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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_backlight= [HW,ACPI]
157 acpi_backlight=vendor
158 acpi_backlight=video
159 If set to vendor, prefer vendor specific driver
160 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
161 of the ACPI video.ko driver.
163 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
164 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
165 Format: <int>
166 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
167 debug output. Bits in debug_layer correspond to a
168 _COMPONENT in an ACPI source file, e.g.,
169 #define _COMPONENT ACPI_PCI_COMPONENT
170 Bits in debug_level correspond to a level in
171 ACPI_DEBUG_PRINT statements, e.g.,
172 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
173 The debug_level mask defaults to "info". See
174 Documentation/acpi/debug.txt for more information about
175 debug layers and levels.
177 Enable processor driver info messages:
178 acpi.debug_layer=0x20000000
179 Enable PCI/PCI interrupt routing info messages:
180 acpi.debug_layer=0x400000
181 Enable AML "Debug" output, i.e., stores to the Debug
182 object while interpreting AML:
183 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
184 Enable all messages related to ACPI hardware:
185 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
187 Some values produce so much output that the system is
188 unusable. The "log_buf_len" parameter may be useful
189 if you need to capture more output.
191 acpi_display_output= [HW,ACPI]
192 acpi_display_output=vendor
193 acpi_display_output=video
194 See above.
196 acpi_irq_balance [HW,ACPI]
197 ACPI will balance active IRQs
198 default in APIC mode
200 acpi_irq_nobalance [HW,ACPI]
201 ACPI will not move active IRQs (default)
202 default in PIC mode
204 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
205 Format: <irq>,<irq>...
207 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
208 use by PCI
209 Format: <irq>,<irq>...
211 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
213 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
214 Format: To spoof as Windows 98: ="Microsoft Windows"
216 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
217 acpi_osi="string1" # add string1 -- only one string
218 acpi_osi="!string2" # remove built-in string2
219 acpi_osi= # disable all strings
221 acpi_pm_good [X86-32,X86-64]
222 Override the pmtimer bug detection: force the kernel
223 to assume that this machine's pmtimer latches its value
224 and always returns good values.
226 acpi.power_nocheck= [HW,ACPI]
227 Format: 1/0 enable/disable the check of power state.
228 On some bogus BIOS the _PSC object/_STA object of
229 power resource can't return the correct device power
230 state. In such case it is unneccessary to check its
231 power state again in power transition.
232 1 : disable the power state check
234 acpi_enforce_resources= [ACPI]
235 { strict | lax | no }
236 Check for resource conflicts between native drivers
237 and ACPI OperationRegions (SystemIO and SystemMemory
238 only). IO ports and memory declared in ACPI might be
239 used by the ACPI subsystem in arbitrary AML code and
240 can interfere with legacy drivers.
241 strict (default): access to resources claimed by ACPI
242 is denied; legacy drivers trying to access reserved
243 resources will fail to bind to device using them.
244 lax: access to resources claimed by ACPI is allowed;
245 legacy drivers trying to access reserved resources
246 will bind successfully but a warning message is logged.
247 no: ACPI OperationRegions are not marked as reserved,
248 no further checks are performed.
250 ad1848= [HW,OSS]
251 Format: <io>,<irq>,<dma>,<dma2>,<type>
253 advansys= [HW,SCSI]
254 See header of drivers/scsi/advansys.c.
256 advwdt= [HW,WDT] Advantech WDT
257 Format: <iostart>,<iostop>
259 aedsp16= [HW,OSS] Audio Excel DSP 16
260 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>
261 See also header of sound/oss/aedsp16.c.
263 agp= [AGP]
264 { off | try_unsupported }
265 off: disable AGP support
266 try_unsupported: try to drive unsupported chipsets
267 (may crash computer or cause data corruption)
269 aha152x= [HW,SCSI]
270 See Documentation/scsi/aha152x.txt.
272 aha1542= [HW,SCSI]
273 Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]
275 aic7xxx= [HW,SCSI]
276 See Documentation/scsi/aic7xxx.txt.
278 aic79xx= [HW,SCSI]
279 See Documentation/scsi/aic79xx.txt.
281 amd_iommu= [HW,X86-84]
282 Pass parameters to the AMD IOMMU driver in the system.
283 Possible values are:
284 isolate - enable device isolation (each device, as far
285 as possible, will get its own protection
286 domain) [default]
287 share - put every device behind one IOMMU into the
288 same protection domain
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
292 is a lot of faster
294 amd_iommu_size= [HW,X86-64]
295 Define the size of the aperture for the AMD IOMMU
296 driver. Possible values are:
297 '32M', '64M' (default), '128M', '256M', '512M', '1G'
299 amijoy.map= [HW,JOY] Amiga joystick support
300 Map of devices attached to JOY0DAT and JOY1DAT
301 Format: <a>,<b>
302 See also Documentation/kernel/input/joystick.txt
304 analog.map= [HW,JOY] Analog joystick and gamepad support
305 Specifies type or capabilities of an analog joystick
306 connected to one of 16 gameports
307 Format: <type1>,<type2>,..<type16>
309 apc= [HW,SPARC]
310 Power management functions (SPARCstation-4/5 + deriv.)
311 Format: noidle
312 Disable APC CPU standby support. SPARCstation-Fox does
313 not play well with APC CPU idle - disable it if you have
314 APC and your system crashes randomly.
316 apic= [APIC,i386] Advanced Programmable Interrupt Controller
317 Change the output verbosity whilst booting
318 Format: { quiet (default) | verbose | debug }
319 Change the amount of debugging information output
320 when initialising the APIC and IO-APIC components.
322 apm= [APM] Advanced Power Management
323 See header of arch/x86/kernel/apm_32.c.
325 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
326 Format: <io>,<irq>,<nodeID>
328 ataflop= [HW,M68k]
330 atarimouse= [HW,MOUSE] Atari Mouse
332 atascsi= [HW,SCSI] Atari SCSI
334 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
335 EzKey and similar keyboards
337 atkbd.reset= [HW] Reset keyboard during initialization
339 atkbd.set= [HW] Select keyboard code set
340 Format: <int> (2 = AT (default), 3 = PS/2)
342 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
343 keyboards
345 atkbd.softraw= [HW] Choose between synthetic and real raw mode
346 Format: <bool> (0 = real, 1 = synthetic (default))
348 atkbd.softrepeat= [HW]
349 Use software keyboard repeat
351 autotest [IA64]
353 baycom_epp= [HW,AX25]
354 Format: <io>,<mode>
356 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
357 Format: <io>,<mode>
358 See header of drivers/net/hamradio/baycom_par.c.
360 baycom_ser_fdx= [HW,AX25]
361 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
362 Format: <io>,<irq>,<mode>[,<baud>]
363 See header of drivers/net/hamradio/baycom_ser_fdx.c.
365 baycom_ser_hdx= [HW,AX25]
366 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
367 Format: <io>,<irq>,<mode>
368 See header of drivers/net/hamradio/baycom_ser_hdx.c.
370 boot_delay= Milliseconds to delay each printk during boot.
371 Values larger than 10 seconds (10000) are changed to
372 no delay (0).
373 Format: integer
375 bootmem_debug [KNL] Enable bootmem allocator debug messages.
377 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
378 bttv.radio= Most important insmod options are available as
379 kernel args too.
380 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
381 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
383 BusLogic= [HW,SCSI]
384 See drivers/scsi/BusLogic.c, comment before function
385 BusLogic_ParseDriverOptions().
387 c101= [NET] Moxa C101 synchronous serial card
389 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
390 Sometimes CPU hardware bugs make them report the cache
391 size incorrectly. The kernel will attempt work arounds
392 to fix known problems, but for some CPUs it is not
393 possible to determine what the correct size should be.
394 This option provides an override for these situations.
396 capability.disable=
397 [SECURITY] Disable capabilities. This would normally
398 be used only if an alternative security model is to be
399 configured. Potentially dangerous and should only be
400 used if you are entirely sure of the consequences.
402 ccw_timeout_log [S390]
403 See Documentation/s390/CommonIO for details.
405 cgroup_disable= [KNL] Disable a particular controller
406 Format: {name of the controller(s) to disable}
407 {Currently supported controllers - "memory"}
409 checkreqprot [SELINUX] Set initial checkreqprot flag value.
410 Format: { "0" | "1" }
411 See security/selinux/Kconfig help text.
412 0 -- check protection applied by kernel (includes
413 any implied execute protection).
414 1 -- check protection requested by application.
415 Default value is set via a kernel config option.
416 Value can be changed at runtime via
417 /selinux/checkreqprot.
419 cio_ignore= [S390]
420 See Documentation/s390/CommonIO for details.
422 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
423 [Deprecated]
424 Forces specified clocksource (if available) to be used
425 when calculating gettimeofday(). If specified
426 clocksource is not available, it defaults to PIT.
427 Format: { pit | tsc | cyclone | pmtmr }
429 clocksource= [GENERIC_TIME] Override the default clocksource
430 Format: <string>
431 Override the default clocksource and use the clocksource
432 with the name specified.
433 Some clocksource names to choose from, depending on
434 the platform:
435 [all] jiffies (this is the base, fallback clocksource)
436 [ACPI] acpi_pm
437 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
438 pxa_timer,timer3,32k_counter,timer0_1
439 [AVR32] avr32
440 [X86-32] pit,hpet,tsc,vmi-timer;
441 scx200_hrt on Geode; cyclone on IBM x440
442 [MIPS] MIPS
443 [PARISC] cr16
444 [S390] tod
445 [SH] SuperH
446 [SPARC64] tick
447 [X86-64] hpet,tsc
449 clearcpuid=BITNUM [X86]
450 Disable CPUID feature X for the kernel. See
451 arch/x86/include/asm/cpufeature.h for the valid bit
452 numbers. Note the Linux specific bits are not necessarily
453 stable over kernel options, but the vendor specific
454 ones should be.
455 Also note that user programs calling CPUID directly
456 or using the feature without checking anything
457 will still see it. This just prevents it from
458 being used by the kernel or shown in /proc/cpuinfo.
459 Also note the kernel might malfunction if you disable
460 some critical bits.
462 code_bytes [IA32/X86_64] How many bytes of object code to print
463 in an oops report.
464 Range: 0 - 8192
465 Default: 64
467 com20020= [HW,NET] ARCnet - COM20020 chipset
468 Format:
469 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
471 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
472 Format: <io>[,<irq>]
474 com90xx= [HW,NET]
475 ARCnet - COM90xx chipset (memory-mapped buffers)
476 Format: <io>[,<irq>[,<memstart>]]
478 condev= [HW,S390] console device
479 conmode=
481 console= [KNL] Output console device and options.
483 tty<n> Use the virtual console device <n>.
485 ttyS<n>[,options]
486 ttyUSB0[,options]
487 Use the specified serial port. The options are of
488 the form "bbbbpnf", where "bbbb" is the baud rate,
489 "p" is parity ("n", "o", or "e"), "n" is number of
490 bits, and "f" is flow control ("r" for RTS or
491 omit it). Default is "9600n8".
493 See Documentation/serial-console.txt for more
494 information. See
495 Documentation/networking/netconsole.txt for an
496 alternative.
498 uart[8250],io,<addr>[,options]
499 uart[8250],mmio,<addr>[,options]
500 Start an early, polled-mode console on the 8250/16550
501 UART at the specified I/O port or MMIO address,
502 switching to the matching ttyS device later. The
503 options are the same as for ttyS, above.
505 If the device connected to the port is not a TTY but a braille
506 device, prepend "brl," before the device type, for instance
507 console=brl,ttyS0
508 For now, only VisioBraille is supported.
510 coredump_filter=
511 [KNL] Change the default value for
512 /proc/<pid>/coredump_filter.
513 See also Documentation/filesystems/proc.txt.
515 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
516 Format:
517 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
519 crashkernel=nn[KMG]@ss[KMG]
520 [KNL] Reserve a chunk of physical memory to
521 hold a kernel to switch to with kexec on panic.
523 crashkernel=range1:size1[,range2:size2,...][@offset]
524 [KNL] Same as above, but depends on the memory
525 in the running system. The syntax of range is
526 start-[end] where start and end are both
527 a memory unit (amount[KMG]). See also
528 Documentation/kdump/kdump.txt for a example.
530 cs89x0_dma= [HW,NET]
531 Format: <dma>
533 cs89x0_media= [HW,NET]
534 Format: { rj45 | aui | bnc }
536 dasd= [HW,NET]
537 See header of drivers/s390/block/dasd_devmap.c.
539 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
540 (one device per port)
541 Format: <port#>,<type>
542 See also Documentation/input/joystick-parport.txt
544 debug [KNL] Enable kernel debugging (events log level).
546 debug_locks_verbose=
547 [KNL] verbose self-tests
548 Format=<0|1>
549 Print debugging info while doing the locking API
550 self-tests.
551 We default to 0 (no extra messages), setting it to
552 1 will print _a lot_ more information - normally
553 only useful to kernel developers.
555 debug_objects [KNL] Enable object debugging
557 no_debug_objects
558 [KNL] Disable object debugging
560 debugpat [X86] Enable PAT debugging
562 decnet.addr= [HW,NET]
563 Format: <area>[,<node>]
564 See also Documentation/networking/decnet.txt.
566 default_hugepagesz=
567 [same as hugepagesz=] The size of the default
568 HugeTLB page size. This is the size represented by
569 the legacy /proc/ hugepages APIs, used for SHM, and
570 default size when mounting hugetlbfs filesystems.
571 Defaults to the default architecture's huge page size
572 if not specified.
574 dhash_entries= [KNL]
575 Set number of hash buckets for dentry cache.
577 digi= [HW,SERIAL]
578 IO parameters + enable/disable command.
580 digiepca= [HW,SERIAL]
581 See drivers/char/README.epca and
582 Documentation/serial/digiepca.txt.
584 disable_mtrr_cleanup [X86]
585 The kernel tries to adjust MTRR layout from continuous
586 to discrete, to make X server driver able to add WB
587 entry later. This parameter disables that.
589 disable_mtrr_trim [X86, Intel and AMD only]
590 By default the kernel will trim any uncacheable
591 memory out of your available memory pool based on
592 MTRR settings. This parameter disables that behavior,
593 possibly causing your machine to run very slowly.
595 disable_timer_pin_1 [i386,x86-64]
596 Disable PIN 1 of APIC timer
597 Can be useful to work around chipset bugs.
599 dmasound= [HW,OSS] Sound subsystem buffers
601 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
602 this option disables the debugging code at boot.
604 dma_debug_entries=<number>
605 This option allows to tune the number of preallocated
606 entries for DMA-API debugging code. One entry is
607 required per DMA-API allocation. Use this if the
608 DMA-API debugging code disables itself because the
609 architectural default is too low.
611 dscc4.setup= [NET]
613 dtc3181e= [HW,SCSI]
615 dynamic_printk Enables pr_debug()/dev_dbg() calls if
616 CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled.
617 These can also be switched on/off via
618 <debugfs>/dynamic_printk/modules
620 earlycon= [KNL] Output early console device and options.
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 Start an early, polled-mode console on the 8250/16550
624 UART at the specified I/O port or MMIO address.
625 The options are the same as for ttyS, above.
627 earlyprintk= [X86-32,X86-64,SH,BLACKFIN]
628 earlyprintk=vga
629 earlyprintk=serial[,ttySn[,baudrate]]
630 earlyprintk=dbgp
632 Append ",keep" to not disable it when the real console
633 takes over.
635 Only vga or serial or usb debug port at a time.
637 Currently only ttyS0 and ttyS1 are supported.
639 Interaction with the standard serial driver is not
640 very good.
642 The VGA output is eventually overwritten by the real
643 console.
645 eata= [HW,SCSI]
647 edd= [EDD]
648 Format: {"off" | "on" | "skip[mbr]"}
650 eisa_irq_edge= [PARISC,HW]
651 See header of drivers/parisc/eisa.c.
653 elanfreq= [X86-32]
654 See comment before function elanfreq_setup() in
655 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
657 elevator= [IOSCHED]
658 Format: {"anticipatory" | "cfq" | "deadline" | "noop"}
659 See Documentation/block/as-iosched.txt and
660 Documentation/block/deadline-iosched.txt for details.
662 elfcorehdr= [IA64,PPC,SH,X86-32,X86_64]
663 Specifies physical address of start of kernel core
664 image elf header. Generally kexec loader will
665 pass this option to capture kernel.
666 See Documentation/kdump/kdump.txt for details.
668 enable_mtrr_cleanup [X86]
669 The kernel tries to adjust MTRR layout from continuous
670 to discrete, to make X server driver able to add WB
671 entry later. This parameter enables that.
673 enable_timer_pin_1 [i386,x86-64]
674 Enable PIN 1 of APIC timer
675 Can be useful to work around chipset bugs
676 (in particular on some ATI chipsets).
677 The kernel tries to set a reasonable default.
679 enforcing [SELINUX] Set initial enforcing status.
680 Format: {"0" | "1"}
681 See security/selinux/Kconfig help text.
682 0 -- permissive (log only, no denials).
683 1 -- enforcing (deny and log).
684 Default value is 0.
685 Value can be changed at runtime via /selinux/enforce.
687 ether= [HW,NET] Ethernet cards parameters
688 This option is obsoleted by the "netdev=" option, which
689 has equivalent usage. See its documentation for details.
691 eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
692 Format: <io>[,<irq>]
694 failslab=
695 fail_page_alloc=
696 fail_make_request=[KNL]
697 General fault injection mechanism.
698 Format: <interval>,<probability>,<space>,<times>
699 See also /Documentation/fault-injection/.
701 fd_mcs= [HW,SCSI]
702 See header of drivers/scsi/fd_mcs.c.
704 fdomain= [HW,SCSI]
705 See header of drivers/scsi/fdomain.c.
707 floppy= [HW]
708 See Documentation/blockdev/floppy.txt.
710 force_pal_cache_flush
711 [IA-64] Avoid check_sal_cache_flush which may hang on
712 buggy SAL_CACHE_FLUSH implementations. Using this
713 parameter will force ia64_sal_cache_flush to call
714 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
716 ftrace=[tracer]
717 [ftrace] will set and start the specified tracer
718 as early as possible in order to facilitate early
719 boot debugging.
721 ftrace_dump_on_oops
722 [ftrace] will dump the trace buffers on oops.
724 gamecon.map[2|3]=
725 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
726 support via parallel port (up to 5 devices per port)
727 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
728 See also Documentation/input/joystick-parport.txt
730 gamma= [HW,DRM]
732 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
733 Format: off | on
734 default: on
736 gdth= [HW,SCSI]
737 See header of drivers/scsi/gdth.c.
739 gpt [EFI] Forces disk with valid GPT signature but
740 invalid Protective MBR to be treated as GPT.
742 gvp11= [HW,SCSI]
744 hashdist= [KNL,NUMA] Large hashes allocated during boot
745 are distributed across NUMA nodes. Defaults on
746 for IA-64, off otherwise.
747 Format: 0 | 1 (for off | on)
749 hcl= [IA-64] SGI's Hardware Graph compatibility layer
751 hd= [EIDE] (E)IDE hard drive subsystem geometry
752 Format: <cyl>,<head>,<sect>
754 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
755 size of <nn>. This works even on boxes that have no
756 highmem otherwise. This also works to reduce highmem
757 size on bigger boxes.
759 highres= [KNL] Enable/disable high resolution timer mode.
760 Valid parameters: "on", "off"
761 Default: "on"
763 hisax= [HW,ISDN]
764 See Documentation/isdn/README.HiSax.
766 hlt [BUGS=ARM,SH]
768 hpet= [X86-32,HPET] option to control HPET usage
769 Format: { enable (default) | disable | force |
770 verbose }
771 disable: disable HPET and use PIT instead
772 force: allow force enabled of undocumented chips (ICH4,
773 VIA, nVidia)
774 verbose: show contents of HPET registers during setup
776 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
777 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
778 On x86-64 and powerpc, this option can be specified
779 multiple times interleaved with hugepages= to reserve
780 huge pages of different sizes. Valid pages sizes on
781 x86-64 are 2M (when the CPU supports "pse") and 1G
782 (when the CPU supports the "pdpe1gb" cpuinfo flag)
783 Note that 1GB pages can only be allocated at boot time
784 using hugepages= and not freed afterwards.
786 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
787 terminal devices. Valid values: 0..8
788 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
789 If specified, z/VM IUCV HVC accepts connections
790 from listed z/VM user IDs only.
792 i2c_bus= [HW] Override the default board specific I2C bus speed
793 or register an additional I2C bus that is not
794 registered from board initialization code.
795 Format:
796 <bus_id>,<clkrate>
798 i8042.debug [HW] Toggle i8042 debug mode
799 i8042.direct [HW] Put keyboard port into non-translated mode
800 i8042.dumbkbd [HW] Pretend that controller can only read data from
801 keyboard and cannot control its state
802 (Don't attempt to blink the leds)
803 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
804 i8042.nokbd [HW] Don't check/create keyboard port
805 i8042.noloop [HW] Disable the AUX Loopback command while probing
806 for the AUX port
807 i8042.nomux [HW] Don't check presence of an active multiplexing
808 controller
809 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
810 controllers
811 i8042.panicblink=
812 [HW] Frequency with which keyboard LEDs should blink
813 when kernel panics (default is 0.5 sec)
814 i8042.reset [HW] Reset the controller during init and cleanup
815 i8042.unlock [HW] Unlock (ignore) the keylock
817 i810= [HW,DRM]
819 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
820 indicates that the driver is running on unsupported
821 hardware.
822 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
823 does not match list of supported models.
824 i8k.power_status
825 [HW] Report power status in /proc/i8k
826 (disabled by default)
827 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
828 capability is set.
830 ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
831 See Documentation/mca.txt.
833 icn= [HW,ISDN]
834 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
836 ide-core.nodma= [HW] (E)IDE subsystem
837 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
838 .vlb_clock .pci_clock .noflush .noprobe .nowerr .cdrom
839 .chs .ignore_cable are additional options
840 See Documentation/ide/ide.txt.
842 idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
843 See Documentation/ide/ide.txt.
845 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
846 Claim all unknown PCI IDE storage controllers.
848 idle= [X86]
849 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
850 Poll forces a polling idle loop that can slightly
851 improve the performance of waking up a idle CPU, but
852 will use a lot of power and make the system run hot.
853 Not recommended.
854 idle=mwait: On systems which support MONITOR/MWAIT but
855 the kernel chose to not use it because it doesn't save
856 as much power as a normal idle loop, use the
857 MONITOR/MWAIT idle loop anyways. Performance should be
858 the same as idle=poll.
859 idle=halt: Halt is forced to be used for CPU idle.
860 In such case C2/C3 won't be used again.
861 idle=nomwait: Disable mwait for CPU C-states
863 ignore_loglevel [KNL]
864 Ignore loglevel setting - this will print /all/
865 kernel messages to the console. Useful for debugging.
867 ihash_entries= [KNL]
868 Set number of hash buckets for inode cache.
870 ima_audit= [IMA]
871 Format: { "0" | "1" }
872 0 -- integrity auditing messages. (Default)
873 1 -- enable informational integrity auditing messages.
875 ima_hash= [IMA]
876 Formt: { "sha1" | "md5" }
877 default: "sha1"
879 in2000= [HW,SCSI]
880 See header of drivers/scsi/in2000.c.
882 init= [KNL]
883 Format: <full_path>
884 Run specified binary instead of /sbin/init as init
885 process.
887 initcall_debug [KNL] Trace initcalls as they are executed. Useful
888 for working out where the kernel is dying during
889 startup.
891 initrd= [BOOT] Specify the location of the initial ramdisk
893 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
894 Format: <irq>
896 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
897 on
898 Enable intel iommu driver.
899 off
900 Disable intel iommu driver.
901 igfx_off [Default Off]
902 By default, gfx is mapped as normal device. If a gfx
903 device has a dedicated DMAR unit, the DMAR unit is
904 bypassed by not enabling DMAR with this option. In
905 this case, gfx device will use physical address for
906 DMA.
907 forcedac [x86_64]
908 With this option iommu will not optimize to look
909 for io virtual address below 32 bit forcing dual
910 address cycle on pci bus for cards supporting greater
911 than 32 bit addressing. The default is to look
912 for translation below 32 bit and if not available
913 then look in the higher range.
914 strict [Default Off]
915 With this option on every unmap_single operation will
916 result in a hardware IOTLB flush operation as opposed
917 to batching them for performance.
919 inttest= [IA64]
921 iomem= Disable strict checking of access to MMIO memory
922 strict regions from userspace.
923 relaxed
925 iommu= [x86]
926 off
927 force
928 noforce
929 biomerge
930 panic
931 nopanic
932 merge
933 nomerge
934 forcesac
935 soft
937 io7= [HW] IO7 for Marvel based alpha systems
938 See comment before marvel_specify_io7 in
939 arch/alpha/kernel/core_marvel.c.
941 io_delay= [X86-32,X86-64] I/O delay method
942 0x80
943 Standard port 0x80 based delay
944 0xed
945 Alternate port 0xed based delay (needed on some systems)
946 udelay
947 Simple two microseconds delay
948 none
949 No delay
951 ip= [IP_PNP]
952 See Documentation/filesystems/nfsroot.txt.
954 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
955 See comment before ip2_setup() in
956 drivers/char/ip2/ip2base.c.
958 ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
959 See header of drivers/scsi/ips.c.
961 irqfixup [HW]
962 When an interrupt is not handled search all handlers
963 for it. Intended to get systems with badly broken
964 firmware running.
966 irqpoll [HW]
967 When an interrupt is not handled search all handlers
968 for it. Also check all handlers each timer
969 interrupt. Intended to get systems with badly broken
970 firmware running.
972 isapnp= [ISAPNP]
973 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
975 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
976 Format:
977 <cpu number>,...,<cpu number>
978 or
979 <cpu number>-<cpu number>
980 (must be a positive range in ascending order)
981 or a mixture
982 <cpu number>,...,<cpu number>-<cpu number>
984 This option can be used to specify one or more CPUs
985 to isolate from the general SMP balancing and scheduling
986 algorithms. You can move a process onto or off an
987 "isolated" CPU via the CPU affinity syscalls or cpuset.
988 <cpu number> begins at 0 and the maximum value is
989 "number of CPUs in system - 1".
991 This option is the preferred way to isolate CPUs. The
992 alternative -- manually setting the CPU mask of all
993 tasks in the system -- can cause problems and
994 suboptimal load balancer performance.
996 iucv= [HW,NET]
998 js= [HW,JOY] Analog joystick
999 See Documentation/input/joystick.txt.
1001 keepinitrd [HW,ARM]
1003 kernelcore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1004 specifies the amount of memory usable by the kernel
1005 for non-movable allocations. The requested amount is
1006 spread evenly throughout all nodes in the system. The
1007 remaining memory in each node is used for Movable
1008 pages. In the event, a node is too small to have both
1009 kernelcore and Movable pages, kernelcore pages will
1010 take priority and other nodes will have a larger number
1011 of kernelcore pages. The Movable zone is used for the
1012 allocation of pages that may be reclaimed or moved
1013 by the page migration subsystem. This means that
1014 HugeTLB pages may not be allocated from this zone.
1015 Note that allocations like PTEs-from-HighMem still
1016 use the HighMem zone if it exists, and the Normal
1017 zone if it does not.
1019 kmemtrace.enable= [KNL,KMEMTRACE] Format: { yes | no }
1020 Controls whether kmemtrace is enabled
1021 at boot-time.
1023 kmemtrace.subbufs=n [KNL,KMEMTRACE] Overrides the number of
1024 subbufs kmemtrace's relay channel has. Set this
1025 higher than default (KMEMTRACE_N_SUBBUFS in code) if
1026 you experience buffer overruns.
1028 kgdboc= [HW] kgdb over consoles.
1029 Requires a tty driver that supports console polling.
1030 (only serial suported for now)
1031 Format: <serial_device>[,baud]
1033 kmac= [MIPS] korina ethernet MAC address.
1034 Configure the RouterBoard 532 series on-chip
1035 Ethernet adapter MAC address.
1037 kstack=N [X86-32,X86-64] Print N words from the kernel stack
1038 in oops dumps.
1040 l2cr= [PPC]
1042 l3cr= [PPC]
1044 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1045 disabled it.
1047 lapic_timer_c2_ok [X86-32,x86-64,APIC] trust the local apic timer
1048 in C2 power state.
1050 libata.dma= [LIBATA] DMA control
1051 libata.dma=0 Disable all PATA and SATA DMA
1052 libata.dma=1 PATA and SATA Disk DMA only
1053 libata.dma=2 ATAPI (CDROM) DMA only
1054 libata.dma=4 Compact Flash DMA only
1055 Combinations also work, so libata.dma=3 enables DMA
1056 for disks and CDROMs, but not CFs.
1058 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1059 when set.
1060 Format: <int>
1062 libata.force= [LIBATA] Force configurations. The format is comma
1063 separated list of "[ID:]VAL" where ID is
1064 PORT[:DEVICE]. PORT and DEVICE are decimal numbers
1065 matching port, link or device. Basically, it matches
1066 the ATA ID string printed on console by libata. If
1067 the whole ID part is omitted, the last PORT and DEVICE
1068 values are used. If ID hasn't been specified yet, the
1069 configuration applies to all ports, links and devices.
1071 If only DEVICE is omitted, the parameter applies to
1072 the port and all links and devices behind it. DEVICE
1073 number of 0 either selects the first device or the
1074 first fan-out link behind PMP device. It does not
1075 select the host link. DEVICE number of 15 selects the
1076 host link and device attached to it.
1078 The VAL specifies the configuration to force. As long
1079 as there's no ambiguity shortcut notation is allowed.
1080 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1081 The following configurations can be forced.
1083 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1084 Any ID with matching PORT is used.
1086 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1088 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1089 udma[/][16,25,33,44,66,100,133] notation is also
1090 allowed.
1092 * [no]ncq: Turn on or off NCQ.
1094 * nohrst, nosrst, norst: suppress hard, soft
1095 and both resets.
1097 If there are multiple matching configurations changing
1098 the same attribute, the last one is used.
1100 lmb=debug [KNL] Enable lmb debug messages.
1102 load_ramdisk= [RAM] List of ramdisks to load from floppy
1103 See Documentation/blockdev/ramdisk.txt.
1105 lockd.nlm_grace_period=P [NFS] Assign grace period.
1106 Format: <integer>
1108 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1109 Format: <integer>
1111 lockd.nlm_timeout=T [NFS] Assign timeout value.
1112 Format: <integer>
1114 lockd.nlm_udpport=M [NFS] Assign UDP port.
1115 Format: <integer>
1117 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1118 Format: <irq>
1120 loglevel= All Kernel Messages with a loglevel smaller than the
1121 console loglevel will be printed to the console. It can
1122 also be changed with klogd or other programs. The
1123 loglevels are defined as follows:
1125 0 (KERN_EMERG) system is unusable
1126 1 (KERN_ALERT) action must be taken immediately
1127 2 (KERN_CRIT) critical conditions
1128 3 (KERN_ERR) error conditions
1129 4 (KERN_WARNING) warning conditions
1130 5 (KERN_NOTICE) normal but significant condition
1131 6 (KERN_INFO) informational
1132 7 (KERN_DEBUG) debug-level messages
1134 log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1135 Format: { n | nk | nM }
1136 n must be a power of two. The default size
1137 is set in the kernel config file.
1139 logo.nologo [FB] Disables display of the built-in Linux logo.
1140 This may be used to provide more screen space for
1141 kernel log messages and is useful when debugging
1142 kernel boot problems.
1144 lp=0 [LP] Specify parallel ports to use, e.g,
1145 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1146 lp=reset first parallel port). 'lp=0' disables the
1147 lp=auto printer driver. 'lp=reset' (which can be
1148 specified in addition to the ports) causes
1149 attached printers to be reset. Using
1150 lp=port1,port2,... specifies the parallel ports
1151 to associate lp devices with, starting with
1152 lp0. A port specification may be 'none' to skip
1153 that lp device, or a parport name such as
1154 'parport0'. Specifying 'lp=auto' instead of a
1155 port specification list means that device IDs
1156 from each port should be examined, to see if
1157 an IEEE 1284-compliant printer is attached; if
1158 so, the driver will manage that printer.
1159 See also header of drivers/char/lp.c.
1161 lpj=n [KNL]
1162 Sets loops_per_jiffy to given constant, thus avoiding
1163 time-consuming boot-time autodetection (up to 250 ms per
1164 CPU). 0 enables autodetection (default). To determine
1165 the correct value for your kernel, boot with normal
1166 autodetection and see what value is printed. Note that
1167 on SMP systems the preset will be applied to all CPUs,
1168 which is likely to cause problems if your CPUs need
1169 significantly divergent settings. An incorrect value
1170 will cause delays in the kernel to be wrong, leading to
1171 unpredictable I/O errors and other breakage. Although
1172 unlikely, in the extreme case this might damage your
1173 hardware.
1175 ltpc= [NET]
1176 Format: <io>,<irq>,<dma>
1178 mac5380= [HW,SCSI] Format:
1179 <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags>
1181 machvec= [IA64] Force the use of a particular machine-vector
1182 (machvec) in a generic kernel.
1183 Example: machvec=hpzx1_swiotlb
1185 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1186 than or equal to this physical address is ignored.
1188 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1189 should make use of. maxcpus=n : n >= 0 limits the
1190 kernel to using 'n' processors. n=0 is a special case,
1191 it is equivalent to "nosmp", which also disables
1192 the IO APIC.
1194 max_loop= [LOOP] Maximum number of loopback devices that can
1195 be mounted
1196 Format: <1-256>
1198 max_luns= [SCSI] Maximum number of LUNs to probe.
1199 Should be between 1 and 2^32-1.
1201 max_report_luns=
1202 [SCSI] Maximum number of LUNs received.
1203 Should be between 1 and 16384.
1205 mcatest= [IA-64]
1207 mce [X86-32] Machine Check Exception
1209 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1211 md= [HW] RAID subsystems devices and level
1212 See Documentation/md.txt.
1214 mdacon= [MDA]
1215 Format: <first>,<last>
1216 Specifies range of consoles to be captured by the MDA.
1218 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1219 Amount of memory to be used when the kernel is not able
1220 to see the whole system memory or for test.
1221 [X86-32] Use together with memmap= to avoid physical
1222 address space collisions. Without memmap= PCI devices
1223 could be placed at addresses belonging to unused RAM.
1225 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1226 memory.
1228 memchunk=nn[KMG]
1229 [KNL,SH] Allow user to override the default size for
1230 per-device physically contiguous DMA buffers.
1232 memmap=exactmap [KNL,X86-32,X86_64] Enable setting of an exact
1233 E820 memory map, as specified by the user.
1234 Such memmap=exactmap lines can be constructed based on
1235 BIOS output or other requirements. See the memmap=nn@ss
1236 option description.
1238 memmap=nn[KMG]@ss[KMG]
1239 [KNL] Force usage of a specific region of memory
1240 Region of memory to be used, from ss to ss+nn.
1242 memmap=nn[KMG]#ss[KMG]
1243 [KNL,ACPI] Mark specific memory as ACPI data.
1244 Region of memory to be used, from ss to ss+nn.
1246 memmap=nn[KMG]$ss[KMG]
1247 [KNL,ACPI] Mark specific memory as reserved.
1248 Region of memory to be used, from ss to ss+nn.
1249 Example: Exclude memory from 0x18690000-0x1869ffff
1250 memmap=64K$0x18690000
1251 or
1252 memmap=0x10000$0x18690000
1254 memory_corruption_check=0/1 [X86]
1255 Some BIOSes seem to corrupt the first 64k of
1256 memory when doing things like suspend/resume.
1257 Setting this option will scan the memory
1258 looking for corruption. Enabling this will
1259 both detect corruption and prevent the kernel
1260 from using the memory being corrupted.
1261 However, its intended as a diagnostic tool; if
1262 repeatable BIOS-originated corruption always
1263 affects the same memory, you can use memmap=
1264 to prevent the kernel from using that memory.
1266 memory_corruption_check_size=size [X86]
1267 By default it checks for corruption in the low
1268 64k, making this memory unavailable for normal
1269 use. Use this parameter to scan for
1270 corruption in more or less memory.
1272 memory_corruption_check_period=seconds [X86]
1273 By default it checks for corruption every 60
1274 seconds. Use this parameter to check at some
1275 other rate. 0 disables periodic checking.
1277 memtest= [KNL,X86] Enable memtest
1278 Format: <integer>
1279 default : 0 <disable>
1280 Specifies the number of memtest passes to be
1281 performed. Each pass selects another test
1282 pattern from a given set of patterns. Memtest
1283 fills the memory with this pattern, validates
1284 memory contents and reserves bad memory
1285 regions that are detected.
1287 meye.*= [HW] Set MotionEye Camera parameters
1288 See Documentation/video4linux/meye.txt.
1290 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1291 Multi-Function General Purpose Timers on AMD Geode
1292 platforms.
1294 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1295 the BIOS has incorrectly applied a workaround. TinyBIOS
1296 version 0.98 is known to be affected, 0.99 fixes the
1297 problem by letting the user disable the workaround.
1299 mga= [HW,DRM]
1301 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1302 physical address is ignored.
1304 mminit_loglevel=
1305 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1306 parameter allows control of the logging verbosity for
1307 the additional memory initialisation checks. A value
1308 of 0 disables mminit logging and a level of 4 will
1309 log everything. Information is printed at KERN_DEBUG
1310 so loglevel=8 may also need to be specified.
1312 mousedev.tap_time=
1313 [MOUSE] Maximum time between finger touching and
1314 leaving touchpad surface for touch to be considered
1315 a tap and be reported as a left button click (for
1316 touchpads working in absolute mode only).
1317 Format: <msecs>
1318 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1319 reporting absolute coordinates, such as tablets
1320 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1321 reporting absolute coordinates, such as tablets
1323 movablecore=nn[KMG] [KNL,X86-32,IA-64,PPC,X86-64] This parameter
1324 is similar to kernelcore except it specifies the
1325 amount of memory used for migratable allocations.
1326 If both kernelcore and movablecore is specified,
1327 then kernelcore will be at *least* the specified
1328 value but may be more. If movablecore on its own
1329 is specified, the administrator must be careful
1330 that the amount of memory usable for all allocations
1331 is not too small.
1333 mpu401= [HW,OSS]
1334 Format: <io>,<irq>
1336 MTD_Partition= [MTD]
1337 Format: <name>,<region-number>,<size>,<offset>
1339 MTD_Region= [MTD] Format:
1340 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1342 mtdparts= [MTD]
1343 See drivers/mtd/cmdlinepart.c.
1345 mtdset= [ARM]
1346 ARM/S3C2412 JIVE boot control
1348 See arch/arm/mach-s3c2412/mach-jive.c
1350 mtouchusb.raw_coordinates=
1351 [HW] Make the MicroTouch USB driver use raw coordinates
1352 ('y', default) or cooked coordinates ('n')
1354 mtrr_chunk_size=nn[KMG] [X86]
1355 used for mtrr cleanup. It is largest continous chunk
1356 that could hold holes aka. UC entries.
1358 mtrr_gran_size=nn[KMG] [X86]
1359 Used for mtrr cleanup. It is granularity of mtrr block.
1360 Default is 1.
1361 Large value could prevent small alignment from
1362 using up MTRRs.
1364 mtrr_spare_reg_nr=n [X86]
1365 Format: <integer>
1366 Range: 0,7 : spare reg number
1367 Default : 1
1368 Used for mtrr cleanup. It is spare mtrr entries number.
1369 Set to 2 or more if your graphical card needs more.
1371 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1373 NCR_D700= [HW,SCSI]
1374 See header of drivers/scsi/NCR_D700.c.
1376 ncr5380= [HW,SCSI]
1378 ncr53c400= [HW,SCSI]
1380 ncr53c400a= [HW,SCSI]
1382 ncr53c406a= [HW,SCSI]
1384 ncr53c8xx= [HW,SCSI]
1386 netdev= [NET] Network devices parameters
1387 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1388 Note that mem_start is often overloaded to mean
1389 something different and driver-specific.
1390 This usage is only documented in each driver source
1391 file if at all.
1393 nf_conntrack.acct=
1394 [NETFILTER] Enable connection tracking flow accounting
1395 0 to disable accounting
1396 1 to enable accounting
1397 Default value depends on CONFIG_NF_CT_ACCT that is
1398 going to be removed in 2.6.29.
1400 nfsaddrs= [NFS]
1401 See Documentation/filesystems/nfsroot.txt.
1403 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1404 See Documentation/filesystems/nfsroot.txt.
1406 nfs.callback_tcpport=
1407 [NFS] set the TCP port on which the NFSv4 callback
1408 channel should listen.
1410 nfs.idmap_cache_timeout=
1411 [NFS] set the maximum lifetime for idmapper cache
1412 entries.
1414 nfs.enable_ino64=
1415 [NFS] enable 64-bit inode numbers.
1416 If zero, the NFS client will fake up a 32-bit inode
1417 number for the readdir() and stat() syscalls instead
1418 of returning the full 64-bit number.
1419 The default is to return 64-bit inode numbers.
1421 nmi_debug= [KNL,AVR32] Specify one or more actions to take
1422 when a NMI is triggered.
1423 Format: [state][,regs][,debounce][,die]
1425 nmi_watchdog= [KNL,BUGS=X86-32,X86-64] Debugging features for SMP kernels
1426 Format: [panic,][num]
1427 Valid num: 0,1,2
1428 0 - turn nmi_watchdog off
1429 1 - use the IO-APIC timer for the NMI watchdog
1430 2 - use the local APIC for the NMI watchdog using
1431 a performance counter. Note: This will use one
1432 performance counter and the local APIC's performance
1433 vector.
1434 When panic is specified, panic when an NMI watchdog
1435 timeout occurs.
1436 This is useful when you use a panic=... timeout and
1437 need the box quickly up again.
1438 Instead of 1 and 2 it is possible to use the following
1439 symbolic names: lapic and ioapic
1440 Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1442 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1443 emulation library even if a 387 maths coprocessor
1444 is present.
1446 no_console_suspend
1447 [HW] Never suspend the console
1448 Disable suspending of consoles during suspend and
1449 hibernate operations. Once disabled, debugging
1450 messages can reach various consoles while the rest
1451 of the system is being put to sleep (ie, while
1452 debugging driver suspend/resume hooks). This may
1453 not work reliably with all consoles, but is known
1454 to work with serial and VGA consoles.
1456 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1457 caches in the slab allocator. Saves per-node memory,
1458 but will impact performance.
1460 noalign [KNL,ARM]
1462 noapic [SMP,APIC] Tells the kernel to not make use of any
1463 IOAPICs that may be present in the system.
1465 nobats [PPC] Do not use BATs for mapping kernel lowmem
1466 on "Classic" PPC cores.
1468 nocache [ARM]
1470 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1472 nodelayacct [KNL] Disable per-task delay accounting
1474 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1476 nodsp [SH] Disable hardware DSP at boot time.
1478 noefi [X86-32,X86-64] Disable EFI runtime services support.
1480 noexec [IA-64]
1482 noexec [X86-32,X86-64]
1483 On X86-32 available only on PAE configured kernels.
1484 noexec=on: enable non-executable mappings (default)
1485 noexec=off: disable non-executable mappings
1487 noexec32 [X86-64]
1488 This affects only 32-bit executables.
1489 noexec32=on: enable non-executable mappings (default)
1490 read doesn't imply executable mappings
1491 noexec32=off: disable non-executable mappings
1492 read implies executable mappings
1494 nofpu [SH] Disable hardware FPU at boot time.
1496 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1497 register save and restore. The kernel will only save
1498 legacy floating-point registers on task switch.
1500 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1501 wfi(ARM) instruction doesn't work correctly and not to
1502 use it. This is also useful when using JTAG debugger.
1504 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1505 instruction doesn't work correctly and not to
1506 use it.
1508 no_file_caps Tells the kernel not to honor file capabilities. The
1509 only way then for a file to be executed with privilege
1510 is to be setuid root or executed by root.
1512 nohalt [IA-64] Tells the kernel not to use the power saving
1513 function PAL_HALT_LIGHT when idle. This increases
1514 power-consumption. On the positive side, it reduces
1515 interrupt wake-up latency, which may improve performance
1516 in certain environments such as networked servers or
1517 real-time systems.
1519 nohz= [KNL] Boottime enable/disable dynamic ticks
1520 Valid arguments: on, off
1521 Default: on
1523 noiotrap [SH] Disables trapped I/O port accesses.
1525 noirqdebug [X86-32] Disables the code which attempts to detect and
1526 disable unhandled interrupt sources.
1528 no_timer_check [X86-32,X86_64,APIC] Disables the code which tests for
1529 broken timer IRQ sources.
1531 noisapnp [ISAPNP] Disables ISA PnP code.
1533 noinitrd [RAM] Tells the kernel not to load any configured
1534 initial RAM disk.
1536 nointroute [IA-64]
1538 nojitter [IA64] Disables jitter checking for ITC timers.
1540 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1542 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1544 noltlbs [PPC] Do not use large page/tlb entries for kernel
1545 lowmem mapping on PPC40x.
1547 nomca [IA-64] Disable machine check abort handling
1549 nomce [X86-32] Machine Check Exception
1551 nomfgpt [X86-32] Disable Multi-Function General Purpose
1552 Timer usage (for AMD Geode machines).
1554 norandmaps Don't use address space randomization. Equivalent to
1555 echo 0 > /proc/sys/kernel/randomize_va_space
1557 noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops
1559 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1560 with UP alternatives
1562 noresidual [PPC] Don't use residual data on PReP machines.
1564 noresume [SWSUSP] Disables resume and restores original swap
1565 space.
1567 no-scroll [VGA] Disables scrollback.
1568 This is required for the Braillex ib80-piezo Braille
1569 reader made by F.H. Papenmeier (Germany).
1571 nosbagart [IA-64]
1573 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1575 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1576 and disable the IO APIC. legacy for "maxcpus=0".
1578 nosoftlockup [KNL] Disable the soft-lockup detector.
1580 noswapaccount [KNL] Disable accounting of swap in memory resource
1581 controller. (See Documentation/cgroups/memory.txt)
1583 nosync [HW,M68K] Disables sync negotiation for all devices.
1585 notsc [BUGS=X86-32] Disable Time Stamp Counter
1587 nousb [USB] Disable the USB subsystem
1589 nowb [ARM]
1591 nptcg= [IA64] Override max number of concurrent global TLB
1592 purges which is reported from either PAL_VM_SUMMARY or
1593 SAL PALO.
1595 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1597 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1598 one of ['zone', 'node', 'default'] can be specified
1599 This can be set from sysctl after boot.
1600 See Documentation/sysctl/vm.txt for details.
1602 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1603 See Documentation/debugging-via-ohci1394.txt for more
1604 info.
1606 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1607 Rather than timing out after 20 ms if an EC
1608 command is not properly ACKed, override the length
1609 of the timeout. We have interrupts disabled while
1610 waiting for the ACK, so if this is set too high
1611 interrupts *may* be lost!
1613 opl3= [HW,OSS]
1614 Format: <io>
1616 oprofile.timer= [HW]
1617 Use timer interrupt instead of performance counters
1619 osst= [HW,SCSI] SCSI Tape Driver
1620 Format: <buffer_size>,<write_threshold>
1621 See also Documentation/scsi/st.txt.
1623 panic= [KNL] Kernel behaviour on panic
1624 Format: <timeout>
1626 parkbd.port= [HW] Parallel port number the keyboard adapter is
1627 connected to, default is 0.
1628 Format: <parport#>
1629 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1630 0 for XT, 1 for AT (default is AT).
1631 Format: <mode>
1633 parport= [HW,PPT] Specify parallel ports. 0 disables.
1634 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1635 Use 'auto' to force the driver to use any
1636 IRQ/DMA settings detected (the default is to
1637 ignore detected IRQ/DMA settings because of
1638 possible conflicts). You can specify the base
1639 address, IRQ, and DMA settings; IRQ and DMA
1640 should be numbers, or 'auto' (for using detected
1641 settings on that particular port), or 'nofifo'
1642 (to avoid using a FIFO even if it is detected).
1643 Parallel ports are assigned in the order they
1644 are specified on the command line, starting
1645 with parport0.
1647 parport_init_mode= [HW,PPT]
1648 Configure VIA parallel port to operate in
1649 a specific mode. This is necessary on Pegasos
1650 computer where firmware has no options for setting
1651 up parallel port mode and sets it to spp.
1652 Currently this function knows 686a and 8231 chips.
1653 Format: [spp|ps2|epp|ecp|ecpepp]
1655 pas2= [HW,OSS] Format:
1656 <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16>
1658 pas16= [HW,SCSI]
1659 See header of drivers/scsi/pas16.c.
1661 pause_on_oops=
1662 Halt all CPUs after the first oops has been printed for
1663 the specified number of seconds. This is to be used if
1664 your oopses keep scrolling off the screen.
1666 pcbit= [HW,ISDN]
1668 pcd. [PARIDE]
1669 See header of drivers/block/paride/pcd.c.
1670 See also Documentation/blockdev/paride.txt.
1672 pci=option[,option...] [PCI] various PCI subsystem options:
1673 earlydump [X86] dump PCI config space before the kernel
1674 changes anything
1675 off [X86] don't probe for the PCI bus
1676 bios [X86-32] force use of PCI BIOS, don't access
1677 the hardware directly. Use this if your machine
1678 has a non-standard PCI host bridge.
1679 nobios [X86-32] disallow use of PCI BIOS, only direct
1680 hardware access methods are allowed. Use this
1681 if you experience crashes upon bootup and you
1682 suspect they are caused by the BIOS.
1683 conf1 [X86] Force use of PCI Configuration
1684 Mechanism 1.
1685 conf2 [X86] Force use of PCI Configuration
1686 Mechanism 2.
1687 noaer [PCIE] If the PCIEAER kernel config parameter is
1688 enabled, this kernel boot option can be used to
1689 disable the use of PCIE advanced error reporting.
1690 nodomains [PCI] Disable support for multiple PCI
1691 root domains (aka PCI segments, in ACPI-speak).
1692 nommconf [X86-32,X86_64] Disable use of MMCONFIG for PCI
1693 Configuration
1694 nomsi [MSI] If the PCI_MSI kernel config parameter is
1695 enabled, this kernel boot option can be used to
1696 disable the use of MSI interrupts system-wide.
1697 noioapicquirk [APIC] Disable all boot interrupt quirks.
1698 Safety option to keep boot IRQs enabled. This
1699 should never be necessary.
1700 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1701 primary IO-APIC for bridges that cannot disable
1702 boot IRQs. This fixes a source of spurious IRQs
1703 when the system masks IRQs.
1704 noioapicreroute [APIC] Disable workaround that uses the
1705 boot IRQ equivalent of an IRQ that connects to
1706 a chipset where boot IRQs cannot be disabled.
1707 The opposite of ioapicreroute.
1708 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1709 routing table. These calls are known to be buggy
1710 on several machines and they hang the machine
1711 when used, but on other computers it's the only
1712 way to get the interrupt routing table. Try
1713 this option if the kernel is unable to allocate
1714 IRQs or discover secondary PCI buses on your
1715 motherboard.
1716 rom [X86] Assign address space to expansion ROMs.
1717 Use with caution as certain devices share
1718 address decoders between ROMs and other
1719 resources.
1720 norom [X86] Do not assign address space to
1721 expansion ROMs that do not already have
1722 BIOS assigned address ranges.
1723 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1724 assigned automatically to PCI devices. You can
1725 make the kernel exclude IRQs of your ISA cards
1726 this way.
1727 pirqaddr=0xAAAAA [X86] Specify the physical address
1728 of the PIRQ table (normally generated
1729 by the BIOS) if it is outside the
1730 F0000h-100000h range.
1731 lastbus=N [X86] Scan all buses thru bus #N. Can be
1732 useful if the kernel is unable to find your
1733 secondary buses and you want to tell it
1734 explicitly which ones they are.
1735 assign-busses [X86] Always assign all PCI bus
1736 numbers ourselves, overriding
1737 whatever the firmware may have done.
1738 usepirqmask [X86] Honor the possible IRQ mask stored
1739 in the BIOS $PIR table. This is needed on
1740 some systems with broken BIOSes, notably
1741 some HP Pavilion N5400 and Omnibook XE3
1742 notebooks. This will have no effect if ACPI
1743 IRQ routing is enabled.
1744 noacpi [X86] Do not use ACPI for IRQ routing
1745 or for PCI scanning.
1746 use_crs [X86] Use _CRS for PCI resource
1747 allocation.
1748 routeirq Do IRQ routing for all PCI devices.
1749 This is normally done in pci_enable_device(),
1750 so this option is a temporary workaround
1751 for broken drivers that don't call it.
1752 skip_isa_align [X86] do not align io start addr, so can
1753 handle more pci cards
1754 firmware [ARM] Do not re-enumerate the bus but instead
1755 just use the configuration from the
1756 bootloader. This is currently used on
1757 IXP2000 systems where the bus has to be
1758 configured a certain way for adjunct CPUs.
1759 noearly [X86] Don't do any early type 1 scanning.
1760 This might help on some broken boards which
1761 machine check when some devices' config space
1762 is read. But various workarounds are disabled
1763 and some IOMMU drivers will not work.
1764 bfsort Sort PCI devices into breadth-first order.
1765 This sorting is done to get a device
1766 order compatible with older (<= 2.4) kernels.
1767 nobfsort Don't sort PCI devices into breadth-first order.
1768 cbiosize=nn[KMG] The fixed amount of bus space which is
1769 reserved for the CardBus bridge's IO window.
1770 The default value is 256 bytes.
1771 cbmemsize=nn[KMG] The fixed amount of bus space which is
1772 reserved for the CardBus bridge's memory
1773 window. The default value is 64 megabytes.
1774 resource_alignment=
1775 Format:
1776 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
1777 Specifies alignment and device to reassign
1778 aligned memory resources.
1779 If <order of align> is not specified,
1780 PAGE_SIZE is used as alignment.
1781 PCI-PCI bridge can be specified, if resource
1782 windows need to be expanded.
1784 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1785 Management.
1786 off Disable ASPM.
1787 force Enable ASPM even on devices that claim not to support it.
1788 WARNING: Forcing ASPM on may cause system lockups.
1790 pcmv= [HW,PCMCIA] BadgePAD 4
1792 pd. [PARIDE]
1793 See Documentation/blockdev/paride.txt.
1795 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
1796 boot time.
1797 Format: { 0 | 1 }
1798 See arch/parisc/kernel/pdc_chassis.c
1800 pf. [PARIDE]
1801 See Documentation/blockdev/paride.txt.
1803 pg. [PARIDE]
1804 See Documentation/blockdev/paride.txt.
1806 pirq= [SMP,APIC] Manual mp-table setup
1807 See Documentation/x86/i386/IO-APIC.txt.
1809 plip= [PPT,NET] Parallel port network link
1810 Format: { parport<nr> | timid | 0 }
1811 See also Documentation/parport.txt.
1813 pmtmr= [X86] Manual setup of pmtmr I/O Port.
1814 Override pmtimer IOPort with a hex value.
1815 e.g. pmtmr=0x508
1817 pnp.debug [PNP]
1818 Enable PNP debug messages. This depends on the
1819 CONFIG_PNP_DEBUG_MESSAGES option.
1821 pnpacpi= [ACPI]
1822 { off }
1824 pnpbios= [ISAPNP]
1825 { on | off | curr | res | no-curr | no-res }
1827 pnp_reserve_irq=
1828 [ISAPNP] Exclude IRQs for the autoconfiguration
1830 pnp_reserve_dma=
1831 [ISAPNP] Exclude DMAs for the autoconfiguration
1833 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
1834 Ranges are in pairs (I/O port base and size).
1836 pnp_reserve_mem=
1837 [ISAPNP] Exclude memory regions for the
1838 autoconfiguration.
1839 Ranges are in pairs (memory base and size).
1841 print-fatal-signals=
1842 [KNL] debug: print fatal signals
1843 print-fatal-signals=1: print segfault info to
1844 the kernel console.
1845 default: off.
1847 printk.time= Show timing data prefixed to each printk message line
1848 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
1850 processor.max_cstate= [HW,ACPI]
1851 Limit processor to maximum C-state
1852 max_cstate=9 overrides any DMI blacklist limit.
1854 processor.nocst [HW,ACPI]
1855 Ignore the _CST method to determine C-states,
1856 instead using the legacy FADT method
1858 profile= [KNL] Enable kernel profiling via /proc/profile
1859 Format: [schedule,]<number>
1860 Param: "schedule" - profile schedule points.
1861 Param: <number> - step/bucket size as a power of 2 for
1862 statistical time based profiling.
1863 Param: "sleep" - profile D-state sleeping (millisecs).
1864 Requires CONFIG_SCHEDSTATS
1865 Param: "kvm" - profile VM exits.
1867 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
1868 before loading.
1869 See Documentation/blockdev/ramdisk.txt.
1871 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
1872 probe for; one of (bare|imps|exps|lifebook|any).
1873 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
1874 per second.
1875 psmouse.resetafter= [HW,MOUSE]
1876 Try to reset the device after so many bad packets
1877 (0 = never).
1878 psmouse.resolution=
1879 [HW,MOUSE] Set desired mouse resolution, in dpi.
1880 psmouse.smartscroll=
1881 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1882 0 = disabled, 1 = enabled (default).
1884 pss= [HW,OSS] Personal Sound System (ECHO ESC614)
1885 Format:
1886 <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq>
1888 pt. [PARIDE]
1889 See Documentation/blockdev/paride.txt.
1891 pty.legacy_count=
1892 [KNL] Number of legacy pty's. Overwrites compiled-in
1893 default number.
1895 quiet [KNL] Disable most log messages
1897 r128= [HW,DRM]
1899 raid= [HW,RAID]
1900 See Documentation/md.txt.
1902 ramdisk_blocksize= [RAM]
1903 See Documentation/blockdev/ramdisk.txt.
1905 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
1906 See Documentation/blockdev/ramdisk.txt.
1908 rcupdate.blimit= [KNL,BOOT]
1909 Set maximum number of finished RCU callbacks to process
1910 in one batch.
1912 rcupdate.qhimark= [KNL,BOOT]
1913 Set threshold of queued
1914 RCU callbacks over which batch limiting is disabled.
1916 rcupdate.qlowmark= [KNL,BOOT]
1917 Set threshold of queued RCU callbacks below which
1918 batch limiting is re-enabled.
1920 rdinit= [KNL]
1921 Format: <full_path>
1922 Run specified binary instead of /init from the ramdisk,
1923 used for early userspace startup. See initrd.
1925 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
1926 Format: <reboot_mode>[,<reboot_mode2>[,...]]
1927 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
1929 relax_domain_level=
1930 [KNL, SMP] Set scheduler's default relax_domain_level.
1931 See Documentation/cgroups/cpusets.txt.
1933 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
1935 reservetop= [X86-32]
1936 Format: nn[KMG]
1937 Reserves a hole at the top of the kernel virtual
1938 address space.
1940 reset_devices [KNL] Force drivers to reset the underlying device
1941 during initialization.
1943 resume= [SWSUSP]
1944 Specify the partition device for software suspend
1946 resume_offset= [SWSUSP]
1947 Specify the offset from the beginning of the partition
1948 given by "resume=" at which the swap header is located,
1949 in <PAGE_SIZE> units (needed only for swap files).
1950 See Documentation/power/swsusp-and-swap-files.txt
1952 retain_initrd [RAM] Keep initrd memory after extraction
1954 rhash_entries= [KNL,NET]
1955 Set number of hash buckets for route cache
1957 riscom8= [HW,SERIAL]
1958 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
1960 ro [KNL] Mount root device read-only on boot
1962 root= [KNL] Root filesystem
1964 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
1965 mount the root filesystem
1967 rootflags= [KNL] Set root filesystem mount option string
1969 rootfstype= [KNL] Set root filesystem type
1971 rootwait [KNL] Wait (indefinitely) for root device to show up.
1972 Useful for devices that are detected asynchronously
1973 (e.g. USB and MMC devices).
1975 root_plug.vendor_id=
1976 [ROOTPLUG] Override the default vendor ID
1978 root_plug.product_id=
1979 [ROOTPLUG] Override the default product ID
1981 root_plug.debug=
1982 [ROOTPLUG] Enable debugging output
1984 rw [KNL] Mount root device read-write on boot
1986 S [KNL] Run init in single mode
1988 sa1100ir [NET]
1989 See drivers/net/irda/sa1100_ir.c.
1991 sbni= [NET] Granch SBNI12 leased line adapter
1993 sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
1994 Format: <io>[,<timeout>[,<isapnp>]]
1996 scsi_debug_*= [SCSI]
1997 See drivers/scsi/scsi_debug.c.
1999 scsi_default_dev_flags=
2000 [SCSI] SCSI default device flags
2001 Format: <integer>
2003 scsi_dev_flags= [SCSI] Black/white list entry for vendor and model
2004 Format: <vendor>:<model>:<flags>
2005 (flags are integer value)
2007 scsi_logging_level= [SCSI] a bit mask of logging levels
2008 See drivers/scsi/scsi_logging.h for bits. Also
2009 settable via sysctl at dev.scsi.logging_level
2010 (/proc/sys/dev/scsi/logging_level).
2011 There is also a nice 'scsi_logging_level' script in the
2012 S390-tools package, available for download at
2013 http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html
2015 scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
2016 discovered. async scans them in kernel threads,
2017 allowing boot to proceed. none ignores them, expecting
2018 user space to do the scan.
2020 security= [SECURITY] Choose a security module to enable at boot.
2021 If this boot parameter is not specified, only the first
2022 security module asking for security registration will be
2023 loaded. An invalid security module name will be treated
2024 as if no module has been chosen.
2026 selinux= [SELINUX] Disable or enable SELinux at boot time.
2027 Format: { "0" | "1" }
2028 See security/selinux/Kconfig help text.
2029 0 -- disable.
2030 1 -- enable.
2031 Default value is set via kernel config option.
2032 If enabled at boot time, /selinux/disable can be used
2033 later to disable prior to initial policy load.
2035 serialnumber [BUGS=X86-32]
2037 shapers= [NET]
2038 Maximal number of shapers.
2040 show_msr= [x86] show boot-time MSR settings
2041 Format: { <integer> }
2042 Show boot-time (BIOS-initialized) MSR settings.
2043 The parameter means the number of CPUs to show,
2044 for example 1 means boot CPU only.
2046 sim710= [SCSI,HW]
2047 See header of drivers/scsi/sim710.c.
2049 simeth= [IA-64]
2050 simscsi=
2052 slram= [HW,MTD]
2054 slub_debug[=options[,slabs]] [MM, SLUB]
2055 Enabling slub_debug allows one to determine the
2056 culprit if slab objects become corrupted. Enabling
2057 slub_debug can create guard zones around objects and
2058 may poison objects when not in use. Also tracks the
2059 last alloc / free. For more information see
2060 Documentation/vm/slub.txt.
2062 slub_max_order= [MM, SLUB]
2063 Determines the maximum allowed order for slabs.
2064 A high setting may cause OOMs due to memory
2065 fragmentation. For more information see
2066 Documentation/vm/slub.txt.
2068 slub_min_objects= [MM, SLUB]
2069 The minimum number of objects per slab. SLUB will
2070 increase the slab order up to slub_max_order to
2071 generate a sufficiently large slab able to contain
2072 the number of objects indicated. The higher the number
2073 of objects the smaller the overhead of tracking slabs
2074 and the less frequently locks need to be acquired.
2075 For more information see Documentation/vm/slub.txt.
2077 slub_min_order= [MM, SLUB]
2078 Determines the mininum page order for slabs. Must be
2079 lower than slub_max_order.
2080 For more information see Documentation/vm/slub.txt.
2082 slub_nomerge [MM, SLUB]
2083 Disable merging of slabs with similar size. May be
2084 necessary if there is some reason to distinguish
2085 allocs to different slabs. Debug options disable
2086 merging on their own.
2087 For more information see Documentation/vm/slub.txt.
2089 smart2= [HW]
2090 Format: <io1>[,<io2>[,...,<io8>]]
2092 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2093 attempt to substitute SMP alternatives once at boot.
2095 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2096 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2097 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2098 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2099 smsc-ircc2.ircc_irq= [HW] IRQ line
2100 smsc-ircc2.ircc_dma= [HW] DMA channel
2101 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2102 0: Toshiba Satellite 1800 (GP data pin select)
2103 1: Fast pin select (default)
2104 2: ATC IRMode
2106 snd-ad1816a= [HW,ALSA]
2108 snd-ad1848= [HW,ALSA]
2110 snd-ali5451= [HW,ALSA]
2112 snd-als100= [HW,ALSA]
2114 snd-als4000= [HW,ALSA]
2116 snd-azt2320= [HW,ALSA]
2118 snd-cmi8330= [HW,ALSA]
2120 snd-cmipci= [HW,ALSA]
2122 snd-cs4231= [HW,ALSA]
2124 snd-cs4232= [HW,ALSA]
2126 snd-cs4236= [HW,ALSA]
2128 snd-cs4281= [HW,ALSA]
2130 snd-cs46xx= [HW,ALSA]
2132 snd-dt019x= [HW,ALSA]
2134 snd-dummy= [HW,ALSA]
2136 snd-emu10k1= [HW,ALSA]
2138 snd-ens1370= [HW,ALSA]
2140 snd-ens1371= [HW,ALSA]
2142 snd-es968= [HW,ALSA]
2144 snd-es1688= [HW,ALSA]
2146 snd-es18xx= [HW,ALSA]
2148 snd-es1938= [HW,ALSA]
2150 snd-es1968= [HW,ALSA]
2152 snd-fm801= [HW,ALSA]
2154 snd-gusclassic= [HW,ALSA]
2156 snd-gusextreme= [HW,ALSA]
2158 snd-gusmax= [HW,ALSA]
2160 snd-hdsp= [HW,ALSA]
2162 snd-ice1712= [HW,ALSA]
2164 snd-intel8x0= [HW,ALSA]
2166 snd-interwave= [HW,ALSA]
2168 snd-interwave-stb=
2169 [HW,ALSA]
2171 snd-korg1212= [HW,ALSA]
2173 snd-maestro3= [HW,ALSA]
2175 snd-mpu401= [HW,ALSA]
2177 snd-mtpav= [HW,ALSA]
2179 snd-nm256= [HW,ALSA]
2181 snd-opl3sa2= [HW,ALSA]
2183 snd-opti92x-ad1848=
2184 [HW,ALSA]
2186 snd-opti92x-cs4231=
2187 [HW,ALSA]
2189 snd-opti93x= [HW,ALSA]
2191 snd-pmac= [HW,ALSA]
2193 snd-rme32= [HW,ALSA]
2195 snd-rme96= [HW,ALSA]
2197 snd-rme9652= [HW,ALSA]
2199 snd-sb8= [HW,ALSA]
2201 snd-sb16= [HW,ALSA]
2203 snd-sbawe= [HW,ALSA]
2205 snd-serial= [HW,ALSA]
2207 snd-sgalaxy= [HW,ALSA]
2209 snd-sonicvibes= [HW,ALSA]
2211 snd-sun-amd7930=
2212 [HW,ALSA]
2214 snd-sun-cs4231= [HW,ALSA]
2216 snd-trident= [HW,ALSA]
2218 snd-usb-audio= [HW,ALSA,USB]
2220 snd-via82xx= [HW,ALSA]
2222 snd-virmidi= [HW,ALSA]
2224 snd-wavefront= [HW,ALSA]
2226 snd-ymfpci= [HW,ALSA]
2228 softlockup_panic=
2229 [KNL] Should the soft-lockup detector generate panics.
2231 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2232 See Documentation/sonypi.txt
2234 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2235 See Documentation/serial/specialix.txt.
2237 spia_io_base= [HW,MTD]
2238 spia_fio_base=
2239 spia_pedr=
2240 spia_peddr=
2242 sscape= [HW,OSS]
2243 Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq>
2245 st= [HW,SCSI] SCSI tape parameters (buffers, etc.)
2246 See Documentation/scsi/st.txt.
2248 stacktrace [FTRACE]
2249 Enabled the stack tracer on boot up.
2251 sti= [PARISC,HW]
2252 Format: <num>
2253 Set the STI (builtin display/keyboard on the HP-PARISC
2254 machines) console (graphic card) which should be used
2255 as the initial boot-console.
2256 See also comment in drivers/video/console/sticore.c.
2258 sti_font= [HW]
2259 See comment in drivers/video/console/sticore.c.
2261 stifb= [HW]
2262 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2264 sunrpc.pool_mode=
2265 [NFS]
2266 Control how the NFS server code allocates CPUs to
2267 service thread pools. Depending on how many NICs
2268 you have and where their interrupts are bound, this
2269 option will affect which CPUs will do NFS serving.
2270 Note: this parameter cannot be changed while the
2271 NFS server is running.
2273 auto the server chooses an appropriate mode
2274 automatically using heuristics
2275 global a single global pool contains all CPUs
2276 percpu one pool for each CPU
2277 pernode one pool for each NUMA node (equivalent
2278 to global on non-NUMA machines)
2280 swiotlb= [IA-64] Number of I/O TLB slabs
2282 switches= [HW,M68k]
2284 sym53c416= [HW,SCSI]
2285 See header of drivers/scsi/sym53c416.c.
2287 sysrq_always_enabled
2288 [KNL]
2289 Ignore sysrq setting - this boot parameter will
2290 neutralize any effect of /proc/sys/kernel/sysrq.
2291 Useful for debugging.
2293 t128= [HW,SCSI]
2294 See header of drivers/scsi/t128.c.
2296 tdfx= [HW,DRM]
2298 test_suspend= [SUSPEND]
2299 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2300 standby suspend) as the system sleep state to briefly
2301 enter during system startup. The system is woken from
2302 this state using a wakeup-capable RTC alarm.
2304 thash_entries= [KNL,NET]
2305 Set number of hash buckets for TCP connection
2307 thermal.act= [HW,ACPI]
2308 -1: disable all active trip points in all thermal zones
2309 <degrees C>: override all lowest active trip points
2311 thermal.crt= [HW,ACPI]
2312 -1: disable all critical trip points in all thermal zones
2313 <degrees C>: override all critical trip points
2315 thermal.nocrt= [HW,ACPI]
2316 Set to disable actions on ACPI thermal zone
2317 critical and hot trip points.
2319 thermal.off= [HW,ACPI]
2320 1: disable ACPI thermal control
2322 thermal.psv= [HW,ACPI]
2323 -1: disable all passive trip points
2324 <degrees C>: override all passive trip points to this
2325 value
2327 thermal.tzp= [HW,ACPI]
2328 Specify global default ACPI thermal zone polling rate
2329 <deci-seconds>: poll all this frequency
2330 0: no polling (default)
2332 tmscsim= [HW,SCSI]
2333 See comment before function dc390_setup() in
2334 drivers/scsi/tmscsim.c.
2336 topology= [S390]
2337 Format: {off | on}
2338 Specify if the kernel should make use of the cpu
2339 topology informations if the hardware supports these.
2340 The scheduler will make use of these informations and
2341 e.g. base its process migration decisions on it.
2342 Default is off.
2344 tp720= [HW,PS2]
2346 trace_buf_size=nn[KMG] [ftrace] will set tracing buffer size.
2348 trix= [HW,OSS] MediaTrix AudioTrix Pro
2349 Format:
2350 <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
2352 tsc= Disable clocksource-must-verify flag for TSC.
2353 Format: <string>
2354 [x86] reliable: mark tsc clocksource as reliable, this
2355 disables clocksource verification at runtime.
2356 Used to enable high-resolution timer mode on older
2357 hardware, and in virtualized environment.
2359 turbografx.map[2|3]= [HW,JOY]
2360 TurboGraFX parallel port interface
2361 Format:
2362 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2363 See also Documentation/input/joystick-parport.txt
2365 u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter
2366 See header of drivers/scsi/u14-34f.c.
2368 uart401= [HW,OSS]
2369 Format: <io>,<irq>
2371 uart6850= [HW,OSS]
2372 Format: <io>,<irq>
2374 uhci-hcd.ignore_oc=
2375 [USB] Ignore overcurrent events (default N).
2376 Some badly-designed motherboards generate lots of
2377 bogus events, for ports that aren't wired to
2378 anything. Set this parameter to avoid log spamming.
2379 Note that genuine overcurrent events won't be
2380 reported either.
2382 unknown_nmi_panic
2383 [X86-32,X86-64]
2384 Set unknown_nmi_panic=1 early on boot.
2386 usbcore.autosuspend=
2387 [USB] The autosuspend time delay (in seconds) used
2388 for newly-detected USB devices (default 2). This
2389 is the time required before an idle device will be
2390 autosuspended. Devices for which the delay is set
2391 to a negative value won't be autosuspended at all.
2393 usbcore.usbfs_snoop=
2394 [USB] Set to log all usbfs traffic (default 0 = off).
2396 usbcore.blinkenlights=
2397 [USB] Set to cycle leds on hubs (default 0 = off).
2399 usbcore.old_scheme_first=
2400 [USB] Start with the old device initialization
2401 scheme (default 0 = off).
2403 usbcore.use_both_schemes=
2404 [USB] Try the other device initialization scheme
2405 if the first one fails (default 1 = enabled).
2407 usbcore.initial_descriptor_timeout=
2408 [USB] Specifies timeout for the initial 64-byte
2409 USB_REQ_GET_DESCRIPTOR request in milliseconds
2410 (default 5000 = 5.0 seconds).
2412 usbhid.mousepoll=
2413 [USBHID] The interval which mice are to be polled at.
2415 usb-storage.delay_use=
2416 [UMS] The delay in seconds before a new device is
2417 scanned for Logical Units (default 5).
2419 usb-storage.quirks=
2420 [UMS] A list of quirks entries to supplement or
2421 override the built-in unusual_devs list. List
2422 entries are separated by commas. Each entry has
2423 the form VID:PID:Flags where VID and PID are Vendor
2424 and Product ID values (4-digit hex numbers) and
2425 Flags is a set of characters, each corresponding
2426 to a common usb-storage quirk flag as follows:
2427 a = SANE_SENSE (collect more than 18 bytes
2428 of sense data);
2429 c = FIX_CAPACITY (decrease the reported
2430 device capacity by one sector);
2431 h = CAPACITY_HEURISTICS (decrease the
2432 reported device capacity by one
2433 sector if the number is odd);
2434 i = IGNORE_DEVICE (don't bind to this
2435 device);
2436 l = NOT_LOCKABLE (don't try to lock and
2437 unlock ejectable media);
2438 m = MAX_SECTORS_64 (don't transfer more
2439 than 64 sectors = 32 KB at a time);
2440 o = CAPACITY_OK (accept the capacity
2441 reported by the device);
2442 r = IGNORE_RESIDUE (the device reports
2443 bogus residue values);
2444 s = SINGLE_LUN (the device has only one
2445 Logical Unit);
2446 w = NO_WP_DETECT (don't test whether the
2447 medium is write-protected).
2448 Example: quirks=0419:aaf5:rl,0421:0433:rc
2450 vdso= [X86-32,SH,x86-64]
2451 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2452 vdso=1: enable VDSO (default)
2453 vdso=0: disable VDSO mapping
2455 vdso32= [X86-32,X86-64]
2456 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2457 vdso32=1: enable 32-bit VDSO (default)
2458 vdso32=0: disable 32-bit VDSO mapping
2460 vector= [IA-64,SMP]
2461 vector=percpu: enable percpu vector domain
2463 video= [FB] Frame buffer configuration
2464 See Documentation/fb/modedb.txt.
2466 vga= [BOOT,X86-32] Select a particular video mode
2467 See Documentation/x86/boot.txt and
2468 Documentation/svga.txt.
2469 Use vga=ask for menu.
2470 This is actually a boot loader parameter; the value is
2471 passed to the kernel using a special protocol.
2473 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2474 size of <nn>. This can be used to increase the
2475 minimum size (128MB on x86). It can also be used to
2476 decrease the size and leave more room for directly
2477 mapped kernel RAM.
2479 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2480 Format: <command>
2482 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2483 Format: <command>
2485 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2486 Format: <command>
2488 vt.default_blu= [VT]
2489 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2490 Change the default blue palette of the console.
2491 This is a 16-member array composed of values
2492 ranging from 0-255.
2494 vt.default_grn= [VT]
2495 Format: <green0>,<green1>,<green2>,...,<green15>
2496 Change the default green palette of the console.
2497 This is a 16-member array composed of values
2498 ranging from 0-255.
2500 vt.default_red= [VT]
2501 Format: <red0>,<red1>,<red2>,...,<red15>
2502 Change the default red palette of the console.
2503 This is a 16-member array composed of values
2504 ranging from 0-255.
2506 vt.default_utf8=
2507 [VT]
2508 Format=<0|1>
2509 Set system-wide default UTF-8 mode for all tty's.
2510 Default is 1, i.e. UTF-8 mode is enabled for all
2511 newly opened terminals.
2513 waveartist= [HW,OSS]
2514 Format: <io>,<irq>,<dma>,<dma2>
2516 wd33c93= [HW,SCSI]
2517 See header of drivers/scsi/wd33c93.c.
2519 wd7000= [HW,SCSI]
2520 See header of drivers/scsi/wd7000.c.
2522 wdt= [WDT] Watchdog
2523 See Documentation/watchdog/wdt.txt.
2525 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2526 default x2apic cluster mode on platforms
2527 supporting x2apic.
2529 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2530 xd_geo= See header of drivers/block/xd.c.
2532 xirc2ps_cs= [NET,PCMCIA]
2533 Format:
2534 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2536 ______________________________________________________________________
2538 TODO:
2540 Add documentation for ALSA options.
2541 Add more DRM drivers.