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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 CLK Common clock infrastructure is enabled.
48 CMA Contiguous Memory Area support is enabled.
49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
54 EVM Extended Verification Module
55 FB The frame buffer device is enabled.
56 FTRACE Function tracing enabled.
57 GCOV GCOV profiling is enabled.
58 HW Appropriate hardware is enabled.
59 IA-64 IA-64 architecture is enabled.
60 IMA Integrity measurement architecture is enabled.
61 IOSCHED More than one I/O scheduler is enabled.
62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
63 IPV6 IPv6 support is enabled.
64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
67 KGDB Kernel debugger support is enabled.
68 KVM Kernel Virtual Machine support is enabled.
69 LIBATA Libata driver is enabled
70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
75 MDA MDA console support is enabled.
76 MIPS MIPS architecture is enabled.
77 MOUSE Appropriate mouse support is enabled.
78 MSI Message Signaled Interrupts (PCI).
79 MTD MTD (Memory Technology Device) support is enabled.
80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
88 PCIE PCI Express support is enabled.
89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
99 SECURITY Different security models are enabled.
100 SELINUX SELinux support is enabled.
101 APPARMOR AppArmor support is enabled.
102 SERIAL Serial support is enabled.
103 SH SuperH architecture is enabled.
104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
108 TPM TPM drivers are enabled.
109 TS Appropriate touchscreen support is enabled.
110 UMS USB Mass Storage support is enabled.
111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
114 VMMIO Driver for memory mapped virtio devices is enabled.
115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
119 X86-32 X86-32, aka i386 architecture is enabled.
120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
122 Documentation/x86/x86_64/boot-options.txt .
123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
124 XEN Xen support is enabled
125
126In addition, the following text indicates that the option:
127
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
131
132Parameters denoted with BOOT are actually interpreted by the boot
133loader, and have no meaning to the kernel directly.
134Do not modify the syntax of boot loader parameters without extreme
135need or coordination with <Documentation/x86/boot.txt>.
136
137There are also arch-specific kernel-parameters not documented here.
138See for example <Documentation/x86/x86_64/boot-options.txt>.
139
140Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141a trailing = on the name of any parameter states that that parameter will
142be entered as an environment variable, whereas its absence indicates that
143it will appear as a kernel argument readable via /proc/cmdline by programs
144running once the system is up.
145
146The number of kernel parameters is not limited, but the length of the
147complete command line (parameters including spaces etc.) is limited to
148a fixed number of characters. This limit depends on the architecture
149and is between 256 and 4096 characters. It is defined in the file
150./include/asm/setup.h as COMMAND_LINE_SIZE.
151
152Finally, the [KMG] suffix is commonly described after a number of kernel
153parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155bytes respectively. Such letter suffixes can also be entirely omitted.
156
157
158 acpi= [HW,ACPI,X86]
159 Advanced Configuration and Power Interface
160 Format: { force | off | strict | noirq | rsdt }
161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
164 strict -- Be less tolerant of platforms that are not
165 strictly ACPI specification compliant.
166 rsdt -- prefer RSDT over (default) XSDT
167 copy_dsdt -- copy DSDT to memory
168
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
170
171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
175
176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
180 default: 0
181
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
188
189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
191 Format: <int>
192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
202
203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
212
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
216
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
220
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
224
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
227
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
231
232 acpi_no_auto_serialize [HW,ACPI]
233 Disable auto-serialization of AML methods
234 AML control methods that contain the opcodes to create
235 named objects will be marked as "Serialized" by the
236 auto-serialization feature.
237 This feature is enabled by default.
238 This option allows to turn off the feature.
239
240 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
241
242 acpica_no_return_repair [HW, ACPI]
243 Disable AML predefined validation mechanism
244 This mechanism can repair the evaluation result to make
245 the return objects more ACPI specification compliant.
246 This option is useful for developers to identify the
247 root cause of an AML interpreter issue when the issue
248 has something to do with the repair mechanism.
249
250 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
251 Format: To spoof as Windows 98: ="Microsoft Windows"
252
253 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
254 acpi_osi="string1" # add string1
255 acpi_osi="!string2" # remove string2
256 acpi_osi=!* # remove all strings
257 acpi_osi=! # disable all built-in OS vendor
258 strings
259 acpi_osi= # disable all strings
260
261 'acpi_osi=!' can be used in combination with single or
262 multiple 'acpi_osi="string1"' to support specific OS
263 vendor string(s). Note that such command can only
264 affect the default state of the OS vendor strings, thus
265 it cannot affect the default state of the feature group
266 strings and the current state of the OS vendor strings,
267 specifying it multiple times through kernel command line
268 is meaningless. This command is useful when one do not
269 care about the state of the feature group strings which
270 should be controlled by the OSPM.
271 Examples:
272 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
273 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
274 can make '_OSI("Windows 2000")' TRUE.
275
276 'acpi_osi=' cannot be used in combination with other
277 'acpi_osi=' command lines, the _OSI method will not
278 exist in the ACPI namespace. NOTE that such command can
279 only affect the _OSI support state, thus specifying it
280 multiple times through kernel command line is also
281 meaningless.
282 Examples:
283 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
284 FALSE.
285
286 'acpi_osi=!*' can be used in combination with single or
287 multiple 'acpi_osi="string1"' to support specific
288 string(s). Note that such command can affect the
289 current state of both the OS vendor strings and the
290 feature group strings, thus specifying it multiple times
291 through kernel command line is meaningful. But it may
292 still not able to affect the final state of a string if
293 there are quirks related to this string. This command
294 is useful when one want to control the state of the
295 feature group strings to debug BIOS issues related to
296 the OSPM features.
297 Examples:
298 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
299 '_OSI("Module Device")' FALSE.
300 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
301 '_OSI("Module Device")' TRUE.
302 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
303 equivalent to
304 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
305 and
306 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
307 they all will make '_OSI("Windows 2000")' TRUE.
308
309 acpi_pm_good [X86]
310 Override the pmtimer bug detection: force the kernel
311 to assume that this machine's pmtimer latches its value
312 and always returns good values.
313
314 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
315 Format: { level | edge | high | low }
316
317 acpi_skip_timer_override [HW,ACPI]
318 Recognize and ignore IRQ0/pin2 Interrupt Override.
319 For broken nForce2 BIOS resulting in XT-PIC timer.
320
321 acpi_sleep= [HW,ACPI] Sleep options
322 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
323 old_ordering, nonvs, sci_force_enable }
324 See Documentation/power/video.txt for information on
325 s3_bios and s3_mode.
326 s3_beep is for debugging; it makes the PC's speaker beep
327 as soon as the kernel's real-mode entry point is called.
328 s4_nohwsig prevents ACPI hardware signature from being
329 used during resume from hibernation.
330 old_ordering causes the ACPI 1.0 ordering of the _PTS
331 control method, with respect to putting devices into
332 low power states, to be enforced (the ACPI 2.0 ordering
333 of _PTS is used by default).
334 nonvs prevents the kernel from saving/restoring the
335 ACPI NVS memory during suspend/hibernation and resume.
336 sci_force_enable causes the kernel to set SCI_EN directly
337 on resume from S1/S3 (which is against the ACPI spec,
338 but some broken systems don't work without it).
339
340 acpi_use_timer_override [HW,ACPI]
341 Use timer override. For some broken Nvidia NF5 boards
342 that require a timer override, but don't have HPET
343
344 acpi_enforce_resources= [ACPI]
345 { strict | lax | no }
346 Check for resource conflicts between native drivers
347 and ACPI OperationRegions (SystemIO and SystemMemory
348 only). IO ports and memory declared in ACPI might be
349 used by the ACPI subsystem in arbitrary AML code and
350 can interfere with legacy drivers.
351 strict (default): access to resources claimed by ACPI
352 is denied; legacy drivers trying to access reserved
353 resources will fail to bind to device using them.
354 lax: access to resources claimed by ACPI is allowed;
355 legacy drivers trying to access reserved resources
356 will bind successfully but a warning message is logged.
357 no: ACPI OperationRegions are not marked as reserved,
358 no further checks are performed.
359
360 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
361 kernels.
362
363 add_efi_memmap [EFI; X86] Include EFI memory map in
364 kernel's map of available physical RAM.
365
366 agp= [AGP]
367 { off | try_unsupported }
368 off: disable AGP support
369 try_unsupported: try to drive unsupported chipsets
370 (may crash computer or cause data corruption)
371
372 ALSA [HW,ALSA]
373 See Documentation/sound/alsa/alsa-parameters.txt
374
375 alignment= [KNL,ARM]
376 Allow the default userspace alignment fault handler
377 behaviour to be specified. Bit 0 enables warnings,
378 bit 1 enables fixups, and bit 2 sends a segfault.
379
380 align_va_addr= [X86-64]
381 Align virtual addresses by clearing slice [14:12] when
382 allocating a VMA at process creation time. This option
383 gives you up to 3% performance improvement on AMD F15h
384 machines (where it is enabled by default) for a
385 CPU-intensive style benchmark, and it can vary highly in
386 a microbenchmark depending on workload and compiler.
387
388 32: only for 32-bit processes
389 64: only for 64-bit processes
390 on: enable for both 32- and 64-bit processes
391 off: disable for both 32- and 64-bit processes
392
393 alloc_snapshot [FTRACE]
394 Allocate the ftrace snapshot buffer on boot up when the
395 main buffer is allocated. This is handy if debugging
396 and you need to use tracing_snapshot() on boot up, and
397 do not want to use tracing_snapshot_alloc() as it needs
398 to be done where GFP_KERNEL allocations are allowed.
399
400 amd_iommu= [HW,X86-64]
401 Pass parameters to the AMD IOMMU driver in the system.
402 Possible values are:
403 fullflush - enable flushing of IO/TLB entries when
404 they are unmapped. Otherwise they are
405 flushed before they will be reused, which
406 is a lot of faster
407 off - do not initialize any AMD IOMMU found in
408 the system
409 force_isolation - Force device isolation for all
410 devices. The IOMMU driver is not
411 allowed anymore to lift isolation
412 requirements as needed. This option
413 does not override iommu=pt
414
415 amd_iommu_dump= [HW,X86-64]
416 Enable AMD IOMMU driver option to dump the ACPI table
417 for AMD IOMMU. With this option enabled, AMD IOMMU
418 driver will print ACPI tables for AMD IOMMU during
419 IOMMU initialization.
420
421 amijoy.map= [HW,JOY] Amiga joystick support
422 Map of devices attached to JOY0DAT and JOY1DAT
423 Format: <a>,<b>
424 See also Documentation/input/joystick.txt
425
426 analog.map= [HW,JOY] Analog joystick and gamepad support
427 Specifies type or capabilities of an analog joystick
428 connected to one of 16 gameports
429 Format: <type1>,<type2>,..<type16>
430
431 apc= [HW,SPARC]
432 Power management functions (SPARCstation-4/5 + deriv.)
433 Format: noidle
434 Disable APC CPU standby support. SPARCstation-Fox does
435 not play well with APC CPU idle - disable it if you have
436 APC and your system crashes randomly.
437
438 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
439 Change the output verbosity whilst booting
440 Format: { quiet (default) | verbose | debug }
441 Change the amount of debugging information output
442 when initialising the APIC and IO-APIC components.
443
444 autoconf= [IPV6]
445 See Documentation/networking/ipv6.txt.
446
447 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
448 Limit apic dumping. The parameter defines the maximal
449 number of local apics being dumped. Also it is possible
450 to set it to "all" by meaning -- no limit here.
451 Format: { 1 (default) | 2 | ... | all }.
452 The parameter valid if only apic=debug or
453 apic=verbose is specified.
454 Example: apic=debug show_lapic=all
455
456 apm= [APM] Advanced Power Management
457 See header of arch/x86/kernel/apm_32.c.
458
459 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
460 Format: <io>,<irq>,<nodeID>
461
462 ataflop= [HW,M68k]
463
464 atarimouse= [HW,MOUSE] Atari Mouse
465
466 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
467 EzKey and similar keyboards
468
469 atkbd.reset= [HW] Reset keyboard during initialization
470
471 atkbd.set= [HW] Select keyboard code set
472 Format: <int> (2 = AT (default), 3 = PS/2)
473
474 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
475 keyboards
476
477 atkbd.softraw= [HW] Choose between synthetic and real raw mode
478 Format: <bool> (0 = real, 1 = synthetic (default))
479
480 atkbd.softrepeat= [HW]
481 Use software keyboard repeat
482
483 audit= [KNL] Enable the audit sub-system
484 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
485 0 - kernel audit is disabled and can not be enabled
486 until the next reboot
487 unset - kernel audit is initialized but disabled and
488 will be fully enabled by the userspace auditd.
489 1 - kernel audit is initialized and partially enabled,
490 storing at most audit_backlog_limit messages in
491 RAM until it is fully enabled by the userspace
492 auditd.
493 Default: unset
494
495 audit_backlog_limit= [KNL] Set the audit queue size limit.
496 Format: <int> (must be >=0)
497 Default: 64
498
499 baycom_epp= [HW,AX25]
500 Format: <io>,<mode>
501
502 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
503 Format: <io>,<mode>
504 See header of drivers/net/hamradio/baycom_par.c.
505
506 baycom_ser_fdx= [HW,AX25]
507 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
508 Format: <io>,<irq>,<mode>[,<baud>]
509 See header of drivers/net/hamradio/baycom_ser_fdx.c.
510
511 baycom_ser_hdx= [HW,AX25]
512 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
513 Format: <io>,<irq>,<mode>
514 See header of drivers/net/hamradio/baycom_ser_hdx.c.
515
516 blkdevparts= Manual partition parsing of block device(s) for
517 embedded devices based on command line input.
518 See Documentation/block/cmdline-partition.txt
519
520 boot_delay= Milliseconds to delay each printk during boot.
521 Values larger than 10 seconds (10000) are changed to
522 no delay (0).
523 Format: integer
524
525 bootmem_debug [KNL] Enable bootmem allocator debug messages.
526
527 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
528 bttv.radio= Most important insmod options are available as
529 kernel args too.
530 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
531 bttv.tuner=
532
533 bulk_remove=off [PPC] This parameter disables the use of the pSeries
534 firmware feature for flushing multiple hpte entries
535 at a time.
536
537 c101= [NET] Moxa C101 synchronous serial card
538
539 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
540 Sometimes CPU hardware bugs make them report the cache
541 size incorrectly. The kernel will attempt work arounds
542 to fix known problems, but for some CPUs it is not
543 possible to determine what the correct size should be.
544 This option provides an override for these situations.
545
546 ccw_timeout_log [S390]
547 See Documentation/s390/CommonIO for details.
548
549 cgroup_disable= [KNL] Disable a particular controller
550 Format: {name of the controller(s) to disable}
551 The effects of cgroup_disable=foo are:
552 - foo isn't auto-mounted if you mount all cgroups in
553 a single hierarchy
554 - foo isn't visible as an individually mountable
555 subsystem
556 {Currently only "memory" controller deal with this and
557 cut the overhead, others just disable the usage. So
558 only cgroup_disable=memory is actually worthy}
559
560 checkreqprot [SELINUX] Set initial checkreqprot flag value.
561 Format: { "0" | "1" }
562 See security/selinux/Kconfig help text.
563 0 -- check protection applied by kernel (includes
564 any implied execute protection).
565 1 -- check protection requested by application.
566 Default value is set via a kernel config option.
567 Value can be changed at runtime via
568 /selinux/checkreqprot.
569
570 cio_ignore= [S390]
571 See Documentation/s390/CommonIO for details.
572 clk_ignore_unused
573 [CLK]
574 Keep all clocks already enabled by bootloader on,
575 even if no driver has claimed them. This is useful
576 for debug and development, but should not be
577 needed on a platform with proper driver support.
578 For more information, see Documentation/clk.txt.
579
580 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
581 [Deprecated]
582 Forces specified clocksource (if available) to be used
583 when calculating gettimeofday(). If specified
584 clocksource is not available, it defaults to PIT.
585 Format: { pit | tsc | cyclone | pmtmr }
586
587 clocksource= Override the default clocksource
588 Format: <string>
589 Override the default clocksource and use the clocksource
590 with the name specified.
591 Some clocksource names to choose from, depending on
592 the platform:
593 [all] jiffies (this is the base, fallback clocksource)
594 [ACPI] acpi_pm
595 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
596 pxa_timer,timer3,32k_counter,timer0_1
597 [AVR32] avr32
598 [X86-32] pit,hpet,tsc;
599 scx200_hrt on Geode; cyclone on IBM x440
600 [MIPS] MIPS
601 [PARISC] cr16
602 [S390] tod
603 [SH] SuperH
604 [SPARC64] tick
605 [X86-64] hpet,tsc
606
607 clearcpuid=BITNUM [X86]
608 Disable CPUID feature X for the kernel. See
609 arch/x86/include/asm/cpufeature.h for the valid bit
610 numbers. Note the Linux specific bits are not necessarily
611 stable over kernel options, but the vendor specific
612 ones should be.
613 Also note that user programs calling CPUID directly
614 or using the feature without checking anything
615 will still see it. This just prevents it from
616 being used by the kernel or shown in /proc/cpuinfo.
617 Also note the kernel might malfunction if you disable
618 some critical bits.
619
620 cma=nn[MG] [ARM,KNL]
621 Sets the size of kernel global memory area for contiguous
622 memory allocations. For more information, see
623 include/linux/dma-contiguous.h
624
625 cmo_free_hint= [PPC] Format: { yes | no }
626 Specify whether pages are marked as being inactive
627 when they are freed. This is used in CMO environments
628 to determine OS memory pressure for page stealing by
629 a hypervisor.
630 Default: yes
631
632 coherent_pool=nn[KMG] [ARM,KNL]
633 Sets the size of memory pool for coherent, atomic dma
634 allocations, by default set to 256K.
635
636 code_bytes [X86] How many bytes of object code to print
637 in an oops report.
638 Range: 0 - 8192
639 Default: 64
640
641 com20020= [HW,NET] ARCnet - COM20020 chipset
642 Format:
643 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
644
645 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
646 Format: <io>[,<irq>]
647
648 com90xx= [HW,NET]
649 ARCnet - COM90xx chipset (memory-mapped buffers)
650 Format: <io>[,<irq>[,<memstart>]]
651
652 condev= [HW,S390] console device
653 conmode=
654
655 console= [KNL] Output console device and options.
656
657 tty<n> Use the virtual console device <n>.
658
659 ttyS<n>[,options]
660 ttyUSB0[,options]
661 Use the specified serial port. The options are of
662 the form "bbbbpnf", where "bbbb" is the baud rate,
663 "p" is parity ("n", "o", or "e"), "n" is number of
664 bits, and "f" is flow control ("r" for RTS or
665 omit it). Default is "9600n8".
666
667 See Documentation/serial-console.txt for more
668 information. See
669 Documentation/networking/netconsole.txt for an
670 alternative.
671
672 uart[8250],io,<addr>[,options]
673 uart[8250],mmio,<addr>[,options]
674 Start an early, polled-mode console on the 8250/16550
675 UART at the specified I/O port or MMIO address,
676 switching to the matching ttyS device later. The
677 options are the same as for ttyS, above.
678 hvc<n> Use the hypervisor console device <n>. This is for
679 both Xen and PowerPC hypervisors.
680
681 If the device connected to the port is not a TTY but a braille
682 device, prepend "brl," before the device type, for instance
683 console=brl,ttyS0
684 For now, only VisioBraille is supported.
685
686 consoleblank= [KNL] The console blank (screen saver) timeout in
687 seconds. Defaults to 10*60 = 10mins. A value of 0
688 disables the blank timer.
689
690 coredump_filter=
691 [KNL] Change the default value for
692 /proc/<pid>/coredump_filter.
693 See also Documentation/filesystems/proc.txt.
694
695 cpuidle.off=1 [CPU_IDLE]
696 disable the cpuidle sub-system
697
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
699 Format:
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
701
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically. Check
708 Documentation/kdump/kdump.txt for further details.
709
710 crashkernel=range1:size1[,range2:size2,...][@offset]
711 [KNL] Same as above, but depends on the memory
712 in the running system. The syntax of range is
713 start-[end] where start and end are both
714 a memory unit (amount[KMG]). See also
715 Documentation/kdump/kdump.txt for an example.
716
717 crashkernel=size[KMG],high
718 [KNL, x86_64] range could be above 4G. Allow kernel
719 to allocate physical memory region from top, so could
720 be above 4G if system have more than 4G ram installed.
721 Otherwise memory region will be allocated below 4G, if
722 available.
723 It will be ignored if crashkernel=X is specified.
724 crashkernel=size[KMG],low
725 [KNL, x86_64] range under 4G. When crashkernel=X,high
726 is passed, kernel could allocate physical memory region
727 above 4G, that cause second kernel crash on system
728 that require some amount of low memory, e.g. swiotlb
729 requires at least 64M+32K low memory. Kernel would
730 try to allocate 72M below 4G automatically.
731 This one let user to specify own low range under 4G
732 for second kernel instead.
733 0: to disable low allocation.
734 It will be ignored when crashkernel=X,high is not used
735 or memory reserved is below 4G.
736
737 cs89x0_dma= [HW,NET]
738 Format: <dma>
739
740 cs89x0_media= [HW,NET]
741 Format: { rj45 | aui | bnc }
742
743 dasd= [HW,NET]
744 See header of drivers/s390/block/dasd_devmap.c.
745
746 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
747 (one device per port)
748 Format: <port#>,<type>
749 See also Documentation/input/joystick-parport.txt
750
751 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
752 time. See Documentation/dynamic-debug-howto.txt for
753 details. Deprecated, see dyndbg.
754
755 debug [KNL] Enable kernel debugging (events log level).
756
757 debug_locks_verbose=
758 [KNL] verbose self-tests
759 Format=<0|1>
760 Print debugging info while doing the locking API
761 self-tests.
762 We default to 0 (no extra messages), setting it to
763 1 will print _a lot_ more information - normally
764 only useful to kernel developers.
765
766 debug_objects [KNL] Enable object debugging
767
768 no_debug_objects
769 [KNL] Disable object debugging
770
771 debug_guardpage_minorder=
772 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
773 parameter allows control of the order of pages that will
774 be intentionally kept free (and hence protected) by the
775 buddy allocator. Bigger value increase the probability
776 of catching random memory corruption, but reduce the
777 amount of memory for normal system use. The maximum
778 possible value is MAX_ORDER/2. Setting this parameter
779 to 1 or 2 should be enough to identify most random
780 memory corruption problems caused by bugs in kernel or
781 driver code when a CPU writes to (or reads from) a
782 random memory location. Note that there exists a class
783 of memory corruptions problems caused by buggy H/W or
784 F/W or by drivers badly programing DMA (basically when
785 memory is written at bus level and the CPU MMU is
786 bypassed) which are not detectable by
787 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
788 tracking down these problems.
789
790 debugpat [X86] Enable PAT debugging
791
792 decnet.addr= [HW,NET]
793 Format: <area>[,<node>]
794 See also Documentation/networking/decnet.txt.
795
796 default_hugepagesz=
797 [same as hugepagesz=] The size of the default
798 HugeTLB page size. This is the size represented by
799 the legacy /proc/ hugepages APIs, used for SHM, and
800 default size when mounting hugetlbfs filesystems.
801 Defaults to the default architecture's huge page size
802 if not specified.
803
804 dhash_entries= [KNL]
805 Set number of hash buckets for dentry cache.
806
807 disable= [IPV6]
808 See Documentation/networking/ipv6.txt.
809
810 disable_cpu_apicid= [X86,APIC,SMP]
811 Format: <int>
812 The number of initial APIC ID for the
813 corresponding CPU to be disabled at boot,
814 mostly used for the kdump 2nd kernel to
815 disable BSP to wake up multiple CPUs without
816 causing system reset or hang due to sending
817 INIT from AP to BSP.
818
819 disable_ddw [PPC/PSERIES]
820 Disable Dynamic DMA Window support. Use this if
821 to workaround buggy firmware.
822
823 disable_ipv6= [IPV6]
824 See Documentation/networking/ipv6.txt.
825
826 disable_mtrr_cleanup [X86]
827 The kernel tries to adjust MTRR layout from continuous
828 to discrete, to make X server driver able to add WB
829 entry later. This parameter disables that.
830
831 disable_mtrr_trim [X86, Intel and AMD only]
832 By default the kernel will trim any uncacheable
833 memory out of your available memory pool based on
834 MTRR settings. This parameter disables that behavior,
835 possibly causing your machine to run very slowly.
836
837 disable_timer_pin_1 [X86]
838 Disable PIN 1 of APIC timer
839 Can be useful to work around chipset bugs.
840
841 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
842 this option disables the debugging code at boot.
843
844 dma_debug_entries=<number>
845 This option allows to tune the number of preallocated
846 entries for DMA-API debugging code. One entry is
847 required per DMA-API allocation. Use this if the
848 DMA-API debugging code disables itself because the
849 architectural default is too low.
850
851 dma_debug_driver=<driver_name>
852 With this option the DMA-API debugging driver
853 filter feature can be enabled at boot time. Just
854 pass the driver to filter for as the parameter.
855 The filter can be disabled or changed to another
856 driver later using sysfs.
857
858 drm_kms_helper.edid_firmware=[<connector>:]<file>
859 Broken monitors, graphic adapters and KVMs may
860 send no or incorrect EDID data sets. This parameter
861 allows to specify an EDID data set in the
862 /lib/firmware directory that is used instead.
863 Generic built-in EDID data sets are used, if one of
864 edid/1024x768.bin, edid/1280x1024.bin,
865 edid/1680x1050.bin, or edid/1920x1080.bin is given
866 and no file with the same name exists. Details and
867 instructions how to build your own EDID data are
868 available in Documentation/EDID/HOWTO.txt. An EDID
869 data set will only be used for a particular connector,
870 if its name and a colon are prepended to the EDID
871 name.
872
873 dscc4.setup= [NET]
874
875 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
876 module.dyndbg[="val"]
877 Enable debug messages at boot time. See
878 Documentation/dynamic-debug-howto.txt for details.
879
880 early_ioremap_debug [KNL]
881 Enable debug messages in early_ioremap support. This
882 is useful for tracking down temporary early mappings
883 which are not unmapped.
884
885 earlycon= [KNL] Output early console device and options.
886 uart[8250],io,<addr>[,options]
887 uart[8250],mmio,<addr>[,options]
888 uart[8250],mmio32,<addr>[,options]
889 Start an early, polled-mode console on the 8250/16550
890 UART at the specified I/O port or MMIO address.
891 MMIO inter-register address stride is either 8-bit
892 (mmio) or 32-bit (mmio32).
893 The options are the same as for ttyS, above.
894
895 earlyprintk= [X86,SH,BLACKFIN,ARM]
896 earlyprintk=vga
897 earlyprintk=efi
898 earlyprintk=xen
899 earlyprintk=serial[,ttySn[,baudrate]]
900 earlyprintk=serial[,0x...[,baudrate]]
901 earlyprintk=ttySn[,baudrate]
902 earlyprintk=dbgp[debugController#]
903
904 earlyprintk is useful when the kernel crashes before
905 the normal console is initialized. It is not enabled by
906 default because it has some cosmetic problems.
907
908 Append ",keep" to not disable it when the real console
909 takes over.
910
911 Only one of vga, efi, serial, or usb debug port can
912 be used at a time.
913
914 Currently only ttyS0 and ttyS1 may be specified by
915 name. Other I/O ports may be explicitly specified
916 on some architectures (x86 and arm at least) by
917 replacing ttySn with an I/O port address, like this:
918 earlyprintk=serial,0x1008,115200
919 You can find the port for a given device in
920 /proc/tty/driver/serial:
921 2: uart:ST16650V2 port:00001008 irq:18 ...
922
923 Interaction with the standard serial driver is not
924 very good.
925
926 The VGA and EFI output is eventually overwritten by
927 the real console.
928
929 The xen output can only be used by Xen PV guests.
930
931 edac_report= [HW,EDAC] Control how to report EDAC event
932 Format: {"on" | "off" | "force"}
933 on: enable EDAC to report H/W event. May be overridden
934 by other higher priority error reporting module.
935 off: disable H/W event reporting through EDAC.
936 force: enforce the use of EDAC to report H/W event.
937 default: on.
938
939 ekgdboc= [X86,KGDB] Allow early kernel console debugging
940 ekgdboc=kbd
941
942 This is designed to be used in conjunction with
943 the boot argument: earlyprintk=vga
944
945 edd= [EDD]
946 Format: {"off" | "on" | "skip[mbr]"}
947
948 efi= [EFI]
949 Format: { "old_map" }
950 old_map [X86-64]: switch to the old ioremap-based EFI
951 runtime services mapping. 32-bit still uses this one by
952 default.
953
954 efi_no_storage_paranoia [EFI; X86]
955 Using this parameter you can use more than 50% of
956 your efi variable storage. Use this parameter only if
957 you are really sure that your UEFI does sane gc and
958 fulfills the spec otherwise your board may brick.
959
960 eisa_irq_edge= [PARISC,HW]
961 See header of drivers/parisc/eisa.c.
962
963 elanfreq= [X86-32]
964 See comment before function elanfreq_setup() in
965 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
966
967 elevator= [IOSCHED]
968 Format: {"cfq" | "deadline" | "noop"}
969 See Documentation/block/cfq-iosched.txt and
970 Documentation/block/deadline-iosched.txt for details.
971
972 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
973 Specifies physical address of start of kernel core
974 image elf header and optionally the size. Generally
975 kexec loader will pass this option to capture kernel.
976 See Documentation/kdump/kdump.txt for details.
977
978 enable_mtrr_cleanup [X86]
979 The kernel tries to adjust MTRR layout from continuous
980 to discrete, to make X server driver able to add WB
981 entry later. This parameter enables that.
982
983 enable_timer_pin_1 [X86]
984 Enable PIN 1 of APIC timer
985 Can be useful to work around chipset bugs
986 (in particular on some ATI chipsets).
987 The kernel tries to set a reasonable default.
988
989 enforcing [SELINUX] Set initial enforcing status.
990 Format: {"0" | "1"}
991 See security/selinux/Kconfig help text.
992 0 -- permissive (log only, no denials).
993 1 -- enforcing (deny and log).
994 Default value is 0.
995 Value can be changed at runtime via /selinux/enforce.
996
997 erst_disable [ACPI]
998 Disable Error Record Serialization Table (ERST)
999 support.
1000
1001 ether= [HW,NET] Ethernet cards parameters
1002 This option is obsoleted by the "netdev=" option, which
1003 has equivalent usage. See its documentation for details.
1004
1005 evm= [EVM]
1006 Format: { "fix" }
1007 Permit 'security.evm' to be updated regardless of
1008 current integrity status.
1009
1010 failslab=
1011 fail_page_alloc=
1012 fail_make_request=[KNL]
1013 General fault injection mechanism.
1014 Format: <interval>,<probability>,<space>,<times>
1015 See also Documentation/fault-injection/.
1016
1017 floppy= [HW]
1018 See Documentation/blockdev/floppy.txt.
1019
1020 force_pal_cache_flush
1021 [IA-64] Avoid check_sal_cache_flush which may hang on
1022 buggy SAL_CACHE_FLUSH implementations. Using this
1023 parameter will force ia64_sal_cache_flush to call
1024 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1025
1026 forcepae [X86-32]
1027 Forcefully enable Physical Address Extension (PAE).
1028 Many Pentium M systems disable PAE but may have a
1029 functionally usable PAE implementation.
1030 Warning: use of this parameter will taint the kernel
1031 and may cause unknown problems.
1032
1033 ftrace=[tracer]
1034 [FTRACE] will set and start the specified tracer
1035 as early as possible in order to facilitate early
1036 boot debugging.
1037
1038 ftrace_dump_on_oops[=orig_cpu]
1039 [FTRACE] will dump the trace buffers on oops.
1040 If no parameter is passed, ftrace will dump
1041 buffers of all CPUs, but if you pass orig_cpu, it will
1042 dump only the buffer of the CPU that triggered the
1043 oops.
1044
1045 ftrace_filter=[function-list]
1046 [FTRACE] Limit the functions traced by the function
1047 tracer at boot up. function-list is a comma separated
1048 list of functions. This list can be changed at run
1049 time by the set_ftrace_filter file in the debugfs
1050 tracing directory.
1051
1052 ftrace_notrace=[function-list]
1053 [FTRACE] Do not trace the functions specified in
1054 function-list. This list can be changed at run time
1055 by the set_ftrace_notrace file in the debugfs
1056 tracing directory.
1057
1058 ftrace_graph_filter=[function-list]
1059 [FTRACE] Limit the top level callers functions traced
1060 by the function graph tracer at boot up.
1061 function-list is a comma separated list of functions
1062 that can be changed at run time by the
1063 set_graph_function file in the debugfs tracing directory.
1064
1065 gamecon.map[2|3]=
1066 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1067 support via parallel port (up to 5 devices per port)
1068 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1069 See also Documentation/input/joystick-parport.txt
1070
1071 gamma= [HW,DRM]
1072
1073 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1074 Format: off | on
1075 default: on
1076
1077 gcov_persist= [GCOV] When non-zero (default), profiling data for
1078 kernel modules is saved and remains accessible via
1079 debugfs, even when the module is unloaded/reloaded.
1080 When zero, profiling data is discarded and associated
1081 debugfs files are removed at module unload time.
1082
1083 gpt [EFI] Forces disk with valid GPT signature but
1084 invalid Protective MBR to be treated as GPT. If the
1085 primary GPT is corrupted, it enables the backup/alternate
1086 GPT to be used instead.
1087
1088 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1089 the "Enable 0" bit of the configuration register.
1090 Format: 0 | 1
1091 Default: 0
1092 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1093 the "Enable 0" bit of the configuration register.
1094 Format: 0 | 1
1095 Default: 0
1096 grcan.select= [HW] Select which physical interface to use.
1097 Format: 0 | 1
1098 Default: 0
1099 grcan.txsize= [HW] Sets the size of the tx buffer.
1100 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1101 Default: 1024
1102 grcan.rxsize= [HW] Sets the size of the rx buffer.
1103 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1104 Default: 1024
1105
1106 hashdist= [KNL,NUMA] Large hashes allocated during boot
1107 are distributed across NUMA nodes. Defaults on
1108 for 64-bit NUMA, off otherwise.
1109 Format: 0 | 1 (for off | on)
1110
1111 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1112
1113 hd= [EIDE] (E)IDE hard drive subsystem geometry
1114 Format: <cyl>,<head>,<sect>
1115
1116 hest_disable [ACPI]
1117 Disable Hardware Error Source Table (HEST) support;
1118 corresponding firmware-first mode error processing
1119 logic will be disabled.
1120
1121 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1122 size of <nn>. This works even on boxes that have no
1123 highmem otherwise. This also works to reduce highmem
1124 size on bigger boxes.
1125
1126 highres= [KNL] Enable/disable high resolution timer mode.
1127 Valid parameters: "on", "off"
1128 Default: "on"
1129
1130 hisax= [HW,ISDN]
1131 See Documentation/isdn/README.HiSax.
1132
1133 hlt [BUGS=ARM,SH]
1134
1135 hpet= [X86-32,HPET] option to control HPET usage
1136 Format: { enable (default) | disable | force |
1137 verbose }
1138 disable: disable HPET and use PIT instead
1139 force: allow force enabled of undocumented chips (ICH4,
1140 VIA, nVidia)
1141 verbose: show contents of HPET registers during setup
1142
1143 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1144 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1145
1146 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1147 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1148 On x86-64 and powerpc, this option can be specified
1149 multiple times interleaved with hugepages= to reserve
1150 huge pages of different sizes. Valid pages sizes on
1151 x86-64 are 2M (when the CPU supports "pse") and 1G
1152 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1153 Note that 1GB pages can only be allocated at boot time
1154 using hugepages= and not freed afterwards.
1155
1156 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1157 terminal devices. Valid values: 0..8
1158 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1159 If specified, z/VM IUCV HVC accepts connections
1160 from listed z/VM user IDs only.
1161
1162 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1163 hardware thread id mappings.
1164 Format: <cpu>:<hwthread>
1165
1166 keep_bootcon [KNL]
1167 Do not unregister boot console at start. This is only
1168 useful for debugging when something happens in the window
1169 between unregistering the boot console and initializing
1170 the real console.
1171
1172 i2c_bus= [HW] Override the default board specific I2C bus speed
1173 or register an additional I2C bus that is not
1174 registered from board initialization code.
1175 Format:
1176 <bus_id>,<clkrate>
1177
1178 i8042.debug [HW] Toggle i8042 debug mode
1179 i8042.direct [HW] Put keyboard port into non-translated mode
1180 i8042.dumbkbd [HW] Pretend that controller can only read data from
1181 keyboard and cannot control its state
1182 (Don't attempt to blink the leds)
1183 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1184 i8042.nokbd [HW] Don't check/create keyboard port
1185 i8042.noloop [HW] Disable the AUX Loopback command while probing
1186 for the AUX port
1187 i8042.nomux [HW] Don't check presence of an active multiplexing
1188 controller
1189 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1190 controllers
1191 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1192 i8042.reset [HW] Reset the controller during init and cleanup
1193 i8042.unlock [HW] Unlock (ignore) the keylock
1194
1195 i810= [HW,DRM]
1196
1197 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1198 indicates that the driver is running on unsupported
1199 hardware.
1200 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1201 does not match list of supported models.
1202 i8k.power_status
1203 [HW] Report power status in /proc/i8k
1204 (disabled by default)
1205 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1206 capability is set.
1207
1208 i915.invert_brightness=
1209 [DRM] Invert the sense of the variable that is used to
1210 set the brightness of the panel backlight. Normally a
1211 brightness value of 0 indicates backlight switched off,
1212 and the maximum of the brightness value sets the backlight
1213 to maximum brightness. If this parameter is set to 0
1214 (default) and the machine requires it, or this parameter
1215 is set to 1, a brightness value of 0 sets the backlight
1216 to maximum brightness, and the maximum of the brightness
1217 value switches the backlight off.
1218 -1 -- never invert brightness
1219 0 -- machine default
1220 1 -- force brightness inversion
1221
1222 icn= [HW,ISDN]
1223 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1224
1225 ide-core.nodma= [HW] (E)IDE subsystem
1226 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1227 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1228 .cdrom .chs .ignore_cable are additional options
1229 See Documentation/ide/ide.txt.
1230
1231 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1232 Claim all unknown PCI IDE storage controllers.
1233
1234 idle= [X86]
1235 Format: idle=poll, idle=halt, idle=nomwait
1236 Poll forces a polling idle loop that can slightly
1237 improve the performance of waking up a idle CPU, but
1238 will use a lot of power and make the system run hot.
1239 Not recommended.
1240 idle=halt: Halt is forced to be used for CPU idle.
1241 In such case C2/C3 won't be used again.
1242 idle=nomwait: Disable mwait for CPU C-states
1243
1244 ignore_loglevel [KNL]
1245 Ignore loglevel setting - this will print /all/
1246 kernel messages to the console. Useful for debugging.
1247 We also add it as printk module parameter, so users
1248 could change it dynamically, usually by
1249 /sys/module/printk/parameters/ignore_loglevel.
1250
1251 ihash_entries= [KNL]
1252 Set number of hash buckets for inode cache.
1253
1254 ima_appraise= [IMA] appraise integrity measurements
1255 Format: { "off" | "enforce" | "fix" }
1256 default: "enforce"
1257
1258 ima_appraise_tcb [IMA]
1259 The builtin appraise policy appraises all files
1260 owned by uid=0.
1261
1262 ima_hash= [IMA]
1263 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1264 | sha512 | ... }
1265 default: "sha1"
1266
1267 The list of supported hash algorithms is defined
1268 in crypto/hash_info.h.
1269
1270 ima_tcb [IMA]
1271 Load a policy which meets the needs of the Trusted
1272 Computing Base. This means IMA will measure all
1273 programs exec'd, files mmap'd for exec, and all files
1274 opened for read by uid=0.
1275
1276 ima_template= [IMA]
1277 Select one of defined IMA measurements template formats.
1278 Formats: { "ima" | "ima-ng" }
1279 Default: "ima-ng"
1280
1281 init= [KNL]
1282 Format: <full_path>
1283 Run specified binary instead of /sbin/init as init
1284 process.
1285
1286 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1287 for working out where the kernel is dying during
1288 startup.
1289
1290 initrd= [BOOT] Specify the location of the initial ramdisk
1291
1292 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1293 Format: <irq>
1294
1295 int_pln_enable [x86] Enable power limit notification interrupt
1296
1297 integrity_audit=[IMA]
1298 Format: { "0" | "1" }
1299 0 -- basic integrity auditing messages. (Default)
1300 1 -- additional integrity auditing messages.
1301
1302 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1303 on
1304 Enable intel iommu driver.
1305 off
1306 Disable intel iommu driver.
1307 igfx_off [Default Off]
1308 By default, gfx is mapped as normal device. If a gfx
1309 device has a dedicated DMAR unit, the DMAR unit is
1310 bypassed by not enabling DMAR with this option. In
1311 this case, gfx device will use physical address for
1312 DMA.
1313 forcedac [x86_64]
1314 With this option iommu will not optimize to look
1315 for io virtual address below 32-bit forcing dual
1316 address cycle on pci bus for cards supporting greater
1317 than 32-bit addressing. The default is to look
1318 for translation below 32-bit and if not available
1319 then look in the higher range.
1320 strict [Default Off]
1321 With this option on every unmap_single operation will
1322 result in a hardware IOTLB flush operation as opposed
1323 to batching them for performance.
1324 sp_off [Default Off]
1325 By default, super page will be supported if Intel IOMMU
1326 has the capability. With this option, super page will
1327 not be supported.
1328
1329 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1330 0 disables intel_idle and fall back on acpi_idle.
1331 1 to 6 specify maximum depth of C-state.
1332
1333 intel_pstate= [X86]
1334 disable
1335 Do not enable intel_pstate as the default
1336 scaling driver for the supported processors
1337
1338 intremap= [X86-64, Intel-IOMMU]
1339 on enable Interrupt Remapping (default)
1340 off disable Interrupt Remapping
1341 nosid disable Source ID checking
1342 no_x2apic_optout
1343 BIOS x2APIC opt-out request will be ignored
1344
1345 iomem= Disable strict checking of access to MMIO memory
1346 strict regions from userspace.
1347 relaxed
1348
1349 iommu= [x86]
1350 off
1351 force
1352 noforce
1353 biomerge
1354 panic
1355 nopanic
1356 merge
1357 nomerge
1358 forcesac
1359 soft
1360 pt [x86, IA-64]
1361
1362
1363 io7= [HW] IO7 for Marvel based alpha systems
1364 See comment before marvel_specify_io7 in
1365 arch/alpha/kernel/core_marvel.c.
1366
1367 io_delay= [X86] I/O delay method
1368 0x80
1369 Standard port 0x80 based delay
1370 0xed
1371 Alternate port 0xed based delay (needed on some systems)
1372 udelay
1373 Simple two microseconds delay
1374 none
1375 No delay
1376
1377 ip= [IP_PNP]
1378 See Documentation/filesystems/nfs/nfsroot.txt.
1379
1380 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1381 See comment before ip2_setup() in
1382 drivers/char/ip2/ip2base.c.
1383
1384 irqfixup [HW]
1385 When an interrupt is not handled search all handlers
1386 for it. Intended to get systems with badly broken
1387 firmware running.
1388
1389 irqpoll [HW]
1390 When an interrupt is not handled search all handlers
1391 for it. Also check all handlers each timer
1392 interrupt. Intended to get systems with badly broken
1393 firmware running.
1394
1395 isapnp= [ISAPNP]
1396 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1397
1398 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1399 Format:
1400 <cpu number>,...,<cpu number>
1401 or
1402 <cpu number>-<cpu number>
1403 (must be a positive range in ascending order)
1404 or a mixture
1405 <cpu number>,...,<cpu number>-<cpu number>
1406
1407 This option can be used to specify one or more CPUs
1408 to isolate from the general SMP balancing and scheduling
1409 algorithms. You can move a process onto or off an
1410 "isolated" CPU via the CPU affinity syscalls or cpuset.
1411 <cpu number> begins at 0 and the maximum value is
1412 "number of CPUs in system - 1".
1413
1414 This option is the preferred way to isolate CPUs. The
1415 alternative -- manually setting the CPU mask of all
1416 tasks in the system -- can cause problems and
1417 suboptimal load balancer performance.
1418
1419 iucv= [HW,NET]
1420
1421 ivrs_ioapic [HW,X86_64]
1422 Provide an override to the IOAPIC-ID<->DEVICE-ID
1423 mapping provided in the IVRS ACPI table. For
1424 example, to map IOAPIC-ID decimal 10 to
1425 PCI device 00:14.0 write the parameter as:
1426 ivrs_ioapic[10]=00:14.0
1427
1428 ivrs_hpet [HW,X86_64]
1429 Provide an override to the HPET-ID<->DEVICE-ID
1430 mapping provided in the IVRS ACPI table. For
1431 example, to map HPET-ID decimal 0 to
1432 PCI device 00:14.0 write the parameter as:
1433 ivrs_hpet[0]=00:14.0
1434
1435 js= [HW,JOY] Analog joystick
1436 See Documentation/input/joystick.txt.
1437
1438 keepinitrd [HW,ARM]
1439
1440 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1441 specifies the amount of memory usable by the kernel
1442 for non-movable allocations. The requested amount is
1443 spread evenly throughout all nodes in the system. The
1444 remaining memory in each node is used for Movable
1445 pages. In the event, a node is too small to have both
1446 kernelcore and Movable pages, kernelcore pages will
1447 take priority and other nodes will have a larger number
1448 of Movable pages. The Movable zone is used for the
1449 allocation of pages that may be reclaimed or moved
1450 by the page migration subsystem. This means that
1451 HugeTLB pages may not be allocated from this zone.
1452 Note that allocations like PTEs-from-HighMem still
1453 use the HighMem zone if it exists, and the Normal
1454 zone if it does not.
1455
1456 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1457 Format: <Controller#>[,poll interval]
1458 The controller # is the number of the ehci usb debug
1459 port as it is probed via PCI. The poll interval is
1460 optional and is the number seconds in between
1461 each poll cycle to the debug port in case you need
1462 the functionality for interrupting the kernel with
1463 gdb or control-c on the dbgp connection. When
1464 not using this parameter you use sysrq-g to break into
1465 the kernel debugger.
1466
1467 kgdboc= [KGDB,HW] kgdb over consoles.
1468 Requires a tty driver that supports console polling,
1469 or a supported polling keyboard driver (non-usb).
1470 Serial only format: <serial_device>[,baud]
1471 keyboard only format: kbd
1472 keyboard and serial format: kbd,<serial_device>[,baud]
1473 Optional Kernel mode setting:
1474 kms, kbd format: kms,kbd
1475 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1476
1477 kgdbwait [KGDB] Stop kernel execution and enter the
1478 kernel debugger at the earliest opportunity.
1479
1480 kmac= [MIPS] korina ethernet MAC address.
1481 Configure the RouterBoard 532 series on-chip
1482 Ethernet adapter MAC address.
1483
1484 kmemleak= [KNL] Boot-time kmemleak enable/disable
1485 Valid arguments: on, off
1486 Default: on
1487
1488 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1489 Valid arguments: 0, 1, 2
1490 kmemcheck=0 (disabled)
1491 kmemcheck=1 (enabled)
1492 kmemcheck=2 (one-shot mode)
1493 Default: 2 (one-shot mode)
1494
1495 kstack=N [X86] Print N words from the kernel stack
1496 in oops dumps.
1497
1498 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1499 Default is 0 (don't ignore, but inject #GP)
1500
1501 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1502 KVM MMU at runtime.
1503 Default is 0 (off)
1504
1505 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1506 Default is 1 (enabled)
1507
1508 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1509 for all guests.
1510 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1511
1512 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1513 (virtualized MMU) support on capable Intel chips.
1514 Default is 1 (enabled)
1515
1516 kvm-intel.emulate_invalid_guest_state=
1517 [KVM,Intel] Enable emulation of invalid guest states
1518 Default is 0 (disabled)
1519
1520 kvm-intel.flexpriority=
1521 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1522 Default is 1 (enabled)
1523
1524 kvm-intel.nested=
1525 [KVM,Intel] Enable VMX nesting (nVMX).
1526 Default is 0 (disabled)
1527
1528 kvm-intel.unrestricted_guest=
1529 [KVM,Intel] Disable unrestricted guest feature
1530 (virtualized real and unpaged mode) on capable
1531 Intel chips. Default is 1 (enabled)
1532
1533 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1534 feature (tagged TLBs) on capable Intel chips.
1535 Default is 1 (enabled)
1536
1537 l2cr= [PPC]
1538
1539 l3cr= [PPC]
1540
1541 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1542 disabled it.
1543
1544 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1545 value for LAPIC timer one-shot implementation. Default
1546 back to the programmable timer unit in the LAPIC.
1547
1548 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1549 in C2 power state.
1550
1551 libata.dma= [LIBATA] DMA control
1552 libata.dma=0 Disable all PATA and SATA DMA
1553 libata.dma=1 PATA and SATA Disk DMA only
1554 libata.dma=2 ATAPI (CDROM) DMA only
1555 libata.dma=4 Compact Flash DMA only
1556 Combinations also work, so libata.dma=3 enables DMA
1557 for disks and CDROMs, but not CFs.
1558
1559 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1560 libata.ignore_hpa=0 keep BIOS limits (default)
1561 libata.ignore_hpa=1 ignore limits, using full disk
1562
1563 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1564 when set.
1565 Format: <int>
1566
1567 libata.force= [LIBATA] Force configurations. The format is comma
1568 separated list of "[ID:]VAL" where ID is
1569 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1570 matching port, link or device. Basically, it matches
1571 the ATA ID string printed on console by libata. If
1572 the whole ID part is omitted, the last PORT and DEVICE
1573 values are used. If ID hasn't been specified yet, the
1574 configuration applies to all ports, links and devices.
1575
1576 If only DEVICE is omitted, the parameter applies to
1577 the port and all links and devices behind it. DEVICE
1578 number of 0 either selects the first device or the
1579 first fan-out link behind PMP device. It does not
1580 select the host link. DEVICE number of 15 selects the
1581 host link and device attached to it.
1582
1583 The VAL specifies the configuration to force. As long
1584 as there's no ambiguity shortcut notation is allowed.
1585 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1586 The following configurations can be forced.
1587
1588 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1589 Any ID with matching PORT is used.
1590
1591 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1592
1593 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1594 udma[/][16,25,33,44,66,100,133] notation is also
1595 allowed.
1596
1597 * [no]ncq: Turn on or off NCQ.
1598
1599 * nohrst, nosrst, norst: suppress hard, soft
1600 and both resets.
1601
1602 * rstonce: only attempt one reset during
1603 hot-unplug link recovery
1604
1605 * dump_id: dump IDENTIFY data.
1606
1607 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1608
1609 * disable: Disable this device.
1610
1611 If there are multiple matching configurations changing
1612 the same attribute, the last one is used.
1613
1614 memblock=debug [KNL] Enable memblock debug messages.
1615
1616 load_ramdisk= [RAM] List of ramdisks to load from floppy
1617 See Documentation/blockdev/ramdisk.txt.
1618
1619 lockd.nlm_grace_period=P [NFS] Assign grace period.
1620 Format: <integer>
1621
1622 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1623 Format: <integer>
1624
1625 lockd.nlm_timeout=T [NFS] Assign timeout value.
1626 Format: <integer>
1627
1628 lockd.nlm_udpport=M [NFS] Assign UDP port.
1629 Format: <integer>
1630
1631 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1632 Format: <irq>
1633
1634 loglevel= All Kernel Messages with a loglevel smaller than the
1635 console loglevel will be printed to the console. It can
1636 also be changed with klogd or other programs. The
1637 loglevels are defined as follows:
1638
1639 0 (KERN_EMERG) system is unusable
1640 1 (KERN_ALERT) action must be taken immediately
1641 2 (KERN_CRIT) critical conditions
1642 3 (KERN_ERR) error conditions
1643 4 (KERN_WARNING) warning conditions
1644 5 (KERN_NOTICE) normal but significant condition
1645 6 (KERN_INFO) informational
1646 7 (KERN_DEBUG) debug-level messages
1647
1648 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1649 in bytes. n must be a power of two. The default
1650 size is set in the kernel config file.
1651
1652 logo.nologo [FB] Disables display of the built-in Linux logo.
1653 This may be used to provide more screen space for
1654 kernel log messages and is useful when debugging
1655 kernel boot problems.
1656
1657 lp=0 [LP] Specify parallel ports to use, e.g,
1658 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1659 lp=reset first parallel port). 'lp=0' disables the
1660 lp=auto printer driver. 'lp=reset' (which can be
1661 specified in addition to the ports) causes
1662 attached printers to be reset. Using
1663 lp=port1,port2,... specifies the parallel ports
1664 to associate lp devices with, starting with
1665 lp0. A port specification may be 'none' to skip
1666 that lp device, or a parport name such as
1667 'parport0'. Specifying 'lp=auto' instead of a
1668 port specification list means that device IDs
1669 from each port should be examined, to see if
1670 an IEEE 1284-compliant printer is attached; if
1671 so, the driver will manage that printer.
1672 See also header of drivers/char/lp.c.
1673
1674 lpj=n [KNL]
1675 Sets loops_per_jiffy to given constant, thus avoiding
1676 time-consuming boot-time autodetection (up to 250 ms per
1677 CPU). 0 enables autodetection (default). To determine
1678 the correct value for your kernel, boot with normal
1679 autodetection and see what value is printed. Note that
1680 on SMP systems the preset will be applied to all CPUs,
1681 which is likely to cause problems if your CPUs need
1682 significantly divergent settings. An incorrect value
1683 will cause delays in the kernel to be wrong, leading to
1684 unpredictable I/O errors and other breakage. Although
1685 unlikely, in the extreme case this might damage your
1686 hardware.
1687
1688 ltpc= [NET]
1689 Format: <io>,<irq>,<dma>
1690
1691 machvec= [IA-64] Force the use of a particular machine-vector
1692 (machvec) in a generic kernel.
1693 Example: machvec=hpzx1_swiotlb
1694
1695 machtype= [Loongson] Share the same kernel image file between different
1696 yeeloong laptop.
1697 Example: machtype=lemote-yeeloong-2f-7inch
1698
1699 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1700 than or equal to this physical address is ignored.
1701
1702 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1703 should make use of. maxcpus=n : n >= 0 limits the
1704 kernel to using 'n' processors. n=0 is a special case,
1705 it is equivalent to "nosmp", which also disables
1706 the IO APIC.
1707
1708 max_loop= [LOOP] The number of loop block devices that get
1709 (loop.max_loop) unconditionally pre-created at init time. The default
1710 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1711 of statically allocating a predefined number, loop
1712 devices can be requested on-demand with the
1713 /dev/loop-control interface.
1714
1715 mce [X86-32] Machine Check Exception
1716
1717 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1718
1719 md= [HW] RAID subsystems devices and level
1720 See Documentation/md.txt.
1721
1722 mdacon= [MDA]
1723 Format: <first>,<last>
1724 Specifies range of consoles to be captured by the MDA.
1725
1726 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1727 Amount of memory to be used when the kernel is not able
1728 to see the whole system memory or for test.
1729 [X86] Work as limiting max address. Use together
1730 with memmap= to avoid physical address space collisions.
1731 Without memmap= PCI devices could be placed at addresses
1732 belonging to unused RAM.
1733
1734 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1735 memory.
1736
1737 memchunk=nn[KMG]
1738 [KNL,SH] Allow user to override the default size for
1739 per-device physically contiguous DMA buffers.
1740
1741 memmap=exactmap [KNL,X86] Enable setting of an exact
1742 E820 memory map, as specified by the user.
1743 Such memmap=exactmap lines can be constructed based on
1744 BIOS output or other requirements. See the memmap=nn@ss
1745 option description.
1746
1747 memmap=nn[KMG]@ss[KMG]
1748 [KNL] Force usage of a specific region of memory.
1749 Region of memory to be used is from ss to ss+nn.
1750
1751 memmap=nn[KMG]#ss[KMG]
1752 [KNL,ACPI] Mark specific memory as ACPI data.
1753 Region of memory to be marked is from ss to ss+nn.
1754
1755 memmap=nn[KMG]$ss[KMG]
1756 [KNL,ACPI] Mark specific memory as reserved.
1757 Region of memory to be reserved is from ss to ss+nn.
1758 Example: Exclude memory from 0x18690000-0x1869ffff
1759 memmap=64K$0x18690000
1760 or
1761 memmap=0x10000$0x18690000
1762
1763 memory_corruption_check=0/1 [X86]
1764 Some BIOSes seem to corrupt the first 64k of
1765 memory when doing things like suspend/resume.
1766 Setting this option will scan the memory
1767 looking for corruption. Enabling this will
1768 both detect corruption and prevent the kernel
1769 from using the memory being corrupted.
1770 However, its intended as a diagnostic tool; if
1771 repeatable BIOS-originated corruption always
1772 affects the same memory, you can use memmap=
1773 to prevent the kernel from using that memory.
1774
1775 memory_corruption_check_size=size [X86]
1776 By default it checks for corruption in the low
1777 64k, making this memory unavailable for normal
1778 use. Use this parameter to scan for
1779 corruption in more or less memory.
1780
1781 memory_corruption_check_period=seconds [X86]
1782 By default it checks for corruption every 60
1783 seconds. Use this parameter to check at some
1784 other rate. 0 disables periodic checking.
1785
1786 memtest= [KNL,X86] Enable memtest
1787 Format: <integer>
1788 default : 0 <disable>
1789 Specifies the number of memtest passes to be
1790 performed. Each pass selects another test
1791 pattern from a given set of patterns. Memtest
1792 fills the memory with this pattern, validates
1793 memory contents and reserves bad memory
1794 regions that are detected.
1795
1796 meye.*= [HW] Set MotionEye Camera parameters
1797 See Documentation/video4linux/meye.txt.
1798
1799 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1800 Multi-Function General Purpose Timers on AMD Geode
1801 platforms.
1802
1803 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1804 the BIOS has incorrectly applied a workaround. TinyBIOS
1805 version 0.98 is known to be affected, 0.99 fixes the
1806 problem by letting the user disable the workaround.
1807
1808 mga= [HW,DRM]
1809
1810 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1811 physical address is ignored.
1812
1813 mini2440= [ARM,HW,KNL]
1814 Format:[0..2][b][c][t]
1815 Default: "0tb"
1816 MINI2440 configuration specification:
1817 0 - The attached screen is the 3.5" TFT
1818 1 - The attached screen is the 7" TFT
1819 2 - The VGA Shield is attached (1024x768)
1820 Leaving out the screen size parameter will not load
1821 the TFT driver, and the framebuffer will be left
1822 unconfigured.
1823 b - Enable backlight. The TFT backlight pin will be
1824 linked to the kernel VESA blanking code and a GPIO
1825 LED. This parameter is not necessary when using the
1826 VGA shield.
1827 c - Enable the s3c camera interface.
1828 t - Reserved for enabling touchscreen support. The
1829 touchscreen support is not enabled in the mainstream
1830 kernel as of 2.6.30, a preliminary port can be found
1831 in the "bleeding edge" mini2440 support kernel at
1832 http://repo.or.cz/w/linux-2.6/mini2440.git
1833
1834 mminit_loglevel=
1835 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1836 parameter allows control of the logging verbosity for
1837 the additional memory initialisation checks. A value
1838 of 0 disables mminit logging and a level of 4 will
1839 log everything. Information is printed at KERN_DEBUG
1840 so loglevel=8 may also need to be specified.
1841
1842 module.sig_enforce
1843 [KNL] When CONFIG_MODULE_SIG is set, this means that
1844 modules without (valid) signatures will fail to load.
1845 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1846 is always true, so this option does nothing.
1847
1848 mousedev.tap_time=
1849 [MOUSE] Maximum time between finger touching and
1850 leaving touchpad surface for touch to be considered
1851 a tap and be reported as a left button click (for
1852 touchpads working in absolute mode only).
1853 Format: <msecs>
1854 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1855 reporting absolute coordinates, such as tablets
1856 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1857 reporting absolute coordinates, such as tablets
1858
1859 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1860 is similar to kernelcore except it specifies the
1861 amount of memory used for migratable allocations.
1862 If both kernelcore and movablecore is specified,
1863 then kernelcore will be at *least* the specified
1864 value but may be more. If movablecore on its own
1865 is specified, the administrator must be careful
1866 that the amount of memory usable for all allocations
1867 is not too small.
1868
1869 movable_node [KNL,X86] Boot-time switch to enable the effects
1870 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1871
1872 MTD_Partition= [MTD]
1873 Format: <name>,<region-number>,<size>,<offset>
1874
1875 MTD_Region= [MTD] Format:
1876 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1877
1878 mtdparts= [MTD]
1879 See drivers/mtd/cmdlinepart.c.
1880
1881 multitce=off [PPC] This parameter disables the use of the pSeries
1882 firmware feature for updating multiple TCE entries
1883 at a time.
1884
1885 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1886
1887 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1888
1889 boundary - index of last SLC block on Flex-OneNAND.
1890 The remaining blocks are configured as MLC blocks.
1891 lock - Configure if Flex-OneNAND boundary should be locked.
1892 Once locked, the boundary cannot be changed.
1893 1 indicates lock status, 0 indicates unlock status.
1894
1895 mtdset= [ARM]
1896 ARM/S3C2412 JIVE boot control
1897
1898 See arch/arm/mach-s3c2412/mach-jive.c
1899
1900 mtouchusb.raw_coordinates=
1901 [HW] Make the MicroTouch USB driver use raw coordinates
1902 ('y', default) or cooked coordinates ('n')
1903
1904 mtrr_chunk_size=nn[KMG] [X86]
1905 used for mtrr cleanup. It is largest continuous chunk
1906 that could hold holes aka. UC entries.
1907
1908 mtrr_gran_size=nn[KMG] [X86]
1909 Used for mtrr cleanup. It is granularity of mtrr block.
1910 Default is 1.
1911 Large value could prevent small alignment from
1912 using up MTRRs.
1913
1914 mtrr_spare_reg_nr=n [X86]
1915 Format: <integer>
1916 Range: 0,7 : spare reg number
1917 Default : 1
1918 Used for mtrr cleanup. It is spare mtrr entries number.
1919 Set to 2 or more if your graphical card needs more.
1920
1921 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1922
1923 netdev= [NET] Network devices parameters
1924 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1925 Note that mem_start is often overloaded to mean
1926 something different and driver-specific.
1927 This usage is only documented in each driver source
1928 file if at all.
1929
1930 nf_conntrack.acct=
1931 [NETFILTER] Enable connection tracking flow accounting
1932 0 to disable accounting
1933 1 to enable accounting
1934 Default value is 0.
1935
1936 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1937 See Documentation/filesystems/nfs/nfsroot.txt.
1938
1939 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1940 See Documentation/filesystems/nfs/nfsroot.txt.
1941
1942 nfsrootdebug [NFS] enable nfsroot debugging messages.
1943 See Documentation/filesystems/nfs/nfsroot.txt.
1944
1945 nfs.callback_tcpport=
1946 [NFS] set the TCP port on which the NFSv4 callback
1947 channel should listen.
1948
1949 nfs.cache_getent=
1950 [NFS] sets the pathname to the program which is used
1951 to update the NFS client cache entries.
1952
1953 nfs.cache_getent_timeout=
1954 [NFS] sets the timeout after which an attempt to
1955 update a cache entry is deemed to have failed.
1956
1957 nfs.idmap_cache_timeout=
1958 [NFS] set the maximum lifetime for idmapper cache
1959 entries.
1960
1961 nfs.enable_ino64=
1962 [NFS] enable 64-bit inode numbers.
1963 If zero, the NFS client will fake up a 32-bit inode
1964 number for the readdir() and stat() syscalls instead
1965 of returning the full 64-bit number.
1966 The default is to return 64-bit inode numbers.
1967
1968 nfs.max_session_slots=
1969 [NFSv4.1] Sets the maximum number of session slots
1970 the client will attempt to negotiate with the server.
1971 This limits the number of simultaneous RPC requests
1972 that the client can send to the NFSv4.1 server.
1973 Note that there is little point in setting this
1974 value higher than the max_tcp_slot_table_limit.
1975
1976 nfs.nfs4_disable_idmapping=
1977 [NFSv4] When set to the default of '1', this option
1978 ensures that both the RPC level authentication
1979 scheme and the NFS level operations agree to use
1980 numeric uids/gids if the mount is using the
1981 'sec=sys' security flavour. In effect it is
1982 disabling idmapping, which can make migration from
1983 legacy NFSv2/v3 systems to NFSv4 easier.
1984 Servers that do not support this mode of operation
1985 will be autodetected by the client, and it will fall
1986 back to using the idmapper.
1987 To turn off this behaviour, set the value to '0'.
1988 nfs.nfs4_unique_id=
1989 [NFS4] Specify an additional fixed unique ident-
1990 ification string that NFSv4 clients can insert into
1991 their nfs_client_id4 string. This is typically a
1992 UUID that is generated at system install time.
1993
1994 nfs.send_implementation_id =
1995 [NFSv4.1] Send client implementation identification
1996 information in exchange_id requests.
1997 If zero, no implementation identification information
1998 will be sent.
1999 The default is to send the implementation identification
2000 information.
2001
2002 nfs.recover_lost_locks =
2003 [NFSv4] Attempt to recover locks that were lost due
2004 to a lease timeout on the server. Please note that
2005 doing this risks data corruption, since there are
2006 no guarantees that the file will remain unchanged
2007 after the locks are lost.
2008 If you want to enable the kernel legacy behaviour of
2009 attempting to recover these locks, then set this
2010 parameter to '1'.
2011 The default parameter value of '0' causes the kernel
2012 not to attempt recovery of lost locks.
2013
2014 nfsd.nfs4_disable_idmapping=
2015 [NFSv4] When set to the default of '1', the NFSv4
2016 server will return only numeric uids and gids to
2017 clients using auth_sys, and will accept numeric uids
2018 and gids from such clients. This is intended to ease
2019 migration from NFSv2/v3.
2020
2021 objlayoutdriver.osd_login_prog=
2022 [NFS] [OBJLAYOUT] sets the pathname to the program which
2023 is used to automatically discover and login into new
2024 osd-targets. Please see:
2025 Documentation/filesystems/pnfs.txt for more explanations
2026
2027 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2028 when a NMI is triggered.
2029 Format: [state][,regs][,debounce][,die]
2030
2031 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2032 Format: [panic,][nopanic,][num]
2033 Valid num: 0
2034 0 - turn nmi_watchdog off
2035 When panic is specified, panic when an NMI watchdog
2036 timeout occurs (or 'nopanic' to override the opposite
2037 default).
2038 This is useful when you use a panic=... timeout and
2039 need the box quickly up again.
2040
2041 netpoll.carrier_timeout=
2042 [NET] Specifies amount of time (in seconds) that
2043 netpoll should wait for a carrier. By default netpoll
2044 waits 4 seconds.
2045
2046 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2047 emulation library even if a 387 maths coprocessor
2048 is present.
2049
2050 no_console_suspend
2051 [HW] Never suspend the console
2052 Disable suspending of consoles during suspend and
2053 hibernate operations. Once disabled, debugging
2054 messages can reach various consoles while the rest
2055 of the system is being put to sleep (ie, while
2056 debugging driver suspend/resume hooks). This may
2057 not work reliably with all consoles, but is known
2058 to work with serial and VGA consoles.
2059 To facilitate more flexible debugging, we also add
2060 console_suspend, a printk module parameter to control
2061 it. Users could use console_suspend (usually
2062 /sys/module/printk/parameters/console_suspend) to
2063 turn on/off it dynamically.
2064
2065 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2066 caches in the slab allocator. Saves per-node memory,
2067 but will impact performance.
2068
2069 noalign [KNL,ARM]
2070
2071 noapic [SMP,APIC] Tells the kernel to not make use of any
2072 IOAPICs that may be present in the system.
2073
2074 nokaslr [X86]
2075 Disable kernel and module base offset ASLR (Address
2076 Space Layout Randomization) if built into the kernel.
2077
2078 noautogroup Disable scheduler automatic task group creation.
2079
2080 nobats [PPC] Do not use BATs for mapping kernel lowmem
2081 on "Classic" PPC cores.
2082
2083 nocache [ARM]
2084
2085 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2086
2087 nodelayacct [KNL] Disable per-task delay accounting
2088
2089 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2090
2091 nodsp [SH] Disable hardware DSP at boot time.
2092
2093 noefi [X86] Disable EFI runtime services support.
2094
2095 noexec [IA-64]
2096
2097 noexec [X86]
2098 On X86-32 available only on PAE configured kernels.
2099 noexec=on: enable non-executable mappings (default)
2100 noexec=off: disable non-executable mappings
2101
2102 nosmap [X86]
2103 Disable SMAP (Supervisor Mode Access Prevention)
2104 even if it is supported by processor.
2105
2106 nosmep [X86]
2107 Disable SMEP (Supervisor Mode Execution Prevention)
2108 even if it is supported by processor.
2109
2110 noexec32 [X86-64]
2111 This affects only 32-bit executables.
2112 noexec32=on: enable non-executable mappings (default)
2113 read doesn't imply executable mappings
2114 noexec32=off: disable non-executable mappings
2115 read implies executable mappings
2116
2117 nofpu [SH] Disable hardware FPU at boot time.
2118
2119 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2120 register save and restore. The kernel will only save
2121 legacy floating-point registers on task switch.
2122
2123 noxsave [BUGS=X86] Disables x86 extended register state save
2124 and restore using xsave. The kernel will fallback to
2125 enabling legacy floating-point and sse state.
2126
2127 eagerfpu= [X86]
2128 on enable eager fpu restore
2129 off disable eager fpu restore
2130 auto selects the default scheme, which automatically
2131 enables eagerfpu restore for xsaveopt.
2132
2133 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2134 wfi(ARM) instruction doesn't work correctly and not to
2135 use it. This is also useful when using JTAG debugger.
2136
2137 no_file_caps Tells the kernel not to honor file capabilities. The
2138 only way then for a file to be executed with privilege
2139 is to be setuid root or executed by root.
2140
2141 nohalt [IA-64] Tells the kernel not to use the power saving
2142 function PAL_HALT_LIGHT when idle. This increases
2143 power-consumption. On the positive side, it reduces
2144 interrupt wake-up latency, which may improve performance
2145 in certain environments such as networked servers or
2146 real-time systems.
2147
2148 nohz= [KNL] Boottime enable/disable dynamic ticks
2149 Valid arguments: on, off
2150 Default: on
2151
2152 nohz_full= [KNL,BOOT]
2153 In kernels built with CONFIG_NO_HZ_FULL=y, set
2154 the specified list of CPUs whose tick will be stopped
2155 whenever possible. The boot CPU will be forced outside
2156 the range to maintain the timekeeping.
2157 The CPUs in this range must also be included in the
2158 rcu_nocbs= set.
2159
2160 noiotrap [SH] Disables trapped I/O port accesses.
2161
2162 noirqdebug [X86-32] Disables the code which attempts to detect and
2163 disable unhandled interrupt sources.
2164
2165 no_timer_check [X86,APIC] Disables the code which tests for
2166 broken timer IRQ sources.
2167
2168 noisapnp [ISAPNP] Disables ISA PnP code.
2169
2170 noinitrd [RAM] Tells the kernel not to load any configured
2171 initial RAM disk.
2172
2173 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2174 remapping.
2175 [Deprecated - use intremap=off]
2176
2177 nointroute [IA-64]
2178
2179 nojitter [IA-64] Disables jitter checking for ITC timers.
2180
2181 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2182
2183 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2184 fault handling.
2185
2186 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2187 steal time is computed, but won't influence scheduler
2188 behaviour
2189
2190 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2191
2192 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2193
2194 noltlbs [PPC] Do not use large page/tlb entries for kernel
2195 lowmem mapping on PPC40x.
2196
2197 nomca [IA-64] Disable machine check abort handling
2198
2199 nomce [X86-32] Machine Check Exception
2200
2201 nomfgpt [X86-32] Disable Multi-Function General Purpose
2202 Timer usage (for AMD Geode machines).
2203
2204 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2205 shutdown the other cpus. Instead use the REBOOT_VECTOR
2206 irq.
2207
2208 nomodule Disable module load
2209
2210 nopat [X86] Disable PAT (page attribute table extension of
2211 pagetables) support.
2212
2213 norandmaps Don't use address space randomization. Equivalent to
2214 echo 0 > /proc/sys/kernel/randomize_va_space
2215
2216 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2217
2218 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2219 with UP alternatives
2220
2221 nordrand [X86] Disable kernel use of the RDRAND and
2222 RDSEED instructions even if they are supported
2223 by the processor. RDRAND and RDSEED are still
2224 available to user space applications.
2225
2226 noresume [SWSUSP] Disables resume and restores original swap
2227 space.
2228
2229 no-scroll [VGA] Disables scrollback.
2230 This is required for the Braillex ib80-piezo Braille
2231 reader made by F.H. Papenmeier (Germany).
2232
2233 nosbagart [IA-64]
2234
2235 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2236
2237 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2238 and disable the IO APIC. legacy for "maxcpus=0".
2239
2240 nosoftlockup [KNL] Disable the soft-lockup detector.
2241
2242 nosync [HW,M68K] Disables sync negotiation for all devices.
2243
2244 notsc [BUGS=X86-32] Disable Time Stamp Counter
2245
2246 nousb [USB] Disable the USB subsystem
2247
2248 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2249
2250 nowb [ARM]
2251
2252 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2253
2254 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2255 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2256 Some features depend on CPU0. Known dependencies are:
2257 1. Resume from suspend/hibernate depends on CPU0.
2258 Suspend/hibernate will fail if CPU0 is offline and you
2259 need to online CPU0 before suspend/hibernate.
2260 2. PIC interrupts also depend on CPU0. CPU0 can't be
2261 removed if a PIC interrupt is detected.
2262 It's said poweroff/reboot may depend on CPU0 on some
2263 machines although I haven't seen such issues so far
2264 after CPU0 is offline on a few tested machines.
2265 If the dependencies are under your control, you can
2266 turn on cpu0_hotplug.
2267
2268 nptcg= [IA-64] Override max number of concurrent global TLB
2269 purges which is reported from either PAL_VM_SUMMARY or
2270 SAL PALO.
2271
2272 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2273 could support. nr_cpus=n : n >= 1 limits the kernel to
2274 supporting 'n' processors. Later in runtime you can not
2275 use hotplug cpu feature to put more cpu back to online.
2276 just like you compile the kernel NR_CPUS=n
2277
2278 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2279
2280 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2281 Allowed values are enable and disable
2282
2283 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2284 one of ['zone', 'node', 'default'] can be specified
2285 This can be set from sysctl after boot.
2286 See Documentation/sysctl/vm.txt for details.
2287
2288 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2289 See Documentation/debugging-via-ohci1394.txt for more
2290 info.
2291
2292 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2293 Rather than timing out after 20 ms if an EC
2294 command is not properly ACKed, override the length
2295 of the timeout. We have interrupts disabled while
2296 waiting for the ACK, so if this is set too high
2297 interrupts *may* be lost!
2298
2299 omap_mux= [OMAP] Override bootloader pin multiplexing.
2300 Format: <mux_mode0.mode_name=value>...
2301 For example, to override I2C bus2:
2302 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2303
2304 oprofile.timer= [HW]
2305 Use timer interrupt instead of performance counters
2306
2307 oprofile.cpu_type= Force an oprofile cpu type
2308 This might be useful if you have an older oprofile
2309 userland or if you want common events.
2310 Format: { arch_perfmon }
2311 arch_perfmon: [X86] Force use of architectural
2312 perfmon on Intel CPUs instead of the
2313 CPU specific event set.
2314 timer: [X86] Force use of architectural NMI
2315 timer mode (see also oprofile.timer
2316 for generic hr timer mode)
2317 [s390] Force legacy basic mode sampling
2318 (report cpu_type "timer")
2319
2320 oops=panic Always panic on oopses. Default is to just kill the
2321 process, but there is a small probability of
2322 deadlocking the machine.
2323 This will also cause panics on machine check exceptions.
2324 Useful together with panic=30 to trigger a reboot.
2325
2326 OSS [HW,OSS]
2327 See Documentation/sound/oss/oss-parameters.txt
2328
2329 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2330 timeout > 0: seconds before rebooting
2331 timeout = 0: wait forever
2332 timeout < 0: reboot immediately
2333 Format: <timeout>
2334
2335 parkbd.port= [HW] Parallel port number the keyboard adapter is
2336 connected to, default is 0.
2337 Format: <parport#>
2338 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2339 0 for XT, 1 for AT (default is AT).
2340 Format: <mode>
2341
2342 parport= [HW,PPT] Specify parallel ports. 0 disables.
2343 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2344 Use 'auto' to force the driver to use any
2345 IRQ/DMA settings detected (the default is to
2346 ignore detected IRQ/DMA settings because of
2347 possible conflicts). You can specify the base
2348 address, IRQ, and DMA settings; IRQ and DMA
2349 should be numbers, or 'auto' (for using detected
2350 settings on that particular port), or 'nofifo'
2351 (to avoid using a FIFO even if it is detected).
2352 Parallel ports are assigned in the order they
2353 are specified on the command line, starting
2354 with parport0.
2355
2356 parport_init_mode= [HW,PPT]
2357 Configure VIA parallel port to operate in
2358 a specific mode. This is necessary on Pegasos
2359 computer where firmware has no options for setting
2360 up parallel port mode and sets it to spp.
2361 Currently this function knows 686a and 8231 chips.
2362 Format: [spp|ps2|epp|ecp|ecpepp]
2363
2364 pause_on_oops=
2365 Halt all CPUs after the first oops has been printed for
2366 the specified number of seconds. This is to be used if
2367 your oopses keep scrolling off the screen.
2368
2369 pcbit= [HW,ISDN]
2370
2371 pcd. [PARIDE]
2372 See header of drivers/block/paride/pcd.c.
2373 See also Documentation/blockdev/paride.txt.
2374
2375 pci=option[,option...] [PCI] various PCI subsystem options:
2376 earlydump [X86] dump PCI config space before the kernel
2377 changes anything
2378 off [X86] don't probe for the PCI bus
2379 bios [X86-32] force use of PCI BIOS, don't access
2380 the hardware directly. Use this if your machine
2381 has a non-standard PCI host bridge.
2382 nobios [X86-32] disallow use of PCI BIOS, only direct
2383 hardware access methods are allowed. Use this
2384 if you experience crashes upon bootup and you
2385 suspect they are caused by the BIOS.
2386 conf1 [X86] Force use of PCI Configuration
2387 Mechanism 1.
2388 conf2 [X86] Force use of PCI Configuration
2389 Mechanism 2.
2390 noaer [PCIE] If the PCIEAER kernel config parameter is
2391 enabled, this kernel boot option can be used to
2392 disable the use of PCIE advanced error reporting.
2393 nodomains [PCI] Disable support for multiple PCI
2394 root domains (aka PCI segments, in ACPI-speak).
2395 nommconf [X86] Disable use of MMCONFIG for PCI
2396 Configuration
2397 check_enable_amd_mmconf [X86] check for and enable
2398 properly configured MMIO access to PCI
2399 config space on AMD family 10h CPU
2400 nomsi [MSI] If the PCI_MSI kernel config parameter is
2401 enabled, this kernel boot option can be used to
2402 disable the use of MSI interrupts system-wide.
2403 noioapicquirk [APIC] Disable all boot interrupt quirks.
2404 Safety option to keep boot IRQs enabled. This
2405 should never be necessary.
2406 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2407 primary IO-APIC for bridges that cannot disable
2408 boot IRQs. This fixes a source of spurious IRQs
2409 when the system masks IRQs.
2410 noioapicreroute [APIC] Disable workaround that uses the
2411 boot IRQ equivalent of an IRQ that connects to
2412 a chipset where boot IRQs cannot be disabled.
2413 The opposite of ioapicreroute.
2414 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2415 routing table. These calls are known to be buggy
2416 on several machines and they hang the machine
2417 when used, but on other computers it's the only
2418 way to get the interrupt routing table. Try
2419 this option if the kernel is unable to allocate
2420 IRQs or discover secondary PCI buses on your
2421 motherboard.
2422 rom [X86] Assign address space to expansion ROMs.
2423 Use with caution as certain devices share
2424 address decoders between ROMs and other
2425 resources.
2426 norom [X86] Do not assign address space to
2427 expansion ROMs that do not already have
2428 BIOS assigned address ranges.
2429 nobar [X86] Do not assign address space to the
2430 BARs that weren't assigned by the BIOS.
2431 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2432 assigned automatically to PCI devices. You can
2433 make the kernel exclude IRQs of your ISA cards
2434 this way.
2435 pirqaddr=0xAAAAA [X86] Specify the physical address
2436 of the PIRQ table (normally generated
2437 by the BIOS) if it is outside the
2438 F0000h-100000h range.
2439 lastbus=N [X86] Scan all buses thru bus #N. Can be
2440 useful if the kernel is unable to find your
2441 secondary buses and you want to tell it
2442 explicitly which ones they are.
2443 assign-busses [X86] Always assign all PCI bus
2444 numbers ourselves, overriding
2445 whatever the firmware may have done.
2446 usepirqmask [X86] Honor the possible IRQ mask stored
2447 in the BIOS $PIR table. This is needed on
2448 some systems with broken BIOSes, notably
2449 some HP Pavilion N5400 and Omnibook XE3
2450 notebooks. This will have no effect if ACPI
2451 IRQ routing is enabled.
2452 noacpi [X86] Do not use ACPI for IRQ routing
2453 or for PCI scanning.
2454 use_crs [X86] Use PCI host bridge window information
2455 from ACPI. On BIOSes from 2008 or later, this
2456 is enabled by default. If you need to use this,
2457 please report a bug.
2458 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2459 If you need to use this, please report a bug.
2460 routeirq Do IRQ routing for all PCI devices.
2461 This is normally done in pci_enable_device(),
2462 so this option is a temporary workaround
2463 for broken drivers that don't call it.
2464 skip_isa_align [X86] do not align io start addr, so can
2465 handle more pci cards
2466 firmware [ARM] Do not re-enumerate the bus but instead
2467 just use the configuration from the
2468 bootloader. This is currently used on
2469 IXP2000 systems where the bus has to be
2470 configured a certain way for adjunct CPUs.
2471 noearly [X86] Don't do any early type 1 scanning.
2472 This might help on some broken boards which
2473 machine check when some devices' config space
2474 is read. But various workarounds are disabled
2475 and some IOMMU drivers will not work.
2476 bfsort Sort PCI devices into breadth-first order.
2477 This sorting is done to get a device
2478 order compatible with older (<= 2.4) kernels.
2479 nobfsort Don't sort PCI devices into breadth-first order.
2480 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2481 tuning and use the BIOS-configured MPS defaults.
2482 pcie_bus_safe Set every device's MPS to the largest value
2483 supported by all devices below the root complex.
2484 pcie_bus_perf Set device MPS to the largest allowable MPS
2485 based on its parent bus. Also set MRRS (Max
2486 Read Request Size) to the largest supported
2487 value (no larger than the MPS that the device
2488 or bus can support) for best performance.
2489 pcie_bus_peer2peer Set every device's MPS to 128B, which
2490 every device is guaranteed to support. This
2491 configuration allows peer-to-peer DMA between
2492 any pair of devices, possibly at the cost of
2493 reduced performance. This also guarantees
2494 that hot-added devices will work.
2495 cbiosize=nn[KMG] The fixed amount of bus space which is
2496 reserved for the CardBus bridge's IO window.
2497 The default value is 256 bytes.
2498 cbmemsize=nn[KMG] The fixed amount of bus space which is
2499 reserved for the CardBus bridge's memory
2500 window. The default value is 64 megabytes.
2501 resource_alignment=
2502 Format:
2503 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2504 Specifies alignment and device to reassign
2505 aligned memory resources.
2506 If <order of align> is not specified,
2507 PAGE_SIZE is used as alignment.
2508 PCI-PCI bridge can be specified, if resource
2509 windows need to be expanded.
2510 ecrc= Enable/disable PCIe ECRC (transaction layer
2511 end-to-end CRC checking).
2512 bios: Use BIOS/firmware settings. This is the
2513 the default.
2514 off: Turn ECRC off
2515 on: Turn ECRC on.
2516 hpiosize=nn[KMG] The fixed amount of bus space which is
2517 reserved for hotplug bridge's IO window.
2518 Default size is 256 bytes.
2519 hpmemsize=nn[KMG] The fixed amount of bus space which is
2520 reserved for hotplug bridge's memory window.
2521 Default size is 2 megabytes.
2522 realloc= Enable/disable reallocating PCI bridge resources
2523 if allocations done by BIOS are too small to
2524 accommodate resources required by all child
2525 devices.
2526 off: Turn realloc off
2527 on: Turn realloc on
2528 realloc same as realloc=on
2529 noari do not use PCIe ARI.
2530 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2531 only look for one device below a PCIe downstream
2532 port.
2533
2534 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2535 Management.
2536 off Disable ASPM.
2537 force Enable ASPM even on devices that claim not to support it.
2538 WARNING: Forcing ASPM on may cause system lockups.
2539
2540 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2541 nomsi Do not use MSI for PCI Express Native Hotplug (this
2542 makes all PCIe ports use INTx for hotplug services).
2543
2544 pcie_ports= [PCIE] PCIe ports handling:
2545 auto Ask the BIOS whether or not to use native PCIe services
2546 associated with PCIe ports (PME, hot-plug, AER). Use
2547 them only if that is allowed by the BIOS.
2548 native Use native PCIe services associated with PCIe ports
2549 unconditionally.
2550 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2551 ports driver.
2552
2553 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2554 nomsi Do not use MSI for native PCIe PME signaling (this makes
2555 all PCIe root ports use INTx for all services).
2556
2557 pcmv= [HW,PCMCIA] BadgePAD 4
2558
2559 pd_ignore_unused
2560 [PM]
2561 Keep all power-domains already enabled by bootloader on,
2562 even if no driver has claimed them. This is useful
2563 for debug and development, but should not be
2564 needed on a platform with proper driver support.
2565
2566 pd. [PARIDE]
2567 See Documentation/blockdev/paride.txt.
2568
2569 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2570 boot time.
2571 Format: { 0 | 1 }
2572 See arch/parisc/kernel/pdc_chassis.c
2573
2574 percpu_alloc= Select which percpu first chunk allocator to use.
2575 Currently supported values are "embed" and "page".
2576 Archs may support subset or none of the selections.
2577 See comments in mm/percpu.c for details on each
2578 allocator. This parameter is primarily for debugging
2579 and performance comparison.
2580
2581 pf. [PARIDE]
2582 See Documentation/blockdev/paride.txt.
2583
2584 pg. [PARIDE]
2585 See Documentation/blockdev/paride.txt.
2586
2587 pirq= [SMP,APIC] Manual mp-table setup
2588 See Documentation/x86/i386/IO-APIC.txt.
2589
2590 plip= [PPT,NET] Parallel port network link
2591 Format: { parport<nr> | timid | 0 }
2592 See also Documentation/parport.txt.
2593
2594 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2595 Override pmtimer IOPort with a hex value.
2596 e.g. pmtmr=0x508
2597
2598 pnp.debug=1 [PNP]
2599 Enable PNP debug messages (depends on the
2600 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2601 via /sys/module/pnp/parameters/debug. We always show
2602 current resource usage; turning this on also shows
2603 possible settings and some assignment information.
2604
2605 pnpacpi= [ACPI]
2606 { off }
2607
2608 pnpbios= [ISAPNP]
2609 { on | off | curr | res | no-curr | no-res }
2610
2611 pnp_reserve_irq=
2612 [ISAPNP] Exclude IRQs for the autoconfiguration
2613
2614 pnp_reserve_dma=
2615 [ISAPNP] Exclude DMAs for the autoconfiguration
2616
2617 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2618 Ranges are in pairs (I/O port base and size).
2619
2620 pnp_reserve_mem=
2621 [ISAPNP] Exclude memory regions for the
2622 autoconfiguration.
2623 Ranges are in pairs (memory base and size).
2624
2625 ports= [IP_VS_FTP] IPVS ftp helper module
2626 Default is 21.
2627 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2628 may be specified.
2629 Format: <port>,<port>....
2630
2631 print-fatal-signals=
2632 [KNL] debug: print fatal signals
2633
2634 If enabled, warn about various signal handling
2635 related application anomalies: too many signals,
2636 too many POSIX.1 timers, fatal signals causing a
2637 coredump - etc.
2638
2639 If you hit the warning due to signal overflow,
2640 you might want to try "ulimit -i unlimited".
2641
2642 default: off.
2643
2644 printk.always_kmsg_dump=
2645 Trigger kmsg_dump for cases other than kernel oops or
2646 panics
2647 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2648 default: disabled
2649
2650 printk.time= Show timing data prefixed to each printk message line
2651 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2652
2653 processor.max_cstate= [HW,ACPI]
2654 Limit processor to maximum C-state
2655 max_cstate=9 overrides any DMI blacklist limit.
2656
2657 processor.nocst [HW,ACPI]
2658 Ignore the _CST method to determine C-states,
2659 instead using the legacy FADT method
2660
2661 profile= [KNL] Enable kernel profiling via /proc/profile
2662 Format: [schedule,]<number>
2663 Param: "schedule" - profile schedule points.
2664 Param: <number> - step/bucket size as a power of 2 for
2665 statistical time based profiling.
2666 Param: "sleep" - profile D-state sleeping (millisecs).
2667 Requires CONFIG_SCHEDSTATS
2668 Param: "kvm" - profile VM exits.
2669
2670 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2671 before loading.
2672 See Documentation/blockdev/ramdisk.txt.
2673
2674 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2675 probe for; one of (bare|imps|exps|lifebook|any).
2676 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2677 per second.
2678 psmouse.resetafter= [HW,MOUSE]
2679 Try to reset the device after so many bad packets
2680 (0 = never).
2681 psmouse.resolution=
2682 [HW,MOUSE] Set desired mouse resolution, in dpi.
2683 psmouse.smartscroll=
2684 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2685 0 = disabled, 1 = enabled (default).
2686
2687 pstore.backend= Specify the name of the pstore backend to use
2688
2689 pt. [PARIDE]
2690 See Documentation/blockdev/paride.txt.
2691
2692 pty.legacy_count=
2693 [KNL] Number of legacy pty's. Overwrites compiled-in
2694 default number.
2695
2696 quiet [KNL] Disable most log messages
2697
2698 r128= [HW,DRM]
2699
2700 raid= [HW,RAID]
2701 See Documentation/md.txt.
2702
2703 ramdisk_blocksize= [RAM]
2704 See Documentation/blockdev/ramdisk.txt.
2705
2706 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2707 See Documentation/blockdev/ramdisk.txt.
2708
2709 rcu_nocbs= [KNL]
2710 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2711 the specified list of CPUs to be no-callback CPUs.
2712 Invocation of these CPUs' RCU callbacks will
2713 be offloaded to "rcuox/N" kthreads created for
2714 that purpose, where "x" is "b" for RCU-bh, "p"
2715 for RCU-preempt, and "s" for RCU-sched, and "N"
2716 is the CPU number. This reduces OS jitter on the
2717 offloaded CPUs, which can be useful for HPC and
2718 real-time workloads. It can also improve energy
2719 efficiency for asymmetric multiprocessors.
2720
2721 rcu_nocb_poll [KNL]
2722 Rather than requiring that offloaded CPUs
2723 (specified by rcu_nocbs= above) explicitly
2724 awaken the corresponding "rcuoN" kthreads,
2725 make these kthreads poll for callbacks.
2726 This improves the real-time response for the
2727 offloaded CPUs by relieving them of the need to
2728 wake up the corresponding kthread, but degrades
2729 energy efficiency by requiring that the kthreads
2730 periodically wake up to do the polling.
2731
2732 rcutree.blimit= [KNL]
2733 Set maximum number of finished RCU callbacks to
2734 process in one batch.
2735
2736 rcutree.rcu_fanout_leaf= [KNL]
2737 Increase the number of CPUs assigned to each
2738 leaf rcu_node structure. Useful for very large
2739 systems.
2740
2741 rcutree.jiffies_till_first_fqs= [KNL]
2742 Set delay from grace-period initialization to
2743 first attempt to force quiescent states.
2744 Units are jiffies, minimum value is zero,
2745 and maximum value is HZ.
2746
2747 rcutree.jiffies_till_next_fqs= [KNL]
2748 Set delay between subsequent attempts to force
2749 quiescent states. Units are jiffies, minimum
2750 value is one, and maximum value is HZ.
2751
2752 rcutree.qhimark= [KNL]
2753 Set threshold of queued RCU callbacks beyond which
2754 batch limiting is disabled.
2755
2756 rcutree.qlowmark= [KNL]
2757 Set threshold of queued RCU callbacks below which
2758 batch limiting is re-enabled.
2759
2760 rcutree.rcu_idle_gp_delay= [KNL]
2761 Set wakeup interval for idle CPUs that have
2762 RCU callbacks (RCU_FAST_NO_HZ=y).
2763
2764 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2765 Set wakeup interval for idle CPUs that have
2766 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2767 Lazy RCU callbacks are those which RCU can
2768 prove do nothing more than free memory.
2769
2770 rcutorture.fqs_duration= [KNL]
2771 Set duration of force_quiescent_state bursts.
2772
2773 rcutorture.fqs_holdoff= [KNL]
2774 Set holdoff time within force_quiescent_state bursts.
2775
2776 rcutorture.fqs_stutter= [KNL]
2777 Set wait time between force_quiescent_state bursts.
2778
2779 rcutorture.gp_exp= [KNL]
2780 Use expedited update-side primitives.
2781
2782 rcutorture.gp_normal= [KNL]
2783 Use normal (non-expedited) update-side primitives.
2784 If both gp_exp and gp_normal are set, do both.
2785 If neither gp_exp nor gp_normal are set, still
2786 do both.
2787
2788 rcutorture.n_barrier_cbs= [KNL]
2789 Set callbacks/threads for rcu_barrier() testing.
2790
2791 rcutorture.nfakewriters= [KNL]
2792 Set number of concurrent RCU writers. These just
2793 stress RCU, they don't participate in the actual
2794 test, hence the "fake".
2795
2796 rcutorture.nreaders= [KNL]
2797 Set number of RCU readers.
2798
2799 rcutorture.object_debug= [KNL]
2800 Enable debug-object double-call_rcu() testing.
2801
2802 rcutorture.onoff_holdoff= [KNL]
2803 Set time (s) after boot for CPU-hotplug testing.
2804
2805 rcutorture.onoff_interval= [KNL]
2806 Set time (s) between CPU-hotplug operations, or
2807 zero to disable CPU-hotplug testing.
2808
2809 rcutorture.rcutorture_runnable= [BOOT]
2810 Start rcutorture running at boot time.
2811
2812 rcutorture.shuffle_interval= [KNL]
2813 Set task-shuffle interval (s). Shuffling tasks
2814 allows some CPUs to go into dyntick-idle mode
2815 during the rcutorture test.
2816
2817 rcutorture.shutdown_secs= [KNL]
2818 Set time (s) after boot system shutdown. This
2819 is useful for hands-off automated testing.
2820
2821 rcutorture.stall_cpu= [KNL]
2822 Duration of CPU stall (s) to test RCU CPU stall
2823 warnings, zero to disable.
2824
2825 rcutorture.stall_cpu_holdoff= [KNL]
2826 Time to wait (s) after boot before inducing stall.
2827
2828 rcutorture.stat_interval= [KNL]
2829 Time (s) between statistics printk()s.
2830
2831 rcutorture.stutter= [KNL]
2832 Time (s) to stutter testing, for example, specifying
2833 five seconds causes the test to run for five seconds,
2834 wait for five seconds, and so on. This tests RCU's
2835 ability to transition abruptly to and from idle.
2836
2837 rcutorture.test_boost= [KNL]
2838 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2839 "Maybe" means test if the RCU implementation
2840 under test support RCU priority boosting.
2841
2842 rcutorture.test_boost_duration= [KNL]
2843 Duration (s) of each individual boost test.
2844
2845 rcutorture.test_boost_interval= [KNL]
2846 Interval (s) between each boost test.
2847
2848 rcutorture.test_no_idle_hz= [KNL]
2849 Test RCU's dyntick-idle handling. See also the
2850 rcutorture.shuffle_interval parameter.
2851
2852 rcutorture.torture_type= [KNL]
2853 Specify the RCU implementation to test.
2854
2855 rcutorture.verbose= [KNL]
2856 Enable additional printk() statements.
2857
2858 rcupdate.rcu_expedited= [KNL]
2859 Use expedited grace-period primitives, for
2860 example, synchronize_rcu_expedited() instead
2861 of synchronize_rcu(). This reduces latency,
2862 but can increase CPU utilization, degrade
2863 real-time latency, and degrade energy efficiency.
2864
2865 rcupdate.rcu_cpu_stall_suppress= [KNL]
2866 Suppress RCU CPU stall warning messages.
2867
2868 rcupdate.rcu_cpu_stall_timeout= [KNL]
2869 Set timeout for RCU CPU stall warning messages.
2870
2871 rdinit= [KNL]
2872 Format: <full_path>
2873 Run specified binary instead of /init from the ramdisk,
2874 used for early userspace startup. See initrd.
2875
2876 reboot= [KNL]
2877 Format (x86 or x86_64):
2878 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2879 [[,]s[mp]#### \
2880 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2881 [[,]f[orce]
2882 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2883 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2884 reboot_force is either force or not specified,
2885 reboot_cpu is s[mp]#### with #### being the processor
2886 to be used for rebooting.
2887
2888 relax_domain_level=
2889 [KNL, SMP] Set scheduler's default relax_domain_level.
2890 See Documentation/cgroups/cpusets.txt.
2891
2892 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2893
2894 reservetop= [X86-32]
2895 Format: nn[KMG]
2896 Reserves a hole at the top of the kernel virtual
2897 address space.
2898
2899 reservelow= [X86]
2900 Format: nn[K]
2901 Set the amount of memory to reserve for BIOS at
2902 the bottom of the address space.
2903
2904 reset_devices [KNL] Force drivers to reset the underlying device
2905 during initialization.
2906
2907 resume= [SWSUSP]
2908 Specify the partition device for software suspend
2909 Format:
2910 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2911
2912 resume_offset= [SWSUSP]
2913 Specify the offset from the beginning of the partition
2914 given by "resume=" at which the swap header is located,
2915 in <PAGE_SIZE> units (needed only for swap files).
2916 See Documentation/power/swsusp-and-swap-files.txt
2917
2918 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2919 read the resume files
2920
2921 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2922 Useful for devices that are detected asynchronously
2923 (e.g. USB and MMC devices).
2924
2925 hibernate= [HIBERNATION]
2926 noresume Don't check if there's a hibernation image
2927 present during boot.
2928 nocompress Don't compress/decompress hibernation images.
2929
2930 retain_initrd [RAM] Keep initrd memory after extraction
2931
2932 rhash_entries= [KNL,NET]
2933 Set number of hash buckets for route cache
2934
2935 ro [KNL] Mount root device read-only on boot
2936
2937 root= [KNL] Root filesystem
2938 See name_to_dev_t comment in init/do_mounts.c.
2939
2940 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2941 mount the root filesystem
2942
2943 rootflags= [KNL] Set root filesystem mount option string
2944
2945 rootfstype= [KNL] Set root filesystem type
2946
2947 rootwait [KNL] Wait (indefinitely) for root device to show up.
2948 Useful for devices that are detected asynchronously
2949 (e.g. USB and MMC devices).
2950
2951 rproc_mem=nn[KMG][@address]
2952 [KNL,ARM,CMA] Remoteproc physical memory block.
2953 Memory area to be used by remote processor image,
2954 managed by CMA.
2955
2956 rw [KNL] Mount root device read-write on boot
2957
2958 S [KNL] Run init in single mode
2959
2960 sa1100ir [NET]
2961 See drivers/net/irda/sa1100_ir.c.
2962
2963 sbni= [NET] Granch SBNI12 leased line adapter
2964
2965 sched_debug [KNL] Enables verbose scheduler debug messages.
2966
2967 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2968 xtime_lock contention on larger systems, and/or RCU lock
2969 contention on all systems with CONFIG_MAXSMP set.
2970 Format: { "0" | "1" }
2971 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2972 1 -- enable.
2973 Note: increases power consumption, thus should only be
2974 enabled if running jitter sensitive (HPC/RT) workloads.
2975
2976 security= [SECURITY] Choose a security module to enable at boot.
2977 If this boot parameter is not specified, only the first
2978 security module asking for security registration will be
2979 loaded. An invalid security module name will be treated
2980 as if no module has been chosen.
2981
2982 selinux= [SELINUX] Disable or enable SELinux at boot time.
2983 Format: { "0" | "1" }
2984 See security/selinux/Kconfig help text.
2985 0 -- disable.
2986 1 -- enable.
2987 Default value is set via kernel config option.
2988 If enabled at boot time, /selinux/disable can be used
2989 later to disable prior to initial policy load.
2990
2991 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2992 Format: { "0" | "1" }
2993 See security/apparmor/Kconfig help text
2994 0 -- disable.
2995 1 -- enable.
2996 Default value is set via kernel config option.
2997
2998 serialnumber [BUGS=X86-32]
2999
3000 shapers= [NET]
3001 Maximal number of shapers.
3002
3003 show_msr= [x86] show boot-time MSR settings
3004 Format: { <integer> }
3005 Show boot-time (BIOS-initialized) MSR settings.
3006 The parameter means the number of CPUs to show,
3007 for example 1 means boot CPU only.
3008
3009 simeth= [IA-64]
3010 simscsi=
3011
3012 slram= [HW,MTD]
3013
3014 slab_max_order= [MM, SLAB]
3015 Determines the maximum allowed order for slabs.
3016 A high setting may cause OOMs due to memory
3017 fragmentation. Defaults to 1 for systems with
3018 more than 32MB of RAM, 0 otherwise.
3019
3020 slub_debug[=options[,slabs]] [MM, SLUB]
3021 Enabling slub_debug allows one to determine the
3022 culprit if slab objects become corrupted. Enabling
3023 slub_debug can create guard zones around objects and
3024 may poison objects when not in use. Also tracks the
3025 last alloc / free. For more information see
3026 Documentation/vm/slub.txt.
3027
3028 slub_max_order= [MM, SLUB]
3029 Determines the maximum allowed order for slabs.
3030 A high setting may cause OOMs due to memory
3031 fragmentation. For more information see
3032 Documentation/vm/slub.txt.
3033
3034 slub_min_objects= [MM, SLUB]
3035 The minimum number of objects per slab. SLUB will
3036 increase the slab order up to slub_max_order to
3037 generate a sufficiently large slab able to contain
3038 the number of objects indicated. The higher the number
3039 of objects the smaller the overhead of tracking slabs
3040 and the less frequently locks need to be acquired.
3041 For more information see Documentation/vm/slub.txt.
3042
3043 slub_min_order= [MM, SLUB]
3044 Determines the minimum page order for slabs. Must be
3045 lower than slub_max_order.
3046 For more information see Documentation/vm/slub.txt.
3047
3048 slub_nomerge [MM, SLUB]
3049 Disable merging of slabs with similar size. May be
3050 necessary if there is some reason to distinguish
3051 allocs to different slabs. Debug options disable
3052 merging on their own.
3053 For more information see Documentation/vm/slub.txt.
3054
3055 smart2= [HW]
3056 Format: <io1>[,<io2>[,...,<io8>]]
3057
3058 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3059 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3060 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3061 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3062 smsc-ircc2.ircc_irq= [HW] IRQ line
3063 smsc-ircc2.ircc_dma= [HW] DMA channel
3064 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3065 0: Toshiba Satellite 1800 (GP data pin select)
3066 1: Fast pin select (default)
3067 2: ATC IRMode
3068
3069 softlockup_panic=
3070 [KNL] Should the soft-lockup detector generate panics.
3071 Format: <integer>
3072
3073 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3074 See Documentation/laptops/sonypi.txt
3075
3076 spia_io_base= [HW,MTD]
3077 spia_fio_base=
3078 spia_pedr=
3079 spia_peddr=
3080
3081 stacktrace [FTRACE]
3082 Enabled the stack tracer on boot up.
3083
3084 stacktrace_filter=[function-list]
3085 [FTRACE] Limit the functions that the stack tracer
3086 will trace at boot up. function-list is a comma separated
3087 list of functions. This list can be changed at run
3088 time by the stack_trace_filter file in the debugfs
3089 tracing directory. Note, this enables stack tracing
3090 and the stacktrace above is not needed.
3091
3092 sti= [PARISC,HW]
3093 Format: <num>
3094 Set the STI (builtin display/keyboard on the HP-PARISC
3095 machines) console (graphic card) which should be used
3096 as the initial boot-console.
3097 See also comment in drivers/video/console/sticore.c.
3098
3099 sti_font= [HW]
3100 See comment in drivers/video/console/sticore.c.
3101
3102 stifb= [HW]
3103 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3104
3105 sunrpc.min_resvport=
3106 sunrpc.max_resvport=
3107 [NFS,SUNRPC]
3108 SunRPC servers often require that client requests
3109 originate from a privileged port (i.e. a port in the
3110 range 0 < portnr < 1024).
3111 An administrator who wishes to reserve some of these
3112 ports for other uses may adjust the range that the
3113 kernel's sunrpc client considers to be privileged
3114 using these two parameters to set the minimum and
3115 maximum port values.
3116
3117 sunrpc.pool_mode=
3118 [NFS]
3119 Control how the NFS server code allocates CPUs to
3120 service thread pools. Depending on how many NICs
3121 you have and where their interrupts are bound, this
3122 option will affect which CPUs will do NFS serving.
3123 Note: this parameter cannot be changed while the
3124 NFS server is running.
3125
3126 auto the server chooses an appropriate mode
3127 automatically using heuristics
3128 global a single global pool contains all CPUs
3129 percpu one pool for each CPU
3130 pernode one pool for each NUMA node (equivalent
3131 to global on non-NUMA machines)
3132
3133 sunrpc.tcp_slot_table_entries=
3134 sunrpc.udp_slot_table_entries=
3135 [NFS,SUNRPC]
3136 Sets the upper limit on the number of simultaneous
3137 RPC calls that can be sent from the client to a
3138 server. Increasing these values may allow you to
3139 improve throughput, but will also increase the
3140 amount of memory reserved for use by the client.
3141
3142 swapaccount=[0|1]
3143 [KNL] Enable accounting of swap in memory resource
3144 controller if no parameter or 1 is given or disable
3145 it if 0 is given (See Documentation/cgroups/memory.txt)
3146
3147 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3148 Format: { <int> | force }
3149 <int> -- Number of I/O TLB slabs
3150 force -- force using of bounce buffers even if they
3151 wouldn't be automatically used by the kernel
3152
3153 switches= [HW,M68k]
3154
3155 sysfs.deprecated=0|1 [KNL]
3156 Enable/disable old style sysfs layout for old udev
3157 on older distributions. When this option is enabled
3158 very new udev will not work anymore. When this option
3159 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3160 in older udev will not work anymore.
3161 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3162 the kernel configuration.
3163
3164 sysrq_always_enabled
3165 [KNL]
3166 Ignore sysrq setting - this boot parameter will
3167 neutralize any effect of /proc/sys/kernel/sysrq.
3168 Useful for debugging.
3169
3170 tdfx= [HW,DRM]
3171
3172 test_suspend= [SUSPEND]
3173 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3174 standby suspend) as the system sleep state to briefly
3175 enter during system startup. The system is woken from
3176 this state using a wakeup-capable RTC alarm.
3177
3178 thash_entries= [KNL,NET]
3179 Set number of hash buckets for TCP connection
3180
3181 thermal.act= [HW,ACPI]
3182 -1: disable all active trip points in all thermal zones
3183 <degrees C>: override all lowest active trip points
3184
3185 thermal.crt= [HW,ACPI]
3186 -1: disable all critical trip points in all thermal zones
3187 <degrees C>: override all critical trip points
3188
3189 thermal.nocrt= [HW,ACPI]
3190 Set to disable actions on ACPI thermal zone
3191 critical and hot trip points.
3192
3193 thermal.off= [HW,ACPI]
3194 1: disable ACPI thermal control
3195
3196 thermal.psv= [HW,ACPI]
3197 -1: disable all passive trip points
3198 <degrees C>: override all passive trip points to this
3199 value
3200
3201 thermal.tzp= [HW,ACPI]
3202 Specify global default ACPI thermal zone polling rate
3203 <deci-seconds>: poll all this frequency
3204 0: no polling (default)
3205
3206 threadirqs [KNL]
3207 Force threading of all interrupt handlers except those
3208 marked explicitly IRQF_NO_THREAD.
3209
3210 tmem [KNL,XEN]
3211 Enable the Transcendent memory driver if built-in.
3212
3213 tmem.cleancache=0|1 [KNL, XEN]
3214 Default is on (1). Disable the usage of the cleancache
3215 API to send anonymous pages to the hypervisor.
3216
3217 tmem.frontswap=0|1 [KNL, XEN]
3218 Default is on (1). Disable the usage of the frontswap
3219 API to send swap pages to the hypervisor. If disabled
3220 the selfballooning and selfshrinking are force disabled.
3221
3222 tmem.selfballooning=0|1 [KNL, XEN]
3223 Default is on (1). Disable the driving of swap pages
3224 to the hypervisor.
3225
3226 tmem.selfshrinking=0|1 [KNL, XEN]
3227 Default is on (1). Partial swapoff that immediately
3228 transfers pages from Xen hypervisor back to the
3229 kernel based on different criteria.
3230
3231 topology= [S390]
3232 Format: {off | on}
3233 Specify if the kernel should make use of the cpu
3234 topology information if the hardware supports this.
3235 The scheduler will make use of this information and
3236 e.g. base its process migration decisions on it.
3237 Default is on.
3238
3239 tp720= [HW,PS2]
3240
3241 tpm_suspend_pcr=[HW,TPM]
3242 Format: integer pcr id
3243 Specify that at suspend time, the tpm driver
3244 should extend the specified pcr with zeros,
3245 as a workaround for some chips which fail to
3246 flush the last written pcr on TPM_SaveState.
3247 This will guarantee that all the other pcrs
3248 are saved.
3249
3250 trace_buf_size=nn[KMG]
3251 [FTRACE] will set tracing buffer size.
3252
3253 trace_event=[event-list]
3254 [FTRACE] Set and start specified trace events in order
3255 to facilitate early boot debugging.
3256 See also Documentation/trace/events.txt
3257
3258 trace_options=[option-list]
3259 [FTRACE] Enable or disable tracer options at boot.
3260 The option-list is a comma delimited list of options
3261 that can be enabled or disabled just as if you were
3262 to echo the option name into
3263
3264 /sys/kernel/debug/tracing/trace_options
3265
3266 For example, to enable stacktrace option (to dump the
3267 stack trace of each event), add to the command line:
3268
3269 trace_options=stacktrace
3270
3271 See also Documentation/trace/ftrace.txt "trace options"
3272 section.
3273
3274 traceoff_on_warning
3275 [FTRACE] enable this option to disable tracing when a
3276 warning is hit. This turns off "tracing_on". Tracing can
3277 be enabled again by echoing '1' into the "tracing_on"
3278 file located in /sys/kernel/debug/tracing/
3279
3280 This option is useful, as it disables the trace before
3281 the WARNING dump is called, which prevents the trace to
3282 be filled with content caused by the warning output.
3283
3284 This option can also be set at run time via the sysctl
3285 option: kernel/traceoff_on_warning
3286
3287 transparent_hugepage=
3288 [KNL]
3289 Format: [always|madvise|never]
3290 Can be used to control the default behavior of the system
3291 with respect to transparent hugepages.
3292 See Documentation/vm/transhuge.txt for more details.
3293
3294 tsc= Disable clocksource stability checks for TSC.
3295 Format: <string>
3296 [x86] reliable: mark tsc clocksource as reliable, this
3297 disables clocksource verification at runtime, as well
3298 as the stability checks done at bootup. Used to enable
3299 high-resolution timer mode on older hardware, and in
3300 virtualized environment.
3301 [x86] noirqtime: Do not use TSC to do irq accounting.
3302 Used to run time disable IRQ_TIME_ACCOUNTING on any
3303 platforms where RDTSC is slow and this accounting
3304 can add overhead.
3305
3306 turbografx.map[2|3]= [HW,JOY]
3307 TurboGraFX parallel port interface
3308 Format:
3309 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3310 See also Documentation/input/joystick-parport.txt
3311
3312 udbg-immortal [PPC] When debugging early kernel crashes that
3313 happen after console_init() and before a proper
3314 console driver takes over, this boot options might
3315 help "seeing" what's going on.
3316
3317 uhash_entries= [KNL,NET]
3318 Set number of hash buckets for UDP/UDP-Lite connections
3319
3320 uhci-hcd.ignore_oc=
3321 [USB] Ignore overcurrent events (default N).
3322 Some badly-designed motherboards generate lots of
3323 bogus events, for ports that aren't wired to
3324 anything. Set this parameter to avoid log spamming.
3325 Note that genuine overcurrent events won't be
3326 reported either.
3327
3328 unknown_nmi_panic
3329 [X86] Cause panic on unknown NMI.
3330
3331 usbcore.authorized_default=
3332 [USB] Default USB device authorization:
3333 (default -1 = authorized except for wireless USB,
3334 0 = not authorized, 1 = authorized)
3335
3336 usbcore.autosuspend=
3337 [USB] The autosuspend time delay (in seconds) used
3338 for newly-detected USB devices (default 2). This
3339 is the time required before an idle device will be
3340 autosuspended. Devices for which the delay is set
3341 to a negative value won't be autosuspended at all.
3342
3343 usbcore.usbfs_snoop=
3344 [USB] Set to log all usbfs traffic (default 0 = off).
3345
3346 usbcore.blinkenlights=
3347 [USB] Set to cycle leds on hubs (default 0 = off).
3348
3349 usbcore.old_scheme_first=
3350 [USB] Start with the old device initialization
3351 scheme (default 0 = off).
3352
3353 usbcore.usbfs_memory_mb=
3354 [USB] Memory limit (in MB) for buffers allocated by
3355 usbfs (default = 16, 0 = max = 2047).
3356
3357 usbcore.use_both_schemes=
3358 [USB] Try the other device initialization scheme
3359 if the first one fails (default 1 = enabled).
3360
3361 usbcore.initial_descriptor_timeout=
3362 [USB] Specifies timeout for the initial 64-byte
3363 USB_REQ_GET_DESCRIPTOR request in milliseconds
3364 (default 5000 = 5.0 seconds).
3365
3366 usbhid.mousepoll=
3367 [USBHID] The interval which mice are to be polled at.
3368
3369 usb-storage.delay_use=
3370 [UMS] The delay in seconds before a new device is
3371 scanned for Logical Units (default 5).
3372
3373 usb-storage.quirks=
3374 [UMS] A list of quirks entries to supplement or
3375 override the built-in unusual_devs list. List
3376 entries are separated by commas. Each entry has
3377 the form VID:PID:Flags where VID and PID are Vendor
3378 and Product ID values (4-digit hex numbers) and
3379 Flags is a set of characters, each corresponding
3380 to a common usb-storage quirk flag as follows:
3381 a = SANE_SENSE (collect more than 18 bytes
3382 of sense data);
3383 b = BAD_SENSE (don't collect more than 18
3384 bytes of sense data);
3385 c = FIX_CAPACITY (decrease the reported
3386 device capacity by one sector);
3387 d = NO_READ_DISC_INFO (don't use
3388 READ_DISC_INFO command);
3389 e = NO_READ_CAPACITY_16 (don't use
3390 READ_CAPACITY_16 command);
3391 h = CAPACITY_HEURISTICS (decrease the
3392 reported device capacity by one
3393 sector if the number is odd);
3394 i = IGNORE_DEVICE (don't bind to this
3395 device);
3396 l = NOT_LOCKABLE (don't try to lock and
3397 unlock ejectable media);
3398 m = MAX_SECTORS_64 (don't transfer more
3399 than 64 sectors = 32 KB at a time);
3400 n = INITIAL_READ10 (force a retry of the
3401 initial READ(10) command);
3402 o = CAPACITY_OK (accept the capacity
3403 reported by the device);
3404 p = WRITE_CACHE (the device cache is ON
3405 by default);
3406 r = IGNORE_RESIDUE (the device reports
3407 bogus residue values);
3408 s = SINGLE_LUN (the device has only one
3409 Logical Unit);
3410 w = NO_WP_DETECT (don't test whether the
3411 medium is write-protected).
3412 Example: quirks=0419:aaf5:rl,0421:0433:rc
3413
3414 user_debug= [KNL,ARM]
3415 Format: <int>
3416 See arch/arm/Kconfig.debug help text.
3417 1 - undefined instruction events
3418 2 - system calls
3419 4 - invalid data aborts
3420 8 - SIGSEGV faults
3421 16 - SIGBUS faults
3422 Example: user_debug=31
3423
3424 userpte=
3425 [X86] Flags controlling user PTE allocations.
3426
3427 nohigh = do not allocate PTE pages in
3428 HIGHMEM regardless of setting
3429 of CONFIG_HIGHPTE.
3430
3431 vdso= [X86,SH]
3432 On X86_32, this is an alias for vdso32=. Otherwise:
3433
3434 vdso=1: enable VDSO (the default)
3435 vdso=0: disable VDSO mapping
3436
3437 vdso32= [X86] Control the 32-bit vDSO
3438 vdso32=1: enable 32-bit VDSO
3439 vdso32=0 or vdso32=2: disable 32-bit VDSO
3440
3441 See the help text for CONFIG_COMPAT_VDSO for more
3442 details. If CONFIG_COMPAT_VDSO is set, the default is
3443 vdso32=0; otherwise, the default is vdso32=1.
3444
3445 For compatibility with older kernels, vdso32=2 is an
3446 alias for vdso32=0.
3447
3448 Try vdso32=0 if you encounter an error that says:
3449 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3450
3451 vector= [IA-64,SMP]
3452 vector=percpu: enable percpu vector domain
3453
3454 video= [FB] Frame buffer configuration
3455 See Documentation/fb/modedb.txt.
3456
3457 video.brightness_switch_enabled= [0,1]
3458 If set to 1, on receiving an ACPI notify event
3459 generated by hotkey, video driver will adjust brightness
3460 level and then send out the event to user space through
3461 the allocated input device; If set to 0, video driver
3462 will only send out the event without touching backlight
3463 brightness level.
3464 default: 1
3465
3466 virtio_mmio.device=
3467 [VMMIO] Memory mapped virtio (platform) device.
3468
3469 <size>@<baseaddr>:<irq>[:<id>]
3470 where:
3471 <size> := size (can use standard suffixes
3472 like K, M and G)
3473 <baseaddr> := physical base address
3474 <irq> := interrupt number (as passed to
3475 request_irq())
3476 <id> := (optional) platform device id
3477 example:
3478 virtio_mmio.device=1K@0x100b0000:48:7
3479
3480 Can be used multiple times for multiple devices.
3481
3482 vga= [BOOT,X86-32] Select a particular video mode
3483 See Documentation/x86/boot.txt and
3484 Documentation/svga.txt.
3485 Use vga=ask for menu.
3486 This is actually a boot loader parameter; the value is
3487 passed to the kernel using a special protocol.
3488
3489 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3490 size of <nn>. This can be used to increase the
3491 minimum size (128MB on x86). It can also be used to
3492 decrease the size and leave more room for directly
3493 mapped kernel RAM.
3494
3495 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3496 Format: <command>
3497
3498 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3499 Format: <command>
3500
3501 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3502 Format: <command>
3503
3504 vsyscall= [X86-64]
3505 Controls the behavior of vsyscalls (i.e. calls to
3506 fixed addresses of 0xffffffffff600x00 from legacy
3507 code). Most statically-linked binaries and older
3508 versions of glibc use these calls. Because these
3509 functions are at fixed addresses, they make nice
3510 targets for exploits that can control RIP.
3511
3512 emulate [default] Vsyscalls turn into traps and are
3513 emulated reasonably safely.
3514
3515 native Vsyscalls are native syscall instructions.
3516 This is a little bit faster than trapping
3517 and makes a few dynamic recompilers work
3518 better than they would in emulation mode.
3519 It also makes exploits much easier to write.
3520
3521 none Vsyscalls don't work at all. This makes
3522 them quite hard to use for exploits but
3523 might break your system.
3524
3525 vt.color= [VT] Default text color.
3526 Format: 0xYX, X = foreground, Y = background.
3527 Default: 0x07 = light gray on black.
3528
3529 vt.cur_default= [VT] Default cursor shape.
3530 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3531 the parameters of the <Esc>[?A;B;Cc escape sequence;
3532 see VGA-softcursor.txt. Default: 2 = underline.
3533
3534 vt.default_blu= [VT]
3535 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3536 Change the default blue palette of the console.
3537 This is a 16-member array composed of values
3538 ranging from 0-255.
3539
3540 vt.default_grn= [VT]
3541 Format: <green0>,<green1>,<green2>,...,<green15>
3542 Change the default green palette of the console.
3543 This is a 16-member array composed of values
3544 ranging from 0-255.
3545
3546 vt.default_red= [VT]
3547 Format: <red0>,<red1>,<red2>,...,<red15>
3548 Change the default red palette of the console.
3549 This is a 16-member array composed of values
3550 ranging from 0-255.
3551
3552 vt.default_utf8=
3553 [VT]
3554 Format=<0|1>
3555 Set system-wide default UTF-8 mode for all tty's.
3556 Default is 1, i.e. UTF-8 mode is enabled for all
3557 newly opened terminals.
3558
3559 vt.global_cursor_default=
3560 [VT]
3561 Format=<-1|0|1>
3562 Set system-wide default for whether a cursor
3563 is shown on new VTs. Default is -1,
3564 i.e. cursors will be created by default unless
3565 overridden by individual drivers. 0 will hide
3566 cursors, 1 will display them.
3567
3568 vt.italic= [VT] Default color for italic text; 0-15.
3569 Default: 2 = green.
3570
3571 vt.underline= [VT] Default color for underlined text; 0-15.
3572 Default: 3 = cyan.
3573
3574 watchdog timers [HW,WDT] For information on watchdog timers,
3575 see Documentation/watchdog/watchdog-parameters.txt
3576 or other driver-specific files in the
3577 Documentation/watchdog/ directory.
3578
3579 workqueue.disable_numa
3580 By default, all work items queued to unbound
3581 workqueues are affine to the NUMA nodes they're
3582 issued on, which results in better behavior in
3583 general. If NUMA affinity needs to be disabled for
3584 whatever reason, this option can be used. Note
3585 that this also can be controlled per-workqueue for
3586 workqueues visible under /sys/bus/workqueue/.
3587
3588 workqueue.power_efficient
3589 Per-cpu workqueues are generally preferred because
3590 they show better performance thanks to cache
3591 locality; unfortunately, per-cpu workqueues tend to
3592 be more power hungry than unbound workqueues.
3593
3594 Enabling this makes the per-cpu workqueues which
3595 were observed to contribute significantly to power
3596 consumption unbound, leading to measurably lower
3597 power usage at the cost of small performance
3598 overhead.
3599
3600 The default value of this parameter is determined by
3601 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3602
3603 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3604 default x2apic cluster mode on platforms
3605 supporting x2apic.
3606
3607 x86_intel_mid_timer= [X86-32,APBT]
3608 Choose timer option for x86 Intel MID platform.
3609 Two valid options are apbt timer only and lapic timer
3610 plus one apbt timer for broadcast timer.
3611 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3612
3613 xen_emul_unplug= [HW,X86,XEN]
3614 Unplug Xen emulated devices
3615 Format: [unplug0,][unplug1]
3616 ide-disks -- unplug primary master IDE devices
3617 aux-ide-disks -- unplug non-primary-master IDE devices
3618 nics -- unplug network devices
3619 all -- unplug all emulated devices (NICs and IDE disks)
3620 unnecessary -- unplugging emulated devices is
3621 unnecessary even if the host did not respond to
3622 the unplug protocol
3623 never -- do not unplug even if version check succeeds
3624
3625 xen_nopvspin [X86,XEN]
3626 Disables the ticketlock slowpath using Xen PV
3627 optimizations.
3628
3629 xirc2ps_cs= [NET,PCMCIA]
3630 Format:
3631 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3632
3633______________________________________________________________________
3634
3635TODO:
3636
3637 Add more DRM drivers.