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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VMMIO Driver for memory mapped virtio devices is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amd_iommu_dump= [HW,X86-64]
339 Enable AMD IOMMU driver option to dump the ACPI table
340 for AMD IOMMU. With this option enabled, AMD IOMMU
341 driver will print ACPI tables for AMD IOMMU during
342 IOMMU initialization.
344 amijoy.map= [HW,JOY] Amiga joystick support
345 Map of devices attached to JOY0DAT and JOY1DAT
346 Format: <a>,<b>
347 See also Documentation/input/joystick.txt
349 analog.map= [HW,JOY] Analog joystick and gamepad support
350 Specifies type or capabilities of an analog joystick
351 connected to one of 16 gameports
352 Format: <type1>,<type2>,..<type16>
354 apc= [HW,SPARC]
355 Power management functions (SPARCstation-4/5 + deriv.)
356 Format: noidle
357 Disable APC CPU standby support. SPARCstation-Fox does
358 not play well with APC CPU idle - disable it if you have
359 APC and your system crashes randomly.
361 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
362 Change the output verbosity whilst booting
363 Format: { quiet (default) | verbose | debug }
364 Change the amount of debugging information output
365 when initialising the APIC and IO-APIC components.
367 autoconf= [IPV6]
368 See Documentation/networking/ipv6.txt.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
385 ataflop= [HW,M68k]
387 atarimouse= [HW,MOUSE] Atari Mouse
389 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
390 EzKey and similar keyboards
392 atkbd.reset= [HW] Reset keyboard during initialization
394 atkbd.set= [HW] Select keyboard code set
395 Format: <int> (2 = AT (default), 3 = PS/2)
397 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
398 keyboards
400 atkbd.softraw= [HW] Choose between synthetic and real raw mode
401 Format: <bool> (0 = real, 1 = synthetic (default))
403 atkbd.softrepeat= [HW]
404 Use software keyboard repeat
406 baycom_epp= [HW,AX25]
407 Format: <io>,<mode>
409 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
410 Format: <io>,<mode>
411 See header of drivers/net/hamradio/baycom_par.c.
413 baycom_ser_fdx= [HW,AX25]
414 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
415 Format: <io>,<irq>,<mode>[,<baud>]
416 See header of drivers/net/hamradio/baycom_ser_fdx.c.
418 baycom_ser_hdx= [HW,AX25]
419 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
420 Format: <io>,<irq>,<mode>
421 See header of drivers/net/hamradio/baycom_ser_hdx.c.
423 boot_delay= Milliseconds to delay each printk during boot.
424 Values larger than 10 seconds (10000) are changed to
425 no delay (0).
426 Format: integer
428 bootmem_debug [KNL] Enable bootmem allocator debug messages.
430 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
431 bttv.radio= Most important insmod options are available as
432 kernel args too.
433 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
434 bttv.tuner=
436 bulk_remove=off [PPC] This parameter disables the use of the pSeries
437 firmware feature for flushing multiple hpte entries
438 at a time.
440 c101= [NET] Moxa C101 synchronous serial card
442 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
443 Sometimes CPU hardware bugs make them report the cache
444 size incorrectly. The kernel will attempt work arounds
445 to fix known problems, but for some CPUs it is not
446 possible to determine what the correct size should be.
447 This option provides an override for these situations.
449 capability.disable=
450 [SECURITY] Disable capabilities. This would normally
451 be used only if an alternative security model is to be
452 configured. Potentially dangerous and should only be
453 used if you are entirely sure of the consequences.
455 ccw_timeout_log [S390]
456 See Documentation/s390/CommonIO for details.
458 cgroup_disable= [KNL] Disable a particular controller
459 Format: {name of the controller(s) to disable}
460 {Currently supported controllers - "memory"}
462 checkreqprot [SELINUX] Set initial checkreqprot flag value.
463 Format: { "0" | "1" }
464 See security/selinux/Kconfig help text.
465 0 -- check protection applied by kernel (includes
466 any implied execute protection).
467 1 -- check protection requested by application.
468 Default value is set via a kernel config option.
469 Value can be changed at runtime via
470 /selinux/checkreqprot.
472 cio_ignore= [S390]
473 See Documentation/s390/CommonIO for details.
475 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
476 [Deprecated]
477 Forces specified clocksource (if available) to be used
478 when calculating gettimeofday(). If specified
479 clocksource is not available, it defaults to PIT.
480 Format: { pit | tsc | cyclone | pmtmr }
482 clocksource= Override the default clocksource
483 Format: <string>
484 Override the default clocksource and use the clocksource
485 with the name specified.
486 Some clocksource names to choose from, depending on
487 the platform:
488 [all] jiffies (this is the base, fallback clocksource)
489 [ACPI] acpi_pm
490 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
491 pxa_timer,timer3,32k_counter,timer0_1
492 [AVR32] avr32
493 [X86-32] pit,hpet,tsc;
494 scx200_hrt on Geode; cyclone on IBM x440
495 [MIPS] MIPS
496 [PARISC] cr16
497 [S390] tod
498 [SH] SuperH
499 [SPARC64] tick
500 [X86-64] hpet,tsc
502 clearcpuid=BITNUM [X86]
503 Disable CPUID feature X for the kernel. See
504 arch/x86/include/asm/cpufeature.h for the valid bit
505 numbers. Note the Linux specific bits are not necessarily
506 stable over kernel options, but the vendor specific
507 ones should be.
508 Also note that user programs calling CPUID directly
509 or using the feature without checking anything
510 will still see it. This just prevents it from
511 being used by the kernel or shown in /proc/cpuinfo.
512 Also note the kernel might malfunction if you disable
513 some critical bits.
515 cma=nn[MG] [ARM,KNL]
516 Sets the size of kernel global memory area for contiguous
517 memory allocations. For more information, see
518 include/linux/dma-contiguous.h
520 cmo_free_hint= [PPC] Format: { yes | no }
521 Specify whether pages are marked as being inactive
522 when they are freed. This is used in CMO environments
523 to determine OS memory pressure for page stealing by
524 a hypervisor.
525 Default: yes
527 coherent_pool=nn[KMG] [ARM,KNL]
528 Sets the size of memory pool for coherent, atomic dma
529 allocations, by default set to 256K.
531 code_bytes [X86] How many bytes of object code to print
532 in an oops report.
533 Range: 0 - 8192
534 Default: 64
536 com20020= [HW,NET] ARCnet - COM20020 chipset
537 Format:
538 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
540 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
541 Format: <io>[,<irq>]
543 com90xx= [HW,NET]
544 ARCnet - COM90xx chipset (memory-mapped buffers)
545 Format: <io>[,<irq>[,<memstart>]]
547 condev= [HW,S390] console device
548 conmode=
550 console= [KNL] Output console device and options.
552 tty<n> Use the virtual console device <n>.
554 ttyS<n>[,options]
555 ttyUSB0[,options]
556 Use the specified serial port. The options are of
557 the form "bbbbpnf", where "bbbb" is the baud rate,
558 "p" is parity ("n", "o", or "e"), "n" is number of
559 bits, and "f" is flow control ("r" for RTS or
560 omit it). Default is "9600n8".
562 See Documentation/serial-console.txt for more
563 information. See
564 Documentation/networking/netconsole.txt for an
565 alternative.
567 uart[8250],io,<addr>[,options]
568 uart[8250],mmio,<addr>[,options]
569 Start an early, polled-mode console on the 8250/16550
570 UART at the specified I/O port or MMIO address,
571 switching to the matching ttyS device later. The
572 options are the same as for ttyS, above.
574 If the device connected to the port is not a TTY but a braille
575 device, prepend "brl," before the device type, for instance
576 console=brl,ttyS0
577 For now, only VisioBraille is supported.
579 consoleblank= [KNL] The console blank (screen saver) timeout in
580 seconds. Defaults to 10*60 = 10mins. A value of 0
581 disables the blank timer.
583 coredump_filter=
584 [KNL] Change the default value for
585 /proc/<pid>/coredump_filter.
586 See also Documentation/filesystems/proc.txt.
588 cpuidle.off=1 [CPU_IDLE]
589 disable the cpuidle sub-system
591 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
592 Format:
593 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
595 crashkernel=size[KMG][@offset[KMG]]
596 [KNL] Using kexec, Linux can switch to a 'crash kernel'
597 upon panic. This parameter reserves the physical
598 memory region [offset, offset + size] for that kernel
599 image. If '@offset' is omitted, then a suitable offset
600 is selected automatically. Check
601 Documentation/kdump/kdump.txt for further details.
603 crashkernel=range1:size1[,range2:size2,...][@offset]
604 [KNL] Same as above, but depends on the memory
605 in the running system. The syntax of range is
606 start-[end] where start and end are both
607 a memory unit (amount[KMG]). See also
608 Documentation/kdump/kdump.txt for an example.
610 cs89x0_dma= [HW,NET]
611 Format: <dma>
613 cs89x0_media= [HW,NET]
614 Format: { rj45 | aui | bnc }
616 dasd= [HW,NET]
617 See header of drivers/s390/block/dasd_devmap.c.
619 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
620 (one device per port)
621 Format: <port#>,<type>
622 See also Documentation/input/joystick-parport.txt
624 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
625 time. See Documentation/dynamic-debug-howto.txt for
626 details. Deprecated, see dyndbg.
628 debug [KNL] Enable kernel debugging (events log level).
630 debug_locks_verbose=
631 [KNL] verbose self-tests
632 Format=<0|1>
633 Print debugging info while doing the locking API
634 self-tests.
635 We default to 0 (no extra messages), setting it to
636 1 will print _a lot_ more information - normally
637 only useful to kernel developers.
639 debug_objects [KNL] Enable object debugging
641 no_debug_objects
642 [KNL] Disable object debugging
644 debug_guardpage_minorder=
645 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
646 parameter allows control of the order of pages that will
647 be intentionally kept free (and hence protected) by the
648 buddy allocator. Bigger value increase the probability
649 of catching random memory corruption, but reduce the
650 amount of memory for normal system use. The maximum
651 possible value is MAX_ORDER/2. Setting this parameter
652 to 1 or 2 should be enough to identify most random
653 memory corruption problems caused by bugs in kernel or
654 driver code when a CPU writes to (or reads from) a
655 random memory location. Note that there exists a class
656 of memory corruptions problems caused by buggy H/W or
657 F/W or by drivers badly programing DMA (basically when
658 memory is written at bus level and the CPU MMU is
659 bypassed) which are not detectable by
660 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
661 tracking down these problems.
663 debugpat [X86] Enable PAT debugging
665 decnet.addr= [HW,NET]
666 Format: <area>[,<node>]
667 See also Documentation/networking/decnet.txt.
669 default_hugepagesz=
670 [same as hugepagesz=] The size of the default
671 HugeTLB page size. This is the size represented by
672 the legacy /proc/ hugepages APIs, used for SHM, and
673 default size when mounting hugetlbfs filesystems.
674 Defaults to the default architecture's huge page size
675 if not specified.
677 dhash_entries= [KNL]
678 Set number of hash buckets for dentry cache.
680 digi= [HW,SERIAL]
681 IO parameters + enable/disable command.
683 digiepca= [HW,SERIAL]
684 See drivers/char/README.epca and
685 Documentation/serial/digiepca.txt.
687 disable= [IPV6]
688 See Documentation/networking/ipv6.txt.
690 disable_ddw [PPC/PSERIES]
691 Disable Dynamic DMA Window support. Use this if
692 to workaround buggy firmware.
694 disable_ipv6= [IPV6]
695 See Documentation/networking/ipv6.txt.
697 disable_mtrr_cleanup [X86]
698 The kernel tries to adjust MTRR layout from continuous
699 to discrete, to make X server driver able to add WB
700 entry later. This parameter disables that.
702 disable_mtrr_trim [X86, Intel and AMD only]
703 By default the kernel will trim any uncacheable
704 memory out of your available memory pool based on
705 MTRR settings. This parameter disables that behavior,
706 possibly causing your machine to run very slowly.
708 disable_timer_pin_1 [X86]
709 Disable PIN 1 of APIC timer
710 Can be useful to work around chipset bugs.
712 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
713 this option disables the debugging code at boot.
715 dma_debug_entries=<number>
716 This option allows to tune the number of preallocated
717 entries for DMA-API debugging code. One entry is
718 required per DMA-API allocation. Use this if the
719 DMA-API debugging code disables itself because the
720 architectural default is too low.
722 dma_debug_driver=<driver_name>
723 With this option the DMA-API debugging driver
724 filter feature can be enabled at boot time. Just
725 pass the driver to filter for as the parameter.
726 The filter can be disabled or changed to another
727 driver later using sysfs.
729 drm_kms_helper.edid_firmware=[<connector>:]<file>
730 Broken monitors, graphic adapters and KVMs may
731 send no or incorrect EDID data sets. This parameter
732 allows to specify an EDID data set in the
733 /lib/firmware directory that is used instead.
734 Generic built-in EDID data sets are used, if one of
735 edid/1024x768.bin, edid/1280x1024.bin,
736 edid/1680x1050.bin, or edid/1920x1080.bin is given
737 and no file with the same name exists. Details and
738 instructions how to build your own EDID data are
739 available in Documentation/EDID/HOWTO.txt. An EDID
740 data set will only be used for a particular connector,
741 if its name and a colon are prepended to the EDID
742 name.
744 dscc4.setup= [NET]
746 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
747 module.dyndbg[="val"]
748 Enable debug messages at boot time. See
749 Documentation/dynamic-debug-howto.txt for details.
751 earlycon= [KNL] Output early console device and options.
752 uart[8250],io,<addr>[,options]
753 uart[8250],mmio,<addr>[,options]
754 uart[8250],mmio32,<addr>[,options]
755 Start an early, polled-mode console on the 8250/16550
756 UART at the specified I/O port or MMIO address.
757 MMIO inter-register address stride is either 8-bit
758 (mmio) or 32-bit (mmio32).
759 The options are the same as for ttyS, above.
761 earlyprintk= [X86,SH,BLACKFIN]
762 earlyprintk=vga
763 earlyprintk=serial[,ttySn[,baudrate]]
764 earlyprintk=ttySn[,baudrate]
765 earlyprintk=dbgp[debugController#]
767 Append ",keep" to not disable it when the real console
768 takes over.
770 Only vga or serial or usb debug port at a time.
772 Currently only ttyS0 and ttyS1 are supported.
774 Interaction with the standard serial driver is not
775 very good.
777 The VGA output is eventually overwritten by the real
778 console.
780 ekgdboc= [X86,KGDB] Allow early kernel console debugging
781 ekgdboc=kbd
783 This is designed to be used in conjunction with
784 the boot argument: earlyprintk=vga
786 edd= [EDD]
787 Format: {"off" | "on" | "skip[mbr]"}
789 eisa_irq_edge= [PARISC,HW]
790 See header of drivers/parisc/eisa.c.
792 elanfreq= [X86-32]
793 See comment before function elanfreq_setup() in
794 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
796 elevator= [IOSCHED]
797 Format: {"cfq" | "deadline" | "noop"}
798 See Documentation/block/cfq-iosched.txt and
799 Documentation/block/deadline-iosched.txt for details.
801 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
802 Specifies physical address of start of kernel core
803 image elf header and optionally the size. Generally
804 kexec loader will pass this option to capture kernel.
805 See Documentation/kdump/kdump.txt for details.
807 enable_mtrr_cleanup [X86]
808 The kernel tries to adjust MTRR layout from continuous
809 to discrete, to make X server driver able to add WB
810 entry later. This parameter enables that.
812 enable_timer_pin_1 [X86]
813 Enable PIN 1 of APIC timer
814 Can be useful to work around chipset bugs
815 (in particular on some ATI chipsets).
816 The kernel tries to set a reasonable default.
818 enforcing [SELINUX] Set initial enforcing status.
819 Format: {"0" | "1"}
820 See security/selinux/Kconfig help text.
821 0 -- permissive (log only, no denials).
822 1 -- enforcing (deny and log).
823 Default value is 0.
824 Value can be changed at runtime via /selinux/enforce.
826 erst_disable [ACPI]
827 Disable Error Record Serialization Table (ERST)
828 support.
830 ether= [HW,NET] Ethernet cards parameters
831 This option is obsoleted by the "netdev=" option, which
832 has equivalent usage. See its documentation for details.
834 evm= [EVM]
835 Format: { "fix" }
836 Permit 'security.evm' to be updated regardless of
837 current integrity status.
839 failslab=
840 fail_page_alloc=
841 fail_make_request=[KNL]
842 General fault injection mechanism.
843 Format: <interval>,<probability>,<space>,<times>
844 See also Documentation/fault-injection/.
846 floppy= [HW]
847 See Documentation/blockdev/floppy.txt.
849 force_pal_cache_flush
850 [IA-64] Avoid check_sal_cache_flush which may hang on
851 buggy SAL_CACHE_FLUSH implementations. Using this
852 parameter will force ia64_sal_cache_flush to call
853 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
855 ftrace=[tracer]
856 [FTRACE] will set and start the specified tracer
857 as early as possible in order to facilitate early
858 boot debugging.
860 ftrace_dump_on_oops[=orig_cpu]
861 [FTRACE] will dump the trace buffers on oops.
862 If no parameter is passed, ftrace will dump
863 buffers of all CPUs, but if you pass orig_cpu, it will
864 dump only the buffer of the CPU that triggered the
865 oops.
867 ftrace_filter=[function-list]
868 [FTRACE] Limit the functions traced by the function
869 tracer at boot up. function-list is a comma separated
870 list of functions. This list can be changed at run
871 time by the set_ftrace_filter file in the debugfs
872 tracing directory.
874 ftrace_notrace=[function-list]
875 [FTRACE] Do not trace the functions specified in
876 function-list. This list can be changed at run time
877 by the set_ftrace_notrace file in the debugfs
878 tracing directory.
880 ftrace_graph_filter=[function-list]
881 [FTRACE] Limit the top level callers functions traced
882 by the function graph tracer at boot up.
883 function-list is a comma separated list of functions
884 that can be changed at run time by the
885 set_graph_function file in the debugfs tracing directory.
887 gamecon.map[2|3]=
888 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
889 support via parallel port (up to 5 devices per port)
890 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
891 See also Documentation/input/joystick-parport.txt
893 gamma= [HW,DRM]
895 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
896 Format: off | on
897 default: on
899 gcov_persist= [GCOV] When non-zero (default), profiling data for
900 kernel modules is saved and remains accessible via
901 debugfs, even when the module is unloaded/reloaded.
902 When zero, profiling data is discarded and associated
903 debugfs files are removed at module unload time.
905 gpt [EFI] Forces disk with valid GPT signature but
906 invalid Protective MBR to be treated as GPT.
908 hashdist= [KNL,NUMA] Large hashes allocated during boot
909 are distributed across NUMA nodes. Defaults on
910 for 64-bit NUMA, off otherwise.
911 Format: 0 | 1 (for off | on)
913 hcl= [IA-64] SGI's Hardware Graph compatibility layer
915 hd= [EIDE] (E)IDE hard drive subsystem geometry
916 Format: <cyl>,<head>,<sect>
918 hest_disable [ACPI]
919 Disable Hardware Error Source Table (HEST) support;
920 corresponding firmware-first mode error processing
921 logic will be disabled.
923 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
924 size of <nn>. This works even on boxes that have no
925 highmem otherwise. This also works to reduce highmem
926 size on bigger boxes.
928 highres= [KNL] Enable/disable high resolution timer mode.
929 Valid parameters: "on", "off"
930 Default: "on"
932 hisax= [HW,ISDN]
933 See Documentation/isdn/README.HiSax.
935 hlt [BUGS=ARM,SH]
937 hpet= [X86-32,HPET] option to control HPET usage
938 Format: { enable (default) | disable | force |
939 verbose }
940 disable: disable HPET and use PIT instead
941 force: allow force enabled of undocumented chips (ICH4,
942 VIA, nVidia)
943 verbose: show contents of HPET registers during setup
945 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
946 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
947 On x86-64 and powerpc, this option can be specified
948 multiple times interleaved with hugepages= to reserve
949 huge pages of different sizes. Valid pages sizes on
950 x86-64 are 2M (when the CPU supports "pse") and 1G
951 (when the CPU supports the "pdpe1gb" cpuinfo flag)
952 Note that 1GB pages can only be allocated at boot time
953 using hugepages= and not freed afterwards.
955 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
956 terminal devices. Valid values: 0..8
957 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
958 If specified, z/VM IUCV HVC accepts connections
959 from listed z/VM user IDs only.
961 keep_bootcon [KNL]
962 Do not unregister boot console at start. This is only
963 useful for debugging when something happens in the window
964 between unregistering the boot console and initializing
965 the real console.
967 i2c_bus= [HW] Override the default board specific I2C bus speed
968 or register an additional I2C bus that is not
969 registered from board initialization code.
970 Format:
971 <bus_id>,<clkrate>
973 i8042.debug [HW] Toggle i8042 debug mode
974 i8042.direct [HW] Put keyboard port into non-translated mode
975 i8042.dumbkbd [HW] Pretend that controller can only read data from
976 keyboard and cannot control its state
977 (Don't attempt to blink the leds)
978 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
979 i8042.nokbd [HW] Don't check/create keyboard port
980 i8042.noloop [HW] Disable the AUX Loopback command while probing
981 for the AUX port
982 i8042.nomux [HW] Don't check presence of an active multiplexing
983 controller
984 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
985 controllers
986 i8042.notimeout [HW] Ignore timeout condition signalled by controller
987 i8042.reset [HW] Reset the controller during init and cleanup
988 i8042.unlock [HW] Unlock (ignore) the keylock
990 i810= [HW,DRM]
992 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
993 indicates that the driver is running on unsupported
994 hardware.
995 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
996 does not match list of supported models.
997 i8k.power_status
998 [HW] Report power status in /proc/i8k
999 (disabled by default)
1000 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1001 capability is set.
1003 i915.invert_brightness=
1004 [DRM] Invert the sense of the variable that is used to
1005 set the brightness of the panel backlight. Normally a
1006 brightness value of 0 indicates backlight switched off,
1007 and the maximum of the brightness value sets the backlight
1008 to maximum brightness. If this parameter is set to 0
1009 (default) and the machine requires it, or this parameter
1010 is set to 1, a brightness value of 0 sets the backlight
1011 to maximum brightness, and the maximum of the brightness
1012 value switches the backlight off.
1013 -1 -- never invert brightness
1014 0 -- machine default
1015 1 -- force brightness inversion
1017 icn= [HW,ISDN]
1018 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1020 ide-core.nodma= [HW] (E)IDE subsystem
1021 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1022 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1023 .cdrom .chs .ignore_cable are additional options
1024 See Documentation/ide/ide.txt.
1026 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1027 Claim all unknown PCI IDE storage controllers.
1029 idle= [X86]
1030 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1031 Poll forces a polling idle loop that can slightly
1032 improve the performance of waking up a idle CPU, but
1033 will use a lot of power and make the system run hot.
1034 Not recommended.
1035 idle=mwait: On systems which support MONITOR/MWAIT but
1036 the kernel chose to not use it because it doesn't save
1037 as much power as a normal idle loop, use the
1038 MONITOR/MWAIT idle loop anyways. Performance should be
1039 the same as idle=poll.
1040 idle=halt: Halt is forced to be used for CPU idle.
1041 In such case C2/C3 won't be used again.
1042 idle=nomwait: Disable mwait for CPU C-states
1044 ignore_loglevel [KNL]
1045 Ignore loglevel setting - this will print /all/
1046 kernel messages to the console. Useful for debugging.
1047 We also add it as printk module parameter, so users
1048 could change it dynamically, usually by
1049 /sys/module/printk/parameters/ignore_loglevel.
1051 ihash_entries= [KNL]
1052 Set number of hash buckets for inode cache.
1054 ima_audit= [IMA]
1055 Format: { "0" | "1" }
1056 0 -- integrity auditing messages. (Default)
1057 1 -- enable informational integrity auditing messages.
1059 ima_hash= [IMA]
1060 Format: { "sha1" | "md5" }
1061 default: "sha1"
1063 ima_tcb [IMA]
1064 Load a policy which meets the needs of the Trusted
1065 Computing Base. This means IMA will measure all
1066 programs exec'd, files mmap'd for exec, and all files
1067 opened for read by uid=0.
1069 init= [KNL]
1070 Format: <full_path>
1071 Run specified binary instead of /sbin/init as init
1072 process.
1074 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1075 for working out where the kernel is dying during
1076 startup.
1078 initrd= [BOOT] Specify the location of the initial ramdisk
1080 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1081 Format: <irq>
1083 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1084 on
1085 Enable intel iommu driver.
1086 off
1087 Disable intel iommu driver.
1088 igfx_off [Default Off]
1089 By default, gfx is mapped as normal device. If a gfx
1090 device has a dedicated DMAR unit, the DMAR unit is
1091 bypassed by not enabling DMAR with this option. In
1092 this case, gfx device will use physical address for
1093 DMA.
1094 forcedac [x86_64]
1095 With this option iommu will not optimize to look
1096 for io virtual address below 32-bit forcing dual
1097 address cycle on pci bus for cards supporting greater
1098 than 32-bit addressing. The default is to look
1099 for translation below 32-bit and if not available
1100 then look in the higher range.
1101 strict [Default Off]
1102 With this option on every unmap_single operation will
1103 result in a hardware IOTLB flush operation as opposed
1104 to batching them for performance.
1105 sp_off [Default Off]
1106 By default, super page will be supported if Intel IOMMU
1107 has the capability. With this option, super page will
1108 not be supported.
1110 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1111 0 disables intel_idle and fall back on acpi_idle.
1112 1 to 6 specify maximum depth of C-state.
1114 intremap= [X86-64, Intel-IOMMU]
1115 on enable Interrupt Remapping (default)
1116 off disable Interrupt Remapping
1117 nosid disable Source ID checking
1118 no_x2apic_optout
1119 BIOS x2APIC opt-out request will be ignored
1121 iomem= Disable strict checking of access to MMIO memory
1122 strict regions from userspace.
1123 relaxed
1125 iommu= [x86]
1126 off
1127 force
1128 noforce
1129 biomerge
1130 panic
1131 nopanic
1132 merge
1133 nomerge
1134 forcesac
1135 soft
1136 pt [x86, IA-64]
1139 io7= [HW] IO7 for Marvel based alpha systems
1140 See comment before marvel_specify_io7 in
1141 arch/alpha/kernel/core_marvel.c.
1143 io_delay= [X86] I/O delay method
1144 0x80
1145 Standard port 0x80 based delay
1146 0xed
1147 Alternate port 0xed based delay (needed on some systems)
1148 udelay
1149 Simple two microseconds delay
1150 none
1151 No delay
1153 ip= [IP_PNP]
1154 See Documentation/filesystems/nfs/nfsroot.txt.
1156 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1157 See comment before ip2_setup() in
1158 drivers/char/ip2/ip2base.c.
1160 irqfixup [HW]
1161 When an interrupt is not handled search all handlers
1162 for it. Intended to get systems with badly broken
1163 firmware running.
1165 irqpoll [HW]
1166 When an interrupt is not handled search all handlers
1167 for it. Also check all handlers each timer
1168 interrupt. Intended to get systems with badly broken
1169 firmware running.
1171 isapnp= [ISAPNP]
1172 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1174 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1175 Format:
1176 <cpu number>,...,<cpu number>
1177 or
1178 <cpu number>-<cpu number>
1179 (must be a positive range in ascending order)
1180 or a mixture
1181 <cpu number>,...,<cpu number>-<cpu number>
1183 This option can be used to specify one or more CPUs
1184 to isolate from the general SMP balancing and scheduling
1185 algorithms. You can move a process onto or off an
1186 "isolated" CPU via the CPU affinity syscalls or cpuset.
1187 <cpu number> begins at 0 and the maximum value is
1188 "number of CPUs in system - 1".
1190 This option is the preferred way to isolate CPUs. The
1191 alternative -- manually setting the CPU mask of all
1192 tasks in the system -- can cause problems and
1193 suboptimal load balancer performance.
1195 iucv= [HW,NET]
1197 js= [HW,JOY] Analog joystick
1198 See Documentation/input/joystick.txt.
1200 keepinitrd [HW,ARM]
1202 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1203 specifies the amount of memory usable by the kernel
1204 for non-movable allocations. The requested amount is
1205 spread evenly throughout all nodes in the system. The
1206 remaining memory in each node is used for Movable
1207 pages. In the event, a node is too small to have both
1208 kernelcore and Movable pages, kernelcore pages will
1209 take priority and other nodes will have a larger number
1210 of kernelcore pages. The Movable zone is used for the
1211 allocation of pages that may be reclaimed or moved
1212 by the page migration subsystem. This means that
1213 HugeTLB pages may not be allocated from this zone.
1214 Note that allocations like PTEs-from-HighMem still
1215 use the HighMem zone if it exists, and the Normal
1216 zone if it does not.
1218 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1219 Format: <Controller#>[,poll interval]
1220 The controller # is the number of the ehci usb debug
1221 port as it is probed via PCI. The poll interval is
1222 optional and is the number seconds in between
1223 each poll cycle to the debug port in case you need
1224 the functionality for interrupting the kernel with
1225 gdb or control-c on the dbgp connection. When
1226 not using this parameter you use sysrq-g to break into
1227 the kernel debugger.
1229 kgdboc= [KGDB,HW] kgdb over consoles.
1230 Requires a tty driver that supports console polling,
1231 or a supported polling keyboard driver (non-usb).
1232 Serial only format: <serial_device>[,baud]
1233 keyboard only format: kbd
1234 keyboard and serial format: kbd,<serial_device>[,baud]
1235 Optional Kernel mode setting:
1236 kms, kbd format: kms,kbd
1237 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1239 kgdbwait [KGDB] Stop kernel execution and enter the
1240 kernel debugger at the earliest opportunity.
1242 kmac= [MIPS] korina ethernet MAC address.
1243 Configure the RouterBoard 532 series on-chip
1244 Ethernet adapter MAC address.
1246 kmemleak= [KNL] Boot-time kmemleak enable/disable
1247 Valid arguments: on, off
1248 Default: on
1250 kstack=N [X86] Print N words from the kernel stack
1251 in oops dumps.
1253 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1254 Default is 0 (don't ignore, but inject #GP)
1256 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1257 KVM MMU at runtime.
1258 Default is 0 (off)
1260 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1261 Default is 1 (enabled)
1263 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1264 for all guests.
1265 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1267 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1268 (virtualized MMU) support on capable Intel chips.
1269 Default is 1 (enabled)
1271 kvm-intel.emulate_invalid_guest_state=
1272 [KVM,Intel] Enable emulation of invalid guest states
1273 Default is 0 (disabled)
1275 kvm-intel.flexpriority=
1276 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1277 Default is 1 (enabled)
1279 kvm-intel.nested=
1280 [KVM,Intel] Enable VMX nesting (nVMX).
1281 Default is 0 (disabled)
1283 kvm-intel.unrestricted_guest=
1284 [KVM,Intel] Disable unrestricted guest feature
1285 (virtualized real and unpaged mode) on capable
1286 Intel chips. Default is 1 (enabled)
1288 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1289 feature (tagged TLBs) on capable Intel chips.
1290 Default is 1 (enabled)
1292 l2cr= [PPC]
1294 l3cr= [PPC]
1296 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1297 disabled it.
1299 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1300 in C2 power state.
1302 libata.dma= [LIBATA] DMA control
1303 libata.dma=0 Disable all PATA and SATA DMA
1304 libata.dma=1 PATA and SATA Disk DMA only
1305 libata.dma=2 ATAPI (CDROM) DMA only
1306 libata.dma=4 Compact Flash DMA only
1307 Combinations also work, so libata.dma=3 enables DMA
1308 for disks and CDROMs, but not CFs.
1310 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1311 libata.ignore_hpa=0 keep BIOS limits (default)
1312 libata.ignore_hpa=1 ignore limits, using full disk
1314 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1315 when set.
1316 Format: <int>
1318 libata.force= [LIBATA] Force configurations. The format is comma
1319 separated list of "[ID:]VAL" where ID is
1320 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1321 matching port, link or device. Basically, it matches
1322 the ATA ID string printed on console by libata. If
1323 the whole ID part is omitted, the last PORT and DEVICE
1324 values are used. If ID hasn't been specified yet, the
1325 configuration applies to all ports, links and devices.
1327 If only DEVICE is omitted, the parameter applies to
1328 the port and all links and devices behind it. DEVICE
1329 number of 0 either selects the first device or the
1330 first fan-out link behind PMP device. It does not
1331 select the host link. DEVICE number of 15 selects the
1332 host link and device attached to it.
1334 The VAL specifies the configuration to force. As long
1335 as there's no ambiguity shortcut notation is allowed.
1336 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1337 The following configurations can be forced.
1339 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1340 Any ID with matching PORT is used.
1342 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1344 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1345 udma[/][16,25,33,44,66,100,133] notation is also
1346 allowed.
1348 * [no]ncq: Turn on or off NCQ.
1350 * nohrst, nosrst, norst: suppress hard, soft
1351 and both resets.
1353 * dump_id: dump IDENTIFY data.
1355 If there are multiple matching configurations changing
1356 the same attribute, the last one is used.
1358 memblock=debug [KNL] Enable memblock debug messages.
1360 load_ramdisk= [RAM] List of ramdisks to load from floppy
1361 See Documentation/blockdev/ramdisk.txt.
1363 lockd.nlm_grace_period=P [NFS] Assign grace period.
1364 Format: <integer>
1366 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1367 Format: <integer>
1369 lockd.nlm_timeout=T [NFS] Assign timeout value.
1370 Format: <integer>
1372 lockd.nlm_udpport=M [NFS] Assign UDP port.
1373 Format: <integer>
1375 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1376 Format: <irq>
1378 loglevel= All Kernel Messages with a loglevel smaller than the
1379 console loglevel will be printed to the console. It can
1380 also be changed with klogd or other programs. The
1381 loglevels are defined as follows:
1383 0 (KERN_EMERG) system is unusable
1384 1 (KERN_ALERT) action must be taken immediately
1385 2 (KERN_CRIT) critical conditions
1386 3 (KERN_ERR) error conditions
1387 4 (KERN_WARNING) warning conditions
1388 5 (KERN_NOTICE) normal but significant condition
1389 6 (KERN_INFO) informational
1390 7 (KERN_DEBUG) debug-level messages
1392 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1393 in bytes. n must be a power of two. The default
1394 size is set in the kernel config file.
1396 logo.nologo [FB] Disables display of the built-in Linux logo.
1397 This may be used to provide more screen space for
1398 kernel log messages and is useful when debugging
1399 kernel boot problems.
1401 lp=0 [LP] Specify parallel ports to use, e.g,
1402 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1403 lp=reset first parallel port). 'lp=0' disables the
1404 lp=auto printer driver. 'lp=reset' (which can be
1405 specified in addition to the ports) causes
1406 attached printers to be reset. Using
1407 lp=port1,port2,... specifies the parallel ports
1408 to associate lp devices with, starting with
1409 lp0. A port specification may be 'none' to skip
1410 that lp device, or a parport name such as
1411 'parport0'. Specifying 'lp=auto' instead of a
1412 port specification list means that device IDs
1413 from each port should be examined, to see if
1414 an IEEE 1284-compliant printer is attached; if
1415 so, the driver will manage that printer.
1416 See also header of drivers/char/lp.c.
1418 lpj=n [KNL]
1419 Sets loops_per_jiffy to given constant, thus avoiding
1420 time-consuming boot-time autodetection (up to 250 ms per
1421 CPU). 0 enables autodetection (default). To determine
1422 the correct value for your kernel, boot with normal
1423 autodetection and see what value is printed. Note that
1424 on SMP systems the preset will be applied to all CPUs,
1425 which is likely to cause problems if your CPUs need
1426 significantly divergent settings. An incorrect value
1427 will cause delays in the kernel to be wrong, leading to
1428 unpredictable I/O errors and other breakage. Although
1429 unlikely, in the extreme case this might damage your
1430 hardware.
1432 ltpc= [NET]
1433 Format: <io>,<irq>,<dma>
1435 machvec= [IA-64] Force the use of a particular machine-vector
1436 (machvec) in a generic kernel.
1437 Example: machvec=hpzx1_swiotlb
1439 machtype= [Loongson] Share the same kernel image file between different
1440 yeeloong laptop.
1441 Example: machtype=lemote-yeeloong-2f-7inch
1443 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1444 than or equal to this physical address is ignored.
1446 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1447 should make use of. maxcpus=n : n >= 0 limits the
1448 kernel to using 'n' processors. n=0 is a special case,
1449 it is equivalent to "nosmp", which also disables
1450 the IO APIC.
1452 max_loop= [LOOP] The number of loop block devices that get
1453 (loop.max_loop) unconditionally pre-created at init time. The default
1454 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1455 of statically allocating a predefined number, loop
1456 devices can be requested on-demand with the
1457 /dev/loop-control interface.
1459 mce [X86-32] Machine Check Exception
1461 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1463 md= [HW] RAID subsystems devices and level
1464 See Documentation/md.txt.
1466 mdacon= [MDA]
1467 Format: <first>,<last>
1468 Specifies range of consoles to be captured by the MDA.
1470 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1471 Amount of memory to be used when the kernel is not able
1472 to see the whole system memory or for test.
1473 [X86-32] Use together with memmap= to avoid physical
1474 address space collisions. Without memmap= PCI devices
1475 could be placed at addresses belonging to unused RAM.
1477 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1478 memory.
1480 memchunk=nn[KMG]
1481 [KNL,SH] Allow user to override the default size for
1482 per-device physically contiguous DMA buffers.
1484 memmap=exactmap [KNL,X86] Enable setting of an exact
1485 E820 memory map, as specified by the user.
1486 Such memmap=exactmap lines can be constructed based on
1487 BIOS output or other requirements. See the memmap=nn@ss
1488 option description.
1490 memmap=nn[KMG]@ss[KMG]
1491 [KNL] Force usage of a specific region of memory
1492 Region of memory to be used, from ss to ss+nn.
1494 memmap=nn[KMG]#ss[KMG]
1495 [KNL,ACPI] Mark specific memory as ACPI data.
1496 Region of memory to be used, from ss to ss+nn.
1498 memmap=nn[KMG]$ss[KMG]
1499 [KNL,ACPI] Mark specific memory as reserved.
1500 Region of memory to be used, from ss to ss+nn.
1501 Example: Exclude memory from 0x18690000-0x1869ffff
1502 memmap=64K$0x18690000
1503 or
1504 memmap=0x10000$0x18690000
1506 memory_corruption_check=0/1 [X86]
1507 Some BIOSes seem to corrupt the first 64k of
1508 memory when doing things like suspend/resume.
1509 Setting this option will scan the memory
1510 looking for corruption. Enabling this will
1511 both detect corruption and prevent the kernel
1512 from using the memory being corrupted.
1513 However, its intended as a diagnostic tool; if
1514 repeatable BIOS-originated corruption always
1515 affects the same memory, you can use memmap=
1516 to prevent the kernel from using that memory.
1518 memory_corruption_check_size=size [X86]
1519 By default it checks for corruption in the low
1520 64k, making this memory unavailable for normal
1521 use. Use this parameter to scan for
1522 corruption in more or less memory.
1524 memory_corruption_check_period=seconds [X86]
1525 By default it checks for corruption every 60
1526 seconds. Use this parameter to check at some
1527 other rate. 0 disables periodic checking.
1529 memtest= [KNL,X86] Enable memtest
1530 Format: <integer>
1531 default : 0 <disable>
1532 Specifies the number of memtest passes to be
1533 performed. Each pass selects another test
1534 pattern from a given set of patterns. Memtest
1535 fills the memory with this pattern, validates
1536 memory contents and reserves bad memory
1537 regions that are detected.
1539 meye.*= [HW] Set MotionEye Camera parameters
1540 See Documentation/video4linux/meye.txt.
1542 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1543 Multi-Function General Purpose Timers on AMD Geode
1544 platforms.
1546 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1547 the BIOS has incorrectly applied a workaround. TinyBIOS
1548 version 0.98 is known to be affected, 0.99 fixes the
1549 problem by letting the user disable the workaround.
1551 mga= [HW,DRM]
1553 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1554 physical address is ignored.
1556 mini2440= [ARM,HW,KNL]
1557 Format:[0..2][b][c][t]
1558 Default: "0tb"
1559 MINI2440 configuration specification:
1560 0 - The attached screen is the 3.5" TFT
1561 1 - The attached screen is the 7" TFT
1562 2 - The VGA Shield is attached (1024x768)
1563 Leaving out the screen size parameter will not load
1564 the TFT driver, and the framebuffer will be left
1565 unconfigured.
1566 b - Enable backlight. The TFT backlight pin will be
1567 linked to the kernel VESA blanking code and a GPIO
1568 LED. This parameter is not necessary when using the
1569 VGA shield.
1570 c - Enable the s3c camera interface.
1571 t - Reserved for enabling touchscreen support. The
1572 touchscreen support is not enabled in the mainstream
1573 kernel as of 2.6.30, a preliminary port can be found
1574 in the "bleeding edge" mini2440 support kernel at
1575 http://repo.or.cz/w/linux-2.6/mini2440.git
1577 mminit_loglevel=
1578 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1579 parameter allows control of the logging verbosity for
1580 the additional memory initialisation checks. A value
1581 of 0 disables mminit logging and a level of 4 will
1582 log everything. Information is printed at KERN_DEBUG
1583 so loglevel=8 may also need to be specified.
1585 mousedev.tap_time=
1586 [MOUSE] Maximum time between finger touching and
1587 leaving touchpad surface for touch to be considered
1588 a tap and be reported as a left button click (for
1589 touchpads working in absolute mode only).
1590 Format: <msecs>
1591 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1592 reporting absolute coordinates, such as tablets
1593 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1594 reporting absolute coordinates, such as tablets
1596 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1597 is similar to kernelcore except it specifies the
1598 amount of memory used for migratable allocations.
1599 If both kernelcore and movablecore is specified,
1600 then kernelcore will be at *least* the specified
1601 value but may be more. If movablecore on its own
1602 is specified, the administrator must be careful
1603 that the amount of memory usable for all allocations
1604 is not too small.
1606 MTD_Partition= [MTD]
1607 Format: <name>,<region-number>,<size>,<offset>
1609 MTD_Region= [MTD] Format:
1610 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1612 mtdparts= [MTD]
1613 See drivers/mtd/cmdlinepart.c.
1615 multitce=off [PPC] This parameter disables the use of the pSeries
1616 firmware feature for updating multiple TCE entries
1617 at a time.
1619 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1621 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1623 boundary - index of last SLC block on Flex-OneNAND.
1624 The remaining blocks are configured as MLC blocks.
1625 lock - Configure if Flex-OneNAND boundary should be locked.
1626 Once locked, the boundary cannot be changed.
1627 1 indicates lock status, 0 indicates unlock status.
1629 mtdset= [ARM]
1630 ARM/S3C2412 JIVE boot control
1632 See arch/arm/mach-s3c2412/mach-jive.c
1634 mtouchusb.raw_coordinates=
1635 [HW] Make the MicroTouch USB driver use raw coordinates
1636 ('y', default) or cooked coordinates ('n')
1638 mtrr_chunk_size=nn[KMG] [X86]
1639 used for mtrr cleanup. It is largest continuous chunk
1640 that could hold holes aka. UC entries.
1642 mtrr_gran_size=nn[KMG] [X86]
1643 Used for mtrr cleanup. It is granularity of mtrr block.
1644 Default is 1.
1645 Large value could prevent small alignment from
1646 using up MTRRs.
1648 mtrr_spare_reg_nr=n [X86]
1649 Format: <integer>
1650 Range: 0,7 : spare reg number
1651 Default : 1
1652 Used for mtrr cleanup. It is spare mtrr entries number.
1653 Set to 2 or more if your graphical card needs more.
1655 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1657 netdev= [NET] Network devices parameters
1658 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1659 Note that mem_start is often overloaded to mean
1660 something different and driver-specific.
1661 This usage is only documented in each driver source
1662 file if at all.
1664 nf_conntrack.acct=
1665 [NETFILTER] Enable connection tracking flow accounting
1666 0 to disable accounting
1667 1 to enable accounting
1668 Default value is 0.
1670 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1671 See Documentation/filesystems/nfs/nfsroot.txt.
1673 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1674 See Documentation/filesystems/nfs/nfsroot.txt.
1676 nfsrootdebug [NFS] enable nfsroot debugging messages.
1677 See Documentation/filesystems/nfs/nfsroot.txt.
1679 nfs.callback_tcpport=
1680 [NFS] set the TCP port on which the NFSv4 callback
1681 channel should listen.
1683 nfs.cache_getent=
1684 [NFS] sets the pathname to the program which is used
1685 to update the NFS client cache entries.
1687 nfs.cache_getent_timeout=
1688 [NFS] sets the timeout after which an attempt to
1689 update a cache entry is deemed to have failed.
1691 nfs.idmap_cache_timeout=
1692 [NFS] set the maximum lifetime for idmapper cache
1693 entries.
1695 nfs.enable_ino64=
1696 [NFS] enable 64-bit inode numbers.
1697 If zero, the NFS client will fake up a 32-bit inode
1698 number for the readdir() and stat() syscalls instead
1699 of returning the full 64-bit number.
1700 The default is to return 64-bit inode numbers.
1702 nfs.max_session_slots=
1703 [NFSv4.1] Sets the maximum number of session slots
1704 the client will attempt to negotiate with the server.
1705 This limits the number of simultaneous RPC requests
1706 that the client can send to the NFSv4.1 server.
1707 Note that there is little point in setting this
1708 value higher than the max_tcp_slot_table_limit.
1710 nfs.nfs4_disable_idmapping=
1711 [NFSv4] When set to the default of '1', this option
1712 ensures that both the RPC level authentication
1713 scheme and the NFS level operations agree to use
1714 numeric uids/gids if the mount is using the
1715 'sec=sys' security flavour. In effect it is
1716 disabling idmapping, which can make migration from
1717 legacy NFSv2/v3 systems to NFSv4 easier.
1718 Servers that do not support this mode of operation
1719 will be autodetected by the client, and it will fall
1720 back to using the idmapper.
1721 To turn off this behaviour, set the value to '0'.
1723 nfs.send_implementation_id =
1724 [NFSv4.1] Send client implementation identification
1725 information in exchange_id requests.
1726 If zero, no implementation identification information
1727 will be sent.
1728 The default is to send the implementation identification
1729 information.
1731 nfsd.nfs4_disable_idmapping=
1732 [NFSv4] When set to the default of '1', the NFSv4
1733 server will return only numeric uids and gids to
1734 clients using auth_sys, and will accept numeric uids
1735 and gids from such clients. This is intended to ease
1736 migration from NFSv2/v3.
1738 objlayoutdriver.osd_login_prog=
1739 [NFS] [OBJLAYOUT] sets the pathname to the program which
1740 is used to automatically discover and login into new
1741 osd-targets. Please see:
1742 Documentation/filesystems/pnfs.txt for more explanations
1744 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1745 when a NMI is triggered.
1746 Format: [state][,regs][,debounce][,die]
1748 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1749 Format: [panic,][nopanic,][num]
1750 Valid num: 0
1751 0 - turn nmi_watchdog off
1752 When panic is specified, panic when an NMI watchdog
1753 timeout occurs (or 'nopanic' to override the opposite
1754 default).
1755 This is useful when you use a panic=... timeout and
1756 need the box quickly up again.
1758 netpoll.carrier_timeout=
1759 [NET] Specifies amount of time (in seconds) that
1760 netpoll should wait for a carrier. By default netpoll
1761 waits 4 seconds.
1763 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1764 emulation library even if a 387 maths coprocessor
1765 is present.
1767 no_console_suspend
1768 [HW] Never suspend the console
1769 Disable suspending of consoles during suspend and
1770 hibernate operations. Once disabled, debugging
1771 messages can reach various consoles while the rest
1772 of the system is being put to sleep (ie, while
1773 debugging driver suspend/resume hooks). This may
1774 not work reliably with all consoles, but is known
1775 to work with serial and VGA consoles.
1776 To facilitate more flexible debugging, we also add
1777 console_suspend, a printk module parameter to control
1778 it. Users could use console_suspend (usually
1779 /sys/module/printk/parameters/console_suspend) to
1780 turn on/off it dynamically.
1782 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1783 caches in the slab allocator. Saves per-node memory,
1784 but will impact performance.
1786 noalign [KNL,ARM]
1788 noapic [SMP,APIC] Tells the kernel to not make use of any
1789 IOAPICs that may be present in the system.
1791 noautogroup Disable scheduler automatic task group creation.
1793 nobats [PPC] Do not use BATs for mapping kernel lowmem
1794 on "Classic" PPC cores.
1796 nocache [ARM]
1798 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1800 nodelayacct [KNL] Disable per-task delay accounting
1802 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1804 nodsp [SH] Disable hardware DSP at boot time.
1806 noefi [X86] Disable EFI runtime services support.
1808 noexec [IA-64]
1810 noexec [X86]
1811 On X86-32 available only on PAE configured kernels.
1812 noexec=on: enable non-executable mappings (default)
1813 noexec=off: disable non-executable mappings
1815 nosmep [X86]
1816 Disable SMEP (Supervisor Mode Execution Protection)
1817 even if it is supported by processor.
1819 noexec32 [X86-64]
1820 This affects only 32-bit executables.
1821 noexec32=on: enable non-executable mappings (default)
1822 read doesn't imply executable mappings
1823 noexec32=off: disable non-executable mappings
1824 read implies executable mappings
1826 nofpu [SH] Disable hardware FPU at boot time.
1828 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1829 register save and restore. The kernel will only save
1830 legacy floating-point registers on task switch.
1832 noxsave [BUGS=X86] Disables x86 extended register state save
1833 and restore using xsave. The kernel will fallback to
1834 enabling legacy floating-point and sse state.
1836 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1837 wfi(ARM) instruction doesn't work correctly and not to
1838 use it. This is also useful when using JTAG debugger.
1840 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1841 instruction doesn't work correctly and not to
1842 use it.
1844 no_file_caps Tells the kernel not to honor file capabilities. The
1845 only way then for a file to be executed with privilege
1846 is to be setuid root or executed by root.
1848 nohalt [IA-64] Tells the kernel not to use the power saving
1849 function PAL_HALT_LIGHT when idle. This increases
1850 power-consumption. On the positive side, it reduces
1851 interrupt wake-up latency, which may improve performance
1852 in certain environments such as networked servers or
1853 real-time systems.
1855 nohz= [KNL] Boottime enable/disable dynamic ticks
1856 Valid arguments: on, off
1857 Default: on
1859 noiotrap [SH] Disables trapped I/O port accesses.
1861 noirqdebug [X86-32] Disables the code which attempts to detect and
1862 disable unhandled interrupt sources.
1864 no_timer_check [X86,APIC] Disables the code which tests for
1865 broken timer IRQ sources.
1867 noisapnp [ISAPNP] Disables ISA PnP code.
1869 noinitrd [RAM] Tells the kernel not to load any configured
1870 initial RAM disk.
1872 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1873 remapping.
1874 [Deprecated - use intremap=off]
1876 nointroute [IA-64]
1878 nojitter [IA-64] Disables jitter checking for ITC timers.
1880 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1882 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1883 fault handling.
1885 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1886 steal time is computed, but won't influence scheduler
1887 behaviour
1889 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1891 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1893 noltlbs [PPC] Do not use large page/tlb entries for kernel
1894 lowmem mapping on PPC40x.
1896 nomca [IA-64] Disable machine check abort handling
1898 nomce [X86-32] Machine Check Exception
1900 nomfgpt [X86-32] Disable Multi-Function General Purpose
1901 Timer usage (for AMD Geode machines).
1903 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1904 shutdown the other cpus. Instead use the REBOOT_VECTOR
1905 irq.
1907 nomodule Disable module load
1909 nopat [X86] Disable PAT (page attribute table extension of
1910 pagetables) support.
1912 norandmaps Don't use address space randomization. Equivalent to
1913 echo 0 > /proc/sys/kernel/randomize_va_space
1915 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1917 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1918 with UP alternatives
1920 noresidual [PPC] Don't use residual data on PReP machines.
1922 nordrand [X86] Disable the direct use of the RDRAND
1923 instruction even if it is supported by the
1924 processor. RDRAND is still available to user
1925 space applications.
1927 noresume [SWSUSP] Disables resume and restores original swap
1928 space.
1930 no-scroll [VGA] Disables scrollback.
1931 This is required for the Braillex ib80-piezo Braille
1932 reader made by F.H. Papenmeier (Germany).
1934 nosbagart [IA-64]
1936 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1938 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1939 and disable the IO APIC. legacy for "maxcpus=0".
1941 nosoftlockup [KNL] Disable the soft-lockup detector.
1943 nosync [HW,M68K] Disables sync negotiation for all devices.
1945 notsc [BUGS=X86-32] Disable Time Stamp Counter
1947 nousb [USB] Disable the USB subsystem
1949 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1951 nowb [ARM]
1953 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1955 nptcg= [IA-64] Override max number of concurrent global TLB
1956 purges which is reported from either PAL_VM_SUMMARY or
1957 SAL PALO.
1959 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1960 could support. nr_cpus=n : n >= 1 limits the kernel to
1961 supporting 'n' processors. Later in runtime you can not
1962 use hotplug cpu feature to put more cpu back to online.
1963 just like you compile the kernel NR_CPUS=n
1965 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1967 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1968 one of ['zone', 'node', 'default'] can be specified
1969 This can be set from sysctl after boot.
1970 See Documentation/sysctl/vm.txt for details.
1972 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1973 See Documentation/debugging-via-ohci1394.txt for more
1974 info.
1976 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1977 Rather than timing out after 20 ms if an EC
1978 command is not properly ACKed, override the length
1979 of the timeout. We have interrupts disabled while
1980 waiting for the ACK, so if this is set too high
1981 interrupts *may* be lost!
1983 omap_mux= [OMAP] Override bootloader pin multiplexing.
1984 Format: <mux_mode0.mode_name=value>...
1985 For example, to override I2C bus2:
1986 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1988 oprofile.timer= [HW]
1989 Use timer interrupt instead of performance counters
1991 oprofile.cpu_type= Force an oprofile cpu type
1992 This might be useful if you have an older oprofile
1993 userland or if you want common events.
1994 Format: { arch_perfmon }
1995 arch_perfmon: [X86] Force use of architectural
1996 perfmon on Intel CPUs instead of the
1997 CPU specific event set.
1998 timer: [X86] Force use of architectural NMI
1999 timer mode (see also oprofile.timer
2000 for generic hr timer mode)
2001 [s390] Force legacy basic mode sampling
2002 (report cpu_type "timer")
2004 oops=panic Always panic on oopses. Default is to just kill the
2005 process, but there is a small probability of
2006 deadlocking the machine.
2007 This will also cause panics on machine check exceptions.
2008 Useful together with panic=30 to trigger a reboot.
2010 OSS [HW,OSS]
2011 See Documentation/sound/oss/oss-parameters.txt
2013 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2014 timeout > 0: seconds before rebooting
2015 timeout = 0: wait forever
2016 timeout < 0: reboot immediately
2017 Format: <timeout>
2019 parkbd.port= [HW] Parallel port number the keyboard adapter is
2020 connected to, default is 0.
2021 Format: <parport#>
2022 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2023 0 for XT, 1 for AT (default is AT).
2024 Format: <mode>
2026 parport= [HW,PPT] Specify parallel ports. 0 disables.
2027 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2028 Use 'auto' to force the driver to use any
2029 IRQ/DMA settings detected (the default is to
2030 ignore detected IRQ/DMA settings because of
2031 possible conflicts). You can specify the base
2032 address, IRQ, and DMA settings; IRQ and DMA
2033 should be numbers, or 'auto' (for using detected
2034 settings on that particular port), or 'nofifo'
2035 (to avoid using a FIFO even if it is detected).
2036 Parallel ports are assigned in the order they
2037 are specified on the command line, starting
2038 with parport0.
2040 parport_init_mode= [HW,PPT]
2041 Configure VIA parallel port to operate in
2042 a specific mode. This is necessary on Pegasos
2043 computer where firmware has no options for setting
2044 up parallel port mode and sets it to spp.
2045 Currently this function knows 686a and 8231 chips.
2046 Format: [spp|ps2|epp|ecp|ecpepp]
2048 pause_on_oops=
2049 Halt all CPUs after the first oops has been printed for
2050 the specified number of seconds. This is to be used if
2051 your oopses keep scrolling off the screen.
2053 pcbit= [HW,ISDN]
2055 pcd. [PARIDE]
2056 See header of drivers/block/paride/pcd.c.
2057 See also Documentation/blockdev/paride.txt.
2059 pci=option[,option...] [PCI] various PCI subsystem options:
2060 earlydump [X86] dump PCI config space before the kernel
2061 changes anything
2062 off [X86] don't probe for the PCI bus
2063 bios [X86-32] force use of PCI BIOS, don't access
2064 the hardware directly. Use this if your machine
2065 has a non-standard PCI host bridge.
2066 nobios [X86-32] disallow use of PCI BIOS, only direct
2067 hardware access methods are allowed. Use this
2068 if you experience crashes upon bootup and you
2069 suspect they are caused by the BIOS.
2070 conf1 [X86] Force use of PCI Configuration
2071 Mechanism 1.
2072 conf2 [X86] Force use of PCI Configuration
2073 Mechanism 2.
2074 noaer [PCIE] If the PCIEAER kernel config parameter is
2075 enabled, this kernel boot option can be used to
2076 disable the use of PCIE advanced error reporting.
2077 nodomains [PCI] Disable support for multiple PCI
2078 root domains (aka PCI segments, in ACPI-speak).
2079 nommconf [X86] Disable use of MMCONFIG for PCI
2080 Configuration
2081 check_enable_amd_mmconf [X86] check for and enable
2082 properly configured MMIO access to PCI
2083 config space on AMD family 10h CPU
2084 nomsi [MSI] If the PCI_MSI kernel config parameter is
2085 enabled, this kernel boot option can be used to
2086 disable the use of MSI interrupts system-wide.
2087 noioapicquirk [APIC] Disable all boot interrupt quirks.
2088 Safety option to keep boot IRQs enabled. This
2089 should never be necessary.
2090 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2091 primary IO-APIC for bridges that cannot disable
2092 boot IRQs. This fixes a source of spurious IRQs
2093 when the system masks IRQs.
2094 noioapicreroute [APIC] Disable workaround that uses the
2095 boot IRQ equivalent of an IRQ that connects to
2096 a chipset where boot IRQs cannot be disabled.
2097 The opposite of ioapicreroute.
2098 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2099 routing table. These calls are known to be buggy
2100 on several machines and they hang the machine
2101 when used, but on other computers it's the only
2102 way to get the interrupt routing table. Try
2103 this option if the kernel is unable to allocate
2104 IRQs or discover secondary PCI buses on your
2105 motherboard.
2106 rom [X86] Assign address space to expansion ROMs.
2107 Use with caution as certain devices share
2108 address decoders between ROMs and other
2109 resources.
2110 norom [X86] Do not assign address space to
2111 expansion ROMs that do not already have
2112 BIOS assigned address ranges.
2113 nobar [X86] Do not assign address space to the
2114 BARs that weren't assigned by the BIOS.
2115 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2116 assigned automatically to PCI devices. You can
2117 make the kernel exclude IRQs of your ISA cards
2118 this way.
2119 pirqaddr=0xAAAAA [X86] Specify the physical address
2120 of the PIRQ table (normally generated
2121 by the BIOS) if it is outside the
2122 F0000h-100000h range.
2123 lastbus=N [X86] Scan all buses thru bus #N. Can be
2124 useful if the kernel is unable to find your
2125 secondary buses and you want to tell it
2126 explicitly which ones they are.
2127 assign-busses [X86] Always assign all PCI bus
2128 numbers ourselves, overriding
2129 whatever the firmware may have done.
2130 usepirqmask [X86] Honor the possible IRQ mask stored
2131 in the BIOS $PIR table. This is needed on
2132 some systems with broken BIOSes, notably
2133 some HP Pavilion N5400 and Omnibook XE3
2134 notebooks. This will have no effect if ACPI
2135 IRQ routing is enabled.
2136 noacpi [X86] Do not use ACPI for IRQ routing
2137 or for PCI scanning.
2138 use_crs [X86] Use PCI host bridge window information
2139 from ACPI. On BIOSes from 2008 or later, this
2140 is enabled by default. If you need to use this,
2141 please report a bug.
2142 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2143 If you need to use this, please report a bug.
2144 routeirq Do IRQ routing for all PCI devices.
2145 This is normally done in pci_enable_device(),
2146 so this option is a temporary workaround
2147 for broken drivers that don't call it.
2148 skip_isa_align [X86] do not align io start addr, so can
2149 handle more pci cards
2150 firmware [ARM] Do not re-enumerate the bus but instead
2151 just use the configuration from the
2152 bootloader. This is currently used on
2153 IXP2000 systems where the bus has to be
2154 configured a certain way for adjunct CPUs.
2155 noearly [X86] Don't do any early type 1 scanning.
2156 This might help on some broken boards which
2157 machine check when some devices' config space
2158 is read. But various workarounds are disabled
2159 and some IOMMU drivers will not work.
2160 bfsort Sort PCI devices into breadth-first order.
2161 This sorting is done to get a device
2162 order compatible with older (<= 2.4) kernels.
2163 nobfsort Don't sort PCI devices into breadth-first order.
2164 cbiosize=nn[KMG] The fixed amount of bus space which is
2165 reserved for the CardBus bridge's IO window.
2166 The default value is 256 bytes.
2167 cbmemsize=nn[KMG] The fixed amount of bus space which is
2168 reserved for the CardBus bridge's memory
2169 window. The default value is 64 megabytes.
2170 resource_alignment=
2171 Format:
2172 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2173 Specifies alignment and device to reassign
2174 aligned memory resources.
2175 If <order of align> is not specified,
2176 PAGE_SIZE is used as alignment.
2177 PCI-PCI bridge can be specified, if resource
2178 windows need to be expanded.
2179 ecrc= Enable/disable PCIe ECRC (transaction layer
2180 end-to-end CRC checking).
2181 bios: Use BIOS/firmware settings. This is the
2182 the default.
2183 off: Turn ECRC off
2184 on: Turn ECRC on.
2185 realloc= Enable/disable reallocating PCI bridge resources
2186 if allocations done by BIOS are too small to
2187 accommodate resources required by all child
2188 devices.
2189 off: Turn realloc off
2190 on: Turn realloc on
2191 realloc same as realloc=on
2192 noari do not use PCIe ARI.
2193 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2194 only look for one device below a PCIe downstream
2195 port.
2197 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2198 Management.
2199 off Disable ASPM.
2200 force Enable ASPM even on devices that claim not to support it.
2201 WARNING: Forcing ASPM on may cause system lockups.
2203 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2204 nomsi Do not use MSI for PCI Express Native Hotplug (this
2205 makes all PCIe ports use INTx for hotplug services).
2207 pcie_ports= [PCIE] PCIe ports handling:
2208 auto Ask the BIOS whether or not to use native PCIe services
2209 associated with PCIe ports (PME, hot-plug, AER). Use
2210 them only if that is allowed by the BIOS.
2211 native Use native PCIe services associated with PCIe ports
2212 unconditionally.
2213 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2214 ports driver.
2216 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2217 nomsi Do not use MSI for native PCIe PME signaling (this makes
2218 all PCIe root ports use INTx for all services).
2220 pcmv= [HW,PCMCIA] BadgePAD 4
2222 pd. [PARIDE]
2223 See Documentation/blockdev/paride.txt.
2225 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2226 boot time.
2227 Format: { 0 | 1 }
2228 See arch/parisc/kernel/pdc_chassis.c
2230 percpu_alloc= Select which percpu first chunk allocator to use.
2231 Currently supported values are "embed" and "page".
2232 Archs may support subset or none of the selections.
2233 See comments in mm/percpu.c for details on each
2234 allocator. This parameter is primarily for debugging
2235 and performance comparison.
2237 pf. [PARIDE]
2238 See Documentation/blockdev/paride.txt.
2240 pg. [PARIDE]
2241 See Documentation/blockdev/paride.txt.
2243 pirq= [SMP,APIC] Manual mp-table setup
2244 See Documentation/x86/i386/IO-APIC.txt.
2246 plip= [PPT,NET] Parallel port network link
2247 Format: { parport<nr> | timid | 0 }
2248 See also Documentation/parport.txt.
2250 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2251 Override pmtimer IOPort with a hex value.
2252 e.g. pmtmr=0x508
2254 pnp.debug=1 [PNP]
2255 Enable PNP debug messages (depends on the
2256 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2257 via /sys/module/pnp/parameters/debug. We always show
2258 current resource usage; turning this on also shows
2259 possible settings and some assignment information.
2261 pnpacpi= [ACPI]
2262 { off }
2264 pnpbios= [ISAPNP]
2265 { on | off | curr | res | no-curr | no-res }
2267 pnp_reserve_irq=
2268 [ISAPNP] Exclude IRQs for the autoconfiguration
2270 pnp_reserve_dma=
2271 [ISAPNP] Exclude DMAs for the autoconfiguration
2273 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2274 Ranges are in pairs (I/O port base and size).
2276 pnp_reserve_mem=
2277 [ISAPNP] Exclude memory regions for the
2278 autoconfiguration.
2279 Ranges are in pairs (memory base and size).
2281 ports= [IP_VS_FTP] IPVS ftp helper module
2282 Default is 21.
2283 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2284 may be specified.
2285 Format: <port>,<port>....
2287 print-fatal-signals=
2288 [KNL] debug: print fatal signals
2290 If enabled, warn about various signal handling
2291 related application anomalies: too many signals,
2292 too many POSIX.1 timers, fatal signals causing a
2293 coredump - etc.
2295 If you hit the warning due to signal overflow,
2296 you might want to try "ulimit -i unlimited".
2298 default: off.
2300 printk.always_kmsg_dump=
2301 Trigger kmsg_dump for cases other than kernel oops or
2302 panics
2303 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2304 default: disabled
2306 printk.time= Show timing data prefixed to each printk message line
2307 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2309 processor.max_cstate= [HW,ACPI]
2310 Limit processor to maximum C-state
2311 max_cstate=9 overrides any DMI blacklist limit.
2313 processor.nocst [HW,ACPI]
2314 Ignore the _CST method to determine C-states,
2315 instead using the legacy FADT method
2317 profile= [KNL] Enable kernel profiling via /proc/profile
2318 Format: [schedule,]<number>
2319 Param: "schedule" - profile schedule points.
2320 Param: <number> - step/bucket size as a power of 2 for
2321 statistical time based profiling.
2322 Param: "sleep" - profile D-state sleeping (millisecs).
2323 Requires CONFIG_SCHEDSTATS
2324 Param: "kvm" - profile VM exits.
2326 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2327 before loading.
2328 See Documentation/blockdev/ramdisk.txt.
2330 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2331 probe for; one of (bare|imps|exps|lifebook|any).
2332 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2333 per second.
2334 psmouse.resetafter= [HW,MOUSE]
2335 Try to reset the device after so many bad packets
2336 (0 = never).
2337 psmouse.resolution=
2338 [HW,MOUSE] Set desired mouse resolution, in dpi.
2339 psmouse.smartscroll=
2340 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2341 0 = disabled, 1 = enabled (default).
2343 pstore.backend= Specify the name of the pstore backend to use
2345 pt. [PARIDE]
2346 See Documentation/blockdev/paride.txt.
2348 pty.legacy_count=
2349 [KNL] Number of legacy pty's. Overwrites compiled-in
2350 default number.
2352 quiet [KNL] Disable most log messages
2354 r128= [HW,DRM]
2356 raid= [HW,RAID]
2357 See Documentation/md.txt.
2359 ramdisk_blocksize= [RAM]
2360 See Documentation/blockdev/ramdisk.txt.
2362 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2363 See Documentation/blockdev/ramdisk.txt.
2365 rcutree.blimit= [KNL,BOOT]
2366 Set maximum number of finished RCU callbacks to process
2367 in one batch.
2369 rcutree.fanout_leaf= [KNL,BOOT]
2370 Increase the number of CPUs assigned to each
2371 leaf rcu_node structure. Useful for very large
2372 systems.
2374 rcutree.qhimark= [KNL,BOOT]
2375 Set threshold of queued
2376 RCU callbacks over which batch limiting is disabled.
2378 rcutree.qlowmark= [KNL,BOOT]
2379 Set threshold of queued RCU callbacks below which
2380 batch limiting is re-enabled.
2382 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2383 Suppress RCU CPU stall warning messages.
2385 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2386 Set timeout for RCU CPU stall warning messages.
2388 rcutorture.fqs_duration= [KNL,BOOT]
2389 Set duration of force_quiescent_state bursts.
2391 rcutorture.fqs_holdoff= [KNL,BOOT]
2392 Set holdoff time within force_quiescent_state bursts.
2394 rcutorture.fqs_stutter= [KNL,BOOT]
2395 Set wait time between force_quiescent_state bursts.
2397 rcutorture.irqreader= [KNL,BOOT]
2398 Test RCU readers from irq handlers.
2400 rcutorture.n_barrier_cbs= [KNL,BOOT]
2401 Set callbacks/threads for rcu_barrier() testing.
2403 rcutorture.nfakewriters= [KNL,BOOT]
2404 Set number of concurrent RCU writers. These just
2405 stress RCU, they don't participate in the actual
2406 test, hence the "fake".
2408 rcutorture.nreaders= [KNL,BOOT]
2409 Set number of RCU readers.
2411 rcutorture.onoff_holdoff= [KNL,BOOT]
2412 Set time (s) after boot for CPU-hotplug testing.
2414 rcutorture.onoff_interval= [KNL,BOOT]
2415 Set time (s) between CPU-hotplug operations, or
2416 zero to disable CPU-hotplug testing.
2418 rcutorture.shuffle_interval= [KNL,BOOT]
2419 Set task-shuffle interval (s). Shuffling tasks
2420 allows some CPUs to go into dyntick-idle mode
2421 during the rcutorture test.
2423 rcutorture.shutdown_secs= [KNL,BOOT]
2424 Set time (s) after boot system shutdown. This
2425 is useful for hands-off automated testing.
2427 rcutorture.stall_cpu= [KNL,BOOT]
2428 Duration of CPU stall (s) to test RCU CPU stall
2429 warnings, zero to disable.
2431 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2432 Time to wait (s) after boot before inducing stall.
2434 rcutorture.stat_interval= [KNL,BOOT]
2435 Time (s) between statistics printk()s.
2437 rcutorture.stutter= [KNL,BOOT]
2438 Time (s) to stutter testing, for example, specifying
2439 five seconds causes the test to run for five seconds,
2440 wait for five seconds, and so on. This tests RCU's
2441 ability to transition abruptly to and from idle.
2443 rcutorture.test_boost= [KNL,BOOT]
2444 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2445 "Maybe" means test if the RCU implementation
2446 under test support RCU priority boosting.
2448 rcutorture.test_boost_duration= [KNL,BOOT]
2449 Duration (s) of each individual boost test.
2451 rcutorture.test_boost_interval= [KNL,BOOT]
2452 Interval (s) between each boost test.
2454 rcutorture.test_no_idle_hz= [KNL,BOOT]
2455 Test RCU's dyntick-idle handling. See also the
2456 rcutorture.shuffle_interval parameter.
2458 rcutorture.torture_type= [KNL,BOOT]
2459 Specify the RCU implementation to test.
2461 rcutorture.verbose= [KNL,BOOT]
2462 Enable additional printk() statements.
2464 rdinit= [KNL]
2465 Format: <full_path>
2466 Run specified binary instead of /init from the ramdisk,
2467 used for early userspace startup. See initrd.
2469 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2470 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2471 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2473 relax_domain_level=
2474 [KNL, SMP] Set scheduler's default relax_domain_level.
2475 See Documentation/cgroups/cpusets.txt.
2477 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2479 reservetop= [X86-32]
2480 Format: nn[KMG]
2481 Reserves a hole at the top of the kernel virtual
2482 address space.
2484 reservelow= [X86]
2485 Format: nn[K]
2486 Set the amount of memory to reserve for BIOS at
2487 the bottom of the address space.
2489 reset_devices [KNL] Force drivers to reset the underlying device
2490 during initialization.
2492 resume= [SWSUSP]
2493 Specify the partition device for software suspend
2494 Format:
2495 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2497 resume_offset= [SWSUSP]
2498 Specify the offset from the beginning of the partition
2499 given by "resume=" at which the swap header is located,
2500 in <PAGE_SIZE> units (needed only for swap files).
2501 See Documentation/power/swsusp-and-swap-files.txt
2503 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2504 read the resume files
2506 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2507 Useful for devices that are detected asynchronously
2508 (e.g. USB and MMC devices).
2510 hibernate= [HIBERNATION]
2511 noresume Don't check if there's a hibernation image
2512 present during boot.
2513 nocompress Don't compress/decompress hibernation images.
2515 retain_initrd [RAM] Keep initrd memory after extraction
2517 rhash_entries= [KNL,NET]
2518 Set number of hash buckets for route cache
2520 riscom8= [HW,SERIAL]
2521 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2523 ro [KNL] Mount root device read-only on boot
2525 root= [KNL] Root filesystem
2526 See name_to_dev_t comment in init/do_mounts.c.
2528 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2529 mount the root filesystem
2531 rootflags= [KNL] Set root filesystem mount option string
2533 rootfstype= [KNL] Set root filesystem type
2535 rootwait [KNL] Wait (indefinitely) for root device to show up.
2536 Useful for devices that are detected asynchronously
2537 (e.g. USB and MMC devices).
2539 rw [KNL] Mount root device read-write on boot
2541 S [KNL] Run init in single mode
2543 sa1100ir [NET]
2544 See drivers/net/irda/sa1100_ir.c.
2546 sbni= [NET] Granch SBNI12 leased line adapter
2548 sched_debug [KNL] Enables verbose scheduler debug messages.
2550 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2551 xtime_lock contention on larger systems, and/or RCU lock
2552 contention on all systems with CONFIG_MAXSMP set.
2553 Format: { "0" | "1" }
2554 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2555 1 -- enable.
2556 Note: increases power consumption, thus should only be
2557 enabled if running jitter sensitive (HPC/RT) workloads.
2559 security= [SECURITY] Choose a security module to enable at boot.
2560 If this boot parameter is not specified, only the first
2561 security module asking for security registration will be
2562 loaded. An invalid security module name will be treated
2563 as if no module has been chosen.
2565 selinux= [SELINUX] Disable or enable SELinux at boot time.
2566 Format: { "0" | "1" }
2567 See security/selinux/Kconfig help text.
2568 0 -- disable.
2569 1 -- enable.
2570 Default value is set via kernel config option.
2571 If enabled at boot time, /selinux/disable can be used
2572 later to disable prior to initial policy load.
2574 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2575 Format: { "0" | "1" }
2576 See security/apparmor/Kconfig help text
2577 0 -- disable.
2578 1 -- enable.
2579 Default value is set via kernel config option.
2581 serialnumber [BUGS=X86-32]
2583 shapers= [NET]
2584 Maximal number of shapers.
2586 show_msr= [x86] show boot-time MSR settings
2587 Format: { <integer> }
2588 Show boot-time (BIOS-initialized) MSR settings.
2589 The parameter means the number of CPUs to show,
2590 for example 1 means boot CPU only.
2592 simeth= [IA-64]
2593 simscsi=
2595 slram= [HW,MTD]
2597 slab_max_order= [MM, SLAB]
2598 Determines the maximum allowed order for slabs.
2599 A high setting may cause OOMs due to memory
2600 fragmentation. Defaults to 1 for systems with
2601 more than 32MB of RAM, 0 otherwise.
2603 slub_debug[=options[,slabs]] [MM, SLUB]
2604 Enabling slub_debug allows one to determine the
2605 culprit if slab objects become corrupted. Enabling
2606 slub_debug can create guard zones around objects and
2607 may poison objects when not in use. Also tracks the
2608 last alloc / free. For more information see
2609 Documentation/vm/slub.txt.
2611 slub_max_order= [MM, SLUB]
2612 Determines the maximum allowed order for slabs.
2613 A high setting may cause OOMs due to memory
2614 fragmentation. For more information see
2615 Documentation/vm/slub.txt.
2617 slub_min_objects= [MM, SLUB]
2618 The minimum number of objects per slab. SLUB will
2619 increase the slab order up to slub_max_order to
2620 generate a sufficiently large slab able to contain
2621 the number of objects indicated. The higher the number
2622 of objects the smaller the overhead of tracking slabs
2623 and the less frequently locks need to be acquired.
2624 For more information see Documentation/vm/slub.txt.
2626 slub_min_order= [MM, SLUB]
2627 Determines the minimum page order for slabs. Must be
2628 lower than slub_max_order.
2629 For more information see Documentation/vm/slub.txt.
2631 slub_nomerge [MM, SLUB]
2632 Disable merging of slabs with similar size. May be
2633 necessary if there is some reason to distinguish
2634 allocs to different slabs. Debug options disable
2635 merging on their own.
2636 For more information see Documentation/vm/slub.txt.
2638 smart2= [HW]
2639 Format: <io1>[,<io2>[,...,<io8>]]
2641 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2642 attempt to substitute SMP alternatives once at boot.
2644 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2645 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2646 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2647 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2648 smsc-ircc2.ircc_irq= [HW] IRQ line
2649 smsc-ircc2.ircc_dma= [HW] DMA channel
2650 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2651 0: Toshiba Satellite 1800 (GP data pin select)
2652 1: Fast pin select (default)
2653 2: ATC IRMode
2655 softlockup_panic=
2656 [KNL] Should the soft-lockup detector generate panics.
2657 Format: <integer>
2659 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2660 See Documentation/laptops/sonypi.txt
2662 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2663 See Documentation/serial/specialix.txt.
2665 spia_io_base= [HW,MTD]
2666 spia_fio_base=
2667 spia_pedr=
2668 spia_peddr=
2670 stacktrace [FTRACE]
2671 Enabled the stack tracer on boot up.
2673 stacktrace_filter=[function-list]
2674 [FTRACE] Limit the functions that the stack tracer
2675 will trace at boot up. function-list is a comma separated
2676 list of functions. This list can be changed at run
2677 time by the stack_trace_filter file in the debugfs
2678 tracing directory. Note, this enables stack tracing
2679 and the stacktrace above is not needed.
2681 sti= [PARISC,HW]
2682 Format: <num>
2683 Set the STI (builtin display/keyboard on the HP-PARISC
2684 machines) console (graphic card) which should be used
2685 as the initial boot-console.
2686 See also comment in drivers/video/console/sticore.c.
2688 sti_font= [HW]
2689 See comment in drivers/video/console/sticore.c.
2691 stifb= [HW]
2692 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2694 sunrpc.min_resvport=
2695 sunrpc.max_resvport=
2696 [NFS,SUNRPC]
2697 SunRPC servers often require that client requests
2698 originate from a privileged port (i.e. a port in the
2699 range 0 < portnr < 1024).
2700 An administrator who wishes to reserve some of these
2701 ports for other uses may adjust the range that the
2702 kernel's sunrpc client considers to be privileged
2703 using these two parameters to set the minimum and
2704 maximum port values.
2706 sunrpc.pool_mode=
2707 [NFS]
2708 Control how the NFS server code allocates CPUs to
2709 service thread pools. Depending on how many NICs
2710 you have and where their interrupts are bound, this
2711 option will affect which CPUs will do NFS serving.
2712 Note: this parameter cannot be changed while the
2713 NFS server is running.
2715 auto the server chooses an appropriate mode
2716 automatically using heuristics
2717 global a single global pool contains all CPUs
2718 percpu one pool for each CPU
2719 pernode one pool for each NUMA node (equivalent
2720 to global on non-NUMA machines)
2722 sunrpc.tcp_slot_table_entries=
2723 sunrpc.udp_slot_table_entries=
2724 [NFS,SUNRPC]
2725 Sets the upper limit on the number of simultaneous
2726 RPC calls that can be sent from the client to a
2727 server. Increasing these values may allow you to
2728 improve throughput, but will also increase the
2729 amount of memory reserved for use by the client.
2731 swapaccount[=0|1]
2732 [KNL] Enable accounting of swap in memory resource
2733 controller if no parameter or 1 is given or disable
2734 it if 0 is given (See Documentation/cgroups/memory.txt)
2736 swiotlb= [IA-64] Number of I/O TLB slabs
2738 switches= [HW,M68k]
2740 sysfs.deprecated=0|1 [KNL]
2741 Enable/disable old style sysfs layout for old udev
2742 on older distributions. When this option is enabled
2743 very new udev will not work anymore. When this option
2744 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2745 in older udev will not work anymore.
2746 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2747 the kernel configuration.
2749 sysrq_always_enabled
2750 [KNL]
2751 Ignore sysrq setting - this boot parameter will
2752 neutralize any effect of /proc/sys/kernel/sysrq.
2753 Useful for debugging.
2755 tdfx= [HW,DRM]
2757 test_suspend= [SUSPEND]
2758 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2759 standby suspend) as the system sleep state to briefly
2760 enter during system startup. The system is woken from
2761 this state using a wakeup-capable RTC alarm.
2763 thash_entries= [KNL,NET]
2764 Set number of hash buckets for TCP connection
2766 thermal.act= [HW,ACPI]
2767 -1: disable all active trip points in all thermal zones
2768 <degrees C>: override all lowest active trip points
2770 thermal.crt= [HW,ACPI]
2771 -1: disable all critical trip points in all thermal zones
2772 <degrees C>: override all critical trip points
2774 thermal.nocrt= [HW,ACPI]
2775 Set to disable actions on ACPI thermal zone
2776 critical and hot trip points.
2778 thermal.off= [HW,ACPI]
2779 1: disable ACPI thermal control
2781 thermal.psv= [HW,ACPI]
2782 -1: disable all passive trip points
2783 <degrees C>: override all passive trip points to this
2784 value
2786 thermal.tzp= [HW,ACPI]
2787 Specify global default ACPI thermal zone polling rate
2788 <deci-seconds>: poll all this frequency
2789 0: no polling (default)
2791 threadirqs [KNL]
2792 Force threading of all interrupt handlers except those
2793 marked explicitly IRQF_NO_THREAD.
2795 topology= [S390]
2796 Format: {off | on}
2797 Specify if the kernel should make use of the cpu
2798 topology information if the hardware supports this.
2799 The scheduler will make use of this information and
2800 e.g. base its process migration decisions on it.
2801 Default is on.
2803 tp720= [HW,PS2]
2805 tpm_suspend_pcr=[HW,TPM]
2806 Format: integer pcr id
2807 Specify that at suspend time, the tpm driver
2808 should extend the specified pcr with zeros,
2809 as a workaround for some chips which fail to
2810 flush the last written pcr on TPM_SaveState.
2811 This will guarantee that all the other pcrs
2812 are saved.
2814 trace_buf_size=nn[KMG]
2815 [FTRACE] will set tracing buffer size.
2817 trace_event=[event-list]
2818 [FTRACE] Set and start specified trace events in order
2819 to facilitate early boot debugging.
2820 See also Documentation/trace/events.txt
2822 transparent_hugepage=
2823 [KNL]
2824 Format: [always|madvise|never]
2825 Can be used to control the default behavior of the system
2826 with respect to transparent hugepages.
2827 See Documentation/vm/transhuge.txt for more details.
2829 tsc= Disable clocksource stability checks for TSC.
2830 Format: <string>
2831 [x86] reliable: mark tsc clocksource as reliable, this
2832 disables clocksource verification at runtime, as well
2833 as the stability checks done at bootup. Used to enable
2834 high-resolution timer mode on older hardware, and in
2835 virtualized environment.
2836 [x86] noirqtime: Do not use TSC to do irq accounting.
2837 Used to run time disable IRQ_TIME_ACCOUNTING on any
2838 platforms where RDTSC is slow and this accounting
2839 can add overhead.
2841 turbografx.map[2|3]= [HW,JOY]
2842 TurboGraFX parallel port interface
2843 Format:
2844 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2845 See also Documentation/input/joystick-parport.txt
2847 udbg-immortal [PPC] When debugging early kernel crashes that
2848 happen after console_init() and before a proper
2849 console driver takes over, this boot options might
2850 help "seeing" what's going on.
2852 uhash_entries= [KNL,NET]
2853 Set number of hash buckets for UDP/UDP-Lite connections
2855 uhci-hcd.ignore_oc=
2856 [USB] Ignore overcurrent events (default N).
2857 Some badly-designed motherboards generate lots of
2858 bogus events, for ports that aren't wired to
2859 anything. Set this parameter to avoid log spamming.
2860 Note that genuine overcurrent events won't be
2861 reported either.
2863 unknown_nmi_panic
2864 [X86] Cause panic on unknown NMI.
2866 usbcore.authorized_default=
2867 [USB] Default USB device authorization:
2868 (default -1 = authorized except for wireless USB,
2869 0 = not authorized, 1 = authorized)
2871 usbcore.autosuspend=
2872 [USB] The autosuspend time delay (in seconds) used
2873 for newly-detected USB devices (default 2). This
2874 is the time required before an idle device will be
2875 autosuspended. Devices for which the delay is set
2876 to a negative value won't be autosuspended at all.
2878 usbcore.usbfs_snoop=
2879 [USB] Set to log all usbfs traffic (default 0 = off).
2881 usbcore.blinkenlights=
2882 [USB] Set to cycle leds on hubs (default 0 = off).
2884 usbcore.old_scheme_first=
2885 [USB] Start with the old device initialization
2886 scheme (default 0 = off).
2888 usbcore.usbfs_memory_mb=
2889 [USB] Memory limit (in MB) for buffers allocated by
2890 usbfs (default = 16, 0 = max = 2047).
2892 usbcore.use_both_schemes=
2893 [USB] Try the other device initialization scheme
2894 if the first one fails (default 1 = enabled).
2896 usbcore.initial_descriptor_timeout=
2897 [USB] Specifies timeout for the initial 64-byte
2898 USB_REQ_GET_DESCRIPTOR request in milliseconds
2899 (default 5000 = 5.0 seconds).
2901 usbhid.mousepoll=
2902 [USBHID] The interval which mice are to be polled at.
2904 usb-storage.delay_use=
2905 [UMS] The delay in seconds before a new device is
2906 scanned for Logical Units (default 5).
2908 usb-storage.quirks=
2909 [UMS] A list of quirks entries to supplement or
2910 override the built-in unusual_devs list. List
2911 entries are separated by commas. Each entry has
2912 the form VID:PID:Flags where VID and PID are Vendor
2913 and Product ID values (4-digit hex numbers) and
2914 Flags is a set of characters, each corresponding
2915 to a common usb-storage quirk flag as follows:
2916 a = SANE_SENSE (collect more than 18 bytes
2917 of sense data);
2918 b = BAD_SENSE (don't collect more than 18
2919 bytes of sense data);
2920 c = FIX_CAPACITY (decrease the reported
2921 device capacity by one sector);
2922 d = NO_READ_DISC_INFO (don't use
2923 READ_DISC_INFO command);
2924 e = NO_READ_CAPACITY_16 (don't use
2925 READ_CAPACITY_16 command);
2926 h = CAPACITY_HEURISTICS (decrease the
2927 reported device capacity by one
2928 sector if the number is odd);
2929 i = IGNORE_DEVICE (don't bind to this
2930 device);
2931 l = NOT_LOCKABLE (don't try to lock and
2932 unlock ejectable media);
2933 m = MAX_SECTORS_64 (don't transfer more
2934 than 64 sectors = 32 KB at a time);
2935 n = INITIAL_READ10 (force a retry of the
2936 initial READ(10) command);
2937 o = CAPACITY_OK (accept the capacity
2938 reported by the device);
2939 p = WRITE_CACHE (the device cache is ON
2940 by default);
2941 r = IGNORE_RESIDUE (the device reports
2942 bogus residue values);
2943 s = SINGLE_LUN (the device has only one
2944 Logical Unit);
2945 w = NO_WP_DETECT (don't test whether the
2946 medium is write-protected).
2947 Example: quirks=0419:aaf5:rl,0421:0433:rc
2949 user_debug= [KNL,ARM]
2950 Format: <int>
2951 See arch/arm/Kconfig.debug help text.
2952 1 - undefined instruction events
2953 2 - system calls
2954 4 - invalid data aborts
2955 8 - SIGSEGV faults
2956 16 - SIGBUS faults
2957 Example: user_debug=31
2959 userpte=
2960 [X86] Flags controlling user PTE allocations.
2962 nohigh = do not allocate PTE pages in
2963 HIGHMEM regardless of setting
2964 of CONFIG_HIGHPTE.
2966 vdso= [X86,SH]
2967 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2968 vdso=1: enable VDSO (default)
2969 vdso=0: disable VDSO mapping
2971 vdso32= [X86]
2972 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2973 vdso32=1: enable 32-bit VDSO (default)
2974 vdso32=0: disable 32-bit VDSO mapping
2976 vector= [IA-64,SMP]
2977 vector=percpu: enable percpu vector domain
2979 video= [FB] Frame buffer configuration
2980 See Documentation/fb/modedb.txt.
2982 virtio_mmio.device=
2983 [VMMIO] Memory mapped virtio (platform) device.
2985 <size>@<baseaddr>:<irq>[:<id>]
2986 where:
2987 <size> := size (can use standard suffixes
2988 like K, M and G)
2989 <baseaddr> := physical base address
2990 <irq> := interrupt number (as passed to
2991 request_irq())
2992 <id> := (optional) platform device id
2993 example:
2994 virtio_mmio.device=1K@0x100b0000:48:7
2996 Can be used multiple times for multiple devices.
2998 vga= [BOOT,X86-32] Select a particular video mode
2999 See Documentation/x86/boot.txt and
3000 Documentation/svga.txt.
3001 Use vga=ask for menu.
3002 This is actually a boot loader parameter; the value is
3003 passed to the kernel using a special protocol.
3005 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3006 size of <nn>. This can be used to increase the
3007 minimum size (128MB on x86). It can also be used to
3008 decrease the size and leave more room for directly
3009 mapped kernel RAM.
3011 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3012 Format: <command>
3014 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3015 Format: <command>
3017 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3018 Format: <command>
3020 vsyscall= [X86-64]
3021 Controls the behavior of vsyscalls (i.e. calls to
3022 fixed addresses of 0xffffffffff600x00 from legacy
3023 code). Most statically-linked binaries and older
3024 versions of glibc use these calls. Because these
3025 functions are at fixed addresses, they make nice
3026 targets for exploits that can control RIP.
3028 emulate [default] Vsyscalls turn into traps and are
3029 emulated reasonably safely.
3031 native Vsyscalls are native syscall instructions.
3032 This is a little bit faster than trapping
3033 and makes a few dynamic recompilers work
3034 better than they would in emulation mode.
3035 It also makes exploits much easier to write.
3037 none Vsyscalls don't work at all. This makes
3038 them quite hard to use for exploits but
3039 might break your system.
3041 vt.cur_default= [VT] Default cursor shape.
3042 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3043 the parameters of the <Esc>[?A;B;Cc escape sequence;
3044 see VGA-softcursor.txt. Default: 2 = underline.
3046 vt.default_blu= [VT]
3047 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3048 Change the default blue palette of the console.
3049 This is a 16-member array composed of values
3050 ranging from 0-255.
3052 vt.default_grn= [VT]
3053 Format: <green0>,<green1>,<green2>,...,<green15>
3054 Change the default green palette of the console.
3055 This is a 16-member array composed of values
3056 ranging from 0-255.
3058 vt.default_red= [VT]
3059 Format: <red0>,<red1>,<red2>,...,<red15>
3060 Change the default red palette of the console.
3061 This is a 16-member array composed of values
3062 ranging from 0-255.
3064 vt.default_utf8=
3065 [VT]
3066 Format=<0|1>
3067 Set system-wide default UTF-8 mode for all tty's.
3068 Default is 1, i.e. UTF-8 mode is enabled for all
3069 newly opened terminals.
3071 vt.global_cursor_default=
3072 [VT]
3073 Format=<-1|0|1>
3074 Set system-wide default for whether a cursor
3075 is shown on new VTs. Default is -1,
3076 i.e. cursors will be created by default unless
3077 overridden by individual drivers. 0 will hide
3078 cursors, 1 will display them.
3080 watchdog timers [HW,WDT] For information on watchdog timers,
3081 see Documentation/watchdog/watchdog-parameters.txt
3082 or other driver-specific files in the
3083 Documentation/watchdog/ directory.
3085 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3086 default x2apic cluster mode on platforms
3087 supporting x2apic.
3089 x86_mrst_timer= [X86-32,APBT]
3090 Choose timer option for x86 Moorestown MID platform.
3091 Two valid options are apbt timer only and lapic timer
3092 plus one apbt timer for broadcast timer.
3093 x86_mrst_timer=apbt_only | lapic_and_apbt
3095 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3096 xd_geo= See header of drivers/block/xd.c.
3098 xen_emul_unplug= [HW,X86,XEN]
3099 Unplug Xen emulated devices
3100 Format: [unplug0,][unplug1]
3101 ide-disks -- unplug primary master IDE devices
3102 aux-ide-disks -- unplug non-primary-master IDE devices
3103 nics -- unplug network devices
3104 all -- unplug all emulated devices (NICs and IDE disks)
3105 unnecessary -- unplugging emulated devices is
3106 unnecessary even if the host did not respond to
3107 the unplug protocol
3108 never -- do not unplug even if version check succeeds
3110 xirc2ps_cs= [NET,PCMCIA]
3111 Format:
3112 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3114 ______________________________________________________________________
3116 TODO:
3118 Add more DRM drivers.