872 kernel debugger at the earliest opportunity.
1874 kmac= [MIPS] korina ethernet MAC address.
1875 Configure the RouterBoard 532 series on-chip
1876 Ethernet adapter MAC address.
1878 kmemleak= [KNL] Boot-time kmemleak enable/disable
1879 Valid arguments: on, off
1881 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1884 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1885 Default is 0 (don't ignore, but inject #GP)
1887 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1891 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1892 Default is 1 (enabled)
1894 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1896 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1898 kvm-arm.vgic_v3_group0_trap=
1899 [KVM,ARM] Trap guest accesses to GICv3 group-0
1902 kvm-arm.vgic_v3_group1_trap=
1903 [KVM,ARM] Trap guest accesses to GICv3 group-1
1906 kvm-arm.vgic_v3_common_trap=
1907 [KVM,ARM] Trap guest accesses to GICv3 common
1910 kvm-arm.vgic_v4_enable=
1911 [KVM,ARM] Allow use of GICv4 for direct injection of
1914 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1915 (virtualized MMU) support on capable Intel chips.
1916 Default is 1 (enabled)
1918 kvm-intel.emulate_invalid_guest_state=
1919 [KVM,Intel] Enable emulation of invalid guest states
1920 Default is 0 (disabled)
1922 kvm-intel.flexpriority=
1923 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1924 Default is 1 (enabled)
1927 [KVM,Intel] Enable VMX nesting (nVMX).
1928 Default is 0 (disabled)
1930 kvm-intel.unrestricted_guest=
1931 [KVM,Intel] Disable unrestricted guest feature
1932 (virtualized real and unpaged mode) on capable
1933 Intel chips. Default is 1 (enabled)
1935 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1938 Valid arguments: never, cond, always
1940 always: L1D cache flush on every VMENTER.
1941 cond: Flush L1D on VMENTER only when the code between
1942 VMEXIT and VMENTER can leak host memory.
1943 never: Disables the mitigation
1945 Default is cond (do L1 cache flush in specific instances)
1947 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1948 feature (tagged TLBs) on capable Intel chips.
1949 Default is 1 (enabled)
1951 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1954 The kernel PTE inversion protection is unconditionally
1955 enabled and cannot be disabled.
1958 Provides all available mitigations for the
1959 L1TF vulnerability. Disables SMT and
1960 enables all mitigations in the
1961 hypervisors, i.e. unconditional L1D flush.
1963 SMT control and L1D flush control via the
1964 sysfs interface is still possible after
1965 boot. Hypervisors will issue a warning
1966 when the first VM is started in a
1967 potentially insecure configuration,
1968 i.e. SMT enabled or L1D flush disabled.
1971 Same as 'full', but disables SMT and L1D
1972 flush runtime control. Implies the
1973 'nosmt=force' command line option.
1974 (i.e. sysfs control of SMT is disabled.)
1977 Leaves SMT enabled and enables the default
1978 hypervisor mitigation, i.e. conditional
1981 SMT control and L1D flush control via the
1982 sysfs interface is still possible after
1983 boot. Hypervisors will issue a warning
1984 when the first VM is started in a
1985 potentially insecure configuration,
1986 i.e. SMT enabled or L1D flush disabled.
1990 Disables SMT and enables the default
1991 hypervisor mitigation.
1993 SMT control and L1D flush control via the
1994 sysfs interface is still possible after
1995 boot. Hypervisors will issue a warning
1996 when the first VM is started in a
1997 potentially insecure configuration,
1998 i.e. SMT enabled or L1D flush disabled.
2001 Same as 'flush', but hypervisors will not
2002 warn when a VM is started in a potentially
2003 insecure configuration.
2006 Disables hypervisor mitigations and doesn't
2011 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2017 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2020 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2021 value for LAPIC timer one-shot implementation. Default
2022 back to the programmable timer unit in the LAPIC.
2024 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2027 libata.dma= [LIBATA] DMA control
2028 libata.dma=0 Disable all PATA and SATA DMA
2029 libata.dma=1 PATA and SATA Disk DMA only
2030 libata.dma=2 ATAPI (CDROM) DMA only
2031 libata.dma=4 Compact Flash DMA only
2032 Combinations also work, so libata.dma=3 enables DMA
2033 for disks and CDROMs, but not CFs.
2035 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2036 libata.ignore_hpa=0 keep BIOS limits (default)
2037 libata.ignore_hpa=1 ignore limits, using full disk
2039 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2043 libata.force= [LIBATA] Force configurations. The format is comma
2044 separated list of "[ID:]VAL" where ID is
2045 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2046 matching port, link or device. Basically, it matches
2047 the ATA ID string printed on console by libata. If
2048 the whole ID part is omitted, the last PORT and DEVICE
2049 values are used. If ID hasn't been specified yet, the
2050 configuration applies to all ports, links and devices.
2052 If only DEVICE is omitted, the parameter applies to
2053 the port and all links and devices behind it. DEVICE
2054 number of 0 either selects the first device or the
2055 first fan-out link behind PMP device. It does not
2056 select the host link. DEVICE number of 15 selects the
2057 host link and device attached to it.
2059 The VAL specifies the configuration to force. As long
2060 as there's no ambiguity shortcut notation is allowed.
2061 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2062 The following configurations can be forced.
2064 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2065 Any ID with matching PORT is used.
2067 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2069 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2070 udma[/][16,25,33,44,66,100,133] notation is also
2073 * [no]ncq: Turn on or off NCQ.
2075 * [no]ncqtrim: Turn off queued DSM TRIM.
2077 * nohrst, nosrst, norst: suppress hard, soft
2080 * rstonce: only attempt one reset during
2081 hot-unplug link recovery
2083 * dump_id: dump IDENTIFY data.
2085 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2087 * disable: Disable this device.
2089 If there are multiple matching configurations changing
2090 the same attribute, the last one is used.
2092 memblock=debug [KNL] Enable memblock debug messages.
2094 load_ramdisk= [RAM] List of ramdisks to load from floppy
2095 See Documentation/blockdev/ramdisk.txt.
2097 lockd.nlm_grace_period=P [NFS] Assign grace period.
2100 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2103 lockd.nlm_timeout=T [NFS] Assign timeout value.
2106 lockd.nlm_udpport=M [NFS] Assign UDP port.
2109 locktorture.nreaders_stress= [KNL]
2110 Set the number of locking read-acquisition kthreads.
2111 Defaults to being automatically set based on the
2112 number of online CPUs.
2114 locktorture.nwriters_stress= [KNL]
2115 Set the number of locking write-acquisition kthreads.
2117 locktorture.onoff_holdoff= [KNL]
2118 Set time (s) after boot for CPU-hotplug testing.
2120 locktorture.onoff_interval= [KNL]
2121 Set time (s) between CPU-hotplug operations, or
2122 zero to disable CPU-hotplug testing.
2124 locktorture.shuffle_interval= [KNL]
2125 Set task-shuffle interval (jiffies). Shuffling
2126 tasks allows some CPUs to go into dyntick-idle
2127 mode during the locktorture test.
2129 locktorture.shutdown_secs= [KNL]
2130 Set time (s) after boot system shutdown. This
2131 is useful for hands-off automated testing.
2133 locktorture.stat_interval= [KNL]
2134 Time (s) between statistics printk()s.
2136 locktorture.stutter= [KNL]
2137 Time (s) to stutter testing, for example,
2138 specifying five seconds causes the test to run for
2139 five seconds, wait for five seconds, and so on.
2140 This tests the locking primitive's ability to
2141 transition abruptly to and from idle.
2143 locktorture.torture_runnable= [BOOT]
2144 Start locktorture running at boot time.
2146 locktorture.torture_type= [KNL]
2147 Specify the locking implementation to test.
2149 locktorture.verbose= [KNL]
2150 Enable additional printk() statements.
2152 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2155 loglevel= All Kernel Messages with a loglevel smaller than the
2156 console loglevel will be printed to the console. It can
2157 also be changed with klogd or other programs. The
2158 loglevels are defined as follows:
2160 0 (KERN_EMERG) system is unusable
2161 1 (KERN_ALERT) action must be taken immediately
2162 2 (KERN_CRIT) critical conditions
2163 3 (KERN_ERR) error conditions
2164 4 (KERN_WARNING) warning conditions
2165 5 (KERN_NOTICE) normal but significant condition
2166 6 (KERN_INFO) informational
2167 7 (KERN_DEBUG) debug-level messages
2169 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2170 in bytes. n must be a power of two and greater
2171 than the minimal size. The minimal size is defined
2172 by LOG_BUF_SHIFT kernel config parameter. There is
2173 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2174 that allows to increase the default size depending on
2175 the number of CPUs. See init/Kconfig for more details.
2177 logo.nologo [FB] Disables display of the built-in Linux logo.
2178 This may be used to provide more screen space for
2179 kernel log messages and is useful when debugging
2180 kernel boot problems.
2182 lp=0 [LP] Specify parallel ports to use, e.g,
2183 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2184 lp=reset first parallel port). 'lp=0' disables the
2185 lp=auto printer driver. 'lp=reset' (which can be
2186 specified in addition to the ports) causes
2187 attached printers to be reset. Using
2188 lp=port1,port2,... specifies the parallel ports
2189 to associate lp devices with, starting with
2190 lp0. A port specification may be 'none' to skip
2191 that lp device, or a parport name such as
2192 'parport0'. Specifying 'lp=auto' instead of a
2193 port specification list means that device IDs
2194 from each port should be examined, to see if
2195 an IEEE 1284-compliant printer is attached; if
2196 so, the driver will manage that printer.
2197 See also header of drivers/char/lp.c.
2200 Sets loops_per_jiffy to given constant, thus avoiding
2201 time-consuming boot-time autodetection (up to 250 ms per
2202 CPU). 0 enables autodetection (default). To determine
2203 the correct value for your kernel, boot with normal
2204 autodetection and see what value is printed. Note that
2205 on SMP systems the preset will be applied to all CPUs,
2206 which is likely to cause problems if your CPUs need
2207 significantly divergent settings. An incorrect value
2208 will cause delays in the kernel to be wrong, leading to
2209 unpredictable I/O errors and other breakage. Although
2210 unlikely, in the extreme case this might damage your
2214 Format: <io>,<irq>,<dma>
2216 machvec= [IA-64] Force the use of a particular machine-vector
2217 (machvec) in a generic kernel.
2218 Example: machvec=hpzx1_swiotlb
2220 machtype= [Loongson] Share the same kernel image file between different
2222 Example: machtype=lemote-yeeloong-2f-7inch
2224 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2225 than or equal to this physical address is ignored.
2227 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2228 will bring up during bootup. maxcpus=n : n >= 0 limits
2229 the kernel to bring up 'n' processors. Surely after
2230 bootup you can bring up the other plugged cpu by executing
2231 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2232 only takes effect during system bootup.
2233 While n=0 is a special case, it is equivalent to "nosmp",
2234 which also disables the IO APIC.
2236 max_loop= [LOOP] The number of loop block devices that get
2237 (loop.max_loop) unconditionally pre-created at init time. The default
2238 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2239 of statically allocating a predefined number, loop
2240 devices can be requested on-demand with the
2241 /dev/loop-control interface.
2243 mce [X86-32] Machine Check Exception
2245 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2247 md= [HW] RAID subsystems devices and level
2248 See Documentation/admin-guide/md.rst.
2251 Format: <first>,<last>
2252 Specifies range of consoles to be captured by the MDA.
2255 Control mitigation for the Micro-architectural Data
2256 Sampling (MDS) vulnerability.
2258 Certain CPUs are vulnerable to an exploit against CPU
2259 internal buffers which can forward information to a
2260 disclosure gadget under certain conditions.
2262 In vulnerable processors, the speculatively
2263 forwarded data can be used in a cache side channel
2264 attack, to access data to which the attacker does
2265 not have direct access.
2267 This parameter controls the MDS mitigation. The
2270 full - Enable MDS mitigation on vulnerable CPUs
2271 full,nosmt - Enable MDS mitigation and disable
2272 SMT on vulnerable CPUs
2273 off - Unconditionally disable MDS mitigation
2275 Not specifying this option is equivalent to
2278 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2280 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2281 Amount of memory to be used when the kernel is not able
2282 to see the whole system memory or for test.
2283 [X86] Work as limiting max address. Use together
2284 with memmap= to avoid physical address space collisions.
2285 Without memmap= PCI devices could be placed at addresses
2286 belonging to unused RAM.
2288 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2292 [KNL,SH] Allow user to override the default size for
2293 per-device physically contiguous DMA buffers.
2295 memhp_default_state=online/offline
2296 [KNL] Set the initial state for the memory hotplug
2297 onlining policy. If not specified, the default value is
2298 set according to the
2299 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2301 See Documentation/memory-hotplug.txt.
2303 memmap=exactmap [KNL,X86] Enable setting of an exact
2304 E820 memory map, as specified by the user.
2305 Such memmap=exactmap lines can be constructed based on
2306 BIOS output or other requirements. See the memmap=nn@ss
2309 memmap=nn[KMG]@ss[KMG]
2310 [KNL] Force usage of a specific region of memory.
2311 Region of memory to be used is from ss to ss+nn.
2312 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2313 which limits max address to nn[KMG].
2314 Multiple different regions can be specified,
2317 memmap=100M@2G,100M#3G,1G!1024G
2319 memmap=nn[KMG]#ss[KMG]
2320 [KNL,ACPI] Mark specific memory as ACPI data.
2321 Region of memory to be marked is from ss to ss+nn.
2323 memmap=nn[KMG]$ss[KMG]
2324 [KNL,ACPI] Mark specific memory as reserved.
2325 Region of memory to be reserved is from ss to ss+nn.
2326 Example: Exclude memory from 0x18690000-0x1869ffff
2327 memmap=64K$0x18690000
2329 memmap=0x10000$0x18690000
2330 Some bootloaders may need an escape character before '$',
2331 like Grub2, otherwise '$' and the following number
2334 memmap=nn[KMG]!ss[KMG]
2335 [KNL,X86] Mark specific memory as protected.
2336 Region of memory to be used, from ss to ss+nn.
2337 The memory region may be marked as e820 type 12 (0xc)
2338 and is NVDIMM or ADR memory.
2340 memory_corruption_check=0/1 [X86]
2341 Some BIOSes seem to corrupt the first 64k of
2342 memory when doing things like suspend/resume.
2343 Setting this option will scan the memory
2344 looking for corruption. Enabling this will
2345 both detect corruption and prevent the kernel
2346 from using the memory being corrupted.
2347 However, its intended as a diagnostic tool; if
2348 repeatable BIOS-originated corruption always
2349 affects the same memory, you can use memmap=
2350 to prevent the kernel from using that memory.
2352 memory_corruption_check_size=size [X86]
2353 By default it checks for corruption in the low
2354 64k, making this memory unavailable for normal
2355 use. Use this parameter to scan for
2356 corruption in more or less memory.
2358 memory_corruption_check_period=seconds [X86]
2359 By default it checks for corruption every 60
2360 seconds. Use this parameter to check at some
2361 other rate. 0 disables periodic checking.
2363 memtest= [KNL,X86,ARM] Enable memtest
2365 default : 0 <disable>
2366 Specifies the number of memtest passes to be
2367 performed. Each pass selects another test
2368 pattern from a given set of patterns. Memtest
2369 fills the memory with this pattern, validates
2370 memory contents and reserves bad memory
2371 regions that are detected.
2373 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2374 Valid arguments: on, off
2375 Default (depends on kernel configuration option):
2376 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2377 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2378 mem_encrypt=on: Activate SME
2379 mem_encrypt=off: Do not activate SME
2381 Refer to Documentation/x86/amd-memory-encryption.txt
2382 for details on when memory encryption can be activated.
2384 mem_sleep_default= [SUSPEND] Default system suspend mode:
2385 s2idle - Suspend-To-Idle
2386 shallow - Power-On Suspend or equivalent (if supported)
2387 deep - Suspend-To-RAM or equivalent (if supported)
2388 See Documentation/admin-guide/pm/sleep-states.rst.
2390 meye.*= [HW] Set MotionEye Camera parameters
2391 See Documentation/media/v4l-drivers/meye.rst.
2393 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2394 Multi-Function General Purpose Timers on AMD Geode
2397 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2398 the BIOS has incorrectly applied a workaround. TinyBIOS
2399 version 0.98 is known to be affected, 0.99 fixes the
2400 problem by letting the user disable the workaround.
2404 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2405 physical address is ignored.
2407 mini2440= [ARM,HW,KNL]
2408 Format:[0..2][b][c][t]
2410 MINI2440 configuration specification:
2411 0 - The attached screen is the 3.5" TFT
2412 1 - The attached screen is the 7" TFT
2413 2 - The VGA Shield is attached (1024x768)
2414 Leaving out the screen size parameter will not load
2415 the TFT driver, and the framebuffer will be left
2417 b - Enable backlight. The TFT backlight pin will be
2418 linked to the kernel VESA blanking code and a GPIO
2419 LED. This parameter is not necessary when using the
2421 c - Enable the s3c camera interface.
2422 t - Reserved for enabling touchscreen support. The
2423 touchscreen support is not enabled in the mainstream
2424 kernel as of 2.6.30, a preliminary port can be found
2425 in the "bleeding edge" mini2440 support kernel at
2426 http://repo.or.cz/w/linux-2.6/mini2440.git
2429 [X86,PPC,S390] Control optional mitigations for CPU
2430 vulnerabilities. This is a set of curated,
2431 arch-independent options, each of which is an
2432 aggregation of existing arch-specific options.
2435 Disable all optional CPU mitigations. This
2436 improves system performance, but it may also
2437 expose users to several CPU vulnerabilities.
2438 Equivalent to: nopti [X86,PPC]
2441 nospectre_v2 [X86,PPC,S390]
2442 spectre_v2_user=off [X86]
2443 spec_store_bypass_disable=off [X86,PPC]
2448 Mitigate all CPU vulnerabilities, but leave SMT
2449 enabled, even if it's vulnerable. This is for
2450 users who don't want to be surprised by SMT
2451 getting disabled across kernel upgrades, or who
2452 have other ways of avoiding SMT-based attacks.
2453 Equivalent to: (default behavior)
2456 Mitigate all CPU vulnerabilities, disabling SMT
2457 if needed. This is for users who always want to
2458 be fully mitigated, even if it means losing SMT.
2459 Equivalent to: l1tf=flush,nosmt [X86]
2460 mds=full,nosmt [X86]
2463 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2464 parameter allows control of the logging verbosity for
2465 the additional memory initialisation checks. A value
2466 of 0 disables mminit logging and a level of 4 will
2467 log everything. Information is printed at KERN_DEBUG
2468 so loglevel=8 may also need to be specified.
2471 [KNL] When CONFIG_MODULE_SIG is set, this means that
2472 modules without (valid) signatures will fail to load.
2473 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2474 is always true, so this option does nothing.
2476 module_blacklist= [KNL] Do not load a comma-separated list of
2477 modules. Useful for debugging problem modules.
2480 [MOUSE] Maximum time between finger touching and
2481 leaving touchpad surface for touch to be considered
2482 a tap and be reported as a left button click (for
2483 touchpads working in absolute mode only).
2485 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2486 reporting absolute coordinates, such as tablets
2487 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2488 reporting absolute coordinates, such as tablets
2490 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2491 is similar to kernelcore except it specifies the
2492 amount of memory used for migratable allocations.
2493 If both kernelcore and movablecore is specified,
2494 then kernelcore will be at *least* the specified
2495 value but may be more. If movablecore on its own
2496 is specified, the administrator must be careful
2497 that the amount of memory usable for all allocations
2500 movable_node [KNL] Boot-time switch to make hotplugable memory
2501 NUMA nodes to be movable. This means that the memory
2502 of such nodes will be usable only for movable
2503 allocations which rules out almost all kernel
2504 allocations. Use with caution!
2506 MTD_Partition= [MTD]
2507 Format: <name>,<region-number>,<size>,<offset>
2509 MTD_Region= [MTD] Format:
2510 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2513 See drivers/mtd/cmdlinepart.c.
2515 multitce=off [PPC] This parameter disables the use of the pSeries
2516 firmware feature for updating multiple TCE entries
2519 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2521 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2523 boundary - index of last SLC block on Flex-OneNAND.
2524 The remaining blocks are configured as MLC blocks.
2525 lock - Configure if Flex-OneNAND boundary should be locked.
2526 Once locked, the boundary cannot be changed.
2527 1 indicates lock status, 0 indicates unlock status.
2530 ARM/S3C2412 JIVE boot control
2532 See arch/arm/mach-s3c2412/mach-jive.c
2534 mtouchusb.raw_coordinates=
2535 [HW] Make the MicroTouch USB driver use raw coordinates
2536 ('y', default) or cooked coordinates ('n')
2538 mtrr_chunk_size=nn[KMG] [X86]
2539 used for mtrr cleanup. It is largest continuous chunk
2540 that could hold holes aka. UC entries.
2542 mtrr_gran_size=nn[KMG] [X86]
2543 Used for mtrr cleanup. It is granularity of mtrr block.
2545 Large value could prevent small alignment from
2548 mtrr_spare_reg_nr=n [X86]
2550 Range: 0,7 : spare reg number
2552 Used for mtrr cleanup. It is spare mtrr entries number.
2553 Set to 2 or more if your graphical card needs more.
2555 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2557 netdev= [NET] Network devices parameters
2558 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2559 Note that mem_start is often overloaded to mean
2560 something different and driver-specific.
2561 This usage is only documented in each driver source
2565 [NETFILTER] Enable connection tracking flow accounting
2566 0 to disable accounting
2567 1 to enable accounting
2570 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2571 See Documentation/filesystems/nfs/nfsroot.txt.
2573 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2574 See Documentation/filesystems/nfs/nfsroot.txt.
2576 nfsrootdebug [NFS] enable nfsroot debugging messages.
2577 See Documentation/filesystems/nfs/nfsroot.txt.
2579 nfs.callback_nr_threads=
2580 [NFSv4] set the total number of threads that the
2581 NFS client will assign to service NFSv4 callback
2584 nfs.callback_tcpport=
2585 [NFS] set the TCP port on which the NFSv4 callback
2586 channel should listen.
2589 [NFS] sets the pathname to the program which is used
2590 to update the NFS client cache entries.
2592 nfs.cache_getent_timeout=
2593 [NFS] sets the timeout after which an attempt to
2594 update a cache entry is deemed to have failed.
2596 nfs.idmap_cache_timeout=
2597 [NFS] set the maximum lifetime for idmapper cache
2601 [NFS] enable 64-bit inode numbers.
2602 If zero, the NFS client will fake up a 32-bit inode
2603 number for the readdir() and stat() syscalls instead
2604 of returning the full 64-bit number.
2605 The default is to return 64-bit inode numbers.
2607 nfs.max_session_cb_slots=
2608 [NFSv4.1] Sets the maximum number of session
2609 slots the client will assign to the callback
2610 channel. This determines the maximum number of
2611 callbacks the client will process in parallel for
2612 a particular server.
2614 nfs.max_session_slots=
2615 [NFSv4.1] Sets the maximum number of session slots
2616 the client will attempt to negotiate with the server.
2617 This limits the number of simultaneous RPC requests
2618 that the client can send to the NFSv4.1 server.
2619 Note that there is little point in setting this
2620 value higher than the max_tcp_slot_table_limit.
2622 nfs.nfs4_disable_idmapping=
2623 [NFSv4] When set to the default of '1', this option
2624 ensures that both the RPC level authentication
2625 scheme and the NFS level operations agree to use
2626 numeric uids/gids if the mount is using the
2627 'sec=sys' security flavour. In effect it is
2628 disabling idmapping, which can make migration from
2629 legacy NFSv2/v3 systems to NFSv4 easier.
2630 Servers that do not support this mode of operation
2631 will be autodetected by the client, and it will fall
2632 back to using the idmapper.
2633 To turn off this behaviour, set the value to '0'.
2635 [NFS4] Specify an additional fixed unique ident-
2636 ification string that NFSv4 clients can insert into
2637 their nfs_client_id4 string. This is typically a
2638 UUID that is generated at system install time.
2640 nfs.send_implementation_id =
2641 [NFSv4.1] Send client implementation identification
2642 information in exchange_id requests.
2643 If zero, no implementation identification information
2645 The default is to send the implementation identification
2648 nfs.recover_lost_locks =
2649 [NFSv4] Attempt to recover locks that were lost due
2650 to a lease timeout on the server. Please note that
2651 doing this risks data corruption, since there are
2652 no guarantees that the file will remain unchanged
2653 after the locks are lost.
2654 If you want to enable the kernel legacy behaviour of
2655 attempting to recover these locks, then set this
2657 The default parameter value of '0' causes the kernel
2658 not to attempt recovery of lost locks.
2660 nfs4.layoutstats_timer =
2661 [NFSv4.2] Change the rate at which the kernel sends
2662 layoutstats to the pNFS metadata server.
2664 Setting this to value to 0 causes the kernel to use
2665 whatever value is the default set by the layout
2666 driver. A non-zero value sets the minimum interval
2667 in seconds between layoutstats transmissions.
2669 nfsd.nfs4_disable_idmapping=
2670 [NFSv4] When set to the default of '1', the NFSv4
2671 server will return only numeric uids and gids to
2672 clients using auth_sys, and will accept numeric uids
2673 and gids from such clients. This is intended to ease
2674 migration from NFSv2/v3.
2676 nmi_debug= [KNL,SH] Specify one or more actions to take
2677 when a NMI is triggered.
2678 Format: [state][,regs][,debounce][,die]
2680 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2681 Format: [panic,][nopanic,][num]
2683 0 - turn hardlockup detector in nmi_watchdog off
2684 1 - turn hardlockup detector in nmi_watchdog on
2685 When panic is specified, panic when an NMI watchdog
2686 timeout occurs (or 'nopanic' to override the opposite
2687 default). To disable both hard and soft lockup detectors,
2688 please see 'nowatchdog'.
2689 This is useful when you use a panic=... timeout and
2690 need the box quickly up again.
2692 netpoll.carrier_timeout=
2693 [NET] Specifies amount of time (in seconds) that
2694 netpoll should wait for a carrier. By default netpoll
2697 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2698 emulation library even if a 387 maths coprocessor
2702 [HW] Never suspend the console
2703 Disable suspending of consoles during suspend and
2704 hibernate operations. Once disabled, debugging
2705 messages can reach various consoles while the rest
2706 of the system is being put to sleep (ie, while
2707 debugging driver suspend/resume hooks). This may
2708 not work reliably with all consoles, but is known
2709 to work with serial and VGA consoles.
2710 To facilitate more flexible debugging, we also add
2711 console_suspend, a printk module parameter to control
2712 it. Users could use console_suspend (usually
2713 /sys/module/printk/parameters/console_suspend) to
2714 turn on/off it dynamically.
2716 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2717 caches in the slab allocator. Saves per-node memory,
2718 but will impact performance.
2722 noaltinstr [S390] Disables alternative instructions patching
2723 (CPU alternatives feature).
2725 noapic [SMP,APIC] Tells the kernel to not make use of any
2726 IOAPICs that may be present in the system.
2728 noautogroup Disable scheduler automatic task group creation.
2730 nobats [PPC] Do not use BATs for mapping kernel lowmem
2731 on "Classic" PPC cores.
2735 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2737 nodelayacct [KNL] Disable per-task delay accounting
2739 nodsp [SH] Disable hardware DSP at boot time.
2741 noefi Disable EFI runtime services support.
2746 On X86-32 available only on PAE configured kernels.
2747 noexec=on: enable non-executable mappings (default)
2748 noexec=off: disable non-executable mappings
2751 Disable SMAP (Supervisor Mode Access Prevention)
2752 even if it is supported by processor.
2755 Disable SMEP (Supervisor Mode Execution Prevention)
2756 even if it is supported by processor.
2759 This affects only 32-bit executables.
2760 noexec32=on: enable non-executable mappings (default)
2761 read doesn't imply executable mappings
2762 noexec32=off: disable non-executable mappings
2763 read implies executable mappings
2765 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2767 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2768 register save and restore. The kernel will only save
2769 legacy floating-point registers on task switch.
2771 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2773 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2774 Equivalent to smt=1.
2776 [KNL,x86] Disable symmetric multithreading (SMT).
2777 nosmt=force: Force disable SMT, cannot be undone
2778 via the sysfs control file.
2780 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2781 (indirect branch prediction) vulnerability. System may
2782 allow data leaks with this option, which is equivalent
2785 nospec_store_bypass_disable
2786 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2788 noxsave [BUGS=X86] Disables x86 extended register state save
2789 and restore using xsave. The kernel will fallback to
2790 enabling legacy floating-point and sse state.
2792 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2793 register states. The kernel will fall back to use
2794 xsave to save the states. By using this parameter,
2795 performance of saving the states is degraded because
2796 xsave doesn't support modified optimization while
2797 xsaveopt supports it on xsaveopt enabled systems.
2799 noxsaves [X86] Disables xsaves and xrstors used in saving and
2800 restoring x86 extended register state in compacted
2801 form of xsave area. The kernel will fall back to use
2802 xsaveopt and xrstor to save and restore the states
2803 in standard form of xsave area. By using this
2804 parameter, xsave area per process might occupy more
2805 memory on xsaves enabled systems.
2807 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2808 wfi(ARM) instruction doesn't work correctly and not to
2809 use it. This is also useful when using JTAG debugger.
2811 no_file_caps Tells the kernel not to honor file capabilities. The
2812 only way then for a file to be executed with privilege
2813 is to be setuid root or executed by root.
2815 nohalt [IA-64] Tells the kernel not to use the power saving
2816 function PAL_HALT_LIGHT when idle. This increases
2817 power-consumption. On the positive side, it reduces
2818 interrupt wake-up latency, which may improve performance
2819 in certain environments such as networked servers or
2822 nohibernate [HIBERNATION] Disable hibernation and resume.
2824 nohz= [KNL] Boottime enable/disable dynamic ticks
2825 Valid arguments: on, off
2828 nohz_full= [KNL,BOOT,SMP,ISOL]
2829 The argument is a cpu list, as described above.
2830 In kernels built with CONFIG_NO_HZ_FULL=y, set
2831 the specified list of CPUs whose tick will be stopped
2832 whenever possible. The boot CPU will be forced outside
2833 the range to maintain the timekeeping. Any CPUs
2834 in this list will have their RCU callbacks offloaded,
2835 just as if they had also been called out in the
2836 rcu_nocbs= boot parameter.
2838 noiotrap [SH] Disables trapped I/O port accesses.
2840 noirqdebug [X86-32] Disables the code which attempts to detect and
2841 disable unhandled interrupt sources.
2843 no_timer_check [X86,APIC] Disables the code which tests for
2844 broken timer IRQ sources.
2846 noisapnp [ISAPNP] Disables ISA PnP code.
2848 noinitrd [RAM] Tells the kernel not to load any configured
2851 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2853 [Deprecated - use intremap=off]
2857 noinvpcid [X86] Disable the INVPCID cpu feature.
2859 nojitter [IA-64] Disables jitter checking for ITC timers.
2861 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2863 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2867 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2868 clock and use the default one.
2870 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2871 steal time is computed, but won't influence scheduler
2874 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2876 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2878 noltlbs [PPC] Do not use large page/tlb entries for kernel
2879 lowmem mapping on PPC40x and PPC8xx
2881 nomca [IA-64] Disable machine check abort handling
2883 nomce [X86-32] Disable Machine Check Exception
2885 nomfgpt [X86-32] Disable Multi-Function General Purpose
2886 Timer usage (for AMD Geode machines).
2888 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2889 shutdown the other cpus. Instead use the REBOOT_VECTOR
2892 nomodule Disable module load
2894 nopat [X86] Disable PAT (page attribute table extension of
2895 pagetables) support.
2897 nopcid [X86-64] Disable the PCID cpu feature.
2899 norandmaps Don't use address space randomization. Equivalent to
2900 echo 0 > /proc/sys/kernel/randomize_va_space
2902 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2903 with UP alternatives
2905 nordrand [X86] Disable kernel use of the RDRAND and
2906 RDSEED instructions even if they are supported
2907 by the processor. RDRAND and RDSEED are still
2908 available to user space applications.
2910 noresume [SWSUSP] Disables resume and restores original swap
2913 no-scroll [VGA] Disables scrollback.
2914 This is required for the Braillex ib80-piezo Braille
2915 reader made by F.H. Papenmeier (Germany).
2919 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2921 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2922 and disable the IO APIC. legacy for "maxcpus=0".
2924 nosoftlockup [KNL] Disable the soft-lockup detector.
2926 nosync [HW,M68K] Disables sync negotiation for all devices.
2928 notsc [BUGS=X86-32] Disable Time Stamp Counter
2930 nowatchdog [KNL] Disable both lockup detectors, i.e.
2931 soft-lockup and NMI watchdog (hard-lockup).
2935 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2937 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2938 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2939 Some features depend on CPU0. Known dependencies are:
2940 1. Resume from suspend/hibernate depends on CPU0.
2941 Suspend/hibernate will fail if CPU0 is offline and you
2942 need to online CPU0 before suspend/hibernate.
2943 2. PIC interrupts also depend on CPU0. CPU0 can't be
2944 removed if a PIC interrupt is detected.
2945 It's said poweroff/reboot may depend on CPU0 on some
2946 machines although I haven't seen such issues so far
2947 after CPU0 is offline on a few tested machines.
2948 If the dependencies are under your control, you can
2949 turn on cpu0_hotplug.
2951 nps_mtm_hs_ctr= [KNL,ARC]
2952 This parameter sets the maximum duration, in
2953 cycles, each HW thread of the CTOP can run
2954 without interruptions, before HW switches it.
2955 The actual maximum duration is 16 times this
2957 Format: integer between 1 and 255
2960 nptcg= [IA-64] Override max number of concurrent global TLB
2961 purges which is reported from either PAL_VM_SUMMARY or
2964 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2965 could support. nr_cpus=n : n >= 1 limits the kernel to
2966 support 'n' processors. It could be larger than the
2967 number of already plugged CPU during bootup, later in
2968 runtime you can physically add extra cpu until it reaches
2969 n. So during boot up some boot time memory for per-cpu
2970 variables need be pre-allocated for later physical cpu
2973 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2975 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2976 Allowed values are enable and disable
2978 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2979 'node', 'default' can be specified
2980 This can be set from sysctl after boot.
2981 See Documentation/sysctl/vm.txt for details.
2983 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2984 See Documentation/debugging-via-ohci1394.txt for more
2987 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2988 Rather than timing out after 20 ms if an EC
2989 command is not properly ACKed, override the length
2990 of the timeout. We have interrupts disabled while
2991 waiting for the ACK, so if this is set too high
2992 interrupts *may* be lost!
2994 omap_mux= [OMAP] Override bootloader pin multiplexing.
2995 Format: <mux_mode0.mode_name=value>...
2996 For example, to override I2C bus2:
2997 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2999 oprofile.timer= [HW]
3000 Use timer interrupt instead of performance counters
3002 oprofile.cpu_type= Force an oprofile cpu type
3003 This might be useful if you have an older oprofile
3004 userland or if you want common events.
3005 Format: { arch_perfmon }
3006 arch_perfmon: [X86] Force use of architectural
3007 perfmon on Intel CPUs instead of the
3008 CPU specific event set.
3009 timer: [X86] Force use of architectural NMI
3010 timer mode (see also oprofile.timer
3011 for generic hr timer mode)
3013 oops=panic Always panic on oopses. Default is to just kill the
3014 process, but there is a small probability of
3015 deadlocking the machine.
3016 This will also cause panics on machine check exceptions.
3017 Useful together with panic=30 to trigger a reboot.
3020 See Documentation/sound/oss/oss-parameters.txt
3022 page_owner= [KNL] Boot-time page_owner enabling option.
3023 Storage of the information about who allocated
3024 each page is disabled in default. With this switch,
3026 on: enable the feature
3028 page_poison= [KNL] Boot-time parameter changing the state of
3029 poisoning on the buddy allocator.
3030 off: turn off poisoning
3031 on: turn on poisoning
3033 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3034 timeout > 0: seconds before rebooting
3035 timeout = 0: wait forever
3036 timeout < 0: reboot immediately
3039 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3042 crash_kexec_post_notifiers
3043 Run kdump after running panic-notifiers and dumping
3044 kmsg. This only for the users who doubt kdump always
3045 succeeds in any situation.
3046 Note that this also increases risks of kdump failure,
3047 because some panic notifiers can make the crashed
3048 kernel more unstable.
3050 parkbd.port= [HW] Parallel port number the keyboard adapter is
3051 connected to, default is 0.
3053 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3054 0 for XT, 1 for AT (default is AT).
3057 parport= [HW,PPT] Specify parallel ports. 0 disables.
3058 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3059 Use 'auto' to force the driver to use any
3060 IRQ/DMA settings detected (the default is to
3061 ignore detected IRQ/DMA settings because of
3062 possible conflicts). You can specify the base
3063 address, IRQ, and DMA settings; IRQ and DMA
3064 should be numbers, or 'auto' (for using detected
3065 settings on that particular port), or 'nofifo'
3066 (to avoid using a FIFO even if it is detected).
3067 Parallel ports are assigned in the order they
3068 are specified on the command line, starting
3071 parport_init_mode= [HW,PPT]
3072 Configure VIA parallel port to operate in
3073 a specific mode. This is necessary on Pegasos
3074 computer where firmware has no options for setting
3075 up parallel port mode and sets it to spp.
3076 Currently this function knows 686a and 8231 chips.
3077 Format: [spp|ps2|epp|ecp|ecpepp]
3080 Halt all CPUs after the first oops has been printed for
3081 the specified number of seconds. This is to be used if
3082 your oopses keep scrolling off the screen.
3087 See header of drivers/block/paride/pcd.c.
3088 See also Documentation/blockdev/paride.txt.
3090 pci=option[,option...] [PCI] various PCI subsystem options:
3091 earlydump [X86] dump PCI config space before the kernel
3093 off [X86] don't probe for the PCI bus
3094 bios [X86-32] force use of PCI BIOS, don't access
3095 the hardware directly. Use this if your machine
3096 has a non-standard PCI host bridge.
3097 nobios [X86-32] disallow use of PCI BIOS, only direct
3098 hardware access methods are allowed. Use this
3099 if you experience crashes upon bootup and you
3100 suspect they are caused by the BIOS.
3101 conf1 [X86] Force use of PCI Configuration Access
3102 Mechanism 1 (config address in IO port 0xCF8,
3103 data in IO port 0xCFC, both 32-bit).
3104 conf2 [X86] Force use of PCI Configuration Access
3105 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3106 the function, IO port 0xCFA, also 8-bit, sets
3107 bus number. The config space is then accessed
3108 through ports 0xC000-0xCFFF).
3109 See http://wiki.osdev.org/PCI for more info
3110 on the configuration access mechanisms.
3111 noaer [PCIE] If the PCIEAER kernel config parameter is
3112 enabled, this kernel boot option can be used to
3113 disable the use of PCIE advanced error reporting.
3114 nodomains [PCI] Disable support for multiple PCI
3115 root domains (aka PCI segments, in ACPI-speak).
3116 nommconf [X86] Disable use of MMCONFIG for PCI
3118 check_enable_amd_mmconf [X86] check for and enable
3119 properly configured MMIO access to PCI
3120 config space on AMD family 10h CPU
3121 nomsi [MSI] If the PCI_MSI kernel config parameter is
3122 enabled, this kernel boot option can be used to
3123 disable the use of MSI interrupts system-wide.
3124 clearmsi [X86] Clears MSI/MSI-X enable bits early in boot
3125 time in order to avoid issues like adapters
3126 screaming irqs and preventing boot progress.
3127 Also, it enforces the PCI Local Bus spec
3128 rule that those bits should be 0 in system reset
3129 events (useful for kexec/kdump cases).
3130 noioapicquirk [APIC] Disable all boot interrupt quirks.
3131 Safety option to keep boot IRQs enabled. This
3132 should never be necessary.
3133 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3134 primary IO-APIC for bridges that cannot disable
3135 boot IRQs. This fixes a source of spurious IRQs
3136 when the system masks IRQs.
3137 noioapicreroute [APIC] Disable workaround that uses the
3138 boot IRQ equivalent of an IRQ that connects to
3139 a chipset where boot IRQs cannot be disabled.
3140 The opposite of ioapicreroute.
3141 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3142 routing table. These calls are known to be buggy
3143 on several machines and they hang the machine
3144 when used, but on other computers it's the only
3145 way to get the interrupt routing table. Try
3146 this option if the kernel is unable to allocate
3147 IRQs or discover secondary PCI buses on your
3149 rom [X86] Assign address space to expansion ROMs.
3150 Use with caution as certain devices share
3151 address decoders between ROMs and other
3153 norom [X86] Do not assign address space to
3154 expansion ROMs that do not already have
3155 BIOS assigned address ranges.
3156 nobar [X86] Do not assign address space to the
3157 BARs that weren't assigned by the BIOS.
3158 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3159 assigned automatically to PCI devices. You can
3160 make the kernel exclude IRQs of your ISA cards
3162 pirqaddr=0xAAAAA [X86] Specify the physical address
3163 of the PIRQ table (normally generated
3164 by the BIOS) if it is outside the
3165 F0000h-100000h range.
3166 lastbus=N [X86] Scan all buses thru bus #N. Can be
3167 useful if the kernel is unable to find your
3168 secondary buses and you want to tell it
3169 explicitly which ones they are.
3170 assign-busses [X86] Always assign all PCI bus
3171 numbers ourselves, overriding
3172 whatever the firmware may have done.
3173 usepirqmask [X86] Honor the possible IRQ mask stored
3174 in the BIOS $PIR table. This is needed on
3175 some systems with broken BIOSes, notably
3176 some HP Pavilion N5400 and Omnibook XE3
3177 notebooks. This will have no effect if ACPI
3178 IRQ routing is enabled.
3179 noacpi [X86] Do not use ACPI for IRQ routing
3180 or for PCI scanning.
3181 use_crs [X86] Use PCI host bridge window information
3182 from ACPI. On BIOSes from 2008 or later, this
3183 is enabled by default. If you need to use this,
3184 please report a bug.
3185 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3186 If you need to use this, please report a bug.
3187 routeirq Do IRQ routing for all PCI devices.
3188 This is normally done in pci_enable_device(),
3189 so this option is a temporary workaround
3190 for broken drivers that don't call it.
3191 skip_isa_align [X86] do not align io start addr, so can
3192 handle more pci cards
3193 noearly [X86] Don't do any early type 1 scanning.
3194 This might help on some broken boards which
3195 machine check when some devices' config space
3196 is read. But various workarounds are disabled
3197 and some IOMMU drivers will not work.
3198 bfsort Sort PCI devices into breadth-first order.
3199 This sorting is done to get a device
3200 order compatible with older (<= 2.4) kernels.
3201 nobfsort Don't sort PCI devices into breadth-first order.
3202 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3203 tuning and use the BIOS-configured MPS defaults.
3204 pcie_bus_safe Set every device's MPS to the largest value
3205 supported by all devices below the root complex.
3206 pcie_bus_perf Set device MPS to the largest allowable MPS
3207 based on its parent bus. Also set MRRS (Max
3208 Read Request Size) to the largest supported
3209 value (no larger than the MPS that the device
3210 or bus can support) for best performance.
3211 pcie_bus_peer2peer Set every device's MPS to 128B, which
3212 every device is guaranteed to support. This
3213 configuration allows peer-to-peer DMA between
3214 any pair of devices, possibly at the cost of
3215 reduced performance. This also guarantees
3216 that hot-added devices will work.
3217 cbiosize=nn[KMG] The fixed amount of bus space which is
3218 reserved for the CardBus bridge's IO window.
3219 The default value is 256 bytes.
3220 cbmemsize=nn[KMG] The fixed amount of bus space which is
3221 reserved for the CardBus bridge's memory
3222 window. The default value is 64 megabytes.
3225 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3226 [<order of align>@]pci:<vendor>:<device>\
3227 [:<subvendor>:<subdevice>][; ...]
3228 Specifies alignment and device to reassign
3229 aligned memory resources.
3230 If <order of align> is not specified,
3231 PAGE_SIZE is used as alignment.
3232 PCI-PCI bridge can be specified, if resource
3233 windows need to be expanded.
3234 To specify the alignment for several
3235 instances of a device, the PCI vendor,
3236 device, subvendor, and subdevice may be
3237 specified, e.g., 4096@pci:8086:9c22:103c:198f
3238 ecrc= Enable/disable PCIe ECRC (transaction layer
3239 end-to-end CRC checking).
3240 bios: Use BIOS/firmware settings. This is the
3244 hpiosize=nn[KMG] The fixed amount of bus space which is
3245 reserved for hotplug bridge's IO window.
3246 Default size is 256 bytes.
3247 hpmemsize=nn[KMG] The fixed amount of bus space which is
3248 reserved for hotplug bridge's memory window.
3249 Default size is 2 megabytes.
3250 hpbussize=nn The minimum amount of additional bus numbers
3251 reserved for buses below a hotplug bridge.
3253 realloc= Enable/disable reallocating PCI bridge resources
3254 if allocations done by BIOS are too small to
3255 accommodate resources required by all child
3257 off: Turn realloc off
3259 realloc same as realloc=on
3260 noari do not use PCIe ARI.
3261 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3262 only look for one device below a PCIe downstream
3264 big_root_window Try to add a big 64bit memory window to the PCIe
3265 root complex on AMD CPUs. Some GFX hardware
3266 can resize a BAR to allow access to all VRAM.
3267 Adding the window is slightly risky (it may
3268 conflict with unreported devices), so this
3271 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3274 force Enable ASPM even on devices that claim not to support it.
3275 WARNING: Forcing ASPM on may cause system lockups.
3277 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3278 nomsi Do not use MSI for PCI Express Native Hotplug (this
3279 makes all PCIe ports use INTx for hotplug services).
3281 pcie_ports= [PCIE] PCIe ports handling:
3282 auto Ask the BIOS whether or not to use native PCIe services
3283 associated with PCIe ports (PME, hot-plug, AER). Use
3284 them only if that is allowed by the BIOS.
3285 native Use native PCIe services associated with PCIe ports
3287 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3290 pcie_port_pm= [PCIE] PCIe port power management handling:
3291 off Disable power management of all PCIe ports
3292 force Forcibly enable power management of all PCIe ports
3294 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3295 nomsi Do not use MSI for native PCIe PME signaling (this makes
3296 all PCIe root ports use INTx for all services).
3298 pcmv= [HW,PCMCIA] BadgePAD 4
3302 Keep all power-domains already enabled by bootloader on,
3303 even if no driver has claimed them. This is useful
3304 for debug and development, but should not be
3305 needed on a platform with proper driver support.
3308 See Documentation/blockdev/paride.txt.
3310 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3313 See arch/parisc/kernel/pdc_chassis.c
3315 percpu_alloc= Select which percpu first chunk allocator to use.
3316 Currently supported values are "embed" and "page".
3317 Archs may support subset or none of the selections.
3318 See comments in mm/percpu.c for details on each
3319 allocator. This parameter is primarily for debugging
3320 and performance comparison.
3323 See Documentation/blockdev/paride.txt.
3326 See Documentation/blockdev/paride.txt.
3328 pirq= [SMP,APIC] Manual mp-table setup
3329 See Documentation/x86/i386/IO-APIC.txt.
3331 plip= [PPT,NET] Parallel port network link
3332 Format: { parport<nr> | timid | 0 }
3333 See also Documentation/admin-guide/parport.rst.
3335 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3336 Override pmtimer IOPort with a hex value.
3340 Enable PNP debug messages (depends on the
3341 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3342 via /sys/module/pnp/parameters/debug. We always show
3343 current resource usage; turning this on also shows
3344 possible settings and some assignment information.
3350 { on | off | curr | res | no-curr | no-res }
3353 [ISAPNP] Exclude IRQs for the autoconfiguration
3356 [ISAPNP] Exclude DMAs for the autoconfiguration
3358 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3359 Ranges are in pairs (I/O port base and size).
3362 [ISAPNP] Exclude memory regions for the
3364 Ranges are in pairs (memory base and size).
3366 ports= [IP_VS_FTP] IPVS ftp helper module
3368 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3370 Format: <port>,<port>....
3372 powersave=off [PPC] This option disables power saving features.
3373 It specifically disables cpuidle and sets the
3374 platform machine description specific power_save
3375 function to NULL. On Idle the CPU just reduces
3378 ppc_strict_facility_enable
3379 [PPC] This option catches any kernel floating point,
3380 Altivec, VSX and SPE outside of regions specifically
3381 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3382 There is some performance impact when enabling this.
3386 Disable Hardware Transactional Memory
3388 print-fatal-signals=
3389 [KNL] debug: print fatal signals
3391 If enabled, warn about various signal handling
3392 related application anomalies: too many signals,
3393 too many POSIX.1 timers, fatal signals causing a
3396 If you hit the warning due to signal overflow,
3397 you might want to try "ulimit -i unlimited".
3401 printk.always_kmsg_dump=
3402 Trigger kmsg_dump for cases other than kernel oops or
3404 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3407 printk.devkmsg={on,off,ratelimit}
3408 Control writing to /dev/kmsg.
3409 on - unlimited logging to /dev/kmsg from userspace
3410 off - logging to /dev/kmsg disabled
3411 ratelimit - ratelimit the logging
3414 printk.time= Show timing data prefixed to each printk message line
3415 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3417 processor.max_cstate= [HW,ACPI]
3418 Limit processor to maximum C-state
3419 max_cstate=9 overrides any DMI blacklist limit.
3421 processor.nocst [HW,ACPI]
3422 Ignore the _CST method to determine C-states,
3423 instead using the legacy FADT method
3425 profile= [KNL] Enable kernel profiling via /proc/profile
3426 Format: [<profiletype>,]<number>
3427 Param: <profiletype>: "schedule", "sleep", or "kvm"
3428 [defaults to kernel profiling]
3429 Param: "schedule" - profile schedule points.
3430 Param: "sleep" - profile D-state sleeping (millisecs).
3431 Requires CONFIG_SCHEDSTATS
3432 Param: "kvm" - profile VM exits.
3433 Param: <number> - step/bucket size as a power of 2 for
3434 statistical time based profiling.
3436 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3438 See Documentation/blockdev/ramdisk.txt.
3440 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3441 probe for; one of (bare|imps|exps|lifebook|any).
3442 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3444 psmouse.resetafter= [HW,MOUSE]
3445 Try to reset the device after so many bad packets
3448 [HW,MOUSE] Set desired mouse resolution, in dpi.
3449 psmouse.smartscroll=
3450 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3451 0 = disabled, 1 = enabled (default).
3453 pstore.backend= Specify the name of the pstore backend to use
3456 See Documentation/blockdev/paride.txt.
3458 pti= [X86_64] Control Page Table Isolation of user and
3459 kernel address spaces. Disabling this feature
3460 removes hardening, but improves performance of
3461 system calls and interrupts.
3463 on - unconditionally enable
3464 off - unconditionally disable
3465 auto - kernel detects whether your CPU model is
3466 vulnerable to issues that PTI mitigates
3468 Not specifying this option is equivalent to pti=auto.
3471 Equivalent to pti=off
3474 [KNL] Number of legacy pty's. Overwrites compiled-in
3477 quiet [KNL] Disable most log messages
3482 See Documentation/admin-guide/md.rst.
3484 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3485 See Documentation/blockdev/ramdisk.txt.
3487 ras=option[,option,...] [KNL] RAS-specific options
3490 Disable the Correctable Errors Collector,
3491 see CONFIG_RAS_CEC help text.
3494 The argument is a cpu list, as described above.
3496 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3497 the specified list of CPUs to be no-callback CPUs.
3498 Invocation of these CPUs' RCU callbacks will
3499 be offloaded to "rcuox/N" kthreads created for
3500 that purpose, where "x" is "b" for RCU-bh, "p"
3501 for RCU-preempt, and "s" for RCU-sched, and "N"
3502 is the CPU number. This reduces OS jitter on the
3503 offloaded CPUs, which can be useful for HPC and
3504 real-time workloads. It can also improve energy
3505 efficiency for asymmetric multiprocessors.
3508 Rather than requiring that offloaded CPUs
3509 (specified by rcu_nocbs= above) explicitly
3510 awaken the corresponding "rcuoN" kthreads,
3511 make these kthreads poll for callbacks.
3512 This improves the real-time response for the
3513 offloaded CPUs by relieving them of the need to
3514 wake up the corresponding kthread, but degrades
3515 energy efficiency by requiring that the kthreads
3516 periodically wake up to do the polling.
3518 rcutree.blimit= [KNL]
3519 Set maximum number of finished RCU callbacks to
3520 process in one batch.
3522 rcutree.dump_tree= [KNL]
3523 Dump the structure of the rcu_node combining tree
3524 out at early boot. This is used for diagnostic
3525 purposes, to verify correct tree setup.
3527 rcutree.gp_cleanup_delay= [KNL]
3528 Set the number of jiffies to delay each step of
3529 RCU grace-period cleanup.
3531 rcutree.gp_init_delay= [KNL]
3532 Set the number of jiffies to delay each step of
3533 RCU grace-period initialization.
3535 rcutree.gp_preinit_delay= [KNL]
3536 Set the number of jiffies to delay each step of
3537 RCU grace-period pre-initialization, that is,
3538 the propagation of recent CPU-hotplug changes up
3539 the rcu_node combining tree.
3541 rcutree.rcu_fanout_exact= [KNL]
3542 Disable autobalancing of the rcu_node combining
3543 tree. This is used by rcutorture, and might
3544 possibly be useful for architectures having high
3545 cache-to-cache transfer latencies.
3547 rcutree.rcu_fanout_leaf= [KNL]
3548 Change the number of CPUs assigned to each
3549 leaf rcu_node structure. Useful for very
3550 large systems, which will choose the value 64,
3551 and for NUMA systems with large remote-access
3552 latencies, which will choose a value aligned
3553 with the appropriate hardware boundaries.
3555 rcutree.jiffies_till_sched_qs= [KNL]
3556 Set required age in jiffies for a
3557 given grace period before RCU starts
3558 soliciting quiescent-state help from
3559 rcu_note_context_switch().
3561 rcutree.jiffies_till_first_fqs= [KNL]
3562 Set delay from grace-period initialization to
3563 first attempt to force quiescent states.
3564 Units are jiffies, minimum value is zero,
3565 and maximum value is HZ.
3567 rcutree.jiffies_till_next_fqs= [KNL]
3568 Set delay between subsequent attempts to force
3569 quiescent states. Units are jiffies, minimum
3570 value is one, and maximum value is HZ.
3572 rcutree.kthread_prio= [KNL,BOOT]
3573 Set the SCHED_FIFO priority of the RCU per-CPU
3574 kthreads (rcuc/N). This value is also used for
3575 the priority of the RCU boost threads (rcub/N)
3576 and for the RCU grace-period kthreads (rcu_bh,
3577 rcu_preempt, and rcu_sched). If RCU_BOOST is
3578 set, valid values are 1-99 and the default is 1
3579 (the least-favored priority). Otherwise, when
3580 RCU_BOOST is not set, valid values are 0-99 and
3581 the default is zero (non-realtime operation).
3583 rcutree.rcu_nocb_leader_stride= [KNL]
3584 Set the number of NOCB kthread groups, which
3585 defaults to the square root of the number of
3586 CPUs. Larger numbers reduces the wakeup overhead
3587 on the per-CPU grace-period kthreads, but increases
3588 that same overhead on each group's leader.
3590 rcutree.qhimark= [KNL]
3591 Set threshold of queued RCU callbacks beyond which
3592 batch limiting is disabled.
3594 rcutree.qlowmark= [KNL]
3595 Set threshold of queued RCU callbacks below which
3596 batch limiting is re-enabled.
3598 rcutree.rcu_idle_gp_delay= [KNL]
3599 Set wakeup interval for idle CPUs that have
3600 RCU callbacks (RCU_FAST_NO_HZ=y).
3602 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3603 Set wakeup interval for idle CPUs that have
3604 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3605 Lazy RCU callbacks are those which RCU can
3606 prove do nothing more than free memory.
3608 rcutree.rcu_kick_kthreads= [KNL]
3609 Cause the grace-period kthread to get an extra
3610 wake_up() if it sleeps three times longer than
3611 it should at force-quiescent-state time.
3612 This wake_up() will be accompanied by a
3613 WARN_ONCE() splat and an ftrace_dump().
3615 rcuperf.gp_async= [KNL]
3616 Measure performance of asynchronous
3617 grace-period primitives such as call_rcu().
3619 rcuperf.gp_async_max= [KNL]
3620 Specify the maximum number of outstanding
3621 callbacks per writer thread. When a writer
3622 thread exceeds this limit, it invokes the
3623 corresponding flavor of rcu_barrier() to allow
3624 previously posted callbacks to drain.
3626 rcuperf.gp_exp= [KNL]
3627 Measure performance of expedited synchronous
3628 grace-period primitives.
3630 rcuperf.holdoff= [KNL]
3631 Set test-start holdoff period. The purpose of
3632 this parameter is to delay the start of the
3633 test until boot completes in order to avoid
3636 rcuperf.nreaders= [KNL]
3637 Set number of RCU readers. The value -1 selects
3638 N, where N is the number of CPUs. A value
3639 "n" less than -1 selects N-n+1, where N is again
3640 the number of CPUs. For example, -2 selects N
3641 (the number of CPUs), -3 selects N+1, and so on.
3642 A value of "n" less than or equal to -N selects
3645 rcuperf.nwriters= [KNL]
3646 Set number of RCU writers. The values operate
3647 the same as for rcuperf.nreaders.
3648 N, where N is the number of CPUs
3650 rcuperf.perf_runnable= [BOOT]
3651 Start rcuperf running at boot time.
3653 rcuperf.perf_type= [KNL]
3654 Specify the RCU implementation to test.
3656 rcuperf.shutdown= [KNL]
3657 Shut the system down after performance tests
3658 complete. This is useful for hands-off automated
3661 rcuperf.verbose= [KNL]
3662 Enable additional printk() statements.
3664 rcuperf.writer_holdoff= [KNL]
3665 Write-side holdoff between grace periods,
3666 in microseconds. The default of zero says
3669 rcutorture.cbflood_inter_holdoff= [KNL]
3670 Set holdoff time (jiffies) between successive
3671 callback-flood tests.
3673 rcutorture.cbflood_intra_holdoff= [KNL]
3674 Set holdoff time (jiffies) between successive
3675 bursts of callbacks within a given callback-flood
3678 rcutorture.cbflood_n_burst= [KNL]
3679 Set the number of bursts making up a given
3680 callback-flood test. Set this to zero to
3681 disable callback-flood testing.
3683 rcutorture.cbflood_n_per_burst= [KNL]
3684 Set the number of callbacks to be registered
3685 in a given burst of a callback-flood test.
3687 rcutorture.fqs_duration= [KNL]
3688 Set duration of force_quiescent_state bursts
3691 rcutorture.fqs_holdoff= [KNL]
3692 Set holdoff time within force_quiescent_state bursts
3695 rcutorture.fqs_stutter= [KNL]
3696 Set wait time between force_quiescent_state bursts
3699 rcutorture.gp_cond= [KNL]
3700 Use conditional/asynchronous update-side
3701 primitives, if available.
3703 rcutorture.gp_exp= [KNL]
3704 Use expedited update-side primitives, if available.
3706 rcutorture.gp_normal= [KNL]
3707 Use normal (non-expedited) asynchronous
3708 update-side primitives, if available.
3710 rcutorture.gp_sync= [KNL]
3711 Use normal (non-expedited) synchronous
3712 update-side primitives, if available. If all
3713 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3714 rcutorture.gp_normal=, and rcutorture.gp_sync=
3715 are zero, rcutorture acts as if is interpreted
3716 they are all non-zero.
3718 rcutorture.n_barrier_cbs= [KNL]
3719 Set callbacks/threads for rcu_barrier() testing.
3721 rcutorture.nfakewriters= [KNL]
3722 Set number of concurrent RCU writers. These just
3723 stress RCU, they don't participate in the actual
3724 test, hence the "fake".
3726 rcutorture.nreaders= [KNL]
3727 Set number of RCU readers. The value -1 selects
3728 N-1, where N is the number of CPUs. A value
3729 "n" less than -1 selects N-n-2, where N is again
3730 the number of CPUs. For example, -2 selects N
3731 (the number of CPUs), -3 selects N+1, and so on.
3733 rcutorture.object_debug= [KNL]
3734 Enable debug-object double-call_rcu() testing.
3736 rcutorture.onoff_holdoff= [KNL]
3737 Set time (s) after boot for CPU-hotplug testing.
3739 rcutorture.onoff_interval= [KNL]
3740 Set time (s) between CPU-hotplug operations, or
3741 zero to disable CPU-hotplug testing.
3743 rcutorture.shuffle_interval= [KNL]
3744 Set task-shuffle interval (s). Shuffling tasks
3745 allows some CPUs to go into dyntick-idle mode
3746 during the rcutorture test.
3748 rcutorture.shutdown_secs= [KNL]
3749 Set time (s) after boot system shutdown. This
3750 is useful for hands-off automated testing.
3752 rcutorture.stall_cpu= [KNL]
3753 Duration of CPU stall (s) to test RCU CPU stall
3754 warnings, zero to disable.
3756 rcutorture.stall_cpu_holdoff= [KNL]
3757 Time to wait (s) after boot before inducing stall.
3759 rcutorture.stall_cpu_irqsoff= [KNL]
3760 Disable interrupts while stalling if set.
3762 rcutorture.stat_interval= [KNL]
3763 Time (s) between statistics printk()s.
3765 rcutorture.stutter= [KNL]
3766 Time (s) to stutter testing, for example, specifying
3767 five seconds causes the test to run for five seconds,
3768 wait for five seconds, and so on. This tests RCU's
3769 ability to transition abruptly to and from idle.
3771 rcutorture.test_boost= [KNL]
3772 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3773 "Maybe" means test if the RCU implementation
3774 under test support RCU priority boosting.
3776 rcutorture.test_boost_duration= [KNL]
3777 Duration (s) of each individual boost test.
3779 rcutorture.test_boost_interval= [KNL]
3780 Interval (s) between each boost test.
3782 rcutorture.test_no_idle_hz= [KNL]
3783 Test RCU's dyntick-idle handling. See also the
3784 rcutorture.shuffle_interval parameter.
3786 rcutorture.torture_runnable= [BOOT]
3787 Start rcutorture running at boot time.
3789 rcutorture.torture_type= [KNL]
3790 Specify the RCU implementation to test.
3792 rcutorture.verbose= [KNL]
3793 Enable additional printk() statements.
3795 rcupdate.rcu_cpu_stall_suppress= [KNL]
3796 Suppress RCU CPU stall warning messages.
3798 rcupdate.rcu_cpu_stall_timeout= [KNL]
3799 Set timeout for RCU CPU stall warning messages.
3801 rcupdate.rcu_expedited= [KNL]
3802 Use expedited grace-period primitives, for
3803 example, synchronize_rcu_expedited() instead
3804 of synchronize_rcu(). This reduces latency,
3805 but can increase CPU utilization, degrade
3806 real-time latency, and degrade energy efficiency.
3807 No effect on CONFIG_TINY_RCU kernels.
3809 rcupdate.rcu_normal= [KNL]
3810 Use only normal grace-period primitives,
3811 for example, synchronize_rcu() instead of
3812 synchronize_rcu_expedited(). This improves
3813 real-time latency, CPU utilization, and
3814 energy efficiency, but can expose users to
3815 increased grace-period latency. This parameter
3816 overrides rcupdate.rcu_expedited. No effect on
3817 CONFIG_TINY_RCU kernels.
3819 rcupdate.rcu_normal_after_boot= [KNL]
3820 Once boot has completed (that is, after
3821 rcu_end_inkernel_boot() has been invoked), use
3822 only normal grace-period primitives. No effect
3823 on CONFIG_TINY_RCU kernels.
3825 rcupdate.rcu_task_stall_timeout= [KNL]
3826 Set timeout in jiffies for RCU task stall warning
3827 messages. Disable with a value less than or equal
3830 rcupdate.rcu_self_test= [KNL]
3831 Run the RCU early boot self tests
3833 rcupdate.rcu_self_test_bh= [KNL]
3834 Run the RCU bh early boot self tests
3836 rcupdate.rcu_self_test_sched= [KNL]
3837 Run the RCU sched early boot self tests
3841 Run specified binary instead of /init from the ramdisk,
3842 used for early userspace startup. See initrd.
3845 Turn on/off individual RDT features. List is:
3846 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3848 E.g. to turn on cmt and turn off mba use:
3852 Format (x86 or x86_64):
3853 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3855 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3857 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3858 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3859 reboot_force is either force or not specified,
3860 reboot_cpu is s[mp]#### with #### being the processor
3861 to be used for rebooting.
3864 [KNL, SMP] Set scheduler's default relax_domain_level.
3865 See Documentation/cgroup-v1/cpusets.txt.
3867 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3869 reservetop= [X86-32]
3871 Reserves a hole at the top of the kernel virtual
3876 Set the amount of memory to reserve for BIOS at
3877 the bottom of the address space.
3879 reset_devices [KNL] Force drivers to reset the underlying device
3880 during initialization.
3883 Specify the partition device for software suspend
3885 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3887 resume_offset= [SWSUSP]
3888 Specify the offset from the beginning of the partition
3889 given by "resume=" at which the swap header is located,
3890 in <PAGE_SIZE> units (needed only for swap files).
3891 See Documentation/power/swsusp-and-swap-files.txt
3893 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3894 read the resume files
3896 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3897 Useful for devices that are detected asynchronously
3898 (e.g. USB and MMC devices).
3900 hibernate= [HIBERNATION]
3901 noresume Don't check if there's a hibernation image
3902 present during boot.
3903 nocompress Don't compress/decompress hibernation images.
3904 no Disable hibernation and resume.
3905 protect_image Turn on image protection during restoration
3906 (that will set all pages holding image data
3907 during restoration read-only).
3909 retain_initrd [RAM] Keep initrd memory after extraction
3911 rfkill.default_state=
3912 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3913 etc. communication is blocked by default.
3916 rfkill.master_switch_mode=
3917 0 The "airplane mode" button does nothing.
3918 1 The "airplane mode" button toggles between everything
3919 blocked and the previous configuration.
3920 2 The "airplane mode" button toggles between everything
3921 blocked and everything unblocked.
3923 rhash_entries= [KNL,NET]
3924 Set number of hash buckets for route cache
3927 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3930 ro [KNL] Mount root device read-only on boot
3933 on Mark read-only kernel memory as read-only (default).
3934 off Leave read-only kernel memory writable for debugging.
3937 Enable the uart passthrough on the designated usb port
3938 on Rockchip SoCs. When active, the signals of the
3939 debug-uart get routed to the D+ and D- pins of the usb
3940 port and the regular usb controller gets disabled.
3942 root= [KNL] Root filesystem
3943 See name_to_dev_t comment in init/do_mounts.c.
3945 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3946 mount the root filesystem
3948 rootflags= [KNL] Set root filesystem mount option string
3950 rootfstype= [KNL] Set root filesystem type
3952 rootwait [KNL] Wait (indefinitely) for root device to show up.
3953 Useful for devices that are detected asynchronously
3954 (e.g. USB and MMC devices).
3956 rproc_mem=nn[KMG][@address]
3957 [KNL,ARM,CMA] Remoteproc physical memory block.
3958 Memory area to be used by remote processor image,
3961 rw [KNL] Mount root device read-write on boot
3963 S [KNL] Run init in single mode
3965 s390_iommu= [HW,S390]
3966 Set s390 IOTLB flushing mode
3968 With strict flushing every unmap operation will result in
3969 an IOTLB flush. Default is lazy flushing before reuse,
3973 See drivers/net/irda/sa1100_ir.c.
3975 sbni= [NET] Granch SBNI12 leased line adapter
3977 sched_debug [KNL] Enables verbose scheduler debug messages.
3979 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3980 Allowed values are enable and disable. This feature
3981 incurs a small amount of overhead in the scheduler
3982 but is useful for debugging and performance tuning.
3984 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3985 xtime_lock contention on larger systems, and/or RCU lock
3986 contention on all systems with CONFIG_MAXSMP set.
3987 Format: { "0" | "1" }
3988 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3990 Note: increases power consumption, thus should only be
3991 enabled if running jitter sensitive (HPC/RT) workloads.
3993 security= [SECURITY] Choose a security module to enable at boot.
3994 If this boot parameter is not specified, only the first
3995 security module asking for security registration will be
3996 loaded. An invalid security module name will be treated
3997 as if no module has been chosen.
3999 selinux= [SELINUX] Disable or enable SELinux at boot time.
4000 Format: { "0" | "1" }
4001 See security/selinux/Kconfig help text.
4004 Default value is set via kernel config option.
4005 If enabled at boot time, /selinux/disable can be used
4006 later to disable prior to initial policy load.
4008 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4009 Format: { "0" | "1" }
4010 See security/apparmor/Kconfig help text
4013 Default value is set via kernel config option.
4015 serialnumber [BUGS=X86-32]
4018 Maximal number of shapers.
4026 Disable merging of slabs with similar size. May be
4027 necessary if there is some reason to distinguish
4028 allocs to different slabs, especially in hardened
4029 environments where the risk of heap overflows and
4030 layout control by attackers can usually be
4031 frustrated by disabling merging. This will reduce
4032 most of the exposure of a heap attack to a single
4033 cache (risks via metadata attacks are mostly
4034 unchanged). Debug options disable merging on their
4036 For more information see Documentation/vm/slub.txt.
4038 slab_max_order= [MM, SLAB]
4039 Determines the maximum allowed order for slabs.
4040 A high setting may cause OOMs due to memory
4041 fragmentation. Defaults to 1 for systems with
4042 more than 32MB of RAM, 0 otherwise.
4044 slub_debug[=options[,slabs]] [MM, SLUB]
4045 Enabling slub_debug allows one to determine the
4046 culprit if slab objects become corrupted. Enabling
4047 slub_debug can create guard zones around objects and
4048 may poison objects when not in use. Also tracks the
4049 last alloc / free. For more information see
4050 Documentation/vm/slub.txt.
4052 slub_memcg_sysfs= [MM, SLUB]
4053 Determines whether to enable sysfs directories for
4054 memory cgroup sub-caches. 1 to enable, 0 to disable.
4055 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4056 Enabling this can lead to a very high number of debug
4057 directories and files being created under
4060 slub_max_order= [MM, SLUB]
4061 Determines the maximum allowed order for slabs.
4062 A high setting may cause OOMs due to memory
4063 fragmentation. For more information see
4064 Documentation/vm/slub.txt.
4066 slub_min_objects= [MM, SLUB]
4067 The minimum number of objects per slab. SLUB will
4068 increase the slab order up to slub_max_order to
4069 generate a sufficiently large slab able to contain
4070 the number of objects indicated. The higher the number
4071 of objects the smaller the overhead of tracking slabs
4072 and the less frequently locks need to be acquired.
4073 For more information see Documentation/vm/slub.txt.
4075 slub_min_order= [MM, SLUB]
4076 Determines the minimum page order for slabs. Must be
4077 lower than slub_max_order.
4078 For more information see Documentation/vm/slub.txt.
4080 slub_nomerge [MM, SLUB]
4081 Same with slab_nomerge. This is supported for legacy.
4082 See slab_nomerge for more information.
4085 Format: <io1>[,<io2>[,...,<io8>]]
4087 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4088 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4089 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4090 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4091 smsc-ircc2.ircc_irq= [HW] IRQ line
4092 smsc-ircc2.ircc_dma= [HW] DMA channel
4093 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4094 0: Toshiba Satellite 1800 (GP data pin select)
4095 1: Fast pin select (default)
4098 smt [KNL,S390] Set the maximum number of threads (logical
4099 CPUs) to use per physical CPU on systems capable of
4100 symmetric multithreading (SMT). Will be capped to the
4101 actual hardware limit.
4103 Default: -1 (no limit)
4106 [KNL] Should the soft-lockup detector generate panics.
4109 A nonzero value instructs the soft-lockup detector
4110 to panic the machine when a soft-lockup occurs. This
4111 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4112 which is the respective build-time switch to that
4115 softlockup_all_cpu_backtrace=
4116 [KNL] Should the soft-lockup detector generate
4117 backtraces on all cpus.
4120 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4121 See Documentation/laptops/sonypi.txt
4123 spectre_v2= [X86] Control mitigation of Spectre variant 2
4124 (indirect branch speculation) vulnerability.
4125 The default operation protects the kernel from
4128 on - unconditionally enable, implies
4130 off - unconditionally disable, implies
4132 auto - kernel detects whether your CPU model is
4135 Selecting 'on' will, and 'auto' may, choose a
4136 mitigation method at run time according to the
4137 CPU, the available microcode, the setting of the
4138 CONFIG_RETPOLINE configuration option, and the
4139 compiler with which the kernel was built.
4141 Selecting 'on' will also enable the mitigation
4142 against user space to user space task attacks.
4144 Selecting 'off' will disable both the kernel and
4145 the user space protections.
4147 Specific mitigations can also be selected manually:
4149 retpoline - replace indirect branches
4150 retpoline,generic - google's original retpoline
4151 retpoline,amd - AMD-specific minimal thunk
4153 Not specifying this option is equivalent to
4157 [X86] Control mitigation of Spectre variant 2
4158 (indirect branch speculation) vulnerability between
4161 on - Unconditionally enable mitigations. Is
4162 enforced by spectre_v2=on
4164 off - Unconditionally disable mitigations. Is
4165 enforced by spectre_v2=off
4167 prctl - Indirect branch speculation is enabled,
4168 but mitigation can be enabled via prctl
4169 per thread. The mitigation control state
4170 is inherited on fork.
4173 - Like "prctl" above, but only STIBP is
4174 controlled per thread. IBPB is issued
4175 always when switching between different user
4179 - Same as "prctl" above, but all seccomp
4180 threads will enable the mitigation unless
4181 they explicitly opt out.
4184 - Like "seccomp" above, but only STIBP is
4185 controlled per thread. IBPB is issued
4186 always when switching between different
4187 user space processes.
4189 auto - Kernel selects the mitigation depending on
4190 the available CPU features and vulnerability.
4193 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4195 Not specifying this option is equivalent to
4196 spectre_v2_user=auto.
4198 spec_store_bypass_disable=
4199 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4200 (Speculative Store Bypass vulnerability)
4202 Certain CPUs are vulnerable to an exploit against a
4203 a common industry wide performance optimization known
4204 as "Speculative Store Bypass" in which recent stores
4205 to the same memory location may not be observed by
4206 later loads during speculative execution. The idea
4207 is that such stores are unlikely and that they can
4208 be detected prior to instruction retirement at the
4209 end of a particular speculation execution window.
4211 In vulnerable processors, the speculatively forwarded
4212 store can be used in a cache side channel attack, for
4213 example to read memory to which the attacker does not
4214 directly have access (e.g. inside sandboxed code).
4216 This parameter controls whether the Speculative Store
4217 Bypass optimization is used.
4219 on - Unconditionally disable Speculative Store Bypass
4220 off - Unconditionally enable Speculative Store Bypass
4221 auto - Kernel detects whether the CPU model contains an
4222 implementation of Speculative Store Bypass and
4223 picks the most appropriate mitigation. If the
4224 CPU is not vulnerable, "off" is selected. If the
4225 CPU is vulnerable the default mitigation is
4226 architecture and Kconfig dependent. See below.
4227 prctl - Control Speculative Store Bypass per thread
4228 via prctl. Speculative Store Bypass is enabled
4229 for a process by default. The state of the control
4230 is inherited on fork.
4231 seccomp - Same as "prctl" above, but all seccomp threads
4232 will disable SSB unless they explicitly opt out.
4234 Not specifying this option is equivalent to
4235 spec_store_bypass_disable=auto.
4237 Default mitigations:
4238 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4240 spia_io_base= [HW,MTD]
4245 srcutree.counter_wrap_check [KNL]
4246 Specifies how frequently to check for
4247 grace-period sequence counter wrap for the
4248 srcu_data structure's ->srcu_gp_seq_needed field.
4249 The greater the number of bits set in this kernel
4250 parameter, the less frequently counter wrap will
4251 be checked for. Note that the bottom two bits
4254 srcutree.exp_holdoff [KNL]
4255 Specifies how many nanoseconds must elapse
4256 since the end of the last SRCU grace period for
4257 a given srcu_struct until the next normal SRCU
4258 grace period will be considered for automatic
4259 expediting. Set to zero to disable automatic
4263 Speculative Store Bypass Disable control
4265 On CPUs that are vulnerable to the Speculative
4266 Store Bypass vulnerability and offer a
4267 firmware based mitigation, this parameter
4268 indicates how the mitigation should be used:
4270 force-on: Unconditionally enable mitigation for
4271 for both kernel and userspace
4272 force-off: Unconditionally disable mitigation for
4273 for both kernel and userspace
4274 kernel: Always enable mitigation in the
4275 kernel, and offer a prctl interface
4276 to allow userspace to register its
4277 interest in being mitigated too.
4279 stack_guard_gap= [MM]
4280 override the default stack gap protection. The value
4281 is in page units and it defines how many pages prior
4282 to (for stacks growing down) resp. after (for stacks
4283 growing up) the main stack are reserved for no other
4284 mapping. Default value is 256 pages.
4287 Enabled the stack tracer on boot up.
4289 stacktrace_filter=[function-list]
4290 [FTRACE] Limit the functions that the stack tracer
4291 will trace at boot up. function-list is a comma separated
4292 list of functions. This list can be changed at run
4293 time by the stack_trace_filter file in the debugfs
4294 tracing directory. Note, this enables stack tracing
4295 and the stacktrace above is not needed.
4299 Set the STI (builtin display/keyboard on the HP-PARISC
4300 machines) console (graphic card) which should be used
4301 as the initial boot-console.
4302 See also comment in drivers/video/console/sticore.c.
4305 See comment in drivers/video/console/sticore.c.
4308 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4310 sunrpc.min_resvport=
4311 sunrpc.max_resvport=
4313 SunRPC servers often require that client requests
4314 originate from a privileged port (i.e. a port in the
4315 range 0 < portnr < 1024).
4316 An administrator who wishes to reserve some of these
4317 ports for other uses may adjust the range that the
4318 kernel's sunrpc client considers to be privileged
4319 using these two parameters to set the minimum and
4320 maximum port values.
4322 sunrpc.svc_rpc_per_connection_limit=
4324 Limit the number of requests that the server will
4325 process in parallel from a single connection.
4326 The default value is 0 (no limit).
4330 Control how the NFS server code allocates CPUs to
4331 service thread pools. Depending on how many NICs
4332 you have and where their interrupts are bound, this
4333 option will affect which CPUs will do NFS serving.
4334 Note: this parameter cannot be changed while the
4335 NFS server is running.
4337 auto the server chooses an appropriate mode
4338 automatically using heuristics
4339 global a single global pool contains all CPUs
4340 percpu one pool for each CPU
4341 pernode one pool for each NUMA node (equivalent
4342 to global on non-NUMA machines)
4344 sunrpc.tcp_slot_table_entries=
4345 sunrpc.udp_slot_table_entries=
4347 Sets the upper limit on the number of simultaneous
4348 RPC calls that can be sent from the client to a
4349 server. Increasing these values may allow you to
4350 improve throughput, but will also increase the
4351 amount of memory reserved for use by the client.
4353 suspend.pm_test_delay=
4355 Sets the number of seconds to remain in a suspend test
4356 mode before resuming the system (see
4357 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4358 is set. Default value is 5.
4361 [KNL] Enable accounting of swap in memory resource
4362 controller if no parameter or 1 is given or disable
4363 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4365 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4366 Format: { <int> | force | noforce }
4367 <int> -- Number of I/O TLB slabs
4368 force -- force using of bounce buffers even if they
4369 wouldn't be automatically used by the kernel
4370 noforce -- Never use bounce buffers (for debugging)
4374 sysfs.deprecated=0|1 [KNL]
4375 Enable/disable old style sysfs layout for old udev
4376 on older distributions. When this option is enabled
4377 very new udev will not work anymore. When this option
4378 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4379 in older udev will not work anymore.
4380 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4381 the kernel configuration.
4383 sysrq_always_enabled
4385 Ignore sysrq setting - this boot parameter will
4386 neutralize any effect of /proc/sys/kernel/sysrq.
4387 Useful for debugging.
4389 tcpmhash_entries= [KNL,NET]
4390 Set the number of tcp_metrics_hash slots.
4391 Default value is 8192 or 16384 depending on total
4392 ram pages. This is used to specify the TCP metrics
4393 cache size. See Documentation/networking/ip-sysctl.txt
4394 "tcp_no_metrics_save" section for more details.
4398 test_suspend= [SUSPEND][,N]
4399 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4400 standby suspend) or "freeze" (for suspend type freeze)
4401 as the system sleep state during system startup with
4402 the optional capability to repeat N number of times.
4403 The system is woken from this state using a
4404 wakeup-capable RTC alarm.
4406 thash_entries= [KNL,NET]
4407 Set number of hash buckets for TCP connection
4409 thermal.act= [HW,ACPI]
4410 -1: disable all active trip points in all thermal zones
4411 <degrees C>: override all lowest active trip points
4413 thermal.crt= [HW,ACPI]
4414 -1: disable all critical trip points in all thermal zones
4415 <degrees C>: override all critical trip points
4417 thermal.nocrt= [HW,ACPI]
4418 Set to disable actions on ACPI thermal zone
4419 critical and hot trip points.
4421 thermal.off= [HW,ACPI]
4422 1: disable ACPI thermal control
4424 thermal.psv= [HW,ACPI]
4425 -1: disable all passive trip points
4426 <degrees C>: override all passive trip points to this
4429 thermal.tzp= [HW,ACPI]
4430 Specify global default ACPI thermal zone polling rate
4431 <deci-seconds>: poll all this frequency
4432 0: no polling (default)
4435 Force threading of all interrupt handlers except those
4436 marked explicitly IRQF_NO_THREAD.
4439 Enable the Transcendent memory driver if built-in.
4441 tmem.cleancache=0|1 [KNL, XEN]
4442 Default is on (1). Disable the usage of the cleancache
4443 API to send anonymous pages to the hypervisor.
4445 tmem.frontswap=0|1 [KNL, XEN]
4446 Default is on (1). Disable the usage of the frontswap
4447 API to send swap pages to the hypervisor. If disabled
4448 the selfballooning and selfshrinking are force disabled.
4450 tmem.selfballooning=0|1 [KNL, XEN]
4451 Default is on (1). Disable the driving of swap pages
4454 tmem.selfshrinking=0|1 [KNL, XEN]
4455 Default is on (1). Partial swapoff that immediately
4456 transfers pages from Xen hypervisor back to the
4457 kernel based on different criteria.
4461 Specify if the kernel should make use of the cpu
4462 topology information if the hardware supports this.
4463 The scheduler will make use of this information and
4464 e.g. base its process migration decisions on it.
4467 topology_updates= [KNL, PPC, NUMA]
4469 Specify if the kernel should ignore (off)
4470 topology updates sent by the hypervisor to this
4475 tpm_suspend_pcr=[HW,TPM]
4476 Format: integer pcr id
4477 Specify that at suspend time, the tpm driver
4478 should extend the specified pcr with zeros,
4479 as a workaround for some chips which fail to
4480 flush the last written pcr on TPM_SaveState.
4481 This will guarantee that all the other pcrs
4484 trace_buf_size=nn[KMG]
4485 [FTRACE] will set tracing buffer size on each cpu.
4487 trace_event=[event-list]
4488 [FTRACE] Set and start specified trace events in order
4489 to facilitate early boot debugging. The event-list is a
4490 comma separated list of trace events to enable. See
4491 also Documentation/trace/events.txt
4493 trace_options=[option-list]
4494 [FTRACE] Enable or disable tracer options at boot.
4495 The option-list is a comma delimited list of options
4496 that can be enabled or disabled just as if you were
4497 to echo the option name into
4499 /sys/kernel/debug/tracing/trace_options
4501 For example, to enable stacktrace option (to dump the
4502 stack trace of each event), add to the command line:
4504 trace_options=stacktrace
4506 See also Documentation/trace/ftrace.txt "trace options"
4510 Have the tracepoints sent to printk as well as the
4511 tracing ring buffer. This is useful for early boot up
4512 where the system hangs or reboots and does not give the
4513 option for reading the tracing buffer or performing a
4514 ftrace_dump_on_oops.
4516 To turn off having tracepoints sent to printk,
4517 echo 0 > /proc/sys/kernel/tracepoint_printk
4518 Note, echoing 1 into this file without the
4519 tracepoint_printk kernel cmdline option has no effect.
4523 Having tracepoints sent to printk() and activating high
4524 frequency tracepoints such as irq or sched, can cause
4525 the system to live lock.
4528 [FTRACE] enable this option to disable tracing when a
4529 warning is hit. This turns off "tracing_on". Tracing can
4530 be enabled again by echoing '1' into the "tracing_on"
4531 file located in /sys/kernel/debug/tracing/
4533 This option is useful, as it disables the trace before
4534 the WARNING dump is called, which prevents the trace to
4535 be filled with content caused by the warning output.
4537 This option can also be set at run time via the sysctl
4538 option: kernel/traceoff_on_warning
4540 transparent_hugepage=
4542 Format: [always|madvise|never]
4543 Can be used to control the default behavior of the system
4544 with respect to transparent hugepages.
4545 See Documentation/vm/transhuge.txt for more details.
4547 tsc= Disable clocksource stability checks for TSC.
4549 [x86] reliable: mark tsc clocksource as reliable, this
4550 disables clocksource verification at runtime, as well
4551 as the stability checks done at bootup. Used to enable
4552 high-resolution timer mode on older hardware, and in
4553 virtualized environment.
4554 [x86] noirqtime: Do not use TSC to do irq accounting.
4555 Used to run time disable IRQ_TIME_ACCOUNTING on any
4556 platforms where RDTSC is slow and this accounting
4558 [x86] unstable: mark the TSC clocksource as unstable, this
4559 marks the TSC unconditionally unstable at bootup and
4560 avoids any further wobbles once the TSC watchdog notices.
4562 turbografx.map[2|3]= [HW,JOY]
4563 TurboGraFX parallel port interface
4565 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4566 See also Documentation/input/devices/joystick-parport.rst
4568 udbg-immortal [PPC] When debugging early kernel crashes that
4569 happen after console_init() and before a proper
4570 console driver takes over, this boot options might
4571 help "seeing" what's going on.
4573 uhash_entries= [KNL,NET]
4574 Set number of hash buckets for UDP/UDP-Lite connections
4577 [USB] Ignore overcurrent events (default N).
4578 Some badly-designed motherboards generate lots of
4579 bogus events, for ports that aren't wired to
4580 anything. Set this parameter to avoid log spamming.
4581 Note that genuine overcurrent events won't be
4585 [X86] Cause panic on unknown NMI.
4587 usbcore.authorized_default=
4588 [USB] Default USB device authorization:
4589 (default -1 = authorized except for wireless USB,
4590 0 = not authorized, 1 = authorized)
4592 usbcore.autosuspend=
4593 [USB] The autosuspend time delay (in seconds) used
4594 for newly-detected USB devices (default 2). This
4595 is the time required before an idle device will be
4596 autosuspended. Devices for which the delay is set
4597 to a negative value won't be autosuspended at all.
4599 usbcore.usbfs_snoop=
4600 [USB] Set to log all usbfs traffic (default 0 = off).
4602 usbcore.usbfs_snoop_max=
4603 [USB] Maximum number of bytes to snoop in each URB
4606 usbcore.blinkenlights=
4607 [USB] Set to cycle leds on hubs (default 0 = off).
4609 usbcore.old_scheme_first=
4610 [USB] Start with the old device initialization
4611 scheme (default 0 = off).
4613 usbcore.usbfs_memory_mb=
4614 [USB] Memory limit (in MB) for buffers allocated by
4615 usbfs (default = 16, 0 = max = 2047).
4617 usbcore.use_both_schemes=
4618 [USB] Try the other device initialization scheme
4619 if the first one fails (default 1 = enabled).
4621 usbcore.initial_descriptor_timeout=
4622 [USB] Specifies timeout for the initial 64-byte
4623 USB_REQ_GET_DESCRIPTOR request in milliseconds
4624 (default 5000 = 5.0 seconds).
4626 usbcore.nousb [USB] Disable the USB subsystem
4629 [USB] A list of quirk entries to augment the built-in
4630 usb core quirk list. List entries are separated by
4631 commas. Each entry has the form
4632 VendorID:ProductID:Flags. The IDs are 4-digit hex
4633 numbers and Flags is a set of letters. Each letter
4634 will change the built-in quirk; setting it if it is
4635 clear and clearing it if it is set. The letters have
4636 the following meanings:
4637 a = USB_QUIRK_STRING_FETCH_255 (string
4638 descriptors must not be fetched using
4640 b = USB_QUIRK_RESET_RESUME (device can't resume
4641 correctly so reset it instead);
4642 c = USB_QUIRK_NO_SET_INTF (device can't handle
4643 Set-Interface requests);
4644 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4645 handle its Configuration or Interface
4647 e = USB_QUIRK_RESET (device can't be reset
4648 (e.g morph devices), don't use reset);
4649 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4650 more interface descriptions than the
4651 bNumInterfaces count, and can't handle
4652 talking to these interfaces);
4653 g = USB_QUIRK_DELAY_INIT (device needs a pause
4654 during initialization, after we read
4655 the device descriptor);
4656 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4657 high speed and super speed interrupt
4658 endpoints, the USB 2.0 and USB 3.0 spec
4659 require the interval in microframes (1
4660 microframe = 125 microseconds) to be
4661 calculated as interval = 2 ^
4663 Devices with this quirk report their
4664 bInterval as the result of this
4665 calculation instead of the exponent
4666 variable used in the calculation);
4667 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4668 handle device_qualifier descriptor
4670 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4671 generates spurious wakeup, ignore
4672 remote wakeup capability);
4673 k = USB_QUIRK_NO_LPM (device can't handle Link
4675 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4676 (Device reports its bInterval as linear
4677 frames instead of the USB 2.0
4679 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4680 to be disconnected before suspend to
4681 prevent spurious wakeup);
4682 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4683 pause after every control message);
4684 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
4685 delay after resetting its port);
4686 Example: quirks=0781:5580:bk,0a5c:5834:gij
4689 [USBHID] The interval which mice are to be polled at.
4692 [USBHID] The interval which joysticks are to be polled at.
4694 usb-storage.delay_use=
4695 [UMS] The delay in seconds before a new device is
4696 scanned for Logical Units (default 1).
4699 [UMS] A list of quirks entries to supplement or
4700 override the built-in unusual_devs list. List
4701 entries are separated by commas. Each entry has
4702 the form VID:PID:Flags where VID and PID are Vendor
4703 and Product ID values (4-digit hex numbers) and
4704 Flags is a set of characters, each corresponding
4705 to a common usb-storage quirk flag as follows:
4706 a = SANE_SENSE (collect more than 18 bytes
4708 b = BAD_SENSE (don't collect more than 18
4709 bytes of sense data);
4710 c = FIX_CAPACITY (decrease the reported
4711 device capacity by one sector);
4712 d = NO_READ_DISC_INFO (don't use
4713 READ_DISC_INFO command);
4714 e = NO_READ_CAPACITY_16 (don't use
4715 READ_CAPACITY_16 command);
4716 f = NO_REPORT_OPCODES (don't use report opcodes
4718 g = MAX_SECTORS_240 (don't transfer more than
4719 240 sectors at a time, uas only);
4720 h = CAPACITY_HEURISTICS (decrease the
4721 reported device capacity by one
4722 sector if the number is odd);
4723 i = IGNORE_DEVICE (don't bind to this
4725 j = NO_REPORT_LUNS (don't use report luns
4727 l = NOT_LOCKABLE (don't try to lock and
4728 unlock ejectable media);
4729 m = MAX_SECTORS_64 (don't transfer more
4730 than 64 sectors = 32 KB at a time);
4731 n = INITIAL_READ10 (force a retry of the
4732 initial READ(10) command);
4733 o = CAPACITY_OK (accept the capacity
4734 reported by the device);
4735 p = WRITE_CACHE (the device cache is ON
4737 r = IGNORE_RESIDUE (the device reports
4738 bogus residue values);
4739 s = SINGLE_LUN (the device has only one
4741 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4742 commands, uas only);
4743 u = IGNORE_UAS (don't bind to the uas driver);
4744 w = NO_WP_DETECT (don't test whether the
4745 medium is write-protected).
4746 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4747 even if the device claims no cache)
4748 Example: quirks=0419:aaf5:rl,0421:0433:rc
4750 user_debug= [KNL,ARM]
4752 See arch/arm/Kconfig.debug help text.
4753 1 - undefined instruction events
4755 4 - invalid data aborts
4758 Example: user_debug=31
4761 [X86] Flags controlling user PTE allocations.
4763 nohigh = do not allocate PTE pages in
4764 HIGHMEM regardless of setting
4768 On X86_32, this is an alias for vdso32=. Otherwise:
4770 vdso=1: enable VDSO (the default)
4771 vdso=0: disable VDSO mapping
4773 vdso32= [X86] Control the 32-bit vDSO
4774 vdso32=1: enable 32-bit VDSO
4775 vdso32=0 or vdso32=2: disable 32-bit VDSO
4777 See the help text for CONFIG_COMPAT_VDSO for more
4778 details. If CONFIG_COMPAT_VDSO is set, the default is
4779 vdso32=0; otherwise, the default is vdso32=1.
4781 For compatibility with older kernels, vdso32=2 is an
4784 Try vdso32=0 if you encounter an error that says:
4785 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4788 vector=percpu: enable percpu vector domain
4790 video= [FB] Frame buffer configuration
4791 See Documentation/fb/modedb.txt.
4793 video.brightness_switch_enabled= [0,1]
4794 If set to 1, on receiving an ACPI notify event
4795 generated by hotkey, video driver will adjust brightness
4796 level and then send out the event to user space through
4797 the allocated input device; If set to 0, video driver
4798 will only send out the event without touching backlight
4803 [VMMIO] Memory mapped virtio (platform) device.
4805 <size>@<baseaddr>:<irq>[:<id>]
4807 <size> := size (can use standard suffixes
4809 <baseaddr> := physical base address
4810 <irq> := interrupt number (as passed to
4812 <id> := (optional) platform device id
4814 virtio_mmio.device=1K@0x100b0000:48:7
4816 Can be used multiple times for multiple devices.
4818 vga= [BOOT,X86-32] Select a particular video mode
4819 See Documentation/x86/boot.txt and
4820 Documentation/svga.txt.
4821 Use vga=ask for menu.
4822 This is actually a boot loader parameter; the value is
4823 passed to the kernel using a special protocol.
4825 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4826 size of <nn>. This can be used to increase the
4827 minimum size (128MB on x86). It can also be used to
4828 decrease the size and leave more room for directly
4831 vmcp_cma=nn[MG] [KNL,S390]
4832 Sets the memory size reserved for contiguous memory
4833 allocations for the vmcp device driver.
4835 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4838 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4841 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4845 Controls the behavior of vsyscalls (i.e. calls to
4846 fixed addresses of 0xffffffffff600x00 from legacy
4847 code). Most statically-linked binaries and older
4848 versions of glibc use these calls. Because these
4849 functions are at fixed addresses, they make nice
4850 targets for exploits that can control RIP.
4852 emulate [default] Vsyscalls turn into traps and are
4853 emulated reasonably safely.
4855 native Vsyscalls are native syscall instructions.
4856 This is a little bit faster than trapping
4857 and makes a few dynamic recompilers work
4858 better than they would in emulation mode.
4859 It also makes exploits much easier to write.
4861 none Vsyscalls don't work at all. This makes
4862 them quite hard to use for exploits but
4863 might break your system.
4865 vt.color= [VT] Default text color.
4866 Format: 0xYX, X = foreground, Y = background.
4867 Default: 0x07 = light gray on black.
4869 vt.cur_default= [VT] Default cursor shape.
4870 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4871 the parameters of the <Esc>[?A;B;Cc escape sequence;
4872 see VGA-softcursor.txt. Default: 2 = underline.
4874 vt.default_blu= [VT]
4875 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4876 Change the default blue palette of the console.
4877 This is a 16-member array composed of values
4880 vt.default_grn= [VT]
4881 Format: <green0>,<green1>,<green2>,...,<green15>
4882 Change the default green palette of the console.
4883 This is a 16-member array composed of values
4886 vt.default_red= [VT]
4887 Format: <red0>,<red1>,<red2>,...,<red15>
4888 Change the default red palette of the console.
4889 This is a 16-member array composed of values
4895 Set system-wide default UTF-8 mode for all tty's.
4896 Default is 1, i.e. UTF-8 mode is enabled for all
4897 newly opened terminals.
4899 vt.global_cursor_default=
4902 Set system-wide default for whether a cursor
4903 is shown on new VTs. Default is -1,
4904 i.e. cursors will be created by default unless
4905 overridden by individual drivers. 0 will hide
4906 cursors, 1 will display them.
4908 vt.italic= [VT] Default color for italic text; 0-15.
4911 vt.underline= [VT] Default color for underlined text; 0-15.
4914 watchdog timers [HW,WDT] For information on watchdog timers,
4915 see Documentation/watchdog/watchdog-parameters.txt
4916 or other driver-specific files in the
4917 Documentation/watchdog/ directory.
4919 workqueue.watchdog_thresh=
4920 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4921 warn stall conditions and dump internal state to
4922 help debugging. 0 disables workqueue stall
4923 detection; otherwise, it's the stall threshold
4924 duration in seconds. The default value is 30 and
4925 it can be updated at runtime by writing to the
4926 corresponding sysfs file.
4928 workqueue.disable_numa
4929 By default, all work items queued to unbound
4930 workqueues are affine to the NUMA nodes they're
4931 issued on, which results in better behavior in
4932 general. If NUMA affinity needs to be disabled for
4933 whatever reason, this option can be used. Note
4934 that this also can be controlled per-workqueue for
4935 workqueues visible under /sys/bus/workqueue/.
4937 workqueue.power_efficient
4938 Per-cpu workqueues are generally preferred because
4939 they show better performance thanks to cache
4940 locality; unfortunately, per-cpu workqueues tend to
4941 be more power hungry than unbound workqueues.
4943 Enabling this makes the per-cpu workqueues which
4944 were observed to contribute significantly to power
4945 consumption unbound, leading to measurably lower
4946 power usage at the cost of small performance
4949 The default value of this parameter is determined by
4950 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4952 workqueue.debug_force_rr_cpu
4953 Workqueue used to implicitly guarantee that work
4954 items queued without explicit CPU specified are put
4955 on the local CPU. This guarantee is no longer true
4956 and while local CPU is still preferred work items
4957 may be put on foreign CPUs. This debug option
4958 forces round-robin CPU selection to flush out
4959 usages which depend on the now broken guarantee.
4960 When enabled, memory and cache locality will be
4963 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4964 default x2apic cluster mode on platforms
4967 x86_intel_mid_timer= [X86-32,APBT]
4968 Choose timer option for x86 Intel MID platform.
4969 Two valid options are apbt timer only and lapic timer
4970 plus one apbt timer for broadcast timer.
4971 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4973 xen_512gb_limit [KNL,X86-64,XEN]
4974 Restricts the kernel running paravirtualized under Xen
4975 to use only up to 512 GB of RAM. The reason to do so is
4976 crash analysis tools and Xen tools for doing domain
4977 save/restore/migration must be enabled to handle larger
4980 xen_emul_unplug= [HW,X86,XEN]
4981 Unplug Xen emulated devices
4982 Format: [unplug0,][unplug1]
4983 ide-disks -- unplug primary master IDE devices
4984 aux-ide-disks -- unplug non-primary-master IDE devices
4985 nics -- unplug network devices
4986 all -- unplug all emulated devices (NICs and IDE disks)
4987 unnecessary -- unplugging emulated devices is
4988 unnecessary even if the host did not respond to
4990 never -- do not unplug even if version check succeeds
4992 xen_nopvspin [X86,XEN]
4993 Disables the ticketlock slowpath using Xen PV
4997 Disables the PV optimizations forcing the HVM guest to
4998 run as generic HVM guest with no PV drivers.
5000 xirc2ps_cs= [NET,PCMCIA]
5002 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]