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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 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MCA MCA bus support is enabled.
74 MDA MDA console support is enabled.
75 MIPS MIPS architecture is enabled.
76 MOUSE Appropriate mouse support is enabled.
77 MSI Message Signaled Interrupts (PCI).
78 MTD MTD (Memory Technology Device) support is enabled.
79 NET Appropriate network support is enabled.
80 NUMA NUMA support is enabled.
81 NFS Appropriate NFS support is enabled.
82 OSS OSS sound support is enabled.
83 PV_OPS A paravirtualized kernel is enabled.
84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
85 PARISC The PA-RISC architecture is enabled.
86 PCI PCI bus support is enabled.
87 PCIE PCI Express support is enabled.
88 PCMCIA The PCMCIA subsystem is enabled.
89 PNP Plug & Play support is enabled.
90 PPC PowerPC architecture is enabled.
91 PPT Parallel port support is enabled.
92 PS2 Appropriate PS/2 support is enabled.
93 RAM RAM disk support is enabled.
94 S390 S390 architecture is enabled.
95 SCSI Appropriate SCSI support is enabled.
96 A lot of drivers have their options described inside
97 the Documentation/scsi/ sub-directory.
98 SECURITY Different security models are enabled.
99 SELINUX SELinux support is enabled.
100 APPARMOR AppArmor support is enabled.
101 SERIAL Serial support is enabled.
102 SH SuperH architecture is enabled.
103 SMP The kernel is an SMP kernel.
104 SPARC Sparc architecture is enabled.
105 SWSUSP Software suspend (hibernation) is enabled.
106 SUSPEND System suspend states are enabled.
107 TPM TPM drivers are enabled.
108 TS Appropriate touchscreen support is enabled.
109 UMS USB Mass Storage support is enabled.
110 USB USB support is enabled.
111 USBHID USB Human Interface Device support is enabled.
112 V4L Video For Linux support is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 amd_iommu= [HW,X86-84]
311 Pass parameters to the AMD IOMMU driver in the system.
312 Possible values are:
313 fullflush - enable flushing of IO/TLB entries when
314 they are unmapped. Otherwise they are
315 flushed before they will be reused, which
316 is a lot of faster
317 off - do not initialize any AMD IOMMU found in
318 the system
320 amijoy.map= [HW,JOY] Amiga joystick support
321 Map of devices attached to JOY0DAT and JOY1DAT
322 Format: <a>,<b>
323 See also Documentation/input/joystick.txt
325 analog.map= [HW,JOY] Analog joystick and gamepad support
326 Specifies type or capabilities of an analog joystick
327 connected to one of 16 gameports
328 Format: <type1>,<type2>,..<type16>
330 apc= [HW,SPARC]
331 Power management functions (SPARCstation-4/5 + deriv.)
332 Format: noidle
333 Disable APC CPU standby support. SPARCstation-Fox does
334 not play well with APC CPU idle - disable it if you have
335 APC and your system crashes randomly.
337 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
338 Change the output verbosity whilst booting
339 Format: { quiet (default) | verbose | debug }
340 Change the amount of debugging information output
341 when initialising the APIC and IO-APIC components.
343 autoconf= [IPV6]
344 See Documentation/networking/ipv6.txt.
346 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
347 Limit apic dumping. The parameter defines the maximal
348 number of local apics being dumped. Also it is possible
349 to set it to "all" by meaning -- no limit here.
350 Format: { 1 (default) | 2 | ... | all }.
351 The parameter valid if only apic=debug or
352 apic=verbose is specified.
353 Example: apic=debug show_lapic=all
355 apm= [APM] Advanced Power Management
356 See header of arch/x86/kernel/apm_32.c.
358 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
359 Format: <io>,<irq>,<nodeID>
361 ataflop= [HW,M68k]
363 atarimouse= [HW,MOUSE] Atari Mouse
365 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
366 EzKey and similar keyboards
368 atkbd.reset= [HW] Reset keyboard during initialization
370 atkbd.set= [HW] Select keyboard code set
371 Format: <int> (2 = AT (default), 3 = PS/2)
373 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
374 keyboards
376 atkbd.softraw= [HW] Choose between synthetic and real raw mode
377 Format: <bool> (0 = real, 1 = synthetic (default))
379 atkbd.softrepeat= [HW]
380 Use software keyboard repeat
382 autotest [IA-64]
384 baycom_epp= [HW,AX25]
385 Format: <io>,<mode>
387 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
388 Format: <io>,<mode>
389 See header of drivers/net/hamradio/baycom_par.c.
391 baycom_ser_fdx= [HW,AX25]
392 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
393 Format: <io>,<irq>,<mode>[,<baud>]
394 See header of drivers/net/hamradio/baycom_ser_fdx.c.
396 baycom_ser_hdx= [HW,AX25]
397 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
398 Format: <io>,<irq>,<mode>
399 See header of drivers/net/hamradio/baycom_ser_hdx.c.
401 boot_delay= Milliseconds to delay each printk during boot.
402 Values larger than 10 seconds (10000) are changed to
403 no delay (0).
404 Format: integer
406 bootmem_debug [KNL] Enable bootmem allocator debug messages.
408 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
409 bttv.radio= Most important insmod options are available as
410 kernel args too.
411 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
412 bttv.tuner=
414 bulk_remove=off [PPC] This parameter disables the use of the pSeries
415 firmware feature for flushing multiple hpte entries
416 at a time.
418 c101= [NET] Moxa C101 synchronous serial card
420 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
421 Sometimes CPU hardware bugs make them report the cache
422 size incorrectly. The kernel will attempt work arounds
423 to fix known problems, but for some CPUs it is not
424 possible to determine what the correct size should be.
425 This option provides an override for these situations.
427 capability.disable=
428 [SECURITY] Disable capabilities. This would normally
429 be used only if an alternative security model is to be
430 configured. Potentially dangerous and should only be
431 used if you are entirely sure of the consequences.
433 ccw_timeout_log [S390]
434 See Documentation/s390/CommonIO for details.
436 cgroup_disable= [KNL] Disable a particular controller
437 Format: {name of the controller(s) to disable}
438 {Currently supported controllers - "memory"}
440 checkreqprot [SELINUX] Set initial checkreqprot flag value.
441 Format: { "0" | "1" }
442 See security/selinux/Kconfig help text.
443 0 -- check protection applied by kernel (includes
444 any implied execute protection).
445 1 -- check protection requested by application.
446 Default value is set via a kernel config option.
447 Value can be changed at runtime via
448 /selinux/checkreqprot.
450 cio_ignore= [S390]
451 See Documentation/s390/CommonIO for details.
453 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
454 [Deprecated]
455 Forces specified clocksource (if available) to be used
456 when calculating gettimeofday(). If specified
457 clocksource is not available, it defaults to PIT.
458 Format: { pit | tsc | cyclone | pmtmr }
460 clocksource= Override the default clocksource
461 Format: <string>
462 Override the default clocksource and use the clocksource
463 with the name specified.
464 Some clocksource names to choose from, depending on
465 the platform:
466 [all] jiffies (this is the base, fallback clocksource)
467 [ACPI] acpi_pm
468 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
469 pxa_timer,timer3,32k_counter,timer0_1
470 [AVR32] avr32
471 [X86-32] pit,hpet,tsc;
472 scx200_hrt on Geode; cyclone on IBM x440
473 [MIPS] MIPS
474 [PARISC] cr16
475 [S390] tod
476 [SH] SuperH
477 [SPARC64] tick
478 [X86-64] hpet,tsc
480 clearcpuid=BITNUM [X86]
481 Disable CPUID feature X for the kernel. See
482 arch/x86/include/asm/cpufeature.h for the valid bit
483 numbers. Note the Linux specific bits are not necessarily
484 stable over kernel options, but the vendor specific
485 ones should be.
486 Also note that user programs calling CPUID directly
487 or using the feature without checking anything
488 will still see it. This just prevents it from
489 being used by the kernel or shown in /proc/cpuinfo.
490 Also note the kernel might malfunction if you disable
491 some critical bits.
493 cmo_free_hint= [PPC] Format: { yes | no }
494 Specify whether pages are marked as being inactive
495 when they are freed. This is used in CMO environments
496 to determine OS memory pressure for page stealing by
497 a hypervisor.
498 Default: yes
500 code_bytes [X86] How many bytes of object code to print
501 in an oops report.
502 Range: 0 - 8192
503 Default: 64
505 com20020= [HW,NET] ARCnet - COM20020 chipset
506 Format:
507 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
509 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
510 Format: <io>[,<irq>]
512 com90xx= [HW,NET]
513 ARCnet - COM90xx chipset (memory-mapped buffers)
514 Format: <io>[,<irq>[,<memstart>]]
516 condev= [HW,S390] console device
517 conmode=
519 console= [KNL] Output console device and options.
521 tty<n> Use the virtual console device <n>.
523 ttyS<n>[,options]
524 ttyUSB0[,options]
525 Use the specified serial port. The options are of
526 the form "bbbbpnf", where "bbbb" is the baud rate,
527 "p" is parity ("n", "o", or "e"), "n" is number of
528 bits, and "f" is flow control ("r" for RTS or
529 omit it). Default is "9600n8".
531 See Documentation/serial-console.txt for more
532 information. See
533 Documentation/networking/netconsole.txt for an
534 alternative.
536 uart[8250],io,<addr>[,options]
537 uart[8250],mmio,<addr>[,options]
538 Start an early, polled-mode console on the 8250/16550
539 UART at the specified I/O port or MMIO address,
540 switching to the matching ttyS device later. The
541 options are the same as for ttyS, above.
543 If the device connected to the port is not a TTY but a braille
544 device, prepend "brl," before the device type, for instance
545 console=brl,ttyS0
546 For now, only VisioBraille is supported.
548 consoleblank= [KNL] The console blank (screen saver) timeout in
549 seconds. Defaults to 10*60 = 10mins. A value of 0
550 disables the blank timer.
552 coredump_filter=
553 [KNL] Change the default value for
554 /proc/<pid>/coredump_filter.
555 See also Documentation/filesystems/proc.txt.
557 cpuidle.off=1 [CPU_IDLE]
558 disable the cpuidle sub-system
560 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
561 Format:
562 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
564 crashkernel=size[KMG][@offset[KMG]]
565 [KNL] Using kexec, Linux can switch to a 'crash kernel'
566 upon panic. This parameter reserves the physical
567 memory region [offset, offset + size] for that kernel
568 image. If '@offset' is omitted, then a suitable offset
569 is selected automatically. Check
570 Documentation/kdump/kdump.txt for further details.
572 crashkernel=range1:size1[,range2:size2,...][@offset]
573 [KNL] Same as above, but depends on the memory
574 in the running system. The syntax of range is
575 start-[end] where start and end are both
576 a memory unit (amount[KMG]). See also
577 Documentation/kdump/kdump.txt for an example.
579 cs89x0_dma= [HW,NET]
580 Format: <dma>
582 cs89x0_media= [HW,NET]
583 Format: { rj45 | aui | bnc }
585 dasd= [HW,NET]
586 See header of drivers/s390/block/dasd_devmap.c.
588 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
589 (one device per port)
590 Format: <port#>,<type>
591 See also Documentation/input/joystick-parport.txt
593 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
594 time. See Documentation/dynamic-debug-howto.txt for
595 details.
597 debug [KNL] Enable kernel debugging (events log level).
599 debug_locks_verbose=
600 [KNL] verbose self-tests
601 Format=<0|1>
602 Print debugging info while doing the locking API
603 self-tests.
604 We default to 0 (no extra messages), setting it to
605 1 will print _a lot_ more information - normally
606 only useful to kernel developers.
608 debug_objects [KNL] Enable object debugging
610 no_debug_objects
611 [KNL] Disable object debugging
613 debugpat [X86] Enable PAT debugging
615 decnet.addr= [HW,NET]
616 Format: <area>[,<node>]
617 See also Documentation/networking/decnet.txt.
619 default_hugepagesz=
620 [same as hugepagesz=] The size of the default
621 HugeTLB page size. This is the size represented by
622 the legacy /proc/ hugepages APIs, used for SHM, and
623 default size when mounting hugetlbfs filesystems.
624 Defaults to the default architecture's huge page size
625 if not specified.
627 dhash_entries= [KNL]
628 Set number of hash buckets for dentry cache.
630 digi= [HW,SERIAL]
631 IO parameters + enable/disable command.
633 digiepca= [HW,SERIAL]
634 See drivers/char/README.epca and
635 Documentation/serial/digiepca.txt.
637 disable= [IPV6]
638 See Documentation/networking/ipv6.txt.
640 disable_ddw [PPC/PSERIES]
641 Disable Dynamic DMA Window support. Use this if
642 to workaround buggy firmware.
644 disable_ipv6= [IPV6]
645 See Documentation/networking/ipv6.txt.
647 disable_mtrr_cleanup [X86]
648 The kernel tries to adjust MTRR layout from continuous
649 to discrete, to make X server driver able to add WB
650 entry later. This parameter disables that.
652 disable_mtrr_trim [X86, Intel and AMD only]
653 By default the kernel will trim any uncacheable
654 memory out of your available memory pool based on
655 MTRR settings. This parameter disables that behavior,
656 possibly causing your machine to run very slowly.
658 disable_timer_pin_1 [X86]
659 Disable PIN 1 of APIC timer
660 Can be useful to work around chipset bugs.
662 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
663 this option disables the debugging code at boot.
665 dma_debug_entries=<number>
666 This option allows to tune the number of preallocated
667 entries for DMA-API debugging code. One entry is
668 required per DMA-API allocation. Use this if the
669 DMA-API debugging code disables itself because the
670 architectural default is too low.
672 dma_debug_driver=<driver_name>
673 With this option the DMA-API debugging driver
674 filter feature can be enabled at boot time. Just
675 pass the driver to filter for as the parameter.
676 The filter can be disabled or changed to another
677 driver later using sysfs.
679 dscc4.setup= [NET]
681 earlycon= [KNL] Output early console device and options.
682 uart[8250],io,<addr>[,options]
683 uart[8250],mmio,<addr>[,options]
684 uart[8250],mmio32,<addr>[,options]
685 Start an early, polled-mode console on the 8250/16550
686 UART at the specified I/O port or MMIO address.
687 MMIO inter-register address stride is either 8-bit
688 (mmio) or 32-bit (mmio32).
689 The options are the same as for ttyS, above.
691 earlyprintk= [X86,SH,BLACKFIN]
692 earlyprintk=vga
693 earlyprintk=serial[,ttySn[,baudrate]]
694 earlyprintk=ttySn[,baudrate]
695 earlyprintk=dbgp[debugController#]
697 Append ",keep" to not disable it when the real console
698 takes over.
700 Only vga or serial or usb debug port at a time.
702 Currently only ttyS0 and ttyS1 are supported.
704 Interaction with the standard serial driver is not
705 very good.
707 The VGA output is eventually overwritten by the real
708 console.
710 ekgdboc= [X86,KGDB] Allow early kernel console debugging
711 ekgdboc=kbd
713 This is designed to be used in conjunction with
714 the boot argument: earlyprintk=vga
716 edd= [EDD]
717 Format: {"off" | "on" | "skip[mbr]"}
719 eisa_irq_edge= [PARISC,HW]
720 See header of drivers/parisc/eisa.c.
722 elanfreq= [X86-32]
723 See comment before function elanfreq_setup() in
724 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
726 elevator= [IOSCHED]
727 Format: {"cfq" | "deadline" | "noop"}
728 See Documentation/block/cfq-iosched.txt and
729 Documentation/block/deadline-iosched.txt for details.
731 elfcorehdr= [IA-64,PPC,SH,X86]
732 Specifies physical address of start of kernel core
733 image elf header. Generally kexec loader will
734 pass this option to capture kernel.
735 See Documentation/kdump/kdump.txt for details.
737 enable_mtrr_cleanup [X86]
738 The kernel tries to adjust MTRR layout from continuous
739 to discrete, to make X server driver able to add WB
740 entry later. This parameter enables that.
742 enable_timer_pin_1 [X86]
743 Enable PIN 1 of APIC timer
744 Can be useful to work around chipset bugs
745 (in particular on some ATI chipsets).
746 The kernel tries to set a reasonable default.
748 enforcing [SELINUX] Set initial enforcing status.
749 Format: {"0" | "1"}
750 See security/selinux/Kconfig help text.
751 0 -- permissive (log only, no denials).
752 1 -- enforcing (deny and log).
753 Default value is 0.
754 Value can be changed at runtime via /selinux/enforce.
756 erst_disable [ACPI]
757 Disable Error Record Serialization Table (ERST)
758 support.
760 ether= [HW,NET] Ethernet cards parameters
761 This option is obsoleted by the "netdev=" option, which
762 has equivalent usage. See its documentation for details.
764 evm= [EVM]
765 Format: { "fix" }
766 Permit 'security.evm' to be updated regardless of
767 current integrity status.
769 failslab=
770 fail_page_alloc=
771 fail_make_request=[KNL]
772 General fault injection mechanism.
773 Format: <interval>,<probability>,<space>,<times>
774 See also Documentation/fault-injection/.
776 floppy= [HW]
777 See Documentation/blockdev/floppy.txt.
779 force_pal_cache_flush
780 [IA-64] Avoid check_sal_cache_flush which may hang on
781 buggy SAL_CACHE_FLUSH implementations. Using this
782 parameter will force ia64_sal_cache_flush to call
783 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
785 ftrace=[tracer]
786 [FTRACE] will set and start the specified tracer
787 as early as possible in order to facilitate early
788 boot debugging.
790 ftrace_dump_on_oops[=orig_cpu]
791 [FTRACE] will dump the trace buffers on oops.
792 If no parameter is passed, ftrace will dump
793 buffers of all CPUs, but if you pass orig_cpu, it will
794 dump only the buffer of the CPU that triggered the
795 oops.
797 ftrace_filter=[function-list]
798 [FTRACE] Limit the functions traced by the function
799 tracer at boot up. function-list is a comma separated
800 list of functions. This list can be changed at run
801 time by the set_ftrace_filter file in the debugfs
802 tracing directory.
804 ftrace_notrace=[function-list]
805 [FTRACE] Do not trace the functions specified in
806 function-list. This list can be changed at run time
807 by the set_ftrace_notrace file in the debugfs
808 tracing directory.
810 ftrace_graph_filter=[function-list]
811 [FTRACE] Limit the top level callers functions traced
812 by the function graph tracer at boot up.
813 function-list is a comma separated list of functions
814 that can be changed at run time by the
815 set_graph_function file in the debugfs tracing directory.
817 gamecon.map[2|3]=
818 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
819 support via parallel port (up to 5 devices per port)
820 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
821 See also Documentation/input/joystick-parport.txt
823 gamma= [HW,DRM]
825 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
826 Format: off | on
827 default: on
829 gcov_persist= [GCOV] When non-zero (default), profiling data for
830 kernel modules is saved and remains accessible via
831 debugfs, even when the module is unloaded/reloaded.
832 When zero, profiling data is discarded and associated
833 debugfs files are removed at module unload time.
835 gpt [EFI] Forces disk with valid GPT signature but
836 invalid Protective MBR to be treated as GPT.
838 hashdist= [KNL,NUMA] Large hashes allocated during boot
839 are distributed across NUMA nodes. Defaults on
840 for 64-bit NUMA, off otherwise.
841 Format: 0 | 1 (for off | on)
843 hcl= [IA-64] SGI's Hardware Graph compatibility layer
845 hd= [EIDE] (E)IDE hard drive subsystem geometry
846 Format: <cyl>,<head>,<sect>
848 hest_disable [ACPI]
849 Disable Hardware Error Source Table (HEST) support;
850 corresponding firmware-first mode error processing
851 logic will be disabled.
853 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
854 size of <nn>. This works even on boxes that have no
855 highmem otherwise. This also works to reduce highmem
856 size on bigger boxes.
858 highres= [KNL] Enable/disable high resolution timer mode.
859 Valid parameters: "on", "off"
860 Default: "on"
862 hisax= [HW,ISDN]
863 See Documentation/isdn/README.HiSax.
865 hlt [BUGS=ARM,SH]
867 hpet= [X86-32,HPET] option to control HPET usage
868 Format: { enable (default) | disable | force |
869 verbose }
870 disable: disable HPET and use PIT instead
871 force: allow force enabled of undocumented chips (ICH4,
872 VIA, nVidia)
873 verbose: show contents of HPET registers during setup
875 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
876 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
877 On x86-64 and powerpc, this option can be specified
878 multiple times interleaved with hugepages= to reserve
879 huge pages of different sizes. Valid pages sizes on
880 x86-64 are 2M (when the CPU supports "pse") and 1G
881 (when the CPU supports the "pdpe1gb" cpuinfo flag)
882 Note that 1GB pages can only be allocated at boot time
883 using hugepages= and not freed afterwards.
885 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
886 terminal devices. Valid values: 0..8
887 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
888 If specified, z/VM IUCV HVC accepts connections
889 from listed z/VM user IDs only.
891 keep_bootcon [KNL]
892 Do not unregister boot console at start. This is only
893 useful for debugging when something happens in the window
894 between unregistering the boot console and initializing
895 the real console.
897 i2c_bus= [HW] Override the default board specific I2C bus speed
898 or register an additional I2C bus that is not
899 registered from board initialization code.
900 Format:
901 <bus_id>,<clkrate>
903 i8042.debug [HW] Toggle i8042 debug mode
904 i8042.direct [HW] Put keyboard port into non-translated mode
905 i8042.dumbkbd [HW] Pretend that controller can only read data from
906 keyboard and cannot control its state
907 (Don't attempt to blink the leds)
908 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
909 i8042.nokbd [HW] Don't check/create keyboard port
910 i8042.noloop [HW] Disable the AUX Loopback command while probing
911 for the AUX port
912 i8042.nomux [HW] Don't check presence of an active multiplexing
913 controller
914 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
915 controllers
916 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
917 i8042.reset [HW] Reset the controller during init and cleanup
918 i8042.unlock [HW] Unlock (ignore) the keylock
920 i810= [HW,DRM]
922 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
923 indicates that the driver is running on unsupported
924 hardware.
925 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
926 does not match list of supported models.
927 i8k.power_status
928 [HW] Report power status in /proc/i8k
929 (disabled by default)
930 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
931 capability is set.
933 icn= [HW,ISDN]
934 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
936 ide-core.nodma= [HW] (E)IDE subsystem
937 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
938 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
939 .cdrom .chs .ignore_cable are additional options
940 See Documentation/ide/ide.txt.
942 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
943 Claim all unknown PCI IDE storage controllers.
945 idle= [X86]
946 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
947 Poll forces a polling idle loop that can slightly
948 improve the performance of waking up a idle CPU, but
949 will use a lot of power and make the system run hot.
950 Not recommended.
951 idle=mwait: On systems which support MONITOR/MWAIT but
952 the kernel chose to not use it because it doesn't save
953 as much power as a normal idle loop, use the
954 MONITOR/MWAIT idle loop anyways. Performance should be
955 the same as idle=poll.
956 idle=halt: Halt is forced to be used for CPU idle.
957 In such case C2/C3 won't be used again.
958 idle=nomwait: Disable mwait for CPU C-states
960 ignore_loglevel [KNL]
961 Ignore loglevel setting - this will print /all/
962 kernel messages to the console. Useful for debugging.
964 ihash_entries= [KNL]
965 Set number of hash buckets for inode cache.
967 ima_audit= [IMA]
968 Format: { "0" | "1" }
969 0 -- integrity auditing messages. (Default)
970 1 -- enable informational integrity auditing messages.
972 ima_hash= [IMA]
973 Format: { "sha1" | "md5" }
974 default: "sha1"
976 ima_tcb [IMA]
977 Load a policy which meets the needs of the Trusted
978 Computing Base. This means IMA will measure all
979 programs exec'd, files mmap'd for exec, and all files
980 opened for read by uid=0.
982 init= [KNL]
983 Format: <full_path>
984 Run specified binary instead of /sbin/init as init
985 process.
987 initcall_debug [KNL] Trace initcalls as they are executed. Useful
988 for working out where the kernel is dying during
989 startup.
991 initrd= [BOOT] Specify the location of the initial ramdisk
993 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
994 Format: <irq>
996 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
997 on
998 Enable intel iommu driver.
999 off
1000 Disable intel iommu driver.
1001 igfx_off [Default Off]
1002 By default, gfx is mapped as normal device. If a gfx
1003 device has a dedicated DMAR unit, the DMAR unit is
1004 bypassed by not enabling DMAR with this option. In
1005 this case, gfx device will use physical address for
1006 DMA.
1007 forcedac [x86_64]
1008 With this option iommu will not optimize to look
1009 for io virtual address below 32-bit forcing dual
1010 address cycle on pci bus for cards supporting greater
1011 than 32-bit addressing. The default is to look
1012 for translation below 32-bit and if not available
1013 then look in the higher range.
1014 strict [Default Off]
1015 With this option on every unmap_single operation will
1016 result in a hardware IOTLB flush operation as opposed
1017 to batching them for performance.
1018 sp_off [Default Off]
1019 By default, super page will be supported if Intel IOMMU
1020 has the capability. With this option, super page will
1021 not be supported.
1022 intremap= [X86-64, Intel-IOMMU]
1023 Format: { on (default) | off | nosid }
1024 on enable Interrupt Remapping (default)
1025 off disable Interrupt Remapping
1026 nosid disable Source ID checking
1028 inttest= [IA-64]
1030 iomem= Disable strict checking of access to MMIO memory
1031 strict regions from userspace.
1032 relaxed
1034 iommu= [x86]
1035 off
1036 force
1037 noforce
1038 biomerge
1039 panic
1040 nopanic
1041 merge
1042 nomerge
1043 forcesac
1044 soft
1045 pt [x86, IA-64]
1047 io7= [HW] IO7 for Marvel based alpha systems
1048 See comment before marvel_specify_io7 in
1049 arch/alpha/kernel/core_marvel.c.
1051 io_delay= [X86] I/O delay method
1052 0x80
1053 Standard port 0x80 based delay
1054 0xed
1055 Alternate port 0xed based delay (needed on some systems)
1056 udelay
1057 Simple two microseconds delay
1058 none
1059 No delay
1061 ip= [IP_PNP]
1062 See Documentation/filesystems/nfs/nfsroot.txt.
1064 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1065 See comment before ip2_setup() in
1066 drivers/char/ip2/ip2base.c.
1068 irqfixup [HW]
1069 When an interrupt is not handled search all handlers
1070 for it. Intended to get systems with badly broken
1071 firmware running.
1073 irqpoll [HW]
1074 When an interrupt is not handled search all handlers
1075 for it. Also check all handlers each timer
1076 interrupt. Intended to get systems with badly broken
1077 firmware running.
1079 isapnp= [ISAPNP]
1080 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1082 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1083 Format:
1084 <cpu number>,...,<cpu number>
1085 or
1086 <cpu number>-<cpu number>
1087 (must be a positive range in ascending order)
1088 or a mixture
1089 <cpu number>,...,<cpu number>-<cpu number>
1091 This option can be used to specify one or more CPUs
1092 to isolate from the general SMP balancing and scheduling
1093 algorithms. You can move a process onto or off an
1094 "isolated" CPU via the CPU affinity syscalls or cpuset.
1095 <cpu number> begins at 0 and the maximum value is
1096 "number of CPUs in system - 1".
1098 This option is the preferred way to isolate CPUs. The
1099 alternative -- manually setting the CPU mask of all
1100 tasks in the system -- can cause problems and
1101 suboptimal load balancer performance.
1103 iucv= [HW,NET]
1105 js= [HW,JOY] Analog joystick
1106 See Documentation/input/joystick.txt.
1108 keepinitrd [HW,ARM]
1110 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1111 specifies the amount of memory usable by the kernel
1112 for non-movable allocations. The requested amount is
1113 spread evenly throughout all nodes in the system. The
1114 remaining memory in each node is used for Movable
1115 pages. In the event, a node is too small to have both
1116 kernelcore and Movable pages, kernelcore pages will
1117 take priority and other nodes will have a larger number
1118 of kernelcore pages. The Movable zone is used for the
1119 allocation of pages that may be reclaimed or moved
1120 by the page migration subsystem. This means that
1121 HugeTLB pages may not be allocated from this zone.
1122 Note that allocations like PTEs-from-HighMem still
1123 use the HighMem zone if it exists, and the Normal
1124 zone if it does not.
1126 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1127 Format: <Controller#>[,poll interval]
1128 The controller # is the number of the ehci usb debug
1129 port as it is probed via PCI. The poll interval is
1130 optional and is the number seconds in between
1131 each poll cycle to the debug port in case you need
1132 the functionality for interrupting the kernel with
1133 gdb or control-c on the dbgp connection. When
1134 not using this parameter you use sysrq-g to break into
1135 the kernel debugger.
1137 kgdboc= [KGDB,HW] kgdb over consoles.
1138 Requires a tty driver that supports console polling,
1139 or a supported polling keyboard driver (non-usb).
1140 Serial only format: <serial_device>[,baud]
1141 keyboard only format: kbd
1142 keyboard and serial format: kbd,<serial_device>[,baud]
1143 Optional Kernel mode setting:
1144 kms, kbd format: kms,kbd
1145 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1147 kgdbwait [KGDB] Stop kernel execution and enter the
1148 kernel debugger at the earliest opportunity.
1150 kmac= [MIPS] korina ethernet MAC address.
1151 Configure the RouterBoard 532 series on-chip
1152 Ethernet adapter MAC address.
1154 kmemleak= [KNL] Boot-time kmemleak enable/disable
1155 Valid arguments: on, off
1156 Default: on
1158 kstack=N [X86] Print N words from the kernel stack
1159 in oops dumps.
1161 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1162 Default is 0 (don't ignore, but inject #GP)
1164 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1165 Default is 1 (enabled)
1167 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1168 KVM MMU at runtime.
1169 Default is 0 (off)
1171 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1172 Default is 1 (enabled)
1174 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1175 for all guests.
1176 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1178 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1179 (virtualized MMU) support on capable Intel chips.
1180 Default is 1 (enabled)
1182 kvm-intel.emulate_invalid_guest_state=
1183 [KVM,Intel] Enable emulation of invalid guest states
1184 Default is 0 (disabled)
1186 kvm-intel.flexpriority=
1187 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1188 Default is 1 (enabled)
1190 kvm-intel.unrestricted_guest=
1191 [KVM,Intel] Disable unrestricted guest feature
1192 (virtualized real and unpaged mode) on capable
1193 Intel chips. Default is 1 (enabled)
1195 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1196 feature (tagged TLBs) on capable Intel chips.
1197 Default is 1 (enabled)
1199 l2cr= [PPC]
1201 l3cr= [PPC]
1203 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1204 disabled it.
1206 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1207 in C2 power state.
1209 libata.dma= [LIBATA] DMA control
1210 libata.dma=0 Disable all PATA and SATA DMA
1211 libata.dma=1 PATA and SATA Disk DMA only
1212 libata.dma=2 ATAPI (CDROM) DMA only
1213 libata.dma=4 Compact Flash DMA only
1214 Combinations also work, so libata.dma=3 enables DMA
1215 for disks and CDROMs, but not CFs.
1217 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1218 libata.ignore_hpa=0 keep BIOS limits (default)
1219 libata.ignore_hpa=1 ignore limits, using full disk
1221 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1222 when set.
1223 Format: <int>
1225 libata.force= [LIBATA] Force configurations. The format is comma
1226 separated list of "[ID:]VAL" where ID is
1227 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1228 matching port, link or device. Basically, it matches
1229 the ATA ID string printed on console by libata. If
1230 the whole ID part is omitted, the last PORT and DEVICE
1231 values are used. If ID hasn't been specified yet, the
1232 configuration applies to all ports, links and devices.
1234 If only DEVICE is omitted, the parameter applies to
1235 the port and all links and devices behind it. DEVICE
1236 number of 0 either selects the first device or the
1237 first fan-out link behind PMP device. It does not
1238 select the host link. DEVICE number of 15 selects the
1239 host link and device attached to it.
1241 The VAL specifies the configuration to force. As long
1242 as there's no ambiguity shortcut notation is allowed.
1243 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1244 The following configurations can be forced.
1246 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1247 Any ID with matching PORT is used.
1249 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1251 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1252 udma[/][16,25,33,44,66,100,133] notation is also
1253 allowed.
1255 * [no]ncq: Turn on or off NCQ.
1257 * nohrst, nosrst, norst: suppress hard, soft
1258 and both resets.
1260 * dump_id: dump IDENTIFY data.
1262 If there are multiple matching configurations changing
1263 the same attribute, the last one is used.
1265 memblock=debug [KNL] Enable memblock debug messages.
1267 load_ramdisk= [RAM] List of ramdisks to load from floppy
1268 See Documentation/blockdev/ramdisk.txt.
1270 lockd.nlm_grace_period=P [NFS] Assign grace period.
1271 Format: <integer>
1273 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1274 Format: <integer>
1276 lockd.nlm_timeout=T [NFS] Assign timeout value.
1277 Format: <integer>
1279 lockd.nlm_udpport=M [NFS] Assign UDP port.
1280 Format: <integer>
1282 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1283 Format: <irq>
1285 loglevel= All Kernel Messages with a loglevel smaller than the
1286 console loglevel will be printed to the console. It can
1287 also be changed with klogd or other programs. The
1288 loglevels are defined as follows:
1290 0 (KERN_EMERG) system is unusable
1291 1 (KERN_ALERT) action must be taken immediately
1292 2 (KERN_CRIT) critical conditions
1293 3 (KERN_ERR) error conditions
1294 4 (KERN_WARNING) warning conditions
1295 5 (KERN_NOTICE) normal but significant condition
1296 6 (KERN_INFO) informational
1297 7 (KERN_DEBUG) debug-level messages
1299 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1300 in bytes. n must be a power of two. The default
1301 size is set in the kernel config file.
1303 logo.nologo [FB] Disables display of the built-in Linux logo.
1304 This may be used to provide more screen space for
1305 kernel log messages and is useful when debugging
1306 kernel boot problems.
1308 lp=0 [LP] Specify parallel ports to use, e.g,
1309 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1310 lp=reset first parallel port). 'lp=0' disables the
1311 lp=auto printer driver. 'lp=reset' (which can be
1312 specified in addition to the ports) causes
1313 attached printers to be reset. Using
1314 lp=port1,port2,... specifies the parallel ports
1315 to associate lp devices with, starting with
1316 lp0. A port specification may be 'none' to skip
1317 that lp device, or a parport name such as
1318 'parport0'. Specifying 'lp=auto' instead of a
1319 port specification list means that device IDs
1320 from each port should be examined, to see if
1321 an IEEE 1284-compliant printer is attached; if
1322 so, the driver will manage that printer.
1323 See also header of drivers/char/lp.c.
1325 lpj=n [KNL]
1326 Sets loops_per_jiffy to given constant, thus avoiding
1327 time-consuming boot-time autodetection (up to 250 ms per
1328 CPU). 0 enables autodetection (default). To determine
1329 the correct value for your kernel, boot with normal
1330 autodetection and see what value is printed. Note that
1331 on SMP systems the preset will be applied to all CPUs,
1332 which is likely to cause problems if your CPUs need
1333 significantly divergent settings. An incorrect value
1334 will cause delays in the kernel to be wrong, leading to
1335 unpredictable I/O errors and other breakage. Although
1336 unlikely, in the extreme case this might damage your
1337 hardware.
1339 ltpc= [NET]
1340 Format: <io>,<irq>,<dma>
1342 machvec= [IA-64] Force the use of a particular machine-vector
1343 (machvec) in a generic kernel.
1344 Example: machvec=hpzx1_swiotlb
1346 machtype= [Loongson] Share the same kernel image file between different
1347 yeeloong laptop.
1348 Example: machtype=lemote-yeeloong-2f-7inch
1350 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1351 than or equal to this physical address is ignored.
1353 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1354 should make use of. maxcpus=n : n >= 0 limits the
1355 kernel to using 'n' processors. n=0 is a special case,
1356 it is equivalent to "nosmp", which also disables
1357 the IO APIC.
1359 max_loop= [LOOP] The number of loop block devices that get
1360 (loop.max_loop) unconditionally pre-created at init time. The default
1361 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1362 of statically allocating a predefined number, loop
1363 devices can be requested on-demand with the
1364 /dev/loop-control interface.
1366 mcatest= [IA-64]
1368 mce [X86-32] Machine Check Exception
1370 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1372 md= [HW] RAID subsystems devices and level
1373 See Documentation/md.txt.
1375 mdacon= [MDA]
1376 Format: <first>,<last>
1377 Specifies range of consoles to be captured by the MDA.
1379 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1380 Amount of memory to be used when the kernel is not able
1381 to see the whole system memory or for test.
1382 [X86-32] Use together with memmap= to avoid physical
1383 address space collisions. Without memmap= PCI devices
1384 could be placed at addresses belonging to unused RAM.
1386 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1387 memory.
1389 memchunk=nn[KMG]
1390 [KNL,SH] Allow user to override the default size for
1391 per-device physically contiguous DMA buffers.
1393 memmap=exactmap [KNL,X86] Enable setting of an exact
1394 E820 memory map, as specified by the user.
1395 Such memmap=exactmap lines can be constructed based on
1396 BIOS output or other requirements. See the memmap=nn@ss
1397 option description.
1399 memmap=nn[KMG]@ss[KMG]
1400 [KNL] Force usage of a specific region of memory
1401 Region of memory to be used, from ss to ss+nn.
1403 memmap=nn[KMG]#ss[KMG]
1404 [KNL,ACPI] Mark specific memory as ACPI data.
1405 Region of memory to be used, from ss to ss+nn.
1407 memmap=nn[KMG]$ss[KMG]
1408 [KNL,ACPI] Mark specific memory as reserved.
1409 Region of memory to be used, from ss to ss+nn.
1410 Example: Exclude memory from 0x18690000-0x1869ffff
1411 memmap=64K$0x18690000
1412 or
1413 memmap=0x10000$0x18690000
1415 memory_corruption_check=0/1 [X86]
1416 Some BIOSes seem to corrupt the first 64k of
1417 memory when doing things like suspend/resume.
1418 Setting this option will scan the memory
1419 looking for corruption. Enabling this will
1420 both detect corruption and prevent the kernel
1421 from using the memory being corrupted.
1422 However, its intended as a diagnostic tool; if
1423 repeatable BIOS-originated corruption always
1424 affects the same memory, you can use memmap=
1425 to prevent the kernel from using that memory.
1427 memory_corruption_check_size=size [X86]
1428 By default it checks for corruption in the low
1429 64k, making this memory unavailable for normal
1430 use. Use this parameter to scan for
1431 corruption in more or less memory.
1433 memory_corruption_check_period=seconds [X86]
1434 By default it checks for corruption every 60
1435 seconds. Use this parameter to check at some
1436 other rate. 0 disables periodic checking.
1438 memtest= [KNL,X86] Enable memtest
1439 Format: <integer>
1440 default : 0 <disable>
1441 Specifies the number of memtest passes to be
1442 performed. Each pass selects another test
1443 pattern from a given set of patterns. Memtest
1444 fills the memory with this pattern, validates
1445 memory contents and reserves bad memory
1446 regions that are detected.
1448 meye.*= [HW] Set MotionEye Camera parameters
1449 See Documentation/video4linux/meye.txt.
1451 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1452 Multi-Function General Purpose Timers on AMD Geode
1453 platforms.
1455 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1456 the BIOS has incorrectly applied a workaround. TinyBIOS
1457 version 0.98 is known to be affected, 0.99 fixes the
1458 problem by letting the user disable the workaround.
1460 mga= [HW,DRM]
1462 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1463 physical address is ignored.
1465 mini2440= [ARM,HW,KNL]
1466 Format:[0..2][b][c][t]
1467 Default: "0tb"
1468 MINI2440 configuration specification:
1469 0 - The attached screen is the 3.5" TFT
1470 1 - The attached screen is the 7" TFT
1471 2 - The VGA Shield is attached (1024x768)
1472 Leaving out the screen size parameter will not load
1473 the TFT driver, and the framebuffer will be left
1474 unconfigured.
1475 b - Enable backlight. The TFT backlight pin will be
1476 linked to the kernel VESA blanking code and a GPIO
1477 LED. This parameter is not necessary when using the
1478 VGA shield.
1479 c - Enable the s3c camera interface.
1480 t - Reserved for enabling touchscreen support. The
1481 touchscreen support is not enabled in the mainstream
1482 kernel as of 2.6.30, a preliminary port can be found
1483 in the "bleeding edge" mini2440 support kernel at
1484 http://repo.or.cz/w/linux-2.6/mini2440.git
1486 mminit_loglevel=
1487 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1488 parameter allows control of the logging verbosity for
1489 the additional memory initialisation checks. A value
1490 of 0 disables mminit logging and a level of 4 will
1491 log everything. Information is printed at KERN_DEBUG
1492 so loglevel=8 may also need to be specified.
1494 mousedev.tap_time=
1495 [MOUSE] Maximum time between finger touching and
1496 leaving touchpad surface for touch to be considered
1497 a tap and be reported as a left button click (for
1498 touchpads working in absolute mode only).
1499 Format: <msecs>
1500 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1501 reporting absolute coordinates, such as tablets
1502 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1503 reporting absolute coordinates, such as tablets
1505 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1506 is similar to kernelcore except it specifies the
1507 amount of memory used for migratable allocations.
1508 If both kernelcore and movablecore is specified,
1509 then kernelcore will be at *least* the specified
1510 value but may be more. If movablecore on its own
1511 is specified, the administrator must be careful
1512 that the amount of memory usable for all allocations
1513 is not too small.
1515 MTD_Partition= [MTD]
1516 Format: <name>,<region-number>,<size>,<offset>
1518 MTD_Region= [MTD] Format:
1519 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1521 mtdparts= [MTD]
1522 See drivers/mtd/cmdlinepart.c.
1524 multitce=off [PPC] This parameter disables the use of the pSeries
1525 firmware feature for updating multiple TCE entries
1526 at a time.
1528 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1530 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1532 boundary - index of last SLC block on Flex-OneNAND.
1533 The remaining blocks are configured as MLC blocks.
1534 lock - Configure if Flex-OneNAND boundary should be locked.
1535 Once locked, the boundary cannot be changed.
1536 1 indicates lock status, 0 indicates unlock status.
1538 mtdset= [ARM]
1539 ARM/S3C2412 JIVE boot control
1541 See arch/arm/mach-s3c2412/mach-jive.c
1543 mtouchusb.raw_coordinates=
1544 [HW] Make the MicroTouch USB driver use raw coordinates
1545 ('y', default) or cooked coordinates ('n')
1547 mtrr_chunk_size=nn[KMG] [X86]
1548 used for mtrr cleanup. It is largest continuous chunk
1549 that could hold holes aka. UC entries.
1551 mtrr_gran_size=nn[KMG] [X86]
1552 Used for mtrr cleanup. It is granularity of mtrr block.
1553 Default is 1.
1554 Large value could prevent small alignment from
1555 using up MTRRs.
1557 mtrr_spare_reg_nr=n [X86]
1558 Format: <integer>
1559 Range: 0,7 : spare reg number
1560 Default : 1
1561 Used for mtrr cleanup. It is spare mtrr entries number.
1562 Set to 2 or more if your graphical card needs more.
1564 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1566 netdev= [NET] Network devices parameters
1567 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1568 Note that mem_start is often overloaded to mean
1569 something different and driver-specific.
1570 This usage is only documented in each driver source
1571 file if at all.
1573 nf_conntrack.acct=
1574 [NETFILTER] Enable connection tracking flow accounting
1575 0 to disable accounting
1576 1 to enable accounting
1577 Default value is 0.
1579 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1580 See Documentation/filesystems/nfs/nfsroot.txt.
1582 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1583 See Documentation/filesystems/nfs/nfsroot.txt.
1585 nfsrootdebug [NFS] enable nfsroot debugging messages.
1586 See Documentation/filesystems/nfs/nfsroot.txt.
1588 nfs.callback_tcpport=
1589 [NFS] set the TCP port on which the NFSv4 callback
1590 channel should listen.
1592 nfs.cache_getent=
1593 [NFS] sets the pathname to the program which is used
1594 to update the NFS client cache entries.
1596 nfs.cache_getent_timeout=
1597 [NFS] sets the timeout after which an attempt to
1598 update a cache entry is deemed to have failed.
1600 nfs.idmap_cache_timeout=
1601 [NFS] set the maximum lifetime for idmapper cache
1602 entries.
1604 nfs.enable_ino64=
1605 [NFS] enable 64-bit inode numbers.
1606 If zero, the NFS client will fake up a 32-bit inode
1607 number for the readdir() and stat() syscalls instead
1608 of returning the full 64-bit number.
1609 The default is to return 64-bit inode numbers.
1611 nfs.nfs4_disable_idmapping=
1612 [NFSv4] When set, this option disables the NFSv4
1613 idmapper on the client, but only if the mount
1614 is using the 'sec=sys' security flavour. This may
1615 make migration from legacy NFSv2/v3 systems easier
1616 provided that the server has the appropriate support.
1617 The default is to always enable NFSv4 idmapping.
1619 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1620 when a NMI is triggered.
1621 Format: [state][,regs][,debounce][,die]
1623 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1624 Format: [panic,][nopanic,][num]
1625 Valid num: 0
1626 0 - turn nmi_watchdog off
1627 When panic is specified, panic when an NMI watchdog
1628 timeout occurs (or 'nopanic' to override the opposite
1629 default).
1630 This is useful when you use a panic=... timeout and
1631 need the box quickly up again.
1633 netpoll.carrier_timeout=
1634 [NET] Specifies amount of time (in seconds) that
1635 netpoll should wait for a carrier. By default netpoll
1636 waits 4 seconds.
1638 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1639 emulation library even if a 387 maths coprocessor
1640 is present.
1642 no_console_suspend
1643 [HW] Never suspend the console
1644 Disable suspending of consoles during suspend and
1645 hibernate operations. Once disabled, debugging
1646 messages can reach various consoles while the rest
1647 of the system is being put to sleep (ie, while
1648 debugging driver suspend/resume hooks). This may
1649 not work reliably with all consoles, but is known
1650 to work with serial and VGA consoles.
1652 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1653 caches in the slab allocator. Saves per-node memory,
1654 but will impact performance.
1656 noalign [KNL,ARM]
1658 noapic [SMP,APIC] Tells the kernel to not make use of any
1659 IOAPICs that may be present in the system.
1661 noautogroup Disable scheduler automatic task group creation.
1663 nobats [PPC] Do not use BATs for mapping kernel lowmem
1664 on "Classic" PPC cores.
1666 nocache [ARM]
1668 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1670 nodelayacct [KNL] Disable per-task delay accounting
1672 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1674 nodsp [SH] Disable hardware DSP at boot time.
1676 noefi [X86] Disable EFI runtime services support.
1678 noexec [IA-64]
1680 noexec [X86]
1681 On X86-32 available only on PAE configured kernels.
1682 noexec=on: enable non-executable mappings (default)
1683 noexec=off: disable non-executable mappings
1685 nosmep [X86]
1686 Disable SMEP (Supervisor Mode Execution Protection)
1687 even if it is supported by processor.
1689 noexec32 [X86-64]
1690 This affects only 32-bit executables.
1691 noexec32=on: enable non-executable mappings (default)
1692 read doesn't imply executable mappings
1693 noexec32=off: disable non-executable mappings
1694 read implies executable mappings
1696 nofpu [SH] Disable hardware FPU at boot time.
1698 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1699 register save and restore. The kernel will only save
1700 legacy floating-point registers on task switch.
1702 noxsave [BUGS=X86] Disables x86 extended register state save
1703 and restore using xsave. The kernel will fallback to
1704 enabling legacy floating-point and sse state.
1706 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1707 wfi(ARM) instruction doesn't work correctly and not to
1708 use it. This is also useful when using JTAG debugger.
1710 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1711 instruction doesn't work correctly and not to
1712 use it.
1714 no_file_caps Tells the kernel not to honor file capabilities. The
1715 only way then for a file to be executed with privilege
1716 is to be setuid root or executed by root.
1718 nohalt [IA-64] Tells the kernel not to use the power saving
1719 function PAL_HALT_LIGHT when idle. This increases
1720 power-consumption. On the positive side, it reduces
1721 interrupt wake-up latency, which may improve performance
1722 in certain environments such as networked servers or
1723 real-time systems.
1725 nohz= [KNL] Boottime enable/disable dynamic ticks
1726 Valid arguments: on, off
1727 Default: on
1729 noiotrap [SH] Disables trapped I/O port accesses.
1731 noirqdebug [X86-32] Disables the code which attempts to detect and
1732 disable unhandled interrupt sources.
1734 no_timer_check [X86,APIC] Disables the code which tests for
1735 broken timer IRQ sources.
1737 noisapnp [ISAPNP] Disables ISA PnP code.
1739 noinitrd [RAM] Tells the kernel not to load any configured
1740 initial RAM disk.
1742 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1743 remapping.
1744 [Deprecated - use intremap=off]
1746 nointroute [IA-64]
1748 nojitter [IA-64] Disables jitter checking for ITC timers.
1750 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1752 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1753 fault handling.
1755 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1756 steal time is computed, but won't influence scheduler
1757 behaviour
1759 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1761 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1763 noltlbs [PPC] Do not use large page/tlb entries for kernel
1764 lowmem mapping on PPC40x.
1766 nomca [IA-64] Disable machine check abort handling
1768 nomce [X86-32] Machine Check Exception
1770 nomfgpt [X86-32] Disable Multi-Function General Purpose
1771 Timer usage (for AMD Geode machines).
1773 nopat [X86] Disable PAT (page attribute table extension of
1774 pagetables) support.
1776 norandmaps Don't use address space randomization. Equivalent to
1777 echo 0 > /proc/sys/kernel/randomize_va_space
1779 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1781 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1782 with UP alternatives
1784 noresidual [PPC] Don't use residual data on PReP machines.
1786 noresume [SWSUSP] Disables resume and restores original swap
1787 space.
1789 no-scroll [VGA] Disables scrollback.
1790 This is required for the Braillex ib80-piezo Braille
1791 reader made by F.H. Papenmeier (Germany).
1793 nosbagart [IA-64]
1795 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1797 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1798 and disable the IO APIC. legacy for "maxcpus=0".
1800 nosoftlockup [KNL] Disable the soft-lockup detector.
1802 nosync [HW,M68K] Disables sync negotiation for all devices.
1804 notsc [BUGS=X86-32] Disable Time Stamp Counter
1806 nousb [USB] Disable the USB subsystem
1808 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1810 nowb [ARM]
1812 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1814 nptcg= [IA-64] Override max number of concurrent global TLB
1815 purges which is reported from either PAL_VM_SUMMARY or
1816 SAL PALO.
1818 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1819 could support. nr_cpus=n : n >= 1 limits the kernel to
1820 supporting 'n' processors. Later in runtime you can not
1821 use hotplug cpu feature to put more cpu back to online.
1822 just like you compile the kernel NR_CPUS=n
1824 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1826 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1827 one of ['zone', 'node', 'default'] can be specified
1828 This can be set from sysctl after boot.
1829 See Documentation/sysctl/vm.txt for details.
1831 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1832 See Documentation/debugging-via-ohci1394.txt for more
1833 info.
1835 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1836 Rather than timing out after 20 ms if an EC
1837 command is not properly ACKed, override the length
1838 of the timeout. We have interrupts disabled while
1839 waiting for the ACK, so if this is set too high
1840 interrupts *may* be lost!
1842 omap_mux= [OMAP] Override bootloader pin multiplexing.
1843 Format: <mux_mode0.mode_name=value>...
1844 For example, to override I2C bus2:
1845 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1847 oprofile.timer= [HW]
1848 Use timer interrupt instead of performance counters
1850 oprofile.cpu_type= Force an oprofile cpu type
1851 This might be useful if you have an older oprofile
1852 userland or if you want common events.
1853 Format: { arch_perfmon }
1854 arch_perfmon: [X86] Force use of architectural
1855 perfmon on Intel CPUs instead of the
1856 CPU specific event set.
1858 oops=panic Always panic on oopses. Default is to just kill the
1859 process, but there is a small probability of
1860 deadlocking the machine.
1861 This will also cause panics on machine check exceptions.
1862 Useful together with panic=30 to trigger a reboot.
1864 OSS [HW,OSS]
1865 See Documentation/sound/oss/oss-parameters.txt
1867 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1868 timeout > 0: seconds before rebooting
1869 timeout = 0: wait forever
1870 timeout < 0: reboot immediately
1871 Format: <timeout>
1873 parkbd.port= [HW] Parallel port number the keyboard adapter is
1874 connected to, default is 0.
1875 Format: <parport#>
1876 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1877 0 for XT, 1 for AT (default is AT).
1878 Format: <mode>
1880 parport= [HW,PPT] Specify parallel ports. 0 disables.
1881 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1882 Use 'auto' to force the driver to use any
1883 IRQ/DMA settings detected (the default is to
1884 ignore detected IRQ/DMA settings because of
1885 possible conflicts). You can specify the base
1886 address, IRQ, and DMA settings; IRQ and DMA
1887 should be numbers, or 'auto' (for using detected
1888 settings on that particular port), or 'nofifo'
1889 (to avoid using a FIFO even if it is detected).
1890 Parallel ports are assigned in the order they
1891 are specified on the command line, starting
1892 with parport0.
1894 parport_init_mode= [HW,PPT]
1895 Configure VIA parallel port to operate in
1896 a specific mode. This is necessary on Pegasos
1897 computer where firmware has no options for setting
1898 up parallel port mode and sets it to spp.
1899 Currently this function knows 686a and 8231 chips.
1900 Format: [spp|ps2|epp|ecp|ecpepp]
1902 pause_on_oops=
1903 Halt all CPUs after the first oops has been printed for
1904 the specified number of seconds. This is to be used if
1905 your oopses keep scrolling off the screen.
1907 pcbit= [HW,ISDN]
1909 pcd. [PARIDE]
1910 See header of drivers/block/paride/pcd.c.
1911 See also Documentation/blockdev/paride.txt.
1913 pci=option[,option...] [PCI] various PCI subsystem options:
1914 earlydump [X86] dump PCI config space before the kernel
1915 changes anything
1916 off [X86] don't probe for the PCI bus
1917 bios [X86-32] force use of PCI BIOS, don't access
1918 the hardware directly. Use this if your machine
1919 has a non-standard PCI host bridge.
1920 nobios [X86-32] disallow use of PCI BIOS, only direct
1921 hardware access methods are allowed. Use this
1922 if you experience crashes upon bootup and you
1923 suspect they are caused by the BIOS.
1924 conf1 [X86] Force use of PCI Configuration
1925 Mechanism 1.
1926 conf2 [X86] Force use of PCI Configuration
1927 Mechanism 2.
1928 noaer [PCIE] If the PCIEAER kernel config parameter is
1929 enabled, this kernel boot option can be used to
1930 disable the use of PCIE advanced error reporting.
1931 nodomains [PCI] Disable support for multiple PCI
1932 root domains (aka PCI segments, in ACPI-speak).
1933 nommconf [X86] Disable use of MMCONFIG for PCI
1934 Configuration
1935 check_enable_amd_mmconf [X86] check for and enable
1936 properly configured MMIO access to PCI
1937 config space on AMD family 10h CPU
1938 nomsi [MSI] If the PCI_MSI kernel config parameter is
1939 enabled, this kernel boot option can be used to
1940 disable the use of MSI interrupts system-wide.
1941 noioapicquirk [APIC] Disable all boot interrupt quirks.
1942 Safety option to keep boot IRQs enabled. This
1943 should never be necessary.
1944 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1945 primary IO-APIC for bridges that cannot disable
1946 boot IRQs. This fixes a source of spurious IRQs
1947 when the system masks IRQs.
1948 noioapicreroute [APIC] Disable workaround that uses the
1949 boot IRQ equivalent of an IRQ that connects to
1950 a chipset where boot IRQs cannot be disabled.
1951 The opposite of ioapicreroute.
1952 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1953 routing table. These calls are known to be buggy
1954 on several machines and they hang the machine
1955 when used, but on other computers it's the only
1956 way to get the interrupt routing table. Try
1957 this option if the kernel is unable to allocate
1958 IRQs or discover secondary PCI buses on your
1959 motherboard.
1960 rom [X86] Assign address space to expansion ROMs.
1961 Use with caution as certain devices share
1962 address decoders between ROMs and other
1963 resources.
1964 norom [X86] Do not assign address space to
1965 expansion ROMs that do not already have
1966 BIOS assigned address ranges.
1967 nobar [X86] Do not assign address space to the
1968 BARs that weren't assigned by the BIOS.
1969 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1970 assigned automatically to PCI devices. You can
1971 make the kernel exclude IRQs of your ISA cards
1972 this way.
1973 pirqaddr=0xAAAAA [X86] Specify the physical address
1974 of the PIRQ table (normally generated
1975 by the BIOS) if it is outside the
1976 F0000h-100000h range.
1977 lastbus=N [X86] Scan all buses thru bus #N. Can be
1978 useful if the kernel is unable to find your
1979 secondary buses and you want to tell it
1980 explicitly which ones they are.
1981 assign-busses [X86] Always assign all PCI bus
1982 numbers ourselves, overriding
1983 whatever the firmware may have done.
1984 usepirqmask [X86] Honor the possible IRQ mask stored
1985 in the BIOS $PIR table. This is needed on
1986 some systems with broken BIOSes, notably
1987 some HP Pavilion N5400 and Omnibook XE3
1988 notebooks. This will have no effect if ACPI
1989 IRQ routing is enabled.
1990 noacpi [X86] Do not use ACPI for IRQ routing
1991 or for PCI scanning.
1992 use_crs [X86] Use PCI host bridge window information
1993 from ACPI. On BIOSes from 2008 or later, this
1994 is enabled by default. If you need to use this,
1995 please report a bug.
1996 nocrs [X86] Ignore PCI host bridge windows from ACPI.
1997 If you need to use this, please report a bug.
1998 routeirq Do IRQ routing for all PCI devices.
1999 This is normally done in pci_enable_device(),
2000 so this option is a temporary workaround
2001 for broken drivers that don't call it.
2002 skip_isa_align [X86] do not align io start addr, so can
2003 handle more pci cards
2004 firmware [ARM] Do not re-enumerate the bus but instead
2005 just use the configuration from the
2006 bootloader. This is currently used on
2007 IXP2000 systems where the bus has to be
2008 configured a certain way for adjunct CPUs.
2009 noearly [X86] Don't do any early type 1 scanning.
2010 This might help on some broken boards which
2011 machine check when some devices' config space
2012 is read. But various workarounds are disabled
2013 and some IOMMU drivers will not work.
2014 bfsort Sort PCI devices into breadth-first order.
2015 This sorting is done to get a device
2016 order compatible with older (<= 2.4) kernels.
2017 nobfsort Don't sort PCI devices into breadth-first order.
2018 cbiosize=nn[KMG] The fixed amount of bus space which is
2019 reserved for the CardBus bridge's IO window.
2020 The default value is 256 bytes.
2021 cbmemsize=nn[KMG] The fixed amount of bus space which is
2022 reserved for the CardBus bridge's memory
2023 window. The default value is 64 megabytes.
2024 resource_alignment=
2025 Format:
2026 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2027 Specifies alignment and device to reassign
2028 aligned memory resources.
2029 If <order of align> is not specified,
2030 PAGE_SIZE is used as alignment.
2031 PCI-PCI bridge can be specified, if resource
2032 windows need to be expanded.
2033 ecrc= Enable/disable PCIe ECRC (transaction layer
2034 end-to-end CRC checking).
2035 bios: Use BIOS/firmware settings. This is the
2036 the default.
2037 off: Turn ECRC off
2038 on: Turn ECRC on.
2039 realloc reallocate PCI resources if allocations done by BIOS
2040 are erroneous.
2042 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2043 Management.
2044 off Disable ASPM.
2045 force Enable ASPM even on devices that claim not to support it.
2046 WARNING: Forcing ASPM on may cause system lockups.
2048 pcie_ports= [PCIE] PCIe ports handling:
2049 auto Ask the BIOS whether or not to use native PCIe services
2050 associated with PCIe ports (PME, hot-plug, AER). Use
2051 them only if that is allowed by the BIOS.
2052 native Use native PCIe services associated with PCIe ports
2053 unconditionally.
2054 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2055 ports driver.
2057 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2058 nomsi Do not use MSI for native PCIe PME signaling (this makes
2059 all PCIe root ports use INTx for all services).
2061 pcmv= [HW,PCMCIA] BadgePAD 4
2063 pd. [PARIDE]
2064 See Documentation/blockdev/paride.txt.
2066 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2067 boot time.
2068 Format: { 0 | 1 }
2069 See arch/parisc/kernel/pdc_chassis.c
2071 percpu_alloc= Select which percpu first chunk allocator to use.
2072 Currently supported values are "embed" and "page".
2073 Archs may support subset or none of the selections.
2074 See comments in mm/percpu.c for details on each
2075 allocator. This parameter is primarily for debugging
2076 and performance comparison.
2078 pf. [PARIDE]
2079 See Documentation/blockdev/paride.txt.
2081 pg. [PARIDE]
2082 See Documentation/blockdev/paride.txt.
2084 pirq= [SMP,APIC] Manual mp-table setup
2085 See Documentation/x86/i386/IO-APIC.txt.
2087 plip= [PPT,NET] Parallel port network link
2088 Format: { parport<nr> | timid | 0 }
2089 See also Documentation/parport.txt.
2091 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2092 Override pmtimer IOPort with a hex value.
2093 e.g. pmtmr=0x508
2095 pnp.debug=1 [PNP]
2096 Enable PNP debug messages (depends on the
2097 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2098 via /sys/module/pnp/parameters/debug. We always show
2099 current resource usage; turning this on also shows
2100 possible settings and some assignment information.
2102 pnpacpi= [ACPI]
2103 { off }
2105 pnpbios= [ISAPNP]
2106 { on | off | curr | res | no-curr | no-res }
2108 pnp_reserve_irq=
2109 [ISAPNP] Exclude IRQs for the autoconfiguration
2111 pnp_reserve_dma=
2112 [ISAPNP] Exclude DMAs for the autoconfiguration
2114 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2115 Ranges are in pairs (I/O port base and size).
2117 pnp_reserve_mem=
2118 [ISAPNP] Exclude memory regions for the
2119 autoconfiguration.
2120 Ranges are in pairs (memory base and size).
2122 ports= [IP_VS_FTP] IPVS ftp helper module
2123 Default is 21.
2124 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2125 may be specified.
2126 Format: <port>,<port>....
2128 print-fatal-signals=
2129 [KNL] debug: print fatal signals
2131 If enabled, warn about various signal handling
2132 related application anomalies: too many signals,
2133 too many POSIX.1 timers, fatal signals causing a
2134 coredump - etc.
2136 If you hit the warning due to signal overflow,
2137 you might want to try "ulimit -i unlimited".
2139 default: off.
2141 printk.time= Show timing data prefixed to each printk message line
2142 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2144 processor.max_cstate= [HW,ACPI]
2145 Limit processor to maximum C-state
2146 max_cstate=9 overrides any DMI blacklist limit.
2148 processor.nocst [HW,ACPI]
2149 Ignore the _CST method to determine C-states,
2150 instead using the legacy FADT method
2152 profile= [KNL] Enable kernel profiling via /proc/profile
2153 Format: [schedule,]<number>
2154 Param: "schedule" - profile schedule points.
2155 Param: <number> - step/bucket size as a power of 2 for
2156 statistical time based profiling.
2157 Param: "sleep" - profile D-state sleeping (millisecs).
2158 Requires CONFIG_SCHEDSTATS
2159 Param: "kvm" - profile VM exits.
2161 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2162 before loading.
2163 See Documentation/blockdev/ramdisk.txt.
2165 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2166 probe for; one of (bare|imps|exps|lifebook|any).
2167 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2168 per second.
2169 psmouse.resetafter= [HW,MOUSE]
2170 Try to reset the device after so many bad packets
2171 (0 = never).
2172 psmouse.resolution=
2173 [HW,MOUSE] Set desired mouse resolution, in dpi.
2174 psmouse.smartscroll=
2175 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2176 0 = disabled, 1 = enabled (default).
2178 pstore.backend= Specify the name of the pstore backend to use
2180 pt. [PARIDE]
2181 See Documentation/blockdev/paride.txt.
2183 pty.legacy_count=
2184 [KNL] Number of legacy pty's. Overwrites compiled-in
2185 default number.
2187 quiet [KNL] Disable most log messages
2189 r128= [HW,DRM]
2191 raid= [HW,RAID]
2192 See Documentation/md.txt.
2194 ramdisk_blocksize= [RAM]
2195 See Documentation/blockdev/ramdisk.txt.
2197 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2198 See Documentation/blockdev/ramdisk.txt.
2200 rcupdate.blimit= [KNL,BOOT]
2201 Set maximum number of finished RCU callbacks to process
2202 in one batch.
2204 rcupdate.qhimark= [KNL,BOOT]
2205 Set threshold of queued
2206 RCU callbacks over which batch limiting is disabled.
2208 rcupdate.qlowmark= [KNL,BOOT]
2209 Set threshold of queued RCU callbacks below which
2210 batch limiting is re-enabled.
2212 rdinit= [KNL]
2213 Format: <full_path>
2214 Run specified binary instead of /init from the ramdisk,
2215 used for early userspace startup. See initrd.
2217 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2218 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2219 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2221 relax_domain_level=
2222 [KNL, SMP] Set scheduler's default relax_domain_level.
2223 See Documentation/cgroups/cpusets.txt.
2225 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2227 reservetop= [X86-32]
2228 Format: nn[KMG]
2229 Reserves a hole at the top of the kernel virtual
2230 address space.
2232 reservelow= [X86]
2233 Format: nn[K]
2234 Set the amount of memory to reserve for BIOS at
2235 the bottom of the address space.
2237 reset_devices [KNL] Force drivers to reset the underlying device
2238 during initialization.
2240 resume= [SWSUSP]
2241 Specify the partition device for software suspend
2243 resume_offset= [SWSUSP]
2244 Specify the offset from the beginning of the partition
2245 given by "resume=" at which the swap header is located,
2246 in <PAGE_SIZE> units (needed only for swap files).
2247 See Documentation/power/swsusp-and-swap-files.txt
2249 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2250 read the resume files
2252 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2253 Useful for devices that are detected asynchronously
2254 (e.g. USB and MMC devices).
2256 hibernate= [HIBERNATION]
2257 noresume Don't check if there's a hibernation image
2258 present during boot.
2259 nocompress Don't compress/decompress hibernation images.
2261 retain_initrd [RAM] Keep initrd memory after extraction
2263 rhash_entries= [KNL,NET]
2264 Set number of hash buckets for route cache
2266 riscom8= [HW,SERIAL]
2267 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2269 ro [KNL] Mount root device read-only on boot
2271 root= [KNL] Root filesystem
2272 See name_to_dev_t comment in init/do_mounts.c.
2274 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2275 mount the root filesystem
2277 rootflags= [KNL] Set root filesystem mount option string
2279 rootfstype= [KNL] Set root filesystem type
2281 rootwait [KNL] Wait (indefinitely) for root device to show up.
2282 Useful for devices that are detected asynchronously
2283 (e.g. USB and MMC devices).
2285 rw [KNL] Mount root device read-write on boot
2287 S [KNL] Run init in single mode
2289 sa1100ir [NET]
2290 See drivers/net/irda/sa1100_ir.c.
2292 sbni= [NET] Granch SBNI12 leased line adapter
2294 sched_debug [KNL] Enables verbose scheduler debug messages.
2296 security= [SECURITY] Choose a security module to enable at boot.
2297 If this boot parameter is not specified, only the first
2298 security module asking for security registration will be
2299 loaded. An invalid security module name will be treated
2300 as if no module has been chosen.
2302 selinux= [SELINUX] Disable or enable SELinux at boot time.
2303 Format: { "0" | "1" }
2304 See security/selinux/Kconfig help text.
2305 0 -- disable.
2306 1 -- enable.
2307 Default value is set via kernel config option.
2308 If enabled at boot time, /selinux/disable can be used
2309 later to disable prior to initial policy load.
2311 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2312 Format: { "0" | "1" }
2313 See security/apparmor/Kconfig help text
2314 0 -- disable.
2315 1 -- enable.
2316 Default value is set via kernel config option.
2318 serialnumber [BUGS=X86-32]
2320 shapers= [NET]
2321 Maximal number of shapers.
2323 show_msr= [x86] show boot-time MSR settings
2324 Format: { <integer> }
2325 Show boot-time (BIOS-initialized) MSR settings.
2326 The parameter means the number of CPUs to show,
2327 for example 1 means boot CPU only.
2329 simeth= [IA-64]
2330 simscsi=
2332 slram= [HW,MTD]
2334 slub_debug[=options[,slabs]] [MM, SLUB]
2335 Enabling slub_debug allows one to determine the
2336 culprit if slab objects become corrupted. Enabling
2337 slub_debug can create guard zones around objects and
2338 may poison objects when not in use. Also tracks the
2339 last alloc / free. For more information see
2340 Documentation/vm/slub.txt.
2342 slub_max_order= [MM, SLUB]
2343 Determines the maximum allowed order for slabs.
2344 A high setting may cause OOMs due to memory
2345 fragmentation. For more information see
2346 Documentation/vm/slub.txt.
2348 slub_min_objects= [MM, SLUB]
2349 The minimum number of objects per slab. SLUB will
2350 increase the slab order up to slub_max_order to
2351 generate a sufficiently large slab able to contain
2352 the number of objects indicated. The higher the number
2353 of objects the smaller the overhead of tracking slabs
2354 and the less frequently locks need to be acquired.
2355 For more information see Documentation/vm/slub.txt.
2357 slub_min_order= [MM, SLUB]
2358 Determines the mininum page order for slabs. Must be
2359 lower than slub_max_order.
2360 For more information see Documentation/vm/slub.txt.
2362 slub_nomerge [MM, SLUB]
2363 Disable merging of slabs with similar size. May be
2364 necessary if there is some reason to distinguish
2365 allocs to different slabs. Debug options disable
2366 merging on their own.
2367 For more information see Documentation/vm/slub.txt.
2369 smart2= [HW]
2370 Format: <io1>[,<io2>[,...,<io8>]]
2372 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2373 attempt to substitute SMP alternatives once at boot.
2375 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2376 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2377 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2378 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2379 smsc-ircc2.ircc_irq= [HW] IRQ line
2380 smsc-ircc2.ircc_dma= [HW] DMA channel
2381 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2382 0: Toshiba Satellite 1800 (GP data pin select)
2383 1: Fast pin select (default)
2384 2: ATC IRMode
2386 softlockup_panic=
2387 [KNL] Should the soft-lockup detector generate panics.
2388 Format: <integer>
2390 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2391 See Documentation/laptops/sonypi.txt
2393 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2394 See Documentation/serial/specialix.txt.
2396 spia_io_base= [HW,MTD]
2397 spia_fio_base=
2398 spia_pedr=
2399 spia_peddr=
2401 stacktrace [FTRACE]
2402 Enabled the stack tracer on boot up.
2404 sti= [PARISC,HW]
2405 Format: <num>
2406 Set the STI (builtin display/keyboard on the HP-PARISC
2407 machines) console (graphic card) which should be used
2408 as the initial boot-console.
2409 See also comment in drivers/video/console/sticore.c.
2411 sti_font= [HW]
2412 See comment in drivers/video/console/sticore.c.
2414 stifb= [HW]
2415 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2417 sunrpc.min_resvport=
2418 sunrpc.max_resvport=
2419 [NFS,SUNRPC]
2420 SunRPC servers often require that client requests
2421 originate from a privileged port (i.e. a port in the
2422 range 0 < portnr < 1024).
2423 An administrator who wishes to reserve some of these
2424 ports for other uses may adjust the range that the
2425 kernel's sunrpc client considers to be privileged
2426 using these two parameters to set the minimum and
2427 maximum port values.
2429 sunrpc.pool_mode=
2430 [NFS]
2431 Control how the NFS server code allocates CPUs to
2432 service thread pools. Depending on how many NICs
2433 you have and where their interrupts are bound, this
2434 option will affect which CPUs will do NFS serving.
2435 Note: this parameter cannot be changed while the
2436 NFS server is running.
2438 auto the server chooses an appropriate mode
2439 automatically using heuristics
2440 global a single global pool contains all CPUs
2441 percpu one pool for each CPU
2442 pernode one pool for each NUMA node (equivalent
2443 to global on non-NUMA machines)
2445 sunrpc.tcp_slot_table_entries=
2446 sunrpc.udp_slot_table_entries=
2447 [NFS,SUNRPC]
2448 Sets the upper limit on the number of simultaneous
2449 RPC calls that can be sent from the client to a
2450 server. Increasing these values may allow you to
2451 improve throughput, but will also increase the
2452 amount of memory reserved for use by the client.
2454 swapaccount[=0|1]
2455 [KNL] Enable accounting of swap in memory resource
2456 controller if no parameter or 1 is given or disable
2457 it if 0 is given (See Documentation/cgroups/memory.txt)
2459 swiotlb= [IA-64] Number of I/O TLB slabs
2461 switches= [HW,M68k]
2463 sysfs.deprecated=0|1 [KNL]
2464 Enable/disable old style sysfs layout for old udev
2465 on older distributions. When this option is enabled
2466 very new udev will not work anymore. When this option
2467 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2468 in older udev will not work anymore.
2469 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2470 the kernel configuration.
2472 sysrq_always_enabled
2473 [KNL]
2474 Ignore sysrq setting - this boot parameter will
2475 neutralize any effect of /proc/sys/kernel/sysrq.
2476 Useful for debugging.
2478 tdfx= [HW,DRM]
2480 test_suspend= [SUSPEND]
2481 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2482 standby suspend) as the system sleep state to briefly
2483 enter during system startup. The system is woken from
2484 this state using a wakeup-capable RTC alarm.
2486 thash_entries= [KNL,NET]
2487 Set number of hash buckets for TCP connection
2489 thermal.act= [HW,ACPI]
2490 -1: disable all active trip points in all thermal zones
2491 <degrees C>: override all lowest active trip points
2493 thermal.crt= [HW,ACPI]
2494 -1: disable all critical trip points in all thermal zones
2495 <degrees C>: override all critical trip points
2497 thermal.nocrt= [HW,ACPI]
2498 Set to disable actions on ACPI thermal zone
2499 critical and hot trip points.
2501 thermal.off= [HW,ACPI]
2502 1: disable ACPI thermal control
2504 thermal.psv= [HW,ACPI]
2505 -1: disable all passive trip points
2506 <degrees C>: override all passive trip points to this
2507 value
2509 thermal.tzp= [HW,ACPI]
2510 Specify global default ACPI thermal zone polling rate
2511 <deci-seconds>: poll all this frequency
2512 0: no polling (default)
2514 threadirqs [KNL]
2515 Force threading of all interrupt handlers except those
2516 marked explicitely IRQF_NO_THREAD.
2518 topology= [S390]
2519 Format: {off | on}
2520 Specify if the kernel should make use of the cpu
2521 topology information if the hardware supports this.
2522 The scheduler will make use of this information and
2523 e.g. base its process migration decisions on it.
2524 Default is on.
2526 tp720= [HW,PS2]
2528 tpm_suspend_pcr=[HW,TPM]
2529 Format: integer pcr id
2530 Specify that at suspend time, the tpm driver
2531 should extend the specified pcr with zeros,
2532 as a workaround for some chips which fail to
2533 flush the last written pcr on TPM_SaveState.
2534 This will guarantee that all the other pcrs
2535 are saved.
2537 trace_buf_size=nn[KMG]
2538 [FTRACE] will set tracing buffer size.
2540 trace_event=[event-list]
2541 [FTRACE] Set and start specified trace events in order
2542 to facilitate early boot debugging.
2543 See also Documentation/trace/events.txt
2545 tsc= Disable clocksource stability checks for TSC.
2546 Format: <string>
2547 [x86] reliable: mark tsc clocksource as reliable, this
2548 disables clocksource verification at runtime, as well
2549 as the stability checks done at bootup. Used to enable
2550 high-resolution timer mode on older hardware, and in
2551 virtualized environment.
2552 [x86] noirqtime: Do not use TSC to do irq accounting.
2553 Used to run time disable IRQ_TIME_ACCOUNTING on any
2554 platforms where RDTSC is slow and this accounting
2555 can add overhead.
2557 turbografx.map[2|3]= [HW,JOY]
2558 TurboGraFX parallel port interface
2559 Format:
2560 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2561 See also Documentation/input/joystick-parport.txt
2563 udbg-immortal [PPC] When debugging early kernel crashes that
2564 happen after console_init() and before a proper
2565 console driver takes over, this boot options might
2566 help "seeing" what's going on.
2568 uhash_entries= [KNL,NET]
2569 Set number of hash buckets for UDP/UDP-Lite connections
2571 uhci-hcd.ignore_oc=
2572 [USB] Ignore overcurrent events (default N).
2573 Some badly-designed motherboards generate lots of
2574 bogus events, for ports that aren't wired to
2575 anything. Set this parameter to avoid log spamming.
2576 Note that genuine overcurrent events won't be
2577 reported either.
2579 unknown_nmi_panic
2580 [X86] Cause panic on unknown NMI.
2582 usbcore.authorized_default=
2583 [USB] Default USB device authorization:
2584 (default -1 = authorized except for wireless USB,
2585 0 = not authorized, 1 = authorized)
2587 usbcore.autosuspend=
2588 [USB] The autosuspend time delay (in seconds) used
2589 for newly-detected USB devices (default 2). This
2590 is the time required before an idle device will be
2591 autosuspended. Devices for which the delay is set
2592 to a negative value won't be autosuspended at all.
2594 usbcore.usbfs_snoop=
2595 [USB] Set to log all usbfs traffic (default 0 = off).
2597 usbcore.blinkenlights=
2598 [USB] Set to cycle leds on hubs (default 0 = off).
2600 usbcore.old_scheme_first=
2601 [USB] Start with the old device initialization
2602 scheme (default 0 = off).
2604 usbcore.use_both_schemes=
2605 [USB] Try the other device initialization scheme
2606 if the first one fails (default 1 = enabled).
2608 usbcore.initial_descriptor_timeout=
2609 [USB] Specifies timeout for the initial 64-byte
2610 USB_REQ_GET_DESCRIPTOR request in milliseconds
2611 (default 5000 = 5.0 seconds).
2613 usbhid.mousepoll=
2614 [USBHID] The interval which mice are to be polled at.
2616 usb-storage.delay_use=
2617 [UMS] The delay in seconds before a new device is
2618 scanned for Logical Units (default 5).
2620 usb-storage.quirks=
2621 [UMS] A list of quirks entries to supplement or
2622 override the built-in unusual_devs list. List
2623 entries are separated by commas. Each entry has
2624 the form VID:PID:Flags where VID and PID are Vendor
2625 and Product ID values (4-digit hex numbers) and
2626 Flags is a set of characters, each corresponding
2627 to a common usb-storage quirk flag as follows:
2628 a = SANE_SENSE (collect more than 18 bytes
2629 of sense data);
2630 b = BAD_SENSE (don't collect more than 18
2631 bytes of sense data);
2632 c = FIX_CAPACITY (decrease the reported
2633 device capacity by one sector);
2634 d = NO_READ_DISC_INFO (don't use
2635 READ_DISC_INFO command);
2636 e = NO_READ_CAPACITY_16 (don't use
2637 READ_CAPACITY_16 command);
2638 h = CAPACITY_HEURISTICS (decrease the
2639 reported device capacity by one
2640 sector if the number is odd);
2641 i = IGNORE_DEVICE (don't bind to this
2642 device);
2643 l = NOT_LOCKABLE (don't try to lock and
2644 unlock ejectable media);
2645 m = MAX_SECTORS_64 (don't transfer more
2646 than 64 sectors = 32 KB at a time);
2647 n = INITIAL_READ10 (force a retry of the
2648 initial READ(10) command);
2649 o = CAPACITY_OK (accept the capacity
2650 reported by the device);
2651 r = IGNORE_RESIDUE (the device reports
2652 bogus residue values);
2653 s = SINGLE_LUN (the device has only one
2654 Logical Unit);
2655 w = NO_WP_DETECT (don't test whether the
2656 medium is write-protected).
2657 Example: quirks=0419:aaf5:rl,0421:0433:rc
2659 user_debug= [KNL,ARM]
2660 Format: <int>
2661 See arch/arm/Kconfig.debug help text.
2662 1 - undefined instruction events
2663 2 - system calls
2664 4 - invalid data aborts
2665 8 - SIGSEGV faults
2666 16 - SIGBUS faults
2667 Example: user_debug=31
2669 userpte=
2670 [X86] Flags controlling user PTE allocations.
2672 nohigh = do not allocate PTE pages in
2673 HIGHMEM regardless of setting
2674 of CONFIG_HIGHPTE.
2676 vdso= [X86,SH]
2677 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2678 vdso=1: enable VDSO (default)
2679 vdso=0: disable VDSO mapping
2681 vdso32= [X86]
2682 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2683 vdso32=1: enable 32-bit VDSO (default)
2684 vdso32=0: disable 32-bit VDSO mapping
2686 vector= [IA-64,SMP]
2687 vector=percpu: enable percpu vector domain
2689 video= [FB] Frame buffer configuration
2690 See Documentation/fb/modedb.txt.
2692 vga= [BOOT,X86-32] Select a particular video mode
2693 See Documentation/x86/boot.txt and
2694 Documentation/svga.txt.
2695 Use vga=ask for menu.
2696 This is actually a boot loader parameter; the value is
2697 passed to the kernel using a special protocol.
2699 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2700 size of <nn>. This can be used to increase the
2701 minimum size (128MB on x86). It can also be used to
2702 decrease the size and leave more room for directly
2703 mapped kernel RAM.
2705 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2706 Format: <command>
2708 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2709 Format: <command>
2711 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2712 Format: <command>
2714 vsyscall= [X86-64]
2715 Controls the behavior of vsyscalls (i.e. calls to
2716 fixed addresses of 0xffffffffff600x00 from legacy
2717 code). Most statically-linked binaries and older
2718 versions of glibc use these calls. Because these
2719 functions are at fixed addresses, they make nice
2720 targets for exploits that can control RIP.
2722 emulate Vsyscalls turn into traps and are emulated
2723 reasonably safely.
2725 native [default] Vsyscalls are native syscall
2726 instructions.
2727 This is a little bit faster than trapping
2728 and makes a few dynamic recompilers work
2729 better than they would in emulation mode.
2730 It also makes exploits much easier to write.
2732 none Vsyscalls don't work at all. This makes
2733 them quite hard to use for exploits but
2734 might break your system.
2736 vt.cur_default= [VT] Default cursor shape.
2737 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2738 the parameters of the <Esc>[?A;B;Cc escape sequence;
2739 see VGA-softcursor.txt. Default: 2 = underline.
2741 vt.default_blu= [VT]
2742 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2743 Change the default blue palette of the console.
2744 This is a 16-member array composed of values
2745 ranging from 0-255.
2747 vt.default_grn= [VT]
2748 Format: <green0>,<green1>,<green2>,...,<green15>
2749 Change the default green palette of the console.
2750 This is a 16-member array composed of values
2751 ranging from 0-255.
2753 vt.default_red= [VT]
2754 Format: <red0>,<red1>,<red2>,...,<red15>
2755 Change the default red palette of the console.
2756 This is a 16-member array composed of values
2757 ranging from 0-255.
2759 vt.default_utf8=
2760 [VT]
2761 Format=<0|1>
2762 Set system-wide default UTF-8 mode for all tty's.
2763 Default is 1, i.e. UTF-8 mode is enabled for all
2764 newly opened terminals.
2766 vt.global_cursor_default=
2767 [VT]
2768 Format=<-1|0|1>
2769 Set system-wide default for whether a cursor
2770 is shown on new VTs. Default is -1,
2771 i.e. cursors will be created by default unless
2772 overridden by individual drivers. 0 will hide
2773 cursors, 1 will display them.
2775 watchdog timers [HW,WDT] For information on watchdog timers,
2776 see Documentation/watchdog/watchdog-parameters.txt
2777 or other driver-specific files in the
2778 Documentation/watchdog/ directory.
2780 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2781 default x2apic cluster mode on platforms
2782 supporting x2apic.
2784 x86_mrst_timer= [X86-32,APBT]
2785 Choose timer option for x86 Moorestown MID platform.
2786 Two valid options are apbt timer only and lapic timer
2787 plus one apbt timer for broadcast timer.
2788 x86_mrst_timer=apbt_only | lapic_and_apbt
2790 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2791 xd_geo= See header of drivers/block/xd.c.
2793 xen_emul_unplug= [HW,X86,XEN]
2794 Unplug Xen emulated devices
2795 Format: [unplug0,][unplug1]
2796 ide-disks -- unplug primary master IDE devices
2797 aux-ide-disks -- unplug non-primary-master IDE devices
2798 nics -- unplug network devices
2799 all -- unplug all emulated devices (NICs and IDE disks)
2800 unnecessary -- unplugging emulated devices is
2801 unnecessary even if the host did not respond to
2802 the unplug protocol
2803 never -- do not unplug even if version check succeeds
2805 xirc2ps_cs= [NET,PCMCIA]
2806 Format:
2807 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2809 ______________________________________________________________________
2811 TODO:
2813 Add more DRM drivers.