1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
117 Support masking of GPEs numbered from 0x00 to 0x7f.
119 acpi_no_auto_serialize [HW,ACPI]
120 Disable auto-serialization of AML methods
121 AML control methods that contain the opcodes to create
122 named objects will be marked as "Serialized" by the
123 auto-serialization feature.
124 This feature is enabled by default.
125 This option allows to turn off the feature.
127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
130 acpi_no_static_ssdt [HW,ACPI]
131 Disable installation of static SSDTs at early boot time
132 By default, SSDTs contained in the RSDT/XSDT will be
133 installed automatically and they will appear under
134 /sys/firmware/acpi/tables.
135 This option turns off this feature.
136 Note that specifying this option does not affect
137 dynamic table installation which will install SSDT
138 tables to /sys/firmware/acpi/tables/dynamic.
140 acpi_rsdp= [ACPI,EFI,KEXEC]
141 Pass the RSDP address to the kernel, mostly used
142 on machines running EFI runtime service to boot the
143 second kernel for kdump.
145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
146 Format: To spoof as Windows 98: ="Microsoft Windows"
148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
149 of 2 which is mandated by ACPI 6) as the supported ACPI
150 specification revision (when using this switch, it may
151 be necessary to carry out a cold reboot _twice_ in a
152 row to make it take effect on the platform firmware).
154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
155 acpi_osi="string1" # add string1
156 acpi_osi="!string2" # remove string2
157 acpi_osi=!* # remove all strings
158 acpi_osi=! # disable all built-in OS vendor
160 acpi_osi=!! # enable all built-in OS vendor
162 acpi_osi= # disable all strings
164 'acpi_osi=!' can be used in combination with single or
165 multiple 'acpi_osi="string1"' to support specific OS
166 vendor string(s). Note that such command can only
167 affect the default state of the OS vendor strings, thus
168 it cannot affect the default state of the feature group
169 strings and the current state of the OS vendor strings,
170 specifying it multiple times through kernel command line
171 is meaningless. This command is useful when one do not
172 care about the state of the feature group strings which
173 should be controlled by the OSPM.
175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
177 can make '_OSI("Windows 2000")' TRUE.
179 'acpi_osi=' cannot be used in combination with other
180 'acpi_osi=' command lines, the _OSI method will not
181 exist in the ACPI namespace. NOTE that such command can
182 only affect the _OSI support state, thus specifying it
183 multiple times through kernel command line is also
186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
189 'acpi_osi=!*' can be used in combination with single or
190 multiple 'acpi_osi="string1"' to support specific
191 string(s). Note that such command can affect the
192 current state of both the OS vendor strings and the
193 feature group strings, thus specifying it multiple times
194 through kernel command line is meaningful. But it may
195 still not able to affect the final state of a string if
196 there are quirks related to this string. This command
197 is useful when one want to control the state of the
198 feature group strings to debug BIOS issues related to
201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
202 '_OSI("Module Device")' FALSE.
203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
204 '_OSI("Module Device")' TRUE.
205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
210 they all will make '_OSI("Windows 2000")' TRUE.
213 Override the pmtimer bug detection: force the kernel
214 to assume that this machine's pmtimer latches its value
215 and always returns good values.
217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
218 Format: { level | edge | high | low }
220 acpi_skip_timer_override [HW,ACPI]
221 Recognize and ignore IRQ0/pin2 Interrupt Override.
222 For broken nForce2 BIOS resulting in XT-PIC timer.
224 acpi_sleep= [HW,ACPI] Sleep options
225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
226 old_ordering, nonvs, sci_force_enable }
227 See Documentation/power/video.txt for information on
229 s3_beep is for debugging; it makes the PC's speaker beep
230 as soon as the kernel's real-mode entry point is called.
231 s4_nohwsig prevents ACPI hardware signature from being
232 used during resume from hibernation.
233 old_ordering causes the ACPI 1.0 ordering of the _PTS
234 control method, with respect to putting devices into
235 low power states, to be enforced (the ACPI 2.0 ordering
236 of _PTS is used by default).
237 nonvs prevents the kernel from saving/restoring the
238 ACPI NVS memory during suspend/hibernation and resume.
239 sci_force_enable causes the kernel to set SCI_EN directly
240 on resume from S1/S3 (which is against the ACPI spec,
241 but some broken systems don't work without it).
243 acpi_use_timer_override [HW,ACPI]
244 Use timer override. For some broken Nvidia NF5 boards
245 that require a timer override, but don't have HPET
247 add_efi_memmap [EFI; X86] Include EFI memory map in
248 kernel's map of available physical RAM.
251 { off | try_unsupported }
252 off: disable AGP support
253 try_unsupported: try to drive unsupported chipsets
254 (may crash computer or cause data corruption)
257 See Documentation/sound/alsa/alsa-parameters.txt
260 Allow the default userspace alignment fault handler
261 behaviour to be specified. Bit 0 enables warnings,
262 bit 1 enables fixups, and bit 2 sends a segfault.
264 align_va_addr= [X86-64]
265 Align virtual addresses by clearing slice [14:12] when
266 allocating a VMA at process creation time. This option
267 gives you up to 3% performance improvement on AMD F15h
268 machines (where it is enabled by default) for a
269 CPU-intensive style benchmark, and it can vary highly in
270 a microbenchmark depending on workload and compiler.
272 32: only for 32-bit processes
273 64: only for 64-bit processes
274 on: enable for both 32- and 64-bit processes
275 off: disable for both 32- and 64-bit processes
277 alloc_snapshot [FTRACE]
278 Allocate the ftrace snapshot buffer on boot up when the
279 main buffer is allocated. This is handy if debugging
280 and you need to use tracing_snapshot() on boot up, and
281 do not want to use tracing_snapshot_alloc() as it needs
282 to be done where GFP_KERNEL allocations are allowed.
284 amd_iommu= [HW,X86-64]
285 Pass parameters to the AMD IOMMU driver in the system.
287 fullflush - enable flushing of IO/TLB entries when
288 they are unmapped. Otherwise they are
289 flushed before they will be reused, which
291 off - do not initialize any AMD IOMMU found in
293 force_isolation - Force device isolation for all
294 devices. The IOMMU driver is not
295 allowed anymore to lift isolation
296 requirements as needed. This option
297 does not override iommu=pt
299 amd_iommu_dump= [HW,X86-64]
300 Enable AMD IOMMU driver option to dump the ACPI table
301 for AMD IOMMU. With this option enabled, AMD IOMMU
302 driver will print ACPI tables for AMD IOMMU during
303 IOMMU initialization.
305 amd_iommu_intr= [HW,X86-64]
306 Specifies one of the following AMD IOMMU interrupt
308 legacy - Use legacy interrupt remapping mode.
309 vapic - Use virtual APIC mode, which allows IOMMU
310 to inject interrupts directly into guest.
311 This mode requires kvm-amd.avic=1.
312 (Default when IOMMU HW support is present.)
314 amijoy.map= [HW,JOY] Amiga joystick support
315 Map of devices attached to JOY0DAT and JOY1DAT
317 See also Documentation/input/joystick.txt
319 analog.map= [HW,JOY] Analog joystick and gamepad support
320 Specifies type or capabilities of an analog joystick
321 connected to one of 16 gameports
322 Format: <type1>,<type2>,..<type16>
325 Power management functions (SPARCstation-4/5 + deriv.)
327 Disable APC CPU standby support. SPARCstation-Fox does
328 not play well with APC CPU idle - disable it if you have
329 APC and your system crashes randomly.
331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
332 Change the output verbosity whilst booting
333 Format: { quiet (default) | verbose | debug }
334 Change the amount of debugging information output
335 when initialising the APIC and IO-APIC components.
337 apic_extnmi= [APIC,X86] External NMI delivery setting
338 Format: { bsp (default) | all | none }
339 bsp: External NMI is delivered only to CPU 0
340 all: External NMIs are broadcast to all CPUs as a
342 none: External NMI is masked for all CPUs. This is
343 useful so that a dump capture kernel won't be
347 See Documentation/networking/ipv6.txt.
349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
350 Limit apic dumping. The parameter defines the maximal
351 number of local apics being dumped. Also it is possible
352 to set it to "all" by meaning -- no limit here.
353 Format: { 1 (default) | 2 | ... | all }.
354 The parameter valid if only apic=debug or
355 apic=verbose is specified.
356 Example: apic=debug show_lapic=all
358 apm= [APM] Advanced Power Management
359 See header of arch/x86/kernel/apm_32.c.
361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
362 Format: <io>,<irq>,<nodeID>
366 atarimouse= [HW,MOUSE] Atari Mouse
368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
369 EzKey and similar keyboards
371 atkbd.reset= [HW] Reset keyboard during initialization
373 atkbd.set= [HW] Select keyboard code set
374 Format: <int> (2 = AT (default), 3 = PS/2)
376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
379 atkbd.softraw= [HW] Choose between synthetic and real raw mode
380 Format: <bool> (0 = real, 1 = synthetic (default))
382 atkbd.softrepeat= [HW]
383 Use software keyboard repeat
385 audit= [KNL] Enable the audit sub-system
386 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
387 0 - kernel audit is disabled and can not be enabled
388 until the next reboot
389 unset - kernel audit is initialized but disabled and
390 will be fully enabled by the userspace auditd.
391 1 - kernel audit is initialized and partially enabled,
392 storing at most audit_backlog_limit messages in
393 RAM until it is fully enabled by the userspace
397 audit_backlog_limit= [KNL] Set the audit queue size limit.
398 Format: <int> (must be >=0)
401 bau= [X86_UV] Enable the BAU on SGI UV. The default
402 behavior is to disable the BAU (i.e. bau=0).
403 Format: { "0" | "1" }
406 unset - Disable the BAU.
408 baycom_epp= [HW,AX25]
411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
413 See header of drivers/net/hamradio/baycom_par.c.
415 baycom_ser_fdx= [HW,AX25]
416 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
417 Format: <io>,<irq>,<mode>[,<baud>]
418 See header of drivers/net/hamradio/baycom_ser_fdx.c.
420 baycom_ser_hdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
422 Format: <io>,<irq>,<mode>
423 See header of drivers/net/hamradio/baycom_ser_hdx.c.
425 blkdevparts= Manual partition parsing of block device(s) for
426 embedded devices based on command line input.
427 See Documentation/block/cmdline-partition.txt
429 boot_delay= Milliseconds to delay each printk during boot.
430 Values larger than 10 seconds (10000) are changed to
434 bootmem_debug [KNL] Enable bootmem allocator debug messages.
437 Disable BERT OS support on buggy BIOSes.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ca_keys= [KEYS] This parameter identifies a specific key(s) on
459 the system trusted keyring to be used for certificate
461 format: { id:<keyid> | builtin }
463 cca= [MIPS] Override the kernel pages' cache coherency
464 algorithm. Accepted values range from 0 to 7
465 inclusive. See arch/mips/include/asm/pgtable-bits.h
466 for platform specific values (SB1, Loongson3 and
469 ccw_timeout_log [S390]
470 See Documentation/s390/CommonIO for details.
472 cgroup_disable= [KNL] Disable a particular controller
473 Format: {name of the controller(s) to disable}
474 The effects of cgroup_disable=foo are:
475 - foo isn't auto-mounted if you mount all cgroups in
477 - foo isn't visible as an individually mountable
479 {Currently only "memory" controller deal with this and
480 cut the overhead, others just disable the usage. So
481 only cgroup_disable=memory is actually worthy}
483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
484 Format: { controller[,controller...] | "all" }
485 Like cgroup_disable, but only applies to cgroup v1;
486 the blacklisted controllers remain available in cgroup2.
488 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
490 nosocket -- Disable socket memory accounting.
491 nokmem -- Disable kernel memory accounting.
493 checkreqprot [SELINUX] Set initial checkreqprot flag value.
494 Format: { "0" | "1" }
495 See security/selinux/Kconfig help text.
496 0 -- check protection applied by kernel (includes
497 any implied execute protection).
498 1 -- check protection requested by application.
499 Default value is set via a kernel config option.
500 Value can be changed at runtime via
501 /selinux/checkreqprot.
504 See Documentation/s390/CommonIO for details.
507 Prevents the clock framework from automatically gating
508 clocks that have not been explicitly enabled by a Linux
509 device driver but are enabled in hardware at reset or
510 by the bootloader/firmware. Note that this does not
511 force such clocks to be always-on nor does it reserve
512 those clocks in any way. This parameter is useful for
513 debug and development, but should not be needed on a
514 platform with proper driver support. For more
515 information, see Documentation/clk.txt.
517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
519 Forces specified clocksource (if available) to be used
520 when calculating gettimeofday(). If specified
521 clocksource is not available, it defaults to PIT.
522 Format: { pit | tsc | cyclone | pmtmr }
524 clocksource= Override the default clocksource
526 Override the default clocksource and use the clocksource
527 with the name specified.
528 Some clocksource names to choose from, depending on
530 [all] jiffies (this is the base, fallback clocksource)
532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
533 pxa_timer,timer3,32k_counter,timer0_1
534 [X86-32] pit,hpet,tsc;
535 scx200_hrt on Geode; cyclone on IBM x440
543 clocksource.arm_arch_timer.evtstrm=
546 Enable/disable the eventstream feature of the ARM
547 architected timer so that code using WFE-based polling
548 loops can be debugged more effectively on production
551 clearcpuid=BITNUM [X86]
552 Disable CPUID feature X for the kernel. See
553 arch/x86/include/asm/cpufeatures.h for the valid bit
554 numbers. Note the Linux specific bits are not necessarily
555 stable over kernel options, but the vendor specific
557 Also note that user programs calling CPUID directly
558 or using the feature without checking anything
559 will still see it. This just prevents it from
560 being used by the kernel or shown in /proc/cpuinfo.
561 Also note the kernel might malfunction if you disable
564 cma=nn[MG]@[start[MG][-end[MG]]]
566 Sets the size of kernel global memory area for
567 contiguous memory allocations and optionally the
568 placement constraint by the physical address range of
569 memory allocations. A value of 0 disables CMA
570 altogether. For more information, see
571 include/linux/dma-contiguous.h
573 cmo_free_hint= [PPC] Format: { yes | no }
574 Specify whether pages are marked as being inactive
575 when they are freed. This is used in CMO environments
576 to determine OS memory pressure for page stealing by
580 coherent_pool=nn[KMG] [ARM,KNL]
581 Sets the size of memory pool for coherent, atomic dma
582 allocations, by default set to 256K.
584 code_bytes [X86] How many bytes of object code to print
589 com20020= [HW,NET] ARCnet - COM20020 chipset
591 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
593 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
597 ARCnet - COM90xx chipset (memory-mapped buffers)
598 Format: <io>[,<irq>[,<memstart>]]
600 condev= [HW,S390] console device
603 console= [KNL] Output console device and options.
605 tty<n> Use the virtual console device <n>.
609 Use the specified serial port. The options are of
610 the form "bbbbpnf", where "bbbb" is the baud rate,
611 "p" is parity ("n", "o", or "e"), "n" is number of
612 bits, and "f" is flow control ("r" for RTS or
613 omit it). Default is "9600n8".
615 See Documentation/admin-guide/serial-console.rst for more
617 Documentation/networking/netconsole.txt for an
620 uart[8250],io,<addr>[,options]
621 uart[8250],mmio,<addr>[,options]
622 uart[8250],mmio16,<addr>[,options]
623 uart[8250],mmio32,<addr>[,options]
624 uart[8250],0x<addr>[,options]
625 Start an early, polled-mode console on the 8250/16550
626 UART at the specified I/O port or MMIO address,
627 switching to the matching ttyS device later.
628 MMIO inter-register address stride is either 8-bit
629 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
630 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
631 to be equivalent to 'mmio'. 'options' are specified in
632 the same format described for ttyS above; if unspecified,
633 the h/w is not re-initialized.
635 hvc<n> Use the hypervisor console device <n>. This is for
636 both Xen and PowerPC hypervisors.
638 If the device connected to the port is not a TTY but a braille
639 device, prepend "brl," before the device type, for instance
641 For now, only VisioBraille is supported.
643 consoleblank= [KNL] The console blank (screen saver) timeout in
644 seconds. Defaults to 10*60 = 10mins. A value of 0
645 disables the blank timer.
648 [KNL] Change the default value for
649 /proc/<pid>/coredump_filter.
650 See also Documentation/filesystems/proc.txt.
652 coresight_cpu_debug.enable
655 Enable/disable the CPU sampling based debugging.
656 0: default value, disable debugging
657 1: enable debugging at boot time
659 cpuidle.off=1 [CPU_IDLE]
660 disable the cpuidle sub-system
662 cpufreq.off=1 [CPU_FREQ]
663 disable the cpufreq sub-system
666 [X86] Delay for N microsec between assert and de-assert
667 of APIC INIT to start processors. This delay occurs
668 on every CPU online, such as boot, and resume from suspend.
671 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
673 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
675 crashkernel=size[KMG][@offset[KMG]]
676 [KNL] Using kexec, Linux can switch to a 'crash kernel'
677 upon panic. This parameter reserves the physical
678 memory region [offset, offset + size] for that kernel
679 image. If '@offset' is omitted, then a suitable offset
680 is selected automatically. Check
681 Documentation/kdump/kdump.txt for further details.
683 crashkernel=range1:size1[,range2:size2,...][@offset]
684 [KNL] Same as above, but depends on the memory
685 in the running system. The syntax of range is
686 start-[end] where start and end are both
687 a memory unit (amount[KMG]). See also
688 Documentation/kdump/kdump.txt for an example.
690 crashkernel=size[KMG],high
691 [KNL, x86_64] range could be above 4G. Allow kernel
692 to allocate physical memory region from top, so could
693 be above 4G if system have more than 4G ram installed.
694 Otherwise memory region will be allocated below 4G, if
696 It will be ignored if crashkernel=X is specified.
697 crashkernel=size[KMG],low
698 [KNL, x86_64] range under 4G. When crashkernel=X,high
699 is passed, kernel could allocate physical memory region
700 above 4G, that cause second kernel crash on system
701 that require some amount of low memory, e.g. swiotlb
702 requires at least 64M+32K low memory, also enough extra
703 low memory is needed to make sure DMA buffers for 32-bit
704 devices won't run out. Kernel would try to allocate at
705 at least 256M below 4G automatically.
706 This one let user to specify own low range under 4G
707 for second kernel instead.
708 0: to disable low allocation.
709 It will be ignored when crashkernel=X,high is not used
710 or memory reserved is below 4G.
713 [KNL] Disable crypto self-tests
718 cs89x0_media= [HW,NET]
719 Format: { rj45 | aui | bnc }
722 See header of drivers/s390/block/dasd_devmap.c.
724 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
725 (one device per port)
726 Format: <port#>,<type>
727 See also Documentation/input/joystick-parport.txt
729 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
731 Documentation/admin-guide/dynamic-debug-howto.rst for
732 details. Deprecated, see dyndbg.
734 debug [KNL] Enable kernel debugging (events log level).
737 [KNL] verbose self-tests
739 Print debugging info while doing the locking API
741 We default to 0 (no extra messages), setting it to
742 1 will print _a lot_ more information - normally
743 only useful to kernel developers.
745 debug_objects [KNL] Enable object debugging
748 [KNL] Disable object debugging
750 debug_guardpage_minorder=
751 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
752 parameter allows control of the order of pages that will
753 be intentionally kept free (and hence protected) by the
754 buddy allocator. Bigger value increase the probability
755 of catching random memory corruption, but reduce the
756 amount of memory for normal system use. The maximum
757 possible value is MAX_ORDER/2. Setting this parameter
758 to 1 or 2 should be enough to identify most random
759 memory corruption problems caused by bugs in kernel or
760 driver code when a CPU writes to (or reads from) a
761 random memory location. Note that there exists a class
762 of memory corruptions problems caused by buggy H/W or
763 F/W or by drivers badly programing DMA (basically when
764 memory is written at bus level and the CPU MMU is
765 bypassed) which are not detectable by
766 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
767 tracking down these problems.
770 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
771 parameter enables the feature at boot time. In
772 default, it is disabled. We can avoid allocating huge
773 chunk of memory for debug pagealloc if we don't enable
774 it at boot time and the system will work mostly same
775 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
776 on: enable the feature
778 debugpat [X86] Enable PAT debugging
780 decnet.addr= [HW,NET]
781 Format: <area>[,<node>]
782 See also Documentation/networking/decnet.txt.
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,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 edac_report= [HW,EDAC] Control how to report EDAC event
1047 Format: {"on" | "off" | "force"}
1048 on: enable EDAC to report H/W event. May be overridden
1049 by other higher priority error reporting module.
1050 off: disable H/W event reporting through EDAC.
1051 force: enforce the use of EDAC to report H/W event.
1054 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1057 This is designed to be used in conjunction with
1058 the boot argument: earlyprintk=vga
1061 Format: {"off" | "on" | "skip[mbr]"}
1064 Format: { "old_map", "nochunk", "noruntime", "debug" }
1065 old_map [X86-64]: switch to the old ioremap-based EFI
1066 runtime services mapping. 32-bit still uses this one by
1068 nochunk: disable reading files in "chunks" in the EFI
1069 boot stub, as chunking can cause problems with some
1070 firmware implementations.
1071 noruntime : disable EFI runtime services support
1072 debug: enable misc debug output
1074 efi_no_storage_paranoia [EFI; X86]
1075 Using this parameter you can use more than 50% of
1076 your efi variable storage. Use this parameter only if
1077 you are really sure that your UEFI does sane gc and
1078 fulfills the spec otherwise your board may brick.
1080 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1081 Add arbitrary attribute to specific memory range by
1082 updating original EFI memory map.
1083 Region of memory which aa attribute is added to is
1085 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1086 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1087 attribute is added to range 0x100000000-0x180000000 and
1088 0x10a0000000-0x1120000000.
1090 Using this parameter you can do debugging of EFI memmap
1091 related feature. For example, you can do debugging of
1092 Address Range Mirroring feature even if your box
1095 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1096 that is to be dynamically loaded by Linux. If there are
1097 multiple variables with the same name but with different
1098 vendor GUIDs, all of them will be loaded. See
1099 Documentation/acpi/ssdt-overlays.txt for details.
1102 eisa_irq_edge= [PARISC,HW]
1103 See header of drivers/parisc/eisa.c.
1106 See comment before function elanfreq_setup() in
1107 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1110 Format: {"cfq" | "deadline" | "noop"}
1111 See Documentation/block/cfq-iosched.txt and
1112 Documentation/block/deadline-iosched.txt for details.
1114 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1115 Specifies physical address of start of kernel core
1116 image elf header and optionally the size. Generally
1117 kexec loader will pass this option to capture kernel.
1118 See Documentation/kdump/kdump.txt for details.
1120 enable_mtrr_cleanup [X86]
1121 The kernel tries to adjust MTRR layout from continuous
1122 to discrete, to make X server driver able to add WB
1123 entry later. This parameter enables that.
1125 enable_timer_pin_1 [X86]
1126 Enable PIN 1 of APIC timer
1127 Can be useful to work around chipset bugs
1128 (in particular on some ATI chipsets).
1129 The kernel tries to set a reasonable default.
1131 enforcing [SELINUX] Set initial enforcing status.
1133 See security/selinux/Kconfig help text.
1134 0 -- permissive (log only, no denials).
1135 1 -- enforcing (deny and log).
1137 Value can be changed at runtime via /selinux/enforce.
1140 Disable Error Record Serialization Table (ERST)
1143 ether= [HW,NET] Ethernet cards parameters
1144 This option is obsoleted by the "netdev=" option, which
1145 has equivalent usage. See its documentation for details.
1149 Permit 'security.evm' to be updated regardless of
1150 current integrity status.
1154 fail_make_request=[KNL]
1155 General fault injection mechanism.
1156 Format: <interval>,<probability>,<space>,<times>
1157 See also Documentation/fault-injection/.
1160 See Documentation/blockdev/floppy.txt.
1162 force_pal_cache_flush
1163 [IA-64] Avoid check_sal_cache_flush which may hang on
1164 buggy SAL_CACHE_FLUSH implementations. Using this
1165 parameter will force ia64_sal_cache_flush to call
1166 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1169 Forcefully enable Physical Address Extension (PAE).
1170 Many Pentium M systems disable PAE but may have a
1171 functionally usable PAE implementation.
1172 Warning: use of this parameter will taint the kernel
1173 and may cause unknown problems.
1176 [FTRACE] will set and start the specified tracer
1177 as early as possible in order to facilitate early
1180 ftrace_dump_on_oops[=orig_cpu]
1181 [FTRACE] will dump the trace buffers on oops.
1182 If no parameter is passed, ftrace will dump
1183 buffers of all CPUs, but if you pass orig_cpu, it will
1184 dump only the buffer of the CPU that triggered the
1187 ftrace_filter=[function-list]
1188 [FTRACE] Limit the functions traced by the function
1189 tracer at boot up. function-list is a comma separated
1190 list of functions. This list can be changed at run
1191 time by the set_ftrace_filter file in the debugfs
1194 ftrace_notrace=[function-list]
1195 [FTRACE] Do not trace the functions specified in
1196 function-list. This list can be changed at run time
1197 by the set_ftrace_notrace file in the debugfs
1200 ftrace_graph_filter=[function-list]
1201 [FTRACE] Limit the top level callers functions traced
1202 by the function graph tracer at boot up.
1203 function-list is a comma separated list of functions
1204 that can be changed at run time by the
1205 set_graph_function file in the debugfs tracing directory.
1207 ftrace_graph_notrace=[function-list]
1208 [FTRACE] Do not trace from the functions specified in
1209 function-list. This list is a comma separated list of
1210 functions that can be changed at run time by the
1211 set_graph_notrace file in the debugfs tracing directory.
1213 ftrace_graph_max_depth=<uint>
1214 [FTRACE] Used with the function graph tracer. This is
1215 the max depth it will trace into a function. This value
1216 can be changed at run time by the max_graph_depth file
1217 in the tracefs tracing directory. default: 0 (no limit)
1220 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1221 support via parallel port (up to 5 devices per port)
1222 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1223 See also Documentation/input/joystick-parport.txt
1227 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1231 gcov_persist= [GCOV] When non-zero (default), profiling data for
1232 kernel modules is saved and remains accessible via
1233 debugfs, even when the module is unloaded/reloaded.
1234 When zero, profiling data is discarded and associated
1235 debugfs files are removed at module unload time.
1237 goldfish [X86] Enable the goldfish android emulator platform.
1238 Don't use this when you are not running on the
1241 gpt [EFI] Forces disk with valid GPT signature but
1242 invalid Protective MBR to be treated as GPT. If the
1243 primary GPT is corrupted, it enables the backup/alternate
1244 GPT to be used instead.
1246 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1247 the "Enable 0" bit of the configuration register.
1250 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1251 the "Enable 0" bit of the configuration register.
1254 grcan.select= [HW] Select which physical interface to use.
1257 grcan.txsize= [HW] Sets the size of the tx buffer.
1258 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1260 grcan.rxsize= [HW] Sets the size of the rx buffer.
1261 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1264 gpio-mockup.gpio_mockup_ranges
1265 [HW] Sets the ranges of gpiochip of for this device.
1266 Format: <start1>,<end1>,<start2>,<end2>...
1268 hardlockup_all_cpu_backtrace=
1269 [KNL] Should the hard-lockup detector generate
1270 backtraces on all cpus.
1273 hashdist= [KNL,NUMA] Large hashes allocated during boot
1274 are distributed across NUMA nodes. Defaults on
1275 for 64-bit NUMA, off otherwise.
1276 Format: 0 | 1 (for off | on)
1278 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1280 hd= [EIDE] (E)IDE hard drive subsystem geometry
1281 Format: <cyl>,<head>,<sect>
1284 Disable Hardware Error Source Table (HEST) support;
1285 corresponding firmware-first mode error processing
1286 logic will be disabled.
1288 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1289 size of <nn>. This works even on boxes that have no
1290 highmem otherwise. This also works to reduce highmem
1291 size on bigger boxes.
1293 highres= [KNL] Enable/disable high resolution timer mode.
1294 Valid parameters: "on", "off"
1298 See Documentation/isdn/README.HiSax.
1302 hpet= [X86-32,HPET] option to control HPET usage
1303 Format: { enable (default) | disable | force |
1305 disable: disable HPET and use PIT instead
1306 force: allow force enabled of undocumented chips (ICH4,
1308 verbose: show contents of HPET registers during setup
1310 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1311 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1313 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1314 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1315 On x86-64 and powerpc, this option can be specified
1316 multiple times interleaved with hugepages= to reserve
1317 huge pages of different sizes. Valid pages sizes on
1318 x86-64 are 2M (when the CPU supports "pse") and 1G
1319 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1321 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1322 terminal devices. Valid values: 0..8
1323 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1324 If specified, z/VM IUCV HVC accepts connections
1325 from listed z/VM user IDs only.
1327 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1328 hardware thread id mappings.
1329 Format: <cpu>:<hwthread>
1332 Do not unregister boot console at start. This is only
1333 useful for debugging when something happens in the window
1334 between unregistering the boot console and initializing
1337 i2c_bus= [HW] Override the default board specific I2C bus speed
1338 or register an additional I2C bus that is not
1339 registered from board initialization code.
1343 i8042.debug [HW] Toggle i8042 debug mode
1344 i8042.unmask_kbd_data
1345 [HW] Enable printing of interrupt data from the KBD port
1346 (disabled by default, and as a pre-condition
1347 requires that i8042.debug=1 be enabled)
1348 i8042.direct [HW] Put keyboard port into non-translated mode
1349 i8042.dumbkbd [HW] Pretend that controller can only read data from
1350 keyboard and cannot control its state
1351 (Don't attempt to blink the leds)
1352 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1353 i8042.nokbd [HW] Don't check/create keyboard port
1354 i8042.noloop [HW] Disable the AUX Loopback command while probing
1356 i8042.nomux [HW] Don't check presence of an active multiplexing
1358 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1360 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1361 i8042.reset [HW] Reset the controller during init, cleanup and
1362 suspend-to-ram transitions, only during s2r
1363 transitions, or never reset
1364 Format: { 1 | Y | y | 0 | N | n }
1365 1, Y, y: always reset controller
1366 0, N, n: don't ever reset controller
1367 Default: only on s2r transitions on x86; most other
1368 architectures force reset to be always executed
1369 i8042.unlock [HW] Unlock (ignore) the keylock
1370 i8042.kbdreset [HW] Reset device connected to KBD port
1374 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1375 indicates that the driver is running on unsupported
1377 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1378 does not match list of supported models.
1380 [HW] Report power status in /proc/i8k
1381 (disabled by default)
1382 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1385 i915.invert_brightness=
1386 [DRM] Invert the sense of the variable that is used to
1387 set the brightness of the panel backlight. Normally a
1388 brightness value of 0 indicates backlight switched off,
1389 and the maximum of the brightness value sets the backlight
1390 to maximum brightness. If this parameter is set to 0
1391 (default) and the machine requires it, or this parameter
1392 is set to 1, a brightness value of 0 sets the backlight
1393 to maximum brightness, and the maximum of the brightness
1394 value switches the backlight off.
1395 -1 -- never invert brightness
1396 0 -- machine default
1397 1 -- force brightness inversion
1400 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1402 ide-core.nodma= [HW] (E)IDE subsystem
1403 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1404 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1405 .cdrom .chs .ignore_cable are additional options
1406 See Documentation/ide/ide.txt.
1408 ide-generic.probe-mask= [HW] (E)IDE subsystem
1410 Probe mask for legacy ISA IDE ports. Depending on
1411 platform up to 6 ports are supported, enabled by
1412 setting corresponding bits in the mask to 1. The
1413 default value is 0x0, which has a special meaning.
1414 On systems that have PCI, it triggers scanning the
1415 PCI bus for the first and the second port, which
1416 are then probed. On systems without PCI the value
1417 of 0x0 enables probing the two first ports as if it
1420 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1421 Claim all unknown PCI IDE storage controllers.
1424 Format: idle=poll, idle=halt, idle=nomwait
1425 Poll forces a polling idle loop that can slightly
1426 improve the performance of waking up a idle CPU, but
1427 will use a lot of power and make the system run hot.
1429 idle=halt: Halt is forced to be used for CPU idle.
1430 In such case C2/C3 won't be used again.
1431 idle=nomwait: Disable mwait for CPU C-states
1433 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1434 Format: { strict | legacy | 2008 | relaxed }
1437 Choose which programs will be accepted for execution
1438 based on the IEEE 754 NaN encoding(s) supported by
1439 the FPU and the NaN encoding requested with the value
1440 of an ELF file header flag individually set by each
1441 binary. Hardware implementations are permitted to
1442 support either or both of the legacy and the 2008 NaN
1445 Available settings are as follows:
1446 strict accept binaries that request a NaN encoding
1447 supported by the FPU
1448 legacy only accept legacy-NaN binaries, if supported
1450 2008 only accept 2008-NaN binaries, if supported
1452 relaxed accept any binaries regardless of whether
1453 supported by the FPU
1455 The FPU emulator is always able to support both NaN
1456 encodings, so if no FPU hardware is present or it has
1457 been disabled with 'nofpu', then the settings of
1458 'legacy' and '2008' strap the emulator accordingly,
1459 'relaxed' straps the emulator for both legacy-NaN and
1460 2008-NaN, whereas 'strict' enables legacy-NaN only on
1461 legacy processors and both NaN encodings on MIPS32 or
1464 The setting for ABS.fmt/NEG.fmt instruction execution
1465 mode generally follows that for the NaN encoding,
1466 except where unsupported by hardware.
1468 ignore_loglevel [KNL]
1469 Ignore loglevel setting - this will print /all/
1470 kernel messages to the console. Useful for debugging.
1471 We also add it as printk module parameter, so users
1472 could change it dynamically, usually by
1473 /sys/module/printk/parameters/ignore_loglevel.
1476 Ignore RLIMIT_DATA setting for data mappings,
1477 print warning at first misuse. Can be changed via
1478 /sys/module/kernel/parameters/ignore_rlimit_data.
1480 ihash_entries= [KNL]
1481 Set number of hash buckets for inode cache.
1483 ima_appraise= [IMA] appraise integrity measurements
1484 Format: { "off" | "enforce" | "fix" | "log" }
1487 ima_appraise_tcb [IMA]
1488 The builtin appraise policy appraises all files
1491 ima_canonical_fmt [IMA]
1492 Use the canonical format for the binary runtime
1493 measurements, instead of host native format.
1496 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1500 The list of supported hash algorithms is defined
1501 in crypto/hash_info.h.
1504 The builtin policies to load during IMA setup.
1505 Format: "tcb | appraise_tcb | secure_boot"
1507 The "tcb" policy measures all programs exec'd, files
1508 mmap'd for exec, and all files opened with the read
1509 mode bit set by either the effective uid (euid=0) or
1512 The "appraise_tcb" policy appraises the integrity of
1513 all files owned by root. (This is the equivalent
1514 of ima_appraise_tcb.)
1516 The "secure_boot" policy appraises the integrity
1517 of files (eg. kexec kernel image, kernel modules,
1518 firmware, policy, etc) based on file signatures.
1520 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1521 Load a policy which meets the needs of the Trusted
1522 Computing Base. This means IMA will measure all
1523 programs exec'd, files mmap'd for exec, and all files
1524 opened for read by uid=0.
1527 Select one of defined IMA measurements template formats.
1528 Formats: { "ima" | "ima-ng" | "ima-sig" }
1532 [IMA] Define a custom template format.
1533 Format: { "field1|...|fieldN" }
1535 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1536 Format: <min_file_size>
1537 Set the minimal file size for using asynchronous hash.
1538 If left unspecified, ahash usage is disabled.
1540 ahash performance varies for different data sizes on
1541 different crypto accelerators. This option can be used
1542 to achieve the best performance for a particular HW.
1544 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1546 Set hashing buffer size. Default: 4k.
1548 ahash performance varies for different chunk sizes on
1549 different crypto accelerators. This option can be used
1550 to achieve best performance for particular HW.
1554 Run specified binary instead of /sbin/init as init
1557 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1558 for working out where the kernel is dying during
1561 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1562 initcall functions. Useful for debugging built-in
1563 modules and initcalls.
1565 initrd= [BOOT] Specify the location of the initial ramdisk
1567 init_pkru= [x86] Specify the default memory protection keys rights
1568 register contents for all processes. 0x55555554 by
1569 default (disallow access to all but pkey 0). Can
1570 override in debugfs after boot.
1572 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1575 int_pln_enable [x86] Enable power limit notification interrupt
1577 integrity_audit=[IMA]
1578 Format: { "0" | "1" }
1579 0 -- basic integrity auditing messages. (Default)
1580 1 -- additional integrity auditing messages.
1582 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1584 Enable intel iommu driver.
1586 Disable intel iommu driver.
1587 igfx_off [Default Off]
1588 By default, gfx is mapped as normal device. If a gfx
1589 device has a dedicated DMAR unit, the DMAR unit is
1590 bypassed by not enabling DMAR with this option. In
1591 this case, gfx device will use physical address for
1594 With this option iommu will not optimize to look
1595 for io virtual address below 32-bit forcing dual
1596 address cycle on pci bus for cards supporting greater
1597 than 32-bit addressing. The default is to look
1598 for translation below 32-bit and if not available
1599 then look in the higher range.
1600 strict [Default Off]
1601 With this option on every unmap_single operation will
1602 result in a hardware IOTLB flush operation as opposed
1603 to batching them for performance.
1604 sp_off [Default Off]
1605 By default, super page will be supported if Intel IOMMU
1606 has the capability. With this option, super page will
1608 ecs_off [Default Off]
1609 By default, extended context tables will be supported if
1610 the hardware advertises that it has support both for the
1611 extended tables themselves, and also PASID support. With
1612 this option set, extended tables will not be used even
1613 on hardware which claims to support them.
1614 tboot_noforce [Default Off]
1615 Do not force the Intel IOMMU enabled under tboot.
1616 By default, tboot will force Intel IOMMU on, which
1617 could harm performance of some high-throughput
1618 devices like 40GBit network cards, even if identity
1620 Note that using this option lowers the security
1621 provided by tboot because it makes the system
1622 vulnerable to DMA attacks.
1624 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1625 0 disables intel_idle and fall back on acpi_idle.
1626 1 to 9 specify maximum depth of C-state.
1630 Do not enable intel_pstate as the default
1631 scaling driver for the supported processors
1633 Use intel_pstate as a scaling driver, but configure it
1634 to work with generic cpufreq governors (instead of
1635 enabling its internal governor). This mode cannot be
1636 used along with the hardware-managed P-states (HWP)
1639 Enable intel_pstate on systems that prohibit it by default
1640 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1641 instead of acpi-cpufreq may disable platform features, such
1642 as thermal controls and power capping, that rely on ACPI
1643 P-States information being indicated to OSPM and therefore
1644 should be used with caution. This option does not work with
1645 processors that aren't supported by the intel_pstate driver
1646 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1648 Do not enable hardware P state control (HWP)
1651 Only load intel_pstate on systems which support
1652 hardware P state control (HWP) if available.
1654 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1655 Description Table, specifies preferred power management
1656 profile as "Enterprise Server" or "Performance Server",
1657 then this feature is turned on by default.
1659 Allow per-logical-CPU P-State performance control limits using
1660 cpufreq sysfs interface
1662 intremap= [X86-64, Intel-IOMMU]
1663 on enable Interrupt Remapping (default)
1664 off disable Interrupt Remapping
1665 nosid disable Source ID checking
1667 BIOS x2APIC opt-out request will be ignored
1668 nopost disable Interrupt Posting
1670 iomem= Disable strict checking of access to MMIO memory
1671 strict regions from userspace.
1686 nobypass [PPC/POWERNV]
1687 Disable IOMMU bypass, using IOMMU for PCI devices.
1690 [ARM64] Configure DMA to bypass the IOMMU by default.
1691 Format: { "0" | "1" }
1692 0 - Use IOMMU translation for DMA.
1693 1 - Bypass the IOMMU for DMA.
1694 unset - Use IOMMU translation for DMA.
1696 io7= [HW] IO7 for Marvel based alpha systems
1697 See comment before marvel_specify_io7 in
1698 arch/alpha/kernel/core_marvel.c.
1700 io_delay= [X86] I/O delay method
1702 Standard port 0x80 based delay
1704 Alternate port 0xed based delay (needed on some systems)
1706 Simple two microseconds delay
1711 See Documentation/filesystems/nfs/nfsroot.txt.
1713 irqaffinity= [SMP] Set the default irq affinity mask
1714 The argument is a cpu list, as described above.
1717 When an interrupt is not handled search all handlers
1718 for it. Intended to get systems with badly broken
1722 When an interrupt is not handled search all handlers
1723 for it. Also check all handlers each timer
1724 interrupt. Intended to get systems with badly broken
1728 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1730 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1731 The argument is a cpu list, as described above.
1733 This option can be used to specify one or more CPUs
1734 to isolate from the general SMP balancing and scheduling
1735 algorithms. You can move a process onto or off an
1736 "isolated" CPU via the CPU affinity syscalls or cpuset.
1737 <cpu number> begins at 0 and the maximum value is
1738 "number of CPUs in system - 1".
1740 This option is the preferred way to isolate CPUs. The
1741 alternative -- manually setting the CPU mask of all
1742 tasks in the system -- can cause problems and
1743 suboptimal load balancer performance.
1747 ivrs_ioapic [HW,X86_64]
1748 Provide an override to the IOAPIC-ID<->DEVICE-ID
1749 mapping provided in the IVRS ACPI table. For
1750 example, to map IOAPIC-ID decimal 10 to
1751 PCI device 00:14.0 write the parameter as:
1752 ivrs_ioapic[10]=00:14.0
1754 ivrs_hpet [HW,X86_64]
1755 Provide an override to the HPET-ID<->DEVICE-ID
1756 mapping provided in the IVRS ACPI table. For
1757 example, to map HPET-ID decimal 0 to
1758 PCI device 00:14.0 write the parameter as:
1759 ivrs_hpet[0]=00:14.0
1761 ivrs_acpihid [HW,X86_64]
1762 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1763 mapping provided in the IVRS ACPI table. For
1764 example, to map UART-HID:UID AMD0020:0 to
1765 PCI device 00:14.5 write the parameter as:
1766 ivrs_acpihid[00:14.5]=AMD0020:0
1768 js= [HW,JOY] Analog joystick
1769 See Documentation/input/joystick.txt.
1772 When CONFIG_RANDOMIZE_BASE is set, this disables
1773 kernel and module base offset ASLR (Address Space
1774 Layout Randomization).
1777 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1778 report on every invalid memory access. Without this
1779 parameter KASAN will print report only for the first
1784 kernelcore= [KNL,X86,IA-64,PPC]
1785 Format: nn[KMGTPE] | "mirror"
1787 specifies the amount of memory usable by the kernel
1788 for non-movable allocations. The requested amount is
1789 spread evenly throughout all nodes in the system. The
1790 remaining memory in each node is used for Movable
1791 pages. In the event, a node is too small to have both
1792 kernelcore and Movable pages, kernelcore pages will
1793 take priority and other nodes will have a larger number
1794 of Movable pages. The Movable zone is used for the
1795 allocation of pages that may be reclaimed or moved
1796 by the page migration subsystem. This means that
1797 HugeTLB pages may not be allocated from this zone.
1798 Note that allocations like PTEs-from-HighMem still
1799 use the HighMem zone if it exists, and the Normal
1800 zone if it does not.
1802 Instead of specifying the amount of memory (nn[KMGTPE]),
1803 you can specify "mirror" option. In case "mirror"
1804 option is specified, mirrored (reliable) memory is used
1805 for non-movable allocations and remaining memory is used
1806 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1807 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1810 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1811 Format: <Controller#>[,poll interval]
1812 The controller # is the number of the ehci usb debug
1813 port as it is probed via PCI. The poll interval is
1814 optional and is the number seconds in between
1815 each poll cycle to the debug port in case you need
1816 the functionality for interrupting the kernel with
1817 gdb or control-c on the dbgp connection. When
1818 not using this parameter you use sysrq-g to break into
1819 the kernel debugger.
1821 kgdboc= [KGDB,HW] kgdb over consoles.
1822 Requires a tty driver that supports console polling,
1823 or a supported polling keyboard driver (non-usb).
1824 Serial only format: <serial_device>[,baud]
1825 keyboard only format: kbd
1826 keyboard and serial format: kbd,<serial_device>[,baud]
1827 Optional Kernel mode setting:
1828 kms, kbd format: kms,kbd
1829 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1831 kgdbwait [KGDB] Stop kernel execution and enter the
1832 kernel debugger at the earliest opportunity.
1834 kmac= [MIPS] korina ethernet MAC address.
1835 Configure the RouterBoard 532 series on-chip
1836 Ethernet adapter MAC address.
1838 kmemleak= [KNL] Boot-time kmemleak enable/disable
1839 Valid arguments: on, off
1841 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1844 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1845 Valid arguments: 0, 1, 2
1846 kmemcheck=0 (disabled)
1847 kmemcheck=1 (enabled)
1848 kmemcheck=2 (one-shot mode)
1849 Default: 2 (one-shot mode)
1851 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1852 Default is 0 (don't ignore, but inject #GP)
1854 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1858 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1859 Default is 1 (enabled)
1861 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1863 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1865 kvm-arm.vgic_v3_group0_trap=
1866 [KVM,ARM] Trap guest accesses to GICv3 group-0
1869 kvm-arm.vgic_v3_group1_trap=
1870 [KVM,ARM] Trap guest accesses to GICv3 group-1
1873 kvm-arm.vgic_v3_common_trap=
1874 [KVM,ARM] Trap guest accesses to GICv3 common
1877 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1878 (virtualized MMU) support on capable Intel chips.
1879 Default is 1 (enabled)
1881 kvm-intel.emulate_invalid_guest_state=
1882 [KVM,Intel] Enable emulation of invalid guest states
1883 Default is 0 (disabled)
1885 kvm-intel.flexpriority=
1886 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1887 Default is 1 (enabled)
1890 [KVM,Intel] Enable VMX nesting (nVMX).
1891 Default is 0 (disabled)
1893 kvm-intel.unrestricted_guest=
1894 [KVM,Intel] Disable unrestricted guest feature
1895 (virtualized real and unpaged mode) on capable
1896 Intel chips. Default is 1 (enabled)
1898 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1899 feature (tagged TLBs) on capable Intel chips.
1900 Default is 1 (enabled)
1906 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1909 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1910 value for LAPIC timer one-shot implementation. Default
1911 back to the programmable timer unit in the LAPIC.
1913 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1916 libata.dma= [LIBATA] DMA control
1917 libata.dma=0 Disable all PATA and SATA DMA
1918 libata.dma=1 PATA and SATA Disk DMA only
1919 libata.dma=2 ATAPI (CDROM) DMA only
1920 libata.dma=4 Compact Flash DMA only
1921 Combinations also work, so libata.dma=3 enables DMA
1922 for disks and CDROMs, but not CFs.
1924 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1925 libata.ignore_hpa=0 keep BIOS limits (default)
1926 libata.ignore_hpa=1 ignore limits, using full disk
1928 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1932 libata.force= [LIBATA] Force configurations. The format is comma
1933 separated list of "[ID:]VAL" where ID is
1934 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1935 matching port, link or device. Basically, it matches
1936 the ATA ID string printed on console by libata. If
1937 the whole ID part is omitted, the last PORT and DEVICE
1938 values are used. If ID hasn't been specified yet, the
1939 configuration applies to all ports, links and devices.
1941 If only DEVICE is omitted, the parameter applies to
1942 the port and all links and devices behind it. DEVICE
1943 number of 0 either selects the first device or the
1944 first fan-out link behind PMP device. It does not
1945 select the host link. DEVICE number of 15 selects the
1946 host link and device attached to it.
1948 The VAL specifies the configuration to force. As long
1949 as there's no ambiguity shortcut notation is allowed.
1950 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1951 The following configurations can be forced.
1953 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1954 Any ID with matching PORT is used.
1956 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1958 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1959 udma[/][16,25,33,44,66,100,133] notation is also
1962 * [no]ncq: Turn on or off NCQ.
1964 * [no]ncqtrim: Turn off queued DSM TRIM.
1966 * nohrst, nosrst, norst: suppress hard, soft
1969 * rstonce: only attempt one reset during
1970 hot-unplug link recovery
1972 * dump_id: dump IDENTIFY data.
1974 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1976 * disable: Disable this device.
1978 If there are multiple matching configurations changing
1979 the same attribute, the last one is used.
1981 memblock=debug [KNL] Enable memblock debug messages.
1983 load_ramdisk= [RAM] List of ramdisks to load from floppy
1984 See Documentation/blockdev/ramdisk.txt.
1986 lockd.nlm_grace_period=P [NFS] Assign grace period.
1989 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1992 lockd.nlm_timeout=T [NFS] Assign timeout value.
1995 lockd.nlm_udpport=M [NFS] Assign UDP port.
1998 locktorture.nreaders_stress= [KNL]
1999 Set the number of locking read-acquisition kthreads.
2000 Defaults to being automatically set based on the
2001 number of online CPUs.
2003 locktorture.nwriters_stress= [KNL]
2004 Set the number of locking write-acquisition kthreads.
2006 locktorture.onoff_holdoff= [KNL]
2007 Set time (s) after boot for CPU-hotplug testing.
2009 locktorture.onoff_interval= [KNL]
2010 Set time (s) between CPU-hotplug operations, or
2011 zero to disable CPU-hotplug testing.
2013 locktorture.shuffle_interval= [KNL]
2014 Set task-shuffle interval (jiffies). Shuffling
2015 tasks allows some CPUs to go into dyntick-idle
2016 mode during the locktorture test.
2018 locktorture.shutdown_secs= [KNL]
2019 Set time (s) after boot system shutdown. This
2020 is useful for hands-off automated testing.
2022 locktorture.stat_interval= [KNL]
2023 Time (s) between statistics printk()s.
2025 locktorture.stutter= [KNL]
2026 Time (s) to stutter testing, for example,
2027 specifying five seconds causes the test to run for
2028 five seconds, wait for five seconds, and so on.
2029 This tests the locking primitive's ability to
2030 transition abruptly to and from idle.
2032 locktorture.torture_runnable= [BOOT]
2033 Start locktorture running at boot time.
2035 locktorture.torture_type= [KNL]
2036 Specify the locking implementation to test.
2038 locktorture.verbose= [KNL]
2039 Enable additional printk() statements.
2041 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2044 loglevel= All Kernel Messages with a loglevel smaller than the
2045 console loglevel will be printed to the console. It can
2046 also be changed with klogd or other programs. The
2047 loglevels are defined as follows:
2049 0 (KERN_EMERG) system is unusable
2050 1 (KERN_ALERT) action must be taken immediately
2051 2 (KERN_CRIT) critical conditions
2052 3 (KERN_ERR) error conditions
2053 4 (KERN_WARNING) warning conditions
2054 5 (KERN_NOTICE) normal but significant condition
2055 6 (KERN_INFO) informational
2056 7 (KERN_DEBUG) debug-level messages
2058 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2059 in bytes. n must be a power of two and greater
2060 than the minimal size. The minimal size is defined
2061 by LOG_BUF_SHIFT kernel config parameter. There is
2062 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2063 that allows to increase the default size depending on
2064 the number of CPUs. See init/Kconfig for more details.
2066 logo.nologo [FB] Disables display of the built-in Linux logo.
2067 This may be used to provide more screen space for
2068 kernel log messages and is useful when debugging
2069 kernel boot problems.
2071 lp=0 [LP] Specify parallel ports to use, e.g,
2072 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2073 lp=reset first parallel port). 'lp=0' disables the
2074 lp=auto printer driver. 'lp=reset' (which can be
2075 specified in addition to the ports) causes
2076 attached printers to be reset. Using
2077 lp=port1,port2,... specifies the parallel ports
2078 to associate lp devices with, starting with
2079 lp0. A port specification may be 'none' to skip
2080 that lp device, or a parport name such as
2081 'parport0'. Specifying 'lp=auto' instead of a
2082 port specification list means that device IDs
2083 from each port should be examined, to see if
2084 an IEEE 1284-compliant printer is attached; if
2085 so, the driver will manage that printer.
2086 See also header of drivers/char/lp.c.
2089 Sets loops_per_jiffy to given constant, thus avoiding
2090 time-consuming boot-time autodetection (up to 250 ms per
2091 CPU). 0 enables autodetection (default). To determine
2092 the correct value for your kernel, boot with normal
2093 autodetection and see what value is printed. Note that
2094 on SMP systems the preset will be applied to all CPUs,
2095 which is likely to cause problems if your CPUs need
2096 significantly divergent settings. An incorrect value
2097 will cause delays in the kernel to be wrong, leading to
2098 unpredictable I/O errors and other breakage. Although
2099 unlikely, in the extreme case this might damage your
2103 Format: <io>,<irq>,<dma>
2105 machvec= [IA-64] Force the use of a particular machine-vector
2106 (machvec) in a generic kernel.
2107 Example: machvec=hpzx1_swiotlb
2109 machtype= [Loongson] Share the same kernel image file between different
2111 Example: machtype=lemote-yeeloong-2f-7inch
2113 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2114 than or equal to this physical address is ignored.
2116 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2117 will bring up during bootup. maxcpus=n : n >= 0 limits
2118 the kernel to bring up 'n' processors. Surely after
2119 bootup you can bring up the other plugged cpu by executing
2120 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2121 only takes effect during system bootup.
2122 While n=0 is a special case, it is equivalent to "nosmp",
2123 which also disables the IO APIC.
2125 max_loop= [LOOP] The number of loop block devices that get
2126 (loop.max_loop) unconditionally pre-created at init time. The default
2127 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2128 of statically allocating a predefined number, loop
2129 devices can be requested on-demand with the
2130 /dev/loop-control interface.
2132 mce [X86-32] Machine Check Exception
2134 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2136 md= [HW] RAID subsystems devices and level
2137 See Documentation/admin-guide/md.rst.
2140 Format: <first>,<last>
2141 Specifies range of consoles to be captured by the MDA.
2143 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2144 Amount of memory to be used when the kernel is not able
2145 to see the whole system memory or for test.
2146 [X86] Work as limiting max address. Use together
2147 with memmap= to avoid physical address space collisions.
2148 Without memmap= PCI devices could be placed at addresses
2149 belonging to unused RAM.
2151 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2155 [KNL,SH] Allow user to override the default size for
2156 per-device physically contiguous DMA buffers.
2158 memhp_default_state=online/offline
2159 [KNL] Set the initial state for the memory hotplug
2160 onlining policy. If not specified, the default value is
2161 set according to the
2162 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2164 See Documentation/memory-hotplug.txt.
2166 memmap=exactmap [KNL,X86] Enable setting of an exact
2167 E820 memory map, as specified by the user.
2168 Such memmap=exactmap lines can be constructed based on
2169 BIOS output or other requirements. See the memmap=nn@ss
2172 memmap=nn[KMG]@ss[KMG]
2173 [KNL] Force usage of a specific region of memory.
2174 Region of memory to be used is from ss to ss+nn.
2175 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2176 which limits max address to nn[KMG].
2177 Multiple different regions can be specified,
2180 memmap=100M@2G,100M#3G,1G!1024G
2182 memmap=nn[KMG]#ss[KMG]
2183 [KNL,ACPI] Mark specific memory as ACPI data.
2184 Region of memory to be marked is from ss to ss+nn.
2186 memmap=nn[KMG]$ss[KMG]
2187 [KNL,ACPI] Mark specific memory as reserved.
2188 Region of memory to be reserved is from ss to ss+nn.
2189 Example: Exclude memory from 0x18690000-0x1869ffff
2190 memmap=64K$0x18690000
2192 memmap=0x10000$0x18690000
2193 Some bootloaders may need an escape character before '$',
2194 like Grub2, otherwise '$' and the following number
2197 memmap=nn[KMG]!ss[KMG]
2198 [KNL,X86] Mark specific memory as protected.
2199 Region of memory to be used, from ss to ss+nn.
2200 The memory region may be marked as e820 type 12 (0xc)
2201 and is NVDIMM or ADR memory.
2203 memory_corruption_check=0/1 [X86]
2204 Some BIOSes seem to corrupt the first 64k of
2205 memory when doing things like suspend/resume.
2206 Setting this option will scan the memory
2207 looking for corruption. Enabling this will
2208 both detect corruption and prevent the kernel
2209 from using the memory being corrupted.
2210 However, its intended as a diagnostic tool; if
2211 repeatable BIOS-originated corruption always
2212 affects the same memory, you can use memmap=
2213 to prevent the kernel from using that memory.
2215 memory_corruption_check_size=size [X86]
2216 By default it checks for corruption in the low
2217 64k, making this memory unavailable for normal
2218 use. Use this parameter to scan for
2219 corruption in more or less memory.
2221 memory_corruption_check_period=seconds [X86]
2222 By default it checks for corruption every 60
2223 seconds. Use this parameter to check at some
2224 other rate. 0 disables periodic checking.
2226 memtest= [KNL,X86,ARM] Enable memtest
2228 default : 0 <disable>
2229 Specifies the number of memtest passes to be
2230 performed. Each pass selects another test
2231 pattern from a given set of patterns. Memtest
2232 fills the memory with this pattern, validates
2233 memory contents and reserves bad memory
2234 regions that are detected.
2236 mem_sleep_default= [SUSPEND] Default system suspend mode:
2237 s2idle - Suspend-To-Idle
2238 shallow - Power-On Suspend or equivalent (if supported)
2239 deep - Suspend-To-RAM or equivalent (if supported)
2240 See Documentation/power/states.txt.
2242 meye.*= [HW] Set MotionEye Camera parameters
2243 See Documentation/video4linux/meye.txt.
2245 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2246 Multi-Function General Purpose Timers on AMD Geode
2249 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2250 the BIOS has incorrectly applied a workaround. TinyBIOS
2251 version 0.98 is known to be affected, 0.99 fixes the
2252 problem by letting the user disable the workaround.
2256 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2257 physical address is ignored.
2259 mini2440= [ARM,HW,KNL]
2260 Format:[0..2][b][c][t]
2262 MINI2440 configuration specification:
2263 0 - The attached screen is the 3.5" TFT
2264 1 - The attached screen is the 7" TFT
2265 2 - The VGA Shield is attached (1024x768)
2266 Leaving out the screen size parameter will not load
2267 the TFT driver, and the framebuffer will be left
2269 b - Enable backlight. The TFT backlight pin will be
2270 linked to the kernel VESA blanking code and a GPIO
2271 LED. This parameter is not necessary when using the
2273 c - Enable the s3c camera interface.
2274 t - Reserved for enabling touchscreen support. The
2275 touchscreen support is not enabled in the mainstream
2276 kernel as of 2.6.30, a preliminary port can be found
2277 in the "bleeding edge" mini2440 support kernel at
2278 http://repo.or.cz/w/linux-2.6/mini2440.git
2281 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2282 parameter allows control of the logging verbosity for
2283 the additional memory initialisation checks. A value
2284 of 0 disables mminit logging and a level of 4 will
2285 log everything. Information is printed at KERN_DEBUG
2286 so loglevel=8 may also need to be specified.
2289 [KNL] When CONFIG_MODULE_SIG is set, this means that
2290 modules without (valid) signatures will fail to load.
2291 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2292 is always true, so this option does nothing.
2294 module_blacklist= [KNL] Do not load a comma-separated list of
2295 modules. Useful for debugging problem modules.
2298 [MOUSE] Maximum time between finger touching and
2299 leaving touchpad surface for touch to be considered
2300 a tap and be reported as a left button click (for
2301 touchpads working in absolute mode only).
2303 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2304 reporting absolute coordinates, such as tablets
2305 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2306 reporting absolute coordinates, such as tablets
2308 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2309 is similar to kernelcore except it specifies the
2310 amount of memory used for migratable allocations.
2311 If both kernelcore and movablecore is specified,
2312 then kernelcore will be at *least* the specified
2313 value but may be more. If movablecore on its own
2314 is specified, the administrator must be careful
2315 that the amount of memory usable for all allocations
2318 movable_node [KNL] Boot-time switch to make hotplugable memory
2319 NUMA nodes to be movable. This means that the memory
2320 of such nodes will be usable only for movable
2321 allocations which rules out almost all kernel
2322 allocations. Use with caution!
2324 MTD_Partition= [MTD]
2325 Format: <name>,<region-number>,<size>,<offset>
2327 MTD_Region= [MTD] Format:
2328 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2331 See drivers/mtd/cmdlinepart.c.
2333 multitce=off [PPC] This parameter disables the use of the pSeries
2334 firmware feature for updating multiple TCE entries
2337 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2339 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2341 boundary - index of last SLC block on Flex-OneNAND.
2342 The remaining blocks are configured as MLC blocks.
2343 lock - Configure if Flex-OneNAND boundary should be locked.
2344 Once locked, the boundary cannot be changed.
2345 1 indicates lock status, 0 indicates unlock status.
2348 ARM/S3C2412 JIVE boot control
2350 See arch/arm/mach-s3c2412/mach-jive.c
2352 mtouchusb.raw_coordinates=
2353 [HW] Make the MicroTouch USB driver use raw coordinates
2354 ('y', default) or cooked coordinates ('n')
2356 mtrr_chunk_size=nn[KMG] [X86]
2357 used for mtrr cleanup. It is largest continuous chunk
2358 that could hold holes aka. UC entries.
2360 mtrr_gran_size=nn[KMG] [X86]
2361 Used for mtrr cleanup. It is granularity of mtrr block.
2363 Large value could prevent small alignment from
2366 mtrr_spare_reg_nr=n [X86]
2368 Range: 0,7 : spare reg number
2370 Used for mtrr cleanup. It is spare mtrr entries number.
2371 Set to 2 or more if your graphical card needs more.
2373 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2375 netdev= [NET] Network devices parameters
2376 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2377 Note that mem_start is often overloaded to mean
2378 something different and driver-specific.
2379 This usage is only documented in each driver source
2383 [NETFILTER] Enable connection tracking flow accounting
2384 0 to disable accounting
2385 1 to enable accounting
2388 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2389 See Documentation/filesystems/nfs/nfsroot.txt.
2391 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2392 See Documentation/filesystems/nfs/nfsroot.txt.
2394 nfsrootdebug [NFS] enable nfsroot debugging messages.
2395 See Documentation/filesystems/nfs/nfsroot.txt.
2397 nfs.callback_nr_threads=
2398 [NFSv4] set the total number of threads that the
2399 NFS client will assign to service NFSv4 callback
2402 nfs.callback_tcpport=
2403 [NFS] set the TCP port on which the NFSv4 callback
2404 channel should listen.
2407 [NFS] sets the pathname to the program which is used
2408 to update the NFS client cache entries.
2410 nfs.cache_getent_timeout=
2411 [NFS] sets the timeout after which an attempt to
2412 update a cache entry is deemed to have failed.
2414 nfs.idmap_cache_timeout=
2415 [NFS] set the maximum lifetime for idmapper cache
2419 [NFS] enable 64-bit inode numbers.
2420 If zero, the NFS client will fake up a 32-bit inode
2421 number for the readdir() and stat() syscalls instead
2422 of returning the full 64-bit number.
2423 The default is to return 64-bit inode numbers.
2425 nfs.max_session_cb_slots=
2426 [NFSv4.1] Sets the maximum number of session
2427 slots the client will assign to the callback
2428 channel. This determines the maximum number of
2429 callbacks the client will process in parallel for
2430 a particular server.
2432 nfs.max_session_slots=
2433 [NFSv4.1] Sets the maximum number of session slots
2434 the client will attempt to negotiate with the server.
2435 This limits the number of simultaneous RPC requests
2436 that the client can send to the NFSv4.1 server.
2437 Note that there is little point in setting this
2438 value higher than the max_tcp_slot_table_limit.
2440 nfs.nfs4_disable_idmapping=
2441 [NFSv4] When set to the default of '1', this option
2442 ensures that both the RPC level authentication
2443 scheme and the NFS level operations agree to use
2444 numeric uids/gids if the mount is using the
2445 'sec=sys' security flavour. In effect it is
2446 disabling idmapping, which can make migration from
2447 legacy NFSv2/v3 systems to NFSv4 easier.
2448 Servers that do not support this mode of operation
2449 will be autodetected by the client, and it will fall
2450 back to using the idmapper.
2451 To turn off this behaviour, set the value to '0'.
2453 [NFS4] Specify an additional fixed unique ident-
2454 ification string that NFSv4 clients can insert into
2455 their nfs_client_id4 string. This is typically a
2456 UUID that is generated at system install time.
2458 nfs.send_implementation_id =
2459 [NFSv4.1] Send client implementation identification
2460 information in exchange_id requests.
2461 If zero, no implementation identification information
2463 The default is to send the implementation identification
2466 nfs.recover_lost_locks =
2467 [NFSv4] Attempt to recover locks that were lost due
2468 to a lease timeout on the server. Please note that
2469 doing this risks data corruption, since there are
2470 no guarantees that the file will remain unchanged
2471 after the locks are lost.
2472 If you want to enable the kernel legacy behaviour of
2473 attempting to recover these locks, then set this
2475 The default parameter value of '0' causes the kernel
2476 not to attempt recovery of lost locks.
2478 nfs4.layoutstats_timer =
2479 [NFSv4.2] Change the rate at which the kernel sends
2480 layoutstats to the pNFS metadata server.
2482 Setting this to value to 0 causes the kernel to use
2483 whatever value is the default set by the layout
2484 driver. A non-zero value sets the minimum interval
2485 in seconds between layoutstats transmissions.
2487 nfsd.nfs4_disable_idmapping=
2488 [NFSv4] When set to the default of '1', the NFSv4
2489 server will return only numeric uids and gids to
2490 clients using auth_sys, and will accept numeric uids
2491 and gids from such clients. This is intended to ease
2492 migration from NFSv2/v3.
2494 nmi_debug= [KNL,SH] Specify one or more actions to take
2495 when a NMI is triggered.
2496 Format: [state][,regs][,debounce][,die]
2498 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2499 Format: [panic,][nopanic,][num]
2501 0 - turn hardlockup detector in nmi_watchdog off
2502 1 - turn hardlockup detector in nmi_watchdog on
2503 When panic is specified, panic when an NMI watchdog
2504 timeout occurs (or 'nopanic' to override the opposite
2505 default). To disable both hard and soft lockup detectors,
2506 please see 'nowatchdog'.
2507 This is useful when you use a panic=... timeout and
2508 need the box quickly up again.
2510 netpoll.carrier_timeout=
2511 [NET] Specifies amount of time (in seconds) that
2512 netpoll should wait for a carrier. By default netpoll
2515 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2516 emulation library even if a 387 maths coprocessor
2520 [HW] Never suspend the console
2521 Disable suspending of consoles during suspend and
2522 hibernate operations. Once disabled, debugging
2523 messages can reach various consoles while the rest
2524 of the system is being put to sleep (ie, while
2525 debugging driver suspend/resume hooks). This may
2526 not work reliably with all consoles, but is known
2527 to work with serial and VGA consoles.
2528 To facilitate more flexible debugging, we also add
2529 console_suspend, a printk module parameter to control
2530 it. Users could use console_suspend (usually
2531 /sys/module/printk/parameters/console_suspend) to
2532 turn on/off it dynamically.
2534 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2535 caches in the slab allocator. Saves per-node memory,
2536 but will impact performance.
2540 noapic [SMP,APIC] Tells the kernel to not make use of any
2541 IOAPICs that may be present in the system.
2543 noautogroup Disable scheduler automatic task group creation.
2545 nobats [PPC] Do not use BATs for mapping kernel lowmem
2546 on "Classic" PPC cores.
2550 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2552 nodelayacct [KNL] Disable per-task delay accounting
2554 nodsp [SH] Disable hardware DSP at boot time.
2556 noefi Disable EFI runtime services support.
2561 On X86-32 available only on PAE configured kernels.
2562 noexec=on: enable non-executable mappings (default)
2563 noexec=off: disable non-executable mappings
2566 Disable SMAP (Supervisor Mode Access Prevention)
2567 even if it is supported by processor.
2570 Disable SMEP (Supervisor Mode Execution Prevention)
2571 even if it is supported by processor.
2574 This affects only 32-bit executables.
2575 noexec32=on: enable non-executable mappings (default)
2576 read doesn't imply executable mappings
2577 noexec32=off: disable non-executable mappings
2578 read implies executable mappings
2580 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2582 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2583 register save and restore. The kernel will only save
2584 legacy floating-point registers on task switch.
2586 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2588 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2589 Equivalent to smt=1.
2591 noxsave [BUGS=X86] Disables x86 extended register state save
2592 and restore using xsave. The kernel will fallback to
2593 enabling legacy floating-point and sse state.
2595 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2596 register states. The kernel will fall back to use
2597 xsave to save the states. By using this parameter,
2598 performance of saving the states is degraded because
2599 xsave doesn't support modified optimization while
2600 xsaveopt supports it on xsaveopt enabled systems.
2602 noxsaves [X86] Disables xsaves and xrstors used in saving and
2603 restoring x86 extended register state in compacted
2604 form of xsave area. The kernel will fall back to use
2605 xsaveopt and xrstor to save and restore the states
2606 in standard form of xsave area. By using this
2607 parameter, xsave area per process might occupy more
2608 memory on xsaves enabled systems.
2610 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2611 wfi(ARM) instruction doesn't work correctly and not to
2612 use it. This is also useful when using JTAG debugger.
2614 no_file_caps Tells the kernel not to honor file capabilities. The
2615 only way then for a file to be executed with privilege
2616 is to be setuid root or executed by root.
2618 nohalt [IA-64] Tells the kernel not to use the power saving
2619 function PAL_HALT_LIGHT when idle. This increases
2620 power-consumption. On the positive side, it reduces
2621 interrupt wake-up latency, which may improve performance
2622 in certain environments such as networked servers or
2625 nohibernate [HIBERNATION] Disable hibernation and resume.
2627 nohz= [KNL] Boottime enable/disable dynamic ticks
2628 Valid arguments: on, off
2631 nohz_full= [KNL,BOOT]
2632 The argument is a cpu list, as described above.
2633 In kernels built with CONFIG_NO_HZ_FULL=y, set
2634 the specified list of CPUs whose tick will be stopped
2635 whenever possible. The boot CPU will be forced outside
2636 the range to maintain the timekeeping.
2637 The CPUs in this range must also be included in the
2640 noiotrap [SH] Disables trapped I/O port accesses.
2642 noirqdebug [X86-32] Disables the code which attempts to detect and
2643 disable unhandled interrupt sources.
2645 no_timer_check [X86,APIC] Disables the code which tests for
2646 broken timer IRQ sources.
2648 noisapnp [ISAPNP] Disables ISA PnP code.
2650 noinitrd [RAM] Tells the kernel not to load any configured
2653 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2655 [Deprecated - use intremap=off]
2659 noinvpcid [X86] Disable the INVPCID cpu feature.
2661 nojitter [IA-64] Disables jitter checking for ITC timers.
2663 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2665 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2669 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2670 clock and use the default one.
2672 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2673 steal time is computed, but won't influence scheduler
2676 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2678 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2680 noltlbs [PPC] Do not use large page/tlb entries for kernel
2681 lowmem mapping on PPC40x and PPC8xx
2683 nomca [IA-64] Disable machine check abort handling
2685 nomce [X86-32] Disable Machine Check Exception
2687 nomfgpt [X86-32] Disable Multi-Function General Purpose
2688 Timer usage (for AMD Geode machines).
2690 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2691 shutdown the other cpus. Instead use the REBOOT_VECTOR
2694 nomodule Disable module load
2696 nopat [X86] Disable PAT (page attribute table extension of
2697 pagetables) support.
2699 norandmaps Don't use address space randomization. Equivalent to
2700 echo 0 > /proc/sys/kernel/randomize_va_space
2702 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2704 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2705 with UP alternatives
2707 nordrand [X86] Disable kernel use of the RDRAND and
2708 RDSEED instructions even if they are supported
2709 by the processor. RDRAND and RDSEED are still
2710 available to user space applications.
2712 noresume [SWSUSP] Disables resume and restores original swap
2715 no-scroll [VGA] Disables scrollback.
2716 This is required for the Braillex ib80-piezo Braille
2717 reader made by F.H. Papenmeier (Germany).
2721 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2723 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2724 and disable the IO APIC. legacy for "maxcpus=0".
2726 nosoftlockup [KNL] Disable the soft-lockup detector.
2728 nosync [HW,M68K] Disables sync negotiation for all devices.
2730 notsc [BUGS=X86-32] Disable Time Stamp Counter
2732 nowatchdog [KNL] Disable both lockup detectors, i.e.
2733 soft-lockup and NMI watchdog (hard-lockup).
2737 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2739 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2740 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2741 Some features depend on CPU0. Known dependencies are:
2742 1. Resume from suspend/hibernate depends on CPU0.
2743 Suspend/hibernate will fail if CPU0 is offline and you
2744 need to online CPU0 before suspend/hibernate.
2745 2. PIC interrupts also depend on CPU0. CPU0 can't be
2746 removed if a PIC interrupt is detected.
2747 It's said poweroff/reboot may depend on CPU0 on some
2748 machines although I haven't seen such issues so far
2749 after CPU0 is offline on a few tested machines.
2750 If the dependencies are under your control, you can
2751 turn on cpu0_hotplug.
2753 nptcg= [IA-64] Override max number of concurrent global TLB
2754 purges which is reported from either PAL_VM_SUMMARY or
2757 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2758 could support. nr_cpus=n : n >= 1 limits the kernel to
2759 support 'n' processors. It could be larger than the
2760 number of already plugged CPU during bootup, later in
2761 runtime you can physically add extra cpu until it reaches
2762 n. So during boot up some boot time memory for per-cpu
2763 variables need be pre-allocated for later physical cpu
2766 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2768 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2769 Allowed values are enable and disable
2771 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2772 one of ['zone', 'node', 'default'] can be specified
2773 This can be set from sysctl after boot.
2774 See Documentation/sysctl/vm.txt for details.
2776 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2777 See Documentation/debugging-via-ohci1394.txt for more
2780 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2781 Rather than timing out after 20 ms if an EC
2782 command is not properly ACKed, override the length
2783 of the timeout. We have interrupts disabled while
2784 waiting for the ACK, so if this is set too high
2785 interrupts *may* be lost!
2787 omap_mux= [OMAP] Override bootloader pin multiplexing.
2788 Format: <mux_mode0.mode_name=value>...
2789 For example, to override I2C bus2:
2790 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2792 oprofile.timer= [HW]
2793 Use timer interrupt instead of performance counters
2795 oprofile.cpu_type= Force an oprofile cpu type
2796 This might be useful if you have an older oprofile
2797 userland or if you want common events.
2798 Format: { arch_perfmon }
2799 arch_perfmon: [X86] Force use of architectural
2800 perfmon on Intel CPUs instead of the
2801 CPU specific event set.
2802 timer: [X86] Force use of architectural NMI
2803 timer mode (see also oprofile.timer
2804 for generic hr timer mode)
2806 oops=panic Always panic on oopses. Default is to just kill the
2807 process, but there is a small probability of
2808 deadlocking the machine.
2809 This will also cause panics on machine check exceptions.
2810 Useful together with panic=30 to trigger a reboot.
2813 See Documentation/sound/oss/oss-parameters.txt
2815 page_owner= [KNL] Boot-time page_owner enabling option.
2816 Storage of the information about who allocated
2817 each page is disabled in default. With this switch,
2819 on: enable the feature
2821 page_poison= [KNL] Boot-time parameter changing the state of
2822 poisoning on the buddy allocator.
2823 off: turn off poisoning
2824 on: turn on poisoning
2826 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2827 timeout > 0: seconds before rebooting
2828 timeout = 0: wait forever
2829 timeout < 0: reboot immediately
2832 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2835 crash_kexec_post_notifiers
2836 Run kdump after running panic-notifiers and dumping
2837 kmsg. This only for the users who doubt kdump always
2838 succeeds in any situation.
2839 Note that this also increases risks of kdump failure,
2840 because some panic notifiers can make the crashed
2841 kernel more unstable.
2843 parkbd.port= [HW] Parallel port number the keyboard adapter is
2844 connected to, default is 0.
2846 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2847 0 for XT, 1 for AT (default is AT).
2850 parport= [HW,PPT] Specify parallel ports. 0 disables.
2851 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2852 Use 'auto' to force the driver to use any
2853 IRQ/DMA settings detected (the default is to
2854 ignore detected IRQ/DMA settings because of
2855 possible conflicts). You can specify the base
2856 address, IRQ, and DMA settings; IRQ and DMA
2857 should be numbers, or 'auto' (for using detected
2858 settings on that particular port), or 'nofifo'
2859 (to avoid using a FIFO even if it is detected).
2860 Parallel ports are assigned in the order they
2861 are specified on the command line, starting
2864 parport_init_mode= [HW,PPT]
2865 Configure VIA parallel port to operate in
2866 a specific mode. This is necessary on Pegasos
2867 computer where firmware has no options for setting
2868 up parallel port mode and sets it to spp.
2869 Currently this function knows 686a and 8231 chips.
2870 Format: [spp|ps2|epp|ecp|ecpepp]
2873 Halt all CPUs after the first oops has been printed for
2874 the specified number of seconds. This is to be used if
2875 your oopses keep scrolling off the screen.
2880 See header of drivers/block/paride/pcd.c.
2881 See also Documentation/blockdev/paride.txt.
2883 pci=option[,option...] [PCI] various PCI subsystem options:
2884 earlydump [X86] dump PCI config space before the kernel
2886 off [X86] don't probe for the PCI bus
2887 bios [X86-32] force use of PCI BIOS, don't access
2888 the hardware directly. Use this if your machine
2889 has a non-standard PCI host bridge.
2890 nobios [X86-32] disallow use of PCI BIOS, only direct
2891 hardware access methods are allowed. Use this
2892 if you experience crashes upon bootup and you
2893 suspect they are caused by the BIOS.
2894 conf1 [X86] Force use of PCI Configuration Access
2895 Mechanism 1 (config address in IO port 0xCF8,
2896 data in IO port 0xCFC, both 32-bit).
2897 conf2 [X86] Force use of PCI Configuration Access
2898 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2899 the function, IO port 0xCFA, also 8-bit, sets
2900 bus number. The config space is then accessed
2901 through ports 0xC000-0xCFFF).
2902 See http://wiki.osdev.org/PCI for more info
2903 on the configuration access mechanisms.
2904 noaer [PCIE] If the PCIEAER kernel config parameter is
2905 enabled, this kernel boot option can be used to
2906 disable the use of PCIE advanced error reporting.
2907 nodomains [PCI] Disable support for multiple PCI
2908 root domains (aka PCI segments, in ACPI-speak).
2909 nommconf [X86] Disable use of MMCONFIG for PCI
2911 check_enable_amd_mmconf [X86] check for and enable
2912 properly configured MMIO access to PCI
2913 config space on AMD family 10h CPU
2914 nomsi [MSI] If the PCI_MSI kernel config parameter is
2915 enabled, this kernel boot option can be used to
2916 disable the use of MSI interrupts system-wide.
2917 noioapicquirk [APIC] Disable all boot interrupt quirks.
2918 Safety option to keep boot IRQs enabled. This
2919 should never be necessary.
2920 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2921 primary IO-APIC for bridges that cannot disable
2922 boot IRQs. This fixes a source of spurious IRQs
2923 when the system masks IRQs.
2924 noioapicreroute [APIC] Disable workaround that uses the
2925 boot IRQ equivalent of an IRQ that connects to
2926 a chipset where boot IRQs cannot be disabled.
2927 The opposite of ioapicreroute.
2928 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2929 routing table. These calls are known to be buggy
2930 on several machines and they hang the machine
2931 when used, but on other computers it's the only
2932 way to get the interrupt routing table. Try
2933 this option if the kernel is unable to allocate
2934 IRQs or discover secondary PCI buses on your
2936 rom [X86] Assign address space to expansion ROMs.
2937 Use with caution as certain devices share
2938 address decoders between ROMs and other
2940 norom [X86] Do not assign address space to
2941 expansion ROMs that do not already have
2942 BIOS assigned address ranges.
2943 nobar [X86] Do not assign address space to the
2944 BARs that weren't assigned by the BIOS.
2945 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2946 assigned automatically to PCI devices. You can
2947 make the kernel exclude IRQs of your ISA cards
2949 pirqaddr=0xAAAAA [X86] Specify the physical address
2950 of the PIRQ table (normally generated
2951 by the BIOS) if it is outside the
2952 F0000h-100000h range.
2953 lastbus=N [X86] Scan all buses thru bus #N. Can be
2954 useful if the kernel is unable to find your
2955 secondary buses and you want to tell it
2956 explicitly which ones they are.
2957 assign-busses [X86] Always assign all PCI bus
2958 numbers ourselves, overriding
2959 whatever the firmware may have done.
2960 usepirqmask [X86] Honor the possible IRQ mask stored
2961 in the BIOS $PIR table. This is needed on
2962 some systems with broken BIOSes, notably
2963 some HP Pavilion N5400 and Omnibook XE3
2964 notebooks. This will have no effect if ACPI
2965 IRQ routing is enabled.
2966 noacpi [X86] Do not use ACPI for IRQ routing
2967 or for PCI scanning.
2968 use_crs [X86] Use PCI host bridge window information
2969 from ACPI. On BIOSes from 2008 or later, this
2970 is enabled by default. If you need to use this,
2971 please report a bug.
2972 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2973 If you need to use this, please report a bug.
2974 routeirq Do IRQ routing for all PCI devices.
2975 This is normally done in pci_enable_device(),
2976 so this option is a temporary workaround
2977 for broken drivers that don't call it.
2978 skip_isa_align [X86] do not align io start addr, so can
2979 handle more pci cards
2980 noearly [X86] Don't do any early type 1 scanning.
2981 This might help on some broken boards which
2982 machine check when some devices' config space
2983 is read. But various workarounds are disabled
2984 and some IOMMU drivers will not work.
2985 bfsort Sort PCI devices into breadth-first order.
2986 This sorting is done to get a device
2987 order compatible with older (<= 2.4) kernels.
2988 nobfsort Don't sort PCI devices into breadth-first order.
2989 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2990 tuning and use the BIOS-configured MPS defaults.
2991 pcie_bus_safe Set every device's MPS to the largest value
2992 supported by all devices below the root complex.
2993 pcie_bus_perf Set device MPS to the largest allowable MPS
2994 based on its parent bus. Also set MRRS (Max
2995 Read Request Size) to the largest supported
2996 value (no larger than the MPS that the device
2997 or bus can support) for best performance.
2998 pcie_bus_peer2peer Set every device's MPS to 128B, which
2999 every device is guaranteed to support. This
3000 configuration allows peer-to-peer DMA between
3001 any pair of devices, possibly at the cost of
3002 reduced performance. This also guarantees
3003 that hot-added devices will work.
3004 cbiosize=nn[KMG] The fixed amount of bus space which is
3005 reserved for the CardBus bridge's IO window.
3006 The default value is 256 bytes.
3007 cbmemsize=nn[KMG] The fixed amount of bus space which is
3008 reserved for the CardBus bridge's memory
3009 window. The default value is 64 megabytes.
3012 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3013 [<order of align>@]pci:<vendor>:<device>\
3014 [:<subvendor>:<subdevice>][; ...]
3015 Specifies alignment and device to reassign
3016 aligned memory resources.
3017 If <order of align> is not specified,
3018 PAGE_SIZE is used as alignment.
3019 PCI-PCI bridge can be specified, if resource
3020 windows need to be expanded.
3021 To specify the alignment for several
3022 instances of a device, the PCI vendor,
3023 device, subvendor, and subdevice may be
3024 specified, e.g., 4096@pci:8086:9c22:103c:198f
3025 ecrc= Enable/disable PCIe ECRC (transaction layer
3026 end-to-end CRC checking).
3027 bios: Use BIOS/firmware settings. This is the
3031 hpiosize=nn[KMG] The fixed amount of bus space which is
3032 reserved for hotplug bridge's IO window.
3033 Default size is 256 bytes.
3034 hpmemsize=nn[KMG] The fixed amount of bus space which is
3035 reserved for hotplug bridge's memory window.
3036 Default size is 2 megabytes.
3037 hpbussize=nn The minimum amount of additional bus numbers
3038 reserved for buses below a hotplug bridge.
3040 realloc= Enable/disable reallocating PCI bridge resources
3041 if allocations done by BIOS are too small to
3042 accommodate resources required by all child
3044 off: Turn realloc off
3046 realloc same as realloc=on
3047 noari do not use PCIe ARI.
3048 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3049 only look for one device below a PCIe downstream
3052 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3055 force Enable ASPM even on devices that claim not to support it.
3056 WARNING: Forcing ASPM on may cause system lockups.
3058 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3059 nomsi Do not use MSI for PCI Express Native Hotplug (this
3060 makes all PCIe ports use INTx for hotplug services).
3062 pcie_ports= [PCIE] PCIe ports handling:
3063 auto Ask the BIOS whether or not to use native PCIe services
3064 associated with PCIe ports (PME, hot-plug, AER). Use
3065 them only if that is allowed by the BIOS.
3066 native Use native PCIe services associated with PCIe ports
3068 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3071 pcie_port_pm= [PCIE] PCIe port power management handling:
3072 off Disable power management of all PCIe ports
3073 force Forcibly enable power management of all PCIe ports
3075 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3076 nomsi Do not use MSI for native PCIe PME signaling (this makes
3077 all PCIe root ports use INTx for all services).
3079 pcmv= [HW,PCMCIA] BadgePAD 4
3083 Keep all power-domains already enabled by bootloader on,
3084 even if no driver has claimed them. This is useful
3085 for debug and development, but should not be
3086 needed on a platform with proper driver support.
3089 See Documentation/blockdev/paride.txt.
3091 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3094 See arch/parisc/kernel/pdc_chassis.c
3096 percpu_alloc= Select which percpu first chunk allocator to use.
3097 Currently supported values are "embed" and "page".
3098 Archs may support subset or none of the selections.
3099 See comments in mm/percpu.c for details on each
3100 allocator. This parameter is primarily for debugging
3101 and performance comparison.
3104 See Documentation/blockdev/paride.txt.
3107 See Documentation/blockdev/paride.txt.
3109 pirq= [SMP,APIC] Manual mp-table setup
3110 See Documentation/x86/i386/IO-APIC.txt.
3112 plip= [PPT,NET] Parallel port network link
3113 Format: { parport<nr> | timid | 0 }
3114 See also Documentation/parport.txt.
3116 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3117 Override pmtimer IOPort with a hex value.
3121 Enable PNP debug messages (depends on the
3122 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3123 via /sys/module/pnp/parameters/debug. We always show
3124 current resource usage; turning this on also shows
3125 possible settings and some assignment information.
3131 { on | off | curr | res | no-curr | no-res }
3134 [ISAPNP] Exclude IRQs for the autoconfiguration
3137 [ISAPNP] Exclude DMAs for the autoconfiguration
3139 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3140 Ranges are in pairs (I/O port base and size).
3143 [ISAPNP] Exclude memory regions for the
3145 Ranges are in pairs (memory base and size).
3147 ports= [IP_VS_FTP] IPVS ftp helper module
3149 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3151 Format: <port>,<port>....
3153 powersave=off [PPC] This option disables power saving features.
3154 It specifically disables cpuidle and sets the
3155 platform machine description specific power_save
3156 function to NULL. On Idle the CPU just reduces
3159 ppc_strict_facility_enable
3160 [PPC] This option catches any kernel floating point,
3161 Altivec, VSX and SPE outside of regions specifically
3162 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3163 There is some performance impact when enabling this.
3165 print-fatal-signals=
3166 [KNL] debug: print fatal signals
3168 If enabled, warn about various signal handling
3169 related application anomalies: too many signals,
3170 too many POSIX.1 timers, fatal signals causing a
3173 If you hit the warning due to signal overflow,
3174 you might want to try "ulimit -i unlimited".
3178 printk.always_kmsg_dump=
3179 Trigger kmsg_dump for cases other than kernel oops or
3181 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3184 printk.devkmsg={on,off,ratelimit}
3185 Control writing to /dev/kmsg.
3186 on - unlimited logging to /dev/kmsg from userspace
3187 off - logging to /dev/kmsg disabled
3188 ratelimit - ratelimit the logging
3191 printk.time= Show timing data prefixed to each printk message line
3192 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3194 processor.max_cstate= [HW,ACPI]
3195 Limit processor to maximum C-state
3196 max_cstate=9 overrides any DMI blacklist limit.
3198 processor.nocst [HW,ACPI]
3199 Ignore the _CST method to determine C-states,
3200 instead using the legacy FADT method
3202 profile= [KNL] Enable kernel profiling via /proc/profile
3203 Format: [schedule,]<number>
3204 Param: "schedule" - profile schedule points.
3205 Param: <number> - step/bucket size as a power of 2 for
3206 statistical time based profiling.
3207 Param: "sleep" - profile D-state sleeping (millisecs).
3208 Requires CONFIG_SCHEDSTATS
3209 Param: "kvm" - profile VM exits.
3211 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3213 See Documentation/blockdev/ramdisk.txt.
3215 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3216 probe for; one of (bare|imps|exps|lifebook|any).
3217 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3219 psmouse.resetafter= [HW,MOUSE]
3220 Try to reset the device after so many bad packets
3223 [HW,MOUSE] Set desired mouse resolution, in dpi.
3224 psmouse.smartscroll=
3225 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3226 0 = disabled, 1 = enabled (default).
3228 pstore.backend= Specify the name of the pstore backend to use
3231 See Documentation/blockdev/paride.txt.
3234 [KNL] Number of legacy pty's. Overwrites compiled-in
3237 quiet [KNL] Disable most log messages
3242 See Documentation/admin-guide/md.rst.
3244 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3245 See Documentation/blockdev/ramdisk.txt.
3247 ras=option[,option,...] [KNL] RAS-specific options
3250 Disable the Correctable Errors Collector,
3251 see CONFIG_RAS_CEC help text.
3254 The argument is a cpu list, as described above.
3256 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3257 the specified list of CPUs to be no-callback CPUs.
3258 Invocation of these CPUs' RCU callbacks will
3259 be offloaded to "rcuox/N" kthreads created for
3260 that purpose, where "x" is "b" for RCU-bh, "p"
3261 for RCU-preempt, and "s" for RCU-sched, and "N"
3262 is the CPU number. This reduces OS jitter on the
3263 offloaded CPUs, which can be useful for HPC and
3264 real-time workloads. It can also improve energy
3265 efficiency for asymmetric multiprocessors.
3268 Rather than requiring that offloaded CPUs
3269 (specified by rcu_nocbs= above) explicitly
3270 awaken the corresponding "rcuoN" kthreads,
3271 make these kthreads poll for callbacks.
3272 This improves the real-time response for the
3273 offloaded CPUs by relieving them of the need to
3274 wake up the corresponding kthread, but degrades
3275 energy efficiency by requiring that the kthreads
3276 periodically wake up to do the polling.
3278 rcutree.blimit= [KNL]
3279 Set maximum number of finished RCU callbacks to
3280 process in one batch.
3282 rcutree.dump_tree= [KNL]
3283 Dump the structure of the rcu_node combining tree
3284 out at early boot. This is used for diagnostic
3285 purposes, to verify correct tree setup.
3287 rcutree.gp_cleanup_delay= [KNL]
3288 Set the number of jiffies to delay each step of
3289 RCU grace-period cleanup.
3291 rcutree.gp_init_delay= [KNL]
3292 Set the number of jiffies to delay each step of
3293 RCU grace-period initialization.
3295 rcutree.gp_preinit_delay= [KNL]
3296 Set the number of jiffies to delay each step of
3297 RCU grace-period pre-initialization, that is,
3298 the propagation of recent CPU-hotplug changes up
3299 the rcu_node combining tree.
3301 rcutree.rcu_fanout_exact= [KNL]
3302 Disable autobalancing of the rcu_node combining
3303 tree. This is used by rcutorture, and might
3304 possibly be useful for architectures having high
3305 cache-to-cache transfer latencies.
3307 rcutree.rcu_fanout_leaf= [KNL]
3308 Change the number of CPUs assigned to each
3309 leaf rcu_node structure. Useful for very
3310 large systems, which will choose the value 64,
3311 and for NUMA systems with large remote-access
3312 latencies, which will choose a value aligned
3313 with the appropriate hardware boundaries.
3315 rcutree.jiffies_till_sched_qs= [KNL]
3316 Set required age in jiffies for a
3317 given grace period before RCU starts
3318 soliciting quiescent-state help from
3319 rcu_note_context_switch().
3321 rcutree.jiffies_till_first_fqs= [KNL]
3322 Set delay from grace-period initialization to
3323 first attempt to force quiescent states.
3324 Units are jiffies, minimum value is zero,
3325 and maximum value is HZ.
3327 rcutree.jiffies_till_next_fqs= [KNL]
3328 Set delay between subsequent attempts to force
3329 quiescent states. Units are jiffies, minimum
3330 value is one, and maximum value is HZ.
3332 rcutree.kthread_prio= [KNL,BOOT]
3333 Set the SCHED_FIFO priority of the RCU per-CPU
3334 kthreads (rcuc/N). This value is also used for
3335 the priority of the RCU boost threads (rcub/N)
3336 and for the RCU grace-period kthreads (rcu_bh,
3337 rcu_preempt, and rcu_sched). If RCU_BOOST is
3338 set, valid values are 1-99 and the default is 1
3339 (the least-favored priority). Otherwise, when
3340 RCU_BOOST is not set, valid values are 0-99 and
3341 the default is zero (non-realtime operation).
3343 rcutree.rcu_nocb_leader_stride= [KNL]
3344 Set the number of NOCB kthread groups, which
3345 defaults to the square root of the number of
3346 CPUs. Larger numbers reduces the wakeup overhead
3347 on the per-CPU grace-period kthreads, but increases
3348 that same overhead on each group's leader.
3350 rcutree.qhimark= [KNL]
3351 Set threshold of queued RCU callbacks beyond which
3352 batch limiting is disabled.
3354 rcutree.qlowmark= [KNL]
3355 Set threshold of queued RCU callbacks below which
3356 batch limiting is re-enabled.
3358 rcutree.rcu_idle_gp_delay= [KNL]
3359 Set wakeup interval for idle CPUs that have
3360 RCU callbacks (RCU_FAST_NO_HZ=y).
3362 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3363 Set wakeup interval for idle CPUs that have
3364 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3365 Lazy RCU callbacks are those which RCU can
3366 prove do nothing more than free memory.
3368 rcutree.rcu_kick_kthreads= [KNL]
3369 Cause the grace-period kthread to get an extra
3370 wake_up() if it sleeps three times longer than
3371 it should at force-quiescent-state time.
3372 This wake_up() will be accompanied by a
3373 WARN_ONCE() splat and an ftrace_dump().
3375 rcuperf.gp_async= [KNL]
3376 Measure performance of asynchronous
3377 grace-period primitives such as call_rcu().
3379 rcuperf.gp_async_max= [KNL]
3380 Specify the maximum number of outstanding
3381 callbacks per writer thread. When a writer
3382 thread exceeds this limit, it invokes the
3383 corresponding flavor of rcu_barrier() to allow
3384 previously posted callbacks to drain.
3386 rcuperf.gp_exp= [KNL]
3387 Measure performance of expedited synchronous
3388 grace-period primitives.
3390 rcuperf.holdoff= [KNL]
3391 Set test-start holdoff period. The purpose of
3392 this parameter is to delay the start of the
3393 test until boot completes in order to avoid
3396 rcuperf.nreaders= [KNL]
3397 Set number of RCU readers. The value -1 selects
3398 N, where N is the number of CPUs. A value
3399 "n" less than -1 selects N-n+1, where N is again
3400 the number of CPUs. For example, -2 selects N
3401 (the number of CPUs), -3 selects N+1, and so on.
3402 A value of "n" less than or equal to -N selects
3405 rcuperf.nwriters= [KNL]
3406 Set number of RCU writers. The values operate
3407 the same as for rcuperf.nreaders.
3408 N, where N is the number of CPUs
3410 rcuperf.perf_runnable= [BOOT]
3411 Start rcuperf running at boot time.
3413 rcuperf.perf_type= [KNL]
3414 Specify the RCU implementation to test.
3416 rcuperf.shutdown= [KNL]
3417 Shut the system down after performance tests
3418 complete. This is useful for hands-off automated
3421 rcuperf.verbose= [KNL]
3422 Enable additional printk() statements.
3424 rcuperf.writer_holdoff= [KNL]
3425 Write-side holdoff between grace periods,
3426 in microseconds. The default of zero says
3429 rcutorture.cbflood_inter_holdoff= [KNL]
3430 Set holdoff time (jiffies) between successive
3431 callback-flood tests.
3433 rcutorture.cbflood_intra_holdoff= [KNL]
3434 Set holdoff time (jiffies) between successive
3435 bursts of callbacks within a given callback-flood
3438 rcutorture.cbflood_n_burst= [KNL]
3439 Set the number of bursts making up a given
3440 callback-flood test. Set this to zero to
3441 disable callback-flood testing.
3443 rcutorture.cbflood_n_per_burst= [KNL]
3444 Set the number of callbacks to be registered
3445 in a given burst of a callback-flood test.
3447 rcutorture.fqs_duration= [KNL]
3448 Set duration of force_quiescent_state bursts
3451 rcutorture.fqs_holdoff= [KNL]
3452 Set holdoff time within force_quiescent_state bursts
3455 rcutorture.fqs_stutter= [KNL]
3456 Set wait time between force_quiescent_state bursts
3459 rcutorture.gp_cond= [KNL]
3460 Use conditional/asynchronous update-side
3461 primitives, if available.
3463 rcutorture.gp_exp= [KNL]
3464 Use expedited update-side primitives, if available.
3466 rcutorture.gp_normal= [KNL]
3467 Use normal (non-expedited) asynchronous
3468 update-side primitives, if available.
3470 rcutorture.gp_sync= [KNL]
3471 Use normal (non-expedited) synchronous
3472 update-side primitives, if available. If all
3473 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3474 rcutorture.gp_normal=, and rcutorture.gp_sync=
3475 are zero, rcutorture acts as if is interpreted
3476 they are all non-zero.
3478 rcutorture.n_barrier_cbs= [KNL]
3479 Set callbacks/threads for rcu_barrier() testing.
3481 rcutorture.nfakewriters= [KNL]
3482 Set number of concurrent RCU writers. These just
3483 stress RCU, they don't participate in the actual
3484 test, hence the "fake".
3486 rcutorture.nreaders= [KNL]
3487 Set number of RCU readers. The value -1 selects
3488 N-1, where N is the number of CPUs. A value
3489 "n" less than -1 selects N-n-2, where N is again
3490 the number of CPUs. For example, -2 selects N
3491 (the number of CPUs), -3 selects N+1, and so on.
3493 rcutorture.object_debug= [KNL]
3494 Enable debug-object double-call_rcu() testing.
3496 rcutorture.onoff_holdoff= [KNL]
3497 Set time (s) after boot for CPU-hotplug testing.
3499 rcutorture.onoff_interval= [KNL]
3500 Set time (s) between CPU-hotplug operations, or
3501 zero to disable CPU-hotplug testing.
3503 rcutorture.shuffle_interval= [KNL]
3504 Set task-shuffle interval (s). Shuffling tasks
3505 allows some CPUs to go into dyntick-idle mode
3506 during the rcutorture test.
3508 rcutorture.shutdown_secs= [KNL]
3509 Set time (s) after boot system shutdown. This
3510 is useful for hands-off automated testing.
3512 rcutorture.stall_cpu= [KNL]
3513 Duration of CPU stall (s) to test RCU CPU stall
3514 warnings, zero to disable.
3516 rcutorture.stall_cpu_holdoff= [KNL]
3517 Time to wait (s) after boot before inducing stall.
3519 rcutorture.stat_interval= [KNL]
3520 Time (s) between statistics printk()s.
3522 rcutorture.stutter= [KNL]
3523 Time (s) to stutter testing, for example, specifying
3524 five seconds causes the test to run for five seconds,
3525 wait for five seconds, and so on. This tests RCU's
3526 ability to transition abruptly to and from idle.
3528 rcutorture.test_boost= [KNL]
3529 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3530 "Maybe" means test if the RCU implementation
3531 under test support RCU priority boosting.
3533 rcutorture.test_boost_duration= [KNL]
3534 Duration (s) of each individual boost test.
3536 rcutorture.test_boost_interval= [KNL]
3537 Interval (s) between each boost test.
3539 rcutorture.test_no_idle_hz= [KNL]
3540 Test RCU's dyntick-idle handling. See also the
3541 rcutorture.shuffle_interval parameter.
3543 rcutorture.torture_runnable= [BOOT]
3544 Start rcutorture running at boot time.
3546 rcutorture.torture_type= [KNL]
3547 Specify the RCU implementation to test.
3549 rcutorture.verbose= [KNL]
3550 Enable additional printk() statements.
3552 rcupdate.rcu_cpu_stall_suppress= [KNL]
3553 Suppress RCU CPU stall warning messages.
3555 rcupdate.rcu_cpu_stall_timeout= [KNL]
3556 Set timeout for RCU CPU stall warning messages.
3558 rcupdate.rcu_expedited= [KNL]
3559 Use expedited grace-period primitives, for
3560 example, synchronize_rcu_expedited() instead
3561 of synchronize_rcu(). This reduces latency,
3562 but can increase CPU utilization, degrade
3563 real-time latency, and degrade energy efficiency.
3564 No effect on CONFIG_TINY_RCU kernels.
3566 rcupdate.rcu_normal= [KNL]
3567 Use only normal grace-period primitives,
3568 for example, synchronize_rcu() instead of
3569 synchronize_rcu_expedited(). This improves
3570 real-time latency, CPU utilization, and
3571 energy efficiency, but can expose users to
3572 increased grace-period latency. This parameter
3573 overrides rcupdate.rcu_expedited. No effect on
3574 CONFIG_TINY_RCU kernels.
3576 rcupdate.rcu_normal_after_boot= [KNL]
3577 Once boot has completed (that is, after
3578 rcu_end_inkernel_boot() has been invoked), use
3579 only normal grace-period primitives. No effect
3580 on CONFIG_TINY_RCU kernels.
3582 rcupdate.rcu_task_stall_timeout= [KNL]
3583 Set timeout in jiffies for RCU task stall warning
3584 messages. Disable with a value less than or equal
3587 rcupdate.rcu_self_test= [KNL]
3588 Run the RCU early boot self tests
3590 rcupdate.rcu_self_test_bh= [KNL]
3591 Run the RCU bh early boot self tests
3593 rcupdate.rcu_self_test_sched= [KNL]
3594 Run the RCU sched early boot self tests
3598 Run specified binary instead of /init from the ramdisk,
3599 used for early userspace startup. See initrd.
3602 Format (x86 or x86_64):
3603 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3605 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3607 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3608 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3609 reboot_force is either force or not specified,
3610 reboot_cpu is s[mp]#### with #### being the processor
3611 to be used for rebooting.
3614 [KNL, SMP] Set scheduler's default relax_domain_level.
3615 See Documentation/cgroup-v1/cpusets.txt.
3617 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3619 reservetop= [X86-32]
3621 Reserves a hole at the top of the kernel virtual
3626 Set the amount of memory to reserve for BIOS at
3627 the bottom of the address space.
3629 reset_devices [KNL] Force drivers to reset the underlying device
3630 during initialization.
3633 Specify the partition device for software suspend
3635 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3637 resume_offset= [SWSUSP]
3638 Specify the offset from the beginning of the partition
3639 given by "resume=" at which the swap header is located,
3640 in <PAGE_SIZE> units (needed only for swap files).
3641 See Documentation/power/swsusp-and-swap-files.txt
3643 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3644 read the resume files
3646 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3647 Useful for devices that are detected asynchronously
3648 (e.g. USB and MMC devices).
3650 hibernate= [HIBERNATION]
3651 noresume Don't check if there's a hibernation image
3652 present during boot.
3653 nocompress Don't compress/decompress hibernation images.
3654 no Disable hibernation and resume.
3655 protect_image Turn on image protection during restoration
3656 (that will set all pages holding image data
3657 during restoration read-only).
3659 retain_initrd [RAM] Keep initrd memory after extraction
3661 rfkill.default_state=
3662 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3663 etc. communication is blocked by default.
3666 rfkill.master_switch_mode=
3667 0 The "airplane mode" button does nothing.
3668 1 The "airplane mode" button toggles between everything
3669 blocked and the previous configuration.
3670 2 The "airplane mode" button toggles between everything
3671 blocked and everything unblocked.
3673 rhash_entries= [KNL,NET]
3674 Set number of hash buckets for route cache
3677 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3680 ro [KNL] Mount root device read-only on boot
3683 on Mark read-only kernel memory as read-only (default).
3684 off Leave read-only kernel memory writable for debugging.
3687 Enable the uart passthrough on the designated usb port
3688 on Rockchip SoCs. When active, the signals of the
3689 debug-uart get routed to the D+ and D- pins of the usb
3690 port and the regular usb controller gets disabled.
3692 root= [KNL] Root filesystem
3693 See name_to_dev_t comment in init/do_mounts.c.
3695 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3696 mount the root filesystem
3698 rootflags= [KNL] Set root filesystem mount option string
3700 rootfstype= [KNL] Set root filesystem type
3702 rootwait [KNL] Wait (indefinitely) for root device to show up.
3703 Useful for devices that are detected asynchronously
3704 (e.g. USB and MMC devices).
3706 rproc_mem=nn[KMG][@address]
3707 [KNL,ARM,CMA] Remoteproc physical memory block.
3708 Memory area to be used by remote processor image,
3711 rw [KNL] Mount root device read-write on boot
3713 S [KNL] Run init in single mode
3715 s390_iommu= [HW,S390]
3716 Set s390 IOTLB flushing mode
3718 With strict flushing every unmap operation will result in
3719 an IOTLB flush. Default is lazy flushing before reuse,
3723 See drivers/net/irda/sa1100_ir.c.
3725 sbni= [NET] Granch SBNI12 leased line adapter
3727 sched_debug [KNL] Enables verbose scheduler debug messages.
3729 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3730 Allowed values are enable and disable. This feature
3731 incurs a small amount of overhead in the scheduler
3732 but is useful for debugging and performance tuning.
3734 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3735 xtime_lock contention on larger systems, and/or RCU lock
3736 contention on all systems with CONFIG_MAXSMP set.
3737 Format: { "0" | "1" }
3738 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3740 Note: increases power consumption, thus should only be
3741 enabled if running jitter sensitive (HPC/RT) workloads.
3743 security= [SECURITY] Choose a security module to enable at boot.
3744 If this boot parameter is not specified, only the first
3745 security module asking for security registration will be
3746 loaded. An invalid security module name will be treated
3747 as if no module has been chosen.
3749 selinux= [SELINUX] Disable or enable SELinux at boot time.
3750 Format: { "0" | "1" }
3751 See security/selinux/Kconfig help text.
3754 Default value is set via kernel config option.
3755 If enabled at boot time, /selinux/disable can be used
3756 later to disable prior to initial policy load.
3758 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3759 Format: { "0" | "1" }
3760 See security/apparmor/Kconfig help text
3763 Default value is set via kernel config option.
3765 serialnumber [BUGS=X86-32]
3768 Maximal number of shapers.
3776 Disable merging of slabs with similar size. May be
3777 necessary if there is some reason to distinguish
3778 allocs to different slabs, especially in hardened
3779 environments where the risk of heap overflows and
3780 layout control by attackers can usually be
3781 frustrated by disabling merging. This will reduce
3782 most of the exposure of a heap attack to a single
3783 cache (risks via metadata attacks are mostly
3784 unchanged). Debug options disable merging on their
3786 For more information see Documentation/vm/slub.txt.
3788 slab_max_order= [MM, SLAB]
3789 Determines the maximum allowed order for slabs.
3790 A high setting may cause OOMs due to memory
3791 fragmentation. Defaults to 1 for systems with
3792 more than 32MB of RAM, 0 otherwise.
3794 slub_debug[=options[,slabs]] [MM, SLUB]
3795 Enabling slub_debug allows one to determine the
3796 culprit if slab objects become corrupted. Enabling
3797 slub_debug can create guard zones around objects and
3798 may poison objects when not in use. Also tracks the
3799 last alloc / free. For more information see
3800 Documentation/vm/slub.txt.
3802 slub_memcg_sysfs= [MM, SLUB]
3803 Determines whether to enable sysfs directories for
3804 memory cgroup sub-caches. 1 to enable, 0 to disable.
3805 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
3806 Enabling this can lead to a very high number of debug
3807 directories and files being created under
3810 slub_max_order= [MM, SLUB]
3811 Determines the maximum allowed order for slabs.
3812 A high setting may cause OOMs due to memory
3813 fragmentation. For more information see
3814 Documentation/vm/slub.txt.
3816 slub_min_objects= [MM, SLUB]
3817 The minimum number of objects per slab. SLUB will
3818 increase the slab order up to slub_max_order to
3819 generate a sufficiently large slab able to contain
3820 the number of objects indicated. The higher the number
3821 of objects the smaller the overhead of tracking slabs
3822 and the less frequently locks need to be acquired.
3823 For more information see Documentation/vm/slub.txt.
3825 slub_min_order= [MM, SLUB]
3826 Determines the minimum page order for slabs. Must be
3827 lower than slub_max_order.
3828 For more information see Documentation/vm/slub.txt.
3830 slub_nomerge [MM, SLUB]
3831 Same with slab_nomerge. This is supported for legacy.
3832 See slab_nomerge for more information.
3835 Format: <io1>[,<io2>[,...,<io8>]]
3837 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3838 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3839 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3840 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3841 smsc-ircc2.ircc_irq= [HW] IRQ line
3842 smsc-ircc2.ircc_dma= [HW] DMA channel
3843 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3844 0: Toshiba Satellite 1800 (GP data pin select)
3845 1: Fast pin select (default)
3848 smt [KNL,S390] Set the maximum number of threads (logical
3849 CPUs) to use per physical CPU on systems capable of
3850 symmetric multithreading (SMT). Will be capped to the
3851 actual hardware limit.
3853 Default: -1 (no limit)
3856 [KNL] Should the soft-lockup detector generate panics.
3859 softlockup_all_cpu_backtrace=
3860 [KNL] Should the soft-lockup detector generate
3861 backtraces on all cpus.
3864 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3865 See Documentation/laptops/sonypi.txt
3867 spia_io_base= [HW,MTD]
3872 srcutree.counter_wrap_check [KNL]
3873 Specifies how frequently to check for
3874 grace-period sequence counter wrap for the
3875 srcu_data structure's ->srcu_gp_seq_needed field.
3876 The greater the number of bits set in this kernel
3877 parameter, the less frequently counter wrap will
3878 be checked for. Note that the bottom two bits
3881 srcutree.exp_holdoff [KNL]
3882 Specifies how many nanoseconds must elapse
3883 since the end of the last SRCU grace period for
3884 a given srcu_struct until the next normal SRCU
3885 grace period will be considered for automatic
3886 expediting. Set to zero to disable automatic
3889 stack_guard_gap= [MM]
3890 override the default stack gap protection. The value
3891 is in page units and it defines how many pages prior
3892 to (for stacks growing down) resp. after (for stacks
3893 growing up) the main stack are reserved for no other
3894 mapping. Default value is 256 pages.
3897 Enabled the stack tracer on boot up.
3899 stacktrace_filter=[function-list]
3900 [FTRACE] Limit the functions that the stack tracer
3901 will trace at boot up. function-list is a comma separated
3902 list of functions. This list can be changed at run
3903 time by the stack_trace_filter file in the debugfs
3904 tracing directory. Note, this enables stack tracing
3905 and the stacktrace above is not needed.
3909 Set the STI (builtin display/keyboard on the HP-PARISC
3910 machines) console (graphic card) which should be used
3911 as the initial boot-console.
3912 See also comment in drivers/video/console/sticore.c.
3915 See comment in drivers/video/console/sticore.c.
3918 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3920 sunrpc.min_resvport=
3921 sunrpc.max_resvport=
3923 SunRPC servers often require that client requests
3924 originate from a privileged port (i.e. a port in the
3925 range 0 < portnr < 1024).
3926 An administrator who wishes to reserve some of these
3927 ports for other uses may adjust the range that the
3928 kernel's sunrpc client considers to be privileged
3929 using these two parameters to set the minimum and
3930 maximum port values.
3932 sunrpc.svc_rpc_per_connection_limit=
3934 Limit the number of requests that the server will
3935 process in parallel from a single connection.
3936 The default value is 0 (no limit).
3940 Control how the NFS server code allocates CPUs to
3941 service thread pools. Depending on how many NICs
3942 you have and where their interrupts are bound, this
3943 option will affect which CPUs will do NFS serving.
3944 Note: this parameter cannot be changed while the
3945 NFS server is running.
3947 auto the server chooses an appropriate mode
3948 automatically using heuristics
3949 global a single global pool contains all CPUs
3950 percpu one pool for each CPU
3951 pernode one pool for each NUMA node (equivalent
3952 to global on non-NUMA machines)
3954 sunrpc.tcp_slot_table_entries=
3955 sunrpc.udp_slot_table_entries=
3957 Sets the upper limit on the number of simultaneous
3958 RPC calls that can be sent from the client to a
3959 server. Increasing these values may allow you to
3960 improve throughput, but will also increase the
3961 amount of memory reserved for use by the client.
3963 suspend.pm_test_delay=
3965 Sets the number of seconds to remain in a suspend test
3966 mode before resuming the system (see
3967 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3968 is set. Default value is 5.
3971 [KNL] Enable accounting of swap in memory resource
3972 controller if no parameter or 1 is given or disable
3973 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3975 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3976 Format: { <int> | force | noforce }
3977 <int> -- Number of I/O TLB slabs
3978 force -- force using of bounce buffers even if they
3979 wouldn't be automatically used by the kernel
3980 noforce -- Never use bounce buffers (for debugging)
3984 sysfs.deprecated=0|1 [KNL]
3985 Enable/disable old style sysfs layout for old udev
3986 on older distributions. When this option is enabled
3987 very new udev will not work anymore. When this option
3988 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3989 in older udev will not work anymore.
3990 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3991 the kernel configuration.
3993 sysrq_always_enabled
3995 Ignore sysrq setting - this boot parameter will
3996 neutralize any effect of /proc/sys/kernel/sysrq.
3997 Useful for debugging.
3999 tcpmhash_entries= [KNL,NET]
4000 Set the number of tcp_metrics_hash slots.
4001 Default value is 8192 or 16384 depending on total
4002 ram pages. This is used to specify the TCP metrics
4003 cache size. See Documentation/networking/ip-sysctl.txt
4004 "tcp_no_metrics_save" section for more details.
4008 test_suspend= [SUSPEND][,N]
4009 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4010 standby suspend) or "freeze" (for suspend type freeze)
4011 as the system sleep state during system startup with
4012 the optional capability to repeat N number of times.
4013 The system is woken from this state using a
4014 wakeup-capable RTC alarm.
4016 thash_entries= [KNL,NET]
4017 Set number of hash buckets for TCP connection
4019 thermal.act= [HW,ACPI]
4020 -1: disable all active trip points in all thermal zones
4021 <degrees C>: override all lowest active trip points
4023 thermal.crt= [HW,ACPI]
4024 -1: disable all critical trip points in all thermal zones
4025 <degrees C>: override all critical trip points
4027 thermal.nocrt= [HW,ACPI]
4028 Set to disable actions on ACPI thermal zone
4029 critical and hot trip points.
4031 thermal.off= [HW,ACPI]
4032 1: disable ACPI thermal control
4034 thermal.psv= [HW,ACPI]
4035 -1: disable all passive trip points
4036 <degrees C>: override all passive trip points to this
4039 thermal.tzp= [HW,ACPI]
4040 Specify global default ACPI thermal zone polling rate
4041 <deci-seconds>: poll all this frequency
4042 0: no polling (default)
4045 Force threading of all interrupt handlers except those
4046 marked explicitly IRQF_NO_THREAD.
4049 Enable the Transcendent memory driver if built-in.
4051 tmem.cleancache=0|1 [KNL, XEN]
4052 Default is on (1). Disable the usage of the cleancache
4053 API to send anonymous pages to the hypervisor.
4055 tmem.frontswap=0|1 [KNL, XEN]
4056 Default is on (1). Disable the usage of the frontswap
4057 API to send swap pages to the hypervisor. If disabled
4058 the selfballooning and selfshrinking are force disabled.
4060 tmem.selfballooning=0|1 [KNL, XEN]
4061 Default is on (1). Disable the driving of swap pages
4064 tmem.selfshrinking=0|1 [KNL, XEN]
4065 Default is on (1). Partial swapoff that immediately
4066 transfers pages from Xen hypervisor back to the
4067 kernel based on different criteria.
4071 Specify if the kernel should make use of the cpu
4072 topology information if the hardware supports this.
4073 The scheduler will make use of this information and
4074 e.g. base its process migration decisions on it.
4077 topology_updates= [KNL, PPC, NUMA]
4079 Specify if the kernel should ignore (off)
4080 topology updates sent by the hypervisor to this
4085 tpm_suspend_pcr=[HW,TPM]
4086 Format: integer pcr id
4087 Specify that at suspend time, the tpm driver
4088 should extend the specified pcr with zeros,
4089 as a workaround for some chips which fail to
4090 flush the last written pcr on TPM_SaveState.
4091 This will guarantee that all the other pcrs
4094 trace_buf_size=nn[KMG]
4095 [FTRACE] will set tracing buffer size on each cpu.
4097 trace_event=[event-list]
4098 [FTRACE] Set and start specified trace events in order
4099 to facilitate early boot debugging. The event-list is a
4100 comma separated list of trace events to enable. See
4101 also Documentation/trace/events.txt
4103 trace_options=[option-list]
4104 [FTRACE] Enable or disable tracer options at boot.
4105 The option-list is a comma delimited list of options
4106 that can be enabled or disabled just as if you were
4107 to echo the option name into
4109 /sys/kernel/debug/tracing/trace_options
4111 For example, to enable stacktrace option (to dump the
4112 stack trace of each event), add to the command line:
4114 trace_options=stacktrace
4116 See also Documentation/trace/ftrace.txt "trace options"
4120 Have the tracepoints sent to printk as well as the
4121 tracing ring buffer. This is useful for early boot up
4122 where the system hangs or reboots and does not give the
4123 option for reading the tracing buffer or performing a
4124 ftrace_dump_on_oops.
4126 To turn off having tracepoints sent to printk,
4127 echo 0 > /proc/sys/kernel/tracepoint_printk
4128 Note, echoing 1 into this file without the
4129 tracepoint_printk kernel cmdline option has no effect.
4133 Having tracepoints sent to printk() and activating high
4134 frequency tracepoints such as irq or sched, can cause
4135 the system to live lock.
4138 [FTRACE] enable this option to disable tracing when a
4139 warning is hit. This turns off "tracing_on". Tracing can
4140 be enabled again by echoing '1' into the "tracing_on"
4141 file located in /sys/kernel/debug/tracing/
4143 This option is useful, as it disables the trace before
4144 the WARNING dump is called, which prevents the trace to
4145 be filled with content caused by the warning output.
4147 This option can also be set at run time via the sysctl
4148 option: kernel/traceoff_on_warning
4150 transparent_hugepage=
4152 Format: [always|madvise|never]
4153 Can be used to control the default behavior of the system
4154 with respect to transparent hugepages.
4155 See Documentation/vm/transhuge.txt for more details.
4157 tsc= Disable clocksource stability checks for TSC.
4159 [x86] reliable: mark tsc clocksource as reliable, this
4160 disables clocksource verification at runtime, as well
4161 as the stability checks done at bootup. Used to enable
4162 high-resolution timer mode on older hardware, and in
4163 virtualized environment.
4164 [x86] noirqtime: Do not use TSC to do irq accounting.
4165 Used to run time disable IRQ_TIME_ACCOUNTING on any
4166 platforms where RDTSC is slow and this accounting
4169 turbografx.map[2|3]= [HW,JOY]
4170 TurboGraFX parallel port interface
4172 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4173 See also Documentation/input/joystick-parport.txt
4175 udbg-immortal [PPC] When debugging early kernel crashes that
4176 happen after console_init() and before a proper
4177 console driver takes over, this boot options might
4178 help "seeing" what's going on.
4180 uhash_entries= [KNL,NET]
4181 Set number of hash buckets for UDP/UDP-Lite connections
4184 [USB] Ignore overcurrent events (default N).
4185 Some badly-designed motherboards generate lots of
4186 bogus events, for ports that aren't wired to
4187 anything. Set this parameter to avoid log spamming.
4188 Note that genuine overcurrent events won't be
4192 [X86] Cause panic on unknown NMI.
4194 usbcore.authorized_default=
4195 [USB] Default USB device authorization:
4196 (default -1 = authorized except for wireless USB,
4197 0 = not authorized, 1 = authorized)
4199 usbcore.autosuspend=
4200 [USB] The autosuspend time delay (in seconds) used
4201 for newly-detected USB devices (default 2). This
4202 is the time required before an idle device will be
4203 autosuspended. Devices for which the delay is set
4204 to a negative value won't be autosuspended at all.
4206 usbcore.usbfs_snoop=
4207 [USB] Set to log all usbfs traffic (default 0 = off).
4209 usbcore.usbfs_snoop_max=
4210 [USB] Maximum number of bytes to snoop in each URB
4213 usbcore.blinkenlights=
4214 [USB] Set to cycle leds on hubs (default 0 = off).
4216 usbcore.old_scheme_first=
4217 [USB] Start with the old device initialization
4218 scheme (default 0 = off).
4220 usbcore.usbfs_memory_mb=
4221 [USB] Memory limit (in MB) for buffers allocated by
4222 usbfs (default = 16, 0 = max = 2047).
4224 usbcore.use_both_schemes=
4225 [USB] Try the other device initialization scheme
4226 if the first one fails (default 1 = enabled).
4228 usbcore.initial_descriptor_timeout=
4229 [USB] Specifies timeout for the initial 64-byte
4230 USB_REQ_GET_DESCRIPTOR request in milliseconds
4231 (default 5000 = 5.0 seconds).
4233 usbcore.nousb [USB] Disable the USB subsystem
4236 [USBHID] The interval which mice are to be polled at.
4239 [USBHID] The interval which joysticks are to be polled at.
4241 usb-storage.delay_use=
4242 [UMS] The delay in seconds before a new device is
4243 scanned for Logical Units (default 1).
4246 [UMS] A list of quirks entries to supplement or
4247 override the built-in unusual_devs list. List
4248 entries are separated by commas. Each entry has
4249 the form VID:PID:Flags where VID and PID are Vendor
4250 and Product ID values (4-digit hex numbers) and
4251 Flags is a set of characters, each corresponding
4252 to a common usb-storage quirk flag as follows:
4253 a = SANE_SENSE (collect more than 18 bytes
4255 b = BAD_SENSE (don't collect more than 18
4256 bytes of sense data);
4257 c = FIX_CAPACITY (decrease the reported
4258 device capacity by one sector);
4259 d = NO_READ_DISC_INFO (don't use
4260 READ_DISC_INFO command);
4261 e = NO_READ_CAPACITY_16 (don't use
4262 READ_CAPACITY_16 command);
4263 f = NO_REPORT_OPCODES (don't use report opcodes
4265 g = MAX_SECTORS_240 (don't transfer more than
4266 240 sectors at a time, uas only);
4267 h = CAPACITY_HEURISTICS (decrease the
4268 reported device capacity by one
4269 sector if the number is odd);
4270 i = IGNORE_DEVICE (don't bind to this
4272 j = NO_REPORT_LUNS (don't use report luns
4274 l = NOT_LOCKABLE (don't try to lock and
4275 unlock ejectable media);
4276 m = MAX_SECTORS_64 (don't transfer more
4277 than 64 sectors = 32 KB at a time);
4278 n = INITIAL_READ10 (force a retry of the
4279 initial READ(10) command);
4280 o = CAPACITY_OK (accept the capacity
4281 reported by the device);
4282 p = WRITE_CACHE (the device cache is ON
4284 r = IGNORE_RESIDUE (the device reports
4285 bogus residue values);
4286 s = SINGLE_LUN (the device has only one
4288 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4289 commands, uas only);
4290 u = IGNORE_UAS (don't bind to the uas driver);
4291 w = NO_WP_DETECT (don't test whether the
4292 medium is write-protected).
4293 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4294 even if the device claims no cache)
4295 Example: quirks=0419:aaf5:rl,0421:0433:rc
4297 user_debug= [KNL,ARM]
4299 See arch/arm/Kconfig.debug help text.
4300 1 - undefined instruction events
4302 4 - invalid data aborts
4305 Example: user_debug=31
4308 [X86] Flags controlling user PTE allocations.
4310 nohigh = do not allocate PTE pages in
4311 HIGHMEM regardless of setting
4315 On X86_32, this is an alias for vdso32=. Otherwise:
4317 vdso=1: enable VDSO (the default)
4318 vdso=0: disable VDSO mapping
4320 vdso32= [X86] Control the 32-bit vDSO
4321 vdso32=1: enable 32-bit VDSO
4322 vdso32=0 or vdso32=2: disable 32-bit VDSO
4324 See the help text for CONFIG_COMPAT_VDSO for more
4325 details. If CONFIG_COMPAT_VDSO is set, the default is
4326 vdso32=0; otherwise, the default is vdso32=1.
4328 For compatibility with older kernels, vdso32=2 is an
4331 Try vdso32=0 if you encounter an error that says:
4332 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4335 vector=percpu: enable percpu vector domain
4337 video= [FB] Frame buffer configuration
4338 See Documentation/fb/modedb.txt.
4340 video.brightness_switch_enabled= [0,1]
4341 If set to 1, on receiving an ACPI notify event
4342 generated by hotkey, video driver will adjust brightness
4343 level and then send out the event to user space through
4344 the allocated input device; If set to 0, video driver
4345 will only send out the event without touching backlight
4350 [VMMIO] Memory mapped virtio (platform) device.
4352 <size>@<baseaddr>:<irq>[:<id>]
4354 <size> := size (can use standard suffixes
4356 <baseaddr> := physical base address
4357 <irq> := interrupt number (as passed to
4359 <id> := (optional) platform device id
4361 virtio_mmio.device=1K@0x100b0000:48:7
4363 Can be used multiple times for multiple devices.
4365 vga= [BOOT,X86-32] Select a particular video mode
4366 See Documentation/x86/boot.txt and
4367 Documentation/svga.txt.
4368 Use vga=ask for menu.
4369 This is actually a boot loader parameter; the value is
4370 passed to the kernel using a special protocol.
4372 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4373 size of <nn>. This can be used to increase the
4374 minimum size (128MB on x86). It can also be used to
4375 decrease the size and leave more room for directly
4378 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4381 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4384 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4388 Controls the behavior of vsyscalls (i.e. calls to
4389 fixed addresses of 0xffffffffff600x00 from legacy
4390 code). Most statically-linked binaries and older
4391 versions of glibc use these calls. Because these
4392 functions are at fixed addresses, they make nice
4393 targets for exploits that can control RIP.
4395 emulate [default] Vsyscalls turn into traps and are
4396 emulated reasonably safely.
4398 native Vsyscalls are native syscall instructions.
4399 This is a little bit faster than trapping
4400 and makes a few dynamic recompilers work
4401 better than they would in emulation mode.
4402 It also makes exploits much easier to write.
4404 none Vsyscalls don't work at all. This makes
4405 them quite hard to use for exploits but
4406 might break your system.
4408 vt.color= [VT] Default text color.
4409 Format: 0xYX, X = foreground, Y = background.
4410 Default: 0x07 = light gray on black.
4412 vt.cur_default= [VT] Default cursor shape.
4413 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4414 the parameters of the <Esc>[?A;B;Cc escape sequence;
4415 see VGA-softcursor.txt. Default: 2 = underline.
4417 vt.default_blu= [VT]
4418 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4419 Change the default blue palette of the console.
4420 This is a 16-member array composed of values
4423 vt.default_grn= [VT]
4424 Format: <green0>,<green1>,<green2>,...,<green15>
4425 Change the default green palette of the console.
4426 This is a 16-member array composed of values
4429 vt.default_red= [VT]
4430 Format: <red0>,<red1>,<red2>,...,<red15>
4431 Change the default red palette of the console.
4432 This is a 16-member array composed of values
4438 Set system-wide default UTF-8 mode for all tty's.
4439 Default is 1, i.e. UTF-8 mode is enabled for all
4440 newly opened terminals.
4442 vt.global_cursor_default=
4445 Set system-wide default for whether a cursor
4446 is shown on new VTs. Default is -1,
4447 i.e. cursors will be created by default unless
4448 overridden by individual drivers. 0 will hide
4449 cursors, 1 will display them.
4451 vt.italic= [VT] Default color for italic text; 0-15.
4454 vt.underline= [VT] Default color for underlined text; 0-15.
4457 watchdog timers [HW,WDT] For information on watchdog timers,
4458 see Documentation/watchdog/watchdog-parameters.txt
4459 or other driver-specific files in the
4460 Documentation/watchdog/ directory.
4462 workqueue.watchdog_thresh=
4463 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4464 warn stall conditions and dump internal state to
4465 help debugging. 0 disables workqueue stall
4466 detection; otherwise, it's the stall threshold
4467 duration in seconds. The default value is 30 and
4468 it can be updated at runtime by writing to the
4469 corresponding sysfs file.
4471 workqueue.disable_numa
4472 By default, all work items queued to unbound
4473 workqueues are affine to the NUMA nodes they're
4474 issued on, which results in better behavior in
4475 general. If NUMA affinity needs to be disabled for
4476 whatever reason, this option can be used. Note
4477 that this also can be controlled per-workqueue for
4478 workqueues visible under /sys/bus/workqueue/.
4480 workqueue.power_efficient
4481 Per-cpu workqueues are generally preferred because
4482 they show better performance thanks to cache
4483 locality; unfortunately, per-cpu workqueues tend to
4484 be more power hungry than unbound workqueues.
4486 Enabling this makes the per-cpu workqueues which
4487 were observed to contribute significantly to power
4488 consumption unbound, leading to measurably lower
4489 power usage at the cost of small performance
4492 The default value of this parameter is determined by
4493 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4495 workqueue.debug_force_rr_cpu
4496 Workqueue used to implicitly guarantee that work
4497 items queued without explicit CPU specified are put
4498 on the local CPU. This guarantee is no longer true
4499 and while local CPU is still preferred work items
4500 may be put on foreign CPUs. This debug option
4501 forces round-robin CPU selection to flush out
4502 usages which depend on the now broken guarantee.
4503 When enabled, memory and cache locality will be
4506 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4507 default x2apic cluster mode on platforms
4510 x86_intel_mid_timer= [X86-32,APBT]
4511 Choose timer option for x86 Intel MID platform.
4512 Two valid options are apbt timer only and lapic timer
4513 plus one apbt timer for broadcast timer.
4514 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4516 xen_512gb_limit [KNL,X86-64,XEN]
4517 Restricts the kernel running paravirtualized under Xen
4518 to use only up to 512 GB of RAM. The reason to do so is
4519 crash analysis tools and Xen tools for doing domain
4520 save/restore/migration must be enabled to handle larger
4523 xen_emul_unplug= [HW,X86,XEN]
4524 Unplug Xen emulated devices
4525 Format: [unplug0,][unplug1]
4526 ide-disks -- unplug primary master IDE devices
4527 aux-ide-disks -- unplug non-primary-master IDE devices
4528 nics -- unplug network devices
4529 all -- unplug all emulated devices (NICs and IDE disks)
4530 unnecessary -- unplugging emulated devices is
4531 unnecessary even if the host did not respond to
4533 never -- do not unplug even if version check succeeds
4535 xen_nopvspin [X86,XEN]
4536 Disables the ticketlock slowpath using Xen PV
4540 Disables the PV optimizations forcing the HVM guest to
4541 run as generic HVM guest with no PV drivers.
4543 xirc2ps_cs= [NET,PCMCIA]
4545 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
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