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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.
1587 intremap= [X86-64, Intel-IOMMU]
1588 on enable Interrupt Remapping (default)
1589 off disable Interrupt Remapping
1590 nosid disable Source ID checking
1591 no_x2apic_optout
1592 BIOS x2APIC opt-out request will be ignored
1593 nopost disable Interrupt Posting
1595 iomem= Disable strict checking of access to MMIO memory
1596 strict regions from userspace.
1597 relaxed
1599 iommu= [x86]
1600 off
1601 force
1602 noforce
1603 biomerge
1604 panic
1605 nopanic
1606 merge
1607 nomerge
1608 forcesac
1609 soft
1610 pt [x86, IA-64]
1611 nobypass [PPC/POWERNV]
1612 Disable IOMMU bypass, using IOMMU for PCI devices.
1615 io7= [HW] IO7 for Marvel based alpha systems
1616 See comment before marvel_specify_io7 in
1617 arch/alpha/kernel/core_marvel.c.
1619 io_delay= [X86] I/O delay method
1620 0x80
1621 Standard port 0x80 based delay
1622 0xed
1623 Alternate port 0xed based delay (needed on some systems)
1624 udelay
1625 Simple two microseconds delay
1626 none
1627 No delay
1629 ip= [IP_PNP]
1630 See Documentation/filesystems/nfs/nfsroot.txt.
1632 irqfixup [HW]
1633 When an interrupt is not handled search all handlers
1634 for it. Intended to get systems with badly broken
1635 firmware running.
1637 irqpoll [HW]
1638 When an interrupt is not handled search all handlers
1639 for it. Also check all handlers each timer
1640 interrupt. Intended to get systems with badly broken
1641 firmware running.
1643 isapnp= [ISAPNP]
1644 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1646 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1647 Format:
1648 <cpu number>,...,<cpu number>
1649 or
1650 <cpu number>-<cpu number>
1651 (must be a positive range in ascending order)
1652 or a mixture
1653 <cpu number>,...,<cpu number>-<cpu number>
1655 This option can be used to specify one or more CPUs
1656 to isolate from the general SMP balancing and scheduling
1657 algorithms. You can move a process onto or off an
1658 "isolated" CPU via the CPU affinity syscalls or cpuset.
1659 <cpu number> begins at 0 and the maximum value is
1660 "number of CPUs in system - 1".
1662 This option is the preferred way to isolate CPUs. The
1663 alternative -- manually setting the CPU mask of all
1664 tasks in the system -- can cause problems and
1665 suboptimal load balancer performance.
1667 iucv= [HW,NET]
1669 ivrs_ioapic [HW,X86_64]
1670 Provide an override to the IOAPIC-ID<->DEVICE-ID
1671 mapping provided in the IVRS ACPI table. For
1672 example, to map IOAPIC-ID decimal 10 to
1673 PCI device 00:14.0 write the parameter as:
1674 ivrs_ioapic[10]=00:14.0
1676 ivrs_hpet [HW,X86_64]
1677 Provide an override to the HPET-ID<->DEVICE-ID
1678 mapping provided in the IVRS ACPI table. For
1679 example, to map HPET-ID decimal 0 to
1680 PCI device 00:14.0 write the parameter as:
1681 ivrs_hpet[0]=00:14.0
1683 js= [HW,JOY] Analog joystick
1684 See Documentation/input/joystick.txt.
1686 kaslr/nokaslr [X86]
1687 Enable/disable kernel and module base offset ASLR
1688 (Address Space Layout Randomization) if built into
1689 the kernel. When CONFIG_HIBERNATION is selected,
1690 kASLR is disabled by default. When kASLR is enabled,
1691 hibernation will be disabled.
1693 keepinitrd [HW,ARM]
1695 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1696 specifies the amount of memory usable by the kernel
1697 for non-movable allocations. The requested amount is
1698 spread evenly throughout all nodes in the system. The
1699 remaining memory in each node is used for Movable
1700 pages. In the event, a node is too small to have both
1701 kernelcore and Movable pages, kernelcore pages will
1702 take priority and other nodes will have a larger number
1703 of Movable pages. The Movable zone is used for the
1704 allocation of pages that may be reclaimed or moved
1705 by the page migration subsystem. This means that
1706 HugeTLB pages may not be allocated from this zone.
1707 Note that allocations like PTEs-from-HighMem still
1708 use the HighMem zone if it exists, and the Normal
1709 zone if it does not.
1711 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1712 Format: <Controller#>[,poll interval]
1713 The controller # is the number of the ehci usb debug
1714 port as it is probed via PCI. The poll interval is
1715 optional and is the number seconds in between
1716 each poll cycle to the debug port in case you need
1717 the functionality for interrupting the kernel with
1718 gdb or control-c on the dbgp connection. When
1719 not using this parameter you use sysrq-g to break into
1720 the kernel debugger.
1722 kgdboc= [KGDB,HW] kgdb over consoles.
1723 Requires a tty driver that supports console polling,
1724 or a supported polling keyboard driver (non-usb).
1725 Serial only format: <serial_device>[,baud]
1726 keyboard only format: kbd
1727 keyboard and serial format: kbd,<serial_device>[,baud]
1728 Optional Kernel mode setting:
1729 kms, kbd format: kms,kbd
1730 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1732 kgdbwait [KGDB] Stop kernel execution and enter the
1733 kernel debugger at the earliest opportunity.
1735 kmac= [MIPS] korina ethernet MAC address.
1736 Configure the RouterBoard 532 series on-chip
1737 Ethernet adapter MAC address.
1739 kmemleak= [KNL] Boot-time kmemleak enable/disable
1740 Valid arguments: on, off
1741 Default: on
1742 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1743 the default is off.
1745 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1746 Valid arguments: 0, 1, 2
1747 kmemcheck=0 (disabled)
1748 kmemcheck=1 (enabled)
1749 kmemcheck=2 (one-shot mode)
1750 Default: 2 (one-shot mode)
1752 kstack=N [X86] Print N words from the kernel stack
1753 in oops dumps.
1755 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1756 Default is 0 (don't ignore, but inject #GP)
1758 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1759 KVM MMU at runtime.
1760 Default is 0 (off)
1762 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1763 Default is 1 (enabled)
1765 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1766 for all guests.
1767 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1769 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1770 (virtualized MMU) support on capable Intel chips.
1771 Default is 1 (enabled)
1773 kvm-intel.emulate_invalid_guest_state=
1774 [KVM,Intel] Enable emulation of invalid guest states
1775 Default is 0 (disabled)
1777 kvm-intel.flexpriority=
1778 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1779 Default is 1 (enabled)
1781 kvm-intel.nested=
1782 [KVM,Intel] Enable VMX nesting (nVMX).
1783 Default is 0 (disabled)
1785 kvm-intel.unrestricted_guest=
1786 [KVM,Intel] Disable unrestricted guest feature
1787 (virtualized real and unpaged mode) on capable
1788 Intel chips. Default is 1 (enabled)
1790 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1791 feature (tagged TLBs) on capable Intel chips.
1792 Default is 1 (enabled)
1794 l2cr= [PPC]
1796 l3cr= [PPC]
1798 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1799 disabled it.
1801 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1802 value for LAPIC timer one-shot implementation. Default
1803 back to the programmable timer unit in the LAPIC.
1805 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1806 in C2 power state.
1808 libata.dma= [LIBATA] DMA control
1809 libata.dma=0 Disable all PATA and SATA DMA
1810 libata.dma=1 PATA and SATA Disk DMA only
1811 libata.dma=2 ATAPI (CDROM) DMA only
1812 libata.dma=4 Compact Flash DMA only
1813 Combinations also work, so libata.dma=3 enables DMA
1814 for disks and CDROMs, but not CFs.
1816 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1817 libata.ignore_hpa=0 keep BIOS limits (default)
1818 libata.ignore_hpa=1 ignore limits, using full disk
1820 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1821 when set.
1822 Format: <int>
1824 libata.force= [LIBATA] Force configurations. The format is comma
1825 separated list of "[ID:]VAL" where ID is
1826 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1827 matching port, link or device. Basically, it matches
1828 the ATA ID string printed on console by libata. If
1829 the whole ID part is omitted, the last PORT and DEVICE
1830 values are used. If ID hasn't been specified yet, the
1831 configuration applies to all ports, links and devices.
1833 If only DEVICE is omitted, the parameter applies to
1834 the port and all links and devices behind it. DEVICE
1835 number of 0 either selects the first device or the
1836 first fan-out link behind PMP device. It does not
1837 select the host link. DEVICE number of 15 selects the
1838 host link and device attached to it.
1840 The VAL specifies the configuration to force. As long
1841 as there's no ambiguity shortcut notation is allowed.
1842 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1843 The following configurations can be forced.
1845 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1846 Any ID with matching PORT is used.
1848 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1850 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1851 udma[/][16,25,33,44,66,100,133] notation is also
1852 allowed.
1854 * [no]ncq: Turn on or off NCQ.
1856 * [no]ncqtrim: Turn off queued DSM TRIM.
1858 * nohrst, nosrst, norst: suppress hard, soft
1859 and both resets.
1861 * rstonce: only attempt one reset during
1862 hot-unplug link recovery
1864 * dump_id: dump IDENTIFY data.
1866 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1868 * disable: Disable this device.
1870 If there are multiple matching configurations changing
1871 the same attribute, the last one is used.
1873 memblock=debug [KNL] Enable memblock debug messages.
1875 load_ramdisk= [RAM] List of ramdisks to load from floppy
1876 See Documentation/blockdev/ramdisk.txt.
1878 lockd.nlm_grace_period=P [NFS] Assign grace period.
1879 Format: <integer>
1881 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1882 Format: <integer>
1884 lockd.nlm_timeout=T [NFS] Assign timeout value.
1885 Format: <integer>
1887 lockd.nlm_udpport=M [NFS] Assign UDP port.
1888 Format: <integer>
1890 locktorture.nreaders_stress= [KNL]
1891 Set the number of locking read-acquisition kthreads.
1892 Defaults to being automatically set based on the
1893 number of online CPUs.
1895 locktorture.nwriters_stress= [KNL]
1896 Set the number of locking write-acquisition kthreads.
1898 locktorture.onoff_holdoff= [KNL]
1899 Set time (s) after boot for CPU-hotplug testing.
1901 locktorture.onoff_interval= [KNL]
1902 Set time (s) between CPU-hotplug operations, or
1903 zero to disable CPU-hotplug testing.
1905 locktorture.shuffle_interval= [KNL]
1906 Set task-shuffle interval (jiffies). Shuffling
1907 tasks allows some CPUs to go into dyntick-idle
1908 mode during the locktorture test.
1910 locktorture.shutdown_secs= [KNL]
1911 Set time (s) after boot system shutdown. This
1912 is useful for hands-off automated testing.
1914 locktorture.stat_interval= [KNL]
1915 Time (s) between statistics printk()s.
1917 locktorture.stutter= [KNL]
1918 Time (s) to stutter testing, for example,
1919 specifying five seconds causes the test to run for
1920 five seconds, wait for five seconds, and so on.
1921 This tests the locking primitive's ability to
1922 transition abruptly to and from idle.
1924 locktorture.torture_runnable= [BOOT]
1925 Start locktorture running at boot time.
1927 locktorture.torture_type= [KNL]
1928 Specify the locking implementation to test.
1930 locktorture.verbose= [KNL]
1931 Enable additional printk() statements.
1933 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1934 Format: <irq>
1936 loglevel= All Kernel Messages with a loglevel smaller than the
1937 console loglevel will be printed to the console. It can
1938 also be changed with klogd or other programs. The
1939 loglevels are defined as follows:
1941 0 (KERN_EMERG) system is unusable
1942 1 (KERN_ALERT) action must be taken immediately
1943 2 (KERN_CRIT) critical conditions
1944 3 (KERN_ERR) error conditions
1945 4 (KERN_WARNING) warning conditions
1946 5 (KERN_NOTICE) normal but significant condition
1947 6 (KERN_INFO) informational
1948 7 (KERN_DEBUG) debug-level messages
1950 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1951 in bytes. n must be a power of two and greater
1952 than the minimal size. The minimal size is defined
1953 by LOG_BUF_SHIFT kernel config parameter. There is
1954 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1955 that allows to increase the default size depending on
1956 the number of CPUs. See init/Kconfig for more details.
1958 logo.nologo [FB] Disables display of the built-in Linux logo.
1959 This may be used to provide more screen space for
1960 kernel log messages and is useful when debugging
1961 kernel boot problems.
1963 lp=0 [LP] Specify parallel ports to use, e.g,
1964 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1965 lp=reset first parallel port). 'lp=0' disables the
1966 lp=auto printer driver. 'lp=reset' (which can be
1967 specified in addition to the ports) causes
1968 attached printers to be reset. Using
1969 lp=port1,port2,... specifies the parallel ports
1970 to associate lp devices with, starting with
1971 lp0. A port specification may be 'none' to skip
1972 that lp device, or a parport name such as
1973 'parport0'. Specifying 'lp=auto' instead of a
1974 port specification list means that device IDs
1975 from each port should be examined, to see if
1976 an IEEE 1284-compliant printer is attached; if
1977 so, the driver will manage that printer.
1978 See also header of drivers/char/lp.c.
1980 lpj=n [KNL]
1981 Sets loops_per_jiffy to given constant, thus avoiding
1982 time-consuming boot-time autodetection (up to 250 ms per
1983 CPU). 0 enables autodetection (default). To determine
1984 the correct value for your kernel, boot with normal
1985 autodetection and see what value is printed. Note that
1986 on SMP systems the preset will be applied to all CPUs,
1987 which is likely to cause problems if your CPUs need
1988 significantly divergent settings. An incorrect value
1989 will cause delays in the kernel to be wrong, leading to
1990 unpredictable I/O errors and other breakage. Although
1991 unlikely, in the extreme case this might damage your
1992 hardware.
1994 ltpc= [NET]
1995 Format: <io>,<irq>,<dma>
1997 machvec= [IA-64] Force the use of a particular machine-vector
1998 (machvec) in a generic kernel.
1999 Example: machvec=hpzx1_swiotlb
2001 machtype= [Loongson] Share the same kernel image file between different
2002 yeeloong laptop.
2003 Example: machtype=lemote-yeeloong-2f-7inch
2005 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2006 than or equal to this physical address is ignored.
2008 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2009 should make use of. maxcpus=n : n >= 0 limits the
2010 kernel to using 'n' processors. n=0 is a special case,
2011 it is equivalent to "nosmp", which also disables
2012 the IO APIC.
2014 max_loop= [LOOP] The number of loop block devices that get
2015 (loop.max_loop) unconditionally pre-created at init time. The default
2016 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2017 of statically allocating a predefined number, loop
2018 devices can be requested on-demand with the
2019 /dev/loop-control interface.
2021 mce [X86-32] Machine Check Exception
2023 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2025 md= [HW] RAID subsystems devices and level
2026 See Documentation/md.txt.
2028 mdacon= [MDA]
2029 Format: <first>,<last>
2030 Specifies range of consoles to be captured by the MDA.
2032 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2033 Amount of memory to be used when the kernel is not able
2034 to see the whole system memory or for test.
2035 [X86] Work as limiting max address. Use together
2036 with memmap= to avoid physical address space collisions.
2037 Without memmap= PCI devices could be placed at addresses
2038 belonging to unused RAM.
2040 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2041 memory.
2043 memchunk=nn[KMG]
2044 [KNL,SH] Allow user to override the default size for
2045 per-device physically contiguous DMA buffers.
2047 memmap=exactmap [KNL,X86] Enable setting of an exact
2048 E820 memory map, as specified by the user.
2049 Such memmap=exactmap lines can be constructed based on
2050 BIOS output or other requirements. See the memmap=nn@ss
2051 option description.
2053 memmap=nn[KMG]@ss[KMG]
2054 [KNL] Force usage of a specific region of memory.
2055 Region of memory to be used is from ss to ss+nn.
2057 memmap=nn[KMG]#ss[KMG]
2058 [KNL,ACPI] Mark specific memory as ACPI data.
2059 Region of memory to be marked is from ss to ss+nn.
2061 memmap=nn[KMG]$ss[KMG]
2062 [KNL,ACPI] Mark specific memory as reserved.
2063 Region of memory to be reserved is from ss to ss+nn.
2064 Example: Exclude memory from 0x18690000-0x1869ffff
2065 memmap=64K$0x18690000
2066 or
2067 memmap=0x10000$0x18690000
2069 memmap=nn[KMG]!ss[KMG]
2070 [KNL,X86] Mark specific memory as protected.
2071 Region of memory to be used, from ss to ss+nn.
2072 The memory region may be marked as e820 type 12 (0xc)
2073 and is NVDIMM or ADR memory.
2075 memory_corruption_check=0/1 [X86]
2076 Some BIOSes seem to corrupt the first 64k of
2077 memory when doing things like suspend/resume.
2078 Setting this option will scan the memory
2079 looking for corruption. Enabling this will
2080 both detect corruption and prevent the kernel
2081 from using the memory being corrupted.
2082 However, its intended as a diagnostic tool; if
2083 repeatable BIOS-originated corruption always
2084 affects the same memory, you can use memmap=
2085 to prevent the kernel from using that memory.
2087 memory_corruption_check_size=size [X86]
2088 By default it checks for corruption in the low
2089 64k, making this memory unavailable for normal
2090 use. Use this parameter to scan for
2091 corruption in more or less memory.
2093 memory_corruption_check_period=seconds [X86]
2094 By default it checks for corruption every 60
2095 seconds. Use this parameter to check at some
2096 other rate. 0 disables periodic checking.
2098 memtest= [KNL,X86,ARM] Enable memtest
2099 Format: <integer>
2100 default : 0 <disable>
2101 Specifies the number of memtest passes to be
2102 performed. Each pass selects another test
2103 pattern from a given set of patterns. Memtest
2104 fills the memory with this pattern, validates
2105 memory contents and reserves bad memory
2106 regions that are detected.
2108 meye.*= [HW] Set MotionEye Camera parameters
2109 See Documentation/video4linux/meye.txt.
2111 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2112 Multi-Function General Purpose Timers on AMD Geode
2113 platforms.
2115 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2116 the BIOS has incorrectly applied a workaround. TinyBIOS
2117 version 0.98 is known to be affected, 0.99 fixes the
2118 problem by letting the user disable the workaround.
2120 mga= [HW,DRM]
2122 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2123 physical address is ignored.
2125 mini2440= [ARM,HW,KNL]
2126 Format:[0..2][b][c][t]
2127 Default: "0tb"
2128 MINI2440 configuration specification:
2129 0 - The attached screen is the 3.5" TFT
2130 1 - The attached screen is the 7" TFT
2131 2 - The VGA Shield is attached (1024x768)
2132 Leaving out the screen size parameter will not load
2133 the TFT driver, and the framebuffer will be left
2134 unconfigured.
2135 b - Enable backlight. The TFT backlight pin will be
2136 linked to the kernel VESA blanking code and a GPIO
2137 LED. This parameter is not necessary when using the
2138 VGA shield.
2139 c - Enable the s3c camera interface.
2140 t - Reserved for enabling touchscreen support. The
2141 touchscreen support is not enabled in the mainstream
2142 kernel as of 2.6.30, a preliminary port can be found
2143 in the "bleeding edge" mini2440 support kernel at
2144 http://repo.or.cz/w/linux-2.6/mini2440.git
2146 mminit_loglevel=
2147 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2148 parameter allows control of the logging verbosity for
2149 the additional memory initialisation checks. A value
2150 of 0 disables mminit logging and a level of 4 will
2151 log everything. Information is printed at KERN_DEBUG
2152 so loglevel=8 may also need to be specified.
2154 module.sig_enforce
2155 [KNL] When CONFIG_MODULE_SIG is set, this means that
2156 modules without (valid) signatures will fail to load.
2157 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2158 is always true, so this option does nothing.
2160 mousedev.tap_time=
2161 [MOUSE] Maximum time between finger touching and
2162 leaving touchpad surface for touch to be considered
2163 a tap and be reported as a left button click (for
2164 touchpads working in absolute mode only).
2165 Format: <msecs>
2166 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2167 reporting absolute coordinates, such as tablets
2168 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2169 reporting absolute coordinates, such as tablets
2171 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2172 is similar to kernelcore except it specifies the
2173 amount of memory used for migratable allocations.
2174 If both kernelcore and movablecore is specified,
2175 then kernelcore will be at *least* the specified
2176 value but may be more. If movablecore on its own
2177 is specified, the administrator must be careful
2178 that the amount of memory usable for all allocations
2179 is not too small.
2181 movable_node [KNL,X86] Boot-time switch to enable the effects
2182 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2184 MTD_Partition= [MTD]
2185 Format: <name>,<region-number>,<size>,<offset>
2187 MTD_Region= [MTD] Format:
2188 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2190 mtdparts= [MTD]
2191 See drivers/mtd/cmdlinepart.c.
2193 multitce=off [PPC] This parameter disables the use of the pSeries
2194 firmware feature for updating multiple TCE entries
2195 at a time.
2197 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2199 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2201 boundary - index of last SLC block on Flex-OneNAND.
2202 The remaining blocks are configured as MLC blocks.
2203 lock - Configure if Flex-OneNAND boundary should be locked.
2204 Once locked, the boundary cannot be changed.
2205 1 indicates lock status, 0 indicates unlock status.
2207 mtdset= [ARM]
2208 ARM/S3C2412 JIVE boot control
2210 See arch/arm/mach-s3c2412/mach-jive.c
2212 mtouchusb.raw_coordinates=
2213 [HW] Make the MicroTouch USB driver use raw coordinates
2214 ('y', default) or cooked coordinates ('n')
2216 mtrr_chunk_size=nn[KMG] [X86]
2217 used for mtrr cleanup. It is largest continuous chunk
2218 that could hold holes aka. UC entries.
2220 mtrr_gran_size=nn[KMG] [X86]
2221 Used for mtrr cleanup. It is granularity of mtrr block.
2222 Default is 1.
2223 Large value could prevent small alignment from
2224 using up MTRRs.
2226 mtrr_spare_reg_nr=n [X86]
2227 Format: <integer>
2228 Range: 0,7 : spare reg number
2229 Default : 1
2230 Used for mtrr cleanup. It is spare mtrr entries number.
2231 Set to 2 or more if your graphical card needs more.
2233 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2235 netdev= [NET] Network devices parameters
2236 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2237 Note that mem_start is often overloaded to mean
2238 something different and driver-specific.
2239 This usage is only documented in each driver source
2240 file if at all.
2242 nf_conntrack.acct=
2243 [NETFILTER] Enable connection tracking flow accounting
2244 0 to disable accounting
2245 1 to enable accounting
2246 Default value is 0.
2248 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2249 See Documentation/filesystems/nfs/nfsroot.txt.
2251 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2252 See Documentation/filesystems/nfs/nfsroot.txt.
2254 nfsrootdebug [NFS] enable nfsroot debugging messages.
2255 See Documentation/filesystems/nfs/nfsroot.txt.
2257 nfs.callback_tcpport=
2258 [NFS] set the TCP port on which the NFSv4 callback
2259 channel should listen.
2261 nfs.cache_getent=
2262 [NFS] sets the pathname to the program which is used
2263 to update the NFS client cache entries.
2265 nfs.cache_getent_timeout=
2266 [NFS] sets the timeout after which an attempt to
2267 update a cache entry is deemed to have failed.
2269 nfs.idmap_cache_timeout=
2270 [NFS] set the maximum lifetime for idmapper cache
2271 entries.
2273 nfs.enable_ino64=
2274 [NFS] enable 64-bit inode numbers.
2275 If zero, the NFS client will fake up a 32-bit inode
2276 number for the readdir() and stat() syscalls instead
2277 of returning the full 64-bit number.
2278 The default is to return 64-bit inode numbers.
2280 nfs.max_session_slots=
2281 [NFSv4.1] Sets the maximum number of session slots
2282 the client will attempt to negotiate with the server.
2283 This limits the number of simultaneous RPC requests
2284 that the client can send to the NFSv4.1 server.
2285 Note that there is little point in setting this
2286 value higher than the max_tcp_slot_table_limit.
2288 nfs.nfs4_disable_idmapping=
2289 [NFSv4] When set to the default of '1', this option
2290 ensures that both the RPC level authentication
2291 scheme and the NFS level operations agree to use
2292 numeric uids/gids if the mount is using the
2293 'sec=sys' security flavour. In effect it is
2294 disabling idmapping, which can make migration from
2295 legacy NFSv2/v3 systems to NFSv4 easier.
2296 Servers that do not support this mode of operation
2297 will be autodetected by the client, and it will fall
2298 back to using the idmapper.
2299 To turn off this behaviour, set the value to '0'.
2300 nfs.nfs4_unique_id=
2301 [NFS4] Specify an additional fixed unique ident-
2302 ification string that NFSv4 clients can insert into
2303 their nfs_client_id4 string. This is typically a
2304 UUID that is generated at system install time.
2306 nfs.send_implementation_id =
2307 [NFSv4.1] Send client implementation identification
2308 information in exchange_id requests.
2309 If zero, no implementation identification information
2310 will be sent.
2311 The default is to send the implementation identification
2312 information.
2314 nfs.recover_lost_locks =
2315 [NFSv4] Attempt to recover locks that were lost due
2316 to a lease timeout on the server. Please note that
2317 doing this risks data corruption, since there are
2318 no guarantees that the file will remain unchanged
2319 after the locks are lost.
2320 If you want to enable the kernel legacy behaviour of
2321 attempting to recover these locks, then set this
2322 parameter to '1'.
2323 The default parameter value of '0' causes the kernel
2324 not to attempt recovery of lost locks.
2326 nfs4.layoutstats_timer =
2327 [NFSv4.2] Change the rate at which the kernel sends
2328 layoutstats to the pNFS metadata server.
2330 Setting this to value to 0 causes the kernel to use
2331 whatever value is the default set by the layout
2332 driver. A non-zero value sets the minimum interval
2333 in seconds between layoutstats transmissions.
2335 nfsd.nfs4_disable_idmapping=
2336 [NFSv4] When set to the default of '1', the NFSv4
2337 server will return only numeric uids and gids to
2338 clients using auth_sys, and will accept numeric uids
2339 and gids from such clients. This is intended to ease
2340 migration from NFSv2/v3.
2342 objlayoutdriver.osd_login_prog=
2343 [NFS] [OBJLAYOUT] sets the pathname to the program which
2344 is used to automatically discover and login into new
2345 osd-targets. Please see:
2346 Documentation/filesystems/pnfs.txt for more explanations
2348 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2349 when a NMI is triggered.
2350 Format: [state][,regs][,debounce][,die]
2352 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2353 Format: [panic,][nopanic,][num]
2354 Valid num: 0 or 1
2355 0 - turn hardlockup detector in nmi_watchdog off
2356 1 - turn hardlockup detector in nmi_watchdog on
2357 When panic is specified, panic when an NMI watchdog
2358 timeout occurs (or 'nopanic' to override the opposite
2359 default). To disable both hard and soft lockup detectors,
2360 please see 'nowatchdog'.
2361 This is useful when you use a panic=... timeout and
2362 need the box quickly up again.
2364 netpoll.carrier_timeout=
2365 [NET] Specifies amount of time (in seconds) that
2366 netpoll should wait for a carrier. By default netpoll
2367 waits 4 seconds.
2369 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2370 emulation library even if a 387 maths coprocessor
2371 is present.
2373 no_console_suspend
2374 [HW] Never suspend the console
2375 Disable suspending of consoles during suspend and
2376 hibernate operations. Once disabled, debugging
2377 messages can reach various consoles while the rest
2378 of the system is being put to sleep (ie, while
2379 debugging driver suspend/resume hooks). This may
2380 not work reliably with all consoles, but is known
2381 to work with serial and VGA consoles.
2382 To facilitate more flexible debugging, we also add
2383 console_suspend, a printk module parameter to control
2384 it. Users could use console_suspend (usually
2385 /sys/module/printk/parameters/console_suspend) to
2386 turn on/off it dynamically.
2388 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2389 caches in the slab allocator. Saves per-node memory,
2390 but will impact performance.
2392 noalign [KNL,ARM]
2394 noapic [SMP,APIC] Tells the kernel to not make use of any
2395 IOAPICs that may be present in the system.
2397 noautogroup Disable scheduler automatic task group creation.
2399 nobats [PPC] Do not use BATs for mapping kernel lowmem
2400 on "Classic" PPC cores.
2402 nocache [ARM]
2404 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2406 nodelayacct [KNL] Disable per-task delay accounting
2408 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2410 nodsp [SH] Disable hardware DSP at boot time.
2412 noefi Disable EFI runtime services support.
2414 noexec [IA-64]
2416 noexec [X86]
2417 On X86-32 available only on PAE configured kernels.
2418 noexec=on: enable non-executable mappings (default)
2419 noexec=off: disable non-executable mappings
2421 nosmap [X86]
2422 Disable SMAP (Supervisor Mode Access Prevention)
2423 even if it is supported by processor.
2425 nosmep [X86]
2426 Disable SMEP (Supervisor Mode Execution Prevention)
2427 even if it is supported by processor.
2429 noexec32 [X86-64]
2430 This affects only 32-bit executables.
2431 noexec32=on: enable non-executable mappings (default)
2432 read doesn't imply executable mappings
2433 noexec32=off: disable non-executable mappings
2434 read implies executable mappings
2436 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2438 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2439 register save and restore. The kernel will only save
2440 legacy floating-point registers on task switch.
2442 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2444 noxsave [BUGS=X86] Disables x86 extended register state save
2445 and restore using xsave. The kernel will fallback to
2446 enabling legacy floating-point and sse state.
2448 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2449 register states. The kernel will fall back to use
2450 xsave to save the states. By using this parameter,
2451 performance of saving the states is degraded because
2452 xsave doesn't support modified optimization while
2453 xsaveopt supports it on xsaveopt enabled systems.
2455 noxsaves [X86] Disables xsaves and xrstors used in saving and
2456 restoring x86 extended register state in compacted
2457 form of xsave area. The kernel will fall back to use
2458 xsaveopt and xrstor to save and restore the states
2459 in standard form of xsave area. By using this
2460 parameter, xsave area per process might occupy more
2461 memory on xsaves enabled systems.
2463 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2464 wfi(ARM) instruction doesn't work correctly and not to
2465 use it. This is also useful when using JTAG debugger.
2467 no_file_caps Tells the kernel not to honor file capabilities. The
2468 only way then for a file to be executed with privilege
2469 is to be setuid root or executed by root.
2471 nohalt [IA-64] Tells the kernel not to use the power saving
2472 function PAL_HALT_LIGHT when idle. This increases
2473 power-consumption. On the positive side, it reduces
2474 interrupt wake-up latency, which may improve performance
2475 in certain environments such as networked servers or
2476 real-time systems.
2478 nohibernate [HIBERNATION] Disable hibernation and resume.
2480 nohz= [KNL] Boottime enable/disable dynamic ticks
2481 Valid arguments: on, off
2482 Default: on
2484 nohz_full= [KNL,BOOT]
2485 In kernels built with CONFIG_NO_HZ_FULL=y, set
2486 the specified list of CPUs whose tick will be stopped
2487 whenever possible. The boot CPU will be forced outside
2488 the range to maintain the timekeeping.
2489 The CPUs in this range must also be included in the
2490 rcu_nocbs= set.
2492 noiotrap [SH] Disables trapped I/O port accesses.
2494 noirqdebug [X86-32] Disables the code which attempts to detect and
2495 disable unhandled interrupt sources.
2497 no_timer_check [X86,APIC] Disables the code which tests for
2498 broken timer IRQ sources.
2500 noisapnp [ISAPNP] Disables ISA PnP code.
2502 noinitrd [RAM] Tells the kernel not to load any configured
2503 initial RAM disk.
2505 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2506 remapping.
2507 [Deprecated - use intremap=off]
2509 nointroute [IA-64]
2511 nojitter [IA-64] Disables jitter checking for ITC timers.
2513 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2515 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2516 fault handling.
2518 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2519 steal time is computed, but won't influence scheduler
2520 behaviour
2522 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2524 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2526 noltlbs [PPC] Do not use large page/tlb entries for kernel
2527 lowmem mapping on PPC40x.
2529 nomca [IA-64] Disable machine check abort handling
2531 nomce [X86-32] Disable Machine Check Exception
2533 nomfgpt [X86-32] Disable Multi-Function General Purpose
2534 Timer usage (for AMD Geode machines).
2536 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2537 shutdown the other cpus. Instead use the REBOOT_VECTOR
2538 irq.
2540 nomodule Disable module load
2542 nopat [X86] Disable PAT (page attribute table extension of
2543 pagetables) support.
2545 norandmaps Don't use address space randomization. Equivalent to
2546 echo 0 > /proc/sys/kernel/randomize_va_space
2548 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2550 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2551 with UP alternatives
2553 nordrand [X86] Disable kernel use of the RDRAND and
2554 RDSEED instructions even if they are supported
2555 by the processor. RDRAND and RDSEED are still
2556 available to user space applications.
2558 noresume [SWSUSP] Disables resume and restores original swap
2559 space.
2561 no-scroll [VGA] Disables scrollback.
2562 This is required for the Braillex ib80-piezo Braille
2563 reader made by F.H. Papenmeier (Germany).
2565 nosbagart [IA-64]
2567 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2569 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2570 and disable the IO APIC. legacy for "maxcpus=0".
2572 nosoftlockup [KNL] Disable the soft-lockup detector.
2574 nosync [HW,M68K] Disables sync negotiation for all devices.
2576 notsc [BUGS=X86-32] Disable Time Stamp Counter
2578 nousb [USB] Disable the USB subsystem
2580 nowatchdog [KNL] Disable both lockup detectors, i.e.
2581 soft-lockup and NMI watchdog (hard-lockup).
2583 nowb [ARM]
2585 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2587 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2588 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2589 Some features depend on CPU0. Known dependencies are:
2590 1. Resume from suspend/hibernate depends on CPU0.
2591 Suspend/hibernate will fail if CPU0 is offline and you
2592 need to online CPU0 before suspend/hibernate.
2593 2. PIC interrupts also depend on CPU0. CPU0 can't be
2594 removed if a PIC interrupt is detected.
2595 It's said poweroff/reboot may depend on CPU0 on some
2596 machines although I haven't seen such issues so far
2597 after CPU0 is offline on a few tested machines.
2598 If the dependencies are under your control, you can
2599 turn on cpu0_hotplug.
2601 nptcg= [IA-64] Override max number of concurrent global TLB
2602 purges which is reported from either PAL_VM_SUMMARY or
2603 SAL PALO.
2605 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2606 could support. nr_cpus=n : n >= 1 limits the kernel to
2607 supporting 'n' processors. Later in runtime you can not
2608 use hotplug cpu feature to put more cpu back to online.
2609 just like you compile the kernel NR_CPUS=n
2611 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2613 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2614 Allowed values are enable and disable
2616 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2617 one of ['zone', 'node', 'default'] can be specified
2618 This can be set from sysctl after boot.
2619 See Documentation/sysctl/vm.txt for details.
2621 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2622 See Documentation/debugging-via-ohci1394.txt for more
2623 info.
2625 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2626 Rather than timing out after 20 ms if an EC
2627 command is not properly ACKed, override the length
2628 of the timeout. We have interrupts disabled while
2629 waiting for the ACK, so if this is set too high
2630 interrupts *may* be lost!
2632 omap_mux= [OMAP] Override bootloader pin multiplexing.
2633 Format: <mux_mode0.mode_name=value>...
2634 For example, to override I2C bus2:
2635 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2637 oprofile.timer= [HW]
2638 Use timer interrupt instead of performance counters
2640 oprofile.cpu_type= Force an oprofile cpu type
2641 This might be useful if you have an older oprofile
2642 userland or if you want common events.
2643 Format: { arch_perfmon }
2644 arch_perfmon: [X86] Force use of architectural
2645 perfmon on Intel CPUs instead of the
2646 CPU specific event set.
2647 timer: [X86] Force use of architectural NMI
2648 timer mode (see also oprofile.timer
2649 for generic hr timer mode)
2650 [s390] Force legacy basic mode sampling
2651 (report cpu_type "timer")
2653 oops=panic Always panic on oopses. Default is to just kill the
2654 process, but there is a small probability of
2655 deadlocking the machine.
2656 This will also cause panics on machine check exceptions.
2657 Useful together with panic=30 to trigger a reboot.
2659 OSS [HW,OSS]
2660 See Documentation/sound/oss/oss-parameters.txt
2662 page_owner= [KNL] Boot-time page_owner enabling option.
2663 Storage of the information about who allocated
2664 each page is disabled in default. With this switch,
2665 we can turn it on.
2666 on: enable the feature
2668 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2669 timeout > 0: seconds before rebooting
2670 timeout = 0: wait forever
2671 timeout < 0: reboot immediately
2672 Format: <timeout>
2674 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2675 on a WARN().
2677 crash_kexec_post_notifiers
2678 Run kdump after running panic-notifiers and dumping
2679 kmsg. This only for the users who doubt kdump always
2680 succeeds in any situation.
2681 Note that this also increases risks of kdump failure,
2682 because some panic notifiers can make the crashed
2683 kernel more unstable.
2685 parkbd.port= [HW] Parallel port number the keyboard adapter is
2686 connected to, default is 0.
2687 Format: <parport#>
2688 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2689 0 for XT, 1 for AT (default is AT).
2690 Format: <mode>
2692 parport= [HW,PPT] Specify parallel ports. 0 disables.
2693 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2694 Use 'auto' to force the driver to use any
2695 IRQ/DMA settings detected (the default is to
2696 ignore detected IRQ/DMA settings because of
2697 possible conflicts). You can specify the base
2698 address, IRQ, and DMA settings; IRQ and DMA
2699 should be numbers, or 'auto' (for using detected
2700 settings on that particular port), or 'nofifo'
2701 (to avoid using a FIFO even if it is detected).
2702 Parallel ports are assigned in the order they
2703 are specified on the command line, starting
2704 with parport0.
2706 parport_init_mode= [HW,PPT]
2707 Configure VIA parallel port to operate in
2708 a specific mode. This is necessary on Pegasos
2709 computer where firmware has no options for setting
2710 up parallel port mode and sets it to spp.
2711 Currently this function knows 686a and 8231 chips.
2712 Format: [spp|ps2|epp|ecp|ecpepp]
2714 pause_on_oops=
2715 Halt all CPUs after the first oops has been printed for
2716 the specified number of seconds. This is to be used if
2717 your oopses keep scrolling off the screen.
2719 pcbit= [HW,ISDN]
2721 pcd. [PARIDE]
2722 See header of drivers/block/paride/pcd.c.
2723 See also Documentation/blockdev/paride.txt.
2725 pci=option[,option...] [PCI] various PCI subsystem options:
2726 earlydump [X86] dump PCI config space before the kernel
2727 changes anything
2728 off [X86] don't probe for the PCI bus
2729 bios [X86-32] force use of PCI BIOS, don't access
2730 the hardware directly. Use this if your machine
2731 has a non-standard PCI host bridge.
2732 nobios [X86-32] disallow use of PCI BIOS, only direct
2733 hardware access methods are allowed. Use this
2734 if you experience crashes upon bootup and you
2735 suspect they are caused by the BIOS.
2736 conf1 [X86] Force use of PCI Configuration
2737 Mechanism 1.
2738 conf2 [X86] Force use of PCI Configuration
2739 Mechanism 2.
2740 noaer [PCIE] If the PCIEAER kernel config parameter is
2741 enabled, this kernel boot option can be used to
2742 disable the use of PCIE advanced error reporting.
2743 nodomains [PCI] Disable support for multiple PCI
2744 root domains (aka PCI segments, in ACPI-speak).
2745 nommconf [X86] Disable use of MMCONFIG for PCI
2746 Configuration
2747 check_enable_amd_mmconf [X86] check for and enable
2748 properly configured MMIO access to PCI
2749 config space on AMD family 10h CPU
2750 nomsi [MSI] If the PCI_MSI kernel config parameter is
2751 enabled, this kernel boot option can be used to
2752 disable the use of MSI interrupts system-wide.
2753 noioapicquirk [APIC] Disable all boot interrupt quirks.
2754 Safety option to keep boot IRQs enabled. This
2755 should never be necessary.
2756 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2757 primary IO-APIC for bridges that cannot disable
2758 boot IRQs. This fixes a source of spurious IRQs
2759 when the system masks IRQs.
2760 noioapicreroute [APIC] Disable workaround that uses the
2761 boot IRQ equivalent of an IRQ that connects to
2762 a chipset where boot IRQs cannot be disabled.
2763 The opposite of ioapicreroute.
2764 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2765 routing table. These calls are known to be buggy
2766 on several machines and they hang the machine
2767 when used, but on other computers it's the only
2768 way to get the interrupt routing table. Try
2769 this option if the kernel is unable to allocate
2770 IRQs or discover secondary PCI buses on your
2771 motherboard.
2772 rom [X86] Assign address space to expansion ROMs.
2773 Use with caution as certain devices share
2774 address decoders between ROMs and other
2775 resources.
2776 norom [X86] Do not assign address space to
2777 expansion ROMs that do not already have
2778 BIOS assigned address ranges.
2779 nobar [X86] Do not assign address space to the
2780 BARs that weren't assigned by the BIOS.
2781 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2782 assigned automatically to PCI devices. You can
2783 make the kernel exclude IRQs of your ISA cards
2784 this way.
2785 pirqaddr=0xAAAAA [X86] Specify the physical address
2786 of the PIRQ table (normally generated
2787 by the BIOS) if it is outside the
2788 F0000h-100000h range.
2789 lastbus=N [X86] Scan all buses thru bus #N. Can be
2790 useful if the kernel is unable to find your
2791 secondary buses and you want to tell it
2792 explicitly which ones they are.
2793 assign-busses [X86] Always assign all PCI bus
2794 numbers ourselves, overriding
2795 whatever the firmware may have done.
2796 usepirqmask [X86] Honor the possible IRQ mask stored
2797 in the BIOS $PIR table. This is needed on
2798 some systems with broken BIOSes, notably
2799 some HP Pavilion N5400 and Omnibook XE3
2800 notebooks. This will have no effect if ACPI
2801 IRQ routing is enabled.
2802 noacpi [X86] Do not use ACPI for IRQ routing
2803 or for PCI scanning.
2804 use_crs [X86] Use PCI host bridge window information
2805 from ACPI. On BIOSes from 2008 or later, this
2806 is enabled by default. If you need to use this,
2807 please report a bug.
2808 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2809 If you need to use this, please report a bug.
2810 routeirq Do IRQ routing for all PCI devices.
2811 This is normally done in pci_enable_device(),
2812 so this option is a temporary workaround
2813 for broken drivers that don't call it.
2814 skip_isa_align [X86] do not align io start addr, so can
2815 handle more pci cards
2816 firmware [ARM] Do not re-enumerate the bus but instead
2817 just use the configuration from the
2818 bootloader. This is currently used on
2819 IXP2000 systems where the bus has to be
2820 configured a certain way for adjunct CPUs.
2821 noearly [X86] Don't do any early type 1 scanning.
2822 This might help on some broken boards which
2823 machine check when some devices' config space
2824 is read. But various workarounds are disabled
2825 and some IOMMU drivers will not work.
2826 bfsort Sort PCI devices into breadth-first order.
2827 This sorting is done to get a device
2828 order compatible with older (<= 2.4) kernels.
2829 nobfsort Don't sort PCI devices into breadth-first order.
2830 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2831 tuning and use the BIOS-configured MPS defaults.
2832 pcie_bus_safe Set every device's MPS to the largest value
2833 supported by all devices below the root complex.
2834 pcie_bus_perf Set device MPS to the largest allowable MPS
2835 based on its parent bus. Also set MRRS (Max
2836 Read Request Size) to the largest supported
2837 value (no larger than the MPS that the device
2838 or bus can support) for best performance.
2839 pcie_bus_peer2peer Set every device's MPS to 128B, which
2840 every device is guaranteed to support. This
2841 configuration allows peer-to-peer DMA between
2842 any pair of devices, possibly at the cost of
2843 reduced performance. This also guarantees
2844 that hot-added devices will work.
2845 cbiosize=nn[KMG] The fixed amount of bus space which is
2846 reserved for the CardBus bridge's IO window.
2847 The default value is 256 bytes.
2848 cbmemsize=nn[KMG] The fixed amount of bus space which is
2849 reserved for the CardBus bridge's memory
2850 window. The default value is 64 megabytes.
2851 resource_alignment=
2852 Format:
2853 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2854 Specifies alignment and device to reassign
2855 aligned memory resources.
2856 If <order of align> is not specified,
2857 PAGE_SIZE is used as alignment.
2858 PCI-PCI bridge can be specified, if resource
2859 windows need to be expanded.
2860 ecrc= Enable/disable PCIe ECRC (transaction layer
2861 end-to-end CRC checking).
2862 bios: Use BIOS/firmware settings. This is the
2863 the default.
2864 off: Turn ECRC off
2865 on: Turn ECRC on.
2866 hpiosize=nn[KMG] The fixed amount of bus space which is
2867 reserved for hotplug bridge's IO window.
2868 Default size is 256 bytes.
2869 hpmemsize=nn[KMG] The fixed amount of bus space which is
2870 reserved for hotplug bridge's memory window.
2871 Default size is 2 megabytes.
2872 realloc= Enable/disable reallocating PCI bridge resources
2873 if allocations done by BIOS are too small to
2874 accommodate resources required by all child
2875 devices.
2876 off: Turn realloc off
2877 on: Turn realloc on
2878 realloc same as realloc=on
2879 noari do not use PCIe ARI.
2880 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2881 only look for one device below a PCIe downstream
2882 port.
2884 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2885 Management.
2886 off Disable ASPM.
2887 force Enable ASPM even on devices that claim not to support it.
2888 WARNING: Forcing ASPM on may cause system lockups.
2890 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2891 nomsi Do not use MSI for PCI Express Native Hotplug (this
2892 makes all PCIe ports use INTx for hotplug services).
2894 pcie_ports= [PCIE] PCIe ports handling:
2895 auto Ask the BIOS whether or not to use native PCIe services
2896 associated with PCIe ports (PME, hot-plug, AER). Use
2897 them only if that is allowed by the BIOS.
2898 native Use native PCIe services associated with PCIe ports
2899 unconditionally.
2900 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2901 ports driver.
2903 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2904 nomsi Do not use MSI for native PCIe PME signaling (this makes
2905 all PCIe root ports use INTx for all services).
2907 pcmv= [HW,PCMCIA] BadgePAD 4
2909 pd_ignore_unused
2910 [PM]
2911 Keep all power-domains already enabled by bootloader on,
2912 even if no driver has claimed them. This is useful
2913 for debug and development, but should not be
2914 needed on a platform with proper driver support.
2916 pd. [PARIDE]
2917 See Documentation/blockdev/paride.txt.
2919 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2920 boot time.
2921 Format: { 0 | 1 }
2922 See arch/parisc/kernel/pdc_chassis.c
2924 percpu_alloc= Select which percpu first chunk allocator to use.
2925 Currently supported values are "embed" and "page".
2926 Archs may support subset or none of the selections.
2927 See comments in mm/percpu.c for details on each
2928 allocator. This parameter is primarily for debugging
2929 and performance comparison.
2931 pf. [PARIDE]
2932 See Documentation/blockdev/paride.txt.
2934 pg. [PARIDE]
2935 See Documentation/blockdev/paride.txt.
2937 pirq= [SMP,APIC] Manual mp-table setup
2938 See Documentation/x86/i386/IO-APIC.txt.
2940 plip= [PPT,NET] Parallel port network link
2941 Format: { parport<nr> | timid | 0 }
2942 See also Documentation/parport.txt.
2944 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2945 Override pmtimer IOPort with a hex value.
2946 e.g. pmtmr=0x508
2948 pnp.debug=1 [PNP]
2949 Enable PNP debug messages (depends on the
2950 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2951 via /sys/module/pnp/parameters/debug. We always show
2952 current resource usage; turning this on also shows
2953 possible settings and some assignment information.
2955 pnpacpi= [ACPI]
2956 { off }
2958 pnpbios= [ISAPNP]
2959 { on | off | curr | res | no-curr | no-res }
2961 pnp_reserve_irq=
2962 [ISAPNP] Exclude IRQs for the autoconfiguration
2964 pnp_reserve_dma=
2965 [ISAPNP] Exclude DMAs for the autoconfiguration
2967 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2968 Ranges are in pairs (I/O port base and size).
2970 pnp_reserve_mem=
2971 [ISAPNP] Exclude memory regions for the
2972 autoconfiguration.
2973 Ranges are in pairs (memory base and size).
2975 ports= [IP_VS_FTP] IPVS ftp helper module
2976 Default is 21.
2977 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2978 may be specified.
2979 Format: <port>,<port>....
2981 print-fatal-signals=
2982 [KNL] debug: print fatal signals
2984 If enabled, warn about various signal handling
2985 related application anomalies: too many signals,
2986 too many POSIX.1 timers, fatal signals causing a
2987 coredump - etc.
2989 If you hit the warning due to signal overflow,
2990 you might want to try "ulimit -i unlimited".
2992 default: off.
2994 printk.always_kmsg_dump=
2995 Trigger kmsg_dump for cases other than kernel oops or
2996 panics
2997 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2998 default: disabled
3000 printk.time= Show timing data prefixed to each printk message line
3001 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3003 processor.max_cstate= [HW,ACPI]
3004 Limit processor to maximum C-state
3005 max_cstate=9 overrides any DMI blacklist limit.
3007 processor.nocst [HW,ACPI]
3008 Ignore the _CST method to determine C-states,
3009 instead using the legacy FADT method
3011 profile= [KNL] Enable kernel profiling via /proc/profile
3012 Format: [schedule,]<number>
3013 Param: "schedule" - profile schedule points.
3014 Param: <number> - step/bucket size as a power of 2 for
3015 statistical time based profiling.
3016 Param: "sleep" - profile D-state sleeping (millisecs).
3017 Requires CONFIG_SCHEDSTATS
3018 Param: "kvm" - profile VM exits.
3020 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3021 before loading.
3022 See Documentation/blockdev/ramdisk.txt.
3024 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3025 probe for; one of (bare|imps|exps|lifebook|any).
3026 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3027 per second.
3028 psmouse.resetafter= [HW,MOUSE]
3029 Try to reset the device after so many bad packets
3030 (0 = never).
3031 psmouse.resolution=
3032 [HW,MOUSE] Set desired mouse resolution, in dpi.
3033 psmouse.smartscroll=
3034 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3035 0 = disabled, 1 = enabled (default).
3037 pstore.backend= Specify the name of the pstore backend to use
3039 pt. [PARIDE]
3040 See Documentation/blockdev/paride.txt.
3042 pty.legacy_count=
3043 [KNL] Number of legacy pty's. Overwrites compiled-in
3044 default number.
3046 quiet [KNL] Disable most log messages
3048 r128= [HW,DRM]
3050 raid= [HW,RAID]
3051 See Documentation/md.txt.
3053 ramdisk_blocksize= [RAM]
3054 See Documentation/blockdev/ramdisk.txt.
3056 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3057 See Documentation/blockdev/ramdisk.txt.
3059 rcu_nocbs= [KNL]
3060 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3061 the specified list of CPUs to be no-callback CPUs.
3062 Invocation of these CPUs' RCU callbacks will
3063 be offloaded to "rcuox/N" kthreads created for
3064 that purpose, where "x" is "b" for RCU-bh, "p"
3065 for RCU-preempt, and "s" for RCU-sched, and "N"
3066 is the CPU number. This reduces OS jitter on the
3067 offloaded CPUs, which can be useful for HPC and
3068 real-time workloads. It can also improve energy
3069 efficiency for asymmetric multiprocessors.
3071 rcu_nocb_poll [KNL]
3072 Rather than requiring that offloaded CPUs
3073 (specified by rcu_nocbs= above) explicitly
3074 awaken the corresponding "rcuoN" kthreads,
3075 make these kthreads poll for callbacks.
3076 This improves the real-time response for the
3077 offloaded CPUs by relieving them of the need to
3078 wake up the corresponding kthread, but degrades
3079 energy efficiency by requiring that the kthreads
3080 periodically wake up to do the polling.
3082 rcutree.blimit= [KNL]
3083 Set maximum number of finished RCU callbacks to
3084 process in one batch.
3086 rcutree.dump_tree= [KNL]
3087 Dump the structure of the rcu_node combining tree
3088 out at early boot. This is used for diagnostic
3089 purposes, to verify correct tree setup.
3091 rcutree.gp_cleanup_delay= [KNL]
3092 Set the number of jiffies to delay each step of
3093 RCU grace-period cleanup. This only has effect
3094 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3096 rcutree.gp_init_delay= [KNL]
3097 Set the number of jiffies to delay each step of
3098 RCU grace-period initialization. This only has
3099 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3100 is set.
3102 rcutree.gp_preinit_delay= [KNL]
3103 Set the number of jiffies to delay each step of
3104 RCU grace-period pre-initialization, that is,
3105 the propagation of recent CPU-hotplug changes up
3106 the rcu_node combining tree. This only has effect
3107 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3109 rcutree.rcu_fanout_exact= [KNL]
3110 Disable autobalancing of the rcu_node combining
3111 tree. This is used by rcutorture, and might
3112 possibly be useful for architectures having high
3113 cache-to-cache transfer latencies.
3115 rcutree.rcu_fanout_leaf= [KNL]
3116 Change the number of CPUs assigned to each
3117 leaf rcu_node structure. Useful for very
3118 large systems, which will choose the value 64,
3119 and for NUMA systems with large remote-access
3120 latencies, which will choose a value aligned
3121 with the appropriate hardware boundaries.
3123 rcutree.jiffies_till_sched_qs= [KNL]
3124 Set required age in jiffies for a
3125 given grace period before RCU starts
3126 soliciting quiescent-state help from
3127 rcu_note_context_switch().
3129 rcutree.jiffies_till_first_fqs= [KNL]
3130 Set delay from grace-period initialization to
3131 first attempt to force quiescent states.
3132 Units are jiffies, minimum value is zero,
3133 and maximum value is HZ.
3135 rcutree.jiffies_till_next_fqs= [KNL]
3136 Set delay between subsequent attempts to force
3137 quiescent states. Units are jiffies, minimum
3138 value is one, and maximum value is HZ.
3140 rcutree.kthread_prio= [KNL,BOOT]
3141 Set the SCHED_FIFO priority of the RCU per-CPU
3142 kthreads (rcuc/N). This value is also used for
3143 the priority of the RCU boost threads (rcub/N)
3144 and for the RCU grace-period kthreads (rcu_bh,
3145 rcu_preempt, and rcu_sched). If RCU_BOOST is
3146 set, valid values are 1-99 and the default is 1
3147 (the least-favored priority). Otherwise, when
3148 RCU_BOOST is not set, valid values are 0-99 and
3149 the default is zero (non-realtime operation).
3151 rcutree.rcu_nocb_leader_stride= [KNL]
3152 Set the number of NOCB kthread groups, which
3153 defaults to the square root of the number of
3154 CPUs. Larger numbers reduces the wakeup overhead
3155 on the per-CPU grace-period kthreads, but increases
3156 that same overhead on each group's leader.
3158 rcutree.qhimark= [KNL]
3159 Set threshold of queued RCU callbacks beyond which
3160 batch limiting is disabled.
3162 rcutree.qlowmark= [KNL]
3163 Set threshold of queued RCU callbacks below which
3164 batch limiting is re-enabled.
3166 rcutree.rcu_idle_gp_delay= [KNL]
3167 Set wakeup interval for idle CPUs that have
3168 RCU callbacks (RCU_FAST_NO_HZ=y).
3170 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3171 Set wakeup interval for idle CPUs that have
3172 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3173 Lazy RCU callbacks are those which RCU can
3174 prove do nothing more than free memory.
3176 rcutorture.cbflood_inter_holdoff= [KNL]
3177 Set holdoff time (jiffies) between successive
3178 callback-flood tests.
3180 rcutorture.cbflood_intra_holdoff= [KNL]
3181 Set holdoff time (jiffies) between successive
3182 bursts of callbacks within a given callback-flood
3183 test.
3185 rcutorture.cbflood_n_burst= [KNL]
3186 Set the number of bursts making up a given
3187 callback-flood test. Set this to zero to
3188 disable callback-flood testing.
3190 rcutorture.cbflood_n_per_burst= [KNL]
3191 Set the number of callbacks to be registered
3192 in a given burst of a callback-flood test.
3194 rcutorture.fqs_duration= [KNL]
3195 Set duration of force_quiescent_state bursts
3196 in microseconds.
3198 rcutorture.fqs_holdoff= [KNL]
3199 Set holdoff time within force_quiescent_state bursts
3200 in microseconds.
3202 rcutorture.fqs_stutter= [KNL]
3203 Set wait time between force_quiescent_state bursts
3204 in seconds.
3206 rcutorture.gp_cond= [KNL]
3207 Use conditional/asynchronous update-side
3208 primitives, if available.
3210 rcutorture.gp_exp= [KNL]
3211 Use expedited update-side primitives, if available.
3213 rcutorture.gp_normal= [KNL]
3214 Use normal (non-expedited) asynchronous
3215 update-side primitives, if available.
3217 rcutorture.gp_sync= [KNL]
3218 Use normal (non-expedited) synchronous
3219 update-side primitives, if available. If all
3220 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3221 rcutorture.gp_normal=, and rcutorture.gp_sync=
3222 are zero, rcutorture acts as if is interpreted
3223 they are all non-zero.
3225 rcutorture.n_barrier_cbs= [KNL]
3226 Set callbacks/threads for rcu_barrier() testing.
3228 rcutorture.nfakewriters= [KNL]
3229 Set number of concurrent RCU writers. These just
3230 stress RCU, they don't participate in the actual
3231 test, hence the "fake".
3233 rcutorture.nreaders= [KNL]
3234 Set number of RCU readers. The value -1 selects
3235 N-1, where N is the number of CPUs. A value
3236 "n" less than -1 selects N-n-2, where N is again
3237 the number of CPUs. For example, -2 selects N
3238 (the number of CPUs), -3 selects N+1, and so on.
3240 rcutorture.object_debug= [KNL]
3241 Enable debug-object double-call_rcu() testing.
3243 rcutorture.onoff_holdoff= [KNL]
3244 Set time (s) after boot for CPU-hotplug testing.
3246 rcutorture.onoff_interval= [KNL]
3247 Set time (s) between CPU-hotplug operations, or
3248 zero to disable CPU-hotplug testing.
3250 rcutorture.shuffle_interval= [KNL]
3251 Set task-shuffle interval (s). Shuffling tasks
3252 allows some CPUs to go into dyntick-idle mode
3253 during the rcutorture test.
3255 rcutorture.shutdown_secs= [KNL]
3256 Set time (s) after boot system shutdown. This
3257 is useful for hands-off automated testing.
3259 rcutorture.stall_cpu= [KNL]
3260 Duration of CPU stall (s) to test RCU CPU stall
3261 warnings, zero to disable.
3263 rcutorture.stall_cpu_holdoff= [KNL]
3264 Time to wait (s) after boot before inducing stall.
3266 rcutorture.stat_interval= [KNL]
3267 Time (s) between statistics printk()s.
3269 rcutorture.stutter= [KNL]
3270 Time (s) to stutter testing, for example, specifying
3271 five seconds causes the test to run for five seconds,
3272 wait for five seconds, and so on. This tests RCU's
3273 ability to transition abruptly to and from idle.
3275 rcutorture.test_boost= [KNL]
3276 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3277 "Maybe" means test if the RCU implementation
3278 under test support RCU priority boosting.
3280 rcutorture.test_boost_duration= [KNL]
3281 Duration (s) of each individual boost test.
3283 rcutorture.test_boost_interval= [KNL]
3284 Interval (s) between each boost test.
3286 rcutorture.test_no_idle_hz= [KNL]
3287 Test RCU's dyntick-idle handling. See also the
3288 rcutorture.shuffle_interval parameter.
3290 rcutorture.torture_runnable= [BOOT]
3291 Start rcutorture running at boot time.
3293 rcutorture.torture_type= [KNL]
3294 Specify the RCU implementation to test.
3296 rcutorture.verbose= [KNL]
3297 Enable additional printk() statements.
3299 rcupdate.rcu_expedited= [KNL]
3300 Use expedited grace-period primitives, for
3301 example, synchronize_rcu_expedited() instead
3302 of synchronize_rcu(). This reduces latency,
3303 but can increase CPU utilization, degrade
3304 real-time latency, and degrade energy efficiency.
3306 rcupdate.rcu_cpu_stall_suppress= [KNL]
3307 Suppress RCU CPU stall warning messages.
3309 rcupdate.rcu_cpu_stall_timeout= [KNL]
3310 Set timeout for RCU CPU stall warning messages.
3312 rcupdate.rcu_task_stall_timeout= [KNL]
3313 Set timeout in jiffies for RCU task stall warning
3314 messages. Disable with a value less than or equal
3315 to zero.
3317 rcupdate.rcu_self_test= [KNL]
3318 Run the RCU early boot self tests
3320 rcupdate.rcu_self_test_bh= [KNL]
3321 Run the RCU bh early boot self tests
3323 rcupdate.rcu_self_test_sched= [KNL]
3324 Run the RCU sched early boot self tests
3326 rdinit= [KNL]
3327 Format: <full_path>
3328 Run specified binary instead of /init from the ramdisk,
3329 used for early userspace startup. See initrd.
3331 reboot= [KNL]
3332 Format (x86 or x86_64):
3333 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3334 [[,]s[mp]#### \
3335 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3336 [[,]f[orce]
3337 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3338 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3339 reboot_force is either force or not specified,
3340 reboot_cpu is s[mp]#### with #### being the processor
3341 to be used for rebooting.
3343 relax_domain_level=
3344 [KNL, SMP] Set scheduler's default relax_domain_level.
3345 See Documentation/cgroups/cpusets.txt.
3347 relative_sleep_states=
3348 [SUSPEND] Use sleep state labeling where the deepest
3349 state available other than hibernation is always "mem".
3350 Format: { "0" | "1" }
3351 0 -- Traditional sleep state labels.
3352 1 -- Relative sleep state labels.
3354 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3356 reservetop= [X86-32]
3357 Format: nn[KMG]
3358 Reserves a hole at the top of the kernel virtual
3359 address space.
3361 reservelow= [X86]
3362 Format: nn[K]
3363 Set the amount of memory to reserve for BIOS at
3364 the bottom of the address space.
3366 reset_devices [KNL] Force drivers to reset the underlying device
3367 during initialization.
3369 resume= [SWSUSP]
3370 Specify the partition device for software suspend
3371 Format:
3372 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3374 resume_offset= [SWSUSP]
3375 Specify the offset from the beginning of the partition
3376 given by "resume=" at which the swap header is located,
3377 in <PAGE_SIZE> units (needed only for swap files).
3378 See Documentation/power/swsusp-and-swap-files.txt
3380 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3381 read the resume files
3383 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3384 Useful for devices that are detected asynchronously
3385 (e.g. USB and MMC devices).
3387 hibernate= [HIBERNATION]
3388 noresume Don't check if there's a hibernation image
3389 present during boot.
3390 nocompress Don't compress/decompress hibernation images.
3391 no Disable hibernation and resume.
3393 retain_initrd [RAM] Keep initrd memory after extraction
3395 rfkill.default_state=
3396 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3397 etc. communication is blocked by default.
3398 1 Unblocked.
3400 rfkill.master_switch_mode=
3401 0 The "airplane mode" button does nothing.
3402 1 The "airplane mode" button toggles between everything
3403 blocked and the previous configuration.
3404 2 The "airplane mode" button toggles between everything
3405 blocked and everything unblocked.
3407 rhash_entries= [KNL,NET]
3408 Set number of hash buckets for route cache
3410 ro [KNL] Mount root device read-only on boot
3412 root= [KNL] Root filesystem
3413 See name_to_dev_t comment in init/do_mounts.c.
3415 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3416 mount the root filesystem
3418 rootflags= [KNL] Set root filesystem mount option string
3420 rootfstype= [KNL] Set root filesystem type
3422 rootwait [KNL] Wait (indefinitely) for root device to show up.
3423 Useful for devices that are detected asynchronously
3424 (e.g. USB and MMC devices).
3426 rproc_mem=nn[KMG][@address]
3427 [KNL,ARM,CMA] Remoteproc physical memory block.
3428 Memory area to be used by remote processor image,
3429 managed by CMA.
3431 rw [KNL] Mount root device read-write on boot
3433 S [KNL] Run init in single mode
3435 s390_iommu= [HW,S390]
3436 Set s390 IOTLB flushing mode
3437 strict
3438 With strict flushing every unmap operation will result in
3439 an IOTLB flush. Default is lazy flushing before reuse,
3440 which is faster.
3442 sa1100ir [NET]
3443 See drivers/net/irda/sa1100_ir.c.
3445 sbni= [NET] Granch SBNI12 leased line adapter
3447 sched_debug [KNL] Enables verbose scheduler debug messages.
3449 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3450 xtime_lock contention on larger systems, and/or RCU lock
3451 contention on all systems with CONFIG_MAXSMP set.
3452 Format: { "0" | "1" }
3453 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3454 1 -- enable.
3455 Note: increases power consumption, thus should only be
3456 enabled if running jitter sensitive (HPC/RT) workloads.
3458 security= [SECURITY] Choose a security module to enable at boot.
3459 If this boot parameter is not specified, only the first
3460 security module asking for security registration will be
3461 loaded. An invalid security module name will be treated
3462 as if no module has been chosen.
3464 selinux= [SELINUX] Disable or enable SELinux at boot time.
3465 Format: { "0" | "1" }
3466 See security/selinux/Kconfig help text.
3467 0 -- disable.
3468 1 -- enable.
3469 Default value is set via kernel config option.
3470 If enabled at boot time, /selinux/disable can be used
3471 later to disable prior to initial policy load.
3473 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3474 Format: { "0" | "1" }
3475 See security/apparmor/Kconfig help text
3476 0 -- disable.
3477 1 -- enable.
3478 Default value is set via kernel config option.
3480 serialnumber [BUGS=X86-32]
3482 shapers= [NET]
3483 Maximal number of shapers.
3485 show_msr= [x86] show boot-time MSR settings
3486 Format: { <integer> }
3487 Show boot-time (BIOS-initialized) MSR settings.
3488 The parameter means the number of CPUs to show,
3489 for example 1 means boot CPU only.
3491 simeth= [IA-64]
3492 simscsi=
3494 slram= [HW,MTD]
3496 slab_nomerge [MM]
3497 Disable merging of slabs with similar size. May be
3498 necessary if there is some reason to distinguish
3499 allocs to different slabs. Debug options disable
3500 merging on their own.
3501 For more information see Documentation/vm/slub.txt.
3503 slab_max_order= [MM, SLAB]
3504 Determines the maximum allowed order for slabs.
3505 A high setting may cause OOMs due to memory
3506 fragmentation. Defaults to 1 for systems with
3507 more than 32MB of RAM, 0 otherwise.
3509 slub_debug[=options[,slabs]] [MM, SLUB]
3510 Enabling slub_debug allows one to determine the
3511 culprit if slab objects become corrupted. Enabling
3512 slub_debug can create guard zones around objects and
3513 may poison objects when not in use. Also tracks the
3514 last alloc / free. For more information see
3515 Documentation/vm/slub.txt.
3517 slub_max_order= [MM, SLUB]
3518 Determines the maximum allowed order for slabs.
3519 A high setting may cause OOMs due to memory
3520 fragmentation. For more information see
3521 Documentation/vm/slub.txt.
3523 slub_min_objects= [MM, SLUB]
3524 The minimum number of objects per slab. SLUB will
3525 increase the slab order up to slub_max_order to
3526 generate a sufficiently large slab able to contain
3527 the number of objects indicated. The higher the number
3528 of objects the smaller the overhead of tracking slabs
3529 and the less frequently locks need to be acquired.
3530 For more information see Documentation/vm/slub.txt.
3532 slub_min_order= [MM, SLUB]
3533 Determines the minimum page order for slabs. Must be
3534 lower than slub_max_order.
3535 For more information see Documentation/vm/slub.txt.
3537 slub_nomerge [MM, SLUB]
3538 Same with slab_nomerge. This is supported for legacy.
3539 See slab_nomerge for more information.
3541 smart2= [HW]
3542 Format: <io1>[,<io2>[,...,<io8>]]
3544 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3545 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3546 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3547 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3548 smsc-ircc2.ircc_irq= [HW] IRQ line
3549 smsc-ircc2.ircc_dma= [HW] DMA channel
3550 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3551 0: Toshiba Satellite 1800 (GP data pin select)
3552 1: Fast pin select (default)
3553 2: ATC IRMode
3555 softlockup_panic=
3556 [KNL] Should the soft-lockup detector generate panics.
3557 Format: <integer>
3559 softlockup_all_cpu_backtrace=
3560 [KNL] Should the soft-lockup detector generate
3561 backtraces on all cpus.
3562 Format: <integer>
3564 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3565 See Documentation/laptops/sonypi.txt
3567 spia_io_base= [HW,MTD]
3568 spia_fio_base=
3569 spia_pedr=
3570 spia_peddr=
3572 stacktrace [FTRACE]
3573 Enabled the stack tracer on boot up.
3575 stacktrace_filter=[function-list]
3576 [FTRACE] Limit the functions that the stack tracer
3577 will trace at boot up. function-list is a comma separated
3578 list of functions. This list can be changed at run
3579 time by the stack_trace_filter file in the debugfs
3580 tracing directory. Note, this enables stack tracing
3581 and the stacktrace above is not needed.
3583 sti= [PARISC,HW]
3584 Format: <num>
3585 Set the STI (builtin display/keyboard on the HP-PARISC
3586 machines) console (graphic card) which should be used
3587 as the initial boot-console.
3588 See also comment in drivers/video/console/sticore.c.
3590 sti_font= [HW]
3591 See comment in drivers/video/console/sticore.c.
3593 stifb= [HW]
3594 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3596 sunrpc.min_resvport=
3597 sunrpc.max_resvport=
3598 [NFS,SUNRPC]
3599 SunRPC servers often require that client requests
3600 originate from a privileged port (i.e. a port in the
3601 range 0 < portnr < 1024).
3602 An administrator who wishes to reserve some of these
3603 ports for other uses may adjust the range that the
3604 kernel's sunrpc client considers to be privileged
3605 using these two parameters to set the minimum and
3606 maximum port values.
3608 sunrpc.pool_mode=
3609 [NFS]
3610 Control how the NFS server code allocates CPUs to
3611 service thread pools. Depending on how many NICs
3612 you have and where their interrupts are bound, this
3613 option will affect which CPUs will do NFS serving.
3614 Note: this parameter cannot be changed while the
3615 NFS server is running.
3617 auto the server chooses an appropriate mode
3618 automatically using heuristics
3619 global a single global pool contains all CPUs
3620 percpu one pool for each CPU
3621 pernode one pool for each NUMA node (equivalent
3622 to global on non-NUMA machines)
3624 sunrpc.tcp_slot_table_entries=
3625 sunrpc.udp_slot_table_entries=
3626 [NFS,SUNRPC]
3627 Sets the upper limit on the number of simultaneous
3628 RPC calls that can be sent from the client to a
3629 server. Increasing these values may allow you to
3630 improve throughput, but will also increase the
3631 amount of memory reserved for use by the client.
3633 suspend.pm_test_delay=
3634 [SUSPEND]
3635 Sets the number of seconds to remain in a suspend test
3636 mode before resuming the system (see
3637 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3638 is set. Default value is 5.
3640 swapaccount=[0|1]
3641 [KNL] Enable accounting of swap in memory resource
3642 controller if no parameter or 1 is given or disable
3643 it if 0 is given (See Documentation/cgroups/memory.txt)
3645 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3646 Format: { <int> | force }
3647 <int> -- Number of I/O TLB slabs
3648 force -- force using of bounce buffers even if they
3649 wouldn't be automatically used by the kernel
3651 switches= [HW,M68k]
3653 sysfs.deprecated=0|1 [KNL]
3654 Enable/disable old style sysfs layout for old udev
3655 on older distributions. When this option is enabled
3656 very new udev will not work anymore. When this option
3657 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3658 in older udev will not work anymore.
3659 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3660 the kernel configuration.
3662 sysrq_always_enabled
3663 [KNL]
3664 Ignore sysrq setting - this boot parameter will
3665 neutralize any effect of /proc/sys/kernel/sysrq.
3666 Useful for debugging.
3668 tcpmhash_entries= [KNL,NET]
3669 Set the number of tcp_metrics_hash slots.
3670 Default value is 8192 or 16384 depending on total
3671 ram pages. This is used to specify the TCP metrics
3672 cache size. See Documentation/networking/ip-sysctl.txt
3673 "tcp_no_metrics_save" section for more details.
3675 tdfx= [HW,DRM]
3677 test_suspend= [SUSPEND][,N]
3678 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3679 standby suspend) or "freeze" (for suspend type freeze)
3680 as the system sleep state during system startup with
3681 the optional capability to repeat N number of times.
3682 The system is woken from this state using a
3683 wakeup-capable RTC alarm.
3685 thash_entries= [KNL,NET]
3686 Set number of hash buckets for TCP connection
3688 thermal.act= [HW,ACPI]
3689 -1: disable all active trip points in all thermal zones
3690 <degrees C>: override all lowest active trip points
3692 thermal.crt= [HW,ACPI]
3693 -1: disable all critical trip points in all thermal zones
3694 <degrees C>: override all critical trip points
3696 thermal.nocrt= [HW,ACPI]
3697 Set to disable actions on ACPI thermal zone
3698 critical and hot trip points.
3700 thermal.off= [HW,ACPI]
3701 1: disable ACPI thermal control
3703 thermal.psv= [HW,ACPI]
3704 -1: disable all passive trip points
3705 <degrees C>: override all passive trip points to this
3706 value
3708 thermal.tzp= [HW,ACPI]
3709 Specify global default ACPI thermal zone polling rate
3710 <deci-seconds>: poll all this frequency
3711 0: no polling (default)
3713 threadirqs [KNL]
3714 Force threading of all interrupt handlers except those
3715 marked explicitly IRQF_NO_THREAD.
3717 tmem [KNL,XEN]
3718 Enable the Transcendent memory driver if built-in.
3720 tmem.cleancache=0|1 [KNL, XEN]
3721 Default is on (1). Disable the usage of the cleancache
3722 API to send anonymous pages to the hypervisor.
3724 tmem.frontswap=0|1 [KNL, XEN]
3725 Default is on (1). Disable the usage of the frontswap
3726 API to send swap pages to the hypervisor. If disabled
3727 the selfballooning and selfshrinking are force disabled.
3729 tmem.selfballooning=0|1 [KNL, XEN]
3730 Default is on (1). Disable the driving of swap pages
3731 to the hypervisor.
3733 tmem.selfshrinking=0|1 [KNL, XEN]
3734 Default is on (1). Partial swapoff that immediately
3735 transfers pages from Xen hypervisor back to the
3736 kernel based on different criteria.
3738 topology= [S390]
3739 Format: {off | on}
3740 Specify if the kernel should make use of the cpu
3741 topology information if the hardware supports this.
3742 The scheduler will make use of this information and
3743 e.g. base its process migration decisions on it.
3744 Default is on.
3746 topology_updates= [KNL, PPC, NUMA]
3747 Format: {off}
3748 Specify if the kernel should ignore (off)
3749 topology updates sent by the hypervisor to this
3750 LPAR.
3752 tp720= [HW,PS2]
3754 tpm_suspend_pcr=[HW,TPM]
3755 Format: integer pcr id
3756 Specify that at suspend time, the tpm driver
3757 should extend the specified pcr with zeros,
3758 as a workaround for some chips which fail to
3759 flush the last written pcr on TPM_SaveState.
3760 This will guarantee that all the other pcrs
3761 are saved.
3763 trace_buf_size=nn[KMG]
3764 [FTRACE] will set tracing buffer size on each cpu.
3766 trace_event=[event-list]
3767 [FTRACE] Set and start specified trace events in order
3768 to facilitate early boot debugging.
3769 See also Documentation/trace/events.txt
3771 trace_options=[option-list]
3772 [FTRACE] Enable or disable tracer options at boot.
3773 The option-list is a comma delimited list of options
3774 that can be enabled or disabled just as if you were
3775 to echo the option name into
3777 /sys/kernel/debug/tracing/trace_options
3779 For example, to enable stacktrace option (to dump the
3780 stack trace of each event), add to the command line:
3782 trace_options=stacktrace
3784 See also Documentation/trace/ftrace.txt "trace options"
3785 section.
3787 tp_printk[FTRACE]
3788 Have the tracepoints sent to printk as well as the
3789 tracing ring buffer. This is useful for early boot up
3790 where the system hangs or reboots and does not give the
3791 option for reading the tracing buffer or performing a
3792 ftrace_dump_on_oops.
3794 To turn off having tracepoints sent to printk,
3795 echo 0 > /proc/sys/kernel/tracepoint_printk
3796 Note, echoing 1 into this file without the
3797 tracepoint_printk kernel cmdline option has no effect.
3799 ** CAUTION **
3801 Having tracepoints sent to printk() and activating high
3802 frequency tracepoints such as irq or sched, can cause
3803 the system to live lock.
3805 traceoff_on_warning
3806 [FTRACE] enable this option to disable tracing when a
3807 warning is hit. This turns off "tracing_on". Tracing can
3808 be enabled again by echoing '1' into the "tracing_on"
3809 file located in /sys/kernel/debug/tracing/
3811 This option is useful, as it disables the trace before
3812 the WARNING dump is called, which prevents the trace to
3813 be filled with content caused by the warning output.
3815 This option can also be set at run time via the sysctl
3816 option: kernel/traceoff_on_warning
3818 transparent_hugepage=
3819 [KNL]
3820 Format: [always|madvise|never]
3821 Can be used to control the default behavior of the system
3822 with respect to transparent hugepages.
3823 See Documentation/vm/transhuge.txt for more details.
3825 tsc= Disable clocksource stability checks for TSC.
3826 Format: <string>
3827 [x86] reliable: mark tsc clocksource as reliable, this
3828 disables clocksource verification at runtime, as well
3829 as the stability checks done at bootup. Used to enable
3830 high-resolution timer mode on older hardware, and in
3831 virtualized environment.
3832 [x86] noirqtime: Do not use TSC to do irq accounting.
3833 Used to run time disable IRQ_TIME_ACCOUNTING on any
3834 platforms where RDTSC is slow and this accounting
3835 can add overhead.
3837 turbografx.map[2|3]= [HW,JOY]
3838 TurboGraFX parallel port interface
3839 Format:
3840 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3841 See also Documentation/input/joystick-parport.txt
3843 udbg-immortal [PPC] When debugging early kernel crashes that
3844 happen after console_init() and before a proper
3845 console driver takes over, this boot options might
3846 help "seeing" what's going on.
3848 uhash_entries= [KNL,NET]
3849 Set number of hash buckets for UDP/UDP-Lite connections
3851 uhci-hcd.ignore_oc=
3852 [USB] Ignore overcurrent events (default N).
3853 Some badly-designed motherboards generate lots of
3854 bogus events, for ports that aren't wired to
3855 anything. Set this parameter to avoid log spamming.
3856 Note that genuine overcurrent events won't be
3857 reported either.
3859 unknown_nmi_panic
3860 [X86] Cause panic on unknown NMI.
3862 usbcore.authorized_default=
3863 [USB] Default USB device authorization:
3864 (default -1 = authorized except for wireless USB,
3865 0 = not authorized, 1 = authorized)
3867 usbcore.autosuspend=
3868 [USB] The autosuspend time delay (in seconds) used
3869 for newly-detected USB devices (default 2). This
3870 is the time required before an idle device will be
3871 autosuspended. Devices for which the delay is set
3872 to a negative value won't be autosuspended at all.
3874 usbcore.usbfs_snoop=
3875 [USB] Set to log all usbfs traffic (default 0 = off).
3877 usbcore.blinkenlights=
3878 [USB] Set to cycle leds on hubs (default 0 = off).
3880 usbcore.old_scheme_first=
3881 [USB] Start with the old device initialization
3882 scheme (default 0 = off).
3884 usbcore.usbfs_memory_mb=
3885 [USB] Memory limit (in MB) for buffers allocated by
3886 usbfs (default = 16, 0 = max = 2047).
3888 usbcore.use_both_schemes=
3889 [USB] Try the other device initialization scheme
3890 if the first one fails (default 1 = enabled).
3892 usbcore.initial_descriptor_timeout=
3893 [USB] Specifies timeout for the initial 64-byte
3894 USB_REQ_GET_DESCRIPTOR request in milliseconds
3895 (default 5000 = 5.0 seconds).
3897 usbhid.mousepoll=
3898 [USBHID] The interval which mice are to be polled at.
3900 usb-storage.delay_use=
3901 [UMS] The delay in seconds before a new device is
3902 scanned for Logical Units (default 1).
3904 usb-storage.quirks=
3905 [UMS] A list of quirks entries to supplement or
3906 override the built-in unusual_devs list. List
3907 entries are separated by commas. Each entry has
3908 the form VID:PID:Flags where VID and PID are Vendor
3909 and Product ID values (4-digit hex numbers) and
3910 Flags is a set of characters, each corresponding
3911 to a common usb-storage quirk flag as follows:
3912 a = SANE_SENSE (collect more than 18 bytes
3913 of sense data);
3914 b = BAD_SENSE (don't collect more than 18
3915 bytes of sense data);
3916 c = FIX_CAPACITY (decrease the reported
3917 device capacity by one sector);
3918 d = NO_READ_DISC_INFO (don't use
3919 READ_DISC_INFO command);
3920 e = NO_READ_CAPACITY_16 (don't use
3921 READ_CAPACITY_16 command);
3922 f = NO_REPORT_OPCODES (don't use report opcodes
3923 command, uas only);
3924 g = MAX_SECTORS_240 (don't transfer more than
3925 240 sectors at a time, uas only);
3926 h = CAPACITY_HEURISTICS (decrease the
3927 reported device capacity by one
3928 sector if the number is odd);
3929 i = IGNORE_DEVICE (don't bind to this
3930 device);
3931 l = NOT_LOCKABLE (don't try to lock and
3932 unlock ejectable media);
3933 m = MAX_SECTORS_64 (don't transfer more
3934 than 64 sectors = 32 KB at a time);
3935 n = INITIAL_READ10 (force a retry of the
3936 initial READ(10) command);
3937 o = CAPACITY_OK (accept the capacity
3938 reported by the device);
3939 p = WRITE_CACHE (the device cache is ON
3940 by default);
3941 r = IGNORE_RESIDUE (the device reports
3942 bogus residue values);
3943 s = SINGLE_LUN (the device has only one
3944 Logical Unit);
3945 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3946 commands, uas only);
3947 u = IGNORE_UAS (don't bind to the uas driver);
3948 w = NO_WP_DETECT (don't test whether the
3949 medium is write-protected).
3950 Example: quirks=0419:aaf5:rl,0421:0433:rc
3952 user_debug= [KNL,ARM]
3953 Format: <int>
3954 See arch/arm/Kconfig.debug help text.
3955 1 - undefined instruction events
3956 2 - system calls
3957 4 - invalid data aborts
3958 8 - SIGSEGV faults
3959 16 - SIGBUS faults
3960 Example: user_debug=31
3962 userpte=
3963 [X86] Flags controlling user PTE allocations.
3965 nohigh = do not allocate PTE pages in
3966 HIGHMEM regardless of setting
3967 of CONFIG_HIGHPTE.
3969 vdso= [X86,SH]
3970 On X86_32, this is an alias for vdso32=. Otherwise:
3972 vdso=1: enable VDSO (the default)
3973 vdso=0: disable VDSO mapping
3975 vdso32= [X86] Control the 32-bit vDSO
3976 vdso32=1: enable 32-bit VDSO
3977 vdso32=0 or vdso32=2: disable 32-bit VDSO
3979 See the help text for CONFIG_COMPAT_VDSO for more
3980 details. If CONFIG_COMPAT_VDSO is set, the default is
3981 vdso32=0; otherwise, the default is vdso32=1.
3983 For compatibility with older kernels, vdso32=2 is an
3984 alias for vdso32=0.
3986 Try vdso32=0 if you encounter an error that says:
3987 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3989 vector= [IA-64,SMP]
3990 vector=percpu: enable percpu vector domain
3992 video= [FB] Frame buffer configuration
3993 See Documentation/fb/modedb.txt.
3995 video.brightness_switch_enabled= [0,1]
3996 If set to 1, on receiving an ACPI notify event
3997 generated by hotkey, video driver will adjust brightness
3998 level and then send out the event to user space through
3999 the allocated input device; If set to 0, video driver
4000 will only send out the event without touching backlight
4001 brightness level.
4002 default: 1
4004 virtio_mmio.device=
4005 [VMMIO] Memory mapped virtio (platform) device.
4007 <size>@<baseaddr>:<irq>[:<id>]
4008 where:
4009 <size> := size (can use standard suffixes
4010 like K, M and G)
4011 <baseaddr> := physical base address
4012 <irq> := interrupt number (as passed to
4013 request_irq())
4014 <id> := (optional) platform device id
4015 example:
4016 virtio_mmio.device=1K@0x100b0000:48:7
4018 Can be used multiple times for multiple devices.
4020 vga= [BOOT,X86-32] Select a particular video mode
4021 See Documentation/x86/boot.txt and
4022 Documentation/svga.txt.
4023 Use vga=ask for menu.
4024 This is actually a boot loader parameter; the value is
4025 passed to the kernel using a special protocol.
4027 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4028 size of <nn>. This can be used to increase the
4029 minimum size (128MB on x86). It can also be used to
4030 decrease the size and leave more room for directly
4031 mapped kernel RAM.
4033 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4034 Format: <command>
4036 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4037 Format: <command>
4039 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4040 Format: <command>
4042 vsyscall= [X86-64]
4043 Controls the behavior of vsyscalls (i.e. calls to
4044 fixed addresses of 0xffffffffff600x00 from legacy
4045 code). Most statically-linked binaries and older
4046 versions of glibc use these calls. Because these
4047 functions are at fixed addresses, they make nice
4048 targets for exploits that can control RIP.
4050 emulate [default] Vsyscalls turn into traps and are
4051 emulated reasonably safely.
4053 native Vsyscalls are native syscall instructions.
4054 This is a little bit faster than trapping
4055 and makes a few dynamic recompilers work
4056 better than they would in emulation mode.
4057 It also makes exploits much easier to write.
4059 none Vsyscalls don't work at all. This makes
4060 them quite hard to use for exploits but
4061 might break your system.
4063 vt.color= [VT] Default text color.
4064 Format: 0xYX, X = foreground, Y = background.
4065 Default: 0x07 = light gray on black.
4067 vt.cur_default= [VT] Default cursor shape.
4068 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4069 the parameters of the <Esc>[?A;B;Cc escape sequence;
4070 see VGA-softcursor.txt. Default: 2 = underline.
4072 vt.default_blu= [VT]
4073 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4074 Change the default blue palette of the console.
4075 This is a 16-member array composed of values
4076 ranging from 0-255.
4078 vt.default_grn= [VT]
4079 Format: <green0>,<green1>,<green2>,...,<green15>
4080 Change the default green palette of the console.
4081 This is a 16-member array composed of values
4082 ranging from 0-255.
4084 vt.default_red= [VT]
4085 Format: <red0>,<red1>,<red2>,...,<red15>
4086 Change the default red palette of the console.
4087 This is a 16-member array composed of values
4088 ranging from 0-255.
4090 vt.default_utf8=
4091 [VT]
4092 Format=<0|1>
4093 Set system-wide default UTF-8 mode for all tty's.
4094 Default is 1, i.e. UTF-8 mode is enabled for all
4095 newly opened terminals.
4097 vt.global_cursor_default=
4098 [VT]
4099 Format=<-1|0|1>
4100 Set system-wide default for whether a cursor
4101 is shown on new VTs. Default is -1,
4102 i.e. cursors will be created by default unless
4103 overridden by individual drivers. 0 will hide
4104 cursors, 1 will display them.
4106 vt.italic= [VT] Default color for italic text; 0-15.
4107 Default: 2 = green.
4109 vt.underline= [VT] Default color for underlined text; 0-15.
4110 Default: 3 = cyan.
4112 watchdog timers [HW,WDT] For information on watchdog timers,
4113 see Documentation/watchdog/watchdog-parameters.txt
4114 or other driver-specific files in the
4115 Documentation/watchdog/ directory.
4117 workqueue.disable_numa
4118 By default, all work items queued to unbound
4119 workqueues are affine to the NUMA nodes they're
4120 issued on, which results in better behavior in
4121 general. If NUMA affinity needs to be disabled for
4122 whatever reason, this option can be used. Note
4123 that this also can be controlled per-workqueue for
4124 workqueues visible under /sys/bus/workqueue/.
4126 workqueue.power_efficient
4127 Per-cpu workqueues are generally preferred because
4128 they show better performance thanks to cache
4129 locality; unfortunately, per-cpu workqueues tend to
4130 be more power hungry than unbound workqueues.
4132 Enabling this makes the per-cpu workqueues which
4133 were observed to contribute significantly to power
4134 consumption unbound, leading to measurably lower
4135 power usage at the cost of small performance
4136 overhead.
4138 The default value of this parameter is determined by
4139 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4141 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4142 default x2apic cluster mode on platforms
4143 supporting x2apic.
4145 x86_intel_mid_timer= [X86-32,APBT]
4146 Choose timer option for x86 Intel MID platform.
4147 Two valid options are apbt timer only and lapic timer
4148 plus one apbt timer for broadcast timer.
4149 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4151 xen_512gb_limit [KNL,X86-64,XEN]
4152 Restricts the kernel running paravirtualized under Xen
4153 to use only up to 512 GB of RAM. The reason to do so is
4154 crash analysis tools and Xen tools for doing domain
4155 save/restore/migration must be enabled to handle larger
4156 domains.
4158 xen_emul_unplug= [HW,X86,XEN]
4159 Unplug Xen emulated devices
4160 Format: [unplug0,][unplug1]
4161 ide-disks -- unplug primary master IDE devices
4162 aux-ide-disks -- unplug non-primary-master IDE devices
4163 nics -- unplug network devices
4164 all -- unplug all emulated devices (NICs and IDE disks)
4165 unnecessary -- unplugging emulated devices is
4166 unnecessary even if the host did not respond to
4167 the unplug protocol
4168 never -- do not unplug even if version check succeeds
4170 xen_nopvspin [X86,XEN]
4171 Disables the ticketlock slowpath using Xen PV
4172 optimizations.
4174 xen_nopv [X86]
4175 Disables the PV optimizations forcing the HVM guest to
4176 run as generic HVM guest with no PV drivers.
4178 xirc2ps_cs= [NET,PCMCIA]
4179 Format:
4180 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4182 ______________________________________________________________________
4184 TODO:
4186 Add more DRM drivers.