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
785 [same as hugepagesz=] The size of the default
786 HugeTLB page size. This is the size represented by
787 the legacy /proc/ hugepages APIs, used for SHM, and
788 default size when mounting hugetlbfs filesystems.
789 Defaults to the default architecture's huge page size
793 Set number of hash buckets for dentry cache.
795 disable_1tb_segments [PPC]
796 Disables the use of 1TB hash page table segments. This
797 causes the kernel to fall back to 256MB segments which
798 can be useful when debugging issues that require an SLB
802 See Documentation/networking/ipv6.txt.
805 Disable RADIX MMU mode on POWER9
807 disable_cpu_apicid= [X86,APIC,SMP]
809 The number of initial APIC ID for the
810 corresponding CPU to be disabled at boot,
811 mostly used for the kdump 2nd kernel to
812 disable BSP to wake up multiple CPUs without
813 causing system reset or hang due to sending
816 disable_ddw [PPC/PSERIES]
817 Disable Dynamic DMA Window support. Use this if
818 to workaround buggy firmware.
821 See Documentation/networking/ipv6.txt.
823 disable_mtrr_cleanup [X86]
824 The kernel tries to adjust MTRR layout from continuous
825 to discrete, to make X server driver able to add WB
826 entry later. This parameter disables that.
828 disable_mtrr_trim [X86, Intel and AMD only]
829 By default the kernel will trim any uncacheable
830 memory out of your available memory pool based on
831 MTRR settings. This parameter disables that behavior,
832 possibly causing your machine to run very slowly.
834 disable_timer_pin_1 [X86]
835 Disable PIN 1 of APIC timer
836 Can be useful to work around chipset bugs.
838 dis_ucode_ldr [X86] Disable the microcode loader.
840 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
841 this option disables the debugging code at boot.
843 dma_debug_entries=<number>
844 This option allows to tune the number of preallocated
845 entries for DMA-API debugging code. One entry is
846 required per DMA-API allocation. Use this if the
847 DMA-API debugging code disables itself because the
848 architectural default is too low.
850 dma_debug_driver=<driver_name>
851 With this option the DMA-API debugging driver
852 filter feature can be enabled at boot time. Just
853 pass the driver to filter for as the parameter.
854 The filter can be disabled or changed to another
855 driver later using sysfs.
857 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
858 Broken monitors, graphic adapters, KVMs and EDIDless
859 panels may send no or incorrect EDID data sets.
860 This parameter allows to specify an EDID data sets
861 in the /lib/firmware directory that are used instead.
862 Generic built-in EDID data sets are used, if one of
863 edid/1024x768.bin, edid/1280x1024.bin,
864 edid/1680x1050.bin, or edid/1920x1080.bin is given
865 and no file with the same name exists. Details and
866 instructions how to build your own EDID data are
867 available in Documentation/EDID/HOWTO.txt. An EDID
868 data set will only be used for a particular connector,
869 if its name and a colon are prepended to the EDID
870 name. Each connector may use a unique EDID data
871 set by separating the files with a comma. An EDID
872 data set with no connector name will be used for
873 any connectors not explicitly specified.
878 Format: {"off" | "known"}
879 Control how the dt_cpu_ftrs device-tree binding is
880 used for CPU feature discovery and setup (if it
882 off: Do not use it, fall back to legacy cpu table.
883 known: Do not pass through unknown features to guests
884 or userspace, only those that the kernel is aware of.
886 dump_apple_properties [X86]
887 Dump name and content of EFI device properties on
888 x86 Macs. Useful for driver authors to determine
889 what data is available or for reverse-engineering.
891 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
892 module.dyndbg[="val"]
893 Enable debug messages at boot time. See
894 Documentation/admin-guide/dynamic-debug-howto.rst
897 nompx [X86] Disables Intel Memory Protection Extensions.
898 See Documentation/x86/intel_mpx.txt for more
899 information about the feature.
901 nopku [X86] Disable Memory Protection Keys CPU feature found
904 module.async_probe [KNL]
905 Enable asynchronous probe on this module.
907 early_ioremap_debug [KNL]
908 Enable debug messages in early_ioremap support. This
909 is useful for tracking down temporary early mappings
910 which are not unmapped.
912 earlycon= [KNL] Output early console device and options.
914 When used with no options, the early console is
915 determined by the stdout-path property in device
918 cdns,<addr>[,options]
919 Start an early, polled-mode console on a Cadence
920 (xuartps) serial port at the specified address. Only
921 supported option is baud rate. If baud rate is not
922 specified, the serial port must already be setup and
925 uart[8250],io,<addr>[,options]
926 uart[8250],mmio,<addr>[,options]
927 uart[8250],mmio32,<addr>[,options]
928 uart[8250],mmio32be,<addr>[,options]
929 uart[8250],0x<addr>[,options]
930 Start an early, polled-mode console on the 8250/16550
931 UART at the specified I/O port or MMIO address.
932 MMIO inter-register address stride is either 8-bit
933 (mmio) or 32-bit (mmio32 or mmio32be).
934 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
935 to be equivalent to 'mmio'. 'options' are specified
936 in the same format described for "console=ttyS<n>"; if
937 unspecified, the h/w is not initialized.
941 Start an early, polled-mode console on a pl011 serial
942 port at the specified address. The pl011 serial port
943 must already be setup and configured. Options are not
944 yet supported. If 'mmio32' is specified, then only
945 the driver will use only 32-bit accessors to read/write
946 the device registers.
949 Start an early, polled-mode console on a meson serial
950 port at the specified address. The serial port must
951 already be setup and configured. Options are not yet
955 Start an early, polled-mode console on an msm serial
956 port at the specified address. The serial port
957 must already be setup and configured. Options are not
961 Start an early, polled-mode console on an msm serial
962 dm port at the specified address. The serial port
963 must already be setup and configured. Options are not
967 Start an early, polled-mode console on a serial port
968 of an Actions Semi SoC, such as S500 or S900, at the
969 specified address. The serial port must already be
970 setup and configured. Options are not yet supported.
972 smh Use ARM semihosting calls for early console.
980 Use early console provided by serial driver available
981 on Samsung SoCs, requires selecting proper type and
982 a correct base address of the selected UART port. The
983 serial port must already be setup and configured.
984 Options are not yet supported.
987 Start an early, polled-mode console on a lantiq serial
988 (lqasc) port at the specified address. The serial port
989 must already be setup and configured. Options are not
994 Use early console provided by Freescale LP UART driver
995 found on Freescale Vybrid and QorIQ LS1021A processors.
996 A valid base address must be provided, and the serial
997 port must already be setup and configured.
1000 Start an early, polled-mode console on the
1001 Armada 3700 serial port at the specified
1002 address. The serial port must already be setup
1003 and configured. Options are not yet supported.
1005 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k,S390]
1010 earlyprintk=serial[,ttySn[,baudrate]]
1011 earlyprintk=serial[,0x...[,baudrate]]
1012 earlyprintk=ttySn[,baudrate]
1013 earlyprintk=dbgp[debugController#]
1014 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1015 earlyprintk=xdbc[xhciController#]
1017 earlyprintk is useful when the kernel crashes before
1018 the normal console is initialized. It is not enabled by
1019 default because it has some cosmetic problems.
1021 Append ",keep" to not disable it when the real console
1024 Only one of vga, efi, serial, or usb debug port can
1027 Currently only ttyS0 and ttyS1 may be specified by
1028 name. Other I/O ports may be explicitly specified
1029 on some architectures (x86 and arm at least) by
1030 replacing ttySn with an I/O port address, like this:
1031 earlyprintk=serial,0x1008,115200
1032 You can find the port for a given device in
1033 /proc/tty/driver/serial:
1034 2: uart:ST16650V2 port:00001008 irq:18 ...
1036 Interaction with the standard serial driver is not
1039 The VGA and EFI output is eventually overwritten by
1042 The xen output can only be used by Xen PV guests.
1044 The sclp output can only be used on s390.
1046 The optional "force" to "pciserial" enables use of a
1047 PCI device even when its classcode is not of the
1050 edac_report= [HW,EDAC] Control how to report EDAC event
1051 Format: {"on" | "off" | "force"}
1052 on: enable EDAC to report H/W event. May be overridden
1053 by other higher priority error reporting module.
1054 off: disable H/W event reporting through EDAC.
1055 force: enforce the use of EDAC to report H/W event.
1058 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1061 This is designed to be used in conjunction with
1062 the boot argument: earlyprintk=vga
1065 Format: {"off" | "on" | "skip[mbr]"}
1068 Format: { "old_map", "nochunk", "noruntime", "debug" }
1069 old_map [X86-64]: switch to the old ioremap-based EFI
1070 runtime services mapping. 32-bit still uses this one by
1072 nochunk: disable reading files in "chunks" in the EFI
1073 boot stub, as chunking can cause problems with some
1074 firmware implementations.
1075 noruntime : disable EFI runtime services support
1076 debug: enable misc debug output
1078 efi_no_storage_paranoia [EFI; X86]
1079 Using this parameter you can use more than 50% of
1080 your efi variable storage. Use this parameter only if
1081 you are really sure that your UEFI does sane gc and
1082 fulfills the spec otherwise your board may brick.
1084 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1085 Add arbitrary attribute to specific memory range by
1086 updating original EFI memory map.
1087 Region of memory which aa attribute is added to is
1089 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1090 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1091 attribute is added to range 0x100000000-0x180000000 and
1092 0x10a0000000-0x1120000000.
1094 Using this parameter you can do debugging of EFI memmap
1095 related feature. For example, you can do debugging of
1096 Address Range Mirroring feature even if your box
1099 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1100 that is to be dynamically loaded by Linux. If there are
1101 multiple variables with the same name but with different
1102 vendor GUIDs, all of them will be loaded. See
1103 Documentation/acpi/ssdt-overlays.txt for details.
1106 eisa_irq_edge= [PARISC,HW]
1107 See header of drivers/parisc/eisa.c.
1110 See comment before function elanfreq_setup() in
1111 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1114 Format: {"cfq" | "deadline" | "noop"}
1115 See Documentation/block/cfq-iosched.txt and
1116 Documentation/block/deadline-iosched.txt for details.
1118 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1119 Specifies physical address of start of kernel core
1120 image elf header and optionally the size. Generally
1121 kexec loader will pass this option to capture kernel.
1122 See Documentation/kdump/kdump.txt for details.
1124 enable_mtrr_cleanup [X86]
1125 The kernel tries to adjust MTRR layout from continuous
1126 to discrete, to make X server driver able to add WB
1127 entry later. This parameter enables that.
1129 enable_timer_pin_1 [X86]
1130 Enable PIN 1 of APIC timer
1131 Can be useful to work around chipset bugs
1132 (in particular on some ATI chipsets).
1133 The kernel tries to set a reasonable default.
1135 enforcing [SELINUX] Set initial enforcing status.
1137 See security/selinux/Kconfig help text.
1138 0 -- permissive (log only, no denials).
1139 1 -- enforcing (deny and log).
1141 Value can be changed at runtime via /selinux/enforce.
1144 Disable Error Record Serialization Table (ERST)
1147 ether= [HW,NET] Ethernet cards parameters
1148 This option is obsoleted by the "netdev=" option, which
1149 has equivalent usage. See its documentation for details.
1153 Permit 'security.evm' to be updated regardless of
1154 current integrity status.
1158 fail_make_request=[KNL]
1159 General fault injection mechanism.
1160 Format: <interval>,<probability>,<space>,<times>
1161 See also Documentation/fault-injection/.
1164 See Documentation/blockdev/floppy.txt.
1166 force_pal_cache_flush
1167 [IA-64] Avoid check_sal_cache_flush which may hang on
1168 buggy SAL_CACHE_FLUSH implementations. Using this
1169 parameter will force ia64_sal_cache_flush to call
1170 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1173 Forcefully enable Physical Address Extension (PAE).
1174 Many Pentium M systems disable PAE but may have a
1175 functionally usable PAE implementation.
1176 Warning: use of this parameter will taint the kernel
1177 and may cause unknown problems.
1180 [FTRACE] will set and start the specified tracer
1181 as early as possible in order to facilitate early
1184 ftrace_dump_on_oops[=orig_cpu]
1185 [FTRACE] will dump the trace buffers on oops.
1186 If no parameter is passed, ftrace will dump
1187 buffers of all CPUs, but if you pass orig_cpu, it will
1188 dump only the buffer of the CPU that triggered the
1191 ftrace_filter=[function-list]
1192 [FTRACE] Limit the functions traced by the function
1193 tracer at boot up. function-list is a comma separated
1194 list of functions. This list can be changed at run
1195 time by the set_ftrace_filter file in the debugfs
1198 ftrace_notrace=[function-list]
1199 [FTRACE] Do not trace the functions specified in
1200 function-list. This list can be changed at run time
1201 by the set_ftrace_notrace file in the debugfs
1204 ftrace_graph_filter=[function-list]
1205 [FTRACE] Limit the top level callers functions traced
1206 by the function graph tracer at boot up.
1207 function-list is a comma separated list of functions
1208 that can be changed at run time by the
1209 set_graph_function file in the debugfs tracing directory.
1211 ftrace_graph_notrace=[function-list]
1212 [FTRACE] Do not trace from the functions specified in
1213 function-list. This list is a comma separated list of
1214 functions that can be changed at run time by the
1215 set_graph_notrace file in the debugfs tracing directory.
1217 ftrace_graph_max_depth=<uint>
1218 [FTRACE] Used with the function graph tracer. This is
1219 the max depth it will trace into a function. This value
1220 can be changed at run time by the max_graph_depth file
1221 in the tracefs tracing directory. default: 0 (no limit)
1224 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1225 support via parallel port (up to 5 devices per port)
1226 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1227 See also Documentation/input/joystick-parport.txt
1231 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1235 gather_data_sampling=
1236 [X86,INTEL] Control the Gather Data Sampling (GDS)
1239 Gather Data Sampling is a hardware vulnerability which
1240 allows unprivileged speculative access to data which was
1241 previously stored in vector registers.
1243 This issue is mitigated by default in updated microcode.
1244 The mitigation may have a performance impact but can be
1245 disabled. On systems without the microcode mitigation
1246 disabling AVX serves as a mitigation.
1248 force: Disable AVX to mitigate systems without
1249 microcode mitigation. No effect if the microcode
1250 mitigation is present. Known to cause crashes in
1251 userspace with buggy AVX enumeration.
1253 off: Disable GDS mitigation.
1255 gcov_persist= [GCOV] When non-zero (default), profiling data for
1256 kernel modules is saved and remains accessible via
1257 debugfs, even when the module is unloaded/reloaded.
1258 When zero, profiling data is discarded and associated
1259 debugfs files are removed at module unload time.
1261 goldfish [X86] Enable the goldfish android emulator platform.
1262 Don't use this when you are not running on the
1265 gpt [EFI] Forces disk with valid GPT signature but
1266 invalid Protective MBR to be treated as GPT. If the
1267 primary GPT is corrupted, it enables the backup/alternate
1268 GPT to be used instead.
1270 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1271 the "Enable 0" bit of the configuration register.
1274 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1275 the "Enable 0" bit of the configuration register.
1278 grcan.select= [HW] Select which physical interface to use.
1281 grcan.txsize= [HW] Sets the size of the tx buffer.
1282 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1284 grcan.rxsize= [HW] Sets the size of the rx buffer.
1285 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1288 gpio-mockup.gpio_mockup_ranges
1289 [HW] Sets the ranges of gpiochip of for this device.
1290 Format: <start1>,<end1>,<start2>,<end2>...
1292 hardlockup_all_cpu_backtrace=
1293 [KNL] Should the hard-lockup detector generate
1294 backtraces on all cpus.
1297 hashdist= [KNL,NUMA] Large hashes allocated during boot
1298 are distributed across NUMA nodes. Defaults on
1299 for 64-bit NUMA, off otherwise.
1300 Format: 0 | 1 (for off | on)
1302 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1304 hd= [EIDE] (E)IDE hard drive subsystem geometry
1305 Format: <cyl>,<head>,<sect>
1308 Disable Hardware Error Source Table (HEST) support;
1309 corresponding firmware-first mode error processing
1310 logic will be disabled.
1312 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1313 size of <nn>. This works even on boxes that have no
1314 highmem otherwise. This also works to reduce highmem
1315 size on bigger boxes.
1317 highres= [KNL] Enable/disable high resolution timer mode.
1318 Valid parameters: "on", "off"
1322 See Documentation/isdn/README.HiSax.
1326 hpet= [X86-32,HPET] option to control HPET usage
1327 Format: { enable (default) | disable | force |
1329 disable: disable HPET and use PIT instead
1330 force: allow force enabled of undocumented chips (ICH4,
1332 verbose: show contents of HPET registers during setup
1334 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1335 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1337 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1338 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1339 On x86-64 and powerpc, this option can be specified
1340 multiple times interleaved with hugepages= to reserve
1341 huge pages of different sizes. Valid pages sizes on
1342 x86-64 are 2M (when the CPU supports "pse") and 1G
1343 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1345 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1346 terminal devices. Valid values: 0..8
1347 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1348 If specified, z/VM IUCV HVC accepts connections
1349 from listed z/VM user IDs only.
1351 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1352 hardware thread id mappings.
1353 Format: <cpu>:<hwthread>
1356 Do not unregister boot console at start. This is only
1357 useful for debugging when something happens in the window
1358 between unregistering the boot console and initializing
1361 i2c_bus= [HW] Override the default board specific I2C bus speed
1362 or register an additional I2C bus that is not
1363 registered from board initialization code.
1367 i8042.debug [HW] Toggle i8042 debug mode
1368 i8042.unmask_kbd_data
1369 [HW] Enable printing of interrupt data from the KBD port
1370 (disabled by default, and as a pre-condition
1371 requires that i8042.debug=1 be enabled)
1372 i8042.direct [HW] Put keyboard port into non-translated mode
1373 i8042.dumbkbd [HW] Pretend that controller can only read data from
1374 keyboard and cannot control its state
1375 (Don't attempt to blink the leds)
1376 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1377 i8042.nokbd [HW] Don't check/create keyboard port
1378 i8042.noloop [HW] Disable the AUX Loopback command while probing
1380 i8042.nomux [HW] Don't check presence of an active multiplexing
1382 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1384 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1385 i8042.reset [HW] Reset the controller during init, cleanup and
1386 suspend-to-ram transitions, only during s2r
1387 transitions, or never reset
1388 Format: { 1 | Y | y | 0 | N | n }
1389 1, Y, y: always reset controller
1390 0, N, n: don't ever reset controller
1391 Default: only on s2r transitions on x86; most other
1392 architectures force reset to be always executed
1393 i8042.unlock [HW] Unlock (ignore) the keylock
1394 i8042.kbdreset [HW] Reset device connected to KBD port
1398 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1399 indicates that the driver is running on unsupported
1401 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1402 does not match list of supported models.
1404 [HW] Report power status in /proc/i8k
1405 (disabled by default)
1406 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1409 i915.invert_brightness=
1410 [DRM] Invert the sense of the variable that is used to
1411 set the brightness of the panel backlight. Normally a
1412 brightness value of 0 indicates backlight switched off,
1413 and the maximum of the brightness value sets the backlight
1414 to maximum brightness. If this parameter is set to 0
1415 (default) and the machine requires it, or this parameter
1416 is set to 1, a brightness value of 0 sets the backlight
1417 to maximum brightness, and the maximum of the brightness
1418 value switches the backlight off.
1419 -1 -- never invert brightness
1420 0 -- machine default
1421 1 -- force brightness inversion
1424 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1426 ide-core.nodma= [HW] (E)IDE subsystem
1427 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1428 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1429 .cdrom .chs .ignore_cable are additional options
1430 See Documentation/ide/ide.txt.
1432 ide-generic.probe-mask= [HW] (E)IDE subsystem
1434 Probe mask for legacy ISA IDE ports. Depending on
1435 platform up to 6 ports are supported, enabled by
1436 setting corresponding bits in the mask to 1. The
1437 default value is 0x0, which has a special meaning.
1438 On systems that have PCI, it triggers scanning the
1439 PCI bus for the first and the second port, which
1440 are then probed. On systems without PCI the value
1441 of 0x0 enables probing the two first ports as if it
1444 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1445 Claim all unknown PCI IDE storage controllers.
1448 Format: idle=poll, idle=halt, idle=nomwait
1449 Poll forces a polling idle loop that can slightly
1450 improve the performance of waking up a idle CPU, but
1451 will use a lot of power and make the system run hot.
1453 idle=halt: Halt is forced to be used for CPU idle.
1454 In such case C2/C3 won't be used again.
1455 idle=nomwait: Disable mwait for CPU C-states
1457 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1458 Format: { strict | legacy | 2008 | relaxed }
1461 Choose which programs will be accepted for execution
1462 based on the IEEE 754 NaN encoding(s) supported by
1463 the FPU and the NaN encoding requested with the value
1464 of an ELF file header flag individually set by each
1465 binary. Hardware implementations are permitted to
1466 support either or both of the legacy and the 2008 NaN
1469 Available settings are as follows:
1470 strict accept binaries that request a NaN encoding
1471 supported by the FPU
1472 legacy only accept legacy-NaN binaries, if supported
1474 2008 only accept 2008-NaN binaries, if supported
1476 relaxed accept any binaries regardless of whether
1477 supported by the FPU
1479 The FPU emulator is always able to support both NaN
1480 encodings, so if no FPU hardware is present or it has
1481 been disabled with 'nofpu', then the settings of
1482 'legacy' and '2008' strap the emulator accordingly,
1483 'relaxed' straps the emulator for both legacy-NaN and
1484 2008-NaN, whereas 'strict' enables legacy-NaN only on
1485 legacy processors and both NaN encodings on MIPS32 or
1488 The setting for ABS.fmt/NEG.fmt instruction execution
1489 mode generally follows that for the NaN encoding,
1490 except where unsupported by hardware.
1492 ignore_loglevel [KNL]
1493 Ignore loglevel setting - this will print /all/
1494 kernel messages to the console. Useful for debugging.
1495 We also add it as printk module parameter, so users
1496 could change it dynamically, usually by
1497 /sys/module/printk/parameters/ignore_loglevel.
1500 Ignore RLIMIT_DATA setting for data mappings,
1501 print warning at first misuse. Can be changed via
1502 /sys/module/kernel/parameters/ignore_rlimit_data.
1504 ihash_entries= [KNL]
1505 Set number of hash buckets for inode cache.
1507 ima_appraise= [IMA] appraise integrity measurements
1508 Format: { "off" | "enforce" | "fix" | "log" }
1511 ima_appraise_tcb [IMA]
1512 The builtin appraise policy appraises all files
1515 ima_canonical_fmt [IMA]
1516 Use the canonical format for the binary runtime
1517 measurements, instead of host native format.
1520 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1524 The list of supported hash algorithms is defined
1525 in crypto/hash_info.h.
1528 The builtin policies to load during IMA setup.
1529 Format: "tcb | appraise_tcb | secure_boot"
1531 The "tcb" policy measures all programs exec'd, files
1532 mmap'd for exec, and all files opened with the read
1533 mode bit set by either the effective uid (euid=0) or
1536 The "appraise_tcb" policy appraises the integrity of
1537 all files owned by root. (This is the equivalent
1538 of ima_appraise_tcb.)
1540 The "secure_boot" policy appraises the integrity
1541 of files (eg. kexec kernel image, kernel modules,
1542 firmware, policy, etc) based on file signatures.
1544 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1545 Load a policy which meets the needs of the Trusted
1546 Computing Base. This means IMA will measure all
1547 programs exec'd, files mmap'd for exec, and all files
1548 opened for read by uid=0.
1551 Select one of defined IMA measurements template formats.
1552 Formats: { "ima" | "ima-ng" | "ima-sig" }
1556 [IMA] Define a custom template format.
1557 Format: { "field1|...|fieldN" }
1559 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1560 Format: <min_file_size>
1561 Set the minimal file size for using asynchronous hash.
1562 If left unspecified, ahash usage is disabled.
1564 ahash performance varies for different data sizes on
1565 different crypto accelerators. This option can be used
1566 to achieve the best performance for a particular HW.
1568 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1570 Set hashing buffer size. Default: 4k.
1572 ahash performance varies for different chunk sizes on
1573 different crypto accelerators. This option can be used
1574 to achieve best performance for particular HW.
1578 Run specified binary instead of /sbin/init as init
1581 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1582 for working out where the kernel is dying during
1585 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1586 initcall functions. Useful for debugging built-in
1587 modules and initcalls.
1589 initrd= [BOOT] Specify the location of the initial ramdisk
1591 init_pkru= [x86] Specify the default memory protection keys rights
1592 register contents for all processes. 0x55555554 by
1593 default (disallow access to all but pkey 0). Can
1594 override in debugfs after boot.
1596 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1599 int_pln_enable [x86] Enable power limit notification interrupt
1601 integrity_audit=[IMA]
1602 Format: { "0" | "1" }
1603 0 -- basic integrity auditing messages. (Default)
1604 1 -- additional integrity auditing messages.
1606 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1608 Enable intel iommu driver.
1610 Disable intel iommu driver.
1611 igfx_off [Default Off]
1612 By default, gfx is mapped as normal device. If a gfx
1613 device has a dedicated DMAR unit, the DMAR unit is
1614 bypassed by not enabling DMAR with this option. In
1615 this case, gfx device will use physical address for
1618 With this option iommu will not optimize to look
1619 for io virtual address below 32-bit forcing dual
1620 address cycle on pci bus for cards supporting greater
1621 than 32-bit addressing. The default is to look
1622 for translation below 32-bit and if not available
1623 then look in the higher range.
1624 strict [Default Off]
1625 With this option on every unmap_single operation will
1626 result in a hardware IOTLB flush operation as opposed
1627 to batching them for performance.
1628 sp_off [Default Off]
1629 By default, super page will be supported if Intel IOMMU
1630 has the capability. With this option, super page will
1632 ecs_off [Default Off]
1633 By default, extended context tables will be supported if
1634 the hardware advertises that it has support both for the
1635 extended tables themselves, and also PASID support. With
1636 this option set, extended tables will not be used even
1637 on hardware which claims to support them.
1638 tboot_noforce [Default Off]
1639 Do not force the Intel IOMMU enabled under tboot.
1640 By default, tboot will force Intel IOMMU on, which
1641 could harm performance of some high-throughput
1642 devices like 40GBit network cards, even if identity
1644 Note that using this option lowers the security
1645 provided by tboot because it makes the system
1646 vulnerable to DMA attacks.
1648 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1649 0 disables intel_idle and fall back on acpi_idle.
1650 1 to 9 specify maximum depth of C-state.
1654 Do not enable intel_pstate as the default
1655 scaling driver for the supported processors
1657 Use intel_pstate as a scaling driver, but configure it
1658 to work with generic cpufreq governors (instead of
1659 enabling its internal governor). This mode cannot be
1660 used along with the hardware-managed P-states (HWP)
1663 Enable intel_pstate on systems that prohibit it by default
1664 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1665 instead of acpi-cpufreq may disable platform features, such
1666 as thermal controls and power capping, that rely on ACPI
1667 P-States information being indicated to OSPM and therefore
1668 should be used with caution. This option does not work with
1669 processors that aren't supported by the intel_pstate driver
1670 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1672 Do not enable hardware P state control (HWP)
1675 Only load intel_pstate on systems which support
1676 hardware P state control (HWP) if available.
1678 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1679 Description Table, specifies preferred power management
1680 profile as "Enterprise Server" or "Performance Server",
1681 then this feature is turned on by default.
1683 Allow per-logical-CPU P-State performance control limits using
1684 cpufreq sysfs interface
1686 intremap= [X86-64, Intel-IOMMU]
1687 on enable Interrupt Remapping (default)
1688 off disable Interrupt Remapping
1689 nosid disable Source ID checking
1691 BIOS x2APIC opt-out request will be ignored
1692 nopost disable Interrupt Posting
1694 iomem= Disable strict checking of access to MMIO memory
1695 strict regions from userspace.
1710 nobypass [PPC/POWERNV]
1711 Disable IOMMU bypass, using IOMMU for PCI devices.
1714 [ARM64] Configure DMA to bypass the IOMMU by default.
1715 Format: { "0" | "1" }
1716 0 - Use IOMMU translation for DMA.
1717 1 - Bypass the IOMMU for DMA.
1718 unset - Use IOMMU translation for DMA.
1720 io7= [HW] IO7 for Marvel based alpha systems
1721 See comment before marvel_specify_io7 in
1722 arch/alpha/kernel/core_marvel.c.
1724 io_delay= [X86] I/O delay method
1726 Standard port 0x80 based delay
1728 Alternate port 0xed based delay (needed on some systems)
1730 Simple two microseconds delay
1735 See Documentation/filesystems/nfs/nfsroot.txt.
1737 irqaffinity= [SMP] Set the default irq affinity mask
1738 The argument is a cpu list, as described above.
1741 When an interrupt is not handled search all handlers
1742 for it. Intended to get systems with badly broken
1746 When an interrupt is not handled search all handlers
1747 for it. Also check all handlers each timer
1748 interrupt. Intended to get systems with badly broken
1752 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1754 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1755 The argument is a cpu list, as described above.
1757 This option can be used to specify one or more CPUs
1758 to isolate from the general SMP balancing and scheduling
1759 algorithms. You can move a process onto or off an
1760 "isolated" CPU via the CPU affinity syscalls or cpuset.
1761 <cpu number> begins at 0 and the maximum value is
1762 "number of CPUs in system - 1".
1764 This option is the preferred way to isolate CPUs. The
1765 alternative -- manually setting the CPU mask of all
1766 tasks in the system -- can cause problems and
1767 suboptimal load balancer performance.
1771 ivrs_ioapic [HW,X86_64]
1772 Provide an override to the IOAPIC-ID<->DEVICE-ID
1773 mapping provided in the IVRS ACPI table. For
1774 example, to map IOAPIC-ID decimal 10 to
1775 PCI device 00:14.0 write the parameter as:
1776 ivrs_ioapic[10]=00:14.0
1778 ivrs_hpet [HW,X86_64]
1779 Provide an override to the HPET-ID<->DEVICE-ID
1780 mapping provided in the IVRS ACPI table. For
1781 example, to map HPET-ID decimal 0 to
1782 PCI device 00:14.0 write the parameter as:
1783 ivrs_hpet[0]=00:14.0
1785 ivrs_acpihid [HW,X86_64]
1786 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1787 mapping provided in the IVRS ACPI table. For
1788 example, to map UART-HID:UID AMD0020:0 to
1789 PCI device 00:14.5 write the parameter as:
1790 ivrs_acpihid[00:14.5]=AMD0020:0
1792 js= [HW,JOY] Analog joystick
1793 See Documentation/input/joystick.txt.
1796 When CONFIG_RANDOMIZE_BASE is set, this disables
1797 kernel and module base offset ASLR (Address Space
1798 Layout Randomization).
1801 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1802 report on every invalid memory access. Without this
1803 parameter KASAN will print report only for the first
1808 kernelcore= [KNL,X86,IA-64,PPC]
1809 Format: nn[KMGTPE] | "mirror"
1811 specifies the amount of memory usable by the kernel
1812 for non-movable allocations. The requested amount is
1813 spread evenly throughout all nodes in the system. The
1814 remaining memory in each node is used for Movable
1815 pages. In the event, a node is too small to have both
1816 kernelcore and Movable pages, kernelcore pages will
1817 take priority and other nodes will have a larger number
1818 of Movable pages. The Movable zone is used for the
1819 allocation of pages that may be reclaimed or moved
1820 by the page migration subsystem. This means that
1821 HugeTLB pages may not be allocated from this zone.
1822 Note that allocations like PTEs-from-HighMem still
1823 use the HighMem zone if it exists, and the Normal
1824 zone if it does not.
1826 Instead of specifying the amount of memory (nn[KMGTPE]),
1827 you can specify "mirror" option. In case "mirror"
1828 option is specified, mirrored (reliable) memory is used
1829 for non-movable allocations and remaining memory is used
1830 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1831 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1834 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1835 Format: <Controller#>[,poll interval]
1836 The controller # is the number of the ehci usb debug
1837 port as it is probed via PCI. The poll interval is
1838 optional and is the number seconds in between
1839 each poll cycle to the debug port in case you need
1840 the functionality for interrupting the kernel with
1841 gdb or control-c on the dbgp connection. When
1842 not using this parameter you use sysrq-g to break into
1843 the kernel debugger.
1845 kgdboc= [KGDB,HW] kgdb over consoles.
1846 Requires a tty driver that supports console polling,
1847 or a supported polling keyboard driver (non-usb).
1848 Serial only format: <serial_device>[,baud]
1849 keyboard only format: kbd
1850 keyboard and serial format: kbd,<serial_device>[,baud]
1851 Optional Kernel mode setting:
1852 kms, kbd format: kms,kbd
1853 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1855 kgdbwait [KGDB] Stop kernel execution and enter the
1856 kernel debugger at the earliest opportunity.
1858 kmac= [MIPS] korina ethernet MAC address.
1859 Configure the RouterBoard 532 series on-chip
1860 Ethernet adapter MAC address.
1862 kmemleak= [KNL] Boot-time kmemleak enable/disable
1863 Valid arguments: on, off
1865 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1868 kpti= [ARM64] Control page table isolation of user
1869 and kernel address spaces.
1870 Default: enabled on cores which need mitigation.
1874 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1875 Default is 0 (don't ignore, but inject #GP)
1877 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1882 [KVM] Controls the software workaround for the
1883 X86_BUG_ITLB_MULTIHIT bug.
1884 force : Always deploy workaround.
1885 off : Never deploy workaround.
1886 auto : Deploy workaround based on the presence of
1887 X86_BUG_ITLB_MULTIHIT.
1891 If the software workaround is enabled for the host,
1892 guests do need not to enable it for nested guests.
1894 kvm.nx_huge_pages_recovery_ratio=
1895 [KVM] Controls how many 4KiB pages are periodically zapped
1896 back to huge pages. 0 disables the recovery, otherwise if
1897 the value is N KVM will zap 1/Nth of the 4KiB pages every
1898 minute. The default is 60.
1900 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1901 Default is 1 (enabled)
1903 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1905 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1907 kvm-arm.vgic_v3_group0_trap=
1908 [KVM,ARM] Trap guest accesses to GICv3 group-0
1911 kvm-arm.vgic_v3_group1_trap=
1912 [KVM,ARM] Trap guest accesses to GICv3 group-1
1915 kvm-arm.vgic_v3_common_trap=
1916 [KVM,ARM] Trap guest accesses to GICv3 common
1919 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1920 (virtualized MMU) support on capable Intel chips.
1921 Default is 1 (enabled)
1923 kvm-intel.emulate_invalid_guest_state=
1924 [KVM,Intel] Disable emulation of invalid guest state.
1925 Ignored if kvm-intel.enable_unrestricted_guest=1, as
1926 guest state is never invalid for unrestricted guests.
1927 This param doesn't apply to nested guests (L2), as KVM
1928 never emulates invalid L2 guest state.
1929 Default is 1 (enabled)
1931 kvm-intel.flexpriority=
1932 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1933 Default is 1 (enabled)
1936 [KVM,Intel] Enable VMX nesting (nVMX).
1937 Default is 0 (disabled)
1939 kvm-intel.unrestricted_guest=
1940 [KVM,Intel] Disable unrestricted guest feature
1941 (virtualized real and unpaged mode) on capable
1942 Intel chips. Default is 1 (enabled)
1944 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1947 Valid arguments: never, cond, always
1949 always: L1D cache flush on every VMENTER.
1950 cond: Flush L1D on VMENTER only when the code between
1951 VMEXIT and VMENTER can leak host memory.
1952 never: Disables the mitigation
1954 Default is cond (do L1 cache flush in specific instances)
1956 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1957 feature (tagged TLBs) on capable Intel chips.
1958 Default is 1 (enabled)
1960 l1tf= [X86] Control mitigation of the L1TF vulnerability on
1963 The kernel PTE inversion protection is unconditionally
1964 enabled and cannot be disabled.
1967 Provides all available mitigations for the
1968 L1TF vulnerability. Disables SMT and
1969 enables all mitigations in the
1970 hypervisors, i.e. unconditional L1D flush.
1972 SMT control and L1D flush control via the
1973 sysfs interface is still possible after
1974 boot. Hypervisors will issue a warning
1975 when the first VM is started in a
1976 potentially insecure configuration,
1977 i.e. SMT enabled or L1D flush disabled.
1980 Same as 'full', but disables SMT and L1D
1981 flush runtime control. Implies the
1982 'nosmt=force' command line option.
1983 (i.e. sysfs control of SMT is disabled.)
1986 Leaves SMT enabled and enables the default
1987 hypervisor mitigation, i.e. conditional
1990 SMT control and L1D flush control via the
1991 sysfs interface is still possible after
1992 boot. Hypervisors will issue a warning
1993 when the first VM is started in a
1994 potentially insecure configuration,
1995 i.e. SMT enabled or L1D flush disabled.
1999 Disables SMT and enables the default
2000 hypervisor mitigation.
2002 SMT control and L1D flush control via the
2003 sysfs interface is still possible after
2004 boot. Hypervisors will issue a warning
2005 when the first VM is started in a
2006 potentially insecure configuration,
2007 i.e. SMT enabled or L1D flush disabled.
2010 Same as 'flush', but hypervisors will not
2011 warn when a VM is started in a potentially
2012 insecure configuration.
2015 Disables hypervisor mitigations and doesn't
2017 It also drops the swap size and available
2018 RAM limit restriction on both hypervisor and
2023 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2029 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2032 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2033 value for LAPIC timer one-shot implementation. Default
2034 back to the programmable timer unit in the LAPIC.
2036 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2039 libata.dma= [LIBATA] DMA control
2040 libata.dma=0 Disable all PATA and SATA DMA
2041 libata.dma=1 PATA and SATA Disk DMA only
2042 libata.dma=2 ATAPI (CDROM) DMA only
2043 libata.dma=4 Compact Flash DMA only
2044 Combinations also work, so libata.dma=3 enables DMA
2045 for disks and CDROMs, but not CFs.
2047 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2048 libata.ignore_hpa=0 keep BIOS limits (default)
2049 libata.ignore_hpa=1 ignore limits, using full disk
2051 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2055 libata.force= [LIBATA] Force configurations. The format is comma
2056 separated list of "[ID:]VAL" where ID is
2057 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2058 matching port, link or device. Basically, it matches
2059 the ATA ID string printed on console by libata. If
2060 the whole ID part is omitted, the last PORT and DEVICE
2061 values are used. If ID hasn't been specified yet, the
2062 configuration applies to all ports, links and devices.
2064 If only DEVICE is omitted, the parameter applies to
2065 the port and all links and devices behind it. DEVICE
2066 number of 0 either selects the first device or the
2067 first fan-out link behind PMP device. It does not
2068 select the host link. DEVICE number of 15 selects the
2069 host link and device attached to it.
2071 The VAL specifies the configuration to force. As long
2072 as there's no ambiguity shortcut notation is allowed.
2073 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2074 The following configurations can be forced.
2076 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2077 Any ID with matching PORT is used.
2079 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2081 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2082 udma[/][16,25,33,44,66,100,133] notation is also
2085 * [no]ncq: Turn on or off NCQ.
2087 * [no]ncqtrim: Turn off queued DSM TRIM.
2089 * nohrst, nosrst, norst: suppress hard, soft
2092 * rstonce: only attempt one reset during
2093 hot-unplug link recovery
2095 * dump_id: dump IDENTIFY data.
2097 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2099 * disable: Disable this device.
2101 If there are multiple matching configurations changing
2102 the same attribute, the last one is used.
2104 memblock=debug [KNL] Enable memblock debug messages.
2106 load_ramdisk= [RAM] List of ramdisks to load from floppy
2107 See Documentation/blockdev/ramdisk.txt.
2109 lockd.nlm_grace_period=P [NFS] Assign grace period.
2112 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2115 lockd.nlm_timeout=T [NFS] Assign timeout value.
2118 lockd.nlm_udpport=M [NFS] Assign UDP port.
2121 locktorture.nreaders_stress= [KNL]
2122 Set the number of locking read-acquisition kthreads.
2123 Defaults to being automatically set based on the
2124 number of online CPUs.
2126 locktorture.nwriters_stress= [KNL]
2127 Set the number of locking write-acquisition kthreads.
2129 locktorture.onoff_holdoff= [KNL]
2130 Set time (s) after boot for CPU-hotplug testing.
2132 locktorture.onoff_interval= [KNL]
2133 Set time (s) between CPU-hotplug operations, or
2134 zero to disable CPU-hotplug testing.
2136 locktorture.shuffle_interval= [KNL]
2137 Set task-shuffle interval (jiffies). Shuffling
2138 tasks allows some CPUs to go into dyntick-idle
2139 mode during the locktorture test.
2141 locktorture.shutdown_secs= [KNL]
2142 Set time (s) after boot system shutdown. This
2143 is useful for hands-off automated testing.
2145 locktorture.stat_interval= [KNL]
2146 Time (s) between statistics printk()s.
2148 locktorture.stutter= [KNL]
2149 Time (s) to stutter testing, for example,
2150 specifying five seconds causes the test to run for
2151 five seconds, wait for five seconds, and so on.
2152 This tests the locking primitive's ability to
2153 transition abruptly to and from idle.
2155 locktorture.torture_runnable= [BOOT]
2156 Start locktorture running at boot time.
2158 locktorture.torture_type= [KNL]
2159 Specify the locking implementation to test.
2161 locktorture.verbose= [KNL]
2162 Enable additional printk() statements.
2164 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2167 loglevel= All Kernel Messages with a loglevel smaller than the
2168 console loglevel will be printed to the console. It can
2169 also be changed with klogd or other programs. The
2170 loglevels are defined as follows:
2172 0 (KERN_EMERG) system is unusable
2173 1 (KERN_ALERT) action must be taken immediately
2174 2 (KERN_CRIT) critical conditions
2175 3 (KERN_ERR) error conditions
2176 4 (KERN_WARNING) warning conditions
2177 5 (KERN_NOTICE) normal but significant condition
2178 6 (KERN_INFO) informational
2179 7 (KERN_DEBUG) debug-level messages
2181 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2182 in bytes. n must be a power of two and greater
2183 than the minimal size. The minimal size is defined
2184 by LOG_BUF_SHIFT kernel config parameter. There is
2185 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2186 that allows to increase the default size depending on
2187 the number of CPUs. See init/Kconfig for more details.
2189 logo.nologo [FB] Disables display of the built-in Linux logo.
2190 This may be used to provide more screen space for
2191 kernel log messages and is useful when debugging
2192 kernel boot problems.
2194 lp=0 [LP] Specify parallel ports to use, e.g,
2195 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2196 lp=reset first parallel port). 'lp=0' disables the
2197 lp=auto printer driver. 'lp=reset' (which can be
2198 specified in addition to the ports) causes
2199 attached printers to be reset. Using
2200 lp=port1,port2,... specifies the parallel ports
2201 to associate lp devices with, starting with
2202 lp0. A port specification may be 'none' to skip
2203 that lp device, or a parport name such as
2204 'parport0'. Specifying 'lp=auto' instead of a
2205 port specification list means that device IDs
2206 from each port should be examined, to see if
2207 an IEEE 1284-compliant printer is attached; if
2208 so, the driver will manage that printer.
2209 See also header of drivers/char/lp.c.
2212 Sets loops_per_jiffy to given constant, thus avoiding
2213 time-consuming boot-time autodetection (up to 250 ms per
2214 CPU). 0 enables autodetection (default). To determine
2215 the correct value for your kernel, boot with normal
2216 autodetection and see what value is printed. Note that
2217 on SMP systems the preset will be applied to all CPUs,
2218 which is likely to cause problems if your CPUs need
2219 significantly divergent settings. An incorrect value
2220 will cause delays in the kernel to be wrong, leading to
2221 unpredictable I/O errors and other breakage. Although
2222 unlikely, in the extreme case this might damage your
2226 Format: <io>,<irq>,<dma>
2228 machvec= [IA-64] Force the use of a particular machine-vector
2229 (machvec) in a generic kernel.
2230 Example: machvec=hpzx1_swiotlb
2232 machtype= [Loongson] Share the same kernel image file between different
2234 Example: machtype=lemote-yeeloong-2f-7inch
2236 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2237 than or equal to this physical address is ignored.
2239 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2240 will bring up during bootup. maxcpus=n : n >= 0 limits
2241 the kernel to bring up 'n' processors. Surely after
2242 bootup you can bring up the other plugged cpu by executing
2243 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2244 only takes effect during system bootup.
2245 While n=0 is a special case, it is equivalent to "nosmp",
2246 which also disables the IO APIC.
2248 max_loop= [LOOP] The number of loop block devices that get
2249 (loop.max_loop) unconditionally pre-created at init time. The default
2250 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2251 of statically allocating a predefined number, loop
2252 devices can be requested on-demand with the
2253 /dev/loop-control interface.
2255 mce [X86-32] Machine Check Exception
2257 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2259 md= [HW] RAID subsystems devices and level
2260 See Documentation/admin-guide/md.rst.
2263 Format: <first>,<last>
2264 Specifies range of consoles to be captured by the MDA.
2267 Control mitigation for the Micro-architectural Data
2268 Sampling (MDS) vulnerability.
2270 Certain CPUs are vulnerable to an exploit against CPU
2271 internal buffers which can forward information to a
2272 disclosure gadget under certain conditions.
2274 In vulnerable processors, the speculatively
2275 forwarded data can be used in a cache side channel
2276 attack, to access data to which the attacker does
2277 not have direct access.
2279 This parameter controls the MDS mitigation. The
2282 full - Enable MDS mitigation on vulnerable CPUs
2283 full,nosmt - Enable MDS mitigation and disable
2284 SMT on vulnerable CPUs
2285 off - Unconditionally disable MDS mitigation
2287 On TAA-affected machines, mds=off can be prevented by
2288 an active TAA mitigation as both vulnerabilities are
2289 mitigated with the same mechanism so in order to disable
2290 this mitigation, you need to specify tsx_async_abort=off
2293 Not specifying this option is equivalent to
2296 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2298 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2299 Amount of memory to be used when the kernel is not able
2300 to see the whole system memory or for test.
2301 [X86] Work as limiting max address. Use together
2302 with memmap= to avoid physical address space collisions.
2303 Without memmap= PCI devices could be placed at addresses
2304 belonging to unused RAM.
2306 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2310 [KNL,SH] Allow user to override the default size for
2311 per-device physically contiguous DMA buffers.
2313 memhp_default_state=online/offline
2314 [KNL] Set the initial state for the memory hotplug
2315 onlining policy. If not specified, the default value is
2316 set according to the
2317 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2319 See Documentation/memory-hotplug.txt.
2321 memmap=exactmap [KNL,X86] Enable setting of an exact
2322 E820 memory map, as specified by the user.
2323 Such memmap=exactmap lines can be constructed based on
2324 BIOS output or other requirements. See the memmap=nn@ss
2327 memmap=nn[KMG]@ss[KMG]
2328 [KNL] Force usage of a specific region of memory.
2329 Region of memory to be used is from ss to ss+nn.
2330 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2331 which limits max address to nn[KMG].
2332 Multiple different regions can be specified,
2335 memmap=100M@2G,100M#3G,1G!1024G
2337 memmap=nn[KMG]#ss[KMG]
2338 [KNL,ACPI] Mark specific memory as ACPI data.
2339 Region of memory to be marked is from ss to ss+nn.
2341 memmap=nn[KMG]$ss[KMG]
2342 [KNL,ACPI] Mark specific memory as reserved.
2343 Region of memory to be reserved is from ss to ss+nn.
2344 Example: Exclude memory from 0x18690000-0x1869ffff
2345 memmap=64K$0x18690000
2347 memmap=0x10000$0x18690000
2348 Some bootloaders may need an escape character before '$',
2349 like Grub2, otherwise '$' and the following number
2352 memmap=nn[KMG]!ss[KMG]
2353 [KNL,X86] Mark specific memory as protected.
2354 Region of memory to be used, from ss to ss+nn.
2355 The memory region may be marked as e820 type 12 (0xc)
2356 and is NVDIMM or ADR memory.
2358 memory_corruption_check=0/1 [X86]
2359 Some BIOSes seem to corrupt the first 64k of
2360 memory when doing things like suspend/resume.
2361 Setting this option will scan the memory
2362 looking for corruption. Enabling this will
2363 both detect corruption and prevent the kernel
2364 from using the memory being corrupted.
2365 However, its intended as a diagnostic tool; if
2366 repeatable BIOS-originated corruption always
2367 affects the same memory, you can use memmap=
2368 to prevent the kernel from using that memory.
2370 memory_corruption_check_size=size [X86]
2371 By default it checks for corruption in the low
2372 64k, making this memory unavailable for normal
2373 use. Use this parameter to scan for
2374 corruption in more or less memory.
2376 memory_corruption_check_period=seconds [X86]
2377 By default it checks for corruption every 60
2378 seconds. Use this parameter to check at some
2379 other rate. 0 disables periodic checking.
2381 memtest= [KNL,X86,ARM] Enable memtest
2383 default : 0 <disable>
2384 Specifies the number of memtest passes to be
2385 performed. Each pass selects another test
2386 pattern from a given set of patterns. Memtest
2387 fills the memory with this pattern, validates
2388 memory contents and reserves bad memory
2389 regions that are detected.
2391 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2392 Valid arguments: on, off
2393 Default (depends on kernel configuration option):
2394 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2395 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2396 mem_encrypt=on: Activate SME
2397 mem_encrypt=off: Do not activate SME
2399 Refer to Documentation/x86/amd-memory-encryption.txt
2400 for details on when memory encryption can be activated.
2402 mem_sleep_default= [SUSPEND] Default system suspend mode:
2403 s2idle - Suspend-To-Idle
2404 shallow - Power-On Suspend or equivalent (if supported)
2405 deep - Suspend-To-RAM or equivalent (if supported)
2406 See Documentation/power/states.txt.
2408 meye.*= [HW] Set MotionEye Camera parameters
2409 See Documentation/video4linux/meye.txt.
2411 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2412 Multi-Function General Purpose Timers on AMD Geode
2415 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2416 the BIOS has incorrectly applied a workaround. TinyBIOS
2417 version 0.98 is known to be affected, 0.99 fixes the
2418 problem by letting the user disable the workaround.
2422 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2423 physical address is ignored.
2425 mini2440= [ARM,HW,KNL]
2426 Format:[0..2][b][c][t]
2428 MINI2440 configuration specification:
2429 0 - The attached screen is the 3.5" TFT
2430 1 - The attached screen is the 7" TFT
2431 2 - The VGA Shield is attached (1024x768)
2432 Leaving out the screen size parameter will not load
2433 the TFT driver, and the framebuffer will be left
2435 b - Enable backlight. The TFT backlight pin will be
2436 linked to the kernel VESA blanking code and a GPIO
2437 LED. This parameter is not necessary when using the
2439 c - Enable the s3c camera interface.
2440 t - Reserved for enabling touchscreen support. The
2441 touchscreen support is not enabled in the mainstream
2442 kernel as of 2.6.30, a preliminary port can be found
2443 in the "bleeding edge" mini2440 support kernel at
2444 http://repo.or.cz/w/linux-2.6/mini2440.git
2447 [X86,PPC,S390,ARM64] Control optional mitigations for
2448 CPU vulnerabilities. This is a set of curated,
2449 arch-independent options, each of which is an
2450 aggregation of existing arch-specific options.
2453 Disable all optional CPU mitigations. This
2454 improves system performance, but it may also
2455 expose users to several CPU vulnerabilities.
2456 Equivalent to: gather_data_sampling=off [X86]
2458 kvm.nx_huge_pages=off [X86]
2461 mmio_stale_data=off [X86]
2462 no_entry_flush [PPC]
2463 no_uaccess_flush [PPC]
2468 nospectre_v2 [X86,PPC,S390,ARM64]
2469 spec_store_bypass_disable=off [X86,PPC]
2470 spectre_v2_user=off [X86]
2471 ssbd=force-off [ARM64]
2472 tsx_async_abort=off [X86]
2475 This does not have any effect on
2476 kvm.nx_huge_pages when
2477 kvm.nx_huge_pages=force.
2480 Mitigate all CPU vulnerabilities, but leave SMT
2481 enabled, even if it's vulnerable. This is for
2482 users who don't want to be surprised by SMT
2483 getting disabled across kernel upgrades, or who
2484 have other ways of avoiding SMT-based attacks.
2485 Equivalent to: (default behavior)
2488 Mitigate all CPU vulnerabilities, disabling SMT
2489 if needed. This is for users who always want to
2490 be fully mitigated, even if it means losing SMT.
2491 Equivalent to: l1tf=flush,nosmt [X86]
2492 mds=full,nosmt [X86]
2493 tsx_async_abort=full,nosmt [X86]
2494 mmio_stale_data=full,nosmt [X86]
2497 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2498 parameter allows control of the logging verbosity for
2499 the additional memory initialisation checks. A value
2500 of 0 disables mminit logging and a level of 4 will
2501 log everything. Information is printed at KERN_DEBUG
2502 so loglevel=8 may also need to be specified.
2505 [X86,INTEL] Control mitigation for the Processor
2506 MMIO Stale Data vulnerabilities.
2508 Processor MMIO Stale Data is a class of
2509 vulnerabilities that may expose data after an MMIO
2510 operation. Exposed data could originate or end in
2511 the same CPU buffers as affected by MDS and TAA.
2512 Therefore, similar to MDS and TAA, the mitigation
2513 is to clear the affected CPU buffers.
2515 This parameter controls the mitigation. The
2518 full - Enable mitigation on vulnerable CPUs
2520 full,nosmt - Enable mitigation and disable SMT on
2523 off - Unconditionally disable mitigation
2525 On MDS or TAA affected machines,
2526 mmio_stale_data=off can be prevented by an active
2527 MDS or TAA mitigation as these vulnerabilities are
2528 mitigated with the same mechanism so in order to
2529 disable this mitigation, you need to specify
2530 mds=off and tsx_async_abort=off too.
2532 Not specifying this option is equivalent to
2533 mmio_stale_data=full.
2536 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
2539 [KNL] When CONFIG_MODULE_SIG is set, this means that
2540 modules without (valid) signatures will fail to load.
2541 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2542 is always true, so this option does nothing.
2544 module_blacklist= [KNL] Do not load a comma-separated list of
2545 modules. Useful for debugging problem modules.
2548 [MOUSE] Maximum time between finger touching and
2549 leaving touchpad surface for touch to be considered
2550 a tap and be reported as a left button click (for
2551 touchpads working in absolute mode only).
2553 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2554 reporting absolute coordinates, such as tablets
2555 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2556 reporting absolute coordinates, such as tablets
2558 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2559 is similar to kernelcore except it specifies the
2560 amount of memory used for migratable allocations.
2561 If both kernelcore and movablecore is specified,
2562 then kernelcore will be at *least* the specified
2563 value but may be more. If movablecore on its own
2564 is specified, the administrator must be careful
2565 that the amount of memory usable for all allocations
2568 movable_node [KNL] Boot-time switch to make hotplugable memory
2569 NUMA nodes to be movable. This means that the memory
2570 of such nodes will be usable only for movable
2571 allocations which rules out almost all kernel
2572 allocations. Use with caution!
2574 MTD_Partition= [MTD]
2575 Format: <name>,<region-number>,<size>,<offset>
2577 MTD_Region= [MTD] Format:
2578 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2581 See drivers/mtd/cmdlinepart.c.
2583 multitce=off [PPC] This parameter disables the use of the pSeries
2584 firmware feature for updating multiple TCE entries
2587 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2589 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2591 boundary - index of last SLC block on Flex-OneNAND.
2592 The remaining blocks are configured as MLC blocks.
2593 lock - Configure if Flex-OneNAND boundary should be locked.
2594 Once locked, the boundary cannot be changed.
2595 1 indicates lock status, 0 indicates unlock status.
2598 ARM/S3C2412 JIVE boot control
2600 See arch/arm/mach-s3c2412/mach-jive.c
2602 mtouchusb.raw_coordinates=
2603 [HW] Make the MicroTouch USB driver use raw coordinates
2604 ('y', default) or cooked coordinates ('n')
2606 mtrr_chunk_size=nn[KMG] [X86]
2607 used for mtrr cleanup. It is largest continuous chunk
2608 that could hold holes aka. UC entries.
2610 mtrr_gran_size=nn[KMG] [X86]
2611 Used for mtrr cleanup. It is granularity of mtrr block.
2613 Large value could prevent small alignment from
2616 mtrr_spare_reg_nr=n [X86]
2618 Range: 0,7 : spare reg number
2620 Used for mtrr cleanup. It is spare mtrr entries number.
2621 Set to 2 or more if your graphical card needs more.
2623 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2625 netdev= [NET] Network devices parameters
2626 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2627 Note that mem_start is often overloaded to mean
2628 something different and driver-specific.
2629 This usage is only documented in each driver source
2633 [NETFILTER] Enable connection tracking flow accounting
2634 0 to disable accounting
2635 1 to enable accounting
2638 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2639 See Documentation/filesystems/nfs/nfsroot.txt.
2641 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2642 See Documentation/filesystems/nfs/nfsroot.txt.
2644 nfsrootdebug [NFS] enable nfsroot debugging messages.
2645 See Documentation/filesystems/nfs/nfsroot.txt.
2647 nfs.callback_nr_threads=
2648 [NFSv4] set the total number of threads that the
2649 NFS client will assign to service NFSv4 callback
2652 nfs.callback_tcpport=
2653 [NFS] set the TCP port on which the NFSv4 callback
2654 channel should listen.
2657 [NFS] sets the pathname to the program which is used
2658 to update the NFS client cache entries.
2660 nfs.cache_getent_timeout=
2661 [NFS] sets the timeout after which an attempt to
2662 update a cache entry is deemed to have failed.
2664 nfs.idmap_cache_timeout=
2665 [NFS] set the maximum lifetime for idmapper cache
2669 [NFS] enable 64-bit inode numbers.
2670 If zero, the NFS client will fake up a 32-bit inode
2671 number for the readdir() and stat() syscalls instead
2672 of returning the full 64-bit number.
2673 The default is to return 64-bit inode numbers.
2675 nfs.max_session_cb_slots=
2676 [NFSv4.1] Sets the maximum number of session
2677 slots the client will assign to the callback
2678 channel. This determines the maximum number of
2679 callbacks the client will process in parallel for
2680 a particular server.
2682 nfs.max_session_slots=
2683 [NFSv4.1] Sets the maximum number of session slots
2684 the client will attempt to negotiate with the server.
2685 This limits the number of simultaneous RPC requests
2686 that the client can send to the NFSv4.1 server.
2687 Note that there is little point in setting this
2688 value higher than the max_tcp_slot_table_limit.
2690 nfs.nfs4_disable_idmapping=
2691 [NFSv4] When set to the default of '1', this option
2692 ensures that both the RPC level authentication
2693 scheme and the NFS level operations agree to use
2694 numeric uids/gids if the mount is using the
2695 'sec=sys' security flavour. In effect it is
2696 disabling idmapping, which can make migration from
2697 legacy NFSv2/v3 systems to NFSv4 easier.
2698 Servers that do not support this mode of operation
2699 will be autodetected by the client, and it will fall
2700 back to using the idmapper.
2701 To turn off this behaviour, set the value to '0'.
2703 [NFS4] Specify an additional fixed unique ident-
2704 ification string that NFSv4 clients can insert into
2705 their nfs_client_id4 string. This is typically a
2706 UUID that is generated at system install time.
2708 nfs.send_implementation_id =
2709 [NFSv4.1] Send client implementation identification
2710 information in exchange_id requests.
2711 If zero, no implementation identification information
2713 The default is to send the implementation identification
2716 nfs.recover_lost_locks =
2717 [NFSv4] Attempt to recover locks that were lost due
2718 to a lease timeout on the server. Please note that
2719 doing this risks data corruption, since there are
2720 no guarantees that the file will remain unchanged
2721 after the locks are lost.
2722 If you want to enable the kernel legacy behaviour of
2723 attempting to recover these locks, then set this
2725 The default parameter value of '0' causes the kernel
2726 not to attempt recovery of lost locks.
2728 nfs4.layoutstats_timer =
2729 [NFSv4.2] Change the rate at which the kernel sends
2730 layoutstats to the pNFS metadata server.
2732 Setting this to value to 0 causes the kernel to use
2733 whatever value is the default set by the layout
2734 driver. A non-zero value sets the minimum interval
2735 in seconds between layoutstats transmissions.
2737 nfsd.nfs4_disable_idmapping=
2738 [NFSv4] When set to the default of '1', the NFSv4
2739 server will return only numeric uids and gids to
2740 clients using auth_sys, and will accept numeric uids
2741 and gids from such clients. This is intended to ease
2742 migration from NFSv2/v3.
2744 nmi_debug= [KNL,SH] Specify one or more actions to take
2745 when a NMI is triggered.
2746 Format: [state][,regs][,debounce][,die]
2748 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2749 Format: [panic,][nopanic,][num]
2751 0 - turn hardlockup detector in nmi_watchdog off
2752 1 - turn hardlockup detector in nmi_watchdog on
2753 When panic is specified, panic when an NMI watchdog
2754 timeout occurs (or 'nopanic' to override the opposite
2755 default). To disable both hard and soft lockup detectors,
2756 please see 'nowatchdog'.
2757 This is useful when you use a panic=... timeout and
2758 need the box quickly up again.
2760 netpoll.carrier_timeout=
2761 [NET] Specifies amount of time (in seconds) that
2762 netpoll should wait for a carrier. By default netpoll
2765 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2766 emulation library even if a 387 maths coprocessor
2770 [HW] Never suspend the console
2771 Disable suspending of consoles during suspend and
2772 hibernate operations. Once disabled, debugging
2773 messages can reach various consoles while the rest
2774 of the system is being put to sleep (ie, while
2775 debugging driver suspend/resume hooks). This may
2776 not work reliably with all consoles, but is known
2777 to work with serial and VGA consoles.
2778 To facilitate more flexible debugging, we also add
2779 console_suspend, a printk module parameter to control
2780 it. Users could use console_suspend (usually
2781 /sys/module/printk/parameters/console_suspend) to
2782 turn on/off it dynamically.
2784 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2785 caches in the slab allocator. Saves per-node memory,
2786 but will impact performance.
2790 noaltinstr [S390] Disables alternative instructions patching
2791 (CPU alternatives feature).
2793 noapic [SMP,APIC] Tells the kernel to not make use of any
2794 IOAPICs that may be present in the system.
2796 noautogroup Disable scheduler automatic task group creation.
2798 nobats [PPC] Do not use BATs for mapping kernel lowmem
2799 on "Classic" PPC cores.
2803 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2805 nodelayacct [KNL] Disable per-task delay accounting
2807 nodsp [SH] Disable hardware DSP at boot time.
2809 noefi Disable EFI runtime services support.
2811 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
2816 On X86-32 available only on PAE configured kernels.
2817 noexec=on: enable non-executable mappings (default)
2818 noexec=off: disable non-executable mappings
2821 Disable SMAP (Supervisor Mode Access Prevention)
2822 even if it is supported by processor.
2825 Disable SMEP (Supervisor Mode Execution Prevention)
2826 even if it is supported by processor.
2829 This affects only 32-bit executables.
2830 noexec32=on: enable non-executable mappings (default)
2831 read doesn't imply executable mappings
2832 noexec32=off: disable non-executable mappings
2833 read implies executable mappings
2835 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2837 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2838 register save and restore. The kernel will only save
2839 legacy floating-point registers on task switch.
2841 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2843 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2844 Equivalent to smt=1.
2846 [KNL,x86] Disable symmetric multithreading (SMT).
2847 nosmt=force: Force disable SMT, cannot be undone
2848 via the sysfs control file.
2850 nospectre_v1 [X66, PPC] Disable mitigations for Spectre Variant 1
2851 (bounds check bypass). With this option data leaks
2852 are possible in the system.
2854 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
2855 the Spectre variant 2 (indirect branch prediction)
2856 vulnerability. System may allow data leaks with this
2859 nospec_store_bypass_disable
2860 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2863 [PPC] Don't flush the L1-D cache after accessing user data.
2865 noxsave [BUGS=X86] Disables x86 extended register state save
2866 and restore using xsave. The kernel will fallback to
2867 enabling legacy floating-point and sse state.
2869 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2870 register states. The kernel will fall back to use
2871 xsave to save the states. By using this parameter,
2872 performance of saving the states is degraded because
2873 xsave doesn't support modified optimization while
2874 xsaveopt supports it on xsaveopt enabled systems.
2876 noxsaves [X86] Disables xsaves and xrstors used in saving and
2877 restoring x86 extended register state in compacted
2878 form of xsave area. The kernel will fall back to use
2879 xsaveopt and xrstor to save and restore the states
2880 in standard form of xsave area. By using this
2881 parameter, xsave area per process might occupy more
2882 memory on xsaves enabled systems.
2884 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2885 wfi(ARM) instruction doesn't work correctly and not to
2886 use it. This is also useful when using JTAG debugger.
2888 no_file_caps Tells the kernel not to honor file capabilities. The
2889 only way then for a file to be executed with privilege
2890 is to be setuid root or executed by root.
2892 nohalt [IA-64] Tells the kernel not to use the power saving
2893 function PAL_HALT_LIGHT when idle. This increases
2894 power-consumption. On the positive side, it reduces
2895 interrupt wake-up latency, which may improve performance
2896 in certain environments such as networked servers or
2899 nohibernate [HIBERNATION] Disable hibernation and resume.
2901 nohz= [KNL] Boottime enable/disable dynamic ticks
2902 Valid arguments: on, off
2905 nohz_full= [KNL,BOOT]
2906 The argument is a cpu list, as described above.
2907 In kernels built with CONFIG_NO_HZ_FULL=y, set
2908 the specified list of CPUs whose tick will be stopped
2909 whenever possible. The boot CPU will be forced outside
2910 the range to maintain the timekeeping. Any CPUs
2911 in this list will have their RCU callbacks offloaded,
2912 just as if they had also been called out in the
2913 rcu_nocbs= boot parameter.
2915 noiotrap [SH] Disables trapped I/O port accesses.
2917 noirqdebug [X86-32] Disables the code which attempts to detect and
2918 disable unhandled interrupt sources.
2920 no_timer_check [X86,APIC] Disables the code which tests for
2921 broken timer IRQ sources.
2923 noisapnp [ISAPNP] Disables ISA PnP code.
2925 noinitrd [RAM] Tells the kernel not to load any configured
2928 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2930 [Deprecated - use intremap=off]
2934 noinvpcid [X86] Disable the INVPCID cpu feature.
2936 nojitter [IA-64] Disables jitter checking for ITC timers.
2938 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2940 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2944 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2945 clock and use the default one.
2947 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2948 steal time is computed, but won't influence scheduler
2951 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2953 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2955 noltlbs [PPC] Do not use large page/tlb entries for kernel
2956 lowmem mapping on PPC40x and PPC8xx
2958 nomca [IA-64] Disable machine check abort handling
2960 nomce [X86-32] Disable Machine Check Exception
2962 nomfgpt [X86-32] Disable Multi-Function General Purpose
2963 Timer usage (for AMD Geode machines).
2965 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2966 shutdown the other cpus. Instead use the REBOOT_VECTOR
2969 nomodule Disable module load
2971 nopat [X86] Disable PAT (page attribute table extension of
2972 pagetables) support.
2974 nopcid [X86-64] Disable the PCID cpu feature.
2976 norandmaps Don't use address space randomization. Equivalent to
2977 echo 0 > /proc/sys/kernel/randomize_va_space
2979 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2980 with UP alternatives
2982 nordrand [X86] Disable kernel use of the RDRAND and
2983 RDSEED instructions even if they are supported
2984 by the processor. RDRAND and RDSEED are still
2985 available to user space applications.
2987 noresume [SWSUSP] Disables resume and restores original swap
2990 no-scroll [VGA] Disables scrollback.
2991 This is required for the Braillex ib80-piezo Braille
2992 reader made by F.H. Papenmeier (Germany).
2996 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2998 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2999 and disable the IO APIC. legacy for "maxcpus=0".
3001 nosoftlockup [KNL] Disable the soft-lockup detector.
3003 nosync [HW,M68K] Disables sync negotiation for all devices.
3005 notsc [BUGS=X86-32] Disable Time Stamp Counter
3007 nowatchdog [KNL] Disable both lockup detectors, i.e.
3008 soft-lockup and NMI watchdog (hard-lockup).
3012 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3014 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3015 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3016 Some features depend on CPU0. Known dependencies are:
3017 1. Resume from suspend/hibernate depends on CPU0.
3018 Suspend/hibernate will fail if CPU0 is offline and you
3019 need to online CPU0 before suspend/hibernate.
3020 2. PIC interrupts also depend on CPU0. CPU0 can't be
3021 removed if a PIC interrupt is detected.
3022 It's said poweroff/reboot may depend on CPU0 on some
3023 machines although I haven't seen such issues so far
3024 after CPU0 is offline on a few tested machines.
3025 If the dependencies are under your control, you can
3026 turn on cpu0_hotplug.
3028 nps_mtm_hs_ctr= [KNL,ARC]
3029 This parameter sets the maximum duration, in
3030 cycles, each HW thread of the CTOP can run
3031 without interruptions, before HW switches it.
3032 The actual maximum duration is 16 times this
3034 Format: integer between 1 and 255
3037 nptcg= [IA-64] Override max number of concurrent global TLB
3038 purges which is reported from either PAL_VM_SUMMARY or
3041 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3042 could support. nr_cpus=n : n >= 1 limits the kernel to
3043 support 'n' processors. It could be larger than the
3044 number of already plugged CPU during bootup, later in
3045 runtime you can physically add extra cpu until it reaches
3046 n. So during boot up some boot time memory for per-cpu
3047 variables need be pre-allocated for later physical cpu
3050 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3052 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3053 Allowed values are enable and disable
3055 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3056 'node', 'default' can be specified
3057 This can be set from sysctl after boot.
3058 See Documentation/sysctl/vm.txt for details.
3060 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3061 See Documentation/debugging-via-ohci1394.txt for more
3064 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3065 Rather than timing out after 20 ms if an EC
3066 command is not properly ACKed, override the length
3067 of the timeout. We have interrupts disabled while
3068 waiting for the ACK, so if this is set too high
3069 interrupts *may* be lost!
3071 omap_mux= [OMAP] Override bootloader pin multiplexing.
3072 Format: <mux_mode0.mode_name=value>...
3073 For example, to override I2C bus2:
3074 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3076 oprofile.timer= [HW]
3077 Use timer interrupt instead of performance counters
3079 oprofile.cpu_type= Force an oprofile cpu type
3080 This might be useful if you have an older oprofile
3081 userland or if you want common events.
3082 Format: { arch_perfmon }
3083 arch_perfmon: [X86] Force use of architectural
3084 perfmon on Intel CPUs instead of the
3085 CPU specific event set.
3086 timer: [X86] Force use of architectural NMI
3087 timer mode (see also oprofile.timer
3088 for generic hr timer mode)
3090 oops=panic Always panic on oopses. Default is to just kill the
3091 process, but there is a small probability of
3092 deadlocking the machine.
3093 This will also cause panics on machine check exceptions.
3094 Useful together with panic=30 to trigger a reboot.
3097 See Documentation/sound/oss/oss-parameters.txt
3099 page_owner= [KNL] Boot-time page_owner enabling option.
3100 Storage of the information about who allocated
3101 each page is disabled in default. With this switch,
3103 on: enable the feature
3105 page_poison= [KNL] Boot-time parameter changing the state of
3106 poisoning on the buddy allocator.
3107 off: turn off poisoning
3108 on: turn on poisoning
3110 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3111 timeout > 0: seconds before rebooting
3112 timeout = 0: wait forever
3113 timeout < 0: reboot immediately
3116 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3119 crash_kexec_post_notifiers
3120 Run kdump after running panic-notifiers and dumping
3121 kmsg. This only for the users who doubt kdump always
3122 succeeds in any situation.
3123 Note that this also increases risks of kdump failure,
3124 because some panic notifiers can make the crashed
3125 kernel more unstable.
3127 parkbd.port= [HW] Parallel port number the keyboard adapter is
3128 connected to, default is 0.
3130 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3131 0 for XT, 1 for AT (default is AT).
3134 parport= [HW,PPT] Specify parallel ports. 0 disables.
3135 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3136 Use 'auto' to force the driver to use any
3137 IRQ/DMA settings detected (the default is to
3138 ignore detected IRQ/DMA settings because of
3139 possible conflicts). You can specify the base
3140 address, IRQ, and DMA settings; IRQ and DMA
3141 should be numbers, or 'auto' (for using detected
3142 settings on that particular port), or 'nofifo'
3143 (to avoid using a FIFO even if it is detected).
3144 Parallel ports are assigned in the order they
3145 are specified on the command line, starting
3148 parport_init_mode= [HW,PPT]
3149 Configure VIA parallel port to operate in
3150 a specific mode. This is necessary on Pegasos
3151 computer where firmware has no options for setting
3152 up parallel port mode and sets it to spp.
3153 Currently this function knows 686a and 8231 chips.
3154 Format: [spp|ps2|epp|ecp|ecpepp]
3157 Halt all CPUs after the first oops has been printed for
3158 the specified number of seconds. This is to be used if
3159 your oopses keep scrolling off the screen.
3164 See header of drivers/block/paride/pcd.c.
3165 See also Documentation/blockdev/paride.txt.
3167 pci=option[,option...] [PCI] various PCI subsystem options:
3168 earlydump [X86] dump PCI config space before the kernel
3170 off [X86] don't probe for the PCI bus
3171 bios [X86-32] force use of PCI BIOS, don't access
3172 the hardware directly. Use this if your machine
3173 has a non-standard PCI host bridge.
3174 nobios [X86-32] disallow use of PCI BIOS, only direct
3175 hardware access methods are allowed. Use this
3176 if you experience crashes upon bootup and you
3177 suspect they are caused by the BIOS.
3178 conf1 [X86] Force use of PCI Configuration Access
3179 Mechanism 1 (config address in IO port 0xCF8,
3180 data in IO port 0xCFC, both 32-bit).
3181 conf2 [X86] Force use of PCI Configuration Access
3182 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3183 the function, IO port 0xCFA, also 8-bit, sets
3184 bus number. The config space is then accessed
3185 through ports 0xC000-0xCFFF).
3186 See http://wiki.osdev.org/PCI for more info
3187 on the configuration access mechanisms.
3188 noaer [PCIE] If the PCIEAER kernel config parameter is
3189 enabled, this kernel boot option can be used to
3190 disable the use of PCIE advanced error reporting.
3191 nodomains [PCI] Disable support for multiple PCI
3192 root domains (aka PCI segments, in ACPI-speak).
3193 nommconf [X86] Disable use of MMCONFIG for PCI
3195 check_enable_amd_mmconf [X86] check for and enable
3196 properly configured MMIO access to PCI
3197 config space on AMD family 10h CPU
3198 nomsi [MSI] If the PCI_MSI kernel config parameter is
3199 enabled, this kernel boot option can be used to
3200 disable the use of MSI interrupts system-wide.
3201 noioapicquirk [APIC] Disable all boot interrupt quirks.
3202 Safety option to keep boot IRQs enabled. This
3203 should never be necessary.
3204 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3205 primary IO-APIC for bridges that cannot disable
3206 boot IRQs. This fixes a source of spurious IRQs
3207 when the system masks IRQs.
3208 noioapicreroute [APIC] Disable workaround that uses the
3209 boot IRQ equivalent of an IRQ that connects to
3210 a chipset where boot IRQs cannot be disabled.
3211 The opposite of ioapicreroute.
3212 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3213 routing table. These calls are known to be buggy
3214 on several machines and they hang the machine
3215 when used, but on other computers it's the only
3216 way to get the interrupt routing table. Try
3217 this option if the kernel is unable to allocate
3218 IRQs or discover secondary PCI buses on your
3220 rom [X86] Assign address space to expansion ROMs.
3221 Use with caution as certain devices share
3222 address decoders between ROMs and other
3224 norom [X86] Do not assign address space to
3225 expansion ROMs that do not already have
3226 BIOS assigned address ranges.
3227 nobar [X86] Do not assign address space to the
3228 BARs that weren't assigned by the BIOS.
3229 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3230 assigned automatically to PCI devices. You can
3231 make the kernel exclude IRQs of your ISA cards
3233 pirqaddr=0xAAAAA [X86] Specify the physical address
3234 of the PIRQ table (normally generated
3235 by the BIOS) if it is outside the
3236 F0000h-100000h range.
3237 lastbus=N [X86] Scan all buses thru bus #N. Can be
3238 useful if the kernel is unable to find your
3239 secondary buses and you want to tell it
3240 explicitly which ones they are.
3241 assign-busses [X86] Always assign all PCI bus
3242 numbers ourselves, overriding
3243 whatever the firmware may have done.
3244 usepirqmask [X86] Honor the possible IRQ mask stored
3245 in the BIOS $PIR table. This is needed on
3246 some systems with broken BIOSes, notably
3247 some HP Pavilion N5400 and Omnibook XE3
3248 notebooks. This will have no effect if ACPI
3249 IRQ routing is enabled.
3250 noacpi [X86] Do not use ACPI for IRQ routing
3251 or for PCI scanning.
3252 use_crs [X86] Use PCI host bridge window information
3253 from ACPI. On BIOSes from 2008 or later, this
3254 is enabled by default. If you need to use this,
3255 please report a bug.
3256 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3257 If you need to use this, please report a bug.
3258 routeirq Do IRQ routing for all PCI devices.
3259 This is normally done in pci_enable_device(),
3260 so this option is a temporary workaround
3261 for broken drivers that don't call it.
3262 skip_isa_align [X86] do not align io start addr, so can
3263 handle more pci cards
3264 noearly [X86] Don't do any early type 1 scanning.
3265 This might help on some broken boards which
3266 machine check when some devices' config space
3267 is read. But various workarounds are disabled
3268 and some IOMMU drivers will not work.
3269 bfsort Sort PCI devices into breadth-first order.
3270 This sorting is done to get a device
3271 order compatible with older (<= 2.4) kernels.
3272 nobfsort Don't sort PCI devices into breadth-first order.
3273 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3274 tuning and use the BIOS-configured MPS defaults.
3275 pcie_bus_safe Set every device's MPS to the largest value
3276 supported by all devices below the root complex.
3277 pcie_bus_perf Set device MPS to the largest allowable MPS
3278 based on its parent bus. Also set MRRS (Max
3279 Read Request Size) to the largest supported
3280 value (no larger than the MPS that the device
3281 or bus can support) for best performance.
3282 pcie_bus_peer2peer Set every device's MPS to 128B, which
3283 every device is guaranteed to support. This
3284 configuration allows peer-to-peer DMA between
3285 any pair of devices, possibly at the cost of
3286 reduced performance. This also guarantees
3287 that hot-added devices will work.
3288 cbiosize=nn[KMG] The fixed amount of bus space which is
3289 reserved for the CardBus bridge's IO window.
3290 The default value is 256 bytes.
3291 cbmemsize=nn[KMG] The fixed amount of bus space which is
3292 reserved for the CardBus bridge's memory
3293 window. The default value is 64 megabytes.
3296 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3297 [<order of align>@]pci:<vendor>:<device>\
3298 [:<subvendor>:<subdevice>][; ...]
3299 Specifies alignment and device to reassign
3300 aligned memory resources.
3301 If <order of align> is not specified,
3302 PAGE_SIZE is used as alignment.
3303 PCI-PCI bridge can be specified, if resource
3304 windows need to be expanded.
3305 To specify the alignment for several
3306 instances of a device, the PCI vendor,
3307 device, subvendor, and subdevice may be
3308 specified, e.g., 4096@pci:8086:9c22:103c:198f
3309 ecrc= Enable/disable PCIe ECRC (transaction layer
3310 end-to-end CRC checking).
3311 bios: Use BIOS/firmware settings. This is the
3315 hpiosize=nn[KMG] The fixed amount of bus space which is
3316 reserved for hotplug bridge's IO window.
3317 Default size is 256 bytes.
3318 hpmemsize=nn[KMG] The fixed amount of bus space which is
3319 reserved for hotplug bridge's memory window.
3320 Default size is 2 megabytes.
3321 hpbussize=nn The minimum amount of additional bus numbers
3322 reserved for buses below a hotplug bridge.
3324 realloc= Enable/disable reallocating PCI bridge resources
3325 if allocations done by BIOS are too small to
3326 accommodate resources required by all child
3328 off: Turn realloc off
3330 realloc same as realloc=on
3331 noari do not use PCIe ARI.
3332 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3333 only look for one device below a PCIe downstream
3336 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3339 force Enable ASPM even on devices that claim not to support it.
3340 WARNING: Forcing ASPM on may cause system lockups.
3342 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3343 nomsi Do not use MSI for PCI Express Native Hotplug (this
3344 makes all PCIe ports use INTx for hotplug services).
3346 pcie_ports= [PCIE] PCIe ports handling:
3347 auto Ask the BIOS whether or not to use native PCIe services
3348 associated with PCIe ports (PME, hot-plug, AER). Use
3349 them only if that is allowed by the BIOS.
3350 native Use native PCIe services associated with PCIe ports
3352 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3355 pcie_port_pm= [PCIE] PCIe port power management handling:
3356 off Disable power management of all PCIe ports
3357 force Forcibly enable power management of all PCIe ports
3359 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3360 nomsi Do not use MSI for native PCIe PME signaling (this makes
3361 all PCIe root ports use INTx for all services).
3363 pcmv= [HW,PCMCIA] BadgePAD 4
3367 Keep all power-domains already enabled by bootloader on,
3368 even if no driver has claimed them. This is useful
3369 for debug and development, but should not be
3370 needed on a platform with proper driver support.
3373 See Documentation/blockdev/paride.txt.
3375 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3378 See arch/parisc/kernel/pdc_chassis.c
3380 percpu_alloc= Select which percpu first chunk allocator to use.
3381 Currently supported values are "embed" and "page".
3382 Archs may support subset or none of the selections.
3383 See comments in mm/percpu.c for details on each
3384 allocator. This parameter is primarily for debugging
3385 and performance comparison.
3388 See Documentation/blockdev/paride.txt.
3391 See Documentation/blockdev/paride.txt.
3393 pirq= [SMP,APIC] Manual mp-table setup
3394 See Documentation/x86/i386/IO-APIC.txt.
3396 plip= [PPT,NET] Parallel port network link
3397 Format: { parport<nr> | timid | 0 }
3398 See also Documentation/parport.txt.
3400 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3401 Override pmtimer IOPort with a hex value.
3405 Enable PNP debug messages (depends on the
3406 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3407 via /sys/module/pnp/parameters/debug. We always show
3408 current resource usage; turning this on also shows
3409 possible settings and some assignment information.
3415 { on | off | curr | res | no-curr | no-res }
3418 [ISAPNP] Exclude IRQs for the autoconfiguration
3421 [ISAPNP] Exclude DMAs for the autoconfiguration
3423 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3424 Ranges are in pairs (I/O port base and size).
3427 [ISAPNP] Exclude memory regions for the
3429 Ranges are in pairs (memory base and size).
3431 ports= [IP_VS_FTP] IPVS ftp helper module
3433 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3435 Format: <port>,<port>....
3437 powersave=off [PPC] This option disables power saving features.
3438 It specifically disables cpuidle and sets the
3439 platform machine description specific power_save
3440 function to NULL. On Idle the CPU just reduces
3443 ppc_strict_facility_enable
3444 [PPC] This option catches any kernel floating point,
3445 Altivec, VSX and SPE outside of regions specifically
3446 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3447 There is some performance impact when enabling this.
3449 print-fatal-signals=
3450 [KNL] debug: print fatal signals
3452 If enabled, warn about various signal handling
3453 related application anomalies: too many signals,
3454 too many POSIX.1 timers, fatal signals causing a
3457 If you hit the warning due to signal overflow,
3458 you might want to try "ulimit -i unlimited".
3462 printk.always_kmsg_dump=
3463 Trigger kmsg_dump for cases other than kernel oops or
3465 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3468 printk.devkmsg={on,off,ratelimit}
3469 Control writing to /dev/kmsg.
3470 on - unlimited logging to /dev/kmsg from userspace
3471 off - logging to /dev/kmsg disabled
3472 ratelimit - ratelimit the logging
3475 printk.time= Show timing data prefixed to each printk message line
3476 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3478 processor.max_cstate= [HW,ACPI]
3479 Limit processor to maximum C-state
3480 max_cstate=9 overrides any DMI blacklist limit.
3482 processor.nocst [HW,ACPI]
3483 Ignore the _CST method to determine C-states,
3484 instead using the legacy FADT method
3486 profile= [KNL] Enable kernel profiling via /proc/profile
3487 Format: [schedule,]<number>
3488 Param: "schedule" - profile schedule points.
3489 Param: <number> - step/bucket size as a power of 2 for
3490 statistical time based profiling.
3491 Param: "sleep" - profile D-state sleeping (millisecs).
3492 Requires CONFIG_SCHEDSTATS
3493 Param: "kvm" - profile VM exits.
3495 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3497 See Documentation/blockdev/ramdisk.txt.
3499 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3500 probe for; one of (bare|imps|exps|lifebook|any).
3501 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3503 psmouse.resetafter= [HW,MOUSE]
3504 Try to reset the device after so many bad packets
3507 [HW,MOUSE] Set desired mouse resolution, in dpi.
3508 psmouse.smartscroll=
3509 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3510 0 = disabled, 1 = enabled (default).
3512 pstore.backend= Specify the name of the pstore backend to use
3515 See Documentation/blockdev/paride.txt.
3517 pti= [X86_64] Control Page Table Isolation of user and
3518 kernel address spaces. Disabling this feature
3519 removes hardening, but improves performance of
3520 system calls and interrupts.
3522 on - unconditionally enable
3523 off - unconditionally disable
3524 auto - kernel detects whether your CPU model is
3525 vulnerable to issues that PTI mitigates
3527 Not specifying this option is equivalent to pti=auto.
3530 Equivalent to pti=off
3533 [KNL] Number of legacy pty's. Overwrites compiled-in
3536 quiet [KNL] Disable most log messages
3541 See Documentation/admin-guide/md.rst.
3543 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3544 See Documentation/blockdev/ramdisk.txt.
3546 random.trust_cpu={on,off}
3547 [KNL] Enable or disable trusting the use of the
3548 CPU's random number generator (if available) to
3549 fully seed the kernel's CRNG. Default is controlled
3550 by CONFIG_RANDOM_TRUST_CPU.
3552 random.trust_bootloader={on,off}
3553 [KNL] Enable or disable trusting the use of a
3554 seed passed by the bootloader (if available) to
3555 fully seed the kernel's CRNG. Default is controlled
3556 by CONFIG_RANDOM_TRUST_BOOTLOADER.
3558 ras=option[,option,...] [KNL] RAS-specific options
3561 Disable the Correctable Errors Collector,
3562 see CONFIG_RAS_CEC help text.
3565 The argument is a cpu list, as described above.
3567 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3568 the specified list of CPUs to be no-callback CPUs.
3569 Invocation of these CPUs' RCU callbacks will
3570 be offloaded to "rcuox/N" kthreads created for
3571 that purpose, where "x" is "b" for RCU-bh, "p"
3572 for RCU-preempt, and "s" for RCU-sched, and "N"
3573 is the CPU number. This reduces OS jitter on the
3574 offloaded CPUs, which can be useful for HPC and
3575 real-time workloads. It can also improve energy
3576 efficiency for asymmetric multiprocessors.
3579 Rather than requiring that offloaded CPUs
3580 (specified by rcu_nocbs= above) explicitly
3581 awaken the corresponding "rcuoN" kthreads,
3582 make these kthreads poll for callbacks.
3583 This improves the real-time response for the
3584 offloaded CPUs by relieving them of the need to
3585 wake up the corresponding kthread, but degrades
3586 energy efficiency by requiring that the kthreads
3587 periodically wake up to do the polling.
3589 rcutree.blimit= [KNL]
3590 Set maximum number of finished RCU callbacks to
3591 process in one batch.
3593 rcutree.dump_tree= [KNL]
3594 Dump the structure of the rcu_node combining tree
3595 out at early boot. This is used for diagnostic
3596 purposes, to verify correct tree setup.
3598 rcutree.gp_cleanup_delay= [KNL]
3599 Set the number of jiffies to delay each step of
3600 RCU grace-period cleanup.
3602 rcutree.gp_init_delay= [KNL]
3603 Set the number of jiffies to delay each step of
3604 RCU grace-period initialization.
3606 rcutree.gp_preinit_delay= [KNL]
3607 Set the number of jiffies to delay each step of
3608 RCU grace-period pre-initialization, that is,
3609 the propagation of recent CPU-hotplug changes up
3610 the rcu_node combining tree.
3612 rcutree.rcu_fanout_exact= [KNL]
3613 Disable autobalancing of the rcu_node combining
3614 tree. This is used by rcutorture, and might
3615 possibly be useful for architectures having high
3616 cache-to-cache transfer latencies.
3618 rcutree.rcu_fanout_leaf= [KNL]
3619 Change the number of CPUs assigned to each
3620 leaf rcu_node structure. Useful for very
3621 large systems, which will choose the value 64,
3622 and for NUMA systems with large remote-access
3623 latencies, which will choose a value aligned
3624 with the appropriate hardware boundaries.
3626 rcutree.jiffies_till_sched_qs= [KNL]
3627 Set required age in jiffies for a
3628 given grace period before RCU starts
3629 soliciting quiescent-state help from
3630 rcu_note_context_switch().
3632 rcutree.jiffies_till_first_fqs= [KNL]
3633 Set delay from grace-period initialization to
3634 first attempt to force quiescent states.
3635 Units are jiffies, minimum value is zero,
3636 and maximum value is HZ.
3638 rcutree.jiffies_till_next_fqs= [KNL]
3639 Set delay between subsequent attempts to force
3640 quiescent states. Units are jiffies, minimum
3641 value is one, and maximum value is HZ.
3643 rcutree.kthread_prio= [KNL,BOOT]
3644 Set the SCHED_FIFO priority of the RCU per-CPU
3645 kthreads (rcuc/N). This value is also used for
3646 the priority of the RCU boost threads (rcub/N)
3647 and for the RCU grace-period kthreads (rcu_bh,
3648 rcu_preempt, and rcu_sched). If RCU_BOOST is
3649 set, valid values are 1-99 and the default is 1
3650 (the least-favored priority). Otherwise, when
3651 RCU_BOOST is not set, valid values are 0-99 and
3652 the default is zero (non-realtime operation).
3654 rcutree.rcu_nocb_leader_stride= [KNL]
3655 Set the number of NOCB kthread groups, which
3656 defaults to the square root of the number of
3657 CPUs. Larger numbers reduces the wakeup overhead
3658 on the per-CPU grace-period kthreads, but increases
3659 that same overhead on each group's leader.
3661 rcutree.qhimark= [KNL]
3662 Set threshold of queued RCU callbacks beyond which
3663 batch limiting is disabled.
3665 rcutree.qlowmark= [KNL]
3666 Set threshold of queued RCU callbacks below which
3667 batch limiting is re-enabled.
3669 rcutree.rcu_idle_gp_delay= [KNL]
3670 Set wakeup interval for idle CPUs that have
3671 RCU callbacks (RCU_FAST_NO_HZ=y).
3673 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3674 Set wakeup interval for idle CPUs that have
3675 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3676 Lazy RCU callbacks are those which RCU can
3677 prove do nothing more than free memory.
3679 rcutree.rcu_kick_kthreads= [KNL]
3680 Cause the grace-period kthread to get an extra
3681 wake_up() if it sleeps three times longer than
3682 it should at force-quiescent-state time.
3683 This wake_up() will be accompanied by a
3684 WARN_ONCE() splat and an ftrace_dump().
3686 rcuperf.gp_async= [KNL]
3687 Measure performance of asynchronous
3688 grace-period primitives such as call_rcu().
3690 rcuperf.gp_async_max= [KNL]
3691 Specify the maximum number of outstanding
3692 callbacks per writer thread. When a writer
3693 thread exceeds this limit, it invokes the
3694 corresponding flavor of rcu_barrier() to allow
3695 previously posted callbacks to drain.
3697 rcuperf.gp_exp= [KNL]
3698 Measure performance of expedited synchronous
3699 grace-period primitives.
3701 rcuperf.holdoff= [KNL]
3702 Set test-start holdoff period. The purpose of
3703 this parameter is to delay the start of the
3704 test until boot completes in order to avoid
3707 rcuperf.nreaders= [KNL]
3708 Set number of RCU readers. The value -1 selects
3709 N, where N is the number of CPUs. A value
3710 "n" less than -1 selects N-n+1, where N is again
3711 the number of CPUs. For example, -2 selects N
3712 (the number of CPUs), -3 selects N+1, and so on.
3713 A value of "n" less than or equal to -N selects
3716 rcuperf.nwriters= [KNL]
3717 Set number of RCU writers. The values operate
3718 the same as for rcuperf.nreaders.
3719 N, where N is the number of CPUs
3721 rcuperf.perf_runnable= [BOOT]
3722 Start rcuperf running at boot time.
3724 rcuperf.perf_type= [KNL]
3725 Specify the RCU implementation to test.
3727 rcuperf.shutdown= [KNL]
3728 Shut the system down after performance tests
3729 complete. This is useful for hands-off automated
3732 rcuperf.verbose= [KNL]
3733 Enable additional printk() statements.
3735 rcuperf.writer_holdoff= [KNL]
3736 Write-side holdoff between grace periods,
3737 in microseconds. The default of zero says
3740 rcutorture.cbflood_inter_holdoff= [KNL]
3741 Set holdoff time (jiffies) between successive
3742 callback-flood tests.
3744 rcutorture.cbflood_intra_holdoff= [KNL]
3745 Set holdoff time (jiffies) between successive
3746 bursts of callbacks within a given callback-flood
3749 rcutorture.cbflood_n_burst= [KNL]
3750 Set the number of bursts making up a given
3751 callback-flood test. Set this to zero to
3752 disable callback-flood testing.
3754 rcutorture.cbflood_n_per_burst= [KNL]
3755 Set the number of callbacks to be registered
3756 in a given burst of a callback-flood test.
3758 rcutorture.fqs_duration= [KNL]
3759 Set duration of force_quiescent_state bursts
3762 rcutorture.fqs_holdoff= [KNL]
3763 Set holdoff time within force_quiescent_state bursts
3766 rcutorture.fqs_stutter= [KNL]
3767 Set wait time between force_quiescent_state bursts
3770 rcutorture.gp_cond= [KNL]
3771 Use conditional/asynchronous update-side
3772 primitives, if available.
3774 rcutorture.gp_exp= [KNL]
3775 Use expedited update-side primitives, if available.
3777 rcutorture.gp_normal= [KNL]
3778 Use normal (non-expedited) asynchronous
3779 update-side primitives, if available.
3781 rcutorture.gp_sync= [KNL]
3782 Use normal (non-expedited) synchronous
3783 update-side primitives, if available. If all
3784 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3785 rcutorture.gp_normal=, and rcutorture.gp_sync=
3786 are zero, rcutorture acts as if is interpreted
3787 they are all non-zero.
3789 rcutorture.n_barrier_cbs= [KNL]
3790 Set callbacks/threads for rcu_barrier() testing.
3792 rcutorture.nfakewriters= [KNL]
3793 Set number of concurrent RCU writers. These just
3794 stress RCU, they don't participate in the actual
3795 test, hence the "fake".
3797 rcutorture.nreaders= [KNL]
3798 Set number of RCU readers. The value -1 selects
3799 N-1, where N is the number of CPUs. A value
3800 "n" less than -1 selects N-n-2, where N is again
3801 the number of CPUs. For example, -2 selects N
3802 (the number of CPUs), -3 selects N+1, and so on.
3804 rcutorture.object_debug= [KNL]
3805 Enable debug-object double-call_rcu() testing.
3807 rcutorture.onoff_holdoff= [KNL]
3808 Set time (s) after boot for CPU-hotplug testing.
3810 rcutorture.onoff_interval= [KNL]
3811 Set time (s) between CPU-hotplug operations, or
3812 zero to disable CPU-hotplug testing.
3814 rcutorture.shuffle_interval= [KNL]
3815 Set task-shuffle interval (s). Shuffling tasks
3816 allows some CPUs to go into dyntick-idle mode
3817 during the rcutorture test.
3819 rcutorture.shutdown_secs= [KNL]
3820 Set time (s) after boot system shutdown. This
3821 is useful for hands-off automated testing.
3823 rcutorture.stall_cpu= [KNL]
3824 Duration of CPU stall (s) to test RCU CPU stall
3825 warnings, zero to disable.
3827 rcutorture.stall_cpu_holdoff= [KNL]
3828 Time to wait (s) after boot before inducing stall.
3830 rcutorture.stat_interval= [KNL]
3831 Time (s) between statistics printk()s.
3833 rcutorture.stutter= [KNL]
3834 Time (s) to stutter testing, for example, specifying
3835 five seconds causes the test to run for five seconds,
3836 wait for five seconds, and so on. This tests RCU's
3837 ability to transition abruptly to and from idle.
3839 rcutorture.test_boost= [KNL]
3840 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3841 "Maybe" means test if the RCU implementation
3842 under test support RCU priority boosting.
3844 rcutorture.test_boost_duration= [KNL]
3845 Duration (s) of each individual boost test.
3847 rcutorture.test_boost_interval= [KNL]
3848 Interval (s) between each boost test.
3850 rcutorture.test_no_idle_hz= [KNL]
3851 Test RCU's dyntick-idle handling. See also the
3852 rcutorture.shuffle_interval parameter.
3854 rcutorture.torture_runnable= [BOOT]
3855 Start rcutorture running at boot time.
3857 rcutorture.torture_type= [KNL]
3858 Specify the RCU implementation to test.
3860 rcutorture.verbose= [KNL]
3861 Enable additional printk() statements.
3863 rcupdate.rcu_cpu_stall_suppress= [KNL]
3864 Suppress RCU CPU stall warning messages.
3866 rcupdate.rcu_cpu_stall_timeout= [KNL]
3867 Set timeout for RCU CPU stall warning messages.
3869 rcupdate.rcu_expedited= [KNL]
3870 Use expedited grace-period primitives, for
3871 example, synchronize_rcu_expedited() instead
3872 of synchronize_rcu(). This reduces latency,
3873 but can increase CPU utilization, degrade
3874 real-time latency, and degrade energy efficiency.
3875 No effect on CONFIG_TINY_RCU kernels.
3877 rcupdate.rcu_normal= [KNL]
3878 Use only normal grace-period primitives,
3879 for example, synchronize_rcu() instead of
3880 synchronize_rcu_expedited(). This improves
3881 real-time latency, CPU utilization, and
3882 energy efficiency, but can expose users to
3883 increased grace-period latency. This parameter
3884 overrides rcupdate.rcu_expedited. No effect on
3885 CONFIG_TINY_RCU kernels.
3887 rcupdate.rcu_normal_after_boot= [KNL]
3888 Once boot has completed (that is, after
3889 rcu_end_inkernel_boot() has been invoked), use
3890 only normal grace-period primitives. No effect
3891 on CONFIG_TINY_RCU kernels.
3893 rcupdate.rcu_task_stall_timeout= [KNL]
3894 Set timeout in jiffies for RCU task stall warning
3895 messages. Disable with a value less than or equal
3898 rcupdate.rcu_self_test= [KNL]
3899 Run the RCU early boot self tests
3901 rcupdate.rcu_self_test_bh= [KNL]
3902 Run the RCU bh early boot self tests
3904 rcupdate.rcu_self_test_sched= [KNL]
3905 Run the RCU sched early boot self tests
3909 Run specified binary instead of /init from the ramdisk,
3910 used for early userspace startup. See initrd.
3913 force - Override the decision by the kernel to hide the
3914 advertisement of RDRAND support (this affects
3915 certain AMD processors because of buggy BIOS
3916 support, specifically around the suspend/resume
3920 Turn on/off individual RDT features. List is:
3921 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, mba.
3922 E.g. to turn on cmt and turn off mba use:
3926 Format (x86 or x86_64):
3927 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3929 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3931 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3932 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3933 reboot_force is either force or not specified,
3934 reboot_cpu is s[mp]#### with #### being the processor
3935 to be used for rebooting.
3938 [KNL, SMP] Set scheduler's default relax_domain_level.
3939 See Documentation/cgroup-v1/cpusets.txt.
3941 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3943 reservetop= [X86-32]
3945 Reserves a hole at the top of the kernel virtual
3950 Set the amount of memory to reserve for BIOS at
3951 the bottom of the address space.
3953 reset_devices [KNL] Force drivers to reset the underlying device
3954 during initialization.
3957 Specify the partition device for software suspend
3959 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3961 resume_offset= [SWSUSP]
3962 Specify the offset from the beginning of the partition
3963 given by "resume=" at which the swap header is located,
3964 in <PAGE_SIZE> units (needed only for swap files).
3965 See Documentation/power/swsusp-and-swap-files.txt
3967 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3968 read the resume files
3970 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3971 Useful for devices that are detected asynchronously
3972 (e.g. USB and MMC devices).
3974 hibernate= [HIBERNATION]
3975 noresume Don't check if there's a hibernation image
3976 present during boot.
3977 nocompress Don't compress/decompress hibernation images.
3978 no Disable hibernation and resume.
3979 protect_image Turn on image protection during restoration
3980 (that will set all pages holding image data
3981 during restoration read-only).
3983 retain_initrd [RAM] Keep initrd memory after extraction
3985 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
3986 Speculative Code Execution with Return Instructions)
3989 off - unconditionally disable
3990 auto - automatically select a migitation
3992 Selecting 'auto' will choose a mitigation method at run
3993 time according to the CPU.
3995 Not specifying this option is equivalent to retbleed=auto.
3997 rfkill.default_state=
3998 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3999 etc. communication is blocked by default.
4002 rfkill.master_switch_mode=
4003 0 The "airplane mode" button does nothing.
4004 1 The "airplane mode" button toggles between everything
4005 blocked and the previous configuration.
4006 2 The "airplane mode" button toggles between everything
4007 blocked and everything unblocked.
4009 rhash_entries= [KNL,NET]
4010 Set number of hash buckets for route cache
4013 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4016 ro [KNL] Mount root device read-only on boot
4019 on Mark read-only kernel memory as read-only (default).
4020 off Leave read-only kernel memory writable for debugging.
4023 Enable the uart passthrough on the designated usb port
4024 on Rockchip SoCs. When active, the signals of the
4025 debug-uart get routed to the D+ and D- pins of the usb
4026 port and the regular usb controller gets disabled.
4028 root= [KNL] Root filesystem
4029 See name_to_dev_t comment in init/do_mounts.c.
4031 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4032 mount the root filesystem
4034 rootflags= [KNL] Set root filesystem mount option string
4036 rootfstype= [KNL] Set root filesystem type
4038 rootwait [KNL] Wait (indefinitely) for root device to show up.
4039 Useful for devices that are detected asynchronously
4040 (e.g. USB and MMC devices).
4042 rproc_mem=nn[KMG][@address]
4043 [KNL,ARM,CMA] Remoteproc physical memory block.
4044 Memory area to be used by remote processor image,
4047 rw [KNL] Mount root device read-write on boot
4049 S [KNL] Run init in single mode
4051 s390_iommu= [HW,S390]
4052 Set s390 IOTLB flushing mode
4054 With strict flushing every unmap operation will result in
4055 an IOTLB flush. Default is lazy flushing before reuse,
4059 See drivers/net/irda/sa1100_ir.c.
4061 sbni= [NET] Granch SBNI12 leased line adapter
4063 sched_debug [KNL] Enables verbose scheduler debug messages.
4065 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4066 Allowed values are enable and disable. This feature
4067 incurs a small amount of overhead in the scheduler
4068 but is useful for debugging and performance tuning.
4070 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4071 xtime_lock contention on larger systems, and/or RCU lock
4072 contention on all systems with CONFIG_MAXSMP set.
4073 Format: { "0" | "1" }
4074 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4076 Note: increases power consumption, thus should only be
4077 enabled if running jitter sensitive (HPC/RT) workloads.
4079 security= [SECURITY] Choose a security module to enable at boot.
4080 If this boot parameter is not specified, only the first
4081 security module asking for security registration will be
4082 loaded. An invalid security module name will be treated
4083 as if no module has been chosen.
4085 selinux= [SELINUX] Disable or enable SELinux at boot time.
4086 Format: { "0" | "1" }
4087 See security/selinux/Kconfig help text.
4090 Default value is set via kernel config option.
4091 If enabled at boot time, /selinux/disable can be used
4092 later to disable prior to initial policy load.
4094 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4095 Format: { "0" | "1" }
4096 See security/apparmor/Kconfig help text
4099 Default value is set via kernel config option.
4101 serialnumber [BUGS=X86-32]
4104 Maximal number of shapers.
4112 Disable merging of slabs with similar size. May be
4113 necessary if there is some reason to distinguish
4114 allocs to different slabs, especially in hardened
4115 environments where the risk of heap overflows and
4116 layout control by attackers can usually be
4117 frustrated by disabling merging. This will reduce
4118 most of the exposure of a heap attack to a single
4119 cache (risks via metadata attacks are mostly
4120 unchanged). Debug options disable merging on their
4122 For more information see Documentation/vm/slub.txt.
4124 slab_max_order= [MM, SLAB]
4125 Determines the maximum allowed order for slabs.
4126 A high setting may cause OOMs due to memory
4127 fragmentation. Defaults to 1 for systems with
4128 more than 32MB of RAM, 0 otherwise.
4130 slub_debug[=options[,slabs]] [MM, SLUB]
4131 Enabling slub_debug allows one to determine the
4132 culprit if slab objects become corrupted. Enabling
4133 slub_debug can create guard zones around objects and
4134 may poison objects when not in use. Also tracks the
4135 last alloc / free. For more information see
4136 Documentation/vm/slub.txt.
4138 slub_memcg_sysfs= [MM, SLUB]
4139 Determines whether to enable sysfs directories for
4140 memory cgroup sub-caches. 1 to enable, 0 to disable.
4141 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4142 Enabling this can lead to a very high number of debug
4143 directories and files being created under
4146 slub_max_order= [MM, SLUB]
4147 Determines the maximum allowed order for slabs.
4148 A high setting may cause OOMs due to memory
4149 fragmentation. For more information see
4150 Documentation/vm/slub.txt.
4152 slub_min_objects= [MM, SLUB]
4153 The minimum number of objects per slab. SLUB will
4154 increase the slab order up to slub_max_order to
4155 generate a sufficiently large slab able to contain
4156 the number of objects indicated. The higher the number
4157 of objects the smaller the overhead of tracking slabs
4158 and the less frequently locks need to be acquired.
4159 For more information see Documentation/vm/slub.txt.
4161 slub_min_order= [MM, SLUB]
4162 Determines the minimum page order for slabs. Must be
4163 lower than slub_max_order.
4164 For more information see Documentation/vm/slub.txt.
4166 slub_nomerge [MM, SLUB]
4167 Same with slab_nomerge. This is supported for legacy.
4168 See slab_nomerge for more information.
4171 Format: <io1>[,<io2>[,...,<io8>]]
4173 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4174 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4175 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4176 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4177 smsc-ircc2.ircc_irq= [HW] IRQ line
4178 smsc-ircc2.ircc_dma= [HW] DMA channel
4179 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4180 0: Toshiba Satellite 1800 (GP data pin select)
4181 1: Fast pin select (default)
4184 smt [KNL,S390] Set the maximum number of threads (logical
4185 CPUs) to use per physical CPU on systems capable of
4186 symmetric multithreading (SMT). Will be capped to the
4187 actual hardware limit.
4189 Default: -1 (no limit)
4192 [KNL] Should the soft-lockup detector generate panics.
4195 softlockup_all_cpu_backtrace=
4196 [KNL] Should the soft-lockup detector generate
4197 backtraces on all cpus.
4200 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4201 See Documentation/laptops/sonypi.txt
4203 spectre_v2= [X86] Control mitigation of Spectre variant 2
4204 (indirect branch speculation) vulnerability.
4205 The default operation protects the kernel from
4208 on - unconditionally enable, implies
4210 off - unconditionally disable, implies
4212 auto - kernel detects whether your CPU model is
4215 Selecting 'on' will, and 'auto' may, choose a
4216 mitigation method at run time according to the
4217 CPU, the available microcode, the setting of the
4218 CONFIG_RETPOLINE configuration option, and the
4219 compiler with which the kernel was built.
4221 Selecting 'on' will also enable the mitigation
4222 against user space to user space task attacks.
4224 Selecting 'off' will disable both the kernel and
4225 the user space protections.
4227 Specific mitigations can also be selected manually:
4229 retpoline - replace indirect branches
4230 retpoline,generic - Retpolines
4231 retpoline,lfence - LFENCE; indirect branch
4232 retpoline,amd - alias for retpoline,lfence
4233 eibrs - enhanced IBRS
4234 eibrs,retpoline - enhanced IBRS + Retpolines
4235 eibrs,lfence - enhanced IBRS + LFENCE
4236 ibrs - use IBRS to protect kernel
4238 Not specifying this option is equivalent to
4242 [X86] Control mitigation of Spectre variant 2
4243 (indirect branch speculation) vulnerability between
4246 on - Unconditionally enable mitigations. Is
4247 enforced by spectre_v2=on
4249 off - Unconditionally disable mitigations. Is
4250 enforced by spectre_v2=off
4252 prctl - Indirect branch speculation is enabled,
4253 but mitigation can be enabled via prctl
4254 per thread. The mitigation control state
4255 is inherited on fork.
4258 - Like "prctl" above, but only STIBP is
4259 controlled per thread. IBPB is issued
4260 always when switching between different user
4264 - Same as "prctl" above, but all seccomp
4265 threads will enable the mitigation unless
4266 they explicitly opt out.
4269 - Like "seccomp" above, but only STIBP is
4270 controlled per thread. IBPB is issued
4271 always when switching between different
4272 user space processes.
4274 auto - Kernel selects the mitigation depending on
4275 the available CPU features and vulnerability.
4278 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4280 Not specifying this option is equivalent to
4281 spectre_v2_user=auto.
4283 spec_store_bypass_disable=
4284 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4285 (Speculative Store Bypass vulnerability)
4287 Certain CPUs are vulnerable to an exploit against a
4288 a common industry wide performance optimization known
4289 as "Speculative Store Bypass" in which recent stores
4290 to the same memory location may not be observed by
4291 later loads during speculative execution. The idea
4292 is that such stores are unlikely and that they can
4293 be detected prior to instruction retirement at the
4294 end of a particular speculation execution window.
4296 In vulnerable processors, the speculatively forwarded
4297 store can be used in a cache side channel attack, for
4298 example to read memory to which the attacker does not
4299 directly have access (e.g. inside sandboxed code).
4301 This parameter controls whether the Speculative Store
4302 Bypass optimization is used.
4304 on - Unconditionally disable Speculative Store Bypass
4305 off - Unconditionally enable Speculative Store Bypass
4306 auto - Kernel detects whether the CPU model contains an
4307 implementation of Speculative Store Bypass and
4308 picks the most appropriate mitigation. If the
4309 CPU is not vulnerable, "off" is selected. If the
4310 CPU is vulnerable the default mitigation is
4311 architecture and Kconfig dependent. See below.
4312 prctl - Control Speculative Store Bypass per thread
4313 via prctl. Speculative Store Bypass is enabled
4314 for a process by default. The state of the control
4315 is inherited on fork.
4316 seccomp - Same as "prctl" above, but all seccomp threads
4317 will disable SSB unless they explicitly opt out.
4319 Not specifying this option is equivalent to
4320 spec_store_bypass_disable=auto.
4322 Default mitigations:
4323 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4325 spia_io_base= [HW,MTD]
4331 Control the Special Register Buffer Data Sampling
4334 Certain CPUs are vulnerable to an MDS-like
4335 exploit which can leak bits from the random
4338 By default, this issue is mitigated by
4339 microcode. However, the microcode fix can cause
4340 the RDRAND and RDSEED instructions to become
4341 much slower. Among other effects, this will
4342 result in reduced throughput from /dev/urandom.
4344 The microcode mitigation can be disabled with
4345 the following option:
4347 off: Disable mitigation and remove
4348 performance impact to RDRAND and RDSEED
4350 srcutree.counter_wrap_check [KNL]
4351 Specifies how frequently to check for
4352 grace-period sequence counter wrap for the
4353 srcu_data structure's ->srcu_gp_seq_needed field.
4354 The greater the number of bits set in this kernel
4355 parameter, the less frequently counter wrap will
4356 be checked for. Note that the bottom two bits
4359 srcutree.exp_holdoff [KNL]
4360 Specifies how many nanoseconds must elapse
4361 since the end of the last SRCU grace period for
4362 a given srcu_struct until the next normal SRCU
4363 grace period will be considered for automatic
4364 expediting. Set to zero to disable automatic
4368 Speculative Store Bypass Disable control
4370 On CPUs that are vulnerable to the Speculative
4371 Store Bypass vulnerability and offer a
4372 firmware based mitigation, this parameter
4373 indicates how the mitigation should be used:
4375 force-on: Unconditionally enable mitigation for
4376 for both kernel and userspace
4377 force-off: Unconditionally disable mitigation for
4378 for both kernel and userspace
4379 kernel: Always enable mitigation in the
4380 kernel, and offer a prctl interface
4381 to allow userspace to register its
4382 interest in being mitigated too.
4384 stack_guard_gap= [MM]
4385 override the default stack gap protection. The value
4386 is in page units and it defines how many pages prior
4387 to (for stacks growing down) resp. after (for stacks
4388 growing up) the main stack are reserved for no other
4389 mapping. Default value is 256 pages.
4392 Enabled the stack tracer on boot up.
4394 stacktrace_filter=[function-list]
4395 [FTRACE] Limit the functions that the stack tracer
4396 will trace at boot up. function-list is a comma separated
4397 list of functions. This list can be changed at run
4398 time by the stack_trace_filter file in the debugfs
4399 tracing directory. Note, this enables stack tracing
4400 and the stacktrace above is not needed.
4404 Set the STI (builtin display/keyboard on the HP-PARISC
4405 machines) console (graphic card) which should be used
4406 as the initial boot-console.
4407 See also comment in drivers/video/console/sticore.c.
4410 See comment in drivers/video/console/sticore.c.
4413 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4415 sunrpc.min_resvport=
4416 sunrpc.max_resvport=
4418 SunRPC servers often require that client requests
4419 originate from a privileged port (i.e. a port in the
4420 range 0 < portnr < 1024).
4421 An administrator who wishes to reserve some of these
4422 ports for other uses may adjust the range that the
4423 kernel's sunrpc client considers to be privileged
4424 using these two parameters to set the minimum and
4425 maximum port values.
4427 sunrpc.svc_rpc_per_connection_limit=
4429 Limit the number of requests that the server will
4430 process in parallel from a single connection.
4431 The default value is 0 (no limit).
4435 Control how the NFS server code allocates CPUs to
4436 service thread pools. Depending on how many NICs
4437 you have and where their interrupts are bound, this
4438 option will affect which CPUs will do NFS serving.
4439 Note: this parameter cannot be changed while the
4440 NFS server is running.
4442 auto the server chooses an appropriate mode
4443 automatically using heuristics
4444 global a single global pool contains all CPUs
4445 percpu one pool for each CPU
4446 pernode one pool for each NUMA node (equivalent
4447 to global on non-NUMA machines)
4449 sunrpc.tcp_slot_table_entries=
4450 sunrpc.udp_slot_table_entries=
4452 Sets the upper limit on the number of simultaneous
4453 RPC calls that can be sent from the client to a
4454 server. Increasing these values may allow you to
4455 improve throughput, but will also increase the
4456 amount of memory reserved for use by the client.
4458 suspend.pm_test_delay=
4460 Sets the number of seconds to remain in a suspend test
4461 mode before resuming the system (see
4462 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4463 is set. Default value is 5.
4466 [KNL] Enable accounting of swap in memory resource
4467 controller if no parameter or 1 is given or disable
4468 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4470 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4471 Format: { <int> | force | noforce }
4472 <int> -- Number of I/O TLB slabs
4473 force -- force using of bounce buffers even if they
4474 wouldn't be automatically used by the kernel
4475 noforce -- Never use bounce buffers (for debugging)
4479 sysfs.deprecated=0|1 [KNL]
4480 Enable/disable old style sysfs layout for old udev
4481 on older distributions. When this option is enabled
4482 very new udev will not work anymore. When this option
4483 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4484 in older udev will not work anymore.
4485 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4486 the kernel configuration.
4488 sysrq_always_enabled
4490 Ignore sysrq setting - this boot parameter will
4491 neutralize any effect of /proc/sys/kernel/sysrq.
4492 Useful for debugging.
4494 tcpmhash_entries= [KNL,NET]
4495 Set the number of tcp_metrics_hash slots.
4496 Default value is 8192 or 16384 depending on total
4497 ram pages. This is used to specify the TCP metrics
4498 cache size. See Documentation/networking/ip-sysctl.txt
4499 "tcp_no_metrics_save" section for more details.
4503 test_suspend= [SUSPEND][,N]
4504 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4505 standby suspend) or "freeze" (for suspend type freeze)
4506 as the system sleep state during system startup with
4507 the optional capability to repeat N number of times.
4508 The system is woken from this state using a
4509 wakeup-capable RTC alarm.
4511 thash_entries= [KNL,NET]
4512 Set number of hash buckets for TCP connection
4514 thermal.act= [HW,ACPI]
4515 -1: disable all active trip points in all thermal zones
4516 <degrees C>: override all lowest active trip points
4518 thermal.crt= [HW,ACPI]
4519 -1: disable all critical trip points in all thermal zones
4520 <degrees C>: override all critical trip points
4522 thermal.nocrt= [HW,ACPI]
4523 Set to disable actions on ACPI thermal zone
4524 critical and hot trip points.
4526 thermal.off= [HW,ACPI]
4527 1: disable ACPI thermal control
4529 thermal.psv= [HW,ACPI]
4530 -1: disable all passive trip points
4531 <degrees C>: override all passive trip points to this
4534 thermal.tzp= [HW,ACPI]
4535 Specify global default ACPI thermal zone polling rate
4536 <deci-seconds>: poll all this frequency
4537 0: no polling (default)
4540 Force threading of all interrupt handlers except those
4541 marked explicitly IRQF_NO_THREAD.
4544 Enable the Transcendent memory driver if built-in.
4546 tmem.cleancache=0|1 [KNL, XEN]
4547 Default is on (1). Disable the usage of the cleancache
4548 API to send anonymous pages to the hypervisor.
4550 tmem.frontswap=0|1 [KNL, XEN]
4551 Default is on (1). Disable the usage of the frontswap
4552 API to send swap pages to the hypervisor. If disabled
4553 the selfballooning and selfshrinking are force disabled.
4555 tmem.selfballooning=0|1 [KNL, XEN]
4556 Default is on (1). Disable the driving of swap pages
4559 tmem.selfshrinking=0|1 [KNL, XEN]
4560 Default is on (1). Partial swapoff that immediately
4561 transfers pages from Xen hypervisor back to the
4562 kernel based on different criteria.
4566 Specify if the kernel should make use of the cpu
4567 topology information if the hardware supports this.
4568 The scheduler will make use of this information and
4569 e.g. base its process migration decisions on it.
4572 topology_updates= [KNL, PPC, NUMA]
4574 Specify if the kernel should ignore (off)
4575 topology updates sent by the hypervisor to this
4580 tpm_suspend_pcr=[HW,TPM]
4581 Format: integer pcr id
4582 Specify that at suspend time, the tpm driver
4583 should extend the specified pcr with zeros,
4584 as a workaround for some chips which fail to
4585 flush the last written pcr on TPM_SaveState.
4586 This will guarantee that all the other pcrs
4589 trace_buf_size=nn[KMG]
4590 [FTRACE] will set tracing buffer size on each cpu.
4592 trace_event=[event-list]
4593 [FTRACE] Set and start specified trace events in order
4594 to facilitate early boot debugging. The event-list is a
4595 comma separated list of trace events to enable. See
4596 also Documentation/trace/events.txt
4598 trace_options=[option-list]
4599 [FTRACE] Enable or disable tracer options at boot.
4600 The option-list is a comma delimited list of options
4601 that can be enabled or disabled just as if you were
4602 to echo the option name into
4604 /sys/kernel/debug/tracing/trace_options
4606 For example, to enable stacktrace option (to dump the
4607 stack trace of each event), add to the command line:
4609 trace_options=stacktrace
4611 See also Documentation/trace/ftrace.txt "trace options"
4615 Have the tracepoints sent to printk as well as the
4616 tracing ring buffer. This is useful for early boot up
4617 where the system hangs or reboots and does not give the
4618 option for reading the tracing buffer or performing a
4619 ftrace_dump_on_oops.
4621 To turn off having tracepoints sent to printk,
4622 echo 0 > /proc/sys/kernel/tracepoint_printk
4623 Note, echoing 1 into this file without the
4624 tracepoint_printk kernel cmdline option has no effect.
4628 Having tracepoints sent to printk() and activating high
4629 frequency tracepoints such as irq or sched, can cause
4630 the system to live lock.
4633 [FTRACE] enable this option to disable tracing when a
4634 warning is hit. This turns off "tracing_on". Tracing can
4635 be enabled again by echoing '1' into the "tracing_on"
4636 file located in /sys/kernel/debug/tracing/
4638 This option is useful, as it disables the trace before
4639 the WARNING dump is called, which prevents the trace to
4640 be filled with content caused by the warning output.
4642 This option can also be set at run time via the sysctl
4643 option: kernel/traceoff_on_warning
4645 transparent_hugepage=
4647 Format: [always|madvise|never]
4648 Can be used to control the default behavior of the system
4649 with respect to transparent hugepages.
4650 See Documentation/vm/transhuge.txt for more details.
4652 tsc= Disable clocksource stability checks for TSC.
4654 [x86] reliable: mark tsc clocksource as reliable, this
4655 disables clocksource verification at runtime, as well
4656 as the stability checks done at bootup. Used to enable
4657 high-resolution timer mode on older hardware, and in
4658 virtualized environment.
4659 [x86] noirqtime: Do not use TSC to do irq accounting.
4660 Used to run time disable IRQ_TIME_ACCOUNTING on any
4661 platforms where RDTSC is slow and this accounting
4664 tsx= [X86] Control Transactional Synchronization
4665 Extensions (TSX) feature in Intel processors that
4666 support TSX control.
4668 This parameter controls the TSX feature. The options are:
4670 on - Enable TSX on the system. Although there are
4671 mitigations for all known security vulnerabilities,
4672 TSX has been known to be an accelerator for
4673 several previous speculation-related CVEs, and
4674 so there may be unknown security risks associated
4675 with leaving it enabled.
4677 off - Disable TSX on the system. (Note that this
4678 option takes effect only on newer CPUs which are
4679 not vulnerable to MDS, i.e., have
4680 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4681 the new IA32_TSX_CTRL MSR through a microcode
4682 update. This new MSR allows for the reliable
4683 deactivation of the TSX functionality.)
4685 auto - Disable TSX if X86_BUG_TAA is present,
4686 otherwise enable TSX on the system.
4688 Not specifying this option is equivalent to tsx=off.
4690 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4693 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4694 Abort (TAA) vulnerability.
4696 Similar to Micro-architectural Data Sampling (MDS)
4697 certain CPUs that support Transactional
4698 Synchronization Extensions (TSX) are vulnerable to an
4699 exploit against CPU internal buffers which can forward
4700 information to a disclosure gadget under certain
4703 In vulnerable processors, the speculatively forwarded
4704 data can be used in a cache side channel attack, to
4705 access data to which the attacker does not have direct
4708 This parameter controls the TAA mitigation. The
4711 full - Enable TAA mitigation on vulnerable CPUs
4714 full,nosmt - Enable TAA mitigation and disable SMT on
4715 vulnerable CPUs. If TSX is disabled, SMT
4716 is not disabled because CPU is not
4717 vulnerable to cross-thread TAA attacks.
4718 off - Unconditionally disable TAA mitigation
4720 On MDS-affected machines, tsx_async_abort=off can be
4721 prevented by an active MDS mitigation as both vulnerabilities
4722 are mitigated with the same mechanism so in order to disable
4723 this mitigation, you need to specify mds=off too.
4725 Not specifying this option is equivalent to
4726 tsx_async_abort=full. On CPUs which are MDS affected
4727 and deploy MDS mitigation, TAA mitigation is not
4728 required and doesn't provide any additional
4732 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
4734 turbografx.map[2|3]= [HW,JOY]
4735 TurboGraFX parallel port interface
4737 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4738 See also Documentation/input/joystick-parport.txt
4740 udbg-immortal [PPC] When debugging early kernel crashes that
4741 happen after console_init() and before a proper
4742 console driver takes over, this boot options might
4743 help "seeing" what's going on.
4745 uhash_entries= [KNL,NET]
4746 Set number of hash buckets for UDP/UDP-Lite connections
4749 [USB] Ignore overcurrent events (default N).
4750 Some badly-designed motherboards generate lots of
4751 bogus events, for ports that aren't wired to
4752 anything. Set this parameter to avoid log spamming.
4753 Note that genuine overcurrent events won't be
4757 [X86] Cause panic on unknown NMI.
4759 usbcore.authorized_default=
4760 [USB] Default USB device authorization:
4761 (default -1 = authorized except for wireless USB,
4762 0 = not authorized, 1 = authorized)
4764 usbcore.autosuspend=
4765 [USB] The autosuspend time delay (in seconds) used
4766 for newly-detected USB devices (default 2). This
4767 is the time required before an idle device will be
4768 autosuspended. Devices for which the delay is set
4769 to a negative value won't be autosuspended at all.
4771 usbcore.usbfs_snoop=
4772 [USB] Set to log all usbfs traffic (default 0 = off).
4774 usbcore.usbfs_snoop_max=
4775 [USB] Maximum number of bytes to snoop in each URB
4778 usbcore.blinkenlights=
4779 [USB] Set to cycle leds on hubs (default 0 = off).
4781 usbcore.old_scheme_first=
4782 [USB] Start with the old device initialization
4783 scheme (default 0 = off).
4785 usbcore.usbfs_memory_mb=
4786 [USB] Memory limit (in MB) for buffers allocated by
4787 usbfs (default = 16, 0 = max = 2047).
4789 usbcore.use_both_schemes=
4790 [USB] Try the other device initialization scheme
4791 if the first one fails (default 1 = enabled).
4793 usbcore.initial_descriptor_timeout=
4794 [USB] Specifies timeout for the initial 64-byte
4795 USB_REQ_GET_DESCRIPTOR request in milliseconds
4796 (default 5000 = 5.0 seconds).
4798 usbcore.nousb [USB] Disable the USB subsystem
4801 [USBHID] The interval which mice are to be polled at.
4804 [USBHID] The interval which joysticks are to be polled at.
4806 usb-storage.delay_use=
4807 [UMS] The delay in seconds before a new device is
4808 scanned for Logical Units (default 1).
4811 [UMS] A list of quirks entries to supplement or
4812 override the built-in unusual_devs list. List
4813 entries are separated by commas. Each entry has
4814 the form VID:PID:Flags where VID and PID are Vendor
4815 and Product ID values (4-digit hex numbers) and
4816 Flags is a set of characters, each corresponding
4817 to a common usb-storage quirk flag as follows:
4818 a = SANE_SENSE (collect more than 18 bytes
4819 of sense data, not on uas);
4820 b = BAD_SENSE (don't collect more than 18
4821 bytes of sense data, not on uas);
4822 c = FIX_CAPACITY (decrease the reported
4823 device capacity by one sector);
4824 d = NO_READ_DISC_INFO (don't use
4825 READ_DISC_INFO command, not on uas);
4826 e = NO_READ_CAPACITY_16 (don't use
4827 READ_CAPACITY_16 command);
4828 f = NO_REPORT_OPCODES (don't use report opcodes
4830 g = MAX_SECTORS_240 (don't transfer more than
4831 240 sectors at a time, uas only);
4832 h = CAPACITY_HEURISTICS (decrease the
4833 reported device capacity by one
4834 sector if the number is odd);
4835 i = IGNORE_DEVICE (don't bind to this
4837 j = NO_REPORT_LUNS (don't use report luns
4839 k = NO_SAME (do not use WRITE_SAME, uas only)
4840 l = NOT_LOCKABLE (don't try to lock and
4841 unlock ejectable media, not on uas);
4842 m = MAX_SECTORS_64 (don't transfer more
4843 than 64 sectors = 32 KB at a time,
4845 n = INITIAL_READ10 (force a retry of the
4846 initial READ(10) command, not on uas);
4847 o = CAPACITY_OK (accept the capacity
4848 reported by the device, not on uas);
4849 p = WRITE_CACHE (the device cache is ON
4850 by default, not on uas);
4851 r = IGNORE_RESIDUE (the device reports
4852 bogus residue values, not on uas);
4853 s = SINGLE_LUN (the device has only one
4855 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4856 commands, uas only);
4857 u = IGNORE_UAS (don't bind to the uas driver);
4858 w = NO_WP_DETECT (don't test whether the
4859 medium is write-protected).
4860 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4861 even if the device claims no cache,
4863 Example: quirks=0419:aaf5:rl,0421:0433:rc
4865 user_debug= [KNL,ARM]
4867 See arch/arm/Kconfig.debug help text.
4868 1 - undefined instruction events
4870 4 - invalid data aborts
4873 Example: user_debug=31
4876 [X86] Flags controlling user PTE allocations.
4878 nohigh = do not allocate PTE pages in
4879 HIGHMEM regardless of setting
4883 On X86_32, this is an alias for vdso32=. Otherwise:
4885 vdso=1: enable VDSO (the default)
4886 vdso=0: disable VDSO mapping
4888 vdso32= [X86] Control the 32-bit vDSO
4889 vdso32=1: enable 32-bit VDSO
4890 vdso32=0 or vdso32=2: disable 32-bit VDSO
4892 See the help text for CONFIG_COMPAT_VDSO for more
4893 details. If CONFIG_COMPAT_VDSO is set, the default is
4894 vdso32=0; otherwise, the default is vdso32=1.
4896 For compatibility with older kernels, vdso32=2 is an
4899 Try vdso32=0 if you encounter an error that says:
4900 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4903 vector=percpu: enable percpu vector domain
4905 video= [FB] Frame buffer configuration
4906 See Documentation/fb/modedb.txt.
4908 video.brightness_switch_enabled= [0,1]
4909 If set to 1, on receiving an ACPI notify event
4910 generated by hotkey, video driver will adjust brightness
4911 level and then send out the event to user space through
4912 the allocated input device; If set to 0, video driver
4913 will only send out the event without touching backlight
4918 [VMMIO] Memory mapped virtio (platform) device.
4920 <size>@<baseaddr>:<irq>[:<id>]
4922 <size> := size (can use standard suffixes
4924 <baseaddr> := physical base address
4925 <irq> := interrupt number (as passed to
4927 <id> := (optional) platform device id
4929 virtio_mmio.device=1K@0x100b0000:48:7
4931 Can be used multiple times for multiple devices.
4933 vga= [BOOT,X86-32] Select a particular video mode
4934 See Documentation/x86/boot.txt and
4935 Documentation/svga.txt.
4936 Use vga=ask for menu.
4937 This is actually a boot loader parameter; the value is
4938 passed to the kernel using a special protocol.
4940 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4941 size of <nn>. This can be used to increase the
4942 minimum size (128MB on x86). It can also be used to
4943 decrease the size and leave more room for directly
4946 vmcp_cma=nn[MG] [KNL,S390]
4947 Sets the memory size reserved for contiguous memory
4948 allocations for the vmcp device driver.
4950 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4953 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4956 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4960 Controls the behavior of vsyscalls (i.e. calls to
4961 fixed addresses of 0xffffffffff600x00 from legacy
4962 code). Most statically-linked binaries and older
4963 versions of glibc use these calls. Because these
4964 functions are at fixed addresses, they make nice
4965 targets for exploits that can control RIP.
4967 emulate [default] Vsyscalls turn into traps and are
4968 emulated reasonably safely.
4970 native Vsyscalls are native syscall instructions.
4971 This is a little bit faster than trapping
4972 and makes a few dynamic recompilers work
4973 better than they would in emulation mode.
4974 It also makes exploits much easier to write.
4976 none Vsyscalls don't work at all. This makes
4977 them quite hard to use for exploits but
4978 might break your system.
4980 vt.color= [VT] Default text color.
4981 Format: 0xYX, X = foreground, Y = background.
4982 Default: 0x07 = light gray on black.
4984 vt.cur_default= [VT] Default cursor shape.
4985 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4986 the parameters of the <Esc>[?A;B;Cc escape sequence;
4987 see VGA-softcursor.txt. Default: 2 = underline.
4989 vt.default_blu= [VT]
4990 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4991 Change the default blue palette of the console.
4992 This is a 16-member array composed of values
4995 vt.default_grn= [VT]
4996 Format: <green0>,<green1>,<green2>,...,<green15>
4997 Change the default green palette of the console.
4998 This is a 16-member array composed of values
5001 vt.default_red= [VT]
5002 Format: <red0>,<red1>,<red2>,...,<red15>
5003 Change the default red palette of the console.
5004 This is a 16-member array composed of values
5010 Set system-wide default UTF-8 mode for all tty's.
5011 Default is 1, i.e. UTF-8 mode is enabled for all
5012 newly opened terminals.
5014 vt.global_cursor_default=
5017 Set system-wide default for whether a cursor
5018 is shown on new VTs. Default is -1,
5019 i.e. cursors will be created by default unless
5020 overridden by individual drivers. 0 will hide
5021 cursors, 1 will display them.
5023 vt.italic= [VT] Default color for italic text; 0-15.
5026 vt.underline= [VT] Default color for underlined text; 0-15.
5029 watchdog timers [HW,WDT] For information on watchdog timers,
5030 see Documentation/watchdog/watchdog-parameters.txt
5031 or other driver-specific files in the
5032 Documentation/watchdog/ directory.
5034 workqueue.watchdog_thresh=
5035 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5036 warn stall conditions and dump internal state to
5037 help debugging. 0 disables workqueue stall
5038 detection; otherwise, it's the stall threshold
5039 duration in seconds. The default value is 30 and
5040 it can be updated at runtime by writing to the
5041 corresponding sysfs file.
5043 workqueue.disable_numa
5044 By default, all work items queued to unbound
5045 workqueues are affine to the NUMA nodes they're
5046 issued on, which results in better behavior in
5047 general. If NUMA affinity needs to be disabled for
5048 whatever reason, this option can be used. Note
5049 that this also can be controlled per-workqueue for
5050 workqueues visible under /sys/bus/workqueue/.
5052 workqueue.power_efficient
5053 Per-cpu workqueues are generally preferred because
5054 they show better performance thanks to cache
5055 locality; unfortunately, per-cpu workqueues tend to
5056 be more power hungry than unbound workqueues.
5058 Enabling this makes the per-cpu workqueues which
5059 were observed to contribute significantly to power
5060 consumption unbound, leading to measurably lower
5061 power usage at the cost of small performance
5064 The default value of this parameter is determined by
5065 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5067 workqueue.debug_force_rr_cpu
5068 Workqueue used to implicitly guarantee that work
5069 items queued without explicit CPU specified are put
5070 on the local CPU. This guarantee is no longer true
5071 and while local CPU is still preferred work items
5072 may be put on foreign CPUs. This debug option
5073 forces round-robin CPU selection to flush out
5074 usages which depend on the now broken guarantee.
5075 When enabled, memory and cache locality will be
5078 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5079 default x2apic cluster mode on platforms
5082 x86_intel_mid_timer= [X86-32,APBT]
5083 Choose timer option for x86 Intel MID platform.
5084 Two valid options are apbt timer only and lapic timer
5085 plus one apbt timer for broadcast timer.
5086 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5088 xen_512gb_limit [KNL,X86-64,XEN]
5089 Restricts the kernel running paravirtualized under Xen
5090 to use only up to 512 GB of RAM. The reason to do so is
5091 crash analysis tools and Xen tools for doing domain
5092 save/restore/migration must be enabled to handle larger
5095 xen_emul_unplug= [HW,X86,XEN]
5096 Unplug Xen emulated devices
5097 Format: [unplug0,][unplug1]
5098 ide-disks -- unplug primary master IDE devices
5099 aux-ide-disks -- unplug non-primary-master IDE devices
5100 nics -- unplug network devices
5101 all -- unplug all emulated devices (NICs and IDE disks)
5102 unnecessary -- unplugging emulated devices is
5103 unnecessary even if the host did not respond to
5105 never -- do not unplug even if version check succeeds
5107 xen_legacy_crash [X86,XEN]
5108 Crash from Xen panic notifier, without executing late
5109 panic() code such as dumping handler.
5111 xen_nopvspin [X86,XEN]
5112 Disables the ticketlock slowpath using Xen PV
5116 Disables the PV optimizations forcing the HVM guest to
5117 run as generic HVM guest with no PV drivers.
5119 xen.balloon_boot_timeout= [XEN]
5120 The time (in seconds) to wait before giving up to boot
5121 in case initial ballooning fails to free enough memory.
5122 Applies only when running as HVM or PVH guest and
5123 started with less memory configured than allowed at
5124 max. Default is 180.
5126 xen.event_eoi_delay= [XEN]
5127 How long to delay EOI handling in case of event
5128 storms (jiffies). Default is 10.
5130 xen.event_loop_timeout= [XEN]
5131 After which time (jiffies) the event handling loop
5132 should start to delay EOI handling. Default is 2.
5134 xirc2ps_cs= [NET,PCMCIA]
5136 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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