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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 debugpat [X86] Enable PAT debugging
834 decnet.addr= [HW,NET]
835 Format: <area>[,<node>]
836 See also Documentation/networking/decnet.txt.
838 default_hugepagesz=
839 [same as hugepagesz=] The size of the default
840 HugeTLB page size. This is the size represented by
841 the legacy /proc/ hugepages APIs, used for SHM, and
842 default size when mounting hugetlbfs filesystems.
843 Defaults to the default architecture's huge page size
844 if not specified.
846 dhash_entries= [KNL]
847 Set number of hash buckets for dentry cache.
849 disable= [IPV6]
850 See Documentation/networking/ipv6.txt.
852 disable_cpu_apicid= [X86,APIC,SMP]
853 Format: <int>
854 The number of initial APIC ID for the
855 corresponding CPU to be disabled at boot,
856 mostly used for the kdump 2nd kernel to
857 disable BSP to wake up multiple CPUs without
858 causing system reset or hang due to sending
859 INIT from AP to BSP.
861 disable_ddw [PPC/PSERIES]
862 Disable Dynamic DMA Window support. Use this if
863 to workaround buggy firmware.
865 disable_ipv6= [IPV6]
866 See Documentation/networking/ipv6.txt.
868 disable_mtrr_cleanup [X86]
869 The kernel tries to adjust MTRR layout from continuous
870 to discrete, to make X server driver able to add WB
871 entry later. This parameter disables that.
873 disable_mtrr_trim [X86, Intel and AMD only]
874 By default the kernel will trim any uncacheable
875 memory out of your available memory pool based on
876 MTRR settings. This parameter disables that behavior,
877 possibly causing your machine to run very slowly.
879 disable_timer_pin_1 [X86]
880 Disable PIN 1 of APIC timer
881 Can be useful to work around chipset bugs.
883 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
884 this option disables the debugging code at boot.
886 dma_debug_entries=<number>
887 This option allows to tune the number of preallocated
888 entries for DMA-API debugging code. One entry is
889 required per DMA-API allocation. Use this if the
890 DMA-API debugging code disables itself because the
891 architectural default is too low.
893 dma_debug_driver=<driver_name>
894 With this option the DMA-API debugging driver
895 filter feature can be enabled at boot time. Just
896 pass the driver to filter for as the parameter.
897 The filter can be disabled or changed to another
898 driver later using sysfs.
900 drm_kms_helper.edid_firmware=[<connector>:]<file>
901 Broken monitors, graphic adapters and KVMs may
902 send no or incorrect EDID data sets. This parameter
903 allows to specify an EDID data set in the
904 /lib/firmware directory that is used instead.
905 Generic built-in EDID data sets are used, if one of
906 edid/1024x768.bin, edid/1280x1024.bin,
907 edid/1680x1050.bin, or edid/1920x1080.bin is given
908 and no file with the same name exists. Details and
909 instructions how to build your own EDID data are
910 available in Documentation/EDID/HOWTO.txt. An EDID
911 data set will only be used for a particular connector,
912 if its name and a colon are prepended to the EDID
913 name.
915 dscc4.setup= [NET]
917 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
918 module.dyndbg[="val"]
919 Enable debug messages at boot time. See
920 Documentation/dynamic-debug-howto.txt for details.
922 early_ioremap_debug [KNL]
923 Enable debug messages in early_ioremap support. This
924 is useful for tracking down temporary early mappings
925 which are not unmapped.
927 earlycon= [KNL] Output early console device and options.
929 cdns,<addr>
930 Start an early, polled-mode console on a cadence serial
931 port at the specified address. The cadence serial port
932 must already be setup and configured. Options are not
933 yet supported.
935 uart[8250],io,<addr>[,options]
936 uart[8250],mmio,<addr>[,options]
937 uart[8250],mmio32,<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32).
942 The options are the same as for ttyS, above.
944 pl011,<addr>
945 Start an early, polled-mode console on a pl011 serial
946 port at the specified address. The pl011 serial port
947 must already be setup and configured. Options are not
948 yet supported.
950 msm_serial,<addr>
951 Start an early, polled-mode console on an msm serial
952 port at the specified address. The serial port
953 must already be setup and configured. Options are not
954 yet supported.
956 msm_serial_dm,<addr>
957 Start an early, polled-mode console on an msm serial
958 dm port at the specified address. The serial port
959 must already be setup and configured. Options are not
960 yet supported.
962 smh Use ARM semihosting calls for early console.
964 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
965 earlyprintk=vga
966 earlyprintk=efi
967 earlyprintk=xen
968 earlyprintk=serial[,ttySn[,baudrate]]
969 earlyprintk=serial[,0x...[,baudrate]]
970 earlyprintk=ttySn[,baudrate]
971 earlyprintk=dbgp[debugController#]
973 earlyprintk is useful when the kernel crashes before
974 the normal console is initialized. It is not enabled by
975 default because it has some cosmetic problems.
977 Append ",keep" to not disable it when the real console
978 takes over.
980 Only one of vga, efi, serial, or usb debug port can
981 be used at a time.
983 Currently only ttyS0 and ttyS1 may be specified by
984 name. Other I/O ports may be explicitly specified
985 on some architectures (x86 and arm at least) by
986 replacing ttySn with an I/O port address, like this:
987 earlyprintk=serial,0x1008,115200
988 You can find the port for a given device in
989 /proc/tty/driver/serial:
990 2: uart:ST16650V2 port:00001008 irq:18 ...
992 Interaction with the standard serial driver is not
993 very good.
995 The VGA and EFI output is eventually overwritten by
996 the real console.
998 The xen output can only be used by Xen PV guests.
1000 edac_report= [HW,EDAC] Control how to report EDAC event
1001 Format: {"on" | "off" | "force"}
1002 on: enable EDAC to report H/W event. May be overridden
1003 by other higher priority error reporting module.
1004 off: disable H/W event reporting through EDAC.
1005 force: enforce the use of EDAC to report H/W event.
1006 default: on.
1008 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1009 ekgdboc=kbd
1011 This is designed to be used in conjunction with
1012 the boot argument: earlyprintk=vga
1014 edd= [EDD]
1015 Format: {"off" | "on" | "skip[mbr]"}
1017 efi= [EFI]
1018 Format: { "old_map", "nochunk", "noruntime" }
1019 old_map [X86-64]: switch to the old ioremap-based EFI
1020 runtime services mapping. 32-bit still uses this one by
1021 default.
1022 nochunk: disable reading files in "chunks" in the EFI
1023 boot stub, as chunking can cause problems with some
1024 firmware implementations.
1025 noruntime : disable EFI runtime services support
1027 efi_no_storage_paranoia [EFI; X86]
1028 Using this parameter you can use more than 50% of
1029 your efi variable storage. Use this parameter only if
1030 you are really sure that your UEFI does sane gc and
1031 fulfills the spec otherwise your board may brick.
1033 eisa_irq_edge= [PARISC,HW]
1034 See header of drivers/parisc/eisa.c.
1036 elanfreq= [X86-32]
1037 See comment before function elanfreq_setup() in
1038 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1040 elevator= [IOSCHED]
1041 Format: {"cfq" | "deadline" | "noop"}
1042 See Documentation/block/cfq-iosched.txt and
1043 Documentation/block/deadline-iosched.txt for details.
1045 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1046 Specifies physical address of start of kernel core
1047 image elf header and optionally the size. Generally
1048 kexec loader will pass this option to capture kernel.
1049 See Documentation/kdump/kdump.txt for details.
1051 enable_mtrr_cleanup [X86]
1052 The kernel tries to adjust MTRR layout from continuous
1053 to discrete, to make X server driver able to add WB
1054 entry later. This parameter enables that.
1056 enable_timer_pin_1 [X86]
1057 Enable PIN 1 of APIC timer
1058 Can be useful to work around chipset bugs
1059 (in particular on some ATI chipsets).
1060 The kernel tries to set a reasonable default.
1062 enforcing [SELINUX] Set initial enforcing status.
1063 Format: {"0" | "1"}
1064 See security/selinux/Kconfig help text.
1065 0 -- permissive (log only, no denials).
1066 1 -- enforcing (deny and log).
1067 Default value is 0.
1068 Value can be changed at runtime via /selinux/enforce.
1070 erst_disable [ACPI]
1071 Disable Error Record Serialization Table (ERST)
1072 support.
1074 ether= [HW,NET] Ethernet cards parameters
1075 This option is obsoleted by the "netdev=" option, which
1076 has equivalent usage. See its documentation for details.
1078 evm= [EVM]
1079 Format: { "fix" }
1080 Permit 'security.evm' to be updated regardless of
1081 current integrity status.
1083 failslab=
1084 fail_page_alloc=
1085 fail_make_request=[KNL]
1086 General fault injection mechanism.
1087 Format: <interval>,<probability>,<space>,<times>
1088 See also Documentation/fault-injection/.
1090 floppy= [HW]
1091 See Documentation/blockdev/floppy.txt.
1093 force_pal_cache_flush
1094 [IA-64] Avoid check_sal_cache_flush which may hang on
1095 buggy SAL_CACHE_FLUSH implementations. Using this
1096 parameter will force ia64_sal_cache_flush to call
1097 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1099 forcepae [X86-32]
1100 Forcefully enable Physical Address Extension (PAE).
1101 Many Pentium M systems disable PAE but may have a
1102 functionally usable PAE implementation.
1103 Warning: use of this parameter will taint the kernel
1104 and may cause unknown problems.
1106 ftrace=[tracer]
1107 [FTRACE] will set and start the specified tracer
1108 as early as possible in order to facilitate early
1109 boot debugging.
1111 ftrace_dump_on_oops[=orig_cpu]
1112 [FTRACE] will dump the trace buffers on oops.
1113 If no parameter is passed, ftrace will dump
1114 buffers of all CPUs, but if you pass orig_cpu, it will
1115 dump only the buffer of the CPU that triggered the
1116 oops.
1118 ftrace_filter=[function-list]
1119 [FTRACE] Limit the functions traced by the function
1120 tracer at boot up. function-list is a comma separated
1121 list of functions. This list can be changed at run
1122 time by the set_ftrace_filter file in the debugfs
1123 tracing directory.
1125 ftrace_notrace=[function-list]
1126 [FTRACE] Do not trace the functions specified in
1127 function-list. This list can be changed at run time
1128 by the set_ftrace_notrace file in the debugfs
1129 tracing directory.
1131 ftrace_graph_filter=[function-list]
1132 [FTRACE] Limit the top level callers functions traced
1133 by the function graph tracer at boot up.
1134 function-list is a comma separated list of functions
1135 that can be changed at run time by the
1136 set_graph_function file in the debugfs tracing directory.
1138 ftrace_graph_notrace=[function-list]
1139 [FTRACE] Do not trace from the functions specified in
1140 function-list. This list is a comma separated list of
1141 functions that can be changed at run time by the
1142 set_graph_notrace file in the debugfs tracing directory.
1144 gamecon.map[2|3]=
1145 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1146 support via parallel port (up to 5 devices per port)
1147 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1148 See also Documentation/input/joystick-parport.txt
1150 gamma= [HW,DRM]
1152 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1153 Format: off | on
1154 default: on
1156 gcov_persist= [GCOV] When non-zero (default), profiling data for
1157 kernel modules is saved and remains accessible via
1158 debugfs, even when the module is unloaded/reloaded.
1159 When zero, profiling data is discarded and associated
1160 debugfs files are removed at module unload time.
1162 gpt [EFI] Forces disk with valid GPT signature but
1163 invalid Protective MBR to be treated as GPT. If the
1164 primary GPT is corrupted, it enables the backup/alternate
1165 GPT to be used instead.
1167 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1168 the "Enable 0" bit of the configuration register.
1169 Format: 0 | 1
1170 Default: 0
1171 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1172 the "Enable 0" bit of the configuration register.
1173 Format: 0 | 1
1174 Default: 0
1175 grcan.select= [HW] Select which physical interface to use.
1176 Format: 0 | 1
1177 Default: 0
1178 grcan.txsize= [HW] Sets the size of the tx buffer.
1179 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1180 Default: 1024
1181 grcan.rxsize= [HW] Sets the size of the rx buffer.
1182 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1183 Default: 1024
1185 hashdist= [KNL,NUMA] Large hashes allocated during boot
1186 are distributed across NUMA nodes. Defaults on
1187 for 64-bit NUMA, off otherwise.
1188 Format: 0 | 1 (for off | on)
1190 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1192 hd= [EIDE] (E)IDE hard drive subsystem geometry
1193 Format: <cyl>,<head>,<sect>
1195 hest_disable [ACPI]
1196 Disable Hardware Error Source Table (HEST) support;
1197 corresponding firmware-first mode error processing
1198 logic will be disabled.
1200 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1201 size of <nn>. This works even on boxes that have no
1202 highmem otherwise. This also works to reduce highmem
1203 size on bigger boxes.
1205 highres= [KNL] Enable/disable high resolution timer mode.
1206 Valid parameters: "on", "off"
1207 Default: "on"
1209 hisax= [HW,ISDN]
1210 See Documentation/isdn/README.HiSax.
1212 hlt [BUGS=ARM,SH]
1214 hpet= [X86-32,HPET] option to control HPET usage
1215 Format: { enable (default) | disable | force |
1216 verbose }
1217 disable: disable HPET and use PIT instead
1218 force: allow force enabled of undocumented chips (ICH4,
1219 VIA, nVidia)
1220 verbose: show contents of HPET registers during setup
1222 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1223 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1225 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1226 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1227 On x86-64 and powerpc, this option can be specified
1228 multiple times interleaved with hugepages= to reserve
1229 huge pages of different sizes. Valid pages sizes on
1230 x86-64 are 2M (when the CPU supports "pse") and 1G
1231 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1232 Note that 1GB pages can only be allocated at boot time
1233 using hugepages= and not freed afterwards.
1235 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1236 terminal devices. Valid values: 0..8
1237 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1238 If specified, z/VM IUCV HVC accepts connections
1239 from listed z/VM user IDs only.
1241 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1242 hardware thread id mappings.
1243 Format: <cpu>:<hwthread>
1245 keep_bootcon [KNL]
1246 Do not unregister boot console at start. This is only
1247 useful for debugging when something happens in the window
1248 between unregistering the boot console and initializing
1249 the real console.
1251 i2c_bus= [HW] Override the default board specific I2C bus speed
1252 or register an additional I2C bus that is not
1253 registered from board initialization code.
1254 Format:
1255 <bus_id>,<clkrate>
1257 i8042.debug [HW] Toggle i8042 debug mode
1258 i8042.direct [HW] Put keyboard port into non-translated mode
1259 i8042.dumbkbd [HW] Pretend that controller can only read data from
1260 keyboard and cannot control its state
1261 (Don't attempt to blink the leds)
1262 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1263 i8042.nokbd [HW] Don't check/create keyboard port
1264 i8042.noloop [HW] Disable the AUX Loopback command while probing
1265 for the AUX port
1266 i8042.nomux [HW] Don't check presence of an active multiplexing
1267 controller
1268 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1269 controllers
1270 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1271 i8042.reset [HW] Reset the controller during init and cleanup
1272 i8042.unlock [HW] Unlock (ignore) the keylock
1273 i8042.kbdreset [HW] Reset device connected to KBD port
1275 i810= [HW,DRM]
1277 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1278 indicates that the driver is running on unsupported
1279 hardware.
1280 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1281 does not match list of supported models.
1282 i8k.power_status
1283 [HW] Report power status in /proc/i8k
1284 (disabled by default)
1285 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1286 capability is set.
1288 i915.invert_brightness=
1289 [DRM] Invert the sense of the variable that is used to
1290 set the brightness of the panel backlight. Normally a
1291 brightness value of 0 indicates backlight switched off,
1292 and the maximum of the brightness value sets the backlight
1293 to maximum brightness. If this parameter is set to 0
1294 (default) and the machine requires it, or this parameter
1295 is set to 1, a brightness value of 0 sets the backlight
1296 to maximum brightness, and the maximum of the brightness
1297 value switches the backlight off.
1298 -1 -- never invert brightness
1299 0 -- machine default
1300 1 -- force brightness inversion
1302 icn= [HW,ISDN]
1303 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1305 ide-core.nodma= [HW] (E)IDE subsystem
1306 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1307 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1308 .cdrom .chs .ignore_cable are additional options
1309 See Documentation/ide/ide.txt.
1311 ide-generic.probe-mask= [HW] (E)IDE subsystem
1312 Format: <int>
1313 Probe mask for legacy ISA IDE ports. Depending on
1314 platform up to 6 ports are supported, enabled by
1315 setting corresponding bits in the mask to 1. The
1316 default value is 0x0, which has a special meaning.
1317 On systems that have PCI, it triggers scanning the
1318 PCI bus for the first and the second port, which
1319 are then probed. On systems without PCI the value
1320 of 0x0 enables probing the two first ports as if it
1321 was 0x3.
1323 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1324 Claim all unknown PCI IDE storage controllers.
1326 idle= [X86]
1327 Format: idle=poll, idle=halt, idle=nomwait
1328 Poll forces a polling idle loop that can slightly
1329 improve the performance of waking up a idle CPU, but
1330 will use a lot of power and make the system run hot.
1331 Not recommended.
1332 idle=halt: Halt is forced to be used for CPU idle.
1333 In such case C2/C3 won't be used again.
1334 idle=nomwait: Disable mwait for CPU C-states
1336 ignore_loglevel [KNL]
1337 Ignore loglevel setting - this will print /all/
1338 kernel messages to the console. Useful for debugging.
1339 We also add it as printk module parameter, so users
1340 could change it dynamically, usually by
1341 /sys/module/printk/parameters/ignore_loglevel.
1343 ihash_entries= [KNL]
1344 Set number of hash buckets for inode cache.
1346 ima_appraise= [IMA] appraise integrity measurements
1347 Format: { "off" | "enforce" | "fix" | "log" }
1348 default: "enforce"
1350 ima_appraise_tcb [IMA]
1351 The builtin appraise policy appraises all files
1352 owned by uid=0.
1354 ima_hash= [IMA]
1355 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1356 | sha512 | ... }
1357 default: "sha1"
1359 The list of supported hash algorithms is defined
1360 in crypto/hash_info.h.
1362 ima_tcb [IMA]
1363 Load a policy which meets the needs of the Trusted
1364 Computing Base. This means IMA will measure all
1365 programs exec'd, files mmap'd for exec, and all files
1366 opened for read by uid=0.
1368 ima_template= [IMA]
1369 Select one of defined IMA measurements template formats.
1370 Formats: { "ima" | "ima-ng" }
1371 Default: "ima-ng"
1373 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1374 Format: <min_file_size>
1375 Set the minimal file size for using asynchronous hash.
1376 If left unspecified, ahash usage is disabled.
1378 ahash performance varies for different data sizes on
1379 different crypto accelerators. This option can be used
1380 to achieve the best performance for a particular HW.
1382 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1383 Format: <bufsize>
1384 Set hashing buffer size. Default: 4k.
1386 ahash performance varies for different chunk sizes on
1387 different crypto accelerators. This option can be used
1388 to achieve best performance for particular HW.
1390 init= [KNL]
1391 Format: <full_path>
1392 Run specified binary instead of /sbin/init as init
1393 process.
1395 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1396 for working out where the kernel is dying during
1397 startup.
1399 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1400 initcall functions. Useful for debugging built-in
1401 modules and initcalls.
1403 initrd= [BOOT] Specify the location of the initial ramdisk
1405 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1406 Format: <irq>
1408 int_pln_enable [x86] Enable power limit notification interrupt
1410 integrity_audit=[IMA]
1411 Format: { "0" | "1" }
1412 0 -- basic integrity auditing messages. (Default)
1413 1 -- additional integrity auditing messages.
1415 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1416 on
1417 Enable intel iommu driver.
1418 off
1419 Disable intel iommu driver.
1420 igfx_off [Default Off]
1421 By default, gfx is mapped as normal device. If a gfx
1422 device has a dedicated DMAR unit, the DMAR unit is
1423 bypassed by not enabling DMAR with this option. In
1424 this case, gfx device will use physical address for
1425 DMA.
1426 forcedac [x86_64]
1427 With this option iommu will not optimize to look
1428 for io virtual address below 32-bit forcing dual
1429 address cycle on pci bus for cards supporting greater
1430 than 32-bit addressing. The default is to look
1431 for translation below 32-bit and if not available
1432 then look in the higher range.
1433 strict [Default Off]
1434 With this option on every unmap_single operation will
1435 result in a hardware IOTLB flush operation as opposed
1436 to batching them for performance.
1437 sp_off [Default Off]
1438 By default, super page will be supported if Intel IOMMU
1439 has the capability. With this option, super page will
1440 not be supported.
1442 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1443 0 disables intel_idle and fall back on acpi_idle.
1444 1 to 6 specify maximum depth of C-state.
1446 intel_pstate= [X86]
1447 disable
1448 Do not enable intel_pstate as the default
1449 scaling driver for the supported processors
1451 intremap= [X86-64, Intel-IOMMU]
1452 on enable Interrupt Remapping (default)
1453 off disable Interrupt Remapping
1454 nosid disable Source ID checking
1455 no_x2apic_optout
1456 BIOS x2APIC opt-out request will be ignored
1458 iomem= Disable strict checking of access to MMIO memory
1459 strict regions from userspace.
1460 relaxed
1462 iommu= [x86]
1463 off
1464 force
1465 noforce
1466 biomerge
1467 panic
1468 nopanic
1469 merge
1470 nomerge
1471 forcesac
1472 soft
1473 pt [x86, IA-64]
1476 io7= [HW] IO7 for Marvel based alpha systems
1477 See comment before marvel_specify_io7 in
1478 arch/alpha/kernel/core_marvel.c.
1480 io_delay= [X86] I/O delay method
1481 0x80
1482 Standard port 0x80 based delay
1483 0xed
1484 Alternate port 0xed based delay (needed on some systems)
1485 udelay
1486 Simple two microseconds delay
1487 none
1488 No delay
1490 ip= [IP_PNP]
1491 See Documentation/filesystems/nfs/nfsroot.txt.
1493 irqfixup [HW]
1494 When an interrupt is not handled search all handlers
1495 for it. Intended to get systems with badly broken
1496 firmware running.
1498 irqpoll [HW]
1499 When an interrupt is not handled search all handlers
1500 for it. Also check all handlers each timer
1501 interrupt. Intended to get systems with badly broken
1502 firmware running.
1504 isapnp= [ISAPNP]
1505 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1507 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1508 Format:
1509 <cpu number>,...,<cpu number>
1510 or
1511 <cpu number>-<cpu number>
1512 (must be a positive range in ascending order)
1513 or a mixture
1514 <cpu number>,...,<cpu number>-<cpu number>
1516 This option can be used to specify one or more CPUs
1517 to isolate from the general SMP balancing and scheduling
1518 algorithms. You can move a process onto or off an
1519 "isolated" CPU via the CPU affinity syscalls or cpuset.
1520 <cpu number> begins at 0 and the maximum value is
1521 "number of CPUs in system - 1".
1523 This option is the preferred way to isolate CPUs. The
1524 alternative -- manually setting the CPU mask of all
1525 tasks in the system -- can cause problems and
1526 suboptimal load balancer performance.
1528 iucv= [HW,NET]
1530 ivrs_ioapic [HW,X86_64]
1531 Provide an override to the IOAPIC-ID<->DEVICE-ID
1532 mapping provided in the IVRS ACPI table. For
1533 example, to map IOAPIC-ID decimal 10 to
1534 PCI device 00:14.0 write the parameter as:
1535 ivrs_ioapic[10]=00:14.0
1537 ivrs_hpet [HW,X86_64]
1538 Provide an override to the HPET-ID<->DEVICE-ID
1539 mapping provided in the IVRS ACPI table. For
1540 example, to map HPET-ID decimal 0 to
1541 PCI device 00:14.0 write the parameter as:
1542 ivrs_hpet[0]=00:14.0
1544 js= [HW,JOY] Analog joystick
1545 See Documentation/input/joystick.txt.
1547 kaslr/nokaslr [X86]
1548 Enable/disable kernel and module base offset ASLR
1549 (Address Space Layout Randomization) if built into
1550 the kernel. When CONFIG_HIBERNATION is selected,
1551 kASLR is disabled by default. When kASLR is enabled,
1552 hibernation will be disabled.
1554 keepinitrd [HW,ARM]
1556 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1557 specifies the amount of memory usable by the kernel
1558 for non-movable allocations. The requested amount is
1559 spread evenly throughout all nodes in the system. The
1560 remaining memory in each node is used for Movable
1561 pages. In the event, a node is too small to have both
1562 kernelcore and Movable pages, kernelcore pages will
1563 take priority and other nodes will have a larger number
1564 of Movable pages. The Movable zone is used for the
1565 allocation of pages that may be reclaimed or moved
1566 by the page migration subsystem. This means that
1567 HugeTLB pages may not be allocated from this zone.
1568 Note that allocations like PTEs-from-HighMem still
1569 use the HighMem zone if it exists, and the Normal
1570 zone if it does not.
1572 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1573 Format: <Controller#>[,poll interval]
1574 The controller # is the number of the ehci usb debug
1575 port as it is probed via PCI. The poll interval is
1576 optional and is the number seconds in between
1577 each poll cycle to the debug port in case you need
1578 the functionality for interrupting the kernel with
1579 gdb or control-c on the dbgp connection. When
1580 not using this parameter you use sysrq-g to break into
1581 the kernel debugger.
1583 kgdboc= [KGDB,HW] kgdb over consoles.
1584 Requires a tty driver that supports console polling,
1585 or a supported polling keyboard driver (non-usb).
1586 Serial only format: <serial_device>[,baud]
1587 keyboard only format: kbd
1588 keyboard and serial format: kbd,<serial_device>[,baud]
1589 Optional Kernel mode setting:
1590 kms, kbd format: kms,kbd
1591 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1593 kgdbwait [KGDB] Stop kernel execution and enter the
1594 kernel debugger at the earliest opportunity.
1596 kmac= [MIPS] korina ethernet MAC address.
1597 Configure the RouterBoard 532 series on-chip
1598 Ethernet adapter MAC address.
1600 kmemleak= [KNL] Boot-time kmemleak enable/disable
1601 Valid arguments: on, off
1602 Default: on
1603 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1604 the default is off.
1606 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1607 Valid arguments: 0, 1, 2
1608 kmemcheck=0 (disabled)
1609 kmemcheck=1 (enabled)
1610 kmemcheck=2 (one-shot mode)
1611 Default: 2 (one-shot mode)
1613 kstack=N [X86] Print N words from the kernel stack
1614 in oops dumps.
1616 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1617 Default is 0 (don't ignore, but inject #GP)
1619 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1620 KVM MMU at runtime.
1621 Default is 0 (off)
1623 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1624 Default is 1 (enabled)
1626 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1627 for all guests.
1628 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1630 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1631 (virtualized MMU) support on capable Intel chips.
1632 Default is 1 (enabled)
1634 kvm-intel.emulate_invalid_guest_state=
1635 [KVM,Intel] Enable emulation of invalid guest states
1636 Default is 0 (disabled)
1638 kvm-intel.flexpriority=
1639 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1640 Default is 1 (enabled)
1642 kvm-intel.nested=
1643 [KVM,Intel] Enable VMX nesting (nVMX).
1644 Default is 0 (disabled)
1646 kvm-intel.unrestricted_guest=
1647 [KVM,Intel] Disable unrestricted guest feature
1648 (virtualized real and unpaged mode) on capable
1649 Intel chips. Default is 1 (enabled)
1651 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1652 feature (tagged TLBs) on capable Intel chips.
1653 Default is 1 (enabled)
1655 l2cr= [PPC]
1657 l3cr= [PPC]
1659 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1660 disabled it.
1662 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1663 value for LAPIC timer one-shot implementation. Default
1664 back to the programmable timer unit in the LAPIC.
1666 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1667 in C2 power state.
1669 libata.dma= [LIBATA] DMA control
1670 libata.dma=0 Disable all PATA and SATA DMA
1671 libata.dma=1 PATA and SATA Disk DMA only
1672 libata.dma=2 ATAPI (CDROM) DMA only
1673 libata.dma=4 Compact Flash DMA only
1674 Combinations also work, so libata.dma=3 enables DMA
1675 for disks and CDROMs, but not CFs.
1677 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1678 libata.ignore_hpa=0 keep BIOS limits (default)
1679 libata.ignore_hpa=1 ignore limits, using full disk
1681 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1682 when set.
1683 Format: <int>
1685 libata.force= [LIBATA] Force configurations. The format is comma
1686 separated list of "[ID:]VAL" where ID is
1687 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1688 matching port, link or device. Basically, it matches
1689 the ATA ID string printed on console by libata. If
1690 the whole ID part is omitted, the last PORT and DEVICE
1691 values are used. If ID hasn't been specified yet, the
1692 configuration applies to all ports, links and devices.
1694 If only DEVICE is omitted, the parameter applies to
1695 the port and all links and devices behind it. DEVICE
1696 number of 0 either selects the first device or the
1697 first fan-out link behind PMP device. It does not
1698 select the host link. DEVICE number of 15 selects the
1699 host link and device attached to it.
1701 The VAL specifies the configuration to force. As long
1702 as there's no ambiguity shortcut notation is allowed.
1703 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1704 The following configurations can be forced.
1706 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1707 Any ID with matching PORT is used.
1709 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1711 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1712 udma[/][16,25,33,44,66,100,133] notation is also
1713 allowed.
1715 * [no]ncq: Turn on or off NCQ.
1717 * nohrst, nosrst, norst: suppress hard, soft
1718 and both resets.
1720 * rstonce: only attempt one reset during
1721 hot-unplug link recovery
1723 * dump_id: dump IDENTIFY data.
1725 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1727 * disable: Disable this device.
1729 If there are multiple matching configurations changing
1730 the same attribute, the last one is used.
1732 memblock=debug [KNL] Enable memblock debug messages.
1734 load_ramdisk= [RAM] List of ramdisks to load from floppy
1735 See Documentation/blockdev/ramdisk.txt.
1737 lockd.nlm_grace_period=P [NFS] Assign grace period.
1738 Format: <integer>
1740 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1741 Format: <integer>
1743 lockd.nlm_timeout=T [NFS] Assign timeout value.
1744 Format: <integer>
1746 lockd.nlm_udpport=M [NFS] Assign UDP port.
1747 Format: <integer>
1749 locktorture.nreaders_stress= [KNL]
1750 Set the number of locking read-acquisition kthreads.
1751 Defaults to being automatically set based on the
1752 number of online CPUs.
1754 locktorture.nwriters_stress= [KNL]
1755 Set the number of locking write-acquisition kthreads.
1757 locktorture.onoff_holdoff= [KNL]
1758 Set time (s) after boot for CPU-hotplug testing.
1760 locktorture.onoff_interval= [KNL]
1761 Set time (s) between CPU-hotplug operations, or
1762 zero to disable CPU-hotplug testing.
1764 locktorture.shuffle_interval= [KNL]
1765 Set task-shuffle interval (jiffies). Shuffling
1766 tasks allows some CPUs to go into dyntick-idle
1767 mode during the locktorture test.
1769 locktorture.shutdown_secs= [KNL]
1770 Set time (s) after boot system shutdown. This
1771 is useful for hands-off automated testing.
1773 locktorture.stat_interval= [KNL]
1774 Time (s) between statistics printk()s.
1776 locktorture.stutter= [KNL]
1777 Time (s) to stutter testing, for example,
1778 specifying five seconds causes the test to run for
1779 five seconds, wait for five seconds, and so on.
1780 This tests the locking primitive's ability to
1781 transition abruptly to and from idle.
1783 locktorture.torture_runnable= [BOOT]
1784 Start locktorture running at boot time.
1786 locktorture.torture_type= [KNL]
1787 Specify the locking implementation to test.
1789 locktorture.verbose= [KNL]
1790 Enable additional printk() statements.
1792 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1793 Format: <irq>
1795 loglevel= All Kernel Messages with a loglevel smaller than the
1796 console loglevel will be printed to the console. It can
1797 also be changed with klogd or other programs. The
1798 loglevels are defined as follows:
1800 0 (KERN_EMERG) system is unusable
1801 1 (KERN_ALERT) action must be taken immediately
1802 2 (KERN_CRIT) critical conditions
1803 3 (KERN_ERR) error conditions
1804 4 (KERN_WARNING) warning conditions
1805 5 (KERN_NOTICE) normal but significant condition
1806 6 (KERN_INFO) informational
1807 7 (KERN_DEBUG) debug-level messages
1809 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1810 in bytes. n must be a power of two and greater
1811 than the minimal size. The minimal size is defined
1812 by LOG_BUF_SHIFT kernel config parameter. There is
1813 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1814 that allows to increase the default size depending on
1815 the number of CPUs. See init/Kconfig for more details.
1817 logo.nologo [FB] Disables display of the built-in Linux logo.
1818 This may be used to provide more screen space for
1819 kernel log messages and is useful when debugging
1820 kernel boot problems.
1822 lp=0 [LP] Specify parallel ports to use, e.g,
1823 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1824 lp=reset first parallel port). 'lp=0' disables the
1825 lp=auto printer driver. 'lp=reset' (which can be
1826 specified in addition to the ports) causes
1827 attached printers to be reset. Using
1828 lp=port1,port2,... specifies the parallel ports
1829 to associate lp devices with, starting with
1830 lp0. A port specification may be 'none' to skip
1831 that lp device, or a parport name such as
1832 'parport0'. Specifying 'lp=auto' instead of a
1833 port specification list means that device IDs
1834 from each port should be examined, to see if
1835 an IEEE 1284-compliant printer is attached; if
1836 so, the driver will manage that printer.
1837 See also header of drivers/char/lp.c.
1839 lpj=n [KNL]
1840 Sets loops_per_jiffy to given constant, thus avoiding
1841 time-consuming boot-time autodetection (up to 250 ms per
1842 CPU). 0 enables autodetection (default). To determine
1843 the correct value for your kernel, boot with normal
1844 autodetection and see what value is printed. Note that
1845 on SMP systems the preset will be applied to all CPUs,
1846 which is likely to cause problems if your CPUs need
1847 significantly divergent settings. An incorrect value
1848 will cause delays in the kernel to be wrong, leading to
1849 unpredictable I/O errors and other breakage. Although
1850 unlikely, in the extreme case this might damage your
1851 hardware.
1853 ltpc= [NET]
1854 Format: <io>,<irq>,<dma>
1856 machvec= [IA-64] Force the use of a particular machine-vector
1857 (machvec) in a generic kernel.
1858 Example: machvec=hpzx1_swiotlb
1860 machtype= [Loongson] Share the same kernel image file between different
1861 yeeloong laptop.
1862 Example: machtype=lemote-yeeloong-2f-7inch
1864 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1865 than or equal to this physical address is ignored.
1867 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1868 should make use of. maxcpus=n : n >= 0 limits the
1869 kernel to using 'n' processors. n=0 is a special case,
1870 it is equivalent to "nosmp", which also disables
1871 the IO APIC.
1873 max_loop= [LOOP] The number of loop block devices that get
1874 (loop.max_loop) unconditionally pre-created at init time. The default
1875 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1876 of statically allocating a predefined number, loop
1877 devices can be requested on-demand with the
1878 /dev/loop-control interface.
1880 mce [X86-32] Machine Check Exception
1882 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1884 md= [HW] RAID subsystems devices and level
1885 See Documentation/md.txt.
1887 mdacon= [MDA]
1888 Format: <first>,<last>
1889 Specifies range of consoles to be captured by the MDA.
1891 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1892 Amount of memory to be used when the kernel is not able
1893 to see the whole system memory or for test.
1894 [X86] Work as limiting max address. Use together
1895 with memmap= to avoid physical address space collisions.
1896 Without memmap= PCI devices could be placed at addresses
1897 belonging to unused RAM.
1899 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1900 memory.
1902 memchunk=nn[KMG]
1903 [KNL,SH] Allow user to override the default size for
1904 per-device physically contiguous DMA buffers.
1906 memmap=exactmap [KNL,X86] Enable setting of an exact
1907 E820 memory map, as specified by the user.
1908 Such memmap=exactmap lines can be constructed based on
1909 BIOS output or other requirements. See the memmap=nn@ss
1910 option description.
1912 memmap=nn[KMG]@ss[KMG]
1913 [KNL] Force usage of a specific region of memory.
1914 Region of memory to be used is from ss to ss+nn.
1916 memmap=nn[KMG]#ss[KMG]
1917 [KNL,ACPI] Mark specific memory as ACPI data.
1918 Region of memory to be marked is from ss to ss+nn.
1920 memmap=nn[KMG]$ss[KMG]
1921 [KNL,ACPI] Mark specific memory as reserved.
1922 Region of memory to be reserved is from ss to ss+nn.
1923 Example: Exclude memory from 0x18690000-0x1869ffff
1924 memmap=64K$0x18690000
1925 or
1926 memmap=0x10000$0x18690000
1928 memory_corruption_check=0/1 [X86]
1929 Some BIOSes seem to corrupt the first 64k of
1930 memory when doing things like suspend/resume.
1931 Setting this option will scan the memory
1932 looking for corruption. Enabling this will
1933 both detect corruption and prevent the kernel
1934 from using the memory being corrupted.
1935 However, its intended as a diagnostic tool; if
1936 repeatable BIOS-originated corruption always
1937 affects the same memory, you can use memmap=
1938 to prevent the kernel from using that memory.
1940 memory_corruption_check_size=size [X86]
1941 By default it checks for corruption in the low
1942 64k, making this memory unavailable for normal
1943 use. Use this parameter to scan for
1944 corruption in more or less memory.
1946 memory_corruption_check_period=seconds [X86]
1947 By default it checks for corruption every 60
1948 seconds. Use this parameter to check at some
1949 other rate. 0 disables periodic checking.
1951 memtest= [KNL,X86] Enable memtest
1952 Format: <integer>
1953 default : 0 <disable>
1954 Specifies the number of memtest passes to be
1955 performed. Each pass selects another test
1956 pattern from a given set of patterns. Memtest
1957 fills the memory with this pattern, validates
1958 memory contents and reserves bad memory
1959 regions that are detected.
1961 meye.*= [HW] Set MotionEye Camera parameters
1962 See Documentation/video4linux/meye.txt.
1964 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1965 Multi-Function General Purpose Timers on AMD Geode
1966 platforms.
1968 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1969 the BIOS has incorrectly applied a workaround. TinyBIOS
1970 version 0.98 is known to be affected, 0.99 fixes the
1971 problem by letting the user disable the workaround.
1973 mga= [HW,DRM]
1975 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1976 physical address is ignored.
1978 mini2440= [ARM,HW,KNL]
1979 Format:[0..2][b][c][t]
1980 Default: "0tb"
1981 MINI2440 configuration specification:
1982 0 - The attached screen is the 3.5" TFT
1983 1 - The attached screen is the 7" TFT
1984 2 - The VGA Shield is attached (1024x768)
1985 Leaving out the screen size parameter will not load
1986 the TFT driver, and the framebuffer will be left
1987 unconfigured.
1988 b - Enable backlight. The TFT backlight pin will be
1989 linked to the kernel VESA blanking code and a GPIO
1990 LED. This parameter is not necessary when using the
1991 VGA shield.
1992 c - Enable the s3c camera interface.
1993 t - Reserved for enabling touchscreen support. The
1994 touchscreen support is not enabled in the mainstream
1995 kernel as of 2.6.30, a preliminary port can be found
1996 in the "bleeding edge" mini2440 support kernel at
1997 http://repo.or.cz/w/linux-2.6/mini2440.git
1999 mminit_loglevel=
2000 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2001 parameter allows control of the logging verbosity for
2002 the additional memory initialisation checks. A value
2003 of 0 disables mminit logging and a level of 4 will
2004 log everything. Information is printed at KERN_DEBUG
2005 so loglevel=8 may also need to be specified.
2007 module.sig_enforce
2008 [KNL] When CONFIG_MODULE_SIG is set, this means that
2009 modules without (valid) signatures will fail to load.
2010 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2011 is always true, so this option does nothing.
2013 mousedev.tap_time=
2014 [MOUSE] Maximum time between finger touching and
2015 leaving touchpad surface for touch to be considered
2016 a tap and be reported as a left button click (for
2017 touchpads working in absolute mode only).
2018 Format: <msecs>
2019 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2020 reporting absolute coordinates, such as tablets
2021 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2022 reporting absolute coordinates, such as tablets
2024 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2025 is similar to kernelcore except it specifies the
2026 amount of memory used for migratable allocations.
2027 If both kernelcore and movablecore is specified,
2028 then kernelcore will be at *least* the specified
2029 value but may be more. If movablecore on its own
2030 is specified, the administrator must be careful
2031 that the amount of memory usable for all allocations
2032 is not too small.
2034 movable_node [KNL,X86] Boot-time switch to enable the effects
2035 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2037 MTD_Partition= [MTD]
2038 Format: <name>,<region-number>,<size>,<offset>
2040 MTD_Region= [MTD] Format:
2041 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2043 mtdparts= [MTD]
2044 See drivers/mtd/cmdlinepart.c.
2046 multitce=off [PPC] This parameter disables the use of the pSeries
2047 firmware feature for updating multiple TCE entries
2048 at a time.
2050 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2052 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2054 boundary - index of last SLC block on Flex-OneNAND.
2055 The remaining blocks are configured as MLC blocks.
2056 lock - Configure if Flex-OneNAND boundary should be locked.
2057 Once locked, the boundary cannot be changed.
2058 1 indicates lock status, 0 indicates unlock status.
2060 mtdset= [ARM]
2061 ARM/S3C2412 JIVE boot control
2063 See arch/arm/mach-s3c2412/mach-jive.c
2065 mtouchusb.raw_coordinates=
2066 [HW] Make the MicroTouch USB driver use raw coordinates
2067 ('y', default) or cooked coordinates ('n')
2069 mtrr_chunk_size=nn[KMG] [X86]
2070 used for mtrr cleanup. It is largest continuous chunk
2071 that could hold holes aka. UC entries.
2073 mtrr_gran_size=nn[KMG] [X86]
2074 Used for mtrr cleanup. It is granularity of mtrr block.
2075 Default is 1.
2076 Large value could prevent small alignment from
2077 using up MTRRs.
2079 mtrr_spare_reg_nr=n [X86]
2080 Format: <integer>
2081 Range: 0,7 : spare reg number
2082 Default : 1
2083 Used for mtrr cleanup. It is spare mtrr entries number.
2084 Set to 2 or more if your graphical card needs more.
2086 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2088 netdev= [NET] Network devices parameters
2089 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2090 Note that mem_start is often overloaded to mean
2091 something different and driver-specific.
2092 This usage is only documented in each driver source
2093 file if at all.
2095 nf_conntrack.acct=
2096 [NETFILTER] Enable connection tracking flow accounting
2097 0 to disable accounting
2098 1 to enable accounting
2099 Default value is 0.
2101 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2102 See Documentation/filesystems/nfs/nfsroot.txt.
2104 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2105 See Documentation/filesystems/nfs/nfsroot.txt.
2107 nfsrootdebug [NFS] enable nfsroot debugging messages.
2108 See Documentation/filesystems/nfs/nfsroot.txt.
2110 nfs.callback_tcpport=
2111 [NFS] set the TCP port on which the NFSv4 callback
2112 channel should listen.
2114 nfs.cache_getent=
2115 [NFS] sets the pathname to the program which is used
2116 to update the NFS client cache entries.
2118 nfs.cache_getent_timeout=
2119 [NFS] sets the timeout after which an attempt to
2120 update a cache entry is deemed to have failed.
2122 nfs.idmap_cache_timeout=
2123 [NFS] set the maximum lifetime for idmapper cache
2124 entries.
2126 nfs.enable_ino64=
2127 [NFS] enable 64-bit inode numbers.
2128 If zero, the NFS client will fake up a 32-bit inode
2129 number for the readdir() and stat() syscalls instead
2130 of returning the full 64-bit number.
2131 The default is to return 64-bit inode numbers.
2133 nfs.max_session_slots=
2134 [NFSv4.1] Sets the maximum number of session slots
2135 the client will attempt to negotiate with the server.
2136 This limits the number of simultaneous RPC requests
2137 that the client can send to the NFSv4.1 server.
2138 Note that there is little point in setting this
2139 value higher than the max_tcp_slot_table_limit.
2141 nfs.nfs4_disable_idmapping=
2142 [NFSv4] When set to the default of '1', this option
2143 ensures that both the RPC level authentication
2144 scheme and the NFS level operations agree to use
2145 numeric uids/gids if the mount is using the
2146 'sec=sys' security flavour. In effect it is
2147 disabling idmapping, which can make migration from
2148 legacy NFSv2/v3 systems to NFSv4 easier.
2149 Servers that do not support this mode of operation
2150 will be autodetected by the client, and it will fall
2151 back to using the idmapper.
2152 To turn off this behaviour, set the value to '0'.
2153 nfs.nfs4_unique_id=
2154 [NFS4] Specify an additional fixed unique ident-
2155 ification string that NFSv4 clients can insert into
2156 their nfs_client_id4 string. This is typically a
2157 UUID that is generated at system install time.
2159 nfs.send_implementation_id =
2160 [NFSv4.1] Send client implementation identification
2161 information in exchange_id requests.
2162 If zero, no implementation identification information
2163 will be sent.
2164 The default is to send the implementation identification
2165 information.
2167 nfs.recover_lost_locks =
2168 [NFSv4] Attempt to recover locks that were lost due
2169 to a lease timeout on the server. Please note that
2170 doing this risks data corruption, since there are
2171 no guarantees that the file will remain unchanged
2172 after the locks are lost.
2173 If you want to enable the kernel legacy behaviour of
2174 attempting to recover these locks, then set this
2175 parameter to '1'.
2176 The default parameter value of '0' causes the kernel
2177 not to attempt recovery of lost locks.
2179 nfsd.nfs4_disable_idmapping=
2180 [NFSv4] When set to the default of '1', the NFSv4
2181 server will return only numeric uids and gids to
2182 clients using auth_sys, and will accept numeric uids
2183 and gids from such clients. This is intended to ease
2184 migration from NFSv2/v3.
2186 objlayoutdriver.osd_login_prog=
2187 [NFS] [OBJLAYOUT] sets the pathname to the program which
2188 is used to automatically discover and login into new
2189 osd-targets. Please see:
2190 Documentation/filesystems/pnfs.txt for more explanations
2192 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2193 when a NMI is triggered.
2194 Format: [state][,regs][,debounce][,die]
2196 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2197 Format: [panic,][nopanic,][num]
2198 Valid num: 0
2199 0 - turn nmi_watchdog off
2200 When panic is specified, panic when an NMI watchdog
2201 timeout occurs (or 'nopanic' to override the opposite
2202 default).
2203 This is useful when you use a panic=... timeout and
2204 need the box quickly up again.
2206 netpoll.carrier_timeout=
2207 [NET] Specifies amount of time (in seconds) that
2208 netpoll should wait for a carrier. By default netpoll
2209 waits 4 seconds.
2211 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2212 emulation library even if a 387 maths coprocessor
2213 is present.
2215 no_console_suspend
2216 [HW] Never suspend the console
2217 Disable suspending of consoles during suspend and
2218 hibernate operations. Once disabled, debugging
2219 messages can reach various consoles while the rest
2220 of the system is being put to sleep (ie, while
2221 debugging driver suspend/resume hooks). This may
2222 not work reliably with all consoles, but is known
2223 to work with serial and VGA consoles.
2224 To facilitate more flexible debugging, we also add
2225 console_suspend, a printk module parameter to control
2226 it. Users could use console_suspend (usually
2227 /sys/module/printk/parameters/console_suspend) to
2228 turn on/off it dynamically.
2230 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2231 caches in the slab allocator. Saves per-node memory,
2232 but will impact performance.
2234 noalign [KNL,ARM]
2236 noapic [SMP,APIC] Tells the kernel to not make use of any
2237 IOAPICs that may be present in the system.
2239 noautogroup Disable scheduler automatic task group creation.
2241 nobats [PPC] Do not use BATs for mapping kernel lowmem
2242 on "Classic" PPC cores.
2244 nocache [ARM]
2246 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2248 nodelayacct [KNL] Disable per-task delay accounting
2250 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2252 nodsp [SH] Disable hardware DSP at boot time.
2254 noefi Disable EFI runtime services support.
2256 noexec [IA-64]
2258 noexec [X86]
2259 On X86-32 available only on PAE configured kernels.
2260 noexec=on: enable non-executable mappings (default)
2261 noexec=off: disable non-executable mappings
2263 nosmap [X86]
2264 Disable SMAP (Supervisor Mode Access Prevention)
2265 even if it is supported by processor.
2267 nosmep [X86]
2268 Disable SMEP (Supervisor Mode Execution Prevention)
2269 even if it is supported by processor.
2271 noexec32 [X86-64]
2272 This affects only 32-bit executables.
2273 noexec32=on: enable non-executable mappings (default)
2274 read doesn't imply executable mappings
2275 noexec32=off: disable non-executable mappings
2276 read implies executable mappings
2278 nofpu [SH] Disable hardware FPU at boot time.
2280 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2281 register save and restore. The kernel will only save
2282 legacy floating-point registers on task switch.
2284 noxsave [BUGS=X86] Disables x86 extended register state save
2285 and restore using xsave. The kernel will fallback to
2286 enabling legacy floating-point and sse state.
2288 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2289 register states. The kernel will fall back to use
2290 xsave to save the states. By using this parameter,
2291 performance of saving the states is degraded because
2292 xsave doesn't support modified optimization while
2293 xsaveopt supports it on xsaveopt enabled systems.
2295 noxsaves [X86] Disables xsaves and xrstors used in saving and
2296 restoring x86 extended register state in compacted
2297 form of xsave area. The kernel will fall back to use
2298 xsaveopt and xrstor to save and restore the states
2299 in standard form of xsave area. By using this
2300 parameter, xsave area per process might occupy more
2301 memory on xsaves enabled systems.
2303 eagerfpu= [X86]
2304 on enable eager fpu restore
2305 off disable eager fpu restore
2306 auto selects the default scheme, which automatically
2307 enables eagerfpu restore for xsaveopt.
2309 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2310 wfi(ARM) instruction doesn't work correctly and not to
2311 use it. This is also useful when using JTAG debugger.
2313 no_file_caps Tells the kernel not to honor file capabilities. The
2314 only way then for a file to be executed with privilege
2315 is to be setuid root or executed by root.
2317 nohalt [IA-64] Tells the kernel not to use the power saving
2318 function PAL_HALT_LIGHT when idle. This increases
2319 power-consumption. On the positive side, it reduces
2320 interrupt wake-up latency, which may improve performance
2321 in certain environments such as networked servers or
2322 real-time systems.
2324 nohibernate [HIBERNATION] Disable hibernation and resume.
2326 nohz= [KNL] Boottime enable/disable dynamic ticks
2327 Valid arguments: on, off
2328 Default: on
2330 nohz_full= [KNL,BOOT]
2331 In kernels built with CONFIG_NO_HZ_FULL=y, set
2332 the specified list of CPUs whose tick will be stopped
2333 whenever possible. The boot CPU will be forced outside
2334 the range to maintain the timekeeping.
2335 The CPUs in this range must also be included in the
2336 rcu_nocbs= set.
2338 noiotrap [SH] Disables trapped I/O port accesses.
2340 noirqdebug [X86-32] Disables the code which attempts to detect and
2341 disable unhandled interrupt sources.
2343 no_timer_check [X86,APIC] Disables the code which tests for
2344 broken timer IRQ sources.
2346 noisapnp [ISAPNP] Disables ISA PnP code.
2348 noinitrd [RAM] Tells the kernel not to load any configured
2349 initial RAM disk.
2351 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2352 remapping.
2353 [Deprecated - use intremap=off]
2355 nointroute [IA-64]
2357 nojitter [IA-64] Disables jitter checking for ITC timers.
2359 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2361 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2362 fault handling.
2364 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2365 steal time is computed, but won't influence scheduler
2366 behaviour
2368 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2370 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2372 noltlbs [PPC] Do not use large page/tlb entries for kernel
2373 lowmem mapping on PPC40x.
2375 nomca [IA-64] Disable machine check abort handling
2377 nomce [X86-32] Machine Check Exception
2379 nomfgpt [X86-32] Disable Multi-Function General Purpose
2380 Timer usage (for AMD Geode machines).
2382 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2383 shutdown the other cpus. Instead use the REBOOT_VECTOR
2384 irq.
2386 nomodule Disable module load
2388 nopat [X86] Disable PAT (page attribute table extension of
2389 pagetables) support.
2391 norandmaps Don't use address space randomization. Equivalent to
2392 echo 0 > /proc/sys/kernel/randomize_va_space
2394 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2396 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2397 with UP alternatives
2399 nordrand [X86] Disable kernel use of the RDRAND and
2400 RDSEED instructions even if they are supported
2401 by the processor. RDRAND and RDSEED are still
2402 available to user space applications.
2404 noresume [SWSUSP] Disables resume and restores original swap
2405 space.
2407 no-scroll [VGA] Disables scrollback.
2408 This is required for the Braillex ib80-piezo Braille
2409 reader made by F.H. Papenmeier (Germany).
2411 nosbagart [IA-64]
2413 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2415 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2416 and disable the IO APIC. legacy for "maxcpus=0".
2418 nosoftlockup [KNL] Disable the soft-lockup detector.
2420 nosync [HW,M68K] Disables sync negotiation for all devices.
2422 notsc [BUGS=X86-32] Disable Time Stamp Counter
2424 nousb [USB] Disable the USB subsystem
2426 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2428 nowb [ARM]
2430 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2432 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2433 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2434 Some features depend on CPU0. Known dependencies are:
2435 1. Resume from suspend/hibernate depends on CPU0.
2436 Suspend/hibernate will fail if CPU0 is offline and you
2437 need to online CPU0 before suspend/hibernate.
2438 2. PIC interrupts also depend on CPU0. CPU0 can't be
2439 removed if a PIC interrupt is detected.
2440 It's said poweroff/reboot may depend on CPU0 on some
2441 machines although I haven't seen such issues so far
2442 after CPU0 is offline on a few tested machines.
2443 If the dependencies are under your control, you can
2444 turn on cpu0_hotplug.
2446 nptcg= [IA-64] Override max number of concurrent global TLB
2447 purges which is reported from either PAL_VM_SUMMARY or
2448 SAL PALO.
2450 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2451 could support. nr_cpus=n : n >= 1 limits the kernel to
2452 supporting 'n' processors. Later in runtime you can not
2453 use hotplug cpu feature to put more cpu back to online.
2454 just like you compile the kernel NR_CPUS=n
2456 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2458 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2459 Allowed values are enable and disable
2461 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2462 one of ['zone', 'node', 'default'] can be specified
2463 This can be set from sysctl after boot.
2464 See Documentation/sysctl/vm.txt for details.
2466 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2467 See Documentation/debugging-via-ohci1394.txt for more
2468 info.
2470 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2471 Rather than timing out after 20 ms if an EC
2472 command is not properly ACKed, override the length
2473 of the timeout. We have interrupts disabled while
2474 waiting for the ACK, so if this is set too high
2475 interrupts *may* be lost!
2477 omap_mux= [OMAP] Override bootloader pin multiplexing.
2478 Format: <mux_mode0.mode_name=value>...
2479 For example, to override I2C bus2:
2480 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2482 oprofile.timer= [HW]
2483 Use timer interrupt instead of performance counters
2485 oprofile.cpu_type= Force an oprofile cpu type
2486 This might be useful if you have an older oprofile
2487 userland or if you want common events.
2488 Format: { arch_perfmon }
2489 arch_perfmon: [X86] Force use of architectural
2490 perfmon on Intel CPUs instead of the
2491 CPU specific event set.
2492 timer: [X86] Force use of architectural NMI
2493 timer mode (see also oprofile.timer
2494 for generic hr timer mode)
2495 [s390] Force legacy basic mode sampling
2496 (report cpu_type "timer")
2498 oops=panic Always panic on oopses. Default is to just kill the
2499 process, but there is a small probability of
2500 deadlocking the machine.
2501 This will also cause panics on machine check exceptions.
2502 Useful together with panic=30 to trigger a reboot.
2504 OSS [HW,OSS]
2505 See Documentation/sound/oss/oss-parameters.txt
2507 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2508 timeout > 0: seconds before rebooting
2509 timeout = 0: wait forever
2510 timeout < 0: reboot immediately
2511 Format: <timeout>
2513 crash_kexec_post_notifiers
2514 Run kdump after running panic-notifiers and dumping
2515 kmsg. This only for the users who doubt kdump always
2516 succeeds in any situation.
2517 Note that this also increases risks of kdump failure,
2518 because some panic notifiers can make the crashed
2519 kernel more unstable.
2521 parkbd.port= [HW] Parallel port number the keyboard adapter is
2522 connected to, default is 0.
2523 Format: <parport#>
2524 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2525 0 for XT, 1 for AT (default is AT).
2526 Format: <mode>
2528 parport= [HW,PPT] Specify parallel ports. 0 disables.
2529 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2530 Use 'auto' to force the driver to use any
2531 IRQ/DMA settings detected (the default is to
2532 ignore detected IRQ/DMA settings because of
2533 possible conflicts). You can specify the base
2534 address, IRQ, and DMA settings; IRQ and DMA
2535 should be numbers, or 'auto' (for using detected
2536 settings on that particular port), or 'nofifo'
2537 (to avoid using a FIFO even if it is detected).
2538 Parallel ports are assigned in the order they
2539 are specified on the command line, starting
2540 with parport0.
2542 parport_init_mode= [HW,PPT]
2543 Configure VIA parallel port to operate in
2544 a specific mode. This is necessary on Pegasos
2545 computer where firmware has no options for setting
2546 up parallel port mode and sets it to spp.
2547 Currently this function knows 686a and 8231 chips.
2548 Format: [spp|ps2|epp|ecp|ecpepp]
2550 pause_on_oops=
2551 Halt all CPUs after the first oops has been printed for
2552 the specified number of seconds. This is to be used if
2553 your oopses keep scrolling off the screen.
2555 pcbit= [HW,ISDN]
2557 pcd. [PARIDE]
2558 See header of drivers/block/paride/pcd.c.
2559 See also Documentation/blockdev/paride.txt.
2561 pci=option[,option...] [PCI] various PCI subsystem options:
2562 earlydump [X86] dump PCI config space before the kernel
2563 changes anything
2564 off [X86] don't probe for the PCI bus
2565 bios [X86-32] force use of PCI BIOS, don't access
2566 the hardware directly. Use this if your machine
2567 has a non-standard PCI host bridge.
2568 nobios [X86-32] disallow use of PCI BIOS, only direct
2569 hardware access methods are allowed. Use this
2570 if you experience crashes upon bootup and you
2571 suspect they are caused by the BIOS.
2572 conf1 [X86] Force use of PCI Configuration
2573 Mechanism 1.
2574 conf2 [X86] Force use of PCI Configuration
2575 Mechanism 2.
2576 noaer [PCIE] If the PCIEAER kernel config parameter is
2577 enabled, this kernel boot option can be used to
2578 disable the use of PCIE advanced error reporting.
2579 nodomains [PCI] Disable support for multiple PCI
2580 root domains (aka PCI segments, in ACPI-speak).
2581 nommconf [X86] Disable use of MMCONFIG for PCI
2582 Configuration
2583 check_enable_amd_mmconf [X86] check for and enable
2584 properly configured MMIO access to PCI
2585 config space on AMD family 10h CPU
2586 nomsi [MSI] If the PCI_MSI kernel config parameter is
2587 enabled, this kernel boot option can be used to
2588 disable the use of MSI interrupts system-wide.
2589 noioapicquirk [APIC] Disable all boot interrupt quirks.
2590 Safety option to keep boot IRQs enabled. This
2591 should never be necessary.
2592 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2593 primary IO-APIC for bridges that cannot disable
2594 boot IRQs. This fixes a source of spurious IRQs
2595 when the system masks IRQs.
2596 noioapicreroute [APIC] Disable workaround that uses the
2597 boot IRQ equivalent of an IRQ that connects to
2598 a chipset where boot IRQs cannot be disabled.
2599 The opposite of ioapicreroute.
2600 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2601 routing table. These calls are known to be buggy
2602 on several machines and they hang the machine
2603 when used, but on other computers it's the only
2604 way to get the interrupt routing table. Try
2605 this option if the kernel is unable to allocate
2606 IRQs or discover secondary PCI buses on your
2607 motherboard.
2608 rom [X86] Assign address space to expansion ROMs.
2609 Use with caution as certain devices share
2610 address decoders between ROMs and other
2611 resources.
2612 norom [X86] Do not assign address space to
2613 expansion ROMs that do not already have
2614 BIOS assigned address ranges.
2615 nobar [X86] Do not assign address space to the
2616 BARs that weren't assigned by the BIOS.
2617 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2618 assigned automatically to PCI devices. You can
2619 make the kernel exclude IRQs of your ISA cards
2620 this way.
2621 pirqaddr=0xAAAAA [X86] Specify the physical address
2622 of the PIRQ table (normally generated
2623 by the BIOS) if it is outside the
2624 F0000h-100000h range.
2625 lastbus=N [X86] Scan all buses thru bus #N. Can be
2626 useful if the kernel is unable to find your
2627 secondary buses and you want to tell it
2628 explicitly which ones they are.
2629 assign-busses [X86] Always assign all PCI bus
2630 numbers ourselves, overriding
2631 whatever the firmware may have done.
2632 usepirqmask [X86] Honor the possible IRQ mask stored
2633 in the BIOS $PIR table. This is needed on
2634 some systems with broken BIOSes, notably
2635 some HP Pavilion N5400 and Omnibook XE3
2636 notebooks. This will have no effect if ACPI
2637 IRQ routing is enabled.
2638 noacpi [X86] Do not use ACPI for IRQ routing
2639 or for PCI scanning.
2640 use_crs [X86] Use PCI host bridge window information
2641 from ACPI. On BIOSes from 2008 or later, this
2642 is enabled by default. If you need to use this,
2643 please report a bug.
2644 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2645 If you need to use this, please report a bug.
2646 routeirq Do IRQ routing for all PCI devices.
2647 This is normally done in pci_enable_device(),
2648 so this option is a temporary workaround
2649 for broken drivers that don't call it.
2650 skip_isa_align [X86] do not align io start addr, so can
2651 handle more pci cards
2652 firmware [ARM] Do not re-enumerate the bus but instead
2653 just use the configuration from the
2654 bootloader. This is currently used on
2655 IXP2000 systems where the bus has to be
2656 configured a certain way for adjunct CPUs.
2657 noearly [X86] Don't do any early type 1 scanning.
2658 This might help on some broken boards which
2659 machine check when some devices' config space
2660 is read. But various workarounds are disabled
2661 and some IOMMU drivers will not work.
2662 bfsort Sort PCI devices into breadth-first order.
2663 This sorting is done to get a device
2664 order compatible with older (<= 2.4) kernels.
2665 nobfsort Don't sort PCI devices into breadth-first order.
2666 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2667 tuning and use the BIOS-configured MPS defaults.
2668 pcie_bus_safe Set every device's MPS to the largest value
2669 supported by all devices below the root complex.
2670 pcie_bus_perf Set device MPS to the largest allowable MPS
2671 based on its parent bus. Also set MRRS (Max
2672 Read Request Size) to the largest supported
2673 value (no larger than the MPS that the device
2674 or bus can support) for best performance.
2675 pcie_bus_peer2peer Set every device's MPS to 128B, which
2676 every device is guaranteed to support. This
2677 configuration allows peer-to-peer DMA between
2678 any pair of devices, possibly at the cost of
2679 reduced performance. This also guarantees
2680 that hot-added devices will work.
2681 cbiosize=nn[KMG] The fixed amount of bus space which is
2682 reserved for the CardBus bridge's IO window.
2683 The default value is 256 bytes.
2684 cbmemsize=nn[KMG] The fixed amount of bus space which is
2685 reserved for the CardBus bridge's memory
2686 window. The default value is 64 megabytes.
2687 resource_alignment=
2688 Format:
2689 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2690 Specifies alignment and device to reassign
2691 aligned memory resources.
2692 If <order of align> is not specified,
2693 PAGE_SIZE is used as alignment.
2694 PCI-PCI bridge can be specified, if resource
2695 windows need to be expanded.
2696 ecrc= Enable/disable PCIe ECRC (transaction layer
2697 end-to-end CRC checking).
2698 bios: Use BIOS/firmware settings. This is the
2699 the default.
2700 off: Turn ECRC off
2701 on: Turn ECRC on.
2702 hpiosize=nn[KMG] The fixed amount of bus space which is
2703 reserved for hotplug bridge's IO window.
2704 Default size is 256 bytes.
2705 hpmemsize=nn[KMG] The fixed amount of bus space which is
2706 reserved for hotplug bridge's memory window.
2707 Default size is 2 megabytes.
2708 realloc= Enable/disable reallocating PCI bridge resources
2709 if allocations done by BIOS are too small to
2710 accommodate resources required by all child
2711 devices.
2712 off: Turn realloc off
2713 on: Turn realloc on
2714 realloc same as realloc=on
2715 noari do not use PCIe ARI.
2716 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2717 only look for one device below a PCIe downstream
2718 port.
2720 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2721 Management.
2722 off Disable ASPM.
2723 force Enable ASPM even on devices that claim not to support it.
2724 WARNING: Forcing ASPM on may cause system lockups.
2726 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2727 nomsi Do not use MSI for PCI Express Native Hotplug (this
2728 makes all PCIe ports use INTx for hotplug services).
2730 pcie_ports= [PCIE] PCIe ports handling:
2731 auto Ask the BIOS whether or not to use native PCIe services
2732 associated with PCIe ports (PME, hot-plug, AER). Use
2733 them only if that is allowed by the BIOS.
2734 native Use native PCIe services associated with PCIe ports
2735 unconditionally.
2736 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2737 ports driver.
2739 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2740 nomsi Do not use MSI for native PCIe PME signaling (this makes
2741 all PCIe root ports use INTx for all services).
2743 pcmv= [HW,PCMCIA] BadgePAD 4
2745 pd_ignore_unused
2746 [PM]
2747 Keep all power-domains already enabled by bootloader on,
2748 even if no driver has claimed them. This is useful
2749 for debug and development, but should not be
2750 needed on a platform with proper driver support.
2752 pd. [PARIDE]
2753 See Documentation/blockdev/paride.txt.
2755 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2756 boot time.
2757 Format: { 0 | 1 }
2758 See arch/parisc/kernel/pdc_chassis.c
2760 percpu_alloc= Select which percpu first chunk allocator to use.
2761 Currently supported values are "embed" and "page".
2762 Archs may support subset or none of the selections.
2763 See comments in mm/percpu.c for details on each
2764 allocator. This parameter is primarily for debugging
2765 and performance comparison.
2767 pf. [PARIDE]
2768 See Documentation/blockdev/paride.txt.
2770 pg. [PARIDE]
2771 See Documentation/blockdev/paride.txt.
2773 pirq= [SMP,APIC] Manual mp-table setup
2774 See Documentation/x86/i386/IO-APIC.txt.
2776 plip= [PPT,NET] Parallel port network link
2777 Format: { parport<nr> | timid | 0 }
2778 See also Documentation/parport.txt.
2780 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2781 Override pmtimer IOPort with a hex value.
2782 e.g. pmtmr=0x508
2784 pnp.debug=1 [PNP]
2785 Enable PNP debug messages (depends on the
2786 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2787 via /sys/module/pnp/parameters/debug. We always show
2788 current resource usage; turning this on also shows
2789 possible settings and some assignment information.
2791 pnpacpi= [ACPI]
2792 { off }
2794 pnpbios= [ISAPNP]
2795 { on | off | curr | res | no-curr | no-res }
2797 pnp_reserve_irq=
2798 [ISAPNP] Exclude IRQs for the autoconfiguration
2800 pnp_reserve_dma=
2801 [ISAPNP] Exclude DMAs for the autoconfiguration
2803 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2804 Ranges are in pairs (I/O port base and size).
2806 pnp_reserve_mem=
2807 [ISAPNP] Exclude memory regions for the
2808 autoconfiguration.
2809 Ranges are in pairs (memory base and size).
2811 ports= [IP_VS_FTP] IPVS ftp helper module
2812 Default is 21.
2813 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2814 may be specified.
2815 Format: <port>,<port>....
2817 print-fatal-signals=
2818 [KNL] debug: print fatal signals
2820 If enabled, warn about various signal handling
2821 related application anomalies: too many signals,
2822 too many POSIX.1 timers, fatal signals causing a
2823 coredump - etc.
2825 If you hit the warning due to signal overflow,
2826 you might want to try "ulimit -i unlimited".
2828 default: off.
2830 printk.always_kmsg_dump=
2831 Trigger kmsg_dump for cases other than kernel oops or
2832 panics
2833 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2834 default: disabled
2836 printk.time= Show timing data prefixed to each printk message line
2837 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2839 processor.max_cstate= [HW,ACPI]
2840 Limit processor to maximum C-state
2841 max_cstate=9 overrides any DMI blacklist limit.
2843 processor.nocst [HW,ACPI]
2844 Ignore the _CST method to determine C-states,
2845 instead using the legacy FADT method
2847 profile= [KNL] Enable kernel profiling via /proc/profile
2848 Format: [schedule,]<number>
2849 Param: "schedule" - profile schedule points.
2850 Param: <number> - step/bucket size as a power of 2 for
2851 statistical time based profiling.
2852 Param: "sleep" - profile D-state sleeping (millisecs).
2853 Requires CONFIG_SCHEDSTATS
2854 Param: "kvm" - profile VM exits.
2856 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2857 before loading.
2858 See Documentation/blockdev/ramdisk.txt.
2860 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2861 probe for; one of (bare|imps|exps|lifebook|any).
2862 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2863 per second.
2864 psmouse.resetafter= [HW,MOUSE]
2865 Try to reset the device after so many bad packets
2866 (0 = never).
2867 psmouse.resolution=
2868 [HW,MOUSE] Set desired mouse resolution, in dpi.
2869 psmouse.smartscroll=
2870 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2871 0 = disabled, 1 = enabled (default).
2873 pstore.backend= Specify the name of the pstore backend to use
2875 pt. [PARIDE]
2876 See Documentation/blockdev/paride.txt.
2878 pty.legacy_count=
2879 [KNL] Number of legacy pty's. Overwrites compiled-in
2880 default number.
2882 quiet [KNL] Disable most log messages
2884 r128= [HW,DRM]
2886 raid= [HW,RAID]
2887 See Documentation/md.txt.
2889 ramdisk_blocksize= [RAM]
2890 See Documentation/blockdev/ramdisk.txt.
2892 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2893 See Documentation/blockdev/ramdisk.txt.
2895 rcu_nocbs= [KNL]
2896 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2897 the specified list of CPUs to be no-callback CPUs.
2898 Invocation of these CPUs' RCU callbacks will
2899 be offloaded to "rcuox/N" kthreads created for
2900 that purpose, where "x" is "b" for RCU-bh, "p"
2901 for RCU-preempt, and "s" for RCU-sched, and "N"
2902 is the CPU number. This reduces OS jitter on the
2903 offloaded CPUs, which can be useful for HPC and
2904 real-time workloads. It can also improve energy
2905 efficiency for asymmetric multiprocessors.
2907 rcu_nocb_poll [KNL]
2908 Rather than requiring that offloaded CPUs
2909 (specified by rcu_nocbs= above) explicitly
2910 awaken the corresponding "rcuoN" kthreads,
2911 make these kthreads poll for callbacks.
2912 This improves the real-time response for the
2913 offloaded CPUs by relieving them of the need to
2914 wake up the corresponding kthread, but degrades
2915 energy efficiency by requiring that the kthreads
2916 periodically wake up to do the polling.
2918 rcutree.blimit= [KNL]
2919 Set maximum number of finished RCU callbacks to
2920 process in one batch.
2922 rcutree.rcu_fanout_leaf= [KNL]
2923 Increase the number of CPUs assigned to each
2924 leaf rcu_node structure. Useful for very large
2925 systems.
2927 rcutree.jiffies_till_sched_qs= [KNL]
2928 Set required age in jiffies for a
2929 given grace period before RCU starts
2930 soliciting quiescent-state help from
2931 rcu_note_context_switch().
2933 rcutree.jiffies_till_first_fqs= [KNL]
2934 Set delay from grace-period initialization to
2935 first attempt to force quiescent states.
2936 Units are jiffies, minimum value is zero,
2937 and maximum value is HZ.
2939 rcutree.jiffies_till_next_fqs= [KNL]
2940 Set delay between subsequent attempts to force
2941 quiescent states. Units are jiffies, minimum
2942 value is one, and maximum value is HZ.
2944 rcutree.rcu_nocb_leader_stride= [KNL]
2945 Set the number of NOCB kthread groups, which
2946 defaults to the square root of the number of
2947 CPUs. Larger numbers reduces the wakeup overhead
2948 on the per-CPU grace-period kthreads, but increases
2949 that same overhead on each group's leader.
2951 rcutree.qhimark= [KNL]
2952 Set threshold of queued RCU callbacks beyond which
2953 batch limiting is disabled.
2955 rcutree.qlowmark= [KNL]
2956 Set threshold of queued RCU callbacks below which
2957 batch limiting is re-enabled.
2959 rcutree.rcu_idle_gp_delay= [KNL]
2960 Set wakeup interval for idle CPUs that have
2961 RCU callbacks (RCU_FAST_NO_HZ=y).
2963 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2964 Set wakeup interval for idle CPUs that have
2965 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2966 Lazy RCU callbacks are those which RCU can
2967 prove do nothing more than free memory.
2969 rcutorture.cbflood_inter_holdoff= [KNL]
2970 Set holdoff time (jiffies) between successive
2971 callback-flood tests.
2973 rcutorture.cbflood_intra_holdoff= [KNL]
2974 Set holdoff time (jiffies) between successive
2975 bursts of callbacks within a given callback-flood
2976 test.
2978 rcutorture.cbflood_n_burst= [KNL]
2979 Set the number of bursts making up a given
2980 callback-flood test. Set this to zero to
2981 disable callback-flood testing.
2983 rcutorture.cbflood_n_per_burst= [KNL]
2984 Set the number of callbacks to be registered
2985 in a given burst of a callback-flood test.
2987 rcutorture.fqs_duration= [KNL]
2988 Set duration of force_quiescent_state bursts.
2990 rcutorture.fqs_holdoff= [KNL]
2991 Set holdoff time within force_quiescent_state bursts.
2993 rcutorture.fqs_stutter= [KNL]
2994 Set wait time between force_quiescent_state bursts.
2996 rcutorture.gp_exp= [KNL]
2997 Use expedited update-side primitives.
2999 rcutorture.gp_normal= [KNL]
3000 Use normal (non-expedited) update-side primitives.
3001 If both gp_exp and gp_normal are set, do both.
3002 If neither gp_exp nor gp_normal are set, still
3003 do both.
3005 rcutorture.n_barrier_cbs= [KNL]
3006 Set callbacks/threads for rcu_barrier() testing.
3008 rcutorture.nfakewriters= [KNL]
3009 Set number of concurrent RCU writers. These just
3010 stress RCU, they don't participate in the actual
3011 test, hence the "fake".
3013 rcutorture.nreaders= [KNL]
3014 Set number of RCU readers.
3016 rcutorture.object_debug= [KNL]
3017 Enable debug-object double-call_rcu() testing.
3019 rcutorture.onoff_holdoff= [KNL]
3020 Set time (s) after boot for CPU-hotplug testing.
3022 rcutorture.onoff_interval= [KNL]
3023 Set time (s) between CPU-hotplug operations, or
3024 zero to disable CPU-hotplug testing.
3026 rcutorture.torture_runnable= [BOOT]
3027 Start rcutorture running at boot time.
3029 rcutorture.shuffle_interval= [KNL]
3030 Set task-shuffle interval (s). Shuffling tasks
3031 allows some CPUs to go into dyntick-idle mode
3032 during the rcutorture test.
3034 rcutorture.shutdown_secs= [KNL]
3035 Set time (s) after boot system shutdown. This
3036 is useful for hands-off automated testing.
3038 rcutorture.stall_cpu= [KNL]
3039 Duration of CPU stall (s) to test RCU CPU stall
3040 warnings, zero to disable.
3042 rcutorture.stall_cpu_holdoff= [KNL]
3043 Time to wait (s) after boot before inducing stall.
3045 rcutorture.stat_interval= [KNL]
3046 Time (s) between statistics printk()s.
3048 rcutorture.stutter= [KNL]
3049 Time (s) to stutter testing, for example, specifying
3050 five seconds causes the test to run for five seconds,
3051 wait for five seconds, and so on. This tests RCU's
3052 ability to transition abruptly to and from idle.
3054 rcutorture.test_boost= [KNL]
3055 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3056 "Maybe" means test if the RCU implementation
3057 under test support RCU priority boosting.
3059 rcutorture.test_boost_duration= [KNL]
3060 Duration (s) of each individual boost test.
3062 rcutorture.test_boost_interval= [KNL]
3063 Interval (s) between each boost test.
3065 rcutorture.test_no_idle_hz= [KNL]
3066 Test RCU's dyntick-idle handling. See also the
3067 rcutorture.shuffle_interval parameter.
3069 rcutorture.torture_type= [KNL]
3070 Specify the RCU implementation to test.
3072 rcutorture.verbose= [KNL]
3073 Enable additional printk() statements.
3075 rcupdate.rcu_expedited= [KNL]
3076 Use expedited grace-period primitives, for
3077 example, synchronize_rcu_expedited() instead
3078 of synchronize_rcu(). This reduces latency,
3079 but can increase CPU utilization, degrade
3080 real-time latency, and degrade energy efficiency.
3082 rcupdate.rcu_cpu_stall_suppress= [KNL]
3083 Suppress RCU CPU stall warning messages.
3085 rcupdate.rcu_cpu_stall_timeout= [KNL]
3086 Set timeout for RCU CPU stall warning messages.
3088 rcupdate.rcu_task_stall_timeout= [KNL]
3089 Set timeout in jiffies for RCU task stall warning
3090 messages. Disable with a value less than or equal
3091 to zero.
3093 rdinit= [KNL]
3094 Format: <full_path>
3095 Run specified binary instead of /init from the ramdisk,
3096 used for early userspace startup. See initrd.
3098 reboot= [KNL]
3099 Format (x86 or x86_64):
3100 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3101 [[,]s[mp]#### \
3102 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3103 [[,]f[orce]
3104 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3105 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3106 reboot_force is either force or not specified,
3107 reboot_cpu is s[mp]#### with #### being the processor
3108 to be used for rebooting.
3110 relax_domain_level=
3111 [KNL, SMP] Set scheduler's default relax_domain_level.
3112 See Documentation/cgroups/cpusets.txt.
3114 relative_sleep_states=
3115 [SUSPEND] Use sleep state labeling where the deepest
3116 state available other than hibernation is always "mem".
3117 Format: { "0" | "1" }
3118 0 -- Traditional sleep state labels.
3119 1 -- Relative sleep state labels.
3121 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3123 reservetop= [X86-32]
3124 Format: nn[KMG]
3125 Reserves a hole at the top of the kernel virtual
3126 address space.
3128 reservelow= [X86]
3129 Format: nn[K]
3130 Set the amount of memory to reserve for BIOS at
3131 the bottom of the address space.
3133 reset_devices [KNL] Force drivers to reset the underlying device
3134 during initialization.
3136 resume= [SWSUSP]
3137 Specify the partition device for software suspend
3138 Format:
3139 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3141 resume_offset= [SWSUSP]
3142 Specify the offset from the beginning of the partition
3143 given by "resume=" at which the swap header is located,
3144 in <PAGE_SIZE> units (needed only for swap files).
3145 See Documentation/power/swsusp-and-swap-files.txt
3147 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3148 read the resume files
3150 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3151 Useful for devices that are detected asynchronously
3152 (e.g. USB and MMC devices).
3154 hibernate= [HIBERNATION]
3155 noresume Don't check if there's a hibernation image
3156 present during boot.
3157 nocompress Don't compress/decompress hibernation images.
3158 no Disable hibernation and resume.
3160 retain_initrd [RAM] Keep initrd memory after extraction
3162 rhash_entries= [KNL,NET]
3163 Set number of hash buckets for route cache
3165 ro [KNL] Mount root device read-only on boot
3167 root= [KNL] Root filesystem
3168 See name_to_dev_t comment in init/do_mounts.c.
3170 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3171 mount the root filesystem
3173 rootflags= [KNL] Set root filesystem mount option string
3175 rootfstype= [KNL] Set root filesystem type
3177 rootwait [KNL] Wait (indefinitely) for root device to show up.
3178 Useful for devices that are detected asynchronously
3179 (e.g. USB and MMC devices).
3181 rproc_mem=nn[KMG][@address]
3182 [KNL,ARM,CMA] Remoteproc physical memory block.
3183 Memory area to be used by remote processor image,
3184 managed by CMA.
3186 rw [KNL] Mount root device read-write on boot
3188 S [KNL] Run init in single mode
3190 s390_iommu= [HW,S390]
3191 Set s390 IOTLB flushing mode
3192 strict
3193 With strict flushing every unmap operation will result in
3194 an IOTLB flush. Default is lazy flushing before reuse,
3195 which is faster.
3197 sa1100ir [NET]
3198 See drivers/net/irda/sa1100_ir.c.
3200 sbni= [NET] Granch SBNI12 leased line adapter
3202 sched_debug [KNL] Enables verbose scheduler debug messages.
3204 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3205 xtime_lock contention on larger systems, and/or RCU lock
3206 contention on all systems with CONFIG_MAXSMP set.
3207 Format: { "0" | "1" }
3208 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3209 1 -- enable.
3210 Note: increases power consumption, thus should only be
3211 enabled if running jitter sensitive (HPC/RT) workloads.
3213 security= [SECURITY] Choose a security module to enable at boot.
3214 If this boot parameter is not specified, only the first
3215 security module asking for security registration will be
3216 loaded. An invalid security module name will be treated
3217 as if no module has been chosen.
3219 selinux= [SELINUX] Disable or enable SELinux at boot time.
3220 Format: { "0" | "1" }
3221 See security/selinux/Kconfig help text.
3222 0 -- disable.
3223 1 -- enable.
3224 Default value is set via kernel config option.
3225 If enabled at boot time, /selinux/disable can be used
3226 later to disable prior to initial policy load.
3228 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3229 Format: { "0" | "1" }
3230 See security/apparmor/Kconfig help text
3231 0 -- disable.
3232 1 -- enable.
3233 Default value is set via kernel config option.
3235 serialnumber [BUGS=X86-32]
3237 shapers= [NET]
3238 Maximal number of shapers.
3240 show_msr= [x86] show boot-time MSR settings
3241 Format: { <integer> }
3242 Show boot-time (BIOS-initialized) MSR settings.
3243 The parameter means the number of CPUs to show,
3244 for example 1 means boot CPU only.
3246 simeth= [IA-64]
3247 simscsi=
3249 slram= [HW,MTD]
3251 slab_nomerge [MM]
3252 Disable merging of slabs with similar size. May be
3253 necessary if there is some reason to distinguish
3254 allocs to different slabs. Debug options disable
3255 merging on their own.
3256 For more information see Documentation/vm/slub.txt.
3258 slab_max_order= [MM, SLAB]
3259 Determines the maximum allowed order for slabs.
3260 A high setting may cause OOMs due to memory
3261 fragmentation. Defaults to 1 for systems with
3262 more than 32MB of RAM, 0 otherwise.
3264 slub_debug[=options[,slabs]] [MM, SLUB]
3265 Enabling slub_debug allows one to determine the
3266 culprit if slab objects become corrupted. Enabling
3267 slub_debug can create guard zones around objects and
3268 may poison objects when not in use. Also tracks the
3269 last alloc / free. For more information see
3270 Documentation/vm/slub.txt.
3272 slub_max_order= [MM, SLUB]
3273 Determines the maximum allowed order for slabs.
3274 A high setting may cause OOMs due to memory
3275 fragmentation. For more information see
3276 Documentation/vm/slub.txt.
3278 slub_min_objects= [MM, SLUB]
3279 The minimum number of objects per slab. SLUB will
3280 increase the slab order up to slub_max_order to
3281 generate a sufficiently large slab able to contain
3282 the number of objects indicated. The higher the number
3283 of objects the smaller the overhead of tracking slabs
3284 and the less frequently locks need to be acquired.
3285 For more information see Documentation/vm/slub.txt.
3287 slub_min_order= [MM, SLUB]
3288 Determines the minimum page order for slabs. Must be
3289 lower than slub_max_order.
3290 For more information see Documentation/vm/slub.txt.
3292 slub_nomerge [MM, SLUB]
3293 Same with slab_nomerge. This is supported for legacy.
3294 See slab_nomerge for more information.
3296 smart2= [HW]
3297 Format: <io1>[,<io2>[,...,<io8>]]
3299 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3300 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3301 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3302 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3303 smsc-ircc2.ircc_irq= [HW] IRQ line
3304 smsc-ircc2.ircc_dma= [HW] DMA channel
3305 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3306 0: Toshiba Satellite 1800 (GP data pin select)
3307 1: Fast pin select (default)
3308 2: ATC IRMode
3310 softlockup_panic=
3311 [KNL] Should the soft-lockup detector generate panics.
3312 Format: <integer>
3314 softlockup_all_cpu_backtrace=
3315 [KNL] Should the soft-lockup detector generate
3316 backtraces on all cpus.
3317 Format: <integer>
3319 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3320 See Documentation/laptops/sonypi.txt
3322 spia_io_base= [HW,MTD]
3323 spia_fio_base=
3324 spia_pedr=
3325 spia_peddr=
3327 stack_guard_gap= [MM]
3328 override the default stack gap protection. The value
3329 is in page units and it defines how many pages prior
3330 to (for stacks growing down) resp. after (for stacks
3331 growing up) the main stack are reserved for no other
3332 mapping. Default value is 256 pages.
3334 stacktrace [FTRACE]
3335 Enabled the stack tracer on boot up.
3337 stacktrace_filter=[function-list]
3338 [FTRACE] Limit the functions that the stack tracer
3339 will trace at boot up. function-list is a comma separated
3340 list of functions. This list can be changed at run
3341 time by the stack_trace_filter file in the debugfs
3342 tracing directory. Note, this enables stack tracing
3343 and the stacktrace above is not needed.
3345 sti= [PARISC,HW]
3346 Format: <num>
3347 Set the STI (builtin display/keyboard on the HP-PARISC
3348 machines) console (graphic card) which should be used
3349 as the initial boot-console.
3350 See also comment in drivers/video/console/sticore.c.
3352 sti_font= [HW]
3353 See comment in drivers/video/console/sticore.c.
3355 stifb= [HW]
3356 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3358 sunrpc.min_resvport=
3359 sunrpc.max_resvport=
3360 [NFS,SUNRPC]
3361 SunRPC servers often require that client requests
3362 originate from a privileged port (i.e. a port in the
3363 range 0 < portnr < 1024).
3364 An administrator who wishes to reserve some of these
3365 ports for other uses may adjust the range that the
3366 kernel's sunrpc client considers to be privileged
3367 using these two parameters to set the minimum and
3368 maximum port values.
3370 sunrpc.pool_mode=
3371 [NFS]
3372 Control how the NFS server code allocates CPUs to
3373 service thread pools. Depending on how many NICs
3374 you have and where their interrupts are bound, this
3375 option will affect which CPUs will do NFS serving.
3376 Note: this parameter cannot be changed while the
3377 NFS server is running.
3379 auto the server chooses an appropriate mode
3380 automatically using heuristics
3381 global a single global pool contains all CPUs
3382 percpu one pool for each CPU
3383 pernode one pool for each NUMA node (equivalent
3384 to global on non-NUMA machines)
3386 sunrpc.tcp_slot_table_entries=
3387 sunrpc.udp_slot_table_entries=
3388 [NFS,SUNRPC]
3389 Sets the upper limit on the number of simultaneous
3390 RPC calls that can be sent from the client to a
3391 server. Increasing these values may allow you to
3392 improve throughput, but will also increase the
3393 amount of memory reserved for use by the client.
3395 swapaccount=[0|1]
3396 [KNL] Enable accounting of swap in memory resource
3397 controller if no parameter or 1 is given or disable
3398 it if 0 is given (See Documentation/cgroups/memory.txt)
3400 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3401 Format: { <int> | force }
3402 <int> -- Number of I/O TLB slabs
3403 force -- force using of bounce buffers even if they
3404 wouldn't be automatically used by the kernel
3406 switches= [HW,M68k]
3408 sysfs.deprecated=0|1 [KNL]
3409 Enable/disable old style sysfs layout for old udev
3410 on older distributions. When this option is enabled
3411 very new udev will not work anymore. When this option
3412 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3413 in older udev will not work anymore.
3414 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3415 the kernel configuration.
3417 sysrq_always_enabled
3418 [KNL]
3419 Ignore sysrq setting - this boot parameter will
3420 neutralize any effect of /proc/sys/kernel/sysrq.
3421 Useful for debugging.
3423 tdfx= [HW,DRM]
3425 test_suspend= [SUSPEND][,N]
3426 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3427 standby suspend) or "freeze" (for suspend type freeze)
3428 as the system sleep state during system startup with
3429 the optional capability to repeat N number of times.
3430 The system is woken from this state using a
3431 wakeup-capable RTC alarm.
3433 thash_entries= [KNL,NET]
3434 Set number of hash buckets for TCP connection
3436 thermal.act= [HW,ACPI]
3437 -1: disable all active trip points in all thermal zones
3438 <degrees C>: override all lowest active trip points
3440 thermal.crt= [HW,ACPI]
3441 -1: disable all critical trip points in all thermal zones
3442 <degrees C>: override all critical trip points
3444 thermal.nocrt= [HW,ACPI]
3445 Set to disable actions on ACPI thermal zone
3446 critical and hot trip points.
3448 thermal.off= [HW,ACPI]
3449 1: disable ACPI thermal control
3451 thermal.psv= [HW,ACPI]
3452 -1: disable all passive trip points
3453 <degrees C>: override all passive trip points to this
3454 value
3456 thermal.tzp= [HW,ACPI]
3457 Specify global default ACPI thermal zone polling rate
3458 <deci-seconds>: poll all this frequency
3459 0: no polling (default)
3461 threadirqs [KNL]
3462 Force threading of all interrupt handlers except those
3463 marked explicitly IRQF_NO_THREAD.
3465 tmem [KNL,XEN]
3466 Enable the Transcendent memory driver if built-in.
3468 tmem.cleancache=0|1 [KNL, XEN]
3469 Default is on (1). Disable the usage of the cleancache
3470 API to send anonymous pages to the hypervisor.
3472 tmem.frontswap=0|1 [KNL, XEN]
3473 Default is on (1). Disable the usage of the frontswap
3474 API to send swap pages to the hypervisor. If disabled
3475 the selfballooning and selfshrinking are force disabled.
3477 tmem.selfballooning=0|1 [KNL, XEN]
3478 Default is on (1). Disable the driving of swap pages
3479 to the hypervisor.
3481 tmem.selfshrinking=0|1 [KNL, XEN]
3482 Default is on (1). Partial swapoff that immediately
3483 transfers pages from Xen hypervisor back to the
3484 kernel based on different criteria.
3486 topology= [S390]
3487 Format: {off | on}
3488 Specify if the kernel should make use of the cpu
3489 topology information if the hardware supports this.
3490 The scheduler will make use of this information and
3491 e.g. base its process migration decisions on it.
3492 Default is on.
3494 topology_updates= [KNL, PPC, NUMA]
3495 Format: {off}
3496 Specify if the kernel should ignore (off)
3497 topology updates sent by the hypervisor to this
3498 LPAR.
3500 tp720= [HW,PS2]
3502 tpm_suspend_pcr=[HW,TPM]
3503 Format: integer pcr id
3504 Specify that at suspend time, the tpm driver
3505 should extend the specified pcr with zeros,
3506 as a workaround for some chips which fail to
3507 flush the last written pcr on TPM_SaveState.
3508 This will guarantee that all the other pcrs
3509 are saved.
3511 trace_buf_size=nn[KMG]
3512 [FTRACE] will set tracing buffer size.
3514 trace_event=[event-list]
3515 [FTRACE] Set and start specified trace events in order
3516 to facilitate early boot debugging.
3517 See also Documentation/trace/events.txt
3519 trace_options=[option-list]
3520 [FTRACE] Enable or disable tracer options at boot.
3521 The option-list is a comma delimited list of options
3522 that can be enabled or disabled just as if you were
3523 to echo the option name into
3525 /sys/kernel/debug/tracing/trace_options
3527 For example, to enable stacktrace option (to dump the
3528 stack trace of each event), add to the command line:
3530 trace_options=stacktrace
3532 See also Documentation/trace/ftrace.txt "trace options"
3533 section.
3535 traceoff_on_warning
3536 [FTRACE] enable this option to disable tracing when a
3537 warning is hit. This turns off "tracing_on". Tracing can
3538 be enabled again by echoing '1' into the "tracing_on"
3539 file located in /sys/kernel/debug/tracing/
3541 This option is useful, as it disables the trace before
3542 the WARNING dump is called, which prevents the trace to
3543 be filled with content caused by the warning output.
3545 This option can also be set at run time via the sysctl
3546 option: kernel/traceoff_on_warning
3548 transparent_hugepage=
3549 [KNL]
3550 Format: [always|madvise|never]
3551 Can be used to control the default behavior of the system
3552 with respect to transparent hugepages.
3553 See Documentation/vm/transhuge.txt for more details.
3555 tsc= Disable clocksource stability checks for TSC.
3556 Format: <string>
3557 [x86] reliable: mark tsc clocksource as reliable, this
3558 disables clocksource verification at runtime, as well
3559 as the stability checks done at bootup. Used to enable
3560 high-resolution timer mode on older hardware, and in
3561 virtualized environment.
3562 [x86] noirqtime: Do not use TSC to do irq accounting.
3563 Used to run time disable IRQ_TIME_ACCOUNTING on any
3564 platforms where RDTSC is slow and this accounting
3565 can add overhead.
3567 turbografx.map[2|3]= [HW,JOY]
3568 TurboGraFX parallel port interface
3569 Format:
3570 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3571 See also Documentation/input/joystick-parport.txt
3573 udbg-immortal [PPC] When debugging early kernel crashes that
3574 happen after console_init() and before a proper
3575 console driver takes over, this boot options might
3576 help "seeing" what's going on.
3578 uhash_entries= [KNL,NET]
3579 Set number of hash buckets for UDP/UDP-Lite connections
3581 uhci-hcd.ignore_oc=
3582 [USB] Ignore overcurrent events (default N).
3583 Some badly-designed motherboards generate lots of
3584 bogus events, for ports that aren't wired to
3585 anything. Set this parameter to avoid log spamming.
3586 Note that genuine overcurrent events won't be
3587 reported either.
3589 unknown_nmi_panic
3590 [X86] Cause panic on unknown NMI.
3592 usbcore.authorized_default=
3593 [USB] Default USB device authorization:
3594 (default -1 = authorized except for wireless USB,
3595 0 = not authorized, 1 = authorized)
3597 usbcore.autosuspend=
3598 [USB] The autosuspend time delay (in seconds) used
3599 for newly-detected USB devices (default 2). This
3600 is the time required before an idle device will be
3601 autosuspended. Devices for which the delay is set
3602 to a negative value won't be autosuspended at all.
3604 usbcore.usbfs_snoop=
3605 [USB] Set to log all usbfs traffic (default 0 = off).
3607 usbcore.blinkenlights=
3608 [USB] Set to cycle leds on hubs (default 0 = off).
3610 usbcore.old_scheme_first=
3611 [USB] Start with the old device initialization
3612 scheme (default 0 = off).
3614 usbcore.usbfs_memory_mb=
3615 [USB] Memory limit (in MB) for buffers allocated by
3616 usbfs (default = 16, 0 = max = 2047).
3618 usbcore.use_both_schemes=
3619 [USB] Try the other device initialization scheme
3620 if the first one fails (default 1 = enabled).
3622 usbcore.initial_descriptor_timeout=
3623 [USB] Specifies timeout for the initial 64-byte
3624 USB_REQ_GET_DESCRIPTOR request in milliseconds
3625 (default 5000 = 5.0 seconds).
3627 usbhid.mousepoll=
3628 [USBHID] The interval which mice are to be polled at.
3630 usb-storage.delay_use=
3631 [UMS] The delay in seconds before a new device is
3632 scanned for Logical Units (default 1).
3634 usb-storage.quirks=
3635 [UMS] A list of quirks entries to supplement or
3636 override the built-in unusual_devs list. List
3637 entries are separated by commas. Each entry has
3638 the form VID:PID:Flags where VID and PID are Vendor
3639 and Product ID values (4-digit hex numbers) and
3640 Flags is a set of characters, each corresponding
3641 to a common usb-storage quirk flag as follows:
3642 a = SANE_SENSE (collect more than 18 bytes
3643 of sense data);
3644 b = BAD_SENSE (don't collect more than 18
3645 bytes of sense data);
3646 c = FIX_CAPACITY (decrease the reported
3647 device capacity by one sector);
3648 d = NO_READ_DISC_INFO (don't use
3649 READ_DISC_INFO command);
3650 e = NO_READ_CAPACITY_16 (don't use
3651 READ_CAPACITY_16 command);
3652 f = NO_REPORT_OPCODES (don't use report opcodes
3653 command, uas only);
3654 g = MAX_SECTORS_240 (don't transfer more than
3655 240 sectors at a time, uas only);
3656 h = CAPACITY_HEURISTICS (decrease the
3657 reported device capacity by one
3658 sector if the number is odd);
3659 i = IGNORE_DEVICE (don't bind to this
3660 device);
3661 j = NO_REPORT_LUNS (don't use report luns
3662 command, uas only);
3663 l = NOT_LOCKABLE (don't try to lock and
3664 unlock ejectable media);
3665 m = MAX_SECTORS_64 (don't transfer more
3666 than 64 sectors = 32 KB at a time);
3667 n = INITIAL_READ10 (force a retry of the
3668 initial READ(10) command);
3669 o = CAPACITY_OK (accept the capacity
3670 reported by the device);
3671 p = WRITE_CACHE (the device cache is ON
3672 by default);
3673 r = IGNORE_RESIDUE (the device reports
3674 bogus residue values);
3675 s = SINGLE_LUN (the device has only one
3676 Logical Unit);
3677 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3678 commands, uas only);
3679 u = IGNORE_UAS (don't bind to the uas driver);
3680 w = NO_WP_DETECT (don't test whether the
3681 medium is write-protected).
3682 Example: quirks=0419:aaf5:rl,0421:0433:rc
3684 user_debug= [KNL,ARM]
3685 Format: <int>
3686 See arch/arm/Kconfig.debug help text.
3687 1 - undefined instruction events
3688 2 - system calls
3689 4 - invalid data aborts
3690 8 - SIGSEGV faults
3691 16 - SIGBUS faults
3692 Example: user_debug=31
3694 userpte=
3695 [X86] Flags controlling user PTE allocations.
3697 nohigh = do not allocate PTE pages in
3698 HIGHMEM regardless of setting
3699 of CONFIG_HIGHPTE.
3701 vdso= [X86,SH]
3702 On X86_32, this is an alias for vdso32=. Otherwise:
3704 vdso=1: enable VDSO (the default)
3705 vdso=0: disable VDSO mapping
3707 vdso32= [X86] Control the 32-bit vDSO
3708 vdso32=1: enable 32-bit VDSO
3709 vdso32=0 or vdso32=2: disable 32-bit VDSO
3711 See the help text for CONFIG_COMPAT_VDSO for more
3712 details. If CONFIG_COMPAT_VDSO is set, the default is
3713 vdso32=0; otherwise, the default is vdso32=1.
3715 For compatibility with older kernels, vdso32=2 is an
3716 alias for vdso32=0.
3718 Try vdso32=0 if you encounter an error that says:
3719 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3721 vector= [IA-64,SMP]
3722 vector=percpu: enable percpu vector domain
3724 video= [FB] Frame buffer configuration
3725 See Documentation/fb/modedb.txt.
3727 video.brightness_switch_enabled= [0,1]
3728 If set to 1, on receiving an ACPI notify event
3729 generated by hotkey, video driver will adjust brightness
3730 level and then send out the event to user space through
3731 the allocated input device; If set to 0, video driver
3732 will only send out the event without touching backlight
3733 brightness level.
3734 default: 1
3736 virtio_mmio.device=
3737 [VMMIO] Memory mapped virtio (platform) device.
3739 <size>@<baseaddr>:<irq>[:<id>]
3740 where:
3741 <size> := size (can use standard suffixes
3742 like K, M and G)
3743 <baseaddr> := physical base address
3744 <irq> := interrupt number (as passed to
3745 request_irq())
3746 <id> := (optional) platform device id
3747 example:
3748 virtio_mmio.device=1K@0x100b0000:48:7
3750 Can be used multiple times for multiple devices.
3752 vga= [BOOT,X86-32] Select a particular video mode
3753 See Documentation/x86/boot.txt and
3754 Documentation/svga.txt.
3755 Use vga=ask for menu.
3756 This is actually a boot loader parameter; the value is
3757 passed to the kernel using a special protocol.
3759 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3760 size of <nn>. This can be used to increase the
3761 minimum size (128MB on x86). It can also be used to
3762 decrease the size and leave more room for directly
3763 mapped kernel RAM.
3765 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3766 Format: <command>
3768 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3769 Format: <command>
3771 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3772 Format: <command>
3774 vsyscall= [X86-64]
3775 Controls the behavior of vsyscalls (i.e. calls to
3776 fixed addresses of 0xffffffffff600x00 from legacy
3777 code). Most statically-linked binaries and older
3778 versions of glibc use these calls. Because these
3779 functions are at fixed addresses, they make nice
3780 targets for exploits that can control RIP.
3782 emulate [default] Vsyscalls turn into traps and are
3783 emulated reasonably safely.
3785 native Vsyscalls are native syscall instructions.
3786 This is a little bit faster than trapping
3787 and makes a few dynamic recompilers work
3788 better than they would in emulation mode.
3789 It also makes exploits much easier to write.
3791 none Vsyscalls don't work at all. This makes
3792 them quite hard to use for exploits but
3793 might break your system.
3795 vt.color= [VT] Default text color.
3796 Format: 0xYX, X = foreground, Y = background.
3797 Default: 0x07 = light gray on black.
3799 vt.cur_default= [VT] Default cursor shape.
3800 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3801 the parameters of the <Esc>[?A;B;Cc escape sequence;
3802 see VGA-softcursor.txt. Default: 2 = underline.
3804 vt.default_blu= [VT]
3805 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3806 Change the default blue palette of the console.
3807 This is a 16-member array composed of values
3808 ranging from 0-255.
3810 vt.default_grn= [VT]
3811 Format: <green0>,<green1>,<green2>,...,<green15>
3812 Change the default green palette of the console.
3813 This is a 16-member array composed of values
3814 ranging from 0-255.
3816 vt.default_red= [VT]
3817 Format: <red0>,<red1>,<red2>,...,<red15>
3818 Change the default red palette of the console.
3819 This is a 16-member array composed of values
3820 ranging from 0-255.
3822 vt.default_utf8=
3823 [VT]
3824 Format=<0|1>
3825 Set system-wide default UTF-8 mode for all tty's.
3826 Default is 1, i.e. UTF-8 mode is enabled for all
3827 newly opened terminals.
3829 vt.global_cursor_default=
3830 [VT]
3831 Format=<-1|0|1>
3832 Set system-wide default for whether a cursor
3833 is shown on new VTs. Default is -1,
3834 i.e. cursors will be created by default unless
3835 overridden by individual drivers. 0 will hide
3836 cursors, 1 will display them.
3838 vt.italic= [VT] Default color for italic text; 0-15.
3839 Default: 2 = green.
3841 vt.underline= [VT] Default color for underlined text; 0-15.
3842 Default: 3 = cyan.
3844 watchdog timers [HW,WDT] For information on watchdog timers,
3845 see Documentation/watchdog/watchdog-parameters.txt
3846 or other driver-specific files in the
3847 Documentation/watchdog/ directory.
3849 workqueue.disable_numa
3850 By default, all work items queued to unbound
3851 workqueues are affine to the NUMA nodes they're
3852 issued on, which results in better behavior in
3853 general. If NUMA affinity needs to be disabled for
3854 whatever reason, this option can be used. Note
3855 that this also can be controlled per-workqueue for
3856 workqueues visible under /sys/bus/workqueue/.
3858 workqueue.power_efficient
3859 Per-cpu workqueues are generally preferred because
3860 they show better performance thanks to cache
3861 locality; unfortunately, per-cpu workqueues tend to
3862 be more power hungry than unbound workqueues.
3864 Enabling this makes the per-cpu workqueues which
3865 were observed to contribute significantly to power
3866 consumption unbound, leading to measurably lower
3867 power usage at the cost of small performance
3868 overhead.
3870 The default value of this parameter is determined by
3871 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3873 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3874 default x2apic cluster mode on platforms
3875 supporting x2apic.
3877 x86_intel_mid_timer= [X86-32,APBT]
3878 Choose timer option for x86 Intel MID platform.
3879 Two valid options are apbt timer only and lapic timer
3880 plus one apbt timer for broadcast timer.
3881 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3883 xen_emul_unplug= [HW,X86,XEN]
3884 Unplug Xen emulated devices
3885 Format: [unplug0,][unplug1]
3886 ide-disks -- unplug primary master IDE devices
3887 aux-ide-disks -- unplug non-primary-master IDE devices
3888 nics -- unplug network devices
3889 all -- unplug all emulated devices (NICs and IDE disks)
3890 unnecessary -- unplugging emulated devices is
3891 unnecessary even if the host did not respond to
3892 the unplug protocol
3893 never -- do not unplug even if version check succeeds
3895 xen_nopvspin [X86,XEN]
3896 Disables the ticketlock slowpath using Xen PV
3897 optimizations.
3899 xen_nopv [X86]
3900 Disables the PV optimizations forcing the HVM guest to
3901 run as generic HVM guest with no PV drivers.
3903 xirc2ps_cs= [NET,PCMCIA]
3904 Format:
3905 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3907 ______________________________________________________________________
3909 TODO:
3911 Add more DRM drivers.