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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 This document may not be entirely up to date and comprehensive. The command
21 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
22 module. Loadable modules, after being loaded into the running kernel, also
23 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
24 parameters may be changed at runtime by the command
25 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
27 The parameters listed below are only valid if certain kernel build options were
28 enabled and if respective hardware is present. The text in square brackets at
29 the beginning of each description states the restrictions within which a
30 parameter is applicable:
32 ACPI ACPI support is enabled.
33 AGP AGP (Accelerated Graphics Port) is enabled.
34 ALSA ALSA sound support is enabled.
35 APIC APIC support is enabled.
36 APM Advanced Power Management support is enabled.
37 AVR32 AVR32 architecture is enabled.
38 AX25 Appropriate AX.25 support is enabled.
39 BLACKFIN Blackfin architecture is enabled.
40 DRM Direct Rendering Management support is enabled.
41 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
42 EFI EFI Partitioning (GPT) is enabled
43 EIDE EIDE/ATAPI support is enabled.
44 FB The frame buffer device is enabled.
45 HW Appropriate hardware is enabled.
46 IA-64 IA-64 architecture is enabled.
47 IMA Integrity measurement architecture is enabled.
48 IOSCHED More than one I/O scheduler is enabled.
49 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
50 ISAPNP ISA PnP code is enabled.
51 ISDN Appropriate ISDN support is enabled.
52 JOY Appropriate joystick support is enabled.
53 LIBATA Libata driver is enabled
54 LP Printer support is enabled.
55 LOOP Loopback device support is enabled.
56 M68k M68k architecture is enabled.
57 These options have more detailed description inside of
58 Documentation/m68k/kernel-options.txt.
59 MCA MCA bus support is enabled.
60 MDA MDA console support is enabled.
61 MOUSE Appropriate mouse support is enabled.
62 MSI Message Signaled Interrupts (PCI).
63 MTD MTD (Memory Technology Device) support is enabled.
64 NET Appropriate network support is enabled.
65 NUMA NUMA support is enabled.
66 GENERIC_TIME The generic timeofday code is enabled.
67 NFS Appropriate NFS support is enabled.
68 OSS OSS sound support is enabled.
69 PV_OPS A paravirtualized kernel is enabled.
70 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
71 PARISC The PA-RISC architecture is enabled.
72 PCI PCI bus support is enabled.
73 PCIE PCI Express support is enabled.
74 PCMCIA The PCMCIA subsystem is enabled.
75 PNP Plug & Play support is enabled.
76 PPC PowerPC architecture is enabled.
77 PPT Parallel port support is enabled.
78 PS2 Appropriate PS/2 support is enabled.
79 RAM RAM disk support is enabled.
80 ROOTPLUG The example Root Plug LSM is enabled.
81 S390 S390 architecture is enabled.
82 SCSI Appropriate SCSI support is enabled.
83 A lot of drivers has their options described inside of
84 Documentation/scsi/.
85 SECURITY Different security models are enabled.
86 SELINUX SELinux support is enabled.
87 SERIAL Serial support is enabled.
88 SH SuperH architecture is enabled.
89 SMP The kernel is an SMP kernel.
90 SPARC Sparc architecture is enabled.
91 SWSUSP Software suspend (hibernation) is enabled.
92 SUSPEND System suspend states are enabled.
93 FTRACE Function tracing enabled.
94 TS Appropriate touchscreen support is enabled.
95 UMS USB Mass Storage support is enabled.
96 USB USB support is enabled.
97 USBHID USB Human Interface Device support is enabled.
98 V4L Video For Linux support is enabled.
99 VGA The VGA console has been enabled.
100 VT Virtual terminal support is enabled.
101 WDT Watchdog support is enabled.
102 XT IBM PC/XT MFM hard disk support is enabled.
103 X86-32 X86-32, aka i386 architecture is enabled.
104 X86-64 X86-64 architecture is enabled.
105 More X86-64 boot options can be found in
106 Documentation/x86/x86_64/boot-options.txt .
107 X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
109 In addition, the following text indicates that the option:
111 BUGS= Relates to possible processor bugs on the said processor.
112 KNL Is a kernel start-up parameter.
113 BOOT Is a boot loader parameter.
115 Parameters denoted with BOOT are actually interpreted by the boot
116 loader, and have no meaning to the kernel directly.
117 Do not modify the syntax of boot loader parameters without extreme
118 need or coordination with <Documentation/x86/boot.txt>.
120 There are also arch-specific kernel-parameters not documented here.
121 See for example <Documentation/x86/x86_64/boot-options.txt>.
123 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
124 a trailing = on the name of any parameter states that that parameter will
125 be entered as an environment variable, whereas its absence indicates that
126 it will appear as a kernel argument readable via /proc/cmdline by programs
127 running once the system is up.
129 The number of kernel parameters is not limited, but the length of the
130 complete command line (parameters including spaces etc.) is limited to
131 a fixed number of characters. This limit depends on the architecture
132 and is between 256 and 4096 characters. It is defined in the file
133 ./include/asm/setup.h as COMMAND_LINE_SIZE.
136 acpi= [HW,ACPI,X86-64,i386]
137 Advanced Configuration and Power Interface
138 Format: { force | off | ht | strict | noirq | rsdt }
139 force -- enable ACPI if default was off
140 off -- disable ACPI if default was on
141 noirq -- do not use ACPI for IRQ routing
142 ht -- run only enough ACPI to enable Hyper Threading
143 strict -- Be less tolerant of platforms that are not
144 strictly ACPI specification compliant.
145 rsdt -- prefer RSDT over (default) XSDT
147 See also Documentation/power/pm.txt, pci=noacpi
149 acpi_apic_instance= [ACPI, IOAPIC]
150 Format: <int>
151 2: use 2nd APIC table, if available
152 1,0: use 1st APIC table
153 default: 0
155 acpi_sleep= [HW,ACPI] Sleep options
156 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
157 old_ordering, s4_nonvs }
158 See Documentation/power/video.txt for information on
159 s3_bios and s3_mode.
160 s3_beep is for debugging; it makes the PC's speaker beep
161 as soon as the kernel's real-mode entry point is called.
162 s4_nohwsig prevents ACPI hardware signature from being
163 used during resume from hibernation.
164 old_ordering causes the ACPI 1.0 ordering of the _PTS
165 control method, with respect to putting devices into
166 low power states, to be enforced (the ACPI 2.0 ordering
167 of _PTS is used by default).
168 s4_nonvs prevents the kernel from saving/restoring the
169 ACPI NVS memory during hibernation.
171 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
172 Format: { level | edge | high | low }
174 acpi_irq_balance [HW,ACPI]
175 ACPI will balance active IRQs
176 default in APIC mode
178 acpi_irq_nobalance [HW,ACPI]
179 ACPI will not move active IRQs (default)
180 default in PIC mode
182 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
183 use by PCI
184 Format: <irq>,<irq>...
186 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
187 Format: <irq>,<irq>...
189 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
191 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
192 Format: To spoof as Windows 98: ="Microsoft Windows"
194 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
195 acpi_osi="string1" # add string1 -- only one string
196 acpi_osi="!string2" # remove built-in string2
197 acpi_osi= # disable all strings
199 acpi_serialize [HW,ACPI] force serialization of AML methods
201 acpi_skip_timer_override [HW,ACPI]
202 Recognize and ignore IRQ0/pin2 Interrupt Override.
203 For broken nForce2 BIOS resulting in XT-PIC timer.
204 acpi_use_timer_override [HW,ACPI]
205 Use timer override. For some broken Nvidia NF5 boards
206 that require a timer override, but don't have
207 HPET
209 acpi_backlight= [HW,ACPI]
210 acpi_backlight=vendor
211 acpi_backlight=video
212 If set to vendor, prefer vendor specific driver
213 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
214 of the ACPI video.ko driver.
216 acpi_display_output= [HW,ACPI]
217 acpi_display_output=vendor
218 acpi_display_output=video
219 See above.
221 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
222 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
223 Format: <int>
224 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
225 debug output. Bits in debug_layer correspond to a
226 _COMPONENT in an ACPI source file, e.g.,
227 #define _COMPONENT ACPI_PCI_COMPONENT
228 Bits in debug_level correspond to a level in
229 ACPI_DEBUG_PRINT statements, e.g.,
230 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
231 The debug_level mask defaults to "info". See
232 Documentation/acpi/debug.txt for more information about
233 debug layers and levels.
235 Enable processor driver info messages:
236 acpi.debug_layer=0x20000000
237 Enable PCI/PCI interrupt routing info messages:
238 acpi.debug_layer=0x400000
239 Enable AML "Debug" output, i.e., stores to the Debug
240 object while interpreting AML:
241 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
242 Enable all messages related to ACPI hardware:
243 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
245 Some values produce so much output that the system is
246 unusable. The "log_buf_len" parameter may be useful
247 if you need to capture more output.
249 acpi.power_nocheck= [HW,ACPI]
250 Format: 1/0 enable/disable the check of power state.
251 On some bogus BIOS the _PSC object/_STA object of
252 power resource can't return the correct device power
253 state. In such case it is unneccessary to check its
254 power state again in power transition.
255 1 : disable the power state check
257 acpi_pm_good [X86-32,X86-64]
258 Override the pmtimer bug detection: force the kernel
259 to assume that this machine's pmtimer latches its value
260 and always returns good values.
262 agp= [AGP]
263 { off | try_unsupported }
264 off: disable AGP support
265 try_unsupported: try to drive unsupported chipsets
266 (may crash computer or cause data corruption)
268 enable_timer_pin_1 [i386,x86-64]
269 Enable PIN 1 of APIC timer
270 Can be useful to work around chipset bugs
271 (in particular on some ATI chipsets).
272 The kernel tries to set a reasonable default.
274 disable_timer_pin_1 [i386,x86-64]
275 Disable PIN 1 of APIC timer
276 Can be useful to work around chipset bugs.
278 ad1848= [HW,OSS]
279 Format: <io>,<irq>,<dma>,<dma2>,<type>
281 advansys= [HW,SCSI]
282 See header of drivers/scsi/advansys.c.
284 advwdt= [HW,WDT] Advantech WDT
285 Format: <iostart>,<iostop>
287 aedsp16= [HW,OSS] Audio Excel DSP 16
288 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>
289 See also header of sound/oss/aedsp16.c.
291 aha152x= [HW,SCSI]
292 See Documentation/scsi/aha152x.txt.
294 aha1542= [HW,SCSI]
295 Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]
297 aic7xxx= [HW,SCSI]
298 See Documentation/scsi/aic7xxx.txt.
300 aic79xx= [HW,SCSI]
301 See Documentation/scsi/aic79xx.txt.
303 amd_iommu= [HW,X86-84]
304 Pass parameters to the AMD IOMMU driver in the system.
305 Possible values are:
306 isolate - enable device isolation (each device, as far
307 as possible, will get its own protection
308 domain) [default]
309 share - put every device behind one IOMMU into the
310 same protection domain
311 fullflush - enable flushing of IO/TLB entries when
312 they are unmapped. Otherwise they are
313 flushed before they will be reused, which
314 is a lot of faster
316 amd_iommu_size= [HW,X86-64]
317 Define the size of the aperture for the AMD IOMMU
318 driver. Possible values are:
319 '32M', '64M' (default), '128M', '256M', '512M', '1G'
321 amijoy.map= [HW,JOY] Amiga joystick support
322 Map of devices attached to JOY0DAT and JOY1DAT
323 Format: <a>,<b>
324 See also Documentation/kernel/input/joystick.txt
326 analog.map= [HW,JOY] Analog joystick and gamepad support
327 Specifies type or capabilities of an analog joystick
328 connected to one of 16 gameports
329 Format: <type1>,<type2>,..<type16>
331 apc= [HW,SPARC]
332 Power management functions (SPARCstation-4/5 + deriv.)
333 Format: noidle
334 Disable APC CPU standby support. SPARCstation-Fox does
335 not play well with APC CPU idle - disable it if you have
336 APC and your system crashes randomly.
338 apic= [APIC,i386] Advanced Programmable Interrupt Controller
339 Change the output verbosity whilst booting
340 Format: { quiet (default) | verbose | debug }
341 Change the amount of debugging information output
342 when initialising the APIC and IO-APIC components.
344 apm= [APM] Advanced Power Management
345 See header of arch/x86/kernel/apm_32.c.
347 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
348 Format: <io>,<irq>,<nodeID>
350 ataflop= [HW,M68k]
352 atarimouse= [HW,MOUSE] Atari Mouse
354 atascsi= [HW,SCSI] Atari SCSI
356 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
357 EzKey and similar keyboards
359 atkbd.reset= [HW] Reset keyboard during initialization
361 atkbd.set= [HW] Select keyboard code set
362 Format: <int> (2 = AT (default), 3 = PS/2)
364 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
365 keyboards
367 atkbd.softraw= [HW] Choose between synthetic and real raw mode
368 Format: <bool> (0 = real, 1 = synthetic (default))
370 atkbd.softrepeat= [HW]
371 Use software keyboard repeat
373 autotest [IA64]
375 baycom_epp= [HW,AX25]
376 Format: <io>,<mode>
378 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
379 Format: <io>,<mode>
380 See header of drivers/net/hamradio/baycom_par.c.
382 baycom_ser_fdx= [HW,AX25]
383 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
384 Format: <io>,<irq>,<mode>[,<baud>]
385 See header of drivers/net/hamradio/baycom_ser_fdx.c.
387 baycom_ser_hdx= [HW,AX25]
388 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
389 Format: <io>,<irq>,<mode>
390 See header of drivers/net/hamradio/baycom_ser_hdx.c.
392 boot_delay= Milliseconds to delay each printk during boot.
393 Values larger than 10 seconds (10000) are changed to
394 no delay (0).
395 Format: integer
397 bootmem_debug [KNL] Enable bootmem allocator debug messages.
399 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
400 bttv.radio= Most important insmod options are available as
401 kernel args too.
402 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
403 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
405 BusLogic= [HW,SCSI]
406 See drivers/scsi/BusLogic.c, comment before function
407 BusLogic_ParseDriverOptions().
409 c101= [NET] Moxa C101 synchronous serial card
411 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
412 Sometimes CPU hardware bugs make them report the cache
413 size incorrectly. The kernel will attempt work arounds
414 to fix known problems, but for some CPUs it is not
415 possible to determine what the correct size should be.
416 This option provides an override for these situations.
418 security= [SECURITY] Choose a security module to enable at boot.
419 If this boot parameter is not specified, only the first
420 security module asking for security registration will be
421 loaded. An invalid security module name will be treated
422 as if no module has been chosen.
424 capability.disable=
425 [SECURITY] Disable capabilities. This would normally
426 be used only if an alternative security model is to be
427 configured. Potentially dangerous and should only be
428 used if you are entirely sure of the consequences.
430 ccw_timeout_log [S390]
431 See Documentation/s390/CommonIO for details.
433 cgroup_disable= [KNL] Disable a particular controller
434 Format: {name of the controller(s) to disable}
435 {Currently supported controllers - "memory"}
437 checkreqprot [SELINUX] Set initial checkreqprot flag value.
438 Format: { "0" | "1" }
439 See security/selinux/Kconfig help text.
440 0 -- check protection applied by kernel (includes
441 any implied execute protection).
442 1 -- check protection requested by application.
443 Default value is set via a kernel config option.
444 Value can be changed at runtime via
445 /selinux/checkreqprot.
447 cio_ignore= [S390]
448 See Documentation/s390/CommonIO for details.
450 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
451 [Deprecated]
452 Forces specified clocksource (if available) to be used
453 when calculating gettimeofday(). If specified
454 clocksource is not available, it defaults to PIT.
455 Format: { pit | tsc | cyclone | pmtmr }
457 clocksource= [GENERIC_TIME] Override the default clocksource
458 Format: <string>
459 Override the default clocksource and use the clocksource
460 with the name specified.
461 Some clocksource names to choose from, depending on
462 the platform:
463 [all] jiffies (this is the base, fallback clocksource)
464 [ACPI] acpi_pm
465 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
466 pxa_timer,timer3,32k_counter,timer0_1
467 [AVR32] avr32
468 [X86-32] pit,hpet,tsc,vmi-timer;
469 scx200_hrt on Geode; cyclone on IBM x440
470 [MIPS] MIPS
471 [PARISC] cr16
472 [S390] tod
473 [SH] SuperH
474 [SPARC64] tick
475 [X86-64] hpet,tsc
477 clearcpuid=BITNUM [X86]
478 Disable CPUID feature X for the kernel. See
479 arch/x86/include/asm/cpufeature.h for the valid bit
480 numbers. Note the Linux specific bits are not necessarily
481 stable over kernel options, but the vendor specific
482 ones should be.
483 Also note that user programs calling CPUID directly
484 or using the feature without checking anything
485 will still see it. This just prevents it from
486 being used by the kernel or shown in /proc/cpuinfo.
487 Also note the kernel might malfunction if you disable
488 some critical bits.
490 code_bytes [IA32/X86_64] How many bytes of object code to print
491 in an oops report.
492 Range: 0 - 8192
493 Default: 64
495 hpet= [X86-32,HPET] option to control HPET usage
496 Format: { enable (default) | disable | force |
497 verbose }
498 disable: disable HPET and use PIT instead
499 force: allow force enabled of undocumented chips (ICH4,
500 VIA, nVidia)
501 verbose: show contents of HPET registers during setup
503 com20020= [HW,NET] ARCnet - COM20020 chipset
504 Format:
505 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
507 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
508 Format: <io>[,<irq>]
510 com90xx= [HW,NET]
511 ARCnet - COM90xx chipset (memory-mapped buffers)
512 Format: <io>[,<irq>[,<memstart>]]
514 condev= [HW,S390] console device
515 conmode=
517 console= [KNL] Output console device and options.
519 tty<n> Use the virtual console device <n>.
521 ttyS<n>[,options]
522 ttyUSB0[,options]
523 Use the specified serial port. The options are of
524 the form "bbbbpnf", where "bbbb" is the baud rate,
525 "p" is parity ("n", "o", or "e"), "n" is number of
526 bits, and "f" is flow control ("r" for RTS or
527 omit it). Default is "9600n8".
529 See Documentation/serial-console.txt for more
530 information. See
531 Documentation/networking/netconsole.txt for an
532 alternative.
534 uart[8250],io,<addr>[,options]
535 uart[8250],mmio,<addr>[,options]
536 Start an early, polled-mode console on the 8250/16550
537 UART at the specified I/O port or MMIO address,
538 switching to the matching ttyS device later. The
539 options are the same as for ttyS, above.
541 If the device connected to the port is not a TTY but a braille
542 device, prepend "brl," before the device type, for instance
543 console=brl,ttyS0
544 For now, only VisioBraille is supported.
546 earlycon= [KNL] Output early console device and options.
547 uart[8250],io,<addr>[,options]
548 uart[8250],mmio,<addr>[,options]
549 Start an early, polled-mode console on the 8250/16550
550 UART at the specified I/O port or MMIO address.
551 The options are the same as for ttyS, above.
553 no_console_suspend
554 [HW] Never suspend the console
555 Disable suspending of consoles during suspend and
556 hibernate operations. Once disabled, debugging
557 messages can reach various consoles while the rest
558 of the system is being put to sleep (ie, while
559 debugging driver suspend/resume hooks). This may
560 not work reliably with all consoles, but is known
561 to work with serial and VGA consoles.
563 coredump_filter=
564 [KNL] Change the default value for
565 /proc/<pid>/coredump_filter.
566 See also Documentation/filesystems/proc.txt.
568 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
569 Format:
570 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
572 crashkernel=nn[KMG]@ss[KMG]
573 [KNL] Reserve a chunk of physical memory to
574 hold a kernel to switch to with kexec on panic.
576 crashkernel=range1:size1[,range2:size2,...][@offset]
577 [KNL] Same as above, but depends on the memory
578 in the running system. The syntax of range is
579 start-[end] where start and end are both
580 a memory unit (amount[KMG]). See also
581 Documentation/kdump/kdump.txt for a example.
583 cs89x0_dma= [HW,NET]
584 Format: <dma>
586 cs89x0_media= [HW,NET]
587 Format: { rj45 | aui | bnc }
589 dasd= [HW,NET]
590 See header of drivers/s390/block/dasd_devmap.c.
592 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
593 (one device per port)
594 Format: <port#>,<type>
595 See also Documentation/input/joystick-parport.txt
597 debug [KNL] Enable kernel debugging (events log level).
599 debug_locks_verbose=
600 [KNL] verbose self-tests
601 Format=<0|1>
602 Print debugging info while doing the locking API
603 self-tests.
604 We default to 0 (no extra messages), setting it to
605 1 will print _a lot_ more information - normally
606 only useful to kernel developers.
608 debug_objects [KNL] Enable object debugging
610 debugpat [X86] Enable PAT debugging
612 decnet.addr= [HW,NET]
613 Format: <area>[,<node>]
614 See also Documentation/networking/decnet.txt.
616 vt.default_blu= [VT]
617 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
618 Change the default blue palette of the console.
619 This is a 16-member array composed of values
620 ranging from 0-255.
622 vt.default_grn= [VT]
623 Format: <green0>,<green1>,<green2>,...,<green15>
624 Change the default green palette of the console.
625 This is a 16-member array composed of values
626 ranging from 0-255.
628 vt.default_red= [VT]
629 Format: <red0>,<red1>,<red2>,...,<red15>
630 Change the default red palette of the console.
631 This is a 16-member array composed of values
632 ranging from 0-255.
634 vt.default_utf8=
635 [VT]
636 Format=<0|1>
637 Set system-wide default UTF-8 mode for all tty's.
638 Default is 1, i.e. UTF-8 mode is enabled for all
639 newly opened terminals.
641 dhash_entries= [KNL]
642 Set number of hash buckets for dentry cache.
644 digi= [HW,SERIAL]
645 IO parameters + enable/disable command.
647 digiepca= [HW,SERIAL]
648 See drivers/char/README.epca and
649 Documentation/serial/digiepca.txt.
651 disable_mtrr_cleanup [X86]
652 enable_mtrr_cleanup [X86]
653 The kernel tries to adjust MTRR layout from continuous
654 to discrete, to make X server driver able to add WB
655 entry later. This parameter enables/disables that.
657 mtrr_chunk_size=nn[KMG] [X86]
658 used for mtrr cleanup. It is largest continous chunk
659 that could hold holes aka. UC entries.
661 mtrr_gran_size=nn[KMG] [X86]
662 Used for mtrr cleanup. It is granularity of mtrr block.
663 Default is 1.
664 Large value could prevent small alignment from
665 using up MTRRs.
667 mtrr_spare_reg_nr=n [X86]
668 Format: <integer>
669 Range: 0,7 : spare reg number
670 Default : 1
671 Used for mtrr cleanup. It is spare mtrr entries number.
672 Set to 2 or more if your graphical card needs more.
674 disable_mtrr_trim [X86, Intel and AMD only]
675 By default the kernel will trim any uncacheable
676 memory out of your available memory pool based on
677 MTRR settings. This parameter disables that behavior,
678 possibly causing your machine to run very slowly.
680 dmasound= [HW,OSS] Sound subsystem buffers
682 dscc4.setup= [NET]
684 dtc3181e= [HW,SCSI]
686 earlyprintk= [X86-32,X86-64,SH,BLACKFIN]
687 earlyprintk=vga
688 earlyprintk=serial[,ttySn[,baudrate]]
689 earlyprintk=dbgp
691 Append ",keep" to not disable it when the real console
692 takes over.
694 Only vga or serial or usb debug port at a time.
696 Currently only ttyS0 and ttyS1 are supported.
698 Interaction with the standard serial driver is not
699 very good.
701 The VGA output is eventually overwritten by the real
702 console.
704 eata= [HW,SCSI]
706 edd= [EDD]
707 Format: {"off" | "on" | "skip[mbr]"}
709 eisa_irq_edge= [PARISC,HW]
710 See header of drivers/parisc/eisa.c.
712 elanfreq= [X86-32]
713 See comment before function elanfreq_setup() in
714 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
716 elevator= [IOSCHED]
717 Format: {"anticipatory" | "cfq" | "deadline" | "noop"}
718 See Documentation/block/as-iosched.txt and
719 Documentation/block/deadline-iosched.txt for details.
721 elfcorehdr= [IA64,PPC,SH,X86-32,X86_64]
722 Specifies physical address of start of kernel core
723 image elf header. Generally kexec loader will
724 pass this option to capture kernel.
725 See Documentation/kdump/kdump.txt for details.
727 enforcing [SELINUX] Set initial enforcing status.
728 Format: {"0" | "1"}
729 See security/selinux/Kconfig help text.
730 0 -- permissive (log only, no denials).
731 1 -- enforcing (deny and log).
732 Default value is 0.
733 Value can be changed at runtime via /selinux/enforce.
735 ether= [HW,NET] Ethernet cards parameters
736 This option is obsoleted by the "netdev=" option, which
737 has equivalent usage. See its documentation for details.
739 eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
740 Format: <io>[,<irq>]
742 failslab=
743 fail_page_alloc=
744 fail_make_request=[KNL]
745 General fault injection mechanism.
746 Format: <interval>,<probability>,<space>,<times>
747 See also /Documentation/fault-injection/.
749 fd_mcs= [HW,SCSI]
750 See header of drivers/scsi/fd_mcs.c.
752 fdomain= [HW,SCSI]
753 See header of drivers/scsi/fdomain.c.
755 floppy= [HW]
756 See Documentation/blockdev/floppy.txt.
758 force_pal_cache_flush
759 [IA-64] Avoid check_sal_cache_flush which may hang on
760 buggy SAL_CACHE_FLUSH implementations. Using this
761 parameter will force ia64_sal_cache_flush to call
762 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
764 ftrace=[tracer]
765 [ftrace] will set and start the specified tracer
766 as early as possible in order to facilitate early
767 boot debugging.
769 ftrace_dump_on_oops
770 [ftrace] will dump the trace buffers on oops.
772 gamecon.map[2|3]=
773 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
774 support via parallel port (up to 5 devices per port)
775 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
776 See also Documentation/input/joystick-parport.txt
778 gamma= [HW,DRM]
780 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
781 Format: off | on
782 default: on
784 gdth= [HW,SCSI]
785 See header of drivers/scsi/gdth.c.
787 gpt [EFI] Forces disk with valid GPT signature but
788 invalid Protective MBR to be treated as GPT.
790 gvp11= [HW,SCSI]
792 hashdist= [KNL,NUMA] Large hashes allocated during boot
793 are distributed across NUMA nodes. Defaults on
794 for IA-64, off otherwise.
795 Format: 0 | 1 (for off | on)
797 hcl= [IA-64] SGI's Hardware Graph compatibility layer
799 hd= [EIDE] (E)IDE hard drive subsystem geometry
800 Format: <cyl>,<head>,<sect>
802 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
803 size of <nn>. This works even on boxes that have no
804 highmem otherwise. This also works to reduce highmem
805 size on bigger boxes.
807 highres= [KNL] Enable/disable high resolution timer mode.
808 Valid parameters: "on", "off"
809 Default: "on"
811 hisax= [HW,ISDN]
812 See Documentation/isdn/README.HiSax.
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.
823 default_hugepagesz=
824 [same as hugepagesz=] The size of the default
825 HugeTLB page size. This is the size represented by
826 the legacy /proc/ hugepages APIs, used for SHM, and
827 default size when mounting hugetlbfs filesystems.
828 Defaults to the default architecture's huge page size
829 if not specified.
831 hlt [BUGS=ARM,SH]
833 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
834 terminal devices. Valid values: 0..8
835 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
836 If specified, z/VM IUCV HVC accepts connections
837 from listed z/VM user IDs only.
839 i2c_bus= [HW] Override the default board specific I2C bus speed
840 or register an additional I2C bus that is not
841 registered from board initialization code.
842 Format:
843 <bus_id>,<clkrate>
845 i8042.debug [HW] Toggle i8042 debug mode
846 i8042.direct [HW] Put keyboard port into non-translated mode
847 i8042.dumbkbd [HW] Pretend that controller can only read data from
848 keyboard and cannot control its state
849 (Don't attempt to blink the leds)
850 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
851 i8042.nokbd [HW] Don't check/create keyboard port
852 i8042.noloop [HW] Disable the AUX Loopback command while probing
853 for the AUX port
854 i8042.nomux [HW] Don't check presence of an active multiplexing
855 controller
856 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
857 controllers
858 i8042.panicblink=
859 [HW] Frequency with which keyboard LEDs should blink
860 when kernel panics (default is 0.5 sec)
861 i8042.reset [HW] Reset the controller during init and cleanup
862 i8042.unlock [HW] Unlock (ignore) the keylock
864 i810= [HW,DRM]
866 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
867 indicates that the driver is running on unsupported
868 hardware.
869 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
870 does not match list of supported models.
871 i8k.power_status
872 [HW] Report power status in /proc/i8k
873 (disabled by default)
874 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
875 capability is set.
877 ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
878 See Documentation/mca.txt.
880 icn= [HW,ISDN]
881 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
883 ide-core.nodma= [HW] (E)IDE subsystem
884 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
885 .vlb_clock .pci_clock .noflush .noprobe .nowerr .cdrom
886 .chs .ignore_cable are additional options
887 See Documentation/ide/ide.txt.
889 idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
890 See Documentation/ide/ide.txt.
892 idle= [X86]
893 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
894 Poll forces a polling idle loop that can slightly
895 improve the performance of waking up a idle CPU, but
896 will use a lot of power and make the system run hot.
897 Not recommended.
898 idle=mwait: On systems which support MONITOR/MWAIT but
899 the kernel chose to not use it because it doesn't save
900 as much power as a normal idle loop, use the
901 MONITOR/MWAIT idle loop anyways. Performance should be
902 the same as idle=poll.
903 idle=halt: Halt is forced to be used for CPU idle.
904 In such case C2/C3 won't be used again.
905 idle=nomwait: Disable mwait for CPU C-states
907 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
908 Claim all unknown PCI IDE storage controllers.
910 ignore_loglevel [KNL]
911 Ignore loglevel setting - this will print /all/
912 kernel messages to the console. Useful for debugging.
914 ihash_entries= [KNL]
915 Set number of hash buckets for inode cache.
917 ima_audit= [IMA]
918 Format: { "0" | "1" }
919 0 -- integrity auditing messages. (Default)
920 1 -- enable informational integrity auditing messages.
922 ima_hash= [IMA]
923 Formt: { "sha1" | "md5" }
924 default: "sha1"
926 in2000= [HW,SCSI]
927 See header of drivers/scsi/in2000.c.
929 init= [KNL]
930 Format: <full_path>
931 Run specified binary instead of /sbin/init as init
932 process.
934 initcall_debug [KNL] Trace initcalls as they are executed. Useful
935 for working out where the kernel is dying during
936 startup.
938 initrd= [BOOT] Specify the location of the initial ramdisk
940 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
941 Format: <irq>
943 inttest= [IA64]
945 iomem= Disable strict checking of access to MMIO memory
946 strict regions from userspace.
947 relaxed
949 iommu= [x86]
950 off
951 force
952 noforce
953 biomerge
954 panic
955 nopanic
956 merge
957 nomerge
958 forcesac
959 soft
962 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
963 on
964 Enable intel iommu driver.
965 off
966 Disable intel iommu driver.
967 igfx_off [Default Off]
968 By default, gfx is mapped as normal device. If a gfx
969 device has a dedicated DMAR unit, the DMAR unit is
970 bypassed by not enabling DMAR with this option. In
971 this case, gfx device will use physical address for
972 DMA.
973 forcedac [x86_64]
974 With this option iommu will not optimize to look
975 for io virtual address below 32 bit forcing dual
976 address cycle on pci bus for cards supporting greater
977 than 32 bit addressing. The default is to look
978 for translation below 32 bit and if not available
979 then look in the higher range.
980 strict [Default Off]
981 With this option on every unmap_single operation will
982 result in a hardware IOTLB flush operation as opposed
983 to batching them for performance.
985 io_delay= [X86-32,X86-64] I/O delay method
986 0x80
987 Standard port 0x80 based delay
988 0xed
989 Alternate port 0xed based delay (needed on some systems)
990 udelay
991 Simple two microseconds delay
992 none
993 No delay
995 io7= [HW] IO7 for Marvel based alpha systems
996 See comment before marvel_specify_io7 in
997 arch/alpha/kernel/core_marvel.c.
999 ip= [IP_PNP]
1000 See Documentation/filesystems/nfsroot.txt.
1002 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1003 See comment before ip2_setup() in
1004 drivers/char/ip2/ip2base.c.
1006 ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
1007 See header of drivers/scsi/ips.c.
1009 ports= [IP_VS_FTP] IPVS ftp helper module
1010 Default is 21.
1011 Up to 8 (IP_VS_APP_MAX_PORTS) ports
1012 may be specified.
1013 Format: <port>,<port>....
1015 irqfixup [HW]
1016 When an interrupt is not handled search all handlers
1017 for it. Intended to get systems with badly broken
1018 firmware running.
1020 irqpoll [HW]
1021 When an interrupt is not handled search all handlers
1022 for it. Also check all handlers each timer
1023 interrupt. Intended to get systems with badly broken
1024 firmware running.
1026 isapnp= [ISAPNP]
1027 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1029 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1030 Format:
1031 <cpu number>,...,<cpu number>
1032 or
1033 <cpu number>-<cpu number>
1034 (must be a positive range in ascending order)
1035 or a mixture
1036 <cpu number>,...,<cpu number>-<cpu number>
1038 This option can be used to specify one or more CPUs
1039 to isolate from the general SMP balancing and scheduling
1040 algorithms. You can move a process onto or off an
1041 "isolated" CPU via the CPU affinity syscalls or cpuset.
1042 <cpu number> begins at 0 and the maximum value is
1043 "number of CPUs in system - 1".
1045 This option is the preferred way to isolate CPUs. The
1046 alternative -- manually setting the CPU mask of all
1047 tasks in the system -- can cause problems and
1048 suboptimal load balancer performance.
1050 iucv= [HW,NET]
1052 js= [HW,JOY] Analog joystick
1053 See Documentation/input/joystick.txt.
1055 kernelcore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1056 specifies the amount of memory usable by the kernel
1057 for non-movable allocations. The requested amount is
1058 spread evenly throughout all nodes in the system. The
1059 remaining memory in each node is used for Movable
1060 pages. In the event, a node is too small to have both
1061 kernelcore and Movable pages, kernelcore pages will
1062 take priority and other nodes will have a larger number
1063 of kernelcore pages. The Movable zone is used for the
1064 allocation of pages that may be reclaimed or moved
1065 by the page migration subsystem. This means that
1066 HugeTLB pages may not be allocated from this zone.
1067 Note that allocations like PTEs-from-HighMem still
1068 use the HighMem zone if it exists, and the Normal
1069 zone if it does not.
1071 movablecore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1072 is similar to kernelcore except it specifies the
1073 amount of memory used for migratable allocations.
1074 If both kernelcore and movablecore is specified,
1075 then kernelcore will be at *least* the specified
1076 value but may be more. If movablecore on its own
1077 is specified, the administrator must be careful
1078 that the amount of memory usable for all allocations
1079 is not too small.
1081 keepinitrd [HW,ARM]
1083 kstack=N [X86-32,X86-64] Print N words from the kernel stack
1084 in oops dumps.
1086 kgdboc= [HW] kgdb over consoles.
1087 Requires a tty driver that supports console polling.
1088 (only serial suported for now)
1089 Format: <serial_device>[,baud]
1091 kmac= [MIPS] korina ethernet MAC address.
1092 Configure the RouterBoard 532 series on-chip
1093 Ethernet adapter MAC address.
1095 l2cr= [PPC]
1097 l3cr= [PPC]
1099 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1100 disabled it.
1102 lapic_timer_c2_ok [X86-32,x86-64,APIC] trust the local apic timer
1103 in C2 power state.
1105 libata.dma= [LIBATA] DMA control
1106 libata.dma=0 Disable all PATA and SATA DMA
1107 libata.dma=1 PATA and SATA Disk DMA only
1108 libata.dma=2 ATAPI (CDROM) DMA only
1109 libata.dma=4 Compact Flash DMA only
1110 Combinations also work, so libata.dma=3 enables DMA
1111 for disks and CDROMs, but not CFs.
1113 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1114 when set.
1115 Format: <int>
1117 libata.force= [LIBATA] Force configurations. The format is comma
1118 separated list of "[ID:]VAL" where ID is
1119 PORT[:DEVICE]. PORT and DEVICE are decimal numbers
1120 matching port, link or device. Basically, it matches
1121 the ATA ID string printed on console by libata. If
1122 the whole ID part is omitted, the last PORT and DEVICE
1123 values are used. If ID hasn't been specified yet, the
1124 configuration applies to all ports, links and devices.
1126 If only DEVICE is omitted, the parameter applies to
1127 the port and all links and devices behind it. DEVICE
1128 number of 0 either selects the first device or the
1129 first fan-out link behind PMP device. It does not
1130 select the host link. DEVICE number of 15 selects the
1131 host link and device attached to it.
1133 The VAL specifies the configuration to force. As long
1134 as there's no ambiguity shortcut notation is allowed.
1135 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1136 The following configurations can be forced.
1138 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1139 Any ID with matching PORT is used.
1141 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1143 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1144 udma[/][16,25,33,44,66,100,133] notation is also
1145 allowed.
1147 * [no]ncq: Turn on or off NCQ.
1149 * nohrst, nosrst, norst: suppress hard, soft
1150 and both resets.
1152 If there are multiple matching configurations changing
1153 the same attribute, the last one is used.
1155 lmb=debug [KNL] Enable lmb debug messages.
1157 load_ramdisk= [RAM] List of ramdisks to load from floppy
1158 See Documentation/blockdev/ramdisk.txt.
1160 lockd.nlm_grace_period=P [NFS] Assign grace period.
1161 Format: <integer>
1163 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1164 Format: <integer>
1166 lockd.nlm_timeout=T [NFS] Assign timeout value.
1167 Format: <integer>
1169 lockd.nlm_udpport=M [NFS] Assign UDP port.
1170 Format: <integer>
1172 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1173 Format: <irq>
1175 loglevel= All Kernel Messages with a loglevel smaller than the
1176 console loglevel will be printed to the console. It can
1177 also be changed with klogd or other programs. The
1178 loglevels are defined as follows:
1180 0 (KERN_EMERG) system is unusable
1181 1 (KERN_ALERT) action must be taken immediately
1182 2 (KERN_CRIT) critical conditions
1183 3 (KERN_ERR) error conditions
1184 4 (KERN_WARNING) warning conditions
1185 5 (KERN_NOTICE) normal but significant condition
1186 6 (KERN_INFO) informational
1187 7 (KERN_DEBUG) debug-level messages
1189 log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1190 Format: { n | nk | nM }
1191 n must be a power of two. The default size
1192 is set in the kernel config file.
1194 logo.nologo [FB] Disables display of the built-in Linux logo.
1195 This may be used to provide more screen space for
1196 kernel log messages and is useful when debugging
1197 kernel boot problems.
1199 lp=0 [LP] Specify parallel ports to use, e.g,
1200 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1201 lp=reset first parallel port). 'lp=0' disables the
1202 lp=auto printer driver. 'lp=reset' (which can be
1203 specified in addition to the ports) causes
1204 attached printers to be reset. Using
1205 lp=port1,port2,... specifies the parallel ports
1206 to associate lp devices with, starting with
1207 lp0. A port specification may be 'none' to skip
1208 that lp device, or a parport name such as
1209 'parport0'. Specifying 'lp=auto' instead of a
1210 port specification list means that device IDs
1211 from each port should be examined, to see if
1212 an IEEE 1284-compliant printer is attached; if
1213 so, the driver will manage that printer.
1214 See also header of drivers/char/lp.c.
1216 lpj=n [KNL]
1217 Sets loops_per_jiffy to given constant, thus avoiding
1218 time-consuming boot-time autodetection (up to 250 ms per
1219 CPU). 0 enables autodetection (default). To determine
1220 the correct value for your kernel, boot with normal
1221 autodetection and see what value is printed. Note that
1222 on SMP systems the preset will be applied to all CPUs,
1223 which is likely to cause problems if your CPUs need
1224 significantly divergent settings. An incorrect value
1225 will cause delays in the kernel to be wrong, leading to
1226 unpredictable I/O errors and other breakage. Although
1227 unlikely, in the extreme case this might damage your
1228 hardware.
1230 ltpc= [NET]
1231 Format: <io>,<irq>,<dma>
1233 mac5380= [HW,SCSI] Format:
1234 <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
1236 machvec= [IA64] Force the use of a particular machine-vector
1237 (machvec) in a generic kernel.
1238 Example: machvec=hpzx1_swiotlb
1240 max_loop= [LOOP] Maximum number of loopback devices that can
1241 be mounted
1242 Format: <1-256>
1244 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1245 should make use of. maxcpus=n : n >= 0 limits the
1246 kernel to using 'n' processors. n=0 is a special case,
1247 it is equivalent to "nosmp", which also disables
1248 the IO APIC.
1250 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater than
1251 or equal to this physical address is ignored.
1253 max_luns= [SCSI] Maximum number of LUNs to probe.
1254 Should be between 1 and 2^32-1.
1256 max_report_luns=
1257 [SCSI] Maximum number of LUNs received.
1258 Should be between 1 and 16384.
1260 mcatest= [IA-64]
1262 mce [X86-32] Machine Check Exception
1264 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1266 md= [HW] RAID subsystems devices and level
1267 See Documentation/md.txt.
1269 mdacon= [MDA]
1270 Format: <first>,<last>
1271 Specifies range of consoles to be captured by the MDA.
1273 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1274 Amount of memory to be used when the kernel is not able
1275 to see the whole system memory or for test.
1276 [X86-32] Use together with memmap= to avoid physical
1277 address space collisions. Without memmap= PCI devices
1278 could be placed at addresses belonging to unused RAM.
1280 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1281 memory.
1283 memchunk=nn[KMG]
1284 [KNL,SH] Allow user to override the default size for
1285 per-device physically contiguous DMA buffers.
1287 memmap=exactmap [KNL,X86-32,X86_64] Enable setting of an exact
1288 E820 memory map, as specified by the user.
1289 Such memmap=exactmap lines can be constructed based on
1290 BIOS output or other requirements. See the memmap=nn@ss
1291 option description.
1293 memmap=nn[KMG]@ss[KMG]
1294 [KNL] Force usage of a specific region of memory
1295 Region of memory to be used, from ss to ss+nn.
1297 memmap=nn[KMG]#ss[KMG]
1298 [KNL,ACPI] Mark specific memory as ACPI data.
1299 Region of memory to be used, from ss to ss+nn.
1301 memmap=nn[KMG]$ss[KMG]
1302 [KNL,ACPI] Mark specific memory as reserved.
1303 Region of memory to be used, from ss to ss+nn.
1304 Example: Exclude memory from 0x18690000-0x1869ffff
1305 memmap=64K$0x18690000
1306 or
1307 memmap=0x10000$0x18690000
1309 memory_corruption_check=0/1 [X86]
1310 Some BIOSes seem to corrupt the first 64k of
1311 memory when doing things like suspend/resume.
1312 Setting this option will scan the memory
1313 looking for corruption. Enabling this will
1314 both detect corruption and prevent the kernel
1315 from using the memory being corrupted.
1316 However, its intended as a diagnostic tool; if
1317 repeatable BIOS-originated corruption always
1318 affects the same memory, you can use memmap=
1319 to prevent the kernel from using that memory.
1321 memory_corruption_check_size=size [X86]
1322 By default it checks for corruption in the low
1323 64k, making this memory unavailable for normal
1324 use. Use this parameter to scan for
1325 corruption in more or less memory.
1327 memory_corruption_check_period=seconds [X86]
1328 By default it checks for corruption every 60
1329 seconds. Use this parameter to check at some
1330 other rate. 0 disables periodic checking.
1332 memtest= [KNL,X86] Enable memtest
1333 Format: <integer>
1334 default : 0 <disable>
1335 Specifies the number of memtest passes to be
1336 performed. Each pass selects another test
1337 pattern from a given set of patterns. Memtest
1338 fills the memory with this pattern, validates
1339 memory contents and reserves bad memory
1340 regions that are detected.
1342 meye.*= [HW] Set MotionEye Camera parameters
1343 See Documentation/video4linux/meye.txt.
1345 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1346 Multi-Function General Purpose Timers on AMD Geode
1347 platforms.
1349 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1350 the BIOS has incorrectly applied a workaround. TinyBIOS
1351 version 0.98 is known to be affected, 0.99 fixes the
1352 problem by letting the user disable the workaround.
1354 mga= [HW,DRM]
1356 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1357 physical address is ignored.
1359 mminit_loglevel=
1360 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1361 parameter allows control of the logging verbosity for
1362 the additional memory initialisation checks. A value
1363 of 0 disables mminit logging and a level of 4 will
1364 log everything. Information is printed at KERN_DEBUG
1365 so loglevel=8 may also need to be specified.
1367 mousedev.tap_time=
1368 [MOUSE] Maximum time between finger touching and
1369 leaving touchpad surface for touch to be considered
1370 a tap and be reported as a left button click (for
1371 touchpads working in absolute mode only).
1372 Format: <msecs>
1373 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1374 reporting absolute coordinates, such as tablets
1375 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1376 reporting absolute coordinates, such as tablets
1378 mpu401= [HW,OSS]
1379 Format: <io>,<irq>
1381 MTD_Partition= [MTD]
1382 Format: <name>,<region-number>,<size>,<offset>
1384 MTD_Region= [MTD] Format:
1385 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1387 mtdparts= [MTD]
1388 See drivers/mtd/cmdlinepart.c.
1390 mtdset= [ARM]
1391 ARM/S3C2412 JIVE boot control
1393 See arch/arm/mach-s3c2412/mach-jive.c
1395 mtouchusb.raw_coordinates=
1396 [HW] Make the MicroTouch USB driver use raw coordinates
1397 ('y', default) or cooked coordinates ('n')
1399 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1401 NCR_D700= [HW,SCSI]
1402 See header of drivers/scsi/NCR_D700.c.
1404 ncr5380= [HW,SCSI]
1406 ncr53c400= [HW,SCSI]
1408 ncr53c400a= [HW,SCSI]
1410 ncr53c406a= [HW,SCSI]
1412 ncr53c8xx= [HW,SCSI]
1414 netdev= [NET] Network devices parameters
1415 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1416 Note that mem_start is often overloaded to mean
1417 something different and driver-specific.
1418 This usage is only documented in each driver source
1419 file if at all.
1421 nf_conntrack.acct=
1422 [NETFILTER] Enable connection tracking flow accounting
1423 0 to disable accounting
1424 1 to enable accounting
1425 Default value depends on CONFIG_NF_CT_ACCT that is
1426 going to be removed in 2.6.29.
1428 nfsaddrs= [NFS]
1429 See Documentation/filesystems/nfsroot.txt.
1431 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1432 See Documentation/filesystems/nfsroot.txt.
1434 nfs.callback_tcpport=
1435 [NFS] set the TCP port on which the NFSv4 callback
1436 channel should listen.
1438 nfs.idmap_cache_timeout=
1439 [NFS] set the maximum lifetime for idmapper cache
1440 entries.
1442 nfs.enable_ino64=
1443 [NFS] enable 64-bit inode numbers.
1444 If zero, the NFS client will fake up a 32-bit inode
1445 number for the readdir() and stat() syscalls instead
1446 of returning the full 64-bit number.
1447 The default is to return 64-bit inode numbers.
1449 nmi_debug= [KNL,AVR32] Specify one or more actions to take
1450 when a NMI is triggered.
1451 Format: [state][,regs][,debounce][,die]
1453 nmi_watchdog= [KNL,BUGS=X86-32,X86-64] Debugging features for SMP kernels
1454 Format: [panic,][num]
1455 Valid num: 0,1,2
1456 0 - turn nmi_watchdog off
1457 1 - use the IO-APIC timer for the NMI watchdog
1458 2 - use the local APIC for the NMI watchdog using
1459 a performance counter. Note: This will use one performance
1460 counter and the local APIC's performance vector.
1461 When panic is specified panic when an NMI watchdog timeout occurs.
1462 This is useful when you use a panic=... timeout and need the box
1463 quickly up again.
1464 Instead of 1 and 2 it is possible to use the following
1465 symbolic names: lapic and ioapic
1466 Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1468 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1469 emulation library even if a 387 maths coprocessor
1470 is present.
1472 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1473 caches in the slab allocator. Saves per-node memory,
1474 but will impact performance.
1476 noalign [KNL,ARM]
1478 noapic [SMP,APIC] Tells the kernel to not make use of any
1479 IOAPICs that may be present in the system.
1481 nobats [PPC] Do not use BATs for mapping kernel lowmem
1482 on "Classic" PPC cores.
1484 nocache [ARM]
1486 nodelayacct [KNL] Disable per-task delay accounting
1488 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1490 nodsp [SH] Disable hardware DSP at boot time.
1492 noefi [X86-32,X86-64] Disable EFI runtime services support.
1494 noexec [IA-64]
1496 noexec [X86-32,X86-64]
1497 On X86-32 available only on PAE configured kernels.
1498 noexec=on: enable non-executable mappings (default)
1499 noexec=off: disable non-executable mappings
1501 noexec32 [X86-64]
1502 This affects only 32-bit executables.
1503 noexec32=on: enable non-executable mappings (default)
1504 read doesn't imply executable mappings
1505 noexec32=off: disable non-executable mappings
1506 read implies executable mappings
1508 nofpu [SH] Disable hardware FPU at boot time.
1510 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1511 register save and restore. The kernel will only save
1512 legacy floating-point registers on task switch.
1514 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1516 nohlt [BUGS=ARM,SH]
1518 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1519 instruction doesn't work correctly and not to
1520 use it.
1522 no_file_caps Tells the kernel not to honor file capabilities. The
1523 only way then for a file to be executed with privilege
1524 is to be setuid root or executed by root.
1526 nohalt [IA-64] Tells the kernel not to use the power saving
1527 function PAL_HALT_LIGHT when idle. This increases
1528 power-consumption. On the positive side, it reduces
1529 interrupt wake-up latency, which may improve performance
1530 in certain environments such as networked servers or
1531 real-time systems.
1533 nohz= [KNL] Boottime enable/disable dynamic ticks
1534 Valid arguments: on, off
1535 Default: on
1537 noirqdebug [X86-32] Disables the code which attempts to detect and
1538 disable unhandled interrupt sources.
1540 no_timer_check [X86-32,X86_64,APIC] Disables the code which tests for
1541 broken timer IRQ sources.
1543 noisapnp [ISAPNP] Disables ISA PnP code.
1545 noinitrd [RAM] Tells the kernel not to load any configured
1546 initial RAM disk.
1548 nointroute [IA-64]
1550 nojitter [IA64] Disables jitter checking for ITC timers.
1552 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1554 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1556 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1558 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
1559 default x2apic cluster mode on platforms
1560 supporting x2apic.
1562 noltlbs [PPC] Do not use large page/tlb entries for kernel
1563 lowmem mapping on PPC40x.
1565 nomca [IA-64] Disable machine check abort handling
1567 nomce [X86-32] Machine Check Exception
1569 nomfgpt [X86-32] Disable Multi-Function General Purpose
1570 Timer usage (for AMD Geode machines).
1572 noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops
1574 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1575 with UP alternatives
1577 noresidual [PPC] Don't use residual data on PReP machines.
1579 noresume [SWSUSP] Disables resume and restores original swap
1580 space.
1582 no-scroll [VGA] Disables scrollback.
1583 This is required for the Braillex ib80-piezo Braille
1584 reader made by F.H. Papenmeier (Germany).
1586 nosbagart [IA-64]
1588 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1590 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1591 and disable the IO APIC. legacy for "maxcpus=0".
1593 nosoftlockup [KNL] Disable the soft-lockup detector.
1595 noswapaccount [KNL] Disable accounting of swap in memory resource
1596 controller. (See Documentation/controllers/memory.txt)
1598 nosync [HW,M68K] Disables sync negotiation for all devices.
1600 notsc [BUGS=X86-32] Disable Time Stamp Counter
1602 nousb [USB] Disable the USB subsystem
1604 nowb [ARM]
1606 nptcg= [IA64] Override max number of concurrent global TLB
1607 purges which is reported from either PAL_VM_SUMMARY or
1608 SAL PALO.
1610 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1611 one of ['zone', 'node', 'default'] can be specified
1612 This can be set from sysctl after boot.
1613 See Documentation/sysctl/vm.txt for details.
1615 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1617 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1618 See Documentation/debugging-via-ohci1394.txt for more
1619 info.
1621 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1622 Rather than timing out after 20 ms if an EC
1623 command is not properly ACKed, override the length
1624 of the timeout. We have interrupts disabled while
1625 waiting for the ACK, so if this is set too high
1626 interrupts *may* be lost!
1628 opl3= [HW,OSS]
1629 Format: <io>
1631 oprofile.timer= [HW]
1632 Use timer interrupt instead of performance counters
1634 osst= [HW,SCSI] SCSI Tape Driver
1635 Format: <buffer_size>,<write_threshold>
1636 See also Documentation/scsi/st.txt.
1638 panic= [KNL] Kernel behaviour on panic
1639 Format: <timeout>
1641 parkbd.port= [HW] Parallel port number the keyboard adapter is
1642 connected to, default is 0.
1643 Format: <parport#>
1644 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1645 0 for XT, 1 for AT (default is AT).
1646 Format: <mode>
1648 parport= [HW,PPT] Specify parallel ports. 0 disables.
1649 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1650 Use 'auto' to force the driver to use any
1651 IRQ/DMA settings detected (the default is to
1652 ignore detected IRQ/DMA settings because of
1653 possible conflicts). You can specify the base
1654 address, IRQ, and DMA settings; IRQ and DMA
1655 should be numbers, or 'auto' (for using detected
1656 settings on that particular port), or 'nofifo'
1657 (to avoid using a FIFO even if it is detected).
1658 Parallel ports are assigned in the order they
1659 are specified on the command line, starting
1660 with parport0.
1662 parport_init_mode= [HW,PPT]
1663 Configure VIA parallel port to operate in
1664 a specific mode. This is necessary on Pegasos
1665 computer where firmware has no options for setting
1666 up parallel port mode and sets it to spp.
1667 Currently this function knows 686a and 8231 chips.
1668 Format: [spp|ps2|epp|ecp|ecpepp]
1670 pas2= [HW,OSS] Format:
1671 <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16>
1673 pas16= [HW,SCSI]
1674 See header of drivers/scsi/pas16.c.
1676 pause_on_oops=
1677 Halt all CPUs after the first oops has been printed for
1678 the specified number of seconds. This is to be used if
1679 your oopses keep scrolling off the screen.
1681 pcbit= [HW,ISDN]
1683 pcd. [PARIDE]
1684 See header of drivers/block/paride/pcd.c.
1685 See also Documentation/blockdev/paride.txt.
1687 pci=option[,option...] [PCI] various PCI subsystem options:
1688 off [X86] don't probe for the PCI bus
1689 bios [X86-32] force use of PCI BIOS, don't access
1690 the hardware directly. Use this if your machine
1691 has a non-standard PCI host bridge.
1692 nobios [X86-32] disallow use of PCI BIOS, only direct
1693 hardware access methods are allowed. Use this
1694 if you experience crashes upon bootup and you
1695 suspect they are caused by the BIOS.
1696 conf1 [X86] Force use of PCI Configuration
1697 Mechanism 1.
1698 conf2 [X86] Force use of PCI Configuration
1699 Mechanism 2.
1700 noaer [PCIE] If the PCIEAER kernel config parameter is
1701 enabled, this kernel boot option can be used to
1702 disable the use of PCIE advanced error reporting.
1703 nodomains [PCI] Disable support for multiple PCI
1704 root domains (aka PCI segments, in ACPI-speak).
1705 nommconf [X86-32,X86_64] Disable use of MMCONFIG for PCI
1706 Configuration
1707 nomsi [MSI] If the PCI_MSI kernel config parameter is
1708 enabled, this kernel boot option can be used to
1709 disable the use of MSI interrupts system-wide.
1710 noioapicquirk [APIC] Disable all boot interrupt quirks.
1711 Safety option to keep boot IRQs enabled. This
1712 should never be necessary.
1713 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1714 primary IO-APIC for bridges that cannot disable
1715 boot IRQs. This fixes a source of spurious IRQs
1716 when the system masks IRQs.
1717 noioapicreroute [APIC] Disable workaround that uses the
1718 boot IRQ equivalent of an IRQ that connects to
1719 a chipset where boot IRQs cannot be disabled.
1720 The opposite of ioapicreroute.
1721 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1722 routing table. These calls are known to be buggy
1723 on several machines and they hang the machine
1724 when used, but on other computers it's the only
1725 way to get the interrupt routing table. Try
1726 this option if the kernel is unable to allocate
1727 IRQs or discover secondary PCI buses on your
1728 motherboard.
1729 rom [X86] Assign address space to expansion ROMs.
1730 Use with caution as certain devices share
1731 address decoders between ROMs and other
1732 resources.
1733 norom [X86] Do not assign address space to
1734 expansion ROMs that do not already have
1735 BIOS assigned address ranges.
1736 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1737 assigned automatically to PCI devices. You can
1738 make the kernel exclude IRQs of your ISA cards
1739 this way.
1740 pirqaddr=0xAAAAA [X86] Specify the physical address
1741 of the PIRQ table (normally generated
1742 by the BIOS) if it is outside the
1743 F0000h-100000h range.
1744 lastbus=N [X86] Scan all buses thru bus #N. Can be
1745 useful if the kernel is unable to find your
1746 secondary buses and you want to tell it
1747 explicitly which ones they are.
1748 assign-busses [X86] Always assign all PCI bus
1749 numbers ourselves, overriding
1750 whatever the firmware may have done.
1751 usepirqmask [X86] Honor the possible IRQ mask stored
1752 in the BIOS $PIR table. This is needed on
1753 some systems with broken BIOSes, notably
1754 some HP Pavilion N5400 and Omnibook XE3
1755 notebooks. This will have no effect if ACPI
1756 IRQ routing is enabled.
1757 noacpi [X86] Do not use ACPI for IRQ routing
1758 or for PCI scanning.
1759 use_crs [X86] Use _CRS for PCI resource
1760 allocation.
1761 routeirq Do IRQ routing for all PCI devices.
1762 This is normally done in pci_enable_device(),
1763 so this option is a temporary workaround
1764 for broken drivers that don't call it.
1765 skip_isa_align [X86] do not align io start addr, so can
1766 handle more pci cards
1767 firmware [ARM] Do not re-enumerate the bus but instead
1768 just use the configuration from the
1769 bootloader. This is currently used on
1770 IXP2000 systems where the bus has to be
1771 configured a certain way for adjunct CPUs.
1772 noearly [X86] Don't do any early type 1 scanning.
1773 This might help on some broken boards which
1774 machine check when some devices' config space
1775 is read. But various workarounds are disabled
1776 and some IOMMU drivers will not work.
1777 bfsort Sort PCI devices into breadth-first order.
1778 This sorting is done to get a device
1779 order compatible with older (<= 2.4) kernels.
1780 nobfsort Don't sort PCI devices into breadth-first order.
1781 cbiosize=nn[KMG] The fixed amount of bus space which is
1782 reserved for the CardBus bridge's IO window.
1783 The default value is 256 bytes.
1784 cbmemsize=nn[KMG] The fixed amount of bus space which is
1785 reserved for the CardBus bridge's memory
1786 window. The default value is 64 megabytes.
1788 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1789 Management.
1790 off Disable ASPM.
1791 force Enable ASPM even on devices that claim not to support it.
1792 WARNING: Forcing ASPM on may cause system lockups.
1794 pcmv= [HW,PCMCIA] BadgePAD 4
1796 pd. [PARIDE]
1797 See Documentation/blockdev/paride.txt.
1799 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
1800 boot time.
1801 Format: { 0 | 1 }
1802 See arch/parisc/kernel/pdc_chassis.c
1804 pf. [PARIDE]
1805 See Documentation/blockdev/paride.txt.
1807 pg. [PARIDE]
1808 See Documentation/blockdev/paride.txt.
1810 pirq= [SMP,APIC] Manual mp-table setup
1811 See Documentation/x86/i386/IO-APIC.txt.
1813 plip= [PPT,NET] Parallel port network link
1814 Format: { parport<nr> | timid | 0 }
1815 See also Documentation/parport.txt.
1817 pmtmr= [X86] Manual setup of pmtmr I/O Port.
1818 Override pmtimer IOPort with a hex value.
1819 e.g. pmtmr=0x508
1821 pnp.debug [PNP]
1822 Enable PNP debug messages. This depends on the
1823 CONFIG_PNP_DEBUG_MESSAGES option.
1825 pnpacpi= [ACPI]
1826 { off }
1828 pnpbios= [ISAPNP]
1829 { on | off | curr | res | no-curr | no-res }
1831 pnp_reserve_irq=
1832 [ISAPNP] Exclude IRQs for the autoconfiguration
1834 pnp_reserve_dma=
1835 [ISAPNP] Exclude DMAs for the autoconfiguration
1837 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
1838 Ranges are in pairs (I/O port base and size).
1840 pnp_reserve_mem=
1841 [ISAPNP] Exclude memory regions for the
1842 autoconfiguration.
1843 Ranges are in pairs (memory base and size).
1845 print-fatal-signals=
1846 [KNL] debug: print fatal signals
1847 print-fatal-signals=1: print segfault info to
1848 the kernel console.
1849 default: off.
1851 printk.time= Show timing data prefixed to each printk message line
1852 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
1854 profile= [KNL] Enable kernel profiling via /proc/profile
1855 Format: [schedule,]<number>
1856 Param: "schedule" - profile schedule points.
1857 Param: <number> - step/bucket size as a power of 2 for
1858 statistical time based profiling.
1859 Param: "sleep" - profile D-state sleeping (millisecs).
1860 Requires CONFIG_SCHEDSTATS
1861 Param: "kvm" - profile VM exits.
1863 processor.max_cstate= [HW,ACPI]
1864 Limit processor to maximum C-state
1865 max_cstate=9 overrides any DMI blacklist limit.
1867 processor.nocst [HW,ACPI]
1868 Ignore the _CST method to determine C-states,
1869 instead using the legacy FADT method
1871 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
1872 before loading.
1873 See Documentation/blockdev/ramdisk.txt.
1875 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
1876 probe for; one of (bare|imps|exps|lifebook|any).
1877 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
1878 per second.
1879 psmouse.resetafter= [HW,MOUSE]
1880 Try to reset the device after so many bad packets
1881 (0 = never).
1882 psmouse.resolution=
1883 [HW,MOUSE] Set desired mouse resolution, in dpi.
1884 psmouse.smartscroll=
1885 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1886 0 = disabled, 1 = enabled (default).
1888 pss= [HW,OSS] Personal Sound System (ECHO ESC614)
1889 Format:
1890 <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq>
1892 pt. [PARIDE]
1893 See Documentation/blockdev/paride.txt.
1895 pty.legacy_count=
1896 [KNL] Number of legacy pty's. Overwrites compiled-in
1897 default number.
1899 quiet [KNL] Disable most log messages
1901 r128= [HW,DRM]
1903 raid= [HW,RAID]
1904 See Documentation/md.txt.
1906 ramdisk_blocksize= [RAM]
1907 See Documentation/blockdev/ramdisk.txt.
1909 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
1910 See Documentation/blockdev/ramdisk.txt.
1912 rcupdate.blimit= [KNL,BOOT]
1913 Set maximum number of finished RCU callbacks to process
1914 in one batch.
1916 rcupdate.qhimark= [KNL,BOOT]
1917 Set threshold of queued
1918 RCU callbacks over which batch limiting is disabled.
1920 rcupdate.qlowmark= [KNL,BOOT]
1921 Set threshold of queued RCU callbacks below which
1922 batch limiting is re-enabled.
1924 rdinit= [KNL]
1925 Format: <full_path>
1926 Run specified binary instead of /init from the ramdisk,
1927 used for early userspace startup. See initrd.
1929 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
1930 Format: <reboot_mode>[,<reboot_mode2>[,...]]
1931 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
1933 relax_domain_level=
1934 [KNL, SMP] Set scheduler's default relax_domain_level.
1935 See Documentation/cpusets.txt.
1937 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
1939 reservetop= [X86-32]
1940 Format: nn[KMG]
1941 Reserves a hole at the top of the kernel virtual
1942 address space.
1944 reset_devices [KNL] Force drivers to reset the underlying device
1945 during initialization.
1947 resume= [SWSUSP]
1948 Specify the partition device for software suspend
1950 resume_offset= [SWSUSP]
1951 Specify the offset from the beginning of the partition
1952 given by "resume=" at which the swap header is located,
1953 in <PAGE_SIZE> units (needed only for swap files).
1954 See Documentation/power/swsusp-and-swap-files.txt
1956 retain_initrd [RAM] Keep initrd memory after extraction
1958 rhash_entries= [KNL,NET]
1959 Set number of hash buckets for route cache
1961 riscom8= [HW,SERIAL]
1962 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
1964 ro [KNL] Mount root device read-only on boot
1966 root= [KNL] Root filesystem
1968 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
1969 mount the root filesystem
1971 rootflags= [KNL] Set root filesystem mount option string
1973 rootfstype= [KNL] Set root filesystem type
1975 rootwait [KNL] Wait (indefinitely) for root device to show up.
1976 Useful for devices that are detected asynchronously
1977 (e.g. USB and MMC devices).
1979 root_plug.vendor_id=
1980 [ROOTPLUG] Override the default vendor ID
1982 root_plug.product_id=
1983 [ROOTPLUG] Override the default product ID
1985 root_plug.debug=
1986 [ROOTPLUG] Enable debugging output
1988 rw [KNL] Mount root device read-write on boot
1990 S [KNL] Run init in single mode
1992 sa1100ir [NET]
1993 See drivers/net/irda/sa1100_ir.c.
1995 sbni= [NET] Granch SBNI12 leased line adapter
1997 sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
1998 Format: <io>[,<timeout>[,<isapnp>]]
2000 scsi_debug_*= [SCSI]
2001 See drivers/scsi/scsi_debug.c.
2003 scsi_default_dev_flags=
2004 [SCSI] SCSI default device flags
2005 Format: <integer>
2007 scsi_dev_flags= [SCSI] Black/white list entry for vendor and model
2008 Format: <vendor>:<model>:<flags>
2009 (flags are integer value)
2011 scsi_logging_level= [SCSI] a bit mask of logging levels
2012 See drivers/scsi/scsi_logging.h for bits. Also
2013 settable via sysctl at dev.scsi.logging_level
2014 (/proc/sys/dev/scsi/logging_level).
2015 There is also a nice 'scsi_logging_level' script in the
2016 S390-tools package, available for download at
2017 http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
2019 scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
2020 discovered. async scans them in kernel threads,
2021 allowing boot to proceed. none ignores them, expecting
2022 user space to do the scan.
2024 selinux [SELINUX] Disable or enable SELinux at boot time.
2025 Format: { "0" | "1" }
2026 See security/selinux/Kconfig help text.
2027 0 -- disable.
2028 1 -- enable.
2029 Default value is set via kernel config option.
2030 If enabled at boot time, /selinux/disable can be used
2031 later to disable prior to initial policy load.
2033 serialnumber [BUGS=X86-32]
2035 shapers= [NET]
2036 Maximal number of shapers.
2038 show_msr= [x86] show boot-time MSR settings
2039 Format: { <integer> }
2040 Show boot-time (BIOS-initialized) MSR settings.
2041 The parameter means the number of CPUs to show,
2042 for example 1 means boot CPU only.
2044 sim710= [SCSI,HW]
2045 See header of drivers/scsi/sim710.c.
2047 simeth= [IA-64]
2048 simscsi=
2050 slram= [HW,MTD]
2052 slub_debug[=options[,slabs]] [MM, SLUB]
2053 Enabling slub_debug allows one to determine the
2054 culprit if slab objects become corrupted. Enabling
2055 slub_debug can create guard zones around objects and
2056 may poison objects when not in use. Also tracks the
2057 last alloc / free. For more information see
2058 Documentation/vm/slub.txt.
2060 slub_max_order= [MM, SLUB]
2061 Determines the maximum allowed order for slabs.
2062 A high setting may cause OOMs due to memory
2063 fragmentation. For more information see
2064 Documentation/vm/slub.txt.
2066 slub_min_objects= [MM, SLUB]
2067 The minimum number of objects per slab. SLUB will
2068 increase the slab order up to slub_max_order to
2069 generate a sufficiently large slab able to contain
2070 the number of objects indicated. The higher the number
2071 of objects the smaller the overhead of tracking slabs
2072 and the less frequently locks need to be acquired.
2073 For more information see Documentation/vm/slub.txt.
2075 slub_min_order= [MM, SLUB]
2076 Determines the mininum page order for slabs. Must be
2077 lower than slub_max_order.
2078 For more information see Documentation/vm/slub.txt.
2080 slub_nomerge [MM, SLUB]
2081 Disable merging of slabs with similar size. May be
2082 necessary if there is some reason to distinguish
2083 allocs to different slabs. Debug options disable
2084 merging on their own.
2085 For more information see Documentation/vm/slub.txt.
2087 smart2= [HW]
2088 Format: <io1>[,<io2>[,...,<io8>]]
2090 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2091 attempt to substitute SMP alternatives once at boot.
2093 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2094 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2095 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2096 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2097 smsc-ircc2.ircc_irq= [HW] IRQ line
2098 smsc-ircc2.ircc_dma= [HW] DMA channel
2099 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2100 0: Toshiba Satellite 1800 (GP data pin select)
2101 1: Fast pin select (default)
2102 2: ATC IRMode
2104 snd-ad1816a= [HW,ALSA]
2106 snd-ad1848= [HW,ALSA]
2108 snd-ali5451= [HW,ALSA]
2110 snd-als100= [HW,ALSA]
2112 snd-als4000= [HW,ALSA]
2114 snd-azt2320= [HW,ALSA]
2116 snd-cmi8330= [HW,ALSA]
2118 snd-cmipci= [HW,ALSA]
2120 snd-cs4231= [HW,ALSA]
2122 snd-cs4232= [HW,ALSA]
2124 snd-cs4236= [HW,ALSA]
2126 snd-cs4281= [HW,ALSA]
2128 snd-cs46xx= [HW,ALSA]
2130 snd-dt019x= [HW,ALSA]
2132 snd-dummy= [HW,ALSA]
2134 snd-emu10k1= [HW,ALSA]
2136 snd-ens1370= [HW,ALSA]
2138 snd-ens1371= [HW,ALSA]
2140 snd-es968= [HW,ALSA]
2142 snd-es1688= [HW,ALSA]
2144 snd-es18xx= [HW,ALSA]
2146 snd-es1938= [HW,ALSA]
2148 snd-es1968= [HW,ALSA]
2150 snd-fm801= [HW,ALSA]
2152 snd-gusclassic= [HW,ALSA]
2154 snd-gusextreme= [HW,ALSA]
2156 snd-gusmax= [HW,ALSA]
2158 snd-hdsp= [HW,ALSA]
2160 snd-ice1712= [HW,ALSA]
2162 snd-intel8x0= [HW,ALSA]
2164 snd-interwave= [HW,ALSA]
2166 snd-interwave-stb=
2167 [HW,ALSA]
2169 snd-korg1212= [HW,ALSA]
2171 snd-maestro3= [HW,ALSA]
2173 snd-mpu401= [HW,ALSA]
2175 snd-mtpav= [HW,ALSA]
2177 snd-nm256= [HW,ALSA]
2179 snd-opl3sa2= [HW,ALSA]
2181 snd-opti92x-ad1848=
2182 [HW,ALSA]
2184 snd-opti92x-cs4231=
2185 [HW,ALSA]
2187 snd-opti93x= [HW,ALSA]
2189 snd-pmac= [HW,ALSA]
2191 snd-rme32= [HW,ALSA]
2193 snd-rme96= [HW,ALSA]
2195 snd-rme9652= [HW,ALSA]
2197 snd-sb8= [HW,ALSA]
2199 snd-sb16= [HW,ALSA]
2201 snd-sbawe= [HW,ALSA]
2203 snd-serial= [HW,ALSA]
2205 snd-sgalaxy= [HW,ALSA]
2207 snd-sonicvibes= [HW,ALSA]
2209 snd-sun-amd7930=
2210 [HW,ALSA]
2212 snd-sun-cs4231= [HW,ALSA]
2214 snd-trident= [HW,ALSA]
2216 snd-usb-audio= [HW,ALSA,USB]
2218 snd-via82xx= [HW,ALSA]
2220 snd-virmidi= [HW,ALSA]
2222 snd-wavefront= [HW,ALSA]
2224 snd-ymfpci= [HW,ALSA]
2226 softlockup_panic=
2227 [KNL] Should the soft-lockup detector generate panics.
2229 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2230 See Documentation/sonypi.txt
2232 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2233 See Documentation/serial/specialix.txt.
2235 spia_io_base= [HW,MTD]
2236 spia_fio_base=
2237 spia_pedr=
2238 spia_peddr=
2240 sscape= [HW,OSS]
2241 Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq>
2243 st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
2244 See Documentation/scsi/st.txt.
2246 stacktrace [FTRACE]
2247 Enabled the stack tracer on boot up.
2249 sti= [PARISC,HW]
2250 Format: <num>
2251 Set the STI (builtin display/keyboard on the HP-PARISC
2252 machines) console (graphic card) which should be used
2253 as the initial boot-console.
2254 See also comment in drivers/video/console/sticore.c.
2256 sti_font= [HW]
2257 See comment in drivers/video/console/sticore.c.
2259 stifb= [HW]
2260 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2262 sunrpc.pool_mode=
2263 [NFS]
2264 Control how the NFS server code allocates CPUs to
2265 service thread pools. Depending on how many NICs
2266 you have and where their interrupts are bound, this
2267 option will affect which CPUs will do NFS serving.
2268 Note: this parameter cannot be changed while the
2269 NFS server is running.
2271 auto the server chooses an appropriate mode
2272 automatically using heuristics
2273 global a single global pool contains all CPUs
2274 percpu one pool for each CPU
2275 pernode one pool for each NUMA node (equivalent
2276 to global on non-NUMA machines)
2278 swiotlb= [IA-64] Number of I/O TLB slabs
2280 switches= [HW,M68k]
2282 sym53c416= [HW,SCSI]
2283 See header of drivers/scsi/sym53c416.c.
2285 sysrq_always_enabled
2286 [KNL]
2287 Ignore sysrq setting - this boot parameter will
2288 neutralize any effect of /proc/sys/kernel/sysrq.
2289 Useful for debugging.
2291 t128= [HW,SCSI]
2292 See header of drivers/scsi/t128.c.
2294 tdfx= [HW,DRM]
2296 test_suspend= [SUSPEND]
2297 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2298 standby suspend) as the system sleep state to briefly
2299 enter during system startup. The system is woken from
2300 this state using a wakeup-capable RTC alarm.
2302 thash_entries= [KNL,NET]
2303 Set number of hash buckets for TCP connection
2305 thermal.act= [HW,ACPI]
2306 -1: disable all active trip points in all thermal zones
2307 <degrees C>: override all lowest active trip points
2309 thermal.crt= [HW,ACPI]
2310 -1: disable all critical trip points in all thermal zones
2311 <degrees C>: override all critical trip points
2313 thermal.nocrt= [HW,ACPI]
2314 Set to disable actions on ACPI thermal zone
2315 critical and hot trip points.
2317 thermal.off= [HW,ACPI]
2318 1: disable ACPI thermal control
2320 thermal.psv= [HW,ACPI]
2321 -1: disable all passive trip points
2322 <degrees C>: override all passive trip points to this
2323 value
2325 thermal.tzp= [HW,ACPI]
2326 Specify global default ACPI thermal zone polling rate
2327 <deci-seconds>: poll all this frequency
2328 0: no polling (default)
2330 tmscsim= [HW,SCSI]
2331 See comment before function dc390_setup() in
2332 drivers/scsi/tmscsim.c.
2334 topology= [S390]
2335 Format: {off | on}
2336 Specify if the kernel should make use of the cpu
2337 topology informations if the hardware supports these.
2338 The scheduler will make use of these informations and
2339 e.g. base its process migration decisions on it.
2340 Default is off.
2342 tp720= [HW,PS2]
2344 trix= [HW,OSS] MediaTrix AudioTrix Pro
2345 Format:
2346 <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
2348 tsc= Disable clocksource-must-verify flag for TSC.
2349 Format: <string>
2350 [x86] reliable: mark tsc clocksource as reliable, this
2351 disables clocksource verification at runtime.
2352 Used to enable high-resolution timer mode on older
2353 hardware, and in virtualized environment.
2355 turbografx.map[2|3]= [HW,JOY]
2356 TurboGraFX parallel port interface
2357 Format:
2358 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2359 See also Documentation/input/joystick-parport.txt
2361 u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter
2362 See header of drivers/scsi/u14-34f.c.
2364 uart401= [HW,OSS]
2365 Format: <io>,<irq>
2367 uart6850= [HW,OSS]
2368 Format: <io>,<irq>
2370 uhci-hcd.ignore_oc=
2371 [USB] Ignore overcurrent events (default N).
2372 Some badly-designed motherboards generate lots of
2373 bogus events, for ports that aren't wired to
2374 anything. Set this parameter to avoid log spamming.
2375 Note that genuine overcurrent events won't be
2376 reported either.
2378 unknown_nmi_panic
2379 [X86-32,X86-64]
2380 Set unknown_nmi_panic=1 early on boot.
2382 usbcore.autosuspend=
2383 [USB] The autosuspend time delay (in seconds) used
2384 for newly-detected USB devices (default 2). This
2385 is the time required before an idle device will be
2386 autosuspended. Devices for which the delay is set
2387 to a negative value won't be autosuspended at all.
2389 usbcore.usbfs_snoop=
2390 [USB] Set to log all usbfs traffic (default 0 = off).
2392 usbcore.blinkenlights=
2393 [USB] Set to cycle leds on hubs (default 0 = off).
2395 usbcore.old_scheme_first=
2396 [USB] Start with the old device initialization
2397 scheme (default 0 = off).
2399 usbcore.use_both_schemes=
2400 [USB] Try the other device initialization scheme
2401 if the first one fails (default 1 = enabled).
2403 usbcore.initial_descriptor_timeout=
2404 [USB] Specifies timeout for the initial 64-byte
2405 USB_REQ_GET_DESCRIPTOR request in milliseconds
2406 (default 5000 = 5.0 seconds).
2408 usbhid.mousepoll=
2409 [USBHID] The interval which mice are to be polled at.
2411 usb-storage.delay_use=
2412 [UMS] The delay in seconds before a new device is
2413 scanned for Logical Units (default 5).
2415 usb-storage.quirks=
2416 [UMS] A list of quirks entries to supplement or
2417 override the built-in unusual_devs list. List
2418 entries are separated by commas. Each entry has
2419 the form VID:PID:Flags where VID and PID are Vendor
2420 and Product ID values (4-digit hex numbers) and
2421 Flags is a set of characters, each corresponding
2422 to a common usb-storage quirk flag as follows:
2423 a = SANE_SENSE (collect more than 18 bytes
2424 of sense data);
2425 c = FIX_CAPACITY (decrease the reported
2426 device capacity by one sector);
2427 h = CAPACITY_HEURISTICS (decrease the
2428 reported device capacity by one
2429 sector if the number is odd);
2430 i = IGNORE_DEVICE (don't bind to this
2431 device);
2432 l = NOT_LOCKABLE (don't try to lock and
2433 unlock ejectable media);
2434 m = MAX_SECTORS_64 (don't transfer more
2435 than 64 sectors = 32 KB at a time);
2436 o = CAPACITY_OK (accept the capacity
2437 reported by the device);
2438 r = IGNORE_RESIDUE (the device reports
2439 bogus residue values);
2440 s = SINGLE_LUN (the device has only one
2441 Logical Unit);
2442 w = NO_WP_DETECT (don't test whether the
2443 medium is write-protected).
2444 Example: quirks=0419:aaf5:rl,0421:0433:rc
2446 add_efi_memmap [EFI; x86-32,X86-64] Include EFI memory map in
2447 kernel's map of available physical RAM.
2449 vdso= [X86-32,SH,x86-64]
2450 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2451 vdso=1: enable VDSO (default)
2452 vdso=0: disable VDSO mapping
2454 vdso32= [X86-32,X86-64]
2455 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2456 vdso32=1: enable 32-bit VDSO (default)
2457 vdso32=0: disable 32-bit VDSO mapping
2459 vector= [IA-64,SMP]
2460 vector=percpu: enable percpu vector domain
2462 video= [FB] Frame buffer configuration
2463 See Documentation/fb/modedb.txt.
2465 vga= [BOOT,X86-32] Select a particular video mode
2466 See Documentation/x86/boot.txt and
2467 Documentation/svga.txt.
2468 Use vga=ask for menu.
2469 This is actually a boot loader parameter; the value is
2470 passed to the kernel using a special protocol.
2472 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2473 size of <nn>. This can be used to increase the
2474 minimum size (128MB on x86). It can also be used to
2475 decrease the size and leave more room for directly
2476 mapped kernel RAM.
2478 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2479 Format: <command>
2481 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2482 Format: <command>
2484 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2485 Format: <command>
2487 waveartist= [HW,OSS]
2488 Format: <io>,<irq>,<dma>,<dma2>
2490 wd33c93= [HW,SCSI]
2491 See header of drivers/scsi/wd33c93.c.
2493 wd7000= [HW,SCSI]
2494 See header of drivers/scsi/wd7000.c.
2496 wdt= [WDT] Watchdog
2497 See Documentation/watchdog/wdt.txt.
2499 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2500 xd_geo= See header of drivers/block/xd.c.
2502 xirc2ps_cs= [NET,PCMCIA]
2503 Format:
2504 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2506 norandmaps Don't use address space randomization. Equivalent to
2507 echo 0 > /proc/sys/kernel/randomize_va_space
2509 ______________________________________________________________________
2511 TODO:
2513 Add documentation for ALSA options.
2514 Add more DRM drivers.