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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 AVR32 AVR32 architecture is enabled.
44 AX25 Appropriate AX.25 support is enabled.
45 BLACKFIN Blackfin architecture is enabled.
46 DRM Direct Rendering Management support is enabled.
47 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
48 EFI EFI Partitioning (GPT) is enabled
49 EIDE EIDE/ATAPI support is enabled.
50 FB The frame buffer device is enabled.
51 HW Appropriate hardware is enabled.
52 IA-64 IA-64 architecture is enabled.
53 IMA Integrity measurement architecture is enabled.
54 IOSCHED More than one I/O scheduler is enabled.
55 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
56 ISAPNP ISA PnP code is enabled.
57 ISDN Appropriate ISDN support is enabled.
58 JOY Appropriate joystick support is enabled.
59 LIBATA Libata driver is enabled
60 LP Printer support is enabled.
61 LOOP Loopback device support is enabled.
62 M68k M68k architecture is enabled.
63 These options have more detailed description inside of
64 Documentation/m68k/kernel-options.txt.
65 MCA MCA bus support is enabled.
66 MDA MDA console support is enabled.
67 MOUSE Appropriate mouse support is enabled.
68 MSI Message Signaled Interrupts (PCI).
69 MTD MTD (Memory Technology Device) support is enabled.
70 NET Appropriate network support is enabled.
71 NUMA NUMA support is enabled.
72 GENERIC_TIME The generic timeofday code is enabled.
73 NFS Appropriate NFS support is enabled.
74 OSS OSS sound support is enabled.
75 PV_OPS A paravirtualized kernel is enabled.
76 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
77 PARISC The PA-RISC architecture is enabled.
78 PCI PCI bus support is enabled.
79 PCIE PCI Express support is enabled.
80 PCMCIA The PCMCIA subsystem is enabled.
81 PNP Plug & Play support is enabled.
82 PPC PowerPC architecture is enabled.
83 PPT Parallel port support is enabled.
84 PS2 Appropriate PS/2 support is enabled.
85 RAM RAM disk support is enabled.
86 ROOTPLUG The example Root Plug LSM is enabled.
87 S390 S390 architecture is enabled.
88 SCSI Appropriate SCSI support is enabled.
89 A lot of drivers has their options described inside of
90 Documentation/scsi/.
91 SECURITY Different security models are enabled.
92 SELINUX SELinux support is enabled.
93 SERIAL Serial support is enabled.
94 SH SuperH architecture is enabled.
95 SMP The kernel is an SMP kernel.
96 SPARC Sparc architecture is enabled.
97 SWSUSP Software suspend (hibernation) is enabled.
98 SUSPEND System suspend states are enabled.
99 FTRACE Function tracing enabled.
100 TS Appropriate touchscreen support is enabled.
101 UMS USB Mass Storage support is enabled.
102 USB USB support is enabled.
103 USBHID USB Human Interface Device support is enabled.
104 V4L Video For Linux support is enabled.
105 VGA The VGA console has been enabled.
106 VT Virtual terminal support is enabled.
107 WDT Watchdog support is enabled.
108 XT IBM PC/XT MFM hard disk support is enabled.
109 X86-32 X86-32, aka i386 architecture is enabled.
110 X86-64 X86-64 architecture is enabled.
111 More X86-64 boot options can be found in
112 Documentation/x86/x86_64/boot-options.txt .
113 X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
115 In addition, the following text indicates that the option:
117 BUGS= Relates to possible processor bugs on the said processor.
118 KNL Is a kernel start-up parameter.
119 BOOT Is a boot loader parameter.
121 Parameters denoted with BOOT are actually interpreted by the boot
122 loader, and have no meaning to the kernel directly.
123 Do not modify the syntax of boot loader parameters without extreme
124 need or coordination with <Documentation/x86/boot.txt>.
126 There are also arch-specific kernel-parameters not documented here.
127 See for example <Documentation/x86/x86_64/boot-options.txt>.
129 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
130 a trailing = on the name of any parameter states that that parameter will
131 be entered as an environment variable, whereas its absence indicates that
132 it will appear as a kernel argument readable via /proc/cmdline by programs
133 running once the system is up.
135 The number of kernel parameters is not limited, but the length of the
136 complete command line (parameters including spaces etc.) is limited to
137 a fixed number of characters. This limit depends on the architecture
138 and is between 256 and 4096 characters. It is defined in the file
139 ./include/asm/setup.h as COMMAND_LINE_SIZE.
142 acpi= [HW,ACPI,X86]
143 Advanced Configuration and Power Interface
144 Format: { force | off | ht | strict | noirq | rsdt }
145 force -- enable ACPI if default was off
146 off -- disable ACPI if default was on
147 noirq -- do not use ACPI for IRQ routing
148 ht -- run only enough ACPI to enable Hyper Threading
149 strict -- Be less tolerant of platforms that are not
150 strictly ACPI specification compliant.
151 rsdt -- prefer RSDT over (default) XSDT
153 See also Documentation/power/pm.txt, pci=noacpi
155 acpi_apic_instance= [ACPI, IOAPIC]
156 Format: <int>
157 2: use 2nd APIC table, if available
158 1,0: use 1st APIC table
159 default: 0
161 acpi_backlight= [HW,ACPI]
162 acpi_backlight=vendor
163 acpi_backlight=video
164 If set to vendor, prefer vendor specific driver
165 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
166 of the ACPI video.ko driver.
168 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
169 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
170 Format: <int>
171 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
172 debug output. Bits in debug_layer correspond to a
173 _COMPONENT in an ACPI source file, e.g.,
174 #define _COMPONENT ACPI_PCI_COMPONENT
175 Bits in debug_level correspond to a level in
176 ACPI_DEBUG_PRINT statements, e.g.,
177 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
178 The debug_level mask defaults to "info". See
179 Documentation/acpi/debug.txt for more information about
180 debug layers and levels.
182 Enable processor driver info messages:
183 acpi.debug_layer=0x20000000
184 Enable PCI/PCI interrupt routing info messages:
185 acpi.debug_layer=0x400000
186 Enable AML "Debug" output, i.e., stores to the Debug
187 object while interpreting AML:
188 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
189 Enable all messages related to ACPI hardware:
190 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
192 Some values produce so much output that the system is
193 unusable. The "log_buf_len" parameter may be useful
194 if you need to capture more output.
196 acpi_display_output= [HW,ACPI]
197 acpi_display_output=vendor
198 acpi_display_output=video
199 See above.
201 acpi_irq_balance [HW,ACPI]
202 ACPI will balance active IRQs
203 default in APIC mode
205 acpi_irq_nobalance [HW,ACPI]
206 ACPI will not move active IRQs (default)
207 default in PIC mode
209 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
210 Format: <irq>,<irq>...
212 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
213 use by PCI
214 Format: <irq>,<irq>...
216 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
218 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
219 Format: To spoof as Windows 98: ="Microsoft Windows"
221 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
222 acpi_osi="string1" # add string1 -- only one string
223 acpi_osi="!string2" # remove built-in string2
224 acpi_osi= # disable all strings
226 acpi_pm_good [X86]
227 Override the pmtimer bug detection: force the kernel
228 to assume that this machine's pmtimer latches its value
229 and always returns good values.
231 acpi.power_nocheck= [HW,ACPI]
232 Format: 1/0 enable/disable the check of power state.
233 On some bogus BIOS the _PSC object/_STA object of
234 power resource can't return the correct device power
235 state. In such case it is unneccessary to check its
236 power state again in power transition.
237 1 : disable the power state check
239 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
240 Format: { level | edge | high | low }
242 acpi_serialize [HW,ACPI] force serialization of AML methods
244 acpi_skip_timer_override [HW,ACPI]
245 Recognize and ignore IRQ0/pin2 Interrupt Override.
246 For broken nForce2 BIOS resulting in XT-PIC timer.
248 acpi_sleep= [HW,ACPI] Sleep options
249 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
250 old_ordering, s4_nonvs }
251 See Documentation/power/video.txt for information on
252 s3_bios and s3_mode.
253 s3_beep is for debugging; it makes the PC's speaker beep
254 as soon as the kernel's real-mode entry point is called.
255 s4_nohwsig prevents ACPI hardware signature from being
256 used during resume from hibernation.
257 old_ordering causes the ACPI 1.0 ordering of the _PTS
258 control method, with respect to putting devices into
259 low power states, to be enforced (the ACPI 2.0 ordering
260 of _PTS is used by default).
261 s4_nonvs prevents the kernel from saving/restoring the
262 ACPI NVS memory during hibernation.
264 acpi_use_timer_override [HW,ACPI]
265 Use timer override. For some broken Nvidia NF5 boards
266 that require a timer override, but don't have HPET
268 acpi_enforce_resources= [ACPI]
269 { strict | lax | no }
270 Check for resource conflicts between native drivers
271 and ACPI OperationRegions (SystemIO and SystemMemory
272 only). IO ports and memory declared in ACPI might be
273 used by the ACPI subsystem in arbitrary AML code and
274 can interfere with legacy drivers.
275 strict (default): access to resources claimed by ACPI
276 is denied; legacy drivers trying to access reserved
277 resources will fail to bind to device using them.
278 lax: access to resources claimed by ACPI is allowed;
279 legacy drivers trying to access reserved resources
280 will bind successfully but a warning message is logged.
281 no: ACPI OperationRegions are not marked as reserved,
282 no further checks are performed.
284 ad1848= [HW,OSS]
285 Format: <io>,<irq>,<dma>,<dma2>,<type>
287 add_efi_memmap [EFI; X86] Include EFI memory map in
288 kernel's map of available physical RAM.
290 advansys= [HW,SCSI]
291 See header of drivers/scsi/advansys.c.
293 advwdt= [HW,WDT] Advantech WDT
294 Format: <iostart>,<iostop>
296 aedsp16= [HW,OSS] Audio Excel DSP 16
297 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>
298 See also header of sound/oss/aedsp16.c.
300 agp= [AGP]
301 { off | try_unsupported }
302 off: disable AGP support
303 try_unsupported: try to drive unsupported chipsets
304 (may crash computer or cause data corruption)
306 aha152x= [HW,SCSI]
307 See Documentation/scsi/aha152x.txt.
309 aha1542= [HW,SCSI]
310 Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]
312 aic7xxx= [HW,SCSI]
313 See Documentation/scsi/aic7xxx.txt.
315 aic79xx= [HW,SCSI]
316 See Documentation/scsi/aic79xx.txt.
318 amd_iommu= [HW,X86-84]
319 Pass parameters to the AMD IOMMU driver in the system.
320 Possible values are:
321 isolate - enable device isolation (each device, as far
322 as possible, will get its own protection
323 domain) [default]
324 share - put every device behind one IOMMU into the
325 same protection domain
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
331 amijoy.map= [HW,JOY] Amiga joystick support
332 Map of devices attached to JOY0DAT and JOY1DAT
333 Format: <a>,<b>
334 See also Documentation/kernel/input/joystick.txt
336 analog.map= [HW,JOY] Analog joystick and gamepad support
337 Specifies type or capabilities of an analog joystick
338 connected to one of 16 gameports
339 Format: <type1>,<type2>,..<type16>
341 apc= [HW,SPARC]
342 Power management functions (SPARCstation-4/5 + deriv.)
343 Format: noidle
344 Disable APC CPU standby support. SPARCstation-Fox does
345 not play well with APC CPU idle - disable it if you have
346 APC and your system crashes randomly.
348 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
349 Change the output verbosity whilst booting
350 Format: { quiet (default) | verbose | debug }
351 Change the amount of debugging information output
352 when initialising the APIC and IO-APIC components.
354 apm= [APM] Advanced Power Management
355 See header of arch/x86/kernel/apm_32.c.
357 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
358 Format: <io>,<irq>,<nodeID>
360 ataflop= [HW,M68k]
362 atarimouse= [HW,MOUSE] Atari Mouse
364 atascsi= [HW,SCSI] Atari SCSI
366 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
367 EzKey and similar keyboards
369 atkbd.reset= [HW] Reset keyboard during initialization
371 atkbd.set= [HW] Select keyboard code set
372 Format: <int> (2 = AT (default), 3 = PS/2)
374 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
375 keyboards
377 atkbd.softraw= [HW] Choose between synthetic and real raw mode
378 Format: <bool> (0 = real, 1 = synthetic (default))
380 atkbd.softrepeat= [HW]
381 Use software keyboard repeat
383 autotest [IA64]
385 baycom_epp= [HW,AX25]
386 Format: <io>,<mode>
388 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
389 Format: <io>,<mode>
390 See header of drivers/net/hamradio/baycom_par.c.
392 baycom_ser_fdx= [HW,AX25]
393 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
394 Format: <io>,<irq>,<mode>[,<baud>]
395 See header of drivers/net/hamradio/baycom_ser_fdx.c.
397 baycom_ser_hdx= [HW,AX25]
398 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
399 Format: <io>,<irq>,<mode>
400 See header of drivers/net/hamradio/baycom_ser_hdx.c.
402 boot_delay= Milliseconds to delay each printk during boot.
403 Values larger than 10 seconds (10000) are changed to
404 no delay (0).
405 Format: integer
407 bootmem_debug [KNL] Enable bootmem allocator debug messages.
409 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
410 bttv.radio= Most important insmod options are available as
411 kernel args too.
412 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
413 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
415 BusLogic= [HW,SCSI]
416 See drivers/scsi/BusLogic.c, comment before function
417 BusLogic_ParseDriverOptions().
419 c101= [NET] Moxa C101 synchronous serial card
421 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
422 Sometimes CPU hardware bugs make them report the cache
423 size incorrectly. The kernel will attempt work arounds
424 to fix known problems, but for some CPUs it is not
425 possible to determine what the correct size should be.
426 This option provides an override for these situations.
428 capability.disable=
429 [SECURITY] Disable capabilities. This would normally
430 be used only if an alternative security model is to be
431 configured. Potentially dangerous and should only be
432 used if you are entirely sure of the consequences.
434 ccw_timeout_log [S390]
435 See Documentation/s390/CommonIO for details.
437 cgroup_disable= [KNL] Disable a particular controller
438 Format: {name of the controller(s) to disable}
439 {Currently supported controllers - "memory"}
441 checkreqprot [SELINUX] Set initial checkreqprot flag value.
442 Format: { "0" | "1" }
443 See security/selinux/Kconfig help text.
444 0 -- check protection applied by kernel (includes
445 any implied execute protection).
446 1 -- check protection requested by application.
447 Default value is set via a kernel config option.
448 Value can be changed at runtime via
449 /selinux/checkreqprot.
451 cio_ignore= [S390]
452 See Documentation/s390/CommonIO for details.
454 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
455 [Deprecated]
456 Forces specified clocksource (if available) to be used
457 when calculating gettimeofday(). If specified
458 clocksource is not available, it defaults to PIT.
459 Format: { pit | tsc | cyclone | pmtmr }
461 clocksource= [GENERIC_TIME] Override the default clocksource
462 Format: <string>
463 Override the default clocksource and use the clocksource
464 with the name specified.
465 Some clocksource names to choose from, depending on
466 the platform:
467 [all] jiffies (this is the base, fallback clocksource)
468 [ACPI] acpi_pm
469 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
470 pxa_timer,timer3,32k_counter,timer0_1
471 [AVR32] avr32
472 [X86-32] pit,hpet,tsc,vmi-timer;
473 scx200_hrt on Geode; cyclone on IBM x440
474 [MIPS] MIPS
475 [PARISC] cr16
476 [S390] tod
477 [SH] SuperH
478 [SPARC64] tick
479 [X86-64] hpet,tsc
481 clearcpuid=BITNUM [X86]
482 Disable CPUID feature X for the kernel. See
483 arch/x86/include/asm/cpufeature.h for the valid bit
484 numbers. Note the Linux specific bits are not necessarily
485 stable over kernel options, but the vendor specific
486 ones should be.
487 Also note that user programs calling CPUID directly
488 or using the feature without checking anything
489 will still see it. This just prevents it from
490 being used by the kernel or shown in /proc/cpuinfo.
491 Also note the kernel might malfunction if you disable
492 some critical bits.
494 cmo_free_hint= [PPC] Format: { yes | no }
495 Specify whether pages are marked as being inactive
496 when they are freed. This is used in CMO environments
497 to determine OS memory pressure for page stealing by
498 a hypervisor.
499 Default: yes
501 code_bytes [X86] How many bytes of object code to print
502 in an oops report.
503 Range: 0 - 8192
504 Default: 64
506 com20020= [HW,NET] ARCnet - COM20020 chipset
507 Format:
508 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
510 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
511 Format: <io>[,<irq>]
513 com90xx= [HW,NET]
514 ARCnet - COM90xx chipset (memory-mapped buffers)
515 Format: <io>[,<irq>[,<memstart>]]
517 condev= [HW,S390] console device
518 conmode=
520 console= [KNL] Output console device and options.
522 tty<n> Use the virtual console device <n>.
524 ttyS<n>[,options]
525 ttyUSB0[,options]
526 Use the specified serial port. The options are of
527 the form "bbbbpnf", where "bbbb" is the baud rate,
528 "p" is parity ("n", "o", or "e"), "n" is number of
529 bits, and "f" is flow control ("r" for RTS or
530 omit it). Default is "9600n8".
532 See Documentation/serial-console.txt for more
533 information. See
534 Documentation/networking/netconsole.txt for an
535 alternative.
537 uart[8250],io,<addr>[,options]
538 uart[8250],mmio,<addr>[,options]
539 Start an early, polled-mode console on the 8250/16550
540 UART at the specified I/O port or MMIO address,
541 switching to the matching ttyS device later. The
542 options are the same as for ttyS, above.
544 If the device connected to the port is not a TTY but a braille
545 device, prepend "brl," before the device type, for instance
546 console=brl,ttyS0
547 For now, only VisioBraille is supported.
549 coredump_filter=
550 [KNL] Change the default value for
551 /proc/<pid>/coredump_filter.
552 See also Documentation/filesystems/proc.txt.
554 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
555 Format:
556 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
558 crashkernel=nn[KMG]@ss[KMG]
559 [KNL] Reserve a chunk of physical memory to
560 hold a kernel to switch to with kexec on panic.
562 crashkernel=range1:size1[,range2:size2,...][@offset]
563 [KNL] Same as above, but depends on the memory
564 in the running system. The syntax of range is
565 start-[end] where start and end are both
566 a memory unit (amount[KMG]). See also
567 Documentation/kdump/kdump.txt for a example.
569 cs89x0_dma= [HW,NET]
570 Format: <dma>
572 cs89x0_media= [HW,NET]
573 Format: { rj45 | aui | bnc }
575 dasd= [HW,NET]
576 See header of drivers/s390/block/dasd_devmap.c.
578 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
579 (one device per port)
580 Format: <port#>,<type>
581 See also Documentation/input/joystick-parport.txt
583 debug [KNL] Enable kernel debugging (events log level).
585 debug_locks_verbose=
586 [KNL] verbose self-tests
587 Format=<0|1>
588 Print debugging info while doing the locking API
589 self-tests.
590 We default to 0 (no extra messages), setting it to
591 1 will print _a lot_ more information - normally
592 only useful to kernel developers.
594 debug_objects [KNL] Enable object debugging
596 no_debug_objects
597 [KNL] Disable object debugging
599 debugpat [X86] Enable PAT debugging
601 decnet.addr= [HW,NET]
602 Format: <area>[,<node>]
603 See also Documentation/networking/decnet.txt.
605 default_hugepagesz=
606 [same as hugepagesz=] The size of the default
607 HugeTLB page size. This is the size represented by
608 the legacy /proc/ hugepages APIs, used for SHM, and
609 default size when mounting hugetlbfs filesystems.
610 Defaults to the default architecture's huge page size
611 if not specified.
613 dhash_entries= [KNL]
614 Set number of hash buckets for dentry cache.
616 digi= [HW,SERIAL]
617 IO parameters + enable/disable command.
619 digiepca= [HW,SERIAL]
620 See drivers/char/README.epca and
621 Documentation/serial/digiepca.txt.
623 disable_mtrr_cleanup [X86]
624 The kernel tries to adjust MTRR layout from continuous
625 to discrete, to make X server driver able to add WB
626 entry later. This parameter disables that.
628 disable_mtrr_trim [X86, Intel and AMD only]
629 By default the kernel will trim any uncacheable
630 memory out of your available memory pool based on
631 MTRR settings. This parameter disables that behavior,
632 possibly causing your machine to run very slowly.
634 disable_timer_pin_1 [X86]
635 Disable PIN 1 of APIC timer
636 Can be useful to work around chipset bugs.
638 dmasound= [HW,OSS] Sound subsystem buffers
640 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
641 this option disables the debugging code at boot.
643 dma_debug_entries=<number>
644 This option allows to tune the number of preallocated
645 entries for DMA-API debugging code. One entry is
646 required per DMA-API allocation. Use this if the
647 DMA-API debugging code disables itself because the
648 architectural default is too low.
650 dma_debug_driver=<driver_name>
651 With this option the DMA-API debugging driver
652 filter feature can be enabled at boot time. Just
653 pass the driver to filter for as the parameter.
654 The filter can be disabled or changed to another
655 driver later using sysfs.
657 dscc4.setup= [NET]
659 dtc3181e= [HW,SCSI]
661 dynamic_printk Enables pr_debug()/dev_dbg() calls if
662 CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled.
663 These can also be switched on/off via
664 <debugfs>/dynamic_printk/modules
666 earlycon= [KNL] Output early console device and options.
667 uart[8250],io,<addr>[,options]
668 uart[8250],mmio,<addr>[,options]
669 Start an early, polled-mode console on the 8250/16550
670 UART at the specified I/O port or MMIO address.
671 The options are the same as for ttyS, above.
673 earlyprintk= [X86,SH,BLACKFIN]
674 earlyprintk=vga
675 earlyprintk=serial[,ttySn[,baudrate]]
676 earlyprintk=dbgp
678 Append ",keep" to not disable it when the real console
679 takes over.
681 Only vga or serial or usb debug port at a time.
683 Currently only ttyS0 and ttyS1 are supported.
685 Interaction with the standard serial driver is not
686 very good.
688 The VGA output is eventually overwritten by the real
689 console.
691 eata= [HW,SCSI]
693 edd= [EDD]
694 Format: {"off" | "on" | "skip[mbr]"}
696 eisa_irq_edge= [PARISC,HW]
697 See header of drivers/parisc/eisa.c.
699 elanfreq= [X86-32]
700 See comment before function elanfreq_setup() in
701 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
703 elevator= [IOSCHED]
704 Format: {"anticipatory" | "cfq" | "deadline" | "noop"}
705 See Documentation/block/as-iosched.txt and
706 Documentation/block/deadline-iosched.txt for details.
708 elfcorehdr= [IA64,PPC,SH,X86]
709 Specifies physical address of start of kernel core
710 image elf header. Generally kexec loader will
711 pass this option to capture kernel.
712 See Documentation/kdump/kdump.txt for details.
714 enable_mtrr_cleanup [X86]
715 The kernel tries to adjust MTRR layout from continuous
716 to discrete, to make X server driver able to add WB
717 entry later. This parameter enables that.
719 enable_timer_pin_1 [X86]
720 Enable PIN 1 of APIC timer
721 Can be useful to work around chipset bugs
722 (in particular on some ATI chipsets).
723 The kernel tries to set a reasonable default.
725 enforcing [SELINUX] Set initial enforcing status.
726 Format: {"0" | "1"}
727 See security/selinux/Kconfig help text.
728 0 -- permissive (log only, no denials).
729 1 -- enforcing (deny and log).
730 Default value is 0.
731 Value can be changed at runtime via /selinux/enforce.
733 ether= [HW,NET] Ethernet cards parameters
734 This option is obsoleted by the "netdev=" option, which
735 has equivalent usage. See its documentation for details.
737 eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
738 Format: <io>[,<irq>]
740 failslab=
741 fail_page_alloc=
742 fail_make_request=[KNL]
743 General fault injection mechanism.
744 Format: <interval>,<probability>,<space>,<times>
745 See also /Documentation/fault-injection/.
747 fd_mcs= [HW,SCSI]
748 See header of drivers/scsi/fd_mcs.c.
750 fdomain= [HW,SCSI]
751 See header of drivers/scsi/fdomain.c.
753 floppy= [HW]
754 See Documentation/blockdev/floppy.txt.
756 force_pal_cache_flush
757 [IA-64] Avoid check_sal_cache_flush which may hang on
758 buggy SAL_CACHE_FLUSH implementations. Using this
759 parameter will force ia64_sal_cache_flush to call
760 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
762 ftrace=[tracer]
763 [FTRACE] will set and start the specified tracer
764 as early as possible in order to facilitate early
765 boot debugging.
767 ftrace_dump_on_oops
768 [FTRACE] will dump the trace buffers on oops.
770 ftrace_filter=[function-list]
771 [FTRACE] Limit the functions traced by the function
772 tracer at boot up. function-list is a comma separated
773 list of functions. This list can be changed at run
774 time by the set_ftrace_filter file in the debugfs
775 tracing directory.
777 ftrace_notrace=[function-list]
778 [FTRACE] Do not trace the functions specified in
779 function-list. This list can be changed at run time
780 by the set_ftrace_notrace file in the debugfs
781 tracing directory.
783 gamecon.map[2|3]=
784 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
785 support via parallel port (up to 5 devices per port)
786 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
787 See also Documentation/input/joystick-parport.txt
789 gamma= [HW,DRM]
791 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
792 Format: off | on
793 default: on
795 gdth= [HW,SCSI]
796 See header of drivers/scsi/gdth.c.
798 gpt [EFI] Forces disk with valid GPT signature but
799 invalid Protective MBR to be treated as GPT.
801 gvp11= [HW,SCSI]
803 hashdist= [KNL,NUMA] Large hashes allocated during boot
804 are distributed across NUMA nodes. Defaults on
805 for 64bit NUMA, off otherwise.
806 Format: 0 | 1 (for off | on)
808 hcl= [IA-64] SGI's Hardware Graph compatibility layer
810 hd= [EIDE] (E)IDE hard drive subsystem geometry
811 Format: <cyl>,<head>,<sect>
813 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
814 size of <nn>. This works even on boxes that have no
815 highmem otherwise. This also works to reduce highmem
816 size on bigger boxes.
818 highres= [KNL] Enable/disable high resolution timer mode.
819 Valid parameters: "on", "off"
820 Default: "on"
822 hisax= [HW,ISDN]
823 See Documentation/isdn/README.HiSax.
825 hlt [BUGS=ARM,SH]
827 hpet= [X86-32,HPET] option to control HPET usage
828 Format: { enable (default) | disable | force |
829 verbose }
830 disable: disable HPET and use PIT instead
831 force: allow force enabled of undocumented chips (ICH4,
832 VIA, nVidia)
833 verbose: show contents of HPET registers during setup
835 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
836 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
837 On x86-64 and powerpc, this option can be specified
838 multiple times interleaved with hugepages= to reserve
839 huge pages of different sizes. Valid pages sizes on
840 x86-64 are 2M (when the CPU supports "pse") and 1G
841 (when the CPU supports the "pdpe1gb" cpuinfo flag)
842 Note that 1GB pages can only be allocated at boot time
843 using hugepages= and not freed afterwards.
845 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
846 terminal devices. Valid values: 0..8
847 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
848 If specified, z/VM IUCV HVC accepts connections
849 from listed z/VM user IDs only.
851 i2c_bus= [HW] Override the default board specific I2C bus speed
852 or register an additional I2C bus that is not
853 registered from board initialization code.
854 Format:
855 <bus_id>,<clkrate>
857 i8042.debug [HW] Toggle i8042 debug mode
858 i8042.direct [HW] Put keyboard port into non-translated mode
859 i8042.dumbkbd [HW] Pretend that controller can only read data from
860 keyboard and cannot control its state
861 (Don't attempt to blink the leds)
862 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
863 i8042.nokbd [HW] Don't check/create keyboard port
864 i8042.noloop [HW] Disable the AUX Loopback command while probing
865 for the AUX port
866 i8042.nomux [HW] Don't check presence of an active multiplexing
867 controller
868 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
869 controllers
870 i8042.panicblink=
871 [HW] Frequency with which keyboard LEDs should blink
872 when kernel panics (default is 0.5 sec)
873 i8042.reset [HW] Reset the controller during init and cleanup
874 i8042.unlock [HW] Unlock (ignore) the keylock
876 i810= [HW,DRM]
878 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
879 indicates that the driver is running on unsupported
880 hardware.
881 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
882 does not match list of supported models.
883 i8k.power_status
884 [HW] Report power status in /proc/i8k
885 (disabled by default)
886 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
887 capability is set.
889 ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
890 See Documentation/mca.txt.
892 icn= [HW,ISDN]
893 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
895 ide-core.nodma= [HW] (E)IDE subsystem
896 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
897 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
898 .cdrom .chs .ignore_cable are additional options
899 See Documentation/ide/ide.txt.
901 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
902 Claim all unknown PCI IDE storage controllers.
904 idle= [X86]
905 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
906 Poll forces a polling idle loop that can slightly
907 improve the performance of waking up a idle CPU, but
908 will use a lot of power and make the system run hot.
909 Not recommended.
910 idle=mwait: On systems which support MONITOR/MWAIT but
911 the kernel chose to not use it because it doesn't save
912 as much power as a normal idle loop, use the
913 MONITOR/MWAIT idle loop anyways. Performance should be
914 the same as idle=poll.
915 idle=halt: Halt is forced to be used for CPU idle.
916 In such case C2/C3 won't be used again.
917 idle=nomwait: Disable mwait for CPU C-states
919 ignore_loglevel [KNL]
920 Ignore loglevel setting - this will print /all/
921 kernel messages to the console. Useful for debugging.
923 ihash_entries= [KNL]
924 Set number of hash buckets for inode cache.
926 ima_audit= [IMA]
927 Format: { "0" | "1" }
928 0 -- integrity auditing messages. (Default)
929 1 -- enable informational integrity auditing messages.
931 ima_hash= [IMA]
932 Formt: { "sha1" | "md5" }
933 default: "sha1"
935 ima_tcb [IMA]
936 Load a policy which meets the needs of the Trusted
937 Computing Base. This means IMA will measure all
938 programs exec'd, files mmap'd for exec, and all files
939 opened for read by uid=0.
941 in2000= [HW,SCSI]
942 See header of drivers/scsi/in2000.c.
944 init= [KNL]
945 Format: <full_path>
946 Run specified binary instead of /sbin/init as init
947 process.
949 initcall_debug [KNL] Trace initcalls as they are executed. Useful
950 for working out where the kernel is dying during
951 startup.
953 initrd= [BOOT] Specify the location of the initial ramdisk
955 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
956 Format: <irq>
958 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
959 on
960 Enable intel iommu driver.
961 off
962 Disable intel iommu driver.
963 igfx_off [Default Off]
964 By default, gfx is mapped as normal device. If a gfx
965 device has a dedicated DMAR unit, the DMAR unit is
966 bypassed by not enabling DMAR with this option. In
967 this case, gfx device will use physical address for
968 DMA.
969 forcedac [x86_64]
970 With this option iommu will not optimize to look
971 for io virtual address below 32 bit forcing dual
972 address cycle on pci bus for cards supporting greater
973 than 32 bit addressing. The default is to look
974 for translation below 32 bit and if not available
975 then look in the higher range.
976 strict [Default Off]
977 With this option on every unmap_single operation will
978 result in a hardware IOTLB flush operation as opposed
979 to batching them for performance.
981 inttest= [IA64]
983 iomem= Disable strict checking of access to MMIO memory
984 strict regions from userspace.
985 relaxed
987 iommu= [x86]
988 off
989 force
990 noforce
991 biomerge
992 panic
993 nopanic
994 merge
995 nomerge
996 forcesac
997 soft
999 io7= [HW] IO7 for Marvel based alpha systems
1000 See comment before marvel_specify_io7 in
1001 arch/alpha/kernel/core_marvel.c.
1003 io_delay= [X86] I/O delay method
1004 0x80
1005 Standard port 0x80 based delay
1006 0xed
1007 Alternate port 0xed based delay (needed on some systems)
1008 udelay
1009 Simple two microseconds delay
1010 none
1011 No delay
1013 ip= [IP_PNP]
1014 See Documentation/filesystems/nfsroot.txt.
1016 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1017 See comment before ip2_setup() in
1018 drivers/char/ip2/ip2base.c.
1020 ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
1021 See header of drivers/scsi/ips.c.
1023 irqfixup [HW]
1024 When an interrupt is not handled search all handlers
1025 for it. Intended to get systems with badly broken
1026 firmware running.
1028 irqpoll [HW]
1029 When an interrupt is not handled search all handlers
1030 for it. Also check all handlers each timer
1031 interrupt. Intended to get systems with badly broken
1032 firmware running.
1034 isapnp= [ISAPNP]
1035 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1037 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1038 Format:
1039 <cpu number>,...,<cpu number>
1040 or
1041 <cpu number>-<cpu number>
1042 (must be a positive range in ascending order)
1043 or a mixture
1044 <cpu number>,...,<cpu number>-<cpu number>
1046 This option can be used to specify one or more CPUs
1047 to isolate from the general SMP balancing and scheduling
1048 algorithms. You can move a process onto or off an
1049 "isolated" CPU via the CPU affinity syscalls or cpuset.
1050 <cpu number> begins at 0 and the maximum value is
1051 "number of CPUs in system - 1".
1053 This option is the preferred way to isolate CPUs. The
1054 alternative -- manually setting the CPU mask of all
1055 tasks in the system -- can cause problems and
1056 suboptimal load balancer performance.
1058 iucv= [HW,NET]
1060 js= [HW,JOY] Analog joystick
1061 See Documentation/input/joystick.txt.
1063 keepinitrd [HW,ARM]
1065 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1066 specifies the amount of memory usable by the kernel
1067 for non-movable allocations. The requested amount is
1068 spread evenly throughout all nodes in the system. The
1069 remaining memory in each node is used for Movable
1070 pages. In the event, a node is too small to have both
1071 kernelcore and Movable pages, kernelcore pages will
1072 take priority and other nodes will have a larger number
1073 of kernelcore pages. The Movable zone is used for the
1074 allocation of pages that may be reclaimed or moved
1075 by the page migration subsystem. This means that
1076 HugeTLB pages may not be allocated from this zone.
1077 Note that allocations like PTEs-from-HighMem still
1078 use the HighMem zone if it exists, and the Normal
1079 zone if it does not.
1081 kgdboc= [HW] kgdb over consoles.
1082 Requires a tty driver that supports console polling.
1083 (only serial supported for now)
1084 Format: <serial_device>[,baud]
1086 kmac= [MIPS] korina ethernet MAC address.
1087 Configure the RouterBoard 532 series on-chip
1088 Ethernet adapter MAC address.
1090 kmemleak= [KNL] Boot-time kmemleak enable/disable
1091 Valid arguments: on, off
1092 Default: on
1094 kstack=N [X86] Print N words from the kernel stack
1095 in oops dumps.
1097 l2cr= [PPC]
1099 l3cr= [PPC]
1101 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1102 disabled it.
1104 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1105 in C2 power state.
1107 libata.dma= [LIBATA] DMA control
1108 libata.dma=0 Disable all PATA and SATA DMA
1109 libata.dma=1 PATA and SATA Disk DMA only
1110 libata.dma=2 ATAPI (CDROM) DMA only
1111 libata.dma=4 Compact Flash DMA only
1112 Combinations also work, so libata.dma=3 enables DMA
1113 for disks and CDROMs, but not CFs.
1115 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1116 when set.
1117 Format: <int>
1119 libata.force= [LIBATA] Force configurations. The format is comma
1120 separated list of "[ID:]VAL" where ID is
1121 PORT[:DEVICE]. PORT and DEVICE are decimal numbers
1122 matching port, link or device. Basically, it matches
1123 the ATA ID string printed on console by libata. If
1124 the whole ID part is omitted, the last PORT and DEVICE
1125 values are used. If ID hasn't been specified yet, the
1126 configuration applies to all ports, links and devices.
1128 If only DEVICE is omitted, the parameter applies to
1129 the port and all links and devices behind it. DEVICE
1130 number of 0 either selects the first device or the
1131 first fan-out link behind PMP device. It does not
1132 select the host link. DEVICE number of 15 selects the
1133 host link and device attached to it.
1135 The VAL specifies the configuration to force. As long
1136 as there's no ambiguity shortcut notation is allowed.
1137 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1138 The following configurations can be forced.
1140 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1141 Any ID with matching PORT is used.
1143 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1145 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1146 udma[/][16,25,33,44,66,100,133] notation is also
1147 allowed.
1149 * [no]ncq: Turn on or off NCQ.
1151 * nohrst, nosrst, norst: suppress hard, soft
1152 and both resets.
1154 If there are multiple matching configurations changing
1155 the same attribute, the last one is used.
1157 lmb=debug [KNL] Enable lmb debug messages.
1159 load_ramdisk= [RAM] List of ramdisks to load from floppy
1160 See Documentation/blockdev/ramdisk.txt.
1162 lockd.nlm_grace_period=P [NFS] Assign grace period.
1163 Format: <integer>
1165 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1166 Format: <integer>
1168 lockd.nlm_timeout=T [NFS] Assign timeout value.
1169 Format: <integer>
1171 lockd.nlm_udpport=M [NFS] Assign UDP port.
1172 Format: <integer>
1174 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1175 Format: <irq>
1177 loglevel= All Kernel Messages with a loglevel smaller than the
1178 console loglevel will be printed to the console. It can
1179 also be changed with klogd or other programs. The
1180 loglevels are defined as follows:
1182 0 (KERN_EMERG) system is unusable
1183 1 (KERN_ALERT) action must be taken immediately
1184 2 (KERN_CRIT) critical conditions
1185 3 (KERN_ERR) error conditions
1186 4 (KERN_WARNING) warning conditions
1187 5 (KERN_NOTICE) normal but significant condition
1188 6 (KERN_INFO) informational
1189 7 (KERN_DEBUG) debug-level messages
1191 log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1192 Format: { n | nk | nM }
1193 n must be a power of two. The default size
1194 is set in the kernel config file.
1196 logo.nologo [FB] Disables display of the built-in Linux logo.
1197 This may be used to provide more screen space for
1198 kernel log messages and is useful when debugging
1199 kernel boot problems.
1201 lp=0 [LP] Specify parallel ports to use, e.g,
1202 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1203 lp=reset first parallel port). 'lp=0' disables the
1204 lp=auto printer driver. 'lp=reset' (which can be
1205 specified in addition to the ports) causes
1206 attached printers to be reset. Using
1207 lp=port1,port2,... specifies the parallel ports
1208 to associate lp devices with, starting with
1209 lp0. A port specification may be 'none' to skip
1210 that lp device, or a parport name such as
1211 'parport0'. Specifying 'lp=auto' instead of a
1212 port specification list means that device IDs
1213 from each port should be examined, to see if
1214 an IEEE 1284-compliant printer is attached; if
1215 so, the driver will manage that printer.
1216 See also header of drivers/char/lp.c.
1218 lpj=n [KNL]
1219 Sets loops_per_jiffy to given constant, thus avoiding
1220 time-consuming boot-time autodetection (up to 250 ms per
1221 CPU). 0 enables autodetection (default). To determine
1222 the correct value for your kernel, boot with normal
1223 autodetection and see what value is printed. Note that
1224 on SMP systems the preset will be applied to all CPUs,
1225 which is likely to cause problems if your CPUs need
1226 significantly divergent settings. An incorrect value
1227 will cause delays in the kernel to be wrong, leading to
1228 unpredictable I/O errors and other breakage. Although
1229 unlikely, in the extreme case this might damage your
1230 hardware.
1232 ltpc= [NET]
1233 Format: <io>,<irq>,<dma>
1235 mac5380= [HW,SCSI] Format:
1236 <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
1238 machvec= [IA64] Force the use of a particular machine-vector
1239 (machvec) in a generic kernel.
1240 Example: machvec=hpzx1_swiotlb
1242 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1243 than or equal to this physical address is ignored.
1245 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1246 should make use of. maxcpus=n : n >= 0 limits the
1247 kernel to using 'n' processors. n=0 is a special case,
1248 it is equivalent to "nosmp", which also disables
1249 the IO APIC.
1251 max_loop= [LOOP] Maximum number of loopback devices that can
1252 be mounted
1253 Format: <1-256>
1255 max_luns= [SCSI] Maximum number of LUNs to probe.
1256 Should be between 1 and 2^32-1.
1258 max_report_luns=
1259 [SCSI] Maximum number of LUNs received.
1260 Should be between 1 and 16384.
1262 mcatest= [IA-64]
1264 mce [X86-32] Machine Check Exception
1266 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1268 md= [HW] RAID subsystems devices and level
1269 See Documentation/md.txt.
1271 mdacon= [MDA]
1272 Format: <first>,<last>
1273 Specifies range of consoles to be captured by the MDA.
1275 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1276 Amount of memory to be used when the kernel is not able
1277 to see the whole system memory or for test.
1278 [X86-32] Use together with memmap= to avoid physical
1279 address space collisions. Without memmap= PCI devices
1280 could be placed at addresses belonging to unused RAM.
1282 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1283 memory.
1285 memchunk=nn[KMG]
1286 [KNL,SH] Allow user to override the default size for
1287 per-device physically contiguous DMA buffers.
1289 memmap=exactmap [KNL,X86] Enable setting of an exact
1290 E820 memory map, as specified by the user.
1291 Such memmap=exactmap lines can be constructed based on
1292 BIOS output or other requirements. See the memmap=nn@ss
1293 option description.
1295 memmap=nn[KMG]@ss[KMG]
1296 [KNL] Force usage of a specific region of memory
1297 Region of memory to be used, from ss to ss+nn.
1299 memmap=nn[KMG]#ss[KMG]
1300 [KNL,ACPI] Mark specific memory as ACPI data.
1301 Region of memory to be used, from ss to ss+nn.
1303 memmap=nn[KMG]$ss[KMG]
1304 [KNL,ACPI] Mark specific memory as reserved.
1305 Region of memory to be used, from ss to ss+nn.
1306 Example: Exclude memory from 0x18690000-0x1869ffff
1307 memmap=64K$0x18690000
1308 or
1309 memmap=0x10000$0x18690000
1311 memory_corruption_check=0/1 [X86]
1312 Some BIOSes seem to corrupt the first 64k of
1313 memory when doing things like suspend/resume.
1314 Setting this option will scan the memory
1315 looking for corruption. Enabling this will
1316 both detect corruption and prevent the kernel
1317 from using the memory being corrupted.
1318 However, its intended as a diagnostic tool; if
1319 repeatable BIOS-originated corruption always
1320 affects the same memory, you can use memmap=
1321 to prevent the kernel from using that memory.
1323 memory_corruption_check_size=size [X86]
1324 By default it checks for corruption in the low
1325 64k, making this memory unavailable for normal
1326 use. Use this parameter to scan for
1327 corruption in more or less memory.
1329 memory_corruption_check_period=seconds [X86]
1330 By default it checks for corruption every 60
1331 seconds. Use this parameter to check at some
1332 other rate. 0 disables periodic checking.
1334 memtest= [KNL,X86] Enable memtest
1335 Format: <integer>
1336 default : 0 <disable>
1337 Specifies the number of memtest passes to be
1338 performed. Each pass selects another test
1339 pattern from a given set of patterns. Memtest
1340 fills the memory with this pattern, validates
1341 memory contents and reserves bad memory
1342 regions that are detected.
1344 meye.*= [HW] Set MotionEye Camera parameters
1345 See Documentation/video4linux/meye.txt.
1347 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1348 Multi-Function General Purpose Timers on AMD Geode
1349 platforms.
1351 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1352 the BIOS has incorrectly applied a workaround. TinyBIOS
1353 version 0.98 is known to be affected, 0.99 fixes the
1354 problem by letting the user disable the workaround.
1356 mga= [HW,DRM]
1358 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1359 physical address is ignored.
1361 mminit_loglevel=
1362 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1363 parameter allows control of the logging verbosity for
1364 the additional memory initialisation checks. A value
1365 of 0 disables mminit logging and a level of 4 will
1366 log everything. Information is printed at KERN_DEBUG
1367 so loglevel=8 may also need to be specified.
1369 mousedev.tap_time=
1370 [MOUSE] Maximum time between finger touching and
1371 leaving touchpad surface for touch to be considered
1372 a tap and be reported as a left button click (for
1373 touchpads working in absolute mode only).
1374 Format: <msecs>
1375 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1376 reporting absolute coordinates, such as tablets
1377 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1378 reporting absolute coordinates, such as tablets
1380 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1381 is similar to kernelcore except it specifies the
1382 amount of memory used for migratable allocations.
1383 If both kernelcore and movablecore is specified,
1384 then kernelcore will be at *least* the specified
1385 value but may be more. If movablecore on its own
1386 is specified, the administrator must be careful
1387 that the amount of memory usable for all allocations
1388 is not too small.
1390 mpu401= [HW,OSS]
1391 Format: <io>,<irq>
1393 MTD_Partition= [MTD]
1394 Format: <name>,<region-number>,<size>,<offset>
1396 MTD_Region= [MTD] Format:
1397 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1399 mtdparts= [MTD]
1400 See drivers/mtd/cmdlinepart.c.
1402 mtdset= [ARM]
1403 ARM/S3C2412 JIVE boot control
1405 See arch/arm/mach-s3c2412/mach-jive.c
1407 mtouchusb.raw_coordinates=
1408 [HW] Make the MicroTouch USB driver use raw coordinates
1409 ('y', default) or cooked coordinates ('n')
1411 mtrr_chunk_size=nn[KMG] [X86]
1412 used for mtrr cleanup. It is largest continuous chunk
1413 that could hold holes aka. UC entries.
1415 mtrr_gran_size=nn[KMG] [X86]
1416 Used for mtrr cleanup. It is granularity of mtrr block.
1417 Default is 1.
1418 Large value could prevent small alignment from
1419 using up MTRRs.
1421 mtrr_spare_reg_nr=n [X86]
1422 Format: <integer>
1423 Range: 0,7 : spare reg number
1424 Default : 1
1425 Used for mtrr cleanup. It is spare mtrr entries number.
1426 Set to 2 or more if your graphical card needs more.
1428 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1430 NCR_D700= [HW,SCSI]
1431 See header of drivers/scsi/NCR_D700.c.
1433 ncr5380= [HW,SCSI]
1435 ncr53c400= [HW,SCSI]
1437 ncr53c400a= [HW,SCSI]
1439 ncr53c406a= [HW,SCSI]
1441 ncr53c8xx= [HW,SCSI]
1443 netdev= [NET] Network devices parameters
1444 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1445 Note that mem_start is often overloaded to mean
1446 something different and driver-specific.
1447 This usage is only documented in each driver source
1448 file if at all.
1450 nf_conntrack.acct=
1451 [NETFILTER] Enable connection tracking flow accounting
1452 0 to disable accounting
1453 1 to enable accounting
1454 Default value depends on CONFIG_NF_CT_ACCT that is
1455 going to be removed in 2.6.29.
1457 nfsaddrs= [NFS]
1458 See Documentation/filesystems/nfsroot.txt.
1460 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1461 See Documentation/filesystems/nfsroot.txt.
1463 nfs.callback_tcpport=
1464 [NFS] set the TCP port on which the NFSv4 callback
1465 channel should listen.
1467 nfs.idmap_cache_timeout=
1468 [NFS] set the maximum lifetime for idmapper cache
1469 entries.
1471 nfs.enable_ino64=
1472 [NFS] enable 64-bit inode numbers.
1473 If zero, the NFS client will fake up a 32-bit inode
1474 number for the readdir() and stat() syscalls instead
1475 of returning the full 64-bit number.
1476 The default is to return 64-bit inode numbers.
1478 nmi_debug= [KNL,AVR32] Specify one or more actions to take
1479 when a NMI is triggered.
1480 Format: [state][,regs][,debounce][,die]
1482 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1483 Format: [panic,][num]
1484 Valid num: 0,1,2
1485 0 - turn nmi_watchdog off
1486 1 - use the IO-APIC timer for the NMI watchdog
1487 2 - use the local APIC for the NMI watchdog using
1488 a performance counter. Note: This will use one
1489 performance counter and the local APIC's performance
1490 vector.
1491 When panic is specified, panic when an NMI watchdog
1492 timeout occurs.
1493 This is useful when you use a panic=... timeout and
1494 need the box quickly up again.
1495 Instead of 1 and 2 it is possible to use the following
1496 symbolic names: lapic and ioapic
1497 Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1499 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1500 emulation library even if a 387 maths coprocessor
1501 is present.
1503 no_console_suspend
1504 [HW] Never suspend the console
1505 Disable suspending of consoles during suspend and
1506 hibernate operations. Once disabled, debugging
1507 messages can reach various consoles while the rest
1508 of the system is being put to sleep (ie, while
1509 debugging driver suspend/resume hooks). This may
1510 not work reliably with all consoles, but is known
1511 to work with serial and VGA consoles.
1513 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1514 caches in the slab allocator. Saves per-node memory,
1515 but will impact performance.
1517 noalign [KNL,ARM]
1519 noapic [SMP,APIC] Tells the kernel to not make use of any
1520 IOAPICs that may be present in the system.
1522 nobats [PPC] Do not use BATs for mapping kernel lowmem
1523 on "Classic" PPC cores.
1525 nocache [ARM]
1527 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1529 nodelayacct [KNL] Disable per-task delay accounting
1531 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1533 nodsp [SH] Disable hardware DSP at boot time.
1535 noefi [X86] Disable EFI runtime services support.
1537 noexec [IA-64]
1539 noexec [X86]
1540 On X86-32 available only on PAE configured kernels.
1541 noexec=on: enable non-executable mappings (default)
1542 noexec=off: disable non-executable mappings
1544 noexec32 [X86-64]
1545 This affects only 32-bit executables.
1546 noexec32=on: enable non-executable mappings (default)
1547 read doesn't imply executable mappings
1548 noexec32=off: disable non-executable mappings
1549 read implies executable mappings
1551 nofpu [SH] Disable hardware FPU at boot time.
1553 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1554 register save and restore. The kernel will only save
1555 legacy floating-point registers on task switch.
1557 noxsave [BUGS=X86] Disables x86 extended register state save
1558 and restore using xsave. The kernel will fallback to
1559 enabling legacy floating-point and sse state.
1561 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1562 wfi(ARM) instruction doesn't work correctly and not to
1563 use it. This is also useful when using JTAG debugger.
1565 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1566 instruction doesn't work correctly and not to
1567 use it.
1569 no_file_caps Tells the kernel not to honor file capabilities. The
1570 only way then for a file to be executed with privilege
1571 is to be setuid root or executed by root.
1573 nohalt [IA-64] Tells the kernel not to use the power saving
1574 function PAL_HALT_LIGHT when idle. This increases
1575 power-consumption. On the positive side, it reduces
1576 interrupt wake-up latency, which may improve performance
1577 in certain environments such as networked servers or
1578 real-time systems.
1580 nohz= [KNL] Boottime enable/disable dynamic ticks
1581 Valid arguments: on, off
1582 Default: on
1584 noiotrap [SH] Disables trapped I/O port accesses.
1586 noirqdebug [X86-32] Disables the code which attempts to detect and
1587 disable unhandled interrupt sources.
1589 no_timer_check [X86,APIC] Disables the code which tests for
1590 broken timer IRQ sources.
1592 noisapnp [ISAPNP] Disables ISA PnP code.
1594 noinitrd [RAM] Tells the kernel not to load any configured
1595 initial RAM disk.
1597 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1598 remapping.
1600 nointroute [IA-64]
1602 nojitter [IA64] Disables jitter checking for ITC timers.
1604 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1606 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1608 noltlbs [PPC] Do not use large page/tlb entries for kernel
1609 lowmem mapping on PPC40x.
1611 nomca [IA-64] Disable machine check abort handling
1613 nomce [X86-32] Machine Check Exception
1615 nomfgpt [X86-32] Disable Multi-Function General Purpose
1616 Timer usage (for AMD Geode machines).
1618 norandmaps Don't use address space randomization. Equivalent to
1619 echo 0 > /proc/sys/kernel/randomize_va_space
1621 noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops
1623 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1624 with UP alternatives
1626 noresidual [PPC] Don't use residual data on PReP machines.
1628 noresume [SWSUSP] Disables resume and restores original swap
1629 space.
1631 no-scroll [VGA] Disables scrollback.
1632 This is required for the Braillex ib80-piezo Braille
1633 reader made by F.H. Papenmeier (Germany).
1635 nosbagart [IA-64]
1637 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1639 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1640 and disable the IO APIC. legacy for "maxcpus=0".
1642 nosoftlockup [KNL] Disable the soft-lockup detector.
1644 noswapaccount [KNL] Disable accounting of swap in memory resource
1645 controller. (See Documentation/cgroups/memory.txt)
1647 nosync [HW,M68K] Disables sync negotiation for all devices.
1649 notsc [BUGS=X86-32] Disable Time Stamp Counter
1651 nousb [USB] Disable the USB subsystem
1653 nowb [ARM]
1655 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1657 nptcg= [IA64] Override max number of concurrent global TLB
1658 purges which is reported from either PAL_VM_SUMMARY or
1659 SAL PALO.
1661 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1663 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1664 one of ['zone', 'node', 'default'] can be specified
1665 This can be set from sysctl after boot.
1666 See Documentation/sysctl/vm.txt for details.
1668 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1669 See Documentation/debugging-via-ohci1394.txt for more
1670 info.
1672 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1673 Rather than timing out after 20 ms if an EC
1674 command is not properly ACKed, override the length
1675 of the timeout. We have interrupts disabled while
1676 waiting for the ACK, so if this is set too high
1677 interrupts *may* be lost!
1679 opl3= [HW,OSS]
1680 Format: <io>
1682 oprofile.timer= [HW]
1683 Use timer interrupt instead of performance counters
1685 oprofile.cpu_type= Force an oprofile cpu type
1686 This might be useful if you have an older oprofile
1687 userland or if you want common events.
1688 Format: { archperfmon }
1689 archperfmon: [X86] Force use of architectural
1690 perfmon on Intel CPUs instead of the
1691 CPU specific event set.
1693 osst= [HW,SCSI] SCSI Tape Driver
1694 Format: <buffer_size>,<write_threshold>
1695 See also Documentation/scsi/st.txt.
1697 panic= [KNL] Kernel behaviour on panic
1698 Format: <timeout>
1700 parkbd.port= [HW] Parallel port number the keyboard adapter is
1701 connected to, default is 0.
1702 Format: <parport#>
1703 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1704 0 for XT, 1 for AT (default is AT).
1705 Format: <mode>
1707 parport= [HW,PPT] Specify parallel ports. 0 disables.
1708 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1709 Use 'auto' to force the driver to use any
1710 IRQ/DMA settings detected (the default is to
1711 ignore detected IRQ/DMA settings because of
1712 possible conflicts). You can specify the base
1713 address, IRQ, and DMA settings; IRQ and DMA
1714 should be numbers, or 'auto' (for using detected
1715 settings on that particular port), or 'nofifo'
1716 (to avoid using a FIFO even if it is detected).
1717 Parallel ports are assigned in the order they
1718 are specified on the command line, starting
1719 with parport0.
1721 parport_init_mode= [HW,PPT]
1722 Configure VIA parallel port to operate in
1723 a specific mode. This is necessary on Pegasos
1724 computer where firmware has no options for setting
1725 up parallel port mode and sets it to spp.
1726 Currently this function knows 686a and 8231 chips.
1727 Format: [spp|ps2|epp|ecp|ecpepp]
1729 pas2= [HW,OSS] Format:
1730 <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16>
1732 pas16= [HW,SCSI]
1733 See header of drivers/scsi/pas16.c.
1735 pause_on_oops=
1736 Halt all CPUs after the first oops has been printed for
1737 the specified number of seconds. This is to be used if
1738 your oopses keep scrolling off the screen.
1740 pcbit= [HW,ISDN]
1742 pcd. [PARIDE]
1743 See header of drivers/block/paride/pcd.c.
1744 See also Documentation/blockdev/paride.txt.
1746 pci=option[,option...] [PCI] various PCI subsystem options:
1747 earlydump [X86] dump PCI config space before the kernel
1748 changes anything
1749 off [X86] don't probe for the PCI bus
1750 bios [X86-32] force use of PCI BIOS, don't access
1751 the hardware directly. Use this if your machine
1752 has a non-standard PCI host bridge.
1753 nobios [X86-32] disallow use of PCI BIOS, only direct
1754 hardware access methods are allowed. Use this
1755 if you experience crashes upon bootup and you
1756 suspect they are caused by the BIOS.
1757 conf1 [X86] Force use of PCI Configuration
1758 Mechanism 1.
1759 conf2 [X86] Force use of PCI Configuration
1760 Mechanism 2.
1761 noaer [PCIE] If the PCIEAER kernel config parameter is
1762 enabled, this kernel boot option can be used to
1763 disable the use of PCIE advanced error reporting.
1764 nodomains [PCI] Disable support for multiple PCI
1765 root domains (aka PCI segments, in ACPI-speak).
1766 nommconf [X86] Disable use of MMCONFIG for PCI
1767 Configuration
1768 nomsi [MSI] If the PCI_MSI kernel config parameter is
1769 enabled, this kernel boot option can be used to
1770 disable the use of MSI interrupts system-wide.
1771 noioapicquirk [APIC] Disable all boot interrupt quirks.
1772 Safety option to keep boot IRQs enabled. This
1773 should never be necessary.
1774 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1775 primary IO-APIC for bridges that cannot disable
1776 boot IRQs. This fixes a source of spurious IRQs
1777 when the system masks IRQs.
1778 noioapicreroute [APIC] Disable workaround that uses the
1779 boot IRQ equivalent of an IRQ that connects to
1780 a chipset where boot IRQs cannot be disabled.
1781 The opposite of ioapicreroute.
1782 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1783 routing table. These calls are known to be buggy
1784 on several machines and they hang the machine
1785 when used, but on other computers it's the only
1786 way to get the interrupt routing table. Try
1787 this option if the kernel is unable to allocate
1788 IRQs or discover secondary PCI buses on your
1789 motherboard.
1790 rom [X86] Assign address space to expansion ROMs.
1791 Use with caution as certain devices share
1792 address decoders between ROMs and other
1793 resources.
1794 norom [X86] Do not assign address space to
1795 expansion ROMs that do not already have
1796 BIOS assigned address ranges.
1797 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1798 assigned automatically to PCI devices. You can
1799 make the kernel exclude IRQs of your ISA cards
1800 this way.
1801 pirqaddr=0xAAAAA [X86] Specify the physical address
1802 of the PIRQ table (normally generated
1803 by the BIOS) if it is outside the
1804 F0000h-100000h range.
1805 lastbus=N [X86] Scan all buses thru bus #N. Can be
1806 useful if the kernel is unable to find your
1807 secondary buses and you want to tell it
1808 explicitly which ones they are.
1809 assign-busses [X86] Always assign all PCI bus
1810 numbers ourselves, overriding
1811 whatever the firmware may have done.
1812 usepirqmask [X86] Honor the possible IRQ mask stored
1813 in the BIOS $PIR table. This is needed on
1814 some systems with broken BIOSes, notably
1815 some HP Pavilion N5400 and Omnibook XE3
1816 notebooks. This will have no effect if ACPI
1817 IRQ routing is enabled.
1818 noacpi [X86] Do not use ACPI for IRQ routing
1819 or for PCI scanning.
1820 use_crs [X86] Use _CRS for PCI resource
1821 allocation.
1822 routeirq Do IRQ routing for all PCI devices.
1823 This is normally done in pci_enable_device(),
1824 so this option is a temporary workaround
1825 for broken drivers that don't call it.
1826 skip_isa_align [X86] do not align io start addr, so can
1827 handle more pci cards
1828 firmware [ARM] Do not re-enumerate the bus but instead
1829 just use the configuration from the
1830 bootloader. This is currently used on
1831 IXP2000 systems where the bus has to be
1832 configured a certain way for adjunct CPUs.
1833 noearly [X86] Don't do any early type 1 scanning.
1834 This might help on some broken boards which
1835 machine check when some devices' config space
1836 is read. But various workarounds are disabled
1837 and some IOMMU drivers will not work.
1838 bfsort Sort PCI devices into breadth-first order.
1839 This sorting is done to get a device
1840 order compatible with older (<= 2.4) kernels.
1841 nobfsort Don't sort PCI devices into breadth-first order.
1842 cbiosize=nn[KMG] The fixed amount of bus space which is
1843 reserved for the CardBus bridge's IO window.
1844 The default value is 256 bytes.
1845 cbmemsize=nn[KMG] The fixed amount of bus space which is
1846 reserved for the CardBus bridge's memory
1847 window. The default value is 64 megabytes.
1848 resource_alignment=
1849 Format:
1850 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
1851 Specifies alignment and device to reassign
1852 aligned memory resources.
1853 If <order of align> is not specified,
1854 PAGE_SIZE is used as alignment.
1855 PCI-PCI bridge can be specified, if resource
1856 windows need to be expanded.
1858 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1859 Management.
1860 off Disable ASPM.
1861 force Enable ASPM even on devices that claim not to support it.
1862 WARNING: Forcing ASPM on may cause system lockups.
1864 pcmv= [HW,PCMCIA] BadgePAD 4
1866 pd. [PARIDE]
1867 See Documentation/blockdev/paride.txt.
1869 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
1870 boot time.
1871 Format: { 0 | 1 }
1872 See arch/parisc/kernel/pdc_chassis.c
1874 pf. [PARIDE]
1875 See Documentation/blockdev/paride.txt.
1877 pg. [PARIDE]
1878 See Documentation/blockdev/paride.txt.
1880 pirq= [SMP,APIC] Manual mp-table setup
1881 See Documentation/x86/i386/IO-APIC.txt.
1883 plip= [PPT,NET] Parallel port network link
1884 Format: { parport<nr> | timid | 0 }
1885 See also Documentation/parport.txt.
1887 pmtmr= [X86] Manual setup of pmtmr I/O Port.
1888 Override pmtimer IOPort with a hex value.
1889 e.g. pmtmr=0x508
1891 pnp.debug [PNP]
1892 Enable PNP debug messages. This depends on the
1893 CONFIG_PNP_DEBUG_MESSAGES option.
1895 pnpacpi= [ACPI]
1896 { off }
1898 pnpbios= [ISAPNP]
1899 { on | off | curr | res | no-curr | no-res }
1901 pnp_reserve_irq=
1902 [ISAPNP] Exclude IRQs for the autoconfiguration
1904 pnp_reserve_dma=
1905 [ISAPNP] Exclude DMAs for the autoconfiguration
1907 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
1908 Ranges are in pairs (I/O port base and size).
1910 pnp_reserve_mem=
1911 [ISAPNP] Exclude memory regions for the
1912 autoconfiguration.
1913 Ranges are in pairs (memory base and size).
1915 ports= [IP_VS_FTP] IPVS ftp helper module
1916 Default is 21.
1917 Up to 8 (IP_VS_APP_MAX_PORTS) ports
1918 may be specified.
1919 Format: <port>,<port>....
1921 print-fatal-signals=
1922 [KNL] debug: print fatal signals
1923 print-fatal-signals=1: print segfault info to
1924 the kernel console.
1925 default: off.
1927 printk.time= Show timing data prefixed to each printk message line
1928 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
1930 processor.max_cstate= [HW,ACPI]
1931 Limit processor to maximum C-state
1932 max_cstate=9 overrides any DMI blacklist limit.
1934 processor.nocst [HW,ACPI]
1935 Ignore the _CST method to determine C-states,
1936 instead using the legacy FADT method
1938 profile= [KNL] Enable kernel profiling via /proc/profile
1939 Format: [schedule,]<number>
1940 Param: "schedule" - profile schedule points.
1941 Param: <number> - step/bucket size as a power of 2 for
1942 statistical time based profiling.
1943 Param: "sleep" - profile D-state sleeping (millisecs).
1944 Requires CONFIG_SCHEDSTATS
1945 Param: "kvm" - profile VM exits.
1947 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
1948 before loading.
1949 See Documentation/blockdev/ramdisk.txt.
1951 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
1952 probe for; one of (bare|imps|exps|lifebook|any).
1953 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
1954 per second.
1955 psmouse.resetafter= [HW,MOUSE]
1956 Try to reset the device after so many bad packets
1957 (0 = never).
1958 psmouse.resolution=
1959 [HW,MOUSE] Set desired mouse resolution, in dpi.
1960 psmouse.smartscroll=
1961 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1962 0 = disabled, 1 = enabled (default).
1964 pss= [HW,OSS] Personal Sound System (ECHO ESC614)
1965 Format:
1966 <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq>
1968 pt. [PARIDE]
1969 See Documentation/blockdev/paride.txt.
1971 pty.legacy_count=
1972 [KNL] Number of legacy pty's. Overwrites compiled-in
1973 default number.
1975 quiet [KNL] Disable most log messages
1977 r128= [HW,DRM]
1979 raid= [HW,RAID]
1980 See Documentation/md.txt.
1982 ramdisk_blocksize= [RAM]
1983 See Documentation/blockdev/ramdisk.txt.
1985 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
1986 See Documentation/blockdev/ramdisk.txt.
1988 rcupdate.blimit= [KNL,BOOT]
1989 Set maximum number of finished RCU callbacks to process
1990 in one batch.
1992 rcupdate.qhimark= [KNL,BOOT]
1993 Set threshold of queued
1994 RCU callbacks over which batch limiting is disabled.
1996 rcupdate.qlowmark= [KNL,BOOT]
1997 Set threshold of queued RCU callbacks below which
1998 batch limiting is re-enabled.
2000 rdinit= [KNL]
2001 Format: <full_path>
2002 Run specified binary instead of /init from the ramdisk,
2003 used for early userspace startup. See initrd.
2005 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2006 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2007 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2009 relax_domain_level=
2010 [KNL, SMP] Set scheduler's default relax_domain_level.
2011 See Documentation/cgroups/cpusets.txt.
2013 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2015 reservetop= [X86-32]
2016 Format: nn[KMG]
2017 Reserves a hole at the top of the kernel virtual
2018 address space.
2020 reset_devices [KNL] Force drivers to reset the underlying device
2021 during initialization.
2023 resume= [SWSUSP]
2024 Specify the partition device for software suspend
2026 resume_offset= [SWSUSP]
2027 Specify the offset from the beginning of the partition
2028 given by "resume=" at which the swap header is located,
2029 in <PAGE_SIZE> units (needed only for swap files).
2030 See Documentation/power/swsusp-and-swap-files.txt
2032 retain_initrd [RAM] Keep initrd memory after extraction
2034 rhash_entries= [KNL,NET]
2035 Set number of hash buckets for route cache
2037 riscom8= [HW,SERIAL]
2038 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2040 ro [KNL] Mount root device read-only on boot
2042 root= [KNL] Root filesystem
2044 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2045 mount the root filesystem
2047 rootflags= [KNL] Set root filesystem mount option string
2049 rootfstype= [KNL] Set root filesystem type
2051 rootwait [KNL] Wait (indefinitely) for root device to show up.
2052 Useful for devices that are detected asynchronously
2053 (e.g. USB and MMC devices).
2055 root_plug.vendor_id=
2056 [ROOTPLUG] Override the default vendor ID
2058 root_plug.product_id=
2059 [ROOTPLUG] Override the default product ID
2061 root_plug.debug=
2062 [ROOTPLUG] Enable debugging output
2064 rw [KNL] Mount root device read-write on boot
2066 S [KNL] Run init in single mode
2068 sa1100ir [NET]
2069 See drivers/net/irda/sa1100_ir.c.
2071 sbni= [NET] Granch SBNI12 leased line adapter
2073 sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
2074 Format: <io>[,<timeout>[,<isapnp>]]
2076 scsi_debug_*= [SCSI]
2077 See drivers/scsi/scsi_debug.c.
2079 scsi_default_dev_flags=
2080 [SCSI] SCSI default device flags
2081 Format: <integer>
2083 scsi_dev_flags= [SCSI] Black/white list entry for vendor and model
2084 Format: <vendor>:<model>:<flags>
2085 (flags are integer value)
2087 scsi_logging_level= [SCSI] a bit mask of logging levels
2088 See drivers/scsi/scsi_logging.h for bits. Also
2089 settable via sysctl at dev.scsi.logging_level
2090 (/proc/sys/dev/scsi/logging_level).
2091 There is also a nice 'scsi_logging_level' script in the
2092 S390-tools package, available for download at
2093 http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
2095 scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
2096 discovered. async scans them in kernel threads,
2097 allowing boot to proceed. none ignores them, expecting
2098 user space to do the scan.
2100 security= [SECURITY] Choose a security module to enable at boot.
2101 If this boot parameter is not specified, only the first
2102 security module asking for security registration will be
2103 loaded. An invalid security module name will be treated
2104 as if no module has been chosen.
2106 selinux= [SELINUX] Disable or enable SELinux at boot time.
2107 Format: { "0" | "1" }
2108 See security/selinux/Kconfig help text.
2109 0 -- disable.
2110 1 -- enable.
2111 Default value is set via kernel config option.
2112 If enabled at boot time, /selinux/disable can be used
2113 later to disable prior to initial policy load.
2115 serialnumber [BUGS=X86-32]
2117 shapers= [NET]
2118 Maximal number of shapers.
2120 show_msr= [x86] show boot-time MSR settings
2121 Format: { <integer> }
2122 Show boot-time (BIOS-initialized) MSR settings.
2123 The parameter means the number of CPUs to show,
2124 for example 1 means boot CPU only.
2126 sim710= [SCSI,HW]
2127 See header of drivers/scsi/sim710.c.
2129 simeth= [IA-64]
2130 simscsi=
2132 slram= [HW,MTD]
2134 slub_debug[=options[,slabs]] [MM, SLUB]
2135 Enabling slub_debug allows one to determine the
2136 culprit if slab objects become corrupted. Enabling
2137 slub_debug can create guard zones around objects and
2138 may poison objects when not in use. Also tracks the
2139 last alloc / free. For more information see
2140 Documentation/vm/slub.txt.
2142 slub_max_order= [MM, SLUB]
2143 Determines the maximum allowed order for slabs.
2144 A high setting may cause OOMs due to memory
2145 fragmentation. For more information see
2146 Documentation/vm/slub.txt.
2148 slub_min_objects= [MM, SLUB]
2149 The minimum number of objects per slab. SLUB will
2150 increase the slab order up to slub_max_order to
2151 generate a sufficiently large slab able to contain
2152 the number of objects indicated. The higher the number
2153 of objects the smaller the overhead of tracking slabs
2154 and the less frequently locks need to be acquired.
2155 For more information see Documentation/vm/slub.txt.
2157 slub_min_order= [MM, SLUB]
2158 Determines the mininum page order for slabs. Must be
2159 lower than slub_max_order.
2160 For more information see Documentation/vm/slub.txt.
2162 slub_nomerge [MM, SLUB]
2163 Disable merging of slabs with similar size. May be
2164 necessary if there is some reason to distinguish
2165 allocs to different slabs. Debug options disable
2166 merging on their own.
2167 For more information see Documentation/vm/slub.txt.
2169 smart2= [HW]
2170 Format: <io1>[,<io2>[,...,<io8>]]
2172 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2173 attempt to substitute SMP alternatives once at boot.
2175 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2176 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2177 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2178 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2179 smsc-ircc2.ircc_irq= [HW] IRQ line
2180 smsc-ircc2.ircc_dma= [HW] DMA channel
2181 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2182 0: Toshiba Satellite 1800 (GP data pin select)
2183 1: Fast pin select (default)
2184 2: ATC IRMode
2186 snd-ad1816a= [HW,ALSA]
2188 snd-ad1848= [HW,ALSA]
2190 snd-ali5451= [HW,ALSA]
2192 snd-als100= [HW,ALSA]
2194 snd-als4000= [HW,ALSA]
2196 snd-azt2320= [HW,ALSA]
2198 snd-cmi8330= [HW,ALSA]
2200 snd-cmipci= [HW,ALSA]
2202 snd-cs4231= [HW,ALSA]
2204 snd-cs4232= [HW,ALSA]
2206 snd-cs4236= [HW,ALSA]
2208 snd-cs4281= [HW,ALSA]
2210 snd-cs46xx= [HW,ALSA]
2212 snd-dt019x= [HW,ALSA]
2214 snd-dummy= [HW,ALSA]
2216 snd-emu10k1= [HW,ALSA]
2218 snd-ens1370= [HW,ALSA]
2220 snd-ens1371= [HW,ALSA]
2222 snd-es968= [HW,ALSA]
2224 snd-es1688= [HW,ALSA]
2226 snd-es18xx= [HW,ALSA]
2228 snd-es1938= [HW,ALSA]
2230 snd-es1968= [HW,ALSA]
2232 snd-fm801= [HW,ALSA]
2234 snd-gusclassic= [HW,ALSA]
2236 snd-gusextreme= [HW,ALSA]
2238 snd-gusmax= [HW,ALSA]
2240 snd-hdsp= [HW,ALSA]
2242 snd-ice1712= [HW,ALSA]
2244 snd-intel8x0= [HW,ALSA]
2246 snd-interwave= [HW,ALSA]
2248 snd-interwave-stb=
2249 [HW,ALSA]
2251 snd-korg1212= [HW,ALSA]
2253 snd-maestro3= [HW,ALSA]
2255 snd-mpu401= [HW,ALSA]
2257 snd-mtpav= [HW,ALSA]
2259 snd-nm256= [HW,ALSA]
2261 snd-opl3sa2= [HW,ALSA]
2263 snd-opti92x-ad1848=
2264 [HW,ALSA]
2266 snd-opti92x-cs4231=
2267 [HW,ALSA]
2269 snd-opti93x= [HW,ALSA]
2271 snd-pmac= [HW,ALSA]
2273 snd-rme32= [HW,ALSA]
2275 snd-rme96= [HW,ALSA]
2277 snd-rme9652= [HW,ALSA]
2279 snd-sb8= [HW,ALSA]
2281 snd-sb16= [HW,ALSA]
2283 snd-sbawe= [HW,ALSA]
2285 snd-serial= [HW,ALSA]
2287 snd-sgalaxy= [HW,ALSA]
2289 snd-sonicvibes= [HW,ALSA]
2291 snd-sun-amd7930=
2292 [HW,ALSA]
2294 snd-sun-cs4231= [HW,ALSA]
2296 snd-trident= [HW,ALSA]
2298 snd-usb-audio= [HW,ALSA,USB]
2300 snd-via82xx= [HW,ALSA]
2302 snd-virmidi= [HW,ALSA]
2304 snd-wavefront= [HW,ALSA]
2306 snd-ymfpci= [HW,ALSA]
2308 softlockup_panic=
2309 [KNL] Should the soft-lockup detector generate panics.
2311 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2312 See Documentation/sonypi.txt
2314 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2315 See Documentation/serial/specialix.txt.
2317 spia_io_base= [HW,MTD]
2318 spia_fio_base=
2319 spia_pedr=
2320 spia_peddr=
2322 sscape= [HW,OSS]
2323 Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq>
2325 st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
2326 See Documentation/scsi/st.txt.
2328 stacktrace [FTRACE]
2329 Enabled the stack tracer on boot up.
2331 sti= [PARISC,HW]
2332 Format: <num>
2333 Set the STI (builtin display/keyboard on the HP-PARISC
2334 machines) console (graphic card) which should be used
2335 as the initial boot-console.
2336 See also comment in drivers/video/console/sticore.c.
2338 sti_font= [HW]
2339 See comment in drivers/video/console/sticore.c.
2341 stifb= [HW]
2342 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2344 sunrpc.pool_mode=
2345 [NFS]
2346 Control how the NFS server code allocates CPUs to
2347 service thread pools. Depending on how many NICs
2348 you have and where their interrupts are bound, this
2349 option will affect which CPUs will do NFS serving.
2350 Note: this parameter cannot be changed while the
2351 NFS server is running.
2353 auto the server chooses an appropriate mode
2354 automatically using heuristics
2355 global a single global pool contains all CPUs
2356 percpu one pool for each CPU
2357 pernode one pool for each NUMA node (equivalent
2358 to global on non-NUMA machines)
2360 swiotlb= [IA-64] Number of I/O TLB slabs
2362 switches= [HW,M68k]
2364 sym53c416= [HW,SCSI]
2365 See header of drivers/scsi/sym53c416.c.
2367 sysrq_always_enabled
2368 [KNL]
2369 Ignore sysrq setting - this boot parameter will
2370 neutralize any effect of /proc/sys/kernel/sysrq.
2371 Useful for debugging.
2373 t128= [HW,SCSI]
2374 See header of drivers/scsi/t128.c.
2376 tdfx= [HW,DRM]
2378 test_suspend= [SUSPEND]
2379 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2380 standby suspend) as the system sleep state to briefly
2381 enter during system startup. The system is woken from
2382 this state using a wakeup-capable RTC alarm.
2384 thash_entries= [KNL,NET]
2385 Set number of hash buckets for TCP connection
2387 thermal.act= [HW,ACPI]
2388 -1: disable all active trip points in all thermal zones
2389 <degrees C>: override all lowest active trip points
2391 thermal.crt= [HW,ACPI]
2392 -1: disable all critical trip points in all thermal zones
2393 <degrees C>: override all critical trip points
2395 thermal.nocrt= [HW,ACPI]
2396 Set to disable actions on ACPI thermal zone
2397 critical and hot trip points.
2399 thermal.off= [HW,ACPI]
2400 1: disable ACPI thermal control
2402 thermal.psv= [HW,ACPI]
2403 -1: disable all passive trip points
2404 <degrees C>: override all passive trip points to this
2405 value
2407 thermal.tzp= [HW,ACPI]
2408 Specify global default ACPI thermal zone polling rate
2409 <deci-seconds>: poll all this frequency
2410 0: no polling (default)
2412 tmscsim= [HW,SCSI]
2413 See comment before function dc390_setup() in
2414 drivers/scsi/tmscsim.c.
2416 topology= [S390]
2417 Format: {off | on}
2418 Specify if the kernel should make use of the cpu
2419 topology informations if the hardware supports these.
2420 The scheduler will make use of these informations and
2421 e.g. base its process migration decisions on it.
2422 Default is off.
2424 tp720= [HW,PS2]
2426 trace_buf_size=nn[KMG] [ftrace] will set tracing buffer size.
2428 trix= [HW,OSS] MediaTrix AudioTrix Pro
2429 Format:
2430 <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
2432 tsc= Disable clocksource-must-verify flag for TSC.
2433 Format: <string>
2434 [x86] reliable: mark tsc clocksource as reliable, this
2435 disables clocksource verification at runtime.
2436 Used to enable high-resolution timer mode on older
2437 hardware, and in virtualized environment.
2439 turbografx.map[2|3]= [HW,JOY]
2440 TurboGraFX parallel port interface
2441 Format:
2442 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2443 See also Documentation/input/joystick-parport.txt
2445 u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter
2446 See header of drivers/scsi/u14-34f.c.
2448 uart401= [HW,OSS]
2449 Format: <io>,<irq>
2451 uart6850= [HW,OSS]
2452 Format: <io>,<irq>
2454 uhci-hcd.ignore_oc=
2455 [USB] Ignore overcurrent events (default N).
2456 Some badly-designed motherboards generate lots of
2457 bogus events, for ports that aren't wired to
2458 anything. Set this parameter to avoid log spamming.
2459 Note that genuine overcurrent events won't be
2460 reported either.
2462 unknown_nmi_panic
2463 [X86]
2464 Set unknown_nmi_panic=1 early on boot.
2466 usbcore.autosuspend=
2467 [USB] The autosuspend time delay (in seconds) used
2468 for newly-detected USB devices (default 2). This
2469 is the time required before an idle device will be
2470 autosuspended. Devices for which the delay is set
2471 to a negative value won't be autosuspended at all.
2473 usbcore.usbfs_snoop=
2474 [USB] Set to log all usbfs traffic (default 0 = off).
2476 usbcore.blinkenlights=
2477 [USB] Set to cycle leds on hubs (default 0 = off).
2479 usbcore.old_scheme_first=
2480 [USB] Start with the old device initialization
2481 scheme (default 0 = off).
2483 usbcore.use_both_schemes=
2484 [USB] Try the other device initialization scheme
2485 if the first one fails (default 1 = enabled).
2487 usbcore.initial_descriptor_timeout=
2488 [USB] Specifies timeout for the initial 64-byte
2489 USB_REQ_GET_DESCRIPTOR request in milliseconds
2490 (default 5000 = 5.0 seconds).
2492 usbhid.mousepoll=
2493 [USBHID] The interval which mice are to be polled at.
2495 usb-storage.delay_use=
2496 [UMS] The delay in seconds before a new device is
2497 scanned for Logical Units (default 5).
2499 usb-storage.quirks=
2500 [UMS] A list of quirks entries to supplement or
2501 override the built-in unusual_devs list. List
2502 entries are separated by commas. Each entry has
2503 the form VID:PID:Flags where VID and PID are Vendor
2504 and Product ID values (4-digit hex numbers) and
2505 Flags is a set of characters, each corresponding
2506 to a common usb-storage quirk flag as follows:
2507 a = SANE_SENSE (collect more than 18 bytes
2508 of sense data);
2509 c = FIX_CAPACITY (decrease the reported
2510 device capacity by one sector);
2511 h = CAPACITY_HEURISTICS (decrease the
2512 reported device capacity by one
2513 sector if the number is odd);
2514 i = IGNORE_DEVICE (don't bind to this
2515 device);
2516 l = NOT_LOCKABLE (don't try to lock and
2517 unlock ejectable media);
2518 m = MAX_SECTORS_64 (don't transfer more
2519 than 64 sectors = 32 KB at a time);
2520 o = CAPACITY_OK (accept the capacity
2521 reported by the device);
2522 r = IGNORE_RESIDUE (the device reports
2523 bogus residue values);
2524 s = SINGLE_LUN (the device has only one
2525 Logical Unit);
2526 w = NO_WP_DETECT (don't test whether the
2527 medium is write-protected).
2528 Example: quirks=0419:aaf5:rl,0421:0433:rc
2530 vdso= [X86,SH]
2531 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2532 vdso=1: enable VDSO (default)
2533 vdso=0: disable VDSO mapping
2535 vdso32= [X86]
2536 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2537 vdso32=1: enable 32-bit VDSO (default)
2538 vdso32=0: disable 32-bit VDSO mapping
2540 vector= [IA-64,SMP]
2541 vector=percpu: enable percpu vector domain
2543 video= [FB] Frame buffer configuration
2544 See Documentation/fb/modedb.txt.
2546 vga= [BOOT,X86-32] Select a particular video mode
2547 See Documentation/x86/boot.txt and
2548 Documentation/svga.txt.
2549 Use vga=ask for menu.
2550 This is actually a boot loader parameter; the value is
2551 passed to the kernel using a special protocol.
2553 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2554 size of <nn>. This can be used to increase the
2555 minimum size (128MB on x86). It can also be used to
2556 decrease the size and leave more room for directly
2557 mapped kernel RAM.
2559 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2560 Format: <command>
2562 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2563 Format: <command>
2565 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2566 Format: <command>
2568 vt.default_blu= [VT]
2569 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2570 Change the default blue palette of the console.
2571 This is a 16-member array composed of values
2572 ranging from 0-255.
2574 vt.default_grn= [VT]
2575 Format: <green0>,<green1>,<green2>,...,<green15>
2576 Change the default green palette of the console.
2577 This is a 16-member array composed of values
2578 ranging from 0-255.
2580 vt.default_red= [VT]
2581 Format: <red0>,<red1>,<red2>,...,<red15>
2582 Change the default red palette of the console.
2583 This is a 16-member array composed of values
2584 ranging from 0-255.
2586 vt.default_utf8=
2587 [VT]
2588 Format=<0|1>
2589 Set system-wide default UTF-8 mode for all tty's.
2590 Default is 1, i.e. UTF-8 mode is enabled for all
2591 newly opened terminals.
2593 waveartist= [HW,OSS]
2594 Format: <io>,<irq>,<dma>,<dma2>
2596 wd33c93= [HW,SCSI]
2597 See header of drivers/scsi/wd33c93.c.
2599 wd7000= [HW,SCSI]
2600 See header of drivers/scsi/wd7000.c.
2602 wdt= [WDT] Watchdog
2603 See Documentation/watchdog/wdt.txt.
2605 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2606 default x2apic cluster mode on platforms
2607 supporting x2apic.
2609 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2610 xd_geo= See header of drivers/block/xd.c.
2612 xirc2ps_cs= [NET,PCMCIA]
2613 Format:
2614 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2616 ______________________________________________________________________
2618 TODO:
2620 Add documentation for ALSA options.
2621 Add more DRM drivers.