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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 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
178 For ARM64, ONLY "acpi=off" or "acpi=force" are available
180 See also Documentation/power/runtime_pm.txt, pci=noacpi
182 acpi_apic_instance= [ACPI, IOAPIC]
183 Format: <int>
184 2: use 2nd APIC table, if available
185 1,0: use 1st APIC table
186 default: 0
188 acpi_backlight= [HW,ACPI]
189 acpi_backlight=vendor
190 acpi_backlight=video
191 If set to vendor, prefer vendor specific driver
192 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
193 of the ACPI video.ko driver.
195 acpica_no_return_repair [HW, ACPI]
196 Disable AML predefined validation mechanism
197 This mechanism can repair the evaluation result to make
198 the return objects more ACPI specification compliant.
199 This option is useful for developers to identify the
200 root cause of an AML interpreter issue when the issue
201 has something to do with the repair mechanism.
203 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
204 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
205 Format: <int>
206 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
207 debug output. Bits in debug_layer correspond to a
208 _COMPONENT in an ACPI source file, e.g.,
209 #define _COMPONENT ACPI_PCI_COMPONENT
210 Bits in debug_level correspond to a level in
211 ACPI_DEBUG_PRINT statements, e.g.,
212 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
213 The debug_level mask defaults to "info". See
214 Documentation/acpi/debug.txt for more information about
215 debug layers and levels.
217 Enable processor driver info messages:
218 acpi.debug_layer=0x20000000
219 Enable PCI/PCI interrupt routing info messages:
220 acpi.debug_layer=0x400000
221 Enable AML "Debug" output, i.e., stores to the Debug
222 object while interpreting AML:
223 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
224 Enable all messages related to ACPI hardware:
225 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
227 Some values produce so much output that the system is
228 unusable. The "log_buf_len" parameter may be useful
229 if you need to capture more output.
231 acpi_enforce_resources= [ACPI]
232 { strict | lax | no }
233 Check for resource conflicts between native drivers
234 and ACPI OperationRegions (SystemIO and SystemMemory
235 only). IO ports and memory declared in ACPI might be
236 used by the ACPI subsystem in arbitrary AML code and
237 can interfere with legacy drivers.
238 strict (default): access to resources claimed by ACPI
239 is denied; legacy drivers trying to access reserved
240 resources will fail to bind to device using them.
241 lax: access to resources claimed by ACPI is allowed;
242 legacy drivers trying to access reserved resources
243 will bind successfully but a warning message is logged.
244 no: ACPI OperationRegions are not marked as reserved,
245 no further checks are performed.
247 acpi_force_table_verification [HW,ACPI]
248 Enable table checksum verification during early stage.
249 By default, this is disabled due to x86 early mapping
250 size limitation.
252 acpi_irq_balance [HW,ACPI]
253 ACPI will balance active IRQs
254 default in APIC mode
256 acpi_irq_nobalance [HW,ACPI]
257 ACPI will not move active IRQs (default)
258 default in PIC mode
260 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
261 Format: <irq>,<irq>...
263 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
264 use by PCI
265 Format: <irq>,<irq>...
267 acpi_no_auto_serialize [HW,ACPI]
268 Disable auto-serialization of AML methods
269 AML control methods that contain the opcodes to create
270 named objects will be marked as "Serialized" by the
271 auto-serialization feature.
272 This feature is enabled by default.
273 This option allows to turn off the feature.
275 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
276 kernels.
278 acpi_no_static_ssdt [HW,ACPI]
279 Disable installation of static SSDTs at early boot time
280 By default, SSDTs contained in the RSDT/XSDT will be
281 installed automatically and they will appear under
282 /sys/firmware/acpi/tables.
283 This option turns off this feature.
284 Note that specifying this option does not affect
285 dynamic table installation which will install SSDT
286 tables to /sys/firmware/acpi/tables/dynamic.
288 acpi_rsdp= [ACPI,EFI,KEXEC]
289 Pass the RSDP address to the kernel, mostly used
290 on machines running EFI runtime service to boot the
291 second kernel for kdump.
293 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
294 Format: To spoof as Windows 98: ="Microsoft Windows"
296 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
297 of 2 which is mandated by ACPI 6) as the supported ACPI
298 specification revision (when using this switch, it may
299 be necessary to carry out a cold reboot _twice_ in a
300 row to make it take effect on the platform firmware).
302 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
303 acpi_osi="string1" # add string1
304 acpi_osi="!string2" # remove string2
305 acpi_osi=!* # remove all strings
306 acpi_osi=! # disable all built-in OS vendor
307 strings
308 acpi_osi= # disable all strings
310 'acpi_osi=!' can be used in combination with single or
311 multiple 'acpi_osi="string1"' to support specific OS
312 vendor string(s). Note that such command can only
313 affect the default state of the OS vendor strings, thus
314 it cannot affect the default state of the feature group
315 strings and the current state of the OS vendor strings,
316 specifying it multiple times through kernel command line
317 is meaningless. This command is useful when one do not
318 care about the state of the feature group strings which
319 should be controlled by the OSPM.
320 Examples:
321 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
322 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
323 can make '_OSI("Windows 2000")' TRUE.
325 'acpi_osi=' cannot be used in combination with other
326 'acpi_osi=' command lines, the _OSI method will not
327 exist in the ACPI namespace. NOTE that such command can
328 only affect the _OSI support state, thus specifying it
329 multiple times through kernel command line is also
330 meaningless.
331 Examples:
332 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
333 FALSE.
335 'acpi_osi=!*' can be used in combination with single or
336 multiple 'acpi_osi="string1"' to support specific
337 string(s). Note that such command can affect the
338 current state of both the OS vendor strings and the
339 feature group strings, thus specifying it multiple times
340 through kernel command line is meaningful. But it may
341 still not able to affect the final state of a string if
342 there are quirks related to this string. This command
343 is useful when one want to control the state of the
344 feature group strings to debug BIOS issues related to
345 the OSPM features.
346 Examples:
347 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
348 '_OSI("Module Device")' FALSE.
349 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
350 '_OSI("Module Device")' TRUE.
351 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
352 equivalent to
353 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
354 and
355 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
356 they all will make '_OSI("Windows 2000")' TRUE.
358 acpi_pm_good [X86]
359 Override the pmtimer bug detection: force the kernel
360 to assume that this machine's pmtimer latches its value
361 and always returns good values.
363 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
364 Format: { level | edge | high | low }
366 acpi_skip_timer_override [HW,ACPI]
367 Recognize and ignore IRQ0/pin2 Interrupt Override.
368 For broken nForce2 BIOS resulting in XT-PIC timer.
370 acpi_sleep= [HW,ACPI] Sleep options
371 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
372 old_ordering, nonvs, sci_force_enable }
373 See Documentation/power/video.txt for information on
374 s3_bios and s3_mode.
375 s3_beep is for debugging; it makes the PC's speaker beep
376 as soon as the kernel's real-mode entry point is called.
377 s4_nohwsig prevents ACPI hardware signature from being
378 used during resume from hibernation.
379 old_ordering causes the ACPI 1.0 ordering of the _PTS
380 control method, with respect to putting devices into
381 low power states, to be enforced (the ACPI 2.0 ordering
382 of _PTS is used by default).
383 nonvs prevents the kernel from saving/restoring the
384 ACPI NVS memory during suspend/hibernation and resume.
385 sci_force_enable causes the kernel to set SCI_EN directly
386 on resume from S1/S3 (which is against the ACPI spec,
387 but some broken systems don't work without it).
389 acpi_use_timer_override [HW,ACPI]
390 Use timer override. For some broken Nvidia NF5 boards
391 that require a timer override, but don't have HPET
393 add_efi_memmap [EFI; X86] Include EFI memory map in
394 kernel's map of available physical RAM.
396 agp= [AGP]
397 { off | try_unsupported }
398 off: disable AGP support
399 try_unsupported: try to drive unsupported chipsets
400 (may crash computer or cause data corruption)
402 ALSA [HW,ALSA]
403 See Documentation/sound/alsa/alsa-parameters.txt
405 alignment= [KNL,ARM]
406 Allow the default userspace alignment fault handler
407 behaviour to be specified. Bit 0 enables warnings,
408 bit 1 enables fixups, and bit 2 sends a segfault.
410 align_va_addr= [X86-64]
411 Align virtual addresses by clearing slice [14:12] when
412 allocating a VMA at process creation time. This option
413 gives you up to 3% performance improvement on AMD F15h
414 machines (where it is enabled by default) for a
415 CPU-intensive style benchmark, and it can vary highly in
416 a microbenchmark depending on workload and compiler.
418 32: only for 32-bit processes
419 64: only for 64-bit processes
420 on: enable for both 32- and 64-bit processes
421 off: disable for both 32- and 64-bit processes
423 alloc_snapshot [FTRACE]
424 Allocate the ftrace snapshot buffer on boot up when the
425 main buffer is allocated. This is handy if debugging
426 and you need to use tracing_snapshot() on boot up, and
427 do not want to use tracing_snapshot_alloc() as it needs
428 to be done where GFP_KERNEL allocations are allowed.
430 amd_iommu= [HW,X86-64]
431 Pass parameters to the AMD IOMMU driver in the system.
432 Possible values are:
433 fullflush - enable flushing of IO/TLB entries when
434 they are unmapped. Otherwise they are
435 flushed before they will be reused, which
436 is a lot of faster
437 off - do not initialize any AMD IOMMU found in
438 the system
439 force_isolation - Force device isolation for all
440 devices. The IOMMU driver is not
441 allowed anymore to lift isolation
442 requirements as needed. This option
443 does not override iommu=pt
445 amd_iommu_dump= [HW,X86-64]
446 Enable AMD IOMMU driver option to dump the ACPI table
447 for AMD IOMMU. With this option enabled, AMD IOMMU
448 driver will print ACPI tables for AMD IOMMU during
449 IOMMU initialization.
451 amijoy.map= [HW,JOY] Amiga joystick support
452 Map of devices attached to JOY0DAT and JOY1DAT
453 Format: <a>,<b>
454 See also Documentation/input/joystick.txt
456 analog.map= [HW,JOY] Analog joystick and gamepad support
457 Specifies type or capabilities of an analog joystick
458 connected to one of 16 gameports
459 Format: <type1>,<type2>,..<type16>
461 apc= [HW,SPARC]
462 Power management functions (SPARCstation-4/5 + deriv.)
463 Format: noidle
464 Disable APC CPU standby support. SPARCstation-Fox does
465 not play well with APC CPU idle - disable it if you have
466 APC and your system crashes randomly.
468 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
469 Change the output verbosity whilst booting
470 Format: { quiet (default) | verbose | debug }
471 Change the amount of debugging information output
472 when initialising the APIC and IO-APIC components.
474 autoconf= [IPV6]
475 See Documentation/networking/ipv6.txt.
477 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
478 Limit apic dumping. The parameter defines the maximal
479 number of local apics being dumped. Also it is possible
480 to set it to "all" by meaning -- no limit here.
481 Format: { 1 (default) | 2 | ... | all }.
482 The parameter valid if only apic=debug or
483 apic=verbose is specified.
484 Example: apic=debug show_lapic=all
486 apm= [APM] Advanced Power Management
487 See header of arch/x86/kernel/apm_32.c.
489 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
490 Format: <io>,<irq>,<nodeID>
492 ataflop= [HW,M68k]
494 atarimouse= [HW,MOUSE] Atari Mouse
496 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
497 EzKey and similar keyboards
499 atkbd.reset= [HW] Reset keyboard during initialization
501 atkbd.set= [HW] Select keyboard code set
502 Format: <int> (2 = AT (default), 3 = PS/2)
504 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
505 keyboards
507 atkbd.softraw= [HW] Choose between synthetic and real raw mode
508 Format: <bool> (0 = real, 1 = synthetic (default))
510 atkbd.softrepeat= [HW]
511 Use software keyboard repeat
513 audit= [KNL] Enable the audit sub-system
514 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
515 0 - kernel audit is disabled and can not be enabled
516 until the next reboot
517 unset - kernel audit is initialized but disabled and
518 will be fully enabled by the userspace auditd.
519 1 - kernel audit is initialized and partially enabled,
520 storing at most audit_backlog_limit messages in
521 RAM until it is fully enabled by the userspace
522 auditd.
523 Default: unset
525 audit_backlog_limit= [KNL] Set the audit queue size limit.
526 Format: <int> (must be >=0)
527 Default: 64
529 baycom_epp= [HW,AX25]
530 Format: <io>,<mode>
532 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
533 Format: <io>,<mode>
534 See header of drivers/net/hamradio/baycom_par.c.
536 baycom_ser_fdx= [HW,AX25]
537 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
538 Format: <io>,<irq>,<mode>[,<baud>]
539 See header of drivers/net/hamradio/baycom_ser_fdx.c.
541 baycom_ser_hdx= [HW,AX25]
542 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
543 Format: <io>,<irq>,<mode>
544 See header of drivers/net/hamradio/baycom_ser_hdx.c.
546 blkdevparts= Manual partition parsing of block device(s) for
547 embedded devices based on command line input.
548 See Documentation/block/cmdline-partition.txt
550 boot_delay= Milliseconds to delay each printk during boot.
551 Values larger than 10 seconds (10000) are changed to
552 no delay (0).
553 Format: integer
555 bootmem_debug [KNL] Enable bootmem allocator debug messages.
557 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
558 bttv.radio= Most important insmod options are available as
559 kernel args too.
560 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
561 bttv.tuner=
563 bulk_remove=off [PPC] This parameter disables the use of the pSeries
564 firmware feature for flushing multiple hpte entries
565 at a time.
567 c101= [NET] Moxa C101 synchronous serial card
569 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
570 Sometimes CPU hardware bugs make them report the cache
571 size incorrectly. The kernel will attempt work arounds
572 to fix known problems, but for some CPUs it is not
573 possible to determine what the correct size should be.
574 This option provides an override for these situations.
576 ca_keys= [KEYS] This parameter identifies a specific key(s) on
577 the system trusted keyring to be used for certificate
578 trust validation.
579 format: { id:<keyid> | builtin }
581 cca= [MIPS] Override the kernel pages' cache coherency
582 algorithm. Accepted values range from 0 to 7
583 inclusive. See arch/mips/include/asm/pgtable-bits.h
584 for platform specific values (SB1, Loongson3 and
585 others).
587 ccw_timeout_log [S390]
588 See Documentation/s390/CommonIO for details.
590 cgroup_disable= [KNL] Disable a particular controller
591 Format: {name of the controller(s) to disable}
592 The effects of cgroup_disable=foo are:
593 - foo isn't auto-mounted if you mount all cgroups in
594 a single hierarchy
595 - foo isn't visible as an individually mountable
596 subsystem
597 {Currently only "memory" controller deal with this and
598 cut the overhead, others just disable the usage. So
599 only cgroup_disable=memory is actually worthy}
601 checkreqprot [SELINUX] Set initial checkreqprot flag value.
602 Format: { "0" | "1" }
603 See security/selinux/Kconfig help text.
604 0 -- check protection applied by kernel (includes
605 any implied execute protection).
606 1 -- check protection requested by application.
607 Default value is set via a kernel config option.
608 Value can be changed at runtime via
609 /selinux/checkreqprot.
611 cio_ignore= [S390]
612 See Documentation/s390/CommonIO for details.
613 clk_ignore_unused
614 [CLK]
615 Prevents the clock framework from automatically gating
616 clocks that have not been explicitly enabled by a Linux
617 device driver but are enabled in hardware at reset or
618 by the bootloader/firmware. Note that this does not
619 force such clocks to be always-on nor does it reserve
620 those clocks in any way. This parameter is useful for
621 debug and development, but should not be needed on a
622 platform with proper driver support. For more
623 information, see Documentation/clk.txt.
625 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
626 [Deprecated]
627 Forces specified clocksource (if available) to be used
628 when calculating gettimeofday(). If specified
629 clocksource is not available, it defaults to PIT.
630 Format: { pit | tsc | cyclone | pmtmr }
632 clocksource= Override the default clocksource
633 Format: <string>
634 Override the default clocksource and use the clocksource
635 with the name specified.
636 Some clocksource names to choose from, depending on
637 the platform:
638 [all] jiffies (this is the base, fallback clocksource)
639 [ACPI] acpi_pm
640 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
641 pxa_timer,timer3,32k_counter,timer0_1
642 [AVR32] avr32
643 [X86-32] pit,hpet,tsc;
644 scx200_hrt on Geode; cyclone on IBM x440
645 [MIPS] MIPS
646 [PARISC] cr16
647 [S390] tod
648 [SH] SuperH
649 [SPARC64] tick
650 [X86-64] hpet,tsc
652 clearcpuid=BITNUM [X86]
653 Disable CPUID feature X for the kernel. See
654 arch/x86/include/asm/cpufeature.h for the valid bit
655 numbers. Note the Linux specific bits are not necessarily
656 stable over kernel options, but the vendor specific
657 ones should be.
658 Also note that user programs calling CPUID directly
659 or using the feature without checking anything
660 will still see it. This just prevents it from
661 being used by the kernel or shown in /proc/cpuinfo.
662 Also note the kernel might malfunction if you disable
663 some critical bits.
665 cma=nn[MG]@[start[MG][-end[MG]]]
666 [ARM,X86,KNL]
667 Sets the size of kernel global memory area for
668 contiguous memory allocations and optionally the
669 placement constraint by the physical address range of
670 memory allocations. A value of 0 disables CMA
671 altogether. For more information, see
672 include/linux/dma-contiguous.h
674 cmo_free_hint= [PPC] Format: { yes | no }
675 Specify whether pages are marked as being inactive
676 when they are freed. This is used in CMO environments
677 to determine OS memory pressure for page stealing by
678 a hypervisor.
679 Default: yes
681 coherent_pool=nn[KMG] [ARM,KNL]
682 Sets the size of memory pool for coherent, atomic dma
683 allocations, by default set to 256K.
685 code_bytes [X86] How many bytes of object code to print
686 in an oops report.
687 Range: 0 - 8192
688 Default: 64
690 com20020= [HW,NET] ARCnet - COM20020 chipset
691 Format:
692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
695 Format: <io>[,<irq>]
697 com90xx= [HW,NET]
698 ARCnet - COM90xx chipset (memory-mapped buffers)
699 Format: <io>[,<irq>[,<memstart>]]
701 condev= [HW,S390] console device
702 conmode=
704 console= [KNL] Output console device and options.
706 tty<n> Use the virtual console device <n>.
708 ttyS<n>[,options]
709 ttyUSB0[,options]
710 Use the specified serial port. The options are of
711 the form "bbbbpnf", where "bbbb" is the baud rate,
712 "p" is parity ("n", "o", or "e"), "n" is number of
713 bits, and "f" is flow control ("r" for RTS or
714 omit it). Default is "9600n8".
716 See Documentation/serial-console.txt for more
717 information. See
718 Documentation/networking/netconsole.txt for an
719 alternative.
721 uart[8250],io,<addr>[,options]
722 uart[8250],mmio,<addr>[,options]
723 uart[8250],mmio32,<addr>[,options]
724 uart[8250],0x<addr>[,options]
725 Start an early, polled-mode console on the 8250/16550
726 UART at the specified I/O port or MMIO address,
727 switching to the matching ttyS device later.
728 MMIO inter-register address stride is either 8-bit
729 (mmio) or 32-bit (mmio32).
730 If none of [io|mmio|mmio32], <addr> is assumed to be
731 equivalent to 'mmio'. 'options' are specified in the
732 same format described for ttyS above; if unspecified,
733 the h/w is not re-initialized.
735 hvc<n> Use the hypervisor console device <n>. This is for
736 both Xen and PowerPC hypervisors.
738 If the device connected to the port is not a TTY but a braille
739 device, prepend "brl," before the device type, for instance
740 console=brl,ttyS0
741 For now, only VisioBraille is supported.
743 consoleblank= [KNL] The console blank (screen saver) timeout in
744 seconds. Defaults to 10*60 = 10mins. A value of 0
745 disables the blank timer.
747 coredump_filter=
748 [KNL] Change the default value for
749 /proc/<pid>/coredump_filter.
750 See also Documentation/filesystems/proc.txt.
752 cpuidle.off=1 [CPU_IDLE]
753 disable the cpuidle sub-system
755 cpu_init_udelay=N
756 [X86] Delay for N microsec between assert and de-assert
757 of APIC INIT to start processors. This delay occurs
758 on every CPU online, such as boot, and resume from suspend.
759 Default: 10000
761 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
762 Format:
763 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
765 crashkernel=size[KMG][@offset[KMG]]
766 [KNL] Using kexec, Linux can switch to a 'crash kernel'
767 upon panic. This parameter reserves the physical
768 memory region [offset, offset + size] for that kernel
769 image. If '@offset' is omitted, then a suitable offset
770 is selected automatically. Check
771 Documentation/kdump/kdump.txt for further details.
773 crashkernel=range1:size1[,range2:size2,...][@offset]
774 [KNL] Same as above, but depends on the memory
775 in the running system. The syntax of range is
776 start-[end] where start and end are both
777 a memory unit (amount[KMG]). See also
778 Documentation/kdump/kdump.txt for an example.
780 crashkernel=size[KMG],high
781 [KNL, x86_64] range could be above 4G. Allow kernel
782 to allocate physical memory region from top, so could
783 be above 4G if system have more than 4G ram installed.
784 Otherwise memory region will be allocated below 4G, if
785 available.
786 It will be ignored if crashkernel=X is specified.
787 crashkernel=size[KMG],low
788 [KNL, x86_64] range under 4G. When crashkernel=X,high
789 is passed, kernel could allocate physical memory region
790 above 4G, that cause second kernel crash on system
791 that require some amount of low memory, e.g. swiotlb
792 requires at least 64M+32K low memory. Kernel would
793 try to allocate 72M below 4G automatically.
794 This one let user to specify own low range under 4G
795 for second kernel instead.
796 0: to disable low allocation.
797 It will be ignored when crashkernel=X,high is not used
798 or memory reserved is below 4G.
800 cs89x0_dma= [HW,NET]
801 Format: <dma>
803 cs89x0_media= [HW,NET]
804 Format: { rj45 | aui | bnc }
806 dasd= [HW,NET]
807 See header of drivers/s390/block/dasd_devmap.c.
809 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
810 (one device per port)
811 Format: <port#>,<type>
812 See also Documentation/input/joystick-parport.txt
814 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
815 time. See Documentation/dynamic-debug-howto.txt for
816 details. Deprecated, see dyndbg.
818 debug [KNL] Enable kernel debugging (events log level).
820 debug_locks_verbose=
821 [KNL] verbose self-tests
822 Format=<0|1>
823 Print debugging info while doing the locking API
824 self-tests.
825 We default to 0 (no extra messages), setting it to
826 1 will print _a lot_ more information - normally
827 only useful to kernel developers.
829 debug_objects [KNL] Enable object debugging
831 no_debug_objects
832 [KNL] Disable object debugging
834 debug_guardpage_minorder=
835 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
836 parameter allows control of the order of pages that will
837 be intentionally kept free (and hence protected) by the
838 buddy allocator. Bigger value increase the probability
839 of catching random memory corruption, but reduce the
840 amount of memory for normal system use. The maximum
841 possible value is MAX_ORDER/2. Setting this parameter
842 to 1 or 2 should be enough to identify most random
843 memory corruption problems caused by bugs in kernel or
844 driver code when a CPU writes to (or reads from) a
845 random memory location. Note that there exists a class
846 of memory corruptions problems caused by buggy H/W or
847 F/W or by drivers badly programing DMA (basically when
848 memory is written at bus level and the CPU MMU is
849 bypassed) which are not detectable by
850 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
851 tracking down these problems.
853 debug_pagealloc=
854 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
855 parameter enables the feature at boot time. In
856 default, it is disabled. We can avoid allocating huge
857 chunk of memory for debug pagealloc if we don't enable
858 it at boot time and the system will work mostly same
859 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
860 on: enable the feature
862 debugpat [X86] Enable PAT debugging
864 decnet.addr= [HW,NET]
865 Format: <area>[,<node>]
866 See also Documentation/networking/decnet.txt.
868 default_hugepagesz=
869 [same as hugepagesz=] The size of the default
870 HugeTLB page size. This is the size represented by
871 the legacy /proc/ hugepages APIs, used for SHM, and
872 default size when mounting hugetlbfs filesystems.
873 Defaults to the default architecture's huge page size
874 if not specified.
876 dhash_entries= [KNL]
877 Set number of hash buckets for dentry cache.
879 disable= [IPV6]
880 See Documentation/networking/ipv6.txt.
882 disable_cpu_apicid= [X86,APIC,SMP]
883 Format: <int>
884 The number of initial APIC ID for the
885 corresponding CPU to be disabled at boot,
886 mostly used for the kdump 2nd kernel to
887 disable BSP to wake up multiple CPUs without
888 causing system reset or hang due to sending
889 INIT from AP to BSP.
891 disable_ddw [PPC/PSERIES]
892 Disable Dynamic DMA Window support. Use this if
893 to workaround buggy firmware.
895 disable_ipv6= [IPV6]
896 See Documentation/networking/ipv6.txt.
898 disable_mtrr_cleanup [X86]
899 The kernel tries to adjust MTRR layout from continuous
900 to discrete, to make X server driver able to add WB
901 entry later. This parameter disables that.
903 disable_mtrr_trim [X86, Intel and AMD only]
904 By default the kernel will trim any uncacheable
905 memory out of your available memory pool based on
906 MTRR settings. This parameter disables that behavior,
907 possibly causing your machine to run very slowly.
909 disable_timer_pin_1 [X86]
910 Disable PIN 1 of APIC timer
911 Can be useful to work around chipset bugs.
913 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
914 this option disables the debugging code at boot.
916 dma_debug_entries=<number>
917 This option allows to tune the number of preallocated
918 entries for DMA-API debugging code. One entry is
919 required per DMA-API allocation. Use this if the
920 DMA-API debugging code disables itself because the
921 architectural default is too low.
923 dma_debug_driver=<driver_name>
924 With this option the DMA-API debugging driver
925 filter feature can be enabled at boot time. Just
926 pass the driver to filter for as the parameter.
927 The filter can be disabled or changed to another
928 driver later using sysfs.
930 drm_kms_helper.edid_firmware=[<connector>:]<file>
931 Broken monitors, graphic adapters and KVMs may
932 send no or incorrect EDID data sets. This parameter
933 allows to specify an EDID data set in the
934 /lib/firmware directory that is used instead.
935 Generic built-in EDID data sets are used, if one of
936 edid/1024x768.bin, edid/1280x1024.bin,
937 edid/1680x1050.bin, or edid/1920x1080.bin is given
938 and no file with the same name exists. Details and
939 instructions how to build your own EDID data are
940 available in Documentation/EDID/HOWTO.txt. An EDID
941 data set will only be used for a particular connector,
942 if its name and a colon are prepended to the EDID
943 name.
945 dscc4.setup= [NET]
947 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
948 module.dyndbg[="val"]
949 Enable debug messages at boot time. See
950 Documentation/dynamic-debug-howto.txt for details.
952 nompx [X86] Disables Intel Memory Protection Extensions.
953 See Documentation/x86/intel_mpx.txt for more
954 information about the feature.
956 eagerfpu= [X86]
957 on enable eager fpu restore
958 off disable eager fpu restore
959 auto selects the default scheme, which automatically
960 enables eagerfpu restore for xsaveopt.
962 module.async_probe [KNL]
963 Enable asynchronous probe on this module.
965 early_ioremap_debug [KNL]
966 Enable debug messages in early_ioremap support. This
967 is useful for tracking down temporary early mappings
968 which are not unmapped.
970 earlycon= [KNL] Output early console device and options.
972 cdns,<addr>
973 Start an early, polled-mode console on a cadence serial
974 port at the specified address. The cadence serial port
975 must already be setup and configured. Options are not
976 yet supported.
978 uart[8250],io,<addr>[,options]
979 uart[8250],mmio,<addr>[,options]
980 uart[8250],mmio32,<addr>[,options]
981 uart[8250],mmio32be,<addr>[,options]
982 uart[8250],0x<addr>[,options]
983 Start an early, polled-mode console on the 8250/16550
984 UART at the specified I/O port or MMIO address.
985 MMIO inter-register address stride is either 8-bit
986 (mmio) or 32-bit (mmio32 or mmio32be).
987 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
988 to be equivalent to 'mmio'. 'options' are specified
989 in the same format described for "console=ttyS<n>"; if
990 unspecified, the h/w is not initialized.
992 pl011,<addr>
993 Start an early, polled-mode console on a pl011 serial
994 port at the specified address. The pl011 serial port
995 must already be setup and configured. Options are not
996 yet supported.
998 msm_serial,<addr>
999 Start an early, polled-mode console on an msm serial
1000 port at the specified address. The serial port
1001 must already be setup and configured. Options are not
1002 yet supported.
1004 msm_serial_dm,<addr>
1005 Start an early, polled-mode console on an msm serial
1006 dm port at the specified address. The serial port
1007 must already be setup and configured. Options are not
1008 yet supported.
1010 smh Use ARM semihosting calls for early console.
1012 s3c2410,<addr>
1013 s3c2412,<addr>
1014 s3c2440,<addr>
1015 s3c6400,<addr>
1016 s5pv210,<addr>
1017 exynos4210,<addr>
1018 Use early console provided by serial driver available
1019 on Samsung SoCs, requires selecting proper type and
1020 a correct base address of the selected UART port. The
1021 serial port must already be setup and configured.
1022 Options are not yet supported.
1024 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1025 earlyprintk=vga
1026 earlyprintk=efi
1027 earlyprintk=xen
1028 earlyprintk=serial[,ttySn[,baudrate]]
1029 earlyprintk=serial[,0x...[,baudrate]]
1030 earlyprintk=ttySn[,baudrate]
1031 earlyprintk=dbgp[debugController#]
1032 earlyprintk=pciserial,bus:device.function[,baudrate]
1034 earlyprintk is useful when the kernel crashes before
1035 the normal console is initialized. It is not enabled by
1036 default because it has some cosmetic problems.
1038 Append ",keep" to not disable it when the real console
1039 takes over.
1041 Only one of vga, efi, serial, or usb debug port can
1042 be used at a time.
1044 Currently only ttyS0 and ttyS1 may be specified by
1045 name. Other I/O ports may be explicitly specified
1046 on some architectures (x86 and arm at least) by
1047 replacing ttySn with an I/O port address, like this:
1048 earlyprintk=serial,0x1008,115200
1049 You can find the port for a given device in
1050 /proc/tty/driver/serial:
1051 2: uart:ST16650V2 port:00001008 irq:18 ...
1053 Interaction with the standard serial driver is not
1054 very good.
1056 The VGA and EFI output is eventually overwritten by
1057 the real console.
1059 The xen output can only be used by Xen PV guests.
1061 edac_report= [HW,EDAC] Control how to report EDAC event
1062 Format: {"on" | "off" | "force"}
1063 on: enable EDAC to report H/W event. May be overridden
1064 by other higher priority error reporting module.
1065 off: disable H/W event reporting through EDAC.
1066 force: enforce the use of EDAC to report H/W event.
1067 default: on.
1069 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1070 ekgdboc=kbd
1072 This is designed to be used in conjunction with
1073 the boot argument: earlyprintk=vga
1075 edd= [EDD]
1076 Format: {"off" | "on" | "skip[mbr]"}
1078 efi= [EFI]
1079 Format: { "old_map", "nochunk", "noruntime", "debug" }
1080 old_map [X86-64]: switch to the old ioremap-based EFI
1081 runtime services mapping. 32-bit still uses this one by
1082 default.
1083 nochunk: disable reading files in "chunks" in the EFI
1084 boot stub, as chunking can cause problems with some
1085 firmware implementations.
1086 noruntime : disable EFI runtime services support
1087 debug: enable misc debug output
1089 efi_no_storage_paranoia [EFI; X86]
1090 Using this parameter you can use more than 50% of
1091 your efi variable storage. Use this parameter only if
1092 you are really sure that your UEFI does sane gc and
1093 fulfills the spec otherwise your board may brick.
1095 eisa_irq_edge= [PARISC,HW]
1096 See header of drivers/parisc/eisa.c.
1098 elanfreq= [X86-32]
1099 See comment before function elanfreq_setup() in
1100 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1102 elevator= [IOSCHED]
1103 Format: {"cfq" | "deadline" | "noop"}
1104 See Documentation/block/cfq-iosched.txt and
1105 Documentation/block/deadline-iosched.txt for details.
1107 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1108 Specifies physical address of start of kernel core
1109 image elf header and optionally the size. Generally
1110 kexec loader will pass this option to capture kernel.
1111 See Documentation/kdump/kdump.txt for details.
1113 enable_mtrr_cleanup [X86]
1114 The kernel tries to adjust MTRR layout from continuous
1115 to discrete, to make X server driver able to add WB
1116 entry later. This parameter enables that.
1118 enable_timer_pin_1 [X86]
1119 Enable PIN 1 of APIC timer
1120 Can be useful to work around chipset bugs
1121 (in particular on some ATI chipsets).
1122 The kernel tries to set a reasonable default.
1124 enforcing [SELINUX] Set initial enforcing status.
1125 Format: {"0" | "1"}
1126 See security/selinux/Kconfig help text.
1127 0 -- permissive (log only, no denials).
1128 1 -- enforcing (deny and log).
1129 Default value is 0.
1130 Value can be changed at runtime via /selinux/enforce.
1132 erst_disable [ACPI]
1133 Disable Error Record Serialization Table (ERST)
1134 support.
1136 ether= [HW,NET] Ethernet cards parameters
1137 This option is obsoleted by the "netdev=" option, which
1138 has equivalent usage. See its documentation for details.
1140 evm= [EVM]
1141 Format: { "fix" }
1142 Permit 'security.evm' to be updated regardless of
1143 current integrity status.
1145 failslab=
1146 fail_page_alloc=
1147 fail_make_request=[KNL]
1148 General fault injection mechanism.
1149 Format: <interval>,<probability>,<space>,<times>
1150 See also Documentation/fault-injection/.
1152 floppy= [HW]
1153 See Documentation/blockdev/floppy.txt.
1155 force_pal_cache_flush
1156 [IA-64] Avoid check_sal_cache_flush which may hang on
1157 buggy SAL_CACHE_FLUSH implementations. Using this
1158 parameter will force ia64_sal_cache_flush to call
1159 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1161 forcepae [X86-32]
1162 Forcefully enable Physical Address Extension (PAE).
1163 Many Pentium M systems disable PAE but may have a
1164 functionally usable PAE implementation.
1165 Warning: use of this parameter will taint the kernel
1166 and may cause unknown problems.
1168 ftrace=[tracer]
1169 [FTRACE] will set and start the specified tracer
1170 as early as possible in order to facilitate early
1171 boot debugging.
1173 ftrace_dump_on_oops[=orig_cpu]
1174 [FTRACE] will dump the trace buffers on oops.
1175 If no parameter is passed, ftrace will dump
1176 buffers of all CPUs, but if you pass orig_cpu, it will
1177 dump only the buffer of the CPU that triggered the
1178 oops.
1180 ftrace_filter=[function-list]
1181 [FTRACE] Limit the functions traced by the function
1182 tracer at boot up. function-list is a comma separated
1183 list of functions. This list can be changed at run
1184 time by the set_ftrace_filter file in the debugfs
1185 tracing directory.
1187 ftrace_notrace=[function-list]
1188 [FTRACE] Do not trace the functions specified in
1189 function-list. This list can be changed at run time
1190 by the set_ftrace_notrace file in the debugfs
1191 tracing directory.
1193 ftrace_graph_filter=[function-list]
1194 [FTRACE] Limit the top level callers functions traced
1195 by the function graph tracer at boot up.
1196 function-list is a comma separated list of functions
1197 that can be changed at run time by the
1198 set_graph_function file in the debugfs tracing directory.
1200 ftrace_graph_notrace=[function-list]
1201 [FTRACE] Do not trace from the functions specified in
1202 function-list. This list is a comma separated list of
1203 functions that can be changed at run time by the
1204 set_graph_notrace file in the debugfs tracing directory.
1206 gamecon.map[2|3]=
1207 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1208 support via parallel port (up to 5 devices per port)
1209 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1210 See also Documentation/input/joystick-parport.txt
1212 gamma= [HW,DRM]
1214 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1215 Format: off | on
1216 default: on
1218 gcov_persist= [GCOV] When non-zero (default), profiling data for
1219 kernel modules is saved and remains accessible via
1220 debugfs, even when the module is unloaded/reloaded.
1221 When zero, profiling data is discarded and associated
1222 debugfs files are removed at module unload time.
1224 gpt [EFI] Forces disk with valid GPT signature but
1225 invalid Protective MBR to be treated as GPT. If the
1226 primary GPT is corrupted, it enables the backup/alternate
1227 GPT to be used instead.
1229 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1230 the "Enable 0" bit of the configuration register.
1231 Format: 0 | 1
1232 Default: 0
1233 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1234 the "Enable 0" bit of the configuration register.
1235 Format: 0 | 1
1236 Default: 0
1237 grcan.select= [HW] Select which physical interface to use.
1238 Format: 0 | 1
1239 Default: 0
1240 grcan.txsize= [HW] Sets the size of the tx buffer.
1241 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1242 Default: 1024
1243 grcan.rxsize= [HW] Sets the size of the rx buffer.
1244 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1245 Default: 1024
1247 hashdist= [KNL,NUMA] Large hashes allocated during boot
1248 are distributed across NUMA nodes. Defaults on
1249 for 64-bit NUMA, off otherwise.
1250 Format: 0 | 1 (for off | on)
1252 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1254 hd= [EIDE] (E)IDE hard drive subsystem geometry
1255 Format: <cyl>,<head>,<sect>
1257 hest_disable [ACPI]
1258 Disable Hardware Error Source Table (HEST) support;
1259 corresponding firmware-first mode error processing
1260 logic will be disabled.
1262 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1263 size of <nn>. This works even on boxes that have no
1264 highmem otherwise. This also works to reduce highmem
1265 size on bigger boxes.
1267 highres= [KNL] Enable/disable high resolution timer mode.
1268 Valid parameters: "on", "off"
1269 Default: "on"
1271 hisax= [HW,ISDN]
1272 See Documentation/isdn/README.HiSax.
1274 hlt [BUGS=ARM,SH]
1276 hpet= [X86-32,HPET] option to control HPET usage
1277 Format: { enable (default) | disable | force |
1278 verbose }
1279 disable: disable HPET and use PIT instead
1280 force: allow force enabled of undocumented chips (ICH4,
1281 VIA, nVidia)
1282 verbose: show contents of HPET registers during setup
1284 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1285 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1287 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1288 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1289 On x86-64 and powerpc, this option can be specified
1290 multiple times interleaved with hugepages= to reserve
1291 huge pages of different sizes. Valid pages sizes on
1292 x86-64 are 2M (when the CPU supports "pse") and 1G
1293 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1295 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1296 terminal devices. Valid values: 0..8
1297 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1298 If specified, z/VM IUCV HVC accepts connections
1299 from listed z/VM user IDs only.
1301 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1302 hardware thread id mappings.
1303 Format: <cpu>:<hwthread>
1305 keep_bootcon [KNL]
1306 Do not unregister boot console at start. This is only
1307 useful for debugging when something happens in the window
1308 between unregistering the boot console and initializing
1309 the real console.
1311 i2c_bus= [HW] Override the default board specific I2C bus speed
1312 or register an additional I2C bus that is not
1313 registered from board initialization code.
1314 Format:
1315 <bus_id>,<clkrate>
1317 i8042.debug [HW] Toggle i8042 debug mode
1318 i8042.direct [HW] Put keyboard port into non-translated mode
1319 i8042.dumbkbd [HW] Pretend that controller can only read data from
1320 keyboard and cannot control its state
1321 (Don't attempt to blink the leds)
1322 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1323 i8042.nokbd [HW] Don't check/create keyboard port
1324 i8042.noloop [HW] Disable the AUX Loopback command while probing
1325 for the AUX port
1326 i8042.nomux [HW] Don't check presence of an active multiplexing
1327 controller
1328 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1329 controllers
1330 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1331 i8042.reset [HW] Reset the controller during init and cleanup
1332 i8042.unlock [HW] Unlock (ignore) the keylock
1333 i8042.kbdreset [HW] Reset device connected to KBD port
1335 i810= [HW,DRM]
1337 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1338 indicates that the driver is running on unsupported
1339 hardware.
1340 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1341 does not match list of supported models.
1342 i8k.power_status
1343 [HW] Report power status in /proc/i8k
1344 (disabled by default)
1345 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1346 capability is set.
1348 i915.invert_brightness=
1349 [DRM] Invert the sense of the variable that is used to
1350 set the brightness of the panel backlight. Normally a
1351 brightness value of 0 indicates backlight switched off,
1352 and the maximum of the brightness value sets the backlight
1353 to maximum brightness. If this parameter is set to 0
1354 (default) and the machine requires it, or this parameter
1355 is set to 1, a brightness value of 0 sets the backlight
1356 to maximum brightness, and the maximum of the brightness
1357 value switches the backlight off.
1358 -1 -- never invert brightness
1359 0 -- machine default
1360 1 -- force brightness inversion
1362 icn= [HW,ISDN]
1363 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1365 ide-core.nodma= [HW] (E)IDE subsystem
1366 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1367 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1368 .cdrom .chs .ignore_cable are additional options
1369 See Documentation/ide/ide.txt.
1371 ide-generic.probe-mask= [HW] (E)IDE subsystem
1372 Format: <int>
1373 Probe mask for legacy ISA IDE ports. Depending on
1374 platform up to 6 ports are supported, enabled by
1375 setting corresponding bits in the mask to 1. The
1376 default value is 0x0, which has a special meaning.
1377 On systems that have PCI, it triggers scanning the
1378 PCI bus for the first and the second port, which
1379 are then probed. On systems without PCI the value
1380 of 0x0 enables probing the two first ports as if it
1381 was 0x3.
1383 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1384 Claim all unknown PCI IDE storage controllers.
1386 idle= [X86]
1387 Format: idle=poll, idle=halt, idle=nomwait
1388 Poll forces a polling idle loop that can slightly
1389 improve the performance of waking up a idle CPU, but
1390 will use a lot of power and make the system run hot.
1391 Not recommended.
1392 idle=halt: Halt is forced to be used for CPU idle.
1393 In such case C2/C3 won't be used again.
1394 idle=nomwait: Disable mwait for CPU C-states
1396 ignore_loglevel [KNL]
1397 Ignore loglevel setting - this will print /all/
1398 kernel messages to the console. Useful for debugging.
1399 We also add it as printk module parameter, so users
1400 could change it dynamically, usually by
1401 /sys/module/printk/parameters/ignore_loglevel.
1403 ihash_entries= [KNL]
1404 Set number of hash buckets for inode cache.
1406 ima_appraise= [IMA] appraise integrity measurements
1407 Format: { "off" | "enforce" | "fix" | "log" }
1408 default: "enforce"
1410 ima_appraise_tcb [IMA]
1411 The builtin appraise policy appraises all files
1412 owned by uid=0.
1414 ima_hash= [IMA]
1415 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1416 | sha512 | ... }
1417 default: "sha1"
1419 The list of supported hash algorithms is defined
1420 in crypto/hash_info.h.
1422 ima_policy= [IMA]
1423 The builtin measurement policy to load during IMA
1424 setup. Specyfing "tcb" as the value, measures all
1425 programs exec'd, files mmap'd for exec, and all files
1426 opened with the read mode bit set by either the
1427 effective uid (euid=0) or uid=0.
1428 Format: "tcb"
1430 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1431 Load a policy which meets the needs of the Trusted
1432 Computing Base. This means IMA will measure all
1433 programs exec'd, files mmap'd for exec, and all files
1434 opened for read by uid=0.
1436 ima_template= [IMA]
1437 Select one of defined IMA measurements template formats.
1438 Formats: { "ima" | "ima-ng" | "ima-sig" }
1439 Default: "ima-ng"
1441 ima_template_fmt=
1442 [IMA] Define a custom template format.
1443 Format: { "field1|...|fieldN" }
1445 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1446 Format: <min_file_size>
1447 Set the minimal file size for using asynchronous hash.
1448 If left unspecified, ahash usage is disabled.
1450 ahash performance varies for different data sizes on
1451 different crypto accelerators. This option can be used
1452 to achieve the best performance for a particular HW.
1454 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1455 Format: <bufsize>
1456 Set hashing buffer size. Default: 4k.
1458 ahash performance varies for different chunk sizes on
1459 different crypto accelerators. This option can be used
1460 to achieve best performance for particular HW.
1462 init= [KNL]
1463 Format: <full_path>
1464 Run specified binary instead of /sbin/init as init
1465 process.
1467 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1468 for working out where the kernel is dying during
1469 startup.
1471 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1472 initcall functions. Useful for debugging built-in
1473 modules and initcalls.
1475 initrd= [BOOT] Specify the location of the initial ramdisk
1477 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1478 Format: <irq>
1480 int_pln_enable [x86] Enable power limit notification interrupt
1482 integrity_audit=[IMA]
1483 Format: { "0" | "1" }
1484 0 -- basic integrity auditing messages. (Default)
1485 1 -- additional integrity auditing messages.
1487 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1488 on
1489 Enable intel iommu driver.
1490 off
1491 Disable intel iommu driver.
1492 igfx_off [Default Off]
1493 By default, gfx is mapped as normal device. If a gfx
1494 device has a dedicated DMAR unit, the DMAR unit is
1495 bypassed by not enabling DMAR with this option. In
1496 this case, gfx device will use physical address for
1497 DMA.
1498 forcedac [x86_64]
1499 With this option iommu will not optimize to look
1500 for io virtual address below 32-bit forcing dual
1501 address cycle on pci bus for cards supporting greater
1502 than 32-bit addressing. The default is to look
1503 for translation below 32-bit and if not available
1504 then look in the higher range.
1505 strict [Default Off]
1506 With this option on every unmap_single operation will
1507 result in a hardware IOTLB flush operation as opposed
1508 to batching them for performance.
1509 sp_off [Default Off]
1510 By default, super page will be supported if Intel IOMMU
1511 has the capability. With this option, super page will
1512 not be supported.
1513 ecs_off [Default Off]
1514 By default, extended context tables will be supported if
1515 the hardware advertises that it has support both for the
1516 extended tables themselves, and also PASID support. With
1517 this option set, extended tables will not be used even
1518 on hardware which claims to support them.
1520 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1521 0 disables intel_idle and fall back on acpi_idle.
1522 1 to 6 specify maximum depth of C-state.
1524 intel_pstate= [X86]
1525 disable
1526 Do not enable intel_pstate as the default
1527 scaling driver for the supported processors
1528 force
1529 Enable intel_pstate on systems that prohibit it by default
1530 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1531 instead of acpi-cpufreq may disable platform features, such
1532 as thermal controls and power capping, that rely on ACPI
1533 P-States information being indicated to OSPM and therefore
1534 should be used with caution. This option does not work with
1535 processors that aren't supported by the intel_pstate driver
1536 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1537 no_hwp
1538 Do not enable hardware P state control (HWP)
1539 if available.
1540 hwp_only
1541 Only load intel_pstate on systems which support
1542 hardware P state control (HWP) if available.
1544 intremap= [X86-64, Intel-IOMMU]
1545 on enable Interrupt Remapping (default)
1546 off disable Interrupt Remapping
1547 nosid disable Source ID checking
1548 no_x2apic_optout
1549 BIOS x2APIC opt-out request will be ignored
1551 iomem= Disable strict checking of access to MMIO memory
1552 strict regions from userspace.
1553 relaxed
1555 iommu= [x86]
1556 off
1557 force
1558 noforce
1559 biomerge
1560 panic
1561 nopanic
1562 merge
1563 nomerge
1564 forcesac
1565 soft
1566 pt [x86, IA-64]
1567 nobypass [PPC/POWERNV]
1568 Disable IOMMU bypass, using IOMMU for PCI devices.
1571 io7= [HW] IO7 for Marvel based alpha systems
1572 See comment before marvel_specify_io7 in
1573 arch/alpha/kernel/core_marvel.c.
1575 io_delay= [X86] I/O delay method
1576 0x80
1577 Standard port 0x80 based delay
1578 0xed
1579 Alternate port 0xed based delay (needed on some systems)
1580 udelay
1581 Simple two microseconds delay
1582 none
1583 No delay
1585 ip= [IP_PNP]
1586 See Documentation/filesystems/nfs/nfsroot.txt.
1588 irqfixup [HW]
1589 When an interrupt is not handled search all handlers
1590 for it. Intended to get systems with badly broken
1591 firmware running.
1593 irqpoll [HW]
1594 When an interrupt is not handled search all handlers
1595 for it. Also check all handlers each timer
1596 interrupt. Intended to get systems with badly broken
1597 firmware running.
1599 isapnp= [ISAPNP]
1600 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1602 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1603 Format:
1604 <cpu number>,...,<cpu number>
1605 or
1606 <cpu number>-<cpu number>
1607 (must be a positive range in ascending order)
1608 or a mixture
1609 <cpu number>,...,<cpu number>-<cpu number>
1611 This option can be used to specify one or more CPUs
1612 to isolate from the general SMP balancing and scheduling
1613 algorithms. You can move a process onto or off an
1614 "isolated" CPU via the CPU affinity syscalls or cpuset.
1615 <cpu number> begins at 0 and the maximum value is
1616 "number of CPUs in system - 1".
1618 This option is the preferred way to isolate CPUs. The
1619 alternative -- manually setting the CPU mask of all
1620 tasks in the system -- can cause problems and
1621 suboptimal load balancer performance.
1623 iucv= [HW,NET]
1625 ivrs_ioapic [HW,X86_64]
1626 Provide an override to the IOAPIC-ID<->DEVICE-ID
1627 mapping provided in the IVRS ACPI table. For
1628 example, to map IOAPIC-ID decimal 10 to
1629 PCI device 00:14.0 write the parameter as:
1630 ivrs_ioapic[10]=00:14.0
1632 ivrs_hpet [HW,X86_64]
1633 Provide an override to the HPET-ID<->DEVICE-ID
1634 mapping provided in the IVRS ACPI table. For
1635 example, to map HPET-ID decimal 0 to
1636 PCI device 00:14.0 write the parameter as:
1637 ivrs_hpet[0]=00:14.0
1639 js= [HW,JOY] Analog joystick
1640 See Documentation/input/joystick.txt.
1642 kaslr/nokaslr [X86]
1643 Enable/disable kernel and module base offset ASLR
1644 (Address Space Layout Randomization) if built into
1645 the kernel. When CONFIG_HIBERNATION is selected,
1646 kASLR is disabled by default. When kASLR is enabled,
1647 hibernation will be disabled.
1649 keepinitrd [HW,ARM]
1651 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1652 specifies the amount of memory usable by the kernel
1653 for non-movable allocations. The requested amount is
1654 spread evenly throughout all nodes in the system. The
1655 remaining memory in each node is used for Movable
1656 pages. In the event, a node is too small to have both
1657 kernelcore and Movable pages, kernelcore pages will
1658 take priority and other nodes will have a larger number
1659 of Movable pages. The Movable zone is used for the
1660 allocation of pages that may be reclaimed or moved
1661 by the page migration subsystem. This means that
1662 HugeTLB pages may not be allocated from this zone.
1663 Note that allocations like PTEs-from-HighMem still
1664 use the HighMem zone if it exists, and the Normal
1665 zone if it does not.
1667 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1668 Format: <Controller#>[,poll interval]
1669 The controller # is the number of the ehci usb debug
1670 port as it is probed via PCI. The poll interval is
1671 optional and is the number seconds in between
1672 each poll cycle to the debug port in case you need
1673 the functionality for interrupting the kernel with
1674 gdb or control-c on the dbgp connection. When
1675 not using this parameter you use sysrq-g to break into
1676 the kernel debugger.
1678 kgdboc= [KGDB,HW] kgdb over consoles.
1679 Requires a tty driver that supports console polling,
1680 or a supported polling keyboard driver (non-usb).
1681 Serial only format: <serial_device>[,baud]
1682 keyboard only format: kbd
1683 keyboard and serial format: kbd,<serial_device>[,baud]
1684 Optional Kernel mode setting:
1685 kms, kbd format: kms,kbd
1686 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1688 kgdbwait [KGDB] Stop kernel execution and enter the
1689 kernel debugger at the earliest opportunity.
1691 kmac= [MIPS] korina ethernet MAC address.
1692 Configure the RouterBoard 532 series on-chip
1693 Ethernet adapter MAC address.
1695 kmemleak= [KNL] Boot-time kmemleak enable/disable
1696 Valid arguments: on, off
1697 Default: on
1698 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1699 the default is off.
1701 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1702 Valid arguments: 0, 1, 2
1703 kmemcheck=0 (disabled)
1704 kmemcheck=1 (enabled)
1705 kmemcheck=2 (one-shot mode)
1706 Default: 2 (one-shot mode)
1708 kstack=N [X86] Print N words from the kernel stack
1709 in oops dumps.
1711 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1712 Default is 0 (don't ignore, but inject #GP)
1714 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1715 KVM MMU at runtime.
1716 Default is 0 (off)
1718 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1719 Default is 1 (enabled)
1721 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1722 for all guests.
1723 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1725 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1726 (virtualized MMU) support on capable Intel chips.
1727 Default is 1 (enabled)
1729 kvm-intel.emulate_invalid_guest_state=
1730 [KVM,Intel] Enable emulation of invalid guest states
1731 Default is 0 (disabled)
1733 kvm-intel.flexpriority=
1734 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1735 Default is 1 (enabled)
1737 kvm-intel.nested=
1738 [KVM,Intel] Enable VMX nesting (nVMX).
1739 Default is 0 (disabled)
1741 kvm-intel.unrestricted_guest=
1742 [KVM,Intel] Disable unrestricted guest feature
1743 (virtualized real and unpaged mode) on capable
1744 Intel chips. Default is 1 (enabled)
1746 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1747 feature (tagged TLBs) on capable Intel chips.
1748 Default is 1 (enabled)
1750 l2cr= [PPC]
1752 l3cr= [PPC]
1754 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1755 disabled it.
1757 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1758 value for LAPIC timer one-shot implementation. Default
1759 back to the programmable timer unit in the LAPIC.
1761 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1762 in C2 power state.
1764 libata.dma= [LIBATA] DMA control
1765 libata.dma=0 Disable all PATA and SATA DMA
1766 libata.dma=1 PATA and SATA Disk DMA only
1767 libata.dma=2 ATAPI (CDROM) DMA only
1768 libata.dma=4 Compact Flash DMA only
1769 Combinations also work, so libata.dma=3 enables DMA
1770 for disks and CDROMs, but not CFs.
1772 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1773 libata.ignore_hpa=0 keep BIOS limits (default)
1774 libata.ignore_hpa=1 ignore limits, using full disk
1776 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1777 when set.
1778 Format: <int>
1780 libata.force= [LIBATA] Force configurations. The format is comma
1781 separated list of "[ID:]VAL" where ID is
1782 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1783 matching port, link or device. Basically, it matches
1784 the ATA ID string printed on console by libata. If
1785 the whole ID part is omitted, the last PORT and DEVICE
1786 values are used. If ID hasn't been specified yet, the
1787 configuration applies to all ports, links and devices.
1789 If only DEVICE is omitted, the parameter applies to
1790 the port and all links and devices behind it. DEVICE
1791 number of 0 either selects the first device or the
1792 first fan-out link behind PMP device. It does not
1793 select the host link. DEVICE number of 15 selects the
1794 host link and device attached to it.
1796 The VAL specifies the configuration to force. As long
1797 as there's no ambiguity shortcut notation is allowed.
1798 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1799 The following configurations can be forced.
1801 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1802 Any ID with matching PORT is used.
1804 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1806 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1807 udma[/][16,25,33,44,66,100,133] notation is also
1808 allowed.
1810 * [no]ncq: Turn on or off NCQ.
1812 * [no]ncqtrim: Turn off queued DSM TRIM.
1814 * nohrst, nosrst, norst: suppress hard, soft
1815 and both resets.
1817 * rstonce: only attempt one reset during
1818 hot-unplug link recovery
1820 * dump_id: dump IDENTIFY data.
1822 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1824 * disable: Disable this device.
1826 If there are multiple matching configurations changing
1827 the same attribute, the last one is used.
1829 memblock=debug [KNL] Enable memblock debug messages.
1831 load_ramdisk= [RAM] List of ramdisks to load from floppy
1832 See Documentation/blockdev/ramdisk.txt.
1834 lockd.nlm_grace_period=P [NFS] Assign grace period.
1835 Format: <integer>
1837 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1838 Format: <integer>
1840 lockd.nlm_timeout=T [NFS] Assign timeout value.
1841 Format: <integer>
1843 lockd.nlm_udpport=M [NFS] Assign UDP port.
1844 Format: <integer>
1846 locktorture.nreaders_stress= [KNL]
1847 Set the number of locking read-acquisition kthreads.
1848 Defaults to being automatically set based on the
1849 number of online CPUs.
1851 locktorture.nwriters_stress= [KNL]
1852 Set the number of locking write-acquisition kthreads.
1854 locktorture.onoff_holdoff= [KNL]
1855 Set time (s) after boot for CPU-hotplug testing.
1857 locktorture.onoff_interval= [KNL]
1858 Set time (s) between CPU-hotplug operations, or
1859 zero to disable CPU-hotplug testing.
1861 locktorture.shuffle_interval= [KNL]
1862 Set task-shuffle interval (jiffies). Shuffling
1863 tasks allows some CPUs to go into dyntick-idle
1864 mode during the locktorture test.
1866 locktorture.shutdown_secs= [KNL]
1867 Set time (s) after boot system shutdown. This
1868 is useful for hands-off automated testing.
1870 locktorture.stat_interval= [KNL]
1871 Time (s) between statistics printk()s.
1873 locktorture.stutter= [KNL]
1874 Time (s) to stutter testing, for example,
1875 specifying five seconds causes the test to run for
1876 five seconds, wait for five seconds, and so on.
1877 This tests the locking primitive's ability to
1878 transition abruptly to and from idle.
1880 locktorture.torture_runnable= [BOOT]
1881 Start locktorture running at boot time.
1883 locktorture.torture_type= [KNL]
1884 Specify the locking implementation to test.
1886 locktorture.verbose= [KNL]
1887 Enable additional printk() statements.
1889 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1890 Format: <irq>
1892 loglevel= All Kernel Messages with a loglevel smaller than the
1893 console loglevel will be printed to the console. It can
1894 also be changed with klogd or other programs. The
1895 loglevels are defined as follows:
1897 0 (KERN_EMERG) system is unusable
1898 1 (KERN_ALERT) action must be taken immediately
1899 2 (KERN_CRIT) critical conditions
1900 3 (KERN_ERR) error conditions
1901 4 (KERN_WARNING) warning conditions
1902 5 (KERN_NOTICE) normal but significant condition
1903 6 (KERN_INFO) informational
1904 7 (KERN_DEBUG) debug-level messages
1906 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1907 in bytes. n must be a power of two and greater
1908 than the minimal size. The minimal size is defined
1909 by LOG_BUF_SHIFT kernel config parameter. There is
1910 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1911 that allows to increase the default size depending on
1912 the number of CPUs. See init/Kconfig for more details.
1914 logo.nologo [FB] Disables display of the built-in Linux logo.
1915 This may be used to provide more screen space for
1916 kernel log messages and is useful when debugging
1917 kernel boot problems.
1919 lp=0 [LP] Specify parallel ports to use, e.g,
1920 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1921 lp=reset first parallel port). 'lp=0' disables the
1922 lp=auto printer driver. 'lp=reset' (which can be
1923 specified in addition to the ports) causes
1924 attached printers to be reset. Using
1925 lp=port1,port2,... specifies the parallel ports
1926 to associate lp devices with, starting with
1927 lp0. A port specification may be 'none' to skip
1928 that lp device, or a parport name such as
1929 'parport0'. Specifying 'lp=auto' instead of a
1930 port specification list means that device IDs
1931 from each port should be examined, to see if
1932 an IEEE 1284-compliant printer is attached; if
1933 so, the driver will manage that printer.
1934 See also header of drivers/char/lp.c.
1936 lpj=n [KNL]
1937 Sets loops_per_jiffy to given constant, thus avoiding
1938 time-consuming boot-time autodetection (up to 250 ms per
1939 CPU). 0 enables autodetection (default). To determine
1940 the correct value for your kernel, boot with normal
1941 autodetection and see what value is printed. Note that
1942 on SMP systems the preset will be applied to all CPUs,
1943 which is likely to cause problems if your CPUs need
1944 significantly divergent settings. An incorrect value
1945 will cause delays in the kernel to be wrong, leading to
1946 unpredictable I/O errors and other breakage. Although
1947 unlikely, in the extreme case this might damage your
1948 hardware.
1950 ltpc= [NET]
1951 Format: <io>,<irq>,<dma>
1953 machvec= [IA-64] Force the use of a particular machine-vector
1954 (machvec) in a generic kernel.
1955 Example: machvec=hpzx1_swiotlb
1957 machtype= [Loongson] Share the same kernel image file between different
1958 yeeloong laptop.
1959 Example: machtype=lemote-yeeloong-2f-7inch
1961 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1962 than or equal to this physical address is ignored.
1964 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1965 should make use of. maxcpus=n : n >= 0 limits the
1966 kernel to using 'n' processors. n=0 is a special case,
1967 it is equivalent to "nosmp", which also disables
1968 the IO APIC.
1970 max_loop= [LOOP] The number of loop block devices that get
1971 (loop.max_loop) unconditionally pre-created at init time. The default
1972 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1973 of statically allocating a predefined number, loop
1974 devices can be requested on-demand with the
1975 /dev/loop-control interface.
1977 mce [X86-32] Machine Check Exception
1979 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1981 md= [HW] RAID subsystems devices and level
1982 See Documentation/md.txt.
1984 mdacon= [MDA]
1985 Format: <first>,<last>
1986 Specifies range of consoles to be captured by the MDA.
1988 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1989 Amount of memory to be used when the kernel is not able
1990 to see the whole system memory or for test.
1991 [X86] Work as limiting max address. Use together
1992 with memmap= to avoid physical address space collisions.
1993 Without memmap= PCI devices could be placed at addresses
1994 belonging to unused RAM.
1996 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1997 memory.
1999 memchunk=nn[KMG]
2000 [KNL,SH] Allow user to override the default size for
2001 per-device physically contiguous DMA buffers.
2003 memmap=exactmap [KNL,X86] Enable setting of an exact
2004 E820 memory map, as specified by the user.
2005 Such memmap=exactmap lines can be constructed based on
2006 BIOS output or other requirements. See the memmap=nn@ss
2007 option description.
2009 memmap=nn[KMG]@ss[KMG]
2010 [KNL] Force usage of a specific region of memory.
2011 Region of memory to be used is from ss to ss+nn.
2013 memmap=nn[KMG]#ss[KMG]
2014 [KNL,ACPI] Mark specific memory as ACPI data.
2015 Region of memory to be marked is from ss to ss+nn.
2017 memmap=nn[KMG]$ss[KMG]
2018 [KNL,ACPI] Mark specific memory as reserved.
2019 Region of memory to be reserved is from ss to ss+nn.
2020 Example: Exclude memory from 0x18690000-0x1869ffff
2021 memmap=64K$0x18690000
2022 or
2023 memmap=0x10000$0x18690000
2025 memmap=nn[KMG]!ss[KMG]
2026 [KNL,X86] Mark specific memory as protected.
2027 Region of memory to be used, from ss to ss+nn.
2028 The memory region may be marked as e820 type 12 (0xc)
2029 and is NVDIMM or ADR memory.
2031 memory_corruption_check=0/1 [X86]
2032 Some BIOSes seem to corrupt the first 64k of
2033 memory when doing things like suspend/resume.
2034 Setting this option will scan the memory
2035 looking for corruption. Enabling this will
2036 both detect corruption and prevent the kernel
2037 from using the memory being corrupted.
2038 However, its intended as a diagnostic tool; if
2039 repeatable BIOS-originated corruption always
2040 affects the same memory, you can use memmap=
2041 to prevent the kernel from using that memory.
2043 memory_corruption_check_size=size [X86]
2044 By default it checks for corruption in the low
2045 64k, making this memory unavailable for normal
2046 use. Use this parameter to scan for
2047 corruption in more or less memory.
2049 memory_corruption_check_period=seconds [X86]
2050 By default it checks for corruption every 60
2051 seconds. Use this parameter to check at some
2052 other rate. 0 disables periodic checking.
2054 memtest= [KNL,X86,ARM] Enable memtest
2055 Format: <integer>
2056 default : 0 <disable>
2057 Specifies the number of memtest passes to be
2058 performed. Each pass selects another test
2059 pattern from a given set of patterns. Memtest
2060 fills the memory with this pattern, validates
2061 memory contents and reserves bad memory
2062 regions that are detected.
2064 meye.*= [HW] Set MotionEye Camera parameters
2065 See Documentation/video4linux/meye.txt.
2067 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2068 Multi-Function General Purpose Timers on AMD Geode
2069 platforms.
2071 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2072 the BIOS has incorrectly applied a workaround. TinyBIOS
2073 version 0.98 is known to be affected, 0.99 fixes the
2074 problem by letting the user disable the workaround.
2076 mga= [HW,DRM]
2078 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2079 physical address is ignored.
2081 mini2440= [ARM,HW,KNL]
2082 Format:[0..2][b][c][t]
2083 Default: "0tb"
2084 MINI2440 configuration specification:
2085 0 - The attached screen is the 3.5" TFT
2086 1 - The attached screen is the 7" TFT
2087 2 - The VGA Shield is attached (1024x768)
2088 Leaving out the screen size parameter will not load
2089 the TFT driver, and the framebuffer will be left
2090 unconfigured.
2091 b - Enable backlight. The TFT backlight pin will be
2092 linked to the kernel VESA blanking code and a GPIO
2093 LED. This parameter is not necessary when using the
2094 VGA shield.
2095 c - Enable the s3c camera interface.
2096 t - Reserved for enabling touchscreen support. The
2097 touchscreen support is not enabled in the mainstream
2098 kernel as of 2.6.30, a preliminary port can be found
2099 in the "bleeding edge" mini2440 support kernel at
2100 http://repo.or.cz/w/linux-2.6/mini2440.git
2102 mminit_loglevel=
2103 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2104 parameter allows control of the logging verbosity for
2105 the additional memory initialisation checks. A value
2106 of 0 disables mminit logging and a level of 4 will
2107 log everything. Information is printed at KERN_DEBUG
2108 so loglevel=8 may also need to be specified.
2110 module.sig_enforce
2111 [KNL] When CONFIG_MODULE_SIG is set, this means that
2112 modules without (valid) signatures will fail to load.
2113 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2114 is always true, so this option does nothing.
2116 mousedev.tap_time=
2117 [MOUSE] Maximum time between finger touching and
2118 leaving touchpad surface for touch to be considered
2119 a tap and be reported as a left button click (for
2120 touchpads working in absolute mode only).
2121 Format: <msecs>
2122 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2123 reporting absolute coordinates, such as tablets
2124 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2125 reporting absolute coordinates, such as tablets
2127 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2128 is similar to kernelcore except it specifies the
2129 amount of memory used for migratable allocations.
2130 If both kernelcore and movablecore is specified,
2131 then kernelcore will be at *least* the specified
2132 value but may be more. If movablecore on its own
2133 is specified, the administrator must be careful
2134 that the amount of memory usable for all allocations
2135 is not too small.
2137 movable_node [KNL,X86] Boot-time switch to enable the effects
2138 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2140 MTD_Partition= [MTD]
2141 Format: <name>,<region-number>,<size>,<offset>
2143 MTD_Region= [MTD] Format:
2144 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2146 mtdparts= [MTD]
2147 See drivers/mtd/cmdlinepart.c.
2149 multitce=off [PPC] This parameter disables the use of the pSeries
2150 firmware feature for updating multiple TCE entries
2151 at a time.
2153 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2155 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2157 boundary - index of last SLC block on Flex-OneNAND.
2158 The remaining blocks are configured as MLC blocks.
2159 lock - Configure if Flex-OneNAND boundary should be locked.
2160 Once locked, the boundary cannot be changed.
2161 1 indicates lock status, 0 indicates unlock status.
2163 mtdset= [ARM]
2164 ARM/S3C2412 JIVE boot control
2166 See arch/arm/mach-s3c2412/mach-jive.c
2168 mtouchusb.raw_coordinates=
2169 [HW] Make the MicroTouch USB driver use raw coordinates
2170 ('y', default) or cooked coordinates ('n')
2172 mtrr_chunk_size=nn[KMG] [X86]
2173 used for mtrr cleanup. It is largest continuous chunk
2174 that could hold holes aka. UC entries.
2176 mtrr_gran_size=nn[KMG] [X86]
2177 Used for mtrr cleanup. It is granularity of mtrr block.
2178 Default is 1.
2179 Large value could prevent small alignment from
2180 using up MTRRs.
2182 mtrr_spare_reg_nr=n [X86]
2183 Format: <integer>
2184 Range: 0,7 : spare reg number
2185 Default : 1
2186 Used for mtrr cleanup. It is spare mtrr entries number.
2187 Set to 2 or more if your graphical card needs more.
2189 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2191 netdev= [NET] Network devices parameters
2192 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2193 Note that mem_start is often overloaded to mean
2194 something different and driver-specific.
2195 This usage is only documented in each driver source
2196 file if at all.
2198 nf_conntrack.acct=
2199 [NETFILTER] Enable connection tracking flow accounting
2200 0 to disable accounting
2201 1 to enable accounting
2202 Default value is 0.
2204 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2205 See Documentation/filesystems/nfs/nfsroot.txt.
2207 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2208 See Documentation/filesystems/nfs/nfsroot.txt.
2210 nfsrootdebug [NFS] enable nfsroot debugging messages.
2211 See Documentation/filesystems/nfs/nfsroot.txt.
2213 nfs.callback_tcpport=
2214 [NFS] set the TCP port on which the NFSv4 callback
2215 channel should listen.
2217 nfs.cache_getent=
2218 [NFS] sets the pathname to the program which is used
2219 to update the NFS client cache entries.
2221 nfs.cache_getent_timeout=
2222 [NFS] sets the timeout after which an attempt to
2223 update a cache entry is deemed to have failed.
2225 nfs.idmap_cache_timeout=
2226 [NFS] set the maximum lifetime for idmapper cache
2227 entries.
2229 nfs.enable_ino64=
2230 [NFS] enable 64-bit inode numbers.
2231 If zero, the NFS client will fake up a 32-bit inode
2232 number for the readdir() and stat() syscalls instead
2233 of returning the full 64-bit number.
2234 The default is to return 64-bit inode numbers.
2236 nfs.max_session_slots=
2237 [NFSv4.1] Sets the maximum number of session slots
2238 the client will attempt to negotiate with the server.
2239 This limits the number of simultaneous RPC requests
2240 that the client can send to the NFSv4.1 server.
2241 Note that there is little point in setting this
2242 value higher than the max_tcp_slot_table_limit.
2244 nfs.nfs4_disable_idmapping=
2245 [NFSv4] When set to the default of '1', this option
2246 ensures that both the RPC level authentication
2247 scheme and the NFS level operations agree to use
2248 numeric uids/gids if the mount is using the
2249 'sec=sys' security flavour. In effect it is
2250 disabling idmapping, which can make migration from
2251 legacy NFSv2/v3 systems to NFSv4 easier.
2252 Servers that do not support this mode of operation
2253 will be autodetected by the client, and it will fall
2254 back to using the idmapper.
2255 To turn off this behaviour, set the value to '0'.
2256 nfs.nfs4_unique_id=
2257 [NFS4] Specify an additional fixed unique ident-
2258 ification string that NFSv4 clients can insert into
2259 their nfs_client_id4 string. This is typically a
2260 UUID that is generated at system install time.
2262 nfs.send_implementation_id =
2263 [NFSv4.1] Send client implementation identification
2264 information in exchange_id requests.
2265 If zero, no implementation identification information
2266 will be sent.
2267 The default is to send the implementation identification
2268 information.
2270 nfs.recover_lost_locks =
2271 [NFSv4] Attempt to recover locks that were lost due
2272 to a lease timeout on the server. Please note that
2273 doing this risks data corruption, since there are
2274 no guarantees that the file will remain unchanged
2275 after the locks are lost.
2276 If you want to enable the kernel legacy behaviour of
2277 attempting to recover these locks, then set this
2278 parameter to '1'.
2279 The default parameter value of '0' causes the kernel
2280 not to attempt recovery of lost locks.
2282 nfsd.nfs4_disable_idmapping=
2283 [NFSv4] When set to the default of '1', the NFSv4
2284 server will return only numeric uids and gids to
2285 clients using auth_sys, and will accept numeric uids
2286 and gids from such clients. This is intended to ease
2287 migration from NFSv2/v3.
2289 objlayoutdriver.osd_login_prog=
2290 [NFS] [OBJLAYOUT] sets the pathname to the program which
2291 is used to automatically discover and login into new
2292 osd-targets. Please see:
2293 Documentation/filesystems/pnfs.txt for more explanations
2295 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2296 when a NMI is triggered.
2297 Format: [state][,regs][,debounce][,die]
2299 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2300 Format: [panic,][nopanic,][num]
2301 Valid num: 0 or 1
2302 0 - turn nmi_watchdog off
2303 1 - turn nmi_watchdog on
2304 When panic is specified, panic when an NMI watchdog
2305 timeout occurs (or 'nopanic' to override the opposite
2306 default).
2307 This is useful when you use a panic=... timeout and
2308 need the box quickly up again.
2310 netpoll.carrier_timeout=
2311 [NET] Specifies amount of time (in seconds) that
2312 netpoll should wait for a carrier. By default netpoll
2313 waits 4 seconds.
2315 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2316 emulation library even if a 387 maths coprocessor
2317 is present.
2319 no_console_suspend
2320 [HW] Never suspend the console
2321 Disable suspending of consoles during suspend and
2322 hibernate operations. Once disabled, debugging
2323 messages can reach various consoles while the rest
2324 of the system is being put to sleep (ie, while
2325 debugging driver suspend/resume hooks). This may
2326 not work reliably with all consoles, but is known
2327 to work with serial and VGA consoles.
2328 To facilitate more flexible debugging, we also add
2329 console_suspend, a printk module parameter to control
2330 it. Users could use console_suspend (usually
2331 /sys/module/printk/parameters/console_suspend) to
2332 turn on/off it dynamically.
2334 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2335 caches in the slab allocator. Saves per-node memory,
2336 but will impact performance.
2338 noalign [KNL,ARM]
2340 noapic [SMP,APIC] Tells the kernel to not make use of any
2341 IOAPICs that may be present in the system.
2343 noautogroup Disable scheduler automatic task group creation.
2345 nobats [PPC] Do not use BATs for mapping kernel lowmem
2346 on "Classic" PPC cores.
2348 nocache [ARM]
2350 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2352 nodelayacct [KNL] Disable per-task delay accounting
2354 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2356 nodsp [SH] Disable hardware DSP at boot time.
2358 noefi Disable EFI runtime services support.
2360 noexec [IA-64]
2362 noexec [X86]
2363 On X86-32 available only on PAE configured kernels.
2364 noexec=on: enable non-executable mappings (default)
2365 noexec=off: disable non-executable mappings
2367 nosmap [X86]
2368 Disable SMAP (Supervisor Mode Access Prevention)
2369 even if it is supported by processor.
2371 nosmep [X86]
2372 Disable SMEP (Supervisor Mode Execution Prevention)
2373 even if it is supported by processor.
2375 noexec32 [X86-64]
2376 This affects only 32-bit executables.
2377 noexec32=on: enable non-executable mappings (default)
2378 read doesn't imply executable mappings
2379 noexec32=off: disable non-executable mappings
2380 read implies executable mappings
2382 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2384 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2385 register save and restore. The kernel will only save
2386 legacy floating-point registers on task switch.
2388 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2390 noxsave [BUGS=X86] Disables x86 extended register state save
2391 and restore using xsave. The kernel will fallback to
2392 enabling legacy floating-point and sse state.
2394 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2395 register states. The kernel will fall back to use
2396 xsave to save the states. By using this parameter,
2397 performance of saving the states is degraded because
2398 xsave doesn't support modified optimization while
2399 xsaveopt supports it on xsaveopt enabled systems.
2401 noxsaves [X86] Disables xsaves and xrstors used in saving and
2402 restoring x86 extended register state in compacted
2403 form of xsave area. The kernel will fall back to use
2404 xsaveopt and xrstor to save and restore the states
2405 in standard form of xsave area. By using this
2406 parameter, xsave area per process might occupy more
2407 memory on xsaves enabled systems.
2409 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2410 wfi(ARM) instruction doesn't work correctly and not to
2411 use it. This is also useful when using JTAG debugger.
2413 no_file_caps Tells the kernel not to honor file capabilities. The
2414 only way then for a file to be executed with privilege
2415 is to be setuid root or executed by root.
2417 nohalt [IA-64] Tells the kernel not to use the power saving
2418 function PAL_HALT_LIGHT when idle. This increases
2419 power-consumption. On the positive side, it reduces
2420 interrupt wake-up latency, which may improve performance
2421 in certain environments such as networked servers or
2422 real-time systems.
2424 nohibernate [HIBERNATION] Disable hibernation and resume.
2426 nohz= [KNL] Boottime enable/disable dynamic ticks
2427 Valid arguments: on, off
2428 Default: on
2430 nohz_full= [KNL,BOOT]
2431 In kernels built with CONFIG_NO_HZ_FULL=y, set
2432 the specified list of CPUs whose tick will be stopped
2433 whenever possible. The boot CPU will be forced outside
2434 the range to maintain the timekeeping.
2435 The CPUs in this range must also be included in the
2436 rcu_nocbs= set.
2438 noiotrap [SH] Disables trapped I/O port accesses.
2440 noirqdebug [X86-32] Disables the code which attempts to detect and
2441 disable unhandled interrupt sources.
2443 no_timer_check [X86,APIC] Disables the code which tests for
2444 broken timer IRQ sources.
2446 noisapnp [ISAPNP] Disables ISA PnP code.
2448 noinitrd [RAM] Tells the kernel not to load any configured
2449 initial RAM disk.
2451 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2452 remapping.
2453 [Deprecated - use intremap=off]
2455 nointroute [IA-64]
2457 nojitter [IA-64] Disables jitter checking for ITC timers.
2459 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2461 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2462 fault handling.
2464 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2465 steal time is computed, but won't influence scheduler
2466 behaviour
2468 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2470 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2472 noltlbs [PPC] Do not use large page/tlb entries for kernel
2473 lowmem mapping on PPC40x.
2475 nomca [IA-64] Disable machine check abort handling
2477 nomce [X86-32] Disable Machine Check Exception
2479 nomfgpt [X86-32] Disable Multi-Function General Purpose
2480 Timer usage (for AMD Geode machines).
2482 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2483 shutdown the other cpus. Instead use the REBOOT_VECTOR
2484 irq.
2486 nomodule Disable module load
2488 nopat [X86] Disable PAT (page attribute table extension of
2489 pagetables) support.
2491 norandmaps Don't use address space randomization. Equivalent to
2492 echo 0 > /proc/sys/kernel/randomize_va_space
2494 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2496 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2497 with UP alternatives
2499 nordrand [X86] Disable kernel use of the RDRAND and
2500 RDSEED instructions even if they are supported
2501 by the processor. RDRAND and RDSEED are still
2502 available to user space applications.
2504 noresume [SWSUSP] Disables resume and restores original swap
2505 space.
2507 no-scroll [VGA] Disables scrollback.
2508 This is required for the Braillex ib80-piezo Braille
2509 reader made by F.H. Papenmeier (Germany).
2511 nosbagart [IA-64]
2513 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2515 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2516 and disable the IO APIC. legacy for "maxcpus=0".
2518 nosoftlockup [KNL] Disable the soft-lockup detector.
2520 nosync [HW,M68K] Disables sync negotiation for all devices.
2522 notsc [BUGS=X86-32] Disable Time Stamp Counter
2524 nousb [USB] Disable the USB subsystem
2526 nowatchdog [KNL] Disable both lockup detectors, i.e.
2527 soft-lockup and NMI watchdog (hard-lockup).
2529 nowb [ARM]
2531 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2533 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2534 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2535 Some features depend on CPU0. Known dependencies are:
2536 1. Resume from suspend/hibernate depends on CPU0.
2537 Suspend/hibernate will fail if CPU0 is offline and you
2538 need to online CPU0 before suspend/hibernate.
2539 2. PIC interrupts also depend on CPU0. CPU0 can't be
2540 removed if a PIC interrupt is detected.
2541 It's said poweroff/reboot may depend on CPU0 on some
2542 machines although I haven't seen such issues so far
2543 after CPU0 is offline on a few tested machines.
2544 If the dependencies are under your control, you can
2545 turn on cpu0_hotplug.
2547 nptcg= [IA-64] Override max number of concurrent global TLB
2548 purges which is reported from either PAL_VM_SUMMARY or
2549 SAL PALO.
2551 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2552 could support. nr_cpus=n : n >= 1 limits the kernel to
2553 supporting 'n' processors. Later in runtime you can not
2554 use hotplug cpu feature to put more cpu back to online.
2555 just like you compile the kernel NR_CPUS=n
2557 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2559 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2560 Allowed values are enable and disable
2562 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2563 one of ['zone', 'node', 'default'] can be specified
2564 This can be set from sysctl after boot.
2565 See Documentation/sysctl/vm.txt for details.
2567 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2568 See Documentation/debugging-via-ohci1394.txt for more
2569 info.
2571 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2572 Rather than timing out after 20 ms if an EC
2573 command is not properly ACKed, override the length
2574 of the timeout. We have interrupts disabled while
2575 waiting for the ACK, so if this is set too high
2576 interrupts *may* be lost!
2578 omap_mux= [OMAP] Override bootloader pin multiplexing.
2579 Format: <mux_mode0.mode_name=value>...
2580 For example, to override I2C bus2:
2581 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2583 oprofile.timer= [HW]
2584 Use timer interrupt instead of performance counters
2586 oprofile.cpu_type= Force an oprofile cpu type
2587 This might be useful if you have an older oprofile
2588 userland or if you want common events.
2589 Format: { arch_perfmon }
2590 arch_perfmon: [X86] Force use of architectural
2591 perfmon on Intel CPUs instead of the
2592 CPU specific event set.
2593 timer: [X86] Force use of architectural NMI
2594 timer mode (see also oprofile.timer
2595 for generic hr timer mode)
2596 [s390] Force legacy basic mode sampling
2597 (report cpu_type "timer")
2599 oops=panic Always panic on oopses. Default is to just kill the
2600 process, but there is a small probability of
2601 deadlocking the machine.
2602 This will also cause panics on machine check exceptions.
2603 Useful together with panic=30 to trigger a reboot.
2605 OSS [HW,OSS]
2606 See Documentation/sound/oss/oss-parameters.txt
2608 page_owner= [KNL] Boot-time page_owner enabling option.
2609 Storage of the information about who allocated
2610 each page is disabled in default. With this switch,
2611 we can turn it on.
2612 on: enable the feature
2614 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2615 timeout > 0: seconds before rebooting
2616 timeout = 0: wait forever
2617 timeout < 0: reboot immediately
2618 Format: <timeout>
2620 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2621 on a WARN().
2623 crash_kexec_post_notifiers
2624 Run kdump after running panic-notifiers and dumping
2625 kmsg. This only for the users who doubt kdump always
2626 succeeds in any situation.
2627 Note that this also increases risks of kdump failure,
2628 because some panic notifiers can make the crashed
2629 kernel more unstable.
2631 parkbd.port= [HW] Parallel port number the keyboard adapter is
2632 connected to, default is 0.
2633 Format: <parport#>
2634 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2635 0 for XT, 1 for AT (default is AT).
2636 Format: <mode>
2638 parport= [HW,PPT] Specify parallel ports. 0 disables.
2639 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2640 Use 'auto' to force the driver to use any
2641 IRQ/DMA settings detected (the default is to
2642 ignore detected IRQ/DMA settings because of
2643 possible conflicts). You can specify the base
2644 address, IRQ, and DMA settings; IRQ and DMA
2645 should be numbers, or 'auto' (for using detected
2646 settings on that particular port), or 'nofifo'
2647 (to avoid using a FIFO even if it is detected).
2648 Parallel ports are assigned in the order they
2649 are specified on the command line, starting
2650 with parport0.
2652 parport_init_mode= [HW,PPT]
2653 Configure VIA parallel port to operate in
2654 a specific mode. This is necessary on Pegasos
2655 computer where firmware has no options for setting
2656 up parallel port mode and sets it to spp.
2657 Currently this function knows 686a and 8231 chips.
2658 Format: [spp|ps2|epp|ecp|ecpepp]
2660 pause_on_oops=
2661 Halt all CPUs after the first oops has been printed for
2662 the specified number of seconds. This is to be used if
2663 your oopses keep scrolling off the screen.
2665 pcbit= [HW,ISDN]
2667 pcd. [PARIDE]
2668 See header of drivers/block/paride/pcd.c.
2669 See also Documentation/blockdev/paride.txt.
2671 pci=option[,option...] [PCI] various PCI subsystem options:
2672 earlydump [X86] dump PCI config space before the kernel
2673 changes anything
2674 off [X86] don't probe for the PCI bus
2675 bios [X86-32] force use of PCI BIOS, don't access
2676 the hardware directly. Use this if your machine
2677 has a non-standard PCI host bridge.
2678 nobios [X86-32] disallow use of PCI BIOS, only direct
2679 hardware access methods are allowed. Use this
2680 if you experience crashes upon bootup and you
2681 suspect they are caused by the BIOS.
2682 conf1 [X86] Force use of PCI Configuration
2683 Mechanism 1.
2684 conf2 [X86] Force use of PCI Configuration
2685 Mechanism 2.
2686 noaer [PCIE] If the PCIEAER kernel config parameter is
2687 enabled, this kernel boot option can be used to
2688 disable the use of PCIE advanced error reporting.
2689 nodomains [PCI] Disable support for multiple PCI
2690 root domains (aka PCI segments, in ACPI-speak).
2691 nommconf [X86] Disable use of MMCONFIG for PCI
2692 Configuration
2693 check_enable_amd_mmconf [X86] check for and enable
2694 properly configured MMIO access to PCI
2695 config space on AMD family 10h CPU
2696 nomsi [MSI] If the PCI_MSI kernel config parameter is
2697 enabled, this kernel boot option can be used to
2698 disable the use of MSI interrupts system-wide.
2699 noioapicquirk [APIC] Disable all boot interrupt quirks.
2700 Safety option to keep boot IRQs enabled. This
2701 should never be necessary.
2702 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2703 primary IO-APIC for bridges that cannot disable
2704 boot IRQs. This fixes a source of spurious IRQs
2705 when the system masks IRQs.
2706 noioapicreroute [APIC] Disable workaround that uses the
2707 boot IRQ equivalent of an IRQ that connects to
2708 a chipset where boot IRQs cannot be disabled.
2709 The opposite of ioapicreroute.
2710 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2711 routing table. These calls are known to be buggy
2712 on several machines and they hang the machine
2713 when used, but on other computers it's the only
2714 way to get the interrupt routing table. Try
2715 this option if the kernel is unable to allocate
2716 IRQs or discover secondary PCI buses on your
2717 motherboard.
2718 rom [X86] Assign address space to expansion ROMs.
2719 Use with caution as certain devices share
2720 address decoders between ROMs and other
2721 resources.
2722 norom [X86] Do not assign address space to
2723 expansion ROMs that do not already have
2724 BIOS assigned address ranges.
2725 nobar [X86] Do not assign address space to the
2726 BARs that weren't assigned by the BIOS.
2727 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2728 assigned automatically to PCI devices. You can
2729 make the kernel exclude IRQs of your ISA cards
2730 this way.
2731 pirqaddr=0xAAAAA [X86] Specify the physical address
2732 of the PIRQ table (normally generated
2733 by the BIOS) if it is outside the
2734 F0000h-100000h range.
2735 lastbus=N [X86] Scan all buses thru bus #N. Can be
2736 useful if the kernel is unable to find your
2737 secondary buses and you want to tell it
2738 explicitly which ones they are.
2739 assign-busses [X86] Always assign all PCI bus
2740 numbers ourselves, overriding
2741 whatever the firmware may have done.
2742 usepirqmask [X86] Honor the possible IRQ mask stored
2743 in the BIOS $PIR table. This is needed on
2744 some systems with broken BIOSes, notably
2745 some HP Pavilion N5400 and Omnibook XE3
2746 notebooks. This will have no effect if ACPI
2747 IRQ routing is enabled.
2748 noacpi [X86] Do not use ACPI for IRQ routing
2749 or for PCI scanning.
2750 use_crs [X86] Use PCI host bridge window information
2751 from ACPI. On BIOSes from 2008 or later, this
2752 is enabled by default. If you need to use this,
2753 please report a bug.
2754 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2755 If you need to use this, please report a bug.
2756 routeirq Do IRQ routing for all PCI devices.
2757 This is normally done in pci_enable_device(),
2758 so this option is a temporary workaround
2759 for broken drivers that don't call it.
2760 skip_isa_align [X86] do not align io start addr, so can
2761 handle more pci cards
2762 firmware [ARM] Do not re-enumerate the bus but instead
2763 just use the configuration from the
2764 bootloader. This is currently used on
2765 IXP2000 systems where the bus has to be
2766 configured a certain way for adjunct CPUs.
2767 noearly [X86] Don't do any early type 1 scanning.
2768 This might help on some broken boards which
2769 machine check when some devices' config space
2770 is read. But various workarounds are disabled
2771 and some IOMMU drivers will not work.
2772 bfsort Sort PCI devices into breadth-first order.
2773 This sorting is done to get a device
2774 order compatible with older (<= 2.4) kernels.
2775 nobfsort Don't sort PCI devices into breadth-first order.
2776 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2777 tuning and use the BIOS-configured MPS defaults.
2778 pcie_bus_safe Set every device's MPS to the largest value
2779 supported by all devices below the root complex.
2780 pcie_bus_perf Set device MPS to the largest allowable MPS
2781 based on its parent bus. Also set MRRS (Max
2782 Read Request Size) to the largest supported
2783 value (no larger than the MPS that the device
2784 or bus can support) for best performance.
2785 pcie_bus_peer2peer Set every device's MPS to 128B, which
2786 every device is guaranteed to support. This
2787 configuration allows peer-to-peer DMA between
2788 any pair of devices, possibly at the cost of
2789 reduced performance. This also guarantees
2790 that hot-added devices will work.
2791 cbiosize=nn[KMG] The fixed amount of bus space which is
2792 reserved for the CardBus bridge's IO window.
2793 The default value is 256 bytes.
2794 cbmemsize=nn[KMG] The fixed amount of bus space which is
2795 reserved for the CardBus bridge's memory
2796 window. The default value is 64 megabytes.
2797 resource_alignment=
2798 Format:
2799 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2800 Specifies alignment and device to reassign
2801 aligned memory resources.
2802 If <order of align> is not specified,
2803 PAGE_SIZE is used as alignment.
2804 PCI-PCI bridge can be specified, if resource
2805 windows need to be expanded.
2806 ecrc= Enable/disable PCIe ECRC (transaction layer
2807 end-to-end CRC checking).
2808 bios: Use BIOS/firmware settings. This is the
2809 the default.
2810 off: Turn ECRC off
2811 on: Turn ECRC on.
2812 hpiosize=nn[KMG] The fixed amount of bus space which is
2813 reserved for hotplug bridge's IO window.
2814 Default size is 256 bytes.
2815 hpmemsize=nn[KMG] The fixed amount of bus space which is
2816 reserved for hotplug bridge's memory window.
2817 Default size is 2 megabytes.
2818 realloc= Enable/disable reallocating PCI bridge resources
2819 if allocations done by BIOS are too small to
2820 accommodate resources required by all child
2821 devices.
2822 off: Turn realloc off
2823 on: Turn realloc on
2824 realloc same as realloc=on
2825 noari do not use PCIe ARI.
2826 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2827 only look for one device below a PCIe downstream
2828 port.
2830 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2831 Management.
2832 off Disable ASPM.
2833 force Enable ASPM even on devices that claim not to support it.
2834 WARNING: Forcing ASPM on may cause system lockups.
2836 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2837 nomsi Do not use MSI for PCI Express Native Hotplug (this
2838 makes all PCIe ports use INTx for hotplug services).
2840 pcie_ports= [PCIE] PCIe ports handling:
2841 auto Ask the BIOS whether or not to use native PCIe services
2842 associated with PCIe ports (PME, hot-plug, AER). Use
2843 them only if that is allowed by the BIOS.
2844 native Use native PCIe services associated with PCIe ports
2845 unconditionally.
2846 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2847 ports driver.
2849 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2850 nomsi Do not use MSI for native PCIe PME signaling (this makes
2851 all PCIe root ports use INTx for all services).
2853 pcmv= [HW,PCMCIA] BadgePAD 4
2855 pd_ignore_unused
2856 [PM]
2857 Keep all power-domains already enabled by bootloader on,
2858 even if no driver has claimed them. This is useful
2859 for debug and development, but should not be
2860 needed on a platform with proper driver support.
2862 pd. [PARIDE]
2863 See Documentation/blockdev/paride.txt.
2865 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2866 boot time.
2867 Format: { 0 | 1 }
2868 See arch/parisc/kernel/pdc_chassis.c
2870 percpu_alloc= Select which percpu first chunk allocator to use.
2871 Currently supported values are "embed" and "page".
2872 Archs may support subset or none of the selections.
2873 See comments in mm/percpu.c for details on each
2874 allocator. This parameter is primarily for debugging
2875 and performance comparison.
2877 pf. [PARIDE]
2878 See Documentation/blockdev/paride.txt.
2880 pg. [PARIDE]
2881 See Documentation/blockdev/paride.txt.
2883 pirq= [SMP,APIC] Manual mp-table setup
2884 See Documentation/x86/i386/IO-APIC.txt.
2886 plip= [PPT,NET] Parallel port network link
2887 Format: { parport<nr> | timid | 0 }
2888 See also Documentation/parport.txt.
2890 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2891 Override pmtimer IOPort with a hex value.
2892 e.g. pmtmr=0x508
2894 pnp.debug=1 [PNP]
2895 Enable PNP debug messages (depends on the
2896 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2897 via /sys/module/pnp/parameters/debug. We always show
2898 current resource usage; turning this on also shows
2899 possible settings and some assignment information.
2901 pnpacpi= [ACPI]
2902 { off }
2904 pnpbios= [ISAPNP]
2905 { on | off | curr | res | no-curr | no-res }
2907 pnp_reserve_irq=
2908 [ISAPNP] Exclude IRQs for the autoconfiguration
2910 pnp_reserve_dma=
2911 [ISAPNP] Exclude DMAs for the autoconfiguration
2913 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2914 Ranges are in pairs (I/O port base and size).
2916 pnp_reserve_mem=
2917 [ISAPNP] Exclude memory regions for the
2918 autoconfiguration.
2919 Ranges are in pairs (memory base and size).
2921 ports= [IP_VS_FTP] IPVS ftp helper module
2922 Default is 21.
2923 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2924 may be specified.
2925 Format: <port>,<port>....
2927 print-fatal-signals=
2928 [KNL] debug: print fatal signals
2930 If enabled, warn about various signal handling
2931 related application anomalies: too many signals,
2932 too many POSIX.1 timers, fatal signals causing a
2933 coredump - etc.
2935 If you hit the warning due to signal overflow,
2936 you might want to try "ulimit -i unlimited".
2938 default: off.
2940 printk.always_kmsg_dump=
2941 Trigger kmsg_dump for cases other than kernel oops or
2942 panics
2943 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2944 default: disabled
2946 printk.time= Show timing data prefixed to each printk message line
2947 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2949 processor.max_cstate= [HW,ACPI]
2950 Limit processor to maximum C-state
2951 max_cstate=9 overrides any DMI blacklist limit.
2953 processor.nocst [HW,ACPI]
2954 Ignore the _CST method to determine C-states,
2955 instead using the legacy FADT method
2957 profile= [KNL] Enable kernel profiling via /proc/profile
2958 Format: [schedule,]<number>
2959 Param: "schedule" - profile schedule points.
2960 Param: <number> - step/bucket size as a power of 2 for
2961 statistical time based profiling.
2962 Param: "sleep" - profile D-state sleeping (millisecs).
2963 Requires CONFIG_SCHEDSTATS
2964 Param: "kvm" - profile VM exits.
2966 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2967 before loading.
2968 See Documentation/blockdev/ramdisk.txt.
2970 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2971 probe for; one of (bare|imps|exps|lifebook|any).
2972 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2973 per second.
2974 psmouse.resetafter= [HW,MOUSE]
2975 Try to reset the device after so many bad packets
2976 (0 = never).
2977 psmouse.resolution=
2978 [HW,MOUSE] Set desired mouse resolution, in dpi.
2979 psmouse.smartscroll=
2980 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2981 0 = disabled, 1 = enabled (default).
2983 pstore.backend= Specify the name of the pstore backend to use
2985 pt. [PARIDE]
2986 See Documentation/blockdev/paride.txt.
2988 pty.legacy_count=
2989 [KNL] Number of legacy pty's. Overwrites compiled-in
2990 default number.
2992 quiet [KNL] Disable most log messages
2994 r128= [HW,DRM]
2996 raid= [HW,RAID]
2997 See Documentation/md.txt.
2999 ramdisk_blocksize= [RAM]
3000 See Documentation/blockdev/ramdisk.txt.
3002 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3003 See Documentation/blockdev/ramdisk.txt.
3005 rcu_nocbs= [KNL]
3006 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3007 the specified list of CPUs to be no-callback CPUs.
3008 Invocation of these CPUs' RCU callbacks will
3009 be offloaded to "rcuox/N" kthreads created for
3010 that purpose, where "x" is "b" for RCU-bh, "p"
3011 for RCU-preempt, and "s" for RCU-sched, and "N"
3012 is the CPU number. This reduces OS jitter on the
3013 offloaded CPUs, which can be useful for HPC and
3014 real-time workloads. It can also improve energy
3015 efficiency for asymmetric multiprocessors.
3017 rcu_nocb_poll [KNL]
3018 Rather than requiring that offloaded CPUs
3019 (specified by rcu_nocbs= above) explicitly
3020 awaken the corresponding "rcuoN" kthreads,
3021 make these kthreads poll for callbacks.
3022 This improves the real-time response for the
3023 offloaded CPUs by relieving them of the need to
3024 wake up the corresponding kthread, but degrades
3025 energy efficiency by requiring that the kthreads
3026 periodically wake up to do the polling.
3028 rcutree.blimit= [KNL]
3029 Set maximum number of finished RCU callbacks to
3030 process in one batch.
3032 rcutree.dump_tree= [KNL]
3033 Dump the structure of the rcu_node combining tree
3034 out at early boot. This is used for diagnostic
3035 purposes, to verify correct tree setup.
3037 rcutree.gp_cleanup_delay= [KNL]
3038 Set the number of jiffies to delay each step of
3039 RCU grace-period cleanup. This only has effect
3040 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3042 rcutree.gp_init_delay= [KNL]
3043 Set the number of jiffies to delay each step of
3044 RCU grace-period initialization. This only has
3045 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3046 is set.
3048 rcutree.gp_preinit_delay= [KNL]
3049 Set the number of jiffies to delay each step of
3050 RCU grace-period pre-initialization, that is,
3051 the propagation of recent CPU-hotplug changes up
3052 the rcu_node combining tree. This only has effect
3053 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3055 rcutree.rcu_fanout_exact= [KNL]
3056 Disable autobalancing of the rcu_node combining
3057 tree. This is used by rcutorture, and might
3058 possibly be useful for architectures having high
3059 cache-to-cache transfer latencies.
3061 rcutree.rcu_fanout_leaf= [KNL]
3062 Increase the number of CPUs assigned to each
3063 leaf rcu_node structure. Useful for very large
3064 systems.
3066 rcutree.jiffies_till_sched_qs= [KNL]
3067 Set required age in jiffies for a
3068 given grace period before RCU starts
3069 soliciting quiescent-state help from
3070 rcu_note_context_switch().
3072 rcutree.jiffies_till_first_fqs= [KNL]
3073 Set delay from grace-period initialization to
3074 first attempt to force quiescent states.
3075 Units are jiffies, minimum value is zero,
3076 and maximum value is HZ.
3078 rcutree.jiffies_till_next_fqs= [KNL]
3079 Set delay between subsequent attempts to force
3080 quiescent states. Units are jiffies, minimum
3081 value is one, and maximum value is HZ.
3083 rcutree.kthread_prio= [KNL,BOOT]
3084 Set the SCHED_FIFO priority of the RCU per-CPU
3085 kthreads (rcuc/N). This value is also used for
3086 the priority of the RCU boost threads (rcub/N)
3087 and for the RCU grace-period kthreads (rcu_bh,
3088 rcu_preempt, and rcu_sched). If RCU_BOOST is
3089 set, valid values are 1-99 and the default is 1
3090 (the least-favored priority). Otherwise, when
3091 RCU_BOOST is not set, valid values are 0-99 and
3092 the default is zero (non-realtime operation).
3094 rcutree.rcu_nocb_leader_stride= [KNL]
3095 Set the number of NOCB kthread groups, which
3096 defaults to the square root of the number of
3097 CPUs. Larger numbers reduces the wakeup overhead
3098 on the per-CPU grace-period kthreads, but increases
3099 that same overhead on each group's leader.
3101 rcutree.qhimark= [KNL]
3102 Set threshold of queued RCU callbacks beyond which
3103 batch limiting is disabled.
3105 rcutree.qlowmark= [KNL]
3106 Set threshold of queued RCU callbacks below which
3107 batch limiting is re-enabled.
3109 rcutree.rcu_idle_gp_delay= [KNL]
3110 Set wakeup interval for idle CPUs that have
3111 RCU callbacks (RCU_FAST_NO_HZ=y).
3113 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3114 Set wakeup interval for idle CPUs that have
3115 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3116 Lazy RCU callbacks are those which RCU can
3117 prove do nothing more than free memory.
3119 rcutorture.cbflood_inter_holdoff= [KNL]
3120 Set holdoff time (jiffies) between successive
3121 callback-flood tests.
3123 rcutorture.cbflood_intra_holdoff= [KNL]
3124 Set holdoff time (jiffies) between successive
3125 bursts of callbacks within a given callback-flood
3126 test.
3128 rcutorture.cbflood_n_burst= [KNL]
3129 Set the number of bursts making up a given
3130 callback-flood test. Set this to zero to
3131 disable callback-flood testing.
3133 rcutorture.cbflood_n_per_burst= [KNL]
3134 Set the number of callbacks to be registered
3135 in a given burst of a callback-flood test.
3137 rcutorture.fqs_duration= [KNL]
3138 Set duration of force_quiescent_state bursts.
3140 rcutorture.fqs_holdoff= [KNL]
3141 Set holdoff time within force_quiescent_state bursts.
3143 rcutorture.fqs_stutter= [KNL]
3144 Set wait time between force_quiescent_state bursts.
3146 rcutorture.gp_exp= [KNL]
3147 Use expedited update-side primitives.
3149 rcutorture.gp_normal= [KNL]
3150 Use normal (non-expedited) update-side primitives.
3151 If both gp_exp and gp_normal are set, do both.
3152 If neither gp_exp nor gp_normal are set, still
3153 do both.
3155 rcutorture.n_barrier_cbs= [KNL]
3156 Set callbacks/threads for rcu_barrier() testing.
3158 rcutorture.nfakewriters= [KNL]
3159 Set number of concurrent RCU writers. These just
3160 stress RCU, they don't participate in the actual
3161 test, hence the "fake".
3163 rcutorture.nreaders= [KNL]
3164 Set number of RCU readers. The value -1 selects
3165 N-1, where N is the number of CPUs. A value
3166 "n" less than -1 selects N-n-2, where N is again
3167 the number of CPUs. For example, -2 selects N
3168 (the number of CPUs), -3 selects N+1, and so on.
3170 rcutorture.object_debug= [KNL]
3171 Enable debug-object double-call_rcu() testing.
3173 rcutorture.onoff_holdoff= [KNL]
3174 Set time (s) after boot for CPU-hotplug testing.
3176 rcutorture.onoff_interval= [KNL]
3177 Set time (s) between CPU-hotplug operations, or
3178 zero to disable CPU-hotplug testing.
3180 rcutorture.torture_runnable= [BOOT]
3181 Start rcutorture running at boot time.
3183 rcutorture.shuffle_interval= [KNL]
3184 Set task-shuffle interval (s). Shuffling tasks
3185 allows some CPUs to go into dyntick-idle mode
3186 during the rcutorture test.
3188 rcutorture.shutdown_secs= [KNL]
3189 Set time (s) after boot system shutdown. This
3190 is useful for hands-off automated testing.
3192 rcutorture.stall_cpu= [KNL]
3193 Duration of CPU stall (s) to test RCU CPU stall
3194 warnings, zero to disable.
3196 rcutorture.stall_cpu_holdoff= [KNL]
3197 Time to wait (s) after boot before inducing stall.
3199 rcutorture.stat_interval= [KNL]
3200 Time (s) between statistics printk()s.
3202 rcutorture.stutter= [KNL]
3203 Time (s) to stutter testing, for example, specifying
3204 five seconds causes the test to run for five seconds,
3205 wait for five seconds, and so on. This tests RCU's
3206 ability to transition abruptly to and from idle.
3208 rcutorture.test_boost= [KNL]
3209 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3210 "Maybe" means test if the RCU implementation
3211 under test support RCU priority boosting.
3213 rcutorture.test_boost_duration= [KNL]
3214 Duration (s) of each individual boost test.
3216 rcutorture.test_boost_interval= [KNL]
3217 Interval (s) between each boost test.
3219 rcutorture.test_no_idle_hz= [KNL]
3220 Test RCU's dyntick-idle handling. See also the
3221 rcutorture.shuffle_interval parameter.
3223 rcutorture.torture_type= [KNL]
3224 Specify the RCU implementation to test.
3226 rcutorture.verbose= [KNL]
3227 Enable additional printk() statements.
3229 rcupdate.rcu_expedited= [KNL]
3230 Use expedited grace-period primitives, for
3231 example, synchronize_rcu_expedited() instead
3232 of synchronize_rcu(). This reduces latency,
3233 but can increase CPU utilization, degrade
3234 real-time latency, and degrade energy efficiency.
3236 rcupdate.rcu_cpu_stall_suppress= [KNL]
3237 Suppress RCU CPU stall warning messages.
3239 rcupdate.rcu_cpu_stall_timeout= [KNL]
3240 Set timeout for RCU CPU stall warning messages.
3242 rcupdate.rcu_task_stall_timeout= [KNL]
3243 Set timeout in jiffies for RCU task stall warning
3244 messages. Disable with a value less than or equal
3245 to zero.
3247 rcupdate.rcu_self_test= [KNL]
3248 Run the RCU early boot self tests
3250 rcupdate.rcu_self_test_bh= [KNL]
3251 Run the RCU bh early boot self tests
3253 rcupdate.rcu_self_test_sched= [KNL]
3254 Run the RCU sched early boot self tests
3256 rdinit= [KNL]
3257 Format: <full_path>
3258 Run specified binary instead of /init from the ramdisk,
3259 used for early userspace startup. See initrd.
3261 reboot= [KNL]
3262 Format (x86 or x86_64):
3263 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3264 [[,]s[mp]#### \
3265 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3266 [[,]f[orce]
3267 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3268 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3269 reboot_force is either force or not specified,
3270 reboot_cpu is s[mp]#### with #### being the processor
3271 to be used for rebooting.
3273 relax_domain_level=
3274 [KNL, SMP] Set scheduler's default relax_domain_level.
3275 See Documentation/cgroups/cpusets.txt.
3277 relative_sleep_states=
3278 [SUSPEND] Use sleep state labeling where the deepest
3279 state available other than hibernation is always "mem".
3280 Format: { "0" | "1" }
3281 0 -- Traditional sleep state labels.
3282 1 -- Relative sleep state labels.
3284 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3286 reservetop= [X86-32]
3287 Format: nn[KMG]
3288 Reserves a hole at the top of the kernel virtual
3289 address space.
3291 reservelow= [X86]
3292 Format: nn[K]
3293 Set the amount of memory to reserve for BIOS at
3294 the bottom of the address space.
3296 reset_devices [KNL] Force drivers to reset the underlying device
3297 during initialization.
3299 resume= [SWSUSP]
3300 Specify the partition device for software suspend
3301 Format:
3302 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3304 resume_offset= [SWSUSP]
3305 Specify the offset from the beginning of the partition
3306 given by "resume=" at which the swap header is located,
3307 in <PAGE_SIZE> units (needed only for swap files).
3308 See Documentation/power/swsusp-and-swap-files.txt
3310 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3311 read the resume files
3313 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3314 Useful for devices that are detected asynchronously
3315 (e.g. USB and MMC devices).
3317 hibernate= [HIBERNATION]
3318 noresume Don't check if there's a hibernation image
3319 present during boot.
3320 nocompress Don't compress/decompress hibernation images.
3321 no Disable hibernation and resume.
3323 retain_initrd [RAM] Keep initrd memory after extraction
3325 rfkill.default_state=
3326 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3327 etc. communication is blocked by default.
3328 1 Unblocked.
3330 rfkill.master_switch_mode=
3331 0 The "airplane mode" button does nothing.
3332 1 The "airplane mode" button toggles between everything
3333 blocked and the previous configuration.
3334 2 The "airplane mode" button toggles between everything
3335 blocked and everything unblocked.
3337 rhash_entries= [KNL,NET]
3338 Set number of hash buckets for route cache
3340 ro [KNL] Mount root device read-only on boot
3342 root= [KNL] Root filesystem
3343 See name_to_dev_t comment in init/do_mounts.c.
3345 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3346 mount the root filesystem
3348 rootflags= [KNL] Set root filesystem mount option string
3350 rootfstype= [KNL] Set root filesystem type
3352 rootwait [KNL] Wait (indefinitely) for root device to show up.
3353 Useful for devices that are detected asynchronously
3354 (e.g. USB and MMC devices).
3356 rproc_mem=nn[KMG][@address]
3357 [KNL,ARM,CMA] Remoteproc physical memory block.
3358 Memory area to be used by remote processor image,
3359 managed by CMA.
3361 rw [KNL] Mount root device read-write on boot
3363 S [KNL] Run init in single mode
3365 s390_iommu= [HW,S390]
3366 Set s390 IOTLB flushing mode
3367 strict
3368 With strict flushing every unmap operation will result in
3369 an IOTLB flush. Default is lazy flushing before reuse,
3370 which is faster.
3372 sa1100ir [NET]
3373 See drivers/net/irda/sa1100_ir.c.
3375 sbni= [NET] Granch SBNI12 leased line adapter
3377 sched_debug [KNL] Enables verbose scheduler debug messages.
3379 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3380 xtime_lock contention on larger systems, and/or RCU lock
3381 contention on all systems with CONFIG_MAXSMP set.
3382 Format: { "0" | "1" }
3383 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3384 1 -- enable.
3385 Note: increases power consumption, thus should only be
3386 enabled if running jitter sensitive (HPC/RT) workloads.
3388 security= [SECURITY] Choose a security module to enable at boot.
3389 If this boot parameter is not specified, only the first
3390 security module asking for security registration will be
3391 loaded. An invalid security module name will be treated
3392 as if no module has been chosen.
3394 selinux= [SELINUX] Disable or enable SELinux at boot time.
3395 Format: { "0" | "1" }
3396 See security/selinux/Kconfig help text.
3397 0 -- disable.
3398 1 -- enable.
3399 Default value is set via kernel config option.
3400 If enabled at boot time, /selinux/disable can be used
3401 later to disable prior to initial policy load.
3403 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3404 Format: { "0" | "1" }
3405 See security/apparmor/Kconfig help text
3406 0 -- disable.
3407 1 -- enable.
3408 Default value is set via kernel config option.
3410 serialnumber [BUGS=X86-32]
3412 shapers= [NET]
3413 Maximal number of shapers.
3415 show_msr= [x86] show boot-time MSR settings
3416 Format: { <integer> }
3417 Show boot-time (BIOS-initialized) MSR settings.
3418 The parameter means the number of CPUs to show,
3419 for example 1 means boot CPU only.
3421 simeth= [IA-64]
3422 simscsi=
3424 slram= [HW,MTD]
3426 slab_nomerge [MM]
3427 Disable merging of slabs with similar size. May be
3428 necessary if there is some reason to distinguish
3429 allocs to different slabs. Debug options disable
3430 merging on their own.
3431 For more information see Documentation/vm/slub.txt.
3433 slab_max_order= [MM, SLAB]
3434 Determines the maximum allowed order for slabs.
3435 A high setting may cause OOMs due to memory
3436 fragmentation. Defaults to 1 for systems with
3437 more than 32MB of RAM, 0 otherwise.
3439 slub_debug[=options[,slabs]] [MM, SLUB]
3440 Enabling slub_debug allows one to determine the
3441 culprit if slab objects become corrupted. Enabling
3442 slub_debug can create guard zones around objects and
3443 may poison objects when not in use. Also tracks the
3444 last alloc / free. For more information see
3445 Documentation/vm/slub.txt.
3447 slub_max_order= [MM, SLUB]
3448 Determines the maximum allowed order for slabs.
3449 A high setting may cause OOMs due to memory
3450 fragmentation. For more information see
3451 Documentation/vm/slub.txt.
3453 slub_min_objects= [MM, SLUB]
3454 The minimum number of objects per slab. SLUB will
3455 increase the slab order up to slub_max_order to
3456 generate a sufficiently large slab able to contain
3457 the number of objects indicated. The higher the number
3458 of objects the smaller the overhead of tracking slabs
3459 and the less frequently locks need to be acquired.
3460 For more information see Documentation/vm/slub.txt.
3462 slub_min_order= [MM, SLUB]
3463 Determines the minimum page order for slabs. Must be
3464 lower than slub_max_order.
3465 For more information see Documentation/vm/slub.txt.
3467 slub_nomerge [MM, SLUB]
3468 Same with slab_nomerge. This is supported for legacy.
3469 See slab_nomerge for more information.
3471 smart2= [HW]
3472 Format: <io1>[,<io2>[,...,<io8>]]
3474 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3475 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3476 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3477 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3478 smsc-ircc2.ircc_irq= [HW] IRQ line
3479 smsc-ircc2.ircc_dma= [HW] DMA channel
3480 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3481 0: Toshiba Satellite 1800 (GP data pin select)
3482 1: Fast pin select (default)
3483 2: ATC IRMode
3485 softlockup_panic=
3486 [KNL] Should the soft-lockup detector generate panics.
3487 Format: <integer>
3489 softlockup_all_cpu_backtrace=
3490 [KNL] Should the soft-lockup detector generate
3491 backtraces on all cpus.
3492 Format: <integer>
3494 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3495 See Documentation/laptops/sonypi.txt
3497 spia_io_base= [HW,MTD]
3498 spia_fio_base=
3499 spia_pedr=
3500 spia_peddr=
3502 stacktrace [FTRACE]
3503 Enabled the stack tracer on boot up.
3505 stacktrace_filter=[function-list]
3506 [FTRACE] Limit the functions that the stack tracer
3507 will trace at boot up. function-list is a comma separated
3508 list of functions. This list can be changed at run
3509 time by the stack_trace_filter file in the debugfs
3510 tracing directory. Note, this enables stack tracing
3511 and the stacktrace above is not needed.
3513 sti= [PARISC,HW]
3514 Format: <num>
3515 Set the STI (builtin display/keyboard on the HP-PARISC
3516 machines) console (graphic card) which should be used
3517 as the initial boot-console.
3518 See also comment in drivers/video/console/sticore.c.
3520 sti_font= [HW]
3521 See comment in drivers/video/console/sticore.c.
3523 stifb= [HW]
3524 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3526 sunrpc.min_resvport=
3527 sunrpc.max_resvport=
3528 [NFS,SUNRPC]
3529 SunRPC servers often require that client requests
3530 originate from a privileged port (i.e. a port in the
3531 range 0 < portnr < 1024).
3532 An administrator who wishes to reserve some of these
3533 ports for other uses may adjust the range that the
3534 kernel's sunrpc client considers to be privileged
3535 using these two parameters to set the minimum and
3536 maximum port values.
3538 sunrpc.pool_mode=
3539 [NFS]
3540 Control how the NFS server code allocates CPUs to
3541 service thread pools. Depending on how many NICs
3542 you have and where their interrupts are bound, this
3543 option will affect which CPUs will do NFS serving.
3544 Note: this parameter cannot be changed while the
3545 NFS server is running.
3547 auto the server chooses an appropriate mode
3548 automatically using heuristics
3549 global a single global pool contains all CPUs
3550 percpu one pool for each CPU
3551 pernode one pool for each NUMA node (equivalent
3552 to global on non-NUMA machines)
3554 sunrpc.tcp_slot_table_entries=
3555 sunrpc.udp_slot_table_entries=
3556 [NFS,SUNRPC]
3557 Sets the upper limit on the number of simultaneous
3558 RPC calls that can be sent from the client to a
3559 server. Increasing these values may allow you to
3560 improve throughput, but will also increase the
3561 amount of memory reserved for use by the client.
3563 suspend.pm_test_delay=
3564 [SUSPEND]
3565 Sets the number of seconds to remain in a suspend test
3566 mode before resuming the system (see
3567 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3568 is set. Default value is 5.
3570 swapaccount=[0|1]
3571 [KNL] Enable accounting of swap in memory resource
3572 controller if no parameter or 1 is given or disable
3573 it if 0 is given (See Documentation/cgroups/memory.txt)
3575 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3576 Format: { <int> | force }
3577 <int> -- Number of I/O TLB slabs
3578 force -- force using of bounce buffers even if they
3579 wouldn't be automatically used by the kernel
3581 switches= [HW,M68k]
3583 sysfs.deprecated=0|1 [KNL]
3584 Enable/disable old style sysfs layout for old udev
3585 on older distributions. When this option is enabled
3586 very new udev will not work anymore. When this option
3587 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3588 in older udev will not work anymore.
3589 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3590 the kernel configuration.
3592 sysrq_always_enabled
3593 [KNL]
3594 Ignore sysrq setting - this boot parameter will
3595 neutralize any effect of /proc/sys/kernel/sysrq.
3596 Useful for debugging.
3598 tcpmhash_entries= [KNL,NET]
3599 Set the number of tcp_metrics_hash slots.
3600 Default value is 8192 or 16384 depending on total
3601 ram pages. This is used to specify the TCP metrics
3602 cache size. See Documentation/networking/ip-sysctl.txt
3603 "tcp_no_metrics_save" section for more details.
3605 tdfx= [HW,DRM]
3607 test_suspend= [SUSPEND][,N]
3608 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3609 standby suspend) or "freeze" (for suspend type freeze)
3610 as the system sleep state during system startup with
3611 the optional capability to repeat N number of times.
3612 The system is woken from this state using a
3613 wakeup-capable RTC alarm.
3615 thash_entries= [KNL,NET]
3616 Set number of hash buckets for TCP connection
3618 thermal.act= [HW,ACPI]
3619 -1: disable all active trip points in all thermal zones
3620 <degrees C>: override all lowest active trip points
3622 thermal.crt= [HW,ACPI]
3623 -1: disable all critical trip points in all thermal zones
3624 <degrees C>: override all critical trip points
3626 thermal.nocrt= [HW,ACPI]
3627 Set to disable actions on ACPI thermal zone
3628 critical and hot trip points.
3630 thermal.off= [HW,ACPI]
3631 1: disable ACPI thermal control
3633 thermal.psv= [HW,ACPI]
3634 -1: disable all passive trip points
3635 <degrees C>: override all passive trip points to this
3636 value
3638 thermal.tzp= [HW,ACPI]
3639 Specify global default ACPI thermal zone polling rate
3640 <deci-seconds>: poll all this frequency
3641 0: no polling (default)
3643 threadirqs [KNL]
3644 Force threading of all interrupt handlers except those
3645 marked explicitly IRQF_NO_THREAD.
3647 tmem [KNL,XEN]
3648 Enable the Transcendent memory driver if built-in.
3650 tmem.cleancache=0|1 [KNL, XEN]
3651 Default is on (1). Disable the usage of the cleancache
3652 API to send anonymous pages to the hypervisor.
3654 tmem.frontswap=0|1 [KNL, XEN]
3655 Default is on (1). Disable the usage of the frontswap
3656 API to send swap pages to the hypervisor. If disabled
3657 the selfballooning and selfshrinking are force disabled.
3659 tmem.selfballooning=0|1 [KNL, XEN]
3660 Default is on (1). Disable the driving of swap pages
3661 to the hypervisor.
3663 tmem.selfshrinking=0|1 [KNL, XEN]
3664 Default is on (1). Partial swapoff that immediately
3665 transfers pages from Xen hypervisor back to the
3666 kernel based on different criteria.
3668 topology= [S390]
3669 Format: {off | on}
3670 Specify if the kernel should make use of the cpu
3671 topology information if the hardware supports this.
3672 The scheduler will make use of this information and
3673 e.g. base its process migration decisions on it.
3674 Default is on.
3676 topology_updates= [KNL, PPC, NUMA]
3677 Format: {off}
3678 Specify if the kernel should ignore (off)
3679 topology updates sent by the hypervisor to this
3680 LPAR.
3682 tp720= [HW,PS2]
3684 tpm_suspend_pcr=[HW,TPM]
3685 Format: integer pcr id
3686 Specify that at suspend time, the tpm driver
3687 should extend the specified pcr with zeros,
3688 as a workaround for some chips which fail to
3689 flush the last written pcr on TPM_SaveState.
3690 This will guarantee that all the other pcrs
3691 are saved.
3693 trace_buf_size=nn[KMG]
3694 [FTRACE] will set tracing buffer size on each cpu.
3696 trace_event=[event-list]
3697 [FTRACE] Set and start specified trace events in order
3698 to facilitate early boot debugging.
3699 See also Documentation/trace/events.txt
3701 trace_options=[option-list]
3702 [FTRACE] Enable or disable tracer options at boot.
3703 The option-list is a comma delimited list of options
3704 that can be enabled or disabled just as if you were
3705 to echo the option name into
3707 /sys/kernel/debug/tracing/trace_options
3709 For example, to enable stacktrace option (to dump the
3710 stack trace of each event), add to the command line:
3712 trace_options=stacktrace
3714 See also Documentation/trace/ftrace.txt "trace options"
3715 section.
3717 tp_printk[FTRACE]
3718 Have the tracepoints sent to printk as well as the
3719 tracing ring buffer. This is useful for early boot up
3720 where the system hangs or reboots and does not give the
3721 option for reading the tracing buffer or performing a
3722 ftrace_dump_on_oops.
3724 To turn off having tracepoints sent to printk,
3725 echo 0 > /proc/sys/kernel/tracepoint_printk
3726 Note, echoing 1 into this file without the
3727 tracepoint_printk kernel cmdline option has no effect.
3729 ** CAUTION **
3731 Having tracepoints sent to printk() and activating high
3732 frequency tracepoints such as irq or sched, can cause
3733 the system to live lock.
3735 traceoff_on_warning
3736 [FTRACE] enable this option to disable tracing when a
3737 warning is hit. This turns off "tracing_on". Tracing can
3738 be enabled again by echoing '1' into the "tracing_on"
3739 file located in /sys/kernel/debug/tracing/
3741 This option is useful, as it disables the trace before
3742 the WARNING dump is called, which prevents the trace to
3743 be filled with content caused by the warning output.
3745 This option can also be set at run time via the sysctl
3746 option: kernel/traceoff_on_warning
3748 transparent_hugepage=
3749 [KNL]
3750 Format: [always|madvise|never]
3751 Can be used to control the default behavior of the system
3752 with respect to transparent hugepages.
3753 See Documentation/vm/transhuge.txt for more details.
3755 tsc= Disable clocksource stability checks for TSC.
3756 Format: <string>
3757 [x86] reliable: mark tsc clocksource as reliable, this
3758 disables clocksource verification at runtime, as well
3759 as the stability checks done at bootup. Used to enable
3760 high-resolution timer mode on older hardware, and in
3761 virtualized environment.
3762 [x86] noirqtime: Do not use TSC to do irq accounting.
3763 Used to run time disable IRQ_TIME_ACCOUNTING on any
3764 platforms where RDTSC is slow and this accounting
3765 can add overhead.
3767 turbografx.map[2|3]= [HW,JOY]
3768 TurboGraFX parallel port interface
3769 Format:
3770 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3771 See also Documentation/input/joystick-parport.txt
3773 udbg-immortal [PPC] When debugging early kernel crashes that
3774 happen after console_init() and before a proper
3775 console driver takes over, this boot options might
3776 help "seeing" what's going on.
3778 uhash_entries= [KNL,NET]
3779 Set number of hash buckets for UDP/UDP-Lite connections
3781 uhci-hcd.ignore_oc=
3782 [USB] Ignore overcurrent events (default N).
3783 Some badly-designed motherboards generate lots of
3784 bogus events, for ports that aren't wired to
3785 anything. Set this parameter to avoid log spamming.
3786 Note that genuine overcurrent events won't be
3787 reported either.
3789 unknown_nmi_panic
3790 [X86] Cause panic on unknown NMI.
3792 usbcore.authorized_default=
3793 [USB] Default USB device authorization:
3794 (default -1 = authorized except for wireless USB,
3795 0 = not authorized, 1 = authorized)
3797 usbcore.autosuspend=
3798 [USB] The autosuspend time delay (in seconds) used
3799 for newly-detected USB devices (default 2). This
3800 is the time required before an idle device will be
3801 autosuspended. Devices for which the delay is set
3802 to a negative value won't be autosuspended at all.
3804 usbcore.usbfs_snoop=
3805 [USB] Set to log all usbfs traffic (default 0 = off).
3807 usbcore.blinkenlights=
3808 [USB] Set to cycle leds on hubs (default 0 = off).
3810 usbcore.old_scheme_first=
3811 [USB] Start with the old device initialization
3812 scheme (default 0 = off).
3814 usbcore.usbfs_memory_mb=
3815 [USB] Memory limit (in MB) for buffers allocated by
3816 usbfs (default = 16, 0 = max = 2047).
3818 usbcore.use_both_schemes=
3819 [USB] Try the other device initialization scheme
3820 if the first one fails (default 1 = enabled).
3822 usbcore.initial_descriptor_timeout=
3823 [USB] Specifies timeout for the initial 64-byte
3824 USB_REQ_GET_DESCRIPTOR request in milliseconds
3825 (default 5000 = 5.0 seconds).
3827 usbhid.mousepoll=
3828 [USBHID] The interval which mice are to be polled at.
3830 usb-storage.delay_use=
3831 [UMS] The delay in seconds before a new device is
3832 scanned for Logical Units (default 1).
3834 usb-storage.quirks=
3835 [UMS] A list of quirks entries to supplement or
3836 override the built-in unusual_devs list. List
3837 entries are separated by commas. Each entry has
3838 the form VID:PID:Flags where VID and PID are Vendor
3839 and Product ID values (4-digit hex numbers) and
3840 Flags is a set of characters, each corresponding
3841 to a common usb-storage quirk flag as follows:
3842 a = SANE_SENSE (collect more than 18 bytes
3843 of sense data);
3844 b = BAD_SENSE (don't collect more than 18
3845 bytes of sense data);
3846 c = FIX_CAPACITY (decrease the reported
3847 device capacity by one sector);
3848 d = NO_READ_DISC_INFO (don't use
3849 READ_DISC_INFO command);
3850 e = NO_READ_CAPACITY_16 (don't use
3851 READ_CAPACITY_16 command);
3852 f = NO_REPORT_OPCODES (don't use report opcodes
3853 command, uas only);
3854 g = MAX_SECTORS_240 (don't transfer more than
3855 240 sectors at a time, uas only);
3856 h = CAPACITY_HEURISTICS (decrease the
3857 reported device capacity by one
3858 sector if the number is odd);
3859 i = IGNORE_DEVICE (don't bind to this
3860 device);
3861 l = NOT_LOCKABLE (don't try to lock and
3862 unlock ejectable media);
3863 m = MAX_SECTORS_64 (don't transfer more
3864 than 64 sectors = 32 KB at a time);
3865 n = INITIAL_READ10 (force a retry of the
3866 initial READ(10) command);
3867 o = CAPACITY_OK (accept the capacity
3868 reported by the device);
3869 p = WRITE_CACHE (the device cache is ON
3870 by default);
3871 r = IGNORE_RESIDUE (the device reports
3872 bogus residue values);
3873 s = SINGLE_LUN (the device has only one
3874 Logical Unit);
3875 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3876 commands, uas only);
3877 u = IGNORE_UAS (don't bind to the uas driver);
3878 w = NO_WP_DETECT (don't test whether the
3879 medium is write-protected).
3880 Example: quirks=0419:aaf5:rl,0421:0433:rc
3882 user_debug= [KNL,ARM]
3883 Format: <int>
3884 See arch/arm/Kconfig.debug help text.
3885 1 - undefined instruction events
3886 2 - system calls
3887 4 - invalid data aborts
3888 8 - SIGSEGV faults
3889 16 - SIGBUS faults
3890 Example: user_debug=31
3892 userpte=
3893 [X86] Flags controlling user PTE allocations.
3895 nohigh = do not allocate PTE pages in
3896 HIGHMEM regardless of setting
3897 of CONFIG_HIGHPTE.
3899 vdso= [X86,SH]
3900 On X86_32, this is an alias for vdso32=. Otherwise:
3902 vdso=1: enable VDSO (the default)
3903 vdso=0: disable VDSO mapping
3905 vdso32= [X86] Control the 32-bit vDSO
3906 vdso32=1: enable 32-bit VDSO
3907 vdso32=0 or vdso32=2: disable 32-bit VDSO
3909 See the help text for CONFIG_COMPAT_VDSO for more
3910 details. If CONFIG_COMPAT_VDSO is set, the default is
3911 vdso32=0; otherwise, the default is vdso32=1.
3913 For compatibility with older kernels, vdso32=2 is an
3914 alias for vdso32=0.
3916 Try vdso32=0 if you encounter an error that says:
3917 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3919 vector= [IA-64,SMP]
3920 vector=percpu: enable percpu vector domain
3922 video= [FB] Frame buffer configuration
3923 See Documentation/fb/modedb.txt.
3925 video.brightness_switch_enabled= [0,1]
3926 If set to 1, on receiving an ACPI notify event
3927 generated by hotkey, video driver will adjust brightness
3928 level and then send out the event to user space through
3929 the allocated input device; If set to 0, video driver
3930 will only send out the event without touching backlight
3931 brightness level.
3932 default: 1
3934 virtio_mmio.device=
3935 [VMMIO] Memory mapped virtio (platform) device.
3937 <size>@<baseaddr>:<irq>[:<id>]
3938 where:
3939 <size> := size (can use standard suffixes
3940 like K, M and G)
3941 <baseaddr> := physical base address
3942 <irq> := interrupt number (as passed to
3943 request_irq())
3944 <id> := (optional) platform device id
3945 example:
3946 virtio_mmio.device=1K@0x100b0000:48:7
3948 Can be used multiple times for multiple devices.
3950 vga= [BOOT,X86-32] Select a particular video mode
3951 See Documentation/x86/boot.txt and
3952 Documentation/svga.txt.
3953 Use vga=ask for menu.
3954 This is actually a boot loader parameter; the value is
3955 passed to the kernel using a special protocol.
3957 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3958 size of <nn>. This can be used to increase the
3959 minimum size (128MB on x86). It can also be used to
3960 decrease the size and leave more room for directly
3961 mapped kernel RAM.
3963 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3964 Format: <command>
3966 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3967 Format: <command>
3969 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3970 Format: <command>
3972 vsyscall= [X86-64]
3973 Controls the behavior of vsyscalls (i.e. calls to
3974 fixed addresses of 0xffffffffff600x00 from legacy
3975 code). Most statically-linked binaries and older
3976 versions of glibc use these calls. Because these
3977 functions are at fixed addresses, they make nice
3978 targets for exploits that can control RIP.
3980 emulate [default] Vsyscalls turn into traps and are
3981 emulated reasonably safely.
3983 native Vsyscalls are native syscall instructions.
3984 This is a little bit faster than trapping
3985 and makes a few dynamic recompilers work
3986 better than they would in emulation mode.
3987 It also makes exploits much easier to write.
3989 none Vsyscalls don't work at all. This makes
3990 them quite hard to use for exploits but
3991 might break your system.
3993 vt.color= [VT] Default text color.
3994 Format: 0xYX, X = foreground, Y = background.
3995 Default: 0x07 = light gray on black.
3997 vt.cur_default= [VT] Default cursor shape.
3998 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3999 the parameters of the <Esc>[?A;B;Cc escape sequence;
4000 see VGA-softcursor.txt. Default: 2 = underline.
4002 vt.default_blu= [VT]
4003 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4004 Change the default blue palette of the console.
4005 This is a 16-member array composed of values
4006 ranging from 0-255.
4008 vt.default_grn= [VT]
4009 Format: <green0>,<green1>,<green2>,...,<green15>
4010 Change the default green palette of the console.
4011 This is a 16-member array composed of values
4012 ranging from 0-255.
4014 vt.default_red= [VT]
4015 Format: <red0>,<red1>,<red2>,...,<red15>
4016 Change the default red palette of the console.
4017 This is a 16-member array composed of values
4018 ranging from 0-255.
4020 vt.default_utf8=
4021 [VT]
4022 Format=<0|1>
4023 Set system-wide default UTF-8 mode for all tty's.
4024 Default is 1, i.e. UTF-8 mode is enabled for all
4025 newly opened terminals.
4027 vt.global_cursor_default=
4028 [VT]
4029 Format=<-1|0|1>
4030 Set system-wide default for whether a cursor
4031 is shown on new VTs. Default is -1,
4032 i.e. cursors will be created by default unless
4033 overridden by individual drivers. 0 will hide
4034 cursors, 1 will display them.
4036 vt.italic= [VT] Default color for italic text; 0-15.
4037 Default: 2 = green.
4039 vt.underline= [VT] Default color for underlined text; 0-15.
4040 Default: 3 = cyan.
4042 watchdog timers [HW,WDT] For information on watchdog timers,
4043 see Documentation/watchdog/watchdog-parameters.txt
4044 or other driver-specific files in the
4045 Documentation/watchdog/ directory.
4047 workqueue.disable_numa
4048 By default, all work items queued to unbound
4049 workqueues are affine to the NUMA nodes they're
4050 issued on, which results in better behavior in
4051 general. If NUMA affinity needs to be disabled for
4052 whatever reason, this option can be used. Note
4053 that this also can be controlled per-workqueue for
4054 workqueues visible under /sys/bus/workqueue/.
4056 workqueue.power_efficient
4057 Per-cpu workqueues are generally preferred because
4058 they show better performance thanks to cache
4059 locality; unfortunately, per-cpu workqueues tend to
4060 be more power hungry than unbound workqueues.
4062 Enabling this makes the per-cpu workqueues which
4063 were observed to contribute significantly to power
4064 consumption unbound, leading to measurably lower
4065 power usage at the cost of small performance
4066 overhead.
4068 The default value of this parameter is determined by
4069 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4071 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4072 default x2apic cluster mode on platforms
4073 supporting x2apic.
4075 x86_intel_mid_timer= [X86-32,APBT]
4076 Choose timer option for x86 Intel MID platform.
4077 Two valid options are apbt timer only and lapic timer
4078 plus one apbt timer for broadcast timer.
4079 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4081 xen_emul_unplug= [HW,X86,XEN]
4082 Unplug Xen emulated devices
4083 Format: [unplug0,][unplug1]
4084 ide-disks -- unplug primary master IDE devices
4085 aux-ide-disks -- unplug non-primary-master IDE devices
4086 nics -- unplug network devices
4087 all -- unplug all emulated devices (NICs and IDE disks)
4088 unnecessary -- unplugging emulated devices is
4089 unnecessary even if the host did not respond to
4090 the unplug protocol
4091 never -- do not unplug even if version check succeeds
4093 xen_nopvspin [X86,XEN]
4094 Disables the ticketlock slowpath using Xen PV
4095 optimizations.
4097 xen_nopv [X86]
4098 Disables the PV optimizations forcing the HVM guest to
4099 run as generic HVM guest with no PV drivers.
4101 xirc2ps_cs= [NET,PCMCIA]
4102 Format:
4103 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4105 ______________________________________________________________________
4107 TODO:
4109 Add more DRM drivers.