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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 KMEMTRACE kmemtrace is enabled.
54 LIBATA Libata driver is enabled
55 LP Printer support is enabled.
56 LOOP Loopback device support is enabled.
57 M68k M68k architecture is enabled.
58 These options have more detailed description inside of
59 Documentation/m68k/kernel-options.txt.
60 MCA MCA bus support is enabled.
61 MDA MDA console support is enabled.
62 MOUSE Appropriate mouse support is enabled.
63 MSI Message Signaled Interrupts (PCI).
64 MTD MTD (Memory Technology Device) support is enabled.
65 NET Appropriate network support is enabled.
66 NUMA NUMA support is enabled.
67 GENERIC_TIME The generic timeofday code is enabled.
68 NFS Appropriate NFS support is enabled.
69 OSS OSS sound support is enabled.
70 PV_OPS A paravirtualized kernel is enabled.
71 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
72 PARISC The PA-RISC architecture is enabled.
73 PCI PCI bus support is enabled.
74 PCIE PCI Express support is enabled.
75 PCMCIA The PCMCIA subsystem is enabled.
76 PNP Plug & Play support is enabled.
77 PPC PowerPC architecture is enabled.
78 PPT Parallel port support is enabled.
79 PS2 Appropriate PS/2 support is enabled.
80 RAM RAM disk support is enabled.
81 ROOTPLUG The example Root Plug LSM is enabled.
82 S390 S390 architecture is enabled.
83 SCSI Appropriate SCSI support is enabled.
84 A lot of drivers has their options described inside of
85 Documentation/scsi/.
86 SECURITY Different security models are enabled.
87 SELINUX SELinux support is enabled.
88 SERIAL Serial support is enabled.
89 SH SuperH architecture is enabled.
90 SMP The kernel is an SMP kernel.
91 SPARC Sparc architecture is enabled.
92 SWSUSP Software suspend (hibernation) is enabled.
93 SUSPEND System suspend states are enabled.
94 FTRACE Function tracing enabled.
95 TS Appropriate touchscreen support is enabled.
96 UMS USB Mass Storage support is enabled.
97 USB USB support is enabled.
98 USBHID USB Human Interface Device support is enabled.
99 V4L Video For Linux support is enabled.
100 VGA The VGA console has been enabled.
101 VT Virtual terminal support is enabled.
102 WDT Watchdog support is enabled.
103 XT IBM PC/XT MFM hard disk support is enabled.
104 X86-32 X86-32, aka i386 architecture is enabled.
105 X86-64 X86-64 architecture is enabled.
106 More X86-64 boot options can be found in
107 Documentation/x86/x86_64/boot-options.txt .
108 X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
110 In addition, the following text indicates that the option:
112 BUGS= Relates to possible processor bugs on the said processor.
113 KNL Is a kernel start-up parameter.
114 BOOT Is a boot loader parameter.
116 Parameters denoted with BOOT are actually interpreted by the boot
117 loader, and have no meaning to the kernel directly.
118 Do not modify the syntax of boot loader parameters without extreme
119 need or coordination with <Documentation/x86/boot.txt>.
121 There are also arch-specific kernel-parameters not documented here.
122 See for example <Documentation/x86/x86_64/boot-options.txt>.
124 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
125 a trailing = on the name of any parameter states that that parameter will
126 be entered as an environment variable, whereas its absence indicates that
127 it will appear as a kernel argument readable via /proc/cmdline by programs
128 running once the system is up.
130 The number of kernel parameters is not limited, but the length of the
131 complete command line (parameters including spaces etc.) is limited to
132 a fixed number of characters. This limit depends on the architecture
133 and is between 256 and 4096 characters. It is defined in the file
134 ./include/asm/setup.h as COMMAND_LINE_SIZE.
137 acpi= [HW,ACPI,X86-64,i386]
138 Advanced Configuration and Power Interface
139 Format: { force | off | ht | strict | noirq | rsdt }
140 force -- enable ACPI if default was off
141 off -- disable ACPI if default was on
142 noirq -- do not use ACPI for IRQ routing
143 ht -- run only enough ACPI to enable Hyper Threading
144 strict -- Be less tolerant of platforms that are not
145 strictly ACPI specification compliant.
146 rsdt -- prefer RSDT over (default) XSDT
148 See also Documentation/power/pm.txt, pci=noacpi
150 acpi_apic_instance= [ACPI, IOAPIC]
151 Format: <int>
152 2: use 2nd APIC table, if available
153 1,0: use 1st APIC table
154 default: 0
156 acpi_sleep= [HW,ACPI] Sleep options
157 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
158 old_ordering, s4_nonvs }
159 See Documentation/power/video.txt for information on
160 s3_bios and s3_mode.
161 s3_beep is for debugging; it makes the PC's speaker beep
162 as soon as the kernel's real-mode entry point is called.
163 s4_nohwsig prevents ACPI hardware signature from being
164 used during resume from hibernation.
165 old_ordering causes the ACPI 1.0 ordering of the _PTS
166 control method, with respect to putting devices into
167 low power states, to be enforced (the ACPI 2.0 ordering
168 of _PTS is used by default).
169 s4_nonvs prevents the kernel from saving/restoring the
170 ACPI NVS memory during hibernation.
172 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
173 Format: { level | edge | high | low }
175 acpi_irq_balance [HW,ACPI]
176 ACPI will balance active IRQs
177 default in APIC mode
179 acpi_irq_nobalance [HW,ACPI]
180 ACPI will not move active IRQs (default)
181 default in PIC mode
183 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
184 use by PCI
185 Format: <irq>,<irq>...
187 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
188 Format: <irq>,<irq>...
190 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
192 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
193 Format: To spoof as Windows 98: ="Microsoft Windows"
195 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
196 acpi_osi="string1" # add string1 -- only one string
197 acpi_osi="!string2" # remove built-in string2
198 acpi_osi= # disable all strings
200 acpi_serialize [HW,ACPI] force serialization of AML methods
202 acpi_skip_timer_override [HW,ACPI]
203 Recognize and ignore IRQ0/pin2 Interrupt Override.
204 For broken nForce2 BIOS resulting in XT-PIC timer.
205 acpi_use_timer_override [HW,ACPI]
206 Use timer override. For some broken Nvidia NF5 boards
207 that require a timer override, but don't have
208 HPET
210 acpi_backlight= [HW,ACPI]
211 acpi_backlight=vendor
212 acpi_backlight=video
213 If set to vendor, prefer vendor specific driver
214 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
215 of the ACPI video.ko driver.
217 acpi_display_output= [HW,ACPI]
218 acpi_display_output=vendor
219 acpi_display_output=video
220 See above.
222 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
223 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
224 Format: <int>
225 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
226 debug output. Bits in debug_layer correspond to a
227 _COMPONENT in an ACPI source file, e.g.,
228 #define _COMPONENT ACPI_PCI_COMPONENT
229 Bits in debug_level correspond to a level in
230 ACPI_DEBUG_PRINT statements, e.g.,
231 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
232 The debug_level mask defaults to "info". See
233 Documentation/acpi/debug.txt for more information about
234 debug layers and levels.
236 Enable processor driver info messages:
237 acpi.debug_layer=0x20000000
238 Enable PCI/PCI interrupt routing info messages:
239 acpi.debug_layer=0x400000
240 Enable AML "Debug" output, i.e., stores to the Debug
241 object while interpreting AML:
242 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
243 Enable all messages related to ACPI hardware:
244 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
246 Some values produce so much output that the system is
247 unusable. The "log_buf_len" parameter may be useful
248 if you need to capture more output.
250 acpi.power_nocheck= [HW,ACPI]
251 Format: 1/0 enable/disable the check of power state.
252 On some bogus BIOS the _PSC object/_STA object of
253 power resource can't return the correct device power
254 state. In such case it is unneccessary to check its
255 power state again in power transition.
256 1 : disable the power state check
258 acpi_pm_good [X86-32,X86-64]
259 Override the pmtimer bug detection: force the kernel
260 to assume that this machine's pmtimer latches its value
261 and always returns good values.
263 acpi_enforce_resources= [ACPI]
264 { strict | lax | no }
265 Check for resource conflicts between native drivers
266 and ACPI OperationRegions (SystemIO and SystemMemory
267 only). IO ports and memory declared in ACPI might be
268 used by the ACPI subsystem in arbitrary AML code and
269 can interfere with legacy drivers.
270 strict (default): access to resources claimed by ACPI
271 is denied; legacy drivers trying to access reserved
272 resources will fail to bind to device using them.
273 lax: access to resources claimed by ACPI is allowed;
274 legacy drivers trying to access reserved resources
275 will bind successfully but a warning message is logged.
276 no: ACPI OperationRegions are not marked as reserved,
277 no further checks are performed.
279 agp= [AGP]
280 { off | try_unsupported }
281 off: disable AGP support
282 try_unsupported: try to drive unsupported chipsets
283 (may crash computer or cause data corruption)
285 enable_timer_pin_1 [i386,x86-64]
286 Enable PIN 1 of APIC timer
287 Can be useful to work around chipset bugs
288 (in particular on some ATI chipsets).
289 The kernel tries to set a reasonable default.
291 disable_timer_pin_1 [i386,x86-64]
292 Disable PIN 1 of APIC timer
293 Can be useful to work around chipset bugs.
295 ad1848= [HW,OSS]
296 Format: <io>,<irq>,<dma>,<dma2>,<type>
298 advansys= [HW,SCSI]
299 See header of drivers/scsi/advansys.c.
301 advwdt= [HW,WDT] Advantech WDT
302 Format: <iostart>,<iostop>
304 aedsp16= [HW,OSS] Audio Excel DSP 16
305 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>
306 See also header of sound/oss/aedsp16.c.
308 aha152x= [HW,SCSI]
309 See Documentation/scsi/aha152x.txt.
311 aha1542= [HW,SCSI]
312 Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]
314 aic7xxx= [HW,SCSI]
315 See Documentation/scsi/aic7xxx.txt.
317 aic79xx= [HW,SCSI]
318 See Documentation/scsi/aic79xx.txt.
320 amd_iommu= [HW,X86-84]
321 Pass parameters to the AMD IOMMU driver in the system.
322 Possible values are:
323 isolate - enable device isolation (each device, as far
324 as possible, will get its own protection
325 domain) [default]
326 share - put every device behind one IOMMU into the
327 same protection domain
328 fullflush - enable flushing of IO/TLB entries when
329 they are unmapped. Otherwise they are
330 flushed before they will be reused, which
331 is a lot of faster
333 amd_iommu_size= [HW,X86-64]
334 Define the size of the aperture for the AMD IOMMU
335 driver. Possible values are:
336 '32M', '64M' (default), '128M', '256M', '512M', '1G'
338 amijoy.map= [HW,JOY] Amiga joystick support
339 Map of devices attached to JOY0DAT and JOY1DAT
340 Format: <a>,<b>
341 See also Documentation/kernel/input/joystick.txt
343 analog.map= [HW,JOY] Analog joystick and gamepad support
344 Specifies type or capabilities of an analog joystick
345 connected to one of 16 gameports
346 Format: <type1>,<type2>,..<type16>
348 apc= [HW,SPARC]
349 Power management functions (SPARCstation-4/5 + deriv.)
350 Format: noidle
351 Disable APC CPU standby support. SPARCstation-Fox does
352 not play well with APC CPU idle - disable it if you have
353 APC and your system crashes randomly.
355 apic= [APIC,i386] Advanced Programmable Interrupt Controller
356 Change the output verbosity whilst booting
357 Format: { quiet (default) | verbose | debug }
358 Change the amount of debugging information output
359 when initialising the APIC and IO-APIC components.
361 apm= [APM] Advanced Power Management
362 See header of arch/x86/kernel/apm_32.c.
364 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
365 Format: <io>,<irq>,<nodeID>
367 ataflop= [HW,M68k]
369 atarimouse= [HW,MOUSE] Atari Mouse
371 atascsi= [HW,SCSI] Atari SCSI
373 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
374 EzKey and similar keyboards
376 atkbd.reset= [HW] Reset keyboard during initialization
378 atkbd.set= [HW] Select keyboard code set
379 Format: <int> (2 = AT (default), 3 = PS/2)
381 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
382 keyboards
384 atkbd.softraw= [HW] Choose between synthetic and real raw mode
385 Format: <bool> (0 = real, 1 = synthetic (default))
387 atkbd.softrepeat= [HW]
388 Use software keyboard repeat
390 autotest [IA64]
392 baycom_epp= [HW,AX25]
393 Format: <io>,<mode>
395 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
396 Format: <io>,<mode>
397 See header of drivers/net/hamradio/baycom_par.c.
399 baycom_ser_fdx= [HW,AX25]
400 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
401 Format: <io>,<irq>,<mode>[,<baud>]
402 See header of drivers/net/hamradio/baycom_ser_fdx.c.
404 baycom_ser_hdx= [HW,AX25]
405 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
406 Format: <io>,<irq>,<mode>
407 See header of drivers/net/hamradio/baycom_ser_hdx.c.
409 boot_delay= Milliseconds to delay each printk during boot.
410 Values larger than 10 seconds (10000) are changed to
411 no delay (0).
412 Format: integer
414 bootmem_debug [KNL] Enable bootmem allocator debug messages.
416 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
417 bttv.radio= Most important insmod options are available as
418 kernel args too.
419 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
420 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
422 BusLogic= [HW,SCSI]
423 See drivers/scsi/BusLogic.c, comment before function
424 BusLogic_ParseDriverOptions().
426 c101= [NET] Moxa C101 synchronous serial card
428 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
429 Sometimes CPU hardware bugs make them report the cache
430 size incorrectly. The kernel will attempt work arounds
431 to fix known problems, but for some CPUs it is not
432 possible to determine what the correct size should be.
433 This option provides an override for these situations.
435 security= [SECURITY] Choose a security module to enable at boot.
436 If this boot parameter is not specified, only the first
437 security module asking for security registration will be
438 loaded. An invalid security module name will be treated
439 as if no module has been chosen.
441 capability.disable=
442 [SECURITY] Disable capabilities. This would normally
443 be used only if an alternative security model is to be
444 configured. Potentially dangerous and should only be
445 used if you are entirely sure of the consequences.
447 ccw_timeout_log [S390]
448 See Documentation/s390/CommonIO for details.
450 cgroup_disable= [KNL] Disable a particular controller
451 Format: {name of the controller(s) to disable}
452 {Currently supported controllers - "memory"}
454 checkreqprot [SELINUX] Set initial checkreqprot flag value.
455 Format: { "0" | "1" }
456 See security/selinux/Kconfig help text.
457 0 -- check protection applied by kernel (includes
458 any implied execute protection).
459 1 -- check protection requested by application.
460 Default value is set via a kernel config option.
461 Value can be changed at runtime via
462 /selinux/checkreqprot.
464 cio_ignore= [S390]
465 See Documentation/s390/CommonIO for details.
467 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
468 [Deprecated]
469 Forces specified clocksource (if available) to be used
470 when calculating gettimeofday(). If specified
471 clocksource is not available, it defaults to PIT.
472 Format: { pit | tsc | cyclone | pmtmr }
474 clocksource= [GENERIC_TIME] Override the default clocksource
475 Format: <string>
476 Override the default clocksource and use the clocksource
477 with the name specified.
478 Some clocksource names to choose from, depending on
479 the platform:
480 [all] jiffies (this is the base, fallback clocksource)
481 [ACPI] acpi_pm
482 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
483 pxa_timer,timer3,32k_counter,timer0_1
484 [AVR32] avr32
485 [X86-32] pit,hpet,tsc,vmi-timer;
486 scx200_hrt on Geode; cyclone on IBM x440
487 [MIPS] MIPS
488 [PARISC] cr16
489 [S390] tod
490 [SH] SuperH
491 [SPARC64] tick
492 [X86-64] hpet,tsc
494 clearcpuid=BITNUM [X86]
495 Disable CPUID feature X for the kernel. See
496 arch/x86/include/asm/cpufeature.h for the valid bit
497 numbers. Note the Linux specific bits are not necessarily
498 stable over kernel options, but the vendor specific
499 ones should be.
500 Also note that user programs calling CPUID directly
501 or using the feature without checking anything
502 will still see it. This just prevents it from
503 being used by the kernel or shown in /proc/cpuinfo.
504 Also note the kernel might malfunction if you disable
505 some critical bits.
507 code_bytes [IA32/X86_64] How many bytes of object code to print
508 in an oops report.
509 Range: 0 - 8192
510 Default: 64
512 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support
513 this option disables the debugging code at boot.
515 dma_debug_entries=<number>
516 This option allows to tune the number of preallocated
517 entries for DMA-API debugging code. One entry is
518 required per DMA-API allocation. Use this if the
519 DMA-API debugging code disables itself because the
520 architectural default is too low.
522 hpet= [X86-32,HPET] option to control HPET usage
523 Format: { enable (default) | disable | force |
524 verbose }
525 disable: disable HPET and use PIT instead
526 force: allow force enabled of undocumented chips (ICH4,
527 VIA, nVidia)
528 verbose: show contents of HPET registers during setup
530 com20020= [HW,NET] ARCnet - COM20020 chipset
531 Format:
532 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
534 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
535 Format: <io>[,<irq>]
537 com90xx= [HW,NET]
538 ARCnet - COM90xx chipset (memory-mapped buffers)
539 Format: <io>[,<irq>[,<memstart>]]
541 condev= [HW,S390] console device
542 conmode=
544 console= [KNL] Output console device and options.
546 tty<n> Use the virtual console device <n>.
548 ttyS<n>[,options]
549 ttyUSB0[,options]
550 Use the specified serial port. The options are of
551 the form "bbbbpnf", where "bbbb" is the baud rate,
552 "p" is parity ("n", "o", or "e"), "n" is number of
553 bits, and "f" is flow control ("r" for RTS or
554 omit it). Default is "9600n8".
556 See Documentation/serial-console.txt for more
557 information. See
558 Documentation/networking/netconsole.txt for an
559 alternative.
561 uart[8250],io,<addr>[,options]
562 uart[8250],mmio,<addr>[,options]
563 Start an early, polled-mode console on the 8250/16550
564 UART at the specified I/O port or MMIO address,
565 switching to the matching ttyS device later. The
566 options are the same as for ttyS, above.
568 If the device connected to the port is not a TTY but a braille
569 device, prepend "brl," before the device type, for instance
570 console=brl,ttyS0
571 For now, only VisioBraille is supported.
573 earlycon= [KNL] Output early console device and options.
574 uart[8250],io,<addr>[,options]
575 uart[8250],mmio,<addr>[,options]
576 Start an early, polled-mode console on the 8250/16550
577 UART at the specified I/O port or MMIO address.
578 The options are the same as for ttyS, above.
580 no_console_suspend
581 [HW] Never suspend the console
582 Disable suspending of consoles during suspend and
583 hibernate operations. Once disabled, debugging
584 messages can reach various consoles while the rest
585 of the system is being put to sleep (ie, while
586 debugging driver suspend/resume hooks). This may
587 not work reliably with all consoles, but is known
588 to work with serial and VGA consoles.
590 coredump_filter=
591 [KNL] Change the default value for
592 /proc/<pid>/coredump_filter.
593 See also Documentation/filesystems/proc.txt.
595 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
596 Format:
597 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
599 crashkernel=nn[KMG]@ss[KMG]
600 [KNL] Reserve a chunk of physical memory to
601 hold a kernel to switch to with kexec on panic.
603 crashkernel=range1:size1[,range2:size2,...][@offset]
604 [KNL] Same as above, but depends on the memory
605 in the running system. The syntax of range is
606 start-[end] where start and end are both
607 a memory unit (amount[KMG]). See also
608 Documentation/kdump/kdump.txt for a example.
610 cs89x0_dma= [HW,NET]
611 Format: <dma>
613 cs89x0_media= [HW,NET]
614 Format: { rj45 | aui | bnc }
616 dasd= [HW,NET]
617 See header of drivers/s390/block/dasd_devmap.c.
619 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
620 (one device per port)
621 Format: <port#>,<type>
622 See also Documentation/input/joystick-parport.txt
624 debug [KNL] Enable kernel debugging (events log level).
626 debug_locks_verbose=
627 [KNL] verbose self-tests
628 Format=<0|1>
629 Print debugging info while doing the locking API
630 self-tests.
631 We default to 0 (no extra messages), setting it to
632 1 will print _a lot_ more information - normally
633 only useful to kernel developers.
635 debug_objects [KNL] Enable object debugging
637 no_debug_objects
638 [KNL] Disable object debugging
640 debugpat [X86] Enable PAT debugging
642 decnet.addr= [HW,NET]
643 Format: <area>[,<node>]
644 See also Documentation/networking/decnet.txt.
646 vt.default_blu= [VT]
647 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
648 Change the default blue palette of the console.
649 This is a 16-member array composed of values
650 ranging from 0-255.
652 vt.default_grn= [VT]
653 Format: <green0>,<green1>,<green2>,...,<green15>
654 Change the default green palette of the console.
655 This is a 16-member array composed of values
656 ranging from 0-255.
658 vt.default_red= [VT]
659 Format: <red0>,<red1>,<red2>,...,<red15>
660 Change the default red palette of the console.
661 This is a 16-member array composed of values
662 ranging from 0-255.
664 vt.default_utf8=
665 [VT]
666 Format=<0|1>
667 Set system-wide default UTF-8 mode for all tty's.
668 Default is 1, i.e. UTF-8 mode is enabled for all
669 newly opened terminals.
671 dhash_entries= [KNL]
672 Set number of hash buckets for dentry cache.
674 digi= [HW,SERIAL]
675 IO parameters + enable/disable command.
677 digiepca= [HW,SERIAL]
678 See drivers/char/README.epca and
679 Documentation/serial/digiepca.txt.
681 disable_mtrr_cleanup [X86]
682 enable_mtrr_cleanup [X86]
683 The kernel tries to adjust MTRR layout from continuous
684 to discrete, to make X server driver able to add WB
685 entry later. This parameter enables/disables that.
687 mtrr_chunk_size=nn[KMG] [X86]
688 used for mtrr cleanup. It is largest continous chunk
689 that could hold holes aka. UC entries.
691 mtrr_gran_size=nn[KMG] [X86]
692 Used for mtrr cleanup. It is granularity of mtrr block.
693 Default is 1.
694 Large value could prevent small alignment from
695 using up MTRRs.
697 mtrr_spare_reg_nr=n [X86]
698 Format: <integer>
699 Range: 0,7 : spare reg number
700 Default : 1
701 Used for mtrr cleanup. It is spare mtrr entries number.
702 Set to 2 or more if your graphical card needs more.
704 disable_mtrr_trim [X86, Intel and AMD only]
705 By default the kernel will trim any uncacheable
706 memory out of your available memory pool based on
707 MTRR settings. This parameter disables that behavior,
708 possibly causing your machine to run very slowly.
710 dmasound= [HW,OSS] Sound subsystem buffers
712 dscc4.setup= [NET]
714 dtc3181e= [HW,SCSI]
716 earlyprintk= [X86-32,X86-64,SH,BLACKFIN]
717 earlyprintk=vga
718 earlyprintk=serial[,ttySn[,baudrate]]
719 earlyprintk=dbgp
721 Append ",keep" to not disable it when the real console
722 takes over.
724 Only vga or serial or usb debug port at a time.
726 Currently only ttyS0 and ttyS1 are supported.
728 Interaction with the standard serial driver is not
729 very good.
731 The VGA output is eventually overwritten by the real
732 console.
734 eata= [HW,SCSI]
736 edd= [EDD]
737 Format: {"off" | "on" | "skip[mbr]"}
739 eisa_irq_edge= [PARISC,HW]
740 See header of drivers/parisc/eisa.c.
742 elanfreq= [X86-32]
743 See comment before function elanfreq_setup() in
744 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
746 elevator= [IOSCHED]
747 Format: {"anticipatory" | "cfq" | "deadline" | "noop"}
748 See Documentation/block/as-iosched.txt and
749 Documentation/block/deadline-iosched.txt for details.
751 elfcorehdr= [IA64,PPC,SH,X86-32,X86_64]
752 Specifies physical address of start of kernel core
753 image elf header. Generally kexec loader will
754 pass this option to capture kernel.
755 See Documentation/kdump/kdump.txt for details.
757 enforcing [SELINUX] Set initial enforcing status.
758 Format: {"0" | "1"}
759 See security/selinux/Kconfig help text.
760 0 -- permissive (log only, no denials).
761 1 -- enforcing (deny and log).
762 Default value is 0.
763 Value can be changed at runtime via /selinux/enforce.
765 ether= [HW,NET] Ethernet cards parameters
766 This option is obsoleted by the "netdev=" option, which
767 has equivalent usage. See its documentation for details.
769 eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
770 Format: <io>[,<irq>]
772 failslab=
773 fail_page_alloc=
774 fail_make_request=[KNL]
775 General fault injection mechanism.
776 Format: <interval>,<probability>,<space>,<times>
777 See also /Documentation/fault-injection/.
779 fd_mcs= [HW,SCSI]
780 See header of drivers/scsi/fd_mcs.c.
782 fdomain= [HW,SCSI]
783 See header of drivers/scsi/fdomain.c.
785 floppy= [HW]
786 See Documentation/blockdev/floppy.txt.
788 force_pal_cache_flush
789 [IA-64] Avoid check_sal_cache_flush which may hang on
790 buggy SAL_CACHE_FLUSH implementations. Using this
791 parameter will force ia64_sal_cache_flush to call
792 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
794 ftrace=[tracer]
795 [ftrace] will set and start the specified tracer
796 as early as possible in order to facilitate early
797 boot debugging.
799 ftrace_dump_on_oops
800 [ftrace] will dump the trace buffers on oops.
802 gamecon.map[2|3]=
803 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
804 support via parallel port (up to 5 devices per port)
805 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
806 See also Documentation/input/joystick-parport.txt
808 gamma= [HW,DRM]
810 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
811 Format: off | on
812 default: on
814 gdth= [HW,SCSI]
815 See header of drivers/scsi/gdth.c.
817 gpt [EFI] Forces disk with valid GPT signature but
818 invalid Protective MBR to be treated as GPT.
820 gvp11= [HW,SCSI]
822 hashdist= [KNL,NUMA] Large hashes allocated during boot
823 are distributed across NUMA nodes. Defaults on
824 for IA-64, off otherwise.
825 Format: 0 | 1 (for off | on)
827 hcl= [IA-64] SGI's Hardware Graph compatibility layer
829 hd= [EIDE] (E)IDE hard drive subsystem geometry
830 Format: <cyl>,<head>,<sect>
832 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
833 size of <nn>. This works even on boxes that have no
834 highmem otherwise. This also works to reduce highmem
835 size on bigger boxes.
837 highres= [KNL] Enable/disable high resolution timer mode.
838 Valid parameters: "on", "off"
839 Default: "on"
841 hisax= [HW,ISDN]
842 See Documentation/isdn/README.HiSax.
844 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
845 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
846 On x86-64 and powerpc, this option can be specified
847 multiple times interleaved with hugepages= to reserve
848 huge pages of different sizes. Valid pages sizes on
849 x86-64 are 2M (when the CPU supports "pse") and 1G
850 (when the CPU supports the "pdpe1gb" cpuinfo flag)
851 Note that 1GB pages can only be allocated at boot time
852 using hugepages= and not freed afterwards.
853 default_hugepagesz=
854 [same as hugepagesz=] The size of the default
855 HugeTLB page size. This is the size represented by
856 the legacy /proc/ hugepages APIs, used for SHM, and
857 default size when mounting hugetlbfs filesystems.
858 Defaults to the default architecture's huge page size
859 if not specified.
861 hlt [BUGS=ARM,SH]
863 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
864 terminal devices. Valid values: 0..8
865 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
866 If specified, z/VM IUCV HVC accepts connections
867 from listed z/VM user IDs only.
869 i2c_bus= [HW] Override the default board specific I2C bus speed
870 or register an additional I2C bus that is not
871 registered from board initialization code.
872 Format:
873 <bus_id>,<clkrate>
875 i8042.debug [HW] Toggle i8042 debug mode
876 i8042.direct [HW] Put keyboard port into non-translated mode
877 i8042.dumbkbd [HW] Pretend that controller can only read data from
878 keyboard and cannot control its state
879 (Don't attempt to blink the leds)
880 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
881 i8042.nokbd [HW] Don't check/create keyboard port
882 i8042.noloop [HW] Disable the AUX Loopback command while probing
883 for the AUX port
884 i8042.nomux [HW] Don't check presence of an active multiplexing
885 controller
886 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
887 controllers
888 i8042.panicblink=
889 [HW] Frequency with which keyboard LEDs should blink
890 when kernel panics (default is 0.5 sec)
891 i8042.reset [HW] Reset the controller during init and cleanup
892 i8042.unlock [HW] Unlock (ignore) the keylock
894 i810= [HW,DRM]
896 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
897 indicates that the driver is running on unsupported
898 hardware.
899 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
900 does not match list of supported models.
901 i8k.power_status
902 [HW] Report power status in /proc/i8k
903 (disabled by default)
904 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
905 capability is set.
907 ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
908 See Documentation/mca.txt.
910 icn= [HW,ISDN]
911 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
913 ide-core.nodma= [HW] (E)IDE subsystem
914 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
915 .vlb_clock .pci_clock .noflush .noprobe .nowerr .cdrom
916 .chs .ignore_cable are additional options
917 See Documentation/ide/ide.txt.
919 idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
920 See Documentation/ide/ide.txt.
922 idle= [X86]
923 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
924 Poll forces a polling idle loop that can slightly
925 improve the performance of waking up a idle CPU, but
926 will use a lot of power and make the system run hot.
927 Not recommended.
928 idle=mwait: On systems which support MONITOR/MWAIT but
929 the kernel chose to not use it because it doesn't save
930 as much power as a normal idle loop, use the
931 MONITOR/MWAIT idle loop anyways. Performance should be
932 the same as idle=poll.
933 idle=halt: Halt is forced to be used for CPU idle.
934 In such case C2/C3 won't be used again.
935 idle=nomwait: Disable mwait for CPU C-states
937 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
938 Claim all unknown PCI IDE storage controllers.
940 ignore_loglevel [KNL]
941 Ignore loglevel setting - this will print /all/
942 kernel messages to the console. Useful for debugging.
944 ihash_entries= [KNL]
945 Set number of hash buckets for inode cache.
947 ima_audit= [IMA]
948 Format: { "0" | "1" }
949 0 -- integrity auditing messages. (Default)
950 1 -- enable informational integrity auditing messages.
952 ima_hash= [IMA]
953 Formt: { "sha1" | "md5" }
954 default: "sha1"
956 in2000= [HW,SCSI]
957 See header of drivers/scsi/in2000.c.
959 init= [KNL]
960 Format: <full_path>
961 Run specified binary instead of /sbin/init as init
962 process.
964 initcall_debug [KNL] Trace initcalls as they are executed. Useful
965 for working out where the kernel is dying during
966 startup.
968 initrd= [BOOT] Specify the location of the initial ramdisk
970 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
971 Format: <irq>
973 inttest= [IA64]
975 iomem= Disable strict checking of access to MMIO memory
976 strict regions from userspace.
977 relaxed
979 iommu= [x86]
980 off
981 force
982 noforce
983 biomerge
984 panic
985 nopanic
986 merge
987 nomerge
988 forcesac
989 soft
992 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
993 on
994 Enable intel iommu driver.
995 off
996 Disable intel iommu driver.
997 igfx_off [Default Off]
998 By default, gfx is mapped as normal device. If a gfx
999 device has a dedicated DMAR unit, the DMAR unit is
1000 bypassed by not enabling DMAR with this option. In
1001 this case, gfx device will use physical address for
1002 DMA.
1003 forcedac [x86_64]
1004 With this option iommu will not optimize to look
1005 for io virtual address below 32 bit forcing dual
1006 address cycle on pci bus for cards supporting greater
1007 than 32 bit addressing. The default is to look
1008 for translation below 32 bit and if not available
1009 then look in the higher range.
1010 strict [Default Off]
1011 With this option on every unmap_single operation will
1012 result in a hardware IOTLB flush operation as opposed
1013 to batching them for performance.
1015 io_delay= [X86-32,X86-64] I/O delay method
1016 0x80
1017 Standard port 0x80 based delay
1018 0xed
1019 Alternate port 0xed based delay (needed on some systems)
1020 udelay
1021 Simple two microseconds delay
1022 none
1023 No delay
1025 io7= [HW] IO7 for Marvel based alpha systems
1026 See comment before marvel_specify_io7 in
1027 arch/alpha/kernel/core_marvel.c.
1029 ip= [IP_PNP]
1030 See Documentation/filesystems/nfsroot.txt.
1032 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1033 See comment before ip2_setup() in
1034 drivers/char/ip2/ip2base.c.
1036 ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
1037 See header of drivers/scsi/ips.c.
1039 ports= [IP_VS_FTP] IPVS ftp helper module
1040 Default is 21.
1041 Up to 8 (IP_VS_APP_MAX_PORTS) ports
1042 may be specified.
1043 Format: <port>,<port>....
1045 irqfixup [HW]
1046 When an interrupt is not handled search all handlers
1047 for it. Intended to get systems with badly broken
1048 firmware running.
1050 irqpoll [HW]
1051 When an interrupt is not handled search all handlers
1052 for it. Also check all handlers each timer
1053 interrupt. Intended to get systems with badly broken
1054 firmware running.
1056 isapnp= [ISAPNP]
1057 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1059 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1060 Format:
1061 <cpu number>,...,<cpu number>
1062 or
1063 <cpu number>-<cpu number>
1064 (must be a positive range in ascending order)
1065 or a mixture
1066 <cpu number>,...,<cpu number>-<cpu number>
1068 This option can be used to specify one or more CPUs
1069 to isolate from the general SMP balancing and scheduling
1070 algorithms. You can move a process onto or off an
1071 "isolated" CPU via the CPU affinity syscalls or cpuset.
1072 <cpu number> begins at 0 and the maximum value is
1073 "number of CPUs in system - 1".
1075 This option is the preferred way to isolate CPUs. The
1076 alternative -- manually setting the CPU mask of all
1077 tasks in the system -- can cause problems and
1078 suboptimal load balancer performance.
1080 iucv= [HW,NET]
1082 js= [HW,JOY] Analog joystick
1083 See Documentation/input/joystick.txt.
1085 kernelcore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1086 specifies the amount of memory usable by the kernel
1087 for non-movable allocations. The requested amount is
1088 spread evenly throughout all nodes in the system. The
1089 remaining memory in each node is used for Movable
1090 pages. In the event, a node is too small to have both
1091 kernelcore and Movable pages, kernelcore pages will
1092 take priority and other nodes will have a larger number
1093 of kernelcore pages. The Movable zone is used for the
1094 allocation of pages that may be reclaimed or moved
1095 by the page migration subsystem. This means that
1096 HugeTLB pages may not be allocated from this zone.
1097 Note that allocations like PTEs-from-HighMem still
1098 use the HighMem zone if it exists, and the Normal
1099 zone if it does not.
1101 kmemtrace.enable= [KNL,KMEMTRACE] Format: { yes | no }
1102 Controls whether kmemtrace is enabled
1103 at boot-time.
1105 kmemtrace.subbufs=n [KNL,KMEMTRACE] Overrides the number of
1106 subbufs kmemtrace's relay channel has. Set this
1107 higher than default (KMEMTRACE_N_SUBBUFS in code) if
1108 you experience buffer overruns.
1110 movablecore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1111 is similar to kernelcore except it specifies the
1112 amount of memory used for migratable allocations.
1113 If both kernelcore and movablecore is specified,
1114 then kernelcore will be at *least* the specified
1115 value but may be more. If movablecore on its own
1116 is specified, the administrator must be careful
1117 that the amount of memory usable for all allocations
1118 is not too small.
1120 keepinitrd [HW,ARM]
1122 kstack=N [X86-32,X86-64] Print N words from the kernel stack
1123 in oops dumps.
1125 kgdboc= [HW] kgdb over consoles.
1126 Requires a tty driver that supports console polling.
1127 (only serial suported for now)
1128 Format: <serial_device>[,baud]
1130 kmac= [MIPS] korina ethernet MAC address.
1131 Configure the RouterBoard 532 series on-chip
1132 Ethernet adapter MAC address.
1134 l2cr= [PPC]
1136 l3cr= [PPC]
1138 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1139 disabled it.
1141 lapic_timer_c2_ok [X86-32,x86-64,APIC] trust the local apic timer
1142 in C2 power state.
1144 libata.dma= [LIBATA] DMA control
1145 libata.dma=0 Disable all PATA and SATA DMA
1146 libata.dma=1 PATA and SATA Disk DMA only
1147 libata.dma=2 ATAPI (CDROM) DMA only
1148 libata.dma=4 Compact Flash DMA only
1149 Combinations also work, so libata.dma=3 enables DMA
1150 for disks and CDROMs, but not CFs.
1152 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1153 when set.
1154 Format: <int>
1156 libata.force= [LIBATA] Force configurations. The format is comma
1157 separated list of "[ID:]VAL" where ID is
1158 PORT[:DEVICE]. PORT and DEVICE are decimal numbers
1159 matching port, link or device. Basically, it matches
1160 the ATA ID string printed on console by libata. If
1161 the whole ID part is omitted, the last PORT and DEVICE
1162 values are used. If ID hasn't been specified yet, the
1163 configuration applies to all ports, links and devices.
1165 If only DEVICE is omitted, the parameter applies to
1166 the port and all links and devices behind it. DEVICE
1167 number of 0 either selects the first device or the
1168 first fan-out link behind PMP device. It does not
1169 select the host link. DEVICE number of 15 selects the
1170 host link and device attached to it.
1172 The VAL specifies the configuration to force. As long
1173 as there's no ambiguity shortcut notation is allowed.
1174 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1175 The following configurations can be forced.
1177 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1178 Any ID with matching PORT is used.
1180 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1182 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1183 udma[/][16,25,33,44,66,100,133] notation is also
1184 allowed.
1186 * [no]ncq: Turn on or off NCQ.
1188 * nohrst, nosrst, norst: suppress hard, soft
1189 and both resets.
1191 If there are multiple matching configurations changing
1192 the same attribute, the last one is used.
1194 lmb=debug [KNL] Enable lmb debug messages.
1196 load_ramdisk= [RAM] List of ramdisks to load from floppy
1197 See Documentation/blockdev/ramdisk.txt.
1199 lockd.nlm_grace_period=P [NFS] Assign grace period.
1200 Format: <integer>
1202 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1203 Format: <integer>
1205 lockd.nlm_timeout=T [NFS] Assign timeout value.
1206 Format: <integer>
1208 lockd.nlm_udpport=M [NFS] Assign UDP port.
1209 Format: <integer>
1211 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1212 Format: <irq>
1214 loglevel= All Kernel Messages with a loglevel smaller than the
1215 console loglevel will be printed to the console. It can
1216 also be changed with klogd or other programs. The
1217 loglevels are defined as follows:
1219 0 (KERN_EMERG) system is unusable
1220 1 (KERN_ALERT) action must be taken immediately
1221 2 (KERN_CRIT) critical conditions
1222 3 (KERN_ERR) error conditions
1223 4 (KERN_WARNING) warning conditions
1224 5 (KERN_NOTICE) normal but significant condition
1225 6 (KERN_INFO) informational
1226 7 (KERN_DEBUG) debug-level messages
1228 log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1229 Format: { n | nk | nM }
1230 n must be a power of two. The default size
1231 is set in the kernel config file.
1233 logo.nologo [FB] Disables display of the built-in Linux logo.
1234 This may be used to provide more screen space for
1235 kernel log messages and is useful when debugging
1236 kernel boot problems.
1238 lp=0 [LP] Specify parallel ports to use, e.g,
1239 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1240 lp=reset first parallel port). 'lp=0' disables the
1241 lp=auto printer driver. 'lp=reset' (which can be
1242 specified in addition to the ports) causes
1243 attached printers to be reset. Using
1244 lp=port1,port2,... specifies the parallel ports
1245 to associate lp devices with, starting with
1246 lp0. A port specification may be 'none' to skip
1247 that lp device, or a parport name such as
1248 'parport0'. Specifying 'lp=auto' instead of a
1249 port specification list means that device IDs
1250 from each port should be examined, to see if
1251 an IEEE 1284-compliant printer is attached; if
1252 so, the driver will manage that printer.
1253 See also header of drivers/char/lp.c.
1255 lpj=n [KNL]
1256 Sets loops_per_jiffy to given constant, thus avoiding
1257 time-consuming boot-time autodetection (up to 250 ms per
1258 CPU). 0 enables autodetection (default). To determine
1259 the correct value for your kernel, boot with normal
1260 autodetection and see what value is printed. Note that
1261 on SMP systems the preset will be applied to all CPUs,
1262 which is likely to cause problems if your CPUs need
1263 significantly divergent settings. An incorrect value
1264 will cause delays in the kernel to be wrong, leading to
1265 unpredictable I/O errors and other breakage. Although
1266 unlikely, in the extreme case this might damage your
1267 hardware.
1269 ltpc= [NET]
1270 Format: <io>,<irq>,<dma>
1272 mac5380= [HW,SCSI] Format:
1273 <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
1275 machvec= [IA64] Force the use of a particular machine-vector
1276 (machvec) in a generic kernel.
1277 Example: machvec=hpzx1_swiotlb
1279 max_loop= [LOOP] Maximum number of loopback devices that can
1280 be mounted
1281 Format: <1-256>
1283 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1284 should make use of. maxcpus=n : n >= 0 limits the
1285 kernel to using 'n' processors. n=0 is a special case,
1286 it is equivalent to "nosmp", which also disables
1287 the IO APIC.
1289 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater than
1290 or equal to this physical address is ignored.
1292 max_luns= [SCSI] Maximum number of LUNs to probe.
1293 Should be between 1 and 2^32-1.
1295 max_report_luns=
1296 [SCSI] Maximum number of LUNs received.
1297 Should be between 1 and 16384.
1299 mcatest= [IA-64]
1301 mce [X86-32] Machine Check Exception
1303 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1305 md= [HW] RAID subsystems devices and level
1306 See Documentation/md.txt.
1308 mdacon= [MDA]
1309 Format: <first>,<last>
1310 Specifies range of consoles to be captured by the MDA.
1312 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1313 Amount of memory to be used when the kernel is not able
1314 to see the whole system memory or for test.
1315 [X86-32] Use together with memmap= to avoid physical
1316 address space collisions. Without memmap= PCI devices
1317 could be placed at addresses belonging to unused RAM.
1319 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1320 memory.
1322 memchunk=nn[KMG]
1323 [KNL,SH] Allow user to override the default size for
1324 per-device physically contiguous DMA buffers.
1326 memmap=exactmap [KNL,X86-32,X86_64] Enable setting of an exact
1327 E820 memory map, as specified by the user.
1328 Such memmap=exactmap lines can be constructed based on
1329 BIOS output or other requirements. See the memmap=nn@ss
1330 option description.
1332 memmap=nn[KMG]@ss[KMG]
1333 [KNL] Force usage of a specific region of memory
1334 Region of memory to be used, from ss to ss+nn.
1336 memmap=nn[KMG]#ss[KMG]
1337 [KNL,ACPI] Mark specific memory as ACPI data.
1338 Region of memory to be used, from ss to ss+nn.
1340 memmap=nn[KMG]$ss[KMG]
1341 [KNL,ACPI] Mark specific memory as reserved.
1342 Region of memory to be used, from ss to ss+nn.
1343 Example: Exclude memory from 0x18690000-0x1869ffff
1344 memmap=64K$0x18690000
1345 or
1346 memmap=0x10000$0x18690000
1348 memory_corruption_check=0/1 [X86]
1349 Some BIOSes seem to corrupt the first 64k of
1350 memory when doing things like suspend/resume.
1351 Setting this option will scan the memory
1352 looking for corruption. Enabling this will
1353 both detect corruption and prevent the kernel
1354 from using the memory being corrupted.
1355 However, its intended as a diagnostic tool; if
1356 repeatable BIOS-originated corruption always
1357 affects the same memory, you can use memmap=
1358 to prevent the kernel from using that memory.
1360 memory_corruption_check_size=size [X86]
1361 By default it checks for corruption in the low
1362 64k, making this memory unavailable for normal
1363 use. Use this parameter to scan for
1364 corruption in more or less memory.
1366 memory_corruption_check_period=seconds [X86]
1367 By default it checks for corruption every 60
1368 seconds. Use this parameter to check at some
1369 other rate. 0 disables periodic checking.
1371 memtest= [KNL,X86] Enable memtest
1372 Format: <integer>
1373 default : 0 <disable>
1374 Specifies the number of memtest passes to be
1375 performed. Each pass selects another test
1376 pattern from a given set of patterns. Memtest
1377 fills the memory with this pattern, validates
1378 memory contents and reserves bad memory
1379 regions that are detected.
1381 meye.*= [HW] Set MotionEye Camera parameters
1382 See Documentation/video4linux/meye.txt.
1384 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1385 Multi-Function General Purpose Timers on AMD Geode
1386 platforms.
1388 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1389 the BIOS has incorrectly applied a workaround. TinyBIOS
1390 version 0.98 is known to be affected, 0.99 fixes the
1391 problem by letting the user disable the workaround.
1393 mga= [HW,DRM]
1395 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1396 physical address is ignored.
1398 mminit_loglevel=
1399 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1400 parameter allows control of the logging verbosity for
1401 the additional memory initialisation checks. A value
1402 of 0 disables mminit logging and a level of 4 will
1403 log everything. Information is printed at KERN_DEBUG
1404 so loglevel=8 may also need to be specified.
1406 mousedev.tap_time=
1407 [MOUSE] Maximum time between finger touching and
1408 leaving touchpad surface for touch to be considered
1409 a tap and be reported as a left button click (for
1410 touchpads working in absolute mode only).
1411 Format: <msecs>
1412 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1413 reporting absolute coordinates, such as tablets
1414 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1415 reporting absolute coordinates, such as tablets
1417 mpu401= [HW,OSS]
1418 Format: <io>,<irq>
1420 MTD_Partition= [MTD]
1421 Format: <name>,<region-number>,<size>,<offset>
1423 MTD_Region= [MTD] Format:
1424 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1426 mtdparts= [MTD]
1427 See drivers/mtd/cmdlinepart.c.
1429 mtdset= [ARM]
1430 ARM/S3C2412 JIVE boot control
1432 See arch/arm/mach-s3c2412/mach-jive.c
1434 mtouchusb.raw_coordinates=
1435 [HW] Make the MicroTouch USB driver use raw coordinates
1436 ('y', default) or cooked coordinates ('n')
1438 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1440 NCR_D700= [HW,SCSI]
1441 See header of drivers/scsi/NCR_D700.c.
1443 ncr5380= [HW,SCSI]
1445 ncr53c400= [HW,SCSI]
1447 ncr53c400a= [HW,SCSI]
1449 ncr53c406a= [HW,SCSI]
1451 ncr53c8xx= [HW,SCSI]
1453 netdev= [NET] Network devices parameters
1454 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1455 Note that mem_start is often overloaded to mean
1456 something different and driver-specific.
1457 This usage is only documented in each driver source
1458 file if at all.
1460 nf_conntrack.acct=
1461 [NETFILTER] Enable connection tracking flow accounting
1462 0 to disable accounting
1463 1 to enable accounting
1464 Default value depends on CONFIG_NF_CT_ACCT that is
1465 going to be removed in 2.6.29.
1467 nfsaddrs= [NFS]
1468 See Documentation/filesystems/nfsroot.txt.
1470 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1471 See Documentation/filesystems/nfsroot.txt.
1473 nfs.callback_tcpport=
1474 [NFS] set the TCP port on which the NFSv4 callback
1475 channel should listen.
1477 nfs.idmap_cache_timeout=
1478 [NFS] set the maximum lifetime for idmapper cache
1479 entries.
1481 nfs.enable_ino64=
1482 [NFS] enable 64-bit inode numbers.
1483 If zero, the NFS client will fake up a 32-bit inode
1484 number for the readdir() and stat() syscalls instead
1485 of returning the full 64-bit number.
1486 The default is to return 64-bit inode numbers.
1488 nmi_debug= [KNL,AVR32] Specify one or more actions to take
1489 when a NMI is triggered.
1490 Format: [state][,regs][,debounce][,die]
1492 nmi_watchdog= [KNL,BUGS=X86-32,X86-64] Debugging features for SMP kernels
1493 Format: [panic,][num]
1494 Valid num: 0,1,2
1495 0 - turn nmi_watchdog off
1496 1 - use the IO-APIC timer for the NMI watchdog
1497 2 - use the local APIC for the NMI watchdog using
1498 a performance counter. Note: This will use one performance
1499 counter and the local APIC's performance vector.
1500 When panic is specified panic when an NMI watchdog timeout occurs.
1501 This is useful when you use a panic=... timeout and need the box
1502 quickly up again.
1503 Instead of 1 and 2 it is possible to use the following
1504 symbolic names: lapic and ioapic
1505 Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1507 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1508 emulation library even if a 387 maths coprocessor
1509 is present.
1511 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1512 caches in the slab allocator. Saves per-node memory,
1513 but will impact performance.
1515 noalign [KNL,ARM]
1517 noapic [SMP,APIC] Tells the kernel to not make use of any
1518 IOAPICs that may be present in the system.
1520 nobats [PPC] Do not use BATs for mapping kernel lowmem
1521 on "Classic" PPC cores.
1523 nocache [ARM]
1525 nodelayacct [KNL] Disable per-task delay accounting
1527 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1529 nodsp [SH] Disable hardware DSP at boot time.
1531 noefi [X86-32,X86-64] Disable EFI runtime services support.
1533 noexec [IA-64]
1535 noexec [X86-32,X86-64]
1536 On X86-32 available only on PAE configured kernels.
1537 noexec=on: enable non-executable mappings (default)
1538 noexec=off: disable non-executable mappings
1540 noexec32 [X86-64]
1541 This affects only 32-bit executables.
1542 noexec32=on: enable non-executable mappings (default)
1543 read doesn't imply executable mappings
1544 noexec32=off: disable non-executable mappings
1545 read implies executable mappings
1547 nofpu [SH] Disable hardware FPU at boot time.
1549 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1550 register save and restore. The kernel will only save
1551 legacy floating-point registers on task switch.
1553 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1555 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1556 wfi(ARM) instruction doesn't work correctly and not to
1557 use it. This is also useful when using JTAG debugger.
1559 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1560 instruction doesn't work correctly and not to
1561 use it.
1563 no_file_caps Tells the kernel not to honor file capabilities. The
1564 only way then for a file to be executed with privilege
1565 is to be setuid root or executed by root.
1567 nohalt [IA-64] Tells the kernel not to use the power saving
1568 function PAL_HALT_LIGHT when idle. This increases
1569 power-consumption. On the positive side, it reduces
1570 interrupt wake-up latency, which may improve performance
1571 in certain environments such as networked servers or
1572 real-time systems.
1574 nohz= [KNL] Boottime enable/disable dynamic ticks
1575 Valid arguments: on, off
1576 Default: on
1578 noiotrap [SH] Disables trapped I/O port accesses.
1580 noirqdebug [X86-32] Disables the code which attempts to detect and
1581 disable unhandled interrupt sources.
1583 no_timer_check [X86-32,X86_64,APIC] Disables the code which tests for
1584 broken timer IRQ sources.
1586 noisapnp [ISAPNP] Disables ISA PnP code.
1588 noinitrd [RAM] Tells the kernel not to load any configured
1589 initial RAM disk.
1591 nointroute [IA-64]
1593 nojitter [IA64] Disables jitter checking for ITC timers.
1595 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1597 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1599 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1601 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
1602 default x2apic cluster mode on platforms
1603 supporting x2apic.
1605 noltlbs [PPC] Do not use large page/tlb entries for kernel
1606 lowmem mapping on PPC40x.
1608 nomca [IA-64] Disable machine check abort handling
1610 nomce [X86-32] Machine Check Exception
1612 nomfgpt [X86-32] Disable Multi-Function General Purpose
1613 Timer usage (for AMD Geode machines).
1615 noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops
1617 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1618 with UP alternatives
1620 noresidual [PPC] Don't use residual data on PReP machines.
1622 noresume [SWSUSP] Disables resume and restores original swap
1623 space.
1625 no-scroll [VGA] Disables scrollback.
1626 This is required for the Braillex ib80-piezo Braille
1627 reader made by F.H. Papenmeier (Germany).
1629 nosbagart [IA-64]
1631 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1633 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1634 and disable the IO APIC. legacy for "maxcpus=0".
1636 nosoftlockup [KNL] Disable the soft-lockup detector.
1638 noswapaccount [KNL] Disable accounting of swap in memory resource
1639 controller. (See Documentation/cgroups/memory.txt)
1641 nosync [HW,M68K] Disables sync negotiation for all devices.
1643 notsc [BUGS=X86-32] Disable Time Stamp Counter
1645 nousb [USB] Disable the USB subsystem
1647 nowb [ARM]
1649 nptcg= [IA64] Override max number of concurrent global TLB
1650 purges which is reported from either PAL_VM_SUMMARY or
1651 SAL PALO.
1653 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1654 one of ['zone', 'node', 'default'] can be specified
1655 This can be set from sysctl after boot.
1656 See Documentation/sysctl/vm.txt for details.
1658 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1660 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1661 See Documentation/debugging-via-ohci1394.txt for more
1662 info.
1664 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1665 Rather than timing out after 20 ms if an EC
1666 command is not properly ACKed, override the length
1667 of the timeout. We have interrupts disabled while
1668 waiting for the ACK, so if this is set too high
1669 interrupts *may* be lost!
1671 opl3= [HW,OSS]
1672 Format: <io>
1674 oprofile.timer= [HW]
1675 Use timer interrupt instead of performance counters
1677 osst= [HW,SCSI] SCSI Tape Driver
1678 Format: <buffer_size>,<write_threshold>
1679 See also Documentation/scsi/st.txt.
1681 panic= [KNL] Kernel behaviour on panic
1682 Format: <timeout>
1684 parkbd.port= [HW] Parallel port number the keyboard adapter is
1685 connected to, default is 0.
1686 Format: <parport#>
1687 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1688 0 for XT, 1 for AT (default is AT).
1689 Format: <mode>
1691 parport= [HW,PPT] Specify parallel ports. 0 disables.
1692 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1693 Use 'auto' to force the driver to use any
1694 IRQ/DMA settings detected (the default is to
1695 ignore detected IRQ/DMA settings because of
1696 possible conflicts). You can specify the base
1697 address, IRQ, and DMA settings; IRQ and DMA
1698 should be numbers, or 'auto' (for using detected
1699 settings on that particular port), or 'nofifo'
1700 (to avoid using a FIFO even if it is detected).
1701 Parallel ports are assigned in the order they
1702 are specified on the command line, starting
1703 with parport0.
1705 parport_init_mode= [HW,PPT]
1706 Configure VIA parallel port to operate in
1707 a specific mode. This is necessary on Pegasos
1708 computer where firmware has no options for setting
1709 up parallel port mode and sets it to spp.
1710 Currently this function knows 686a and 8231 chips.
1711 Format: [spp|ps2|epp|ecp|ecpepp]
1713 pas2= [HW,OSS] Format:
1714 <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16>
1716 pas16= [HW,SCSI]
1717 See header of drivers/scsi/pas16.c.
1719 pause_on_oops=
1720 Halt all CPUs after the first oops has been printed for
1721 the specified number of seconds. This is to be used if
1722 your oopses keep scrolling off the screen.
1724 pcbit= [HW,ISDN]
1726 pcd. [PARIDE]
1727 See header of drivers/block/paride/pcd.c.
1728 See also Documentation/blockdev/paride.txt.
1730 pci=option[,option...] [PCI] various PCI subsystem options:
1731 earlydump [X86] dump PCI config space before the kernel
1732 changes anything
1733 off [X86] don't probe for the PCI bus
1734 bios [X86-32] force use of PCI BIOS, don't access
1735 the hardware directly. Use this if your machine
1736 has a non-standard PCI host bridge.
1737 nobios [X86-32] disallow use of PCI BIOS, only direct
1738 hardware access methods are allowed. Use this
1739 if you experience crashes upon bootup and you
1740 suspect they are caused by the BIOS.
1741 conf1 [X86] Force use of PCI Configuration
1742 Mechanism 1.
1743 conf2 [X86] Force use of PCI Configuration
1744 Mechanism 2.
1745 noaer [PCIE] If the PCIEAER kernel config parameter is
1746 enabled, this kernel boot option can be used to
1747 disable the use of PCIE advanced error reporting.
1748 nodomains [PCI] Disable support for multiple PCI
1749 root domains (aka PCI segments, in ACPI-speak).
1750 nommconf [X86-32,X86_64] Disable use of MMCONFIG for PCI
1751 Configuration
1752 nomsi [MSI] If the PCI_MSI kernel config parameter is
1753 enabled, this kernel boot option can be used to
1754 disable the use of MSI interrupts system-wide.
1755 noioapicquirk [APIC] Disable all boot interrupt quirks.
1756 Safety option to keep boot IRQs enabled. This
1757 should never be necessary.
1758 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1759 primary IO-APIC for bridges that cannot disable
1760 boot IRQs. This fixes a source of spurious IRQs
1761 when the system masks IRQs.
1762 noioapicreroute [APIC] Disable workaround that uses the
1763 boot IRQ equivalent of an IRQ that connects to
1764 a chipset where boot IRQs cannot be disabled.
1765 The opposite of ioapicreroute.
1766 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1767 routing table. These calls are known to be buggy
1768 on several machines and they hang the machine
1769 when used, but on other computers it's the only
1770 way to get the interrupt routing table. Try
1771 this option if the kernel is unable to allocate
1772 IRQs or discover secondary PCI buses on your
1773 motherboard.
1774 rom [X86] Assign address space to expansion ROMs.
1775 Use with caution as certain devices share
1776 address decoders between ROMs and other
1777 resources.
1778 norom [X86] Do not assign address space to
1779 expansion ROMs that do not already have
1780 BIOS assigned address ranges.
1781 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1782 assigned automatically to PCI devices. You can
1783 make the kernel exclude IRQs of your ISA cards
1784 this way.
1785 pirqaddr=0xAAAAA [X86] Specify the physical address
1786 of the PIRQ table (normally generated
1787 by the BIOS) if it is outside the
1788 F0000h-100000h range.
1789 lastbus=N [X86] Scan all buses thru bus #N. Can be
1790 useful if the kernel is unable to find your
1791 secondary buses and you want to tell it
1792 explicitly which ones they are.
1793 assign-busses [X86] Always assign all PCI bus
1794 numbers ourselves, overriding
1795 whatever the firmware may have done.
1796 usepirqmask [X86] Honor the possible IRQ mask stored
1797 in the BIOS $PIR table. This is needed on
1798 some systems with broken BIOSes, notably
1799 some HP Pavilion N5400 and Omnibook XE3
1800 notebooks. This will have no effect if ACPI
1801 IRQ routing is enabled.
1802 noacpi [X86] Do not use ACPI for IRQ routing
1803 or for PCI scanning.
1804 use_crs [X86] Use _CRS for PCI resource
1805 allocation.
1806 routeirq Do IRQ routing for all PCI devices.
1807 This is normally done in pci_enable_device(),
1808 so this option is a temporary workaround
1809 for broken drivers that don't call it.
1810 skip_isa_align [X86] do not align io start addr, so can
1811 handle more pci cards
1812 firmware [ARM] Do not re-enumerate the bus but instead
1813 just use the configuration from the
1814 bootloader. This is currently used on
1815 IXP2000 systems where the bus has to be
1816 configured a certain way for adjunct CPUs.
1817 noearly [X86] Don't do any early type 1 scanning.
1818 This might help on some broken boards which
1819 machine check when some devices' config space
1820 is read. But various workarounds are disabled
1821 and some IOMMU drivers will not work.
1822 bfsort Sort PCI devices into breadth-first order.
1823 This sorting is done to get a device
1824 order compatible with older (<= 2.4) kernels.
1825 nobfsort Don't sort PCI devices into breadth-first order.
1826 cbiosize=nn[KMG] The fixed amount of bus space which is
1827 reserved for the CardBus bridge's IO window.
1828 The default value is 256 bytes.
1829 cbmemsize=nn[KMG] The fixed amount of bus space which is
1830 reserved for the CardBus bridge's memory
1831 window. The default value is 64 megabytes.
1832 resource_alignment=
1833 Format:
1834 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
1835 Specifies alignment and device to reassign
1836 aligned memory resources.
1837 If <order of align> is not specified,
1838 PAGE_SIZE is used as alignment.
1839 PCI-PCI bridge can be specified, if resource
1840 windows need to be expanded.
1842 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1843 Management.
1844 off Disable ASPM.
1845 force Enable ASPM even on devices that claim not to support it.
1846 WARNING: Forcing ASPM on may cause system lockups.
1848 pcmv= [HW,PCMCIA] BadgePAD 4
1850 pd. [PARIDE]
1851 See Documentation/blockdev/paride.txt.
1853 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
1854 boot time.
1855 Format: { 0 | 1 }
1856 See arch/parisc/kernel/pdc_chassis.c
1858 pf. [PARIDE]
1859 See Documentation/blockdev/paride.txt.
1861 pg. [PARIDE]
1862 See Documentation/blockdev/paride.txt.
1864 pirq= [SMP,APIC] Manual mp-table setup
1865 See Documentation/x86/i386/IO-APIC.txt.
1867 plip= [PPT,NET] Parallel port network link
1868 Format: { parport<nr> | timid | 0 }
1869 See also Documentation/parport.txt.
1871 pmtmr= [X86] Manual setup of pmtmr I/O Port.
1872 Override pmtimer IOPort with a hex value.
1873 e.g. pmtmr=0x508
1875 pnp.debug [PNP]
1876 Enable PNP debug messages. This depends on the
1877 CONFIG_PNP_DEBUG_MESSAGES option.
1879 pnpacpi= [ACPI]
1880 { off }
1882 pnpbios= [ISAPNP]
1883 { on | off | curr | res | no-curr | no-res }
1885 pnp_reserve_irq=
1886 [ISAPNP] Exclude IRQs for the autoconfiguration
1888 pnp_reserve_dma=
1889 [ISAPNP] Exclude DMAs for the autoconfiguration
1891 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
1892 Ranges are in pairs (I/O port base and size).
1894 pnp_reserve_mem=
1895 [ISAPNP] Exclude memory regions for the
1896 autoconfiguration.
1897 Ranges are in pairs (memory base and size).
1899 print-fatal-signals=
1900 [KNL] debug: print fatal signals
1901 print-fatal-signals=1: print segfault info to
1902 the kernel console.
1903 default: off.
1905 printk.time= Show timing data prefixed to each printk message line
1906 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
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 processor.max_cstate= [HW,ACPI]
1918 Limit processor to maximum C-state
1919 max_cstate=9 overrides any DMI blacklist limit.
1921 processor.nocst [HW,ACPI]
1922 Ignore the _CST method to determine C-states,
1923 instead using the legacy FADT method
1925 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
1926 before loading.
1927 See Documentation/blockdev/ramdisk.txt.
1929 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
1930 probe for; one of (bare|imps|exps|lifebook|any).
1931 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
1932 per second.
1933 psmouse.resetafter= [HW,MOUSE]
1934 Try to reset the device after so many bad packets
1935 (0 = never).
1936 psmouse.resolution=
1937 [HW,MOUSE] Set desired mouse resolution, in dpi.
1938 psmouse.smartscroll=
1939 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1940 0 = disabled, 1 = enabled (default).
1942 pss= [HW,OSS] Personal Sound System (ECHO ESC614)
1943 Format:
1944 <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq>
1946 pt. [PARIDE]
1947 See Documentation/blockdev/paride.txt.
1949 pty.legacy_count=
1950 [KNL] Number of legacy pty's. Overwrites compiled-in
1951 default number.
1953 quiet [KNL] Disable most log messages
1955 r128= [HW,DRM]
1957 raid= [HW,RAID]
1958 See Documentation/md.txt.
1960 ramdisk_blocksize= [RAM]
1961 See Documentation/blockdev/ramdisk.txt.
1963 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
1964 See Documentation/blockdev/ramdisk.txt.
1966 rcupdate.blimit= [KNL,BOOT]
1967 Set maximum number of finished RCU callbacks to process
1968 in one batch.
1970 rcupdate.qhimark= [KNL,BOOT]
1971 Set threshold of queued
1972 RCU callbacks over which batch limiting is disabled.
1974 rcupdate.qlowmark= [KNL,BOOT]
1975 Set threshold of queued RCU callbacks below which
1976 batch limiting is re-enabled.
1978 rdinit= [KNL]
1979 Format: <full_path>
1980 Run specified binary instead of /init from the ramdisk,
1981 used for early userspace startup. See initrd.
1983 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
1984 Format: <reboot_mode>[,<reboot_mode2>[,...]]
1985 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
1987 relax_domain_level=
1988 [KNL, SMP] Set scheduler's default relax_domain_level.
1989 See Documentation/cgroups/cpusets.txt.
1991 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
1993 reservetop= [X86-32]
1994 Format: nn[KMG]
1995 Reserves a hole at the top of the kernel virtual
1996 address space.
1998 reset_devices [KNL] Force drivers to reset the underlying device
1999 during initialization.
2001 resume= [SWSUSP]
2002 Specify the partition device for software suspend
2004 resume_offset= [SWSUSP]
2005 Specify the offset from the beginning of the partition
2006 given by "resume=" at which the swap header is located,
2007 in <PAGE_SIZE> units (needed only for swap files).
2008 See Documentation/power/swsusp-and-swap-files.txt
2010 retain_initrd [RAM] Keep initrd memory after extraction
2012 rhash_entries= [KNL,NET]
2013 Set number of hash buckets for route cache
2015 riscom8= [HW,SERIAL]
2016 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2018 ro [KNL] Mount root device read-only on boot
2020 root= [KNL] Root filesystem
2022 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2023 mount the root filesystem
2025 rootflags= [KNL] Set root filesystem mount option string
2027 rootfstype= [KNL] Set root filesystem type
2029 rootwait [KNL] Wait (indefinitely) for root device to show up.
2030 Useful for devices that are detected asynchronously
2031 (e.g. USB and MMC devices).
2033 root_plug.vendor_id=
2034 [ROOTPLUG] Override the default vendor ID
2036 root_plug.product_id=
2037 [ROOTPLUG] Override the default product ID
2039 root_plug.debug=
2040 [ROOTPLUG] Enable debugging output
2042 rw [KNL] Mount root device read-write on boot
2044 S [KNL] Run init in single mode
2046 sa1100ir [NET]
2047 See drivers/net/irda/sa1100_ir.c.
2049 sbni= [NET] Granch SBNI12 leased line adapter
2051 sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
2052 Format: <io>[,<timeout>[,<isapnp>]]
2054 scsi_debug_*= [SCSI]
2055 See drivers/scsi/scsi_debug.c.
2057 scsi_default_dev_flags=
2058 [SCSI] SCSI default device flags
2059 Format: <integer>
2061 scsi_dev_flags= [SCSI] Black/white list entry for vendor and model
2062 Format: <vendor>:<model>:<flags>
2063 (flags are integer value)
2065 scsi_logging_level= [SCSI] a bit mask of logging levels
2066 See drivers/scsi/scsi_logging.h for bits. Also
2067 settable via sysctl at dev.scsi.logging_level
2068 (/proc/sys/dev/scsi/logging_level).
2069 There is also a nice 'scsi_logging_level' script in the
2070 S390-tools package, available for download at
2071 http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
2073 scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
2074 discovered. async scans them in kernel threads,
2075 allowing boot to proceed. none ignores them, expecting
2076 user space to do the scan.
2078 selinux [SELINUX] Disable or enable SELinux at boot time.
2079 Format: { "0" | "1" }
2080 See security/selinux/Kconfig help text.
2081 0 -- disable.
2082 1 -- enable.
2083 Default value is set via kernel config option.
2084 If enabled at boot time, /selinux/disable can be used
2085 later to disable prior to initial policy load.
2087 serialnumber [BUGS=X86-32]
2089 shapers= [NET]
2090 Maximal number of shapers.
2092 show_msr= [x86] show boot-time MSR settings
2093 Format: { <integer> }
2094 Show boot-time (BIOS-initialized) MSR settings.
2095 The parameter means the number of CPUs to show,
2096 for example 1 means boot CPU only.
2098 sim710= [SCSI,HW]
2099 See header of drivers/scsi/sim710.c.
2101 simeth= [IA-64]
2102 simscsi=
2104 slram= [HW,MTD]
2106 slub_debug[=options[,slabs]] [MM, SLUB]
2107 Enabling slub_debug allows one to determine the
2108 culprit if slab objects become corrupted. Enabling
2109 slub_debug can create guard zones around objects and
2110 may poison objects when not in use. Also tracks the
2111 last alloc / free. For more information see
2112 Documentation/vm/slub.txt.
2114 slub_max_order= [MM, SLUB]
2115 Determines the maximum allowed order for slabs.
2116 A high setting may cause OOMs due to memory
2117 fragmentation. For more information see
2118 Documentation/vm/slub.txt.
2120 slub_min_objects= [MM, SLUB]
2121 The minimum number of objects per slab. SLUB will
2122 increase the slab order up to slub_max_order to
2123 generate a sufficiently large slab able to contain
2124 the number of objects indicated. The higher the number
2125 of objects the smaller the overhead of tracking slabs
2126 and the less frequently locks need to be acquired.
2127 For more information see Documentation/vm/slub.txt.
2129 slub_min_order= [MM, SLUB]
2130 Determines the mininum page order for slabs. Must be
2131 lower than slub_max_order.
2132 For more information see Documentation/vm/slub.txt.
2134 slub_nomerge [MM, SLUB]
2135 Disable merging of slabs with similar size. May be
2136 necessary if there is some reason to distinguish
2137 allocs to different slabs. Debug options disable
2138 merging on their own.
2139 For more information see Documentation/vm/slub.txt.
2141 smart2= [HW]
2142 Format: <io1>[,<io2>[,...,<io8>]]
2144 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2145 attempt to substitute SMP alternatives once at boot.
2147 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2148 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2149 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2150 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2151 smsc-ircc2.ircc_irq= [HW] IRQ line
2152 smsc-ircc2.ircc_dma= [HW] DMA channel
2153 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2154 0: Toshiba Satellite 1800 (GP data pin select)
2155 1: Fast pin select (default)
2156 2: ATC IRMode
2158 snd-ad1816a= [HW,ALSA]
2160 snd-ad1848= [HW,ALSA]
2162 snd-ali5451= [HW,ALSA]
2164 snd-als100= [HW,ALSA]
2166 snd-als4000= [HW,ALSA]
2168 snd-azt2320= [HW,ALSA]
2170 snd-cmi8330= [HW,ALSA]
2172 snd-cmipci= [HW,ALSA]
2174 snd-cs4231= [HW,ALSA]
2176 snd-cs4232= [HW,ALSA]
2178 snd-cs4236= [HW,ALSA]
2180 snd-cs4281= [HW,ALSA]
2182 snd-cs46xx= [HW,ALSA]
2184 snd-dt019x= [HW,ALSA]
2186 snd-dummy= [HW,ALSA]
2188 snd-emu10k1= [HW,ALSA]
2190 snd-ens1370= [HW,ALSA]
2192 snd-ens1371= [HW,ALSA]
2194 snd-es968= [HW,ALSA]
2196 snd-es1688= [HW,ALSA]
2198 snd-es18xx= [HW,ALSA]
2200 snd-es1938= [HW,ALSA]
2202 snd-es1968= [HW,ALSA]
2204 snd-fm801= [HW,ALSA]
2206 snd-gusclassic= [HW,ALSA]
2208 snd-gusextreme= [HW,ALSA]
2210 snd-gusmax= [HW,ALSA]
2212 snd-hdsp= [HW,ALSA]
2214 snd-ice1712= [HW,ALSA]
2216 snd-intel8x0= [HW,ALSA]
2218 snd-interwave= [HW,ALSA]
2220 snd-interwave-stb=
2221 [HW,ALSA]
2223 snd-korg1212= [HW,ALSA]
2225 snd-maestro3= [HW,ALSA]
2227 snd-mpu401= [HW,ALSA]
2229 snd-mtpav= [HW,ALSA]
2231 snd-nm256= [HW,ALSA]
2233 snd-opl3sa2= [HW,ALSA]
2235 snd-opti92x-ad1848=
2236 [HW,ALSA]
2238 snd-opti92x-cs4231=
2239 [HW,ALSA]
2241 snd-opti93x= [HW,ALSA]
2243 snd-pmac= [HW,ALSA]
2245 snd-rme32= [HW,ALSA]
2247 snd-rme96= [HW,ALSA]
2249 snd-rme9652= [HW,ALSA]
2251 snd-sb8= [HW,ALSA]
2253 snd-sb16= [HW,ALSA]
2255 snd-sbawe= [HW,ALSA]
2257 snd-serial= [HW,ALSA]
2259 snd-sgalaxy= [HW,ALSA]
2261 snd-sonicvibes= [HW,ALSA]
2263 snd-sun-amd7930=
2264 [HW,ALSA]
2266 snd-sun-cs4231= [HW,ALSA]
2268 snd-trident= [HW,ALSA]
2270 snd-usb-audio= [HW,ALSA,USB]
2272 snd-via82xx= [HW,ALSA]
2274 snd-virmidi= [HW,ALSA]
2276 snd-wavefront= [HW,ALSA]
2278 snd-ymfpci= [HW,ALSA]
2280 softlockup_panic=
2281 [KNL] Should the soft-lockup detector generate panics.
2283 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2284 See Documentation/sonypi.txt
2286 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2287 See Documentation/serial/specialix.txt.
2289 spia_io_base= [HW,MTD]
2290 spia_fio_base=
2291 spia_pedr=
2292 spia_peddr=
2294 sscape= [HW,OSS]
2295 Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq>
2297 st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
2298 See Documentation/scsi/st.txt.
2300 stacktrace [FTRACE]
2301 Enabled the stack tracer on boot up.
2303 sti= [PARISC,HW]
2304 Format: <num>
2305 Set the STI (builtin display/keyboard on the HP-PARISC
2306 machines) console (graphic card) which should be used
2307 as the initial boot-console.
2308 See also comment in drivers/video/console/sticore.c.
2310 sti_font= [HW]
2311 See comment in drivers/video/console/sticore.c.
2313 stifb= [HW]
2314 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2316 sunrpc.pool_mode=
2317 [NFS]
2318 Control how the NFS server code allocates CPUs to
2319 service thread pools. Depending on how many NICs
2320 you have and where their interrupts are bound, this
2321 option will affect which CPUs will do NFS serving.
2322 Note: this parameter cannot be changed while the
2323 NFS server is running.
2325 auto the server chooses an appropriate mode
2326 automatically using heuristics
2327 global a single global pool contains all CPUs
2328 percpu one pool for each CPU
2329 pernode one pool for each NUMA node (equivalent
2330 to global on non-NUMA machines)
2332 swiotlb= [IA-64] Number of I/O TLB slabs
2334 switches= [HW,M68k]
2336 sym53c416= [HW,SCSI]
2337 See header of drivers/scsi/sym53c416.c.
2339 sysrq_always_enabled
2340 [KNL]
2341 Ignore sysrq setting - this boot parameter will
2342 neutralize any effect of /proc/sys/kernel/sysrq.
2343 Useful for debugging.
2345 t128= [HW,SCSI]
2346 See header of drivers/scsi/t128.c.
2348 tdfx= [HW,DRM]
2350 test_suspend= [SUSPEND]
2351 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2352 standby suspend) as the system sleep state to briefly
2353 enter during system startup. The system is woken from
2354 this state using a wakeup-capable RTC alarm.
2356 thash_entries= [KNL,NET]
2357 Set number of hash buckets for TCP connection
2359 thermal.act= [HW,ACPI]
2360 -1: disable all active trip points in all thermal zones
2361 <degrees C>: override all lowest active trip points
2363 thermal.crt= [HW,ACPI]
2364 -1: disable all critical trip points in all thermal zones
2365 <degrees C>: override all critical trip points
2367 thermal.nocrt= [HW,ACPI]
2368 Set to disable actions on ACPI thermal zone
2369 critical and hot trip points.
2371 thermal.off= [HW,ACPI]
2372 1: disable ACPI thermal control
2374 thermal.psv= [HW,ACPI]
2375 -1: disable all passive trip points
2376 <degrees C>: override all passive trip points to this
2377 value
2379 thermal.tzp= [HW,ACPI]
2380 Specify global default ACPI thermal zone polling rate
2381 <deci-seconds>: poll all this frequency
2382 0: no polling (default)
2384 tmscsim= [HW,SCSI]
2385 See comment before function dc390_setup() in
2386 drivers/scsi/tmscsim.c.
2388 topology= [S390]
2389 Format: {off | on}
2390 Specify if the kernel should make use of the cpu
2391 topology informations if the hardware supports these.
2392 The scheduler will make use of these informations and
2393 e.g. base its process migration decisions on it.
2394 Default is off.
2396 tp720= [HW,PS2]
2398 trace_buf_size=nn[KMG] [ftrace] will set tracing buffer size.
2400 trix= [HW,OSS] MediaTrix AudioTrix Pro
2401 Format:
2402 <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
2404 tsc= Disable clocksource-must-verify flag for TSC.
2405 Format: <string>
2406 [x86] reliable: mark tsc clocksource as reliable, this
2407 disables clocksource verification at runtime.
2408 Used to enable high-resolution timer mode on older
2409 hardware, and in virtualized environment.
2411 turbografx.map[2|3]= [HW,JOY]
2412 TurboGraFX parallel port interface
2413 Format:
2414 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2415 See also Documentation/input/joystick-parport.txt
2417 u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter
2418 See header of drivers/scsi/u14-34f.c.
2420 uart401= [HW,OSS]
2421 Format: <io>,<irq>
2423 uart6850= [HW,OSS]
2424 Format: <io>,<irq>
2426 uhci-hcd.ignore_oc=
2427 [USB] Ignore overcurrent events (default N).
2428 Some badly-designed motherboards generate lots of
2429 bogus events, for ports that aren't wired to
2430 anything. Set this parameter to avoid log spamming.
2431 Note that genuine overcurrent events won't be
2432 reported either.
2434 unknown_nmi_panic
2435 [X86-32,X86-64]
2436 Set unknown_nmi_panic=1 early on boot.
2438 usbcore.autosuspend=
2439 [USB] The autosuspend time delay (in seconds) used
2440 for newly-detected USB devices (default 2). This
2441 is the time required before an idle device will be
2442 autosuspended. Devices for which the delay is set
2443 to a negative value won't be autosuspended at all.
2445 usbcore.usbfs_snoop=
2446 [USB] Set to log all usbfs traffic (default 0 = off).
2448 usbcore.blinkenlights=
2449 [USB] Set to cycle leds on hubs (default 0 = off).
2451 usbcore.old_scheme_first=
2452 [USB] Start with the old device initialization
2453 scheme (default 0 = off).
2455 usbcore.use_both_schemes=
2456 [USB] Try the other device initialization scheme
2457 if the first one fails (default 1 = enabled).
2459 usbcore.initial_descriptor_timeout=
2460 [USB] Specifies timeout for the initial 64-byte
2461 USB_REQ_GET_DESCRIPTOR request in milliseconds
2462 (default 5000 = 5.0 seconds).
2464 usbhid.mousepoll=
2465 [USBHID] The interval which mice are to be polled at.
2467 usb-storage.delay_use=
2468 [UMS] The delay in seconds before a new device is
2469 scanned for Logical Units (default 5).
2471 usb-storage.quirks=
2472 [UMS] A list of quirks entries to supplement or
2473 override the built-in unusual_devs list. List
2474 entries are separated by commas. Each entry has
2475 the form VID:PID:Flags where VID and PID are Vendor
2476 and Product ID values (4-digit hex numbers) and
2477 Flags is a set of characters, each corresponding
2478 to a common usb-storage quirk flag as follows:
2479 a = SANE_SENSE (collect more than 18 bytes
2480 of sense data);
2481 c = FIX_CAPACITY (decrease the reported
2482 device capacity by one sector);
2483 h = CAPACITY_HEURISTICS (decrease the
2484 reported device capacity by one
2485 sector if the number is odd);
2486 i = IGNORE_DEVICE (don't bind to this
2487 device);
2488 l = NOT_LOCKABLE (don't try to lock and
2489 unlock ejectable media);
2490 m = MAX_SECTORS_64 (don't transfer more
2491 than 64 sectors = 32 KB at a time);
2492 o = CAPACITY_OK (accept the capacity
2493 reported by the device);
2494 r = IGNORE_RESIDUE (the device reports
2495 bogus residue values);
2496 s = SINGLE_LUN (the device has only one
2497 Logical Unit);
2498 w = NO_WP_DETECT (don't test whether the
2499 medium is write-protected).
2500 Example: quirks=0419:aaf5:rl,0421:0433:rc
2502 add_efi_memmap [EFI; x86-32,X86-64] Include EFI memory map in
2503 kernel's map of available physical RAM.
2505 vdso= [X86-32,SH,x86-64]
2506 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2507 vdso=1: enable VDSO (default)
2508 vdso=0: disable VDSO mapping
2510 vdso32= [X86-32,X86-64]
2511 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2512 vdso32=1: enable 32-bit VDSO (default)
2513 vdso32=0: disable 32-bit VDSO mapping
2515 vector= [IA-64,SMP]
2516 vector=percpu: enable percpu vector domain
2518 video= [FB] Frame buffer configuration
2519 See Documentation/fb/modedb.txt.
2521 vga= [BOOT,X86-32] Select a particular video mode
2522 See Documentation/x86/boot.txt and
2523 Documentation/svga.txt.
2524 Use vga=ask for menu.
2525 This is actually a boot loader parameter; the value is
2526 passed to the kernel using a special protocol.
2528 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2529 size of <nn>. This can be used to increase the
2530 minimum size (128MB on x86). It can also be used to
2531 decrease the size and leave more room for directly
2532 mapped kernel RAM.
2534 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2535 Format: <command>
2537 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2538 Format: <command>
2540 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2541 Format: <command>
2543 waveartist= [HW,OSS]
2544 Format: <io>,<irq>,<dma>,<dma2>
2546 wd33c93= [HW,SCSI]
2547 See header of drivers/scsi/wd33c93.c.
2549 wd7000= [HW,SCSI]
2550 See header of drivers/scsi/wd7000.c.
2552 wdt= [WDT] Watchdog
2553 See Documentation/watchdog/wdt.txt.
2555 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2556 xd_geo= See header of drivers/block/xd.c.
2558 xirc2ps_cs= [NET,PCMCIA]
2559 Format:
2560 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2562 norandmaps Don't use address space randomization. Equivalent to
2563 echo 0 > /proc/sys/kernel/randomize_va_space
2565 ______________________________________________________________________
2567 TODO:
2569 Add documentation for ALSA options.
2570 Add more DRM drivers.