1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_no_watchdog [HW,ACPI,WDT]
141 Ignore the ACPI-based watchdog interface (WDAT) and let
142 a native driver control the watchdog device instead.
144 acpi_rsdp= [ACPI,EFI,KEXEC]
145 Pass the RSDP address to the kernel, mostly used
146 on machines running EFI runtime service to boot the
147 second kernel for kdump.
149 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
150 Format: To spoof as Windows 98: ="Microsoft Windows"
152 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
153 of 2 which is mandated by ACPI 6) as the supported ACPI
154 specification revision (when using this switch, it may
155 be necessary to carry out a cold reboot _twice_ in a
156 row to make it take effect on the platform firmware).
158 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
159 acpi_osi="string1" # add string1
160 acpi_osi="!string2" # remove string2
161 acpi_osi=!* # remove all strings
162 acpi_osi=! # disable all built-in OS vendor
164 acpi_osi=!! # enable all built-in OS vendor
166 acpi_osi= # disable all strings
168 'acpi_osi=!' can be used in combination with single or
169 multiple 'acpi_osi="string1"' to support specific OS
170 vendor string(s). Note that such command can only
171 affect the default state of the OS vendor strings, thus
172 it cannot affect the default state of the feature group
173 strings and the current state of the OS vendor strings,
174 specifying it multiple times through kernel command line
175 is meaningless. This command is useful when one do not
176 care about the state of the feature group strings which
177 should be controlled by the OSPM.
179 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
180 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
181 can make '_OSI("Windows 2000")' TRUE.
183 'acpi_osi=' cannot be used in combination with other
184 'acpi_osi=' command lines, the _OSI method will not
185 exist in the ACPI namespace. NOTE that such command can
186 only affect the _OSI support state, thus specifying it
187 multiple times through kernel command line is also
190 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
193 'acpi_osi=!*' can be used in combination with single or
194 multiple 'acpi_osi="string1"' to support specific
195 string(s). Note that such command can affect the
196 current state of both the OS vendor strings and the
197 feature group strings, thus specifying it multiple times
198 through kernel command line is meaningful. But it may
199 still not able to affect the final state of a string if
200 there are quirks related to this string. This command
201 is useful when one want to control the state of the
202 feature group strings to debug BIOS issues related to
205 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
206 '_OSI("Module Device")' FALSE.
207 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
208 '_OSI("Module Device")' TRUE.
209 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
211 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
213 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
214 they all will make '_OSI("Windows 2000")' TRUE.
217 Override the pmtimer bug detection: force the kernel
218 to assume that this machine's pmtimer latches its value
219 and always returns good values.
221 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
222 Format: { level | edge | high | low }
224 acpi_skip_timer_override [HW,ACPI]
225 Recognize and ignore IRQ0/pin2 Interrupt Override.
226 For broken nForce2 BIOS resulting in XT-PIC timer.
228 acpi_sleep= [HW,ACPI] Sleep options
229 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
230 old_ordering, nonvs, sci_force_enable }
231 See Documentation/power/video.txt for information on
233 s3_beep is for debugging; it makes the PC's speaker beep
234 as soon as the kernel's real-mode entry point is called.
235 s4_nohwsig prevents ACPI hardware signature from being
236 used during resume from hibernation.
237 old_ordering causes the ACPI 1.0 ordering of the _PTS
238 control method, with respect to putting devices into
239 low power states, to be enforced (the ACPI 2.0 ordering
240 of _PTS is used by default).
241 nonvs prevents the kernel from saving/restoring the
242 ACPI NVS memory during suspend/hibernation and resume.
243 sci_force_enable causes the kernel to set SCI_EN directly
244 on resume from S1/S3 (which is against the ACPI spec,
245 but some broken systems don't work without it).
247 acpi_use_timer_override [HW,ACPI]
248 Use timer override. For some broken Nvidia NF5 boards
249 that require a timer override, but don't have HPET
251 add_efi_memmap [EFI; X86] Include EFI memory map in
252 kernel's map of available physical RAM.
255 { off | try_unsupported }
256 off: disable AGP support
257 try_unsupported: try to drive unsupported chipsets
258 (may crash computer or cause data corruption)
261 See Documentation/sound/alsa/alsa-parameters.txt
264 Allow the default userspace alignment fault handler
265 behaviour to be specified. Bit 0 enables warnings,
266 bit 1 enables fixups, and bit 2 sends a segfault.
268 align_va_addr= [X86-64]
269 Align virtual addresses by clearing slice [14:12] when
270 allocating a VMA at process creation time. This option
271 gives you up to 3% performance improvement on AMD F15h
272 machines (where it is enabled by default) for a
273 CPU-intensive style benchmark, and it can vary highly in
274 a microbenchmark depending on workload and compiler.
276 32: only for 32-bit processes
277 64: only for 64-bit processes
278 on: enable for both 32- and 64-bit processes
279 off: disable for both 32- and 64-bit processes
281 alloc_snapshot [FTRACE]
282 Allocate the ftrace snapshot buffer on boot up when the
283 main buffer is allocated. This is handy if debugging
284 and you need to use tracing_snapshot() on boot up, and
285 do not want to use tracing_snapshot_alloc() as it needs
286 to be done where GFP_KERNEL allocations are allowed.
288 amd_iommu= [HW,X86-64]
289 Pass parameters to the AMD IOMMU driver in the system.
291 fullflush - enable flushing of IO/TLB entries when
292 they are unmapped. Otherwise they are
293 flushed before they will be reused, which
295 off - do not initialize any AMD IOMMU found in
297 force_isolation - Force device isolation for all
298 devices. The IOMMU driver is not
299 allowed anymore to lift isolation
300 requirements as needed. This option
301 does not override iommu=pt
303 amd_iommu_dump= [HW,X86-64]
304 Enable AMD IOMMU driver option to dump the ACPI table
305 for AMD IOMMU. With this option enabled, AMD IOMMU
306 driver will print ACPI tables for AMD IOMMU during
307 IOMMU initialization.
309 amd_iommu_intr= [HW,X86-64]
310 Specifies one of the following AMD IOMMU interrupt
312 legacy - Use legacy interrupt remapping mode.
313 vapic - Use virtual APIC mode, which allows IOMMU
314 to inject interrupts directly into guest.
315 This mode requires kvm-amd.avic=1.
316 (Default when IOMMU HW support is present.)
318 amijoy.map= [HW,JOY] Amiga joystick support
319 Map of devices attached to JOY0DAT and JOY1DAT
321 See also Documentation/input/joystick.txt
323 analog.map= [HW,JOY] Analog joystick and gamepad support
324 Specifies type or capabilities of an analog joystick
325 connected to one of 16 gameports
326 Format: <type1>,<type2>,..<type16>
329 Power management functions (SPARCstation-4/5 + deriv.)
331 Disable APC CPU standby support. SPARCstation-Fox does
332 not play well with APC CPU idle - disable it if you have
333 APC and your system crashes randomly.
335 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
336 Change the output verbosity whilst booting
337 Format: { quiet (default) | verbose | debug }
338 Change the amount of debugging information output
339 when initialising the APIC and IO-APIC components.
341 apic_extnmi= [APIC,X86] External NMI delivery setting
342 Format: { bsp (default) | all | none }
343 bsp: External NMI is delivered only to CPU 0
344 all: External NMIs are broadcast to all CPUs as a
346 none: External NMI is masked for all CPUs. This is
347 useful so that a dump capture kernel won't be
351 See Documentation/networking/ipv6.txt.
353 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
354 Limit apic dumping. The parameter defines the maximal
355 number of local apics being dumped. Also it is possible
356 to set it to "all" by meaning -- no limit here.
357 Format: { 1 (default) | 2 | ... | all }.
358 The parameter valid if only apic=debug or
359 apic=verbose is specified.
360 Example: apic=debug show_lapic=all
362 apm= [APM] Advanced Power Management
363 See header of arch/x86/kernel/apm_32.c.
365 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
366 Format: <io>,<irq>,<nodeID>
370 atarimouse= [HW,MOUSE] Atari Mouse
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
375 atkbd.reset= [HW] Reset keyboard during initialization
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
389 audit= [KNL] Enable the audit sub-system
390 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
391 0 - kernel audit is disabled and can not be enabled
392 until the next reboot
393 unset - kernel audit is initialized but disabled and
394 will be fully enabled by the userspace auditd.
395 1 - kernel audit is initialized and partially enabled,
396 storing at most audit_backlog_limit messages in
397 RAM until it is fully enabled by the userspace
401 audit_backlog_limit= [KNL] Set the audit queue size limit.
402 Format: <int> (must be >=0)
405 bau= [X86_UV] Enable the BAU on SGI UV. The default
406 behavior is to disable the BAU (i.e. bau=0).
407 Format: { "0" | "1" }
410 unset - Disable the BAU.
412 baycom_epp= [HW,AX25]
415 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
417 See header of drivers/net/hamradio/baycom_par.c.
419 baycom_ser_fdx= [HW,AX25]
420 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
421 Format: <io>,<irq>,<mode>[,<baud>]
422 See header of drivers/net/hamradio/baycom_ser_fdx.c.
424 baycom_ser_hdx= [HW,AX25]
425 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
426 Format: <io>,<irq>,<mode>
427 See header of drivers/net/hamradio/baycom_ser_hdx.c.
429 blkdevparts= Manual partition parsing of block device(s) for
430 embedded devices based on command line input.
431 See Documentation/block/cmdline-partition.txt
433 boot_delay= Milliseconds to delay each printk during boot.
434 Values larger than 10 seconds (10000) are changed to
438 bootmem_debug [KNL] Enable bootmem allocator debug messages.
441 Disable BERT OS support on buggy BIOSes.
443 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
444 bttv.radio= Most important insmod options are available as
446 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
449 bulk_remove=off [PPC] This parameter disables the use of the pSeries
450 firmware feature for flushing multiple hpte entries
453 c101= [NET] Moxa C101 synchronous serial card
455 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
456 Sometimes CPU hardware bugs make them report the cache
457 size incorrectly. The kernel will attempt work arounds
458 to fix known problems, but for some CPUs it is not
459 possible to determine what the correct size should be.
460 This option provides an override for these situations.
462 ca_keys= [KEYS] This parameter identifies a specific key(s) on
463 the system trusted keyring to be used for certificate
465 format: { id:<keyid> | builtin }
467 cca= [MIPS] Override the kernel pages' cache coherency
468 algorithm. Accepted values range from 0 to 7
469 inclusive. See arch/mips/include/asm/pgtable-bits.h
470 for platform specific values (SB1, Loongson3 and
473 ccw_timeout_log [S390]
474 See Documentation/s390/CommonIO for details.
476 cgroup_disable= [KNL] Disable a particular controller
477 Format: {name of the controller(s) to disable}
478 The effects of cgroup_disable=foo are:
479 - foo isn't auto-mounted if you mount all cgroups in
481 - foo isn't visible as an individually mountable
483 {Currently only "memory" controller deal with this and
484 cut the overhead, others just disable the usage. So
485 only cgroup_disable=memory is actually worthy}
487 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
488 Format: { controller[,controller...] | "all" }
489 Like cgroup_disable, but only applies to cgroup v1;
490 the blacklisted controllers remain available in cgroup2.
492 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
494 nosocket -- Disable socket memory accounting.
495 nokmem -- Disable kernel memory accounting.
497 checkreqprot [SELINUX] Set initial checkreqprot flag value.
498 Format: { "0" | "1" }
499 See security/selinux/Kconfig help text.
500 0 -- check protection applied by kernel (includes
501 any implied execute protection).
502 1 -- check protection requested by application.
503 Default value is set via a kernel config option.
504 Value can be changed at runtime via
505 /selinux/checkreqprot.
508 See Documentation/s390/CommonIO for details.
511 Prevents the clock framework from automatically gating
512 clocks that have not been explicitly enabled by a Linux
513 device driver but are enabled in hardware at reset or
514 by the bootloader/firmware. Note that this does not
515 force such clocks to be always-on nor does it reserve
516 those clocks in any way. This parameter is useful for
517 debug and development, but should not be needed on a
518 platform with proper driver support. For more
519 information, see Documentation/clk.txt.
521 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
523 Forces specified clocksource (if available) to be used
524 when calculating gettimeofday(). If specified
525 clocksource is not available, it defaults to PIT.
526 Format: { pit | tsc | cyclone | pmtmr }
528 clocksource= Override the default clocksource
530 Override the default clocksource and use the clocksource
531 with the name specified.
532 Some clocksource names to choose from, depending on
534 [all] jiffies (this is the base, fallback clocksource)
536 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
537 pxa_timer,timer3,32k_counter,timer0_1
538 [X86-32] pit,hpet,tsc;
539 scx200_hrt on Geode; cyclone on IBM x440
547 clocksource.arm_arch_timer.evtstrm=
550 Enable/disable the eventstream feature of the ARM
551 architected timer so that code using WFE-based polling
552 loops can be debugged more effectively on production
555 clearcpuid=BITNUM[,BITNUM...] [X86]
556 Disable CPUID feature X for the kernel. See
557 arch/x86/include/asm/cpufeatures.h for the valid bit
558 numbers. Note the Linux specific bits are not necessarily
559 stable over kernel options, but the vendor specific
561 Also note that user programs calling CPUID directly
562 or using the feature without checking anything
563 will still see it. This just prevents it from
564 being used by the kernel or shown in /proc/cpuinfo.
565 Also note the kernel might malfunction if you disable
568 cma=nn[MG]@[start[MG][-end[MG]]]
570 Sets the size of kernel global memory area for
571 contiguous memory allocations and optionally the
572 placement constraint by the physical address range of
573 memory allocations. A value of 0 disables CMA
574 altogether. For more information, see
575 include/linux/dma-contiguous.h
577 cmo_free_hint= [PPC] Format: { yes | no }
578 Specify whether pages are marked as being inactive
579 when they are freed. This is used in CMO environments
580 to determine OS memory pressure for page stealing by
584 coherent_pool=nn[KMG] [ARM,KNL]
585 Sets the size of memory pool for coherent, atomic dma
586 allocations, by default set to 256K.
588 code_bytes [X86] How many bytes of object code to print
593 com20020= [HW,NET] ARCnet - COM20020 chipset
595 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
597 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
601 ARCnet - COM90xx chipset (memory-mapped buffers)
602 Format: <io>[,<irq>[,<memstart>]]
604 condev= [HW,S390] console device
607 console= [KNL] Output console device and options.
609 tty<n> Use the virtual console device <n>.
613 Use the specified serial port. The options are of
614 the form "bbbbpnf", where "bbbb" is the baud rate,
615 "p" is parity ("n", "o", or "e"), "n" is number of
616 bits, and "f" is flow control ("r" for RTS or
617 omit it). Default is "9600n8".
619 See Documentation/admin-guide/serial-console.rst for more
621 Documentation/networking/netconsole.txt for an
624 uart[8250],io,<addr>[,options]
625 uart[8250],mmio,<addr>[,options]
626 uart[8250],mmio16,<addr>[,options]
627 uart[8250],mmio32,<addr>[,options]
628 uart[8250],0x<addr>[,options]
629 Start an early, polled-mode console on the 8250/16550
630 UART at the specified I/O port or MMIO address,
631 switching to the matching ttyS device later.
632 MMIO inter-register address stride is either 8-bit
633 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
634 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
635 to be equivalent to 'mmio'. 'options' are specified in
636 the same format described for ttyS above; if unspecified,
637 the h/w is not re-initialized.
639 hvc<n> Use the hypervisor console device <n>. This is for
640 both Xen and PowerPC hypervisors.
642 If the device connected to the port is not a TTY but a braille
643 device, prepend "brl," before the device type, for instance
645 For now, only VisioBraille is supported.
647 consoleblank= [KNL] The console blank (screen saver) timeout in
648 seconds. Defaults to 10*60 = 10mins. A value of 0
649 disables the blank timer.
652 [KNL] Change the default value for
653 /proc/<pid>/coredump_filter.
654 See also Documentation/filesystems/proc.txt.
656 coresight_cpu_debug.enable
659 Enable/disable the CPU sampling based debugging.
660 0: default value, disable debugging
661 1: enable debugging at boot time
663 cpuidle.off=1 [CPU_IDLE]
664 disable the cpuidle sub-system
666 cpufreq.off=1 [CPU_FREQ]
667 disable the cpufreq sub-system
670 [X86] Delay for N microsec between assert and de-assert
671 of APIC INIT to start processors. This delay occurs
672 on every CPU online, such as boot, and resume from suspend.
675 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
677 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
679 crashkernel=size[KMG][@offset[KMG]]
680 [KNL] Using kexec, Linux can switch to a 'crash kernel'
681 upon panic. This parameter reserves the physical
682 memory region [offset, offset + size] for that kernel
683 image. If '@offset' is omitted, then a suitable offset
684 is selected automatically. Check
685 Documentation/kdump/kdump.txt for further details.
687 crashkernel=range1:size1[,range2:size2,...][@offset]
688 [KNL] Same as above, but depends on the memory
689 in the running system. The syntax of range is
690 start-[end] where start and end are both
691 a memory unit (amount[KMG]). See also
692 Documentation/kdump/kdump.txt for an example.
694 crashkernel=size[KMG],high
695 [KNL, x86_64] range could be above 4G. Allow kernel
696 to allocate physical memory region from top, so could
697 be above 4G if system have more than 4G ram installed.
698 Otherwise memory region will be allocated below 4G, if
700 It will be ignored if crashkernel=X is specified.
701 crashkernel=size[KMG],low
702 [KNL, x86_64] range under 4G. When crashkernel=X,high
703 is passed, kernel could allocate physical memory region
704 above 4G, that cause second kernel crash on system
705 that require some amount of low memory, e.g. swiotlb
706 requires at least 64M+32K low memory, also enough extra
707 low memory is needed to make sure DMA buffers for 32-bit
708 devices won't run out. Kernel would try to allocate at
709 at least 256M below 4G automatically.
710 This one let user to specify own low range under 4G
711 for second kernel instead.
712 0: to disable low allocation.
713 It will be ignored when crashkernel=X,high is not used
714 or memory reserved is below 4G.
717 [KNL] Disable crypto self-tests
722 cs89x0_media= [HW,NET]
723 Format: { rj45 | aui | bnc }
726 See header of drivers/s390/block/dasd_devmap.c.
728 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
729 (one device per port)
730 Format: <port#>,<type>
731 See also Documentation/input/joystick-parport.txt
733 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
735 Documentation/admin-guide/dynamic-debug-howto.rst for
736 details. Deprecated, see dyndbg.
738 debug [KNL] Enable kernel debugging (events log level).
741 [KNL] verbose self-tests
743 Print debugging info while doing the locking API
745 We default to 0 (no extra messages), setting it to
746 1 will print _a lot_ more information - normally
747 only useful to kernel developers.
749 debug_objects [KNL] Enable object debugging
752 [KNL] Disable object debugging
754 debug_guardpage_minorder=
755 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
756 parameter allows control of the order of pages that will
757 be intentionally kept free (and hence protected) by the
758 buddy allocator. Bigger value increase the probability
759 of catching random memory corruption, but reduce the
760 amount of memory for normal system use. The maximum
761 possible value is MAX_ORDER/2. Setting this parameter
762 to 1 or 2 should be enough to identify most random
763 memory corruption problems caused by bugs in kernel or
764 driver code when a CPU writes to (or reads from) a
765 random memory location. Note that there exists a class
766 of memory corruptions problems caused by buggy H/W or
767 F/W or by drivers badly programing DMA (basically when
768 memory is written at bus level and the CPU MMU is
769 bypassed) which are not detectable by
770 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
771 tracking down these problems.
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter enables the feature at boot time. In
776 default, it is disabled. We can avoid allocating huge
777 chunk of memory for debug pagealloc if we don't enable
778 it at boot time and the system will work mostly same
779 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
780 on: enable the feature
782 debugpat [X86] Enable PAT debugging
784 decnet.addr= [HW,NET]
785 Format: <area>[,<node>]
786 See also Documentation/networking/decnet.txt.
789 [same as hugepagesz=] The size of the default
790 HugeTLB page size. This is the size represented by
791 the legacy /proc/ hugepages APIs, used for SHM, and
792 default size when mounting hugetlbfs filesystems.
793 Defaults to the default architecture's huge page size
797 Set number of hash buckets for dentry cache.
799 disable_1tb_segments [PPC]
800 Disables the use of 1TB hash page table segments. This
801 causes the kernel to fall back to 256MB segments which
802 can be useful when debugging issues that require an SLB
806 See Documentation/networking/ipv6.txt.
809 Disable RADIX MMU mode on POWER9
811 disable_cpu_apicid= [X86,APIC,SMP]
813 The number of initial APIC ID for the
814 corresponding CPU to be disabled at boot,
815 mostly used for the kdump 2nd kernel to
816 disable BSP to wake up multiple CPUs without
817 causing system reset or hang due to sending
820 disable_ddw [PPC/PSERIES]
821 Disable Dynamic DMA Window support. Use this if
822 to workaround buggy firmware.
825 See Documentation/networking/ipv6.txt.
827 disable_mtrr_cleanup [X86]
828 The kernel tries to adjust MTRR layout from continuous
829 to discrete, to make X server driver able to add WB
830 entry later. This parameter disables that.
832 disable_mtrr_trim [X86, Intel and AMD only]
833 By default the kernel will trim any uncacheable
834 memory out of your available memory pool based on
835 MTRR settings. This parameter disables that behavior,
836 possibly causing your machine to run very slowly.
838 disable_timer_pin_1 [X86]
839 Disable PIN 1 of APIC timer
840 Can be useful to work around chipset bugs.
842 dis_ucode_ldr [X86] Disable the microcode loader.
844 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
845 this option disables the debugging code at boot.
847 dma_debug_entries=<number>
848 This option allows to tune the number of preallocated
849 entries for DMA-API debugging code. One entry is
850 required per DMA-API allocation. Use this if the
851 DMA-API debugging code disables itself because the
852 architectural default is too low.
854 dma_debug_driver=<driver_name>
855 With this option the DMA-API debugging driver
856 filter feature can be enabled at boot time. Just
857 pass the driver to filter for as the parameter.
858 The filter can be disabled or changed to another
859 driver later using sysfs.
861 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
862 Broken monitors, graphic adapters, KVMs and EDIDless
863 panels may send no or incorrect EDID data sets.
864 This parameter allows to specify an EDID data sets
865 in the /lib/firmware directory that are used instead.
866 Generic built-in EDID data sets are used, if one of
867 edid/1024x768.bin, edid/1280x1024.bin,
868 edid/1680x1050.bin, or edid/1920x1080.bin is given
869 and no file with the same name exists. Details and
870 instructions how to build your own EDID data are
871 available in Documentation/EDID/HOWTO.txt. An EDID
872 data set will only be used for a particular connector,
873 if its name and a colon are prepended to the EDID
874 name. Each connector may use a unique EDID data
875 set by separating the files with a comma. An EDID
876 data set with no connector name will be used for
877 any connectors not explicitly specified.
882 Format: {"off" | "known"}
883 Control how the dt_cpu_ftrs device-tree binding is
884 used for CPU feature discovery and setup (if it
886 off: Do not use it, fall back to legacy cpu table.
887 known: Do not pass through unknown features to guests
888 or userspace, only those that the kernel is aware of.
890 dump_apple_properties [X86]
891 Dump name and content of EFI device properties on
892 x86 Macs. Useful for driver authors to determine
893 what data is available or for reverse-engineering.
895 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
896 module.dyndbg[="val"]
897 Enable debug messages at boot time. See
898 Documentation/admin-guide/dynamic-debug-howto.rst
901 nompx [X86] Disables Intel Memory Protection Extensions.
902 See Documentation/x86/intel_mpx.txt for more
903 information about the feature.
905 nopku [X86] Disable Memory Protection Keys CPU feature found
908 module.async_probe [KNL]
909 Enable asynchronous probe on this module.
911 early_ioremap_debug [KNL]
912 Enable debug messages in early_ioremap support. This
913 is useful for tracking down temporary early mappings
914 which are not unmapped.
916 earlycon= [KNL] Output early console device and options.
918 When used with no options, the early console is
919 determined by the stdout-path property in device
922 cdns,<addr>[,options]
923 Start an early, polled-mode console on a Cadence
924 (xuartps) serial port at the specified address. Only
925 supported option is baud rate. If baud rate is not
926 specified, the serial port must already be setup and
929 uart[8250],io,<addr>[,options]
930 uart[8250],mmio,<addr>[,options]
931 uart[8250],mmio32,<addr>[,options]
932 uart[8250],mmio32be,<addr>[,options]
933 uart[8250],0x<addr>[,options]
934 Start an early, polled-mode console on the 8250/16550
935 UART at the specified I/O port or MMIO address.
936 MMIO inter-register address stride is either 8-bit
937 (mmio) or 32-bit (mmio32 or mmio32be).
938 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
939 to be equivalent to 'mmio'. 'options' are specified
940 in the same format described for "console=ttyS<n>"; if
941 unspecified, the h/w is not initialized.
945 Start an early, polled-mode console on a pl011 serial
946 port at the specified address. The pl011 serial port
947 must already be setup and configured. Options are not
948 yet supported. If 'mmio32' is specified, then only
949 the driver will use only 32-bit accessors to read/write
950 the device registers.
953 Start an early, polled-mode console on a meson serial
954 port at the specified address. The serial port must
955 already be setup and configured. Options are not yet
959 Start an early, polled-mode console on an msm serial
960 port at the specified address. The serial port
961 must already be setup and configured. Options are not
965 Start an early, polled-mode console on an msm serial
966 dm port at the specified address. The serial port
967 must already be setup and configured. Options are not
971 Start an early, polled-mode console on a serial port
972 of an Actions Semi SoC, such as S500 or S900, at the
973 specified address. The serial port must already be
974 setup and configured. Options are not yet supported.
976 smh Use ARM semihosting calls for early console.
984 Use early console provided by serial driver available
985 on Samsung SoCs, requires selecting proper type and
986 a correct base address of the selected UART port. The
987 serial port must already be setup and configured.
988 Options are not yet supported.
991 Start an early, polled-mode console on a lantiq serial
992 (lqasc) port at the specified address. The serial port
993 must already be setup and configured. Options are not
998 Use early console provided by Freescale LP UART driver
999 found on Freescale Vybrid and QorIQ LS1021A processors.
1000 A valid base address must be provided, and the serial
1001 port must already be setup and configured.
1004 Start an early, polled-mode console on the
1005 Armada 3700 serial port at the specified
1006 address. The serial port must already be setup
1007 and configured. Options are not yet supported.
1009 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1014 earlyprintk=serial[,ttySn[,baudrate]]
1015 earlyprintk=serial[,0x...[,baudrate]]
1016 earlyprintk=ttySn[,baudrate]
1017 earlyprintk=dbgp[debugController#]
1018 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1019 earlyprintk=xdbc[xhciController#]
1021 earlyprintk is useful when the kernel crashes before
1022 the normal console is initialized. It is not enabled by
1023 default because it has some cosmetic problems.
1025 Append ",keep" to not disable it when the real console
1028 Only one of vga, efi, serial, or usb debug port can
1031 Currently only ttyS0 and ttyS1 may be specified by
1032 name. Other I/O ports may be explicitly specified
1033 on some architectures (x86 and arm at least) by
1034 replacing ttySn with an I/O port address, like this:
1035 earlyprintk=serial,0x1008,115200
1036 You can find the port for a given device in
1037 /proc/tty/driver/serial:
1038 2: uart:ST16650V2 port:00001008 irq:18 ...
1040 Interaction with the standard serial driver is not
1043 The VGA and EFI output is eventually overwritten by
1046 The xen output can only be used by Xen PV guests.
1048 The sclp output can only be used on s390.
1050 The optional "force" to "pciserial" enables use of a
1051 PCI device even when its classcode is not of the
1054 edac_report= [HW,EDAC] Control how to report EDAC event
1055 Format: {"on" | "off" | "force"}
1056 on: enable EDAC to report H/W event. May be overridden
1057 by other higher priority error reporting module.
1058 off: disable H/W event reporting through EDAC.
1059 force: enforce the use of EDAC to report H/W event.
1062 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1065 This is designed to be used in conjunction with
1066 the boot argument: earlyprintk=vga
1069 Format: {"off" | "on" | "skip[mbr]"}
1072 Format: { "old_map", "nochunk", "noruntime", "debug" }
1073 old_map [X86-64]: switch to the old ioremap-based EFI
1074 runtime services mapping. 32-bit still uses this one by
1076 nochunk: disable reading files in "chunks" in the EFI
1077 boot stub, as chunking can cause problems with some
1078 firmware implementations.
1079 noruntime : disable EFI runtime services support
1080 debug: enable misc debug output
1082 efi_no_storage_paranoia [EFI; X86]
1083 Using this parameter you can use more than 50% of
1084 your efi variable storage. Use this parameter only if
1085 you are really sure that your UEFI does sane gc and
1086 fulfills the spec otherwise your board may brick.
1088 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1089 Add arbitrary attribute to specific memory range by
1090 updating original EFI memory map.
1091 Region of memory which aa attribute is added to is
1093 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1094 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1095 attribute is added to range 0x100000000-0x180000000 and
1096 0x10a0000000-0x1120000000.
1098 Using this parameter you can do debugging of EFI memmap
1099 related feature. For example, you can do debugging of
1100 Address Range Mirroring feature even if your box
1103 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1104 that is to be dynamically loaded by Linux. If there are
1105 multiple variables with the same name but with different
1106 vendor GUIDs, all of them will be loaded. See
1107 Documentation/acpi/ssdt-overlays.txt for details.
1110 eisa_irq_edge= [PARISC,HW]
1111 See header of drivers/parisc/eisa.c.
1114 See comment before function elanfreq_setup() in
1115 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1118 Format: {"cfq" | "deadline" | "noop"}
1119 See Documentation/block/cfq-iosched.txt and
1120 Documentation/block/deadline-iosched.txt for details.
1122 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1123 Specifies physical address of start of kernel core
1124 image elf header and optionally the size. Generally
1125 kexec loader will pass this option to capture kernel.
1126 See Documentation/kdump/kdump.txt for details.
1128 enable_mtrr_cleanup [X86]
1129 The kernel tries to adjust MTRR layout from continuous
1130 to discrete, to make X server driver able to add WB
1131 entry later. This parameter enables that.
1133 enable_timer_pin_1 [X86]
1134 Enable PIN 1 of APIC timer
1135 Can be useful to work around chipset bugs
1136 (in particular on some ATI chipsets).
1137 The kernel tries to set a reasonable default.
1139 enforcing [SELINUX] Set initial enforcing status.
1141 See security/selinux/Kconfig help text.
1142 0 -- permissive (log only, no denials).
1143 1 -- enforcing (deny and log).
1145 Value can be changed at runtime via /selinux/enforce.
1148 Disable Error Record Serialization Table (ERST)
1151 ether= [HW,NET] Ethernet cards parameters
1152 This option is obsoleted by the "netdev=" option, which
1153 has equivalent usage. See its documentation for details.
1157 Permit 'security.evm' to be updated regardless of
1158 current integrity status.
1162 fail_make_request=[KNL]
1163 General fault injection mechanism.
1164 Format: <interval>,<probability>,<space>,<times>
1165 See also Documentation/fault-injection/.
1168 See Documentation/blockdev/floppy.txt.
1170 force_pal_cache_flush
1171 [IA-64] Avoid check_sal_cache_flush which may hang on
1172 buggy SAL_CACHE_FLUSH implementations. Using this
1173 parameter will force ia64_sal_cache_flush to call
1174 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1177 Forcefully enable Physical Address Extension (PAE).
1178 Many Pentium M systems disable PAE but may have a
1179 functionally usable PAE implementation.
1180 Warning: use of this parameter will taint the kernel
1181 and may cause unknown problems.
1184 [FTRACE] will set and start the specified tracer
1185 as early as possible in order to facilitate early
1188 ftrace_dump_on_oops[=orig_cpu]
1189 [FTRACE] will dump the trace buffers on oops.
1190 If no parameter is passed, ftrace will dump
1191 buffers of all CPUs, but if you pass orig_cpu, it will
1192 dump only the buffer of the CPU that triggered the
1195 ftrace_filter=[function-list]
1196 [FTRACE] Limit the functions traced by the function
1197 tracer at boot up. function-list is a comma separated
1198 list of functions. This list can be changed at run
1199 time by the set_ftrace_filter file in the debugfs
1202 ftrace_notrace=[function-list]
1203 [FTRACE] Do not trace the functions specified in
1204 function-list. This list can be changed at run time
1205 by the set_ftrace_notrace file in the debugfs
1208 ftrace_graph_filter=[function-list]
1209 [FTRACE] Limit the top level callers functions traced
1210 by the function graph tracer at boot up.
1211 function-list is a comma separated list of functions
1212 that can be changed at run time by the
1213 set_graph_function file in the debugfs tracing directory.
1215 ftrace_graph_notrace=[function-list]
1216 [FTRACE] Do not trace from the functions specified in
1217 function-list. This list is a comma separated list of
1218 functions that can be changed at run time by the
1219 set_graph_notrace file in the debugfs tracing directory.
1221 ftrace_graph_max_depth=<uint>
1222 [FTRACE] Used with the function graph tracer. This is
1223 the max depth it will trace into a function. This value
1224 can be changed at run time by the max_graph_depth file
1225 in the tracefs tracing directory. default: 0 (no limit)
1228 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1229 support via parallel port (up to 5 devices per port)
1230 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1231 See also Documentation/input/joystick-parport.txt
1235 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1239 gcov_persist= [GCOV] When non-zero (default), profiling data for
1240 kernel modules is saved and remains accessible via
1241 debugfs, even when the module is unloaded/reloaded.
1242 When zero, profiling data is discarded and associated
1243 debugfs files are removed at module unload time.
1245 goldfish [X86] Enable the goldfish android emulator platform.
1246 Don't use this when you are not running on the
1249 gpt [EFI] Forces disk with valid GPT signature but
1250 invalid Protective MBR to be treated as GPT. If the
1251 primary GPT is corrupted, it enables the backup/alternate
1252 GPT to be used instead.
1254 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1255 the "Enable 0" bit of the configuration register.
1258 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1259 the "Enable 0" bit of the configuration register.
1262 grcan.select= [HW] Select which physical interface to use.
1265 grcan.txsize= [HW] Sets the size of the tx buffer.
1266 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1268 grcan.rxsize= [HW] Sets the size of the rx buffer.
1269 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1272 gpio-mockup.gpio_mockup_ranges
1273 [HW] Sets the ranges of gpiochip of for this device.
1274 Format: <start1>,<end1>,<start2>,<end2>...
1276 hardlockup_all_cpu_backtrace=
1277 [KNL] Should the hard-lockup detector generate
1278 backtraces on all cpus.
1281 hashdist= [KNL,NUMA] Large hashes allocated during boot
1282 are distributed across NUMA nodes. Defaults on
1283 for 64-bit NUMA, off otherwise.
1284 Format: 0 | 1 (for off | on)
1286 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1288 hd= [EIDE] (E)IDE hard drive subsystem geometry
1289 Format: <cyl>,<head>,<sect>
1292 Disable Hardware Error Source Table (HEST) support;
1293 corresponding firmware-first mode error processing
1294 logic will be disabled.
1296 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1297 size of <nn>. This works even on boxes that have no
1298 highmem otherwise. This also works to reduce highmem
1299 size on bigger boxes.
1301 highres= [KNL] Enable/disable high resolution timer mode.
1302 Valid parameters: "on", "off"
1306 See Documentation/isdn/README.HiSax.
1310 hpet= [X86-32,HPET] option to control HPET usage
1311 Format: { enable (default) | disable | force |
1313 disable: disable HPET and use PIT instead
1314 force: allow force enabled of undocumented chips (ICH4,
1316 verbose: show contents of HPET registers during setup
1318 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1319 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1321 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1322 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1323 On x86-64 and powerpc, this option can be specified
1324 multiple times interleaved with hugepages= to reserve
1325 huge pages of different sizes. Valid pages sizes on
1326 x86-64 are 2M (when the CPU supports "pse") and 1G
1327 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1329 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1330 terminal devices. Valid values: 0..8
1331 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1332 If specified, z/VM IUCV HVC accepts connections
1333 from listed z/VM user IDs only.
1335 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1336 hardware thread id mappings.
1337 Format: <cpu>:<hwthread>
1340 Do not unregister boot console at start. This is only
1341 useful for debugging when something happens in the window
1342 between unregistering the boot console and initializing
1345 i2c_bus= [HW] Override the default board specific I2C bus speed
1346 or register an additional I2C bus that is not
1347 registered from board initialization code.
1351 i8042.debug [HW] Toggle i8042 debug mode
1352 i8042.unmask_kbd_data
1353 [HW] Enable printing of interrupt data from the KBD port
1354 (disabled by default, and as a pre-condition
1355 requires that i8042.debug=1 be enabled)
1356 i8042.direct [HW] Put keyboard port into non-translated mode
1357 i8042.dumbkbd [HW] Pretend that controller can only read data from
1358 keyboard and cannot control its state
1359 (Don't attempt to blink the leds)
1360 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1361 i8042.nokbd [HW] Don't check/create keyboard port
1362 i8042.noloop [HW] Disable the AUX Loopback command while probing
1364 i8042.nomux [HW] Don't check presence of an active multiplexing
1366 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1368 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1369 i8042.reset [HW] Reset the controller during init, cleanup and
1370 suspend-to-ram transitions, only during s2r
1371 transitions, or never reset
1372 Format: { 1 | Y | y | 0 | N | n }
1373 1, Y, y: always reset controller
1374 0, N, n: don't ever reset controller
1375 Default: only on s2r transitions on x86; most other
1376 architectures force reset to be always executed
1377 i8042.unlock [HW] Unlock (ignore) the keylock
1378 i8042.kbdreset [HW] Reset device connected to KBD port
1382 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1383 indicates that the driver is running on unsupported
1385 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1386 does not match list of supported models.
1388 [HW] Report power status in /proc/i8k
1389 (disabled by default)
1390 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1393 i915.invert_brightness=
1394 [DRM] Invert the sense of the variable that is used to
1395 set the brightness of the panel backlight. Normally a
1396 brightness value of 0 indicates backlight switched off,
1397 and the maximum of the brightness value sets the backlight
1398 to maximum brightness. If this parameter is set to 0
1399 (default) and the machine requires it, or this parameter
1400 is set to 1, a brightness value of 0 sets the backlight
1401 to maximum brightness, and the maximum of the brightness
1402 value switches the backlight off.
1403 -1 -- never invert brightness
1404 0 -- machine default
1405 1 -- force brightness inversion
1408 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1410 ide-core.nodma= [HW] (E)IDE subsystem
1411 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1412 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1413 .cdrom .chs .ignore_cable are additional options
1414 See Documentation/ide/ide.txt.
1416 ide-generic.probe-mask= [HW] (E)IDE subsystem
1418 Probe mask for legacy ISA IDE ports. Depending on
1419 platform up to 6 ports are supported, enabled by
1420 setting corresponding bits in the mask to 1. The
1421 default value is 0x0, which has a special meaning.
1422 On systems that have PCI, it triggers scanning the
1423 PCI bus for the first and the second port, which
1424 are then probed. On systems without PCI the value
1425 of 0x0 enables probing the two first ports as if it
1428 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1429 Claim all unknown PCI IDE storage controllers.
1432 Format: idle=poll, idle=halt, idle=nomwait
1433 Poll forces a polling idle loop that can slightly
1434 improve the performance of waking up a idle CPU, but
1435 will use a lot of power and make the system run hot.
1437 idle=halt: Halt is forced to be used for CPU idle.
1438 In such case C2/C3 won't be used again.
1439 idle=nomwait: Disable mwait for CPU C-states
1441 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1442 Format: { strict | legacy | 2008 | relaxed }
1445 Choose which programs will be accepted for execution
1446 based on the IEEE 754 NaN encoding(s) supported by
1447 the FPU and the NaN encoding requested with the value
1448 of an ELF file header flag individually set by each
1449 binary. Hardware implementations are permitted to
1450 support either or both of the legacy and the 2008 NaN
1453 Available settings are as follows:
1454 strict accept binaries that request a NaN encoding
1455 supported by the FPU
1456 legacy only accept legacy-NaN binaries, if supported
1458 2008 only accept 2008-NaN binaries, if supported
1460 relaxed accept any binaries regardless of whether
1461 supported by the FPU
1463 The FPU emulator is always able to support both NaN
1464 encodings, so if no FPU hardware is present or it has
1465 been disabled with 'nofpu', then the settings of
1466 'legacy' and '2008' strap the emulator accordingly,
1467 'relaxed' straps the emulator for both legacy-NaN and
1468 2008-NaN, whereas 'strict' enables legacy-NaN only on
1469 legacy processors and both NaN encodings on MIPS32 or
1472 The setting for ABS.fmt/NEG.fmt instruction execution
1473 mode generally follows that for the NaN encoding,
1474 except where unsupported by hardware.
1476 ignore_loglevel [KNL]
1477 Ignore loglevel setting - this will print /all/
1478 kernel messages to the console. Useful for debugging.
1479 We also add it as printk module parameter, so users
1480 could change it dynamically, usually by
1481 /sys/module/printk/parameters/ignore_loglevel.
1484 Ignore RLIMIT_DATA setting for data mappings,
1485 print warning at first misuse. Can be changed via
1486 /sys/module/kernel/parameters/ignore_rlimit_data.
1488 ihash_entries= [KNL]
1489 Set number of hash buckets for inode cache.
1491 ima_appraise= [IMA] appraise integrity measurements
1492 Format: { "off" | "enforce" | "fix" | "log" }
1495 ima_appraise_tcb [IMA]
1496 The builtin appraise policy appraises all files
1499 ima_canonical_fmt [IMA]
1500 Use the canonical format for the binary runtime
1501 measurements, instead of host native format.
1504 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1508 The list of supported hash algorithms is defined
1509 in crypto/hash_info.h.
1512 The builtin policies to load during IMA setup.
1513 Format: "tcb | appraise_tcb | secure_boot"
1515 The "tcb" policy measures all programs exec'd, files
1516 mmap'd for exec, and all files opened with the read
1517 mode bit set by either the effective uid (euid=0) or
1520 The "appraise_tcb" policy appraises the integrity of
1521 all files owned by root. (This is the equivalent
1522 of ima_appraise_tcb.)
1524 The "secure_boot" policy appraises the integrity
1525 of files (eg. kexec kernel image, kernel modules,
1526 firmware, policy, etc) based on file signatures.
1528 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1529 Load a policy which meets the needs of the Trusted
1530 Computing Base. This means IMA will measure all
1531 programs exec'd, files mmap'd for exec, and all files
1532 opened for read by uid=0.
1535 Select one of defined IMA measurements template formats.
1536 Formats: { "ima" | "ima-ng" | "ima-sig" }
1540 [IMA] Define a custom template format.
1541 Format: { "field1|...|fieldN" }
1543 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1544 Format: <min_file_size>
1545 Set the minimal file size for using asynchronous hash.
1546 If left unspecified, ahash usage is disabled.
1548 ahash performance varies for different data sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve the best performance for a particular HW.
1552 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1554 Set hashing buffer size. Default: 4k.
1556 ahash performance varies for different chunk sizes on
1557 different crypto accelerators. This option can be used
1558 to achieve best performance for particular HW.
1562 Run specified binary instead of /sbin/init as init
1565 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1566 for working out where the kernel is dying during
1569 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1570 initcall functions. Useful for debugging built-in
1571 modules and initcalls.
1573 initrd= [BOOT] Specify the location of the initial ramdisk
1575 init_pkru= [x86] Specify the default memory protection keys rights
1576 register contents for all processes. 0x55555554 by
1577 default (disallow access to all but pkey 0). Can
1578 override in debugfs after boot.
1580 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1583 int_pln_enable [x86] Enable power limit notification interrupt
1585 integrity_audit=[IMA]
1586 Format: { "0" | "1" }
1587 0 -- basic integrity auditing messages. (Default)
1588 1 -- additional integrity auditing messages.
1590 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1592 Enable intel iommu driver.
1594 Disable intel iommu driver.
1595 igfx_off [Default Off]
1596 By default, gfx is mapped as normal device. If a gfx
1597 device has a dedicated DMAR unit, the DMAR unit is
1598 bypassed by not enabling DMAR with this option. In
1599 this case, gfx device will use physical address for
1602 With this option iommu will not optimize to look
1603 for io virtual address below 32-bit forcing dual
1604 address cycle on pci bus for cards supporting greater
1605 than 32-bit addressing. The default is to look
1606 for translation below 32-bit and if not available
1607 then look in the higher range.
1608 strict [Default Off]
1609 With this option on every unmap_single operation will
1610 result in a hardware IOTLB flush operation as opposed
1611 to batching them for performance.
1612 sp_off [Default Off]
1613 By default, super page will be supported if Intel IOMMU
1614 has the capability. With this option, super page will
1616 ecs_off [Default Off]
1617 By default, extended context tables will be supported if
1618 the hardware advertises that it has support both for the
1619 extended tables themselves, and also PASID support. With
1620 this option set, extended tables will not be used even
1621 on hardware which claims to support them.
1622 tboot_noforce [Default Off]
1623 Do not force the Intel IOMMU enabled under tboot.
1624 By default, tboot will force Intel IOMMU on, which
1625 could harm performance of some high-throughput
1626 devices like 40GBit network cards, even if identity
1628 Note that using this option lowers the security
1629 provided by tboot because it makes the system
1630 vulnerable to DMA attacks.
1632 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1633 0 disables intel_idle and fall back on acpi_idle.
1634 1 to 9 specify maximum depth of C-state.
1638 Do not enable intel_pstate as the default
1639 scaling driver for the supported processors
1641 Use intel_pstate as a scaling driver, but configure it
1642 to work with generic cpufreq governors (instead of
1643 enabling its internal governor). This mode cannot be
1644 used along with the hardware-managed P-states (HWP)
1647 Enable intel_pstate on systems that prohibit it by default
1648 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1649 instead of acpi-cpufreq may disable platform features, such
1650 as thermal controls and power capping, that rely on ACPI
1651 P-States information being indicated to OSPM and therefore
1652 should be used with caution. This option does not work with
1653 processors that aren't supported by the intel_pstate driver
1654 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1656 Do not enable hardware P state control (HWP)
1659 Only load intel_pstate on systems which support
1660 hardware P state control (HWP) if available.
1662 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1663 Description Table, specifies preferred power management
1664 profile as "Enterprise Server" or "Performance Server",
1665 then this feature is turned on by default.
1667 Allow per-logical-CPU P-State performance control limits using
1668 cpufreq sysfs interface
1670 intremap= [X86-64, Intel-IOMMU]
1671 on enable Interrupt Remapping (default)
1672 off disable Interrupt Remapping
1673 nosid disable Source ID checking
1675 BIOS x2APIC opt-out request will be ignored
1676 nopost disable Interrupt Posting
1678 iomem= Disable strict checking of access to MMIO memory
1679 strict regions from userspace.
1694 nobypass [PPC/POWERNV]
1695 Disable IOMMU bypass, using IOMMU for PCI devices.
1698 [ARM64] Configure DMA to bypass the IOMMU by default.
1699 Format: { "0" | "1" }
1700 0 - Use IOMMU translation for DMA.
1701 1 - Bypass the IOMMU for DMA.
1702 unset - Use IOMMU translation for DMA.
1704 io7= [HW] IO7 for Marvel based alpha systems
1705 See comment before marvel_specify_io7 in
1706 arch/alpha/kernel/core_marvel.c.
1708 io_delay= [X86] I/O delay method
1710 Standard port 0x80 based delay
1712 Alternate port 0xed based delay (needed on some systems)
1714 Simple two microseconds delay
1719 See Documentation/filesystems/nfs/nfsroot.txt.
1721 irqaffinity= [SMP] Set the default irq affinity mask
1722 The argument is a cpu list, as described above.
1725 When an interrupt is not handled search all handlers
1726 for it. Intended to get systems with badly broken
1730 When an interrupt is not handled search all handlers
1731 for it. Also check all handlers each timer
1732 interrupt. Intended to get systems with badly broken
1736 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1738 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1739 The argument is a cpu list, as described above.
1741 This option can be used to specify one or more CPUs
1742 to isolate from the general SMP balancing and scheduling
1743 algorithms. You can move a process onto or off an
1744 "isolated" CPU via the CPU affinity syscalls or cpuset.
1745 <cpu number> begins at 0 and the maximum value is
1746 "number of CPUs in system - 1".
1748 This option is the preferred way to isolate CPUs. The
1749 alternative -- manually setting the CPU mask of all
1750 tasks in the system -- can cause problems and
1751 suboptimal load balancer performance.
1755 ivrs_ioapic [HW,X86_64]
1756 Provide an override to the IOAPIC-ID<->DEVICE-ID
1757 mapping provided in the IVRS ACPI table. For
1758 example, to map IOAPIC-ID decimal 10 to
1759 PCI device 00:14.0 write the parameter as:
1760 ivrs_ioapic[10]=00:14.0
1762 ivrs_hpet [HW,X86_64]
1763 Provide an override to the HPET-ID<->DEVICE-ID
1764 mapping provided in the IVRS ACPI table. For
1765 example, to map HPET-ID decimal 0 to
1766 PCI device 00:14.0 write the parameter as:
1767 ivrs_hpet[0]=00:14.0
1769 ivrs_acpihid [HW,X86_64]
1770 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1771 mapping provided in the IVRS ACPI table. For
1772 example, to map UART-HID:UID AMD0020:0 to
1773 PCI device 00:14.5 write the parameter as:
1774 ivrs_acpihid[00:14.5]=AMD0020:0
1776 js= [HW,JOY] Analog joystick
1777 See Documentation/input/joystick.txt.
1780 When CONFIG_RANDOMIZE_BASE is set, this disables
1781 kernel and module base offset ASLR (Address Space
1782 Layout Randomization).
1785 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1786 report on every invalid memory access. Without this
1787 parameter KASAN will print report only for the first
1792 kernelcore= [KNL,X86,IA-64,PPC]
1793 Format: nn[KMGTPE] | "mirror"
1795 specifies the amount of memory usable by the kernel
1796 for non-movable allocations. The requested amount is
1797 spread evenly throughout all nodes in the system. The
1798 remaining memory in each node is used for Movable
1799 pages. In the event, a node is too small to have both
1800 kernelcore and Movable pages, kernelcore pages will
1801 take priority and other nodes will have a larger number
1802 of Movable pages. The Movable zone is used for the
1803 allocation of pages that may be reclaimed or moved
1804 by the page migration subsystem. This means that
1805 HugeTLB pages may not be allocated from this zone.
1806 Note that allocations like PTEs-from-HighMem still
1807 use the HighMem zone if it exists, and the Normal
1808 zone if it does not.
1810 Instead of specifying the amount of memory (nn[KMGTPE]),
1811 you can specify "mirror" option. In case "mirror"
1812 option is specified, mirrored (reliable) memory is used
1813 for non-movable allocations and remaining memory is used
1814 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1815 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1818 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1819 Format: <Controller#>[,poll interval]
1820 The controller # is the number of the ehci usb debug
1821 port as it is probed via PCI. The poll interval is
1822 optional and is the number seconds in between
1823 each poll cycle to the debug port in case you need
1824 the functionality for interrupting the kernel with
1825 gdb or control-c on the dbgp connection. When
1826 not using this parameter you use sysrq-g to break into
1827 the kernel debugger.
1829 kgdboc= [KGDB,HW] kgdb over consoles.
1830 Requires a tty driver that supports console polling,
1831 or a supported polling keyboard driver (non-usb).
1832 Serial only format: <serial_device>[,baud]
1833 keyboard only format: kbd
1834 keyboard and serial format: kbd,<serial_device>[,baud]
1835 Optional Kernel mode setting:
1836 kms, kbd format: kms,kbd
1837 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1839 kgdbwait [KGDB] Stop kernel execution and enter the
1840 kernel debugger at the earliest opportunity.
1842 kmac= [MIPS] korina ethernet MAC address.
1843 Configure the RouterBoard 532 series on-chip
1844 Ethernet adapter MAC address.
1846 kmemleak= [KNL] Boot-time kmemleak enable/disable
1847 Valid arguments: on, off
1849 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1852 kpti= [ARM64] Control page table isolation of user
1853 and kernel address spaces.
1854 Default: enabled on cores which need mitigation.
1858 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1859 Default is 0 (don't ignore, but inject #GP)
1861 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1866 [KVM] Controls the software workaround for the
1867 X86_BUG_ITLB_MULTIHIT bug.
1868 force : Always deploy workaround.
1869 off : Never deploy workaround.
1870 auto : Deploy workaround based on the presence of
1871 X86_BUG_ITLB_MULTIHIT.
1875 If the software workaround is enabled for the host,
1876 guests do need not to enable it for nested guests.
1878 kvm.nx_huge_pages_recovery_ratio=
1879 [KVM] Controls how many 4KiB pages are periodically zapped
1880 back to huge pages. 0 disables the recovery, otherwise if
1881 the value is N KVM will zap 1/Nth of the 4KiB pages every
1882 minute. The default is 60.
1884 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1885 Default is 1 (enabled)
1887 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1889 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1891 kvm-arm.vgic_v3_group0_trap=
1892 [KVM,ARM] Trap guest accesses to GICv3 group-0
1895 kvm-arm.vgic_v3_group1_trap=
1896 [KVM,ARM] Trap guest accesses to GICv3 group-1
1899 kvm-arm.vgic_v3_common_trap=
1900 [KVM,ARM] Trap guest accesses to GICv3 common
1903 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1904 (virtualized MMU) support on capable Intel chips.
1905 Default is 1 (enabled)
1907 kvm-intel.emulate_invalid_guest_state=
1908 [KVM,Intel] Disable emulation of invalid guest state.
1909 Ignored if kvm-intel.enable_unrestricted_guest=1, as
1910 guest state is never invalid for unrestricted guests.
1911 This param doesn't apply to nested guests (L2), as KVM
1912 never emulates invalid L2 guest state.
1913 Default is 1 (enabled)
1915 kvm-intel.flexpriority=
1916 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1917 Default is 1 (enabled)
1920 [KVM,Intel] Enable VMX nesting (nVMX).
1921 Default is 0 (disabled)
1923 kvm-intel.unrestricted_guest=
1924 [KVM,Intel] Disable unrestricted guest feature
1925 (virtualized real and unpaged mode) on capable
1926 Intel chips. Default is 1 (enabled)
1928 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1931 Valid arguments: never, cond, always
1933 always: L1D cache flush on every VMENTER.
1934 cond: Flush L1D on VMENTER only when the code between
1935 VMEXIT and VMENTER can leak host memory.
1936 never: Disables the mitigation
1938 Default is cond (do L1 cache flush in specific instances)
1940 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1941 feature (tagged TLBs) on capable Intel chips.
1942 Default is 1 (enabled)
1944 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1947 The kernel PTE inversion protection is unconditionally
1948 enabled and cannot be disabled.
1951 Provides all available mitigations for the
1952 L1TF vulnerability. Disables SMT and
1953 enables all mitigations in the
1954 hypervisors, i.e. unconditional L1D flush.
1956 SMT control and L1D flush control via the
1957 sysfs interface is still possible after
1958 boot. Hypervisors will issue a warning
1959 when the first VM is started in a
1960 potentially insecure configuration,
1961 i.e. SMT enabled or L1D flush disabled.
1964 Same as 'full', but disables SMT and L1D
1965 flush runtime control. Implies the
1966 'nosmt=force' command line option.
1967 (i.e. sysfs control of SMT is disabled.)
1970 Leaves SMT enabled and enables the default
1971 hypervisor mitigation, i.e. conditional
1974 SMT control and L1D flush control via the
1975 sysfs interface is still possible after
1976 boot. Hypervisors will issue a warning
1977 when the first VM is started in a
1978 potentially insecure configuration,
1979 i.e. SMT enabled or L1D flush disabled.
1983 Disables SMT and enables the default
1984 hypervisor mitigation.
1986 SMT control and L1D flush control via the
1987 sysfs interface is still possible after
1988 boot. Hypervisors will issue a warning
1989 when the first VM is started in a
1990 potentially insecure configuration,
1991 i.e. SMT enabled or L1D flush disabled.
1994 Same as 'flush', but hypervisors will not
1995 warn when a VM is started in a potentially
1996 insecure configuration.
1999 Disables hypervisor mitigations and doesn't
2001 It also drops the swap size and available
2002 RAM limit restriction on both hypervisor and
2007 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2013 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2016 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2017 value for LAPIC timer one-shot implementation. Default
2018 back to the programmable timer unit in the LAPIC.
2020 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2023 libata.dma= [LIBATA] DMA control
2024 libata.dma=0 Disable all PATA and SATA DMA
2025 libata.dma=1 PATA and SATA Disk DMA only
2026 libata.dma=2 ATAPI (CDROM) DMA only
2027 libata.dma=4 Compact Flash DMA only
2028 Combinations also work, so libata.dma=3 enables DMA
2029 for disks and CDROMs, but not CFs.
2031 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2032 libata.ignore_hpa=0 keep BIOS limits (default)
2033 libata.ignore_hpa=1 ignore limits, using full disk
2035 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2039 libata.force= [LIBATA] Force configurations. The format is comma
2040 separated list of "[ID:]VAL" where ID is
2041 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2042 matching port, link or device. Basically, it matches
2043 the ATA ID string printed on console by libata. If
2044 the whole ID part is omitted, the last PORT and DEVICE
2045 values are used. If ID hasn't been specified yet, the
2046 configuration applies to all ports, links and devices.
2048 If only DEVICE is omitted, the parameter applies to
2049 the port and all links and devices behind it. DEVICE
2050 number of 0 either selects the first device or the
2051 first fan-out link behind PMP device. It does not
2052 select the host link. DEVICE number of 15 selects the
2053 host link and device attached to it.
2055 The VAL specifies the configuration to force. As long
2056 as there's no ambiguity shortcut notation is allowed.
2057 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2058 The following configurations can be forced.
2060 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2061 Any ID with matching PORT is used.
2063 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2065 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2066 udma[/][16,25,33,44,66,100,133] notation is also
2069 * [no]ncq: Turn on or off NCQ.
2071 * [no]ncqtrim: Turn off queued DSM TRIM.
2073 * nohrst, nosrst, norst: suppress hard, soft
2076 * rstonce: only attempt one reset during
2077 hot-unplug link recovery
2079 * dump_id: dump IDENTIFY data.
2081 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2083 * disable: Disable this device.
2085 If there are multiple matching configurations changing
2086 the same attribute, the last one is used.
2088 memblock=debug [KNL] Enable memblock debug messages.
2090 load_ramdisk= [RAM] List of ramdisks to load from floppy
2091 See Documentation/blockdev/ramdisk.txt.
2093 lockd.nlm_grace_period=P [NFS] Assign grace period.
2096 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2099 lockd.nlm_timeout=T [NFS] Assign timeout value.
2102 lockd.nlm_udpport=M [NFS] Assign UDP port.
2105 locktorture.nreaders_stress= [KNL]
2106 Set the number of locking read-acquisition kthreads.
2107 Defaults to being automatically set based on the
2108 number of online CPUs.
2110 locktorture.nwriters_stress= [KNL]
2111 Set the number of locking write-acquisition kthreads.
2113 locktorture.onoff_holdoff= [KNL]
2114 Set time (s) after boot for CPU-hotplug testing.
2116 locktorture.onoff_interval= [KNL]
2117 Set time (s) between CPU-hotplug operations, or
2118 zero to disable CPU-hotplug testing.
2120 locktorture.shuffle_interval= [KNL]
2121 Set task-shuffle interval (jiffies). Shuffling
2122 tasks allows some CPUs to go into dyntick-idle
2123 mode during the locktorture test.
2125 locktorture.shutdown_secs= [KNL]
2126 Set time (s) after boot system shutdown. This
2127 is useful for hands-off automated testing.
2129 locktorture.stat_interval= [KNL]
2130 Time (s) between statistics printk()s.
2132 locktorture.stutter= [KNL]
2133 Time (s) to stutter testing, for example,
2134 specifying five seconds causes the test to run for
2135 five seconds, wait for five seconds, and so on.
2136 This tests the locking primitive's ability to
2137 transition abruptly to and from idle.
2139 locktorture.torture_runnable= [BOOT]
2140 Start locktorture running at boot time.
2142 locktorture.torture_type= [KNL]
2143 Specify the locking implementation to test.
2145 locktorture.verbose= [KNL]
2146 Enable additional printk() statements.
2148 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2151 loglevel= All Kernel Messages with a loglevel smaller than the
2152 console loglevel will be printed to the console. It can
2153 also be changed with klogd or other programs. The
2154 loglevels are defined as follows:
2156 0 (KERN_EMERG) system is unusable
2157 1 (KERN_ALERT) action must be taken immediately
2158 2 (KERN_CRIT) critical conditions
2159 3 (KERN_ERR) error conditions
2160 4 (KERN_WARNING) warning conditions
2161 5 (KERN_NOTICE) normal but significant condition
2162 6 (KERN_INFO) informational
2163 7 (KERN_DEBUG) debug-level messages
2165 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2166 in bytes. n must be a power of two and greater
2167 than the minimal size. The minimal size is defined
2168 by LOG_BUF_SHIFT kernel config parameter. There is
2169 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2170 that allows to increase the default size depending on
2171 the number of CPUs. See init/Kconfig for more details.
2173 logo.nologo [FB] Disables display of the built-in Linux logo.
2174 This may be used to provide more screen space for
2175 kernel log messages and is useful when debugging
2176 kernel boot problems.
2178 lp=0 [LP] Specify parallel ports to use, e.g,
2179 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2180 lp=reset first parallel port). 'lp=0' disables the
2181 lp=auto printer driver. 'lp=reset' (which can be
2182 specified in addition to the ports) causes
2183 attached printers to be reset. Using
2184 lp=port1,port2,... specifies the parallel ports
2185 to associate lp devices with, starting with
2186 lp0. A port specification may be 'none' to skip
2187 that lp device, or a parport name such as
2188 'parport0'. Specifying 'lp=auto' instead of a
2189 port specification list means that device IDs
2190 from each port should be examined, to see if
2191 an IEEE 1284-compliant printer is attached; if
2192 so, the driver will manage that printer.
2193 See also header of drivers/char/lp.c.
2196 Sets loops_per_jiffy to given constant, thus avoiding
2197 time-consuming boot-time autodetection (up to 250 ms per
2198 CPU). 0 enables autodetection (default). To determine
2199 the correct value for your kernel, boot with normal
2200 autodetection and see what value is printed. Note that
2201 on SMP systems the preset will be applied to all CPUs,
2202 which is likely to cause problems if your CPUs need
2203 significantly divergent settings. An incorrect value
2204 will cause delays in the kernel to be wrong, leading to
2205 unpredictable I/O errors and other breakage. Although
2206 unlikely, in the extreme case this might damage your
2210 Format: <io>,<irq>,<dma>
2212 machvec= [IA-64] Force the use of a particular machine-vector
2213 (machvec) in a generic kernel.
2214 Example: machvec=hpzx1_swiotlb
2216 machtype= [Loongson] Share the same kernel image file between different
2218 Example: machtype=lemote-yeeloong-2f-7inch
2220 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2221 than or equal to this physical address is ignored.
2223 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2224 will bring up during bootup. maxcpus=n : n >= 0 limits
2225 the kernel to bring up 'n' processors. Surely after
2226 bootup you can bring up the other plugged cpu by executing
2227 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2228 only takes effect during system bootup.
2229 While n=0 is a special case, it is equivalent to "nosmp",
2230 which also disables the IO APIC.
2232 max_loop= [LOOP] The number of loop block devices that get
2233 (loop.max_loop) unconditionally pre-created at init time. The default
2234 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2235 of statically allocating a predefined number, loop
2236 devices can be requested on-demand with the
2237 /dev/loop-control interface.
2239 mce [X86-32] Machine Check Exception
2241 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2243 md= [HW] RAID subsystems devices and level
2244 See Documentation/admin-guide/md.rst.
2247 Format: <first>,<last>
2248 Specifies range of consoles to be captured by the MDA.
2251 Control mitigation for the Micro-architectural Data
2252 Sampling (MDS) vulnerability.
2254 Certain CPUs are vulnerable to an exploit against CPU
2255 internal buffers which can forward information to a
2256 disclosure gadget under certain conditions.
2258 In vulnerable processors, the speculatively
2259 forwarded data can be used in a cache side channel
2260 attack, to access data to which the attacker does
2261 not have direct access.
2263 This parameter controls the MDS mitigation. The
2266 full - Enable MDS mitigation on vulnerable CPUs
2267 full,nosmt - Enable MDS mitigation and disable
2268 SMT on vulnerable CPUs
2269 off - Unconditionally disable MDS mitigation
2271 On TAA-affected machines, mds=off can be prevented by
2272 an active TAA mitigation as both vulnerabilities are
2273 mitigated with the same mechanism so in order to disable
2274 this mitigation, you need to specify tsx_async_abort=off
2277 Not specifying this option is equivalent to
2280 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2282 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2283 Amount of memory to be used when the kernel is not able
2284 to see the whole system memory or for test.
2285 [X86] Work as limiting max address. Use together
2286 with memmap= to avoid physical address space collisions.
2287 Without memmap= PCI devices could be placed at addresses
2288 belonging to unused RAM.
2290 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2294 [KNL,SH] Allow user to override the default size for
2295 per-device physically contiguous DMA buffers.
2297 memhp_default_state=online/offline
2298 [KNL] Set the initial state for the memory hotplug
2299 onlining policy. If not specified, the default value is
2300 set according to the
2301 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2303 See Documentation/memory-hotplug.txt.
2305 memmap=exactmap [KNL,X86] Enable setting of an exact
2306 E820 memory map, as specified by the user.
2307 Such memmap=exactmap lines can be constructed based on
2308 BIOS output or other requirements. See the memmap=nn@ss
2311 memmap=nn[KMG]@ss[KMG]
2312 [KNL] Force usage of a specific region of memory.
2313 Region of memory to be used is from ss to ss+nn.
2314 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2315 which limits max address to nn[KMG].
2316 Multiple different regions can be specified,
2319 memmap=100M@2G,100M#3G,1G!1024G
2321 memmap=nn[KMG]#ss[KMG]
2322 [KNL,ACPI] Mark specific memory as ACPI data.
2323 Region of memory to be marked is from ss to ss+nn.
2325 memmap=nn[KMG]$ss[KMG]
2326 [KNL,ACPI] Mark specific memory as reserved.
2327 Region of memory to be reserved is from ss to ss+nn.
2328 Example: Exclude memory from 0x18690000-0x1869ffff
2329 memmap=64K$0x18690000
2331 memmap=0x10000$0x18690000
2332 Some bootloaders may need an escape character before '$',
2333 like Grub2, otherwise '$' and the following number
2336 memmap=nn[KMG]!ss[KMG]
2337 [KNL,X86] Mark specific memory as protected.
2338 Region of memory to be used, from ss to ss+nn.
2339 The memory region may be marked as e820 type 12 (0xc)
2340 and is NVDIMM or ADR memory.
2342 memory_corruption_check=0/1 [X86]
2343 Some BIOSes seem to corrupt the first 64k of
2344 memory when doing things like suspend/resume.
2345 Setting this option will scan the memory
2346 looking for corruption. Enabling this will
2347 both detect corruption and prevent the kernel
2348 from using the memory being corrupted.
2349 However, its intended as a diagnostic tool; if
2350 repeatable BIOS-originated corruption always
2351 affects the same memory, you can use memmap=
2352 to prevent the kernel from using that memory.
2354 memory_corruption_check_size=size [X86]
2355 By default it checks for corruption in the low
2356 64k, making this memory unavailable for normal
2357 use. Use this parameter to scan for
2358 corruption in more or less memory.
2360 memory_corruption_check_period=seconds [X86]
2361 By default it checks for corruption every 60
2362 seconds. Use this parameter to check at some
2363 other rate. 0 disables periodic checking.
2365 memtest= [KNL,X86,ARM] Enable memtest
2367 default : 0 <disable>
2368 Specifies the number of memtest passes to be
2369 performed. Each pass selects another test
2370 pattern from a given set of patterns. Memtest
2371 fills the memory with this pattern, validates
2372 memory contents and reserves bad memory
2373 regions that are detected.
2375 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2376 Valid arguments: on, off
2377 Default (depends on kernel configuration option):
2378 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2379 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2380 mem_encrypt=on: Activate SME
2381 mem_encrypt=off: Do not activate SME
2383 Refer to Documentation/x86/amd-memory-encryption.txt
2384 for details on when memory encryption can be activated.
2386 mem_sleep_default= [SUSPEND] Default system suspend mode:
2387 s2idle - Suspend-To-Idle
2388 shallow - Power-On Suspend or equivalent (if supported)
2389 deep - Suspend-To-RAM or equivalent (if supported)
2390 See Documentation/power/states.txt.
2392 meye.*= [HW] Set MotionEye Camera parameters
2393 See Documentation/video4linux/meye.txt.
2395 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2396 Multi-Function General Purpose Timers on AMD Geode
2399 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2400 the BIOS has incorrectly applied a workaround. TinyBIOS
2401 version 0.98 is known to be affected, 0.99 fixes the
2402 problem by letting the user disable the workaround.
2406 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2407 physical address is ignored.
2409 mini2440= [ARM,HW,KNL]
2410 Format:[0..2][b][c][t]
2412 MINI2440 configuration specification:
2413 0 - The attached screen is the 3.5" TFT
2414 1 - The attached screen is the 7" TFT
2415 2 - The VGA Shield is attached (1024x768)
2416 Leaving out the screen size parameter will not load
2417 the TFT driver, and the framebuffer will be left
2419 b - Enable backlight. The TFT backlight pin will be
2420 linked to the kernel VESA blanking code and a GPIO
2421 LED. This parameter is not necessary when using the
2423 c - Enable the s3c camera interface.
2424 t - Reserved for enabling touchscreen support. The
2425 touchscreen support is not enabled in the mainstream
2426 kernel as of 2.6.30, a preliminary port can be found
2427 in the "bleeding edge" mini2440 support kernel at
2428 http://repo.or.cz/w/linux-2.6/mini2440.git
2431 [X86,PPC,S390,ARM64] Control optional mitigations for
2432 CPU vulnerabilities. This is a set of curated,
2433 arch-independent options, each of which is an
2434 aggregation of existing arch-specific options.
2437 Disable all optional CPU mitigations. This
2438 improves system performance, but it may also
2439 expose users to several CPU vulnerabilities.
2440 Equivalent to: nopti [X86,PPC]
2445 nospectre_v2 [X86,PPC,S390,ARM64]
2446 spectre_v2_user=off [X86]
2447 spec_store_bypass_disable=off [X86,PPC]
2448 ssbd=force-off [ARM64]
2451 tsx_async_abort=off [X86]
2452 kvm.nx_huge_pages=off [X86]
2453 no_entry_flush [PPC]
2454 no_uaccess_flush [PPC]
2455 mmio_stale_data=off [X86]
2458 This does not have any effect on
2459 kvm.nx_huge_pages when
2460 kvm.nx_huge_pages=force.
2463 Mitigate all CPU vulnerabilities, but leave SMT
2464 enabled, even if it's vulnerable. This is for
2465 users who don't want to be surprised by SMT
2466 getting disabled across kernel upgrades, or who
2467 have other ways of avoiding SMT-based attacks.
2468 Equivalent to: (default behavior)
2471 Mitigate all CPU vulnerabilities, disabling SMT
2472 if needed. This is for users who always want to
2473 be fully mitigated, even if it means losing SMT.
2474 Equivalent to: l1tf=flush,nosmt [X86]
2475 mds=full,nosmt [X86]
2476 tsx_async_abort=full,nosmt [X86]
2477 mmio_stale_data=full,nosmt [X86]
2480 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2481 parameter allows control of the logging verbosity for
2482 the additional memory initialisation checks. A value
2483 of 0 disables mminit logging and a level of 4 will
2484 log everything. Information is printed at KERN_DEBUG
2485 so loglevel=8 may also need to be specified.
2488 [X86,INTEL] Control mitigation for the Processor
2489 MMIO Stale Data vulnerabilities.
2491 Processor MMIO Stale Data is a class of
2492 vulnerabilities that may expose data after an MMIO
2493 operation. Exposed data could originate or end in
2494 the same CPU buffers as affected by MDS and TAA.
2495 Therefore, similar to MDS and TAA, the mitigation
2496 is to clear the affected CPU buffers.
2498 This parameter controls the mitigation. The
2501 full - Enable mitigation on vulnerable CPUs
2503 full,nosmt - Enable mitigation and disable SMT on
2506 off - Unconditionally disable mitigation
2508 On MDS or TAA affected machines,
2509 mmio_stale_data=off can be prevented by an active
2510 MDS or TAA mitigation as these vulnerabilities are
2511 mitigated with the same mechanism so in order to
2512 disable this mitigation, you need to specify
2513 mds=off and tsx_async_abort=off too.
2515 Not specifying this option is equivalent to
2516 mmio_stale_data=full.
2519 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
2522 [KNL] When CONFIG_MODULE_SIG is set, this means that
2523 modules without (valid) signatures will fail to load.
2524 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2525 is always true, so this option does nothing.
2527 module_blacklist= [KNL] Do not load a comma-separated list of
2528 modules. Useful for debugging problem modules.
2531 [MOUSE] Maximum time between finger touching and
2532 leaving touchpad surface for touch to be considered
2533 a tap and be reported as a left button click (for
2534 touchpads working in absolute mode only).
2536 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2537 reporting absolute coordinates, such as tablets
2538 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2539 reporting absolute coordinates, such as tablets
2541 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2542 is similar to kernelcore except it specifies the
2543 amount of memory used for migratable allocations.
2544 If both kernelcore and movablecore is specified,
2545 then kernelcore will be at *least* the specified
2546 value but may be more. If movablecore on its own
2547 is specified, the administrator must be careful
2548 that the amount of memory usable for all allocations
2551 movable_node [KNL] Boot-time switch to make hotplugable memory
2552 NUMA nodes to be movable. This means that the memory
2553 of such nodes will be usable only for movable
2554 allocations which rules out almost all kernel
2555 allocations. Use with caution!
2557 MTD_Partition= [MTD]
2558 Format: <name>,<region-number>,<size>,<offset>
2560 MTD_Region= [MTD] Format:
2561 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2564 See drivers/mtd/cmdlinepart.c.
2566 multitce=off [PPC] This parameter disables the use of the pSeries
2567 firmware feature for updating multiple TCE entries
2570 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2572 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2574 boundary - index of last SLC block on Flex-OneNAND.
2575 The remaining blocks are configured as MLC blocks.
2576 lock - Configure if Flex-OneNAND boundary should be locked.
2577 Once locked, the boundary cannot be changed.
2578 1 indicates lock status, 0 indicates unlock status.
2581 ARM/S3C2412 JIVE boot control
2583 See arch/arm/mach-s3c2412/mach-jive.c
2585 mtouchusb.raw_coordinates=
2586 [HW] Make the MicroTouch USB driver use raw coordinates
2587 ('y', default) or cooked coordinates ('n')
2589 mtrr_chunk_size=nn[KMG] [X86]
2590 used for mtrr cleanup. It is largest continuous chunk
2591 that could hold holes aka. UC entries.
2593 mtrr_gran_size=nn[KMG] [X86]
2594 Used for mtrr cleanup. It is granularity of mtrr block.
2596 Large value could prevent small alignment from
2599 mtrr_spare_reg_nr=n [X86]
2601 Range: 0,7 : spare reg number
2603 Used for mtrr cleanup. It is spare mtrr entries number.
2604 Set to 2 or more if your graphical card needs more.
2606 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2608 netdev= [NET] Network devices parameters
2609 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2610 Note that mem_start is often overloaded to mean
2611 something different and driver-specific.
2612 This usage is only documented in each driver source
2616 [NETFILTER] Enable connection tracking flow accounting
2617 0 to disable accounting
2618 1 to enable accounting
2621 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2622 See Documentation/filesystems/nfs/nfsroot.txt.
2624 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2625 See Documentation/filesystems/nfs/nfsroot.txt.
2627 nfsrootdebug [NFS] enable nfsroot debugging messages.
2628 See Documentation/filesystems/nfs/nfsroot.txt.
2630 nfs.callback_nr_threads=
2631 [NFSv4] set the total number of threads that the
2632 NFS client will assign to service NFSv4 callback
2635 nfs.callback_tcpport=
2636 [NFS] set the TCP port on which the NFSv4 callback
2637 channel should listen.
2640 [NFS] sets the pathname to the program which is used
2641 to update the NFS client cache entries.
2643 nfs.cache_getent_timeout=
2644 [NFS] sets the timeout after which an attempt to
2645 update a cache entry is deemed to have failed.
2647 nfs.idmap_cache_timeout=
2648 [NFS] set the maximum lifetime for idmapper cache
2652 [NFS] enable 64-bit inode numbers.
2653 If zero, the NFS client will fake up a 32-bit inode
2654 number for the readdir() and stat() syscalls instead
2655 of returning the full 64-bit number.
2656 The default is to return 64-bit inode numbers.
2658 nfs.max_session_cb_slots=
2659 [NFSv4.1] Sets the maximum number of session
2660 slots the client will assign to the callback
2661 channel. This determines the maximum number of
2662 callbacks the client will process in parallel for
2663 a particular server.
2665 nfs.max_session_slots=
2666 [NFSv4.1] Sets the maximum number of session slots
2667 the client will attempt to negotiate with the server.
2668 This limits the number of simultaneous RPC requests
2669 that the client can send to the NFSv4.1 server.
2670 Note that there is little point in setting this
2671 value higher than the max_tcp_slot_table_limit.
2673 nfs.nfs4_disable_idmapping=
2674 [NFSv4] When set to the default of '1', this option
2675 ensures that both the RPC level authentication
2676 scheme and the NFS level operations agree to use
2677 numeric uids/gids if the mount is using the
2678 'sec=sys' security flavour. In effect it is
2679 disabling idmapping, which can make migration from
2680 legacy NFSv2/v3 systems to NFSv4 easier.
2681 Servers that do not support this mode of operation
2682 will be autodetected by the client, and it will fall
2683 back to using the idmapper.
2684 To turn off this behaviour, set the value to '0'.
2686 [NFS4] Specify an additional fixed unique ident-
2687 ification string that NFSv4 clients can insert into
2688 their nfs_client_id4 string. This is typically a
2689 UUID that is generated at system install time.
2691 nfs.send_implementation_id =
2692 [NFSv4.1] Send client implementation identification
2693 information in exchange_id requests.
2694 If zero, no implementation identification information
2696 The default is to send the implementation identification
2699 nfs.recover_lost_locks =
2700 [NFSv4] Attempt to recover locks that were lost due
2701 to a lease timeout on the server. Please note that
2702 doing this risks data corruption, since there are
2703 no guarantees that the file will remain unchanged
2704 after the locks are lost.
2705 If you want to enable the kernel legacy behaviour of
2706 attempting to recover these locks, then set this
2708 The default parameter value of '0' causes the kernel
2709 not to attempt recovery of lost locks.
2711 nfs4.layoutstats_timer =
2712 [NFSv4.2] Change the rate at which the kernel sends
2713 layoutstats to the pNFS metadata server.
2715 Setting this to value to 0 causes the kernel to use
2716 whatever value is the default set by the layout
2717 driver. A non-zero value sets the minimum interval
2718 in seconds between layoutstats transmissions.
2720 nfsd.nfs4_disable_idmapping=
2721 [NFSv4] When set to the default of '1', the NFSv4
2722 server will return only numeric uids and gids to
2723 clients using auth_sys, and will accept numeric uids
2724 and gids from such clients. This is intended to ease
2725 migration from NFSv2/v3.
2727 nmi_debug= [KNL,SH] Specify one or more actions to take
2728 when a NMI is triggered.
2729 Format: [state][,regs][,debounce][,die]
2731 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2732 Format: [panic,][nopanic,][num]
2734 0 - turn hardlockup detector in nmi_watchdog off
2735 1 - turn hardlockup detector in nmi_watchdog on
2736 When panic is specified, panic when an NMI watchdog
2737 timeout occurs (or 'nopanic' to override the opposite
2738 default). To disable both hard and soft lockup detectors,
2739 please see 'nowatchdog'.
2740 This is useful when you use a panic=... timeout and
2741 need the box quickly up again.
2743 netpoll.carrier_timeout=
2744 [NET] Specifies amount of time (in seconds) that
2745 netpoll should wait for a carrier. By default netpoll
2748 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2749 emulation library even if a 387 maths coprocessor
2753 [HW] Never suspend the console
2754 Disable suspending of consoles during suspend and
2755 hibernate operations. Once disabled, debugging
2756 messages can reach various consoles while the rest
2757 of the system is being put to sleep (ie, while
2758 debugging driver suspend/resume hooks). This may
2759 not work reliably with all consoles, but is known
2760 to work with serial and VGA consoles.
2761 To facilitate more flexible debugging, we also add
2762 console_suspend, a printk module parameter to control
2763 it. Users could use console_suspend (usually
2764 /sys/module/printk/parameters/console_suspend) to
2765 turn on/off it dynamically.
2767 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2768 caches in the slab allocator. Saves per-node memory,
2769 but will impact performance.
2773 noaltinstr [S390] Disables alternative instructions patching
2774 (CPU alternatives feature).
2776 noapic [SMP,APIC] Tells the kernel to not make use of any
2777 IOAPICs that may be present in the system.
2779 noautogroup Disable scheduler automatic task group creation.
2781 nobats [PPC] Do not use BATs for mapping kernel lowmem
2782 on "Classic" PPC cores.
2786 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2788 nodelayacct [KNL] Disable per-task delay accounting
2790 nodsp [SH] Disable hardware DSP at boot time.
2792 noefi Disable EFI runtime services support.
2794 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
2799 On X86-32 available only on PAE configured kernels.
2800 noexec=on: enable non-executable mappings (default)
2801 noexec=off: disable non-executable mappings
2804 Disable SMAP (Supervisor Mode Access Prevention)
2805 even if it is supported by processor.
2808 Disable SMEP (Supervisor Mode Execution Prevention)
2809 even if it is supported by processor.
2812 This affects only 32-bit executables.
2813 noexec32=on: enable non-executable mappings (default)
2814 read doesn't imply executable mappings
2815 noexec32=off: disable non-executable mappings
2816 read implies executable mappings
2818 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2820 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2821 register save and restore. The kernel will only save
2822 legacy floating-point registers on task switch.
2824 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2826 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2827 Equivalent to smt=1.
2829 [KNL,x86] Disable symmetric multithreading (SMT).
2830 nosmt=force: Force disable SMT, cannot be undone
2831 via the sysfs control file.
2833 nospectre_v1 [X66, PPC] Disable mitigations for Spectre Variant 1
2834 (bounds check bypass). With this option data leaks
2835 are possible in the system.
2837 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2838 the Spectre variant 2 (indirect branch prediction)
2839 vulnerability. System may allow data leaks with this
2842 nospec_store_bypass_disable
2843 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2846 [PPC] Don't flush the L1-D cache after accessing user data.
2848 noxsave [BUGS=X86] Disables x86 extended register state save
2849 and restore using xsave. The kernel will fallback to
2850 enabling legacy floating-point and sse state.
2852 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2853 register states. The kernel will fall back to use
2854 xsave to save the states. By using this parameter,
2855 performance of saving the states is degraded because
2856 xsave doesn't support modified optimization while
2857 xsaveopt supports it on xsaveopt enabled systems.
2859 noxsaves [X86] Disables xsaves and xrstors used in saving and
2860 restoring x86 extended register state in compacted
2861 form of xsave area. The kernel will fall back to use
2862 xsaveopt and xrstor to save and restore the states
2863 in standard form of xsave area. By using this
2864 parameter, xsave area per process might occupy more
2865 memory on xsaves enabled systems.
2867 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2868 wfi(ARM) instruction doesn't work correctly and not to
2869 use it. This is also useful when using JTAG debugger.
2871 no_file_caps Tells the kernel not to honor file capabilities. The
2872 only way then for a file to be executed with privilege
2873 is to be setuid root or executed by root.
2875 nohalt [IA-64] Tells the kernel not to use the power saving
2876 function PAL_HALT_LIGHT when idle. This increases
2877 power-consumption. On the positive side, it reduces
2878 interrupt wake-up latency, which may improve performance
2879 in certain environments such as networked servers or
2882 nohibernate [HIBERNATION] Disable hibernation and resume.
2884 nohz= [KNL] Boottime enable/disable dynamic ticks
2885 Valid arguments: on, off
2888 nohz_full= [KNL,BOOT]
2889 The argument is a cpu list, as described above.
2890 In kernels built with CONFIG_NO_HZ_FULL=y, set
2891 the specified list of CPUs whose tick will be stopped
2892 whenever possible. The boot CPU will be forced outside
2893 the range to maintain the timekeeping. Any CPUs
2894 in this list will have their RCU callbacks offloaded,
2895 just as if they had also been called out in the
2896 rcu_nocbs= boot parameter.
2898 noiotrap [SH] Disables trapped I/O port accesses.
2900 noirqdebug [X86-32] Disables the code which attempts to detect and
2901 disable unhandled interrupt sources.
2903 no_timer_check [X86,APIC] Disables the code which tests for
2904 broken timer IRQ sources.
2906 noisapnp [ISAPNP] Disables ISA PnP code.
2908 noinitrd [RAM] Tells the kernel not to load any configured
2911 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2913 [Deprecated - use intremap=off]
2917 noinvpcid [X86] Disable the INVPCID cpu feature.
2919 nojitter [IA-64] Disables jitter checking for ITC timers.
2921 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2923 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2927 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2928 clock and use the default one.
2930 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2931 steal time is computed, but won't influence scheduler
2934 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2936 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2938 noltlbs [PPC] Do not use large page/tlb entries for kernel
2939 lowmem mapping on PPC40x and PPC8xx
2941 nomca [IA-64] Disable machine check abort handling
2943 nomce [X86-32] Disable Machine Check Exception
2945 nomfgpt [X86-32] Disable Multi-Function General Purpose
2946 Timer usage (for AMD Geode machines).
2948 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2949 shutdown the other cpus. Instead use the REBOOT_VECTOR
2952 nomodule Disable module load
2954 nopat [X86] Disable PAT (page attribute table extension of
2955 pagetables) support.
2957 nopcid [X86-64] Disable the PCID cpu feature.
2959 norandmaps Don't use address space randomization. Equivalent to
2960 echo 0 > /proc/sys/kernel/randomize_va_space
2962 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2963 with UP alternatives
2965 nordrand [X86] Disable kernel use of the RDRAND and
2966 RDSEED instructions even if they are supported
2967 by the processor. RDRAND and RDSEED are still
2968 available to user space applications.
2970 noresume [SWSUSP] Disables resume and restores original swap
2973 no-scroll [VGA] Disables scrollback.
2974 This is required for the Braillex ib80-piezo Braille
2975 reader made by F.H. Papenmeier (Germany).
2979 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2981 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2982 and disable the IO APIC. legacy for "maxcpus=0".
2984 nosoftlockup [KNL] Disable the soft-lockup detector.
2986 nosync [HW,M68K] Disables sync negotiation for all devices.
2988 notsc [BUGS=X86-32] Disable Time Stamp Counter
2990 nowatchdog [KNL] Disable both lockup detectors, i.e.
2991 soft-lockup and NMI watchdog (hard-lockup).
2995 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2997 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2998 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2999 Some features depend on CPU0. Known dependencies are:
3000 1. Resume from suspend/hibernate depends on CPU0.
3001 Suspend/hibernate will fail if CPU0 is offline and you
3002 need to online CPU0 before suspend/hibernate.
3003 2. PIC interrupts also depend on CPU0. CPU0 can't be
3004 removed if a PIC interrupt is detected.
3005 It's said poweroff/reboot may depend on CPU0 on some
3006 machines although I haven't seen such issues so far
3007 after CPU0 is offline on a few tested machines.
3008 If the dependencies are under your control, you can
3009 turn on cpu0_hotplug.
3011 nps_mtm_hs_ctr= [KNL,ARC]
3012 This parameter sets the maximum duration, in
3013 cycles, each HW thread of the CTOP can run
3014 without interruptions, before HW switches it.
3015 The actual maximum duration is 16 times this
3017 Format: integer between 1 and 255
3020 nptcg= [IA-64] Override max number of concurrent global TLB
3021 purges which is reported from either PAL_VM_SUMMARY or
3024 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3025 could support. nr_cpus=n : n >= 1 limits the kernel to
3026 support 'n' processors. It could be larger than the
3027 number of already plugged CPU during bootup, later in
3028 runtime you can physically add extra cpu until it reaches
3029 n. So during boot up some boot time memory for per-cpu
3030 variables need be pre-allocated for later physical cpu
3033 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3035 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3036 Allowed values are enable and disable
3038 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3039 'node', 'default' can be specified
3040 This can be set from sysctl after boot.
3041 See Documentation/sysctl/vm.txt for details.
3043 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3044 See Documentation/debugging-via-ohci1394.txt for more
3047 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3048 Rather than timing out after 20 ms if an EC
3049 command is not properly ACKed, override the length
3050 of the timeout. We have interrupts disabled while
3051 waiting for the ACK, so if this is set too high
3052 interrupts *may* be lost!
3054 omap_mux= [OMAP] Override bootloader pin multiplexing.
3055 Format: <mux_mode0.mode_name=value>...
3056 For example, to override I2C bus2:
3057 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3059 oprofile.timer= [HW]
3060 Use timer interrupt instead of performance counters
3062 oprofile.cpu_type= Force an oprofile cpu type
3063 This might be useful if you have an older oprofile
3064 userland or if you want common events.
3065 Format: { arch_perfmon }
3066 arch_perfmon: [X86] Force use of architectural
3067 perfmon on Intel CPUs instead of the
3068 CPU specific event set.
3069 timer: [X86] Force use of architectural NMI
3070 timer mode (see also oprofile.timer
3071 for generic hr timer mode)
3073 oops=panic Always panic on oopses. Default is to just kill the
3074 process, but there is a small probability of
3075 deadlocking the machine.
3076 This will also cause panics on machine check exceptions.
3077 Useful together with panic=30 to trigger a reboot.
3080 See Documentation/sound/oss/oss-parameters.txt
3082 page_owner= [KNL] Boot-time page_owner enabling option.
3083 Storage of the information about who allocated
3084 each page is disabled in default. With this switch,
3086 on: enable the feature
3088 page_poison= [KNL] Boot-time parameter changing the state of
3089 poisoning on the buddy allocator.
3090 off: turn off poisoning
3091 on: turn on poisoning
3093 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3094 timeout > 0: seconds before rebooting
3095 timeout = 0: wait forever
3096 timeout < 0: reboot immediately
3099 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3102 crash_kexec_post_notifiers
3103 Run kdump after running panic-notifiers and dumping
3104 kmsg. This only for the users who doubt kdump always
3105 succeeds in any situation.
3106 Note that this also increases risks of kdump failure,
3107 because some panic notifiers can make the crashed
3108 kernel more unstable.
3110 parkbd.port= [HW] Parallel port number the keyboard adapter is
3111 connected to, default is 0.
3113 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3114 0 for XT, 1 for AT (default is AT).
3117 parport= [HW,PPT] Specify parallel ports. 0 disables.
3118 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3119 Use 'auto' to force the driver to use any
3120 IRQ/DMA settings detected (the default is to
3121 ignore detected IRQ/DMA settings because of
3122 possible conflicts). You can specify the base
3123 address, IRQ, and DMA settings; IRQ and DMA
3124 should be numbers, or 'auto' (for using detected
3125 settings on that particular port), or 'nofifo'
3126 (to avoid using a FIFO even if it is detected).
3127 Parallel ports are assigned in the order they
3128 are specified on the command line, starting
3131 parport_init_mode= [HW,PPT]
3132 Configure VIA parallel port to operate in
3133 a specific mode. This is necessary on Pegasos
3134 computer where firmware has no options for setting
3135 up parallel port mode and sets it to spp.
3136 Currently this function knows 686a and 8231 chips.
3137 Format: [spp|ps2|epp|ecp|ecpepp]
3140 Halt all CPUs after the first oops has been printed for
3141 the specified number of seconds. This is to be used if
3142 your oopses keep scrolling off the screen.
3147 See header of drivers/block/paride/pcd.c.
3148 See also Documentation/blockdev/paride.txt.
3150 pci=option[,option...] [PCI] various PCI subsystem options:
3151 earlydump [X86] dump PCI config space before the kernel
3153 off [X86] don't probe for the PCI bus
3154 bios [X86-32] force use of PCI BIOS, don't access
3155 the hardware directly. Use this if your machine
3156 has a non-standard PCI host bridge.
3157 nobios [X86-32] disallow use of PCI BIOS, only direct
3158 hardware access methods are allowed. Use this
3159 if you experience crashes upon bootup and you
3160 suspect they are caused by the BIOS.
3161 conf1 [X86] Force use of PCI Configuration Access
3162 Mechanism 1 (config address in IO port 0xCF8,
3163 data in IO port 0xCFC, both 32-bit).
3164 conf2 [X86] Force use of PCI Configuration Access
3165 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3166 the function, IO port 0xCFA, also 8-bit, sets
3167 bus number. The config space is then accessed
3168 through ports 0xC000-0xCFFF).
3169 See http://wiki.osdev.org/PCI for more info
3170 on the configuration access mechanisms.
3171 noaer [PCIE] If the PCIEAER kernel config parameter is
3172 enabled, this kernel boot option can be used to
3173 disable the use of PCIE advanced error reporting.
3174 nodomains [PCI] Disable support for multiple PCI
3175 root domains (aka PCI segments, in ACPI-speak).
3176 nommconf [X86] Disable use of MMCONFIG for PCI
3178 check_enable_amd_mmconf [X86] check for and enable
3179 properly configured MMIO access to PCI
3180 config space on AMD family 10h CPU
3181 nomsi [MSI] If the PCI_MSI kernel config parameter is
3182 enabled, this kernel boot option can be used to
3183 disable the use of MSI interrupts system-wide.
3184 noioapicquirk [APIC] Disable all boot interrupt quirks.
3185 Safety option to keep boot IRQs enabled. This
3186 should never be necessary.
3187 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3188 primary IO-APIC for bridges that cannot disable
3189 boot IRQs. This fixes a source of spurious IRQs
3190 when the system masks IRQs.
3191 noioapicreroute [APIC] Disable workaround that uses the
3192 boot IRQ equivalent of an IRQ that connects to
3193 a chipset where boot IRQs cannot be disabled.
3194 The opposite of ioapicreroute.
3195 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3196 routing table. These calls are known to be buggy
3197 on several machines and they hang the machine
3198 when used, but on other computers it's the only
3199 way to get the interrupt routing table. Try
3200 this option if the kernel is unable to allocate
3201 IRQs or discover secondary PCI buses on your
3203 rom [X86] Assign address space to expansion ROMs.
3204 Use with caution as certain devices share
3205 address decoders between ROMs and other
3207 norom [X86] Do not assign address space to
3208 expansion ROMs that do not already have
3209 BIOS assigned address ranges.
3210 nobar [X86] Do not assign address space to the
3211 BARs that weren't assigned by the BIOS.
3212 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3213 assigned automatically to PCI devices. You can
3214 make the kernel exclude IRQs of your ISA cards
3216 pirqaddr=0xAAAAA [X86] Specify the physical address
3217 of the PIRQ table (normally generated
3218 by the BIOS) if it is outside the
3219 F0000h-100000h range.
3220 lastbus=N [X86] Scan all buses thru bus #N. Can be
3221 useful if the kernel is unable to find your
3222 secondary buses and you want to tell it
3223 explicitly which ones they are.
3224 assign-busses [X86] Always assign all PCI bus
3225 numbers ourselves, overriding
3226 whatever the firmware may have done.
3227 usepirqmask [X86] Honor the possible IRQ mask stored
3228 in the BIOS $PIR table. This is needed on
3229 some systems with broken BIOSes, notably
3230 some HP Pavilion N5400 and Omnibook XE3
3231 notebooks. This will have no effect if ACPI
3232 IRQ routing is enabled.
3233 noacpi [X86] Do not use ACPI for IRQ routing
3234 or for PCI scanning.
3235 use_crs [X86] Use PCI host bridge window information
3236 from ACPI. On BIOSes from 2008 or later, this
3237 is enabled by default. If you need to use this,
3238 please report a bug.
3239 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3240 If you need to use this, please report a bug.
3241 routeirq Do IRQ routing for all PCI devices.
3242 This is normally done in pci_enable_device(),
3243 so this option is a temporary workaround
3244 for broken drivers that don't call it.
3245 skip_isa_align [X86] do not align io start addr, so can
3246 handle more pci cards
3247 noearly [X86] Don't do any early type 1 scanning.
3248 This might help on some broken boards which
3249 machine check when some devices' config space
3250 is read. But various workarounds are disabled
3251 and some IOMMU drivers will not work.
3252 bfsort Sort PCI devices into breadth-first order.
3253 This sorting is done to get a device
3254 order compatible with older (<= 2.4) kernels.
3255 nobfsort Don't sort PCI devices into breadth-first order.
3256 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3257 tuning and use the BIOS-configured MPS defaults.
3258 pcie_bus_safe Set every device's MPS to the largest value
3259 supported by all devices below the root complex.
3260 pcie_bus_perf Set device MPS to the largest allowable MPS
3261 based on its parent bus. Also set MRRS (Max
3262 Read Request Size) to the largest supported
3263 value (no larger than the MPS that the device
3264 or bus can support) for best performance.
3265 pcie_bus_peer2peer Set every device's MPS to 128B, which
3266 every device is guaranteed to support. This
3267 configuration allows peer-to-peer DMA between
3268 any pair of devices, possibly at the cost of
3269 reduced performance. This also guarantees
3270 that hot-added devices will work.
3271 cbiosize=nn[KMG] The fixed amount of bus space which is
3272 reserved for the CardBus bridge's IO window.
3273 The default value is 256 bytes.
3274 cbmemsize=nn[KMG] The fixed amount of bus space which is
3275 reserved for the CardBus bridge's memory
3276 window. The default value is 64 megabytes.
3279 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3280 [<order of align>@]pci:<vendor>:<device>\
3281 [:<subvendor>:<subdevice>][; ...]
3282 Specifies alignment and device to reassign
3283 aligned memory resources.
3284 If <order of align> is not specified,
3285 PAGE_SIZE is used as alignment.
3286 PCI-PCI bridge can be specified, if resource
3287 windows need to be expanded.
3288 To specify the alignment for several
3289 instances of a device, the PCI vendor,
3290 device, subvendor, and subdevice may be
3291 specified, e.g., 4096@pci:8086:9c22:103c:198f
3292 ecrc= Enable/disable PCIe ECRC (transaction layer
3293 end-to-end CRC checking).
3294 bios: Use BIOS/firmware settings. This is the
3298 hpiosize=nn[KMG] The fixed amount of bus space which is
3299 reserved for hotplug bridge's IO window.
3300 Default size is 256 bytes.
3301 hpmemsize=nn[KMG] The fixed amount of bus space which is
3302 reserved for hotplug bridge's memory window.
3303 Default size is 2 megabytes.
3304 hpbussize=nn The minimum amount of additional bus numbers
3305 reserved for buses below a hotplug bridge.
3307 realloc= Enable/disable reallocating PCI bridge resources
3308 if allocations done by BIOS are too small to
3309 accommodate resources required by all child
3311 off: Turn realloc off
3313 realloc same as realloc=on
3314 noari do not use PCIe ARI.
3315 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3316 only look for one device below a PCIe downstream
3319 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3322 force Enable ASPM even on devices that claim not to support it.
3323 WARNING: Forcing ASPM on may cause system lockups.
3325 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3326 nomsi Do not use MSI for PCI Express Native Hotplug (this
3327 makes all PCIe ports use INTx for hotplug services).
3329 pcie_ports= [PCIE] PCIe ports handling:
3330 auto Ask the BIOS whether or not to use native PCIe services
3331 associated with PCIe ports (PME, hot-plug, AER). Use
3332 them only if that is allowed by the BIOS.
3333 native Use native PCIe services associated with PCIe ports
3335 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3338 pcie_port_pm= [PCIE] PCIe port power management handling:
3339 off Disable power management of all PCIe ports
3340 force Forcibly enable power management of all PCIe ports
3342 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3343 nomsi Do not use MSI for native PCIe PME signaling (this makes
3344 all PCIe root ports use INTx for all services).
3346 pcmv= [HW,PCMCIA] BadgePAD 4
3350 Keep all power-domains already enabled by bootloader on,
3351 even if no driver has claimed them. This is useful
3352 for debug and development, but should not be
3353 needed on a platform with proper driver support.
3356 See Documentation/blockdev/paride.txt.
3358 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3361 See arch/parisc/kernel/pdc_chassis.c
3363 percpu_alloc= Select which percpu first chunk allocator to use.
3364 Currently supported values are "embed" and "page".
3365 Archs may support subset or none of the selections.
3366 See comments in mm/percpu.c for details on each
3367 allocator. This parameter is primarily for debugging
3368 and performance comparison.
3371 See Documentation/blockdev/paride.txt.
3374 See Documentation/blockdev/paride.txt.
3376 pirq= [SMP,APIC] Manual mp-table setup
3377 See Documentation/x86/i386/IO-APIC.txt.
3379 plip= [PPT,NET] Parallel port network link
3380 Format: { parport<nr> | timid | 0 }
3381 See also Documentation/parport.txt.
3383 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3384 Override pmtimer IOPort with a hex value.
3388 Enable PNP debug messages (depends on the
3389 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3390 via /sys/module/pnp/parameters/debug. We always show
3391 current resource usage; turning this on also shows
3392 possible settings and some assignment information.
3398 { on | off | curr | res | no-curr | no-res }
3401 [ISAPNP] Exclude IRQs for the autoconfiguration
3404 [ISAPNP] Exclude DMAs for the autoconfiguration
3406 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3407 Ranges are in pairs (I/O port base and size).
3410 [ISAPNP] Exclude memory regions for the
3412 Ranges are in pairs (memory base and size).
3414 ports= [IP_VS_FTP] IPVS ftp helper module
3416 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3418 Format: <port>,<port>....
3420 powersave=off [PPC] This option disables power saving features.
3421 It specifically disables cpuidle and sets the
3422 platform machine description specific power_save
3423 function to NULL. On Idle the CPU just reduces
3426 ppc_strict_facility_enable
3427 [PPC] This option catches any kernel floating point,
3428 Altivec, VSX and SPE outside of regions specifically
3429 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3430 There is some performance impact when enabling this.
3432 print-fatal-signals=
3433 [KNL] debug: print fatal signals
3435 If enabled, warn about various signal handling
3436 related application anomalies: too many signals,
3437 too many POSIX.1 timers, fatal signals causing a
3440 If you hit the warning due to signal overflow,
3441 you might want to try "ulimit -i unlimited".
3445 printk.always_kmsg_dump=
3446 Trigger kmsg_dump for cases other than kernel oops or
3448 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3451 printk.devkmsg={on,off,ratelimit}
3452 Control writing to /dev/kmsg.
3453 on - unlimited logging to /dev/kmsg from userspace
3454 off - logging to /dev/kmsg disabled
3455 ratelimit - ratelimit the logging
3458 printk.time= Show timing data prefixed to each printk message line
3459 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3461 processor.max_cstate= [HW,ACPI]
3462 Limit processor to maximum C-state
3463 max_cstate=9 overrides any DMI blacklist limit.
3465 processor.nocst [HW,ACPI]
3466 Ignore the _CST method to determine C-states,
3467 instead using the legacy FADT method
3469 profile= [KNL] Enable kernel profiling via /proc/profile
3470 Format: [schedule,]<number>
3471 Param: "schedule" - profile schedule points.
3472 Param: <number> - step/bucket size as a power of 2 for
3473 statistical time based profiling.
3474 Param: "sleep" - profile D-state sleeping (millisecs).
3475 Requires CONFIG_SCHEDSTATS
3476 Param: "kvm" - profile VM exits.
3478 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3480 See Documentation/blockdev/ramdisk.txt.
3482 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3483 probe for; one of (bare|imps|exps|lifebook|any).
3484 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3486 psmouse.resetafter= [HW,MOUSE]
3487 Try to reset the device after so many bad packets
3490 [HW,MOUSE] Set desired mouse resolution, in dpi.
3491 psmouse.smartscroll=
3492 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3493 0 = disabled, 1 = enabled (default).
3495 pstore.backend= Specify the name of the pstore backend to use
3498 See Documentation/blockdev/paride.txt.
3500 pti= [X86_64] Control Page Table Isolation of user and
3501 kernel address spaces. Disabling this feature
3502 removes hardening, but improves performance of
3503 system calls and interrupts.
3505 on - unconditionally enable
3506 off - unconditionally disable
3507 auto - kernel detects whether your CPU model is
3508 vulnerable to issues that PTI mitigates
3510 Not specifying this option is equivalent to pti=auto.
3513 Equivalent to pti=off
3516 [KNL] Number of legacy pty's. Overwrites compiled-in
3519 quiet [KNL] Disable most log messages
3524 See Documentation/admin-guide/md.rst.
3526 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3527 See Documentation/blockdev/ramdisk.txt.
3529 random.trust_cpu={on,off}
3530 [KNL] Enable or disable trusting the use of the
3531 CPU's random number generator (if available) to
3532 fully seed the kernel's CRNG. Default is controlled
3533 by CONFIG_RANDOM_TRUST_CPU.
3535 random.trust_bootloader={on,off}
3536 [KNL] Enable or disable trusting the use of a
3537 seed passed by the bootloader (if available) to
3538 fully seed the kernel's CRNG. Default is controlled
3539 by CONFIG_RANDOM_TRUST_BOOTLOADER.
3541 ras=option[,option,...] [KNL] RAS-specific options
3544 Disable the Correctable Errors Collector,
3545 see CONFIG_RAS_CEC help text.
3548 The argument is a cpu list, as described above.
3550 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3551 the specified list of CPUs to be no-callback CPUs.
3552 Invocation of these CPUs' RCU callbacks will
3553 be offloaded to "rcuox/N" kthreads created for
3554 that purpose, where "x" is "b" for RCU-bh, "p"
3555 for RCU-preempt, and "s" for RCU-sched, and "N"
3556 is the CPU number. This reduces OS jitter on the
3557 offloaded CPUs, which can be useful for HPC and
3558 real-time workloads. It can also improve energy
3559 efficiency for asymmetric multiprocessors.
3562 Rather than requiring that offloaded CPUs
3563 (specified by rcu_nocbs= above) explicitly
3564 awaken the corresponding "rcuoN" kthreads,
3565 make these kthreads poll for callbacks.
3566 This improves the real-time response for the
3567 offloaded CPUs by relieving them of the need to
3568 wake up the corresponding kthread, but degrades
3569 energy efficiency by requiring that the kthreads
3570 periodically wake up to do the polling.
3572 rcutree.blimit= [KNL]
3573 Set maximum number of finished RCU callbacks to
3574 process in one batch.
3576 rcutree.dump_tree= [KNL]
3577 Dump the structure of the rcu_node combining tree
3578 out at early boot. This is used for diagnostic
3579 purposes, to verify correct tree setup.
3581 rcutree.gp_cleanup_delay= [KNL]
3582 Set the number of jiffies to delay each step of
3583 RCU grace-period cleanup.
3585 rcutree.gp_init_delay= [KNL]
3586 Set the number of jiffies to delay each step of
3587 RCU grace-period initialization.
3589 rcutree.gp_preinit_delay= [KNL]
3590 Set the number of jiffies to delay each step of
3591 RCU grace-period pre-initialization, that is,
3592 the propagation of recent CPU-hotplug changes up
3593 the rcu_node combining tree.
3595 rcutree.rcu_fanout_exact= [KNL]
3596 Disable autobalancing of the rcu_node combining
3597 tree. This is used by rcutorture, and might
3598 possibly be useful for architectures having high
3599 cache-to-cache transfer latencies.
3601 rcutree.rcu_fanout_leaf= [KNL]
3602 Change the number of CPUs assigned to each
3603 leaf rcu_node structure. Useful for very
3604 large systems, which will choose the value 64,
3605 and for NUMA systems with large remote-access
3606 latencies, which will choose a value aligned
3607 with the appropriate hardware boundaries.
3609 rcutree.jiffies_till_sched_qs= [KNL]
3610 Set required age in jiffies for a
3611 given grace period before RCU starts
3612 soliciting quiescent-state help from
3613 rcu_note_context_switch().
3615 rcutree.jiffies_till_first_fqs= [KNL]
3616 Set delay from grace-period initialization to
3617 first attempt to force quiescent states.
3618 Units are jiffies, minimum value is zero,
3619 and maximum value is HZ.
3621 rcutree.jiffies_till_next_fqs= [KNL]
3622 Set delay between subsequent attempts to force
3623 quiescent states. Units are jiffies, minimum
3624 value is one, and maximum value is HZ.
3626 rcutree.kthread_prio= [KNL,BOOT]
3627 Set the SCHED_FIFO priority of the RCU per-CPU
3628 kthreads (rcuc/N). This value is also used for
3629 the priority of the RCU boost threads (rcub/N)
3630 and for the RCU grace-period kthreads (rcu_bh,
3631 rcu_preempt, and rcu_sched). If RCU_BOOST is
3632 set, valid values are 1-99 and the default is 1
3633 (the least-favored priority). Otherwise, when
3634 RCU_BOOST is not set, valid values are 0-99 and
3635 the default is zero (non-realtime operation).
3637 rcutree.rcu_nocb_leader_stride= [KNL]
3638 Set the number of NOCB kthread groups, which
3639 defaults to the square root of the number of
3640 CPUs. Larger numbers reduces the wakeup overhead
3641 on the per-CPU grace-period kthreads, but increases
3642 that same overhead on each group's leader.
3644 rcutree.qhimark= [KNL]
3645 Set threshold of queued RCU callbacks beyond which
3646 batch limiting is disabled.
3648 rcutree.qlowmark= [KNL]
3649 Set threshold of queued RCU callbacks below which
3650 batch limiting is re-enabled.
3652 rcutree.rcu_idle_gp_delay= [KNL]
3653 Set wakeup interval for idle CPUs that have
3654 RCU callbacks (RCU_FAST_NO_HZ=y).
3656 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3657 Set wakeup interval for idle CPUs that have
3658 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3659 Lazy RCU callbacks are those which RCU can
3660 prove do nothing more than free memory.
3662 rcutree.rcu_kick_kthreads= [KNL]
3663 Cause the grace-period kthread to get an extra
3664 wake_up() if it sleeps three times longer than
3665 it should at force-quiescent-state time.
3666 This wake_up() will be accompanied by a
3667 WARN_ONCE() splat and an ftrace_dump().
3669 rcuperf.gp_async= [KNL]
3670 Measure performance of asynchronous
3671 grace-period primitives such as call_rcu().
3673 rcuperf.gp_async_max= [KNL]
3674 Specify the maximum number of outstanding
3675 callbacks per writer thread. When a writer
3676 thread exceeds this limit, it invokes the
3677 corresponding flavor of rcu_barrier() to allow
3678 previously posted callbacks to drain.
3680 rcuperf.gp_exp= [KNL]
3681 Measure performance of expedited synchronous
3682 grace-period primitives.
3684 rcuperf.holdoff= [KNL]
3685 Set test-start holdoff period. The purpose of
3686 this parameter is to delay the start of the
3687 test until boot completes in order to avoid
3690 rcuperf.nreaders= [KNL]
3691 Set number of RCU readers. The value -1 selects
3692 N, where N is the number of CPUs. A value
3693 "n" less than -1 selects N-n+1, where N is again
3694 the number of CPUs. For example, -2 selects N
3695 (the number of CPUs), -3 selects N+1, and so on.
3696 A value of "n" less than or equal to -N selects
3699 rcuperf.nwriters= [KNL]
3700 Set number of RCU writers. The values operate
3701 the same as for rcuperf.nreaders.
3702 N, where N is the number of CPUs
3704 rcuperf.perf_runnable= [BOOT]
3705 Start rcuperf running at boot time.
3707 rcuperf.perf_type= [KNL]
3708 Specify the RCU implementation to test.
3710 rcuperf.shutdown= [KNL]
3711 Shut the system down after performance tests
3712 complete. This is useful for hands-off automated
3715 rcuperf.verbose= [KNL]
3716 Enable additional printk() statements.
3718 rcuperf.writer_holdoff= [KNL]
3719 Write-side holdoff between grace periods,
3720 in microseconds. The default of zero says
3723 rcutorture.cbflood_inter_holdoff= [KNL]
3724 Set holdoff time (jiffies) between successive
3725 callback-flood tests.
3727 rcutorture.cbflood_intra_holdoff= [KNL]
3728 Set holdoff time (jiffies) between successive
3729 bursts of callbacks within a given callback-flood
3732 rcutorture.cbflood_n_burst= [KNL]
3733 Set the number of bursts making up a given
3734 callback-flood test. Set this to zero to
3735 disable callback-flood testing.
3737 rcutorture.cbflood_n_per_burst= [KNL]
3738 Set the number of callbacks to be registered
3739 in a given burst of a callback-flood test.
3741 rcutorture.fqs_duration= [KNL]
3742 Set duration of force_quiescent_state bursts
3745 rcutorture.fqs_holdoff= [KNL]
3746 Set holdoff time within force_quiescent_state bursts
3749 rcutorture.fqs_stutter= [KNL]
3750 Set wait time between force_quiescent_state bursts
3753 rcutorture.gp_cond= [KNL]
3754 Use conditional/asynchronous update-side
3755 primitives, if available.
3757 rcutorture.gp_exp= [KNL]
3758 Use expedited update-side primitives, if available.
3760 rcutorture.gp_normal= [KNL]
3761 Use normal (non-expedited) asynchronous
3762 update-side primitives, if available.
3764 rcutorture.gp_sync= [KNL]
3765 Use normal (non-expedited) synchronous
3766 update-side primitives, if available. If all
3767 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3768 rcutorture.gp_normal=, and rcutorture.gp_sync=
3769 are zero, rcutorture acts as if is interpreted
3770 they are all non-zero.
3772 rcutorture.n_barrier_cbs= [KNL]
3773 Set callbacks/threads for rcu_barrier() testing.
3775 rcutorture.nfakewriters= [KNL]
3776 Set number of concurrent RCU writers. These just
3777 stress RCU, they don't participate in the actual
3778 test, hence the "fake".
3780 rcutorture.nreaders= [KNL]
3781 Set number of RCU readers. The value -1 selects
3782 N-1, where N is the number of CPUs. A value
3783 "n" less than -1 selects N-n-2, where N is again
3784 the number of CPUs. For example, -2 selects N
3785 (the number of CPUs), -3 selects N+1, and so on.
3787 rcutorture.object_debug= [KNL]
3788 Enable debug-object double-call_rcu() testing.
3790 rcutorture.onoff_holdoff= [KNL]
3791 Set time (s) after boot for CPU-hotplug testing.
3793 rcutorture.onoff_interval= [KNL]
3794 Set time (s) between CPU-hotplug operations, or
3795 zero to disable CPU-hotplug testing.
3797 rcutorture.shuffle_interval= [KNL]
3798 Set task-shuffle interval (s). Shuffling tasks
3799 allows some CPUs to go into dyntick-idle mode
3800 during the rcutorture test.
3802 rcutorture.shutdown_secs= [KNL]
3803 Set time (s) after boot system shutdown. This
3804 is useful for hands-off automated testing.
3806 rcutorture.stall_cpu= [KNL]
3807 Duration of CPU stall (s) to test RCU CPU stall
3808 warnings, zero to disable.
3810 rcutorture.stall_cpu_holdoff= [KNL]
3811 Time to wait (s) after boot before inducing stall.
3813 rcutorture.stat_interval= [KNL]
3814 Time (s) between statistics printk()s.
3816 rcutorture.stutter= [KNL]
3817 Time (s) to stutter testing, for example, specifying
3818 five seconds causes the test to run for five seconds,
3819 wait for five seconds, and so on. This tests RCU's
3820 ability to transition abruptly to and from idle.
3822 rcutorture.test_boost= [KNL]
3823 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3824 "Maybe" means test if the RCU implementation
3825 under test support RCU priority boosting.
3827 rcutorture.test_boost_duration= [KNL]
3828 Duration (s) of each individual boost test.
3830 rcutorture.test_boost_interval= [KNL]
3831 Interval (s) between each boost test.
3833 rcutorture.test_no_idle_hz= [KNL]
3834 Test RCU's dyntick-idle handling. See also the
3835 rcutorture.shuffle_interval parameter.
3837 rcutorture.torture_runnable= [BOOT]
3838 Start rcutorture running at boot time.
3840 rcutorture.torture_type= [KNL]
3841 Specify the RCU implementation to test.
3843 rcutorture.verbose= [KNL]
3844 Enable additional printk() statements.
3846 rcupdate.rcu_cpu_stall_suppress= [KNL]
3847 Suppress RCU CPU stall warning messages.
3849 rcupdate.rcu_cpu_stall_timeout= [KNL]
3850 Set timeout for RCU CPU stall warning messages.
3852 rcupdate.rcu_expedited= [KNL]
3853 Use expedited grace-period primitives, for
3854 example, synchronize_rcu_expedited() instead
3855 of synchronize_rcu(). This reduces latency,
3856 but can increase CPU utilization, degrade
3857 real-time latency, and degrade energy efficiency.
3858 No effect on CONFIG_TINY_RCU kernels.
3860 rcupdate.rcu_normal= [KNL]
3861 Use only normal grace-period primitives,
3862 for example, synchronize_rcu() instead of
3863 synchronize_rcu_expedited(). This improves
3864 real-time latency, CPU utilization, and
3865 energy efficiency, but can expose users to
3866 increased grace-period latency. This parameter
3867 overrides rcupdate.rcu_expedited. No effect on
3868 CONFIG_TINY_RCU kernels.
3870 rcupdate.rcu_normal_after_boot= [KNL]
3871 Once boot has completed (that is, after
3872 rcu_end_inkernel_boot() has been invoked), use
3873 only normal grace-period primitives. No effect
3874 on CONFIG_TINY_RCU kernels.
3876 rcupdate.rcu_task_stall_timeout= [KNL]
3877 Set timeout in jiffies for RCU task stall warning
3878 messages. Disable with a value less than or equal
3881 rcupdate.rcu_self_test= [KNL]
3882 Run the RCU early boot self tests
3884 rcupdate.rcu_self_test_bh= [KNL]
3885 Run the RCU bh early boot self tests
3887 rcupdate.rcu_self_test_sched= [KNL]
3888 Run the RCU sched early boot self tests
3892 Run specified binary instead of /init from the ramdisk,
3893 used for early userspace startup. See initrd.
3896 force - Override the decision by the kernel to hide the
3897 advertisement of RDRAND support (this affects
3898 certain AMD processors because of buggy BIOS
3899 support, specifically around the suspend/resume
3903 Turn on/off individual RDT features. List is:
3904 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3905 E.g. to turn on cmt and turn off mba use:
3909 Format (x86 or x86_64):
3910 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3912 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3914 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3915 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3916 reboot_force is either force or not specified,
3917 reboot_cpu is s[mp]#### with #### being the processor
3918 to be used for rebooting.
3921 [KNL, SMP] Set scheduler's default relax_domain_level.
3922 See Documentation/cgroup-v1/cpusets.txt.
3924 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3926 reservetop= [X86-32]
3928 Reserves a hole at the top of the kernel virtual
3933 Set the amount of memory to reserve for BIOS at
3934 the bottom of the address space.
3936 reset_devices [KNL] Force drivers to reset the underlying device
3937 during initialization.
3940 Specify the partition device for software suspend
3942 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3944 resume_offset= [SWSUSP]
3945 Specify the offset from the beginning of the partition
3946 given by "resume=" at which the swap header is located,
3947 in <PAGE_SIZE> units (needed only for swap files).
3948 See Documentation/power/swsusp-and-swap-files.txt
3950 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3951 read the resume files
3953 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3954 Useful for devices that are detected asynchronously
3955 (e.g. USB and MMC devices).
3957 hibernate= [HIBERNATION]
3958 noresume Don't check if there's a hibernation image
3959 present during boot.
3960 nocompress Don't compress/decompress hibernation images.
3961 no Disable hibernation and resume.
3962 protect_image Turn on image protection during restoration
3963 (that will set all pages holding image data
3964 during restoration read-only).
3966 retain_initrd [RAM] Keep initrd memory after extraction
3968 rfkill.default_state=
3969 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3970 etc. communication is blocked by default.
3973 rfkill.master_switch_mode=
3974 0 The "airplane mode" button does nothing.
3975 1 The "airplane mode" button toggles between everything
3976 blocked and the previous configuration.
3977 2 The "airplane mode" button toggles between everything
3978 blocked and everything unblocked.
3980 rhash_entries= [KNL,NET]
3981 Set number of hash buckets for route cache
3984 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3987 ro [KNL] Mount root device read-only on boot
3990 on Mark read-only kernel memory as read-only (default).
3991 off Leave read-only kernel memory writable for debugging.
3994 Enable the uart passthrough on the designated usb port
3995 on Rockchip SoCs. When active, the signals of the
3996 debug-uart get routed to the D+ and D- pins of the usb
3997 port and the regular usb controller gets disabled.
3999 root= [KNL] Root filesystem
4000 See name_to_dev_t comment in init/do_mounts.c.
4002 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4003 mount the root filesystem
4005 rootflags= [KNL] Set root filesystem mount option string
4007 rootfstype= [KNL] Set root filesystem type
4009 rootwait [KNL] Wait (indefinitely) for root device to show up.
4010 Useful for devices that are detected asynchronously
4011 (e.g. USB and MMC devices).
4013 rproc_mem=nn[KMG][@address]
4014 [KNL,ARM,CMA] Remoteproc physical memory block.
4015 Memory area to be used by remote processor image,
4018 rw [KNL] Mount root device read-write on boot
4020 S [KNL] Run init in single mode
4022 s390_iommu= [HW,S390]
4023 Set s390 IOTLB flushing mode
4025 With strict flushing every unmap operation will result in
4026 an IOTLB flush. Default is lazy flushing before reuse,
4030 See drivers/net/irda/sa1100_ir.c.
4032 sbni= [NET] Granch SBNI12 leased line adapter
4034 sched_debug [KNL] Enables verbose scheduler debug messages.
4036 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4037 Allowed values are enable and disable. This feature
4038 incurs a small amount of overhead in the scheduler
4039 but is useful for debugging and performance tuning.
4041 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4042 xtime_lock contention on larger systems, and/or RCU lock
4043 contention on all systems with CONFIG_MAXSMP set.
4044 Format: { "0" | "1" }
4045 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4047 Note: increases power consumption, thus should only be
4048 enabled if running jitter sensitive (HPC/RT) workloads.
4050 security= [SECURITY] Choose a security module to enable at boot.
4051 If this boot parameter is not specified, only the first
4052 security module asking for security registration will be
4053 loaded. An invalid security module name will be treated
4054 as if no module has been chosen.
4056 selinux= [SELINUX] Disable or enable SELinux at boot time.
4057 Format: { "0" | "1" }
4058 See security/selinux/Kconfig help text.
4061 Default value is set via kernel config option.
4062 If enabled at boot time, /selinux/disable can be used
4063 later to disable prior to initial policy load.
4065 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4066 Format: { "0" | "1" }
4067 See security/apparmor/Kconfig help text
4070 Default value is set via kernel config option.
4072 serialnumber [BUGS=X86-32]
4075 Maximal number of shapers.
4083 Disable merging of slabs with similar size. May be
4084 necessary if there is some reason to distinguish
4085 allocs to different slabs, especially in hardened
4086 environments where the risk of heap overflows and
4087 layout control by attackers can usually be
4088 frustrated by disabling merging. This will reduce
4089 most of the exposure of a heap attack to a single
4090 cache (risks via metadata attacks are mostly
4091 unchanged). Debug options disable merging on their
4093 For more information see Documentation/vm/slub.txt.
4095 slab_max_order= [MM, SLAB]
4096 Determines the maximum allowed order for slabs.
4097 A high setting may cause OOMs due to memory
4098 fragmentation. Defaults to 1 for systems with
4099 more than 32MB of RAM, 0 otherwise.
4101 slub_debug[=options[,slabs]] [MM, SLUB]
4102 Enabling slub_debug allows one to determine the
4103 culprit if slab objects become corrupted. Enabling
4104 slub_debug can create guard zones around objects and
4105 may poison objects when not in use. Also tracks the
4106 last alloc / free. For more information see
4107 Documentation/vm/slub.txt.
4109 slub_memcg_sysfs= [MM, SLUB]
4110 Determines whether to enable sysfs directories for
4111 memory cgroup sub-caches. 1 to enable, 0 to disable.
4112 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4113 Enabling this can lead to a very high number of debug
4114 directories and files being created under
4117 slub_max_order= [MM, SLUB]
4118 Determines the maximum allowed order for slabs.
4119 A high setting may cause OOMs due to memory
4120 fragmentation. For more information see
4121 Documentation/vm/slub.txt.
4123 slub_min_objects= [MM, SLUB]
4124 The minimum number of objects per slab. SLUB will
4125 increase the slab order up to slub_max_order to
4126 generate a sufficiently large slab able to contain
4127 the number of objects indicated. The higher the number
4128 of objects the smaller the overhead of tracking slabs
4129 and the less frequently locks need to be acquired.
4130 For more information see Documentation/vm/slub.txt.
4132 slub_min_order= [MM, SLUB]
4133 Determines the minimum page order for slabs. Must be
4134 lower than slub_max_order.
4135 For more information see Documentation/vm/slub.txt.
4137 slub_nomerge [MM, SLUB]
4138 Same with slab_nomerge. This is supported for legacy.
4139 See slab_nomerge for more information.
4142 Format: <io1>[,<io2>[,...,<io8>]]
4144 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4145 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4146 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4147 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4148 smsc-ircc2.ircc_irq= [HW] IRQ line
4149 smsc-ircc2.ircc_dma= [HW] DMA channel
4150 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4151 0: Toshiba Satellite 1800 (GP data pin select)
4152 1: Fast pin select (default)
4155 smt [KNL,S390] Set the maximum number of threads (logical
4156 CPUs) to use per physical CPU on systems capable of
4157 symmetric multithreading (SMT). Will be capped to the
4158 actual hardware limit.
4160 Default: -1 (no limit)
4163 [KNL] Should the soft-lockup detector generate panics.
4166 softlockup_all_cpu_backtrace=
4167 [KNL] Should the soft-lockup detector generate
4168 backtraces on all cpus.
4171 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4172 See Documentation/laptops/sonypi.txt
4174 spectre_v2= [X86] Control mitigation of Spectre variant 2
4175 (indirect branch speculation) vulnerability.
4176 The default operation protects the kernel from
4179 on - unconditionally enable, implies
4181 off - unconditionally disable, implies
4183 auto - kernel detects whether your CPU model is
4186 Selecting 'on' will, and 'auto' may, choose a
4187 mitigation method at run time according to the
4188 CPU, the available microcode, the setting of the
4189 CONFIG_RETPOLINE configuration option, and the
4190 compiler with which the kernel was built.
4192 Selecting 'on' will also enable the mitigation
4193 against user space to user space task attacks.
4195 Selecting 'off' will disable both the kernel and
4196 the user space protections.
4198 Specific mitigations can also be selected manually:
4200 retpoline - replace indirect branches
4201 retpoline,generic - Retpolines
4202 retpoline,lfence - LFENCE; indirect branch
4203 retpoline,amd - alias for retpoline,lfence
4204 eibrs - enhanced IBRS
4205 eibrs,retpoline - enhanced IBRS + Retpolines
4206 eibrs,lfence - enhanced IBRS + LFENCE
4208 Not specifying this option is equivalent to
4212 [X86] Control mitigation of Spectre variant 2
4213 (indirect branch speculation) vulnerability between
4216 on - Unconditionally enable mitigations. Is
4217 enforced by spectre_v2=on
4219 off - Unconditionally disable mitigations. Is
4220 enforced by spectre_v2=off
4222 prctl - Indirect branch speculation is enabled,
4223 but mitigation can be enabled via prctl
4224 per thread. The mitigation control state
4225 is inherited on fork.
4228 - Like "prctl" above, but only STIBP is
4229 controlled per thread. IBPB is issued
4230 always when switching between different user
4234 - Same as "prctl" above, but all seccomp
4235 threads will enable the mitigation unless
4236 they explicitly opt out.
4239 - Like "seccomp" above, but only STIBP is
4240 controlled per thread. IBPB is issued
4241 always when switching between different
4242 user space processes.
4244 auto - Kernel selects the mitigation depending on
4245 the available CPU features and vulnerability.
4248 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4250 Not specifying this option is equivalent to
4251 spectre_v2_user=auto.
4253 spec_store_bypass_disable=
4254 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4255 (Speculative Store Bypass vulnerability)
4257 Certain CPUs are vulnerable to an exploit against a
4258 a common industry wide performance optimization known
4259 as "Speculative Store Bypass" in which recent stores
4260 to the same memory location may not be observed by
4261 later loads during speculative execution. The idea
4262 is that such stores are unlikely and that they can
4263 be detected prior to instruction retirement at the
4264 end of a particular speculation execution window.
4266 In vulnerable processors, the speculatively forwarded
4267 store can be used in a cache side channel attack, for
4268 example to read memory to which the attacker does not
4269 directly have access (e.g. inside sandboxed code).
4271 This parameter controls whether the Speculative Store
4272 Bypass optimization is used.
4274 on - Unconditionally disable Speculative Store Bypass
4275 off - Unconditionally enable Speculative Store Bypass
4276 auto - Kernel detects whether the CPU model contains an
4277 implementation of Speculative Store Bypass and
4278 picks the most appropriate mitigation. If the
4279 CPU is not vulnerable, "off" is selected. If the
4280 CPU is vulnerable the default mitigation is
4281 architecture and Kconfig dependent. See below.
4282 prctl - Control Speculative Store Bypass per thread
4283 via prctl. Speculative Store Bypass is enabled
4284 for a process by default. The state of the control
4285 is inherited on fork.
4286 seccomp - Same as "prctl" above, but all seccomp threads
4287 will disable SSB unless they explicitly opt out.
4289 Not specifying this option is equivalent to
4290 spec_store_bypass_disable=auto.
4292 Default mitigations:
4293 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4295 spia_io_base= [HW,MTD]
4301 Control the Special Register Buffer Data Sampling
4304 Certain CPUs are vulnerable to an MDS-like
4305 exploit which can leak bits from the random
4308 By default, this issue is mitigated by
4309 microcode. However, the microcode fix can cause
4310 the RDRAND and RDSEED instructions to become
4311 much slower. Among other effects, this will
4312 result in reduced throughput from /dev/urandom.
4314 The microcode mitigation can be disabled with
4315 the following option:
4317 off: Disable mitigation and remove
4318 performance impact to RDRAND and RDSEED
4320 srcutree.counter_wrap_check [KNL]
4321 Specifies how frequently to check for
4322 grace-period sequence counter wrap for the
4323 srcu_data structure's ->srcu_gp_seq_needed field.
4324 The greater the number of bits set in this kernel
4325 parameter, the less frequently counter wrap will
4326 be checked for. Note that the bottom two bits
4329 srcutree.exp_holdoff [KNL]
4330 Specifies how many nanoseconds must elapse
4331 since the end of the last SRCU grace period for
4332 a given srcu_struct until the next normal SRCU
4333 grace period will be considered for automatic
4334 expediting. Set to zero to disable automatic
4338 Speculative Store Bypass Disable control
4340 On CPUs that are vulnerable to the Speculative
4341 Store Bypass vulnerability and offer a
4342 firmware based mitigation, this parameter
4343 indicates how the mitigation should be used:
4345 force-on: Unconditionally enable mitigation for
4346 for both kernel and userspace
4347 force-off: Unconditionally disable mitigation for
4348 for both kernel and userspace
4349 kernel: Always enable mitigation in the
4350 kernel, and offer a prctl interface
4351 to allow userspace to register its
4352 interest in being mitigated too.
4354 stack_guard_gap= [MM]
4355 override the default stack gap protection. The value
4356 is in page units and it defines how many pages prior
4357 to (for stacks growing down) resp. after (for stacks
4358 growing up) the main stack are reserved for no other
4359 mapping. Default value is 256 pages.
4362 Enabled the stack tracer on boot up.
4364 stacktrace_filter=[function-list]
4365 [FTRACE] Limit the functions that the stack tracer
4366 will trace at boot up. function-list is a comma separated
4367 list of functions. This list can be changed at run
4368 time by the stack_trace_filter file in the debugfs
4369 tracing directory. Note, this enables stack tracing
4370 and the stacktrace above is not needed.
4374 Set the STI (builtin display/keyboard on the HP-PARISC
4375 machines) console (graphic card) which should be used
4376 as the initial boot-console.
4377 See also comment in drivers/video/console/sticore.c.
4380 See comment in drivers/video/console/sticore.c.
4383 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4385 sunrpc.min_resvport=
4386 sunrpc.max_resvport=
4388 SunRPC servers often require that client requests
4389 originate from a privileged port (i.e. a port in the
4390 range 0 < portnr < 1024).
4391 An administrator who wishes to reserve some of these
4392 ports for other uses may adjust the range that the
4393 kernel's sunrpc client considers to be privileged
4394 using these two parameters to set the minimum and
4395 maximum port values.
4397 sunrpc.svc_rpc_per_connection_limit=
4399 Limit the number of requests that the server will
4400 process in parallel from a single connection.
4401 The default value is 0 (no limit).
4405 Control how the NFS server code allocates CPUs to
4406 service thread pools. Depending on how many NICs
4407 you have and where their interrupts are bound, this
4408 option will affect which CPUs will do NFS serving.
4409 Note: this parameter cannot be changed while the
4410 NFS server is running.
4412 auto the server chooses an appropriate mode
4413 automatically using heuristics
4414 global a single global pool contains all CPUs
4415 percpu one pool for each CPU
4416 pernode one pool for each NUMA node (equivalent
4417 to global on non-NUMA machines)
4419 sunrpc.tcp_slot_table_entries=
4420 sunrpc.udp_slot_table_entries=
4422 Sets the upper limit on the number of simultaneous
4423 RPC calls that can be sent from the client to a
4424 server. Increasing these values may allow you to
4425 improve throughput, but will also increase the
4426 amount of memory reserved for use by the client.
4428 suspend.pm_test_delay=
4430 Sets the number of seconds to remain in a suspend test
4431 mode before resuming the system (see
4432 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4433 is set. Default value is 5.
4436 [KNL] Enable accounting of swap in memory resource
4437 controller if no parameter or 1 is given or disable
4438 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4440 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4441 Format: { <int> | force | noforce }
4442 <int> -- Number of I/O TLB slabs
4443 force -- force using of bounce buffers even if they
4444 wouldn't be automatically used by the kernel
4445 noforce -- Never use bounce buffers (for debugging)
4449 sysfs.deprecated=0|1 [KNL]
4450 Enable/disable old style sysfs layout for old udev
4451 on older distributions. When this option is enabled
4452 very new udev will not work anymore. When this option
4453 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4454 in older udev will not work anymore.
4455 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4456 the kernel configuration.
4458 sysrq_always_enabled
4460 Ignore sysrq setting - this boot parameter will
4461 neutralize any effect of /proc/sys/kernel/sysrq.
4462 Useful for debugging.
4464 tcpmhash_entries= [KNL,NET]
4465 Set the number of tcp_metrics_hash slots.
4466 Default value is 8192 or 16384 depending on total
4467 ram pages. This is used to specify the TCP metrics
4468 cache size. See Documentation/networking/ip-sysctl.txt
4469 "tcp_no_metrics_save" section for more details.
4473 test_suspend= [SUSPEND][,N]
4474 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4475 standby suspend) or "freeze" (for suspend type freeze)
4476 as the system sleep state during system startup with
4477 the optional capability to repeat N number of times.
4478 The system is woken from this state using a
4479 wakeup-capable RTC alarm.
4481 thash_entries= [KNL,NET]
4482 Set number of hash buckets for TCP connection
4484 thermal.act= [HW,ACPI]
4485 -1: disable all active trip points in all thermal zones
4486 <degrees C>: override all lowest active trip points
4488 thermal.crt= [HW,ACPI]
4489 -1: disable all critical trip points in all thermal zones
4490 <degrees C>: override all critical trip points
4492 thermal.nocrt= [HW,ACPI]
4493 Set to disable actions on ACPI thermal zone
4494 critical and hot trip points.
4496 thermal.off= [HW,ACPI]
4497 1: disable ACPI thermal control
4499 thermal.psv= [HW,ACPI]
4500 -1: disable all passive trip points
4501 <degrees C>: override all passive trip points to this
4504 thermal.tzp= [HW,ACPI]
4505 Specify global default ACPI thermal zone polling rate
4506 <deci-seconds>: poll all this frequency
4507 0: no polling (default)
4510 Force threading of all interrupt handlers except those
4511 marked explicitly IRQF_NO_THREAD.
4514 Enable the Transcendent memory driver if built-in.
4516 tmem.cleancache=0|1 [KNL, XEN]
4517 Default is on (1). Disable the usage of the cleancache
4518 API to send anonymous pages to the hypervisor.
4520 tmem.frontswap=0|1 [KNL, XEN]
4521 Default is on (1). Disable the usage of the frontswap
4522 API to send swap pages to the hypervisor. If disabled
4523 the selfballooning and selfshrinking are force disabled.
4525 tmem.selfballooning=0|1 [KNL, XEN]
4526 Default is on (1). Disable the driving of swap pages
4529 tmem.selfshrinking=0|1 [KNL, XEN]
4530 Default is on (1). Partial swapoff that immediately
4531 transfers pages from Xen hypervisor back to the
4532 kernel based on different criteria.
4536 Specify if the kernel should make use of the cpu
4537 topology information if the hardware supports this.
4538 The scheduler will make use of this information and
4539 e.g. base its process migration decisions on it.
4542 topology_updates= [KNL, PPC, NUMA]
4544 Specify if the kernel should ignore (off)
4545 topology updates sent by the hypervisor to this
4550 tpm_suspend_pcr=[HW,TPM]
4551 Format: integer pcr id
4552 Specify that at suspend time, the tpm driver
4553 should extend the specified pcr with zeros,
4554 as a workaround for some chips which fail to
4555 flush the last written pcr on TPM_SaveState.
4556 This will guarantee that all the other pcrs
4559 trace_buf_size=nn[KMG]
4560 [FTRACE] will set tracing buffer size on each cpu.
4562 trace_event=[event-list]
4563 [FTRACE] Set and start specified trace events in order
4564 to facilitate early boot debugging. The event-list is a
4565 comma separated list of trace events to enable. See
4566 also Documentation/trace/events.txt
4568 trace_options=[option-list]
4569 [FTRACE] Enable or disable tracer options at boot.
4570 The option-list is a comma delimited list of options
4571 that can be enabled or disabled just as if you were
4572 to echo the option name into
4574 /sys/kernel/debug/tracing/trace_options
4576 For example, to enable stacktrace option (to dump the
4577 stack trace of each event), add to the command line:
4579 trace_options=stacktrace
4581 See also Documentation/trace/ftrace.txt "trace options"
4585 Have the tracepoints sent to printk as well as the
4586 tracing ring buffer. This is useful for early boot up
4587 where the system hangs or reboots and does not give the
4588 option for reading the tracing buffer or performing a
4589 ftrace_dump_on_oops.
4591 To turn off having tracepoints sent to printk,
4592 echo 0 > /proc/sys/kernel/tracepoint_printk
4593 Note, echoing 1 into this file without the
4594 tracepoint_printk kernel cmdline option has no effect.
4598 Having tracepoints sent to printk() and activating high
4599 frequency tracepoints such as irq or sched, can cause
4600 the system to live lock.
4603 [FTRACE] enable this option to disable tracing when a
4604 warning is hit. This turns off "tracing_on". Tracing can
4605 be enabled again by echoing '1' into the "tracing_on"
4606 file located in /sys/kernel/debug/tracing/
4608 This option is useful, as it disables the trace before
4609 the WARNING dump is called, which prevents the trace to
4610 be filled with content caused by the warning output.
4612 This option can also be set at run time via the sysctl
4613 option: kernel/traceoff_on_warning
4615 transparent_hugepage=
4617 Format: [always|madvise|never]
4618 Can be used to control the default behavior of the system
4619 with respect to transparent hugepages.
4620 See Documentation/vm/transhuge.txt for more details.
4622 tsc= Disable clocksource stability checks for TSC.
4624 [x86] reliable: mark tsc clocksource as reliable, this
4625 disables clocksource verification at runtime, as well
4626 as the stability checks done at bootup. Used to enable
4627 high-resolution timer mode on older hardware, and in
4628 virtualized environment.
4629 [x86] noirqtime: Do not use TSC to do irq accounting.
4630 Used to run time disable IRQ_TIME_ACCOUNTING on any
4631 platforms where RDTSC is slow and this accounting
4634 tsx= [X86] Control Transactional Synchronization
4635 Extensions (TSX) feature in Intel processors that
4636 support TSX control.
4638 This parameter controls the TSX feature. The options are:
4640 on - Enable TSX on the system. Although there are
4641 mitigations for all known security vulnerabilities,
4642 TSX has been known to be an accelerator for
4643 several previous speculation-related CVEs, and
4644 so there may be unknown security risks associated
4645 with leaving it enabled.
4647 off - Disable TSX on the system. (Note that this
4648 option takes effect only on newer CPUs which are
4649 not vulnerable to MDS, i.e., have
4650 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4651 the new IA32_TSX_CTRL MSR through a microcode
4652 update. This new MSR allows for the reliable
4653 deactivation of the TSX functionality.)
4655 auto - Disable TSX if X86_BUG_TAA is present,
4656 otherwise enable TSX on the system.
4658 Not specifying this option is equivalent to tsx=off.
4660 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4663 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4664 Abort (TAA) vulnerability.
4666 Similar to Micro-architectural Data Sampling (MDS)
4667 certain CPUs that support Transactional
4668 Synchronization Extensions (TSX) are vulnerable to an
4669 exploit against CPU internal buffers which can forward
4670 information to a disclosure gadget under certain
4673 In vulnerable processors, the speculatively forwarded
4674 data can be used in a cache side channel attack, to
4675 access data to which the attacker does not have direct
4678 This parameter controls the TAA mitigation. The
4681 full - Enable TAA mitigation on vulnerable CPUs
4684 full,nosmt - Enable TAA mitigation and disable SMT on
4685 vulnerable CPUs. If TSX is disabled, SMT
4686 is not disabled because CPU is not
4687 vulnerable to cross-thread TAA attacks.
4688 off - Unconditionally disable TAA mitigation
4690 On MDS-affected machines, tsx_async_abort=off can be
4691 prevented by an active MDS mitigation as both vulnerabilities
4692 are mitigated with the same mechanism so in order to disable
4693 this mitigation, you need to specify mds=off too.
4695 Not specifying this option is equivalent to
4696 tsx_async_abort=full. On CPUs which are MDS affected
4697 and deploy MDS mitigation, TAA mitigation is not
4698 required and doesn't provide any additional
4702 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4704 turbografx.map[2|3]= [HW,JOY]
4705 TurboGraFX parallel port interface
4707 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4708 See also Documentation/input/joystick-parport.txt
4710 udbg-immortal [PPC] When debugging early kernel crashes that
4711 happen after console_init() and before a proper
4712 console driver takes over, this boot options might
4713 help "seeing" what's going on.
4715 uhash_entries= [KNL,NET]
4716 Set number of hash buckets for UDP/UDP-Lite connections
4719 [USB] Ignore overcurrent events (default N).
4720 Some badly-designed motherboards generate lots of
4721 bogus events, for ports that aren't wired to
4722 anything. Set this parameter to avoid log spamming.
4723 Note that genuine overcurrent events won't be
4727 [X86] Cause panic on unknown NMI.
4729 usbcore.authorized_default=
4730 [USB] Default USB device authorization:
4731 (default -1 = authorized except for wireless USB,
4732 0 = not authorized, 1 = authorized)
4734 usbcore.autosuspend=
4735 [USB] The autosuspend time delay (in seconds) used
4736 for newly-detected USB devices (default 2). This
4737 is the time required before an idle device will be
4738 autosuspended. Devices for which the delay is set
4739 to a negative value won't be autosuspended at all.
4741 usbcore.usbfs_snoop=
4742 [USB] Set to log all usbfs traffic (default 0 = off).
4744 usbcore.usbfs_snoop_max=
4745 [USB] Maximum number of bytes to snoop in each URB
4748 usbcore.blinkenlights=
4749 [USB] Set to cycle leds on hubs (default 0 = off).
4751 usbcore.old_scheme_first=
4752 [USB] Start with the old device initialization
4753 scheme (default 0 = off).
4755 usbcore.usbfs_memory_mb=
4756 [USB] Memory limit (in MB) for buffers allocated by
4757 usbfs (default = 16, 0 = max = 2047).
4759 usbcore.use_both_schemes=
4760 [USB] Try the other device initialization scheme
4761 if the first one fails (default 1 = enabled).
4763 usbcore.initial_descriptor_timeout=
4764 [USB] Specifies timeout for the initial 64-byte
4765 USB_REQ_GET_DESCRIPTOR request in milliseconds
4766 (default 5000 = 5.0 seconds).
4768 usbcore.nousb [USB] Disable the USB subsystem
4771 [USBHID] The interval which mice are to be polled at.
4774 [USBHID] The interval which joysticks are to be polled at.
4776 usb-storage.delay_use=
4777 [UMS] The delay in seconds before a new device is
4778 scanned for Logical Units (default 1).
4781 [UMS] A list of quirks entries to supplement or
4782 override the built-in unusual_devs list. List
4783 entries are separated by commas. Each entry has
4784 the form VID:PID:Flags where VID and PID are Vendor
4785 and Product ID values (4-digit hex numbers) and
4786 Flags is a set of characters, each corresponding
4787 to a common usb-storage quirk flag as follows:
4788 a = SANE_SENSE (collect more than 18 bytes
4789 of sense data, not on uas);
4790 b = BAD_SENSE (don't collect more than 18
4791 bytes of sense data, not on uas);
4792 c = FIX_CAPACITY (decrease the reported
4793 device capacity by one sector);
4794 d = NO_READ_DISC_INFO (don't use
4795 READ_DISC_INFO command, not on uas);
4796 e = NO_READ_CAPACITY_16 (don't use
4797 READ_CAPACITY_16 command);
4798 f = NO_REPORT_OPCODES (don't use report opcodes
4800 g = MAX_SECTORS_240 (don't transfer more than
4801 240 sectors at a time, uas only);
4802 h = CAPACITY_HEURISTICS (decrease the
4803 reported device capacity by one
4804 sector if the number is odd);
4805 i = IGNORE_DEVICE (don't bind to this
4807 j = NO_REPORT_LUNS (don't use report luns
4809 k = NO_SAME (do not use WRITE_SAME, uas only)
4810 l = NOT_LOCKABLE (don't try to lock and
4811 unlock ejectable media, not on uas);
4812 m = MAX_SECTORS_64 (don't transfer more
4813 than 64 sectors = 32 KB at a time,
4815 n = INITIAL_READ10 (force a retry of the
4816 initial READ(10) command, not on uas);
4817 o = CAPACITY_OK (accept the capacity
4818 reported by the device, not on uas);
4819 p = WRITE_CACHE (the device cache is ON
4820 by default, not on uas);
4821 r = IGNORE_RESIDUE (the device reports
4822 bogus residue values, not on uas);
4823 s = SINGLE_LUN (the device has only one
4825 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4826 commands, uas only);
4827 u = IGNORE_UAS (don't bind to the uas driver);
4828 w = NO_WP_DETECT (don't test whether the
4829 medium is write-protected).
4830 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4831 even if the device claims no cache,
4833 Example: quirks=0419:aaf5:rl,0421:0433:rc
4835 user_debug= [KNL,ARM]
4837 See arch/arm/Kconfig.debug help text.
4838 1 - undefined instruction events
4840 4 - invalid data aborts
4843 Example: user_debug=31
4846 [X86] Flags controlling user PTE allocations.
4848 nohigh = do not allocate PTE pages in
4849 HIGHMEM regardless of setting
4853 On X86_32, this is an alias for vdso32=. Otherwise:
4855 vdso=1: enable VDSO (the default)
4856 vdso=0: disable VDSO mapping
4858 vdso32= [X86] Control the 32-bit vDSO
4859 vdso32=1: enable 32-bit VDSO
4860 vdso32=0 or vdso32=2: disable 32-bit VDSO
4862 See the help text for CONFIG_COMPAT_VDSO for more
4863 details. If CONFIG_COMPAT_VDSO is set, the default is
4864 vdso32=0; otherwise, the default is vdso32=1.
4866 For compatibility with older kernels, vdso32=2 is an
4869 Try vdso32=0 if you encounter an error that says:
4870 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4873 vector=percpu: enable percpu vector domain
4875 video= [FB] Frame buffer configuration
4876 See Documentation/fb/modedb.txt.
4878 video.brightness_switch_enabled= [0,1]
4879 If set to 1, on receiving an ACPI notify event
4880 generated by hotkey, video driver will adjust brightness
4881 level and then send out the event to user space through
4882 the allocated input device; If set to 0, video driver
4883 will only send out the event without touching backlight
4888 [VMMIO] Memory mapped virtio (platform) device.
4890 <size>@<baseaddr>:<irq>[:<id>]
4892 <size> := size (can use standard suffixes
4894 <baseaddr> := physical base address
4895 <irq> := interrupt number (as passed to
4897 <id> := (optional) platform device id
4899 virtio_mmio.device=1K@0x100b0000:48:7
4901 Can be used multiple times for multiple devices.
4903 vga= [BOOT,X86-32] Select a particular video mode
4904 See Documentation/x86/boot.txt and
4905 Documentation/svga.txt.
4906 Use vga=ask for menu.
4907 This is actually a boot loader parameter; the value is
4908 passed to the kernel using a special protocol.
4910 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4911 size of <nn>. This can be used to increase the
4912 minimum size (128MB on x86). It can also be used to
4913 decrease the size and leave more room for directly
4916 vmcp_cma=nn[MG] [KNL,S390]
4917 Sets the memory size reserved for contiguous memory
4918 allocations for the vmcp device driver.
4920 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4923 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4926 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4930 Controls the behavior of vsyscalls (i.e. calls to
4931 fixed addresses of 0xffffffffff600x00 from legacy
4932 code). Most statically-linked binaries and older
4933 versions of glibc use these calls. Because these
4934 functions are at fixed addresses, they make nice
4935 targets for exploits that can control RIP.
4937 emulate [default] Vsyscalls turn into traps and are
4938 emulated reasonably safely.
4940 native Vsyscalls are native syscall instructions.
4941 This is a little bit faster than trapping
4942 and makes a few dynamic recompilers work
4943 better than they would in emulation mode.
4944 It also makes exploits much easier to write.
4946 none Vsyscalls don't work at all. This makes
4947 them quite hard to use for exploits but
4948 might break your system.
4950 vt.color= [VT] Default text color.
4951 Format: 0xYX, X = foreground, Y = background.
4952 Default: 0x07 = light gray on black.
4954 vt.cur_default= [VT] Default cursor shape.
4955 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4956 the parameters of the <Esc>[?A;B;Cc escape sequence;
4957 see VGA-softcursor.txt. Default: 2 = underline.
4959 vt.default_blu= [VT]
4960 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4961 Change the default blue palette of the console.
4962 This is a 16-member array composed of values
4965 vt.default_grn= [VT]
4966 Format: <green0>,<green1>,<green2>,...,<green15>
4967 Change the default green palette of the console.
4968 This is a 16-member array composed of values
4971 vt.default_red= [VT]
4972 Format: <red0>,<red1>,<red2>,...,<red15>
4973 Change the default red palette of the console.
4974 This is a 16-member array composed of values
4980 Set system-wide default UTF-8 mode for all tty's.
4981 Default is 1, i.e. UTF-8 mode is enabled for all
4982 newly opened terminals.
4984 vt.global_cursor_default=
4987 Set system-wide default for whether a cursor
4988 is shown on new VTs. Default is -1,
4989 i.e. cursors will be created by default unless
4990 overridden by individual drivers. 0 will hide
4991 cursors, 1 will display them.
4993 vt.italic= [VT] Default color for italic text; 0-15.
4996 vt.underline= [VT] Default color for underlined text; 0-15.
4999 watchdog timers [HW,WDT] For information on watchdog timers,
5000 see Documentation/watchdog/watchdog-parameters.txt
5001 or other driver-specific files in the
5002 Documentation/watchdog/ directory.
5004 workqueue.watchdog_thresh=
5005 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5006 warn stall conditions and dump internal state to
5007 help debugging. 0 disables workqueue stall
5008 detection; otherwise, it's the stall threshold
5009 duration in seconds. The default value is 30 and
5010 it can be updated at runtime by writing to the
5011 corresponding sysfs file.
5013 workqueue.disable_numa
5014 By default, all work items queued to unbound
5015 workqueues are affine to the NUMA nodes they're
5016 issued on, which results in better behavior in
5017 general. If NUMA affinity needs to be disabled for
5018 whatever reason, this option can be used. Note
5019 that this also can be controlled per-workqueue for
5020 workqueues visible under /sys/bus/workqueue/.
5022 workqueue.power_efficient
5023 Per-cpu workqueues are generally preferred because
5024 they show better performance thanks to cache
5025 locality; unfortunately, per-cpu workqueues tend to
5026 be more power hungry than unbound workqueues.
5028 Enabling this makes the per-cpu workqueues which
5029 were observed to contribute significantly to power
5030 consumption unbound, leading to measurably lower
5031 power usage at the cost of small performance
5034 The default value of this parameter is determined by
5035 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5037 workqueue.debug_force_rr_cpu
5038 Workqueue used to implicitly guarantee that work
5039 items queued without explicit CPU specified are put
5040 on the local CPU. This guarantee is no longer true
5041 and while local CPU is still preferred work items
5042 may be put on foreign CPUs. This debug option
5043 forces round-robin CPU selection to flush out
5044 usages which depend on the now broken guarantee.
5045 When enabled, memory and cache locality will be
5048 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5049 default x2apic cluster mode on platforms
5052 x86_intel_mid_timer= [X86-32,APBT]
5053 Choose timer option for x86 Intel MID platform.
5054 Two valid options are apbt timer only and lapic timer
5055 plus one apbt timer for broadcast timer.
5056 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5058 xen_512gb_limit [KNL,X86-64,XEN]
5059 Restricts the kernel running paravirtualized under Xen
5060 to use only up to 512 GB of RAM. The reason to do so is
5061 crash analysis tools and Xen tools for doing domain
5062 save/restore/migration must be enabled to handle larger
5065 xen_emul_unplug= [HW,X86,XEN]
5066 Unplug Xen emulated devices
5067 Format: [unplug0,][unplug1]
5068 ide-disks -- unplug primary master IDE devices
5069 aux-ide-disks -- unplug non-primary-master IDE devices
5070 nics -- unplug network devices
5071 all -- unplug all emulated devices (NICs and IDE disks)
5072 unnecessary -- unplugging emulated devices is
5073 unnecessary even if the host did not respond to
5075 never -- do not unplug even if version check succeeds
5077 xen_legacy_crash [X86,XEN]
5078 Crash from Xen panic notifier, without executing late
5079 panic() code such as dumping handler.
5081 xen_nopvspin [X86,XEN]
5082 Disables the ticketlock slowpath using Xen PV
5086 Disables the PV optimizations forcing the HVM guest to
5087 run as generic HVM guest with no PV drivers.
5089 xen.balloon_boot_timeout= [XEN]
5090 The time (in seconds) to wait before giving up to boot
5091 in case initial ballooning fails to free enough memory.
5092 Applies only when running as HVM or PVH guest and
5093 started with less memory configured than allowed at
5094 max. Default is 180.
5096 xen.event_eoi_delay= [XEN]
5097 How long to delay EOI handling in case of event
5098 storms (jiffies). Default is 10.
5100 xen.event_loop_timeout= [XEN]
5101 After which time (jiffies) the event handling loop
5102 should start to delay EOI handling. Default is 2.
5104 xirc2ps_cs= [NET,PCMCIA]
5106 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]