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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
3
4The 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
7case insensitive manner), and with descriptions where known.
8
9Module parameters for loadable modules are specified only as the
10parameter name with optional '=' and value as appropriate, such as:
11
12 modprobe usbcore blinkenlights=1
13
14Module parameters for modules that are built into the kernel image
15are specified on the kernel command line with the module name plus
16'.' plus parameter name, with '=' and value if appropriate, such as:
17
18 usbcore.blinkenlights=1
19
20Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22can also be entered as
23 log-buf-len=1M print_fatal_signals=1
24
25
26This document may not be entirely up to date and comprehensive. The command
27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28module. Loadable modules, after being loaded into the running kernel, also
29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30parameters may be changed at runtime by the command
31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
32
33The parameters listed below are only valid if certain kernel build options were
34enabled and if respective hardware is present. The text in square brackets at
35the beginning of each description states the restrictions within which a
36parameter is applicable:
37
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 FB The frame buffer device is enabled.
53 FTRACE Function tracing enabled.
54 GCOV GCOV profiling is enabled.
55 HW Appropriate hardware is enabled.
56 IA-64 IA-64 architecture is enabled.
57 IMA Integrity measurement architecture is enabled.
58 IOSCHED More than one I/O scheduler is enabled.
59 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
60 IPV6 IPv6 support is enabled.
61 ISAPNP ISA PnP code is enabled.
62 ISDN Appropriate ISDN support is enabled.
63 JOY Appropriate joystick support is enabled.
64 KGDB Kernel debugger support is enabled.
65 KVM Kernel Virtual Machine support is enabled.
66 LIBATA Libata driver is enabled
67 LP Printer support is enabled.
68 LOOP Loopback device support is enabled.
69 M68k M68k architecture is enabled.
70 These options have more detailed description inside of
71 Documentation/m68k/kernel-options.txt.
72 MCA MCA bus support is enabled.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VGA The VGA console has been enabled.
113 VT Virtual terminal support is enabled.
114 WDT Watchdog support is enabled.
115 XT IBM PC/XT MFM hard disk support is enabled.
116 X86-32 X86-32, aka i386 architecture is enabled.
117 X86-64 X86-64 architecture is enabled.
118 More X86-64 boot options can be found in
119 Documentation/x86/x86_64/boot-options.txt .
120 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
121 XEN Xen support is enabled
122
123In addition, the following text indicates that the option:
124
125 BUGS= Relates to possible processor bugs on the said processor.
126 KNL Is a kernel start-up parameter.
127 BOOT Is a boot loader parameter.
128
129Parameters denoted with BOOT are actually interpreted by the boot
130loader, and have no meaning to the kernel directly.
131Do not modify the syntax of boot loader parameters without extreme
132need or coordination with <Documentation/x86/boot.txt>.
133
134There are also arch-specific kernel-parameters not documented here.
135See for example <Documentation/x86/x86_64/boot-options.txt>.
136
137Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
138a trailing = on the name of any parameter states that that parameter will
139be entered as an environment variable, whereas its absence indicates that
140it will appear as a kernel argument readable via /proc/cmdline by programs
141running once the system is up.
142
143The number of kernel parameters is not limited, but the length of the
144complete command line (parameters including spaces etc.) is limited to
145a fixed number of characters. This limit depends on the architecture
146and is between 256 and 4096 characters. It is defined in the file
147./include/asm/setup.h as COMMAND_LINE_SIZE.
148
149Finally, the [KMG] suffix is commonly described after a number of kernel
150parameter values. These 'K', 'M', and 'G' letters represent the _binary_
151multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
152bytes respectively. Such letter suffixes can also be entirely omitted.
153
154
155 acpi= [HW,ACPI,X86]
156 Advanced Configuration and Power Interface
157 Format: { force | off | strict | noirq | rsdt }
158 force -- enable ACPI if default was off
159 off -- disable ACPI if default was on
160 noirq -- do not use ACPI for IRQ routing
161 strict -- Be less tolerant of platforms that are not
162 strictly ACPI specification compliant.
163 rsdt -- prefer RSDT over (default) XSDT
164 copy_dsdt -- copy DSDT to memory
165
166 See also Documentation/power/pm.txt, pci=noacpi
167
168 acpi_rsdp= [ACPI,EFI,KEXEC]
169 Pass the RSDP address to the kernel, mostly used
170 on machines running EFI runtime service to boot the
171 second kernel for kdump.
172
173 acpi_apic_instance= [ACPI, IOAPIC]
174 Format: <int>
175 2: use 2nd APIC table, if available
176 1,0: use 1st APIC table
177 default: 0
178
179 acpi_backlight= [HW,ACPI]
180 acpi_backlight=vendor
181 acpi_backlight=video
182 If set to vendor, prefer vendor specific driver
183 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
184 of the ACPI video.ko driver.
185
186 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
187 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
188 Format: <int>
189 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
190 debug output. Bits in debug_layer correspond to a
191 _COMPONENT in an ACPI source file, e.g.,
192 #define _COMPONENT ACPI_PCI_COMPONENT
193 Bits in debug_level correspond to a level in
194 ACPI_DEBUG_PRINT statements, e.g.,
195 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
196 The debug_level mask defaults to "info". See
197 Documentation/acpi/debug.txt for more information about
198 debug layers and levels.
199
200 Enable processor driver info messages:
201 acpi.debug_layer=0x20000000
202 Enable PCI/PCI interrupt routing info messages:
203 acpi.debug_layer=0x400000
204 Enable AML "Debug" output, i.e., stores to the Debug
205 object while interpreting AML:
206 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
207 Enable all messages related to ACPI hardware:
208 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
209
210 Some values produce so much output that the system is
211 unusable. The "log_buf_len" parameter may be useful
212 if you need to capture more output.
213
214 acpi_irq_balance [HW,ACPI]
215 ACPI will balance active IRQs
216 default in APIC mode
217
218 acpi_irq_nobalance [HW,ACPI]
219 ACPI will not move active IRQs (default)
220 default in PIC mode
221
222 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
223 Format: <irq>,<irq>...
224
225 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
226 use by PCI
227 Format: <irq>,<irq>...
228
229 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
230
231 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
232 Format: To spoof as Windows 98: ="Microsoft Windows"
233
234 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
235 acpi_osi="string1" # add string1 -- only one string
236 acpi_osi="!string2" # remove built-in string2
237 acpi_osi= # disable all strings
238
239 acpi_pm_good [X86]
240 Override the pmtimer bug detection: force the kernel
241 to assume that this machine's pmtimer latches its value
242 and always returns good values.
243
244 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
245 Format: { level | edge | high | low }
246
247 acpi_serialize [HW,ACPI] force serialization of AML methods
248
249 acpi_skip_timer_override [HW,ACPI]
250 Recognize and ignore IRQ0/pin2 Interrupt Override.
251 For broken nForce2 BIOS resulting in XT-PIC timer.
252
253 acpi_sleep= [HW,ACPI] Sleep options
254 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
255 old_ordering, nonvs, sci_force_enable }
256 See Documentation/power/video.txt for information on
257 s3_bios and s3_mode.
258 s3_beep is for debugging; it makes the PC's speaker beep
259 as soon as the kernel's real-mode entry point is called.
260 s4_nohwsig prevents ACPI hardware signature from being
261 used during resume from hibernation.
262 old_ordering causes the ACPI 1.0 ordering of the _PTS
263 control method, with respect to putting devices into
264 low power states, to be enforced (the ACPI 2.0 ordering
265 of _PTS is used by default).
266 nonvs prevents the kernel from saving/restoring the
267 ACPI NVS memory during suspend/hibernation and resume.
268 sci_force_enable causes the kernel to set SCI_EN directly
269 on resume from S1/S3 (which is against the ACPI spec,
270 but some broken systems don't work without it).
271
272 acpi_use_timer_override [HW,ACPI]
273 Use timer override. For some broken Nvidia NF5 boards
274 that require a timer override, but don't have HPET
275
276 acpi_enforce_resources= [ACPI]
277 { strict | lax | no }
278 Check for resource conflicts between native drivers
279 and ACPI OperationRegions (SystemIO and SystemMemory
280 only). IO ports and memory declared in ACPI might be
281 used by the ACPI subsystem in arbitrary AML code and
282 can interfere with legacy drivers.
283 strict (default): access to resources claimed by ACPI
284 is denied; legacy drivers trying to access reserved
285 resources will fail to bind to device using them.
286 lax: access to resources claimed by ACPI is allowed;
287 legacy drivers trying to access reserved resources
288 will bind successfully but a warning message is logged.
289 no: ACPI OperationRegions are not marked as reserved,
290 no further checks are performed.
291
292 add_efi_memmap [EFI; X86] Include EFI memory map in
293 kernel's map of available physical RAM.
294
295 agp= [AGP]
296 { off | try_unsupported }
297 off: disable AGP support
298 try_unsupported: try to drive unsupported chipsets
299 (may crash computer or cause data corruption)
300
301 ALSA [HW,ALSA]
302 See Documentation/sound/alsa/alsa-parameters.txt
303
304 alignment= [KNL,ARM]
305 Allow the default userspace alignment fault handler
306 behaviour to be specified. Bit 0 enables warnings,
307 bit 1 enables fixups, and bit 2 sends a segfault.
308
309 amd_iommu= [HW,X86-84]
310 Pass parameters to the AMD IOMMU driver in the system.
311 Possible values are:
312 fullflush - enable flushing of IO/TLB entries when
313 they are unmapped. Otherwise they are
314 flushed before they will be reused, which
315 is a lot of faster
316 off - do not initialize any AMD IOMMU found in
317 the system
318
319 amijoy.map= [HW,JOY] Amiga joystick support
320 Map of devices attached to JOY0DAT and JOY1DAT
321 Format: <a>,<b>
322 See also Documentation/kernel/input/joystick.txt
323
324 analog.map= [HW,JOY] Analog joystick and gamepad support
325 Specifies type or capabilities of an analog joystick
326 connected to one of 16 gameports
327 Format: <type1>,<type2>,..<type16>
328
329 apc= [HW,SPARC]
330 Power management functions (SPARCstation-4/5 + deriv.)
331 Format: noidle
332 Disable APC CPU standby support. SPARCstation-Fox does
333 not play well with APC CPU idle - disable it if you have
334 APC and your system crashes randomly.
335
336 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
337 Change the output verbosity whilst booting
338 Format: { quiet (default) | verbose | debug }
339 Change the amount of debugging information output
340 when initialising the APIC and IO-APIC components.
341
342 autoconf= [IPV6]
343 See Documentation/networking/ipv6.txt.
344
345 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
346 Limit apic dumping. The parameter defines the maximal
347 number of local apics being dumped. Also it is possible
348 to set it to "all" by meaning -- no limit here.
349 Format: { 1 (default) | 2 | ... | all }.
350 The parameter valid if only apic=debug or
351 apic=verbose is specified.
352 Example: apic=debug show_lapic=all
353
354 apm= [APM] Advanced Power Management
355 See header of arch/x86/kernel/apm_32.c.
356
357 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
358 Format: <io>,<irq>,<nodeID>
359
360 ataflop= [HW,M68k]
361
362 atarimouse= [HW,MOUSE] Atari Mouse
363
364 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
365 EzKey and similar keyboards
366
367 atkbd.reset= [HW] Reset keyboard during initialization
368
369 atkbd.set= [HW] Select keyboard code set
370 Format: <int> (2 = AT (default), 3 = PS/2)
371
372 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
373 keyboards
374
375 atkbd.softraw= [HW] Choose between synthetic and real raw mode
376 Format: <bool> (0 = real, 1 = synthetic (default))
377
378 atkbd.softrepeat= [HW]
379 Use software keyboard repeat
380
381 autotest [IA-64]
382
383 baycom_epp= [HW,AX25]
384 Format: <io>,<mode>
385
386 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
387 Format: <io>,<mode>
388 See header of drivers/net/hamradio/baycom_par.c.
389
390 baycom_ser_fdx= [HW,AX25]
391 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
392 Format: <io>,<irq>,<mode>[,<baud>]
393 See header of drivers/net/hamradio/baycom_ser_fdx.c.
394
395 baycom_ser_hdx= [HW,AX25]
396 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
397 Format: <io>,<irq>,<mode>
398 See header of drivers/net/hamradio/baycom_ser_hdx.c.
399
400 boot_delay= Milliseconds to delay each printk during boot.
401 Values larger than 10 seconds (10000) are changed to
402 no delay (0).
403 Format: integer
404
405 bootmem_debug [KNL] Enable bootmem allocator debug messages.
406
407 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
408 bttv.radio= Most important insmod options are available as
409 kernel args too.
410 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
411 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
412
413 bulk_remove=off [PPC] This parameter disables the use of the pSeries
414 firmware feature for flushing multiple hpte entries
415 at a time.
416
417 c101= [NET] Moxa C101 synchronous serial card
418
419 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
420 Sometimes CPU hardware bugs make them report the cache
421 size incorrectly. The kernel will attempt work arounds
422 to fix known problems, but for some CPUs it is not
423 possible to determine what the correct size should be.
424 This option provides an override for these situations.
425
426 capability.disable=
427 [SECURITY] Disable capabilities. This would normally
428 be used only if an alternative security model is to be
429 configured. Potentially dangerous and should only be
430 used if you are entirely sure of the consequences.
431
432 ccw_timeout_log [S390]
433 See Documentation/s390/CommonIO for details.
434
435 cgroup_disable= [KNL] Disable a particular controller
436 Format: {name of the controller(s) to disable}
437 {Currently supported controllers - "memory"}
438
439 checkreqprot [SELINUX] Set initial checkreqprot flag value.
440 Format: { "0" | "1" }
441 See security/selinux/Kconfig help text.
442 0 -- check protection applied by kernel (includes
443 any implied execute protection).
444 1 -- check protection requested by application.
445 Default value is set via a kernel config option.
446 Value can be changed at runtime via
447 /selinux/checkreqprot.
448
449 cio_ignore= [S390]
450 See Documentation/s390/CommonIO for details.
451
452 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
453 [Deprecated]
454 Forces specified clocksource (if available) to be used
455 when calculating gettimeofday(). If specified
456 clocksource is not available, it defaults to PIT.
457 Format: { pit | tsc | cyclone | pmtmr }
458
459 clocksource= Override the default clocksource
460 Format: <string>
461 Override the default clocksource and use the clocksource
462 with the name specified.
463 Some clocksource names to choose from, depending on
464 the platform:
465 [all] jiffies (this is the base, fallback clocksource)
466 [ACPI] acpi_pm
467 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
468 pxa_timer,timer3,32k_counter,timer0_1
469 [AVR32] avr32
470 [X86-32] pit,hpet,tsc;
471 scx200_hrt on Geode; cyclone on IBM x440
472 [MIPS] MIPS
473 [PARISC] cr16
474 [S390] tod
475 [SH] SuperH
476 [SPARC64] tick
477 [X86-64] hpet,tsc
478
479 clearcpuid=BITNUM [X86]
480 Disable CPUID feature X for the kernel. See
481 arch/x86/include/asm/cpufeature.h for the valid bit
482 numbers. Note the Linux specific bits are not necessarily
483 stable over kernel options, but the vendor specific
484 ones should be.
485 Also note that user programs calling CPUID directly
486 or using the feature without checking anything
487 will still see it. This just prevents it from
488 being used by the kernel or shown in /proc/cpuinfo.
489 Also note the kernel might malfunction if you disable
490 some critical bits.
491
492 cmo_free_hint= [PPC] Format: { yes | no }
493 Specify whether pages are marked as being inactive
494 when they are freed. This is used in CMO environments
495 to determine OS memory pressure for page stealing by
496 a hypervisor.
497 Default: yes
498
499 code_bytes [X86] How many bytes of object code to print
500 in an oops report.
501 Range: 0 - 8192
502 Default: 64
503
504 com20020= [HW,NET] ARCnet - COM20020 chipset
505 Format:
506 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
507
508 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
509 Format: <io>[,<irq>]
510
511 com90xx= [HW,NET]
512 ARCnet - COM90xx chipset (memory-mapped buffers)
513 Format: <io>[,<irq>[,<memstart>]]
514
515 condev= [HW,S390] console device
516 conmode=
517
518 console= [KNL] Output console device and options.
519
520 tty<n> Use the virtual console device <n>.
521
522 ttyS<n>[,options]
523 ttyUSB0[,options]
524 Use the specified serial port. The options are of
525 the form "bbbbpnf", where "bbbb" is the baud rate,
526 "p" is parity ("n", "o", or "e"), "n" is number of
527 bits, and "f" is flow control ("r" for RTS or
528 omit it). Default is "9600n8".
529
530 See Documentation/serial-console.txt for more
531 information. See
532 Documentation/networking/netconsole.txt for an
533 alternative.
534
535 uart[8250],io,<addr>[,options]
536 uart[8250],mmio,<addr>[,options]
537 Start an early, polled-mode console on the 8250/16550
538 UART at the specified I/O port or MMIO address,
539 switching to the matching ttyS device later. The
540 options are the same as for ttyS, above.
541
542 If the device connected to the port is not a TTY but a braille
543 device, prepend "brl," before the device type, for instance
544 console=brl,ttyS0
545 For now, only VisioBraille is supported.
546
547 consoleblank= [KNL] The console blank (screen saver) timeout in
548 seconds. Defaults to 10*60 = 10mins. A value of 0
549 disables the blank timer.
550
551 coredump_filter=
552 [KNL] Change the default value for
553 /proc/<pid>/coredump_filter.
554 See also Documentation/filesystems/proc.txt.
555
556 cpuidle.off=1 [CPU_IDLE]
557 disable the cpuidle sub-system
558
559 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
560 Format:
561 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
562
563 crashkernel=size[KMG][@offset[KMG]]
564 [KNL] Using kexec, Linux can switch to a 'crash kernel'
565 upon panic. This parameter reserves the physical
566 memory region [offset, offset + size] for that kernel
567 image. If '@offset' is omitted, then a suitable offset
568 is selected automatically. Check
569 Documentation/kdump/kdump.txt for further details.
570
571 crashkernel=range1:size1[,range2:size2,...][@offset]
572 [KNL] Same as above, but depends on the memory
573 in the running system. The syntax of range is
574 start-[end] where start and end are both
575 a memory unit (amount[KMG]). See also
576 Documentation/kdump/kdump.txt for an example.
577
578 cs89x0_dma= [HW,NET]
579 Format: <dma>
580
581 cs89x0_media= [HW,NET]
582 Format: { rj45 | aui | bnc }
583
584 dasd= [HW,NET]
585 See header of drivers/s390/block/dasd_devmap.c.
586
587 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
588 (one device per port)
589 Format: <port#>,<type>
590 See also Documentation/input/joystick-parport.txt
591
592 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
593 time. See Documentation/dynamic-debug-howto.txt for
594 details.
595
596 debug [KNL] Enable kernel debugging (events log level).
597
598 debug_locks_verbose=
599 [KNL] verbose self-tests
600 Format=<0|1>
601 Print debugging info while doing the locking API
602 self-tests.
603 We default to 0 (no extra messages), setting it to
604 1 will print _a lot_ more information - normally
605 only useful to kernel developers.
606
607 debug_objects [KNL] Enable object debugging
608
609 no_debug_objects
610 [KNL] Disable object debugging
611
612 debugpat [X86] Enable PAT debugging
613
614 decnet.addr= [HW,NET]
615 Format: <area>[,<node>]
616 See also Documentation/networking/decnet.txt.
617
618 default_hugepagesz=
619 [same as hugepagesz=] The size of the default
620 HugeTLB page size. This is the size represented by
621 the legacy /proc/ hugepages APIs, used for SHM, and
622 default size when mounting hugetlbfs filesystems.
623 Defaults to the default architecture's huge page size
624 if not specified.
625
626 dhash_entries= [KNL]
627 Set number of hash buckets for dentry cache.
628
629 digi= [HW,SERIAL]
630 IO parameters + enable/disable command.
631
632 digiepca= [HW,SERIAL]
633 See drivers/char/README.epca and
634 Documentation/serial/digiepca.txt.
635
636 disable= [IPV6]
637 See Documentation/networking/ipv6.txt.
638
639 disable_ddw [PPC/PSERIES]
640 Disable Dynamic DMA Window support. Use this if
641 to workaround buggy firmware.
642
643 disable_ipv6= [IPV6]
644 See Documentation/networking/ipv6.txt.
645
646 disable_mtrr_cleanup [X86]
647 The kernel tries to adjust MTRR layout from continuous
648 to discrete, to make X server driver able to add WB
649 entry later. This parameter disables that.
650
651 disable_mtrr_trim [X86, Intel and AMD only]
652 By default the kernel will trim any uncacheable
653 memory out of your available memory pool based on
654 MTRR settings. This parameter disables that behavior,
655 possibly causing your machine to run very slowly.
656
657 disable_timer_pin_1 [X86]
658 Disable PIN 1 of APIC timer
659 Can be useful to work around chipset bugs.
660
661 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
662 this option disables the debugging code at boot.
663
664 dma_debug_entries=<number>
665 This option allows to tune the number of preallocated
666 entries for DMA-API debugging code. One entry is
667 required per DMA-API allocation. Use this if the
668 DMA-API debugging code disables itself because the
669 architectural default is too low.
670
671 dma_debug_driver=<driver_name>
672 With this option the DMA-API debugging driver
673 filter feature can be enabled at boot time. Just
674 pass the driver to filter for as the parameter.
675 The filter can be disabled or changed to another
676 driver later using sysfs.
677
678 dscc4.setup= [NET]
679
680 earlycon= [KNL] Output early console device and options.
681 uart[8250],io,<addr>[,options]
682 uart[8250],mmio,<addr>[,options]
683 uart[8250],mmio32,<addr>[,options]
684 Start an early, polled-mode console on the 8250/16550
685 UART at the specified I/O port or MMIO address.
686 MMIO inter-register address stride is either 8-bit
687 (mmio) or 32-bit (mmio32).
688 The options are the same as for ttyS, above.
689
690 earlyprintk= [X86,SH,BLACKFIN]
691 earlyprintk=vga
692 earlyprintk=serial[,ttySn[,baudrate]]
693 earlyprintk=ttySn[,baudrate]
694 earlyprintk=dbgp[debugController#]
695
696 Append ",keep" to not disable it when the real console
697 takes over.
698
699 Only vga or serial or usb debug port at a time.
700
701 Currently only ttyS0 and ttyS1 are supported.
702
703 Interaction with the standard serial driver is not
704 very good.
705
706 The VGA output is eventually overwritten by the real
707 console.
708
709 ekgdboc= [X86,KGDB] Allow early kernel console debugging
710 ekgdboc=kbd
711
712 This is designed to be used in conjunction with
713 the boot argument: earlyprintk=vga
714
715 edd= [EDD]
716 Format: {"off" | "on" | "skip[mbr]"}
717
718 eisa_irq_edge= [PARISC,HW]
719 See header of drivers/parisc/eisa.c.
720
721 elanfreq= [X86-32]
722 See comment before function elanfreq_setup() in
723 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
724
725 elevator= [IOSCHED]
726 Format: {"cfq" | "deadline" | "noop"}
727 See Documentation/block/as-iosched.txt and
728 Documentation/block/deadline-iosched.txt for details.
729
730 elfcorehdr= [IA-64,PPC,SH,X86]
731 Specifies physical address of start of kernel core
732 image elf header. Generally kexec loader will
733 pass this option to capture kernel.
734 See Documentation/kdump/kdump.txt for details.
735
736 enable_mtrr_cleanup [X86]
737 The kernel tries to adjust MTRR layout from continuous
738 to discrete, to make X server driver able to add WB
739 entry later. This parameter enables that.
740
741 enable_timer_pin_1 [X86]
742 Enable PIN 1 of APIC timer
743 Can be useful to work around chipset bugs
744 (in particular on some ATI chipsets).
745 The kernel tries to set a reasonable default.
746
747 enforcing [SELINUX] Set initial enforcing status.
748 Format: {"0" | "1"}
749 See security/selinux/Kconfig help text.
750 0 -- permissive (log only, no denials).
751 1 -- enforcing (deny and log).
752 Default value is 0.
753 Value can be changed at runtime via /selinux/enforce.
754
755 erst_disable [ACPI]
756 Disable Error Record Serialization Table (ERST)
757 support.
758
759 ether= [HW,NET] Ethernet cards parameters
760 This option is obsoleted by the "netdev=" option, which
761 has equivalent usage. See its documentation for details.
762
763 failslab=
764 fail_page_alloc=
765 fail_make_request=[KNL]
766 General fault injection mechanism.
767 Format: <interval>,<probability>,<space>,<times>
768 See also /Documentation/fault-injection/.
769
770 floppy= [HW]
771 See Documentation/blockdev/floppy.txt.
772
773 force_pal_cache_flush
774 [IA-64] Avoid check_sal_cache_flush which may hang on
775 buggy SAL_CACHE_FLUSH implementations. Using this
776 parameter will force ia64_sal_cache_flush to call
777 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
778
779 ftrace=[tracer]
780 [FTRACE] will set and start the specified tracer
781 as early as possible in order to facilitate early
782 boot debugging.
783
784 ftrace_dump_on_oops[=orig_cpu]
785 [FTRACE] will dump the trace buffers on oops.
786 If no parameter is passed, ftrace will dump
787 buffers of all CPUs, but if you pass orig_cpu, it will
788 dump only the buffer of the CPU that triggered the
789 oops.
790
791 ftrace_filter=[function-list]
792 [FTRACE] Limit the functions traced by the function
793 tracer at boot up. function-list is a comma separated
794 list of functions. This list can be changed at run
795 time by the set_ftrace_filter file in the debugfs
796 tracing directory.
797
798 ftrace_notrace=[function-list]
799 [FTRACE] Do not trace the functions specified in
800 function-list. This list can be changed at run time
801 by the set_ftrace_notrace file in the debugfs
802 tracing directory.
803
804 ftrace_graph_filter=[function-list]
805 [FTRACE] Limit the top level callers functions traced
806 by the function graph tracer at boot up.
807 function-list is a comma separated list of functions
808 that can be changed at run time by the
809 set_graph_function file in the debugfs tracing directory.
810
811 gamecon.map[2|3]=
812 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
813 support via parallel port (up to 5 devices per port)
814 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
815 See also Documentation/input/joystick-parport.txt
816
817 gamma= [HW,DRM]
818
819 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
820 Format: off | on
821 default: on
822
823 gcov_persist= [GCOV] When non-zero (default), profiling data for
824 kernel modules is saved and remains accessible via
825 debugfs, even when the module is unloaded/reloaded.
826 When zero, profiling data is discarded and associated
827 debugfs files are removed at module unload time.
828
829 gpt [EFI] Forces disk with valid GPT signature but
830 invalid Protective MBR to be treated as GPT.
831
832 hashdist= [KNL,NUMA] Large hashes allocated during boot
833 are distributed across NUMA nodes. Defaults on
834 for 64-bit NUMA, off otherwise.
835 Format: 0 | 1 (for off | on)
836
837 hcl= [IA-64] SGI's Hardware Graph compatibility layer
838
839 hd= [EIDE] (E)IDE hard drive subsystem geometry
840 Format: <cyl>,<head>,<sect>
841
842 hest_disable [ACPI]
843 Disable Hardware Error Source Table (HEST) support;
844 corresponding firmware-first mode error processing
845 logic will be disabled.
846
847 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
848 size of <nn>. This works even on boxes that have no
849 highmem otherwise. This also works to reduce highmem
850 size on bigger boxes.
851
852 highres= [KNL] Enable/disable high resolution timer mode.
853 Valid parameters: "on", "off"
854 Default: "on"
855
856 hisax= [HW,ISDN]
857 See Documentation/isdn/README.HiSax.
858
859 hlt [BUGS=ARM,SH]
860
861 hpet= [X86-32,HPET] option to control HPET usage
862 Format: { enable (default) | disable | force |
863 verbose }
864 disable: disable HPET and use PIT instead
865 force: allow force enabled of undocumented chips (ICH4,
866 VIA, nVidia)
867 verbose: show contents of HPET registers during setup
868
869 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
870 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
871 On x86-64 and powerpc, this option can be specified
872 multiple times interleaved with hugepages= to reserve
873 huge pages of different sizes. Valid pages sizes on
874 x86-64 are 2M (when the CPU supports "pse") and 1G
875 (when the CPU supports the "pdpe1gb" cpuinfo flag)
876 Note that 1GB pages can only be allocated at boot time
877 using hugepages= and not freed afterwards.
878
879 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
880 terminal devices. Valid values: 0..8
881 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
882 If specified, z/VM IUCV HVC accepts connections
883 from listed z/VM user IDs only.
884
885 keep_bootcon [KNL]
886 Do not unregister boot console at start. This is only
887 useful for debugging when something happens in the window
888 between unregistering the boot console and initializing
889 the real console.
890
891 i2c_bus= [HW] Override the default board specific I2C bus speed
892 or register an additional I2C bus that is not
893 registered from board initialization code.
894 Format:
895 <bus_id>,<clkrate>
896
897 i8042.debug [HW] Toggle i8042 debug mode
898 i8042.direct [HW] Put keyboard port into non-translated mode
899 i8042.dumbkbd [HW] Pretend that controller can only read data from
900 keyboard and cannot control its state
901 (Don't attempt to blink the leds)
902 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
903 i8042.nokbd [HW] Don't check/create keyboard port
904 i8042.noloop [HW] Disable the AUX Loopback command while probing
905 for the AUX port
906 i8042.nomux [HW] Don't check presence of an active multiplexing
907 controller
908 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
909 controllers
910 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
911 i8042.reset [HW] Reset the controller during init and cleanup
912 i8042.unlock [HW] Unlock (ignore) the keylock
913
914 i810= [HW,DRM]
915
916 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
917 indicates that the driver is running on unsupported
918 hardware.
919 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
920 does not match list of supported models.
921 i8k.power_status
922 [HW] Report power status in /proc/i8k
923 (disabled by default)
924 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
925 capability is set.
926
927 icn= [HW,ISDN]
928 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
929
930 ide-core.nodma= [HW] (E)IDE subsystem
931 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
932 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
933 .cdrom .chs .ignore_cable are additional options
934 See Documentation/ide/ide.txt.
935
936 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
937 Claim all unknown PCI IDE storage controllers.
938
939 idle= [X86]
940 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
941 Poll forces a polling idle loop that can slightly
942 improve the performance of waking up a idle CPU, but
943 will use a lot of power and make the system run hot.
944 Not recommended.
945 idle=mwait: On systems which support MONITOR/MWAIT but
946 the kernel chose to not use it because it doesn't save
947 as much power as a normal idle loop, use the
948 MONITOR/MWAIT idle loop anyways. Performance should be
949 the same as idle=poll.
950 idle=halt: Halt is forced to be used for CPU idle.
951 In such case C2/C3 won't be used again.
952 idle=nomwait: Disable mwait for CPU C-states
953
954 ignore_loglevel [KNL]
955 Ignore loglevel setting - this will print /all/
956 kernel messages to the console. Useful for debugging.
957
958 ihash_entries= [KNL]
959 Set number of hash buckets for inode cache.
960
961 ima_audit= [IMA]
962 Format: { "0" | "1" }
963 0 -- integrity auditing messages. (Default)
964 1 -- enable informational integrity auditing messages.
965
966 ima_hash= [IMA]
967 Format: { "sha1" | "md5" }
968 default: "sha1"
969
970 ima_tcb [IMA]
971 Load a policy which meets the needs of the Trusted
972 Computing Base. This means IMA will measure all
973 programs exec'd, files mmap'd for exec, and all files
974 opened for read by uid=0.
975
976 init= [KNL]
977 Format: <full_path>
978 Run specified binary instead of /sbin/init as init
979 process.
980
981 initcall_debug [KNL] Trace initcalls as they are executed. Useful
982 for working out where the kernel is dying during
983 startup.
984
985 initrd= [BOOT] Specify the location of the initial ramdisk
986
987 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
988 Format: <irq>
989
990 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
991 on
992 Enable intel iommu driver.
993 off
994 Disable intel iommu driver.
995 igfx_off [Default Off]
996 By default, gfx is mapped as normal device. If a gfx
997 device has a dedicated DMAR unit, the DMAR unit is
998 bypassed by not enabling DMAR with this option. In
999 this case, gfx device will use physical address for
1000 DMA.
1001 forcedac [x86_64]
1002 With this option iommu will not optimize to look
1003 for io virtual address below 32-bit forcing dual
1004 address cycle on pci bus for cards supporting greater
1005 than 32-bit addressing. The default is to look
1006 for translation below 32-bit and if not available
1007 then look in the higher range.
1008 strict [Default Off]
1009 With this option on every unmap_single operation will
1010 result in a hardware IOTLB flush operation as opposed
1011 to batching them for performance.
1012 sp_off [Default Off]
1013 By default, super page will be supported if Intel IOMMU
1014 has the capability. With this option, super page will
1015 not be supported.
1016 intremap= [X86-64, Intel-IOMMU]
1017 Format: { on (default) | off | nosid }
1018 on enable Interrupt Remapping (default)
1019 off disable Interrupt Remapping
1020 nosid disable Source ID checking
1021
1022 inttest= [IA-64]
1023
1024 iomem= Disable strict checking of access to MMIO memory
1025 strict regions from userspace.
1026 relaxed
1027
1028 iommu= [x86]
1029 off
1030 force
1031 noforce
1032 biomerge
1033 panic
1034 nopanic
1035 merge
1036 nomerge
1037 forcesac
1038 soft
1039 pt [x86, IA-64]
1040
1041 io7= [HW] IO7 for Marvel based alpha systems
1042 See comment before marvel_specify_io7 in
1043 arch/alpha/kernel/core_marvel.c.
1044
1045 io_delay= [X86] I/O delay method
1046 0x80
1047 Standard port 0x80 based delay
1048 0xed
1049 Alternate port 0xed based delay (needed on some systems)
1050 udelay
1051 Simple two microseconds delay
1052 none
1053 No delay
1054
1055 ip= [IP_PNP]
1056 See Documentation/filesystems/nfs/nfsroot.txt.
1057
1058 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1059 See comment before ip2_setup() in
1060 drivers/char/ip2/ip2base.c.
1061
1062 irqfixup [HW]
1063 When an interrupt is not handled search all handlers
1064 for it. Intended to get systems with badly broken
1065 firmware running.
1066
1067 irqpoll [HW]
1068 When an interrupt is not handled search all handlers
1069 for it. Also check all handlers each timer
1070 interrupt. Intended to get systems with badly broken
1071 firmware running.
1072
1073 isapnp= [ISAPNP]
1074 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1075
1076 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1077 Format:
1078 <cpu number>,...,<cpu number>
1079 or
1080 <cpu number>-<cpu number>
1081 (must be a positive range in ascending order)
1082 or a mixture
1083 <cpu number>,...,<cpu number>-<cpu number>
1084
1085 This option can be used to specify one or more CPUs
1086 to isolate from the general SMP balancing and scheduling
1087 algorithms. You can move a process onto or off an
1088 "isolated" CPU via the CPU affinity syscalls or cpuset.
1089 <cpu number> begins at 0 and the maximum value is
1090 "number of CPUs in system - 1".
1091
1092 This option is the preferred way to isolate CPUs. The
1093 alternative -- manually setting the CPU mask of all
1094 tasks in the system -- can cause problems and
1095 suboptimal load balancer performance.
1096
1097 iucv= [HW,NET]
1098
1099 js= [HW,JOY] Analog joystick
1100 See Documentation/input/joystick.txt.
1101
1102 keepinitrd [HW,ARM]
1103
1104 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1105 specifies the amount of memory usable by the kernel
1106 for non-movable allocations. The requested amount is
1107 spread evenly throughout all nodes in the system. The
1108 remaining memory in each node is used for Movable
1109 pages. In the event, a node is too small to have both
1110 kernelcore and Movable pages, kernelcore pages will
1111 take priority and other nodes will have a larger number
1112 of kernelcore pages. The Movable zone is used for the
1113 allocation of pages that may be reclaimed or moved
1114 by the page migration subsystem. This means that
1115 HugeTLB pages may not be allocated from this zone.
1116 Note that allocations like PTEs-from-HighMem still
1117 use the HighMem zone if it exists, and the Normal
1118 zone if it does not.
1119
1120 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1121 Format: <Controller#>[,poll interval]
1122 The controller # is the number of the ehci usb debug
1123 port as it is probed via PCI. The poll interval is
1124 optional and is the number seconds in between
1125 each poll cycle to the debug port in case you need
1126 the functionality for interrupting the kernel with
1127 gdb or control-c on the dbgp connection. When
1128 not using this parameter you use sysrq-g to break into
1129 the kernel debugger.
1130
1131 kgdboc= [KGDB,HW] kgdb over consoles.
1132 Requires a tty driver that supports console polling,
1133 or a supported polling keyboard driver (non-usb).
1134 Serial only format: <serial_device>[,baud]
1135 keyboard only format: kbd
1136 keyboard and serial format: kbd,<serial_device>[,baud]
1137 Optional Kernel mode setting:
1138 kms, kbd format: kms,kbd
1139 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1140
1141 kgdbwait [KGDB] Stop kernel execution and enter the
1142 kernel debugger at the earliest opportunity.
1143
1144 kmac= [MIPS] korina ethernet MAC address.
1145 Configure the RouterBoard 532 series on-chip
1146 Ethernet adapter MAC address.
1147
1148 kmemleak= [KNL] Boot-time kmemleak enable/disable
1149 Valid arguments: on, off
1150 Default: on
1151
1152 kstack=N [X86] Print N words from the kernel stack
1153 in oops dumps.
1154
1155 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1156 Default is 0 (don't ignore, but inject #GP)
1157
1158 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1159 Default is 1 (enabled)
1160
1161 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1162 KVM MMU at runtime.
1163 Default is 0 (off)
1164
1165 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1166 Default is 1 (enabled)
1167
1168 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1169 for all guests.
1170 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1171
1172 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1173 (virtualized MMU) support on capable Intel chips.
1174 Default is 1 (enabled)
1175
1176 kvm-intel.emulate_invalid_guest_state=
1177 [KVM,Intel] Enable emulation of invalid guest states
1178 Default is 0 (disabled)
1179
1180 kvm-intel.flexpriority=
1181 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1182 Default is 1 (enabled)
1183
1184 kvm-intel.unrestricted_guest=
1185 [KVM,Intel] Disable unrestricted guest feature
1186 (virtualized real and unpaged mode) on capable
1187 Intel chips. Default is 1 (enabled)
1188
1189 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1190 feature (tagged TLBs) on capable Intel chips.
1191 Default is 1 (enabled)
1192
1193 l2cr= [PPC]
1194
1195 l3cr= [PPC]
1196
1197 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1198 disabled it.
1199
1200 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1201 in C2 power state.
1202
1203 libata.dma= [LIBATA] DMA control
1204 libata.dma=0 Disable all PATA and SATA DMA
1205 libata.dma=1 PATA and SATA Disk DMA only
1206 libata.dma=2 ATAPI (CDROM) DMA only
1207 libata.dma=4 Compact Flash DMA only
1208 Combinations also work, so libata.dma=3 enables DMA
1209 for disks and CDROMs, but not CFs.
1210
1211 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1212 libata.ignore_hpa=0 keep BIOS limits (default)
1213 libata.ignore_hpa=1 ignore limits, using full disk
1214
1215 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1216 when set.
1217 Format: <int>
1218
1219 libata.force= [LIBATA] Force configurations. The format is comma
1220 separated list of "[ID:]VAL" where ID is
1221 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1222 matching port, link or device. Basically, it matches
1223 the ATA ID string printed on console by libata. If
1224 the whole ID part is omitted, the last PORT and DEVICE
1225 values are used. If ID hasn't been specified yet, the
1226 configuration applies to all ports, links and devices.
1227
1228 If only DEVICE is omitted, the parameter applies to
1229 the port and all links and devices behind it. DEVICE
1230 number of 0 either selects the first device or the
1231 first fan-out link behind PMP device. It does not
1232 select the host link. DEVICE number of 15 selects the
1233 host link and device attached to it.
1234
1235 The VAL specifies the configuration to force. As long
1236 as there's no ambiguity shortcut notation is allowed.
1237 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1238 The following configurations can be forced.
1239
1240 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1241 Any ID with matching PORT is used.
1242
1243 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1244
1245 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1246 udma[/][16,25,33,44,66,100,133] notation is also
1247 allowed.
1248
1249 * [no]ncq: Turn on or off NCQ.
1250
1251 * nohrst, nosrst, norst: suppress hard, soft
1252 and both resets.
1253
1254 * dump_id: dump IDENTIFY data.
1255
1256 If there are multiple matching configurations changing
1257 the same attribute, the last one is used.
1258
1259 memblock=debug [KNL] Enable memblock debug messages.
1260
1261 load_ramdisk= [RAM] List of ramdisks to load from floppy
1262 See Documentation/blockdev/ramdisk.txt.
1263
1264 lockd.nlm_grace_period=P [NFS] Assign grace period.
1265 Format: <integer>
1266
1267 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1268 Format: <integer>
1269
1270 lockd.nlm_timeout=T [NFS] Assign timeout value.
1271 Format: <integer>
1272
1273 lockd.nlm_udpport=M [NFS] Assign UDP port.
1274 Format: <integer>
1275
1276 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1277 Format: <irq>
1278
1279 loglevel= All Kernel Messages with a loglevel smaller than the
1280 console loglevel will be printed to the console. It can
1281 also be changed with klogd or other programs. The
1282 loglevels are defined as follows:
1283
1284 0 (KERN_EMERG) system is unusable
1285 1 (KERN_ALERT) action must be taken immediately
1286 2 (KERN_CRIT) critical conditions
1287 3 (KERN_ERR) error conditions
1288 4 (KERN_WARNING) warning conditions
1289 5 (KERN_NOTICE) normal but significant condition
1290 6 (KERN_INFO) informational
1291 7 (KERN_DEBUG) debug-level messages
1292
1293 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1294 in bytes. n must be a power of two. The default
1295 size is set in the kernel config file.
1296
1297 logo.nologo [FB] Disables display of the built-in Linux logo.
1298 This may be used to provide more screen space for
1299 kernel log messages and is useful when debugging
1300 kernel boot problems.
1301
1302 lp=0 [LP] Specify parallel ports to use, e.g,
1303 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1304 lp=reset first parallel port). 'lp=0' disables the
1305 lp=auto printer driver. 'lp=reset' (which can be
1306 specified in addition to the ports) causes
1307 attached printers to be reset. Using
1308 lp=port1,port2,... specifies the parallel ports
1309 to associate lp devices with, starting with
1310 lp0. A port specification may be 'none' to skip
1311 that lp device, or a parport name such as
1312 'parport0'. Specifying 'lp=auto' instead of a
1313 port specification list means that device IDs
1314 from each port should be examined, to see if
1315 an IEEE 1284-compliant printer is attached; if
1316 so, the driver will manage that printer.
1317 See also header of drivers/char/lp.c.
1318
1319 lpj=n [KNL]
1320 Sets loops_per_jiffy to given constant, thus avoiding
1321 time-consuming boot-time autodetection (up to 250 ms per
1322 CPU). 0 enables autodetection (default). To determine
1323 the correct value for your kernel, boot with normal
1324 autodetection and see what value is printed. Note that
1325 on SMP systems the preset will be applied to all CPUs,
1326 which is likely to cause problems if your CPUs need
1327 significantly divergent settings. An incorrect value
1328 will cause delays in the kernel to be wrong, leading to
1329 unpredictable I/O errors and other breakage. Although
1330 unlikely, in the extreme case this might damage your
1331 hardware.
1332
1333 ltpc= [NET]
1334 Format: <io>,<irq>,<dma>
1335
1336 machvec= [IA-64] Force the use of a particular machine-vector
1337 (machvec) in a generic kernel.
1338 Example: machvec=hpzx1_swiotlb
1339
1340 machtype= [Loongson] Share the same kernel image file between different
1341 yeeloong laptop.
1342 Example: machtype=lemote-yeeloong-2f-7inch
1343
1344 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1345 than or equal to this physical address is ignored.
1346
1347 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1348 should make use of. maxcpus=n : n >= 0 limits the
1349 kernel to using 'n' processors. n=0 is a special case,
1350 it is equivalent to "nosmp", which also disables
1351 the IO APIC.
1352
1353 max_loop= [LOOP] The number of loop block devices that get
1354 (loop.max_loop) unconditionally pre-created at init time. The default
1355 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1356 of statically allocating a predefined number, loop
1357 devices can be requested on-demand with the
1358 /dev/loop-control interface.
1359
1360 mcatest= [IA-64]
1361
1362 mce [X86-32] Machine Check Exception
1363
1364 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1365
1366 md= [HW] RAID subsystems devices and level
1367 See Documentation/md.txt.
1368
1369 mdacon= [MDA]
1370 Format: <first>,<last>
1371 Specifies range of consoles to be captured by the MDA.
1372
1373 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1374 Amount of memory to be used when the kernel is not able
1375 to see the whole system memory or for test.
1376 [X86-32] Use together with memmap= to avoid physical
1377 address space collisions. Without memmap= PCI devices
1378 could be placed at addresses belonging to unused RAM.
1379
1380 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1381 memory.
1382
1383 memchunk=nn[KMG]
1384 [KNL,SH] Allow user to override the default size for
1385 per-device physically contiguous DMA buffers.
1386
1387 memmap=exactmap [KNL,X86] Enable setting of an exact
1388 E820 memory map, as specified by the user.
1389 Such memmap=exactmap lines can be constructed based on
1390 BIOS output or other requirements. See the memmap=nn@ss
1391 option description.
1392
1393 memmap=nn[KMG]@ss[KMG]
1394 [KNL] Force usage of a specific region of memory
1395 Region of memory to be used, from ss to ss+nn.
1396
1397 memmap=nn[KMG]#ss[KMG]
1398 [KNL,ACPI] Mark specific memory as ACPI data.
1399 Region of memory to be used, from ss to ss+nn.
1400
1401 memmap=nn[KMG]$ss[KMG]
1402 [KNL,ACPI] Mark specific memory as reserved.
1403 Region of memory to be used, from ss to ss+nn.
1404 Example: Exclude memory from 0x18690000-0x1869ffff
1405 memmap=64K$0x18690000
1406 or
1407 memmap=0x10000$0x18690000
1408
1409 memory_corruption_check=0/1 [X86]
1410 Some BIOSes seem to corrupt the first 64k of
1411 memory when doing things like suspend/resume.
1412 Setting this option will scan the memory
1413 looking for corruption. Enabling this will
1414 both detect corruption and prevent the kernel
1415 from using the memory being corrupted.
1416 However, its intended as a diagnostic tool; if
1417 repeatable BIOS-originated corruption always
1418 affects the same memory, you can use memmap=
1419 to prevent the kernel from using that memory.
1420
1421 memory_corruption_check_size=size [X86]
1422 By default it checks for corruption in the low
1423 64k, making this memory unavailable for normal
1424 use. Use this parameter to scan for
1425 corruption in more or less memory.
1426
1427 memory_corruption_check_period=seconds [X86]
1428 By default it checks for corruption every 60
1429 seconds. Use this parameter to check at some
1430 other rate. 0 disables periodic checking.
1431
1432 memtest= [KNL,X86] Enable memtest
1433 Format: <integer>
1434 default : 0 <disable>
1435 Specifies the number of memtest passes to be
1436 performed. Each pass selects another test
1437 pattern from a given set of patterns. Memtest
1438 fills the memory with this pattern, validates
1439 memory contents and reserves bad memory
1440 regions that are detected.
1441
1442 meye.*= [HW] Set MotionEye Camera parameters
1443 See Documentation/video4linux/meye.txt.
1444
1445 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1446 Multi-Function General Purpose Timers on AMD Geode
1447 platforms.
1448
1449 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1450 the BIOS has incorrectly applied a workaround. TinyBIOS
1451 version 0.98 is known to be affected, 0.99 fixes the
1452 problem by letting the user disable the workaround.
1453
1454 mga= [HW,DRM]
1455
1456 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1457 physical address is ignored.
1458
1459 mini2440= [ARM,HW,KNL]
1460 Format:[0..2][b][c][t]
1461 Default: "0tb"
1462 MINI2440 configuration specification:
1463 0 - The attached screen is the 3.5" TFT
1464 1 - The attached screen is the 7" TFT
1465 2 - The VGA Shield is attached (1024x768)
1466 Leaving out the screen size parameter will not load
1467 the TFT driver, and the framebuffer will be left
1468 unconfigured.
1469 b - Enable backlight. The TFT backlight pin will be
1470 linked to the kernel VESA blanking code and a GPIO
1471 LED. This parameter is not necessary when using the
1472 VGA shield.
1473 c - Enable the s3c camera interface.
1474 t - Reserved for enabling touchscreen support. The
1475 touchscreen support is not enabled in the mainstream
1476 kernel as of 2.6.30, a preliminary port can be found
1477 in the "bleeding edge" mini2440 support kernel at
1478 http://repo.or.cz/w/linux-2.6/mini2440.git
1479
1480 mminit_loglevel=
1481 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1482 parameter allows control of the logging verbosity for
1483 the additional memory initialisation checks. A value
1484 of 0 disables mminit logging and a level of 4 will
1485 log everything. Information is printed at KERN_DEBUG
1486 so loglevel=8 may also need to be specified.
1487
1488 mousedev.tap_time=
1489 [MOUSE] Maximum time between finger touching and
1490 leaving touchpad surface for touch to be considered
1491 a tap and be reported as a left button click (for
1492 touchpads working in absolute mode only).
1493 Format: <msecs>
1494 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1495 reporting absolute coordinates, such as tablets
1496 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1497 reporting absolute coordinates, such as tablets
1498
1499 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1500 is similar to kernelcore except it specifies the
1501 amount of memory used for migratable allocations.
1502 If both kernelcore and movablecore is specified,
1503 then kernelcore will be at *least* the specified
1504 value but may be more. If movablecore on its own
1505 is specified, the administrator must be careful
1506 that the amount of memory usable for all allocations
1507 is not too small.
1508
1509 MTD_Partition= [MTD]
1510 Format: <name>,<region-number>,<size>,<offset>
1511
1512 MTD_Region= [MTD] Format:
1513 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1514
1515 mtdparts= [MTD]
1516 See drivers/mtd/cmdlinepart.c.
1517
1518 multitce=off [PPC] This parameter disables the use of the pSeries
1519 firmware feature for updating multiple TCE entries
1520 at a time.
1521
1522 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1523
1524 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1525
1526 boundary - index of last SLC block on Flex-OneNAND.
1527 The remaining blocks are configured as MLC blocks.
1528 lock - Configure if Flex-OneNAND boundary should be locked.
1529 Once locked, the boundary cannot be changed.
1530 1 indicates lock status, 0 indicates unlock status.
1531
1532 mtdset= [ARM]
1533 ARM/S3C2412 JIVE boot control
1534
1535 See arch/arm/mach-s3c2412/mach-jive.c
1536
1537 mtouchusb.raw_coordinates=
1538 [HW] Make the MicroTouch USB driver use raw coordinates
1539 ('y', default) or cooked coordinates ('n')
1540
1541 mtrr_chunk_size=nn[KMG] [X86]
1542 used for mtrr cleanup. It is largest continuous chunk
1543 that could hold holes aka. UC entries.
1544
1545 mtrr_gran_size=nn[KMG] [X86]
1546 Used for mtrr cleanup. It is granularity of mtrr block.
1547 Default is 1.
1548 Large value could prevent small alignment from
1549 using up MTRRs.
1550
1551 mtrr_spare_reg_nr=n [X86]
1552 Format: <integer>
1553 Range: 0,7 : spare reg number
1554 Default : 1
1555 Used for mtrr cleanup. It is spare mtrr entries number.
1556 Set to 2 or more if your graphical card needs more.
1557
1558 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1559
1560 netdev= [NET] Network devices parameters
1561 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1562 Note that mem_start is often overloaded to mean
1563 something different and driver-specific.
1564 This usage is only documented in each driver source
1565 file if at all.
1566
1567 nf_conntrack.acct=
1568 [NETFILTER] Enable connection tracking flow accounting
1569 0 to disable accounting
1570 1 to enable accounting
1571 Default value is 0.
1572
1573 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1574 See Documentation/filesystems/nfs/nfsroot.txt.
1575
1576 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1577 See Documentation/filesystems/nfs/nfsroot.txt.
1578
1579 nfsrootdebug [NFS] enable nfsroot debugging messages.
1580 See Documentation/filesystems/nfs/nfsroot.txt.
1581
1582 nfs.callback_tcpport=
1583 [NFS] set the TCP port on which the NFSv4 callback
1584 channel should listen.
1585
1586 nfs.cache_getent=
1587 [NFS] sets the pathname to the program which is used
1588 to update the NFS client cache entries.
1589
1590 nfs.cache_getent_timeout=
1591 [NFS] sets the timeout after which an attempt to
1592 update a cache entry is deemed to have failed.
1593
1594 nfs.idmap_cache_timeout=
1595 [NFS] set the maximum lifetime for idmapper cache
1596 entries.
1597
1598 nfs.enable_ino64=
1599 [NFS] enable 64-bit inode numbers.
1600 If zero, the NFS client will fake up a 32-bit inode
1601 number for the readdir() and stat() syscalls instead
1602 of returning the full 64-bit number.
1603 The default is to return 64-bit inode numbers.
1604
1605 nfs.nfs4_disable_idmapping=
1606 [NFSv4] When set, this option disables the NFSv4
1607 idmapper on the client, but only if the mount
1608 is using the 'sec=sys' security flavour. This may
1609 make migration from legacy NFSv2/v3 systems easier
1610 provided that the server has the appropriate support.
1611 The default is to always enable NFSv4 idmapping.
1612
1613 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1614 when a NMI is triggered.
1615 Format: [state][,regs][,debounce][,die]
1616
1617 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1618 Format: [panic,][nopanic,][num]
1619 Valid num: 0
1620 0 - turn nmi_watchdog off
1621 When panic is specified, panic when an NMI watchdog
1622 timeout occurs (or 'nopanic' to override the opposite
1623 default).
1624 This is useful when you use a panic=... timeout and
1625 need the box quickly up again.
1626
1627 netpoll.carrier_timeout=
1628 [NET] Specifies amount of time (in seconds) that
1629 netpoll should wait for a carrier. By default netpoll
1630 waits 4 seconds.
1631
1632 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1633 emulation library even if a 387 maths coprocessor
1634 is present.
1635
1636 no_console_suspend
1637 [HW] Never suspend the console
1638 Disable suspending of consoles during suspend and
1639 hibernate operations. Once disabled, debugging
1640 messages can reach various consoles while the rest
1641 of the system is being put to sleep (ie, while
1642 debugging driver suspend/resume hooks). This may
1643 not work reliably with all consoles, but is known
1644 to work with serial and VGA consoles.
1645
1646 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1647 caches in the slab allocator. Saves per-node memory,
1648 but will impact performance.
1649
1650 noalign [KNL,ARM]
1651
1652 noapic [SMP,APIC] Tells the kernel to not make use of any
1653 IOAPICs that may be present in the system.
1654
1655 noautogroup Disable scheduler automatic task group creation.
1656
1657 nobats [PPC] Do not use BATs for mapping kernel lowmem
1658 on "Classic" PPC cores.
1659
1660 nocache [ARM]
1661
1662 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1663
1664 nodelayacct [KNL] Disable per-task delay accounting
1665
1666 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1667
1668 nodsp [SH] Disable hardware DSP at boot time.
1669
1670 noefi [X86] Disable EFI runtime services support.
1671
1672 noexec [IA-64]
1673
1674 noexec [X86]
1675 On X86-32 available only on PAE configured kernels.
1676 noexec=on: enable non-executable mappings (default)
1677 noexec=off: disable non-executable mappings
1678
1679 nosmep [X86]
1680 Disable SMEP (Supervisor Mode Execution Protection)
1681 even if it is supported by processor.
1682
1683 noexec32 [X86-64]
1684 This affects only 32-bit executables.
1685 noexec32=on: enable non-executable mappings (default)
1686 read doesn't imply executable mappings
1687 noexec32=off: disable non-executable mappings
1688 read implies executable mappings
1689
1690 nofpu [SH] Disable hardware FPU at boot time.
1691
1692 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1693 register save and restore. The kernel will only save
1694 legacy floating-point registers on task switch.
1695
1696 noxsave [BUGS=X86] Disables x86 extended register state save
1697 and restore using xsave. The kernel will fallback to
1698 enabling legacy floating-point and sse state.
1699
1700 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1701 wfi(ARM) instruction doesn't work correctly and not to
1702 use it. This is also useful when using JTAG debugger.
1703
1704 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1705 instruction doesn't work correctly and not to
1706 use it.
1707
1708 no_file_caps Tells the kernel not to honor file capabilities. The
1709 only way then for a file to be executed with privilege
1710 is to be setuid root or executed by root.
1711
1712 nohalt [IA-64] Tells the kernel not to use the power saving
1713 function PAL_HALT_LIGHT when idle. This increases
1714 power-consumption. On the positive side, it reduces
1715 interrupt wake-up latency, which may improve performance
1716 in certain environments such as networked servers or
1717 real-time systems.
1718
1719 nohz= [KNL] Boottime enable/disable dynamic ticks
1720 Valid arguments: on, off
1721 Default: on
1722
1723 noiotrap [SH] Disables trapped I/O port accesses.
1724
1725 noirqdebug [X86-32] Disables the code which attempts to detect and
1726 disable unhandled interrupt sources.
1727
1728 no_timer_check [X86,APIC] Disables the code which tests for
1729 broken timer IRQ sources.
1730
1731 noisapnp [ISAPNP] Disables ISA PnP code.
1732
1733 noinitrd [RAM] Tells the kernel not to load any configured
1734 initial RAM disk.
1735
1736 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1737 remapping.
1738 [Deprecated - use intremap=off]
1739
1740 nointroute [IA-64]
1741
1742 nojitter [IA-64] Disables jitter checking for ITC timers.
1743
1744 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1745
1746 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1747 fault handling.
1748
1749 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1750 steal time is computed, but won't influence scheduler
1751 behaviour
1752
1753 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1754
1755 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1756
1757 noltlbs [PPC] Do not use large page/tlb entries for kernel
1758 lowmem mapping on PPC40x.
1759
1760 nomca [IA-64] Disable machine check abort handling
1761
1762 nomce [X86-32] Machine Check Exception
1763
1764 nomfgpt [X86-32] Disable Multi-Function General Purpose
1765 Timer usage (for AMD Geode machines).
1766
1767 nopat [X86] Disable PAT (page attribute table extension of
1768 pagetables) support.
1769
1770 norandmaps Don't use address space randomization. Equivalent to
1771 echo 0 > /proc/sys/kernel/randomize_va_space
1772
1773 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1774
1775 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1776 with UP alternatives
1777
1778 noresidual [PPC] Don't use residual data on PReP machines.
1779
1780 noresume [SWSUSP] Disables resume and restores original swap
1781 space.
1782
1783 no-scroll [VGA] Disables scrollback.
1784 This is required for the Braillex ib80-piezo Braille
1785 reader made by F.H. Papenmeier (Germany).
1786
1787 nosbagart [IA-64]
1788
1789 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1790
1791 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1792 and disable the IO APIC. legacy for "maxcpus=0".
1793
1794 nosoftlockup [KNL] Disable the soft-lockup detector.
1795
1796 nosync [HW,M68K] Disables sync negotiation for all devices.
1797
1798 notsc [BUGS=X86-32] Disable Time Stamp Counter
1799
1800 nousb [USB] Disable the USB subsystem
1801
1802 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1803
1804 nowb [ARM]
1805
1806 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1807
1808 nptcg= [IA-64] Override max number of concurrent global TLB
1809 purges which is reported from either PAL_VM_SUMMARY or
1810 SAL PALO.
1811
1812 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1813 could support. nr_cpus=n : n >= 1 limits the kernel to
1814 supporting 'n' processors. Later in runtime you can not
1815 use hotplug cpu feature to put more cpu back to online.
1816 just like you compile the kernel NR_CPUS=n
1817
1818 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1819
1820 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1821 one of ['zone', 'node', 'default'] can be specified
1822 This can be set from sysctl after boot.
1823 See Documentation/sysctl/vm.txt for details.
1824
1825 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1826 See Documentation/debugging-via-ohci1394.txt for more
1827 info.
1828
1829 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1830 Rather than timing out after 20 ms if an EC
1831 command is not properly ACKed, override the length
1832 of the timeout. We have interrupts disabled while
1833 waiting for the ACK, so if this is set too high
1834 interrupts *may* be lost!
1835
1836 omap_mux= [OMAP] Override bootloader pin multiplexing.
1837 Format: <mux_mode0.mode_name=value>...
1838 For example, to override I2C bus2:
1839 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1840
1841 oprofile.timer= [HW]
1842 Use timer interrupt instead of performance counters
1843
1844 oprofile.cpu_type= Force an oprofile cpu type
1845 This might be useful if you have an older oprofile
1846 userland or if you want common events.
1847 Format: { arch_perfmon }
1848 arch_perfmon: [X86] Force use of architectural
1849 perfmon on Intel CPUs instead of the
1850 CPU specific event set.
1851
1852 oops=panic Always panic on oopses. Default is to just kill the
1853 process, but there is a small probability of
1854 deadlocking the machine.
1855 This will also cause panics on machine check exceptions.
1856 Useful together with panic=30 to trigger a reboot.
1857
1858 OSS [HW,OSS]
1859 See Documentation/sound/oss/oss-parameters.txt
1860
1861 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1862 timeout > 0: seconds before rebooting
1863 timeout = 0: wait forever
1864 timeout < 0: reboot immediately
1865 Format: <timeout>
1866
1867 parkbd.port= [HW] Parallel port number the keyboard adapter is
1868 connected to, default is 0.
1869 Format: <parport#>
1870 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1871 0 for XT, 1 for AT (default is AT).
1872 Format: <mode>
1873
1874 parport= [HW,PPT] Specify parallel ports. 0 disables.
1875 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1876 Use 'auto' to force the driver to use any
1877 IRQ/DMA settings detected (the default is to
1878 ignore detected IRQ/DMA settings because of
1879 possible conflicts). You can specify the base
1880 address, IRQ, and DMA settings; IRQ and DMA
1881 should be numbers, or 'auto' (for using detected
1882 settings on that particular port), or 'nofifo'
1883 (to avoid using a FIFO even if it is detected).
1884 Parallel ports are assigned in the order they
1885 are specified on the command line, starting
1886 with parport0.
1887
1888 parport_init_mode= [HW,PPT]
1889 Configure VIA parallel port to operate in
1890 a specific mode. This is necessary on Pegasos
1891 computer where firmware has no options for setting
1892 up parallel port mode and sets it to spp.
1893 Currently this function knows 686a and 8231 chips.
1894 Format: [spp|ps2|epp|ecp|ecpepp]
1895
1896 pause_on_oops=
1897 Halt all CPUs after the first oops has been printed for
1898 the specified number of seconds. This is to be used if
1899 your oopses keep scrolling off the screen.
1900
1901 pcbit= [HW,ISDN]
1902
1903 pcd. [PARIDE]
1904 See header of drivers/block/paride/pcd.c.
1905 See also Documentation/blockdev/paride.txt.
1906
1907 pci=option[,option...] [PCI] various PCI subsystem options:
1908 earlydump [X86] dump PCI config space before the kernel
1909 changes anything
1910 off [X86] don't probe for the PCI bus
1911 bios [X86-32] force use of PCI BIOS, don't access
1912 the hardware directly. Use this if your machine
1913 has a non-standard PCI host bridge.
1914 nobios [X86-32] disallow use of PCI BIOS, only direct
1915 hardware access methods are allowed. Use this
1916 if you experience crashes upon bootup and you
1917 suspect they are caused by the BIOS.
1918 conf1 [X86] Force use of PCI Configuration
1919 Mechanism 1.
1920 conf2 [X86] Force use of PCI Configuration
1921 Mechanism 2.
1922 noaer [PCIE] If the PCIEAER kernel config parameter is
1923 enabled, this kernel boot option can be used to
1924 disable the use of PCIE advanced error reporting.
1925 nodomains [PCI] Disable support for multiple PCI
1926 root domains (aka PCI segments, in ACPI-speak).
1927 nommconf [X86] Disable use of MMCONFIG for PCI
1928 Configuration
1929 check_enable_amd_mmconf [X86] check for and enable
1930 properly configured MMIO access to PCI
1931 config space on AMD family 10h CPU
1932 nomsi [MSI] If the PCI_MSI kernel config parameter is
1933 enabled, this kernel boot option can be used to
1934 disable the use of MSI interrupts system-wide.
1935 noioapicquirk [APIC] Disable all boot interrupt quirks.
1936 Safety option to keep boot IRQs enabled. This
1937 should never be necessary.
1938 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1939 primary IO-APIC for bridges that cannot disable
1940 boot IRQs. This fixes a source of spurious IRQs
1941 when the system masks IRQs.
1942 noioapicreroute [APIC] Disable workaround that uses the
1943 boot IRQ equivalent of an IRQ that connects to
1944 a chipset where boot IRQs cannot be disabled.
1945 The opposite of ioapicreroute.
1946 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1947 routing table. These calls are known to be buggy
1948 on several machines and they hang the machine
1949 when used, but on other computers it's the only
1950 way to get the interrupt routing table. Try
1951 this option if the kernel is unable to allocate
1952 IRQs or discover secondary PCI buses on your
1953 motherboard.
1954 rom [X86] Assign address space to expansion ROMs.
1955 Use with caution as certain devices share
1956 address decoders between ROMs and other
1957 resources.
1958 norom [X86] Do not assign address space to
1959 expansion ROMs that do not already have
1960 BIOS assigned address ranges.
1961 nobar [X86] Do not assign address space to the
1962 BARs that weren't assigned by the BIOS.
1963 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1964 assigned automatically to PCI devices. You can
1965 make the kernel exclude IRQs of your ISA cards
1966 this way.
1967 pirqaddr=0xAAAAA [X86] Specify the physical address
1968 of the PIRQ table (normally generated
1969 by the BIOS) if it is outside the
1970 F0000h-100000h range.
1971 lastbus=N [X86] Scan all buses thru bus #N. Can be
1972 useful if the kernel is unable to find your
1973 secondary buses and you want to tell it
1974 explicitly which ones they are.
1975 assign-busses [X86] Always assign all PCI bus
1976 numbers ourselves, overriding
1977 whatever the firmware may have done.
1978 usepirqmask [X86] Honor the possible IRQ mask stored
1979 in the BIOS $PIR table. This is needed on
1980 some systems with broken BIOSes, notably
1981 some HP Pavilion N5400 and Omnibook XE3
1982 notebooks. This will have no effect if ACPI
1983 IRQ routing is enabled.
1984 noacpi [X86] Do not use ACPI for IRQ routing
1985 or for PCI scanning.
1986 use_crs [X86] Use PCI host bridge window information
1987 from ACPI. On BIOSes from 2008 or later, this
1988 is enabled by default. If you need to use this,
1989 please report a bug.
1990 nocrs [X86] Ignore PCI host bridge windows from ACPI.
1991 If you need to use this, please report a bug.
1992 routeirq Do IRQ routing for all PCI devices.
1993 This is normally done in pci_enable_device(),
1994 so this option is a temporary workaround
1995 for broken drivers that don't call it.
1996 skip_isa_align [X86] do not align io start addr, so can
1997 handle more pci cards
1998 firmware [ARM] Do not re-enumerate the bus but instead
1999 just use the configuration from the
2000 bootloader. This is currently used on
2001 IXP2000 systems where the bus has to be
2002 configured a certain way for adjunct CPUs.
2003 noearly [X86] Don't do any early type 1 scanning.
2004 This might help on some broken boards which
2005 machine check when some devices' config space
2006 is read. But various workarounds are disabled
2007 and some IOMMU drivers will not work.
2008 bfsort Sort PCI devices into breadth-first order.
2009 This sorting is done to get a device
2010 order compatible with older (<= 2.4) kernels.
2011 nobfsort Don't sort PCI devices into breadth-first order.
2012 cbiosize=nn[KMG] The fixed amount of bus space which is
2013 reserved for the CardBus bridge's IO window.
2014 The default value is 256 bytes.
2015 cbmemsize=nn[KMG] The fixed amount of bus space which is
2016 reserved for the CardBus bridge's memory
2017 window. The default value is 64 megabytes.
2018 resource_alignment=
2019 Format:
2020 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2021 Specifies alignment and device to reassign
2022 aligned memory resources.
2023 If <order of align> is not specified,
2024 PAGE_SIZE is used as alignment.
2025 PCI-PCI bridge can be specified, if resource
2026 windows need to be expanded.
2027 ecrc= Enable/disable PCIe ECRC (transaction layer
2028 end-to-end CRC checking).
2029 bios: Use BIOS/firmware settings. This is the
2030 the default.
2031 off: Turn ECRC off
2032 on: Turn ECRC on.
2033 realloc reallocate PCI resources if allocations done by BIOS
2034 are erroneous.
2035
2036 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2037 Management.
2038 off Disable ASPM.
2039 force Enable ASPM even on devices that claim not to support it.
2040 WARNING: Forcing ASPM on may cause system lockups.
2041
2042 pcie_ports= [PCIE] PCIe ports handling:
2043 auto Ask the BIOS whether or not to use native PCIe services
2044 associated with PCIe ports (PME, hot-plug, AER). Use
2045 them only if that is allowed by the BIOS.
2046 native Use native PCIe services associated with PCIe ports
2047 unconditionally.
2048 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2049 ports driver.
2050
2051 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2052 nomsi Do not use MSI for native PCIe PME signaling (this makes
2053 all PCIe root ports use INTx for all services).
2054
2055 pcmv= [HW,PCMCIA] BadgePAD 4
2056
2057 pd. [PARIDE]
2058 See Documentation/blockdev/paride.txt.
2059
2060 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2061 boot time.
2062 Format: { 0 | 1 }
2063 See arch/parisc/kernel/pdc_chassis.c
2064
2065 percpu_alloc= Select which percpu first chunk allocator to use.
2066 Currently supported values are "embed" and "page".
2067 Archs may support subset or none of the selections.
2068 See comments in mm/percpu.c for details on each
2069 allocator. This parameter is primarily for debugging
2070 and performance comparison.
2071
2072 pf. [PARIDE]
2073 See Documentation/blockdev/paride.txt.
2074
2075 pg. [PARIDE]
2076 See Documentation/blockdev/paride.txt.
2077
2078 pirq= [SMP,APIC] Manual mp-table setup
2079 See Documentation/x86/i386/IO-APIC.txt.
2080
2081 plip= [PPT,NET] Parallel port network link
2082 Format: { parport<nr> | timid | 0 }
2083 See also Documentation/parport.txt.
2084
2085 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2086 Override pmtimer IOPort with a hex value.
2087 e.g. pmtmr=0x508
2088
2089 pnp.debug=1 [PNP]
2090 Enable PNP debug messages (depends on the
2091 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2092 via /sys/module/pnp/parameters/debug. We always show
2093 current resource usage; turning this on also shows
2094 possible settings and some assignment information.
2095
2096 pnpacpi= [ACPI]
2097 { off }
2098
2099 pnpbios= [ISAPNP]
2100 { on | off | curr | res | no-curr | no-res }
2101
2102 pnp_reserve_irq=
2103 [ISAPNP] Exclude IRQs for the autoconfiguration
2104
2105 pnp_reserve_dma=
2106 [ISAPNP] Exclude DMAs for the autoconfiguration
2107
2108 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2109 Ranges are in pairs (I/O port base and size).
2110
2111 pnp_reserve_mem=
2112 [ISAPNP] Exclude memory regions for the
2113 autoconfiguration.
2114 Ranges are in pairs (memory base and size).
2115
2116 ports= [IP_VS_FTP] IPVS ftp helper module
2117 Default is 21.
2118 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2119 may be specified.
2120 Format: <port>,<port>....
2121
2122 print-fatal-signals=
2123 [KNL] debug: print fatal signals
2124
2125 If enabled, warn about various signal handling
2126 related application anomalies: too many signals,
2127 too many POSIX.1 timers, fatal signals causing a
2128 coredump - etc.
2129
2130 If you hit the warning due to signal overflow,
2131 you might want to try "ulimit -i unlimited".
2132
2133 default: off.
2134
2135 printk.time= Show timing data prefixed to each printk message line
2136 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2137
2138 processor.max_cstate= [HW,ACPI]
2139 Limit processor to maximum C-state
2140 max_cstate=9 overrides any DMI blacklist limit.
2141
2142 processor.nocst [HW,ACPI]
2143 Ignore the _CST method to determine C-states,
2144 instead using the legacy FADT method
2145
2146 profile= [KNL] Enable kernel profiling via /proc/profile
2147 Format: [schedule,]<number>
2148 Param: "schedule" - profile schedule points.
2149 Param: <number> - step/bucket size as a power of 2 for
2150 statistical time based profiling.
2151 Param: "sleep" - profile D-state sleeping (millisecs).
2152 Requires CONFIG_SCHEDSTATS
2153 Param: "kvm" - profile VM exits.
2154
2155 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2156 before loading.
2157 See Documentation/blockdev/ramdisk.txt.
2158
2159 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2160 probe for; one of (bare|imps|exps|lifebook|any).
2161 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2162 per second.
2163 psmouse.resetafter= [HW,MOUSE]
2164 Try to reset the device after so many bad packets
2165 (0 = never).
2166 psmouse.resolution=
2167 [HW,MOUSE] Set desired mouse resolution, in dpi.
2168 psmouse.smartscroll=
2169 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2170 0 = disabled, 1 = enabled (default).
2171
2172 pstore.backend= Specify the name of the pstore backend to use
2173
2174 pt. [PARIDE]
2175 See Documentation/blockdev/paride.txt.
2176
2177 pty.legacy_count=
2178 [KNL] Number of legacy pty's. Overwrites compiled-in
2179 default number.
2180
2181 quiet [KNL] Disable most log messages
2182
2183 r128= [HW,DRM]
2184
2185 raid= [HW,RAID]
2186 See Documentation/md.txt.
2187
2188 ramdisk_blocksize= [RAM]
2189 See Documentation/blockdev/ramdisk.txt.
2190
2191 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2192 See Documentation/blockdev/ramdisk.txt.
2193
2194 rcupdate.blimit= [KNL,BOOT]
2195 Set maximum number of finished RCU callbacks to process
2196 in one batch.
2197
2198 rcupdate.qhimark= [KNL,BOOT]
2199 Set threshold of queued
2200 RCU callbacks over which batch limiting is disabled.
2201
2202 rcupdate.qlowmark= [KNL,BOOT]
2203 Set threshold of queued RCU callbacks below which
2204 batch limiting is re-enabled.
2205
2206 rdinit= [KNL]
2207 Format: <full_path>
2208 Run specified binary instead of /init from the ramdisk,
2209 used for early userspace startup. See initrd.
2210
2211 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2212 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2213 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2214
2215 relax_domain_level=
2216 [KNL, SMP] Set scheduler's default relax_domain_level.
2217 See Documentation/cgroups/cpusets.txt.
2218
2219 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2220
2221 reservetop= [X86-32]
2222 Format: nn[KMG]
2223 Reserves a hole at the top of the kernel virtual
2224 address space.
2225
2226 reservelow= [X86]
2227 Format: nn[K]
2228 Set the amount of memory to reserve for BIOS at
2229 the bottom of the address space.
2230
2231 reset_devices [KNL] Force drivers to reset the underlying device
2232 during initialization.
2233
2234 resume= [SWSUSP]
2235 Specify the partition device for software suspend
2236
2237 resume_offset= [SWSUSP]
2238 Specify the offset from the beginning of the partition
2239 given by "resume=" at which the swap header is located,
2240 in <PAGE_SIZE> units (needed only for swap files).
2241 See Documentation/power/swsusp-and-swap-files.txt
2242
2243 hibernate= [HIBERNATION]
2244 noresume Don't check if there's a hibernation image
2245 present during boot.
2246 nocompress Don't compress/decompress hibernation images.
2247
2248 retain_initrd [RAM] Keep initrd memory after extraction
2249
2250 rhash_entries= [KNL,NET]
2251 Set number of hash buckets for route cache
2252
2253 riscom8= [HW,SERIAL]
2254 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2255
2256 ro [KNL] Mount root device read-only on boot
2257
2258 root= [KNL] Root filesystem
2259 See name_to_dev_t comment in init/do_mounts.c.
2260
2261 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2262 mount the root filesystem
2263
2264 rootflags= [KNL] Set root filesystem mount option string
2265
2266 rootfstype= [KNL] Set root filesystem type
2267
2268 rootwait [KNL] Wait (indefinitely) for root device to show up.
2269 Useful for devices that are detected asynchronously
2270 (e.g. USB and MMC devices).
2271
2272 rw [KNL] Mount root device read-write on boot
2273
2274 S [KNL] Run init in single mode
2275
2276 sa1100ir [NET]
2277 See drivers/net/irda/sa1100_ir.c.
2278
2279 sbni= [NET] Granch SBNI12 leased line adapter
2280
2281 sched_debug [KNL] Enables verbose scheduler debug messages.
2282
2283 security= [SECURITY] Choose a security module to enable at boot.
2284 If this boot parameter is not specified, only the first
2285 security module asking for security registration will be
2286 loaded. An invalid security module name will be treated
2287 as if no module has been chosen.
2288
2289 selinux= [SELINUX] Disable or enable SELinux at boot time.
2290 Format: { "0" | "1" }
2291 See security/selinux/Kconfig help text.
2292 0 -- disable.
2293 1 -- enable.
2294 Default value is set via kernel config option.
2295 If enabled at boot time, /selinux/disable can be used
2296 later to disable prior to initial policy load.
2297
2298 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2299 Format: { "0" | "1" }
2300 See security/apparmor/Kconfig help text
2301 0 -- disable.
2302 1 -- enable.
2303 Default value is set via kernel config option.
2304
2305 serialnumber [BUGS=X86-32]
2306
2307 shapers= [NET]
2308 Maximal number of shapers.
2309
2310 show_msr= [x86] show boot-time MSR settings
2311 Format: { <integer> }
2312 Show boot-time (BIOS-initialized) MSR settings.
2313 The parameter means the number of CPUs to show,
2314 for example 1 means boot CPU only.
2315
2316 simeth= [IA-64]
2317 simscsi=
2318
2319 slram= [HW,MTD]
2320
2321 slub_debug[=options[,slabs]] [MM, SLUB]
2322 Enabling slub_debug allows one to determine the
2323 culprit if slab objects become corrupted. Enabling
2324 slub_debug can create guard zones around objects and
2325 may poison objects when not in use. Also tracks the
2326 last alloc / free. For more information see
2327 Documentation/vm/slub.txt.
2328
2329 slub_max_order= [MM, SLUB]
2330 Determines the maximum allowed order for slabs.
2331 A high setting may cause OOMs due to memory
2332 fragmentation. For more information see
2333 Documentation/vm/slub.txt.
2334
2335 slub_min_objects= [MM, SLUB]
2336 The minimum number of objects per slab. SLUB will
2337 increase the slab order up to slub_max_order to
2338 generate a sufficiently large slab able to contain
2339 the number of objects indicated. The higher the number
2340 of objects the smaller the overhead of tracking slabs
2341 and the less frequently locks need to be acquired.
2342 For more information see Documentation/vm/slub.txt.
2343
2344 slub_min_order= [MM, SLUB]
2345 Determines the mininum page order for slabs. Must be
2346 lower than slub_max_order.
2347 For more information see Documentation/vm/slub.txt.
2348
2349 slub_nomerge [MM, SLUB]
2350 Disable merging of slabs with similar size. May be
2351 necessary if there is some reason to distinguish
2352 allocs to different slabs. Debug options disable
2353 merging on their own.
2354 For more information see Documentation/vm/slub.txt.
2355
2356 smart2= [HW]
2357 Format: <io1>[,<io2>[,...,<io8>]]
2358
2359 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2360 attempt to substitute SMP alternatives once at boot.
2361
2362 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2363 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2364 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2365 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2366 smsc-ircc2.ircc_irq= [HW] IRQ line
2367 smsc-ircc2.ircc_dma= [HW] DMA channel
2368 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2369 0: Toshiba Satellite 1800 (GP data pin select)
2370 1: Fast pin select (default)
2371 2: ATC IRMode
2372
2373 softlockup_panic=
2374 [KNL] Should the soft-lockup detector generate panics.
2375 Format: <integer>
2376
2377 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2378 See Documentation/sonypi.txt
2379
2380 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2381 See Documentation/serial/specialix.txt.
2382
2383 spia_io_base= [HW,MTD]
2384 spia_fio_base=
2385 spia_pedr=
2386 spia_peddr=
2387
2388 stacktrace [FTRACE]
2389 Enabled the stack tracer on boot up.
2390
2391 sti= [PARISC,HW]
2392 Format: <num>
2393 Set the STI (builtin display/keyboard on the HP-PARISC
2394 machines) console (graphic card) which should be used
2395 as the initial boot-console.
2396 See also comment in drivers/video/console/sticore.c.
2397
2398 sti_font= [HW]
2399 See comment in drivers/video/console/sticore.c.
2400
2401 stifb= [HW]
2402 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2403
2404 sunrpc.min_resvport=
2405 sunrpc.max_resvport=
2406 [NFS,SUNRPC]
2407 SunRPC servers often require that client requests
2408 originate from a privileged port (i.e. a port in the
2409 range 0 < portnr < 1024).
2410 An administrator who wishes to reserve some of these
2411 ports for other uses may adjust the range that the
2412 kernel's sunrpc client considers to be privileged
2413 using these two parameters to set the minimum and
2414 maximum port values.
2415
2416 sunrpc.pool_mode=
2417 [NFS]
2418 Control how the NFS server code allocates CPUs to
2419 service thread pools. Depending on how many NICs
2420 you have and where their interrupts are bound, this
2421 option will affect which CPUs will do NFS serving.
2422 Note: this parameter cannot be changed while the
2423 NFS server is running.
2424
2425 auto the server chooses an appropriate mode
2426 automatically using heuristics
2427 global a single global pool contains all CPUs
2428 percpu one pool for each CPU
2429 pernode one pool for each NUMA node (equivalent
2430 to global on non-NUMA machines)
2431
2432 sunrpc.tcp_slot_table_entries=
2433 sunrpc.udp_slot_table_entries=
2434 [NFS,SUNRPC]
2435 Sets the upper limit on the number of simultaneous
2436 RPC calls that can be sent from the client to a
2437 server. Increasing these values may allow you to
2438 improve throughput, but will also increase the
2439 amount of memory reserved for use by the client.
2440
2441 swapaccount[=0|1]
2442 [KNL] Enable accounting of swap in memory resource
2443 controller if no parameter or 1 is given or disable
2444 it if 0 is given (See Documentation/cgroups/memory.txt)
2445
2446 swiotlb= [IA-64] Number of I/O TLB slabs
2447
2448 switches= [HW,M68k]
2449
2450 sysfs.deprecated=0|1 [KNL]
2451 Enable/disable old style sysfs layout for old udev
2452 on older distributions. When this option is enabled
2453 very new udev will not work anymore. When this option
2454 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2455 in older udev will not work anymore.
2456 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2457 the kernel configuration.
2458
2459 sysrq_always_enabled
2460 [KNL]
2461 Ignore sysrq setting - this boot parameter will
2462 neutralize any effect of /proc/sys/kernel/sysrq.
2463 Useful for debugging.
2464
2465 tdfx= [HW,DRM]
2466
2467 test_suspend= [SUSPEND]
2468 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2469 standby suspend) as the system sleep state to briefly
2470 enter during system startup. The system is woken from
2471 this state using a wakeup-capable RTC alarm.
2472
2473 thash_entries= [KNL,NET]
2474 Set number of hash buckets for TCP connection
2475
2476 thermal.act= [HW,ACPI]
2477 -1: disable all active trip points in all thermal zones
2478 <degrees C>: override all lowest active trip points
2479
2480 thermal.crt= [HW,ACPI]
2481 -1: disable all critical trip points in all thermal zones
2482 <degrees C>: override all critical trip points
2483
2484 thermal.nocrt= [HW,ACPI]
2485 Set to disable actions on ACPI thermal zone
2486 critical and hot trip points.
2487
2488 thermal.off= [HW,ACPI]
2489 1: disable ACPI thermal control
2490
2491 thermal.psv= [HW,ACPI]
2492 -1: disable all passive trip points
2493 <degrees C>: override all passive trip points to this
2494 value
2495
2496 thermal.tzp= [HW,ACPI]
2497 Specify global default ACPI thermal zone polling rate
2498 <deci-seconds>: poll all this frequency
2499 0: no polling (default)
2500
2501 threadirqs [KNL]
2502 Force threading of all interrupt handlers except those
2503 marked explicitely IRQF_NO_THREAD.
2504
2505 topology= [S390]
2506 Format: {off | on}
2507 Specify if the kernel should make use of the cpu
2508 topology information if the hardware supports this.
2509 The scheduler will make use of this information and
2510 e.g. base its process migration decisions on it.
2511 Default is on.
2512
2513 tp720= [HW,PS2]
2514
2515 tpm_suspend_pcr=[HW,TPM]
2516 Format: integer pcr id
2517 Specify that at suspend time, the tpm driver
2518 should extend the specified pcr with zeros,
2519 as a workaround for some chips which fail to
2520 flush the last written pcr on TPM_SaveState.
2521 This will guarantee that all the other pcrs
2522 are saved.
2523
2524 trace_buf_size=nn[KMG]
2525 [FTRACE] will set tracing buffer size.
2526
2527 trace_event=[event-list]
2528 [FTRACE] Set and start specified trace events in order
2529 to facilitate early boot debugging.
2530 See also Documentation/trace/events.txt
2531
2532 tsc= Disable clocksource stability checks for TSC.
2533 Format: <string>
2534 [x86] reliable: mark tsc clocksource as reliable, this
2535 disables clocksource verification at runtime, as well
2536 as the stability checks done at bootup. Used to enable
2537 high-resolution timer mode on older hardware, and in
2538 virtualized environment.
2539 [x86] noirqtime: Do not use TSC to do irq accounting.
2540 Used to run time disable IRQ_TIME_ACCOUNTING on any
2541 platforms where RDTSC is slow and this accounting
2542 can add overhead.
2543
2544 turbografx.map[2|3]= [HW,JOY]
2545 TurboGraFX parallel port interface
2546 Format:
2547 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2548 See also Documentation/input/joystick-parport.txt
2549
2550 udbg-immortal [PPC] When debugging early kernel crashes that
2551 happen after console_init() and before a proper
2552 console driver takes over, this boot options might
2553 help "seeing" what's going on.
2554
2555 uhash_entries= [KNL,NET]
2556 Set number of hash buckets for UDP/UDP-Lite connections
2557
2558 uhci-hcd.ignore_oc=
2559 [USB] Ignore overcurrent events (default N).
2560 Some badly-designed motherboards generate lots of
2561 bogus events, for ports that aren't wired to
2562 anything. Set this parameter to avoid log spamming.
2563 Note that genuine overcurrent events won't be
2564 reported either.
2565
2566 unknown_nmi_panic
2567 [X86] Cause panic on unknown NMI.
2568
2569 usbcore.authorized_default=
2570 [USB] Default USB device authorization:
2571 (default -1 = authorized except for wireless USB,
2572 0 = not authorized, 1 = authorized)
2573
2574 usbcore.autosuspend=
2575 [USB] The autosuspend time delay (in seconds) used
2576 for newly-detected USB devices (default 2). This
2577 is the time required before an idle device will be
2578 autosuspended. Devices for which the delay is set
2579 to a negative value won't be autosuspended at all.
2580
2581 usbcore.usbfs_snoop=
2582 [USB] Set to log all usbfs traffic (default 0 = off).
2583
2584 usbcore.blinkenlights=
2585 [USB] Set to cycle leds on hubs (default 0 = off).
2586
2587 usbcore.old_scheme_first=
2588 [USB] Start with the old device initialization
2589 scheme (default 0 = off).
2590
2591 usbcore.use_both_schemes=
2592 [USB] Try the other device initialization scheme
2593 if the first one fails (default 1 = enabled).
2594
2595 usbcore.initial_descriptor_timeout=
2596 [USB] Specifies timeout for the initial 64-byte
2597 USB_REQ_GET_DESCRIPTOR request in milliseconds
2598 (default 5000 = 5.0 seconds).
2599
2600 usbhid.mousepoll=
2601 [USBHID] The interval which mice are to be polled at.
2602
2603 usb-storage.delay_use=
2604 [UMS] The delay in seconds before a new device is
2605 scanned for Logical Units (default 5).
2606
2607 usb-storage.quirks=
2608 [UMS] A list of quirks entries to supplement or
2609 override the built-in unusual_devs list. List
2610 entries are separated by commas. Each entry has
2611 the form VID:PID:Flags where VID and PID are Vendor
2612 and Product ID values (4-digit hex numbers) and
2613 Flags is a set of characters, each corresponding
2614 to a common usb-storage quirk flag as follows:
2615 a = SANE_SENSE (collect more than 18 bytes
2616 of sense data);
2617 b = BAD_SENSE (don't collect more than 18
2618 bytes of sense data);
2619 c = FIX_CAPACITY (decrease the reported
2620 device capacity by one sector);
2621 d = NO_READ_DISC_INFO (don't use
2622 READ_DISC_INFO command);
2623 e = NO_READ_CAPACITY_16 (don't use
2624 READ_CAPACITY_16 command);
2625 h = CAPACITY_HEURISTICS (decrease the
2626 reported device capacity by one
2627 sector if the number is odd);
2628 i = IGNORE_DEVICE (don't bind to this
2629 device);
2630 l = NOT_LOCKABLE (don't try to lock and
2631 unlock ejectable media);
2632 m = MAX_SECTORS_64 (don't transfer more
2633 than 64 sectors = 32 KB at a time);
2634 n = INITIAL_READ10 (force a retry of the
2635 initial READ(10) command);
2636 o = CAPACITY_OK (accept the capacity
2637 reported by the device);
2638 r = IGNORE_RESIDUE (the device reports
2639 bogus residue values);
2640 s = SINGLE_LUN (the device has only one
2641 Logical Unit);
2642 w = NO_WP_DETECT (don't test whether the
2643 medium is write-protected).
2644 Example: quirks=0419:aaf5:rl,0421:0433:rc
2645
2646 user_debug= [KNL,ARM]
2647 Format: <int>
2648 See arch/arm/Kconfig.debug help text.
2649 1 - undefined instruction events
2650 2 - system calls
2651 4 - invalid data aborts
2652 8 - SIGSEGV faults
2653 16 - SIGBUS faults
2654 Example: user_debug=31
2655
2656 userpte=
2657 [X86] Flags controlling user PTE allocations.
2658
2659 nohigh = do not allocate PTE pages in
2660 HIGHMEM regardless of setting
2661 of CONFIG_HIGHPTE.
2662
2663 vdso= [X86,SH]
2664 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2665 vdso=1: enable VDSO (default)
2666 vdso=0: disable VDSO mapping
2667
2668 vdso32= [X86]
2669 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2670 vdso32=1: enable 32-bit VDSO (default)
2671 vdso32=0: disable 32-bit VDSO mapping
2672
2673 vector= [IA-64,SMP]
2674 vector=percpu: enable percpu vector domain
2675
2676 video= [FB] Frame buffer configuration
2677 See Documentation/fb/modedb.txt.
2678
2679 vga= [BOOT,X86-32] Select a particular video mode
2680 See Documentation/x86/boot.txt and
2681 Documentation/svga.txt.
2682 Use vga=ask for menu.
2683 This is actually a boot loader parameter; the value is
2684 passed to the kernel using a special protocol.
2685
2686 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2687 size of <nn>. This can be used to increase the
2688 minimum size (128MB on x86). It can also be used to
2689 decrease the size and leave more room for directly
2690 mapped kernel RAM.
2691
2692 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2693 Format: <command>
2694
2695 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2696 Format: <command>
2697
2698 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2699 Format: <command>
2700
2701 vsyscall= [X86-64]
2702 Controls the behavior of vsyscalls (i.e. calls to
2703 fixed addresses of 0xffffffffff600x00 from legacy
2704 code). Most statically-linked binaries and older
2705 versions of glibc use these calls. Because these
2706 functions are at fixed addresses, they make nice
2707 targets for exploits that can control RIP.
2708
2709 emulate Vsyscalls turn into traps and are emulated
2710 reasonably safely.
2711
2712 native [default] Vsyscalls are native syscall
2713 instructions.
2714 This is a little bit faster than trapping
2715 and makes a few dynamic recompilers work
2716 better than they would in emulation mode.
2717 It also makes exploits much easier to write.
2718
2719 none Vsyscalls don't work at all. This makes
2720 them quite hard to use for exploits but
2721 might break your system.
2722
2723 vt.cur_default= [VT] Default cursor shape.
2724 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2725 the parameters of the <Esc>[?A;B;Cc escape sequence;
2726 see VGA-softcursor.txt. Default: 2 = underline.
2727
2728 vt.default_blu= [VT]
2729 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2730 Change the default blue palette of the console.
2731 This is a 16-member array composed of values
2732 ranging from 0-255.
2733
2734 vt.default_grn= [VT]
2735 Format: <green0>,<green1>,<green2>,...,<green15>
2736 Change the default green palette of the console.
2737 This is a 16-member array composed of values
2738 ranging from 0-255.
2739
2740 vt.default_red= [VT]
2741 Format: <red0>,<red1>,<red2>,...,<red15>
2742 Change the default red palette of the console.
2743 This is a 16-member array composed of values
2744 ranging from 0-255.
2745
2746 vt.default_utf8=
2747 [VT]
2748 Format=<0|1>
2749 Set system-wide default UTF-8 mode for all tty's.
2750 Default is 1, i.e. UTF-8 mode is enabled for all
2751 newly opened terminals.
2752
2753 vt.global_cursor_default=
2754 [VT]
2755 Format=<-1|0|1>
2756 Set system-wide default for whether a cursor
2757 is shown on new VTs. Default is -1,
2758 i.e. cursors will be created by default unless
2759 overridden by individual drivers. 0 will hide
2760 cursors, 1 will display them.
2761
2762 watchdog timers [HW,WDT] For information on watchdog timers,
2763 see Documentation/watchdog/watchdog-parameters.txt
2764 or other driver-specific files in the
2765 Documentation/watchdog/ directory.
2766
2767 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2768 default x2apic cluster mode on platforms
2769 supporting x2apic.
2770
2771 x86_mrst_timer= [X86-32,APBT]
2772 Choose timer option for x86 Moorestown MID platform.
2773 Two valid options are apbt timer only and lapic timer
2774 plus one apbt timer for broadcast timer.
2775 x86_mrst_timer=apbt_only | lapic_and_apbt
2776
2777 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2778 xd_geo= See header of drivers/block/xd.c.
2779
2780 xen_emul_unplug= [HW,X86,XEN]
2781 Unplug Xen emulated devices
2782 Format: [unplug0,][unplug1]
2783 ide-disks -- unplug primary master IDE devices
2784 aux-ide-disks -- unplug non-primary-master IDE devices
2785 nics -- unplug network devices
2786 all -- unplug all emulated devices (NICs and IDE disks)
2787 unnecessary -- unplugging emulated devices is
2788 unnecessary even if the host did not respond to
2789 the unplug protocol
2790 never -- do not unplug even if version check succeeds
2791
2792 xirc2ps_cs= [NET,PCMCIA]
2793 Format:
2794 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2795
2796______________________________________________________________________
2797
2798TODO:
2799
2800 Add more DRM drivers.