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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 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 FB The frame buffer device is enabled.
53 FTRACE Function tracing enabled.
54 GCOV GCOV profiling is enabled.
55 HW Appropriate hardware is enabled.
56 IA-64 IA-64 architecture is enabled.
57 IMA Integrity measurement architecture is enabled.
58 IOSCHED More than one I/O scheduler is enabled.
59 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
60 IPV6 IPv6 support is enabled.
61 ISAPNP ISA PnP code is enabled.
62 ISDN Appropriate ISDN support is enabled.
63 JOY Appropriate joystick support is enabled.
64 KGDB Kernel debugger support is enabled.
65 KVM Kernel Virtual Machine support is enabled.
66 LIBATA Libata driver is enabled
67 LP Printer support is enabled.
68 LOOP Loopback device support is enabled.
69 M68k M68k architecture is enabled.
70 These options have more detailed description inside of
71 Documentation/m68k/kernel-options.txt.
72 MCA MCA bus support is enabled.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VGA The VGA console has been enabled.
113 VT Virtual terminal support is enabled.
114 WDT Watchdog support is enabled.
115 XT IBM PC/XT MFM hard disk support is enabled.
116 X86-32 X86-32, aka i386 architecture is enabled.
117 X86-64 X86-64 architecture is enabled.
118 More X86-64 boot options can be found in
119 Documentation/x86/x86_64/boot-options.txt .
120 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
121 XEN Xen support is enabled
123 In addition, the following text indicates that the option:
125 BUGS= Relates to possible processor bugs on the said processor.
126 KNL Is a kernel start-up parameter.
127 BOOT Is a boot loader parameter.
129 Parameters denoted with BOOT are actually interpreted by the boot
130 loader, and have no meaning to the kernel directly.
131 Do not modify the syntax of boot loader parameters without extreme
132 need or coordination with <Documentation/x86/boot.txt>.
134 There are also arch-specific kernel-parameters not documented here.
135 See for example <Documentation/x86/x86_64/boot-options.txt>.
137 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
138 a trailing = on the name of any parameter states that that parameter will
139 be entered as an environment variable, whereas its absence indicates that
140 it will appear as a kernel argument readable via /proc/cmdline by programs
141 running once the system is up.
143 The number of kernel parameters is not limited, but the length of the
144 complete command line (parameters including spaces etc.) is limited to
145 a fixed number of characters. This limit depends on the architecture
146 and is between 256 and 4096 characters. It is defined in the file
147 ./include/asm/setup.h as COMMAND_LINE_SIZE.
149 Finally, the [KMG] suffix is commonly described after a number of kernel
150 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
151 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
152 bytes respectively. Such letter suffixes can also be entirely omitted.
155 acpi= [HW,ACPI,X86]
156 Advanced Configuration and Power Interface
157 Format: { force | off | strict | noirq | rsdt }
158 force -- enable ACPI if default was off
159 off -- disable ACPI if default was on
160 noirq -- do not use ACPI for IRQ routing
161 strict -- Be less tolerant of platforms that are not
162 strictly ACPI specification compliant.
163 rsdt -- prefer RSDT over (default) XSDT
164 copy_dsdt -- copy DSDT to memory
166 See also Documentation/power/pm.txt, pci=noacpi
168 acpi_rsdp= [ACPI,EFI,KEXEC]
169 Pass the RSDP address to the kernel, mostly used
170 on machines running EFI runtime service to boot the
171 second kernel for kdump.
173 acpi_apic_instance= [ACPI, IOAPIC]
174 Format: <int>
175 2: use 2nd APIC table, if available
176 1,0: use 1st APIC table
177 default: 0
179 acpi_backlight= [HW,ACPI]
180 acpi_backlight=vendor
181 acpi_backlight=video
182 If set to vendor, prefer vendor specific driver
183 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
184 of the ACPI video.ko driver.
186 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
187 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
188 Format: <int>
189 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
190 debug output. Bits in debug_layer correspond to a
191 _COMPONENT in an ACPI source file, e.g.,
192 #define _COMPONENT ACPI_PCI_COMPONENT
193 Bits in debug_level correspond to a level in
194 ACPI_DEBUG_PRINT statements, e.g.,
195 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
196 The debug_level mask defaults to "info". See
197 Documentation/acpi/debug.txt for more information about
198 debug layers and levels.
200 Enable processor driver info messages:
201 acpi.debug_layer=0x20000000
202 Enable PCI/PCI interrupt routing info messages:
203 acpi.debug_layer=0x400000
204 Enable AML "Debug" output, i.e., stores to the Debug
205 object while interpreting AML:
206 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
207 Enable all messages related to ACPI hardware:
208 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
210 Some values produce so much output that the system is
211 unusable. The "log_buf_len" parameter may be useful
212 if you need to capture more output.
214 acpi_irq_balance [HW,ACPI]
215 ACPI will balance active IRQs
216 default in APIC mode
218 acpi_irq_nobalance [HW,ACPI]
219 ACPI will not move active IRQs (default)
220 default in PIC mode
222 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
223 Format: <irq>,<irq>...
225 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
226 use by PCI
227 Format: <irq>,<irq>...
229 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
231 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
232 Format: To spoof as Windows 98: ="Microsoft Windows"
234 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
235 acpi_osi="string1" # add string1 -- only one string
236 acpi_osi="!string2" # remove built-in string2
237 acpi_osi= # disable all strings
239 acpi_pm_good [X86]
240 Override the pmtimer bug detection: force the kernel
241 to assume that this machine's pmtimer latches its value
242 and always returns good values.
244 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
245 Format: { level | edge | high | low }
247 acpi_serialize [HW,ACPI] force serialization of AML methods
249 acpi_skip_timer_override [HW,ACPI]
250 Recognize and ignore IRQ0/pin2 Interrupt Override.
251 For broken nForce2 BIOS resulting in XT-PIC timer.
253 acpi_sleep= [HW,ACPI] Sleep options
254 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
255 old_ordering, nonvs, sci_force_enable }
256 See Documentation/power/video.txt for information on
257 s3_bios and s3_mode.
258 s3_beep is for debugging; it makes the PC's speaker beep
259 as soon as the kernel's real-mode entry point is called.
260 s4_nohwsig prevents ACPI hardware signature from being
261 used during resume from hibernation.
262 old_ordering causes the ACPI 1.0 ordering of the _PTS
263 control method, with respect to putting devices into
264 low power states, to be enforced (the ACPI 2.0 ordering
265 of _PTS is used by default).
266 nonvs prevents the kernel from saving/restoring the
267 ACPI NVS memory during suspend/hibernation and resume.
268 sci_force_enable causes the kernel to set SCI_EN directly
269 on resume from S1/S3 (which is against the ACPI spec,
270 but some broken systems don't work without it).
272 acpi_use_timer_override [HW,ACPI]
273 Use timer override. For some broken Nvidia NF5 boards
274 that require a timer override, but don't have HPET
276 acpi_enforce_resources= [ACPI]
277 { strict | lax | no }
278 Check for resource conflicts between native drivers
279 and ACPI OperationRegions (SystemIO and SystemMemory
280 only). IO ports and memory declared in ACPI might be
281 used by the ACPI subsystem in arbitrary AML code and
282 can interfere with legacy drivers.
283 strict (default): access to resources claimed by ACPI
284 is denied; legacy drivers trying to access reserved
285 resources will fail to bind to device using them.
286 lax: access to resources claimed by ACPI is allowed;
287 legacy drivers trying to access reserved resources
288 will bind successfully but a warning message is logged.
289 no: ACPI OperationRegions are not marked as reserved,
290 no further checks are performed.
292 add_efi_memmap [EFI; X86] Include EFI memory map in
293 kernel's map of available physical RAM.
295 agp= [AGP]
296 { off | try_unsupported }
297 off: disable AGP support
298 try_unsupported: try to drive unsupported chipsets
299 (may crash computer or cause data corruption)
301 ALSA [HW,ALSA]
302 See Documentation/sound/alsa/alsa-parameters.txt
304 alignment= [KNL,ARM]
305 Allow the default userspace alignment fault handler
306 behaviour to be specified. Bit 0 enables warnings,
307 bit 1 enables fixups, and bit 2 sends a segfault.
309 align_va_addr= [X86-64]
310 Align virtual addresses by clearing slice [14:12] when
311 allocating a VMA at process creation time. This option
312 gives you up to 3% performance improvement on AMD F15h
313 machines (where it is enabled by default) for a
314 CPU-intensive style benchmark, and it can vary highly in
315 a microbenchmark depending on workload and compiler.
317 1: only for 32-bit processes
318 2: only for 64-bit processes
319 on: enable for both 32- and 64-bit processes
320 off: disable for both 32- and 64-bit processes
322 amd_iommu= [HW,X86-84]
323 Pass parameters to the AMD IOMMU driver in the system.
324 Possible values are:
325 fullflush - enable flushing of IO/TLB entries when
326 they are unmapped. Otherwise they are
327 flushed before they will be reused, which
328 is a lot of faster
329 off - do not initialize any AMD IOMMU found in
330 the system
332 amijoy.map= [HW,JOY] Amiga joystick support
333 Map of devices attached to JOY0DAT and JOY1DAT
334 Format: <a>,<b>
335 See also Documentation/kernel/input/joystick.txt
337 analog.map= [HW,JOY] Analog joystick and gamepad support
338 Specifies type or capabilities of an analog joystick
339 connected to one of 16 gameports
340 Format: <type1>,<type2>,..<type16>
342 apc= [HW,SPARC]
343 Power management functions (SPARCstation-4/5 + deriv.)
344 Format: noidle
345 Disable APC CPU standby support. SPARCstation-Fox does
346 not play well with APC CPU idle - disable it if you have
347 APC and your system crashes randomly.
349 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
350 Change the output verbosity whilst booting
351 Format: { quiet (default) | verbose | debug }
352 Change the amount of debugging information output
353 when initialising the APIC and IO-APIC components.
355 autoconf= [IPV6]
356 See Documentation/networking/ipv6.txt.
358 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
359 Limit apic dumping. The parameter defines the maximal
360 number of local apics being dumped. Also it is possible
361 to set it to "all" by meaning -- no limit here.
362 Format: { 1 (default) | 2 | ... | all }.
363 The parameter valid if only apic=debug or
364 apic=verbose is specified.
365 Example: apic=debug show_lapic=all
367 apm= [APM] Advanced Power Management
368 See header of arch/x86/kernel/apm_32.c.
370 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
371 Format: <io>,<irq>,<nodeID>
373 ataflop= [HW,M68k]
375 atarimouse= [HW,MOUSE] Atari Mouse
377 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
378 EzKey and similar keyboards
380 atkbd.reset= [HW] Reset keyboard during initialization
382 atkbd.set= [HW] Select keyboard code set
383 Format: <int> (2 = AT (default), 3 = PS/2)
385 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
386 keyboards
388 atkbd.softraw= [HW] Choose between synthetic and real raw mode
389 Format: <bool> (0 = real, 1 = synthetic (default))
391 atkbd.softrepeat= [HW]
392 Use software keyboard repeat
394 autotest [IA-64]
396 baycom_epp= [HW,AX25]
397 Format: <io>,<mode>
399 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
400 Format: <io>,<mode>
401 See header of drivers/net/hamradio/baycom_par.c.
403 baycom_ser_fdx= [HW,AX25]
404 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
405 Format: <io>,<irq>,<mode>[,<baud>]
406 See header of drivers/net/hamradio/baycom_ser_fdx.c.
408 baycom_ser_hdx= [HW,AX25]
409 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
410 Format: <io>,<irq>,<mode>
411 See header of drivers/net/hamradio/baycom_ser_hdx.c.
413 boot_delay= Milliseconds to delay each printk during boot.
414 Values larger than 10 seconds (10000) are changed to
415 no delay (0).
416 Format: integer
418 bootmem_debug [KNL] Enable bootmem allocator debug messages.
420 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
421 bttv.radio= Most important insmod options are available as
422 kernel args too.
423 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
424 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
426 bulk_remove=off [PPC] This parameter disables the use of the pSeries
427 firmware feature for flushing multiple hpte entries
428 at a time.
430 c101= [NET] Moxa C101 synchronous serial card
432 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
433 Sometimes CPU hardware bugs make them report the cache
434 size incorrectly. The kernel will attempt work arounds
435 to fix known problems, but for some CPUs it is not
436 possible to determine what the correct size should be.
437 This option provides an override for these situations.
439 capability.disable=
440 [SECURITY] Disable capabilities. This would normally
441 be used only if an alternative security model is to be
442 configured. Potentially dangerous and should only be
443 used if you are entirely sure of the consequences.
445 ccw_timeout_log [S390]
446 See Documentation/s390/CommonIO for details.
448 cgroup_disable= [KNL] Disable a particular controller
449 Format: {name of the controller(s) to disable}
450 {Currently supported controllers - "memory"}
452 checkreqprot [SELINUX] Set initial checkreqprot flag value.
453 Format: { "0" | "1" }
454 See security/selinux/Kconfig help text.
455 0 -- check protection applied by kernel (includes
456 any implied execute protection).
457 1 -- check protection requested by application.
458 Default value is set via a kernel config option.
459 Value can be changed at runtime via
460 /selinux/checkreqprot.
462 cio_ignore= [S390]
463 See Documentation/s390/CommonIO for details.
465 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
466 [Deprecated]
467 Forces specified clocksource (if available) to be used
468 when calculating gettimeofday(). If specified
469 clocksource is not available, it defaults to PIT.
470 Format: { pit | tsc | cyclone | pmtmr }
472 clocksource= Override the default clocksource
473 Format: <string>
474 Override the default clocksource and use the clocksource
475 with the name specified.
476 Some clocksource names to choose from, depending on
477 the platform:
478 [all] jiffies (this is the base, fallback clocksource)
479 [ACPI] acpi_pm
480 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
481 pxa_timer,timer3,32k_counter,timer0_1
482 [AVR32] avr32
483 [X86-32] pit,hpet,tsc;
484 scx200_hrt on Geode; cyclone on IBM x440
485 [MIPS] MIPS
486 [PARISC] cr16
487 [S390] tod
488 [SH] SuperH
489 [SPARC64] tick
490 [X86-64] hpet,tsc
492 clearcpuid=BITNUM [X86]
493 Disable CPUID feature X for the kernel. See
494 arch/x86/include/asm/cpufeature.h for the valid bit
495 numbers. Note the Linux specific bits are not necessarily
496 stable over kernel options, but the vendor specific
497 ones should be.
498 Also note that user programs calling CPUID directly
499 or using the feature without checking anything
500 will still see it. This just prevents it from
501 being used by the kernel or shown in /proc/cpuinfo.
502 Also note the kernel might malfunction if you disable
503 some critical bits.
505 cmo_free_hint= [PPC] Format: { yes | no }
506 Specify whether pages are marked as being inactive
507 when they are freed. This is used in CMO environments
508 to determine OS memory pressure for page stealing by
509 a hypervisor.
510 Default: yes
512 code_bytes [X86] How many bytes of object code to print
513 in an oops report.
514 Range: 0 - 8192
515 Default: 64
517 com20020= [HW,NET] ARCnet - COM20020 chipset
518 Format:
519 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
521 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
522 Format: <io>[,<irq>]
524 com90xx= [HW,NET]
525 ARCnet - COM90xx chipset (memory-mapped buffers)
526 Format: <io>[,<irq>[,<memstart>]]
528 condev= [HW,S390] console device
529 conmode=
531 console= [KNL] Output console device and options.
533 tty<n> Use the virtual console device <n>.
535 ttyS<n>[,options]
536 ttyUSB0[,options]
537 Use the specified serial port. The options are of
538 the form "bbbbpnf", where "bbbb" is the baud rate,
539 "p" is parity ("n", "o", or "e"), "n" is number of
540 bits, and "f" is flow control ("r" for RTS or
541 omit it). Default is "9600n8".
543 See Documentation/serial-console.txt for more
544 information. See
545 Documentation/networking/netconsole.txt for an
546 alternative.
548 uart[8250],io,<addr>[,options]
549 uart[8250],mmio,<addr>[,options]
550 Start an early, polled-mode console on the 8250/16550
551 UART at the specified I/O port or MMIO address,
552 switching to the matching ttyS device later. The
553 options are the same as for ttyS, above.
555 If the device connected to the port is not a TTY but a braille
556 device, prepend "brl," before the device type, for instance
557 console=brl,ttyS0
558 For now, only VisioBraille is supported.
560 consoleblank= [KNL] The console blank (screen saver) timeout in
561 seconds. Defaults to 10*60 = 10mins. A value of 0
562 disables the blank timer.
564 coredump_filter=
565 [KNL] Change the default value for
566 /proc/<pid>/coredump_filter.
567 See also Documentation/filesystems/proc.txt.
569 cpuidle.off=1 [CPU_IDLE]
570 disable the cpuidle sub-system
572 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
573 Format:
574 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
576 crashkernel=size[KMG][@offset[KMG]]
577 [KNL] Using kexec, Linux can switch to a 'crash kernel'
578 upon panic. This parameter reserves the physical
579 memory region [offset, offset + size] for that kernel
580 image. If '@offset' is omitted, then a suitable offset
581 is selected automatically. Check
582 Documentation/kdump/kdump.txt for further details.
584 crashkernel=range1:size1[,range2:size2,...][@offset]
585 [KNL] Same as above, but depends on the memory
586 in the running system. The syntax of range is
587 start-[end] where start and end are both
588 a memory unit (amount[KMG]). See also
589 Documentation/kdump/kdump.txt for an example.
591 cs89x0_dma= [HW,NET]
592 Format: <dma>
594 cs89x0_media= [HW,NET]
595 Format: { rj45 | aui | bnc }
597 dasd= [HW,NET]
598 See header of drivers/s390/block/dasd_devmap.c.
600 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
601 (one device per port)
602 Format: <port#>,<type>
603 See also Documentation/input/joystick-parport.txt
605 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
606 time. See Documentation/dynamic-debug-howto.txt for
607 details.
609 debug [KNL] Enable kernel debugging (events log level).
611 debug_locks_verbose=
612 [KNL] verbose self-tests
613 Format=<0|1>
614 Print debugging info while doing the locking API
615 self-tests.
616 We default to 0 (no extra messages), setting it to
617 1 will print _a lot_ more information - normally
618 only useful to kernel developers.
620 debug_objects [KNL] Enable object debugging
622 no_debug_objects
623 [KNL] Disable object debugging
625 debugpat [X86] Enable PAT debugging
627 decnet.addr= [HW,NET]
628 Format: <area>[,<node>]
629 See also Documentation/networking/decnet.txt.
631 default_hugepagesz=
632 [same as hugepagesz=] The size of the default
633 HugeTLB page size. This is the size represented by
634 the legacy /proc/ hugepages APIs, used for SHM, and
635 default size when mounting hugetlbfs filesystems.
636 Defaults to the default architecture's huge page size
637 if not specified.
639 dhash_entries= [KNL]
640 Set number of hash buckets for dentry cache.
642 digi= [HW,SERIAL]
643 IO parameters + enable/disable command.
645 digiepca= [HW,SERIAL]
646 See drivers/char/README.epca and
647 Documentation/serial/digiepca.txt.
649 disable= [IPV6]
650 See Documentation/networking/ipv6.txt.
652 disable_ddw [PPC/PSERIES]
653 Disable Dynamic DMA Window support. Use this if
654 to workaround buggy firmware.
656 disable_ipv6= [IPV6]
657 See Documentation/networking/ipv6.txt.
659 disable_mtrr_cleanup [X86]
660 The kernel tries to adjust MTRR layout from continuous
661 to discrete, to make X server driver able to add WB
662 entry later. This parameter disables that.
664 disable_mtrr_trim [X86, Intel and AMD only]
665 By default the kernel will trim any uncacheable
666 memory out of your available memory pool based on
667 MTRR settings. This parameter disables that behavior,
668 possibly causing your machine to run very slowly.
670 disable_timer_pin_1 [X86]
671 Disable PIN 1 of APIC timer
672 Can be useful to work around chipset bugs.
674 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
675 this option disables the debugging code at boot.
677 dma_debug_entries=<number>
678 This option allows to tune the number of preallocated
679 entries for DMA-API debugging code. One entry is
680 required per DMA-API allocation. Use this if the
681 DMA-API debugging code disables itself because the
682 architectural default is too low.
684 dma_debug_driver=<driver_name>
685 With this option the DMA-API debugging driver
686 filter feature can be enabled at boot time. Just
687 pass the driver to filter for as the parameter.
688 The filter can be disabled or changed to another
689 driver later using sysfs.
691 dscc4.setup= [NET]
693 earlycon= [KNL] Output early console device and options.
694 uart[8250],io,<addr>[,options]
695 uart[8250],mmio,<addr>[,options]
696 uart[8250],mmio32,<addr>[,options]
697 Start an early, polled-mode console on the 8250/16550
698 UART at the specified I/O port or MMIO address.
699 MMIO inter-register address stride is either 8-bit
700 (mmio) or 32-bit (mmio32).
701 The options are the same as for ttyS, above.
703 earlyprintk= [X86,SH,BLACKFIN]
704 earlyprintk=vga
705 earlyprintk=serial[,ttySn[,baudrate]]
706 earlyprintk=ttySn[,baudrate]
707 earlyprintk=dbgp[debugController#]
709 Append ",keep" to not disable it when the real console
710 takes over.
712 Only vga or serial or usb debug port at a time.
714 Currently only ttyS0 and ttyS1 are supported.
716 Interaction with the standard serial driver is not
717 very good.
719 The VGA output is eventually overwritten by the real
720 console.
722 ekgdboc= [X86,KGDB] Allow early kernel console debugging
723 ekgdboc=kbd
725 This is designed to be used in conjunction with
726 the boot argument: earlyprintk=vga
728 edd= [EDD]
729 Format: {"off" | "on" | "skip[mbr]"}
731 eisa_irq_edge= [PARISC,HW]
732 See header of drivers/parisc/eisa.c.
734 elanfreq= [X86-32]
735 See comment before function elanfreq_setup() in
736 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
738 elevator= [IOSCHED]
739 Format: {"cfq" | "deadline" | "noop"}
740 See Documentation/block/as-iosched.txt and
741 Documentation/block/deadline-iosched.txt for details.
743 elfcorehdr= [IA-64,PPC,SH,X86]
744 Specifies physical address of start of kernel core
745 image elf header. Generally kexec loader will
746 pass this option to capture kernel.
747 See Documentation/kdump/kdump.txt for details.
749 enable_mtrr_cleanup [X86]
750 The kernel tries to adjust MTRR layout from continuous
751 to discrete, to make X server driver able to add WB
752 entry later. This parameter enables that.
754 enable_timer_pin_1 [X86]
755 Enable PIN 1 of APIC timer
756 Can be useful to work around chipset bugs
757 (in particular on some ATI chipsets).
758 The kernel tries to set a reasonable default.
760 enforcing [SELINUX] Set initial enforcing status.
761 Format: {"0" | "1"}
762 See security/selinux/Kconfig help text.
763 0 -- permissive (log only, no denials).
764 1 -- enforcing (deny and log).
765 Default value is 0.
766 Value can be changed at runtime via /selinux/enforce.
768 erst_disable [ACPI]
769 Disable Error Record Serialization Table (ERST)
770 support.
772 ether= [HW,NET] Ethernet cards parameters
773 This option is obsoleted by the "netdev=" option, which
774 has equivalent usage. See its documentation for details.
776 failslab=
777 fail_page_alloc=
778 fail_make_request=[KNL]
779 General fault injection mechanism.
780 Format: <interval>,<probability>,<space>,<times>
781 See also /Documentation/fault-injection/.
783 floppy= [HW]
784 See Documentation/blockdev/floppy.txt.
786 force_pal_cache_flush
787 [IA-64] Avoid check_sal_cache_flush which may hang on
788 buggy SAL_CACHE_FLUSH implementations. Using this
789 parameter will force ia64_sal_cache_flush to call
790 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
792 ftrace=[tracer]
793 [FTRACE] will set and start the specified tracer
794 as early as possible in order to facilitate early
795 boot debugging.
797 ftrace_dump_on_oops[=orig_cpu]
798 [FTRACE] will dump the trace buffers on oops.
799 If no parameter is passed, ftrace will dump
800 buffers of all CPUs, but if you pass orig_cpu, it will
801 dump only the buffer of the CPU that triggered the
802 oops.
804 ftrace_filter=[function-list]
805 [FTRACE] Limit the functions traced by the function
806 tracer at boot up. function-list is a comma separated
807 list of functions. This list can be changed at run
808 time by the set_ftrace_filter file in the debugfs
809 tracing directory.
811 ftrace_notrace=[function-list]
812 [FTRACE] Do not trace the functions specified in
813 function-list. This list can be changed at run time
814 by the set_ftrace_notrace file in the debugfs
815 tracing directory.
817 ftrace_graph_filter=[function-list]
818 [FTRACE] Limit the top level callers functions traced
819 by the function graph tracer at boot up.
820 function-list is a comma separated list of functions
821 that can be changed at run time by the
822 set_graph_function file in the debugfs tracing directory.
824 gamecon.map[2|3]=
825 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
826 support via parallel port (up to 5 devices per port)
827 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
828 See also Documentation/input/joystick-parport.txt
830 gamma= [HW,DRM]
832 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
833 Format: off | on
834 default: on
836 gcov_persist= [GCOV] When non-zero (default), profiling data for
837 kernel modules is saved and remains accessible via
838 debugfs, even when the module is unloaded/reloaded.
839 When zero, profiling data is discarded and associated
840 debugfs files are removed at module unload time.
842 gpt [EFI] Forces disk with valid GPT signature but
843 invalid Protective MBR to be treated as GPT.
845 hashdist= [KNL,NUMA] Large hashes allocated during boot
846 are distributed across NUMA nodes. Defaults on
847 for 64-bit NUMA, off otherwise.
848 Format: 0 | 1 (for off | on)
850 hcl= [IA-64] SGI's Hardware Graph compatibility layer
852 hd= [EIDE] (E)IDE hard drive subsystem geometry
853 Format: <cyl>,<head>,<sect>
855 hest_disable [ACPI]
856 Disable Hardware Error Source Table (HEST) support;
857 corresponding firmware-first mode error processing
858 logic will be disabled.
860 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
861 size of <nn>. This works even on boxes that have no
862 highmem otherwise. This also works to reduce highmem
863 size on bigger boxes.
865 highres= [KNL] Enable/disable high resolution timer mode.
866 Valid parameters: "on", "off"
867 Default: "on"
869 hisax= [HW,ISDN]
870 See Documentation/isdn/README.HiSax.
872 hlt [BUGS=ARM,SH]
874 hpet= [X86-32,HPET] option to control HPET usage
875 Format: { enable (default) | disable | force |
876 verbose }
877 disable: disable HPET and use PIT instead
878 force: allow force enabled of undocumented chips (ICH4,
879 VIA, nVidia)
880 verbose: show contents of HPET registers during setup
882 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
883 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
884 On x86-64 and powerpc, this option can be specified
885 multiple times interleaved with hugepages= to reserve
886 huge pages of different sizes. Valid pages sizes on
887 x86-64 are 2M (when the CPU supports "pse") and 1G
888 (when the CPU supports the "pdpe1gb" cpuinfo flag)
889 Note that 1GB pages can only be allocated at boot time
890 using hugepages= and not freed afterwards.
892 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
893 terminal devices. Valid values: 0..8
894 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
895 If specified, z/VM IUCV HVC accepts connections
896 from listed z/VM user IDs only.
898 keep_bootcon [KNL]
899 Do not unregister boot console at start. This is only
900 useful for debugging when something happens in the window
901 between unregistering the boot console and initializing
902 the real console.
904 i2c_bus= [HW] Override the default board specific I2C bus speed
905 or register an additional I2C bus that is not
906 registered from board initialization code.
907 Format:
908 <bus_id>,<clkrate>
910 i8042.debug [HW] Toggle i8042 debug mode
911 i8042.direct [HW] Put keyboard port into non-translated mode
912 i8042.dumbkbd [HW] Pretend that controller can only read data from
913 keyboard and cannot control its state
914 (Don't attempt to blink the leds)
915 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
916 i8042.nokbd [HW] Don't check/create keyboard port
917 i8042.noloop [HW] Disable the AUX Loopback command while probing
918 for the AUX port
919 i8042.nomux [HW] Don't check presence of an active multiplexing
920 controller
921 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
922 controllers
923 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
924 i8042.reset [HW] Reset the controller during init and cleanup
925 i8042.unlock [HW] Unlock (ignore) the keylock
927 i810= [HW,DRM]
929 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
930 indicates that the driver is running on unsupported
931 hardware.
932 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
933 does not match list of supported models.
934 i8k.power_status
935 [HW] Report power status in /proc/i8k
936 (disabled by default)
937 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
938 capability is set.
940 icn= [HW,ISDN]
941 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
943 ide-core.nodma= [HW] (E)IDE subsystem
944 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
945 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
946 .cdrom .chs .ignore_cable are additional options
947 See Documentation/ide/ide.txt.
949 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
950 Claim all unknown PCI IDE storage controllers.
952 idle= [X86]
953 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
954 Poll forces a polling idle loop that can slightly
955 improve the performance of waking up a idle CPU, but
956 will use a lot of power and make the system run hot.
957 Not recommended.
958 idle=mwait: On systems which support MONITOR/MWAIT but
959 the kernel chose to not use it because it doesn't save
960 as much power as a normal idle loop, use the
961 MONITOR/MWAIT idle loop anyways. Performance should be
962 the same as idle=poll.
963 idle=halt: Halt is forced to be used for CPU idle.
964 In such case C2/C3 won't be used again.
965 idle=nomwait: Disable mwait for CPU C-states
967 ignore_loglevel [KNL]
968 Ignore loglevel setting - this will print /all/
969 kernel messages to the console. Useful for debugging.
971 ihash_entries= [KNL]
972 Set number of hash buckets for inode cache.
974 ima_audit= [IMA]
975 Format: { "0" | "1" }
976 0 -- integrity auditing messages. (Default)
977 1 -- enable informational integrity auditing messages.
979 ima_hash= [IMA]
980 Format: { "sha1" | "md5" }
981 default: "sha1"
983 ima_tcb [IMA]
984 Load a policy which meets the needs of the Trusted
985 Computing Base. This means IMA will measure all
986 programs exec'd, files mmap'd for exec, and all files
987 opened for read by uid=0.
989 init= [KNL]
990 Format: <full_path>
991 Run specified binary instead of /sbin/init as init
992 process.
994 initcall_debug [KNL] Trace initcalls as they are executed. Useful
995 for working out where the kernel is dying during
996 startup.
998 initrd= [BOOT] Specify the location of the initial ramdisk
1000 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1001 Format: <irq>
1003 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1004 on
1005 Enable intel iommu driver.
1006 off
1007 Disable intel iommu driver.
1008 igfx_off [Default Off]
1009 By default, gfx is mapped as normal device. If a gfx
1010 device has a dedicated DMAR unit, the DMAR unit is
1011 bypassed by not enabling DMAR with this option. In
1012 this case, gfx device will use physical address for
1013 DMA.
1014 forcedac [x86_64]
1015 With this option iommu will not optimize to look
1016 for io virtual address below 32-bit forcing dual
1017 address cycle on pci bus for cards supporting greater
1018 than 32-bit addressing. The default is to look
1019 for translation below 32-bit and if not available
1020 then look in the higher range.
1021 strict [Default Off]
1022 With this option on every unmap_single operation will
1023 result in a hardware IOTLB flush operation as opposed
1024 to batching them for performance.
1025 sp_off [Default Off]
1026 By default, super page will be supported if Intel IOMMU
1027 has the capability. With this option, super page will
1028 not be supported.
1029 intremap= [X86-64, Intel-IOMMU]
1030 Format: { on (default) | off | nosid }
1031 on enable Interrupt Remapping (default)
1032 off disable Interrupt Remapping
1033 nosid disable Source ID checking
1035 inttest= [IA-64]
1037 iomem= Disable strict checking of access to MMIO memory
1038 strict regions from userspace.
1039 relaxed
1041 iommu= [x86]
1042 off
1043 force
1044 noforce
1045 biomerge
1046 panic
1047 nopanic
1048 merge
1049 nomerge
1050 forcesac
1051 soft
1052 pt [x86, IA-64]
1054 io7= [HW] IO7 for Marvel based alpha systems
1055 See comment before marvel_specify_io7 in
1056 arch/alpha/kernel/core_marvel.c.
1058 io_delay= [X86] I/O delay method
1059 0x80
1060 Standard port 0x80 based delay
1061 0xed
1062 Alternate port 0xed based delay (needed on some systems)
1063 udelay
1064 Simple two microseconds delay
1065 none
1066 No delay
1068 ip= [IP_PNP]
1069 See Documentation/filesystems/nfs/nfsroot.txt.
1071 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1072 See comment before ip2_setup() in
1073 drivers/char/ip2/ip2base.c.
1075 irqfixup [HW]
1076 When an interrupt is not handled search all handlers
1077 for it. Intended to get systems with badly broken
1078 firmware running.
1080 irqpoll [HW]
1081 When an interrupt is not handled search all handlers
1082 for it. Also check all handlers each timer
1083 interrupt. Intended to get systems with badly broken
1084 firmware running.
1086 isapnp= [ISAPNP]
1087 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1089 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1090 Format:
1091 <cpu number>,...,<cpu number>
1092 or
1093 <cpu number>-<cpu number>
1094 (must be a positive range in ascending order)
1095 or a mixture
1096 <cpu number>,...,<cpu number>-<cpu number>
1098 This option can be used to specify one or more CPUs
1099 to isolate from the general SMP balancing and scheduling
1100 algorithms. You can move a process onto or off an
1101 "isolated" CPU via the CPU affinity syscalls or cpuset.
1102 <cpu number> begins at 0 and the maximum value is
1103 "number of CPUs in system - 1".
1105 This option is the preferred way to isolate CPUs. The
1106 alternative -- manually setting the CPU mask of all
1107 tasks in the system -- can cause problems and
1108 suboptimal load balancer performance.
1110 iucv= [HW,NET]
1112 js= [HW,JOY] Analog joystick
1113 See Documentation/input/joystick.txt.
1115 keepinitrd [HW,ARM]
1117 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1118 specifies the amount of memory usable by the kernel
1119 for non-movable allocations. The requested amount is
1120 spread evenly throughout all nodes in the system. The
1121 remaining memory in each node is used for Movable
1122 pages. In the event, a node is too small to have both
1123 kernelcore and Movable pages, kernelcore pages will
1124 take priority and other nodes will have a larger number
1125 of kernelcore pages. The Movable zone is used for the
1126 allocation of pages that may be reclaimed or moved
1127 by the page migration subsystem. This means that
1128 HugeTLB pages may not be allocated from this zone.
1129 Note that allocations like PTEs-from-HighMem still
1130 use the HighMem zone if it exists, and the Normal
1131 zone if it does not.
1133 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1134 Format: <Controller#>[,poll interval]
1135 The controller # is the number of the ehci usb debug
1136 port as it is probed via PCI. The poll interval is
1137 optional and is the number seconds in between
1138 each poll cycle to the debug port in case you need
1139 the functionality for interrupting the kernel with
1140 gdb or control-c on the dbgp connection. When
1141 not using this parameter you use sysrq-g to break into
1142 the kernel debugger.
1144 kgdboc= [KGDB,HW] kgdb over consoles.
1145 Requires a tty driver that supports console polling,
1146 or a supported polling keyboard driver (non-usb).
1147 Serial only format: <serial_device>[,baud]
1148 keyboard only format: kbd
1149 keyboard and serial format: kbd,<serial_device>[,baud]
1150 Optional Kernel mode setting:
1151 kms, kbd format: kms,kbd
1152 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1154 kgdbwait [KGDB] Stop kernel execution and enter the
1155 kernel debugger at the earliest opportunity.
1157 kmac= [MIPS] korina ethernet MAC address.
1158 Configure the RouterBoard 532 series on-chip
1159 Ethernet adapter MAC address.
1161 kmemleak= [KNL] Boot-time kmemleak enable/disable
1162 Valid arguments: on, off
1163 Default: on
1165 kstack=N [X86] Print N words from the kernel stack
1166 in oops dumps.
1168 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1169 Default is 0 (don't ignore, but inject #GP)
1171 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1172 Default is 1 (enabled)
1174 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1175 KVM MMU at runtime.
1176 Default is 0 (off)
1178 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1179 Default is 1 (enabled)
1181 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1182 for all guests.
1183 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1185 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1186 (virtualized MMU) support on capable Intel chips.
1187 Default is 1 (enabled)
1189 kvm-intel.emulate_invalid_guest_state=
1190 [KVM,Intel] Enable emulation of invalid guest states
1191 Default is 0 (disabled)
1193 kvm-intel.flexpriority=
1194 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1195 Default is 1 (enabled)
1197 kvm-intel.unrestricted_guest=
1198 [KVM,Intel] Disable unrestricted guest feature
1199 (virtualized real and unpaged mode) on capable
1200 Intel chips. Default is 1 (enabled)
1202 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1203 feature (tagged TLBs) on capable Intel chips.
1204 Default is 1 (enabled)
1206 l2cr= [PPC]
1208 l3cr= [PPC]
1210 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1211 disabled it.
1213 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1214 in C2 power state.
1216 libata.dma= [LIBATA] DMA control
1217 libata.dma=0 Disable all PATA and SATA DMA
1218 libata.dma=1 PATA and SATA Disk DMA only
1219 libata.dma=2 ATAPI (CDROM) DMA only
1220 libata.dma=4 Compact Flash DMA only
1221 Combinations also work, so libata.dma=3 enables DMA
1222 for disks and CDROMs, but not CFs.
1224 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1225 libata.ignore_hpa=0 keep BIOS limits (default)
1226 libata.ignore_hpa=1 ignore limits, using full disk
1228 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1229 when set.
1230 Format: <int>
1232 libata.force= [LIBATA] Force configurations. The format is comma
1233 separated list of "[ID:]VAL" where ID is
1234 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1235 matching port, link or device. Basically, it matches
1236 the ATA ID string printed on console by libata. If
1237 the whole ID part is omitted, the last PORT and DEVICE
1238 values are used. If ID hasn't been specified yet, the
1239 configuration applies to all ports, links and devices.
1241 If only DEVICE is omitted, the parameter applies to
1242 the port and all links and devices behind it. DEVICE
1243 number of 0 either selects the first device or the
1244 first fan-out link behind PMP device. It does not
1245 select the host link. DEVICE number of 15 selects the
1246 host link and device attached to it.
1248 The VAL specifies the configuration to force. As long
1249 as there's no ambiguity shortcut notation is allowed.
1250 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1251 The following configurations can be forced.
1253 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1254 Any ID with matching PORT is used.
1256 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1258 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1259 udma[/][16,25,33,44,66,100,133] notation is also
1260 allowed.
1262 * [no]ncq: Turn on or off NCQ.
1264 * nohrst, nosrst, norst: suppress hard, soft
1265 and both resets.
1267 * dump_id: dump IDENTIFY data.
1269 If there are multiple matching configurations changing
1270 the same attribute, the last one is used.
1272 memblock=debug [KNL] Enable memblock debug messages.
1274 load_ramdisk= [RAM] List of ramdisks to load from floppy
1275 See Documentation/blockdev/ramdisk.txt.
1277 lockd.nlm_grace_period=P [NFS] Assign grace period.
1278 Format: <integer>
1280 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1281 Format: <integer>
1283 lockd.nlm_timeout=T [NFS] Assign timeout value.
1284 Format: <integer>
1286 lockd.nlm_udpport=M [NFS] Assign UDP port.
1287 Format: <integer>
1289 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1290 Format: <irq>
1292 loglevel= All Kernel Messages with a loglevel smaller than the
1293 console loglevel will be printed to the console. It can
1294 also be changed with klogd or other programs. The
1295 loglevels are defined as follows:
1297 0 (KERN_EMERG) system is unusable
1298 1 (KERN_ALERT) action must be taken immediately
1299 2 (KERN_CRIT) critical conditions
1300 3 (KERN_ERR) error conditions
1301 4 (KERN_WARNING) warning conditions
1302 5 (KERN_NOTICE) normal but significant condition
1303 6 (KERN_INFO) informational
1304 7 (KERN_DEBUG) debug-level messages
1306 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1307 in bytes. n must be a power of two. The default
1308 size is set in the kernel config file.
1310 logo.nologo [FB] Disables display of the built-in Linux logo.
1311 This may be used to provide more screen space for
1312 kernel log messages and is useful when debugging
1313 kernel boot problems.
1315 lp=0 [LP] Specify parallel ports to use, e.g,
1316 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1317 lp=reset first parallel port). 'lp=0' disables the
1318 lp=auto printer driver. 'lp=reset' (which can be
1319 specified in addition to the ports) causes
1320 attached printers to be reset. Using
1321 lp=port1,port2,... specifies the parallel ports
1322 to associate lp devices with, starting with
1323 lp0. A port specification may be 'none' to skip
1324 that lp device, or a parport name such as
1325 'parport0'. Specifying 'lp=auto' instead of a
1326 port specification list means that device IDs
1327 from each port should be examined, to see if
1328 an IEEE 1284-compliant printer is attached; if
1329 so, the driver will manage that printer.
1330 See also header of drivers/char/lp.c.
1332 lpj=n [KNL]
1333 Sets loops_per_jiffy to given constant, thus avoiding
1334 time-consuming boot-time autodetection (up to 250 ms per
1335 CPU). 0 enables autodetection (default). To determine
1336 the correct value for your kernel, boot with normal
1337 autodetection and see what value is printed. Note that
1338 on SMP systems the preset will be applied to all CPUs,
1339 which is likely to cause problems if your CPUs need
1340 significantly divergent settings. An incorrect value
1341 will cause delays in the kernel to be wrong, leading to
1342 unpredictable I/O errors and other breakage. Although
1343 unlikely, in the extreme case this might damage your
1344 hardware.
1346 ltpc= [NET]
1347 Format: <io>,<irq>,<dma>
1349 machvec= [IA-64] Force the use of a particular machine-vector
1350 (machvec) in a generic kernel.
1351 Example: machvec=hpzx1_swiotlb
1353 machtype= [Loongson] Share the same kernel image file between different
1354 yeeloong laptop.
1355 Example: machtype=lemote-yeeloong-2f-7inch
1357 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1358 than or equal to this physical address is ignored.
1360 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1361 should make use of. maxcpus=n : n >= 0 limits the
1362 kernel to using 'n' processors. n=0 is a special case,
1363 it is equivalent to "nosmp", which also disables
1364 the IO APIC.
1366 max_loop= [LOOP] The number of loop block devices that get
1367 (loop.max_loop) unconditionally pre-created at init time. The default
1368 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1369 of statically allocating a predefined number, loop
1370 devices can be requested on-demand with the
1371 /dev/loop-control interface.
1373 mcatest= [IA-64]
1375 mce [X86-32] Machine Check Exception
1377 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1379 md= [HW] RAID subsystems devices and level
1380 See Documentation/md.txt.
1382 mdacon= [MDA]
1383 Format: <first>,<last>
1384 Specifies range of consoles to be captured by the MDA.
1386 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1387 Amount of memory to be used when the kernel is not able
1388 to see the whole system memory or for test.
1389 [X86-32] Use together with memmap= to avoid physical
1390 address space collisions. Without memmap= PCI devices
1391 could be placed at addresses belonging to unused RAM.
1393 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1394 memory.
1396 memchunk=nn[KMG]
1397 [KNL,SH] Allow user to override the default size for
1398 per-device physically contiguous DMA buffers.
1400 memmap=exactmap [KNL,X86] Enable setting of an exact
1401 E820 memory map, as specified by the user.
1402 Such memmap=exactmap lines can be constructed based on
1403 BIOS output or other requirements. See the memmap=nn@ss
1404 option description.
1406 memmap=nn[KMG]@ss[KMG]
1407 [KNL] Force usage of a specific region of memory
1408 Region of memory to be used, from ss to ss+nn.
1410 memmap=nn[KMG]#ss[KMG]
1411 [KNL,ACPI] Mark specific memory as ACPI data.
1412 Region of memory to be used, from ss to ss+nn.
1414 memmap=nn[KMG]$ss[KMG]
1415 [KNL,ACPI] Mark specific memory as reserved.
1416 Region of memory to be used, from ss to ss+nn.
1417 Example: Exclude memory from 0x18690000-0x1869ffff
1418 memmap=64K$0x18690000
1419 or
1420 memmap=0x10000$0x18690000
1422 memory_corruption_check=0/1 [X86]
1423 Some BIOSes seem to corrupt the first 64k of
1424 memory when doing things like suspend/resume.
1425 Setting this option will scan the memory
1426 looking for corruption. Enabling this will
1427 both detect corruption and prevent the kernel
1428 from using the memory being corrupted.
1429 However, its intended as a diagnostic tool; if
1430 repeatable BIOS-originated corruption always
1431 affects the same memory, you can use memmap=
1432 to prevent the kernel from using that memory.
1434 memory_corruption_check_size=size [X86]
1435 By default it checks for corruption in the low
1436 64k, making this memory unavailable for normal
1437 use. Use this parameter to scan for
1438 corruption in more or less memory.
1440 memory_corruption_check_period=seconds [X86]
1441 By default it checks for corruption every 60
1442 seconds. Use this parameter to check at some
1443 other rate. 0 disables periodic checking.
1445 memtest= [KNL,X86] Enable memtest
1446 Format: <integer>
1447 default : 0 <disable>
1448 Specifies the number of memtest passes to be
1449 performed. Each pass selects another test
1450 pattern from a given set of patterns. Memtest
1451 fills the memory with this pattern, validates
1452 memory contents and reserves bad memory
1453 regions that are detected.
1455 meye.*= [HW] Set MotionEye Camera parameters
1456 See Documentation/video4linux/meye.txt.
1458 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1459 Multi-Function General Purpose Timers on AMD Geode
1460 platforms.
1462 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1463 the BIOS has incorrectly applied a workaround. TinyBIOS
1464 version 0.98 is known to be affected, 0.99 fixes the
1465 problem by letting the user disable the workaround.
1467 mga= [HW,DRM]
1469 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1470 physical address is ignored.
1472 mini2440= [ARM,HW,KNL]
1473 Format:[0..2][b][c][t]
1474 Default: "0tb"
1475 MINI2440 configuration specification:
1476 0 - The attached screen is the 3.5" TFT
1477 1 - The attached screen is the 7" TFT
1478 2 - The VGA Shield is attached (1024x768)
1479 Leaving out the screen size parameter will not load
1480 the TFT driver, and the framebuffer will be left
1481 unconfigured.
1482 b - Enable backlight. The TFT backlight pin will be
1483 linked to the kernel VESA blanking code and a GPIO
1484 LED. This parameter is not necessary when using the
1485 VGA shield.
1486 c - Enable the s3c camera interface.
1487 t - Reserved for enabling touchscreen support. The
1488 touchscreen support is not enabled in the mainstream
1489 kernel as of 2.6.30, a preliminary port can be found
1490 in the "bleeding edge" mini2440 support kernel at
1491 http://repo.or.cz/w/linux-2.6/mini2440.git
1493 mminit_loglevel=
1494 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1495 parameter allows control of the logging verbosity for
1496 the additional memory initialisation checks. A value
1497 of 0 disables mminit logging and a level of 4 will
1498 log everything. Information is printed at KERN_DEBUG
1499 so loglevel=8 may also need to be specified.
1501 mousedev.tap_time=
1502 [MOUSE] Maximum time between finger touching and
1503 leaving touchpad surface for touch to be considered
1504 a tap and be reported as a left button click (for
1505 touchpads working in absolute mode only).
1506 Format: <msecs>
1507 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1508 reporting absolute coordinates, such as tablets
1509 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1510 reporting absolute coordinates, such as tablets
1512 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1513 is similar to kernelcore except it specifies the
1514 amount of memory used for migratable allocations.
1515 If both kernelcore and movablecore is specified,
1516 then kernelcore will be at *least* the specified
1517 value but may be more. If movablecore on its own
1518 is specified, the administrator must be careful
1519 that the amount of memory usable for all allocations
1520 is not too small.
1522 MTD_Partition= [MTD]
1523 Format: <name>,<region-number>,<size>,<offset>
1525 MTD_Region= [MTD] Format:
1526 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1528 mtdparts= [MTD]
1529 See drivers/mtd/cmdlinepart.c.
1531 multitce=off [PPC] This parameter disables the use of the pSeries
1532 firmware feature for updating multiple TCE entries
1533 at a time.
1535 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1537 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1539 boundary - index of last SLC block on Flex-OneNAND.
1540 The remaining blocks are configured as MLC blocks.
1541 lock - Configure if Flex-OneNAND boundary should be locked.
1542 Once locked, the boundary cannot be changed.
1543 1 indicates lock status, 0 indicates unlock status.
1545 mtdset= [ARM]
1546 ARM/S3C2412 JIVE boot control
1548 See arch/arm/mach-s3c2412/mach-jive.c
1550 mtouchusb.raw_coordinates=
1551 [HW] Make the MicroTouch USB driver use raw coordinates
1552 ('y', default) or cooked coordinates ('n')
1554 mtrr_chunk_size=nn[KMG] [X86]
1555 used for mtrr cleanup. It is largest continuous chunk
1556 that could hold holes aka. UC entries.
1558 mtrr_gran_size=nn[KMG] [X86]
1559 Used for mtrr cleanup. It is granularity of mtrr block.
1560 Default is 1.
1561 Large value could prevent small alignment from
1562 using up MTRRs.
1564 mtrr_spare_reg_nr=n [X86]
1565 Format: <integer>
1566 Range: 0,7 : spare reg number
1567 Default : 1
1568 Used for mtrr cleanup. It is spare mtrr entries number.
1569 Set to 2 or more if your graphical card needs more.
1571 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1573 netdev= [NET] Network devices parameters
1574 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1575 Note that mem_start is often overloaded to mean
1576 something different and driver-specific.
1577 This usage is only documented in each driver source
1578 file if at all.
1580 nf_conntrack.acct=
1581 [NETFILTER] Enable connection tracking flow accounting
1582 0 to disable accounting
1583 1 to enable accounting
1584 Default value is 0.
1586 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1587 See Documentation/filesystems/nfs/nfsroot.txt.
1589 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1590 See Documentation/filesystems/nfs/nfsroot.txt.
1592 nfsrootdebug [NFS] enable nfsroot debugging messages.
1593 See Documentation/filesystems/nfs/nfsroot.txt.
1595 nfs.callback_tcpport=
1596 [NFS] set the TCP port on which the NFSv4 callback
1597 channel should listen.
1599 nfs.cache_getent=
1600 [NFS] sets the pathname to the program which is used
1601 to update the NFS client cache entries.
1603 nfs.cache_getent_timeout=
1604 [NFS] sets the timeout after which an attempt to
1605 update a cache entry is deemed to have failed.
1607 nfs.idmap_cache_timeout=
1608 [NFS] set the maximum lifetime for idmapper cache
1609 entries.
1611 nfs.enable_ino64=
1612 [NFS] enable 64-bit inode numbers.
1613 If zero, the NFS client will fake up a 32-bit inode
1614 number for the readdir() and stat() syscalls instead
1615 of returning the full 64-bit number.
1616 The default is to return 64-bit inode numbers.
1618 nfs.nfs4_disable_idmapping=
1619 [NFSv4] When set, this option disables the NFSv4
1620 idmapper on the client, but only if the mount
1621 is using the 'sec=sys' security flavour. This may
1622 make migration from legacy NFSv2/v3 systems easier
1623 provided that the server has the appropriate support.
1624 The default is to always enable NFSv4 idmapping.
1626 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1627 when a NMI is triggered.
1628 Format: [state][,regs][,debounce][,die]
1630 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1631 Format: [panic,][nopanic,][num]
1632 Valid num: 0
1633 0 - turn nmi_watchdog off
1634 When panic is specified, panic when an NMI watchdog
1635 timeout occurs (or 'nopanic' to override the opposite
1636 default).
1637 This is useful when you use a panic=... timeout and
1638 need the box quickly up again.
1640 netpoll.carrier_timeout=
1641 [NET] Specifies amount of time (in seconds) that
1642 netpoll should wait for a carrier. By default netpoll
1643 waits 4 seconds.
1645 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1646 emulation library even if a 387 maths coprocessor
1647 is present.
1649 no_console_suspend
1650 [HW] Never suspend the console
1651 Disable suspending of consoles during suspend and
1652 hibernate operations. Once disabled, debugging
1653 messages can reach various consoles while the rest
1654 of the system is being put to sleep (ie, while
1655 debugging driver suspend/resume hooks). This may
1656 not work reliably with all consoles, but is known
1657 to work with serial and VGA consoles.
1659 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1660 caches in the slab allocator. Saves per-node memory,
1661 but will impact performance.
1663 noalign [KNL,ARM]
1665 noapic [SMP,APIC] Tells the kernel to not make use of any
1666 IOAPICs that may be present in the system.
1668 noautogroup Disable scheduler automatic task group creation.
1670 nobats [PPC] Do not use BATs for mapping kernel lowmem
1671 on "Classic" PPC cores.
1673 nocache [ARM]
1675 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1677 nodelayacct [KNL] Disable per-task delay accounting
1679 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1681 nodsp [SH] Disable hardware DSP at boot time.
1683 noefi [X86] Disable EFI runtime services support.
1685 noexec [IA-64]
1687 noexec [X86]
1688 On X86-32 available only on PAE configured kernels.
1689 noexec=on: enable non-executable mappings (default)
1690 noexec=off: disable non-executable mappings
1692 nosmep [X86]
1693 Disable SMEP (Supervisor Mode Execution Protection)
1694 even if it is supported by processor.
1696 noexec32 [X86-64]
1697 This affects only 32-bit executables.
1698 noexec32=on: enable non-executable mappings (default)
1699 read doesn't imply executable mappings
1700 noexec32=off: disable non-executable mappings
1701 read implies executable mappings
1703 nofpu [SH] Disable hardware FPU at boot time.
1705 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1706 register save and restore. The kernel will only save
1707 legacy floating-point registers on task switch.
1709 noxsave [BUGS=X86] Disables x86 extended register state save
1710 and restore using xsave. The kernel will fallback to
1711 enabling legacy floating-point and sse state.
1713 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1714 wfi(ARM) instruction doesn't work correctly and not to
1715 use it. This is also useful when using JTAG debugger.
1717 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1718 instruction doesn't work correctly and not to
1719 use it.
1721 no_file_caps Tells the kernel not to honor file capabilities. The
1722 only way then for a file to be executed with privilege
1723 is to be setuid root or executed by root.
1725 nohalt [IA-64] Tells the kernel not to use the power saving
1726 function PAL_HALT_LIGHT when idle. This increases
1727 power-consumption. On the positive side, it reduces
1728 interrupt wake-up latency, which may improve performance
1729 in certain environments such as networked servers or
1730 real-time systems.
1732 nohz= [KNL] Boottime enable/disable dynamic ticks
1733 Valid arguments: on, off
1734 Default: on
1736 noiotrap [SH] Disables trapped I/O port accesses.
1738 noirqdebug [X86-32] Disables the code which attempts to detect and
1739 disable unhandled interrupt sources.
1741 no_timer_check [X86,APIC] Disables the code which tests for
1742 broken timer IRQ sources.
1744 noisapnp [ISAPNP] Disables ISA PnP code.
1746 noinitrd [RAM] Tells the kernel not to load any configured
1747 initial RAM disk.
1749 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1750 remapping.
1751 [Deprecated - use intremap=off]
1753 nointroute [IA-64]
1755 nojitter [IA-64] Disables jitter checking for ITC timers.
1757 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1759 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1760 fault handling.
1762 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1763 steal time is computed, but won't influence scheduler
1764 behaviour
1766 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1768 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1770 noltlbs [PPC] Do not use large page/tlb entries for kernel
1771 lowmem mapping on PPC40x.
1773 nomca [IA-64] Disable machine check abort handling
1775 nomce [X86-32] Machine Check Exception
1777 nomfgpt [X86-32] Disable Multi-Function General Purpose
1778 Timer usage (for AMD Geode machines).
1780 nopat [X86] Disable PAT (page attribute table extension of
1781 pagetables) support.
1783 norandmaps Don't use address space randomization. Equivalent to
1784 echo 0 > /proc/sys/kernel/randomize_va_space
1786 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1788 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1789 with UP alternatives
1791 noresidual [PPC] Don't use residual data on PReP machines.
1793 nordrand [X86] Disable the direct use of the RDRAND
1794 instruction even if it is supported by the
1795 processor. RDRAND is still available to user
1796 space applications.
1798 noresume [SWSUSP] Disables resume and restores original swap
1799 space.
1801 no-scroll [VGA] Disables scrollback.
1802 This is required for the Braillex ib80-piezo Braille
1803 reader made by F.H. Papenmeier (Germany).
1805 nosbagart [IA-64]
1807 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1809 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1810 and disable the IO APIC. legacy for "maxcpus=0".
1812 nosoftlockup [KNL] Disable the soft-lockup detector.
1814 nosync [HW,M68K] Disables sync negotiation for all devices.
1816 notsc [BUGS=X86-32] Disable Time Stamp Counter
1818 nousb [USB] Disable the USB subsystem
1820 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1822 nowb [ARM]
1824 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1826 nptcg= [IA-64] Override max number of concurrent global TLB
1827 purges which is reported from either PAL_VM_SUMMARY or
1828 SAL PALO.
1830 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1831 could support. nr_cpus=n : n >= 1 limits the kernel to
1832 supporting 'n' processors. Later in runtime you can not
1833 use hotplug cpu feature to put more cpu back to online.
1834 just like you compile the kernel NR_CPUS=n
1836 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1838 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1839 one of ['zone', 'node', 'default'] can be specified
1840 This can be set from sysctl after boot.
1841 See Documentation/sysctl/vm.txt for details.
1843 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1844 See Documentation/debugging-via-ohci1394.txt for more
1845 info.
1847 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1848 Rather than timing out after 20 ms if an EC
1849 command is not properly ACKed, override the length
1850 of the timeout. We have interrupts disabled while
1851 waiting for the ACK, so if this is set too high
1852 interrupts *may* be lost!
1854 omap_mux= [OMAP] Override bootloader pin multiplexing.
1855 Format: <mux_mode0.mode_name=value>...
1856 For example, to override I2C bus2:
1857 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1859 oprofile.timer= [HW]
1860 Use timer interrupt instead of performance counters
1862 oprofile.cpu_type= Force an oprofile cpu type
1863 This might be useful if you have an older oprofile
1864 userland or if you want common events.
1865 Format: { arch_perfmon }
1866 arch_perfmon: [X86] Force use of architectural
1867 perfmon on Intel CPUs instead of the
1868 CPU specific event set.
1870 oops=panic Always panic on oopses. Default is to just kill the
1871 process, but there is a small probability of
1872 deadlocking the machine.
1873 This will also cause panics on machine check exceptions.
1874 Useful together with panic=30 to trigger a reboot.
1876 OSS [HW,OSS]
1877 See Documentation/sound/oss/oss-parameters.txt
1879 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1880 timeout > 0: seconds before rebooting
1881 timeout = 0: wait forever
1882 timeout < 0: reboot immediately
1883 Format: <timeout>
1885 parkbd.port= [HW] Parallel port number the keyboard adapter is
1886 connected to, default is 0.
1887 Format: <parport#>
1888 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1889 0 for XT, 1 for AT (default is AT).
1890 Format: <mode>
1892 parport= [HW,PPT] Specify parallel ports. 0 disables.
1893 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1894 Use 'auto' to force the driver to use any
1895 IRQ/DMA settings detected (the default is to
1896 ignore detected IRQ/DMA settings because of
1897 possible conflicts). You can specify the base
1898 address, IRQ, and DMA settings; IRQ and DMA
1899 should be numbers, or 'auto' (for using detected
1900 settings on that particular port), or 'nofifo'
1901 (to avoid using a FIFO even if it is detected).
1902 Parallel ports are assigned in the order they
1903 are specified on the command line, starting
1904 with parport0.
1906 parport_init_mode= [HW,PPT]
1907 Configure VIA parallel port to operate in
1908 a specific mode. This is necessary on Pegasos
1909 computer where firmware has no options for setting
1910 up parallel port mode and sets it to spp.
1911 Currently this function knows 686a and 8231 chips.
1912 Format: [spp|ps2|epp|ecp|ecpepp]
1914 pause_on_oops=
1915 Halt all CPUs after the first oops has been printed for
1916 the specified number of seconds. This is to be used if
1917 your oopses keep scrolling off the screen.
1919 pcbit= [HW,ISDN]
1921 pcd. [PARIDE]
1922 See header of drivers/block/paride/pcd.c.
1923 See also Documentation/blockdev/paride.txt.
1925 pci=option[,option...] [PCI] various PCI subsystem options:
1926 earlydump [X86] dump PCI config space before the kernel
1927 changes anything
1928 off [X86] don't probe for the PCI bus
1929 bios [X86-32] force use of PCI BIOS, don't access
1930 the hardware directly. Use this if your machine
1931 has a non-standard PCI host bridge.
1932 nobios [X86-32] disallow use of PCI BIOS, only direct
1933 hardware access methods are allowed. Use this
1934 if you experience crashes upon bootup and you
1935 suspect they are caused by the BIOS.
1936 conf1 [X86] Force use of PCI Configuration
1937 Mechanism 1.
1938 conf2 [X86] Force use of PCI Configuration
1939 Mechanism 2.
1940 noaer [PCIE] If the PCIEAER kernel config parameter is
1941 enabled, this kernel boot option can be used to
1942 disable the use of PCIE advanced error reporting.
1943 nodomains [PCI] Disable support for multiple PCI
1944 root domains (aka PCI segments, in ACPI-speak).
1945 nommconf [X86] Disable use of MMCONFIG for PCI
1946 Configuration
1947 check_enable_amd_mmconf [X86] check for and enable
1948 properly configured MMIO access to PCI
1949 config space on AMD family 10h CPU
1950 nomsi [MSI] If the PCI_MSI kernel config parameter is
1951 enabled, this kernel boot option can be used to
1952 disable the use of MSI interrupts system-wide.
1953 noioapicquirk [APIC] Disable all boot interrupt quirks.
1954 Safety option to keep boot IRQs enabled. This
1955 should never be necessary.
1956 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1957 primary IO-APIC for bridges that cannot disable
1958 boot IRQs. This fixes a source of spurious IRQs
1959 when the system masks IRQs.
1960 noioapicreroute [APIC] Disable workaround that uses the
1961 boot IRQ equivalent of an IRQ that connects to
1962 a chipset where boot IRQs cannot be disabled.
1963 The opposite of ioapicreroute.
1964 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1965 routing table. These calls are known to be buggy
1966 on several machines and they hang the machine
1967 when used, but on other computers it's the only
1968 way to get the interrupt routing table. Try
1969 this option if the kernel is unable to allocate
1970 IRQs or discover secondary PCI buses on your
1971 motherboard.
1972 rom [X86] Assign address space to expansion ROMs.
1973 Use with caution as certain devices share
1974 address decoders between ROMs and other
1975 resources.
1976 norom [X86] Do not assign address space to
1977 expansion ROMs that do not already have
1978 BIOS assigned address ranges.
1979 nobar [X86] Do not assign address space to the
1980 BARs that weren't assigned by the BIOS.
1981 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1982 assigned automatically to PCI devices. You can
1983 make the kernel exclude IRQs of your ISA cards
1984 this way.
1985 pirqaddr=0xAAAAA [X86] Specify the physical address
1986 of the PIRQ table (normally generated
1987 by the BIOS) if it is outside the
1988 F0000h-100000h range.
1989 lastbus=N [X86] Scan all buses thru bus #N. Can be
1990 useful if the kernel is unable to find your
1991 secondary buses and you want to tell it
1992 explicitly which ones they are.
1993 assign-busses [X86] Always assign all PCI bus
1994 numbers ourselves, overriding
1995 whatever the firmware may have done.
1996 usepirqmask [X86] Honor the possible IRQ mask stored
1997 in the BIOS $PIR table. This is needed on
1998 some systems with broken BIOSes, notably
1999 some HP Pavilion N5400 and Omnibook XE3
2000 notebooks. This will have no effect if ACPI
2001 IRQ routing is enabled.
2002 noacpi [X86] Do not use ACPI for IRQ routing
2003 or for PCI scanning.
2004 use_crs [X86] Use PCI host bridge window information
2005 from ACPI. On BIOSes from 2008 or later, this
2006 is enabled by default. If you need to use this,
2007 please report a bug.
2008 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2009 If you need to use this, please report a bug.
2010 routeirq Do IRQ routing for all PCI devices.
2011 This is normally done in pci_enable_device(),
2012 so this option is a temporary workaround
2013 for broken drivers that don't call it.
2014 skip_isa_align [X86] do not align io start addr, so can
2015 handle more pci cards
2016 firmware [ARM] Do not re-enumerate the bus but instead
2017 just use the configuration from the
2018 bootloader. This is currently used on
2019 IXP2000 systems where the bus has to be
2020 configured a certain way for adjunct CPUs.
2021 noearly [X86] Don't do any early type 1 scanning.
2022 This might help on some broken boards which
2023 machine check when some devices' config space
2024 is read. But various workarounds are disabled
2025 and some IOMMU drivers will not work.
2026 bfsort Sort PCI devices into breadth-first order.
2027 This sorting is done to get a device
2028 order compatible with older (<= 2.4) kernels.
2029 nobfsort Don't sort PCI devices into breadth-first order.
2030 cbiosize=nn[KMG] The fixed amount of bus space which is
2031 reserved for the CardBus bridge's IO window.
2032 The default value is 256 bytes.
2033 cbmemsize=nn[KMG] The fixed amount of bus space which is
2034 reserved for the CardBus bridge's memory
2035 window. The default value is 64 megabytes.
2036 resource_alignment=
2037 Format:
2038 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2039 Specifies alignment and device to reassign
2040 aligned memory resources.
2041 If <order of align> is not specified,
2042 PAGE_SIZE is used as alignment.
2043 PCI-PCI bridge can be specified, if resource
2044 windows need to be expanded.
2045 ecrc= Enable/disable PCIe ECRC (transaction layer
2046 end-to-end CRC checking).
2047 bios: Use BIOS/firmware settings. This is the
2048 the default.
2049 off: Turn ECRC off
2050 on: Turn ECRC on.
2051 realloc reallocate PCI resources if allocations done by BIOS
2052 are erroneous.
2054 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2055 Management.
2056 off Disable ASPM.
2057 force Enable ASPM even on devices that claim not to support it.
2058 WARNING: Forcing ASPM on may cause system lockups.
2060 pcie_ports= [PCIE] PCIe ports handling:
2061 auto Ask the BIOS whether or not to use native PCIe services
2062 associated with PCIe ports (PME, hot-plug, AER). Use
2063 them only if that is allowed by the BIOS.
2064 native Use native PCIe services associated with PCIe ports
2065 unconditionally.
2066 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2067 ports driver.
2069 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2070 nomsi Do not use MSI for native PCIe PME signaling (this makes
2071 all PCIe root ports use INTx for all services).
2073 pcmv= [HW,PCMCIA] BadgePAD 4
2075 pd. [PARIDE]
2076 See Documentation/blockdev/paride.txt.
2078 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2079 boot time.
2080 Format: { 0 | 1 }
2081 See arch/parisc/kernel/pdc_chassis.c
2083 percpu_alloc= Select which percpu first chunk allocator to use.
2084 Currently supported values are "embed" and "page".
2085 Archs may support subset or none of the selections.
2086 See comments in mm/percpu.c for details on each
2087 allocator. This parameter is primarily for debugging
2088 and performance comparison.
2090 pf. [PARIDE]
2091 See Documentation/blockdev/paride.txt.
2093 pg. [PARIDE]
2094 See Documentation/blockdev/paride.txt.
2096 pirq= [SMP,APIC] Manual mp-table setup
2097 See Documentation/x86/i386/IO-APIC.txt.
2099 plip= [PPT,NET] Parallel port network link
2100 Format: { parport<nr> | timid | 0 }
2101 See also Documentation/parport.txt.
2103 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2104 Override pmtimer IOPort with a hex value.
2105 e.g. pmtmr=0x508
2107 pnp.debug [PNP]
2108 Enable PNP debug messages. This depends on the
2109 CONFIG_PNP_DEBUG_MESSAGES option.
2111 pnpacpi= [ACPI]
2112 { off }
2114 pnpbios= [ISAPNP]
2115 { on | off | curr | res | no-curr | no-res }
2117 pnp_reserve_irq=
2118 [ISAPNP] Exclude IRQs for the autoconfiguration
2120 pnp_reserve_dma=
2121 [ISAPNP] Exclude DMAs for the autoconfiguration
2123 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2124 Ranges are in pairs (I/O port base and size).
2126 pnp_reserve_mem=
2127 [ISAPNP] Exclude memory regions for the
2128 autoconfiguration.
2129 Ranges are in pairs (memory base and size).
2131 ports= [IP_VS_FTP] IPVS ftp helper module
2132 Default is 21.
2133 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2134 may be specified.
2135 Format: <port>,<port>....
2137 print-fatal-signals=
2138 [KNL] debug: print fatal signals
2140 If enabled, warn about various signal handling
2141 related application anomalies: too many signals,
2142 too many POSIX.1 timers, fatal signals causing a
2143 coredump - etc.
2145 If you hit the warning due to signal overflow,
2146 you might want to try "ulimit -i unlimited".
2148 default: off.
2150 printk.time= Show timing data prefixed to each printk message line
2151 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2153 processor.max_cstate= [HW,ACPI]
2154 Limit processor to maximum C-state
2155 max_cstate=9 overrides any DMI blacklist limit.
2157 processor.nocst [HW,ACPI]
2158 Ignore the _CST method to determine C-states,
2159 instead using the legacy FADT method
2161 profile= [KNL] Enable kernel profiling via /proc/profile
2162 Format: [schedule,]<number>
2163 Param: "schedule" - profile schedule points.
2164 Param: <number> - step/bucket size as a power of 2 for
2165 statistical time based profiling.
2166 Param: "sleep" - profile D-state sleeping (millisecs).
2167 Requires CONFIG_SCHEDSTATS
2168 Param: "kvm" - profile VM exits.
2170 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2171 before loading.
2172 See Documentation/blockdev/ramdisk.txt.
2174 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2175 probe for; one of (bare|imps|exps|lifebook|any).
2176 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2177 per second.
2178 psmouse.resetafter= [HW,MOUSE]
2179 Try to reset the device after so many bad packets
2180 (0 = never).
2181 psmouse.resolution=
2182 [HW,MOUSE] Set desired mouse resolution, in dpi.
2183 psmouse.smartscroll=
2184 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2185 0 = disabled, 1 = enabled (default).
2187 pstore.backend= Specify the name of the pstore backend to use
2189 pt. [PARIDE]
2190 See Documentation/blockdev/paride.txt.
2192 pty.legacy_count=
2193 [KNL] Number of legacy pty's. Overwrites compiled-in
2194 default number.
2196 quiet [KNL] Disable most log messages
2198 r128= [HW,DRM]
2200 raid= [HW,RAID]
2201 See Documentation/md.txt.
2203 ramdisk_blocksize= [RAM]
2204 See Documentation/blockdev/ramdisk.txt.
2206 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2207 See Documentation/blockdev/ramdisk.txt.
2209 rcupdate.blimit= [KNL,BOOT]
2210 Set maximum number of finished RCU callbacks to process
2211 in one batch.
2213 rcupdate.qhimark= [KNL,BOOT]
2214 Set threshold of queued
2215 RCU callbacks over which batch limiting is disabled.
2217 rcupdate.qlowmark= [KNL,BOOT]
2218 Set threshold of queued RCU callbacks below which
2219 batch limiting is re-enabled.
2221 rdinit= [KNL]
2222 Format: <full_path>
2223 Run specified binary instead of /init from the ramdisk,
2224 used for early userspace startup. See initrd.
2226 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2227 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2228 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2230 relax_domain_level=
2231 [KNL, SMP] Set scheduler's default relax_domain_level.
2232 See Documentation/cgroups/cpusets.txt.
2234 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2236 reservetop= [X86-32]
2237 Format: nn[KMG]
2238 Reserves a hole at the top of the kernel virtual
2239 address space.
2241 reservelow= [X86]
2242 Format: nn[K]
2243 Set the amount of memory to reserve for BIOS at
2244 the bottom of the address space.
2246 reset_devices [KNL] Force drivers to reset the underlying device
2247 during initialization.
2249 resume= [SWSUSP]
2250 Specify the partition device for software suspend
2252 resume_offset= [SWSUSP]
2253 Specify the offset from the beginning of the partition
2254 given by "resume=" at which the swap header is located,
2255 in <PAGE_SIZE> units (needed only for swap files).
2256 See Documentation/power/swsusp-and-swap-files.txt
2258 hibernate= [HIBERNATION]
2259 noresume Don't check if there's a hibernation image
2260 present during boot.
2261 nocompress Don't compress/decompress hibernation images.
2263 retain_initrd [RAM] Keep initrd memory after extraction
2265 rhash_entries= [KNL,NET]
2266 Set number of hash buckets for route cache
2268 riscom8= [HW,SERIAL]
2269 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2271 ro [KNL] Mount root device read-only on boot
2273 root= [KNL] Root filesystem
2274 See name_to_dev_t comment in init/do_mounts.c.
2276 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2277 mount the root filesystem
2279 rootflags= [KNL] Set root filesystem mount option string
2281 rootfstype= [KNL] Set root filesystem type
2283 rootwait [KNL] Wait (indefinitely) for root device to show up.
2284 Useful for devices that are detected asynchronously
2285 (e.g. USB and MMC devices).
2287 rw [KNL] Mount root device read-write on boot
2289 S [KNL] Run init in single mode
2291 sa1100ir [NET]
2292 See drivers/net/irda/sa1100_ir.c.
2294 sbni= [NET] Granch SBNI12 leased line adapter
2296 sched_debug [KNL] Enables verbose scheduler debug messages.
2298 security= [SECURITY] Choose a security module to enable at boot.
2299 If this boot parameter is not specified, only the first
2300 security module asking for security registration will be
2301 loaded. An invalid security module name will be treated
2302 as if no module has been chosen.
2304 selinux= [SELINUX] Disable or enable SELinux at boot time.
2305 Format: { "0" | "1" }
2306 See security/selinux/Kconfig help text.
2307 0 -- disable.
2308 1 -- enable.
2309 Default value is set via kernel config option.
2310 If enabled at boot time, /selinux/disable can be used
2311 later to disable prior to initial policy load.
2313 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2314 Format: { "0" | "1" }
2315 See security/apparmor/Kconfig help text
2316 0 -- disable.
2317 1 -- enable.
2318 Default value is set via kernel config option.
2320 serialnumber [BUGS=X86-32]
2322 shapers= [NET]
2323 Maximal number of shapers.
2325 show_msr= [x86] show boot-time MSR settings
2326 Format: { <integer> }
2327 Show boot-time (BIOS-initialized) MSR settings.
2328 The parameter means the number of CPUs to show,
2329 for example 1 means boot CPU only.
2331 simeth= [IA-64]
2332 simscsi=
2334 slram= [HW,MTD]
2336 slub_debug[=options[,slabs]] [MM, SLUB]
2337 Enabling slub_debug allows one to determine the
2338 culprit if slab objects become corrupted. Enabling
2339 slub_debug can create guard zones around objects and
2340 may poison objects when not in use. Also tracks the
2341 last alloc / free. For more information see
2342 Documentation/vm/slub.txt.
2344 slub_max_order= [MM, SLUB]
2345 Determines the maximum allowed order for slabs.
2346 A high setting may cause OOMs due to memory
2347 fragmentation. For more information see
2348 Documentation/vm/slub.txt.
2350 slub_min_objects= [MM, SLUB]
2351 The minimum number of objects per slab. SLUB will
2352 increase the slab order up to slub_max_order to
2353 generate a sufficiently large slab able to contain
2354 the number of objects indicated. The higher the number
2355 of objects the smaller the overhead of tracking slabs
2356 and the less frequently locks need to be acquired.
2357 For more information see Documentation/vm/slub.txt.
2359 slub_min_order= [MM, SLUB]
2360 Determines the mininum page order for slabs. Must be
2361 lower than slub_max_order.
2362 For more information see Documentation/vm/slub.txt.
2364 slub_nomerge [MM, SLUB]
2365 Disable merging of slabs with similar size. May be
2366 necessary if there is some reason to distinguish
2367 allocs to different slabs. Debug options disable
2368 merging on their own.
2369 For more information see Documentation/vm/slub.txt.
2371 smart2= [HW]
2372 Format: <io1>[,<io2>[,...,<io8>]]
2374 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2375 attempt to substitute SMP alternatives once at boot.
2377 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2378 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2379 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2380 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2381 smsc-ircc2.ircc_irq= [HW] IRQ line
2382 smsc-ircc2.ircc_dma= [HW] DMA channel
2383 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2384 0: Toshiba Satellite 1800 (GP data pin select)
2385 1: Fast pin select (default)
2386 2: ATC IRMode
2388 softlockup_panic=
2389 [KNL] Should the soft-lockup detector generate panics.
2390 Format: <integer>
2392 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2393 See Documentation/sonypi.txt
2395 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2396 See Documentation/serial/specialix.txt.
2398 spia_io_base= [HW,MTD]
2399 spia_fio_base=
2400 spia_pedr=
2401 spia_peddr=
2403 stacktrace [FTRACE]
2404 Enabled the stack tracer on boot up.
2406 sti= [PARISC,HW]
2407 Format: <num>
2408 Set the STI (builtin display/keyboard on the HP-PARISC
2409 machines) console (graphic card) which should be used
2410 as the initial boot-console.
2411 See also comment in drivers/video/console/sticore.c.
2413 sti_font= [HW]
2414 See comment in drivers/video/console/sticore.c.
2416 stifb= [HW]
2417 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2419 sunrpc.min_resvport=
2420 sunrpc.max_resvport=
2421 [NFS,SUNRPC]
2422 SunRPC servers often require that client requests
2423 originate from a privileged port (i.e. a port in the
2424 range 0 < portnr < 1024).
2425 An administrator who wishes to reserve some of these
2426 ports for other uses may adjust the range that the
2427 kernel's sunrpc client considers to be privileged
2428 using these two parameters to set the minimum and
2429 maximum port values.
2431 sunrpc.pool_mode=
2432 [NFS]
2433 Control how the NFS server code allocates CPUs to
2434 service thread pools. Depending on how many NICs
2435 you have and where their interrupts are bound, this
2436 option will affect which CPUs will do NFS serving.
2437 Note: this parameter cannot be changed while the
2438 NFS server is running.
2440 auto the server chooses an appropriate mode
2441 automatically using heuristics
2442 global a single global pool contains all CPUs
2443 percpu one pool for each CPU
2444 pernode one pool for each NUMA node (equivalent
2445 to global on non-NUMA machines)
2447 sunrpc.tcp_slot_table_entries=
2448 sunrpc.udp_slot_table_entries=
2449 [NFS,SUNRPC]
2450 Sets the upper limit on the number of simultaneous
2451 RPC calls that can be sent from the client to a
2452 server. Increasing these values may allow you to
2453 improve throughput, but will also increase the
2454 amount of memory reserved for use by the client.
2456 swapaccount[=0|1]
2457 [KNL] Enable accounting of swap in memory resource
2458 controller if no parameter or 1 is given or disable
2459 it if 0 is given (See Documentation/cgroups/memory.txt)
2461 swiotlb= [IA-64] Number of I/O TLB slabs
2463 switches= [HW,M68k]
2465 sysfs.deprecated=0|1 [KNL]
2466 Enable/disable old style sysfs layout for old udev
2467 on older distributions. When this option is enabled
2468 very new udev will not work anymore. When this option
2469 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2470 in older udev will not work anymore.
2471 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2472 the kernel configuration.
2474 sysrq_always_enabled
2475 [KNL]
2476 Ignore sysrq setting - this boot parameter will
2477 neutralize any effect of /proc/sys/kernel/sysrq.
2478 Useful for debugging.
2480 tdfx= [HW,DRM]
2482 test_suspend= [SUSPEND]
2483 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2484 standby suspend) as the system sleep state to briefly
2485 enter during system startup. The system is woken from
2486 this state using a wakeup-capable RTC alarm.
2488 thash_entries= [KNL,NET]
2489 Set number of hash buckets for TCP connection
2491 thermal.act= [HW,ACPI]
2492 -1: disable all active trip points in all thermal zones
2493 <degrees C>: override all lowest active trip points
2495 thermal.crt= [HW,ACPI]
2496 -1: disable all critical trip points in all thermal zones
2497 <degrees C>: override all critical trip points
2499 thermal.nocrt= [HW,ACPI]
2500 Set to disable actions on ACPI thermal zone
2501 critical and hot trip points.
2503 thermal.off= [HW,ACPI]
2504 1: disable ACPI thermal control
2506 thermal.psv= [HW,ACPI]
2507 -1: disable all passive trip points
2508 <degrees C>: override all passive trip points to this
2509 value
2511 thermal.tzp= [HW,ACPI]
2512 Specify global default ACPI thermal zone polling rate
2513 <deci-seconds>: poll all this frequency
2514 0: no polling (default)
2516 threadirqs [KNL]
2517 Force threading of all interrupt handlers except those
2518 marked explicitely IRQF_NO_THREAD.
2520 topology= [S390]
2521 Format: {off | on}
2522 Specify if the kernel should make use of the cpu
2523 topology information if the hardware supports this.
2524 The scheduler will make use of this information and
2525 e.g. base its process migration decisions on it.
2526 Default is on.
2528 tp720= [HW,PS2]
2530 tpm_suspend_pcr=[HW,TPM]
2531 Format: integer pcr id
2532 Specify that at suspend time, the tpm driver
2533 should extend the specified pcr with zeros,
2534 as a workaround for some chips which fail to
2535 flush the last written pcr on TPM_SaveState.
2536 This will guarantee that all the other pcrs
2537 are saved.
2539 trace_buf_size=nn[KMG]
2540 [FTRACE] will set tracing buffer size.
2542 trace_event=[event-list]
2543 [FTRACE] Set and start specified trace events in order
2544 to facilitate early boot debugging.
2545 See also Documentation/trace/events.txt
2547 tsc= Disable clocksource stability checks for TSC.
2548 Format: <string>
2549 [x86] reliable: mark tsc clocksource as reliable, this
2550 disables clocksource verification at runtime, as well
2551 as the stability checks done at bootup. Used to enable
2552 high-resolution timer mode on older hardware, and in
2553 virtualized environment.
2554 [x86] noirqtime: Do not use TSC to do irq accounting.
2555 Used to run time disable IRQ_TIME_ACCOUNTING on any
2556 platforms where RDTSC is slow and this accounting
2557 can add overhead.
2559 turbografx.map[2|3]= [HW,JOY]
2560 TurboGraFX parallel port interface
2561 Format:
2562 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2563 See also Documentation/input/joystick-parport.txt
2565 udbg-immortal [PPC] When debugging early kernel crashes that
2566 happen after console_init() and before a proper
2567 console driver takes over, this boot options might
2568 help "seeing" what's going on.
2570 uhash_entries= [KNL,NET]
2571 Set number of hash buckets for UDP/UDP-Lite connections
2573 uhci-hcd.ignore_oc=
2574 [USB] Ignore overcurrent events (default N).
2575 Some badly-designed motherboards generate lots of
2576 bogus events, for ports that aren't wired to
2577 anything. Set this parameter to avoid log spamming.
2578 Note that genuine overcurrent events won't be
2579 reported either.
2581 unknown_nmi_panic
2582 [X86] Cause panic on unknown NMI.
2584 usbcore.authorized_default=
2585 [USB] Default USB device authorization:
2586 (default -1 = authorized except for wireless USB,
2587 0 = not authorized, 1 = authorized)
2589 usbcore.autosuspend=
2590 [USB] The autosuspend time delay (in seconds) used
2591 for newly-detected USB devices (default 2). This
2592 is the time required before an idle device will be
2593 autosuspended. Devices for which the delay is set
2594 to a negative value won't be autosuspended at all.
2596 usbcore.usbfs_snoop=
2597 [USB] Set to log all usbfs traffic (default 0 = off).
2599 usbcore.blinkenlights=
2600 [USB] Set to cycle leds on hubs (default 0 = off).
2602 usbcore.old_scheme_first=
2603 [USB] Start with the old device initialization
2604 scheme (default 0 = off).
2606 usbcore.use_both_schemes=
2607 [USB] Try the other device initialization scheme
2608 if the first one fails (default 1 = enabled).
2610 usbcore.initial_descriptor_timeout=
2611 [USB] Specifies timeout for the initial 64-byte
2612 USB_REQ_GET_DESCRIPTOR request in milliseconds
2613 (default 5000 = 5.0 seconds).
2615 usbhid.mousepoll=
2616 [USBHID] The interval which mice are to be polled at.
2618 usb-storage.delay_use=
2619 [UMS] The delay in seconds before a new device is
2620 scanned for Logical Units (default 5).
2622 usb-storage.quirks=
2623 [UMS] A list of quirks entries to supplement or
2624 override the built-in unusual_devs list. List
2625 entries are separated by commas. Each entry has
2626 the form VID:PID:Flags where VID and PID are Vendor
2627 and Product ID values (4-digit hex numbers) and
2628 Flags is a set of characters, each corresponding
2629 to a common usb-storage quirk flag as follows:
2630 a = SANE_SENSE (collect more than 18 bytes
2631 of sense data);
2632 b = BAD_SENSE (don't collect more than 18
2633 bytes of sense data);
2634 c = FIX_CAPACITY (decrease the reported
2635 device capacity by one sector);
2636 d = NO_READ_DISC_INFO (don't use
2637 READ_DISC_INFO command);
2638 e = NO_READ_CAPACITY_16 (don't use
2639 READ_CAPACITY_16 command);
2640 h = CAPACITY_HEURISTICS (decrease the
2641 reported device capacity by one
2642 sector if the number is odd);
2643 i = IGNORE_DEVICE (don't bind to this
2644 device);
2645 l = NOT_LOCKABLE (don't try to lock and
2646 unlock ejectable media);
2647 m = MAX_SECTORS_64 (don't transfer more
2648 than 64 sectors = 32 KB at a time);
2649 n = INITIAL_READ10 (force a retry of the
2650 initial READ(10) command);
2651 o = CAPACITY_OK (accept the capacity
2652 reported by the device);
2653 r = IGNORE_RESIDUE (the device reports
2654 bogus residue values);
2655 s = SINGLE_LUN (the device has only one
2656 Logical Unit);
2657 w = NO_WP_DETECT (don't test whether the
2658 medium is write-protected).
2659 Example: quirks=0419:aaf5:rl,0421:0433:rc
2661 user_debug= [KNL,ARM]
2662 Format: <int>
2663 See arch/arm/Kconfig.debug help text.
2664 1 - undefined instruction events
2665 2 - system calls
2666 4 - invalid data aborts
2667 8 - SIGSEGV faults
2668 16 - SIGBUS faults
2669 Example: user_debug=31
2671 userpte=
2672 [X86] Flags controlling user PTE allocations.
2674 nohigh = do not allocate PTE pages in
2675 HIGHMEM regardless of setting
2676 of CONFIG_HIGHPTE.
2678 vdso= [X86,SH]
2679 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2680 vdso=1: enable VDSO (default)
2681 vdso=0: disable VDSO mapping
2683 vdso32= [X86]
2684 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2685 vdso32=1: enable 32-bit VDSO (default)
2686 vdso32=0: disable 32-bit VDSO mapping
2688 vector= [IA-64,SMP]
2689 vector=percpu: enable percpu vector domain
2691 video= [FB] Frame buffer configuration
2692 See Documentation/fb/modedb.txt.
2694 vga= [BOOT,X86-32] Select a particular video mode
2695 See Documentation/x86/boot.txt and
2696 Documentation/svga.txt.
2697 Use vga=ask for menu.
2698 This is actually a boot loader parameter; the value is
2699 passed to the kernel using a special protocol.
2701 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2702 size of <nn>. This can be used to increase the
2703 minimum size (128MB on x86). It can also be used to
2704 decrease the size and leave more room for directly
2705 mapped kernel RAM.
2707 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2708 Format: <command>
2710 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2711 Format: <command>
2713 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2714 Format: <command>
2716 vsyscall= [X86-64]
2717 Controls the behavior of vsyscalls (i.e. calls to
2718 fixed addresses of 0xffffffffff600x00 from legacy
2719 code). Most statically-linked binaries and older
2720 versions of glibc use these calls. Because these
2721 functions are at fixed addresses, they make nice
2722 targets for exploits that can control RIP.
2724 emulate [default] Vsyscalls turn into traps and are
2725 emulated reasonably safely.
2727 native Vsyscalls are native syscall instructions.
2728 This is a little bit faster than trapping
2729 and makes a few dynamic recompilers work
2730 better than they would in emulation mode.
2731 It also makes exploits much easier to write.
2733 none Vsyscalls don't work at all. This makes
2734 them quite hard to use for exploits but
2735 might break your system.
2737 vt.cur_default= [VT] Default cursor shape.
2738 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2739 the parameters of the <Esc>[?A;B;Cc escape sequence;
2740 see VGA-softcursor.txt. Default: 2 = underline.
2742 vt.default_blu= [VT]
2743 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2744 Change the default blue palette of the console.
2745 This is a 16-member array composed of values
2746 ranging from 0-255.
2748 vt.default_grn= [VT]
2749 Format: <green0>,<green1>,<green2>,...,<green15>
2750 Change the default green palette of the console.
2751 This is a 16-member array composed of values
2752 ranging from 0-255.
2754 vt.default_red= [VT]
2755 Format: <red0>,<red1>,<red2>,...,<red15>
2756 Change the default red palette of the console.
2757 This is a 16-member array composed of values
2758 ranging from 0-255.
2760 vt.default_utf8=
2761 [VT]
2762 Format=<0|1>
2763 Set system-wide default UTF-8 mode for all tty's.
2764 Default is 1, i.e. UTF-8 mode is enabled for all
2765 newly opened terminals.
2767 vt.global_cursor_default=
2768 [VT]
2769 Format=<-1|0|1>
2770 Set system-wide default for whether a cursor
2771 is shown on new VTs. Default is -1,
2772 i.e. cursors will be created by default unless
2773 overridden by individual drivers. 0 will hide
2774 cursors, 1 will display them.
2776 watchdog timers [HW,WDT] For information on watchdog timers,
2777 see Documentation/watchdog/watchdog-parameters.txt
2778 or other driver-specific files in the
2779 Documentation/watchdog/ directory.
2781 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2782 default x2apic cluster mode on platforms
2783 supporting x2apic.
2785 x86_mrst_timer= [X86-32,APBT]
2786 Choose timer option for x86 Moorestown MID platform.
2787 Two valid options are apbt timer only and lapic timer
2788 plus one apbt timer for broadcast timer.
2789 x86_mrst_timer=apbt_only | lapic_and_apbt
2791 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2792 xd_geo= See header of drivers/block/xd.c.
2794 xen_emul_unplug= [HW,X86,XEN]
2795 Unplug Xen emulated devices
2796 Format: [unplug0,][unplug1]
2797 ide-disks -- unplug primary master IDE devices
2798 aux-ide-disks -- unplug non-primary-master IDE devices
2799 nics -- unplug network devices
2800 all -- unplug all emulated devices (NICs and IDE disks)
2801 unnecessary -- unplugging emulated devices is
2802 unnecessary even if the host did not respond to
2803 the unplug protocol
2804 never -- do not unplug even if version check succeeds
2806 xirc2ps_cs= [NET,PCMCIA]
2807 Format:
2808 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2810 ______________________________________________________________________
2812 TODO:
2814 Add more DRM drivers.