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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]
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
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
187 Format: <int>
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
190 default: 0
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
194 acpi_backlight=video
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
201 Format: <int>
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
230 size limitation.
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
234 default in APIC mode
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
238 default in PIC mode
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
244 use by PCI
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
281 strings
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
294 Examples:
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
304 meaningless.
305 Examples:
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
307 FALSE.
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
319 the OSPM features.
320 Examples:
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
326 equivalent to
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
328 and
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
332 acpi_pm_good [X86]
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
348 s3_bios and s3_mode.
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
384 kernels.
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
389 agp= [AGP]
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
395 ALSA [HW,ALSA]
396 See Documentation/sound/alsa/alsa-parameters.txt
398 alignment= [KNL,ARM]
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
425 Possible values are:
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
429 is a lot of faster
430 off - do not initialize any AMD IOMMU found in
431 the system
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
446 Format: <a>,<b>
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
454 apc= [HW,SPARC]
455 Power management functions (SPARCstation-4/5 + deriv.)
456 Format: noidle
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
467 autoconf= [IPV6]
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
485 ataflop= [HW,M68k]
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
498 keyboards
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
515 auditd.
516 Default: unset
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
520 Default: 64
522 baycom_epp= [HW,AX25]
523 Format: <io>,<mode>
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
526 Format: <io>,<mode>
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
545 no delay (0).
546 Format: integer
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
552 kernel args too.
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
554 bttv.tuner=
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
558 at a time.
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ca_keys= [KEYS] This parameter identifies a specific key(s) on
570 the system trusted keyring to be used for certificate
571 trust validation.
572 format: { id:<keyid> | builtin }
574 cca= [MIPS] Override the kernel pages' cache coherency
575 algorithm. Accepted values range from 0 to 7
576 inclusive. See arch/mips/include/asm/pgtable-bits.h
577 for platform specific values (SB1, Loongson3 and
578 others).
580 ccw_timeout_log [S390]
581 See Documentation/s390/CommonIO for details.
583 cgroup_disable= [KNL] Disable a particular controller
584 Format: {name of the controller(s) to disable}
585 The effects of cgroup_disable=foo are:
586 - foo isn't auto-mounted if you mount all cgroups in
587 a single hierarchy
588 - foo isn't visible as an individually mountable
589 subsystem
590 {Currently only "memory" controller deal with this and
591 cut the overhead, others just disable the usage. So
592 only cgroup_disable=memory is actually worthy}
594 checkreqprot [SELINUX] Set initial checkreqprot flag value.
595 Format: { "0" | "1" }
596 See security/selinux/Kconfig help text.
597 0 -- check protection applied by kernel (includes
598 any implied execute protection).
599 1 -- check protection requested by application.
600 Default value is set via a kernel config option.
601 Value can be changed at runtime via
602 /selinux/checkreqprot.
604 cio_ignore= [S390]
605 See Documentation/s390/CommonIO for details.
606 clk_ignore_unused
607 [CLK]
608 Prevents the clock framework from automatically gating
609 clocks that have not been explicitly enabled by a Linux
610 device driver but are enabled in hardware at reset or
611 by the bootloader/firmware. Note that this does not
612 force such clocks to be always-on nor does it reserve
613 those clocks in any way. This parameter is useful for
614 debug and development, but should not be needed on a
615 platform with proper driver support. For more
616 information, see Documentation/clk.txt.
618 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
619 [Deprecated]
620 Forces specified clocksource (if available) to be used
621 when calculating gettimeofday(). If specified
622 clocksource is not available, it defaults to PIT.
623 Format: { pit | tsc | cyclone | pmtmr }
625 clocksource= Override the default clocksource
626 Format: <string>
627 Override the default clocksource and use the clocksource
628 with the name specified.
629 Some clocksource names to choose from, depending on
630 the platform:
631 [all] jiffies (this is the base, fallback clocksource)
632 [ACPI] acpi_pm
633 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
634 pxa_timer,timer3,32k_counter,timer0_1
635 [AVR32] avr32
636 [X86-32] pit,hpet,tsc;
637 scx200_hrt on Geode; cyclone on IBM x440
638 [MIPS] MIPS
639 [PARISC] cr16
640 [S390] tod
641 [SH] SuperH
642 [SPARC64] tick
643 [X86-64] hpet,tsc
645 clearcpuid=BITNUM [X86]
646 Disable CPUID feature X for the kernel. See
647 arch/x86/include/asm/cpufeature.h for the valid bit
648 numbers. Note the Linux specific bits are not necessarily
649 stable over kernel options, but the vendor specific
650 ones should be.
651 Also note that user programs calling CPUID directly
652 or using the feature without checking anything
653 will still see it. This just prevents it from
654 being used by the kernel or shown in /proc/cpuinfo.
655 Also note the kernel might malfunction if you disable
656 some critical bits.
658 cma=nn[MG]@[start[MG][-end[MG]]]
659 [ARM,X86,KNL]
660 Sets the size of kernel global memory area for
661 contiguous memory allocations and optionally the
662 placement constraint by the physical address range of
663 memory allocations. A value of 0 disables CMA
664 altogether. For more information, see
665 include/linux/dma-contiguous.h
667 cmo_free_hint= [PPC] Format: { yes | no }
668 Specify whether pages are marked as being inactive
669 when they are freed. This is used in CMO environments
670 to determine OS memory pressure for page stealing by
671 a hypervisor.
672 Default: yes
674 coherent_pool=nn[KMG] [ARM,KNL]
675 Sets the size of memory pool for coherent, atomic dma
676 allocations, by default set to 256K.
678 code_bytes [X86] How many bytes of object code to print
679 in an oops report.
680 Range: 0 - 8192
681 Default: 64
683 com20020= [HW,NET] ARCnet - COM20020 chipset
684 Format:
685 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
687 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
688 Format: <io>[,<irq>]
690 com90xx= [HW,NET]
691 ARCnet - COM90xx chipset (memory-mapped buffers)
692 Format: <io>[,<irq>[,<memstart>]]
694 condev= [HW,S390] console device
695 conmode=
697 console= [KNL] Output console device and options.
699 tty<n> Use the virtual console device <n>.
701 ttyS<n>[,options]
702 ttyUSB0[,options]
703 Use the specified serial port. The options are of
704 the form "bbbbpnf", where "bbbb" is the baud rate,
705 "p" is parity ("n", "o", or "e"), "n" is number of
706 bits, and "f" is flow control ("r" for RTS or
707 omit it). Default is "9600n8".
709 See Documentation/serial-console.txt for more
710 information. See
711 Documentation/networking/netconsole.txt for an
712 alternative.
714 uart[8250],io,<addr>[,options]
715 uart[8250],mmio,<addr>[,options]
716 Start an early, polled-mode console on the 8250/16550
717 UART at the specified I/O port or MMIO address,
718 switching to the matching ttyS device later. The
719 options are the same as for ttyS, above.
720 hvc<n> Use the hypervisor console device <n>. This is for
721 both Xen and PowerPC hypervisors.
723 If the device connected to the port is not a TTY but a braille
724 device, prepend "brl," before the device type, for instance
725 console=brl,ttyS0
726 For now, only VisioBraille is supported.
728 consoleblank= [KNL] The console blank (screen saver) timeout in
729 seconds. Defaults to 10*60 = 10mins. A value of 0
730 disables the blank timer.
732 coredump_filter=
733 [KNL] Change the default value for
734 /proc/<pid>/coredump_filter.
735 See also Documentation/filesystems/proc.txt.
737 cpuidle.off=1 [CPU_IDLE]
738 disable the cpuidle sub-system
740 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
741 Format:
742 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
744 crashkernel=size[KMG][@offset[KMG]]
745 [KNL] Using kexec, Linux can switch to a 'crash kernel'
746 upon panic. This parameter reserves the physical
747 memory region [offset, offset + size] for that kernel
748 image. If '@offset' is omitted, then a suitable offset
749 is selected automatically. Check
750 Documentation/kdump/kdump.txt for further details.
752 crashkernel=range1:size1[,range2:size2,...][@offset]
753 [KNL] Same as above, but depends on the memory
754 in the running system. The syntax of range is
755 start-[end] where start and end are both
756 a memory unit (amount[KMG]). See also
757 Documentation/kdump/kdump.txt for an example.
759 crashkernel=size[KMG],high
760 [KNL, x86_64] range could be above 4G. Allow kernel
761 to allocate physical memory region from top, so could
762 be above 4G if system have more than 4G ram installed.
763 Otherwise memory region will be allocated below 4G, if
764 available.
765 It will be ignored if crashkernel=X is specified.
766 crashkernel=size[KMG],low
767 [KNL, x86_64] range under 4G. When crashkernel=X,high
768 is passed, kernel could allocate physical memory region
769 above 4G, that cause second kernel crash on system
770 that require some amount of low memory, e.g. swiotlb
771 requires at least 64M+32K low memory. Kernel would
772 try to allocate 72M below 4G automatically.
773 This one let user to specify own low range under 4G
774 for second kernel instead.
775 0: to disable low allocation.
776 It will be ignored when crashkernel=X,high is not used
777 or memory reserved is below 4G.
779 cs89x0_dma= [HW,NET]
780 Format: <dma>
782 cs89x0_media= [HW,NET]
783 Format: { rj45 | aui | bnc }
785 dasd= [HW,NET]
786 See header of drivers/s390/block/dasd_devmap.c.
788 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
789 (one device per port)
790 Format: <port#>,<type>
791 See also Documentation/input/joystick-parport.txt
793 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
794 time. See Documentation/dynamic-debug-howto.txt for
795 details. Deprecated, see dyndbg.
797 debug [KNL] Enable kernel debugging (events log level).
799 debug_locks_verbose=
800 [KNL] verbose self-tests
801 Format=<0|1>
802 Print debugging info while doing the locking API
803 self-tests.
804 We default to 0 (no extra messages), setting it to
805 1 will print _a lot_ more information - normally
806 only useful to kernel developers.
808 debug_objects [KNL] Enable object debugging
810 no_debug_objects
811 [KNL] Disable object debugging
813 debug_guardpage_minorder=
814 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
815 parameter allows control of the order of pages that will
816 be intentionally kept free (and hence protected) by the
817 buddy allocator. Bigger value increase the probability
818 of catching random memory corruption, but reduce the
819 amount of memory for normal system use. The maximum
820 possible value is MAX_ORDER/2. Setting this parameter
821 to 1 or 2 should be enough to identify most random
822 memory corruption problems caused by bugs in kernel or
823 driver code when a CPU writes to (or reads from) a
824 random memory location. Note that there exists a class
825 of memory corruptions problems caused by buggy H/W or
826 F/W or by drivers badly programing DMA (basically when
827 memory is written at bus level and the CPU MMU is
828 bypassed) which are not detectable by
829 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
830 tracking down these problems.
832 debug_pagealloc=
833 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
834 parameter enables the feature at boot time. In
835 default, it is disabled. We can avoid allocating huge
836 chunk of memory for debug pagealloc if we don't enable
837 it at boot time and the system will work mostly same
838 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
839 on: enable the feature
841 debugpat [X86] Enable PAT debugging
843 decnet.addr= [HW,NET]
844 Format: <area>[,<node>]
845 See also Documentation/networking/decnet.txt.
847 default_hugepagesz=
848 [same as hugepagesz=] The size of the default
849 HugeTLB page size. This is the size represented by
850 the legacy /proc/ hugepages APIs, used for SHM, and
851 default size when mounting hugetlbfs filesystems.
852 Defaults to the default architecture's huge page size
853 if not specified.
855 dhash_entries= [KNL]
856 Set number of hash buckets for dentry cache.
858 disable= [IPV6]
859 See Documentation/networking/ipv6.txt.
861 disable_cpu_apicid= [X86,APIC,SMP]
862 Format: <int>
863 The number of initial APIC ID for the
864 corresponding CPU to be disabled at boot,
865 mostly used for the kdump 2nd kernel to
866 disable BSP to wake up multiple CPUs without
867 causing system reset or hang due to sending
868 INIT from AP to BSP.
870 disable_ddw [PPC/PSERIES]
871 Disable Dynamic DMA Window support. Use this if
872 to workaround buggy firmware.
874 disable_ipv6= [IPV6]
875 See Documentation/networking/ipv6.txt.
877 disable_mtrr_cleanup [X86]
878 The kernel tries to adjust MTRR layout from continuous
879 to discrete, to make X server driver able to add WB
880 entry later. This parameter disables that.
882 disable_mtrr_trim [X86, Intel and AMD only]
883 By default the kernel will trim any uncacheable
884 memory out of your available memory pool based on
885 MTRR settings. This parameter disables that behavior,
886 possibly causing your machine to run very slowly.
888 disable_timer_pin_1 [X86]
889 Disable PIN 1 of APIC timer
890 Can be useful to work around chipset bugs.
892 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
893 this option disables the debugging code at boot.
895 dma_debug_entries=<number>
896 This option allows to tune the number of preallocated
897 entries for DMA-API debugging code. One entry is
898 required per DMA-API allocation. Use this if the
899 DMA-API debugging code disables itself because the
900 architectural default is too low.
902 dma_debug_driver=<driver_name>
903 With this option the DMA-API debugging driver
904 filter feature can be enabled at boot time. Just
905 pass the driver to filter for as the parameter.
906 The filter can be disabled or changed to another
907 driver later using sysfs.
909 drm_kms_helper.edid_firmware=[<connector>:]<file>
910 Broken monitors, graphic adapters and KVMs may
911 send no or incorrect EDID data sets. This parameter
912 allows to specify an EDID data set in the
913 /lib/firmware directory that is used instead.
914 Generic built-in EDID data sets are used, if one of
915 edid/1024x768.bin, edid/1280x1024.bin,
916 edid/1680x1050.bin, or edid/1920x1080.bin is given
917 and no file with the same name exists. Details and
918 instructions how to build your own EDID data are
919 available in Documentation/EDID/HOWTO.txt. An EDID
920 data set will only be used for a particular connector,
921 if its name and a colon are prepended to the EDID
922 name.
924 dscc4.setup= [NET]
926 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
927 module.dyndbg[="val"]
928 Enable debug messages at boot time. See
929 Documentation/dynamic-debug-howto.txt for details.
931 early_ioremap_debug [KNL]
932 Enable debug messages in early_ioremap support. This
933 is useful for tracking down temporary early mappings
934 which are not unmapped.
936 earlycon= [KNL] Output early console device and options.
938 cdns,<addr>
939 Start an early, polled-mode console on a cadence serial
940 port at the specified address. The cadence serial port
941 must already be setup and configured. Options are not
942 yet supported.
944 uart[8250],io,<addr>[,options]
945 uart[8250],mmio,<addr>[,options]
946 uart[8250],mmio32,<addr>[,options]
947 Start an early, polled-mode console on the 8250/16550
948 UART at the specified I/O port or MMIO address.
949 MMIO inter-register address stride is either 8-bit
950 (mmio) or 32-bit (mmio32).
951 The options are the same as for ttyS, above.
953 pl011,<addr>
954 Start an early, polled-mode console on a pl011 serial
955 port at the specified address. The pl011 serial port
956 must already be setup and configured. Options are not
957 yet supported.
959 msm_serial,<addr>
960 Start an early, polled-mode console on an msm serial
961 port at the specified address. The serial port
962 must already be setup and configured. Options are not
963 yet supported.
965 msm_serial_dm,<addr>
966 Start an early, polled-mode console on an msm serial
967 dm port at the specified address. The serial port
968 must already be setup and configured. Options are not
969 yet supported.
971 smh Use ARM semihosting calls for early console.
973 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
974 earlyprintk=vga
975 earlyprintk=efi
976 earlyprintk=xen
977 earlyprintk=serial[,ttySn[,baudrate]]
978 earlyprintk=serial[,0x...[,baudrate]]
979 earlyprintk=ttySn[,baudrate]
980 earlyprintk=dbgp[debugController#]
982 earlyprintk is useful when the kernel crashes before
983 the normal console is initialized. It is not enabled by
984 default because it has some cosmetic problems.
986 Append ",keep" to not disable it when the real console
987 takes over.
989 Only one of vga, efi, serial, or usb debug port can
990 be used at a time.
992 Currently only ttyS0 and ttyS1 may be specified by
993 name. Other I/O ports may be explicitly specified
994 on some architectures (x86 and arm at least) by
995 replacing ttySn with an I/O port address, like this:
996 earlyprintk=serial,0x1008,115200
997 You can find the port for a given device in
998 /proc/tty/driver/serial:
999 2: uart:ST16650V2 port:00001008 irq:18 ...
1001 Interaction with the standard serial driver is not
1002 very good.
1004 The VGA and EFI output is eventually overwritten by
1005 the real console.
1007 The xen output can only be used by Xen PV guests.
1009 edac_report= [HW,EDAC] Control how to report EDAC event
1010 Format: {"on" | "off" | "force"}
1011 on: enable EDAC to report H/W event. May be overridden
1012 by other higher priority error reporting module.
1013 off: disable H/W event reporting through EDAC.
1014 force: enforce the use of EDAC to report H/W event.
1015 default: on.
1017 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1018 ekgdboc=kbd
1020 This is designed to be used in conjunction with
1021 the boot argument: earlyprintk=vga
1023 edd= [EDD]
1024 Format: {"off" | "on" | "skip[mbr]"}
1026 efi= [EFI]
1027 Format: { "old_map", "nochunk", "noruntime" }
1028 old_map [X86-64]: switch to the old ioremap-based EFI
1029 runtime services mapping. 32-bit still uses this one by
1030 default.
1031 nochunk: disable reading files in "chunks" in the EFI
1032 boot stub, as chunking can cause problems with some
1033 firmware implementations.
1034 noruntime : disable EFI runtime services support
1036 efi_no_storage_paranoia [EFI; X86]
1037 Using this parameter you can use more than 50% of
1038 your efi variable storage. Use this parameter only if
1039 you are really sure that your UEFI does sane gc and
1040 fulfills the spec otherwise your board may brick.
1042 eisa_irq_edge= [PARISC,HW]
1043 See header of drivers/parisc/eisa.c.
1045 elanfreq= [X86-32]
1046 See comment before function elanfreq_setup() in
1047 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1049 elevator= [IOSCHED]
1050 Format: {"cfq" | "deadline" | "noop"}
1051 See Documentation/block/cfq-iosched.txt and
1052 Documentation/block/deadline-iosched.txt for details.
1054 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1055 Specifies physical address of start of kernel core
1056 image elf header and optionally the size. Generally
1057 kexec loader will pass this option to capture kernel.
1058 See Documentation/kdump/kdump.txt for details.
1060 enable_mtrr_cleanup [X86]
1061 The kernel tries to adjust MTRR layout from continuous
1062 to discrete, to make X server driver able to add WB
1063 entry later. This parameter enables that.
1065 enable_timer_pin_1 [X86]
1066 Enable PIN 1 of APIC timer
1067 Can be useful to work around chipset bugs
1068 (in particular on some ATI chipsets).
1069 The kernel tries to set a reasonable default.
1071 enforcing [SELINUX] Set initial enforcing status.
1072 Format: {"0" | "1"}
1073 See security/selinux/Kconfig help text.
1074 0 -- permissive (log only, no denials).
1075 1 -- enforcing (deny and log).
1076 Default value is 0.
1077 Value can be changed at runtime via /selinux/enforce.
1079 erst_disable [ACPI]
1080 Disable Error Record Serialization Table (ERST)
1081 support.
1083 ether= [HW,NET] Ethernet cards parameters
1084 This option is obsoleted by the "netdev=" option, which
1085 has equivalent usage. See its documentation for details.
1087 evm= [EVM]
1088 Format: { "fix" }
1089 Permit 'security.evm' to be updated regardless of
1090 current integrity status.
1092 failslab=
1093 fail_page_alloc=
1094 fail_make_request=[KNL]
1095 General fault injection mechanism.
1096 Format: <interval>,<probability>,<space>,<times>
1097 See also Documentation/fault-injection/.
1099 floppy= [HW]
1100 See Documentation/blockdev/floppy.txt.
1102 force_pal_cache_flush
1103 [IA-64] Avoid check_sal_cache_flush which may hang on
1104 buggy SAL_CACHE_FLUSH implementations. Using this
1105 parameter will force ia64_sal_cache_flush to call
1106 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1108 forcepae [X86-32]
1109 Forcefully enable Physical Address Extension (PAE).
1110 Many Pentium M systems disable PAE but may have a
1111 functionally usable PAE implementation.
1112 Warning: use of this parameter will taint the kernel
1113 and may cause unknown problems.
1115 ftrace=[tracer]
1116 [FTRACE] will set and start the specified tracer
1117 as early as possible in order to facilitate early
1118 boot debugging.
1120 ftrace_dump_on_oops[=orig_cpu]
1121 [FTRACE] will dump the trace buffers on oops.
1122 If no parameter is passed, ftrace will dump
1123 buffers of all CPUs, but if you pass orig_cpu, it will
1124 dump only the buffer of the CPU that triggered the
1125 oops.
1127 ftrace_filter=[function-list]
1128 [FTRACE] Limit the functions traced by the function
1129 tracer at boot up. function-list is a comma separated
1130 list of functions. This list can be changed at run
1131 time by the set_ftrace_filter file in the debugfs
1132 tracing directory.
1134 ftrace_notrace=[function-list]
1135 [FTRACE] Do not trace the functions specified in
1136 function-list. This list can be changed at run time
1137 by the set_ftrace_notrace file in the debugfs
1138 tracing directory.
1140 ftrace_graph_filter=[function-list]
1141 [FTRACE] Limit the top level callers functions traced
1142 by the function graph tracer at boot up.
1143 function-list is a comma separated list of functions
1144 that can be changed at run time by the
1145 set_graph_function file in the debugfs tracing directory.
1147 ftrace_graph_notrace=[function-list]
1148 [FTRACE] Do not trace from the functions specified in
1149 function-list. This list is a comma separated list of
1150 functions that can be changed at run time by the
1151 set_graph_notrace file in the debugfs tracing directory.
1153 gamecon.map[2|3]=
1154 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1155 support via parallel port (up to 5 devices per port)
1156 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1157 See also Documentation/input/joystick-parport.txt
1159 gamma= [HW,DRM]
1161 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1162 Format: off | on
1163 default: on
1165 gcov_persist= [GCOV] When non-zero (default), profiling data for
1166 kernel modules is saved and remains accessible via
1167 debugfs, even when the module is unloaded/reloaded.
1168 When zero, profiling data is discarded and associated
1169 debugfs files are removed at module unload time.
1171 gpt [EFI] Forces disk with valid GPT signature but
1172 invalid Protective MBR to be treated as GPT. If the
1173 primary GPT is corrupted, it enables the backup/alternate
1174 GPT to be used instead.
1176 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1177 the "Enable 0" bit of the configuration register.
1178 Format: 0 | 1
1179 Default: 0
1180 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1181 the "Enable 0" bit of the configuration register.
1182 Format: 0 | 1
1183 Default: 0
1184 grcan.select= [HW] Select which physical interface to use.
1185 Format: 0 | 1
1186 Default: 0
1187 grcan.txsize= [HW] Sets the size of the tx buffer.
1188 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1189 Default: 1024
1190 grcan.rxsize= [HW] Sets the size of the rx buffer.
1191 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1192 Default: 1024
1194 hashdist= [KNL,NUMA] Large hashes allocated during boot
1195 are distributed across NUMA nodes. Defaults on
1196 for 64-bit NUMA, off otherwise.
1197 Format: 0 | 1 (for off | on)
1199 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1201 hd= [EIDE] (E)IDE hard drive subsystem geometry
1202 Format: <cyl>,<head>,<sect>
1204 hest_disable [ACPI]
1205 Disable Hardware Error Source Table (HEST) support;
1206 corresponding firmware-first mode error processing
1207 logic will be disabled.
1209 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1210 size of <nn>. This works even on boxes that have no
1211 highmem otherwise. This also works to reduce highmem
1212 size on bigger boxes.
1214 highres= [KNL] Enable/disable high resolution timer mode.
1215 Valid parameters: "on", "off"
1216 Default: "on"
1218 hisax= [HW,ISDN]
1219 See Documentation/isdn/README.HiSax.
1221 hlt [BUGS=ARM,SH]
1223 hpet= [X86-32,HPET] option to control HPET usage
1224 Format: { enable (default) | disable | force |
1225 verbose }
1226 disable: disable HPET and use PIT instead
1227 force: allow force enabled of undocumented chips (ICH4,
1228 VIA, nVidia)
1229 verbose: show contents of HPET registers during setup
1231 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1232 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1234 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1235 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1236 On x86-64 and powerpc, this option can be specified
1237 multiple times interleaved with hugepages= to reserve
1238 huge pages of different sizes. Valid pages sizes on
1239 x86-64 are 2M (when the CPU supports "pse") and 1G
1240 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1242 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1243 terminal devices. Valid values: 0..8
1244 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1245 If specified, z/VM IUCV HVC accepts connections
1246 from listed z/VM user IDs only.
1248 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1249 hardware thread id mappings.
1250 Format: <cpu>:<hwthread>
1252 keep_bootcon [KNL]
1253 Do not unregister boot console at start. This is only
1254 useful for debugging when something happens in the window
1255 between unregistering the boot console and initializing
1256 the real console.
1258 i2c_bus= [HW] Override the default board specific I2C bus speed
1259 or register an additional I2C bus that is not
1260 registered from board initialization code.
1261 Format:
1262 <bus_id>,<clkrate>
1264 i8042.debug [HW] Toggle i8042 debug mode
1265 i8042.direct [HW] Put keyboard port into non-translated mode
1266 i8042.dumbkbd [HW] Pretend that controller can only read data from
1267 keyboard and cannot control its state
1268 (Don't attempt to blink the leds)
1269 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1270 i8042.nokbd [HW] Don't check/create keyboard port
1271 i8042.noloop [HW] Disable the AUX Loopback command while probing
1272 for the AUX port
1273 i8042.nomux [HW] Don't check presence of an active multiplexing
1274 controller
1275 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1276 controllers
1277 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1278 i8042.reset [HW] Reset the controller during init and cleanup
1279 i8042.unlock [HW] Unlock (ignore) the keylock
1281 i810= [HW,DRM]
1283 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1284 indicates that the driver is running on unsupported
1285 hardware.
1286 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1287 does not match list of supported models.
1288 i8k.power_status
1289 [HW] Report power status in /proc/i8k
1290 (disabled by default)
1291 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1292 capability is set.
1294 i915.invert_brightness=
1295 [DRM] Invert the sense of the variable that is used to
1296 set the brightness of the panel backlight. Normally a
1297 brightness value of 0 indicates backlight switched off,
1298 and the maximum of the brightness value sets the backlight
1299 to maximum brightness. If this parameter is set to 0
1300 (default) and the machine requires it, or this parameter
1301 is set to 1, a brightness value of 0 sets the backlight
1302 to maximum brightness, and the maximum of the brightness
1303 value switches the backlight off.
1304 -1 -- never invert brightness
1305 0 -- machine default
1306 1 -- force brightness inversion
1308 icn= [HW,ISDN]
1309 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1311 ide-core.nodma= [HW] (E)IDE subsystem
1312 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1313 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1314 .cdrom .chs .ignore_cable are additional options
1315 See Documentation/ide/ide.txt.
1317 ide-generic.probe-mask= [HW] (E)IDE subsystem
1318 Format: <int>
1319 Probe mask for legacy ISA IDE ports. Depending on
1320 platform up to 6 ports are supported, enabled by
1321 setting corresponding bits in the mask to 1. The
1322 default value is 0x0, which has a special meaning.
1323 On systems that have PCI, it triggers scanning the
1324 PCI bus for the first and the second port, which
1325 are then probed. On systems without PCI the value
1326 of 0x0 enables probing the two first ports as if it
1327 was 0x3.
1329 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1330 Claim all unknown PCI IDE storage controllers.
1332 idle= [X86]
1333 Format: idle=poll, idle=halt, idle=nomwait
1334 Poll forces a polling idle loop that can slightly
1335 improve the performance of waking up a idle CPU, but
1336 will use a lot of power and make the system run hot.
1337 Not recommended.
1338 idle=halt: Halt is forced to be used for CPU idle.
1339 In such case C2/C3 won't be used again.
1340 idle=nomwait: Disable mwait for CPU C-states
1342 ignore_loglevel [KNL]
1343 Ignore loglevel setting - this will print /all/
1344 kernel messages to the console. Useful for debugging.
1345 We also add it as printk module parameter, so users
1346 could change it dynamically, usually by
1347 /sys/module/printk/parameters/ignore_loglevel.
1349 ihash_entries= [KNL]
1350 Set number of hash buckets for inode cache.
1352 ima_appraise= [IMA] appraise integrity measurements
1353 Format: { "off" | "enforce" | "fix" | "log" }
1354 default: "enforce"
1356 ima_appraise_tcb [IMA]
1357 The builtin appraise policy appraises all files
1358 owned by uid=0.
1360 ima_hash= [IMA]
1361 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1362 | sha512 | ... }
1363 default: "sha1"
1365 The list of supported hash algorithms is defined
1366 in crypto/hash_info.h.
1368 ima_tcb [IMA]
1369 Load a policy which meets the needs of the Trusted
1370 Computing Base. This means IMA will measure all
1371 programs exec'd, files mmap'd for exec, and all files
1372 opened for read by uid=0.
1374 ima_template= [IMA]
1375 Select one of defined IMA measurements template formats.
1376 Formats: { "ima" | "ima-ng" }
1377 Default: "ima-ng"
1379 ima_template_fmt=
1380 [IMA] Define a custom template format.
1381 Format: { "field1|...|fieldN" }
1383 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1384 Format: <min_file_size>
1385 Set the minimal file size for using asynchronous hash.
1386 If left unspecified, ahash usage is disabled.
1388 ahash performance varies for different data sizes on
1389 different crypto accelerators. This option can be used
1390 to achieve the best performance for a particular HW.
1392 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1393 Format: <bufsize>
1394 Set hashing buffer size. Default: 4k.
1396 ahash performance varies for different chunk sizes on
1397 different crypto accelerators. This option can be used
1398 to achieve best performance for particular HW.
1400 init= [KNL]
1401 Format: <full_path>
1402 Run specified binary instead of /sbin/init as init
1403 process.
1405 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1406 for working out where the kernel is dying during
1407 startup.
1409 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1410 initcall functions. Useful for debugging built-in
1411 modules and initcalls.
1413 initrd= [BOOT] Specify the location of the initial ramdisk
1415 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1416 Format: <irq>
1418 int_pln_enable [x86] Enable power limit notification interrupt
1420 integrity_audit=[IMA]
1421 Format: { "0" | "1" }
1422 0 -- basic integrity auditing messages. (Default)
1423 1 -- additional integrity auditing messages.
1425 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1426 on
1427 Enable intel iommu driver.
1428 off
1429 Disable intel iommu driver.
1430 igfx_off [Default Off]
1431 By default, gfx is mapped as normal device. If a gfx
1432 device has a dedicated DMAR unit, the DMAR unit is
1433 bypassed by not enabling DMAR with this option. In
1434 this case, gfx device will use physical address for
1435 DMA.
1436 forcedac [x86_64]
1437 With this option iommu will not optimize to look
1438 for io virtual address below 32-bit forcing dual
1439 address cycle on pci bus for cards supporting greater
1440 than 32-bit addressing. The default is to look
1441 for translation below 32-bit and if not available
1442 then look in the higher range.
1443 strict [Default Off]
1444 With this option on every unmap_single operation will
1445 result in a hardware IOTLB flush operation as opposed
1446 to batching them for performance.
1447 sp_off [Default Off]
1448 By default, super page will be supported if Intel IOMMU
1449 has the capability. With this option, super page will
1450 not be supported.
1452 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1453 0 disables intel_idle and fall back on acpi_idle.
1454 1 to 6 specify maximum depth of C-state.
1456 intel_pstate= [X86]
1457 disable
1458 Do not enable intel_pstate as the default
1459 scaling driver for the supported processors
1460 force
1461 Enable intel_pstate on systems that prohibit it by default
1462 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1463 instead of acpi-cpufreq may disable platform features, such
1464 as thermal controls and power capping, that rely on ACPI
1465 P-States information being indicated to OSPM and therefore
1466 should be used with caution. This option does not work with
1467 processors that aren't supported by the intel_pstate driver
1468 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1469 no_hwp
1470 Do not enable hardware P state control (HWP)
1471 if available.
1473 intremap= [X86-64, Intel-IOMMU]
1474 on enable Interrupt Remapping (default)
1475 off disable Interrupt Remapping
1476 nosid disable Source ID checking
1477 no_x2apic_optout
1478 BIOS x2APIC opt-out request will be ignored
1480 iomem= Disable strict checking of access to MMIO memory
1481 strict regions from userspace.
1482 relaxed
1484 iommu= [x86]
1485 off
1486 force
1487 noforce
1488 biomerge
1489 panic
1490 nopanic
1491 merge
1492 nomerge
1493 forcesac
1494 soft
1495 pt [x86, IA-64]
1498 io7= [HW] IO7 for Marvel based alpha systems
1499 See comment before marvel_specify_io7 in
1500 arch/alpha/kernel/core_marvel.c.
1502 io_delay= [X86] I/O delay method
1503 0x80
1504 Standard port 0x80 based delay
1505 0xed
1506 Alternate port 0xed based delay (needed on some systems)
1507 udelay
1508 Simple two microseconds delay
1509 none
1510 No delay
1512 ip= [IP_PNP]
1513 See Documentation/filesystems/nfs/nfsroot.txt.
1515 irqfixup [HW]
1516 When an interrupt is not handled search all handlers
1517 for it. Intended to get systems with badly broken
1518 firmware running.
1520 irqpoll [HW]
1521 When an interrupt is not handled search all handlers
1522 for it. Also check all handlers each timer
1523 interrupt. Intended to get systems with badly broken
1524 firmware running.
1526 isapnp= [ISAPNP]
1527 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1529 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1530 Format:
1531 <cpu number>,...,<cpu number>
1532 or
1533 <cpu number>-<cpu number>
1534 (must be a positive range in ascending order)
1535 or a mixture
1536 <cpu number>,...,<cpu number>-<cpu number>
1538 This option can be used to specify one or more CPUs
1539 to isolate from the general SMP balancing and scheduling
1540 algorithms. You can move a process onto or off an
1541 "isolated" CPU via the CPU affinity syscalls or cpuset.
1542 <cpu number> begins at 0 and the maximum value is
1543 "number of CPUs in system - 1".
1545 This option is the preferred way to isolate CPUs. The
1546 alternative -- manually setting the CPU mask of all
1547 tasks in the system -- can cause problems and
1548 suboptimal load balancer performance.
1550 iucv= [HW,NET]
1552 ivrs_ioapic [HW,X86_64]
1553 Provide an override to the IOAPIC-ID<->DEVICE-ID
1554 mapping provided in the IVRS ACPI table. For
1555 example, to map IOAPIC-ID decimal 10 to
1556 PCI device 00:14.0 write the parameter as:
1557 ivrs_ioapic[10]=00:14.0
1559 ivrs_hpet [HW,X86_64]
1560 Provide an override to the HPET-ID<->DEVICE-ID
1561 mapping provided in the IVRS ACPI table. For
1562 example, to map HPET-ID decimal 0 to
1563 PCI device 00:14.0 write the parameter as:
1564 ivrs_hpet[0]=00:14.0
1566 js= [HW,JOY] Analog joystick
1567 See Documentation/input/joystick.txt.
1569 kaslr/nokaslr [X86]
1570 Enable/disable kernel and module base offset ASLR
1571 (Address Space Layout Randomization) if built into
1572 the kernel. When CONFIG_HIBERNATION is selected,
1573 kASLR is disabled by default. When kASLR is enabled,
1574 hibernation will be disabled.
1576 keepinitrd [HW,ARM]
1578 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1579 specifies the amount of memory usable by the kernel
1580 for non-movable allocations. The requested amount is
1581 spread evenly throughout all nodes in the system. The
1582 remaining memory in each node is used for Movable
1583 pages. In the event, a node is too small to have both
1584 kernelcore and Movable pages, kernelcore pages will
1585 take priority and other nodes will have a larger number
1586 of Movable pages. The Movable zone is used for the
1587 allocation of pages that may be reclaimed or moved
1588 by the page migration subsystem. This means that
1589 HugeTLB pages may not be allocated from this zone.
1590 Note that allocations like PTEs-from-HighMem still
1591 use the HighMem zone if it exists, and the Normal
1592 zone if it does not.
1594 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1595 Format: <Controller#>[,poll interval]
1596 The controller # is the number of the ehci usb debug
1597 port as it is probed via PCI. The poll interval is
1598 optional and is the number seconds in between
1599 each poll cycle to the debug port in case you need
1600 the functionality for interrupting the kernel with
1601 gdb or control-c on the dbgp connection. When
1602 not using this parameter you use sysrq-g to break into
1603 the kernel debugger.
1605 kgdboc= [KGDB,HW] kgdb over consoles.
1606 Requires a tty driver that supports console polling,
1607 or a supported polling keyboard driver (non-usb).
1608 Serial only format: <serial_device>[,baud]
1609 keyboard only format: kbd
1610 keyboard and serial format: kbd,<serial_device>[,baud]
1611 Optional Kernel mode setting:
1612 kms, kbd format: kms,kbd
1613 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1615 kgdbwait [KGDB] Stop kernel execution and enter the
1616 kernel debugger at the earliest opportunity.
1618 kmac= [MIPS] korina ethernet MAC address.
1619 Configure the RouterBoard 532 series on-chip
1620 Ethernet adapter MAC address.
1622 kmemleak= [KNL] Boot-time kmemleak enable/disable
1623 Valid arguments: on, off
1624 Default: on
1625 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1626 the default is off.
1628 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1629 Valid arguments: 0, 1, 2
1630 kmemcheck=0 (disabled)
1631 kmemcheck=1 (enabled)
1632 kmemcheck=2 (one-shot mode)
1633 Default: 2 (one-shot mode)
1635 kstack=N [X86] Print N words from the kernel stack
1636 in oops dumps.
1638 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1639 Default is 0 (don't ignore, but inject #GP)
1641 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1642 KVM MMU at runtime.
1643 Default is 0 (off)
1645 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1646 Default is 1 (enabled)
1648 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1649 for all guests.
1650 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1652 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1653 (virtualized MMU) support on capable Intel chips.
1654 Default is 1 (enabled)
1656 kvm-intel.emulate_invalid_guest_state=
1657 [KVM,Intel] Enable emulation of invalid guest states
1658 Default is 0 (disabled)
1660 kvm-intel.flexpriority=
1661 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1662 Default is 1 (enabled)
1664 kvm-intel.nested=
1665 [KVM,Intel] Enable VMX nesting (nVMX).
1666 Default is 0 (disabled)
1668 kvm-intel.unrestricted_guest=
1669 [KVM,Intel] Disable unrestricted guest feature
1670 (virtualized real and unpaged mode) on capable
1671 Intel chips. Default is 1 (enabled)
1673 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1674 feature (tagged TLBs) on capable Intel chips.
1675 Default is 1 (enabled)
1677 l2cr= [PPC]
1679 l3cr= [PPC]
1681 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1682 disabled it.
1684 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1685 value for LAPIC timer one-shot implementation. Default
1686 back to the programmable timer unit in the LAPIC.
1688 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1689 in C2 power state.
1691 libata.dma= [LIBATA] DMA control
1692 libata.dma=0 Disable all PATA and SATA DMA
1693 libata.dma=1 PATA and SATA Disk DMA only
1694 libata.dma=2 ATAPI (CDROM) DMA only
1695 libata.dma=4 Compact Flash DMA only
1696 Combinations also work, so libata.dma=3 enables DMA
1697 for disks and CDROMs, but not CFs.
1699 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1700 libata.ignore_hpa=0 keep BIOS limits (default)
1701 libata.ignore_hpa=1 ignore limits, using full disk
1703 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1704 when set.
1705 Format: <int>
1707 libata.force= [LIBATA] Force configurations. The format is comma
1708 separated list of "[ID:]VAL" where ID is
1709 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1710 matching port, link or device. Basically, it matches
1711 the ATA ID string printed on console by libata. If
1712 the whole ID part is omitted, the last PORT and DEVICE
1713 values are used. If ID hasn't been specified yet, the
1714 configuration applies to all ports, links and devices.
1716 If only DEVICE is omitted, the parameter applies to
1717 the port and all links and devices behind it. DEVICE
1718 number of 0 either selects the first device or the
1719 first fan-out link behind PMP device. It does not
1720 select the host link. DEVICE number of 15 selects the
1721 host link and device attached to it.
1723 The VAL specifies the configuration to force. As long
1724 as there's no ambiguity shortcut notation is allowed.
1725 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1726 The following configurations can be forced.
1728 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1729 Any ID with matching PORT is used.
1731 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1733 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1734 udma[/][16,25,33,44,66,100,133] notation is also
1735 allowed.
1737 * [no]ncq: Turn on or off NCQ.
1739 * nohrst, nosrst, norst: suppress hard, soft
1740 and both resets.
1742 * rstonce: only attempt one reset during
1743 hot-unplug link recovery
1745 * dump_id: dump IDENTIFY data.
1747 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1749 * disable: Disable this device.
1751 If there are multiple matching configurations changing
1752 the same attribute, the last one is used.
1754 memblock=debug [KNL] Enable memblock debug messages.
1756 load_ramdisk= [RAM] List of ramdisks to load from floppy
1757 See Documentation/blockdev/ramdisk.txt.
1759 lockd.nlm_grace_period=P [NFS] Assign grace period.
1760 Format: <integer>
1762 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1763 Format: <integer>
1765 lockd.nlm_timeout=T [NFS] Assign timeout value.
1766 Format: <integer>
1768 lockd.nlm_udpport=M [NFS] Assign UDP port.
1769 Format: <integer>
1771 locktorture.nreaders_stress= [KNL]
1772 Set the number of locking read-acquisition kthreads.
1773 Defaults to being automatically set based on the
1774 number of online CPUs.
1776 locktorture.nwriters_stress= [KNL]
1777 Set the number of locking write-acquisition kthreads.
1779 locktorture.onoff_holdoff= [KNL]
1780 Set time (s) after boot for CPU-hotplug testing.
1782 locktorture.onoff_interval= [KNL]
1783 Set time (s) between CPU-hotplug operations, or
1784 zero to disable CPU-hotplug testing.
1786 locktorture.shuffle_interval= [KNL]
1787 Set task-shuffle interval (jiffies). Shuffling
1788 tasks allows some CPUs to go into dyntick-idle
1789 mode during the locktorture test.
1791 locktorture.shutdown_secs= [KNL]
1792 Set time (s) after boot system shutdown. This
1793 is useful for hands-off automated testing.
1795 locktorture.stat_interval= [KNL]
1796 Time (s) between statistics printk()s.
1798 locktorture.stutter= [KNL]
1799 Time (s) to stutter testing, for example,
1800 specifying five seconds causes the test to run for
1801 five seconds, wait for five seconds, and so on.
1802 This tests the locking primitive's ability to
1803 transition abruptly to and from idle.
1805 locktorture.torture_runnable= [BOOT]
1806 Start locktorture running at boot time.
1808 locktorture.torture_type= [KNL]
1809 Specify the locking implementation to test.
1811 locktorture.verbose= [KNL]
1812 Enable additional printk() statements.
1814 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1815 Format: <irq>
1817 loglevel= All Kernel Messages with a loglevel smaller than the
1818 console loglevel will be printed to the console. It can
1819 also be changed with klogd or other programs. The
1820 loglevels are defined as follows:
1822 0 (KERN_EMERG) system is unusable
1823 1 (KERN_ALERT) action must be taken immediately
1824 2 (KERN_CRIT) critical conditions
1825 3 (KERN_ERR) error conditions
1826 4 (KERN_WARNING) warning conditions
1827 5 (KERN_NOTICE) normal but significant condition
1828 6 (KERN_INFO) informational
1829 7 (KERN_DEBUG) debug-level messages
1831 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1832 in bytes. n must be a power of two and greater
1833 than the minimal size. The minimal size is defined
1834 by LOG_BUF_SHIFT kernel config parameter. There is
1835 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1836 that allows to increase the default size depending on
1837 the number of CPUs. See init/Kconfig for more details.
1839 logo.nologo [FB] Disables display of the built-in Linux logo.
1840 This may be used to provide more screen space for
1841 kernel log messages and is useful when debugging
1842 kernel boot problems.
1844 lp=0 [LP] Specify parallel ports to use, e.g,
1845 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1846 lp=reset first parallel port). 'lp=0' disables the
1847 lp=auto printer driver. 'lp=reset' (which can be
1848 specified in addition to the ports) causes
1849 attached printers to be reset. Using
1850 lp=port1,port2,... specifies the parallel ports
1851 to associate lp devices with, starting with
1852 lp0. A port specification may be 'none' to skip
1853 that lp device, or a parport name such as
1854 'parport0'. Specifying 'lp=auto' instead of a
1855 port specification list means that device IDs
1856 from each port should be examined, to see if
1857 an IEEE 1284-compliant printer is attached; if
1858 so, the driver will manage that printer.
1859 See also header of drivers/char/lp.c.
1861 lpj=n [KNL]
1862 Sets loops_per_jiffy to given constant, thus avoiding
1863 time-consuming boot-time autodetection (up to 250 ms per
1864 CPU). 0 enables autodetection (default). To determine
1865 the correct value for your kernel, boot with normal
1866 autodetection and see what value is printed. Note that
1867 on SMP systems the preset will be applied to all CPUs,
1868 which is likely to cause problems if your CPUs need
1869 significantly divergent settings. An incorrect value
1870 will cause delays in the kernel to be wrong, leading to
1871 unpredictable I/O errors and other breakage. Although
1872 unlikely, in the extreme case this might damage your
1873 hardware.
1875 ltpc= [NET]
1876 Format: <io>,<irq>,<dma>
1878 machvec= [IA-64] Force the use of a particular machine-vector
1879 (machvec) in a generic kernel.
1880 Example: machvec=hpzx1_swiotlb
1882 machtype= [Loongson] Share the same kernel image file between different
1883 yeeloong laptop.
1884 Example: machtype=lemote-yeeloong-2f-7inch
1886 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1887 than or equal to this physical address is ignored.
1889 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1890 should make use of. maxcpus=n : n >= 0 limits the
1891 kernel to using 'n' processors. n=0 is a special case,
1892 it is equivalent to "nosmp", which also disables
1893 the IO APIC.
1895 max_loop= [LOOP] The number of loop block devices that get
1896 (loop.max_loop) unconditionally pre-created at init time. The default
1897 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1898 of statically allocating a predefined number, loop
1899 devices can be requested on-demand with the
1900 /dev/loop-control interface.
1902 mce [X86-32] Machine Check Exception
1904 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1906 md= [HW] RAID subsystems devices and level
1907 See Documentation/md.txt.
1909 mdacon= [MDA]
1910 Format: <first>,<last>
1911 Specifies range of consoles to be captured by the MDA.
1913 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1914 Amount of memory to be used when the kernel is not able
1915 to see the whole system memory or for test.
1916 [X86] Work as limiting max address. Use together
1917 with memmap= to avoid physical address space collisions.
1918 Without memmap= PCI devices could be placed at addresses
1919 belonging to unused RAM.
1921 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1922 memory.
1924 memchunk=nn[KMG]
1925 [KNL,SH] Allow user to override the default size for
1926 per-device physically contiguous DMA buffers.
1928 memmap=exactmap [KNL,X86] Enable setting of an exact
1929 E820 memory map, as specified by the user.
1930 Such memmap=exactmap lines can be constructed based on
1931 BIOS output or other requirements. See the memmap=nn@ss
1932 option description.
1934 memmap=nn[KMG]@ss[KMG]
1935 [KNL] Force usage of a specific region of memory.
1936 Region of memory to be used is from ss to ss+nn.
1938 memmap=nn[KMG]#ss[KMG]
1939 [KNL,ACPI] Mark specific memory as ACPI data.
1940 Region of memory to be marked is from ss to ss+nn.
1942 memmap=nn[KMG]$ss[KMG]
1943 [KNL,ACPI] Mark specific memory as reserved.
1944 Region of memory to be reserved is from ss to ss+nn.
1945 Example: Exclude memory from 0x18690000-0x1869ffff
1946 memmap=64K$0x18690000
1947 or
1948 memmap=0x10000$0x18690000
1950 memory_corruption_check=0/1 [X86]
1951 Some BIOSes seem to corrupt the first 64k of
1952 memory when doing things like suspend/resume.
1953 Setting this option will scan the memory
1954 looking for corruption. Enabling this will
1955 both detect corruption and prevent the kernel
1956 from using the memory being corrupted.
1957 However, its intended as a diagnostic tool; if
1958 repeatable BIOS-originated corruption always
1959 affects the same memory, you can use memmap=
1960 to prevent the kernel from using that memory.
1962 memory_corruption_check_size=size [X86]
1963 By default it checks for corruption in the low
1964 64k, making this memory unavailable for normal
1965 use. Use this parameter to scan for
1966 corruption in more or less memory.
1968 memory_corruption_check_period=seconds [X86]
1969 By default it checks for corruption every 60
1970 seconds. Use this parameter to check at some
1971 other rate. 0 disables periodic checking.
1973 memtest= [KNL,X86] Enable memtest
1974 Format: <integer>
1975 default : 0 <disable>
1976 Specifies the number of memtest passes to be
1977 performed. Each pass selects another test
1978 pattern from a given set of patterns. Memtest
1979 fills the memory with this pattern, validates
1980 memory contents and reserves bad memory
1981 regions that are detected.
1983 meye.*= [HW] Set MotionEye Camera parameters
1984 See Documentation/video4linux/meye.txt.
1986 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1987 Multi-Function General Purpose Timers on AMD Geode
1988 platforms.
1990 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1991 the BIOS has incorrectly applied a workaround. TinyBIOS
1992 version 0.98 is known to be affected, 0.99 fixes the
1993 problem by letting the user disable the workaround.
1995 mga= [HW,DRM]
1997 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1998 physical address is ignored.
2000 mini2440= [ARM,HW,KNL]
2001 Format:[0..2][b][c][t]
2002 Default: "0tb"
2003 MINI2440 configuration specification:
2004 0 - The attached screen is the 3.5" TFT
2005 1 - The attached screen is the 7" TFT
2006 2 - The VGA Shield is attached (1024x768)
2007 Leaving out the screen size parameter will not load
2008 the TFT driver, and the framebuffer will be left
2009 unconfigured.
2010 b - Enable backlight. The TFT backlight pin will be
2011 linked to the kernel VESA blanking code and a GPIO
2012 LED. This parameter is not necessary when using the
2013 VGA shield.
2014 c - Enable the s3c camera interface.
2015 t - Reserved for enabling touchscreen support. The
2016 touchscreen support is not enabled in the mainstream
2017 kernel as of 2.6.30, a preliminary port can be found
2018 in the "bleeding edge" mini2440 support kernel at
2019 http://repo.or.cz/w/linux-2.6/mini2440.git
2021 mminit_loglevel=
2022 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2023 parameter allows control of the logging verbosity for
2024 the additional memory initialisation checks. A value
2025 of 0 disables mminit logging and a level of 4 will
2026 log everything. Information is printed at KERN_DEBUG
2027 so loglevel=8 may also need to be specified.
2029 module.sig_enforce
2030 [KNL] When CONFIG_MODULE_SIG is set, this means that
2031 modules without (valid) signatures will fail to load.
2032 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2033 is always true, so this option does nothing.
2035 mousedev.tap_time=
2036 [MOUSE] Maximum time between finger touching and
2037 leaving touchpad surface for touch to be considered
2038 a tap and be reported as a left button click (for
2039 touchpads working in absolute mode only).
2040 Format: <msecs>
2041 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2042 reporting absolute coordinates, such as tablets
2043 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2044 reporting absolute coordinates, such as tablets
2046 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2047 is similar to kernelcore except it specifies the
2048 amount of memory used for migratable allocations.
2049 If both kernelcore and movablecore is specified,
2050 then kernelcore will be at *least* the specified
2051 value but may be more. If movablecore on its own
2052 is specified, the administrator must be careful
2053 that the amount of memory usable for all allocations
2054 is not too small.
2056 movable_node [KNL,X86] Boot-time switch to enable the effects
2057 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2059 MTD_Partition= [MTD]
2060 Format: <name>,<region-number>,<size>,<offset>
2062 MTD_Region= [MTD] Format:
2063 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2065 mtdparts= [MTD]
2066 See drivers/mtd/cmdlinepart.c.
2068 multitce=off [PPC] This parameter disables the use of the pSeries
2069 firmware feature for updating multiple TCE entries
2070 at a time.
2072 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2074 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2076 boundary - index of last SLC block on Flex-OneNAND.
2077 The remaining blocks are configured as MLC blocks.
2078 lock - Configure if Flex-OneNAND boundary should be locked.
2079 Once locked, the boundary cannot be changed.
2080 1 indicates lock status, 0 indicates unlock status.
2082 mtdset= [ARM]
2083 ARM/S3C2412 JIVE boot control
2085 See arch/arm/mach-s3c2412/mach-jive.c
2087 mtouchusb.raw_coordinates=
2088 [HW] Make the MicroTouch USB driver use raw coordinates
2089 ('y', default) or cooked coordinates ('n')
2091 mtrr_chunk_size=nn[KMG] [X86]
2092 used for mtrr cleanup. It is largest continuous chunk
2093 that could hold holes aka. UC entries.
2095 mtrr_gran_size=nn[KMG] [X86]
2096 Used for mtrr cleanup. It is granularity of mtrr block.
2097 Default is 1.
2098 Large value could prevent small alignment from
2099 using up MTRRs.
2101 mtrr_spare_reg_nr=n [X86]
2102 Format: <integer>
2103 Range: 0,7 : spare reg number
2104 Default : 1
2105 Used for mtrr cleanup. It is spare mtrr entries number.
2106 Set to 2 or more if your graphical card needs more.
2108 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2110 netdev= [NET] Network devices parameters
2111 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2112 Note that mem_start is often overloaded to mean
2113 something different and driver-specific.
2114 This usage is only documented in each driver source
2115 file if at all.
2117 nf_conntrack.acct=
2118 [NETFILTER] Enable connection tracking flow accounting
2119 0 to disable accounting
2120 1 to enable accounting
2121 Default value is 0.
2123 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2124 See Documentation/filesystems/nfs/nfsroot.txt.
2126 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2127 See Documentation/filesystems/nfs/nfsroot.txt.
2129 nfsrootdebug [NFS] enable nfsroot debugging messages.
2130 See Documentation/filesystems/nfs/nfsroot.txt.
2132 nfs.callback_tcpport=
2133 [NFS] set the TCP port on which the NFSv4 callback
2134 channel should listen.
2136 nfs.cache_getent=
2137 [NFS] sets the pathname to the program which is used
2138 to update the NFS client cache entries.
2140 nfs.cache_getent_timeout=
2141 [NFS] sets the timeout after which an attempt to
2142 update a cache entry is deemed to have failed.
2144 nfs.idmap_cache_timeout=
2145 [NFS] set the maximum lifetime for idmapper cache
2146 entries.
2148 nfs.enable_ino64=
2149 [NFS] enable 64-bit inode numbers.
2150 If zero, the NFS client will fake up a 32-bit inode
2151 number for the readdir() and stat() syscalls instead
2152 of returning the full 64-bit number.
2153 The default is to return 64-bit inode numbers.
2155 nfs.max_session_slots=
2156 [NFSv4.1] Sets the maximum number of session slots
2157 the client will attempt to negotiate with the server.
2158 This limits the number of simultaneous RPC requests
2159 that the client can send to the NFSv4.1 server.
2160 Note that there is little point in setting this
2161 value higher than the max_tcp_slot_table_limit.
2163 nfs.nfs4_disable_idmapping=
2164 [NFSv4] When set to the default of '1', this option
2165 ensures that both the RPC level authentication
2166 scheme and the NFS level operations agree to use
2167 numeric uids/gids if the mount is using the
2168 'sec=sys' security flavour. In effect it is
2169 disabling idmapping, which can make migration from
2170 legacy NFSv2/v3 systems to NFSv4 easier.
2171 Servers that do not support this mode of operation
2172 will be autodetected by the client, and it will fall
2173 back to using the idmapper.
2174 To turn off this behaviour, set the value to '0'.
2175 nfs.nfs4_unique_id=
2176 [NFS4] Specify an additional fixed unique ident-
2177 ification string that NFSv4 clients can insert into
2178 their nfs_client_id4 string. This is typically a
2179 UUID that is generated at system install time.
2181 nfs.send_implementation_id =
2182 [NFSv4.1] Send client implementation identification
2183 information in exchange_id requests.
2184 If zero, no implementation identification information
2185 will be sent.
2186 The default is to send the implementation identification
2187 information.
2189 nfs.recover_lost_locks =
2190 [NFSv4] Attempt to recover locks that were lost due
2191 to a lease timeout on the server. Please note that
2192 doing this risks data corruption, since there are
2193 no guarantees that the file will remain unchanged
2194 after the locks are lost.
2195 If you want to enable the kernel legacy behaviour of
2196 attempting to recover these locks, then set this
2197 parameter to '1'.
2198 The default parameter value of '0' causes the kernel
2199 not to attempt recovery of lost locks.
2201 nfsd.nfs4_disable_idmapping=
2202 [NFSv4] When set to the default of '1', the NFSv4
2203 server will return only numeric uids and gids to
2204 clients using auth_sys, and will accept numeric uids
2205 and gids from such clients. This is intended to ease
2206 migration from NFSv2/v3.
2208 objlayoutdriver.osd_login_prog=
2209 [NFS] [OBJLAYOUT] sets the pathname to the program which
2210 is used to automatically discover and login into new
2211 osd-targets. Please see:
2212 Documentation/filesystems/pnfs.txt for more explanations
2214 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2215 when a NMI is triggered.
2216 Format: [state][,regs][,debounce][,die]
2218 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2219 Format: [panic,][nopanic,][num]
2220 Valid num: 0
2221 0 - turn nmi_watchdog off
2222 When panic is specified, panic when an NMI watchdog
2223 timeout occurs (or 'nopanic' to override the opposite
2224 default).
2225 This is useful when you use a panic=... timeout and
2226 need the box quickly up again.
2228 netpoll.carrier_timeout=
2229 [NET] Specifies amount of time (in seconds) that
2230 netpoll should wait for a carrier. By default netpoll
2231 waits 4 seconds.
2233 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2234 emulation library even if a 387 maths coprocessor
2235 is present.
2237 no_console_suspend
2238 [HW] Never suspend the console
2239 Disable suspending of consoles during suspend and
2240 hibernate operations. Once disabled, debugging
2241 messages can reach various consoles while the rest
2242 of the system is being put to sleep (ie, while
2243 debugging driver suspend/resume hooks). This may
2244 not work reliably with all consoles, but is known
2245 to work with serial and VGA consoles.
2246 To facilitate more flexible debugging, we also add
2247 console_suspend, a printk module parameter to control
2248 it. Users could use console_suspend (usually
2249 /sys/module/printk/parameters/console_suspend) to
2250 turn on/off it dynamically.
2252 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2253 caches in the slab allocator. Saves per-node memory,
2254 but will impact performance.
2256 noalign [KNL,ARM]
2258 noapic [SMP,APIC] Tells the kernel to not make use of any
2259 IOAPICs that may be present in the system.
2261 noautogroup Disable scheduler automatic task group creation.
2263 nobats [PPC] Do not use BATs for mapping kernel lowmem
2264 on "Classic" PPC cores.
2266 nocache [ARM]
2268 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2270 nodelayacct [KNL] Disable per-task delay accounting
2272 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2274 nodsp [SH] Disable hardware DSP at boot time.
2276 noefi Disable EFI runtime services support.
2278 noexec [IA-64]
2280 noexec [X86]
2281 On X86-32 available only on PAE configured kernels.
2282 noexec=on: enable non-executable mappings (default)
2283 noexec=off: disable non-executable mappings
2285 nosmap [X86]
2286 Disable SMAP (Supervisor Mode Access Prevention)
2287 even if it is supported by processor.
2289 nosmep [X86]
2290 Disable SMEP (Supervisor Mode Execution Prevention)
2291 even if it is supported by processor.
2293 noexec32 [X86-64]
2294 This affects only 32-bit executables.
2295 noexec32=on: enable non-executable mappings (default)
2296 read doesn't imply executable mappings
2297 noexec32=off: disable non-executable mappings
2298 read implies executable mappings
2300 nofpu [SH] Disable hardware FPU at boot time.
2302 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2303 register save and restore. The kernel will only save
2304 legacy floating-point registers on task switch.
2306 noxsave [BUGS=X86] Disables x86 extended register state save
2307 and restore using xsave. The kernel will fallback to
2308 enabling legacy floating-point and sse state.
2310 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2311 register states. The kernel will fall back to use
2312 xsave to save the states. By using this parameter,
2313 performance of saving the states is degraded because
2314 xsave doesn't support modified optimization while
2315 xsaveopt supports it on xsaveopt enabled systems.
2317 noxsaves [X86] Disables xsaves and xrstors used in saving and
2318 restoring x86 extended register state in compacted
2319 form of xsave area. The kernel will fall back to use
2320 xsaveopt and xrstor to save and restore the states
2321 in standard form of xsave area. By using this
2322 parameter, xsave area per process might occupy more
2323 memory on xsaves enabled systems.
2325 eagerfpu= [X86]
2326 on enable eager fpu restore
2327 off disable eager fpu restore
2328 auto selects the default scheme, which automatically
2329 enables eagerfpu restore for xsaveopt.
2331 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2332 wfi(ARM) instruction doesn't work correctly and not to
2333 use it. This is also useful when using JTAG debugger.
2335 no_file_caps Tells the kernel not to honor file capabilities. The
2336 only way then for a file to be executed with privilege
2337 is to be setuid root or executed by root.
2339 nohalt [IA-64] Tells the kernel not to use the power saving
2340 function PAL_HALT_LIGHT when idle. This increases
2341 power-consumption. On the positive side, it reduces
2342 interrupt wake-up latency, which may improve performance
2343 in certain environments such as networked servers or
2344 real-time systems.
2346 nohibernate [HIBERNATION] Disable hibernation and resume.
2348 nohz= [KNL] Boottime enable/disable dynamic ticks
2349 Valid arguments: on, off
2350 Default: on
2352 nohz_full= [KNL,BOOT]
2353 In kernels built with CONFIG_NO_HZ_FULL=y, set
2354 the specified list of CPUs whose tick will be stopped
2355 whenever possible. The boot CPU will be forced outside
2356 the range to maintain the timekeeping.
2357 The CPUs in this range must also be included in the
2358 rcu_nocbs= set.
2360 noiotrap [SH] Disables trapped I/O port accesses.
2362 noirqdebug [X86-32] Disables the code which attempts to detect and
2363 disable unhandled interrupt sources.
2365 no_timer_check [X86,APIC] Disables the code which tests for
2366 broken timer IRQ sources.
2368 noisapnp [ISAPNP] Disables ISA PnP code.
2370 noinitrd [RAM] Tells the kernel not to load any configured
2371 initial RAM disk.
2373 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2374 remapping.
2375 [Deprecated - use intremap=off]
2377 nointroute [IA-64]
2379 nojitter [IA-64] Disables jitter checking for ITC timers.
2381 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2383 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2384 fault handling.
2386 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2387 steal time is computed, but won't influence scheduler
2388 behaviour
2390 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2392 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2394 noltlbs [PPC] Do not use large page/tlb entries for kernel
2395 lowmem mapping on PPC40x.
2397 nomca [IA-64] Disable machine check abort handling
2399 nomce [X86-32] Machine Check Exception
2401 nomfgpt [X86-32] Disable Multi-Function General Purpose
2402 Timer usage (for AMD Geode machines).
2404 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2405 shutdown the other cpus. Instead use the REBOOT_VECTOR
2406 irq.
2408 nomodule Disable module load
2410 nopat [X86] Disable PAT (page attribute table extension of
2411 pagetables) support.
2413 norandmaps Don't use address space randomization. Equivalent to
2414 echo 0 > /proc/sys/kernel/randomize_va_space
2416 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2418 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2419 with UP alternatives
2421 nordrand [X86] Disable kernel use of the RDRAND and
2422 RDSEED instructions even if they are supported
2423 by the processor. RDRAND and RDSEED are still
2424 available to user space applications.
2426 noresume [SWSUSP] Disables resume and restores original swap
2427 space.
2429 no-scroll [VGA] Disables scrollback.
2430 This is required for the Braillex ib80-piezo Braille
2431 reader made by F.H. Papenmeier (Germany).
2433 nosbagart [IA-64]
2435 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2437 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2438 and disable the IO APIC. legacy for "maxcpus=0".
2440 nosoftlockup [KNL] Disable the soft-lockup detector.
2442 nosync [HW,M68K] Disables sync negotiation for all devices.
2444 notsc [BUGS=X86-32] Disable Time Stamp Counter
2446 nousb [USB] Disable the USB subsystem
2448 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2450 nowb [ARM]
2452 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2454 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2455 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2456 Some features depend on CPU0. Known dependencies are:
2457 1. Resume from suspend/hibernate depends on CPU0.
2458 Suspend/hibernate will fail if CPU0 is offline and you
2459 need to online CPU0 before suspend/hibernate.
2460 2. PIC interrupts also depend on CPU0. CPU0 can't be
2461 removed if a PIC interrupt is detected.
2462 It's said poweroff/reboot may depend on CPU0 on some
2463 machines although I haven't seen such issues so far
2464 after CPU0 is offline on a few tested machines.
2465 If the dependencies are under your control, you can
2466 turn on cpu0_hotplug.
2468 nptcg= [IA-64] Override max number of concurrent global TLB
2469 purges which is reported from either PAL_VM_SUMMARY or
2470 SAL PALO.
2472 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2473 could support. nr_cpus=n : n >= 1 limits the kernel to
2474 supporting 'n' processors. Later in runtime you can not
2475 use hotplug cpu feature to put more cpu back to online.
2476 just like you compile the kernel NR_CPUS=n
2478 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2480 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2481 Allowed values are enable and disable
2483 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2484 one of ['zone', 'node', 'default'] can be specified
2485 This can be set from sysctl after boot.
2486 See Documentation/sysctl/vm.txt for details.
2488 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2489 See Documentation/debugging-via-ohci1394.txt for more
2490 info.
2492 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2493 Rather than timing out after 20 ms if an EC
2494 command is not properly ACKed, override the length
2495 of the timeout. We have interrupts disabled while
2496 waiting for the ACK, so if this is set too high
2497 interrupts *may* be lost!
2499 omap_mux= [OMAP] Override bootloader pin multiplexing.
2500 Format: <mux_mode0.mode_name=value>...
2501 For example, to override I2C bus2:
2502 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2504 oprofile.timer= [HW]
2505 Use timer interrupt instead of performance counters
2507 oprofile.cpu_type= Force an oprofile cpu type
2508 This might be useful if you have an older oprofile
2509 userland or if you want common events.
2510 Format: { arch_perfmon }
2511 arch_perfmon: [X86] Force use of architectural
2512 perfmon on Intel CPUs instead of the
2513 CPU specific event set.
2514 timer: [X86] Force use of architectural NMI
2515 timer mode (see also oprofile.timer
2516 for generic hr timer mode)
2517 [s390] Force legacy basic mode sampling
2518 (report cpu_type "timer")
2520 oops=panic Always panic on oopses. Default is to just kill the
2521 process, but there is a small probability of
2522 deadlocking the machine.
2523 This will also cause panics on machine check exceptions.
2524 Useful together with panic=30 to trigger a reboot.
2526 OSS [HW,OSS]
2527 See Documentation/sound/oss/oss-parameters.txt
2529 page_owner= [KNL] Boot-time page_owner enabling option.
2530 Storage of the information about who allocated
2531 each page is disabled in default. With this switch,
2532 we can turn it on.
2533 on: enable the feature
2535 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2536 timeout > 0: seconds before rebooting
2537 timeout = 0: wait forever
2538 timeout < 0: reboot immediately
2539 Format: <timeout>
2541 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2542 on a WARN().
2544 crash_kexec_post_notifiers
2545 Run kdump after running panic-notifiers and dumping
2546 kmsg. This only for the users who doubt kdump always
2547 succeeds in any situation.
2548 Note that this also increases risks of kdump failure,
2549 because some panic notifiers can make the crashed
2550 kernel more unstable.
2552 parkbd.port= [HW] Parallel port number the keyboard adapter is
2553 connected to, default is 0.
2554 Format: <parport#>
2555 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2556 0 for XT, 1 for AT (default is AT).
2557 Format: <mode>
2559 parport= [HW,PPT] Specify parallel ports. 0 disables.
2560 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2561 Use 'auto' to force the driver to use any
2562 IRQ/DMA settings detected (the default is to
2563 ignore detected IRQ/DMA settings because of
2564 possible conflicts). You can specify the base
2565 address, IRQ, and DMA settings; IRQ and DMA
2566 should be numbers, or 'auto' (for using detected
2567 settings on that particular port), or 'nofifo'
2568 (to avoid using a FIFO even if it is detected).
2569 Parallel ports are assigned in the order they
2570 are specified on the command line, starting
2571 with parport0.
2573 parport_init_mode= [HW,PPT]
2574 Configure VIA parallel port to operate in
2575 a specific mode. This is necessary on Pegasos
2576 computer where firmware has no options for setting
2577 up parallel port mode and sets it to spp.
2578 Currently this function knows 686a and 8231 chips.
2579 Format: [spp|ps2|epp|ecp|ecpepp]
2581 pause_on_oops=
2582 Halt all CPUs after the first oops has been printed for
2583 the specified number of seconds. This is to be used if
2584 your oopses keep scrolling off the screen.
2586 pcbit= [HW,ISDN]
2588 pcd. [PARIDE]
2589 See header of drivers/block/paride/pcd.c.
2590 See also Documentation/blockdev/paride.txt.
2592 pci=option[,option...] [PCI] various PCI subsystem options:
2593 earlydump [X86] dump PCI config space before the kernel
2594 changes anything
2595 off [X86] don't probe for the PCI bus
2596 bios [X86-32] force use of PCI BIOS, don't access
2597 the hardware directly. Use this if your machine
2598 has a non-standard PCI host bridge.
2599 nobios [X86-32] disallow use of PCI BIOS, only direct
2600 hardware access methods are allowed. Use this
2601 if you experience crashes upon bootup and you
2602 suspect they are caused by the BIOS.
2603 conf1 [X86] Force use of PCI Configuration
2604 Mechanism 1.
2605 conf2 [X86] Force use of PCI Configuration
2606 Mechanism 2.
2607 noaer [PCIE] If the PCIEAER kernel config parameter is
2608 enabled, this kernel boot option can be used to
2609 disable the use of PCIE advanced error reporting.
2610 nodomains [PCI] Disable support for multiple PCI
2611 root domains (aka PCI segments, in ACPI-speak).
2612 nommconf [X86] Disable use of MMCONFIG for PCI
2613 Configuration
2614 check_enable_amd_mmconf [X86] check for and enable
2615 properly configured MMIO access to PCI
2616 config space on AMD family 10h CPU
2617 nomsi [MSI] If the PCI_MSI kernel config parameter is
2618 enabled, this kernel boot option can be used to
2619 disable the use of MSI interrupts system-wide.
2620 noioapicquirk [APIC] Disable all boot interrupt quirks.
2621 Safety option to keep boot IRQs enabled. This
2622 should never be necessary.
2623 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2624 primary IO-APIC for bridges that cannot disable
2625 boot IRQs. This fixes a source of spurious IRQs
2626 when the system masks IRQs.
2627 noioapicreroute [APIC] Disable workaround that uses the
2628 boot IRQ equivalent of an IRQ that connects to
2629 a chipset where boot IRQs cannot be disabled.
2630 The opposite of ioapicreroute.
2631 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2632 routing table. These calls are known to be buggy
2633 on several machines and they hang the machine
2634 when used, but on other computers it's the only
2635 way to get the interrupt routing table. Try
2636 this option if the kernel is unable to allocate
2637 IRQs or discover secondary PCI buses on your
2638 motherboard.
2639 rom [X86] Assign address space to expansion ROMs.
2640 Use with caution as certain devices share
2641 address decoders between ROMs and other
2642 resources.
2643 norom [X86] Do not assign address space to
2644 expansion ROMs that do not already have
2645 BIOS assigned address ranges.
2646 nobar [X86] Do not assign address space to the
2647 BARs that weren't assigned by the BIOS.
2648 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2649 assigned automatically to PCI devices. You can
2650 make the kernel exclude IRQs of your ISA cards
2651 this way.
2652 pirqaddr=0xAAAAA [X86] Specify the physical address
2653 of the PIRQ table (normally generated
2654 by the BIOS) if it is outside the
2655 F0000h-100000h range.
2656 lastbus=N [X86] Scan all buses thru bus #N. Can be
2657 useful if the kernel is unable to find your
2658 secondary buses and you want to tell it
2659 explicitly which ones they are.
2660 assign-busses [X86] Always assign all PCI bus
2661 numbers ourselves, overriding
2662 whatever the firmware may have done.
2663 usepirqmask [X86] Honor the possible IRQ mask stored
2664 in the BIOS $PIR table. This is needed on
2665 some systems with broken BIOSes, notably
2666 some HP Pavilion N5400 and Omnibook XE3
2667 notebooks. This will have no effect if ACPI
2668 IRQ routing is enabled.
2669 noacpi [X86] Do not use ACPI for IRQ routing
2670 or for PCI scanning.
2671 use_crs [X86] Use PCI host bridge window information
2672 from ACPI. On BIOSes from 2008 or later, this
2673 is enabled by default. If you need to use this,
2674 please report a bug.
2675 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2676 If you need to use this, please report a bug.
2677 routeirq Do IRQ routing for all PCI devices.
2678 This is normally done in pci_enable_device(),
2679 so this option is a temporary workaround
2680 for broken drivers that don't call it.
2681 skip_isa_align [X86] do not align io start addr, so can
2682 handle more pci cards
2683 firmware [ARM] Do not re-enumerate the bus but instead
2684 just use the configuration from the
2685 bootloader. This is currently used on
2686 IXP2000 systems where the bus has to be
2687 configured a certain way for adjunct CPUs.
2688 noearly [X86] Don't do any early type 1 scanning.
2689 This might help on some broken boards which
2690 machine check when some devices' config space
2691 is read. But various workarounds are disabled
2692 and some IOMMU drivers will not work.
2693 bfsort Sort PCI devices into breadth-first order.
2694 This sorting is done to get a device
2695 order compatible with older (<= 2.4) kernels.
2696 nobfsort Don't sort PCI devices into breadth-first order.
2697 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2698 tuning and use the BIOS-configured MPS defaults.
2699 pcie_bus_safe Set every device's MPS to the largest value
2700 supported by all devices below the root complex.
2701 pcie_bus_perf Set device MPS to the largest allowable MPS
2702 based on its parent bus. Also set MRRS (Max
2703 Read Request Size) to the largest supported
2704 value (no larger than the MPS that the device
2705 or bus can support) for best performance.
2706 pcie_bus_peer2peer Set every device's MPS to 128B, which
2707 every device is guaranteed to support. This
2708 configuration allows peer-to-peer DMA between
2709 any pair of devices, possibly at the cost of
2710 reduced performance. This also guarantees
2711 that hot-added devices will work.
2712 cbiosize=nn[KMG] The fixed amount of bus space which is
2713 reserved for the CardBus bridge's IO window.
2714 The default value is 256 bytes.
2715 cbmemsize=nn[KMG] The fixed amount of bus space which is
2716 reserved for the CardBus bridge's memory
2717 window. The default value is 64 megabytes.
2718 resource_alignment=
2719 Format:
2720 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2721 Specifies alignment and device to reassign
2722 aligned memory resources.
2723 If <order of align> is not specified,
2724 PAGE_SIZE is used as alignment.
2725 PCI-PCI bridge can be specified, if resource
2726 windows need to be expanded.
2727 ecrc= Enable/disable PCIe ECRC (transaction layer
2728 end-to-end CRC checking).
2729 bios: Use BIOS/firmware settings. This is the
2730 the default.
2731 off: Turn ECRC off
2732 on: Turn ECRC on.
2733 hpiosize=nn[KMG] The fixed amount of bus space which is
2734 reserved for hotplug bridge's IO window.
2735 Default size is 256 bytes.
2736 hpmemsize=nn[KMG] The fixed amount of bus space which is
2737 reserved for hotplug bridge's memory window.
2738 Default size is 2 megabytes.
2739 realloc= Enable/disable reallocating PCI bridge resources
2740 if allocations done by BIOS are too small to
2741 accommodate resources required by all child
2742 devices.
2743 off: Turn realloc off
2744 on: Turn realloc on
2745 realloc same as realloc=on
2746 noari do not use PCIe ARI.
2747 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2748 only look for one device below a PCIe downstream
2749 port.
2751 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2752 Management.
2753 off Disable ASPM.
2754 force Enable ASPM even on devices that claim not to support it.
2755 WARNING: Forcing ASPM on may cause system lockups.
2757 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2758 nomsi Do not use MSI for PCI Express Native Hotplug (this
2759 makes all PCIe ports use INTx for hotplug services).
2761 pcie_ports= [PCIE] PCIe ports handling:
2762 auto Ask the BIOS whether or not to use native PCIe services
2763 associated with PCIe ports (PME, hot-plug, AER). Use
2764 them only if that is allowed by the BIOS.
2765 native Use native PCIe services associated with PCIe ports
2766 unconditionally.
2767 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2768 ports driver.
2770 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2771 nomsi Do not use MSI for native PCIe PME signaling (this makes
2772 all PCIe root ports use INTx for all services).
2774 pcmv= [HW,PCMCIA] BadgePAD 4
2776 pd_ignore_unused
2777 [PM]
2778 Keep all power-domains already enabled by bootloader on,
2779 even if no driver has claimed them. This is useful
2780 for debug and development, but should not be
2781 needed on a platform with proper driver support.
2783 pd. [PARIDE]
2784 See Documentation/blockdev/paride.txt.
2786 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2787 boot time.
2788 Format: { 0 | 1 }
2789 See arch/parisc/kernel/pdc_chassis.c
2791 percpu_alloc= Select which percpu first chunk allocator to use.
2792 Currently supported values are "embed" and "page".
2793 Archs may support subset or none of the selections.
2794 See comments in mm/percpu.c for details on each
2795 allocator. This parameter is primarily for debugging
2796 and performance comparison.
2798 pf. [PARIDE]
2799 See Documentation/blockdev/paride.txt.
2801 pg. [PARIDE]
2802 See Documentation/blockdev/paride.txt.
2804 pirq= [SMP,APIC] Manual mp-table setup
2805 See Documentation/x86/i386/IO-APIC.txt.
2807 plip= [PPT,NET] Parallel port network link
2808 Format: { parport<nr> | timid | 0 }
2809 See also Documentation/parport.txt.
2811 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2812 Override pmtimer IOPort with a hex value.
2813 e.g. pmtmr=0x508
2815 pnp.debug=1 [PNP]
2816 Enable PNP debug messages (depends on the
2817 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2818 via /sys/module/pnp/parameters/debug. We always show
2819 current resource usage; turning this on also shows
2820 possible settings and some assignment information.
2822 pnpacpi= [ACPI]
2823 { off }
2825 pnpbios= [ISAPNP]
2826 { on | off | curr | res | no-curr | no-res }
2828 pnp_reserve_irq=
2829 [ISAPNP] Exclude IRQs for the autoconfiguration
2831 pnp_reserve_dma=
2832 [ISAPNP] Exclude DMAs for the autoconfiguration
2834 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2835 Ranges are in pairs (I/O port base and size).
2837 pnp_reserve_mem=
2838 [ISAPNP] Exclude memory regions for the
2839 autoconfiguration.
2840 Ranges are in pairs (memory base and size).
2842 ports= [IP_VS_FTP] IPVS ftp helper module
2843 Default is 21.
2844 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2845 may be specified.
2846 Format: <port>,<port>....
2848 print-fatal-signals=
2849 [KNL] debug: print fatal signals
2851 If enabled, warn about various signal handling
2852 related application anomalies: too many signals,
2853 too many POSIX.1 timers, fatal signals causing a
2854 coredump - etc.
2856 If you hit the warning due to signal overflow,
2857 you might want to try "ulimit -i unlimited".
2859 default: off.
2861 printk.always_kmsg_dump=
2862 Trigger kmsg_dump for cases other than kernel oops or
2863 panics
2864 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2865 default: disabled
2867 printk.time= Show timing data prefixed to each printk message line
2868 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2870 processor.max_cstate= [HW,ACPI]
2871 Limit processor to maximum C-state
2872 max_cstate=9 overrides any DMI blacklist limit.
2874 processor.nocst [HW,ACPI]
2875 Ignore the _CST method to determine C-states,
2876 instead using the legacy FADT method
2878 profile= [KNL] Enable kernel profiling via /proc/profile
2879 Format: [schedule,]<number>
2880 Param: "schedule" - profile schedule points.
2881 Param: <number> - step/bucket size as a power of 2 for
2882 statistical time based profiling.
2883 Param: "sleep" - profile D-state sleeping (millisecs).
2884 Requires CONFIG_SCHEDSTATS
2885 Param: "kvm" - profile VM exits.
2887 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2888 before loading.
2889 See Documentation/blockdev/ramdisk.txt.
2891 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2892 probe for; one of (bare|imps|exps|lifebook|any).
2893 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2894 per second.
2895 psmouse.resetafter= [HW,MOUSE]
2896 Try to reset the device after so many bad packets
2897 (0 = never).
2898 psmouse.resolution=
2899 [HW,MOUSE] Set desired mouse resolution, in dpi.
2900 psmouse.smartscroll=
2901 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2902 0 = disabled, 1 = enabled (default).
2904 pstore.backend= Specify the name of the pstore backend to use
2906 pt. [PARIDE]
2907 See Documentation/blockdev/paride.txt.
2909 pty.legacy_count=
2910 [KNL] Number of legacy pty's. Overwrites compiled-in
2911 default number.
2913 quiet [KNL] Disable most log messages
2915 r128= [HW,DRM]
2917 raid= [HW,RAID]
2918 See Documentation/md.txt.
2920 ramdisk_blocksize= [RAM]
2921 See Documentation/blockdev/ramdisk.txt.
2923 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2924 See Documentation/blockdev/ramdisk.txt.
2926 rcu_nocbs= [KNL]
2927 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2928 the specified list of CPUs to be no-callback CPUs.
2929 Invocation of these CPUs' RCU callbacks will
2930 be offloaded to "rcuox/N" kthreads created for
2931 that purpose, where "x" is "b" for RCU-bh, "p"
2932 for RCU-preempt, and "s" for RCU-sched, and "N"
2933 is the CPU number. This reduces OS jitter on the
2934 offloaded CPUs, which can be useful for HPC and
2935 real-time workloads. It can also improve energy
2936 efficiency for asymmetric multiprocessors.
2938 rcu_nocb_poll [KNL]
2939 Rather than requiring that offloaded CPUs
2940 (specified by rcu_nocbs= above) explicitly
2941 awaken the corresponding "rcuoN" kthreads,
2942 make these kthreads poll for callbacks.
2943 This improves the real-time response for the
2944 offloaded CPUs by relieving them of the need to
2945 wake up the corresponding kthread, but degrades
2946 energy efficiency by requiring that the kthreads
2947 periodically wake up to do the polling.
2949 rcutree.blimit= [KNL]
2950 Set maximum number of finished RCU callbacks to
2951 process in one batch.
2953 rcutree.rcu_fanout_leaf= [KNL]
2954 Increase the number of CPUs assigned to each
2955 leaf rcu_node structure. Useful for very large
2956 systems.
2958 rcutree.jiffies_till_sched_qs= [KNL]
2959 Set required age in jiffies for a
2960 given grace period before RCU starts
2961 soliciting quiescent-state help from
2962 rcu_note_context_switch().
2964 rcutree.jiffies_till_first_fqs= [KNL]
2965 Set delay from grace-period initialization to
2966 first attempt to force quiescent states.
2967 Units are jiffies, minimum value is zero,
2968 and maximum value is HZ.
2970 rcutree.jiffies_till_next_fqs= [KNL]
2971 Set delay between subsequent attempts to force
2972 quiescent states. Units are jiffies, minimum
2973 value is one, and maximum value is HZ.
2975 rcutree.kthread_prio= [KNL,BOOT]
2976 Set the SCHED_FIFO priority of the RCU
2977 per-CPU kthreads (rcuc/N). This value is also
2978 used for the priority of the RCU boost threads
2979 (rcub/N). Valid values are 1-99 and the default
2980 is 1 (the least-favored priority).
2982 rcutree.rcu_nocb_leader_stride= [KNL]
2983 Set the number of NOCB kthread groups, which
2984 defaults to the square root of the number of
2985 CPUs. Larger numbers reduces the wakeup overhead
2986 on the per-CPU grace-period kthreads, but increases
2987 that same overhead on each group's leader.
2989 rcutree.qhimark= [KNL]
2990 Set threshold of queued RCU callbacks beyond which
2991 batch limiting is disabled.
2993 rcutree.qlowmark= [KNL]
2994 Set threshold of queued RCU callbacks below which
2995 batch limiting is re-enabled.
2997 rcutree.rcu_idle_gp_delay= [KNL]
2998 Set wakeup interval for idle CPUs that have
2999 RCU callbacks (RCU_FAST_NO_HZ=y).
3001 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3002 Set wakeup interval for idle CPUs that have
3003 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3004 Lazy RCU callbacks are those which RCU can
3005 prove do nothing more than free memory.
3007 rcutorture.cbflood_inter_holdoff= [KNL]
3008 Set holdoff time (jiffies) between successive
3009 callback-flood tests.
3011 rcutorture.cbflood_intra_holdoff= [KNL]
3012 Set holdoff time (jiffies) between successive
3013 bursts of callbacks within a given callback-flood
3014 test.
3016 rcutorture.cbflood_n_burst= [KNL]
3017 Set the number of bursts making up a given
3018 callback-flood test. Set this to zero to
3019 disable callback-flood testing.
3021 rcutorture.cbflood_n_per_burst= [KNL]
3022 Set the number of callbacks to be registered
3023 in a given burst of a callback-flood test.
3025 rcutorture.fqs_duration= [KNL]
3026 Set duration of force_quiescent_state bursts.
3028 rcutorture.fqs_holdoff= [KNL]
3029 Set holdoff time within force_quiescent_state bursts.
3031 rcutorture.fqs_stutter= [KNL]
3032 Set wait time between force_quiescent_state bursts.
3034 rcutorture.gp_exp= [KNL]
3035 Use expedited update-side primitives.
3037 rcutorture.gp_normal= [KNL]
3038 Use normal (non-expedited) update-side primitives.
3039 If both gp_exp and gp_normal are set, do both.
3040 If neither gp_exp nor gp_normal are set, still
3041 do both.
3043 rcutorture.n_barrier_cbs= [KNL]
3044 Set callbacks/threads for rcu_barrier() testing.
3046 rcutorture.nfakewriters= [KNL]
3047 Set number of concurrent RCU writers. These just
3048 stress RCU, they don't participate in the actual
3049 test, hence the "fake".
3051 rcutorture.nreaders= [KNL]
3052 Set number of RCU readers.
3054 rcutorture.object_debug= [KNL]
3055 Enable debug-object double-call_rcu() testing.
3057 rcutorture.onoff_holdoff= [KNL]
3058 Set time (s) after boot for CPU-hotplug testing.
3060 rcutorture.onoff_interval= [KNL]
3061 Set time (s) between CPU-hotplug operations, or
3062 zero to disable CPU-hotplug testing.
3064 rcutorture.torture_runnable= [BOOT]
3065 Start rcutorture running at boot time.
3067 rcutorture.shuffle_interval= [KNL]
3068 Set task-shuffle interval (s). Shuffling tasks
3069 allows some CPUs to go into dyntick-idle mode
3070 during the rcutorture test.
3072 rcutorture.shutdown_secs= [KNL]
3073 Set time (s) after boot system shutdown. This
3074 is useful for hands-off automated testing.
3076 rcutorture.stall_cpu= [KNL]
3077 Duration of CPU stall (s) to test RCU CPU stall
3078 warnings, zero to disable.
3080 rcutorture.stall_cpu_holdoff= [KNL]
3081 Time to wait (s) after boot before inducing stall.
3083 rcutorture.stat_interval= [KNL]
3084 Time (s) between statistics printk()s.
3086 rcutorture.stutter= [KNL]
3087 Time (s) to stutter testing, for example, specifying
3088 five seconds causes the test to run for five seconds,
3089 wait for five seconds, and so on. This tests RCU's
3090 ability to transition abruptly to and from idle.
3092 rcutorture.test_boost= [KNL]
3093 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3094 "Maybe" means test if the RCU implementation
3095 under test support RCU priority boosting.
3097 rcutorture.test_boost_duration= [KNL]
3098 Duration (s) of each individual boost test.
3100 rcutorture.test_boost_interval= [KNL]
3101 Interval (s) between each boost test.
3103 rcutorture.test_no_idle_hz= [KNL]
3104 Test RCU's dyntick-idle handling. See also the
3105 rcutorture.shuffle_interval parameter.
3107 rcutorture.torture_type= [KNL]
3108 Specify the RCU implementation to test.
3110 rcutorture.verbose= [KNL]
3111 Enable additional printk() statements.
3113 rcupdate.rcu_expedited= [KNL]
3114 Use expedited grace-period primitives, for
3115 example, synchronize_rcu_expedited() instead
3116 of synchronize_rcu(). This reduces latency,
3117 but can increase CPU utilization, degrade
3118 real-time latency, and degrade energy efficiency.
3120 rcupdate.rcu_cpu_stall_suppress= [KNL]
3121 Suppress RCU CPU stall warning messages.
3123 rcupdate.rcu_cpu_stall_timeout= [KNL]
3124 Set timeout for RCU CPU stall warning messages.
3126 rcupdate.rcu_task_stall_timeout= [KNL]
3127 Set timeout in jiffies for RCU task stall warning
3128 messages. Disable with a value less than or equal
3129 to zero.
3131 rcupdate.rcu_self_test= [KNL]
3132 Run the RCU early boot self tests
3134 rcupdate.rcu_self_test_bh= [KNL]
3135 Run the RCU bh early boot self tests
3137 rcupdate.rcu_self_test_sched= [KNL]
3138 Run the RCU sched early boot self tests
3140 rdinit= [KNL]
3141 Format: <full_path>
3142 Run specified binary instead of /init from the ramdisk,
3143 used for early userspace startup. See initrd.
3145 reboot= [KNL]
3146 Format (x86 or x86_64):
3147 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3148 [[,]s[mp]#### \
3149 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3150 [[,]f[orce]
3151 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3152 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3153 reboot_force is either force or not specified,
3154 reboot_cpu is s[mp]#### with #### being the processor
3155 to be used for rebooting.
3157 relax_domain_level=
3158 [KNL, SMP] Set scheduler's default relax_domain_level.
3159 See Documentation/cgroups/cpusets.txt.
3161 relative_sleep_states=
3162 [SUSPEND] Use sleep state labeling where the deepest
3163 state available other than hibernation is always "mem".
3164 Format: { "0" | "1" }
3165 0 -- Traditional sleep state labels.
3166 1 -- Relative sleep state labels.
3168 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3170 reservetop= [X86-32]
3171 Format: nn[KMG]
3172 Reserves a hole at the top of the kernel virtual
3173 address space.
3175 reservelow= [X86]
3176 Format: nn[K]
3177 Set the amount of memory to reserve for BIOS at
3178 the bottom of the address space.
3180 reset_devices [KNL] Force drivers to reset the underlying device
3181 during initialization.
3183 resume= [SWSUSP]
3184 Specify the partition device for software suspend
3185 Format:
3186 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3188 resume_offset= [SWSUSP]
3189 Specify the offset from the beginning of the partition
3190 given by "resume=" at which the swap header is located,
3191 in <PAGE_SIZE> units (needed only for swap files).
3192 See Documentation/power/swsusp-and-swap-files.txt
3194 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3195 read the resume files
3197 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3198 Useful for devices that are detected asynchronously
3199 (e.g. USB and MMC devices).
3201 hibernate= [HIBERNATION]
3202 noresume Don't check if there's a hibernation image
3203 present during boot.
3204 nocompress Don't compress/decompress hibernation images.
3205 no Disable hibernation and resume.
3207 retain_initrd [RAM] Keep initrd memory after extraction
3209 rhash_entries= [KNL,NET]
3210 Set number of hash buckets for route cache
3212 ro [KNL] Mount root device read-only on boot
3214 root= [KNL] Root filesystem
3215 See name_to_dev_t comment in init/do_mounts.c.
3217 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3218 mount the root filesystem
3220 rootflags= [KNL] Set root filesystem mount option string
3222 rootfstype= [KNL] Set root filesystem type
3224 rootwait [KNL] Wait (indefinitely) for root device to show up.
3225 Useful for devices that are detected asynchronously
3226 (e.g. USB and MMC devices).
3228 rproc_mem=nn[KMG][@address]
3229 [KNL,ARM,CMA] Remoteproc physical memory block.
3230 Memory area to be used by remote processor image,
3231 managed by CMA.
3233 rw [KNL] Mount root device read-write on boot
3235 S [KNL] Run init in single mode
3237 s390_iommu= [HW,S390]
3238 Set s390 IOTLB flushing mode
3239 strict
3240 With strict flushing every unmap operation will result in
3241 an IOTLB flush. Default is lazy flushing before reuse,
3242 which is faster.
3244 sa1100ir [NET]
3245 See drivers/net/irda/sa1100_ir.c.
3247 sbni= [NET] Granch SBNI12 leased line adapter
3249 sched_debug [KNL] Enables verbose scheduler debug messages.
3251 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3252 xtime_lock contention on larger systems, and/or RCU lock
3253 contention on all systems with CONFIG_MAXSMP set.
3254 Format: { "0" | "1" }
3255 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3256 1 -- enable.
3257 Note: increases power consumption, thus should only be
3258 enabled if running jitter sensitive (HPC/RT) workloads.
3260 security= [SECURITY] Choose a security module to enable at boot.
3261 If this boot parameter is not specified, only the first
3262 security module asking for security registration will be
3263 loaded. An invalid security module name will be treated
3264 as if no module has been chosen.
3266 selinux= [SELINUX] Disable or enable SELinux at boot time.
3267 Format: { "0" | "1" }
3268 See security/selinux/Kconfig help text.
3269 0 -- disable.
3270 1 -- enable.
3271 Default value is set via kernel config option.
3272 If enabled at boot time, /selinux/disable can be used
3273 later to disable prior to initial policy load.
3275 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3276 Format: { "0" | "1" }
3277 See security/apparmor/Kconfig help text
3278 0 -- disable.
3279 1 -- enable.
3280 Default value is set via kernel config option.
3282 serialnumber [BUGS=X86-32]
3284 shapers= [NET]
3285 Maximal number of shapers.
3287 show_msr= [x86] show boot-time MSR settings
3288 Format: { <integer> }
3289 Show boot-time (BIOS-initialized) MSR settings.
3290 The parameter means the number of CPUs to show,
3291 for example 1 means boot CPU only.
3293 simeth= [IA-64]
3294 simscsi=
3296 slram= [HW,MTD]
3298 slab_nomerge [MM]
3299 Disable merging of slabs with similar size. May be
3300 necessary if there is some reason to distinguish
3301 allocs to different slabs. Debug options disable
3302 merging on their own.
3303 For more information see Documentation/vm/slub.txt.
3305 slab_max_order= [MM, SLAB]
3306 Determines the maximum allowed order for slabs.
3307 A high setting may cause OOMs due to memory
3308 fragmentation. Defaults to 1 for systems with
3309 more than 32MB of RAM, 0 otherwise.
3311 slub_debug[=options[,slabs]] [MM, SLUB]
3312 Enabling slub_debug allows one to determine the
3313 culprit if slab objects become corrupted. Enabling
3314 slub_debug can create guard zones around objects and
3315 may poison objects when not in use. Also tracks the
3316 last alloc / free. For more information see
3317 Documentation/vm/slub.txt.
3319 slub_max_order= [MM, SLUB]
3320 Determines the maximum allowed order for slabs.
3321 A high setting may cause OOMs due to memory
3322 fragmentation. For more information see
3323 Documentation/vm/slub.txt.
3325 slub_min_objects= [MM, SLUB]
3326 The minimum number of objects per slab. SLUB will
3327 increase the slab order up to slub_max_order to
3328 generate a sufficiently large slab able to contain
3329 the number of objects indicated. The higher the number
3330 of objects the smaller the overhead of tracking slabs
3331 and the less frequently locks need to be acquired.
3332 For more information see Documentation/vm/slub.txt.
3334 slub_min_order= [MM, SLUB]
3335 Determines the minimum page order for slabs. Must be
3336 lower than slub_max_order.
3337 For more information see Documentation/vm/slub.txt.
3339 slub_nomerge [MM, SLUB]
3340 Same with slab_nomerge. This is supported for legacy.
3341 See slab_nomerge for more information.
3343 smart2= [HW]
3344 Format: <io1>[,<io2>[,...,<io8>]]
3346 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3347 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3348 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3349 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3350 smsc-ircc2.ircc_irq= [HW] IRQ line
3351 smsc-ircc2.ircc_dma= [HW] DMA channel
3352 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3353 0: Toshiba Satellite 1800 (GP data pin select)
3354 1: Fast pin select (default)
3355 2: ATC IRMode
3357 softlockup_panic=
3358 [KNL] Should the soft-lockup detector generate panics.
3359 Format: <integer>
3361 softlockup_all_cpu_backtrace=
3362 [KNL] Should the soft-lockup detector generate
3363 backtraces on all cpus.
3364 Format: <integer>
3366 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3367 See Documentation/laptops/sonypi.txt
3369 spia_io_base= [HW,MTD]
3370 spia_fio_base=
3371 spia_pedr=
3372 spia_peddr=
3374 stacktrace [FTRACE]
3375 Enabled the stack tracer on boot up.
3377 stacktrace_filter=[function-list]
3378 [FTRACE] Limit the functions that the stack tracer
3379 will trace at boot up. function-list is a comma separated
3380 list of functions. This list can be changed at run
3381 time by the stack_trace_filter file in the debugfs
3382 tracing directory. Note, this enables stack tracing
3383 and the stacktrace above is not needed.
3385 sti= [PARISC,HW]
3386 Format: <num>
3387 Set the STI (builtin display/keyboard on the HP-PARISC
3388 machines) console (graphic card) which should be used
3389 as the initial boot-console.
3390 See also comment in drivers/video/console/sticore.c.
3392 sti_font= [HW]
3393 See comment in drivers/video/console/sticore.c.
3395 stifb= [HW]
3396 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3398 sunrpc.min_resvport=
3399 sunrpc.max_resvport=
3400 [NFS,SUNRPC]
3401 SunRPC servers often require that client requests
3402 originate from a privileged port (i.e. a port in the
3403 range 0 < portnr < 1024).
3404 An administrator who wishes to reserve some of these
3405 ports for other uses may adjust the range that the
3406 kernel's sunrpc client considers to be privileged
3407 using these two parameters to set the minimum and
3408 maximum port values.
3410 sunrpc.pool_mode=
3411 [NFS]
3412 Control how the NFS server code allocates CPUs to
3413 service thread pools. Depending on how many NICs
3414 you have and where their interrupts are bound, this
3415 option will affect which CPUs will do NFS serving.
3416 Note: this parameter cannot be changed while the
3417 NFS server is running.
3419 auto the server chooses an appropriate mode
3420 automatically using heuristics
3421 global a single global pool contains all CPUs
3422 percpu one pool for each CPU
3423 pernode one pool for each NUMA node (equivalent
3424 to global on non-NUMA machines)
3426 sunrpc.tcp_slot_table_entries=
3427 sunrpc.udp_slot_table_entries=
3428 [NFS,SUNRPC]
3429 Sets the upper limit on the number of simultaneous
3430 RPC calls that can be sent from the client to a
3431 server. Increasing these values may allow you to
3432 improve throughput, but will also increase the
3433 amount of memory reserved for use by the client.
3435 swapaccount=[0|1]
3436 [KNL] Enable accounting of swap in memory resource
3437 controller if no parameter or 1 is given or disable
3438 it if 0 is given (See Documentation/cgroups/memory.txt)
3440 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3441 Format: { <int> | force }
3442 <int> -- Number of I/O TLB slabs
3443 force -- force using of bounce buffers even if they
3444 wouldn't be automatically used by the kernel
3446 switches= [HW,M68k]
3448 sysfs.deprecated=0|1 [KNL]
3449 Enable/disable old style sysfs layout for old udev
3450 on older distributions. When this option is enabled
3451 very new udev will not work anymore. When this option
3452 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3453 in older udev will not work anymore.
3454 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3455 the kernel configuration.
3457 sysrq_always_enabled
3458 [KNL]
3459 Ignore sysrq setting - this boot parameter will
3460 neutralize any effect of /proc/sys/kernel/sysrq.
3461 Useful for debugging.
3463 tcpmhash_entries= [KNL,NET]
3464 Set the number of tcp_metrics_hash slots.
3465 Default value is 8192 or 16384 depending on total
3466 ram pages. This is used to specify the TCP metrics
3467 cache size. See Documentation/networking/ip-sysctl.txt
3468 "tcp_no_metrics_save" section for more details.
3470 tdfx= [HW,DRM]
3472 test_suspend= [SUSPEND][,N]
3473 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3474 standby suspend) or "freeze" (for suspend type freeze)
3475 as the system sleep state during system startup with
3476 the optional capability to repeat N number of times.
3477 The system is woken from this state using a
3478 wakeup-capable RTC alarm.
3480 thash_entries= [KNL,NET]
3481 Set number of hash buckets for TCP connection
3483 thermal.act= [HW,ACPI]
3484 -1: disable all active trip points in all thermal zones
3485 <degrees C>: override all lowest active trip points
3487 thermal.crt= [HW,ACPI]
3488 -1: disable all critical trip points in all thermal zones
3489 <degrees C>: override all critical trip points
3491 thermal.nocrt= [HW,ACPI]
3492 Set to disable actions on ACPI thermal zone
3493 critical and hot trip points.
3495 thermal.off= [HW,ACPI]
3496 1: disable ACPI thermal control
3498 thermal.psv= [HW,ACPI]
3499 -1: disable all passive trip points
3500 <degrees C>: override all passive trip points to this
3501 value
3503 thermal.tzp= [HW,ACPI]
3504 Specify global default ACPI thermal zone polling rate
3505 <deci-seconds>: poll all this frequency
3506 0: no polling (default)
3508 threadirqs [KNL]
3509 Force threading of all interrupt handlers except those
3510 marked explicitly IRQF_NO_THREAD.
3512 tmem [KNL,XEN]
3513 Enable the Transcendent memory driver if built-in.
3515 tmem.cleancache=0|1 [KNL, XEN]
3516 Default is on (1). Disable the usage of the cleancache
3517 API to send anonymous pages to the hypervisor.
3519 tmem.frontswap=0|1 [KNL, XEN]
3520 Default is on (1). Disable the usage of the frontswap
3521 API to send swap pages to the hypervisor. If disabled
3522 the selfballooning and selfshrinking are force disabled.
3524 tmem.selfballooning=0|1 [KNL, XEN]
3525 Default is on (1). Disable the driving of swap pages
3526 to the hypervisor.
3528 tmem.selfshrinking=0|1 [KNL, XEN]
3529 Default is on (1). Partial swapoff that immediately
3530 transfers pages from Xen hypervisor back to the
3531 kernel based on different criteria.
3533 topology= [S390]
3534 Format: {off | on}
3535 Specify if the kernel should make use of the cpu
3536 topology information if the hardware supports this.
3537 The scheduler will make use of this information and
3538 e.g. base its process migration decisions on it.
3539 Default is on.
3541 topology_updates= [KNL, PPC, NUMA]
3542 Format: {off}
3543 Specify if the kernel should ignore (off)
3544 topology updates sent by the hypervisor to this
3545 LPAR.
3547 tp720= [HW,PS2]
3549 tpm_suspend_pcr=[HW,TPM]
3550 Format: integer pcr id
3551 Specify that at suspend time, the tpm driver
3552 should extend the specified pcr with zeros,
3553 as a workaround for some chips which fail to
3554 flush the last written pcr on TPM_SaveState.
3555 This will guarantee that all the other pcrs
3556 are saved.
3558 trace_buf_size=nn[KMG]
3559 [FTRACE] will set tracing buffer size on each cpu.
3561 trace_event=[event-list]
3562 [FTRACE] Set and start specified trace events in order
3563 to facilitate early boot debugging.
3564 See also Documentation/trace/events.txt
3566 trace_options=[option-list]
3567 [FTRACE] Enable or disable tracer options at boot.
3568 The option-list is a comma delimited list of options
3569 that can be enabled or disabled just as if you were
3570 to echo the option name into
3572 /sys/kernel/debug/tracing/trace_options
3574 For example, to enable stacktrace option (to dump the
3575 stack trace of each event), add to the command line:
3577 trace_options=stacktrace
3579 See also Documentation/trace/ftrace.txt "trace options"
3580 section.
3582 tp_printk[FTRACE]
3583 Have the tracepoints sent to printk as well as the
3584 tracing ring buffer. This is useful for early boot up
3585 where the system hangs or reboots and does not give the
3586 option for reading the tracing buffer or performing a
3587 ftrace_dump_on_oops.
3589 To turn off having tracepoints sent to printk,
3590 echo 0 > /proc/sys/kernel/tracepoint_printk
3591 Note, echoing 1 into this file without the
3592 tracepoint_printk kernel cmdline option has no effect.
3594 ** CAUTION **
3596 Having tracepoints sent to printk() and activating high
3597 frequency tracepoints such as irq or sched, can cause
3598 the system to live lock.
3600 traceoff_on_warning
3601 [FTRACE] enable this option to disable tracing when a
3602 warning is hit. This turns off "tracing_on". Tracing can
3603 be enabled again by echoing '1' into the "tracing_on"
3604 file located in /sys/kernel/debug/tracing/
3606 This option is useful, as it disables the trace before
3607 the WARNING dump is called, which prevents the trace to
3608 be filled with content caused by the warning output.
3610 This option can also be set at run time via the sysctl
3611 option: kernel/traceoff_on_warning
3613 transparent_hugepage=
3614 [KNL]
3615 Format: [always|madvise|never]
3616 Can be used to control the default behavior of the system
3617 with respect to transparent hugepages.
3618 See Documentation/vm/transhuge.txt for more details.
3620 tsc= Disable clocksource stability checks for TSC.
3621 Format: <string>
3622 [x86] reliable: mark tsc clocksource as reliable, this
3623 disables clocksource verification at runtime, as well
3624 as the stability checks done at bootup. Used to enable
3625 high-resolution timer mode on older hardware, and in
3626 virtualized environment.
3627 [x86] noirqtime: Do not use TSC to do irq accounting.
3628 Used to run time disable IRQ_TIME_ACCOUNTING on any
3629 platforms where RDTSC is slow and this accounting
3630 can add overhead.
3632 turbografx.map[2|3]= [HW,JOY]
3633 TurboGraFX parallel port interface
3634 Format:
3635 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3636 See also Documentation/input/joystick-parport.txt
3638 udbg-immortal [PPC] When debugging early kernel crashes that
3639 happen after console_init() and before a proper
3640 console driver takes over, this boot options might
3641 help "seeing" what's going on.
3643 uhash_entries= [KNL,NET]
3644 Set number of hash buckets for UDP/UDP-Lite connections
3646 uhci-hcd.ignore_oc=
3647 [USB] Ignore overcurrent events (default N).
3648 Some badly-designed motherboards generate lots of
3649 bogus events, for ports that aren't wired to
3650 anything. Set this parameter to avoid log spamming.
3651 Note that genuine overcurrent events won't be
3652 reported either.
3654 unknown_nmi_panic
3655 [X86] Cause panic on unknown NMI.
3657 usbcore.authorized_default=
3658 [USB] Default USB device authorization:
3659 (default -1 = authorized except for wireless USB,
3660 0 = not authorized, 1 = authorized)
3662 usbcore.autosuspend=
3663 [USB] The autosuspend time delay (in seconds) used
3664 for newly-detected USB devices (default 2). This
3665 is the time required before an idle device will be
3666 autosuspended. Devices for which the delay is set
3667 to a negative value won't be autosuspended at all.
3669 usbcore.usbfs_snoop=
3670 [USB] Set to log all usbfs traffic (default 0 = off).
3672 usbcore.blinkenlights=
3673 [USB] Set to cycle leds on hubs (default 0 = off).
3675 usbcore.old_scheme_first=
3676 [USB] Start with the old device initialization
3677 scheme (default 0 = off).
3679 usbcore.usbfs_memory_mb=
3680 [USB] Memory limit (in MB) for buffers allocated by
3681 usbfs (default = 16, 0 = max = 2047).
3683 usbcore.use_both_schemes=
3684 [USB] Try the other device initialization scheme
3685 if the first one fails (default 1 = enabled).
3687 usbcore.initial_descriptor_timeout=
3688 [USB] Specifies timeout for the initial 64-byte
3689 USB_REQ_GET_DESCRIPTOR request in milliseconds
3690 (default 5000 = 5.0 seconds).
3692 usbhid.mousepoll=
3693 [USBHID] The interval which mice are to be polled at.
3695 usb-storage.delay_use=
3696 [UMS] The delay in seconds before a new device is
3697 scanned for Logical Units (default 1).
3699 usb-storage.quirks=
3700 [UMS] A list of quirks entries to supplement or
3701 override the built-in unusual_devs list. List
3702 entries are separated by commas. Each entry has
3703 the form VID:PID:Flags where VID and PID are Vendor
3704 and Product ID values (4-digit hex numbers) and
3705 Flags is a set of characters, each corresponding
3706 to a common usb-storage quirk flag as follows:
3707 a = SANE_SENSE (collect more than 18 bytes
3708 of sense data);
3709 b = BAD_SENSE (don't collect more than 18
3710 bytes of sense data);
3711 c = FIX_CAPACITY (decrease the reported
3712 device capacity by one sector);
3713 d = NO_READ_DISC_INFO (don't use
3714 READ_DISC_INFO command);
3715 e = NO_READ_CAPACITY_16 (don't use
3716 READ_CAPACITY_16 command);
3717 f = NO_REPORT_OPCODES (don't use report opcodes
3718 command, uas only);
3719 h = CAPACITY_HEURISTICS (decrease the
3720 reported device capacity by one
3721 sector if the number is odd);
3722 i = IGNORE_DEVICE (don't bind to this
3723 device);
3724 l = NOT_LOCKABLE (don't try to lock and
3725 unlock ejectable media);
3726 m = MAX_SECTORS_64 (don't transfer more
3727 than 64 sectors = 32 KB at a time);
3728 n = INITIAL_READ10 (force a retry of the
3729 initial READ(10) command);
3730 o = CAPACITY_OK (accept the capacity
3731 reported by the device);
3732 p = WRITE_CACHE (the device cache is ON
3733 by default);
3734 r = IGNORE_RESIDUE (the device reports
3735 bogus residue values);
3736 s = SINGLE_LUN (the device has only one
3737 Logical Unit);
3738 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3739 commands, uas only);
3740 u = IGNORE_UAS (don't bind to the uas driver);
3741 w = NO_WP_DETECT (don't test whether the
3742 medium is write-protected).
3743 Example: quirks=0419:aaf5:rl,0421:0433:rc
3745 user_debug= [KNL,ARM]
3746 Format: <int>
3747 See arch/arm/Kconfig.debug help text.
3748 1 - undefined instruction events
3749 2 - system calls
3750 4 - invalid data aborts
3751 8 - SIGSEGV faults
3752 16 - SIGBUS faults
3753 Example: user_debug=31
3755 userpte=
3756 [X86] Flags controlling user PTE allocations.
3758 nohigh = do not allocate PTE pages in
3759 HIGHMEM regardless of setting
3760 of CONFIG_HIGHPTE.
3762 vdso= [X86,SH]
3763 On X86_32, this is an alias for vdso32=. Otherwise:
3765 vdso=1: enable VDSO (the default)
3766 vdso=0: disable VDSO mapping
3768 vdso32= [X86] Control the 32-bit vDSO
3769 vdso32=1: enable 32-bit VDSO
3770 vdso32=0 or vdso32=2: disable 32-bit VDSO
3772 See the help text for CONFIG_COMPAT_VDSO for more
3773 details. If CONFIG_COMPAT_VDSO is set, the default is
3774 vdso32=0; otherwise, the default is vdso32=1.
3776 For compatibility with older kernels, vdso32=2 is an
3777 alias for vdso32=0.
3779 Try vdso32=0 if you encounter an error that says:
3780 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3782 vector= [IA-64,SMP]
3783 vector=percpu: enable percpu vector domain
3785 video= [FB] Frame buffer configuration
3786 See Documentation/fb/modedb.txt.
3788 video.brightness_switch_enabled= [0,1]
3789 If set to 1, on receiving an ACPI notify event
3790 generated by hotkey, video driver will adjust brightness
3791 level and then send out the event to user space through
3792 the allocated input device; If set to 0, video driver
3793 will only send out the event without touching backlight
3794 brightness level.
3795 default: 1
3797 virtio_mmio.device=
3798 [VMMIO] Memory mapped virtio (platform) device.
3800 <size>@<baseaddr>:<irq>[:<id>]
3801 where:
3802 <size> := size (can use standard suffixes
3803 like K, M and G)
3804 <baseaddr> := physical base address
3805 <irq> := interrupt number (as passed to
3806 request_irq())
3807 <id> := (optional) platform device id
3808 example:
3809 virtio_mmio.device=1K@0x100b0000:48:7
3811 Can be used multiple times for multiple devices.
3813 vga= [BOOT,X86-32] Select a particular video mode
3814 See Documentation/x86/boot.txt and
3815 Documentation/svga.txt.
3816 Use vga=ask for menu.
3817 This is actually a boot loader parameter; the value is
3818 passed to the kernel using a special protocol.
3820 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3821 size of <nn>. This can be used to increase the
3822 minimum size (128MB on x86). It can also be used to
3823 decrease the size and leave more room for directly
3824 mapped kernel RAM.
3826 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3827 Format: <command>
3829 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3830 Format: <command>
3832 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3833 Format: <command>
3835 vsyscall= [X86-64]
3836 Controls the behavior of vsyscalls (i.e. calls to
3837 fixed addresses of 0xffffffffff600x00 from legacy
3838 code). Most statically-linked binaries and older
3839 versions of glibc use these calls. Because these
3840 functions are at fixed addresses, they make nice
3841 targets for exploits that can control RIP.
3843 emulate [default] Vsyscalls turn into traps and are
3844 emulated reasonably safely.
3846 native Vsyscalls are native syscall instructions.
3847 This is a little bit faster than trapping
3848 and makes a few dynamic recompilers work
3849 better than they would in emulation mode.
3850 It also makes exploits much easier to write.
3852 none Vsyscalls don't work at all. This makes
3853 them quite hard to use for exploits but
3854 might break your system.
3856 vt.color= [VT] Default text color.
3857 Format: 0xYX, X = foreground, Y = background.
3858 Default: 0x07 = light gray on black.
3860 vt.cur_default= [VT] Default cursor shape.
3861 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3862 the parameters of the <Esc>[?A;B;Cc escape sequence;
3863 see VGA-softcursor.txt. Default: 2 = underline.
3865 vt.default_blu= [VT]
3866 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3867 Change the default blue palette of the console.
3868 This is a 16-member array composed of values
3869 ranging from 0-255.
3871 vt.default_grn= [VT]
3872 Format: <green0>,<green1>,<green2>,...,<green15>
3873 Change the default green palette of the console.
3874 This is a 16-member array composed of values
3875 ranging from 0-255.
3877 vt.default_red= [VT]
3878 Format: <red0>,<red1>,<red2>,...,<red15>
3879 Change the default red palette of the console.
3880 This is a 16-member array composed of values
3881 ranging from 0-255.
3883 vt.default_utf8=
3884 [VT]
3885 Format=<0|1>
3886 Set system-wide default UTF-8 mode for all tty's.
3887 Default is 1, i.e. UTF-8 mode is enabled for all
3888 newly opened terminals.
3890 vt.global_cursor_default=
3891 [VT]
3892 Format=<-1|0|1>
3893 Set system-wide default for whether a cursor
3894 is shown on new VTs. Default is -1,
3895 i.e. cursors will be created by default unless
3896 overridden by individual drivers. 0 will hide
3897 cursors, 1 will display them.
3899 vt.italic= [VT] Default color for italic text; 0-15.
3900 Default: 2 = green.
3902 vt.underline= [VT] Default color for underlined text; 0-15.
3903 Default: 3 = cyan.
3905 watchdog timers [HW,WDT] For information on watchdog timers,
3906 see Documentation/watchdog/watchdog-parameters.txt
3907 or other driver-specific files in the
3908 Documentation/watchdog/ directory.
3910 workqueue.disable_numa
3911 By default, all work items queued to unbound
3912 workqueues are affine to the NUMA nodes they're
3913 issued on, which results in better behavior in
3914 general. If NUMA affinity needs to be disabled for
3915 whatever reason, this option can be used. Note
3916 that this also can be controlled per-workqueue for
3917 workqueues visible under /sys/bus/workqueue/.
3919 workqueue.power_efficient
3920 Per-cpu workqueues are generally preferred because
3921 they show better performance thanks to cache
3922 locality; unfortunately, per-cpu workqueues tend to
3923 be more power hungry than unbound workqueues.
3925 Enabling this makes the per-cpu workqueues which
3926 were observed to contribute significantly to power
3927 consumption unbound, leading to measurably lower
3928 power usage at the cost of small performance
3929 overhead.
3931 The default value of this parameter is determined by
3932 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3934 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3935 default x2apic cluster mode on platforms
3936 supporting x2apic.
3938 x86_intel_mid_timer= [X86-32,APBT]
3939 Choose timer option for x86 Intel MID platform.
3940 Two valid options are apbt timer only and lapic timer
3941 plus one apbt timer for broadcast timer.
3942 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3944 xen_emul_unplug= [HW,X86,XEN]
3945 Unplug Xen emulated devices
3946 Format: [unplug0,][unplug1]
3947 ide-disks -- unplug primary master IDE devices
3948 aux-ide-disks -- unplug non-primary-master IDE devices
3949 nics -- unplug network devices
3950 all -- unplug all emulated devices (NICs and IDE disks)
3951 unnecessary -- unplugging emulated devices is
3952 unnecessary even if the host did not respond to
3953 the unplug protocol
3954 never -- do not unplug even if version check succeeds
3956 xen_nopvspin [X86,XEN]
3957 Disables the ticketlock slowpath using Xen PV
3958 optimizations.
3960 xen_nopv [X86]
3961 Disables the PV optimizations forcing the HVM guest to
3962 run as generic HVM guest with no PV drivers.
3964 xirc2ps_cs= [NET,PCMCIA]
3965 Format:
3966 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3968 ______________________________________________________________________
3970 TODO:
3972 Add more DRM drivers.