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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
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
26 loadable modules too.
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 |
171 copy_dsdt }
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]
184 Format: <int>
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
187 default: 0
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
191 acpi_backlight=video
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]
206 Format: <int>
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
251 size limitation.
253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
255 default in APIC mode
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
259 default in PIC mode
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
265 use by PCI
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
277 kernels.
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
308 strings
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.
321 Examples:
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
331 meaningless.
332 Examples:
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
334 FALSE.
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
346 the OSPM features.
347 Examples:
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
353 equivalent to
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
355 and
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
359 acpi_pm_good [X86]
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
375 s3_bios and s3_mode.
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.
397 agp= [AGP]
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)
403 ALSA [HW,ALSA]
404 See Documentation/sound/alsa/alsa-parameters.txt
406 alignment= [KNL,ARM]
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.
433 Possible values are:
434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
437 is a lot of faster
438 off - do not initialize any AMD IOMMU found in
439 the system
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
454 Format: <a>,<b>
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>
462 apc= [HW,SPARC]
463 Power management functions (SPARCstation-4/5 + deriv.)
464 Format: noidle
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.
475 autoconf= [IPV6]
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>
493 ataflop= [HW,M68k]
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
506 keyboards
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
523 auditd.
524 Default: unset
526 audit_backlog_limit= [KNL] Set the audit queue size limit.
527 Format: <int> (must be >=0)
528 Default: 64
530 baycom_epp= [HW,AX25]
531 Format: <io>,<mode>
533 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
534 Format: <io>,<mode>
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
553 no delay (0).
554 Format: integer
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
560 kernel args too.
561 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
562 bttv.tuner=
564 bulk_remove=off [PPC] This parameter disables the use of the pSeries
565 firmware feature for flushing multiple hpte entries
566 at a time.
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
579 trust validation.
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
586 others).
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
595 a single hierarchy
596 - foo isn't visible as an individually mountable
597 subsystem
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.
612 cio_ignore= [S390]
613 See Documentation/s390/CommonIO for details.
614 clk_ignore_unused
615 [CLK]
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.
627 [Deprecated]
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
634 Format: <string>
635 Override the default clocksource and use the clocksource
636 with the name specified.
637 Some clocksource names to choose from, depending on
638 the platform:
639 [all] jiffies (this is the base, fallback clocksource)
640 [ACPI] acpi_pm
641 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
642 pxa_timer,timer3,32k_counter,timer0_1
643 [AVR32] avr32
644 [X86-32] pit,hpet,tsc;
645 scx200_hrt on Geode; cyclone on IBM x440
646 [MIPS] MIPS
647 [PARISC] cr16
648 [S390] tod
649 [SH] SuperH
650 [SPARC64] tick
651 [X86-64] hpet,tsc
653 clearcpuid=BITNUM [X86]
654 Disable CPUID feature X for the kernel. See
655 arch/x86/include/asm/cpufeature.h for the valid bit
656 numbers. Note the Linux specific bits are not necessarily
657 stable over kernel options, but the vendor specific
658 ones should be.
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
664 some critical bits.
666 cma=nn[MG]@[start[MG][-end[MG]]]
667 [ARM,X86,KNL]
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
679 a hypervisor.
680 Default: yes
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
687 in an oops report.
688 Range: 0 - 8192
689 Default: 64
691 com20020= [HW,NET] ARCnet - COM20020 chipset
692 Format:
693 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
695 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
696 Format: <io>[,<irq>]
698 com90xx= [HW,NET]
699 ARCnet - COM90xx chipset (memory-mapped buffers)
700 Format: <io>[,<irq>[,<memstart>]]
702 condev= [HW,S390] console device
703 conmode=
705 console= [KNL] Output console device and options.
707 tty<n> Use the virtual console device <n>.
709 ttyS<n>[,options]
710 ttyUSB0[,options]
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
718 information. See
719 Documentation/networking/netconsole.txt for an
720 alternative.
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
741 console=brl,ttyS0
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.
748 coredump_filter=
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
756 cpu_init_udelay=N
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.
760 Default: 10000
762 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
763 Format:
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
786 available.
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.
803 cs89x0_dma= [HW,NET]
804 Format: <dma>
806 cs89x0_media= [HW,NET]
807 Format: { rj45 | aui | bnc }
809 dasd= [HW,NET]
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).
823 debug_locks_verbose=
824 [KNL] verbose self-tests
825 Format=<0|1>
826 Print debugging info while doing the locking API
827 self-tests.
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
834 no_debug_objects
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.
856 debug_pagealloc=
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.
871 default_hugepagesz=
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
877 if not specified.
879 dhash_entries= [KNL]
880 Set number of hash buckets for dentry cache.
882 disable= [IPV6]
883 See Documentation/networking/ipv6.txt.
885 disable_cpu_apicid= [X86,APIC,SMP]
886 Format: <int>
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
892 INIT from AP to BSP.
894 disable_ddw [PPC/PSERIES]
895 Disable Dynamic DMA Window support. Use this if
896 to workaround buggy firmware.
898 disable_ipv6= [IPV6]
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.
953 dscc4.setup= [NET]
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.
964 eagerfpu= [X86]
965 on enable eager fpu restore
966 off disable eager fpu restore
967 auto selects the default scheme, which automatically
968 enables eagerfpu restore for xsaveopt.
970 module.async_probe [KNL]
971 Enable asynchronous probe on this module.
973 early_ioremap_debug [KNL]
974 Enable debug messages in early_ioremap support. This
975 is useful for tracking down temporary early mappings
976 which are not unmapped.
978 earlycon= [KNL] Output early console device and options.
980 When used with no options, the early console is
981 determined by the stdout-path property in device
982 tree's chosen node.
984 cdns,<addr>
985 Start an early, polled-mode console on a cadence serial
986 port at the specified address. The cadence serial port
987 must already be setup and configured. Options are not
988 yet supported.
990 uart[8250],io,<addr>[,options]
991 uart[8250],mmio,<addr>[,options]
992 uart[8250],mmio32,<addr>[,options]
993 uart[8250],mmio32be,<addr>[,options]
994 uart[8250],0x<addr>[,options]
995 Start an early, polled-mode console on the 8250/16550
996 UART at the specified I/O port or MMIO address.
997 MMIO inter-register address stride is either 8-bit
998 (mmio) or 32-bit (mmio32 or mmio32be).
999 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1000 to be equivalent to 'mmio'. 'options' are specified
1001 in the same format described for "console=ttyS<n>"; if
1002 unspecified, the h/w is not initialized.
1004 pl011,<addr>
1005 Start an early, polled-mode console on a pl011 serial
1006 port at the specified address. The pl011 serial port
1007 must already be setup and configured. Options are not
1008 yet supported.
1010 msm_serial,<addr>
1011 Start an early, polled-mode console on an msm serial
1012 port at the specified address. The serial port
1013 must already be setup and configured. Options are not
1014 yet supported.
1016 msm_serial_dm,<addr>
1017 Start an early, polled-mode console on an msm serial
1018 dm port at the specified address. The serial port
1019 must already be setup and configured. Options are not
1020 yet supported.
1022 smh Use ARM semihosting calls for early console.
1024 s3c2410,<addr>
1025 s3c2412,<addr>
1026 s3c2440,<addr>
1027 s3c6400,<addr>
1028 s5pv210,<addr>
1029 exynos4210,<addr>
1030 Use early console provided by serial driver available
1031 on Samsung SoCs, requires selecting proper type and
1032 a correct base address of the selected UART port. The
1033 serial port must already be setup and configured.
1034 Options are not yet supported.
1036 lpuart,<addr>
1037 lpuart32,<addr>
1038 Use early console provided by Freescale LP UART driver
1039 found on Freescale Vybrid and QorIQ LS1021A processors.
1040 A valid base address must be provided, and the serial
1041 port must already be setup and configured.
1043 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1044 earlyprintk=vga
1045 earlyprintk=efi
1046 earlyprintk=xen
1047 earlyprintk=serial[,ttySn[,baudrate]]
1048 earlyprintk=serial[,0x...[,baudrate]]
1049 earlyprintk=ttySn[,baudrate]
1050 earlyprintk=dbgp[debugController#]
1051 earlyprintk=pciserial,bus:device.function[,baudrate]
1053 earlyprintk is useful when the kernel crashes before
1054 the normal console is initialized. It is not enabled by
1055 default because it has some cosmetic problems.
1057 Append ",keep" to not disable it when the real console
1058 takes over.
1060 Only one of vga, efi, serial, or usb debug port can
1061 be used at a time.
1063 Currently only ttyS0 and ttyS1 may be specified by
1064 name. Other I/O ports may be explicitly specified
1065 on some architectures (x86 and arm at least) by
1066 replacing ttySn with an I/O port address, like this:
1067 earlyprintk=serial,0x1008,115200
1068 You can find the port for a given device in
1069 /proc/tty/driver/serial:
1070 2: uart:ST16650V2 port:00001008 irq:18 ...
1072 Interaction with the standard serial driver is not
1073 very good.
1075 The VGA and EFI output is eventually overwritten by
1076 the real console.
1078 The xen output can only be used by Xen PV guests.
1080 edac_report= [HW,EDAC] Control how to report EDAC event
1081 Format: {"on" | "off" | "force"}
1082 on: enable EDAC to report H/W event. May be overridden
1083 by other higher priority error reporting module.
1084 off: disable H/W event reporting through EDAC.
1085 force: enforce the use of EDAC to report H/W event.
1086 default: on.
1088 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1089 ekgdboc=kbd
1091 This is designed to be used in conjunction with
1092 the boot argument: earlyprintk=vga
1094 edd= [EDD]
1095 Format: {"off" | "on" | "skip[mbr]"}
1097 efi= [EFI]
1098 Format: { "old_map", "nochunk", "noruntime", "debug" }
1099 old_map [X86-64]: switch to the old ioremap-based EFI
1100 runtime services mapping. 32-bit still uses this one by
1101 default.
1102 nochunk: disable reading files in "chunks" in the EFI
1103 boot stub, as chunking can cause problems with some
1104 firmware implementations.
1105 noruntime : disable EFI runtime services support
1106 debug: enable misc debug output
1108 efi_no_storage_paranoia [EFI; X86]
1109 Using this parameter you can use more than 50% of
1110 your efi variable storage. Use this parameter only if
1111 you are really sure that your UEFI does sane gc and
1112 fulfills the spec otherwise your board may brick.
1114 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1115 Add arbitrary attribute to specific memory range by
1116 updating original EFI memory map.
1117 Region of memory which aa attribute is added to is
1118 from ss to ss+nn.
1119 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1120 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1121 attribute is added to range 0x100000000-0x180000000 and
1122 0x10a0000000-0x1120000000.
1124 Using this parameter you can do debugging of EFI memmap
1125 related feature. For example, you can do debugging of
1126 Address Range Mirroring feature even if your box
1127 doesn't support it.
1129 eisa_irq_edge= [PARISC,HW]
1130 See header of drivers/parisc/eisa.c.
1132 elanfreq= [X86-32]
1133 See comment before function elanfreq_setup() in
1134 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1136 elevator= [IOSCHED]
1137 Format: {"cfq" | "deadline" | "noop"}
1138 See Documentation/block/cfq-iosched.txt and
1139 Documentation/block/deadline-iosched.txt for details.
1141 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1142 Specifies physical address of start of kernel core
1143 image elf header and optionally the size. Generally
1144 kexec loader will pass this option to capture kernel.
1145 See Documentation/kdump/kdump.txt for details.
1147 enable_mtrr_cleanup [X86]
1148 The kernel tries to adjust MTRR layout from continuous
1149 to discrete, to make X server driver able to add WB
1150 entry later. This parameter enables that.
1152 enable_timer_pin_1 [X86]
1153 Enable PIN 1 of APIC timer
1154 Can be useful to work around chipset bugs
1155 (in particular on some ATI chipsets).
1156 The kernel tries to set a reasonable default.
1158 enforcing [SELINUX] Set initial enforcing status.
1159 Format: {"0" | "1"}
1160 See security/selinux/Kconfig help text.
1161 0 -- permissive (log only, no denials).
1162 1 -- enforcing (deny and log).
1163 Default value is 0.
1164 Value can be changed at runtime via /selinux/enforce.
1166 erst_disable [ACPI]
1167 Disable Error Record Serialization Table (ERST)
1168 support.
1170 ether= [HW,NET] Ethernet cards parameters
1171 This option is obsoleted by the "netdev=" option, which
1172 has equivalent usage. See its documentation for details.
1174 evm= [EVM]
1175 Format: { "fix" }
1176 Permit 'security.evm' to be updated regardless of
1177 current integrity status.
1179 failslab=
1180 fail_page_alloc=
1181 fail_make_request=[KNL]
1182 General fault injection mechanism.
1183 Format: <interval>,<probability>,<space>,<times>
1184 See also Documentation/fault-injection/.
1186 floppy= [HW]
1187 See Documentation/blockdev/floppy.txt.
1189 force_pal_cache_flush
1190 [IA-64] Avoid check_sal_cache_flush which may hang on
1191 buggy SAL_CACHE_FLUSH implementations. Using this
1192 parameter will force ia64_sal_cache_flush to call
1193 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1195 forcepae [X86-32]
1196 Forcefully enable Physical Address Extension (PAE).
1197 Many Pentium M systems disable PAE but may have a
1198 functionally usable PAE implementation.
1199 Warning: use of this parameter will taint the kernel
1200 and may cause unknown problems.
1202 ftrace=[tracer]
1203 [FTRACE] will set and start the specified tracer
1204 as early as possible in order to facilitate early
1205 boot debugging.
1207 ftrace_dump_on_oops[=orig_cpu]
1208 [FTRACE] will dump the trace buffers on oops.
1209 If no parameter is passed, ftrace will dump
1210 buffers of all CPUs, but if you pass orig_cpu, it will
1211 dump only the buffer of the CPU that triggered the
1212 oops.
1214 ftrace_filter=[function-list]
1215 [FTRACE] Limit the functions traced by the function
1216 tracer at boot up. function-list is a comma separated
1217 list of functions. This list can be changed at run
1218 time by the set_ftrace_filter file in the debugfs
1219 tracing directory.
1221 ftrace_notrace=[function-list]
1222 [FTRACE] Do not trace the functions specified in
1223 function-list. This list can be changed at run time
1224 by the set_ftrace_notrace file in the debugfs
1225 tracing directory.
1227 ftrace_graph_filter=[function-list]
1228 [FTRACE] Limit the top level callers functions traced
1229 by the function graph tracer at boot up.
1230 function-list is a comma separated list of functions
1231 that can be changed at run time by the
1232 set_graph_function file in the debugfs tracing directory.
1234 ftrace_graph_notrace=[function-list]
1235 [FTRACE] Do not trace from the functions specified in
1236 function-list. This list is a comma separated list of
1237 functions that can be changed at run time by the
1238 set_graph_notrace file in the debugfs tracing directory.
1240 gamecon.map[2|3]=
1241 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1242 support via parallel port (up to 5 devices per port)
1243 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1244 See also Documentation/input/joystick-parport.txt
1246 gamma= [HW,DRM]
1248 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1249 Format: off | on
1250 default: on
1252 gcov_persist= [GCOV] When non-zero (default), profiling data for
1253 kernel modules is saved and remains accessible via
1254 debugfs, even when the module is unloaded/reloaded.
1255 When zero, profiling data is discarded and associated
1256 debugfs files are removed at module unload time.
1258 gpt [EFI] Forces disk with valid GPT signature but
1259 invalid Protective MBR to be treated as GPT. If the
1260 primary GPT is corrupted, it enables the backup/alternate
1261 GPT to be used instead.
1263 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1264 the "Enable 0" bit of the configuration register.
1265 Format: 0 | 1
1266 Default: 0
1267 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1268 the "Enable 0" bit of the configuration register.
1269 Format: 0 | 1
1270 Default: 0
1271 grcan.select= [HW] Select which physical interface to use.
1272 Format: 0 | 1
1273 Default: 0
1274 grcan.txsize= [HW] Sets the size of the tx buffer.
1275 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1276 Default: 1024
1277 grcan.rxsize= [HW] Sets the size of the rx buffer.
1278 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1279 Default: 1024
1281 hardlockup_all_cpu_backtrace=
1282 [KNL] Should the hard-lockup detector generate
1283 backtraces on all cpus.
1284 Format: <integer>
1286 hashdist= [KNL,NUMA] Large hashes allocated during boot
1287 are distributed across NUMA nodes. Defaults on
1288 for 64-bit NUMA, off otherwise.
1289 Format: 0 | 1 (for off | on)
1291 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1293 hd= [EIDE] (E)IDE hard drive subsystem geometry
1294 Format: <cyl>,<head>,<sect>
1296 hest_disable [ACPI]
1297 Disable Hardware Error Source Table (HEST) support;
1298 corresponding firmware-first mode error processing
1299 logic will be disabled.
1301 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1302 size of <nn>. This works even on boxes that have no
1303 highmem otherwise. This also works to reduce highmem
1304 size on bigger boxes.
1306 highres= [KNL] Enable/disable high resolution timer mode.
1307 Valid parameters: "on", "off"
1308 Default: "on"
1310 hisax= [HW,ISDN]
1311 See Documentation/isdn/README.HiSax.
1313 hlt [BUGS=ARM,SH]
1315 hpet= [X86-32,HPET] option to control HPET usage
1316 Format: { enable (default) | disable | force |
1317 verbose }
1318 disable: disable HPET and use PIT instead
1319 force: allow force enabled of undocumented chips (ICH4,
1320 VIA, nVidia)
1321 verbose: show contents of HPET registers during setup
1323 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1324 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1326 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1327 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1328 On x86-64 and powerpc, this option can be specified
1329 multiple times interleaved with hugepages= to reserve
1330 huge pages of different sizes. Valid pages sizes on
1331 x86-64 are 2M (when the CPU supports "pse") and 1G
1332 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1334 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1335 terminal devices. Valid values: 0..8
1336 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1337 If specified, z/VM IUCV HVC accepts connections
1338 from listed z/VM user IDs only.
1340 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1341 hardware thread id mappings.
1342 Format: <cpu>:<hwthread>
1344 keep_bootcon [KNL]
1345 Do not unregister boot console at start. This is only
1346 useful for debugging when something happens in the window
1347 between unregistering the boot console and initializing
1348 the real console.
1350 i2c_bus= [HW] Override the default board specific I2C bus speed
1351 or register an additional I2C bus that is not
1352 registered from board initialization code.
1353 Format:
1354 <bus_id>,<clkrate>
1356 i8042.debug [HW] Toggle i8042 debug mode
1357 i8042.unmask_kbd_data
1358 [HW] Enable printing of interrupt data from the KBD port
1359 (disabled by default, and as a pre-condition
1360 requires that i8042.debug=1 be enabled)
1361 i8042.direct [HW] Put keyboard port into non-translated mode
1362 i8042.dumbkbd [HW] Pretend that controller can only read data from
1363 keyboard and cannot control its state
1364 (Don't attempt to blink the leds)
1365 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1366 i8042.nokbd [HW] Don't check/create keyboard port
1367 i8042.noloop [HW] Disable the AUX Loopback command while probing
1368 for the AUX port
1369 i8042.nomux [HW] Don't check presence of an active multiplexing
1370 controller
1371 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1372 controllers
1373 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1374 i8042.reset [HW] Reset the controller during init and cleanup
1375 i8042.unlock [HW] Unlock (ignore) the keylock
1376 i8042.kbdreset [HW] Reset device connected to KBD port
1378 i810= [HW,DRM]
1380 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1381 indicates that the driver is running on unsupported
1382 hardware.
1383 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1384 does not match list of supported models.
1385 i8k.power_status
1386 [HW] Report power status in /proc/i8k
1387 (disabled by default)
1388 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1389 capability is set.
1391 i915.invert_brightness=
1392 [DRM] Invert the sense of the variable that is used to
1393 set the brightness of the panel backlight. Normally a
1394 brightness value of 0 indicates backlight switched off,
1395 and the maximum of the brightness value sets the backlight
1396 to maximum brightness. If this parameter is set to 0
1397 (default) and the machine requires it, or this parameter
1398 is set to 1, a brightness value of 0 sets the backlight
1399 to maximum brightness, and the maximum of the brightness
1400 value switches the backlight off.
1401 -1 -- never invert brightness
1402 0 -- machine default
1403 1 -- force brightness inversion
1405 icn= [HW,ISDN]
1406 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1408 ide-core.nodma= [HW] (E)IDE subsystem
1409 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1410 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1411 .cdrom .chs .ignore_cable are additional options
1412 See Documentation/ide/ide.txt.
1414 ide-generic.probe-mask= [HW] (E)IDE subsystem
1415 Format: <int>
1416 Probe mask for legacy ISA IDE ports. Depending on
1417 platform up to 6 ports are supported, enabled by
1418 setting corresponding bits in the mask to 1. The
1419 default value is 0x0, which has a special meaning.
1420 On systems that have PCI, it triggers scanning the
1421 PCI bus for the first and the second port, which
1422 are then probed. On systems without PCI the value
1423 of 0x0 enables probing the two first ports as if it
1424 was 0x3.
1426 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1427 Claim all unknown PCI IDE storage controllers.
1429 idle= [X86]
1430 Format: idle=poll, idle=halt, idle=nomwait
1431 Poll forces a polling idle loop that can slightly
1432 improve the performance of waking up a idle CPU, but
1433 will use a lot of power and make the system run hot.
1434 Not recommended.
1435 idle=halt: Halt is forced to be used for CPU idle.
1436 In such case C2/C3 won't be used again.
1437 idle=nomwait: Disable mwait for CPU C-states
1439 ignore_loglevel [KNL]
1440 Ignore loglevel setting - this will print /all/
1441 kernel messages to the console. Useful for debugging.
1442 We also add it as printk module parameter, so users
1443 could change it dynamically, usually by
1444 /sys/module/printk/parameters/ignore_loglevel.
1446 ihash_entries= [KNL]
1447 Set number of hash buckets for inode cache.
1449 ima_appraise= [IMA] appraise integrity measurements
1450 Format: { "off" | "enforce" | "fix" | "log" }
1451 default: "enforce"
1453 ima_appraise_tcb [IMA]
1454 The builtin appraise policy appraises all files
1455 owned by uid=0.
1457 ima_hash= [IMA]
1458 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1459 | sha512 | ... }
1460 default: "sha1"
1462 The list of supported hash algorithms is defined
1463 in crypto/hash_info.h.
1465 ima_policy= [IMA]
1466 The builtin measurement policy to load during IMA
1467 setup. Specyfing "tcb" as the value, measures all
1468 programs exec'd, files mmap'd for exec, and all files
1469 opened with the read mode bit set by either the
1470 effective uid (euid=0) or uid=0.
1471 Format: "tcb"
1473 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1474 Load a policy which meets the needs of the Trusted
1475 Computing Base. This means IMA will measure all
1476 programs exec'd, files mmap'd for exec, and all files
1477 opened for read by uid=0.
1479 ima_template= [IMA]
1480 Select one of defined IMA measurements template formats.
1481 Formats: { "ima" | "ima-ng" | "ima-sig" }
1482 Default: "ima-ng"
1484 ima_template_fmt=
1485 [IMA] Define a custom template format.
1486 Format: { "field1|...|fieldN" }
1488 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1489 Format: <min_file_size>
1490 Set the minimal file size for using asynchronous hash.
1491 If left unspecified, ahash usage is disabled.
1493 ahash performance varies for different data sizes on
1494 different crypto accelerators. This option can be used
1495 to achieve the best performance for a particular HW.
1497 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1498 Format: <bufsize>
1499 Set hashing buffer size. Default: 4k.
1501 ahash performance varies for different chunk sizes on
1502 different crypto accelerators. This option can be used
1503 to achieve best performance for particular HW.
1505 init= [KNL]
1506 Format: <full_path>
1507 Run specified binary instead of /sbin/init as init
1508 process.
1510 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1511 for working out where the kernel is dying during
1512 startup.
1514 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1515 initcall functions. Useful for debugging built-in
1516 modules and initcalls.
1518 initrd= [BOOT] Specify the location of the initial ramdisk
1520 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1521 Format: <irq>
1523 int_pln_enable [x86] Enable power limit notification interrupt
1525 integrity_audit=[IMA]
1526 Format: { "0" | "1" }
1527 0 -- basic integrity auditing messages. (Default)
1528 1 -- additional integrity auditing messages.
1530 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1531 on
1532 Enable intel iommu driver.
1533 off
1534 Disable intel iommu driver.
1535 igfx_off [Default Off]
1536 By default, gfx is mapped as normal device. If a gfx
1537 device has a dedicated DMAR unit, the DMAR unit is
1538 bypassed by not enabling DMAR with this option. In
1539 this case, gfx device will use physical address for
1540 DMA.
1541 forcedac [x86_64]
1542 With this option iommu will not optimize to look
1543 for io virtual address below 32-bit forcing dual
1544 address cycle on pci bus for cards supporting greater
1545 than 32-bit addressing. The default is to look
1546 for translation below 32-bit and if not available
1547 then look in the higher range.
1548 strict [Default Off]
1549 With this option on every unmap_single operation will
1550 result in a hardware IOTLB flush operation as opposed
1551 to batching them for performance.
1552 sp_off [Default Off]
1553 By default, super page will be supported if Intel IOMMU
1554 has the capability. With this option, super page will
1555 not be supported.
1556 ecs_off [Default Off]
1557 By default, extended context tables will be supported if
1558 the hardware advertises that it has support both for the
1559 extended tables themselves, and also PASID support. With
1560 this option set, extended tables will not be used even
1561 on hardware which claims to support them.
1563 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1564 0 disables intel_idle and fall back on acpi_idle.
1565 1 to 6 specify maximum depth of C-state.
1567 intel_pstate= [X86]
1568 disable
1569 Do not enable intel_pstate as the default
1570 scaling driver for the supported processors
1571 force
1572 Enable intel_pstate on systems that prohibit it by default
1573 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1574 instead of acpi-cpufreq may disable platform features, such
1575 as thermal controls and power capping, that rely on ACPI
1576 P-States information being indicated to OSPM and therefore
1577 should be used with caution. This option does not work with
1578 processors that aren't supported by the intel_pstate driver
1579 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1580 no_hwp
1581 Do not enable hardware P state control (HWP)
1582 if available.
1583 hwp_only
1584 Only load intel_pstate on systems which support
1585 hardware P state control (HWP) if available.
1586 no_acpi
1587 Don't use ACPI processor performance control objects
1588 _PSS and _PPC specified limits.
1590 intremap= [X86-64, Intel-IOMMU]
1591 on enable Interrupt Remapping (default)
1592 off disable Interrupt Remapping
1593 nosid disable Source ID checking
1594 no_x2apic_optout
1595 BIOS x2APIC opt-out request will be ignored
1596 nopost disable Interrupt Posting
1598 iomem= Disable strict checking of access to MMIO memory
1599 strict regions from userspace.
1600 relaxed
1602 iommu= [x86]
1603 off
1604 force
1605 noforce
1606 biomerge
1607 panic
1608 nopanic
1609 merge
1610 nomerge
1611 forcesac
1612 soft
1613 pt [x86, IA-64]
1614 nobypass [PPC/POWERNV]
1615 Disable IOMMU bypass, using IOMMU for PCI devices.
1618 io7= [HW] IO7 for Marvel based alpha systems
1619 See comment before marvel_specify_io7 in
1620 arch/alpha/kernel/core_marvel.c.
1622 io_delay= [X86] I/O delay method
1623 0x80
1624 Standard port 0x80 based delay
1625 0xed
1626 Alternate port 0xed based delay (needed on some systems)
1627 udelay
1628 Simple two microseconds delay
1629 none
1630 No delay
1632 ip= [IP_PNP]
1633 See Documentation/filesystems/nfs/nfsroot.txt.
1635 irqfixup [HW]
1636 When an interrupt is not handled search all handlers
1637 for it. Intended to get systems with badly broken
1638 firmware running.
1640 irqpoll [HW]
1641 When an interrupt is not handled search all handlers
1642 for it. Also check all handlers each timer
1643 interrupt. Intended to get systems with badly broken
1644 firmware running.
1646 isapnp= [ISAPNP]
1647 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1649 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1650 Format:
1651 <cpu number>,...,<cpu number>
1652 or
1653 <cpu number>-<cpu number>
1654 (must be a positive range in ascending order)
1655 or a mixture
1656 <cpu number>,...,<cpu number>-<cpu number>
1658 This option can be used to specify one or more CPUs
1659 to isolate from the general SMP balancing and scheduling
1660 algorithms. You can move a process onto or off an
1661 "isolated" CPU via the CPU affinity syscalls or cpuset.
1662 <cpu number> begins at 0 and the maximum value is
1663 "number of CPUs in system - 1".
1665 This option is the preferred way to isolate CPUs. The
1666 alternative -- manually setting the CPU mask of all
1667 tasks in the system -- can cause problems and
1668 suboptimal load balancer performance.
1670 iucv= [HW,NET]
1672 ivrs_ioapic [HW,X86_64]
1673 Provide an override to the IOAPIC-ID<->DEVICE-ID
1674 mapping provided in the IVRS ACPI table. For
1675 example, to map IOAPIC-ID decimal 10 to
1676 PCI device 00:14.0 write the parameter as:
1677 ivrs_ioapic[10]=00:14.0
1679 ivrs_hpet [HW,X86_64]
1680 Provide an override to the HPET-ID<->DEVICE-ID
1681 mapping provided in the IVRS ACPI table. For
1682 example, to map HPET-ID decimal 0 to
1683 PCI device 00:14.0 write the parameter as:
1684 ivrs_hpet[0]=00:14.0
1686 js= [HW,JOY] Analog joystick
1687 See Documentation/input/joystick.txt.
1689 kaslr/nokaslr [X86]
1690 Enable/disable kernel and module base offset ASLR
1691 (Address Space Layout Randomization) if built into
1692 the kernel. When CONFIG_HIBERNATION is selected,
1693 kASLR is disabled by default. When kASLR is enabled,
1694 hibernation will be disabled.
1696 keepinitrd [HW,ARM]
1698 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1699 specifies the amount of memory usable by the kernel
1700 for non-movable allocations. The requested amount is
1701 spread evenly throughout all nodes in the system. The
1702 remaining memory in each node is used for Movable
1703 pages. In the event, a node is too small to have both
1704 kernelcore and Movable pages, kernelcore pages will
1705 take priority and other nodes will have a larger number
1706 of Movable pages. The Movable zone is used for the
1707 allocation of pages that may be reclaimed or moved
1708 by the page migration subsystem. This means that
1709 HugeTLB pages may not be allocated from this zone.
1710 Note that allocations like PTEs-from-HighMem still
1711 use the HighMem zone if it exists, and the Normal
1712 zone if it does not.
1714 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1715 Format: <Controller#>[,poll interval]
1716 The controller # is the number of the ehci usb debug
1717 port as it is probed via PCI. The poll interval is
1718 optional and is the number seconds in between
1719 each poll cycle to the debug port in case you need
1720 the functionality for interrupting the kernel with
1721 gdb or control-c on the dbgp connection. When
1722 not using this parameter you use sysrq-g to break into
1723 the kernel debugger.
1725 kgdboc= [KGDB,HW] kgdb over consoles.
1726 Requires a tty driver that supports console polling,
1727 or a supported polling keyboard driver (non-usb).
1728 Serial only format: <serial_device>[,baud]
1729 keyboard only format: kbd
1730 keyboard and serial format: kbd,<serial_device>[,baud]
1731 Optional Kernel mode setting:
1732 kms, kbd format: kms,kbd
1733 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1735 kgdbwait [KGDB] Stop kernel execution and enter the
1736 kernel debugger at the earliest opportunity.
1738 kmac= [MIPS] korina ethernet MAC address.
1739 Configure the RouterBoard 532 series on-chip
1740 Ethernet adapter MAC address.
1742 kmemleak= [KNL] Boot-time kmemleak enable/disable
1743 Valid arguments: on, off
1744 Default: on
1745 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1746 the default is off.
1748 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1749 Valid arguments: 0, 1, 2
1750 kmemcheck=0 (disabled)
1751 kmemcheck=1 (enabled)
1752 kmemcheck=2 (one-shot mode)
1753 Default: 2 (one-shot mode)
1755 kstack=N [X86] Print N words from the kernel stack
1756 in oops dumps.
1758 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1759 Default is 0 (don't ignore, but inject #GP)
1761 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1762 KVM MMU at runtime.
1763 Default is 0 (off)
1765 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1766 Default is 1 (enabled)
1768 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1769 for all guests.
1770 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1772 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1773 (virtualized MMU) support on capable Intel chips.
1774 Default is 1 (enabled)
1776 kvm-intel.emulate_invalid_guest_state=
1777 [KVM,Intel] Enable emulation of invalid guest states
1778 Default is 0 (disabled)
1780 kvm-intel.flexpriority=
1781 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1782 Default is 1 (enabled)
1784 kvm-intel.nested=
1785 [KVM,Intel] Enable VMX nesting (nVMX).
1786 Default is 0 (disabled)
1788 kvm-intel.unrestricted_guest=
1789 [KVM,Intel] Disable unrestricted guest feature
1790 (virtualized real and unpaged mode) on capable
1791 Intel chips. Default is 1 (enabled)
1793 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1794 feature (tagged TLBs) on capable Intel chips.
1795 Default is 1 (enabled)
1797 l2cr= [PPC]
1799 l3cr= [PPC]
1801 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1802 disabled it.
1804 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1805 value for LAPIC timer one-shot implementation. Default
1806 back to the programmable timer unit in the LAPIC.
1808 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1809 in C2 power state.
1811 libata.dma= [LIBATA] DMA control
1812 libata.dma=0 Disable all PATA and SATA DMA
1813 libata.dma=1 PATA and SATA Disk DMA only
1814 libata.dma=2 ATAPI (CDROM) DMA only
1815 libata.dma=4 Compact Flash DMA only
1816 Combinations also work, so libata.dma=3 enables DMA
1817 for disks and CDROMs, but not CFs.
1819 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1820 libata.ignore_hpa=0 keep BIOS limits (default)
1821 libata.ignore_hpa=1 ignore limits, using full disk
1823 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1824 when set.
1825 Format: <int>
1827 libata.force= [LIBATA] Force configurations. The format is comma
1828 separated list of "[ID:]VAL" where ID is
1829 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1830 matching port, link or device. Basically, it matches
1831 the ATA ID string printed on console by libata. If
1832 the whole ID part is omitted, the last PORT and DEVICE
1833 values are used. If ID hasn't been specified yet, the
1834 configuration applies to all ports, links and devices.
1836 If only DEVICE is omitted, the parameter applies to
1837 the port and all links and devices behind it. DEVICE
1838 number of 0 either selects the first device or the
1839 first fan-out link behind PMP device. It does not
1840 select the host link. DEVICE number of 15 selects the
1841 host link and device attached to it.
1843 The VAL specifies the configuration to force. As long
1844 as there's no ambiguity shortcut notation is allowed.
1845 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1846 The following configurations can be forced.
1848 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1849 Any ID with matching PORT is used.
1851 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1853 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1854 udma[/][16,25,33,44,66,100,133] notation is also
1855 allowed.
1857 * [no]ncq: Turn on or off NCQ.
1859 * [no]ncqtrim: Turn off queued DSM TRIM.
1861 * nohrst, nosrst, norst: suppress hard, soft
1862 and both resets.
1864 * rstonce: only attempt one reset during
1865 hot-unplug link recovery
1867 * dump_id: dump IDENTIFY data.
1869 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1871 * disable: Disable this device.
1873 If there are multiple matching configurations changing
1874 the same attribute, the last one is used.
1876 memblock=debug [KNL] Enable memblock debug messages.
1878 load_ramdisk= [RAM] List of ramdisks to load from floppy
1879 See Documentation/blockdev/ramdisk.txt.
1881 lockd.nlm_grace_period=P [NFS] Assign grace period.
1882 Format: <integer>
1884 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1885 Format: <integer>
1887 lockd.nlm_timeout=T [NFS] Assign timeout value.
1888 Format: <integer>
1890 lockd.nlm_udpport=M [NFS] Assign UDP port.
1891 Format: <integer>
1893 locktorture.nreaders_stress= [KNL]
1894 Set the number of locking read-acquisition kthreads.
1895 Defaults to being automatically set based on the
1896 number of online CPUs.
1898 locktorture.nwriters_stress= [KNL]
1899 Set the number of locking write-acquisition kthreads.
1901 locktorture.onoff_holdoff= [KNL]
1902 Set time (s) after boot for CPU-hotplug testing.
1904 locktorture.onoff_interval= [KNL]
1905 Set time (s) between CPU-hotplug operations, or
1906 zero to disable CPU-hotplug testing.
1908 locktorture.shuffle_interval= [KNL]
1909 Set task-shuffle interval (jiffies). Shuffling
1910 tasks allows some CPUs to go into dyntick-idle
1911 mode during the locktorture test.
1913 locktorture.shutdown_secs= [KNL]
1914 Set time (s) after boot system shutdown. This
1915 is useful for hands-off automated testing.
1917 locktorture.stat_interval= [KNL]
1918 Time (s) between statistics printk()s.
1920 locktorture.stutter= [KNL]
1921 Time (s) to stutter testing, for example,
1922 specifying five seconds causes the test to run for
1923 five seconds, wait for five seconds, and so on.
1924 This tests the locking primitive's ability to
1925 transition abruptly to and from idle.
1927 locktorture.torture_runnable= [BOOT]
1928 Start locktorture running at boot time.
1930 locktorture.torture_type= [KNL]
1931 Specify the locking implementation to test.
1933 locktorture.verbose= [KNL]
1934 Enable additional printk() statements.
1936 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1937 Format: <irq>
1939 loglevel= All Kernel Messages with a loglevel smaller than the
1940 console loglevel will be printed to the console. It can
1941 also be changed with klogd or other programs. The
1942 loglevels are defined as follows:
1944 0 (KERN_EMERG) system is unusable
1945 1 (KERN_ALERT) action must be taken immediately
1946 2 (KERN_CRIT) critical conditions
1947 3 (KERN_ERR) error conditions
1948 4 (KERN_WARNING) warning conditions
1949 5 (KERN_NOTICE) normal but significant condition
1950 6 (KERN_INFO) informational
1951 7 (KERN_DEBUG) debug-level messages
1953 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1954 in bytes. n must be a power of two and greater
1955 than the minimal size. The minimal size is defined
1956 by LOG_BUF_SHIFT kernel config parameter. There is
1957 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1958 that allows to increase the default size depending on
1959 the number of CPUs. See init/Kconfig for more details.
1961 logo.nologo [FB] Disables display of the built-in Linux logo.
1962 This may be used to provide more screen space for
1963 kernel log messages and is useful when debugging
1964 kernel boot problems.
1966 lp=0 [LP] Specify parallel ports to use, e.g,
1967 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1968 lp=reset first parallel port). 'lp=0' disables the
1969 lp=auto printer driver. 'lp=reset' (which can be
1970 specified in addition to the ports) causes
1971 attached printers to be reset. Using
1972 lp=port1,port2,... specifies the parallel ports
1973 to associate lp devices with, starting with
1974 lp0. A port specification may be 'none' to skip
1975 that lp device, or a parport name such as
1976 'parport0'. Specifying 'lp=auto' instead of a
1977 port specification list means that device IDs
1978 from each port should be examined, to see if
1979 an IEEE 1284-compliant printer is attached; if
1980 so, the driver will manage that printer.
1981 See also header of drivers/char/lp.c.
1983 lpj=n [KNL]
1984 Sets loops_per_jiffy to given constant, thus avoiding
1985 time-consuming boot-time autodetection (up to 250 ms per
1986 CPU). 0 enables autodetection (default). To determine
1987 the correct value for your kernel, boot with normal
1988 autodetection and see what value is printed. Note that
1989 on SMP systems the preset will be applied to all CPUs,
1990 which is likely to cause problems if your CPUs need
1991 significantly divergent settings. An incorrect value
1992 will cause delays in the kernel to be wrong, leading to
1993 unpredictable I/O errors and other breakage. Although
1994 unlikely, in the extreme case this might damage your
1995 hardware.
1997 ltpc= [NET]
1998 Format: <io>,<irq>,<dma>
2000 machvec= [IA-64] Force the use of a particular machine-vector
2001 (machvec) in a generic kernel.
2002 Example: machvec=hpzx1_swiotlb
2004 machtype= [Loongson] Share the same kernel image file between different
2005 yeeloong laptop.
2006 Example: machtype=lemote-yeeloong-2f-7inch
2008 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2009 than or equal to this physical address is ignored.
2011 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2012 should make use of. maxcpus=n : n >= 0 limits the
2013 kernel to using 'n' processors. n=0 is a special case,
2014 it is equivalent to "nosmp", which also disables
2015 the IO APIC.
2017 max_loop= [LOOP] The number of loop block devices that get
2018 (loop.max_loop) unconditionally pre-created at init time. The default
2019 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2020 of statically allocating a predefined number, loop
2021 devices can be requested on-demand with the
2022 /dev/loop-control interface.
2024 mce [X86-32] Machine Check Exception
2026 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2028 md= [HW] RAID subsystems devices and level
2029 See Documentation/md.txt.
2031 mdacon= [MDA]
2032 Format: <first>,<last>
2033 Specifies range of consoles to be captured by the MDA.
2035 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2036 Amount of memory to be used when the kernel is not able
2037 to see the whole system memory or for test.
2038 [X86] Work as limiting max address. Use together
2039 with memmap= to avoid physical address space collisions.
2040 Without memmap= PCI devices could be placed at addresses
2041 belonging to unused RAM.
2043 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2044 memory.
2046 memchunk=nn[KMG]
2047 [KNL,SH] Allow user to override the default size for
2048 per-device physically contiguous DMA buffers.
2050 memmap=exactmap [KNL,X86] Enable setting of an exact
2051 E820 memory map, as specified by the user.
2052 Such memmap=exactmap lines can be constructed based on
2053 BIOS output or other requirements. See the memmap=nn@ss
2054 option description.
2056 memmap=nn[KMG]@ss[KMG]
2057 [KNL] Force usage of a specific region of memory.
2058 Region of memory to be used is from ss to ss+nn.
2060 memmap=nn[KMG]#ss[KMG]
2061 [KNL,ACPI] Mark specific memory as ACPI data.
2062 Region of memory to be marked is from ss to ss+nn.
2064 memmap=nn[KMG]$ss[KMG]
2065 [KNL,ACPI] Mark specific memory as reserved.
2066 Region of memory to be reserved is from ss to ss+nn.
2067 Example: Exclude memory from 0x18690000-0x1869ffff
2068 memmap=64K$0x18690000
2069 or
2070 memmap=0x10000$0x18690000
2072 memmap=nn[KMG]!ss[KMG]
2073 [KNL,X86] Mark specific memory as protected.
2074 Region of memory to be used, from ss to ss+nn.
2075 The memory region may be marked as e820 type 12 (0xc)
2076 and is NVDIMM or ADR memory.
2078 memory_corruption_check=0/1 [X86]
2079 Some BIOSes seem to corrupt the first 64k of
2080 memory when doing things like suspend/resume.
2081 Setting this option will scan the memory
2082 looking for corruption. Enabling this will
2083 both detect corruption and prevent the kernel
2084 from using the memory being corrupted.
2085 However, its intended as a diagnostic tool; if
2086 repeatable BIOS-originated corruption always
2087 affects the same memory, you can use memmap=
2088 to prevent the kernel from using that memory.
2090 memory_corruption_check_size=size [X86]
2091 By default it checks for corruption in the low
2092 64k, making this memory unavailable for normal
2093 use. Use this parameter to scan for
2094 corruption in more or less memory.
2096 memory_corruption_check_period=seconds [X86]
2097 By default it checks for corruption every 60
2098 seconds. Use this parameter to check at some
2099 other rate. 0 disables periodic checking.
2101 memtest= [KNL,X86,ARM] Enable memtest
2102 Format: <integer>
2103 default : 0 <disable>
2104 Specifies the number of memtest passes to be
2105 performed. Each pass selects another test
2106 pattern from a given set of patterns. Memtest
2107 fills the memory with this pattern, validates
2108 memory contents and reserves bad memory
2109 regions that are detected.
2111 meye.*= [HW] Set MotionEye Camera parameters
2112 See Documentation/video4linux/meye.txt.
2114 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2115 Multi-Function General Purpose Timers on AMD Geode
2116 platforms.
2118 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2119 the BIOS has incorrectly applied a workaround. TinyBIOS
2120 version 0.98 is known to be affected, 0.99 fixes the
2121 problem by letting the user disable the workaround.
2123 mga= [HW,DRM]
2125 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2126 physical address is ignored.
2128 mini2440= [ARM,HW,KNL]
2129 Format:[0..2][b][c][t]
2130 Default: "0tb"
2131 MINI2440 configuration specification:
2132 0 - The attached screen is the 3.5" TFT
2133 1 - The attached screen is the 7" TFT
2134 2 - The VGA Shield is attached (1024x768)
2135 Leaving out the screen size parameter will not load
2136 the TFT driver, and the framebuffer will be left
2137 unconfigured.
2138 b - Enable backlight. The TFT backlight pin will be
2139 linked to the kernel VESA blanking code and a GPIO
2140 LED. This parameter is not necessary when using the
2141 VGA shield.
2142 c - Enable the s3c camera interface.
2143 t - Reserved for enabling touchscreen support. The
2144 touchscreen support is not enabled in the mainstream
2145 kernel as of 2.6.30, a preliminary port can be found
2146 in the "bleeding edge" mini2440 support kernel at
2147 http://repo.or.cz/w/linux-2.6/mini2440.git
2149 mminit_loglevel=
2150 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2151 parameter allows control of the logging verbosity for
2152 the additional memory initialisation checks. A value
2153 of 0 disables mminit logging and a level of 4 will
2154 log everything. Information is printed at KERN_DEBUG
2155 so loglevel=8 may also need to be specified.
2157 module.sig_enforce
2158 [KNL] When CONFIG_MODULE_SIG is set, this means that
2159 modules without (valid) signatures will fail to load.
2160 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2161 is always true, so this option does nothing.
2163 mousedev.tap_time=
2164 [MOUSE] Maximum time between finger touching and
2165 leaving touchpad surface for touch to be considered
2166 a tap and be reported as a left button click (for
2167 touchpads working in absolute mode only).
2168 Format: <msecs>
2169 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2170 reporting absolute coordinates, such as tablets
2171 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2172 reporting absolute coordinates, such as tablets
2174 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2175 is similar to kernelcore except it specifies the
2176 amount of memory used for migratable allocations.
2177 If both kernelcore and movablecore is specified,
2178 then kernelcore will be at *least* the specified
2179 value but may be more. If movablecore on its own
2180 is specified, the administrator must be careful
2181 that the amount of memory usable for all allocations
2182 is not too small.
2184 movable_node [KNL,X86] Boot-time switch to enable the effects
2185 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2187 MTD_Partition= [MTD]
2188 Format: <name>,<region-number>,<size>,<offset>
2190 MTD_Region= [MTD] Format:
2191 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2193 mtdparts= [MTD]
2194 See drivers/mtd/cmdlinepart.c.
2196 multitce=off [PPC] This parameter disables the use of the pSeries
2197 firmware feature for updating multiple TCE entries
2198 at a time.
2200 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2202 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2204 boundary - index of last SLC block on Flex-OneNAND.
2205 The remaining blocks are configured as MLC blocks.
2206 lock - Configure if Flex-OneNAND boundary should be locked.
2207 Once locked, the boundary cannot be changed.
2208 1 indicates lock status, 0 indicates unlock status.
2210 mtdset= [ARM]
2211 ARM/S3C2412 JIVE boot control
2213 See arch/arm/mach-s3c2412/mach-jive.c
2215 mtouchusb.raw_coordinates=
2216 [HW] Make the MicroTouch USB driver use raw coordinates
2217 ('y', default) or cooked coordinates ('n')
2219 mtrr_chunk_size=nn[KMG] [X86]
2220 used for mtrr cleanup. It is largest continuous chunk
2221 that could hold holes aka. UC entries.
2223 mtrr_gran_size=nn[KMG] [X86]
2224 Used for mtrr cleanup. It is granularity of mtrr block.
2225 Default is 1.
2226 Large value could prevent small alignment from
2227 using up MTRRs.
2229 mtrr_spare_reg_nr=n [X86]
2230 Format: <integer>
2231 Range: 0,7 : spare reg number
2232 Default : 1
2233 Used for mtrr cleanup. It is spare mtrr entries number.
2234 Set to 2 or more if your graphical card needs more.
2236 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2238 netdev= [NET] Network devices parameters
2239 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2240 Note that mem_start is often overloaded to mean
2241 something different and driver-specific.
2242 This usage is only documented in each driver source
2243 file if at all.
2245 nf_conntrack.acct=
2246 [NETFILTER] Enable connection tracking flow accounting
2247 0 to disable accounting
2248 1 to enable accounting
2249 Default value is 0.
2251 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2252 See Documentation/filesystems/nfs/nfsroot.txt.
2254 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2255 See Documentation/filesystems/nfs/nfsroot.txt.
2257 nfsrootdebug [NFS] enable nfsroot debugging messages.
2258 See Documentation/filesystems/nfs/nfsroot.txt.
2260 nfs.callback_tcpport=
2261 [NFS] set the TCP port on which the NFSv4 callback
2262 channel should listen.
2264 nfs.cache_getent=
2265 [NFS] sets the pathname to the program which is used
2266 to update the NFS client cache entries.
2268 nfs.cache_getent_timeout=
2269 [NFS] sets the timeout after which an attempt to
2270 update a cache entry is deemed to have failed.
2272 nfs.idmap_cache_timeout=
2273 [NFS] set the maximum lifetime for idmapper cache
2274 entries.
2276 nfs.enable_ino64=
2277 [NFS] enable 64-bit inode numbers.
2278 If zero, the NFS client will fake up a 32-bit inode
2279 number for the readdir() and stat() syscalls instead
2280 of returning the full 64-bit number.
2281 The default is to return 64-bit inode numbers.
2283 nfs.max_session_slots=
2284 [NFSv4.1] Sets the maximum number of session slots
2285 the client will attempt to negotiate with the server.
2286 This limits the number of simultaneous RPC requests
2287 that the client can send to the NFSv4.1 server.
2288 Note that there is little point in setting this
2289 value higher than the max_tcp_slot_table_limit.
2291 nfs.nfs4_disable_idmapping=
2292 [NFSv4] When set to the default of '1', this option
2293 ensures that both the RPC level authentication
2294 scheme and the NFS level operations agree to use
2295 numeric uids/gids if the mount is using the
2296 'sec=sys' security flavour. In effect it is
2297 disabling idmapping, which can make migration from
2298 legacy NFSv2/v3 systems to NFSv4 easier.
2299 Servers that do not support this mode of operation
2300 will be autodetected by the client, and it will fall
2301 back to using the idmapper.
2302 To turn off this behaviour, set the value to '0'.
2303 nfs.nfs4_unique_id=
2304 [NFS4] Specify an additional fixed unique ident-
2305 ification string that NFSv4 clients can insert into
2306 their nfs_client_id4 string. This is typically a
2307 UUID that is generated at system install time.
2309 nfs.send_implementation_id =
2310 [NFSv4.1] Send client implementation identification
2311 information in exchange_id requests.
2312 If zero, no implementation identification information
2313 will be sent.
2314 The default is to send the implementation identification
2315 information.
2317 nfs.recover_lost_locks =
2318 [NFSv4] Attempt to recover locks that were lost due
2319 to a lease timeout on the server. Please note that
2320 doing this risks data corruption, since there are
2321 no guarantees that the file will remain unchanged
2322 after the locks are lost.
2323 If you want to enable the kernel legacy behaviour of
2324 attempting to recover these locks, then set this
2325 parameter to '1'.
2326 The default parameter value of '0' causes the kernel
2327 not to attempt recovery of lost locks.
2329 nfs4.layoutstats_timer =
2330 [NFSv4.2] Change the rate at which the kernel sends
2331 layoutstats to the pNFS metadata server.
2333 Setting this to value to 0 causes the kernel to use
2334 whatever value is the default set by the layout
2335 driver. A non-zero value sets the minimum interval
2336 in seconds between layoutstats transmissions.
2338 nfsd.nfs4_disable_idmapping=
2339 [NFSv4] When set to the default of '1', the NFSv4
2340 server will return only numeric uids and gids to
2341 clients using auth_sys, and will accept numeric uids
2342 and gids from such clients. This is intended to ease
2343 migration from NFSv2/v3.
2345 objlayoutdriver.osd_login_prog=
2346 [NFS] [OBJLAYOUT] sets the pathname to the program which
2347 is used to automatically discover and login into new
2348 osd-targets. Please see:
2349 Documentation/filesystems/pnfs.txt for more explanations
2351 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2352 when a NMI is triggered.
2353 Format: [state][,regs][,debounce][,die]
2355 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2356 Format: [panic,][nopanic,][num]
2357 Valid num: 0 or 1
2358 0 - turn hardlockup detector in nmi_watchdog off
2359 1 - turn hardlockup detector in nmi_watchdog on
2360 When panic is specified, panic when an NMI watchdog
2361 timeout occurs (or 'nopanic' to override the opposite
2362 default). To disable both hard and soft lockup detectors,
2363 please see 'nowatchdog'.
2364 This is useful when you use a panic=... timeout and
2365 need the box quickly up again.
2367 netpoll.carrier_timeout=
2368 [NET] Specifies amount of time (in seconds) that
2369 netpoll should wait for a carrier. By default netpoll
2370 waits 4 seconds.
2372 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2373 emulation library even if a 387 maths coprocessor
2374 is present.
2376 no_console_suspend
2377 [HW] Never suspend the console
2378 Disable suspending of consoles during suspend and
2379 hibernate operations. Once disabled, debugging
2380 messages can reach various consoles while the rest
2381 of the system is being put to sleep (ie, while
2382 debugging driver suspend/resume hooks). This may
2383 not work reliably with all consoles, but is known
2384 to work with serial and VGA consoles.
2385 To facilitate more flexible debugging, we also add
2386 console_suspend, a printk module parameter to control
2387 it. Users could use console_suspend (usually
2388 /sys/module/printk/parameters/console_suspend) to
2389 turn on/off it dynamically.
2391 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2392 caches in the slab allocator. Saves per-node memory,
2393 but will impact performance.
2395 noalign [KNL,ARM]
2397 noapic [SMP,APIC] Tells the kernel to not make use of any
2398 IOAPICs that may be present in the system.
2400 noautogroup Disable scheduler automatic task group creation.
2402 nobats [PPC] Do not use BATs for mapping kernel lowmem
2403 on "Classic" PPC cores.
2405 nocache [ARM]
2407 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2409 nodelayacct [KNL] Disable per-task delay accounting
2411 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2413 nodsp [SH] Disable hardware DSP at boot time.
2415 noefi Disable EFI runtime services support.
2417 noexec [IA-64]
2419 noexec [X86]
2420 On X86-32 available only on PAE configured kernels.
2421 noexec=on: enable non-executable mappings (default)
2422 noexec=off: disable non-executable mappings
2424 nosmap [X86]
2425 Disable SMAP (Supervisor Mode Access Prevention)
2426 even if it is supported by processor.
2428 nosmep [X86]
2429 Disable SMEP (Supervisor Mode Execution Prevention)
2430 even if it is supported by processor.
2432 noexec32 [X86-64]
2433 This affects only 32-bit executables.
2434 noexec32=on: enable non-executable mappings (default)
2435 read doesn't imply executable mappings
2436 noexec32=off: disable non-executable mappings
2437 read implies executable mappings
2439 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2441 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2442 register save and restore. The kernel will only save
2443 legacy floating-point registers on task switch.
2445 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2447 noxsave [BUGS=X86] Disables x86 extended register state save
2448 and restore using xsave. The kernel will fallback to
2449 enabling legacy floating-point and sse state.
2451 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2452 register states. The kernel will fall back to use
2453 xsave to save the states. By using this parameter,
2454 performance of saving the states is degraded because
2455 xsave doesn't support modified optimization while
2456 xsaveopt supports it on xsaveopt enabled systems.
2458 noxsaves [X86] Disables xsaves and xrstors used in saving and
2459 restoring x86 extended register state in compacted
2460 form of xsave area. The kernel will fall back to use
2461 xsaveopt and xrstor to save and restore the states
2462 in standard form of xsave area. By using this
2463 parameter, xsave area per process might occupy more
2464 memory on xsaves enabled systems.
2466 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2467 wfi(ARM) instruction doesn't work correctly and not to
2468 use it. This is also useful when using JTAG debugger.
2470 no_file_caps Tells the kernel not to honor file capabilities. The
2471 only way then for a file to be executed with privilege
2472 is to be setuid root or executed by root.
2474 nohalt [IA-64] Tells the kernel not to use the power saving
2475 function PAL_HALT_LIGHT when idle. This increases
2476 power-consumption. On the positive side, it reduces
2477 interrupt wake-up latency, which may improve performance
2478 in certain environments such as networked servers or
2479 real-time systems.
2481 nohibernate [HIBERNATION] Disable hibernation and resume.
2483 nohz= [KNL] Boottime enable/disable dynamic ticks
2484 Valid arguments: on, off
2485 Default: on
2487 nohz_full= [KNL,BOOT]
2488 In kernels built with CONFIG_NO_HZ_FULL=y, set
2489 the specified list of CPUs whose tick will be stopped
2490 whenever possible. The boot CPU will be forced outside
2491 the range to maintain the timekeeping.
2492 The CPUs in this range must also be included in the
2493 rcu_nocbs= set.
2495 noiotrap [SH] Disables trapped I/O port accesses.
2497 noirqdebug [X86-32] Disables the code which attempts to detect and
2498 disable unhandled interrupt sources.
2500 no_timer_check [X86,APIC] Disables the code which tests for
2501 broken timer IRQ sources.
2503 noisapnp [ISAPNP] Disables ISA PnP code.
2505 noinitrd [RAM] Tells the kernel not to load any configured
2506 initial RAM disk.
2508 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2509 remapping.
2510 [Deprecated - use intremap=off]
2512 nointroute [IA-64]
2514 nojitter [IA-64] Disables jitter checking for ITC timers.
2516 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2518 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2519 fault handling.
2521 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2522 steal time is computed, but won't influence scheduler
2523 behaviour
2525 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2527 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2529 noltlbs [PPC] Do not use large page/tlb entries for kernel
2530 lowmem mapping on PPC40x.
2532 nomca [IA-64] Disable machine check abort handling
2534 nomce [X86-32] Disable Machine Check Exception
2536 nomfgpt [X86-32] Disable Multi-Function General Purpose
2537 Timer usage (for AMD Geode machines).
2539 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2540 shutdown the other cpus. Instead use the REBOOT_VECTOR
2541 irq.
2543 nomodule Disable module load
2545 nopat [X86] Disable PAT (page attribute table extension of
2546 pagetables) support.
2548 norandmaps Don't use address space randomization. Equivalent to
2549 echo 0 > /proc/sys/kernel/randomize_va_space
2551 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2553 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2554 with UP alternatives
2556 nordrand [X86] Disable kernel use of the RDRAND and
2557 RDSEED instructions even if they are supported
2558 by the processor. RDRAND and RDSEED are still
2559 available to user space applications.
2561 noresume [SWSUSP] Disables resume and restores original swap
2562 space.
2564 no-scroll [VGA] Disables scrollback.
2565 This is required for the Braillex ib80-piezo Braille
2566 reader made by F.H. Papenmeier (Germany).
2568 nosbagart [IA-64]
2570 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2572 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2573 and disable the IO APIC. legacy for "maxcpus=0".
2575 nosoftlockup [KNL] Disable the soft-lockup detector.
2577 nosync [HW,M68K] Disables sync negotiation for all devices.
2579 notsc [BUGS=X86-32] Disable Time Stamp Counter
2581 nousb [USB] Disable the USB subsystem
2583 nowatchdog [KNL] Disable both lockup detectors, i.e.
2584 soft-lockup and NMI watchdog (hard-lockup).
2586 nowb [ARM]
2588 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2590 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2591 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2592 Some features depend on CPU0. Known dependencies are:
2593 1. Resume from suspend/hibernate depends on CPU0.
2594 Suspend/hibernate will fail if CPU0 is offline and you
2595 need to online CPU0 before suspend/hibernate.
2596 2. PIC interrupts also depend on CPU0. CPU0 can't be
2597 removed if a PIC interrupt is detected.
2598 It's said poweroff/reboot may depend on CPU0 on some
2599 machines although I haven't seen such issues so far
2600 after CPU0 is offline on a few tested machines.
2601 If the dependencies are under your control, you can
2602 turn on cpu0_hotplug.
2604 nptcg= [IA-64] Override max number of concurrent global TLB
2605 purges which is reported from either PAL_VM_SUMMARY or
2606 SAL PALO.
2608 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2609 could support. nr_cpus=n : n >= 1 limits the kernel to
2610 supporting 'n' processors. Later in runtime you can not
2611 use hotplug cpu feature to put more cpu back to online.
2612 just like you compile the kernel NR_CPUS=n
2614 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2616 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2617 Allowed values are enable and disable
2619 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2620 one of ['zone', 'node', 'default'] can be specified
2621 This can be set from sysctl after boot.
2622 See Documentation/sysctl/vm.txt for details.
2624 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2625 See Documentation/debugging-via-ohci1394.txt for more
2626 info.
2628 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2629 Rather than timing out after 20 ms if an EC
2630 command is not properly ACKed, override the length
2631 of the timeout. We have interrupts disabled while
2632 waiting for the ACK, so if this is set too high
2633 interrupts *may* be lost!
2635 omap_mux= [OMAP] Override bootloader pin multiplexing.
2636 Format: <mux_mode0.mode_name=value>...
2637 For example, to override I2C bus2:
2638 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2640 oprofile.timer= [HW]
2641 Use timer interrupt instead of performance counters
2643 oprofile.cpu_type= Force an oprofile cpu type
2644 This might be useful if you have an older oprofile
2645 userland or if you want common events.
2646 Format: { arch_perfmon }
2647 arch_perfmon: [X86] Force use of architectural
2648 perfmon on Intel CPUs instead of the
2649 CPU specific event set.
2650 timer: [X86] Force use of architectural NMI
2651 timer mode (see also oprofile.timer
2652 for generic hr timer mode)
2653 [s390] Force legacy basic mode sampling
2654 (report cpu_type "timer")
2656 oops=panic Always panic on oopses. Default is to just kill the
2657 process, but there is a small probability of
2658 deadlocking the machine.
2659 This will also cause panics on machine check exceptions.
2660 Useful together with panic=30 to trigger a reboot.
2662 OSS [HW,OSS]
2663 See Documentation/sound/oss/oss-parameters.txt
2665 page_owner= [KNL] Boot-time page_owner enabling option.
2666 Storage of the information about who allocated
2667 each page is disabled in default. With this switch,
2668 we can turn it on.
2669 on: enable the feature
2671 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2672 timeout > 0: seconds before rebooting
2673 timeout = 0: wait forever
2674 timeout < 0: reboot immediately
2675 Format: <timeout>
2677 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2678 on a WARN().
2680 crash_kexec_post_notifiers
2681 Run kdump after running panic-notifiers and dumping
2682 kmsg. This only for the users who doubt kdump always
2683 succeeds in any situation.
2684 Note that this also increases risks of kdump failure,
2685 because some panic notifiers can make the crashed
2686 kernel more unstable.
2688 parkbd.port= [HW] Parallel port number the keyboard adapter is
2689 connected to, default is 0.
2690 Format: <parport#>
2691 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2692 0 for XT, 1 for AT (default is AT).
2693 Format: <mode>
2695 parport= [HW,PPT] Specify parallel ports. 0 disables.
2696 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2697 Use 'auto' to force the driver to use any
2698 IRQ/DMA settings detected (the default is to
2699 ignore detected IRQ/DMA settings because of
2700 possible conflicts). You can specify the base
2701 address, IRQ, and DMA settings; IRQ and DMA
2702 should be numbers, or 'auto' (for using detected
2703 settings on that particular port), or 'nofifo'
2704 (to avoid using a FIFO even if it is detected).
2705 Parallel ports are assigned in the order they
2706 are specified on the command line, starting
2707 with parport0.
2709 parport_init_mode= [HW,PPT]
2710 Configure VIA parallel port to operate in
2711 a specific mode. This is necessary on Pegasos
2712 computer where firmware has no options for setting
2713 up parallel port mode and sets it to spp.
2714 Currently this function knows 686a and 8231 chips.
2715 Format: [spp|ps2|epp|ecp|ecpepp]
2717 pause_on_oops=
2718 Halt all CPUs after the first oops has been printed for
2719 the specified number of seconds. This is to be used if
2720 your oopses keep scrolling off the screen.
2722 pcbit= [HW,ISDN]
2724 pcd. [PARIDE]
2725 See header of drivers/block/paride/pcd.c.
2726 See also Documentation/blockdev/paride.txt.
2728 pci=option[,option...] [PCI] various PCI subsystem options:
2729 earlydump [X86] dump PCI config space before the kernel
2730 changes anything
2731 off [X86] don't probe for the PCI bus
2732 bios [X86-32] force use of PCI BIOS, don't access
2733 the hardware directly. Use this if your machine
2734 has a non-standard PCI host bridge.
2735 nobios [X86-32] disallow use of PCI BIOS, only direct
2736 hardware access methods are allowed. Use this
2737 if you experience crashes upon bootup and you
2738 suspect they are caused by the BIOS.
2739 conf1 [X86] Force use of PCI Configuration
2740 Mechanism 1.
2741 conf2 [X86] Force use of PCI Configuration
2742 Mechanism 2.
2743 noaer [PCIE] If the PCIEAER kernel config parameter is
2744 enabled, this kernel boot option can be used to
2745 disable the use of PCIE advanced error reporting.
2746 nodomains [PCI] Disable support for multiple PCI
2747 root domains (aka PCI segments, in ACPI-speak).
2748 nommconf [X86] Disable use of MMCONFIG for PCI
2749 Configuration
2750 check_enable_amd_mmconf [X86] check for and enable
2751 properly configured MMIO access to PCI
2752 config space on AMD family 10h CPU
2753 nomsi [MSI] If the PCI_MSI kernel config parameter is
2754 enabled, this kernel boot option can be used to
2755 disable the use of MSI interrupts system-wide.
2756 noioapicquirk [APIC] Disable all boot interrupt quirks.
2757 Safety option to keep boot IRQs enabled. This
2758 should never be necessary.
2759 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2760 primary IO-APIC for bridges that cannot disable
2761 boot IRQs. This fixes a source of spurious IRQs
2762 when the system masks IRQs.
2763 noioapicreroute [APIC] Disable workaround that uses the
2764 boot IRQ equivalent of an IRQ that connects to
2765 a chipset where boot IRQs cannot be disabled.
2766 The opposite of ioapicreroute.
2767 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2768 routing table. These calls are known to be buggy
2769 on several machines and they hang the machine
2770 when used, but on other computers it's the only
2771 way to get the interrupt routing table. Try
2772 this option if the kernel is unable to allocate
2773 IRQs or discover secondary PCI buses on your
2774 motherboard.
2775 rom [X86] Assign address space to expansion ROMs.
2776 Use with caution as certain devices share
2777 address decoders between ROMs and other
2778 resources.
2779 norom [X86] Do not assign address space to
2780 expansion ROMs that do not already have
2781 BIOS assigned address ranges.
2782 nobar [X86] Do not assign address space to the
2783 BARs that weren't assigned by the BIOS.
2784 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2785 assigned automatically to PCI devices. You can
2786 make the kernel exclude IRQs of your ISA cards
2787 this way.
2788 pirqaddr=0xAAAAA [X86] Specify the physical address
2789 of the PIRQ table (normally generated
2790 by the BIOS) if it is outside the
2791 F0000h-100000h range.
2792 lastbus=N [X86] Scan all buses thru bus #N. Can be
2793 useful if the kernel is unable to find your
2794 secondary buses and you want to tell it
2795 explicitly which ones they are.
2796 assign-busses [X86] Always assign all PCI bus
2797 numbers ourselves, overriding
2798 whatever the firmware may have done.
2799 usepirqmask [X86] Honor the possible IRQ mask stored
2800 in the BIOS $PIR table. This is needed on
2801 some systems with broken BIOSes, notably
2802 some HP Pavilion N5400 and Omnibook XE3
2803 notebooks. This will have no effect if ACPI
2804 IRQ routing is enabled.
2805 noacpi [X86] Do not use ACPI for IRQ routing
2806 or for PCI scanning.
2807 use_crs [X86] Use PCI host bridge window information
2808 from ACPI. On BIOSes from 2008 or later, this
2809 is enabled by default. If you need to use this,
2810 please report a bug.
2811 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2812 If you need to use this, please report a bug.
2813 routeirq Do IRQ routing for all PCI devices.
2814 This is normally done in pci_enable_device(),
2815 so this option is a temporary workaround
2816 for broken drivers that don't call it.
2817 skip_isa_align [X86] do not align io start addr, so can
2818 handle more pci cards
2819 firmware [ARM] Do not re-enumerate the bus but instead
2820 just use the configuration from the
2821 bootloader. This is currently used on
2822 IXP2000 systems where the bus has to be
2823 configured a certain way for adjunct CPUs.
2824 noearly [X86] Don't do any early type 1 scanning.
2825 This might help on some broken boards which
2826 machine check when some devices' config space
2827 is read. But various workarounds are disabled
2828 and some IOMMU drivers will not work.
2829 bfsort Sort PCI devices into breadth-first order.
2830 This sorting is done to get a device
2831 order compatible with older (<= 2.4) kernels.
2832 nobfsort Don't sort PCI devices into breadth-first order.
2833 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2834 tuning and use the BIOS-configured MPS defaults.
2835 pcie_bus_safe Set every device's MPS to the largest value
2836 supported by all devices below the root complex.
2837 pcie_bus_perf Set device MPS to the largest allowable MPS
2838 based on its parent bus. Also set MRRS (Max
2839 Read Request Size) to the largest supported
2840 value (no larger than the MPS that the device
2841 or bus can support) for best performance.
2842 pcie_bus_peer2peer Set every device's MPS to 128B, which
2843 every device is guaranteed to support. This
2844 configuration allows peer-to-peer DMA between
2845 any pair of devices, possibly at the cost of
2846 reduced performance. This also guarantees
2847 that hot-added devices will work.
2848 cbiosize=nn[KMG] The fixed amount of bus space which is
2849 reserved for the CardBus bridge's IO window.
2850 The default value is 256 bytes.
2851 cbmemsize=nn[KMG] The fixed amount of bus space which is
2852 reserved for the CardBus bridge's memory
2853 window. The default value is 64 megabytes.
2854 resource_alignment=
2855 Format:
2856 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2857 Specifies alignment and device to reassign
2858 aligned memory resources.
2859 If <order of align> is not specified,
2860 PAGE_SIZE is used as alignment.
2861 PCI-PCI bridge can be specified, if resource
2862 windows need to be expanded.
2863 ecrc= Enable/disable PCIe ECRC (transaction layer
2864 end-to-end CRC checking).
2865 bios: Use BIOS/firmware settings. This is the
2866 the default.
2867 off: Turn ECRC off
2868 on: Turn ECRC on.
2869 hpiosize=nn[KMG] The fixed amount of bus space which is
2870 reserved for hotplug bridge's IO window.
2871 Default size is 256 bytes.
2872 hpmemsize=nn[KMG] The fixed amount of bus space which is
2873 reserved for hotplug bridge's memory window.
2874 Default size is 2 megabytes.
2875 realloc= Enable/disable reallocating PCI bridge resources
2876 if allocations done by BIOS are too small to
2877 accommodate resources required by all child
2878 devices.
2879 off: Turn realloc off
2880 on: Turn realloc on
2881 realloc same as realloc=on
2882 noari do not use PCIe ARI.
2883 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2884 only look for one device below a PCIe downstream
2885 port.
2887 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2888 Management.
2889 off Disable ASPM.
2890 force Enable ASPM even on devices that claim not to support it.
2891 WARNING: Forcing ASPM on may cause system lockups.
2893 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2894 nomsi Do not use MSI for PCI Express Native Hotplug (this
2895 makes all PCIe ports use INTx for hotplug services).
2897 pcie_ports= [PCIE] PCIe ports handling:
2898 auto Ask the BIOS whether or not to use native PCIe services
2899 associated with PCIe ports (PME, hot-plug, AER). Use
2900 them only if that is allowed by the BIOS.
2901 native Use native PCIe services associated with PCIe ports
2902 unconditionally.
2903 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2904 ports driver.
2906 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2907 nomsi Do not use MSI for native PCIe PME signaling (this makes
2908 all PCIe root ports use INTx for all services).
2910 pcmv= [HW,PCMCIA] BadgePAD 4
2912 pd_ignore_unused
2913 [PM]
2914 Keep all power-domains already enabled by bootloader on,
2915 even if no driver has claimed them. This is useful
2916 for debug and development, but should not be
2917 needed on a platform with proper driver support.
2919 pd. [PARIDE]
2920 See Documentation/blockdev/paride.txt.
2922 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2923 boot time.
2924 Format: { 0 | 1 }
2925 See arch/parisc/kernel/pdc_chassis.c
2927 percpu_alloc= Select which percpu first chunk allocator to use.
2928 Currently supported values are "embed" and "page".
2929 Archs may support subset or none of the selections.
2930 See comments in mm/percpu.c for details on each
2931 allocator. This parameter is primarily for debugging
2932 and performance comparison.
2934 pf. [PARIDE]
2935 See Documentation/blockdev/paride.txt.
2937 pg. [PARIDE]
2938 See Documentation/blockdev/paride.txt.
2940 pirq= [SMP,APIC] Manual mp-table setup
2941 See Documentation/x86/i386/IO-APIC.txt.
2943 plip= [PPT,NET] Parallel port network link
2944 Format: { parport<nr> | timid | 0 }
2945 See also Documentation/parport.txt.
2947 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2948 Override pmtimer IOPort with a hex value.
2949 e.g. pmtmr=0x508
2951 pnp.debug=1 [PNP]
2952 Enable PNP debug messages (depends on the
2953 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2954 via /sys/module/pnp/parameters/debug. We always show
2955 current resource usage; turning this on also shows
2956 possible settings and some assignment information.
2958 pnpacpi= [ACPI]
2959 { off }
2961 pnpbios= [ISAPNP]
2962 { on | off | curr | res | no-curr | no-res }
2964 pnp_reserve_irq=
2965 [ISAPNP] Exclude IRQs for the autoconfiguration
2967 pnp_reserve_dma=
2968 [ISAPNP] Exclude DMAs for the autoconfiguration
2970 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2971 Ranges are in pairs (I/O port base and size).
2973 pnp_reserve_mem=
2974 [ISAPNP] Exclude memory regions for the
2975 autoconfiguration.
2976 Ranges are in pairs (memory base and size).
2978 ports= [IP_VS_FTP] IPVS ftp helper module
2979 Default is 21.
2980 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2981 may be specified.
2982 Format: <port>,<port>....
2984 print-fatal-signals=
2985 [KNL] debug: print fatal signals
2987 If enabled, warn about various signal handling
2988 related application anomalies: too many signals,
2989 too many POSIX.1 timers, fatal signals causing a
2990 coredump - etc.
2992 If you hit the warning due to signal overflow,
2993 you might want to try "ulimit -i unlimited".
2995 default: off.
2997 printk.always_kmsg_dump=
2998 Trigger kmsg_dump for cases other than kernel oops or
2999 panics
3000 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3001 default: disabled
3003 printk.time= Show timing data prefixed to each printk message line
3004 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3006 processor.max_cstate= [HW,ACPI]
3007 Limit processor to maximum C-state
3008 max_cstate=9 overrides any DMI blacklist limit.
3010 processor.nocst [HW,ACPI]
3011 Ignore the _CST method to determine C-states,
3012 instead using the legacy FADT method
3014 profile= [KNL] Enable kernel profiling via /proc/profile
3015 Format: [schedule,]<number>
3016 Param: "schedule" - profile schedule points.
3017 Param: <number> - step/bucket size as a power of 2 for
3018 statistical time based profiling.
3019 Param: "sleep" - profile D-state sleeping (millisecs).
3020 Requires CONFIG_SCHEDSTATS
3021 Param: "kvm" - profile VM exits.
3023 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3024 before loading.
3025 See Documentation/blockdev/ramdisk.txt.
3027 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3028 probe for; one of (bare|imps|exps|lifebook|any).
3029 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3030 per second.
3031 psmouse.resetafter= [HW,MOUSE]
3032 Try to reset the device after so many bad packets
3033 (0 = never).
3034 psmouse.resolution=
3035 [HW,MOUSE] Set desired mouse resolution, in dpi.
3036 psmouse.smartscroll=
3037 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3038 0 = disabled, 1 = enabled (default).
3040 pstore.backend= Specify the name of the pstore backend to use
3042 pt. [PARIDE]
3043 See Documentation/blockdev/paride.txt.
3045 pty.legacy_count=
3046 [KNL] Number of legacy pty's. Overwrites compiled-in
3047 default number.
3049 quiet [KNL] Disable most log messages
3051 r128= [HW,DRM]
3053 raid= [HW,RAID]
3054 See Documentation/md.txt.
3056 ramdisk_blocksize= [RAM]
3057 See Documentation/blockdev/ramdisk.txt.
3059 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3060 See Documentation/blockdev/ramdisk.txt.
3062 rcu_nocbs= [KNL]
3063 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3064 the specified list of CPUs to be no-callback CPUs.
3065 Invocation of these CPUs' RCU callbacks will
3066 be offloaded to "rcuox/N" kthreads created for
3067 that purpose, where "x" is "b" for RCU-bh, "p"
3068 for RCU-preempt, and "s" for RCU-sched, and "N"
3069 is the CPU number. This reduces OS jitter on the
3070 offloaded CPUs, which can be useful for HPC and
3071 real-time workloads. It can also improve energy
3072 efficiency for asymmetric multiprocessors.
3074 rcu_nocb_poll [KNL]
3075 Rather than requiring that offloaded CPUs
3076 (specified by rcu_nocbs= above) explicitly
3077 awaken the corresponding "rcuoN" kthreads,
3078 make these kthreads poll for callbacks.
3079 This improves the real-time response for the
3080 offloaded CPUs by relieving them of the need to
3081 wake up the corresponding kthread, but degrades
3082 energy efficiency by requiring that the kthreads
3083 periodically wake up to do the polling.
3085 rcutree.blimit= [KNL]
3086 Set maximum number of finished RCU callbacks to
3087 process in one batch.
3089 rcutree.dump_tree= [KNL]
3090 Dump the structure of the rcu_node combining tree
3091 out at early boot. This is used for diagnostic
3092 purposes, to verify correct tree setup.
3094 rcutree.gp_cleanup_delay= [KNL]
3095 Set the number of jiffies to delay each step of
3096 RCU grace-period cleanup. This only has effect
3097 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3099 rcutree.gp_init_delay= [KNL]
3100 Set the number of jiffies to delay each step of
3101 RCU grace-period initialization. This only has
3102 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3103 is set.
3105 rcutree.gp_preinit_delay= [KNL]
3106 Set the number of jiffies to delay each step of
3107 RCU grace-period pre-initialization, that is,
3108 the propagation of recent CPU-hotplug changes up
3109 the rcu_node combining tree. This only has effect
3110 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3112 rcutree.rcu_fanout_exact= [KNL]
3113 Disable autobalancing of the rcu_node combining
3114 tree. This is used by rcutorture, and might
3115 possibly be useful for architectures having high
3116 cache-to-cache transfer latencies.
3118 rcutree.rcu_fanout_leaf= [KNL]
3119 Change the number of CPUs assigned to each
3120 leaf rcu_node structure. Useful for very
3121 large systems, which will choose the value 64,
3122 and for NUMA systems with large remote-access
3123 latencies, which will choose a value aligned
3124 with the appropriate hardware boundaries.
3126 rcutree.jiffies_till_sched_qs= [KNL]
3127 Set required age in jiffies for a
3128 given grace period before RCU starts
3129 soliciting quiescent-state help from
3130 rcu_note_context_switch().
3132 rcutree.jiffies_till_first_fqs= [KNL]
3133 Set delay from grace-period initialization to
3134 first attempt to force quiescent states.
3135 Units are jiffies, minimum value is zero,
3136 and maximum value is HZ.
3138 rcutree.jiffies_till_next_fqs= [KNL]
3139 Set delay between subsequent attempts to force
3140 quiescent states. Units are jiffies, minimum
3141 value is one, and maximum value is HZ.
3143 rcutree.kthread_prio= [KNL,BOOT]
3144 Set the SCHED_FIFO priority of the RCU per-CPU
3145 kthreads (rcuc/N). This value is also used for
3146 the priority of the RCU boost threads (rcub/N)
3147 and for the RCU grace-period kthreads (rcu_bh,
3148 rcu_preempt, and rcu_sched). If RCU_BOOST is
3149 set, valid values are 1-99 and the default is 1
3150 (the least-favored priority). Otherwise, when
3151 RCU_BOOST is not set, valid values are 0-99 and
3152 the default is zero (non-realtime operation).
3154 rcutree.rcu_nocb_leader_stride= [KNL]
3155 Set the number of NOCB kthread groups, which
3156 defaults to the square root of the number of
3157 CPUs. Larger numbers reduces the wakeup overhead
3158 on the per-CPU grace-period kthreads, but increases
3159 that same overhead on each group's leader.
3161 rcutree.qhimark= [KNL]
3162 Set threshold of queued RCU callbacks beyond which
3163 batch limiting is disabled.
3165 rcutree.qlowmark= [KNL]
3166 Set threshold of queued RCU callbacks below which
3167 batch limiting is re-enabled.
3169 rcutree.rcu_idle_gp_delay= [KNL]
3170 Set wakeup interval for idle CPUs that have
3171 RCU callbacks (RCU_FAST_NO_HZ=y).
3173 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3174 Set wakeup interval for idle CPUs that have
3175 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3176 Lazy RCU callbacks are those which RCU can
3177 prove do nothing more than free memory.
3179 rcutorture.cbflood_inter_holdoff= [KNL]
3180 Set holdoff time (jiffies) between successive
3181 callback-flood tests.
3183 rcutorture.cbflood_intra_holdoff= [KNL]
3184 Set holdoff time (jiffies) between successive
3185 bursts of callbacks within a given callback-flood
3186 test.
3188 rcutorture.cbflood_n_burst= [KNL]
3189 Set the number of bursts making up a given
3190 callback-flood test. Set this to zero to
3191 disable callback-flood testing.
3193 rcutorture.cbflood_n_per_burst= [KNL]
3194 Set the number of callbacks to be registered
3195 in a given burst of a callback-flood test.
3197 rcutorture.fqs_duration= [KNL]
3198 Set duration of force_quiescent_state bursts
3199 in microseconds.
3201 rcutorture.fqs_holdoff= [KNL]
3202 Set holdoff time within force_quiescent_state bursts
3203 in microseconds.
3205 rcutorture.fqs_stutter= [KNL]
3206 Set wait time between force_quiescent_state bursts
3207 in seconds.
3209 rcutorture.gp_cond= [KNL]
3210 Use conditional/asynchronous update-side
3211 primitives, if available.
3213 rcutorture.gp_exp= [KNL]
3214 Use expedited update-side primitives, if available.
3216 rcutorture.gp_normal= [KNL]
3217 Use normal (non-expedited) asynchronous
3218 update-side primitives, if available.
3220 rcutorture.gp_sync= [KNL]
3221 Use normal (non-expedited) synchronous
3222 update-side primitives, if available. If all
3223 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3224 rcutorture.gp_normal=, and rcutorture.gp_sync=
3225 are zero, rcutorture acts as if is interpreted
3226 they are all non-zero.
3228 rcutorture.n_barrier_cbs= [KNL]
3229 Set callbacks/threads for rcu_barrier() testing.
3231 rcutorture.nfakewriters= [KNL]
3232 Set number of concurrent RCU writers. These just
3233 stress RCU, they don't participate in the actual
3234 test, hence the "fake".
3236 rcutorture.nreaders= [KNL]
3237 Set number of RCU readers. The value -1 selects
3238 N-1, where N is the number of CPUs. A value
3239 "n" less than -1 selects N-n-2, where N is again
3240 the number of CPUs. For example, -2 selects N
3241 (the number of CPUs), -3 selects N+1, and so on.
3243 rcutorture.object_debug= [KNL]
3244 Enable debug-object double-call_rcu() testing.
3246 rcutorture.onoff_holdoff= [KNL]
3247 Set time (s) after boot for CPU-hotplug testing.
3249 rcutorture.onoff_interval= [KNL]
3250 Set time (s) between CPU-hotplug operations, or
3251 zero to disable CPU-hotplug testing.
3253 rcutorture.shuffle_interval= [KNL]
3254 Set task-shuffle interval (s). Shuffling tasks
3255 allows some CPUs to go into dyntick-idle mode
3256 during the rcutorture test.
3258 rcutorture.shutdown_secs= [KNL]
3259 Set time (s) after boot system shutdown. This
3260 is useful for hands-off automated testing.
3262 rcutorture.stall_cpu= [KNL]
3263 Duration of CPU stall (s) to test RCU CPU stall
3264 warnings, zero to disable.
3266 rcutorture.stall_cpu_holdoff= [KNL]
3267 Time to wait (s) after boot before inducing stall.
3269 rcutorture.stat_interval= [KNL]
3270 Time (s) between statistics printk()s.
3272 rcutorture.stutter= [KNL]
3273 Time (s) to stutter testing, for example, specifying
3274 five seconds causes the test to run for five seconds,
3275 wait for five seconds, and so on. This tests RCU's
3276 ability to transition abruptly to and from idle.
3278 rcutorture.test_boost= [KNL]
3279 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3280 "Maybe" means test if the RCU implementation
3281 under test support RCU priority boosting.
3283 rcutorture.test_boost_duration= [KNL]
3284 Duration (s) of each individual boost test.
3286 rcutorture.test_boost_interval= [KNL]
3287 Interval (s) between each boost test.
3289 rcutorture.test_no_idle_hz= [KNL]
3290 Test RCU's dyntick-idle handling. See also the
3291 rcutorture.shuffle_interval parameter.
3293 rcutorture.torture_runnable= [BOOT]
3294 Start rcutorture running at boot time.
3296 rcutorture.torture_type= [KNL]
3297 Specify the RCU implementation to test.
3299 rcutorture.verbose= [KNL]
3300 Enable additional printk() statements.
3302 rcupdate.rcu_expedited= [KNL]
3303 Use expedited grace-period primitives, for
3304 example, synchronize_rcu_expedited() instead
3305 of synchronize_rcu(). This reduces latency,
3306 but can increase CPU utilization, degrade
3307 real-time latency, and degrade energy efficiency.
3309 rcupdate.rcu_cpu_stall_suppress= [KNL]
3310 Suppress RCU CPU stall warning messages.
3312 rcupdate.rcu_cpu_stall_timeout= [KNL]
3313 Set timeout for RCU CPU stall warning messages.
3315 rcupdate.rcu_task_stall_timeout= [KNL]
3316 Set timeout in jiffies for RCU task stall warning
3317 messages. Disable with a value less than or equal
3318 to zero.
3320 rcupdate.rcu_self_test= [KNL]
3321 Run the RCU early boot self tests
3323 rcupdate.rcu_self_test_bh= [KNL]
3324 Run the RCU bh early boot self tests
3326 rcupdate.rcu_self_test_sched= [KNL]
3327 Run the RCU sched early boot self tests
3329 rdinit= [KNL]
3330 Format: <full_path>
3331 Run specified binary instead of /init from the ramdisk,
3332 used for early userspace startup. See initrd.
3334 reboot= [KNL]
3335 Format (x86 or x86_64):
3336 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3337 [[,]s[mp]#### \
3338 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3339 [[,]f[orce]
3340 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3341 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3342 reboot_force is either force or not specified,
3343 reboot_cpu is s[mp]#### with #### being the processor
3344 to be used for rebooting.
3346 relax_domain_level=
3347 [KNL, SMP] Set scheduler's default relax_domain_level.
3348 See Documentation/cgroups/cpusets.txt.
3350 relative_sleep_states=
3351 [SUSPEND] Use sleep state labeling where the deepest
3352 state available other than hibernation is always "mem".
3353 Format: { "0" | "1" }
3354 0 -- Traditional sleep state labels.
3355 1 -- Relative sleep state labels.
3357 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3359 reservetop= [X86-32]
3360 Format: nn[KMG]
3361 Reserves a hole at the top of the kernel virtual
3362 address space.
3364 reservelow= [X86]
3365 Format: nn[K]
3366 Set the amount of memory to reserve for BIOS at
3367 the bottom of the address space.
3369 reset_devices [KNL] Force drivers to reset the underlying device
3370 during initialization.
3372 resume= [SWSUSP]
3373 Specify the partition device for software suspend
3374 Format:
3375 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3377 resume_offset= [SWSUSP]
3378 Specify the offset from the beginning of the partition
3379 given by "resume=" at which the swap header is located,
3380 in <PAGE_SIZE> units (needed only for swap files).
3381 See Documentation/power/swsusp-and-swap-files.txt
3383 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3384 read the resume files
3386 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3387 Useful for devices that are detected asynchronously
3388 (e.g. USB and MMC devices).
3390 hibernate= [HIBERNATION]
3391 noresume Don't check if there's a hibernation image
3392 present during boot.
3393 nocompress Don't compress/decompress hibernation images.
3394 no Disable hibernation and resume.
3396 retain_initrd [RAM] Keep initrd memory after extraction
3398 rfkill.default_state=
3399 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3400 etc. communication is blocked by default.
3401 1 Unblocked.
3403 rfkill.master_switch_mode=
3404 0 The "airplane mode" button does nothing.
3405 1 The "airplane mode" button toggles between everything
3406 blocked and the previous configuration.
3407 2 The "airplane mode" button toggles between everything
3408 blocked and everything unblocked.
3410 rhash_entries= [KNL,NET]
3411 Set number of hash buckets for route cache
3413 ro [KNL] Mount root device read-only on boot
3415 root= [KNL] Root filesystem
3416 See name_to_dev_t comment in init/do_mounts.c.
3418 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3419 mount the root filesystem
3421 rootflags= [KNL] Set root filesystem mount option string
3423 rootfstype= [KNL] Set root filesystem type
3425 rootwait [KNL] Wait (indefinitely) for root device to show up.
3426 Useful for devices that are detected asynchronously
3427 (e.g. USB and MMC devices).
3429 rproc_mem=nn[KMG][@address]
3430 [KNL,ARM,CMA] Remoteproc physical memory block.
3431 Memory area to be used by remote processor image,
3432 managed by CMA.
3434 rw [KNL] Mount root device read-write on boot
3436 S [KNL] Run init in single mode
3438 s390_iommu= [HW,S390]
3439 Set s390 IOTLB flushing mode
3440 strict
3441 With strict flushing every unmap operation will result in
3442 an IOTLB flush. Default is lazy flushing before reuse,
3443 which is faster.
3445 sa1100ir [NET]
3446 See drivers/net/irda/sa1100_ir.c.
3448 sbni= [NET] Granch SBNI12 leased line adapter
3450 sched_debug [KNL] Enables verbose scheduler debug messages.
3452 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3453 xtime_lock contention on larger systems, and/or RCU lock
3454 contention on all systems with CONFIG_MAXSMP set.
3455 Format: { "0" | "1" }
3456 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3457 1 -- enable.
3458 Note: increases power consumption, thus should only be
3459 enabled if running jitter sensitive (HPC/RT) workloads.
3461 security= [SECURITY] Choose a security module to enable at boot.
3462 If this boot parameter is not specified, only the first
3463 security module asking for security registration will be
3464 loaded. An invalid security module name will be treated
3465 as if no module has been chosen.
3467 selinux= [SELINUX] Disable or enable SELinux at boot time.
3468 Format: { "0" | "1" }
3469 See security/selinux/Kconfig help text.
3470 0 -- disable.
3471 1 -- enable.
3472 Default value is set via kernel config option.
3473 If enabled at boot time, /selinux/disable can be used
3474 later to disable prior to initial policy load.
3476 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3477 Format: { "0" | "1" }
3478 See security/apparmor/Kconfig help text
3479 0 -- disable.
3480 1 -- enable.
3481 Default value is set via kernel config option.
3483 serialnumber [BUGS=X86-32]
3485 shapers= [NET]
3486 Maximal number of shapers.
3488 show_msr= [x86] show boot-time MSR settings
3489 Format: { <integer> }
3490 Show boot-time (BIOS-initialized) MSR settings.
3491 The parameter means the number of CPUs to show,
3492 for example 1 means boot CPU only.
3494 simeth= [IA-64]
3495 simscsi=
3497 slram= [HW,MTD]
3499 slab_nomerge [MM]
3500 Disable merging of slabs with similar size. May be
3501 necessary if there is some reason to distinguish
3502 allocs to different slabs. Debug options disable
3503 merging on their own.
3504 For more information see Documentation/vm/slub.txt.
3506 slab_max_order= [MM, SLAB]
3507 Determines the maximum allowed order for slabs.
3508 A high setting may cause OOMs due to memory
3509 fragmentation. Defaults to 1 for systems with
3510 more than 32MB of RAM, 0 otherwise.
3512 slub_debug[=options[,slabs]] [MM, SLUB]
3513 Enabling slub_debug allows one to determine the
3514 culprit if slab objects become corrupted. Enabling
3515 slub_debug can create guard zones around objects and
3516 may poison objects when not in use. Also tracks the
3517 last alloc / free. For more information see
3518 Documentation/vm/slub.txt.
3520 slub_max_order= [MM, SLUB]
3521 Determines the maximum allowed order for slabs.
3522 A high setting may cause OOMs due to memory
3523 fragmentation. For more information see
3524 Documentation/vm/slub.txt.
3526 slub_min_objects= [MM, SLUB]
3527 The minimum number of objects per slab. SLUB will
3528 increase the slab order up to slub_max_order to
3529 generate a sufficiently large slab able to contain
3530 the number of objects indicated. The higher the number
3531 of objects the smaller the overhead of tracking slabs
3532 and the less frequently locks need to be acquired.
3533 For more information see Documentation/vm/slub.txt.
3535 slub_min_order= [MM, SLUB]
3536 Determines the minimum page order for slabs. Must be
3537 lower than slub_max_order.
3538 For more information see Documentation/vm/slub.txt.
3540 slub_nomerge [MM, SLUB]
3541 Same with slab_nomerge. This is supported for legacy.
3542 See slab_nomerge for more information.
3544 smart2= [HW]
3545 Format: <io1>[,<io2>[,...,<io8>]]
3547 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3548 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3549 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3550 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3551 smsc-ircc2.ircc_irq= [HW] IRQ line
3552 smsc-ircc2.ircc_dma= [HW] DMA channel
3553 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3554 0: Toshiba Satellite 1800 (GP data pin select)
3555 1: Fast pin select (default)
3556 2: ATC IRMode
3558 softlockup_panic=
3559 [KNL] Should the soft-lockup detector generate panics.
3560 Format: <integer>
3562 softlockup_all_cpu_backtrace=
3563 [KNL] Should the soft-lockup detector generate
3564 backtraces on all cpus.
3565 Format: <integer>
3567 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3568 See Documentation/laptops/sonypi.txt
3570 spia_io_base= [HW,MTD]
3571 spia_fio_base=
3572 spia_pedr=
3573 spia_peddr=
3575 stacktrace [FTRACE]
3576 Enabled the stack tracer on boot up.
3578 stacktrace_filter=[function-list]
3579 [FTRACE] Limit the functions that the stack tracer
3580 will trace at boot up. function-list is a comma separated
3581 list of functions. This list can be changed at run
3582 time by the stack_trace_filter file in the debugfs
3583 tracing directory. Note, this enables stack tracing
3584 and the stacktrace above is not needed.
3586 sti= [PARISC,HW]
3587 Format: <num>
3588 Set the STI (builtin display/keyboard on the HP-PARISC
3589 machines) console (graphic card) which should be used
3590 as the initial boot-console.
3591 See also comment in drivers/video/console/sticore.c.
3593 sti_font= [HW]
3594 See comment in drivers/video/console/sticore.c.
3596 stifb= [HW]
3597 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3599 sunrpc.min_resvport=
3600 sunrpc.max_resvport=
3601 [NFS,SUNRPC]
3602 SunRPC servers often require that client requests
3603 originate from a privileged port (i.e. a port in the
3604 range 0 < portnr < 1024).
3605 An administrator who wishes to reserve some of these
3606 ports for other uses may adjust the range that the
3607 kernel's sunrpc client considers to be privileged
3608 using these two parameters to set the minimum and
3609 maximum port values.
3611 sunrpc.pool_mode=
3612 [NFS]
3613 Control how the NFS server code allocates CPUs to
3614 service thread pools. Depending on how many NICs
3615 you have and where their interrupts are bound, this
3616 option will affect which CPUs will do NFS serving.
3617 Note: this parameter cannot be changed while the
3618 NFS server is running.
3620 auto the server chooses an appropriate mode
3621 automatically using heuristics
3622 global a single global pool contains all CPUs
3623 percpu one pool for each CPU
3624 pernode one pool for each NUMA node (equivalent
3625 to global on non-NUMA machines)
3627 sunrpc.tcp_slot_table_entries=
3628 sunrpc.udp_slot_table_entries=
3629 [NFS,SUNRPC]
3630 Sets the upper limit on the number of simultaneous
3631 RPC calls that can be sent from the client to a
3632 server. Increasing these values may allow you to
3633 improve throughput, but will also increase the
3634 amount of memory reserved for use by the client.
3636 suspend.pm_test_delay=
3637 [SUSPEND]
3638 Sets the number of seconds to remain in a suspend test
3639 mode before resuming the system (see
3640 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3641 is set. Default value is 5.
3643 swapaccount=[0|1]
3644 [KNL] Enable accounting of swap in memory resource
3645 controller if no parameter or 1 is given or disable
3646 it if 0 is given (See Documentation/cgroups/memory.txt)
3648 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3649 Format: { <int> | force }
3650 <int> -- Number of I/O TLB slabs
3651 force -- force using of bounce buffers even if they
3652 wouldn't be automatically used by the kernel
3654 switches= [HW,M68k]
3656 sysfs.deprecated=0|1 [KNL]
3657 Enable/disable old style sysfs layout for old udev
3658 on older distributions. When this option is enabled
3659 very new udev will not work anymore. When this option
3660 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3661 in older udev will not work anymore.
3662 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3663 the kernel configuration.
3665 sysrq_always_enabled
3666 [KNL]
3667 Ignore sysrq setting - this boot parameter will
3668 neutralize any effect of /proc/sys/kernel/sysrq.
3669 Useful for debugging.
3671 tcpmhash_entries= [KNL,NET]
3672 Set the number of tcp_metrics_hash slots.
3673 Default value is 8192 or 16384 depending on total
3674 ram pages. This is used to specify the TCP metrics
3675 cache size. See Documentation/networking/ip-sysctl.txt
3676 "tcp_no_metrics_save" section for more details.
3678 tdfx= [HW,DRM]
3680 test_suspend= [SUSPEND][,N]
3681 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3682 standby suspend) or "freeze" (for suspend type freeze)
3683 as the system sleep state during system startup with
3684 the optional capability to repeat N number of times.
3685 The system is woken from this state using a
3686 wakeup-capable RTC alarm.
3688 thash_entries= [KNL,NET]
3689 Set number of hash buckets for TCP connection
3691 thermal.act= [HW,ACPI]
3692 -1: disable all active trip points in all thermal zones
3693 <degrees C>: override all lowest active trip points
3695 thermal.crt= [HW,ACPI]
3696 -1: disable all critical trip points in all thermal zones
3697 <degrees C>: override all critical trip points
3699 thermal.nocrt= [HW,ACPI]
3700 Set to disable actions on ACPI thermal zone
3701 critical and hot trip points.
3703 thermal.off= [HW,ACPI]
3704 1: disable ACPI thermal control
3706 thermal.psv= [HW,ACPI]
3707 -1: disable all passive trip points
3708 <degrees C>: override all passive trip points to this
3709 value
3711 thermal.tzp= [HW,ACPI]
3712 Specify global default ACPI thermal zone polling rate
3713 <deci-seconds>: poll all this frequency
3714 0: no polling (default)
3716 threadirqs [KNL]
3717 Force threading of all interrupt handlers except those
3718 marked explicitly IRQF_NO_THREAD.
3720 tmem [KNL,XEN]
3721 Enable the Transcendent memory driver if built-in.
3723 tmem.cleancache=0|1 [KNL, XEN]
3724 Default is on (1). Disable the usage of the cleancache
3725 API to send anonymous pages to the hypervisor.
3727 tmem.frontswap=0|1 [KNL, XEN]
3728 Default is on (1). Disable the usage of the frontswap
3729 API to send swap pages to the hypervisor. If disabled
3730 the selfballooning and selfshrinking are force disabled.
3732 tmem.selfballooning=0|1 [KNL, XEN]
3733 Default is on (1). Disable the driving of swap pages
3734 to the hypervisor.
3736 tmem.selfshrinking=0|1 [KNL, XEN]
3737 Default is on (1). Partial swapoff that immediately
3738 transfers pages from Xen hypervisor back to the
3739 kernel based on different criteria.
3741 topology= [S390]
3742 Format: {off | on}
3743 Specify if the kernel should make use of the cpu
3744 topology information if the hardware supports this.
3745 The scheduler will make use of this information and
3746 e.g. base its process migration decisions on it.
3747 Default is on.
3749 topology_updates= [KNL, PPC, NUMA]
3750 Format: {off}
3751 Specify if the kernel should ignore (off)
3752 topology updates sent by the hypervisor to this
3753 LPAR.
3755 tp720= [HW,PS2]
3757 tpm_suspend_pcr=[HW,TPM]
3758 Format: integer pcr id
3759 Specify that at suspend time, the tpm driver
3760 should extend the specified pcr with zeros,
3761 as a workaround for some chips which fail to
3762 flush the last written pcr on TPM_SaveState.
3763 This will guarantee that all the other pcrs
3764 are saved.
3766 trace_buf_size=nn[KMG]
3767 [FTRACE] will set tracing buffer size on each cpu.
3769 trace_event=[event-list]
3770 [FTRACE] Set and start specified trace events in order
3771 to facilitate early boot debugging.
3772 See also Documentation/trace/events.txt
3774 trace_options=[option-list]
3775 [FTRACE] Enable or disable tracer options at boot.
3776 The option-list is a comma delimited list of options
3777 that can be enabled or disabled just as if you were
3778 to echo the option name into
3780 /sys/kernel/debug/tracing/trace_options
3782 For example, to enable stacktrace option (to dump the
3783 stack trace of each event), add to the command line:
3785 trace_options=stacktrace
3787 See also Documentation/trace/ftrace.txt "trace options"
3788 section.
3790 tp_printk[FTRACE]
3791 Have the tracepoints sent to printk as well as the
3792 tracing ring buffer. This is useful for early boot up
3793 where the system hangs or reboots and does not give the
3794 option for reading the tracing buffer or performing a
3795 ftrace_dump_on_oops.
3797 To turn off having tracepoints sent to printk,
3798 echo 0 > /proc/sys/kernel/tracepoint_printk
3799 Note, echoing 1 into this file without the
3800 tracepoint_printk kernel cmdline option has no effect.
3802 ** CAUTION **
3804 Having tracepoints sent to printk() and activating high
3805 frequency tracepoints such as irq or sched, can cause
3806 the system to live lock.
3808 traceoff_on_warning
3809 [FTRACE] enable this option to disable tracing when a
3810 warning is hit. This turns off "tracing_on". Tracing can
3811 be enabled again by echoing '1' into the "tracing_on"
3812 file located in /sys/kernel/debug/tracing/
3814 This option is useful, as it disables the trace before
3815 the WARNING dump is called, which prevents the trace to
3816 be filled with content caused by the warning output.
3818 This option can also be set at run time via the sysctl
3819 option: kernel/traceoff_on_warning
3821 transparent_hugepage=
3822 [KNL]
3823 Format: [always|madvise|never]
3824 Can be used to control the default behavior of the system
3825 with respect to transparent hugepages.
3826 See Documentation/vm/transhuge.txt for more details.
3828 tsc= Disable clocksource stability checks for TSC.
3829 Format: <string>
3830 [x86] reliable: mark tsc clocksource as reliable, this
3831 disables clocksource verification at runtime, as well
3832 as the stability checks done at bootup. Used to enable
3833 high-resolution timer mode on older hardware, and in
3834 virtualized environment.
3835 [x86] noirqtime: Do not use TSC to do irq accounting.
3836 Used to run time disable IRQ_TIME_ACCOUNTING on any
3837 platforms where RDTSC is slow and this accounting
3838 can add overhead.
3840 turbografx.map[2|3]= [HW,JOY]
3841 TurboGraFX parallel port interface
3842 Format:
3843 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3844 See also Documentation/input/joystick-parport.txt
3846 udbg-immortal [PPC] When debugging early kernel crashes that
3847 happen after console_init() and before a proper
3848 console driver takes over, this boot options might
3849 help "seeing" what's going on.
3851 uhash_entries= [KNL,NET]
3852 Set number of hash buckets for UDP/UDP-Lite connections
3854 uhci-hcd.ignore_oc=
3855 [USB] Ignore overcurrent events (default N).
3856 Some badly-designed motherboards generate lots of
3857 bogus events, for ports that aren't wired to
3858 anything. Set this parameter to avoid log spamming.
3859 Note that genuine overcurrent events won't be
3860 reported either.
3862 unknown_nmi_panic
3863 [X86] Cause panic on unknown NMI.
3865 usbcore.authorized_default=
3866 [USB] Default USB device authorization:
3867 (default -1 = authorized except for wireless USB,
3868 0 = not authorized, 1 = authorized)
3870 usbcore.autosuspend=
3871 [USB] The autosuspend time delay (in seconds) used
3872 for newly-detected USB devices (default 2). This
3873 is the time required before an idle device will be
3874 autosuspended. Devices for which the delay is set
3875 to a negative value won't be autosuspended at all.
3877 usbcore.usbfs_snoop=
3878 [USB] Set to log all usbfs traffic (default 0 = off).
3880 usbcore.blinkenlights=
3881 [USB] Set to cycle leds on hubs (default 0 = off).
3883 usbcore.old_scheme_first=
3884 [USB] Start with the old device initialization
3885 scheme (default 0 = off).
3887 usbcore.usbfs_memory_mb=
3888 [USB] Memory limit (in MB) for buffers allocated by
3889 usbfs (default = 16, 0 = max = 2047).
3891 usbcore.use_both_schemes=
3892 [USB] Try the other device initialization scheme
3893 if the first one fails (default 1 = enabled).
3895 usbcore.initial_descriptor_timeout=
3896 [USB] Specifies timeout for the initial 64-byte
3897 USB_REQ_GET_DESCRIPTOR request in milliseconds
3898 (default 5000 = 5.0 seconds).
3900 usbhid.mousepoll=
3901 [USBHID] The interval which mice are to be polled at.
3903 usb-storage.delay_use=
3904 [UMS] The delay in seconds before a new device is
3905 scanned for Logical Units (default 1).
3907 usb-storage.quirks=
3908 [UMS] A list of quirks entries to supplement or
3909 override the built-in unusual_devs list. List
3910 entries are separated by commas. Each entry has
3911 the form VID:PID:Flags where VID and PID are Vendor
3912 and Product ID values (4-digit hex numbers) and
3913 Flags is a set of characters, each corresponding
3914 to a common usb-storage quirk flag as follows:
3915 a = SANE_SENSE (collect more than 18 bytes
3916 of sense data);
3917 b = BAD_SENSE (don't collect more than 18
3918 bytes of sense data);
3919 c = FIX_CAPACITY (decrease the reported
3920 device capacity by one sector);
3921 d = NO_READ_DISC_INFO (don't use
3922 READ_DISC_INFO command);
3923 e = NO_READ_CAPACITY_16 (don't use
3924 READ_CAPACITY_16 command);
3925 f = NO_REPORT_OPCODES (don't use report opcodes
3926 command, uas only);
3927 g = MAX_SECTORS_240 (don't transfer more than
3928 240 sectors at a time, uas only);
3929 h = CAPACITY_HEURISTICS (decrease the
3930 reported device capacity by one
3931 sector if the number is odd);
3932 i = IGNORE_DEVICE (don't bind to this
3933 device);
3934 l = NOT_LOCKABLE (don't try to lock and
3935 unlock ejectable media);
3936 m = MAX_SECTORS_64 (don't transfer more
3937 than 64 sectors = 32 KB at a time);
3938 n = INITIAL_READ10 (force a retry of the
3939 initial READ(10) command);
3940 o = CAPACITY_OK (accept the capacity
3941 reported by the device);
3942 p = WRITE_CACHE (the device cache is ON
3943 by default);
3944 r = IGNORE_RESIDUE (the device reports
3945 bogus residue values);
3946 s = SINGLE_LUN (the device has only one
3947 Logical Unit);
3948 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3949 commands, uas only);
3950 u = IGNORE_UAS (don't bind to the uas driver);
3951 w = NO_WP_DETECT (don't test whether the
3952 medium is write-protected).
3953 Example: quirks=0419:aaf5:rl,0421:0433:rc
3955 user_debug= [KNL,ARM]
3956 Format: <int>
3957 See arch/arm/Kconfig.debug help text.
3958 1 - undefined instruction events
3959 2 - system calls
3960 4 - invalid data aborts
3961 8 - SIGSEGV faults
3962 16 - SIGBUS faults
3963 Example: user_debug=31
3965 userpte=
3966 [X86] Flags controlling user PTE allocations.
3968 nohigh = do not allocate PTE pages in
3969 HIGHMEM regardless of setting
3970 of CONFIG_HIGHPTE.
3972 vdso= [X86,SH]
3973 On X86_32, this is an alias for vdso32=. Otherwise:
3975 vdso=1: enable VDSO (the default)
3976 vdso=0: disable VDSO mapping
3978 vdso32= [X86] Control the 32-bit vDSO
3979 vdso32=1: enable 32-bit VDSO
3980 vdso32=0 or vdso32=2: disable 32-bit VDSO
3982 See the help text for CONFIG_COMPAT_VDSO for more
3983 details. If CONFIG_COMPAT_VDSO is set, the default is
3984 vdso32=0; otherwise, the default is vdso32=1.
3986 For compatibility with older kernels, vdso32=2 is an
3987 alias for vdso32=0.
3989 Try vdso32=0 if you encounter an error that says:
3990 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3992 vector= [IA-64,SMP]
3993 vector=percpu: enable percpu vector domain
3995 video= [FB] Frame buffer configuration
3996 See Documentation/fb/modedb.txt.
3998 video.brightness_switch_enabled= [0,1]
3999 If set to 1, on receiving an ACPI notify event
4000 generated by hotkey, video driver will adjust brightness
4001 level and then send out the event to user space through
4002 the allocated input device; If set to 0, video driver
4003 will only send out the event without touching backlight
4004 brightness level.
4005 default: 1
4007 virtio_mmio.device=
4008 [VMMIO] Memory mapped virtio (platform) device.
4010 <size>@<baseaddr>:<irq>[:<id>]
4011 where:
4012 <size> := size (can use standard suffixes
4013 like K, M and G)
4014 <baseaddr> := physical base address
4015 <irq> := interrupt number (as passed to
4016 request_irq())
4017 <id> := (optional) platform device id
4018 example:
4019 virtio_mmio.device=1K@0x100b0000:48:7
4021 Can be used multiple times for multiple devices.
4023 vga= [BOOT,X86-32] Select a particular video mode
4024 See Documentation/x86/boot.txt and
4025 Documentation/svga.txt.
4026 Use vga=ask for menu.
4027 This is actually a boot loader parameter; the value is
4028 passed to the kernel using a special protocol.
4030 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4031 size of <nn>. This can be used to increase the
4032 minimum size (128MB on x86). It can also be used to
4033 decrease the size and leave more room for directly
4034 mapped kernel RAM.
4036 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4037 Format: <command>
4039 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4040 Format: <command>
4042 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4043 Format: <command>
4045 vsyscall= [X86-64]
4046 Controls the behavior of vsyscalls (i.e. calls to
4047 fixed addresses of 0xffffffffff600x00 from legacy
4048 code). Most statically-linked binaries and older
4049 versions of glibc use these calls. Because these
4050 functions are at fixed addresses, they make nice
4051 targets for exploits that can control RIP.
4053 emulate [default] Vsyscalls turn into traps and are
4054 emulated reasonably safely.
4056 native Vsyscalls are native syscall instructions.
4057 This is a little bit faster than trapping
4058 and makes a few dynamic recompilers work
4059 better than they would in emulation mode.
4060 It also makes exploits much easier to write.
4062 none Vsyscalls don't work at all. This makes
4063 them quite hard to use for exploits but
4064 might break your system.
4066 vt.color= [VT] Default text color.
4067 Format: 0xYX, X = foreground, Y = background.
4068 Default: 0x07 = light gray on black.
4070 vt.cur_default= [VT] Default cursor shape.
4071 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4072 the parameters of the <Esc>[?A;B;Cc escape sequence;
4073 see VGA-softcursor.txt. Default: 2 = underline.
4075 vt.default_blu= [VT]
4076 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4077 Change the default blue palette of the console.
4078 This is a 16-member array composed of values
4079 ranging from 0-255.
4081 vt.default_grn= [VT]
4082 Format: <green0>,<green1>,<green2>,...,<green15>
4083 Change the default green palette of the console.
4084 This is a 16-member array composed of values
4085 ranging from 0-255.
4087 vt.default_red= [VT]
4088 Format: <red0>,<red1>,<red2>,...,<red15>
4089 Change the default red palette of the console.
4090 This is a 16-member array composed of values
4091 ranging from 0-255.
4093 vt.default_utf8=
4094 [VT]
4095 Format=<0|1>
4096 Set system-wide default UTF-8 mode for all tty's.
4097 Default is 1, i.e. UTF-8 mode is enabled for all
4098 newly opened terminals.
4100 vt.global_cursor_default=
4101 [VT]
4102 Format=<-1|0|1>
4103 Set system-wide default for whether a cursor
4104 is shown on new VTs. Default is -1,
4105 i.e. cursors will be created by default unless
4106 overridden by individual drivers. 0 will hide
4107 cursors, 1 will display them.
4109 vt.italic= [VT] Default color for italic text; 0-15.
4110 Default: 2 = green.
4112 vt.underline= [VT] Default color for underlined text; 0-15.
4113 Default: 3 = cyan.
4115 watchdog timers [HW,WDT] For information on watchdog timers,
4116 see Documentation/watchdog/watchdog-parameters.txt
4117 or other driver-specific files in the
4118 Documentation/watchdog/ directory.
4120 workqueue.disable_numa
4121 By default, all work items queued to unbound
4122 workqueues are affine to the NUMA nodes they're
4123 issued on, which results in better behavior in
4124 general. If NUMA affinity needs to be disabled for
4125 whatever reason, this option can be used. Note
4126 that this also can be controlled per-workqueue for
4127 workqueues visible under /sys/bus/workqueue/.
4129 workqueue.power_efficient
4130 Per-cpu workqueues are generally preferred because
4131 they show better performance thanks to cache
4132 locality; unfortunately, per-cpu workqueues tend to
4133 be more power hungry than unbound workqueues.
4135 Enabling this makes the per-cpu workqueues which
4136 were observed to contribute significantly to power
4137 consumption unbound, leading to measurably lower
4138 power usage at the cost of small performance
4139 overhead.
4141 The default value of this parameter is determined by
4142 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4144 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4145 default x2apic cluster mode on platforms
4146 supporting x2apic.
4148 x86_intel_mid_timer= [X86-32,APBT]
4149 Choose timer option for x86 Intel MID platform.
4150 Two valid options are apbt timer only and lapic timer
4151 plus one apbt timer for broadcast timer.
4152 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4154 xen_512gb_limit [KNL,X86-64,XEN]
4155 Restricts the kernel running paravirtualized under Xen
4156 to use only up to 512 GB of RAM. The reason to do so is
4157 crash analysis tools and Xen tools for doing domain
4158 save/restore/migration must be enabled to handle larger
4159 domains.
4161 xen_emul_unplug= [HW,X86,XEN]
4162 Unplug Xen emulated devices
4163 Format: [unplug0,][unplug1]
4164 ide-disks -- unplug primary master IDE devices
4165 aux-ide-disks -- unplug non-primary-master IDE devices
4166 nics -- unplug network devices
4167 all -- unplug all emulated devices (NICs and IDE disks)
4168 unnecessary -- unplugging emulated devices is
4169 unnecessary even if the host did not respond to
4170 the unplug protocol
4171 never -- do not unplug even if version check succeeds
4173 xen_nopvspin [X86,XEN]
4174 Disables the ticketlock slowpath using Xen PV
4175 optimizations.
4177 xen_nopv [X86]
4178 Disables the PV optimizations forcing the HVM guest to
4179 run as generic HVM guest with no PV drivers.
4181 xirc2ps_cs= [NET,PCMCIA]
4182 Format:
4183 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4185 ______________________________________________________________________
4187 TODO:
4189 Add more DRM drivers.