4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt |
172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
175 strict -- Be less tolerant of platforms that are not
176 strictly ACPI specification compliant.
177 rsdt -- prefer RSDT over (default) XSDT
178 copy_dsdt -- copy DSDT to memory
179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
181 See also Documentation/power/runtime_pm.txt, pci=noacpi
183 acpi_apic_instance= [ACPI, IOAPIC]
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
196 acpica_no_return_repair [HW, ACPI]
197 Disable AML predefined validation mechanism
198 This mechanism can repair the evaluation result to make
199 the return objects more ACPI specification compliant.
200 This option is useful for developers to identify the
201 root cause of an AML interpreter issue when the issue
202 has something to do with the repair mechanism.
204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
208 debug output. Bits in debug_layer correspond to a
209 _COMPONENT in an ACPI source file, e.g.,
210 #define _COMPONENT ACPI_PCI_COMPONENT
211 Bits in debug_level correspond to a level in
212 ACPI_DEBUG_PRINT statements, e.g.,
213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
214 The debug_level mask defaults to "info". See
215 Documentation/acpi/debug.txt for more information about
216 debug layers and levels.
218 Enable processor driver info messages:
219 acpi.debug_layer=0x20000000
220 Enable PCI/PCI interrupt routing info messages:
221 acpi.debug_layer=0x400000
222 Enable AML "Debug" output, i.e., stores to the Debug
223 object while interpreting AML:
224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
225 Enable all messages related to ACPI hardware:
226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
228 Some values produce so much output that the system is
229 unusable. The "log_buf_len" parameter may be useful
230 if you need to capture more output.
232 acpi_enforce_resources= [ACPI]
233 { strict | lax | no }
234 Check for resource conflicts between native drivers
235 and ACPI OperationRegions (SystemIO and SystemMemory
236 only). IO ports and memory declared in ACPI might be
237 used by the ACPI subsystem in arbitrary AML code and
238 can interfere with legacy drivers.
239 strict (default): access to resources claimed by ACPI
240 is denied; legacy drivers trying to access reserved
241 resources will fail to bind to device using them.
242 lax: access to resources claimed by ACPI is allowed;
243 legacy drivers trying to access reserved resources
244 will bind successfully but a warning message is logged.
245 no: ACPI OperationRegions are not marked as reserved,
246 no further checks are performed.
248 acpi_force_table_verification [HW,ACPI]
249 Enable table checksum verification during early stage.
250 By default, this is disabled due to x86 early mapping
253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
262 Format: <irq>,<irq>...
264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
266 Format: <irq>,<irq>...
268 acpi_no_auto_serialize [HW,ACPI]
269 Disable auto-serialization of AML methods
270 AML control methods that contain the opcodes to create
271 named objects will be marked as "Serialized" by the
272 auto-serialization feature.
273 This feature is enabled by default.
274 This option allows to turn off the feature.
276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
279 acpi_no_static_ssdt [HW,ACPI]
280 Disable installation of static SSDTs at early boot time
281 By default, SSDTs contained in the RSDT/XSDT will be
282 installed automatically and they will appear under
283 /sys/firmware/acpi/tables.
284 This option turns off this feature.
285 Note that specifying this option does not affect
286 dynamic table installation which will install SSDT
287 tables to /sys/firmware/acpi/tables/dynamic.
289 acpi_rsdp= [ACPI,EFI,KEXEC]
290 Pass the RSDP address to the kernel, mostly used
291 on machines running EFI runtime service to boot the
292 second kernel for kdump.
294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
295 Format: To spoof as Windows 98: ="Microsoft Windows"
297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
298 of 2 which is mandated by ACPI 6) as the supported ACPI
299 specification revision (when using this switch, it may
300 be necessary to carry out a cold reboot _twice_ in a
301 row to make it take effect on the platform firmware).
303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
304 acpi_osi="string1" # add string1
305 acpi_osi="!string2" # remove string2
306 acpi_osi=!* # remove all strings
307 acpi_osi=! # disable all built-in OS vendor
309 acpi_osi= # disable all strings
311 'acpi_osi=!' can be used in combination with single or
312 multiple 'acpi_osi="string1"' to support specific OS
313 vendor string(s). Note that such command can only
314 affect the default state of the OS vendor strings, thus
315 it cannot affect the default state of the feature group
316 strings and the current state of the OS vendor strings,
317 specifying it multiple times through kernel command line
318 is meaningless. This command is useful when one do not
319 care about the state of the feature group strings which
320 should be controlled by the OSPM.
322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
324 can make '_OSI("Windows 2000")' TRUE.
326 'acpi_osi=' cannot be used in combination with other
327 'acpi_osi=' command lines, the _OSI method will not
328 exist in the ACPI namespace. NOTE that such command can
329 only affect the _OSI support state, thus specifying it
330 multiple times through kernel command line is also
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
336 'acpi_osi=!*' can be used in combination with single or
337 multiple 'acpi_osi="string1"' to support specific
338 string(s). Note that such command can affect the
339 current state of both the OS vendor strings and the
340 feature group strings, thus specifying it multiple times
341 through kernel command line is meaningful. But it may
342 still not able to affect the final state of a string if
343 there are quirks related to this string. This command
344 is useful when one want to control the state of the
345 feature group strings to debug BIOS issues related to
348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
349 '_OSI("Module Device")' FALSE.
350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
351 '_OSI("Module Device")' TRUE.
352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
360 Override the pmtimer bug detection: force the kernel
361 to assume that this machine's pmtimer latches its value
362 and always returns good values.
364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
365 Format: { level | edge | high | low }
367 acpi_skip_timer_override [HW,ACPI]
368 Recognize and ignore IRQ0/pin2 Interrupt Override.
369 For broken nForce2 BIOS resulting in XT-PIC timer.
371 acpi_sleep= [HW,ACPI] Sleep options
372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
373 old_ordering, nonvs, sci_force_enable }
374 See Documentation/power/video.txt for information on
376 s3_beep is for debugging; it makes the PC's speaker beep
377 as soon as the kernel's real-mode entry point is called.
378 s4_nohwsig prevents ACPI hardware signature from being
379 used during resume from hibernation.
380 old_ordering causes the ACPI 1.0 ordering of the _PTS
381 control method, with respect to putting devices into
382 low power states, to be enforced (the ACPI 2.0 ordering
383 of _PTS is used by default).
384 nonvs prevents the kernel from saving/restoring the
385 ACPI NVS memory during suspend/hibernation and resume.
386 sci_force_enable causes the kernel to set SCI_EN directly
387 on resume from S1/S3 (which is against the ACPI spec,
388 but some broken systems don't work without it).
390 acpi_use_timer_override [HW,ACPI]
391 Use timer override. For some broken Nvidia NF5 boards
392 that require a timer override, but don't have HPET
394 add_efi_memmap [EFI; X86] Include EFI memory map in
395 kernel's map of available physical RAM.
398 { off | try_unsupported }
399 off: disable AGP support
400 try_unsupported: try to drive unsupported chipsets
401 (may crash computer or cause data corruption)
404 See Documentation/sound/alsa/alsa-parameters.txt
407 Allow the default userspace alignment fault handler
408 behaviour to be specified. Bit 0 enables warnings,
409 bit 1 enables fixups, and bit 2 sends a segfault.
411 align_va_addr= [X86-64]
412 Align virtual addresses by clearing slice [14:12] when
413 allocating a VMA at process creation time. This option
414 gives you up to 3% performance improvement on AMD F15h
415 machines (where it is enabled by default) for a
416 CPU-intensive style benchmark, and it can vary highly in
417 a microbenchmark depending on workload and compiler.
419 32: only for 32-bit processes
420 64: only for 64-bit processes
421 on: enable for both 32- and 64-bit processes
422 off: disable for both 32- and 64-bit processes
424 alloc_snapshot [FTRACE]
425 Allocate the ftrace snapshot buffer on boot up when the
426 main buffer is allocated. This is handy if debugging
427 and you need to use tracing_snapshot() on boot up, and
428 do not want to use tracing_snapshot_alloc() as it needs
429 to be done where GFP_KERNEL allocations are allowed.
431 amd_iommu= [HW,X86-64]
432 Pass parameters to the AMD IOMMU driver in the system.
434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
438 off - do not initialize any AMD IOMMU found in
440 force_isolation - Force device isolation for all
441 devices. The IOMMU driver is not
442 allowed anymore to lift isolation
443 requirements as needed. This option
444 does not override iommu=pt
446 amd_iommu_dump= [HW,X86-64]
447 Enable AMD IOMMU driver option to dump the ACPI table
448 for AMD IOMMU. With this option enabled, AMD IOMMU
449 driver will print ACPI tables for AMD IOMMU during
450 IOMMU initialization.
452 amijoy.map= [HW,JOY] Amiga joystick support
453 Map of devices attached to JOY0DAT and JOY1DAT
455 See also Documentation/input/joystick.txt
457 analog.map= [HW,JOY] Analog joystick and gamepad support
458 Specifies type or capabilities of an analog joystick
459 connected to one of 16 gameports
460 Format: <type1>,<type2>,..<type16>
463 Power management functions (SPARCstation-4/5 + deriv.)
465 Disable APC CPU standby support. SPARCstation-Fox does
466 not play well with APC CPU idle - disable it if you have
467 APC and your system crashes randomly.
469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
470 Change the output verbosity whilst booting
471 Format: { quiet (default) | verbose | debug }
472 Change the amount of debugging information output
473 when initialising the APIC and IO-APIC components.
476 See Documentation/networking/ipv6.txt.
478 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
479 Limit apic dumping. The parameter defines the maximal
480 number of local apics being dumped. Also it is possible
481 to set it to "all" by meaning -- no limit here.
482 Format: { 1 (default) | 2 | ... | all }.
483 The parameter valid if only apic=debug or
484 apic=verbose is specified.
485 Example: apic=debug show_lapic=all
487 apm= [APM] Advanced Power Management
488 See header of arch/x86/kernel/apm_32.c.
490 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
491 Format: <io>,<irq>,<nodeID>
495 atarimouse= [HW,MOUSE] Atari Mouse
497 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
498 EzKey and similar keyboards
500 atkbd.reset= [HW] Reset keyboard during initialization
502 atkbd.set= [HW] Select keyboard code set
503 Format: <int> (2 = AT (default), 3 = PS/2)
505 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
508 atkbd.softraw= [HW] Choose between synthetic and real raw mode
509 Format: <bool> (0 = real, 1 = synthetic (default))
511 atkbd.softrepeat= [HW]
512 Use software keyboard repeat
514 audit= [KNL] Enable the audit sub-system
515 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
516 0 - kernel audit is disabled and can not be enabled
517 until the next reboot
518 unset - kernel audit is initialized but disabled and
519 will be fully enabled by the userspace auditd.
520 1 - kernel audit is initialized and partially enabled,
521 storing at most audit_backlog_limit messages in
522 RAM until it is fully enabled by the userspace
526 audit_backlog_limit= [KNL] Set the audit queue size limit.
527 Format: <int> (must be >=0)
530 baycom_epp= [HW,AX25]
533 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
535 See header of drivers/net/hamradio/baycom_par.c.
537 baycom_ser_fdx= [HW,AX25]
538 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
539 Format: <io>,<irq>,<mode>[,<baud>]
540 See header of drivers/net/hamradio/baycom_ser_fdx.c.
542 baycom_ser_hdx= [HW,AX25]
543 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
544 Format: <io>,<irq>,<mode>
545 See header of drivers/net/hamradio/baycom_ser_hdx.c.
547 blkdevparts= Manual partition parsing of block device(s) for
548 embedded devices based on command line input.
549 See Documentation/block/cmdline-partition.txt
551 boot_delay= Milliseconds to delay each printk during boot.
552 Values larger than 10 seconds (10000) are changed to
556 bootmem_debug [KNL] Enable bootmem allocator debug messages.
558 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
559 bttv.radio= Most important insmod options are available as
561 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
564 bulk_remove=off [PPC] This parameter disables the use of the pSeries
565 firmware feature for flushing multiple hpte entries
568 c101= [NET] Moxa C101 synchronous serial card
570 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
571 Sometimes CPU hardware bugs make them report the cache
572 size incorrectly. The kernel will attempt work arounds
573 to fix known problems, but for some CPUs it is not
574 possible to determine what the correct size should be.
575 This option provides an override for these situations.
577 ca_keys= [KEYS] This parameter identifies a specific key(s) on
578 the system trusted keyring to be used for certificate
580 format: { id:<keyid> | builtin }
582 cca= [MIPS] Override the kernel pages' cache coherency
583 algorithm. Accepted values range from 0 to 7
584 inclusive. See arch/mips/include/asm/pgtable-bits.h
585 for platform specific values (SB1, Loongson3 and
588 ccw_timeout_log [S390]
589 See Documentation/s390/CommonIO for details.
591 cgroup_disable= [KNL] Disable a particular controller
592 Format: {name of the controller(s) to disable}
593 The effects of cgroup_disable=foo are:
594 - foo isn't auto-mounted if you mount all cgroups in
596 - foo isn't visible as an individually mountable
598 {Currently only "memory" controller deal with this and
599 cut the overhead, others just disable the usage. So
600 only cgroup_disable=memory is actually worthy}
602 checkreqprot [SELINUX] Set initial checkreqprot flag value.
603 Format: { "0" | "1" }
604 See security/selinux/Kconfig help text.
605 0 -- check protection applied by kernel (includes
606 any implied execute protection).
607 1 -- check protection requested by application.
608 Default value is set via a kernel config option.
609 Value can be changed at runtime via
610 /selinux/checkreqprot.
613 See Documentation/s390/CommonIO for details.
616 Prevents the clock framework from automatically gating
617 clocks that have not been explicitly enabled by a Linux
618 device driver but are enabled in hardware at reset or
619 by the bootloader/firmware. Note that this does not
620 force such clocks to be always-on nor does it reserve
621 those clocks in any way. This parameter is useful for
622 debug and development, but should not be needed on a
623 platform with proper driver support. For more
624 information, see Documentation/clk.txt.
626 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
628 Forces specified clocksource (if available) to be used
629 when calculating gettimeofday(). If specified
630 clocksource is not available, it defaults to PIT.
631 Format: { pit | tsc | cyclone | pmtmr }
633 clocksource= Override the default clocksource
635 Override the default clocksource and use the clocksource
636 with the name specified.
637 Some clocksource names to choose from, depending on
639 [all] jiffies (this is the base, fallback clocksource)
641 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
642 pxa_timer,timer3,32k_counter,timer0_1
644 [X86-32] pit,hpet,tsc;
645 scx200_hrt on Geode; cyclone on IBM x440
653 clearcpuid=BITNUM [X86]
654 Disable CPUID feature X for the kernel. See
655 arch/x86/include/asm/cpufeatures.h for the valid bit
656 numbers. Note the Linux specific bits are not necessarily
657 stable over kernel options, but the vendor specific
659 Also note that user programs calling CPUID directly
660 or using the feature without checking anything
661 will still see it. This just prevents it from
662 being used by the kernel or shown in /proc/cpuinfo.
663 Also note the kernel might malfunction if you disable
666 cma=nn[MG]@[start[MG][-end[MG]]]
668 Sets the size of kernel global memory area for
669 contiguous memory allocations and optionally the
670 placement constraint by the physical address range of
671 memory allocations. A value of 0 disables CMA
672 altogether. For more information, see
673 include/linux/dma-contiguous.h
675 cmo_free_hint= [PPC] Format: { yes | no }
676 Specify whether pages are marked as being inactive
677 when they are freed. This is used in CMO environments
678 to determine OS memory pressure for page stealing by
682 coherent_pool=nn[KMG] [ARM,KNL]
683 Sets the size of memory pool for coherent, atomic dma
684 allocations, by default set to 256K.
686 code_bytes [X86] How many bytes of object code to print
691 com20020= [HW,NET] ARCnet - COM20020 chipset
693 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
695 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
699 ARCnet - COM90xx chipset (memory-mapped buffers)
700 Format: <io>[,<irq>[,<memstart>]]
702 condev= [HW,S390] console device
705 console= [KNL] Output console device and options.
707 tty<n> Use the virtual console device <n>.
711 Use the specified serial port. The options are of
712 the form "bbbbpnf", where "bbbb" is the baud rate,
713 "p" is parity ("n", "o", or "e"), "n" is number of
714 bits, and "f" is flow control ("r" for RTS or
715 omit it). Default is "9600n8".
717 See Documentation/serial-console.txt for more
719 Documentation/networking/netconsole.txt for an
722 uart[8250],io,<addr>[,options]
723 uart[8250],mmio,<addr>[,options]
724 uart[8250],mmio32,<addr>[,options]
725 uart[8250],0x<addr>[,options]
726 Start an early, polled-mode console on the 8250/16550
727 UART at the specified I/O port or MMIO address,
728 switching to the matching ttyS device later.
729 MMIO inter-register address stride is either 8-bit
730 (mmio) or 32-bit (mmio32).
731 If none of [io|mmio|mmio32], <addr> is assumed to be
732 equivalent to 'mmio'. 'options' are specified in the
733 same format described for ttyS above; if unspecified,
734 the h/w is not re-initialized.
736 hvc<n> Use the hypervisor console device <n>. This is for
737 both Xen and PowerPC hypervisors.
739 If the device connected to the port is not a TTY but a braille
740 device, prepend "brl," before the device type, for instance
742 For now, only VisioBraille is supported.
744 consoleblank= [KNL] The console blank (screen saver) timeout in
745 seconds. Defaults to 10*60 = 10mins. A value of 0
746 disables the blank timer.
749 [KNL] Change the default value for
750 /proc/<pid>/coredump_filter.
751 See also Documentation/filesystems/proc.txt.
753 cpuidle.off=1 [CPU_IDLE]
754 disable the cpuidle sub-system
757 [X86] Delay for N microsec between assert and de-assert
758 of APIC INIT to start processors. This delay occurs
759 on every CPU online, such as boot, and resume from suspend.
762 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
764 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
766 crashkernel=size[KMG][@offset[KMG]]
767 [KNL] Using kexec, Linux can switch to a 'crash kernel'
768 upon panic. This parameter reserves the physical
769 memory region [offset, offset + size] for that kernel
770 image. If '@offset' is omitted, then a suitable offset
771 is selected automatically. Check
772 Documentation/kdump/kdump.txt for further details.
774 crashkernel=range1:size1[,range2:size2,...][@offset]
775 [KNL] Same as above, but depends on the memory
776 in the running system. The syntax of range is
777 start-[end] where start and end are both
778 a memory unit (amount[KMG]). See also
779 Documentation/kdump/kdump.txt for an example.
781 crashkernel=size[KMG],high
782 [KNL, x86_64] range could be above 4G. Allow kernel
783 to allocate physical memory region from top, so could
784 be above 4G if system have more than 4G ram installed.
785 Otherwise memory region will be allocated below 4G, if
787 It will be ignored if crashkernel=X is specified.
788 crashkernel=size[KMG],low
789 [KNL, x86_64] range under 4G. When crashkernel=X,high
790 is passed, kernel could allocate physical memory region
791 above 4G, that cause second kernel crash on system
792 that require some amount of low memory, e.g. swiotlb
793 requires at least 64M+32K low memory, also enough extra
794 low memory is needed to make sure DMA buffers for 32-bit
795 devices won't run out. Kernel would try to allocate at
796 at least 256M below 4G automatically.
797 This one let user to specify own low range under 4G
798 for second kernel instead.
799 0: to disable low allocation.
800 It will be ignored when crashkernel=X,high is not used
801 or memory reserved is below 4G.
806 cs89x0_media= [HW,NET]
807 Format: { rj45 | aui | bnc }
810 See header of drivers/s390/block/dasd_devmap.c.
812 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
813 (one device per port)
814 Format: <port#>,<type>
815 See also Documentation/input/joystick-parport.txt
817 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
818 time. See Documentation/dynamic-debug-howto.txt for
819 details. Deprecated, see dyndbg.
821 debug [KNL] Enable kernel debugging (events log level).
824 [KNL] verbose self-tests
826 Print debugging info while doing the locking API
828 We default to 0 (no extra messages), setting it to
829 1 will print _a lot_ more information - normally
830 only useful to kernel developers.
832 debug_objects [KNL] Enable object debugging
835 [KNL] Disable object debugging
837 debug_guardpage_minorder=
838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
839 parameter allows control of the order of pages that will
840 be intentionally kept free (and hence protected) by the
841 buddy allocator. Bigger value increase the probability
842 of catching random memory corruption, but reduce the
843 amount of memory for normal system use. The maximum
844 possible value is MAX_ORDER/2. Setting this parameter
845 to 1 or 2 should be enough to identify most random
846 memory corruption problems caused by bugs in kernel or
847 driver code when a CPU writes to (or reads from) a
848 random memory location. Note that there exists a class
849 of memory corruptions problems caused by buggy H/W or
850 F/W or by drivers badly programing DMA (basically when
851 memory is written at bus level and the CPU MMU is
852 bypassed) which are not detectable by
853 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
854 tracking down these problems.
857 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
858 parameter enables the feature at boot time. In
859 default, it is disabled. We can avoid allocating huge
860 chunk of memory for debug pagealloc if we don't enable
861 it at boot time and the system will work mostly same
862 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
863 on: enable the feature
865 debugpat [X86] Enable PAT debugging
867 decnet.addr= [HW,NET]
868 Format: <area>[,<node>]
869 See also Documentation/networking/decnet.txt.
872 [same as hugepagesz=] The size of the default
873 HugeTLB page size. This is the size represented by
874 the legacy /proc/ hugepages APIs, used for SHM, and
875 default size when mounting hugetlbfs filesystems.
876 Defaults to the default architecture's huge page size
880 Set number of hash buckets for dentry cache.
883 See Documentation/networking/ipv6.txt.
885 disable_cpu_apicid= [X86,APIC,SMP]
887 The number of initial APIC ID for the
888 corresponding CPU to be disabled at boot,
889 mostly used for the kdump 2nd kernel to
890 disable BSP to wake up multiple CPUs without
891 causing system reset or hang due to sending
894 disable_ddw [PPC/PSERIES]
895 Disable Dynamic DMA Window support. Use this if
896 to workaround buggy firmware.
899 See Documentation/networking/ipv6.txt.
901 disable_mtrr_cleanup [X86]
902 The kernel tries to adjust MTRR layout from continuous
903 to discrete, to make X server driver able to add WB
904 entry later. This parameter disables that.
906 disable_mtrr_trim [X86, Intel and AMD only]
907 By default the kernel will trim any uncacheable
908 memory out of your available memory pool based on
909 MTRR settings. This parameter disables that behavior,
910 possibly causing your machine to run very slowly.
912 disable_timer_pin_1 [X86]
913 Disable PIN 1 of APIC timer
914 Can be useful to work around chipset bugs.
916 dis_ucode_ldr [X86] Disable the microcode loader.
918 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
919 this option disables the debugging code at boot.
921 dma_debug_entries=<number>
922 This option allows to tune the number of preallocated
923 entries for DMA-API debugging code. One entry is
924 required per DMA-API allocation. Use this if the
925 DMA-API debugging code disables itself because the
926 architectural default is too low.
928 dma_debug_driver=<driver_name>
929 With this option the DMA-API debugging driver
930 filter feature can be enabled at boot time. Just
931 pass the driver to filter for as the parameter.
932 The filter can be disabled or changed to another
933 driver later using sysfs.
935 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
936 Broken monitors, graphic adapters, KVMs and EDIDless
937 panels may send no or incorrect EDID data sets.
938 This parameter allows to specify an EDID data sets
939 in the /lib/firmware directory that are used instead.
940 Generic built-in EDID data sets are used, if one of
941 edid/1024x768.bin, edid/1280x1024.bin,
942 edid/1680x1050.bin, or edid/1920x1080.bin is given
943 and no file with the same name exists. Details and
944 instructions how to build your own EDID data are
945 available in Documentation/EDID/HOWTO.txt. An EDID
946 data set will only be used for a particular connector,
947 if its name and a colon are prepended to the EDID
948 name. Each connector may use a unique EDID data
949 set by separating the files with a comma. An EDID
950 data set with no connector name will be used for
951 any connectors not explicitly specified.
955 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
956 module.dyndbg[="val"]
957 Enable debug messages at boot time. See
958 Documentation/dynamic-debug-howto.txt for details.
960 nompx [X86] Disables Intel Memory Protection Extensions.
961 See Documentation/x86/intel_mpx.txt for more
962 information about the feature.
965 module.async_probe [KNL]
966 Enable asynchronous probe on this module.
968 early_ioremap_debug [KNL]
969 Enable debug messages in early_ioremap support. This
970 is useful for tracking down temporary early mappings
971 which are not unmapped.
973 earlycon= [KNL] Output early console device and options.
975 When used with no options, the early console is
976 determined by the stdout-path property in device
980 Start an early, polled-mode console on a cadence serial
981 port at the specified address. The cadence serial port
982 must already be setup and configured. Options are not
985 uart[8250],io,<addr>[,options]
986 uart[8250],mmio,<addr>[,options]
987 uart[8250],mmio32,<addr>[,options]
988 uart[8250],mmio32be,<addr>[,options]
989 uart[8250],0x<addr>[,options]
990 Start an early, polled-mode console on the 8250/16550
991 UART at the specified I/O port or MMIO address.
992 MMIO inter-register address stride is either 8-bit
993 (mmio) or 32-bit (mmio32 or mmio32be).
994 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
995 to be equivalent to 'mmio'. 'options' are specified
996 in the same format described for "console=ttyS<n>"; if
997 unspecified, the h/w is not initialized.
1000 Start an early, polled-mode console on a pl011 serial
1001 port at the specified address. The pl011 serial port
1002 must already be setup and configured. Options are not
1006 Start an early, polled-mode console on an msm serial
1007 port at the specified address. The serial port
1008 must already be setup and configured. Options are not
1011 msm_serial_dm,<addr>
1012 Start an early, polled-mode console on an msm serial
1013 dm port at the specified address. The serial port
1014 must already be setup and configured. Options are not
1017 smh Use ARM semihosting calls for early console.
1025 Use early console provided by serial driver available
1026 on Samsung SoCs, requires selecting proper type and
1027 a correct base address of the selected UART port. The
1028 serial port must already be setup and configured.
1029 Options are not yet supported.
1033 Use early console provided by Freescale LP UART driver
1034 found on Freescale Vybrid and QorIQ LS1021A processors.
1035 A valid base address must be provided, and the serial
1036 port must already be setup and configured.
1038 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1042 earlyprintk=serial[,ttySn[,baudrate]]
1043 earlyprintk=serial[,0x...[,baudrate]]
1044 earlyprintk=ttySn[,baudrate]
1045 earlyprintk=dbgp[debugController#]
1046 earlyprintk=pciserial,bus:device.function[,baudrate]
1048 earlyprintk is useful when the kernel crashes before
1049 the normal console is initialized. It is not enabled by
1050 default because it has some cosmetic problems.
1052 Append ",keep" to not disable it when the real console
1055 Only one of vga, efi, serial, or usb debug port can
1058 Currently only ttyS0 and ttyS1 may be specified by
1059 name. Other I/O ports may be explicitly specified
1060 on some architectures (x86 and arm at least) by
1061 replacing ttySn with an I/O port address, like this:
1062 earlyprintk=serial,0x1008,115200
1063 You can find the port for a given device in
1064 /proc/tty/driver/serial:
1065 2: uart:ST16650V2 port:00001008 irq:18 ...
1067 Interaction with the standard serial driver is not
1070 The VGA and EFI output is eventually overwritten by
1073 The xen output can only be used by Xen PV guests.
1075 edac_report= [HW,EDAC] Control how to report EDAC event
1076 Format: {"on" | "off" | "force"}
1077 on: enable EDAC to report H/W event. May be overridden
1078 by other higher priority error reporting module.
1079 off: disable H/W event reporting through EDAC.
1080 force: enforce the use of EDAC to report H/W event.
1083 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1086 This is designed to be used in conjunction with
1087 the boot argument: earlyprintk=vga
1090 Format: {"off" | "on" | "skip[mbr]"}
1093 Format: { "old_map", "nochunk", "noruntime", "debug" }
1094 old_map [X86-64]: switch to the old ioremap-based EFI
1095 runtime services mapping. 32-bit still uses this one by
1097 nochunk: disable reading files in "chunks" in the EFI
1098 boot stub, as chunking can cause problems with some
1099 firmware implementations.
1100 noruntime : disable EFI runtime services support
1101 debug: enable misc debug output
1103 efi_no_storage_paranoia [EFI; X86]
1104 Using this parameter you can use more than 50% of
1105 your efi variable storage. Use this parameter only if
1106 you are really sure that your UEFI does sane gc and
1107 fulfills the spec otherwise your board may brick.
1109 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1110 Add arbitrary attribute to specific memory range by
1111 updating original EFI memory map.
1112 Region of memory which aa attribute is added to is
1114 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1115 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1116 attribute is added to range 0x100000000-0x180000000 and
1117 0x10a0000000-0x1120000000.
1119 Using this parameter you can do debugging of EFI memmap
1120 related feature. For example, you can do debugging of
1121 Address Range Mirroring feature even if your box
1124 eisa_irq_edge= [PARISC,HW]
1125 See header of drivers/parisc/eisa.c.
1128 See comment before function elanfreq_setup() in
1129 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1132 Format: {"cfq" | "deadline" | "noop"}
1133 See Documentation/block/cfq-iosched.txt and
1134 Documentation/block/deadline-iosched.txt for details.
1136 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1137 Specifies physical address of start of kernel core
1138 image elf header and optionally the size. Generally
1139 kexec loader will pass this option to capture kernel.
1140 See Documentation/kdump/kdump.txt for details.
1142 enable_mtrr_cleanup [X86]
1143 The kernel tries to adjust MTRR layout from continuous
1144 to discrete, to make X server driver able to add WB
1145 entry later. This parameter enables that.
1147 enable_timer_pin_1 [X86]
1148 Enable PIN 1 of APIC timer
1149 Can be useful to work around chipset bugs
1150 (in particular on some ATI chipsets).
1151 The kernel tries to set a reasonable default.
1153 enforcing [SELINUX] Set initial enforcing status.
1155 See security/selinux/Kconfig help text.
1156 0 -- permissive (log only, no denials).
1157 1 -- enforcing (deny and log).
1159 Value can be changed at runtime via /selinux/enforce.
1162 Disable Error Record Serialization Table (ERST)
1165 ether= [HW,NET] Ethernet cards parameters
1166 This option is obsoleted by the "netdev=" option, which
1167 has equivalent usage. See its documentation for details.
1171 Permit 'security.evm' to be updated regardless of
1172 current integrity status.
1176 fail_make_request=[KNL]
1177 General fault injection mechanism.
1178 Format: <interval>,<probability>,<space>,<times>
1179 See also Documentation/fault-injection/.
1182 See Documentation/blockdev/floppy.txt.
1184 force_pal_cache_flush
1185 [IA-64] Avoid check_sal_cache_flush which may hang on
1186 buggy SAL_CACHE_FLUSH implementations. Using this
1187 parameter will force ia64_sal_cache_flush to call
1188 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1191 Forcefully enable Physical Address Extension (PAE).
1192 Many Pentium M systems disable PAE but may have a
1193 functionally usable PAE implementation.
1194 Warning: use of this parameter will taint the kernel
1195 and may cause unknown problems.
1198 [FTRACE] will set and start the specified tracer
1199 as early as possible in order to facilitate early
1202 ftrace_dump_on_oops[=orig_cpu]
1203 [FTRACE] will dump the trace buffers on oops.
1204 If no parameter is passed, ftrace will dump
1205 buffers of all CPUs, but if you pass orig_cpu, it will
1206 dump only the buffer of the CPU that triggered the
1209 ftrace_filter=[function-list]
1210 [FTRACE] Limit the functions traced by the function
1211 tracer at boot up. function-list is a comma separated
1212 list of functions. This list can be changed at run
1213 time by the set_ftrace_filter file in the debugfs
1216 ftrace_notrace=[function-list]
1217 [FTRACE] Do not trace the functions specified in
1218 function-list. This list can be changed at run time
1219 by the set_ftrace_notrace file in the debugfs
1222 ftrace_graph_filter=[function-list]
1223 [FTRACE] Limit the top level callers functions traced
1224 by the function graph tracer at boot up.
1225 function-list is a comma separated list of functions
1226 that can be changed at run time by the
1227 set_graph_function file in the debugfs tracing directory.
1229 ftrace_graph_notrace=[function-list]
1230 [FTRACE] Do not trace from the functions specified in
1231 function-list. This list is a comma separated list of
1232 functions that can be changed at run time by the
1233 set_graph_notrace file in the debugfs tracing directory.
1236 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1237 support via parallel port (up to 5 devices per port)
1238 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1239 See also Documentation/input/joystick-parport.txt
1243 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1247 gcov_persist= [GCOV] When non-zero (default), profiling data for
1248 kernel modules is saved and remains accessible via
1249 debugfs, even when the module is unloaded/reloaded.
1250 When zero, profiling data is discarded and associated
1251 debugfs files are removed at module unload time.
1253 goldfish [X86] Enable the goldfish android emulator platform.
1254 Don't use this when you are not running on the
1257 gpt [EFI] Forces disk with valid GPT signature but
1258 invalid Protective MBR to be treated as GPT. If the
1259 primary GPT is corrupted, it enables the backup/alternate
1260 GPT to be used instead.
1262 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1263 the "Enable 0" bit of the configuration register.
1266 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1267 the "Enable 0" bit of the configuration register.
1270 grcan.select= [HW] Select which physical interface to use.
1273 grcan.txsize= [HW] Sets the size of the tx buffer.
1274 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1276 grcan.rxsize= [HW] Sets the size of the rx buffer.
1277 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1280 hardlockup_all_cpu_backtrace=
1281 [KNL] Should the hard-lockup detector generate
1282 backtraces on all cpus.
1285 hashdist= [KNL,NUMA] Large hashes allocated during boot
1286 are distributed across NUMA nodes. Defaults on
1287 for 64-bit NUMA, off otherwise.
1288 Format: 0 | 1 (for off | on)
1290 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1292 hd= [EIDE] (E)IDE hard drive subsystem geometry
1293 Format: <cyl>,<head>,<sect>
1296 Disable Hardware Error Source Table (HEST) support;
1297 corresponding firmware-first mode error processing
1298 logic will be disabled.
1300 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1301 size of <nn>. This works even on boxes that have no
1302 highmem otherwise. This also works to reduce highmem
1303 size on bigger boxes.
1305 highres= [KNL] Enable/disable high resolution timer mode.
1306 Valid parameters: "on", "off"
1310 See Documentation/isdn/README.HiSax.
1314 hpet= [X86-32,HPET] option to control HPET usage
1315 Format: { enable (default) | disable | force |
1317 disable: disable HPET and use PIT instead
1318 force: allow force enabled of undocumented chips (ICH4,
1320 verbose: show contents of HPET registers during setup
1322 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1323 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1325 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1326 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1327 On x86-64 and powerpc, this option can be specified
1328 multiple times interleaved with hugepages= to reserve
1329 huge pages of different sizes. Valid pages sizes on
1330 x86-64 are 2M (when the CPU supports "pse") and 1G
1331 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1333 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1334 terminal devices. Valid values: 0..8
1335 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1336 If specified, z/VM IUCV HVC accepts connections
1337 from listed z/VM user IDs only.
1339 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1340 hardware thread id mappings.
1341 Format: <cpu>:<hwthread>
1344 Do not unregister boot console at start. This is only
1345 useful for debugging when something happens in the window
1346 between unregistering the boot console and initializing
1349 i2c_bus= [HW] Override the default board specific I2C bus speed
1350 or register an additional I2C bus that is not
1351 registered from board initialization code.
1355 i8042.debug [HW] Toggle i8042 debug mode
1356 i8042.unmask_kbd_data
1357 [HW] Enable printing of interrupt data from the KBD port
1358 (disabled by default, and as a pre-condition
1359 requires that i8042.debug=1 be enabled)
1360 i8042.direct [HW] Put keyboard port into non-translated mode
1361 i8042.dumbkbd [HW] Pretend that controller can only read data from
1362 keyboard and cannot control its state
1363 (Don't attempt to blink the leds)
1364 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1365 i8042.nokbd [HW] Don't check/create keyboard port
1366 i8042.noloop [HW] Disable the AUX Loopback command while probing
1368 i8042.nomux [HW] Don't check presence of an active multiplexing
1370 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1372 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1373 i8042.reset [HW] Reset the controller during init, cleanup and
1374 suspend-to-ram transitions, only during s2r
1375 transitions, or never reset
1376 Format: { 1 | Y | y | 0 | N | n }
1377 1, Y, y: always reset controller
1378 0, N, n: don't ever reset controller
1379 Default: only on s2r transitions on x86; most other
1380 architectures force reset to be always executed
1381 i8042.unlock [HW] Unlock (ignore) the keylock
1382 i8042.kbdreset [HW] Reset device connected to KBD port
1386 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1387 indicates that the driver is running on unsupported
1389 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1390 does not match list of supported models.
1392 [HW] Report power status in /proc/i8k
1393 (disabled by default)
1394 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1397 i915.invert_brightness=
1398 [DRM] Invert the sense of the variable that is used to
1399 set the brightness of the panel backlight. Normally a
1400 brightness value of 0 indicates backlight switched off,
1401 and the maximum of the brightness value sets the backlight
1402 to maximum brightness. If this parameter is set to 0
1403 (default) and the machine requires it, or this parameter
1404 is set to 1, a brightness value of 0 sets the backlight
1405 to maximum brightness, and the maximum of the brightness
1406 value switches the backlight off.
1407 -1 -- never invert brightness
1408 0 -- machine default
1409 1 -- force brightness inversion
1412 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1414 ide-core.nodma= [HW] (E)IDE subsystem
1415 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1416 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1417 .cdrom .chs .ignore_cable are additional options
1418 See Documentation/ide/ide.txt.
1420 ide-generic.probe-mask= [HW] (E)IDE subsystem
1422 Probe mask for legacy ISA IDE ports. Depending on
1423 platform up to 6 ports are supported, enabled by
1424 setting corresponding bits in the mask to 1. The
1425 default value is 0x0, which has a special meaning.
1426 On systems that have PCI, it triggers scanning the
1427 PCI bus for the first and the second port, which
1428 are then probed. On systems without PCI the value
1429 of 0x0 enables probing the two first ports as if it
1432 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1433 Claim all unknown PCI IDE storage controllers.
1436 Format: idle=poll, idle=halt, idle=nomwait
1437 Poll forces a polling idle loop that can slightly
1438 improve the performance of waking up a idle CPU, but
1439 will use a lot of power and make the system run hot.
1441 idle=halt: Halt is forced to be used for CPU idle.
1442 In such case C2/C3 won't be used again.
1443 idle=nomwait: Disable mwait for CPU C-states
1445 ignore_loglevel [KNL]
1446 Ignore loglevel setting - this will print /all/
1447 kernel messages to the console. Useful for debugging.
1448 We also add it as printk module parameter, so users
1449 could change it dynamically, usually by
1450 /sys/module/printk/parameters/ignore_loglevel.
1452 ihash_entries= [KNL]
1453 Set number of hash buckets for inode cache.
1455 ima_appraise= [IMA] appraise integrity measurements
1456 Format: { "off" | "enforce" | "fix" | "log" }
1459 ima_appraise_tcb [IMA]
1460 The builtin appraise policy appraises all files
1464 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1468 The list of supported hash algorithms is defined
1469 in crypto/hash_info.h.
1472 The builtin measurement policy to load during IMA
1473 setup. Specyfing "tcb" as the value, measures all
1474 programs exec'd, files mmap'd for exec, and all files
1475 opened with the read mode bit set by either the
1476 effective uid (euid=0) or uid=0.
1479 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1480 Load a policy which meets the needs of the Trusted
1481 Computing Base. This means IMA will measure all
1482 programs exec'd, files mmap'd for exec, and all files
1483 opened for read by uid=0.
1486 Select one of defined IMA measurements template formats.
1487 Formats: { "ima" | "ima-ng" | "ima-sig" }
1491 [IMA] Define a custom template format.
1492 Format: { "field1|...|fieldN" }
1494 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1495 Format: <min_file_size>
1496 Set the minimal file size for using asynchronous hash.
1497 If left unspecified, ahash usage is disabled.
1499 ahash performance varies for different data sizes on
1500 different crypto accelerators. This option can be used
1501 to achieve the best performance for a particular HW.
1503 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1505 Set hashing buffer size. Default: 4k.
1507 ahash performance varies for different chunk sizes on
1508 different crypto accelerators. This option can be used
1509 to achieve best performance for particular HW.
1513 Run specified binary instead of /sbin/init as init
1516 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1517 for working out where the kernel is dying during
1520 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1521 initcall functions. Useful for debugging built-in
1522 modules and initcalls.
1524 initrd= [BOOT] Specify the location of the initial ramdisk
1526 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1529 int_pln_enable [x86] Enable power limit notification interrupt
1531 integrity_audit=[IMA]
1532 Format: { "0" | "1" }
1533 0 -- basic integrity auditing messages. (Default)
1534 1 -- additional integrity auditing messages.
1536 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1538 Enable intel iommu driver.
1540 Disable intel iommu driver.
1541 igfx_off [Default Off]
1542 By default, gfx is mapped as normal device. If a gfx
1543 device has a dedicated DMAR unit, the DMAR unit is
1544 bypassed by not enabling DMAR with this option. In
1545 this case, gfx device will use physical address for
1548 With this option iommu will not optimize to look
1549 for io virtual address below 32-bit forcing dual
1550 address cycle on pci bus for cards supporting greater
1551 than 32-bit addressing. The default is to look
1552 for translation below 32-bit and if not available
1553 then look in the higher range.
1554 strict [Default Off]
1555 With this option on every unmap_single operation will
1556 result in a hardware IOTLB flush operation as opposed
1557 to batching them for performance.
1558 sp_off [Default Off]
1559 By default, super page will be supported if Intel IOMMU
1560 has the capability. With this option, super page will
1562 ecs_off [Default Off]
1563 By default, extended context tables will be supported if
1564 the hardware advertises that it has support both for the
1565 extended tables themselves, and also PASID support. With
1566 this option set, extended tables will not be used even
1567 on hardware which claims to support them.
1569 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1570 0 disables intel_idle and fall back on acpi_idle.
1571 1 to 6 specify maximum depth of C-state.
1575 Do not enable intel_pstate as the default
1576 scaling driver for the supported processors
1578 Enable intel_pstate on systems that prohibit it by default
1579 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1580 instead of acpi-cpufreq may disable platform features, such
1581 as thermal controls and power capping, that rely on ACPI
1582 P-States information being indicated to OSPM and therefore
1583 should be used with caution. This option does not work with
1584 processors that aren't supported by the intel_pstate driver
1585 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1587 Do not enable hardware P state control (HWP)
1590 Only load intel_pstate on systems which support
1591 hardware P state control (HWP) if available.
1593 intremap= [X86-64, Intel-IOMMU]
1594 on enable Interrupt Remapping (default)
1595 off disable Interrupt Remapping
1596 nosid disable Source ID checking
1598 BIOS x2APIC opt-out request will be ignored
1599 nopost disable Interrupt Posting
1601 iomem= Disable strict checking of access to MMIO memory
1602 strict regions from userspace.
1617 nobypass [PPC/POWERNV]
1618 Disable IOMMU bypass, using IOMMU for PCI devices.
1621 io7= [HW] IO7 for Marvel based alpha systems
1622 See comment before marvel_specify_io7 in
1623 arch/alpha/kernel/core_marvel.c.
1625 io_delay= [X86] I/O delay method
1627 Standard port 0x80 based delay
1629 Alternate port 0xed based delay (needed on some systems)
1631 Simple two microseconds delay
1636 See Documentation/filesystems/nfs/nfsroot.txt.
1639 When an interrupt is not handled search all handlers
1640 for it. Intended to get systems with badly broken
1644 When an interrupt is not handled search all handlers
1645 for it. Also check all handlers each timer
1646 interrupt. Intended to get systems with badly broken
1650 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1652 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1654 <cpu number>,...,<cpu number>
1656 <cpu number>-<cpu number>
1657 (must be a positive range in ascending order)
1659 <cpu number>,...,<cpu number>-<cpu number>
1661 This option can be used to specify one or more CPUs
1662 to isolate from the general SMP balancing and scheduling
1663 algorithms. You can move a process onto or off an
1664 "isolated" CPU via the CPU affinity syscalls or cpuset.
1665 <cpu number> begins at 0 and the maximum value is
1666 "number of CPUs in system - 1".
1668 This option is the preferred way to isolate CPUs. The
1669 alternative -- manually setting the CPU mask of all
1670 tasks in the system -- can cause problems and
1671 suboptimal load balancer performance.
1675 ivrs_ioapic [HW,X86_64]
1676 Provide an override to the IOAPIC-ID<->DEVICE-ID
1677 mapping provided in the IVRS ACPI table. For
1678 example, to map IOAPIC-ID decimal 10 to
1679 PCI device 00:14.0 write the parameter as:
1680 ivrs_ioapic[10]=00:14.0
1682 ivrs_hpet [HW,X86_64]
1683 Provide an override to the HPET-ID<->DEVICE-ID
1684 mapping provided in the IVRS ACPI table. For
1685 example, to map HPET-ID decimal 0 to
1686 PCI device 00:14.0 write the parameter as:
1687 ivrs_hpet[0]=00:14.0
1689 js= [HW,JOY] Analog joystick
1690 See Documentation/input/joystick.txt.
1693 Enable/disable kernel and module base offset ASLR
1694 (Address Space Layout Randomization) if built into
1695 the kernel. When CONFIG_HIBERNATION is selected,
1696 kASLR is disabled by default. When kASLR is enabled,
1697 hibernation will be disabled.
1701 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1702 specifies the amount of memory usable by the kernel
1703 for non-movable allocations. The requested amount is
1704 spread evenly throughout all nodes in the system. The
1705 remaining memory in each node is used for Movable
1706 pages. In the event, a node is too small to have both
1707 kernelcore and Movable pages, kernelcore pages will
1708 take priority and other nodes will have a larger number
1709 of Movable pages. The Movable zone is used for the
1710 allocation of pages that may be reclaimed or moved
1711 by the page migration subsystem. This means that
1712 HugeTLB pages may not be allocated from this zone.
1713 Note that allocations like PTEs-from-HighMem still
1714 use the HighMem zone if it exists, and the Normal
1715 zone if it does not.
1717 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1718 Format: <Controller#>[,poll interval]
1719 The controller # is the number of the ehci usb debug
1720 port as it is probed via PCI. The poll interval is
1721 optional and is the number seconds in between
1722 each poll cycle to the debug port in case you need
1723 the functionality for interrupting the kernel with
1724 gdb or control-c on the dbgp connection. When
1725 not using this parameter you use sysrq-g to break into
1726 the kernel debugger.
1728 kgdboc= [KGDB,HW] kgdb over consoles.
1729 Requires a tty driver that supports console polling,
1730 or a supported polling keyboard driver (non-usb).
1731 Serial only format: <serial_device>[,baud]
1732 keyboard only format: kbd
1733 keyboard and serial format: kbd,<serial_device>[,baud]
1734 Optional Kernel mode setting:
1735 kms, kbd format: kms,kbd
1736 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1738 kgdbwait [KGDB] Stop kernel execution and enter the
1739 kernel debugger at the earliest opportunity.
1741 kmac= [MIPS] korina ethernet MAC address.
1742 Configure the RouterBoard 532 series on-chip
1743 Ethernet adapter MAC address.
1745 kmemleak= [KNL] Boot-time kmemleak enable/disable
1746 Valid arguments: on, off
1748 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1751 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1752 Valid arguments: 0, 1, 2
1753 kmemcheck=0 (disabled)
1754 kmemcheck=1 (enabled)
1755 kmemcheck=2 (one-shot mode)
1756 Default: 2 (one-shot mode)
1758 kstack=N [X86] Print N words from the kernel stack
1761 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1762 Default is 0 (don't ignore, but inject #GP)
1764 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1768 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1769 Default is 1 (enabled)
1771 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1773 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1775 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1776 (virtualized MMU) support on capable Intel chips.
1777 Default is 1 (enabled)
1779 kvm-intel.emulate_invalid_guest_state=
1780 [KVM,Intel] Enable emulation of invalid guest states
1781 Default is 0 (disabled)
1783 kvm-intel.flexpriority=
1784 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1785 Default is 1 (enabled)
1788 [KVM,Intel] Enable VMX nesting (nVMX).
1789 Default is 0 (disabled)
1791 kvm-intel.unrestricted_guest=
1792 [KVM,Intel] Disable unrestricted guest feature
1793 (virtualized real and unpaged mode) on capable
1794 Intel chips. Default is 1 (enabled)
1796 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1797 feature (tagged TLBs) on capable Intel chips.
1798 Default is 1 (enabled)
1804 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1807 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1808 value for LAPIC timer one-shot implementation. Default
1809 back to the programmable timer unit in the LAPIC.
1811 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1814 libata.dma= [LIBATA] DMA control
1815 libata.dma=0 Disable all PATA and SATA DMA
1816 libata.dma=1 PATA and SATA Disk DMA only
1817 libata.dma=2 ATAPI (CDROM) DMA only
1818 libata.dma=4 Compact Flash DMA only
1819 Combinations also work, so libata.dma=3 enables DMA
1820 for disks and CDROMs, but not CFs.
1822 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1823 libata.ignore_hpa=0 keep BIOS limits (default)
1824 libata.ignore_hpa=1 ignore limits, using full disk
1826 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1830 libata.force= [LIBATA] Force configurations. The format is comma
1831 separated list of "[ID:]VAL" where ID is
1832 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1833 matching port, link or device. Basically, it matches
1834 the ATA ID string printed on console by libata. If
1835 the whole ID part is omitted, the last PORT and DEVICE
1836 values are used. If ID hasn't been specified yet, the
1837 configuration applies to all ports, links and devices.
1839 If only DEVICE is omitted, the parameter applies to
1840 the port and all links and devices behind it. DEVICE
1841 number of 0 either selects the first device or the
1842 first fan-out link behind PMP device. It does not
1843 select the host link. DEVICE number of 15 selects the
1844 host link and device attached to it.
1846 The VAL specifies the configuration to force. As long
1847 as there's no ambiguity shortcut notation is allowed.
1848 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1849 The following configurations can be forced.
1851 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1852 Any ID with matching PORT is used.
1854 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1856 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1857 udma[/][16,25,33,44,66,100,133] notation is also
1860 * [no]ncq: Turn on or off NCQ.
1862 * [no]ncqtrim: Turn off queued DSM TRIM.
1864 * nohrst, nosrst, norst: suppress hard, soft
1867 * rstonce: only attempt one reset during
1868 hot-unplug link recovery
1870 * dump_id: dump IDENTIFY data.
1872 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1874 * disable: Disable this device.
1876 If there are multiple matching configurations changing
1877 the same attribute, the last one is used.
1879 memblock=debug [KNL] Enable memblock debug messages.
1881 load_ramdisk= [RAM] List of ramdisks to load from floppy
1882 See Documentation/blockdev/ramdisk.txt.
1884 lockd.nlm_grace_period=P [NFS] Assign grace period.
1887 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1890 lockd.nlm_timeout=T [NFS] Assign timeout value.
1893 lockd.nlm_udpport=M [NFS] Assign UDP port.
1896 locktorture.nreaders_stress= [KNL]
1897 Set the number of locking read-acquisition kthreads.
1898 Defaults to being automatically set based on the
1899 number of online CPUs.
1901 locktorture.nwriters_stress= [KNL]
1902 Set the number of locking write-acquisition kthreads.
1904 locktorture.onoff_holdoff= [KNL]
1905 Set time (s) after boot for CPU-hotplug testing.
1907 locktorture.onoff_interval= [KNL]
1908 Set time (s) between CPU-hotplug operations, or
1909 zero to disable CPU-hotplug testing.
1911 locktorture.shuffle_interval= [KNL]
1912 Set task-shuffle interval (jiffies). Shuffling
1913 tasks allows some CPUs to go into dyntick-idle
1914 mode during the locktorture test.
1916 locktorture.shutdown_secs= [KNL]
1917 Set time (s) after boot system shutdown. This
1918 is useful for hands-off automated testing.
1920 locktorture.stat_interval= [KNL]
1921 Time (s) between statistics printk()s.
1923 locktorture.stutter= [KNL]
1924 Time (s) to stutter testing, for example,
1925 specifying five seconds causes the test to run for
1926 five seconds, wait for five seconds, and so on.
1927 This tests the locking primitive's ability to
1928 transition abruptly to and from idle.
1930 locktorture.torture_runnable= [BOOT]
1931 Start locktorture running at boot time.
1933 locktorture.torture_type= [KNL]
1934 Specify the locking implementation to test.
1936 locktorture.verbose= [KNL]
1937 Enable additional printk() statements.
1939 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1942 loglevel= All Kernel Messages with a loglevel smaller than the
1943 console loglevel will be printed to the console. It can
1944 also be changed with klogd or other programs. The
1945 loglevels are defined as follows:
1947 0 (KERN_EMERG) system is unusable
1948 1 (KERN_ALERT) action must be taken immediately
1949 2 (KERN_CRIT) critical conditions
1950 3 (KERN_ERR) error conditions
1951 4 (KERN_WARNING) warning conditions
1952 5 (KERN_NOTICE) normal but significant condition
1953 6 (KERN_INFO) informational
1954 7 (KERN_DEBUG) debug-level messages
1956 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1957 in bytes. n must be a power of two and greater
1958 than the minimal size. The minimal size is defined
1959 by LOG_BUF_SHIFT kernel config parameter. There is
1960 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1961 that allows to increase the default size depending on
1962 the number of CPUs. See init/Kconfig for more details.
1964 logo.nologo [FB] Disables display of the built-in Linux logo.
1965 This may be used to provide more screen space for
1966 kernel log messages and is useful when debugging
1967 kernel boot problems.
1969 lp=0 [LP] Specify parallel ports to use, e.g,
1970 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1971 lp=reset first parallel port). 'lp=0' disables the
1972 lp=auto printer driver. 'lp=reset' (which can be
1973 specified in addition to the ports) causes
1974 attached printers to be reset. Using
1975 lp=port1,port2,... specifies the parallel ports
1976 to associate lp devices with, starting with
1977 lp0. A port specification may be 'none' to skip
1978 that lp device, or a parport name such as
1979 'parport0'. Specifying 'lp=auto' instead of a
1980 port specification list means that device IDs
1981 from each port should be examined, to see if
1982 an IEEE 1284-compliant printer is attached; if
1983 so, the driver will manage that printer.
1984 See also header of drivers/char/lp.c.
1987 Sets loops_per_jiffy to given constant, thus avoiding
1988 time-consuming boot-time autodetection (up to 250 ms per
1989 CPU). 0 enables autodetection (default). To determine
1990 the correct value for your kernel, boot with normal
1991 autodetection and see what value is printed. Note that
1992 on SMP systems the preset will be applied to all CPUs,
1993 which is likely to cause problems if your CPUs need
1994 significantly divergent settings. An incorrect value
1995 will cause delays in the kernel to be wrong, leading to
1996 unpredictable I/O errors and other breakage. Although
1997 unlikely, in the extreme case this might damage your
2001 Format: <io>,<irq>,<dma>
2003 machvec= [IA-64] Force the use of a particular machine-vector
2004 (machvec) in a generic kernel.
2005 Example: machvec=hpzx1_swiotlb
2007 machtype= [Loongson] Share the same kernel image file between different
2009 Example: machtype=lemote-yeeloong-2f-7inch
2011 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2012 than or equal to this physical address is ignored.
2014 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2015 should make use of. maxcpus=n : n >= 0 limits the
2016 kernel to using 'n' processors. n=0 is a special case,
2017 it is equivalent to "nosmp", which also disables
2020 max_loop= [LOOP] The number of loop block devices that get
2021 (loop.max_loop) unconditionally pre-created at init time. The default
2022 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2023 of statically allocating a predefined number, loop
2024 devices can be requested on-demand with the
2025 /dev/loop-control interface.
2027 mce [X86-32] Machine Check Exception
2029 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2031 md= [HW] RAID subsystems devices and level
2032 See Documentation/md.txt.
2035 Format: <first>,<last>
2036 Specifies range of consoles to be captured by the MDA.
2039 Control mitigation for the Micro-architectural Data
2040 Sampling (MDS) vulnerability.
2042 Certain CPUs are vulnerable to an exploit against CPU
2043 internal buffers which can forward information to a
2044 disclosure gadget under certain conditions.
2046 In vulnerable processors, the speculatively
2047 forwarded data can be used in a cache side channel
2048 attack, to access data to which the attacker does
2049 not have direct access.
2051 This parameter controls the MDS mitigation. The
2054 full - Enable MDS mitigation on vulnerable CPUs
2055 off - Unconditionally disable MDS mitigation
2057 Not specifying this option is equivalent to
2060 For details see: Documentation/hw-vuln/mds.rst
2062 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2063 Amount of memory to be used when the kernel is not able
2064 to see the whole system memory or for test.
2065 [X86] Work as limiting max address. Use together
2066 with memmap= to avoid physical address space collisions.
2067 Without memmap= PCI devices could be placed at addresses
2068 belonging to unused RAM.
2070 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2074 [KNL,SH] Allow user to override the default size for
2075 per-device physically contiguous DMA buffers.
2077 memmap=exactmap [KNL,X86] Enable setting of an exact
2078 E820 memory map, as specified by the user.
2079 Such memmap=exactmap lines can be constructed based on
2080 BIOS output or other requirements. See the memmap=nn@ss
2083 memmap=nn[KMG]@ss[KMG]
2084 [KNL] Force usage of a specific region of memory.
2085 Region of memory to be used is from ss to ss+nn.
2087 memmap=nn[KMG]#ss[KMG]
2088 [KNL,ACPI] Mark specific memory as ACPI data.
2089 Region of memory to be marked is from ss to ss+nn.
2091 memmap=nn[KMG]$ss[KMG]
2092 [KNL,ACPI] Mark specific memory as reserved.
2093 Region of memory to be reserved is from ss to ss+nn.
2094 Example: Exclude memory from 0x18690000-0x1869ffff
2095 memmap=64K$0x18690000
2097 memmap=0x10000$0x18690000
2099 memmap=nn[KMG]!ss[KMG]
2100 [KNL,X86] Mark specific memory as protected.
2101 Region of memory to be used, from ss to ss+nn.
2102 The memory region may be marked as e820 type 12 (0xc)
2103 and is NVDIMM or ADR memory.
2105 memory_corruption_check=0/1 [X86]
2106 Some BIOSes seem to corrupt the first 64k of
2107 memory when doing things like suspend/resume.
2108 Setting this option will scan the memory
2109 looking for corruption. Enabling this will
2110 both detect corruption and prevent the kernel
2111 from using the memory being corrupted.
2112 However, its intended as a diagnostic tool; if
2113 repeatable BIOS-originated corruption always
2114 affects the same memory, you can use memmap=
2115 to prevent the kernel from using that memory.
2117 memory_corruption_check_size=size [X86]
2118 By default it checks for corruption in the low
2119 64k, making this memory unavailable for normal
2120 use. Use this parameter to scan for
2121 corruption in more or less memory.
2123 memory_corruption_check_period=seconds [X86]
2124 By default it checks for corruption every 60
2125 seconds. Use this parameter to check at some
2126 other rate. 0 disables periodic checking.
2128 memtest= [KNL,X86,ARM] Enable memtest
2130 default : 0 <disable>
2131 Specifies the number of memtest passes to be
2132 performed. Each pass selects another test
2133 pattern from a given set of patterns. Memtest
2134 fills the memory with this pattern, validates
2135 memory contents and reserves bad memory
2136 regions that are detected.
2138 meye.*= [HW] Set MotionEye Camera parameters
2139 See Documentation/video4linux/meye.txt.
2141 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2142 Multi-Function General Purpose Timers on AMD Geode
2145 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2146 the BIOS has incorrectly applied a workaround. TinyBIOS
2147 version 0.98 is known to be affected, 0.99 fixes the
2148 problem by letting the user disable the workaround.
2152 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2153 physical address is ignored.
2155 mini2440= [ARM,HW,KNL]
2156 Format:[0..2][b][c][t]
2158 MINI2440 configuration specification:
2159 0 - The attached screen is the 3.5" TFT
2160 1 - The attached screen is the 7" TFT
2161 2 - The VGA Shield is attached (1024x768)
2162 Leaving out the screen size parameter will not load
2163 the TFT driver, and the framebuffer will be left
2165 b - Enable backlight. The TFT backlight pin will be
2166 linked to the kernel VESA blanking code and a GPIO
2167 LED. This parameter is not necessary when using the
2169 c - Enable the s3c camera interface.
2170 t - Reserved for enabling touchscreen support. The
2171 touchscreen support is not enabled in the mainstream
2172 kernel as of 2.6.30, a preliminary port can be found
2173 in the "bleeding edge" mini2440 support kernel at
2174 http://repo.or.cz/w/linux-2.6/mini2440.git
2177 [X86] Control optional mitigations for CPU
2178 vulnerabilities. This is a set of curated,
2179 arch-independent options, each of which is an
2180 aggregation of existing arch-specific options.
2183 Disable all optional CPU mitigations. This
2184 improves system performance, but it may also
2185 expose users to several CPU vulnerabilities.
2186 Equivalent to: nopti [X86]
2188 spectre_v2_user=off [X86]
2189 spec_store_bypass_disable=off [X86]
2193 Mitigate all CPU vulnerabilities, but leave SMT
2194 enabled, even if it's vulnerable. This is for
2195 users who don't want to be surprised by SMT
2196 getting disabled across kernel upgrades, or who
2197 have other ways of avoiding SMT-based attacks.
2198 Equivalent to: (default behavior)
2201 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2202 parameter allows control of the logging verbosity for
2203 the additional memory initialisation checks. A value
2204 of 0 disables mminit logging and a level of 4 will
2205 log everything. Information is printed at KERN_DEBUG
2206 so loglevel=8 may also need to be specified.
2209 [KNL] When CONFIG_MODULE_SIG is set, this means that
2210 modules without (valid) signatures will fail to load.
2211 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2212 is always true, so this option does nothing.
2215 [MOUSE] Maximum time between finger touching and
2216 leaving touchpad surface for touch to be considered
2217 a tap and be reported as a left button click (for
2218 touchpads working in absolute mode only).
2220 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2221 reporting absolute coordinates, such as tablets
2222 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2223 reporting absolute coordinates, such as tablets
2225 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2226 is similar to kernelcore except it specifies the
2227 amount of memory used for migratable allocations.
2228 If both kernelcore and movablecore is specified,
2229 then kernelcore will be at *least* the specified
2230 value but may be more. If movablecore on its own
2231 is specified, the administrator must be careful
2232 that the amount of memory usable for all allocations
2235 movable_node [KNL,X86] Boot-time switch to enable the effects
2236 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2238 MTD_Partition= [MTD]
2239 Format: <name>,<region-number>,<size>,<offset>
2241 MTD_Region= [MTD] Format:
2242 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2245 See drivers/mtd/cmdlinepart.c.
2247 multitce=off [PPC] This parameter disables the use of the pSeries
2248 firmware feature for updating multiple TCE entries
2251 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2253 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2255 boundary - index of last SLC block on Flex-OneNAND.
2256 The remaining blocks are configured as MLC blocks.
2257 lock - Configure if Flex-OneNAND boundary should be locked.
2258 Once locked, the boundary cannot be changed.
2259 1 indicates lock status, 0 indicates unlock status.
2262 ARM/S3C2412 JIVE boot control
2264 See arch/arm/mach-s3c2412/mach-jive.c
2266 mtouchusb.raw_coordinates=
2267 [HW] Make the MicroTouch USB driver use raw coordinates
2268 ('y', default) or cooked coordinates ('n')
2270 mtrr_chunk_size=nn[KMG] [X86]
2271 used for mtrr cleanup. It is largest continuous chunk
2272 that could hold holes aka. UC entries.
2274 mtrr_gran_size=nn[KMG] [X86]
2275 Used for mtrr cleanup. It is granularity of mtrr block.
2277 Large value could prevent small alignment from
2280 mtrr_spare_reg_nr=n [X86]
2282 Range: 0,7 : spare reg number
2284 Used for mtrr cleanup. It is spare mtrr entries number.
2285 Set to 2 or more if your graphical card needs more.
2287 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2289 netdev= [NET] Network devices parameters
2290 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2291 Note that mem_start is often overloaded to mean
2292 something different and driver-specific.
2293 This usage is only documented in each driver source
2297 [NETFILTER] Enable connection tracking flow accounting
2298 0 to disable accounting
2299 1 to enable accounting
2302 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2303 See Documentation/filesystems/nfs/nfsroot.txt.
2305 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2306 See Documentation/filesystems/nfs/nfsroot.txt.
2308 nfsrootdebug [NFS] enable nfsroot debugging messages.
2309 See Documentation/filesystems/nfs/nfsroot.txt.
2311 nfs.callback_tcpport=
2312 [NFS] set the TCP port on which the NFSv4 callback
2313 channel should listen.
2316 [NFS] sets the pathname to the program which is used
2317 to update the NFS client cache entries.
2319 nfs.cache_getent_timeout=
2320 [NFS] sets the timeout after which an attempt to
2321 update a cache entry is deemed to have failed.
2323 nfs.idmap_cache_timeout=
2324 [NFS] set the maximum lifetime for idmapper cache
2328 [NFS] enable 64-bit inode numbers.
2329 If zero, the NFS client will fake up a 32-bit inode
2330 number for the readdir() and stat() syscalls instead
2331 of returning the full 64-bit number.
2332 The default is to return 64-bit inode numbers.
2334 nfs.max_session_slots=
2335 [NFSv4.1] Sets the maximum number of session slots
2336 the client will attempt to negotiate with the server.
2337 This limits the number of simultaneous RPC requests
2338 that the client can send to the NFSv4.1 server.
2339 Note that there is little point in setting this
2340 value higher than the max_tcp_slot_table_limit.
2342 nfs.nfs4_disable_idmapping=
2343 [NFSv4] When set to the default of '1', this option
2344 ensures that both the RPC level authentication
2345 scheme and the NFS level operations agree to use
2346 numeric uids/gids if the mount is using the
2347 'sec=sys' security flavour. In effect it is
2348 disabling idmapping, which can make migration from
2349 legacy NFSv2/v3 systems to NFSv4 easier.
2350 Servers that do not support this mode of operation
2351 will be autodetected by the client, and it will fall
2352 back to using the idmapper.
2353 To turn off this behaviour, set the value to '0'.
2355 [NFS4] Specify an additional fixed unique ident-
2356 ification string that NFSv4 clients can insert into
2357 their nfs_client_id4 string. This is typically a
2358 UUID that is generated at system install time.
2360 nfs.send_implementation_id =
2361 [NFSv4.1] Send client implementation identification
2362 information in exchange_id requests.
2363 If zero, no implementation identification information
2365 The default is to send the implementation identification
2368 nfs.recover_lost_locks =
2369 [NFSv4] Attempt to recover locks that were lost due
2370 to a lease timeout on the server. Please note that
2371 doing this risks data corruption, since there are
2372 no guarantees that the file will remain unchanged
2373 after the locks are lost.
2374 If you want to enable the kernel legacy behaviour of
2375 attempting to recover these locks, then set this
2377 The default parameter value of '0' causes the kernel
2378 not to attempt recovery of lost locks.
2380 nfs4.layoutstats_timer =
2381 [NFSv4.2] Change the rate at which the kernel sends
2382 layoutstats to the pNFS metadata server.
2384 Setting this to value to 0 causes the kernel to use
2385 whatever value is the default set by the layout
2386 driver. A non-zero value sets the minimum interval
2387 in seconds between layoutstats transmissions.
2389 nfsd.nfs4_disable_idmapping=
2390 [NFSv4] When set to the default of '1', the NFSv4
2391 server will return only numeric uids and gids to
2392 clients using auth_sys, and will accept numeric uids
2393 and gids from such clients. This is intended to ease
2394 migration from NFSv2/v3.
2396 objlayoutdriver.osd_login_prog=
2397 [NFS] [OBJLAYOUT] sets the pathname to the program which
2398 is used to automatically discover and login into new
2399 osd-targets. Please see:
2400 Documentation/filesystems/pnfs.txt for more explanations
2402 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2403 when a NMI is triggered.
2404 Format: [state][,regs][,debounce][,die]
2406 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2407 Format: [panic,][nopanic,][num]
2409 0 - turn hardlockup detector in nmi_watchdog off
2410 1 - turn hardlockup detector in nmi_watchdog on
2411 When panic is specified, panic when an NMI watchdog
2412 timeout occurs (or 'nopanic' to override the opposite
2413 default). To disable both hard and soft lockup detectors,
2414 please see 'nowatchdog'.
2415 This is useful when you use a panic=... timeout and
2416 need the box quickly up again.
2418 netpoll.carrier_timeout=
2419 [NET] Specifies amount of time (in seconds) that
2420 netpoll should wait for a carrier. By default netpoll
2423 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2424 emulation library even if a 387 maths coprocessor
2428 [HW] Never suspend the console
2429 Disable suspending of consoles during suspend and
2430 hibernate operations. Once disabled, debugging
2431 messages can reach various consoles while the rest
2432 of the system is being put to sleep (ie, while
2433 debugging driver suspend/resume hooks). This may
2434 not work reliably with all consoles, but is known
2435 to work with serial and VGA consoles.
2436 To facilitate more flexible debugging, we also add
2437 console_suspend, a printk module parameter to control
2438 it. Users could use console_suspend (usually
2439 /sys/module/printk/parameters/console_suspend) to
2440 turn on/off it dynamically.
2442 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2443 caches in the slab allocator. Saves per-node memory,
2444 but will impact performance.
2448 noaltinstr [S390] Disables alternative instructions patching
2449 (CPU alternatives feature).
2451 noapic [SMP,APIC] Tells the kernel to not make use of any
2452 IOAPICs that may be present in the system.
2454 noautogroup Disable scheduler automatic task group creation.
2456 nobats [PPC] Do not use BATs for mapping kernel lowmem
2457 on "Classic" PPC cores.
2461 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2463 nodelayacct [KNL] Disable per-task delay accounting
2465 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2467 nodsp [SH] Disable hardware DSP at boot time.
2469 noefi Disable EFI runtime services support.
2474 On X86-32 available only on PAE configured kernels.
2475 noexec=on: enable non-executable mappings (default)
2476 noexec=off: disable non-executable mappings
2479 Disable SMAP (Supervisor Mode Access Prevention)
2480 even if it is supported by processor.
2483 Disable SMEP (Supervisor Mode Execution Prevention)
2484 even if it is supported by processor.
2487 This affects only 32-bit executables.
2488 noexec32=on: enable non-executable mappings (default)
2489 read doesn't imply executable mappings
2490 noexec32=off: disable non-executable mappings
2491 read implies executable mappings
2493 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2495 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2496 register save and restore. The kernel will only save
2497 legacy floating-point registers on task switch.
2499 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2501 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2502 check bypass). With this option data leaks are possible
2505 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2506 (indirect branch prediction) vulnerability. System may
2507 allow data leaks with this option, which is equivalent
2510 nospec_store_bypass_disable
2511 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2513 noxsave [BUGS=X86] Disables x86 extended register state save
2514 and restore using xsave. The kernel will fallback to
2515 enabling legacy floating-point and sse state.
2517 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2518 register states. The kernel will fall back to use
2519 xsave to save the states. By using this parameter,
2520 performance of saving the states is degraded because
2521 xsave doesn't support modified optimization while
2522 xsaveopt supports it on xsaveopt enabled systems.
2524 noxsaves [X86] Disables xsaves and xrstors used in saving and
2525 restoring x86 extended register state in compacted
2526 form of xsave area. The kernel will fall back to use
2527 xsaveopt and xrstor to save and restore the states
2528 in standard form of xsave area. By using this
2529 parameter, xsave area per process might occupy more
2530 memory on xsaves enabled systems.
2532 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2533 wfi(ARM) instruction doesn't work correctly and not to
2534 use it. This is also useful when using JTAG debugger.
2536 no_file_caps Tells the kernel not to honor file capabilities. The
2537 only way then for a file to be executed with privilege
2538 is to be setuid root or executed by root.
2540 nohalt [IA-64] Tells the kernel not to use the power saving
2541 function PAL_HALT_LIGHT when idle. This increases
2542 power-consumption. On the positive side, it reduces
2543 interrupt wake-up latency, which may improve performance
2544 in certain environments such as networked servers or
2547 nohibernate [HIBERNATION] Disable hibernation and resume.
2549 nohz= [KNL] Boottime enable/disable dynamic ticks
2550 Valid arguments: on, off
2553 nohz_full= [KNL,BOOT]
2554 In kernels built with CONFIG_NO_HZ_FULL=y, set
2555 the specified list of CPUs whose tick will be stopped
2556 whenever possible. The boot CPU will be forced outside
2557 the range to maintain the timekeeping.
2558 The CPUs in this range must also be included in the
2561 noiotrap [SH] Disables trapped I/O port accesses.
2563 noirqdebug [X86-32] Disables the code which attempts to detect and
2564 disable unhandled interrupt sources.
2566 no_timer_check [X86,APIC] Disables the code which tests for
2567 broken timer IRQ sources.
2569 noisapnp [ISAPNP] Disables ISA PnP code.
2571 noinitrd [RAM] Tells the kernel not to load any configured
2574 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2576 [Deprecated - use intremap=off]
2580 noinvpcid [X86] Disable the INVPCID cpu feature.
2582 nojitter [IA-64] Disables jitter checking for ITC timers.
2584 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2586 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2589 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2590 steal time is computed, but won't influence scheduler
2593 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2595 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2597 noltlbs [PPC] Do not use large page/tlb entries for kernel
2598 lowmem mapping on PPC40x.
2600 nomca [IA-64] Disable machine check abort handling
2602 nomce [X86-32] Disable Machine Check Exception
2604 nomfgpt [X86-32] Disable Multi-Function General Purpose
2605 Timer usage (for AMD Geode machines).
2607 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2608 shutdown the other cpus. Instead use the REBOOT_VECTOR
2611 nomodule Disable module load
2613 nopat [X86] Disable PAT (page attribute table extension of
2614 pagetables) support.
2616 nopcid [X86-64] Disable the PCID cpu feature.
2618 norandmaps Don't use address space randomization. Equivalent to
2619 echo 0 > /proc/sys/kernel/randomize_va_space
2621 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2622 with UP alternatives
2624 nordrand [X86] Disable kernel use of the RDRAND and
2625 RDSEED instructions even if they are supported
2626 by the processor. RDRAND and RDSEED are still
2627 available to user space applications.
2629 noresume [SWSUSP] Disables resume and restores original swap
2632 no-scroll [VGA] Disables scrollback.
2633 This is required for the Braillex ib80-piezo Braille
2634 reader made by F.H. Papenmeier (Germany).
2638 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2640 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2641 and disable the IO APIC. legacy for "maxcpus=0".
2643 nosoftlockup [KNL] Disable the soft-lockup detector.
2645 nosync [HW,M68K] Disables sync negotiation for all devices.
2647 notsc [BUGS=X86-32] Disable Time Stamp Counter
2649 nousb [USB] Disable the USB subsystem
2651 nowatchdog [KNL] Disable both lockup detectors, i.e.
2652 soft-lockup and NMI watchdog (hard-lockup).
2656 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2658 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2659 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2660 Some features depend on CPU0. Known dependencies are:
2661 1. Resume from suspend/hibernate depends on CPU0.
2662 Suspend/hibernate will fail if CPU0 is offline and you
2663 need to online CPU0 before suspend/hibernate.
2664 2. PIC interrupts also depend on CPU0. CPU0 can't be
2665 removed if a PIC interrupt is detected.
2666 It's said poweroff/reboot may depend on CPU0 on some
2667 machines although I haven't seen such issues so far
2668 after CPU0 is offline on a few tested machines.
2669 If the dependencies are under your control, you can
2670 turn on cpu0_hotplug.
2672 nptcg= [IA-64] Override max number of concurrent global TLB
2673 purges which is reported from either PAL_VM_SUMMARY or
2676 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2677 could support. nr_cpus=n : n >= 1 limits the kernel to
2678 supporting 'n' processors. Later in runtime you can not
2679 use hotplug cpu feature to put more cpu back to online.
2680 just like you compile the kernel NR_CPUS=n
2682 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2684 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2685 Allowed values are enable and disable
2687 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2688 one of ['zone', 'node', 'default'] can be specified
2689 This can be set from sysctl after boot.
2690 See Documentation/sysctl/vm.txt for details.
2692 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2693 See Documentation/debugging-via-ohci1394.txt for more
2696 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2697 Rather than timing out after 20 ms if an EC
2698 command is not properly ACKed, override the length
2699 of the timeout. We have interrupts disabled while
2700 waiting for the ACK, so if this is set too high
2701 interrupts *may* be lost!
2703 omap_mux= [OMAP] Override bootloader pin multiplexing.
2704 Format: <mux_mode0.mode_name=value>...
2705 For example, to override I2C bus2:
2706 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2708 oprofile.timer= [HW]
2709 Use timer interrupt instead of performance counters
2711 oprofile.cpu_type= Force an oprofile cpu type
2712 This might be useful if you have an older oprofile
2713 userland or if you want common events.
2714 Format: { arch_perfmon }
2715 arch_perfmon: [X86] Force use of architectural
2716 perfmon on Intel CPUs instead of the
2717 CPU specific event set.
2718 timer: [X86] Force use of architectural NMI
2719 timer mode (see also oprofile.timer
2720 for generic hr timer mode)
2721 [s390] Force legacy basic mode sampling
2722 (report cpu_type "timer")
2724 oops=panic Always panic on oopses. Default is to just kill the
2725 process, but there is a small probability of
2726 deadlocking the machine.
2727 This will also cause panics on machine check exceptions.
2728 Useful together with panic=30 to trigger a reboot.
2731 See Documentation/sound/oss/oss-parameters.txt
2733 page_owner= [KNL] Boot-time page_owner enabling option.
2734 Storage of the information about who allocated
2735 each page is disabled in default. With this switch,
2737 on: enable the feature
2739 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2740 timeout > 0: seconds before rebooting
2741 timeout = 0: wait forever
2742 timeout < 0: reboot immediately
2745 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2748 crash_kexec_post_notifiers
2749 Run kdump after running panic-notifiers and dumping
2750 kmsg. This only for the users who doubt kdump always
2751 succeeds in any situation.
2752 Note that this also increases risks of kdump failure,
2753 because some panic notifiers can make the crashed
2754 kernel more unstable.
2756 parkbd.port= [HW] Parallel port number the keyboard adapter is
2757 connected to, default is 0.
2759 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2760 0 for XT, 1 for AT (default is AT).
2763 parport= [HW,PPT] Specify parallel ports. 0 disables.
2764 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2765 Use 'auto' to force the driver to use any
2766 IRQ/DMA settings detected (the default is to
2767 ignore detected IRQ/DMA settings because of
2768 possible conflicts). You can specify the base
2769 address, IRQ, and DMA settings; IRQ and DMA
2770 should be numbers, or 'auto' (for using detected
2771 settings on that particular port), or 'nofifo'
2772 (to avoid using a FIFO even if it is detected).
2773 Parallel ports are assigned in the order they
2774 are specified on the command line, starting
2777 parport_init_mode= [HW,PPT]
2778 Configure VIA parallel port to operate in
2779 a specific mode. This is necessary on Pegasos
2780 computer where firmware has no options for setting
2781 up parallel port mode and sets it to spp.
2782 Currently this function knows 686a and 8231 chips.
2783 Format: [spp|ps2|epp|ecp|ecpepp]
2786 Halt all CPUs after the first oops has been printed for
2787 the specified number of seconds. This is to be used if
2788 your oopses keep scrolling off the screen.
2793 See header of drivers/block/paride/pcd.c.
2794 See also Documentation/blockdev/paride.txt.
2796 pci=option[,option...] [PCI] various PCI subsystem options:
2797 earlydump [X86] dump PCI config space before the kernel
2799 off [X86] don't probe for the PCI bus
2800 bios [X86-32] force use of PCI BIOS, don't access
2801 the hardware directly. Use this if your machine
2802 has a non-standard PCI host bridge.
2803 nobios [X86-32] disallow use of PCI BIOS, only direct
2804 hardware access methods are allowed. Use this
2805 if you experience crashes upon bootup and you
2806 suspect they are caused by the BIOS.
2807 conf1 [X86] Force use of PCI Configuration
2809 conf2 [X86] Force use of PCI Configuration
2811 noaer [PCIE] If the PCIEAER kernel config parameter is
2812 enabled, this kernel boot option can be used to
2813 disable the use of PCIE advanced error reporting.
2814 nodomains [PCI] Disable support for multiple PCI
2815 root domains (aka PCI segments, in ACPI-speak).
2816 nommconf [X86] Disable use of MMCONFIG for PCI
2818 check_enable_amd_mmconf [X86] check for and enable
2819 properly configured MMIO access to PCI
2820 config space on AMD family 10h CPU
2821 nomsi [MSI] If the PCI_MSI kernel config parameter is
2822 enabled, this kernel boot option can be used to
2823 disable the use of MSI interrupts system-wide.
2824 noioapicquirk [APIC] Disable all boot interrupt quirks.
2825 Safety option to keep boot IRQs enabled. This
2826 should never be necessary.
2827 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2828 primary IO-APIC for bridges that cannot disable
2829 boot IRQs. This fixes a source of spurious IRQs
2830 when the system masks IRQs.
2831 noioapicreroute [APIC] Disable workaround that uses the
2832 boot IRQ equivalent of an IRQ that connects to
2833 a chipset where boot IRQs cannot be disabled.
2834 The opposite of ioapicreroute.
2835 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2836 routing table. These calls are known to be buggy
2837 on several machines and they hang the machine
2838 when used, but on other computers it's the only
2839 way to get the interrupt routing table. Try
2840 this option if the kernel is unable to allocate
2841 IRQs or discover secondary PCI buses on your
2843 rom [X86] Assign address space to expansion ROMs.
2844 Use with caution as certain devices share
2845 address decoders between ROMs and other
2847 norom [X86] Do not assign address space to
2848 expansion ROMs that do not already have
2849 BIOS assigned address ranges.
2850 nobar [X86] Do not assign address space to the
2851 BARs that weren't assigned by the BIOS.
2852 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2853 assigned automatically to PCI devices. You can
2854 make the kernel exclude IRQs of your ISA cards
2856 pirqaddr=0xAAAAA [X86] Specify the physical address
2857 of the PIRQ table (normally generated
2858 by the BIOS) if it is outside the
2859 F0000h-100000h range.
2860 lastbus=N [X86] Scan all buses thru bus #N. Can be
2861 useful if the kernel is unable to find your
2862 secondary buses and you want to tell it
2863 explicitly which ones they are.
2864 assign-busses [X86] Always assign all PCI bus
2865 numbers ourselves, overriding
2866 whatever the firmware may have done.
2867 usepirqmask [X86] Honor the possible IRQ mask stored
2868 in the BIOS $PIR table. This is needed on
2869 some systems with broken BIOSes, notably
2870 some HP Pavilion N5400 and Omnibook XE3
2871 notebooks. This will have no effect if ACPI
2872 IRQ routing is enabled.
2873 noacpi [X86] Do not use ACPI for IRQ routing
2874 or for PCI scanning.
2875 use_crs [X86] Use PCI host bridge window information
2876 from ACPI. On BIOSes from 2008 or later, this
2877 is enabled by default. If you need to use this,
2878 please report a bug.
2879 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2880 If you need to use this, please report a bug.
2881 routeirq Do IRQ routing for all PCI devices.
2882 This is normally done in pci_enable_device(),
2883 so this option is a temporary workaround
2884 for broken drivers that don't call it.
2885 skip_isa_align [X86] do not align io start addr, so can
2886 handle more pci cards
2887 firmware [ARM] Do not re-enumerate the bus but instead
2888 just use the configuration from the
2889 bootloader. This is currently used on
2890 IXP2000 systems where the bus has to be
2891 configured a certain way for adjunct CPUs.
2892 noearly [X86] Don't do any early type 1 scanning.
2893 This might help on some broken boards which
2894 machine check when some devices' config space
2895 is read. But various workarounds are disabled
2896 and some IOMMU drivers will not work.
2897 bfsort Sort PCI devices into breadth-first order.
2898 This sorting is done to get a device
2899 order compatible with older (<= 2.4) kernels.
2900 nobfsort Don't sort PCI devices into breadth-first order.
2901 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2902 tuning and use the BIOS-configured MPS defaults.
2903 pcie_bus_safe Set every device's MPS to the largest value
2904 supported by all devices below the root complex.
2905 pcie_bus_perf Set device MPS to the largest allowable MPS
2906 based on its parent bus. Also set MRRS (Max
2907 Read Request Size) to the largest supported
2908 value (no larger than the MPS that the device
2909 or bus can support) for best performance.
2910 pcie_bus_peer2peer Set every device's MPS to 128B, which
2911 every device is guaranteed to support. This
2912 configuration allows peer-to-peer DMA between
2913 any pair of devices, possibly at the cost of
2914 reduced performance. This also guarantees
2915 that hot-added devices will work.
2916 cbiosize=nn[KMG] The fixed amount of bus space which is
2917 reserved for the CardBus bridge's IO window.
2918 The default value is 256 bytes.
2919 cbmemsize=nn[KMG] The fixed amount of bus space which is
2920 reserved for the CardBus bridge's memory
2921 window. The default value is 64 megabytes.
2924 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2925 Specifies alignment and device to reassign
2926 aligned memory resources.
2927 If <order of align> is not specified,
2928 PAGE_SIZE is used as alignment.
2929 PCI-PCI bridge can be specified, if resource
2930 windows need to be expanded.
2931 ecrc= Enable/disable PCIe ECRC (transaction layer
2932 end-to-end CRC checking).
2933 bios: Use BIOS/firmware settings. This is the
2937 hpiosize=nn[KMG] The fixed amount of bus space which is
2938 reserved for hotplug bridge's IO window.
2939 Default size is 256 bytes.
2940 hpmemsize=nn[KMG] The fixed amount of bus space which is
2941 reserved for hotplug bridge's memory window.
2942 Default size is 2 megabytes.
2943 realloc= Enable/disable reallocating PCI bridge resources
2944 if allocations done by BIOS are too small to
2945 accommodate resources required by all child
2947 off: Turn realloc off
2949 realloc same as realloc=on
2950 noari do not use PCIe ARI.
2951 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2952 only look for one device below a PCIe downstream
2955 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2958 force Enable ASPM even on devices that claim not to support it.
2959 WARNING: Forcing ASPM on may cause system lockups.
2961 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2962 nomsi Do not use MSI for PCI Express Native Hotplug (this
2963 makes all PCIe ports use INTx for hotplug services).
2965 pcie_ports= [PCIE] PCIe ports handling:
2966 auto Ask the BIOS whether or not to use native PCIe services
2967 associated with PCIe ports (PME, hot-plug, AER). Use
2968 them only if that is allowed by the BIOS.
2969 native Use native PCIe services associated with PCIe ports
2971 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2974 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2975 nomsi Do not use MSI for native PCIe PME signaling (this makes
2976 all PCIe root ports use INTx for all services).
2978 pcmv= [HW,PCMCIA] BadgePAD 4
2982 Keep all power-domains already enabled by bootloader on,
2983 even if no driver has claimed them. This is useful
2984 for debug and development, but should not be
2985 needed on a platform with proper driver support.
2988 See Documentation/blockdev/paride.txt.
2990 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2993 See arch/parisc/kernel/pdc_chassis.c
2995 percpu_alloc= Select which percpu first chunk allocator to use.
2996 Currently supported values are "embed" and "page".
2997 Archs may support subset or none of the selections.
2998 See comments in mm/percpu.c for details on each
2999 allocator. This parameter is primarily for debugging
3000 and performance comparison.
3003 See Documentation/blockdev/paride.txt.
3006 See Documentation/blockdev/paride.txt.
3008 pirq= [SMP,APIC] Manual mp-table setup
3009 See Documentation/x86/i386/IO-APIC.txt.
3011 plip= [PPT,NET] Parallel port network link
3012 Format: { parport<nr> | timid | 0 }
3013 See also Documentation/parport.txt.
3015 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3016 Override pmtimer IOPort with a hex value.
3020 Enable PNP debug messages (depends on the
3021 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3022 via /sys/module/pnp/parameters/debug. We always show
3023 current resource usage; turning this on also shows
3024 possible settings and some assignment information.
3030 { on | off | curr | res | no-curr | no-res }
3033 [ISAPNP] Exclude IRQs for the autoconfiguration
3036 [ISAPNP] Exclude DMAs for the autoconfiguration
3038 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3039 Ranges are in pairs (I/O port base and size).
3042 [ISAPNP] Exclude memory regions for the
3044 Ranges are in pairs (memory base and size).
3046 ports= [IP_VS_FTP] IPVS ftp helper module
3048 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3050 Format: <port>,<port>....
3052 print-fatal-signals=
3053 [KNL] debug: print fatal signals
3055 If enabled, warn about various signal handling
3056 related application anomalies: too many signals,
3057 too many POSIX.1 timers, fatal signals causing a
3060 If you hit the warning due to signal overflow,
3061 you might want to try "ulimit -i unlimited".
3065 printk.always_kmsg_dump=
3066 Trigger kmsg_dump for cases other than kernel oops or
3068 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3071 printk.time= Show timing data prefixed to each printk message line
3072 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3074 processor.max_cstate= [HW,ACPI]
3075 Limit processor to maximum C-state
3076 max_cstate=9 overrides any DMI blacklist limit.
3078 processor.nocst [HW,ACPI]
3079 Ignore the _CST method to determine C-states,
3080 instead using the legacy FADT method
3082 profile= [KNL] Enable kernel profiling via /proc/profile
3083 Format: [schedule,]<number>
3084 Param: "schedule" - profile schedule points.
3085 Param: <number> - step/bucket size as a power of 2 for
3086 statistical time based profiling.
3087 Param: "sleep" - profile D-state sleeping (millisecs).
3088 Requires CONFIG_SCHEDSTATS
3089 Param: "kvm" - profile VM exits.
3091 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3093 See Documentation/blockdev/ramdisk.txt.
3095 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3096 probe for; one of (bare|imps|exps|lifebook|any).
3097 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3099 psmouse.resetafter= [HW,MOUSE]
3100 Try to reset the device after so many bad packets
3103 [HW,MOUSE] Set desired mouse resolution, in dpi.
3104 psmouse.smartscroll=
3105 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3106 0 = disabled, 1 = enabled (default).
3108 pstore.backend= Specify the name of the pstore backend to use
3111 See Documentation/blockdev/paride.txt.
3113 pti= [X86_64] Control Page Table Isolation of user and
3114 kernel address spaces. Disabling this feature
3115 removes hardening, but improves performance of
3116 system calls and interrupts.
3118 on - unconditionally enable
3119 off - unconditionally disable
3120 auto - kernel detects whether your CPU model is
3121 vulnerable to issues that PTI mitigates
3123 Not specifying this option is equivalent to pti=auto.
3126 Equivalent to pti=off
3129 [KNL] Number of legacy pty's. Overwrites compiled-in
3132 quiet [KNL] Disable most log messages
3137 See Documentation/md.txt.
3139 ramdisk_blocksize= [RAM]
3140 See Documentation/blockdev/ramdisk.txt.
3142 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3143 See Documentation/blockdev/ramdisk.txt.
3146 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3147 the specified list of CPUs to be no-callback CPUs.
3148 Invocation of these CPUs' RCU callbacks will
3149 be offloaded to "rcuox/N" kthreads created for
3150 that purpose, where "x" is "b" for RCU-bh, "p"
3151 for RCU-preempt, and "s" for RCU-sched, and "N"
3152 is the CPU number. This reduces OS jitter on the
3153 offloaded CPUs, which can be useful for HPC and
3154 real-time workloads. It can also improve energy
3155 efficiency for asymmetric multiprocessors.
3158 Rather than requiring that offloaded CPUs
3159 (specified by rcu_nocbs= above) explicitly
3160 awaken the corresponding "rcuoN" kthreads,
3161 make these kthreads poll for callbacks.
3162 This improves the real-time response for the
3163 offloaded CPUs by relieving them of the need to
3164 wake up the corresponding kthread, but degrades
3165 energy efficiency by requiring that the kthreads
3166 periodically wake up to do the polling.
3168 rcutree.blimit= [KNL]
3169 Set maximum number of finished RCU callbacks to
3170 process in one batch.
3172 rcutree.dump_tree= [KNL]
3173 Dump the structure of the rcu_node combining tree
3174 out at early boot. This is used for diagnostic
3175 purposes, to verify correct tree setup.
3177 rcutree.gp_cleanup_delay= [KNL]
3178 Set the number of jiffies to delay each step of
3179 RCU grace-period cleanup. This only has effect
3180 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3182 rcutree.gp_init_delay= [KNL]
3183 Set the number of jiffies to delay each step of
3184 RCU grace-period initialization. This only has
3185 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3188 rcutree.gp_preinit_delay= [KNL]
3189 Set the number of jiffies to delay each step of
3190 RCU grace-period pre-initialization, that is,
3191 the propagation of recent CPU-hotplug changes up
3192 the rcu_node combining tree. This only has effect
3193 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3195 rcutree.rcu_fanout_exact= [KNL]
3196 Disable autobalancing of the rcu_node combining
3197 tree. This is used by rcutorture, and might
3198 possibly be useful for architectures having high
3199 cache-to-cache transfer latencies.
3201 rcutree.rcu_fanout_leaf= [KNL]
3202 Change the number of CPUs assigned to each
3203 leaf rcu_node structure. Useful for very
3204 large systems, which will choose the value 64,
3205 and for NUMA systems with large remote-access
3206 latencies, which will choose a value aligned
3207 with the appropriate hardware boundaries.
3209 rcutree.jiffies_till_sched_qs= [KNL]
3210 Set required age in jiffies for a
3211 given grace period before RCU starts
3212 soliciting quiescent-state help from
3213 rcu_note_context_switch().
3215 rcutree.jiffies_till_first_fqs= [KNL]
3216 Set delay from grace-period initialization to
3217 first attempt to force quiescent states.
3218 Units are jiffies, minimum value is zero,
3219 and maximum value is HZ.
3221 rcutree.jiffies_till_next_fqs= [KNL]
3222 Set delay between subsequent attempts to force
3223 quiescent states. Units are jiffies, minimum
3224 value is one, and maximum value is HZ.
3226 rcutree.kthread_prio= [KNL,BOOT]
3227 Set the SCHED_FIFO priority of the RCU per-CPU
3228 kthreads (rcuc/N). This value is also used for
3229 the priority of the RCU boost threads (rcub/N)
3230 and for the RCU grace-period kthreads (rcu_bh,
3231 rcu_preempt, and rcu_sched). If RCU_BOOST is
3232 set, valid values are 1-99 and the default is 1
3233 (the least-favored priority). Otherwise, when
3234 RCU_BOOST is not set, valid values are 0-99 and
3235 the default is zero (non-realtime operation).
3237 rcutree.rcu_nocb_leader_stride= [KNL]
3238 Set the number of NOCB kthread groups, which
3239 defaults to the square root of the number of
3240 CPUs. Larger numbers reduces the wakeup overhead
3241 on the per-CPU grace-period kthreads, but increases
3242 that same overhead on each group's leader.
3244 rcutree.qhimark= [KNL]
3245 Set threshold of queued RCU callbacks beyond which
3246 batch limiting is disabled.
3248 rcutree.qlowmark= [KNL]
3249 Set threshold of queued RCU callbacks below which
3250 batch limiting is re-enabled.
3252 rcutree.rcu_idle_gp_delay= [KNL]
3253 Set wakeup interval for idle CPUs that have
3254 RCU callbacks (RCU_FAST_NO_HZ=y).
3256 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3257 Set wakeup interval for idle CPUs that have
3258 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3259 Lazy RCU callbacks are those which RCU can
3260 prove do nothing more than free memory.
3262 rcutorture.cbflood_inter_holdoff= [KNL]
3263 Set holdoff time (jiffies) between successive
3264 callback-flood tests.
3266 rcutorture.cbflood_intra_holdoff= [KNL]
3267 Set holdoff time (jiffies) between successive
3268 bursts of callbacks within a given callback-flood
3271 rcutorture.cbflood_n_burst= [KNL]
3272 Set the number of bursts making up a given
3273 callback-flood test. Set this to zero to
3274 disable callback-flood testing.
3276 rcutorture.cbflood_n_per_burst= [KNL]
3277 Set the number of callbacks to be registered
3278 in a given burst of a callback-flood test.
3280 rcutorture.fqs_duration= [KNL]
3281 Set duration of force_quiescent_state bursts
3284 rcutorture.fqs_holdoff= [KNL]
3285 Set holdoff time within force_quiescent_state bursts
3288 rcutorture.fqs_stutter= [KNL]
3289 Set wait time between force_quiescent_state bursts
3292 rcutorture.gp_cond= [KNL]
3293 Use conditional/asynchronous update-side
3294 primitives, if available.
3296 rcutorture.gp_exp= [KNL]
3297 Use expedited update-side primitives, if available.
3299 rcutorture.gp_normal= [KNL]
3300 Use normal (non-expedited) asynchronous
3301 update-side primitives, if available.
3303 rcutorture.gp_sync= [KNL]
3304 Use normal (non-expedited) synchronous
3305 update-side primitives, if available. If all
3306 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3307 rcutorture.gp_normal=, and rcutorture.gp_sync=
3308 are zero, rcutorture acts as if is interpreted
3309 they are all non-zero.
3311 rcutorture.n_barrier_cbs= [KNL]
3312 Set callbacks/threads for rcu_barrier() testing.
3314 rcutorture.nfakewriters= [KNL]
3315 Set number of concurrent RCU writers. These just
3316 stress RCU, they don't participate in the actual
3317 test, hence the "fake".
3319 rcutorture.nreaders= [KNL]
3320 Set number of RCU readers. The value -1 selects
3321 N-1, where N is the number of CPUs. A value
3322 "n" less than -1 selects N-n-2, where N is again
3323 the number of CPUs. For example, -2 selects N
3324 (the number of CPUs), -3 selects N+1, and so on.
3326 rcutorture.object_debug= [KNL]
3327 Enable debug-object double-call_rcu() testing.
3329 rcutorture.onoff_holdoff= [KNL]
3330 Set time (s) after boot for CPU-hotplug testing.
3332 rcutorture.onoff_interval= [KNL]
3333 Set time (s) between CPU-hotplug operations, or
3334 zero to disable CPU-hotplug testing.
3336 rcutorture.shuffle_interval= [KNL]
3337 Set task-shuffle interval (s). Shuffling tasks
3338 allows some CPUs to go into dyntick-idle mode
3339 during the rcutorture test.
3341 rcutorture.shutdown_secs= [KNL]
3342 Set time (s) after boot system shutdown. This
3343 is useful for hands-off automated testing.
3345 rcutorture.stall_cpu= [KNL]
3346 Duration of CPU stall (s) to test RCU CPU stall
3347 warnings, zero to disable.
3349 rcutorture.stall_cpu_holdoff= [KNL]
3350 Time to wait (s) after boot before inducing stall.
3352 rcutorture.stat_interval= [KNL]
3353 Time (s) between statistics printk()s.
3355 rcutorture.stutter= [KNL]
3356 Time (s) to stutter testing, for example, specifying
3357 five seconds causes the test to run for five seconds,
3358 wait for five seconds, and so on. This tests RCU's
3359 ability to transition abruptly to and from idle.
3361 rcutorture.test_boost= [KNL]
3362 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3363 "Maybe" means test if the RCU implementation
3364 under test support RCU priority boosting.
3366 rcutorture.test_boost_duration= [KNL]
3367 Duration (s) of each individual boost test.
3369 rcutorture.test_boost_interval= [KNL]
3370 Interval (s) between each boost test.
3372 rcutorture.test_no_idle_hz= [KNL]
3373 Test RCU's dyntick-idle handling. See also the
3374 rcutorture.shuffle_interval parameter.
3376 rcutorture.torture_runnable= [BOOT]
3377 Start rcutorture running at boot time.
3379 rcutorture.torture_type= [KNL]
3380 Specify the RCU implementation to test.
3382 rcutorture.verbose= [KNL]
3383 Enable additional printk() statements.
3385 rcupdate.rcu_expedited= [KNL]
3386 Use expedited grace-period primitives, for
3387 example, synchronize_rcu_expedited() instead
3388 of synchronize_rcu(). This reduces latency,
3389 but can increase CPU utilization, degrade
3390 real-time latency, and degrade energy efficiency.
3392 rcupdate.rcu_cpu_stall_suppress= [KNL]
3393 Suppress RCU CPU stall warning messages.
3395 rcupdate.rcu_cpu_stall_timeout= [KNL]
3396 Set timeout for RCU CPU stall warning messages.
3398 rcupdate.rcu_task_stall_timeout= [KNL]
3399 Set timeout in jiffies for RCU task stall warning
3400 messages. Disable with a value less than or equal
3403 rcupdate.rcu_self_test= [KNL]
3404 Run the RCU early boot self tests
3406 rcupdate.rcu_self_test_bh= [KNL]
3407 Run the RCU bh early boot self tests
3409 rcupdate.rcu_self_test_sched= [KNL]
3410 Run the RCU sched early boot self tests
3414 Run specified binary instead of /init from the ramdisk,
3415 used for early userspace startup. See initrd.
3418 Format (x86 or x86_64):
3419 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3421 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3423 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3424 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3425 reboot_force is either force or not specified,
3426 reboot_cpu is s[mp]#### with #### being the processor
3427 to be used for rebooting.
3430 [KNL, SMP] Set scheduler's default relax_domain_level.
3431 See Documentation/cgroups/cpusets.txt.
3433 relative_sleep_states=
3434 [SUSPEND] Use sleep state labeling where the deepest
3435 state available other than hibernation is always "mem".
3436 Format: { "0" | "1" }
3437 0 -- Traditional sleep state labels.
3438 1 -- Relative sleep state labels.
3440 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3442 reservetop= [X86-32]
3444 Reserves a hole at the top of the kernel virtual
3449 Set the amount of memory to reserve for BIOS at
3450 the bottom of the address space.
3452 reset_devices [KNL] Force drivers to reset the underlying device
3453 during initialization.
3456 Specify the partition device for software suspend
3458 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3460 resume_offset= [SWSUSP]
3461 Specify the offset from the beginning of the partition
3462 given by "resume=" at which the swap header is located,
3463 in <PAGE_SIZE> units (needed only for swap files).
3464 See Documentation/power/swsusp-and-swap-files.txt
3466 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3467 read the resume files
3469 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3470 Useful for devices that are detected asynchronously
3471 (e.g. USB and MMC devices).
3473 hibernate= [HIBERNATION]
3474 noresume Don't check if there's a hibernation image
3475 present during boot.
3476 nocompress Don't compress/decompress hibernation images.
3477 no Disable hibernation and resume.
3479 retain_initrd [RAM] Keep initrd memory after extraction
3481 rfkill.default_state=
3482 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3483 etc. communication is blocked by default.
3486 rfkill.master_switch_mode=
3487 0 The "airplane mode" button does nothing.
3488 1 The "airplane mode" button toggles between everything
3489 blocked and the previous configuration.
3490 2 The "airplane mode" button toggles between everything
3491 blocked and everything unblocked.
3493 rhash_entries= [KNL,NET]
3494 Set number of hash buckets for route cache
3496 ro [KNL] Mount root device read-only on boot
3498 root= [KNL] Root filesystem
3499 See name_to_dev_t comment in init/do_mounts.c.
3501 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3502 mount the root filesystem
3504 rootflags= [KNL] Set root filesystem mount option string
3506 rootfstype= [KNL] Set root filesystem type
3508 rootwait [KNL] Wait (indefinitely) for root device to show up.
3509 Useful for devices that are detected asynchronously
3510 (e.g. USB and MMC devices).
3512 rproc_mem=nn[KMG][@address]
3513 [KNL,ARM,CMA] Remoteproc physical memory block.
3514 Memory area to be used by remote processor image,
3517 rw [KNL] Mount root device read-write on boot
3519 S [KNL] Run init in single mode
3521 s390_iommu= [HW,S390]
3522 Set s390 IOTLB flushing mode
3524 With strict flushing every unmap operation will result in
3525 an IOTLB flush. Default is lazy flushing before reuse,
3529 See drivers/net/irda/sa1100_ir.c.
3531 sbni= [NET] Granch SBNI12 leased line adapter
3533 sched_debug [KNL] Enables verbose scheduler debug messages.
3535 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3536 xtime_lock contention on larger systems, and/or RCU lock
3537 contention on all systems with CONFIG_MAXSMP set.
3538 Format: { "0" | "1" }
3539 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3541 Note: increases power consumption, thus should only be
3542 enabled if running jitter sensitive (HPC/RT) workloads.
3544 security= [SECURITY] Choose a security module to enable at boot.
3545 If this boot parameter is not specified, only the first
3546 security module asking for security registration will be
3547 loaded. An invalid security module name will be treated
3548 as if no module has been chosen.
3550 selinux= [SELINUX] Disable or enable SELinux at boot time.
3551 Format: { "0" | "1" }
3552 See security/selinux/Kconfig help text.
3555 Default value is set via kernel config option.
3556 If enabled at boot time, /selinux/disable can be used
3557 later to disable prior to initial policy load.
3559 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3560 Format: { "0" | "1" }
3561 See security/apparmor/Kconfig help text
3564 Default value is set via kernel config option.
3566 serialnumber [BUGS=X86-32]
3569 Maximal number of shapers.
3571 show_msr= [x86] show boot-time MSR settings
3572 Format: { <integer> }
3573 Show boot-time (BIOS-initialized) MSR settings.
3574 The parameter means the number of CPUs to show,
3575 for example 1 means boot CPU only.
3583 Disable merging of slabs with similar size. May be
3584 necessary if there is some reason to distinguish
3585 allocs to different slabs. Debug options disable
3586 merging on their own.
3587 For more information see Documentation/vm/slub.txt.
3589 slab_max_order= [MM, SLAB]
3590 Determines the maximum allowed order for slabs.
3591 A high setting may cause OOMs due to memory
3592 fragmentation. Defaults to 1 for systems with
3593 more than 32MB of RAM, 0 otherwise.
3595 slub_debug[=options[,slabs]] [MM, SLUB]
3596 Enabling slub_debug allows one to determine the
3597 culprit if slab objects become corrupted. Enabling
3598 slub_debug can create guard zones around objects and
3599 may poison objects when not in use. Also tracks the
3600 last alloc / free. For more information see
3601 Documentation/vm/slub.txt.
3603 slub_max_order= [MM, SLUB]
3604 Determines the maximum allowed order for slabs.
3605 A high setting may cause OOMs due to memory
3606 fragmentation. For more information see
3607 Documentation/vm/slub.txt.
3609 slub_min_objects= [MM, SLUB]
3610 The minimum number of objects per slab. SLUB will
3611 increase the slab order up to slub_max_order to
3612 generate a sufficiently large slab able to contain
3613 the number of objects indicated. The higher the number
3614 of objects the smaller the overhead of tracking slabs
3615 and the less frequently locks need to be acquired.
3616 For more information see Documentation/vm/slub.txt.
3618 slub_min_order= [MM, SLUB]
3619 Determines the minimum page order for slabs. Must be
3620 lower than slub_max_order.
3621 For more information see Documentation/vm/slub.txt.
3623 slub_nomerge [MM, SLUB]
3624 Same with slab_nomerge. This is supported for legacy.
3625 See slab_nomerge for more information.
3628 Format: <io1>[,<io2>[,...,<io8>]]
3630 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3631 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3632 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3633 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3634 smsc-ircc2.ircc_irq= [HW] IRQ line
3635 smsc-ircc2.ircc_dma= [HW] DMA channel
3636 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3637 0: Toshiba Satellite 1800 (GP data pin select)
3638 1: Fast pin select (default)
3642 [KNL] Should the soft-lockup detector generate panics.
3645 softlockup_all_cpu_backtrace=
3646 [KNL] Should the soft-lockup detector generate
3647 backtraces on all cpus.
3650 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3651 See Documentation/laptops/sonypi.txt
3653 spectre_v2= [X86] Control mitigation of Spectre variant 2
3654 (indirect branch speculation) vulnerability.
3655 The default operation protects the kernel from
3658 on - unconditionally enable, implies
3660 off - unconditionally disable, implies
3662 auto - kernel detects whether your CPU model is
3665 Selecting 'on' will, and 'auto' may, choose a
3666 mitigation method at run time according to the
3667 CPU, the available microcode, the setting of the
3668 CONFIG_RETPOLINE configuration option, and the
3669 compiler with which the kernel was built.
3671 Selecting 'on' will also enable the mitigation
3672 against user space to user space task attacks.
3674 Selecting 'off' will disable both the kernel and
3675 the user space protections.
3677 Specific mitigations can also be selected manually:
3679 retpoline - replace indirect branches
3680 retpoline,generic - google's original retpoline
3681 retpoline,amd - AMD-specific minimal thunk
3683 Not specifying this option is equivalent to
3687 [X86] Control mitigation of Spectre variant 2
3688 (indirect branch speculation) vulnerability between
3691 on - Unconditionally enable mitigations. Is
3692 enforced by spectre_v2=on
3694 off - Unconditionally disable mitigations. Is
3695 enforced by spectre_v2=off
3697 prctl - Indirect branch speculation is enabled,
3698 but mitigation can be enabled via prctl
3699 per thread. The mitigation control state
3700 is inherited on fork.
3703 - Like "prctl" above, but only STIBP is
3704 controlled per thread. IBPB is issued
3705 always when switching between different user
3709 - Same as "prctl" above, but all seccomp
3710 threads will enable the mitigation unless
3711 they explicitly opt out.
3714 - Like "seccomp" above, but only STIBP is
3715 controlled per thread. IBPB is issued
3716 always when switching between different
3717 user space processes.
3719 auto - Kernel selects the mitigation depending on
3720 the available CPU features and vulnerability.
3723 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
3725 Not specifying this option is equivalent to
3726 spectre_v2_user=auto.
3728 spec_store_bypass_disable=
3729 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
3730 (Speculative Store Bypass vulnerability)
3732 Certain CPUs are vulnerable to an exploit against a
3733 a common industry wide performance optimization known
3734 as "Speculative Store Bypass" in which recent stores
3735 to the same memory location may not be observed by
3736 later loads during speculative execution. The idea
3737 is that such stores are unlikely and that they can
3738 be detected prior to instruction retirement at the
3739 end of a particular speculation execution window.
3741 In vulnerable processors, the speculatively forwarded
3742 store can be used in a cache side channel attack, for
3743 example to read memory to which the attacker does not
3744 directly have access (e.g. inside sandboxed code).
3746 This parameter controls whether the Speculative Store
3747 Bypass optimization is used.
3749 on - Unconditionally disable Speculative Store Bypass
3750 off - Unconditionally enable Speculative Store Bypass
3751 auto - Kernel detects whether the CPU model contains an
3752 implementation of Speculative Store Bypass and
3753 picks the most appropriate mitigation. If the
3754 CPU is not vulnerable, "off" is selected. If the
3755 CPU is vulnerable the default mitigation is
3756 architecture and Kconfig dependent. See below.
3757 prctl - Control Speculative Store Bypass per thread
3758 via prctl. Speculative Store Bypass is enabled
3759 for a process by default. The state of the control
3760 is inherited on fork.
3761 seccomp - Same as "prctl" above, but all seccomp threads
3762 will disable SSB unless they explicitly opt out.
3764 Not specifying this option is equivalent to
3765 spec_store_bypass_disable=auto.
3767 Default mitigations:
3768 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
3770 spia_io_base= [HW,MTD]
3775 stack_guard_gap= [MM]
3776 override the default stack gap protection. The value
3777 is in page units and it defines how many pages prior
3778 to (for stacks growing down) resp. after (for stacks
3779 growing up) the main stack are reserved for no other
3780 mapping. Default value is 256 pages.
3783 Enabled the stack tracer on boot up.
3785 stacktrace_filter=[function-list]
3786 [FTRACE] Limit the functions that the stack tracer
3787 will trace at boot up. function-list is a comma separated
3788 list of functions. This list can be changed at run
3789 time by the stack_trace_filter file in the debugfs
3790 tracing directory. Note, this enables stack tracing
3791 and the stacktrace above is not needed.
3795 Set the STI (builtin display/keyboard on the HP-PARISC
3796 machines) console (graphic card) which should be used
3797 as the initial boot-console.
3798 See also comment in drivers/video/console/sticore.c.
3801 See comment in drivers/video/console/sticore.c.
3804 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3806 sunrpc.min_resvport=
3807 sunrpc.max_resvport=
3809 SunRPC servers often require that client requests
3810 originate from a privileged port (i.e. a port in the
3811 range 0 < portnr < 1024).
3812 An administrator who wishes to reserve some of these
3813 ports for other uses may adjust the range that the
3814 kernel's sunrpc client considers to be privileged
3815 using these two parameters to set the minimum and
3816 maximum port values.
3820 Control how the NFS server code allocates CPUs to
3821 service thread pools. Depending on how many NICs
3822 you have and where their interrupts are bound, this
3823 option will affect which CPUs will do NFS serving.
3824 Note: this parameter cannot be changed while the
3825 NFS server is running.
3827 auto the server chooses an appropriate mode
3828 automatically using heuristics
3829 global a single global pool contains all CPUs
3830 percpu one pool for each CPU
3831 pernode one pool for each NUMA node (equivalent
3832 to global on non-NUMA machines)
3834 sunrpc.tcp_slot_table_entries=
3835 sunrpc.udp_slot_table_entries=
3837 Sets the upper limit on the number of simultaneous
3838 RPC calls that can be sent from the client to a
3839 server. Increasing these values may allow you to
3840 improve throughput, but will also increase the
3841 amount of memory reserved for use by the client.
3843 suspend.pm_test_delay=
3845 Sets the number of seconds to remain in a suspend test
3846 mode before resuming the system (see
3847 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3848 is set. Default value is 5.
3851 [KNL] Enable accounting of swap in memory resource
3852 controller if no parameter or 1 is given or disable
3853 it if 0 is given (See Documentation/cgroups/memory.txt)
3855 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3856 Format: { <int> | force }
3857 <int> -- Number of I/O TLB slabs
3858 force -- force using of bounce buffers even if they
3859 wouldn't be automatically used by the kernel
3863 sysfs.deprecated=0|1 [KNL]
3864 Enable/disable old style sysfs layout for old udev
3865 on older distributions. When this option is enabled
3866 very new udev will not work anymore. When this option
3867 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3868 in older udev will not work anymore.
3869 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3870 the kernel configuration.
3872 sysrq_always_enabled
3874 Ignore sysrq setting - this boot parameter will
3875 neutralize any effect of /proc/sys/kernel/sysrq.
3876 Useful for debugging.
3878 tcpmhash_entries= [KNL,NET]
3879 Set the number of tcp_metrics_hash slots.
3880 Default value is 8192 or 16384 depending on total
3881 ram pages. This is used to specify the TCP metrics
3882 cache size. See Documentation/networking/ip-sysctl.txt
3883 "tcp_no_metrics_save" section for more details.
3887 test_suspend= [SUSPEND][,N]
3888 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3889 standby suspend) or "freeze" (for suspend type freeze)
3890 as the system sleep state during system startup with
3891 the optional capability to repeat N number of times.
3892 The system is woken from this state using a
3893 wakeup-capable RTC alarm.
3895 thash_entries= [KNL,NET]
3896 Set number of hash buckets for TCP connection
3898 thermal.act= [HW,ACPI]
3899 -1: disable all active trip points in all thermal zones
3900 <degrees C>: override all lowest active trip points
3902 thermal.crt= [HW,ACPI]
3903 -1: disable all critical trip points in all thermal zones
3904 <degrees C>: override all critical trip points
3906 thermal.nocrt= [HW,ACPI]
3907 Set to disable actions on ACPI thermal zone
3908 critical and hot trip points.
3910 thermal.off= [HW,ACPI]
3911 1: disable ACPI thermal control
3913 thermal.psv= [HW,ACPI]
3914 -1: disable all passive trip points
3915 <degrees C>: override all passive trip points to this
3918 thermal.tzp= [HW,ACPI]
3919 Specify global default ACPI thermal zone polling rate
3920 <deci-seconds>: poll all this frequency
3921 0: no polling (default)
3924 Force threading of all interrupt handlers except those
3925 marked explicitly IRQF_NO_THREAD.
3928 Enable the Transcendent memory driver if built-in.
3930 tmem.cleancache=0|1 [KNL, XEN]
3931 Default is on (1). Disable the usage of the cleancache
3932 API to send anonymous pages to the hypervisor.
3934 tmem.frontswap=0|1 [KNL, XEN]
3935 Default is on (1). Disable the usage of the frontswap
3936 API to send swap pages to the hypervisor. If disabled
3937 the selfballooning and selfshrinking are force disabled.
3939 tmem.selfballooning=0|1 [KNL, XEN]
3940 Default is on (1). Disable the driving of swap pages
3943 tmem.selfshrinking=0|1 [KNL, XEN]
3944 Default is on (1). Partial swapoff that immediately
3945 transfers pages from Xen hypervisor back to the
3946 kernel based on different criteria.
3950 Specify if the kernel should make use of the cpu
3951 topology information if the hardware supports this.
3952 The scheduler will make use of this information and
3953 e.g. base its process migration decisions on it.
3956 topology_updates= [KNL, PPC, NUMA]
3958 Specify if the kernel should ignore (off)
3959 topology updates sent by the hypervisor to this
3964 tpm_suspend_pcr=[HW,TPM]
3965 Format: integer pcr id
3966 Specify that at suspend time, the tpm driver
3967 should extend the specified pcr with zeros,
3968 as a workaround for some chips which fail to
3969 flush the last written pcr on TPM_SaveState.
3970 This will guarantee that all the other pcrs
3973 trace_buf_size=nn[KMG]
3974 [FTRACE] will set tracing buffer size on each cpu.
3976 trace_event=[event-list]
3977 [FTRACE] Set and start specified trace events in order
3978 to facilitate early boot debugging.
3979 See also Documentation/trace/events.txt
3981 trace_options=[option-list]
3982 [FTRACE] Enable or disable tracer options at boot.
3983 The option-list is a comma delimited list of options
3984 that can be enabled or disabled just as if you were
3985 to echo the option name into
3987 /sys/kernel/debug/tracing/trace_options
3989 For example, to enable stacktrace option (to dump the
3990 stack trace of each event), add to the command line:
3992 trace_options=stacktrace
3994 See also Documentation/trace/ftrace.txt "trace options"
3998 Have the tracepoints sent to printk as well as the
3999 tracing ring buffer. This is useful for early boot up
4000 where the system hangs or reboots and does not give the
4001 option for reading the tracing buffer or performing a
4002 ftrace_dump_on_oops.
4004 To turn off having tracepoints sent to printk,
4005 echo 0 > /proc/sys/kernel/tracepoint_printk
4006 Note, echoing 1 into this file without the
4007 tracepoint_printk kernel cmdline option has no effect.
4011 Having tracepoints sent to printk() and activating high
4012 frequency tracepoints such as irq or sched, can cause
4013 the system to live lock.
4016 [FTRACE] enable this option to disable tracing when a
4017 warning is hit. This turns off "tracing_on". Tracing can
4018 be enabled again by echoing '1' into the "tracing_on"
4019 file located in /sys/kernel/debug/tracing/
4021 This option is useful, as it disables the trace before
4022 the WARNING dump is called, which prevents the trace to
4023 be filled with content caused by the warning output.
4025 This option can also be set at run time via the sysctl
4026 option: kernel/traceoff_on_warning
4028 transparent_hugepage=
4030 Format: [always|madvise|never]
4031 Can be used to control the default behavior of the system
4032 with respect to transparent hugepages.
4033 See Documentation/vm/transhuge.txt for more details.
4035 tsc= Disable clocksource stability checks for TSC.
4037 [x86] reliable: mark tsc clocksource as reliable, this
4038 disables clocksource verification at runtime, as well
4039 as the stability checks done at bootup. Used to enable
4040 high-resolution timer mode on older hardware, and in
4041 virtualized environment.
4042 [x86] noirqtime: Do not use TSC to do irq accounting.
4043 Used to run time disable IRQ_TIME_ACCOUNTING on any
4044 platforms where RDTSC is slow and this accounting
4047 turbografx.map[2|3]= [HW,JOY]
4048 TurboGraFX parallel port interface
4050 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4051 See also Documentation/input/joystick-parport.txt
4053 udbg-immortal [PPC] When debugging early kernel crashes that
4054 happen after console_init() and before a proper
4055 console driver takes over, this boot options might
4056 help "seeing" what's going on.
4058 uhash_entries= [KNL,NET]
4059 Set number of hash buckets for UDP/UDP-Lite connections
4062 [USB] Ignore overcurrent events (default N).
4063 Some badly-designed motherboards generate lots of
4064 bogus events, for ports that aren't wired to
4065 anything. Set this parameter to avoid log spamming.
4066 Note that genuine overcurrent events won't be
4070 [X86] Cause panic on unknown NMI.
4072 usbcore.authorized_default=
4073 [USB] Default USB device authorization:
4074 (default -1 = authorized except for wireless USB,
4075 0 = not authorized, 1 = authorized)
4077 usbcore.autosuspend=
4078 [USB] The autosuspend time delay (in seconds) used
4079 for newly-detected USB devices (default 2). This
4080 is the time required before an idle device will be
4081 autosuspended. Devices for which the delay is set
4082 to a negative value won't be autosuspended at all.
4084 usbcore.usbfs_snoop=
4085 [USB] Set to log all usbfs traffic (default 0 = off).
4087 usbcore.blinkenlights=
4088 [USB] Set to cycle leds on hubs (default 0 = off).
4090 usbcore.old_scheme_first=
4091 [USB] Start with the old device initialization
4092 scheme (default 0 = off).
4094 usbcore.usbfs_memory_mb=
4095 [USB] Memory limit (in MB) for buffers allocated by
4096 usbfs (default = 16, 0 = max = 2047).
4098 usbcore.use_both_schemes=
4099 [USB] Try the other device initialization scheme
4100 if the first one fails (default 1 = enabled).
4102 usbcore.initial_descriptor_timeout=
4103 [USB] Specifies timeout for the initial 64-byte
4104 USB_REQ_GET_DESCRIPTOR request in milliseconds
4105 (default 5000 = 5.0 seconds).
4108 [USBHID] The interval which mice are to be polled at.
4110 usb-storage.delay_use=
4111 [UMS] The delay in seconds before a new device is
4112 scanned for Logical Units (default 1).
4115 [UMS] A list of quirks entries to supplement or
4116 override the built-in unusual_devs list. List
4117 entries are separated by commas. Each entry has
4118 the form VID:PID:Flags where VID and PID are Vendor
4119 and Product ID values (4-digit hex numbers) and
4120 Flags is a set of characters, each corresponding
4121 to a common usb-storage quirk flag as follows:
4122 a = SANE_SENSE (collect more than 18 bytes
4124 b = BAD_SENSE (don't collect more than 18
4125 bytes of sense data);
4126 c = FIX_CAPACITY (decrease the reported
4127 device capacity by one sector);
4128 d = NO_READ_DISC_INFO (don't use
4129 READ_DISC_INFO command);
4130 e = NO_READ_CAPACITY_16 (don't use
4131 READ_CAPACITY_16 command);
4132 f = NO_REPORT_OPCODES (don't use report opcodes
4134 g = MAX_SECTORS_240 (don't transfer more than
4135 240 sectors at a time, uas only);
4136 h = CAPACITY_HEURISTICS (decrease the
4137 reported device capacity by one
4138 sector if the number is odd);
4139 i = IGNORE_DEVICE (don't bind to this
4141 j = NO_REPORT_LUNS (don't use report luns
4143 l = NOT_LOCKABLE (don't try to lock and
4144 unlock ejectable media);
4145 m = MAX_SECTORS_64 (don't transfer more
4146 than 64 sectors = 32 KB at a time);
4147 n = INITIAL_READ10 (force a retry of the
4148 initial READ(10) command);
4149 o = CAPACITY_OK (accept the capacity
4150 reported by the device);
4151 p = WRITE_CACHE (the device cache is ON
4153 r = IGNORE_RESIDUE (the device reports
4154 bogus residue values);
4155 s = SINGLE_LUN (the device has only one
4157 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4158 commands, uas only);
4159 u = IGNORE_UAS (don't bind to the uas driver);
4160 w = NO_WP_DETECT (don't test whether the
4161 medium is write-protected).
4162 Example: quirks=0419:aaf5:rl,0421:0433:rc
4164 user_debug= [KNL,ARM]
4166 See arch/arm/Kconfig.debug help text.
4167 1 - undefined instruction events
4169 4 - invalid data aborts
4172 Example: user_debug=31
4175 [X86] Flags controlling user PTE allocations.
4177 nohigh = do not allocate PTE pages in
4178 HIGHMEM regardless of setting
4182 On X86_32, this is an alias for vdso32=. Otherwise:
4184 vdso=1: enable VDSO (the default)
4185 vdso=0: disable VDSO mapping
4187 vdso32= [X86] Control the 32-bit vDSO
4188 vdso32=1: enable 32-bit VDSO
4189 vdso32=0 or vdso32=2: disable 32-bit VDSO
4191 See the help text for CONFIG_COMPAT_VDSO for more
4192 details. If CONFIG_COMPAT_VDSO is set, the default is
4193 vdso32=0; otherwise, the default is vdso32=1.
4195 For compatibility with older kernels, vdso32=2 is an
4198 Try vdso32=0 if you encounter an error that says:
4199 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4202 vector=percpu: enable percpu vector domain
4204 video= [FB] Frame buffer configuration
4205 See Documentation/fb/modedb.txt.
4207 video.brightness_switch_enabled= [0,1]
4208 If set to 1, on receiving an ACPI notify event
4209 generated by hotkey, video driver will adjust brightness
4210 level and then send out the event to user space through
4211 the allocated input device; If set to 0, video driver
4212 will only send out the event without touching backlight
4217 [VMMIO] Memory mapped virtio (platform) device.
4219 <size>@<baseaddr>:<irq>[:<id>]
4221 <size> := size (can use standard suffixes
4223 <baseaddr> := physical base address
4224 <irq> := interrupt number (as passed to
4226 <id> := (optional) platform device id
4228 virtio_mmio.device=1K@0x100b0000:48:7
4230 Can be used multiple times for multiple devices.
4232 vga= [BOOT,X86-32] Select a particular video mode
4233 See Documentation/x86/boot.txt and
4234 Documentation/svga.txt.
4235 Use vga=ask for menu.
4236 This is actually a boot loader parameter; the value is
4237 passed to the kernel using a special protocol.
4239 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4240 size of <nn>. This can be used to increase the
4241 minimum size (128MB on x86). It can also be used to
4242 decrease the size and leave more room for directly
4245 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4248 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4251 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4255 Controls the behavior of vsyscalls (i.e. calls to
4256 fixed addresses of 0xffffffffff600x00 from legacy
4257 code). Most statically-linked binaries and older
4258 versions of glibc use these calls. Because these
4259 functions are at fixed addresses, they make nice
4260 targets for exploits that can control RIP.
4262 emulate [default] Vsyscalls turn into traps and are
4263 emulated reasonably safely.
4265 native Vsyscalls are native syscall instructions.
4266 This is a little bit faster than trapping
4267 and makes a few dynamic recompilers work
4268 better than they would in emulation mode.
4269 It also makes exploits much easier to write.
4271 none Vsyscalls don't work at all. This makes
4272 them quite hard to use for exploits but
4273 might break your system.
4275 vt.color= [VT] Default text color.
4276 Format: 0xYX, X = foreground, Y = background.
4277 Default: 0x07 = light gray on black.
4279 vt.cur_default= [VT] Default cursor shape.
4280 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4281 the parameters of the <Esc>[?A;B;Cc escape sequence;
4282 see VGA-softcursor.txt. Default: 2 = underline.
4284 vt.default_blu= [VT]
4285 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4286 Change the default blue palette of the console.
4287 This is a 16-member array composed of values
4290 vt.default_grn= [VT]
4291 Format: <green0>,<green1>,<green2>,...,<green15>
4292 Change the default green palette of the console.
4293 This is a 16-member array composed of values
4296 vt.default_red= [VT]
4297 Format: <red0>,<red1>,<red2>,...,<red15>
4298 Change the default red palette of the console.
4299 This is a 16-member array composed of values
4305 Set system-wide default UTF-8 mode for all tty's.
4306 Default is 1, i.e. UTF-8 mode is enabled for all
4307 newly opened terminals.
4309 vt.global_cursor_default=
4312 Set system-wide default for whether a cursor
4313 is shown on new VTs. Default is -1,
4314 i.e. cursors will be created by default unless
4315 overridden by individual drivers. 0 will hide
4316 cursors, 1 will display them.
4318 vt.italic= [VT] Default color for italic text; 0-15.
4321 vt.underline= [VT] Default color for underlined text; 0-15.
4324 watchdog timers [HW,WDT] For information on watchdog timers,
4325 see Documentation/watchdog/watchdog-parameters.txt
4326 or other driver-specific files in the
4327 Documentation/watchdog/ directory.
4329 workqueue.disable_numa
4330 By default, all work items queued to unbound
4331 workqueues are affine to the NUMA nodes they're
4332 issued on, which results in better behavior in
4333 general. If NUMA affinity needs to be disabled for
4334 whatever reason, this option can be used. Note
4335 that this also can be controlled per-workqueue for
4336 workqueues visible under /sys/bus/workqueue/.
4338 workqueue.power_efficient
4339 Per-cpu workqueues are generally preferred because
4340 they show better performance thanks to cache
4341 locality; unfortunately, per-cpu workqueues tend to
4342 be more power hungry than unbound workqueues.
4344 Enabling this makes the per-cpu workqueues which
4345 were observed to contribute significantly to power
4346 consumption unbound, leading to measurably lower
4347 power usage at the cost of small performance
4350 The default value of this parameter is determined by
4351 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4353 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4354 default x2apic cluster mode on platforms
4357 x86_intel_mid_timer= [X86-32,APBT]
4358 Choose timer option for x86 Intel MID platform.
4359 Two valid options are apbt timer only and lapic timer
4360 plus one apbt timer for broadcast timer.
4361 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4363 xen_512gb_limit [KNL,X86-64,XEN]
4364 Restricts the kernel running paravirtualized under Xen
4365 to use only up to 512 GB of RAM. The reason to do so is
4366 crash analysis tools and Xen tools for doing domain
4367 save/restore/migration must be enabled to handle larger
4370 xen_emul_unplug= [HW,X86,XEN]
4371 Unplug Xen emulated devices
4372 Format: [unplug0,][unplug1]
4373 ide-disks -- unplug primary master IDE devices
4374 aux-ide-disks -- unplug non-primary-master IDE devices
4375 nics -- unplug network devices
4376 all -- unplug all emulated devices (NICs and IDE disks)
4377 unnecessary -- unplugging emulated devices is
4378 unnecessary even if the host did not respond to
4380 never -- do not unplug even if version check succeeds
4382 xen_nopvspin [X86,XEN]
4383 Disables the ticketlock slowpath using Xen PV
4387 Disables the PV optimizations forcing the HVM guest to
4388 run as generic HVM guest with no PV drivers.
4390 xirc2ps_cs= [NET,PCMCIA]
4392 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4394 ______________________________________________________________________
4398 Add more DRM drivers.
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