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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 AVR32 AVR32 architecture is enabled.
44 AX25 Appropriate AX.25 support is enabled.
45 BLACKFIN Blackfin architecture is enabled.
46 DRM Direct Rendering Management support is enabled.
47 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
48 EFI EFI Partitioning (GPT) is enabled
49 EIDE EIDE/ATAPI support is enabled.
50 FB The frame buffer device is enabled.
51 HW Appropriate hardware is enabled.
52 IA-64 IA-64 architecture is enabled.
53 IMA Integrity measurement architecture is enabled.
54 IOSCHED More than one I/O scheduler is enabled.
55 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
56 ISAPNP ISA PnP code is enabled.
57 ISDN Appropriate ISDN support is enabled.
58 JOY Appropriate joystick support is enabled.
59 KMEMTRACE kmemtrace is enabled.
60 LIBATA Libata driver is enabled
61 LP Printer support is enabled.
62 LOOP Loopback device support is enabled.
63 M68k M68k architecture is enabled.
64 These options have more detailed description inside of
65 Documentation/m68k/kernel-options.txt.
66 MCA MCA bus support is enabled.
67 MDA MDA console support is enabled.
68 MOUSE Appropriate mouse support is enabled.
69 MSI Message Signaled Interrupts (PCI).
70 MTD MTD (Memory Technology Device) support is enabled.
71 NET Appropriate network support is enabled.
72 NUMA NUMA support is enabled.
73 GENERIC_TIME The generic timeofday code is enabled.
74 NFS Appropriate NFS support is enabled.
75 OSS OSS sound support is enabled.
76 PV_OPS A paravirtualized kernel is enabled.
77 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
78 PARISC The PA-RISC architecture is enabled.
79 PCI PCI bus support is enabled.
80 PCIE PCI Express support is enabled.
81 PCMCIA The PCMCIA subsystem is enabled.
82 PNP Plug & Play support is enabled.
83 PPC PowerPC architecture is enabled.
84 PPT Parallel port support is enabled.
85 PS2 Appropriate PS/2 support is enabled.
86 RAM RAM disk support is enabled.
87 ROOTPLUG The example Root Plug LSM is enabled.
88 S390 S390 architecture is enabled.
89 SCSI Appropriate SCSI support is enabled.
90 A lot of drivers has their options described inside of
91 Documentation/scsi/.
92 SECURITY Different security models are enabled.
93 SELINUX SELinux support is enabled.
94 SERIAL Serial support is enabled.
95 SH SuperH architecture is enabled.
96 SMP The kernel is an SMP kernel.
97 SPARC Sparc architecture is enabled.
98 SWSUSP Software suspend (hibernation) is enabled.
99 SUSPEND System suspend states are enabled.
100 FTRACE Function tracing enabled.
101 TS Appropriate touchscreen support is enabled.
102 UMS USB Mass Storage support is enabled.
103 USB USB support is enabled.
104 USBHID USB Human Interface Device support is enabled.
105 V4L Video For Linux support is enabled.
106 VGA The VGA console has been enabled.
107 VT Virtual terminal support is enabled.
108 WDT Watchdog support is enabled.
109 XT IBM PC/XT MFM hard disk support is enabled.
110 X86-32 X86-32, aka i386 architecture is enabled.
111 X86-64 X86-64 architecture is enabled.
112 More X86-64 boot options can be found in
113 Documentation/x86/x86_64/boot-options.txt .
114 X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
116 In addition, the following text indicates that the option:
118 BUGS= Relates to possible processor bugs on the said processor.
119 KNL Is a kernel start-up parameter.
120 BOOT Is a boot loader parameter.
122 Parameters denoted with BOOT are actually interpreted by the boot
123 loader, and have no meaning to the kernel directly.
124 Do not modify the syntax of boot loader parameters without extreme
125 need or coordination with <Documentation/x86/boot.txt>.
127 There are also arch-specific kernel-parameters not documented here.
128 See for example <Documentation/x86/x86_64/boot-options.txt>.
130 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
131 a trailing = on the name of any parameter states that that parameter will
132 be entered as an environment variable, whereas its absence indicates that
133 it will appear as a kernel argument readable via /proc/cmdline by programs
134 running once the system is up.
136 The number of kernel parameters is not limited, but the length of the
137 complete command line (parameters including spaces etc.) is limited to
138 a fixed number of characters. This limit depends on the architecture
139 and is between 256 and 4096 characters. It is defined in the file
140 ./include/asm/setup.h as COMMAND_LINE_SIZE.
143 acpi= [HW,ACPI,X86]
144 Advanced Configuration and Power Interface
145 Format: { force | off | ht | strict | noirq | rsdt }
146 force -- enable ACPI if default was off
147 off -- disable ACPI if default was on
148 noirq -- do not use ACPI for IRQ routing
149 ht -- run only enough ACPI to enable Hyper Threading
150 strict -- Be less tolerant of platforms that are not
151 strictly ACPI specification compliant.
152 rsdt -- prefer RSDT over (default) XSDT
154 See also Documentation/power/pm.txt, pci=noacpi
156 acpi_apic_instance= [ACPI, IOAPIC]
157 Format: <int>
158 2: use 2nd APIC table, if available
159 1,0: use 1st APIC table
160 default: 0
162 acpi_backlight= [HW,ACPI]
163 acpi_backlight=vendor
164 acpi_backlight=video
165 If set to vendor, prefer vendor specific driver
166 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
167 of the ACPI video.ko driver.
169 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
170 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
171 Format: <int>
172 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
173 debug output. Bits in debug_layer correspond to a
174 _COMPONENT in an ACPI source file, e.g.,
175 #define _COMPONENT ACPI_PCI_COMPONENT
176 Bits in debug_level correspond to a level in
177 ACPI_DEBUG_PRINT statements, e.g.,
178 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
179 The debug_level mask defaults to "info". See
180 Documentation/acpi/debug.txt for more information about
181 debug layers and levels.
183 Enable processor driver info messages:
184 acpi.debug_layer=0x20000000
185 Enable PCI/PCI interrupt routing info messages:
186 acpi.debug_layer=0x400000
187 Enable AML "Debug" output, i.e., stores to the Debug
188 object while interpreting AML:
189 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
190 Enable all messages related to ACPI hardware:
191 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
193 Some values produce so much output that the system is
194 unusable. The "log_buf_len" parameter may be useful
195 if you need to capture more output.
197 acpi_display_output= [HW,ACPI]
198 acpi_display_output=vendor
199 acpi_display_output=video
200 See above.
202 acpi_irq_balance [HW,ACPI]
203 ACPI will balance active IRQs
204 default in APIC mode
206 acpi_irq_nobalance [HW,ACPI]
207 ACPI will not move active IRQs (default)
208 default in PIC mode
210 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
211 Format: <irq>,<irq>...
213 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
214 use by PCI
215 Format: <irq>,<irq>...
217 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
219 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
220 Format: To spoof as Windows 98: ="Microsoft Windows"
222 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
223 acpi_osi="string1" # add string1 -- only one string
224 acpi_osi="!string2" # remove built-in string2
225 acpi_osi= # disable all strings
227 acpi_pm_good [X86]
228 Override the pmtimer bug detection: force the kernel
229 to assume that this machine's pmtimer latches its value
230 and always returns good values.
232 acpi.power_nocheck= [HW,ACPI]
233 Format: 1/0 enable/disable the check of power state.
234 On some bogus BIOS the _PSC object/_STA object of
235 power resource can't return the correct device power
236 state. In such case it is unneccessary to check its
237 power state again in power transition.
238 1 : disable the power state check
240 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
241 Format: { level | edge | high | low }
243 acpi_serialize [HW,ACPI] force serialization of AML methods
245 acpi_skip_timer_override [HW,ACPI]
246 Recognize and ignore IRQ0/pin2 Interrupt Override.
247 For broken nForce2 BIOS resulting in XT-PIC timer.
249 acpi_sleep= [HW,ACPI] Sleep options
250 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
251 old_ordering, s4_nonvs }
252 See Documentation/power/video.txt for information on
253 s3_bios and s3_mode.
254 s3_beep is for debugging; it makes the PC's speaker beep
255 as soon as the kernel's real-mode entry point is called.
256 s4_nohwsig prevents ACPI hardware signature from being
257 used during resume from hibernation.
258 old_ordering causes the ACPI 1.0 ordering of the _PTS
259 control method, with respect to putting devices into
260 low power states, to be enforced (the ACPI 2.0 ordering
261 of _PTS is used by default).
262 s4_nonvs prevents the kernel from saving/restoring the
263 ACPI NVS memory during hibernation.
265 acpi_use_timer_override [HW,ACPI]
266 Use timer override. For some broken Nvidia NF5 boards
267 that require a timer override, but don't have HPET
269 acpi_enforce_resources= [ACPI]
270 { strict | lax | no }
271 Check for resource conflicts between native drivers
272 and ACPI OperationRegions (SystemIO and SystemMemory
273 only). IO ports and memory declared in ACPI might be
274 used by the ACPI subsystem in arbitrary AML code and
275 can interfere with legacy drivers.
276 strict (default): access to resources claimed by ACPI
277 is denied; legacy drivers trying to access reserved
278 resources will fail to bind to device using them.
279 lax: access to resources claimed by ACPI is allowed;
280 legacy drivers trying to access reserved resources
281 will bind successfully but a warning message is logged.
282 no: ACPI OperationRegions are not marked as reserved,
283 no further checks are performed.
285 ad1848= [HW,OSS]
286 Format: <io>,<irq>,<dma>,<dma2>,<type>
288 add_efi_memmap [EFI; X86] Include EFI memory map in
289 kernel's map of available physical RAM.
291 advansys= [HW,SCSI]
292 See header of drivers/scsi/advansys.c.
294 advwdt= [HW,WDT] Advantech WDT
295 Format: <iostart>,<iostop>
297 aedsp16= [HW,OSS] Audio Excel DSP 16
298 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>
299 See also header of sound/oss/aedsp16.c.
301 agp= [AGP]
302 { off | try_unsupported }
303 off: disable AGP support
304 try_unsupported: try to drive unsupported chipsets
305 (may crash computer or cause data corruption)
307 aha152x= [HW,SCSI]
308 See Documentation/scsi/aha152x.txt.
310 aha1542= [HW,SCSI]
311 Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]
313 aic7xxx= [HW,SCSI]
314 See Documentation/scsi/aic7xxx.txt.
316 aic79xx= [HW,SCSI]
317 See Documentation/scsi/aic79xx.txt.
319 amd_iommu= [HW,X86-84]
320 Pass parameters to the AMD IOMMU driver in the system.
321 Possible values are:
322 isolate - enable device isolation (each device, as far
323 as possible, will get its own protection
324 domain) [default]
325 share - put every device behind one IOMMU into the
326 same protection domain
327 fullflush - enable flushing of IO/TLB entries when
328 they are unmapped. Otherwise they are
329 flushed before they will be reused, which
330 is a lot of faster
332 amd_iommu_size= [HW,X86-64]
333 Define the size of the aperture for the AMD IOMMU
334 driver. Possible values are:
335 '32M', '64M' (default), '128M', '256M', '512M', '1G'
337 amijoy.map= [HW,JOY] Amiga joystick support
338 Map of devices attached to JOY0DAT and JOY1DAT
339 Format: <a>,<b>
340 See also Documentation/kernel/input/joystick.txt
342 analog.map= [HW,JOY] Analog joystick and gamepad support
343 Specifies type or capabilities of an analog joystick
344 connected to one of 16 gameports
345 Format: <type1>,<type2>,..<type16>
347 apc= [HW,SPARC]
348 Power management functions (SPARCstation-4/5 + deriv.)
349 Format: noidle
350 Disable APC CPU standby support. SPARCstation-Fox does
351 not play well with APC CPU idle - disable it if you have
352 APC and your system crashes randomly.
354 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
355 Change the output verbosity whilst booting
356 Format: { quiet (default) | verbose | debug }
357 Change the amount of debugging information output
358 when initialising the APIC and IO-APIC components.
360 apm= [APM] Advanced Power Management
361 See header of arch/x86/kernel/apm_32.c.
363 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
364 Format: <io>,<irq>,<nodeID>
366 ataflop= [HW,M68k]
368 atarimouse= [HW,MOUSE] Atari Mouse
370 atascsi= [HW,SCSI] Atari SCSI
372 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
373 EzKey and similar keyboards
375 atkbd.reset= [HW] Reset keyboard during initialization
377 atkbd.set= [HW] Select keyboard code set
378 Format: <int> (2 = AT (default), 3 = PS/2)
380 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
381 keyboards
383 atkbd.softraw= [HW] Choose between synthetic and real raw mode
384 Format: <bool> (0 = real, 1 = synthetic (default))
386 atkbd.softrepeat= [HW]
387 Use software keyboard repeat
389 autotest [IA64]
391 baycom_epp= [HW,AX25]
392 Format: <io>,<mode>
394 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
395 Format: <io>,<mode>
396 See header of drivers/net/hamradio/baycom_par.c.
398 baycom_ser_fdx= [HW,AX25]
399 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
400 Format: <io>,<irq>,<mode>[,<baud>]
401 See header of drivers/net/hamradio/baycom_ser_fdx.c.
403 baycom_ser_hdx= [HW,AX25]
404 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
405 Format: <io>,<irq>,<mode>
406 See header of drivers/net/hamradio/baycom_ser_hdx.c.
408 boot_delay= Milliseconds to delay each printk during boot.
409 Values larger than 10 seconds (10000) are changed to
410 no delay (0).
411 Format: integer
413 bootmem_debug [KNL] Enable bootmem allocator debug messages.
415 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
416 bttv.radio= Most important insmod options are available as
417 kernel args too.
418 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
419 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
421 BusLogic= [HW,SCSI]
422 See drivers/scsi/BusLogic.c, comment before function
423 BusLogic_ParseDriverOptions().
425 c101= [NET] Moxa C101 synchronous serial card
427 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
428 Sometimes CPU hardware bugs make them report the cache
429 size incorrectly. The kernel will attempt work arounds
430 to fix known problems, but for some CPUs it is not
431 possible to determine what the correct size should be.
432 This option provides an override for these situations.
434 capability.disable=
435 [SECURITY] Disable capabilities. This would normally
436 be used only if an alternative security model is to be
437 configured. Potentially dangerous and should only be
438 used if you are entirely sure of the consequences.
440 ccw_timeout_log [S390]
441 See Documentation/s390/CommonIO for details.
443 cgroup_disable= [KNL] Disable a particular controller
444 Format: {name of the controller(s) to disable}
445 {Currently supported controllers - "memory"}
447 checkreqprot [SELINUX] Set initial checkreqprot flag value.
448 Format: { "0" | "1" }
449 See security/selinux/Kconfig help text.
450 0 -- check protection applied by kernel (includes
451 any implied execute protection).
452 1 -- check protection requested by application.
453 Default value is set via a kernel config option.
454 Value can be changed at runtime via
455 /selinux/checkreqprot.
457 cio_ignore= [S390]
458 See Documentation/s390/CommonIO for details.
460 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
461 [Deprecated]
462 Forces specified clocksource (if available) to be used
463 when calculating gettimeofday(). If specified
464 clocksource is not available, it defaults to PIT.
465 Format: { pit | tsc | cyclone | pmtmr }
467 clocksource= [GENERIC_TIME] Override the default clocksource
468 Format: <string>
469 Override the default clocksource and use the clocksource
470 with the name specified.
471 Some clocksource names to choose from, depending on
472 the platform:
473 [all] jiffies (this is the base, fallback clocksource)
474 [ACPI] acpi_pm
475 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
476 pxa_timer,timer3,32k_counter,timer0_1
477 [AVR32] avr32
478 [X86-32] pit,hpet,tsc,vmi-timer;
479 scx200_hrt on Geode; cyclone on IBM x440
480 [MIPS] MIPS
481 [PARISC] cr16
482 [S390] tod
483 [SH] SuperH
484 [SPARC64] tick
485 [X86-64] hpet,tsc
487 clearcpuid=BITNUM [X86]
488 Disable CPUID feature X for the kernel. See
489 arch/x86/include/asm/cpufeature.h for the valid bit
490 numbers. Note the Linux specific bits are not necessarily
491 stable over kernel options, but the vendor specific
492 ones should be.
493 Also note that user programs calling CPUID directly
494 or using the feature without checking anything
495 will still see it. This just prevents it from
496 being used by the kernel or shown in /proc/cpuinfo.
497 Also note the kernel might malfunction if you disable
498 some critical bits.
500 code_bytes [X86] How many bytes of object code to print
501 in an oops report.
502 Range: 0 - 8192
503 Default: 64
505 com20020= [HW,NET] ARCnet - COM20020 chipset
506 Format:
507 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
509 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
510 Format: <io>[,<irq>]
512 com90xx= [HW,NET]
513 ARCnet - COM90xx chipset (memory-mapped buffers)
514 Format: <io>[,<irq>[,<memstart>]]
516 condev= [HW,S390] console device
517 conmode=
519 console= [KNL] Output console device and options.
521 tty<n> Use the virtual console device <n>.
523 ttyS<n>[,options]
524 ttyUSB0[,options]
525 Use the specified serial port. The options are of
526 the form "bbbbpnf", where "bbbb" is the baud rate,
527 "p" is parity ("n", "o", or "e"), "n" is number of
528 bits, and "f" is flow control ("r" for RTS or
529 omit it). Default is "9600n8".
531 See Documentation/serial-console.txt for more
532 information. See
533 Documentation/networking/netconsole.txt for an
534 alternative.
536 uart[8250],io,<addr>[,options]
537 uart[8250],mmio,<addr>[,options]
538 Start an early, polled-mode console on the 8250/16550
539 UART at the specified I/O port or MMIO address,
540 switching to the matching ttyS device later. The
541 options are the same as for ttyS, above.
543 If the device connected to the port is not a TTY but a braille
544 device, prepend "brl," before the device type, for instance
545 console=brl,ttyS0
546 For now, only VisioBraille is supported.
548 coredump_filter=
549 [KNL] Change the default value for
550 /proc/<pid>/coredump_filter.
551 See also Documentation/filesystems/proc.txt.
553 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
554 Format:
555 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
557 crashkernel=nn[KMG]@ss[KMG]
558 [KNL] Reserve a chunk of physical memory to
559 hold a kernel to switch to with kexec on panic.
561 crashkernel=range1:size1[,range2:size2,...][@offset]
562 [KNL] Same as above, but depends on the memory
563 in the running system. The syntax of range is
564 start-[end] where start and end are both
565 a memory unit (amount[KMG]). See also
566 Documentation/kdump/kdump.txt for a example.
568 cs89x0_dma= [HW,NET]
569 Format: <dma>
571 cs89x0_media= [HW,NET]
572 Format: { rj45 | aui | bnc }
574 dasd= [HW,NET]
575 See header of drivers/s390/block/dasd_devmap.c.
577 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
578 (one device per port)
579 Format: <port#>,<type>
580 See also Documentation/input/joystick-parport.txt
582 debug [KNL] Enable kernel debugging (events log level).
584 debug_locks_verbose=
585 [KNL] verbose self-tests
586 Format=<0|1>
587 Print debugging info while doing the locking API
588 self-tests.
589 We default to 0 (no extra messages), setting it to
590 1 will print _a lot_ more information - normally
591 only useful to kernel developers.
593 debug_objects [KNL] Enable object debugging
595 no_debug_objects
596 [KNL] Disable object debugging
598 debugpat [X86] Enable PAT debugging
600 decnet.addr= [HW,NET]
601 Format: <area>[,<node>]
602 See also Documentation/networking/decnet.txt.
604 default_hugepagesz=
605 [same as hugepagesz=] The size of the default
606 HugeTLB page size. This is the size represented by
607 the legacy /proc/ hugepages APIs, used for SHM, and
608 default size when mounting hugetlbfs filesystems.
609 Defaults to the default architecture's huge page size
610 if not specified.
612 dhash_entries= [KNL]
613 Set number of hash buckets for dentry cache.
615 digi= [HW,SERIAL]
616 IO parameters + enable/disable command.
618 digiepca= [HW,SERIAL]
619 See drivers/char/README.epca and
620 Documentation/serial/digiepca.txt.
622 disable_mtrr_cleanup [X86]
623 The kernel tries to adjust MTRR layout from continuous
624 to discrete, to make X server driver able to add WB
625 entry later. This parameter disables that.
627 disable_mtrr_trim [X86, Intel and AMD only]
628 By default the kernel will trim any uncacheable
629 memory out of your available memory pool based on
630 MTRR settings. This parameter disables that behavior,
631 possibly causing your machine to run very slowly.
633 disable_timer_pin_1 [X86]
634 Disable PIN 1 of APIC timer
635 Can be useful to work around chipset bugs.
637 dmasound= [HW,OSS] Sound subsystem buffers
639 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
640 this option disables the debugging code at boot.
642 dma_debug_entries=<number>
643 This option allows to tune the number of preallocated
644 entries for DMA-API debugging code. One entry is
645 required per DMA-API allocation. Use this if the
646 DMA-API debugging code disables itself because the
647 architectural default is too low.
649 dscc4.setup= [NET]
651 dtc3181e= [HW,SCSI]
653 dynamic_printk Enables pr_debug()/dev_dbg() calls if
654 CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled.
655 These can also be switched on/off via
656 <debugfs>/dynamic_printk/modules
658 earlycon= [KNL] Output early console device and options.
659 uart[8250],io,<addr>[,options]
660 uart[8250],mmio,<addr>[,options]
661 Start an early, polled-mode console on the 8250/16550
662 UART at the specified I/O port or MMIO address.
663 The options are the same as for ttyS, above.
665 earlyprintk= [X86,SH,BLACKFIN]
666 earlyprintk=vga
667 earlyprintk=serial[,ttySn[,baudrate]]
668 earlyprintk=dbgp
670 Append ",keep" to not disable it when the real console
671 takes over.
673 Only vga or serial or usb debug port at a time.
675 Currently only ttyS0 and ttyS1 are supported.
677 Interaction with the standard serial driver is not
678 very good.
680 The VGA output is eventually overwritten by the real
681 console.
683 eata= [HW,SCSI]
685 edd= [EDD]
686 Format: {"off" | "on" | "skip[mbr]"}
688 eisa_irq_edge= [PARISC,HW]
689 See header of drivers/parisc/eisa.c.
691 elanfreq= [X86-32]
692 See comment before function elanfreq_setup() in
693 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
695 elevator= [IOSCHED]
696 Format: {"anticipatory" | "cfq" | "deadline" | "noop"}
697 See Documentation/block/as-iosched.txt and
698 Documentation/block/deadline-iosched.txt for details.
700 elfcorehdr= [IA64,PPC,SH,X86]
701 Specifies physical address of start of kernel core
702 image elf header. Generally kexec loader will
703 pass this option to capture kernel.
704 See Documentation/kdump/kdump.txt for details.
706 enable_mtrr_cleanup [X86]
707 The kernel tries to adjust MTRR layout from continuous
708 to discrete, to make X server driver able to add WB
709 entry later. This parameter enables that.
711 enable_timer_pin_1 [X86]
712 Enable PIN 1 of APIC timer
713 Can be useful to work around chipset bugs
714 (in particular on some ATI chipsets).
715 The kernel tries to set a reasonable default.
717 enforcing [SELINUX] Set initial enforcing status.
718 Format: {"0" | "1"}
719 See security/selinux/Kconfig help text.
720 0 -- permissive (log only, no denials).
721 1 -- enforcing (deny and log).
722 Default value is 0.
723 Value can be changed at runtime via /selinux/enforce.
725 ether= [HW,NET] Ethernet cards parameters
726 This option is obsoleted by the "netdev=" option, which
727 has equivalent usage. See its documentation for details.
729 eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
730 Format: <io>[,<irq>]
732 failslab=
733 fail_page_alloc=
734 fail_make_request=[KNL]
735 General fault injection mechanism.
736 Format: <interval>,<probability>,<space>,<times>
737 See also /Documentation/fault-injection/.
739 fd_mcs= [HW,SCSI]
740 See header of drivers/scsi/fd_mcs.c.
742 fdomain= [HW,SCSI]
743 See header of drivers/scsi/fdomain.c.
745 floppy= [HW]
746 See Documentation/blockdev/floppy.txt.
748 force_pal_cache_flush
749 [IA-64] Avoid check_sal_cache_flush which may hang on
750 buggy SAL_CACHE_FLUSH implementations. Using this
751 parameter will force ia64_sal_cache_flush to call
752 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
754 ftrace=[tracer]
755 [ftrace] will set and start the specified tracer
756 as early as possible in order to facilitate early
757 boot debugging.
759 ftrace_dump_on_oops
760 [ftrace] will dump the trace buffers on oops.
762 gamecon.map[2|3]=
763 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
764 support via parallel port (up to 5 devices per port)
765 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
766 See also Documentation/input/joystick-parport.txt
768 gamma= [HW,DRM]
770 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
771 Format: off | on
772 default: on
774 gdth= [HW,SCSI]
775 See header of drivers/scsi/gdth.c.
777 gpt [EFI] Forces disk with valid GPT signature but
778 invalid Protective MBR to be treated as GPT.
780 gvp11= [HW,SCSI]
782 hashdist= [KNL,NUMA] Large hashes allocated during boot
783 are distributed across NUMA nodes. Defaults on
784 for 64bit NUMA, off otherwise.
785 Format: 0 | 1 (for off | on)
787 hcl= [IA-64] SGI's Hardware Graph compatibility layer
789 hd= [EIDE] (E)IDE hard drive subsystem geometry
790 Format: <cyl>,<head>,<sect>
792 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
793 size of <nn>. This works even on boxes that have no
794 highmem otherwise. This also works to reduce highmem
795 size on bigger boxes.
797 highres= [KNL] Enable/disable high resolution timer mode.
798 Valid parameters: "on", "off"
799 Default: "on"
801 hisax= [HW,ISDN]
802 See Documentation/isdn/README.HiSax.
804 hlt [BUGS=ARM,SH]
806 hpet= [X86-32,HPET] option to control HPET usage
807 Format: { enable (default) | disable | force |
808 verbose }
809 disable: disable HPET and use PIT instead
810 force: allow force enabled of undocumented chips (ICH4,
811 VIA, nVidia)
812 verbose: show contents of HPET registers during setup
814 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
815 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
816 On x86-64 and powerpc, this option can be specified
817 multiple times interleaved with hugepages= to reserve
818 huge pages of different sizes. Valid pages sizes on
819 x86-64 are 2M (when the CPU supports "pse") and 1G
820 (when the CPU supports the "pdpe1gb" cpuinfo flag)
821 Note that 1GB pages can only be allocated at boot time
822 using hugepages= and not freed afterwards.
824 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
825 terminal devices. Valid values: 0..8
826 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
827 If specified, z/VM IUCV HVC accepts connections
828 from listed z/VM user IDs only.
830 i2c_bus= [HW] Override the default board specific I2C bus speed
831 or register an additional I2C bus that is not
832 registered from board initialization code.
833 Format:
834 <bus_id>,<clkrate>
836 i8042.debug [HW] Toggle i8042 debug mode
837 i8042.direct [HW] Put keyboard port into non-translated mode
838 i8042.dumbkbd [HW] Pretend that controller can only read data from
839 keyboard and cannot control its state
840 (Don't attempt to blink the leds)
841 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
842 i8042.nokbd [HW] Don't check/create keyboard port
843 i8042.noloop [HW] Disable the AUX Loopback command while probing
844 for the AUX port
845 i8042.nomux [HW] Don't check presence of an active multiplexing
846 controller
847 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
848 controllers
849 i8042.panicblink=
850 [HW] Frequency with which keyboard LEDs should blink
851 when kernel panics (default is 0.5 sec)
852 i8042.reset [HW] Reset the controller during init and cleanup
853 i8042.unlock [HW] Unlock (ignore) the keylock
855 i810= [HW,DRM]
857 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
858 indicates that the driver is running on unsupported
859 hardware.
860 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
861 does not match list of supported models.
862 i8k.power_status
863 [HW] Report power status in /proc/i8k
864 (disabled by default)
865 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
866 capability is set.
868 ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
869 See Documentation/mca.txt.
871 icn= [HW,ISDN]
872 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
874 ide-core.nodma= [HW] (E)IDE subsystem
875 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
876 .vlb_clock .pci_clock .noflush .noprobe .nowerr .cdrom
877 .chs .ignore_cable are additional options
878 See Documentation/ide/ide.txt.
880 idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
881 See Documentation/ide/ide.txt.
883 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
884 Claim all unknown PCI IDE storage controllers.
886 idle= [X86]
887 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
888 Poll forces a polling idle loop that can slightly
889 improve the performance of waking up a idle CPU, but
890 will use a lot of power and make the system run hot.
891 Not recommended.
892 idle=mwait: On systems which support MONITOR/MWAIT but
893 the kernel chose to not use it because it doesn't save
894 as much power as a normal idle loop, use the
895 MONITOR/MWAIT idle loop anyways. Performance should be
896 the same as idle=poll.
897 idle=halt: Halt is forced to be used for CPU idle.
898 In such case C2/C3 won't be used again.
899 idle=nomwait: Disable mwait for CPU C-states
901 ignore_loglevel [KNL]
902 Ignore loglevel setting - this will print /all/
903 kernel messages to the console. Useful for debugging.
905 ihash_entries= [KNL]
906 Set number of hash buckets for inode cache.
908 ima_audit= [IMA]
909 Format: { "0" | "1" }
910 0 -- integrity auditing messages. (Default)
911 1 -- enable informational integrity auditing messages.
913 ima_hash= [IMA]
914 Formt: { "sha1" | "md5" }
915 default: "sha1"
917 in2000= [HW,SCSI]
918 See header of drivers/scsi/in2000.c.
920 init= [KNL]
921 Format: <full_path>
922 Run specified binary instead of /sbin/init as init
923 process.
925 initcall_debug [KNL] Trace initcalls as they are executed. Useful
926 for working out where the kernel is dying during
927 startup.
929 initrd= [BOOT] Specify the location of the initial ramdisk
931 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
932 Format: <irq>
934 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
935 on
936 Enable intel iommu driver.
937 off
938 Disable intel iommu driver.
939 igfx_off [Default Off]
940 By default, gfx is mapped as normal device. If a gfx
941 device has a dedicated DMAR unit, the DMAR unit is
942 bypassed by not enabling DMAR with this option. In
943 this case, gfx device will use physical address for
944 DMA.
945 forcedac [x86_64]
946 With this option iommu will not optimize to look
947 for io virtual address below 32 bit forcing dual
948 address cycle on pci bus for cards supporting greater
949 than 32 bit addressing. The default is to look
950 for translation below 32 bit and if not available
951 then look in the higher range.
952 strict [Default Off]
953 With this option on every unmap_single operation will
954 result in a hardware IOTLB flush operation as opposed
955 to batching them for performance.
957 inttest= [IA64]
959 iomem= Disable strict checking of access to MMIO memory
960 strict regions from userspace.
961 relaxed
963 iommu= [x86]
964 off
965 force
966 noforce
967 biomerge
968 panic
969 nopanic
970 merge
971 nomerge
972 forcesac
973 soft
975 io7= [HW] IO7 for Marvel based alpha systems
976 See comment before marvel_specify_io7 in
977 arch/alpha/kernel/core_marvel.c.
979 io_delay= [X86] I/O delay method
980 0x80
981 Standard port 0x80 based delay
982 0xed
983 Alternate port 0xed based delay (needed on some systems)
984 udelay
985 Simple two microseconds delay
986 none
987 No delay
989 ip= [IP_PNP]
990 See Documentation/filesystems/nfsroot.txt.
992 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
993 See comment before ip2_setup() in
994 drivers/char/ip2/ip2base.c.
996 ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
997 See header of drivers/scsi/ips.c.
999 irqfixup [HW]
1000 When an interrupt is not handled search all handlers
1001 for it. Intended to get systems with badly broken
1002 firmware running.
1004 irqpoll [HW]
1005 When an interrupt is not handled search all handlers
1006 for it. Also check all handlers each timer
1007 interrupt. Intended to get systems with badly broken
1008 firmware running.
1010 isapnp= [ISAPNP]
1011 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1013 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1014 Format:
1015 <cpu number>,...,<cpu number>
1016 or
1017 <cpu number>-<cpu number>
1018 (must be a positive range in ascending order)
1019 or a mixture
1020 <cpu number>,...,<cpu number>-<cpu number>
1022 This option can be used to specify one or more CPUs
1023 to isolate from the general SMP balancing and scheduling
1024 algorithms. You can move a process onto or off an
1025 "isolated" CPU via the CPU affinity syscalls or cpuset.
1026 <cpu number> begins at 0 and the maximum value is
1027 "number of CPUs in system - 1".
1029 This option is the preferred way to isolate CPUs. The
1030 alternative -- manually setting the CPU mask of all
1031 tasks in the system -- can cause problems and
1032 suboptimal load balancer performance.
1034 iucv= [HW,NET]
1036 js= [HW,JOY] Analog joystick
1037 See Documentation/input/joystick.txt.
1039 keepinitrd [HW,ARM]
1041 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1042 specifies the amount of memory usable by the kernel
1043 for non-movable allocations. The requested amount is
1044 spread evenly throughout all nodes in the system. The
1045 remaining memory in each node is used for Movable
1046 pages. In the event, a node is too small to have both
1047 kernelcore and Movable pages, kernelcore pages will
1048 take priority and other nodes will have a larger number
1049 of kernelcore pages. The Movable zone is used for the
1050 allocation of pages that may be reclaimed or moved
1051 by the page migration subsystem. This means that
1052 HugeTLB pages may not be allocated from this zone.
1053 Note that allocations like PTEs-from-HighMem still
1054 use the HighMem zone if it exists, and the Normal
1055 zone if it does not.
1057 kmemtrace.enable= [KNL,KMEMTRACE] Format: { yes | no }
1058 Controls whether kmemtrace is enabled
1059 at boot-time.
1061 kmemtrace.subbufs=n [KNL,KMEMTRACE] Overrides the number of
1062 subbufs kmemtrace's relay channel has. Set this
1063 higher than default (KMEMTRACE_N_SUBBUFS in code) if
1064 you experience buffer overruns.
1066 kgdboc= [HW] kgdb over consoles.
1067 Requires a tty driver that supports console polling.
1068 (only serial suported for now)
1069 Format: <serial_device>[,baud]
1071 kmac= [MIPS] korina ethernet MAC address.
1072 Configure the RouterBoard 532 series on-chip
1073 Ethernet adapter MAC address.
1075 kstack=N [X86] Print N words from the kernel stack
1076 in oops dumps.
1078 l2cr= [PPC]
1080 l3cr= [PPC]
1082 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1083 disabled it.
1085 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1086 in C2 power state.
1088 libata.dma= [LIBATA] DMA control
1089 libata.dma=0 Disable all PATA and SATA DMA
1090 libata.dma=1 PATA and SATA Disk DMA only
1091 libata.dma=2 ATAPI (CDROM) DMA only
1092 libata.dma=4 Compact Flash DMA only
1093 Combinations also work, so libata.dma=3 enables DMA
1094 for disks and CDROMs, but not CFs.
1096 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1097 when set.
1098 Format: <int>
1100 libata.force= [LIBATA] Force configurations. The format is comma
1101 separated list of "[ID:]VAL" where ID is
1102 PORT[:DEVICE]. PORT and DEVICE are decimal numbers
1103 matching port, link or device. Basically, it matches
1104 the ATA ID string printed on console by libata. If
1105 the whole ID part is omitted, the last PORT and DEVICE
1106 values are used. If ID hasn't been specified yet, the
1107 configuration applies to all ports, links and devices.
1109 If only DEVICE is omitted, the parameter applies to
1110 the port and all links and devices behind it. DEVICE
1111 number of 0 either selects the first device or the
1112 first fan-out link behind PMP device. It does not
1113 select the host link. DEVICE number of 15 selects the
1114 host link and device attached to it.
1116 The VAL specifies the configuration to force. As long
1117 as there's no ambiguity shortcut notation is allowed.
1118 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1119 The following configurations can be forced.
1121 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1122 Any ID with matching PORT is used.
1124 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1126 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1127 udma[/][16,25,33,44,66,100,133] notation is also
1128 allowed.
1130 * [no]ncq: Turn on or off NCQ.
1132 * nohrst, nosrst, norst: suppress hard, soft
1133 and both resets.
1135 If there are multiple matching configurations changing
1136 the same attribute, the last one is used.
1138 lmb=debug [KNL] Enable lmb debug messages.
1140 load_ramdisk= [RAM] List of ramdisks to load from floppy
1141 See Documentation/blockdev/ramdisk.txt.
1143 lockd.nlm_grace_period=P [NFS] Assign grace period.
1144 Format: <integer>
1146 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1147 Format: <integer>
1149 lockd.nlm_timeout=T [NFS] Assign timeout value.
1150 Format: <integer>
1152 lockd.nlm_udpport=M [NFS] Assign UDP port.
1153 Format: <integer>
1155 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1156 Format: <irq>
1158 loglevel= All Kernel Messages with a loglevel smaller than the
1159 console loglevel will be printed to the console. It can
1160 also be changed with klogd or other programs. The
1161 loglevels are defined as follows:
1163 0 (KERN_EMERG) system is unusable
1164 1 (KERN_ALERT) action must be taken immediately
1165 2 (KERN_CRIT) critical conditions
1166 3 (KERN_ERR) error conditions
1167 4 (KERN_WARNING) warning conditions
1168 5 (KERN_NOTICE) normal but significant condition
1169 6 (KERN_INFO) informational
1170 7 (KERN_DEBUG) debug-level messages
1172 log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1173 Format: { n | nk | nM }
1174 n must be a power of two. The default size
1175 is set in the kernel config file.
1177 logo.nologo [FB] Disables display of the built-in Linux logo.
1178 This may be used to provide more screen space for
1179 kernel log messages and is useful when debugging
1180 kernel boot problems.
1182 lp=0 [LP] Specify parallel ports to use, e.g,
1183 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1184 lp=reset first parallel port). 'lp=0' disables the
1185 lp=auto printer driver. 'lp=reset' (which can be
1186 specified in addition to the ports) causes
1187 attached printers to be reset. Using
1188 lp=port1,port2,... specifies the parallel ports
1189 to associate lp devices with, starting with
1190 lp0. A port specification may be 'none' to skip
1191 that lp device, or a parport name such as
1192 'parport0'. Specifying 'lp=auto' instead of a
1193 port specification list means that device IDs
1194 from each port should be examined, to see if
1195 an IEEE 1284-compliant printer is attached; if
1196 so, the driver will manage that printer.
1197 See also header of drivers/char/lp.c.
1199 lpj=n [KNL]
1200 Sets loops_per_jiffy to given constant, thus avoiding
1201 time-consuming boot-time autodetection (up to 250 ms per
1202 CPU). 0 enables autodetection (default). To determine
1203 the correct value for your kernel, boot with normal
1204 autodetection and see what value is printed. Note that
1205 on SMP systems the preset will be applied to all CPUs,
1206 which is likely to cause problems if your CPUs need
1207 significantly divergent settings. An incorrect value
1208 will cause delays in the kernel to be wrong, leading to
1209 unpredictable I/O errors and other breakage. Although
1210 unlikely, in the extreme case this might damage your
1211 hardware.
1213 ltpc= [NET]
1214 Format: <io>,<irq>,<dma>
1216 mac5380= [HW,SCSI] Format:
1217 <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
1219 machvec= [IA64] Force the use of a particular machine-vector
1220 (machvec) in a generic kernel.
1221 Example: machvec=hpzx1_swiotlb
1223 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1224 than or equal to this physical address is ignored.
1226 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1227 should make use of. maxcpus=n : n >= 0 limits the
1228 kernel to using 'n' processors. n=0 is a special case,
1229 it is equivalent to "nosmp", which also disables
1230 the IO APIC.
1232 max_loop= [LOOP] Maximum number of loopback devices that can
1233 be mounted
1234 Format: <1-256>
1236 max_luns= [SCSI] Maximum number of LUNs to probe.
1237 Should be between 1 and 2^32-1.
1239 max_report_luns=
1240 [SCSI] Maximum number of LUNs received.
1241 Should be between 1 and 16384.
1243 mcatest= [IA-64]
1245 mce [X86-32] Machine Check Exception
1247 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1249 md= [HW] RAID subsystems devices and level
1250 See Documentation/md.txt.
1252 mdacon= [MDA]
1253 Format: <first>,<last>
1254 Specifies range of consoles to be captured by the MDA.
1256 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1257 Amount of memory to be used when the kernel is not able
1258 to see the whole system memory or for test.
1259 [X86-32] Use together with memmap= to avoid physical
1260 address space collisions. Without memmap= PCI devices
1261 could be placed at addresses belonging to unused RAM.
1263 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1264 memory.
1266 memchunk=nn[KMG]
1267 [KNL,SH] Allow user to override the default size for
1268 per-device physically contiguous DMA buffers.
1270 memmap=exactmap [KNL,X86] Enable setting of an exact
1271 E820 memory map, as specified by the user.
1272 Such memmap=exactmap lines can be constructed based on
1273 BIOS output or other requirements. See the memmap=nn@ss
1274 option description.
1276 memmap=nn[KMG]@ss[KMG]
1277 [KNL] Force usage of a specific region of memory
1278 Region of memory to be used, from ss to ss+nn.
1280 memmap=nn[KMG]#ss[KMG]
1281 [KNL,ACPI] Mark specific memory as ACPI data.
1282 Region of memory to be used, from ss to ss+nn.
1284 memmap=nn[KMG]$ss[KMG]
1285 [KNL,ACPI] Mark specific memory as reserved.
1286 Region of memory to be used, from ss to ss+nn.
1287 Example: Exclude memory from 0x18690000-0x1869ffff
1288 memmap=64K$0x18690000
1289 or
1290 memmap=0x10000$0x18690000
1292 memory_corruption_check=0/1 [X86]
1293 Some BIOSes seem to corrupt the first 64k of
1294 memory when doing things like suspend/resume.
1295 Setting this option will scan the memory
1296 looking for corruption. Enabling this will
1297 both detect corruption and prevent the kernel
1298 from using the memory being corrupted.
1299 However, its intended as a diagnostic tool; if
1300 repeatable BIOS-originated corruption always
1301 affects the same memory, you can use memmap=
1302 to prevent the kernel from using that memory.
1304 memory_corruption_check_size=size [X86]
1305 By default it checks for corruption in the low
1306 64k, making this memory unavailable for normal
1307 use. Use this parameter to scan for
1308 corruption in more or less memory.
1310 memory_corruption_check_period=seconds [X86]
1311 By default it checks for corruption every 60
1312 seconds. Use this parameter to check at some
1313 other rate. 0 disables periodic checking.
1315 memtest= [KNL,X86] Enable memtest
1316 Format: <integer>
1317 default : 0 <disable>
1318 Specifies the number of memtest passes to be
1319 performed. Each pass selects another test
1320 pattern from a given set of patterns. Memtest
1321 fills the memory with this pattern, validates
1322 memory contents and reserves bad memory
1323 regions that are detected.
1325 meye.*= [HW] Set MotionEye Camera parameters
1326 See Documentation/video4linux/meye.txt.
1328 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1329 Multi-Function General Purpose Timers on AMD Geode
1330 platforms.
1332 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1333 the BIOS has incorrectly applied a workaround. TinyBIOS
1334 version 0.98 is known to be affected, 0.99 fixes the
1335 problem by letting the user disable the workaround.
1337 mga= [HW,DRM]
1339 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1340 physical address is ignored.
1342 mminit_loglevel=
1343 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1344 parameter allows control of the logging verbosity for
1345 the additional memory initialisation checks. A value
1346 of 0 disables mminit logging and a level of 4 will
1347 log everything. Information is printed at KERN_DEBUG
1348 so loglevel=8 may also need to be specified.
1350 mousedev.tap_time=
1351 [MOUSE] Maximum time between finger touching and
1352 leaving touchpad surface for touch to be considered
1353 a tap and be reported as a left button click (for
1354 touchpads working in absolute mode only).
1355 Format: <msecs>
1356 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1357 reporting absolute coordinates, such as tablets
1358 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1359 reporting absolute coordinates, such as tablets
1361 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1362 is similar to kernelcore except it specifies the
1363 amount of memory used for migratable allocations.
1364 If both kernelcore and movablecore is specified,
1365 then kernelcore will be at *least* the specified
1366 value but may be more. If movablecore on its own
1367 is specified, the administrator must be careful
1368 that the amount of memory usable for all allocations
1369 is not too small.
1371 mpu401= [HW,OSS]
1372 Format: <io>,<irq>
1374 MTD_Partition= [MTD]
1375 Format: <name>,<region-number>,<size>,<offset>
1377 MTD_Region= [MTD] Format:
1378 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1380 mtdparts= [MTD]
1381 See drivers/mtd/cmdlinepart.c.
1383 mtdset= [ARM]
1384 ARM/S3C2412 JIVE boot control
1386 See arch/arm/mach-s3c2412/mach-jive.c
1388 mtouchusb.raw_coordinates=
1389 [HW] Make the MicroTouch USB driver use raw coordinates
1390 ('y', default) or cooked coordinates ('n')
1392 mtrr_chunk_size=nn[KMG] [X86]
1393 used for mtrr cleanup. It is largest continous chunk
1394 that could hold holes aka. UC entries.
1396 mtrr_gran_size=nn[KMG] [X86]
1397 Used for mtrr cleanup. It is granularity of mtrr block.
1398 Default is 1.
1399 Large value could prevent small alignment from
1400 using up MTRRs.
1402 mtrr_spare_reg_nr=n [X86]
1403 Format: <integer>
1404 Range: 0,7 : spare reg number
1405 Default : 1
1406 Used for mtrr cleanup. It is spare mtrr entries number.
1407 Set to 2 or more if your graphical card needs more.
1409 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1411 NCR_D700= [HW,SCSI]
1412 See header of drivers/scsi/NCR_D700.c.
1414 ncr5380= [HW,SCSI]
1416 ncr53c400= [HW,SCSI]
1418 ncr53c400a= [HW,SCSI]
1420 ncr53c406a= [HW,SCSI]
1422 ncr53c8xx= [HW,SCSI]
1424 netdev= [NET] Network devices parameters
1425 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1426 Note that mem_start is often overloaded to mean
1427 something different and driver-specific.
1428 This usage is only documented in each driver source
1429 file if at all.
1431 nf_conntrack.acct=
1432 [NETFILTER] Enable connection tracking flow accounting
1433 0 to disable accounting
1434 1 to enable accounting
1435 Default value depends on CONFIG_NF_CT_ACCT that is
1436 going to be removed in 2.6.29.
1438 nfsaddrs= [NFS]
1439 See Documentation/filesystems/nfsroot.txt.
1441 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1442 See Documentation/filesystems/nfsroot.txt.
1444 nfs.callback_tcpport=
1445 [NFS] set the TCP port on which the NFSv4 callback
1446 channel should listen.
1448 nfs.idmap_cache_timeout=
1449 [NFS] set the maximum lifetime for idmapper cache
1450 entries.
1452 nfs.enable_ino64=
1453 [NFS] enable 64-bit inode numbers.
1454 If zero, the NFS client will fake up a 32-bit inode
1455 number for the readdir() and stat() syscalls instead
1456 of returning the full 64-bit number.
1457 The default is to return 64-bit inode numbers.
1459 nmi_debug= [KNL,AVR32] Specify one or more actions to take
1460 when a NMI is triggered.
1461 Format: [state][,regs][,debounce][,die]
1463 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1464 Format: [panic,][num]
1465 Valid num: 0,1,2
1466 0 - turn nmi_watchdog off
1467 1 - use the IO-APIC timer for the NMI watchdog
1468 2 - use the local APIC for the NMI watchdog using
1469 a performance counter. Note: This will use one
1470 performance counter and the local APIC's performance
1471 vector.
1472 When panic is specified, panic when an NMI watchdog
1473 timeout occurs.
1474 This is useful when you use a panic=... timeout and
1475 need the box quickly up again.
1476 Instead of 1 and 2 it is possible to use the following
1477 symbolic names: lapic and ioapic
1478 Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1480 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1481 emulation library even if a 387 maths coprocessor
1482 is present.
1484 no_console_suspend
1485 [HW] Never suspend the console
1486 Disable suspending of consoles during suspend and
1487 hibernate operations. Once disabled, debugging
1488 messages can reach various consoles while the rest
1489 of the system is being put to sleep (ie, while
1490 debugging driver suspend/resume hooks). This may
1491 not work reliably with all consoles, but is known
1492 to work with serial and VGA consoles.
1494 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1495 caches in the slab allocator. Saves per-node memory,
1496 but will impact performance.
1498 noalign [KNL,ARM]
1500 noapic [SMP,APIC] Tells the kernel to not make use of any
1501 IOAPICs that may be present in the system.
1503 nobats [PPC] Do not use BATs for mapping kernel lowmem
1504 on "Classic" PPC cores.
1506 nocache [ARM]
1508 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1510 nodelayacct [KNL] Disable per-task delay accounting
1512 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1514 nodsp [SH] Disable hardware DSP at boot time.
1516 noefi [X86] Disable EFI runtime services support.
1518 noexec [IA-64]
1520 noexec [X86]
1521 On X86-32 available only on PAE configured kernels.
1522 noexec=on: enable non-executable mappings (default)
1523 noexec=off: disable non-executable mappings
1525 noexec32 [X86-64]
1526 This affects only 32-bit executables.
1527 noexec32=on: enable non-executable mappings (default)
1528 read doesn't imply executable mappings
1529 noexec32=off: disable non-executable mappings
1530 read implies executable mappings
1532 nofpu [SH] Disable hardware FPU at boot time.
1534 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1535 register save and restore. The kernel will only save
1536 legacy floating-point registers on task switch.
1538 noxsave [BUGS=X86] Disables x86 extended register state save
1539 and restore using xsave. The kernel will fallback to
1540 enabling legacy floating-point and sse state.
1542 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1543 wfi(ARM) instruction doesn't work correctly and not to
1544 use it. This is also useful when using JTAG debugger.
1546 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1547 instruction doesn't work correctly and not to
1548 use it.
1550 no_file_caps Tells the kernel not to honor file capabilities. The
1551 only way then for a file to be executed with privilege
1552 is to be setuid root or executed by root.
1554 nohalt [IA-64] Tells the kernel not to use the power saving
1555 function PAL_HALT_LIGHT when idle. This increases
1556 power-consumption. On the positive side, it reduces
1557 interrupt wake-up latency, which may improve performance
1558 in certain environments such as networked servers or
1559 real-time systems.
1561 nohz= [KNL] Boottime enable/disable dynamic ticks
1562 Valid arguments: on, off
1563 Default: on
1565 noiotrap [SH] Disables trapped I/O port accesses.
1567 noirqdebug [X86-32] Disables the code which attempts to detect and
1568 disable unhandled interrupt sources.
1570 no_timer_check [X86,APIC] Disables the code which tests for
1571 broken timer IRQ sources.
1573 noisapnp [ISAPNP] Disables ISA PnP code.
1575 noinitrd [RAM] Tells the kernel not to load any configured
1576 initial RAM disk.
1578 nointroute [IA-64]
1580 nojitter [IA64] Disables jitter checking for ITC timers.
1582 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1584 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1586 noltlbs [PPC] Do not use large page/tlb entries for kernel
1587 lowmem mapping on PPC40x.
1589 nomca [IA-64] Disable machine check abort handling
1591 nomce [X86-32] Machine Check Exception
1593 nomfgpt [X86-32] Disable Multi-Function General Purpose
1594 Timer usage (for AMD Geode machines).
1596 norandmaps Don't use address space randomization. Equivalent to
1597 echo 0 > /proc/sys/kernel/randomize_va_space
1599 noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops
1601 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1602 with UP alternatives
1604 noresidual [PPC] Don't use residual data on PReP machines.
1606 noresume [SWSUSP] Disables resume and restores original swap
1607 space.
1609 no-scroll [VGA] Disables scrollback.
1610 This is required for the Braillex ib80-piezo Braille
1611 reader made by F.H. Papenmeier (Germany).
1613 nosbagart [IA-64]
1615 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1617 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1618 and disable the IO APIC. legacy for "maxcpus=0".
1620 nosoftlockup [KNL] Disable the soft-lockup detector.
1622 noswapaccount [KNL] Disable accounting of swap in memory resource
1623 controller. (See Documentation/cgroups/memory.txt)
1625 nosync [HW,M68K] Disables sync negotiation for all devices.
1627 notsc [BUGS=X86-32] Disable Time Stamp Counter
1629 nousb [USB] Disable the USB subsystem
1631 nowb [ARM]
1633 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1635 nptcg= [IA64] Override max number of concurrent global TLB
1636 purges which is reported from either PAL_VM_SUMMARY or
1637 SAL PALO.
1639 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1641 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1642 one of ['zone', 'node', 'default'] can be specified
1643 This can be set from sysctl after boot.
1644 See Documentation/sysctl/vm.txt for details.
1646 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1647 See Documentation/debugging-via-ohci1394.txt for more
1648 info.
1650 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1651 Rather than timing out after 20 ms if an EC
1652 command is not properly ACKed, override the length
1653 of the timeout. We have interrupts disabled while
1654 waiting for the ACK, so if this is set too high
1655 interrupts *may* be lost!
1657 opl3= [HW,OSS]
1658 Format: <io>
1660 oprofile.timer= [HW]
1661 Use timer interrupt instead of performance counters
1663 osst= [HW,SCSI] SCSI Tape Driver
1664 Format: <buffer_size>,<write_threshold>
1665 See also Documentation/scsi/st.txt.
1667 panic= [KNL] Kernel behaviour on panic
1668 Format: <timeout>
1670 parkbd.port= [HW] Parallel port number the keyboard adapter is
1671 connected to, default is 0.
1672 Format: <parport#>
1673 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1674 0 for XT, 1 for AT (default is AT).
1675 Format: <mode>
1677 parport= [HW,PPT] Specify parallel ports. 0 disables.
1678 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1679 Use 'auto' to force the driver to use any
1680 IRQ/DMA settings detected (the default is to
1681 ignore detected IRQ/DMA settings because of
1682 possible conflicts). You can specify the base
1683 address, IRQ, and DMA settings; IRQ and DMA
1684 should be numbers, or 'auto' (for using detected
1685 settings on that particular port), or 'nofifo'
1686 (to avoid using a FIFO even if it is detected).
1687 Parallel ports are assigned in the order they
1688 are specified on the command line, starting
1689 with parport0.
1691 parport_init_mode= [HW,PPT]
1692 Configure VIA parallel port to operate in
1693 a specific mode. This is necessary on Pegasos
1694 computer where firmware has no options for setting
1695 up parallel port mode and sets it to spp.
1696 Currently this function knows 686a and 8231 chips.
1697 Format: [spp|ps2|epp|ecp|ecpepp]
1699 pas2= [HW,OSS] Format:
1700 <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16>
1702 pas16= [HW,SCSI]
1703 See header of drivers/scsi/pas16.c.
1705 pause_on_oops=
1706 Halt all CPUs after the first oops has been printed for
1707 the specified number of seconds. This is to be used if
1708 your oopses keep scrolling off the screen.
1710 pcbit= [HW,ISDN]
1712 pcd. [PARIDE]
1713 See header of drivers/block/paride/pcd.c.
1714 See also Documentation/blockdev/paride.txt.
1716 pci=option[,option...] [PCI] various PCI subsystem options:
1717 earlydump [X86] dump PCI config space before the kernel
1718 changes anything
1719 off [X86] don't probe for the PCI bus
1720 bios [X86-32] force use of PCI BIOS, don't access
1721 the hardware directly. Use this if your machine
1722 has a non-standard PCI host bridge.
1723 nobios [X86-32] disallow use of PCI BIOS, only direct
1724 hardware access methods are allowed. Use this
1725 if you experience crashes upon bootup and you
1726 suspect they are caused by the BIOS.
1727 conf1 [X86] Force use of PCI Configuration
1728 Mechanism 1.
1729 conf2 [X86] Force use of PCI Configuration
1730 Mechanism 2.
1731 noaer [PCIE] If the PCIEAER kernel config parameter is
1732 enabled, this kernel boot option can be used to
1733 disable the use of PCIE advanced error reporting.
1734 nodomains [PCI] Disable support for multiple PCI
1735 root domains (aka PCI segments, in ACPI-speak).
1736 nommconf [X86] Disable use of MMCONFIG for PCI
1737 Configuration
1738 nomsi [MSI] If the PCI_MSI kernel config parameter is
1739 enabled, this kernel boot option can be used to
1740 disable the use of MSI interrupts system-wide.
1741 noioapicquirk [APIC] Disable all boot interrupt quirks.
1742 Safety option to keep boot IRQs enabled. This
1743 should never be necessary.
1744 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1745 primary IO-APIC for bridges that cannot disable
1746 boot IRQs. This fixes a source of spurious IRQs
1747 when the system masks IRQs.
1748 noioapicreroute [APIC] Disable workaround that uses the
1749 boot IRQ equivalent of an IRQ that connects to
1750 a chipset where boot IRQs cannot be disabled.
1751 The opposite of ioapicreroute.
1752 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1753 routing table. These calls are known to be buggy
1754 on several machines and they hang the machine
1755 when used, but on other computers it's the only
1756 way to get the interrupt routing table. Try
1757 this option if the kernel is unable to allocate
1758 IRQs or discover secondary PCI buses on your
1759 motherboard.
1760 rom [X86] Assign address space to expansion ROMs.
1761 Use with caution as certain devices share
1762 address decoders between ROMs and other
1763 resources.
1764 norom [X86] Do not assign address space to
1765 expansion ROMs that do not already have
1766 BIOS assigned address ranges.
1767 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1768 assigned automatically to PCI devices. You can
1769 make the kernel exclude IRQs of your ISA cards
1770 this way.
1771 pirqaddr=0xAAAAA [X86] Specify the physical address
1772 of the PIRQ table (normally generated
1773 by the BIOS) if it is outside the
1774 F0000h-100000h range.
1775 lastbus=N [X86] Scan all buses thru bus #N. Can be
1776 useful if the kernel is unable to find your
1777 secondary buses and you want to tell it
1778 explicitly which ones they are.
1779 assign-busses [X86] Always assign all PCI bus
1780 numbers ourselves, overriding
1781 whatever the firmware may have done.
1782 usepirqmask [X86] Honor the possible IRQ mask stored
1783 in the BIOS $PIR table. This is needed on
1784 some systems with broken BIOSes, notably
1785 some HP Pavilion N5400 and Omnibook XE3
1786 notebooks. This will have no effect if ACPI
1787 IRQ routing is enabled.
1788 noacpi [X86] Do not use ACPI for IRQ routing
1789 or for PCI scanning.
1790 use_crs [X86] Use _CRS for PCI resource
1791 allocation.
1792 routeirq Do IRQ routing for all PCI devices.
1793 This is normally done in pci_enable_device(),
1794 so this option is a temporary workaround
1795 for broken drivers that don't call it.
1796 skip_isa_align [X86] do not align io start addr, so can
1797 handle more pci cards
1798 firmware [ARM] Do not re-enumerate the bus but instead
1799 just use the configuration from the
1800 bootloader. This is currently used on
1801 IXP2000 systems where the bus has to be
1802 configured a certain way for adjunct CPUs.
1803 noearly [X86] Don't do any early type 1 scanning.
1804 This might help on some broken boards which
1805 machine check when some devices' config space
1806 is read. But various workarounds are disabled
1807 and some IOMMU drivers will not work.
1808 bfsort Sort PCI devices into breadth-first order.
1809 This sorting is done to get a device
1810 order compatible with older (<= 2.4) kernels.
1811 nobfsort Don't sort PCI devices into breadth-first order.
1812 cbiosize=nn[KMG] The fixed amount of bus space which is
1813 reserved for the CardBus bridge's IO window.
1814 The default value is 256 bytes.
1815 cbmemsize=nn[KMG] The fixed amount of bus space which is
1816 reserved for the CardBus bridge's memory
1817 window. The default value is 64 megabytes.
1818 resource_alignment=
1819 Format:
1820 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
1821 Specifies alignment and device to reassign
1822 aligned memory resources.
1823 If <order of align> is not specified,
1824 PAGE_SIZE is used as alignment.
1825 PCI-PCI bridge can be specified, if resource
1826 windows need to be expanded.
1828 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1829 Management.
1830 off Disable ASPM.
1831 force Enable ASPM even on devices that claim not to support it.
1832 WARNING: Forcing ASPM on may cause system lockups.
1834 pcmv= [HW,PCMCIA] BadgePAD 4
1836 pd. [PARIDE]
1837 See Documentation/blockdev/paride.txt.
1839 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
1840 boot time.
1841 Format: { 0 | 1 }
1842 See arch/parisc/kernel/pdc_chassis.c
1844 pf. [PARIDE]
1845 See Documentation/blockdev/paride.txt.
1847 pg. [PARIDE]
1848 See Documentation/blockdev/paride.txt.
1850 pirq= [SMP,APIC] Manual mp-table setup
1851 See Documentation/x86/i386/IO-APIC.txt.
1853 plip= [PPT,NET] Parallel port network link
1854 Format: { parport<nr> | timid | 0 }
1855 See also Documentation/parport.txt.
1857 pmtmr= [X86] Manual setup of pmtmr I/O Port.
1858 Override pmtimer IOPort with a hex value.
1859 e.g. pmtmr=0x508
1861 pnp.debug [PNP]
1862 Enable PNP debug messages. This depends on the
1863 CONFIG_PNP_DEBUG_MESSAGES option.
1865 pnpacpi= [ACPI]
1866 { off }
1868 pnpbios= [ISAPNP]
1869 { on | off | curr | res | no-curr | no-res }
1871 pnp_reserve_irq=
1872 [ISAPNP] Exclude IRQs for the autoconfiguration
1874 pnp_reserve_dma=
1875 [ISAPNP] Exclude DMAs for the autoconfiguration
1877 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
1878 Ranges are in pairs (I/O port base and size).
1880 pnp_reserve_mem=
1881 [ISAPNP] Exclude memory regions for the
1882 autoconfiguration.
1883 Ranges are in pairs (memory base and size).
1885 ports= [IP_VS_FTP] IPVS ftp helper module
1886 Default is 21.
1887 Up to 8 (IP_VS_APP_MAX_PORTS) ports
1888 may be specified.
1889 Format: <port>,<port>....
1891 print-fatal-signals=
1892 [KNL] debug: print fatal signals
1893 print-fatal-signals=1: print segfault info to
1894 the kernel console.
1895 default: off.
1897 printk.time= Show timing data prefixed to each printk message line
1898 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
1900 processor.max_cstate= [HW,ACPI]
1901 Limit processor to maximum C-state
1902 max_cstate=9 overrides any DMI blacklist limit.
1904 processor.nocst [HW,ACPI]
1905 Ignore the _CST method to determine C-states,
1906 instead using the legacy FADT method
1908 profile= [KNL] Enable kernel profiling via /proc/profile
1909 Format: [schedule,]<number>
1910 Param: "schedule" - profile schedule points.
1911 Param: <number> - step/bucket size as a power of 2 for
1912 statistical time based profiling.
1913 Param: "sleep" - profile D-state sleeping (millisecs).
1914 Requires CONFIG_SCHEDSTATS
1915 Param: "kvm" - profile VM exits.
1917 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
1918 before loading.
1919 See Documentation/blockdev/ramdisk.txt.
1921 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
1922 probe for; one of (bare|imps|exps|lifebook|any).
1923 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
1924 per second.
1925 psmouse.resetafter= [HW,MOUSE]
1926 Try to reset the device after so many bad packets
1927 (0 = never).
1928 psmouse.resolution=
1929 [HW,MOUSE] Set desired mouse resolution, in dpi.
1930 psmouse.smartscroll=
1931 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1932 0 = disabled, 1 = enabled (default).
1934 pss= [HW,OSS] Personal Sound System (ECHO ESC614)
1935 Format:
1936 <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq>
1938 pt. [PARIDE]
1939 See Documentation/blockdev/paride.txt.
1941 pty.legacy_count=
1942 [KNL] Number of legacy pty's. Overwrites compiled-in
1943 default number.
1945 quiet [KNL] Disable most log messages
1947 r128= [HW,DRM]
1949 raid= [HW,RAID]
1950 See Documentation/md.txt.
1952 ramdisk_blocksize= [RAM]
1953 See Documentation/blockdev/ramdisk.txt.
1955 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
1956 See Documentation/blockdev/ramdisk.txt.
1958 rcupdate.blimit= [KNL,BOOT]
1959 Set maximum number of finished RCU callbacks to process
1960 in one batch.
1962 rcupdate.qhimark= [KNL,BOOT]
1963 Set threshold of queued
1964 RCU callbacks over which batch limiting is disabled.
1966 rcupdate.qlowmark= [KNL,BOOT]
1967 Set threshold of queued RCU callbacks below which
1968 batch limiting is re-enabled.
1970 rdinit= [KNL]
1971 Format: <full_path>
1972 Run specified binary instead of /init from the ramdisk,
1973 used for early userspace startup. See initrd.
1975 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
1976 Format: <reboot_mode>[,<reboot_mode2>[,...]]
1977 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
1979 relax_domain_level=
1980 [KNL, SMP] Set scheduler's default relax_domain_level.
1981 See Documentation/cgroups/cpusets.txt.
1983 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
1985 reservetop= [X86-32]
1986 Format: nn[KMG]
1987 Reserves a hole at the top of the kernel virtual
1988 address space.
1990 reset_devices [KNL] Force drivers to reset the underlying device
1991 during initialization.
1993 resume= [SWSUSP]
1994 Specify the partition device for software suspend
1996 resume_offset= [SWSUSP]
1997 Specify the offset from the beginning of the partition
1998 given by "resume=" at which the swap header is located,
1999 in <PAGE_SIZE> units (needed only for swap files).
2000 See Documentation/power/swsusp-and-swap-files.txt
2002 retain_initrd [RAM] Keep initrd memory after extraction
2004 rhash_entries= [KNL,NET]
2005 Set number of hash buckets for route cache
2007 riscom8= [HW,SERIAL]
2008 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2010 ro [KNL] Mount root device read-only on boot
2012 root= [KNL] Root filesystem
2014 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2015 mount the root filesystem
2017 rootflags= [KNL] Set root filesystem mount option string
2019 rootfstype= [KNL] Set root filesystem type
2021 rootwait [KNL] Wait (indefinitely) for root device to show up.
2022 Useful for devices that are detected asynchronously
2023 (e.g. USB and MMC devices).
2025 root_plug.vendor_id=
2026 [ROOTPLUG] Override the default vendor ID
2028 root_plug.product_id=
2029 [ROOTPLUG] Override the default product ID
2031 root_plug.debug=
2032 [ROOTPLUG] Enable debugging output
2034 rw [KNL] Mount root device read-write on boot
2036 S [KNL] Run init in single mode
2038 sa1100ir [NET]
2039 See drivers/net/irda/sa1100_ir.c.
2041 sbni= [NET] Granch SBNI12 leased line adapter
2043 sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
2044 Format: <io>[,<timeout>[,<isapnp>]]
2046 scsi_debug_*= [SCSI]
2047 See drivers/scsi/scsi_debug.c.
2049 scsi_default_dev_flags=
2050 [SCSI] SCSI default device flags
2051 Format: <integer>
2053 scsi_dev_flags= [SCSI] Black/white list entry for vendor and model
2054 Format: <vendor>:<model>:<flags>
2055 (flags are integer value)
2057 scsi_logging_level= [SCSI] a bit mask of logging levels
2058 See drivers/scsi/scsi_logging.h for bits. Also
2059 settable via sysctl at dev.scsi.logging_level
2060 (/proc/sys/dev/scsi/logging_level).
2061 There is also a nice 'scsi_logging_level' script in the
2062 S390-tools package, available for download at
2063 http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
2065 scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
2066 discovered. async scans them in kernel threads,
2067 allowing boot to proceed. none ignores them, expecting
2068 user space to do the scan.
2070 security= [SECURITY] Choose a security module to enable at boot.
2071 If this boot parameter is not specified, only the first
2072 security module asking for security registration will be
2073 loaded. An invalid security module name will be treated
2074 as if no module has been chosen.
2076 selinux= [SELINUX] Disable or enable SELinux at boot time.
2077 Format: { "0" | "1" }
2078 See security/selinux/Kconfig help text.
2079 0 -- disable.
2080 1 -- enable.
2081 Default value is set via kernel config option.
2082 If enabled at boot time, /selinux/disable can be used
2083 later to disable prior to initial policy load.
2085 serialnumber [BUGS=X86-32]
2087 shapers= [NET]
2088 Maximal number of shapers.
2090 show_msr= [x86] show boot-time MSR settings
2091 Format: { <integer> }
2092 Show boot-time (BIOS-initialized) MSR settings.
2093 The parameter means the number of CPUs to show,
2094 for example 1 means boot CPU only.
2096 sim710= [SCSI,HW]
2097 See header of drivers/scsi/sim710.c.
2099 simeth= [IA-64]
2100 simscsi=
2102 slram= [HW,MTD]
2104 slub_debug[=options[,slabs]] [MM, SLUB]
2105 Enabling slub_debug allows one to determine the
2106 culprit if slab objects become corrupted. Enabling
2107 slub_debug can create guard zones around objects and
2108 may poison objects when not in use. Also tracks the
2109 last alloc / free. For more information see
2110 Documentation/vm/slub.txt.
2112 slub_max_order= [MM, SLUB]
2113 Determines the maximum allowed order for slabs.
2114 A high setting may cause OOMs due to memory
2115 fragmentation. For more information see
2116 Documentation/vm/slub.txt.
2118 slub_min_objects= [MM, SLUB]
2119 The minimum number of objects per slab. SLUB will
2120 increase the slab order up to slub_max_order to
2121 generate a sufficiently large slab able to contain
2122 the number of objects indicated. The higher the number
2123 of objects the smaller the overhead of tracking slabs
2124 and the less frequently locks need to be acquired.
2125 For more information see Documentation/vm/slub.txt.
2127 slub_min_order= [MM, SLUB]
2128 Determines the mininum page order for slabs. Must be
2129 lower than slub_max_order.
2130 For more information see Documentation/vm/slub.txt.
2132 slub_nomerge [MM, SLUB]
2133 Disable merging of slabs with similar size. May be
2134 necessary if there is some reason to distinguish
2135 allocs to different slabs. Debug options disable
2136 merging on their own.
2137 For more information see Documentation/vm/slub.txt.
2139 smart2= [HW]
2140 Format: <io1>[,<io2>[,...,<io8>]]
2142 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2143 attempt to substitute SMP alternatives once at boot.
2145 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2146 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2147 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2148 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2149 smsc-ircc2.ircc_irq= [HW] IRQ line
2150 smsc-ircc2.ircc_dma= [HW] DMA channel
2151 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2152 0: Toshiba Satellite 1800 (GP data pin select)
2153 1: Fast pin select (default)
2154 2: ATC IRMode
2156 snd-ad1816a= [HW,ALSA]
2158 snd-ad1848= [HW,ALSA]
2160 snd-ali5451= [HW,ALSA]
2162 snd-als100= [HW,ALSA]
2164 snd-als4000= [HW,ALSA]
2166 snd-azt2320= [HW,ALSA]
2168 snd-cmi8330= [HW,ALSA]
2170 snd-cmipci= [HW,ALSA]
2172 snd-cs4231= [HW,ALSA]
2174 snd-cs4232= [HW,ALSA]
2176 snd-cs4236= [HW,ALSA]
2178 snd-cs4281= [HW,ALSA]
2180 snd-cs46xx= [HW,ALSA]
2182 snd-dt019x= [HW,ALSA]
2184 snd-dummy= [HW,ALSA]
2186 snd-emu10k1= [HW,ALSA]
2188 snd-ens1370= [HW,ALSA]
2190 snd-ens1371= [HW,ALSA]
2192 snd-es968= [HW,ALSA]
2194 snd-es1688= [HW,ALSA]
2196 snd-es18xx= [HW,ALSA]
2198 snd-es1938= [HW,ALSA]
2200 snd-es1968= [HW,ALSA]
2202 snd-fm801= [HW,ALSA]
2204 snd-gusclassic= [HW,ALSA]
2206 snd-gusextreme= [HW,ALSA]
2208 snd-gusmax= [HW,ALSA]
2210 snd-hdsp= [HW,ALSA]
2212 snd-ice1712= [HW,ALSA]
2214 snd-intel8x0= [HW,ALSA]
2216 snd-interwave= [HW,ALSA]
2218 snd-interwave-stb=
2219 [HW,ALSA]
2221 snd-korg1212= [HW,ALSA]
2223 snd-maestro3= [HW,ALSA]
2225 snd-mpu401= [HW,ALSA]
2227 snd-mtpav= [HW,ALSA]
2229 snd-nm256= [HW,ALSA]
2231 snd-opl3sa2= [HW,ALSA]
2233 snd-opti92x-ad1848=
2234 [HW,ALSA]
2236 snd-opti92x-cs4231=
2237 [HW,ALSA]
2239 snd-opti93x= [HW,ALSA]
2241 snd-pmac= [HW,ALSA]
2243 snd-rme32= [HW,ALSA]
2245 snd-rme96= [HW,ALSA]
2247 snd-rme9652= [HW,ALSA]
2249 snd-sb8= [HW,ALSA]
2251 snd-sb16= [HW,ALSA]
2253 snd-sbawe= [HW,ALSA]
2255 snd-serial= [HW,ALSA]
2257 snd-sgalaxy= [HW,ALSA]
2259 snd-sonicvibes= [HW,ALSA]
2261 snd-sun-amd7930=
2262 [HW,ALSA]
2264 snd-sun-cs4231= [HW,ALSA]
2266 snd-trident= [HW,ALSA]
2268 snd-usb-audio= [HW,ALSA,USB]
2270 snd-via82xx= [HW,ALSA]
2272 snd-virmidi= [HW,ALSA]
2274 snd-wavefront= [HW,ALSA]
2276 snd-ymfpci= [HW,ALSA]
2278 softlockup_panic=
2279 [KNL] Should the soft-lockup detector generate panics.
2281 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2282 See Documentation/sonypi.txt
2284 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2285 See Documentation/serial/specialix.txt.
2287 spia_io_base= [HW,MTD]
2288 spia_fio_base=
2289 spia_pedr=
2290 spia_peddr=
2292 sscape= [HW,OSS]
2293 Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq>
2295 st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
2296 See Documentation/scsi/st.txt.
2298 stacktrace [FTRACE]
2299 Enabled the stack tracer on boot up.
2301 sti= [PARISC,HW]
2302 Format: <num>
2303 Set the STI (builtin display/keyboard on the HP-PARISC
2304 machines) console (graphic card) which should be used
2305 as the initial boot-console.
2306 See also comment in drivers/video/console/sticore.c.
2308 sti_font= [HW]
2309 See comment in drivers/video/console/sticore.c.
2311 stifb= [HW]
2312 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2314 sunrpc.pool_mode=
2315 [NFS]
2316 Control how the NFS server code allocates CPUs to
2317 service thread pools. Depending on how many NICs
2318 you have and where their interrupts are bound, this
2319 option will affect which CPUs will do NFS serving.
2320 Note: this parameter cannot be changed while the
2321 NFS server is running.
2323 auto the server chooses an appropriate mode
2324 automatically using heuristics
2325 global a single global pool contains all CPUs
2326 percpu one pool for each CPU
2327 pernode one pool for each NUMA node (equivalent
2328 to global on non-NUMA machines)
2330 swiotlb= [IA-64] Number of I/O TLB slabs
2332 switches= [HW,M68k]
2334 sym53c416= [HW,SCSI]
2335 See header of drivers/scsi/sym53c416.c.
2337 sysrq_always_enabled
2338 [KNL]
2339 Ignore sysrq setting - this boot parameter will
2340 neutralize any effect of /proc/sys/kernel/sysrq.
2341 Useful for debugging.
2343 t128= [HW,SCSI]
2344 See header of drivers/scsi/t128.c.
2346 tdfx= [HW,DRM]
2348 test_suspend= [SUSPEND]
2349 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2350 standby suspend) as the system sleep state to briefly
2351 enter during system startup. The system is woken from
2352 this state using a wakeup-capable RTC alarm.
2354 thash_entries= [KNL,NET]
2355 Set number of hash buckets for TCP connection
2357 thermal.act= [HW,ACPI]
2358 -1: disable all active trip points in all thermal zones
2359 <degrees C>: override all lowest active trip points
2361 thermal.crt= [HW,ACPI]
2362 -1: disable all critical trip points in all thermal zones
2363 <degrees C>: override all critical trip points
2365 thermal.nocrt= [HW,ACPI]
2366 Set to disable actions on ACPI thermal zone
2367 critical and hot trip points.
2369 thermal.off= [HW,ACPI]
2370 1: disable ACPI thermal control
2372 thermal.psv= [HW,ACPI]
2373 -1: disable all passive trip points
2374 <degrees C>: override all passive trip points to this
2375 value
2377 thermal.tzp= [HW,ACPI]
2378 Specify global default ACPI thermal zone polling rate
2379 <deci-seconds>: poll all this frequency
2380 0: no polling (default)
2382 tmscsim= [HW,SCSI]
2383 See comment before function dc390_setup() in
2384 drivers/scsi/tmscsim.c.
2386 topology= [S390]
2387 Format: {off | on}
2388 Specify if the kernel should make use of the cpu
2389 topology informations if the hardware supports these.
2390 The scheduler will make use of these informations and
2391 e.g. base its process migration decisions on it.
2392 Default is off.
2394 tp720= [HW,PS2]
2396 trace_buf_size=nn[KMG] [ftrace] will set tracing buffer size.
2398 trix= [HW,OSS] MediaTrix AudioTrix Pro
2399 Format:
2400 <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
2402 tsc= Disable clocksource-must-verify flag for TSC.
2403 Format: <string>
2404 [x86] reliable: mark tsc clocksource as reliable, this
2405 disables clocksource verification at runtime.
2406 Used to enable high-resolution timer mode on older
2407 hardware, and in virtualized environment.
2409 turbografx.map[2|3]= [HW,JOY]
2410 TurboGraFX parallel port interface
2411 Format:
2412 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2413 See also Documentation/input/joystick-parport.txt
2415 u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter
2416 See header of drivers/scsi/u14-34f.c.
2418 uart401= [HW,OSS]
2419 Format: <io>,<irq>
2421 uart6850= [HW,OSS]
2422 Format: <io>,<irq>
2424 uhci-hcd.ignore_oc=
2425 [USB] Ignore overcurrent events (default N).
2426 Some badly-designed motherboards generate lots of
2427 bogus events, for ports that aren't wired to
2428 anything. Set this parameter to avoid log spamming.
2429 Note that genuine overcurrent events won't be
2430 reported either.
2432 unknown_nmi_panic
2433 [X86]
2434 Set unknown_nmi_panic=1 early on boot.
2436 usbcore.autosuspend=
2437 [USB] The autosuspend time delay (in seconds) used
2438 for newly-detected USB devices (default 2). This
2439 is the time required before an idle device will be
2440 autosuspended. Devices for which the delay is set
2441 to a negative value won't be autosuspended at all.
2443 usbcore.usbfs_snoop=
2444 [USB] Set to log all usbfs traffic (default 0 = off).
2446 usbcore.blinkenlights=
2447 [USB] Set to cycle leds on hubs (default 0 = off).
2449 usbcore.old_scheme_first=
2450 [USB] Start with the old device initialization
2451 scheme (default 0 = off).
2453 usbcore.use_both_schemes=
2454 [USB] Try the other device initialization scheme
2455 if the first one fails (default 1 = enabled).
2457 usbcore.initial_descriptor_timeout=
2458 [USB] Specifies timeout for the initial 64-byte
2459 USB_REQ_GET_DESCRIPTOR request in milliseconds
2460 (default 5000 = 5.0 seconds).
2462 usbhid.mousepoll=
2463 [USBHID] The interval which mice are to be polled at.
2465 usb-storage.delay_use=
2466 [UMS] The delay in seconds before a new device is
2467 scanned for Logical Units (default 5).
2469 usb-storage.quirks=
2470 [UMS] A list of quirks entries to supplement or
2471 override the built-in unusual_devs list. List
2472 entries are separated by commas. Each entry has
2473 the form VID:PID:Flags where VID and PID are Vendor
2474 and Product ID values (4-digit hex numbers) and
2475 Flags is a set of characters, each corresponding
2476 to a common usb-storage quirk flag as follows:
2477 a = SANE_SENSE (collect more than 18 bytes
2478 of sense data);
2479 c = FIX_CAPACITY (decrease the reported
2480 device capacity by one sector);
2481 h = CAPACITY_HEURISTICS (decrease the
2482 reported device capacity by one
2483 sector if the number is odd);
2484 i = IGNORE_DEVICE (don't bind to this
2485 device);
2486 l = NOT_LOCKABLE (don't try to lock and
2487 unlock ejectable media);
2488 m = MAX_SECTORS_64 (don't transfer more
2489 than 64 sectors = 32 KB at a time);
2490 o = CAPACITY_OK (accept the capacity
2491 reported by the device);
2492 r = IGNORE_RESIDUE (the device reports
2493 bogus residue values);
2494 s = SINGLE_LUN (the device has only one
2495 Logical Unit);
2496 w = NO_WP_DETECT (don't test whether the
2497 medium is write-protected).
2498 Example: quirks=0419:aaf5:rl,0421:0433:rc
2500 vdso= [X86,SH]
2501 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2502 vdso=1: enable VDSO (default)
2503 vdso=0: disable VDSO mapping
2505 vdso32= [X86]
2506 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2507 vdso32=1: enable 32-bit VDSO (default)
2508 vdso32=0: disable 32-bit VDSO mapping
2510 vector= [IA-64,SMP]
2511 vector=percpu: enable percpu vector domain
2513 video= [FB] Frame buffer configuration
2514 See Documentation/fb/modedb.txt.
2516 vga= [BOOT,X86-32] Select a particular video mode
2517 See Documentation/x86/boot.txt and
2518 Documentation/svga.txt.
2519 Use vga=ask for menu.
2520 This is actually a boot loader parameter; the value is
2521 passed to the kernel using a special protocol.
2523 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2524 size of <nn>. This can be used to increase the
2525 minimum size (128MB on x86). It can also be used to
2526 decrease the size and leave more room for directly
2527 mapped kernel RAM.
2529 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2530 Format: <command>
2532 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2533 Format: <command>
2535 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2536 Format: <command>
2538 vt.default_blu= [VT]
2539 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2540 Change the default blue palette of the console.
2541 This is a 16-member array composed of values
2542 ranging from 0-255.
2544 vt.default_grn= [VT]
2545 Format: <green0>,<green1>,<green2>,...,<green15>
2546 Change the default green palette of the console.
2547 This is a 16-member array composed of values
2548 ranging from 0-255.
2550 vt.default_red= [VT]
2551 Format: <red0>,<red1>,<red2>,...,<red15>
2552 Change the default red palette of the console.
2553 This is a 16-member array composed of values
2554 ranging from 0-255.
2556 vt.default_utf8=
2557 [VT]
2558 Format=<0|1>
2559 Set system-wide default UTF-8 mode for all tty's.
2560 Default is 1, i.e. UTF-8 mode is enabled for all
2561 newly opened terminals.
2563 waveartist= [HW,OSS]
2564 Format: <io>,<irq>,<dma>,<dma2>
2566 wd33c93= [HW,SCSI]
2567 See header of drivers/scsi/wd33c93.c.
2569 wd7000= [HW,SCSI]
2570 See header of drivers/scsi/wd7000.c.
2572 wdt= [WDT] Watchdog
2573 See Documentation/watchdog/wdt.txt.
2575 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2576 default x2apic cluster mode on platforms
2577 supporting x2apic.
2579 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2580 xd_geo= See header of drivers/block/xd.c.
2582 xirc2ps_cs= [NET,PCMCIA]
2583 Format:
2584 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2586 ______________________________________________________________________
2588 TODO:
2590 Add documentation for ALSA options.
2591 Add more DRM drivers.