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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_rsdp= [ACPI,EFI,KEXEC]
183 Pass the RSDP address to the kernel, mostly used
184 on machines running EFI runtime service to boot the
185 second kernel for kdump.
187 acpi_apic_instance= [ACPI, IOAPIC]
188 Format: <int>
189 2: use 2nd APIC table, if available
190 1,0: use 1st APIC table
191 default: 0
193 acpi_backlight= [HW,ACPI]
194 acpi_backlight=vendor
195 acpi_backlight=video
196 If set to vendor, prefer vendor specific driver
197 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
198 of the ACPI video.ko driver.
200 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
201 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
202 Format: <int>
203 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
204 debug output. Bits in debug_layer correspond to a
205 _COMPONENT in an ACPI source file, e.g.,
206 #define _COMPONENT ACPI_PCI_COMPONENT
207 Bits in debug_level correspond to a level in
208 ACPI_DEBUG_PRINT statements, e.g.,
209 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
210 The debug_level mask defaults to "info". See
211 Documentation/acpi/debug.txt for more information about
212 debug layers and levels.
214 Enable processor driver info messages:
215 acpi.debug_layer=0x20000000
216 Enable PCI/PCI interrupt routing info messages:
217 acpi.debug_layer=0x400000
218 Enable AML "Debug" output, i.e., stores to the Debug
219 object while interpreting AML:
220 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
221 Enable all messages related to ACPI hardware:
222 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
224 Some values produce so much output that the system is
225 unusable. The "log_buf_len" parameter may be useful
226 if you need to capture more output.
228 acpi_force_table_verification [HW,ACPI]
229 Enable table checksum verification during early stage.
230 By default, this is disabled due to x86 early mapping
231 size limitation.
233 acpi_irq_balance [HW,ACPI]
234 ACPI will balance active IRQs
235 default in APIC mode
237 acpi_irq_nobalance [HW,ACPI]
238 ACPI will not move active IRQs (default)
239 default in PIC mode
241 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
242 Format: <irq>,<irq>...
244 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
245 use by PCI
246 Format: <irq>,<irq>...
248 acpi_no_auto_serialize [HW,ACPI]
249 Disable auto-serialization of AML methods
250 AML control methods that contain the opcodes to create
251 named objects will be marked as "Serialized" by the
252 auto-serialization feature.
253 This feature is enabled by default.
254 This option allows to turn off the feature.
256 acpi_no_static_ssdt [HW,ACPI]
257 Disable installation of static SSDTs at early boot time
258 By default, SSDTs contained in the RSDT/XSDT will be
259 installed automatically and they will appear under
260 /sys/firmware/acpi/tables.
261 This option turns off this feature.
262 Note that specifying this option does not affect
263 dynamic table installation which will install SSDT
264 tables to /sys/firmware/acpi/tables/dynamic.
266 acpica_no_return_repair [HW, ACPI]
267 Disable AML predefined validation mechanism
268 This mechanism can repair the evaluation result to make
269 the return objects more ACPI specification compliant.
270 This option is useful for developers to identify the
271 root cause of an AML interpreter issue when the issue
272 has something to do with the repair mechanism.
274 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
275 Format: To spoof as Windows 98: ="Microsoft Windows"
277 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
278 acpi_osi="string1" # add string1
279 acpi_osi="!string2" # remove string2
280 acpi_osi=!* # remove all strings
281 acpi_osi=! # disable all built-in OS vendor
282 strings
283 acpi_osi= # disable all strings
285 'acpi_osi=!' can be used in combination with single or
286 multiple 'acpi_osi="string1"' to support specific OS
287 vendor string(s). Note that such command can only
288 affect the default state of the OS vendor strings, thus
289 it cannot affect the default state of the feature group
290 strings and the current state of the OS vendor strings,
291 specifying it multiple times through kernel command line
292 is meaningless. This command is useful when one do not
293 care about the state of the feature group strings which
294 should be controlled by the OSPM.
295 Examples:
296 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
297 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
298 can make '_OSI("Windows 2000")' TRUE.
300 'acpi_osi=' cannot be used in combination with other
301 'acpi_osi=' command lines, the _OSI method will not
302 exist in the ACPI namespace. NOTE that such command can
303 only affect the _OSI support state, thus specifying it
304 multiple times through kernel command line is also
305 meaningless.
306 Examples:
307 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
308 FALSE.
310 'acpi_osi=!*' can be used in combination with single or
311 multiple 'acpi_osi="string1"' to support specific
312 string(s). Note that such command can affect the
313 current state of both the OS vendor strings and the
314 feature group strings, thus specifying it multiple times
315 through kernel command line is meaningful. But it may
316 still not able to affect the final state of a string if
317 there are quirks related to this string. This command
318 is useful when one want to control the state of the
319 feature group strings to debug BIOS issues related to
320 the OSPM features.
321 Examples:
322 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
323 '_OSI("Module Device")' FALSE.
324 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
325 '_OSI("Module Device")' TRUE.
326 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
327 equivalent to
328 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
329 and
330 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
331 they all will make '_OSI("Windows 2000")' TRUE.
333 acpi_pm_good [X86]
334 Override the pmtimer bug detection: force the kernel
335 to assume that this machine's pmtimer latches its value
336 and always returns good values.
338 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
339 Format: { level | edge | high | low }
341 acpi_skip_timer_override [HW,ACPI]
342 Recognize and ignore IRQ0/pin2 Interrupt Override.
343 For broken nForce2 BIOS resulting in XT-PIC timer.
345 acpi_sleep= [HW,ACPI] Sleep options
346 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
347 old_ordering, nonvs, sci_force_enable }
348 See Documentation/power/video.txt for information on
349 s3_bios and s3_mode.
350 s3_beep is for debugging; it makes the PC's speaker beep
351 as soon as the kernel's real-mode entry point is called.
352 s4_nohwsig prevents ACPI hardware signature from being
353 used during resume from hibernation.
354 old_ordering causes the ACPI 1.0 ordering of the _PTS
355 control method, with respect to putting devices into
356 low power states, to be enforced (the ACPI 2.0 ordering
357 of _PTS is used by default).
358 nonvs prevents the kernel from saving/restoring the
359 ACPI NVS memory during suspend/hibernation and resume.
360 sci_force_enable causes the kernel to set SCI_EN directly
361 on resume from S1/S3 (which is against the ACPI spec,
362 but some broken systems don't work without it).
364 acpi_use_timer_override [HW,ACPI]
365 Use timer override. For some broken Nvidia NF5 boards
366 that require a timer override, but don't have HPET
368 acpi_enforce_resources= [ACPI]
369 { strict | lax | no }
370 Check for resource conflicts between native drivers
371 and ACPI OperationRegions (SystemIO and SystemMemory
372 only). IO ports and memory declared in ACPI might be
373 used by the ACPI subsystem in arbitrary AML code and
374 can interfere with legacy drivers.
375 strict (default): access to resources claimed by ACPI
376 is denied; legacy drivers trying to access reserved
377 resources will fail to bind to device using them.
378 lax: access to resources claimed by ACPI is allowed;
379 legacy drivers trying to access reserved resources
380 will bind successfully but a warning message is logged.
381 no: ACPI OperationRegions are not marked as reserved,
382 no further checks are performed.
384 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
385 kernels.
387 add_efi_memmap [EFI; X86] Include EFI memory map in
388 kernel's map of available physical RAM.
390 agp= [AGP]
391 { off | try_unsupported }
392 off: disable AGP support
393 try_unsupported: try to drive unsupported chipsets
394 (may crash computer or cause data corruption)
396 ALSA [HW,ALSA]
397 See Documentation/sound/alsa/alsa-parameters.txt
399 alignment= [KNL,ARM]
400 Allow the default userspace alignment fault handler
401 behaviour to be specified. Bit 0 enables warnings,
402 bit 1 enables fixups, and bit 2 sends a segfault.
404 align_va_addr= [X86-64]
405 Align virtual addresses by clearing slice [14:12] when
406 allocating a VMA at process creation time. This option
407 gives you up to 3% performance improvement on AMD F15h
408 machines (where it is enabled by default) for a
409 CPU-intensive style benchmark, and it can vary highly in
410 a microbenchmark depending on workload and compiler.
412 32: only for 32-bit processes
413 64: only for 64-bit processes
414 on: enable for both 32- and 64-bit processes
415 off: disable for both 32- and 64-bit processes
417 alloc_snapshot [FTRACE]
418 Allocate the ftrace snapshot buffer on boot up when the
419 main buffer is allocated. This is handy if debugging
420 and you need to use tracing_snapshot() on boot up, and
421 do not want to use tracing_snapshot_alloc() as it needs
422 to be done where GFP_KERNEL allocations are allowed.
424 amd_iommu= [HW,X86-64]
425 Pass parameters to the AMD IOMMU driver in the system.
426 Possible values are:
427 fullflush - enable flushing of IO/TLB entries when
428 they are unmapped. Otherwise they are
429 flushed before they will be reused, which
430 is a lot of faster
431 off - do not initialize any AMD IOMMU found in
432 the system
433 force_isolation - Force device isolation for all
434 devices. The IOMMU driver is not
435 allowed anymore to lift isolation
436 requirements as needed. This option
437 does not override iommu=pt
439 amd_iommu_dump= [HW,X86-64]
440 Enable AMD IOMMU driver option to dump the ACPI table
441 for AMD IOMMU. With this option enabled, AMD IOMMU
442 driver will print ACPI tables for AMD IOMMU during
443 IOMMU initialization.
445 amijoy.map= [HW,JOY] Amiga joystick support
446 Map of devices attached to JOY0DAT and JOY1DAT
447 Format: <a>,<b>
448 See also Documentation/input/joystick.txt
450 analog.map= [HW,JOY] Analog joystick and gamepad support
451 Specifies type or capabilities of an analog joystick
452 connected to one of 16 gameports
453 Format: <type1>,<type2>,..<type16>
455 apc= [HW,SPARC]
456 Power management functions (SPARCstation-4/5 + deriv.)
457 Format: noidle
458 Disable APC CPU standby support. SPARCstation-Fox does
459 not play well with APC CPU idle - disable it if you have
460 APC and your system crashes randomly.
462 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
463 Change the output verbosity whilst booting
464 Format: { quiet (default) | verbose | debug }
465 Change the amount of debugging information output
466 when initialising the APIC and IO-APIC components.
468 autoconf= [IPV6]
469 See Documentation/networking/ipv6.txt.
471 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
472 Limit apic dumping. The parameter defines the maximal
473 number of local apics being dumped. Also it is possible
474 to set it to "all" by meaning -- no limit here.
475 Format: { 1 (default) | 2 | ... | all }.
476 The parameter valid if only apic=debug or
477 apic=verbose is specified.
478 Example: apic=debug show_lapic=all
480 apm= [APM] Advanced Power Management
481 See header of arch/x86/kernel/apm_32.c.
483 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
484 Format: <io>,<irq>,<nodeID>
486 ataflop= [HW,M68k]
488 atarimouse= [HW,MOUSE] Atari Mouse
490 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
491 EzKey and similar keyboards
493 atkbd.reset= [HW] Reset keyboard during initialization
495 atkbd.set= [HW] Select keyboard code set
496 Format: <int> (2 = AT (default), 3 = PS/2)
498 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
499 keyboards
501 atkbd.softraw= [HW] Choose between synthetic and real raw mode
502 Format: <bool> (0 = real, 1 = synthetic (default))
504 atkbd.softrepeat= [HW]
505 Use software keyboard repeat
507 audit= [KNL] Enable the audit sub-system
508 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
509 0 - kernel audit is disabled and can not be enabled
510 until the next reboot
511 unset - kernel audit is initialized but disabled and
512 will be fully enabled by the userspace auditd.
513 1 - kernel audit is initialized and partially enabled,
514 storing at most audit_backlog_limit messages in
515 RAM until it is fully enabled by the userspace
516 auditd.
517 Default: unset
519 audit_backlog_limit= [KNL] Set the audit queue size limit.
520 Format: <int> (must be >=0)
521 Default: 64
523 baycom_epp= [HW,AX25]
524 Format: <io>,<mode>
526 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
527 Format: <io>,<mode>
528 See header of drivers/net/hamradio/baycom_par.c.
530 baycom_ser_fdx= [HW,AX25]
531 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
532 Format: <io>,<irq>,<mode>[,<baud>]
533 See header of drivers/net/hamradio/baycom_ser_fdx.c.
535 baycom_ser_hdx= [HW,AX25]
536 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
537 Format: <io>,<irq>,<mode>
538 See header of drivers/net/hamradio/baycom_ser_hdx.c.
540 blkdevparts= Manual partition parsing of block device(s) for
541 embedded devices based on command line input.
542 See Documentation/block/cmdline-partition.txt
544 boot_delay= Milliseconds to delay each printk during boot.
545 Values larger than 10 seconds (10000) are changed to
546 no delay (0).
547 Format: integer
549 bootmem_debug [KNL] Enable bootmem allocator debug messages.
551 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
552 bttv.radio= Most important insmod options are available as
553 kernel args too.
554 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
555 bttv.tuner=
557 bulk_remove=off [PPC] This parameter disables the use of the pSeries
558 firmware feature for flushing multiple hpte entries
559 at a time.
561 c101= [NET] Moxa C101 synchronous serial card
563 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
564 Sometimes CPU hardware bugs make them report the cache
565 size incorrectly. The kernel will attempt work arounds
566 to fix known problems, but for some CPUs it is not
567 possible to determine what the correct size should be.
568 This option provides an override for these situations.
570 ca_keys= [KEYS] This parameter identifies a specific key(s) on
571 the system trusted keyring to be used for certificate
572 trust validation.
573 format: { id:<keyid> | builtin }
575 cca= [MIPS] Override the kernel pages' cache coherency
576 algorithm. Accepted values range from 0 to 7
577 inclusive. See arch/mips/include/asm/pgtable-bits.h
578 for platform specific values (SB1, Loongson3 and
579 others).
581 ccw_timeout_log [S390]
582 See Documentation/s390/CommonIO for details.
584 cgroup_disable= [KNL] Disable a particular controller
585 Format: {name of the controller(s) to disable}
586 The effects of cgroup_disable=foo are:
587 - foo isn't auto-mounted if you mount all cgroups in
588 a single hierarchy
589 - foo isn't visible as an individually mountable
590 subsystem
591 {Currently only "memory" controller deal with this and
592 cut the overhead, others just disable the usage. So
593 only cgroup_disable=memory is actually worthy}
595 checkreqprot [SELINUX] Set initial checkreqprot flag value.
596 Format: { "0" | "1" }
597 See security/selinux/Kconfig help text.
598 0 -- check protection applied by kernel (includes
599 any implied execute protection).
600 1 -- check protection requested by application.
601 Default value is set via a kernel config option.
602 Value can be changed at runtime via
603 /selinux/checkreqprot.
605 cio_ignore= [S390]
606 See Documentation/s390/CommonIO for details.
607 clk_ignore_unused
608 [CLK]
609 Prevents the clock framework from automatically gating
610 clocks that have not been explicitly enabled by a Linux
611 device driver but are enabled in hardware at reset or
612 by the bootloader/firmware. Note that this does not
613 force such clocks to be always-on nor does it reserve
614 those clocks in any way. This parameter is useful for
615 debug and development, but should not be needed on a
616 platform with proper driver support. For more
617 information, see Documentation/clk.txt.
619 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
620 [Deprecated]
621 Forces specified clocksource (if available) to be used
622 when calculating gettimeofday(). If specified
623 clocksource is not available, it defaults to PIT.
624 Format: { pit | tsc | cyclone | pmtmr }
626 clocksource= Override the default clocksource
627 Format: <string>
628 Override the default clocksource and use the clocksource
629 with the name specified.
630 Some clocksource names to choose from, depending on
631 the platform:
632 [all] jiffies (this is the base, fallback clocksource)
633 [ACPI] acpi_pm
634 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
635 pxa_timer,timer3,32k_counter,timer0_1
636 [AVR32] avr32
637 [X86-32] pit,hpet,tsc;
638 scx200_hrt on Geode; cyclone on IBM x440
639 [MIPS] MIPS
640 [PARISC] cr16
641 [S390] tod
642 [SH] SuperH
643 [SPARC64] tick
644 [X86-64] hpet,tsc
646 clearcpuid=BITNUM [X86]
647 Disable CPUID feature X for the kernel. See
648 arch/x86/include/asm/cpufeature.h for the valid bit
649 numbers. Note the Linux specific bits are not necessarily
650 stable over kernel options, but the vendor specific
651 ones should be.
652 Also note that user programs calling CPUID directly
653 or using the feature without checking anything
654 will still see it. This just prevents it from
655 being used by the kernel or shown in /proc/cpuinfo.
656 Also note the kernel might malfunction if you disable
657 some critical bits.
659 cma=nn[MG]@[start[MG][-end[MG]]]
660 [ARM,X86,KNL]
661 Sets the size of kernel global memory area for
662 contiguous memory allocations and optionally the
663 placement constraint by the physical address range of
664 memory allocations. A value of 0 disables CMA
665 altogether. For more information, see
666 include/linux/dma-contiguous.h
668 cmo_free_hint= [PPC] Format: { yes | no }
669 Specify whether pages are marked as being inactive
670 when they are freed. This is used in CMO environments
671 to determine OS memory pressure for page stealing by
672 a hypervisor.
673 Default: yes
675 coherent_pool=nn[KMG] [ARM,KNL]
676 Sets the size of memory pool for coherent, atomic dma
677 allocations, by default set to 256K.
679 code_bytes [X86] How many bytes of object code to print
680 in an oops report.
681 Range: 0 - 8192
682 Default: 64
684 com20020= [HW,NET] ARCnet - COM20020 chipset
685 Format:
686 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
688 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
689 Format: <io>[,<irq>]
691 com90xx= [HW,NET]
692 ARCnet - COM90xx chipset (memory-mapped buffers)
693 Format: <io>[,<irq>[,<memstart>]]
695 condev= [HW,S390] console device
696 conmode=
698 console= [KNL] Output console device and options.
700 tty<n> Use the virtual console device <n>.
702 ttyS<n>[,options]
703 ttyUSB0[,options]
704 Use the specified serial port. The options are of
705 the form "bbbbpnf", where "bbbb" is the baud rate,
706 "p" is parity ("n", "o", or "e"), "n" is number of
707 bits, and "f" is flow control ("r" for RTS or
708 omit it). Default is "9600n8".
710 See Documentation/serial-console.txt for more
711 information. See
712 Documentation/networking/netconsole.txt for an
713 alternative.
715 uart[8250],io,<addr>[,options]
716 uart[8250],mmio,<addr>[,options]
717 uart[8250],mmio32,<addr>[,options]
718 uart[8250],0x<addr>[,options]
719 Start an early, polled-mode console on the 8250/16550
720 UART at the specified I/O port or MMIO address,
721 switching to the matching ttyS device later.
722 MMIO inter-register address stride is either 8-bit
723 (mmio) or 32-bit (mmio32).
724 If none of [io|mmio|mmio32], <addr> is assumed to be
725 equivalent to 'mmio'. 'options' are specified in the
726 same format described for ttyS above; if unspecified,
727 the h/w is not re-initialized.
729 hvc<n> Use the hypervisor console device <n>. This is for
730 both Xen and PowerPC hypervisors.
732 If the device connected to the port is not a TTY but a braille
733 device, prepend "brl," before the device type, for instance
734 console=brl,ttyS0
735 For now, only VisioBraille is supported.
737 consoleblank= [KNL] The console blank (screen saver) timeout in
738 seconds. Defaults to 10*60 = 10mins. A value of 0
739 disables the blank timer.
741 coredump_filter=
742 [KNL] Change the default value for
743 /proc/<pid>/coredump_filter.
744 See also Documentation/filesystems/proc.txt.
746 cpuidle.off=1 [CPU_IDLE]
747 disable the cpuidle sub-system
749 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
750 Format:
751 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
753 crashkernel=size[KMG][@offset[KMG]]
754 [KNL] Using kexec, Linux can switch to a 'crash kernel'
755 upon panic. This parameter reserves the physical
756 memory region [offset, offset + size] for that kernel
757 image. If '@offset' is omitted, then a suitable offset
758 is selected automatically. Check
759 Documentation/kdump/kdump.txt for further details.
761 crashkernel=range1:size1[,range2:size2,...][@offset]
762 [KNL] Same as above, but depends on the memory
763 in the running system. The syntax of range is
764 start-[end] where start and end are both
765 a memory unit (amount[KMG]). See also
766 Documentation/kdump/kdump.txt for an example.
768 crashkernel=size[KMG],high
769 [KNL, x86_64] range could be above 4G. Allow kernel
770 to allocate physical memory region from top, so could
771 be above 4G if system have more than 4G ram installed.
772 Otherwise memory region will be allocated below 4G, if
773 available.
774 It will be ignored if crashkernel=X is specified.
775 crashkernel=size[KMG],low
776 [KNL, x86_64] range under 4G. When crashkernel=X,high
777 is passed, kernel could allocate physical memory region
778 above 4G, that cause second kernel crash on system
779 that require some amount of low memory, e.g. swiotlb
780 requires at least 64M+32K low memory. Kernel would
781 try to allocate 72M below 4G automatically.
782 This one let user to specify own low range under 4G
783 for second kernel instead.
784 0: to disable low allocation.
785 It will be ignored when crashkernel=X,high is not used
786 or memory reserved is below 4G.
788 cs89x0_dma= [HW,NET]
789 Format: <dma>
791 cs89x0_media= [HW,NET]
792 Format: { rj45 | aui | bnc }
794 dasd= [HW,NET]
795 See header of drivers/s390/block/dasd_devmap.c.
797 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
798 (one device per port)
799 Format: <port#>,<type>
800 See also Documentation/input/joystick-parport.txt
802 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
803 time. See Documentation/dynamic-debug-howto.txt for
804 details. Deprecated, see dyndbg.
806 debug [KNL] Enable kernel debugging (events log level).
808 debug_locks_verbose=
809 [KNL] verbose self-tests
810 Format=<0|1>
811 Print debugging info while doing the locking API
812 self-tests.
813 We default to 0 (no extra messages), setting it to
814 1 will print _a lot_ more information - normally
815 only useful to kernel developers.
817 debug_objects [KNL] Enable object debugging
819 no_debug_objects
820 [KNL] Disable object debugging
822 debug_guardpage_minorder=
823 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
824 parameter allows control of the order of pages that will
825 be intentionally kept free (and hence protected) by the
826 buddy allocator. Bigger value increase the probability
827 of catching random memory corruption, but reduce the
828 amount of memory for normal system use. The maximum
829 possible value is MAX_ORDER/2. Setting this parameter
830 to 1 or 2 should be enough to identify most random
831 memory corruption problems caused by bugs in kernel or
832 driver code when a CPU writes to (or reads from) a
833 random memory location. Note that there exists a class
834 of memory corruptions problems caused by buggy H/W or
835 F/W or by drivers badly programing DMA (basically when
836 memory is written at bus level and the CPU MMU is
837 bypassed) which are not detectable by
838 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
839 tracking down these problems.
841 debug_pagealloc=
842 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
843 parameter enables the feature at boot time. In
844 default, it is disabled. We can avoid allocating huge
845 chunk of memory for debug pagealloc if we don't enable
846 it at boot time and the system will work mostly same
847 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
848 on: enable the feature
850 debugpat [X86] Enable PAT debugging
852 decnet.addr= [HW,NET]
853 Format: <area>[,<node>]
854 See also Documentation/networking/decnet.txt.
856 default_hugepagesz=
857 [same as hugepagesz=] The size of the default
858 HugeTLB page size. This is the size represented by
859 the legacy /proc/ hugepages APIs, used for SHM, and
860 default size when mounting hugetlbfs filesystems.
861 Defaults to the default architecture's huge page size
862 if not specified.
864 dhash_entries= [KNL]
865 Set number of hash buckets for dentry cache.
867 disable= [IPV6]
868 See Documentation/networking/ipv6.txt.
870 disable_cpu_apicid= [X86,APIC,SMP]
871 Format: <int>
872 The number of initial APIC ID for the
873 corresponding CPU to be disabled at boot,
874 mostly used for the kdump 2nd kernel to
875 disable BSP to wake up multiple CPUs without
876 causing system reset or hang due to sending
877 INIT from AP to BSP.
879 disable_ddw [PPC/PSERIES]
880 Disable Dynamic DMA Window support. Use this if
881 to workaround buggy firmware.
883 disable_ipv6= [IPV6]
884 See Documentation/networking/ipv6.txt.
886 disable_mtrr_cleanup [X86]
887 The kernel tries to adjust MTRR layout from continuous
888 to discrete, to make X server driver able to add WB
889 entry later. This parameter disables that.
891 disable_mtrr_trim [X86, Intel and AMD only]
892 By default the kernel will trim any uncacheable
893 memory out of your available memory pool based on
894 MTRR settings. This parameter disables that behavior,
895 possibly causing your machine to run very slowly.
897 disable_timer_pin_1 [X86]
898 Disable PIN 1 of APIC timer
899 Can be useful to work around chipset bugs.
901 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
902 this option disables the debugging code at boot.
904 dma_debug_entries=<number>
905 This option allows to tune the number of preallocated
906 entries for DMA-API debugging code. One entry is
907 required per DMA-API allocation. Use this if the
908 DMA-API debugging code disables itself because the
909 architectural default is too low.
911 dma_debug_driver=<driver_name>
912 With this option the DMA-API debugging driver
913 filter feature can be enabled at boot time. Just
914 pass the driver to filter for as the parameter.
915 The filter can be disabled or changed to another
916 driver later using sysfs.
918 drm_kms_helper.edid_firmware=[<connector>:]<file>
919 Broken monitors, graphic adapters and KVMs may
920 send no or incorrect EDID data sets. This parameter
921 allows to specify an EDID data set in the
922 /lib/firmware directory that is used instead.
923 Generic built-in EDID data sets are used, if one of
924 edid/1024x768.bin, edid/1280x1024.bin,
925 edid/1680x1050.bin, or edid/1920x1080.bin is given
926 and no file with the same name exists. Details and
927 instructions how to build your own EDID data are
928 available in Documentation/EDID/HOWTO.txt. An EDID
929 data set will only be used for a particular connector,
930 if its name and a colon are prepended to the EDID
931 name.
933 dscc4.setup= [NET]
935 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
936 module.dyndbg[="val"]
937 Enable debug messages at boot time. See
938 Documentation/dynamic-debug-howto.txt for details.
940 eagerfpu= [X86]
941 on enable eager fpu restore
942 off disable eager fpu restore
943 auto selects the default scheme, which automatically
944 enables eagerfpu restore for xsaveopt.
946 early_ioremap_debug [KNL]
947 Enable debug messages in early_ioremap support. This
948 is useful for tracking down temporary early mappings
949 which are not unmapped.
951 earlycon= [KNL] Output early console device and options.
953 cdns,<addr>
954 Start an early, polled-mode console on a cadence serial
955 port at the specified address. The cadence serial port
956 must already be setup and configured. Options are not
957 yet supported.
959 uart[8250],io,<addr>[,options]
960 uart[8250],mmio,<addr>[,options]
961 uart[8250],mmio32,<addr>[,options]
962 uart[8250],0x<addr>[,options]
963 Start an early, polled-mode console on the 8250/16550
964 UART at the specified I/O port or MMIO address.
965 MMIO inter-register address stride is either 8-bit
966 (mmio) or 32-bit (mmio32).
967 If none of [io|mmio|mmio32], <addr> is assumed to be
968 equivalent to 'mmio'. 'options' are specified in the
969 same format described for "console=ttyS<n>"; if
970 unspecified, the h/w is not initialized.
972 pl011,<addr>
973 Start an early, polled-mode console on a pl011 serial
974 port at the specified address. The pl011 serial port
975 must already be setup and configured. Options are not
976 yet supported.
978 msm_serial,<addr>
979 Start an early, polled-mode console on an msm serial
980 port at the specified address. The serial port
981 must already be setup and configured. Options are not
982 yet supported.
984 msm_serial_dm,<addr>
985 Start an early, polled-mode console on an msm serial
986 dm port at the specified address. The serial port
987 must already be setup and configured. Options are not
988 yet supported.
990 smh Use ARM semihosting calls for early console.
992 s3c2410,<addr>
993 s3c2412,<addr>
994 s3c2440,<addr>
995 s3c6400,<addr>
996 s5pv210,<addr>
997 exynos4210,<addr>
998 Use early console provided by serial driver available
999 on Samsung SoCs, requires selecting proper type and
1000 a correct base address of the selected UART port. The
1001 serial port must already be setup and configured.
1002 Options are not yet supported.
1004 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1005 earlyprintk=vga
1006 earlyprintk=efi
1007 earlyprintk=xen
1008 earlyprintk=serial[,ttySn[,baudrate]]
1009 earlyprintk=serial[,0x...[,baudrate]]
1010 earlyprintk=ttySn[,baudrate]
1011 earlyprintk=dbgp[debugController#]
1013 earlyprintk is useful when the kernel crashes before
1014 the normal console is initialized. It is not enabled by
1015 default because it has some cosmetic problems.
1017 Append ",keep" to not disable it when the real console
1018 takes over.
1020 Only one of vga, efi, serial, or usb debug port can
1021 be used at a time.
1023 Currently only ttyS0 and ttyS1 may be specified by
1024 name. Other I/O ports may be explicitly specified
1025 on some architectures (x86 and arm at least) by
1026 replacing ttySn with an I/O port address, like this:
1027 earlyprintk=serial,0x1008,115200
1028 You can find the port for a given device in
1029 /proc/tty/driver/serial:
1030 2: uart:ST16650V2 port:00001008 irq:18 ...
1032 Interaction with the standard serial driver is not
1033 very good.
1035 The VGA and EFI output is eventually overwritten by
1036 the real console.
1038 The xen output can only be used by Xen PV guests.
1040 edac_report= [HW,EDAC] Control how to report EDAC event
1041 Format: {"on" | "off" | "force"}
1042 on: enable EDAC to report H/W event. May be overridden
1043 by other higher priority error reporting module.
1044 off: disable H/W event reporting through EDAC.
1045 force: enforce the use of EDAC to report H/W event.
1046 default: on.
1048 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1049 ekgdboc=kbd
1051 This is designed to be used in conjunction with
1052 the boot argument: earlyprintk=vga
1054 edd= [EDD]
1055 Format: {"off" | "on" | "skip[mbr]"}
1057 efi= [EFI]
1058 Format: { "old_map", "nochunk", "noruntime", "debug" }
1059 old_map [X86-64]: switch to the old ioremap-based EFI
1060 runtime services mapping. 32-bit still uses this one by
1061 default.
1062 nochunk: disable reading files in "chunks" in the EFI
1063 boot stub, as chunking can cause problems with some
1064 firmware implementations.
1065 noruntime : disable EFI runtime services support
1066 debug: enable misc debug output
1068 efi_no_storage_paranoia [EFI; X86]
1069 Using this parameter you can use more than 50% of
1070 your efi variable storage. Use this parameter only if
1071 you are really sure that your UEFI does sane gc and
1072 fulfills the spec otherwise your board may brick.
1074 eisa_irq_edge= [PARISC,HW]
1075 See header of drivers/parisc/eisa.c.
1077 elanfreq= [X86-32]
1078 See comment before function elanfreq_setup() in
1079 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1081 elevator= [IOSCHED]
1082 Format: {"cfq" | "deadline" | "noop"}
1083 See Documentation/block/cfq-iosched.txt and
1084 Documentation/block/deadline-iosched.txt for details.
1086 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1087 Specifies physical address of start of kernel core
1088 image elf header and optionally the size. Generally
1089 kexec loader will pass this option to capture kernel.
1090 See Documentation/kdump/kdump.txt for details.
1092 enable_mtrr_cleanup [X86]
1093 The kernel tries to adjust MTRR layout from continuous
1094 to discrete, to make X server driver able to add WB
1095 entry later. This parameter enables that.
1097 enable_timer_pin_1 [X86]
1098 Enable PIN 1 of APIC timer
1099 Can be useful to work around chipset bugs
1100 (in particular on some ATI chipsets).
1101 The kernel tries to set a reasonable default.
1103 enforcing [SELINUX] Set initial enforcing status.
1104 Format: {"0" | "1"}
1105 See security/selinux/Kconfig help text.
1106 0 -- permissive (log only, no denials).
1107 1 -- enforcing (deny and log).
1108 Default value is 0.
1109 Value can be changed at runtime via /selinux/enforce.
1111 erst_disable [ACPI]
1112 Disable Error Record Serialization Table (ERST)
1113 support.
1115 ether= [HW,NET] Ethernet cards parameters
1116 This option is obsoleted by the "netdev=" option, which
1117 has equivalent usage. See its documentation for details.
1119 evm= [EVM]
1120 Format: { "fix" }
1121 Permit 'security.evm' to be updated regardless of
1122 current integrity status.
1124 failslab=
1125 fail_page_alloc=
1126 fail_make_request=[KNL]
1127 General fault injection mechanism.
1128 Format: <interval>,<probability>,<space>,<times>
1129 See also Documentation/fault-injection/.
1131 floppy= [HW]
1132 See Documentation/blockdev/floppy.txt.
1134 force_pal_cache_flush
1135 [IA-64] Avoid check_sal_cache_flush which may hang on
1136 buggy SAL_CACHE_FLUSH implementations. Using this
1137 parameter will force ia64_sal_cache_flush to call
1138 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1140 forcepae [X86-32]
1141 Forcefully enable Physical Address Extension (PAE).
1142 Many Pentium M systems disable PAE but may have a
1143 functionally usable PAE implementation.
1144 Warning: use of this parameter will taint the kernel
1145 and may cause unknown problems.
1147 ftrace=[tracer]
1148 [FTRACE] will set and start the specified tracer
1149 as early as possible in order to facilitate early
1150 boot debugging.
1152 ftrace_dump_on_oops[=orig_cpu]
1153 [FTRACE] will dump the trace buffers on oops.
1154 If no parameter is passed, ftrace will dump
1155 buffers of all CPUs, but if you pass orig_cpu, it will
1156 dump only the buffer of the CPU that triggered the
1157 oops.
1159 ftrace_filter=[function-list]
1160 [FTRACE] Limit the functions traced by the function
1161 tracer at boot up. function-list is a comma separated
1162 list of functions. This list can be changed at run
1163 time by the set_ftrace_filter file in the debugfs
1164 tracing directory.
1166 ftrace_notrace=[function-list]
1167 [FTRACE] Do not trace the functions specified in
1168 function-list. This list can be changed at run time
1169 by the set_ftrace_notrace file in the debugfs
1170 tracing directory.
1172 ftrace_graph_filter=[function-list]
1173 [FTRACE] Limit the top level callers functions traced
1174 by the function graph tracer at boot up.
1175 function-list is a comma separated list of functions
1176 that can be changed at run time by the
1177 set_graph_function file in the debugfs tracing directory.
1179 ftrace_graph_notrace=[function-list]
1180 [FTRACE] Do not trace from the functions specified in
1181 function-list. This list is a comma separated list of
1182 functions that can be changed at run time by the
1183 set_graph_notrace file in the debugfs tracing directory.
1185 gamecon.map[2|3]=
1186 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1187 support via parallel port (up to 5 devices per port)
1188 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1189 See also Documentation/input/joystick-parport.txt
1191 gamma= [HW,DRM]
1193 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1194 Format: off | on
1195 default: on
1197 gcov_persist= [GCOV] When non-zero (default), profiling data for
1198 kernel modules is saved and remains accessible via
1199 debugfs, even when the module is unloaded/reloaded.
1200 When zero, profiling data is discarded and associated
1201 debugfs files are removed at module unload time.
1203 gpt [EFI] Forces disk with valid GPT signature but
1204 invalid Protective MBR to be treated as GPT. If the
1205 primary GPT is corrupted, it enables the backup/alternate
1206 GPT to be used instead.
1208 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1209 the "Enable 0" bit of the configuration register.
1210 Format: 0 | 1
1211 Default: 0
1212 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1213 the "Enable 0" bit of the configuration register.
1214 Format: 0 | 1
1215 Default: 0
1216 grcan.select= [HW] Select which physical interface to use.
1217 Format: 0 | 1
1218 Default: 0
1219 grcan.txsize= [HW] Sets the size of the tx buffer.
1220 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1221 Default: 1024
1222 grcan.rxsize= [HW] Sets the size of the rx buffer.
1223 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1224 Default: 1024
1226 hashdist= [KNL,NUMA] Large hashes allocated during boot
1227 are distributed across NUMA nodes. Defaults on
1228 for 64-bit NUMA, off otherwise.
1229 Format: 0 | 1 (for off | on)
1231 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1233 hd= [EIDE] (E)IDE hard drive subsystem geometry
1234 Format: <cyl>,<head>,<sect>
1236 hest_disable [ACPI]
1237 Disable Hardware Error Source Table (HEST) support;
1238 corresponding firmware-first mode error processing
1239 logic will be disabled.
1241 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1242 size of <nn>. This works even on boxes that have no
1243 highmem otherwise. This also works to reduce highmem
1244 size on bigger boxes.
1246 highres= [KNL] Enable/disable high resolution timer mode.
1247 Valid parameters: "on", "off"
1248 Default: "on"
1250 hisax= [HW,ISDN]
1251 See Documentation/isdn/README.HiSax.
1253 hlt [BUGS=ARM,SH]
1255 hpet= [X86-32,HPET] option to control HPET usage
1256 Format: { enable (default) | disable | force |
1257 verbose }
1258 disable: disable HPET and use PIT instead
1259 force: allow force enabled of undocumented chips (ICH4,
1260 VIA, nVidia)
1261 verbose: show contents of HPET registers during setup
1263 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1264 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1266 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1267 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1268 On x86-64 and powerpc, this option can be specified
1269 multiple times interleaved with hugepages= to reserve
1270 huge pages of different sizes. Valid pages sizes on
1271 x86-64 are 2M (when the CPU supports "pse") and 1G
1272 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1274 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1275 terminal devices. Valid values: 0..8
1276 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1277 If specified, z/VM IUCV HVC accepts connections
1278 from listed z/VM user IDs only.
1280 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1281 hardware thread id mappings.
1282 Format: <cpu>:<hwthread>
1284 keep_bootcon [KNL]
1285 Do not unregister boot console at start. This is only
1286 useful for debugging when something happens in the window
1287 between unregistering the boot console and initializing
1288 the real console.
1290 i2c_bus= [HW] Override the default board specific I2C bus speed
1291 or register an additional I2C bus that is not
1292 registered from board initialization code.
1293 Format:
1294 <bus_id>,<clkrate>
1296 i8042.debug [HW] Toggle i8042 debug mode
1297 i8042.direct [HW] Put keyboard port into non-translated mode
1298 i8042.dumbkbd [HW] Pretend that controller can only read data from
1299 keyboard and cannot control its state
1300 (Don't attempt to blink the leds)
1301 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1302 i8042.nokbd [HW] Don't check/create keyboard port
1303 i8042.noloop [HW] Disable the AUX Loopback command while probing
1304 for the AUX port
1305 i8042.nomux [HW] Don't check presence of an active multiplexing
1306 controller
1307 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1308 controllers
1309 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1310 i8042.reset [HW] Reset the controller during init and cleanup
1311 i8042.unlock [HW] Unlock (ignore) the keylock
1312 i8042.kbdreset [HW] Reset device connected to KBD port
1314 i810= [HW,DRM]
1316 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1317 indicates that the driver is running on unsupported
1318 hardware.
1319 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1320 does not match list of supported models.
1321 i8k.power_status
1322 [HW] Report power status in /proc/i8k
1323 (disabled by default)
1324 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1325 capability is set.
1327 i915.invert_brightness=
1328 [DRM] Invert the sense of the variable that is used to
1329 set the brightness of the panel backlight. Normally a
1330 brightness value of 0 indicates backlight switched off,
1331 and the maximum of the brightness value sets the backlight
1332 to maximum brightness. If this parameter is set to 0
1333 (default) and the machine requires it, or this parameter
1334 is set to 1, a brightness value of 0 sets the backlight
1335 to maximum brightness, and the maximum of the brightness
1336 value switches the backlight off.
1337 -1 -- never invert brightness
1338 0 -- machine default
1339 1 -- force brightness inversion
1341 icn= [HW,ISDN]
1342 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1344 ide-core.nodma= [HW] (E)IDE subsystem
1345 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1346 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1347 .cdrom .chs .ignore_cable are additional options
1348 See Documentation/ide/ide.txt.
1350 ide-generic.probe-mask= [HW] (E)IDE subsystem
1351 Format: <int>
1352 Probe mask for legacy ISA IDE ports. Depending on
1353 platform up to 6 ports are supported, enabled by
1354 setting corresponding bits in the mask to 1. The
1355 default value is 0x0, which has a special meaning.
1356 On systems that have PCI, it triggers scanning the
1357 PCI bus for the first and the second port, which
1358 are then probed. On systems without PCI the value
1359 of 0x0 enables probing the two first ports as if it
1360 was 0x3.
1362 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1363 Claim all unknown PCI IDE storage controllers.
1365 idle= [X86]
1366 Format: idle=poll, idle=halt, idle=nomwait
1367 Poll forces a polling idle loop that can slightly
1368 improve the performance of waking up a idle CPU, but
1369 will use a lot of power and make the system run hot.
1370 Not recommended.
1371 idle=halt: Halt is forced to be used for CPU idle.
1372 In such case C2/C3 won't be used again.
1373 idle=nomwait: Disable mwait for CPU C-states
1375 ignore_loglevel [KNL]
1376 Ignore loglevel setting - this will print /all/
1377 kernel messages to the console. Useful for debugging.
1378 We also add it as printk module parameter, so users
1379 could change it dynamically, usually by
1380 /sys/module/printk/parameters/ignore_loglevel.
1382 ihash_entries= [KNL]
1383 Set number of hash buckets for inode cache.
1385 ima_appraise= [IMA] appraise integrity measurements
1386 Format: { "off" | "enforce" | "fix" | "log" }
1387 default: "enforce"
1389 ima_appraise_tcb [IMA]
1390 The builtin appraise policy appraises all files
1391 owned by uid=0.
1393 ima_hash= [IMA]
1394 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1395 | sha512 | ... }
1396 default: "sha1"
1398 The list of supported hash algorithms is defined
1399 in crypto/hash_info.h.
1401 ima_policy= [IMA]
1402 The builtin measurement policy to load during IMA
1403 setup. Specyfing "tcb" as the value, measures all
1404 programs exec'd, files mmap'd for exec, and all files
1405 opened with the read mode bit set by either the
1406 effective uid (euid=0) or uid=0.
1407 Format: "tcb"
1409 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1410 Load a policy which meets the needs of the Trusted
1411 Computing Base. This means IMA will measure all
1412 programs exec'd, files mmap'd for exec, and all files
1413 opened for read by uid=0.
1415 ima_template= [IMA]
1416 Select one of defined IMA measurements template formats.
1417 Formats: { "ima" | "ima-ng" }
1418 Default: "ima-ng"
1420 ima_template_fmt=
1421 [IMA] Define a custom template format.
1422 Format: { "field1|...|fieldN" }
1424 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1425 Format: <min_file_size>
1426 Set the minimal file size for using asynchronous hash.
1427 If left unspecified, ahash usage is disabled.
1429 ahash performance varies for different data sizes on
1430 different crypto accelerators. This option can be used
1431 to achieve the best performance for a particular HW.
1433 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1434 Format: <bufsize>
1435 Set hashing buffer size. Default: 4k.
1437 ahash performance varies for different chunk sizes on
1438 different crypto accelerators. This option can be used
1439 to achieve best performance for particular HW.
1441 init= [KNL]
1442 Format: <full_path>
1443 Run specified binary instead of /sbin/init as init
1444 process.
1446 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1447 for working out where the kernel is dying during
1448 startup.
1450 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1451 initcall functions. Useful for debugging built-in
1452 modules and initcalls.
1454 initrd= [BOOT] Specify the location of the initial ramdisk
1456 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1457 Format: <irq>
1459 int_pln_enable [x86] Enable power limit notification interrupt
1461 integrity_audit=[IMA]
1462 Format: { "0" | "1" }
1463 0 -- basic integrity auditing messages. (Default)
1464 1 -- additional integrity auditing messages.
1466 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1467 on
1468 Enable intel iommu driver.
1469 off
1470 Disable intel iommu driver.
1471 igfx_off [Default Off]
1472 By default, gfx is mapped as normal device. If a gfx
1473 device has a dedicated DMAR unit, the DMAR unit is
1474 bypassed by not enabling DMAR with this option. In
1475 this case, gfx device will use physical address for
1476 DMA.
1477 forcedac [x86_64]
1478 With this option iommu will not optimize to look
1479 for io virtual address below 32-bit forcing dual
1480 address cycle on pci bus for cards supporting greater
1481 than 32-bit addressing. The default is to look
1482 for translation below 32-bit and if not available
1483 then look in the higher range.
1484 strict [Default Off]
1485 With this option on every unmap_single operation will
1486 result in a hardware IOTLB flush operation as opposed
1487 to batching them for performance.
1488 sp_off [Default Off]
1489 By default, super page will be supported if Intel IOMMU
1490 has the capability. With this option, super page will
1491 not be supported.
1492 ecs_off [Default Off]
1493 By default, extended context tables will be supported if
1494 the hardware advertises that it has support both for the
1495 extended tables themselves, and also PASID support. With
1496 this option set, extended tables will not be used even
1497 on hardware which claims to support them.
1499 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1500 0 disables intel_idle and fall back on acpi_idle.
1501 1 to 6 specify maximum depth of C-state.
1503 intel_pstate= [X86]
1504 disable
1505 Do not enable intel_pstate as the default
1506 scaling driver for the supported processors
1507 force
1508 Enable intel_pstate on systems that prohibit it by default
1509 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1510 instead of acpi-cpufreq may disable platform features, such
1511 as thermal controls and power capping, that rely on ACPI
1512 P-States information being indicated to OSPM and therefore
1513 should be used with caution. This option does not work with
1514 processors that aren't supported by the intel_pstate driver
1515 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1516 no_hwp
1517 Do not enable hardware P state control (HWP)
1518 if available.
1519 hwp_only
1520 Only load intel_pstate on systems which support
1521 hardware P state control (HWP) if available.
1523 intremap= [X86-64, Intel-IOMMU]
1524 on enable Interrupt Remapping (default)
1525 off disable Interrupt Remapping
1526 nosid disable Source ID checking
1527 no_x2apic_optout
1528 BIOS x2APIC opt-out request will be ignored
1530 iomem= Disable strict checking of access to MMIO memory
1531 strict regions from userspace.
1532 relaxed
1534 iommu= [x86]
1535 off
1536 force
1537 noforce
1538 biomerge
1539 panic
1540 nopanic
1541 merge
1542 nomerge
1543 forcesac
1544 soft
1545 pt [x86, IA-64]
1546 nobypass [PPC/POWERNV]
1547 Disable IOMMU bypass, using IOMMU for PCI devices.
1550 io7= [HW] IO7 for Marvel based alpha systems
1551 See comment before marvel_specify_io7 in
1552 arch/alpha/kernel/core_marvel.c.
1554 io_delay= [X86] I/O delay method
1555 0x80
1556 Standard port 0x80 based delay
1557 0xed
1558 Alternate port 0xed based delay (needed on some systems)
1559 udelay
1560 Simple two microseconds delay
1561 none
1562 No delay
1564 ip= [IP_PNP]
1565 See Documentation/filesystems/nfs/nfsroot.txt.
1567 irqfixup [HW]
1568 When an interrupt is not handled search all handlers
1569 for it. Intended to get systems with badly broken
1570 firmware running.
1572 irqpoll [HW]
1573 When an interrupt is not handled search all handlers
1574 for it. Also check all handlers each timer
1575 interrupt. Intended to get systems with badly broken
1576 firmware running.
1578 isapnp= [ISAPNP]
1579 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1581 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1582 Format:
1583 <cpu number>,...,<cpu number>
1584 or
1585 <cpu number>-<cpu number>
1586 (must be a positive range in ascending order)
1587 or a mixture
1588 <cpu number>,...,<cpu number>-<cpu number>
1590 This option can be used to specify one or more CPUs
1591 to isolate from the general SMP balancing and scheduling
1592 algorithms. You can move a process onto or off an
1593 "isolated" CPU via the CPU affinity syscalls or cpuset.
1594 <cpu number> begins at 0 and the maximum value is
1595 "number of CPUs in system - 1".
1597 This option is the preferred way to isolate CPUs. The
1598 alternative -- manually setting the CPU mask of all
1599 tasks in the system -- can cause problems and
1600 suboptimal load balancer performance.
1602 iucv= [HW,NET]
1604 ivrs_ioapic [HW,X86_64]
1605 Provide an override to the IOAPIC-ID<->DEVICE-ID
1606 mapping provided in the IVRS ACPI table. For
1607 example, to map IOAPIC-ID decimal 10 to
1608 PCI device 00:14.0 write the parameter as:
1609 ivrs_ioapic[10]=00:14.0
1611 ivrs_hpet [HW,X86_64]
1612 Provide an override to the HPET-ID<->DEVICE-ID
1613 mapping provided in the IVRS ACPI table. For
1614 example, to map HPET-ID decimal 0 to
1615 PCI device 00:14.0 write the parameter as:
1616 ivrs_hpet[0]=00:14.0
1618 js= [HW,JOY] Analog joystick
1619 See Documentation/input/joystick.txt.
1621 kaslr/nokaslr [X86]
1622 Enable/disable kernel and module base offset ASLR
1623 (Address Space Layout Randomization) if built into
1624 the kernel. When CONFIG_HIBERNATION is selected,
1625 kASLR is disabled by default. When kASLR is enabled,
1626 hibernation will be disabled.
1628 keepinitrd [HW,ARM]
1630 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1631 specifies the amount of memory usable by the kernel
1632 for non-movable allocations. The requested amount is
1633 spread evenly throughout all nodes in the system. The
1634 remaining memory in each node is used for Movable
1635 pages. In the event, a node is too small to have both
1636 kernelcore and Movable pages, kernelcore pages will
1637 take priority and other nodes will have a larger number
1638 of Movable pages. The Movable zone is used for the
1639 allocation of pages that may be reclaimed or moved
1640 by the page migration subsystem. This means that
1641 HugeTLB pages may not be allocated from this zone.
1642 Note that allocations like PTEs-from-HighMem still
1643 use the HighMem zone if it exists, and the Normal
1644 zone if it does not.
1646 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1647 Format: <Controller#>[,poll interval]
1648 The controller # is the number of the ehci usb debug
1649 port as it is probed via PCI. The poll interval is
1650 optional and is the number seconds in between
1651 each poll cycle to the debug port in case you need
1652 the functionality for interrupting the kernel with
1653 gdb or control-c on the dbgp connection. When
1654 not using this parameter you use sysrq-g to break into
1655 the kernel debugger.
1657 kgdboc= [KGDB,HW] kgdb over consoles.
1658 Requires a tty driver that supports console polling,
1659 or a supported polling keyboard driver (non-usb).
1660 Serial only format: <serial_device>[,baud]
1661 keyboard only format: kbd
1662 keyboard and serial format: kbd,<serial_device>[,baud]
1663 Optional Kernel mode setting:
1664 kms, kbd format: kms,kbd
1665 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1667 kgdbwait [KGDB] Stop kernel execution and enter the
1668 kernel debugger at the earliest opportunity.
1670 kmac= [MIPS] korina ethernet MAC address.
1671 Configure the RouterBoard 532 series on-chip
1672 Ethernet adapter MAC address.
1674 kmemleak= [KNL] Boot-time kmemleak enable/disable
1675 Valid arguments: on, off
1676 Default: on
1677 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1678 the default is off.
1680 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1681 Valid arguments: 0, 1, 2
1682 kmemcheck=0 (disabled)
1683 kmemcheck=1 (enabled)
1684 kmemcheck=2 (one-shot mode)
1685 Default: 2 (one-shot mode)
1687 kstack=N [X86] Print N words from the kernel stack
1688 in oops dumps.
1690 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1691 Default is 0 (don't ignore, but inject #GP)
1693 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1694 KVM MMU at runtime.
1695 Default is 0 (off)
1697 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1698 Default is 1 (enabled)
1700 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1701 for all guests.
1702 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1704 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1705 (virtualized MMU) support on capable Intel chips.
1706 Default is 1 (enabled)
1708 kvm-intel.emulate_invalid_guest_state=
1709 [KVM,Intel] Enable emulation of invalid guest states
1710 Default is 0 (disabled)
1712 kvm-intel.flexpriority=
1713 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1714 Default is 1 (enabled)
1716 kvm-intel.nested=
1717 [KVM,Intel] Enable VMX nesting (nVMX).
1718 Default is 0 (disabled)
1720 kvm-intel.unrestricted_guest=
1721 [KVM,Intel] Disable unrestricted guest feature
1722 (virtualized real and unpaged mode) on capable
1723 Intel chips. Default is 1 (enabled)
1725 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1726 feature (tagged TLBs) on capable Intel chips.
1727 Default is 1 (enabled)
1729 l2cr= [PPC]
1731 l3cr= [PPC]
1733 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1734 disabled it.
1736 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1737 value for LAPIC timer one-shot implementation. Default
1738 back to the programmable timer unit in the LAPIC.
1740 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1741 in C2 power state.
1743 libata.dma= [LIBATA] DMA control
1744 libata.dma=0 Disable all PATA and SATA DMA
1745 libata.dma=1 PATA and SATA Disk DMA only
1746 libata.dma=2 ATAPI (CDROM) DMA only
1747 libata.dma=4 Compact Flash DMA only
1748 Combinations also work, so libata.dma=3 enables DMA
1749 for disks and CDROMs, but not CFs.
1751 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1752 libata.ignore_hpa=0 keep BIOS limits (default)
1753 libata.ignore_hpa=1 ignore limits, using full disk
1755 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1756 when set.
1757 Format: <int>
1759 libata.force= [LIBATA] Force configurations. The format is comma
1760 separated list of "[ID:]VAL" where ID is
1761 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1762 matching port, link or device. Basically, it matches
1763 the ATA ID string printed on console by libata. If
1764 the whole ID part is omitted, the last PORT and DEVICE
1765 values are used. If ID hasn't been specified yet, the
1766 configuration applies to all ports, links and devices.
1768 If only DEVICE is omitted, the parameter applies to
1769 the port and all links and devices behind it. DEVICE
1770 number of 0 either selects the first device or the
1771 first fan-out link behind PMP device. It does not
1772 select the host link. DEVICE number of 15 selects the
1773 host link and device attached to it.
1775 The VAL specifies the configuration to force. As long
1776 as there's no ambiguity shortcut notation is allowed.
1777 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1778 The following configurations can be forced.
1780 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1781 Any ID with matching PORT is used.
1783 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1785 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1786 udma[/][16,25,33,44,66,100,133] notation is also
1787 allowed.
1789 * [no]ncq: Turn on or off NCQ.
1791 * nohrst, nosrst, norst: suppress hard, soft
1792 and both resets.
1794 * rstonce: only attempt one reset during
1795 hot-unplug link recovery
1797 * dump_id: dump IDENTIFY data.
1799 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1801 * disable: Disable this device.
1803 If there are multiple matching configurations changing
1804 the same attribute, the last one is used.
1806 memblock=debug [KNL] Enable memblock debug messages.
1808 load_ramdisk= [RAM] List of ramdisks to load from floppy
1809 See Documentation/blockdev/ramdisk.txt.
1811 lockd.nlm_grace_period=P [NFS] Assign grace period.
1812 Format: <integer>
1814 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1815 Format: <integer>
1817 lockd.nlm_timeout=T [NFS] Assign timeout value.
1818 Format: <integer>
1820 lockd.nlm_udpport=M [NFS] Assign UDP port.
1821 Format: <integer>
1823 locktorture.nreaders_stress= [KNL]
1824 Set the number of locking read-acquisition kthreads.
1825 Defaults to being automatically set based on the
1826 number of online CPUs.
1828 locktorture.nwriters_stress= [KNL]
1829 Set the number of locking write-acquisition kthreads.
1831 locktorture.onoff_holdoff= [KNL]
1832 Set time (s) after boot for CPU-hotplug testing.
1834 locktorture.onoff_interval= [KNL]
1835 Set time (s) between CPU-hotplug operations, or
1836 zero to disable CPU-hotplug testing.
1838 locktorture.shuffle_interval= [KNL]
1839 Set task-shuffle interval (jiffies). Shuffling
1840 tasks allows some CPUs to go into dyntick-idle
1841 mode during the locktorture test.
1843 locktorture.shutdown_secs= [KNL]
1844 Set time (s) after boot system shutdown. This
1845 is useful for hands-off automated testing.
1847 locktorture.stat_interval= [KNL]
1848 Time (s) between statistics printk()s.
1850 locktorture.stutter= [KNL]
1851 Time (s) to stutter testing, for example,
1852 specifying five seconds causes the test to run for
1853 five seconds, wait for five seconds, and so on.
1854 This tests the locking primitive's ability to
1855 transition abruptly to and from idle.
1857 locktorture.torture_runnable= [BOOT]
1858 Start locktorture running at boot time.
1860 locktorture.torture_type= [KNL]
1861 Specify the locking implementation to test.
1863 locktorture.verbose= [KNL]
1864 Enable additional printk() statements.
1866 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1867 Format: <irq>
1869 loglevel= All Kernel Messages with a loglevel smaller than the
1870 console loglevel will be printed to the console. It can
1871 also be changed with klogd or other programs. The
1872 loglevels are defined as follows:
1874 0 (KERN_EMERG) system is unusable
1875 1 (KERN_ALERT) action must be taken immediately
1876 2 (KERN_CRIT) critical conditions
1877 3 (KERN_ERR) error conditions
1878 4 (KERN_WARNING) warning conditions
1879 5 (KERN_NOTICE) normal but significant condition
1880 6 (KERN_INFO) informational
1881 7 (KERN_DEBUG) debug-level messages
1883 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1884 in bytes. n must be a power of two and greater
1885 than the minimal size. The minimal size is defined
1886 by LOG_BUF_SHIFT kernel config parameter. There is
1887 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1888 that allows to increase the default size depending on
1889 the number of CPUs. See init/Kconfig for more details.
1891 logo.nologo [FB] Disables display of the built-in Linux logo.
1892 This may be used to provide more screen space for
1893 kernel log messages and is useful when debugging
1894 kernel boot problems.
1896 lp=0 [LP] Specify parallel ports to use, e.g,
1897 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1898 lp=reset first parallel port). 'lp=0' disables the
1899 lp=auto printer driver. 'lp=reset' (which can be
1900 specified in addition to the ports) causes
1901 attached printers to be reset. Using
1902 lp=port1,port2,... specifies the parallel ports
1903 to associate lp devices with, starting with
1904 lp0. A port specification may be 'none' to skip
1905 that lp device, or a parport name such as
1906 'parport0'. Specifying 'lp=auto' instead of a
1907 port specification list means that device IDs
1908 from each port should be examined, to see if
1909 an IEEE 1284-compliant printer is attached; if
1910 so, the driver will manage that printer.
1911 See also header of drivers/char/lp.c.
1913 lpj=n [KNL]
1914 Sets loops_per_jiffy to given constant, thus avoiding
1915 time-consuming boot-time autodetection (up to 250 ms per
1916 CPU). 0 enables autodetection (default). To determine
1917 the correct value for your kernel, boot with normal
1918 autodetection and see what value is printed. Note that
1919 on SMP systems the preset will be applied to all CPUs,
1920 which is likely to cause problems if your CPUs need
1921 significantly divergent settings. An incorrect value
1922 will cause delays in the kernel to be wrong, leading to
1923 unpredictable I/O errors and other breakage. Although
1924 unlikely, in the extreme case this might damage your
1925 hardware.
1927 ltpc= [NET]
1928 Format: <io>,<irq>,<dma>
1930 machvec= [IA-64] Force the use of a particular machine-vector
1931 (machvec) in a generic kernel.
1932 Example: machvec=hpzx1_swiotlb
1934 machtype= [Loongson] Share the same kernel image file between different
1935 yeeloong laptop.
1936 Example: machtype=lemote-yeeloong-2f-7inch
1938 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1939 than or equal to this physical address is ignored.
1941 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1942 should make use of. maxcpus=n : n >= 0 limits the
1943 kernel to using 'n' processors. n=0 is a special case,
1944 it is equivalent to "nosmp", which also disables
1945 the IO APIC.
1947 max_loop= [LOOP] The number of loop block devices that get
1948 (loop.max_loop) unconditionally pre-created at init time. The default
1949 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1950 of statically allocating a predefined number, loop
1951 devices can be requested on-demand with the
1952 /dev/loop-control interface.
1954 mce [X86-32] Machine Check Exception
1956 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1958 md= [HW] RAID subsystems devices and level
1959 See Documentation/md.txt.
1961 mdacon= [MDA]
1962 Format: <first>,<last>
1963 Specifies range of consoles to be captured by the MDA.
1965 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1966 Amount of memory to be used when the kernel is not able
1967 to see the whole system memory or for test.
1968 [X86] Work as limiting max address. Use together
1969 with memmap= to avoid physical address space collisions.
1970 Without memmap= PCI devices could be placed at addresses
1971 belonging to unused RAM.
1973 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1974 memory.
1976 memchunk=nn[KMG]
1977 [KNL,SH] Allow user to override the default size for
1978 per-device physically contiguous DMA buffers.
1980 memmap=exactmap [KNL,X86] Enable setting of an exact
1981 E820 memory map, as specified by the user.
1982 Such memmap=exactmap lines can be constructed based on
1983 BIOS output or other requirements. See the memmap=nn@ss
1984 option description.
1986 memmap=nn[KMG]@ss[KMG]
1987 [KNL] Force usage of a specific region of memory.
1988 Region of memory to be used is from ss to ss+nn.
1990 memmap=nn[KMG]#ss[KMG]
1991 [KNL,ACPI] Mark specific memory as ACPI data.
1992 Region of memory to be marked is from ss to ss+nn.
1994 memmap=nn[KMG]$ss[KMG]
1995 [KNL,ACPI] Mark specific memory as reserved.
1996 Region of memory to be reserved is from ss to ss+nn.
1997 Example: Exclude memory from 0x18690000-0x1869ffff
1998 memmap=64K$0x18690000
1999 or
2000 memmap=0x10000$0x18690000
2002 memmap=nn[KMG]!ss[KMG]
2003 [KNL,X86] Mark specific memory as protected.
2004 Region of memory to be used, from ss to ss+nn.
2005 The memory region may be marked as e820 type 12 (0xc)
2006 and is NVDIMM or ADR memory.
2008 memory_corruption_check=0/1 [X86]
2009 Some BIOSes seem to corrupt the first 64k of
2010 memory when doing things like suspend/resume.
2011 Setting this option will scan the memory
2012 looking for corruption. Enabling this will
2013 both detect corruption and prevent the kernel
2014 from using the memory being corrupted.
2015 However, its intended as a diagnostic tool; if
2016 repeatable BIOS-originated corruption always
2017 affects the same memory, you can use memmap=
2018 to prevent the kernel from using that memory.
2020 memory_corruption_check_size=size [X86]
2021 By default it checks for corruption in the low
2022 64k, making this memory unavailable for normal
2023 use. Use this parameter to scan for
2024 corruption in more or less memory.
2026 memory_corruption_check_period=seconds [X86]
2027 By default it checks for corruption every 60
2028 seconds. Use this parameter to check at some
2029 other rate. 0 disables periodic checking.
2031 memtest= [KNL,X86,ARM] Enable memtest
2032 Format: <integer>
2033 default : 0 <disable>
2034 Specifies the number of memtest passes to be
2035 performed. Each pass selects another test
2036 pattern from a given set of patterns. Memtest
2037 fills the memory with this pattern, validates
2038 memory contents and reserves bad memory
2039 regions that are detected.
2041 meye.*= [HW] Set MotionEye Camera parameters
2042 See Documentation/video4linux/meye.txt.
2044 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2045 Multi-Function General Purpose Timers on AMD Geode
2046 platforms.
2048 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2049 the BIOS has incorrectly applied a workaround. TinyBIOS
2050 version 0.98 is known to be affected, 0.99 fixes the
2051 problem by letting the user disable the workaround.
2053 mga= [HW,DRM]
2055 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2056 physical address is ignored.
2058 mini2440= [ARM,HW,KNL]
2059 Format:[0..2][b][c][t]
2060 Default: "0tb"
2061 MINI2440 configuration specification:
2062 0 - The attached screen is the 3.5" TFT
2063 1 - The attached screen is the 7" TFT
2064 2 - The VGA Shield is attached (1024x768)
2065 Leaving out the screen size parameter will not load
2066 the TFT driver, and the framebuffer will be left
2067 unconfigured.
2068 b - Enable backlight. The TFT backlight pin will be
2069 linked to the kernel VESA blanking code and a GPIO
2070 LED. This parameter is not necessary when using the
2071 VGA shield.
2072 c - Enable the s3c camera interface.
2073 t - Reserved for enabling touchscreen support. The
2074 touchscreen support is not enabled in the mainstream
2075 kernel as of 2.6.30, a preliminary port can be found
2076 in the "bleeding edge" mini2440 support kernel at
2077 http://repo.or.cz/w/linux-2.6/mini2440.git
2079 mminit_loglevel=
2080 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2081 parameter allows control of the logging verbosity for
2082 the additional memory initialisation checks. A value
2083 of 0 disables mminit logging and a level of 4 will
2084 log everything. Information is printed at KERN_DEBUG
2085 so loglevel=8 may also need to be specified.
2087 module.sig_enforce
2088 [KNL] When CONFIG_MODULE_SIG is set, this means that
2089 modules without (valid) signatures will fail to load.
2090 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2091 is always true, so this option does nothing.
2093 mousedev.tap_time=
2094 [MOUSE] Maximum time between finger touching and
2095 leaving touchpad surface for touch to be considered
2096 a tap and be reported as a left button click (for
2097 touchpads working in absolute mode only).
2098 Format: <msecs>
2099 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2100 reporting absolute coordinates, such as tablets
2101 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2102 reporting absolute coordinates, such as tablets
2104 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2105 is similar to kernelcore except it specifies the
2106 amount of memory used for migratable allocations.
2107 If both kernelcore and movablecore is specified,
2108 then kernelcore will be at *least* the specified
2109 value but may be more. If movablecore on its own
2110 is specified, the administrator must be careful
2111 that the amount of memory usable for all allocations
2112 is not too small.
2114 movable_node [KNL,X86] Boot-time switch to enable the effects
2115 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2117 MTD_Partition= [MTD]
2118 Format: <name>,<region-number>,<size>,<offset>
2120 MTD_Region= [MTD] Format:
2121 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2123 mtdparts= [MTD]
2124 See drivers/mtd/cmdlinepart.c.
2126 multitce=off [PPC] This parameter disables the use of the pSeries
2127 firmware feature for updating multiple TCE entries
2128 at a time.
2130 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2132 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2134 boundary - index of last SLC block on Flex-OneNAND.
2135 The remaining blocks are configured as MLC blocks.
2136 lock - Configure if Flex-OneNAND boundary should be locked.
2137 Once locked, the boundary cannot be changed.
2138 1 indicates lock status, 0 indicates unlock status.
2140 mtdset= [ARM]
2141 ARM/S3C2412 JIVE boot control
2143 See arch/arm/mach-s3c2412/mach-jive.c
2145 mtouchusb.raw_coordinates=
2146 [HW] Make the MicroTouch USB driver use raw coordinates
2147 ('y', default) or cooked coordinates ('n')
2149 mtrr_chunk_size=nn[KMG] [X86]
2150 used for mtrr cleanup. It is largest continuous chunk
2151 that could hold holes aka. UC entries.
2153 mtrr_gran_size=nn[KMG] [X86]
2154 Used for mtrr cleanup. It is granularity of mtrr block.
2155 Default is 1.
2156 Large value could prevent small alignment from
2157 using up MTRRs.
2159 mtrr_spare_reg_nr=n [X86]
2160 Format: <integer>
2161 Range: 0,7 : spare reg number
2162 Default : 1
2163 Used for mtrr cleanup. It is spare mtrr entries number.
2164 Set to 2 or more if your graphical card needs more.
2166 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2168 netdev= [NET] Network devices parameters
2169 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2170 Note that mem_start is often overloaded to mean
2171 something different and driver-specific.
2172 This usage is only documented in each driver source
2173 file if at all.
2175 nf_conntrack.acct=
2176 [NETFILTER] Enable connection tracking flow accounting
2177 0 to disable accounting
2178 1 to enable accounting
2179 Default value is 0.
2181 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2182 See Documentation/filesystems/nfs/nfsroot.txt.
2184 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2185 See Documentation/filesystems/nfs/nfsroot.txt.
2187 nfsrootdebug [NFS] enable nfsroot debugging messages.
2188 See Documentation/filesystems/nfs/nfsroot.txt.
2190 nfs.callback_tcpport=
2191 [NFS] set the TCP port on which the NFSv4 callback
2192 channel should listen.
2194 nfs.cache_getent=
2195 [NFS] sets the pathname to the program which is used
2196 to update the NFS client cache entries.
2198 nfs.cache_getent_timeout=
2199 [NFS] sets the timeout after which an attempt to
2200 update a cache entry is deemed to have failed.
2202 nfs.idmap_cache_timeout=
2203 [NFS] set the maximum lifetime for idmapper cache
2204 entries.
2206 nfs.enable_ino64=
2207 [NFS] enable 64-bit inode numbers.
2208 If zero, the NFS client will fake up a 32-bit inode
2209 number for the readdir() and stat() syscalls instead
2210 of returning the full 64-bit number.
2211 The default is to return 64-bit inode numbers.
2213 nfs.max_session_slots=
2214 [NFSv4.1] Sets the maximum number of session slots
2215 the client will attempt to negotiate with the server.
2216 This limits the number of simultaneous RPC requests
2217 that the client can send to the NFSv4.1 server.
2218 Note that there is little point in setting this
2219 value higher than the max_tcp_slot_table_limit.
2221 nfs.nfs4_disable_idmapping=
2222 [NFSv4] When set to the default of '1', this option
2223 ensures that both the RPC level authentication
2224 scheme and the NFS level operations agree to use
2225 numeric uids/gids if the mount is using the
2226 'sec=sys' security flavour. In effect it is
2227 disabling idmapping, which can make migration from
2228 legacy NFSv2/v3 systems to NFSv4 easier.
2229 Servers that do not support this mode of operation
2230 will be autodetected by the client, and it will fall
2231 back to using the idmapper.
2232 To turn off this behaviour, set the value to '0'.
2233 nfs.nfs4_unique_id=
2234 [NFS4] Specify an additional fixed unique ident-
2235 ification string that NFSv4 clients can insert into
2236 their nfs_client_id4 string. This is typically a
2237 UUID that is generated at system install time.
2239 nfs.send_implementation_id =
2240 [NFSv4.1] Send client implementation identification
2241 information in exchange_id requests.
2242 If zero, no implementation identification information
2243 will be sent.
2244 The default is to send the implementation identification
2245 information.
2247 nfs.recover_lost_locks =
2248 [NFSv4] Attempt to recover locks that were lost due
2249 to a lease timeout on the server. Please note that
2250 doing this risks data corruption, since there are
2251 no guarantees that the file will remain unchanged
2252 after the locks are lost.
2253 If you want to enable the kernel legacy behaviour of
2254 attempting to recover these locks, then set this
2255 parameter to '1'.
2256 The default parameter value of '0' causes the kernel
2257 not to attempt recovery of lost locks.
2259 nfsd.nfs4_disable_idmapping=
2260 [NFSv4] When set to the default of '1', the NFSv4
2261 server will return only numeric uids and gids to
2262 clients using auth_sys, and will accept numeric uids
2263 and gids from such clients. This is intended to ease
2264 migration from NFSv2/v3.
2266 objlayoutdriver.osd_login_prog=
2267 [NFS] [OBJLAYOUT] sets the pathname to the program which
2268 is used to automatically discover and login into new
2269 osd-targets. Please see:
2270 Documentation/filesystems/pnfs.txt for more explanations
2272 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2273 when a NMI is triggered.
2274 Format: [state][,regs][,debounce][,die]
2276 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2277 Format: [panic,][nopanic,][num]
2278 Valid num: 0 or 1
2279 0 - turn nmi_watchdog off
2280 1 - turn nmi_watchdog on
2281 When panic is specified, panic when an NMI watchdog
2282 timeout occurs (or 'nopanic' to override the opposite
2283 default).
2284 This is useful when you use a panic=... timeout and
2285 need the box quickly up again.
2287 netpoll.carrier_timeout=
2288 [NET] Specifies amount of time (in seconds) that
2289 netpoll should wait for a carrier. By default netpoll
2290 waits 4 seconds.
2292 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2293 emulation library even if a 387 maths coprocessor
2294 is present.
2296 no_console_suspend
2297 [HW] Never suspend the console
2298 Disable suspending of consoles during suspend and
2299 hibernate operations. Once disabled, debugging
2300 messages can reach various consoles while the rest
2301 of the system is being put to sleep (ie, while
2302 debugging driver suspend/resume hooks). This may
2303 not work reliably with all consoles, but is known
2304 to work with serial and VGA consoles.
2305 To facilitate more flexible debugging, we also add
2306 console_suspend, a printk module parameter to control
2307 it. Users could use console_suspend (usually
2308 /sys/module/printk/parameters/console_suspend) to
2309 turn on/off it dynamically.
2311 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2312 caches in the slab allocator. Saves per-node memory,
2313 but will impact performance.
2315 noalign [KNL,ARM]
2317 noapic [SMP,APIC] Tells the kernel to not make use of any
2318 IOAPICs that may be present in the system.
2320 noautogroup Disable scheduler automatic task group creation.
2322 nobats [PPC] Do not use BATs for mapping kernel lowmem
2323 on "Classic" PPC cores.
2325 nocache [ARM]
2327 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2329 nodelayacct [KNL] Disable per-task delay accounting
2331 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2333 nodsp [SH] Disable hardware DSP at boot time.
2335 noefi Disable EFI runtime services support.
2337 noexec [IA-64]
2339 noexec [X86]
2340 On X86-32 available only on PAE configured kernels.
2341 noexec=on: enable non-executable mappings (default)
2342 noexec=off: disable non-executable mappings
2344 nosmap [X86]
2345 Disable SMAP (Supervisor Mode Access Prevention)
2346 even if it is supported by processor.
2348 nosmep [X86]
2349 Disable SMEP (Supervisor Mode Execution Prevention)
2350 even if it is supported by processor.
2352 noexec32 [X86-64]
2353 This affects only 32-bit executables.
2354 noexec32=on: enable non-executable mappings (default)
2355 read doesn't imply executable mappings
2356 noexec32=off: disable non-executable mappings
2357 read implies executable mappings
2359 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2361 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2362 register save and restore. The kernel will only save
2363 legacy floating-point registers on task switch.
2365 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2367 noxsave [BUGS=X86] Disables x86 extended register state save
2368 and restore using xsave. The kernel will fallback to
2369 enabling legacy floating-point and sse state.
2371 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2372 register states. The kernel will fall back to use
2373 xsave to save the states. By using this parameter,
2374 performance of saving the states is degraded because
2375 xsave doesn't support modified optimization while
2376 xsaveopt supports it on xsaveopt enabled systems.
2378 noxsaves [X86] Disables xsaves and xrstors used in saving and
2379 restoring x86 extended register state in compacted
2380 form of xsave area. The kernel will fall back to use
2381 xsaveopt and xrstor to save and restore the states
2382 in standard form of xsave area. By using this
2383 parameter, xsave area per process might occupy more
2384 memory on xsaves enabled systems.
2386 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2387 wfi(ARM) instruction doesn't work correctly and not to
2388 use it. This is also useful when using JTAG debugger.
2390 no_file_caps Tells the kernel not to honor file capabilities. The
2391 only way then for a file to be executed with privilege
2392 is to be setuid root or executed by root.
2394 nohalt [IA-64] Tells the kernel not to use the power saving
2395 function PAL_HALT_LIGHT when idle. This increases
2396 power-consumption. On the positive side, it reduces
2397 interrupt wake-up latency, which may improve performance
2398 in certain environments such as networked servers or
2399 real-time systems.
2401 nohibernate [HIBERNATION] Disable hibernation and resume.
2403 nohz= [KNL] Boottime enable/disable dynamic ticks
2404 Valid arguments: on, off
2405 Default: on
2407 nohz_full= [KNL,BOOT]
2408 In kernels built with CONFIG_NO_HZ_FULL=y, set
2409 the specified list of CPUs whose tick will be stopped
2410 whenever possible. The boot CPU will be forced outside
2411 the range to maintain the timekeeping.
2412 The CPUs in this range must also be included in the
2413 rcu_nocbs= set.
2415 noiotrap [SH] Disables trapped I/O port accesses.
2417 noirqdebug [X86-32] Disables the code which attempts to detect and
2418 disable unhandled interrupt sources.
2420 no_timer_check [X86,APIC] Disables the code which tests for
2421 broken timer IRQ sources.
2423 noisapnp [ISAPNP] Disables ISA PnP code.
2425 noinitrd [RAM] Tells the kernel not to load any configured
2426 initial RAM disk.
2428 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2429 remapping.
2430 [Deprecated - use intremap=off]
2432 nointroute [IA-64]
2434 nojitter [IA-64] Disables jitter checking for ITC timers.
2436 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2438 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2439 fault handling.
2441 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2442 steal time is computed, but won't influence scheduler
2443 behaviour
2445 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2447 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2449 noltlbs [PPC] Do not use large page/tlb entries for kernel
2450 lowmem mapping on PPC40x.
2452 nomca [IA-64] Disable machine check abort handling
2454 nomce [X86-32] Machine Check Exception
2456 nomfgpt [X86-32] Disable Multi-Function General Purpose
2457 Timer usage (for AMD Geode machines).
2459 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2460 shutdown the other cpus. Instead use the REBOOT_VECTOR
2461 irq.
2463 nomodule Disable module load
2465 nopat [X86] Disable PAT (page attribute table extension of
2466 pagetables) support.
2468 norandmaps Don't use address space randomization. Equivalent to
2469 echo 0 > /proc/sys/kernel/randomize_va_space
2471 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2473 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2474 with UP alternatives
2476 nordrand [X86] Disable kernel use of the RDRAND and
2477 RDSEED instructions even if they are supported
2478 by the processor. RDRAND and RDSEED are still
2479 available to user space applications.
2481 noresume [SWSUSP] Disables resume and restores original swap
2482 space.
2484 no-scroll [VGA] Disables scrollback.
2485 This is required for the Braillex ib80-piezo Braille
2486 reader made by F.H. Papenmeier (Germany).
2488 nosbagart [IA-64]
2490 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2492 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2493 and disable the IO APIC. legacy for "maxcpus=0".
2495 nosoftlockup [KNL] Disable the soft-lockup detector.
2497 nosync [HW,M68K] Disables sync negotiation for all devices.
2499 notsc [BUGS=X86-32] Disable Time Stamp Counter
2501 nousb [USB] Disable the USB subsystem
2503 nowatchdog [KNL] Disable both lockup detectors, i.e.
2504 soft-lockup and NMI watchdog (hard-lockup).
2506 nowb [ARM]
2508 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2510 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2511 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2512 Some features depend on CPU0. Known dependencies are:
2513 1. Resume from suspend/hibernate depends on CPU0.
2514 Suspend/hibernate will fail if CPU0 is offline and you
2515 need to online CPU0 before suspend/hibernate.
2516 2. PIC interrupts also depend on CPU0. CPU0 can't be
2517 removed if a PIC interrupt is detected.
2518 It's said poweroff/reboot may depend on CPU0 on some
2519 machines although I haven't seen such issues so far
2520 after CPU0 is offline on a few tested machines.
2521 If the dependencies are under your control, you can
2522 turn on cpu0_hotplug.
2524 nptcg= [IA-64] Override max number of concurrent global TLB
2525 purges which is reported from either PAL_VM_SUMMARY or
2526 SAL PALO.
2528 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2529 could support. nr_cpus=n : n >= 1 limits the kernel to
2530 supporting 'n' processors. Later in runtime you can not
2531 use hotplug cpu feature to put more cpu back to online.
2532 just like you compile the kernel NR_CPUS=n
2534 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2536 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2537 Allowed values are enable and disable
2539 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2540 one of ['zone', 'node', 'default'] can be specified
2541 This can be set from sysctl after boot.
2542 See Documentation/sysctl/vm.txt for details.
2544 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2545 See Documentation/debugging-via-ohci1394.txt for more
2546 info.
2548 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2549 Rather than timing out after 20 ms if an EC
2550 command is not properly ACKed, override the length
2551 of the timeout. We have interrupts disabled while
2552 waiting for the ACK, so if this is set too high
2553 interrupts *may* be lost!
2555 omap_mux= [OMAP] Override bootloader pin multiplexing.
2556 Format: <mux_mode0.mode_name=value>...
2557 For example, to override I2C bus2:
2558 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2560 oprofile.timer= [HW]
2561 Use timer interrupt instead of performance counters
2563 oprofile.cpu_type= Force an oprofile cpu type
2564 This might be useful if you have an older oprofile
2565 userland or if you want common events.
2566 Format: { arch_perfmon }
2567 arch_perfmon: [X86] Force use of architectural
2568 perfmon on Intel CPUs instead of the
2569 CPU specific event set.
2570 timer: [X86] Force use of architectural NMI
2571 timer mode (see also oprofile.timer
2572 for generic hr timer mode)
2573 [s390] Force legacy basic mode sampling
2574 (report cpu_type "timer")
2576 oops=panic Always panic on oopses. Default is to just kill the
2577 process, but there is a small probability of
2578 deadlocking the machine.
2579 This will also cause panics on machine check exceptions.
2580 Useful together with panic=30 to trigger a reboot.
2582 OSS [HW,OSS]
2583 See Documentation/sound/oss/oss-parameters.txt
2585 page_owner= [KNL] Boot-time page_owner enabling option.
2586 Storage of the information about who allocated
2587 each page is disabled in default. With this switch,
2588 we can turn it on.
2589 on: enable the feature
2591 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2592 timeout > 0: seconds before rebooting
2593 timeout = 0: wait forever
2594 timeout < 0: reboot immediately
2595 Format: <timeout>
2597 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2598 on a WARN().
2600 crash_kexec_post_notifiers
2601 Run kdump after running panic-notifiers and dumping
2602 kmsg. This only for the users who doubt kdump always
2603 succeeds in any situation.
2604 Note that this also increases risks of kdump failure,
2605 because some panic notifiers can make the crashed
2606 kernel more unstable.
2608 parkbd.port= [HW] Parallel port number the keyboard adapter is
2609 connected to, default is 0.
2610 Format: <parport#>
2611 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2612 0 for XT, 1 for AT (default is AT).
2613 Format: <mode>
2615 parport= [HW,PPT] Specify parallel ports. 0 disables.
2616 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2617 Use 'auto' to force the driver to use any
2618 IRQ/DMA settings detected (the default is to
2619 ignore detected IRQ/DMA settings because of
2620 possible conflicts). You can specify the base
2621 address, IRQ, and DMA settings; IRQ and DMA
2622 should be numbers, or 'auto' (for using detected
2623 settings on that particular port), or 'nofifo'
2624 (to avoid using a FIFO even if it is detected).
2625 Parallel ports are assigned in the order they
2626 are specified on the command line, starting
2627 with parport0.
2629 parport_init_mode= [HW,PPT]
2630 Configure VIA parallel port to operate in
2631 a specific mode. This is necessary on Pegasos
2632 computer where firmware has no options for setting
2633 up parallel port mode and sets it to spp.
2634 Currently this function knows 686a and 8231 chips.
2635 Format: [spp|ps2|epp|ecp|ecpepp]
2637 pause_on_oops=
2638 Halt all CPUs after the first oops has been printed for
2639 the specified number of seconds. This is to be used if
2640 your oopses keep scrolling off the screen.
2642 pcbit= [HW,ISDN]
2644 pcd. [PARIDE]
2645 See header of drivers/block/paride/pcd.c.
2646 See also Documentation/blockdev/paride.txt.
2648 pci=option[,option...] [PCI] various PCI subsystem options:
2649 earlydump [X86] dump PCI config space before the kernel
2650 changes anything
2651 off [X86] don't probe for the PCI bus
2652 bios [X86-32] force use of PCI BIOS, don't access
2653 the hardware directly. Use this if your machine
2654 has a non-standard PCI host bridge.
2655 nobios [X86-32] disallow use of PCI BIOS, only direct
2656 hardware access methods are allowed. Use this
2657 if you experience crashes upon bootup and you
2658 suspect they are caused by the BIOS.
2659 conf1 [X86] Force use of PCI Configuration
2660 Mechanism 1.
2661 conf2 [X86] Force use of PCI Configuration
2662 Mechanism 2.
2663 noaer [PCIE] If the PCIEAER kernel config parameter is
2664 enabled, this kernel boot option can be used to
2665 disable the use of PCIE advanced error reporting.
2666 nodomains [PCI] Disable support for multiple PCI
2667 root domains (aka PCI segments, in ACPI-speak).
2668 nommconf [X86] Disable use of MMCONFIG for PCI
2669 Configuration
2670 check_enable_amd_mmconf [X86] check for and enable
2671 properly configured MMIO access to PCI
2672 config space on AMD family 10h CPU
2673 nomsi [MSI] If the PCI_MSI kernel config parameter is
2674 enabled, this kernel boot option can be used to
2675 disable the use of MSI interrupts system-wide.
2676 noioapicquirk [APIC] Disable all boot interrupt quirks.
2677 Safety option to keep boot IRQs enabled. This
2678 should never be necessary.
2679 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2680 primary IO-APIC for bridges that cannot disable
2681 boot IRQs. This fixes a source of spurious IRQs
2682 when the system masks IRQs.
2683 noioapicreroute [APIC] Disable workaround that uses the
2684 boot IRQ equivalent of an IRQ that connects to
2685 a chipset where boot IRQs cannot be disabled.
2686 The opposite of ioapicreroute.
2687 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2688 routing table. These calls are known to be buggy
2689 on several machines and they hang the machine
2690 when used, but on other computers it's the only
2691 way to get the interrupt routing table. Try
2692 this option if the kernel is unable to allocate
2693 IRQs or discover secondary PCI buses on your
2694 motherboard.
2695 rom [X86] Assign address space to expansion ROMs.
2696 Use with caution as certain devices share
2697 address decoders between ROMs and other
2698 resources.
2699 norom [X86] Do not assign address space to
2700 expansion ROMs that do not already have
2701 BIOS assigned address ranges.
2702 nobar [X86] Do not assign address space to the
2703 BARs that weren't assigned by the BIOS.
2704 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2705 assigned automatically to PCI devices. You can
2706 make the kernel exclude IRQs of your ISA cards
2707 this way.
2708 pirqaddr=0xAAAAA [X86] Specify the physical address
2709 of the PIRQ table (normally generated
2710 by the BIOS) if it is outside the
2711 F0000h-100000h range.
2712 lastbus=N [X86] Scan all buses thru bus #N. Can be
2713 useful if the kernel is unable to find your
2714 secondary buses and you want to tell it
2715 explicitly which ones they are.
2716 assign-busses [X86] Always assign all PCI bus
2717 numbers ourselves, overriding
2718 whatever the firmware may have done.
2719 usepirqmask [X86] Honor the possible IRQ mask stored
2720 in the BIOS $PIR table. This is needed on
2721 some systems with broken BIOSes, notably
2722 some HP Pavilion N5400 and Omnibook XE3
2723 notebooks. This will have no effect if ACPI
2724 IRQ routing is enabled.
2725 noacpi [X86] Do not use ACPI for IRQ routing
2726 or for PCI scanning.
2727 use_crs [X86] Use PCI host bridge window information
2728 from ACPI. On BIOSes from 2008 or later, this
2729 is enabled by default. If you need to use this,
2730 please report a bug.
2731 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2732 If you need to use this, please report a bug.
2733 routeirq Do IRQ routing for all PCI devices.
2734 This is normally done in pci_enable_device(),
2735 so this option is a temporary workaround
2736 for broken drivers that don't call it.
2737 skip_isa_align [X86] do not align io start addr, so can
2738 handle more pci cards
2739 firmware [ARM] Do not re-enumerate the bus but instead
2740 just use the configuration from the
2741 bootloader. This is currently used on
2742 IXP2000 systems where the bus has to be
2743 configured a certain way for adjunct CPUs.
2744 noearly [X86] Don't do any early type 1 scanning.
2745 This might help on some broken boards which
2746 machine check when some devices' config space
2747 is read. But various workarounds are disabled
2748 and some IOMMU drivers will not work.
2749 bfsort Sort PCI devices into breadth-first order.
2750 This sorting is done to get a device
2751 order compatible with older (<= 2.4) kernels.
2752 nobfsort Don't sort PCI devices into breadth-first order.
2753 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2754 tuning and use the BIOS-configured MPS defaults.
2755 pcie_bus_safe Set every device's MPS to the largest value
2756 supported by all devices below the root complex.
2757 pcie_bus_perf Set device MPS to the largest allowable MPS
2758 based on its parent bus. Also set MRRS (Max
2759 Read Request Size) to the largest supported
2760 value (no larger than the MPS that the device
2761 or bus can support) for best performance.
2762 pcie_bus_peer2peer Set every device's MPS to 128B, which
2763 every device is guaranteed to support. This
2764 configuration allows peer-to-peer DMA between
2765 any pair of devices, possibly at the cost of
2766 reduced performance. This also guarantees
2767 that hot-added devices will work.
2768 cbiosize=nn[KMG] The fixed amount of bus space which is
2769 reserved for the CardBus bridge's IO window.
2770 The default value is 256 bytes.
2771 cbmemsize=nn[KMG] The fixed amount of bus space which is
2772 reserved for the CardBus bridge's memory
2773 window. The default value is 64 megabytes.
2774 resource_alignment=
2775 Format:
2776 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2777 Specifies alignment and device to reassign
2778 aligned memory resources.
2779 If <order of align> is not specified,
2780 PAGE_SIZE is used as alignment.
2781 PCI-PCI bridge can be specified, if resource
2782 windows need to be expanded.
2783 ecrc= Enable/disable PCIe ECRC (transaction layer
2784 end-to-end CRC checking).
2785 bios: Use BIOS/firmware settings. This is the
2786 the default.
2787 off: Turn ECRC off
2788 on: Turn ECRC on.
2789 hpiosize=nn[KMG] The fixed amount of bus space which is
2790 reserved for hotplug bridge's IO window.
2791 Default size is 256 bytes.
2792 hpmemsize=nn[KMG] The fixed amount of bus space which is
2793 reserved for hotplug bridge's memory window.
2794 Default size is 2 megabytes.
2795 realloc= Enable/disable reallocating PCI bridge resources
2796 if allocations done by BIOS are too small to
2797 accommodate resources required by all child
2798 devices.
2799 off: Turn realloc off
2800 on: Turn realloc on
2801 realloc same as realloc=on
2802 noari do not use PCIe ARI.
2803 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2804 only look for one device below a PCIe downstream
2805 port.
2807 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2808 Management.
2809 off Disable ASPM.
2810 force Enable ASPM even on devices that claim not to support it.
2811 WARNING: Forcing ASPM on may cause system lockups.
2813 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2814 nomsi Do not use MSI for PCI Express Native Hotplug (this
2815 makes all PCIe ports use INTx for hotplug services).
2817 pcie_ports= [PCIE] PCIe ports handling:
2818 auto Ask the BIOS whether or not to use native PCIe services
2819 associated with PCIe ports (PME, hot-plug, AER). Use
2820 them only if that is allowed by the BIOS.
2821 native Use native PCIe services associated with PCIe ports
2822 unconditionally.
2823 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2824 ports driver.
2826 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2827 nomsi Do not use MSI for native PCIe PME signaling (this makes
2828 all PCIe root ports use INTx for all services).
2830 pcmv= [HW,PCMCIA] BadgePAD 4
2832 pd_ignore_unused
2833 [PM]
2834 Keep all power-domains already enabled by bootloader on,
2835 even if no driver has claimed them. This is useful
2836 for debug and development, but should not be
2837 needed on a platform with proper driver support.
2839 pd. [PARIDE]
2840 See Documentation/blockdev/paride.txt.
2842 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2843 boot time.
2844 Format: { 0 | 1 }
2845 See arch/parisc/kernel/pdc_chassis.c
2847 percpu_alloc= Select which percpu first chunk allocator to use.
2848 Currently supported values are "embed" and "page".
2849 Archs may support subset or none of the selections.
2850 See comments in mm/percpu.c for details on each
2851 allocator. This parameter is primarily for debugging
2852 and performance comparison.
2854 pf. [PARIDE]
2855 See Documentation/blockdev/paride.txt.
2857 pg. [PARIDE]
2858 See Documentation/blockdev/paride.txt.
2860 pirq= [SMP,APIC] Manual mp-table setup
2861 See Documentation/x86/i386/IO-APIC.txt.
2863 plip= [PPT,NET] Parallel port network link
2864 Format: { parport<nr> | timid | 0 }
2865 See also Documentation/parport.txt.
2867 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2868 Override pmtimer IOPort with a hex value.
2869 e.g. pmtmr=0x508
2871 pnp.debug=1 [PNP]
2872 Enable PNP debug messages (depends on the
2873 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2874 via /sys/module/pnp/parameters/debug. We always show
2875 current resource usage; turning this on also shows
2876 possible settings and some assignment information.
2878 pnpacpi= [ACPI]
2879 { off }
2881 pnpbios= [ISAPNP]
2882 { on | off | curr | res | no-curr | no-res }
2884 pnp_reserve_irq=
2885 [ISAPNP] Exclude IRQs for the autoconfiguration
2887 pnp_reserve_dma=
2888 [ISAPNP] Exclude DMAs for the autoconfiguration
2890 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2891 Ranges are in pairs (I/O port base and size).
2893 pnp_reserve_mem=
2894 [ISAPNP] Exclude memory regions for the
2895 autoconfiguration.
2896 Ranges are in pairs (memory base and size).
2898 ports= [IP_VS_FTP] IPVS ftp helper module
2899 Default is 21.
2900 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2901 may be specified.
2902 Format: <port>,<port>....
2904 print-fatal-signals=
2905 [KNL] debug: print fatal signals
2907 If enabled, warn about various signal handling
2908 related application anomalies: too many signals,
2909 too many POSIX.1 timers, fatal signals causing a
2910 coredump - etc.
2912 If you hit the warning due to signal overflow,
2913 you might want to try "ulimit -i unlimited".
2915 default: off.
2917 printk.always_kmsg_dump=
2918 Trigger kmsg_dump for cases other than kernel oops or
2919 panics
2920 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2921 default: disabled
2923 printk.time= Show timing data prefixed to each printk message line
2924 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2926 processor.max_cstate= [HW,ACPI]
2927 Limit processor to maximum C-state
2928 max_cstate=9 overrides any DMI blacklist limit.
2930 processor.nocst [HW,ACPI]
2931 Ignore the _CST method to determine C-states,
2932 instead using the legacy FADT method
2934 profile= [KNL] Enable kernel profiling via /proc/profile
2935 Format: [schedule,]<number>
2936 Param: "schedule" - profile schedule points.
2937 Param: <number> - step/bucket size as a power of 2 for
2938 statistical time based profiling.
2939 Param: "sleep" - profile D-state sleeping (millisecs).
2940 Requires CONFIG_SCHEDSTATS
2941 Param: "kvm" - profile VM exits.
2943 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2944 before loading.
2945 See Documentation/blockdev/ramdisk.txt.
2947 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2948 probe for; one of (bare|imps|exps|lifebook|any).
2949 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2950 per second.
2951 psmouse.resetafter= [HW,MOUSE]
2952 Try to reset the device after so many bad packets
2953 (0 = never).
2954 psmouse.resolution=
2955 [HW,MOUSE] Set desired mouse resolution, in dpi.
2956 psmouse.smartscroll=
2957 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2958 0 = disabled, 1 = enabled (default).
2960 pstore.backend= Specify the name of the pstore backend to use
2962 pt. [PARIDE]
2963 See Documentation/blockdev/paride.txt.
2965 pty.legacy_count=
2966 [KNL] Number of legacy pty's. Overwrites compiled-in
2967 default number.
2969 quiet [KNL] Disable most log messages
2971 r128= [HW,DRM]
2973 raid= [HW,RAID]
2974 See Documentation/md.txt.
2976 ramdisk_blocksize= [RAM]
2977 See Documentation/blockdev/ramdisk.txt.
2979 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2980 See Documentation/blockdev/ramdisk.txt.
2982 rcu_nocbs= [KNL]
2983 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2984 the specified list of CPUs to be no-callback CPUs.
2985 Invocation of these CPUs' RCU callbacks will
2986 be offloaded to "rcuox/N" kthreads created for
2987 that purpose, where "x" is "b" for RCU-bh, "p"
2988 for RCU-preempt, and "s" for RCU-sched, and "N"
2989 is the CPU number. This reduces OS jitter on the
2990 offloaded CPUs, which can be useful for HPC and
2991 real-time workloads. It can also improve energy
2992 efficiency for asymmetric multiprocessors.
2994 rcu_nocb_poll [KNL]
2995 Rather than requiring that offloaded CPUs
2996 (specified by rcu_nocbs= above) explicitly
2997 awaken the corresponding "rcuoN" kthreads,
2998 make these kthreads poll for callbacks.
2999 This improves the real-time response for the
3000 offloaded CPUs by relieving them of the need to
3001 wake up the corresponding kthread, but degrades
3002 energy efficiency by requiring that the kthreads
3003 periodically wake up to do the polling.
3005 rcutree.blimit= [KNL]
3006 Set maximum number of finished RCU callbacks to
3007 process in one batch.
3009 rcutree.gp_init_delay= [KNL]
3010 Set the number of jiffies to delay each step of
3011 RCU grace-period initialization. This only has
3012 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT is
3013 set.
3015 rcutree.rcu_fanout_leaf= [KNL]
3016 Increase the number of CPUs assigned to each
3017 leaf rcu_node structure. Useful for very large
3018 systems.
3020 rcutree.jiffies_till_sched_qs= [KNL]
3021 Set required age in jiffies for a
3022 given grace period before RCU starts
3023 soliciting quiescent-state help from
3024 rcu_note_context_switch().
3026 rcutree.jiffies_till_first_fqs= [KNL]
3027 Set delay from grace-period initialization to
3028 first attempt to force quiescent states.
3029 Units are jiffies, minimum value is zero,
3030 and maximum value is HZ.
3032 rcutree.jiffies_till_next_fqs= [KNL]
3033 Set delay between subsequent attempts to force
3034 quiescent states. Units are jiffies, minimum
3035 value is one, and maximum value is HZ.
3037 rcutree.kthread_prio= [KNL,BOOT]
3038 Set the SCHED_FIFO priority of the RCU per-CPU
3039 kthreads (rcuc/N). This value is also used for
3040 the priority of the RCU boost threads (rcub/N)
3041 and for the RCU grace-period kthreads (rcu_bh,
3042 rcu_preempt, and rcu_sched). If RCU_BOOST is
3043 set, valid values are 1-99 and the default is 1
3044 (the least-favored priority). Otherwise, when
3045 RCU_BOOST is not set, valid values are 0-99 and
3046 the default is zero (non-realtime operation).
3048 rcutree.rcu_nocb_leader_stride= [KNL]
3049 Set the number of NOCB kthread groups, which
3050 defaults to the square root of the number of
3051 CPUs. Larger numbers reduces the wakeup overhead
3052 on the per-CPU grace-period kthreads, but increases
3053 that same overhead on each group's leader.
3055 rcutree.qhimark= [KNL]
3056 Set threshold of queued RCU callbacks beyond which
3057 batch limiting is disabled.
3059 rcutree.qlowmark= [KNL]
3060 Set threshold of queued RCU callbacks below which
3061 batch limiting is re-enabled.
3063 rcutree.rcu_idle_gp_delay= [KNL]
3064 Set wakeup interval for idle CPUs that have
3065 RCU callbacks (RCU_FAST_NO_HZ=y).
3067 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3068 Set wakeup interval for idle CPUs that have
3069 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3070 Lazy RCU callbacks are those which RCU can
3071 prove do nothing more than free memory.
3073 rcutorture.cbflood_inter_holdoff= [KNL]
3074 Set holdoff time (jiffies) between successive
3075 callback-flood tests.
3077 rcutorture.cbflood_intra_holdoff= [KNL]
3078 Set holdoff time (jiffies) between successive
3079 bursts of callbacks within a given callback-flood
3080 test.
3082 rcutorture.cbflood_n_burst= [KNL]
3083 Set the number of bursts making up a given
3084 callback-flood test. Set this to zero to
3085 disable callback-flood testing.
3087 rcutorture.cbflood_n_per_burst= [KNL]
3088 Set the number of callbacks to be registered
3089 in a given burst of a callback-flood test.
3091 rcutorture.fqs_duration= [KNL]
3092 Set duration of force_quiescent_state bursts.
3094 rcutorture.fqs_holdoff= [KNL]
3095 Set holdoff time within force_quiescent_state bursts.
3097 rcutorture.fqs_stutter= [KNL]
3098 Set wait time between force_quiescent_state bursts.
3100 rcutorture.gp_exp= [KNL]
3101 Use expedited update-side primitives.
3103 rcutorture.gp_normal= [KNL]
3104 Use normal (non-expedited) update-side primitives.
3105 If both gp_exp and gp_normal are set, do both.
3106 If neither gp_exp nor gp_normal are set, still
3107 do both.
3109 rcutorture.n_barrier_cbs= [KNL]
3110 Set callbacks/threads for rcu_barrier() testing.
3112 rcutorture.nfakewriters= [KNL]
3113 Set number of concurrent RCU writers. These just
3114 stress RCU, they don't participate in the actual
3115 test, hence the "fake".
3117 rcutorture.nreaders= [KNL]
3118 Set number of RCU readers.
3120 rcutorture.object_debug= [KNL]
3121 Enable debug-object double-call_rcu() testing.
3123 rcutorture.onoff_holdoff= [KNL]
3124 Set time (s) after boot for CPU-hotplug testing.
3126 rcutorture.onoff_interval= [KNL]
3127 Set time (s) between CPU-hotplug operations, or
3128 zero to disable CPU-hotplug testing.
3130 rcutorture.torture_runnable= [BOOT]
3131 Start rcutorture running at boot time.
3133 rcutorture.shuffle_interval= [KNL]
3134 Set task-shuffle interval (s). Shuffling tasks
3135 allows some CPUs to go into dyntick-idle mode
3136 during the rcutorture test.
3138 rcutorture.shutdown_secs= [KNL]
3139 Set time (s) after boot system shutdown. This
3140 is useful for hands-off automated testing.
3142 rcutorture.stall_cpu= [KNL]
3143 Duration of CPU stall (s) to test RCU CPU stall
3144 warnings, zero to disable.
3146 rcutorture.stall_cpu_holdoff= [KNL]
3147 Time to wait (s) after boot before inducing stall.
3149 rcutorture.stat_interval= [KNL]
3150 Time (s) between statistics printk()s.
3152 rcutorture.stutter= [KNL]
3153 Time (s) to stutter testing, for example, specifying
3154 five seconds causes the test to run for five seconds,
3155 wait for five seconds, and so on. This tests RCU's
3156 ability to transition abruptly to and from idle.
3158 rcutorture.test_boost= [KNL]
3159 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3160 "Maybe" means test if the RCU implementation
3161 under test support RCU priority boosting.
3163 rcutorture.test_boost_duration= [KNL]
3164 Duration (s) of each individual boost test.
3166 rcutorture.test_boost_interval= [KNL]
3167 Interval (s) between each boost test.
3169 rcutorture.test_no_idle_hz= [KNL]
3170 Test RCU's dyntick-idle handling. See also the
3171 rcutorture.shuffle_interval parameter.
3173 rcutorture.torture_type= [KNL]
3174 Specify the RCU implementation to test.
3176 rcutorture.verbose= [KNL]
3177 Enable additional printk() statements.
3179 rcupdate.rcu_expedited= [KNL]
3180 Use expedited grace-period primitives, for
3181 example, synchronize_rcu_expedited() instead
3182 of synchronize_rcu(). This reduces latency,
3183 but can increase CPU utilization, degrade
3184 real-time latency, and degrade energy efficiency.
3186 rcupdate.rcu_cpu_stall_suppress= [KNL]
3187 Suppress RCU CPU stall warning messages.
3189 rcupdate.rcu_cpu_stall_timeout= [KNL]
3190 Set timeout for RCU CPU stall warning messages.
3192 rcupdate.rcu_task_stall_timeout= [KNL]
3193 Set timeout in jiffies for RCU task stall warning
3194 messages. Disable with a value less than or equal
3195 to zero.
3197 rcupdate.rcu_self_test= [KNL]
3198 Run the RCU early boot self tests
3200 rcupdate.rcu_self_test_bh= [KNL]
3201 Run the RCU bh early boot self tests
3203 rcupdate.rcu_self_test_sched= [KNL]
3204 Run the RCU sched early boot self tests
3206 rdinit= [KNL]
3207 Format: <full_path>
3208 Run specified binary instead of /init from the ramdisk,
3209 used for early userspace startup. See initrd.
3211 reboot= [KNL]
3212 Format (x86 or x86_64):
3213 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3214 [[,]s[mp]#### \
3215 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3216 [[,]f[orce]
3217 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3218 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3219 reboot_force is either force or not specified,
3220 reboot_cpu is s[mp]#### with #### being the processor
3221 to be used for rebooting.
3223 relax_domain_level=
3224 [KNL, SMP] Set scheduler's default relax_domain_level.
3225 See Documentation/cgroups/cpusets.txt.
3227 relative_sleep_states=
3228 [SUSPEND] Use sleep state labeling where the deepest
3229 state available other than hibernation is always "mem".
3230 Format: { "0" | "1" }
3231 0 -- Traditional sleep state labels.
3232 1 -- Relative sleep state labels.
3234 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3236 reservetop= [X86-32]
3237 Format: nn[KMG]
3238 Reserves a hole at the top of the kernel virtual
3239 address space.
3241 reservelow= [X86]
3242 Format: nn[K]
3243 Set the amount of memory to reserve for BIOS at
3244 the bottom of the address space.
3246 reset_devices [KNL] Force drivers to reset the underlying device
3247 during initialization.
3249 resume= [SWSUSP]
3250 Specify the partition device for software suspend
3251 Format:
3252 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3254 resume_offset= [SWSUSP]
3255 Specify the offset from the beginning of the partition
3256 given by "resume=" at which the swap header is located,
3257 in <PAGE_SIZE> units (needed only for swap files).
3258 See Documentation/power/swsusp-and-swap-files.txt
3260 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3261 read the resume files
3263 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3264 Useful for devices that are detected asynchronously
3265 (e.g. USB and MMC devices).
3267 hibernate= [HIBERNATION]
3268 noresume Don't check if there's a hibernation image
3269 present during boot.
3270 nocompress Don't compress/decompress hibernation images.
3271 no Disable hibernation and resume.
3273 retain_initrd [RAM] Keep initrd memory after extraction
3275 rfkill.default_state=
3276 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3277 etc. communication is blocked by default.
3278 1 Unblocked.
3280 rfkill.master_switch_mode=
3281 0 The "airplane mode" button does nothing.
3282 1 The "airplane mode" button toggles between everything
3283 blocked and the previous configuration.
3284 2 The "airplane mode" button toggles between everything
3285 blocked and everything unblocked.
3287 rhash_entries= [KNL,NET]
3288 Set number of hash buckets for route cache
3290 ro [KNL] Mount root device read-only on boot
3292 root= [KNL] Root filesystem
3293 See name_to_dev_t comment in init/do_mounts.c.
3295 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3296 mount the root filesystem
3298 rootflags= [KNL] Set root filesystem mount option string
3300 rootfstype= [KNL] Set root filesystem type
3302 rootwait [KNL] Wait (indefinitely) for root device to show up.
3303 Useful for devices that are detected asynchronously
3304 (e.g. USB and MMC devices).
3306 rproc_mem=nn[KMG][@address]
3307 [KNL,ARM,CMA] Remoteproc physical memory block.
3308 Memory area to be used by remote processor image,
3309 managed by CMA.
3311 rw [KNL] Mount root device read-write on boot
3313 S [KNL] Run init in single mode
3315 s390_iommu= [HW,S390]
3316 Set s390 IOTLB flushing mode
3317 strict
3318 With strict flushing every unmap operation will result in
3319 an IOTLB flush. Default is lazy flushing before reuse,
3320 which is faster.
3322 sa1100ir [NET]
3323 See drivers/net/irda/sa1100_ir.c.
3325 sbni= [NET] Granch SBNI12 leased line adapter
3327 sched_debug [KNL] Enables verbose scheduler debug messages.
3329 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3330 xtime_lock contention on larger systems, and/or RCU lock
3331 contention on all systems with CONFIG_MAXSMP set.
3332 Format: { "0" | "1" }
3333 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3334 1 -- enable.
3335 Note: increases power consumption, thus should only be
3336 enabled if running jitter sensitive (HPC/RT) workloads.
3338 security= [SECURITY] Choose a security module to enable at boot.
3339 If this boot parameter is not specified, only the first
3340 security module asking for security registration will be
3341 loaded. An invalid security module name will be treated
3342 as if no module has been chosen.
3344 selinux= [SELINUX] Disable or enable SELinux at boot time.
3345 Format: { "0" | "1" }
3346 See security/selinux/Kconfig help text.
3347 0 -- disable.
3348 1 -- enable.
3349 Default value is set via kernel config option.
3350 If enabled at boot time, /selinux/disable can be used
3351 later to disable prior to initial policy load.
3353 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3354 Format: { "0" | "1" }
3355 See security/apparmor/Kconfig help text
3356 0 -- disable.
3357 1 -- enable.
3358 Default value is set via kernel config option.
3360 serialnumber [BUGS=X86-32]
3362 shapers= [NET]
3363 Maximal number of shapers.
3365 show_msr= [x86] show boot-time MSR settings
3366 Format: { <integer> }
3367 Show boot-time (BIOS-initialized) MSR settings.
3368 The parameter means the number of CPUs to show,
3369 for example 1 means boot CPU only.
3371 simeth= [IA-64]
3372 simscsi=
3374 slram= [HW,MTD]
3376 slab_nomerge [MM]
3377 Disable merging of slabs with similar size. May be
3378 necessary if there is some reason to distinguish
3379 allocs to different slabs. Debug options disable
3380 merging on their own.
3381 For more information see Documentation/vm/slub.txt.
3383 slab_max_order= [MM, SLAB]
3384 Determines the maximum allowed order for slabs.
3385 A high setting may cause OOMs due to memory
3386 fragmentation. Defaults to 1 for systems with
3387 more than 32MB of RAM, 0 otherwise.
3389 slub_debug[=options[,slabs]] [MM, SLUB]
3390 Enabling slub_debug allows one to determine the
3391 culprit if slab objects become corrupted. Enabling
3392 slub_debug can create guard zones around objects and
3393 may poison objects when not in use. Also tracks the
3394 last alloc / free. For more information see
3395 Documentation/vm/slub.txt.
3397 slub_max_order= [MM, SLUB]
3398 Determines the maximum allowed order for slabs.
3399 A high setting may cause OOMs due to memory
3400 fragmentation. For more information see
3401 Documentation/vm/slub.txt.
3403 slub_min_objects= [MM, SLUB]
3404 The minimum number of objects per slab. SLUB will
3405 increase the slab order up to slub_max_order to
3406 generate a sufficiently large slab able to contain
3407 the number of objects indicated. The higher the number
3408 of objects the smaller the overhead of tracking slabs
3409 and the less frequently locks need to be acquired.
3410 For more information see Documentation/vm/slub.txt.
3412 slub_min_order= [MM, SLUB]
3413 Determines the minimum page order for slabs. Must be
3414 lower than slub_max_order.
3415 For more information see Documentation/vm/slub.txt.
3417 slub_nomerge [MM, SLUB]
3418 Same with slab_nomerge. This is supported for legacy.
3419 See slab_nomerge for more information.
3421 smart2= [HW]
3422 Format: <io1>[,<io2>[,...,<io8>]]
3424 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3425 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3426 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3427 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3428 smsc-ircc2.ircc_irq= [HW] IRQ line
3429 smsc-ircc2.ircc_dma= [HW] DMA channel
3430 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3431 0: Toshiba Satellite 1800 (GP data pin select)
3432 1: Fast pin select (default)
3433 2: ATC IRMode
3435 softlockup_panic=
3436 [KNL] Should the soft-lockup detector generate panics.
3437 Format: <integer>
3439 softlockup_all_cpu_backtrace=
3440 [KNL] Should the soft-lockup detector generate
3441 backtraces on all cpus.
3442 Format: <integer>
3444 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3445 See Documentation/laptops/sonypi.txt
3447 spia_io_base= [HW,MTD]
3448 spia_fio_base=
3449 spia_pedr=
3450 spia_peddr=
3452 stacktrace [FTRACE]
3453 Enabled the stack tracer on boot up.
3455 stacktrace_filter=[function-list]
3456 [FTRACE] Limit the functions that the stack tracer
3457 will trace at boot up. function-list is a comma separated
3458 list of functions. This list can be changed at run
3459 time by the stack_trace_filter file in the debugfs
3460 tracing directory. Note, this enables stack tracing
3461 and the stacktrace above is not needed.
3463 sti= [PARISC,HW]
3464 Format: <num>
3465 Set the STI (builtin display/keyboard on the HP-PARISC
3466 machines) console (graphic card) which should be used
3467 as the initial boot-console.
3468 See also comment in drivers/video/console/sticore.c.
3470 sti_font= [HW]
3471 See comment in drivers/video/console/sticore.c.
3473 stifb= [HW]
3474 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3476 sunrpc.min_resvport=
3477 sunrpc.max_resvport=
3478 [NFS,SUNRPC]
3479 SunRPC servers often require that client requests
3480 originate from a privileged port (i.e. a port in the
3481 range 0 < portnr < 1024).
3482 An administrator who wishes to reserve some of these
3483 ports for other uses may adjust the range that the
3484 kernel's sunrpc client considers to be privileged
3485 using these two parameters to set the minimum and
3486 maximum port values.
3488 sunrpc.pool_mode=
3489 [NFS]
3490 Control how the NFS server code allocates CPUs to
3491 service thread pools. Depending on how many NICs
3492 you have and where their interrupts are bound, this
3493 option will affect which CPUs will do NFS serving.
3494 Note: this parameter cannot be changed while the
3495 NFS server is running.
3497 auto the server chooses an appropriate mode
3498 automatically using heuristics
3499 global a single global pool contains all CPUs
3500 percpu one pool for each CPU
3501 pernode one pool for each NUMA node (equivalent
3502 to global on non-NUMA machines)
3504 sunrpc.tcp_slot_table_entries=
3505 sunrpc.udp_slot_table_entries=
3506 [NFS,SUNRPC]
3507 Sets the upper limit on the number of simultaneous
3508 RPC calls that can be sent from the client to a
3509 server. Increasing these values may allow you to
3510 improve throughput, but will also increase the
3511 amount of memory reserved for use by the client.
3513 suspend.pm_test_delay=
3514 [SUSPEND]
3515 Sets the number of seconds to remain in a suspend test
3516 mode before resuming the system (see
3517 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3518 is set. Default value is 5.
3520 swapaccount=[0|1]
3521 [KNL] Enable accounting of swap in memory resource
3522 controller if no parameter or 1 is given or disable
3523 it if 0 is given (See Documentation/cgroups/memory.txt)
3525 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3526 Format: { <int> | force }
3527 <int> -- Number of I/O TLB slabs
3528 force -- force using of bounce buffers even if they
3529 wouldn't be automatically used by the kernel
3531 switches= [HW,M68k]
3533 sysfs.deprecated=0|1 [KNL]
3534 Enable/disable old style sysfs layout for old udev
3535 on older distributions. When this option is enabled
3536 very new udev will not work anymore. When this option
3537 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3538 in older udev will not work anymore.
3539 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3540 the kernel configuration.
3542 sysrq_always_enabled
3543 [KNL]
3544 Ignore sysrq setting - this boot parameter will
3545 neutralize any effect of /proc/sys/kernel/sysrq.
3546 Useful for debugging.
3548 tcpmhash_entries= [KNL,NET]
3549 Set the number of tcp_metrics_hash slots.
3550 Default value is 8192 or 16384 depending on total
3551 ram pages. This is used to specify the TCP metrics
3552 cache size. See Documentation/networking/ip-sysctl.txt
3553 "tcp_no_metrics_save" section for more details.
3555 tdfx= [HW,DRM]
3557 test_suspend= [SUSPEND][,N]
3558 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3559 standby suspend) or "freeze" (for suspend type freeze)
3560 as the system sleep state during system startup with
3561 the optional capability to repeat N number of times.
3562 The system is woken from this state using a
3563 wakeup-capable RTC alarm.
3565 thash_entries= [KNL,NET]
3566 Set number of hash buckets for TCP connection
3568 thermal.act= [HW,ACPI]
3569 -1: disable all active trip points in all thermal zones
3570 <degrees C>: override all lowest active trip points
3572 thermal.crt= [HW,ACPI]
3573 -1: disable all critical trip points in all thermal zones
3574 <degrees C>: override all critical trip points
3576 thermal.nocrt= [HW,ACPI]
3577 Set to disable actions on ACPI thermal zone
3578 critical and hot trip points.
3580 thermal.off= [HW,ACPI]
3581 1: disable ACPI thermal control
3583 thermal.psv= [HW,ACPI]
3584 -1: disable all passive trip points
3585 <degrees C>: override all passive trip points to this
3586 value
3588 thermal.tzp= [HW,ACPI]
3589 Specify global default ACPI thermal zone polling rate
3590 <deci-seconds>: poll all this frequency
3591 0: no polling (default)
3593 threadirqs [KNL]
3594 Force threading of all interrupt handlers except those
3595 marked explicitly IRQF_NO_THREAD.
3597 tmem [KNL,XEN]
3598 Enable the Transcendent memory driver if built-in.
3600 tmem.cleancache=0|1 [KNL, XEN]
3601 Default is on (1). Disable the usage of the cleancache
3602 API to send anonymous pages to the hypervisor.
3604 tmem.frontswap=0|1 [KNL, XEN]
3605 Default is on (1). Disable the usage of the frontswap
3606 API to send swap pages to the hypervisor. If disabled
3607 the selfballooning and selfshrinking are force disabled.
3609 tmem.selfballooning=0|1 [KNL, XEN]
3610 Default is on (1). Disable the driving of swap pages
3611 to the hypervisor.
3613 tmem.selfshrinking=0|1 [KNL, XEN]
3614 Default is on (1). Partial swapoff that immediately
3615 transfers pages from Xen hypervisor back to the
3616 kernel based on different criteria.
3618 topology= [S390]
3619 Format: {off | on}
3620 Specify if the kernel should make use of the cpu
3621 topology information if the hardware supports this.
3622 The scheduler will make use of this information and
3623 e.g. base its process migration decisions on it.
3624 Default is on.
3626 topology_updates= [KNL, PPC, NUMA]
3627 Format: {off}
3628 Specify if the kernel should ignore (off)
3629 topology updates sent by the hypervisor to this
3630 LPAR.
3632 tp720= [HW,PS2]
3634 tpm_suspend_pcr=[HW,TPM]
3635 Format: integer pcr id
3636 Specify that at suspend time, the tpm driver
3637 should extend the specified pcr with zeros,
3638 as a workaround for some chips which fail to
3639 flush the last written pcr on TPM_SaveState.
3640 This will guarantee that all the other pcrs
3641 are saved.
3643 trace_buf_size=nn[KMG]
3644 [FTRACE] will set tracing buffer size on each cpu.
3646 trace_event=[event-list]
3647 [FTRACE] Set and start specified trace events in order
3648 to facilitate early boot debugging.
3649 See also Documentation/trace/events.txt
3651 trace_options=[option-list]
3652 [FTRACE] Enable or disable tracer options at boot.
3653 The option-list is a comma delimited list of options
3654 that can be enabled or disabled just as if you were
3655 to echo the option name into
3657 /sys/kernel/debug/tracing/trace_options
3659 For example, to enable stacktrace option (to dump the
3660 stack trace of each event), add to the command line:
3662 trace_options=stacktrace
3664 See also Documentation/trace/ftrace.txt "trace options"
3665 section.
3667 tp_printk[FTRACE]
3668 Have the tracepoints sent to printk as well as the
3669 tracing ring buffer. This is useful for early boot up
3670 where the system hangs or reboots and does not give the
3671 option for reading the tracing buffer or performing a
3672 ftrace_dump_on_oops.
3674 To turn off having tracepoints sent to printk,
3675 echo 0 > /proc/sys/kernel/tracepoint_printk
3676 Note, echoing 1 into this file without the
3677 tracepoint_printk kernel cmdline option has no effect.
3679 ** CAUTION **
3681 Having tracepoints sent to printk() and activating high
3682 frequency tracepoints such as irq or sched, can cause
3683 the system to live lock.
3685 traceoff_on_warning
3686 [FTRACE] enable this option to disable tracing when a
3687 warning is hit. This turns off "tracing_on". Tracing can
3688 be enabled again by echoing '1' into the "tracing_on"
3689 file located in /sys/kernel/debug/tracing/
3691 This option is useful, as it disables the trace before
3692 the WARNING dump is called, which prevents the trace to
3693 be filled with content caused by the warning output.
3695 This option can also be set at run time via the sysctl
3696 option: kernel/traceoff_on_warning
3698 transparent_hugepage=
3699 [KNL]
3700 Format: [always|madvise|never]
3701 Can be used to control the default behavior of the system
3702 with respect to transparent hugepages.
3703 See Documentation/vm/transhuge.txt for more details.
3705 tsc= Disable clocksource stability checks for TSC.
3706 Format: <string>
3707 [x86] reliable: mark tsc clocksource as reliable, this
3708 disables clocksource verification at runtime, as well
3709 as the stability checks done at bootup. Used to enable
3710 high-resolution timer mode on older hardware, and in
3711 virtualized environment.
3712 [x86] noirqtime: Do not use TSC to do irq accounting.
3713 Used to run time disable IRQ_TIME_ACCOUNTING on any
3714 platforms where RDTSC is slow and this accounting
3715 can add overhead.
3717 turbografx.map[2|3]= [HW,JOY]
3718 TurboGraFX parallel port interface
3719 Format:
3720 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3721 See also Documentation/input/joystick-parport.txt
3723 udbg-immortal [PPC] When debugging early kernel crashes that
3724 happen after console_init() and before a proper
3725 console driver takes over, this boot options might
3726 help "seeing" what's going on.
3728 uhash_entries= [KNL,NET]
3729 Set number of hash buckets for UDP/UDP-Lite connections
3731 uhci-hcd.ignore_oc=
3732 [USB] Ignore overcurrent events (default N).
3733 Some badly-designed motherboards generate lots of
3734 bogus events, for ports that aren't wired to
3735 anything. Set this parameter to avoid log spamming.
3736 Note that genuine overcurrent events won't be
3737 reported either.
3739 unknown_nmi_panic
3740 [X86] Cause panic on unknown NMI.
3742 usbcore.authorized_default=
3743 [USB] Default USB device authorization:
3744 (default -1 = authorized except for wireless USB,
3745 0 = not authorized, 1 = authorized)
3747 usbcore.autosuspend=
3748 [USB] The autosuspend time delay (in seconds) used
3749 for newly-detected USB devices (default 2). This
3750 is the time required before an idle device will be
3751 autosuspended. Devices for which the delay is set
3752 to a negative value won't be autosuspended at all.
3754 usbcore.usbfs_snoop=
3755 [USB] Set to log all usbfs traffic (default 0 = off).
3757 usbcore.blinkenlights=
3758 [USB] Set to cycle leds on hubs (default 0 = off).
3760 usbcore.old_scheme_first=
3761 [USB] Start with the old device initialization
3762 scheme (default 0 = off).
3764 usbcore.usbfs_memory_mb=
3765 [USB] Memory limit (in MB) for buffers allocated by
3766 usbfs (default = 16, 0 = max = 2047).
3768 usbcore.use_both_schemes=
3769 [USB] Try the other device initialization scheme
3770 if the first one fails (default 1 = enabled).
3772 usbcore.initial_descriptor_timeout=
3773 [USB] Specifies timeout for the initial 64-byte
3774 USB_REQ_GET_DESCRIPTOR request in milliseconds
3775 (default 5000 = 5.0 seconds).
3777 usbhid.mousepoll=
3778 [USBHID] The interval which mice are to be polled at.
3780 usb-storage.delay_use=
3781 [UMS] The delay in seconds before a new device is
3782 scanned for Logical Units (default 1).
3784 usb-storage.quirks=
3785 [UMS] A list of quirks entries to supplement or
3786 override the built-in unusual_devs list. List
3787 entries are separated by commas. Each entry has
3788 the form VID:PID:Flags where VID and PID are Vendor
3789 and Product ID values (4-digit hex numbers) and
3790 Flags is a set of characters, each corresponding
3791 to a common usb-storage quirk flag as follows:
3792 a = SANE_SENSE (collect more than 18 bytes
3793 of sense data);
3794 b = BAD_SENSE (don't collect more than 18
3795 bytes of sense data);
3796 c = FIX_CAPACITY (decrease the reported
3797 device capacity by one sector);
3798 d = NO_READ_DISC_INFO (don't use
3799 READ_DISC_INFO command);
3800 e = NO_READ_CAPACITY_16 (don't use
3801 READ_CAPACITY_16 command);
3802 f = NO_REPORT_OPCODES (don't use report opcodes
3803 command, uas only);
3804 g = MAX_SECTORS_240 (don't transfer more than
3805 240 sectors at a time, uas only);
3806 h = CAPACITY_HEURISTICS (decrease the
3807 reported device capacity by one
3808 sector if the number is odd);
3809 i = IGNORE_DEVICE (don't bind to this
3810 device);
3811 l = NOT_LOCKABLE (don't try to lock and
3812 unlock ejectable media);
3813 m = MAX_SECTORS_64 (don't transfer more
3814 than 64 sectors = 32 KB at a time);
3815 n = INITIAL_READ10 (force a retry of the
3816 initial READ(10) command);
3817 o = CAPACITY_OK (accept the capacity
3818 reported by the device);
3819 p = WRITE_CACHE (the device cache is ON
3820 by default);
3821 r = IGNORE_RESIDUE (the device reports
3822 bogus residue values);
3823 s = SINGLE_LUN (the device has only one
3824 Logical Unit);
3825 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3826 commands, uas only);
3827 u = IGNORE_UAS (don't bind to the uas driver);
3828 w = NO_WP_DETECT (don't test whether the
3829 medium is write-protected).
3830 Example: quirks=0419:aaf5:rl,0421:0433:rc
3832 user_debug= [KNL,ARM]
3833 Format: <int>
3834 See arch/arm/Kconfig.debug help text.
3835 1 - undefined instruction events
3836 2 - system calls
3837 4 - invalid data aborts
3838 8 - SIGSEGV faults
3839 16 - SIGBUS faults
3840 Example: user_debug=31
3842 userpte=
3843 [X86] Flags controlling user PTE allocations.
3845 nohigh = do not allocate PTE pages in
3846 HIGHMEM regardless of setting
3847 of CONFIG_HIGHPTE.
3849 vdso= [X86,SH]
3850 On X86_32, this is an alias for vdso32=. Otherwise:
3852 vdso=1: enable VDSO (the default)
3853 vdso=0: disable VDSO mapping
3855 vdso32= [X86] Control the 32-bit vDSO
3856 vdso32=1: enable 32-bit VDSO
3857 vdso32=0 or vdso32=2: disable 32-bit VDSO
3859 See the help text for CONFIG_COMPAT_VDSO for more
3860 details. If CONFIG_COMPAT_VDSO is set, the default is
3861 vdso32=0; otherwise, the default is vdso32=1.
3863 For compatibility with older kernels, vdso32=2 is an
3864 alias for vdso32=0.
3866 Try vdso32=0 if you encounter an error that says:
3867 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3869 vector= [IA-64,SMP]
3870 vector=percpu: enable percpu vector domain
3872 video= [FB] Frame buffer configuration
3873 See Documentation/fb/modedb.txt.
3875 video.brightness_switch_enabled= [0,1]
3876 If set to 1, on receiving an ACPI notify event
3877 generated by hotkey, video driver will adjust brightness
3878 level and then send out the event to user space through
3879 the allocated input device; If set to 0, video driver
3880 will only send out the event without touching backlight
3881 brightness level.
3882 default: 1
3884 virtio_mmio.device=
3885 [VMMIO] Memory mapped virtio (platform) device.
3887 <size>@<baseaddr>:<irq>[:<id>]
3888 where:
3889 <size> := size (can use standard suffixes
3890 like K, M and G)
3891 <baseaddr> := physical base address
3892 <irq> := interrupt number (as passed to
3893 request_irq())
3894 <id> := (optional) platform device id
3895 example:
3896 virtio_mmio.device=1K@0x100b0000:48:7
3898 Can be used multiple times for multiple devices.
3900 vga= [BOOT,X86-32] Select a particular video mode
3901 See Documentation/x86/boot.txt and
3902 Documentation/svga.txt.
3903 Use vga=ask for menu.
3904 This is actually a boot loader parameter; the value is
3905 passed to the kernel using a special protocol.
3907 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3908 size of <nn>. This can be used to increase the
3909 minimum size (128MB on x86). It can also be used to
3910 decrease the size and leave more room for directly
3911 mapped kernel RAM.
3913 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3914 Format: <command>
3916 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3917 Format: <command>
3919 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3920 Format: <command>
3922 vsyscall= [X86-64]
3923 Controls the behavior of vsyscalls (i.e. calls to
3924 fixed addresses of 0xffffffffff600x00 from legacy
3925 code). Most statically-linked binaries and older
3926 versions of glibc use these calls. Because these
3927 functions are at fixed addresses, they make nice
3928 targets for exploits that can control RIP.
3930 emulate [default] Vsyscalls turn into traps and are
3931 emulated reasonably safely.
3933 native Vsyscalls are native syscall instructions.
3934 This is a little bit faster than trapping
3935 and makes a few dynamic recompilers work
3936 better than they would in emulation mode.
3937 It also makes exploits much easier to write.
3939 none Vsyscalls don't work at all. This makes
3940 them quite hard to use for exploits but
3941 might break your system.
3943 vt.color= [VT] Default text color.
3944 Format: 0xYX, X = foreground, Y = background.
3945 Default: 0x07 = light gray on black.
3947 vt.cur_default= [VT] Default cursor shape.
3948 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3949 the parameters of the <Esc>[?A;B;Cc escape sequence;
3950 see VGA-softcursor.txt. Default: 2 = underline.
3952 vt.default_blu= [VT]
3953 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3954 Change the default blue palette of the console.
3955 This is a 16-member array composed of values
3956 ranging from 0-255.
3958 vt.default_grn= [VT]
3959 Format: <green0>,<green1>,<green2>,...,<green15>
3960 Change the default green palette of the console.
3961 This is a 16-member array composed of values
3962 ranging from 0-255.
3964 vt.default_red= [VT]
3965 Format: <red0>,<red1>,<red2>,...,<red15>
3966 Change the default red palette of the console.
3967 This is a 16-member array composed of values
3968 ranging from 0-255.
3970 vt.default_utf8=
3971 [VT]
3972 Format=<0|1>
3973 Set system-wide default UTF-8 mode for all tty's.
3974 Default is 1, i.e. UTF-8 mode is enabled for all
3975 newly opened terminals.
3977 vt.global_cursor_default=
3978 [VT]
3979 Format=<-1|0|1>
3980 Set system-wide default for whether a cursor
3981 is shown on new VTs. Default is -1,
3982 i.e. cursors will be created by default unless
3983 overridden by individual drivers. 0 will hide
3984 cursors, 1 will display them.
3986 vt.italic= [VT] Default color for italic text; 0-15.
3987 Default: 2 = green.
3989 vt.underline= [VT] Default color for underlined text; 0-15.
3990 Default: 3 = cyan.
3992 watchdog timers [HW,WDT] For information on watchdog timers,
3993 see Documentation/watchdog/watchdog-parameters.txt
3994 or other driver-specific files in the
3995 Documentation/watchdog/ directory.
3997 workqueue.disable_numa
3998 By default, all work items queued to unbound
3999 workqueues are affine to the NUMA nodes they're
4000 issued on, which results in better behavior in
4001 general. If NUMA affinity needs to be disabled for
4002 whatever reason, this option can be used. Note
4003 that this also can be controlled per-workqueue for
4004 workqueues visible under /sys/bus/workqueue/.
4006 workqueue.power_efficient
4007 Per-cpu workqueues are generally preferred because
4008 they show better performance thanks to cache
4009 locality; unfortunately, per-cpu workqueues tend to
4010 be more power hungry than unbound workqueues.
4012 Enabling this makes the per-cpu workqueues which
4013 were observed to contribute significantly to power
4014 consumption unbound, leading to measurably lower
4015 power usage at the cost of small performance
4016 overhead.
4018 The default value of this parameter is determined by
4019 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4021 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4022 default x2apic cluster mode on platforms
4023 supporting x2apic.
4025 x86_intel_mid_timer= [X86-32,APBT]
4026 Choose timer option for x86 Intel MID platform.
4027 Two valid options are apbt timer only and lapic timer
4028 plus one apbt timer for broadcast timer.
4029 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4031 xen_emul_unplug= [HW,X86,XEN]
4032 Unplug Xen emulated devices
4033 Format: [unplug0,][unplug1]
4034 ide-disks -- unplug primary master IDE devices
4035 aux-ide-disks -- unplug non-primary-master IDE devices
4036 nics -- unplug network devices
4037 all -- unplug all emulated devices (NICs and IDE disks)
4038 unnecessary -- unplugging emulated devices is
4039 unnecessary even if the host did not respond to
4040 the unplug protocol
4041 never -- do not unplug even if version check succeeds
4043 xen_nopvspin [X86,XEN]
4044 Disables the ticketlock slowpath using Xen PV
4045 optimizations.
4047 xen_nopv [X86]
4048 Disables the PV optimizations forcing the HVM guest to
4049 run as generic HVM guest with no PV drivers.
4051 xirc2ps_cs= [NET,PCMCIA]
4052 Format:
4053 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4055 ______________________________________________________________________
4057 TODO:
4059 Add more DRM drivers.