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_no_watchdog [HW,ACPI,WDT]
141 Ignore the ACPI-based watchdog interface (WDAT) and let
142 a native driver control the watchdog device instead.
144 acpi_rsdp= [ACPI,EFI,KEXEC]
145 Pass the RSDP address to the kernel, mostly used
146 on machines running EFI runtime service to boot the
147 second kernel for kdump.
149 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
150 Format: To spoof as Windows 98: ="Microsoft Windows"
152 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
153 of 2 which is mandated by ACPI 6) as the supported ACPI
154 specification revision (when using this switch, it may
155 be necessary to carry out a cold reboot _twice_ in a
156 row to make it take effect on the platform firmware).
158 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
159 acpi_osi="string1" # add string1
160 acpi_osi="!string2" # remove string2
161 acpi_osi=!* # remove all strings
162 acpi_osi=! # disable all built-in OS vendor
164 acpi_osi=!! # enable all built-in OS vendor
166 acpi_osi= # disable all strings
168 'acpi_osi=!' can be used in combination with single or
169 multiple 'acpi_osi="string1"' to support specific OS
170 vendor string(s). Note that such command can only
171 affect the default state of the OS vendor strings, thus
172 it cannot affect the default state of the feature group
173 strings and the current state of the OS vendor strings,
174 specifying it multiple times through kernel command line
175 is meaningless. This command is useful when one do not
176 care about the state of the feature group strings which
177 should be controlled by the OSPM.
179 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
180 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
181 can make '_OSI("Windows 2000")' TRUE.
183 'acpi_osi=' cannot be used in combination with other
184 'acpi_osi=' command lines, the _OSI method will not
185 exist in the ACPI namespace. NOTE that such command can
186 only affect the _OSI support state, thus specifying it
187 multiple times through kernel command line is also
190 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
193 'acpi_osi=!*' can be used in combination with single or
194 multiple 'acpi_osi="string1"' to support specific
195 string(s). Note that such command can affect the
196 current state of both the OS vendor strings and the
197 feature group strings, thus specifying it multiple times
198 through kernel command line is meaningful. But it may
199 still not able to affect the final state of a string if
200 there are quirks related to this string. This command
201 is useful when one want to control the state of the
202 feature group strings to debug BIOS issues related to
205 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
206 '_OSI("Module Device")' FALSE.
207 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
208 '_OSI("Module Device")' TRUE.
209 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
211 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
213 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
214 they all will make '_OSI("Windows 2000")' TRUE.
217 Override the pmtimer bug detection: force the kernel
218 to assume that this machine's pmtimer latches its value
219 and always returns good values.
221 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
222 Format: { level | edge | high | low }
224 acpi_skip_timer_override [HW,ACPI]
225 Recognize and ignore IRQ0/pin2 Interrupt Override.
226 For broken nForce2 BIOS resulting in XT-PIC timer.
228 acpi_sleep= [HW,ACPI] Sleep options
229 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
230 old_ordering, nonvs, sci_force_enable }
231 See Documentation/power/video.txt for information on
233 s3_beep is for debugging; it makes the PC's speaker beep
234 as soon as the kernel's real-mode entry point is called.
235 s4_nohwsig prevents ACPI hardware signature from being
236 used during resume from hibernation.
237 old_ordering causes the ACPI 1.0 ordering of the _PTS
238 control method, with respect to putting devices into
239 low power states, to be enforced (the ACPI 2.0 ordering
240 of _PTS is used by default).
241 nonvs prevents the kernel from saving/restoring the
242 ACPI NVS memory during suspend/hibernation and resume.
243 sci_force_enable causes the kernel to set SCI_EN directly
244 on resume from S1/S3 (which is against the ACPI spec,
245 but some broken systems don't work without it).
247 acpi_use_timer_override [HW,ACPI]
248 Use timer override. For some broken Nvidia NF5 boards
249 that require a timer override, but don't have HPET
251 add_efi_memmap [EFI; X86] Include EFI memory map in
252 kernel's map of available physical RAM.
255 { off | try_unsupported }
256 off: disable AGP support
257 try_unsupported: try to drive unsupported chipsets
258 (may crash computer or cause data corruption)
261 See Documentation/sound/alsa/alsa-parameters.txt
264 Allow the default userspace alignment fault handler
265 behaviour to be specified. Bit 0 enables warnings,
266 bit 1 enables fixups, and bit 2 sends a segfault.
268 align_va_addr= [X86-64]
269 Align virtual addresses by clearing slice [14:12] when
270 allocating a VMA at process creation time. This option
271 gives you up to 3% performance improvement on AMD F15h
272 machines (where it is enabled by default) for a
273 CPU-intensive style benchmark, and it can vary highly in
274 a microbenchmark depending on workload and compiler.
276 32: only for 32-bit processes
277 64: only for 64-bit processes
278 on: enable for both 32- and 64-bit processes
279 off: disable for both 32- and 64-bit processes
281 alloc_snapshot [FTRACE]
282 Allocate the ftrace snapshot buffer on boot up when the
283 main buffer is allocated. This is handy if debugging
284 and you need to use tracing_snapshot() on boot up, and
285 do not want to use tracing_snapshot_alloc() as it needs
286 to be done where GFP_KERNEL allocations are allowed.
288 amd_iommu= [HW,X86-64]
289 Pass parameters to the AMD IOMMU driver in the system.
291 fullflush - enable flushing of IO/TLB entries when
292 they are unmapped. Otherwise they are
293 flushed before they will be reused, which
295 off - do not initialize any AMD IOMMU found in
297 force_isolation - Force device isolation for all
298 devices. The IOMMU driver is not
299 allowed anymore to lift isolation
300 requirements as needed. This option
301 does not override iommu=pt
303 amd_iommu_dump= [HW,X86-64]
304 Enable AMD IOMMU driver option to dump the ACPI table
305 for AMD IOMMU. With this option enabled, AMD IOMMU
306 driver will print ACPI tables for AMD IOMMU during
307 IOMMU initialization.
309 amd_iommu_intr= [HW,X86-64]
310 Specifies one of the following AMD IOMMU interrupt
312 legacy - Use legacy interrupt remapping mode.
313 vapic - Use virtual APIC mode, which allows IOMMU
314 to inject interrupts directly into guest.
315 This mode requires kvm-amd.avic=1.
316 (Default when IOMMU HW support is present.)
318 amijoy.map= [HW,JOY] Amiga joystick support
319 Map of devices attached to JOY0DAT and JOY1DAT
321 See also Documentation/input/joystick.txt
323 analog.map= [HW,JOY] Analog joystick and gamepad support
324 Specifies type or capabilities of an analog joystick
325 connected to one of 16 gameports
326 Format: <type1>,<type2>,..<type16>
329 Power management functions (SPARCstation-4/5 + deriv.)
331 Disable APC CPU standby support. SPARCstation-Fox does
332 not play well with APC CPU idle - disable it if you have
333 APC and your system crashes randomly.
335 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
336 Change the output verbosity whilst booting
337 Format: { quiet (default) | verbose | debug }
338 Change the amount of debugging information output
339 when initialising the APIC and IO-APIC components.
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/video4linux/bttv/Insmod-options
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[,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. Defaults to 10*60 = 10mins. A value of 0
649 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 cpuidle.off=1 [CPU_IDLE]
664 disable the cpuidle sub-system
666 cpufreq.off=1 [CPU_FREQ]
667 disable the cpufreq sub-system
670 [X86] Delay for N microsec between assert and de-assert
671 of APIC INIT to start processors. This delay occurs
672 on every CPU online, such as boot, and resume from suspend.
675 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
677 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
679 crashkernel=size[KMG][@offset[KMG]]
680 [KNL] Using kexec, Linux can switch to a 'crash kernel'
681 upon panic. This parameter reserves the physical
682 memory region [offset, offset + size] for that kernel
683 image. If '@offset' is omitted, then a suitable offset
684 is selected automatically. Check
685 Documentation/kdump/kdump.txt for further details.
687 crashkernel=range1:size1[,range2:size2,...][@offset]
688 [KNL] Same as above, but depends on the memory
689 in the running system. The syntax of range is
690 start-[end] where start and end are both
691 a memory unit (amount[KMG]). See also
692 Documentation/kdump/kdump.txt for an example.
694 crashkernel=size[KMG],high
695 [KNL, x86_64] range could be above 4G. Allow kernel
696 to allocate physical memory region from top, so could
697 be above 4G if system have more than 4G ram installed.
698 Otherwise memory region will be allocated below 4G, if
700 It will be ignored if crashkernel=X is specified.
701 crashkernel=size[KMG],low
702 [KNL, x86_64] range under 4G. When crashkernel=X,high
703 is passed, kernel could allocate physical memory region
704 above 4G, that cause second kernel crash on system
705 that require some amount of low memory, e.g. swiotlb
706 requires at least 64M+32K low memory, also enough extra
707 low memory is needed to make sure DMA buffers for 32-bit
708 devices won't run out. Kernel would try to allocate at
709 at least 256M below 4G automatically.
710 This one let user to specify own low range under 4G
711 for second kernel instead.
712 0: to disable low allocation.
713 It will be ignored when crashkernel=X,high is not used
714 or memory reserved is below 4G.
717 [KNL] Disable crypto self-tests
722 cs89x0_media= [HW,NET]
723 Format: { rj45 | aui | bnc }
726 See header of drivers/s390/block/dasd_devmap.c.
728 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
729 (one device per port)
730 Format: <port#>,<type>
731 See also Documentation/input/joystick-parport.txt
733 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
735 Documentation/admin-guide/dynamic-debug-howto.rst for
736 details. Deprecated, see dyndbg.
738 debug [KNL] Enable kernel debugging (events log level).
741 [KNL] verbose self-tests
743 Print debugging info while doing the locking API
745 We default to 0 (no extra messages), setting it to
746 1 will print _a lot_ more information - normally
747 only useful to kernel developers.
749 debug_objects [KNL] Enable object debugging
752 [KNL] Disable object debugging
754 debug_guardpage_minorder=
755 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
756 parameter allows control of the order of pages that will
757 be intentionally kept free (and hence protected) by the
758 buddy allocator. Bigger value increase the probability
759 of catching random memory corruption, but reduce the
760 amount of memory for normal system use. The maximum
761 possible value is MAX_ORDER/2. Setting this parameter
762 to 1 or 2 should be enough to identify most random
763 memory corruption problems caused by bugs in kernel or
764 driver code when a CPU writes to (or reads from) a
765 random memory location. Note that there exists a class
766 of memory corruptions problems caused by buggy H/W or
767 F/W or by drivers badly programing DMA (basically when
768 memory is written at bus level and the CPU MMU is
769 bypassed) which are not detectable by
770 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
771 tracking down these problems.
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter enables the feature at boot time. In
776 default, it is disabled. We can avoid allocating huge
777 chunk of memory for debug pagealloc if we don't enable
778 it at boot time and the system will work mostly same
779 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
780 on: enable the feature
782 debugpat [X86] Enable PAT debugging
784 decnet.addr= [HW,NET]
785 Format: <area>[,<node>]
786 See also Documentation/networking/decnet.txt.
789 [same as hugepagesz=] The size of the default
790 HugeTLB page size. This is the size represented by
791 the legacy /proc/ hugepages APIs, used for SHM, and
792 default size when mounting hugetlbfs filesystems.
793 Defaults to the default architecture's huge page size
797 Set number of hash buckets for dentry cache.
799 disable_1tb_segments [PPC]
800 Disables the use of 1TB hash page table segments. This
801 causes the kernel to fall back to 256MB segments which
802 can be useful when debugging issues that require an SLB
806 See Documentation/networking/ipv6.txt.
809 Disable RADIX MMU mode on POWER9
811 disable_cpu_apicid= [X86,APIC,SMP]
813 The number of initial APIC ID for the
814 corresponding CPU to be disabled at boot,
815 mostly used for the kdump 2nd kernel to
816 disable BSP to wake up multiple CPUs without
817 causing system reset or hang due to sending
820 disable_ddw [PPC/PSERIES]
821 Disable Dynamic DMA Window support. Use this if
822 to workaround buggy firmware.
825 See Documentation/networking/ipv6.txt.
827 disable_mtrr_cleanup [X86]
828 The kernel tries to adjust MTRR layout from continuous
829 to discrete, to make X server driver able to add WB
830 entry later. This parameter disables that.
832 disable_mtrr_trim [X86, Intel and AMD only]
833 By default the kernel will trim any uncacheable
834 memory out of your available memory pool based on
835 MTRR settings. This parameter disables that behavior,
836 possibly causing your machine to run very slowly.
838 disable_timer_pin_1 [X86]
839 Disable PIN 1 of APIC timer
840 Can be useful to work around chipset bugs.
842 dis_ucode_ldr [X86] Disable the microcode loader.
844 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
845 this option disables the debugging code at boot.
847 dma_debug_entries=<number>
848 This option allows to tune the number of preallocated
849 entries for DMA-API debugging code. One entry is
850 required per DMA-API allocation. Use this if the
851 DMA-API debugging code disables itself because the
852 architectural default is too low.
854 dma_debug_driver=<driver_name>
855 With this option the DMA-API debugging driver
856 filter feature can be enabled at boot time. Just
857 pass the driver to filter for as the parameter.
858 The filter can be disabled or changed to another
859 driver later using sysfs.
861 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
862 Broken monitors, graphic adapters, KVMs and EDIDless
863 panels may send no or incorrect EDID data sets.
864 This parameter allows to specify an EDID data sets
865 in the /lib/firmware directory that are used instead.
866 Generic built-in EDID data sets are used, if one of
867 edid/1024x768.bin, edid/1280x1024.bin,
868 edid/1680x1050.bin, or edid/1920x1080.bin is given
869 and no file with the same name exists. Details and
870 instructions how to build your own EDID data are
871 available in Documentation/EDID/HOWTO.txt. An EDID
872 data set will only be used for a particular connector,
873 if its name and a colon are prepended to the EDID
874 name. Each connector may use a unique EDID data
875 set by separating the files with a comma. An EDID
876 data set with no connector name will be used for
877 any connectors not explicitly specified.
882 Format: {"off" | "known"}
883 Control how the dt_cpu_ftrs device-tree binding is
884 used for CPU feature discovery and setup (if it
886 off: Do not use it, fall back to legacy cpu table.
887 known: Do not pass through unknown features to guests
888 or userspace, only those that the kernel is aware of.
890 dump_apple_properties [X86]
891 Dump name and content of EFI device properties on
892 x86 Macs. Useful for driver authors to determine
893 what data is available or for reverse-engineering.
895 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
896 module.dyndbg[="val"]
897 Enable debug messages at boot time. See
898 Documentation/admin-guide/dynamic-debug-howto.rst
901 nompx [X86] Disables Intel Memory Protection Extensions.
902 See Documentation/x86/intel_mpx.txt for more
903 information about the feature.
905 nopku [X86] Disable Memory Protection Keys CPU feature found
908 module.async_probe [KNL]
909 Enable asynchronous probe on this module.
911 early_ioremap_debug [KNL]
912 Enable debug messages in early_ioremap support. This
913 is useful for tracking down temporary early mappings
914 which are not unmapped.
916 earlycon= [KNL] Output early console device and options.
918 When used with no options, the early console is
919 determined by the stdout-path property in device
922 cdns,<addr>[,options]
923 Start an early, polled-mode console on a Cadence
924 (xuartps) serial port at the specified address. Only
925 supported option is baud rate. If baud rate is not
926 specified, the serial port must already be setup and
929 uart[8250],io,<addr>[,options]
930 uart[8250],mmio,<addr>[,options]
931 uart[8250],mmio32,<addr>[,options]
932 uart[8250],mmio32be,<addr>[,options]
933 uart[8250],0x<addr>[,options]
934 Start an early, polled-mode console on the 8250/16550
935 UART at the specified I/O port or MMIO address.
936 MMIO inter-register address stride is either 8-bit
937 (mmio) or 32-bit (mmio32 or mmio32be).
938 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
939 to be equivalent to 'mmio'. 'options' are specified
940 in the same format described for "console=ttyS<n>"; if
941 unspecified, the h/w is not initialized.
945 Start an early, polled-mode console on a pl011 serial
946 port at the specified address. The pl011 serial port
947 must already be setup and configured. Options are not
948 yet supported. If 'mmio32' is specified, then only
949 the driver will use only 32-bit accessors to read/write
950 the device registers.
953 Start an early, polled-mode console on a meson serial
954 port at the specified address. The serial port must
955 already be setup and configured. Options are not yet
959 Start an early, polled-mode console on an msm serial
960 port at the specified address. The serial port
961 must already be setup and configured. Options are not
965 Start an early, polled-mode console on an msm serial
966 dm port at the specified address. The serial port
967 must already be setup and configured. Options are not
971 Start an early, polled-mode console on a serial port
972 of an Actions Semi SoC, such as S500 or S900, at the
973 specified address. The serial port must already be
974 setup and configured. Options are not yet supported.
976 smh Use ARM semihosting calls for early console.
984 Use early console provided by serial driver available
985 on Samsung SoCs, requires selecting proper type and
986 a correct base address of the selected UART port. The
987 serial port must already be setup and configured.
988 Options are not yet supported.
991 Start an early, polled-mode console on a lantiq serial
992 (lqasc) port at the specified address. The serial port
993 must already be setup and configured. Options are not
998 Use early console provided by Freescale LP UART driver
999 found on Freescale Vybrid and QorIQ LS1021A processors.
1000 A valid base address must be provided, and the serial
1001 port must already be setup and configured.
1004 Start an early, polled-mode console on the
1005 Armada 3700 serial port at the specified
1006 address. The serial port must already be setup
1007 and configured. Options are not yet supported.
1009 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1014 earlyprintk=serial[,ttySn[,baudrate]]
1015 earlyprintk=serial[,0x...[,baudrate]]
1016 earlyprintk=ttySn[,baudrate]
1017 earlyprintk=dbgp[debugController#]
1018 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1019 earlyprintk=xdbc[xhciController#]
1021 earlyprintk is useful when the kernel crashes before
1022 the normal console is initialized. It is not enabled by
1023 default because it has some cosmetic problems.
1025 Append ",keep" to not disable it when the real console
1028 Only one of vga, efi, serial, or usb debug port can
1031 Currently only ttyS0 and ttyS1 may be specified by
1032 name. Other I/O ports may be explicitly specified
1033 on some architectures (x86 and arm at least) by
1034 replacing ttySn with an I/O port address, like this:
1035 earlyprintk=serial,0x1008,115200
1036 You can find the port for a given device in
1037 /proc/tty/driver/serial:
1038 2: uart:ST16650V2 port:00001008 irq:18 ...
1040 Interaction with the standard serial driver is not
1043 The VGA and EFI output is eventually overwritten by
1046 The xen output can only be used by Xen PV guests.
1048 The sclp output can only be used on s390.
1050 The optional "force" to "pciserial" enables use of a
1051 PCI device even when its classcode is not of the
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/joystick-parport.txt
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.
1698 [ARM64] Configure DMA to bypass the IOMMU by default.
1699 Format: { "0" | "1" }
1700 0 - Use IOMMU translation for DMA.
1701 1 - Bypass the IOMMU for DMA.
1702 unset - Use IOMMU translation for DMA.
1704 io7= [HW] IO7 for Marvel based alpha systems
1705 See comment before marvel_specify_io7 in
1706 arch/alpha/kernel/core_marvel.c.
1708 io_delay= [X86] I/O delay method
1710 Standard port 0x80 based delay
1712 Alternate port 0xed based delay (needed on some systems)
1714 Simple two microseconds delay
1719 See Documentation/filesystems/nfs/nfsroot.txt.
1721 irqaffinity= [SMP] Set the default irq affinity mask
1722 The argument is a cpu list, as described above.
1725 When an interrupt is not handled search all handlers
1726 for it. Intended to get systems with badly broken
1730 When an interrupt is not handled search all handlers
1731 for it. Also check all handlers each timer
1732 interrupt. Intended to get systems with badly broken
1736 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1738 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1739 The argument is a cpu list, as described above.
1741 This option can be used to specify one or more CPUs
1742 to isolate from the general SMP balancing and scheduling
1743 algorithms. You can move a process onto or off an
1744 "isolated" CPU via the CPU affinity syscalls or cpuset.
1745 <cpu number> begins at 0 and the maximum value is
1746 "number of CPUs in system - 1".
1748 This option is the preferred way to isolate CPUs. The
1749 alternative -- manually setting the CPU mask of all
1750 tasks in the system -- can cause problems and
1751 suboptimal load balancer performance.
1755 ivrs_ioapic [HW,X86_64]
1756 Provide an override to the IOAPIC-ID<->DEVICE-ID
1757 mapping provided in the IVRS ACPI table. For
1758 example, to map IOAPIC-ID decimal 10 to
1759 PCI device 00:14.0 write the parameter as:
1760 ivrs_ioapic[10]=00:14.0
1762 ivrs_hpet [HW,X86_64]
1763 Provide an override to the HPET-ID<->DEVICE-ID
1764 mapping provided in the IVRS ACPI table. For
1765 example, to map HPET-ID decimal 0 to
1766 PCI device 00:14.0 write the parameter as:
1767 ivrs_hpet[0]=00:14.0
1769 ivrs_acpihid [HW,X86_64]
1770 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1771 mapping provided in the IVRS ACPI table. For
1772 example, to map UART-HID:UID AMD0020:0 to
1773 PCI device 00:14.5 write the parameter as:
1774 ivrs_acpihid[00:14.5]=AMD0020:0
1776 js= [HW,JOY] Analog joystick
1777 See Documentation/input/joystick.txt.
1780 When CONFIG_RANDOMIZE_BASE is set, this disables
1781 kernel and module base offset ASLR (Address Space
1782 Layout Randomization).
1785 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1786 report on every invalid memory access. Without this
1787 parameter KASAN will print report only for the first
1792 kernelcore= [KNL,X86,IA-64,PPC]
1793 Format: nn[KMGTPE] | "mirror"
1795 specifies the amount of memory usable by the kernel
1796 for non-movable allocations. The requested amount is
1797 spread evenly throughout all nodes in the system. The
1798 remaining memory in each node is used for Movable
1799 pages. In the event, a node is too small to have both
1800 kernelcore and Movable pages, kernelcore pages will
1801 take priority and other nodes will have a larger number
1802 of Movable pages. The Movable zone is used for the
1803 allocation of pages that may be reclaimed or moved
1804 by the page migration subsystem. This means that
1805 HugeTLB pages may not be allocated from this zone.
1806 Note that allocations like PTEs-from-HighMem still
1807 use the HighMem zone if it exists, and the Normal
1808 zone if it does not.
1810 Instead of specifying the amount of memory (nn[KMGTPE]),
1811 you can specify "mirror" option. In case "mirror"
1812 option is specified, mirrored (reliable) memory is used
1813 for non-movable allocations and remaining memory is used
1814 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1815 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1818 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1819 Format: <Controller#>[,poll interval]
1820 The controller # is the number of the ehci usb debug
1821 port as it is probed via PCI. The poll interval is
1822 optional and is the number seconds in between
1823 each poll cycle to the debug port in case you need
1824 the functionality for interrupting the kernel with
1825 gdb or control-c on the dbgp connection. When
1826 not using this parameter you use sysrq-g to break into
1827 the kernel debugger.
1829 kgdboc= [KGDB,HW] kgdb over consoles.
1830 Requires a tty driver that supports console polling,
1831 or a supported polling keyboard driver (non-usb).
1832 Serial only format: <serial_device>[,baud]
1833 keyboard only format: kbd
1834 keyboard and serial format: kbd,<serial_device>[,baud]
1835 Optional Kernel mode setting:
1836 kms, kbd format: kms,kbd
1837 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1839 kgdbwait [KGDB] Stop kernel execution and enter the
1840 kernel debugger at the earliest opportunity.
1842 kmac= [MIPS] korina ethernet MAC address.
1843 Configure the RouterBoard 532 series on-chip
1844 Ethernet adapter MAC address.
1846 kmemleak= [KNL] Boot-time kmemleak enable/disable
1847 Valid arguments: on, off
1849 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1852 kpti= [ARM64] Control page table isolation of user
1853 and kernel address spaces.
1854 Default: enabled on cores which need mitigation.
1858 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1859 Default is 0 (don't ignore, but inject #GP)
1861 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1866 [KVM] Controls the software workaround for the
1867 X86_BUG_ITLB_MULTIHIT bug.
1868 force : Always deploy workaround.
1869 off : Never deploy workaround.
1870 auto : Deploy workaround based on the presence of
1871 X86_BUG_ITLB_MULTIHIT.
1875 If the software workaround is enabled for the host,
1876 guests do need not to enable it for nested guests.
1878 kvm.nx_huge_pages_recovery_ratio=
1879 [KVM] Controls how many 4KiB pages are periodically zapped
1880 back to huge pages. 0 disables the recovery, otherwise if
1881 the value is N KVM will zap 1/Nth of the 4KiB pages every
1882 minute. The default is 60.
1884 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1885 Default is 1 (enabled)
1887 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1889 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1891 kvm-arm.vgic_v3_group0_trap=
1892 [KVM,ARM] Trap guest accesses to GICv3 group-0
1895 kvm-arm.vgic_v3_group1_trap=
1896 [KVM,ARM] Trap guest accesses to GICv3 group-1
1899 kvm-arm.vgic_v3_common_trap=
1900 [KVM,ARM] Trap guest accesses to GICv3 common
1903 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1904 (virtualized MMU) support on capable Intel chips.
1905 Default is 1 (enabled)
1907 kvm-intel.emulate_invalid_guest_state=
1908 [KVM,Intel] Disable emulation of invalid guest state.
1909 Ignored if kvm-intel.enable_unrestricted_guest=1, as
1910 guest state is never invalid for unrestricted guests.
1911 This param doesn't apply to nested guests (L2), as KVM
1912 never emulates invalid L2 guest state.
1913 Default is 1 (enabled)
1915 kvm-intel.flexpriority=
1916 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1917 Default is 1 (enabled)
1920 [KVM,Intel] Enable VMX nesting (nVMX).
1921 Default is 0 (disabled)
1923 kvm-intel.unrestricted_guest=
1924 [KVM,Intel] Disable unrestricted guest feature
1925 (virtualized real and unpaged mode) on capable
1926 Intel chips. Default is 1 (enabled)
1928 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1931 Valid arguments: never, cond, always
1933 always: L1D cache flush on every VMENTER.
1934 cond: Flush L1D on VMENTER only when the code between
1935 VMEXIT and VMENTER can leak host memory.
1936 never: Disables the mitigation
1938 Default is cond (do L1 cache flush in specific instances)
1940 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1941 feature (tagged TLBs) on capable Intel chips.
1942 Default is 1 (enabled)
1944 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1947 The kernel PTE inversion protection is unconditionally
1948 enabled and cannot be disabled.
1951 Provides all available mitigations for the
1952 L1TF vulnerability. Disables SMT and
1953 enables all mitigations in the
1954 hypervisors, i.e. unconditional L1D flush.
1956 SMT control and L1D flush control via the
1957 sysfs interface is still possible after
1958 boot. Hypervisors will issue a warning
1959 when the first VM is started in a
1960 potentially insecure configuration,
1961 i.e. SMT enabled or L1D flush disabled.
1964 Same as 'full', but disables SMT and L1D
1965 flush runtime control. Implies the
1966 'nosmt=force' command line option.
1967 (i.e. sysfs control of SMT is disabled.)
1970 Leaves SMT enabled and enables the default
1971 hypervisor mitigation, i.e. conditional
1974 SMT control and L1D flush control via the
1975 sysfs interface is still possible after
1976 boot. Hypervisors will issue a warning
1977 when the first VM is started in a
1978 potentially insecure configuration,
1979 i.e. SMT enabled or L1D flush disabled.
1983 Disables SMT and enables the default
1984 hypervisor mitigation.
1986 SMT control and L1D flush control via the
1987 sysfs interface is still possible after
1988 boot. Hypervisors will issue a warning
1989 when the first VM is started in a
1990 potentially insecure configuration,
1991 i.e. SMT enabled or L1D flush disabled.
1994 Same as 'flush', but hypervisors will not
1995 warn when a VM is started in a potentially
1996 insecure configuration.
1999 Disables hypervisor mitigations and doesn't
2001 It also drops the swap size and available
2002 RAM limit restriction on both hypervisor and
2007 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2013 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2016 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2017 value for LAPIC timer one-shot implementation. Default
2018 back to the programmable timer unit in the LAPIC.
2020 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2023 libata.dma= [LIBATA] DMA control
2024 libata.dma=0 Disable all PATA and SATA DMA
2025 libata.dma=1 PATA and SATA Disk DMA only
2026 libata.dma=2 ATAPI (CDROM) DMA only
2027 libata.dma=4 Compact Flash DMA only
2028 Combinations also work, so libata.dma=3 enables DMA
2029 for disks and CDROMs, but not CFs.
2031 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2032 libata.ignore_hpa=0 keep BIOS limits (default)
2033 libata.ignore_hpa=1 ignore limits, using full disk
2035 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2039 libata.force= [LIBATA] Force configurations. The format is comma
2040 separated list of "[ID:]VAL" where ID is
2041 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2042 matching port, link or device. Basically, it matches
2043 the ATA ID string printed on console by libata. If
2044 the whole ID part is omitted, the last PORT and DEVICE
2045 values are used. If ID hasn't been specified yet, the
2046 configuration applies to all ports, links and devices.
2048 If only DEVICE is omitted, the parameter applies to
2049 the port and all links and devices behind it. DEVICE
2050 number of 0 either selects the first device or the
2051 first fan-out link behind PMP device. It does not
2052 select the host link. DEVICE number of 15 selects the
2053 host link and device attached to it.
2055 The VAL specifies the configuration to force. As long
2056 as there's no ambiguity shortcut notation is allowed.
2057 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2058 The following configurations can be forced.
2060 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2061 Any ID with matching PORT is used.
2063 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2065 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2066 udma[/][16,25,33,44,66,100,133] notation is also
2069 * [no]ncq: Turn on or off NCQ.
2071 * [no]ncqtrim: Turn off queued DSM TRIM.
2073 * nohrst, nosrst, norst: suppress hard, soft
2076 * rstonce: only attempt one reset during
2077 hot-unplug link recovery
2079 * dump_id: dump IDENTIFY data.
2081 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2083 * disable: Disable this device.
2085 If there are multiple matching configurations changing
2086 the same attribute, the last one is used.
2088 memblock=debug [KNL] Enable memblock debug messages.
2090 load_ramdisk= [RAM] List of ramdisks to load from floppy
2091 See Documentation/blockdev/ramdisk.txt.
2093 lockd.nlm_grace_period=P [NFS] Assign grace period.
2096 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2099 lockd.nlm_timeout=T [NFS] Assign timeout value.
2102 lockd.nlm_udpport=M [NFS] Assign UDP port.
2105 locktorture.nreaders_stress= [KNL]
2106 Set the number of locking read-acquisition kthreads.
2107 Defaults to being automatically set based on the
2108 number of online CPUs.
2110 locktorture.nwriters_stress= [KNL]
2111 Set the number of locking write-acquisition kthreads.
2113 locktorture.onoff_holdoff= [KNL]
2114 Set time (s) after boot for CPU-hotplug testing.
2116 locktorture.onoff_interval= [KNL]
2117 Set time (s) between CPU-hotplug operations, or
2118 zero to disable CPU-hotplug testing.
2120 locktorture.shuffle_interval= [KNL]
2121 Set task-shuffle interval (jiffies). Shuffling
2122 tasks allows some CPUs to go into dyntick-idle
2123 mode during the locktorture test.
2125 locktorture.shutdown_secs= [KNL]
2126 Set time (s) after boot system shutdown. This
2127 is useful for hands-off automated testing.
2129 locktorture.stat_interval= [KNL]
2130 Time (s) between statistics printk()s.
2132 locktorture.stutter= [KNL]
2133 Time (s) to stutter testing, for example,
2134 specifying five seconds causes the test to run for
2135 five seconds, wait for five seconds, and so on.
2136 This tests the locking primitive's ability to
2137 transition abruptly to and from idle.
2139 locktorture.torture_runnable= [BOOT]
2140 Start locktorture running at boot time.
2142 locktorture.torture_type= [KNL]
2143 Specify the locking implementation to test.
2145 locktorture.verbose= [KNL]
2146 Enable additional printk() statements.
2148 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2151 loglevel= All Kernel Messages with a loglevel smaller than the
2152 console loglevel will be printed to the console. It can
2153 also be changed with klogd or other programs. The
2154 loglevels are defined as follows:
2156 0 (KERN_EMERG) system is unusable
2157 1 (KERN_ALERT) action must be taken immediately
2158 2 (KERN_CRIT) critical conditions
2159 3 (KERN_ERR) error conditions
2160 4 (KERN_WARNING) warning conditions
2161 5 (KERN_NOTICE) normal but significant condition
2162 6 (KERN_INFO) informational
2163 7 (KERN_DEBUG) debug-level messages
2165 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2166 in bytes. n must be a power of two and greater
2167 than the minimal size. The minimal size is defined
2168 by LOG_BUF_SHIFT kernel config parameter. There is
2169 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2170 that allows to increase the default size depending on
2171 the number of CPUs. See init/Kconfig for more details.
2173 logo.nologo [FB] Disables display of the built-in Linux logo.
2174 This may be used to provide more screen space for
2175 kernel log messages and is useful when debugging
2176 kernel boot problems.
2178 lp=0 [LP] Specify parallel ports to use, e.g,
2179 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2180 lp=reset first parallel port). 'lp=0' disables the
2181 lp=auto printer driver. 'lp=reset' (which can be
2182 specified in addition to the ports) causes
2183 attached printers to be reset. Using
2184 lp=port1,port2,... specifies the parallel ports
2185 to associate lp devices with, starting with
2186 lp0. A port specification may be 'none' to skip
2187 that lp device, or a parport name such as
2188 'parport0'. Specifying 'lp=auto' instead of a
2189 port specification list means that device IDs
2190 from each port should be examined, to see if
2191 an IEEE 1284-compliant printer is attached; if
2192 so, the driver will manage that printer.
2193 See also header of drivers/char/lp.c.
2196 Sets loops_per_jiffy to given constant, thus avoiding
2197 time-consuming boot-time autodetection (up to 250 ms per
2198 CPU). 0 enables autodetection (default). To determine
2199 the correct value for your kernel, boot with normal
2200 autodetection and see what value is printed. Note that
2201 on SMP systems the preset will be applied to all CPUs,
2202 which is likely to cause problems if your CPUs need
2203 significantly divergent settings. An incorrect value
2204 will cause delays in the kernel to be wrong, leading to
2205 unpredictable I/O errors and other breakage. Although
2206 unlikely, in the extreme case this might damage your
2210 Format: <io>,<irq>,<dma>
2212 machvec= [IA-64] Force the use of a particular machine-vector
2213 (machvec) in a generic kernel.
2214 Example: machvec=hpzx1_swiotlb
2216 machtype= [Loongson] Share the same kernel image file between different
2218 Example: machtype=lemote-yeeloong-2f-7inch
2220 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2221 than or equal to this physical address is ignored.
2223 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2224 will bring up during bootup. maxcpus=n : n >= 0 limits
2225 the kernel to bring up 'n' processors. Surely after
2226 bootup you can bring up the other plugged cpu by executing
2227 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2228 only takes effect during system bootup.
2229 While n=0 is a special case, it is equivalent to "nosmp",
2230 which also disables the IO APIC.
2232 max_loop= [LOOP] The number of loop block devices that get
2233 (loop.max_loop) unconditionally pre-created at init time. The default
2234 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2235 of statically allocating a predefined number, loop
2236 devices can be requested on-demand with the
2237 /dev/loop-control interface.
2239 mce [X86-32] Machine Check Exception
2241 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2243 md= [HW] RAID subsystems devices and level
2244 See Documentation/admin-guide/md.rst.
2247 Format: <first>,<last>
2248 Specifies range of consoles to be captured by the MDA.
2251 Control mitigation for the Micro-architectural Data
2252 Sampling (MDS) vulnerability.
2254 Certain CPUs are vulnerable to an exploit against CPU
2255 internal buffers which can forward information to a
2256 disclosure gadget under certain conditions.
2258 In vulnerable processors, the speculatively
2259 forwarded data can be used in a cache side channel
2260 attack, to access data to which the attacker does
2261 not have direct access.
2263 This parameter controls the MDS mitigation. The
2266 full - Enable MDS mitigation on vulnerable CPUs
2267 full,nosmt - Enable MDS mitigation and disable
2268 SMT on vulnerable CPUs
2269 off - Unconditionally disable MDS mitigation
2271 On TAA-affected machines, mds=off can be prevented by
2272 an active TAA mitigation as both vulnerabilities are
2273 mitigated with the same mechanism so in order to disable
2274 this mitigation, you need to specify tsx_async_abort=off
2277 Not specifying this option is equivalent to
2280 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2282 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2283 Amount of memory to be used when the kernel is not able
2284 to see the whole system memory or for test.
2285 [X86] Work as limiting max address. Use together
2286 with memmap= to avoid physical address space collisions.
2287 Without memmap= PCI devices could be placed at addresses
2288 belonging to unused RAM.
2290 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2294 [KNL,SH] Allow user to override the default size for
2295 per-device physically contiguous DMA buffers.
2297 memhp_default_state=online/offline
2298 [KNL] Set the initial state for the memory hotplug
2299 onlining policy. If not specified, the default value is
2300 set according to the
2301 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2303 See Documentation/memory-hotplug.txt.
2305 memmap=exactmap [KNL,X86] Enable setting of an exact
2306 E820 memory map, as specified by the user.
2307 Such memmap=exactmap lines can be constructed based on
2308 BIOS output or other requirements. See the memmap=nn@ss
2311 memmap=nn[KMG]@ss[KMG]
2312 [KNL] Force usage of a specific region of memory.
2313 Region of memory to be used is from ss to ss+nn.
2314 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2315 which limits max address to nn[KMG].
2316 Multiple different regions can be specified,
2319 memmap=100M@2G,100M#3G,1G!1024G
2321 memmap=nn[KMG]#ss[KMG]
2322 [KNL,ACPI] Mark specific memory as ACPI data.
2323 Region of memory to be marked is from ss to ss+nn.
2325 memmap=nn[KMG]$ss[KMG]
2326 [KNL,ACPI] Mark specific memory as reserved.
2327 Region of memory to be reserved is from ss to ss+nn.
2328 Example: Exclude memory from 0x18690000-0x1869ffff
2329 memmap=64K$0x18690000
2331 memmap=0x10000$0x18690000
2332 Some bootloaders may need an escape character before '$',
2333 like Grub2, otherwise '$' and the following number
2336 memmap=nn[KMG]!ss[KMG]
2337 [KNL,X86] Mark specific memory as protected.
2338 Region of memory to be used, from ss to ss+nn.
2339 The memory region may be marked as e820 type 12 (0xc)
2340 and is NVDIMM or ADR memory.
2342 memory_corruption_check=0/1 [X86]
2343 Some BIOSes seem to corrupt the first 64k of
2344 memory when doing things like suspend/resume.
2345 Setting this option will scan the memory
2346 looking for corruption. Enabling this will
2347 both detect corruption and prevent the kernel
2348 from using the memory being corrupted.
2349 However, its intended as a diagnostic tool; if
2350 repeatable BIOS-originated corruption always
2351 affects the same memory, you can use memmap=
2352 to prevent the kernel from using that memory.
2354 memory_corruption_check_size=size [X86]
2355 By default it checks for corruption in the low
2356 64k, making this memory unavailable for normal
2357 use. Use this parameter to scan for
2358 corruption in more or less memory.
2360 memory_corruption_check_period=seconds [X86]
2361 By default it checks for corruption every 60
2362 seconds. Use this parameter to check at some
2363 other rate. 0 disables periodic checking.
2365 memtest= [KNL,X86,ARM] Enable memtest
2367 default : 0 <disable>
2368 Specifies the number of memtest passes to be
2369 performed. Each pass selects another test
2370 pattern from a given set of patterns. Memtest
2371 fills the memory with this pattern, validates
2372 memory contents and reserves bad memory
2373 regions that are detected.
2375 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2376 Valid arguments: on, off
2377 Default (depends on kernel configuration option):
2378 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2379 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2380 mem_encrypt=on: Activate SME
2381 mem_encrypt=off: Do not activate SME
2383 Refer to Documentation/x86/amd-memory-encryption.txt
2384 for details on when memory encryption can be activated.
2386 mem_sleep_default= [SUSPEND] Default system suspend mode:
2387 s2idle - Suspend-To-Idle
2388 shallow - Power-On Suspend or equivalent (if supported)
2389 deep - Suspend-To-RAM or equivalent (if supported)
2390 See Documentation/power/states.txt.
2392 meye.*= [HW] Set MotionEye Camera parameters
2393 See Documentation/video4linux/meye.txt.
2395 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2396 Multi-Function General Purpose Timers on AMD Geode
2399 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2400 the BIOS has incorrectly applied a workaround. TinyBIOS
2401 version 0.98 is known to be affected, 0.99 fixes the
2402 problem by letting the user disable the workaround.
2406 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2407 physical address is ignored.
2409 mini2440= [ARM,HW,KNL]
2410 Format:[0..2][b][c][t]
2412 MINI2440 configuration specification:
2413 0 - The attached screen is the 3.5" TFT
2414 1 - The attached screen is the 7" TFT
2415 2 - The VGA Shield is attached (1024x768)
2416 Leaving out the screen size parameter will not load
2417 the TFT driver, and the framebuffer will be left
2419 b - Enable backlight. The TFT backlight pin will be
2420 linked to the kernel VESA blanking code and a GPIO
2421 LED. This parameter is not necessary when using the
2423 c - Enable the s3c camera interface.
2424 t - Reserved for enabling touchscreen support. The
2425 touchscreen support is not enabled in the mainstream
2426 kernel as of 2.6.30, a preliminary port can be found
2427 in the "bleeding edge" mini2440 support kernel at
2428 http://repo.or.cz/w/linux-2.6/mini2440.git
2431 [X86,PPC,S390,ARM64] Control optional mitigations for
2432 CPU vulnerabilities. This is a set of curated,
2433 arch-independent options, each of which is an
2434 aggregation of existing arch-specific options.
2437 Disable all optional CPU mitigations. This
2438 improves system performance, but it may also
2439 expose users to several CPU vulnerabilities.
2440 Equivalent to: nopti [X86,PPC]
2445 nospectre_v2 [X86,PPC,S390,ARM64]
2446 spectre_v2_user=off [X86]
2447 spec_store_bypass_disable=off [X86,PPC]
2448 ssbd=force-off [ARM64]
2451 tsx_async_abort=off [X86]
2452 kvm.nx_huge_pages=off [X86]
2453 no_entry_flush [PPC]
2454 no_uaccess_flush [PPC]
2457 This does not have any effect on
2458 kvm.nx_huge_pages when
2459 kvm.nx_huge_pages=force.
2462 Mitigate all CPU vulnerabilities, but leave SMT
2463 enabled, even if it's vulnerable. This is for
2464 users who don't want to be surprised by SMT
2465 getting disabled across kernel upgrades, or who
2466 have other ways of avoiding SMT-based attacks.
2467 Equivalent to: (default behavior)
2470 Mitigate all CPU vulnerabilities, disabling SMT
2471 if needed. This is for users who always want to
2472 be fully mitigated, even if it means losing SMT.
2473 Equivalent to: l1tf=flush,nosmt [X86]
2474 mds=full,nosmt [X86]
2475 tsx_async_abort=full,nosmt [X86]
2478 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2479 parameter allows control of the logging verbosity for
2480 the additional memory initialisation checks. A value
2481 of 0 disables mminit logging and a level of 4 will
2482 log everything. Information is printed at KERN_DEBUG
2483 so loglevel=8 may also need to be specified.
2486 [KNL] When CONFIG_MODULE_SIG is set, this means that
2487 modules without (valid) signatures will fail to load.
2488 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2489 is always true, so this option does nothing.
2491 module_blacklist= [KNL] Do not load a comma-separated list of
2492 modules. Useful for debugging problem modules.
2495 [MOUSE] Maximum time between finger touching and
2496 leaving touchpad surface for touch to be considered
2497 a tap and be reported as a left button click (for
2498 touchpads working in absolute mode only).
2500 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2501 reporting absolute coordinates, such as tablets
2502 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2503 reporting absolute coordinates, such as tablets
2505 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2506 is similar to kernelcore except it specifies the
2507 amount of memory used for migratable allocations.
2508 If both kernelcore and movablecore is specified,
2509 then kernelcore will be at *least* the specified
2510 value but may be more. If movablecore on its own
2511 is specified, the administrator must be careful
2512 that the amount of memory usable for all allocations
2515 movable_node [KNL] Boot-time switch to make hotplugable memory
2516 NUMA nodes to be movable. This means that the memory
2517 of such nodes will be usable only for movable
2518 allocations which rules out almost all kernel
2519 allocations. Use with caution!
2521 MTD_Partition= [MTD]
2522 Format: <name>,<region-number>,<size>,<offset>
2524 MTD_Region= [MTD] Format:
2525 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2528 See drivers/mtd/cmdlinepart.c.
2530 multitce=off [PPC] This parameter disables the use of the pSeries
2531 firmware feature for updating multiple TCE entries
2534 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2536 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2538 boundary - index of last SLC block on Flex-OneNAND.
2539 The remaining blocks are configured as MLC blocks.
2540 lock - Configure if Flex-OneNAND boundary should be locked.
2541 Once locked, the boundary cannot be changed.
2542 1 indicates lock status, 0 indicates unlock status.
2545 ARM/S3C2412 JIVE boot control
2547 See arch/arm/mach-s3c2412/mach-jive.c
2549 mtouchusb.raw_coordinates=
2550 [HW] Make the MicroTouch USB driver use raw coordinates
2551 ('y', default) or cooked coordinates ('n')
2553 mtrr_chunk_size=nn[KMG] [X86]
2554 used for mtrr cleanup. It is largest continuous chunk
2555 that could hold holes aka. UC entries.
2557 mtrr_gran_size=nn[KMG] [X86]
2558 Used for mtrr cleanup. It is granularity of mtrr block.
2560 Large value could prevent small alignment from
2563 mtrr_spare_reg_nr=n [X86]
2565 Range: 0,7 : spare reg number
2567 Used for mtrr cleanup. It is spare mtrr entries number.
2568 Set to 2 or more if your graphical card needs more.
2570 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2572 netdev= [NET] Network devices parameters
2573 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2574 Note that mem_start is often overloaded to mean
2575 something different and driver-specific.
2576 This usage is only documented in each driver source
2580 [NETFILTER] Enable connection tracking flow accounting
2581 0 to disable accounting
2582 1 to enable accounting
2585 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2586 See Documentation/filesystems/nfs/nfsroot.txt.
2588 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2589 See Documentation/filesystems/nfs/nfsroot.txt.
2591 nfsrootdebug [NFS] enable nfsroot debugging messages.
2592 See Documentation/filesystems/nfs/nfsroot.txt.
2594 nfs.callback_nr_threads=
2595 [NFSv4] set the total number of threads that the
2596 NFS client will assign to service NFSv4 callback
2599 nfs.callback_tcpport=
2600 [NFS] set the TCP port on which the NFSv4 callback
2601 channel should listen.
2604 [NFS] sets the pathname to the program which is used
2605 to update the NFS client cache entries.
2607 nfs.cache_getent_timeout=
2608 [NFS] sets the timeout after which an attempt to
2609 update a cache entry is deemed to have failed.
2611 nfs.idmap_cache_timeout=
2612 [NFS] set the maximum lifetime for idmapper cache
2616 [NFS] enable 64-bit inode numbers.
2617 If zero, the NFS client will fake up a 32-bit inode
2618 number for the readdir() and stat() syscalls instead
2619 of returning the full 64-bit number.
2620 The default is to return 64-bit inode numbers.
2622 nfs.max_session_cb_slots=
2623 [NFSv4.1] Sets the maximum number of session
2624 slots the client will assign to the callback
2625 channel. This determines the maximum number of
2626 callbacks the client will process in parallel for
2627 a particular server.
2629 nfs.max_session_slots=
2630 [NFSv4.1] Sets the maximum number of session slots
2631 the client will attempt to negotiate with the server.
2632 This limits the number of simultaneous RPC requests
2633 that the client can send to the NFSv4.1 server.
2634 Note that there is little point in setting this
2635 value higher than the max_tcp_slot_table_limit.
2637 nfs.nfs4_disable_idmapping=
2638 [NFSv4] When set to the default of '1', this option
2639 ensures that both the RPC level authentication
2640 scheme and the NFS level operations agree to use
2641 numeric uids/gids if the mount is using the
2642 'sec=sys' security flavour. In effect it is
2643 disabling idmapping, which can make migration from
2644 legacy NFSv2/v3 systems to NFSv4 easier.
2645 Servers that do not support this mode of operation
2646 will be autodetected by the client, and it will fall
2647 back to using the idmapper.
2648 To turn off this behaviour, set the value to '0'.
2650 [NFS4] Specify an additional fixed unique ident-
2651 ification string that NFSv4 clients can insert into
2652 their nfs_client_id4 string. This is typically a
2653 UUID that is generated at system install time.
2655 nfs.send_implementation_id =
2656 [NFSv4.1] Send client implementation identification
2657 information in exchange_id requests.
2658 If zero, no implementation identification information
2660 The default is to send the implementation identification
2663 nfs.recover_lost_locks =
2664 [NFSv4] Attempt to recover locks that were lost due
2665 to a lease timeout on the server. Please note that
2666 doing this risks data corruption, since there are
2667 no guarantees that the file will remain unchanged
2668 after the locks are lost.
2669 If you want to enable the kernel legacy behaviour of
2670 attempting to recover these locks, then set this
2672 The default parameter value of '0' causes the kernel
2673 not to attempt recovery of lost locks.
2675 nfs4.layoutstats_timer =
2676 [NFSv4.2] Change the rate at which the kernel sends
2677 layoutstats to the pNFS metadata server.
2679 Setting this to value to 0 causes the kernel to use
2680 whatever value is the default set by the layout
2681 driver. A non-zero value sets the minimum interval
2682 in seconds between layoutstats transmissions.
2684 nfsd.nfs4_disable_idmapping=
2685 [NFSv4] When set to the default of '1', the NFSv4
2686 server will return only numeric uids and gids to
2687 clients using auth_sys, and will accept numeric uids
2688 and gids from such clients. This is intended to ease
2689 migration from NFSv2/v3.
2691 nmi_debug= [KNL,SH] Specify one or more actions to take
2692 when a NMI is triggered.
2693 Format: [state][,regs][,debounce][,die]
2695 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2696 Format: [panic,][nopanic,][num]
2698 0 - turn hardlockup detector in nmi_watchdog off
2699 1 - turn hardlockup detector in nmi_watchdog on
2700 When panic is specified, panic when an NMI watchdog
2701 timeout occurs (or 'nopanic' to override the opposite
2702 default). To disable both hard and soft lockup detectors,
2703 please see 'nowatchdog'.
2704 This is useful when you use a panic=... timeout and
2705 need the box quickly up again.
2707 netpoll.carrier_timeout=
2708 [NET] Specifies amount of time (in seconds) that
2709 netpoll should wait for a carrier. By default netpoll
2712 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2713 emulation library even if a 387 maths coprocessor
2717 [HW] Never suspend the console
2718 Disable suspending of consoles during suspend and
2719 hibernate operations. Once disabled, debugging
2720 messages can reach various consoles while the rest
2721 of the system is being put to sleep (ie, while
2722 debugging driver suspend/resume hooks). This may
2723 not work reliably with all consoles, but is known
2724 to work with serial and VGA consoles.
2725 To facilitate more flexible debugging, we also add
2726 console_suspend, a printk module parameter to control
2727 it. Users could use console_suspend (usually
2728 /sys/module/printk/parameters/console_suspend) to
2729 turn on/off it dynamically.
2731 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2732 caches in the slab allocator. Saves per-node memory,
2733 but will impact performance.
2737 noaltinstr [S390] Disables alternative instructions patching
2738 (CPU alternatives feature).
2740 noapic [SMP,APIC] Tells the kernel to not make use of any
2741 IOAPICs that may be present in the system.
2743 noautogroup Disable scheduler automatic task group creation.
2745 nobats [PPC] Do not use BATs for mapping kernel lowmem
2746 on "Classic" PPC cores.
2750 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2752 nodelayacct [KNL] Disable per-task delay accounting
2754 nodsp [SH] Disable hardware DSP at boot time.
2756 noefi Disable EFI runtime services support.
2758 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
2763 On X86-32 available only on PAE configured kernels.
2764 noexec=on: enable non-executable mappings (default)
2765 noexec=off: disable non-executable mappings
2768 Disable SMAP (Supervisor Mode Access Prevention)
2769 even if it is supported by processor.
2772 Disable SMEP (Supervisor Mode Execution Prevention)
2773 even if it is supported by processor.
2776 This affects only 32-bit executables.
2777 noexec32=on: enable non-executable mappings (default)
2778 read doesn't imply executable mappings
2779 noexec32=off: disable non-executable mappings
2780 read implies executable mappings
2782 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2784 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2785 register save and restore. The kernel will only save
2786 legacy floating-point registers on task switch.
2788 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2790 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2791 Equivalent to smt=1.
2793 [KNL,x86] Disable symmetric multithreading (SMT).
2794 nosmt=force: Force disable SMT, cannot be undone
2795 via the sysfs control file.
2797 nospectre_v1 [X66, PPC] Disable mitigations for Spectre Variant 1
2798 (bounds check bypass). With this option data leaks
2799 are possible in the system.
2801 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2802 the Spectre variant 2 (indirect branch prediction)
2803 vulnerability. System may allow data leaks with this
2806 nospec_store_bypass_disable
2807 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2810 [PPC] Don't flush the L1-D cache after accessing user data.
2812 noxsave [BUGS=X86] Disables x86 extended register state save
2813 and restore using xsave. The kernel will fallback to
2814 enabling legacy floating-point and sse state.
2816 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2817 register states. The kernel will fall back to use
2818 xsave to save the states. By using this parameter,
2819 performance of saving the states is degraded because
2820 xsave doesn't support modified optimization while
2821 xsaveopt supports it on xsaveopt enabled systems.
2823 noxsaves [X86] Disables xsaves and xrstors used in saving and
2824 restoring x86 extended register state in compacted
2825 form of xsave area. The kernel will fall back to use
2826 xsaveopt and xrstor to save and restore the states
2827 in standard form of xsave area. By using this
2828 parameter, xsave area per process might occupy more
2829 memory on xsaves enabled systems.
2831 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2832 wfi(ARM) instruction doesn't work correctly and not to
2833 use it. This is also useful when using JTAG debugger.
2835 no_file_caps Tells the kernel not to honor file capabilities. The
2836 only way then for a file to be executed with privilege
2837 is to be setuid root or executed by root.
2839 nohalt [IA-64] Tells the kernel not to use the power saving
2840 function PAL_HALT_LIGHT when idle. This increases
2841 power-consumption. On the positive side, it reduces
2842 interrupt wake-up latency, which may improve performance
2843 in certain environments such as networked servers or
2846 nohibernate [HIBERNATION] Disable hibernation and resume.
2848 nohz= [KNL] Boottime enable/disable dynamic ticks
2849 Valid arguments: on, off
2852 nohz_full= [KNL,BOOT]
2853 The argument is a cpu list, as described above.
2854 In kernels built with CONFIG_NO_HZ_FULL=y, set
2855 the specified list of CPUs whose tick will be stopped
2856 whenever possible. The boot CPU will be forced outside
2857 the range to maintain the timekeeping. Any CPUs
2858 in this list will have their RCU callbacks offloaded,
2859 just as if they had also been called out in the
2860 rcu_nocbs= boot parameter.
2862 noiotrap [SH] Disables trapped I/O port accesses.
2864 noirqdebug [X86-32] Disables the code which attempts to detect and
2865 disable unhandled interrupt sources.
2867 no_timer_check [X86,APIC] Disables the code which tests for
2868 broken timer IRQ sources.
2870 noisapnp [ISAPNP] Disables ISA PnP code.
2872 noinitrd [RAM] Tells the kernel not to load any configured
2875 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2877 [Deprecated - use intremap=off]
2881 noinvpcid [X86] Disable the INVPCID cpu feature.
2883 nojitter [IA-64] Disables jitter checking for ITC timers.
2885 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2887 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2891 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2892 clock and use the default one.
2894 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2895 steal time is computed, but won't influence scheduler
2898 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2900 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2902 noltlbs [PPC] Do not use large page/tlb entries for kernel
2903 lowmem mapping on PPC40x and PPC8xx
2905 nomca [IA-64] Disable machine check abort handling
2907 nomce [X86-32] Disable Machine Check Exception
2909 nomfgpt [X86-32] Disable Multi-Function General Purpose
2910 Timer usage (for AMD Geode machines).
2912 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2913 shutdown the other cpus. Instead use the REBOOT_VECTOR
2916 nomodule Disable module load
2918 nopat [X86] Disable PAT (page attribute table extension of
2919 pagetables) support.
2921 nopcid [X86-64] Disable the PCID cpu feature.
2923 norandmaps Don't use address space randomization. Equivalent to
2924 echo 0 > /proc/sys/kernel/randomize_va_space
2926 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2927 with UP alternatives
2929 nordrand [X86] Disable kernel use of the RDRAND and
2930 RDSEED instructions even if they are supported
2931 by the processor. RDRAND and RDSEED are still
2932 available to user space applications.
2934 noresume [SWSUSP] Disables resume and restores original swap
2937 no-scroll [VGA] Disables scrollback.
2938 This is required for the Braillex ib80-piezo Braille
2939 reader made by F.H. Papenmeier (Germany).
2943 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2945 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2946 and disable the IO APIC. legacy for "maxcpus=0".
2948 nosoftlockup [KNL] Disable the soft-lockup detector.
2950 nosync [HW,M68K] Disables sync negotiation for all devices.
2952 notsc [BUGS=X86-32] Disable Time Stamp Counter
2954 nowatchdog [KNL] Disable both lockup detectors, i.e.
2955 soft-lockup and NMI watchdog (hard-lockup).
2959 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2961 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2962 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2963 Some features depend on CPU0. Known dependencies are:
2964 1. Resume from suspend/hibernate depends on CPU0.
2965 Suspend/hibernate will fail if CPU0 is offline and you
2966 need to online CPU0 before suspend/hibernate.
2967 2. PIC interrupts also depend on CPU0. CPU0 can't be
2968 removed if a PIC interrupt is detected.
2969 It's said poweroff/reboot may depend on CPU0 on some
2970 machines although I haven't seen such issues so far
2971 after CPU0 is offline on a few tested machines.
2972 If the dependencies are under your control, you can
2973 turn on cpu0_hotplug.
2975 nps_mtm_hs_ctr= [KNL,ARC]
2976 This parameter sets the maximum duration, in
2977 cycles, each HW thread of the CTOP can run
2978 without interruptions, before HW switches it.
2979 The actual maximum duration is 16 times this
2981 Format: integer between 1 and 255
2984 nptcg= [IA-64] Override max number of concurrent global TLB
2985 purges which is reported from either PAL_VM_SUMMARY or
2988 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2989 could support. nr_cpus=n : n >= 1 limits the kernel to
2990 support 'n' processors. It could be larger than the
2991 number of already plugged CPU during bootup, later in
2992 runtime you can physically add extra cpu until it reaches
2993 n. So during boot up some boot time memory for per-cpu
2994 variables need be pre-allocated for later physical cpu
2997 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2999 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3000 Allowed values are enable and disable
3002 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3003 'node', 'default' can be specified
3004 This can be set from sysctl after boot.
3005 See Documentation/sysctl/vm.txt for details.
3007 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3008 See Documentation/debugging-via-ohci1394.txt for more
3011 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3012 Rather than timing out after 20 ms if an EC
3013 command is not properly ACKed, override the length
3014 of the timeout. We have interrupts disabled while
3015 waiting for the ACK, so if this is set too high
3016 interrupts *may* be lost!
3018 omap_mux= [OMAP] Override bootloader pin multiplexing.
3019 Format: <mux_mode0.mode_name=value>...
3020 For example, to override I2C bus2:
3021 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3023 oprofile.timer= [HW]
3024 Use timer interrupt instead of performance counters
3026 oprofile.cpu_type= Force an oprofile cpu type
3027 This might be useful if you have an older oprofile
3028 userland or if you want common events.
3029 Format: { arch_perfmon }
3030 arch_perfmon: [X86] Force use of architectural
3031 perfmon on Intel CPUs instead of the
3032 CPU specific event set.
3033 timer: [X86] Force use of architectural NMI
3034 timer mode (see also oprofile.timer
3035 for generic hr timer mode)
3037 oops=panic Always panic on oopses. Default is to just kill the
3038 process, but there is a small probability of
3039 deadlocking the machine.
3040 This will also cause panics on machine check exceptions.
3041 Useful together with panic=30 to trigger a reboot.
3044 See Documentation/sound/oss/oss-parameters.txt
3046 page_owner= [KNL] Boot-time page_owner enabling option.
3047 Storage of the information about who allocated
3048 each page is disabled in default. With this switch,
3050 on: enable the feature
3052 page_poison= [KNL] Boot-time parameter changing the state of
3053 poisoning on the buddy allocator.
3054 off: turn off poisoning
3055 on: turn on poisoning
3057 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3058 timeout > 0: seconds before rebooting
3059 timeout = 0: wait forever
3060 timeout < 0: reboot immediately
3063 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3066 crash_kexec_post_notifiers
3067 Run kdump after running panic-notifiers and dumping
3068 kmsg. This only for the users who doubt kdump always
3069 succeeds in any situation.
3070 Note that this also increases risks of kdump failure,
3071 because some panic notifiers can make the crashed
3072 kernel more unstable.
3074 parkbd.port= [HW] Parallel port number the keyboard adapter is
3075 connected to, default is 0.
3077 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3078 0 for XT, 1 for AT (default is AT).
3081 parport= [HW,PPT] Specify parallel ports. 0 disables.
3082 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3083 Use 'auto' to force the driver to use any
3084 IRQ/DMA settings detected (the default is to
3085 ignore detected IRQ/DMA settings because of
3086 possible conflicts). You can specify the base
3087 address, IRQ, and DMA settings; IRQ and DMA
3088 should be numbers, or 'auto' (for using detected
3089 settings on that particular port), or 'nofifo'
3090 (to avoid using a FIFO even if it is detected).
3091 Parallel ports are assigned in the order they
3092 are specified on the command line, starting
3095 parport_init_mode= [HW,PPT]
3096 Configure VIA parallel port to operate in
3097 a specific mode. This is necessary on Pegasos
3098 computer where firmware has no options for setting
3099 up parallel port mode and sets it to spp.
3100 Currently this function knows 686a and 8231 chips.
3101 Format: [spp|ps2|epp|ecp|ecpepp]
3104 Halt all CPUs after the first oops has been printed for
3105 the specified number of seconds. This is to be used if
3106 your oopses keep scrolling off the screen.
3111 See header of drivers/block/paride/pcd.c.
3112 See also Documentation/blockdev/paride.txt.
3114 pci=option[,option...] [PCI] various PCI subsystem options:
3115 earlydump [X86] dump PCI config space before the kernel
3117 off [X86] don't probe for the PCI bus
3118 bios [X86-32] force use of PCI BIOS, don't access
3119 the hardware directly. Use this if your machine
3120 has a non-standard PCI host bridge.
3121 nobios [X86-32] disallow use of PCI BIOS, only direct
3122 hardware access methods are allowed. Use this
3123 if you experience crashes upon bootup and you
3124 suspect they are caused by the BIOS.
3125 conf1 [X86] Force use of PCI Configuration Access
3126 Mechanism 1 (config address in IO port 0xCF8,
3127 data in IO port 0xCFC, both 32-bit).
3128 conf2 [X86] Force use of PCI Configuration Access
3129 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3130 the function, IO port 0xCFA, also 8-bit, sets
3131 bus number. The config space is then accessed
3132 through ports 0xC000-0xCFFF).
3133 See http://wiki.osdev.org/PCI for more info
3134 on the configuration access mechanisms.
3135 noaer [PCIE] If the PCIEAER kernel config parameter is
3136 enabled, this kernel boot option can be used to
3137 disable the use of PCIE advanced error reporting.
3138 nodomains [PCI] Disable support for multiple PCI
3139 root domains (aka PCI segments, in ACPI-speak).
3140 nommconf [X86] Disable use of MMCONFIG for PCI
3142 check_enable_amd_mmconf [X86] check for and enable
3143 properly configured MMIO access to PCI
3144 config space on AMD family 10h CPU
3145 nomsi [MSI] If the PCI_MSI kernel config parameter is
3146 enabled, this kernel boot option can be used to
3147 disable the use of MSI interrupts system-wide.
3148 noioapicquirk [APIC] Disable all boot interrupt quirks.
3149 Safety option to keep boot IRQs enabled. This
3150 should never be necessary.
3151 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3152 primary IO-APIC for bridges that cannot disable
3153 boot IRQs. This fixes a source of spurious IRQs
3154 when the system masks IRQs.
3155 noioapicreroute [APIC] Disable workaround that uses the
3156 boot IRQ equivalent of an IRQ that connects to
3157 a chipset where boot IRQs cannot be disabled.
3158 The opposite of ioapicreroute.
3159 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3160 routing table. These calls are known to be buggy
3161 on several machines and they hang the machine
3162 when used, but on other computers it's the only
3163 way to get the interrupt routing table. Try
3164 this option if the kernel is unable to allocate
3165 IRQs or discover secondary PCI buses on your
3167 rom [X86] Assign address space to expansion ROMs.
3168 Use with caution as certain devices share
3169 address decoders between ROMs and other
3171 norom [X86] Do not assign address space to
3172 expansion ROMs that do not already have
3173 BIOS assigned address ranges.
3174 nobar [X86] Do not assign address space to the
3175 BARs that weren't assigned by the BIOS.
3176 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3177 assigned automatically to PCI devices. You can
3178 make the kernel exclude IRQs of your ISA cards
3180 pirqaddr=0xAAAAA [X86] Specify the physical address
3181 of the PIRQ table (normally generated
3182 by the BIOS) if it is outside the
3183 F0000h-100000h range.
3184 lastbus=N [X86] Scan all buses thru bus #N. Can be
3185 useful if the kernel is unable to find your
3186 secondary buses and you want to tell it
3187 explicitly which ones they are.
3188 assign-busses [X86] Always assign all PCI bus
3189 numbers ourselves, overriding
3190 whatever the firmware may have done.
3191 usepirqmask [X86] Honor the possible IRQ mask stored
3192 in the BIOS $PIR table. This is needed on
3193 some systems with broken BIOSes, notably
3194 some HP Pavilion N5400 and Omnibook XE3
3195 notebooks. This will have no effect if ACPI
3196 IRQ routing is enabled.
3197 noacpi [X86] Do not use ACPI for IRQ routing
3198 or for PCI scanning.
3199 use_crs [X86] Use PCI host bridge window information
3200 from ACPI. On BIOSes from 2008 or later, this
3201 is enabled by default. If you need to use this,
3202 please report a bug.
3203 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3204 If you need to use this, please report a bug.
3205 routeirq Do IRQ routing for all PCI devices.
3206 This is normally done in pci_enable_device(),
3207 so this option is a temporary workaround
3208 for broken drivers that don't call it.
3209 skip_isa_align [X86] do not align io start addr, so can
3210 handle more pci cards
3211 noearly [X86] Don't do any early type 1 scanning.
3212 This might help on some broken boards which
3213 machine check when some devices' config space
3214 is read. But various workarounds are disabled
3215 and some IOMMU drivers will not work.
3216 bfsort Sort PCI devices into breadth-first order.
3217 This sorting is done to get a device
3218 order compatible with older (<= 2.4) kernels.
3219 nobfsort Don't sort PCI devices into breadth-first order.
3220 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3221 tuning and use the BIOS-configured MPS defaults.
3222 pcie_bus_safe Set every device's MPS to the largest value
3223 supported by all devices below the root complex.
3224 pcie_bus_perf Set device MPS to the largest allowable MPS
3225 based on its parent bus. Also set MRRS (Max
3226 Read Request Size) to the largest supported
3227 value (no larger than the MPS that the device
3228 or bus can support) for best performance.
3229 pcie_bus_peer2peer Set every device's MPS to 128B, which
3230 every device is guaranteed to support. This
3231 configuration allows peer-to-peer DMA between
3232 any pair of devices, possibly at the cost of
3233 reduced performance. This also guarantees
3234 that hot-added devices will work.
3235 cbiosize=nn[KMG] The fixed amount of bus space which is
3236 reserved for the CardBus bridge's IO window.
3237 The default value is 256 bytes.
3238 cbmemsize=nn[KMG] The fixed amount of bus space which is
3239 reserved for the CardBus bridge's memory
3240 window. The default value is 64 megabytes.
3243 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3244 [<order of align>@]pci:<vendor>:<device>\
3245 [:<subvendor>:<subdevice>][; ...]
3246 Specifies alignment and device to reassign
3247 aligned memory resources.
3248 If <order of align> is not specified,
3249 PAGE_SIZE is used as alignment.
3250 PCI-PCI bridge can be specified, if resource
3251 windows need to be expanded.
3252 To specify the alignment for several
3253 instances of a device, the PCI vendor,
3254 device, subvendor, and subdevice may be
3255 specified, e.g., 4096@pci:8086:9c22:103c:198f
3256 ecrc= Enable/disable PCIe ECRC (transaction layer
3257 end-to-end CRC checking).
3258 bios: Use BIOS/firmware settings. This is the
3262 hpiosize=nn[KMG] The fixed amount of bus space which is
3263 reserved for hotplug bridge's IO window.
3264 Default size is 256 bytes.
3265 hpmemsize=nn[KMG] The fixed amount of bus space which is
3266 reserved for hotplug bridge's memory window.
3267 Default size is 2 megabytes.
3268 hpbussize=nn The minimum amount of additional bus numbers
3269 reserved for buses below a hotplug bridge.
3271 realloc= Enable/disable reallocating PCI bridge resources
3272 if allocations done by BIOS are too small to
3273 accommodate resources required by all child
3275 off: Turn realloc off
3277 realloc same as realloc=on
3278 noari do not use PCIe ARI.
3279 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3280 only look for one device below a PCIe downstream
3283 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3286 force Enable ASPM even on devices that claim not to support it.
3287 WARNING: Forcing ASPM on may cause system lockups.
3289 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3290 nomsi Do not use MSI for PCI Express Native Hotplug (this
3291 makes all PCIe ports use INTx for hotplug services).
3293 pcie_ports= [PCIE] PCIe ports handling:
3294 auto Ask the BIOS whether or not to use native PCIe services
3295 associated with PCIe ports (PME, hot-plug, AER). Use
3296 them only if that is allowed by the BIOS.
3297 native Use native PCIe services associated with PCIe ports
3299 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3302 pcie_port_pm= [PCIE] PCIe port power management handling:
3303 off Disable power management of all PCIe ports
3304 force Forcibly enable power management of all PCIe ports
3306 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3307 nomsi Do not use MSI for native PCIe PME signaling (this makes
3308 all PCIe root ports use INTx for all services).
3310 pcmv= [HW,PCMCIA] BadgePAD 4
3314 Keep all power-domains already enabled by bootloader on,
3315 even if no driver has claimed them. This is useful
3316 for debug and development, but should not be
3317 needed on a platform with proper driver support.
3320 See Documentation/blockdev/paride.txt.
3322 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3325 See arch/parisc/kernel/pdc_chassis.c
3327 percpu_alloc= Select which percpu first chunk allocator to use.
3328 Currently supported values are "embed" and "page".
3329 Archs may support subset or none of the selections.
3330 See comments in mm/percpu.c for details on each
3331 allocator. This parameter is primarily for debugging
3332 and performance comparison.
3335 See Documentation/blockdev/paride.txt.
3338 See Documentation/blockdev/paride.txt.
3340 pirq= [SMP,APIC] Manual mp-table setup
3341 See Documentation/x86/i386/IO-APIC.txt.
3343 plip= [PPT,NET] Parallel port network link
3344 Format: { parport<nr> | timid | 0 }
3345 See also Documentation/parport.txt.
3347 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3348 Override pmtimer IOPort with a hex value.
3352 Enable PNP debug messages (depends on the
3353 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3354 via /sys/module/pnp/parameters/debug. We always show
3355 current resource usage; turning this on also shows
3356 possible settings and some assignment information.
3362 { on | off | curr | res | no-curr | no-res }
3365 [ISAPNP] Exclude IRQs for the autoconfiguration
3368 [ISAPNP] Exclude DMAs for the autoconfiguration
3370 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3371 Ranges are in pairs (I/O port base and size).
3374 [ISAPNP] Exclude memory regions for the
3376 Ranges are in pairs (memory base and size).
3378 ports= [IP_VS_FTP] IPVS ftp helper module
3380 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3382 Format: <port>,<port>....
3384 powersave=off [PPC] This option disables power saving features.
3385 It specifically disables cpuidle and sets the
3386 platform machine description specific power_save
3387 function to NULL. On Idle the CPU just reduces
3390 ppc_strict_facility_enable
3391 [PPC] This option catches any kernel floating point,
3392 Altivec, VSX and SPE outside of regions specifically
3393 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3394 There is some performance impact when enabling this.
3396 print-fatal-signals=
3397 [KNL] debug: print fatal signals
3399 If enabled, warn about various signal handling
3400 related application anomalies: too many signals,
3401 too many POSIX.1 timers, fatal signals causing a
3404 If you hit the warning due to signal overflow,
3405 you might want to try "ulimit -i unlimited".
3409 printk.always_kmsg_dump=
3410 Trigger kmsg_dump for cases other than kernel oops or
3412 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3415 printk.devkmsg={on,off,ratelimit}
3416 Control writing to /dev/kmsg.
3417 on - unlimited logging to /dev/kmsg from userspace
3418 off - logging to /dev/kmsg disabled
3419 ratelimit - ratelimit the logging
3422 printk.time= Show timing data prefixed to each printk message line
3423 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3425 processor.max_cstate= [HW,ACPI]
3426 Limit processor to maximum C-state
3427 max_cstate=9 overrides any DMI blacklist limit.
3429 processor.nocst [HW,ACPI]
3430 Ignore the _CST method to determine C-states,
3431 instead using the legacy FADT method
3433 profile= [KNL] Enable kernel profiling via /proc/profile
3434 Format: [schedule,]<number>
3435 Param: "schedule" - profile schedule points.
3436 Param: <number> - step/bucket size as a power of 2 for
3437 statistical time based profiling.
3438 Param: "sleep" - profile D-state sleeping (millisecs).
3439 Requires CONFIG_SCHEDSTATS
3440 Param: "kvm" - profile VM exits.
3442 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3444 See Documentation/blockdev/ramdisk.txt.
3446 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3447 probe for; one of (bare|imps|exps|lifebook|any).
3448 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3450 psmouse.resetafter= [HW,MOUSE]
3451 Try to reset the device after so many bad packets
3454 [HW,MOUSE] Set desired mouse resolution, in dpi.
3455 psmouse.smartscroll=
3456 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3457 0 = disabled, 1 = enabled (default).
3459 pstore.backend= Specify the name of the pstore backend to use
3462 See Documentation/blockdev/paride.txt.
3464 pti= [X86_64] Control Page Table Isolation of user and
3465 kernel address spaces. Disabling this feature
3466 removes hardening, but improves performance of
3467 system calls and interrupts.
3469 on - unconditionally enable
3470 off - unconditionally disable
3471 auto - kernel detects whether your CPU model is
3472 vulnerable to issues that PTI mitigates
3474 Not specifying this option is equivalent to pti=auto.
3477 Equivalent to pti=off
3480 [KNL] Number of legacy pty's. Overwrites compiled-in
3483 quiet [KNL] Disable most log messages
3488 See Documentation/admin-guide/md.rst.
3490 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3491 See Documentation/blockdev/ramdisk.txt.
3493 ras=option[,option,...] [KNL] RAS-specific options
3496 Disable the Correctable Errors Collector,
3497 see CONFIG_RAS_CEC help text.
3500 The argument is a cpu list, as described above.
3502 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3503 the specified list of CPUs to be no-callback CPUs.
3504 Invocation of these CPUs' RCU callbacks will
3505 be offloaded to "rcuox/N" kthreads created for
3506 that purpose, where "x" is "b" for RCU-bh, "p"
3507 for RCU-preempt, and "s" for RCU-sched, and "N"
3508 is the CPU number. This reduces OS jitter on the
3509 offloaded CPUs, which can be useful for HPC and
3510 real-time workloads. It can also improve energy
3511 efficiency for asymmetric multiprocessors.
3514 Rather than requiring that offloaded CPUs
3515 (specified by rcu_nocbs= above) explicitly
3516 awaken the corresponding "rcuoN" kthreads,
3517 make these kthreads poll for callbacks.
3518 This improves the real-time response for the
3519 offloaded CPUs by relieving them of the need to
3520 wake up the corresponding kthread, but degrades
3521 energy efficiency by requiring that the kthreads
3522 periodically wake up to do the polling.
3524 rcutree.blimit= [KNL]
3525 Set maximum number of finished RCU callbacks to
3526 process in one batch.
3528 rcutree.dump_tree= [KNL]
3529 Dump the structure of the rcu_node combining tree
3530 out at early boot. This is used for diagnostic
3531 purposes, to verify correct tree setup.
3533 rcutree.gp_cleanup_delay= [KNL]
3534 Set the number of jiffies to delay each step of
3535 RCU grace-period cleanup.
3537 rcutree.gp_init_delay= [KNL]
3538 Set the number of jiffies to delay each step of
3539 RCU grace-period initialization.
3541 rcutree.gp_preinit_delay= [KNL]
3542 Set the number of jiffies to delay each step of
3543 RCU grace-period pre-initialization, that is,
3544 the propagation of recent CPU-hotplug changes up
3545 the rcu_node combining tree.
3547 rcutree.rcu_fanout_exact= [KNL]
3548 Disable autobalancing of the rcu_node combining
3549 tree. This is used by rcutorture, and might
3550 possibly be useful for architectures having high
3551 cache-to-cache transfer latencies.
3553 rcutree.rcu_fanout_leaf= [KNL]
3554 Change the number of CPUs assigned to each
3555 leaf rcu_node structure. Useful for very
3556 large systems, which will choose the value 64,
3557 and for NUMA systems with large remote-access
3558 latencies, which will choose a value aligned
3559 with the appropriate hardware boundaries.
3561 rcutree.jiffies_till_sched_qs= [KNL]
3562 Set required age in jiffies for a
3563 given grace period before RCU starts
3564 soliciting quiescent-state help from
3565 rcu_note_context_switch().
3567 rcutree.jiffies_till_first_fqs= [KNL]
3568 Set delay from grace-period initialization to
3569 first attempt to force quiescent states.
3570 Units are jiffies, minimum value is zero,
3571 and maximum value is HZ.
3573 rcutree.jiffies_till_next_fqs= [KNL]
3574 Set delay between subsequent attempts to force
3575 quiescent states. Units are jiffies, minimum
3576 value is one, and maximum value is HZ.
3578 rcutree.kthread_prio= [KNL,BOOT]
3579 Set the SCHED_FIFO priority of the RCU per-CPU
3580 kthreads (rcuc/N). This value is also used for
3581 the priority of the RCU boost threads (rcub/N)
3582 and for the RCU grace-period kthreads (rcu_bh,
3583 rcu_preempt, and rcu_sched). If RCU_BOOST is
3584 set, valid values are 1-99 and the default is 1
3585 (the least-favored priority). Otherwise, when
3586 RCU_BOOST is not set, valid values are 0-99 and
3587 the default is zero (non-realtime operation).
3589 rcutree.rcu_nocb_leader_stride= [KNL]
3590 Set the number of NOCB kthread groups, which
3591 defaults to the square root of the number of
3592 CPUs. Larger numbers reduces the wakeup overhead
3593 on the per-CPU grace-period kthreads, but increases
3594 that same overhead on each group's leader.
3596 rcutree.qhimark= [KNL]
3597 Set threshold of queued RCU callbacks beyond which
3598 batch limiting is disabled.
3600 rcutree.qlowmark= [KNL]
3601 Set threshold of queued RCU callbacks below which
3602 batch limiting is re-enabled.
3604 rcutree.rcu_idle_gp_delay= [KNL]
3605 Set wakeup interval for idle CPUs that have
3606 RCU callbacks (RCU_FAST_NO_HZ=y).
3608 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3609 Set wakeup interval for idle CPUs that have
3610 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3611 Lazy RCU callbacks are those which RCU can
3612 prove do nothing more than free memory.
3614 rcutree.rcu_kick_kthreads= [KNL]
3615 Cause the grace-period kthread to get an extra
3616 wake_up() if it sleeps three times longer than
3617 it should at force-quiescent-state time.
3618 This wake_up() will be accompanied by a
3619 WARN_ONCE() splat and an ftrace_dump().
3621 rcuperf.gp_async= [KNL]
3622 Measure performance of asynchronous
3623 grace-period primitives such as call_rcu().
3625 rcuperf.gp_async_max= [KNL]
3626 Specify the maximum number of outstanding
3627 callbacks per writer thread. When a writer
3628 thread exceeds this limit, it invokes the
3629 corresponding flavor of rcu_barrier() to allow
3630 previously posted callbacks to drain.
3632 rcuperf.gp_exp= [KNL]
3633 Measure performance of expedited synchronous
3634 grace-period primitives.
3636 rcuperf.holdoff= [KNL]
3637 Set test-start holdoff period. The purpose of
3638 this parameter is to delay the start of the
3639 test until boot completes in order to avoid
3642 rcuperf.nreaders= [KNL]
3643 Set number of RCU readers. The value -1 selects
3644 N, where N is the number of CPUs. A value
3645 "n" less than -1 selects N-n+1, where N is again
3646 the number of CPUs. For example, -2 selects N
3647 (the number of CPUs), -3 selects N+1, and so on.
3648 A value of "n" less than or equal to -N selects
3651 rcuperf.nwriters= [KNL]
3652 Set number of RCU writers. The values operate
3653 the same as for rcuperf.nreaders.
3654 N, where N is the number of CPUs
3656 rcuperf.perf_runnable= [BOOT]
3657 Start rcuperf running at boot time.
3659 rcuperf.perf_type= [KNL]
3660 Specify the RCU implementation to test.
3662 rcuperf.shutdown= [KNL]
3663 Shut the system down after performance tests
3664 complete. This is useful for hands-off automated
3667 rcuperf.verbose= [KNL]
3668 Enable additional printk() statements.
3670 rcuperf.writer_holdoff= [KNL]
3671 Write-side holdoff between grace periods,
3672 in microseconds. The default of zero says
3675 rcutorture.cbflood_inter_holdoff= [KNL]
3676 Set holdoff time (jiffies) between successive
3677 callback-flood tests.
3679 rcutorture.cbflood_intra_holdoff= [KNL]
3680 Set holdoff time (jiffies) between successive
3681 bursts of callbacks within a given callback-flood
3684 rcutorture.cbflood_n_burst= [KNL]
3685 Set the number of bursts making up a given
3686 callback-flood test. Set this to zero to
3687 disable callback-flood testing.
3689 rcutorture.cbflood_n_per_burst= [KNL]
3690 Set the number of callbacks to be registered
3691 in a given burst of a callback-flood test.
3693 rcutorture.fqs_duration= [KNL]
3694 Set duration of force_quiescent_state bursts
3697 rcutorture.fqs_holdoff= [KNL]
3698 Set holdoff time within force_quiescent_state bursts
3701 rcutorture.fqs_stutter= [KNL]
3702 Set wait time between force_quiescent_state bursts
3705 rcutorture.gp_cond= [KNL]
3706 Use conditional/asynchronous update-side
3707 primitives, if available.
3709 rcutorture.gp_exp= [KNL]
3710 Use expedited update-side primitives, if available.
3712 rcutorture.gp_normal= [KNL]
3713 Use normal (non-expedited) asynchronous
3714 update-side primitives, if available.
3716 rcutorture.gp_sync= [KNL]
3717 Use normal (non-expedited) synchronous
3718 update-side primitives, if available. If all
3719 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3720 rcutorture.gp_normal=, and rcutorture.gp_sync=
3721 are zero, rcutorture acts as if is interpreted
3722 they are all non-zero.
3724 rcutorture.n_barrier_cbs= [KNL]
3725 Set callbacks/threads for rcu_barrier() testing.
3727 rcutorture.nfakewriters= [KNL]
3728 Set number of concurrent RCU writers. These just
3729 stress RCU, they don't participate in the actual
3730 test, hence the "fake".
3732 rcutorture.nreaders= [KNL]
3733 Set number of RCU readers. The value -1 selects
3734 N-1, where N is the number of CPUs. A value
3735 "n" less than -1 selects N-n-2, where N is again
3736 the number of CPUs. For example, -2 selects N
3737 (the number of CPUs), -3 selects N+1, and so on.
3739 rcutorture.object_debug= [KNL]
3740 Enable debug-object double-call_rcu() testing.
3742 rcutorture.onoff_holdoff= [KNL]
3743 Set time (s) after boot for CPU-hotplug testing.
3745 rcutorture.onoff_interval= [KNL]
3746 Set time (s) between CPU-hotplug operations, or
3747 zero to disable CPU-hotplug testing.
3749 rcutorture.shuffle_interval= [KNL]
3750 Set task-shuffle interval (s). Shuffling tasks
3751 allows some CPUs to go into dyntick-idle mode
3752 during the rcutorture test.
3754 rcutorture.shutdown_secs= [KNL]
3755 Set time (s) after boot system shutdown. This
3756 is useful for hands-off automated testing.
3758 rcutorture.stall_cpu= [KNL]
3759 Duration of CPU stall (s) to test RCU CPU stall
3760 warnings, zero to disable.
3762 rcutorture.stall_cpu_holdoff= [KNL]
3763 Time to wait (s) after boot before inducing stall.
3765 rcutorture.stat_interval= [KNL]
3766 Time (s) between statistics printk()s.
3768 rcutorture.stutter= [KNL]
3769 Time (s) to stutter testing, for example, specifying
3770 five seconds causes the test to run for five seconds,
3771 wait for five seconds, and so on. This tests RCU's
3772 ability to transition abruptly to and from idle.
3774 rcutorture.test_boost= [KNL]
3775 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3776 "Maybe" means test if the RCU implementation
3777 under test support RCU priority boosting.
3779 rcutorture.test_boost_duration= [KNL]
3780 Duration (s) of each individual boost test.
3782 rcutorture.test_boost_interval= [KNL]
3783 Interval (s) between each boost test.
3785 rcutorture.test_no_idle_hz= [KNL]
3786 Test RCU's dyntick-idle handling. See also the
3787 rcutorture.shuffle_interval parameter.
3789 rcutorture.torture_runnable= [BOOT]
3790 Start rcutorture running at boot time.
3792 rcutorture.torture_type= [KNL]
3793 Specify the RCU implementation to test.
3795 rcutorture.verbose= [KNL]
3796 Enable additional printk() statements.
3798 rcupdate.rcu_cpu_stall_suppress= [KNL]
3799 Suppress RCU CPU stall warning messages.
3801 rcupdate.rcu_cpu_stall_timeout= [KNL]
3802 Set timeout for RCU CPU stall warning messages.
3804 rcupdate.rcu_expedited= [KNL]
3805 Use expedited grace-period primitives, for
3806 example, synchronize_rcu_expedited() instead
3807 of synchronize_rcu(). This reduces latency,
3808 but can increase CPU utilization, degrade
3809 real-time latency, and degrade energy efficiency.
3810 No effect on CONFIG_TINY_RCU kernels.
3812 rcupdate.rcu_normal= [KNL]
3813 Use only normal grace-period primitives,
3814 for example, synchronize_rcu() instead of
3815 synchronize_rcu_expedited(). This improves
3816 real-time latency, CPU utilization, and
3817 energy efficiency, but can expose users to
3818 increased grace-period latency. This parameter
3819 overrides rcupdate.rcu_expedited. No effect on
3820 CONFIG_TINY_RCU kernels.
3822 rcupdate.rcu_normal_after_boot= [KNL]
3823 Once boot has completed (that is, after
3824 rcu_end_inkernel_boot() has been invoked), use
3825 only normal grace-period primitives. No effect
3826 on CONFIG_TINY_RCU kernels.
3828 rcupdate.rcu_task_stall_timeout= [KNL]
3829 Set timeout in jiffies for RCU task stall warning
3830 messages. Disable with a value less than or equal
3833 rcupdate.rcu_self_test= [KNL]
3834 Run the RCU early boot self tests
3836 rcupdate.rcu_self_test_bh= [KNL]
3837 Run the RCU bh early boot self tests
3839 rcupdate.rcu_self_test_sched= [KNL]
3840 Run the RCU sched early boot self tests
3844 Run specified binary instead of /init from the ramdisk,
3845 used for early userspace startup. See initrd.
3848 force - Override the decision by the kernel to hide the
3849 advertisement of RDRAND support (this affects
3850 certain AMD processors because of buggy BIOS
3851 support, specifically around the suspend/resume
3855 Turn on/off individual RDT features. List is:
3856 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3857 E.g. to turn on cmt and turn off mba use:
3861 Format (x86 or x86_64):
3862 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3864 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3866 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3867 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3868 reboot_force is either force or not specified,
3869 reboot_cpu is s[mp]#### with #### being the processor
3870 to be used for rebooting.
3873 [KNL, SMP] Set scheduler's default relax_domain_level.
3874 See Documentation/cgroup-v1/cpusets.txt.
3876 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3878 reservetop= [X86-32]
3880 Reserves a hole at the top of the kernel virtual
3885 Set the amount of memory to reserve for BIOS at
3886 the bottom of the address space.
3888 reset_devices [KNL] Force drivers to reset the underlying device
3889 during initialization.
3892 Specify the partition device for software suspend
3894 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3896 resume_offset= [SWSUSP]
3897 Specify the offset from the beginning of the partition
3898 given by "resume=" at which the swap header is located,
3899 in <PAGE_SIZE> units (needed only for swap files).
3900 See Documentation/power/swsusp-and-swap-files.txt
3902 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3903 read the resume files
3905 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3906 Useful for devices that are detected asynchronously
3907 (e.g. USB and MMC devices).
3909 hibernate= [HIBERNATION]
3910 noresume Don't check if there's a hibernation image
3911 present during boot.
3912 nocompress Don't compress/decompress hibernation images.
3913 no Disable hibernation and resume.
3914 protect_image Turn on image protection during restoration
3915 (that will set all pages holding image data
3916 during restoration read-only).
3918 retain_initrd [RAM] Keep initrd memory after extraction
3920 rfkill.default_state=
3921 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3922 etc. communication is blocked by default.
3925 rfkill.master_switch_mode=
3926 0 The "airplane mode" button does nothing.
3927 1 The "airplane mode" button toggles between everything
3928 blocked and the previous configuration.
3929 2 The "airplane mode" button toggles between everything
3930 blocked and everything unblocked.
3932 rhash_entries= [KNL,NET]
3933 Set number of hash buckets for route cache
3936 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3939 ro [KNL] Mount root device read-only on boot
3942 on Mark read-only kernel memory as read-only (default).
3943 off Leave read-only kernel memory writable for debugging.
3946 Enable the uart passthrough on the designated usb port
3947 on Rockchip SoCs. When active, the signals of the
3948 debug-uart get routed to the D+ and D- pins of the usb
3949 port and the regular usb controller gets disabled.
3951 root= [KNL] Root filesystem
3952 See name_to_dev_t comment in init/do_mounts.c.
3954 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3955 mount the root filesystem
3957 rootflags= [KNL] Set root filesystem mount option string
3959 rootfstype= [KNL] Set root filesystem type
3961 rootwait [KNL] Wait (indefinitely) for root device to show up.
3962 Useful for devices that are detected asynchronously
3963 (e.g. USB and MMC devices).
3965 rproc_mem=nn[KMG][@address]
3966 [KNL,ARM,CMA] Remoteproc physical memory block.
3967 Memory area to be used by remote processor image,
3970 rw [KNL] Mount root device read-write on boot
3972 S [KNL] Run init in single mode
3974 s390_iommu= [HW,S390]
3975 Set s390 IOTLB flushing mode
3977 With strict flushing every unmap operation will result in
3978 an IOTLB flush. Default is lazy flushing before reuse,
3982 See drivers/net/irda/sa1100_ir.c.
3984 sbni= [NET] Granch SBNI12 leased line adapter
3986 sched_debug [KNL] Enables verbose scheduler debug messages.
3988 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3989 Allowed values are enable and disable. This feature
3990 incurs a small amount of overhead in the scheduler
3991 but is useful for debugging and performance tuning.
3993 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3994 xtime_lock contention on larger systems, and/or RCU lock
3995 contention on all systems with CONFIG_MAXSMP set.
3996 Format: { "0" | "1" }
3997 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3999 Note: increases power consumption, thus should only be
4000 enabled if running jitter sensitive (HPC/RT) workloads.
4002 security= [SECURITY] Choose a security module to enable at boot.
4003 If this boot parameter is not specified, only the first
4004 security module asking for security registration will be
4005 loaded. An invalid security module name will be treated
4006 as if no module has been chosen.
4008 selinux= [SELINUX] Disable or enable SELinux at boot time.
4009 Format: { "0" | "1" }
4010 See security/selinux/Kconfig help text.
4013 Default value is set via kernel config option.
4014 If enabled at boot time, /selinux/disable can be used
4015 later to disable prior to initial policy load.
4017 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4018 Format: { "0" | "1" }
4019 See security/apparmor/Kconfig help text
4022 Default value is set via kernel config option.
4024 serialnumber [BUGS=X86-32]
4027 Maximal number of shapers.
4035 Disable merging of slabs with similar size. May be
4036 necessary if there is some reason to distinguish
4037 allocs to different slabs, especially in hardened
4038 environments where the risk of heap overflows and
4039 layout control by attackers can usually be
4040 frustrated by disabling merging. This will reduce
4041 most of the exposure of a heap attack to a single
4042 cache (risks via metadata attacks are mostly
4043 unchanged). Debug options disable merging on their
4045 For more information see Documentation/vm/slub.txt.
4047 slab_max_order= [MM, SLAB]
4048 Determines the maximum allowed order for slabs.
4049 A high setting may cause OOMs due to memory
4050 fragmentation. Defaults to 1 for systems with
4051 more than 32MB of RAM, 0 otherwise.
4053 slub_debug[=options[,slabs]] [MM, SLUB]
4054 Enabling slub_debug allows one to determine the
4055 culprit if slab objects become corrupted. Enabling
4056 slub_debug can create guard zones around objects and
4057 may poison objects when not in use. Also tracks the
4058 last alloc / free. For more information see
4059 Documentation/vm/slub.txt.
4061 slub_memcg_sysfs= [MM, SLUB]
4062 Determines whether to enable sysfs directories for
4063 memory cgroup sub-caches. 1 to enable, 0 to disable.
4064 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4065 Enabling this can lead to a very high number of debug
4066 directories and files being created under
4069 slub_max_order= [MM, SLUB]
4070 Determines the maximum allowed order for slabs.
4071 A high setting may cause OOMs due to memory
4072 fragmentation. For more information see
4073 Documentation/vm/slub.txt.
4075 slub_min_objects= [MM, SLUB]
4076 The minimum number of objects per slab. SLUB will
4077 increase the slab order up to slub_max_order to
4078 generate a sufficiently large slab able to contain
4079 the number of objects indicated. The higher the number
4080 of objects the smaller the overhead of tracking slabs
4081 and the less frequently locks need to be acquired.
4082 For more information see Documentation/vm/slub.txt.
4084 slub_min_order= [MM, SLUB]
4085 Determines the minimum page order for slabs. Must be
4086 lower than slub_max_order.
4087 For more information see Documentation/vm/slub.txt.
4089 slub_nomerge [MM, SLUB]
4090 Same with slab_nomerge. This is supported for legacy.
4091 See slab_nomerge for more information.
4094 Format: <io1>[,<io2>[,...,<io8>]]
4096 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4097 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4098 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4099 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4100 smsc-ircc2.ircc_irq= [HW] IRQ line
4101 smsc-ircc2.ircc_dma= [HW] DMA channel
4102 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4103 0: Toshiba Satellite 1800 (GP data pin select)
4104 1: Fast pin select (default)
4107 smt [KNL,S390] Set the maximum number of threads (logical
4108 CPUs) to use per physical CPU on systems capable of
4109 symmetric multithreading (SMT). Will be capped to the
4110 actual hardware limit.
4112 Default: -1 (no limit)
4115 [KNL] Should the soft-lockup detector generate panics.
4118 softlockup_all_cpu_backtrace=
4119 [KNL] Should the soft-lockup detector generate
4120 backtraces on all cpus.
4123 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4124 See Documentation/laptops/sonypi.txt
4126 spectre_v2= [X86] Control mitigation of Spectre variant 2
4127 (indirect branch speculation) vulnerability.
4128 The default operation protects the kernel from
4131 on - unconditionally enable, implies
4133 off - unconditionally disable, implies
4135 auto - kernel detects whether your CPU model is
4138 Selecting 'on' will, and 'auto' may, choose a
4139 mitigation method at run time according to the
4140 CPU, the available microcode, the setting of the
4141 CONFIG_RETPOLINE configuration option, and the
4142 compiler with which the kernel was built.
4144 Selecting 'on' will also enable the mitigation
4145 against user space to user space task attacks.
4147 Selecting 'off' will disable both the kernel and
4148 the user space protections.
4150 Specific mitigations can also be selected manually:
4152 retpoline - replace indirect branches
4153 retpoline,generic - google's original retpoline
4154 retpoline,amd - AMD-specific minimal thunk
4156 Not specifying this option is equivalent to
4160 [X86] Control mitigation of Spectre variant 2
4161 (indirect branch speculation) vulnerability between
4164 on - Unconditionally enable mitigations. Is
4165 enforced by spectre_v2=on
4167 off - Unconditionally disable mitigations. Is
4168 enforced by spectre_v2=off
4170 prctl - Indirect branch speculation is enabled,
4171 but mitigation can be enabled via prctl
4172 per thread. The mitigation control state
4173 is inherited on fork.
4176 - Like "prctl" above, but only STIBP is
4177 controlled per thread. IBPB is issued
4178 always when switching between different user
4182 - Same as "prctl" above, but all seccomp
4183 threads will enable the mitigation unless
4184 they explicitly opt out.
4187 - Like "seccomp" above, but only STIBP is
4188 controlled per thread. IBPB is issued
4189 always when switching between different
4190 user space processes.
4192 auto - Kernel selects the mitigation depending on
4193 the available CPU features and vulnerability.
4196 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4198 Not specifying this option is equivalent to
4199 spectre_v2_user=auto.
4201 spec_store_bypass_disable=
4202 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4203 (Speculative Store Bypass vulnerability)
4205 Certain CPUs are vulnerable to an exploit against a
4206 a common industry wide performance optimization known
4207 as "Speculative Store Bypass" in which recent stores
4208 to the same memory location may not be observed by
4209 later loads during speculative execution. The idea
4210 is that such stores are unlikely and that they can
4211 be detected prior to instruction retirement at the
4212 end of a particular speculation execution window.
4214 In vulnerable processors, the speculatively forwarded
4215 store can be used in a cache side channel attack, for
4216 example to read memory to which the attacker does not
4217 directly have access (e.g. inside sandboxed code).
4219 This parameter controls whether the Speculative Store
4220 Bypass optimization is used.
4222 on - Unconditionally disable Speculative Store Bypass
4223 off - Unconditionally enable Speculative Store Bypass
4224 auto - Kernel detects whether the CPU model contains an
4225 implementation of Speculative Store Bypass and
4226 picks the most appropriate mitigation. If the
4227 CPU is not vulnerable, "off" is selected. If the
4228 CPU is vulnerable the default mitigation is
4229 architecture and Kconfig dependent. See below.
4230 prctl - Control Speculative Store Bypass per thread
4231 via prctl. Speculative Store Bypass is enabled
4232 for a process by default. The state of the control
4233 is inherited on fork.
4234 seccomp - Same as "prctl" above, but all seccomp threads
4235 will disable SSB unless they explicitly opt out.
4237 Not specifying this option is equivalent to
4238 spec_store_bypass_disable=auto.
4240 Default mitigations:
4241 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4243 spia_io_base= [HW,MTD]
4249 Control the Special Register Buffer Data Sampling
4252 Certain CPUs are vulnerable to an MDS-like
4253 exploit which can leak bits from the random
4256 By default, this issue is mitigated by
4257 microcode. However, the microcode fix can cause
4258 the RDRAND and RDSEED instructions to become
4259 much slower. Among other effects, this will
4260 result in reduced throughput from /dev/urandom.
4262 The microcode mitigation can be disabled with
4263 the following option:
4265 off: Disable mitigation and remove
4266 performance impact to RDRAND and RDSEED
4268 srcutree.counter_wrap_check [KNL]
4269 Specifies how frequently to check for
4270 grace-period sequence counter wrap for the
4271 srcu_data structure's ->srcu_gp_seq_needed field.
4272 The greater the number of bits set in this kernel
4273 parameter, the less frequently counter wrap will
4274 be checked for. Note that the bottom two bits
4277 srcutree.exp_holdoff [KNL]
4278 Specifies how many nanoseconds must elapse
4279 since the end of the last SRCU grace period for
4280 a given srcu_struct until the next normal SRCU
4281 grace period will be considered for automatic
4282 expediting. Set to zero to disable automatic
4286 Speculative Store Bypass Disable control
4288 On CPUs that are vulnerable to the Speculative
4289 Store Bypass vulnerability and offer a
4290 firmware based mitigation, this parameter
4291 indicates how the mitigation should be used:
4293 force-on: Unconditionally enable mitigation for
4294 for both kernel and userspace
4295 force-off: Unconditionally disable mitigation for
4296 for both kernel and userspace
4297 kernel: Always enable mitigation in the
4298 kernel, and offer a prctl interface
4299 to allow userspace to register its
4300 interest in being mitigated too.
4302 stack_guard_gap= [MM]
4303 override the default stack gap protection. The value
4304 is in page units and it defines how many pages prior
4305 to (for stacks growing down) resp. after (for stacks
4306 growing up) the main stack are reserved for no other
4307 mapping. Default value is 256 pages.
4310 Enabled the stack tracer on boot up.
4312 stacktrace_filter=[function-list]
4313 [FTRACE] Limit the functions that the stack tracer
4314 will trace at boot up. function-list is a comma separated
4315 list of functions. This list can be changed at run
4316 time by the stack_trace_filter file in the debugfs
4317 tracing directory. Note, this enables stack tracing
4318 and the stacktrace above is not needed.
4322 Set the STI (builtin display/keyboard on the HP-PARISC
4323 machines) console (graphic card) which should be used
4324 as the initial boot-console.
4325 See also comment in drivers/video/console/sticore.c.
4328 See comment in drivers/video/console/sticore.c.
4331 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4333 sunrpc.min_resvport=
4334 sunrpc.max_resvport=
4336 SunRPC servers often require that client requests
4337 originate from a privileged port (i.e. a port in the
4338 range 0 < portnr < 1024).
4339 An administrator who wishes to reserve some of these
4340 ports for other uses may adjust the range that the
4341 kernel's sunrpc client considers to be privileged
4342 using these two parameters to set the minimum and
4343 maximum port values.
4345 sunrpc.svc_rpc_per_connection_limit=
4347 Limit the number of requests that the server will
4348 process in parallel from a single connection.
4349 The default value is 0 (no limit).
4353 Control how the NFS server code allocates CPUs to
4354 service thread pools. Depending on how many NICs
4355 you have and where their interrupts are bound, this
4356 option will affect which CPUs will do NFS serving.
4357 Note: this parameter cannot be changed while the
4358 NFS server is running.
4360 auto the server chooses an appropriate mode
4361 automatically using heuristics
4362 global a single global pool contains all CPUs
4363 percpu one pool for each CPU
4364 pernode one pool for each NUMA node (equivalent
4365 to global on non-NUMA machines)
4367 sunrpc.tcp_slot_table_entries=
4368 sunrpc.udp_slot_table_entries=
4370 Sets the upper limit on the number of simultaneous
4371 RPC calls that can be sent from the client to a
4372 server. Increasing these values may allow you to
4373 improve throughput, but will also increase the
4374 amount of memory reserved for use by the client.
4376 suspend.pm_test_delay=
4378 Sets the number of seconds to remain in a suspend test
4379 mode before resuming the system (see
4380 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4381 is set. Default value is 5.
4384 [KNL] Enable accounting of swap in memory resource
4385 controller if no parameter or 1 is given or disable
4386 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4388 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4389 Format: { <int> | force | noforce }
4390 <int> -- Number of I/O TLB slabs
4391 force -- force using of bounce buffers even if they
4392 wouldn't be automatically used by the kernel
4393 noforce -- Never use bounce buffers (for debugging)
4397 sysfs.deprecated=0|1 [KNL]
4398 Enable/disable old style sysfs layout for old udev
4399 on older distributions. When this option is enabled
4400 very new udev will not work anymore. When this option
4401 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4402 in older udev will not work anymore.
4403 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4404 the kernel configuration.
4406 sysrq_always_enabled
4408 Ignore sysrq setting - this boot parameter will
4409 neutralize any effect of /proc/sys/kernel/sysrq.
4410 Useful for debugging.
4412 tcpmhash_entries= [KNL,NET]
4413 Set the number of tcp_metrics_hash slots.
4414 Default value is 8192 or 16384 depending on total
4415 ram pages. This is used to specify the TCP metrics
4416 cache size. See Documentation/networking/ip-sysctl.txt
4417 "tcp_no_metrics_save" section for more details.
4421 test_suspend= [SUSPEND][,N]
4422 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4423 standby suspend) or "freeze" (for suspend type freeze)
4424 as the system sleep state during system startup with
4425 the optional capability to repeat N number of times.
4426 The system is woken from this state using a
4427 wakeup-capable RTC alarm.
4429 thash_entries= [KNL,NET]
4430 Set number of hash buckets for TCP connection
4432 thermal.act= [HW,ACPI]
4433 -1: disable all active trip points in all thermal zones
4434 <degrees C>: override all lowest active trip points
4436 thermal.crt= [HW,ACPI]
4437 -1: disable all critical trip points in all thermal zones
4438 <degrees C>: override all critical trip points
4440 thermal.nocrt= [HW,ACPI]
4441 Set to disable actions on ACPI thermal zone
4442 critical and hot trip points.
4444 thermal.off= [HW,ACPI]
4445 1: disable ACPI thermal control
4447 thermal.psv= [HW,ACPI]
4448 -1: disable all passive trip points
4449 <degrees C>: override all passive trip points to this
4452 thermal.tzp= [HW,ACPI]
4453 Specify global default ACPI thermal zone polling rate
4454 <deci-seconds>: poll all this frequency
4455 0: no polling (default)
4458 Force threading of all interrupt handlers except those
4459 marked explicitly IRQF_NO_THREAD.
4462 Enable the Transcendent memory driver if built-in.
4464 tmem.cleancache=0|1 [KNL, XEN]
4465 Default is on (1). Disable the usage of the cleancache
4466 API to send anonymous pages to the hypervisor.
4468 tmem.frontswap=0|1 [KNL, XEN]
4469 Default is on (1). Disable the usage of the frontswap
4470 API to send swap pages to the hypervisor. If disabled
4471 the selfballooning and selfshrinking are force disabled.
4473 tmem.selfballooning=0|1 [KNL, XEN]
4474 Default is on (1). Disable the driving of swap pages
4477 tmem.selfshrinking=0|1 [KNL, XEN]
4478 Default is on (1). Partial swapoff that immediately
4479 transfers pages from Xen hypervisor back to the
4480 kernel based on different criteria.
4484 Specify if the kernel should make use of the cpu
4485 topology information if the hardware supports this.
4486 The scheduler will make use of this information and
4487 e.g. base its process migration decisions on it.
4490 topology_updates= [KNL, PPC, NUMA]
4492 Specify if the kernel should ignore (off)
4493 topology updates sent by the hypervisor to this
4498 tpm_suspend_pcr=[HW,TPM]
4499 Format: integer pcr id
4500 Specify that at suspend time, the tpm driver
4501 should extend the specified pcr with zeros,
4502 as a workaround for some chips which fail to
4503 flush the last written pcr on TPM_SaveState.
4504 This will guarantee that all the other pcrs
4507 trace_buf_size=nn[KMG]
4508 [FTRACE] will set tracing buffer size on each cpu.
4510 trace_event=[event-list]
4511 [FTRACE] Set and start specified trace events in order
4512 to facilitate early boot debugging. The event-list is a
4513 comma separated list of trace events to enable. See
4514 also Documentation/trace/events.txt
4516 trace_options=[option-list]
4517 [FTRACE] Enable or disable tracer options at boot.
4518 The option-list is a comma delimited list of options
4519 that can be enabled or disabled just as if you were
4520 to echo the option name into
4522 /sys/kernel/debug/tracing/trace_options
4524 For example, to enable stacktrace option (to dump the
4525 stack trace of each event), add to the command line:
4527 trace_options=stacktrace
4529 See also Documentation/trace/ftrace.txt "trace options"
4533 Have the tracepoints sent to printk as well as the
4534 tracing ring buffer. This is useful for early boot up
4535 where the system hangs or reboots and does not give the
4536 option for reading the tracing buffer or performing a
4537 ftrace_dump_on_oops.
4539 To turn off having tracepoints sent to printk,
4540 echo 0 > /proc/sys/kernel/tracepoint_printk
4541 Note, echoing 1 into this file without the
4542 tracepoint_printk kernel cmdline option has no effect.
4546 Having tracepoints sent to printk() and activating high
4547 frequency tracepoints such as irq or sched, can cause
4548 the system to live lock.
4551 [FTRACE] enable this option to disable tracing when a
4552 warning is hit. This turns off "tracing_on". Tracing can
4553 be enabled again by echoing '1' into the "tracing_on"
4554 file located in /sys/kernel/debug/tracing/
4556 This option is useful, as it disables the trace before
4557 the WARNING dump is called, which prevents the trace to
4558 be filled with content caused by the warning output.
4560 This option can also be set at run time via the sysctl
4561 option: kernel/traceoff_on_warning
4563 transparent_hugepage=
4565 Format: [always|madvise|never]
4566 Can be used to control the default behavior of the system
4567 with respect to transparent hugepages.
4568 See Documentation/vm/transhuge.txt for more details.
4570 tsc= Disable clocksource stability checks for TSC.
4572 [x86] reliable: mark tsc clocksource as reliable, this
4573 disables clocksource verification at runtime, as well
4574 as the stability checks done at bootup. Used to enable
4575 high-resolution timer mode on older hardware, and in
4576 virtualized environment.
4577 [x86] noirqtime: Do not use TSC to do irq accounting.
4578 Used to run time disable IRQ_TIME_ACCOUNTING on any
4579 platforms where RDTSC is slow and this accounting
4582 tsx= [X86] Control Transactional Synchronization
4583 Extensions (TSX) feature in Intel processors that
4584 support TSX control.
4586 This parameter controls the TSX feature. The options are:
4588 on - Enable TSX on the system. Although there are
4589 mitigations for all known security vulnerabilities,
4590 TSX has been known to be an accelerator for
4591 several previous speculation-related CVEs, and
4592 so there may be unknown security risks associated
4593 with leaving it enabled.
4595 off - Disable TSX on the system. (Note that this
4596 option takes effect only on newer CPUs which are
4597 not vulnerable to MDS, i.e., have
4598 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4599 the new IA32_TSX_CTRL MSR through a microcode
4600 update. This new MSR allows for the reliable
4601 deactivation of the TSX functionality.)
4603 auto - Disable TSX if X86_BUG_TAA is present,
4604 otherwise enable TSX on the system.
4606 Not specifying this option is equivalent to tsx=off.
4608 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4611 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4612 Abort (TAA) vulnerability.
4614 Similar to Micro-architectural Data Sampling (MDS)
4615 certain CPUs that support Transactional
4616 Synchronization Extensions (TSX) are vulnerable to an
4617 exploit against CPU internal buffers which can forward
4618 information to a disclosure gadget under certain
4621 In vulnerable processors, the speculatively forwarded
4622 data can be used in a cache side channel attack, to
4623 access data to which the attacker does not have direct
4626 This parameter controls the TAA mitigation. The
4629 full - Enable TAA mitigation on vulnerable CPUs
4632 full,nosmt - Enable TAA mitigation and disable SMT on
4633 vulnerable CPUs. If TSX is disabled, SMT
4634 is not disabled because CPU is not
4635 vulnerable to cross-thread TAA attacks.
4636 off - Unconditionally disable TAA mitigation
4638 On MDS-affected machines, tsx_async_abort=off can be
4639 prevented by an active MDS mitigation as both vulnerabilities
4640 are mitigated with the same mechanism so in order to disable
4641 this mitigation, you need to specify mds=off too.
4643 Not specifying this option is equivalent to
4644 tsx_async_abort=full. On CPUs which are MDS affected
4645 and deploy MDS mitigation, TAA mitigation is not
4646 required and doesn't provide any additional
4650 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4652 turbografx.map[2|3]= [HW,JOY]
4653 TurboGraFX parallel port interface
4655 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4656 See also Documentation/input/joystick-parport.txt
4658 udbg-immortal [PPC] When debugging early kernel crashes that
4659 happen after console_init() and before a proper
4660 console driver takes over, this boot options might
4661 help "seeing" what's going on.
4663 uhash_entries= [KNL,NET]
4664 Set number of hash buckets for UDP/UDP-Lite connections
4667 [USB] Ignore overcurrent events (default N).
4668 Some badly-designed motherboards generate lots of
4669 bogus events, for ports that aren't wired to
4670 anything. Set this parameter to avoid log spamming.
4671 Note that genuine overcurrent events won't be
4675 [X86] Cause panic on unknown NMI.
4677 usbcore.authorized_default=
4678 [USB] Default USB device authorization:
4679 (default -1 = authorized except for wireless USB,
4680 0 = not authorized, 1 = authorized)
4682 usbcore.autosuspend=
4683 [USB] The autosuspend time delay (in seconds) used
4684 for newly-detected USB devices (default 2). This
4685 is the time required before an idle device will be
4686 autosuspended. Devices for which the delay is set
4687 to a negative value won't be autosuspended at all.
4689 usbcore.usbfs_snoop=
4690 [USB] Set to log all usbfs traffic (default 0 = off).
4692 usbcore.usbfs_snoop_max=
4693 [USB] Maximum number of bytes to snoop in each URB
4696 usbcore.blinkenlights=
4697 [USB] Set to cycle leds on hubs (default 0 = off).
4699 usbcore.old_scheme_first=
4700 [USB] Start with the old device initialization
4701 scheme (default 0 = off).
4703 usbcore.usbfs_memory_mb=
4704 [USB] Memory limit (in MB) for buffers allocated by
4705 usbfs (default = 16, 0 = max = 2047).
4707 usbcore.use_both_schemes=
4708 [USB] Try the other device initialization scheme
4709 if the first one fails (default 1 = enabled).
4711 usbcore.initial_descriptor_timeout=
4712 [USB] Specifies timeout for the initial 64-byte
4713 USB_REQ_GET_DESCRIPTOR request in milliseconds
4714 (default 5000 = 5.0 seconds).
4716 usbcore.nousb [USB] Disable the USB subsystem
4719 [USBHID] The interval which mice are to be polled at.
4722 [USBHID] The interval which joysticks are to be polled at.
4724 usb-storage.delay_use=
4725 [UMS] The delay in seconds before a new device is
4726 scanned for Logical Units (default 1).
4729 [UMS] A list of quirks entries to supplement or
4730 override the built-in unusual_devs list. List
4731 entries are separated by commas. Each entry has
4732 the form VID:PID:Flags where VID and PID are Vendor
4733 and Product ID values (4-digit hex numbers) and
4734 Flags is a set of characters, each corresponding
4735 to a common usb-storage quirk flag as follows:
4736 a = SANE_SENSE (collect more than 18 bytes
4737 of sense data, not on uas);
4738 b = BAD_SENSE (don't collect more than 18
4739 bytes of sense data, not on uas);
4740 c = FIX_CAPACITY (decrease the reported
4741 device capacity by one sector);
4742 d = NO_READ_DISC_INFO (don't use
4743 READ_DISC_INFO command, not on uas);
4744 e = NO_READ_CAPACITY_16 (don't use
4745 READ_CAPACITY_16 command);
4746 f = NO_REPORT_OPCODES (don't use report opcodes
4748 g = MAX_SECTORS_240 (don't transfer more than
4749 240 sectors at a time, uas only);
4750 h = CAPACITY_HEURISTICS (decrease the
4751 reported device capacity by one
4752 sector if the number is odd);
4753 i = IGNORE_DEVICE (don't bind to this
4755 j = NO_REPORT_LUNS (don't use report luns
4757 k = NO_SAME (do not use WRITE_SAME, uas only)
4758 l = NOT_LOCKABLE (don't try to lock and
4759 unlock ejectable media, not on uas);
4760 m = MAX_SECTORS_64 (don't transfer more
4761 than 64 sectors = 32 KB at a time,
4763 n = INITIAL_READ10 (force a retry of the
4764 initial READ(10) command, not on uas);
4765 o = CAPACITY_OK (accept the capacity
4766 reported by the device, not on uas);
4767 p = WRITE_CACHE (the device cache is ON
4768 by default, not on uas);
4769 r = IGNORE_RESIDUE (the device reports
4770 bogus residue values, not on uas);
4771 s = SINGLE_LUN (the device has only one
4773 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4774 commands, uas only);
4775 u = IGNORE_UAS (don't bind to the uas driver);
4776 w = NO_WP_DETECT (don't test whether the
4777 medium is write-protected).
4778 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4779 even if the device claims no cache,
4781 Example: quirks=0419:aaf5:rl,0421:0433:rc
4783 user_debug= [KNL,ARM]
4785 See arch/arm/Kconfig.debug help text.
4786 1 - undefined instruction events
4788 4 - invalid data aborts
4791 Example: user_debug=31
4794 [X86] Flags controlling user PTE allocations.
4796 nohigh = do not allocate PTE pages in
4797 HIGHMEM regardless of setting
4801 On X86_32, this is an alias for vdso32=. Otherwise:
4803 vdso=1: enable VDSO (the default)
4804 vdso=0: disable VDSO mapping
4806 vdso32= [X86] Control the 32-bit vDSO
4807 vdso32=1: enable 32-bit VDSO
4808 vdso32=0 or vdso32=2: disable 32-bit VDSO
4810 See the help text for CONFIG_COMPAT_VDSO for more
4811 details. If CONFIG_COMPAT_VDSO is set, the default is
4812 vdso32=0; otherwise, the default is vdso32=1.
4814 For compatibility with older kernels, vdso32=2 is an
4817 Try vdso32=0 if you encounter an error that says:
4818 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4821 vector=percpu: enable percpu vector domain
4823 video= [FB] Frame buffer configuration
4824 See Documentation/fb/modedb.txt.
4826 video.brightness_switch_enabled= [0,1]
4827 If set to 1, on receiving an ACPI notify event
4828 generated by hotkey, video driver will adjust brightness
4829 level and then send out the event to user space through
4830 the allocated input device; If set to 0, video driver
4831 will only send out the event without touching backlight
4836 [VMMIO] Memory mapped virtio (platform) device.
4838 <size>@<baseaddr>:<irq>[:<id>]
4840 <size> := size (can use standard suffixes
4842 <baseaddr> := physical base address
4843 <irq> := interrupt number (as passed to
4845 <id> := (optional) platform device id
4847 virtio_mmio.device=1K@0x100b0000:48:7
4849 Can be used multiple times for multiple devices.
4851 vga= [BOOT,X86-32] Select a particular video mode
4852 See Documentation/x86/boot.txt and
4853 Documentation/svga.txt.
4854 Use vga=ask for menu.
4855 This is actually a boot loader parameter; the value is
4856 passed to the kernel using a special protocol.
4858 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4859 size of <nn>. This can be used to increase the
4860 minimum size (128MB on x86). It can also be used to
4861 decrease the size and leave more room for directly
4864 vmcp_cma=nn[MG] [KNL,S390]
4865 Sets the memory size reserved for contiguous memory
4866 allocations for the vmcp device driver.
4868 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4871 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4874 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4878 Controls the behavior of vsyscalls (i.e. calls to
4879 fixed addresses of 0xffffffffff600x00 from legacy
4880 code). Most statically-linked binaries and older
4881 versions of glibc use these calls. Because these
4882 functions are at fixed addresses, they make nice
4883 targets for exploits that can control RIP.
4885 emulate [default] Vsyscalls turn into traps and are
4886 emulated reasonably safely.
4888 native Vsyscalls are native syscall instructions.
4889 This is a little bit faster than trapping
4890 and makes a few dynamic recompilers work
4891 better than they would in emulation mode.
4892 It also makes exploits much easier to write.
4894 none Vsyscalls don't work at all. This makes
4895 them quite hard to use for exploits but
4896 might break your system.
4898 vt.color= [VT] Default text color.
4899 Format: 0xYX, X = foreground, Y = background.
4900 Default: 0x07 = light gray on black.
4902 vt.cur_default= [VT] Default cursor shape.
4903 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4904 the parameters of the <Esc>[?A;B;Cc escape sequence;
4905 see VGA-softcursor.txt. Default: 2 = underline.
4907 vt.default_blu= [VT]
4908 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4909 Change the default blue palette of the console.
4910 This is a 16-member array composed of values
4913 vt.default_grn= [VT]
4914 Format: <green0>,<green1>,<green2>,...,<green15>
4915 Change the default green palette of the console.
4916 This is a 16-member array composed of values
4919 vt.default_red= [VT]
4920 Format: <red0>,<red1>,<red2>,...,<red15>
4921 Change the default red palette of the console.
4922 This is a 16-member array composed of values
4928 Set system-wide default UTF-8 mode for all tty's.
4929 Default is 1, i.e. UTF-8 mode is enabled for all
4930 newly opened terminals.
4932 vt.global_cursor_default=
4935 Set system-wide default for whether a cursor
4936 is shown on new VTs. Default is -1,
4937 i.e. cursors will be created by default unless
4938 overridden by individual drivers. 0 will hide
4939 cursors, 1 will display them.
4941 vt.italic= [VT] Default color for italic text; 0-15.
4944 vt.underline= [VT] Default color for underlined text; 0-15.
4947 watchdog timers [HW,WDT] For information on watchdog timers,
4948 see Documentation/watchdog/watchdog-parameters.txt
4949 or other driver-specific files in the
4950 Documentation/watchdog/ directory.
4952 workqueue.watchdog_thresh=
4953 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4954 warn stall conditions and dump internal state to
4955 help debugging. 0 disables workqueue stall
4956 detection; otherwise, it's the stall threshold
4957 duration in seconds. The default value is 30 and
4958 it can be updated at runtime by writing to the
4959 corresponding sysfs file.
4961 workqueue.disable_numa
4962 By default, all work items queued to unbound
4963 workqueues are affine to the NUMA nodes they're
4964 issued on, which results in better behavior in
4965 general. If NUMA affinity needs to be disabled for
4966 whatever reason, this option can be used. Note
4967 that this also can be controlled per-workqueue for
4968 workqueues visible under /sys/bus/workqueue/.
4970 workqueue.power_efficient
4971 Per-cpu workqueues are generally preferred because
4972 they show better performance thanks to cache
4973 locality; unfortunately, per-cpu workqueues tend to
4974 be more power hungry than unbound workqueues.
4976 Enabling this makes the per-cpu workqueues which
4977 were observed to contribute significantly to power
4978 consumption unbound, leading to measurably lower
4979 power usage at the cost of small performance
4982 The default value of this parameter is determined by
4983 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4985 workqueue.debug_force_rr_cpu
4986 Workqueue used to implicitly guarantee that work
4987 items queued without explicit CPU specified are put
4988 on the local CPU. This guarantee is no longer true
4989 and while local CPU is still preferred work items
4990 may be put on foreign CPUs. This debug option
4991 forces round-robin CPU selection to flush out
4992 usages which depend on the now broken guarantee.
4993 When enabled, memory and cache locality will be
4996 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4997 default x2apic cluster mode on platforms
5000 x86_intel_mid_timer= [X86-32,APBT]
5001 Choose timer option for x86 Intel MID platform.
5002 Two valid options are apbt timer only and lapic timer
5003 plus one apbt timer for broadcast timer.
5004 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5006 xen_512gb_limit [KNL,X86-64,XEN]
5007 Restricts the kernel running paravirtualized under Xen
5008 to use only up to 512 GB of RAM. The reason to do so is
5009 crash analysis tools and Xen tools for doing domain
5010 save/restore/migration must be enabled to handle larger
5013 xen_emul_unplug= [HW,X86,XEN]
5014 Unplug Xen emulated devices
5015 Format: [unplug0,][unplug1]
5016 ide-disks -- unplug primary master IDE devices
5017 aux-ide-disks -- unplug non-primary-master IDE devices
5018 nics -- unplug network devices
5019 all -- unplug all emulated devices (NICs and IDE disks)
5020 unnecessary -- unplugging emulated devices is
5021 unnecessary even if the host did not respond to
5023 never -- do not unplug even if version check succeeds
5025 xen_legacy_crash [X86,XEN]
5026 Crash from Xen panic notifier, without executing late
5027 panic() code such as dumping handler.
5029 xen_nopvspin [X86,XEN]
5030 Disables the ticketlock slowpath using Xen PV
5034 Disables the PV optimizations forcing the HVM guest to
5035 run as generic HVM guest with no PV drivers.
5037 xen.balloon_boot_timeout= [XEN]
5038 The time (in seconds) to wait before giving up to boot
5039 in case initial ballooning fails to free enough memory.
5040 Applies only when running as HVM or PVH guest and
5041 started with less memory configured than allowed at
5042 max. Default is 180.
5044 xen.event_eoi_delay= [XEN]
5045 How long to delay EOI handling in case of event
5046 storms (jiffies). Default is 10.
5048 xen.event_loop_timeout= [XEN]
5049 After which time (jiffies) the event handling loop
5050 should start to delay EOI handling. Default is 2.
5052 xirc2ps_cs= [NET,PCMCIA]
5054 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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