1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joydev/joystick.rst
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
336 For X86-32, this can also be used to specify an APIC
338 Format: apic=driver_name
339 Examples: apic=bigsmp
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
351 See Documentation/networking/ipv6.txt.
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
370 atarimouse= [HW,MOUSE] Atari Mouse
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
375 atkbd.reset= [HW] Reset keyboard during initialization
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
410 unset - Disable the BAU.
412 baycom_epp= [HW,AX25]
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
417 See header of drivers/net/hamradio/baycom_par.c.
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441 Disable BERT OS support on buggy BIOSes.
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
446 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
453 c101= [NET] Moxa C101 synchronous serial card
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
465 format: { id:<keyid> | builtin }
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
481 - foo isn't visible as an individually mountable
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
508 See Documentation/s390/CommonIO for details.
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
528 clocksource= Override the default clocksource
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
534 [all] jiffies (this is the base, fallback clocksource)
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
547 clocksource.arm_arch_timer.evtstrm=
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
555 clearcpuid=BITNUM [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
568 cma=nn[MG]@[start[MG][-end[MG]]]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
588 code_bytes [X86] How many bytes of object code to print
593 com20020= [HW,NET] ARCnet - COM20020 chipset
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
604 condev= [HW,S390] console device
607 console= [KNL] Output console device and options.
609 tty<n> Use the virtual console device <n>.
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
619 See Documentation/admin-guide/serial-console.rst for more
621 Documentation/networking/netconsole.txt for an
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
645 For now, only VisioBraille is supported.
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. A value of 0 disables the blank timer.
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
656 coresight_cpu_debug.enable
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
663 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
664 to register. Example: cpufreq_driver=powernow-k8
665 Format: { none | STRING }
667 cpuidle.off=1 [CPU_IDLE]
668 disable the cpuidle sub-system
670 cpufreq.off=1 [CPU_FREQ]
671 disable the cpufreq sub-system
674 [X86] Delay for N microsec between assert and de-assert
675 of APIC INIT to start processors. This delay occurs
676 on every CPU online, such as boot, and resume from suspend.
679 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
681 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
683 crashkernel=size[KMG][@offset[KMG]]
684 [KNL] Using kexec, Linux can switch to a 'crash kernel'
685 upon panic. This parameter reserves the physical
686 memory region [offset, offset + size] for that kernel
687 image. If '@offset' is omitted, then a suitable offset
688 is selected automatically. Check
689 Documentation/kdump/kdump.txt for further details.
691 crashkernel=range1:size1[,range2:size2,...][@offset]
692 [KNL] Same as above, but depends on the memory
693 in the running system. The syntax of range is
694 start-[end] where start and end are both
695 a memory unit (amount[KMG]). See also
696 Documentation/kdump/kdump.txt for an example.
698 crashkernel=size[KMG],high
699 [KNL, x86_64] range could be above 4G. Allow kernel
700 to allocate physical memory region from top, so could
701 be above 4G if system have more than 4G ram installed.
702 Otherwise memory region will be allocated below 4G, if
704 It will be ignored if crashkernel=X is specified.
705 crashkernel=size[KMG],low
706 [KNL, x86_64] range under 4G. When crashkernel=X,high
707 is passed, kernel could allocate physical memory region
708 above 4G, that cause second kernel crash on system
709 that require some amount of low memory, e.g. swiotlb
710 requires at least 64M+32K low memory, also enough extra
711 low memory is needed to make sure DMA buffers for 32-bit
712 devices won't run out. Kernel would try to allocate at
713 at least 256M below 4G automatically.
714 This one let user to specify own low range under 4G
715 for second kernel instead.
716 0: to disable low allocation.
717 It will be ignored when crashkernel=X,high is not used
718 or memory reserved is below 4G.
721 [KNL] Disable crypto self-tests
726 cs89x0_media= [HW,NET]
727 Format: { rj45 | aui | bnc }
730 See header of drivers/s390/block/dasd_devmap.c.
732 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
733 (one device per port)
734 Format: <port#>,<type>
735 See also Documentation/input/devices/joystick-parport.rst
737 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
739 Documentation/admin-guide/dynamic-debug-howto.rst for
740 details. Deprecated, see dyndbg.
742 debug [KNL] Enable kernel debugging (events log level).
745 [KNL] verbose self-tests
747 Print debugging info while doing the locking API
749 We default to 0 (no extra messages), setting it to
750 1 will print _a lot_ more information - normally
751 only useful to kernel developers.
753 debug_objects [KNL] Enable object debugging
756 [KNL] Disable object debugging
758 debug_guardpage_minorder=
759 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
760 parameter allows control of the order of pages that will
761 be intentionally kept free (and hence protected) by the
762 buddy allocator. Bigger value increase the probability
763 of catching random memory corruption, but reduce the
764 amount of memory for normal system use. The maximum
765 possible value is MAX_ORDER/2. Setting this parameter
766 to 1 or 2 should be enough to identify most random
767 memory corruption problems caused by bugs in kernel or
768 driver code when a CPU writes to (or reads from) a
769 random memory location. Note that there exists a class
770 of memory corruptions problems caused by buggy H/W or
771 F/W or by drivers badly programing DMA (basically when
772 memory is written at bus level and the CPU MMU is
773 bypassed) which are not detectable by
774 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
775 tracking down these problems.
778 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
779 parameter enables the feature at boot time. In
780 default, it is disabled. We can avoid allocating huge
781 chunk of memory for debug pagealloc if we don't enable
782 it at boot time and the system will work mostly same
783 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
784 on: enable the feature
786 debugpat [X86] Enable PAT debugging
788 decnet.addr= [HW,NET]
789 Format: <area>[,<node>]
790 See also Documentation/networking/decnet.txt.
793 [same as hugepagesz=] The size of the default
794 HugeTLB page size. This is the size represented by
795 the legacy /proc/ hugepages APIs, used for SHM, and
796 default size when mounting hugetlbfs filesystems.
797 Defaults to the default architecture's huge page size
801 Set number of hash buckets for dentry cache.
803 disable_1tb_segments [PPC]
804 Disables the use of 1TB hash page table segments. This
805 causes the kernel to fall back to 256MB segments which
806 can be useful when debugging issues that require an SLB
810 See Documentation/networking/ipv6.txt.
813 Disable RADIX MMU mode on POWER9
815 disable_cpu_apicid= [X86,APIC,SMP]
817 The number of initial APIC ID for the
818 corresponding CPU to be disabled at boot,
819 mostly used for the kdump 2nd kernel to
820 disable BSP to wake up multiple CPUs without
821 causing system reset or hang due to sending
824 disable_ddw [PPC/PSERIES]
825 Disable Dynamic DMA Window support. Use this if
826 to workaround buggy firmware.
829 See Documentation/networking/ipv6.txt.
831 disable_mtrr_cleanup [X86]
832 The kernel tries to adjust MTRR layout from continuous
833 to discrete, to make X server driver able to add WB
834 entry later. This parameter disables that.
836 disable_mtrr_trim [X86, Intel and AMD only]
837 By default the kernel will trim any uncacheable
838 memory out of your available memory pool based on
839 MTRR settings. This parameter disables that behavior,
840 possibly causing your machine to run very slowly.
842 disable_timer_pin_1 [X86]
843 Disable PIN 1 of APIC timer
844 Can be useful to work around chipset bugs.
846 dis_ucode_ldr [X86] Disable the microcode loader.
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
865 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
866 Broken monitors, graphic adapters, KVMs and EDIDless
867 panels may send no or incorrect EDID data sets.
868 This parameter allows to specify an EDID data sets
869 in the /lib/firmware directory that are used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name. Each connector may use a unique EDID data
879 set by separating the files with a comma. An EDID
880 data set with no connector name will be used for
881 any connectors not explicitly specified.
886 Format: {"off" | "known"}
887 Control how the dt_cpu_ftrs device-tree binding is
888 used for CPU feature discovery and setup (if it
890 off: Do not use it, fall back to legacy cpu table.
891 known: Do not pass through unknown features to guests
892 or userspace, only those that the kernel is aware of.
894 dump_apple_properties [X86]
895 Dump name and content of EFI device properties on
896 x86 Macs. Useful for driver authors to determine
897 what data is available or for reverse-engineering.
899 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
900 module.dyndbg[="val"]
901 Enable debug messages at boot time. See
902 Documentation/admin-guide/dynamic-debug-howto.rst
905 nompx [X86] Disables Intel Memory Protection Extensions.
906 See Documentation/x86/intel_mpx.txt for more
907 information about the feature.
909 nopku [X86] Disable Memory Protection Keys CPU feature found
912 module.async_probe [KNL]
913 Enable asynchronous probe on this module.
915 early_ioremap_debug [KNL]
916 Enable debug messages in early_ioremap support. This
917 is useful for tracking down temporary early mappings
918 which are not unmapped.
920 earlycon= [KNL] Output early console device and options.
922 When used with no options, the early console is
923 determined by the stdout-path property in device
926 cdns,<addr>[,options]
927 Start an early, polled-mode console on a Cadence
928 (xuartps) serial port at the specified address. Only
929 supported option is baud rate. If baud rate is not
930 specified, the serial port must already be setup and
933 uart[8250],io,<addr>[,options]
934 uart[8250],mmio,<addr>[,options]
935 uart[8250],mmio32,<addr>[,options]
936 uart[8250],mmio32be,<addr>[,options]
937 uart[8250],0x<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32 or mmio32be).
942 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
943 to be equivalent to 'mmio'. 'options' are specified
944 in the same format described for "console=ttyS<n>"; if
945 unspecified, the h/w is not initialized.
949 Start an early, polled-mode console on a pl011 serial
950 port at the specified address. The pl011 serial port
951 must already be setup and configured. Options are not
952 yet supported. If 'mmio32' is specified, then only
953 the driver will use only 32-bit accessors to read/write
954 the device registers.
957 Start an early, polled-mode console on a meson serial
958 port at the specified address. The serial port must
959 already be setup and configured. Options are not yet
963 Start an early, polled-mode console on an msm serial
964 port at the specified address. The serial port
965 must already be setup and configured. Options are not
969 Start an early, polled-mode console on an msm serial
970 dm port at the specified address. The serial port
971 must already be setup and configured. Options are not
975 Start an early, polled-mode console on a serial port
976 of an Actions Semi SoC, such as S500 or S900, at the
977 specified address. The serial port must already be
978 setup and configured. Options are not yet supported.
980 smh Use ARM semihosting calls for early console.
988 Use early console provided by serial driver available
989 on Samsung SoCs, requires selecting proper type and
990 a correct base address of the selected UART port. The
991 serial port must already be setup and configured.
992 Options are not yet supported.
995 Start an early, polled-mode console on a lantiq serial
996 (lqasc) port at the specified address. The serial port
997 must already be setup and configured. Options are not
1002 Use early console provided by Freescale LP UART driver
1003 found on Freescale Vybrid and QorIQ LS1021A processors.
1004 A valid base address must be provided, and the serial
1005 port must already be setup and configured.
1008 Start an early, polled-mode console on the
1009 Armada 3700 serial port at the specified
1010 address. The serial port must already be setup
1011 and configured. Options are not yet supported.
1013 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1018 earlyprintk=serial[,ttySn[,baudrate]]
1019 earlyprintk=serial[,0x...[,baudrate]]
1020 earlyprintk=ttySn[,baudrate]
1021 earlyprintk=dbgp[debugController#]
1022 earlyprintk=pciserial,bus:device.function[,baudrate]
1023 earlyprintk=xdbc[xhciController#]
1025 earlyprintk is useful when the kernel crashes before
1026 the normal console is initialized. It is not enabled by
1027 default because it has some cosmetic problems.
1029 Append ",keep" to not disable it when the real console
1032 Only one of vga, efi, serial, or usb debug port can
1035 Currently only ttyS0 and ttyS1 may be specified by
1036 name. Other I/O ports may be explicitly specified
1037 on some architectures (x86 and arm at least) by
1038 replacing ttySn with an I/O port address, like this:
1039 earlyprintk=serial,0x1008,115200
1040 You can find the port for a given device in
1041 /proc/tty/driver/serial:
1042 2: uart:ST16650V2 port:00001008 irq:18 ...
1044 Interaction with the standard serial driver is not
1047 The VGA and EFI output is eventually overwritten by
1050 The xen output can only be used by Xen PV guests.
1052 The sclp output can only be used on s390.
1054 edac_report= [HW,EDAC] Control how to report EDAC event
1055 Format: {"on" | "off" | "force"}
1056 on: enable EDAC to report H/W event. May be overridden
1057 by other higher priority error reporting module.
1058 off: disable H/W event reporting through EDAC.
1059 force: enforce the use of EDAC to report H/W event.
1062 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1065 This is designed to be used in conjunction with
1066 the boot argument: earlyprintk=vga
1069 Format: {"off" | "on" | "skip[mbr]"}
1072 Format: { "old_map", "nochunk", "noruntime", "debug" }
1073 old_map [X86-64]: switch to the old ioremap-based EFI
1074 runtime services mapping. 32-bit still uses this one by
1076 nochunk: disable reading files in "chunks" in the EFI
1077 boot stub, as chunking can cause problems with some
1078 firmware implementations.
1079 noruntime : disable EFI runtime services support
1080 debug: enable misc debug output
1082 efi_no_storage_paranoia [EFI; X86]
1083 Using this parameter you can use more than 50% of
1084 your efi variable storage. Use this parameter only if
1085 you are really sure that your UEFI does sane gc and
1086 fulfills the spec otherwise your board may brick.
1088 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1089 Add arbitrary attribute to specific memory range by
1090 updating original EFI memory map.
1091 Region of memory which aa attribute is added to is
1093 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1094 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1095 attribute is added to range 0x100000000-0x180000000 and
1096 0x10a0000000-0x1120000000.
1098 Using this parameter you can do debugging of EFI memmap
1099 related feature. For example, you can do debugging of
1100 Address Range Mirroring feature even if your box
1103 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1104 that is to be dynamically loaded by Linux. If there are
1105 multiple variables with the same name but with different
1106 vendor GUIDs, all of them will be loaded. See
1107 Documentation/acpi/ssdt-overlays.txt for details.
1110 eisa_irq_edge= [PARISC,HW]
1111 See header of drivers/parisc/eisa.c.
1114 See comment before function elanfreq_setup() in
1115 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1118 Format: {"cfq" | "deadline" | "noop"}
1119 See Documentation/block/cfq-iosched.txt and
1120 Documentation/block/deadline-iosched.txt for details.
1122 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1123 Specifies physical address of start of kernel core
1124 image elf header and optionally the size. Generally
1125 kexec loader will pass this option to capture kernel.
1126 See Documentation/kdump/kdump.txt for details.
1128 enable_mtrr_cleanup [X86]
1129 The kernel tries to adjust MTRR layout from continuous
1130 to discrete, to make X server driver able to add WB
1131 entry later. This parameter enables that.
1133 enable_timer_pin_1 [X86]
1134 Enable PIN 1 of APIC timer
1135 Can be useful to work around chipset bugs
1136 (in particular on some ATI chipsets).
1137 The kernel tries to set a reasonable default.
1139 enforcing [SELINUX] Set initial enforcing status.
1141 See security/selinux/Kconfig help text.
1142 0 -- permissive (log only, no denials).
1143 1 -- enforcing (deny and log).
1145 Value can be changed at runtime via /selinux/enforce.
1148 Disable Error Record Serialization Table (ERST)
1151 ether= [HW,NET] Ethernet cards parameters
1152 This option is obsoleted by the "netdev=" option, which
1153 has equivalent usage. See its documentation for details.
1157 Permit 'security.evm' to be updated regardless of
1158 current integrity status.
1162 fail_make_request=[KNL]
1163 General fault injection mechanism.
1164 Format: <interval>,<probability>,<space>,<times>
1165 See also Documentation/fault-injection/.
1168 See Documentation/blockdev/floppy.txt.
1170 force_pal_cache_flush
1171 [IA-64] Avoid check_sal_cache_flush which may hang on
1172 buggy SAL_CACHE_FLUSH implementations. Using this
1173 parameter will force ia64_sal_cache_flush to call
1174 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1177 Forcefully enable Physical Address Extension (PAE).
1178 Many Pentium M systems disable PAE but may have a
1179 functionally usable PAE implementation.
1180 Warning: use of this parameter will taint the kernel
1181 and may cause unknown problems.
1184 [FTRACE] will set and start the specified tracer
1185 as early as possible in order to facilitate early
1188 ftrace_dump_on_oops[=orig_cpu]
1189 [FTRACE] will dump the trace buffers on oops.
1190 If no parameter is passed, ftrace will dump
1191 buffers of all CPUs, but if you pass orig_cpu, it will
1192 dump only the buffer of the CPU that triggered the
1195 ftrace_filter=[function-list]
1196 [FTRACE] Limit the functions traced by the function
1197 tracer at boot up. function-list is a comma separated
1198 list of functions. This list can be changed at run
1199 time by the set_ftrace_filter file in the debugfs
1202 ftrace_notrace=[function-list]
1203 [FTRACE] Do not trace the functions specified in
1204 function-list. This list can be changed at run time
1205 by the set_ftrace_notrace file in the debugfs
1208 ftrace_graph_filter=[function-list]
1209 [FTRACE] Limit the top level callers functions traced
1210 by the function graph tracer at boot up.
1211 function-list is a comma separated list of functions
1212 that can be changed at run time by the
1213 set_graph_function file in the debugfs tracing directory.
1215 ftrace_graph_notrace=[function-list]
1216 [FTRACE] Do not trace from the functions specified in
1217 function-list. This list is a comma separated list of
1218 functions that can be changed at run time by the
1219 set_graph_notrace file in the debugfs tracing directory.
1221 ftrace_graph_max_depth=<uint>
1222 [FTRACE] Used with the function graph tracer. This is
1223 the max depth it will trace into a function. This value
1224 can be changed at run time by the max_graph_depth file
1225 in the tracefs tracing directory. default: 0 (no limit)
1228 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1229 support via parallel port (up to 5 devices per port)
1230 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1231 See also Documentation/input/devices/joystick-parport.rst
1235 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1239 gcov_persist= [GCOV] When non-zero (default), profiling data for
1240 kernel modules is saved and remains accessible via
1241 debugfs, even when the module is unloaded/reloaded.
1242 When zero, profiling data is discarded and associated
1243 debugfs files are removed at module unload time.
1245 goldfish [X86] Enable the goldfish android emulator platform.
1246 Don't use this when you are not running on the
1249 gpt [EFI] Forces disk with valid GPT signature but
1250 invalid Protective MBR to be treated as GPT. If the
1251 primary GPT is corrupted, it enables the backup/alternate
1252 GPT to be used instead.
1254 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1255 the "Enable 0" bit of the configuration register.
1258 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1259 the "Enable 0" bit of the configuration register.
1262 grcan.select= [HW] Select which physical interface to use.
1265 grcan.txsize= [HW] Sets the size of the tx buffer.
1266 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1268 grcan.rxsize= [HW] Sets the size of the rx buffer.
1269 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1272 gpio-mockup.gpio_mockup_ranges
1273 [HW] Sets the ranges of gpiochip of for this device.
1274 Format: <start1>,<end1>,<start2>,<end2>...
1276 hardlockup_all_cpu_backtrace=
1277 [KNL] Should the hard-lockup detector generate
1278 backtraces on all cpus.
1281 hashdist= [KNL,NUMA] Large hashes allocated during boot
1282 are distributed across NUMA nodes. Defaults on
1283 for 64-bit NUMA, off otherwise.
1284 Format: 0 | 1 (for off | on)
1286 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1288 hd= [EIDE] (E)IDE hard drive subsystem geometry
1289 Format: <cyl>,<head>,<sect>
1292 Disable Hardware Error Source Table (HEST) support;
1293 corresponding firmware-first mode error processing
1294 logic will be disabled.
1296 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1297 size of <nn>. This works even on boxes that have no
1298 highmem otherwise. This also works to reduce highmem
1299 size on bigger boxes.
1301 highres= [KNL] Enable/disable high resolution timer mode.
1302 Valid parameters: "on", "off"
1306 See Documentation/isdn/README.HiSax.
1310 hpet= [X86-32,HPET] option to control HPET usage
1311 Format: { enable (default) | disable | force |
1313 disable: disable HPET and use PIT instead
1314 force: allow force enabled of undocumented chips (ICH4,
1316 verbose: show contents of HPET registers during setup
1318 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1319 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1321 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1322 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1323 On x86-64 and powerpc, this option can be specified
1324 multiple times interleaved with hugepages= to reserve
1325 huge pages of different sizes. Valid pages sizes on
1326 x86-64 are 2M (when the CPU supports "pse") and 1G
1327 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1329 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1330 terminal devices. Valid values: 0..8
1331 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1332 If specified, z/VM IUCV HVC accepts connections
1333 from listed z/VM user IDs only.
1335 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1336 hardware thread id mappings.
1337 Format: <cpu>:<hwthread>
1340 Do not unregister boot console at start. This is only
1341 useful for debugging when something happens in the window
1342 between unregistering the boot console and initializing
1345 i2c_bus= [HW] Override the default board specific I2C bus speed
1346 or register an additional I2C bus that is not
1347 registered from board initialization code.
1351 i8042.debug [HW] Toggle i8042 debug mode
1352 i8042.unmask_kbd_data
1353 [HW] Enable printing of interrupt data from the KBD port
1354 (disabled by default, and as a pre-condition
1355 requires that i8042.debug=1 be enabled)
1356 i8042.direct [HW] Put keyboard port into non-translated mode
1357 i8042.dumbkbd [HW] Pretend that controller can only read data from
1358 keyboard and cannot control its state
1359 (Don't attempt to blink the leds)
1360 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1361 i8042.nokbd [HW] Don't check/create keyboard port
1362 i8042.noloop [HW] Disable the AUX Loopback command while probing
1364 i8042.nomux [HW] Don't check presence of an active multiplexing
1366 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1368 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1369 i8042.reset [HW] Reset the controller during init, cleanup and
1370 suspend-to-ram transitions, only during s2r
1371 transitions, or never reset
1372 Format: { 1 | Y | y | 0 | N | n }
1373 1, Y, y: always reset controller
1374 0, N, n: don't ever reset controller
1375 Default: only on s2r transitions on x86; most other
1376 architectures force reset to be always executed
1377 i8042.unlock [HW] Unlock (ignore) the keylock
1378 i8042.kbdreset [HW] Reset device connected to KBD port
1382 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1383 indicates that the driver is running on unsupported
1385 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1386 does not match list of supported models.
1388 [HW] Report power status in /proc/i8k
1389 (disabled by default)
1390 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1393 i915.invert_brightness=
1394 [DRM] Invert the sense of the variable that is used to
1395 set the brightness of the panel backlight. Normally a
1396 brightness value of 0 indicates backlight switched off,
1397 and the maximum of the brightness value sets the backlight
1398 to maximum brightness. If this parameter is set to 0
1399 (default) and the machine requires it, or this parameter
1400 is set to 1, a brightness value of 0 sets the backlight
1401 to maximum brightness, and the maximum of the brightness
1402 value switches the backlight off.
1403 -1 -- never invert brightness
1404 0 -- machine default
1405 1 -- force brightness inversion
1408 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1410 ide-core.nodma= [HW] (E)IDE subsystem
1411 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1412 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1413 .cdrom .chs .ignore_cable are additional options
1414 See Documentation/ide/ide.txt.
1416 ide-generic.probe-mask= [HW] (E)IDE subsystem
1418 Probe mask for legacy ISA IDE ports. Depending on
1419 platform up to 6 ports are supported, enabled by
1420 setting corresponding bits in the mask to 1. The
1421 default value is 0x0, which has a special meaning.
1422 On systems that have PCI, it triggers scanning the
1423 PCI bus for the first and the second port, which
1424 are then probed. On systems without PCI the value
1425 of 0x0 enables probing the two first ports as if it
1428 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1429 Claim all unknown PCI IDE storage controllers.
1432 Format: idle=poll, idle=halt, idle=nomwait
1433 Poll forces a polling idle loop that can slightly
1434 improve the performance of waking up a idle CPU, but
1435 will use a lot of power and make the system run hot.
1437 idle=halt: Halt is forced to be used for CPU idle.
1438 In such case C2/C3 won't be used again.
1439 idle=nomwait: Disable mwait for CPU C-states
1441 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1442 Format: { strict | legacy | 2008 | relaxed }
1445 Choose which programs will be accepted for execution
1446 based on the IEEE 754 NaN encoding(s) supported by
1447 the FPU and the NaN encoding requested with the value
1448 of an ELF file header flag individually set by each
1449 binary. Hardware implementations are permitted to
1450 support either or both of the legacy and the 2008 NaN
1453 Available settings are as follows:
1454 strict accept binaries that request a NaN encoding
1455 supported by the FPU
1456 legacy only accept legacy-NaN binaries, if supported
1458 2008 only accept 2008-NaN binaries, if supported
1460 relaxed accept any binaries regardless of whether
1461 supported by the FPU
1463 The FPU emulator is always able to support both NaN
1464 encodings, so if no FPU hardware is present or it has
1465 been disabled with 'nofpu', then the settings of
1466 'legacy' and '2008' strap the emulator accordingly,
1467 'relaxed' straps the emulator for both legacy-NaN and
1468 2008-NaN, whereas 'strict' enables legacy-NaN only on
1469 legacy processors and both NaN encodings on MIPS32 or
1472 The setting for ABS.fmt/NEG.fmt instruction execution
1473 mode generally follows that for the NaN encoding,
1474 except where unsupported by hardware.
1476 ignore_loglevel [KNL]
1477 Ignore loglevel setting - this will print /all/
1478 kernel messages to the console. Useful for debugging.
1479 We also add it as printk module parameter, so users
1480 could change it dynamically, usually by
1481 /sys/module/printk/parameters/ignore_loglevel.
1484 Ignore RLIMIT_DATA setting for data mappings,
1485 print warning at first misuse. Can be changed via
1486 /sys/module/kernel/parameters/ignore_rlimit_data.
1488 ihash_entries= [KNL]
1489 Set number of hash buckets for inode cache.
1491 ima_appraise= [IMA] appraise integrity measurements
1492 Format: { "off" | "enforce" | "fix" | "log" }
1495 ima_appraise_tcb [IMA]
1496 The builtin appraise policy appraises all files
1499 ima_canonical_fmt [IMA]
1500 Use the canonical format for the binary runtime
1501 measurements, instead of host native format.
1504 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1508 The list of supported hash algorithms is defined
1509 in crypto/hash_info.h.
1512 The builtin policies to load during IMA setup.
1513 Format: "tcb | appraise_tcb | secure_boot"
1515 The "tcb" policy measures all programs exec'd, files
1516 mmap'd for exec, and all files opened with the read
1517 mode bit set by either the effective uid (euid=0) or
1520 The "appraise_tcb" policy appraises the integrity of
1521 all files owned by root. (This is the equivalent
1522 of ima_appraise_tcb.)
1524 The "secure_boot" policy appraises the integrity
1525 of files (eg. kexec kernel image, kernel modules,
1526 firmware, policy, etc) based on file signatures.
1528 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1529 Load a policy which meets the needs of the Trusted
1530 Computing Base. This means IMA will measure all
1531 programs exec'd, files mmap'd for exec, and all files
1532 opened for read by uid=0.
1535 Select one of defined IMA measurements template formats.
1536 Formats: { "ima" | "ima-ng" | "ima-sig" }
1540 [IMA] Define a custom template format.
1541 Format: { "field1|...|fieldN" }
1543 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1544 Format: <min_file_size>
1545 Set the minimal file size for using asynchronous hash.
1546 If left unspecified, ahash usage is disabled.
1548 ahash performance varies for different data sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve the best performance for a particular HW.
1552 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1554 Set hashing buffer size. Default: 4k.
1556 ahash performance varies for different chunk sizes on
1557 different crypto accelerators. This option can be used
1558 to achieve best performance for particular HW.
1562 Run specified binary instead of /sbin/init as init
1565 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1566 for working out where the kernel is dying during
1569 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1570 initcall functions. Useful for debugging built-in
1571 modules and initcalls.
1573 initrd= [BOOT] Specify the location of the initial ramdisk
1575 init_pkru= [x86] Specify the default memory protection keys rights
1576 register contents for all processes. 0x55555554 by
1577 default (disallow access to all but pkey 0). Can
1578 override in debugfs after boot.
1580 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1583 int_pln_enable [x86] Enable power limit notification interrupt
1585 integrity_audit=[IMA]
1586 Format: { "0" | "1" }
1587 0 -- basic integrity auditing messages. (Default)
1588 1 -- additional integrity auditing messages.
1590 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1592 Enable intel iommu driver.
1594 Disable intel iommu driver.
1595 igfx_off [Default Off]
1596 By default, gfx is mapped as normal device. If a gfx
1597 device has a dedicated DMAR unit, the DMAR unit is
1598 bypassed by not enabling DMAR with this option. In
1599 this case, gfx device will use physical address for
1602 With this option iommu will not optimize to look
1603 for io virtual address below 32-bit forcing dual
1604 address cycle on pci bus for cards supporting greater
1605 than 32-bit addressing. The default is to look
1606 for translation below 32-bit and if not available
1607 then look in the higher range.
1608 strict [Default Off]
1609 With this option on every unmap_single operation will
1610 result in a hardware IOTLB flush operation as opposed
1611 to batching them for performance.
1612 sp_off [Default Off]
1613 By default, super page will be supported if Intel IOMMU
1614 has the capability. With this option, super page will
1616 ecs_off [Default Off]
1617 By default, extended context tables will be supported if
1618 the hardware advertises that it has support both for the
1619 extended tables themselves, and also PASID support. With
1620 this option set, extended tables will not be used even
1621 on hardware which claims to support them.
1622 tboot_noforce [Default Off]
1623 Do not force the Intel IOMMU enabled under tboot.
1624 By default, tboot will force Intel IOMMU on, which
1625 could harm performance of some high-throughput
1626 devices like 40GBit network cards, even if identity
1628 Note that using this option lowers the security
1629 provided by tboot because it makes the system
1630 vulnerable to DMA attacks.
1632 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1633 0 disables intel_idle and fall back on acpi_idle.
1634 1 to 9 specify maximum depth of C-state.
1638 Do not enable intel_pstate as the default
1639 scaling driver for the supported processors
1641 Use intel_pstate as a scaling driver, but configure it
1642 to work with generic cpufreq governors (instead of
1643 enabling its internal governor). This mode cannot be
1644 used along with the hardware-managed P-states (HWP)
1647 Enable intel_pstate on systems that prohibit it by default
1648 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1649 instead of acpi-cpufreq may disable platform features, such
1650 as thermal controls and power capping, that rely on ACPI
1651 P-States information being indicated to OSPM and therefore
1652 should be used with caution. This option does not work with
1653 processors that aren't supported by the intel_pstate driver
1654 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1656 Do not enable hardware P state control (HWP)
1659 Only load intel_pstate on systems which support
1660 hardware P state control (HWP) if available.
1662 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1663 Description Table, specifies preferred power management
1664 profile as "Enterprise Server" or "Performance Server",
1665 then this feature is turned on by default.
1667 Allow per-logical-CPU P-State performance control limits using
1668 cpufreq sysfs interface
1670 intremap= [X86-64, Intel-IOMMU]
1671 on enable Interrupt Remapping (default)
1672 off disable Interrupt Remapping
1673 nosid disable Source ID checking
1675 BIOS x2APIC opt-out request will be ignored
1676 nopost disable Interrupt Posting
1678 iomem= Disable strict checking of access to MMIO memory
1679 strict regions from userspace.
1694 nobypass [PPC/POWERNV]
1695 Disable IOMMU bypass, using IOMMU for PCI devices.
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.
1724 irqchip.gicv2_force_probe=
1727 Force the kernel to look for the second 4kB page
1728 of a GICv2 controller even if the memory range
1729 exposed by the device tree is too small.
1732 When an interrupt is not handled search all handlers
1733 for it. Intended to get systems with badly broken
1737 When an interrupt is not handled search all handlers
1738 for it. Also check all handlers each timer
1739 interrupt. Intended to get systems with badly broken
1743 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1745 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1746 [Deprecated - use cpusets instead]
1747 Format: [flag-list,]<cpu-list>
1749 Specify one or more CPUs to isolate from disturbances
1750 specified in the flag list (default: domain):
1753 Disable the tick when a single task runs.
1755 Isolate from the general SMP balancing and scheduling
1756 algorithms. Note that performing domain isolation this way
1757 is irreversible: it's not possible to bring back a CPU to
1758 the domains once isolated through isolcpus. It's strongly
1759 advised to use cpusets instead to disable scheduler load
1760 balancing through the "cpuset.sched_load_balance" file.
1761 It offers a much more flexible interface where CPUs can
1762 move in and out of an isolated set anytime.
1764 You can move a process onto or off an "isolated" CPU via
1765 the CPU affinity syscalls or cpuset.
1766 <cpu number> begins at 0 and the maximum value is
1767 "number of CPUs in system - 1".
1769 The format of <cpu-list> is described above.
1775 ivrs_ioapic [HW,X86_64]
1776 Provide an override to the IOAPIC-ID<->DEVICE-ID
1777 mapping provided in the IVRS ACPI table. For
1778 example, to map IOAPIC-ID decimal 10 to
1779 PCI device 00:14.0 write the parameter as:
1780 ivrs_ioapic[10]=00:14.0
1782 ivrs_hpet [HW,X86_64]
1783 Provide an override to the HPET-ID<->DEVICE-ID
1784 mapping provided in the IVRS ACPI table. For
1785 example, to map HPET-ID decimal 0 to
1786 PCI device 00:14.0 write the parameter as:
1787 ivrs_hpet[0]=00:14.0
1789 ivrs_acpihid [HW,X86_64]
1790 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1791 mapping provided in the IVRS ACPI table. For
1792 example, to map UART-HID:UID AMD0020:0 to
1793 PCI device 00:14.5 write the parameter as:
1794 ivrs_acpihid[00:14.5]=AMD0020:0
1796 js= [HW,JOY] Analog joystick
1797 See Documentation/input/joydev/joystick.rst.
1800 When CONFIG_RANDOMIZE_BASE is set, this disables
1801 kernel and module base offset ASLR (Address Space
1802 Layout Randomization).
1805 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1806 report on every invalid memory access. Without this
1807 parameter KASAN will print report only for the first
1812 kernelcore= [KNL,X86,IA-64,PPC]
1813 Format: nn[KMGTPE] | "mirror"
1815 specifies the amount of memory usable by the kernel
1816 for non-movable allocations. The requested amount is
1817 spread evenly throughout all nodes in the system. The
1818 remaining memory in each node is used for Movable
1819 pages. In the event, a node is too small to have both
1820 kernelcore and Movable pages, kernelcore pages will
1821 take priority and other nodes will have a larger number
1822 of Movable pages. The Movable zone is used for the
1823 allocation of pages that may be reclaimed or moved
1824 by the page migration subsystem. This means that
1825 HugeTLB pages may not be allocated from this zone.
1826 Note that allocations like PTEs-from-HighMem still
1827 use the HighMem zone if it exists, and the Normal
1828 zone if it does not.
1830 Instead of specifying the amount of memory (nn[KMGTPE]),
1831 you can specify "mirror" option. In case "mirror"
1832 option is specified, mirrored (reliable) memory is used
1833 for non-movable allocations and remaining memory is used
1834 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1835 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1838 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1839 Format: <Controller#>[,poll interval]
1840 The controller # is the number of the ehci usb debug
1841 port as it is probed via PCI. The poll interval is
1842 optional and is the number seconds in between
1843 each poll cycle to the debug port in case you need
1844 the functionality for interrupting the kernel with
1845 gdb or control-c on the dbgp connection. When
1846 not using this parameter you use sysrq-g to break into
1847 the kernel debugger.
1849 kgdboc= [KGDB,HW] kgdb over consoles.
1850 Requires a tty driver that supports console polling,
1851 or a supported polling keyboard driver (non-usb).
1852 Serial only format: <serial_device>[,baud]
1853 keyboard only format: kbd
1854 keyboard and serial format: kbd,<serial_device>[,baud]
1855 Optional Kernel mode setting:
1856 kms, kbd format: kms,kbd
1857 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1859 kgdbwait [KGDB] Stop kernel execution and enter the
1860 kernel debugger at the earliest opportunity.
1862 kmac= [MIPS] korina ethernet MAC address.
1863 Configure the RouterBoard 532 series on-chip
1864 Ethernet adapter MAC address.
1866 kmemleak= [KNL] Boot-time kmemleak enable/disable
1867 Valid arguments: on, off
1869 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1872 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1873 Default is 0 (don't ignore, but inject #GP)
1875 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1879 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1880 Default is 1 (enabled)
1882 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1884 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1886 kvm-arm.vgic_v3_group0_trap=
1887 [KVM,ARM] Trap guest accesses to GICv3 group-0
1890 kvm-arm.vgic_v3_group1_trap=
1891 [KVM,ARM] Trap guest accesses to GICv3 group-1
1894 kvm-arm.vgic_v3_common_trap=
1895 [KVM,ARM] Trap guest accesses to GICv3 common
1898 kvm-arm.vgic_v4_enable=
1899 [KVM,ARM] Allow use of GICv4 for direct injection of
1902 kvm-intel.nosmt=[KVM,Intel] If the L1TF CPU bug is present (CVE-2018-3620)
1903 and the system has SMT (aka Hyper-Threading) enabled then
1904 don't allow guests to be created.
1906 Default is 0 (allow guests to be created).
1908 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1909 (virtualized MMU) support on capable Intel chips.
1910 Default is 1 (enabled)
1912 kvm-intel.emulate_invalid_guest_state=
1913 [KVM,Intel] Enable emulation of invalid guest states
1914 Default is 0 (disabled)
1916 kvm-intel.flexpriority=
1917 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1918 Default is 1 (enabled)
1921 [KVM,Intel] Enable VMX nesting (nVMX).
1922 Default is 0 (disabled)
1924 kvm-intel.unrestricted_guest=
1925 [KVM,Intel] Disable unrestricted guest feature
1926 (virtualized real and unpaged mode) on capable
1927 Intel chips. Default is 1 (enabled)
1929 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1932 Valid arguments: never, cond, always
1934 always: L1D cache flush on every VMENTER.
1935 cond: Flush L1D on VMENTER only when the code between
1936 VMEXIT and VMENTER can leak host memory.
1937 never: Disables the mitigation
1939 Default is cond (do L1 cache flush in specific instances)
1941 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1942 feature (tagged TLBs) on capable Intel chips.
1943 Default is 1 (enabled)
1949 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1952 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1953 value for LAPIC timer one-shot implementation. Default
1954 back to the programmable timer unit in the LAPIC.
1956 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1959 libata.dma= [LIBATA] DMA control
1960 libata.dma=0 Disable all PATA and SATA DMA
1961 libata.dma=1 PATA and SATA Disk DMA only
1962 libata.dma=2 ATAPI (CDROM) DMA only
1963 libata.dma=4 Compact Flash DMA only
1964 Combinations also work, so libata.dma=3 enables DMA
1965 for disks and CDROMs, but not CFs.
1967 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1968 libata.ignore_hpa=0 keep BIOS limits (default)
1969 libata.ignore_hpa=1 ignore limits, using full disk
1971 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1975 libata.force= [LIBATA] Force configurations. The format is comma
1976 separated list of "[ID:]VAL" where ID is
1977 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1978 matching port, link or device. Basically, it matches
1979 the ATA ID string printed on console by libata. If
1980 the whole ID part is omitted, the last PORT and DEVICE
1981 values are used. If ID hasn't been specified yet, the
1982 configuration applies to all ports, links and devices.
1984 If only DEVICE is omitted, the parameter applies to
1985 the port and all links and devices behind it. DEVICE
1986 number of 0 either selects the first device or the
1987 first fan-out link behind PMP device. It does not
1988 select the host link. DEVICE number of 15 selects the
1989 host link and device attached to it.
1991 The VAL specifies the configuration to force. As long
1992 as there's no ambiguity shortcut notation is allowed.
1993 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1994 The following configurations can be forced.
1996 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1997 Any ID with matching PORT is used.
1999 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2001 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2002 udma[/][16,25,33,44,66,100,133] notation is also
2005 * [no]ncq: Turn on or off NCQ.
2007 * [no]ncqtrim: Turn off queued DSM TRIM.
2009 * nohrst, nosrst, norst: suppress hard, soft
2012 * rstonce: only attempt one reset during
2013 hot-unplug link recovery
2015 * dump_id: dump IDENTIFY data.
2017 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2019 * disable: Disable this device.
2021 If there are multiple matching configurations changing
2022 the same attribute, the last one is used.
2024 memblock=debug [KNL] Enable memblock debug messages.
2026 load_ramdisk= [RAM] List of ramdisks to load from floppy
2027 See Documentation/blockdev/ramdisk.txt.
2029 lockd.nlm_grace_period=P [NFS] Assign grace period.
2032 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2035 lockd.nlm_timeout=T [NFS] Assign timeout value.
2038 lockd.nlm_udpport=M [NFS] Assign UDP port.
2041 locktorture.nreaders_stress= [KNL]
2042 Set the number of locking read-acquisition kthreads.
2043 Defaults to being automatically set based on the
2044 number of online CPUs.
2046 locktorture.nwriters_stress= [KNL]
2047 Set the number of locking write-acquisition kthreads.
2049 locktorture.onoff_holdoff= [KNL]
2050 Set time (s) after boot for CPU-hotplug testing.
2052 locktorture.onoff_interval= [KNL]
2053 Set time (s) between CPU-hotplug operations, or
2054 zero to disable CPU-hotplug testing.
2056 locktorture.shuffle_interval= [KNL]
2057 Set task-shuffle interval (jiffies). Shuffling
2058 tasks allows some CPUs to go into dyntick-idle
2059 mode during the locktorture test.
2061 locktorture.shutdown_secs= [KNL]
2062 Set time (s) after boot system shutdown. This
2063 is useful for hands-off automated testing.
2065 locktorture.stat_interval= [KNL]
2066 Time (s) between statistics printk()s.
2068 locktorture.stutter= [KNL]
2069 Time (s) to stutter testing, for example,
2070 specifying five seconds causes the test to run for
2071 five seconds, wait for five seconds, and so on.
2072 This tests the locking primitive's ability to
2073 transition abruptly to and from idle.
2075 locktorture.torture_runnable= [BOOT]
2076 Start locktorture running at boot time.
2078 locktorture.torture_type= [KNL]
2079 Specify the locking implementation to test.
2081 locktorture.verbose= [KNL]
2082 Enable additional printk() statements.
2084 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2087 loglevel= All Kernel Messages with a loglevel smaller than the
2088 console loglevel will be printed to the console. It can
2089 also be changed with klogd or other programs. The
2090 loglevels are defined as follows:
2092 0 (KERN_EMERG) system is unusable
2093 1 (KERN_ALERT) action must be taken immediately
2094 2 (KERN_CRIT) critical conditions
2095 3 (KERN_ERR) error conditions
2096 4 (KERN_WARNING) warning conditions
2097 5 (KERN_NOTICE) normal but significant condition
2098 6 (KERN_INFO) informational
2099 7 (KERN_DEBUG) debug-level messages
2101 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2102 in bytes. n must be a power of two and greater
2103 than the minimal size. The minimal size is defined
2104 by LOG_BUF_SHIFT kernel config parameter. There is
2105 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2106 that allows to increase the default size depending on
2107 the number of CPUs. See init/Kconfig for more details.
2109 logo.nologo [FB] Disables display of the built-in Linux logo.
2110 This may be used to provide more screen space for
2111 kernel log messages and is useful when debugging
2112 kernel boot problems.
2114 lp=0 [LP] Specify parallel ports to use, e.g,
2115 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2116 lp=reset first parallel port). 'lp=0' disables the
2117 lp=auto printer driver. 'lp=reset' (which can be
2118 specified in addition to the ports) causes
2119 attached printers to be reset. Using
2120 lp=port1,port2,... specifies the parallel ports
2121 to associate lp devices with, starting with
2122 lp0. A port specification may be 'none' to skip
2123 that lp device, or a parport name such as
2124 'parport0'. Specifying 'lp=auto' instead of a
2125 port specification list means that device IDs
2126 from each port should be examined, to see if
2127 an IEEE 1284-compliant printer is attached; if
2128 so, the driver will manage that printer.
2129 See also header of drivers/char/lp.c.
2132 Sets loops_per_jiffy to given constant, thus avoiding
2133 time-consuming boot-time autodetection (up to 250 ms per
2134 CPU). 0 enables autodetection (default). To determine
2135 the correct value for your kernel, boot with normal
2136 autodetection and see what value is printed. Note that
2137 on SMP systems the preset will be applied to all CPUs,
2138 which is likely to cause problems if your CPUs need
2139 significantly divergent settings. An incorrect value
2140 will cause delays in the kernel to be wrong, leading to
2141 unpredictable I/O errors and other breakage. Although
2142 unlikely, in the extreme case this might damage your
2146 Format: <io>,<irq>,<dma>
2148 machvec= [IA-64] Force the use of a particular machine-vector
2149 (machvec) in a generic kernel.
2150 Example: machvec=hpzx1_swiotlb
2152 machtype= [Loongson] Share the same kernel image file between different
2154 Example: machtype=lemote-yeeloong-2f-7inch
2156 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2157 than or equal to this physical address is ignored.
2159 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2160 will bring up during bootup. maxcpus=n : n >= 0 limits
2161 the kernel to bring up 'n' processors. Surely after
2162 bootup you can bring up the other plugged cpu by executing
2163 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2164 only takes effect during system bootup.
2165 While n=0 is a special case, it is equivalent to "nosmp",
2166 which also disables the IO APIC.
2168 max_loop= [LOOP] The number of loop block devices that get
2169 (loop.max_loop) unconditionally pre-created at init time. The default
2170 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2171 of statically allocating a predefined number, loop
2172 devices can be requested on-demand with the
2173 /dev/loop-control interface.
2175 mce [X86-32] Machine Check Exception
2177 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2179 md= [HW] RAID subsystems devices and level
2180 See Documentation/admin-guide/md.rst.
2183 Format: <first>,<last>
2184 Specifies range of consoles to be captured by the MDA.
2186 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2187 Amount of memory to be used when the kernel is not able
2188 to see the whole system memory or for test.
2189 [X86] Work as limiting max address. Use together
2190 with memmap= to avoid physical address space collisions.
2191 Without memmap= PCI devices could be placed at addresses
2192 belonging to unused RAM.
2194 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2198 [KNL,SH] Allow user to override the default size for
2199 per-device physically contiguous DMA buffers.
2201 memhp_default_state=online/offline
2202 [KNL] Set the initial state for the memory hotplug
2203 onlining policy. If not specified, the default value is
2204 set according to the
2205 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2207 See Documentation/memory-hotplug.txt.
2209 memmap=exactmap [KNL,X86] Enable setting of an exact
2210 E820 memory map, as specified by the user.
2211 Such memmap=exactmap lines can be constructed based on
2212 BIOS output or other requirements. See the memmap=nn@ss
2215 memmap=nn[KMG]@ss[KMG]
2216 [KNL] Force usage of a specific region of memory.
2217 Region of memory to be used is from ss to ss+nn.
2218 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2219 which limits max address to nn[KMG].
2220 Multiple different regions can be specified,
2223 memmap=100M@2G,100M#3G,1G!1024G
2225 memmap=nn[KMG]#ss[KMG]
2226 [KNL,ACPI] Mark specific memory as ACPI data.
2227 Region of memory to be marked is from ss to ss+nn.
2229 memmap=nn[KMG]$ss[KMG]
2230 [KNL,ACPI] Mark specific memory as reserved.
2231 Region of memory to be reserved is from ss to ss+nn.
2232 Example: Exclude memory from 0x18690000-0x1869ffff
2233 memmap=64K$0x18690000
2235 memmap=0x10000$0x18690000
2236 Some bootloaders may need an escape character before '$',
2237 like Grub2, otherwise '$' and the following number
2240 memmap=nn[KMG]!ss[KMG]
2241 [KNL,X86] Mark specific memory as protected.
2242 Region of memory to be used, from ss to ss+nn.
2243 The memory region may be marked as e820 type 12 (0xc)
2244 and is NVDIMM or ADR memory.
2246 memory_corruption_check=0/1 [X86]
2247 Some BIOSes seem to corrupt the first 64k of
2248 memory when doing things like suspend/resume.
2249 Setting this option will scan the memory
2250 looking for corruption. Enabling this will
2251 both detect corruption and prevent the kernel
2252 from using the memory being corrupted.
2253 However, its intended as a diagnostic tool; if
2254 repeatable BIOS-originated corruption always
2255 affects the same memory, you can use memmap=
2256 to prevent the kernel from using that memory.
2258 memory_corruption_check_size=size [X86]
2259 By default it checks for corruption in the low
2260 64k, making this memory unavailable for normal
2261 use. Use this parameter to scan for
2262 corruption in more or less memory.
2264 memory_corruption_check_period=seconds [X86]
2265 By default it checks for corruption every 60
2266 seconds. Use this parameter to check at some
2267 other rate. 0 disables periodic checking.
2269 memtest= [KNL,X86,ARM] Enable memtest
2271 default : 0 <disable>
2272 Specifies the number of memtest passes to be
2273 performed. Each pass selects another test
2274 pattern from a given set of patterns. Memtest
2275 fills the memory with this pattern, validates
2276 memory contents and reserves bad memory
2277 regions that are detected.
2279 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2280 Valid arguments: on, off
2281 Default (depends on kernel configuration option):
2282 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2283 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2284 mem_encrypt=on: Activate SME
2285 mem_encrypt=off: Do not activate SME
2287 Refer to Documentation/x86/amd-memory-encryption.txt
2288 for details on when memory encryption can be activated.
2290 mem_sleep_default= [SUSPEND] Default system suspend mode:
2291 s2idle - Suspend-To-Idle
2292 shallow - Power-On Suspend or equivalent (if supported)
2293 deep - Suspend-To-RAM or equivalent (if supported)
2294 See Documentation/admin-guide/pm/sleep-states.rst.
2296 meye.*= [HW] Set MotionEye Camera parameters
2297 See Documentation/media/v4l-drivers/meye.rst.
2299 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2300 Multi-Function General Purpose Timers on AMD Geode
2303 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2304 the BIOS has incorrectly applied a workaround. TinyBIOS
2305 version 0.98 is known to be affected, 0.99 fixes the
2306 problem by letting the user disable the workaround.
2310 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2311 physical address is ignored.
2313 mini2440= [ARM,HW,KNL]
2314 Format:[0..2][b][c][t]
2316 MINI2440 configuration specification:
2317 0 - The attached screen is the 3.5" TFT
2318 1 - The attached screen is the 7" TFT
2319 2 - The VGA Shield is attached (1024x768)
2320 Leaving out the screen size parameter will not load
2321 the TFT driver, and the framebuffer will be left
2323 b - Enable backlight. The TFT backlight pin will be
2324 linked to the kernel VESA blanking code and a GPIO
2325 LED. This parameter is not necessary when using the
2327 c - Enable the s3c camera interface.
2328 t - Reserved for enabling touchscreen support. The
2329 touchscreen support is not enabled in the mainstream
2330 kernel as of 2.6.30, a preliminary port can be found
2331 in the "bleeding edge" mini2440 support kernel at
2332 http://repo.or.cz/w/linux-2.6/mini2440.git
2335 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2336 parameter allows control of the logging verbosity for
2337 the additional memory initialisation checks. A value
2338 of 0 disables mminit logging and a level of 4 will
2339 log everything. Information is printed at KERN_DEBUG
2340 so loglevel=8 may also need to be specified.
2343 [KNL] When CONFIG_MODULE_SIG is set, this means that
2344 modules without (valid) signatures will fail to load.
2345 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2346 is always true, so this option does nothing.
2348 module_blacklist= [KNL] Do not load a comma-separated list of
2349 modules. Useful for debugging problem modules.
2352 [MOUSE] Maximum time between finger touching and
2353 leaving touchpad surface for touch to be considered
2354 a tap and be reported as a left button click (for
2355 touchpads working in absolute mode only).
2357 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2358 reporting absolute coordinates, such as tablets
2359 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2360 reporting absolute coordinates, such as tablets
2362 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2363 is similar to kernelcore except it specifies the
2364 amount of memory used for migratable allocations.
2365 If both kernelcore and movablecore is specified,
2366 then kernelcore will be at *least* the specified
2367 value but may be more. If movablecore on its own
2368 is specified, the administrator must be careful
2369 that the amount of memory usable for all allocations
2372 movable_node [KNL] Boot-time switch to make hotplugable memory
2373 NUMA nodes to be movable. This means that the memory
2374 of such nodes will be usable only for movable
2375 allocations which rules out almost all kernel
2376 allocations. Use with caution!
2378 MTD_Partition= [MTD]
2379 Format: <name>,<region-number>,<size>,<offset>
2381 MTD_Region= [MTD] Format:
2382 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2385 See drivers/mtd/cmdlinepart.c.
2387 multitce=off [PPC] This parameter disables the use of the pSeries
2388 firmware feature for updating multiple TCE entries
2391 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2393 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2395 boundary - index of last SLC block on Flex-OneNAND.
2396 The remaining blocks are configured as MLC blocks.
2397 lock - Configure if Flex-OneNAND boundary should be locked.
2398 Once locked, the boundary cannot be changed.
2399 1 indicates lock status, 0 indicates unlock status.
2402 ARM/S3C2412 JIVE boot control
2404 See arch/arm/mach-s3c2412/mach-jive.c
2406 mtouchusb.raw_coordinates=
2407 [HW] Make the MicroTouch USB driver use raw coordinates
2408 ('y', default) or cooked coordinates ('n')
2410 mtrr_chunk_size=nn[KMG] [X86]
2411 used for mtrr cleanup. It is largest continuous chunk
2412 that could hold holes aka. UC entries.
2414 mtrr_gran_size=nn[KMG] [X86]
2415 Used for mtrr cleanup. It is granularity of mtrr block.
2417 Large value could prevent small alignment from
2420 mtrr_spare_reg_nr=n [X86]
2422 Range: 0,7 : spare reg number
2424 Used for mtrr cleanup. It is spare mtrr entries number.
2425 Set to 2 or more if your graphical card needs more.
2427 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2429 netdev= [NET] Network devices parameters
2430 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2431 Note that mem_start is often overloaded to mean
2432 something different and driver-specific.
2433 This usage is only documented in each driver source
2437 [NETFILTER] Enable connection tracking flow accounting
2438 0 to disable accounting
2439 1 to enable accounting
2442 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2443 See Documentation/filesystems/nfs/nfsroot.txt.
2445 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2446 See Documentation/filesystems/nfs/nfsroot.txt.
2448 nfsrootdebug [NFS] enable nfsroot debugging messages.
2449 See Documentation/filesystems/nfs/nfsroot.txt.
2451 nfs.callback_nr_threads=
2452 [NFSv4] set the total number of threads that the
2453 NFS client will assign to service NFSv4 callback
2456 nfs.callback_tcpport=
2457 [NFS] set the TCP port on which the NFSv4 callback
2458 channel should listen.
2461 [NFS] sets the pathname to the program which is used
2462 to update the NFS client cache entries.
2464 nfs.cache_getent_timeout=
2465 [NFS] sets the timeout after which an attempt to
2466 update a cache entry is deemed to have failed.
2468 nfs.idmap_cache_timeout=
2469 [NFS] set the maximum lifetime for idmapper cache
2473 [NFS] enable 64-bit inode numbers.
2474 If zero, the NFS client will fake up a 32-bit inode
2475 number for the readdir() and stat() syscalls instead
2476 of returning the full 64-bit number.
2477 The default is to return 64-bit inode numbers.
2479 nfs.max_session_cb_slots=
2480 [NFSv4.1] Sets the maximum number of session
2481 slots the client will assign to the callback
2482 channel. This determines the maximum number of
2483 callbacks the client will process in parallel for
2484 a particular server.
2486 nfs.max_session_slots=
2487 [NFSv4.1] Sets the maximum number of session slots
2488 the client will attempt to negotiate with the server.
2489 This limits the number of simultaneous RPC requests
2490 that the client can send to the NFSv4.1 server.
2491 Note that there is little point in setting this
2492 value higher than the max_tcp_slot_table_limit.
2494 nfs.nfs4_disable_idmapping=
2495 [NFSv4] When set to the default of '1', this option
2496 ensures that both the RPC level authentication
2497 scheme and the NFS level operations agree to use
2498 numeric uids/gids if the mount is using the
2499 'sec=sys' security flavour. In effect it is
2500 disabling idmapping, which can make migration from
2501 legacy NFSv2/v3 systems to NFSv4 easier.
2502 Servers that do not support this mode of operation
2503 will be autodetected by the client, and it will fall
2504 back to using the idmapper.
2505 To turn off this behaviour, set the value to '0'.
2507 [NFS4] Specify an additional fixed unique ident-
2508 ification string that NFSv4 clients can insert into
2509 their nfs_client_id4 string. This is typically a
2510 UUID that is generated at system install time.
2512 nfs.send_implementation_id =
2513 [NFSv4.1] Send client implementation identification
2514 information in exchange_id requests.
2515 If zero, no implementation identification information
2517 The default is to send the implementation identification
2520 nfs.recover_lost_locks =
2521 [NFSv4] Attempt to recover locks that were lost due
2522 to a lease timeout on the server. Please note that
2523 doing this risks data corruption, since there are
2524 no guarantees that the file will remain unchanged
2525 after the locks are lost.
2526 If you want to enable the kernel legacy behaviour of
2527 attempting to recover these locks, then set this
2529 The default parameter value of '0' causes the kernel
2530 not to attempt recovery of lost locks.
2532 nfs4.layoutstats_timer =
2533 [NFSv4.2] Change the rate at which the kernel sends
2534 layoutstats to the pNFS metadata server.
2536 Setting this to value to 0 causes the kernel to use
2537 whatever value is the default set by the layout
2538 driver. A non-zero value sets the minimum interval
2539 in seconds between layoutstats transmissions.
2541 nfsd.nfs4_disable_idmapping=
2542 [NFSv4] When set to the default of '1', the NFSv4
2543 server will return only numeric uids and gids to
2544 clients using auth_sys, and will accept numeric uids
2545 and gids from such clients. This is intended to ease
2546 migration from NFSv2/v3.
2548 nmi_debug= [KNL,SH] Specify one or more actions to take
2549 when a NMI is triggered.
2550 Format: [state][,regs][,debounce][,die]
2552 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2553 Format: [panic,][nopanic,][num]
2555 0 - turn hardlockup detector in nmi_watchdog off
2556 1 - turn hardlockup detector in nmi_watchdog on
2557 When panic is specified, panic when an NMI watchdog
2558 timeout occurs (or 'nopanic' to override the opposite
2559 default). To disable both hard and soft lockup detectors,
2560 please see 'nowatchdog'.
2561 This is useful when you use a panic=... timeout and
2562 need the box quickly up again.
2564 netpoll.carrier_timeout=
2565 [NET] Specifies amount of time (in seconds) that
2566 netpoll should wait for a carrier. By default netpoll
2569 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2570 emulation library even if a 387 maths coprocessor
2574 [HW] Never suspend the console
2575 Disable suspending of consoles during suspend and
2576 hibernate operations. Once disabled, debugging
2577 messages can reach various consoles while the rest
2578 of the system is being put to sleep (ie, while
2579 debugging driver suspend/resume hooks). This may
2580 not work reliably with all consoles, but is known
2581 to work with serial and VGA consoles.
2582 To facilitate more flexible debugging, we also add
2583 console_suspend, a printk module parameter to control
2584 it. Users could use console_suspend (usually
2585 /sys/module/printk/parameters/console_suspend) to
2586 turn on/off it dynamically.
2588 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2589 caches in the slab allocator. Saves per-node memory,
2590 but will impact performance.
2594 noaltinstr [S390] Disables alternative instructions patching
2595 (CPU alternatives feature).
2597 noapic [SMP,APIC] Tells the kernel to not make use of any
2598 IOAPICs that may be present in the system.
2600 noautogroup Disable scheduler automatic task group creation.
2602 nobats [PPC] Do not use BATs for mapping kernel lowmem
2603 on "Classic" PPC cores.
2607 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2609 nodelayacct [KNL] Disable per-task delay accounting
2611 nodsp [SH] Disable hardware DSP at boot time.
2613 noefi Disable EFI runtime services support.
2618 On X86-32 available only on PAE configured kernels.
2619 noexec=on: enable non-executable mappings (default)
2620 noexec=off: disable non-executable mappings
2623 Disable SMAP (Supervisor Mode Access Prevention)
2624 even if it is supported by processor.
2627 Disable SMEP (Supervisor Mode Execution Prevention)
2628 even if it is supported by processor.
2631 This affects only 32-bit executables.
2632 noexec32=on: enable non-executable mappings (default)
2633 read doesn't imply executable mappings
2634 noexec32=off: disable non-executable mappings
2635 read implies executable mappings
2637 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2639 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2640 register save and restore. The kernel will only save
2641 legacy floating-point registers on task switch.
2643 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2645 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2646 Equivalent to smt=1.
2648 [KNL,x86] Disable symmetric multithreading (SMT).
2649 nosmt=force: Force disable SMT, cannot be undone
2650 via the sysfs control file.
2652 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2653 (indirect branch prediction) vulnerability. System may
2654 allow data leaks with this option, which is equivalent
2657 nospec_store_bypass_disable
2658 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2660 noxsave [BUGS=X86] Disables x86 extended register state save
2661 and restore using xsave. The kernel will fallback to
2662 enabling legacy floating-point and sse state.
2664 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2665 register states. The kernel will fall back to use
2666 xsave to save the states. By using this parameter,
2667 performance of saving the states is degraded because
2668 xsave doesn't support modified optimization while
2669 xsaveopt supports it on xsaveopt enabled systems.
2671 noxsaves [X86] Disables xsaves and xrstors used in saving and
2672 restoring x86 extended register state in compacted
2673 form of xsave area. The kernel will fall back to use
2674 xsaveopt and xrstor to save and restore the states
2675 in standard form of xsave area. By using this
2676 parameter, xsave area per process might occupy more
2677 memory on xsaves enabled systems.
2679 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2680 wfi(ARM) instruction doesn't work correctly and not to
2681 use it. This is also useful when using JTAG debugger.
2683 no_file_caps Tells the kernel not to honor file capabilities. The
2684 only way then for a file to be executed with privilege
2685 is to be setuid root or executed by root.
2687 nohalt [IA-64] Tells the kernel not to use the power saving
2688 function PAL_HALT_LIGHT when idle. This increases
2689 power-consumption. On the positive side, it reduces
2690 interrupt wake-up latency, which may improve performance
2691 in certain environments such as networked servers or
2694 nohibernate [HIBERNATION] Disable hibernation and resume.
2696 nohz= [KNL] Boottime enable/disable dynamic ticks
2697 Valid arguments: on, off
2700 nohz_full= [KNL,BOOT,SMP,ISOL]
2701 The argument is a cpu list, as described above.
2702 In kernels built with CONFIG_NO_HZ_FULL=y, set
2703 the specified list of CPUs whose tick will be stopped
2704 whenever possible. The boot CPU will be forced outside
2705 the range to maintain the timekeeping. Any CPUs
2706 in this list will have their RCU callbacks offloaded,
2707 just as if they had also been called out in the
2708 rcu_nocbs= boot parameter.
2710 noiotrap [SH] Disables trapped I/O port accesses.
2712 noirqdebug [X86-32] Disables the code which attempts to detect and
2713 disable unhandled interrupt sources.
2715 no_timer_check [X86,APIC] Disables the code which tests for
2716 broken timer IRQ sources.
2718 noisapnp [ISAPNP] Disables ISA PnP code.
2720 noinitrd [RAM] Tells the kernel not to load any configured
2723 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2725 [Deprecated - use intremap=off]
2729 noinvpcid [X86] Disable the INVPCID cpu feature.
2731 nojitter [IA-64] Disables jitter checking for ITC timers.
2733 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2735 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2739 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2740 clock and use the default one.
2742 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2743 steal time is computed, but won't influence scheduler
2746 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2748 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2750 noltlbs [PPC] Do not use large page/tlb entries for kernel
2751 lowmem mapping on PPC40x and PPC8xx
2753 nomca [IA-64] Disable machine check abort handling
2755 nomce [X86-32] Disable Machine Check Exception
2757 nomfgpt [X86-32] Disable Multi-Function General Purpose
2758 Timer usage (for AMD Geode machines).
2760 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2761 shutdown the other cpus. Instead use the REBOOT_VECTOR
2764 nomodule Disable module load
2766 nopat [X86] Disable PAT (page attribute table extension of
2767 pagetables) support.
2769 nopcid [X86-64] Disable the PCID cpu feature.
2771 norandmaps Don't use address space randomization. Equivalent to
2772 echo 0 > /proc/sys/kernel/randomize_va_space
2774 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2775 with UP alternatives
2777 nordrand [X86] Disable kernel use of the RDRAND and
2778 RDSEED instructions even if they are supported
2779 by the processor. RDRAND and RDSEED are still
2780 available to user space applications.
2782 noresume [SWSUSP] Disables resume and restores original swap
2785 no-scroll [VGA] Disables scrollback.
2786 This is required for the Braillex ib80-piezo Braille
2787 reader made by F.H. Papenmeier (Germany).
2791 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2793 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2794 and disable the IO APIC. legacy for "maxcpus=0".
2796 nosoftlockup [KNL] Disable the soft-lockup detector.
2798 nosync [HW,M68K] Disables sync negotiation for all devices.
2800 notsc [BUGS=X86-32] Disable Time Stamp Counter
2802 nowatchdog [KNL] Disable both lockup detectors, i.e.
2803 soft-lockup and NMI watchdog (hard-lockup).
2807 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2809 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2810 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2811 Some features depend on CPU0. Known dependencies are:
2812 1. Resume from suspend/hibernate depends on CPU0.
2813 Suspend/hibernate will fail if CPU0 is offline and you
2814 need to online CPU0 before suspend/hibernate.
2815 2. PIC interrupts also depend on CPU0. CPU0 can't be
2816 removed if a PIC interrupt is detected.
2817 It's said poweroff/reboot may depend on CPU0 on some
2818 machines although I haven't seen such issues so far
2819 after CPU0 is offline on a few tested machines.
2820 If the dependencies are under your control, you can
2821 turn on cpu0_hotplug.
2823 nps_mtm_hs_ctr= [KNL,ARC]
2824 This parameter sets the maximum duration, in
2825 cycles, each HW thread of the CTOP can run
2826 without interruptions, before HW switches it.
2827 The actual maximum duration is 16 times this
2829 Format: integer between 1 and 255
2832 nptcg= [IA-64] Override max number of concurrent global TLB
2833 purges which is reported from either PAL_VM_SUMMARY or
2836 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2837 could support. nr_cpus=n : n >= 1 limits the kernel to
2838 support 'n' processors. It could be larger than the
2839 number of already plugged CPU during bootup, later in
2840 runtime you can physically add extra cpu until it reaches
2841 n. So during boot up some boot time memory for per-cpu
2842 variables need be pre-allocated for later physical cpu
2845 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2847 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2848 Allowed values are enable and disable
2850 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2851 'node', 'default' can be specified
2852 This can be set from sysctl after boot.
2853 See Documentation/sysctl/vm.txt for details.
2855 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2856 See Documentation/debugging-via-ohci1394.txt for more
2859 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2860 Rather than timing out after 20 ms if an EC
2861 command is not properly ACKed, override the length
2862 of the timeout. We have interrupts disabled while
2863 waiting for the ACK, so if this is set too high
2864 interrupts *may* be lost!
2866 omap_mux= [OMAP] Override bootloader pin multiplexing.
2867 Format: <mux_mode0.mode_name=value>...
2868 For example, to override I2C bus2:
2869 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2871 oprofile.timer= [HW]
2872 Use timer interrupt instead of performance counters
2874 oprofile.cpu_type= Force an oprofile cpu type
2875 This might be useful if you have an older oprofile
2876 userland or if you want common events.
2877 Format: { arch_perfmon }
2878 arch_perfmon: [X86] Force use of architectural
2879 perfmon on Intel CPUs instead of the
2880 CPU specific event set.
2881 timer: [X86] Force use of architectural NMI
2882 timer mode (see also oprofile.timer
2883 for generic hr timer mode)
2885 oops=panic Always panic on oopses. Default is to just kill the
2886 process, but there is a small probability of
2887 deadlocking the machine.
2888 This will also cause panics on machine check exceptions.
2889 Useful together with panic=30 to trigger a reboot.
2892 See Documentation/sound/oss/oss-parameters.txt
2894 page_owner= [KNL] Boot-time page_owner enabling option.
2895 Storage of the information about who allocated
2896 each page is disabled in default. With this switch,
2898 on: enable the feature
2900 page_poison= [KNL] Boot-time parameter changing the state of
2901 poisoning on the buddy allocator.
2902 off: turn off poisoning
2903 on: turn on poisoning
2905 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2906 timeout > 0: seconds before rebooting
2907 timeout = 0: wait forever
2908 timeout < 0: reboot immediately
2911 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2914 crash_kexec_post_notifiers
2915 Run kdump after running panic-notifiers and dumping
2916 kmsg. This only for the users who doubt kdump always
2917 succeeds in any situation.
2918 Note that this also increases risks of kdump failure,
2919 because some panic notifiers can make the crashed
2920 kernel more unstable.
2922 parkbd.port= [HW] Parallel port number the keyboard adapter is
2923 connected to, default is 0.
2925 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2926 0 for XT, 1 for AT (default is AT).
2929 parport= [HW,PPT] Specify parallel ports. 0 disables.
2930 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2931 Use 'auto' to force the driver to use any
2932 IRQ/DMA settings detected (the default is to
2933 ignore detected IRQ/DMA settings because of
2934 possible conflicts). You can specify the base
2935 address, IRQ, and DMA settings; IRQ and DMA
2936 should be numbers, or 'auto' (for using detected
2937 settings on that particular port), or 'nofifo'
2938 (to avoid using a FIFO even if it is detected).
2939 Parallel ports are assigned in the order they
2940 are specified on the command line, starting
2943 parport_init_mode= [HW,PPT]
2944 Configure VIA parallel port to operate in
2945 a specific mode. This is necessary on Pegasos
2946 computer where firmware has no options for setting
2947 up parallel port mode and sets it to spp.
2948 Currently this function knows 686a and 8231 chips.
2949 Format: [spp|ps2|epp|ecp|ecpepp]
2952 Halt all CPUs after the first oops has been printed for
2953 the specified number of seconds. This is to be used if
2954 your oopses keep scrolling off the screen.
2959 See header of drivers/block/paride/pcd.c.
2960 See also Documentation/blockdev/paride.txt.
2962 pci=option[,option...] [PCI] various PCI subsystem options:
2963 earlydump [X86] dump PCI config space before the kernel
2965 off [X86] don't probe for the PCI bus
2966 bios [X86-32] force use of PCI BIOS, don't access
2967 the hardware directly. Use this if your machine
2968 has a non-standard PCI host bridge.
2969 nobios [X86-32] disallow use of PCI BIOS, only direct
2970 hardware access methods are allowed. Use this
2971 if you experience crashes upon bootup and you
2972 suspect they are caused by the BIOS.
2973 conf1 [X86] Force use of PCI Configuration Access
2974 Mechanism 1 (config address in IO port 0xCF8,
2975 data in IO port 0xCFC, both 32-bit).
2976 conf2 [X86] Force use of PCI Configuration Access
2977 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2978 the function, IO port 0xCFA, also 8-bit, sets
2979 bus number. The config space is then accessed
2980 through ports 0xC000-0xCFFF).
2981 See http://wiki.osdev.org/PCI for more info
2982 on the configuration access mechanisms.
2983 noaer [PCIE] If the PCIEAER kernel config parameter is
2984 enabled, this kernel boot option can be used to
2985 disable the use of PCIE advanced error reporting.
2986 nodomains [PCI] Disable support for multiple PCI
2987 root domains (aka PCI segments, in ACPI-speak).
2988 nommconf [X86] Disable use of MMCONFIG for PCI
2990 check_enable_amd_mmconf [X86] check for and enable
2991 properly configured MMIO access to PCI
2992 config space on AMD family 10h CPU
2993 nomsi [MSI] If the PCI_MSI kernel config parameter is
2994 enabled, this kernel boot option can be used to
2995 disable the use of MSI interrupts system-wide.
2996 noioapicquirk [APIC] Disable all boot interrupt quirks.
2997 Safety option to keep boot IRQs enabled. This
2998 should never be necessary.
2999 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3000 primary IO-APIC for bridges that cannot disable
3001 boot IRQs. This fixes a source of spurious IRQs
3002 when the system masks IRQs.
3003 noioapicreroute [APIC] Disable workaround that uses the
3004 boot IRQ equivalent of an IRQ that connects to
3005 a chipset where boot IRQs cannot be disabled.
3006 The opposite of ioapicreroute.
3007 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3008 routing table. These calls are known to be buggy
3009 on several machines and they hang the machine
3010 when used, but on other computers it's the only
3011 way to get the interrupt routing table. Try
3012 this option if the kernel is unable to allocate
3013 IRQs or discover secondary PCI buses on your
3015 rom [X86] Assign address space to expansion ROMs.
3016 Use with caution as certain devices share
3017 address decoders between ROMs and other
3019 norom [X86] Do not assign address space to
3020 expansion ROMs that do not already have
3021 BIOS assigned address ranges.
3022 nobar [X86] Do not assign address space to the
3023 BARs that weren't assigned by the BIOS.
3024 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3025 assigned automatically to PCI devices. You can
3026 make the kernel exclude IRQs of your ISA cards
3028 pirqaddr=0xAAAAA [X86] Specify the physical address
3029 of the PIRQ table (normally generated
3030 by the BIOS) if it is outside the
3031 F0000h-100000h range.
3032 lastbus=N [X86] Scan all buses thru bus #N. Can be
3033 useful if the kernel is unable to find your
3034 secondary buses and you want to tell it
3035 explicitly which ones they are.
3036 assign-busses [X86] Always assign all PCI bus
3037 numbers ourselves, overriding
3038 whatever the firmware may have done.
3039 usepirqmask [X86] Honor the possible IRQ mask stored
3040 in the BIOS $PIR table. This is needed on
3041 some systems with broken BIOSes, notably
3042 some HP Pavilion N5400 and Omnibook XE3
3043 notebooks. This will have no effect if ACPI
3044 IRQ routing is enabled.
3045 noacpi [X86] Do not use ACPI for IRQ routing
3046 or for PCI scanning.
3047 use_crs [X86] Use PCI host bridge window information
3048 from ACPI. On BIOSes from 2008 or later, this
3049 is enabled by default. If you need to use this,
3050 please report a bug.
3051 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3052 If you need to use this, please report a bug.
3053 routeirq Do IRQ routing for all PCI devices.
3054 This is normally done in pci_enable_device(),
3055 so this option is a temporary workaround
3056 for broken drivers that don't call it.
3057 skip_isa_align [X86] do not align io start addr, so can
3058 handle more pci cards
3059 noearly [X86] Don't do any early type 1 scanning.
3060 This might help on some broken boards which
3061 machine check when some devices' config space
3062 is read. But various workarounds are disabled
3063 and some IOMMU drivers will not work.
3064 bfsort Sort PCI devices into breadth-first order.
3065 This sorting is done to get a device
3066 order compatible with older (<= 2.4) kernels.
3067 nobfsort Don't sort PCI devices into breadth-first order.
3068 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3069 tuning and use the BIOS-configured MPS defaults.
3070 pcie_bus_safe Set every device's MPS to the largest value
3071 supported by all devices below the root complex.
3072 pcie_bus_perf Set device MPS to the largest allowable MPS
3073 based on its parent bus. Also set MRRS (Max
3074 Read Request Size) to the largest supported
3075 value (no larger than the MPS that the device
3076 or bus can support) for best performance.
3077 pcie_bus_peer2peer Set every device's MPS to 128B, which
3078 every device is guaranteed to support. This
3079 configuration allows peer-to-peer DMA between
3080 any pair of devices, possibly at the cost of
3081 reduced performance. This also guarantees
3082 that hot-added devices will work.
3083 cbiosize=nn[KMG] The fixed amount of bus space which is
3084 reserved for the CardBus bridge's IO window.
3085 The default value is 256 bytes.
3086 cbmemsize=nn[KMG] The fixed amount of bus space which is
3087 reserved for the CardBus bridge's memory
3088 window. The default value is 64 megabytes.
3091 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3092 [<order of align>@]pci:<vendor>:<device>\
3093 [:<subvendor>:<subdevice>][; ...]
3094 Specifies alignment and device to reassign
3095 aligned memory resources.
3096 If <order of align> is not specified,
3097 PAGE_SIZE is used as alignment.
3098 PCI-PCI bridge can be specified, if resource
3099 windows need to be expanded.
3100 To specify the alignment for several
3101 instances of a device, the PCI vendor,
3102 device, subvendor, and subdevice may be
3103 specified, e.g., 4096@pci:8086:9c22:103c:198f
3104 ecrc= Enable/disable PCIe ECRC (transaction layer
3105 end-to-end CRC checking).
3106 bios: Use BIOS/firmware settings. This is the
3110 hpiosize=nn[KMG] The fixed amount of bus space which is
3111 reserved for hotplug bridge's IO window.
3112 Default size is 256 bytes.
3113 hpmemsize=nn[KMG] The fixed amount of bus space which is
3114 reserved for hotplug bridge's memory window.
3115 Default size is 2 megabytes.
3116 hpbussize=nn The minimum amount of additional bus numbers
3117 reserved for buses below a hotplug bridge.
3119 realloc= Enable/disable reallocating PCI bridge resources
3120 if allocations done by BIOS are too small to
3121 accommodate resources required by all child
3123 off: Turn realloc off
3125 realloc same as realloc=on
3126 noari do not use PCIe ARI.
3127 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3128 only look for one device below a PCIe downstream
3130 big_root_window Try to add a big 64bit memory window to the PCIe
3131 root complex on AMD CPUs. Some GFX hardware
3132 can resize a BAR to allow access to all VRAM.
3133 Adding the window is slightly risky (it may
3134 conflict with unreported devices), so this
3137 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3140 force Enable ASPM even on devices that claim not to support it.
3141 WARNING: Forcing ASPM on may cause system lockups.
3143 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3144 nomsi Do not use MSI for PCI Express Native Hotplug (this
3145 makes all PCIe ports use INTx for hotplug services).
3147 pcie_ports= [PCIE] PCIe ports handling:
3148 auto Ask the BIOS whether or not to use native PCIe services
3149 associated with PCIe ports (PME, hot-plug, AER). Use
3150 them only if that is allowed by the BIOS.
3151 native Use native PCIe services associated with PCIe ports
3153 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3156 pcie_port_pm= [PCIE] PCIe port power management handling:
3157 off Disable power management of all PCIe ports
3158 force Forcibly enable power management of all PCIe ports
3160 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3161 nomsi Do not use MSI for native PCIe PME signaling (this makes
3162 all PCIe root ports use INTx for all services).
3164 pcmv= [HW,PCMCIA] BadgePAD 4
3168 Keep all power-domains already enabled by bootloader on,
3169 even if no driver has claimed them. This is useful
3170 for debug and development, but should not be
3171 needed on a platform with proper driver support.
3174 See Documentation/blockdev/paride.txt.
3176 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3179 See arch/parisc/kernel/pdc_chassis.c
3181 percpu_alloc= Select which percpu first chunk allocator to use.
3182 Currently supported values are "embed" and "page".
3183 Archs may support subset or none of the selections.
3184 See comments in mm/percpu.c for details on each
3185 allocator. This parameter is primarily for debugging
3186 and performance comparison.
3189 See Documentation/blockdev/paride.txt.
3192 See Documentation/blockdev/paride.txt.
3194 pirq= [SMP,APIC] Manual mp-table setup
3195 See Documentation/x86/i386/IO-APIC.txt.
3197 plip= [PPT,NET] Parallel port network link
3198 Format: { parport<nr> | timid | 0 }
3199 See also Documentation/admin-guide/parport.rst.
3201 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3202 Override pmtimer IOPort with a hex value.
3206 Enable PNP debug messages (depends on the
3207 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3208 via /sys/module/pnp/parameters/debug. We always show
3209 current resource usage; turning this on also shows
3210 possible settings and some assignment information.
3216 { on | off | curr | res | no-curr | no-res }
3219 [ISAPNP] Exclude IRQs for the autoconfiguration
3222 [ISAPNP] Exclude DMAs for the autoconfiguration
3224 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3225 Ranges are in pairs (I/O port base and size).
3228 [ISAPNP] Exclude memory regions for the
3230 Ranges are in pairs (memory base and size).
3232 ports= [IP_VS_FTP] IPVS ftp helper module
3234 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3236 Format: <port>,<port>....
3238 powersave=off [PPC] This option disables power saving features.
3239 It specifically disables cpuidle and sets the
3240 platform machine description specific power_save
3241 function to NULL. On Idle the CPU just reduces
3244 ppc_strict_facility_enable
3245 [PPC] This option catches any kernel floating point,
3246 Altivec, VSX and SPE outside of regions specifically
3247 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3248 There is some performance impact when enabling this.
3252 Disable Hardware Transactional Memory
3254 print-fatal-signals=
3255 [KNL] debug: print fatal signals
3257 If enabled, warn about various signal handling
3258 related application anomalies: too many signals,
3259 too many POSIX.1 timers, fatal signals causing a
3262 If you hit the warning due to signal overflow,
3263 you might want to try "ulimit -i unlimited".
3267 printk.always_kmsg_dump=
3268 Trigger kmsg_dump for cases other than kernel oops or
3270 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3273 printk.devkmsg={on,off,ratelimit}
3274 Control writing to /dev/kmsg.
3275 on - unlimited logging to /dev/kmsg from userspace
3276 off - logging to /dev/kmsg disabled
3277 ratelimit - ratelimit the logging
3280 printk.time= Show timing data prefixed to each printk message line
3281 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3283 processor.max_cstate= [HW,ACPI]
3284 Limit processor to maximum C-state
3285 max_cstate=9 overrides any DMI blacklist limit.
3287 processor.nocst [HW,ACPI]
3288 Ignore the _CST method to determine C-states,
3289 instead using the legacy FADT method
3291 profile= [KNL] Enable kernel profiling via /proc/profile
3292 Format: [<profiletype>,]<number>
3293 Param: <profiletype>: "schedule", "sleep", or "kvm"
3294 [defaults to kernel profiling]
3295 Param: "schedule" - profile schedule points.
3296 Param: "sleep" - profile D-state sleeping (millisecs).
3297 Requires CONFIG_SCHEDSTATS
3298 Param: "kvm" - profile VM exits.
3299 Param: <number> - step/bucket size as a power of 2 for
3300 statistical time based profiling.
3302 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3304 See Documentation/blockdev/ramdisk.txt.
3306 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3307 probe for; one of (bare|imps|exps|lifebook|any).
3308 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3310 psmouse.resetafter= [HW,MOUSE]
3311 Try to reset the device after so many bad packets
3314 [HW,MOUSE] Set desired mouse resolution, in dpi.
3315 psmouse.smartscroll=
3316 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3317 0 = disabled, 1 = enabled (default).
3319 pstore.backend= Specify the name of the pstore backend to use
3322 See Documentation/blockdev/paride.txt.
3324 pti= [X86_64] Control Page Table Isolation of user and
3325 kernel address spaces. Disabling this feature
3326 removes hardening, but improves performance of
3327 system calls and interrupts.
3329 on - unconditionally enable
3330 off - unconditionally disable
3331 auto - kernel detects whether your CPU model is
3332 vulnerable to issues that PTI mitigates
3334 Not specifying this option is equivalent to pti=auto.
3337 Equivalent to pti=off
3340 [KNL] Number of legacy pty's. Overwrites compiled-in
3343 quiet [KNL] Disable most log messages
3348 See Documentation/admin-guide/md.rst.
3350 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3351 See Documentation/blockdev/ramdisk.txt.
3353 ras=option[,option,...] [KNL] RAS-specific options
3356 Disable the Correctable Errors Collector,
3357 see CONFIG_RAS_CEC help text.
3360 The argument is a cpu list, as described above.
3362 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3363 the specified list of CPUs to be no-callback CPUs.
3364 Invocation of these CPUs' RCU callbacks will
3365 be offloaded to "rcuox/N" kthreads created for
3366 that purpose, where "x" is "b" for RCU-bh, "p"
3367 for RCU-preempt, and "s" for RCU-sched, and "N"
3368 is the CPU number. This reduces OS jitter on the
3369 offloaded CPUs, which can be useful for HPC and
3370 real-time workloads. It can also improve energy
3371 efficiency for asymmetric multiprocessors.
3374 Rather than requiring that offloaded CPUs
3375 (specified by rcu_nocbs= above) explicitly
3376 awaken the corresponding "rcuoN" kthreads,
3377 make these kthreads poll for callbacks.
3378 This improves the real-time response for the
3379 offloaded CPUs by relieving them of the need to
3380 wake up the corresponding kthread, but degrades
3381 energy efficiency by requiring that the kthreads
3382 periodically wake up to do the polling.
3384 rcutree.blimit= [KNL]
3385 Set maximum number of finished RCU callbacks to
3386 process in one batch.
3388 rcutree.dump_tree= [KNL]
3389 Dump the structure of the rcu_node combining tree
3390 out at early boot. This is used for diagnostic
3391 purposes, to verify correct tree setup.
3393 rcutree.gp_cleanup_delay= [KNL]
3394 Set the number of jiffies to delay each step of
3395 RCU grace-period cleanup.
3397 rcutree.gp_init_delay= [KNL]
3398 Set the number of jiffies to delay each step of
3399 RCU grace-period initialization.
3401 rcutree.gp_preinit_delay= [KNL]
3402 Set the number of jiffies to delay each step of
3403 RCU grace-period pre-initialization, that is,
3404 the propagation of recent CPU-hotplug changes up
3405 the rcu_node combining tree.
3407 rcutree.rcu_fanout_exact= [KNL]
3408 Disable autobalancing of the rcu_node combining
3409 tree. This is used by rcutorture, and might
3410 possibly be useful for architectures having high
3411 cache-to-cache transfer latencies.
3413 rcutree.rcu_fanout_leaf= [KNL]
3414 Change the number of CPUs assigned to each
3415 leaf rcu_node structure. Useful for very
3416 large systems, which will choose the value 64,
3417 and for NUMA systems with large remote-access
3418 latencies, which will choose a value aligned
3419 with the appropriate hardware boundaries.
3421 rcutree.jiffies_till_sched_qs= [KNL]
3422 Set required age in jiffies for a
3423 given grace period before RCU starts
3424 soliciting quiescent-state help from
3425 rcu_note_context_switch().
3427 rcutree.jiffies_till_first_fqs= [KNL]
3428 Set delay from grace-period initialization to
3429 first attempt to force quiescent states.
3430 Units are jiffies, minimum value is zero,
3431 and maximum value is HZ.
3433 rcutree.jiffies_till_next_fqs= [KNL]
3434 Set delay between subsequent attempts to force
3435 quiescent states. Units are jiffies, minimum
3436 value is one, and maximum value is HZ.
3438 rcutree.kthread_prio= [KNL,BOOT]
3439 Set the SCHED_FIFO priority of the RCU per-CPU
3440 kthreads (rcuc/N). This value is also used for
3441 the priority of the RCU boost threads (rcub/N)
3442 and for the RCU grace-period kthreads (rcu_bh,
3443 rcu_preempt, and rcu_sched). If RCU_BOOST is
3444 set, valid values are 1-99 and the default is 1
3445 (the least-favored priority). Otherwise, when
3446 RCU_BOOST is not set, valid values are 0-99 and
3447 the default is zero (non-realtime operation).
3449 rcutree.rcu_nocb_leader_stride= [KNL]
3450 Set the number of NOCB kthread groups, which
3451 defaults to the square root of the number of
3452 CPUs. Larger numbers reduces the wakeup overhead
3453 on the per-CPU grace-period kthreads, but increases
3454 that same overhead on each group's leader.
3456 rcutree.qhimark= [KNL]
3457 Set threshold of queued RCU callbacks beyond which
3458 batch limiting is disabled.
3460 rcutree.qlowmark= [KNL]
3461 Set threshold of queued RCU callbacks below which
3462 batch limiting is re-enabled.
3464 rcutree.rcu_idle_gp_delay= [KNL]
3465 Set wakeup interval for idle CPUs that have
3466 RCU callbacks (RCU_FAST_NO_HZ=y).
3468 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3469 Set wakeup interval for idle CPUs that have
3470 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3471 Lazy RCU callbacks are those which RCU can
3472 prove do nothing more than free memory.
3474 rcutree.rcu_kick_kthreads= [KNL]
3475 Cause the grace-period kthread to get an extra
3476 wake_up() if it sleeps three times longer than
3477 it should at force-quiescent-state time.
3478 This wake_up() will be accompanied by a
3479 WARN_ONCE() splat and an ftrace_dump().
3481 rcuperf.gp_async= [KNL]
3482 Measure performance of asynchronous
3483 grace-period primitives such as call_rcu().
3485 rcuperf.gp_async_max= [KNL]
3486 Specify the maximum number of outstanding
3487 callbacks per writer thread. When a writer
3488 thread exceeds this limit, it invokes the
3489 corresponding flavor of rcu_barrier() to allow
3490 previously posted callbacks to drain.
3492 rcuperf.gp_exp= [KNL]
3493 Measure performance of expedited synchronous
3494 grace-period primitives.
3496 rcuperf.holdoff= [KNL]
3497 Set test-start holdoff period. The purpose of
3498 this parameter is to delay the start of the
3499 test until boot completes in order to avoid
3502 rcuperf.nreaders= [KNL]
3503 Set number of RCU readers. The value -1 selects
3504 N, where N is the number of CPUs. A value
3505 "n" less than -1 selects N-n+1, where N is again
3506 the number of CPUs. For example, -2 selects N
3507 (the number of CPUs), -3 selects N+1, and so on.
3508 A value of "n" less than or equal to -N selects
3511 rcuperf.nwriters= [KNL]
3512 Set number of RCU writers. The values operate
3513 the same as for rcuperf.nreaders.
3514 N, where N is the number of CPUs
3516 rcuperf.perf_runnable= [BOOT]
3517 Start rcuperf running at boot time.
3519 rcuperf.perf_type= [KNL]
3520 Specify the RCU implementation to test.
3522 rcuperf.shutdown= [KNL]
3523 Shut the system down after performance tests
3524 complete. This is useful for hands-off automated
3527 rcuperf.verbose= [KNL]
3528 Enable additional printk() statements.
3530 rcuperf.writer_holdoff= [KNL]
3531 Write-side holdoff between grace periods,
3532 in microseconds. The default of zero says
3535 rcutorture.cbflood_inter_holdoff= [KNL]
3536 Set holdoff time (jiffies) between successive
3537 callback-flood tests.
3539 rcutorture.cbflood_intra_holdoff= [KNL]
3540 Set holdoff time (jiffies) between successive
3541 bursts of callbacks within a given callback-flood
3544 rcutorture.cbflood_n_burst= [KNL]
3545 Set the number of bursts making up a given
3546 callback-flood test. Set this to zero to
3547 disable callback-flood testing.
3549 rcutorture.cbflood_n_per_burst= [KNL]
3550 Set the number of callbacks to be registered
3551 in a given burst of a callback-flood test.
3553 rcutorture.fqs_duration= [KNL]
3554 Set duration of force_quiescent_state bursts
3557 rcutorture.fqs_holdoff= [KNL]
3558 Set holdoff time within force_quiescent_state bursts
3561 rcutorture.fqs_stutter= [KNL]
3562 Set wait time between force_quiescent_state bursts
3565 rcutorture.gp_cond= [KNL]
3566 Use conditional/asynchronous update-side
3567 primitives, if available.
3569 rcutorture.gp_exp= [KNL]
3570 Use expedited update-side primitives, if available.
3572 rcutorture.gp_normal= [KNL]
3573 Use normal (non-expedited) asynchronous
3574 update-side primitives, if available.
3576 rcutorture.gp_sync= [KNL]
3577 Use normal (non-expedited) synchronous
3578 update-side primitives, if available. If all
3579 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3580 rcutorture.gp_normal=, and rcutorture.gp_sync=
3581 are zero, rcutorture acts as if is interpreted
3582 they are all non-zero.
3584 rcutorture.n_barrier_cbs= [KNL]
3585 Set callbacks/threads for rcu_barrier() testing.
3587 rcutorture.nfakewriters= [KNL]
3588 Set number of concurrent RCU writers. These just
3589 stress RCU, they don't participate in the actual
3590 test, hence the "fake".
3592 rcutorture.nreaders= [KNL]
3593 Set number of RCU readers. The value -1 selects
3594 N-1, where N is the number of CPUs. A value
3595 "n" less than -1 selects N-n-2, where N is again
3596 the number of CPUs. For example, -2 selects N
3597 (the number of CPUs), -3 selects N+1, and so on.
3599 rcutorture.object_debug= [KNL]
3600 Enable debug-object double-call_rcu() testing.
3602 rcutorture.onoff_holdoff= [KNL]
3603 Set time (s) after boot for CPU-hotplug testing.
3605 rcutorture.onoff_interval= [KNL]
3606 Set time (s) between CPU-hotplug operations, or
3607 zero to disable CPU-hotplug testing.
3609 rcutorture.shuffle_interval= [KNL]
3610 Set task-shuffle interval (s). Shuffling tasks
3611 allows some CPUs to go into dyntick-idle mode
3612 during the rcutorture test.
3614 rcutorture.shutdown_secs= [KNL]
3615 Set time (s) after boot system shutdown. This
3616 is useful for hands-off automated testing.
3618 rcutorture.stall_cpu= [KNL]
3619 Duration of CPU stall (s) to test RCU CPU stall
3620 warnings, zero to disable.
3622 rcutorture.stall_cpu_holdoff= [KNL]
3623 Time to wait (s) after boot before inducing stall.
3625 rcutorture.stall_cpu_irqsoff= [KNL]
3626 Disable interrupts while stalling if set.
3628 rcutorture.stat_interval= [KNL]
3629 Time (s) between statistics printk()s.
3631 rcutorture.stutter= [KNL]
3632 Time (s) to stutter testing, for example, specifying
3633 five seconds causes the test to run for five seconds,
3634 wait for five seconds, and so on. This tests RCU's
3635 ability to transition abruptly to and from idle.
3637 rcutorture.test_boost= [KNL]
3638 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3639 "Maybe" means test if the RCU implementation
3640 under test support RCU priority boosting.
3642 rcutorture.test_boost_duration= [KNL]
3643 Duration (s) of each individual boost test.
3645 rcutorture.test_boost_interval= [KNL]
3646 Interval (s) between each boost test.
3648 rcutorture.test_no_idle_hz= [KNL]
3649 Test RCU's dyntick-idle handling. See also the
3650 rcutorture.shuffle_interval parameter.
3652 rcutorture.torture_runnable= [BOOT]
3653 Start rcutorture running at boot time.
3655 rcutorture.torture_type= [KNL]
3656 Specify the RCU implementation to test.
3658 rcutorture.verbose= [KNL]
3659 Enable additional printk() statements.
3661 rcupdate.rcu_cpu_stall_suppress= [KNL]
3662 Suppress RCU CPU stall warning messages.
3664 rcupdate.rcu_cpu_stall_timeout= [KNL]
3665 Set timeout for RCU CPU stall warning messages.
3667 rcupdate.rcu_expedited= [KNL]
3668 Use expedited grace-period primitives, for
3669 example, synchronize_rcu_expedited() instead
3670 of synchronize_rcu(). This reduces latency,
3671 but can increase CPU utilization, degrade
3672 real-time latency, and degrade energy efficiency.
3673 No effect on CONFIG_TINY_RCU kernels.
3675 rcupdate.rcu_normal= [KNL]
3676 Use only normal grace-period primitives,
3677 for example, synchronize_rcu() instead of
3678 synchronize_rcu_expedited(). This improves
3679 real-time latency, CPU utilization, and
3680 energy efficiency, but can expose users to
3681 increased grace-period latency. This parameter
3682 overrides rcupdate.rcu_expedited. No effect on
3683 CONFIG_TINY_RCU kernels.
3685 rcupdate.rcu_normal_after_boot= [KNL]
3686 Once boot has completed (that is, after
3687 rcu_end_inkernel_boot() has been invoked), use
3688 only normal grace-period primitives. No effect
3689 on CONFIG_TINY_RCU kernels.
3691 rcupdate.rcu_task_stall_timeout= [KNL]
3692 Set timeout in jiffies for RCU task stall warning
3693 messages. Disable with a value less than or equal
3696 rcupdate.rcu_self_test= [KNL]
3697 Run the RCU early boot self tests
3699 rcupdate.rcu_self_test_bh= [KNL]
3700 Run the RCU bh early boot self tests
3702 rcupdate.rcu_self_test_sched= [KNL]
3703 Run the RCU sched early boot self tests
3707 Run specified binary instead of /init from the ramdisk,
3708 used for early userspace startup. See initrd.
3711 Turn on/off individual RDT features. List is:
3712 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3714 E.g. to turn on cmt and turn off mba use:
3718 Format (x86 or x86_64):
3719 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3721 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3723 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3724 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3725 reboot_force is either force or not specified,
3726 reboot_cpu is s[mp]#### with #### being the processor
3727 to be used for rebooting.
3730 [KNL, SMP] Set scheduler's default relax_domain_level.
3731 See Documentation/cgroup-v1/cpusets.txt.
3733 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3735 reservetop= [X86-32]
3737 Reserves a hole at the top of the kernel virtual
3742 Set the amount of memory to reserve for BIOS at
3743 the bottom of the address space.
3745 reset_devices [KNL] Force drivers to reset the underlying device
3746 during initialization.
3749 Specify the partition device for software suspend
3751 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3753 resume_offset= [SWSUSP]
3754 Specify the offset from the beginning of the partition
3755 given by "resume=" at which the swap header is located,
3756 in <PAGE_SIZE> units (needed only for swap files).
3757 See Documentation/power/swsusp-and-swap-files.txt
3759 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3760 read the resume files
3762 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3763 Useful for devices that are detected asynchronously
3764 (e.g. USB and MMC devices).
3766 hibernate= [HIBERNATION]
3767 noresume Don't check if there's a hibernation image
3768 present during boot.
3769 nocompress Don't compress/decompress hibernation images.
3770 no Disable hibernation and resume.
3771 protect_image Turn on image protection during restoration
3772 (that will set all pages holding image data
3773 during restoration read-only).
3775 retain_initrd [RAM] Keep initrd memory after extraction
3777 rfkill.default_state=
3778 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3779 etc. communication is blocked by default.
3782 rfkill.master_switch_mode=
3783 0 The "airplane mode" button does nothing.
3784 1 The "airplane mode" button toggles between everything
3785 blocked and the previous configuration.
3786 2 The "airplane mode" button toggles between everything
3787 blocked and everything unblocked.
3789 rhash_entries= [KNL,NET]
3790 Set number of hash buckets for route cache
3793 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3796 ro [KNL] Mount root device read-only on boot
3799 on Mark read-only kernel memory as read-only (default).
3800 off Leave read-only kernel memory writable for debugging.
3803 Enable the uart passthrough on the designated usb port
3804 on Rockchip SoCs. When active, the signals of the
3805 debug-uart get routed to the D+ and D- pins of the usb
3806 port and the regular usb controller gets disabled.
3808 root= [KNL] Root filesystem
3809 See name_to_dev_t comment in init/do_mounts.c.
3811 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3812 mount the root filesystem
3814 rootflags= [KNL] Set root filesystem mount option string
3816 rootfstype= [KNL] Set root filesystem type
3818 rootwait [KNL] Wait (indefinitely) for root device to show up.
3819 Useful for devices that are detected asynchronously
3820 (e.g. USB and MMC devices).
3822 rproc_mem=nn[KMG][@address]
3823 [KNL,ARM,CMA] Remoteproc physical memory block.
3824 Memory area to be used by remote processor image,
3827 rw [KNL] Mount root device read-write on boot
3829 S [KNL] Run init in single mode
3831 s390_iommu= [HW,S390]
3832 Set s390 IOTLB flushing mode
3834 With strict flushing every unmap operation will result in
3835 an IOTLB flush. Default is lazy flushing before reuse,
3839 See drivers/net/irda/sa1100_ir.c.
3841 sbni= [NET] Granch SBNI12 leased line adapter
3843 sched_debug [KNL] Enables verbose scheduler debug messages.
3845 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3846 Allowed values are enable and disable. This feature
3847 incurs a small amount of overhead in the scheduler
3848 but is useful for debugging and performance tuning.
3850 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3851 xtime_lock contention on larger systems, and/or RCU lock
3852 contention on all systems with CONFIG_MAXSMP set.
3853 Format: { "0" | "1" }
3854 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3856 Note: increases power consumption, thus should only be
3857 enabled if running jitter sensitive (HPC/RT) workloads.
3859 security= [SECURITY] Choose a security module to enable at boot.
3860 If this boot parameter is not specified, only the first
3861 security module asking for security registration will be
3862 loaded. An invalid security module name will be treated
3863 as if no module has been chosen.
3865 selinux= [SELINUX] Disable or enable SELinux at boot time.
3866 Format: { "0" | "1" }
3867 See security/selinux/Kconfig help text.
3870 Default value is set via kernel config option.
3871 If enabled at boot time, /selinux/disable can be used
3872 later to disable prior to initial policy load.
3874 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3875 Format: { "0" | "1" }
3876 See security/apparmor/Kconfig help text
3879 Default value is set via kernel config option.
3881 serialnumber [BUGS=X86-32]
3884 Maximal number of shapers.
3892 Disable merging of slabs with similar size. May be
3893 necessary if there is some reason to distinguish
3894 allocs to different slabs, especially in hardened
3895 environments where the risk of heap overflows and
3896 layout control by attackers can usually be
3897 frustrated by disabling merging. This will reduce
3898 most of the exposure of a heap attack to a single
3899 cache (risks via metadata attacks are mostly
3900 unchanged). Debug options disable merging on their
3902 For more information see Documentation/vm/slub.txt.
3904 slab_max_order= [MM, SLAB]
3905 Determines the maximum allowed order for slabs.
3906 A high setting may cause OOMs due to memory
3907 fragmentation. Defaults to 1 for systems with
3908 more than 32MB of RAM, 0 otherwise.
3910 slub_debug[=options[,slabs]] [MM, SLUB]
3911 Enabling slub_debug allows one to determine the
3912 culprit if slab objects become corrupted. Enabling
3913 slub_debug can create guard zones around objects and
3914 may poison objects when not in use. Also tracks the
3915 last alloc / free. For more information see
3916 Documentation/vm/slub.txt.
3918 slub_memcg_sysfs= [MM, SLUB]
3919 Determines whether to enable sysfs directories for
3920 memory cgroup sub-caches. 1 to enable, 0 to disable.
3921 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3922 Enabling this can lead to a very high number of debug
3923 directories and files being created under
3926 slub_max_order= [MM, SLUB]
3927 Determines the maximum allowed order for slabs.
3928 A high setting may cause OOMs due to memory
3929 fragmentation. For more information see
3930 Documentation/vm/slub.txt.
3932 slub_min_objects= [MM, SLUB]
3933 The minimum number of objects per slab. SLUB will
3934 increase the slab order up to slub_max_order to
3935 generate a sufficiently large slab able to contain
3936 the number of objects indicated. The higher the number
3937 of objects the smaller the overhead of tracking slabs
3938 and the less frequently locks need to be acquired.
3939 For more information see Documentation/vm/slub.txt.
3941 slub_min_order= [MM, SLUB]
3942 Determines the minimum page order for slabs. Must be
3943 lower than slub_max_order.
3944 For more information see Documentation/vm/slub.txt.
3946 slub_nomerge [MM, SLUB]
3947 Same with slab_nomerge. This is supported for legacy.
3948 See slab_nomerge for more information.
3951 Format: <io1>[,<io2>[,...,<io8>]]
3953 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3954 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3955 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3956 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3957 smsc-ircc2.ircc_irq= [HW] IRQ line
3958 smsc-ircc2.ircc_dma= [HW] DMA channel
3959 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3960 0: Toshiba Satellite 1800 (GP data pin select)
3961 1: Fast pin select (default)
3964 smt [KNL,S390] Set the maximum number of threads (logical
3965 CPUs) to use per physical CPU on systems capable of
3966 symmetric multithreading (SMT). Will be capped to the
3967 actual hardware limit.
3969 Default: -1 (no limit)
3972 [KNL] Should the soft-lockup detector generate panics.
3975 A nonzero value instructs the soft-lockup detector
3976 to panic the machine when a soft-lockup occurs. This
3977 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
3978 which is the respective build-time switch to that
3981 softlockup_all_cpu_backtrace=
3982 [KNL] Should the soft-lockup detector generate
3983 backtraces on all cpus.
3986 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3987 See Documentation/laptops/sonypi.txt
3989 spectre_v2= [X86] Control mitigation of Spectre variant 2
3990 (indirect branch speculation) vulnerability.
3992 on - unconditionally enable
3993 off - unconditionally disable
3994 auto - kernel detects whether your CPU model is
3997 Selecting 'on' will, and 'auto' may, choose a
3998 mitigation method at run time according to the
3999 CPU, the available microcode, the setting of the
4000 CONFIG_RETPOLINE configuration option, and the
4001 compiler with which the kernel was built.
4003 Specific mitigations can also be selected manually:
4005 retpoline - replace indirect branches
4006 retpoline,generic - google's original retpoline
4007 retpoline,amd - AMD-specific minimal thunk
4009 Not specifying this option is equivalent to
4012 spec_store_bypass_disable=
4013 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4014 (Speculative Store Bypass vulnerability)
4016 Certain CPUs are vulnerable to an exploit against a
4017 a common industry wide performance optimization known
4018 as "Speculative Store Bypass" in which recent stores
4019 to the same memory location may not be observed by
4020 later loads during speculative execution. The idea
4021 is that such stores are unlikely and that they can
4022 be detected prior to instruction retirement at the
4023 end of a particular speculation execution window.
4025 In vulnerable processors, the speculatively forwarded
4026 store can be used in a cache side channel attack, for
4027 example to read memory to which the attacker does not
4028 directly have access (e.g. inside sandboxed code).
4030 This parameter controls whether the Speculative Store
4031 Bypass optimization is used.
4033 on - Unconditionally disable Speculative Store Bypass
4034 off - Unconditionally enable Speculative Store Bypass
4035 auto - Kernel detects whether the CPU model contains an
4036 implementation of Speculative Store Bypass and
4037 picks the most appropriate mitigation. If the
4038 CPU is not vulnerable, "off" is selected. If the
4039 CPU is vulnerable the default mitigation is
4040 architecture and Kconfig dependent. See below.
4041 prctl - Control Speculative Store Bypass per thread
4042 via prctl. Speculative Store Bypass is enabled
4043 for a process by default. The state of the control
4044 is inherited on fork.
4045 seccomp - Same as "prctl" above, but all seccomp threads
4046 will disable SSB unless they explicitly opt out.
4048 Not specifying this option is equivalent to
4049 spec_store_bypass_disable=auto.
4051 Default mitigations:
4052 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4054 spia_io_base= [HW,MTD]
4059 srcutree.counter_wrap_check [KNL]
4060 Specifies how frequently to check for
4061 grace-period sequence counter wrap for the
4062 srcu_data structure's ->srcu_gp_seq_needed field.
4063 The greater the number of bits set in this kernel
4064 parameter, the less frequently counter wrap will
4065 be checked for. Note that the bottom two bits
4068 srcutree.exp_holdoff [KNL]
4069 Specifies how many nanoseconds must elapse
4070 since the end of the last SRCU grace period for
4071 a given srcu_struct until the next normal SRCU
4072 grace period will be considered for automatic
4073 expediting. Set to zero to disable automatic
4076 stack_guard_gap= [MM]
4077 override the default stack gap protection. The value
4078 is in page units and it defines how many pages prior
4079 to (for stacks growing down) resp. after (for stacks
4080 growing up) the main stack are reserved for no other
4081 mapping. Default value is 256 pages.
4084 Enabled the stack tracer on boot up.
4086 stacktrace_filter=[function-list]
4087 [FTRACE] Limit the functions that the stack tracer
4088 will trace at boot up. function-list is a comma separated
4089 list of functions. This list can be changed at run
4090 time by the stack_trace_filter file in the debugfs
4091 tracing directory. Note, this enables stack tracing
4092 and the stacktrace above is not needed.
4096 Set the STI (builtin display/keyboard on the HP-PARISC
4097 machines) console (graphic card) which should be used
4098 as the initial boot-console.
4099 See also comment in drivers/video/console/sticore.c.
4102 See comment in drivers/video/console/sticore.c.
4105 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4107 sunrpc.min_resvport=
4108 sunrpc.max_resvport=
4110 SunRPC servers often require that client requests
4111 originate from a privileged port (i.e. a port in the
4112 range 0 < portnr < 1024).
4113 An administrator who wishes to reserve some of these
4114 ports for other uses may adjust the range that the
4115 kernel's sunrpc client considers to be privileged
4116 using these two parameters to set the minimum and
4117 maximum port values.
4119 sunrpc.svc_rpc_per_connection_limit=
4121 Limit the number of requests that the server will
4122 process in parallel from a single connection.
4123 The default value is 0 (no limit).
4127 Control how the NFS server code allocates CPUs to
4128 service thread pools. Depending on how many NICs
4129 you have and where their interrupts are bound, this
4130 option will affect which CPUs will do NFS serving.
4131 Note: this parameter cannot be changed while the
4132 NFS server is running.
4134 auto the server chooses an appropriate mode
4135 automatically using heuristics
4136 global a single global pool contains all CPUs
4137 percpu one pool for each CPU
4138 pernode one pool for each NUMA node (equivalent
4139 to global on non-NUMA machines)
4141 sunrpc.tcp_slot_table_entries=
4142 sunrpc.udp_slot_table_entries=
4144 Sets the upper limit on the number of simultaneous
4145 RPC calls that can be sent from the client to a
4146 server. Increasing these values may allow you to
4147 improve throughput, but will also increase the
4148 amount of memory reserved for use by the client.
4150 suspend.pm_test_delay=
4152 Sets the number of seconds to remain in a suspend test
4153 mode before resuming the system (see
4154 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4155 is set. Default value is 5.
4158 [KNL] Enable accounting of swap in memory resource
4159 controller if no parameter or 1 is given or disable
4160 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4162 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4163 Format: { <int> | force | noforce }
4164 <int> -- Number of I/O TLB slabs
4165 force -- force using of bounce buffers even if they
4166 wouldn't be automatically used by the kernel
4167 noforce -- Never use bounce buffers (for debugging)
4171 sysfs.deprecated=0|1 [KNL]
4172 Enable/disable old style sysfs layout for old udev
4173 on older distributions. When this option is enabled
4174 very new udev will not work anymore. When this option
4175 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4176 in older udev will not work anymore.
4177 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4178 the kernel configuration.
4180 sysrq_always_enabled
4182 Ignore sysrq setting - this boot parameter will
4183 neutralize any effect of /proc/sys/kernel/sysrq.
4184 Useful for debugging.
4186 tcpmhash_entries= [KNL,NET]
4187 Set the number of tcp_metrics_hash slots.
4188 Default value is 8192 or 16384 depending on total
4189 ram pages. This is used to specify the TCP metrics
4190 cache size. See Documentation/networking/ip-sysctl.txt
4191 "tcp_no_metrics_save" section for more details.
4195 test_suspend= [SUSPEND][,N]
4196 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4197 standby suspend) or "freeze" (for suspend type freeze)
4198 as the system sleep state during system startup with
4199 the optional capability to repeat N number of times.
4200 The system is woken from this state using a
4201 wakeup-capable RTC alarm.
4203 thash_entries= [KNL,NET]
4204 Set number of hash buckets for TCP connection
4206 thermal.act= [HW,ACPI]
4207 -1: disable all active trip points in all thermal zones
4208 <degrees C>: override all lowest active trip points
4210 thermal.crt= [HW,ACPI]
4211 -1: disable all critical trip points in all thermal zones
4212 <degrees C>: override all critical trip points
4214 thermal.nocrt= [HW,ACPI]
4215 Set to disable actions on ACPI thermal zone
4216 critical and hot trip points.
4218 thermal.off= [HW,ACPI]
4219 1: disable ACPI thermal control
4221 thermal.psv= [HW,ACPI]
4222 -1: disable all passive trip points
4223 <degrees C>: override all passive trip points to this
4226 thermal.tzp= [HW,ACPI]
4227 Specify global default ACPI thermal zone polling rate
4228 <deci-seconds>: poll all this frequency
4229 0: no polling (default)
4232 Force threading of all interrupt handlers except those
4233 marked explicitly IRQF_NO_THREAD.
4236 Enable the Transcendent memory driver if built-in.
4238 tmem.cleancache=0|1 [KNL, XEN]
4239 Default is on (1). Disable the usage of the cleancache
4240 API to send anonymous pages to the hypervisor.
4242 tmem.frontswap=0|1 [KNL, XEN]
4243 Default is on (1). Disable the usage of the frontswap
4244 API to send swap pages to the hypervisor. If disabled
4245 the selfballooning and selfshrinking are force disabled.
4247 tmem.selfballooning=0|1 [KNL, XEN]
4248 Default is on (1). Disable the driving of swap pages
4251 tmem.selfshrinking=0|1 [KNL, XEN]
4252 Default is on (1). Partial swapoff that immediately
4253 transfers pages from Xen hypervisor back to the
4254 kernel based on different criteria.
4258 Specify if the kernel should make use of the cpu
4259 topology information if the hardware supports this.
4260 The scheduler will make use of this information and
4261 e.g. base its process migration decisions on it.
4264 topology_updates= [KNL, PPC, NUMA]
4266 Specify if the kernel should ignore (off)
4267 topology updates sent by the hypervisor to this
4272 tpm_suspend_pcr=[HW,TPM]
4273 Format: integer pcr id
4274 Specify that at suspend time, the tpm driver
4275 should extend the specified pcr with zeros,
4276 as a workaround for some chips which fail to
4277 flush the last written pcr on TPM_SaveState.
4278 This will guarantee that all the other pcrs
4281 trace_buf_size=nn[KMG]
4282 [FTRACE] will set tracing buffer size on each cpu.
4284 trace_event=[event-list]
4285 [FTRACE] Set and start specified trace events in order
4286 to facilitate early boot debugging. The event-list is a
4287 comma separated list of trace events to enable. See
4288 also Documentation/trace/events.txt
4290 trace_options=[option-list]
4291 [FTRACE] Enable or disable tracer options at boot.
4292 The option-list is a comma delimited list of options
4293 that can be enabled or disabled just as if you were
4294 to echo the option name into
4296 /sys/kernel/debug/tracing/trace_options
4298 For example, to enable stacktrace option (to dump the
4299 stack trace of each event), add to the command line:
4301 trace_options=stacktrace
4303 See also Documentation/trace/ftrace.txt "trace options"
4307 Have the tracepoints sent to printk as well as the
4308 tracing ring buffer. This is useful for early boot up
4309 where the system hangs or reboots and does not give the
4310 option for reading the tracing buffer or performing a
4311 ftrace_dump_on_oops.
4313 To turn off having tracepoints sent to printk,
4314 echo 0 > /proc/sys/kernel/tracepoint_printk
4315 Note, echoing 1 into this file without the
4316 tracepoint_printk kernel cmdline option has no effect.
4320 Having tracepoints sent to printk() and activating high
4321 frequency tracepoints such as irq or sched, can cause
4322 the system to live lock.
4325 [FTRACE] enable this option to disable tracing when a
4326 warning is hit. This turns off "tracing_on". Tracing can
4327 be enabled again by echoing '1' into the "tracing_on"
4328 file located in /sys/kernel/debug/tracing/
4330 This option is useful, as it disables the trace before
4331 the WARNING dump is called, which prevents the trace to
4332 be filled with content caused by the warning output.
4334 This option can also be set at run time via the sysctl
4335 option: kernel/traceoff_on_warning
4337 transparent_hugepage=
4339 Format: [always|madvise|never]
4340 Can be used to control the default behavior of the system
4341 with respect to transparent hugepages.
4342 See Documentation/vm/transhuge.txt for more details.
4344 tsc= Disable clocksource stability checks for TSC.
4346 [x86] reliable: mark tsc clocksource as reliable, this
4347 disables clocksource verification at runtime, as well
4348 as the stability checks done at bootup. Used to enable
4349 high-resolution timer mode on older hardware, and in
4350 virtualized environment.
4351 [x86] noirqtime: Do not use TSC to do irq accounting.
4352 Used to run time disable IRQ_TIME_ACCOUNTING on any
4353 platforms where RDTSC is slow and this accounting
4355 [x86] unstable: mark the TSC clocksource as unstable, this
4356 marks the TSC unconditionally unstable at bootup and
4357 avoids any further wobbles once the TSC watchdog notices.
4359 turbografx.map[2|3]= [HW,JOY]
4360 TurboGraFX parallel port interface
4362 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4363 See also Documentation/input/devices/joystick-parport.rst
4365 udbg-immortal [PPC] When debugging early kernel crashes that
4366 happen after console_init() and before a proper
4367 console driver takes over, this boot options might
4368 help "seeing" what's going on.
4370 uhash_entries= [KNL,NET]
4371 Set number of hash buckets for UDP/UDP-Lite connections
4374 [USB] Ignore overcurrent events (default N).
4375 Some badly-designed motherboards generate lots of
4376 bogus events, for ports that aren't wired to
4377 anything. Set this parameter to avoid log spamming.
4378 Note that genuine overcurrent events won't be
4382 [X86] Cause panic on unknown NMI.
4384 usbcore.authorized_default=
4385 [USB] Default USB device authorization:
4386 (default -1 = authorized except for wireless USB,
4387 0 = not authorized, 1 = authorized)
4389 usbcore.autosuspend=
4390 [USB] The autosuspend time delay (in seconds) used
4391 for newly-detected USB devices (default 2). This
4392 is the time required before an idle device will be
4393 autosuspended. Devices for which the delay is set
4394 to a negative value won't be autosuspended at all.
4396 usbcore.usbfs_snoop=
4397 [USB] Set to log all usbfs traffic (default 0 = off).
4399 usbcore.usbfs_snoop_max=
4400 [USB] Maximum number of bytes to snoop in each URB
4403 usbcore.blinkenlights=
4404 [USB] Set to cycle leds on hubs (default 0 = off).
4406 usbcore.old_scheme_first=
4407 [USB] Start with the old device initialization
4408 scheme (default 0 = off).
4410 usbcore.usbfs_memory_mb=
4411 [USB] Memory limit (in MB) for buffers allocated by
4412 usbfs (default = 16, 0 = max = 2047).
4414 usbcore.use_both_schemes=
4415 [USB] Try the other device initialization scheme
4416 if the first one fails (default 1 = enabled).
4418 usbcore.initial_descriptor_timeout=
4419 [USB] Specifies timeout for the initial 64-byte
4420 USB_REQ_GET_DESCRIPTOR request in milliseconds
4421 (default 5000 = 5.0 seconds).
4423 usbcore.nousb [USB] Disable the USB subsystem
4426 [USB] A list of quirk entries to augment the built-in
4427 usb core quirk list. List entries are separated by
4428 commas. Each entry has the form
4429 VendorID:ProductID:Flags. The IDs are 4-digit hex
4430 numbers and Flags is a set of letters. Each letter
4431 will change the built-in quirk; setting it if it is
4432 clear and clearing it if it is set. The letters have
4433 the following meanings:
4434 a = USB_QUIRK_STRING_FETCH_255 (string
4435 descriptors must not be fetched using
4437 b = USB_QUIRK_RESET_RESUME (device can't resume
4438 correctly so reset it instead);
4439 c = USB_QUIRK_NO_SET_INTF (device can't handle
4440 Set-Interface requests);
4441 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4442 handle its Configuration or Interface
4444 e = USB_QUIRK_RESET (device can't be reset
4445 (e.g morph devices), don't use reset);
4446 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4447 more interface descriptions than the
4448 bNumInterfaces count, and can't handle
4449 talking to these interfaces);
4450 g = USB_QUIRK_DELAY_INIT (device needs a pause
4451 during initialization, after we read
4452 the device descriptor);
4453 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4454 high speed and super speed interrupt
4455 endpoints, the USB 2.0 and USB 3.0 spec
4456 require the interval in microframes (1
4457 microframe = 125 microseconds) to be
4458 calculated as interval = 2 ^
4460 Devices with this quirk report their
4461 bInterval as the result of this
4462 calculation instead of the exponent
4463 variable used in the calculation);
4464 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4465 handle device_qualifier descriptor
4467 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4468 generates spurious wakeup, ignore
4469 remote wakeup capability);
4470 k = USB_QUIRK_NO_LPM (device can't handle Link
4472 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4473 (Device reports its bInterval as linear
4474 frames instead of the USB 2.0
4476 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4477 to be disconnected before suspend to
4478 prevent spurious wakeup);
4479 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4480 pause after every control message);
4481 Example: quirks=0781:5580:bk,0a5c:5834:gij
4484 [USBHID] The interval which mice are to be polled at.
4487 [USBHID] The interval which joysticks are to be polled at.
4489 usb-storage.delay_use=
4490 [UMS] The delay in seconds before a new device is
4491 scanned for Logical Units (default 1).
4494 [UMS] A list of quirks entries to supplement or
4495 override the built-in unusual_devs list. List
4496 entries are separated by commas. Each entry has
4497 the form VID:PID:Flags where VID and PID are Vendor
4498 and Product ID values (4-digit hex numbers) and
4499 Flags is a set of characters, each corresponding
4500 to a common usb-storage quirk flag as follows:
4501 a = SANE_SENSE (collect more than 18 bytes
4503 b = BAD_SENSE (don't collect more than 18
4504 bytes of sense data);
4505 c = FIX_CAPACITY (decrease the reported
4506 device capacity by one sector);
4507 d = NO_READ_DISC_INFO (don't use
4508 READ_DISC_INFO command);
4509 e = NO_READ_CAPACITY_16 (don't use
4510 READ_CAPACITY_16 command);
4511 f = NO_REPORT_OPCODES (don't use report opcodes
4513 g = MAX_SECTORS_240 (don't transfer more than
4514 240 sectors at a time, uas only);
4515 h = CAPACITY_HEURISTICS (decrease the
4516 reported device capacity by one
4517 sector if the number is odd);
4518 i = IGNORE_DEVICE (don't bind to this
4520 j = NO_REPORT_LUNS (don't use report luns
4522 l = NOT_LOCKABLE (don't try to lock and
4523 unlock ejectable media);
4524 m = MAX_SECTORS_64 (don't transfer more
4525 than 64 sectors = 32 KB at a time);
4526 n = INITIAL_READ10 (force a retry of the
4527 initial READ(10) command);
4528 o = CAPACITY_OK (accept the capacity
4529 reported by the device);
4530 p = WRITE_CACHE (the device cache is ON
4532 r = IGNORE_RESIDUE (the device reports
4533 bogus residue values);
4534 s = SINGLE_LUN (the device has only one
4536 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4537 commands, uas only);
4538 u = IGNORE_UAS (don't bind to the uas driver);
4539 w = NO_WP_DETECT (don't test whether the
4540 medium is write-protected).
4541 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4542 even if the device claims no cache)
4543 Example: quirks=0419:aaf5:rl,0421:0433:rc
4545 user_debug= [KNL,ARM]
4547 See arch/arm/Kconfig.debug help text.
4548 1 - undefined instruction events
4550 4 - invalid data aborts
4553 Example: user_debug=31
4556 [X86] Flags controlling user PTE allocations.
4558 nohigh = do not allocate PTE pages in
4559 HIGHMEM regardless of setting
4563 On X86_32, this is an alias for vdso32=. Otherwise:
4565 vdso=1: enable VDSO (the default)
4566 vdso=0: disable VDSO mapping
4568 vdso32= [X86] Control the 32-bit vDSO
4569 vdso32=1: enable 32-bit VDSO
4570 vdso32=0 or vdso32=2: disable 32-bit VDSO
4572 See the help text for CONFIG_COMPAT_VDSO for more
4573 details. If CONFIG_COMPAT_VDSO is set, the default is
4574 vdso32=0; otherwise, the default is vdso32=1.
4576 For compatibility with older kernels, vdso32=2 is an
4579 Try vdso32=0 if you encounter an error that says:
4580 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4583 vector=percpu: enable percpu vector domain
4585 video= [FB] Frame buffer configuration
4586 See Documentation/fb/modedb.txt.
4588 video.brightness_switch_enabled= [0,1]
4589 If set to 1, on receiving an ACPI notify event
4590 generated by hotkey, video driver will adjust brightness
4591 level and then send out the event to user space through
4592 the allocated input device; If set to 0, video driver
4593 will only send out the event without touching backlight
4598 [VMMIO] Memory mapped virtio (platform) device.
4600 <size>@<baseaddr>:<irq>[:<id>]
4602 <size> := size (can use standard suffixes
4604 <baseaddr> := physical base address
4605 <irq> := interrupt number (as passed to
4607 <id> := (optional) platform device id
4609 virtio_mmio.device=1K@0x100b0000:48:7
4611 Can be used multiple times for multiple devices.
4613 vga= [BOOT,X86-32] Select a particular video mode
4614 See Documentation/x86/boot.txt and
4615 Documentation/svga.txt.
4616 Use vga=ask for menu.
4617 This is actually a boot loader parameter; the value is
4618 passed to the kernel using a special protocol.
4620 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4621 size of <nn>. This can be used to increase the
4622 minimum size (128MB on x86). It can also be used to
4623 decrease the size and leave more room for directly
4626 vmcp_cma=nn[MG] [KNL,S390]
4627 Sets the memory size reserved for contiguous memory
4628 allocations for the vmcp device driver.
4630 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4633 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4636 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4640 Controls the behavior of vsyscalls (i.e. calls to
4641 fixed addresses of 0xffffffffff600x00 from legacy
4642 code). Most statically-linked binaries and older
4643 versions of glibc use these calls. Because these
4644 functions are at fixed addresses, they make nice
4645 targets for exploits that can control RIP.
4647 emulate [default] Vsyscalls turn into traps and are
4648 emulated reasonably safely.
4650 native Vsyscalls are native syscall instructions.
4651 This is a little bit faster than trapping
4652 and makes a few dynamic recompilers work
4653 better than they would in emulation mode.
4654 It also makes exploits much easier to write.
4656 none Vsyscalls don't work at all. This makes
4657 them quite hard to use for exploits but
4658 might break your system.
4660 vt.color= [VT] Default text color.
4661 Format: 0xYX, X = foreground, Y = background.
4662 Default: 0x07 = light gray on black.
4664 vt.cur_default= [VT] Default cursor shape.
4665 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4666 the parameters of the <Esc>[?A;B;Cc escape sequence;
4667 see VGA-softcursor.txt. Default: 2 = underline.
4669 vt.default_blu= [VT]
4670 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4671 Change the default blue palette of the console.
4672 This is a 16-member array composed of values
4675 vt.default_grn= [VT]
4676 Format: <green0>,<green1>,<green2>,...,<green15>
4677 Change the default green palette of the console.
4678 This is a 16-member array composed of values
4681 vt.default_red= [VT]
4682 Format: <red0>,<red1>,<red2>,...,<red15>
4683 Change the default red palette of the console.
4684 This is a 16-member array composed of values
4690 Set system-wide default UTF-8 mode for all tty's.
4691 Default is 1, i.e. UTF-8 mode is enabled for all
4692 newly opened terminals.
4694 vt.global_cursor_default=
4697 Set system-wide default for whether a cursor
4698 is shown on new VTs. Default is -1,
4699 i.e. cursors will be created by default unless
4700 overridden by individual drivers. 0 will hide
4701 cursors, 1 will display them.
4703 vt.italic= [VT] Default color for italic text; 0-15.
4706 vt.underline= [VT] Default color for underlined text; 0-15.
4709 watchdog timers [HW,WDT] For information on watchdog timers,
4710 see Documentation/watchdog/watchdog-parameters.txt
4711 or other driver-specific files in the
4712 Documentation/watchdog/ directory.
4714 workqueue.watchdog_thresh=
4715 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4716 warn stall conditions and dump internal state to
4717 help debugging. 0 disables workqueue stall
4718 detection; otherwise, it's the stall threshold
4719 duration in seconds. The default value is 30 and
4720 it can be updated at runtime by writing to the
4721 corresponding sysfs file.
4723 workqueue.disable_numa
4724 By default, all work items queued to unbound
4725 workqueues are affine to the NUMA nodes they're
4726 issued on, which results in better behavior in
4727 general. If NUMA affinity needs to be disabled for
4728 whatever reason, this option can be used. Note
4729 that this also can be controlled per-workqueue for
4730 workqueues visible under /sys/bus/workqueue/.
4732 workqueue.power_efficient
4733 Per-cpu workqueues are generally preferred because
4734 they show better performance thanks to cache
4735 locality; unfortunately, per-cpu workqueues tend to
4736 be more power hungry than unbound workqueues.
4738 Enabling this makes the per-cpu workqueues which
4739 were observed to contribute significantly to power
4740 consumption unbound, leading to measurably lower
4741 power usage at the cost of small performance
4744 The default value of this parameter is determined by
4745 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4747 workqueue.debug_force_rr_cpu
4748 Workqueue used to implicitly guarantee that work
4749 items queued without explicit CPU specified are put
4750 on the local CPU. This guarantee is no longer true
4751 and while local CPU is still preferred work items
4752 may be put on foreign CPUs. This debug option
4753 forces round-robin CPU selection to flush out
4754 usages which depend on the now broken guarantee.
4755 When enabled, memory and cache locality will be
4758 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4759 default x2apic cluster mode on platforms
4762 x86_intel_mid_timer= [X86-32,APBT]
4763 Choose timer option for x86 Intel MID platform.
4764 Two valid options are apbt timer only and lapic timer
4765 plus one apbt timer for broadcast timer.
4766 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4768 xen_512gb_limit [KNL,X86-64,XEN]
4769 Restricts the kernel running paravirtualized under Xen
4770 to use only up to 512 GB of RAM. The reason to do so is
4771 crash analysis tools and Xen tools for doing domain
4772 save/restore/migration must be enabled to handle larger
4775 xen_emul_unplug= [HW,X86,XEN]
4776 Unplug Xen emulated devices
4777 Format: [unplug0,][unplug1]
4778 ide-disks -- unplug primary master IDE devices
4779 aux-ide-disks -- unplug non-primary-master IDE devices
4780 nics -- unplug network devices
4781 all -- unplug all emulated devices (NICs and IDE disks)
4782 unnecessary -- unplugging emulated devices is
4783 unnecessary even if the host did not respond to
4785 never -- do not unplug even if version check succeeds
4787 xen_nopvspin [X86,XEN]
4788 Disables the ticketlock slowpath using Xen PV
4792 Disables the PV optimizations forcing the HVM guest to
4793 run as generic HVM guest with no PV drivers.
4795 xirc2ps_cs= [NET,PCMCIA]
4797 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]