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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 goldfish [X86] Enable the goldfish android emulator platform.
1259 Don't use this when you are not running on the
1260 android emulator
1262 gpt [EFI] Forces disk with valid GPT signature but
1263 invalid Protective MBR to be treated as GPT. If the
1264 primary GPT is corrupted, it enables the backup/alternate
1265 GPT to be used instead.
1267 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1268 the "Enable 0" bit of the configuration register.
1269 Format: 0 | 1
1270 Default: 0
1271 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1272 the "Enable 0" bit of the configuration register.
1273 Format: 0 | 1
1274 Default: 0
1275 grcan.select= [HW] Select which physical interface to use.
1276 Format: 0 | 1
1277 Default: 0
1278 grcan.txsize= [HW] Sets the size of the tx buffer.
1279 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1280 Default: 1024
1281 grcan.rxsize= [HW] Sets the size of the rx buffer.
1282 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1283 Default: 1024
1285 hardlockup_all_cpu_backtrace=
1286 [KNL] Should the hard-lockup detector generate
1287 backtraces on all cpus.
1288 Format: <integer>
1290 hashdist= [KNL,NUMA] Large hashes allocated during boot
1291 are distributed across NUMA nodes. Defaults on
1292 for 64-bit NUMA, off otherwise.
1293 Format: 0 | 1 (for off | on)
1295 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1297 hd= [EIDE] (E)IDE hard drive subsystem geometry
1298 Format: <cyl>,<head>,<sect>
1300 hest_disable [ACPI]
1301 Disable Hardware Error Source Table (HEST) support;
1302 corresponding firmware-first mode error processing
1303 logic will be disabled.
1305 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1306 size of <nn>. This works even on boxes that have no
1307 highmem otherwise. This also works to reduce highmem
1308 size on bigger boxes.
1310 highres= [KNL] Enable/disable high resolution timer mode.
1311 Valid parameters: "on", "off"
1312 Default: "on"
1314 hisax= [HW,ISDN]
1315 See Documentation/isdn/README.HiSax.
1317 hlt [BUGS=ARM,SH]
1319 hpet= [X86-32,HPET] option to control HPET usage
1320 Format: { enable (default) | disable | force |
1321 verbose }
1322 disable: disable HPET and use PIT instead
1323 force: allow force enabled of undocumented chips (ICH4,
1324 VIA, nVidia)
1325 verbose: show contents of HPET registers during setup
1327 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1328 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1330 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1331 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1332 On x86-64 and powerpc, this option can be specified
1333 multiple times interleaved with hugepages= to reserve
1334 huge pages of different sizes. Valid pages sizes on
1335 x86-64 are 2M (when the CPU supports "pse") and 1G
1336 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1338 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1339 terminal devices. Valid values: 0..8
1340 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1341 If specified, z/VM IUCV HVC accepts connections
1342 from listed z/VM user IDs only.
1344 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1345 hardware thread id mappings.
1346 Format: <cpu>:<hwthread>
1348 keep_bootcon [KNL]
1349 Do not unregister boot console at start. This is only
1350 useful for debugging when something happens in the window
1351 between unregistering the boot console and initializing
1352 the real console.
1354 i2c_bus= [HW] Override the default board specific I2C bus speed
1355 or register an additional I2C bus that is not
1356 registered from board initialization code.
1357 Format:
1358 <bus_id>,<clkrate>
1360 i8042.debug [HW] Toggle i8042 debug mode
1361 i8042.unmask_kbd_data
1362 [HW] Enable printing of interrupt data from the KBD port
1363 (disabled by default, and as a pre-condition
1364 requires that i8042.debug=1 be enabled)
1365 i8042.direct [HW] Put keyboard port into non-translated mode
1366 i8042.dumbkbd [HW] Pretend that controller can only read data from
1367 keyboard and cannot control its state
1368 (Don't attempt to blink the leds)
1369 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1370 i8042.nokbd [HW] Don't check/create keyboard port
1371 i8042.noloop [HW] Disable the AUX Loopback command while probing
1372 for the AUX port
1373 i8042.nomux [HW] Don't check presence of an active multiplexing
1374 controller
1375 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1376 controllers
1377 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1378 i8042.reset [HW] Reset the controller during init, cleanup and
1379 suspend-to-ram transitions, only during s2r
1380 transitions, or never reset
1381 Format: { 1 | Y | y | 0 | N | n }
1382 1, Y, y: always reset controller
1383 0, N, n: don't ever reset controller
1384 Default: only on s2r transitions on x86; most other
1385 architectures force reset to be always executed
1386 i8042.unlock [HW] Unlock (ignore) the keylock
1387 i8042.kbdreset [HW] Reset device connected to KBD port
1389 i810= [HW,DRM]
1391 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1392 indicates that the driver is running on unsupported
1393 hardware.
1394 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1395 does not match list of supported models.
1396 i8k.power_status
1397 [HW] Report power status in /proc/i8k
1398 (disabled by default)
1399 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1400 capability is set.
1402 i915.invert_brightness=
1403 [DRM] Invert the sense of the variable that is used to
1404 set the brightness of the panel backlight. Normally a
1405 brightness value of 0 indicates backlight switched off,
1406 and the maximum of the brightness value sets the backlight
1407 to maximum brightness. If this parameter is set to 0
1408 (default) and the machine requires it, or this parameter
1409 is set to 1, a brightness value of 0 sets the backlight
1410 to maximum brightness, and the maximum of the brightness
1411 value switches the backlight off.
1412 -1 -- never invert brightness
1413 0 -- machine default
1414 1 -- force brightness inversion
1416 icn= [HW,ISDN]
1417 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1419 ide-core.nodma= [HW] (E)IDE subsystem
1420 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1421 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1422 .cdrom .chs .ignore_cable are additional options
1423 See Documentation/ide/ide.txt.
1425 ide-generic.probe-mask= [HW] (E)IDE subsystem
1426 Format: <int>
1427 Probe mask for legacy ISA IDE ports. Depending on
1428 platform up to 6 ports are supported, enabled by
1429 setting corresponding bits in the mask to 1. The
1430 default value is 0x0, which has a special meaning.
1431 On systems that have PCI, it triggers scanning the
1432 PCI bus for the first and the second port, which
1433 are then probed. On systems without PCI the value
1434 of 0x0 enables probing the two first ports as if it
1435 was 0x3.
1437 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1438 Claim all unknown PCI IDE storage controllers.
1440 idle= [X86]
1441 Format: idle=poll, idle=halt, idle=nomwait
1442 Poll forces a polling idle loop that can slightly
1443 improve the performance of waking up a idle CPU, but
1444 will use a lot of power and make the system run hot.
1445 Not recommended.
1446 idle=halt: Halt is forced to be used for CPU idle.
1447 In such case C2/C3 won't be used again.
1448 idle=nomwait: Disable mwait for CPU C-states
1450 ignore_loglevel [KNL]
1451 Ignore loglevel setting - this will print /all/
1452 kernel messages to the console. Useful for debugging.
1453 We also add it as printk module parameter, so users
1454 could change it dynamically, usually by
1455 /sys/module/printk/parameters/ignore_loglevel.
1457 ihash_entries= [KNL]
1458 Set number of hash buckets for inode cache.
1460 ima_appraise= [IMA] appraise integrity measurements
1461 Format: { "off" | "enforce" | "fix" | "log" }
1462 default: "enforce"
1464 ima_appraise_tcb [IMA]
1465 The builtin appraise policy appraises all files
1466 owned by uid=0.
1468 ima_hash= [IMA]
1469 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1470 | sha512 | ... }
1471 default: "sha1"
1473 The list of supported hash algorithms is defined
1474 in crypto/hash_info.h.
1476 ima_policy= [IMA]
1477 The builtin measurement policy to load during IMA
1478 setup. Specyfing "tcb" as the value, measures all
1479 programs exec'd, files mmap'd for exec, and all files
1480 opened with the read mode bit set by either the
1481 effective uid (euid=0) or uid=0.
1482 Format: "tcb"
1484 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1485 Load a policy which meets the needs of the Trusted
1486 Computing Base. This means IMA will measure all
1487 programs exec'd, files mmap'd for exec, and all files
1488 opened for read by uid=0.
1490 ima_template= [IMA]
1491 Select one of defined IMA measurements template formats.
1492 Formats: { "ima" | "ima-ng" | "ima-sig" }
1493 Default: "ima-ng"
1495 ima_template_fmt=
1496 [IMA] Define a custom template format.
1497 Format: { "field1|...|fieldN" }
1499 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1500 Format: <min_file_size>
1501 Set the minimal file size for using asynchronous hash.
1502 If left unspecified, ahash usage is disabled.
1504 ahash performance varies for different data sizes on
1505 different crypto accelerators. This option can be used
1506 to achieve the best performance for a particular HW.
1508 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1509 Format: <bufsize>
1510 Set hashing buffer size. Default: 4k.
1512 ahash performance varies for different chunk sizes on
1513 different crypto accelerators. This option can be used
1514 to achieve best performance for particular HW.
1516 init= [KNL]
1517 Format: <full_path>
1518 Run specified binary instead of /sbin/init as init
1519 process.
1521 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1522 for working out where the kernel is dying during
1523 startup.
1525 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1526 initcall functions. Useful for debugging built-in
1527 modules and initcalls.
1529 initrd= [BOOT] Specify the location of the initial ramdisk
1531 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1532 Format: <irq>
1534 int_pln_enable [x86] Enable power limit notification interrupt
1536 integrity_audit=[IMA]
1537 Format: { "0" | "1" }
1538 0 -- basic integrity auditing messages. (Default)
1539 1 -- additional integrity auditing messages.
1541 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1542 on
1543 Enable intel iommu driver.
1544 off
1545 Disable intel iommu driver.
1546 igfx_off [Default Off]
1547 By default, gfx is mapped as normal device. If a gfx
1548 device has a dedicated DMAR unit, the DMAR unit is
1549 bypassed by not enabling DMAR with this option. In
1550 this case, gfx device will use physical address for
1551 DMA.
1552 forcedac [x86_64]
1553 With this option iommu will not optimize to look
1554 for io virtual address below 32-bit forcing dual
1555 address cycle on pci bus for cards supporting greater
1556 than 32-bit addressing. The default is to look
1557 for translation below 32-bit and if not available
1558 then look in the higher range.
1559 strict [Default Off]
1560 With this option on every unmap_single operation will
1561 result in a hardware IOTLB flush operation as opposed
1562 to batching them for performance.
1563 sp_off [Default Off]
1564 By default, super page will be supported if Intel IOMMU
1565 has the capability. With this option, super page will
1566 not be supported.
1567 ecs_off [Default Off]
1568 By default, extended context tables will be supported if
1569 the hardware advertises that it has support both for the
1570 extended tables themselves, and also PASID support. With
1571 this option set, extended tables will not be used even
1572 on hardware which claims to support them.
1574 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1575 0 disables intel_idle and fall back on acpi_idle.
1576 1 to 6 specify maximum depth of C-state.
1578 intel_pstate= [X86]
1579 disable
1580 Do not enable intel_pstate as the default
1581 scaling driver for the supported processors
1582 force
1583 Enable intel_pstate on systems that prohibit it by default
1584 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1585 instead of acpi-cpufreq may disable platform features, such
1586 as thermal controls and power capping, that rely on ACPI
1587 P-States information being indicated to OSPM and therefore
1588 should be used with caution. This option does not work with
1589 processors that aren't supported by the intel_pstate driver
1590 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1591 no_hwp
1592 Do not enable hardware P state control (HWP)
1593 if available.
1594 hwp_only
1595 Only load intel_pstate on systems which support
1596 hardware P state control (HWP) if available.
1598 intremap= [X86-64, Intel-IOMMU]
1599 on enable Interrupt Remapping (default)
1600 off disable Interrupt Remapping
1601 nosid disable Source ID checking
1602 no_x2apic_optout
1603 BIOS x2APIC opt-out request will be ignored
1604 nopost disable Interrupt Posting
1606 iomem= Disable strict checking of access to MMIO memory
1607 strict regions from userspace.
1608 relaxed
1610 iommu= [x86]
1611 off
1612 force
1613 noforce
1614 biomerge
1615 panic
1616 nopanic
1617 merge
1618 nomerge
1619 forcesac
1620 soft
1621 pt [x86, IA-64]
1622 nobypass [PPC/POWERNV]
1623 Disable IOMMU bypass, using IOMMU for PCI devices.
1626 io7= [HW] IO7 for Marvel based alpha systems
1627 See comment before marvel_specify_io7 in
1628 arch/alpha/kernel/core_marvel.c.
1630 io_delay= [X86] I/O delay method
1631 0x80
1632 Standard port 0x80 based delay
1633 0xed
1634 Alternate port 0xed based delay (needed on some systems)
1635 udelay
1636 Simple two microseconds delay
1637 none
1638 No delay
1640 ip= [IP_PNP]
1641 See Documentation/filesystems/nfs/nfsroot.txt.
1643 irqfixup [HW]
1644 When an interrupt is not handled search all handlers
1645 for it. Intended to get systems with badly broken
1646 firmware running.
1648 irqpoll [HW]
1649 When an interrupt is not handled search all handlers
1650 for it. Also check all handlers each timer
1651 interrupt. Intended to get systems with badly broken
1652 firmware running.
1654 isapnp= [ISAPNP]
1655 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1657 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1658 Format:
1659 <cpu number>,...,<cpu number>
1660 or
1661 <cpu number>-<cpu number>
1662 (must be a positive range in ascending order)
1663 or a mixture
1664 <cpu number>,...,<cpu number>-<cpu number>
1666 This option can be used to specify one or more CPUs
1667 to isolate from the general SMP balancing and scheduling
1668 algorithms. You can move a process onto or off an
1669 "isolated" CPU via the CPU affinity syscalls or cpuset.
1670 <cpu number> begins at 0 and the maximum value is
1671 "number of CPUs in system - 1".
1673 This option is the preferred way to isolate CPUs. The
1674 alternative -- manually setting the CPU mask of all
1675 tasks in the system -- can cause problems and
1676 suboptimal load balancer performance.
1678 iucv= [HW,NET]
1680 ivrs_ioapic [HW,X86_64]
1681 Provide an override to the IOAPIC-ID<->DEVICE-ID
1682 mapping provided in the IVRS ACPI table. For
1683 example, to map IOAPIC-ID decimal 10 to
1684 PCI device 00:14.0 write the parameter as:
1685 ivrs_ioapic[10]=00:14.0
1687 ivrs_hpet [HW,X86_64]
1688 Provide an override to the HPET-ID<->DEVICE-ID
1689 mapping provided in the IVRS ACPI table. For
1690 example, to map HPET-ID decimal 0 to
1691 PCI device 00:14.0 write the parameter as:
1692 ivrs_hpet[0]=00:14.0
1694 js= [HW,JOY] Analog joystick
1695 See Documentation/input/joystick.txt.
1697 kaslr/nokaslr [X86]
1698 Enable/disable kernel and module base offset ASLR
1699 (Address Space Layout Randomization) if built into
1700 the kernel. When CONFIG_HIBERNATION is selected,
1701 kASLR is disabled by default. When kASLR is enabled,
1702 hibernation will be disabled.
1704 keepinitrd [HW,ARM]
1706 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1707 specifies the amount of memory usable by the kernel
1708 for non-movable allocations. The requested amount is
1709 spread evenly throughout all nodes in the system. The
1710 remaining memory in each node is used for Movable
1711 pages. In the event, a node is too small to have both
1712 kernelcore and Movable pages, kernelcore pages will
1713 take priority and other nodes will have a larger number
1714 of Movable pages. The Movable zone is used for the
1715 allocation of pages that may be reclaimed or moved
1716 by the page migration subsystem. This means that
1717 HugeTLB pages may not be allocated from this zone.
1718 Note that allocations like PTEs-from-HighMem still
1719 use the HighMem zone if it exists, and the Normal
1720 zone if it does not.
1722 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1723 Format: <Controller#>[,poll interval]
1724 The controller # is the number of the ehci usb debug
1725 port as it is probed via PCI. The poll interval is
1726 optional and is the number seconds in between
1727 each poll cycle to the debug port in case you need
1728 the functionality for interrupting the kernel with
1729 gdb or control-c on the dbgp connection. When
1730 not using this parameter you use sysrq-g to break into
1731 the kernel debugger.
1733 kgdboc= [KGDB,HW] kgdb over consoles.
1734 Requires a tty driver that supports console polling,
1735 or a supported polling keyboard driver (non-usb).
1736 Serial only format: <serial_device>[,baud]
1737 keyboard only format: kbd
1738 keyboard and serial format: kbd,<serial_device>[,baud]
1739 Optional Kernel mode setting:
1740 kms, kbd format: kms,kbd
1741 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1743 kgdbwait [KGDB] Stop kernel execution and enter the
1744 kernel debugger at the earliest opportunity.
1746 kmac= [MIPS] korina ethernet MAC address.
1747 Configure the RouterBoard 532 series on-chip
1748 Ethernet adapter MAC address.
1750 kmemleak= [KNL] Boot-time kmemleak enable/disable
1751 Valid arguments: on, off
1752 Default: on
1753 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1754 the default is off.
1756 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1757 Valid arguments: 0, 1, 2
1758 kmemcheck=0 (disabled)
1759 kmemcheck=1 (enabled)
1760 kmemcheck=2 (one-shot mode)
1761 Default: 2 (one-shot mode)
1763 kstack=N [X86] Print N words from the kernel stack
1764 in oops dumps.
1766 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1767 Default is 0 (don't ignore, but inject #GP)
1769 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1770 KVM MMU at runtime.
1771 Default is 0 (off)
1773 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1774 Default is 1 (enabled)
1776 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1777 for all guests.
1778 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1780 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1781 (virtualized MMU) support on capable Intel chips.
1782 Default is 1 (enabled)
1784 kvm-intel.emulate_invalid_guest_state=
1785 [KVM,Intel] Enable emulation of invalid guest states
1786 Default is 0 (disabled)
1788 kvm-intel.flexpriority=
1789 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1790 Default is 1 (enabled)
1792 kvm-intel.nested=
1793 [KVM,Intel] Enable VMX nesting (nVMX).
1794 Default is 0 (disabled)
1796 kvm-intel.unrestricted_guest=
1797 [KVM,Intel] Disable unrestricted guest feature
1798 (virtualized real and unpaged mode) on capable
1799 Intel chips. Default is 1 (enabled)
1801 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1802 feature (tagged TLBs) on capable Intel chips.
1803 Default is 1 (enabled)
1805 l2cr= [PPC]
1807 l3cr= [PPC]
1809 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1810 disabled it.
1812 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1813 value for LAPIC timer one-shot implementation. Default
1814 back to the programmable timer unit in the LAPIC.
1816 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1817 in C2 power state.
1819 libata.dma= [LIBATA] DMA control
1820 libata.dma=0 Disable all PATA and SATA DMA
1821 libata.dma=1 PATA and SATA Disk DMA only
1822 libata.dma=2 ATAPI (CDROM) DMA only
1823 libata.dma=4 Compact Flash DMA only
1824 Combinations also work, so libata.dma=3 enables DMA
1825 for disks and CDROMs, but not CFs.
1827 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1828 libata.ignore_hpa=0 keep BIOS limits (default)
1829 libata.ignore_hpa=1 ignore limits, using full disk
1831 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1832 when set.
1833 Format: <int>
1835 libata.force= [LIBATA] Force configurations. The format is comma
1836 separated list of "[ID:]VAL" where ID is
1837 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1838 matching port, link or device. Basically, it matches
1839 the ATA ID string printed on console by libata. If
1840 the whole ID part is omitted, the last PORT and DEVICE
1841 values are used. If ID hasn't been specified yet, the
1842 configuration applies to all ports, links and devices.
1844 If only DEVICE is omitted, the parameter applies to
1845 the port and all links and devices behind it. DEVICE
1846 number of 0 either selects the first device or the
1847 first fan-out link behind PMP device. It does not
1848 select the host link. DEVICE number of 15 selects the
1849 host link and device attached to it.
1851 The VAL specifies the configuration to force. As long
1852 as there's no ambiguity shortcut notation is allowed.
1853 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1854 The following configurations can be forced.
1856 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1857 Any ID with matching PORT is used.
1859 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1861 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1862 udma[/][16,25,33,44,66,100,133] notation is also
1863 allowed.
1865 * [no]ncq: Turn on or off NCQ.
1867 * [no]ncqtrim: Turn off queued DSM TRIM.
1869 * nohrst, nosrst, norst: suppress hard, soft
1870 and both resets.
1872 * rstonce: only attempt one reset during
1873 hot-unplug link recovery
1875 * dump_id: dump IDENTIFY data.
1877 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1879 * disable: Disable this device.
1881 If there are multiple matching configurations changing
1882 the same attribute, the last one is used.
1884 memblock=debug [KNL] Enable memblock debug messages.
1886 load_ramdisk= [RAM] List of ramdisks to load from floppy
1887 See Documentation/blockdev/ramdisk.txt.
1889 lockd.nlm_grace_period=P [NFS] Assign grace period.
1890 Format: <integer>
1892 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1893 Format: <integer>
1895 lockd.nlm_timeout=T [NFS] Assign timeout value.
1896 Format: <integer>
1898 lockd.nlm_udpport=M [NFS] Assign UDP port.
1899 Format: <integer>
1901 locktorture.nreaders_stress= [KNL]
1902 Set the number of locking read-acquisition kthreads.
1903 Defaults to being automatically set based on the
1904 number of online CPUs.
1906 locktorture.nwriters_stress= [KNL]
1907 Set the number of locking write-acquisition kthreads.
1909 locktorture.onoff_holdoff= [KNL]
1910 Set time (s) after boot for CPU-hotplug testing.
1912 locktorture.onoff_interval= [KNL]
1913 Set time (s) between CPU-hotplug operations, or
1914 zero to disable CPU-hotplug testing.
1916 locktorture.shuffle_interval= [KNL]
1917 Set task-shuffle interval (jiffies). Shuffling
1918 tasks allows some CPUs to go into dyntick-idle
1919 mode during the locktorture test.
1921 locktorture.shutdown_secs= [KNL]
1922 Set time (s) after boot system shutdown. This
1923 is useful for hands-off automated testing.
1925 locktorture.stat_interval= [KNL]
1926 Time (s) between statistics printk()s.
1928 locktorture.stutter= [KNL]
1929 Time (s) to stutter testing, for example,
1930 specifying five seconds causes the test to run for
1931 five seconds, wait for five seconds, and so on.
1932 This tests the locking primitive's ability to
1933 transition abruptly to and from idle.
1935 locktorture.torture_runnable= [BOOT]
1936 Start locktorture running at boot time.
1938 locktorture.torture_type= [KNL]
1939 Specify the locking implementation to test.
1941 locktorture.verbose= [KNL]
1942 Enable additional printk() statements.
1944 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1945 Format: <irq>
1947 loglevel= All Kernel Messages with a loglevel smaller than the
1948 console loglevel will be printed to the console. It can
1949 also be changed with klogd or other programs. The
1950 loglevels are defined as follows:
1952 0 (KERN_EMERG) system is unusable
1953 1 (KERN_ALERT) action must be taken immediately
1954 2 (KERN_CRIT) critical conditions
1955 3 (KERN_ERR) error conditions
1956 4 (KERN_WARNING) warning conditions
1957 5 (KERN_NOTICE) normal but significant condition
1958 6 (KERN_INFO) informational
1959 7 (KERN_DEBUG) debug-level messages
1961 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1962 in bytes. n must be a power of two and greater
1963 than the minimal size. The minimal size is defined
1964 by LOG_BUF_SHIFT kernel config parameter. There is
1965 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1966 that allows to increase the default size depending on
1967 the number of CPUs. See init/Kconfig for more details.
1969 logo.nologo [FB] Disables display of the built-in Linux logo.
1970 This may be used to provide more screen space for
1971 kernel log messages and is useful when debugging
1972 kernel boot problems.
1974 lp=0 [LP] Specify parallel ports to use, e.g,
1975 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1976 lp=reset first parallel port). 'lp=0' disables the
1977 lp=auto printer driver. 'lp=reset' (which can be
1978 specified in addition to the ports) causes
1979 attached printers to be reset. Using
1980 lp=port1,port2,... specifies the parallel ports
1981 to associate lp devices with, starting with
1982 lp0. A port specification may be 'none' to skip
1983 that lp device, or a parport name such as
1984 'parport0'. Specifying 'lp=auto' instead of a
1985 port specification list means that device IDs
1986 from each port should be examined, to see if
1987 an IEEE 1284-compliant printer is attached; if
1988 so, the driver will manage that printer.
1989 See also header of drivers/char/lp.c.
1991 lpj=n [KNL]
1992 Sets loops_per_jiffy to given constant, thus avoiding
1993 time-consuming boot-time autodetection (up to 250 ms per
1994 CPU). 0 enables autodetection (default). To determine
1995 the correct value for your kernel, boot with normal
1996 autodetection and see what value is printed. Note that
1997 on SMP systems the preset will be applied to all CPUs,
1998 which is likely to cause problems if your CPUs need
1999 significantly divergent settings. An incorrect value
2000 will cause delays in the kernel to be wrong, leading to
2001 unpredictable I/O errors and other breakage. Although
2002 unlikely, in the extreme case this might damage your
2003 hardware.
2005 ltpc= [NET]
2006 Format: <io>,<irq>,<dma>
2008 machvec= [IA-64] Force the use of a particular machine-vector
2009 (machvec) in a generic kernel.
2010 Example: machvec=hpzx1_swiotlb
2012 machtype= [Loongson] Share the same kernel image file between different
2013 yeeloong laptop.
2014 Example: machtype=lemote-yeeloong-2f-7inch
2016 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2017 than or equal to this physical address is ignored.
2019 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2020 should make use of. maxcpus=n : n >= 0 limits the
2021 kernel to using 'n' processors. n=0 is a special case,
2022 it is equivalent to "nosmp", which also disables
2023 the IO APIC.
2025 max_loop= [LOOP] The number of loop block devices that get
2026 (loop.max_loop) unconditionally pre-created at init time. The default
2027 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2028 of statically allocating a predefined number, loop
2029 devices can be requested on-demand with the
2030 /dev/loop-control interface.
2032 mce [X86-32] Machine Check Exception
2034 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2036 md= [HW] RAID subsystems devices and level
2037 See Documentation/md.txt.
2039 mdacon= [MDA]
2040 Format: <first>,<last>
2041 Specifies range of consoles to be captured by the MDA.
2043 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2044 Amount of memory to be used when the kernel is not able
2045 to see the whole system memory or for test.
2046 [X86] Work as limiting max address. Use together
2047 with memmap= to avoid physical address space collisions.
2048 Without memmap= PCI devices could be placed at addresses
2049 belonging to unused RAM.
2051 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2052 memory.
2054 memchunk=nn[KMG]
2055 [KNL,SH] Allow user to override the default size for
2056 per-device physically contiguous DMA buffers.
2058 memmap=exactmap [KNL,X86] Enable setting of an exact
2059 E820 memory map, as specified by the user.
2060 Such memmap=exactmap lines can be constructed based on
2061 BIOS output or other requirements. See the memmap=nn@ss
2062 option description.
2064 memmap=nn[KMG]@ss[KMG]
2065 [KNL] Force usage of a specific region of memory.
2066 Region of memory to be used is from ss to ss+nn.
2068 memmap=nn[KMG]#ss[KMG]
2069 [KNL,ACPI] Mark specific memory as ACPI data.
2070 Region of memory to be marked is from ss to ss+nn.
2072 memmap=nn[KMG]$ss[KMG]
2073 [KNL,ACPI] Mark specific memory as reserved.
2074 Region of memory to be reserved is from ss to ss+nn.
2075 Example: Exclude memory from 0x18690000-0x1869ffff
2076 memmap=64K$0x18690000
2077 or
2078 memmap=0x10000$0x18690000
2080 memmap=nn[KMG]!ss[KMG]
2081 [KNL,X86] Mark specific memory as protected.
2082 Region of memory to be used, from ss to ss+nn.
2083 The memory region may be marked as e820 type 12 (0xc)
2084 and is NVDIMM or ADR memory.
2086 memory_corruption_check=0/1 [X86]
2087 Some BIOSes seem to corrupt the first 64k of
2088 memory when doing things like suspend/resume.
2089 Setting this option will scan the memory
2090 looking for corruption. Enabling this will
2091 both detect corruption and prevent the kernel
2092 from using the memory being corrupted.
2093 However, its intended as a diagnostic tool; if
2094 repeatable BIOS-originated corruption always
2095 affects the same memory, you can use memmap=
2096 to prevent the kernel from using that memory.
2098 memory_corruption_check_size=size [X86]
2099 By default it checks for corruption in the low
2100 64k, making this memory unavailable for normal
2101 use. Use this parameter to scan for
2102 corruption in more or less memory.
2104 memory_corruption_check_period=seconds [X86]
2105 By default it checks for corruption every 60
2106 seconds. Use this parameter to check at some
2107 other rate. 0 disables periodic checking.
2109 memtest= [KNL,X86,ARM] Enable memtest
2110 Format: <integer>
2111 default : 0 <disable>
2112 Specifies the number of memtest passes to be
2113 performed. Each pass selects another test
2114 pattern from a given set of patterns. Memtest
2115 fills the memory with this pattern, validates
2116 memory contents and reserves bad memory
2117 regions that are detected.
2119 meye.*= [HW] Set MotionEye Camera parameters
2120 See Documentation/video4linux/meye.txt.
2122 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2123 Multi-Function General Purpose Timers on AMD Geode
2124 platforms.
2126 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2127 the BIOS has incorrectly applied a workaround. TinyBIOS
2128 version 0.98 is known to be affected, 0.99 fixes the
2129 problem by letting the user disable the workaround.
2131 mga= [HW,DRM]
2133 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2134 physical address is ignored.
2136 mini2440= [ARM,HW,KNL]
2137 Format:[0..2][b][c][t]
2138 Default: "0tb"
2139 MINI2440 configuration specification:
2140 0 - The attached screen is the 3.5" TFT
2141 1 - The attached screen is the 7" TFT
2142 2 - The VGA Shield is attached (1024x768)
2143 Leaving out the screen size parameter will not load
2144 the TFT driver, and the framebuffer will be left
2145 unconfigured.
2146 b - Enable backlight. The TFT backlight pin will be
2147 linked to the kernel VESA blanking code and a GPIO
2148 LED. This parameter is not necessary when using the
2149 VGA shield.
2150 c - Enable the s3c camera interface.
2151 t - Reserved for enabling touchscreen support. The
2152 touchscreen support is not enabled in the mainstream
2153 kernel as of 2.6.30, a preliminary port can be found
2154 in the "bleeding edge" mini2440 support kernel at
2155 http://repo.or.cz/w/linux-2.6/mini2440.git
2157 mminit_loglevel=
2158 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2159 parameter allows control of the logging verbosity for
2160 the additional memory initialisation checks. A value
2161 of 0 disables mminit logging and a level of 4 will
2162 log everything. Information is printed at KERN_DEBUG
2163 so loglevel=8 may also need to be specified.
2165 module.sig_enforce
2166 [KNL] When CONFIG_MODULE_SIG is set, this means that
2167 modules without (valid) signatures will fail to load.
2168 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2169 is always true, so this option does nothing.
2171 mousedev.tap_time=
2172 [MOUSE] Maximum time between finger touching and
2173 leaving touchpad surface for touch to be considered
2174 a tap and be reported as a left button click (for
2175 touchpads working in absolute mode only).
2176 Format: <msecs>
2177 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2178 reporting absolute coordinates, such as tablets
2179 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2180 reporting absolute coordinates, such as tablets
2182 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2183 is similar to kernelcore except it specifies the
2184 amount of memory used for migratable allocations.
2185 If both kernelcore and movablecore is specified,
2186 then kernelcore will be at *least* the specified
2187 value but may be more. If movablecore on its own
2188 is specified, the administrator must be careful
2189 that the amount of memory usable for all allocations
2190 is not too small.
2192 movable_node [KNL,X86] Boot-time switch to enable the effects
2193 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2195 MTD_Partition= [MTD]
2196 Format: <name>,<region-number>,<size>,<offset>
2198 MTD_Region= [MTD] Format:
2199 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2201 mtdparts= [MTD]
2202 See drivers/mtd/cmdlinepart.c.
2204 multitce=off [PPC] This parameter disables the use of the pSeries
2205 firmware feature for updating multiple TCE entries
2206 at a time.
2208 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2210 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2212 boundary - index of last SLC block on Flex-OneNAND.
2213 The remaining blocks are configured as MLC blocks.
2214 lock - Configure if Flex-OneNAND boundary should be locked.
2215 Once locked, the boundary cannot be changed.
2216 1 indicates lock status, 0 indicates unlock status.
2218 mtdset= [ARM]
2219 ARM/S3C2412 JIVE boot control
2221 See arch/arm/mach-s3c2412/mach-jive.c
2223 mtouchusb.raw_coordinates=
2224 [HW] Make the MicroTouch USB driver use raw coordinates
2225 ('y', default) or cooked coordinates ('n')
2227 mtrr_chunk_size=nn[KMG] [X86]
2228 used for mtrr cleanup. It is largest continuous chunk
2229 that could hold holes aka. UC entries.
2231 mtrr_gran_size=nn[KMG] [X86]
2232 Used for mtrr cleanup. It is granularity of mtrr block.
2233 Default is 1.
2234 Large value could prevent small alignment from
2235 using up MTRRs.
2237 mtrr_spare_reg_nr=n [X86]
2238 Format: <integer>
2239 Range: 0,7 : spare reg number
2240 Default : 1
2241 Used for mtrr cleanup. It is spare mtrr entries number.
2242 Set to 2 or more if your graphical card needs more.
2244 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2246 netdev= [NET] Network devices parameters
2247 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2248 Note that mem_start is often overloaded to mean
2249 something different and driver-specific.
2250 This usage is only documented in each driver source
2251 file if at all.
2253 nf_conntrack.acct=
2254 [NETFILTER] Enable connection tracking flow accounting
2255 0 to disable accounting
2256 1 to enable accounting
2257 Default value is 0.
2259 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2260 See Documentation/filesystems/nfs/nfsroot.txt.
2262 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2263 See Documentation/filesystems/nfs/nfsroot.txt.
2265 nfsrootdebug [NFS] enable nfsroot debugging messages.
2266 See Documentation/filesystems/nfs/nfsroot.txt.
2268 nfs.callback_tcpport=
2269 [NFS] set the TCP port on which the NFSv4 callback
2270 channel should listen.
2272 nfs.cache_getent=
2273 [NFS] sets the pathname to the program which is used
2274 to update the NFS client cache entries.
2276 nfs.cache_getent_timeout=
2277 [NFS] sets the timeout after which an attempt to
2278 update a cache entry is deemed to have failed.
2280 nfs.idmap_cache_timeout=
2281 [NFS] set the maximum lifetime for idmapper cache
2282 entries.
2284 nfs.enable_ino64=
2285 [NFS] enable 64-bit inode numbers.
2286 If zero, the NFS client will fake up a 32-bit inode
2287 number for the readdir() and stat() syscalls instead
2288 of returning the full 64-bit number.
2289 The default is to return 64-bit inode numbers.
2291 nfs.max_session_slots=
2292 [NFSv4.1] Sets the maximum number of session slots
2293 the client will attempt to negotiate with the server.
2294 This limits the number of simultaneous RPC requests
2295 that the client can send to the NFSv4.1 server.
2296 Note that there is little point in setting this
2297 value higher than the max_tcp_slot_table_limit.
2299 nfs.nfs4_disable_idmapping=
2300 [NFSv4] When set to the default of '1', this option
2301 ensures that both the RPC level authentication
2302 scheme and the NFS level operations agree to use
2303 numeric uids/gids if the mount is using the
2304 'sec=sys' security flavour. In effect it is
2305 disabling idmapping, which can make migration from
2306 legacy NFSv2/v3 systems to NFSv4 easier.
2307 Servers that do not support this mode of operation
2308 will be autodetected by the client, and it will fall
2309 back to using the idmapper.
2310 To turn off this behaviour, set the value to '0'.
2311 nfs.nfs4_unique_id=
2312 [NFS4] Specify an additional fixed unique ident-
2313 ification string that NFSv4 clients can insert into
2314 their nfs_client_id4 string. This is typically a
2315 UUID that is generated at system install time.
2317 nfs.send_implementation_id =
2318 [NFSv4.1] Send client implementation identification
2319 information in exchange_id requests.
2320 If zero, no implementation identification information
2321 will be sent.
2322 The default is to send the implementation identification
2323 information.
2325 nfs.recover_lost_locks =
2326 [NFSv4] Attempt to recover locks that were lost due
2327 to a lease timeout on the server. Please note that
2328 doing this risks data corruption, since there are
2329 no guarantees that the file will remain unchanged
2330 after the locks are lost.
2331 If you want to enable the kernel legacy behaviour of
2332 attempting to recover these locks, then set this
2333 parameter to '1'.
2334 The default parameter value of '0' causes the kernel
2335 not to attempt recovery of lost locks.
2337 nfs4.layoutstats_timer =
2338 [NFSv4.2] Change the rate at which the kernel sends
2339 layoutstats to the pNFS metadata server.
2341 Setting this to value to 0 causes the kernel to use
2342 whatever value is the default set by the layout
2343 driver. A non-zero value sets the minimum interval
2344 in seconds between layoutstats transmissions.
2346 nfsd.nfs4_disable_idmapping=
2347 [NFSv4] When set to the default of '1', the NFSv4
2348 server will return only numeric uids and gids to
2349 clients using auth_sys, and will accept numeric uids
2350 and gids from such clients. This is intended to ease
2351 migration from NFSv2/v3.
2353 objlayoutdriver.osd_login_prog=
2354 [NFS] [OBJLAYOUT] sets the pathname to the program which
2355 is used to automatically discover and login into new
2356 osd-targets. Please see:
2357 Documentation/filesystems/pnfs.txt for more explanations
2359 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2360 when a NMI is triggered.
2361 Format: [state][,regs][,debounce][,die]
2363 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2364 Format: [panic,][nopanic,][num]
2365 Valid num: 0 or 1
2366 0 - turn hardlockup detector in nmi_watchdog off
2367 1 - turn hardlockup detector in nmi_watchdog on
2368 When panic is specified, panic when an NMI watchdog
2369 timeout occurs (or 'nopanic' to override the opposite
2370 default). To disable both hard and soft lockup detectors,
2371 please see 'nowatchdog'.
2372 This is useful when you use a panic=... timeout and
2373 need the box quickly up again.
2375 netpoll.carrier_timeout=
2376 [NET] Specifies amount of time (in seconds) that
2377 netpoll should wait for a carrier. By default netpoll
2378 waits 4 seconds.
2380 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2381 emulation library even if a 387 maths coprocessor
2382 is present.
2384 no_console_suspend
2385 [HW] Never suspend the console
2386 Disable suspending of consoles during suspend and
2387 hibernate operations. Once disabled, debugging
2388 messages can reach various consoles while the rest
2389 of the system is being put to sleep (ie, while
2390 debugging driver suspend/resume hooks). This may
2391 not work reliably with all consoles, but is known
2392 to work with serial and VGA consoles.
2393 To facilitate more flexible debugging, we also add
2394 console_suspend, a printk module parameter to control
2395 it. Users could use console_suspend (usually
2396 /sys/module/printk/parameters/console_suspend) to
2397 turn on/off it dynamically.
2399 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2400 caches in the slab allocator. Saves per-node memory,
2401 but will impact performance.
2403 noalign [KNL,ARM]
2405 noapic [SMP,APIC] Tells the kernel to not make use of any
2406 IOAPICs that may be present in the system.
2408 noautogroup Disable scheduler automatic task group creation.
2410 nobats [PPC] Do not use BATs for mapping kernel lowmem
2411 on "Classic" PPC cores.
2413 nocache [ARM]
2415 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2417 nodelayacct [KNL] Disable per-task delay accounting
2419 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2421 nodsp [SH] Disable hardware DSP at boot time.
2423 noefi Disable EFI runtime services support.
2425 noexec [IA-64]
2427 noexec [X86]
2428 On X86-32 available only on PAE configured kernels.
2429 noexec=on: enable non-executable mappings (default)
2430 noexec=off: disable non-executable mappings
2432 nosmap [X86]
2433 Disable SMAP (Supervisor Mode Access Prevention)
2434 even if it is supported by processor.
2436 nosmep [X86]
2437 Disable SMEP (Supervisor Mode Execution Prevention)
2438 even if it is supported by processor.
2440 noexec32 [X86-64]
2441 This affects only 32-bit executables.
2442 noexec32=on: enable non-executable mappings (default)
2443 read doesn't imply executable mappings
2444 noexec32=off: disable non-executable mappings
2445 read implies executable mappings
2447 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2449 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2450 register save and restore. The kernel will only save
2451 legacy floating-point registers on task switch.
2453 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2455 noxsave [BUGS=X86] Disables x86 extended register state save
2456 and restore using xsave. The kernel will fallback to
2457 enabling legacy floating-point and sse state.
2459 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2460 register states. The kernel will fall back to use
2461 xsave to save the states. By using this parameter,
2462 performance of saving the states is degraded because
2463 xsave doesn't support modified optimization while
2464 xsaveopt supports it on xsaveopt enabled systems.
2466 noxsaves [X86] Disables xsaves and xrstors used in saving and
2467 restoring x86 extended register state in compacted
2468 form of xsave area. The kernel will fall back to use
2469 xsaveopt and xrstor to save and restore the states
2470 in standard form of xsave area. By using this
2471 parameter, xsave area per process might occupy more
2472 memory on xsaves enabled systems.
2474 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2475 wfi(ARM) instruction doesn't work correctly and not to
2476 use it. This is also useful when using JTAG debugger.
2478 no_file_caps Tells the kernel not to honor file capabilities. The
2479 only way then for a file to be executed with privilege
2480 is to be setuid root or executed by root.
2482 nohalt [IA-64] Tells the kernel not to use the power saving
2483 function PAL_HALT_LIGHT when idle. This increases
2484 power-consumption. On the positive side, it reduces
2485 interrupt wake-up latency, which may improve performance
2486 in certain environments such as networked servers or
2487 real-time systems.
2489 nohibernate [HIBERNATION] Disable hibernation and resume.
2491 nohz= [KNL] Boottime enable/disable dynamic ticks
2492 Valid arguments: on, off
2493 Default: on
2495 nohz_full= [KNL,BOOT]
2496 In kernels built with CONFIG_NO_HZ_FULL=y, set
2497 the specified list of CPUs whose tick will be stopped
2498 whenever possible. The boot CPU will be forced outside
2499 the range to maintain the timekeeping.
2500 The CPUs in this range must also be included in the
2501 rcu_nocbs= set.
2503 noiotrap [SH] Disables trapped I/O port accesses.
2505 noirqdebug [X86-32] Disables the code which attempts to detect and
2506 disable unhandled interrupt sources.
2508 no_timer_check [X86,APIC] Disables the code which tests for
2509 broken timer IRQ sources.
2511 noisapnp [ISAPNP] Disables ISA PnP code.
2513 noinitrd [RAM] Tells the kernel not to load any configured
2514 initial RAM disk.
2516 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2517 remapping.
2518 [Deprecated - use intremap=off]
2520 nointroute [IA-64]
2522 nojitter [IA-64] Disables jitter checking for ITC timers.
2524 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2526 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2527 fault handling.
2529 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2530 steal time is computed, but won't influence scheduler
2531 behaviour
2533 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2535 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2537 noltlbs [PPC] Do not use large page/tlb entries for kernel
2538 lowmem mapping on PPC40x.
2540 nomca [IA-64] Disable machine check abort handling
2542 nomce [X86-32] Disable Machine Check Exception
2544 nomfgpt [X86-32] Disable Multi-Function General Purpose
2545 Timer usage (for AMD Geode machines).
2547 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2548 shutdown the other cpus. Instead use the REBOOT_VECTOR
2549 irq.
2551 nomodule Disable module load
2553 nopat [X86] Disable PAT (page attribute table extension of
2554 pagetables) support.
2556 norandmaps Don't use address space randomization. Equivalent to
2557 echo 0 > /proc/sys/kernel/randomize_va_space
2559 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2561 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2562 with UP alternatives
2564 nordrand [X86] Disable kernel use of the RDRAND and
2565 RDSEED instructions even if they are supported
2566 by the processor. RDRAND and RDSEED are still
2567 available to user space applications.
2569 noresume [SWSUSP] Disables resume and restores original swap
2570 space.
2572 no-scroll [VGA] Disables scrollback.
2573 This is required for the Braillex ib80-piezo Braille
2574 reader made by F.H. Papenmeier (Germany).
2576 nosbagart [IA-64]
2578 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2580 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2581 and disable the IO APIC. legacy for "maxcpus=0".
2583 nosoftlockup [KNL] Disable the soft-lockup detector.
2585 nosync [HW,M68K] Disables sync negotiation for all devices.
2587 notsc [BUGS=X86-32] Disable Time Stamp Counter
2589 nousb [USB] Disable the USB subsystem
2591 nowatchdog [KNL] Disable both lockup detectors, i.e.
2592 soft-lockup and NMI watchdog (hard-lockup).
2594 nowb [ARM]
2596 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2598 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2599 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2600 Some features depend on CPU0. Known dependencies are:
2601 1. Resume from suspend/hibernate depends on CPU0.
2602 Suspend/hibernate will fail if CPU0 is offline and you
2603 need to online CPU0 before suspend/hibernate.
2604 2. PIC interrupts also depend on CPU0. CPU0 can't be
2605 removed if a PIC interrupt is detected.
2606 It's said poweroff/reboot may depend on CPU0 on some
2607 machines although I haven't seen such issues so far
2608 after CPU0 is offline on a few tested machines.
2609 If the dependencies are under your control, you can
2610 turn on cpu0_hotplug.
2612 nptcg= [IA-64] Override max number of concurrent global TLB
2613 purges which is reported from either PAL_VM_SUMMARY or
2614 SAL PALO.
2616 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2617 could support. nr_cpus=n : n >= 1 limits the kernel to
2618 supporting 'n' processors. Later in runtime you can not
2619 use hotplug cpu feature to put more cpu back to online.
2620 just like you compile the kernel NR_CPUS=n
2622 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2624 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2625 Allowed values are enable and disable
2627 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2628 one of ['zone', 'node', 'default'] can be specified
2629 This can be set from sysctl after boot.
2630 See Documentation/sysctl/vm.txt for details.
2632 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2633 See Documentation/debugging-via-ohci1394.txt for more
2634 info.
2636 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2637 Rather than timing out after 20 ms if an EC
2638 command is not properly ACKed, override the length
2639 of the timeout. We have interrupts disabled while
2640 waiting for the ACK, so if this is set too high
2641 interrupts *may* be lost!
2643 omap_mux= [OMAP] Override bootloader pin multiplexing.
2644 Format: <mux_mode0.mode_name=value>...
2645 For example, to override I2C bus2:
2646 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2648 oprofile.timer= [HW]
2649 Use timer interrupt instead of performance counters
2651 oprofile.cpu_type= Force an oprofile cpu type
2652 This might be useful if you have an older oprofile
2653 userland or if you want common events.
2654 Format: { arch_perfmon }
2655 arch_perfmon: [X86] Force use of architectural
2656 perfmon on Intel CPUs instead of the
2657 CPU specific event set.
2658 timer: [X86] Force use of architectural NMI
2659 timer mode (see also oprofile.timer
2660 for generic hr timer mode)
2661 [s390] Force legacy basic mode sampling
2662 (report cpu_type "timer")
2664 oops=panic Always panic on oopses. Default is to just kill the
2665 process, but there is a small probability of
2666 deadlocking the machine.
2667 This will also cause panics on machine check exceptions.
2668 Useful together with panic=30 to trigger a reboot.
2670 OSS [HW,OSS]
2671 See Documentation/sound/oss/oss-parameters.txt
2673 page_owner= [KNL] Boot-time page_owner enabling option.
2674 Storage of the information about who allocated
2675 each page is disabled in default. With this switch,
2676 we can turn it on.
2677 on: enable the feature
2679 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2680 timeout > 0: seconds before rebooting
2681 timeout = 0: wait forever
2682 timeout < 0: reboot immediately
2683 Format: <timeout>
2685 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2686 on a WARN().
2688 crash_kexec_post_notifiers
2689 Run kdump after running panic-notifiers and dumping
2690 kmsg. This only for the users who doubt kdump always
2691 succeeds in any situation.
2692 Note that this also increases risks of kdump failure,
2693 because some panic notifiers can make the crashed
2694 kernel more unstable.
2696 parkbd.port= [HW] Parallel port number the keyboard adapter is
2697 connected to, default is 0.
2698 Format: <parport#>
2699 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2700 0 for XT, 1 for AT (default is AT).
2701 Format: <mode>
2703 parport= [HW,PPT] Specify parallel ports. 0 disables.
2704 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2705 Use 'auto' to force the driver to use any
2706 IRQ/DMA settings detected (the default is to
2707 ignore detected IRQ/DMA settings because of
2708 possible conflicts). You can specify the base
2709 address, IRQ, and DMA settings; IRQ and DMA
2710 should be numbers, or 'auto' (for using detected
2711 settings on that particular port), or 'nofifo'
2712 (to avoid using a FIFO even if it is detected).
2713 Parallel ports are assigned in the order they
2714 are specified on the command line, starting
2715 with parport0.
2717 parport_init_mode= [HW,PPT]
2718 Configure VIA parallel port to operate in
2719 a specific mode. This is necessary on Pegasos
2720 computer where firmware has no options for setting
2721 up parallel port mode and sets it to spp.
2722 Currently this function knows 686a and 8231 chips.
2723 Format: [spp|ps2|epp|ecp|ecpepp]
2725 pause_on_oops=
2726 Halt all CPUs after the first oops has been printed for
2727 the specified number of seconds. This is to be used if
2728 your oopses keep scrolling off the screen.
2730 pcbit= [HW,ISDN]
2732 pcd. [PARIDE]
2733 See header of drivers/block/paride/pcd.c.
2734 See also Documentation/blockdev/paride.txt.
2736 pci=option[,option...] [PCI] various PCI subsystem options:
2737 earlydump [X86] dump PCI config space before the kernel
2738 changes anything
2739 off [X86] don't probe for the PCI bus
2740 bios [X86-32] force use of PCI BIOS, don't access
2741 the hardware directly. Use this if your machine
2742 has a non-standard PCI host bridge.
2743 nobios [X86-32] disallow use of PCI BIOS, only direct
2744 hardware access methods are allowed. Use this
2745 if you experience crashes upon bootup and you
2746 suspect they are caused by the BIOS.
2747 conf1 [X86] Force use of PCI Configuration
2748 Mechanism 1.
2749 conf2 [X86] Force use of PCI Configuration
2750 Mechanism 2.
2751 noaer [PCIE] If the PCIEAER kernel config parameter is
2752 enabled, this kernel boot option can be used to
2753 disable the use of PCIE advanced error reporting.
2754 nodomains [PCI] Disable support for multiple PCI
2755 root domains (aka PCI segments, in ACPI-speak).
2756 nommconf [X86] Disable use of MMCONFIG for PCI
2757 Configuration
2758 check_enable_amd_mmconf [X86] check for and enable
2759 properly configured MMIO access to PCI
2760 config space on AMD family 10h CPU
2761 nomsi [MSI] If the PCI_MSI kernel config parameter is
2762 enabled, this kernel boot option can be used to
2763 disable the use of MSI interrupts system-wide.
2764 noioapicquirk [APIC] Disable all boot interrupt quirks.
2765 Safety option to keep boot IRQs enabled. This
2766 should never be necessary.
2767 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2768 primary IO-APIC for bridges that cannot disable
2769 boot IRQs. This fixes a source of spurious IRQs
2770 when the system masks IRQs.
2771 noioapicreroute [APIC] Disable workaround that uses the
2772 boot IRQ equivalent of an IRQ that connects to
2773 a chipset where boot IRQs cannot be disabled.
2774 The opposite of ioapicreroute.
2775 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2776 routing table. These calls are known to be buggy
2777 on several machines and they hang the machine
2778 when used, but on other computers it's the only
2779 way to get the interrupt routing table. Try
2780 this option if the kernel is unable to allocate
2781 IRQs or discover secondary PCI buses on your
2782 motherboard.
2783 rom [X86] Assign address space to expansion ROMs.
2784 Use with caution as certain devices share
2785 address decoders between ROMs and other
2786 resources.
2787 norom [X86] Do not assign address space to
2788 expansion ROMs that do not already have
2789 BIOS assigned address ranges.
2790 nobar [X86] Do not assign address space to the
2791 BARs that weren't assigned by the BIOS.
2792 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2793 assigned automatically to PCI devices. You can
2794 make the kernel exclude IRQs of your ISA cards
2795 this way.
2796 pirqaddr=0xAAAAA [X86] Specify the physical address
2797 of the PIRQ table (normally generated
2798 by the BIOS) if it is outside the
2799 F0000h-100000h range.
2800 lastbus=N [X86] Scan all buses thru bus #N. Can be
2801 useful if the kernel is unable to find your
2802 secondary buses and you want to tell it
2803 explicitly which ones they are.
2804 assign-busses [X86] Always assign all PCI bus
2805 numbers ourselves, overriding
2806 whatever the firmware may have done.
2807 usepirqmask [X86] Honor the possible IRQ mask stored
2808 in the BIOS $PIR table. This is needed on
2809 some systems with broken BIOSes, notably
2810 some HP Pavilion N5400 and Omnibook XE3
2811 notebooks. This will have no effect if ACPI
2812 IRQ routing is enabled.
2813 noacpi [X86] Do not use ACPI for IRQ routing
2814 or for PCI scanning.
2815 use_crs [X86] Use PCI host bridge window information
2816 from ACPI. On BIOSes from 2008 or later, this
2817 is enabled by default. If you need to use this,
2818 please report a bug.
2819 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2820 If you need to use this, please report a bug.
2821 routeirq Do IRQ routing for all PCI devices.
2822 This is normally done in pci_enable_device(),
2823 so this option is a temporary workaround
2824 for broken drivers that don't call it.
2825 skip_isa_align [X86] do not align io start addr, so can
2826 handle more pci cards
2827 firmware [ARM] Do not re-enumerate the bus but instead
2828 just use the configuration from the
2829 bootloader. This is currently used on
2830 IXP2000 systems where the bus has to be
2831 configured a certain way for adjunct CPUs.
2832 noearly [X86] Don't do any early type 1 scanning.
2833 This might help on some broken boards which
2834 machine check when some devices' config space
2835 is read. But various workarounds are disabled
2836 and some IOMMU drivers will not work.
2837 bfsort Sort PCI devices into breadth-first order.
2838 This sorting is done to get a device
2839 order compatible with older (<= 2.4) kernels.
2840 nobfsort Don't sort PCI devices into breadth-first order.
2841 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2842 tuning and use the BIOS-configured MPS defaults.
2843 pcie_bus_safe Set every device's MPS to the largest value
2844 supported by all devices below the root complex.
2845 pcie_bus_perf Set device MPS to the largest allowable MPS
2846 based on its parent bus. Also set MRRS (Max
2847 Read Request Size) to the largest supported
2848 value (no larger than the MPS that the device
2849 or bus can support) for best performance.
2850 pcie_bus_peer2peer Set every device's MPS to 128B, which
2851 every device is guaranteed to support. This
2852 configuration allows peer-to-peer DMA between
2853 any pair of devices, possibly at the cost of
2854 reduced performance. This also guarantees
2855 that hot-added devices will work.
2856 cbiosize=nn[KMG] The fixed amount of bus space which is
2857 reserved for the CardBus bridge's IO window.
2858 The default value is 256 bytes.
2859 cbmemsize=nn[KMG] The fixed amount of bus space which is
2860 reserved for the CardBus bridge's memory
2861 window. The default value is 64 megabytes.
2862 resource_alignment=
2863 Format:
2864 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2865 Specifies alignment and device to reassign
2866 aligned memory resources.
2867 If <order of align> is not specified,
2868 PAGE_SIZE is used as alignment.
2869 PCI-PCI bridge can be specified, if resource
2870 windows need to be expanded.
2871 ecrc= Enable/disable PCIe ECRC (transaction layer
2872 end-to-end CRC checking).
2873 bios: Use BIOS/firmware settings. This is the
2874 the default.
2875 off: Turn ECRC off
2876 on: Turn ECRC on.
2877 hpiosize=nn[KMG] The fixed amount of bus space which is
2878 reserved for hotplug bridge's IO window.
2879 Default size is 256 bytes.
2880 hpmemsize=nn[KMG] The fixed amount of bus space which is
2881 reserved for hotplug bridge's memory window.
2882 Default size is 2 megabytes.
2883 realloc= Enable/disable reallocating PCI bridge resources
2884 if allocations done by BIOS are too small to
2885 accommodate resources required by all child
2886 devices.
2887 off: Turn realloc off
2888 on: Turn realloc on
2889 realloc same as realloc=on
2890 noari do not use PCIe ARI.
2891 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2892 only look for one device below a PCIe downstream
2893 port.
2895 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2896 Management.
2897 off Disable ASPM.
2898 force Enable ASPM even on devices that claim not to support it.
2899 WARNING: Forcing ASPM on may cause system lockups.
2901 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2902 nomsi Do not use MSI for PCI Express Native Hotplug (this
2903 makes all PCIe ports use INTx for hotplug services).
2905 pcie_ports= [PCIE] PCIe ports handling:
2906 auto Ask the BIOS whether or not to use native PCIe services
2907 associated with PCIe ports (PME, hot-plug, AER). Use
2908 them only if that is allowed by the BIOS.
2909 native Use native PCIe services associated with PCIe ports
2910 unconditionally.
2911 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2912 ports driver.
2914 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2915 nomsi Do not use MSI for native PCIe PME signaling (this makes
2916 all PCIe root ports use INTx for all services).
2918 pcmv= [HW,PCMCIA] BadgePAD 4
2920 pd_ignore_unused
2921 [PM]
2922 Keep all power-domains already enabled by bootloader on,
2923 even if no driver has claimed them. This is useful
2924 for debug and development, but should not be
2925 needed on a platform with proper driver support.
2927 pd. [PARIDE]
2928 See Documentation/blockdev/paride.txt.
2930 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2931 boot time.
2932 Format: { 0 | 1 }
2933 See arch/parisc/kernel/pdc_chassis.c
2935 percpu_alloc= Select which percpu first chunk allocator to use.
2936 Currently supported values are "embed" and "page".
2937 Archs may support subset or none of the selections.
2938 See comments in mm/percpu.c for details on each
2939 allocator. This parameter is primarily for debugging
2940 and performance comparison.
2942 pf. [PARIDE]
2943 See Documentation/blockdev/paride.txt.
2945 pg. [PARIDE]
2946 See Documentation/blockdev/paride.txt.
2948 pirq= [SMP,APIC] Manual mp-table setup
2949 See Documentation/x86/i386/IO-APIC.txt.
2951 plip= [PPT,NET] Parallel port network link
2952 Format: { parport<nr> | timid | 0 }
2953 See also Documentation/parport.txt.
2955 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2956 Override pmtimer IOPort with a hex value.
2957 e.g. pmtmr=0x508
2959 pnp.debug=1 [PNP]
2960 Enable PNP debug messages (depends on the
2961 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2962 via /sys/module/pnp/parameters/debug. We always show
2963 current resource usage; turning this on also shows
2964 possible settings and some assignment information.
2966 pnpacpi= [ACPI]
2967 { off }
2969 pnpbios= [ISAPNP]
2970 { on | off | curr | res | no-curr | no-res }
2972 pnp_reserve_irq=
2973 [ISAPNP] Exclude IRQs for the autoconfiguration
2975 pnp_reserve_dma=
2976 [ISAPNP] Exclude DMAs for the autoconfiguration
2978 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2979 Ranges are in pairs (I/O port base and size).
2981 pnp_reserve_mem=
2982 [ISAPNP] Exclude memory regions for the
2983 autoconfiguration.
2984 Ranges are in pairs (memory base and size).
2986 ports= [IP_VS_FTP] IPVS ftp helper module
2987 Default is 21.
2988 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2989 may be specified.
2990 Format: <port>,<port>....
2992 print-fatal-signals=
2993 [KNL] debug: print fatal signals
2995 If enabled, warn about various signal handling
2996 related application anomalies: too many signals,
2997 too many POSIX.1 timers, fatal signals causing a
2998 coredump - etc.
3000 If you hit the warning due to signal overflow,
3001 you might want to try "ulimit -i unlimited".
3003 default: off.
3005 printk.always_kmsg_dump=
3006 Trigger kmsg_dump for cases other than kernel oops or
3007 panics
3008 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3009 default: disabled
3011 printk.time= Show timing data prefixed to each printk message line
3012 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3014 processor.max_cstate= [HW,ACPI]
3015 Limit processor to maximum C-state
3016 max_cstate=9 overrides any DMI blacklist limit.
3018 processor.nocst [HW,ACPI]
3019 Ignore the _CST method to determine C-states,
3020 instead using the legacy FADT method
3022 profile= [KNL] Enable kernel profiling via /proc/profile
3023 Format: [schedule,]<number>
3024 Param: "schedule" - profile schedule points.
3025 Param: <number> - step/bucket size as a power of 2 for
3026 statistical time based profiling.
3027 Param: "sleep" - profile D-state sleeping (millisecs).
3028 Requires CONFIG_SCHEDSTATS
3029 Param: "kvm" - profile VM exits.
3031 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3032 before loading.
3033 See Documentation/blockdev/ramdisk.txt.
3035 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3036 probe for; one of (bare|imps|exps|lifebook|any).
3037 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3038 per second.
3039 psmouse.resetafter= [HW,MOUSE]
3040 Try to reset the device after so many bad packets
3041 (0 = never).
3042 psmouse.resolution=
3043 [HW,MOUSE] Set desired mouse resolution, in dpi.
3044 psmouse.smartscroll=
3045 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3046 0 = disabled, 1 = enabled (default).
3048 pstore.backend= Specify the name of the pstore backend to use
3050 pt. [PARIDE]
3051 See Documentation/blockdev/paride.txt.
3053 pty.legacy_count=
3054 [KNL] Number of legacy pty's. Overwrites compiled-in
3055 default number.
3057 quiet [KNL] Disable most log messages
3059 r128= [HW,DRM]
3061 raid= [HW,RAID]
3062 See Documentation/md.txt.
3064 ramdisk_blocksize= [RAM]
3065 See Documentation/blockdev/ramdisk.txt.
3067 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3068 See Documentation/blockdev/ramdisk.txt.
3070 rcu_nocbs= [KNL]
3071 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3072 the specified list of CPUs to be no-callback CPUs.
3073 Invocation of these CPUs' RCU callbacks will
3074 be offloaded to "rcuox/N" kthreads created for
3075 that purpose, where "x" is "b" for RCU-bh, "p"
3076 for RCU-preempt, and "s" for RCU-sched, and "N"
3077 is the CPU number. This reduces OS jitter on the
3078 offloaded CPUs, which can be useful for HPC and
3079 real-time workloads. It can also improve energy
3080 efficiency for asymmetric multiprocessors.
3082 rcu_nocb_poll [KNL]
3083 Rather than requiring that offloaded CPUs
3084 (specified by rcu_nocbs= above) explicitly
3085 awaken the corresponding "rcuoN" kthreads,
3086 make these kthreads poll for callbacks.
3087 This improves the real-time response for the
3088 offloaded CPUs by relieving them of the need to
3089 wake up the corresponding kthread, but degrades
3090 energy efficiency by requiring that the kthreads
3091 periodically wake up to do the polling.
3093 rcutree.blimit= [KNL]
3094 Set maximum number of finished RCU callbacks to
3095 process in one batch.
3097 rcutree.dump_tree= [KNL]
3098 Dump the structure of the rcu_node combining tree
3099 out at early boot. This is used for diagnostic
3100 purposes, to verify correct tree setup.
3102 rcutree.gp_cleanup_delay= [KNL]
3103 Set the number of jiffies to delay each step of
3104 RCU grace-period cleanup. This only has effect
3105 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3107 rcutree.gp_init_delay= [KNL]
3108 Set the number of jiffies to delay each step of
3109 RCU grace-period initialization. This only has
3110 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3111 is set.
3113 rcutree.gp_preinit_delay= [KNL]
3114 Set the number of jiffies to delay each step of
3115 RCU grace-period pre-initialization, that is,
3116 the propagation of recent CPU-hotplug changes up
3117 the rcu_node combining tree. This only has effect
3118 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3120 rcutree.rcu_fanout_exact= [KNL]
3121 Disable autobalancing of the rcu_node combining
3122 tree. This is used by rcutorture, and might
3123 possibly be useful for architectures having high
3124 cache-to-cache transfer latencies.
3126 rcutree.rcu_fanout_leaf= [KNL]
3127 Change the number of CPUs assigned to each
3128 leaf rcu_node structure. Useful for very
3129 large systems, which will choose the value 64,
3130 and for NUMA systems with large remote-access
3131 latencies, which will choose a value aligned
3132 with the appropriate hardware boundaries.
3134 rcutree.jiffies_till_sched_qs= [KNL]
3135 Set required age in jiffies for a
3136 given grace period before RCU starts
3137 soliciting quiescent-state help from
3138 rcu_note_context_switch().
3140 rcutree.jiffies_till_first_fqs= [KNL]
3141 Set delay from grace-period initialization to
3142 first attempt to force quiescent states.
3143 Units are jiffies, minimum value is zero,
3144 and maximum value is HZ.
3146 rcutree.jiffies_till_next_fqs= [KNL]
3147 Set delay between subsequent attempts to force
3148 quiescent states. Units are jiffies, minimum
3149 value is one, and maximum value is HZ.
3151 rcutree.kthread_prio= [KNL,BOOT]
3152 Set the SCHED_FIFO priority of the RCU per-CPU
3153 kthreads (rcuc/N). This value is also used for
3154 the priority of the RCU boost threads (rcub/N)
3155 and for the RCU grace-period kthreads (rcu_bh,
3156 rcu_preempt, and rcu_sched). If RCU_BOOST is
3157 set, valid values are 1-99 and the default is 1
3158 (the least-favored priority). Otherwise, when
3159 RCU_BOOST is not set, valid values are 0-99 and
3160 the default is zero (non-realtime operation).
3162 rcutree.rcu_nocb_leader_stride= [KNL]
3163 Set the number of NOCB kthread groups, which
3164 defaults to the square root of the number of
3165 CPUs. Larger numbers reduces the wakeup overhead
3166 on the per-CPU grace-period kthreads, but increases
3167 that same overhead on each group's leader.
3169 rcutree.qhimark= [KNL]
3170 Set threshold of queued RCU callbacks beyond which
3171 batch limiting is disabled.
3173 rcutree.qlowmark= [KNL]
3174 Set threshold of queued RCU callbacks below which
3175 batch limiting is re-enabled.
3177 rcutree.rcu_idle_gp_delay= [KNL]
3178 Set wakeup interval for idle CPUs that have
3179 RCU callbacks (RCU_FAST_NO_HZ=y).
3181 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3182 Set wakeup interval for idle CPUs that have
3183 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3184 Lazy RCU callbacks are those which RCU can
3185 prove do nothing more than free memory.
3187 rcutorture.cbflood_inter_holdoff= [KNL]
3188 Set holdoff time (jiffies) between successive
3189 callback-flood tests.
3191 rcutorture.cbflood_intra_holdoff= [KNL]
3192 Set holdoff time (jiffies) between successive
3193 bursts of callbacks within a given callback-flood
3194 test.
3196 rcutorture.cbflood_n_burst= [KNL]
3197 Set the number of bursts making up a given
3198 callback-flood test. Set this to zero to
3199 disable callback-flood testing.
3201 rcutorture.cbflood_n_per_burst= [KNL]
3202 Set the number of callbacks to be registered
3203 in a given burst of a callback-flood test.
3205 rcutorture.fqs_duration= [KNL]
3206 Set duration of force_quiescent_state bursts
3207 in microseconds.
3209 rcutorture.fqs_holdoff= [KNL]
3210 Set holdoff time within force_quiescent_state bursts
3211 in microseconds.
3213 rcutorture.fqs_stutter= [KNL]
3214 Set wait time between force_quiescent_state bursts
3215 in seconds.
3217 rcutorture.gp_cond= [KNL]
3218 Use conditional/asynchronous update-side
3219 primitives, if available.
3221 rcutorture.gp_exp= [KNL]
3222 Use expedited update-side primitives, if available.
3224 rcutorture.gp_normal= [KNL]
3225 Use normal (non-expedited) asynchronous
3226 update-side primitives, if available.
3228 rcutorture.gp_sync= [KNL]
3229 Use normal (non-expedited) synchronous
3230 update-side primitives, if available. If all
3231 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3232 rcutorture.gp_normal=, and rcutorture.gp_sync=
3233 are zero, rcutorture acts as if is interpreted
3234 they are all non-zero.
3236 rcutorture.n_barrier_cbs= [KNL]
3237 Set callbacks/threads for rcu_barrier() testing.
3239 rcutorture.nfakewriters= [KNL]
3240 Set number of concurrent RCU writers. These just
3241 stress RCU, they don't participate in the actual
3242 test, hence the "fake".
3244 rcutorture.nreaders= [KNL]
3245 Set number of RCU readers. The value -1 selects
3246 N-1, where N is the number of CPUs. A value
3247 "n" less than -1 selects N-n-2, where N is again
3248 the number of CPUs. For example, -2 selects N
3249 (the number of CPUs), -3 selects N+1, and so on.
3251 rcutorture.object_debug= [KNL]
3252 Enable debug-object double-call_rcu() testing.
3254 rcutorture.onoff_holdoff= [KNL]
3255 Set time (s) after boot for CPU-hotplug testing.
3257 rcutorture.onoff_interval= [KNL]
3258 Set time (s) between CPU-hotplug operations, or
3259 zero to disable CPU-hotplug testing.
3261 rcutorture.shuffle_interval= [KNL]
3262 Set task-shuffle interval (s). Shuffling tasks
3263 allows some CPUs to go into dyntick-idle mode
3264 during the rcutorture test.
3266 rcutorture.shutdown_secs= [KNL]
3267 Set time (s) after boot system shutdown. This
3268 is useful for hands-off automated testing.
3270 rcutorture.stall_cpu= [KNL]
3271 Duration of CPU stall (s) to test RCU CPU stall
3272 warnings, zero to disable.
3274 rcutorture.stall_cpu_holdoff= [KNL]
3275 Time to wait (s) after boot before inducing stall.
3277 rcutorture.stat_interval= [KNL]
3278 Time (s) between statistics printk()s.
3280 rcutorture.stutter= [KNL]
3281 Time (s) to stutter testing, for example, specifying
3282 five seconds causes the test to run for five seconds,
3283 wait for five seconds, and so on. This tests RCU's
3284 ability to transition abruptly to and from idle.
3286 rcutorture.test_boost= [KNL]
3287 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3288 "Maybe" means test if the RCU implementation
3289 under test support RCU priority boosting.
3291 rcutorture.test_boost_duration= [KNL]
3292 Duration (s) of each individual boost test.
3294 rcutorture.test_boost_interval= [KNL]
3295 Interval (s) between each boost test.
3297 rcutorture.test_no_idle_hz= [KNL]
3298 Test RCU's dyntick-idle handling. See also the
3299 rcutorture.shuffle_interval parameter.
3301 rcutorture.torture_runnable= [BOOT]
3302 Start rcutorture running at boot time.
3304 rcutorture.torture_type= [KNL]
3305 Specify the RCU implementation to test.
3307 rcutorture.verbose= [KNL]
3308 Enable additional printk() statements.
3310 rcupdate.rcu_expedited= [KNL]
3311 Use expedited grace-period primitives, for
3312 example, synchronize_rcu_expedited() instead
3313 of synchronize_rcu(). This reduces latency,
3314 but can increase CPU utilization, degrade
3315 real-time latency, and degrade energy efficiency.
3317 rcupdate.rcu_cpu_stall_suppress= [KNL]
3318 Suppress RCU CPU stall warning messages.
3320 rcupdate.rcu_cpu_stall_timeout= [KNL]
3321 Set timeout for RCU CPU stall warning messages.
3323 rcupdate.rcu_task_stall_timeout= [KNL]
3324 Set timeout in jiffies for RCU task stall warning
3325 messages. Disable with a value less than or equal
3326 to zero.
3328 rcupdate.rcu_self_test= [KNL]
3329 Run the RCU early boot self tests
3331 rcupdate.rcu_self_test_bh= [KNL]
3332 Run the RCU bh early boot self tests
3334 rcupdate.rcu_self_test_sched= [KNL]
3335 Run the RCU sched early boot self tests
3337 rdinit= [KNL]
3338 Format: <full_path>
3339 Run specified binary instead of /init from the ramdisk,
3340 used for early userspace startup. See initrd.
3342 reboot= [KNL]
3343 Format (x86 or x86_64):
3344 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3345 [[,]s[mp]#### \
3346 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3347 [[,]f[orce]
3348 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3349 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3350 reboot_force is either force or not specified,
3351 reboot_cpu is s[mp]#### with #### being the processor
3352 to be used for rebooting.
3354 relax_domain_level=
3355 [KNL, SMP] Set scheduler's default relax_domain_level.
3356 See Documentation/cgroups/cpusets.txt.
3358 relative_sleep_states=
3359 [SUSPEND] Use sleep state labeling where the deepest
3360 state available other than hibernation is always "mem".
3361 Format: { "0" | "1" }
3362 0 -- Traditional sleep state labels.
3363 1 -- Relative sleep state labels.
3365 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3367 reservetop= [X86-32]
3368 Format: nn[KMG]
3369 Reserves a hole at the top of the kernel virtual
3370 address space.
3372 reservelow= [X86]
3373 Format: nn[K]
3374 Set the amount of memory to reserve for BIOS at
3375 the bottom of the address space.
3377 reset_devices [KNL] Force drivers to reset the underlying device
3378 during initialization.
3380 resume= [SWSUSP]
3381 Specify the partition device for software suspend
3382 Format:
3383 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3385 resume_offset= [SWSUSP]
3386 Specify the offset from the beginning of the partition
3387 given by "resume=" at which the swap header is located,
3388 in <PAGE_SIZE> units (needed only for swap files).
3389 See Documentation/power/swsusp-and-swap-files.txt
3391 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3392 read the resume files
3394 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3395 Useful for devices that are detected asynchronously
3396 (e.g. USB and MMC devices).
3398 hibernate= [HIBERNATION]
3399 noresume Don't check if there's a hibernation image
3400 present during boot.
3401 nocompress Don't compress/decompress hibernation images.
3402 no Disable hibernation and resume.
3404 retain_initrd [RAM] Keep initrd memory after extraction
3406 rfkill.default_state=
3407 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3408 etc. communication is blocked by default.
3409 1 Unblocked.
3411 rfkill.master_switch_mode=
3412 0 The "airplane mode" button does nothing.
3413 1 The "airplane mode" button toggles between everything
3414 blocked and the previous configuration.
3415 2 The "airplane mode" button toggles between everything
3416 blocked and everything unblocked.
3418 rhash_entries= [KNL,NET]
3419 Set number of hash buckets for route cache
3421 ro [KNL] Mount root device read-only on boot
3423 root= [KNL] Root filesystem
3424 See name_to_dev_t comment in init/do_mounts.c.
3426 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3427 mount the root filesystem
3429 rootflags= [KNL] Set root filesystem mount option string
3431 rootfstype= [KNL] Set root filesystem type
3433 rootwait [KNL] Wait (indefinitely) for root device to show up.
3434 Useful for devices that are detected asynchronously
3435 (e.g. USB and MMC devices).
3437 rproc_mem=nn[KMG][@address]
3438 [KNL,ARM,CMA] Remoteproc physical memory block.
3439 Memory area to be used by remote processor image,
3440 managed by CMA.
3442 rw [KNL] Mount root device read-write on boot
3444 S [KNL] Run init in single mode
3446 s390_iommu= [HW,S390]
3447 Set s390 IOTLB flushing mode
3448 strict
3449 With strict flushing every unmap operation will result in
3450 an IOTLB flush. Default is lazy flushing before reuse,
3451 which is faster.
3453 sa1100ir [NET]
3454 See drivers/net/irda/sa1100_ir.c.
3456 sbni= [NET] Granch SBNI12 leased line adapter
3458 sched_debug [KNL] Enables verbose scheduler debug messages.
3460 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3461 xtime_lock contention on larger systems, and/or RCU lock
3462 contention on all systems with CONFIG_MAXSMP set.
3463 Format: { "0" | "1" }
3464 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3465 1 -- enable.
3466 Note: increases power consumption, thus should only be
3467 enabled if running jitter sensitive (HPC/RT) workloads.
3469 security= [SECURITY] Choose a security module to enable at boot.
3470 If this boot parameter is not specified, only the first
3471 security module asking for security registration will be
3472 loaded. An invalid security module name will be treated
3473 as if no module has been chosen.
3475 selinux= [SELINUX] Disable or enable SELinux at boot time.
3476 Format: { "0" | "1" }
3477 See security/selinux/Kconfig help text.
3478 0 -- disable.
3479 1 -- enable.
3480 Default value is set via kernel config option.
3481 If enabled at boot time, /selinux/disable can be used
3482 later to disable prior to initial policy load.
3484 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3485 Format: { "0" | "1" }
3486 See security/apparmor/Kconfig help text
3487 0 -- disable.
3488 1 -- enable.
3489 Default value is set via kernel config option.
3491 serialnumber [BUGS=X86-32]
3493 shapers= [NET]
3494 Maximal number of shapers.
3496 show_msr= [x86] show boot-time MSR settings
3497 Format: { <integer> }
3498 Show boot-time (BIOS-initialized) MSR settings.
3499 The parameter means the number of CPUs to show,
3500 for example 1 means boot CPU only.
3502 simeth= [IA-64]
3503 simscsi=
3505 slram= [HW,MTD]
3507 slab_nomerge [MM]
3508 Disable merging of slabs with similar size. May be
3509 necessary if there is some reason to distinguish
3510 allocs to different slabs. Debug options disable
3511 merging on their own.
3512 For more information see Documentation/vm/slub.txt.
3514 slab_max_order= [MM, SLAB]
3515 Determines the maximum allowed order for slabs.
3516 A high setting may cause OOMs due to memory
3517 fragmentation. Defaults to 1 for systems with
3518 more than 32MB of RAM, 0 otherwise.
3520 slub_debug[=options[,slabs]] [MM, SLUB]
3521 Enabling slub_debug allows one to determine the
3522 culprit if slab objects become corrupted. Enabling
3523 slub_debug can create guard zones around objects and
3524 may poison objects when not in use. Also tracks the
3525 last alloc / free. For more information see
3526 Documentation/vm/slub.txt.
3528 slub_max_order= [MM, SLUB]
3529 Determines the maximum allowed order for slabs.
3530 A high setting may cause OOMs due to memory
3531 fragmentation. For more information see
3532 Documentation/vm/slub.txt.
3534 slub_min_objects= [MM, SLUB]
3535 The minimum number of objects per slab. SLUB will
3536 increase the slab order up to slub_max_order to
3537 generate a sufficiently large slab able to contain
3538 the number of objects indicated. The higher the number
3539 of objects the smaller the overhead of tracking slabs
3540 and the less frequently locks need to be acquired.
3541 For more information see Documentation/vm/slub.txt.
3543 slub_min_order= [MM, SLUB]
3544 Determines the minimum page order for slabs. Must be
3545 lower than slub_max_order.
3546 For more information see Documentation/vm/slub.txt.
3548 slub_nomerge [MM, SLUB]
3549 Same with slab_nomerge. This is supported for legacy.
3550 See slab_nomerge for more information.
3552 smart2= [HW]
3553 Format: <io1>[,<io2>[,...,<io8>]]
3555 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3556 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3557 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3558 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3559 smsc-ircc2.ircc_irq= [HW] IRQ line
3560 smsc-ircc2.ircc_dma= [HW] DMA channel
3561 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3562 0: Toshiba Satellite 1800 (GP data pin select)
3563 1: Fast pin select (default)
3564 2: ATC IRMode
3566 softlockup_panic=
3567 [KNL] Should the soft-lockup detector generate panics.
3568 Format: <integer>
3570 softlockup_all_cpu_backtrace=
3571 [KNL] Should the soft-lockup detector generate
3572 backtraces on all cpus.
3573 Format: <integer>
3575 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3576 See Documentation/laptops/sonypi.txt
3578 spia_io_base= [HW,MTD]
3579 spia_fio_base=
3580 spia_pedr=
3581 spia_peddr=
3583 stack_guard_gap= [MM]
3584 override the default stack gap protection. The value
3585 is in page units and it defines how many pages prior
3586 to (for stacks growing down) resp. after (for stacks
3587 growing up) the main stack are reserved for no other
3588 mapping. Default value is 256 pages.
3590 stacktrace [FTRACE]
3591 Enabled the stack tracer on boot up.
3593 stacktrace_filter=[function-list]
3594 [FTRACE] Limit the functions that the stack tracer
3595 will trace at boot up. function-list is a comma separated
3596 list of functions. This list can be changed at run
3597 time by the stack_trace_filter file in the debugfs
3598 tracing directory. Note, this enables stack tracing
3599 and the stacktrace above is not needed.
3601 sti= [PARISC,HW]
3602 Format: <num>
3603 Set the STI (builtin display/keyboard on the HP-PARISC
3604 machines) console (graphic card) which should be used
3605 as the initial boot-console.
3606 See also comment in drivers/video/console/sticore.c.
3608 sti_font= [HW]
3609 See comment in drivers/video/console/sticore.c.
3611 stifb= [HW]
3612 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3614 sunrpc.min_resvport=
3615 sunrpc.max_resvport=
3616 [NFS,SUNRPC]
3617 SunRPC servers often require that client requests
3618 originate from a privileged port (i.e. a port in the
3619 range 0 < portnr < 1024).
3620 An administrator who wishes to reserve some of these
3621 ports for other uses may adjust the range that the
3622 kernel's sunrpc client considers to be privileged
3623 using these two parameters to set the minimum and
3624 maximum port values.
3626 sunrpc.pool_mode=
3627 [NFS]
3628 Control how the NFS server code allocates CPUs to
3629 service thread pools. Depending on how many NICs
3630 you have and where their interrupts are bound, this
3631 option will affect which CPUs will do NFS serving.
3632 Note: this parameter cannot be changed while the
3633 NFS server is running.
3635 auto the server chooses an appropriate mode
3636 automatically using heuristics
3637 global a single global pool contains all CPUs
3638 percpu one pool for each CPU
3639 pernode one pool for each NUMA node (equivalent
3640 to global on non-NUMA machines)
3642 sunrpc.tcp_slot_table_entries=
3643 sunrpc.udp_slot_table_entries=
3644 [NFS,SUNRPC]
3645 Sets the upper limit on the number of simultaneous
3646 RPC calls that can be sent from the client to a
3647 server. Increasing these values may allow you to
3648 improve throughput, but will also increase the
3649 amount of memory reserved for use by the client.
3651 suspend.pm_test_delay=
3652 [SUSPEND]
3653 Sets the number of seconds to remain in a suspend test
3654 mode before resuming the system (see
3655 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3656 is set. Default value is 5.
3658 swapaccount=[0|1]
3659 [KNL] Enable accounting of swap in memory resource
3660 controller if no parameter or 1 is given or disable
3661 it if 0 is given (See Documentation/cgroups/memory.txt)
3663 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3664 Format: { <int> | force }
3665 <int> -- Number of I/O TLB slabs
3666 force -- force using of bounce buffers even if they
3667 wouldn't be automatically used by the kernel
3669 switches= [HW,M68k]
3671 sysfs.deprecated=0|1 [KNL]
3672 Enable/disable old style sysfs layout for old udev
3673 on older distributions. When this option is enabled
3674 very new udev will not work anymore. When this option
3675 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3676 in older udev will not work anymore.
3677 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3678 the kernel configuration.
3680 sysrq_always_enabled
3681 [KNL]
3682 Ignore sysrq setting - this boot parameter will
3683 neutralize any effect of /proc/sys/kernel/sysrq.
3684 Useful for debugging.
3686 tcpmhash_entries= [KNL,NET]
3687 Set the number of tcp_metrics_hash slots.
3688 Default value is 8192 or 16384 depending on total
3689 ram pages. This is used to specify the TCP metrics
3690 cache size. See Documentation/networking/ip-sysctl.txt
3691 "tcp_no_metrics_save" section for more details.
3693 tdfx= [HW,DRM]
3695 test_suspend= [SUSPEND][,N]
3696 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3697 standby suspend) or "freeze" (for suspend type freeze)
3698 as the system sleep state during system startup with
3699 the optional capability to repeat N number of times.
3700 The system is woken from this state using a
3701 wakeup-capable RTC alarm.
3703 thash_entries= [KNL,NET]
3704 Set number of hash buckets for TCP connection
3706 thermal.act= [HW,ACPI]
3707 -1: disable all active trip points in all thermal zones
3708 <degrees C>: override all lowest active trip points
3710 thermal.crt= [HW,ACPI]
3711 -1: disable all critical trip points in all thermal zones
3712 <degrees C>: override all critical trip points
3714 thermal.nocrt= [HW,ACPI]
3715 Set to disable actions on ACPI thermal zone
3716 critical and hot trip points.
3718 thermal.off= [HW,ACPI]
3719 1: disable ACPI thermal control
3721 thermal.psv= [HW,ACPI]
3722 -1: disable all passive trip points
3723 <degrees C>: override all passive trip points to this
3724 value
3726 thermal.tzp= [HW,ACPI]
3727 Specify global default ACPI thermal zone polling rate
3728 <deci-seconds>: poll all this frequency
3729 0: no polling (default)
3731 threadirqs [KNL]
3732 Force threading of all interrupt handlers except those
3733 marked explicitly IRQF_NO_THREAD.
3735 tmem [KNL,XEN]
3736 Enable the Transcendent memory driver if built-in.
3738 tmem.cleancache=0|1 [KNL, XEN]
3739 Default is on (1). Disable the usage of the cleancache
3740 API to send anonymous pages to the hypervisor.
3742 tmem.frontswap=0|1 [KNL, XEN]
3743 Default is on (1). Disable the usage of the frontswap
3744 API to send swap pages to the hypervisor. If disabled
3745 the selfballooning and selfshrinking are force disabled.
3747 tmem.selfballooning=0|1 [KNL, XEN]
3748 Default is on (1). Disable the driving of swap pages
3749 to the hypervisor.
3751 tmem.selfshrinking=0|1 [KNL, XEN]
3752 Default is on (1). Partial swapoff that immediately
3753 transfers pages from Xen hypervisor back to the
3754 kernel based on different criteria.
3756 topology= [S390]
3757 Format: {off | on}
3758 Specify if the kernel should make use of the cpu
3759 topology information if the hardware supports this.
3760 The scheduler will make use of this information and
3761 e.g. base its process migration decisions on it.
3762 Default is on.
3764 topology_updates= [KNL, PPC, NUMA]
3765 Format: {off}
3766 Specify if the kernel should ignore (off)
3767 topology updates sent by the hypervisor to this
3768 LPAR.
3770 tp720= [HW,PS2]
3772 tpm_suspend_pcr=[HW,TPM]
3773 Format: integer pcr id
3774 Specify that at suspend time, the tpm driver
3775 should extend the specified pcr with zeros,
3776 as a workaround for some chips which fail to
3777 flush the last written pcr on TPM_SaveState.
3778 This will guarantee that all the other pcrs
3779 are saved.
3781 trace_buf_size=nn[KMG]
3782 [FTRACE] will set tracing buffer size on each cpu.
3784 trace_event=[event-list]
3785 [FTRACE] Set and start specified trace events in order
3786 to facilitate early boot debugging.
3787 See also Documentation/trace/events.txt
3789 trace_options=[option-list]
3790 [FTRACE] Enable or disable tracer options at boot.
3791 The option-list is a comma delimited list of options
3792 that can be enabled or disabled just as if you were
3793 to echo the option name into
3795 /sys/kernel/debug/tracing/trace_options
3797 For example, to enable stacktrace option (to dump the
3798 stack trace of each event), add to the command line:
3800 trace_options=stacktrace
3802 See also Documentation/trace/ftrace.txt "trace options"
3803 section.
3805 tp_printk[FTRACE]
3806 Have the tracepoints sent to printk as well as the
3807 tracing ring buffer. This is useful for early boot up
3808 where the system hangs or reboots and does not give the
3809 option for reading the tracing buffer or performing a
3810 ftrace_dump_on_oops.
3812 To turn off having tracepoints sent to printk,
3813 echo 0 > /proc/sys/kernel/tracepoint_printk
3814 Note, echoing 1 into this file without the
3815 tracepoint_printk kernel cmdline option has no effect.
3817 ** CAUTION **
3819 Having tracepoints sent to printk() and activating high
3820 frequency tracepoints such as irq or sched, can cause
3821 the system to live lock.
3823 traceoff_on_warning
3824 [FTRACE] enable this option to disable tracing when a
3825 warning is hit. This turns off "tracing_on". Tracing can
3826 be enabled again by echoing '1' into the "tracing_on"
3827 file located in /sys/kernel/debug/tracing/
3829 This option is useful, as it disables the trace before
3830 the WARNING dump is called, which prevents the trace to
3831 be filled with content caused by the warning output.
3833 This option can also be set at run time via the sysctl
3834 option: kernel/traceoff_on_warning
3836 transparent_hugepage=
3837 [KNL]
3838 Format: [always|madvise|never]
3839 Can be used to control the default behavior of the system
3840 with respect to transparent hugepages.
3841 See Documentation/vm/transhuge.txt for more details.
3843 tsc= Disable clocksource stability checks for TSC.
3844 Format: <string>
3845 [x86] reliable: mark tsc clocksource as reliable, this
3846 disables clocksource verification at runtime, as well
3847 as the stability checks done at bootup. Used to enable
3848 high-resolution timer mode on older hardware, and in
3849 virtualized environment.
3850 [x86] noirqtime: Do not use TSC to do irq accounting.
3851 Used to run time disable IRQ_TIME_ACCOUNTING on any
3852 platforms where RDTSC is slow and this accounting
3853 can add overhead.
3855 turbografx.map[2|3]= [HW,JOY]
3856 TurboGraFX parallel port interface
3857 Format:
3858 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3859 See also Documentation/input/joystick-parport.txt
3861 udbg-immortal [PPC] When debugging early kernel crashes that
3862 happen after console_init() and before a proper
3863 console driver takes over, this boot options might
3864 help "seeing" what's going on.
3866 uhash_entries= [KNL,NET]
3867 Set number of hash buckets for UDP/UDP-Lite connections
3869 uhci-hcd.ignore_oc=
3870 [USB] Ignore overcurrent events (default N).
3871 Some badly-designed motherboards generate lots of
3872 bogus events, for ports that aren't wired to
3873 anything. Set this parameter to avoid log spamming.
3874 Note that genuine overcurrent events won't be
3875 reported either.
3877 unknown_nmi_panic
3878 [X86] Cause panic on unknown NMI.
3880 usbcore.authorized_default=
3881 [USB] Default USB device authorization:
3882 (default -1 = authorized except for wireless USB,
3883 0 = not authorized, 1 = authorized)
3885 usbcore.autosuspend=
3886 [USB] The autosuspend time delay (in seconds) used
3887 for newly-detected USB devices (default 2). This
3888 is the time required before an idle device will be
3889 autosuspended. Devices for which the delay is set
3890 to a negative value won't be autosuspended at all.
3892 usbcore.usbfs_snoop=
3893 [USB] Set to log all usbfs traffic (default 0 = off).
3895 usbcore.blinkenlights=
3896 [USB] Set to cycle leds on hubs (default 0 = off).
3898 usbcore.old_scheme_first=
3899 [USB] Start with the old device initialization
3900 scheme (default 0 = off).
3902 usbcore.usbfs_memory_mb=
3903 [USB] Memory limit (in MB) for buffers allocated by
3904 usbfs (default = 16, 0 = max = 2047).
3906 usbcore.use_both_schemes=
3907 [USB] Try the other device initialization scheme
3908 if the first one fails (default 1 = enabled).
3910 usbcore.initial_descriptor_timeout=
3911 [USB] Specifies timeout for the initial 64-byte
3912 USB_REQ_GET_DESCRIPTOR request in milliseconds
3913 (default 5000 = 5.0 seconds).
3915 usbhid.mousepoll=
3916 [USBHID] The interval which mice are to be polled at.
3918 usb-storage.delay_use=
3919 [UMS] The delay in seconds before a new device is
3920 scanned for Logical Units (default 1).
3922 usb-storage.quirks=
3923 [UMS] A list of quirks entries to supplement or
3924 override the built-in unusual_devs list. List
3925 entries are separated by commas. Each entry has
3926 the form VID:PID:Flags where VID and PID are Vendor
3927 and Product ID values (4-digit hex numbers) and
3928 Flags is a set of characters, each corresponding
3929 to a common usb-storage quirk flag as follows:
3930 a = SANE_SENSE (collect more than 18 bytes
3931 of sense data);
3932 b = BAD_SENSE (don't collect more than 18
3933 bytes of sense data);
3934 c = FIX_CAPACITY (decrease the reported
3935 device capacity by one sector);
3936 d = NO_READ_DISC_INFO (don't use
3937 READ_DISC_INFO command);
3938 e = NO_READ_CAPACITY_16 (don't use
3939 READ_CAPACITY_16 command);
3940 f = NO_REPORT_OPCODES (don't use report opcodes
3941 command, uas only);
3942 g = MAX_SECTORS_240 (don't transfer more than
3943 240 sectors at a time, uas only);
3944 h = CAPACITY_HEURISTICS (decrease the
3945 reported device capacity by one
3946 sector if the number is odd);
3947 i = IGNORE_DEVICE (don't bind to this
3948 device);
3949 j = NO_REPORT_LUNS (don't use report luns
3950 command, uas only);
3951 l = NOT_LOCKABLE (don't try to lock and
3952 unlock ejectable media);
3953 m = MAX_SECTORS_64 (don't transfer more
3954 than 64 sectors = 32 KB at a time);
3955 n = INITIAL_READ10 (force a retry of the
3956 initial READ(10) command);
3957 o = CAPACITY_OK (accept the capacity
3958 reported by the device);
3959 p = WRITE_CACHE (the device cache is ON
3960 by default);
3961 r = IGNORE_RESIDUE (the device reports
3962 bogus residue values);
3963 s = SINGLE_LUN (the device has only one
3964 Logical Unit);
3965 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3966 commands, uas only);
3967 u = IGNORE_UAS (don't bind to the uas driver);
3968 w = NO_WP_DETECT (don't test whether the
3969 medium is write-protected).
3970 Example: quirks=0419:aaf5:rl,0421:0433:rc
3972 user_debug= [KNL,ARM]
3973 Format: <int>
3974 See arch/arm/Kconfig.debug help text.
3975 1 - undefined instruction events
3976 2 - system calls
3977 4 - invalid data aborts
3978 8 - SIGSEGV faults
3979 16 - SIGBUS faults
3980 Example: user_debug=31
3982 userpte=
3983 [X86] Flags controlling user PTE allocations.
3985 nohigh = do not allocate PTE pages in
3986 HIGHMEM regardless of setting
3987 of CONFIG_HIGHPTE.
3989 vdso= [X86,SH]
3990 On X86_32, this is an alias for vdso32=. Otherwise:
3992 vdso=1: enable VDSO (the default)
3993 vdso=0: disable VDSO mapping
3995 vdso32= [X86] Control the 32-bit vDSO
3996 vdso32=1: enable 32-bit VDSO
3997 vdso32=0 or vdso32=2: disable 32-bit VDSO
3999 See the help text for CONFIG_COMPAT_VDSO for more
4000 details. If CONFIG_COMPAT_VDSO is set, the default is
4001 vdso32=0; otherwise, the default is vdso32=1.
4003 For compatibility with older kernels, vdso32=2 is an
4004 alias for vdso32=0.
4006 Try vdso32=0 if you encounter an error that says:
4007 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4009 vector= [IA-64,SMP]
4010 vector=percpu: enable percpu vector domain
4012 video= [FB] Frame buffer configuration
4013 See Documentation/fb/modedb.txt.
4015 video.brightness_switch_enabled= [0,1]
4016 If set to 1, on receiving an ACPI notify event
4017 generated by hotkey, video driver will adjust brightness
4018 level and then send out the event to user space through
4019 the allocated input device; If set to 0, video driver
4020 will only send out the event without touching backlight
4021 brightness level.
4022 default: 1
4024 virtio_mmio.device=
4025 [VMMIO] Memory mapped virtio (platform) device.
4027 <size>@<baseaddr>:<irq>[:<id>]
4028 where:
4029 <size> := size (can use standard suffixes
4030 like K, M and G)
4031 <baseaddr> := physical base address
4032 <irq> := interrupt number (as passed to
4033 request_irq())
4034 <id> := (optional) platform device id
4035 example:
4036 virtio_mmio.device=1K@0x100b0000:48:7
4038 Can be used multiple times for multiple devices.
4040 vga= [BOOT,X86-32] Select a particular video mode
4041 See Documentation/x86/boot.txt and
4042 Documentation/svga.txt.
4043 Use vga=ask for menu.
4044 This is actually a boot loader parameter; the value is
4045 passed to the kernel using a special protocol.
4047 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4048 size of <nn>. This can be used to increase the
4049 minimum size (128MB on x86). It can also be used to
4050 decrease the size and leave more room for directly
4051 mapped kernel RAM.
4053 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4054 Format: <command>
4056 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4057 Format: <command>
4059 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4060 Format: <command>
4062 vsyscall= [X86-64]
4063 Controls the behavior of vsyscalls (i.e. calls to
4064 fixed addresses of 0xffffffffff600x00 from legacy
4065 code). Most statically-linked binaries and older
4066 versions of glibc use these calls. Because these
4067 functions are at fixed addresses, they make nice
4068 targets for exploits that can control RIP.
4070 emulate [default] Vsyscalls turn into traps and are
4071 emulated reasonably safely.
4073 native Vsyscalls are native syscall instructions.
4074 This is a little bit faster than trapping
4075 and makes a few dynamic recompilers work
4076 better than they would in emulation mode.
4077 It also makes exploits much easier to write.
4079 none Vsyscalls don't work at all. This makes
4080 them quite hard to use for exploits but
4081 might break your system.
4083 vt.color= [VT] Default text color.
4084 Format: 0xYX, X = foreground, Y = background.
4085 Default: 0x07 = light gray on black.
4087 vt.cur_default= [VT] Default cursor shape.
4088 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4089 the parameters of the <Esc>[?A;B;Cc escape sequence;
4090 see VGA-softcursor.txt. Default: 2 = underline.
4092 vt.default_blu= [VT]
4093 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4094 Change the default blue palette of the console.
4095 This is a 16-member array composed of values
4096 ranging from 0-255.
4098 vt.default_grn= [VT]
4099 Format: <green0>,<green1>,<green2>,...,<green15>
4100 Change the default green palette of the console.
4101 This is a 16-member array composed of values
4102 ranging from 0-255.
4104 vt.default_red= [VT]
4105 Format: <red0>,<red1>,<red2>,...,<red15>
4106 Change the default red palette of the console.
4107 This is a 16-member array composed of values
4108 ranging from 0-255.
4110 vt.default_utf8=
4111 [VT]
4112 Format=<0|1>
4113 Set system-wide default UTF-8 mode for all tty's.
4114 Default is 1, i.e. UTF-8 mode is enabled for all
4115 newly opened terminals.
4117 vt.global_cursor_default=
4118 [VT]
4119 Format=<-1|0|1>
4120 Set system-wide default for whether a cursor
4121 is shown on new VTs. Default is -1,
4122 i.e. cursors will be created by default unless
4123 overridden by individual drivers. 0 will hide
4124 cursors, 1 will display them.
4126 vt.italic= [VT] Default color for italic text; 0-15.
4127 Default: 2 = green.
4129 vt.underline= [VT] Default color for underlined text; 0-15.
4130 Default: 3 = cyan.
4132 watchdog timers [HW,WDT] For information on watchdog timers,
4133 see Documentation/watchdog/watchdog-parameters.txt
4134 or other driver-specific files in the
4135 Documentation/watchdog/ directory.
4137 workqueue.disable_numa
4138 By default, all work items queued to unbound
4139 workqueues are affine to the NUMA nodes they're
4140 issued on, which results in better behavior in
4141 general. If NUMA affinity needs to be disabled for
4142 whatever reason, this option can be used. Note
4143 that this also can be controlled per-workqueue for
4144 workqueues visible under /sys/bus/workqueue/.
4146 workqueue.power_efficient
4147 Per-cpu workqueues are generally preferred because
4148 they show better performance thanks to cache
4149 locality; unfortunately, per-cpu workqueues tend to
4150 be more power hungry than unbound workqueues.
4152 Enabling this makes the per-cpu workqueues which
4153 were observed to contribute significantly to power
4154 consumption unbound, leading to measurably lower
4155 power usage at the cost of small performance
4156 overhead.
4158 The default value of this parameter is determined by
4159 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4161 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4162 default x2apic cluster mode on platforms
4163 supporting x2apic.
4165 x86_intel_mid_timer= [X86-32,APBT]
4166 Choose timer option for x86 Intel MID platform.
4167 Two valid options are apbt timer only and lapic timer
4168 plus one apbt timer for broadcast timer.
4169 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4171 xen_512gb_limit [KNL,X86-64,XEN]
4172 Restricts the kernel running paravirtualized under Xen
4173 to use only up to 512 GB of RAM. The reason to do so is
4174 crash analysis tools and Xen tools for doing domain
4175 save/restore/migration must be enabled to handle larger
4176 domains.
4178 xen_emul_unplug= [HW,X86,XEN]
4179 Unplug Xen emulated devices
4180 Format: [unplug0,][unplug1]
4181 ide-disks -- unplug primary master IDE devices
4182 aux-ide-disks -- unplug non-primary-master IDE devices
4183 nics -- unplug network devices
4184 all -- unplug all emulated devices (NICs and IDE disks)
4185 unnecessary -- unplugging emulated devices is
4186 unnecessary even if the host did not respond to
4187 the unplug protocol
4188 never -- do not unplug even if version check succeeds
4190 xen_nopvspin [X86,XEN]
4191 Disables the ticketlock slowpath using Xen PV
4192 optimizations.
4194 xen_nopv [X86]
4195 Disables the PV optimizations forcing the HVM guest to
4196 run as generic HVM guest with no PV drivers.
4198 xirc2ps_cs= [NET,PCMCIA]
4199 Format:
4200 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4202 ______________________________________________________________________
4204 TODO:
4206 Add more DRM drivers.